EP2 and EP3 receptors as therapeutic targets for underactive bladder/detrusor underactivity due to diabetic cystopathy in a type 1 diabetic rat model.

OBJECTIVES: Diabetic cystopathy (DC) is recognized as one of the major etiologies of underactive bladder (UAB)/detrusor underactivity (DU). Although DC was first reported about three decades ago, there is a distinct lack of effective pharmacological management methods for UAB/DU due to DC with a robust certainty of evidence. In this study, we investigated whether EP2 and EP3 receptors are promising targets of pharmacological management of UAB/DU due to DC. METHODS: We used streptozotocin (STZ)-induced diabetic Sprague-Dawley rats with postvoid residual urine (PVR) greater than 0.1 mL. Sixteen weeks after induction of diabetes, we performed awake single cystometry after oral administration of the vehicle, an α-blocker (tamsulosin [TAM], 0.1 and 0.3 mg/kg), a cholinesterase inhibitor (distigmine [DIS], 0.3 and 1.0 mg/kg), or an EP2/3 dual agonist (ONO-8055, 0.01 and 0.03 mg/kg). We compared cystometric parameters after administration of the vehicle and drugs using a paired t test. P < .05 was considered to be statistically significant. RESULTS: Compared with the vehicle, TAM significantly decreased maximum intravesical pressure during voiding (Pmax), while DIS significantly increased it. However, neither drug significantly affected PVR or the residual urine rate (RUR). On the other hand, ONO-8055 significantly decreased PVR and tended to decrease RUR, although it did not significantly affect Pmax. CONCLUSION: The present study was unable to demonstrate that stimulation of EP2 and EP3 receptors caused major improvements in UAB/DU due to DC. However, this equivocal result could arise from inherent limitations of the STZ-induced diabetic rat as a UAB/DU model.

Prostaglandin E2 sequentially activates E-prostanoid receptor-3 and thromboxane prostanoid receptor to evoke contraction and increase in resistance of the mouse renal vasculature.

Although recognized to have an in vivo vasodepressor effect blunted by the vasoconstrictor effect of E-prostanoid receptor-3 (EP3), prostaglandin E2 (PGE2 ) evokes contractions of many vascular beds that are sensitive to antagonizing the thromboxane prostanoid receptor (TP). This study aimed to determine the direct effect of PGE2 on renal arteries and/or the whole renal vasculature and how each of these two receptors is involved in the responses. Experiments were performed on isolated vessels and perfused kidneys of wild-type mice and/or mice with deficiency in TP (TP-/- ), EP3 (EP3-/- ), or both TP and EP3 (TP-/- /EP3-/- ). Here we show that PGE2 (0.001-30 µM) evoked not only contraction of main renal arteries, but also a decrease of flow in perfused kidneys. EP3-/- diminished the response to 0.001-0.3 µM PGE2 , while TP-/- reduced that to the prostanoid of higher concentrations. In TP-/- /EP3-/- vessels and perfused kidneys, PGE2 did not evoke contraction but instead resulted in vasodilator responses. These results demonstrate that PGE2 functions as an overall direct vasoconstrictor of the mouse renal vasculature with an effect reflecting the vasoconstrictor activities outweighing that of dilation. Also, our results suggest that EP3 dominates the vasoconstrictor effect of PGE2 of low concentrations (≤0.001-0.3 µM), but its effect is further added by that of TP, which has a higher efficacy, although activated by higher concentrations (from 0.01 µM) of the same prostanoid PGE2 .

Enriching Islet Phospholipids With Eicosapentaenoic Acid Reduces Prostaglandin E2 Signaling and Enhances Diabetic ß-Cell Function.

