Novel aspects of the activation of NADPH oxidase in neutrophils of rheumatic patients on biological therapy.

The relationship between inflammation and formation of reactive oxygen species (ROS) is still not completely understood and excessive inflammatory reaction is attributed to increased yet also to reduced ROS formation. To compare ROS formation in severe and low inflammation, neutrophil oxidative burst was analyzed in rheumatic patients before and during therapy with TNFα- or interleukin-6 receptor-neutralizing antibodies. Intracellular and extracellular ROS productions were evaluated on the basis of luminol- and isoluminol-enhanced chemiluminescence in isolated peripheral neutrophils. Disease activity score DAS28 and platelet to lymphocyte ratio were used as markers of arthritis activity and the intensity of systemic inflammation. Biological therapy effectively reduced the intensity of inflammation. Of the twenty-six patients studied eighteen achieved remission or low disease activity. Highly active arthritis persisted only in one patient, though prior to the therapy it was evident in all subjects tested. In patients receiving biological therapy, intracellular chemiluminescence was significantly higher than in patients before this therapy; ROS produced by neutrophils extracellularly were not affected. The increased ROS formation associated with reduced inflammation supports the need to revise the view of the role of ROS in inflammation - from toxic agents promoting inflammation towards a more complex view of ROS as regulators of immune pathways with inflammation-limiting capacity. From this perspective, the interference with neutrophil-derived oxidants may represent a new mechanism involved in the anti-inflammatory activity of biological therapy.

Increased intracellular and extracellular oxidant production in phagocytes of rheumatic patients treated with biological therapy - whole blood quantification.

Infectious complications, resulting from reduced activity of immune cells, are the most severe and common adverse effects of biological therapy. This study analyzed the effect of biological therapy on blood phagocytes, focusing on the formation of reactive oxygen species (ROS), an important factor in the defence against invading pathogens. Intra- and extracellular ROS production were recorded separately, on the basis of luminol and isoluminol chemiluminescence in patients treated with antibodies against tumor necrosis factor-α or against interleukin-6 receptor. In comparison to healthy donors or to rheumatic patients treated with classical immunosuppressive drugs, biological therapy increased ROS formation in both compartments. This indicates that the anti-microbial activity of blood phagocytes was not reduced by TNFα- or IL-6-neutralizing therapy, at least in terms of ROS. The method presented does not require blood fractionation, which could modify activity of phagocytes and cause loss of some subpopulations of these cells. The technique is simple, requires microliter volumes of blood and is thus well applicable to clinical studies.

Effect of N-Feruloylserotonin and Methotrexate on Severity of Experimental Arthritis and on Messenger RNA Expression of Key Proinflammatory Markers in Liver.

Rheumatoid arthritis (RA) is a chronic inflammatory disease, leading to progressive destruction of joints and extra-articular tissues, including organs such as liver and spleen. The purpose of this study was to compare the effects of a potential immunomodulator, natural polyphenol N-feruloylserotonin (N-f-5HT), with methotrexate (MTX), the standard in RA therapy, in the chronic phase of adjuvant-induced arthritis (AA) in male Lewis rats. The experiment included healthy controls (CO), arthritic animals (AA), AA given N-f-5HT (AA-N-f-5HT), and AA given MTX (AA-MTX). N-f-5HT did not affect the body weight change and clinical parameters until the 14th experimental day. Its positive effect was rising during the 28-day experiment, indicating a delayed onset of N-f-5HT action. Administration of either N-f-5HT or MTX caused reduction of inflammation measured as the level of CRP in plasma and the activity of LOX in the liver. mRNA transcription of TNF-α and iNOS in the liver was significantly attenuated in both MTX and N-f-5HT treated groups of arthritic rats. Interestingly, in contrast to MTX, N-f-5HT significantly lowered the level of IL-1ß in plasma and IL-1ß mRNA expression in the liver and spleen of arthritic rats. This speaks for future investigations of N-f-5HT as an agent in the treatment of RA in combination therapy with MTX.

Ex Vivo and In Vitro Studies on the Cytotoxicity and Immunomodulative Properties of Poly(2-isopropenyl-2-oxazoline) as a New Type of Biomedical Polymer.

