Down-regulation by prostaglandins of type-II phospholipase A2 expression in guinea-pig alveolar macrophages: a possible involvement of cAMP

Fluoride as a factor initiating and potentiating inflammation in THP1 differentiated monocytes/macrophages

It is well known that exposure to fluorides lead to an increased ROS production and enhances the inflammatory reactions. Therefore we decided to examine whether cyclooxygenases (particular COX-2) activity and expression may be changed by fluoride in THP1 macrophages and in this way may change the prostanoids biosynthesis. In the present work we demonstrate that fluoride increased concentration of PGE2 and TXA2 in THP1 macrophages. Following exposure to 1-10 μM NaF, COX-2 protein and COX-2 transcript increased markedly. COX-2 protein up-regulation probably is mediated by ROS, produced during fluoride-induced inflammatory reactions. Additional fluoride activates the transcription factor, nuclear factor (NF)-kappaB, which is involved in the up-regulation of COX-2 gene expression. This study indicated that even in small concentrations fluoride changes the amounts and activity of COX-1 and COX-2 enzymes taking part in the initiating and development of inflammatory process.

Prostaglandin E2 EP3 receptor regulates cyclooxygenase-2 expression in the kidney

Cyclooxygenase-2 (COX-2) is constitutively expressed and highly regulated in the thick ascending limb (TAL). As COX-2 inhibitors (Coxibs) increase COX-2 expression, we tested the hypothesis that a negative feedback mechanism involving PGE(2) EP3 receptors regulates COX-2 expression in the TAL. Sprague-Dawley rats were treated with a Coxib [celecoxib (20 mg·kg(-1)·day(-1)) or rofecoxib (10 mg·kg(-1)·day(-1))], with or without sulprostone (20 μg·kg(-1)·day(-1)). Sulprostone was given using two protocols, namely, previous to Coxib treatment (prevention effect; Sulp7-Coxib5 group) and 5 days after initiation of Coxib treatment (regression effect; Coxib10-Sulp5 group). Immunohistochemical and morphometric analysis revealed that the stained area for COX-2-positive TAL cells (μm(2)/field) increased in Coxib-treated rats (Sham: 412 ± 56.3, Coxib: 794 ± 153.3). The Coxib effect was inhibited when sulprostone was used in either the prevention (285 ± 56.9) or regression (345 ± 51.1) protocols. Western blot analysis revealed a 2.1 ± 0.3-fold increase in COX-2 protein expression in the Coxib-treated group, an effect abolished by sulprostone using either the prevention (1.2 ± 0.3-fold) or regression (0.6 ± 0.4-fold vs. control, P < 0.05) protocols. Similarly, the 6.4 ± 0.6-fold increase in COX-2 mRNA abundance induced by Coxibs (P < 0.05) was inhibited by sulprostone; prevention: 0.9 ± 0.3-fold (P < 0.05) and regression: 0.6 ± 0.1 (P < 0.05). Administration of a selective EP3 receptor antagonist, L-798106, also increased the area for COX-2-stained cells, COX-2 mRNA accumulation, and protein expression in the TAL. Collectively, the data suggest that COX-2 levels are regulated by a novel negative feedback loop mediated by PGE(2) acting on its EP3 receptor in the TAL.

Ischemic injury enhances dendritic cell immunogenicity via TLR4 and NF-kappa B activation

