Inhibition of the alpha-ketoglutarate dehydrogenase-mediated reactive oxygen species generation by lipoic acid.
Dihydrolipoamide dehydrogenase (LADH) is a flavo-enzyme that serves as a subunit of alpha-ketoglutarate dehydrogenase complex (alpha-KGDHC). Reactive oxygen species (ROS) generation by alpha-KGDHC has been assigned to LADH (E3 subunit) and explained by the diaphorase activity of E3. Dysfunctions of alpha-KGDHC and concurrent ROS production have been implicated in neurodegeneration, ischemia-reperfusion, and other pathological conditions. In this work we investigated the in-depth details of ROS generation by isolated LADH and alpha-KGDHC. We found a parallel generation of superoxide and hydrogen peroxide by the E3 subunit of alpha-KGDHC which could be blocked by lipoic acid (LA) acting on a site upstream of the E3 subunit. The pathologically relevant ROS generation (at high NADH/NAD+ ratio and low pH) in the reverse mode of alpha-KGDHC could also be inhibited by LA. Our results contradict the previously proposed mechanism for pH-dependent ROS generation by LADH, showing no disassembling of the E3 functional homodimer at acidic pH using a physiologically relevant method for the examination. It is also suggested that LA could be beneficial in reducing the cell damage related to excessive ROS generation under pathological conditions.
Ambrus
Attila
A
Department of Medical Biochemistry, Neurobiochemical Research Group, Hungarian Academy of Sciences and Szentagothai Janos Knowledge Center, Semmelweis University, Budapest, Hungary.
Tretter
László
L
Adam-Vizi
Vera
V
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D008058:Dihydrolipoamide Dehydrogenase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007655:Ketoglutarate Dehydrogenase Complex / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010783:Photometry; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013481:Superoxides / Q000378:metabolism; D008063:Thioctic Acid / Q000494:pharmacology*
D000975:Antioxidants; D017382:Reactive Oxygen Species; D013481:Superoxides; D008063:Thioctic Acid; D006861:Hydrogen Peroxide; D007655:Ketoglutarate Dehydrogenase Complex; D008058:Dihydrolipoamide Dehydrogenase