L-arginine chlorination products inhibit endothelial nitric oxide production

The myeloperoxidase-derived oxidant hypochlorous acid (HOCl) is thought to contribute to endothelial dysfunction, but the mechanisms underlying this i nhibitory effect are unknown. The present study tested the hypothesis that HOCl and L-arginine (L-Arg) react to form novel compounds that adversely af fect endothelial function by inhibiting nitric oxide (NO) formation. Using spectrophotometric techniques, we found that HOCl and L-Arg react rapidly ( k = 7.1 x 10(5) M-1 s(-1)) to form two major products that were identified by mass spectrometry as monochlorinated and dichlorinated adducts of L-Arg. Pretreatment of bovine aortic endothelial cells with the chlorinated L-Arg metabolites (Cl-L-Arg) inhibited the A23187-induced formation of the NO me tabolites nitrate (NO3-) and nitrite (NO2-) in a concentration-dependent ma nner. Preincubation of rat aortic ring segments with Cl-L-Arg resulted in c oncentration-dependent inhibition of acetylcholine-induced relaxation, In c ontrast, blood vessels relaxed normally to the endothelium-independent vaso dilator sodium nitroprusside, In vivo administration of Cl-L-Arg to anesthe tized rats increased carotid artery vascular resistance. A greater than 10- fold excess of L-Arg was required to reverse the inhibitory effects of Cl-L -Arg in vivo and in vitro. Reaction of HOCl with D-arginine (D-Arg) did not result in the formation of inhibitory products. These results suggest that HOCl reacts with L-Arg to form chlorinated products that act as nitric-oxi de synthase inhibitors.