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Plasma levels of oxidative stress-responsive apoptosis inducing protein (ORAIP) in patients with atrial fibrillation
International Journal of Cardiology 222 (2016) 528–530
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Correspondence
Plasma levels of oxidative stress-responsive apoptosis inducing protein (ORAIP) in patients with atrial fibrillation Takako Yao a, Kentaro Tanaka b, Tsutomu Fujimura c, Kimie Murayama d, Shuichi Fukuda e, Ko Okumura f, Yoshinori Seko a,⁎ a
Division of Cardiovascular Medicine, The Institute for Adult Diseases, Asahi Life Foundation, Tokyo, Japan Higashiyamato Nangai Clinic, Tokyo, Japan Laboratory of Bioanalytical Chemistry, Tohoku Pharmaceutical University, Miyagi, Japan d Division of Proteomics and Biomolecular Science, BioMedical Research Center, Graduate School of Medicine, Juntendo University, Tokyo, Japan e Wakakusa Clinic, Tochigi, Japan f Department of Atopy Research Center, Juntendo University School of Medicine, Tokyo, Japan b c
a r t i c l e
i n f o
Article history: Received 4 May 2016 Received in revised form 25 July 2016 Accepted 2 August 2016 Available online 3 August 2016
Keywords: Atrial fibrillation (AF) Cardiac injury Eukaryotic translation initiation factor (eIF) 5 A Ischemia/reperfusion Oxidative stress
Atrial fibrillation (AF) is frequently associated with congestive heart failure, valvular heart diseases, hypertension, and diabetes mellitus (DM) [1], but is also an important causative factor of cerebral infarction, congestive heart failure, and other cardiac disorders. Although oxidative stress has been implicated in the pathogenesis of AF [2–4], the precise mechanism of cardiotoxicity involved in AF remains unclear. Oxidative stress causes cell damage that leads to apoptosis via uncertain mechanisms. To investigate the mechanisms involved, we previously analyzed the molecular mechanism involved in hypoxia/reoxygenationinduced apoptosis of cultured cardiac myocytes [5]. Because hypoxia/ reoxygenation-conditioned medium of cardiac myocytes could induce
Abbreviations: AF, atrial fibrillation; cTnT, cardiac troponin T; DM, diabetes mellitus; eIF5A, eukaryotic translation initiation factor 5A; ELISA, enzyme-linked immunosorbent assay; HRP, horseradish peroxidase; mAb, monoclonal antibody; NT-proBNP, N-terminal pro-brain natriuretic peptide; 8-OHdG, 8-hydroxy-2′-deoxyguanosine; ORAIP, oxidative stress-responsive apoptosis inducing protein; RyR2, type 2 ryanodine receptor; SE, standard error; ROS, reactive oxygen species; UV, ultraviolet. ⁎ Corresponding author at: Division of Cardiovascular Medicine, The Institute for Adult Diseases, Asahi Life Foundation, 2-2-6 Nihonbashi-Bakurocho, Chuo-ku, Tokyo 103-0002, Japan. E-mail address: [email protected] (Y. Seko).
http://dx.doi.org/10.1016/j.ijcard.2016.08.005 0167-5273/© 2016 Elsevier Ireland Ltd. All rights reserved.
