title: In vitro metabolism of diphenyl diselenide in rat liver fractions. Conjugation with GSH and binding to thiol groups.
abstract: In spite of an extensive literature reporting pharmacological properties of diphenyl diselenide, (PhSe)(2), little is known about its metabolism. The aim of this study was to identify possible metabolic pathways of (PhSe)(2) in vitro to get insights into the mechanism of its toxicity. Rat liver preparations, namely total homogenate, S9 fraction, cytosol and microsomes were used in the incubations. Samples were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), high-performance liquid chromatography (HPLC) or inductively coupled plasma (ICP). A reduced glutathione (GSH)-selenol adduct (m/z 462) was identified in all liver fraction incubations by LC-MS/MS, suggesting a reaction between (PhSe)(2) and GSH in tissues. Results from incubation of (PhSe)(2) with microsomal fraction showed that (PhSe)(2) disappears from the supernatant without formation of phase I metabolites. The addition of exogenous GSH maintained constant (PhSe)(2) levels in supernatant and significantly reduced the amount of selenium in the precipitate obtained when microsomal incubations were treated with methanol. Addition of N-acetylcysteine (NAC) had a similar effect; moreover, a NAC-selenol adduct similar to the GSH-selenol adduct was identified by LC-MS/MS (m/z 318) in the NAC incubations. The data indicates that (PhSe)(2) probably binds covalently to microsomal components and that GSH and NAC can prevent binding. The depletion of GSH levels in vitro may be related to (PhSe)(2) toxicity. The inhibition of cytochrome P450 (CYP) activity by carbon monoxide or proadifen did not change the amount of (PhSe)(2) in supernatant and selenium levels in the precipitate, neither did the inactivation of the microsomes by heat indicating that binding was not mediated by cytochrome P450 metabolism and was probably due to a direct reaction between (PhSe)(2) and microsomal components. Due to the covalent binding of (PhSe)(2) to microsomal components the potential of (PhSe)(2) to inhibit cytochrome P450 was examined. (PhSe)(2) at a concentration as low as 1 μM reduced monooxygenase activity with an IC(50) value of 78 μM.
authors.affiliation: Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, Santa Maria, CEP 97105-900 RS, Brazil.
authors.forename: Marina
authors.initials: M
authors.lastname: Prigol
authors.forename: Cristina W
authors.initials: CW
authors.lastname: Nogueira
authors.forename: Gilson
authors.initials: G
authors.lastname: Zeni
authors.forename: Maria Rosário
authors.initials: MR
authors.lastname: Bronze
authors.forename: Luís
authors.initials: L
authors.lastname: Constantino
mesh_terms: D000818:Animals; D001555:Benzene Derivatives / Q000378:metabolism / Q000493:pharmacokinetics*; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D016566:Organoselenium Compounds / Q000378:metabolism / Q000493:pharmacokinetics*; D051381:Rats; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D053719:Tandem Mass Spectrometry
chemical_list: D001555:Benzene Derivatives; D016566:Organoselenium Compounds; D013438:Sulfhydryl Compounds; C061132:diphenyldiselenide; D003577:Cytochrome P-450 Enzyme System; D005978:Glutathione