Studies on the induction of cyclooxygenase isozymes by various prostaglandins in mouse osteoblastic cell line with reference to signal transduction pathways

Prostaglandin E2 inhibits the proliferation of human gingival fibroblasts via the EP2 receptor and Epac

Elevated levels of prostaglandins such as PGE(2) in inflamed gingiva play a significant role in the tissue destruction caused by periodontitis, partly by targeting local fibroblasts. Only very few studies have shown that PGE(2) inhibits the proliferation of a gingival fibroblast (GF) cell line, and we expanded this research by using primary human GFs (hGFs) and looking into the mechanisms of the PGE(2) effect. GFs derived from healthy human gingiva were treated with PGE(2) and proliferation was assessed by measuring cell number and DNA synthesis and potential signaling pathways were investigated using selective activators or inhibitors. PGE(2) inhibited the proliferation of hGFs dose-dependently. The effect was mimicked by forskolin (adenylate cyclase stimulator) and augmented by IBMX (a cAMP-breakdown inhibitor), pointing to involvement of cAMP. Indeed, PGE(2) and forskolin induced cAMP generation in these cells. Using selective EP receptor agonists we found that the anti-proliferative effect of PGE(2) is mediated via the EP(2) receptor (which is coupled to adenylate cyclase activation). We also found that the effect of PGE(2) involved activation of Epac (exchange protein directly activated by cAMP), an intracellular cAMP sensor, and not PKA. While serum increased the amount of phospho-ERK in hGFs by approximately 300%, PGE(2) decreased it by approximately 50%. Finally, the PGE(2) effect does not require endogenous production of prostaglandins since it was not abrogated by two COX-inhibitors. In conclusion, in human gingival fibroblasts PGE(2) activates the EP(2)-cAMP-Epac pathway, reducing ERK phosphorylation and inhibiting proliferation. This effect could hamper periodontal healing and provide further insights into the pathogenesis of inflammatory periodontal disease.

The Interaction between Orally Administered Non-Steroidal Anti-Inflammatory Drugs and Prednisolone in Healthy Dogs

The interaction between oral non-steroidal anti-inflammatory drugs (NSAIDs) and prednisolone administered concurrently for 30 days was studied in 18 healthy dogs divided into 3 groups of 6 dogs each: a drug-free negative control group (NC group) given 2 gelatin capsules; a group given meloxicam (0.1 mg/kg) and prednisolone (0.5 mg/kg) (MP group); and a group given a reduced dosage of ketoprofen (0.25 mg/kg, p.o.) and prednisolone (0.5 mg/kg, p.o.) (KP group). The dogs were periodically monitored by physical examinations, blood analyses, endoscopic examinations, fecal occult blood tests, renal function tests [effective renal plasma flow (ERPF) and glomerular filtration rate (GFR)], urinalyses [urinary sediments, and urinary micro-albumin to creatinine ratio (UAlb/Cre)], urinary enzyme indices, and haemostatic function tests [buccal mucosa bleeding time (BMBT), cuticle bleeding time (CBT)]. Significant changes were observed in the KP group, including a decrease of ERPF and GFR, an increased UAlb/Cre ratio, prolonged BMBT and CBT, as well as the presence of more severe grades of endoscopic lesions and fecal occult blood. In both the MP and KP groups, abnormal enzymuria with exfoliation of renal tubular epithelial cells in the urine was found. However, no significant changes in any of the other tests were observed in the MP group compared with the NC group. These findings suggest that the combination of NSAIDs, even selective COX-2 inhibitors, with prednisolone may be contraindicated due to the potential for serious adverse effects on the kidneys, the platelets, and the gastrointestinal tract.

Stimulation of prostaglandin E2 (PGE2) production by arachidonic acid, oestrogen and parathyroid hormone in MG-63 and MC3T3-E1 osteoblast-like cells

Polyunsaturated fatty acids (PUFAs) as well as oestrogen (E2) and parathyroid hormone (PTH) affect bone cells. The aim of the study was to determine whether arachidonic acid (AA), E2, and PTH increase prostaglandin E(2) (PGE(2)) synthesis in MG-63 and MC3T3-E1 osteoblastic cells and the level of mediation by COX-1 and COX-2. PGE(2) levels were determined in the conditioned culture media of MG-63 and MC3T3-E1 osteoblasts after exposure to AA, PTH and E2. Cells were pre-incubated in some experiments with the unselective COX inhibitor indomethacin or the COX-2 specific blocker NS-398. Indirect immunofluorescence was performed on MG-63 cells to detect the presence and location of the two enzymes involved. AA increased PGE(2) secretion in both cell lines; production by MC3T3-E1 cells, however, was significantly higher than that of MG-63 cells. This could be due to autoamplification via the EP(1) subtype of PGE receptors in mouse MC3T3-E1 osteoblasts. Both COX-1 and COX-2 affected the regulation of PGE(2) synthesis in MG-63 cells. E2 had no effect on PGE(2) secretion in both cell lines, while PTH caused a slight increase in PGE(2) synthesis in the MG-63 cell line.

Cyclooxygenase-2-specific inhibitor improves functional outcomes, provides neuroprotection, and reduces inflammation in a rat model of traumatic brain injury

OBJECTIVE

Increases in brain cyclooxygenase-2 (COX2) are associated with the central inflammatory response and with delayed neuronal death, events that cause secondary insults after traumatic brain injury. A growing literature supports the benefit of COX2-specific inhibitors in treating brain injuries.

METHODS

DFU [5,5-dimethyl-3(3-fluorophenyl)-4(4-methylsulfonyl)phenyl-2(5)H)-furanone] is a third-generation, highly specific COX2 enzyme inhibitor. DFU treatments (1 or 10 mg/kg intraperitoneally, twice daily for 3 d) were initiated either before or after traumatic brain injury in a lateral cortical contusion rat model.

RESULTS

DFU treatments initiated 10 minutes before injury or up to 6 hours after injury enhanced functional recovery at 3 days compared with vehicle-treated controls. Significant improvements in neurological reflexes and memory were observed. DFU initiated 10 minutes before injury improved histopathology and altered eicosanoid profiles in the brain. DFU 1 mg/kg reduced the rise in prostaglandin E2 in the brain at 24 hours after injury. DFU 10 mg/kg attenuated injury-induced COX2 immunoreactivity in the cortex (24 and 72 h) and hippocampus (6 and 72 h). This treatment also decreased the total number of activated caspase-3-immunoreactive cells in the injured cortex and hippocampus, significantly reducing the number of activated caspase-3-immunoreactive neurons at 72 hours after injury. DFU 1 mg/kg amplified potentially anti-inflammatory epoxyeicosatrienoic acid levels by more than fourfold in the injured brain. DFU 10 mg/kg protected the levels of 2-arachidonoyl glycerol, a neuroprotective endocannabinoid, in the injured brain.

