Accumulation of Myeloperoxidase-Positive Neutrophils in Atherosclerotic Lesions in LDLR–/– Mice

Objective—
Atherosclerosis is a chronic inflammatory disease in which the immune system plays an important role. Neutrophils have not been thoroughly studied in the context of atherogenesis. Here, we investigated neutrophils in the development of murine atherosclerotic lesions.

Methods and Results—
LDLR–/– mice were given a high-fat diet for different time periods and subsequently atherosclerotic lesions were studied by immunohistochemistry. Staining with anti–Ly-6G monoclonal antibody, a specific marker for neutrophils, revealed a marked accumulation of neutrophils during atherosclerosis development. Neutrophils were observed in the lesion, attached to the cap, and in the arterial adventitia. In addition, at some sites, neutrophil accumulation colocalized with endothelial E-selectin expression. Immunofluorescence double staining with anti-myeloperoxidase and anti–Ly-6G antibodies demonstrated the presence of myeloperoxidase in atherosclerotic lesions and its colocalization with neutrophils. After introducing the high-fat diet, levels of circulating myeloperoxidase in plasma strongly increased, with a peak at 6 weeks and a subsequent decrease to almost normal levels after 16 weeks of diet.

Conclusions—
We here demonstrate for the first time the presence of neutrophils and myeloperoxidase in murine atherosclerotic lesions. As a major cell type in inflammatory responses the neutrophil may also be an important mediator in the development of atherosclerosis.

We identified myeloperoxidase-positive neutrophils in mouse atherosclerotic lesions. Although neutrophils were not detected in early lesions, they were abundantly present in more advanced stages. In addition, circulating myeloperoxidase levels were strongly increased by high-fat feeding of the mice. Therefore, neutrophils should be considered as a potential important cellular mediator in atherogenesis.

Chitin oligosaccharides inhibit oxidative stress in live cells

The aim of this research is to identify the cellular antioxidant effects of Chitin oligosaccharides inhibit oxidative stress in live cells

(NA-COS; Mw 229.21–593.12 Da) produced by acidic hydrolysis of crab chitin. The inhibitory effect of NA-COS on myeloperoxidase (MPO) activity in human myeloid cells (HL-60) and oxidation of DNA and protein in mouse macrophages (Raw 264.7) were identified. Furthermore, their direct radical scavenging effect by 2′,7′-dichlorofluorescein (DCF) intensity and intracellular glutathione (GSH) level were significantly increased in a time dependent manner, respectively. These results suggest that NA-COS act as a potent antioxidant in live cells.

ARTICLE

Myeloperoxidase levels are not associated with carotid atherosclerosis progression in patients with familial hypercholesterolemia

Introduction
myeloperoxidase (MPO), an antimicrobial enzyme of the innate immune system, has been proposed to exert a wide array of pro-atherogenic effects throughout all stages of the atherosclerotic process. In view of the potent anti-inflammatory effects of statins in vitro, we evaluated the impact of statin therapy on plasma MPO levels in patients with heterozygous familial hypercholesterolemia (FH), treated with either intensive or conventional lipid-lowering therapy. Furthermore, we evaluated the relation between myeloperoxidase (MPO)levels and atherosclerosis progression, as determined by intima media thickness (IMT).

Methods
We measured plasma MPO levels, lipoprotein profiles, high sensitivity-C-reactive protein (hs-CRP) as well as IMT of carotid artery segments in 122 FH patients at baseline and after 2-year treatment with atorvastatin 80mg or simvastatin 40mg QD.

Results
Baseline median myeloperoxidase (MPO)values were 147pM (interquartile range (IQR) 122–217) and 144pM (IQR 118–216) and these increased significantly to 221pM (IQR 144–290) and 255pM (IQR 152–324) during 2-year follow-up in both the atorvastatin 80mg and simvastatin 40mg group, respectively. There was no correlation between MPO levels and IMT progression, change in lipoproteins or hs-CRP.

Conclusion
In FH patients, statins do not prevent an increase in MPO levels during follow-up. Moreover, MPO levels are not associated with atherosclerosis progression in these patients.

Evaluation of the ameliorative effects of immunosuppressants on crescentic glomerulonephritis in SCG/Kj mice

The therapeutic efficacy of immunosuppressants for treating rapidly progressive glomerulonephritis (RPGN) with crescent formation remains controversial. SCG/Kj mice spontaneously develop RPGN-like symptoms, characteristic of crescentic glomerulonephritis and systemic small vessel vasculitis, associated with the presence of anti-neutrophil cytoplasmic antibodies (ANCA). We evaluated the “ameliorative”, not prophylactic, effects of immunosuppressive agents, deoxyspergualin (DSG), cyclophosphamide (CYC) and prednisolone (PDN), on RPGN in these mice. DSG at intraperitoneal doses of 3 and 6 mg/kg, CYC at an oral dose of 12 mg/kg, or PDN at an intraperitoneal dose of 120 mg/kg was administered once a day for 21 days to female mice “at the onset of hematuria”. A set of control SCG/Kj mice received only saline injections. DSG and CYC significantly prolonged survival, improved the proteinuria, hematuria and hyperuremia, and decreased the serum level of myeloperoxidase-ANCA. Moreover, DSG significantly suppressed the formation of crescents in glomeruli. PDN failed to affect any of the parameters. DSG might be useful for inducing remission in crescentic glomerulonephritis involved in RPGN.

ARTICLE

Kinetic evidence for rapid oxidation of (–)-epicatechin by human myeloperoxidase

Apocynin has been reported to require dimerization by myeloperoxidase (MPO) to inhibit leukocyte NADPH oxidase. (–)-Epicatechin, a dietary flavan-3-ol, has been identified as a ‘prodrug’ of apocynin-like metabolites that inhibit endothelial NADPH oxidase activity and elevate the cellular level of nitric oxide. Since (–)-epicatechin has tentatively been identified as substrate of myeloperoxidase (MPO), we studied the one-electron oxidation of (–)-epicatechin by MPO. By using multi-mixing stopped-flow technique, we demonstrate that (–)-epicatechin is one of the most efficient electron donors for heme peroxidases investigated so far. Second order rate constants for the (–)-epicatechin-mediated conversion of MPO-compound I to compound II and compound II to resting enzyme were estimated to be 1.9 × 107 and 4.5 × 106 M−1 s−1, respectively (pH 7, 25 °C). The data indicate that (–)-epicatechin is capable of undergoing fast MPO-mediated one-electron oxidation.

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