Neutrophil erythrotoxicity induced by phorbol myristate acetate: mechanisms involved in neutrophil activation

Proline-arginine rich (PR-39) cathelicidin: Structure, expression and functional implication in intestinal health

Proline-Arginine-39 (PR-39) is a small cationic, proline and arginine rich, cathelicidin that plays an important role in the porcine innate immune system. Although PR-39 was first discovered in intestinal cell lysates of pigs, subsequent research has indicated that it is primarily expressed in bone marrow and other lymphoid tissues including the thymus and spleen, as well as in leukocytes. Mature PR-39 cathelicidin has anti-microbial activity against many gram-negative and some gram-positive bacteria. PR-39 is also a bridge between the innate and adaptive immune system with recognized immunomodulatory, wound healing, anti-apoptotic, and pro-angiogenic functions. The purpose of this review is to summarize our current knowledge about the structure, expression, and functions of PR-39 and its potential to promote intestinal homeostasis. This understanding is relevant in the search of alternative therapeutics against diarrheic enterocolitis, a major problem faced by pork producers both in terms of costs and risk of zoonosis.

The hydroxypyridinone iron chelator CP94 increases methyl-aminolevulinate-based photodynamic cell killing by increasing the generation of reactive oxygen species

Methyl-aminolevulinate-based photodynamic therapy (MAL-PDT) is utilised clinically for the treatment of non-melanoma skin cancers and pre-cancers and the hydroxypyridinone iron chelator, CP94, has successfully been demonstrated to increase MAL-PDT efficacy in an initial clinical pilot study. However, the biochemical and photochemical processes leading to CP94-enhanced photodynamic cell death, beyond the well-documented increases in accumulation of the photosensitiser protoporphyrin IX (PpIX), have not yet been fully elucidated. This investigation demonstrated that MAL-based photodynamic cell killing of cultured human squamous carcinoma cells (A431) occurred in a predominantly necrotic manner following the generation of singlet oxygen and ROS. Augmenting MAL-based photodynamic cell killing with CP94 co-treatment resulted in increased PpIX accumulation, MitoSOX-detectable ROS generation (probably of mitochondrial origin) and necrotic cell death, but did not affect singlet oxygen generation. We also report (to our knowledge, for the first time) the detection of intracellular PpIX-generated singlet oxygen in whole cells via electron paramagnetic resonance spectroscopy in conjunction with a spin trap.

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Augmentation of MAL-based photodynamic cell killing with CP94 increases necrosis.

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CP94 augmentation increases generation of ROS, likely to be mitochondria-localised.

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PpIX-generated ¹O₂ was detected in whole cells by EPR spectroscopy.

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Photodynamic cell killing was dependent primarily on ¹O₂.

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Superoxide/other ROS also contributed to the efficacy of photodynamic cell killing.

Chemical and biological activity of free radical 'scavengers' in allergic diseases

Reactive oxygen species (ROS) are generated constantly in vivo. They can lead to lipid peroxidation and oxidation of some enzymes, as well as protein oxidation and degradation. Cells possess several biological systems, defined as 'scavengers', to protect themselves from the radical-mediated damage. Immune cells may discharge their arsenal of toxic agents against host tissues, resulting in oxidative damage and inflammation. Therefore, free radical production and disturbance in redox status can modulate the expression of a variety of immune and inflammatory molecules, leading to inflammatory processes, both exacerbating inflammation and effecting tissue damage. Recently, abnormal immunity has been related to oxidative imbalance, and antioxidant functions are linked to anti-inflammatory and/or immunosuppressive properties. Currently, allergy is one of the most important human diseases. We studied the role of the primary antioxidant defence system, constituted by the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase, protecting cells from toxic oxygen. We analyzed how they are involved in blood cells detoxification, and how the imbalance of reactive oxygen species is related to inflammation in allergic diseases by affecting immune cells. Finally, we discuss the published data that relates anti-free radical therapy to the management of human allergic diseases.

Effect of Nitric Oxide Donors on Oxygen-Dependent Cytotoxic Responses Mediated by Neutrophils

We analyzed the effect of nitric oxide (NO) on oxygen-dependent cytotoxic responses mediated by neutrophils against unopsonized erythrocytes using three NO donors: S-nitrosoglutathione (GSNO), S-nitroso-N-acetylpenicillamine (SNAP), and sodium nitroprusside (SNP). Neutrophils were treated with these compounds for 1–2 min at 37°C and cytotoxicity was then triggered in the presence of NO donors by precipitating immune complexes, aggregated IgG, the chemotactic peptide FMLP, or opsonized zymosan. GSNO induced, in all cases, a marked increase in cytotoxic responses, while SNAP moderately increased cytotoxicity triggered by immune complexes, aggregated IgG, or Z, opsonized zymosen, without modifying those responses induced by FMLP. By contrast, SNP dramatically suppressed cytotoxicity triggered by all of the stimuli assessed. The enhancing effects mediated by GSNO and SNAP did not depend on the stimulation of guanylyl cyclase and were prevented by the NO scavengers hemoglobin and PTIO (2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide). The inhibitory activity of SNP, on the other hand, was not prevented by NO scavengers, suggesting that it cannot be ascribed to the release of NO. In another set of experiments, neutrophils were pretreated with GSNO or SNAP for different times. Then cells were washed to remove NO donors from the culture medium, and cytotoxicity was triggered by different stimuli. It was found that neutrophils must be pretreated with NO donors for at least 4 h to increase cytotoxic responses, and pretreatment for longer periods (i.e., 8 or 18 h) further increased cytotoxicity. Not only cytotoxic responses, but also the production of O2− and H2O2, and the release of myeloperoxidase were increased under these conditions.

