Thiol-containing molecules interact with the myeloperoxidase/H2O2/chloride system to inhibit LDL oxidation

Mechanisms, Pathophysiology and Currently Proposed Treatments of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is one of the leading global causes of morbidity and mortality. A hallmark of COPD is progressive airflow obstruction primarily caused by cigarette smoke (CS). CS exposure causes an imbalance favoring pro- over antioxidants (oxidative stress), leading to transcription factor activation and increased expression of inflammatory mediators and proteases. Different cell types, including macrophages, epithelial cells, neutrophils, and T lymphocytes, contribute to COPD pathophysiology. Alteration in cell functions results in the generation of an oxidative and inflammatory microenvironment, which contributes to disease progression. Current treatments include inhaled corticosteroids and bronchodilator therapy. However, these therapies do not effectively halt disease progression. Due to the complexity of its pathophysiology, and the risk of exacerbating symptoms with existing therapies, other specific and effective treatment options are required. Therapies directly or indirectly targeting the oxidative imbalance may be promising alternatives. This review briefly discusses COPD pathophysiology, and provides an update on the development and clinical testing of novel COPD treatments.

Impact of MPO-ANCA-mediated oxidative imbalance on renal vasculitis

Glomerulonephritis is a severe complication of microscopic polyangiitis (MPA), a small-vessel vasculitis associated with anti-myeloperoxidase antibodies (MPO-ANCA). We previously showed the pathogenic effects of MPO-ANCA that activate MPO to trigger an oxidative burst mainly through HOCl production, contributing to endothelial injury and lung fibrosis. The aim of this study was to investigate the relationship between MPO-induced oxidative stress, anti-oxidant defenses and renal histological lesions in MPA patients. We therefore analyzed histological data from a prospective cohort of ANCA-associated glomerulonephritis. Serum-mediated HOCl production, advanced oxidation protein products (AOPP), and thiol concentration in sera were determined. From 38 patients included, histological classification noted 50% focal glomerulonephritis, 15.8% crescentic-glomerulonephritis, and 34.2% mixed-glomerulonephritis. MPA patients’ sera displayed higher HOCl production by MPO ( P < 0.001), higher AOPP ( P < 0.001) and thiol ( P < 0.01) levels, compared with healthy subjects. The presence of cellular crescents was associated with higher serum-mediated HOCl production ( P = 0.049) and lower thiol levels ( P = 0.022) at disease onset. Higher thiol concentrations were associated with focal glomerulonephritis ( P = 0.042), less interstitial fibrosis ( P = 0.039) and hyalinosis ( P = 0.066). In remission, HOCl production was decreased ( P < 0.01), and thiol concentration remained high ( P = 0.39). Our findings suggest that HOCl production by activated MPO could contribute to the very early stage of glomerulonephritis, whereas thiol may exert a protective effect against the development of renal vasculitis and glomerulosclerosis. This study highlights the importance of oxidative defenses to counteract the process of MPO-ANCA associated glomerulonephritis.

Enzymatic synthesis of a thiolated chitosan-based wound dressing crosslinked with chicoric acid

This work describes the enzymatic synthesis of multifunctional hydrogels for chronic wound treatment using thiolated chitosan and the natural polyphenol chicoric acid. Gelation was achieved by laccase-catalyzed oxidation of chicoric acid, a natural compound used for the first time as a homobifunctional crosslinker, reacting subsequently with nucleophilic thiol and amino groups from the chitosan derivative. This approach allowed for twice as fast gelation at a three-fold reduced crosslinking reagent concentration, compared to reported enzymatic synthesis of hydrogels using gallic acid as a phenolic provider. Hydrogels with 600% swelling capacity, coupled with only 20% weight loss after 6 days under physiological conditions, were obtained. The clinically relevant Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa were reduced by up to 4.5 and 5.5 logs, respectively. A tunable, in the range of 20-95%, ex vivo inhibition of myeloperoxidase (MPO) activity in chronic wound exudate was achieved, together with control over the total matrix metalloproteinase (MMP) activities.

