Mitochondrial toxicity of nanomaterials

Journal Pre-proofs Review Mitochondrial toxicity of nanomaterials Daming Wu, Ying Ma, Yuna Cao, Ting Zhang PII: DOI: Reference:

S0048-9697(19)34986-1 https://doi.org/10.1016/j.scitotenv.2019.134994 STOTEN 134994

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Science of the Total Environment

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2 September 2019 11 October 2019 14 October 2019

Please cite this article as: D. Wu, Y. Ma, Y. Cao, T. Zhang, Mitochondrial toxicity of nanomaterials, Science of the Total Environment (2019), doi: https://doi.org/10.1016/j.scitotenv.2019.134994

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Mitochondrial toxicity of nanomaterials Daming Wu, Ying Ma, Yuna Cao, Ting Zhang*

Key Laboratory of Environmental Medicine Engineering, Ministry of Education, School of Public Health, Southeast University, Nanjing, 210009, China.

*Corresponding

author. Email address: [email protected]

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Abstract In recent years, nanomaterials have been widely applied in electronics, food, biomedicine and other fields, resulting in increased human exposure and consequent research focus on their biological and toxic effects. Mitochondria, the main target organelle for nanomaterials (NM), play a critical role in their toxic activities. Several studies to date have shown that nanomaterials cause alterations in mitochondrial morphology, mitochondrial membrane potential, opening of the mitochondrial permeability transition pore (MPTP) and mitochondrial respiratory function, and promote cytochrome C release. An earlier mitochondrial toxicity study of NMs additionally reported induction of mitochondrial dynamic changes. Here, we have reviewed the mitochondrial toxicity of NMs and provided a scientific basis for the contribution of mitochondria to the toxicological effects of different NMs along with approaches to reduce mitochondrial and, consequently, overall toxicity of NMs.

Keywords: Nanomaterials; Mitochondria; Mitochondrial toxicity; Mitochondrial dynamic; Mitochondrial homeostasis

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1 Introduction With the rapid development of nanotechnology and its widespread application in multiple fields, such as electronics (Jariwala et al., 2013; Kim et al., 2014), food (Handford et al., 2014), cosmetics (Cao et al., 2016), agriculture (Handford et al., 2014), and biomedicine (Teradal and Jelinek, 2017), the commercial demand for nanomaterials (NM) has increased dramatically (Vance et al., 2015; Lai et al., 2018). Owing to their expanding use, NMs are inevitably released into the environment or directly absorbed by the body (Lead et al., 2018). Every step in the production, processing, transportation, application and disposal of NMs may lead to release into the ambient atmosphere (Caballero-Guzman and Nowack, 2016). In addition, high concentrations of NMs can be released during accidents, such as explosions, fires or transportation collisions (John et al., 2017). The respiratory tract is the main route for NM entry into the human body. NMs also enter aquatic systems and soils through application to agriculture and industrial discharge (Rai et al., 2018), where the majority are aggregated and transformed by colloids, particles and organisms in water and soil (Batley et al., 2013; Lead et al., 2018). The extensive use of NMs in pharmaceuticals, cosmetics, textiles, food and tableware has led to direct contact with human skin and entry into the body through the gastrointestinal tract and intravenous injection (Blaser et al., 2008; Handford et al., 2014; Cao et al., 2016; Rathor et al., 2017). NMs in the body penetrate cells via free diffusion, phagocytosis and pinocytosis (Karlsson et al., 2009), exerting diverse biological effects that cause potential harm to health. Accordingly, determination of the 3

biological effects and safety of NMs, in particular, their interactions with subcellular structures, is essential (Service, 2003). Mitochondria are key organelles involved in numerous biological processes. In addition to their function as an “energy plant”, mitochondria are involved in the initiation of apoptosis (Raimundo et al., 2012), calcium signaling and homeostasis (Marchi et al., 2018), biomacromolecule synthesis (Ahn and Metallo, 2015), ion exchange (Shoshan-Barmatz et al., 2015) and metabolite transport (Ellenrieder et al., 2017). Numerous environmental contaminants exert toxic effects by inducing mitochondrial impairment, including dioxins (Hwang et al., 2016), acrylamide (Zamani et al., 2017), cigarette smoke (He et al., 2017), and heavy metals (Belyaeva et al., 2012). Mitochondrial damage also occurs in human diseases including common aging disorders, such as Parkinson's disease, Alzheimer's disease and cancer (Wallace, 2005), as well as liver disease (Nassir and Ibdah, 2014; Simoes et al., 2018), muscle disease (Russell et al., 2014; Zulian et al., 2016) and heart disease (Santiago et al., 2015). Therefore, mitochondria are suggested to play a key role in diseases caused by environmental pollutants. NMs clearly cause damage to mitochondria (Yu et al., 2013; Maurer and Meyer, 2016; Xue et al., 2017), inducing morphological changes (Nguyen et al., 2015), mitochondrial membrane potential (MMP) decrease (Huerta-Garcia et al., 2014), suppression of mitochondrial respiratory function (Yu et al., 2015) and promotion of cytochrome C release (Jaworski et al., 2019). These toxic effects ultimately lead to decreased ATP production and apoptosis. Changes in mitochondrial dynamics (Yamada et al., 2018) and mitophagy (Wang et al., 2018a) were 4

simultaneously reported from toxicity studies of NMs, which play an important role in the occurrence and development of neurodegenerative diseases, cancer and metabolic disorders (Bertholet et al., 2016; Serasinghe and Chipuk, 2017; Srinivasan et al., 2017; Um and Yun, 2017). This review aids in improving understanding of the biosafety of NMs by highlighting the mitochondrial toxicity of common nanomaterials and provides a reference for subsequent evaluation of mitochondrial contribution to the toxicological effects of different NMs.

2 Structure and function of mitochondria The structure and functions of mitochondria, important sites for cell energy metabolism, are depicted in Fig.1. The organelle can be divided into four functional regions from the inside to outside: matrix, mitochondrial inner membrane (MIM), intermembrane space and mitochondrial outer membrane (MOM). The mitochondrial permeability transition pore (MPTP) is composed of transmembrane proteins on MIM and MOM (Tsujimoto and Shimizu, 2007). The main physiological role of MPTP is regulation of intracellular calcium homeostasis (Hurst et al., 2017), transport of ATP/ADP and energy metabolism (Mnatsakanyan et al., 2017). Continuous opening of MPTP can lead to collapse of transmembrane potential, oxidative phosphorylation uncoupling and release of cytochrome C (Mashayekhi et al., 2014; Mnatsakanyan et al., 2017). MIM folds inwards to form mitochondrial cristae. Most respiratory complexes responsible for oxidative phosphorylation and ATP production are embedded in cristae (Quintana-Cabrera et al., 2018). The shape of mitochondrial cristae 5

determines mitochondrial respiratory complex assembly and efficiency of energy metabolism (Cogliati et al., 2013; Cogliati et al., 2016). ROS (Sarniak et al., 2016) and MMP (Brand and Nicholls, 2011) are generated during electron transport in the respiratory chain in which complexes I and III are the main sources of mitochondrial ROS (mtROS) (Bleier and Drose, 2013; Vinogradov and Grivennikova, 2016; Basit et al., 2017), which may be involved in organism development (Coffman et al., 2009), immune processes (Pinegin et al., 2018) and signal transduction (Scialo et al., 2017). Excess ROS can be eliminated by antioxidants or antioxidant enzymes in cells (Larosa and Remacle, 2018). Normal MMP is a prerequisite for maintaining oxidative phosphorylation and ATP production (Chen, 1988). When the respiratory chain complex is affected by exogenous factors, excessive production of mtROS, altered MMP and decreased ATP production may be triggered (Zhou and Huang, 2018). Mitochondrial DNA (mtDNA) and ribosomes in the mitochondrial matrix encode ~13 proteins that primarily form enzyme complexes of the oxidative phosphorylation system (Friedman and Nunnari, 2014; Mazunin et al., 2015). MtDNA is transcribed at high rates in some high-energy active tissues, such as heart (Mercer et al., 2011).

3 Role of mitochondria in NM-induced toxicity ROS generation is one of the important mechanisms underlying nanoparticleinduced toxicity (Abdal Dayem et al., 2017; Jayaram et al., 2017). On the one hand, NMs themselves produce ROS, causing damage to mitochondria, in turn, triggering a series of mitochondria-mediated toxic effects (Abdal Dayem et al., 2017). On the other 6

hand, decreased levels or activities of mitochondrial respiratory chain complexes lead to overproduction of ROS (Sun et al., 2016; Passmore et al., 2017; Zhang et al., 2018a). NMs may directly trigger overproduction of mitochondrial ROS by affecting the expression or activity of the respiratory chain complex. A study by Nguyen et al. (2015) on the effects of cadmium telluride quantum dots (CdTe QDs) on mitochondria of human hepatocellular carcinoma cells (HepG2) consistently disclosed that CdTe QDs suppress the activities of electron transport chain complexes II, III and IV. Costa and co-workers (2010) reported the that silver nanoparticles (Ag-NPs; 10, 25 and 50 mg/L) suppress the activities of mitochondrial respiratory chain complexes I, II, III and IV in rat brain, skeletal muscle, heart and liver. The role of the mitochondrial respiratory chain in ROS generation and cytotoxicity in keratinocyte cells induced by nano-TiO2 under UVA irradiation was examined by Xue et al. (2016a). In this study, complexes I and III were determined as the major sites of ROS generation and mitochondrial respiratory chain as the main source of intracellular ROS induced by nano-TiO2. In addition, damage to mtDNA further leading to decreased expression of respiratory chain complexes has been reported in a recent toxicity study of multi-walled carbon nanotubes (MWCNT) (Xu et al., 2016). The collective findings support the theory that NMs trigger increased mtROS levels by affecting respiratory chain complexes and promote oxidative stress (Song et al., 2016; Tee et al., 2016). Upon exposure to environmental stress (such as elevated ROS levels), cells regulate mitochondrial dynamics and mitophagy to control mitochondrial quality and maintain homeostasis (Youle and van der Bliek, 2012; Ni et al., 2015; Vigie and 7

Camougrand, 2017; Palikaras et al., 2018). Changes in mitochondrial dynamics have been detected in nanomaterial-induced toxicity. Mitochondria show a high degree of fusion at low doses and high degree of fragmentation at high doses (Wilson et al., 2015). Mitochondrial fusion may serve as an adaptive response (Meyer et al., 2017). Proper mitochondrial fission protects healthy regions from being eliminated (Burman et al., 2017) and promotes clearance of damaged regions via mitophagy. Wei et al. (2017) showed a protective role of PINK1/parkin-mediated mitophagy against cytotoxicity induced by ZnO-NPs. Mitochondria play critical role in intrinsic apoptosis (Galluzzi et al., 2018). Mitochondria-mediated apoptosis is associated with the toxicological effects of most nanomaterials. Recent experiments on the effects of Ag-NPs on SH-SY5Y cells by Li et al. (2018) demonstrated that Ag-NPs increase the length of endoplasmic reticulummitochondrial contact sites, enhance transfer of Ca2+ from the endoplasmic reticulum to mitochondria, cause Ca2+ overload and disrupt homeostasis in mitochondriatriggered apoptosis. The group of Zhao (2016) demonstrated that ZnO-NPs cause reduction of the Bcl-2/Bax ratio and release of cytochrome C into the cytosol, and ultimately, mitochondria-mediated apoptosis in zebrafish embryos. Induction of mitochondria-mediated apoptosis by single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and Fe2O3 NPs in melanoma cells was further documented by Naserzadeh et al. (2018). In summary, mitochondria act as targets and mediators of the toxic effects of NMs. An overview of mitochondrial toxicity by NMs is shown in Figure 2. 8

