Selective downregulation of mitochondrial electron transport chain activity and increased oxidative stress in human atrial fibrillation

Mitochondria are critical for maintaining normal cardiac function, and a deficit in mitochondrial energetics can be associated with the development of the substrate that promotes atrial fibrillation (AF) and its progression. The link, however, between mitochondrial dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate differences in the functional activities of mitochondrial oxidative phosphorylation (OXPHOS) complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF (AF) who were undergoing open-heart surgery and were well matched for presence of major comorbidities. The overall functional activity of the electron transport chain, NADH:O2 oxidoreductase activity, was reduced by 30% in atrial tissue from AF compared to non-AF patients. This was predominantly due to a selective reduction in complex I activity in AF compared to non-AF (0.10±0.01 vs. 0.13±0.01 nmol/min/citrate synthase activity, p=0.03). In addition, the AF patients had a higher level of 4-hydroxynonenal (4-HNE) (77.64±30.2 vs 9.83±2.83 ng/mg protein, p=0.05), a marker of oxidative stress. Our findings suggest that functional activity of complex I is selectively downregulated in patients with AF and could contribute to oxidative stress and the progression of the substrate for AF

Selective downregulation of mitochondrial electron transport chain activity and increased oxidative stress in human atrial fibrillation

Mitochondria are critical for maintaining normal cardiac function, and a deficit in mitochondrial energetics can lead to the development of the substrate that promotes atrial fibrillation (AF) and its progression. However, the link between mitochondrial dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate differences in the functional activity of mitochondrial oxidative phosphorylation (OXPHOS) complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF (AF) who were undergoing open-heart surgery and were not significantly different for age, sex, major comorbidities, and medications. The overall functional activity of the electron transport chain (ETC), NADH:O(2) oxidoreductase activity, was reduced by 30% in atrial tissue from AF compared with non-AF patients. This was predominantly due to a selective reduction in complex I (0.06 ± 0.007 vs. 0.09 ± 0.006 nmol·min(−1)·citrate synthase activity(−1), P = 0.02) and II (0.11 ± 0.012 vs. 0.16 ± 0.012 nmol·min(−1)·citrate synthase activity(−1), P = 0.003) functional activity in AF patients. Conversely, complex V activity was significantly increased in AF patients (0.21 ± 0.027 vs. 0.12 ± 0.01 nmol·min(−1)·citrate synthase activity(−1), P = 0.005). In addition, AF patients exhibited a higher oxidative stress with increased production of mitochondrial superoxide (73 ± 17 vs. 11 ± 2 arbitrary units, P = 0.03) and 4-hydroxynonenal level (77.64 ± 30.2 vs. 9.83 ± 2.83 ng·mg(−1) protein, P = 0.048). Our findings suggest that AF is associated with selective downregulation of ETC activity and increased oxidative stress that can contribute to the progression of the substrate for AF