Studies on prostanoid receptors in ocular tissues

A Prostacyclin Analog, Cicaprost, Exhibits Potent Anti-Inflammatory Activity in Human Primary Immune Cells and a Uveitis Model

PURPOSE

To investigate the therapeutic potential of a prostacyclin (IP) receptor agonist for ocular inflammation and the effect on immune cells.

METHODS

The anti-inflammatory activities of cicaprost were determined in primary human monocyte-derived macrophages and human monocyte-derived dendritic cells (MoDC), as well as a lipopolysaccharides (LPS)-induced rat uveitis model. Multiple cytokine release was measured by utilizing Luminex Technology. Prostacyclin (IP) Receptor expression was detected by reverse transcription-polymerase chain receptor. Leukocyte infiltration and protein exudation in the rat uveitis model were measured using a hemocytometer and protein concentration by a NanoDrop instrument.

RESULTS

Cicapost, an IP receptor agonist, potently inhibits proinflammatory chemokines/cytokine production not only from LPS- or TNFα (tumor necrosis factor-alpha)-induced primary human monocyte-derived macrophages, but also from LPS-stimulated MoDC. While constitutively expressed in macrophages, the IP receptor was inducible by LPS stimulation in MoDCs. In a LPS-induced rat uveitis model, cicaprost efficaciously prevents ocular inflammatory cell and protein leakage, as well as inflammatory cytokine release.

CONCLUSION

The IP receptor agonist cicaprost is a potent anti-inflammatory agent, implicating that the tightly controlled PGI₂/IP signaling pathway is important in regulating inflammation. This response could be harnessed in ocular inflammatory disease where steroids are currently the standard of care.

Effects of tylosin, tilmicosin and tulathromycin on inflammatory mediators in bronchoalveolar lavage fluid of lipopolysaccharide-induced lung injury

The aim of this study was to determine the anti-inflammatory effects of macrolides through kinetic parameters in bronchoalveolar lavage fluid (BALF) of lipopolysaccharide-induced lung injury. Rats were divided into four groups: lipopolysaccharide (LPS), LPS + tylosin, LPS + tilmicosin and LPS + tulathromycin. BALF samples were collected at sampling times. TNF, IL-1β, IL-6, IL-10 and 13,14-dihydro-15-keto-prostaglandin F2α (PGM) and C-reactive protein (CRP) were analysed. Area under the curve (AUC) and maximum plasma concentration (Cmax) values of inflammatory mediators were determined by a pharmacokinetic computer programme. When inflammatory mediator concentrations were compared between the LPS group and other groups for each sampling time, the three macrolides had no pronounced depressor effect on cytokine levels, but they depressed PGM and CRP levels. In addition, tylosin and tilmicosin decreased the AUC0-24 level of TNF, while tilmicosin decreased the AUC0-24 level of IL-10. Tylosin and tulathromycin decreased the AUC0-24 of PGM, and all three macrolides decreased the AUC0-24 of CRP. Especially tylosin and tulathromycin may have more expressed anti-inflammatory effects than tilmicosin, via depressing the production of inflammatory mediators in the lung. The AUC may be used for determining the effects of drugs on inflammation. In this study, the antiinflammatory effects of these antibiotics were evaluated with kinetic parameters as a new and different approach.

Feline glaucoma--a comprehensive review

Cats with glaucoma typically present late in the course of disease. It is likely that glaucoma in cats is under-diagnosed due to its insidious onset and gradual progression, as well as limitations of some commonly used tonometers in this species. Treatment of glaucoma in feline patients presents a clinical challenge, particularly as glaucoma is often secondary to other disease processes in cats. In this review, we consider the clinical features, pathophysiology, and classification of the feline glaucomas and provide current evidence to direct selection of appropriate treatment strategies for feline glaucoma patients.

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.

Cyclooxygenase-2 expression in the cornea of dogs with keratitis

Cyclooxygenase-2 (COX-2) can be overexpressed at inflammatory sites, leading to the generation of proinflammatory prostanoids. Selective inhibitors of COX-2 have potential use in treating inflammatory conditions including ophthalmic diseases in veterinary medicine. Keratitis is considered the most common inflammatory eye disease in dogs. In this study we evaluated the expression of COX-2 in normal dog eyes and in dog eyes with keratitis by immunohistochemistry using isoform-specific antibodies. In the normal eye (n = 4), no COX-2 immunoreactivity was observed in the cornea. In keratitis, COX-2 (n = 12) expression was observed in all corneal layers (epithelium, stromal cells, and endothelium). COX-2 immunoreactivity was also noted in the stromal and epithelial cells of the iris and the stromal cells of the trabecular meshwork. These data indicate that COX-2 may play a pathophysiologic role in keratitis and suggest potential therapeutic implications of prostaglandin modulation in inflammatory eye diseases.

Quantitative autoradiographic visualization and pharmacology of FP-prostaglandin receptors in human eyes using the novel phosphor-imaging technology

Quantitative autoradiographic visualization of FP prostaglandin receptors was determined in postmortem human eye sections using [3H]PGF2alpha and the novel phosphor-imaging technology coupled with computerized image analysis. Densitometric analysis of digital images obtained after a 19-day screen-exposure revealed FP receptors to be highly concentrated in the longitudinal ciliary muscle (12,741 digital light units [DLU/mm2]), iris sphincter muscle (19,261 DLU/mm2) and retina (9,544 DLU/mm2), with lesser amounts (1,558-3,776 DLU/mm2) in five other ocular structures (n = 3-4 donors). The highest percentage specific binding was in the iris sphincter and longitudinal ciliary muscle (78-73%) and lowest in the lens (12%). Binding of [3H]PGF2alpha to the longitudinal ciliary and iris sphincter muscles and retina was concentration-dependently and potently displaced by known FP-receptor-selective compounds such as cloprostenol (Ki = 13-37 nM), fluprostenol (Ki = 56-98 nM), PHXA85 (Ki = 181-206 nM) and latanoprost (isopropyl ester of PHXA85; Ki = 0.43-4.5 microM) (from up to 4 donor eyes). These quantitative phosphor-imaging autoradiography data provide further evidence for the presence of FP receptors in human longitudinal ciliary muscle, one of the tissues involved in the intraocular pressure lowering effects of FP-class prostaglandins. The quantitative localization of FP receptors in the human iris, iris sphincter muscle, and retina represent interesting new observations.

