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Research ArticleArticle

Comparison of Stably Expressed Rat UGT1.1 and UGT2B1 in the Glucuronidation of Opioid Compounds

Christopher D. King, Gladys R. Rios, Mitchell D. Green, Peter I. Mackenzie and Thomas R. Tephly
Drug Metabolism and Disposition February 1997, 25 (2) 251-255;
Christopher D. King
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Gladys R. Rios
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Mitchell D. Green
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Peter I. Mackenzie
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Thomas R. Tephly
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Abstract

Opioids are important drugs used as analgesics, antitussives, antidiarrheals, and in the therapy of myocardial infarctions, and as antagonists of opioid intoxication. The glucuronidation of these compounds, catalyzed by UDP-glucuronosyltransferases (UGTs), is well known to be a primary step in their metabolism to hydrophilic products and in their ultimate excretion. The present study was designed to compare the reactivity and relative glucuronidation efficiencies of opioid agonists, antagonists, and partial agonists with two rat UGT isoforms; UGT1.1, which is generally considered the “bilirubin UGT,” and UGT2B1, which has previously been shown to catalyze the glucuronidation of testosterone, chloramphenicol, and (−)-morphine. Rat UGT2B1, stably expressed in HK293 cells, exhibited high glucuronidation rates and catalytic efficiencies for many opioids, although values for (−)-morphine and nalorphine were the highest. In contrast, these compounds were very poor substrates for expressed rat UGT1.1. Comparably high glucuronidation rates and efficiencies were found for buprenorphine and diprenorphine with both UGT isoforms. These results suggest that opioids with morphinan-based chemical structures similar to (−)-morphine interact with UGTs differently than those with oripavine-based chemical structures similar to buprenorphine. To investigate the contribution of rat UGT1.1 and UGT2B1 in the overall rate of glucuronidation of buprenorphine in the rat liver, hepatic microsomes from Gunn rats (where UGT1.1 activity is absent) and Wistar rats (where UGT1.1 activity is present) were studied. Buprenorphine glucuronidation activity in Gunn rat liver microsomes exhibit ∼25% of rates observed in Wistar rat liver microsomes, whereas (−)-morphine, naloxone, and naltrexone glucuronidation rates were not significantly different in microsomal preparations from Gunn and Wistar rats. These data suggest that UGT2B1 is the major hepatic enzyme involved in the glucuronidation of (−)-morphine and naloxone in livers from untreated rats, whereas buprenorphine glucuronidation is preferentially catalyzed by rat UGT1.1.

Footnotes

  • Send reprint requests to: Dr. Thomas R. Tephly, Department of Pharmacology, University of Iowa, 2-452 Bowen Science Building, Iowa City, IA 52242.

  • This research was supported by the National Institutes of Health Grant GM26221.

  • ↵2 B. L. Coffman et al., manuscript in preparation.

  • Abbreviations used are::
    UDP-GlcUA
    UDP-glucuronic acid
    UGT
    UDP-glucuronosyltransferase
    HK293 cell
    human embryonic kidney 293 cell
    IgG
    immunoglobulin G
    OH
    hydroxy
    • Received August 19, 1996.
    • Accepted November 7, 1996.
  • The American Society for Pharmacology and Experimental Therapeutics
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Drug Metabolism and Disposition
Vol. 25, Issue 2
1 Feb 1997
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Research ArticleArticle

Comparison of Stably Expressed Rat UGT1.1 and UGT2B1 in the Glucuronidation of Opioid Compounds

Christopher D. King, Gladys R. Rios, Mitchell D. Green, Peter I. Mackenzie and Thomas R. Tephly
Drug Metabolism and Disposition February 1, 1997, 25 (2) 251-255;

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Research ArticleArticle

Comparison of Stably Expressed Rat UGT1.1 and UGT2B1 in the Glucuronidation of Opioid Compounds

Christopher D. King, Gladys R. Rios, Mitchell D. Green, Peter I. Mackenzie and Thomas R. Tephly
Drug Metabolism and Disposition February 1, 1997, 25 (2) 251-255;
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