Poly(2-alkenyl-2-oxazoline)s are promising functional polymers for a variety of biomedical applications, such as drug delivery systems, peptide conjugates, or gene delivery. In this study, poly(2-isopropenyl-2-oxazoline) (PIPOx) is prepared through free-radical polymerization initiated with azobisisobutyronitrile. Reactive 2-oxazoline units in the side chain support an addition reaction with different compounds containing a carboxylic group, which facilitates the preparation of polymers labeled with two different fluorescent dyes. The cytotoxicities of 2-oxazoline monomers, PIPOx, and fluorescently labeled PIPOx are evaluated in vitro using an 3-(4,5-Dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and ex vivo using a cell proliferation assay with adenosine triphosphate bioluminescence. The cell uptake of labeled PIPOx is used to determine the colocalization of PIPOx with cell organelles that are part of the endocytic pathway. For the first time, it is shown that poly(2-isopropenyl-2-oxazoline) is a biocompatible material and is suitable for biomedical applications; further, its immunomodulative properties are evaluated.

Equol Effectively Inhibits Toxic Activity of Human Neutrophils without Influencing Their Viability.

Equol (7,4'-dihydroxy-isoflavan, or 4',7-isoflavandiol) is a chroman derivative produced by intestinal bacteria in response to soy isoflavone intake in some, but not in all, humans. Equol shows strong anti-oxidant, anti-estrogenic, anti-cancerous and anti-inflammatory properties. The antioxidative capacity of equol has recently received considerable attention, and it has been used for preventing and treating several diseases. We investigated the effect of equol on human neutrophils, extra- and intracellular formation of oxidants, the phosphorylation of protein regulating NADPH oxidase and its effect on apoptosis. Neutrophils, isolated from blood from healthy subjects, were tested upon activation with various stimulants, proper for reactive oxygen species (ROS) production and treated by equol. Equol has the ability to reduce the toxic action of neutrophils. With increasing concentrations, equol decreased the amount of oxidants produced by neutrophils both extra- and intracellularly. The phosphorylation of p40(phox) (a component of NADPH oxidase, responsible for the assembly of functional oxidase in intracellular membranes) was reduced in the presence of equol. The experiments showed that equol did not change the number of viable, apoptotic or dead neutrophils significantly in all concentrations used. These results indicate the promising effect of equol in the operation of ROS in different mechanisms in the model of inflammation.

Selective inhibition of extracellular oxidants liberated from human neutrophils--A new mechanism potentially involved in the anti-inflammatory activity of hydroxychloroquine.

Hydroxychloroquine is used in the therapy of rheumatoid arthritis or lupus erythematosus. Although these diseases are often accompanied by activation of neutrophils, there are still few data relating to the impact of hydroxychloroquine on these cells. We investigated the effect of orally administered hydroxychloroquine on neutrophil oxidative burst in rats with adjuvant arthritis. In human neutrophils, extra- and intracellular formation of oxidants, mobilisation of intracellular calcium and the phosphorylation of proteins regulating NADPH oxidase assembly were analysed. Administration of hydroxychloroquine decreased the concentration of oxidants in blood of arthritic rats. The inhibition was comparable with the reference drug methotrexate, yet it was not accompanied by a reduction in neutrophil count. When both drugs were co-applied, the effect became more pronounced. In isolated human neutrophils, treatment with hydroxychloroquine resulted in reduced mobilisation of intracellular calcium, diminished concentration of external oxidants and in decreased phosphorylation of Ca(2+)-dependent protein kinase C isoforms PKCα and PKCßII, which regulate activation of NADPH oxidase on plasma membrane. On the other hand, no reduction was observed in intracellular oxidants or in the phosphorylation of p40(phox) and PKCδ, two proteins directing the oxidase assembly to intracellular membranes. Hydroxychloroquine reduced neutrophil-derived oxidants potentially involved in tissue damage and protected those capable to suppress inflammation. The observed effects may represent a new mechanism involved in the anti-inflammatory activity of this drug.

Molecular pharmacology of antihistamines in inhibition of oxidative burst of professional phagocytes.

Antihistamines of the H1and H3/H4groups interfere with oxidative burst of human professional phagocytes in vitro. In the concentration of 10 µM, H1antihistamines of the 1st and 2nd generation inhibited oxidative burst of human neutrophils in the rank order of potency: dithiaden > loratadine > brompheniramine > chlorpheniramine > pheniramine. Of the H1antihistamines, the most effective was dithiaden in suppressing oxidative burst of whole human blood and dose-dependently the chemiluminescence of isolated neutrophils at extra- and intracellular level. Inhibition of free oxygen radical generation in isolated neutrophils by dithiaden resulted from the inhibition of protein kinase C activation. The potentiation of recombinant caspase-3 by dithiaden is supportive of the antiinflammatory effect of dithiaden and suggestive of increasing the apoptosis of professional phagocytes. Of the H3/H4antihistamines, the most effective was JNJ7777120 in decreasing chemiluminescence in whole blood and also at extra- and intracellular sites of isolated neutrophils. JNJ 10191584 and thioperamide were less effective and the latter significantly potentiated free oxygen radical generation intracellularly. The results demonstrated that, compared with the H3/H4antihistamines investigated, H1antihistamines were much more potent in inhibiting free oxygen radical generation in human professional phagocytes. This finding should be taken into account therapeutically.