Mediation by prostaglandins of the stimulatory effect of substance P on cyclic AMP production in dog iris sphincter smooth muscle

The purpose of the present study was to examine the mechanism of the stimulatory effect of substance P (SP) on cyclic AMP (cAMP) accumulation in dog iris sphincter. We found that: (1) SP increased cAMP accumulation in a time- and concentration-dependent manner, the T1/2 and EC50 values being 1.2 min and 44 nM, respectively. SP has no effect on inositol trisphosphate and muscle contraction in this tissue. (2) SP-stimulated cAMP formation was inhibited by quinacrine, a non-specific phospholipase A2 inhibitor (IC50 = 9.5 microM), and by indomethacin (Indo), a cyclooxygenase inhibitor (IC50 = 3.5 nM), in a concentration-dependent manner, suggesting that SP induces cAMP accumulation via an Indo-sensitive pathway. (3) SP-induced arachidonic acid release and SP-induced prostaglandin E2 (PGE2) release were inhibited concentration dependently by quinacrine and Indo, with IC50 values of 11 microM and 0.8 nM, respectively. (4) PGE2 (1 microM) increased cAMP formation in the sphincter muscle by 94%, and, furthermore, the PG, but not SP, stimulated the activity of adenylyl cyclase in membrane fractions isolated from this tissue. (5) Indo (1 microM) blocked the relaxing effect of SP (1 microM) in iris sphincter precontracted with carbachol (1 microM). (6) The inhibitory effect of Indo on SP-induced cAMP accumulation was species specific. Increases in cAMP represent a mechanism by which extracellular SP can regulate smooth muscle function. Thus, we conclude from these studies that in dog iris sphincter SP-induced cAMP accumulation is mediated through PGs, and that in this cholinergically innervated muscle SP via cAMP could function, in part, to modulate the physiological responses to muscarinic receptor stimulation.

The effects of prostaglandins E2 and F2 alpha on porcine ciliary muscle cells in culture

The purpose of this work is to investigate the effect of prostaglandins (PGs) on the contraction of ciliary muscle cells. It has been proposed that PGs induce relaxation of ciliary muscle and facilitate uveoscleral outflow, and reduce intraocular pressure (IOP). The ocular response to PGs is complicated because the relative contributions of uveoscleral flow and the conventional outflow to lowering IOP and the type of PG receptors associated with ciliary muscle may vary depending on animal species. In order to obtain insights into prostaglandin receptors of ciliary muscle, ciliary muscle cells from porcine eye were grown in culture and characterized immunocytochemically with antibodies against smooth muscle-alpha-actin and PGE2 receptor subtypes. As in ciliary muscle tissues, positive immunostaining for alpha-actin and EP2 and EP3 subtypes was observed in cultured cells. Time-dependent contraction of cultured cells induced by 10(-4) M carbachol was recorded by taking sequential photographs and analyzed. Using this assay method, the effect of prostaglandins E2 and F2 alpha to inhibit the carbachol-induced contraction was studied. PGE2 showed potent inhibition of cell contraction; 10(-7) approximately 10(-8) M PGE2 inhibited 50% of full contraction in 15 min. PGF2 alpha at 10(-4) M neither caused cell contraction by itself nor blocked carbachol-induced contraction. The EP2 agonist 11-deoxy-16, 16-dimethyl PGE2 at 10(-4) M inhibited cell contraction but the EP3 agonist sulprostone had no effect. Dibutyryl cAMP at 3 x 10(-5) M inhibited contraction by 50%. In the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), less than 10(-7) M dibutyryl cAMP caused 50% inhibition. In support of the cAMP effect, the addition of 10(-4) M PGE2 to cultured cells in the presence of indomethacin and IBMX was shown to cause an 80% increase in intracellular cAMP concentration compared with the basal (i.e. unstimulated) level of cAMP. Stimulation of cells with 10(-4) M PGF2 alpha caused no increase in cellular cAMP. These results indicate that PGE2 receptor EP2 subtype, but not PGF2 alpha receptor, is involved in the inhibition (hence relaxation by inference) of carbachol-induced porcine ciliary muscle cell contraction. It awaits further studies to determine whether cultured ciliary muscle cells of other species respond similarly to different PGs.

Immunocytochemical localization of prostaglandin E2 receptor subtypes in porcine ocular tissues. I. Uveal tissues

Polyclonal antibodies were raised against 15-residue sequences in the carboxyl terminal region of mouse EP1, EP2, and EP3 subtypes. The selected sequences are well conserved in different species. Using the antibodies, the localization of the receptor subtypes in porcine uveal tissues was investigated by immunoperoxidase reaction (by light microscopy) and immunogold labeling (by electron microscopy). EP1 immunoreactivity was found in ciliary nonpigmented epithelium and iris muscles (both sphincter and dilator). EP2 was localized to ciliary nonpigmented epithelium and muscle, iris sphincter muscle, and trabecular meshwork. EP3 immunoreactivity was detected in all uveal tissues examined.

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.