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Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice
Chemosphere xxx (2016) 1e2
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Discussion
Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice Fankun Zhou, Chang Feng, Guangqin Fan* Department of Occupational Health and Toxicology, School of Public Health, Nanchang University, BaYi Road 461, Nanchang 330006, China
h i g h l i g h t s The study by Cobbina et al. published in Chemosphere in 2015 deserve critiques. Levels of toxic metals measured in the control mice are extremely high. Accumulation of toxic metal in mice is inconsistent with the exposure. Oxidative stress indices altered by toxic metal are inconsistent with the literature.
a r t i c l e i n f o Article history: Received 20 June 2016 Received in revised form 12 August 2016 Accepted 28 August 2016 Available online xxx Handling Editor: A. Gies
Pb-exposed mice, where brain Pb concentration in the control is either below 0.1 mg/g or undetectable (Liu et al., 2014; Ferlemi et al., 2014; Li et al., 2014; Chang et al., 2014; Ivanova et al., 2016; Li et al., 2016). The value 810 ng/g of control in this study is even higher than that of a high level Pb-exposed group in other studies (Ferlemi et al., 2014; Li et al., 2014, 2016; Ivanova et al., 2016). This implies that the control in this study is polluted by Pb. 2. The ingestion of individual toxic metal is inconsistent with the accumulation in organs of mice
A paper concerning low concentration toxic metal mixture interactions was published in 2015 by Cobbina et al. (2015a). Despite of the significance attached to interactions among low concentration toxic metals, the paper misses its scientific accuracy because, (1) the levels of toxic metals in control are extremely high, (2) the ingestion of toxic metals is inconsistent with their accumulation in organs of mice, (3) the changes of routine oxidative stress indices induced by low concentration toxic metal exposure are incomprehensible. The conclusion made from the study is alarming and may mislead health officials, and hence warrant critique. 1. The levels of toxic metals in controls are extremely high In this study, there are extremely high background concentrations of toxic metals in the control shown in Table S2 (Cobbina et al., 2015a). In the experiments where mice were exposed to Pb for 30 days, for example, the average value in the control is 0.81 mg/g (810 ng/g). This is much higher than most researches concerning
DOI of original article: http://dx.doi.org/10.1016/j.chemosphere.2015.03.013. * Corresponding author. E-mail address: [email protected] (G. Fan).
For example, Pb-only exposed mice are subjected to a low concentration of 0.01 mg L1 Pb (Cobbina et al., 2015a), and an average daily water intake of 4.0 ml/day/mouse for 30 days in their another paper (see Table S3) based on the same mice model (Cobbina et al., 2015b). So, the total amount of Pb exposure is 1.20 mg after being exposed with 0.01 mg L1 Pb for 30 days (see the following Equation (1)). However, the calculated total amount of Pb accumulated in organs is 5.29 mg via Pb concentration of brain, liver and kidney supplied in the following Table 1. If the mice exposed to 0.01 mg L1 Pb accumulated 100% of the toxic metal ion, the amount (1.20 mg) is only about a quarter of the total content (5.29 mg) measured in the organs. Where does the additional Pb come from?
4:0 ml=day=mice*0:01 mg L1 *30 days ¼ 1:20 mg
(1)
3. The changes of oxidative stress indices like MDA, SOD and GPx after low concentration toxic metal exposure individually are inconsistent with the literature Take Pb-only exposed mice for example. The change of the conventional index without high sensitivity as MDA, SOD and GPx
http://dx.doi.org/10.1016/j.chemosphere.2016.08.132 0045-6535/© 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Zhou, F., et al., Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice, Chemosphere (2016), http://dx.doi.org/10.1016/j.chemosphere.2016.08.132
2
F. Zhou et al. / Chemosphere xxx (2016) 1e2
Table 1 Total amount of Pb accumulated in organs reported by Cobbina et al. (2015a,b). Tissue
Concentrations of Pb
Brain Liver Kidney Total
1.91 mg/g 2.65 mg/g 3.20 mg/g
a b
a
Absolute weights 0.4114 g 1.2318 g 0.3868 g
b
Amount of Pb 0.7858 mg 3.2643 mg 1.2378 mg 5.2879 mg
See Table S2 reported by Cobbina et al. (2015a). See Table S2a-c reported by Cobbina et al. (2015b).
