ubiquinol and dihydrolipoic-acid

Inflamed tissues generate reactive nitrogen oxide species (RNO(x)), such as peroxynitrite (ONOO-)and nitryl chloride (NO2Cl), which lead to formation of nitrated DNA and protein adducts, including 8-nitroguanine (8NG), 8-nitroxanthine (8NX), and 3-nitrotyrosine (3NT). Once formed, the two nitrated DNA adducts are not stable in DNA and undergo spontaneous depurination. Nitration of protein tyrosine leads to inactivation of protein functions and 3NT has been detected in various disease states. We herein report that reduction of these nitro adducts to their corresponding amino analogues can be catalyzed by lipoyl dehydrogenases (EC 1.8.1.4) from Clostridium kluyveri (ck) and from porcine heart (ph) using NAD(P)H as the cofactor. We also found that dihydrolipoic acid (DHLA) and ubiquinol can be used as effective cofactors for reduction of 8NG, 8NX, and 3NT by these lipoyl dehydrogenases. The reduction efficiency of the mammalian enzyme is higher than the bacterial isozyme. The preference of cofactors by both lipoyl dehydrogenases is DHLA>NAD(P)H>ubiquinol. In all the systems examined, the nitrated purines are reduced to a greater extent than 3NT under the same conditions. We also demonstrate that this lipoyl dehydrogenase/antioxidant system is effective in reducing nitrated purine on NO2Cl-treated double stranded calf thymus DNA, and thus decreases apurinic site formation. The nitroreductase activity for lipoyl dehydrogenase might represent a possible metabolic pathway to reverse the process of biological nitration.

Topics: Dihydrolipoamide Dehydrogenase; Guanine; NADP; Nitrogen Oxides; Oxidation-Reduction; Reactive Nitrogen Species; Thioctic Acid; Tyrosine; Ubiquinone; Xanthines

Topics: Antioxidants; Cells, Cultured; Culture Media, Serum-Free; Dose-Response Relationship, Drug; Humans; Keratinocytes; Oxidation-Reduction; Oxidative Stress; Reactive Oxygen Species; Solubility; Thioctic Acid; Ubiquinone; Ultraviolet Rays; Vitamin E

Ubiquinol (QH2, reduced coenzyme Q) is increasingly reported to exert antioxidant functions besides its implication in mitochondrial energy metabolism. On the other hand ubisemiquinones (SQ-.) of the respiratory chain are considered to account for the production of superoxide radicals as a byproduct of cellular respiration. Since the formation of potentially prooxidative ubisemiquinones can be expected to result from the antioxidant activity of ubiquinol, the evaluation whether or not QH2 exerts antioxidant activities depends on the fate of antioxidant-derived metabolites and the existence of a natural recycling system for oxidized QH2. We have recently shown that SQ increasingly undergo autoxidation when approaching the external more polar phase of the membrane. In contrast to mitochondria where the QH2/ SQ-./Q pools are dynamically kept in relatively stable relationships the fate of semi and fully oxidized QH2 is not at all clear in LDL particles where QH2 is suggested to exert important antioxidant functions. Therefore, the antioxidant-derived metabolites of QH2 in liposomes following lipid peroxidation were studied with respect to their localization in the bilayer and the possibility to recycle oxidized QH2 via dihydrolipoic acid (DHLA). The results revealed a considerable fraction of QH2 existing in the outer membrane section where protons from the aqueous phase have access to allow autoxidation. DHLA was found to recycle oxidized QH2 although due to slow partition equilibration the reduction velocity appears to be not sufficient for therapeutic application.

Topics: Antioxidants; Electron Spin Resonance Spectroscopy; Lipid Peroxidation; Lipoproteins, LDL; Liposomes; Oxidation-Reduction; Oxidative Stress; Peroxides; Photolysis; Thioctic Acid; Ubiquinone