4 Different types of nanomaterials inducing mitochondrial toxicity According to composition and application, we have divided nanomaterial subtypes into metal and metal oxides (MNM), metal-free carbon (CNM) and quantum dots (QD). This article mainly focuses on the mitochondrial toxicity of these three NM types (presented in Tables 1, 2 and 3). 4.1 Metal and metal oxide nanomaterials The latest Nanotechnology Consumer Products Inventory highlights that MNMs are the most highly used NM types, accounting for 37% nanoproducts worldwide (Vance et al., 2015). Among these, titanium dioxide nanoparticles (TiO2-NP) and zinc oxide nanoparticles (ZnO-NP) have the largest yield and are the most widely used in various applications including paints, coatings, catalysts, pharmaceuticals, food, cosmetics and toothpaste (Shi et al., 2013; Madhumitha et al., 2016). Although the annual production of Ag-NPs accounts for only 2% TiO2-NPs, more than 400 products contain this subtype (Vance et al., 2015). Moreover, Ag-NPs are widely used in medical fields, such as antibacterial, biological imaging, drug delivery and tumor hyperthermia (Abbasi et al., 2016; Mathur et al., 2018). TiO2-NPs, Ag-NPs and ZnO-NPs cause morphological changes in mitochondria (Hou et al., 2014; Jain et al., 2017; Jia et al., 2017; Ostaszewska et al., 2018; Pereira et al., 2018), MMP collapse and cytochrome C release leading to mitochondria-mediated apoptosis in various cell types (Huerta-Garcia et al., 2014; Sheng et al., 2015; Hong et al., 2016; Kovacs et al., 2016; Liang et al., 2016; Tan et al., 2016; Xin et al., 2016; Xue et al., 2016b; Zhao et al., 2016; Choudhury et al., 2017; Han et al., 2017; Reshma and Mohanan, 2017; Sruthi et al., 2017; George et al., 2018; Wang et al., 2018a; Wang et 9

al., 2018b; Tang et al., 2019). In addition, MNMs are reported to affect mitochondrial respiratory function. Yu et al. (2017) studied the effects of TiO2-NPs (anatase, rutile) on mouse macrophages. Data from the reverse electron transfer (RET) assay showed significant inhibition of mitochondrial respiration by TiO2-NPs. Moreover, the inhibitory effect of anatase was stronger, indicating a greater impact on mitochondria. Chen et al. (2018) performed GC-MS-based metabolic flux analysis of macrophages exposed to TiO2-NP, which showed a dose-dependent decrease in flux of metabolites in the Krebs cycle. Additionally, TiO2-NPs suppressed expression of mitochondrial respiratory chain complexes I, II and IV (Yu et al., 2015) and inhibited complex II activity (Ghanbary et al., 2018). Ag-NPs inhibit activity of liver mitochondrial complexes II, IV and ATP synthase in Sprague-Dawley male rats (Teodoro et al., 2016). The effects of these MNMs on mitochondrial respiration ultimately result in decreased ATP production and mitochondrial dysfunction (Park et al., 2014a; Tan et al., 2016; Sharma et al., 2017). MNMs have been shown to affect mitochondrial dynamics. Natarajan et al. (2015) examined the toxic effects of three different TiO2-NPs (rutile, anatase and P25) on primary rat hepatocytes. Their results showed that gene expression levels of OPA1 and MFN1 associated with mitochondrial fusion events were significantly downregulated upon exposure to 50 ppm P25 and anatase, with P25 exerting the highest effect. High levels of mitochondrial fragmentation were observed using the fluorescent stain MitoTracker FM for imaging mitochondria while downregulation of the fusion-related gene in the rutile treatment group was not significant. Wilson and co-workers (2015) 10

investigated the effects of rutile, anatase and P25 TiO2-NPs on mitochondrial dynamics of primary rat cortical astrocytes by determining the relative expression levels of Mfn1, Mfn2, and Drp1. At a concentration of 25 ppm, P25 induced marked upregulation of Mfn1 and Mfn2 transcript levels while astrocytes treated with anatase showed a significant increase in Mfn1, but not Mfn2, and those treated with rutile showed a significant increase in Mfn2, but not Mfn1. The three TiO2-NPs exerted no significant effects on Drp1 transcript levels. At a concentration of 100 ppm, all three TiO2-NPs enhanced the levels of Mfn1, Mfn2 and Drp1. Confocal imaging of mitochondrial morphology revealed that mitochondria of astrocytes treated with 25 ppm P25 showed the greatest degree of fusion while those treated with 100 ppm P25 and anatase displayed highest fragmentation. In a study by Yamada et al. (2018) on the effects of Ag-NPs on human embryonic stem cell-derived neural progenitor cells (NPCs), AgNPs induced mitochondrial fragmentation and reduced the level of mitochondrial fusion related protein Mfn-1. Mitochondrial division and fusion are closely related to mitophagy. Recent studies have demonstrated that MNMs also activate mitophagy (Wei et al., 2017; Wang et al., 2018a; Zhang et al., 2018b). Wei and co-workers (2017) showed that PINK1/parkin-mediated mitophagy exerts protective effects against toxicity to mouse microglial cell line BV-2 induced by ZnO-NPs. 4.2 Carbon nanomaterials CNMs are considered the most promising products of nanotechnology (Hirsch, 2010) and widely used in biomedicine (Saeed et al., 2014; Kim et al., 2017; Teradal 11

and Jelinek, 2017), electronic components (Wang and Dai, 2015) and architecture (Hincapie et al., 2015). Common CNMs include zero-dimensional fullerenes (C60), onedimensional carbon nanotubes (CNTs) and the two-dimensional carbon allotrope graphene (Teradal and Jelinek, 2017). We have mainly focused on the mitochondrial toxicities of these three CNMs and their derivatives. In experiments on mitochondrial toxicity induced by C60 and its derivatives, Yang et al. (2016) extracted rat liver mitochondria followed by direct exposure to polyhydroxylated fullerenes (C60(OH)44), which resulted in mitochondrial swelling, mitochondrial membrane fluidity changes, MMP collapse and mitochondrial permeability transition (MPT) in addition to causing a decrease in mitochondrial respiratory control ratio (RCR; ratio of state 3 to state 4 respiration rates, which is an important parameter reflecting the coupling of mitochondrial oxidative phosphorylation) by promoting status 4 respiration and inhibiting state 3 respiration. The low respiration rate of state 4 (when ADP is exhausted) indicates intact mitochondrial inner membrane, which is necessary to maintain a sufficiently high potential to limit electron transport. The high respiratory rate of state 3 in the presence of ADP indicates the integrity of the respiratory chain (Adlam et al., 2005). The findings suggest impairment of the integrity of the mitochondrial inner membrane and respiratory chain by C60(OH)44. Santos et al. (2014) reported that C60 has higher affinity for the mitochondrial membrane than C60(OH)18–22 with a greater inhibitory effect on mitochondrial function, indicating that the surface chemistry of fullerene nanoparticles influences their toxic effects on mitochondria. In addition, C60 is reported to stimulate translocation of the pro-apoptotic 12

protein, Bax, to mitochondria, leading to mitochondria-mediated apoptosis (Song et al., 2012). Other fullerene derivatives, such as C60OH and C60(OH)24, are reported to cause a decrease in ATP generation and MMP (Johnson-Lyles et al., 2010; Nakagawa et al., 2015). Numerous studies have explored the toxicity of accumulating CNTs to mitochondria (Zhou et al., 2011; Xu et al., 2016). Furthermore, some researchers have utilized this property and combined drugs with CNTs to activate apoptosis (Yoong et al., 2015; Kim et al., 2017). Carbon nanotubes and their derivatives cause a variety of mitochondrial toxicities as specified earlier (mitochondrial morphological changes, decreased MMP, MPTP opening and cyto C release (Ma et al., 2012; Park et al., 2014b; Zhu et al., 2016; Visalli et al., 2017; Naserzadeh et al., 2018; Zhu et al., 2018; Visalli et al., 2019)), along with mtDNA damage (Xu et al., 2016). CNTs and their derivatives have multiple effects on mitochondrial respiratory function, including significant decrease in mitochondrial oxygen consumption (Ma et al., 2012; Xu et al., 2016), expression of MT-ND2 (mitochondria-NADH dehydrogenase subunit 2) and MT-ND3 (mitochondria-NADH dehydrogenase subunit 3) (Xu et al., 2016), decreased activity of mitochondrial respiratory chain complex II and ATP synthase (Ghanbari et al., 2017; Chen et al., 2012), attenuated electron transfer and conformational changes of cytochrome C (Ma et al., 2012). Different CNTs and their derivatives exert distinct mitochondrial toxicity effects. Ghanbari et al. (2017) compared the effects of equivalent doses of SWCNTs and MWCNTs on rat skin cells and found that mitochondrial toxicity caused by SWCNTs was higher than that of MWCNTs in terms of complex II activity, 13

cytochrome c release, reduction of MMP and ATP production. Moreover, levels of MMP decline and cytochrome C release induced by modified MWCNTs, such as MWCNT-COOH (hydroxylation) (Liu et al., 2014a), MWCNT -OH(hydroxylation) (Liu et al., 2014b) and tau-MWCNT (taurine functionalization) (Chen et al., 2012; Wang et al., 2012) were lower than those by raw MWCNTs. Similar to CNTs, mitochondria may be the main site of distribution of graphene and its derivatives in cells (Li et al., 2014; Zhou et al., 2014a). These compounds have a substantial impact on the respiratory function of mitochondria. Zhou et al. (2014a) reported that graphene and graphene oxide affect activity of mitochondrial respiratory chain complexes I, II, III and IV through effects on electron transfer between iron-sulfur centers but not the activity of complex V, potentially due to the absence of an ironsulfur center in this complex. The group additionally evaluated the effect of PEGmodified graphene oxide (PEG-GO) on mitochondrial oxidative phosphorylation system (OXPHOS) activity in breast cancer cell lines MDA-MB-231, MDA-MB-436 and SK-BR-3 using the Seahorse XF24-3 Extracellular Flux Analyzer to monitor mitochondrial oxygen consumption rate (OCR). PEG-GO reduced basal and maximal OCR to a significant extent, suggesting inhibition of mitochondrial OXPHOS activity, and downregulated mitochondrial respiratory chain complexes II and III in breast cancer cells, resulting in suppression of ATP production (Zhou et al., 2014b). In terms of the influence of graphene and its derivatives, the majority of studies to date have reported a decrease in MMP (Lammel et al., 2013; Hu et al., 2015; Zou et al., 2018; Jaworski et al., 2019), but with the use of higher concentrations of graphene and its 14

derivatives. Moreover, the results were obtained at a single time-point. Mari et al. (2016) studied the effects of low-dose (2 μg/mL) graphene oxide on mitochondria of neuroblastoma cell lines, SK-N-BE (2) and SH-SY5Y, at different time-points. MMP decreased in the first 4 h, followed by a gradual increase, and structurally disordered mitochondria were observed in the autophagosome after 48 h of GO exposure, indicating the occurrence of mitophagy. Moreover, extremely low doses (0.01–1 μg/L) of graphene oxide have been shown to cause changes in mitochondrial morphology and structures of adult zebrafish (Ren et al., 2016), indicating that graphene and its derivatives are more toxic to mitochondria. Additionally, graphene and derivatives are capable of inducing cytochrome C release, resulting in mitochondria-mediated apoptosis (Park et al., 2015; Jaworski et al., 2019). 4.3 Quantum dots Quantum dots (QD), also known as semiconductor nanocrystals, consist of II-IV or III-V elements with physical dimensions smaller than the exciton Bohr radius (Alivisatos, 1996). Their optical properties can be altered by adjusting the physical QD size (Esteve-Turrillas and Abad-Fuentes, 2013). Compared with traditional organic dyes, QDs have a longer fluorescence lifetime (Volkov, 2015) and are therefore more widely used in bioimaging (Mukherjee et al., 2016; Liu et al., 2017; Ma et al., 2017; Matea et al., 2017). Several in vitro experiments have identified mitochondria as one of the distribution sites of QDs (Clift et al., 2011; Wang et al., 2016; Han et al., 2019). In experiments by Li et al. (2011) involving direct exposure of rat liver mitochondria to 15

NAC-coated CdTe QDs, state 3 respiration was significantly decreased while state 4 respiration initially increased and then decreased with increasing QD doses, along with mitochondrial swelling and membrane lipid peroxidation. In the majority of in vitro studies, different cell types were exposed to QDs, which caused a range of mitochondrial toxicities including mitochondrial swelling and cristae disappearance, reduction of MMP and oxygen consumption, decreased levels of mitochondrial respiratory chain complexes II-IV and concomitantly increased complex V, MPTP opening, and cytochrome C release, with consequent mitochondria-mediated apoptosis (Chan et al., 2006; Nguyen et al., 2013; Wu et al., 2013; Lai et al., 2015; Nguyen et al., 2015), but no mtDNA damage (Paesano et al., 2016; Pasquali et al., 2017). In an in vivo study, Lin et al. (2012) treated mice with a single dose of QD (intravenous; 40 pmol) and examined mitochondrial toxicity in kidney at 4, 12, 16 and 24 weeks. Disorientation and decreased numbers of mitochondria were detected early, followed by mitochondrial swelling and compensatory hypertrophy, and finally an increase in number. Other studies have shown that toxic effects of QDs on mitochondria are affected by surface modification and particle size. Xiang et al. (2018) investigated the mitochondrial toxicity of CdTe QDs coated with thioglycolic acid (TGA), mercaptoethylamine (MEA) and 1-cysteine (1-Cys) in liver of female Wistar rats. All three types of QDs reduced mitochondrial respiration rates of state 3, state 4 and unconjugated states in a dosedependent manner. TGA-CdTe QDs exerted greater effects on mitochondria morphology, MMP and MPTP proteins than the other two QD types. MEA-CdTe QDs induced a dose-dependent decrease in mitochondrial membrane fluidity and l-Cys16

CdTe QDs had no significant effect while TGA-CdTe QDs increased mitochondrial membrane fluidity in a dose-dependent manner. The group of Lai (2016) reported greater effects of larger particle sizes of CdTe QDs on mitochondrial morphology, MMP and permeability. Therefore, toxic effects on mitochondria may be reduced by adjusting the modifications and particle sizes of QDs.

