The endothelial nitric oxide synthase (eNOS) derived NO. plays an important role in maintaining vascular tone and vasoreactivity, vasodialation, platelet aggregation and in maintaining balance between smooth muscle cell growth and differentiation. Decreased NO bioavailabilty is the one of the major feature of the CVDs [249]. During reduced availability of BH4 or L-Arg, eNOS becomes uncoupled from a NO2 to a O2À state [164]. The O•- formed can 2 2interact with NO• to produce ONOO-, a damaging and cytotoxic free radical with potential to disturb cardiovascular function. ONOO- reduces the bioavailability of NO leading to reduced endothelial vascular regulatory capacity and increased vascular dysfunction. ONOO2 also inactivates the BH4 cofactor effectively amplifying the damaging effects of eNOS uncoupling the endothelium [164]. Mitochondrial DNA damage is frequently observed in human atherosclerosis in both circulating and vessel wall cells [165]. Oxidative stress mediated damaged mitochondrial DNA that escape autophagy induces a potent inflammatory response in atherosclerosis [166]. Malfunction of DNA repair leads to defects in cell proliferation, apoptosis, and mitochondrial dysfunction, which in turn leads to ketosis, hyperlipidemia, and increased fat storage, promoting atherosclerosis and the metabolic syndrome [167].
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