Abstract 11922: Defective Glutathione Reductase Results in Systolic Dysfunction Associated with Impaired Mitochondrial Integrity, Increased Uncoupling Respiration, and Enhanced S-Glutathionylation of Complex I
Mitochondrial function is determined in part by its redox state, which reflects a balance between the amount of oxidants produced and the antioxidant defenses. Glutathione reductase (GR) is a key antioxidant enzyme, which reduces GSSG to its reduced form (GSH), and regulates the redox state via modulation of the GSSG/GSH ratio. Because of this key role, we hypothesized that impaired GR activity may deteriorate mitochondrial integrity and result in heart dysfunction. Rats subjected to 30 min of coronary ligation followed by 24 hr of reperfusion showed a decrease in mitochondrial GR activity (75±4%). This result corroborates reports of an increased ratio of GSSG/GSH and protein S-glutathionylation (PrSSG) of complex I in the post-ischemic heart. Intravenous administration of the anticancer agent 1, 3-bis (2-chloroethyl)-1-nitrosourea (BCNU) inhibited mitochondrial GR activity by 80±3% in heart, but modestly enhanced the complex I activity to 113±3% from the mitochondria. Cardiac function of BCNU-treated rat was analyzed by echocardiography, revealing a reduction of ejection fraction (from 76±3% to 58±2%) and cardiac output (from 119±5 to 81±7 ml/min). Also, BCNU treatment increased in left ventricular internal dimension (LVID, from 4.1±0.3 to 5.4±0.3 mm) and left ventricular volume (from 77±13 to 139±14 µl) in systole, without changing LVID in diastole, suggesting systolic dysfunction after GR inhibition. The respiratory control index of isolated mitochondria from myocardial tissue was moderately decreased by 16±4% after BCNU treatment, indicating impaired mitochondrial integrity. NADH-linked uncoupling O2 consumption was boosted by 39±6%. Extracellular flux analysis to measure the fatty acid oxidation of myocyte indicated a 19±3% enhancement after BCNU treatment. When mitochondrial proteins were immunoprecipitated with antibody against complex I and probed with an antibody against GSH, PrSSG was significantly enhanced at the 51-kDa (by 88±14%) and 75-kDa (by 106±19%) subunits, indicating increasing oxidative stress in mitochondria. In conclusion, our data suggest that BCNU-induced GR defect compromises systolic function of rat heart by impairing mitochondrial integrity, uncoupling respiration, and enhancing PrSSG of complex I.
- © 2011 by American Heart Association, Inc.