title: The effect of L-arginine and creatine on vascular function and homocysteine metabolism.
abstract: Studies with L-arginine supplementation have shown inconsistent effects on endothelial function. The generation of guanidinoacetate (GAA) from L-arginine with subsequent formation of creatine and homocysteine and consumption of methionine may reduce the pool of L-arginine available for nitric oxide generation. Experimental studies suggest that creatine supplementation might block this pathway. We sought to determine the effects of L-arginine, creatine, or the combination on endothelium-dependent vasodilation and homocysteine metabolism in patients with coronary artery disease. Patients with coronary artery disease were randomized to L-arginine (9 g/day), creatine (21 g/day), L-arginine plus creatine, or placebo for 4 days (n = 26-29/group). Brachial artery flow-mediated dilation and plasma levels of L-arginine, creatine, homocysteine, methionine, and GAA were measured at baseline and follow-up. L-arginine and creatine supplementation had no effects on vascular function. L-arginine alone increased GAA (p < 0.01) and the ratio of homocysteine to methionine (p < 0.01), suggesting increased methylation demand. The combination of creatinine and L-arginine did not suppress GAA production or prevent the increase in homocysteine-to-methionine ratio. Unexpectedly, creatine supplementation (alone or in combination with L-arginine) was associated with an 11-20% increase in homocysteine concentration (p < 0.05), which was not attributable to worsened renal function, providing evidence against an effect of creatine on decreasing methylation demand. In conclusion, the present study provides no evidence that L-arginine supplementation improves endothelial function and suggests that l-arginine may increase methylation demand. Creatine supplementation failed to alter the actions of L-arginine on vascular function or suppress methylation demand. The unexpected increase in homocysteine levels following creatine supplementation could have adverse effects and merits further study, since creatine is a commonly used dietary supplement.
authors: Boston University School of Medicine, Boston, MA 02118, USA.
authors: Eiman
authors: E
authors: Jahangir
authors: Joseph A
authors: JA
authors: Vita
authors: Diane
authors: D
authors: Handy
authors: Monica
authors: M
authors: Holbrook
authors: Joseph
authors: J
authors: Palmisano
authors: Ryan
authors: R
authors: Beal
authors: Joseph
authors: J
authors: Loscalzo
authors: Robert T
authors: RT
authors: Eberhardt
mesh_terms: D000368:Aged; D001120:Arginine / Q000097:blood / Q000627:therapeutic use*; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000503:physiopathology; D003324:Coronary Artery Disease / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D003401:Creatine / Q000097:blood / Q000627:therapeutic use*; D019587:Dietary Supplements; D005260:Female; D005998:Glycine / Q000031:analogs & derivatives / Q000097:blood; D006710:Homocysteine / Q000097:blood; D006801:Humans; D006940:Hyperemia / Q000503:physiopathology; D008297:Male; D008715:Methionine / Q000097:blood; D008875:Middle Aged; D012039:Regional Blood Flow; D016896:Treatment Outcome; D014463:Ultrasonography; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D006710:Homocysteine; D001120:Arginine; D008715:Methionine; C004946:glycocyamine; D003401:Creatine; D005998:Glycine