CONCLUSION

These improvements, particularly when treatment began up to 6 hours after injury, suggest exciting neuroprotective potential for COX2 inhibitors in the treatment of traumatic brain injury and support the consideration of Phase I/II clinical trials.

Salicylate Regulates COX‐2 Expression Through ERK and Subsequent NF‐κB Activation in Osteoblasts

The expression of cyclooxygenase-2 (COX-2) is a characteristic response to inflammation and can be inhibited with sodium salicylate. TNF-alpha plus IFN-gamma can induce extracellular signal-regulated kinase (ERK), IKK, IkappaB degradation and NF-kappaB activation. The inhibition of the ERK pathway with selective inhibitor, PD098059, blocked cytokine-induced COX-2 expression and PGE2 release. Salicylate treatment inhibited COX-2 expression induced by TNF-alpha/IFN-gamma and regulated the activation of ERK, IKK and IkappaB degradation and subsequent NF-kappaB activation in MC3T3E1 osteoblasts. As well, antioxidant-catalase, N-acetyl-cysteine or reduced glutathione-attenuated COX-2 expression in combined cytokines-treated cells. These antioxidants also inhibited the activation of ERK, IKK and NF-kappaB in MC3T3E1 osteoblasts. In addition, TNF-alpha/IFN-gamma stimulated ROS release in the osteoblasts. However salicylate had no obvious effect on ROS release in DCFDA assay. The results showed that salicylate inhibited the activation of ERK and IKK, IkappaB degradation and NF-kappaB activation independent of ROS release and suggested that salicylate exerts its anti-inflammatory action in part through inhibition of the ERK, IKK, IkappaB, NF-kappaB and resultant COX-2 expression pathway.

Microarray evaluation of EP4 receptor-mediated prostaglandin E2 suppression of 3T3-L1 adipocyte differentiation

Prostaglandin E(2) (PGE(2)) has been shown to negatively regulate adipogenesis. To explore to what extent PGE(2) inhibits the differentiation of cells to adipocytes and to examine whether its effect could be due to EP4 receptor signaling, we used microarrays to analyze the gene expression profiles of 3T3-L1 cells exposed to a differentiation cocktail supplemented with PGE(2), AE1-329 (an EP4 agonist), or vehicle. The differentiation-associated responses in genes such as adipocytokines and enzymes related to lipid metabolism were largely weakened upon PGE(2) treatment. In particular, the expression of peroxisome proliferator activated receptor-gamma and CCAAT/enhancer binding protein-alpha, genes playing a central role in adipogenesis, was greatly suppressed. PGE(2) appears to be ineffective to a subclass of insulin target genes such as hexokinase 2 and phosphofructokinase. Similar responses were produced in the differentiation-associated genes upon AE1-329 treatment. These results suggest that PGE(2) inhibits a crucial step of the adipocyte differentiation process by acting on the EP4 receptor in 3T3-L1 cells.

Entamoeba histolytica: induction of cyclooxygenase-2 expression during amoebic liver abscess formation in hamsters (Mesocricetus auratus)

Experimental amoebic liver abscess in hamsters curses with an increase in both, systemic levels of prostaglandin E2 (PGE(2)) and local cyclooxygenase activity in liver microsomes. The cellular source of PGE(2) and the isoform of cyclooxygenase responsible are not completely evidenced. Cyclooxygenase-2 (COX-2) protein and gene expression were demonstrated on macrophages and polymorphonuclear cells as a result of Entamoeba histolytica infection in hamsters at 2, 4, and 7 days postinfection by immunohistochemistry and RT-PCR. E. histolytica trophozoites located in the lesion showed a strong positive signal for COX-2, however the enzyme was not detected in cultured trophozoites by Western blot. Our results indicate that the increment in PGE(2) is the result of COX-2 activity from cells of the reticuloendothelial system and reinforce the possibility that PGE(2) production by enzyme induction in macrophages may be a mechanism by which E. histolytica modulates the host immune response in this parasitic infection.

Role of prostaglandin H2 synthase 2 in murine parturition: study on ovariectomy-induced parturition in prostaglandin F receptor-deficient mice

To determine the prostaglandin (PG) H2 synthase (generally referred to as cyclooxygenase [COX]) isozyme responsible for producing uterotonic PGs during parturition, we used PGF2alpha receptor-deficient mice, which exhibit parturition failure due to impaired withdrawal of serum progesterone at term. On ovariectomy-induced parturition in these mice, uterine COX-2 mRNA expression was drastically induced in the myometrium, whereas COX-1 mRNA expression in the endometrial epithelium decreased. The concomitant administration of progesterone with ovariectomy resulted in a delay in parturition and the disappearance of both the increase in COX-2 mRNA and the decrease in COX-1 mRNA. Thus, the expression of myometrial COX-2 and the occurrence of parturition are closely associated in this model. Furthermore, administration of the COX-nonselective inhibitor, indomethacin, or the COX-2-selective inhibitor, Dup-697 or JTE-522, effectively delayed ovariectomy-induced parturition in these mice. These findings suggest that COX-2-derived PGs contribute to the onset of parturition after the decrease in serum progesterone level.

Increase in IP3 and intracellular Ca2+ induced by phosphate depletion in LLC-PK 1 cells

The mechanisms by which Pi depletion rapidly regulates gene expression and cellular function have not been clarified. Here, we found a rapid increase in intracellular ionized calcium [Ca(2+)](i) by phosphate depletion in LLC-PK(1) cells using confocal microscopy with the green-fluorescence protein based calcium indicator "yellow cameleon 2.1." The increase of [Ca(2+)](i) was observed in the presence or absence of extracellular Ca(2+). At the same time, an approximately twofold increase in intracellular inositol 1,4,5-triphosphate (IP(3)) occurred in response to the acute Pi depletion in the medium. Furthermore, 2-aminoethoxydiphenyl borate completely blocked the [Ca(2+)](i) increase induced by Pi depletion. These results suggest that Pi depletion causes IP(3)-mediated release of Ca(2+) from intracellular Ca(2+) pools and rapidly increases [Ca(2+)](i) in LLC-PK(1) cells.

