Delta12-prostaglandin D2 is a potent and selective CRTH2 receptor agonist and causes activation of human eosinophils and Th2 lymphocytes

Prostaglandin D2 (PGD2) is a lipid mediator produced by mast cells, macrophages and Th2 lymphocytes and has been detected in high concentrations in the airways of asthmatic patients. There are two receptors for PGD2, namely the D prostanoid (DP) receptor and the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). The proinflammatory effects of PGD2 leading to recruitment of eosinophils and Th2 lymphocytes into inflamed tissues is thought to be predominantly due to action on CRTH2. Several PGD2 metabolites have been described as potent and selective agonists for CRTH2. In this study we have characterized the activity of delta12-PGD2, a product of PGD2 isomerization by albumin. Delta12-PGD2 induced calcium mobilization in CHO cells expressing human CRTH2 receptor, with efficacy and potency similar to those of PGD2. These effects were blocked by the TP/CRTH2 antagonist ramatroban. delta12-PGD2 bound to CRTH2 receptor with a pKi of 7.63, and a 55-fold selectivity for CRTH2 compared to DP. In Th2 lymphocytes, delta12-PGD2 induced calcium mobilization with high potency and an efficacy similar to that of PGD2. delta12-PGD2 also caused activation of eosinophils as measured by shape change. Taken together, these results show that delta12-PGD2 is a potent and selective agonist for CRTH2 receptor and can cause activation of eosinophils and Th2 lymphocytes. These data also confirm the selective effect of other PGD2 metabolites on CRTH2 and illustrate how the metabolism of PGD2 may influence the pattern of leukocyte infiltration at sites of allergic inflammation.

Synthesis of 15R-PGD2: a potential DP2 receptor agonist

The first total synthesis of 15R-PGD(2)3 was accomplished. The approach used in this report is also an efficient method to produce 15R-PGE(2). 15R-PGD(2), a potential DP(2) receptor agonist, could be an important novel tool for defining the role of this receptor in inflammatory diseases.

Ocular hypotensive DP-class prostaglandin receptor affinities determined by quantitative autoradiography on human eye sections

The aim of this study was to define the localization and pharmacology of DP-prostaglandin receptors in human eye sections using a novel DP-antagonist radioligand ([3H]-BWA868C), using various intraocular pressure (IOP)-lowering DP-prostaglandins and the technique of quantitative autoradiography on 20-microm sections of frozen human eyes. [3H]BWA868C yielded well-defined autoradiograms of DP-receptors in human eyes with up to 82% specific binding. High densities of DP-receptors were associated with the ciliary epithelium/process, iris, choroid, longitudinal and circular ciliary muscles, and retina. Low specific binding was observed in the lens and cornea. The DP-receptor agonists, BW245C (Ki = 4-8 nM), SQ27986 (Ki = 6-9 nM), ZK118182 (Ki = 12-33 nM), 3,4-dihydro-ZK118182 (AL-6556; Ki = 1.6-4.3 (microM) and 3,4-dihydro-ZK118182 isopropyl ester (AL-6598; Ki = 2.9-9.7 microM), exhibited varying affinities for human DP-receptors in the ciliary process, longitudinal and circular ciliary muscles, and iris, respectively. These human ocular tissue affinity values correlated well with nonocular tissue affinities and functional potencies of these prostaglandins in cultured cells (r = 0.93-0.99). In conclusion, these quantitative autoradiographic studies revealed a high density of DP-prostaglandin receptors in human ciliary muscles, ciliary process, and iris, indicating that this class of prostaglandin may lower IOP by uveoscleral pathway and also by inhibiting aqueous humor production. The pharmacological attributes of [3H]BWA868C-labeled receptor sites studied using in situ quantitative autoradiography matched those previously documented for several other DP-receptor-containing cells and tissues.

Prostaglandins E(2) and F(2alpha) enhance differentiation of cementoblastic cells

BACKGROUND

The prostaglandins (PG) E(2) and PGF(2alpha) are important cytokines in periodontal physiology and pathology. PGE(2) and PGF(2alpha) alter cell function by binding and activating the plasmamembrane G-protein-coupled PG receptors. In this study, we examined the PGE(2) and PGF(2alpha) effects on the immortalized cementoblastic OCCM cells.

METHODS

Confluent OCCM cells were treated with PGE(2), PGF(2alpha), specific activators/inhibitors of the EP prostanoid receptors, a specific activator of the FP prostanoid receptor, and direct activators/inhibitors of the protein kinase C (PKC) signaling pathway. Mineral nodule formation was assessed by the von Kossa stain.

