An intracellular signaling pathway linking lipopolysaccharide stimulation to cellular responses of the human neutrophil: the p38 MAP kinase cascade and its functional significance

The guidance receptor neogenin promotes pulmonary inflammation during lung injury

Lung injury is marked by a persistent self-propagating inflammation within the pulmonary tissue that is initiated by the migration of leukocytes into the alveolar space. Recent work has demonstrated that neuronal guidance proteins are involved into the orchestration of leukocyte migration. Neogenin is a crucial guidance receptor for axonal migration, yet its role during leukocyte migration and acute inflammation is to date unknown. Here, we report that neogenin influences neutrophil migration across endothelial HMEC-1 and alveolar A549 monolayers in vitro. In vivo, Neo1(-/-) mice demonstrated 59% reduced cell count, 41% reduced TNF-α, and 76% reduced IL-6 levels within the alveolar space during lung injury. In studies employing chimeric animals, the presence of Neo1(-/-) bone marrow was associated with a 42% reduction of cell count and reduced inflammatory changes within pulmonary tissue during lung injury. The functional inhibition of neogenin through antibody injection confirmed these results and the role of neogenin for the inflammatory changes within the alveolar space. Previously unappreciated, the guidance receptor neogenin has a significant effect on the orchestration of leukocyte migration and the control of acute inflammation.

Anti-inflammatory effects of anti-hypertensive agents: influence on interleukin-1β secretion by peripheral blood polymorphonuclear leukocytes from patients with essential hypertension

The effects of clinically relevant concentrations of anti-hypertensive agents on lipopolysaccharide (LPS)-induced interleukin-1beta (IL-1β) secretion by polymorphonuclear leukocytes (PMNs) were investigated in vitro. Lipopolysaccharide-induced secretion of IL-1β by PMNs from 15 hypertensive and 15 normotensive subjects after incubation with losartan, captopril, amlodipine, atenolol, and hydrochlorothiazide were assessed. IL-1β secretion by PMNs markedly increased in hypertensive patients versus normotensive subjects. Losartan, captopril, and amlodipine caused a concentration-dependent attenuation of IL-1β levels in both groups. Losartan, captopril, and amlodipine demonstrated marked in vitro anti-inflammatory effects at clinically relevant serum concentrations but atenolol and hydrochlorothiazide did not.

Aspirin and indomethacin reduce lung inflammation of mice exposed to cigarette smoke

Neutrophil accumulation response to cigarette smoke (CS) in humans and animal models is believed to play an important role in pathogenesis of many tobacco-related lung diseases. Here we evaluated the lung anti-inflammatory effect of aspirin and indomethacin in mice exposed to CS. C57BL/6 mice were exposed to four cigarettes per day during 4 days and were treated i.p. with aspirin or indomethacin, administered each day 1h before CS exposure. Twenty four hours after the last exposure, cells and inflammatory mediators were assessed in bronchoalveolar lavage (BAL) fluid and the lungs used for evaluation of lipid peroxidation, p38 mitogen-activated protein kinase (MAPK) phosphorylation and nuclear transcription factor kappaB (NF-kappaB) activation. Exposure to CS resulted in a marked lung neutrophilia. Moreover, the levels of oxidative stress-related lipid peroxidation, prostaglandin E(2) (PGE(2)), interleukin 1beta (IL-1beta), monocyte chemotactic protein 1 (MCP-1), and activated NF-kappaB and p38 MAPK were greatly increased in CS group. Aspirin or indomethacin treatment led to a significant reduction of neutrophil influx, but only aspirin resulted in dramatic decrease of inflammatory mediators. Moreover, both drugs reduced lung p38 MAPK and NF-kappaB activation induced by CS. These results demonstrate that short-term CS exposure has profound airway inflammatory effects counteracted by the anti-inflammatory agents aspirin and indomethacin, probably through COX-dependent and -independent mechanisms.

Role of NF-kappaB in transcriptional regulation of the phagocyte NADPH oxidase by tumor necrosis factor-alpha

