Protective effects of coenzyme Q10 and α-tocopherol against free radical-mediated liver cell injury

In an attempt to provide further confirmation of the antioxidant role of reduced form of coenzyme Q homologue (CoQnH2) and α-tocopherol (α-Toc), we incubated isolated rat hepatocytes with a water-soluble radical initiator, 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) in the presence or absence of exogenously added coenzyme Q10 (CoQ10) or α-Toc for 3 h at 37°C under an atmosphere of 95% oxygen and 5% carbon dioxide. In the control experiment without adding AAPH it was confirmed that added CoQ10 and α-Toc were incorporated into the cells and some CoQ10 were converted to CoQ10H2. Incubation of hepatocytes with 50 mM AAPH resulted in the formation of thiobarbituric acid-reactive substances and the decrease in cell viability and both were inhibited by exogenously added CoQ10 or α-Toc in a dose-dependent manner. The decrease in endogenous CoQ9H2 and α-Toc levels was observed by the addition of AAPH. Addition of CoQ10 inhibited the oxidation of CoQ9H2 to CoQ9 dose-dependently while the addition of α-Toc did not. These data suggest that both CoQnH2 and α-Toc act as antioxidants and can inhibit free radical-mediated cell injury.