in organs would not be observed if the Pb exposure concentration below 50 mg L1 in most of studies concerning Pb exposed mice and rats (Moreira et al., 2001; Berrahal et al., 2007; Ferlemi et al., 2014; Alya et al., 2015; Ferreira et al., 2016). However, with the same chromogenic substrate assay, there is a significant change of MDA, SOD and GPx in organs after being exposed with an extremely low Pb concentration of 0.01 mg L1 in this study (Cobbina et al., 2015b). The results are inconsistent with that of the current studies. In view of the above two issues that the extremely high Pb concentration in control and impossible accumulation of Pb in organs, is there a real relationship between 0.01 mg L1 Pb exposure and the changes of oxidative stress indices like MDA, SOD and GPx? In summary, there are critical problems in design and quality control in this study which involved in the control group, the doses of metals exposure as well as the relationships between the metals exposure and their response indicators. Thus, the animal model of a low concentration toxic metal mixture exposure was unreliable and the conclusions drawn were alarmist in this study. In addition, the doses of toxic metals used in this study were the permissible by the National Standard of The Republic of China for Municipal Water Standards (GB5749-2006) (MHPRC, 2006), whose influence is widespread. Thus, the conclusions need to be revaluated.
biochemical alterations, and hyperlipidemia in female rats induced by lead chronic toxicity during puberty and post puberty periods. Iran. J. Basic. Med. Sci. 18, 1034e1043. Berrahal, A. Annabi, Nehdi, A., Hajjaji, N., Gharbi, N., El-Faz^ aa, S., 2007. Antioxidant enzymes activities and bilirubin level in adult rat treated with lead. C. R. Biol. 330, 581e588. Chang, J., Kueon, C., Kim, J., 2014. Influence of lead on repetitive behavior and dopamine metabolism in a mouse model of iron overload. Toxicol. Res. 30, 267e276. Cobbina, S.J., Chen, Y., Zhou, Z., Wu, X., Feng, W., Wang, W., Mao, G., Xu, H., Zhang, Z., Wu, X., Yang, L., 2015a. Low concentration toxic metal mixture interactions: effects on essential and non-essential metals in brain, liver, and kidneys of mice on sub-chronic exposure. Chemosphere 132, 79e86. Cobbina, S.J., Chen, Y., Zhou, Z., Wu, X., Zhao, T., Zhang, Z., Feng, W., Wang, W., Li, Q., Wu, X., Yang, L., 2015b. Toxicity assessment due to sub-chronic exposure to individual and mixtures of four toxic heavy metals. J. Hazard. Mater. 294, 109e120. Ferlemi, A.V., Avgoustatos, D., Kokkosis, A.G., Protonotarios, V., Constantinou, C., Margarity, M., 2014. Lead-induced effects on learning/memory and fear/anxiety are correlated with disturbances in specific cholinesterase isoform activity and redox imbalance in adult brain. Physiol. Behav. 131, 115e122. Ferreira, M.C., Zucki, F., Duarte, J.L., Iano, F.G., Ximenes, V.F., Buzalaf, M.A., Oliveira, R.C., 2016. Influence of iron on modulation of the antioxidant system in rat brains exposed to lead. Environ. Toxicol. http://dx.doi.org/10.1002/tox.22281 [Epub ahead of print]. Ivanova, J., Gluhcheva, Y., Dimova, D., Pavlova, E., Arpadjan, S., 2016. Comparative assessment of the effects of salinomycin and monensin on the biodistribution of lead and some essential metal ions in mice, subjected to subacute lead intoxication. J. Trace Elem. Med. Biol. 33, 31e36. Li, N., Yang, G., Wang, Y., Qiao, M., Zhang, P., Shao, J., Yang, G., 2016. Decreased IDE and IGF2 expression but increased Ab40 in the cerebral cortex of mouse pups by early life lead exposure. Brain Res. Bull. 121, 84e90. Li, N., Zhao, G., Qiao, M., Shao, J., Liu, X., Li, H., Li, X., Yu, Z., 2014. The effects of early life lead exposure on the expression of insulin-like growth factor 1 and 2 (IGF1, IGF2) in the hippocampus of mouse pups. Food Chem. Toxicol. 63, 48e52. Liu, F., Xue, Z., Li, N., Huang, H., Ying, Y., Li, J., Wang, L., Li, W., 2014. Effects of lead exposure on the expression of amyloid b and phosphorylated tau proteins in the C57BL/6 mouse hippocampus at different life stages. J. Trace Elem. Med. Biol. 28, 227e232. MHPRC (Minister of Health of the People's Republic of China), 2006. National Standard of the Republic of China for Drinking Water Quality Standards (GB5749-2006). China, Beijing. Moreira, E.G., Rosa, G.J., Barros, S.B., Vassilieff, V.S., Vassillieff, I., 2001. Antioxidant defense in rat brain regions after developmental lead exposure. Toxicology 169, 145e151.
