Nimesulide reduces interleukin-1beta-induced cyclooxygenase-2 gene expression in human synovial fibroblasts

Potential role of mitochondria in synoviocytes

Synoviocytes are located in the synovium lining layer, which is composed of macrophage-like synoviocytes (MLS) and fibroblast-like synoviocytes (FLS) with different characteristics. Mitochondria, which exist in most cells, are two membrane-covered organelles. In addition to providing the necessary ATP for synoviocytes, mitochondria are involved in the regulation of redox homeostasis and the integration of synoviocytes death signals. In recent years, mitochondrial dysfunction has been found in rheumatoid arthritis (RA) and osteoarthritis (OA). Interestingly, recent studies have started uncovering that mitochondria that were previously reported to play a role in chondrocytes or immune cells, but not known to have pronounced roles in synoviocytes, can actually play crucial roles in the regulation of the pathological properties of the synoviocytes. The purpose of this review is to summarize our current understanding of the key role of mitochondria in synoviocytes, including mitochondrial dysfunction in synoviocytes can induce and aggravate inflammatory responses and changes in mitochondrial structure and function with the involvement of multiple cytokines, signal pathway, and hypoxic state of synovial tissue alter the response of synoviocytes to apoptotic stimulation. Also, mitochondrial abnormalities in synoviocytes promote the synoviocytes invasion and proliferation.

The relatively selective cyclooxygenase-2 inhibitor nimesulide: What's going on?

Nimesulide is a relatively selective cyclooxygenase (COX)-2 inhibitor, non-steroidal anti-inflammatory drug; it has been discovered in 1971 and firstly commercialized in Italy in 1985. There is much evidence that the pharmacological profile of nimesulide is peculiar and not shared with the other COX-2 selective inhibitors, suggesting that other molecular mechanisms besides inhibition of COX-2 derived prostaglandins are involved. Similarly, experimental data suggest that the gastrointestinal safety of nimesulide cannot be ascribed only to a COX-1 sparing effect. On the inflammatory process, the efficacy of nimesulide is dependent upon a wide spectrum of actions, due to the combination of effects on immune and non-immune cells. Early data demonstrated a central role for cyclic AMP (cAMP) in the anti-inflammatory effect of nimesulide; more recently, we have shown the involvement of the pathway ecto-5'-nucleotidase/adenosine A_2A receptor. To date, the molecular mechanism(s) that confers uniqueness to nimesulide have not yet been defined. To go inside the mechanism of action of an existing drug, such as nimesulide, would be helpful to refine its therapeutic use but also to identify new targets for novel therapeutic anti-inflammatory approach. Here, we focus on accumulated evidence for a peculiar pharmacological profile of nimesulide.

Protective effects of curcumin against doxorubicin-induced toxicity and resistance: A review

Doxorubicin (DOX)-induced toxicity and resistance are major obstacles in chemotherapeutic approaches. Despite effective in the treatment of numerous malignancies, some clinicians have voiced concern that DOX has the potential to cause debilitating consequences in organ tissues, especially the heart. The mechanisms of toxicity and resistance are respectively related to induction of reactive oxygen species (ROS) and up-regulation of ATP-binding cassette (ABC) transporter. Curcumin (CUR) with several biological and pharmacological properties is expected to restore DOX-mediated impairments to tissues. This review is intended to address the current knowledge on DOX adverse effects and CUR protective actions in the heart, kidneys, liver, brain, and reproductive organs. Coadministration of CUR and DOX is capable of ameliorating DOX toxicity pertained to antioxidant, apoptosis, autophagy, and mitochondrial permeability.

Metamizol Relieves Pain Without Interfering With Cerulein-Induced Acute Pancreatitis in Mice

OBJECTIVES

Animal models are essential to understand the pathogenesis of acute pancreatitis (AP) and to develop new therapeutic strategies. Although it has been shown that cerulein-induced AP is associated with pain in experimental animals, most experiments are carried out without any pain-relieving treatment because researchers are apprehensive of an interference of the analgetic agent with AP-associated inflammation. In light of the growing ethical concerns and the legal tightening regarding animal welfare during experiments, this attitude should be changed.

METHODS

Acute pancreatitis was induced by cerulein in the C57BL/6J and FVB/N mouse inbred strains. One group received vehicle only, and the other was treated with metamizol as analgetic agent. Pain sensation and parameters of AP were analyzed as well as the effect of metamizol in the pancreas and its actions in the brain.

