Myeloperoxidase: a key regulator of neutrophil oxidant production

Myeloperoxidase-derived oxidants rapidly oxidize and disrupt zinc-cysteine/histidine clusters in proteins

Zinc is an abundant cellular transition metal ion, which binds avidly to protein cysteine (Cys) and histidine (His) residues to form zinc-Cys/His clusters; these play a key role in the function of many proteins (e.g., DNA binding and repair enzymes, transcription factors, nitric oxide synthase). Leukocyte-derived myeloperoxidase generates powerful oxidants including hypochlorous (HOCl), hypobromous (HOBr), and hypothiocyanous (HOSCN) acids from H(2)O(2) and (pseudo)halide ions. Excessive or misplaced formation of these species is associated with cellular dysfunction, apoptosis and necrosis, and multiple inflammatory diseases. HOCl and HOBr react rapidly with sulfur-containing compounds, and HOSCN reacts specifically with thiols. Consequently, we hypothesized that zinc-Cys/His clusters would be targets for these oxidants, and the activity of such enzymes would be perturbed. This hypothesis has been tested using yeast alcohol dehydrogenase (YADH), which contains a well-characterized Zn(1)Cys(2)His(1) cluster. Incubation of YADH with pathologically relevant concentrations of HOSCN, HOCl, and HOBr resulted in rapid oxidation of the protein (rate constants, determined by competition kinetics, for reaction of HOCl and HOSCN with YADH being (3.3±0.9)×10(8) and (2.9±0.4)×10(4) M(-1) s(-1) per YADH monomer, respectively), loss of enzyme activity, Zn(2+) release, changes in protein structure (particularly formation of disulfide cross-links), and oxidation of Cys residues. The loss of enzyme activity correlated with Zn(2+) release, loss of thiols, and changes in protein structure. We conclude that exposure of zinc-Cys/His clusters to inflammatory oxidants can result in impaired protein activity, thiol oxidation, and Zn(2+) release. These reactions may contribute to inflammation-induced tissue damage.

Effects of halides on reaction of nucleosides with ozone

Ozone (O(3)), a major component of photochemical oxidants, is used recently as a deodorizer in living spaces. It has been reported that O(3) can directly react with DNA, causing mutagenesis in human cells and carcinogenesis in mice. However, little is known about the effects of coexistent ions in the reaction of O(3). In the present study, we analyzed the effects of halides on the reaction of O(3) with nucleosides using reversed-phase high-performance liquid chromatography with ultraviolet detection. When aqueous O(3) solution was added to a nucleoside mixture in potassium phosphate buffer (pH 7.3), the nucleosides were consumed with the following decreasing order of importance: dGuo > Thd > dCyd > dAdo. The effects of addition of fluoride and chloride in the system were slight. Bromide suppressed the reactions of dGuo, Thd, and dAdo but enhanced the reaction of dCyd. The major products were 5-hydroxy-2'-deoxycytidine, 5-bromo-2'-deoxycytidine, and 8-bromo-2'-deoxyguanosine. The time course and pH dependence of the product yield indicated formation of hypobromous acid as the reactive agent. Iodide suppressed all the reactions effectively. The results suggest that bromide may alter the mutation spectrum by O(3) in humans.

Interaction profile of diphenyl diselenide with pharmacologically significant thiols

Diphenyl diselenide has shown interesting biological activities in various free-radical-induced damage models and can be considered as a potential candidate drug against oxidative stress. Apart from its anti-oxidant activity, this compound can oxidize various thiols. However there are no detailed studies in the literature about the thiol oxidase-like activity of this compound against biologically significant mono and di-thiols with respect to various pH conditions. Keeping in mind the scarcity of data in this area of organochalcogen chemistry, we report for the first time the kinetics of thiol oxidation by diphenyl diselenide, which was carried out in a commonly used phosphate buffer, not only at physiological pH, but also at a number of acidic values. The relative reactivities of the different thiols with diphenyl diselenide were independent of the pKa of the thiol group, such that at pH 7.4, cysteine and dithiothreitol were the most reactive, while 2,3-dimercapto-1-propanesulfonic acid and glutathione were weakly reactive and extremely low reactivity was observed with dimercaptosuccinic acid. Rate of oxidation was dependent on the pH of the incubation medium. The results obtained will help us in the design of rational strategies for the safe pharmacological use of diphenyl diselenide.

Validation of a surgical technique for rat intestinal irradiation: potential side effects prevention by dietary grape phenolics

AIMS

This study evaluates and defines the histological and biochemical consequences of irradiation on the Hauer-Jensen intestinal model and investigates the potential effects of dietary polyphenols.

MAIN METHODS

Sprague-Dawley rats were orchiectomized, and an ileal loop was transposed to the left part of the scrotum, then irradiated 2 weeks after surgery with a single dose of 21 Gy (4.49 Gy/min). Four groups of rats received either phenolic extracts from grape seeds (EGS) and from red wine (ACYS, EGT), or pure quercetin 3-O-β-glucoside (Q3G), for 5 days before the irradiation and were sacrificed 2 weeks after. Antioxidant enzyme activities, i.e. superoxide dismutase (SOD) and glutathione peroxidase activity (GSHPx), and oxidative markers such as myeloperoxidase activity (MPO) and thiobarbituric acid reactive substances (MDA) were measured as well as cytokine-induced neutrophil chemoattractant level (CINC-1), a chemokine involved in inflammation.