Interaperitoneal Administration of Αlpha-Tocopherol Loaded Nanoparticles Improves Ischemia-Reperfusion Injury in Rat Ovaries Torsion and Detorsion Model

Objective:

To investigate effects of intraperitoneally administration of α-tocopherol loaded nanoparticles (TNP) on ischemia-reperfusion injury in ovaries.

Methods:

Thirty-five healthy female Wistar rats ~250g were randomized into seven experimental groups (n = 5): Group SHAM: The rats underwent only laparotomy. Group Ischemia: A 3- hour ischemia only. Group I/R: A 3-hour ischemia and a 3-hour reperfusion. Group I/T: A 3-hour ischemia only and 100 mg/kg intraperitoneal administration (IP) of α-tocopherol 2.5 hours after induction of ischemia. Group I/R/T: A 3-hour ischemia, a 3-hour reperfusion and 100 mg/kg IP of α-tocopherol 2.5 hours after induction of ischemia. Group I/TNP: A 3-hour ischemia only and 1 mg/kg IP of TNP 2.5 hours after induction of ischemia. Group I/R/TNP: A 3-hour ischemia, a 3-hour reperfusion and 1 mg/kg IP of TNP 2.5 hours after induction of ischemia.  

Results:

Animals treated with αTNP showed significantly ameliorated development of ischemia and reperfusion tissue injury compared to those of other groups (p=0.001). The significant higher values of SOD, tGSH, GPO, GSHRd and GST were observed in I/R/NC animals compared to those of other groups (p=0.001). Damage indicators (NOS, MDA, MPO and DNA damage level) were significantly lower in I/R/NC animal compared to those of other groups (p=0.001).

Conclusion:

Intraperitoneal administration of TNP could be helpful in minimizing ischemia-reperfusion injury in ovarian tissue exposed to ischemia.

Protective effects of intraperitoneal administration of nimodipine on ischemia-reperfusion injury in ovaries: Histological and biochemical assessments in a rat model

PURPOSE

Ovarian torsion must be diagnosed and treated as much early as possible. The aim of the present study was to investigate effects of intraperitoneal administration of nimodipine on ischemia-reperfusion injury in ovaries.

METHODS

Thirty healthy male Wistar rats weighing approximately 250g were randomized into six experimental groups (n=5): Group Sham: The rats underwent only laparotomy. Group I: A 3-h ischemia only. Group I/R: A 3-h ischemia and a 3-h reperfusion. Group I/Nimodipine: A 3-h ischemia only and 1mg/kg intraperitoneal administration of nimodipine 2.5h after induction of ischemia. Group I/R/Nimodipine: A 3-h ischemia, a 3-h reperfusion and 1mg/kg intraperitoneal administration of nimodipine 2.5h after induction of ischemia.

RESULTS

Nimodipine treated animals showed significantly ameliorated development of ischemia and reperfusion tissue injury compared to those of other groups (P<0.05). The significant higher values of SOD, tGSH, GPO, GSHRd and GST were observed in I/R/Nimodipine animals compared to those of other groups (P<0.05). The damage indicators (NOS, MDA, MPO and DNA damage level) were significantly lower in I/R/Nimodipine animal compared to those of other groups (P<0.05).

CONCLUSIONS

Intraperitoneal administration of nimodipine could be helpful in minimizing ischemia-reperfusion injury in ovarian tissue exposed to ischemia.

