Activation of Nitric Oxide Release and Oxidative Metabolism by Leukotrienes B4, C4, and D4 in Human Polymorphonuclear Leukocytes

Metabolic regulation of neutrophil functions in homeostasis and diseases

Neutrophils are the most abundant leukocytes in humans and play a role in the innate immune response by being the first cells attracted to the site of infection. While early studies presented neutrophils as almost exclusively glycolytic cells, recent advances show that these cells use several metabolic pathways other than glycolysis, such as the pentose phosphate pathway, oxidative phosphorylation, fatty acid oxidation, and glutaminolysis, which they modulate to perform their functions. Metabolism shifts from fatty acid oxidation-mediated mitochondrial respiration in immature neutrophils to glycolysis in mature neutrophils. Tissue environments largely influence neutrophil metabolism according to nutrient sources, inflammatory mediators, and oxygen availability. Inhibition of metabolic pathways in neutrophils results in impairment of certain effector functions, such as NETosis, chemotaxis, degranulation, and reactive oxygen species generation. Alteration of these neutrophil functions is implicated in certain human diseases, such as antiphospholipid syndrome, coronavirus disease 2019, and bronchiectasis. Metabolic regulators such as AMPK, HIF-1α, mTOR, and Arf6 are linked to neutrophil metabolism and function and could potentially be targeted for the treatment of diseases associated with neutrophil dysfunction. This review details the effects of alterations in neutrophil metabolism on the effector functions of these cells.

The nitric oxide-cyclic GMP-KATP channels pathway contributes to the effects of montelukast against gastric damage induced by ethanol

The leukotrienes, lipid mediators, have a role in gastric damage induced by ethanol. Here, the gastroprotective effect of montelukast, an antagonist of the leukotriene receptor, and the involvement of the NO-cGMP-KATP channel pathway, were evaluated in gastric damage induced by ethanol in rats. For this, l-arginine, l-NAME, methylene blue (guanylate cyclase inhibitor), sildenafil, diazoxide, or glibenclamide (ATP-sensitive potassium channel blocker) were administered 30 min before montelukast (0.1, 1, 10, and 20 mg/kg, by mouth [p.o.]). After 1 h, to induce gastric damage, the rats received absolute ethanol (4 mL/kg, p.o.), and then microscopic, macroscopic, and pro-inflammatory parameters (TNF-α and IL-1β) were assessed. Results obtained here revealed that montelukast significantly attenuated the macroscopic and microscopic lesions induced by ethanol. Montelukast also reduced IL-1β and TNF-α levels. It was also observed that NOS inhibitor (l-NAME), methylene blue, and glibenclamide inhibited the effects of montelukast in the stomach. Moreover, the NO precursor (l-arginine), the PDE-5 inhibitor (sildenafil), and a potassium channel opener (diazoxide) before montelukast produced gastroprotective effects. In conclusion, the effect of montelukast against gastric lesions induced by ethanol is mediated, at least in part, through the pathway of the NO-cGMP-KATP channel.

The emerging role for metabolism in fueling neutrophilic inflammation

Neutrophils are a critical element of host defense and are rapidly recruited to inflammatory sites. Such sites are frequently limited in oxygen and/or nutrient availability, presenting a metabolic challenge for infiltrating cells. Long believed to be uniquely dependent on glycolysis, it is now clear that neutrophils possess far greater metabolic plasticity than previously thought, with the capacity to generate energy stores and utilize extracellular proteins to fuel central carbon metabolism and biosynthetic activity. Out-with cellular energetics, metabolic programs have also been implicated in the production of neutrophils and their progenitors in the bone marrow compartment, activation of neutrophil antimicrobial responses, inflammatory and cell survival signaling cascades, and training of the innate immune response. Thus, understanding the mechanisms by which metabolic processes sustain changes in neutrophil effector functions and how these are subverted in disease states provides exciting new avenues for the treatment of dysfunctional neutrophilic inflammation which are lacking in clinical practice to date.

Montelukast, a cysteinyl leukotriene receptor antagonist, exerts local antinociception in animal model of pain through the L-arginine/nitric oxide/cyclic GMP/KATP channel pathway and PPARγ receptors

OBJECTIVE

The leukotrienes are inflammatory mediators. In the present study, the analgesic role of local montelukast, a cysteinyl leukotriene receptor antagonist, and the possible involvement of L-arginine/NO/cGMP/KATP channel pathway and PPARγ receptors was assessed in the formalin test in rats.

METHODS AND RESULTS

The local administration of montelukast into the hind paw produced dose-related analgesia during both phases of the formalin test. Furthermore, pre-treatment with L-NAME, methylene blue, and glibenclamide prevented montelukast (10 μg/paw)-induced antinociception in both early and late phases of the test. Moreover, the local L-arginine and diazoxide before the sub-effective dose of montelukast (3 μg/paw) produced an analgesic effect. Also, local GW-9662 blocked antinociception induced by montelukast plus pioglitazone (10 μg/paw).

CONCLUSION

In conclusion, montelukast produced peripheral analgesia through PPARγ receptors and activation of the L-arginine/NO/cGMP/KATP channel pathway, with potential for a new topical analgesic drug.

Comorbidity of Neurally Mediated Syncope and Allergic Disease in Children

Neurally mediated syncope (NMS) is the most common underlying disease of pediatric syncope, which generally includes vasovagal syncope (VVS), postural tachycardia syndrome (POTS), and situational syncope. Allergic diseases involving the respiratory system, digestive system, skin, and other systems are prevalent in children. In recent years, increasing attention has been paid to children with the comorbidity of NMS and allergic diseases. This article reviews the featured clinical manifestations and pathogenesis of the comorbidity according to the progress of related studies. Clinical studies have shown that the comorbidity rate of pediatric VVS and/or POTS with allergic diseases amounts to ~30-40%, referring to the whole population of children with VVS and/or POTS. Additionally, children with the comorbidity present some relatively special clinical characteristics. A series of mechanisms or regulatory factors relating to allergies, such as the imbalance of vasoactive elements, dysfunction of the autonomic nervous system (ANS), and autoimmunity may play a role in the development of the comorbidity. Moreover, 90% of children with cough syncope, a type of situational syncope, have a history of asthma, indicating a potential relationship between asthma and NMS. Further studies exploring the clinical characteristics and pathogenesis of the comorbidity are still needed to aid in the diagnosis and treatment of children with NMS.

Differences in cNOS/iNOS Activity during Resistance to Trypanosoma cruzi Infection in 5-Lipoxygenase Knockout Mice

Infection with the protozoan Trypanosoma cruzi causes Chagas disease and consequently leads to severe inflammatory heart condition; however, the mechanisms driving this inflammatory response have not been completely elucidated. Nitric oxide (NO) is a key mediator of parasite killing in T. cruzi-infected mice, and previous studies have suggested that leukotrienes (LTs) essentially regulate the NO activity in the heart. We used infected 5-lipoxygenase-deficient mice (5-LO^−/−) to explore the participation of nitric oxide synthase isoforms, inducible (iNOS) and constitutive (cNOS), in heart injury, cytokine profile, and oxidative stress during the early stage of T. cruzi infection. Our evidence suggests that the cNOS of the host is involved in the resistance of 5-LO^−/− mice during T. cruzi infection. iNOS inhibition generated a remarkable increase in T. cruzi infection in the blood and heart of mice, whereas cNOS inhibition reduced cardiac parasitism (amastigote nests). Furthermore, this inhibition associates with a higher IFN-γ production and lower lipid peroxidation status. These data provide a better understanding about the influence of NO-interfering therapies for the inflammatory response toward T. cruzi infection.