RESULTS

PGE(2) and PGF(2alpha) significantly increased mineralization of OCCM cells. The EP1 and EP3 PG receptor activators 16,16-dimethyl-prostaglandin E(2) and sulprostone, also increased mineralization. In contrast, specific activators of the EP2 or the EP2/EP3/EP4 receptors did not have any effect. Fluprostenol, a specific activator of the FP receptor, significantly increased mineralization of OCCM cells. FP and EP (1 or 3) receptors signal through activation of the protein kinase C (PKC) pathway. Indeed, phorbol 12-myristate 13-acetate (PMA), a direct activator of the PKC pathway, significantly increase OCCM mineralization, while pre-treatment of OCCM cells with the PKC inhibitor GF109203x (bisindolylmaleimide) significantly decreased mineralization.

CONCLUSION

We conclude that PGE(2) and PGF(2alpha) exert an anabolic effect on OCCM mineralization through activation of PKC signaling.

Prostaglandin D2 mediates neuronal protection via the DP1 receptor

Cyclo-oxygenases (COXs) catalyze the first committed step in the synthesis of the prostaglandins PGE(2), PGD(2), PGF(2alpha), PGI(2) and thomboxane A(2). Expression and enzymatic activity of COX-2, the inducible isoform of COX, are observed in several neurological diseases and result in significant neuronal injury. The neurotoxic effect of COX-2 is believed to occur through downstream effects of its prostaglandin products. In this study, we examined the function of PGD(2) and its two receptors DP1 and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) (DP2) in neuronal survival. PGD(2) is the most abundant prostaglandin in brain and regulates sleep, temperature and nociception. It signals through two distinct G protein-coupled receptors, DP1 and DP2, that have opposing effects on cyclic AMP (cAMP) production. Physiological concentrations of PGD(2) potently and unexpectedly rescued neurons in paradigms of glutamate toxicity in cultured hippocampal neurons and organotypic slices. This effect was mimicked by the DP1-selective agonist BW245C but not by the PGD(2) metabolite 15d-PGJ(2), suggesting that neuroprotection was mediated by the DP1 receptor. Conversely, activation of the DP2 receptor promoted neuronal loss. The protein kinase A inhibitors H89 and KT5720 reversed the protective effect of PGD(2), indicating that PGD(2)-mediated neuroprotection was dependent on cAMP signaling. These studies indicate that activation of the PGD(2) DP1 receptor protects against excitotoxic injury in a cAMP-dependent manner, consistent with recent studies of PGE(2) receptors that also suggest a neuroprotective effect of prostaglandin receptors. Taken together, these data support an emerging and paradoxical neuroprotective role of prostaglandins in the CNS.

Piglet saphenous vein contains multiple relaxatory prostanoid receptors: evidence for EP4, EP2, DP and IP receptor subtypes

Prostaglandin E(2) produced endothelium-independent relaxation of phenylephrine- and 5-HT-contracted piglet saphenous vein (PSV; pEC(50)=8.6+/-0.2; n=6). The prostanoid EP(4) receptor antagonist GW627368X (30-300 nM) produced parallel rightward displacement of PGE(2) concentration-effect (E/[A]) curves (pK(b)=9.2+/-0.2; slope=1). Higher concentrations of GW627368X did not produce further rightward shifts, revealing the presence of non-EP(4) prostanoid receptors. In all, 18 other prostanoid receptor agonists relaxed PSV in a concentration-related manner. Relative potencies of agonists most sensitive to 10 muM GW627368X (and therefore predominantly activating EP(4) receptors) correlated well with those at human recombinant EP(4) receptors in human embryonic kidney (HEK-293) cells (r(2)=0.74). In the presence of 10 microM GW627368X, the rank order of agonist relative potency matched that of the human recombinant EP(2) receptor in Chinese hamster ovary cells (r(2)=0.72). Iloprost, cicaprost and PGI(2) relaxed PSV maximally and were antagonised by 10 microM GW627368X, demonstrating that they were full EP(4) receptor agonists. Residual responses to these compounds in the presence of GW627368X suggested the presence of IP receptors.BW245C relaxed PSV maximally (pEC(50)=6.8+/-0.1). In the presence of 10 microM GW627368X, BW245C produced biphasic E/[A] curves (phase one pEC(50)=6.6; alpha=24%; phase two pEC(50)=5.1; alpha=112%). Phase two was antagonised by the DP receptor antagonist BW A868C (1 microM), demonstrating that BW245C is an agonist at DP and EP4 receptors. We conclude that PSV contains EP(4), EP(2), DP and IP receptors; IP receptor agonists are also porcine EP(4) receptor agonists.

Minor structural modifications convert the dual TP/CRTH2 antagonist ramatroban into a highly selective and potent CRTH2 antagonist

Ramatroban, a thromboxane A(2) receptor (TP) antagonist with clinical efficacy in asthma and allergic rhinitis, was recently shown to also antagonize the prostaglandin D(2) receptor CRTH2. Here we report that minor structural changes to ramatroban result in a compound (13) with complete lack of activity on TP but sub-nanomolar potency toward CRTH2. This is the first selective CRTH2 antagonist described to date, and should prove highly valuable in further elucidating the biological significance of CRTH2.