extensive apoptosis of cardiac myocytes under normoxia, we thought that some humoral factor was rapidly released from cardiac myocytes, then mediated apoptosis. And, we identified the apoptosis-inducing humoral factor in the hypoxia/reoxygenation-conditioned medium by a proteomic approach. We found that eukaryotic translation initiation factor 5A (eIF5A) undergoes sulfation of 69th tyrosine residue in the trans-Golgi as well as more hypusination, and is rapidly secreted from cardiac myocytes in response to hypoxia/reoxygenation, then induces apoptosis of the cells as a pro-apoptotic ligand [5]. We named this novel post-translationally modified secreted form of eIF5A, Oxidative stress-Responsive Apoptosis Inducing Protein (ORAIP). Rat model of myocardial ischemia/reperfusion (but not ischemia alone) markedly increased plasma levels of ORAIP. Another oxidative stress, ultraviolet (UV)-irradiation to the heart of rats also markedly increased plasma levels of ORAIP. The apoptosis induction of cardiac myocytes by hypoxia/reoxygenation and UV-irradiation was significantly suppressed by neutralizing anti-ORAIP monoclonal antibodies (mAbs) in vitro [5]. In vivo administration of anti-ORAIP mAbs significantly reduced myocardial ischemia/reperfusion injury. These data [5] indicate that the apoptosis induction of cardiac myocytes by these stimuli are critically mediated by ORAIP. We confirmed that ORAIP is specifically secreted in response to the oxidative stresses including ischemia/reperfusion, hypoxia/ reoxygenation, ultraviolet-irradiation, ionizing radiation, cold/warmstress (heat shock), and blood acidification [6], then acts as a proapoptotic ligand to induce apoptosis of target cells. In this study, to investigate the role of ORAIP in the mechanism of oxidative stressinduced myocardial injury in AF, we analyzed plasma levels of ORAIP, cardiac troponin T (cTnT), and N-terminal pro-brain natriuretic peptide (NT-proBNP) in patients with AF. This study was carried out in accordance with the Declaration of Helsinki (2000) of the World Medical Association, and was approved by the institutional ethical committee. All patients gave written informed consent after full explanation of the purpose, nature and risk of all procedures used. Thirty patients (30 males; age, 73.5 ± 1.6 [mean ± SE] years) with AF and 23 control subjects (23 males; age, 72.7 ± 1.3 [mean ± SE] years) without AF were studied. The characteristics of the patient and control groups are summarized in Table 1. Plasma ORAIP levels were analyzed by the sandwich enzyme-linked immunosorbent
Correspondence Table 1 Characteristics of the patient and control groups. Controls
AF patients
n
23
30
Sex (male/female) Age (years) Smoking (n) Hypertension (n) Diabetes mellitus (n) Dislipidemia (n)
23/0 72.7 ± 1.3 13 (56.5%) 15 (65.2%) 18 (78.3%) 10 (43.5%)
30/0 73.5 ± 1.6 15 (50.0%) 19 (63.3%) 16 (53.3%) 11 (36.7%)
p valuea
0.701 0.638 0.886 0.0603 0.616
Data given as (mean ± SE) or numbers (%). a Quantitative data, Welch's t-test; qualitative data, chi-square test.
assay using blocking-less type plates (Sumitomo Bakelite Co., Ltd., Tokyo, Japan) as described previously [5]. The (mean ± SE) plasma ORAIP concentrations (64.75 ± 10.68 ng/ml) in 30 patients with AF were significantly (p = 0.0000190, Welch's t-test) increased as compared with those (9.92 ± 2.11 ng/ml) in 23 control subjects without AF (Fig. 1A). To investigate the effect of significant elevation of plasma ORAIP levels on myocardial injury, we analyzed plasma levels of cTnT (normal range b 14.0 pg/ml) and found that plasma cTnT levels (43.4 ± 13.1 [mean ± SE] pg/ml) were significantly (p = 0.0217, Welch's t-test) elevated as compared with those in 23 control subjects without AF (11.4 ± 1.3 [mean ± SE] pg/ml), and there was a positive correlation (r = 0.453, p = 0.0120) between plasma levels of ORAIP and cTnT (Fig. 1B). There was also a positive correlation (r = 0.492, p = 0.0057) between plasma levels of ORAIP and NT-proBNP (Fig. 1C). We also analyzed the plasma levels of 8-hydroxy-2′-deoxyguanosine (8-OHdG) as one of the oxidative stress markers. There was a tendency for positive correlation (but not significant p = 0.0904) between plasma levels of ORAIP and those of 8-OHdG (data not shown). We have demonstrated that plasma ORAIP levels were significantly increased in AF patients, indicating that oxidative stress levels were elevated in AF. The correlation between plasma levels of ORAIP and cTnT as well as NT-proBNP strongly suggests that ORAIP plays a critical role in cardiac injury in patients with AF. There have been several studies reporting the mechanisms of oxidative stress induction in AF. Xanthine oxidase (XO) is an enzyme involved in purine metabolism and also produces reactive oxygen species (ROS). Sakabe et al. [7] demonstrated that XO inhibitor allopurinol suppressed AF promotion by preventing both electrical and structural remodeling in dogs with atrial tachypacing,