Early Production of the Neutrophil-Derived Lipid Mediators LTB4 and LXA4 Is Modulated by Intracellular Infection with Leishmania major

Recruitment of neutrophil granulocytes to sites of infectious tissue damage is an early event in innate immune responses. Following chemotactic signals neutrophils establish a first line of defense in a swarm-like manner. Intracellular pathogens such as Leishmania major can, however, evade neutrophil-mediated killing and survive inside neutrophils. To achieve this the parasites evolved potent evasion mechanisms. Since neutrophils are a major source of inflammation regulating lipid mediators, we hypothesized that intracellular infection modifies the release of pro- and anti-inflammatory lipid mediators like leukotriene B4 (LTB₄) and lipoxin A4 (LXA₄), respectively. In the present study, we demonstrated in vitro that L. major-infected primary human neutrophils release an increased amount of LTB₄, whereas LXA₄ liberation is reduced during the first hours of infection. To investigate whether lipid mediator modulation is a common feature in intracellular infections, we tested the impact of an infection with Anaplasma phagocytophilum. Similarly to L. major, neutrophil infection with A. phagocytophilum led to an enhanced release of LTB₄ and decreased LXA₄ production. Together, our findings indicate that intracellular infections modulate the lipid mediator profile of neutrophils. This effect is likely to contribute to the survival of the pathogens in neutrophils and to the outcome of the infections.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

Biomarkers for differentiation of causes of respiratory distress in dogs and cats: Part 2--Lower airway, thromboembolic, and inflammatory diseases

OBJECTIVES

To review the current veterinary and relevant human literature regarding biomarkers of respiratory diseases leading to dyspnea and to summarize the availability, feasibility, and practicality of using respiratory biomarkers in the veterinary setting.

DATA SOURCES

Veterinary and human medical literature: original research articles, scientific reviews, consensus statements, and recent textbooks.

HUMAN DATA SYNTHESIS

Numerous biomarkers have been evaluated in people for discriminating respiratory disease processes with varying degrees of success.

VETERINARY DATA SYNTHESIS

Although biomarkers should not dictate clinical decisions in lieu of gold standard diagnostics, their use may be useful in directing care in the stabilization process. Serum immunoglobulins have shown promise as an indicator of asthma in cats. A group of biomarkers has also been evaluated in exhaled breath. Of these, hydrogen peroxide has shown the most potential as a marker of inflammation in asthma and potentially aspiration pneumonia, but methods for measurement are not standardized. D-dimers may be useful in screening for thromboembolic disease in dogs. There are a variety of markers of inflammation and oxidative stress, which are being evaluated for their ability to assess the severity and type of underlying disease process. Of these, amino terminal pro-C-type natriuretic peptide may be the most useful in determining if antibiotic therapy is warranted. Although critically evaluated for their use in respiratory disorders, many of the biomarkers which have been evaluated have been found to be affected by more than one type of respiratory or systemic disease.

CONCLUSION

At this time, there are point-of-care biomarkers that have been shown to reliably differentiate between causes of dyspnea in dogs and cats. Future clinical research is warranted to understand of how various diseases affect the biomarkers and more bedside tests for their utilization.

V-PYRRO/NO downregulates mRNA expression levels of leukotriene C4 synthase during hepatic ischemia reperfusion injury in rats via inhibition of the nuclear factor-κB activation pathway

The aim of the present study was to explore the mechanism underlying the effects of a selective liver nitric oxide (NO) donor, O²-vinyl1-(pyrrolidin-1-yl)-diazen-1-ium-1,2-diolate (V-PYRRO/NO), on the gene expression of leukotriene C4 synthase (LTC4S) during hepatic ischemia/reperfusion (I/R). Adult male Sprague-Dawley rats were divided into 3 groups: Sham (control), I/R and V-PYRRO/NO + I/R groups. The liver was subjected to 1 h of partial hepatic ischemia followed by 5 h of reperfusion, saline or V-PYRRO/NO (1.06 µmol/kg/h) administered intravenously. The mRNA expression levels of LTC4S in rat liver tissue were examined by the reverse transcription-polymerase chain reaction method, the protein expression levels of nuclear factor-κB (NF-κB) p65, p50 and IκBα in liver cell lysates and nuclear extracts were detected by western blot analysis. Hepatic mRNA expression of LTC4S was lower in V-PYRRO/NO + I/R group compared to the I/R group. In addition, the protein expression levels of NF-κB p65 and p50 in the nucleus extract were lower in the V-PYRRO/NO + I/R group when compared with the I/R group. However, the IκBα protein in the 3 groups was not changed. Immunohistochemistry staining revealed that the I/R liver exhibited strong cytoplasmic and nuclear staining for NF-κB p65; however, the V-PYRRO/NO + I/R group liver presented slight cytoplasmic and nuclear staining. In conclusion, V-PYRRO/NO may downregulate LTC4S mRNA expression by inhibiting NF-κB activation independent of IκBα during hepatic I/R injury.

Degranulating Neutrophils Promote Leukotriene B4 Production by Infected Macrophages To Kill Leishmania amazonensis Parasites

Neutrophils mediate early responses against pathogens, and they become activated during endothelial transmigration toward the inflammatory site. In the current study, human neutrophils were activated in vitro with immobilized extracellular matrix proteins, such as fibronectin (FN), collagen, and laminin. Neutrophil activation by FN, but not other extracellular matrix proteins, induces the release of the granules' contents, measured as matrix metalloproteinase 9 and neutrophil elastase activity in culture supernatant, as well as reactive oxygen species production. Upon contact with Leishmania amazonensis-infected macrophages, these FN-activated neutrophils reduce the parasite burden through a mechanism independent of cell contact. The release of granule proteases, such as myeloperoxidase, neutrophil elastase, and matrix metalloproteinase 9, activates macrophages through TLRs, leading to the production of inflammatory mediators, TNF-α and leukotriene B4 (LTB4), which are involved in parasite killing by infected macrophages. The pharmacological inhibition of degranulation reverted this effect, abolishing LTB4 and TNF production. Together, these results suggest that FN-driven degranulation of neutrophils induces the production of LTB4 and TNF by infected macrophages, leading to the control of Leishmania infection.

Role of leukotrienes in diabetic retinopathy

The pathophysiology of diabetic retinopathy is highly complex and encompasses the detrimental roles of numerous factors/mediators in inducing various molecular pathological alterations. Although the roles of many inflammatory mediators, involved in the progression of this complication, have been thoroughly researched and studied, the part played by leukotrienes remains widely neglected. This review focuses on leukotrienes-induced mediation and aggravation of the pathological pathways, such as inflammation, oxidative stress and retinal angiogenesis, responsible for exhibition of various characteristic events including leukostasis, macular edema, retinal neovascularization and vitreous hemorrhages, hence, marking the advent of diabetic retinopathy. Acknowledging these roles, it might be possible to potentially utilize leukotrienes antagonists for suppressing or reducing the intensity of the mentioned pathological alterations. Hence, leukotrienes antagonists may act as an effective adjuvant therapy either along with other developing novel therapies (such as anti-VEGF or anti-TNF-α therapy), or with the established conventional laser photocoagulation treatment, to provide additional symptomatic relief or, possibly prevent the progression of diabetic retinopathy.

Matrikines are key regulators in modulating the amplitude of lung inflammation in acute pulmonary infection

Bioactive matrix fragments (matrikines) have been identified in a myriad of disorders, but their impact on the evolution of airway inflammation has not been demonstrated. We recently described a pathway where the matrikine and neutrophil chemoattractant proline–glycine–proline (PGP) could be degraded by the enzyme leukotriene A₄ hydrolase (LTA₄H). LTA₄H classically functions in the generation of pro-inflammatory leukotriene B₄, thus LTA₄H exhibits opposing pro- and anti-inflammatory activities. The physiological significance of this secondary anti-inflammatory activity remains unknown. Here we show, using readily resolving pulmonary inflammation models, that loss of this secondary activity leads to more pronounced and sustained inflammation and illness owing to PGP accumulation. PGP elicits an exacerbated neutrophilic inflammation and protease imbalance that further degrades the extracellular matrix, generating fragments that perpetuate inflammation. This highlights a critical role for the secondary anti-inflammatory activity of LTA₄H and thus has consequences for the generation of global LTA₄H inhibitors currently being developed.

Proteases degrade extracellular matrix during inflammation, releasing peptides that can recruit neutrophils. Here the authors show that degradation of such bioactive peptide by the enzyme leukotriene A4 hydrolase is critical to limit pulmonary inflammation during bacterial infection in mice.

Microvesicles: ubiquitous contributors to infection and immunity

MVs, which can be subgrouped into exosomes, SVs, and OMVs, are secreted by eukaryotic and prokaryotic cells. Many previously inexplicable phenomena can be explained by the existence of these vesicles, as they appear to be important in a wide range of biologic processes, such as intercellular communication and transfer of functional genetic information. In this review, we discuss the immunologic roles of MVs during sterile insult and infectious disease. MVs contribute to clotting initiation, cell recruitment, and neovascularization during wound healing. In the context of pathogen infection, both the host and the pathogen use MVs for communication and defense. MVs are exploited by various viruses to evade the host immune response and contribute to viral spread. Bacteria produce MVs that contain virulence factors that contribute to disease pathology and antibiotic resistance. This review summarizes the role of MVs in the pathology and resolution of disease.

