142 - Alterations of Endogenous Coenzyme Q10 Levels in Human Cells after the Induction of Lipid Peroxidation by an Organic Peroxide

Abstract

Coenzyme Q10 (CoQ10) is an essential electron carrier in the mitochondrial electron transport chain and also an endogenously synthesized lipid-soluble antioxidant. We have previously demonstrated that hydrogen peroxide increased CoQ10 levels, but disruption of mitochondrial membrane potential by the chemical uncoupler FCCP suppressed CoQ10 levels in the human 143B cells. Mor bioeover, we have also shown that the COQ5 protein, which is required for CoQ biosynthesis in yeast, is essential for maintaining CoQ10 levels in 143B cells. In this study, we investigated how the condition of enhanced lipid peroxidation affected levels of the reduced form (ubiquinol-10) and oxidized form (ubiquinone-10) of CoQ10. The organic peroxide tert-butyl hydroperoxide (TBHP) was used to induce lipid peroxidation in 143B cells. Levels of esterified F2-isoprostanes (F2-IsoPs) in cells, detected by the gas chromatography/mass spectrometry method, were confirmed to be elevated by a low, medium, or high dose of TBHP as early as after 4 h of treatment. The levels remained augmented after 18 h of TBHP treatment but the degree of the increase was less. Only the medium-dose and high-dose TBHP treatments enhanced total CoQ10 levels after 18 h or 24 h of treatment, but the high-dose TBHP treatment also enhanced ubiquinol-10 levels after 4 h of treatment. Transient knockdown of COQ5, which decreased CoQ10 levels, suppressed the increase of both ubiquinol-10 and ubiquinone-10 levels after 24-h TBHP treatment. These results demonstrate for the first time that specific augmentation of lipid peroxidation could up-regulate formation of endogenous CoQ10 levels and ubiquinol-10 could be the initially generated form.