KEY FINDINGS

Irradiated rats exhibited a high radiation injury score (RIS) with a thickened serosa, mucosal loss and ulceration, and epithelial atypicality. Intestinal MPO activity and CINC-1 concentration were significantly increased in irradiated animals (60 and 66 %, respectively). Higher plasma MDA levels (58 %) and SOD activity (32 %) were accompanied by a reduced GSHPx activity (79 %). However, feeding phenolic extracts remarkably reduced levels of blood SOD activity (34 % on average), intestinal CINC-1 (25-75 % range) and MPO activity (36-84 %). Except for Q3G, phenolics preserved the intestinal structure.

SIGNIFICANCE

These findings show that irradiation triggers an inflammation, and an oxidative stress by disturbing the pro-oxidant/antioxidant balance and indicate that phenolics supply exerts preventive effects against radio-induced intestinal impairment.

Myeloperoxidase and oxidative stress in rheumatoid arthritis

OBJECTIVE

To determine whether MPO contributes to oxidative stress and disease activity in RA and whether it produces hypochlorous acid in SF.

METHODS

Plasma and where possible SF were collected from 77 RA patients while 120 healthy controls supplied plasma only. MPO and protein carbonyls were measured by ELISAs. 3-Chlorotyrosine in proteins and allantoin in plasma were measured by mass spectrometry.

RESULTS

Plasma MPO concentrations were significantly higher in patients with RA compared with healthy controls [10.8 ng/ml, inter-quartile range (IQR): 7.2-14.2; P<0.05], but there was no significant difference in plasma MPO protein concentrations between RA patients with high disease activity (HDA; DAS-28 >3.2) and those with low disease activity (LDA; DAS-28 ≤ 3.2) (HDA 27.9 ng/ml, 20.2-34.1 vs LDA 22.1 ng/ml, 16.9-34.9; P>0.05). There was a significant relationship between plasma MPO and DAS-28 (r=0.35; P=0.005). Plasma protein carbonyls and allantoin were significantly higher in patients with RA compared with the healthy controls. MPO protein was significantly higher in SF compared with plasma (median 624.0 ng/ml, IQR 258.4-2433.0 vs 30.2 ng/ml, IQR 25.1-50.9; P<0.0001). The MPO present in SF was mostly active. 3-Chlorotyrosine, a specific biomarker of hypochlorous acid, was present in proteins from SF and related to the concentration of MPO (r=0.69; P=0.001). Protein carbonyls in SF were associated with MPO protein concentration (r=0.40; P=0.019) and 3-chlorotyrosine (r=0.66; P=0.003).

CONCLUSION

MPO is elevated in patients with RA and promotes oxidative stress through the production of hypochlorous acid.

Protective Effects of Nigella sativa Oil in Hyperoxia-Induced Lung Injury

BACKGROUND

Oxygen-induced lung injury is believed to lead to the development of bronchopulmonary dysplasia in premature infants. We have evaluated the beneficial effects of Nigella sativa oil (NSO) on rats with hyperoxia-induced lung injury.

METHODS

Thirty newborn Sprague-Dawley rats were randomly divided into 3 groups as hyperoxia (95% O(2)), hyperoxia+NSO and control (21% O(2)). Pups in the hyperoxia+NSO group were administered intraperitoneal NSO at a dose of 4ml/kg daily during the study period. Histopathologic, immunochemical, and biochemical evaluations (superoxide dismutase [SOD], glutathione peroxidase [GSH-Px], malonaldehyde [MDA] and myeloperoxidase [MPO]) were performed.

RESULTS

In the histopathologic and immunochemical evaluation, severity of lung damage was significantly lower in the hyperoxia+NOS group (P<.05). Tissue GSH-Px and SOD levels were significantly preserved, and MDA, MPO levels were significantly lower in the hyperoxia+NSO group (P<.05).

CONCLUSION

NSO significantly reduced the severity of lung damage due to hyperoxia.

Beneficial effects of Nigella sativa oil on intestinal damage in necrotizing enterocolitis

AIM

The aim of this study was to determine the beneficial effects of Nigella sativa oil (NSO) on rats with necrotizing enterocolitis (NEC).

MATERIAL AND METHODS

Thirty newborn Sprague-Dawley rats were randomly divided into three groups as NEC, NEC + NSO, and control. NEC was induced by enteral formula feeding, exposure to hypoxia-hyperoxia and cold stress. Pups in the NEC + NSO group were administered NOS at a dose of 2 ml/kg daily by intraperitoneal route from the first day until the end of the study. Proximal colon and ileum were excised for histopathologic, apoptosis (TUNEL) and biochemical evaluation, including xanthine oxidase (XO), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malonaldehyde (MDA), and myeloperoxdase (MPO) activities.

RESULTS

Pups in the NEC + NOS group had better clinical sickness scores and weight gain compared to the NEC group (p < 0.05). In the macroscopic assessment, histopathologic and apoptosis evaluation (TUNEL), severity of bowel damage was significantly lower in the NEC + NOS group compared to the NEC group (p < 0.05). Tissue GSH-Px and SOD levels were significantly preserved in the NEC + NSO group (p < 0.05), whereas, tissue MDA, MPO levels of the NEC + NSO group were significantly lower than those in the NEC group (p < 0.05).

CONCLUSION

NSO significantly reduced the severity of intestinal damage in NEC.