Cysteinyl leukotriene receptor-1 antagonists as modulators of innate immune cell function

Cysteinyl leukotrienes (cysLTs) are produced predominantly by cells of the innate immune system, especially basophils, eosinophils, mast cells, and monocytes/macrophages. Notwithstanding potent bronchoconstrictor activity, cysLTs are also proinflammatory consequent to their autocrine and paracrine interactions with G-protein-coupled receptors expressed not only on the aforementioned cell types, but also on Th2 lymphocytes, as well as structural cells, and to a lesser extent neutrophils and CD8⁺ cells. Recognition of the involvement of cysLTs in the immunopathogenesis of various types of acute and chronic inflammatory disorders, especially bronchial asthma, prompted the development of selective cysLT receptor-1 (cysLTR1) antagonists, specifically montelukast, pranlukast, and zafirlukast. More recently these agents have also been reported to possess secondary anti-inflammatory activities, distinct from cysLTR1 antagonism, which appear to be particularly effective in targeting neutrophils and monocytes/macrophages. Underlying mechanisms include interference with cyclic nucleotide phosphodiesterases, 5′-lipoxygenase, and the proinflammatory transcription factor, nuclear factor kappa B. These and other secondary anti-inflammatory mechanisms of the commonly used cysLTR1 antagonists are the major focus of the current review, which also includes a comparison of the anti-inflammatory effects of montelukast, pranlukast, and zafirlukast on human neutrophils in vitro, as well as an overview of both the current clinical applications of these agents and potential future applications based on preclinical and early clinical studies.

Understanding the mechanisms controlling Leishmania amazonensis infection in vitro: the role of LTB4 derived from human neutrophils

Neutrophils are rapidly recruited to the site of Leishmania infection and play an active role in capturing and killing parasites. They are the main source of leukotriene B₄ (LTB₄), a potent proinflammatory lipid mediator. However, the role of LTB₄ in neutrophil infection by Leishmania amazonensis is not clear. In this study, we show that L. amazonensis or its lipophosphoglycan can induce neutrophil activation, degranulation, and LTB₄ production. Using pharmacological inhibitors of leukotriene synthesis, our findings reveal an LTB₄-driven autocrine/paracrine regulatory effect. In particular, neutrophil-derived LTB₄ controls L. amazonensis killing, degranulation, and reactive oxygen species production. In addition, L. amazonensis infection induces an early increase in Toll-like receptor 2 expression, which facilitates parasite internalization. Nuclear factor kappa B (NFkB) pathway activation represents a required upstream event for L. amazonensis–induced LTB₄ synthesis. These leishmanicidal mechanisms mediated by neutrophil-derived LTB₄ act through activation of its receptor, B leukotriene receptor 1 (BLT1).

The pivotal role of 5-lipoxygenase-derived LTB4 in controlling pulmonary paracoccidioidomycosis

Leukotrienes (LTs) produced from arachidonic acid by the action of 5-lipoxygenase (5-LO) are classical mediators of inflammatory responses. However, studies published in the literature regarding these mediators are contradictory and it remains uncertain whether these lipid mediators play a role in host defense against the fungal pathogen Paracoccidioides brasiliensis. To determine the involvement of LTs in the host response to pulmonary infection, wild-type and LT-deficient mice by targeted disruption of the 5-lipoxygenase gene (knockout mice) were studied following intratracheal challenge with P. brasiliensis yeasts. The results showed that infection is uniformly fatal in 5-LO-deficient mice and the mechanisms that account for this phenotype are an exacerbated lung injury and higher fungal pulmonary burden. Genetic ablation or pharmacological inhibition of LTs resulted in lower phagocytosis and fungicidal activity of macrophages in vitro, suggesting that deficiency in fungal clearance seems to be secondary to the absence of activation in 5-LO(-/-) macrophages. Exogenous LTB4 restored phagocytosis and fungicidal activity of 5-LO(-/-) macrophages. Moreover, P. brasiliensis killing promoted by LTB4 was dependent on nitric oxide (NO) production by macrophages. Taken together, these results reveal a fundamental role for 5-LO-derived LTB4 in the protective response to P. brasiliensis infection and identify relevant mechanisms for the control of fungal infection during the early stages of the host immune response.

Role of cysteinyl leukotriene receptor-1 antagonists in treatment of experimentally induced mammary tumor

It has been reported that a leukotriene (LT)-D4 receptor (i.e. cysteinyl LT1 receptor; CysLT1R) has an important role in carcinogenesis. The current study was carried out to assess the possible antitumor effects of montelukast (MON), a CysLT1R antagonist, in a mouse mammary carcinoma model, that is, a solid Ehrlich carcinoma (SEC). Effects of MON on tumor-induced immune dysfunction and the possibility that MON may modulate the antitumor and immunomodulatory effects of doxorubicin (DOX) were also studied. The effects in tumor-bearing hosts of several dosings with MON (10 mg/kg, per os), with and without the added presence of DOX (2 mg/kg, intraperitoneal), were investigated in vivo; end points evaluated included assessment of tumor volume, splenic lymphocyte profiles/functionality, tumor necrosis factor-α content, as well as apoptosis and expression of nuclear factor-κB (NF-κB) among the tumor cells. The data indicate that MON induced significant antitumor activity against the SEC. MON treatments also significantly mitigated both tumor- and DOX-induced declines in immune parameters assessed here. Moreover, MON led to decreased NF-κB nuclear expression and, in doing so, appeared to chemosensitize these tumor cells to DOX-induced apoptosis.

Eicosanoids and respiratory viral infection: coordinators of inflammation and potential therapeutic targets

Viruses are frequent causes of respiratory infection, and viral respiratory infections are significant causes of hospitalization, morbidity, and sometimes mortality in a variety of patient populations. Lung inflammation induced by infection with common respiratory pathogens such as influenza and respiratory syncytial virus is accompanied by increased lung production of prostaglandins and leukotrienes, lipid mediators with a wide range of effects on host immune function. Deficiency or pharmacologic inhibition of prostaglandin and leukotriene production often results in a dampened inflammatory response to acute infection with a respiratory virus. These mediators may, therefore, serve as appealing therapeutic targets for disease caused by respiratory viral infection.

Bacterial toll-like receptor agonists induce sequential NF-κB-mediated leukotriene B4 and prostaglandin E2 production in chicken heterophils

Studies of the response of the primary avian polymorphonuclear leukocyte, the heterophil, to microbe associated molecular patterns (MAMPs) through toll-like receptors (TLR) has concentrated on the activation of the respiratory burst, release of intracellular granules, and the induction of cytokine and chemokine expression. Virtually no studies have been described on the role of lipid mediators, leukotrienes and prostaglandins, as effectors of the avian inflammatory response. We have previously shown that flagellin (FLG), the bacterial lipoprotein mimic palmitoly-3-cysteine-serine-lysine-4 (PAM), and unmethylated CpG motifs of bacteria DNA (CpG) are all potent activators of the avian innate immune system. In the present studies, we hypothesized that FLG, PAM, and CpG are also capable of eliciting the production of these lipid mediators of inflammation by avian heterophils. Compared to non-stimulated control heterophils, all three TLR agonists were potent inducers (3-5-fold increase) of a rapid production (30 min) of leukotriene B(4) (LTB(4)) followed by a later release (60-120 min) of prostaglandin (PGE(2)) by the heterophils. LTB(4) and PGE(2) production were derived from lipoxygenase-5 (5-LO) and cyclooxygenase-2 (COX-2) enzymatic activities, respectively, as the selective 5-LO (caffeic acid) and COX-2 (NS-398) inhibitors eliminated LTB(4) and PGE(2) production from the MAMP-stimulated heterophils. These results demonstrate that both the lipoxygenase and cycloxygenase pathways are operational in avian heterophils in response to bacterial MAMPs. Treatment of heterophils with either FLG, PAM, or CpG also induced a significant increase in DNA binding by NF-κB family members' p50, c-Rel, and RelB. Additionally, the production of LTB(4) and PGE(2) were inhibited following treatment of heterophils with the specific pharmacologic inhibitor of NF-κB (Bay 11-7086), thus suggesting that TLR pathway activation of NF-κB controls LTB(4) and PGE(2) production. This the first report of the production of lipid mediators of inflammation by avian heterophils in response to PAMPs. Since FLG, lipoproteins, and bacterial CpG DNA are abundant during bacterial infections, these data support their role in the inflammatory response mediated by avian heterophils.

