Inhibition of p38 mitogen-activated protein kinase: dose-dependent suppression of leukocyte and endothelial response after endotoxin challenge in humans

Unlocking the Untapped Potential of Endothelial Kinase and Phosphatase Involvement in Sepsis for Drug Treatment Design

Sepsis is a devastating clinical condition that can lead to multiple organ failure and death. Despite advancements in our understanding of molecular mechanisms underlying sepsis and sepsis-associated multiple organ failure, no effective therapeutic treatment to directly counteract it has yet been established. The endothelium is considered to play an important role in sepsis. This review highlights a number of signal transduction pathways involved in endothelial inflammatory activation and dysregulated endothelial barrier function in response to sepsis conditions. Within these pathways – NF-κB, Rac1/RhoA GTPases, AP-1, APC/S1P, Angpt/Tie2, and VEGF/VEGFR2 – we focus on the role of kinases and phosphatases as potential druggable targets for therapeutic intervention. Animal studies and clinical trials that have been conducted for this purpose are discussed, highlighting reasons why they might not have resulted in the expected outcomes, and which lessons can be learned from this. Lastly, opportunities and challenges that sepsis and sepsis-associated multiple organ failure research are currently facing are presented, including recommendations on improved experimental design to increase the translational power of preclinical research to the clinic.

Renal microvascular endothelial cell responses in sepsis-induced acute kidney injury

Microvascular endothelial cells in the kidney have been a neglected cell type in sepsis-induced acute kidney injury (sepsis-AKI) research; yet, they offer tremendous potential as pharmacological targets. As endothelial cells in distinct cortical microvascular segments are highly heterogeneous, this Review focuses on endothelial cells in their anatomical niche. In animal models of sepsis-AKI, reduced glomerular blood flow has been attributed to inhibition of endothelial nitric oxide synthase activation in arterioles and glomeruli, whereas decreased cortex peritubular capillary perfusion is associated with epithelial redox stress. Elevated systemic levels of vascular endothelial growth factor, reduced levels of circulating sphingosine 1-phosphate and loss of components of the glycocalyx from glomerular endothelial cells lead to increased microvascular permeability. Although coagulation disbalance occurs in all microvascular segments, the molecules involved differ between segments. Induction of the expression of adhesion molecules and leukocyte recruitment also occurs in a heterogeneous manner. Evidence of similar endothelial cell responses has been found in kidney and blood samples from patients with sepsis. Comprehensive studies are needed to investigate the relationships between segment-specific changes in the microvasculature and kidney function loss in sepsis-AKI. The application of omics technologies to kidney tissues from animals and patients will be key in identifying these relationships and in developing novel therapeutics for sepsis.

Characterization of immune cell, endothelial, and renal responses upon experimental human endotoxemia

INTRODUCTION

Although the effects of relatively high concentrations of endotoxin on endothelial activation/dysfunction and kidney markers has been described in literature, detailed insight in the LPS concentration-effect relationship, the magnitude, variability and timing of the response, and potential effects of endotoxemia on the kidneys is lacking. A study was performed to assess the effects of low- to moderate dose (0.5, 1 or 2ng/kg) endotoxemia on the endothelium and kidneys as measured by a panel of novel highly sensitive kidney injury markers.

METHODS

This was a randomized, double-blind, placebo-controlled study with single ascending doses of LPS (0.5, 1 or 2ng/kg) administered to healthy male volunteers (3 cohorts of 8 subjects, LPS:placebo 6:2). Endothelial measures included selectins, cell adhesion molecules, and thrombomodulin. Renal measures included novel, sensitive and specific biomarkers of acute kidney injury.

RESULTS

Endotoxin exposure resulted in consistent LPS dose-dependent responses in inflammatory markers, E- and P- Selectin, VCAM1, ICAM1, and thrombomodulin. The observed biological responses were transient, reaching a level of significance of at least <0.01 in the highest dose group and with an effect size which was dependent on the administered LPS dose. LPS-induced inflammatory and endothelial effects did not translate into a change in renal damage biomarkers, although at 2ng/kg LPS, subtle and transient biomarker changes were observed that may relate to (subclinical) tubular damage.

