Substrates and products of eosinophil peroxidase

2001 ◽  
Vol 358 (1) ◽  
pp. 233-239 ◽  
Author(s):  
Christine J. van DALEN ◽  
Anthony J. KETTLE
Keyword(s):  
Hypochlorous Acid ◽  
Plasma Concentrations ◽  
Oxidation Products ◽  
Inflammatory Conditions ◽  
Eosinophil Peroxidase ◽  
Hypohalous Acids ◽  
Hypobromous Acid ◽  
Michaelis Constants ◽  
The One ◽  
Compound Ii

Eosinophil peroxidase has been implicated in promoting oxidative tissue damage in a variety of inflammatory conditions, including asthma. It uses H2O2 to oxidize chloride, bromide and thiocyanate to their respective hypohalous acids. The aim of this study was to establish which oxidants eosinophil peroxidase produces under physiological conditions. By measuring rates of H2O2 utilization by the enzyme at neutral pH, we determined the catalytic rate constants for bromide and thiocyanate as 248 and 223s−1 and the Michaelis constants as 0.5 and 0.15mM respectively. On the basis of these values thiocyanate is preferred 2.8-fold over bromide as a substrate for eosinophil peroxidase. Eosinophil peroxidase catalysed substantive oxidation of chloride only below pH6.5. We found that when eosinophil peroxidase or myeloperoxidase oxidized thiocyanate, another product besides hypothiocyanite was formed; it also converted methionine into methionine sulphoxide. During the oxidation of thiocyanate, the peroxidases were present as their compound II forms. Compound II did not form when GSH was included to scavenge hypothiocyanite. We propose that the unidentified oxidant was derived from a radical species produced by the one-electron oxidation of hypothiocyanite. We conclude that at plasma concentrations of bromide (20–120μM) and thiocyanate (20–100μM), hypobromous acid and oxidation products of thiocyanate are produced by eosinophil peroxidase. Hypochlorous acid is likely to be produced only when substrates preferred over chloride are depleted. Thiocyanate should be considered to augment peroxidase-mediated toxicity because these enzymes can convert relatively benign hypothiocyanite into a stronger oxidant.

scholarly journals Thiocyanate and chloride as competing substrates for myeloperoxidase

1997 ◽  
Vol 327 (2) ◽  
pp. 487-492 ◽  
Author(s):  
J. Christine van DALEN ◽  
W. Michael WHITEHOUSE ◽  
C. Christine WINTERBOURN ◽  
J. Anthony KETTLE
Keyword(s):  
Kinetic Study ◽  
Acid Production ◽  
Plasma Concentrations ◽  
Host Defence ◽  
Oxidation Products ◽  
Substrate Preference ◽  
Hypohalous Acids ◽  
Relative Specificity ◽  
The Individual

The neutrophil enzyme myeloperoxidase uses H2O2 to oxidize chloride, bromide, iodide and thiocyanate to their respective hypohalous acids. Chloride is considered to be the physiological substrate. However, a detailed kinetic study of its substrate preference has not been undertaken. Our aim was to establish whether myeloperoxidase oxidizes thiocyanate in the presence of chloride at physiological concentrations of these substrates. We determined this by measuring the rate of H2O2 loss in reactions catalysed by the enzyme at various concentrations of each substrate. The relative specificity constants for chloride, bromide and thiocyanate were 1:60:730 respectively, indicating that thiocyanate is by far the most favoured substrate for myeloperoxidase. In the presence of 100 mM chloride, myeloperoxidase catalysed the production of hypothiocyanite at concentrations of thiocyanate as low as 25 μM. With 100 μM thiocyanate, about 50% of the H2O2 present was converted into hypothiocyanite, and the rate of hypohalous acid production equalled the sum of the individual rates obtained when each of these anions was present alone. The rate of H2O2 loss catalysed by myeloperoxidase in the presence of 100 mM chloride doubled when 100 μM thiocyanate was added, and was maximal with 1 mM thiocyanate. This indicates that at plasma concentrations of thiocyanate and chloride, myeloperoxidase is far from saturated. We conclude that thiocyanate is a major physiological substrate of myeloperoxidase, regardless of where the enzyme acts. As a consequence, more consideration should be given to the oxidation products of thiocyanate and to the role they play in host defence and inflammation.

scholarly journals Mechanism of nitrite oxidation by eosinophil peroxidase: implications for oxidant production and nitration by eosinophils

2006 ◽  
Vol 394 (3) ◽  
pp. 707-713 ◽  
Author(s):  
Christine J. van Dalen ◽  
Christine C. Winterbourn ◽  
Anthony J. Kettle
Keyword(s):  
Nitrogen Dioxide ◽  
Active Site ◽  
Tissue Injury ◽  
Spectral Studies ◽  
Compound I ◽  
Eosinophil Peroxidase ◽  
Hypohalous Acids ◽  
Low Concentrations ◽  
Oxidant Production ◽  
Compound Ii

