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

SUMMARY

In an attempt to provide further confirmation of the antioxidant role of reduced form of coenzyme Q homologue (CoQ_nH₂) 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 CoQ_nH₂ and α-Toc act as antioxidants and can inhibit free radical-mediated cell injury.