Leishmania donovani-induced macrophages cyclooxygenase-2 and prostaglandin E2 synthesis

Prostaglandin E2 (PGE2) secretion during Leishmania infection has been reported. However, the signalling mechanisms mediating this response are not well understood. Since cyclooxygenase-2 (COX-2) and cytosolic phospholipase A2 (cPLA2) are involved in PGE2 synthesis in response to various stimuli, the implication of these enzymes was evaluated in Leishmania-infected phorbol myristate acetate-differentiated U937 human monocytic cell line. Time-course experiments showed that PGE2 synthesis increased significantly in parallel with COX-2 expression when cells were incubated in the presence of Leishmania donovani promastigotes or lipopolysaccharides (LPS). Increase in cPLA2 mRNA expression was only detected when cells were stimulated with LPS. Indomethacin, genistein, and H7, which are antagonists of COX-2, protein tyrosine kinase (PTK) and protein kinase C (PKC), respectively, inhibited PGE2 production induced by L. donovani and LPS. However, only H7 inhibited COX-2 mRNA synthesis, and there was a significant correlation between PGE2 inhibition and reduced COX-2 expression. Collectively, our results indicate that infection of U937 by L. donovani leads to the generation of PGE2 in part through a PKC-dependent signalling pathway involving COX-2 expression. They further reveal that PTK-dependent events are necessary for Leishmania-induced PGE2 generation, but not for COX-2 expression. A better understanding of the mechanisms by which Leishmania can induce PGE2 production could provide insight into the pathophysiology of leishmaniasis and may help to improve therapeutic approaches.     

Increased Leishmania replication in HIV-1-infected macrophages is mediated by tat protein through cyclooxygenase-2 expression and prostaglandin E2 synthesis

Protozoan parasites of the genus Leishmania frequently occur as opportunistic pathogens in human immunodeficiency virus type 1 (HIV-1)-infected individuals, but the mechanisms underlying protozoan growth in this context are poorly understood. Here, we demonstrate that the HIV-1 Tat protein drives Leishmania replication in primary human macrophages. We found that Leishmania growth doubled in HIV-1-infected macrophages and that anti-Tat antibodies reduced the exacerbated protozoan replication by 70%. Recombinant Tat increased Leishmania replication and overrode the leishmanicidal effect induced by interferon-gamma , allowing Leishmania replication even in the presence of this cytokine. Tat induced cyclooxygenase (COX)-2 expression and prostaglandin E2 (PGE2) synthesis, and a COX-2 inhibitor abolished the Tat-mediated augmentation of Leishmania replication. Moreover, PGE2 increased Leishmania growth, which was abrogated by anti-transforming growth factor (TGF)- beta1 monoclonal antibodies. Neutralization of TGF-beta1 reduced parasite growth in Leishmania-infected macrophages exposed to Tat by 50%. Our findings suggest that Tat generates a milieu permissive to Leishmania growth in individuals infected with HIV-1.     

Coexpression of microsomal prostaglandin E synthase with cyclooxygenase-2 in human rheumatoid synovial cells

OBJECTIVE: Recently, microsomal prostaglandin (PG) E synthase (mPGES) was cloned as a terminal enzyme catalyzing PGH2 to PGE2. We investigated mPGES as well as cyclooxygenase (COX)-2, catalyzing arachidonic acid to PGH2, in synovial cells from patients with rheumatoid arthritis (RA). The effect of dexamethasone on mPGES expression was also studied. METHODS: Synovial cells were treated with interleukin 1beta (IL-1beta) and dexamethasone under various conditions, and expression of mPGES mRNA and protein was analyzed by Northern blot and Western blot, respectively. Conversions of arachidonic acid or PGH2 to PGE2 were measured by ELISA. Subcellular localization of mPGES and COX-2 was determined by immunofluorescent microscopic analysis. RESULTS: mPGES mRNA and protein expression were significantly upregulated by IL-1beta in synovial cells. COX-2 mRNA and protein were also upregulated by IL-1beta, but with a different time course from that of mPGES. Conversion of PGH2 to PGE2 increased by IL-1beta and was correlated with mPGES expression. Increased conversion of arachidonic acid to PGE2 was maintained when mPGES and COX-2 were coexpressed. Subcellular localization of mPGES and COX-2 overlapped in the perinuclear region in IL-1beta stimulated synovial cells. Dexamethasone inhibited mRNA and protein expression for mPGES and increased conversion of arachidonic acid to PGE2, but inhibition of mPGES was weaker compared with that of COX-2 in IL-1beta stimulated cells. CONCLUSION: The results suggest that abundant PGE2 production at inflammation sites such as rheumatoid synovia is caused by the coordinated upregulation of mPGES and COX-2. Thus mPGES might be a potential new target for therapeutic strategies to control PGE2 synthesis specifically in patients with RA and other inflammatory diseases.     