Ketoconazole suppresses prostaglandin E(2)-induced cyclooxygenase-2 expression in human epidermoid carcinoma A-431 cells

Cyclooxygenase-2 is a key enzyme in the conversion of arachidonic acid to prostaglandins. The overexpression of cyclooxygenase-2 has been reported in skin cancer cells, and may be involved in carcinogenesis. Prostaglandin E2, the end product of cyclooxygenase-2-induced catalysis, autoamplifies the cyclooxygenase-2 expression. It is suggested that an anti-mycotic drug, ketoconazole may inhibit carcinogenesis. We herein investigated if ketoconazole may inhibit prostaglandin E2-induced cyclooxygenase-2 expression in human epidermoid carcinoma A-431 cells. Ketoconazole suppressed prostaglandin E2-induced cyclooxygenase-2 protein and mRNA expression and promoter activation in A-431; the suppressive effects of ketoconazole were counteracted by cyclic adenosine monophosphate analog. Analyses using deleted or mutated cyclooxygenase-2 promoters revealed that cyclic adenosine monophosphate response element (- 59 to - 53 bp) on the promoter was involved in prostaglandin E2-induced stimulation and ketoconazole-induced inhibition of the promoter activity. Electrophoretic mobility shift assays indicated that cyclic adenosine monophosphate response element binding protein and activating transcription factor-1 may constitutively bind to cyclic adenosine monophosphate response element on cyclooxygenase-2 promoter. Prostaglandin E2 increased the proportion of phosphorylated forms among total bound cyclic adenosine monophosphate response element binding protein/activating transcription factor-1, and the effect was suppressed by ketoconazole. Prostaglandin E2 induced the phosphorylation of cyclic adenosine monophosphate response element binding protein and activating transcription factor-1, and the phosphorylation was suppressed by cyclic adenosine monophosphate-dependent protein kinase (protein kinase A) inhibitor, indicating protein kinase A-mediated phosphorylation. Ketoconazole suppressed the prostaglandin E2-induced phosphorylation of cyclic adenosine monophosphate response element binding protein/activating transcription factor-1. Prostaglandin E2 increased intracellular cyclic adenosine monophosphate level by activating adenylate cyclase in A-431, and the increase was suppressed by ketoconazole. These results suggest that ketoconazole may suppress prostaglandin E2-induced cyclooxygenase-2 expression by inhibiting the cyclic adenosine monophosphate signal in A-431, and stress its anti-cancer effect.

Obligatory role of cyclic adenosine monophosphate response element in cyclooxygenase-2 promoter induction and feedback regulation by inflammatory mediators

BACKGROUND

Cyclooxygenase-2 (COX-2) plays a key role in human inflammatory disorders such as vascular inflammation. COX-2 promoter activity is induced by proinflammatory mediators, but the role of cyclic adenosine monophosphate response element (CRE) in promoter stimulation remains unclear.

METHODS AND RESULTS

Transient transfection of a 0.9-kb COX-2 promoter fragment bearing CRE mutation abrogated COX-2 promoter activity induced by proinflammatory mediators in human endothelial cells and fibroblasts. Dual mutations of CRE and an upstream CCAAT/enhancer binding protein (C/EBP) site did not have an additional effect. Binding of CREB-2, ATF-2, USF-2, and c-Jun transactivators to a wild-type and CRE-mutated oligonucleotide was analyzed by a novel DNA-binding assay. CREB-2 and ATF-2 in nuclear extracts of unstimulated endothelial cells bound to CRE, whereas USF-2 and c-Jun or c-Fos bound to non-CRE sites. CREB-2 and c-Fos binding was increased by phorbol 12-myristate 13-acetate but not tumor necrosis factor-alpha. The binding assay and chromatin immunoprecipitation revealed binding of P300 coactivator to the COX-2 promoter region.

CONCLUSIONS

CRE plays an obligatory role in COX-2 promoter activation by diverse stimuli. CREB-2 and ATF-2 bound to CRE serve as an anchor for P300 interaction with upstream transactivators and downstream transcription machinery.

PGE(2) is essential for gap junction-mediated intercellular communication between osteocyte-like MLO-Y4 cells in response to mechanical strain

We have observed, in our previous studies, that fluid flow increases gap junction-mediated intercellular coupling and the expression of a gap junction protein, connexin 43, in osteocyte-like MLO-Y4 cells. Interestingly, this stimulation is further enhanced during the poststress period, indicating that a released factor(s) is likely to be involved. Here, we report that the conditioned medium obtained from the fluid flow-treated MLO-Y4 cells increased the number of functional gap junctions and connexin 43 protein. These changes are similar to those observed in MLO-Y4 cells directly exposed to fluid flow. Fluid flow was found to induce PGE(2) release and increase cyclooxygenase 2 expression. Treatment of the cells with PGE(2) had the same effect as fluid flow, suggesting that PGE(2) could be responsible for these autocrine effects. When PGE(2) was depleted from the fluid flow-conditioned medium, the stimulatory effect on gap junctions was partially, but significantly, decreased. Addition of the cyclooxygenase inhibitor, indomethacin, partially blocked the stimulatory effects of mechanical strain on gap junctions. Taken together, these studies suggest that the stimulatory effect of fluid flow on gap junctions is mediated, in part, by the release of PGE(2). Hence, PGE(2) is an essential mediator between mechanical strain and gap junctions in osteocyte-like cells.

Modulation of cyclooxygenase-2 and brain reactive astrogliosis by purinergic P2 receptors

Astroglial cells respond to trauma and ischemia with reactive gliosis, a reaction characterized by increased astrocytic proliferation and hypertrophy. Although beneficial to a certain extent, excessive gliosis may be detrimental, contributing to neuronal death in neurodegenerative diseases. We have tested the hypothesis that ATP may act as a trigger of reactive gliosis in an in vitro model (rat brain primary astrocytes) where reactive astrogliosis can be quantified as elongation of astrocytic processes. Challenge of cells with the ATP analog alpha,beta methyleneATP (alpha,beta meATP) resulted in concentration dependent elongation of astrocytic processes, an effect that was fully counteracted by the non-selective ATP/P2 receptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). Signalling studies revealed that alpha,beta meATP-induced gliosis is mediated by a novel G-protein-coupled receptor (a P2Y receptor) coupled to an early release of arachidonic acid. Challenge of cells with alpha,beta meATP also resulted in an increase of inducible cyclooxygenase-2 (COX-2), the activity of which has been reported to be pathologically increased in a variety of neurodegenerative diseases characterized by inflammation and astrocytic activation. Induction of COX-2 by alpha,beta meATP was causally related to reactive astrogliosis, since the selective COX-2 inhibitor NS-398 prevented both the purine-induced elongation of astrocytic processes and the associated COX-2 increase. Preliminary data on the putative receptor-to-nucleus pathways responsible for purine-induced gliosis suggest that induction of the COX-2 gene may occur through the protein kinase C/mitogen activated protein kinase system, and may involve the formation of activated AP-1 transcription complexes. We speculate that antagonists selective at this novel P2Y receptor subtype may represent a novel class of neuroprotective agents able to slow down neurodegeneration by counteracting the inflammatory events contributing to neuronal cell death.

