Exposure of macrophages to an enzymatically inactive macrophage mannose receptor ligand augments killing of Candida albicans

Development, optimization and validation of an absolute specific assay for active myeloperoxidase (MPO) and its application in a clinical context: role of MPO specific activity in coronary artery disease

Background Myeloperoxidase (MPO) is an enzyme with a recognized prognostic role in coronary artery disease (CAD), which is also emerging as a promising biomarker for cardiac risk stratification. However, the lack of a consensus method for its quantification has hindered its implementation in clinical practice. The aim of our work was to optimize an absolute sensitive assay for active MPO without external standards, to validate the method in the clinical context of CAD patients, and to estimate the enzyme specific activity. Methods In order to determine the MPO concentration using fluorescence readings, this ELISA assay exploits the activity of the enzyme recognized by specific antibodies. The assay was validated in a small cohort of patients that included: healthy subjects (n=60); patients with acute myocardial infarction (AMI, n=25); patients with stable CAD (SCAD, n=25) and a concomitant chronic obstructive pulmonary disease (COPD). Then, total MPO concentration and specific activity (activity/total MPO) were determined. Results The assay showed an intra- and inter-assay coefficient of variation of 5.8% and 10.4%, respectively, with a limit of detection (LoD) of 0.074 μU. Both AMI and SCAD patients had higher active and total MPO than controls (p<0.0001 and p<0.01, respectively). The specific activity of MPO was higher in SCAD patients compared to both controls and AMI (p<0.0001). Conclusions The study presents a robust and sensitive method for assaying MPO activity in biological fluids with low variability. Moreover, the determination of the specific activity could provide novel insight into the role of MPO in cardiovascular diseases (CVDs).

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

Syzygium aromaticum aqueous extract inhibits human neutrophils myeloperoxidase and protects mice from LPS-induced lung inflammation

CONTEXT

Syzygium aromaticum (L.) Merr. & Perry (Myrtaceae), commonly known as clove, originally found in the Muluku Islands in East Indonesia, is widely used as a spice and has numerous medicinal properties.

OBJECTIVE

This study investigated the antioxidant potential of S. aromaticum aqueous extract (SAAE) in vitro and its protective effects on lipopolysaccharide (LPS)-induced lung inflammation in mice.

MATERIAL AND METHODS

Neutrophils were isolated from healthy donors and reactive oxygen species (ROS) generation was measured by luminol-amplified chemiluminescence. Superoxide anion generation was detected by cytochrome c reduction assay. H₂O₂ was detected by DCFH fluorescence assay. Myeloperoxidase (MPO) activity was mesured by tetramethyl benzidine oxidation method. To study the anti-inflammatory activity of SAAE, lung inflammation was induced in mice (BALB/c) by intra-tracheal instillation of lypopolysaccharide (5 µg/mouse), and SAAE (200 mg/kg body weight) was injected intraperitoneally prior to LPS administration. Bronchoalveolar lavage and lung tissue were collected to assess inflammatory cells count and total protein content. Metalloproteinases activity was detected by zymography technique.

RESULTS

SAAE inhibited luminol-amplified chemiluminescence of resting neutrophils and N-formyl-methionyl-leucyl-phenylalanine- or phorbol myristate acetate-stimulated neutrophils, with an inhibitory effect starting at a concentration as low as 0.5 µg/mL. Moreover, SAAE reduced significantly MPO activity and it exhibits a dose-dependent action (IC₅₀ = 0.5 µg/mL). In vivo results showed that SAAE decreased markedly neutrophil count (From 61% to 15%) and proteins leakage into bronchoalveolar lavage fluid. Gelatin zymography assay showed that S. aromaticum inhibited MMP-2 (15%) and MMP-9 (18%) activity in lung homogenates.

DISCUSSION AND CONCLUSION

Our results suggest that the anti-inflammatory activity of SAAE, in vivo, is due to the inhibition of ROS production and metalloproteinases activity via its action on MPO. According to these findings, SAAE could be a potential source of new compounds with anti-inflammatory activity.

