The role of natural antioxidants in preserving the biological activity of endothelium-derived nitric oxide.

Endothelium-derived nitric oxide (EDNO) is a pivotal molecule in the regulation of vascular tone via the stimulation of vascular smooth muscle cell relaxation and concomitant vasodilation. In addition, EDNO exerts a number of other potent antiatherogenic effects, including inhibition of leukocyte-endothelial interactions, smooth muscle cell proliferation, and platelet aggregation. Endothelial vasodilator dysfunction has been observed in patients with CAD or coronary risk factors such as hypercholesterolemia, hyperhomocysteinemia, essential hypertension, diabetes mellitus, smoking, and aging. Most of these conditions are associated with increased oxidative stress, particularly increased production of superoxide radicals and elevated levels of oxidized LDL, both of which can attenuate the biological activity of EDNO. The levels of superoxide and oxidized LDL can be decreased by administering the small molecule antioxidants vitamins E and C. Vitamin C also spares intracellular thiols, which in turn can stabilize EDNO through the formation of biologically active S-nitrosothiols. Here we review the role that vitamins E and C and thiol compounds play in endothelium-dependent vasodilation. Understanding the mechanisms of the reversal of endothelial dysfunction by natural antioxidants will lead to successful therapeutic interventions of CAD and its clinical sequelae.