Lack of cyclooxygenase-2 inhibits growth of teratocarcinomas in mice

Two isoforms of cyclooxygenase (COX-1 or COX-2) have been identified in the prostanoid biosynthetic pathway. The constitutive form, COX-1, is thought to maintain cellular homeostasis and the inducible form, COX-2, is recognized as a primary response gene thought to be involved in modulating cell proliferation and differentiation. To further characterize the role of the cyclooxygenases in cell proliferation, differentiation, and tumorigenicity we developed embryonic stem (ES) cell lines which contain homozygous disruptions in either the COX-1 or the COX-2 gene. These lines were then examined in terms of their viability, proliferation, and in vitro differentiation potential. Our results demonstrate that the wild-type ES cells do not express either COX-1 or COX-2 until the cells undergo differentiation. And the lack of either cyclooxygenase has no apparent effect on ES cell proliferation in vitro. However, the absence of a functional COX-2 gene leads to a dramatic reduction in the formation and growth of teratocarcinomas that appear when ES cells are injected into syngeneic mice. Histological microscopy shows that the few very small tumors that were generated from ES cells lacking COX-2 appear more differentiated than tumors emerging from COX-1 -/- or wild-type cells by exhibiting greater keratinization in the areas of squamous epithelium and the ossification of bone-forming cartilage. We conclude that the presence of a functional COX-2 enzyme is necessary for the efficient growth of these teratocarcinomas in animals.

Suppression of cyclooxygenase-2 gene transcription by humulon of beer hop extract studied with reference to glucocorticoid

In murine osteoblastic MC3T3-E1 cells which produced prostaglandin E2 as a bone resorption factor, the cyclooxygenase-2 induction by tumor necrosis factor alpha (TNFalpha) was suppressed by dexamethasone with an IC(50) of 1 nM. Humulon isolated from hop extract for beer brewing was reported previously as an inhibitor of bone resorption [Tobe, H. et al. (1997) Biosci. Biotech. Biochem. 61, 158-159]. We showed that the compound suppressed the TNFalpha-dependent cyclooxygenase-2 induction with an IC(50) of as low as about 30 nM as demonstrated experimentally by catalytic activity assay, Northern blot analysis and promoter analysis. Reporter gene experiments suggested that humulon blocked the cyclooxygenase-2 expression mediated by NFkappaB and NF-IL6, but the intracellular glucocorticoid receptor was not involved. The catalytic activity of cyclooxygenase-2 was inhibited by humulon with an IC(50) of as high as 1.6 microM. These results showed that humulon suppressed cyclooxygenase-2 induction at the step of transcription.

Transcriptional regulation of cyclooxygenase-2 in the human microvascular endothelial cell line, HMEC-1: control by the combinatorial actions of AP2, NF-IL-6 and CRE elements

Interleukin-1beta (IL-1) is a potent inducer of cyclooxygenase-2 (COX-2) and prostaglandin biosynthesis in many types of cells, yet little is known about the molecular mechanisms regulating IL-1 mediated prostanoid biosynthesis in the endothelium of the microvasculature. Therefore, we examined the cis- and trans-acting factors regulating IL-1-induced COX-2 expression in the human microvascular endothelial cell line, HMEC-1. IL-1 enhanced steady state levels of COX-2 protein and mRNA synthesis by approximately 2-fold which preceded a 2-fold increase in PGF(alpha) biosynthesis. Expression of a series of COX-2 promoter-luciferase constructs in IL-1 treated HMEC-1 cells revealed that the 'full length' (-1432/+59 bp) promoter was 10 times more active than the SV-40 promoter/enhancer and that it could be further activated by IL-1. Surprisingly however, all except for the shortest COX-2 promoter construct retained the ability to respond to IL-1 and luciferase activity driven by -191/+59 bp COX-2 promoter was as responsive to IL-1 as the full-length promoter. Moreover, site-directed promoter mutagenesis and electophoretic mobility shift assays (EMSA) indicate that the combinatorial actions of AP2, NF-IL6, and CRE elements are critical for both constitutive and IL-1-inducible COX-2 promoter activity. Understanding the mechanism(s) regulating COX-2 gene expression and prostaglandin biosynthesis in the microvasculature has important implications with regard to inflammation and angiogenesis in vivo.

Induction of prostaglandin I(2) receptor by tumor necrosis factor alpha in osteoblastic MC3T3-E1 cells

Mouse osteoblastic cells MC3T3-E1 produced prostaglandin E(2) via the reaction of cyclooxygenase-2 enzyme induced by tumor necrosis factor alpha (TNFalpha). Originally, the mRNA level for prostaglandin I(2) receptor (IP) was low in the cells. However, the addition of TNFalpha brought about a marked increase in the IP mRNA with a lag of about 3 h up to an about 8-fold higher level for 24 h. In addition, the induction of IP was supported by a binding experiment of [(3)H]iloprost (a stable analogue of prostaglandin I(2)). The amount of iloprost bound to the TNFalpha-stimulated cell membranes increased to a saturation level around 30 nM. Dexamethasone, cycloheximide and cyclooxygenase inhibitor suppressed the IP mRNA induction. The finding with the latter two compounds suggested a TNFalpha-dependent de novo synthesis of a protein, which is involved in the IP mRNA induction and may be attributed partially to the induced cyclooxygenase-2.

Differential regulation of cyclooxygenase isoenzymes by cAMP-elevating agents

Bovine aortic endothelial cells produce prostacyclin as their major arachidonic acid metabolite. cAMP, in turn, is the second messenger for prostacyclin. In the present study, we investigated the effects of cAMP-elevating agents on prostacyclin production by bovine aortic endothelial cells. Treatment of resting bovine aortic endothelial cells with cAMP-elevating agents inhibited prostacyclin production and cyclooxygenase activity, without affecting arachidonic acid release. No change was detected in cyclooxygenase-1 protein expression. The specific inhibitor of protein kinase A, Rp-cAMPS (adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer, triethylammonium salt), and the phosphatase inhibitor, okadaic acid, both suppressed cAMP-induced inhibition, suggesting that this inhibition is mediated by a phosphorylation-dephosphorylation cascade, which is possibly protein kinase A-dependent. In lipopolysaccharide-treated cyclooxygenase-2 expressing bovine aortic endothelial cells, where cyclooxygenase-1 activity was selectively inhibited, dibutyryl cAMP failed to inhibit cyclooxygenase-2 activity. Cyclooxygenase-2 protein was induced upon treatment with dibutyryl cAMP and further induction of cyclooxygenase-2 protein was effected by IBMX (3-isobutyl-1-methyl-xanthine) and dibutyryl cAMP in bacterial lipopolysaccharide-stimulated cells. These results suggest that increased cellular cAMP selectively inhibits cyclooxygenase-1 activity without altering cyclooxygenase-1 protein expression, and at the same time, up-regulates cyclooxygenase-2 protein. This complex regulation of cyclooxygenase activity and protein expression by cAMP may represent a prostacyclin-induced autoregulatory mechanism in bovine aortic endothelial cells.