Ischemic (isc) injury during the course of transplantation enhances the immunogenicity of allografts and thus results in poorer graft outcome. Given the central role of dendritic cells (DCs) in mounting alloimmune responses, activation of donor DCs by ischemia may have a primary function in the increased immunogenicity of isc allografts. In this study, we sought to investigate the effect of ischemia on DC activity in vitro. Following induction of ischemia, bone marrow-derived DCs were shown to augment allogeneic T cell proliferation as well as the IFN-gamma response. Isc DCs produced greater levels of IL-6, and isc insult was concurrent with NF-kappaB activation. TLR4 ligation was also shown to occur in isc DCs, most likely in response to the endogenous ligand heat shock protein 70, which was found to be elevated in DCs following isc injury, and lack of TLR4 abrogated the observed effects of isc DCs. As compared with control DCs, isc DCs injected into the footpads of mice demonstrated enhanced migration, which was concomitant with increased recipient T cell activity. Moreover, isc DCs underwent a greater degree of apoptosis in the lymph nodes of injected mice, which may further demonstrate enhanced immunogenicity of isc DCs. We thus show that isc injury of DCs enhances DC function, augments the allogeneic T cell response, and occurs via ligation of TLR4, followed by activation of NF-kappaB. These data may serve to identify novel therapeutic targets to attenuate graft immunogenicity following ischemia.

CCK-8 inhibits LPS-induced IL-1beta production in pulmonary interstitial macrophages by modulating PKA, p38, and NF-kappaB pathway

The neuropeptide cholecystokinin octapeptide (CCK-8) inhibits inflammation by downregulating the expression of proinflammatory cytokines, such as tumor necrosis factor alpha and interleukin (IL) 1beta during endotoxin shock. However, the signaling mechanism of CCK-8 action has not yet been clearly elucidated. In this study, we have examined the possible signaling pathways by which CCK-8 inhibits lipopolysaccharide (LPS)-induced IL-1beta production in rat pulmonary interstitial macrophages. In macrophages, LPS is known to activate p38 kinase, which, in turn, activates nuclear factor (NF)-kappaB to induce IL-1beta production. We found that the pretreatment of cells with CCK-8 blocked the LPS-induced p38 kinase, NF-kappaB activation, and IL-1beta production. Furthermore, CCK-8 treatment activated the cyclic adenosine monophosphate-protein kinase A signaling pathway and H-89 (a protein kinase A inhibitor), abrogated the inhibitory effects of CCK-8 on p38 kinase activation and NF-kappaB activation. In addition, we also demonstrate that the specific antagonist to CCK-1 receptor (CCK-1R) and CCK-2 receptor (CCK-2R) abrogate the CCK action, and that the effects of the antagonist specific to CCK-1R is more significant. These results suggest that these responses were mediated through CCK-1R and CCK-2R, and CCK-1R might be the major receptor responsible for the anti-inflammatory effect of CCK-8. Taken together, our results indicate that the stimulation of cyclic adenosine monophosphate-protein kinase A signaling pathway by CCK-8 through CCK-1R and CCK-2R inhibits the LPS-induced activation of p38 kinase and NF-kappaB to block the IL-1beta production in rat pulmonary interstitial macrophages.

Inhibition of phospholipase A2 activity by conjugated linoleic acids in human macrophages

The objective of this study was to assess the effect of conjugated linoleic acid isomers (CLAs) on the expression and activity of phospholipases A(2) (PLA(2)) in human macrophages. Macrophages were incubated with 30 microM cis-9, trans-11 and trans-10, cis-12 CLAs for 48 h. After incubation, the total activity of phospholipases as well as the expression of mRNA for cytosolic (cPLA(2)) and secretory (sPLA(2)) phospholipases and activity of sPLA(2) were measured. Both CLA isomers reduced the total activity of PLA(2) (by 30.2%, P < 0.01 for cis-9, trans-11 CLA and by 30%, P < 0.001 for trans-10, cis-12 CLA). Trans-10, cis-12 CLA isomer downregulated the expression of mRNA of sPLA(2) and decreased the enzymatic activity of this enzyme (by 23%, P = 0.02) in macrophages. Conjugated linoleic acid isomers can significantly reduce the activity of PLA(2) in macrophages and downregulate sPLA(2) expression. The consequence of this effect may be reduction of releasing the arachidonic acid (AA) from the cellular membranes of macrophages.