Inhibitory Effect of the 4-Aminotetrahydroquinoline Derivatives, Selective Chemoattractant Receptor-Homologous Molecule Expressed on T Helper 2 Cell Antagonists, on Eosinophil Migration Induced by Prostaglandin D2

Prostaglandin (PG) D2, a major cyclooxygenase metabolite generated from immunologically stimulated mast cells, is known to induce activation and chemotaxis in eosinophils, basophils, and T helper 2 (Th2) lymphocytes via a newly identified PGD2 receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). CRTH2 is hypothesized to play an important role in the outcome of allergic responses. However, the absence of selective CRTH2 antagonists has prevented the elucidation of the role of CRTH2 in pathogenesis of allergic diseases. We now report compounds discovered as selective CRTH2 antagonists, (2R*,4S*)-N-(1-benzoyl-2-methyl-1,2,3,4-tetrahydroquinolin-4-yl)-N-phenylisobutyramide (K117) and (2R*,4S*)-N-(1-benzoyl-2-methyl-1,2,3,4-tetrahydroquinolin-4-yl)-N-phenylcyclopropanecarboxamide (K604). K117 and K604 have inhibitory effects on human CRTH2 with Ki values of 5.5 and 11 nM, respectively. The effect of these compounds is CRTH2-specific with no cross-reactivity against 15 other receptors and four arachidonic acid-metabolizing enzymes. K117 and K604 has no effect on the basal Ca2+ level and inhibited the Ca2+ response induced by PGD2 in 293EBNA cells expressing human CRTH2. Also, K117 and K604 inhibit PGD2-induced human eosinophil chemotaxis with IC50 values of 7.8 and 42.2 nM, respectively, but they do not inhibit the CC-chemokine receptor 3 agonist eotaxin-induced chemotaxis. These results indicate that K117 and K604 are highly potent and selective antagonists for human CRTH2. These compounds have possibilities to become useful tools to explore CRTH2 functions in allergic diseases.

Identification of a potent and selective synthetic agonist at the CRTH2 receptor

The chemoattractant receptor-homologous molecule expressed on T-helper type 2 cells (CRTH2) is a G protein-coupled receptor whose function in vivo has been incompletely characterized. One of the reasons is that its current known ligands, prostaglandin D(2) and some of its metabolites, have either poor selectivity for CRTH2 or are metabolically unstable in vivo. In this study, we describe the biological and pharmacological properties of L-888,607, the first synthetic potent and selective CRTH2 agonist. We show that L-888,607 exhibits 1) subnanomolar affinity for the human CRTH2 receptor, 2) high selectivity over all other prostanoid receptors and other receptors tested, 3) agonistic activity on recombinant and endogenously expressed CRTH2 receptor, and 4) relative stability in vivo. L-888,607 thus represents a suitable tool to investigate the in vivo function of CRTH2.

Studies using isolated uterine and other preparations show bimatoprost and prostanoid FP agonists have different activity profiles

1. The pharmacology of bimatoprost, a synthetic prostaglandin-amide, was examined in prostaglandin F(2alpha) (PGF(2alpha))-sensitive preparations. Bimatoprost potently contracted the rabbit isolated uterus (pEC(50)=7.92+/-0.16). In contrast, bimatoprost exhibited weak excitatory activity in human myometrium from pregnant and nonpregnant donors, mouse uterus, rat uterus, and endothelium-intact rabbit jugular veins, and did not stimulate DNA synthesis in mouse fibroblasts. 2. The possibility that the effects of bimatoprost may reflect partial agonism at prostanoid FP receptors was examined and the contractile effects of full agonists, 17-phenyl PGF(2alpha) (FP) and U-46619 (TP, a control), were determined in the absence and presence of 1 muM bimatoprost on the mouse uterus. Analyses of the agonist-agonist functional studies showed no antagonism, indicating that bimatoprost is not a partial agonist. 3. Bioassay metabolism studies of bimatoprost and latanoprost (FP receptor agonist prodrug) in the rabbit uterus were conducted using recipient mouse uterus. Results indicated that the potent responses to bimatoprost in the rabbit uterus are produced by the intact molecule and not by its putative free acid metabolite, 17-phenyl PGF(2alpha). Some hydrolysis of latanoprost to latanoprost free acid appears to have occurred in the rabbit uterus, according to biological detection. 4. The pharmacology of bimatoprost could not be explained by its interaction with known prostanoid FP receptors and was independent of species-, tissue-, or preparation-related factors. The potent contractile effects of bimatoprost in the rabbit uterus provide further pharmacological evidence for the presence of a novel receptor population that preferentially recognises bimatoprost.