Markers of inflammation and oxidative stress studied in adjuvant-induced arthritis in the rat on systemic and local level affected by pinosylvin and methotrexate and their combination.

Oxidative stress (OS) is important in the pathogenesis of autoimmune diseases such as rheumatoid arthritis (RA) and its experimental model--adjuvant arthritis (AA). Antioxidants are scarcely studied in autoimmunity, and future analyses are needed to assess its effects in ameliorating these diseases. Although there are studies about antioxidants effects on the course of RA, their role in combination therapy has not yet been studied in detail, especially on extra-articular manifestations of AA. During the 28-d administration of pinosylvin (PIN) in monotherapy and in combination with methotrexate (MTX) to AA rats, we evaluated the impact of the treatment on selected parameters. The experiment included: healthy controls, untreated AA, AA administered 50 mg/kg b.w. of PIN daily p.o., AA administered 0.4 mg/kg b.w. of MTX twice weekly p.o. and AA treated with a combination of PIN+MTX. AA was monitored using: hind paw volume, C-reactive protein, monocyte chemotactic protein-1 (MCP-1), thiobarbituric acid reactive substances (TBARS) and F2-isoprostanes in plasma, γ-glutamyltransferase activity in spleen, activity of lipoxygenase (LOX) in lung, heme oxygenase-1 (HO-1) and nuclear factor kappa B (NF-κB) in liver and lung. PIN monotherapy significantly improved the activation of NF-κB in liver and lung, HO-1 expression and activity of LOX in the lung, MCP-1 levels in plasma (on 14th d) and plasmatic levels of F2-isoprostanes. An important contribution of PIN to MTX effect was the reduction of OS (an increase of HO-1 expression in lung and reduction of plasmatic TBARS) and decrease of LOX activity in the lung.

N-feruloylserotonin in preventive combination therapy with methotrexate reduced inflammation in adjuvant arthritis.

Many of disease-modifying anti-rheumatic drugs often have side effects at high doses and/or during long-term administration. Increased efficacy without increased toxicity is expected for combination therapy of rheumatoid arthritis (RA). The aim of the study was to examine the effect of N-feruloylserotonin (N-f-5HT) and methotrexate (MTX) in monotherapy and in combination therapy on disease progression and inflammation in arthritic rats. Adjuvant arthritis was induced by intradermal injection of Mycobacterium butyricum in incomplete Freund's adjuvant in Lewis rats. The experiment included healthy animals, arthritic animals without any drug administration, arthritic animals with administration of N-f-5HT in the oral daily dose of 15 mg/kg b.w., arthritic animals with administration of MTX in the oral dose of 0.3 mg/kg b.w. twice a week and arthritic animals treated with the combination of N-f-5HT and MTX. N-f-5HT in monotherapy reduced only activation of NF-κB and did not have any significant effect on other parameters monitored. Low-dose treatment of MTX decreased the level of IL-1ß and MCP-1 on day 14 and activation of NF-κB in liver without significant effect on other parameters. N-f-5HT and MTX combination showed both the anti-arthritic (hind paw volume and arthritic score) and anti-inflammatory effect (plasmatic levels of IL-1ß, IL-17, MCP-1, CRP, and activation of NF-κB in liver). In combination with MTX, N-f-5HT markedly potentiated the therapeutic effect of MTX low dose, which resulted in significant improvement of all parameters measured. The findings showed that the combination therapy simultaneously decreased multiple markers of inflammation, a result crucial for future therapy of RA.

On the molecular pharmacology of resveratrol on oxidative burst inhibition in professional phagocytes.