529
suggesting that XO plays a critical role in inducing oxidative stress in AF. Xie W, et al. [8] reported that intracellular Ca2+ release via the atrial type 2 ryanodine receptor (RyR2) increases RyR2 oxidation and mitochondrial ROS production, which leads to AF. Goette et al. [9] demonstrated that rapid atrial pacing induces angiotensin II type 1-receptor-mediated oxidative stress in ventricular myocardium that is accompanied by impaired microvascular blood flow and cardiac troponin-I release. Saito et al. [10] reported that glucose fluctuation in streptozotocin-induced diabetic rats increased ROS levels, which promote cardiac fibrosis and increase the incidence of AF. This may be one of the mechanisms of increased association of AF with DM. Although the precise mechanism of oxidative stress generation in AF is still uncertain, plasma ORAIP levels can be a novel biomarker for the oxidative stress involved and the elevated levels of ORAIP will cause myocardial injury and fibrosis, resulting in the progression of AF and cardiac dysfunction. Thus, ORAIP may play a critical role in AF-associated cardiac disorders as well as AF itself. Our findings warrant elimination of plasma ORAIP with a neutralizing antibody against ORAIP [5] to protect from cardiovascular injury in patients with oxidative stress-associated disorders such as AF. Conflict of interest The authors have no conflicts of interest to disclose. Source of funding This work was supported by Research Fund of Mitsukoshi Health and Welfare Foundation 2015 and a grant from Takeda Research Support. Author contribution Y.S. designed the study. T.Y., Y.S., and K.O. produced mAbs, developed ELISA. T.Y., Y.S., K.T., and S.F. collected and measured the patients' samples. T.F. and K.M. did proteomic analyses and identified ORAIP. All authors discussed the results and commented the study. Acknowledgments We thank co-medical staffs of The Institute for Adult Diseases, Asahi Life Foundation for technical supports.
Fig. 1. (A) Plasma levels of ORAIP in patients with AF and control subjects without AF. (mean ± SE, n = 30 and 23, respectively, *p = 0.0000190, Welch's t-test). (B) Correlation between plasma levels of ORAIP and those of cTnT. There was a significant positive correlation (r = 0.453, p = 0.0120). (C) Correlation between plasma levels of ORAIP and those of NT-proBNP. There was a significant positive correlation (r = 0.492, p = 0.0057). (B and C; Spearman's rank correlations between the data were calculated).
530
Correspondence
References [1] K. Aizawa, J. Fujui, Y. Seko, Diabetes mellitus is important as a risk factor of atrial fibrillation, Integr. Mol. Med. 1 (2014) 73–75. [2] K. Toyama, H. Yamabe, T. Uemura, et al., Analysis of oxidative stress expressed by urinary level of 8-hydroxy-2′-deoxyguanosine and biopyrrin in atrial fibrillation: effect of sinus rhythm restoration, Int. J. Cardiol. 168 (2013) 80–85. [3] F. Violi, D. Pastori, P. Pignatelli, L. Loffredo, Antioxidants for prevention of atrial fibrillation: a potentially useful future therapeutic approach? A review of the literature and meta-analysis, Europace 16 (2014) 1107–1116. [4] M.T. Ziolo, P.J. Mohler, Defining the role of oxidative stress in atrial fibrillation and diabetes, J. Cardiovasc. Electrophysiol. 26 (2015) 223–225. [5] Y. Seko, T. Fujimura, T. Yao, et al., Secreted tyrosine sulfated-eIF5A mediates oxidative stress-induced apoptosis, Sci. Rep. 5 (2015) 13737 (510.1038/ srep13737).
[6] T. Yao, T. Fujimura, K. Murayama, Y. Seko, Plasma levels of oxidative stress-responsive apoptosis inducing protein (ORAIP) in rats subjected to various types of oxidative stress, Biosci. Rep. 36 (2016) e00317 (10.1042BSR20160044). [7] M. Sakabe, A. Fujiki, T. Sakamoto, Y. Nakatani, K. Mizumaki, H. Inoue, Xanthine oxidase inhibition prevents atrial fibrillation in a canine model of atrial pacing-induced left ventricular dysfunction, J. Cardiovasc. Electrophysiol. 10 (2012) 1130–1135. [8] W. Xie, G. Santulli, S.R. Reiken, et al., Mitochondrial oxidative stress promotes atrial fibrillation, Sci. Rep. 5 (2015) 11427. [9] A. Goettel, A. Bukowska, D. Dobrev, et al., Acute atrial tachyarrhythmia induces angiotensin II type 1 receptor-mediated oxidative stressand microvascular flow abnormalities in the ventricles, Eur. Heart J. 30 (2009) 1411–1420. [10] S. Saito, Y. Teshima, A. Fukui, et al., Glucose fluctuations increase the incidence of atrial fibrillation in diabetic rats, Cardiovasc. Res. 104 (2014) 5–14.