Salicylic acid attenuates gentamicin-induced nephrotoxicity in rats

Gentamicin (GM) is a widely used antibiotic against serious and life-threatening infections, but its usefulness is limited by the development of nephrotoxicity. The present study was designed to determine the protective effect of salicylic acid (SA) in gentamicin-induced nephrotoxicity in rats. Quantitative evaluation of gentamicin-induced structural alterations and degree of functional alterations in the kidneys were performed by histopathological and biochemical analyses in order to determine potential beneficial effects of SA coadministration with gentamicin. Gentamicin was observed to cause a severe nephrotoxicity which was evidenced by an elevation of serum urea and creatinine levels. The significant increases in malondialdehyde (MDA) levels and protein carbonyl groups indicated that GM-induced tissue injury was mediated through oxidative reactions. On the other hand, simultaneous SA administration protected kidney tissue against the oxidative damage and the nephrotoxic effect caused by GM treatment. Exposure to GM caused necrosis of tubular epithelial cells. Necrosis of tubules was found to be prevented by SA pretreatment. The results from our study indicate that SA supplement attenuates oxidative-stress associated renal injury by reducing oxygen free radicals and lipid peroxidation in gentamicin-treated rats.

Myeloperoxidase-derived oxidants inhibit sarco/endoplasmic reticulum Ca2+-ATPase activity and perturb Ca2+ homeostasis in human coronary artery endothelial cells

The sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) plays a critical role in Ca(2+) homeostasis via sequestration of this ion in the sarco/endoplasmic reticulum. The activity of this pump is inhibited by oxidants and impaired in aging tissues and cardiovascular disease. We have shown previously that the myeloperoxidase (MPO)-derived oxidants HOCl and HOSCN target thiols and mediate cellular dysfunction. As SERCA contains Cys residues critical to ATPase activity, we hypothesized that HOCl and HOSCN might inhibit SERCA activity, via thiol oxidation, and increase cytosolic Ca(2+) levels in human coronary artery endothelial cells (HCAEC). Exposure of sarcoplasmic reticulum vesicles to preformed or enzymatically generated HOCl and HOSCN resulted in a concentration-dependent decrease in ATPase activity; this was also inhibited by the SERCA inhibitor thapsigargin. Decomposed HOSCN and incomplete MPO enzyme systems did not decrease activity. Loss of ATPase activity occurred concurrent with oxidation of SERCA Cys residues and protein modification. Exposure of HCAEC, with or without external Ca(2+), to HOSCN or HOCl resulted in a time- and concentration-dependent increase in intracellular Ca(2+) under conditions that did not result in immediate loss of cell viability. Thapsigargin, but not inhibitors of plasma membrane or mitochondrial Ca(2+) pumps/channels, completely attenuated the increase in intracellular Ca(2+) consistent with a critical role for SERCA in maintaining endothelial cell Ca(2+) homeostasis. Angiotensin II pretreatment potentiated the effect of HOSCN at low concentrations. MPO-mediated modulation of intracellular Ca(2+) levels may exacerbate endothelial dysfunction, a key early event in atherosclerosis, and be more marked in smokers because of their higher SCN(-) levels.

Garlic extract ameliorates renal and cardiopulmonary injury in the rats with chronic renal failure

Chronic renal failure (CRF) is associated with oxidative stress that promotes production of reactive oxygen species and cytokine release. We aimed to investigate the possible protective and antioxidant effects of aqueous garlic extract (AGE) in a rat model of CRF. Male Sprague-Dawley rats were randomly assigned as either CRF group with 5/6 reduction in the renal mass or sham-operated control group. CRF group received either saline or AGE (250 mg/kg/day/1 mL) orally for 3 weeks. At the end of the 3 weeks, rats were decapitated and trunk blood was collected. Creatinine, blood urea nitrogen (BUN) and lactate dehydrogenase (LDH) activity, and TNF-α and IL-1β levels were measured in the serum samples, while malondialdehyde (MDA), glutathione (GSH) levels, and myeloperoxidase (MPO) activity were determined in the kidney, lung, and heart samples. CRF caused significant decreases in tissue GSH, which were accompanied with significant increases in MDA levels and MPO activities, while the circulating levels of the LDH activity, creatinine, BUN, TNF-α, and IL-1β were elevated. AGE treatment alleviated CRF-induced oxidative changes in the injured tissues, while CRF-induced elevations in the blood levels of the pro-inflammatory cytokines and LDH were reduced. In conclusion, CRF-induced oxidative tissue injury occurs via the activation of pro-inflammatory mediators and by neutrophil infiltration into tissues and that the protective effects of garlic on CRF-induced injury can be attributed to its ability to inhibit neutrophil infiltration and pro-inflammatory mediators. These findings suggest that garlic, as a supplementary to diet, may have a potential therapeutic use in delimitating the systemic oxidant effects of CRF on remote organs.

Protective effects of caffeic acid phenethyl ester (CAPE) on intestinal damage in necrotizing enterocolitis

OBJECTIVE

To determine the preventative effect of caffeic acid phenethyl ester (CAPE) in necrotizing enterocolitis (NEC) in an experimental rat model of NEC.

MATERIALS AND METHODS

Thirty newborn Sprague-Dawley rats were randomly divided into three groups; as NEC, NEC + CAPE and control. NEC was induced by enteral formula feeding, subjected to hypoxia-hyperoxia and cold stress. Pups in the NEC + CAPE group were treated with CAPE at a dose of 30 mg/kg daily by intraperitoneal route from the first day to the end of the study. All pups were executed on the fourth day. Proximal colon and ileum were allocated for histopathologic and biochemical evaluation, including xanthine oxidase (XO), total antioxidant status (TAS), total oxidant status (TOS), malonaldehyde (MDA) and myeloperoxidase (MPO) activities.

