The marmoset cytochrome P450 superfamily: Sequence/phylogenetic analyses, genomic structure, and catalytic function

Abstract

The common marmoset (Callithrix jacchus) is a New World monkey that has attracted much attention as a potentially useful primate model for preclinical testing. A total of 36 marmoset cytochrome P450 (P450) isoforms in the P450 1–51 subfamilies have been identified and characterized by the application of genome analysis and molecular functional characterization. In this mini-review, we provide an overview of the genomic structures, sequence identities, and substrate selectivities of marmoset P450s compared with those of human P450s. Based on the sequence identity, phylogeny, and genomic organization of marmoset P450s, orthologous relationships were established between human and marmoset P450s. Twenty-four members of the marmoset P450 1A, 2A, 2B, 2C, 2D, 2E, 3A, 4A, and 4F subfamilies shared high degrees of homology in terms of cDNA (>89%) and amino acid sequences (>85%) with the corresponding human P450s; P450 2C76 was among the exceptions. Phylogenetic analysis using amino acid sequences revealed that marmoset P450s in the P450 1–51 families were located in the same clades as their human and macaque P450 homologs. This finding underlines the evolutionary closeness of marmoset P450s to their human and macaque homologs. Most marmoset P450 1–4 enzymes catalyzed the typical drug-metabolizing reactions of the corresponding human P450 homologs, except for some differences of P450 2A6 and 2B6. Consequently, it appears that the substrate specificities of enzymes in the P450 1–4 families are generally similar in marmosets and humans. The information presented here supports a better understanding of the functional characteristics of marmoset P450s and their similarities and differences with human P450s. It is hoped that this mini-review will facilitate the successful use of marmosets as primate models in drug metabolism and pharmacokinetic studies.

Introduction

Because of their close genetic and physiological similarities to humans, nonhuman primates are important species for evaluating the safety and therapeutic efficacy of candidates for drug development. The common marmoset (Callithrix jacchus), a New World monkey, is a potentially useful primate in efficacy/pharmacology, safety/toxicology, and drug metabolism and pharmacokinetic studies for preclinical testing. The common marmoset has various advantages, such as genetic closeness to humans, small size, fast maturation, high fertility, and ease of handling [1]. Marmosets have been favored for biomedical research in fields such as neurobiology [2], immunology [3], obesity [4], and aging [5]. The cynomolgus macaque (Macaca fascicularis), an Old World monkey, has been widely used as a preclinical model in drug metabolism and pharmacokinetic studies because of its availability and its long history of use as a laboratory animal species.

Cytochromes P450 (P450) constitute a superfamily of heme-thiolate enzymes that mediate the biotransformation and metabolism of endogenous steroid hormones, xenobiotics, and drugs. Currently known human P450 isoforms are encoded by 57 functional genes and 58 pseudogenes [6]. P450 enzymes in the P450 1A, 2B, 2C, 2D, 2E, and 3A subfamilies are major drug-metabolizing enzymes [7], whereas those in the P450 4 family are involved in the metabolism of endogenous [8] and exogenous compounds [9]. P450 enzymes can catalyze various types of enzymatic reactions, including hydroxylation, dealkylation, sulfoxidation, epoxidation, and N-oxidation [10]. Interspecies differences of P450-mediated drug metabolism have been identified in commonly used preclinical animal species, including mice, rats, dogs, pigs, and cynomolgus macaques [11]. Consequently, to select appropriate animal species for drug metabolism and pharmacokinetic studies, it is important to understand the orthologous relationships and functional characteristics of their P450 isoforms.

In 2013, the Brain Mapping by Integrated Neurotechnologies for Disease Studies (Brain/MINDS) project was set up. Its aims were to accelerate the understanding of human brain disorders using marmosets and to facilitate the use of marmosets for drug development [12]. However, despite the importance of the marmoset as a preclinical nonhuman primate species, only limited numbers of P450 isoforms have been identified, including P450 1A2, 2B6, 2C8, 2D6, 2E1, 3A4, 3A5, and 3A90. We participated in the Brain/MINDS project to investigate the characteristics of drug metabolism and pharmacokinetics in marmosets. By using transcriptome data of marmoset tissues obtained by next-generation high-throughput RNA sequencing analysis [13] and by using marmoset genome data based on whole-genome shotgun sequencing and assembly [14], we identified and characterized a large number of marmoset P450 isoforms in the P450 1–51 families (see http://drnelson.uthsc.edu/CytochromeP450.html). Our understanding of P450-mediated drug metabolism has been accelerated by the comprehensive cDNA cloning and functional analyses of marmoset P450 isoforms carried out as part of the Brain/MINDS project. This mini-review compares the characteristics of the P450 1A, 2A, 2B, 2C, 2D, 2E, and 3A subfamilies in marmosets and humans.