GTP cyclohydrolase I gene transfer reverses tetrahydrobiopterin deficiency and increases nitric oxide synthesis in endothelial cells and isolated vessels from diabetic rats

Nitric oxide ( NO) synthesis in endothelial cells is impaired in diabetes. We previously showed that impaired NO synthesis in the spontaneously diabetic BB (BBd) rat is due to decreased levels of tetrahydrobiopterin (BH4), secondary to decreased expression of GTP cyclohydrolase I (GTPCH). The aim of this study was to utilize adenoviral GTPCH gene transfer to reverse BH4 deficiency and repair the ability of endothelial cells to produce NO. GTPCH gene transfer increased BH4 levels in BBd endothelial cells from 0.17 +/- 0.02 ( mean +/- SE) to 73.37 +/- 14.42 pmol/million cells and NO production from 0.77 +/- 0.07 to 18.74 +/- 5.52 nmol/24 h/million cells. To demonstrate a functional effect of increasing BH4 concentrations in tissues, we transferred GTPCH into aortic rings from BBd and Zucker diabetic fatty (ZDF) rats, models of human type I and type II diabetes, respectively. GTPCH gene transfer led to a dose-dependent increase in acetylcholine-induced vasorelaxation, preventable by inhibiting NO synthase. Maximal relaxation of virus-treated rings (10(10) virus particles/ml) to acetylcholine was significantly higher than sham-treated rings (BBd 64% vs. 37%, P< 0.005; ZDF 80% vs. 44%, P< 0.05). This study demonstrates that GTPCH gene transfer can reverse BH4 deficiency in both type I and type II diabetes and provides an experimental basis for using gene therapy to treat cardiovascular complications in diabetic patients.