Phenobarbital and Phenytoin Increased Acetaminophen Hepatotoxicity Due to Inhibition of UDP-Glucuronosyltransferases in Cultured Human Hepatocytes

Here we present a preclinical model to assess drug–drug interactions due to inhibition of glucuronidation. Treatment with the antiepileptics phenobarbital (PB) or phenytoin (PH) has been associated with increased incidence of acetaminophen (APAP) hepatotoxicity in patients. In human hepatocytes, we...

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Bibliographic Details
Published in:Toxicological sciences 2005-09, Vol.87 (1), p.146-155
Main Authors: Kostrubsky, Seva E., Sinclair, Jacqueline F., Strom, Stephen C., Wood, Sheryl, Urda, Ellen, Stolz, Donna Beer, Wen, Yuan H., Kulkarni, Shaila, Mutlib, Abdul
Format: Article
Language:English
Subjects:
acetaminophen
Acetaminophen - metabolism
Acetaminophen - toxicity
Cells, Cultured
Drug Interactions
Glucuronides - metabolism
Glucuronosyltransferase - antagonists & inhibitors
Glutathione - metabolism
hepatocytes
Hepatocytes - drug effects
Hepatocytes - enzymology
hepatotoxicity
Humans
inhibition
Liver - drug effects
microsomes
phenobarbital
Phenobarbital - pharmacology
Phenytoin - pharmacology
UGT1A
UGT2B
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Summary:Here we present a preclinical model to assess drug–drug interactions due to inhibition of glucuronidation. Treatment with the antiepileptics phenobarbital (PB) or phenytoin (PH) has been associated with increased incidence of acetaminophen (APAP) hepatotoxicity in patients. In human hepatocytes, we found that the toxicity of APAP (5 mM) was increased by simultaneous treatment with phenobarbital (2 mM) or phenytoin (0.2 mM). In contrast, pretreatment with PB for 48 h prior to APAP treatment did not increase APAP toxicity unless both drugs were present simultaneously. Cells treated with APAP in combination with PB or PH experienced decreases in protein synthesis as early as 1 h, ultrastructural changes by 24 h, and release of liver enzymes by 48 h. Toxicity correlated with inhibition of APAP glucuronidation. PB or PH also inhibited APAP glucuronidation in rat and human liver microsomes and expressed human UGT1A6, 1A9, and 2B15. As with intact hepatocytes, PB and PH were neither hydroxylated nor glucuronidated, suggesting the direct inhibition of UGTs. Our findings suggest that, in multiple drug therapy, an inhibitory complex between UGT and one of the drugs can lead to decreased glucuronidation and increased systemic exposure and toxicity of a coadministered drug.
ISSN:1096-6080
1096-0929
DOI:10.1093/toxsci/kfi211