RGD Reference Report - Glucuronidation of acetaminophen catalyzed by multiple rat phenol UDP-glucuronosyltransferases. - Rat Genome Database

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Glucuronidation of acetaminophen catalyzed by multiple rat phenol UDP-glucuronosyltransferases.

Authors: Kessler, FK  Kessler, MR  Auyeung, DJ  Ritter, JK 
Citation: Kessler FK, etal., Drug Metab Dispos 2002 Mar;30(3):324-30.
RGD ID: 634454
Pubmed: (View Article at PubMed) PMID:11854153

Gunn rats glucuronidate acetaminophen (APAP) at reduced rates and show increased susceptibility to APAP-induced hepatotoxicity. This defect is presumed to involve UDP-glucuronosyltransferase (UGT) 1A6, which is nonfunctional in Gunn rats, but it is currently unclear whether other 1A family members are also involved. In humans, two 1A isoforms are known to be active (1A6 and 1A9) but 1A6 form has a 25-fold lower apparent K(m) (2 mM). Rat liver microsomal APAP UGT activity is induced by in vivo treatment with beta-naphthoflavone or oltipraz, an effect correlating with induction of 1A6 and 1A7. To address a possible role of 1A7 in APAP glucuronidation relative to other 1A forms, cDNAs encoding UGTs 1A1, 1A5, 1A6, 1A7, and 1A8 were expressed in human embryonic kidney cells and the contents of expressed enzyme in prepared membrane fractions determined by quantitative immunoblotting. At 2.5 mM APAP, 1A7 showed the highest specific activity (2.8 nmol/min/nmol 1A7 protein), followed by 1A6 (1.1 nmol/min/nmol), and 1A8 (0.27 nmol/min/nmol). 1A1 and 1A5 were essentially inactive. Kinetic comparisons indicated 1A7 had a similar apparent K(m) as 1A6 (4.7 versus 3.9 mM, respectively) but a 2.4-fold higher catalytic activity. These data suggest that in rats, 1A7 plays a major role in APAP glucuronidation and contributes to protection against APAP-induced hepatotoxicity. The involvement of other UGTs besides 1A6 is further underscored by the presence of significant residual APAP-glucuronidating activity by Gunn rat hepatocytes, indicating the activity of an unknown UGT2 family member.

Annotation

Gene Ontology Annotations    

Biological Process

Molecular Function

Objects Annotated

Genes (Rattus norvegicus)
Ugt1a6  (UDP glucuronosyltransferase family 1 member A6)
Ugt1a8  (UDP glucuronosyltransferase family 1 member A8)

Objects referenced in this article
Gene Ugt1a1 UDP glucuronosyltransferase family 1 member A1 Rattus norvegicus
Gene Ugt1a7c UDP glucuronosyltransferase 1 family, polypeptide A7C Rattus norvegicus

Additional Information