Abstract 597: Tetrahydrobiopterin Prevents Progression To End-stage Heart Failure In A Mouse Model Of Pressure-overload Induced Remodeling
Background: Decreased bioavailability of tetrahydrobiopterin (BH4), an essential cofactor of eNOS, leads to eNOS uncoupling and thus increased generation of free radicals and reduced nitric oxide. Exogenous BH4 prevents eNOS uncoupling and the onset of pressure-overload remodeling. Here, we tested whether once daily oral BH4 attenuates the progression of advanced hypertrophic remodeling to end-stage heart failure in mice, using a placebo-controlled dose-response study design.
Methods: C57/bl6 mice (n=53) underwent 5wks of transverse aortic constriction (TAC) to induce hypertrophy (LV mass: 180±6mg vs. 95±5mg control), chamber dilation (end-diastolic dimension, EDD: 3.94±0.08mm vs. 3.26±0.06mm) and dysfunction (EF: 54±2% vs. 87±0.6% control). Animals were then randomized to 0, 12, 36, 200 or 400 mg/kg/d BH4 (po) for an additional 5 wks of TAC. Sham-mice (n=20) received placebo or BH4 (400mg/kg/d). Echocardiography was performed at 5 and 10wks; fibrosis evaluated by Trichrome-Masson (score 0–3), and O2− by lucigenin-enhanced chemiluminescence. Myocardial BH4 was measured by HPLC.
Results: Placebo treated animals developed worsening failure (EF 31±2%), dilation (EDD 5.0 ±0.1 mm), and hypertrophy (LV mass 263±11g). This was prevented by doses of BH4≥36 mg/kg/d (EF 45±6%, 53±6% and 45±5%, all p<0.05), with similar blunting of LV mass increase (208±19mg, 225±20mg and 234±23mg, all p<0.05) and dilation (4.27±0.26mm, 4.45±0.22mm and 4.37±0.37mm, all p<0.05). Myocardial fibrosis maximally declined at 36 mg/kg/d BH4 (1.17±0.4 AU vs. 2.73±0.12 AU, p<0.001), and this dose also lowered O2− (3.3±0.4 vs. 7.62±1.1 (placebo) cpm·104, p=0.05), to levels in controls (3.4±0.2 cpm·104). Myocardial BH4 rose in a dose-dependent manner (5.5 and 12.1 fold at 36 and 200 mg/kg/d, resp). Doses > 36 mg/kg/d had little incremental pharmacological activity. This dose represents ~15% of that previously reported to prevent eNOS uncoupling.
Conclusion: BH4 therapy prevents progression to end-stage failure in hearts subjected to pressure-overload. Despite increasing myocardial BH4, the dose-response curve is rather flat, with 36 mg/kg/d being sufficient.
This supports a practical use of BH4 and studies of its efficacy in humans with hypertrophic heart disease.