Abstract 13243: Oxidative Stress From Upregulation of Cardiac β3-AR-Activated iNOS Uncoupling Promotes Diabetic Cardiomyopathy in Cynomolgous Monkeys With Naturally-Occurring Type 2 Diabetes
Background: Recent evidence highlights oxidative stress as an important mechanism to cardiac dysfunction in diabetic cardiomyopathy (DM) and altered β3-adrenergic receptor (AR)-activated nitric oxide synthase (NOS) pathway contributing to this process. However, the NOS isoforms involved are controversial. The mechanism of how β3-AR stimulation impacts ROS, SERCA2a, and cardiac function in diabetes is unclear. We tested the hypothesis that oxidant stress from upregulation of LV β3-AR-activated iNOS uncoupling promotes DM.
Methods: We compared myocyte β1- and β3-AR, 3 NOS, peroxynitrite (NT), NADPH and SERCA2a expressions and myocyte functional responses to β- and β3-AR stimulation with isoproterenol (ISO,10-8M) and BRL-37344 (BRL,10-8 M), respectively, in the absence and presence of iNOS inhibitor, 1400W (10-5 M), of 10 male monkeys: 5 normal and 5 with naturally-occurring type 2 diabetes. Myocytes were freshly isolated from LV tissue collected during terminal study.
Results: Compared to normal myocytes, DM myocytes had significantly increased protein levels of β3-AR (0.27 vs 0.15) and iNOS (0.46 vs 0.23) accompanied with increased oxidative stress indicated by significantly-elevated NT formation, NADPH (P67-phox, 33% and p22-phox, 25%) and decreased GTPCH expression (0.48 vs 0.82) and activity. DM myocytes had significantly-decreased protein levels of β1-AR (0.38 vs 0.59) and SERCA2a (0.95 vs 1.15). These changes were associated with reduced basal cell contraction of dL/dtmax (68.4 vs 121.1 μm/s), relaxation (-63.4 vs -110.2 μm/s), and [Ca2+]iT (0.15 vs 0.27) accompanied by diminished β-AR-stimulated positive inotropic response, but enhanced β3-AR-induced negative inotropic response. Only in DM myocytes, pretreatment with 1400W improved basal cell function and augmented ISO-increased dL/dtmax (63.2%) and [Ca2+]iT (27.8%), but significantly limited BRL-induced decrease in dL/dtmax (-13.8%) and [Ca2+]iT (-10.9%).
Conclusions: DM is associated with contrasting changes on myocyte β1- and β3-AR expression with decreased SERCA2a and increased iNOS. Upregulation of β3-AR triggers iNOS uncoupling, leading to oxidative stress, thus promoting intrinsic myocyte dysfunction with impaired [Ca2+]i regulation and reduced β-AR reserve.
- © 2013 by American Heart Association, Inc.