An aqueous pomegranate peel extract inhibits neutrophil myeloperoxidase in vitro and attenuates lung inflammation in mice

Punica granatum peel aqueous extract (PGE) is widely used to treat disorders such as inflammation, ulcers and infections, but its pharmacological target is not known. In this study we investigated the effect of PGE on human neutrophil reactive oxygen species (ROS) production in vitro and on LPS-induced lung inflammation in vivo in mice. Neutrophils were isolated and ROS generation was measured by luminol-amplified chemiluminescence. Superoxide anion generation was detected by the cytochrome c reduction assay. H(2)O(2) was detected by DCFH fluorescence assay. Myeloperoxidase (MPO) activity was measured by the tetramethyl benzidine oxidation method. Lung inflammation was induced in mice by LPS instillation. PGE inhibited luminol-amplified chemiluminescence of resting neutrophils and N-formyl-methionyl-leucyl-phenylalanine (fMLF)- or phorbol myristate acetate (PMA)-stimulated neutrophils, in a concentration-dependent manner. PGE had no effect on superoxide anion generation, suggesting that it does not directly inhibit NADPH oxidase activity or activation pathways, or scavenge superoxide anions. PGE did not scavenge H(2)O(2) but directly inhibited myeloperoxidase activity in vitro. In vivo studies showed that PGE also attenuated LPS-induced lung inflammation in mice. So this study reveals that PGE inhibits neutrophil MPO activity and attenuates LPS-induced lung inflammation in mice. Inhibition of MPO activity by PGE could explain its anti-inflammatory action.

Neutrophils: Cinderella of innate immune system

Neutrophils are the first line of innate immune defense against infectious diseases. However, since their discovery by Elie Metchnikoff, they have always been considered tissue-destructive cells responsible for inflammatory tissue damage occurring during acute infections. Now, extensive research in the field of neutrophil cell biology and their role skewing the immune response in various infections or inflammatory disorders revealed their importance in the regulation of immune response. Along with releasing various antimicrobial molecules, neutrophils also release neutrophil extracellular traps (NETs) for the containment of infection and inflammation. Activated neutrophils provide signals for the activation and maturation of macrophages as well as dendritic cells. Neutrophils are also involved in the regulation of T-cell immune response against various pathogens and tumor antigens. Thus, the present review is intended to highlight the emerging role of neutrophils in the regulation of both innate and adaptive immunity during acute infectious or inflammatory conditions.

Microglia and myeloperoxidase: a deadly partnership in neurodegenerative disease

The role of inflammation in Alzheimer's disease, Parkinson's disease, and multiple sclerosis has recently come under increased scrutiny. Associated with these inflammatory responses are tumor necrosis factor-alpha (TNF-alpha) and reactive oxygen species (ROS), both believed to be derived from brain microglia. In addition to the above, the presence of myeloperoxidase (MPO) in these diseased brains has been reported by a number of investigators. However, the possible role of MPO and enzymatically inactive MPO (iMPO) as the "choreographers" of the destruction done by TNF-alpha and ROS is not generally recognized. Previously, our laboratory has reported that MPO/iMPO enhance macrophage generation of ROS and expression of proinflammatory cytokine genes as well as gene products. Recent studies in our laboratory indicate that the same response occurs with microglia. A paradigm is presented for the perpetuation of inflammation associated with neurodegenerative diseases. This model describes the unrecognized consequences of the stimulation of microglia by MPO or iMPO. Both MPO and iMPO and/or its receptor may represent new therapeutic targets for the treatment of these diseases.

An evaluation of the biological and toxicological properties of Aloe barbadensis (miller), Aloe vera

Aloe barbadensis (Miller), Aloe vera, has a long history of use as a topical and oral therapeutic. The plant is the source of two products, gel and latex, which are obtained from its fleshy leaves. Aloe vera products contain multiple constituents with potential biological and toxicological activities, yet the active components elude definition. Ingestion of Aloe vera is associated with diarrhea, electrolyte imbalance, kidney dysfunction, and conventional drug interactions; episodes of contact dermatitis, erythema, and phototoxicity have been reported from topical applications. This review examines the botany, physical and chemical properties, and biological activities of the Aloe vera plant.

Dietary supplementation with phosphorylated mannans improves growth response and modulates immune function of weanling pigs