N-acetylcysteine a possible protector against indomethacin-induced peptic ulcer: crosstalk between antioxidant, anti-inflammatory, and antiapoptotic mechanisms

This study investigated the gastroprotective effects of N-acetylcysteine (NAC) against indomethacin-induced gastric ulcer in rats. Ulceration was induced by a single oral administration of indomethacin (30 mg/kg). 50 male albino rats were allocated into 5 equal groups: control group received normal saline orally, indomethacin group rats received normal saline orally for 5 days and indomethacin (50 mg/kg) on the last day, ranitidine group received ranitidine (reference drug) orally for 5 days (50 mg/kg) before receiving indomethacin (50 mg/kg) on the last day, and NAC groups received NAC orally at 300 and 500 mg/kg, respectively, for 5 days before receiving indomethacin (50 mg/kg) on the last day. Gastric tissue interleukin-1β (IL-1β), interferon-γ (IFN-γ), and caspase-3 levels were immunoassayed. Total thiol (T-SH), myeloperoxidase (MPO), and glucose-6-phosphate dehydrogenase (G6PD) were determined by spectrophotometry. Cytokine-induced neutrophil chemoattractant 2α (CINC-2α) gene expression was evaluated in addition to Bcl-2 immunohistochemistry. Pretreatment with NAC improved the inflammatory, apoptotic, and redox status in a dose-dependent manner particularly in NAC 500 mg/kg pretreated group. These results show a role for NAC in improving indomethacin-induced gastric ulceration via antioxidative, antiapoptotic, and anti-inflammatory interactive mechanisms.

Sex-specific effects of N-acetylcysteine in neonatal rats treated with hypothermia after severe hypoxia-ischemia

Approximately half of moderate to severely hypoxic-ischemic (HI) newborns do not respond to hypothermia, the only proven neuroprotective treatment. N-acetylcysteine (NAC), an antioxidant and glutathione precursor, shows promise for neuroprotection in combination with hypothermia, mitigating post-HI neuroinflammation due to oxidative stress. As mechanisms of HI injury and cell death differ in males and females, sex differences must be considered in translational research of neuroprotection. We assessed the potential toxicity and efficacy of NAC in combination with hypothermia, in male and female neonatal rats after severe HI injury. NAC 50mg/kg/d administered 1h after initiation of hypothermia significantly decreased iNOS expression and caspase 3 activation in the injured hemisphere versus hypothermia alone. However, only females treated with hypothermia +NAC 50mg/kg showed improvement in short-term infarct volumes compared with saline treated animals. Hypothermia alone had no effect in this severe model. When NAC was continued for 6 weeks, significant improvement in long-term neuromotor outcomes over hypothermia treatment alone was observed, controlling for sex. Antioxidants may provide insufficient neuroprotection after HI for neonatal males in the short term, while long-term therapy may benefit both sexes.

Protective effect of N-acetylcysteine against ethanol-induced gastric ulcer: A pharmacological assessment in mice

Aim:

Since there is an increasing need for gastric ulcer therapies with optimum benefit-risk profile. This study was conducted to investigate gastro-protective effects of N-acetylcysteine (NAC) against ethanol-induced gastric ulcer models in mice.

Materials and Methods:

A total of 41 mice were allocated into six groups consisted of 7 mice each. Groups 1 (normal control) and 2 (ulcer control) received distilled water at a dose of 10 ml/kg, groups 3, 4 and 5 were given NAC at doses 100, 300 and 500 mg/kg, respectively, and the 6^th group received ranitidine (50 mg/kg). All drugs administered orally once daily for 7 days, on the 8^th day absolute ethanol (7 ml/kg) was administrated orally to all mice to induce the acute ulcer except normal control group. Then 3 h after, all animals were sacrificed then consequently the stomachs were excised for examination.

Results:

NAC administration at the tested doses showed a dose-related potent gastro-protective effect with significant increase in curative ratio, PH of gastric juice and mucus content viscosity seen with the highest dose of NAC and it is comparable with that observed in ranitidine group.

Conclusion:

The present findings demonstrate that, oral NAC shows significant gastro-protective effects comparable to ranitidine confirmed by anti-secretory, cytoprotective, histological and biochemical data, but the molecular mechanisms behind such protection are complex.

