Impact of Oral Glycine Propionyl-L-Carnitine on Oxidative Stress, Antioxidant Status, and Exercise Performance

Abstract

Various forms of L-carnitine have been shown to have antioxidant properties and to improve circulation and exercise performance in individuals with vascular disease, possibly mediated by enhanced nitric oxide production. PURPOSE: To compare the effects of a novel form of L-carnitine (glycine propionyl-L-carnitine {GPLC})to a placebo on markers of aerobic and anaerobic exercise performance, antioxidant status, oxidative stress, nitric oxide, and skeletal muscle carnitine content. METHODS: 32 healthy men or women (27±5 years) were randomly assigned in double-blind manner to receive either a placebo (n=9), GPLC at 1 g/d (n=12), or GPLC at 3g/d (n=11) in conjunction with an eight week program of supervised aerobic training. VO2peak, time to fatigue, and anaerobic threshold was assessed using a graded exercise treadmill test. Anaerobic power and work was assessed using a Wingate cycle test. Resting blood samples were analyzed for total whole blood glutathione, total plasma antioxidant capacity, and plasma nitric oxide. Muscle samples were analyzed for total, free, and acyl carnitine. All above variables were determined before and following the eight week intervention. Malondialdehyde (MDA) was measured pre and post both exercise tests; pre and post intervention. RESULTS: With the exception of a significant (P<0.05) increased anaerobic threshold for both GPLC groups (9-10%) compared to placebo (2%), no exercise performance effects were observed (p<0.05). While both glutathione and antioxidant status were higher in the GPLC groups compared to placebo, these differences were not statistically significant (P>0.05). The percent change for nitric oxide was statistically greater for GPLC 3g/d (55±15) compared to GPLC 1g/d (10±15) and placebo (7±17, P<0.05). Muscle carnitine content was maintained at 3g/d of GPLC, but decreased following training in the other groups. Resting MDA was decreased 22-30% in the GPLC groups compared to no change in the placebo group following the intervention, but the same pattern of change was present in all groups in response to both exercise tests (p<0.05). CONCLUSION: These findings indicate that GPLC supplementation may increase the anaerobic threshold, maintain muscle carnitine content at 3g/d, increase resting nitric oxide production, and decrease resting lipid peroxidation.