Investigation of hepatic and intestinal mycophenolic acid glucuronidation in relation to gastrointestinal toxicity in rat

Mycophenolic acid (MPA), an immunosuppressant used in anti-rejection therapy, is detoxified by UDP-glucuronosyltransferases (UGTs). Unfortunately, gastrointestinal (GI) toxicity is frequently associated with MPA. Overall objectives were to characterize MPA glucuronidation in rat and to determine if intestinal MPA UGTs mediate a protective role against MPA-induced GI toxicity.; Liver microsomel MPA glucuronidation was evaluated for rats and humans. Rat liver microsomes (RLM) demonstrated a lower affinity and activity towards MPA as compared to human liver microsomes (HLM). Hepatic MPA glucuronidation was shown to be primarily mediated by UGT1A1, 1A6 and 1A7 in rats. Kinetic analysis indicated UGT1A1 and 1A7 as having major roles in RLM, whereas 1A9 was shown to be the primary contributor in HLM. Results indicate a species difference in hepatic MPA glucuronidation.; MPA glucuronidation was characterized for rat small intestine and colon. Gunn (j/j) rat microsomes prepared from these regions were unable to glucuronidate MPA, indicating an exclusive UGTIA role. Highest MPA affinities and activities were found in proximal intestine and progressively declined longitudinally. Quantitative immunoblotting revealed differential distribution of UGT1A1, 1A6 and 1A7 in the intestine and activities significantly correlated with UGT1A7 content. Data support UGT1A7 as being the primary form involved in intestinal MPA glucuronidation.; Recombinant adenoviruses (AdV) encoding UGT1A1, 1A6 and 1A7 were administered to Gunn (j/j) rats in order to reconstitute normal hepatic MPA glucuronidation. Animals were infected with high (HD), intermediate (ID) or low (LD) doses of AdV and injected with 80 mg/kg MPA. Similar MPA and MPA glucuronide plasma pharmacokinetics were observed for ID and control rats. RLM prepared from j/j ID animals displayed MPA activities and UGT1A1, 1A6 and 1A7 protein levels that mimicked controls.; Development of MPA-induced diarrhea was evaluated for Gunn rats expressing (j/+) or lacking (j/j) intestinal MPA UGTs. Animals were infected with a HD or ID of control or MPA UGT-encoding AdV and a received daily injection of 20 mg/kg MPA equivalents for 10 days. Severe diarrhea developed for j/j ID rats, whereas other groups were unaffected. Results do not support a protective role for intestinal MPA UGTs against MPA-induced GI toxicity.