Prostaglandin E2 produced by inducible COX-2 and mPGES-1 promoting cancer cell proliferation in vitro and in vivo

Aim

Many cancers originate and flourish in a prolonged inflammatory environment. Our aim is to understand the mechanisms of how the pathway of prostaglandin E₂ (PGE₂) biosynthesis and signaling can promote cancer growth in inflammatory environment at cellular and animal model levels.

Main methods

In this study, a chronic inflammation pathway was mimicked with a stable cell line that over-expressed a novel human enzyme consisting of cyclooxygenase isoform-2 (COX-2) linked to microsomal (PGE₂ synthase-1 (mPGES-1)) for the overproduction of pathogenic PGE₂. This PGE₂-producing cell line was co-cultured and co-implanted with three human cancer cell lines including prostate, lung, and colon cancers in vitro and in vivo, respectively.

Key findings

Increases in cell doubling rates for the three cancer cell types in the presence of the PGE₂-producing cell line were clearly observed. In addition, one of the four human PGE₂ subtype receptors, EP₁, was used as a model to identify PGE₂-signaling involved in promoting the cancer cell growth. This finding was further proven in vivo by co-implanting the PGE₂-producing cells line and the EP₁-positive cancer cells into the immune deficient mice, after that, it was observed that the PGE₂-producing cells promoted all three types of cancer formation in the mice.

Significance

This study clearly demonstrated that the human COX-2 linked to mPGES-1 is a pathway that, when mediated by the EP, is linked to promoting cancer growth in a chronic inflammatory environment. The identified pathway could be used as a novel target for developing and advancing anti-inflammation and anti-cancer interventions.     

Prostaglandin E2 modulates components of the Wnt signaling system in bone and prostate cancer cells

Both Wnt signaling and prostaglandin E₂ (PGE₂) play pivotal roles in bone development, remodeling, osteoporosis and prostate cancer (PCa) bone metastases. We investigated the effects of PGE₂ on Wnt signaling in osteoblast-lineage cells and Wnt-inhibitor expression in PCa cells. We demonstrate that low dose PGE₂ (0.1 μM) promotes Wnt signaling while higher doses of PGE₂ (1.0-10 μM) inhibit these same parameters in osteoblast-lineage cells. The differential effects of low vs high-dose PGE₂ on pre-osteoblasts may be attributed to dose-dependent modulation of prostaglandin receptor (EP) subtype expression; with lower doses increasing the expression the cAMP-stimulatory EP4 receptor subtype and higher doses increasing the expression of the cAMP-inhibitory EP3 receptor subtype. Moreover, we demonstrate that high expression levels of COX-2 and PGE₂ promote the secretion of Wnt inhibitors from prostate cancer cells. These data demonstrate that there are dose-dependent effects of PGE₂ on Wnt activation in osteoblast-lineage cells and Wnt-inhibitor expression in PCa cells which may have clinical implications in the management.     

Prostaglandin E1 or E2 inhibits an oxytocin-induced premature luteolysis in ewes when oxytocin is given early in the estrous cycle

The objective of this study was to determine whether PGE₁ or PGE₂ prevents a premature luteolysis when oxytocin is given on Days 1 to 6 of the ovine estrous cycle. Oxytocin given into the jugular vein every 8 hours on Days 1 to 6 postestrus in ewes decreased (P ≤ 0.05) luteal weights on Day 8 postestrus. Plasma progesterone differed (P ≤ 0.05) among the treatment groups; toward the end of the experimental period, concentrations of circulating progesterone in the oxytocin-only treatment group decreased (P ≤ 0.05) when compared with the other treatment groups. Plasma progesterone concentrations in ewes receiving PGE₁ or PGE₁ + oxytocin were greater (P ≤ 0.05) than in vehicle controls or in ewes receiving PGE₂ or PGE₂ + oxytocin and was greater (P ≤ 0.05) in all treatment groups receiving PGE₁ or PGE₂ than in ewes treated only with oxytocin. Chronic intrauterine treatment with PGE₁ or PGE₂ also prevented (P ≤ 0.05) oxytocin decreases in luteal unoccupied and occupied LH receptors on Day 8 postestrus. Oxytocin given alone on Days 1 to 6 postestrus in ewes advanced (P ≤ 0.05) increases in PGF_2α in inferior vena cava or uterine venous blood. PGE₁ or PGE₂ given alone did not affect (P ≥ 0.05) concentrations of PGF_2α in inferior vena cava and uterine venous blood when compared with vehicle controls or oxytocin-induced PGF_2α increases (P ≤ 0.05) in inferior vena cava or uterine venous blood. We concluded that PGE₁ or PGE₂ prevented oxytocin-induced premature luteolysis by preventing a loss of luteal unoccupied and occupied LH receptors.     

