Increased NADPH oxidase activity and alteration in antioxidant enzymes in the right and the left ventricle from human failing heart

During pathophysiological conditions, the balance between reactive oxygen species (ROS) and antioxidants may shift towards a relative increase of ROS resulting in oxidative stress. Conflicting data are available on antioxidant defences in human failing heart and they are limited to the left ventricle. We aimed to investigate and compare a major source of ROS, a NADPH oxidase system, and antioxidant enzyme activities in the right (RV) and left (LV) ventricles of human failing hearts. Methods. The molecular and biochemical analyses were performed in RV and LV from non failing (NF) (n=5) and failing hearts secondary to idiopathic dilated cardiomyopathy or ischemic heart disease (n=13). NADPH oxidase activity, as major source of ROS, was determined by lucigenin-enhanced chemiluminescence and NOX2 and NOX4 gene expression by RT-PCR. The analysis of catalase (CAT), glutathione peroxidase (GPx) and Mn-superoxide dismutase (Mn-SOD) was performed by measuring their mRNA (by real-time PCR) and protein levels (by Western blotting) as well as their enzymatic activities (by spectrophotometric methods). The level of lipid peroxidation was evaluated by measuring the contents of malonildialdheyde (MDA). Results. A significant increase in NADPH oxidase activity was found in both failing ventricles, more marked in RV. As for antioxidant enzymes, despite unchanged mRNA or protein expression, the enzymatic activity of CAT and GPx was increased, whereas Mn-SOD activity appeared decreased. We attributed the changes in catalytic activity of these antioxidant enzymes to post-translational modifications (notably, tyrosine phosphorylation). The increase in NADPH oxidase activity positively and significantly correlated with the activation of both CAT and GPx. However, the slope of the linear correlation (m) was steeper in LV than in RV for GPx (LV: m = 2.416; RV: m = 1.485) and CAT (LV: m = 1.007; RV: m = 0.354). MDA levels, measured as an indirect index of oxidative stress, were significantly higher in the RV than LV. Conclusions. We concluded that in human failing RV and LV, oxidative stress was correlated to activation of antioxidant enzymes CAT and GPx. This activation appeared less evident in RV than RV. Thus, although qualitatively similar changes appeared in both the RV and LV of the same hearts, our data suggest a reduced protection of RV against oxidative stress damage and support the involvement of the right ventricle in the pathophysiology of heart disease.