Mechanisms of Disease & Translational Research, Department of Pathology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia; School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
Biochem Pharmacol. 2017 Jul 1;135:90-115. doi: 10.1016/j.bcp.2017.03.016. Epub 2017 Mar 24.
The leukocyte-derived heme enzyme myeloperoxidase (MPO) is released extracellularly during inflammation and impairs nitric oxide (NO) bioavailability by directly oxidizing NO or producing NO-consuming substrate radicals. Here, structurally diverse pharmacological agents with activities as MPO substrates/inhibitors or antioxidants were screened for their effects on MPO NO oxidase activity in human plasma and physiological model systems containing endogenous MPO substrates/antioxidants (tyrosine, urate, ascorbate). Hydrazide-based irreversible/reversible MPO inhibitors (4-ABAH, isoniazid) or the sickle cell anaemia drug, hydroxyurea, all promoted MPO NO oxidase activity. This involved the capacity of NO to antagonize MPO inhibition by hydrazide-derived radicals and/or the ability of drug-derived radicals to stimulate MPO turnover thereby increasing NO consumption by MPO redox intermediates or NO-consuming radicals. In contrast, the mechanism-based irreversible MPO inhibitor 2-thioxanthine, potently inhibited MPO turnover and NO consumption. Although the phenolics acetaminophen and resveratrol initially increased MPO turnover and NO consumption, they limited the overall extent of NO loss by rapidly depleting HO and promoting the formation of ascorbyl radicals, which inefficiently consume NO. The vitamin E analogue trolox inhibited MPO NO oxidase activity in ascorbate-depleted fluids by scavenging NO-consuming tyrosyl and urate radicals. Tempol and related nitroxides decreased NO consumption in ascorbate-replete fluids by scavenging MPO-derived ascorbyl radicals. Indoles or apocynin yielded marginal effects. Kinetic analyses rationalized differences in drug activities and identified criteria for the improved inhibition of MPO NO oxidase activity. This study reveals that widely used agents have important implications for MPO NO oxidase activity under physiological conditions, highlighting new pharmacological strategies for preserving NO bioavailability during inflammation.
白细胞来源的血红素酶髓过氧化物酶 (MPO) 在炎症期间被释放到细胞外，并通过直接氧化 NO 或产生消耗 NO 的底物自由基来损害一氧化氮 (NO) 的生物利用度。在这里，具有作为 MPO 底物/抑制剂或抗氧化剂的活性的结构多样的药理学试剂被筛选用于其对人血浆中 MPO-NO 氧化酶活性和含有内源性 MPO 底物/抗氧化剂（酪氨酸、尿酸、抗坏血酸）的生理模型系统的影响。基于酰肼的不可逆/可逆 MPO 抑制剂（4-ABAH、异烟肼）或镰状细胞贫血药物羟基脲都促进了 MPO-NO 氧化酶活性。这涉及到 NO 拮抗酰肼衍生自由基对 MPO 抑制的能力和/或药物衍生自由基刺激 MPO 周转的能力，从而增加 MPO 氧化还原中间体或消耗 NO 的自由基对 NO 的消耗。相比之下，机制不可逆 MPO 抑制剂 2-硫代嘌呤强烈抑制 MPO 周转和 NO 消耗。尽管酚类化合物对乙酰氨基酚和白藜芦醇最初增加了 MPO 周转和 NO 消耗，但它们通过快速耗尽 HO 和促进抗坏血酸自由基的形成来限制 NO 损失的整体程度，抗坏血酸自由基效率低下地消耗 NO。维生素 E 类似物 Trolox 通过清除消耗 NO 的酪氨酸和尿酸自由基来抑制缺乏抗坏血酸的液体中的 MPO-NO 氧化酶活性。Tempol 和相关的氮氧化物通过清除 MPO 衍生的抗坏血酸自由基减少富含抗坏血酸的液体中的 NO 消耗。吲哚或阿朴肉桂酸酯产生微不足道的影响。动力学分析使药物活性的差异合理化，并确定了改善 MPO-NO 氧化酶活性抑制的标准。这项研究揭示了在生理条件下，广泛使用的药物对 MPO-NO 氧化酶活性有重要影响，强调了在炎症期间保护 NO 生物利用度的新药理学策略。
