Inhibition of microsomal prostaglandin E-synthase-1 (mPGES-1) selectively suppresses PGE2 in an in vitro equine inflammation model

Expression of mPGES1 and p16 in feline and human oral squamous cell carcinoma: A comparative oncology approach

Comparative cancer studies help us determine if discoveries in one species apply to another. Feline and human oral squamous cell carcinoma (FOSCC and HOSCC) are invasive tumours in which inflammation and abnormal p16 expression are reported. Immunohistochemistry was used to determine the expression of p16 and microsomal prostaglandin E2 synthase 1 (mPGES1) in 42 HOSCC and 45 FOSCC samples with known expression of cyclooxygenase 2 (COX2) and cluster of differentiation 147 (CD147). High p16 expression was more common in HOSCC tumour cells compared to adjacent stroma and oral epithelium (p < .05), with a similar but statistically nonsignificant pattern in FOSCC. Interestingly, high mPGES1 expression in FOSCC was more common in the adjacent epithelium compared to the other compartments (p < .05). In HOSCC, mPGES1 was more similar between compartments but was numerically more common in the tumour compartment (p > .05). There were nominal (p > 0.05) differences in marker expression between high and low mPGES1 expressing tumours in both species, including high p16 observed more commonly in high mPGES1 tumours, and COX-2 positive tumours being more common in low mPGES1 tumours. High CD147 HOSCC tumours were more common in the high mPGES1 HOSCC group (p < .05). In the FOSCC cohort, where there was no statistical difference in CD147 expression between high and low mPGES1 tumours, there were numerically higher CD147 cases in the high mPGES1group. Different expression patterns in FOSCC and HOSCC could be related to different risk factors. For example, p16 is a marker of papillomavirus-driven HOSCC, but a causal relationship between papillomaviruses and FOSCC has yet to be definitively demonstrated. The significance of high P16 expression in the absence of papillomavirus infection deserves further study, and the relative contributions of COX2 and mPGES1 to tumour inflammation and progression should be explored. The findings reveal potential similarities in FOSCC and HOSCC biology, while also demonstrating differences that may relate to risk factors and pathogenesis that are unique to each species.

Role of prostanoids, nitric oxide and endothelin pathways in pulmonary hypertension due to COPD

Pulmonary hypertension (PH) due to chronic obstructive pulmonary disease (COPD) is classified as Group 3 PH, with no current proven targeted therapies. Studies suggest that cigarette smoke, the most risk factor for COPD can cause vascular remodelling and eventually PH as a result of dysfunction and proliferation of pulmonary artery smooth muscle cells (PASMCs) and pulmonary artery endothelial cells (PAECs). In addition, hypoxia is a known driver of pulmonary vascular remodelling in COPD, and it is also thought that the presence of hypoxia in patients with COPD may further exaggerate cigarette smoke-induced vascular remodelling; however, the underlying cause is not fully understood. Three main pathways (prostanoids, nitric oxide and endothelin) are currently used as a therapeutic target for the treatment of patients with different groups of PH. However, drugs targeting these three pathways are not approved for patients with COPD-associated PH due to lack of evidence. Thus, this review aims to shed light on the role of impaired prostanoids, nitric oxide and endothelin pathways in cigarette smoke- and hypoxia-induced pulmonary vascular remodelling and also discusses the potential of using these pathways as therapeutic target for patients with PH secondary to COPD.

Prostaglandin E2 increases the expression of cyclooxygenase-2 in cultured rat microglia