Prostaglandin E2 increases the calcium concentration in rat brown adipocytes and their consumption of oxygen

Effects of prostaglandin E₂ (PGE₁) were examined on the oxygen consumption and intracellular calcium concentration of rat brown adipose tissue (BAT). PGE₂ 0.1 nM-1 μM increased oxygen consumption of the tissue blocks of BAT, with a maximum 2–13 min after PGE2 administration. PGE₂ was most effective at 1 and 10 nM, and the oxygen consumption was elevated for over 40 min. Pretreatment of BAT with indomethacin, a prostaglandin synthesis inhibitor, did not affect the increase in oxygen consumption induced by noradrenaline. PGE₂ at 1–10 nM gradually increased the intracellular calcium concentration of freshly dispersed single brown adipocytes by 3–4 times in 30 min. PGE₂ also increased the intracellular calcium concentration of brown adipocytes in calcium-free medium. These results raise the possibility that PGE₂ and noradrenaline affect heat genesis and metabolism of BAT independently.     

Effects of prostaglandin E2 on the micronucleus formation in mouse bone marrow cells by various mutagens

The effects of prostaglandin E₂ (PGE)₂, as trigger of erythroid progenitor cells into the cell cycle, were studied on the induction of micronucleu by various mutagens; with mitomicin C (MMC) the optimal protocol was established. dose-response relationship between PGE₂ doses and micronucleus frequency were observed 30 h after injection of MMC to mice administered PGE₂ 24 h previously. Sensitazion by PGE₂ pretreatment was also found for other mutagens, such as vincristine, 5-fluorouracil, benzo[a]pyrene, 1,1-dimethylhydrazine and 2-naphthylamine. These results support the hypothesis that accelerating the erythropoiesis increases the frequency of micronucleic induced by mutagens.     

Prostaglandin E1 decreases circulating endothelial cells

Prostaglandin E₁ (PGE₁) has been claimed to have cytoprotective effects and also to decrease thrombogenicity. The effect of intraarterial (i.a.) and intravenous (i.v.) administration of PGE₁ on the number of circulating endothelial cells (CEC) was investigated in patients with peripheral vascular disease (PVD). Patients with hyperlipoproteinemia and also smokers exhibited higher numbers of CEC. PGE₁ significantly (p < 0.01) decreased CEC. In parallel, plate let survival was prolonged (r = −0.82). This effect lasted for more than a month after stopping PGE₁-therapy. The observed decrease in CEC reflects the decreased thrombogenicity and improved haemostasis achieved after PGE₁.     

Applications and limitations of measurement of 15-keto,13,14-dihydro prostaglandin E2 in human blood by radioimmunoassay