Phosphorylated mannans derived from the yeast cell wall of Saccharomyces cerevisiae may beneficially modulate immune function in the weanling pig, possibly providing an alternative to the use of dietary growth-promoting antibiotics. Therefore, in this study, 32 pigs averaging 19 d of age and 5.7 +/- 0.2 kg initial BW were randomly assigned to 16 pens in an environmentally controlled nursery to determine the effects of dietary supplementation with phosphorylated mannans on growth and immune function. Average daily gain and G:F ratio increased (P < 0.05) when pigs were fed diets supplemented with mannans from d 0 to 14 after weaning and in the overall experiment. Percentage of neutrophils was lower (P < 0.08) and percentage of lymphocytes was higher (P < 0.05) in blood from pigs fed mannans than when pigs were fed the basal diet. Lamina propria macrophages isolated from pigs fed diets containing mannans phagocytosed a greater (P < 0.05) number of sheep red blood cells (2.63 +/- 0.11) than did lamina propria macrophages isolated from pigs fed the basal diet (2.31 +/- 0.11). On d 19 after weaning, pigs fed diets supplemented with mannans tended to have a greater (P < 0.10) percentage of CD14+ lamina propria leukocytes than did pigs fed the basal diet. On d 21 following weaning, the percentage of CD14+MHCII+ leukocytes isolated from lamina propria tissue tended (P < 0.10) to be lower when pigs were fed mannans than when pigs were fed the basal diet. Pigs fed diets containing mannans had a lower (P < 0.05) ratio of CD3+CD4+:CD3+CD8+ T lymphocytes isolated from jejunal lamina propria tissue only on d 21 after weaning compared with pigs fed the basal diet. Supplementation of mannans in the diets of weanling pigs improved gain and efficiency, and intermittently affected selected components of the young pigs' immune function both systemically and enterically.

The expression of mannose receptors in skin fibroblast and their involvement in Leishmania (L.) amazonensis invasion

Leishmania are protozoa that invade mononuclear phagocytes with the involvement of different ligand-receptor systems, including mannose receptors. Until now, scant data are available concerning the mechanisms that govern the infection of Leishmania in other host cell types such as fibroblasts. Our aim was to analyze the expression of mannose receptors in primary cultures of skin fibroblasts (SF) further characterizing their role during the invasion of promastigotes of Leishmania (L.) amazonensis. Both fluorescent, light, and electron microscopy assays revealed that SF have mannose receptors since they bound and internalized mannosylated ligands in addition to being positively labeled by fuc-BSA-FITC probes. d-mannose competition assays revealed the participation of mannose receptors during the parasite association with SF presenting upregulated receptor expression during the initial steps of the infection. After longer periods of Leishmania:fibroblasts contact, the modulation noted in the host mannose receptors was reverted concomitantly to the infection control, suggesting that the parasites were required for the alteration maintenance and providing evidences that the SF may display microbicidal mechanisms to control the Leishmania infection.

Alveolar macrophage activation by myeloperoxidase: a model for exacerbation of lung inflammation

Inflammation of the lung is characterized by the influx of increased numbers of various leukocytes including polymorphonuclear leukocyte (PMN) neutrophils. In addition to cells, numerous studies have pointed to the role of tumor necrosis factor-alpha in the inflammatory process. This study addresses a previously unrecognized interaction between neutrophil-derived myeloperoxidase (MPO) and resident alveolar macrophages (AMø). Rat AMø exposed to either enzymatically active recombinant MPO or enzymatically inactive MPO (iMPO) exhibited an increased respiratory burst (RB). When iMPO was employed, the enhancement of the RB was greater than that observed with MPO. Although the RB was greater with iMPO, macrophage (Mø)-mediated intracellular candidic activity was equivalent for both MPO and iMPO. It is known that pro- inflammatory cytokines contribute to the inflammatory process. When rat AMø were exposed to both forms of myeloperoxidase, iMPO demonstrated greater upregulation of cytokine genes as well as product. These data suggest that at the site of inflammation, neutrophil-derived MPO and iMPO stimulate AMø, resulting in an increased inflammatory and cytotoxic state, and thereby contributing to the general lung inflammatory response.

Macrophage-neutrophil interaction: a paradigm for chronic inflammation revisited

Macrophages have been described as 'factories' of pro-inflammatory cytokines. Several years ago the present investigators reported that binding of inactive myeloperoxidase (iMPO) to the macrophage-mannose receptor resulted in the induction of TNF and other cytokines. Also, if endothelial cells were incubated with iMPO, but not enzymatically active myeloperoxidase (MPO), upregulation of cytokine mRNA and cytokines was observed. Taken in their entirety, the data suggest a dichotomy of function for myeloperoxidase; that is, enzymatically active MPO functions primarily in cell killing through the 'cytotoxic triad' and iMPO functions as an immunoregulatory molecule through the induction of numerous cytokines. These studies underscore a previously unrecognized interaction among neutrophils, endothelial cells and macrophages, resulting in the induction of TNF and perpetuation of inflammation. The inflammation induced could be relevant in a number of diseases in which neutrophils play a prominent role. The importance of this interaction in the pathogenesis of rheumatoid arthritis is currently under investigation.