Macrophages play an important role in the pathogenesis of chronic inflammatory disease. Activation of these phagocytes induces the production of proinflammatory cytokines, such as IL-1 and TNF-alpha and the generation of reactive oxygen species (ROS), such as superoxide anion (O2*-). Recently, we found that TNF-alpha treatment of human monocytic cells (MonoMac1) and isolated human monocytes resulted in up-regulation of the NADPH oxidase gene, neutrophil cytosolic factor 2 (NCF2). These results suggested that TNF-alpha, produced by activated macrophages, could serve as an autocrine/paracrine regulator of the oxidase, resulting in increased and/or prolonged production of O2*-. To gain a better understanding of the mechanisms involved in NADPH oxidase regulation by TNF-alpha, we evaluated transcriptional regulation of oxidase genes in MonoMac1 cells and human monocytes. We show that TNF-alpha-treated cells have increased levels of mRNA and up-regulated expression of NADPH oxidase subunits p47(phox), p67(phox), and gp91(phox), as well as increased oxidase activity. Pharmacological inhibitors of NF-kappaB activation blocked TNF-alpha-induced up-regulation of NCF1, NCF2, and CYBB message, which correlated with a reduction in expression of the corresponding oxidase proteins and decreased O2*- production. These data demonstrate that the increase in and/or maintenance of O2*- production in TNF-alpha-treated MonoMac1 cells and monocytes are a result, in part, of transcriptional up-regulation of three essential NADPH oxidase genes via the NF-kappaB pathway. This novel finding supports a model, whereby TNF-alpha-dependent activation of NF-kappaB up-regulates phagocyte NADPH oxidase activity, leading to enhanced ROS production and further NF-kappaB activation, potentially contributing to sustained oxidant production in chronic inflammation.

Highly purified lipopolysaccharides from Burkholderia cepacia complex clinical isolates induce inflammatory cytokine responses via TLR4-mediated MAPK signalling pathways and activation of NFkappaB

In cystic fibrosis (CF), bacteria of the Burkholderia cepacia complex (Bcc) can induce a fulminant inflammation with pneumonitis and sepsis. Lipopolysaccharide (LPS) may be an important virulence factor associated with this decline but little is known about the molecular pathogenesis of Bcc LPS. In this study we have investigated the inflammatory response to highly purified LPS from different Bcc clinical isolates and the cellular signalling pathways employed. The inflammatory response (TNFalpha, IL-6) was measured in human MonoMac 6 monocytes and inhibition experiments were used to investigate the Toll-like receptors and associated adaptor molecules and pathways utilized. LPS from all clinical Bcc isolates induced significant pro-inflammatory cytokines and utilized TLR4 and CD14 to mediate activation of mitogen-activated protein kinase pathways, IkappaB-alpha degradation and NFkappaB activation. However, LPS from different clinical isolates of the same clonal strain of Burkholderia cenocepacia were found to induce a varied inflammatory response. LPS from clinical isolates of Burkholderia multivorans was found to activate the inflammatory response via MyD88-independent pathways. This study suggests that LPS alone from clinical isolates of Bcc is an important virulence factor in CF and utilizes TLR4-mediated signalling pathways to induce a significant inflammatory response.

Crohn's disease: future anti-tumor necrosis factor therapies beyond infliximab

The dramatic benefit experienced by many Crohn's disease patients treated with the anti-tumor necrosis factor-alpha (TNF-alpha) antibody infliximab underscores the centrality of this cytokine in the pathogenesis of Crohn's disease and the potential use of the therapeutic strategy of blocking TNF-alpha in this disease. In the hopes of emulating and improving on the success of infliximab, numerous strategies are being devised and studied to inhibit the actions of TNF-alpha. This article focuses on those agents, other than infliximab, which target TNF-alpha to treat inflammatory bowel disease as their central mechanism of action.

Modulation of bone marrow-derived neutrophil signaling by H2O2: disparate effects on kinases, NF-kappaB, and cytokine expression

Reactive oxygen species (ROS), including hydrogen peroxide (H2O2), are generated in increased amounts in pathological, biological processes and can play a role in signal transduction. Neutrophils often accumulate in acute inflammatory reactions, at sites where elevated concentrations of ROS are present. ROS have been demonstrated to participate in the activation of intracellular signaling pathways, including those involved in modulating nuclear accumulation and transcriptional activity of NF-kappaB. However, the role of ROS in affecting such events in neutrophils has not been examined. Using exposure of murine bone marrow neutrophils to H2O2 as a model of oxidative stress, we found both strong and persistent activation of ERK1/2, p38, JNK, and PKB, but not the p21-activated kinase. Stimulating the bone marrow-derived neutrophils with H2O2 did not affect nuclear translocation of NF-kappaB. However, production and secretion of the proinflammatory cytokine TNF-alpha in LPS-stimulated neutrophils were inhibited by H2O2. Exposure of LPS- or TNF-alpha-stimulated neutrophils to H2O2 decreased nuclear translocation of NF-kappaB. LPS-induced activation of the transcriptional factor AP-1 was also inhibited by H2O2. This inhibition of nuclear accumulation of NF-kappaB by H2O2 was not caused by an impaired capacity of LPS to stimulate the IKK pathway or to direct oxidative effects on NF-kappaB but rather reflected diminished degradation of IkappaB-alpha. These results indicate that oxidative stress, despite being able to selectively activate intracellular kinases in bone marrow-derived neutrophils, also inhibits NF-kappaB activation and associated TNF-alpha expression. Such inhibitory effects on neutrophil activation may limit tissue damage produced by oxidative stress.