Anovulation in cyclooxygenase-2-deficient mice is restored by prostaglandin E2 and interleukin-1beta.

Mice carrying a null mutation for either of the two cyclooxygenase (COX) isoenzymes, necessary for prostanoid production, exhibit several isotype-specific reproductive abnormalities. Mice deficient in COX-1 are fertile but have decreased pup viability, whereas mice deficient in COX-2 fail to ovulate and have abnormal implantation and decidualization responses. The present study identifies the specific contribution of each COX isoenzyme in hypothalamic, pituitary, and ovarian function and establishes the pathology and rescue of the anovulatory syndrome in the COX-2-deficient mouse. In both COX-1- and COX-2-deficient mice, pituitary gonadotropins were selectively increased, whereas hypothalamic LHRH and serum gonadotropin levels were similar to those in wild-type animals (+/+). No significant differences in serum estrogen or progesterone were noted among the three genotypes. Exogenous gonadotropin stimulation with PMSG and hCG produced a comparable 4-fold increase in ovarian PGE2 levels in wild-type and COX-1(-/-) mice. COX-2(-/-) mice had no increase in PGE2 over PMSG-stimulated levels. Wild-type and COX-1(-/-) mice ovulated in response to PMSG/hCG; very few COX-2(-/-) animals responded to this regimen. The defect in ovulation in COX-2 mutants was attributed to both an abnormal cumulus oophorum expansion and subsequent stigmata formation. Gonadotropin stimulation and concurrent treatment with PGE2 or interleukin-1beta resulted in ovulation of COX-2(-/-) mice comparable to that in COX-2(+/+), whereas treatment with PGF2alpha was less effective. Collectively, these data demonstrate that COX-2, but not COX-1, is required for the gonadotropin induction of ovarian PG levels; that COX-2-related prostanoids are required for stabilization of the cumulus oophorum during ovulation; and that ovulation can be restored in the COX-2(-/-) animals by simultaneous treatment with gonadotropins and PGE2 or interleukin-1beta.     

环氧合酶-1和前列腺素E2在多潘立酮对大鼠胃黏膜保护中的作用

目的　研究多潘立酮对大鼠胃黏膜损伤是否具有保护作用 ,并探讨胃黏膜细胞中环氧合酶 1(COX 1)及前列腺素 (PG)E2是否参与其中。方法　研究分为对照组和实验组。后者分别用多潘立酮 0 .5mg/kg、1mg/kg和 2mg/kg灌胃 ,3次 /d ,连续 3d。各组大鼠灌入无水乙醇后 ,肉眼观察胃黏膜损伤指数 (LI) ,光镜下观察黏膜缺损深度 ,并计算黏膜缺损深度与胃壁全层厚度百分比。放射免疫法测定各组胃黏膜PGE2的水平。免疫组织化学方法检测COX 1和COX 2蛋白表达水平并以平均吸光度值表示其强度。RT PCR检测胃黏膜COX 1和COX 2mRNA表达变化。结果　多潘立酮 1mg/kg组的LI及黏膜缺损深度与胃壁全层厚度百分比显著低于对照组 (P <0 .0 5 ) ,0 .5mg/kg组和 2mg/kg的组LI亦显著低于对照组 (P <0 .0 5 )。多潘立酮 1mg/kg组大鼠胃黏膜COX 1蛋白表达水平及PGE2水平显著高于空白对照组 (P <0 .0 1)。各实验组和对照组在胃黏膜细胞内均无COX 2蛋白表达。三个实验组COX 1mRNA表达量与对照组比较差异均有显著性 (P <0 .0 1)。各组均未检测到COX 2mRNA表达。结论　多潘立酮对胃黏膜损伤具有保护作用 ,其机制之一可能与其增加胃黏膜COX 1mRNA和COX 1蛋白表达及促进胃黏膜PGE2分泌有关。     

Multidrug resistance associated protein 2 mediates transport of prostaglandin E2.