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Correspondence
Plasma levels of oxidative stress-responsive apoptosis inducing protein (ORAIP) in patients with atrial fibrillation Takako Yao a, Kentaro Tanaka b, Tsutomu Fujimura c, Kimie Murayama d, Shuichi Fukuda e, Ko Okumura f, Yoshinori Seko a,⁎ a
Division of Cardiovascular Medicine, The Institute for Adult Diseases, Asahi Life Foundation, Tokyo, Japan Higashiyamato Nangai Clinic, Tokyo, Japan Laboratory of Bioanalytical Chemistry, Tohoku Pharmaceutical University, Miyagi, Japan d Division of Proteomics and Biomolecular Science, BioMedical Research Center, Graduate School of Medicine, Juntendo University, Tokyo, Japan e Wakakusa Clinic, Tochigi, Japan f Department of Atopy Research Center, Juntendo University School of Medicine, Tokyo, Japan b c
a r t i c l e
i n f o
Article history: Received 4 May 2016 Received in revised form 25 July 2016 Accepted 2 August 2016 Available online 3 August 2016
Keywords: Atrial fibrillation (AF) Cardiac injury Eukaryotic translation initiation factor (eIF) 5 A Ischemia/reperfusion Oxidative stress
Atrial fibrillation (AF) is frequently associated with congestive heart failure, valvular heart diseases, hypertension, and diabetes mellitus (DM) [1], but is also an important causative factor of cerebral infarction, congestive heart failure, and other cardiac disorders. Although oxidative stress has been implicated in the pathogenesis of AF [2–4], the precise mechanism of cardiotoxicity involved in AF remains unclear. Oxidative stress causes cell damage that leads to apoptosis via uncertain mechanisms. To investigate the mechanisms involved, we previously analyzed the molecular mechanism involved in hypoxia/reoxygenationinduced apoptosis of cultured cardiac myocytes [5]. Because hypoxia/ reoxygenation-conditioned medium of cardiac myocytes could induce
Abbreviations: AF, atrial fibrillation; cTnT, cardiac troponin T; DM, diabetes mellitus; eIF5A, eukaryotic translation initiation factor 5A; ELISA, enzyme-linked immunosorbent assay; HRP, horseradish peroxidase; mAb, monoclonal antibody; NT-proBNP, N-terminal pro-brain natriuretic peptide; 8-OHdG, 8-hydroxy-2′-deoxyguanosine; ORAIP, oxidative stress-responsive apoptosis inducing protein; RyR2, type 2 ryanodine receptor; SE, standard error; ROS, reactive oxygen species; UV, ultraviolet. ⁎ Corresponding author at: Division of Cardiovascular Medicine, The Institute for Adult Diseases, Asahi Life Foundation, 2-2-6 Nihonbashi-Bakurocho, Chuo-ku, Tokyo 103-0002, Japan. E-mail address: [email protected] (Y. Seko).
http://dx.doi.org/10.1016/j.ijcard.2016.08.005 0167-5273/© 2016 Elsevier Ireland Ltd. All rights reserved.