RESULTS

The pups in the NEC + CAPE group had better histopathologic and apoptosis evaluations (TUNEL and caspase-9) and the severity of bowel damage was significantly lower in the NEC + CAPE group compared to the NEC group (P < 0.01). The clinical sickness scores and body weight in the NEC + CAPE group was significantly better compared to the NEC group (P < 0.05). Tissue MDA, MPO, XO levels and TOS were remarkably reduced in the NEC + CAPE group, however, TAS was significantly increased in the NEC + CAPE group (P < 0.05).

CONCLUSION

Treatment with CAPE reduces the intestinal damage in NEC.

2-thioxanthines are mechanism-based inactivators of myeloperoxidase that block oxidative stress during inflammation

Myeloperoxidase (MPO) is a prime candidate for promoting oxidative stress during inflammation. This abundant enzyme of neutrophils uses hydrogen peroxide to oxidize chloride to highly reactive and toxic chlorine bleach. We have identified 2-thioxanthines as potent mechanism-based inactivators of MPO. Mass spectrometry and x-ray crystal structures revealed that these inhibitors become covalently attached to the heme prosthetic groups of the enzyme. We propose a mechanism whereby 2-thioxanthines are oxidized, and their incipient free radicals react with the heme groups of the enzyme before they can exit the active site. 2-Thioxanthines inhibited MPO in plasma and decreased protein chlorination in a mouse model of peritonitis. They slowed but did not prevent neutrophils from killing bacteria and were poor inhibitors of thyroid peroxidase. Our study shows that MPO is susceptible to the free radicals it generates, and this Achilles' heel of the enzyme can be exploited to block oxidative stress during inflammation.

Roles of superoxide and myeloperoxidase in ascorbate oxidation in stimulated neutrophils and H2O2-treated HL60 cells

Ascorbate is present at high concentrations in neutrophils and becomes oxidized when the cells are stimulated. We have investigated the mechanism of oxidation by studying cultured HL60 cells and isolated neutrophils. Addition of H(2)O(2) to ascorbate-loaded HL60 cells resulted in substantial oxidation of intracellular ascorbate. Oxidation was myeloperoxidase-dependent, but not attributable to hypochlorous acid, and can be explained by myeloperoxidase (MPO) exhibiting direct ascorbate peroxidase activity. When neutrophils were stimulated with phorbol myristate acetate, about 40% of their intracellular ascorbate was oxidized over 20 min. Ascorbate loss required NADPH oxidase activity but in contrast to the HL60 cells did not involve myeloperoxidase. It did not occur when exogenous H(2)O(2) was added, was not inhibited by myeloperoxidase inhibitors, and was the same for normal and myeloperoxidase-deficient cells. Neutrophil ascorbate loss was enhanced when endogenous superoxide dismutase was inhibited by cyanide or diethyldithiocarbamate and appears to be due to oxidation by superoxide. We propose that in HL60 cells, MPO-dependent ascorbate oxidation occurs because cellular ascorbate can access newly synthesized MPO before it becomes packaged in granules: a mechanism not possible in neutrophils. In neutrophils, we estimate that ascorbate is capable of competing with superoxide dismutase for a small fraction of the superoxide they generate and propose that the superoxide responsible is likely to come from previously identified sites of intracellular NADPH oxidase activity. We speculate that ascorbate might protect the neutrophil against intracellular effects of superoxide generated at these sites.

Involvement of vascular peroxidase 1 in angiotensin II-induced vascular smooth muscle cell proliferation

AIMS

Vascular peroxidase 1 (VPO1) is a newly identified haem-containing peroxidase that catalyses the oxidation of a variety of substrates by hydrogen peroxide (H(2)O(2)). Considering the well-defined effects of H(2)O(2) on the vascular remodelling during hypertension, and that VPO1 can utilize H(2)O(2) generated from co-expressed NADPH oxidases to catalyse peroxidative reactions, the aims of this study were to determine the potential role of VPO1 in vascular remodelling during hypertension.

METHODS AND RESULTS

The vascular morphology and the expression of VPO1 in arterial tissues of spontaneously hypertensive rats and Wistar-Kyoto rats were assessed. The VPO1 expression was significantly increased concomitantly with definite vascular remodelling assessed by evaluating the media thickness, lumen diameter, media thickness-to-lumen diameter ratio and mean nuclear area in artery media in spontaneously hypertensive rats. In addition, in cultured rat aortic smooth muscle cells we found that the angiotensin II-mediated cell proliferation was inhibited by knockdown of VPO1 using small hairpin RNA. Moreover, the NADPH oxidase inhibitor, apocynin, and the hydrogen peroxide scavenger, catalase, but not the ERK1/2 inhibitor, PD98059, attenuated angiotensin II-mediated up-regulation of VPO1 and generation of hypochlorous acid.

CONCLUSION

VPO1 is a novel regulator of vascular smooth muscle cell proliferation via NADPH oxidase-H(2)O(2)-VPO1-hypochlorous acid-ERK1/2 pathways, which may contribute to vascular remodelling in hypertension.