Resveratrol-3,5,4'-trihydroxystilbene-possesses antioxidant activities in vitro. It dose-dependently inhibited the generation of peroxyl, hydroxyl, peroxides, and lipid peroxidation products in cell free systems. Oxidative burst of whole human blood stimulated with PMA, fMLP, OpZ, and A23187 was inhibited in a concentration-dependent way, indicating suppression of both receptor and nonreceptor activated chemiluminescence by resveratrol. Results from isolated human neutrophils revealed that resveratrol was active extracellularly as well as intracellularly in inhibiting the generation of reactive oxygen species. Liberation of ATP and analysis of apoptosis showed that in the concentration of 100 µM, resveratrol did not change the viability and integrity of isolated neutrophils. Western blot analysis documented that resveratrol in concentrations of 10 and 100 µM significantly decreased PMA-induced phosphorylation of PKC α/ß II. Dose-dependent inhibition of nitrite production and iNOS protein expression in RAW 264.7 cells indicated possible interference of resveratrol with reactive nitrogen radical generation in professional phagocytes. The results suggest that resveratrol represents an effective naturally occurring substance with potent pharmacological effect on oxidative burst of human neutrophils and nitric oxide production by macrophages. It should be further investigated for its pharmacological activity against oxidative stress in ischaemia reperfusion, inflammation, and other pathological conditions, particularly neoplasia.

Role of histamine receptors in the effects of histamine on the production of reactive oxygen species by whole blood phagocytes.

AIMS: The diverse physiological functions of histamine are mediated through distinct histamine receptors. In this study we investigated the role of H2R and H4R in the effects of histamine on the production of reactive oxygen species by phagocytes in whole blood. MAIN METHODS: Changes in reactive oxygen species (ROS) production by whole blood phagocytes after treatment with histamine, H4R agonists (4-methylhistamine, VUF8430), H2R agonist (dimaprit) and their combinations with H4R antagonist (JNJ10191584) and H2R antagonist (ranitidine) were determined using the chemiluminescence (CL) assay. To exclude the direct scavenging effects of the studied compounds on the CL response, the antioxidant properties of all compounds were measured using several methods (TRAP, ORAC, and luminol-HRP-H2O2 based CL). KEY FINDINGS: Histamine, 4-methylhistamine, VUF8430 and dimaprit inhibited the spontaneous and OZP-activated whole blood CL in a dose-dependent manner. On the other hand, only VUF8430 was able to inhibit PMA-activated whole blood CL. Ranitidine, but not JNJ10191584, completely reduced the effects of histamine, 4-methylhistamine and dimaprit. The direct scavenging ability of tested compounds was negligible. SIGNIFICANCE: Our results demonstrate that the inhibitory effects of histamine on ROS production in whole blood phagocytes were caused by H2R. Our results also suggest that H4R agonists in concentrations higher than 10(-6)M may also influence ROS production via binding to H2R.

Arbutin and decrease of potentially toxic substances generated in human blood neutrophils.

Neutrophils, highly motile phagocytic cells, constitute the first line of host defense and simultaneously they are considered to be central cells of chronic inflammation. In combination with standard therapeutic procedures, natural substances are gaining interest as an option for enhancing the effectiveness of treatment of inflammatory diseases. We investigated the effect of arbutin and carvedilol and of their combination on 4ß-phorbol-12ß-myristate-13α-acetate- stimulated functions of human isolated neutrophils. Cells were preincubated with the drugs tested and subsequently stimulated. Superoxide (with or without blood platelets, in the rate close to physiological conditions [1:50]) and HOCl generation, elastase and myeloperoxidase release were determined spectrophotometrically and phospholipase D activation spectrofluorometrically. The combined effect of arbutin and carvedilol was found to be more effective than the effect of each compound alone. Our study provided evidence supporting the potential beneficial effect of arbutin alone or in combination with carvedilol in diminishing tissue damage by decreasing phospholipase D, myeloperoxidase and elastase activity and by attenuating the generation of superoxide and the subsequently derived reactive oxygen species. The presented data indicate the ability of arbutin to suppress the onset and progression of inflammation.

Can semi-synthetic flavonoids return old microglia to their youthful state?