RESULTS

We report that oral administration of metamizol protects cerulein-treated mice from abdominal pain without influencing the clinical and histopathological course of the disease. In addition, it could be shown that metamizol reduces the central pain response.

CONCLUSIONS

This study reveals that oral administered metamizol has no influence on the cerulein-induced AP and can be given as an analgesic to increase animal welfare in experiments with induced AP.

Acute pain: a multifaceted challenge - the role of nimesulide

BACKGROUND

This article summarizes the outcome from an international consensus meeting, which took place in Vienna on 4 November 2014.

SCOPE

The aim of the meeting was to provide the state of the art on the pathophysiology and treatment of acute pain with special emphasis on nimesulide, a non-steroidal anti-inflammatory drug (NSAID) indicated for the treatment of acute pain and primary dysmenorrhea. Besides the data on the mechanisms of acute inflammatory pain and on the efficacy and safety of nimesulide in patients affected by different forms of acute pain, the clinical experience of attending experts was discussed based on selected case reports.

RESULTS

The members of this consensus group recognized that nimesulide is a NSAID highly effective in the treatment of several painful situations with an acute inflammatory component including primary dysmenorrhea. Although safety concerns regarding nimesulide have emerged in recent years, both robust new epidemiological data and clinical experience confirm a positive benefit/risk profile of nimesulide in the treatment of several forms of acute pain.

CONCLUSIONS

The members of this international consensus group concluded that nimesulide, when used appropriately, remains a particularly valuable and safe option for the treatment of several conditions characterized by the presence of acute inflammatory pain because of the rapid onset of the analgesic action, and the positive evidence-based benefit/risk profile.

Crosstalk Among Disrupted Glutamatergic and Cholinergic Homeostasis and Inflammatory Response in Mechanisms Elicited by Proline in Astrocytes

Hyperprolinemias are inherited disorder of proline (Pro) metabolism. Patients affected may present neurological manifestations, but the mechanisms of neural excitotoxicity elicited by hyperprolinemia are far from being understood. Considering that the astrocytes are important players in neurological disorders, the aim of the present work was to study the effects 1 mM Pro on glutamatergic and inflammatory parameters in cultured astrocytes from cerebral cortex of rats, exploring some molecular mechanisms underlying the disrupted homeostasis of astrocytes exposed to this toxic Pro concentration. We showed that cortical astrocytes of rats exposed to 1 mM Pro presented significantly elevated extracellular glutamate and glutamine levels, suggesting glutamate excitotoxicity. The excess of glutamate elicited by Pro together with increased glutamate uptake and upregulated glutamine synthetase (GS) activity supported misregulated glutamate homeostasis in astrocytic cells. High Pro levels also induced production/release of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6. We also evidenced misregulation of cholinergic anti-inflammatory system with increased acetylcholinesterase (AChE) activity and decreased acetylcholine (ACh) levels, contributing to the inflammatory status in Pro-treated astrocytes. Our findings highlighted a crosstalk among disrupted glutamate homeostasis, cholinergic mechanisms, and inflammatory cytokines, since ionotropic (DL-AP5 and CNQX) and metabotropic (MCPG and MPEP) glutamate antagonists were able to restore the extracellular glutamate and glutamine levels; downregulate TNFα and IL6 production/release, modulate GS and AChE activities; and restore ACh levels. Otherwise, the non-steroidal anti-inflammatory drugs nimesulide, acetylsalicylic acid, ibuprofen, and diclofenac sodium decreased the extracellular glutamate and glutamine levels, downregulated GS and AChE activities, and restored ACh levels in Pro-treated astrocytes. Altogether, our results evidence that the vulnerability of metabolic homeostasis in cortical astrocytes might have important implications in the neurotoxicity of Pro.