Inhibition of myeloperoxidase activity by the alkaloids of Peganum harmala L. (Zygophyllaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Seeds and aerial parts of Peganum harmala L. are widely used in Algeria as anti-inflammatory remedies. Evaluation of Peganum harmala total alkaloids extracts and pure β-carboline compounds as an anti-inflammatory treatment by the inhibition of an enzyme key of inflammatory, myeloperoxidase (MPO) and HPLC quantification of the alkaloids from the different parts of plant.

MATERIALS AND METHODS

MPO inhibition was tested using taurine chloramine test. The inhibition of LDL oxidation induced by MPO was carried out. The molecular docking analysis of Peganum harmala alkaloids on MPO was performed using the Glide XP docking protocol and scoring function and the redox potential of alkaloids was determined using an Epsilon potentiostat. The concentration of harmala alkaloids was determined using HPLC analysis.

RESULTS

The HPLC profiling of the active total alkaloids indicates that β-carboline e.g. harmine, harmaline, harmane, harmol and harmalol are major components. As β-carbolines resemble tryptamine, of which derivatives are efficient inhibitors of MPO, the harmala alkaloids were tested for their activity on this enzyme. Total alkaloids of the seeds and of the aerial parts strongly inhibited MPO at 20µg/mL (97±5% and 43±4%, respectively) whereas, at the same concentration, those of the roots showed very low inhibition (15±6%). Harmine, harmaline and harmane demonstrated a significant inhibition of MPO at IC50 of 0.26, 0.08 and 0.72µM respectively. These alkaloids exerted a similar inhibition effects on MPO-induced LDL oxidation. Molecular docking analysis of Peganum harmala alkaloids on MPO showed that all active Peganum harmala alkaloids have a high affinity on the active site of MPO (predicted free energies of binding up to -3.1kcal/mol). Measurement of redox potentials versus the normal hydrogen electrode clearly differentiated (i) the high MPO inhibitory activity of harmine, harmaline and harmane (+1014, 1014 and 1003mV, respectively); and (ii) the low activity of harmalol and harmol (+629/778 and 532/644mV, respectively). A reverse phase HPLC method has been developed to determine simultaneously five alkaloids of Peganum harmala. Seeds contained all five β-carboline derivatives with the main active alkaloids, harmaline and harmine, being up to 3.8% and 2.9%, respectively. Up to 3.2% of harmine was determined in the roots. The four β-carboline derivatives, harmine, harmaline, harmane and harmalol were identified in the aerial parts. The highest inhibitory effect observed in seeds and the moderate effect of aerial parts could be explained by their harmine and harmaline content. In contrast, the very weak inhibition of the root extract, despite the presence of harmine, may tentatively be explained by the high concentration of harmol which can reduce Compound II of MPO to the native form.

CONCLUSION

The inhibition of MPO by Peganum harmala β-carboline alkaloids, herein reported for the first time, may explain the anti-inflammatory effect traditionally attributed to its herbal medicine.

Characterization and antioxidant properties of six Algerian propolis extracts: ethyl acetate extracts inhibit myeloperoxidase activity

Because propolis contains many types of antioxidant compounds such as polyphenols and flavonoids, it can be useful in preventing oxidative damages. Ethyl acetate extracts of propolis from several Algerian regions show high activity by scavenging free radicals, preventing lipid peroxidation and inhibiting myeloperoxidase (MPO). By fractioning and assaying ethyl acetate extracts, it was observed that both polyphenols and flavonoids contribute to these activities. A correlation was observed between the polyphenol content and the MPO inhibition. However, it seems that kaempferol, a flavonoid, contributes mainly to the MPO inhibition. This molecule is in a high amount in the ethyl acetate extract and demonstrates the best efficiency towards the enzyme with an inhibiting concentration at 50% of 4 ± 2 µM.