Eosinophil peroxidase is a haem enzyme of eosinophils that is implicated in oxidative tissue injury in asthma. It uses hydrogen peroxide to oxidize thiocyanate and bromide to their respective hypohalous acids. Nitrite is also a substrate for eosinophil peroxidase. We have investigated the mechanisms by which the enzyme oxidizes nitrite. Nitrite was very effective at inhibiting hypothiocyanous acid (‘cyanosulphenic acid’) and hypobromous acid production. Spectral studies showed that nitrite reduced the enzyme to its compound II form, which is a redox intermediate containing FeIV in the haem active site. Compound II does not oxidize thiocyanate or bromide. These results demonstrate that nitrite is readily oxidized by compound I, which contains FeV at the active site. However, it reacts more slowly with compound II. The observed rate constant for reduction of compound II by nitrite was determined to be 5.6×103 M−1·s−1. Eosinophils were at least 4-fold more effective at promoting nitration of a heptapeptide than neutrophils. This result is explained by our finding that nitrite reacts 10-fold faster with compound II of eosinophil peroxidase than with the analogous redox intermediate of myeloperoxidase. Nitration by eosinophils was increased 3-fold by superoxide dismutase, which indicates that superoxide interferes with nitration. We propose that at sites of eosinophilic inflammation, low concentrations of nitrite will retard oxidant production by eosinophil peroxidase, whereas at higher concentrations nitrogen dioxide will be a major oxidant formed by these cells. The efficiency of protein nitration will be decreased by the diffusion-controlled reaction of superoxide with nitrogen dioxide.

scholarly journals Peroxidasin and eosinophil peroxidase, but not myeloperoxidase, contribute to renal fibrosis in the murine unilateral ureteral obstruction model

2019 ◽  
Vol 316 (2) ◽  
pp. F360-F371 ◽  
Author(s):  
Selene Colon ◽  
Haiyan Luan ◽  
Yan Liu ◽  
Cameron Meyer ◽  
Leslie Gewin ◽  
...  
Keyword(s):  
Ureteral Obstruction ◽  
Renal Fibrosis ◽  
Hypochlorous Acid ◽  
Unilateral Ureteral Obstruction ◽  
Tubulointerstitial Fibrosis ◽  
Renal Inflammation ◽  
Eosinophil Peroxidase ◽  
Hypohalous Acids ◽  
Heme Peroxidases

Renal fibrosis is the pathological hallmark of chronic kidney disease (CKD) and manifests as glomerulosclerosis and tubulointerstitial fibrosis. Reactive oxygen species contribute significantly to renal inflammation and fibrosis, but most research has focused on superoxide and hydrogen peroxide (H2O2). The animal heme peroxidases myeloperoxidase (MPO), eosinophil peroxidase (EPX), and peroxidasin (PXDN) uniquely metabolize H2O2 into highly reactive and destructive hypohalous acids, such as hypobromous and hypochlorous acid. However, the role of these peroxidases and their downstream hypohalous acids in the pathogenesis of renal fibrosis is unclear. Our study defines the contribution of MPO, EPX, and PXDN to renal inflammation and tubulointerstitial fibrosis in the murine unilateral ureteral obstruction (UUO) model. Using a nonspecific inhibitor of animal heme peroxidases and peroxidase-specific knockout mice, we find that loss of EPX or PXDN, but not MPO, reduces renal fibrosis. Furthermore, we demonstrate that eosinophils, the source of EPX, accumulate in the renal interstitium after UUO. These findings point to EPX and PXDN as potential therapeutic targets for renal fibrosis and CKD and suggest that eosinophils modulate the response to renal injury.

scholarly journals Bromide-dependent toxicity of eosinophil peroxidase for endothelium and isolated working rat hearts: a model for eosinophilic endocarditis.

1991 ◽  
Vol 173 (1) ◽  
pp. 117-126 ◽  
Author(s):  
A Slungaard ◽  
J R Mahoney
Keyword(s):  
Endothelial Cells ◽  
Hypochlorous Acid ◽  
Cell Damage ◽  
Cardiac Metabolism ◽  
Rate Pressure Product ◽  
Cell Monolayers ◽  
Eosinophil Peroxidase ◽  
Rat Hearts ◽  
Hypobromous Acid ◽  
Flowing Blood