Electromagnetic fields (EMFs) and adenosine receptors modulate prostaglandin E(2) and cytokine release in human osteoarthritic synovial fibroblasts

Synovial fibroblasts (SFs) contribute to the development of osteoarthritis (OA) by the secretion of a wide range of pro-inflammatory mediators, including cytokines and lipid mediators of inflammation. Previous studies suggest that electromagnetic fields (EMFs) may represent a potential therapeutic approach to limit cartilage degradation and control inflammation associated to OA, and that they may act through the adenosine pathway. Therefore, we investigated whether EMFs might modulate inflammatory activities of human SFs from OA patients (OASFs) treated with interleukin-1β (IL-1β), and the possible involvement of adenosine receptors (ARs) in mediating EMF effects. EMF exposure induced a selective increase in A(2A) and A(3) ARs. These increases were associated to changes in cAMP levels, indicating that ARs were functionally active also in EMF-exposed cells. Functional data obtained in the presence of selective A(2A) and A(3) adenosine agonists and antagonists showed that EMFs inhibit the release of prostaglandin E(2) (PGE(2)) and the proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8), while stimulating the release of interleukin-10 (IL-10), an antinflammatory cytokine. These effects seem to be mediated by the EMF-induced upregulation of A(2A) and A(3) ARs. No effects of EMFs or ARs have been observed on matrix degrading enzyme production. In conclusion, this study shows that EMFs display anti-inflammatory effects in human OASFs, and that these EMF-induced effects are in part mediated by the adenosine pathway, specifically by the A(2A) and A(3) AR activation. Taken together, these results open new clinical perspectives to the control of inflammation associated to joint diseases.

Effect of selective and non-selective cyclooxygenase inhibitors on doxorubicin-induced cardiotoxicity and nephrotoxicity in rats

CONTEXT

Doxorubicin (DX) is a highly effective chemotherapeutic agent used widely in the treatment of solid tumors; however, its optimal use was associated with cardiotoxicity and nephrotoxicity. The exact mechanism of DX-induced cardiotoxicity and nephrotoxicity is not fully explored. Induction of cyclooxygenase-2 (COX-2) activity in either cardiac or renal tissue by DX has been previously reported, indicating a possible role of COX-2 in DX-induced tissue injury. However, the nature of this role in either tissue injury is an issue of controversy.

OBJECTIVE

This study was the first that simultaneously evaluated the effects of a selective COX-2 inhibitor, nimesulide, and a non-selective COX-inhibitor, indomethacin, on DX-induced cardiotoxicity and nephrotoxicity in male Wistar rats.

MATERIALS AND METHODS

Rats were allocated into four groups. Control group, DX group (received 15 mg/kg, ip), DX + nimesulide (10 mg/kg/day, po) group, and DX + indomethacin (2 mg/kg/day, po) group. Nimesulide and indomethacin were started at the same day of DX injection and continued for 5 days.

RESULTS

The results of the present study showed that inhibition of COX-2 either by selective or non-selective COX-2 inhibitor ameliorated DX-induced cardiotoxicity but aggravated DX-induced nephrotoxicity in rats, as evidenced biochemically and histopathologically.

DISCUSSION AND CONCLUSION

Our study indicates that production of COX-2 is organ specific; consequently, the differential effect of COX-inhibitors should be considered in DX-treated patients. However, a wide scale experiment is needed for further confirmation and testing other members of COX-inhibitors (e.g. celecoxib and diclofenac).

Adenosine analogs and electromagnetic fields inhibit prostaglandin E2 release in bovine synovial fibroblasts

OBJECTIVE

To investigate the role of adenosine analogs and electromagnetic field (EMF) stimulation on prostaglandin E(2) (PGE(2)) release and cyclooxygenase-2 (COX-2) expression in bovine synovial fibroblasts (SFs).

METHODS

SFs isolated from synovia were cultured in monolayer. Saturation and binding experiments were performed by using typical adenosine agonists: N6-cyclohexyladenosine (CHA, A(1)), 2-[p-(2-carboxyethyl)-phenetyl-amino]-5'-N-ethylcarboxamidoadenosine (CGS 21680, A(2A)), 5'-N-ethylcarboxamidoadenosine (NECA, non-selective), N6-(3-iodobenzyl)2-chloroadenosine-5'-N-methyluronamide (Cl-IB-MECA, A(3)). SFs were treated with TNF-alpha (10 ng/ml) and lipopolysaccharide (LPS) (1 microg/ml) to activate inflammatory response. Adenosine analogs were added to control and TNF-alpha- or LPS-treated cultures both in the absence and in the presence of adenosine deaminase (ADA) which is used to deplete endogenous adenosine. Parallel cultures were exposed to EMFs (75 Hz, 1.5 mT) during the period in culture (24h). PGE(2) release was measured by immunoassay. COX-2 expression was evaluated by RT-PCR.