It has been anticipated that the inherent limitations of radioimmunoassays for prostaglandin E (PGE) would be obviated by assays for its major circulating metabolite, 15-keto, 13,14-dihydro PGE₂ (KH₂-PGE₂) which has a longer half-life in blood. We examined the effects of PGE₂ infusion and alterations in lipolysis , and of clotting, prolonged storage and hemolysis , on KH₂-PGE₂ immunoreactivity in unextracted human plasma and serum samples. Indeed KH₂-PGE₂ levels rose several hundred fold during infusions of PGE₂ at doses which cause little or no increment in peripheral PGE levels. During stimulation of lipolysis by infusions of epinephrine, apparent KH₂-PGE₂ levels rose five-fold. However, the dilution curve of plasma obtained during stimulation of lipolysis was not parallel to the standard curve; furthermore, apparent KH₂-PGE₂ levels were correlated strongly with free fatty acid (FFA) levels, suggesting that FFA's cross-reacted in the RIA weakly but significantly due to their very high molar concentration in blood. Clotting and prolonged storage of samples, but not hemolysis, also caused marked apparent increments in KH₂-PGE₂ levels. Competition curves using dilutions of such samples were again not parallel to the standard curves in plasma or buffer, but resembled dilution curves of samples containing high levels of FFA. These results suggest that handling of human blood samples for KH₂-PGE₂ measurement must be carefully standardized to avoid significant artifacts which presumably are due in part to fatty acids released from triglyceride stores or from disrupted membrane phospholipids . Unextracted plasma appears to be unsatisfactory for use in this RIA.     

Prostaglandin E2 production in astrocytes: regulation by cytokines, extracellular ATP, and oxidative agents

Upregulation and activation of phospholipases A₂ (PLA₂) and cyclooxygenases (COX) leading to prostaglandin E₂(PGE₂) production have been implicated in a number of neurodegenerative diseases. In this study, we investigated PGE₂ production in primary rat astrocytes in response to agents that activate PLA₂ including pro-inflammatory cytokines (IL-1β, TNFα and IFNγ), the P2 nucleotide receptor agonist ATP, and oxidants (H₂O₂ and menadione). Exposure of astrocytes to cytokines resulted in a time-dependent increase in PGE₂ production that was marked by increased expression of secretory sPLA₂ and COX-2, but not COX-1 and cytosolic cPLA₂. Although astrocytes responded to ATP or phorbol ester (PMA) with increased cPLA₂ phosphorylation and arachidonic acid release, ATP or PMA only caused a small increase in levels of PGE₂. However, when astrocytes were first treated with cytokines, further exposure to ATP or PMA, but not H₂O₂ or menadione, markedly increased PGE₂ production. These results suggest that ATP release during neuronal excitation or injury can enhance the inflammatory effects of cytokines on PGE₂ production and may contribute to chronic inflammation seen in Alzheimer's disease.     

Controlled trial of induction of labor by vaginal suppositories containing prostaglandin E2

A group of 84 women at 39 – 43 weeks of pregnancy were randomly allocated to a blind trial of induction of labor with vaginal suppositories containing inert material or either 0.2 mg or 0.4 mg of prostaglandin E₂. The suppositories were self-administered every two hours during waking hours on two successive days until labor started or 15 had been used. Side-effects were absent. Labor was established within 48 hr of insertion of the first suppository in 9.3% of control patients, 65.4% of those treated with 0.2 mg PGE₂ and 85.7% of those treated with 0.4 mg PGE₂. The mean Apgar scores in the three groups were the same. The mean total dose of PGE₂ were 2.0 mg (0.2 mg group) and 2.3 mg (0.4 mg group). It is concluded that vaginal PGE₂ is an effective and acceptable method of inducing labor at term.     

The use of oral prostaglandin E2 in the management of intrauterine fetal death

12 otherwise healthy patients with intrauterine fetal death 1 to 6 weeks earlier were treated with oral prostaglandin E₂. 9 of the 12 patients delivered within 48 hours after treatment began. 2 others delivered within 48 hours after unsuccessful treatment ceased. In a third patient the cervix relaxed after treatment, and the uterine contents were removed by curettage. No serious complications, such as hemorrhage occurred. The uterus seemed surprisingly responsive to oral prostaglandin E₂ in cases of intrauterine fetal death.     

