Genetic deficiency of inducible nitric oxide synthase reduces atherosclerosis and lowers plasma lipid peroxides in apolipoprotein E-knockout mice

Abstract

Background. Inducible nitric oxide synthase (iNOS) is expressed by leukocytes and smooth muscle cells in atherosclerotic lesions. To test whether NO produced by iNOS deficiency affects atherosclerosis, we studied apoE/iNOS-double knockout (dKO) and apoE-knockout (KO) control animals fed a "Western-type" diet. Methods and Results. After 16 weeks of Western-type diet, the aortic lesion area in apoE/iNOS-dKO males and females was significantly reduced, by 22% and 21%, respectively, compared with apoE-KO males and females. This effect was more pronounced after 24 weeks of Western-type diet, after which lesion formation in male and female dKO mice was reduced by 38% and 40%, respectively. Plasma levels of lipoperoxides in apoE/iNOS-dKO mice (2.0±0.23 μmol/L) were significantly lower than in apoE-KO control animals (3.2±0.44 μmol/L; P=0.02). To test whether substrate deficiency plays a role in the proatherogenic actions of iNOS, we administered L-arginine to apoE-KO animals for 16 and 24 weeks. L-Arginine treatment did not affect lesion formation in apoE-KO animals fed a Western-type diet. Conclusions. Genetic deficiency of iNOS decreases diet-induced atherosclerosis and lowers plasma levels of lipoperoxides, a marker for oxidative stress, in apoE-KO animals. Reduction in iNOS-mediated oxidative stress could partly explain protection from lesion formation in dKO animals. L-Arginine supplementation did not change lesion area in apoE-KO mice, indicating that substrate deficiency is not a likely cause for iNOS-mediated injury in this model of atherosclerosis.