Role of prostaglandin H synthase isoforms in murine ear edema induced by phorbol ester application on skin

Topical application of TPA to a murine ear induced an edema that was accompanied by eicosanoid biosynthesis and an early enhancement of prostaglandin H synthase 2 (PGHS-2) expression. PGHS-2 induction may be correlated with the time-course of TPA-induced edema formation. Treatment with drugs that inhibit AA mobilization such as dexamethasone or manoalide or inhibitors of leukotriene formation such as zileuton or baicalein, reduced TPA-induced edema development and PGHS-2 levels. On the other hand, arachidonic acid (AA) application on the murine ear induced rapid expression of PGHS-2. This effect was not reproduced by other fatty acids such as oleic, linoleic, eicosatetraynoic or eicosapentaenoic acids. PGHS-2 expression induced by AA application was independent of PGHS and lipoxygenase metabolite synthesis. However, topical application of PGE2 on skin induced PGHS-2 overexpression. This study suggests that AA release and/or subsequent metabolism by PGHS may be involved in the induction of PGHS-2 expression in murine TPA- and AA-induced ear oedema.

Regulation of type II renal Na+-dependent inorganic phosphate transporters by 1,25-dihydroxyvitamin D3. Identification of a vitamin D-responsive element in the human NAPi-3 gene

Vitamin D is an important regulator of phosphate homeostasis. The effects of vitamin D on the expression of renal Na+-dependent inorganic phosphate (Pi) transporters (types I and II) were investigated. In vitamin D-deficient rats, the amounts of type II Na+-dependent Pi transporter (NaPi-2) protein and mRNA were decreased in the juxtamedullary kidney cortex, but not in the superficial cortex, compared with control rats. The administration of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) to vitamin D-deficient rats increased the initial rate of Pi uptake as well as the amounts of NaPi-2 mRNA and protein in the juxtamedullary cortex. The transcriptional activity of a luciferase reporter plasmid containing the promoter region of the human type II Na+-dependent Pi transporter NaPi-3 gene was increased markedly by 1,25-(OH)2D3 in COS-7 cells expressing the human vitamin D receptor. A deletion and mutation analysis of the NaPi-3 gene promoter identified the vitamin D-responsive element as the sequence 5'-GGGGCAGCAAGGGCA-3' nucleotides -1977 to -1963 relative to the transcription start site. This element bound a heterodimer of the vitamin D receptor and retinoid X receptor, and it enhanced the basal transcriptional activity of the promoter of the herpes simplex virus thymidine kinase gene in an orientation-independent manner. Thus, one mechanism by which vitamin D regulates Pi homeostasis is through the modulation of the expression of type II Na+-dependent Pi transporter genes in the juxtamedullary kidney cortex.

Production of mice deficient in genes for interleukin (IL)-1alpha, IL-1beta, IL-1alpha/beta, and IL-1 receptor antagonist shows that IL-1beta is crucial in turpentine-induced fever development and glucocorticoid secretion

Interleukin (IL)-1 is a major mediator of inflammation and exerts pleiotropic effects on the neuro-immuno-endocrine system. To elucidate pathophysiological roles of IL-1, we have first produced IL-1alpha/beta doubly deficient (KO) mice together with mice deficient in either the IL-1alpha, IL-1beta, or IL-1 receptor antagonist (IL-1ra) genes. These mice were born healthy, and their growth was normal except for IL-1ra KO mice, which showed growth retardation after weaning. Fever development upon injection with turpentine was suppressed in IL-1beta as well as IL-1alpha/beta KO mice, but not in IL-1alpha KO mice, whereas IL-1ra KO mice showed an elevated response. At this time, expression of IL-1beta mRNA in the diencephalon decreased 1.5-fold in IL-1alpha KO mice, whereas expression of IL-1alpha mRNA decreased >30-fold in IL-1beta KO mice, suggesting mutual induction between IL-1alpha and IL-1beta. This mutual induction was also suggested in peritoneal macrophages stimulated with lipopolysaccharide in vitro. In IL-1beta KO mice treated with turpentine, the induction of cyclooxygenase-2 (EC 1.14.99.1) in the diencephalon was suppressed, whereas it was enhanced in IL-1ra KO mice. We also found that glucocorticoid induction 8 h after turpentine treatment was suppressed in IL-1beta but not IL-1alpha KO mice. These observations suggest that IL-1beta but not IL-1alpha is crucial in febrile and neuro-immuno-endocrine responses, and that this is because IL-1alpha expression in the brain is dependent on IL-1beta. The importance of IL-1ra both in normal physiology and under stress is also suggested.

Up-regulation of COX2 expression by uni-axial cyclic stretch in human lung fibroblast cells

The effect of uni-axial cyclic mechanical stretch on the expression of cyclooxygenases (COX) was investigated in a human lung fibroblast cell line (TIG-1). In response to uni-axial cyclic stretch, the level of COX2 mRNA significantly increased and peaked at 3 h (9.09 +/- 3.82-fold, mean +/- standard error, n = 6, compared with that at 1 h). The level of the expression of COX2 protein peaked at 6 h, whereas the level of COX1 protein was not significantly changed. The involvement of stretch-activated (SA) channel was investigated in the stretch-induced COX2 production. The application of Gd3-, a blocker for SA channel, or the removal of extracellular Ca2+ inhibited the production of COX2 mRNA without any effect on the production of COX1 or GAPDH mRNA. These data strongly suggest that COX2 expression is up-regulated by uni-axial cyclic stretch via the activation of SA channel in human lung fibroblasts.

Sustained increase in intracellular free calcium and activation of cyclooxygenase-2 expression in mouse hepatoma cells treated with dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a non-genotoxic environmental pollutant that causes multiple adverse effects in experimental animals and in humans. We show here that TCDD treatment of mouse hepatoma cells causes a rapid mobilization of intracellular calcium both in wild type Hepa-1 cells and in its c2 variant, a cell line that has highly reduced levels of functional aromatic hydrocarbon (Ah) receptor (AHR). In wild type cells, but not in the c2 variant, TCDD treatment leads to a sustained elevation of cytosolic free calcium. TCDD also induces elevated levels of cyclooxygenase-2 (COX-2) mRNA in wild type and in c37, a CYP1A1-deficient cell line, but not in c2 cells. Induction of Cox-2 is in fact dependent on the presence of a functional Ah receptor, since it can be blocked by antisense oligonucleotides to Ah receptor mRNA. Most likely as a consequence of Cox-2 induction, we find a significant increase in the level of 12-hydroxyheptadecatrienoic acid (12-HHT) secreted from TCDD-treated Hepa-1 cells. In addition, we observe elevated levels of 6-keto prostaglandin F1alpha in c2 cells and high levels of secreted prostaglandin F2alpha in c2, c37 and c4, the variant cell line lacking aromatic hydrocarbon nuclear translocator protein. These data suggest that Cox-2 activation by TCDD leads to the release of prostaglandins, eicosanoids and other mediators which may have an important role in the biological and toxic effects of TCDD.