Secretory phospholipase A2 of group IIA: Is it an offensive or a defensive player during atherosclerosis and other inflammatory diseases?

Since its discovery in the serum of patients with severe inflammation and in rheumatoid arthritic fluids, the secretory phospholipase A2 of group IIA (sPLA2-IIA) has been chiefly considered as a proinflammatory enzyme, the result of which has been very intense interest in selective inhibitors of sPLA2-IIA in the hope of developing new and efficient therapies for inflammatory diseases. The recent discovery of the antibacterial properties of sPLA2-IIA, however, has raised the question of whether the upregulation of sPLA2-IIA during inflammation is to be considered uniformly negative and the hindrance of sPLA2-IIA in every instance beneficial. The aim of this review is for this reason, along with the results of various investigations which argue for the proinflammatory and proatherogenic effects of an upregulation of sPLA2-IIA, also to array data alongside which point to a protective function of sPLA2-IIA during inflammation. Thus, it could be shown that sPLA2-IIA, apart from the bactericidal effects, possesses also antithrombotic properties and indeed plays a possible role in the resolution of inflammation and the accelerated clearance of oxidatively modified lipoproteins during inflammation via the liver and adrenals. Based on these multipotent properties the knowledge of the function of sPLA2-IIA during inflammation is a fundamental prerequisite for the development and establishment of new therapeutic strategies to prevent and treat severe inflammatory diseases up to and including sepsis.

Regulation of interleukin-12 gene expression and its anti-tumor activities by prostaglandin E2 derived from mammary carcinomas

Interleukin-12 (IL-12)-mediated immune responses are critical for the control of malignant development. Tumors can actively resist detrimental immunity of the host via many routes. Prostaglandin E2 (PGE2) is one of the major immune-suppressive factors derived from many types of tumors. Here, we show that systemic administration of recombinant IL-12 could therapeutically control the growth of aggressive TS/A and 4T1 mouse mammary carcinomas. However, PGE2 produced by tumors potently inhibits the production of endogenous IL-12 at the level of protein secretion, mRNA synthesis, and transcription of the constituent p40 and p35 genes. The inhibition can be reversed by NS-398, a selective inhibitor of the enzymatic activity of cyclooxygenase 2 in PGE2 synthesis. Moreover, PGE2-mediated inhibition of IL-12 production requires the functional cooperation of AP-1 and AP-1 strongly suppresses IL-12 p40 transcription. Blocking PGE2 production in vivo results in a marked reduction in lung metastasis of 4T1 tumors, accompanied by enhanced ability of peritoneal macrophages to produce IL-12 and spleen lymphocytes to produce interferon-gamma. This study contributes to the elucidation of the molecular mechanisms underlying the interaction between a progressive malignancy and the immune defense apparatus.

Pertussis toxin-sensitive secretory phospholipase A2 expression and motility in activated primary human keratinocytes

Secretory phospholipase A2 and cycloxygenase-2 are coexpressed in activated primary keratinocytes. These proteins are known to be functionally linked, mediating proliferation of human keratinocytes during epidermal wound repair. Primary human keratinocytes grown at low densities (15-30%; nonconfluent) produce high levels of prostaglandin E2 important for proliferation and are a good model for studying activated keratinocytes after injury. In this study, we used this model to assess the role of secretory phospholipase A2 and cycloxygenase-2 in keratinocyte motility. Initial work showed 24 h pretreatment with 20 ng pertussis toxin per ml, an inhibitor of the inhibitory G-protein, decreased prostaglandin E2 production and both secretory phospholipase A2 and cycloxygenase-2 protein expression. This suggested that inhibitory G-protein may be involved in mediating expression of these proteins. Pertussis toxin also caused changes in cell morphology, actin organization, and keratinocyte motility. Pretreatment with 5 microm 12-epi-scalaradial, a secretory phospholipase A2 inhibitor, caused similar changes in cell motility and actin organization; however, the specific cycloxygenase-2 inhibitor, SC-58236 (20 nm) was much less effective. These results suggested that secretory phospholipase A2 plays a part in keratinocyte motility that is independent of its functional linkage to cycloxygenase-2 and prostaglandin E2 biosynthesis.

