Abstract 1683: Tetrahydrobiopterin Reverses Pressure-Load Remodeling by Preventing eNOS Uncoupling
Background: Pressure overload leads to oxidative uncoupling of endothelial nitric oxide synthase (eNOS), which in turn serves as a prominent source of myocardial reactive oxygen species (ROS) contributing to dilatory remodelling and cardiac dysfunction. Concomitant administration of the NOS cofactor tetrahydrobiopterin (BH4) prevents these changes. In this study, we tested whether BH4 can reverse already established non-decompensated hypertrophy by re-coupling eNOS.
Methods: 30 mice underwent transverse aortic constriction (TAC) for 4 weeks to establish hypertrophy and early dilation-remodeling. Mice were then randomized to receive BH4 (5mg/d, n=10) or placebo (n=10) for 5 additional weeks of TAC. Five additional mice underwent sham-surgery, and 5 were sacrificed at 4-wks. Echocardiography was performed at baseline and after 4 and 9wks. Cold SDS-PAGE was used to assess eNOS dimer/monomer. ROS generation was evaluated with dihydroethidium (DHE) confocal staining (score 1-absent; 4-markedly present) and lucigenin-enhanced chemiluminescence. Myocyte dimensions and fibrosis (PAS Methenimine Silverstain score 0–3) were assessed histologically.
Results: At 9 weeks, animals receiving BH4 had reduced myocyte hypertrophy (20.9μm±0.6 μm vs. 15.1± 0.6 μm, p< .001); left ventricular wall thickness (0.91±0.04 mm vs 1.11±0.03 , p<0.001), total wet heart weight (200.2± 13.1 vs 317±18.1 mg, p<0.001), LV mass (164.2±6.0 vs 221. 5 ± 8.7, p=0.004), and fibrosis (0.75 ± 0.48 vs 2.5±0.22 , p=0.026). Additionally, BH4 prevented functional deterioration (fractional shortening: 32.94 ±4.82% vs 20.28± 1.41%, p=0.01). Superoxide generation was markedly reduced by BH4 (n=10, DHE-stain: 2 versus 4; lucigenin: 23% reduction with BH4, both p<0.05). eNOS monomers on SDS gels were reduced by BH4 treatment, supporting NOS re-coupling.
Conclusion: BH4 can reverse established cardiac remodelling by re-coupling uncoupled NOS and as a consequence reducing ROS generation. The result is suppression of hypertrophy progression, reduced fibrosis, and improvement in cardiac function. These data support BH4 treatment as a novel therapy for established hypertrophic heart disease and evolving cardiac failure