5. Conclusions and Future Perspectives In this review, we have provided an overview of the multiple subcellular, cellular and in vivo toxic effects of NMs on mitochondria, including morphological and dynamic changes, decreased MMP, opening of MPTP, impaired mitochondrial respiratory function, and apoptosis caused by increased cytochrome C release. The differences in mitochondrial toxicity between NMs with various modifications and particle sizes are additionally explored. Although the included studies have provided valuable insights into the mitochondrial toxicity of NMs, a number of aspects require further research. Firstly, the majority of studies to date have investigated the toxic effects of NMs on mitochondria in vitro, and further in vivo evaluation is required. Secondly, changes in mitochondrial dynamics were detected in mitochondrial toxicity studies on MNMs, but not those on CNMs and QDs. The reasons for this discrepancy require further clarification. Thirdly, CNTs cause damage to mitochondrial DNA, but not QDs. Therefore, in further research on the mitochondrial toxicity of different NMs, the integrity of mitochondrial DNA should be routinely analyzed. Fourthly, in most studies, the exposure concentration was high and mitochondrial toxicity of NMs was 17

observed at a single time-point. Future analyses should be conducted using low concentrations and the toxic effects of NMs on mitochondria examined at different time-points. Harnessing the mitochondrial toxicity of NMs is emerging as a promising research strategy. Given the diverse functions of mitochondria in both physiological and pathological contexts, damaged mitochondria serve to balance survival and death and ultimately dictate cellular fate. A key objective of upcoming studies in this field will be to clarify the mechanisms associated with mitochondrial toxicity and enhance its applicability to nanotoxicity studies and risk assessment of exposure in the near future.

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Acknowledgments This work was Supported by the National Natural Science Funds of China (No. 81673218) and the Fundamental Research Funds for the Central Universities (No. 2242019K40223).

Disclosure The author reports no conflicts of interest in this work.

Reference Abbasi, E., Milani, M., Fekri Aval, S., Kouhi, M., Akbarzadeh, A., Tayefi Nasrabadi, H., Nikasa, P., Joo, S.W., Hanifehpour, Y., Nejati-Koshki, K., Samiei, M., 2016. Silver nanoparticles: Synthesis methods, bio-applications and properties. Crit. Rev. Microbiol. 42,173-180. Abdal Dayem, A., Hossain, M.K., Lee, S.B., Kim, K., Saha, S.K., Yang, G.M., Choi, H.Y., Cho, S.G., 2017. The Role of Reactive Oxygen Species (ROS) in the Biological Activities of Metallic Nanoparticles. Int J Mol Sci. 18. Adlam, V.J., Harrison, J.C., Porteous, C.M., James, A.M., Smith, R.A.J., Murphy, M.P., Sammut, I.A., 2005. Targeting an antioxidant to mitochondria decreases cardiac ischemiareperfusion injury. FASEB J. 19,1088-1095. Ahn, C.S., Metallo, C.M., 2015. Mitochondria as biosynthetic factories for cancer proliferation. Cancer & Metabolism. 3. Alivisatos, A.P., 1996. Semiconductor clusters, nanocrystals, and quantum dots. Science. 271,933-937. Basit, F., van Oppen, L.M., Schockel, L., Bossenbroek, H.M., van Emst-de Vries, S.E., 19

Hermeling, J.C., Grefte, S., Kopitz, C., Heroult, M., Hgm Willems, P., Koopman, W.J., 2017. Mitochondrial complex I inhibition triggers a mitophagy-dependent ROS increase leading to necroptosis and ferroptosis in melanoma cells. Cell Death Dis. 8,e2716. Batley, G.E., Kirby, J.K., McLaughlin, M.J., 2013. Fate and Risks of Nanomaterials in Aquatic and Terrestrial Environments. Accounts Chem Res. 46,854-862. Belyaeva, E.A., Sokolova, T.V., Emelyanova, L.V., Zakharova, I.O., 2012. Mitochondrial Electron Transport Chain in Heavy Metal-Induced Neurotoxicity: Effects of Cadmium, Mercury, and Copper. Sci World J. Bertholet, A.M., Delerue, T., Millet, A.M., Moulis, M.F., David, C., Daloyau, M., ArnaunePelloquin, L., Davezac, N., Mils, V., Miquel, M.C., Rojo, M., Belenguer, P., 2016. Mitochondrial fusion/fission dynamics in neurodegeneration and neuronal plasticity. Neurobiol Dis. 90,3-19. Blaser, S.A., Scheringer, M., MacLeod, M., Hungerbuhler, K., 2008. Estimation of cumulative aquatic exposure and risk due to silver: Contribution of nano-functionalized plastics and textiles. Sci. Total Environ. 390,396-409. Bleier, L., Drose, S., 2013. Superoxide generation by complex III: from mechanistic rationales to functional consequences. Biochim. Biophys. Acta. 1827,1320-1331. Brand, M.D., Nicholls, D.G., 2011. Assessing mitochondrial dysfunction in cells. Biochem. J. 435,297-312. Burman, J.L., Pickles, S., Wang, C., Sekine, S., Vargas, J.N.S., Zhang, Z., Youle, A.M., Nezich, C.L., Wu, X., Hammer, J.A., Youle, R.J., 2017. Mitochondrial fission facilitates the selective mitophagy of protein aggregates. J. Cell Biol. 216,3231-3247. 20

Caballero-Guzman, A., Nowack, B., 2016. A critical review of engineered nanomaterial release data: Are current data useful for material flow modeling? Environ. Pollut. 213,502-517. Cao, M.J., Li, J.Y., Tang, J.L., Chen, C.Y., Zhao, Y.L., 2016. Gold Nanomaterials in Consumer Cosmetics Nanoproducts: Analyses, Characterization, and Dermal Safety Assessment. Small. 12,5488-5496. Chan, W.H., Shiao, N.H., Lu, P.Z., 2006. CdSe quantum dots induce apoptosis in human neuroblastoma cells via mitochondrial-dependent pathways and inhibition of survival signals. Toxicol. Lett. 167,191-200. Chen, L.B., 1988. Mitochondrial-Membrane Potential in Living Cells. Annual Review of Cell Biology. 4,155-181. Chen, Q., Wang, N.N., Zhu, M.J., Lu, J.H., Zhong, H.Q., Xue, X.L., Guo, S.Y., Li, M., Wei, X.B., Tao, Y.Z., Yin, H.Y., 2018. TiO2 nanoparticles cause mitochondrial dysfunction, activate inflammatory responses, and attenuate phagocytosis in macrophages: A proteomic and metabolomic insight. Redox Biology. 15,266-276. Chen, T., Zang, J.J., Wang, H.F., Nie, H.Y., Wang, X., Shen, Z.L., Tang, S.C., Yang, J.L., Jia, G., 2012. Water-Soluble Taurine-Functionalized Multi-Walled Carbon Nanotubes Induce Less Damage to Mitochondria of RAW 264.7 Cells. Journal of Nanoscience and Nanotechnology. 12,8008-8016. Choudhury, S.R., Ordaz, J., Lo, C.L., Damayanti, N.P., Zhou, F., Irudayaraj, J., 2017. From the Cover: Zinc oxide Nanoparticles-Induced Reactive Oxygen Species Promotes Multimodal Cyto- and Epigenetic Toxicity. Toxicol. Sci. 156,261-274. Clift, M.J.D., Brandenberger, C., Rothen-Rutishauser, B., Brown, D.M., Stone, V., 2011. The 21

uptake and intracellular fate of a series of different surface coated quantum dots in vitro. Toxicology. 286,58-68. Coffman, J.A., Coluccio, A., Planchart, A., Robertson, A.J., 2009. Oral-aboral axis specification in the sea urchin embryo III. Role of mitochondrial redox signaling via H2O2. Dev. Biol. 330,123-130. Cogliati, S., Enriquez, J.A., Scorrano, L., 2016. Mitochondrial Cristae: Where Beauty Meets Functionality. Trends Biochem. Sci. 41,261-273. Cogliati, S., Frezza, C., Soriano, M.E., Varanita, T., Quintana-Cabrera, R., Corrado, M., Cipolat, S., Costa, V., Casarin, A., Gomes, L.C., Perales-Clemente, E., Salviati, L., FernandezSilva, P., Enriquez, J.A., Scorrano, L., 2013. Mitochondrial Cristae Shape Determines Respiratory Chain Supercomplexes Assembly and Respiratory Efficiency. Cell. 155,160171. Costa, C.S., Ronconi, J.V., Daufenbach, J.F., Goncalves, C.L., Rezin, G.T., Streck, E.L., Paula, M.M., 2010. In vitro effects of silver nanoparticles on the mitochondrial respiratory chain. Mol. Cell. Biochem. 342,51-56. Ellenrieder, L., Rampelt, H., Becker, T., 2017. Connection of Protein Transport and Organelle Contact Sites in Mitochondria. J. Mol. Biol. 429,2148-2160. Esteve-Turrillas, F.A., Abad-Fuentes, A., 2013. Applications of quantum dots as probes in immunosensing of small-sized analytes. Biosensors & Bioelectronics. 41,12-29. Friedman, J.R., Nunnari, J., 2014. Mitochondrial form and function. Nature. 505,335-343. Galluzzi, L., Vitale, I., Aaronson, S.A., Abrams, J.M., Adam, D., Agostinis, P., Alnemri, E.S., Altucci, L., Amelio, I., Andrews, D.W., Annicchiarico-Petruzzelli, M., Antonov, A.V., 22

Arama, E., Baehrecke, E.H., Barlev, N.A., Bazan, N.G., Bernassola, F., Bertrand, M.J.M., Bianchi, K., Blagosklonny, M.V., Blomgren, K., Borner, C., Boya, P., Brenner, C., Campanella, M., Candi, E., Carmona-Gutierrez, D., Cecconi, F., Chan, F.K.M., Chandel, N.S., Cheng, E.H., Chipuk, J.E., Cidlowski, J.A., Ciechanover, A., Cohen, G.M., Conrad, M., Cubillos-Ruiz, J.R., Czabotar, P.E., D'Angiolella, V., Dawson, T.M., Dawson, V.L., De Laurenzi, V., De Maria, R., Debatin, K.M., DeBerardinis, R.J., Deshmukh, M., Di Daniele, N., Di Virgilio, F., Dixit, V.M., Dixon, S.J., Duckett, C.S., Dynlacht, B.D., ElDeiry, W.S., Elrod, J.W., Fimia, G.M., Fulda, S., Garcia-Saez, A.J., Garg, A.D., Garrido, C., Gavathiotis, E., Golstein, P., Gottlieb, E., Green, D.R., Greene, L.A., Gronemeyer, H., Gross, A., Hajnoczky, G., Hardwick, J.M., Harris, I.S., Hengartner, M.O., Hetz, C., Ichijo, H., Jaattela, M., Joseph, B., Jost, P.J., Juin, P.P., Kaiser, W.J., Karin, M., Kaufmann, T., Kepp, O., Kimchi, A., Kitsis, R.N., Klionsky, D.J., Knight, R.A., Kumar, S., Lee, S.W., Lemasters, J.J., Levine, B., Linkermann, A., Lipton, S.A., Lockshin, R.A., Lopez-Otin, C., Lowe, S.W., Luedde, T., Lugli, E., MacFarlane, M., Madeo, F., Malewicz, M., Malorni, W., Manic, G., Marine, J.C., Martin, S.J., Martinou, J.C., Medema, J.P., Mehlen, P., Meier, P., Melino, S., Miao, E.A., Molkentin, J.D., Moll, U.M., Munoz-Pinedo, C., Nagata, S., Nunez, G., Oberst, A., Oren, M., Overholtzer, M., Pagano, M., Panaretakis, T., Pasparakis, M., Penninger, J.M., Pereira, D.M., Pervaiz, S., Peter, M.E., Piacentini, M., Pinton, P., Prehn, J.H.M., Puthalakath, H., Rabinovich, G.A., Rehm, M., Rizzuto, R., Rodrigues, C.M.P., Rubinsztein, D.C., Rudel, T., Ryan, K.M., Sayan, E., Scorrano, L., Shao, F., Shi, Y.F., Silke, J., Simon, H.U., Sistigu, A., Stockwell, B.R., Strasser, A., Szabadkai, G., Tait, S.W.G., Tang, D.L., Tavernarakis, N., Thorburn, A., Tsujimoto, Y., Turk, B., Vanden 23

