Studies on the reactivity of acyl glucuronides—II: Interaction of diflunisal acyl glucuronide and its isomers with human serum albumin in vitro

doi:10.1016/0006-2952(91)90233-U

Biochemical Pharmacology

Volume 42, Issue 12, 27 November 1991, Pages 2301-2306

https://doi.org/10.1016/0006-2952(91)90233-U Get rights and content

Abstract

A major metabolite of diflunisal (DF) is its reactive acyl glucuronide conjugate (DAG) which can undergo hydrolysis (regeneration of DF), intramolecular rearrangement (isomerization via acyl migration) and intermolecular reactions with nucleophiles. We have compared the fate of DAG and its individual 2-, 3- and 4-O-acyl positional isomers (at ca. 55 μg DF equivalents/mL) after incubation with human serum albumin (HSA, 40 mg/mL) at pH 7.4 and 37°. Initial half-lives $(T_{12})$ for DAG and its 2-, 3- and 4-isomers were 53, 75, 61 and 26 min, respectively. DAG was more labile to hydrolysis than any of its isomers but the latter, in particular the 4-isomer, were much better substrates for formation of covalent DF-HSA adducts. After a 2-hr incubation, 2.4, 8.2, 13.7 and 36.6% of substrate DAG and its 2-, 3- and 4-isomers (respectively) were present as DF-HSA adducts. With long term incubation, the concentrations of adducts so generated in situ declined in a biphasic manner, with apparent terminal $T_{12}$ values of ca. 28 days. DAG was much more labile to transacylation with methanol (i.e. formation of DF methyl ester) than an equimolar mixture of its isomers after incubation in a 1:1 methanol:pH 7.4 buffer solution at 37° ( $T_{12}$ values of 5 and 70 min, respectively). The data do not support direct transacylation with nucleophilic groups on protein as the predominant mechanism of formation of covalent DF-HSA adducts in vitro.

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Acyl glucuronides can be reactive metabolites capable of undergoing hydrolysis, intramolecular acyl migration, and covalent binding to proteins, both in vitro and in vivo. Glucuronidation occurs primarily in the liver and intestines, and is the major route of elimination for many xenobiotic and endogenous compounds containing a carboxylic acid function. Although glucuronidation is recognized as a detoxification process, acyl-linked glucuronides are considered chemically reactive electrophiles capable of covalent modification with nucleophilic sites on proteins. The extent of covalent binding with lysine amino groups of proteins correlates well with acyl glucuronide degradation rates (acyl migration and hydrolysis) and occurs either through a direct transacylation reaction or by a Schiff base mechanism via the open-chain aldehyde form of the acyl-migrated isomer. Subsequent formation of drug protein adducts has been proposed to elicit a direct toxicity or an immune-based reaction, both of which are consistent with the idiosyncratic toxicity commonly associated with carboxylic acid-containing drugs.
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Studies on the reactivity of acyl glucuronides—II: Interaction of diflunisal acyl glucuronide and its isomers with human serum albumin in vitro

Abstract

Life Sci

J Biol Chem

J Biol Chem

J Biol Chem

J Chromatogr

J Chromatogr

J Pharmaceut Biomed Anal

Biochem Pharmacol

Biochem Pharmacol

Biochem Pharmacol

Properties of acyl glucuronides: implications for studies of the pharmacokinetics and metabolism of acidic drugs

Drug Metab Rev

Acylation of albumin by 1-O-acyl glucuronides

Drug Metab Dispos

Reactions of oxaprozin-1-O-acyl glucuronide in solutions of human plasma and albumin

Acylation of amino acids and other endobiotics by xenobiotic carboxylic acids

Acyl migration and covalent binding of drug glucuronides — potential toxicity mediators

Structural and stereochemical aspects of acyl glucuronide formation and reactivity

Studies of intramolecular rearrangements of acyl-linked glucuronides using salicylic acid, flufenamic acid, and (S)- and (R)-benoxaprofen and confirmation of isomerization in acyl-linked Δ9-11-carboxytetrahydrocannabinol glucuronide

Chem Res Toxicol

Reaction of 1-O-acyl glucuronides with 4-(P-nitrobenzyl)pyridine

Drug Metab Dispos

Studies of intramolecular rearrangements of acyl-linked glucuronides using salicylic acid, flufenamic acid, and (S)- and (R)-benoxaprofen and confirmation of isomerization in acyl-linked Δ⁹-11-carboxytetrahydrocannabinol glucuronide