Arginase Reciprocally Regulates Nitric Oxide Synthase Activity and Contributes to Endothelial Dysfunction in Aging Blood Vessels

Abstract

Background— Although abnormal l -arginine NO signaling contributes to endothelial dysfunction in the aging cardiovascular system, the biochemical mechanisms remain controversial. l -arginine, the NO synthase (NOS) precursor, is also a substrate for arginase. We tested the hypotheses that arginase reciprocally regulates NOS by modulating l -arginine bioavailability and that arginase is upregulated in aging vasculature, contributing to depressed endothelial function. Methods and Results— Inhibition of arginase with (S)-(2-boronoethyl)- l -cysteine, HCl (BEC) produced vasodilation in aortic rings from young (Y) adult rats (maximum effect, 46.4±9.4% at 10 −5 mol/L, P <0.01). Similar vasorelaxation was elicited with the additional arginase inhibitors N -hydroxy-nor- l -arginine (nor-NOHA) and difluoromethylornithine (DFMO). This effect required intact endothelium and was prevented by 1H-oxadiazole quinoxalin-1-one ( P <0.05 and P <0.001, respectively), a soluble guanylyl cyclase inhibitor. DFMO-elicited vasodilation was greater in old (O) compared with Y rat aortic rings (60±6% versus 39±6%, P <0.05). In addition, BEC restored depressed l -arginine (10 −4 mol/L)–dependent vasorelaxant responses in O rings to those of Y. Arginase activity and expression were increased in O rings, whereas NOS activity and cyclic GMP levels were decreased. BEC and DFMO suppressed arginase activity and restored NOS activity and cyclic GMP levels in O vessels to those of Y. Conclusions— These findings demonstrate that arginase modulates NOS activity, likely by regulating intracellular l -arginine availability. Arginase upregulation contributes to endothelial dysfunction of aging and may therefore be a therapeutic target.