Prostaglandin E2 amplifies cytosolic phospholipase A2- and cyclooxygenase-2-dependent delayed prostaglandin E2 generation in mouse osteoblastic cells. Enhancement by secretory phospholipase A2

We used the MC3T3-E1 cell line, which originates from C57BL/6J mouse that is genetically type IIA secretory phospholipase A2 (sPLA2)-deficient, to reveal the type IIA sPLA2-independent route of the prostanglandin (PG) biosynthetic pathway. Kinetic and pharmacological studies showed that delayed PGE2 generation by this cell line in response to interleukin (IL)-1beta and tumor necrosis factor alpha (TNFalpha) was dependent upon cytosolic phospholipase A2 (cPLA2) and cyclooxygenase (COX)-2. Expression of these two enzymes was reduced by cPLA2 or COX-2 inhibitors and restored by adding exogenous arachidonic acid or PGE2, indicating that PGE2 produced by these cells acted as an autocrine amplifier of delayed PGE2 generation through enhanced cPLA2 and COX-2 expression. Exogenous addition or enforced expression of type IIA sPLA2 significantly increased IL-1beta/TNFalpha-initiated PGE2 generation, which was accompanied by increased expression of both cPLA2 and COX-2 and suppressed by inhibitors of these enzymes. Thus, our results revealed a particular cross-talk between the two PLA2 enzymes and COX-2 for delayed PGE2 biosynthesis by a type IIA sPLA2-deficient cell line. cPLA2 is responsible for initiating COX-2-dependent delayed PGE2 generation, and sPLA2, if introduced, enhances PGE2 generation by increasing cPLA2 and COX-2 expression via endogenous PGE2.

Expression of recombinant human cyclooxygenase isoenzymes in transfected COS-7 cells in vitro and inhibition by tenoxicam, indomethacin and aspirin

The recent discovery of cyclooxygenase-2 (COX-2), an isoenzyme associated mainly with inflammation created the need to reevaluate cyclooxygenase inhibitors with reliable screening methods. In the present study we standardized a technique to determine the IC50S of cyclooxygenase inhibitors on recombinant human COX-1 and COX-2 expressed in mammalian cells and used it to study the compounds tenoxicam, aspirin and indomethacin. The IC50S of aspirin, indomethacin and tenoxicam for human COX-1 were 0.41 +/- 0.07 microgram/ml, 0.008 +/- 0.003 microgram/ml, and 7.94 +/- 3.28 micrograms/ml, respectively, and for human COX-20.64 +/- 0.16 microgram/ml, 0.09 +/- 0.05 microgram/ml, and 10.61 +/- 1.50 micrograms/ml, for aspirin, indomethacin, and tenoxicam. Tenoxicam had the lowest IC50hCOX-2/IC50hCOX-1 ratio (1.34), followed by aspirin (1.53) and indomethacin (10.82). The system described in the present study provides a simple and efficient way to determine the specificity of NSAID inhibition for each of the human cyclooxygenase isoenzymes separately.

Induction of cyclooxygenase-1 in a human megakaryoblastic cell line (CMK) differentiated by phorbol ester

Human megakaryoblastic cells (CMK line) are known to differentiate to mature megakaryocyte-like cells by treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA). There are two isozymes of prostaglandin-forming cyclooxygenase enzyme. Constitutive cyclooxygenase-1 and inducible cyclooxygenase-2 were followed during differentiation of CMK cells. Treatment of the cells with 0.1 microM TPA for 4 days resulted in a 5-20-fold increase in cyclooxygenase activity. Northern and Western blot analyses revealed that cyclooxygenase-1 mRNA and protein increased in parallel with the enzyme activity. In contrast, cyclooxygenase-2 mRNA was detected only at 3 h. Furthermore, most of the increased cyclooxygenase activity was immunoprecipitated with anti-cyclooxygenase-1 antibody, and was not affected by a cyclooxygenase-2-specific inhibitor, NS-398. These results indicated that cyclooxygenase-1 rather than cyclooxygenase-2 was predominantly induced depending on TPA. The enzyme thus induced was localized by immunoelectron microscopy in nuclear envelope and endoplasmic reticulum of the CMK cells.

Induction of cyclo-oxygenase-2 mRNA by prostaglandin E2 in human prostatic carcinoma cells

Prostaglandins are synthesized from arachidonic acid by the enzyme cyclo-oxygenase. There are two isoforms of cyclooxygenases: COX-1 (a constitutive form) and COX-2 (an inducible form). COX-2 has recently been categorized as an immediate-early gene and is associated with cellular growth and differentiation. The purpose of this study was to investigate the effects of exogenous dimethylprostaglandin E2 (dmPGE2) on prostate cancer cell growth. Results of these experiments demonstrate that administration of dmPGE2 to growing PC-3 cells significantly increased cellular proliferation (as measured by the cell number), total DNA content and endogenous PGE2 concentration. DmPGE2 also increased the steady-state mRNA levels of its own inducible synthesizing enzyme, COX-2, as well as cellular growth to levels similar to those seen with fetal calf serum and phorbol ester. The same results were observed in other human cancer cell types, such as the androgen-dependent LNCaP cells, breast cancer MDA-MB-134 cells and human colorectal carcinoma DiFi cells. In PC-3 cells, the dmPGE2 regulation of the COX-2 mRNA levels was both time dependent, with maximum stimulation seen 2 h after addition, and dose dependent on dmPGE2 concentration, with maximum stimulation seen at 5 microg ml(-1). The non-steroidal anti-inflammatory drug flurbiprofen (5 microM), in the presence of exogenous dmPGE2, inhibited the up-regulation of COX-2 mRNA and PC-3 cell growth. Taken together, these data suggest that PGE2 has a specific role in the maintenance of human cancer cell growth and that the activation of COX-2 expression depends primarily upon newly synthesized PGE2, perhaps resulting from changes in local cellular PGE2 concentrations.

Effect of vitamin E on expression of cyclooxygenase-2 in lipopolysaccharide-stimulated rat macrophages

To clarify the role of vitamin E (alpha-tocopherol) for the induction of cyclooxygenase-2 (COX-2) in rat macrophages stimulated by lipopolysaccharide (LPS), vitamin E-enriched macrophages were prepared by intraperitoneal injection of vitamin E for 6 days at a rate of 5 mg per day. The production of PGE2 was increased in dose- and time-dependent manners by addition of LPS in both control and vitamin E-enriched peritoneal macrophages. The maximum effect of LPS was observed in 12 h at concentration of 5 micrograms/ml. By analyzing COX-2 mRNA level by Northern blot and COX-2 enzyme mass and phosphotyrosine by Western blot, it was revealed that the increase of PGE2 production reflected the induction of COX-2 expression through activation of tyrosine kinase. Vitamin E failed to inhibit PGE2 production in LPS-stimulated macrophages; however, genistein, a tyrosine kinase inhibitor, completely inhibited the production at 100 microM. These results suggest that vitamin E does not inhibit COX-2 expression via LPS-mediated tyrosine kinase signal transduction pathway.

