[7] Covalent binding of electrophilic metabolites to macromolecules

Pohl, Lance R.; Branchflower, Richard V.

doi:10.1016/s0076-6879(81)77009-5

Cited by 34 publications

(11 citation statements)

References 23 publications

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“…The Z-protein adduct was stable under the conditions used to wash the protein, with -2.5% of adduct lost during the washing procedure, as estimated from 24-h stability studies conducted in methanol/ether (3:1). Drug not removed from plasma protein by the washing procedure but liberated only on treatment with strong base is defined in this paper as "irreversibly bound" (20). A clinical study of the effect of probenecid on Z disposition was conducted in our laboratory in September 1982 (18).…”

Section: Methodsmentioning

confidence: 99%

Irreversible binding of zomepirac to plasma protein in vitro and in vivo.

Smith¹,

McDonagh²,

Benet³

1986

J. Clin. Invest.

164

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Zomepirac is a nonsteroidal anti-inflammatory drug recently withdrawn from use because of an unexplained high incidence of immunological reactions. It is metabolized in humans to a reactive, unstable acyl glucuronide which accumulates in plasma. Because of the similarity of zomepirac glucuronide to bilirubin glucuronide in structure and stability and the documented irreversible binding of bilirubin to albumin through its acyl glucuronide, we studied the reaction of zomepirac acyl glucuronide with albumin in vitro from pH 5 to 9 and in vivo in six healthy human volunteers who had received a single 100-mg oral dose of zomepirac. Irreversible binding of zomepirac to protein was determined by exhaustive washing of protein, followed by hydrolysis of bound zomepirac-protein adduct with base, extraction of the liberated drug, and chromatographic measurement. Irreversible binding was observed both in vitro and in vivo. The extent of binding in vitro was time-and pH-dependent. In vitro drug binding was also observed for the isomers of zomepirac glucuronide which were formed by intramolecular acyl migration. Irreversible binding in vivo correlated with overall exposure to zomepirac glucuronide when exposure was expressed as the area under the plasma concentration vs. time curve. When probenecid (500 mg, twice daily), which decreases the plasma clearance of zomepirac glucuronide, was administered concurrently with zomepirac, irreversible binding of zomepirac was increased. The nature of the zomepirac protein binding is probably covalent. Formation of irreversibly protein-bound zomepirac occurs via the acyl glucuronide as previously shown for bilirubin glucuronide, and the reaction may be general for other drugs that are metabolized to acyl glucuronides.

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Section: Methodsmentioning

confidence: 99%

Irreversible binding of zomepirac to plasma protein in vitro and in vivo.

Smith¹,

McDonagh²,

Benet³

1986

J. Clin. Invest.

164

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“…Incubation conditions for binding to microsomal proteins consisted of 2 mg/ml renal cortex microsomal protein (obtained from untreated male Syrian hamsters), 1.5mM CuOOH, 50/zM 2-hydroxy-[6,7-3H]-estradiol (6/zCi) in a final volume of 1.0 ml of 10 mM phosphate buffer, pH 7.5. Irreversible binding to proteins was determined as described previously [24]. Reactions were carried out at 37 ° C in a shaking water bath and stopped by addition of 4 ml of cold 0.8 M trichloroacetic acid.…”

Section: Irreversible Bindingmentioning

confidence: 99%

“…The oxidation of catechol estrogens or DES to their corresponding quinones has previously been shown to be dependent on the availability of organic hydroperox- Incubations contained kidney cortex microsomes, (2 mg/ml), 1.5 mM CuOOH, 50 mM 2-hydroxy-[6,7-3H]-estradiol (6/xCi) in a final volume of 1 ml of 10 mM phosphate buffer, pH7.5. Irreversible binding was measured as described previously [24]. Control reactions were carried out in the absence of substrate or cofactor.…”

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confidence: 99%

Target organ-specific inactivation of drug metabolizing enzymes in kidney of hamsters treated with estradiol

Roy

Liehr

1992

Mol Cell Biochem

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Chronic treatment of hamsters with estradiol for several months has previously been shown to decrease the specific content of cytochrome P450 in the kidney, a target of hormonal carcinogenesis, but not in liver. The reason for this decrease in metabolic enzyme activity is unknown and has been examined in this investigation. We now report that the decrease in specific content of renal cytochrome P450 by 73% in response to estradiol was not affected by co-treatment with tamoxifen for 1 month. The subcutaneous infusion of 250 micrograms/day estradiol for 7 days lowered renal cytochrome P450 by 71% from control values and was therefore used for further mechanistic studies. This treatment decreased renal activities of estradiol 2- or 4-hydroxylase by 77 to 80%, of 7-ethoxycoumarin-O-deethylase by 66% of control values, respectively, and completely eliminated aryl hydrocarbon hydroxylase activities, whereas liver enzymes remained unaffected. After 7 days of infusion of estradiol, fluorescent products of lipid peroxidation were more than doubled in hamster kidney but remained unchanged in liver. The possibility of enzyme destruction by binding of estradiol 2,3-quinone to metabolizing enzymes was investigated in vitro. In the presence of 2-hydroxyestradiol, cumene hydroperoxide, and microsomes, conditions known to favor the oxidation of the steroid to quinone, the binding of catechol estrogen metabolite to microsomal protein increased 60 fold over control values in the absence of cofactor. Purified rat liver cytochrome P450c also oxidized 2-hydroxyestradiol to 2,3-estradiol quinone. The rate of oxidation was linear for the first 2-3 min, but thereafter decreased with time.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…It is known, however, especially at higher concentrations of DEM, that many effects, not directly related to GSH depletion, may show up. It may react with all available thiols, bind to a variety of macromolecules [23] and increase heme-catabolism [5]. The hydrolysis product of DEM, maleic acid, as well as DEM-conjugates may alter several metabolic pathways in the cell [25].…”

Section: Discussionmentioning

confidence: 99%

Radio- and thermosensitivity of E. coli K1060 after thiol depletion by diethylmaleate

Konings

Gipp

Yatvin

1984

Radiat Environ Biophys

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The Escherichia coli auxotroph K1060 has been grown in a medium supplemented with either oleic acid (18:1) or linolenic acid (18:3) and its radiosensitivity and thermosensitivity established using bacterial cell survival as the assay system. No difference in radiosensitivity was observed when oleic and linolenic grown cells were exposed to gamma-radiation at room temperature. When heated at 49 degrees C linolenic grown cells were more sensitive than oleic grown cells. To investigate whether soluble -SH compounds, e.g., glutathione (GSH), were critical in protecting cells against radiation or heat, studies were performed using cells depleted of -SH by incubation with diethylmaleate (DEM). After reduction of water-soluble non-protein thiol compounds to 25% (10 mM DEM treatment) of control value, no major changes in radiosensitivity under oxic conditions were found. Radioresistance increased slightly when irradiation was performed under hypoxic conditions. Thermoresistance was clearly stimulated after DEM treatments between 1 and 10 mM DEM. The main conclusion of these experiments is that lowering the cellular level of reduced glutathione may not generally be correlated with a higher radio- and thermosensitivity.

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[7] Covalent binding of electrophilic metabolites to macromolecules

Cited by 34 publications

References 23 publications

Irreversible binding of zomepirac to plasma protein in vitro and in vivo.

Irreversible binding of zomepirac to plasma protein in vitro and in vivo.

Target organ-specific inactivation of drug metabolizing enzymes in kidney of hamsters treated with estradiol

Radio- and thermosensitivity of E. coli K1060 after thiol depletion by diethylmaleate

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