Old and new generation lipid mediators in acute inflammation and resolution

Originally regarded as just membrane constituents and energy storing molecules, lipids are now recognised as potent signalling molecules that regulate a multitude of cellular responses via receptor-mediated pathways, including cell growth and death, and inflammation/infection. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. The diversity of their actions arises because such metabolites are synthesised via discrete enzymatic pathways and because they elicit their response via different receptors. This review will collate the bioactive lipid research to date and summarise the findings in terms of the major pathways involved in their biosynthesis and their role in inflammation and its resolution. It will include lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins and maresins).

Intrapulmonary administration of leukotriene B4 enhances pulmonary host defense against pneumococcal pneumonia

Leukotriene B(4) (LTB(4)) is a potent lipid mediator of inflammation formed by the 5-lipoxygenase (5-LO)-catalyzed oxidation of arachidonic acid. We have previously shown that (i) LTB(4) is generated during infection, (ii) its biosynthesis is essential for optimal antimicrobial host defense, (iii) LT deficiency is associated with clinical states of immunocompromise, and (iv) exogenous LTB(4) augments antimicrobial functions in phagocytes. Here, we sought to determine whether the administration of LTB(4) has therapeutic potential in a mouse model of pneumonia. Wild-type and 5-LO knockout mice were challenged with Streptococcus pneumoniae via the intranasal route, and bacterial burdens, leukocyte counts, and cytokine levels were determined. LTB(4) was administered via the intraperitoneal, intravenous, and intranasal routes prior to pneumococcal infection and by aerosol 24 h following infection. Leukocytes recovered from mice given S. pneumoniae and treated with aerosolized LTB(4) were evaluated for expression levels of the p47phox subunit of NADPH oxidase. Intrapulmonary but not systemic pretreatment with LTB(4) significantly reduced the lung S. pneumoniae burden in wild-type mice. Aerosolized LTB(4) was effective at improving lung bacterial clearance when administered postinoculation in animals with established infection and exhibited greater potency in 5-LO knockout animals, which also exhibited greater baseline susceptibility. Augmented bacterial clearance in response to LTB(4) was associated with enhanced monocyte recruitment and leukocyte expression of p47phox. The results of the current study in an animal model serve as a proof of concept for the potential utility of treatment with aerosolized LTB(4) as an immunostimulatory strategy in patients with bacterial pneumonia.

Convergence of nitric oxide and lipid signaling: anti-inflammatory nitro-fatty acids

The signaling mediators nitric oxide ( NO) and oxidized lipids, once viewed to transduce metabolic and inflammatory information via discrete and independent pathways, are now appreciated as interdependent regulators of immune response and metabolic homeostasis. The interactions between these two classes of mediators result in reciprocal control of mediator synthesis that is strongly influenced by the local chemical environment. The relationship between the two pathways extends beyond coregulation of NO and eicosanoid formation to converge via the nitration of unsaturated fatty acids to yield nitro derivatives (NO(2)-FA). These pluripotent signaling molecules are generated in vivo as an adaptive response to oxidative inflammatory conditions and manifest predominantly anti-inflammatory signaling reactions. These actions of NO(2)-FA are diverse, with these species serving as a potential chemical reserve of NO, reacting with cellular nucleophiles to posttranslationally modify protein structure, function, and localization. In this regard these species act as potent endogenous ligands for peroxisome proliferator-activated receptor gamma. Functional consequences of these signaling mechanisms have been shown in multiple model systems, including the inhibition of platelet and neutrophil functions, induction of heme oxygenase-1, inhibition of LPS-induced cytokine release in monocytes, increased insulin sensitivity and glucose uptake in adipocytes, and relaxation of preconstricted rat aortic segments. These observations have propelled further in vitro and in vivo studies of mechanisms of NO(2)-FA signaling and metabolism, highlighting the therapeutic potential of this class of molecules as anti-inflammatory drug candidates.

Montelukast inhibits neutrophil pro-inflammatory activity by a cyclic AMP-dependent mechanism

BACKGROUND AND PURPOSE

The objective of this study was to characterize the effects of the cysteinyl leukotriene receptor antagonist, montelukast (0.1-2 micromol x L(-1)), on Ca(2+)-dependent pro-inflammatory activities, cytosolic Ca(2+) fluxes and intracellular cAMP in isolated human neutrophils activated with the chemoattractants, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (1 micromol x L(-1)) and platelet-activating factor (200 nmol x L(-1)).

EXPERIMENTAL APPROACH

Generation of reactive oxygen species was measured by lucigenin- and luminol-enhanced chemiluminescence, elastase release by a colourimetric assay, leukotriene B(4) and cAMP by competitive binding ELISA procedures, and Ca(2+) fluxes by fura-2/AM-based spectrofluorimetric and radiometric ((45)Ca(2+)) procedures.

KEY RESULTS

Pre-incubation of neutrophils with montelukast resulted in dose-related inhibition of the generation of reactive oxygen species and leukotriene B(4) by chemoattractant-activated neutrophils, as well as release of elastase, all of which were maximal at 2 micromol x L(-1) (mean percentages of the control values of 30 +/- 1, 12 +/- 3 and 21 +/- 3 respectively; P < 0.05). From a mechanistic perspective, treatment of chemoattractant-activated neutrophils with montelukast resulted in significant reductions in both post-peak cytosolic Ca(2+) concentrations and store-operated Ca(2+) influx. These montelukast-mediated alterations in Ca(2+) handling by the cells were associated with a significant elevation in basal cAMP levels, which resulted from inhibition of cyclic nucleotide phosphodiesterases.

CONCLUSIONS AND IMPLICATIONS

Montelukast, primarily a cysteinyl leukotriene (CysLT(1)) receptor antagonist, exhibited previously undocumented, secondary, neutrophil-directed anti-inflammatory properties, which appeared to be cAMP-dependent.

Tolerance and rebound with zafirlukast in patients with persistent asthma

BACKGROUND

The potential for tolerance to develop to zafirlukast, a cysteinyl leukotriene (CysLT) receptor antagonist (LRA) in persistent asthma, has not been specifically examined.

OBJECTIVE

To look for any evidence of tolerance and potential for short-term clinical worsening on LRA withdrawal. Outcome measures included changes in; airway hyperresponsiveness to inhaled methacholine (PD20FEV1), daily symptoms and peak expiratory flows (PEF), sputum and blood cell profiles, sputum CysLT and prostaglandin (PG)E2 and exhaled nitric oxide (eNO) levels.

METHODS

A double blind, placebo-controlled study of zafirlukast, 20 mg twice daily over 12 weeks in 21 asthmatics taking beta2-agonists only (Group I), and 24 subjects treated with ICS (Group II).

RESULTS

In Group I, zafirlukast significantly improved morning PEF and FEV1compared to placebo (p < 0.01), and reduced morning waking with asthma from baseline after two weeks (p < 0.05). Similarly in Group II, FEV1 improved compared to placebo (p < 0.05), and there were early within-treatment group improvements in morning PEF, beta2-agonist use and asthma severity scores (p < 0.05). However, most improvements with zafirlukast in Group I and to a lesser extent in Group II deteriorated toward baseline values over 12 weeks. In both groups, one week following zafirlukast withdrawal there were significant deteriorations in morning and evening PEFs and FEV1 compared with placebo (p < or = 0.05) and increased nocturnal awakenings in Group II (p < 0.05). There were no changes in PD20FEV1, sputum CysLT concentrations or exhaled nitric oxide (eNO) levels. However, blood neutrophils significantly increased in both groups following zafirlukast withdrawal compared to placebo (p = 0.007).

CONCLUSION

Tolerance appears to develop to zafirlukast and there is rebound clinical deterioration on drug withdrawal, accompanied by a blood neutrophilia.

