Solubilization and characterization of PGE2 receptor in porcine ciliary epithelium

Molecular pharmacology of the DP/EP2 class prostaglandin AL-6598 and quantitative autoradiographic visualization of DP and EP2 receptor sites in human eyes

DP-class prostaglandins and prostaglandin analogs (collectively, prostaglandins or PGs) such as PGD2, BW245C, ZK110841, and ZK118182, lower intraocular pressure (IOP) in animal models of ocular hypertension. A new analog of ZK118182 (AL-6556; 13,14-dihydro-ZK118182) was synthesized, and the isopropyl ester of AL-6556 (AL-6598) was shown recently to lower IOP in the ocular hypertensive cynomolgus monkey model of glaucoma and in human subjects. AL-6556 and AL-6598 had an affinity (Ki) of 2.66-4.43 microM for DP receptors but a much lower affinity (K(i)s = 38-103 microM) for EP3, FP, IP, and TP receptors (n = 3-5). In addition, AL-6556 and AL-6598 exhibited K(i)s > 100 microM for 19 nonprostanoid receptors. Both PGs stimulated cAMP production (EC50 = 1.07 +/- 0.1 microM and EC50 = 2.64 +/- 0.84 microM; n = 3) by way of DP receptors in embryonic bovine tracheal fibroblasts. While AL-6556 and AL-6598 were partial agonists (EC(50)s = 0.47-0.69 microM; E(max) = 35%-46%) at EP2 receptors in human nonpigmented epithelial cells, neither had any agonist activity at EP4, IP, or FP receptors. The DP antagonist, BWA868C, effectively antagonized the effects of AL-6556 with a high potency (IC50 = 22.8 +/- 3.9 nM; n = 3). DP receptors radiolabeled with [3H]BWA868C on human eye sections by quantitative autoradiography were highly concentrated in the ciliary process (CP), longitudinal (LCM) and circular (CCM) ciliary muscles, and iris with much lower specific binding in the cornea (CN), lens (LNS), and retina (RET). EP2 receptors labeled with [3H]PGE2 were concentrated in the LCM, CM, RET, and iris. In conclusion, AL-6598 and AL-6556 are relatively DP-receptor-selective PGs with full agonist activity at the DP and partial agonist activity at the EP2 receptor. The IOP-lowering activities of these compounds may involve both the inflow and outflow mechanisms, as DP and EP2 receptors were visualized in human ocular tissues involved in such aqueous humor dynamics.

Prostaglandin-stimulated adenylyl cyclase activity via a pharmacologically defined EP2 receptor in human nonpigmented ciliary epithelial cells

The goal of these studies was to compare the effects of several prostaglandin (PG) receptor agonists on adenylyl cyclase activity in transformed human nonpigmented ciliary epithelial (NPE) cells. In order to define the pharmacology of the PG receptors present on these cells, cyclic AMP production was measured by both manual and robotic radioimmunoassay (RIA) techniques. In NPE cells, the rank order of potency for the PGs tested in the current study (n = up to 46) was PGE2 (EC50 = 67 nM) > 13,14-dihydro-PGE1 (EC50 = 231 nM) > 11-deoxy-PGE1 (EC50 = 500 nM) = 16,16-dimethyl-PGE2 (EC50 = 872 nM) = 11-deoxy-16,16-dimethyl-PGE2 (EC50 = 1135 nM) >> PGF2 alpha (EC50 > 10,000 nM) = PGD2 (EC50 > 10,000 nM) = PGI2 (EC50 > 10,000 nM). The EP2-receptor selective PG, butaprost, exhibited a potency of 212 nM (Emax = 55%). The response to 1 microM PGE2 was antagonized by AH6809 (IC50 = approximately 50 microM, Kb = 4 microM). The relative potencies of the EP agonists mentioned above were significantly weaker in EbTr and NCB-20 cells expressing DP and IP receptors, respectively (1). These data provide a detailed pharmacological identification and characterization of EP2 receptors on NPE cells.

Activation of the phospholipase/cyclooxygenase cascade in the rabbit cornea by platelet-activating factor is challenged by PAF receptor antagonists

Platelet-activating factor (PAF) is a potent lipid inflammatory mediator which is generated in the cornea after injury. Its activity is regulated by interaction with specific receptors. The binding of PAF to its receptors initiates biochemical sequences that cluminate in the release of additional lipid mediators. An arachidonoyl-dependent phospholipase A2 is activated to release arachidonic acid from membrane phospholipids, especially phosphatidylcholine and ethanolamine. Arachidonic acid is then predominantly metabolized by the cyclooxygenase pathway to prostaglandins F2 alpha, E2 and D2, whereas the lipoxygenase pathway is not influenced by PAF. The release of arachidonic acid and prostaglandins stimulated by PAF is challenged by the PAF receptor antagonists BN 50727 and BN 50730. PAF acting intracellularly may also induce the synthesis of cyclooxygenase, presumably the 'inducible' isoform PGHS2, which has been implicated in the inflammatory response. Thus, the therapeutic use of PAF receptor angatonists could be potentially beneficial in the management of ocular inflammatory disease.