Berghe, T., Vandenabeele, P., Heiden, M.G.V., Villunger, A., Virgin, H.W., Vousden, K.H., Vucic, D., Wagner, E.F., Walczak, H., Wallach, D., Wang, Y., Wells, J.A., Wood, W., Yuan, J.Y., Zakeri, Z., Zhivotovsky, B., Zitvogel, L., Melino, G., Kroemer, G., 2018. Molecular mechanisms of cell death: recommendations of the Nomenclature Committee on Cell Death 2018. Cell Death Differ. 25,486-541. Plackal Adimuriyil George, B., Kumar, N., Abrahamse, H., Ray, S.S., 2018. Apoptotic efficacy of multifaceted biosynthesized silver nanoparticles on human adenocarcinoma cells. Sci Rep. 8,14368. Ghanbari, F., Nasarzadeh, P., Seydi, E., Ghasemi, A., Taghi Joghataei, M., Ashtari, K., Akbari, M., 2017. Mitochondrial oxidative stress and dysfunction induced by single- and multiwall carbon nanotubes: A comparative study. J. Biomed. Mater. Res. A. 105,2047-2055. Ghanbary, F., Seydi, E., Naserzadeh, P., Salimi, A., 2018. Toxicity of nanotitanium dioxide (TiO2-NP) on human monocytes and their mitochondria. Environmental Science and Pollution Research. 25,6739-6750. Han, J.W., Gurunathan, S., Choi, Y.J., Kim, J.H., 2017. Dual functions of silver nanoparticles in F9 teratocarcinoma stem cells, a suitable model for evaluating cytotoxicity- and differentiation-mediated cancer therapy. Int J Nanomedicine. 12,7529-7549. Han, X., Lei, J., Chen, K., Li, Q., Hao, H., Zhou, T., Jiang, F.L., Li, M., Liu, Y., 2019. Cytotoxicity of CdTe quantum dots with different surface coatings against yeast Saccharomyces cerevisiae. Ecotoxicol. Environ. Saf. 174,467-474. Handford, C.E., Dean, M., Henchion, M., Spence, M., Elliott, C.T., Campbell, K., 2014. Implications of nanotechnology for the agri-food industry: Opportunities, benefits and 24

risks. Trends Food Sci. Technol. 40,226-241. He, L., You, S., Gong, H., Zhang, J., Wang, L., Zhang, C., Huang, Y., Zhong, C., Zou, Y., 2017. Cigarette smoke induces rat testicular injury via mitochondrial apoptotic pathway. Mol. Reprod. Dev. 84,1053-1065. Hincapie, I., Caballero-Guzman, A., Hiltbrunner, D., Nowack, B., 2015. Use of engineered nanomaterials in the construction industry with specific emphasis on paints and their flows in construction and demolition waste in Switzerland. Waste Manag. 43,398-406. Hirsch, A., 2010. The era of carbon allotropes. Nat Mater. 9,868-871. Hong, F.S., Zhao, X.Y., Chen, M., Zhou, Y.J., Ze, Y.G., Wang, L., Wang, Y.J., Ge, Y.S., Zhang, Q., Ye, L.Q., 2016. TiO2 nanoparticles-induced apoptosis of primary cultured Sertoli cells of mice. Journal of Biomedical Materials Research Part A. 104,124-135. Hou, Y.H., Lai, M., Chen, X.Y., Li, J.H., Hu, Y., Luo, Z., Ding, X.W., Cai, K.Y., 2014. Effects of mesoporous SiO2, Fe3O4, and TiO2 nanoparticles on the biological functions of endothelial cells in vitro. Journal of Biomedical Materials Research Part A. 102,17261736. Hu, X.G., Ouyang, S.H., Mu, L., An, J., Zhou, Q., 2015. Effects of Graphene Oxide and Oxidized Carbon Nanotubes on the Cellular Division, Microstructure, Uptake, Oxidative Stress, and Metabolic Profiles. Environ. Sci. Technol. 49,10825-10833. Huerta-Garcia, E., Perez-Arizti, J.A., Marquez-Ramirez, S.G., Delgado-Buenrostro, N.L., Chirino, Y.I., Iglesias, G.G., Lopez-Marure, R., 2014. Titanium dioxide nanoparticles induce strong oxidative stress and mitochondrial damage in glial cells. Free Radic Biol Med. 73,84-94. 25

Hurst, S., Hoek, J., Sheu, S.S., 2017. Mitochondrial Ca(2+) and regulation of the permeability transition pore. J. Bioenerg. Biomembr. 49,27-47. Hwang, H.J., Dornbos, P., Steidemann, M., Dunivin, T.K., Rizzo, M., LaPres, J.J., 2016. Mitochondrial-targeted aryl hydrocarbon receptor and the impact of 2,3,7,8tetrachlorodibenzo-p-dioxin on cellular respiration and the mitochondrial proteome. Toxicol. Appl. Pharmacol. 304,121-132. Jain, A.K., Senapati, V.A., Singh, D., Dubey, K., Maurya, R., Pandey, A.K., 2017. Impact of anatase titanium dioxide nanoparticles on mutagenic and genotoxic response in Chinese hamster lung fibroblast cells (V-79): The role of cellular uptake. Food Chem. Toxicol. 105,127-139. Jariwala, D., Sangwan, V.K., Lauhon, L.J., Marks, T.J., Hersam, M.C., 2013. Carbon nanomaterials for electronics, optoelectronics, photovoltaics, and sensing. Chem Soc Rev. 42,2824-2860. Jaworski, S., Strojny, B., Sawosz, E., Wierzbicki, M., Grodzik, M., Kutwin, M., Daniluk, K., Chwalibog, A., 2019. Degradation of Mitochondria and Oxidative Stress as the Main Mechanism of Toxicity of Pristine Graphene on U87 Glioblastoma Cells and Tumors and HS-5 Cells. International Journal of Molecular Sciences. 20. Jayaram, D.T., Runa, S., Kemp, M.L., Payne, C.K., 2017. Nanoparticle-induced oxidation of corona proteins initiates an oxidative stress response in cells. Nanoscale. 9,7595-7601. Jia, X.C., Wang, S., Zhou, L., Sun, L., 2017. The Potential Liver, Brain, and Embryo Toxicity of Titanium Dioxide Nanoparticles on Mice. Nanoscale Research Letters. 12. John, A.C., Kupper, M., Manders-Groot, A.M.M., Debray, B., Lacome, J.M., Kuhlbusch, 26

T.A.J., 2017. Emissions and Possible Environmental Implication of Engineered Nanomaterials (ENMs) in the Atmosphere. Atmosphere-Basel. 8. Johnson-Lyles, D.N., Peifley, K., Lockett, S., Neun, B.W., Hansen, M., Clogston, J., Stern, S.T., McNeil, S.E., 2010. Fullerenol cytotoxicity in kidney cells is associated with cytoskeleton disruption, autophagic vacuole accumulation, and mitochondrial dysfunction. Toxicol. Appl. Pharmacol. 248,249-258. Karlsson, H.L., Gustafsson, J., Cronholm, P., Moller, L., 2009. Size-dependent toxicity of metal oxide particles-A comparison between nano- and micrometer size. Toxicol. Lett. 188,112118. Kim, G.H., Ramesh, S., Kim, J.H., Jung, D., Kim, H.S., 2014. Cellulose-silica/gold nanomaterials for electronic applications. J Nanosci Nanotechnol. 14,7495-7501. Kim, S.W., Lee, Y.K., Lee, J.Y., Hong, J.H., Khang, D., 2017. PEGylated anticancer-carbon nanotubes complex targeting mitochondria of lung cancer cells. Nanotechnology. 28. Kovacs, D., Igaz, N., Keskeny, C., Belteky, P., Toth, T., Gaspar, R., Madarasz, D., Razga, Z., Konya, Z., Boros, I.M., Kiricsi, M., 2016. Silver nanoparticles defeat p53-positive and p53-negative osteosarcoma cells by triggering mitochondrial stress and apoptosis. Sci Rep. 6,27902. Lai, L., Jin, J.C., Xu, Z.Q., Mei, P., Jiang, F.L., Liu, Y., 2015. Necrotic cell death induced by the protein-mediated intercellular uptake of CdTe quantum dots. Chemosphere. 135,240249. Lai, L., Li, Y.P., Mei, P., Chen, W., Jiang, F.L., Liu, Y., 2016. Size Effects on the Interaction of QDs with the Mitochondrial Membrane In Vitro. J. Membr. Biol. 249,757-767. 27

Lai, R.W.S., Yeung, K.W.Y., Yung, M.M.N., Djurisic, A.B., Giesy, J.P., Leung, K.M.Y., 2018. Regulation of engineered nanomaterials: current challenges, insights and future directions. Environmental Science and Pollution Research. 25,3060-3077. Lammel, T., Boisseaux, P., Fernandez-Cruz, M.L., Navas, J.M., 2013. Internalization and cytotoxicity of graphene oxide and carboxyl graphene nanoplatelets in the human hepatocellular carcinoma cell line Hep G2. Particle and Fibre Toxicology. 10. Larosa, V., Remacle, C., 2018. Insights into the respiratory chain and oxidative stress. Bioscience Reports. 38. Lead, J.R., Batley, G.E., Alvarez, P.J.J., Croteau, M.N., Handy, R.D., McLaughlin, M.J., Judy, J.D., Schirmer, K., 2018. Nanomaterials in the environment: Behavior, fate, bioavailability, and effects-An updated review. Environ. Toxicol. Chem. 37,2029-2063. Li, J.H., Zhang, Y., Xiao, Q., Tian, F.F., Liu, X.R., Li, R., Zhao, G.Y., Jiang, F.L., Liu, Y., 2011. Mitochondria as target of Quantum dots toxicity. J. Hazard. Mater. 194,440-444. Li, L., Cui, J., Liu, Z., Zhou, X., Li, Z., Yu, Y., Jia, Y., Zuo, D., Wu, Y., 2018. Silver nanoparticles induce SH-SY5Y cell apoptosis via endoplasmic reticulum- and mitochondrial pathways that lengthen endoplasmic reticulum-mitochondria contact sites and alter inositol-3-phosphate receptor function. Toxicol. Lett. 285,156-167. Li, Y.P., Wu, Q.L., Zhao, Y.L., Bai, Y.F., Chen, P.S., Xia, T., Wang, D.Y., 2014. Response of MicroRNAs to In Vitro Treatment with Graphene Oxide. Acs Nano. 8,2100-2110. Liang, S., Sun, K., Wang, Y., Dong, S., Wang, C., Liu, L., Wu, Y., 2016. Role of CytC/caspases-9,3, Bax/Bcl-2 and the FAS death receptor pathway in apoptosis induced by zinc oxide nanoparticles in human aortic endothelial cells and the protective effect by 28

alpha-lipoic acid. Chem Biol Interact. 258,40-51. Lin, C.H., Chang, L.W., Wei, Y.H., Wu, S.B., Yang, C.S., Chang, W.H., Chen, Y.C., Lin, P.P., 2012. Electronic microscopy evidence for mitochondria as targets for Cd/Se/Te-based quantum dot 705 toxicity in vivo. Kaohsiung Journal of Medical Sciences. 28,S53-S62. Liu, X.Y., Braun, G.B., Qin, M.D., Ruoslahti, E., Sugahara, K.N., 2017. In vivo cation exchange in quantum dots for tumor-specific imaging. Nature Communications. 8. Liu, Z., Dong, X., Song, L., Zhang, H., Liu, L., Zhu, D., Song, C., Leng, X., 2014a. Carboxylation of multiwalled carbon nanotube enhanced its biocompatibility with L02 cells through decreased activation of mitochondrial apoptotic pathway. J. Biomed. Mater. Res. A. 102,665-673. Liu, Z.B., Liu, Y.F., Peng, D.M., 2014b. Hydroxylation of multi-walled carbon nanotubes reduces their cytotoxicity by limiting the activation of mitochondrial mediated apoptotic pathway. Journal of Materials Science-Materials in Medicine. 25,1033-1044. Ma, X., Zhang, L.H., Wang, L.R., Xue, X., Sun, J.H., Wu, Y., Zou, G., Wu, X., Wang, P.C., Wamer, W.G., Yin, J.J., Zheng, K., Liang, X.J., 2012. Single-walled carbon nanotubes alter cytochrome c electron transfer and modulate mitochondrial function. ACS Nano. 6,10486-10496. Ma, Y.X., Wang, M.X., Li, W., Zhang, Z.P., Zhang, X.W., Tan, T.W., Zhang, X.E., Cui, Z.Q., 2017. Live cell imaging of single genomic loci with quantum dot-labeled TALEs. Nature Communications. 8. Madhumitha, G., Elango, G., Roopan, S.M., 2016. Biotechnological aspects of ZnO nanoparticles: overview on synthesis and its applications. Appl. Microbiol. Biotechnol. 29

