Comparison of the effect of alpha-lipoic acid and alpha-tocopherol supplementation on measures of oxidative stress

In vitro studies have shown that cr-lipoic acid (LA) is an antioxidant. The re is a paucity of studies on LA supplementation in humans. Therefore, the aim of this study was to assess the effect of oral supplementation with LA alone and in combination with alpha-tocopherol (AT) on measures of oxidativ e stress. A total of 31 healthy adults were supplemented for 2 months eithe r with LA (600 mg/d, n = 16), or with AT (400 IU/d, n = 15) alone, and then with the combination of both for 2 additional months. At baseline, after 2 and 4 months of supplementation, urine for F-2-isoprostanes, plasma for pr otein carbonyl measurement and low-density lipoprotein (LDL) oxidative susc eptibility was collected. plasma oxidizability was assessed after incubatio n with 100 mM 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) for 4 h a t 37 degrees C. LDL was subjected to copper- and AAPH-catalyzed oxidation a t 37 degrees C over 5 h and the lag time was computed. LA significantly inc reased the lag time of LDL lipid peroxide formation for both copper-catalyz ed and AAPH-induced LDL oxidation (p < .05), decreased urinary F-2-isoprost anes levels (p < .05), and plasma carbonyl levels after AAPH oxidation (p < .001). AT prolonged LDL lag time of lipid peroxide formation (p < .01) and conjugated dienes (p < .01) after copper-catalyzed LDL oxidation, decrease d urinary F-2-isoprostanes (p < .002), but had no effect on plasma carbonyl s. The addition of LA to AT did not produce an additional significant impro vement in the measures of oxidative stress. In conclusion, LA supplementati on functions as an antioxidant, because it decreases plasma- and LDL-oxidat ion and urinary isoprostanes. (C) 1999 Elsevier Science Inc.