van Zyl J M, Basson K, Kriegler A, van der Walt B J
Department of Pharmacology, Medical School, University of Stellenbosch, Tygerberg, South Africa.
Biochem Pharmacol. 1991 Jul 15;42(3):599-608. doi: 10.1016/0006-2952(91)90323-w.
The 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.
研究了两种均具有抗炎特性的抗麻风病药物（氯法齐明和氨苯砜）抑制髓过氧化物酶（MPO）催化反应的机制。利用NADH荧光的消失作为其氧化的检测方法。氯离子以浓度依赖性方式刺激MPO-H2O2系统中NADH的氧化（在150 mM NaCl时为50倍）。在这些条件下，Cl-被氧化，形成的氧化剂大概是次氯酸（HOCl），它氧化NADH。证明药物对MPO系统有影响的观察结果如下：（1）抑制Cl(-)刺激的NADH氧化。（2）抑制模型蛋白甲状腺球蛋白（TG）中的多肽修饰。（3）保护MPO免受系统产生的氯化氧化剂导致的催化活性丧失。（4）抑制血红蛋白氧化。在此处只有氨苯砜有活性。HPLC分析表明，在没有Cl-的情况下，药物在MPO-H2O2系统中没有明显代谢。MPO系统中的Cl-刺激氯法齐明的漂白，表明HOCl参与其中。当使用试剂HOCl抑制NADH氧化作为检测方法时，发现氯法齐明是比氨苯砜更有效的HOCl清除剂。HPLC分析也支持这一发现，其表明HOCl对氯法齐明的敏感性高于氨苯砜。相对低浓度的氨苯砜抑制氧合血红蛋白（HbO2）的氧化,这表明该药物没有代谢为其N-羟基化衍生物，而该衍生物被认为在体内负责高铁血红蛋白（metHb）的形成。有人提出，氯法齐明的抑制作用机制是清除MPO-Cl(-)-H2O2系统产生的氯化氧化剂，而氨苯砜则将MPO转化为其无活性的化合物II（高铁）形式。氯法齐明和氨苯砜对MPO系统的不同抑制机制可能有助于这些药物的抗炎作用。