extensive apoptosis of cardiac myocytes under normoxia, we thought that some humoral factor was rapidly released from cardiac myocytes, then mediated apoptosis. And, we identified the apoptosis-inducing humoral factor in the hypoxia/reoxygenation-conditioned medium by a proteomic approach. We found that eukaryotic translation initiation factor 5A (eIF5A) undergoes sulfation of 69th tyrosine residue in the trans-Golgi as well as more hypusination, and is rapidly secreted from cardiac myocytes in response to hypoxia/reoxygenation, then induces apoptosis of the cells as a pro-apoptotic ligand [5]. We named this novel post-translationally modified secreted form of eIF5A, Oxidative stress-Responsive Apoptosis Inducing Protein (ORAIP). Rat model of myocardial ischemia/reperfusion (but not ischemia alone) markedly increased plasma levels of ORAIP. Another oxidative stress, ultraviolet (UV)-irradiation to the heart of rats also markedly increased plasma levels of ORAIP. The apoptosis induction of cardiac myocytes by hypoxia/reoxygenation and UV-irradiation was significantly suppressed by neutralizing anti-ORAIP monoclonal antibodies (mAbs) in vitro [5]. In vivo administration of anti-ORAIP mAbs significantly reduced myocardial ischemia/reperfusion injury. These data [5] indicate that the apoptosis induction of cardiac myocytes by these stimuli are critically mediated by ORAIP. We confirmed that ORAIP is specifically secreted in response to the oxidative stresses including ischemia/reperfusion, hypoxia/ reoxygenation, ultraviolet-irradiation, ionizing radiation, cold/warmstress (heat shock), and blood acidification [6], then acts as a proapoptotic ligand to induce apoptosis of target cells. In this study, to investigate the role of ORAIP in the mechanism of oxidative stressinduced myocardial injury in AF, we analyzed plasma levels of ORAIP, cardiac troponin T (cTnT), and N-terminal pro-brain natriuretic peptide (NT-proBNP) in patients with AF. This study was carried out in accordance with the Declaration of Helsinki (2000) of the World Medical Association, and was approved by the institutional ethical committee. All patients gave written informed consent after full explanation of the purpose, nature and risk of all procedures used. Thirty patients (30 males; age, 73.5 ± 1.6 [mean ± SE] years) with AF and 23 control subjects (23 males; age, 72.7 ± 1.3 [mean ± SE] years) without AF were studied. The characteristics of the patient and control groups are summarized in Table 1. Plasma ORAIP levels were analyzed by the sandwich enzyme-linked immunosorbent
Correspondence Table 1 Characteristics of the patient and control groups. Controls
AF patients
n
23
30
Sex (male/female) Age (years) Smoking (n) Hypertension (n) Diabetes mellitus (n) Dislipidemia (n)
23/0 72.7 ± 1.3 13 (56.5%) 15 (65.2%) 18 (78.3%) 10 (43.5%)
30/0 73.5 ± 1.6 15 (50.0%) 19 (63.3%) 16 (53.3%) 11 (36.7%)
p valuea
0.701 0.638 0.886 0.0603 0.616
Data given as (mean ± SE) or numbers (%). a Quantitative data, Welch's t-test; qualitative data, chi-square test.
assay using blocking-less type plates (Sumitomo Bakelite Co., Ltd., Tokyo, Japan) as described previously [5]. The (mean ± SE) plasma ORAIP concentrations (64.75 ± 10.68 ng/ml) in 30 patients with AF were significantly (p = 0.0000190, Welch's t-test) increased as compared with those (9.92 ± 2.11 ng/ml) in 23 control subjects without AF (Fig. 1A). To investigate the effect of significant elevation of plasma ORAIP levels on myocardial injury, we analyzed plasma levels of cTnT (normal range b 14.0 pg/ml) and found that plasma cTnT levels (43.4 ± 13.1 [mean ± SE] pg/ml) were significantly (p = 0.0217, Welch's t-test) elevated as compared with those in 23 control subjects without AF (11.4 ± 1.3 [mean ± SE] pg/ml), and there was a positive correlation (r = 0.453, p = 0.0120) between plasma levels of ORAIP and cTnT (Fig. 1B). There was also a positive correlation (r = 0.492, p = 0.0057) between plasma levels of ORAIP and NT-proBNP (Fig. 1C). We also analyzed the plasma levels of 8-hydroxy-2′-deoxyguanosine (8-OHdG) as one of the oxidative stress markers. There was a tendency for positive correlation (but not significant p = 0.0904) between plasma levels of ORAIP and those of 8-OHdG (data not shown). We have demonstrated that plasma ORAIP levels were significantly increased in AF patients, indicating that oxidative stress levels were elevated in AF. The correlation between plasma levels of ORAIP and cTnT as well as NT-proBNP strongly suggests that ORAIP plays a critical role in cardiac injury in patients with AF. There have been several studies reporting the mechanisms of oxidative stress induction in AF. Xanthine oxidase (XO) is an enzyme involved in purine metabolism and also produces reactive oxygen species (ROS). Sakabe et al. [7] demonstrated that XO inhibitor allopurinol suppressed AF promotion by preventing both electrical and structural remodeling in dogs with atrial tachypacing,