Prostaglandin E2 (PGE2) is derived from arachidonic acid, whereas PGE3 is derived from eicosapentaenoic acid (EPA) using the same downstream metabolic enzymes. Little is known about the impact of EPA and PGE3 on ß-cell function, particularly in the diabetic state. In this work, we determined that PGE3 elicits a 10-fold weaker reduction in glucose-stimulated insulin secretion through the EP3 receptor as compared with PGE2 We tested the hypothesis that enriching pancreatic islet cell membranes with EPA, thereby reducing arachidonic acid abundance, would positively impact ß-cell function in the diabetic state. EPA-enriched islets isolated from diabetic BTBR Leptinob/ob mice produced significantly less PGE2 and more PGE3 than controls, correlating with improved glucose-stimulated insulin secretion. NAD(P)H fluorescence lifetime imaging showed that EPA acts downstream and independently of mitochondrial function. EPA treatment also reduced islet interleukin-1ß expression, a proinflammatory cytokine known to stimulate prostaglandin production and EP3 expression. Finally, EPA feeding improved glucose tolerance and ß-cell function in a mouse model of diabetes that incorporates a strong immune phenotype: the NOD mouse. In sum, increasing pancreatic islet EPA abundance improves diabetic ß-cell function through both direct and indirect mechanisms that converge on reduced EP3 signaling.

Novel prostaglandin receptor modulators--part II: EP receptor modulators; a patent review (2002 - 2012).

INTRODUCTION: Prostaglandins and their G-protein-coupled receptors play numerous physiological and pathophysiological roles, especially in inflammation and its resolution. The variety of effects mediated by prostanoids makes prostanoid receptors valuable drug targets and the research on prostaglandin receptor modulators is intensive. The physiological and pathophysiological effects of prostaglandin E(2) are especially complex and numerous. The four subtypes of EP receptor have gained a lot of industrial and academic interest, in particular EP(2) and EP(4) for various indications. AREAS COVERED: Evaluation of the patent activity over the last decade (2002 - 2012) illustrates several potent compounds targeting the distinct prostaglandin E(2) receptors. Many novel methods for the use of EP receptor modulators have been developed, in addition to the classical indications for agents modulating the arachidonic acid cascade such as pain and inflammation. EXPERT OPINION: Several EP targeting agents with good potency and selectivity have been developed but their pharmacological use and utility has not yet been satisfactorily investigated. More research is necessary, and clinical use of these agents might therefore take some more time.

Distinct roles of central and peripheral prostaglandin E2 and EP subtypes in blood pressure regulation.

Prostaglandin E(2) (PGE(2)) is a major prostanoid with a wide variety of biological activities. PGE(2) can influence blood pressure (BP) both positively and negatively. In particular, centrally administered PGE(2) induces hypertension whereas systemic administration of PGE(2) produces a hypotensive effect. These physiologically opposing effects are generated by the existence of multiple EP receptors, namely EP(1-4), which are G protein-coupled receptors with distinct signaling properties. This review highlights the distinct roles of PGE(2) in BP regulation and the involvement of specific EP receptor subtypes.

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

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

EP3 receptor-mediated contraction of human pulmonary arteries and inhibition of neurogenic tachycardia in pithed rats.

BACKGROUND: The aim of our study was (1) the pharmacological characterization of EP(3) receptors in human pulmonary arteries and (2) the examination of the potential involvement of these receptors in the regulation of neurogenic tachycardia in pithed rats. L-826266 served as the EP(3) receptor antagonist. METHODS: Experiments were performed on isolated human pulmonary arteries and pithed rats. RESULTS: The prostanoid EP(1)/EP(3) receptor agonist sulprostone (1 nM - 100 µM) concentration-dependently contracted isolated human pulmonary arteries (pEC50, 6.88 ± 0.10). The EP(1) receptor antagonist SC 19920 (100 µM) did not affect the vasoconstriction induced by sulprostone, the TP receptor antagonist sulotroban (10 µM) only slightly attenuated the effects elicited by sulprostone >>3 µM, whereas L-826266 (10 µM) shifted its concentration-response curve to the right (apparent pA(2) value 6.18; incubation time 0.5 h). In rings exposed to L-826266 (0.1, 1 or 10 µM) for 3 h, a concentration-dependent inhibitory effect against the sulprostone-induced vasoconstriction was obtained, yielding a Schild plot-based pA(2) value of 7.39. In pithed rats, sulprostone (10 - 1,000 nmol/kg), but not the IP/EP(1) receptor agonist iloprost (1-100 nmol/kg), inhibited the electrically evoked increase in heart rate (HR) dose-dependently, maximally by at least 80%. L-826266 (3 µmol/kg) did not affect basal HR and diastolic blood pressure, but reduced the inhibitory effect of sulprostone 1,000 nmol/kg by about 20%. CONCLUSION: EP(3) receptors (1) located postsynaptically strongly contract human pulmonary arteries and (2) located presynaptically on sympathetic nerve fibers supplying the heart of pithed rats strongly inhibit the neurogenic tachycardia.

