A possible involvement of crosstalk between advanced glycation end products (AGEs) and asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor in accelerated atherosclerosis in diabetes.

Endothelial dysfunction due to reduced bioavailability of nitric oxide (NO) is an early step in the course of atherosclerotic cardiovascular disease (CVD). NO is synthesized from L-arginine via the action of NO synthase (NOS), which is known to be blocked by endogenous L-arginine analogues such as asymmetric dimethylarginine (ADMA). ADMA is a naturally occurring amino acid found in plasma and various types of tissues. Recently, it has been demonstrated that plasma levels of ADMA are elevated in patients with diabetes. It has also been reported that elevated plasma levels of ADMA are associated with increased risks of nonfatal stroke and myocardial infarction in patients with early diabetic nephropathy. These findings suggest that the elevated ADMA in diabetes could contribute to acceleration of atherosclerosis in this population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress. There is a growing body of evidence to show that AGEs are involved in the development and progression of atherosclerosis in patients with diabetes. Since ADMA is mainly metabolized by dimethylarginine dimethylaminohydrolase (DDAH), it is conceivable that the impairment of DDAH actions by AGEs could be one possible molecular mechanism of the ADMA elevation in diabetic patients. In this paper, we would like to propose the possible ways of testing our hypotheses. Does treatment with metformin, which has a potential effect on the inhibition of glycation reactions in vivo, decrease the levels of ADMA in diabetic patients? If the answer is yes, is this beneficial effect of metformin superior to that of other anti-diabetic agents with equihypoglycemic properties? Does treatment with pyridoxamine, a post-Amadori inhibitor (so-called Amadorins) of AGE formation, also reduce the levels of ADMA and subsequently improve endothelial dysfunction in diabetic patients? Are the ADMA-lowering effects of these agents associated with an increase of DDAH expression and/or activity in endothelial cells? These clinical studies could clarify whether AGEs are involved in the elevation of ADMA in patients with diabetes via suppression of DDAH expression and/or activity, thus providing a novel molecular mechanism for accelerated atherosclerosis in diabetes.