DISCUSSION

We demonstrated that administration of a single LPS dose of 2ng/kg to healthy volunteers results in significant inflammatory and endothelial responses, without inducing clinically relevant signs of kidney injury. These findings support the application of the human endotoxemia model in future clinical pharmacology studies.

p38-MAPK inhibition and endotoxin induced tubular dysfunction in men

Background: To evaluate the possibility of preventing endotoxin induced renal damage by p38-MAPK inhibition in a human model.

Design and Methods: Twenty-one healthy young male volunteers received 4 ng/kg Escherichia coli endotoxin as a single dose. Four groups of volunteers received an oral dose of placebo or 350, 700 or 1400 mg RWJ-67657, a p38-MAPK inhibitor, 20 min before endotoxin infusion. Urine samples were collected at set time intervals. The urinary excretion rate of β2-microglobulin and N-acetyl-β-D-glucosaminidase, as indicators of tubular dysfunction was determined.

Results: There was a significant increase of β2-microglobulin and N-acetyl-β-D-glucosaminidase urine excretion rate after endotoxin infusion in the placebo group. p38-MAPK inhibition prevented the increase of markers for tubulopathy.

Conclusions: Endotoxin infusion induces measurable tubular damage. Blocking the p38-MAPK may prevent this damage. The mechanism is unclear, but blocking TNF-α release is a possible explanation.

Indoleamine-2,3-dioxygenase activity in experimental human endotoxemia

Background

Excessive tryptophan metabolism to kynurenine by the rate-limiting enzyme endothelial indoleamine 2,3-dioxygenase 1 (IDO) controls arterial vessel relaxation and causes hypotension in murine endotoxemia. However, its relevance in human endotoxemia has not been investigated so far. We thus aimed to study changes in blood pressure in parallel with tryptophan and kynurenine levels during experimental endotoxemia in humans.

Findings

Six healthy male volunteers were given E. coli lipopolysaccharide (LPS; 4 ng/kg) as a 1-min intravenous infusion. They had levels of soluble E-Selectin and soluble vascular cell adhesion molecule-1 as well as IDO activity assessed as the kynurenine-to-tryptophan plasma ratio by liquid chromatography-tandem mass spectrometry at various time points during a 24 h time course. During endotoxemia, IDO activity significantly increased, reaching peak levels at 8 h after LPS infusion (44.0 ± 15.2 vs. 29.4 ± 6.8 at baseline, P<0.0001). IDO activity correlated inversely with the development of hypotension as shown by random effects linear regression models. Finally, IDO activity exhibited a kinetic profile similar to that of soluble endothelial-specific adhesion molecules.

Conclusions

LPS is a triggering factor for the induction of IDO in men. Our findings strongly support the concept that the induction of IDO in the vascular endothelium contributes to hypotension in human sepsis.

SB203580, a p38 inhibitor, improved cardiac function but worsened lung injury and survival during Escherichia coli pneumonia in mice

BACKGROUND

Supporting its therapeutic application in sepsis, p38 mitogen-activated protein kinase (MAPK) inhibition decreases cardiopulmonary injury and lethality with lipopolysaccharide challenge. However, only one preclinical study has reported the survival effects of a p38 inhibitor (SB203580, 100 mg/kg) during infection. We therefore tested SB203580 in mice (n = 763) challenged with intratracheal Escherichia coli and treated with antibiotics and fluids.

METHODS AND RESULTS

Compared with placebo, high dose SB203580 (100 mg/kg) pretreatment increased the hazards ratio of death (95% confidence interval) (3.6 [2.1, 6.1], p < 0.0001). Decreasing doses (10, 1, or 0.1 mg/kg) went from being harmful to having no significant effect (p < 0.0001 for the effect of decreasing dose). At 48 hours, but not 24 hours after E. coli, high and low dose SB203580 pretreatment decreased cardiac phosphorylated p38 MAPK levels and improved cardiac output either (p <or= 0.07). Low dose SB203580 did not alter lung neutrophils significantly but increased lung injury at 48 hours (p = 0.05). High dose decreased lung neutrophils and injury at 24 hours (p = 0.09 and 0.01, respectively) but then increased them at 48 hours (both p <or= 0.01). Lung injury was greater with high versus low dose at 48 hours (p = 0.002).

CONCLUSION

Thus, SB203580 had divergent effects on cardiac and lung function in E. coli challenged mice. Furthermore, high dose worsened survival and low dose did not improve it. Altogether, these findings suggest that clearly defining the risks and benefits of p38 MAPK inhibition is important before such treatment is applied in patients with or at risk of serious infection.