Neutrophil-independence of the initiation of colonic injury. Comparison of results from three models of experimental colitis in the rat

Although the role of neutrophils in the pathogenesis of several forms of gastrointestinal injury has been well demonstrated, their role in the development of experimental colonic injury is less clear. To examine whether neutrophils play a role in the development of experimental colitides, the effects of a sustained neutropenia on multiple indices of colonic injury in rats was examined 24 hr following the initiation of colitis with the intrarectal application of acetic acid, trinitrobenzene sulfonic acid (TNBS)-ethanol, or the potent proinflammatory agent, phorbol-12-myristate-13-acetate (PMA). In comparison to animals with normal neutrophil counts and colitis induced by any of the three agents, no attenuation in macroscopic damage or histopathologic injury was observed in neutropenic animals exhibiting a greater than 95% reduction in circulating neutrophils and 85% reduction in tissue-associated myeloperoxidase activity. Although the tissue edema associated with acetic acid or PMA-induced colitis was not reduced by neutropenia, the colonic edema associated with TNBS colitis was attenuated by prior neutrophil depletion with anti-neutrophil antiserum. Despite our initial hypothesis that neutrophils played a key role in the genesis of experimental colitis (especially that induced by PMA), the results demonstrated that these cells are not essential for the development of the major pathological features of colitis induced by this agent, acetic acid, or TNBS. Although these results support the proposal that in these models of colitis, inflammation develops secondary to injury (rather than the converse), further studies will be necessary to elucidate the role of inflammatory cells other than neutrophils in the genesis of experimental colitides.

LDL modification by activated polymorphonuclear leukocytes: a cellular model of mild oxidative stress

The purpose of this study was to determine the most potent activator of the respiratory burst of polymorphonuclear leukocytes (PMN) with respect to the oxidative modification of low density lipoprotein (LDL). Phorbol-12-myristate-13-acetate (PMA), n-formyl-methionyl-leucylphenylalanine (nFMLP), lipopolysaccharide (LPS), and opsonized zymosan (OZ) were tested. The generation of reactive oxygen species by PMN was assayed as superoxide anion production. Oxidative modification of LDL was monitored by thiobarbituric acid reactive substance (TBARS) activity, by conjugated dienes formation at 234nm and by electrophoretic mobility on agarose gel. PMA was the most potent activator of PMN, inducing a 6-fold increase in the superoxide anion production, followed by OZ (3-fold increase). PMA activation also induced the greatest modification of LDL by PMN: 700% increase of conjugated dienes formation, 222% increase of TBARS, and 70% increase in the electrophoretic mobility. The indices of oxidative modification significantly correlated with the superoxide anion generated by different activators. Also, LDL oxidation by PMN was inhibited by superoxide dismutase but not by catalase, methionine, or hydroxyl radical scavengers. Our data indicate that PMNs activated by PMA produce a mildly oxidized form of LDL by a mechanism that appears to involve the superoxide anion.

The paraproteins in systemic capillary leak syndrome

Systemic capillary leak syndrome (SCLS) is a rare disease characterized by episodes of collapse due to rapid transfer of considerable volumes of plasma from the intravascular to the extravascular compartment. The pathogenesis of this disease is unknown. The diagnosis is made largely on clinical grounds, and investigations are unhelpful. The only consistent abnormality is that an IgG paraprotein is found in most patients, raising the possibility that the paraprotein may be involved in the pathogenesis of the disease. Reduction of the paraprotein level in our patient was associated with remission. Blood samples from three SCLS patients and one probable SCLS have been studied. All patients had monoclonal IgG paraproteins. The purified paraproteins were all of IgG1 subclass and had kappa light chains. However, they differed in size and charge. Antibodies against each of the paraproteins were raised in rabbits. Affinity-purified anti-idiotypic antibodies were tested for cross-reactivity against the other paraproteins using immunoblotting and Ouchterlony assay. These assays showed that the anti-idiotypic antibodies reacted only with the immunizing paraprotein and not with any of the other paraproteins, i.e. that the paraproteins do not share a common idiotype. Paraproteins did not bind to cultured endothelial cells, either unactivated or following activation with interferon-gamma (IFN-gamma), IL-2 or IL-6. In addition, we were unable to demonstrate any cytotoxicity towards cultured human endothelial cells by paraprotein alone, or in the presence of neutrophils (pronounced neutrophilia being a feature of attacks). The relationship between the paraproteins and the disease remains unclear. It is likely that additional, as yet unidentified, factors are required for the paraprotein to lead to capillary leak.

Extracellular acidic pH modulates oxygen-dependent cytotoxic responses mediated by polymorphonuclear leucocytes and monocytes

In the present study, we compared the ability of human neutrophils and monocytes to display oxygen-dependent cytotoxic responses at pH 7.4 and 6.2. Our results show that cytotoxicity induced by immune complexes (IC), zymosan, N-formyl-methionyl-leucyl-phenylalanine (FMLP) and concanavalin A (Con A) were markedly increased when they were carried out at pH 6.2 instead of pH 7.4. Cytotoxicity induced by phorbol myristate acetate (PMA), on the contrary, was significantly decreased at pH 6.2. It is noteworthy that cytotoxic responses induced by IC, zymosan and Con A were also increased when, 2 h after effector cell stimulation at pH 6.2, cytotoxicity was measured at pH 7.4. Finally, when we examined possible mechanisms involved in the augmentation of cytotoxicity, we observed that the oxidative response of IC-stimulated neutrophils, measured as chemiluminescence emission, was not increased at pH 6.2, on the contrary, it was significantly decreased. The relevance of these results is discussed.