Platelet particle formation by anti GPIIIa49-66 Ab, Ca2+ ionophore A23187, and phorbol myristate acetate is induced by reactive oxygen species and inhibited by dexamethasone blockade of platelet phospholipase A2, 12-lipoxygenase, and NADPH oxidase

An HIV antibody (Ab) against platelet integrin GPIIIa49-66 induces complement-independent platelet particle formation by the elaboration of reactive oxygen species (ROS) downstream of the activation of the platelet NADPH oxidase by the 12-lipoxygenase (12-LO) product 12(S)-HETE. To determine whether other inducers of platelet particle formation also function via the induction of ROS, we examined the effects of the Ca(2+) ionophore A23187 and phorbol myristate acetate (PMA). Both agents induced oxidative platelet particle formation in an identical fashion as Ab, requiring Ca(2+) flux and 12(S)-HETE production as well as intact NADPH oxidase and 12-LO pathways. Since HIV-ITP patients with this Ab correct their platelet counts with dexamethasone (Dex), we examined the role of this steroid in this unique autoimmune disorder. Dex at therapeutic concentrations inhibited Ab-, A23187-, or PMA-induced platelet particle formation by inhibiting platelet PLA(2), 12-LO, and NADPH oxidase. The operational requirement of translocation of PLA(2), 12-LO, and NADPH oxidase components (p67 phox) from cytosol to membrane for induction of ROS was both inhibited and partially reversed by Dex in platelets. We conclude that (1) platelet particle formation can be induced by the generation of ROS; and (2) platelet PLA(2), 12-LO, NADPH oxidase, and cytosol membrane translocation, requirements for ROS production, are inhibited by Dex.

Sodium nitroprusside regulates mRNA expressions of LTC4 synthesis enzymes in hepatic ischemia/reperfusion injury rats via NF-kappaB signaling pathway

Leukotriene (LT) C4 (LTC4) synthesis enzymes including LTC4 synthase (LTC4S), microsomal glutathione S-transferase (MGST) 2 and MGST3 can all conjugate LTA4 and reduced glutathione (GSH) to form LTC4, which is related to hepatic ischemia/reperfusion (I/R) injury. The relationship between nitric oxide (NO) and cysteinyl LTs has been shown in previous studies. However, the mechanisms of NO action on gene expression of LTC4 synthesis enzymes are still largely unclear during hepatic I/R. Adult male Sprague-Dawley rats were divided into 5 groups: a sham group (control), an I/R group, and sodium nitroprusside (SNP, 2.5, 5 and 10 microg/kg/min)+I/R groups. Livers were subjected to 60 min of partial hepatic ischemia followed by 5 h of reperfusion, saline or SNP (2.5, 5 and 10 microg/kg/min) administered intravenously. The mRNA levels of LTC4 synthesis enzymes, inducible NO synthase (iNOS) and endothelial No synthase (eNOS) in rat liver tissue were examined by RT-PCR; the protein expressions of NF-kappaB p65, p50 and IkappaBalpha in liver cell lysates and nuclear extracts were detected by Western blot analysis, and serum NO2. levels were also evaluated. Serum NO2. levels, the protein expressions of NF-kappaB p65 and p50 in the nucleus extract, and hepatic mRNA expressions of LTC4S and iNOS were decreased while hepatic mRNA of eNOS was increased in the SNP (5 and 10 microg/kg/min)+I/R groups when compared with those in the I/R group. SNP (2.5 microg/kg/min) promoted the mRNA expressions of both MGST2 and MGST3, whereas SNP (10 microg/kg/min) increased MGST2 mRNA but decreased MGST3 mRNA compared to those in I/R group. Compared with control, the mRNA expression of MGST2 and MGST3 were elevated in SNP (2.5 microg/kg/min)+I/R group, MGST3 mRNA was significantly declined in the SNP (5 and 10 microg/kg/min)+I/R groups. Immunohistochemistry staining revealed that I/R liver exhibited strong cytoplasmic and nuclear staining for NF-kappaB p65, but the livers of the SNP (2.5 microg/kg/min)+I/R group presented slight cytoplasmic and nuclear staining. But IkappaBalpha protein in all groups remains unchanged. It was concluded that SNP downregulated LTC4S mRNA expression by inhibiting NF-kappaB activation independent of IkappaBalpha, but appeared to have a dual influence on the mRNA expressions of MGST2 and MGST3 by other signaling pathways during hepatic I/R injury.

Inhibition of leukotriene biosynthesis abrogates the host control of Mycobacterium tuberculosis

Leukotrienes produced from arachidonic acid by the action of 5-lipoxygenase (5-LO) are classical mediators of inflammatory responses. Recently, it has been demonstrated that leukotrienes also play an important role in host defense against microorganisms. In vitro studies have shown that leukotrienes augmented the anti-mycobacterial activity of neutrophils. In this study, we examined the role of leukotrienes in regulating host response and cytokine generation in a murine model of tuberculosis. Administration of the 5-LO pathway inhibitor MK 886, which reduced lung levels of both the leukotriene B(4) and the anti-inflammatory substance lipoxin A(4) by approximately 50%, increased 60-day mortality from 14% to approximately 57% in Mycobacterium tuberculosis-infected mice, and increased lung bacterial burden by approximately 15-fold. Although MK 886-treated animals exhibited no reduction in pulmonary leukocyte accumulation, they did manifest reduced levels of nitric oxide generation and of the protective type 1 cytokines interleukin-12 and gamma interferon. Together our results demonstrate that 5-LO pathway product(s) - presumably leukotrienes - positively regulate protective Th1 responses against mycobacterial infection in vivo. Moreover, the immunosuppressive phenotype in infected mice observed with MK 886 is most consistent with inhibition of an activator (LTB(4)) rather than a suppressor (LXA(4)) of antimicrobial defense, suggesting the major effect of leukotrienes.

Sodium nitroprusside decreased leukotriene C4 generation by inhibiting leukotriene C4 synthase expression and activity in hepatic ischemia-reperfusion injured rats

The effects of NO on LTC4 generation during hepatic ischemia-reperfusion (I/R) are largely unclear. Sprague-Dawley rats were divided into control, I/R and sodium nitroprusside (SNP, 2.5, 5 and 10 microg/kg/min)+I/R groups. Liver was subjected to I/R injury, saline or SNP administered intravenously. The protein expressions of LTC4 synthesis enzymes including LTC4 synthase (LTC4S), microsomal glutathione-S-transferase (mGST)2 and mGST3 were detected with immunoblotting, the LTC4 synthesis enzymes' activities and LTC4 content were measured by RP-HPLC, the mRNA expressions of inducible nitric oxide synthase (iNOS) and endogenous nitric oxide synthase (eNOS) in liver were measured by RT-PCR. Tissue injuries were assessed by serum ALT and AST and histological changes. Serum NO(2)(-) and liver tissue GSH were also examined. Compared with I/R group, SNP markedly decreased LTC4 content, LTC4S protein and iNOS mRNA levels, and the LTC4 synthesis enzymes' activities (P<0.05), but significantly enhanced eNOS mRNA expression in liver (P<0.05). The decline in serum ALT, AST and NO(2)(-) levels (P<0.05) together with hepatic GSH elevation (P<0.05) in SNP+I/R groups were also observed. LTC4S expression in hepatocytes and sinusoidal endothelial cells in SNP+I/R groups was lower than that in I/R group. But no significant differences in the protein expressions of mGST3 and mGST2 existed between control, I/R and SNP+I/R groups (P>0.05). These results demonstrated that the decline in LTC4 production by SNP treatment during hepatic I/R could be partially resulted from SNP down-regulating the protein expression of LTC4S rather than mGST2 or mGST3 and its inhibiting the LTC4 synthesis enzymes' activities.

Effect of montelukast on bacterial sinusitis in allergic mice

BACKGROUND

In mice, allergic rhinitis augments the infectious and inflammatory response to Streptococcus pneumoniae-induced sinusitis.

OBJECTIVE

To investigate the effects of cysteinyl leukotriene antagonism on the severity of bacterial infection.

METHODS

We performed 3 parallel, placebo-controlled experiments. In the first, mice were ovalbumin sensitized and ovalbumin challenged to show the effects of montelukast on the allergic inflammation; in the second, we evaluated the effect of montelukast on S. pneumoniae infection; in the third, we used mice that were both allergic and infected. Montelukast was given starting 2 days after sensitization until the day before euthanasia. One day after drug treatment began, the mice were inoculated intranasally with S. pneumoniae in the infected groups. Nasal hypersensitivity was measured with histamine challenges before the first sensitization and on the day before euthanasia. On the fifth day after infection, mice were euthanized, nasal lavage was performed, bacteria were cultured, and inflammatory cells in the sinuses were quantified.