A novel bovine lactoferrin peptide, FKCRRWQWRM, suppresses Candida cell growth and activates neutrophils

To identify potent new antifungal agents, the Candida cell growth inhibitory activities of six lactoferrin (Lf) peptides consisting of 6-25 amino acid residues (peptide 1, FKCRRWQWRMKKLGAPSITCVRRAF lactoferricin B; peptide 2, FKCRRWQWRM; peptide 2', FKARRWQWRM; peptide 3, GAPSITCVRRAF; peptide 4, RRWQWR; and peptide 5, RWQWRM) were examined. Of these, peptide 2 strongly suppressed the multiplication of Candida cells, but other peptides showed only weak activities. In two strains of C. albicans, the minimum inhibitory concentration 100 of peptide 2 (17.3+/-2.2 microM and 17.5+/-2.4 microM) was close to that of miconazole (13.0+/-1.7 microM and 13.1+/-1.6 microM) but markedly different from that of amphotericin B (0.52+/-0.09 microM and 0.56+/-0.11 microM). The suppression of Candida cell growth was additively increased by a combination of peptide 2 with amphotericin B and miconazole. Peptides 1, 3, 4 and 5 and Lf suppressed iron uptake by Candida cells, inversely correlated with their Candida cell growth inhibition activities. However, iron uptake was not inhibited by peptide 2. In addition, peptide 2 upregulated Candida cell killing activity of polymorphonuclear leukocytes (PMN) increasing their superoxide generation, protein kinase C activity, p38 MAPK activity and the expression of p47phox. These results indicated that the main antimicrobial activity of the Lf peptides is dependent on the N-terminal half of Lf and that the PMN upregulatory activity of peptide 2 and additive function of peptide 2 with antifungal drugs are useful for prophylaxis and control of candidiasis.

Effects of a glyconutrient on macrophage functions

Previous studies have shown that mannosylated bovine serum albumin (mBSA) enhances the respiratory burst (RB), phagocytosis, and killing of Candida albicans and Escherichia coli by resident murine peritoneal macrophages (Mphi). Upregulation of the above Mphi functions was associated with the binding of mBSA to the macrophage mannose receptor. The present study was done to determine if certain glyconutrients could stimulate Mphi functions in a similar manner. Resident peritoneal murine Mphi collected from C57BL/6 mice were exposed to the glyconutrients for 10 and 60 min. The RB was measured using chemiluminescence. Both phagocytosis and killing were measured after incubation with each of the following microorganisms: Candida albicans, Escherichia coli and Staphylococcus aureus. The percent phagocytosis and killing were determined using fluorescence microscopy. Results indicated that certain glyconutrients, caused a dose and time dependent effect on Mphi-induced killing of all three microorganisms.

Cellular and molecular mechanisms of glial scarring and progressive cavitation: in vivo and in vitro analysis of inflammation-induced secondary injury after CNS trauma

Post-traumatic cystic cavitation, in which the size and severity of a CNS injury progress from a small area of direct trauma to a greatly enlarged secondary injury surrounded by glial scar tissue, is a poorly understood complication of damage to the brain and spinal cord. Using minimally invasive techniques to avoid primary physical injury, this study demonstrates in vivo that inflammatory processes alone initiate a cascade of secondary tissue damage, progressive cavitation, and glial scarring in the CNS. An in vitro model allowed us to test the hypothesis that specific molecules that stimulate macrophage inflammatory activation are an important step in initiating secondary neuropathology. Time-lapse video analyses of inflammation-induced cavitation in our in vitro model revealed that this process occurs primarily via a previously undescribed cellular mechanism involving dramatic astrocyte morphological changes and rapid migration. The physical process of cavitation leads to astrocyte abandonment of neuronal processes, neurite stretching, and secondary injury. The macrophage mannose receptor and the complement receptor type 3 beta2-integrin are implicated in the cascade that induces cavity and scar formation. We also demonstrate that anti-inflammatory agents modulating transcription via the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma may be therapeutic in preventing progressive cavitation by limiting inflammation and subsequent secondary damage after CNS injury.

Neutrophilic myeloperoxidase-macrophage interactions perpetuate chronic inflammation associated with experimental arthritis

Rheumatoid arthritis is a systemic disease of unknown etiology. The purpose of this study was to elucidate an unrecognized interaction between neutrophilic myeloperoxidase (MPO) and macrophages (Mphi) which could perpetuate the inflammatory response associated with arthritis. A monoarticular arthritis was induced by intra-articular injection of group A streptococcus cell wall fragments (PG-APS) into the ankle joint of female Lewis rats. After swelling/erythema subsided, joints were reinjected with either recombinant MPO or enzymatically inactive MPO (iMPO). Joint measurements were made daily and arthritis was confirmed by histology. Neither iMPO nor MPO could initiate "clinical" arthritis; however, either form of the enzyme injected after PG-APS induced a dose-dependent increase in erythema and swelling. Mannans, which block the binding of MPO to Mo, ablated clinical symptoms. Also, the presence of tumor necrosis factor alpha was observed only in diseased joints using immunocytochemistry.