100,571-581. Marchi, S., Patergnani, S., Missiroli, S., Morciano, G., Rimessi, A., Wieckowski, M.R., Giorgi, C., Pinton, P., 2018. Mitochondrial and endoplasmic reticulum calcium homeostasis and cell death. Cell Calcium. 69,62-72. Mari, E., Mardente, S., Morgante, E., Tafani, M., Lococo, E., Fico, F., Valentini, F., Zicari, A., 2016. Graphene Oxide Nanoribbons Induce Autophagic Vacuoles in Neuroblastoma Cell Lines. International Journal of Molecular Sciences. 17. Mashayekhi, V., Eskandari, M.R., Kobarfard, F., Khajeamiri, A., Hosseini, M.J., 2014. Induction of mitochondrial permeability transition (MPT) pore opening and ROS formation as a mechanism for methamphetamine-induced mitochondrial toxicity. NaunynSchmiedeberg's Arch. Pharmacol. 387,47-58. Matea, C.T., Mocan, T., Tabaran, F., Pop, T., Mosteanu, O., Puia, C., Iancu, C., Mocan, L., 2017. Quantum dots in imaging, drug delivery and sensor applications. International Journal of Nanomedicine. 12,5421-5431. Mathur, P., Jha, S., Ramteke, S., Jain, N.K., 2018. Pharmaceutical aspects of silver nanoparticles. Artif Cells Nanomed Biotechnol. 46,115-126. Maurer, L.L., Meyer, J.N., 2016. A systematic review of evidence for silver nanoparticleinduced mitochondrial toxicity. Environmental Science-Nano. 3,311-322. Mazunin, I.O., Levitskii, S.A., Patrushev, M.V., Kamenski, P.A., 2015. Mitochondrial Matrix Processes. Biochemistry (Mosc). 80,1418-1428. Mercer, T.R., Neph, S., Dinger, M.E., Crawford, J., Smith, M.A., Shearwood, A.M.J., Haugen, E., Bracken, C.P., Rackham, O., Stamatoyannopoulos, J.A., Filipovska, A., Mattick, J.S., 30

2011. The Human Mitochondrial Transcriptome. Cell. 146,645-658. Meyer, J.N., Leuthner, T.C., Luz, A.L., 2017. Mitochondrial fusion, fission, and mitochondrial toxicity. Toxicology. 391,42-53. Mnatsakanyan, N., Beutner, G., Porter, G.A., Alavian, K.N., Jonas, E.A., 2017. Physiological roles of the mitochondrial permeability transition pore. J. Bioenerg. Biomembr. 49,13-25. Mukherjee, A., Shim, Y., Song, J.M., 2016. Quantum dot as probe for disease diagnosis and monitoring. Biotechnology Journal. 11,31-42. Nakagawa, Y., Inomata, A., Ogata, A., Nakae, D., 2015. Comparative effects of sulfhydryl compounds on target organellae, nuclei and mitochondria, of hydroxylated fullereneinduced cytotoxicity in isolated rat hepatocytes. J. Appl. Toxicol. 35,1465-1472. Naserzadeh, P., Ansari Esfeh, F., Kaviani, M., Ashtari, K., Kheirbakhsh, R., Salimi, A., Pourahmad, J., 2018. Single-walled carbon nanotube, multi-walled carbon nanotube and Fe2O3 nanoparticles induced mitochondria mediated apoptosis in melanoma cells. Cutan. Ocul. Toxicol. 37,157-166. Nassir, F., Ibdah, J.A., 2014. Role of mitochondria in alcoholic liver disease. World Journal of Gastroenterology. 20,2136-2142. Natarajan, V., Wilson, C.L., Hayward, S.L., Kidambi, S., 2015. Titanium Dioxide Nanoparticles Trigger Loss of Function and Perturbation of Mitochondrial Dynamics in Primary Hepatocytes. PloS one. 10. Nguyen, K.C., Rippstein, P., Tayabali, A.F., Willmore, W.G., 2015. Mitochondrial Toxicity of Cadmium Telluride Quantum Dot Nanoparticles in Mammalian Hepatocytes. Toxicol. Sci. 146,31-42. 31

Nguyen, K.C., Willmore, W.G., Tayabali, A.F., 2013. Cadmium telluride quantum dots cause oxidative stress leading to extrinsic and intrinsic apoptosis in hepatocellular carcinoma HepG2 cells. Toxicology. 306,114-123. Ni, H.M., Williams, J.A., Ding, W.X., 2015. Mitochondrial dynamics and mitochondrial quality control. Redox Biol. 4,6-13. Ostaszewska, T., Sliwinski, J., Kamaszewski, M., Sysa, P., Chojnacki, M., 2018. Cytotoxicity of silver and copper nanoparticles on rainbow trout (Oncorhynchus mykiss) hepatocytes. Environ Sci Pollut Res Int. 25,908-915. Paesano, L., Perotti, A., Buschini, A., Carubbi, C., Marmiroli, M., Maestri, E., Iannotta, S., Marmiroli, N., 2016. Markers for toxicity to HepG2 exposed to cadmium sulphide quantum dots; damage to mitochondria. Toxicology. 374,18-28. Palikaras, K., Lionaki, E., Tavernarakis, N., 2018. Mechanisms of mitophagy in cellular homeostasis, physiology and pathology. Nat. Cell Biol. 20,1013-1022. Park, E.J., Lee, G.H., Han, B.S., Lee, B.S., Lee, S., Cho, M.H., Kim, J.H., Kim, D.W., 2015. Toxic response of graphene nanoplatelets in vivo and in vitro. Arch. Toxicol. 89,15571568. Park, E.J., Lee, S.Y., Lee, G.H., Kim, D.W., Kim, Y., Cho, M.H., Kim, J.H., 2014a. Sheet-type titania, but not P25, induced paraptosis accompanying apoptosis in murine alveolar macrophage cells. Toxicol. Lett. 230,69-79. Park, E.J., Zahari, N.E.M., Lee, E.W., Song, J., Lee, J.H., Cho, M.H., Kim, J.H., 2014b. SWCNTs induced autophagic cell death in human bronchial epithelial cells. Toxicol. In Vitro. 28,442-450. 32

Pasquali, F., Agrimonti, C., Pagano, L., Zappettini, A., Villani, M., Marmiroli, M., White, J.C., Marmiroli, N., 2017. Nucleo-mitochondrial interaction of yeast in response to cadmium sulfide quantum dot exposure. J. Hazard. Mater. 324,744-752. Passmore, J.B., Pinho, S., Gomez-Lazaro, M., Schrader, M., 2017. The respiratory chain inhibitor rotenone affects peroxisomal dynamics via its microtubule-destabilising activity. Histochem Cell Biol. 148,331-341. Pereira, L.C., Pazin, M., Franco-Bernardes, M.F., Martins, A.D.C., Jr., Barcelos, G.R.M., Pereira, M.C., Mesquita, J.P., Rodrigues, J.L., Barbosa, F., Jr., Dorta, D.J., 2018. A perspective of mitochondrial dysfunction in rats treated with silver and titanium nanoparticles (AgNPs and TiNPs). J Trace Elem Med Biol. 47,63-69. Pinegin, B., Vorobjeva, N., Pashenkov, M., Chernyak, B., 2018. The role of mitochondrial ROS in antibacterial immunity. J Cell Physiol. 233,3745-3754. Quintana-Cabrera, R., Mehrotra, A., Rigoni, G., Soriano, M.E., 2018. Who and how in the regulation of mitochondrial cristae shape and function. Biochem. Biophys. Res. Commun. 500,94-101. Rai, P.K., Kumar, V., Lee, S., Raza, N., Kim, K.H., Ok, Y.S., Tsang, D.C.W., 2018. Nanoparticle-plant interaction: Implications in energy, environment, and agriculture. Environ. Int. 119,1-19. Raimundo, N., Song, L., Shutt, T.E., McKay, S.E., Cotney, J., Guan, M.X., Gilliland, T.C., Hohuan, D., Santos-Sacchi, J., Shadel, G.S., 2012. Mitochondrial stress engages E2F1 apoptotic signaling to cause deafness. Cell. 148,716-726. Rathor, S., Bhatt, D.C., Aamir, S., Singh, S.K., Kumar, V., 2017. A Comprehensive Review on 33

Role of Nanoparticles in Therapeutic Delivery of Medicine. Pharm Nanotechnol. 5,263275. Ren, C.X., Hu, X.G., Li, X.Y., Zhou, Q.X., 2016. Ultra-trace graphene oxide in a water environment triggers Parkinson's disease-like symptoms and metabolic disturbance in zebrafish larvae. Biomaterials. 93,83-94. Reshma, V.G., Mohanan, P.V., 2017. Cellular interactions of zinc oxide nanoparticles with human embryonic kidney (HEK 293) cells. Colloid Surface B. 157,182-190. Russell, A.P., Foletta, V.C., Snow, R.J., Wadley, G.D., 2014. Skeletal muscle mitochondria: A major player in exercise, health and disease. Biochimica Et Biophysica Acta-General Subjects. 1840,1276-1284. Saeed, L.M., Mahmood, M., Pyrek, S.J., Fahmi, T., Xu, Y., Mustafa, T., Nima, Z.A., Bratton, S.M., Casciano, D., Dervishi, E., Radominska-Pandya, A., Biris, A.S., 2014. Singlewalled carbon nanotube and graphene nanodelivery of gambogic acid increases its cytotoxicity in breast and pancreatic cancer cells. J. Appl. Toxicol. 34,1188-1199. Santiago, D.J., Dries, E., Lenaerts, I., Sipido, K.R., 2015. Altered Ryanodine Receptor Function in Ischemic Heart Disease: Is there a Role for Mitochondria? Biophys. J. 108,567a-567a. Santos, S.M., Dinis, A.M., Peixoto, F., Ferreira, L., Jurado, A.S., Videira, R.A., 2014. Interaction of fullerene nanoparticles with biomembranes: from the partition in lipid membranes to effects on mitochondrial bioenergetics. Toxicol. Sci. 138,117-129. Sarniak, A., Lipinska, J., Tytman, K., Lipinska, S., 2016. Endogenous mechanisms of reactive oxygen species (ROS) generation. Postepy Hig Med Dosw (Online). 70,1150-1165. Scialo, F., Fernandez-Ayala, D.J., Sanz, A., 2017. Role of Mitochondrial Reverse Electron 34

Transport in ROS Signaling: Potential Roles in Health and Disease. Front Physiol. 8,428. Serasinghe, M.N., Chipuk, J.E., 2017. Mitochondrial Fission in Human Diseases. Handb Exp Pharmacol. 240,159-188. Service, R.F., 2003. American Chemical Society meeting: Nanomaterials show signs of toxicity. Science. 300,243-243. Sharma, A.K., Singh, V., Gera, R., Purohit, M.P., Ghosh, D., 2017. Zinc Oxide Nanoparticle Induces Microglial Death by NADPH-Oxidase-Independent Reactive Oxygen Species as well as Energy Depletion. Mol. Neurobiol. 54,6273-6286. Sheng, L., Ze, Y.G., Wang, L., Yu, X.H., Hong, J., Zhao, X.Y., Ze, X., Liu, D., Xu, B.Q., Zhu, Y., Long, Y., Lin, A.A., Zhang, C., Zhao, Y., Hong, F.H., 2015. Mechanisms of TiO2 nanoparticle-induced neuronal apoptosis in rat primary cultured hippocampal neurons. Journal of Biomedical Materials Research Part A. 103,1141-1149. Shi, H.B., Magaye, R., Castranova, V., Zhao, J.S., 2013. Titanium dioxide nanoparticles: a review of current toxicological data. Particle and Fibre Toxicology. 10. Shoshan-Barmatz, V., Ben-Hail, D., Admoni, L., Krelin, Y., Tripathi, S.S., 2015. The mitochondrial voltage-dependent anion channel 1 in tumor cells. Biochimica Et Biophysica Acta-Biomembranes. 1848,2547-2575. Simoes, I.C.M., Fontes, A., Pinton, P., Zischka, H., Wieckowski, M.R., 2018. Mitochondria in non-alcoholic fatty liver disease. International Journal of Biochemistry & Cell Biology. 95,93-99. Song, B., Zhou, T., Yang, W., Liu, J., Shao, L., 2016. Contribution of oxidative stress to TiO2 nanoparticle-induced toxicity. Environ. Toxicol. Pharmacol. 48,130-140. 35