RESULTS

Mice that were infected only tended toward having increased bacterial counts from nasal lavage in the montelukast-treated group. The mice that were allergic and infected experienced significantly higher bacterial counts (P < .05). All 3 montelukast treatment groups had significantly decreased eosinophil counts as well as T-lymphocyte counts.

CONCLUSIONS

Montelukast reduces the manifestations of allergic rhinitis in mice. Surprisingly, montelukast led to an increase in bacterial growth in infected mice. This suggests an effect of the cysteinyl leukotrienes on the innate response to bacterial infection.

Cysteinyl leukotrienes: multi-functional mediators in allergic rhinitis

Cysteinyl leukotrienes (CysLTs) are a family of inflammatory lipid mediators synthesized from arachidonic acid by a variety of cells, including mast cells, eosinophils, basophils, and macrophages. This article reviews the data for the role of CysLTs as multi-functional mediators in allergic rhinitis (AR). We review the evidence that: (1) CysLTs are released from inflammatory cells that participate in AR, (2) receptors for CysLTs are located in nasal tissue, (3) CysLTs are increased in patients with AR and are released following allergen exposure, (4) administration of CysLTs reproduces the symptoms of AR, (5) CysLTs play roles in the maturation, as well as tissue recruitment, of inflammatory cells, and (6) a complex inter-regulation between CysLTs and a variety of other inflammatory mediators exists.

Nitric oxide produced in response to engagement of beta2 integrins on human neutrophils activates the monomeric GTPases Rap1 and Rap2 and promotes adhesion

We found that engagement of beta2 integrins on human neutrophils increased the levels of GTP-bound Rap1 and Rap2. Also, the activation of Rap1 was blocked by PP1, SU6656, LY294002, GF109203X, or BAPTA-AM, which indicates that the downstream signaling events in Rap1 activation involve Src tyrosine kinases, phosphoinositide 3-kinase, protein kinase C, and release of calcium. Surprisingly, the beta2 integrin-induced activation of Rap2 was not regulated by any of the signaling pathways mentioned above. However, we identified nitric oxide as the signaling molecule involved in beta2 integrin-induced activation of Rap1 and Rap2. This was illustrated by the fact that engagement of beta2 integrins increased the production of nitrite, a stable end-product of nitric oxide. Furthermore, pretreatment of neutrophils with Nomega-monomethyl-L-arginine, or 1400W, which are inhibitors of inducible nitric-oxide synthase, blocked beta2 integrin-induced activation of Rap1 and Rap2. Similarly, Rp-8pCPT-cGMPS, an inhibitor of cGMP-dependent serine/threonine kinases, also blunted the beta2 integrin-induced activation of Rap GTPases. Also nitric oxide production and its downstream activation of cGMP-dependent serine/threonine kinases were essential for proper neutrophil adhesion by beta2 integrins. Thus, we made the novel findings that beta2 integrin engagement on human neutrophils triggers production of nitric oxide and its downstream signaling is essential for activation of Rap GTPases and neutrophil adhesion.

Fatty acid transduction of nitric oxide signaling: multiple nitrated unsaturated fatty acid derivatives exist in human blood and urine and serve as endogenous peroxisome proliferator-activated receptor ligands

Mass spectrometric analysis of human plasma and urine revealed abundant nitrated derivatives of all principal unsaturated fatty acids. Nitrated palmitoleic, oleic, linoleic, linolenic, arachidonic and eicosapentaenoic acids were detected in concert with their nitrohydroxy derivatives. Two nitroalkene derivatives of the most prevalent fatty acid, oleic acid, were synthesized (9- and 10-nitro-9-cis-octadecenoic acid; OA-NO2), structurally characterized and determined to be identical to OA-NO2 found in plasma, red cells, and urine of healthy humans. These regioisomers of OA-NO2 were quantified in clinical samples using 13C isotope dilution. Plasma free and esterified OA-NO2 concentrations were 619 +/- 52 and 302 +/- 369 nm, respectively, and packed red blood cell free and esterified OA-NO2 was 59 +/- 11 and 155 +/- 65 nm. The OA-NO2 concentration of blood is approximately 50% greater than that of nitrated linoleic acid, with the combined free and esterified blood levels of these two fatty acid derivatives exceeding 1 microm. OA-NO2 is a potent ligand for peroxisome proliferator activated receptors at physiological concentrations. CV-1 cells co-transfected with the luciferase gene under peroxisome proliferator-activated receptor (PPAR) response element regulation, in concert with PPARgamma, PPARalpha, or PPARdelta expression plasmids, showed dose-dependent activation of all PPARs by OA-NO2. PPARgamma showed the greatest response, with significant activation at 100 nm, while PPARalpha and PPARdelta were activated at approximately 300 nm OA-NO2. OA-NO2 also induced PPAR gamma-dependent adipogenesis and deoxyglucose uptake in 3T3-L1 preadipocytes at a potency exceeding nitrolinoleic acid and rivaling synthetic thiazo-lidinediones. These data reveal that nitrated fatty acids comprise a class of nitric oxide-derived, receptor-dependent, cell signaling mediators that act within physiological concentration ranges.

The role of leukotrienes in allergic rhinitis

OBJECTIVE

To review the role of cysteinyl leukotrienes (cysLTs) in allergic rhinitis and the scientific rationale for therapy with leukotriene receptor antagonists (LTRAs).

DATA SOURCES

Relevant basic science and clinical articles were identified by a search of the PubMed database for articles published from 1984 to 2004 using the following keywords: allergic rhinitis; nose; immune response; allergen challenge; leukotrienes C, D, and E; cysteinyl leukotriene; cysteinyl leukotriene receptor; cytokine; leukocyte; montelukast; zafirlukast; and pranlukast.

STUDY SELECTION

The authors' expert opinion was used to select studies for inclusion in this review.

RESULTS

CysLTs are synthesized via 5-lipoxygenase metabolism of arachidonic acid by mast cells and basophils during the early-phase response to antigen and by eosinophils and macrophages during the late phase. The cysLT levels in nasal secretions are elevated after short-term allergen instillation and in allergy season in patients with allergic rhinitis. These lipid mediators act locally and systemically by interacting with receptors, particularly the cysLT1 receptor, on target cells. Evidence derived from topical application of cysLTs in the nose and from the effects of LTRAs indicates that cysLTs contribute to nasal mucous secretion, congestion, and inflammation. CysLTs promote allergic inflammation by enhancing immune responses and the production, adhesion, migration, and survival of inflammatory cells such as eosinophils. They also increase the generation of an array of other proinflammatory mediators, such as cytokines, which in turn increase the production of and receptors for cysLTs. Clinical trials have demonstrated that LTRAs have significant but modest efficacy as single agents but additive efficacy when used with other classes of agents.

CONCLUSIONS

CysLTs fulfill the criteria for relevant mediators of allergic rhinitis via their diverse effects on immune, inflammatory, and local structural components of disease. By blocking the cysLT1 receptor responsible for most of these effects, LTRAs represent a useful approach to treatment of this important and prevalent disorder.

Leukotriene B4mediates p47phox phosphorylation and membrane translocation in polyunsaturated fatty acid-stimulated neutrophils

Polyunsaturated fatty acids (PUFAs) and leukotriene B(4) (LTB(4)) are involved in many inflammatory and physiological conditions. The role of arachidonic acid (AA) and linoleic acid (LA) in promoting the assembly of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits is well known, but the involvement of LTB(4) and other 5-lipoxygenase (5-LO) pathway metabolites of AA in hydrogen peroxide (H(2)O(2)) production by PUFA-stimulated polymorphonuclear leukocytes (PMNs) has not been investigated. We examined this question by determining H(2)O(2) production as well as phosphorylation and membrane translocation of the p47phox subunit of NADPH oxidase. Elicited peritoneal PMNs from rats and from 5-LO-deficient or wild-type mice were pretreated with or without inhibitors of LT biosynthesis and antagonists of the receptors for LTB(4) and cysteinyl LTs for 20 min before stimulation with AA (at 5 and 20 microM) or LA (at 20 microM). PUFAs elicited H(2)O(2) production in a dose-dependent manner, and pharmacologic or genetic inhibition of LT synthesis decreased H(2)O(2) production by approximately 40% when compared with untreated controls. LTB(4) was the moiety responsible for H(2)O(2) production, as revealed by studies using receptor antagonists and its exogenous addition. LTB(4) itself also promoted p47phox phosphorylation and translocation. These results identify a heretofore unrecognized role for activation of 5-LO and subsequent production of LTB(4) in stimulation of PMN NADPH oxidase activation by PUFAs.