Flavonoids and 5-aminosalicylic acid inhibit the formation of neutrophil extracellular traps

Neutrophil extracellular traps (NETs) have been suggested to play a pathophysiological role in several autoimmune diseases. Since NET-formation in response to several biological and chemical stimuli is mostly ROS dependent, in theory any substance that inhibits or scavenges ROS could prevent ROS-dependent NET release. Therefore, in the present comprehensive study, several antioxidative substances were assessed for their capacity to inhibit NET formation of primary human neutrophils in vitro. We could show that the flavonoids (-)-epicatechin, (+)-catechin hydrate, and rutin trihydrate as well as vitamin C and the pharmacological substances N-acetyl-L-cysteine and 5-aminosalicylic acid inhibited PMA induced ROS production and NET formation. Therefore, a broad spectrum of antioxidative substances that reduce ROS production of primary human neutrophils also inhibits ROS-dependent NET formation. It is tempting to speculate that such antioxidants can have beneficial therapeutic effects in diseases associated with ROS-dependent NET formation.

Design, synthesis, and structure-activity relationship studies of novel 3-alkylindole derivatives as selective and highly potent myeloperoxidase inhibitors

Due to its production of potent antimicrobial oxidants including hypochlorous acid, human myeloperoxidase (MPO) plays a critical role in innate immunity and inflammatory diseases. Thus MPO is an attractive target in drug design. (Aminoalkyl)fluoroindole derivatives were detected to be very potent MPO inhibitors; however, they also promote inhibition of the serotonin reuptake transporter (SERT) at the same concentration range. Via structure-based drug design, a new series of MPO inhibitors derived from 3-alkylindole were synthesized and their effects were assessed on MPO-mediated taurine chlorination and low-density lipoprotein oxidation as well as on inhibition of SERT. The fluoroindole compound with three carbons in the side chain and one amide group exhibited a selectivity index of 35 (Ki/IC50) with high inhibition of MPO activity (IC50 = 18 nM), whereas its effect on SERT was in the micromolar range. Structure-function relationships, mechanism of action, and safety of the molecule are discussed.

S-carbamoylation impairs the oxidant scavenging activity of cysteine: its possible impact on increased LDL modification in uraemia

Carbamoylation is the non-enzymatic reaction of cyanate with amino-, hydroxy- or thiol groups. In vivo, amino group modification (N-carbamoylation) resulting in altered function of proteins/amino acids has been observed in patients suffering from uraemia due to urea-derived cyanate. Uraemia has been linked to impaired antioxidant defense. As thiol-compounds like cysteine, N-acetyl cysteine and GSH have oxidant scavenging properties one may speculate that thiol-group carbamoylation (S-carbamoylation) may impair their protective activity. Here we report on the effect of S-carbamoylation on the ABTS free radical and HOCl scavenging property of cysteine as well on its ability to protect LDL from atherogenic modification induced by AAPH generated peroxylradicals or HOCl. The results show that S-carbamoylation impaired the ABTS free radical and HOCl scavenging property of the thiol-compounds tested. The ability of the thiols to protect LDL from lipid oxidation and apolipoprotein modification was strongly diminished by S-carbamoylation. The data indicate that S-carbamoylation could impair the free radical and HOCl scavenging of thiol-amino acids reducing their protective property against LDL atherogenic modification by these oxidant species. As S-carbamoylation is most effective at pH 7 to 5 in vivo thiol-carbamoylation may especially occur at sites of acidic extracellular pH as in hypoxic/inflammatory macrophage rich areas like the atherosclerotic plaque where increased LDL oxidation has been found and may contribute to the higher oxidative stress in uraemia.