Song, M., Yuan, S., Yin, J., Wang, X., Meng, Z., Wang, H., Jiang, G., 2012. Size-dependent toxicity of nano-C60 aggregates: more sensitive indication by apoptosis-related Bax translocation in cultured human cells. Environ. Sci. Technol. 46,3457-3464. Srinivasan, S., Guha, M., Kashina, A., Avadhani, N.G., 2017. Mitochondrial dysfunction and mitochondrial dynamics-The cancer connection. Biochim Biophys Acta Bioenerg. 1858,602-614. Sruthi, S., Millot, N., Mohanan, P.V., 2017. Zinc oxide nanoparticles mediated cytotoxicity, mitochondrial membrane potential and level of antioxidants in presence of melatonin. Int J Biol Macromol. 103,808-818. Sun, Q., Zhong, W., Zhang, W., Zhou, Z., 2016. Defect of mitochondrial respiratory chain is a mechanism of ROS overproduction in a rat model of alcoholic liver disease: role of zinc deficiency. Am J Physiol Gastrointest Liver Physiol. 310,G205-214. Tan, J.W., Ho, C.F., Ng, Y.K., Ong, W.Y., 2016. Docosahexaenoic acid and L-Carnitine prevent ATP loss in SH-SY5Y neuroblastoma cells after exposure to silver nanoparticles. Environ. Toxicol. 31,224-232. Tang, J., Lu, X., Chen, B., Cai, E., Liu, W., Jiang, J., Chen, F., Shan, X., Zhang, H., 2019. Mechanisms of silver nanoparticles-induced cytotoxicity and apoptosis in rat tracheal epithelial cells. J. Toxicol. Sci. 44,155-165. Tee, J.K., Ong, C.N., Bay, B.H., Ho, H.K., Leong, D.T., 2016. Oxidative stress by inorganic nanoparticles. Wiley Interdiscip Rev Nanomed Nanobiotechnol. 8,414-438. Teodoro, J.S., Silva, R., Varela, A.T., Duarte, F.V., Rolo, A.P., Hussain, S., Palmeira, C.M., 2016. Low-dose, subchronic exposure to silver nanoparticles causes mitochondrial 36

alterations in Sprague-Dawley rats. Nanomedicine (Lond). 11,1359-1375. Teradal, N.L., Jelinek, R., 2017. Carbon Nanomaterials in Biological Studies and Biomedicine. Adv Healthc Mater. 6. Tsujimoto, Y., Shimizu, S., 2007. Role of the mitochondrial membrane permeability transition in cell death. Apoptosis. 12,835-840. Um, J.H., Yun, J., 2017. Emerging role of mitophagy in human diseases and physiology. BMB Rep. 50,299-307. Vance, M.E., Kuiken, T., Vejerano, E.P., McGinnis, S.P., Hochella, M.F., Rejeski, D., Hull, M.S., 2015. Nanotechnology in the real world: Redeveloping the nanomaterial consumer products inventory. Beilstein Journal of Nanotechnology. 6,1769-1780. Vigie, P., Camougrand, N., 2017. [Role of mitophagy in the mitochondrial quality control]. Med Sci (Paris). 33,231-237. Vinogradov, A.D., Grivennikova, V.G., 2016. Oxidation of NADH and ROS production by respiratory complex I. Biochim. Biophys. Acta. 1857,863-871. Visalli, G., Curro, M., Iannazzo, D., Pistone, A., Pruiti Ciarello, M., Acri, G., Testagrossa, B., Bertuccio, M.P., Squeri, R., Di Pietro, A., 2017. In vitro assessment of neurotoxicity and neuroinflammation of homemade MWCNTs. Environ. Toxicol. Pharmacol. 56,121-128. Visalli, G., Facciola, A., Curro, M., Lagana, P., La Fauci, V., Iannazzo, D., Pistone, A., Di Pietro, A., 2019. Mitochondrial Impairment Induced by Sub-Chronic Exposure to MultiWalled Carbon Nanotubes. Int. J. Env. Res. Public Health. 16. Volkov, Y., 2015. Quantum dots in nanomedicine: recent trends, advances and unresolved issues. Biochem. Biophys. Res. Commun. 468,419-427. 37

Wallace, D.C., 2005. A mitochondrial paradigm of metabolic and degenerative diseases, aging, and cancer: a dawn for evolutionary medicine. Annu. Rev. Genet. 39,359-407. Wang, G., Guo, Y.M., Yang, G., Yang, L., Ma, X.M., Wang, K., Zhu, L., Sun, J.J., Wang, X.B., Zhang, H., 2016. Mitochondria-Mediated Protein Regulation Mechanism of PolymorphsDependent Inhibition of Nanoselenium on Cancer Cells. Sci Rep. 6,31427. Wang, J., Gao, S., Wang, S., Xu, Z., Wei, L., 2018a. Zinc oxide nanoparticles induce toxicity in CAL 27 oral cancer cell lines by activating PINK1/Parkin-mediated mitophagy. Int J Nanomedicine. 13,3441-3450. Wang, L., Chen, C., Guo, L., Li, Q., Ding, H., Bi, H., Guo, D., 2018b. Zinc oxide nanoparticles induce murine photoreceptor cell death via mitochondria-related signaling pathway. Artif Cells Nanomed Biotechnol. 46,1102-1113. Wang, X., Guo, J., Chen, T., Nie, H.Y., Wang, H.F., Zang, J.J., Cui, X.X., Jia, G., 2012. Multiwalled carbon nanotubes induce apoptosis via mitochondrial pathway and scavenger receptor. Toxicol. In Vitro. 26,799-806. Wang, Z., Dai, Z., 2015. Carbon nanomaterial-based electrochemical biosensors: an overview. Nanoscale. 7,6420-6431. Wei, L., Wang, J., Chen, A., Liu, J., Feng, X., Shao, L., 2017. Involvement of PINK1/parkinmediated mitophagy in ZnO nanoparticle-induced toxicity in BV-2 cells. Int J Nanomedicine. 12,1891-1903. Wilson, C.L., Natarajan, V., Hayward, S.L., Khalimonchuk, O., Kidambi, S., 2015. Mitochondrial dysfunction and loss of glutamate uptake in primary astrocytes exposed to titanium dioxide nanoparticles. Nanoscale. 7,18477-18488. 38

Wu, C.Y., Wang, C., Han, T., Zhou, X.J., Guo, S.W., Zhang, J.Y., 2013. Insight into the Cellular Internalization and Cytotoxicity of Graphene Quantum Dots. Advanced Healthcare Materials. 2,1613-1619. Xiang, X., Gao, T., Zhang, B.R., Jiang, F.L., Liu, Y., 2018. Surface functional groups affect CdTe QDs behavior at mitochondrial level. Toxicology Research. 7,1071-1080. Xin, L., Wang, J., Fan, G., Che, B., Wu, Y., Guo, S., Tong, J., 2016. Oxidative stress and mitochondrial injury-mediated cytotoxicity induced by silver nanoparticles in human A549 and HepG2 cells. Environ. Toxicol. 31,1691-1699. Xu, C., Liu, Q., Liu, H., Zhang, C., Shao, W., Gu, A., 2016. Toxicological assessment of multiwalled carbon nanotubes in vitro: potential mitochondria effects on male reproductive cells. Oncotarget. 7,39270-39278. Xue, C., Li, X., Liu, G., Liu, W., 2016a. Evaluation of Mitochondrial Respiratory Chain on the Generation of Reactive Oxygen Species and Cytotoxicity in HaCaT Cells Induced by Nanosized Titanium Dioxide Under UVA Irradiation. Int. J. Toxicol. 35,644-653. Xue, Y., Chen, Q.Q., Sun, J., 2017. Hydroxyapatite nanoparticle-induced mitochondrial energy metabolism impairment in liver cells: in vitro and in vivo studies. J. Appl. Toxicol. 37,1004-1016. Xue, Y., Zhang, T., Zhang, B., Gong, F., Huang, Y., Tang, M., 2016b. Cytotoxicity and apoptosis induced by silver nanoparticles in human liver HepG2 cells in different dispersion media. J. Appl. Toxicol. 36,352-360. Yamada, S., Yamazaki, D., Kanda, Y., 2018. Silver nanoparticles inhibit neural induction in human induced pluripotent stem cells. Nanotoxicology,1-11. 39

Yang, L.Y., Gao, J.L., Gao, T., Dong, P., Ma, L., Jiang, F.L., Liu, Y., 2016. Toxicity of polyhydroxylated fullerene to mitochondria. J. Hazard. Mater. 301,119-126. Yoong, S.L., Lau, W.L., Liu, A.Y., Prendergast, D., Ho, H.K., Yu, V.C.K., Lee, C., Ang, W.H., Pastorin, G., 2015. Mitochondria-acting hexokinase II peptides carried by short-length carbon nanotubes with increased cellular uptake, endosomal evasion, and enhanced bioactivity against cancer cells. Nanoscale. 7,13907-13917. Youle, R.J., van der Bliek, A.M., 2012. Mitochondrial fission, fusion, and stress. Science. 337,1062-1065. Yu, K.N., Chang, S.H., Park, S.J., Lim, J., Lee, J., Yoon, T.J., Kim, J.S., Cho, M.H., 2015. Titanium Dioxide Nanoparticles Induce Endoplasmic Reticulum Stress-Mediated Autophagic Cell Death via Mitochondria-Associated Endoplasmic Reticulum Membrane Disruption in Normal Lung Cells. Plos One. 10. Yu, K.N., Yoon, T.J., Minai-Tehrani, A., Kim, J.E., Park, S.J., Jeong, M.S., Ha, S.W., Lee, J.K., Kim, J.S., Cho, M.H., 2013. Zinc oxide nanoparticle induced autophagic cell death and mitochondrial damage via reactive oxygen species generation. Toxicol. In Vitro. 27,1187-1195. Yu, Q., Wang, H., Peng, Q., Li, Y., Liu, Z., Li, M., 2017. Different toxicity of anatase and rutile TiO2 nanoparticles on macrophages: Involvement of difference in affinity to proteins and phospholipids. J. Hazard. Mater. 335,125-134. Zamani, E., Shaki, F., AbedianKenari, S., Shokrzadeh, M., 2017. Acrylamide induces immunotoxicity through reactive oxygen species production and caspase-dependent apoptosis in mice splenocytes via the mitochondria-dependent signaling pathways. 40

Biomedicine & Pharmacotherapy. 94,523-530. Zhang, P., Li, H., Cheng, J., Sun, A.Y., Wang, L., Mirchevska, G., Calderone, R., Li, D., 2018a. Respiratory stress in mitochondrial electron transport chain complex mutants of Candida albicans activates Snf1 kinase response. Fungal Genet. Biol. 111,73-84. Zhang, Y.Q., Xu, B., Yao, M.M., Dong, T.Y., Mao, Z.L., Hang, B., Han, X.M., Lin, Z.N., Bian, Q., Li, M., Xia, Y.K., 2018b. Titanium dioxide nanoparticles induce proteostasis disruption and autophagy in human trophoblast cells. Chem.-Biol. Interact. 296,124-133. Zhao, X., Ren, X., Zhu, R., Luo, Z., Ren, B., 2016. Zinc oxide nanoparticles induce oxidative DNA damage and ROS-triggered mitochondria-mediated apoptosis in zebrafish embryos. Aquat. Toxicol. 180,56-70. Zhou, F.F., Wu, S.N., Wu, B.Y., Chen, W.R., Xing, D., 2011. Mitochondria-Targeting SingleWalled Carbon Nanotubes for Cancer Photothermal Therapy. Small. 7,2727-2735. Zhou, H.J., Zhang, B., Zheng, J.J., Yu, M.F., Zhou, T., Zhao, K., Jia, Y.X., Gao, X.F., Chen, C.Y., Wei, T.T., 2014a. The inhibition of migration and invasion of cancer cells by graphene via the impairment of mitochondrial respiration. Biomaterials. 35,1597-1607. Zhou, P.K., Huang, R.X., 2018. Targeting of the respiratory chain by toxicants: beyond the toxicities to mitochondrial morphology. Toxicol Res (Camb). 7,1008-1011. Zhou, T., Zhang, B., Wei, P., Du, Y.P., Zhou, H.J., Yu, M.F., Yan, L., Zhang, W.D., Nie, G.J., Chen, C.Y., Tu, Y.P., Wei, T.T., 2014b. Energy metabolism analysis reveals the mechanism of inhibition of breast cancer cell metastasis by PEG-modified graphene oxide nanosheets. Biomaterials. 35,9833-9843. Zhu, S., Luo, F., Li, J., Zhu, B., Wang, G.X., 2018. Biocompatibility assessment of single41

walled carbon nanotubes using Saccharomyces cerevisiae as a model organism. Journal of Nanobiotechnology. 16. Zhu, S., Zhu, B., Huang, A., Hu, Y., Wang, G., Ling, F., 2016. Toxicological effects of multiwalled carbon nanotubes on Saccharomyces cerevisiae: The uptake kinetics and mechanisms and the toxic responses. J. Hazard. Mater. 318,650-662. Zou, W., Zhou, Q.X., Zhang, X.L., Mu, L., Hu, X.G., 2018. Characterization of the effects of trace concentrations of graphene oxide on zebrafish larvae through proteomic and standard methods. Ecotoxicol. Environ. Saf. 159,221-231. Zulian, A., Schiavone, M., Giorgio, V., Bernardi, P., 2016. Forty years later: Mitochondria as therapeutic targets in muscle diseases. Pharmacol. Res. 113,563-573.