A randomized, placebo-controlled study of the effects of the p38 MAPK inhibitor SB-681323 on blood biomarkers of inflammation in COPD patients

The p38 mitogen-activated protein kinase (MAPK) signaling upregulates inflammation and is known to be increased in chronic obstructive pulmonary disease (COPD). The authors assessed the pharmacology of the novel p38 MAPK inhibitor SB-681323 using blood biomarkers in COPD. Seventeen COPD patients (forced expiratory volume in 1 second 50%-80% predicted) using short-acting bronchodilators participated in a double-blind, double-dummy, randomized, crossover study. Patients received single oral doses of SB-681323 7.5 mg and 25 mg, prednisolone 10 mg and 30 mg, and placebo. Blood was obtained predose and at 1, 2, 6, and 24 hours postdose. Whole-blood sorbitol-induced phosphorylated (p) heat shock protein (HSP) 27 levels as a marker of p38 pathway activation and lipopolysaccharide-induced tumor necrosis factor (TNF)-alpha production were assessed. Both doses of SB-681323, but not prednisolone, significantly (P < .0001) reduced weighted mean (WM) pHSP27 (0-6 hours) by 58% compared with placebo. WM TNF-alpha production (0-24 hours) was significantly reduced compared with placebo by SB-681323 25 mg (40%, P = .005) and 7.5 mg (33.4%, P = .02), while prednisolone 30 mg and 10 mg caused 81.5% and 58.2% suppression, respectively (both P < .0001). SB-681323 inhibited the p38 MAPK pathway to a greater degree than prednisolone did. SB-681323 inhibited TNF-alpha production. SB-681323 is a potent p38 MAPK inhibitor that potentially suppresses inflammation in COPD.

Time course of angiopoietin-2 release during experimental human endotoxemia and sepsis

Introduction

Endothelial activation leading to vascular barrier breakdown denotes a devastating event in sepsis. Angiopoietin (Ang)-2, a circulating antagonistic ligand of the endothelial specific Tie2 receptor, is rapidly released from Weibel-Palade and has been identified as a non-redundant gatekeeper of endothelial activation. We aimed to study: the time course of Ang-2 release during human experimental endotoxemia; the association of Ang-2 with soluble adhesion molecules and inflammatory cytokines; and the early time course of Ang-2 release during sepsis in critically ill patients.

Methods

In 22 healthy volunteers during a 24-hour period after a single intravenous injection of lipopolysaccharide (LPS; 4 ng/kg) the following measurement were taken by immuno luminometric assay (ILMA), ELISA, and bead-based multiplex technology: circulating Ang-1, Ang-2, soluble Tie2 receptor, the inflammatory molecules TNF-alpha, IL-6, IL-8 and C-reactive protein, and the soluble endothelial adhesion molecules inter-cellular adhesion molecule-1 (ICAM-1), E-selectin, and P-selectin. A single oral dose of placebo or the p38 mitogen activated protein (MAP) kinase inhibitor drug, RWJ-67657, was administered 30 minutes before the endotoxin infusion. In addition, the course of circulating Ang-2 was analyzed in 21 septic patients at intensive care unit (ICU) admission and after 24 and 72 hours, respectively.

Results

During endotoxemia, circulating Ang-2 levels were significantly elevated, reaching peak levels 4.5 hours after LPS infusion. Ang-2 exhibited a kinetic profile similar to early pro-inflammatory cytokines TNF-alpha, IL-6, and IL-8. Ang-2 levels peaked prior to soluble endothelial-specific adhesion molecules. Finally, Ang-2 correlated with TNF-alpha levels (r = 0.61, P = 0.003), soluble E-selectin levels (r = 0.64, P < 0.002), and the heart rate/mean arterial pressure index (r = 0.75, P < 0.0001). In septic patients, Ang-2 increased in non-survivors only, and was significantly higher compared with survivors at baseline, 24 hours, and 72 hours.

Conclusions

LPS is a triggering factor for Ang-2 release in men. Circulating Ang-2 appears in the systemic circulation during experimental human endotoxemia in a distinctive temporal sequence and correlates with TNF-alpha and E-selectin levels. In addition, not only higher baseline Ang-2 concentrations, but also a persistent increase in Ang-2 during the early course identifies septic patients with unfavorable outcome.