RESULTS

TNF-alpha and LPS stimulated PGE(2) release. All adenosine agonists, except for Cl-IB-MECA, significantly inhibited PGE(2) production. EMFs inhibited PGE(2) production in the absence of adenosine agonists and increased the effects of CHA, CGS 21680 and NECA. In ADA, the inhibition on PGE(2) release induced by CHA, CGS and NECA was stronger than in the absence of ADA and the EMF-inhibitory effect was lost. Changes in PGE(2) levels were associated to modification of COX-2 expression.

CONCLUSIONS

This study supports anti-inflammatory activities of A(1) and A(2A) adenosine receptors and EMFs in bovine SFs. EMF activity appears mediated by an EMF-induced up-regulation of A(2A) receptors. Biophysical and/or pharmacological modulation of adenosine pathways may play an important role to control joint inflammation.

Mitochondrial dysfunction activates cyclooxygenase 2 expression in cultured normal human chondrocytes

OBJECTIVE

Mitochondrial alterations play a key role in the pathogenesis of osteoarthritis (OA). This study evaluated a potential role of mitochondrial respiratory chain (MRC) dysfunction in the inflammatory response of normal human chondrocytes.

METHODS

Commonly used inhibitors of the MRC were utilized to induce mitochondrial dysfunction in normal human chondrocytes. Levels of prostaglandin E(2) (PGE(2)) protein and expression of cyclooxygenase 2 (COX-2) and COX-1 messenger RNA (mRNA) and protein were analyzed. To identify the underlying mechanisms responsible for PGE(2) liberation, reactive oxygen species (ROS) were measured. Inhibitors of ROS, including vitamin E, and inhibitors of mitochondrial Ca(2+) and NF-kappaB were used to test their effects on the MRC.

RESULTS

Antimycin A and oligomycin (inhibitors of mitochondrial complexes III and V, respectively) significantly increased the levels of PGE(2) (mean +/- SEM 505 +/- 132 pg/50,000 cells and 288 +/- 104 pg/50,000 cells, respectively, at 24 hours versus a basal level of 29 +/- 9 pg/50,000 cells; P < 0.05) and increased the expression of COX-2 at both the mRNA and protein levels. Expression of COX-1 did not show any modulation with either inhibitor. Further experiments revealed that antimycin A and oligomycin induced a marked increase in the levels of ROS. Production of PGE(2) and expression of COX-2 protein were inhibited by antioxidants, vitamin E, and mitochondrial Ca(2+) and NF-kappaB inhibitors. The response to blockers of mitochondrial Ca(2+) movement showed that ROS production was dependent on mitochondrial Ca(2+) accumulation.

CONCLUSION

These results strongly suggest that, in human chondrocytes, the inhibition of complexes III and V of the MRC induces an inflammatory response, which could be especially relevant in relation to PGE(2) production via mitochondrial Ca(2+) exchange, ROS production, and NF-kappaB activation. These data may prove valuable for a better understanding of the participation of mitochondria in the pathogenesis of OA.

Long term NSAID treatment inhibits COX-2 synthesis in the knee synovial membrane of patients with osteoarthritis: differential proinflammatory cytokine profile between celecoxib and aceclofenac

OBJECTIVE

To compare the effect of celecoxib with that of a classic non-steroidal anti-inflammatory drug (NSAID) on synovial inflammation and on the synovial expression of proinflammatory genes in patients with knee osteoarthritis (OA).

METHODS

30 patients with severe knee OA scheduled for total knee replacement surgery were included in a 3 month clinical trial. They were randomised to two groups: patients treated with celecoxib (CBX) (200 mg/24 h) and patients treated with aceclofenac (ACF) (100 mg/12 h). Those patients with OA who did not want to be treated with NSAIDs served as a control group. During knee surgery, synovial fluid (SF) and synovial membrane (SM) were collected. A SM specimen was fixed and embedded in paraffin and another part was frozen for molecular biology studies.

RESULTS

At the end of study both CBX and ACF treated patients showed a significant improvement in pain and knee function compared with controls. Both drugs significantly reduced prostaglandin E(2) (PGE(2)) SF concentration and down regulated COX-2 mRNA and protein expression at the SM. However, synovial macrophage infiltration (CD68 antigen staining) and expression of proinflammatory mediators, such as interleukin 1beta and tumour necrosis factor alpha, were decreased only by CBX treatment.

