Protection by Exogenously Added Coenzyme Q₉ against Free Radical-Induced Injuries in Human Liver Cells

Abstract

Reduced coenzyme Q₁₀ (CoQ₁₀H₂) is known as a potent antioxidant in biological systems. However, it is not yet known whether CoQ₉H₂ could act as an antioxidant in human cells. The aim of this study is to assess whether exogenously added CoQ₉ can protect human liver cells against injuries induced by a water-soluble radical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) and a lipid-soluble radical initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). CoQ₉-enriched cells were obtained by treatment of HepG2 cells with 10 μM CoQ₉ liposomes for 24 h. CoQ₉-enriched cells were exposed to 10 mM AAPH and 500 μM AMVN over 4 h and 24 h, respectively. The loss of viability after treatment with AAPH or AMVN was much less in CoQ₉-enriched cells than in naive HepG2 cells. The decrease in glutathione and the increase in thiobarbituric acid-reactive substance after treatment with AAPH or AMVN were also suppressed in CoQ₉-enriched cells. The incubation of CoQ₉-enriched cells with AAPH or AMVN led to a decrease in cellular CoQ₉H₂ and reciprocal increase in cellular CoQ₉ resulting from its antioxidant function. Taken together, it was demonstrated for the first time that exogenously added CoQ₉ could prevent oxidative stress-mediated damage to human cells by virtue of its antioxidant activity.