Eosinophilic endocarditis is a potentially lethal complication of chronic peripheral blood hypereosinophilia. We hypothesized that eosinophil peroxidase (EPO), an abundant eosinophil (EO) cationic granule protein, promotes eosinophilic endocarditis by binding to negatively charged endocardium, and there generating cytotoxic oxidants. Using an immunocytochemical technique, we demonstrated endocardial deposition of EPO in the heart of a patient with hypereosinophilic heart disease. Because EPO preferentially oxidizes Br- to hypobromous acid (HOBr) rather than Cl- to hypochlorous acid (HOCl) at physiologic halide concentrations, we characterized the Br(-)-dependent toxicity of both activated EOs and purified human EPO towards several types of endothelial cells and isolated working rat hearts. In RPMI supplemented with 100 microM Br-, phorbol myristate acetate-activated EOs, but not polymorphonuclear leukocytes, caused 1.8-3.6 times as much 51Cr release from four types of endothelial cell monolayers as in RPMI alone. H2O2 and purified human EPO, especially when bound to cell surfaces, mediated extraordinarily potent, completely Br(-)-dependent cytolysis of endothelial cells that was reversed by peroxidase inhibitors, HOBr scavengers, and competitive substrates. We further modeled eosinophilic endocarditis by instilling EPO into the left ventricles of isolated rat hearts, flushing unbound EPO, then perfusing them with a buffer containing 100 microM Br- and 1 microM H2O2. Acute congestive heart failure (evidenced by a precipitous decrement in rate pressure product, stroke volume work, aortic output, and MVO2 to 0-33% of control values) ensued over 20 min, which deletion of EPO, Br-, or H2O2 completely abrogated. These findings raise the possibility that EPO bound to endocardial cells might utilize H2O2 generated either by overlying phagocytes or endogenous cardiac metabolism along with the virtually inexhaustible supply of Br- from flowing blood to fuel HOBr-mediated cell damage. By this mechanism, EPO may play an important role in the pathogenesis of eosinophilic endocarditis.

scholarly journals The Responses of Bioactive Betanin Pigment and Its Derivatives from a Red Beetroot (Beta vulgaris L.) Betalain-Rich Extract to Hypochlorous Acid

2021 ◽  
Vol 22 (3) ◽  
pp. 1155
Author(s):  
Karolina Starzak ◽  
Katarzyna Sutor ◽  
Tomasz Świergosz ◽  
Boris Nemzer ◽  
Zbigniew Pietrzkowski ◽  
...  
Keyword(s):  
Beta Vulgaris ◽  
Hypochlorous Acid ◽  
Innate Immune ◽  
Inflammatory Factors ◽  
Oxygen Species ◽  
Plant Pigments ◽  
Important Food ◽  
Inflammatory Conditions ◽  
Ph Range

Neutrophils produce hypochlorous acid (HOCl) as well as other reactive oxygen species as part of a natural innate immune response in the human body; however, excessive levels of HOCl can ultimately be detrimental to health. Recent reports suggest that betacyanin plant pigments can act as potent scavengers of inflammatory factors and are notably effective against HOCl. Comparison of the in vitro anti-hypochlorite activities of a novel betalain-rich red beetroot (Beta vulgaris L.) extract with its pure betalainic pigments revealed that the extract had the highest anti-hypochlorite activity, far exceeding the activity of all of the betalainic derivatives and selected reference antioxidants. This suggests that it may be an important food-based candidate for management of inflammatory conditions induced by excessive HOCl production. Among all pigments studied, betanidin exhibited the highest activity across the pH range.

PLASMA PROLACTIN AND PROGESTERONE RESPONSES TO MATING ARE ALTERED IN AGED RATS

1981 ◽  
Vol 90 (2) ◽  
pp. 179-191 ◽  
Author(s):  
S. HENDRICKS ◽  
C. A. BLAKE
Keyword(s):  
Plasma Concentrations ◽  
External Jugular Vein ◽  
Female Rats ◽  
Plasma Prolactin ◽  
Aged Rats ◽  
Pregnant Rats ◽  
Pregnant Rat ◽  
Plasma Progesterone ◽  
The One ◽  
The Right