Signal transduction pathways involved in brain death-induced renal injury

Kidneys derived from brain death organ donors show an inferior survival when compared to kidneys derived from living donors. Brain death is known to induce organ injury by evoking an inflammatory response in the donor. Neuronal injury triggers an inflammatory response in the brain, leading to endothelial dysfunction and the release of cytokines in the circulation. Serum levels of interleukin-6, -8, -10, and monocyte chemoattractant protein-1 (MCP-1) are increased after brain death. Binding with cytokine-receptors in kidneys stimulates activation of nuclear factor-kappa B (NF-kappaB), selectins, adhesion molecules and production of chemokines leading to cellular influx. Mitogen-activated protein kinases (MAP-kinases) mediate inflammatory responses and together with NF-kappaB they seem to play an important role in brain death induced renal injury. Altering the activation state of MAP-kinases could be a promising drug target for early intervention to reduce cerebral injury related donor kidney damage and improve outcome after transplantation.

New approaches to the treatment of inflammatory disease : focus on small-molecule inhibitors of signal transduction pathways

This 'state-of-the-art' review specifically focuses on alternative signalling pathways deeply involved in acute and chronic inflammatory responses initiated by various pathological stimuli. The accumulated scientific knowledge has already revealed key biological targets, such as COX-2, and related pro-inflammatory mediators (cytokines and chemokines, interleukins [ILs], tumour necrosis factor [TNF]-alpha, migration inhibition factor [MIF], interferon [IFN]-gamma and matrix metalloproteinases [MMPs]) implicated in uncontrolled, destructive inflammatory reaction. A number of physiologically active agents are currently approved for market or are under active investigation in different clinical trials. However, recent findings have exposed the fatal adverse effects directly associated with drug therapy based on COX-2 inhibition. Given these possible harmful outcomes, a range of novel therapeutically relevant biological targets that include nuclear transcription factor (NF-kappaB), p38 mitogen-activated protein kinases (MAPK) and Janus protein tyrosine kinases and signal transducers and activators of transcription (JAK/STAT) signalling pathways has received growing attention. Here we discuss recent progress in the identification and development of novel, clinically approved or evaluated small-molecule regulators of these signalling cascades as promising anti-inflammatory drugs.

Macrophage glucocorticoid receptors regulate Toll-like receptor 4-mediated inflammatory responses by selective inhibition of p38 MAP kinase

To explore the role of glucocorticoids in regulation of kinase pathways during innate immune responses, we generated mice with conditional deletion of glucocorticoid receptor (GR) in macrophages (MGRKO). Activation of toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS) caused greater mortality and cytokine production in MGRKO mice than in controls. Ex vivo, treatment with dexamethasone (Dex) markedly inhibited LPS-mediated induction of inflammatory genes in control but not GR-deficient macrophages. We show that Dex inhibits p38 MAPK, but not PI3K/Akt, ERK, or JNK, in control macrophages. Associated with p38 inhibition, Dex induced MAP kinase phosphatase-1 (MKP-1) in control, but not MGRKO, macrophages. Consistent with the ex vivo studies, treatment with a p38 MAPK-specific inhibitor resulted in rescue of MGRKO mice from LPS-induced lethality. Taken together, we identify p38 MAPK and its downstream targets as essential for GR-mediated immunosuppression in macrophages.

The many paths to p38 mitogen-activated protein kinase activation in the immune system

Signals emanating from many cell-surface receptors and environmental cues converge on mitogen-activated protein kinases (MAPKs), which in turn phosphorylate and activate various transcription factors and other molecular effectors. Members of the p38 MAPK family, which respond to pro-inflammatory cytokines and cellular stresses, are typically activated by serial phosphorylation and activation of upstream kinases (the MAPK cascade). In this Review, I highlight the recent studies that indicate that p38-subfamily members can also be activated by non-canonical mechanisms, at least one of which seems to have an important role in antigen-receptor-activated T cells. These alternative pathways might have particular relevance for cells that participate in immune and inflammatory responses.

