Inhibitory effect of alpha-lipoic acid and its positively charged amide analogue on nitric oxide production in RAW 264.7 macrophages

The aim of this study was to investigate the effect of the mitochondrial co factor cr-lipoic acid [R (+) LA] or its Lipoamide analogue, 2-(N,N-dimethyl amine) ethylamido lipoate [R (+) LA-plus], on nitric oxide (NO) production in RAW 264.7 macrophages. NO production from RAW 264.7 cells stimulated wit h 10 mug/mL of lipopolysaccharide and 50 U/mL of interferon-gamma was measu red directly by electron spin resonance using spin-trapping techniques. R ( +) LA or R (+) LA-plus was found to inhibit NO production at pharmacologica lly relevant concentrations. However, in a cell-free chemical system, neith er R (+) LA nor R (+) LA-plus was able to directly scavenge NO. Furthermore , in the presence of 2.5 or 25 mM glucose, the inhibitory effects of R (+) LA and R (+) LA-plus on NO production were decreased markedly, while they s howed more potent inhibitory effects in the presence of 2 muM rotenone or 5 mug/mL of antimycin A, inhibitors of mitochondrial complex I and complex I II, respectively. Glucose, rotenone, or antimycin A alone resulted in an in crease of NO production. These results suggest that NO production in macrop hages can be regulated by glucose and mitochondrial respiration, and that m odulation of NO production by lipoic acid or lipoamide analogues in inflamm atory situations is attributed not to their radical scavenging activity but to their redox properties. (C) 2001 Elsevier Science Inc. All rights reser ved.