BACKGROUND/AIM: Inactivation of prostaglandin E(2) (PGE(2)) in the liver is a rapid process and occurs mainly through beta-oxidation in the peroxisome of the hepatocyte. Biliary excretion of PGE(2) is also a means of elimination from the liver. We investigated the role of multidrug resistance-associated protein 2 (MRP2) in the transport of PGE(2). METHODS: Biliary PGE(2) elimination was measured in liver perfusions in Wistar and MRP2-deficient TR(-) rats. Furthermore, transport experiments were performed in membrane vesicles from human MRP2-infected Spodoptera frugiperda 21 (Sf21) insect cells. RESULTS: The liver perfusions showed a 3.5 times higher percentage of undegraded [(3)H]PGE(2) in bile of Wistar rats in comparison with MRP2 deficient (TR(-)) rats (3.6% vs. 1.1%, respectively; P<0.05). MRP2-mediated transport of the model substrate [(3)H]DNP-SG was inhibited by PGE(2). Half maximal inhibition was achieved at a concentration of approximately 15 microM PGE(2). In addition, [(3)H]PGE(2) uptake in these vesicles was detected, and determined to be ATP dependent. CONCLUSION: MRP2 mediates the transport of PGE(2) and its breakdown products. The biliary excretion of PGE(2) via MRP2 may contribute to rapid elimination of the prostaglandin but might also serve to relay prostaglandin signalling to the biliary tree.     

Selective inhibition of cyclooxygenase-2 (COX-2) reduces prostaglandin E2 production and attenuates systemic disease sequelae in experimental pancreatitis

BACKGROUND/AIMS: Prostaglandins and prostaglandin-derived mediators play an important role in mediating the systemic inflammatory response in acute pancreatitis. COX (cyclooxygenase) is the key enzyme of prostaglandin synthesis. Whereas COX-1 produces prostaglandin mediators for physiological reactions, COX-2 is overexpressed in acute pancreatitis. The aim of this study was to investigate whether a selective COX-2 inhibitor alters prostaglandin production and attenuates systemic disease sequelae in severe acute pancreatitis in rats. METHODOLOGY: Severe acute pancreatitis was induced in 36 rats by standardized intraductal infusion of bile salt and intravenous cerulein infusion. Six hours after acute pancreatitis induction, rats were randomized to receive either no COX inhibition (saline), nonselective COX inhibition by indomethacin (3 mg/kg, i.v.) or selective COX-2 inhibition by NS-398 (10 mg/kg, i.v.). Serum concentrations of prostaglandin E2 were measured before and after acute pancreatitis induction and 24 hrs after starting therapy. Routine cardiorespiratory and renal parameters were monitored to assess organ function. RESULTS: Animals treated with the selective COX-2 inhibitor had significantly lower prostaglandin E2 values (211 +/- 17 vs. 366 +/- 37 and 435 +/- 13 pg/mL), produced more urine (18 +/- 4 vs. 13 +/- 3 and 12 +/- 3 mL/6-24 h) and had significantly fewer episodes of respiratory distress (defined as a pO2 < 80 mmHg or pCO2 > 50 mmHg for > 15 min; 12 vs. 57 and 71%) during the observation period than animals without or with nonselective COX inhibition. CONCLUSIONS: Selective inhibition of COX-2 reduces prostaglandin E2 serum levels in this model of acute pancreatitis. This together with improved renal and respiratory function suggests an attenuation of the systemic response to pancreatic injury. COX-2 inhibition may be another step toward optimizing therapy in severe acute pancreatitis.     

Inverse relationship of plasma prostaglandin E2 and blood mononuclear cell cyclooxygenase-2 with disease severity in children with Plasmodium falciparum malaria

Prostaglandins (PGs) derived from inducible cyclooxygenase (COX)-2 are important proinflammatory mediators of the host-immune response to infection. Since the role of host-derived PG in human malaria is unknown, plasma bicyclo-PGE2 (a stable catabolite of PGE2), peripheral blood mononuclear cell COX-2 protein, and mRNA were measured in Gabonese children with and without malaria (n=129). Relative to healthy children, bicyclo-PGE2 and COX-2 protein were lower in children with mild (P=.007 and P=.026, respectively) and severe malaria (P=.002 and P=.010, respectively). COX-2 mRNA was also reduced in children with malaria. Investigation of COX-2 regulatory cytokines revealed an inverse correlation (P<.001) between plasma levels of bicyclo-PGE2 and interleukin (IL)-10, a cytokine that suppresses COX-2 expression. On the basis of these results, elevated PGE2 in healthy malaria-exposed children may protect against malaria, whereas IL-10-induced decreases in PGE2 during acute malaria may increase susceptibility to severe disease.     

