Mechanisms by which clofazimine and dapsone inhibit the myeloperoxidase system. A possible correlation with their anti-inflammatory properties

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dc.contributor.authorVan Zijl J.M.
dc.contributor.authorBasson K.
dc.contributor.authorKriegler A.
dc.contributor.authorVan der Walt B.J.
dc.date.accessioned2011-05-15T16:01:18Z
dc.date.available2011-05-15T16:01:18Z
dc.date.issued1991
dc.description.abstractThe mechanisms by which two anti-leprotic drugs (clofazimine and dapsone), both with anti-inflammatory properties, inhibit myeloperoxidase (MPO)-catalysed reactions, were investigated. The disappearance of NADH fluorescence was used as an assay for its oxidation. Chloride stimulated the oxidation of NADH in the MPO-H2O2 system in a concentration-dependent manner (50-fold at 150 mM NaCl). Under these conditions Cl- is oxidized and the oxidant formed, presumably hypochlorous acid (HOCl), oxidizes NADH. Observations demonstrating the effect of the drugs on the MPO system, are: (1) Inhibition of Cl--stimulated oxidation of NADH. (2) Inhibition of polypeptide modification in a model protein, thyroglobulin (TG). (3) Protection of MPO against loss of catalytic activity caused by chlorinating oxidants generated by the system. (4) Inhibition of haemoglobin oxidation. Only dapsone was active here. HPLC analyses suggested that the drugs were not significantly metabolized in the MPO-H2O2 system in the absence of Cl-. Bleaching of clofazimine was stimulated by Cl- in the MPO system, suggesting the involvement of HOCl. Clofazimine was found to be a more potent scavenger of HOCl than dapsone when the inhibition of NADH oxidation by reagent HOCl was used as an assay. This finding is also supported by HPLC analyses which indicated a greater sensitivity of HOCl for clofazimine than for dapsone. Relatively low concentrations of dapsone inhibited the oxidation of oxygenated haemoglobin (HbO2), suggesting that the drug was not metabolized to its N-hydroxylated derivative which is thought to be responsible for methaemoglobin (metHb) formation in vivo. It is proposed that the inhibitory mechanism of action of clofazimine is to scavenge chlorinating oxidants generated by the MPO-Cl--H2O2 system, while dapsone converts MPO into its inactive compound II (ferryl) form. The different inhibitory mechanisms of clofazimine and dapsone towards the MPO system may contribute to the anti-inflammatory actions of the drugs.
dc.description.versionArticle
dc.identifier.citationBiochemical Pharmacology
dc.identifier.citation42
dc.identifier.citation3
dc.identifier.issn62952
dc.identifier.other10.1016/0006-2952(91)90323-W
dc.identifier.urihttp://hdl.handle.net/10019.1/11908
dc.subjectchloride
dc.subjectclofazimine
dc.subjectdapsone
dc.subjecthemoglobin
dc.subjecthydrogen peroxide
dc.subjectmyeloperoxidase
dc.subjectreduced nicotinamide adenine dinucleotide
dc.subjectabsorption spectroscopy
dc.subjectantiinflammatory activity
dc.subjectarticle
dc.subjectconcentration response
dc.subjectcontrolled study
dc.subjecthigh performance liquid chromatography
dc.subjectoxidation
dc.subjectpriority journal
dc.subjectscavenging system
dc.subjectAnti-Inflammatory Agents, Non-Steroidal
dc.subjectChlorides
dc.subjectChromatography, High Pressure Liquid
dc.subjectClofazimine
dc.subjectComparative Study
dc.subjectDapsone
dc.subjectHuman
dc.subjectHydrogen Peroxide
dc.subjectHypochlorous Acid
dc.subjectNAD
dc.subjectNeutrophils
dc.subjectOxidation-Reduction
dc.subjectPeroxidase
dc.subjectThyroglobulin
dc.titleMechanisms by which clofazimine and dapsone inhibit the myeloperoxidase system. A possible correlation with their anti-inflammatory properties
dc.typeArticle
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