Prostaglandin E₂ (PGE₂) plays pivotal roles in controlling microglial activation with the EP₂ receptor, a PGE₂ receptor subtype. Activated microglia are often reported to increase cyclooxygenase (COX)-2 expression, followed by PGE₂ production, but it is unclear whether extracellular PGE₂ is involved in microglial PGE₂ synthesis. In the present study, we report that PGE₂ increases COX-2 protein in microglia. In a culture system, PGE₂ at 10^-6 M for 3 h increased COX-2 and microsomal PGE synthase (mPGES)-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cytosolic PGE synthase (cPGES) in microglia. PGE₂ at 10^-6 M for 3 h also increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. An EP₂ agonist, ONO-AE1-259-01, also increased COX-2 and mPGES-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cPGES, whereas an EP₁ agonist, ONO-DI-004, an EP₃ agonist, ONO-AE-248, and an EP₄ agonist, ONO-AE1-329, had no effect. Similar to PGE₂, ONO-AE1-259-01 increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. In addition, the effects of PGE₂ were inhibited by an EP₂ antagonist, PF-04418948, but not by an EP₁ antagonist, ONO-8713, an EP₃ antagonist, ONO-AE3-240, or an EP₄ antagonist, ONO-AE3-208, at 10^-6 M. On the other hand, lipopolysaccharide (LPS) increased PGE₂ production, but the LPS-induced PGE₂ production was not affected by ONO-8713, PF-04418948, ONO-AE3-240, or ONO-AE3-208. These results indicate that PGE₂ increases COX-2 protein in microglia through the EP₂ receptor supporting the idea that extracellular PGE₂ has a triggering aspect for microglial activation.

Microsomal prostaglandin E2 synthase-1 and its inhibitors: Molecular mechanisms and therapeutic significance

Inflammation is closely linked to the abnormal phospholipid metabolism chain of cyclooxygenase-2/microsomal prostaglandin E₂ synthase-1/prostaglandin E₂ (COX-2/mPGES-1/PGE₂). In clinical practice, non-steroidal anti-inflammatory drugs (NSAIDs) as upstream COX-2 enzyme activity inhibitors are widely used to block COX-2 cascade to relieve inflammatory response. However, NSAIDs could also cause cardiovascular and gastrointestinal side effects due to its inhibition on other prostaglandins generation. To avoid this, targeting downstream mPGES-1 instead of upstream COX is preferable to selectively block overexpressed PGE₂ in inflammatory diseases. Some mPGES-1 inhibitor candidates including synthetic compounds, natural products and existing anti-inflammatory drugs have been proved to be effective in in vitro experiments. After 20 years of in-depth research on mPGES-1 and its inhibitors, ISC 27864 have completed phase II clinical trial. In this review, we intend to summarize mPGES-1 inhibitors focused on their inhibitory specificity with perspectives for future drug development.

Enhanced mPGES-1 Contributes to PD-Related Peritoneal Fibrosis via Activation of the NLRP3 Inflammasome

Background: Microsomal prostaglandin E synthase-1 (mPGES-1)-derived prostaglandin E₂ (PGE2) is a chief mediator of inflammation. However, the role and mechanism of mPGES-1 in peritoneal dialysis (PD)-associated peritoneal fibrosis have not been investigated.

Material and Methods: In PD patients, mPGES-1 expression in peritoneum tissues and the levels of PGE2, IL-1β, and IL-18 in the dialysate were examined. In rat peritoneal mesothelial cells (RPMCs), the regulation and function of mPGES-1 and NLRP3 inflammasome were investigated. The expression of extracellular matrix proteins and the components of NLRP3 inflammasome were detected by Western blotting or real-time quantitative PCR.

Results: In PD patients with ultrafiltration failure (UFF), mPGES-1 was enhanced in the peritoneum, which was associated with the degree of peritoneal fibrosis. Accordingly, the intraperitoneal PGE2 levels were also positively related to the PD duration, serum C-reactive protein levels, and serum creatinine levels in incident PD patients. In RPMCs, high-glucose treatment significantly induced mPGES-1 expression and PGE2 secretion without affecting the expressions of mPGES-2 and cPGES. Inhibition of mPGES-1 via short hairpin RNA significantly ameliorated the expression of extracellular matrix proteins of RPMCs induced by high glucose. Additionally, high glucose markedly activated NLRP3 inflammasome in RPMCs that was blunted by mPGES-1 inhibition. Furthermore, silencing NLRP3 with siRNA significantly abrogated the expression of extracellular matrix proteins in RPMCs treated with high glucose. Finally, we observed increased IL-1β and IL-18 levels in the dialysate of incident PD patients, showing a positive correlation with PGE2.

Conclusion: These data demonstrate that mPGES-1-derived PGE2 plays a critical role in PD-associated peritoneal fibrosis through activation of the NLRP3 inflammasome. Targeting mPGES-1 may offer a novel strategy to treat peritoneal fibrosis during PD.