529
suggesting that XO plays a critical role in inducing oxidative stress in AF. Xie W, et al. [8] reported that intracellular Ca2+ release via the atrial type 2 ryanodine receptor (RyR2) increases RyR2 oxidation and mitochondrial ROS production, which leads to AF. Goette et al. [9] demonstrated that rapid atrial pacing induces angiotensin II type 1-receptor-mediated oxidative stress in ventricular myocardium that is accompanied by impaired microvascular blood flow and cardiac troponin-I release. Saito et al. [10] reported that glucose fluctuation in streptozotocin-induced diabetic rats increased ROS levels, which promote cardiac fibrosis and increase the incidence of AF. This may be one of the mechanisms of increased association of AF with DM. Although the precise mechanism of oxidative stress generation in AF is still uncertain, plasma ORAIP levels can be a novel biomarker for the oxidative stress involved and the elevated levels of ORAIP will cause myocardial injury and fibrosis, resulting in the progression of AF and cardiac dysfunction. Thus, ORAIP may play a critical role in AF-associated cardiac disorders as well as AF itself. Our findings warrant elimination of plasma ORAIP with a neutralizing antibody against ORAIP [5] to protect from cardiovascular injury in patients with oxidative stress-associated disorders such as AF. Conflict of interest The authors have no conflicts of interest to disclose. Source of funding This work was supported by Research Fund of Mitsukoshi Health and Welfare Foundation 2015 and a grant from Takeda Research Support. Author contribution Y.S. designed the study. T.Y., Y.S., and K.O. produced mAbs, developed ELISA. T.Y., Y.S., K.T., and S.F. collected and measured the patients' samples. T.F. and K.M. did proteomic analyses and identified ORAIP. All authors discussed the results and commented the study. Acknowledgments We thank co-medical staffs of The Institute for Adult Diseases, Asahi Life Foundation for technical supports.
Fig. 1. (A) Plasma levels of ORAIP in patients with AF and control subjects without AF. (mean ± SE, n = 30 and 23, respectively, *p = 0.0000190, Welch's t-test). (B) Correlation between plasma levels of ORAIP and those of cTnT. There was a significant positive correlation (r = 0.453, p = 0.0120). (C) Correlation between plasma levels of ORAIP and those of NT-proBNP. There was a significant positive correlation (r = 0.492, p = 0.0057). (B and C; Spearman's rank correlations between the data were calculated).
530
Correspondence
References [1] K. Aizawa, J. Fujui, Y. Seko, Diabetes mellitus is important as a risk factor of atrial fibrillation, Integr. Mol. Med. 1 (2014) 73–75. [2] K. Toyama, H. Yamabe, T. Uemura, et al., Analysis of oxidative stress expressed by urinary level of 8-hydroxy-2′-deoxyguanosine and biopyrrin in atrial fibrillation: effect of sinus rhythm restoration, Int. J. Cardiol. 168 (2013) 80–85. [3] F. Violi, D. Pastori, P. Pignatelli, L. Loffredo, Antioxidants for prevention of atrial fibrillation: a potentially useful future therapeutic approach? A review of the literature and meta-analysis, Europace 16 (2014) 1107–1116. [4] M.T. Ziolo, P.J. Mohler, Defining the role of oxidative stress in atrial fibrillation and diabetes, J. Cardiovasc. Electrophysiol. 26 (2015) 223–225. [5] Y. Seko, T. Fujimura, T. Yao, et al., Secreted tyrosine sulfated-eIF5A mediates oxidative stress-induced apoptosis, Sci. Rep. 5 (2015) 13737 (510.1038/ srep13737).
[6] T. Yao, T. Fujimura, K. Murayama, Y. Seko, Plasma levels of oxidative stress-responsive apoptosis inducing protein (ORAIP) in rats subjected to various types of oxidative stress, Biosci. Rep. 36 (2016) e00317 (10.1042BSR20160044). [7] M. Sakabe, A. Fujiki, T. Sakamoto, Y. Nakatani, K. Mizumaki, H. Inoue, Xanthine oxidase inhibition prevents atrial fibrillation in a canine model of atrial pacing-induced left ventricular dysfunction, J. Cardiovasc. Electrophysiol. 10 (2012) 1130–1135. [8] W. Xie, G. Santulli, S.R. Reiken, et al., Mitochondrial oxidative stress promotes atrial fibrillation, Sci. Rep. 5 (2015) 11427. [9] A. Goettel, A. Bukowska, D. Dobrev, et al., Acute atrial tachyarrhythmia induces angiotensin II type 1 receptor-mediated oxidative stressand microvascular flow abnormalities in the ventricles, Eur. Heart J. 30 (2009) 1411–1420. [10] S. Saito, Y. Teshima, A. Fukui, et al., Glucose fluctuations increase the incidence of atrial fibrillation in diabetic rats, Cardiovasc. Res. 104 (2014) 5–14.