Arachidonic acid differentially affects basal and lipopolysaccharide-induced sPLA(2)-IIA expression in alveolar macrophages through NF-kappaB and PPAR-gamma-dependent pathways

Secretory type IIA phospholipase A(2) (sPLA(2)-IIA) is a critical enzyme involved in inflammatory diseases. We have previously identified alveolar macrophages (AMs) as the major pulmonary source of lipopolysaccharide (LPS)-induced sPLA(2)-IIA expression in a guinea pig model of acute lung injury (ALI). Here, we examined the role of arachidonic acid (AA) in the regulation of basal and LPS-induced sPLA(2)-IIA expression in AMs. We showed that both AA and its nonmetabolizable analog, 5,8,11,14-eicosatetraynoic acid (ETYA), inhibited sPLA(2)-IIA synthesis in unstimulated AMs. However, only AA inhibited sPLA(2)-IIA expression in LPS-stimulated cells, suggesting that this effect requires metabolic conversion of AA. Indeed, cyclooxygenase inhibitors abolished this down-regulation. Prostaglandins PGE(2), PGA(2), and 15d-PGJ(2) also inhibited the LPS-induced sPLA(2)-IIA expression. Nuclear factor-kappaB (NF-kappaB) was found to regulate sPLA(2)-IIA expression in AMs. Both AA and ETYA inhibited basal activation of NF-kappaB but had no effect on LPS-induced NF-kappaB translocation, suggesting that suppression of sPLA(2)-IIA synthesis by AA in LPS-stimulated cells occurs via a NF-kappaB-independent pathway. 15-Deoxy-Delta(12,14)-PGJ(2) and ciglitazone, which are, respectively, natural and synthetic ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma), inhibited LPS-induced sPLA(2)-IIA synthesis, whereas PPAR-alpha ligands were ineffective. Moreover, electrophoretic mobility shift assay showed PPAR activation by AA and PPAR-gamma ligands in LPS-stimulated AMs. Our results suggest that the down-regulation of basal sPLA(2)-IIA expression is unrelated to the metabolic conversion of AA but is dependent on the impairment of NF-kappaB activation. In contrast, the inhibition of LPS-stimulated sPLA(2)-IIA expression is mediated by cyclooxygenase-derived metabolites of AA and involves a PPAR-gamma-dependent pathway. These findings provide new insights for the treatment of ALI.

Prostaglandin E2 concentrations in gingival crevicular fluid: observations in untreated chronic periodontitis

OBJECTIVES

We set out to monitor gingival crevicular fluid prostaglandin E2 (GCF-PGE2) concentrations longitudinally in a cohort of subjects with chronic periodontitis, given that we had noted an unexplained trend for GCF-PGE2 concentrations to gradually increase in control groups and placebo populations in previously published clinical trials.

MATERIAL AND METHODS

41 adults with moderate-severe chronic periodontitis were recruited. GCF samples were collected from 8 test sites (with 5-8 mm probing depths and attachment loss) every 30 days for 150 days, and assayed for PGE2. Clinical measurements (probing depths, attachment levels, bleeding on probing) were recorded at days 0 and 150.

RESULTS

A gradual and statistically significant increase in GCF-PGE2 concentrations was observed over the course of the study, from 40.3 ng/ml to 83.1 ng/ml (p<0.001). When data were expressed as absolute PGE2 content, a similar statistically significant increase from baseline to day 150 was observed (p<0.001). GCF volumes did not vary significantly during the study (p>0.05). Over the same time period, no statistically significant changes in clinical parameters were recorded, with the exception of mean probing depths, which decreased slightly from 5.73 mm to 5.51 mm (p<0.05).