New fluoroprostaglandin F(2alpha) derivatives with prostanoid FP-receptor agonistic activity as potent ocular-hypotensive agents

To find new prostanoid FP-receptor agonists possessing potent ocular-hypotensive effects with minimal side effects, we evaluated the agonistic activities of newly synthesized prostaglandin F(2alpha) derivatives for the prostanoid FP-receptor both in vitro and in vivo. The iris constrictions induced by the derivatives and their effects on melanin content were examined using cat isolated iris sphincters and cultured B16 melanoma cells, respectively. The effects of derivative ester forms on miosis and intraocular pressure (IOP) were evaluated in cats and cynomolgus monkeys, respectively. Of these derivatives, 6 out of 12 compounds were more potent iris constrictors, with EC(50) values of 0.6 to 9.4 nM, than a carboxylic acid of latanoprost (EC(50)=13.6 nM). A carboxylic acid of latanoprost (100 microM) significantly increased the melanin content of cultured B16 melanoma cells, but some 15,15-difluoro derivatives, such as AFP-157 and AFP-172, did not. Topically applied AFP-168, AFP-169 and AFP-175 (isopropyl ester, methyl ester and ethyl ester forms, respectively, of AFP-172) induced miosis in cats more potently than latanoprost. AFP-168 (0.0005%) reduced IOP to the same extent as 0.005% latanoprost (for at least 8 h). These findings indicate that 15,15-difluoroprostaglandin F(2alpha) derivatives, especially AFP-168, have more potent prostanoid FP-receptor agonistic activities than latanoprost. Hence, AFP-168 may be worthy of further evaluation as an ocular-hypotensive agent.

Effects of Prostaglandin D2, 15-Deoxy-Δ12,14-prostaglandin J2, and Selective DP1and DP2Receptor Agonists on Pulmonary Infiltration of Eosinophils in Brown Norway Rats

Prostaglandin (PG) D2 is an arachidonic acid metabolite that is released by allergen-stimulated mast cells. It is a potent in vitro chemoattractant for human eosinophils, acting through the DP2 receptor/chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). Furthermore, there is in vivo evidence that PGD2 contributes to allergen-induced pulmonary eosinophilia via its classic DP1 receptor. The PGD2-derived product 15-deoxy-Delta12,14-PGJ2 is widely used as a peroxisome proliferator-activated receptor gamma agonist and has been shown to have anti-inflammatory properties. However, this substance can also activate eosinophils in vitro through the DP2 receptor. The objectives of the present study were to determine whether PGD2 and 15-deoxy-Delta12,14-PGJ2 can induce pulmonary eosinophilia, and, if so, to examine the abilities of selective DP1 and DP2 receptor agonists to induce this response. Brown Norway rats were treated by intratracheal instillation of PGs. Vehicle and 5-oxo-6,8,11,14-eicosatetraenoic acid were used as negative and positive controls, respectively. Lung eosinophils were identified by immunostaining of lung sections with an antibody to major basic protein. Both PGD2 and 15-deoxy-Delta12,14-PGJ2 induced robust eosinophilic responses that were apparent by 12 h and persisted for at least 48 h. Two selective DP2 receptor agonists, 15R-methyl-PGD2 and 13-14-dihydro-15-keto-PGD2, induced similar responses, the former being more potent than PGD2, whereas the latter was less potent. The selective DP1 receptor agonist BW245C [(4S)-(3-[(3R,S)-3-cyclohexyl-3-hydroxypropyl]-2,5-dioxo)-4-imidazolidineheptanoic acid] was completely inactive. We conclude that PGD2 and 15-deoxy-Delta12,14-PGJ2 induce eosinophil infiltration into the lungs through the DP2 receptor. The potent in vitro DP2 receptor agonist 15R-methyl-PGD2 is also very active in vivo and should be a useful tool in examining the role of this receptor.

New insights into the intracellular mechanisms by which PGI2 analogues elicit vascular relaxation: cyclic AMP-independent, Gs-protein mediated-activation of MaxiK channel

Prostaglandin I2 (PGI2, prostacyclin), an eicosanoid of the cyclooxygenase pathway, causes relaxation of vascular smooth muscle in most blood vessels and inhibits platelet aggregation. PGI2 and its stable analogues activate a specific cell-surface receptor (IP receptor, IPR), which is coupled to adenylyl cyclase through G(s)-protein. Elevation of 3': 5'-cyclic monophosphate (cyclic AMP, cAMP) levels has been considered to be a key cellular event to trigger blood vessel relaxation by IP agonists; however, its exclusive role has been recently challenged. Downstream effectors of the IP agonist metabolic cascade are plasma membrane K+ channels that upon activation would cause smooth muscle cell hyperpolarization and relaxation. The K+ channel candidates include ATP-sensitive K+ (KATP) channel and large conductance, Ca2+ -activated K+ (MaxiK, BK) channel. The contribution of each K+ channel subtype would be governed by their relative expression and/or particular co-localization with different proteins of the IPR signaling cascade in each vascular bed. Scrutiny of the cellular mechanisms underlying IPR-activated vascular relaxation of a large conduit artery revealed that relaxation by an IP agonist, beraprost, is elicited through cAMP-independent pathway as well as by a cAMP-dependent route. Both mechanisms include activation of MaxiK channels. The cAMP-independent vasorelaxant mechanism is partly attributed to a direct activation of MaxiK channel by G(s)-protein. In this review article, we discuss cAMP-dependent and -independent mechanisms by which IPR stimulation activates MaxiK channel. Our recent work demonstrates a functional tight coupling between IPR and MaxiK channel through a cAMP-independent, G(s)-protein mediated mechanism(s) in vascular smooth muscle.

