title: Influence of pH on the reactivity of diphenyl ditelluride with thiols and anti-oxidant potential in rat brain.
abstract: Thiol oxidation by diphenyl ditelluride is a favorable reaction and may be responsible for alteration in regulatory or signaling pathways. We have measured rate constants for reactions of diphenyl ditelluride with cysteine, dimercaptosuccinic acid, glutathione and dithiothreitol in phosphate buffer. The relative reactivities of the different thiols with diphenyl ditelluride were independent of the pK(a) of the thiol group, such that at pH 7.4, cysteine and dithiothreitol were the most reactive and low reactivity was observed with glutathione and dimercaptosuccinic acid. The reactivity of diphenyl ditelluride was not modified by change in pH. Rate of oxidation increased with increasing pH for all thiols except dimercaptosuccinic acid, where the rate of oxidation was faster at low pH. The lipid peroxidation product malonaldehyde (MDA) was measured in rat brain homogenate and phospholipids extract from egg yolk after incubation in phosphate buffer at various pHs ranging from 7.4 to 5.4. TBARS production increased when homogenates were incubated in the pH (5.4-6.8) medium both in the absence and presence of Fe(II). These data indicate that lipid peroxidation processes, mediated by iron, are enhanced with decreasing pH. The iron mobilization may come from reserves where it is weakly bound. Diphenyl ditelluride significantly protected TBARS production at all studied pH values in a concentration dependent manner in brain homogenate. This study provides in vitro evidence for acidosis induced oxidative stress and anti-oxidant action of diphenyl ditelluride.
authors.affiliation: Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade, Federal de Santa Maria, Santa Maria, RS, Brazil. waseem_anw@yahoo.com
authors.forename: Waseem
authors.initials: W
authors.lastname: Hassan
authors.forename: Mohammad
authors.initials: M
authors.lastname: Ibrahim
authors.forename: Cristina Wayne
authors.initials: CW
authors.lastname: Nogueira
authors.forename: Antonio Luis
authors.initials: AL
authors.lastname: Braga
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Deobald
authors.forename: Imdad Ullah
authors.initials: IU
authors.lastname: Mohammadzai
authors.forename: Joao Batista Teixeira
authors.initials: JB
authors.lastname: Rocha
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry* / Q000494:pharmacology*; D001555:Benzene Derivatives / Q000737:chemistry* / Q000494:pharmacology*; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008297:Male; D009942:Organometallic Compounds / Q000737:chemistry* / Q000494:pharmacology*; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D001555:Benzene Derivatives; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; C434247:diphenylditelluride