Inhibitor Of Myeloperoxidase Activity Research Articles

Myeloperoxidase Deficiency Alters the Process of the Regulated Cell Death of Polymorphonuclear Neutrophils.

Polymorphonuclear neutrophils (PMNs) play a key role in host defense. However, their massive accumulation at the site of inflammation can delay regenerative healing processes and can initiate pathological inflammatory processes. Thus, the efficient clearance of PMNs mediated by the induction of regulated cell death is a key process preventing the development of these pathological conditions. Myeloperoxidase (MPO), a highly abundant enzyme in PMN granules, primarily connected with PMN defense machinery, is suggested to play a role in PMN-regulated cell death. However, the contribution of MPO to the mechanisms of PMN cell death remains incompletely characterized. Herein, the process of the cell death of mouse PMNs induced by three different stimuli – phorbol 12-myristate 13-acetate (PMA), opsonized streptococcus (OST), and N-formyl-met-leu-phe (fMLP) – was investigated. MPO-deficient PMNs revealed a significantly decreased rate of cell death characterized by phosphatidylserine surface exposure and cell membrane permeabilization. An inhibitor of MPO activity, 4-aminobenzoic acid hydrazide, did not exhibit a significant effect on PMA-induced cell death compared to MPO deficiency. Interestingly, only the limited activation of markers related to apoptotic cell death was observed (e.g. caspase 8 activation, Bax expression) and they mostly did not correspond to phosphatidylserine surface exposure. Furthermore, a marker characterizing autophagy, cleavage of LC3 protein, as well as histone H3 citrullination and its surface expression was observed. Collectively, the data show the ability of MPO to modulate the life span of PMNs primarily through the potentiation of cell membrane permeabilization and phosphatidylserine surface exposure.

Inhibition of Myeloperoxidase Activity in Cystic Fibrosis Sputum by Peptide Inhibitor of Complement C1 (PIC1).

Myeloperoxidase is the major peroxidase enzyme in neutrophil granules and implicated in contributing to inflammatory lung damage in cystic fibrosis. Free myeloperoxidase is present in cystic fibrosis lung fluid and generates hypochlorous acid. Here we report a new inhibitor of myeloperoxidase activity, Peptide Inhibitor of Complement C1 (PIC1). Using TMB as the oxidizing substrate, PIC1 inhibited myeloperoxidase activity in cystic fibrosis sputum soluble fractions by an average of a 3.4-fold decrease (P = 0.02). PIC1 also dose-dependently inhibited myeloperoxidase activity in a neutrophil lysate or purified myeloperoxidase by up to 28-fold (P < 0.001). PIC1 inhibited myeloperoxidase activity similarly, on a molar basis, as the specific myeloperoxidase inhibitor 4-Aminobenzoic acid hydrazide (ABAH) for various oxidizing substrates. PIC1 was able to protect the heme ring of myeloperoxidase from destruction by NaOCl, assayed by spectral analysis. PIC1 incubated with oxidized TMB reversed the oxidation state of TMB, as measured by absorbance at 450 nm, with a 20-fold reduction in oxidized TMB (P = 0.02). This result was consistent with an antioxidant mechanism for PIC1. In summary, PIC1 inhibits the peroxidase activity of myeloperoxidase in CF sputum likely via an antioxidant mechanism.

Nucleic acid binding of arylamines during the respiratory burst of human granulocytes

Following stimulation with phorbol myristate acetate, human granulocytes were found to incorporate a series of arylamines into cellular nucleic acid. No such binding occurred if the granulocytes were not induced to undergo the respiratory burst. The relative amount of covalent binding to cellular DNA and RNA was found to depend strongly on the chemical structure of the arylamine. 2-Aminofluorene gave the highest ratio of DNA/RNA binding, while 4-nitroaniline showed a very low ratio of DNA/RNA binding. 4-Nitroaniline may bind only to RNA, since the degree of binding to DNA was at the level of detectability. Two other substrates, 4-chloroaniline and 4-methylaniline, gave intermediary ratios of DNA/RNA binding. Studies on the possible role of the granulocyte enzyme myeloperoxidase in the activation and binding of these arylamines were conducted in vitro and also through the use of azide, an inhibitor of myeloperoxidase activity in cells. The results indicate that myeloperoxidase probably plays only a limited role in causing the covalent binding of arylamines to nucleic acid in human granulocytes. It is probable that other reactive oxygen species, which are not dependent upon myeloperoxidase for their production, are necessary for the bioactivation of some arylamines, especially for substrates such as 4-nitroaniline. A free-radical mechanism for arylamine bioactivation, and its potential role in arylamine toxicity, was presented in the context of the current scientific literature.

Influence of 13-cis retinoic acid on zymosan-induced chemiluminescence of granulocytes

The effect of 13-cis retinoic acid (Ro-4-3780) on zymosan-induced chemiluminescence (CL) of freshly drawn human blood and isolated granulocytes has been examined in vitro. A marked enhancement was observed; optimal concentrations were 100 μg/ml in whole blood CL and 10 μg/ml in isolated granulocyte CL. It was found that already 5 μg/ml of 13-cis retinoic acid in isolated granulocytes showed a significant enhancement in zymosan-induced CL. The enhancement by 13-cis retinoic acid was completely inhibited by 10-5 M sodium azide, which is an inhibitor of myeloperoxidase activity. CL response was not enhanced by retinoic acid in mouse bone marrow originated cultured macrophages, which do not have myeloperoxidase activity. These findings strongly suggest that 13-cis retinoic acid might stimulate myeloperoxidase-dependent CL.