Inhibition of mPGES-1 attenuates efficient resolution of acute inflammation by enhancing CX3CL1 expression

Despite the progress to understand inflammatory reactions, mechanisms causing their resolution remain poorly understood. Prostanoids, especially prostaglandin E2 (PGE2), are well-characterized mediators of inflammation. PGE2 is produced in an inducible manner in macrophages (Mϕ) by microsomal PGE2-synthase-1 (mPGES-1), with the notion that it also conveys pro-resolving properties. We aimed to characterize the role of mPGES-1 during resolution of acute, zymosan-induced peritonitis. Experimentally, we applied the mPGES-1 inhibitor compound III (CIII) once the inflammatory response was established and confirmed its potent PGE2-blocking efficacy. mPGES-1 inhibition resulted in an incomplete removal of neutrophils and a concomitant increase in monocytes and Mϕ during the resolution process. The mRNA-seq analysis identified enhanced C-X3-C motif receptor 1 (CX3CR1) expression in resident and infiltrating Mϕ upon mPGES-1 inhibition. Besides elevated Cx3cr1 expression, its ligand CX3CL1 was enriched in the peritoneal lavage of the mice, produced by epithelial cells upon mPGES-1 inhibition. CX3CL1 not only increased adhesion and survival of Mϕ but its neutralization also completely reversed elevated inflammatory cell numbers, thereby normalizing the cellular, peritoneal composition during resolution. Our data suggest that mPGES-1-derived PGE2 contributes to the resolution of inflammation by preventing CX3CL1-mediated retention of activated myeloid cells at sites of injury.

Targeting microsomal prostaglandin E synthase 1 to develop drugs treating the inflammatory diseases

Microsomal prostaglandin E synthase 1 (mPGES-1) is the terminal synthase of prostaglandin E2 (PGE2) which plays a crucial role in inflammatory diseases. Thus, mPGES-1 inhibitors are promising agents for their better specificity in blocking the production of PGE2, a potent inflammatory mediator, compared with non-steroidal anti-inflammatory drugs (NSAIDs). Currently, two mPGES-1 inhibitors are undergoing clinical trials and more novel inhibitors are being developed. In this review, we focus on the advances in the development of mPGES-1 inhibitors and the potential of these inhibitors to treat different inflammatory diseases, and discuss the existing challenges. The insights from this review will increase the understanding on the current status of mPGES-1-targeted anti-inflammatory drug development and the potential of these drugs in treating inflammation in diseases.

Exploring relationships between body condition score, body fat, activity level and inflammatory biomarkers

Obesity is associated with inflammatory disorders in humans, including degenerative joint disease. While obesity is endemic in horses, its relationship to equine degenerative joint disease has not been explored. The current study sought to describe relationships between: body weight (BW), body condition score (BCS), lameness grade (AAEP), total body fat mass (kg; FM) and fat per cent (FP) [multifrequency bioelectrical impedance analysis (mfBIA)], age, gender, activity level (AL), synovial fluid (SF) and plasma (PL) PGE₂ and glycosaminoglycan (GAG) in horses. During this field investigation, the BCS (of nine) of 54 horses at multiple farms in southern Ontario, Canada, was determined. Horses were categorized as thin (BCS=3/9; n = 6), moderate (BCS=4 or 5/9; n = 18), overweight (BCS=6 or 7/9; n = 19) or obese (BCS=8 or 9/9; n = 11). Total fat mass (kg) and body fat% was measured using mfBIA, lameness was assessed (AAEP lameness scale) and synovial fluid was collected via aseptic arthrocentesis from the left intercarpal joint for assessment of inflammatory biomarkers (PGE₂ , GAG). Means were compared with a one-way ANOVA; correlation coefficients were calculated using a Spearman Rank Order Correlation to reveal correlations between variables. BCS was positively correlated with BW, FM, FP, AL and PL-PGE₂ . BW was also significantly positively correlated with PL-PGE₂ . It is concluded that BCS is significantly correlated with PL-PGE₂ , due in part to the combined effect of AL and body condition. Net inflammatory effects of body fat on risk for joint disease require further study.