SiO2 nanoparticles induce global genomic hypomethylation in HaCaT cells

The increasing amount of nanotechnological products, found in our environment and those applicable in engineering, material sciences and medicine has stimulated a growing interest in examining their long-term impact on genetic and epigenetic processes. We examined here the epigenomic response to nm-SiO₂ particles in human HaCaT cells and methyltransferases (DNMTs) and DNA-binding domain proteins (MBDs) induced by nano-SiO₂ particles. Nm-SiO₂ treatment induced global hypoacetylation implying a global epigenomic response. The levels of DNMT1, DNMT3a and methyl-CpG binding protein 2 (MBD2) were also decreased in a dose dependent manner at mRNA and protein level. Epigenetic changes may have long-term effects on gene expression programming long after the initial signal has been removed, and if these changes remain undetected, it could lead to long-term untoward effects in biological systems. These studies suggest that nanoparticles could cause more subtle epigenetic changes which merit thorough examination of environmental nanoparticles and novel candidate nanomaterials for medical applications.     

Prostaglandin I2 as a potentiator of acute inflammation in rats

Prostaglandin I₂ potentiated the paw swelling induced by carrageenin in rats. Prostaglandin I₂ (0.1 μg) showed similar activity to PGE₁ (0.01 μg). This potentiating property disappeared in 60 minutes and was completely abolished by diphenhydramine (25 mg kg⁻¹, i.p.). In vascular permeability tests, PGI₂ itself (2.5 × 10⁻¹⁰ mol, 88 ng) caused no dye leakage reaction, but PGE₁ (2.5 × 10⁻¹⁰ mol, 88.5 ng) caused a significant dye leakage. This effect of PGE₁ was statistically significant compared with vehicle- or PGI₂-treated group (p<0.05). Prostaglandin I₂ potentiated the increased vascular permeability induced by 5-hydroxytriptamine (2.5 × 10⁻¹⁰ mol), bradykinin (5 × 10⁻¹⁰ mol) and histamine (2 × 10⁻¹⁰ to 2 × 10⁻⁸ mol). The potentiation was the most evidence in the case of histamine.     

Green tea epigallocatechin-3-gallate inhibits microsomal prostaglandin E2 synthase-1

Prostaglandin (PG)E₂ is a critical lipid mediator connecting chronic inflammation to cancer. The anti-carcinogenic epigallocatechin-3-gallate (EGCG) from green tea (Camellia sinensis) suppresses cellular PGE₂ biosynthesis, but the underlying molecular mechanisms are unclear. Here, we investigated the interference of EGCG with enzymes involved in PGE₂ biosynthesis, namely cytosolic phospholipase (cPL)A₂, cyclooxygenase (COX)-1 and -2, and microsomal prostaglandin E₂ synthase-1 (mPGES-1). EGCG failed to significantly inhibit isolated COX-2 and cPLA₂ up to 30 μM and moderately blocked isolated COX-1 (IC₅₀ > 30 μM). However, EGCG efficiently inhibited the transformation of PGH₂ to PGE₂ catalyzed by mPGES-1 (IC₅₀ = 1.8 μM). In lipopolysaccharide-stimulated human whole blood, EGCG significantly inhibited PGE₂ generation, whereas the concomitant synthesis of other prostanoids (i.e., 12(S)-hydroxy-5-cis-8,10-trans-heptadecatrienoic acid and 6-keto PGF_1α) was not suppressed. Conclusively, mPGES-1 is a molecular target of EGCG, and inhibition of mPGES-1 is seemingly the predominant mechanism underlying suppression of cellular PGE₂ biosynthesis by EGCG.     

