Common marmosets (Callithrix jacchus), New World monkeys, are a promising primate model for preclinical drug metabolism studies because of the similarities of cytochrome P450 (P450) enzyme function to those of humans. Despite an increasing number of drug candidates catalyzed by non-P450 enzymes, drug metabolizing enzymes other than P450s have been hardly identified or characterized in marmosets. In this study, we identified aldehyde oxidase (AOX) 1 gene by marmoset genome analysis. AOX1 cDNA was cloned from marmoset livers by reverse transcription-polymerase chain reaction. Deduced amino acid sequences of AOX1 cDNA showed high sequence identities (92-93%) with primate AOX1s. Phylogenetic analysis showed that marmoset AOX1 was closely clustered with primate AOX1s, unlike nonprimate animal model AOX1s of pig, rabbit, rat, and mouse used in drug metabolism. The tissue expression analyses by real-time reverse-transcription polymerase chain reaction and immunoblotting showed that marmoset AOX1 mRNA and protein were abundantly expressed in livers, similar to cynomolgus monkeys and humans. Marmoset AOX1 heterologously expressed in Escherichia coli catalyzed the oxidation of carbazeran and phthalazine, typical AOX1 substrates, similar to cynomolgus monkey and human AOX1s. Human and marmoset AOX1 effectively catalyzed phthalazine oxidation when assessed with Michaelis-Menten kinetics, but cynomolgus monkey AOX1 catalyzed this reaction with cooperative kinetics with high capacity. These results indicated that tissue distribution and enzymatic function of AOX1 enzyme is similar between marmosets and humans, suggesting that marmosets are a suitable primate model for AOXdependent drug metabolism in preclinical studies.