Prostanoid DP1 receptor agonist inhibits the pruritic activity in NC/Nga mice with atopic dermatitis

NC/Nga mice have similar pathological and behavioral features of human atopic dermatitis and are used as a model of the disease. Under conventional circumstances, spontaneous and persistent scratching is frequent and can lead to the onset of skin inflammation. We examined the effects of several prostanoids and their related compounds on the scratching behavior of NC/Nga mice. Among them, topically applied prostaglandin D2, prostaglandin E1, prostaglandin E2 and prostaglandin I2 significantly suppressed the scratching, the order of inhibitory activities being prostaglandin D2>>prostaglandin I2>prostaglandin E1=prostaglandin E2. Prostaglandin D2 metabolite, prostaglandin J2 also significantly suppressed the scratching but not so 13,14-dihydro-15-keto-prostaglandin D2, and 15-deoxy-Delta12,14-prostaglandin J2. The order of the inhibitory activities of these prostaglandin D2 metabolites depended on affinity of the prostanoid DP1 receptor but not on the DP2 receptor (chemoattractant receptor-homologous molecule expressed on T helper2 cells, CRTH2) and PPAR-gamma receptors. Likewise, topically applied arachidonic acid significantly suppressed the scratching while indomethacin enhanced it. Pretreatment of arachidonic acid increased the skin prostaglandins (prostaglandin D2, prostaglandin E2, prostaglandin F2alpha and 6-keto-prostaglandin F1alpha) contents, but indomethacin decreased the prostaglandin D2 and prostaglandin E2 contents. On the other hand, prostaglandin D2 and indomethacin had no apparent effects on histamine-induced scratching of ICR mice. These results suggested that prostaglandin D2 plays a physiological role in inhibiting pruritus of NC/Nga mice via their specific prostanoid DP1 receptors, and that prostaglandin D2 and/or a prostanoid DP1 receptor agonist may have therapeutic effects for cases of consecutive skin inflammation.

15-Fluoro prostaglandin FP agonists: a new class of topical ocular hypotensives

A novel series of 15-fluoro prostaglandins with phenoxy termination of the omega-chain was synthesized and evaluated for binding and functional activation of the prostaglandin FP receptor in vitro and for side effect potential and topical ocular hypotensive efficacy in vivo. Compounds with the 15alpha-fluoride relative stereochemistry displayed EC50 values of <or=20 nM, comparable to the value for the endogenous ligand PGF2alpha. Evaluation of selected ester prodrugs of these 15-fluoro prostaglandins in vivo highlighted their generally low propensity to elicit hyperemia or ocular irritation in rabbits and efficacious intraocular pressure-lowering property in monkeys. In particular 13,14-dihydro-15-deoxy-15alpha-fluoro-16-aryloxy-omega-tetranor-cis-Delta4-PGF2alpha isopropyl ester (24) caused relatively little ocular irritation in rabbits while lowering intraocular pressure in conscious ocular hypertensive monkeys by 39% following a topical ocular dose of 3 microg.

Partial Agonism of Taprostene at Prostanoid IP Receptors in Vascular Preparations from Guinea-Pig, Rat, and Mouse

This study investigates whether incomplete relaxation of vascular smooth muscle preparations induced by the prostacyclin analogue taprostene is due to partial agonism at prostanoid IP receptors. In the presence of the prostanoid EP4 receptor antagonist AH 23848, 3 microM taprostene induced 45% relaxation of phenylephrine-contracted guinea-pig saphenous vein rings and displaced log concentration-response curves for the prostacyclin analogues AFP-07, TEI-9063, and cicaprost to the right, parallel to their predicted addition curves. In contrast, taprostene interacted additively with prostaglandin E2 (PGE2), ONO-AE1-259 (selective EP2 agonist), and acetylcholine. Similarly, on rat tail artery contracted with phenylephrine, 3 microM taprostene (20% relaxation) opposed AFP-07- but not PGE2-induced relaxation. However, under U-46619-induced tone (AH 23848 absent), taprostene antagonized AFP-07 and cicaprost more than TEI-9063, suggesting that the latter has more than one relaxation mechanism. The presence of a sensitive EP3 contractile system in mouse aorta interfered with IP receptor-mediated relaxation. By generating tone with phenylephrine and the potent EP3 agonist sulprostone, it was possible to show that 3 microM taprostene (15% relaxation) selectively opposed relaxations induced by AFP-07, TEI-9063, and cicaprost. Our experiments indicate that taprostene is a partial agonist at prostanoid IP receptors, and may be a lead to an IP receptor antagonist.