Glycosylation pattern of mature dimeric leukocyte and recombinant monomeric myeloperoxidase: glycosylation is required for optimal enzymatic activity

The involvement of myeloperoxidase (MPO) in various inflammatory conditions has been the scope of many recent studies. Besides its well studied catalytic activity, the role of its overall structure and glycosylation pattern in biological function is barely known. Here, the N-glycan composition of native dimeric human MPO purified from neutrophils and of monomeric MPO recombinantly expressed in Chinese hamster ovary cells has been investigated. Analyses showed the presence of five N-glycans at positions 323, 355, 391, 483, 729 in both proteins. Site by site analysis demonstrated a well conserved micro- and macro-heterogeneity and more complex-type N-glycans for the recombinant form. Comparison of biological functionality of glycosylated and deglycosylated recombinant MPO suggests that glycosylation is required for optimal enzymatic activity. Data are discussed with regard to biosynthesis and the three-dimensional structure of MPO.

Hydrogen sulphide: A novel physiological inhibitor of LDL atherogenic modification by HOCl

Hypochlorite (HOCl), the product of the activated myeloperoxidase/H(2)O(2)/chloride (MPO/H(2)O(2)/Cl(- )) system is favored as a trigger of LDL modifications, which may play a pivotal role in early atherogenesis. As HOCl has been shown to react with thiol-containing compounds like glutathione and N-acetylcysteine protecting LDL from HOCl modification, we have tested the ability of hydrogen sulfide (H(2)S) - which has recently been identified as an endogenous vasorelaxant - to counteract the action of HOCl on LDL. The results show that H(2)S could inhibit the atherogenic modification of LDL induced by HOCl, as measured by apolipoprotein alterations. Beside its HOCl scavenging potential, H(2)S was found to inhibit MPO (one may speculate that this occurs via H(2)S/heme interaction) and destroy H(2)O(2). Thus, H(2)S may interfere with the reactants and reaction products of the activated MPO/H(2)O(2)/Cl(- ) system. Our data add to the evidence of an anti-atherosclerotic action of this gasotransmitter taking the role of HOCl in the atherogenic modification of LDL into account.

Mammalian heme peroxidases: from molecular mechanisms to health implications

A marked increase in interest has occurred over the last few years in the role that mammalian heme peroxidase enzymes, primarily myeloperoxidase, eosinophil peroxidase, and lactoperoxidase, may play in both disease prevention and human pathologies. This increased interest has been sparked by developments in our understanding of polymorphisms that control the levels of these enzymes, a greater understanding of the basic chemistry and biochemistry of the oxidants formed by these species, the development of specific biomarkers that can be used in vivo to detect damage induced by these oxidants, the detection of active forms of these peroxidases at most, if not all, sites of inflammation, and a correlation between the levels of these enzymes and a number of major human pathologies. This article reviews recent developments in our understanding of the enzymology, chemistry, biochemistry and biologic roles of mammalian peroxidases and the oxidants that they generate, the potential role of these oxidants in human disease, and the use of the levels of these enzymes in disease prognosis.

Lipid peroxidation and decomposition--conflicting roles in plaque vulnerability and stability

The low density lipoprotein (LDL) oxidation hypothesis has generated considerable interest in oxidative stress and how it might affect atherosclerosis. However, the failure of antioxidants, particularly vitamin E, to affect the progression of the disease in humans has convinced even staunch supporters of the hypothesis to take a step backwards and reconsider alternatives. Preponderant evidence for the hypothesis came from animal antioxidant intervention studies. In this review we point out basic differences between animal and human atherosclerosis development and suggest that human disease starts where animal studies end. While initial oxidative steps in the generation of early fatty streak lesions might be common, the differences might be in the steps involved in the decomposition of peroxidized lipids into aldehydes and their further oxidation into carboxylic acids. We suggest that these steps may not be amenable to attenuation by antioxidants and antioxidants might actually counter the stabilization of plaque by preventing the formation of carboxylic acids which are anti-inflammatory in nature. The formation of such dicarboxylic acids may also be conducive to plaque stabilization by trapping calcium. We suggest that agents that would prevent the decomposition of lipid peroxides and promote the formation and removal of lipid hydroxides, such as paraoxonase (PON 1) or apo A1/high density lipoprotein (HDL) might be more conducive to plaque regression.

