Characterization of the ZebrafishUgtRepertoire Reveals a New Class of Drug-Metabolizing UDP Glucuronosyltransferases

Abstract

The zebrafish genome contains a gene superfamily of 40 Ugt genes that can be divided into Ugt1, Ugt2, and Ugt5 families. Because the encoded zebrafish UDP glucuronosyltransferase (UGT) proteins do not display orthologous relationships to any of the mammalian and avian UGT enzymes based on molecular phylogeny, it is difficult to predict their substrate specificity. Here, we mapped their tissue-specific expression patterns. We showed that the zebrafish UGT enzymes can be glycosylated. We determined their substrate specificity and catalytic activity toward diverse aglycone substrates. Specifically, we measured mRNA levels of each of the 40 zebrafish Ugt genes in 11 adult tissues and found that they are expressed in a tissue-specific manner. Moreover, functional analyses with the donor of UDP glucuronic acid (UDPGA) for each of the 40 zebrafish UGT proteins revealed their substrate specificity toward 10 important aglycones. In particular, UGT1A1, UGT1A7, and UGT1B1 displayed good glucuronidation activities toward most phenolic aglycones (4-methylumbelliferone, 4-nitrophenol, 1-naphthol, bisphenol A, and mycophenolic acid) and the two carboxylic acids (bilirubin and diclofenac). Importantly, some members of the UGT5, a novel UGT family identified recently, are capable of glucuronidating multiple aglycones with the donor cofactor of UDPGA. In particular, UGT5A5, UGT5B2, and UGT5E1 glucuronidate phenols and steroids with high specificity toward steroid hormones of estradiol and testosterone and estrogenic alkylphenols 4-tert-octylphenol. These results shed new insights into the mechanisms by which fish species defend themselves against vast numbers of xenobiotics via glucuronidation conjugations and may facilitate the establishment of zebrafish as a model vertebrate in toxicological, developmental, and pathologic studies.

Metabolomic Characterizations of Liver Injury Caused by Acute Arsenic Toxicity in Zebrafish

“…Bilirubin conjugation in zebrafish has not been well studied. A recent in vitro study has shown that only ugt1 family could conjugate bilirubin, among which ugt1b7 has the highest catalytic activity and it is detected in the liver [ 53 ]. However, in a liver transcriptomic profile we obtained under the same As exposure conditions, none of the ugt1 genes is deregulated [ 3 ].…”

Comparison of the In Vivo Biotransformation of Two Emerging Estrogenic Contaminants, BP2 and BPS, in Zebrafish Embryos and Adults

“…The comparison of the metabolic pattern of BP2 and BPS suggests the involvement of different sulfotransferases (SULT) and glucuronidases (UGT) in their respective biotransformation. Zebrafish UGTs 1A1, 1A7 and 1B1, and in particular UGT1A1 in the case of BPA, have been shown to be the major isoforms involved in the conjugation of phenolic and carboxylic compounds in HEK293T modified cells [34], and SULTs are known to participate in the metabolism of both endogenous and exogenous substrates. BPA sulfation in zebrafish has been shown to involve three SULTs from two families, namely SULT1 ST5, SULT 3 ST1 and SULT3 ST3 [35,36].…”

Comparative metabolism of mycophenolic acid by glucuronic acid and glucose conjugation in human, dog, and cat liver microsomes

“…Although glucosidation is the major pathway for conjugative metabolism of xenobiotics in nonvertebrate species (including insects and plants), glucuronidation is the dominant conjugative clearance mechanism in all vertebrates studied to date (Shipkova et al, 2001;Huang et al, 2008;Wang et al, 2014;Bock, 2016). This is despite the ready availability of UDPglucose as a cofactor in hepatocytes.…”