References Alya, A., Ines, D.B., Montassar, L., Najoua, G., Saloua, elF., 2015. Oxidative stress,
Please cite this article in press as: Zhou, F., et al., Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice, Chemosphere (2016), http://dx.doi.org/10.1016/j.chemosphere.2016.08.132
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Discussion
Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice Fankun Zhou, Chang Feng, Guangqin Fan* Department of Occupational Health and Toxicology, School of Public Health, Nanchang University, BaYi Road 461, Nanchang 330006, China
h i g h l i g h t s The study by Cobbina et al. published in Chemosphere in 2015 deserve critiques. Levels of toxic metals measured in the control mice are extremely high. Accumulation of toxic metal in mice is inconsistent with the exposure. Oxidative stress indices altered by toxic metal are inconsistent with the literature.
a r t i c l e i n f o Article history: Received 20 June 2016 Received in revised form 12 August 2016 Accepted 28 August 2016 Available online xxx Handling Editor: A. Gies
Pb-exposed mice, where brain Pb concentration in the control is either below 0.1 mg/g or undetectable (Liu et al., 2014; Ferlemi et al., 2014; Li et al., 2014; Chang et al., 2014; Ivanova et al., 2016; Li et al., 2016). The value 810 ng/g of control in this study is even higher than that of a high level Pb-exposed group in other studies (Ferlemi et al., 2014; Li et al., 2014, 2016; Ivanova et al., 2016). This implies that the control in this study is polluted by Pb. 2. The ingestion of individual toxic metal is inconsistent with the accumulation in organs of mice
A paper concerning low concentration toxic metal mixture interactions was published in 2015 by Cobbina et al. (2015a). Despite of the significance attached to interactions among low concentration toxic metals, the paper misses its scientific accuracy because, (1) the levels of toxic metals in control are extremely high, (2) the ingestion of toxic metals is inconsistent with their accumulation in organs of mice, (3) the changes of routine oxidative stress indices induced by low concentration toxic metal exposure are incomprehensible. The conclusion made from the study is alarming and may mislead health officials, and hence warrant critique. 1. The levels of toxic metals in controls are extremely high In this study, there are extremely high background concentrations of toxic metals in the control shown in Table S2 (Cobbina et al., 2015a). In the experiments where mice were exposed to Pb for 30 days, for example, the average value in the control is 0.81 mg/g (810 ng/g). This is much higher than most researches concerning
DOI of original article: http://dx.doi.org/10.1016/j.chemosphere.2015.03.013. * Corresponding author. E-mail address: [email protected] (G. Fan).
For example, Pb-only exposed mice are subjected to a low concentration of 0.01 mg L1 Pb (Cobbina et al., 2015a), and an average daily water intake of 4.0 ml/day/mouse for 30 days in their another paper (see Table S3) based on the same mice model (Cobbina et al., 2015b). So, the total amount of Pb exposure is 1.20 mg after being exposed with 0.01 mg L1 Pb for 30 days (see the following Equation (1)). However, the calculated total amount of Pb accumulated in organs is 5.29 mg via Pb concentration of brain, liver and kidney supplied in the following Table 1. If the mice exposed to 0.01 mg L1 Pb accumulated 100% of the toxic metal ion, the amount (1.20 mg) is only about a quarter of the total content (5.29 mg) measured in the organs. Where does the additional Pb come from?
4:0 ml=day=mice*0:01 mg L1 *30 days ¼ 1:20 mg
(1)
3. The changes of oxidative stress indices like MDA, SOD and GPx after low concentration toxic metal exposure individually are inconsistent with the literature Take Pb-only exposed mice for example. The change of the conventional index without high sensitivity as MDA, SOD and GPx
http://dx.doi.org/10.1016/j.chemosphere.2016.08.132 0045-6535/© 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Zhou, F., et al., Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice, Chemosphere (2016), http://dx.doi.org/10.1016/j.chemosphere.2016.08.132
2
F. Zhou et al. / Chemosphere xxx (2016) 1e2
Table 1 Total amount of Pb accumulated in organs reported by Cobbina et al. (2015a,b). Tissue
Concentrations of Pb
Brain Liver Kidney Total
1.91 mg/g 2.65 mg/g 3.20 mg/g
a b
a
Absolute weights 0.4114 g 1.2318 g 0.3868 g
b
Amount of Pb 0.7858 mg 3.2643 mg 1.2378 mg 5.2879 mg
See Table S2 reported by Cobbina et al. (2015a). See Table S2a-c reported by Cobbina et al. (2015b).