Inflammatory response to sputum induction measured by exhaled markers

BACKGROUND

Sputum induction is increasingly used to study both cellular and biochemical composition of the airways. However, there is a significant rise in the percentage of neutrophils at 8 h after inhalation with hypertonic saline.

OBJECTIVE

The aim of this study was to assess whether markers of inflammation in exhaled air and exhaled air condensate change after sputum induction in normal and asthmatic subjects.

METHODS

We measured leukotriene B(4) (LTB(4)) and a marker of oxidative stress, 8-isoprostane, (by enzyme immunoassay) in exhaled air condensate and exhaled nitric oxide (NO; by chemiluminescence analyzer) in 15 healthy subjects (8 females, mean age 35 +/- 4 years, FEV(1) 97.4% predicted) and in 8 mild asthmatic subjects (5 males, mean age 34 +/- 2 years, FEV(1) 70.5% predicted).

RESULTS

LTB(4) was significantly higher compared with baseline at 6 h but did not remain increased at 24 h after sputum induction (134.3 +/- 30.15 and 75.4 +/- 14.32 vs. 64.6 +/- 11.6 pg/ml at baseline; p < 0.02 and p > 0.05, respectively) in healthy subjects. An inverse correlation between LTB(4) and exhaled NO at 6 h after sputum induction was observed in healthy subjects (r = -0.66, p < 0.03). No increase in LTB(4) levels was observed in asthmatic patients. Baseline 8-isoprostane levels were higher in asthmatic patients than in healthy subjects (47.3 +/- 37.1 vs. 17.5 +/- 8.8 pg/ml; p < 0.01). A trend towards increased levels of 8-isoprostane could be observed at 6 and 24 h after inhalation in healthy subjects (26.2 +/- 3.7 and 26.7 +/- 3.9 pg/ml; p = 0.09 and p = 0.07, respectively). In healthy subjects, exhaled NO was significantly higher compared with baseline at 6 h and remained increased 24 h after sputum induction (7.96 +/- 3.5 vs. 5.61 +/- 1.86 ppb; p < 0.01 and p < 0.05, respectively). Exhaled NO levels were increased in asthmatic patients but did not further increase after sputum induction.

CONCLUSIONS

Sputum induction with hypertonic saline causes an inflammatory response which should be considered when using the technique to monitor airway inflammation.

Leukotrienes and isocyanate-induced asthma: a pilot study

BACKGROUND

The role of leukotrienes (LTs) in the pathophysiology of isocyanate-induced asthma is not well known.

OBJECTIVE

We sought to characterize the type of airway inflammation induced by exposure to isocyanates and to investigate whether exposure to isocyanates induced an increase in LT receptor cysteinyl leukotriene ((CysLT)(1), CysLT(2) and leukotriene B(4) receptor (BLT(1))) expression, as well as a release of LT (LTC(4) and leukotriene B(4) (LTB(4))) and IL-8 in both asthmatics with isocyanate-induced asthma and healthy subjects.

METHODS

We investigated eight subjects with isocyanate-induced asthma and eight healthy subjects. Both groups underwent specific inhalation challenges to isocyanates in the laboratory. Induced sputum was collected before and after exposure to isocyanates. CysLT(1), CysLT(2) and BLT(1) expression was assessed by flow cytometry, whereas LTC(4), LTB(4) and IL-8 were measured in the sputum supernatants by enzyme immunoassay.

RESULTS

Exposure to isocyanates induced an increase in sputum neutrophils only in subjects with occupational asthma. There was a significant increase in CysLT(1) and BLT(1) receptor expression, as well as a release of LTB(4) and IL-8 after exposure to isocyanates compared with the baseline, only in subjects with isocyanate-induced asthma, whereas there was no increase in LTC(4). Exposure to isocyanates did not induce any change in LT receptor expression nor in the levels of LTC(4), LTB(4) and IL-8, in healthy subjects.

CONCLUSION

The neutrophilia observed after exposure to isocyanates is likely to be related to the release of LTB(4), probably enhanced by the increased expression of BLT(1) on neutrophils as well as by the release of IL-8. The significance of the increase of CysLT1 receptor expression on neutrophils is unknown and needs further investigation.

Leukotrienes: underappreciated mediators of innate immune responses

Leukotrienes are bronchoconstrictor and vasoactive lipid mediators that are targets in the treatment of asthma. Although they are increasingly recognized to exert broad proinflammatory effects, their role in innate immune responses is less well appreciated. These molecules are indeed synthesized by resident and recruited leukocytes during infection. Acting via cell surface G protein-coupled receptors and subsequent intracellular signaling events, they enhance leukocyte accumulation, phagocyte capacity for microbial ingestion and killing, and generation of other proinflammatory mediators. Interestingly, a variety of acquired states of immunodeficiency, such as HIV infection and malnutrition, are characterized by a relative deficiency of leukotriene synthesis. The data reviewed herein point to leukotrienes as underappreciated yet highly relevant mediators of innate immunity.

Leukotrienes enhance the bactericidal activity of alveolar macrophages against Klebsiella pneumoniae through the activation of NADPH oxidase

Leukotrienes (LTs) are lipid mediators that participate in inflammatory diseases and innate immune function. We sought to investigate the importance of LTs in regulating the microbicidal activity of alveolar macrophages (AMs) and the molecular mechanisms by which this occurs. The role of LTs in enhancing AM microbicidal activity was evaluated pharmacologically and genetically using in vitro challenge with Klebsiella pneumoniae. Exogenous LTs increased AM microbicidal activity in a dose- and receptor-dependent manner, and endogenous production of LTs was necessary for optimal killing. Leukotriene B4 (LTB4) was more potent than cysteinyl LTs. An important role for nicotinamide adenine dinucleotide (NADPH) oxidase in LT-induced microbicidal activity was indicated by the fact that bacterial killing was abrogated by the NADPH oxidase inhibitor diphenyleneiodonium (DPI; 10 microM) and in AMs derived from gp91phox-deficient mice. By contrast, LT-induced microbicidal activity was independent of the generation of nitric oxide. LTs increased H2O2 production, and LTB4 was again the more potent agonist. Both classes of LTs elicited translocation of p47phox to the cell membrane, and LTB4 induced phosphorylation of p47phox in a manner dependent on protein kinase C-delta (PKC-delta) activity. In addition, the enhancement of microbicidal activity by LTs was also dependent on PKC-delta activity. Our results demonstrate that LTs, especially LTB4, enhanceAM microbicidal activity through the PKC-delta-dependent activation of NADPH oxidase.

Effects of Carbon Monoxide Poisoning on Neutrophil Responses in Patients Treated with Hyperbaric Oxygen

Background

Carbon monoxide (CO) poisoning can cause tissue injury. Neutrophil granulocytes have been proposed to contribute to the injury, which may be ameliorated by hyperbaric oxygen (HBO2) treatment. We sought to assess the relationship between acute CO poisoning and blood neutrophil count, plasma cytokine, and Cortisol responses, as well as the mechanism behind the observed beneficiary effects of HBO2 treatment.

Methods

Eight patients (age 26–82 years) with severe acute CO poisoning were enrolled, concomitant with eight healthy controls (age 27–42 years), in a prospective, controlled, clinical study. The patients were given three HBO2 treatments (2.8 atmospheres absolute, 100 minutes) within the first 24 hours. The controls were given identical simultaneous HBO2 treatments. Venous blood samples were taken before and after each treatment.

Results

At the start of the HBO2 treatment, patients displayed significantly higher blood neutrophil counts ( p < .0001) and plasma Cortisol levels (p = .020) than controls, but the two groups had similar values for interleukin-8, granulocyte colony-stimulating factor (G-CSF), neutrophil H2O2 generation, and CD16 and CD18 surface expression. During the observation time, neutrophil H2O2 accumulation declined in patients and in controls ( p = .031), whereas the up-regulation of CD18 expression increased ( p = .002) in both groups. Moreover, G-CSF levels became significantly higher in patients than in controls ( p = .015). G-CSF levels also correlated significantly with neutrophil counts.

