Hypercholesterolemia inhibits angiogenesis in response to hindlimb ischemia - Nitric oxide-dependent mechanism

Background-Endothelium-derived nitric oxide (EDNO) plays an important role in the regulation of angiogenesis, whereas hypercholesterolemia (HC) impair s EDNO release. We examined the hypothesis that HC may inhibit ischemia-ind uced angiogenesis by inhibition of EDNO in a rat model of unilateral hindli mb ischemia and that oral L-arginine supplementation, a substrate for NO sy nthase, may prevent HC-related impairment of angiogenesis. Methods and Results-Male Sprague-Dawley rats were fed (A) standard diet (co ntrol), (B) 2% high-cholesterol diet (HC group), or (C) high-cholesterol di et with oral L-arginine (2.25% in drinking water) (HC+L-arg group). At 2 we eks of the dietary intervention, unilateral limb ischemia was surgically in duced in all animals. Dietary HC groups (B and C) revealed elevated total a nd LDL cholesterol levels compared with control animals. Laser Doppler bloo d flow analyses showed significant decreases in the ischemic/normal limb bl ood flow ratio in the HC group compared with controls (P<0.05) when followe d up until 4 weeks after surgery. Selective angiography and immunohistochem ical analyses in the ischemic limb at postoperative day 14 revealed signifi cantly lower angiographic scores (P<0.01) and capillary densities (P<0.01) in the HC group than controls, which were associated with decreased tissue contents of NO, and cGMP. Oral L-arginine supplementation (HC+L-arg) signif icantly improved all parameters of the laser Doppler blood perfusion ratio, angiographic scores, and capillary densities (P<0.01 versus HC group), whi ch were accompanied by significant elevations in serum L-arginine levels an d tissue NOx and cGMP contents. Conclusions-Collateral vessel formation and angiogenesis in response to hin dlimb ischemia were significantly attenuated in rats with dietary HC. The m echanism may be related to the reduced NO bioactivity in the ischemic tissu es. Augmentation of the tissue NO activity by oral L-arginine supplementati on restored the impaired angiogenesis in HC.