CONCLUSION

Both drugs improved joint pain and function, inhibited SF PGE(2) concentration, and induced a decrease in synovial COX-2 expression and synthesis not related to the tissue inflammatory status. These data suggest that PGE(2) blocking agents may decrease PGE(2) production not only by direct COX-2 inhibition but also by down regulating COX-2 expression and synthesis. However, CBX and ACF appear to have different anti-inflammatory profiles in controlling OA synovial macrophage infiltration and proinflammatory expression.

Immunohistochemical localization of cyclooxygenase-1 and -2 in synovial tissues from patients with internal derangement or osteoarthritis of the temporomandibular joint

This study examined the immunohistochemical expression and localization of cyclooxygenase-1 and -2 (COX-1 and COX-2) in synovial tissues from patients with internal derangement (ID) or osteoarthritis (OA) of the temporomandibular joint (TMJ). Synovial tissues from patients with condylar fractures of the mandible were studied as control. Synovial tissues from 13 TMJs of 10 patients with ID or OA and from 5 TMJs of 4 patients with fractures were examined for COX-1 and COX-2 expression by immunohistochemical staining using two monoclonal antibodies. In addition, whether the COX-2 expression grade correlated with the synovitis score and clinical findings was assessed. COX-2 was expressed in the synovial lining, infiltrating mononuclear cells, fibroblast-like cells, and blood vessels, including CD31-positive endothelial cells, in the synovium of patients with ID or OA. Expression levels of COX-1 in synovial lining cells and endothelial cells were similar in the specimens obtained from the patients with ID or OA and those obtained from the controls. The expression of COX-2 positively correlated with arthroscopic findings of synovitis (p = 0.55, P = 0.023) and with joint pain (p = 0.56, P = 0.021). These results suggest that up-regulation of COX-2 in synovium may play a part in the pathogenesis of synovitis in patients with ID or OA of the TMJ.

Nimesulide, a preferential cyclooxygenase 2 inhibitor, suppresses peroxisome proliferator-activated receptor induction of cyclooxygenase 2 gene expression in human synovial fibroblasts: evidence for receptor antagonism

OBJECTIVE

To characterize the inhibitory effects of therapeutic concentrations of the nonsteroidal antiinflammatory drug nimesulide (NIM) on peroxisome proliferator-activated receptor (PPAR)-induced cyclooxygenase 2 (COX-2) gene expression in human synovial fibroblasts (HSFs) from patients with osteoarthritis (OA) and to define the intracellular mechanisms mediating the response.

METHODS

PPARalpha and PPARgamma messenger RNA (mRNA) expression and protein synthesis in OA HSFs were measured by reverse transcription-polymerase chain reaction and electrophoretic mobility shift assay, respectively. Experiments investigating endogenous and overexpressed PPARalpha and PPARgamma activation of COX-2 mRNA and protein were conducted by incubating nontransfected and transfected cells with increasing concentrations of cognate ligands WY-14,643 (alpha agonist), ciglitasone (gamma agonist), and 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) in the absence or presence of NIM and NS-398 (1 microM). COX-2 mRNA and protein were measured by Northern and Western blotting procedures, respectively. Receptor activation studies were evaluated by cotransfecting pSG5-Gal 4 DNA binding domain (DBD)-PPARalpha ligand binding domain (LBD) or pSG5-Gal 4 DBD-PPARgamma LBD chimeric constructs with a 5x Gal 4 enhancer site tk-tataa-luciferase reporter under ligand stimulation in the presence or absence of increasing concentrations of NIM. Gene transactivation analyses were conducted by treating cells overexpressing cytomegalovirus (CMV)-PPARalpha or CMV-PPARgamma expression constructs with either a PPAR response element (PPRE)-luciferase construct containing 3 DR1 acyl-coenzyme A (acyl-CoA) oxidase gene response elements or human COX-2 promoter constructs with WY-14,643, ciglitasone, and 15d-PGJ(2) in the presence or absence of increasing concentrations of NIM.

