Effect of L-Citrulline Supplementation on Arginase Activity and Vascular Function in Type II Diabetes Mellitus

Vascular dysfunction is a major cause of morbidity and mortality in diabetic patients. The pathological process is characterized by impaired endothelial cell production of the vasodilator and antiplatelet adhesion factor nitric oxide (NO) and/or decreased NO bioavailability. NO is a major regulator of vascular tone and integrity. In endothelial cells, NO is produced by activity of endothelial NO synthase (eNOS) on its substrate L-arginine. Reduced availability of L-arginine to eNOS has been implicated in vascular dysfunction in diabetes and a variety of other disease conditions. Arginase, which metabolizes L-arginine to urea and ornithine, competes directly with NOS for L-arginine. Hence increases in arginase activity can decrease tissue and cellular arginine levels, reducing its availability to eNOS and decreasing No production. During diabetes, elevated levels of arginase can compete with NOS for available arginine thus reducing vascular NO. We have recently shown that arginase activity is elevated in diabetes. In this proposal we implement a method of flow mediate dilation (FMD) to assess vascular function in diabetic patients. We will study the relation of our vascular function findings with arginase activity levels. We propose that arginase activity measurements could be novel marker of vascular dysfunction in diabetes. The effect of the natural amino acid supplements (L-citrulline) on levels of arginase activity in diabetic patients and vascular function will also be studied.