Abstract 351: Efficacy Of Targeting enos-generated Oxidant Stress To Reverse Cardiac Pressure-overload Induced Hypertrophy
Background: Uncoupling of endothelial nitric oxide synthase (eNOS) is linked to depletion of its essential cofactor tetrahydrobiopterin (BH4) and the resulting reactive oxygen species (ROS) generation plays an important role in pressure-overload induced remodeling. We hypothesized that re-coupling of eNOS by exogenous BH4 can reverse established ventricular remodeling more effectively than a similarly potent but less targeted superoxide scavenger.
Methods: Mice (n=120) were subjected to transverse aortic-constriction (TAC), and after 4wks randomized to receive BH4 (200mg/kg/d, n=30), the superoxide dismutase mimetic Tempol (5mg/d, n=8), or placebo (n=30) for the ensuing 5wks of TAC.
Results: TAC for 4 wks (no treatment) induced marked ventricular and myocyte hypertrophy, fibrosis and chamber dysfunction (Table⇓). These continued to worsen with TAC 9 wk in mice receiving placebo, but all significantly improved to levels better than at the start of treatment in mice receiving BH4. In contrast, Tempol did not reverse hypertrophy or fibrosis, but partially blunted progressive myocyte enlargement and EF decline. Importantly, both BH4 and Tempol similarly reduced superoxide (BH4:4.45 ± 0.80; Tempol: 5.16 ± 0.63; placebo: 8.7 ± 0.77 cpm ·103, both p<0.05 vs placebo). BH4 but not Tempol recoupled eNOS as reflected by monomer/dimer SDS-Page analysis, supporting a targeted role of eNOS function and ROS generation. Microarray analysis revealed both BH4 and Tempol altered the expression of principally metabolic genes, but with directionally opposite changes and essentially no overlap in the specific genes induced.
Conclusion: Targeting eNOS dependent ROS generation by BH4 rather than using a less-focused antioxidant blocks pre-existing pressure-overload induced hypertrophy, fibrosis, and improves function by recoupling eNOS. This indicates that the effect of BH4 is more potent than a general antioxidant, and enhances its potential for heart disease treatment.