Long-term agonist stimulation of IP prostanoid receptor depletes the cognate G(s)alpha protein in membrane domains but does not change the receptor level

Iloprost (IP) stimulation (1 microM, 2 h) of Flag-epitope-tagged human IP prostanoid receptor (FhIPR) expressed in HEK293 cells resulted in specific decrease of endogenous G(s)alpha protein in detergent-insensitive, caveolin-enriched, membrane domains (DIMs). Receptor protein FhIPR, caveolin, G(i)alpha and GPI-linked, domain markers CD55 and CD59 were unchanged. The same result was obtained in HEK293 cells expressing FhIPR-G(s)alpha fusion protein. The endogenous G(s)alpha decreased, but the level of Flag-hIPR-G(s)alpha protein did not change. The specific depletion of domain-bound pool of G(s)alpha as consequence of iloprost stimulation was also demonstrated in membrane domains prepared according to alkaline treatment plus sonication protocol (detergent-free procedure of Song et al.). Our data further indicated that in control, quiescent cells only a very small amount of IP prostanoid receptor was present in DIMs together with large amount of its cognate G(s)alpha protein. Expressed in quantitative terms, DIMs contained 30-40% of the total cellular amount of G proteins whereas the content of IP prostanoid receptors was 1-3%. The dominant portion (>95%) of FhIPR as well as FhIPR-G(s)alpha was localised in high-density area of the gradient containing detergent-solubilised proteins. FhIPR and FhIPR-G(s)alpha distribution was similar to that of transmembrane plasma membrane (PM) markers (CD147, MHCI, CD29, Tapa1, the alpha subunit of Na,K-ATPase, transmembrane form of CD58 and CD44). All these proteins are known to be fully solubilised by detergent and thus unable to float in density gradient. Our data indicate that (i) long-term agonist stimulation of IP prostanoid receptor is associated with preferential decrease of its cognate G protein G(s)alpha from membrane domains; receptor level is unchanged. (ii) Very small fraction (1-3%) of total cellular amount of receptors is recovered in DIMs together with roughly 40% of G proteins. These data suggest a "supra-stoichiometric" arrangement of G proteins and corresponding receptors in DIMs.

Agonists can discriminate between cloned human and mouse prostacyclin receptors

The ability of prostacyclin analogues to stimulate adenylyl cyclase (AC) and phospholipase C (PLC) in Chinese hamster ovary (CHO) cells expressing cloned human (hIP) or cloned mouse (mIP) prostacyclin receptors has been compared. For hIP, the order of potency (pEC(50)) for stimulating AC and PLC pathways was similar: AFP-07 (9.3, 8.4)>cicaprost (8.3, 6.9), iloprost (7.9, 6.8)>taprostene (7.4, 6.8)>carbacyclin (6.9, 6.6), PGE(1) (6.6, 5.1). Although the standard IP agonists cicaprost and iloprost behaved similarly in both hIP and mIP receptor-expressing cells, carbacyclin and PGE(1) showed significantly higher potency at the mIP receptor, suggesting that the agonist recognition sites on hIP and mIP receptors are not identical. A further distinction between hIP and mIP receptors was found with taprostene, which had greater efficacy at hIP receptors (AC 94%, PLC 14%) than at mIP receptors (AC 77%, PLC 0%) (cicaprost=100% in each assay).

Stimulation of cAMP production and cyclooxygenase-2 by prostaglandin E(2) and selective prostaglandin receptor agonists in murine osteoblastic cells

Prostaglandins (PGs), particularly PGE(2), can stimulate bone resorption and formation and auto-amplify their effects by inducing cyclooxygenase (COX)-2. We examined the role of different PG receptors in stimulating cAMP production and COX-2 expression in murine calvarial osteoblasts. Cells were obtained from PGE(2) receptor (EP2R and EP4R) wild-type and knockout (KO) mice and from mice transgenic for the COX-2 promoter fused to a luciferase reporter. We analyzed effects of selective agonists, EP2A and EP4A, for EP2R and EP4R, which mediate the increase in cAMP in response to PGE(2). We also tested agonists for other PGE(2) receptors (EP1A and EP3A) and for prostacyclin (IPA), prostaglandin D(2) (DPA), thromboxane (TPA), and prostaglandin F(2alpha) (FPA) receptors. PGE(2) and EP2A were the most effective stimulators of cAMP production. EP4A, IPA, and DPA produced smaller responses, and EP1A, EP3A, FPA, and TPA were ineffective. In EP2R KO cells, cAMP responses to PGE(2) were reduced by 80%, and responses to EP2A were abrogated. In EP4R KO cells, cAMP responses to PGE(2) and EP2A showed a small reduction, while the response to EP4A was abrogated. Pretreatment with PGE(2), EP2A, or EP4A down-regulated the subsequent response to the respective ligands. COX-2 induction was measured by increased luciferase activity and mRNA expression. PGE(2) was the most effective agonist; EP2A and another selective EP2R agonist, butaprost, showed similar efficacy, and EP4A was less effective. EP2A and EP4A effects on luciferase activity were additive, and effects of the combination were similar to PGE(2) itself. IPA, TPA, and DPA produced 2- to 6-fold increases in COX-2 expression. FPA was a weak agonist, while EP1A and EP3A were inactive. Treatment with specific inhibitors indicated that PGE(2), EP2A, and EP4A induced COX-2 expression largely through protein kinase A (PKA). We conclude that the PG induction of COX-2 in this system generally paralleled effects on cAMP production and was mediated predominantly via the PKA pathway.