Kinase inhibitors and airway inflammation

Kinases are believed to play a crucial role in the expression and activation of inflammatory mediators in the airway, in T-cell function and airway remodelling. Important kinases such as Inhibitor of kappaB kinase (IKK)2, mitogen activated protein (MAP) kinases and phsopho-inositol (PI)3 kinase regulate inflammation either through activation of pro-inflammatory transcription factors such as activating protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB), which are activated in airway disease, or through regulation of mRNA half-life. Selective kinase inhibitors have been developed which reduce inflammation and some characteristics of disease in animal models. Targeting specific kinases that are overexpressed or over active in disease should allow for selective treatment of respiratory diseases. Interest in this area has intensified due to the success of the specific Abelson murine leukaemia viral oncogene (Abl) kinase inhibitor imatinib mesylate (Gleevec) in the treatment of chronic myelogenous leukaemia. Encouraging data from animal models and primary cells and early Phase I and II studies in other diseases suggest that inhibitors of p38 MAP kinase and IKK2 may prove to be useful novel therapies in the treatment of severe asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis and other inflammatory airway diseases.

New anti-inflammatory therapies and targets for asthma and chronic obstructive pulmonary disease

Asthma and chronic obstructive pulmonary disease (COPD) are diseases of the airways with an underlying inflammatory component. The prevalence and healthcare burden of asthma and COPD is still rising and is predicted to continue to rise in the foreseeable future. Beta-agonists and corticosteroids form the basis of the therapies available to treat asthma. However, the treatments available for COPD, corticosteroids and anticholinergics, reduce the number and severity of exacerbations, but have a limited effect on slowing the progression of the disease. The inflammatory processes underlying the pathology of asthma have received a great deal of attention and more recently, those underlying COPD have begun to be elucidated. This has resulted in the identification of new targets that will allow the development of novel approaches by the pharmaceutical industry, which will be able to focus its efforts in an attempt to provide new and improved therapies to treat these debilitating diseases. The resultant therapies should impinge on the underlying development of these diseases rather than providing symptomatic relief or palliative treatment alone. This review will outline new targets and novel approaches currently under investigation, which may provide opportunities for novel anti-inflammatory therapeutic interventions that slow or halt disease progression in asthma and COPD.

Chemokine production and E-selectin expression in activated endothelial cells are inhibited by p38 MAPK (mitogen activated protein kinase) inhibitor RWJ 67657

Endothelial cells play an important role in inflammatory diseases like rheumatoid arthritis by recruitment of inflammatory cells. The cytokines TNF-alpha and IL-1beta are major inducers of endothelial cell activation and are stimulators of inflammatory signal transduction pathway involving p38 MAPK (mitogen-activated protein kinase). The present study investigated the effects of p38 MAPK inhibition on cell adhesion molecule (CAM) expression and chemokine production by endothelial cells both on mRNA and protein level. Pre-treatment of endothelial cells with the pharmacologically relevant concentration of 1 microM of the p38 MAPK inhibitor RWJ 67657 reduced TNF-alpha and IL-1beta induced mRNA and membrane expression of E-selectin. Moderate inhibitory effects on ICAM-1 and VCAM-1 expression were found. Significant reduction of mRNA expression and protein production of the inflammatory cytokine IL-6 and the chemokines IL-8 and MCP-1 was demonstrated. Treatment with RWJ 67657 could lead to reduced leukocyte infiltration by the reduction of E-selectin expression and chemokine production.

Kinase targets and inhibitors for the treatment of airway inflammatory diseases: the next generation of drugs for severe asthma and COPD?

Kinases are believed to play a crucial role in the expression and activation of inflammatory mediators in the airway, in T-cell function, and in airway remodeling. Important pro-inflammatory transcription factors such as activating protein-1 and nuclear factor kappaB, which are activated in airway disease, require kinase activation to switch on inflammatory genes, while other kinases can regulate mRNA half-life. Selective kinase inhibitors have been developed that reduce inflammatory gene expression and some characteristics of disease in animal models. Targeting specific kinases that are overexpressed or overactive in disease should allow for selective treatment of airway inflammatory diseases. Interest in this area has intensified due to the success of the specific Abelson murine leukemia viral oncogene homolog tyrosine kinase inhibitor, imatinib mesylate, in the treatment of chronic myelogenous leukemia. Encouraging data from animal models and primary cells and early phase I and II studies in other diseases suggest that inhibitors of p38 mitogen-activated protein kinase and inhibitor of kappaB kinase-2 may prove to be useful novel therapies in the treatment of severe asthma and chronic obstructive pulmonary disease.