Resveratrol inhibits the activity of equine neutrophil myeloperoxidase by a direct interaction with the enzyme

Resveratrol is a polyphenolic antioxidant present in beverage and food known for its multiple protective effects. We report the inhibitory effects of resveratrol on equine myeloperoxidase (MPO), a hemic peroxidase present in the granules of the neutrophils involved in the inflammatory response. Resveratrol inhibited the production of reactive oxygen species (ROS) by stimulated equine neutrophils by acting as a direct scavenger of the ROS released by the cells but did not modify the degranulation of the stimulated neutrophils as the amounts of released MPO were unchanged. Resveratrol strongly inhibited the chlorination, oxidation, and nitration activities of MPO in a dose-dependent manner. By an original technique of specific immunological extraction followed by enzymatic detection (SIEFED), we demonstrated that resveratrol inhibited the peroxidasic activity of the MPO measured by a direct interaction such as the fixation of resveratrol on the enzyme. The observation of a decrease of the accumulation of compound II suggested that resveratrol acts as an electron donor for MPO reduction.

Inhibition of the myeloperoxidase chlorinating activity by non-steroidal anti-inflammatory drugs: Flufenamic acid and its 5-chloro-derivative directly interact with a recombinant human myeloperoxidase to inhibit the synthesis of hypochlorous acid

The present in vitro study was designed to assess the inhibition of the myeloperoxidase (MPO)/H(2)O(2)/Cl(-) system by several non steroidal anti-inflammatory drugs (NSAIDs) of the oxicam family and of nimesulide and to compare their effect with flufenamic acid in order to investigate their influence on the chlorinating activity of MPO as a protective mechanism during chronic inflammatory syndromes. The inhibition of the system was assessed by measurement of the taurine chlorination while the accumulation of compound II was used to investigate the mechanism of inhibition. The oxidation products of NSAIDs by the MPO/H(2)O(2)/Cl(-) system were identified and flufenamic acid and derivatives were also assessed in the inhibition of LDL oxidation in two models. Flufenamic acid (IC(50) = 1.1+/-0.3 microM) is the most efficient inhibitor of the MPO/H(2)O(2)/Cl(-) system and nimesulide (IC(50) = 2.1+/-0.3 microM) is more active than the other NSAIDs of the oxicam family (IC(50) = 8-12 microM). The accumulation of compound II revealed that flufenamic acid acts as an electron donor while the other NSAIDs are antagonists of chloride anions. The identification of the oxidation products confirms that flufenamic behaves like an electron donor and is directly oxidized in the 5-hydroxy-derivative but gives also the 5-chloro-derivative which similarly inhibits the MPO/H(2)O(2)/Cl(-) system. Flufenamic acid has the best inhibiting activity towards the MPO/H(2)O(2)/Cl(-) system. However, in models that assess the LDL oxidation, flufenamic acid and its derivatives were unable to properly inhibit MPO activity as the enzyme is adsorbed on macrostructures such as LDL molecules.

Increased hydrogen peroxide concentration in the exhaled breath condensate of stable COPD patients after nebulized N-acetylcysteine

BACKGROUND

The oxidative burden in the airways is a hallmark of chronic obstructive pulmonary disease (COPD).

AIMS

This prospective, cross-over, placebo (PL)-controlled study was designed to investigate the effect of N-acetyl-l-cysteine (NAC) on hydrogen peroxide (H(2)O(2)), nitrites and nitrates (NO(2)(-)+NO(3)(-)), and thiol (RSH) concentrations in exhaled breath condensate (EBC) in stable COPD patients (n=19, aged 52.6+/-15.6 years, 10 females, mean FEV(1) 95.2+/-23.8%, FEV(1)/FVC 69.1+/-11.4%).

METHODS

H(2)O(2), NO(2)(-)+NO(3)(-) and RSH concentrations in EBC were determined with homovanillic acid, NADPH-nitrite reductase assays and Ellman's reaction, respectively.