Sensitive and selective off-on rhodamine hydrazide fluorescent chemosensor for hypochlorous acid detection and bioimaging

A rhodamine 6G hydrazide fluorescent chemosensor was prepared for the rapid HOCl detection in aqueous media. The system makes good use of the irreversible HOCl-mediated selective oxidation reaction to generate fluorescent response proportional to the amount of HOCl in neutral buffer. This probe exhibits great photostability, high sensitivity, and good selectivity for HOCl over other reactive species and most of the common metal ions. Furthermore, the probe is cell membrane permeable, and its applicability has been successfully demonstrated for fluorescence imaging of both exogenous and endogenous HOCl within living cells. Cytotoxicity assays prove that this probe is almost nontoxic to the cultured cell lines under the experimental conditions.

Urate as a physiological substrate for myeloperoxidase: implications for hyperuricemia and inflammation

Urate and myeloperoxidase (MPO) are associated with adverse outcomes in cardiovascular disease. In this study, we assessed whether urate is a likely physiological substrate for MPO and if the products of their interaction have the potential to exacerbate inflammation. Urate was readily oxidized by MPO and hydrogen peroxide to 5-hydroxyisourate, which decayed to predominantly allantoin. The redox intermediates of MPO were reduced by urate with rate constants of 4.6 × 10(5) M(-1) s(-1) for compound I and 1.7 × 10(4) M(-1) s(-1) for compound II. Urate competed with chloride for oxidation by MPO and at hyperuricemic levels is expected to be a substantive substrate for the enzyme. Oxidation of urate promoted super-stoichiometric consumption of glutathione, which indicates that it is converted to a free radical intermediate. In combination with superoxide and hydrogen peroxide, MPO oxidized urate to a reactive hydroperoxide. This would form by addition of superoxide to the urate radical. Urate also enhanced MPO-dependent consumption of nitric oxide. In human plasma, stimulated neutrophils produced allantoin in a reaction dependent on the NADPH oxidase, MPO and superoxide. We propose that urate is a physiological substrate for MPO that is oxidized to the urate radical. The reactions of this radical with superoxide and nitric oxide provide a plausible link between urate and MPO in cardiovascular disease.

(1→3)-β-D-Glucan inhibits a dual mechanism of peroxynitrite stroke

AIM

The antioxidative and antinitrative activities of (1→3)-β-D-glucan (1-4μg/ml) from the yeast cell walls of Saccharomyces cerevisiae in human plasma treated with strong oxidants - peroxynitrite (ONOO(-)) (0.1mM) and hydrogen peroxide (H(2)O(2)) (2mM) were studied in vitro. The main purpose of this study was to assess if (1→3)-β-D-glucan, a well known strong immunostimulatory agent, possesses a protective function against dual mechanism of ONOO(-) stroke associated with nitrative and oxidative damages to human plasma biomolecules.

SCOPE

The protein changes were determined in vitro by estimating the level of oxidative stress markers - carbonyl groups, and nitrative products - 3-nitrotyrosine residues. The plasma lipid peroxidation was also investigated. The obtained results show that (1→3)-β-D-glucan inhibits in vitro ONOO(-)-induced oxidation and nitration of plasma proteins, even by 50% and 30%, respectively. The antioxidative activity of (1→3)-β-D-glucan was confirmed by its inhibitory effect on plasma lipids peroxidation induced by ONOO(-) or by H(2)O(2).

CONCLUSIONS

The obtained results demonstrate that (1→3)-β-D-glucan from S. cerevisiae protects plasma components against toxic effects of ONOO(-) and H(2)O(2) due to its antioxidative and antinitrative activities. Therefore (1→3)-β-D-glucan supplementation during inflammatory may be beneficial not only regard for its ability to stimulate the immune system but also by antioxidative properties.

Pharmacophore modelling and synthesis of quinoline-3-carbohydrazide as antioxidants

From well-known antioxidants agents, we developed a first pharmacophore model containing four common chemical features: one aromatic ring and three hydrogen bond acceptors. This model served as a template in virtual screening of Maybridge and NCI databases that resulted in selection of sixteen compounds. The selected compounds showed a good antioxidant activity measured by three chemical tests: DPPH radical, OH° radical, and superoxide radical scavenging. New synthetic compounds with a good correlation with the model were prepared, and some of them presented a good antioxidant activity.

Myeloperoxidase-derived oxidation: mechanisms of biological damage and its prevention

There is considerable interest in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase and lactoperoxidase, may play in a wide range of human pathologies. This has been sparked by rapid developments in our understanding of the basic biochemistry of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of biomarkers that can be used damage induced by these oxidants in vivo, and the recent identification of a number of compounds that show promise as inhibitors of these enzymes. Such compounds offer the possibility of modulating damage in a number of human pathologies. This reviews recent developments in our understanding of the biochemistry of myeloperoxidase, the oxidants that this enzyme generates, and the use of inhibitors to inhibit such damage.

Ability of hypochlorous acid and N-chloramines to chlorinate DNA and its constituents