ENDOTOXIN INCREASES PLASMA SOLUBLE TUMOR NECROSIS FACTOR-RELATED APOPTOSIS-INDUCING LIGAND LEVEL MEDIATED BY THE p38 MITOGEN-ACTIVATED PROTEIN KINASE SIGNALING PATHWAY

Despite extensive knowledge about the mechanisms behind sepsis, this syndrome still caries a large morbidity and mortality rate. Dysregulated immune and coagulation systems are held responsible. However, additional pathophysiological mechanisms such as uncontrolled apoptosis induced by death receptor ligands might well play a role. P38 mitogen-activated protein (MAP) kinase inhibitors are considered as potential drugs in inflammatory diseases. Therefore, the effect of endotoxin administration on the response of soluble(s) tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL), a death receptor ligand, and the role of p38 MAP kinase inhibition was studied in 21 human volunteers. The volunteers received 30 min before the endotoxin infusion a single oral dose of placebo or the selective p38 MAP kinase inhibitor drug, RWJ-67657. Plasma sTRAIL increased 10-fold to 6564 +/- 511 pg/mL after 2.5 h. This increase was blocked completely by the highest dose of RW-J6765. This is the first report showing that endotoxin increases sTRAIL where the p38 MAP kinase signaling pathway is involved.

Signals mediating cleavage of intercellular adhesion molecule-1

ICAM-1, a membrane-bound receptor, is released as soluble ICAM-1 in inflammatory diseases. To delineate mechanisms regulating ICAM-1 cleavage, studies were performed in endothelial cells (EC), human embryonic kidney (HEK)-293 cells transfected with wild-type (WT) ICAM-1, and ICAM-1 containing single tyrosine-to-alanine substitutions (Y474A, Y476A, and Y485A) in the cytoplasmic region. Tyrosine residues at 474 and 485 become phosphorylated upon ICAM-1 ligation and associate with signaling modules. Cleavage was assessed by using an antibody against the cytoplasmic tail of ICAM-1, which recognizes intact ICAM-1 and the 7-kDa membrane-bound fragment remaining after cleavage. Cleavage in HEK-293 WT cells was accelerated by phorbol ester PMA, whereas in EC it was induced by tumor necrosis factor-alpha. In both cell types, a 7-kDa ICAM-1 remnant was detected. Tyrosine phosphatase inhibitors dephostatin and sodium orthovanadate augmented cleavage. PD-98059 (MEK kinase inhibitor), geldanamycin and PP2 (Src kinase inhibitors), and wortmannin (phosphatidylinositol 3-kinase inhibitor) dose-dependently inhibited cleavage in both cell types. SB-203580 (p38 inhibitor) was more effective in EC, and D609 (PLC inhibitor) mostly affected cleavage in HEK-293 cells. Cleavage was drastically decreased in Y474A and Y485A, whereas it was marginally reduced in Y476A. Surprisingly, phosphorylation was not detectable on the 7-kDa fragment of ICAM-1. These results implicate distinct pathways in the cleavage process and suggest a preferred signal transmission route for ICAM-1 shedding in the two cell systems tested. Tyrosine residues Y474 and Y485 within the cytoplasmic sequence of ICAM-1 regulate the cleavage process.

Activation of p38 mitogen-activated protein kinase in spinal microglia is a critical link in inflammation-induced spinal pain processing

We examined the effect of p38 mitogen-activated protein kinase (MAPK) inhibitors in models of nociception and correlated this effect with localization and expression levels of p38 MAPK in spinal cord. There was a rapid increase in phosphorylated p38 MAPK in spinal cord following intrathecal administration of substance P or intradermal injection of formalin. Immunocytochemistry revealed that phosphorylated p38 MAPK-immunoreactive cells were predominantly present in laminae I-IV of the dorsal horn. Double-staining with markers for neurons, microglia, astrocytes and oligodendrocytes unexpectedly revealed co-localization with microglia but not with neurons or other glia. Pretreatment with p38 MAPK inhibitors (SB20358 or SD-282) had no effect on acute thermal thresholds. However, they attenuated hyperalgesia in several nociceptive models associated with spinal sensitization including direct spinal activation (intrathecal substance P) and peripheral tissue inflammation (intraplantar formalin or carrageenan). Spinal sensitization, manifested by enhanced expression of cyclo-oxygenase-2 and inflammation-induced appearance of Fos-positive neurons, was blocked by pretreatment, but not post-treatment, with p38 MAPK inhibitors. Taken together, these results indicate that spinal p38 MAPK is involved in inflammation-induced pain and that activated spinal microglia play a direct role in spinal nociceptive processing.