RESULTS

Thirty minutes after nebulization, H(2)O(2) concentration increased if levels after NAC (0.45+/-0.25microM) and PL (0.17+/-0.17microM) were compared in COPD patients (p=0.002). This increased H(2)O(2) level in EBC was no longer observed either after 90min: 0.16+/-0.09microM (PL 0.17+/-0.15microM) or 3h: 0.12+/-0.07microM (PL 0.21+/-0.23microM) (p=0.5 and 0.2, respectively). The levels of NO(2)(-) and NO(3)(-) did not differ between NAC and PL. There was no significant difference in RSH levels between nebulized NAC and PL. After nebulized NAC, however, exhaled RSH increased from 1.42+/-1.69microM (0min) to 2.49+/-2.00microM (30min), and 1.71+/-1.83microM (180min) (p=0.009 and 0.03, respectively, compared with 0min).

CONCLUSIONS

These data demonstrate that nebulized NAC transiently increases exhaled H(2)O(2) level, whereas it has no effect on other oxidative parameters.

Captopril inhibits the oxidative modification of apolipoprotein B-100 caused by myeloperoxydase in a comparative in vitro assay of angiotensin converting enzyme inhibitors

The oxidative modification of low-density lipoproteins (LDL) is a key event in the formation of atheromatous lesions. Indeed, oxidized derivatives accumulate in the vascular wall and promote a local inflammatory process which triggers the progression of the atheromatous plaque. Myeloperoxidase (MPO) has been mentioned as a major contributor to this oxidative process. It takes part in the oxidation both of lipids by chlorination and peroxidation and of apolipoprotein B-100. Based on recent observations with several anti-inflammatory and thiol-containing drugs, the present study was designed to test the hypothesis that anti-hypertensive agents from the angiotensin converting enzyme (ACE) inhibitors group inhibit the oxidative modifications of Apo B-100 caused by MPO. Captopril, ramipril, enalapril, lisinopril and fosinopril were assessed by measuring: their inhibiting effect on the MPO/H(2)O(2)/Cl(-) system, the accumulation of compound II, which reflects the inhibition of the synthesis of HOCl and the LDL oxidation by MPO in presence of several concentrations of ACE inhibitors. Only captopril, a thiol-containing ACE inhibitor, was able to significantly decrease the oxidative modification of LDL in a dose dependent manner and this by scavenging HOCl. This efficient anti-hypertensive drug therefore appears to also protect against the atherosclerotic process by this newly documented mechanism.

Role of N-acetylcysteine in the management of COPD

The importance of the underlying local and systemic oxidative stress and inflammation in chronic obstructive pulmonary disease (COPD) has long been established. In view of the lack of therapy that might inhibit the progress of the disease, there is an urgent need for a successful therapeutic approach that, through affecting the pathological processes, will influence the subsequent issues in COPD management such as lung function, airway clearance, dyspnoea, exacerbation, and quality of life. N-acetylcysteine (NAC) is a mucolytic and antioxidant drug that may also influence several inflammatory pathways. It provides the sulfhydryl groups and acts both as a precursor of reduced glutathione and as a direct reactive oxygen species (ROS) scavenger, hence regulating the redox status in the cells. The changed redox status may, in turn, influence the inflammation-controlling pathways. Moreover, as a mucolytic drug, it may, by means of decreasing viscosity of the sputum, clean the bronchi leading to a decrease in dyspnoea and improved lung function. Nevertheless, as successful as it is in the in vitro studies and in vivo studies with high dosage, its actions at the dosages used in COPD management are debatable. It seems to influence exacerbation rate and limit the number of hospitalization days, however, with little or no influence on the lung function parameters. Despite these considerations and in view of the present lack of effective therapies to inhibit disease progression in COPD, NAC and its derivatives with their multiple molecular modes of action remain promising medication once doses and route of administration are optimized.