Myeloperoxidase is a heme enzyme released by activated phagocytes that is responsible for the generation of the strong oxidant hypochlorous acid (HOCl). Although HOCl has potent bactericidal properties and plays an important role in the human immune system, this oxidant also causes damage to tissues, particularly under inflammatory conditions. There is a strong link between chronic inflammation and the incidence of many cancers, which may be associated with the ability of HOCl and related oxidants such as N-chloramines to damage DNA. However, in contrast to HOCl, little is known about the reactivity of N-chloramines with DNA and its constituents. In this study, we examine the ability of HOCl and various N-chloramines to form chlorinated base products on nucleosides, nucleotides, DNA, and in cellular systems. Experiments were performed with N-chloramines formed on Nalpha-acetyl-histidine (His-C), Nalpha-acetyl-lysine (Lys-C), glycine (Gly-C), taurine (Tau-C), and ammonia (Mono-C). Treatment of DNA and related materials with HOCl and His-C resulted in the formation of 5-chloro-2'-deoxycytidine (5CldC), 8-chloro-2'-deoxyadenosine (8CldA) and 8-chloro-2'-deoxyguanosine (8CldG). With the nucleosides, 8CldG was the favored product in each case, and HOCl was the most efficient chlorinating agent. 5Cl(d)C was the most abundant product on exposure of the nucleotides and DNA to HOCl and His-C, with only low levels of chlorinated products observed with Lys-C, Gly-C, Tau-C, and Mono-C. 5CldC was also formed on exposure of smooth muscle cells to either HOCl or His-C. Cellular RNA was also a target for HOCl and His-C, with evidence for the formation of 5-chloro-cytidine (5ClC). This study shows that HOCl and the model N-chloramine, His-C, are able to chlorinate cellular genetic material, which may play a role in the development of various inflammatory cancers.

Resveratrol protects against irradiation-induced hepatic and ileal damage via its anti-oxidative activity

The present study was undertaken to determine whether resveratrol (RVT) could ameliorate ionizing radiation-induced oxidative injury. After a 10-days pre-treatment with RVT (10 mg/kg/day p.o.), rats were exposed to whole-body IR (800 cGy) and the RVT treatment was continued for 10 more days after the irradiation. Irradiation caused a significant decrease in glutathione level, while malondialdehyde levels, myeloperoxidase activity and collagen content were increased in the liver and ileum tissues. Similarly, plasma lactate dehydrogenase and pro-inflammatory cytokine levels, 8-hydroxy-2'-deoxyguanosine and leukocyte apoptosis were elevated, while antioxidant-capacity was reduced in the irradiated rats as compared with the control group. Furthermore, Na(+), K(+)-ATPase activity was inhibited and DNA fragmentation was increased in the ileal tissues. Resveratrol treatment reversed all these biochemical indices, as well as histopathological alterations induced by irradiation. In conclusion, supplementing cancer patients with adjuvant therapy of resveratrol may have some benefit for a more successful radiotherapy.

Montelukast, a selective cysteinyl leukotriene receptor 1 antagonist, reduces cerulein-induced pancreatic injury in rats

OBJECTIVES

This study was designed to evaluate the protective effect of the cysteinyl leukotriene receptor antagonist montelukast against pancreatic injury during acute pancreatitis.

METHODS

Acute pancreatitis was induced in rats by 20-μg/kg (intraperitoneal) cerulein given at 1-hour intervals within 4 hours. Montelukast was administered intraperitoneally at a dose of 10 mg/kg 15 minutes before the first cerulein injection. Six hours after the cerulein or saline injections, the animals were killed by decapitation. Blood samples were collected to analyze amylase, lipase, and the proinflammatory cytokines tumor necrosis factor α and interleukin 1β. Pancreas tissues were taken for the determination of tissue glutathione and malondialdehyde levels and Na,K-adenosine triphosphatase and myeloperoxidase activities. The extent of tissue injury was analyzed microscopically.

RESULTS

Acute pancreatitis caused significant decreases in tissue glutathione level and Na,K-adenosine triphosphatase activity, which were accompanied with significant increases in the pancreatic malondialdehyde level, myeloperoxidase activity, and plasma cytokine level. On the other hand, montelukast treatment reversed all these biochemical indices and histopathological alterations that were induced by cerulein.

CONCLUSIONS

These results suggest that cysteinyl leukotrienes may be involved in the pathogenesis of acute pancreatitis and that the cysteinyl leukotriene receptor antagonist, montelukast, might be of therapeutic value for treatment of acute pancreatitis.

The myeloperoxidase-derived oxidant HOSCN inhibits protein tyrosine phosphatases and modulates cell signalling via the mitogen-activated protein kinase (MAPK) pathway in macrophages

MPO (myeloperoxidase) catalyses the oxidation of chloride, bromide and thiocyanate by hydrogen peroxide to HOCl (hypochlorous acid), HOBr (hypobromous acid) and HOSCN (hypothiocyanous acid) respectively. Specificity constants indicate that SCN⁻ is a major substrate for MPO. HOSCN is also a major oxidant generated by other peroxidases including salivary, gastric and eosinophil peroxidases. While HOCl and HOBr are powerful oxidizing agents, HOSCN is a less reactive, but more specific, oxidant which targets thiols and especially low pK_a species. In the present study we show that HOSCN targets cysteine residues present in PTPs (protein tyrosine phosphatases) with this resulting in a loss of PTP activity for the isolated enzyme, in cell lysates and intact J774A.1 macrophage-like cells. Inhibition also occurs with MPO-generated HOCl and HOBr, but is more marked with MPO-generated HOSCN, particularly at longer incubation times. This inhibition is reversed by dithiothreitol, particularly at early time points, consistent with the reversible oxidation of the active site cysteine residue to give either a cysteine–SCN adduct or a sulfenic acid. Inhibition of PTP activity is associated with increased phosphorylation of p38a and ERK2 (extracellular-signal-regulated kinase 2) as detected by Western blot analysis and phosphoprotein arrays, and results in altered MAPK (mitogen-activated protein kinase) signalling. These data indicate that the highly selective targeting of some protein thiols by HOSCN can result in perturbation of cellular phosphorylation and altered cell signalling. These changes occur with (patho)physiological concentrations of SCN⁻ ions, and implicate HOSCN as an important mediator of inflammation-induced oxidative damage, particularly in smokers who have elevated plasma levels of SCN⁻.