CONCLUSION

A trend for gradually increasing GCF-PGE2 concentrations in the absence of any clinical signs of disease progression was noted in a group of patients monitored longitudinally. We suggest that this phenomenon is to be expected in longitudinal clinical trials, and propose a new model for the role of PGE2 in the pathogenesis of periodontal destruction. We feel that if GCF mediators are to be monitored in clinical studies, then both concentrations and absolute mediator content should be calculated, and a standardised sampling protocol should be employed.

Protein kinase A-dependent stimulation of rat type II secreted phospholipase A(2) gene transcription involves C/EBP-beta and -delta in vascular smooth muscle cells

Type II secreted phospholipase A(2) (sPLA(2)) releases precursors of important inflammatory lipid mediators from phospholipids. Some observations have indicated that the sPLA(2), which has been implicated in chronic inflammatory conditions such as arthritis, contributes to atherosclerosis in the arterial wall. sPLA(2) was not detected in control vascular smooth muscle cells (VSMC). Treatment of VSMC with agents that increase intracellular cAMP (eg, forskolin, dibutyryl [db]-cAMP) resulted in a time- and concentration-dependent increase in sPLA(2) gene expression. Semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) showed a marked dose-dependent inhibition of forskolin-induced mRNA by protein kinase A inhibitor. Electrophoretic mobility shift analysis of nuclear proteins from forskolin-treated and db-cAMP-treated VSMC with C/EBP consensus oligonucleotides and C/EBP oligonucleotides from the rat promoter revealed greater binding than in control VSMC. Incubation of VSMC with H89, a specific protein kinase inhibitor, also blocked the binding of nuclear C/EBP to the C/EBP site of the rat promoter induced by db-cAMP and forskolin. Binding was unchanged with the use of CRE consensus oligonucleotides. Antibodies revealed the specific formation of C/EBP/DNA complexes, the majority of which were supershifted by C/EBP-ss and -delta antibodies. Functional activation of C/EBP was confirmed by a luciferase reporter gene assay. A construct comprising 4 tandem repeat copies of the C/EBP element from the rat sPLA(2) promoter linked to luciferase was transcriptionally activated in VSMC by cotransfection with expression vector for the protein kinase A catalytic subunit. It was also significantly activated in transfected VSMC treated by forskolin or db-cAMP. H89 inhibited this activations. We therefore conclude that the increases in sPLA(2) mRNA and enzyme activity produced by cAMP-elevating agents is controlled by a mechanism involving nuclear C/EBP-ss and -delta acting through a protein kinase A signaling pathway.

Tumor necrosis factor has positive and negative self regulatory feed back cycles centered around cAMP

This paper reviews data that allow recognition of, (1) two opposing intracellular chains of events occurring subsequent to an increase in tumor necrosis factor, TNF, and (2) that these two chains have opposing effects on intracellular cyclic adenosine monophosphate, cAMP. The two chains - attenuation cycle, where TNF results in prostaglandin E mediated increased cAMP and, consequent to this, suppression of TNF levels; and an amplification cycle, where increased TNF increases intracellular cyclic adenosine phosphodiesterase, lowering cAMP, thereby raising TNF levels further. TNF is a central mediator in several inflammatory diseases. Understanding TNF control systems will allow better delineation of pathophysiology and clinical care.

