Atheroprotective effects of antioxidants through inhibition of mitogen-activated protein kinases

Reactive oxygen species (ROS) have been known to play an important role in the pathogenesis of atherosclerosis and several other cardiovascular diseases. It is now apparent that ROS induce endothelial cell damage and vascular smooth muscle cell (VSMC) growth and cardiac remodeling, which are associated with hypertension, atherosclerosis, heart failure, and restenosis. Several lines of evidence have indicated that ROS and mitogen-activated protein (MAP) kinases were involved in vascular remodeling under various pathological conditions. Recently, it was also reported that MAP kinases were sensitive to oxidative stress. MAP kinases play an important role in cell differentiation, growth, apoptosis, and the regulation of a variety of transcription factors and gene expressions. Bioflavonoids and polyphenolic compounds are believed to be beneficial for the prevention and treatment of atherosclerosis and cardiovascular diseases. One of the most widely distributed bioflavonoids, 3,3',4',5,7-penta-hydroxyflavone (quercetin) and its metabolite quercetin 3-O-beta-D-glucuronide (Q3GA) inhibited Angiotensin II-stimulated JNK activation and resultant hypertrophy of VSMC. Several studies have suggested that various antioxidants including probucol, N-acetyl-L-cysteine, diphenylene iodonium, Trolox C (vitamin E analogue), and vitamin C inhibit VSMC growth, which is associated with pathogenesis of cardiovascular diseases. Therefore, inhibition of MAP kinases by antioxidant treatment may prove to be a therapeutic strategy for cardiovascular diseases. In contrast, some clinical studies have reported that antioxidant vitamins did not show beneficial effects in coronary artery disease or in a number of high-risk people. Thus, further studies are needed to clarify why antioxidants showed beneficial effects in vitro, whereas less satisfactory results were obtained in some clinical conditions.