Cadmium intoxication of pregnant rats and fetuses: interactions of copper supplementation

BACKGROUND AND AIMS

Cadmium (Cd) is an industrial and environmental pollutant that was shown to be involved in the development of some diseases. Due to high amounts of Cd in cigarettes, smokers and passive smokers are exposed to high amount of Cd. We aimed to determine whether Copper (Cu) supplementation would have a protective effect against Cd intoxication in pregnant rats and their fetuses.

METHODS

Experiments were performed on 27 adult female Wistar albino rats divided into three experimental groups. CdCl(2), CdCl(2) plus CuSO(4) and only drinking water was given to different groups for 21 days. We measured cadmium (Cd), malondialdehyde (MDA), reduced glutathione (GSH), myeloperoxidase (MPO), superoxide dismutase (SOD) and catalase (CAT) levels in dams' liver, dams' kidney, fetus liver, fetus kidney, and placenta of rats.

RESULTS

In all tissues of Cd and Cd + Cu-treated groups, Cd levels were found to be increased significantly when compared to control group. MDA levels and MPO activities were significantly increased whereas GSH levels, activities of SOD and CAT were decreased in Cd groups when compared to control group. Cu supplementation significantly prevented the increment in MDA levels and brought MPO activities back to control levels or below. Cd-induced reductions in GSH levels and SOD activities were also prevented by Cu supplementation. An increase of CAT activity after Cu supplementation was enough to revert to the control levels in some tissues.

CONCLUSIONS

Our findings suggest that Cu supplementation may have a protective effect against the Cd-induced oxidative stress in liver, kidney and placental tissues of pregnant rats and fetuses.

Quercetin attenuates inflammatory processes after spinal cord injury in an animal model

OBJECTIVES

We have shown earlier that administration of the flavonoid quercetin significantly contributed to recovery of motor function after spinal cord compression injury in the adult rat. Using the same animal model, we have now designed a set of experiments to test the hypothesis that quercetin attenuates oxidative stress-related inflammatory processes early after spinal cord trauma.

METHODS

Mid-thoracic spinal cord compression injury in adult male Wistar rats was caused by extradural application and closure of a 50 g calibrated aneurysm clip for 5 s. Myeloperoxidase (MPO) levels were determined in spinal cord tissue and serum of quercetin-treated animals and controls at 6, 12, 24 and 72 h after injury. The white blood count was followed until 72 h after injury.

RESULTS

In quercetin-treated animals, MPO activity was significantly decreased in tissue at 12 and 24 h and in serum at 6, 12 and 24 h after injury, compared with saline controls. In quercetin-treated animals, the prevalence of ED-1 and MPO positive cells was significantly lower than in saline controls. White blood count in venous blood was significantly decreased in quercetin-treated animals at 12 and 24 h after injury.

CONCLUSION

Quercetin attenuated the recruitment of neutrophils to the site of injury. The resulting lower MPO release in the injured tissue is likely to decrease the extent of secondary injury and might at least partially explain the neuroprotective effect of the flavonoid quercetin.

Protective effect of aqueous garlic extract against naphthalene-induced oxidative stress in mice

The aim of this study was to investigate the possible protective effects of aqueous garlic extract (AGE) against naphthalene-induced oxidative changes in liver, kidney, lung and brain of mice. Balb/c mice (25–30 g) of either sex were divided into five groups each comprising 10 animals. Mice received for 30 days: 0.9% NaCl, i.p. (control); corn oil, i.p; AGE in a dose of 125 mg kg−1, i.p.; naphthalene in a dose of 100 mg kg−1, i.p. (dissolved in corn oil); and AGE (in a dose of 125 mg kg−1, i.p.) plus naphthalene (in a dose of 100 mg kg−1, i.p.). After decapitation, liver, kidney, lung and brain tissues were excised. Malondialdehyde (MDA) and glutathione (GSH) levels and myeloperoxidase activity (MPO) were determined in the tissues, while oxidant-induced tissue fibrosis was determined by collagen content. Tissues were also examined microscopically. Serum aspartate aminotransferase, alanine aminotransferase levels and blood urea nitrogen and creatinine concentrations were measured for the evaluation of hepatic and renal function, respectively. MDA and GSH levels were also assayed in serum samples. In the naphthalene-treated group, GSH levels decreased significantly, while MDA levels, MPO activity and collagen content increased in the tissues (P&lt; 0.01–0.001), suggesting oxidative organ damage, which was also verified histologically. In the AGE-treated naphthalene group, all of these oxidant responses were reversed significantly (P&lt; 0.05–0.01). Hepatic and renal function test parameters, which increased significantly (P&lt; 0.001) following naphthalene administration, decreased (P&lt; 0.05–0.001) after AGE treatment. The results demonstrate the role of oxidative mechanisms in naphthalene-induced tissue damage. The antioxidant properties of AGE ameliorated oxidative organ injury due to naphthalene toxicity.