Partial prevention of ethanol damage of human gastroduodenal mucosa by prostaglandin E2 in vitro

Biopsies were taken endoscopically from the fundic, antral, and upper duodenal region of healthy volunteers and gastric ulcer patients and were incubated in carbogen-saturated and buffered Medium 199 at 37 degrees C. The rate of DNA synthesis, estimated as incorporation of tritiated thymidine into tissue DNA, was determined as an index of cellular integrity. During the 30-min incubation, ethanol (25% v/v) significantly (p less than 0.01) depressed DNA synthesis by about 50% in the gastroduodenal mucosa of normal subjects and even by two thirds in the gastric mucosa of gastric ulcer patients. Prostaglandin E2 (PGE2) by itself (1 mg/50 ml) had no stimulatory effect on DNA synthesis; it did, however, reduce the drastic fall in DNA synthesis due to ethanol (p less than 0.005) when administered concomitantly. The basic process underlying cytoprotection by PGE2 in vitro remains to be elucidated. Some indirect mechanisms, such as stimulation of gastric mucosal blood flow, are ruled out by these experiments.     

Distribution of prostaglandin E2 and prostaglandin F2 alpha receptors in human myometrium

Human myometrium was studied for specific binding of PGE2 and PGF2 alpha. PGF2 alpha-binding was almost undetectable, but specific binding sites for PGE2 with high affinity (KD = 2.7 +/- 0.4 x 10(-9) M were demonstrated. The binding capacity for PGE2 exhibited a topically different distribution pattern with the highest values in the central parts and low to undetectable levels in the cervical region. Binding characteristics were analyzed by receptor kinetics, revealing a homogeneous receptor population. Binding capacity in uteri obtained from post-menopausal women was of the order of 900-940 fmol/mg protein. Oestrogen pre-treatment and pregnancy were associated with a 3-fold reduction of the PGE2-binding capacity.     

阿托伐他汀对颈动脉斑块中环氧化物酶-2及诱导型前列腺素合成酶-1表达的影响

目的 探讨阿托伐他汀对兔颈动脉斑块中环氧化物酶-2(COX-2)、诱导型前列腺素合成酶-1 (mPGES-l)表达的影响.方法 选择月龄≥36个月的33只雄性新西兰大白兔,其中正常对照组8只,另25只建立兔颈动脉粥样斑块狭窄动物模型,除外1只用于实验确认造模成功外,将其余24只模型兔随机分为颈动脉狭窄造模组、塞来昔布治疗组(15 mg· kg-1·d-1,2次/d)和阿托伐他汀治疗组(5 mg· kg-1·d-1,1次/d),每组各8只.治疗4周后分别测定颈动脉斑块COX-2及mPGES-1的表达.结果 与正常对照组0.23±0.04、0.17±0.03比较,造模组、塞来昔布治疗组、阿托伐他汀治疗组颈动脉粥样硬化模型兔的斑块中COX-2mRNA及mPGES-1mRNA表达上调,分别为0.97±0.09、0.44±0.05、0.60±0.04;0.92±0.07、0.41±0.04、0.61±0.03,差异有统计学意义(F=56.77、54.87,均P＜0.01);与造模组比较,塞来昔布治疗组和阿托伐他汀治疗组颈动脉斑块的COx-2mRNA及mPGES-1 mRNA表达显著下调(均P＜0.01);与正常对照组0.18±0.05、0.21±0.04比较,造模组、塞来昔布治疗组、阿托伐他汀治疗组颈动脉粥样硬化模型兔的斑块中COX-2蛋白及mPGES-1蛋白表达上调,分别为0.89±0.06、0.42±0.07、0.62±0.04;0.91±0.05、0.44±0.05、0.63±0.05,差异有统计学意义(F=61.75、86.44,均P＜0.01);与造模组比较,塞来昔布治疗组和阿托伐他汀治疗组颈动脉斑块的COX-2蛋白及mPGES-1蛋白表达显著下调(均P＜0.01);塞来昔布治疗组与阿托伐他汀治疗组COX-2 mRNA、mPGES-1 mRNA、COx-2蛋白及mPGES-1蛋白比较差异均有统计学意义(均P＜0.01).结论 在颈动脉粥样硬化斑块的病理过程中炎性反应可能起主导作用,阿托伐他汀与既往研究已明确的COX-2抑制剂塞来昔布相同,可抑制COX-2及mPGES-1的表达水平,减缓颈动脉粥样硬化的炎性反应,进而抑制颈动脉斑块的进程.     

Elevated interleukin 6 is induced by prostaglandin E2 in a murine model of inflammation: possible role of cyclooxygenase-2.