Prostaglandin E2 activates outwardly rectifying Cl(-) channels via a cAMP-dependent pathway and reduces cell motility in rat osteoclasts

We examined changes in electrical and morphological properties of rat osteoclasts in response to prostaglandin (PG)E(2). PGE(2) (>10 nM) stimulated an outwardly rectifying Cl(-) current in a concentration-dependent manner and caused a long-lasting depolarization of cell membrane. This PGE(2)-induced Cl(-) current was reversibly inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), and tamoxifen. The anion permeability sequence of this current was I(-) > Br(-) approximately Cl(-) > gluconate(-). When outwardly rectifying Cl(-) current was induced by hyposmotic extracellular solution, no further stimulatory effect of PGE(2) was seen. Forskolin and dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) mimicked the effect of PGE(2). The PGE(2)-induced Cl(-) current was inhibited by pretreatment with guanosine 5'-O-2-(thiodiphosphate) (GDPbetaS), Rp-adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS), N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide dihydrochloride (H-89), and protein kinase A inhibitors. Even in the absence of nonosteoclastic cells, PGE(2) (1 microM) reduced cell surface area and suppressed motility of osteoclasts, and these effects were abolished by Rp-cAMPS or H-89. PGE(2) is known to exert its effects through four subtypes of PGE receptors (EP1-EP4). EP2 and EP4 agonists (ONO-AE1-259 and ONO-AE1-329, respectively), but not EP1 and EP3 agonists (ONO-DI-004 and ONO-AE-248, respectively), mimicked the electrical and morphological actions of PGE(2) on osteoclasts. Our results show that PGE(2) stimulates rat osteoclast Cl(-) current by activation of a cAMP-dependent pathway through EP2 and, to a lesser degree, EP4 receptors and reduces osteoclast motility. This effect is likely to reduce bone resorption.

Activation of the D Prostanoid Receptor 1 Regulates Immune and Skin Allergic Responses

The mobilization of Langerhans cells (LCs) from epithelia to the draining lymph nodes is an essential process to initiate primary immune responses. We have recently shown that in mice, PGD2 is a potent inhibitor of epidermal LC emigration. In this study, we demonstrate that activation of the D prostanoid receptor 1 (DP1) impedes the TNF-alpha-induced migration of human LCs from skin explants and strongly inhibits the chemotactic responses of human LC precursors and of maturing LCs to CC chemokine ligands 20 and 19, respectively. Using a murine model of atopic dermatitis, a chronic Th2-type allergic inflammatory disease, we demonstrate that the potent DP1 agonist BW245C dramatically decreases the Ag-specific T cell activation in the skin draining lymph nodes and markedly prevents the skin lesions following repeated epicutaneous sensitization with OVA. Interestingly, analysis of the local response indicates that BW245C treatment strongly reduces the recruitment of inflammatory cells into the dermis and disrupts the Th1/Th2 balance, probably through the increased production of the immunoregulatory cytokine IL-10, in the skin of sensitized mice. Taken together, our results suggest a new function for DP1 in the regulation of the immune and inflammatory responses. We propose that DP1 activation by specific agonists may represent a strategy to control cutaneous inflammatory Th2-associated diseases.

Nuclear prostaglandin receptors: role in pregnancy and parturition?

The key regulatory role of prostanoids [prostaglandins (PGs) and thromboxanes (TXs)] in the maintenance of pregnancy and initiation of parturition has been established. However, our understanding of how these events are fine-tuned by the recruitment of specific signaling pathways remains unclear. Whereas, initial thoughts were that PGs were lipophilic and would easily cross cell membranes without specific receptors or transport processes, it has since been realized that PG signaling occurs via specific cell surface G-protein coupled receptors (GPCRs) coupled to classical adenylate cyclase or inositol phosphate signaling pathways. Furthermore, specific PG transporters have been identified and cloned adding a further level of complexity to the regulation of paracrine action of these potent bioactive molecules. It is now apparent that PGs also activate nuclear receptors, opening the possibility of novel intracrine signaling mechanisms. The existence of intracrine signaling pathways is further supported by accumulating evidence linking the perinuclear localization of PG synthesizing enzymes with intracellular PG synthesis. This review will focus on the evidence for a role of nuclear actions of PGs in the regulation of pregnancy and parturition.

