Only a few years ago, it was generally accepted by pharmaceutical scientists that phase II metabolites of drugs, such as acyl glucuronide conjugates, are rapidly excreted following their formation in the body and that these metabolites are not active or reactive. It has recently become recognized that acyl glucuronides of carboxylic acids are unstable and reactive metabolites. At physiologic pH they can undergo isomerization, facile hydrolysis, reversible and irreversible binding to proteins. The general aims of this grant proposal are to determine the scope and biological significance of the rearrangement and protein binding reactions of acyl glucuronides, and to establish whether irreversible binding of these metabolites to macromolecules is responsible for some of the major toxicological side-effect of NSAIDs. We hypothesize that four determinants, related to disposition of the drug acyl glucuronide, may be predictive of the potential for immunotoxicity. These are: the ability of the acyl glucuronide to lead to irreversible binding with proteins (in vitro); the plasma-concentration-time profile of the acyl glucuronide; and the stability of the in vivo adduct. We will study acyl glucuronides of several commonly used acidic drugs (tolmetin, naproxen, carprofen, ibuprofen and fenoprofen), as well as drugs of known serious toxicity to humans (zomepirac and benoxaprofen), some experimental (flunoxaprofen and oxaprozin), and endogenous (bilirubin) compounds.
Specific aims of the proposal are: 1). elucidate the interrelationship between irreversible protein binding and acyl glucuronide reactivity. Here the acyl glucuronides of a group of five primary compounds (tolmetin, zomepirac, benoxaprofen, flunoxaprofen and carprofen) will be isolated, and their acyl migration, reversible and irreversible binding to human serum albumin, will be determined. For chiral compounds, diastereomeric acyl glucuronides of R and S enantiomers will be investigated individually and compared; 2). investigate the relationship for the group of primary compounds between the reversible binding of acyl glucuronides to plasma protein and their irreversible binding; 3). establish the chemical structures of the irreversibly bound drug/protein complexes, determine the mechanism by which they are formed, pinpoint the site of binding and the role of isomeric glucuronides, and determine whether a single mechanism prevails for most acyl glucuronide; 4). measure the stability and disposition of selected albumin adducts in vivo in animals; 5). undertake dosing of approved drugs in healthy volunteers and patients; 6). determine whether acyl glucuronide adducts with proteins are effective immunogens and whether there is immunological cross reactivity between adducts from different glucuronides; and 7). investigate the relationship between irreversible binding in vivo and immunological toxicity.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
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Pharmacology A Study Section (PHRA)
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University of California San Francisco
Schools of Pharmacy
San Francisco
United States
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Horng, Howard; Benet, Leslie Z (2013) The nonenzymatic reactivity of the acyl-linked metabolites of mefenamic acid toward amino and thiol functional group bionucleophiles. Drug Metab Dispos 41:1923-33
Horng, Howard; Benet, Leslie Z (2013) Characterization of the acyl-adenylate linked metabolite of mefenamic Acid. Chem Res Toxicol 26:465-76
Grillo, Mark P; Wait, Jill C M; Tadano Lohr, Michelle et al. (2010) Stereoselective flunoxaprofen-S-acyl-glutathione thioester formation mediated by acyl-CoA formation in rat hepatocytes. Drug Metab Dispos 38:133-42
Grillo, Mark P; Hua, Fengmei; March, Kristi L et al. (2008) Gamma-glutamyltranspeptidase-mediated degradation of diclofenac-S-acyl-glutathione in vitro and in vivo in rat. Chem Res Toxicol 21:1933-8
Li, Chunze; Grillo, Mark P; Badagnani, Ilaria et al. (2008) Differential effects of fibrates on the metabolic activation of 2-phenylpropionic acid in rats. Drug Metab Dispos 36:682-7
Olsen, Jorgen; Li, Chunze; Skonberg, Christian et al. (2007) Studies on the metabolism of tolmetin to the chemically reactive acyl-coenzyme A thioester intermediate in rats. Drug Metab Dispos 35:758-64
Olsen, Jorgen; Li, Chunze; Bjornsdottir, Inga et al. (2005) In vitro and in vivo studies on acyl-coenzyme A-dependent bioactivation of zomepirac in rats. Chem Res Toxicol 18:1729-36
Wu, Chi-Yuan; Benet, Leslie Z (2005) Predicting drug disposition via application of BCS: transport/absorption/ elimination interplay and development of a biopharmaceutics drug disposition classification system. Pharm Res 22:11-23
Chang, Jae H; Benet, Leslie Z (2005) Glucuronidation and the transport of the glucuronide metabolites in LLC-PK1 cells. Mol Pharm 2:428-34
Mohri, Kiminori; Okada, Kenji; Benet, Leslie Z (2005) Stereoselective taurine conjugation of (R)-benoxaprofen enantiomer in rats: in vivo and in vitro studies using rat hepatic mitochondria and microsomes. Pharm Res 22:79-85

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