Endothelial-specific tetrahydrobiopterin expression accelerates refractory wound healing by suppressing oxidative stress in diabetes.

Refractory wound is a severe complication that leads to limb amputation in diabetes. Endothelial nitric oxide synthase (eNOS) plays a key role in normal wound repair, but is uncoupled in streptozotocin (STZ)-induced type 1 diabetes due to reduced cofactor tetrahydrobiopterin (BH4). We tested the hypothesis that overexpression of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for de novo BH4 synthesis, retards NOS uncoupling and accelerates wound healing in STZ mice. Blood glucose levels were significantly increased in both male endothelial-specific GTPCH I transgenic mice (Tg-GCH via a tie-2 promoter) and the wild-type (WT) littermates 5 days after STZ regimen. A full-thickness excisional wound was created on mouse dorsal skin by a 4-mm punch biopsy. Wound closure was delayed in STZ mice, which was rescued in STZ Tg-GCH mice. Cutaneous BH4 level was significantly reduced in STZ mice vs. WT mice, which was maintained in STZ Tg-GCH mice. In STZ mice, constitutive nitric oxide synthase (cNOS) activity and nitrite levels were decreased compared to WT mice, paralleled by increased superoxide anion (O2(-)) level and inducible nitric oxide synthase (iNOS) activity. In STZ Tg-GCH mice, nitrite level and cNOS activity were potentiated, O2(-) level and iNOS activity were suppressed compared to STZ mice. Thus, endothelial-specific BH4 overexpression accelerates wound healing in type 1 diabetic mice by suppressing oxidative stress. Key words: GTP cyclohydrolase I, BH4, oxidative stress, wound healing.