During a systemic inflammatory response, the effect of non-steroidal anti-inflammatory drugs on seizure susceptibility in the immature brain may depend on the proconvulsant and anticonvulsant mechanisms simultaneously induced by the elevation of parenchymal prostaglandin E2 levels

Clinical evidence from paediatric neurology supports the possibility that a protracted inflammatory state in the central nervous system (CNS) may enhance the predisposition of brain tissue to develop seizures. Consequently, non-steroidal anti-inflammatory drugs (NSAIDs) as well as selective cyclooxygenase-2 (COX-2) inhibitors were expected to positively modulate seizure susceptibility during a systemic inflammatory response. Nevertheless, experimental findings and clinical evidence provide controversial results. As a possible explanation for these apparent discrepancies, it is hypothesised that the amount of prostaglandin E₂ (PGE₂) induced in the immature brain parenchyma during systemic inflammatory response is crucial since PGE₂ plays a dual role. Indeed, on the one hand, this prostaglandin increases seizure susceptibility by stimulation of glutamate release from neurons and astrocytes. On the other hand, however, the same prostaglandin induces a massive release of corticosterone, being this hormone known to inhibit efficiently the seizure susceptibility of the immature brain. Hence, the dose-response curve of any given NSAID/COX-2 inhibitor on seizure susceptibility is expected to show different patterns, depending on the amount of PGE₂ levels produced in the brain parenchyma during the effect of drug. The proposed hypothesis also suggests that mild to moderate increase of PGE₂ levels in the immature brain parenchyma may act as a ‘preconditioning’ stimulus, i.e., it may confer a transient resistance to develop seizure-induced brain injury, besides to efficiently counteract seizure susceptibility.     

Dietary arachidonic acid suppresses bone turnover in contrast to low dosage exogenous prostaglandin E2 that elevates bone formation in the piglet

This study was designed to compare the effects of dietary arachidonic acid (AA) versus prostaglandin E₂ (PGE₂) on bone cell metabolism and bone mass. Twenty-eight piglets from 7 litters were randomized to 1 of 4 treatments for 15 days: fatty acid supplemented formula (FA: 0.8% of total fatty acids as AA and 0.1% of total fatty acids as DHA)+PGE₂ injections (0.1 mg/kg/day), FA+saline injections, standard formula (STD: n-6:n-3 of 8:1) + PGE₂ injections or STD+saline injections. PGE₂ resulted in elevated osteoblast activity as indicated by plasma osteocalcin and also reduced urinary calcium excretion. Dietary FA resulted in reduced bone resorption as indicated by urinary N-telopeptide and reduced bone PGE₂. Both PGE₂ and FA treatments independently lead to elevated femur mineral content, but the combined treatment caused a reduction. Thus the mechanisms by which PGE₂ and FA lead to enhanced bone mass are distinct.     

A calcitonin-like action of prostaglandin E1

The pharmacological effects of PGE₁ (6 and 9 days, 21,250 μg/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE₁ hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE₁ clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth >dentin formation >incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE₁, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE₁ lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE₁ may induce a calcitonin-like action, a part of which may dependent on the calcinonin secretion is suggested.     

七氟烷联合右美托咪定对腹腔镜下子宫肌瘤切除术患者生命体征、血清炎性因子和疼痛介质P物质、前列腺素E2的影响

摘要 目的：探讨七氟烷联合右美托咪定对腹腔镜下子宫肌瘤切除术患者生命体征、血清炎性因子和疼痛介质P物质（SP）、前列腺素E2（PGE2）的影响。方法：选取安徽医科大学附属合肥医院2019年8月~2022年1月期间择期行腹腔镜下子宫肌瘤切除术患者92例。根据随机数字表法将入选患者分为对照组（46例）和研究组（46例）。对照组接受七氟烷麻醉,研究组接受七氟烷联合右美托咪定麻醉,比较两组生命体征、血清炎性因子[肿瘤坏死因子-α（TNF-α）、白介素-6（IL-6）、白介素-1β（IL-1β）]、疼痛指标[视觉疼痛模拟评分（VAS）、SP、PGE2]、苏醒质量和不良反应发生率。结果：研究组插管后5 min（T1）、术毕（T2）心率（HR）、平均动脉压（MAP）低于对照组（P<0.05）。研究组术后24 h（T3）、术后48 h（T4）TNF-α、IL-6、IL-1β低于对照组（P<0.05）。研究组T3、T4时VAS、PGE2、SP低于对照组（P<0.05）。两组苏醒时间、拔管时间无显著差异（P>0.05）。研究组的躁动评分小于对照组（P<0.05）。两组不良反应发生率组间对比无差异（P>0.05）。结论：腹腔镜下子宫肌瘤切除术中应用七氟烷联合右美托咪定,可使术后躁动减轻,血流动力学稳定,有效改善术后疼痛和炎性反应。     

