11:15 〜 11:30
[MZZ51-09] Genetic and evolutional features of xenobiotic metabolism enzymes in Carnivora (Mammalia, Laurasiatheria)
キーワード：生体外異物代謝、食肉目、環境毒性学、野生動物医学
Wildlife mammals are continuously exposed to wide variety of environmental chemicals such as polyhalogenated aromatic hydrocarbons and organochlorine pesticides. Since their higher position in their each food chains, Carnivorans (order of placental mammals includes; dogs, pinnipeds, weasels, racoons, bears, felines, mongooses, hyenas and so on) are one of the most significant species which accumulate severe amount of lipophilic environmental contaminants. Therefore, toxicological assessment of these species has been highly required, nonetheless xenobiotic metabolism as a defense system in wildlife mammals have not been clearly understood.
Xenobiotic metabolism primarily consists of 2 phases which is phase I and II reaction catalyzed by various xenobiotics metabolism enzymes. Phase I reactions are characterized as hydration, oxidation, and reduction and mainly catalyzed by Cytochrome P450 (CYP450) and esterase. Phase II reaction are conducted as conjugation reaction which transfer some moiety to the acceptor compounds and alter their bioactivity to mostly less active and more water-soluble forms accelerating excretion of their substrate compounds. Enzymes related to these reactions are UDP-glucuronosyltransferase (UGTs), Sulfotransferase (SULTs), Glutathione-S transferase (GSTs), N-acetyltransferase (NATs) and some others.
Most of previous reports about xenobiotic enzyme in wildlife mammals regarded phase I enzymes, especially CYP450 since these enzymes are fist step of xenobiotic metabolism and considered as main factor deciding clearance of xenobiotics. However, some chemicals such as carcinogens are metabolically activated after phase I reactions and that feature makes phase II reactions more important pathway as detoxification of xenobiotics.
We recently reported genetic deficiency and enzymatic disfunction in vitro of some UGTs (UGT1A6s and 2B31s) in feline and pinniped species, which suggest these species may poorly metabolize chemical compounds, nonetheless genetical features of other Carnivorans which are closely related species in their phylogeny are completely unknown.
Such importance of phase II reaction in xenobiotic metabolism, and lack of information of them motivated our research to reveal genetic features of these enzymes among wildlife Carnivorans including Ursidae (bears), Mustelidae (ferrets and weasels), Pinniped and other Carnivorans.
In our present study, genetic information of phase II enzymes, especially UGTs and SULTs of various carnivorans are collected from NCBI GenBank data, and in silico phylogenetic analysis was conducted. In addition, gene loci coding each UGTs and SULTs isoforms of these species were investigated and compared to understand the evolutional background of each isoform.
We compared UGT1 gene coding loci synteny, and we revealed limited number of UGT1 isoforms in Mustelidae, especially river otter and sea otter and only 1 or 2 isoforms are observed in these species. Also, as a result of Synteny analysis of UGT2Bs, although Canidae (dog and red fox) have more than 3 possible functional UGT2 isoforms, Ursidae (Polar bears, giant pandas, and brown bears) have only 1 or none isoforms similar to pinnipeds. Moreover, in Mustelidae (ferret, river otter, sea otter, and ermine) some variation of isoform numbers was observed. Ermine has possible 3 isoforms but others (ferrets, river and sea otters) have 2 or 1 isoforms. These genetic features suggest there are huge diversity of xenobiotic metabolism even among Carnivorans and some Carnivora might have limited capacity of xenobiotic metabolism. Although further study is needed for enzymatic or functional analysis of these enzymes of these species, these results surely provide us fundamental information of xenobiotic metabolism among carnivorans.
Xenobiotic metabolism primarily consists of 2 phases which is phase I and II reaction catalyzed by various xenobiotics metabolism enzymes. Phase I reactions are characterized as hydration, oxidation, and reduction and mainly catalyzed by Cytochrome P450 (CYP450) and esterase. Phase II reaction are conducted as conjugation reaction which transfer some moiety to the acceptor compounds and alter their bioactivity to mostly less active and more water-soluble forms accelerating excretion of their substrate compounds. Enzymes related to these reactions are UDP-glucuronosyltransferase (UGTs), Sulfotransferase (SULTs), Glutathione-S transferase (GSTs), N-acetyltransferase (NATs) and some others.
Most of previous reports about xenobiotic enzyme in wildlife mammals regarded phase I enzymes, especially CYP450 since these enzymes are fist step of xenobiotic metabolism and considered as main factor deciding clearance of xenobiotics. However, some chemicals such as carcinogens are metabolically activated after phase I reactions and that feature makes phase II reactions more important pathway as detoxification of xenobiotics.
We recently reported genetic deficiency and enzymatic disfunction in vitro of some UGTs (UGT1A6s and 2B31s) in feline and pinniped species, which suggest these species may poorly metabolize chemical compounds, nonetheless genetical features of other Carnivorans which are closely related species in their phylogeny are completely unknown.
Such importance of phase II reaction in xenobiotic metabolism, and lack of information of them motivated our research to reveal genetic features of these enzymes among wildlife Carnivorans including Ursidae (bears), Mustelidae (ferrets and weasels), Pinniped and other Carnivorans.
In our present study, genetic information of phase II enzymes, especially UGTs and SULTs of various carnivorans are collected from NCBI GenBank data, and in silico phylogenetic analysis was conducted. In addition, gene loci coding each UGTs and SULTs isoforms of these species were investigated and compared to understand the evolutional background of each isoform.
We compared UGT1 gene coding loci synteny, and we revealed limited number of UGT1 isoforms in Mustelidae, especially river otter and sea otter and only 1 or 2 isoforms are observed in these species. Also, as a result of Synteny analysis of UGT2Bs, although Canidae (dog and red fox) have more than 3 possible functional UGT2 isoforms, Ursidae (Polar bears, giant pandas, and brown bears) have only 1 or none isoforms similar to pinnipeds. Moreover, in Mustelidae (ferret, river otter, sea otter, and ermine) some variation of isoform numbers was observed. Ermine has possible 3 isoforms but others (ferrets, river and sea otters) have 2 or 1 isoforms. These genetic features suggest there are huge diversity of xenobiotic metabolism even among Carnivorans and some Carnivora might have limited capacity of xenobiotic metabolism. Although further study is needed for enzymatic or functional analysis of these enzymes of these species, these results surely provide us fundamental information of xenobiotic metabolism among carnivorans.