A number of studies have indicated that brain inflammation may deteriorate during normal aging and that neuroinflammation is amplified in age-related neurodegenerative diseases. A pivotal role in age-related neuroinflammatory pathologies is attributed to amplified and prolonged activation of microglia. In addition, microglia from the aged brain were reported as senescent displaying many functional impairments. Flavonoids were shown to be promising molecules in modulation of neuroinflammation. Quercetin, a naturally occurring flavonoid, was proven to downregulate inflammatory genes in microglia. Synthetically modified quercetin, 3´-O-(3-chloropivaloyl)quercetin (CPQ), is assumed to posses better biological availability and enhanced antioxidant properties. In the present study, the antineuroinflammatory capacity of CPQ was assessed in BV-2 microglial cells and rat primary microglia. CPQ suppressed more efficiently than its precursor quercetin LPS-induced NO production and iNOS protein expression. However, neither of the compounds tested influenced significantly phagocytosis of BV-2 cells. In addition, CPQ showed a somewhat better suppression of PMA-induced generation of superoxide than did quercetin. Unlike quercetin, CPQ caused a decline in BV-2 microglia proliferation (without any impact on cell viability) along with interference with cell cycle progression. Both compounds tested at 10uM concentration notably enhanced viability of microglia-enriched cultures prepared from 22-month-old rat brains. This was followed by suppression of lipofuscin-like autofluorescence, improvement of lysosomal function and protection of mitochondria in the old microglia. These results can highlight the therapeutic potential of CPQ as a novel antiinflammatory drug in neurodegenerative diseases. In addition, our data suggest that both natural and semisynthetic flavonoids might protect functions of old microglia [VEGA2/0031/12,1/0076/13;APVV-0052-10;ITMS26240220040].

Study of possible mechanisms involved in the inhibitory effects of coumarin derivatives on neutrophil activity.

To specify the site of action of the synthetic coumarin derivatives 7-hydroxy-3-(4'-hydroxyphenyl) coumarin (HHC) and 7-hydroxy-3-(4'-hydroxyphenyl) dihydrocoumarin (HHDC), we evaluated their effects on extra- and intracellular reactive oxygen species (ROS) formation in phorbol-myristate-13-acetate (PMA) stimulated human neutrophils. We studied also the effects of HHC and HHDC on possible molecular mechanisms which participate in the activation of NADPH oxidase, that is, on PKC activity, on phosphorylation of some PKC isoforms (α, ßII, and δ), and on phosphorylation of the NADPH oxidase subunit p40(phox). Without affecting cytotoxicity, both coumarines tested were effective inhibitors/scavengers of ROS produced by neutrophils on extracellular level. HHC markedly diminished oxidant production and also, intracellularly, decreased PKC activity and partly phosphorylation of PKCα, ßII. On the other hand, we did not observe any effect of coumarin derivatives on phosphorylation of PKC δ and on phosphorylation of the NADPH oxidase subunit p40(phox), which were suggested to be involved in the PMA-dependent intracellular activation process. In agreement with our previous findings, we assume that the different molecular structures of HHC and HHDC with their different physicochemical and free radical scavenging characteristics are responsible for their diverse effects on the parameters tested.

The effects of pterostilbene on neutrophil activity in experimental model of arthritis.

It has been demonstrated that pterostilbene inhibits reactive oxygen species production in neutrophils in vitro. However, little is known about its effects on neutrophils during inflammation in vivo. In this study, the effect of pterostilbene on neutrophil activity was investigated in experimental arthritis model. Lewis rats were injected by a single intradermal injection of heat-killed Mycobacterium butyricum in Freund's adjuvant to develop arthritis. Another group of arthritic animals received pterostilbene 30 mg/kg, daily, p.o. The number and activity of neutrophils in blood were measured on a weekly basis during the whole experiment. Moreover, the total radical trapping potential in plasma was measured at the end of the experiment. In the pterostilbene treated arthritic group, the treatment significantly lowered the number of neutrophils in blood on days 14 and 21 without significant downregulation of neutrophil oxidative burst. Pterostilbene nonsignificantly increased total radical trapping potential in arthritic animals. These results indicate that the promising effects of pterostilbene on reactive oxygen species operate by different mechanisms in vitro and in the animal model of inflammation. In conclusion, the positive effects of pterostilbene in the model of arthritis may be attributed to regulation of neutrophil number.

The natural stilbenoid piceatannol decreases activity and accelerates apoptosis of human neutrophils: involvement of protein kinase C.

Neutrophils are able to release cytotoxic substances and inflammatory mediators, which, along with their delayed apoptosis, have a potential to maintain permanent inflammation. Therefore, treatment of diseases associated with chronic inflammation should be focused on neutrophils; formation of reactive oxygen species and apoptosis of these cells represent two promising targets for pharmacological intervention. Piceatannol, a naturally occurring stilbenoid, has the ability to reduce the toxic action of neutrophils. This substance decreased the amount of oxidants produced by neutrophils both extra- and intracellularly. Radicals formed within neutrophils (fulfilling a regulatory role) were reduced to a lesser extent than extracellular oxidants, potentially dangerous for host tissues. Moreover, piceatannol did not affect the phosphorylation of p40(phox)-a component of NADPH oxidase, responsible for the assembly of functional oxidase in intracellular (granular) membranes. The stilbenoid tested elevated the percentage of early apoptotic neutrophils, inhibited the activity of protein kinase C (PKC)-the main regulatory enzyme in neutrophils, and reduced phosphorylation of PKC isoforms α , ß II, and δ on their catalytic region. The results indicated that piceatannol may be useful as a complementary medicine in states associated with persisting neutrophil activation and with oxidative damage of tissues.