in organs would not be observed if the Pb exposure concentration below 50 mg L1 in most of studies concerning Pb exposed mice and rats (Moreira et al., 2001; Berrahal et al., 2007; Ferlemi et al., 2014; Alya et al., 2015; Ferreira et al., 2016). However, with the same chromogenic substrate assay, there is a significant change of MDA, SOD and GPx in organs after being exposed with an extremely low Pb concentration of 0.01 mg L1 in this study (Cobbina et al., 2015b). The results are inconsistent with that of the current studies. In view of the above two issues that the extremely high Pb concentration in control and impossible accumulation of Pb in organs, is there a real relationship between 0.01 mg L1 Pb exposure and the changes of oxidative stress indices like MDA, SOD and GPx? In summary, there are critical problems in design and quality control in this study which involved in the control group, the doses of metals exposure as well as the relationships between the metals exposure and their response indicators. Thus, the animal model of a low concentration toxic metal mixture exposure was unreliable and the conclusions drawn were alarmist in this study. In addition, the doses of toxic metals used in this study were the permissible by the National Standard of The Republic of China for Municipal Water Standards (GB5749-2006) (MHPRC, 2006), whose influence is widespread. Thus, the conclusions need to be revaluated.
biochemical alterations, and hyperlipidemia in female rats induced by lead chronic toxicity during puberty and post puberty periods. Iran. J. Basic. Med. Sci. 18, 1034e1043. Berrahal, A. Annabi, Nehdi, A., Hajjaji, N., Gharbi, N., El-Faz^ aa, S., 2007. Antioxidant enzymes activities and bilirubin level in adult rat treated with lead. C. R. Biol. 330, 581e588. Chang, J., Kueon, C., Kim, J., 2014. Influence of lead on repetitive behavior and dopamine metabolism in a mouse model of iron overload. Toxicol. Res. 30, 267e276. Cobbina, S.J., Chen, Y., Zhou, Z., Wu, X., Feng, W., Wang, W., Mao, G., Xu, H., Zhang, Z., Wu, X., Yang, L., 2015a. Low concentration toxic metal mixture interactions: effects on essential and non-essential metals in brain, liver, and kidneys of mice on sub-chronic exposure. Chemosphere 132, 79e86. Cobbina, S.J., Chen, Y., Zhou, Z., Wu, X., Zhao, T., Zhang, Z., Feng, W., Wang, W., Li, Q., Wu, X., Yang, L., 2015b. Toxicity assessment due to sub-chronic exposure to individual and mixtures of four toxic heavy metals. J. Hazard. Mater. 294, 109e120. Ferlemi, A.V., Avgoustatos, D., Kokkosis, A.G., Protonotarios, V., Constantinou, C., Margarity, M., 2014. Lead-induced effects on learning/memory and fear/anxiety are correlated with disturbances in specific cholinesterase isoform activity and redox imbalance in adult brain. Physiol. Behav. 131, 115e122. Ferreira, M.C., Zucki, F., Duarte, J.L., Iano, F.G., Ximenes, V.F., Buzalaf, M.A., Oliveira, R.C., 2016. Influence of iron on modulation of the antioxidant system in rat brains exposed to lead. Environ. Toxicol. http://dx.doi.org/10.1002/tox.22281 [Epub ahead of print]. Ivanova, J., Gluhcheva, Y., Dimova, D., Pavlova, E., Arpadjan, S., 2016. Comparative assessment of the effects of salinomycin and monensin on the biodistribution of lead and some essential metal ions in mice, subjected to subacute lead intoxication. J. Trace Elem. Med. Biol. 33, 31e36. Li, N., Yang, G., Wang, Y., Qiao, M., Zhang, P., Shao, J., Yang, G., 2016. Decreased IDE and IGF2 expression but increased Ab40 in the cerebral cortex of mouse pups by early life lead exposure. Brain Res. Bull. 121, 84e90. Li, N., Zhao, G., Qiao, M., Shao, J., Liu, X., Li, H., Li, X., Yu, Z., 2014. The effects of early life lead exposure on the expression of insulin-like growth factor 1 and 2 (IGF1, IGF2) in the hippocampus of mouse pups. Food Chem. Toxicol. 63, 48e52. Liu, F., Xue, Z., Li, N., Huang, H., Ying, Y., Li, J., Wang, L., Li, W., 2014. Effects of lead exposure on the expression of amyloid b and phosphorylated tau proteins in the C57BL/6 mouse hippocampus at different life stages. J. Trace Elem. Med. Biol. 28, 227e232. MHPRC (Minister of Health of the People's Republic of China), 2006. National Standard of the Republic of China for Drinking Water Quality Standards (GB5749-2006). China, Beijing. Moreira, E.G., Rosa, G.J., Barros, S.B., Vassilieff, V.S., Vassillieff, I., 2001. Antioxidant defense in rat brain regions after developmental lead exposure. Toxicology 169, 145e151.
References Alya, A., Ines, D.B., Montassar, L., Najoua, G., Saloua, elF., 2015. Oxidative stress,
Please cite this article in press as: Zhou, F., et al., Combined exposure of low dose lead, cadmium, arsenic, and mercury in mice, Chemosphere (2016), http://dx.doi.org/10.1016/j.chemosphere.2016.08.132