Conclusion

CO poisoning was associated with discrete changes of blood neutrophil counts, Cortisol, and G-CSF plasma concentrations. HBO2 treatment modulated neutrophil generation of H2O2 and surface expression of CD18. These changes may be part of the cascade of events leading to the sequelae of CO poisoning and their attenuation by HBO2.

Comparison of glucocorticoid and cysteinyl leukotriene receptor antagonist treatments in an experimental model of chronic airway inflammation in guinea-pigs

BACKGROUND

Leukotriene receptor antagonists have been demonstrated in several studies to possess bronchodilating and anti-inflammatory properties in asthma. However, there are few experimental studies performed to compare the effects of anti-leukotrienes and glucocorticoids, most used anti-inflammatory agents in asthma. In the present study, we evaluated the effects of treatment with dexamethasone or montelukast on eosinophil and mononuclear cell recruitment in an experimental model of allergen-induced chronic airway inflammation in guinea-pigs (GP).

METHODS

GP were submitted to increasing concentrations of aerosols of ovalbumin (OVA) twice a week for 4 weeks. After 2 weeks, animals were treated daily with dexamethasone, montelukast or saline solution. After this period, GP were anaesthetized, tracheostomized, mechanically ventilated and challenged with OVA aerosol.

RESULTS

Maximal changes of respiratory system resistance and elastance induced by OVA challenge were attenuated by dexamethasone (P<0.001), but not by montelukast treatment. Neither dexamethasone nor montelukast significantly influenced bronchial oedema formation. Dexamethasone but not montelukast induced a decrease in mononuclear cells in airways (P<0.001). Eosinophil infiltration in the bronchial wall was reduced by both dexamethasone and montelukast (P<0.005). Only dexamethasone treatment reduced the levels of exhaled nitric oxide (P<0.025).

CONCLUSION

Although leukotriene receptor antagonist treatment reduces eosinophil accumulation induced by multiple antigen challenges, glucocorticoid treatment attenuates both eosinophil and mononuclear cell infiltration.

Blockade of endogenous leukotrienes exacerbates pulmonary histoplasmosis

Leukotrienes are classical mediators of inflammatory response. New aspects of leukotriene function have recently been described. We examine here the previously unreported role that leukotrienes play in the regulation of cytokines in a murine model of histoplasmosis. We demonstrate that administration of MK 886, a leukotriene synthesis inhibitor, caused Histoplasma capsulatum-infected mice to die by the day 15 of infection, whereas the correlating death rate in untreated infected mice was 0%. Treating infected animals with MK 886 inhibited leukotriene synthesis but increased leukocyte recruitment to the lungs. Subsequent to this phenomenon, levels of tumor necrosis factor alpha, interleukin-1 (IL-1), IL-6, and KC chemoattractant cytokines and fungi in the lung parenchyma increased, as did inflammatory response. In contrast, IL-2, IL-5, IL-12, and gamma interferon cytokine levels actually decreased. Thus, murine response to pulmonary histoplasmosis may be leukotriene modulated. This finding may enable us to alter the course of the immune response and inflammation caused by histoplasmosis. The data from the present study suggest an important new strategy for immunologic or drug intervention in human patients.

Effect of montelukast pretreatment on inducible nitric oxide synthase mRNA expression in the lungs of antigen-challenged allergic mice

BACKGROUND

Growing evidence suggests that inducible nitric oxide synthase (iNOS) is the main source of the high output of exhaled nitric oxide (NO) in asthma. Treatment of asthmatic patients with glucocorticoids reduces high levels of exhaled NO mainly by inhibiting the transcription of iNOS. A similar reduction in exhaled NO was recently observed in patients treated with the leukotriene receptor antagonists, but the exact interaction between these drugs and iNOS remains obscure.

OBJECTIVE

The purpose of this study was to evaluate the effect of a leukotriene receptor antagonist, montelukast, on the expression and activity of iNOS in a murine model of allergic asthma.

METHODS

Twenty-four BALB/c mice were sensitized to OVA and were equally divided into 3 groups (Groups 1-3). Eight additional mice were sham sensitized and served as a negative control group (Group 4). Group 1 received montelukast 1 mg/kg/day in their drinking water, Group 2 received dexamethasone 1 mg/kg/day in their drinking water and Groups 3 and 4 received plain tap water. After 1 week, the animals were challenged by inhalation of OVA and, 3 h later, they were killed and their lung cells were isolated by enzymatic tissue digestion. NO generation was measured by a Griess assay, and iNOS mRNA was studied by RT-PCR.

RESULTS

A significant increase in iNOS mRNA expression and in NO generation was evident after allergen challenge compared with the controls. Pretreatment with montelukast mildly decreased NO production without producing a concomitant significant decrease in iNOS mRNA expression.

CONCLUSION

Unlike pretreatment with glucocorticoids, we failed to find compelling evidence for a major role for montelukast treatment in the modulation of iNOS mRNA in a murine model of acute asthma.

Comparison of iNOS Inhibition by Antisense and Pharmacological Inhibitors after Spinal Cord Injury

Inducible nitric oxide synthase (iNOS) is a key mediator of inflammation during pathological conditions. We examined, through the use of selective iNOS inhibitors, the role of iNOS in specific pathophysiological processes after spinal cord injury (SCI), including astrogliosis, blood-spinal cord barrier (BSCB) permeability, polymorphonuclear leukocyte infiltration, and neuronal cell death. Administration of iNOS antisense oligonucleotides (ASOs) (intraspinally at 3 h) or the pharmacological inhibitors, N-[3(Aminomethyl) benzyl] acetamidine (1400 W) (i.v./i.p. 3 and 9 h) or aminoguanidine (i.p. at 3 and 9 h) after moderate contusive injury decreased the number of iNOS immunoreactive cells at the injury site by 65.6% (iNOS ASOs), 62.1% (1400 W), or 59% (aminoguanidine) 24 h postinjury. iNOS activity was reduced 81.8% (iNOS ASOs), 56.7% (1400 W), or 67.9% (aminoguanidine) at this time. All iNOS inhibitors reduced the degree of BSCB disruption (plasma leakage of rat immunoglobulins), with iNOS ASO inhibition being more effective (reduced by 58%). Neutrophil accumulation within the injury site was significantly reduced by iNOS ASOs and 1400 W by 78.8% and 20.9%, respectively. Increased astrogliosis was diminished with iNOS ASOs but enhanced following aminoguanidine. Detection of necrotic and apoptotic neuronal cell death by propidium iodide and an FITC-conjugated Annexin V antibody showed that iNOS inhibition could significantly retard neuronal cell death rostral and caudal to the injury site. These novel findings indicate that acute inhibition of iNOS is beneficial in reducing several pathophysiological processes after SCI. Furthermore, we demonstrate that the antisense inhibition of iNOS is more efficacious than currently available pharmacological agents.

Elevated urinary excretion of nitric oxide metabolites in young infants with Zellweger syndrome

BACKGROUND

Children with Zellweger syndrome (ZS), a rare peroxisome deficiency disorder, excrete into the urine highly elevated amounts of urinary metabolites of the arachidonic acid cascade. This pathway may interact in vivo with the L-arginine/nitric oxide (NO) pathway. The aim of this study was to investigate NO production in ZS.

METHODS

We studied 11 infants aged 2-12 months with ZS and 30 healthy controls (HC) aged 1-12 months. Urinary excretion of nitrite plus nitrate (U(NO(x))), which is a reliable measure of whole body NO formation, was determined by gas chromatography-mass spectrometry (GC-MS) and corrected for creatinine excretion.

RESULTS

In the subjects aged 1-6 months, U(NO(x)) was more than twofolds higher in ZS (median, 666 micromol/mmol creatinine) as compared to HC (median, 257 micromol/mmol creatinine) (P=0.014 by Mann-Whitney U-test). In children aged 7-12 months, U(NO(x)) was similar for ZS subjects and HC (P=0.96). U(NO(x)) correlated negatively with age in ZS (Kendall's rank correlation coefficient, tau=-0.75, P=0.001). By contrast, no such correlation was found in HC (tau=0.06, P=0.6).

CONCLUSIONS

NO production is highly elevated during the first 6 months of life in infants with ZS and falls to normal levels within the following 6 months, suggesting a dramatic decrease in NO synthesis in ZS.