Effect of stilbene derivative on superoxide generation and enzyme release from human neutrophils in vitro.

Neutrophils represent the body's primary line of defense against invading pathogens. They most rapidly reach the site of injury or infection, liberate antimicrobial proteins, proteases and produce reactive oxygen species. Prolonged or excessive liberation of these very effective and toxic substances could intensify the inflammatory process and enhance tissue damage in many diseases, such as allergies, infections and rheumatoid arthritis. Pterostilbene belongs to stilbenoids, structural analogues of resveratrol, which act as natural protective agents in defending the plant against viral and microbial attack. It possesses anticancerous, antidiabetic and anti-inflammatory properties.The study provides new information on the effect of pterostilbene [0.01-100 µmol/l] on superoxide generation in and myeloperoxidase (MPO) release from azurophil granules of isolated human neutrophils. PMA [1µmol/l], which activates NADPH-oxidase via protein kinase C, was used for stimulation of neutrophils Unstimulated cells showed neither superoxide generation nor myelopereoxidase release after preincubation with the drug studied. Pterostilbene dose dependently decreased superoxide generation in and MPO release from stimulated human neutrophils, however a significant decrease was recorded only in the concentration 100 µmol/l. The effect of pterostilbene was more pronounced on superoxide generation in comparison to MPO release. Our results suggest that the effect of pterostilbene may prove beneficial in controlling inflammation.

Decreased activity and accelerated apoptosis of neutrophils in the presence of natural polyphenols.

Prolonged or excessive formation and liberation of cytotoxic substances from neutrophils intensifies inflammation and the risk of tissue damage. From this perspective, administration of substances which are able to reduce activity of neutrophils and to enhance apoptosis of these cells may improve the therapy of pathological states connected with persistent inflammation. In this short review, neutrophil oxidative burst and apoptosis are presented as potential targets for pharmacological intervention. Effects of natural polyphenols (resveratrol, pterostilbene, pinosylvin, piceatannol, curcumin, N-feruloylserotonin) are summarised, considering the ability of these compounds to affect inflammation and particularly neutrophil activity. The intended neutrophil inhibition is introduced as a part of a new strategy for pharmacological modulation of chronic inflammatory processes, focused on supporting innate anti-inflammatory mechanisms and enhancing resolution of inflammation.

Polyphenol derivatives - potential regulators of neutrophil activity.

The study provides new information on the effect of natural polyphenols (derivatives of stilbene - resveratrol, pterostilbene, pinosylvin and piceatannol and derivatives of ferulic acid - curcumin, N-feruloylserotonin) on the activity of human neutrophils in influencing oxidative burst. All the polyphenols tested were found to reduce markedly the production of reactive oxygen species released by human neutrophils on extra-and intracellular levels as well as in cell free system. Moreover, pinosylvin, curcumin, N-feruloylserotonin and resveratrol decreased protein kinase C activity involved in neutrophil signalling and reactive oxygen species production. Our results suggest that due to their anti-neutrophil activity, the polyphenols tested might be attractive candidates in therapeutic development.

Quercetin inhibits degranulation and superoxide generation in PMA stimulated neutrophils.

Activated neutrophils represent the main source of myeloperoxidase (MPO), superoxide (SO) and subsequently derived oxygen metabolites. They have important microbicidal activities, however in inflammatory conditions they may secondarily attack surrounding tissues. Overproduction of reactive oxygen species, prolonged or excessive liberation of MPO and other effective yet also toxic substances from neutrophils may participate in disturbed apoptosis, intensify the inflammatory processes and result in serious human diseases. The inhibitory effect of quercetin on PMA stimulated SO generation in isolated human neutrophils was found to be dose-dependent, without affecting the activity of intact isolated neutrophils. At comparable conditions, quercetin was more potent in inhibiting MPO release than SO generation. Our results indicate that quercetin could support resolution of inflammation through decreased activity of neutrophils, i.e. respiratory burst and degranulation.