Attenuation of macrophage apoptosis by the cAMP-signaling system

Previous studies revealed that expression and activation of cyclooxygenase-2 (Cox-2) conveyed a protective principle in murine macrophages, thus attenuating pro-apoptotic actions of chemotherapeutic agents or programmed cell death as a result of massive nitric oxide (NO) generation. Expression of Cox-2 was achieved by treatment of cells with lipopolysaccharide/interferon-gamma or nontoxic doses of NO releasing agents. We reasoned E-type prostanoid formation, and in turn an intracellular cAMP increase as the underlying protective mechanism. To prove our hypothesis, we analyzed the effects of lipophilic cAMP-analogs on NO, cisplatin, or etoposide induced apoptosis in RAW 264.7 macrophages. Selected apoptotic parameters comprised DNA fragmentation (diphenylamine assay), annexin V staining of phosphatidylserine, caspase activity (quantitated by the cleavage of a fluorogenic caspase-3-like substrate Ac-DEVD-AMC), and mitochondrial membrane depolarisation (delta psi). Western blots detected accumulation of the tumor suppressor protein p53, relocation of cytochrome c to the cytosol, and expression of the anti-apoptotic protein Bcl-xL. Prestimulation with lipophilic cAMP-analogs attenuated apoptosis with the notion that cell death parameters were basically absent. To verify gene induction by cAMP in association with protection we established activation of cAMP response element binding protein (CREB) by gel-shift analysis and moreover, treated macrophages with oligonucleotides containing a cAMP-responsive element (CRE) in order to scavenge CREB. Decoy oligonucleotides, but not control oligonucleotides, attenuated cAMP-evoked protection and reestablished pro-apoptotic parameters. We conclude that gene induction by cAMP protects macrophages towards apoptosis that occurs as a result of excessive NO formation or addition of chemotherapeutica. Attenuating programmed cell death by the cAMP-signaling system may be found in association with Cox-2 expression and tumor formation.

Inhibition by unsaturated fatty acids of type II secretory phospholipase A2 synthesis in guinea-pig alveolar macrophages evidence for the eicosanoid-independent pathway

The effect of arachidonic acid (C20:4) on the production of secretory type II phospholipase A2 (sPLA2-II) by guinea-pig alveolar macrophages was investigated. We show that incubation of these cells with 1-30 microM of arachidonic acid inhibits the synthesis of sPLA2-II in a concentration-dependent manner with an IC50 of approximately 7.5 microM. The inhibition by low concentrations (5 microM) of arachidonic acid was partially reduced by pretreatment of alveolar macrophages with cyclooxygenase or cytochrome P450 inhibitors (aspirin and 1-aminobenzotriazole, respectively), but not by lipoxygenase inhibitor, BW A4C. However, these inhibitors failed to interfere with the effect of high concentrations (30 microM) of arachidonic acid, suggesting that the latter may act on the expression of sPLA2-II, at least in part, independently of eicosanoid generation. Indeed, a similar inhibitory effect on sPLA2-II activity and mRNA expression was observed with other unsaturated fatty acids such as eicosapentaenoic (C20:5) and oleic (C18:1) acids, but not with the saturated fatty acid, palmitic acid (C16:0). In addition, arachidonic acid partially reduced the secretion of tumor necrosis factor alpha, an important intermediate in the induction of sPLA2-II synthesis by guinea-pig alveolar macrophages. However, addition of recombinant tumor necrosis factor alpha failed to reverse the inhibitory effect of arachidonic acid on sPLA2-II expression, suggesting that this process occurs downstream of tumor necrosis factor alpha secretion. We conclude that the expression of sPLA2-II in alveolar macrophages is down-regulated at the transcriptional level by arachidonic acid either directly or via its cyclooxygenase and cytochrome P450-derived metabolites.

Prostaglandin E2 stimulates AP-1-mediated CD14 expression in mouse macrophages via cyclic AMP-dependent protein kinase A