Down-regulated circulating PMN function after injury despite enhanced p38 MAPK activity

BACKGROUND

Neutrophils (PMN) are initially primed by injury. However, remaining PMN found in the circulation postinjury demonstrate a down-regulated phenotype with inhibited apoptosis, CXCR2 expression, and endotoxin (LPS) responsiveness that may contribute to infectious complications and organ dysfunction. The p38 mitogen activated protein kinase (MAPK) signal transduction pathway has been implicated in regulating each of these PMN functions. We, therefore, hypothesize that p38 signaling is similarly down-regulated in postinjury circulating PMN.

MATERIALS AND METHODS

PMN were isolated from trauma patients (ISS > 20, postinjury day 3) and concurrently from healthy volunteers (control). PMN were cultured with LPS (100 ng/mL) and p38 activity assessed by Western blotting of cell lysates using a dual phosphospecific antibody for phosphorylated, active p38. In separate experiments, PMN from healthy volunteers were cultured in plasma from either healthy or injured subjects +/- LPS and p38 activity assessed by a cell-free in vitro kinase assay using the transcription factor, ATF-2, as a substrate. Apoptosis and IL-1beta secretion of the cultured PMN from each experimental condition were also quantified.

RESULTS

Circulating PMN from trauma patients have an upregulated LPS signaled p38 MAPK response (threefold) compared to PMN from healthy volunteers (p < 0.05). Furthermore, circulating factors present in trauma plasma can transfer this response to normal PMN. There was no significant alteration in apoptosis following LPS treatment between control and trauma patient's PMN (control: 62 +/- 3% vs. trauma: 55 +/- 5%), but there was decreased secretion of IL-1beta (control: 100 +/- 28 pg/mL vs. trauma: 12 +/- 5 pg/mL, p < 0.05).

CONCLUSION

We conclude that injury down-regulates selective PMN function despite enhanced p38 activity. These results suggest a shift in the role of PMN p38 signal transduction following injury with additional critical regulation of LPS responses downstream to p38 MAPK activity.

Heme oxygenase-1 and carbon monoxide in pulmonary medicine

Heme oxygenase-1 (HO-1), an inducible stress protein, confers cytoprotection against oxidative stress in vitro and in vivo. In addition to its physiological role in heme degradation, HO-1 may influence a number of cellular processes, including growth, inflammation, and apoptosis. By virtue of anti-inflammatory effects, HO-1 limits tissue damage in response to proinflammatory stimuli and prevents allograft rejection after transplantation. The transcriptional upregulation of HO-1 responds to many agents, such as hypoxia, bacterial lipopolysaccharide, and reactive oxygen/nitrogen species. HO-1 and its constitutively expressed isozyme, heme oxygenase-2, catalyze the rate-limiting step in the conversion of heme to its metabolites, bilirubin IXalpha, ferrous iron, and carbon monoxide (CO). The mechanisms by which HO-1 provides protection most likely involve its enzymatic reaction products. Remarkably, administration of CO at low concentrations can substitute for HO-1 with respect to anti-inflammatory and anti-apoptotic effects, suggesting a role for CO as a key mediator of HO-1 function. Chronic, low-level, exogenous exposure to CO from cigarette smoking contributes to the importance of CO in pulmonary medicine. The implications of the HO-1/CO system in pulmonary diseases will be discussed in this review, with an emphasis on inflammatory states.

A genomic and proteomic analysis of activation of the human neutrophil by lipopolysaccharide and its mediation by p38 mitogen-activated protein kinase

Bacterial lipopolysaccharide (LPS) evokes several functional responses in the neutrophil that contribute to innate immunity. Although certain responses, such as adhesion and synthesis of tumor necrosis factor-alpha, are inhibited by pretreatment with an inhibitor of p38 mitogen-activated protein kinase, others, such as actin assembly, are unaffected. The aim of the present study was to investigate the changes in neutrophil gene transcription and protein expression following lipopolysaccharide exposure and to establish their dependence on p38 signaling. Microarray analysis indicated expression of 13% of the 7070 Affymetrix gene set in nonstimulated neutrophils, and LPS up-regulation of 100 distinct genes, including cytokines and chemokines, signaling molecules, and regulators of transcription. Proteomic analysis yielded a separate list of up-regulated modulators of inflammation, signaling molecules, and cytoskeletal proteins. Poor concordance between mRNA transcript and protein expression changes was noted. Pretreatment with the p38 inhibitor SB203580 attenuated 23% of LPS-regulated genes and 18% of LPS-regulated proteins by > or = 40%. This study indicates that p38 plays a selective role in regulation of neutrophil transcripts and proteins following lipopolysaccharide exposure, clarifies that several of the effects of lipopolysaccharide are post-transcriptional and post-translational, and identifies several proteins not previously reported to be involved in the innate immune response.