Constitutive expression of prostaglandin endoperoxide G/H synthetase (PGHS)-2 but not PGHS-1 in hum an tracheal epithelial cells in vitro

Primary cultures of human tracheal epithelial (HTE) cells cultured in vitro, in defined serum-free media, express prostaglandin endoperoxide G/H synthase (PGHS) activity and produce prostaglandin E2 (PGE2). In contrast to every other cell type studied to date, HTE cells appear to constitutively express PGHS-2, the 'inducible' form of the enzyme, while expressing little or no PGHS-1, the 'housekeeping' isoenzyme in vitro. Prostaglandin synthesis in HTE cells was reduced by a selective PGHS-2 inhibitor, N-[2-cyclohexyloyl-4-nitrophenyl] methane-sulfonamide (NS398), with an IC50 of approximately 1 microM. Immunoblotting and immunoprecipitation of enzymatic activity with isozyme-specific antisera revealed only the PGHS-2 isoform. Full length human cDNA probes detected only PGHS-2 message in Northern blots. Neither PGHS-2 activity nor mRNA levels were dependent on, nor stimulated by peptide growth factors present in the defined serum-free growth medium, or by serum. Prolonged maintenance in the absence of retinoic acid, however, lead to a decline in PGHS activity. Phorbol-myristate acetate (PMA) induced PGHS-2 activity and mRNA and neither PMA-induced, nor constitutive PGHS-2 expression was suppressed by corticosteroids. Actinomycin D-treatment for six hours reduced the PGHS-2 activity and mRNA to only 50% that of untreated cells, suggesting that PGHS-2 mRNA is extremely stable in these cells. HTE cells, at least in vitro, appear unique among prostaglandin-producing cells in that they express PGHS-2, constitutively, independent of regulation by growth factors, serum, or corticosteroids and fail to express PGHS-1 under any culture condition studied.

Arachidonic acid up-regulates and prostaglandin E2 down-regulates the expression of pancreatic-type phospholipase A2 and prostaglandin-endoperoxide synthase 2 in uterine stromal cells

It is well known that arachidonic acid, as a substrate of prostaglandin G/H synthase (PGHS), is converted into prostaglandins of the two-series. In this work, we attempted to determine whether arachidonic acid and prostaglandin E2 might regulate the expression of PGHS and the pancreatic-type phospholipase A2 (PLA2I), which may be involved in the liberation of arachidonic acid from membrane phospholipids. For this purpose, we used the uterine stromal cell line UIII, which produces prostaglandin E2 and expresses both the constitutive and inducible PGHS enzymes (PGHS1 and PGHS2) and PLA2 I. The results show that PGHS1, which is expressed at a high level in UIII cells, was not modified by arachidonic acid. The expression of PGHS2 and PLA2 I was up-regulated by increasing arachidonate concentrations (1-10 microM). The maximal response was obtained at 24 h, reaching a 2.3-fold and 2.6-fold increase for PGHS2 and PLA2 I expression, respectively, compared to the control level. To discriminate between the effect of arachidonic acid and that of prostaglandins, which are highly increased in the presence of exogenous arachidonic acid, we treated the cells with two inhibitors of PGHS activity, aspirin and meclofenamic acid. Both inhibitors failed to suppress the arachidonate-induced increase of PLA2 I and PGHS2 expression and even enhanced it either in the presence or absence of arachidonic acid. In contrast, the addition of prostaglandin E2 to the culture medium decreased the expression of both enzymes in a dose-dependent manner, the maximal response being reached at 1 microM. We conclude that arachidonic acid up-regulates the expression of PLA2 I and PGHS2 in the uterine stromal cells, independently of prostanoids, and that prostaglandin E2 is capable of down-regulating enzyme expression.

Effect of in vitro aging on Campylobacter rectus lipopolysaccharide-stimulated PGE2 release from human gingival fibroblasts

OBJECTIVE

We examined the influence of in vitro aging on Campylobacter rectus (C. rectus) lipopolysaccharide (LPS)-stimulated prostaglandin (PG), E2 release frOm human gingival fibroblasts (HGFs).

MATERIALS AND METHODS

LPS was prepared from C. rectus ATCC33238. HGFs were established from healing gingival tissue removed from three patients (donors A, B and C), aged 10-12 years. Aging of the cells in culture was determined with increasing population doubling. The cells were cultured until confluence, then stimulated with LPS (1.0 micrograms ml-1), and the levels of PGE2 in the medium were measured after 24 h by radioimmunoassay.

RESULTS

The LPS-stimulated PGE2 production in each old cell (passage 17-20) was significantly increased to about 1.6-2.6 times than that in the corresponding young cells (passage 5-6). The gene expression of cyclooxygenase-2 mRNA in the old cells was higher than that in the young cells in response to LPS. In the absence of LPS, PGE2 production levels in both the young and old cells were very low, and also at the same level. However, there was a higher level of LPS-stimulated PGE2 production in the young cells from donor C compared to that in the old cells from donor B. The LPS-stimulated PGE2 production in each young cell from donors A and C was almost equal to that in each old cell from donors B and A, respectively.

CONCLUSIONS

The results suggested that aging in HGFs may be one of the factors that take part in the stimulation of C. rectus LPS-stimulated PGE2 production in old cells.

Stimulation of prostaglandin E2 synthesis by interleukin-1beta is amplified by interferons but inhibited by interleukin-4 in human amnion-derived WISH cells

Human amnion-derived WISH cells synthesize little prostaglandin E2 at the basal state. However, the cells were stimulated greatly to synthesize prostaglandin E2 by interleukin-1beta in a dose-dependent manner. Stimulation by interleukin-1beta was synergistically increased by pretreatment of the cells with interferon alpha or gamma, which alone were inactive. Synergism by interferons was dose-dependent. Stimulation by interleukin-1beta, on the contrary, was inhibited by preincubation of the cells with interleukin-4. Inhibition by interleukin-4 was also dose-dependent. Regulation of prostaglandin E2 synthesis by cytokines was further examined at the m-RNA level of cyclooxygenase-2. Quantitative reverse transcription-polymerase chain reaction indicated that the m-RNA level was not increased by interferon-gamma but was synergistically increased by interferon-gamma plus interleukin-1beta. Furthermore, the m-RNA level increased by interleukin-1beta was attenuated by interleukin-4. These results indicate that regulation of interleukin-1beta-stimulated prostaglandin E2 synthesis by interferons and interleukin-4 is controlled at the m-RNA level of cyclooxygenase-2.