The effects of varying amounts of copulatory stimulation on patterns of plasma concentrations of prolactin and progesterone were evaluated in 3- and 12-month-old female rats. The 12-month-old group included rats which still exhibited oestrous cycles and rats in persistent vaginal oestrus (PVO). The extent of copulatory stimulation was defined by the number of intromissions received during mating: ≤5,15 or > 50. Blood samples were drawn over the 8 days after mating through a cannula inserted into the right external jugular vein. Plasma from the samples was assayed for prolactin and progesterone. In aged but still cyclic rats, pregnancy rates were positively correlated with the number of intromissions received during mating. Only one rat in PVO became pregnant. All animals which became pregnant and rats in PVO which, after mating, exhibited a disruption of the pattern of PVO, showed the nocturnal surge of plasma prolactin characteristic of pregnant and pseudopregnant rats. While these surges persisted until day 8 after mating in pregnant animals, they were absent by this time in the rats in PVO. Prolactin surges were present in some but not all of the aged rats which did not become pregnant. Progesterone concentrations were raised in all pregnant animals except the one pregnant rat in PVO and, while not related to the number of intromissions, concentrations were higher 8 days after mating in young compared with those in aged pregnant rats. Plasma progesterone was low in rats in PVO regardless of disruption of the pattern of PVO. We have concluded that the failure of limited copulatory stimulation to induce pregnancy in older rats results, at least in part, from its failure to initiate nocturnal prolactin surges. Nevertheless, our data suggest that matings which are not experimentally limited should provide ample stimulation to establish such surges. Although reduced plasma concentrations of prolactin and progesterone at pro-oestrus and reduced plasma progesterone through part of gestation may contribute to decreasing fertility in aged rats, other unidentified factors appear to be involved in mediating the capacity of extensive copulatory stimulation to induce pregnancy in these animals.

scholarly journals 308-nm excimer laser in the treatment of a localized recalcitrant form of perioral dermatitis: Case report

2022 ◽  
Vol 13 (e) ◽  
pp. e5-e5
Author(s):  
Catarina Queirós ◽  
Luís Uva ◽  
Paulo Filipe
Keyword(s):  
Case Report ◽  
Excimer Laser ◽  
Excellent Result ◽  
Adjacent Tissue ◽  
Therapeutic Alternative ◽  
Inflammatory Conditions ◽  
Perioral Dermatitis ◽  
Topical Treatments ◽  
Uv Dose ◽  
The One

In the last two decades, 308-nm excimer laser has been increasingly recognized as a therapeutic alternative for several dermatological conditions, being currently FDA approved for the treatment of localized vitiligo and moderately severe localized psoriasis unresponsive to topical treatments. We describe the case of a 17-year-old with a recalcitrant form of dermatitis occupying the entire perioral region, previously unresponsive to several treatments, who was treated with 308-nm excimer laser with an excellent result. 308-nm monochromatic excimer laser has several advantages over other types of phototherapy, including lower UV dose exposure, shorter courses of therapy and a better sparing of adjacent tissue. Although infrequently used, 308-nm excimer laser certainly has a vast potential in Dermatology, particularly regarding recalcitrant and localized inflammatory conditions, such as the one we present.

scholarly journals Structural Diversity, Characterization and Toxicology of Microcystins

Toxins ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 714 ◽  
Author(s):  
Noureddine Bouaïcha ◽  
Christopher Miles ◽  
Daniel Beach ◽  
Zineb Labidi ◽  
Amina Djabri ◽  
...  
Keyword(s):  
Methyl Esters ◽  
Structural Diversity ◽  
Oxidation Products ◽  
Future Research ◽  
Analytical Methodology ◽  
Environmental Controls ◽  
Scientific Disciplines ◽  
Comprehensive Information ◽  
The One ◽  
The Impact

Hepatotoxic microcystins (MCs) are the most widespread class of cyanotoxins and the one that has most often been implicated in cyanobacterial toxicosis. One of the main challenges in studying and monitoring MCs is the great structural diversity within the class. The full chemical structure of the first MC was elucidated in the early 1980s and since then, the number of reported structural analogues has grown steadily and continues to do so, thanks largely to advances in analytical methodology. The structures of some of these analogues have been definitively elucidated after chemical isolation using a combination of techniques including nuclear magnetic resonance, amino acid analysis, and tandem mass spectrometry (MS/MS). Others have only been tentatively identified using liquid chromatography-MS/MS without chemical isolation. An understanding of the structural diversity of MCs, the genetic and environmental controls for this diversity and the impact of structure on toxicity are all essential to the ongoing study of MCs across several scientific disciplines. However, because of the diversity of MCs and the range of approaches that have been taken for characterizing them, comprehensive information on the state of knowledge in each of these areas can be challenging to gather. We have conducted an in-depth review of the literature surrounding the identification and toxicity of known MCs and present here a concise review of these topics. At present, at least 279 MCs have been reported and are tabulated here. Among these, about 20% (55 of 279) appear to be the result of chemical or biochemical transformations of MCs that can occur in the environment or during sample handling and extraction of cyanobacteria, including oxidation products, methyl esters, or post-biosynthetic metabolites. The toxicity of many MCs has also been studied using a range of different approaches and a great deal of variability can be observed between reported toxicities, even for the same congener. This review will help clarify the current state of knowledge on the structural diversity of MCs as a class and the impacts of structure on toxicity, as well as to identify gaps in knowledge that should be addressed in future research.

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