Suppression of the clinical and cytokine response to endotoxin by RWJ-67657, a p38 mitogen-activated protein-kinase inhibitor, in healthy human volunteers

Sepsis resulting in multiorgan failure and death is still a major problem in intensive care medicine, despite extensive attempts to interfere in the supposed underlying mechanism of a deranged immune system. This is not only due to the persistent lacunae in knowledge about the immune system in sepsis but also due to the lack of sufficient instruments for intervention. Inhibitors of the p38 mitogen-activated protein kinase (p38MAPK) have been used to study the signalling pathway of the immune response. In vitro and animal studies have demonstrated that blocking p38MAPK could mitigate the pro-inflammatory response and improve survival after endotoxaemia. Using an endotoxaemia model in healthy human volunteers we evaluated the attenuation of clinical and cytokine response to endotoxin after inhibition of p38MAPK by an oral dose of RWJ-67657, a pyrindinyl imidazole. We measured the clinical parameters temperature, blood pressure and heart rate. The proinflammatory cytokines tumour necrosis factor-alpha, interleukin-6 and interleukin-8 were measured by ELISA at various points during a 24-h period. Drug toxicity was evaluated by routine clinical and laboratory examinations. After a single dose dose of RWJ-67657 the temperature and blood pressure response remained at the basal level. The inhibition of TNF-alpha, IL-6 and IL-8 response was a dose dependent. With the maximum dosage, reduction in peak serum levels of the proinflammatory cytokines was greater than 90%. There was no drug-related toxicity.

INTERPRETATION

We conclude that inhibition of p38MAPK by RWJ-67657 might be a tool to intervene in the deranged immune response in sepsis and other inflammatory diseases.

FR167653 attenuates ischemia and reperfusion injury of the rat lung with suppressing p38 mitogen-activated protein kinase

BACKGROUND

FR167653 is a potent suppressant of tumor necrosis factor (TNF)-alpha and interleukin-1 (IL-1) production, and was shown to attenuate ischemia and reperfusion (I/R) organ injury in our previous experiment. Because p38 mitogen-activated protein (MAP) kinase has been reported to regulate the production of TNF-alpha and IL-1, we examined the effects of FR167653 in the rat lung I/R model and determined the expression and activation of p38 MAP kinase.

METHODS

Experiment 1: After 1 hour of ischemia, p38 MAP kinase, phosphorylated p38 MAP kinase (active form), histologic changes of the lung, and serum levels of TNF-alpha and IL-1beta were examined. Experiment 2: After 2 hours of reperfusion, arterial oxygen content (PaO(2)) and saturation (SaO(2)), serum TNF-alpha and IL-1beta levels, and histologic changes in the lung were examined. Rats were divided into three groups in Experiment 1. In the control group, a saline solution was administered and, in the FR group, 0.1 mg/kg per hour of FR167653 was administered, intravenously throughout the experiment, beginning 30 minutes before ischemia. In the non-ischemic group, samples were taken soon after thoracotomy. The rats were divided into control and FR groups in Experiment 2.

RESULTS

Experiment 1: One hour of ischemia induced almost no changes in the lung or serum cytokine levels. Meanwhile, FR167653 markedly attenuated the expression of phosphorylated p38 MAP kinase. Experiment 2: SaO(2) and PaO(2) were improved, serum cytokines were lower, and lung damage was less extensive in the FR group than in the control group.

CONCLUSION

FR167653 attenuates I/R injury of the lung and this attenuation is associated with suppression of p38 MAP kinase activation.

Neutrophil activation and acute lung injury

Neutrophils are considered to be central to the pathogenesis of most forms of acute lung injury (ALI). For the sake of clarity, neutrophil involvement in ALI can be conceptualized as consisting of sequential stages, beginning with their sequestration in the pulmonary microvasculature, followed by adhesion and activation, and culminating in the production of a microbicidal or "effector" response, such as the generation of reactive oxygen species or release of proteolytic enzymes. Great strides have been made in elucidating these various stages of neutrophil involvement. Recent studies have focused on the intracellular signaling pathways that govern neutrophil activation and have elucidated complex cascades of kinases and other intracellular signaling molecules that allow for amplication of the neutrophil response, yet simultaneously confer specificity of a response. We believe that the inflammatory response in ALI may initially be adaptive, such as the pivotal role played by neutrophils in a bacterial or fungal infection. Ultimately, it is the persistence or the dysregulation of neutrophil activation that may lead to ALI. An increased understanding of how neutrophils function will facilitate the design of therapeutic strategies that retain the beneficial aspects of the inflammatory response, while avoiding unnecessary tissue damage.