RESULTS

Human synovial cells expressed functional PPAR isoforms, PPARalpha and PPARgamma. Neither receptor agonists nor antagonists modulated the intracellular protein levels of PPAR. PPARalpha and, especially, PPARgamma mediated the induction of COX-2 gene expression by receptor agonists. Stimulation of COX-2 mRNA expression and protein synthesis by 15d-PGJ(2) appeared to occur through a receptor-independent process. NIM inhibited PPAR agonist stimulation of COX-2 expression and synthesis in a dose-dependent manner in both nontransfected cells and cells overexpressing both receptor isoforms. NIM potently abrogated basal and ligand-stimulated PPRE(3X) DR1 acyl-CoA oxidase-driven luciferase activity and also human PPRE-containing COX-2 promoter activity.

CONCLUSION

PPAR-mediated induction of COX-2 expression and synthesis in human OA synovial fibroblasts is inhibited by therapeutic concentrations of NIM through the functional antagonism of ligand-dependent receptor activation, with the resultant suppression of PPAR-dependent transactivation of target genes (e.g., COX-2).

COX-2 inhibitors compared and contrasted

Non-steroidal anti-inflammatory drugs (NSAIDs) are the principal drug treatments for inflammation, pain and fever. They act primarily by inhibiting prostaglandin (PG) synthesis but this can cause adverse events (AEs). Since the discovery of two PG synthesising enzymes, COX-1 and COX-2, and the substantial evidence that sparing COX-1 is advantageous for gastric safety, great interest has focused on selective COX-2 inhibitors. Much of the impetus has come from the most recently developed compounds celecoxib and rofecoxib, which have shown spectacular sales growth. However, the older drugs etodolac, nimesulide and meloxicam, made before COX-2 was discovered, are also COX-1-sparing and have good GI safety and therapeutic activities. These five compounds show similarities and differences that are discussed in relation to aspects that include their uses, efficacy, actions and safety.

Prostaglandin E(2) regulates the level and stability of cyclooxygenase-2 mRNA through activation of p38 mitogen-activated protein kinase in interleukin-1 beta-treated human synovial fibroblasts

The p38 MAPK mediates transcriptional and post-transcriptional control of cyclooxygenase-2 (COX-2) mRNA following interleukin-1(IL-1)/lipopolysaccharide cellular activation. We explored a positive feedback, prostaglandin E(2) (PGE(2))-dependent stabilization of COX-2 mRNA mediated by the p38 MAPK cascade in IL-1 beta-stimulated human synovial fibroblasts. We observed a rapid (5 min), massive (>30-fold), and sustained (>48 h) increase in COX-2 mRNA, protein, and PGE(2) release following a recombinant human (rh) IL-1 beta signal that was inhibited by NS-398, a COX-2 inhibitor, and SB202190, a selective, cell-permeable p38 MAPK inhibitor. PGE(2) completely reversed NS-398-mediated inhibition but not SB202190-dependent inhibition. The eicosanoid didn't potentiate IL-1 beta-induced COX-2 expression nor did it activate COX-2 gene expression in quiescent cells. Transfection experiments with a human COX-2 promoter construct revealed a minor element of p38 MAPK-dependent transcriptional control after IL-1 beta stimulation. p38 MAPK synergized with the cAMP/cAMP-dependent protein kinase cascade to transactivate the COX-2 promoter. When human synovial fibroblasts were activated with rhIL-1 beta for 3-4 h (steady state) followed by washout, the elevated levels of COX-2 mRNA declined rapidly (<2 h) to control levels. If PGE(2), unlike EP2/3 agonists butaprost and sulprostone, was added to fresh medium, COX-2 mRNA levels remained elevated for up to 16 h. SB202190 or anti-PGE(2) monoclonal antibody compromised the stabilization of COX-2 mRNA by PGE(2). Deletion analysis using transfected chimeric luciferase-COX-2 mRNA 3'-untranslated region reporter constructs revealed that IL-1 beta increased reporter gene mRNA stability and translation via AU-containing distal regions of the untranslated region. This response was mediated entirely by a PGE(2)/p38 MAPK-dependent process. We conclude that the magnitude and duration of the induction of COX-2 mRNA, protein, and PGE(2) release by rhIL-1 beta is primarily the result of PGE(2)-dependent stabilization of COX-2 mRNA and stimulation of translation, a process involving a positive feedback loop mediated by the EP4 receptor and the downstream kinases p38 MAPK and, perhaps, cAMP-dependent protein kinase.