PGs play a functional role in the early stage of Gram-negative bacterial infections, because this prostanoid is produced rapidly by epithelial cells after a bacterial infection. CD14, one of the LPS receptors, is a key molecule in triggering the response to bacterial LPS in association with a Toll-like molecule. Therefore, in this study, we investigated the effect of PG on CD14 expression in mouse macrophages. PGE1, PGE2, and PGA1 among the PGs tested strongly stimulated the expression of the CD14 gene in the cells. The stimulatory action also was observed by Western blot analysis. cAMP-elevating agents stimulated expression of CD14 gene as well. Protein kinase A inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not protein kinase C inhibitor 3-(1-[3-(dimethylamino)propyl]-1H-indol-3-yl)-4-(1H-indol-3-yl)-1H-py rrole-2,5-dione (GF109203X), abolished the stimulated expression of CD14. A run-on assay showed that PGE2 stimulated the CD14 gene expression at the transcriptional level via protein kinase A. PGE2 also stimulated activation of AP-1, a heterodimer of c-Jun and c-Fos, because the prostanoid increased specific binding of nuclear proteins to the AP-1 consensus sequence and stimulated AP-1-promoted luciferase activity. PGE2-stimulated expression of CD14 was inhibited by antisense c-fos and c-jun oligonucleotides, but not by their sense oligonucleotides. Finally, PGE2 pretreatment synergistically stimulated LPS-induced expression of IL-1beta and IL-6 genes in mouse macrophages. Therefore, the present study demonstrates that PGE2 has the ability to stimulate AP-1-mediated expression of CD14 in mouse macrophages via cAMP-dependent protein kinase A.

NO-Evoked macrophage apoptosis is attenuated by cAMP-induced gene expression

BACKGROUND

Previous work has suggested that an increase in expression of cyclooxygenase-2, concomitant formation of E-type prostanoids, and in turn intracellular cAMP conveys macrophage resistance against apoptosis.

MATERIALS AND METHODS

We analyzed the effects of lipophilic cAMP analogs on nitric oxide (NO)-induced apoptosis in RAW 264.7 macrophages and human primary monocyte-derived macrophages. Parameters comprised DNA fragmentation (diphenylamine assay), annexin V staining of phosphatidylserine, caspase activity (quantitated by the cleavage of a fluorogenic caspase-3-like substrate Ac-DEVD-AMC), and mitochondrial membrane depolarization (DeltaPsi), analyzed using DiOC(6)(3). Western blots detected accumulation of the tumor suppressor protein p53, relocation of cytochrome c, and expression of the antiapoptotic protein Bcl-X(L). A cAMP response-element decoy approach confirmed cAMP-dependent gene induction.

RESULTS

We verified resistance of murine and human macrophages against NO donors such as S-nitrosoglutathione or spermine-NO by pre-exposing cells to lipophilic cAMP analogs or by pretreatment with lipopolysaccaride, interferon-gamma, and N(G)-nitroarginine-methylester for 15 hr. Cellular prestimulation decreased NO-evoked apoptosis, as apoptotic parameters were basically absent. Macrophage protection was not achieved during a short period of preexposure, i.e., 1 hr. To verify gene induction as the underlying protective principle, we treated RAW cells with oligonucleotides containing a cAMP-responsive element in order to scavenge cAMP response element-binding protein prior to its promoter-activating ability. Decoy oligonucleotides, but not an unrelated control oligonucleotide, weakened cAMP-evoked protection and re-established a p53 response following NO addition.

CONCLUSION

Gene induction by cAMP protects macrophages against apoptosis that occurs as a result of excessive NO formation. Decreasing programmed cell death of macrophages may perpetuate inflammatory conditions in humans when macrophages become activated in close association with innate immune responses.

A role for phospholipase A2 in ARDS pathogenesis

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury that is characterized by arterial hypoxemia and noncardiogenic pulmonary oedema. One feature of ARDS is an alteration of pulmonary surfactant that increases surface tension at the air-liquid interface and results in alveolar collapse and the impairment of gas exchange. Type-II secretory phospholipase A2 (sPLA2-II) plays a major role in the hydrolysis of surfactant phospholipids and its expression is inhibited by surfactant. Here, we discuss the evidence that in pathological situations, such as ARDS, in which surfactant is altered, sPLA2-II production is exacerbated, leading to further surfactant alteration and the establishment of a vicious cycle.