Regulation of the nitric oxide oxidase activity of myeloperoxidase by pharmacological agents.
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 H2O2and 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.
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.
Sophie L
SL
Maiocchi
School of Chemistry, University of New South Wales, Sydney, NSW 2052, Australia.
Jonathan C
JC
Morris
Mechanisms of Disease & Translational Research, Department of Pathology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: martdrees@gmail.com.
Martin D
MD
Rees
Mechanisms of Disease & Translational Research, Department of Pathology, School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, NSW 2052, Australia. Electronic address: shane.thomas@unsw.edu.au.
Shane R
SR
Thomas
D000975:Antioxidants / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D009569:Nitric Oxide / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009195:Peroxidase / Q000037:antagonists & inhibitors* / Q000378:metabolism*
D000975:Antioxidants; D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D010088:Oxidoreductases; D009195:Peroxidase
2-Thioxanthine; 2-Thioxanthine (PubChem CID: 10264211); 4-AminoTEMPO (PubChem CID: 550942); 4-CarboxyTEMPO (PubChem CID: 3080786); ABAH (PubChem CID: 21450); Apocynin (PubChem CID: 2214); Endothelial dysfunction; Hydroxyurea (PubChem CID: 3657); Isoniazid (PubChem CID: 3767); Melatonin (PubChem CID: 896); Myeloperoxidase; Nitric oxide; Oxidative stress; Paracetamol (PubChem CID: 1983); Resveratrol (PubChem CID: 445154); Tempol (PubChem CID: 137994); Trolox (PubChem CID: 40634); Tryptophan (PubChem CID: 6305)