Avian Cytochrome P450 (CYP) 1-3 Family Genes: Isoforms, Evolutionary Relationships, and mRNA Expression in Chicken Liver

Abstract

Cytochrome P450 (CYP) of chicken and other avian species have been studied primarily with microsomes or characterized by cloning and protein expression. However, the overall existing isoforms in avian CYP1-3 families or dominant isoforms in avian xenobiotic metabolism have not yet been elucidated. In this study, we aimed to clarify and classify all of the existing isoforms of CYP1-3 in avian species using available genome assemblies for chicken, zebra finch, and turkey. Furthermore, we performed qRT-PCR assay to identify dominant CYP genes in chicken liver. Our results suggested that avian xenobiotic-metabolizing CYP genes have undergone unique evolution such as CYP2C and CYP3A genes, which have undergone avian-specific gene duplications. qRT-PCR experiments showed that CYP2C45 was the most highly expressed isoform in chicken liver, while CYP2C23b was the most highly induced gene by phenobarbital. Considering together with the result of further enzymatic characterization, CYP2C45 may have a dominant role in chicken xenobiotic metabolism due to the constitutive high expression levels, while CYP2C23a and CYP2C23b can be greatly induced by chicken xenobiotic receptor (CXR) activators. These findings will provide not only novel insights into avian xenobiotic metabolism, but also a basis for the further characterization of each CYP gene.

Vibrational biospectroscopy characterizes biochemical differences between cell types used for toxicological investigations and identifies alterations induced by environmental contaminants

“…Previous work has found that MCF‐7 cells preferentially express CYP1A1 , whereas in avian species, other isoforms such as CYP1A4 or CYP1A5 may be more important . However, it is important to recognize that although some mallard isoforms are orthologous to mammalian CYP1A1, the degree of homology is not perfect, which could interfere with the efficacy of antibody‐based assays . Therefore, cytochrome P450 metabolism differences cannot be determined with certainty until the strength of avian CYP isoform binding to CYP antibodies has been fully validated.…”

Partial cloning of CYP2C23a genes and hepatic protein expression in eight representative avian species

“…We have previously reported large interspecies differences in in vitro microsomal warfarin metabolic activity among several bird species (Watanabe et al ., ). A recent study has revealed that CYP2C23a and CYP2C23b were the isoforms most induced by phenobarbital in chicken liver (Watanabe et al ., ). In xenobiotic metabolism, CYP2C proteins seem to be more important than other CYP isoforms in avian species (Watanabe et al ., ).…”

“…Signal intensity for microsomal band of CYP2C45 was similar to that of 0.5 pmol of expressed protein, whereas CYP2C23 band gave much weaker signal than 0.5 pmol expressed protein. This result suggested that CYP2C45 protein had higher expression level than CYP2C23a and CYP2C23b at the basal levels, and it was consistent with our previous report showing comparative mRNA expression levels in chicken liver (Watanabe et al ., ).…”

“…). The collected phylogeny was consistent with the previous report (Watanabe et al ., ) that the two chicken CYP2C23 genes compose one clade within avian CYP2C23 genes, while other birds have only one gene, which should be orthologous to chicken CYP2C23a . The high identity and homology between chicken CYP2C23a and CYP2C23b also supports the idea that the divergence of chicken CYP2C23 genes happened after speciation of Galloanserae ; Neoaves and Paleognathae species have only one CYP2C23a gene.…”

“…A recent study has revealed that CYP2C23a and CYP2C23b were the isoforms most induced by phenobarbital in chicken liver (Watanabe et al, 2013). In xenobiotic metabolism, CYP2C proteins seem to be more important than other CYP isoforms in avian species (Watanabe et al, 2013). In the present study, we aimed to clarify the species differences of avian CYP2C23 proteins among the whole avian lineage, that is, Paleognathae (e.g., ostrich and emu), Galloanserae (e.g., chicken and most poultry species), and Neoaves (more than 95% of all the avian species belong to this superorder, according to classification by Hackett et al, 2008).…”