Alpha-lipoic acid supplementation protects enzymes from damage by nitrosative and oxidative stress

•We identified new antioxidant protein targets for α-lipoic acid activity.•α-Lipoic acid supplementation restores mitochondrial enzymatic activities.•α-Lipoic acid improves ATP generation inhibited by nitrosative stress.•Our findings disclose a novel redox regulatory function of α-lipoic acid.•Our data suggest a novel strategy for treatment of inflammation-related diseases.

BackgroundS-nitrosylation of mitochondrial enzymes involved in energy transfer under nitrosative stress may result in ATP deficiency. We investigated whether α-lipoic acid, a powerful antioxidant, could alleviate nitrosative stress by regulating S-nitrosylation, which could result in retaining the mitochondrial enzyme activity.MethodsIn this study, we have identified the S-nitrosylated forms of subunit 1 of dihydrolipoyllysine succinyltransferase (complex III), and subunit 2 of the α-ketoglutarate dehydrogenase complex by implementing a fluorescence-based differential quantitative proteomics method.ResultsWe found that the activities of these two mitochondrial enzymes were partially but reversibly inhibited by S-nitrosylation in cultured endothelial cells, and that their activities were partially restored by supplementation of α-lipoic acid. We show that protein S-nitrosylation affects the activity of mitochondrial enzymes that are central to energy supply, and that α-lipoic acid protects mitochondrial enzymes by altering S-nitrosylation levels.ConclusionsInhibiting protein S-nitrosylation with α-lipoic acid seems to be a protective mechanism against nitrosative stress.General significanceIdentification and characterization of these new protein targets should contribute to expanding the therapeutic power of α-lipoic acid and to a better understanding of the underlying antioxidant mechanisms.