The smoking-associated oxidant hypothiocyanous acid induces endothelial nitric oxide synthase dysfunction

Author:

Talib Jihan12,Kwan Jair12,Suryo Rahmanto Aldwin12,Witting Paul K.3,Davies Michael J.12

Affiliation:

1. The Heart Research Institute, 7 Eliza Street, Newtown, Sydney, NSW 2042, Australia

2. Faculty of Medicine, University of Sydney, Sydney, NSW 2006, Australia

3. Discipline of Pathology, School of Medical Sciences, University of Sydney, Sydney, NSW 2006, Australia

Abstract

Smokers have an elevated risk of cardiovascular disease but the origin(s) of this increased risk are incompletely defined. Considerable evidence supports an accumulation of the oxidant-generating enzyme MPO (myeloperoxidase) in the inflamed artery wall, and smokers have high levels of SCN−, a preferred MPO substrate, with this resulting in HOSCN (hypothiocyanous acid) formation. We hypothesized that this thiol-specific oxidant may target the Zn2+–thiol cluster of eNOS (endothelial nitric oxide synthase), resulting in enzyme dysfunction and reduced formation of the critical signalling molecule NO•. Decreased NO• bioavailability is an early and critical event in atherogenesis, and HOSCN-mediated damage to eNOS may contribute to smoking-associated disease. In the present study it is shown that exposure of isolated eNOS to HOSCN or MPO/H2O2/SCN− decreased active dimeric eNOS levels, and increased inactive monomer and Zn2+ release, compared with controls, HOCl (hypochlorous acid)- or MPO/H2O2/Cl−-treated samples. eNOS activity was increasingly compromised by MPO/H2O2/Cl− with increasing SCN− concentrations. Exposure of HCAEC (human coronary artery endothelial cell) lysates to pre-formed HOSCN, or MPO/H2O2/Cl− with increasing SCN−, increased eNOS monomerization and Zn2+ release, and decreased activity. Intact HCAECs exposed to HOCl and HOSCN had decreased eNOS activity and NO2−/NO3− formation (products of NO• decomposition), and increased free Zn2+. Exposure of isolated rat aortic rings to HOSCN resulted in thiol loss, and decreased eNOS activity and cGMP levels. Overall these data indicate that high SCN− levels, as seen in smokers, can increase HOSCN formation and enhance eNOS dysfunction in human endothelial cells, with this potentially contributing to increased atherogenesis in smokers.

Publisher

Portland Press Ltd.

Subject

Cell Biology,Molecular Biology,Biochemistry

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