Abstract 856: Augmentation of Vascular Remodeling due to Uncoupled eNOS in Diabetes
Background: Diabetes mellitus is associated with increased oxidative stress in vessels, which oxidizes tetrahydrobiopterin (BH4) required for endothelial nitric oxide synthase (eNOS) bioactivity. In the presence of reduced BH4, eNOS is uncoupled to L-arginine and produces superoxide rather than NO. However, it is unknown whether increased oxidative stress caused by uncoupled eNOS augments vascular remodeling in diabetes.
Methods and Results: Diabetes mellitus was produced by streptozotocin in C57BL/6J wild-type mice. Under stable hyperglycemia, the common carotid artery was ligated, and neointimal formation proximal to the ligated site was examined 4 weeks later. In diabetic mice, the neointimal area was dramatically augmented (5470±1460 vs. 1330±410μm2, P<0.05, n=10 per group), in association with increased superoxide formation in aortas by 1.8-fold. In diabetic mice, the ratio of BH4/BH2 in the aorta was reduced by 45%, eNOS dimer to monomer ratio in the lung by 44%, and plasma NOx levels by 28% compared with non-diabetic mice. Chronic supplementation with exogenous BH4 (10mg/kg/day) reduced the neointimal area (2060±790μm2, n=10) in diabetic mice. Along with this reduction, there were preserved BH4/BH2 ratio, eNOS dimer to monomer ratio, and plasma NOx levels, which resulted in suppression of superoxide production possibly via maintained eNOS coupling. Further, expressions of ICAM-1 and VCAM-1, and leukocyte accumulation were decreased in the endothelial layer of carotid arteries of BH4-treated diabetic mice. To further examine the effects of uncoupled eNOS on vascular remodeling, we used endothelial-targeted eNOS-transgenic mice. In the absence of diabetes, overexpression of eNOS inhibited neointimal formation. In the presence of diabetes, however, overexpression of eNOS resulted in marked augmentation of neointimal area (10130±1580μm2), which was accompanied by increased superoxide production and expression of adhesion molecules in the endothelium.
Conclusions: Therefore, increased oxidative stress derived from uncoupled eNOS leads to augmentation of vascular remodeling under hyperglycemia. Preservation of eNOS coupling by BH4 may be a rational therapeutic strategy for preventing vascular complications in diabetes.