Injection of mineral oils such as pristane into the peritoneal cavities of BALB/c mice results in a chronic peritonitis associated with high tissue levels of interleukin 6 (IL-6). Here we show that increased prostaglandin E2 (PGE2) synthesis causes induction of IL-6 and that expression of an inducible cyclooxygenase, Cox-2, may mediate this process. Levels of both PGE2 and IL-6 are elevated in inflammatory exudates from pristane-treated mice compared with lavage samples from untreated mice. The Cox-2 gene is induced in the peritoneal macrophage fraction isolated from the mice. A cause and effect relationship between increased macrophage PGE2 and IL-6 production is shown in vitro. When peritoneal macrophages are activated with an inflammatory stimulus (polymerized albumin), the Cox-2 gene is induced and secretion of PGE2 and IL-6 increases, with elevated PGE2 appearing before IL-6. Cotreatment with 1 microM indomethacin inhibits PGE2 production by the cells and reduces the induction of IL-6 mRNA but has no effect on Cox-2 mRNA, consistent with the fact that the drug inhibits catalytic activity of the cyclooxygenase but does not affect expression of the gene. Addition of exogenous PGE2 to macrophages induces IL-6 protein and mRNA synthesis, indicating that the eicosanoid stimulates IL-6 production at the level of gene expression. PGE2-stimulated IL-6 production is unaffected by addition of indomethacin. Taken together with the earlier finding that indomethacin diminishes the elevation of IL-6 in pristane-treated mice, the results show that PGE2 can induce IL-6 production in vivo and implicate expression of the Cox-2 gene in the regulation of this cytokine.     

The role of prostaglandin E2 (PGE 2) in toll-like receptor 4 (TLR4)-mediated colitis-associated neoplasia

Background

We have previously found that TLR4-deficient (TLR4-/-) mice demonstrate decreased expression of mucosal PGE ₂ and are protected against colitis-associated neoplasia. However, it is still unclear whether PGE ₂ is the central factor downstream of TLR4 signaling that promotes intestinal tumorigenesis. To further elucidate critical downstream pathways involving TLR4-mediated intestinal tumorigenesis, we examined the effects of exogenously administered PGE ₂ in TLR4-/- mice to see if PGE ₂ bypasses the protection from colitis-associated tumorigenesis.

Method

Mouse colitis-associated neoplasia was induced by azoxymethane (AOM) injection followed by two cycles of dextran sodium sulfate (DSS) treatment. Two different doses of PGE ₂ (high dose group, 200 μg, n = 8; and low dose group, 100 μg, n = 6) were administered daily during recovery period of colitis by gavage feeding. Another group was given PGE ₂ during DSS treatment (200 μg, n = 5). Inflammation and dysplasia were assessed histologically. Mucosal Cox-2 and amphiregulin (AR) expression, prostanoid synthesis, and EGFR activation were analyzed.

Results

In control mice treated with PBS, the average number of tumors was greater in WT mice (n = 13) than in TLR4-/- mice (n = 7). High dose but not low dose PGE ₂ treatment caused an increase in epithelial proliferation. 28.6% of PBS-treated TLR4-/- mice developed dysplasia (tumors/animal: 0.4 ± 0.2). By contrast, 75.0% (tumors/animal: 1.5 ± 1.2, P < 0.05) of the high dose group and 33.3% (tumors/animal: 0.3 ± 0.5) of the low dose group developed dysplasia in TLR4-/- mice. Tumor size was also increased by high dose PGE ₂ treatment. Endogenous prostanoid synthesis was differentially affected by PGE ₂ treatment during acute and recovery phases of colitis. Exogenous administration of PGE ₂ increased colitis-associated tumorigenesis but this only occurred during the recovery phase. Lastly, PGE ₂ treatment increased mucosal expression of AR and Cox-2, thus inducing EGFR activation and forming a positive feedback mechanism to amplify mucosal Cox-2.

Conclusions

These results highlight the importance of PGE ₂ as a central downstream molecule involving TLR4-mediated intestinal tumorigenesis.     

Relationship between blood plasma prostaglandin E2 and liver and lung metastases in colorectal cancer

The relationship of prostaglandin E ₂,of which a large amount is produced in various neoplasms, and hematogenous distant metastases was investigated in a total of 44 colorectal cancer patients because of its varied pathophysiologic potentials. The authors found significantly high levels of PGE ₂ in local venous blood draining the carcinoma and in peripheral blood in cases with liver or lung metastasis, as well as a significantly large amount of PGE ₂ production in the carcinoma tissue. The results suggest that increased local blood PGE ₂ could enhance the metastasis formation, and increased peripheral blood PGE ₂ may be useful in the detection of such metastasis in colorectal cancer.Supported in part by a Grant-in-Aid for Cancer Research from the Ministry of Health and Welfare, Japan.