Prostaglandin D2 inhibits airway dendritic cell migration and function in steady state conditions by selective activation of the D prostanoid receptor 1

PGD(2) is the major mediator released by mast cells during allergic responses, and it acts through two different receptors, the D prostanoid receptor 1 (DP1) and DP2, also known as CRTH2. Recently, it has been shown that PGD(2) inhibits the migration of epidermal Langerhans cells to the skin draining lymph nodes (LNs) and affects the subsequent cutaneous inflammatory reaction. However, the role of PGD(2) in the pulmonary immune response remains unclear. Here, we show that the intratracheal instillation of FITC-OVA together with PGD(2) inhibits the migration of FITC(+) lung DC to draining LNs. This process is mimicked by the DP1 agonist BW245C, but not by the DP2 agonist DK-PGD(2). The ligation of DP1 inhibits the migration of FITC-OVA(+) DCs only temporarily, but still inhibits the proliferation of adoptively transferred, OVA-specific, CFSE-labeled, naive T cells in draining LNs. These T cells produced lower amounts of the T cell cytokines IL-4, IL-10, and IFN-gamma compared with T cells from mice that received FITC-OVA alone. Taken together, our data suggest that the activation of DP receptor by PGD(2) may represent a pathway to control airway DC migration and to limit the activation of T cells in the LNs under steady state conditions, possibly contributing to homeostasis in the lung.

Ocular Hypotensive FP Prostaglandin (PG) Analogs: PG Receptor Subtype Binding Affinities and Selectivities, and Agonist Potencies at FP and Other PG Receptors in Cultured Cells

Natural prostaglandins (PGs) such as PGD2, PGE2, PGF2(2alpha), and PGI2 exhibited the highest affinity for their respective cognate receptors, but were the least selective agents when tested in receptor binding assays. Travoprost acid ([+]-fluprostenol) was the most FP-receptor-selective compound, exhibiting a high affinity (Ki = 35 +/- 5 nM) for the FP receptor, and minimal affinity for DP (Ki = 52,000 nM), EP1 (Ki = 9540 nM), EP3 (Ki = 3501 nM), EP4 (Ki = 41,000 nM), IP (Ki > 90,000 nM), and TP (Ki = 121,000 nM) receptors. Travoprost acid was the most potent PG analog tested in FP receptor functional phosphoinositide turnover assays in the following cell types: human ciliary muscle (EC50 = 1.4 nM), human trabecular meshwork (EC50 = 3.6 nM), and mouse fibroblasts and rat aortic smooth muscle cells (EC50 = 2.6 nM). Although latanoprost acid exhibited a relatively high affinity for the FP receptor (Ki = 98 nM), it had significant functional activity at FP (EC50 = 32-124 nM) and EP1 (EC50 = 119 nM) receptors. Bimatoprost acid was less selective, exhibiting a relatively high affinity for the FP (Ki = 83 nM), EP1 (Ki = 95 nM), and EP3 (Ki = 387 nM) receptors. Bimatoprost acid exhibited functional activity at the EP1 (EC50 = 2.7 nM) and FP (EC50 = 2.8-3.8 nM in most cells) receptors. Bimatoprost (nonhydrolyzed amide) also behaved as an FP agonist at the cloned human FP receptor (EC50 = 681 nM), in h-TM (EC50 = 3245 nM) and other cell types. Unoprostone and S-1033 bound with low affinity (Ki = 5.9 microM to > 22 microM) to the FP receptor, were not selective, but activated the FP receptor. In conclusion, travoprost acid has the highest affinity, the highest FP-receptor-selectivity, and the highest potency at the FP receptor as compared to the other ocular hypotensive PG analogs known so far, including free acids of latanoprost, bimatoprost, and unoprostone isopropyl ester.

Prostanoid receptors and the urogenital tract

Prostanoids are the metabolic product of cyclooxygenase-mediated metabolism of arachidonic acid. These prostanoids interact with a family of eight G protein-coupled transmembrane receptors, which are abundantly expressed along the genitourinary tract and mediate the critical physiological actions of the prostanoids. These actions include modulation of renal glomerular hemodynamics, promotion of renal salt excretion, and maintenance of uroepithelial function and integrity. Normal functioning of prostanoid receptors is also a prerequisite for fertility and reproduction. Prostanoid receptor selective agonists and antagonists are likely to affect these processes quite differently from the simultaneous and global inhibition of all prostanoid synthesis that is achieved through the use of non-steroidal anti-inflammatory drugs.