The mannose receptor mediates uptake of pathogenic and nonpathogenic mycobacteria and bypasses bactericidal responses in human macrophages

The mannose receptor (MR) is involved in the phagocytosis of pathogenic microorganisms. Here we investigated its role in the bactericidal functions of human monocyte-derived macrophages (MDMs), using (i) trimannoside-bovine serum albumin (BSA)-coated latex beads and zymosan as particulate ligands of the MR, and (ii) mannan and mannose-BSA as soluble ligands. We show that phagocytosis of mannosylated latex beads did not elicit the production of O2-. Zymosan, which is composed of alpha-mannan and beta-glucan, was internalized by the MR and a beta-glucan receptor, but the production of O2- was triggered only by phagocytosis through the beta-glucan receptor. Activation and translocation of Hck, a Src family tyrosine kinase located on lysosomes, has previously been used as a marker of fusion between lysosomes and phagosomes in human neutrophils. In MDMs, Hck was activated and recruited to phagosomes containing zymosan later than LAMP-1 and CD63. Phagosomes containing mannosylated latex beads fused with LAMP-1 and CD63 vesicles but not with the Hck compartment, and the kinase was not activated. We also demonstrate that the MR was unable to distinguish between nonpathogenic and pathogenic mycobacteria, as they were internalized at similar rates by this receptor, indicating that this route of entry cannot be considered as a differential determinant of the intracellular fate of mycobacteria. In conclusion, MR-dependent phagocytosis is coupled neither to the activation of NADPH oxidase nor to the maturation of phagosomes until fusion with the Hck compartment and therefore constitutes a safe portal of entry for microorganisms.

Inhibition of tumor necrosis factor and subsequent endotoxin shock by pirfenidone

Tumor necrosis factor-alpha (TNF) is an extremely potent cytokine which is involved in the pathogenesis of a number of diseases. Interruption of its synthesis can result in a reduction of inflammation and subsequent pathology. A new experimental drug pirfenidone (5-methyl-L-phenyl-2-(1H)-pyridone, trade name: Deskar) has been reported to have beneficial effects for the treatment of certain fibrotic diseases. The present study describes the inhibition of TNF in vitro as well as the inhibition of circulating TNF in vivo by pirfenidone. Isolated, thioglycollate-induced peritoneal macrophages (Mphi) from C57BL/6 mice were exposed to either lipopolysaccharide (LPS) or mannosylated bovine serum albumin then incubated with 0.1-0.9 mg/ml of pirfenidone. This substance inhibited the production of TNF in a dose-dependent manner as measured by ELISA. One i.p. injection of either 100 or 200 mg/kg pirfenidone inhibited the induction of circulating TNF following a single i.v. injection of LPS. Endotoxin shock was induced in mice using an i.p. injection of galactosamine and LPS. The higher dose of pirfenidone (200 mg/kg) completely inhibited shock and subsequent mortality. Lower doses of pirfenidone or administration either prior to or post challenge only partially inhibited symptoms. These results indicate that pirfenidone is able to inhibit both TNF induction and subsequent endotoxin shock. Additional studies are warranted to establish this drug as a potential treatment for diseases where TNF plays a major role.

Perpetuation of inflammation associated with experimental arthritis: the role of macrophage activation by neutrophilic myeloperoxidase

Rheumatoid arthritis (RA) is characterized by an abnormal cellular and cytokine infiltration of inflamed joints. This study addresses a previously unrecognized interaction between neutrophilic-myeloperoxidase (MPO) and macrophages (Mphi) which could explain the perpetuation of inflammation associated with RA. A monoarticular arthritis was induced in female Lewis rats by injection of streptococcal cell wall extracts (PG-APS). After swelling and erythema subsided, joints were re-injected with one of the following: porcine MPO or partially inactivated MPO (iMPO). Injection with either MPO or iMPO induced a 'flare' of experimental RA. Blocking the Mphi-mannose receptor by mannans, ablated exacerbation of disease. These results indicate that MPO or iMPO can play a pivotal role in the perpetuation but not initiation of this RA model.