Abstract 547: 7-Ketocholesterol-Mediated Alterations in Vascular Function: A Link Between Vascular and Metabolic Complications of Chronic Particulate Matter Exposure

Abstract

BACKGROUND: Both human and animal studies have suggested a compelling link between inhaled particulate matter <2.5nm (PM2.5) exposure and acceleration of atherosclerosis. In this study, we assessed the hypothesis that 7-Ketocholesterol (7KC), a major redox product of cholesterol may mediate adverse vascular and metabolic effects of PM2.5 exposure. METHODS: Apolipoprotein E -/- (apoE-/-) mice were exposed to concentrated ambient PM2.5 or filtered air (FA) for 6 hours per day, 5 days per week for a total of 6 months in a versatile aerosol concentrator exposure system. Vasomotor tone changes were assessed in and atherosclerosis lesion quantification performed. 7KC and total cholesterol levels were determined by LC-MS in various tissues including aorta and 7KC accumulation and reverse transport studies in cultured murine macrophages subjected to PM2.5 exposure. eNOS activation and NO generation in response to 7KC exposure was assessed in cultured endothelial cells. RESULTS: PM2.5 increased aortic plaque (1.4-fold, p<0.05 vs. FA; n=7). Relaxation to the endothelium-dependent agonist acetylcholine was attenuated (Rmax, 74.86±6.2 vs. 94.55±7.29%, p<0.05 for PM2.5 vs. FA; n=7). 7KC levels in the aorta of PM2.5-exposed mice was significantly higher than that of FA (1251±453 vs. 8588±2088 ng/g tissue, p<0.05 PM2.5 vs. FA; n=5) while levels in liver were 1-fold higher (p=0.06; n=5). 7KC reduced eNOS activation in cultured endothelial cells through regulation of 1177, 495 and 113 phosphorylation sites of eNOS in a time and dose dependent manner and reduced NO generation when assessed by EPR. Enhanced uptake of 7KC was demonstrated in cultured macrophages after PM2.5 pre-exposure (56.2±0.3 vs. 47.8± 0.9 % p =0.01 for PM2.5 vs. control; n=3) while reverse transport of 7-KC did not differ in the presence of HDL (50 μg/ml). CD36 expression inside macrophages increased after PM2.5 exposure (1.5-fold, p<0.01; n=5) suggesting internalization of 7-KC via CD36 dependent mechanisms. CONCLUSIONS: Chronic PM2.5 exposure enhances 7KC levels paralleled by alterations in endothelial function through eNOS dependent pathways. These findings suggest novel secondary mediators by which air-pollution may modulate adverse vascular effects.