Difference in antioxidant activity between reduced coenzyme Q 9 and reduced coenzyme Q 10 in the cell: studies with isolated rat and guinea pig hepatocytes treated with a water-soluble radical initiator

Abstract

A possible difference in antioxidant activity between reduced coenzyme Q 9 (CoQ 9H 2) and reduced coenzyme Q 10 (CoQ 10H 2) in animal cells was studied by incubation of hepatocytes with a hydrophilic radical initiator, 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH). Two kinds of hepatocytes differing in their content of CoQ homologs were used: rat, total (oxidized plus reduced) CoQ 9: total CoQ 10 6:1, guinea pig, 1:5. The sum of total CoQ 9 and CoQ 10 in rat and guinea-pig hepatocytes was about 780 and 400 pmol/mg protein, respectively. The concentration of CoQ 9H 2 in rat hepatocytes decreased linearly after the addition of AAPH, whereas that of oxidized CoQ 9 showed a reciprocal increase. No loss of cell viability or increase of lipid peroxidation was observed until most of the CoQ 9H 2 had been consumed. Cellular CoQ 9H 2 was consumed probably through scavenging of lipid peroxyl radicals produced by incubation with AAPH. On the other hand, CoQ 10H 2 was not significantly consumed in the AAPH-treated rat hepatocytes during incubation compared with the control cells. In guinea-pig hepatocytes, cellular CoQ 10H 2 as well as CoQ 9H 2 was consumed by addition of AAPH. α-Tocopherol also showed linear consumption with incubation time regardless of the cell types used. It is concluded that CoQ 9H 2, together with α-tocopherol, constantly acts as a potential antioxidant in hepatocytes when incubated with AAPH, whereas CoQ 10H 2 mainly exhibits its antioxidant activity in cells containing CoQ 10 as the predominant CoQ homolog.