Capsaicin-induced vasodilatation in human nasal vasculature is mediated by modulation of cyclooxygenase-2 activity and abrogated by sulprostone.

Extensively based on evidence gained from experimental animal models, the transient receptor potential vanilloid receptor type 1 (TRPV1)-activator capsaicin is regarded as a valuable tool in the research on neurogenic inflammation. Although capsaicin-related drugs gained renewed interest as a therapeutic tool, there is also controversy as whether neurogenic inflammation actually takes place in humans. In this study, we verified the involvement of capsaicin in vascular responses that are regarded to be implicated in the cascade of neurogenic inflammatory mechanisms. By means of ex vivo functional experiments on human nasal mucosal vascular beds, the effect and mechanism of action of capsaicin was assessed in the absence and presence of various agents that interfere with potentially related transduction pathways. Ten micromolars of capsaicin induced vasodilatations that were reduced by the selective EP(1) prostanoid receptor antagonist SC19220 (10 µM) and almost abolished by the selective COX-2 inhibitor NS398 (1 µM) and the EP(1/3) receptor agonist sulprostone (0.1-10 nM), but not affected by the TRPV1-antagonists capsazepine (5 µM), the neurokinin NK(1) receptor antagonist GR20517A (1 µM), and the calcitonin-gene-related peptide (CGRP) receptor antagonist CGRP8-37 (100 nM). Spontaneously released PGE(2) and PGD(2) levels were significantly reduced in the presence of capsaicin. In conclusion, capsaicin-at concentrations clinically applied or under investigation for diverse disease backgrounds-induces a vasodilatory response in human nasal mucosa via a mechanism involving TRPV1-independent reduction of PGE(2) production by modulation of COX-2 enzymatic activity. These vasodilatations can be suppressed by the EP(1/3) receptor agonist sulprostone at subnanomolar concentrations.

Sodium butyrate induces the production of cyclooxygenases and prostaglandin E2 in ROS 17/2.8 osteoblastic cells.

OBJECTIVE: Sodium butyrate (butyric acid; BA) is a major metabolic by-product of the anaerobic periodontopathic bacteria present in subgingival plaque. We examined the effects of BA and/or indomethacin on cell proliferation, the expression of cyclooxygenases (COXs), prostaglandin (PG) receptors (EP1-4), extracellular matrix proteins, such as type I collagen and osteopontin, and PGE(2) production, using ROS17/2.8 cells as osteoblasts. METHODS: The rat clonal cell line ROS 17/2.8 was cultured with 0, 10(-5), 10(-4), and 10(-3)M BA in the presence or absence of 0.5 µM indomethacin, for up to 7 days. The expression of COX-1, COX-2, EP1, EP2, EP3, EP4, type I collagen, and osteopontin was examined at the mRNA and protein levels using real-time PCR and Western blotting, respectively. The amount of PGE(2) in the culture medium was measured by ELISA. RESULTS: Proliferation of ROS 17/2.8 cells was not affected by the addition of BA. However, PGE(2) production and the expression of COX-1 and COX-2 increased with the addition of BA. In contrast, indomethacin, an inhibitor of COX, blocked the stimulatory effect of BA. Furthermore, EP2 expression increased with BA treatment, whereas EP1 expression was not affected and the expression of EP3 and EP4 was not detected. The addition of BA also increased the expression of type I collagen and osteopontin. Indomethacin blocked about 50% of the stimulatory effect of BA on type I collagen, whereas it did not block the effect on osteopontin. CONCLUSIONS: These results suggest that BA induces PGE(2) production by increasing the expression of COX-1 and COX-2 in osteoblasts, and that an autocrine action of the produced PGE(2), via EP1 or BA-induced EP2, is related to an increase in type I collagen expression by BA.