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Figure legends Figure 1. Mitochondrial structure and function. The main function of mitochondria is to produce ATP, which is achieved via electron transport of respiratory chain complexes embedded in the cristae. ROS are generated during electron transport, and complexes I and III are the main source of mtROS. mtDNA in the mitochondrial matrix encodes the majority of oxidative phosphorylation enzyme complexes. MPTPs are composed of transmembrane proteins on the inner and outer membranes of mitochondria and involved in the regulation of intracellular calcium homeostasis and ATP/ADP transport. Figure 2. Role of mitochondria in nanomaterial-induced toxicity. When cells are exposed to environmental stress (such as elevated ROS) induced by nanomaterials, mitochondrial dynamics are regulated to control mitochondrial quality and maintain cell homeostasis. Under slight environmental stress, mitochondria promote production of ATP and reduce the influence of stress through fusion. Under high environmental stress, cells are protected through proper fission of mitochondria and mitophagy. Nanomaterials also cause production of excess ROS by affecting the activity or expression of respiratory chain complexes, thereby further affecting mitochondrial dynamics and structure and leading to decreased MMP and ATP production. In addition, some nanomaterials induce structural damage upon entry into mitochondria, causing a decrease in the bcl-2/bax ratio and opening of MPTP. Eventually, cytochrome C is released into the cytoplasm, triggering mitochondria-mediated apoptosis.

43

Table legends Table 1. Physicochemical properties of metal and metal oxide nanomaterials and corresponding tissue-specific and cell-specific mitochondrial toxicity Table 2. Physicochemical properties of carbon nanomaterials and corresponding tissuespecific and cell-specific mitochondrial toxicity Table 3. Physicochemical properties of quantum dots and corresponding tissue-specific and cell-specific mitochondrial toxicity

44

45

46

Table 1. Physicochemical properties of metal and metal oxide nanomaterials and corresponding tissue-specific and cell-specific mitochondrial toxicity S.

NMs type

Size(nm)

No.

Target organ or cell

Concentration or exposure

type used

route,

time

Mitochondrial effects

Reference

and

concentration 1

TiO2-NPs

<50nm

Rat and human glial

20µg/cm2

Mitochondrial depolarization

Huerta-

cells(C6 and U373)

Garcia et al. (2014)

2

TiO2-NPs

117±19nm

Endothelial cells

0.1, 0.15, 0.2 mg/mL

Decreased number of mitochondria, mitochondrial swelling

3

TiO2-NPs

5-6nm

Primary hippocampal

5, 15, 30µg/mL

Hou et al. (2014)

Decreased MMP, increased release of Cyto-c

neurons in Sprague-

Sheng et al. (2015)

Dawley rats 4

TiO2-NPs

5-6nm.

Primary Sertoli cells

5, 15, 30µg/mL

Decreased MMP and increased

release of Cyto-c

isolated from mice 5

TiO2-

21-50nm

NPs(rutile, anatase

Primary

Hong et al. (2016)

rat

20, 50,100ppm

hepatocytes and

MMP reduction, OPA-1 and Mfn-1 expression

Natarajan

levels were significantly down-regulated when

et al. (2015)

exposed to 50ppm P25 and anatase

P25) 6

TiO2-NPs

20nm

Human monocyte

10, 20, 50, 100µg/mL

Mitochondrial swelling, decreased MMP and ATP

Ghanbary

production, increased Cyto-c release, decreased

et al. (2018)

activity of mitochondrial respiratory chain complex II 7

TiO2-NPs

250nm

Human

bronchial

epithelial

50, 100µg/mL

cells

Mitochondrial swelling, reduction in mitochondrial number, decreased VDAC1 expression, decreased

(16HBE14o-)

Yu et al. (2015)

expression of respiratory chain complexes I, II and IV, reduced ATP production

8

TiO2-NPs

73.29 ± 5.75nm

Human

trophoblast

1, 10, 100µg/mL

Activation of mitophagy

Zhang et al.

HTR-8/SVneo cells 9

TiO2-NPs

20-100nm

(rutile, anatase

Primary rat cortical

(2018b) 25, 50, 100ppm

astrocytes

Decreased MMP, when the exposure concentration was

and P25)

25ppm,

P25

significantly

up-regulated

Wilson

et

al. (2015)

transcript levels of Mfn1 and Mfn2, while anatase significantly

up-regulated

Mfn1

transcription

levels and rutile significantly up-regulated Mfn2 transcription

levels,

when

the

exposure

concentration was 100ppm, all three TiO2-NPs significantly increased the transcript levels of Mfn1, Mfn2 and Drp1 10

TiO2-NPs

100-300 nm

Macrophages

10, 100µg/ml

Increased mitochondrial reactive oxygen species (ROS) levels ,decreased ATP content, and

47

Chen et al. (2018)

decreased metabolic flux in tricarboxylic acid (TCA) cycle 11

TiO2-

12-25nm

NPs(anatase) 12

TiO2-

Chinese hamster lung

1, 10, 25, 50, 100µg/ml

Mitochondrial swelling

fibroblast cells (V-79) 20-40nm

NPs(anatase,

Mouse

macrophage

(2017) 12.5, 25, 50, 200µg/ml

Decreased mitochondrial membrane potential,

line RAW264.7 7

inhibition of mitochondrial reverse electron

rutile) 13

TiO2-NPs

Jain et al.

Yu et al. (2017)

transport(RET) activity 223.6±21.5nm

Mouse

alveolar

2.5, 5, 10, 20µg/mL

ATP generation reduction

Park et al.

macrophage cell line

（Sheet-type）

(2014a)

(MH-S) 14

TiO2-NPs

10-90nm

ICR mice liver, brain

Intraperitoneal injection 5,

Mitochondrial

and embryo

10,

vacuoles

50,

200mg/kg,

100,

150,

observed

swelling

and

mitochondrial

Jia et al. (2017)

2

weeks 15

Ag-NPs

13.5 -43.8nm

A549, HepG2

12.5,

25,

50,

100,

Decreased MMP

Xin et al.

200µg/mL 16

Citrate-coated

2-15n, 10-70nm

Ag-NPs 17

Ag-NPs

235.5±25.1nm

(2016)

Saos-2 osteosarcoma

50, 10, 15, 20, 25μM;

Decrease in MMP, increased mitochondrial Cyto-c

cell

20, 40, 60, 80, 100μM

release

1.5mg/L

Mitochondrial swelling

Rainbow

trout

Kovacs et al. (2016)

hepatocytes

Ostaszewsk a

et

al.

(2018) 18

Ag-NPs

2-100nm

F9 mouse embryonic

12.5μg/mL

Decreased MMP

Han et al.

carcinoma cells 19

Ag-NPs

20-26nm

SH-SY5Y

(2017) 50μg/mL

Decreased MMP and production of ATP

Tan et al.

neuroblastoma cells 20

Ag-NPs

10-30nm

HepG2

(2016) 40, 80, 160μg/mL

Decreased MMP

Xue et al. (2016b)

21

Ag-NPs

10nm

Human stem

22

Ag-NPs

10nm, 100nm

embryonic

0.1, 0.2, 0.3μg/mL

cell-derived

mitochondrial fragmentation and decreased the

neural progenitor cells

level of the mitochondrial fusion protein mitofusin

(NPCs)

1 (Mfn1)

Rat tracheal epithelial

100,10000μg/L

Increased Cyto-c release and caused mitochondria-

cells (RTE) 23

Rubus-

30-150nm

conjugated Ag

Decreased ATP production and MMP, induced

Human breast cancer

mediated apoptosis 2.5, 5, 10μg/ml

al. (2018)

Tang et al. (2019)

Decreased MMP, increased release of Cyto-c

cell MCF-7

Yamada et

caused mitochondria-mediated apoptosis

George et al. (2018)

NPs 24

sodium citrate-

10,75nm

coated Ag-NPs

Sprague-Dawley male

Intraperitoneal

injection

Mitochondrial

swelling,

decreased

MMP,

rat liver

250 µM/kg weekly, for 4

mitochondrial permeability transition (MPT),

weeks.

decreased activity of mitochondrial respiratory

Teodoro et al. (2016)

chain complex II, IV and ATP synthase activity 25

Ag-NPs, TiO2NPs

<100nm

Male Wistar rat live

Gavage

treatment,

100µg/kg/day for 21 days

Mitochondrial swelling, uncoupling effect in

Pereira

oxidative phosphorylation system, GSH/GSSG

al. (2018)

ratio reduction

48

et

26

ZnO-NPs

50-100nm

C6 cells

5, 10, 20, 40, 80µg/mL

Decreased MMP

Sruthi et al. (2017)

27

ZnO-NPs

25-40nm

Human kidney

embryonic (HEK

293)

5,

15,

25,

50,

75,

Decreased MMP

Reshma and

100μg/mL

Mohanan

cells 28

ZnO-NPs

85-130nm

(2017)

HEK-293 cells

25, 50µg/mL

Increased mitochondrial Cyto-c release, decreased MMP

29

ZnO-NPs

40-170nm

Zebrafish embryo

10, 30, 60, 90, 120mg/L

et al. (2017)

Decreased MMP, increased release of Cyto-c caused mitochondria-mediated apoptosis

30

ZnO-NPs

~50nm

CAL 27 oral cancer

25µg/mL

Mitochondrial

cell lines 31

ZnO-NPs

38.52 ± 2.82nm

swelling,

decreased

activation of PINK1/Parkin-mediated

Mouse microglial cell

6.6μg/ml

Zhao et al. (2016)

MMP,

mitophagy

Decreased ATP production and MMP, increased

line, N9

Choudhury

release of Cyto-c caused mitochondria-mediated

Wang et al. (2018a) Sharma et al. (2017)

apoptosis 32

ZnO-NPs

50nm

Murine microglia cell

10μg/mL

Mitochondrial

line, BV-2

swelling,

decreased

activation of PINK1/Parkin-mediated

MMP,

mitophagy

Wei et al. (2017)

and PINK1/parkin-mediated mitophagy plays a protective role in ZnO-NPs-induced cytotoxicity. 33

ZnO-NPs

70nm

Human

aortic

8, 15, 25, 50μg/mL

endothelial cells 34

ZnO-NPs

10-35nm

Murine photoreceptor

Decreased MMP, increased release of Cyto-c caused mitochondria-mediated apoptosis

31.25, 62.5, 125μmol/L

cells

Reduction of ATP levels, collapse of MMP, Cytoc caused mitochondria-mediated apoptosis

49

Liang et al. (2016) Wang et al. (2018b)

Table 2. Physicochemical properties of carbon nanomaterials and corresponding tissue-specific and cell-specific mitochondrial toxicity S.

NMs type

No.