Transcriptional roles of nuclear factor kappa B and nuclear factor-interleukin-6 in the tumor necrosis factor alpha-dependent induction of cyclooxygenase-2 in MC3T3-E1 cells

When a mouse osteoblastic cell line MC3T3-E1 was cultured in the presence of tumor necrosis factor alpha (TNF alpha), the release of prostaglandin E2 and the cyclooxygenase activity increased in a dose- and time-dependent manner. The increase of the enzyme activity was attributed mostly to the induction of cyclooxygenase-2 rather than cyclooxygenase-1 as judged by the inhibitory effect of NS398, Western blotting, and Northern blotting. In this system we attempted to elucidate the transcriptional regulation of the cyclooxygenase-2 gene. As examined by the luciferase assay, two positive regulatory regions (-186 to -131 and -512 to -385 base pairs) were found in the 5'-flanking promoter region of the mouse cyclooxygenase-2 gene in the TNF alpha-stimulated cells. The former included putative NF-IL6 (C/EBP beta) and AP2 elements, and the latter contained the NF kappa B motif. A DNA probe including the NF-IL6 and AP2 sites gave positive bands upon electrophoretic mobility shift assay using the nuclear extracts of MC3T3-E1 cells. The bands were supershifted by the addition of anti-NF-IL6 antibody but not by anti-AP2 antibody. A probe including the NF kappa B site also gave positive bands, which were supershifted by anti-NF kappa B p50 and p65 antibodies. Furthermore, when the motif of NF-IL6 or NF kappa B or both was subjected to point mutation, the luciferase activity was markedly reduced. These data suggested a potential role of both NF-IL6 and NF kappa B in the induction of cyclooxygenase-2 by TNF alpha.

Eicosanoid production by parasites:

In this review, Adam Belley and Kris Chadee discuss eicosanoid production by various parasites and propose roles they may play in pathogenesis and immunomodulation. The commonality between parasites is prostaglandin production and, therefore, special attention is given to the cyclooxygenase pathway, highlighting the enzymes and functions of prostaglandins.

Regulation of two isozymes of prostaglandin endoperoxide synthase and thromboxane synthase in human monoblastoid cell line U937

The mechanism responsible for the rapid increase of thromboxane A2 synthesis by cells of the human monoblastoid cell line U937, which were differentiated with 12-O-tetradecanoyl-phorbol-13-acetate, induced by lipopolysaccharide (LPS) was studied. Both RNA blot and immunoblot analyses showed that LPS increased the levels of prostaglandin endoperoxide synthase-1 (PES-1) and -2 (PES-2) in a time-dependent manner, and the modes of induction of the two isozymes differed. The maximum PES-1 mRNA level was 1.6 times higher 36 h after than before stimulation by LPS, and that of PES-2 mRNA was elevated about 20-fold at its peak at 12 h after stimulation. Consequently, the immunoreactive PES-1 and PES-2 protein levels also increased time-dependently after LPS stimulation. However, the effects of LPS on the thromboxane synthase mRNA and protein levels were much less marked. These results indicate that LPS-induced thromboxane synthesis by the differentiated cells was regulated at the levels of the two PES isozymes, predominantly at the PES-2 level.

Characterisation of cyclooxygenase 1 and 2 expression in mouse resident peritoneal macrophages in vitro; interactions of non steroidal anti-inflammatory drugs with COX2

Resident peritoneal macrophages exposed to inflammatory stimuli (zymosan, lipopolysaccharide (LPS)) represent a widely used model for studying arachidonic acid metabolism and for screening of prostaglandin (PG) synthesis inhibitors. In the present study, cyclooxygenase 1 (COX1) was shown constitutively expressed in mouse adherent and non-adherent macrophages whereas expression of COX2 was observed only in adherent cells, even when cultured in minimal conditions (Ca-, Mg- and serum-free medium). The COX2 expression was amplified by arachidonic acid cascade stimulating agents (Ca, Mg, zymosan) and by LPS in a time-dependant manner; PGE2 by itself amplified LPS-induced COX2 expression. In well-defined experimental conditions of COX2 expression (LPS-stimulated adherent macrophages), we studied specific interactions of some representative anti-inflammatory drugs with COX2 enzymatic activity and expression. By contrast with dexamethasone, which reduced PGE2 release together with a strong reduction of COX2 expression (protein and mRNA), non steroidal anti-inflammatory drugs (NSAIDs) reduced PGE2 synthesis without any effect at the COX2 mRNA level. This reduction of PGE2 production by NSAIDs resulted from either an exclusive enzymatic inhibition (aspirin, NS398, 6-Methoxy naphtyl acetic acid) or an enzymatic inhibition associated with a slight decrease of COX2 protein level (indomethacin). For paracetamol and salicylic acid, two weak inhibitors of COX enzymatic activity, reduction of PGE2 synthesis appeared to be related to reduced level of COX2. These findings show that the macrophage can be used as a cellular model to study specifically COX1 and COX2. In this cell type, COX2 expression is dependent on adhesion, enhanced by stimulation of arachidonic acid metabolism, and auto amplified by PGE2. Furthermore, the results indicate that known NSAIDs differ in their interaction with cyclooxygenase, being able to inhibit either COX2 enzymatic activity, and/or COX2 expression. However, further studies are required to determine the mechanism and the role of COX2 expression during inflammation in vivo, and to define more precisely the best target for new potent and safe NSAIDs.

Autoregulation of inducible prostaglandin G/H synthase in osteoblastic cells by prostaglandins

Prostaglandins (PGs) have been postulated to amplify their own production by stimulating cyclic adenosine monophosphate activity, which in turn stimulates PG production. We examined regulation of messenger RNA levels for the inducible and constitutive prostaglandin G/H synthases, PGHS-2 and PGHS-1, in murine osteoblastic MC3T3-E1 cells, which express both PGHS-1 and PGHS-2, and in rat osteoblastic Py1a cells, which express only PGHS-2. Prostaglandins E2, F2 alpha, and D2 induced PGHS-2 mRNA in both cell lines under serum-free conditions and stimulated small increases in PGHS-1 mRNA levels in MC3T3-E1 cells. PGE2 (1 microM) increased the transcription rate of PGHS-2 mRNA 9-fold at 2 h in serum-free cells and also induced PGHS-2 protein. In the presence of arachidonic acid or serum, PGs also increased medium PGE2. Both forskolin, a protein kinase A activator, and phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, have previously been shown to induce PGHS-2 mRNA in MC3T3-E1 cells, but in the present study only PMA induced PGHS-2 expression in Py1a cells. The induction of PGHS-2 mRNA in Py1a cells by PGs was inhibited by chelerythrine, a PKC inhibitor, and blocked by 24 h of pretreatment with PMA. The 2 h serum stimulation of PGHS-2 mRNA in MC3T3-E1 cells was inhibited 40-50% by three structurally unrelated nonsteroidal anti-inflammatory drugs (NSAIDs), suggesting that endogenous PGs also amplify PG production through induction of PGHS-2.(ABSTRACT TRUNCATED AT 250 WORDS)