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Atherosclerosis is the main pathophysiological process underlying coronary artery disease (CAD). Acute complications of atherosclerosis, such as myocardial infarction, are caused by the rupture of vulnerable atherosclerotic plaques, which are characterized by thin, highly inflamed, and collagen-poor fibrous caps. Several lines of evidence mechanistically link the heme peroxidase myeloperoxidase (MPO), inflammation as well as acute and chronic manifestations of atherosclerosis. MPO and MPO-derived oxidants have been shown to contribute to the formation of foam cells, endothelial dysfunction and apoptosis, the activation of latent matrix metalloproteinases, and the expression of tissue factor that can promote the development of vulnerable plaque. As such, detection, quantification and imaging of MPO mass and activity have become useful in cardiac risk stratification, both for disease assessment and in the identification of patients at risk of plaque rupture. This review summarizes the current knowledge about the role of MPO in CAD with a focus on its possible roles in plaque rupture and recent advances to quantify and image MPO in plasma and atherosclerotic plaques. [ABSTRACT FROM AUTHOR]

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 oxidantgenerating 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 signallingmoleculeNO·.DecreasedNO· bioavailability is an early and critical event in atherogenesis, and HOSCN-mediated damage to eNOS may contribute to smokingassociated 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 byMPO/H2O2/Cl- with increasing SCN- concentrations. Exposure ofHCAEC (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. [ABSTRACT FROM AUTHOR]

Electrospray ionisation (ESI) mass spectrometry was used to examine the reactions of the clinically used antiarthritic agent [Au(S2O3)2]3−, and AuPEt3Cl, a derivative of another clinically used agent auranofin, with human serum albumin (HSA) obtained from a human volunteer. Both compounds reacted readily with HSA to form complexes containing one or more covalently attached gold fragments. In the case of AuPEt3Cl, binding was accompanied by the loss of the chloride ligand, while for [Au(S2O3)2]3− the mass spectral data indicated binding of Au(S2O3) groups. Experiments performed using HSA with Cys34 blocked by reaction with iodoacetamide were consistent with reaction of both gold compounds with this amino acid. Separate blocking experiments using diethylpyrocarbonate and AuPEt3Cl also provided evidence for histidine residues acting as lower-affinity binding sites for this gold compound. ESI mass spectra of solutions containing [Au(S2O3)2]3− or [Au(CN)2]−, and HSA, provided evidence for the formation of protein complexes in which intact gold molecules were non-covalently bound. In the case of [Au(S2O3)2]3−, these non-covalent complexes proved to be transitory in nature. However, for [Au(CN)2]− a non-covalent complex containing a single gold molecule bound to HSA was found to be stable, and constituted the main adduct formed in solutions containing low-to-medium Au-to-HSA ratios. Evidence was also obtained for the formation of a covalent adduct in which a single Au(CN) moiety was bonded to Cys34 of the protein. AuPEt3Cl reacted to a much lower extent with HSA that had Cys34 modified by formation of a disulfide bond to added cysteine, than with unmodified HSA. This suggests that the extent of modification of the protein in vivo may have an important influence on the transport and bioavailability of gold antiarthritic drugs. [ABSTRACT FROM AUTHOR]

Oxidative damage catalysed by the heme enzyme myeloperoxidase (MPO) has been linked with multiple inflammatory pathologies. The major oxidant species generated by MPO are hypochlorous (HOCl) and hypothiocyanous acids (HOSCN). The damage induced by HOCl is well characterized and has been linked to multiple diseases, however the role of HOSCN is less well understood. It is known that HOSCN can cause selective damage, as this oxidant selectively targets thiol (e.g. Cys) residues and selenium-containing species. The aim of the current study was to assess whether HOCl and HOSCN can disrupt the [4Fe-4 S] cluster of aconitase causing iron release and loss of activity. It is shown that HOSCN induces rapid and efficient release of iron from aconitase, with 80% removed at an oxidant concentration of 3 micromoles/mg protein; this is markedly more efficient than HOCl. In contrast the extent of loss of enzymatic activity was comparable between the two oxidants at the same concentration. Blocking the [4Fe-4 S] cluster inhibited HOSCN-mediated inactivation, but did not have dramatic effects on HOCl-mediated damage, consistent with HOSCN, but not HOCl, interacting with the cluster. This data is supported by peptide mass mapping studies that indicate that HOSCN oxidises Cys385 of the [4Fe-4 S] cluster. In contrast HOCl damaged multiple sites. Exposure of human coronary artery endothelial cells (HCAEC) to 0-50 micromolar HOCl or 0-150 micromolar HOSCN resulted in an increase in intracellular iron, loss of aconitase activity and a loss of mitochondrial aconitase protein. In contrast cytosolic aconitase was not affected. These data indicate that aconitase - and particularly the mitochondrial form - is a target for MPO-mediated damage with HOSCN showing a selectivity for the [4Fe-4 S] cluster and inducing greater iron release. This damage, and the release of iron, may exacerbate oxidative stress in cells at sites of inflammation where active MPO is present. [ABSTRACT FROM AUTHOR]