Diameter(D)

Target organ or cell

Concentration

Length(L)

type used

exposure route, time and

Thickness(T) 1

C60

D:179.3±3.4nm,

or

Mitochondrial effects

Reference

concentration Human

lung

123.4±4.9nm,

adenocarcinoma

108.6±3.5nm,

line A549

60mg/L

Bax

cell

translocated

to

mitochondria,

causing

mitochondria-mediated apoptosis

Song et al. (2012)

228.2±7.5nm 2

C60(OH)44

D:26.96 nm

Rat liver mitochondria

0, 5, 25, 50, 100, 150,

Mitochondrial

permeability

transition,

200μg/mL

mitochondrial

swelling,

decreased

mitochondrial

membrane

fluidity

MMP,

Yang et al. (2016)

changed,

decreased respiration rate of state 3 and increased respiration rate of state 4 3

C60(OH)24

Rat hepatocytes

—

50μM

Decreased ATP production and MMP

Nakagawa et al. (2015)

4

Fullerenol

D:15.7nm

The

porcine

proximal

(C₆₀OHx)

cell

renal

0.2-60mM

Decreased ATP production and MMP

Johnson-

line

Lyles et al.

(LLC-PK1 cells) 5

MWCNTs

L:180nm

Mice

spermatocyte

cell line (GC-2spd)

(2010) 0.05,

0.25,

0.5,

1,

5μg/mL

mtDNA

damaged,

oxygen

consumption

decreased

decreased and

expression

mitochondrial

ATP

levels

production,

of

Xu et al. (2016)

MT-ND2

(mitochondria-NADH dehydrogenase subunit 2) and

MT-ND3

(mitochondria-NADH

dehydrogenase subunit 3) 6

SWCNTs, MWCNTs

D:1.3-2.3nm,

Male mouse skin

0.1, 0.2, 0.4μg/mL

Decreased activity of mitochondrial respiratory

5nm

chain complex II,

L:1.5um,

mitochondrial swelling,

Ghanbari et al. (2017)

decreased mitochondrial GSH, ATP and MMP,

5um

increased

release

of

Cyto-c

(SWCNTs>

MWCNTs) 7

MWCNTs，

D:10-20nm,

MWCNT-

L:10-30μm

L02 cells

12.5,

25,

200μg/mL

COOH 8

SWCNTs,

50,

100,

Decreased MMP and increased Cyto-c release caused

mitochondria-mediated

apoptosis

Liu et al. (2014a)

(MWCNTs-COOH
Melanoma cells

0-0.4μg/mL

MWCNTs

Mitochondrial swelling, increased

mtROS,

decreased MMP,

Cyto-c

release

caused

Naserzadeh et al. (2018)

mitochondria-mediated apoptosis 9

Oxidized

L:60-500nm

MWCNTs 10

MWCNTs,

Saccharomyces

0-600mg/L

cerevisiae L:10-20μm

Decreased MMP, release of Cyto-c in dosedependent manners

SH-SY5Y cells

25μg/mL

Zhu et al. (2016)

Decreased MMP

Visalli

MWCNT-

et

al. (2017)

COOH 11

SWCNTs

Not specified

Human

epithelial

0-60μg/ml

50

Mitochondria

swelling

and

round,

cristae

Ma et al.

carcinoma cells

disappeared, decreased

mitochondrial oxygen

(2012)

consumption and MMP, decreased Cyto-c in mitochondria, disrupting

electron transfer of

Cyto-c 12

MWCNTs,

D:10-20nm

MWCNTs-OH

L:10-30μm

L02 cells

12.5,

25,

50,

100,

200μg/ml

Decreased MMP and increased Cyto-c release caused

mitochondria-mediated

apoptosis

Liu et al. (2014b)

（ MWCNTs-OH< MWCNTs） 13

SWCNTs

D:4±2nm

Human

L:335±154nm

epithelial

bronchial

0.8, 1.7, 3.3 6.6μg/ml

Reduced ATP production, mitochondrial damaged

cells

Park et al. (2014b)

(BEAS-2B) 14

15

SWCNTs，

L:3.16μm

O-SWCNTs

263nm

MWCNTs，

Not specified

Saccharomyces

23.5, 47.1, 94.1, 188.2,

cerevisiae

376.4mg/L

Mouse

peritoneal

5, 20, 40, 80μg/ml

Decreased MMP and ATP production

Zhu et al. (2018)

Decreased MMP, release of cytochrome C,

tau-MWCNTs

macrophage cell line

decreased activity of ATP synthase and succinate

(Taurine-

(RAW 264.7)

dehydrogenase

Functionalized

Chen et al. (2012)

(tau-MWCNTs< MWCNTs)

) 16

Aci-MWCNT

D:10–20nm

Mouse

peritoneal

5, 20, 40, 80μg/ml

Mitochondrial swelling, decreased MMP, and

( acid-treated)， L:0.3–0.6μm

macrophage cell line

release of Cyto-c caused mitochondria-mediated

tau-MWCNTs

(RAW 264.7)

apoptosis

(

Wang et al. (2012)

taurine-

functionalized) 17

Not specified

MWCNTs， MWCNTs

Human alveolar cell

2,20μg/ml

line A549

-

Dose dependent higher levels of dehydrogenase kinase 1

COOH

pyruvate

in the short time, and

then decreased, MMP declined,

Visalli

et

al. (2019)

increased

release of Cyto-c, MPTP opening 18

Graphene

D:42.0±11.3nm

oxide,

382.9±22.0nm

carboxyl

4672.5±414.9nm

graphene

HepG2 cells

1, 2, 4, 8, 16μg/ml,

Decreased MMP

Lammel et al. (2013)

2, 4, 8, 16, 32μg/ml

D:349.5±42.6nm 1805.6±616.8nm 4827.3±497.5nm

19

Graphene,

D:100-200nm

MDA-MB-231 human

graphene oxide

T:3-4nm

breast cancer cells,

20, 40, 60, 80, 100μg/ml

Decreased MMP and ATP production, inhibited activity

succinate of dehydrogenase by affecting

Zhou et al. (2014a)

the function of iron-sulfur center in succinate dehydrogenase, decreased

activity of complexes

I, II, III and IV in a dose-dependent manner

20

Graphene

D:0.5-5μm

oxide

T:0.8-1.2nm

C. vulgaris

0.01, 0.1, 1, 10mg/L

Decreased MMP

Hu et al., (2015)

51

21

22

Polyethylene

D:100-200nm

MDA-MB-231

glycol-

T:2-3nm

MDA-MB-436,

of complex II and complex III was significantly

modified

SK-BR-3(breast

down-regulated

graphene oxide

cancer cells)

，

Graphene

D:<2μm

Human

bronchial

nanoplatelets

T:3-4nm

epithelial cell (BEAS-

40μg/ml

2.5, 5, 10, 20μg/mL

Decreased ATP production, the expression levels

Decreased ATP production,

release of Cyto-c

caused mitochondria-mediated apoptosis

Zhou et al. (2014b)

Park et al. (2015)

2B)

23

Graphene

D:22-26nm

oxide

Neuroblastoma Lines

Cell

2μg/mL

(SK-N-BE(2),

MMP decreased in the first 4 hours, then gradually increased, and returned to normal in 72 hours. At

SH-SY5Y)

Mari et al. (2016)

48 hours, mitochondria swelling and disintegrating were observed. At 72 hours, mitochondrial conformational condensation and mitochondria with structural dysfunction in autophagosomes were observed.

24

Graphene

D:0.5μm

oxide

T:1.02±0.15nm

Adult zebrafish

0.01, 0.1, 1μg/L

The structures of the mitochondria were obscured, with the intact crista structure being fractured and

Ren et al. (2016)

reduced in size

25

Graphene

D:420nm-1.6μm

Human

glioblastoma

20, 50, 100, 200μg/mL

Mitochondrial swelling, decreased MMP and ATP

U87 cell line and non-

production,

cancer

mitochondria-mediated apoptosis

cells

HS-5

release

of

Cyto-c

caused

Jaworski et al. (2019)

(bone marrow/stroma)

26

Graphene

D:0.3-2.6µm

oxide

T:1.01±0.05nm

Zebrafish larva

1, 10, 100μg/L

Decreased MMP AND Na+/K+-ATPase activity, and

up-regulated

proteins

associated

with

mitochondrial respiratory chain and intramolecular oxidoreductase activity, including ndufa8, ndufa2, ndufc2, ndufa10, mthfd1b, cox6a1, ndufs4, aifm4, acadsb and qsox1

52

Zou et al. (2018)

Table 3. Physicochemical properties of quantum dots and corresponding tissuespecific and cell-specific mitochondrial toxicity S.

NMs type

Size

No.

Diameter(D)

or and

Target organ or cell

Concentration

type used

exposure route, time and

Thickness(T) 1

ZnS-CdSe

3.5nm

QDs

or

Mitochondrial effects

Reference

concentration Human

150, 300nM

Increased

neuroblastoma IMR-

Cyto-c

release

and

caused

mitochondria-mediated apoptosis

Chan et al. (2006)

32 cells 2

NAC-capped

~5.5nm

CdTe QDs

Mitochondria isolated

200,

400,

from rat livers

800,1000nmol/mg

600,

Low concentration of QDs

Li

stimulated respiration rate of state 4 while high

et

al.

(2011)

concentration of QDs inhibited respiration rate of state 4, the respiration rate of state 3 decreased with the addition of QDs. mitochondrial swelling,

mitochondrial

membrane

lipid

peroxidation 3

Cd/Se/Te-

20nm

Mice kidneys

based QDs

Intravenous,40pmol, 4,

Mitochondrial

12, 16, and 24 weeks

mitochondrial

dysplasia, number and

decreased mitochondrial

Lin et al. (2012)

swelling (early changes), later compensatory mitochondrial hypertrophy and mitochondrial hyperplasia 4

5

CdTe QDs

CdTe QDs

14±2.8nm

13.98 ± 2.79 nm

HepG2 cells

HepG2 cells

0.001, 0.01, 0.1, 1, 10,

Increased

100μg/ml

mitochondria-mediated apoptosis

1, 10μg/ml

Mitochondrial swelling and cristae disappeared, MMP

Cyto-c

decreased,

release

and

caused

Nguyen et al. (2013)

mitochondrial

oxygen

Nguyen et al. (2015)

consumption and ATP production decreased, mitochondrial respiratory chain complex II-IV content and activity decreased significantly, and complex V content increased significantly. Stimulating mitochondrial biogenesis 6

7

GSH-CdTe

5.22±0.17nm,

Human

embryonic

QDs

7.21±0.19nm,

kidney

9.34±0.37nm

293)

MEA-CdTe

2.20 ± 0.60nm,

Female Wistar rats

QDs,

l-Cys-

2.35 ± 0.55nm,

liver mitochondria

CdTe

QDs,

2.35 ± 0.40nm

cells

1, 2, 4μM

(HEK

Decreased MMP, mitochondrial swelling and increased

mitochondrial

inner

membrane

Lai et al. (2016)

permeability 100, 200, 300, 400nM

Three types of CdTe QD reduced mitochondrial respiration rates of state 3, state 4 and unconjugated state in a dose-dependent manner.

TGA-CdTe

Mitochondrial swelling and decreased MMP

QDs

caused by TGA-CdTe QDs were stronger than the

other

two.

MEA-CdTe

QDs

reduce

mitochondrial membrane fluidity in a dosedependent manner. LCA-CdTe QDs increase

53

Xiang et al. (2018)

mitochondrial membrane fluidity in a dosedependent manner. TGA-CdTe QD has greater effects on MPTP proteins than the other two 8

Graphene QDs

D: ~20nm

Human gastric cancer

T:1nm

MGC‐803 and breast

20, 100, 200, 400μg/mL

Decreased MMP

Wu et al. (2013)

cancer MCF‐7 cells 9

MPA-CdTe

~4nm

HEK293 cells

25, 50, 100, 200nm

QDs 10

CdS QDs

Mitochondrial

swelling,

Decreased

MMP,

MPTP opening 6nm

Bakers' yeast strain

75, 100, 150mg/L

BY4742

(2015)

Decreased MMP and oxygen consumption, mitochondrial

Lai et al.

morphology

changes,

Pasquali et al. (2017)

morphological changes in mitochondria, but mtDNA was not damaged 11

CdS QDs

∼5nm

HepG2 cells

3, 7, 14μg/ml

Decreased MMP, no damage to

mtDNA

Paesano et al. (2016)

54

Highlights: 1. We provided an overview of the role of mitochondria in toxicity caused by nanomaterials. 2. We reviewed current knowledge of mitochondrial toxicity induced by nanomaterials. 3. We highlighted the challenges and opportunities regarding mitochondrial toxicity studies of nanomaterials.

55

Graphical abstract

56