Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
For the antioxidant effect of lipoic acid, reduction to dihydrolipoic acid is considered to be important. Dihydrolipoamide dehydrogenase (LipHD) preferentially reduces R-lipoic acid and in a subsequent reaction, the R-dihydrolipoic acid formed may non-enzymatically reduce S-lipoic acid. Using circular dichroism (CD) spectroscopy, the second order rate constant of the latter reaction was determined (k2 = 15 M-1 sec-1). In vitro, it was found that S-lipoic acid is reduced by LipDH using R-lipoic acid as a catalyst. The non-enzymatic dithiol-disulfide reaction leads to synergistic reduction of the enantiomers which can explain the higher antioxidant activity of racemic lipoic acid found in vivo (Maitra et al. Biochem. Biophys. Res. Commun. 221:422-429, 1996) in comparison to the enantiomers. Lipoic acid is therapeutically active in several diseases via antioxidant activity. These findings suggest that racemic lipoic acid can be therapeutically more active than the separate enantiomers. Chirality 9:362-366, 1997. © 1997 Wiley-Liss, Inc.
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