Hypochlorite scavenging activity of flavonoids

Scavengers of hypochlorite, a highly reactive oxidant produced by activated phagocytes, could have potential therapeutic effects in diseases in which this oxidant plays a pathogenic role. Flavonoids are polyphenolic substances present in food plants and have been extensively studied for their antioxidant properties against various free radicals. Less is known about their reactivity with hypochlorite. In this study, the hypochlorite scavenging activity of flavonoids was investigated using a microplate assay recently developed in our laboratory. This method evaluates the ability of a substance to inhibit the formation of chloramines in human serum albumin upon oxidation by hypochlorite. Thirteen flavonoids were tested. Most of them inhibited human serum albumin oxidation at micro-molar concentrations and appeared more active than Trolox, a water-soluble equivalent of vitamin E. It was observed that the greater the number of hydroxyl substitutions, the greater the scavenging activity. The 3-hydroxy substitution seemed to be particularly important for scavenging activity, whereas the presence of a 2,3-double bond in the C ring did not. Flavonoids were found to be good hypochlorite scavengers in-vitro and further information is provided about the chemical aspects important for scavenging activity. Thus, flavonoids could have beneficial effects in diseases such as atherosclerosis in which hypochlorite plays a pathogenic role.

Aqueous garlic extract alleviates ischaemia-reperfusion-induced oxidative hepatic injury in rats

This study was designed to examine the effects of aqueous garlic extract (AGE) on hepatic ischaemia-reperfusion (I/R) injury in rats. For this purpose, Wistar albino rats were subjected to 45 min of hepatic ischaemia, followed by a 60-min reperfusion period. AGE (1 mL kg−1, i.p., corresponding to 500 mg kg−1) or saline was administered twice, 15 min before ischaemia and immediately before the reperfusion period. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were determined to assess liver functions. Liver tissues were taken for the determination of malondialdehyde (MDA) levels, an end product of lipid peroxidation; glutathione (GSH) levels, a key antioxidant; and myeloperoxidase (MPO) activity, as an indirect index of neutrophil infiltration. Hepatic collagen content, as a fibrosis marker, was also determined. Plasma ALT and AST activities were elevated in the I/R group as compared with the control group, while these increases were significantly decreased by AGE treatment. Hepatic GSH levels, significantly depressed by I/R, were elevated back to control levels in the AGE-treated I/R group. Increases in tissue MDA levels and MPO activity due to I/R injury were reduced back to control levels by AGE treatment. Similarly, increased hepatic collagen content in the I/R group was reduced to the control level with AGE treatment. Since AGE administration alleviated the I/R-induced injury of the liver and improved the hepatic structure and function, it seems likely that AGE, with its antioxidant and oxidant-scavenging properties, may be of potential therapeutic value in protecting the liver against oxidative injury due to ischaemia-reperfusion.

Calprotectin (S100A8/S100A9) and myeloperoxidase: co-regulators of formation of reactive oxygen species

Inflammatory mediators trigger polymorphonuclear neutrophils (PMN) to produce reactive oxygen species (ROS: O₂^-, H₂O₂, ∙OH). Mediated by myeloperoxidase in PMN, HOCl is formed, detectable in a chemiluminescence (CL) assay. We have shown that the abundant cytosolic PMN protein calprotectin (S100A8/A9) similarly elicits CL in response to H₂O₂ in a cell-free system. Myeloperoxidase and calprotectin worked synergistically. Calprotectin-induced CL increased, whereas myeloperoxidase-triggered CL decreased with pH > 7.5. Myeloperoxidase needed NaCl for CL, calprotectin did not. 4-hydroxybenzoic acid, binding ∙OH, almost abrogated calprotectin CL, but moderately increased myeloperoxidase activity. The combination of native calprotectin, or recombinant S100A8/A9 proteins, with NaOCl markedly enhanced CL. NaOCl may be the synergistic link between myeloperoxidase and calprotectin. Surprisingly- and unexplained- at higher concentration of S100A9 the stimulation vanished, suggesting a switch from pro-oxidant to anti-oxidant function. We propose that the ∙OH is predominant in ROS production by calprotectin, a function not described before.

Protective effects of pycnogenol against ischemia reperfusion-induced oxidative renal injury in rats

INTRODUCTION

Oxygen free radicals are involved in pathophysiology of ischemia/reperfusion (I/R) injury. This study was designed to assess the possible protective effect of pycnogenol (PYC) against I/R-induced oxidative renal damage.

MATERIALS AND METHODS

Wistar albino rats were unilaterally nephrectomized and subjected to 45 min of renal pedicle occlusion followed by 3 h of reperfusion. PYC (10 mg kg(-1), i.p.) or saline was administered at 15 min prior to ischemia and immediately before the reperfusion period. At the end of the 3 h, rats were decapitated and trunk blood was collected. Creatinine, blood urea nitrogen (BUN), and lactate dehydrogenase (LDH) activity were measured in the serum samples, while proinflammatory cytokines, TNF-alpha, IL-1beta, and IL-6 levels were assayed in plasma samples. Kidney samples were taken for the determination of tissue malondialdehyde (MDA), glutathione (GSH) levels, Na+, K+-ATPase, and myeloperoxidase (MPO) activities, and the extent of tissue injury was analyzed microscopically.

RESULTS

Ischemia/reperfusion caused a significant decrease in tissue GSH level and Na+, K+-ATPase activity, which was accompanied with significant increases in the renal MDA level and MPO activity. Similarly, serum creatinine and BUN levels, as well as LDH and IL-1beta, IL-6, and TNF-alpha levels, were elevated in the saline-treated I/R group as compared to saline-treated control group. On the other hand, PYC treatment reversed all these biochemical indices, as well as histopathological alterations that were induced by I/R.

CONCLUSIONS

Findings of the present study suggest that pycnogenol exerts renoprotective effects, via its free radical scavenging and antioxidant activities, that appear to involve the inhibition of tissue neutrophil infiltration.