ABSTRACT
Peroxynitrite, a potent pro-inflammatory and cytotoxic species, interacts with a variety of heme containing proteins. We addressed the question whether (i) the interaction of myeloperoxidase (MPO, an enzyme generating hypochlorous acid from hydrogen peroxide and chloride ions) with peroxynitrite affects the clearance of peroxynitrite, and (ii) if peroxynitrite could modulate the chlorinating activity of MPO. Our results show that this interaction promotes the decomposition of the highly reactive pro-inflammatory oxidant, whereby MPO Compound II (but not Compound I) is formed. The efficiency of MPO to remove peroxynitrite was enhanced by L-tyrosine, nitrite and (-)-epicatechin, substances known to reduce Compound II with high reaction rate. Next, peroxynitrite (added as reagent) diminished the chlorinating activity of MPO in the presence of hydrogen peroxide. Alternatively, SIN-1, a peroxynitrite donor, reduced hypochlorous acid formation by MPO, as measured by aminophenyl fluorescein oxidation (time kinetics) and taurine chloramine formation (end point measurement). At inflammatory loci, scavenging of peroxynitrite by MPO may overcome the uncontrolled peroxynitrite decomposition and formation of reactive species, which lead to cell/tissue damage.
Subject(s)
Anti-Inflammatory Agents/chemistry , Peroxidase/chemistry , Peroxynitrous Acid/chemistry , Aniline Compounds/chemistry , Catechin/chemistry , Fluoresceins/chemistry , Halogenation , Humans , Hydrogen Peroxide/chemistry , Hydrogen-Ion Concentration , Kinetics , Molsidomine/analogs & derivatives , Molsidomine/chemistry , Nitrites/chemistry , Oxidants/chemistry , Oxidation-Reduction , Tyrosine/chemistryABSTRACT
Polymorphonuclear leukocytes (PMNs) are important players in innate and acquired immunity. These cells accumulate at inflammatory sites and contribute to host defence, regulation of the inflammatory process, and also to tissue injury. One of the key components of PMNs is the heme-containing enzyme myeloperoxidase (MPO) that is stored in large amount in azurophilic granules of resting cells. Here we review the (patho)physiological role of MPO from the viewpoint of participation of PMNs in immune reactions. Myeloperoxidase is able to catalyse a wide range of one- and two-electron substrate oxidations. With special products, MPO contributes to apoptosis induction in PMNs and other cells, and, thus, to termination of inflammatory response. On the other hand, MPO released from necrotic cells promotes an inflammation by further recruitment of PMNs, and chemical modification of proteins and other tissue constituents. Myeloperoxidase is a fascinating, multifunctional, and challenging enzyme that has not yet revealed all its secrets.
Subject(s)
Adaptive Immunity , Immunity, Innate , Peroxidase/immunology , Animals , Humans , Inflammation/enzymology , Inflammation/immunology , Models, Molecular , Neutrophils/enzymology , Neutrophils/immunology , Peroxidase/chemistryABSTRACT
The close association of the heme enzyme myeloperoxidase to phosphatidylserine epitopes on the surface of non-vital polymorphonuclear leukocytes (PMNs) and other apoptotic cells at inflammatory sites favours modifications of this phospholipid by myeloperoxidase products. As detected by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, ammonium ions inhibit in a concentration-dependent manner the hypochlorous acid-mediated formation of aldehyde and nitrile products from 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS). Concomitantly, the formation of monochloramine (NH(2)Cl) raises with increasing NH(4)(+) concentrations. A transchlorination from monochlorinated O-phospho-L-serine to NH(4)(+) with the formation of NH(2)Cl occurs only when extraordinary high NH(4)(+) concentrations are applied. Due to the low rate of 0.044 M(-1) s(-1) for this process, a transhalogenation reaction from transient chlorinated intermediates of the serine moiety to NH(4)(+) can be ruled out as an important process contributing to the HOCl-mediated formation of NH(2)Cl. A significant formation of NH(2)Cl by myeloperoxidase interacting with DPPS in the presence of ammonium ions takes only place at acidic pH values around 5, a scenario that may occur in phagosomes of macrophages after the uptake of apoptotic PMNs.
Subject(s)
Hypochlorous Acid/chemistry , Peroxidase/metabolism , Phosphatidylserines/metabolism , Quaternary Ammonium Compounds/chemistry , Apoptosis , Cells, Cultured , Humans , Hydrogen-Ion Concentration , Macrophages/enzymology , Neutrophils/metabolism , Peroxidase/chemistry , Phagosomes/enzymology , Phagosomes/metabolism , Phosphatidylserines/chemistryABSTRACT
The binding of the heme enzyme myeloperoxidase to phosphatidylserine epitopes on the surface of non-vital polymorphonuclear leukocytes and other cells at inflammatory sites favours modifications of this phospholipid by myeloperoxidase products. As detected by MALDI-TOF mass spectrometry hypochlorous acid and the myeloperoxidase-hydrogen peroxide-chloride system convert 1,2-dipalmitoyl-sn-glycero-3-phosphoserine into 1,2-dipalmitoyl-sn-glycero-3-phosphoacetaldehyde and 1,2-dipalmitoyl-sn-glycero-3-phosphonitrile. A transient chlorimine derivative was detected using 4-chloro-alpha-cyanocinnamic acid as matrix in mass spectrometry only at short incubation times and supplying HOCl in two-fold excess. The decay of transient chlorinated products was followed by changes in absorbance spectra using O-phospho-l-serine to model the behavior of the serine head group in phosphatidylserine. N-Chlorimine and N-monochloramine derivatives decayed with half-life times of 1.5 and 57 min, respectively, at 22 degrees C and pH 7.4. N-Dichloramines decayed within few seconds under these conditions.