Prostaglandin E2 receptors in asthma and in chronic rhinosinusitis/nasal polyps with and without aspirin hypersensitivity

Chronic rhinosinusitis with nasal polyps (CRSwNP) and asthma frequently coexist and are always present in patients with aspirin exacerbated respiratory disease (AERD). Although the pathogenic mechanisms of this condition are still unknown, AERD may be due, at least in part, to an imbalance in eicosanoid metabolism (increased production of cysteinyl leukotrienes (CysLTs) and reduced biosynthesis of prostaglandin (PG) E₂), possibly increasing and perpetuating the process of inflammation. PGE₂ results from the metabolism of arachidonic acid (AA) by cyclooxygenase (COX) enzymes, and seems to play a central role in homeostasis maintenance and inflammatory response modulation in airways. Therefore, the abnormal regulation of PGE₂ could contribute to the exacerbated processes observed in AERD. PGE₂ exerts its actions through four G-protein-coupled receptors designated E-prostanoid (EP) receptors EP1, EP2, EP3, and EP4. Altered PGE₂ production as well as differential EP receptor expression has been reported in both upper and lower airways of patients with AERD. Since the heterogeneity of these receptors is the key for the multiple biological effects of PGE₂ this review focuses on the studies available to elucidate the importance of these receptors in inflammatory airway diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-014-0100-7) contains supplementary material, which is available to authorized users.     

Effects of hypothalamic microinjection of PGE2 on body temperature and sympathetic nervous activities in the rabbit

The febrile response and sympathetic nervous response to hypothalamic microinjections of prostaglandin E₂ (PGE₂) were investigated in anesthetized rabbits. Microninjection of PGE₂ (500–1000 ng) caused an increase in rectal temperature of more than 0.3°C in 13 of 50 loci in the preoptic and anterior hypothalamic area (PO/AH). At 8 of these 13 loci, PGE₂ elicited response patterns in the sympathetic nervous system, such as an increase in cutaneous sympathetic nervous activity and decrease in renal sympathetic nervous activity. This pattern of sympathetic nervous responses was induced with a simultaneous increase in rectal temperature of more than 0.5°C. The 8 loci were distributed in the preoptic area, especially in the vicinity of the supraoptic nucleus. Electrolytic lesions of this region were made bilaterally, and intracerebroventricular injection of PGE₂ (8 µg/kg) was found to inhibit fever and sympathetic activity. The results demonstrate that the action of PGE₂ is responsible for the response patterns of sympathetic twigs during fever. The preoptic area, especially in the vicinity of the supraoptic nucleus, is most sensitive to PGE₂ for the patternized response of sympathetic neurons and fever.     

The prostaglandin transporter PGT transports PGH2

Prostaglandin H₂ not only serves as the common precursor of all other PGs, but also directly triggers signals (e.g. platelet aggregation), depending on its location and translocation. The prostaglandin carrier PGT mediates the transport of several prostanoids, such as PGE₂, and PGF_2α. Here we used PGT in the plasma membrane as a model system to test the hypothesis that PGT also transports PGH₂. Using wild-type and PGT-expressing MDCK cells, we show that PGH₂ uptake is mediated both by simple diffusion and by PGT. The PGH₂ influx permeability coefficient for diffusion is (5.66 ± 0.63) × 10⁻⁶ cm/s. The kinetic parameters of PGH₂ transport by PGT are K_m = 376 ± 34 nM and V_max = 210.2 ± 11.4 fmol/mg protein/s. PGH₂ transport by PGT can be inhibited by excess PGE₂ or by a PGT inhibitor. We conclude that PGT may play a role in transporting PGH₂ across cellular membranes.