Abstract
The effect of probenecid (PRB) on factors regulating the hepatic disposition of acetaminophen glucuronide (AG) was investigated in vitro. Potential interactions in metabolism or binding to cytosolic proteins were examined. In the absence of PRB, AG formation in rat hepatic S9 fractions was saturable (Vmax = 2.77 ± 0.36 nmol/min/mg protein; KM = 18.0 ± 0.92 mM). PRB significantly decreased Vmax, but notKM , for AG formation, consistent with noncompetitive inhibition. Various models were fit to the AG formation rate vs. acetaminophen (APAP) and PRB concentration data to elucidate the mechanism of inhibition by PRB. A partial noncompetitive inhibition model (Ki = 1.10 ± 0.01 mM) described the data best based on model selection criteria. AG did not bind to the cytosolic protein ligandin (glutathioneS-transferase A1). These data indicate that PRB is a potent partial noncompetitive inhibitor of acetaminophen glucuronidationin vitro. PRB-associated alterations in AG hepatic disposition in vivo are not due to altered binding of AG to GSTA1 but may be attributed in part to impaired AG formation.
Footnotes
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Send reprint requests to: Kim L. R. Brouwer, Pharm.D., Ph.D., School of Pharmacy, Division of Pharmaceutics, The University of North Carolina at Chapel Hill, CB# 7360, Beard Hall, Chapel Hill, NC 27599-7360
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This work was supported by grant GM41935 from the National Institutes of Health.
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This work was presented in part at the 1993 annual meeting of the American Association of Pharmaceutical Scientists, November 14–18, 1993, Lake Buena Vista (Orlando), Florida.
- Abbreviations used are::
- APAP
- acetaminophen
- PRB
- probenecid
- AG
- acetaminophen glucuronide
- GSTA1
- glutathioneS-transferase A1
- DBSP
- dibromosulfophthalein
- BSP
- bromosulfophthalein
- BSA
- bovine serum albumin
- UDPGA
- uridine 5′-diphosphoglucuronic acid
- HPLC
- high-performance liquid chromotography
- AIC
- Akaike’s Information Criterion
- UDP
- uridine diphosphate
- Received October 14, 1996.
- Accepted April 22, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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