Adenylyl cyclase activity mediated by beta-adrenoceptors in immortalized human trabecular meshwork and non-pigmented ciliary epithelial cells

Adrenoceptors in the Eye - Physiological and Pathophysiological Relevance

The autonomic nervous system plays a crucial role in the innervation of the eye. Consequently, it comes as no surprise that catecholamines and their corresponding receptors have been extensively studied and characterized in numerous ocular structures, including the cornea, conjunctiva, lacrimal gland, trabecular meshwork, uvea, and retina. These investigations have unveiled substantial clinical implications, particularly in the context of treating glaucoma, a progressive neurodegenerative disorder responsible for irreversible vision loss on a global scale. The primary therapeutic approaches for glaucoma frequently involve the modulation of α1-, α2-, and β-adrenoceptors, making them pivotal targets. In this chapter, we offer a comprehensive overview of the expression, distribution, and functional roles of adrenoceptors within various components of the eye and its associated structures. Additionally, we delve into the pivotal role of adrenoceptors in the pathophysiology of glaucoma. Furthermore, we provide a concise historical perspective on adrenoceptor research, examine the distinct contributions of individual adrenoceptor subtypes to the treatment of various ocular conditions, and propose potential future avenues of exploration in this field.

β-Adrenoreceptors as Therapeutic Targets for Ocular Tumors and Other Eye Diseases-Historical Aspects and Nowadays Understanding

β-adrenoreceptors (ARs) are members of the superfamily of G-protein-coupled receptors (GPCRs), and are activated by catecholamines, such as epinephrine and norepinephrine. Three subtypes of β-ARs (β₁, β₂, and β₃) have been identified with different distributions among ocular tissues. Importantly, β-ARs are an established target in the treatment of glaucoma. Moreover, β-adrenergic signaling has been associated with the development and progression of various tumor types. Hence, β-ARs are a potential therapeutic target for ocular neoplasms, such as ocular hemangioma and uveal melanoma. This review aims to discuss the expression and function of individual β-AR subtypes in ocular structures, as well as their role in the treatment of ocular diseases, including ocular tumors.

β-blocker eye drops affect ocular surface through β2 adrenoceptor of corneal limbal stem cells

Background

Topical application of β-blocker eye drops induces damage to the ocular surface in clinical. However, the mechanism involved remains incompletely understood. The purpose of this study was to investigate the influence and mechanism of β-blocker eye drops on corneal epithelial wound healing.

Methods

Corneal epithelial wound healing models were constructed by epithelial scraping including in the limbal region and unceasingly received eye drops containing 5 mg/mL β-blocker levobunolol, β1-adrenoceptor (β1AR)-specific antagonist atenolol or β2-adrenoceptor (β2AR)-specific antagonist ICI 118, 551. For the migration assay, the murine corneal epithelial stem/progenitor cells (TKE2) were wounded and subsequently incubated with levobunolol, atenolol, or ICI 118, 551. The proliferation and colony formation abilities of TKE2 cells treated with levobunolol, atenolol, or ICI 118, 551 were investigated by CCK-8 kit and crystal violet staining. The differentiation marker Cytokeratin 3 (CK3), the stem cell markers-Cytokeratin 14 (CK14) and Cytokeratin 19 (CK19), and corneal epithelium regeneration-related signaling including in Ki67 and the phosphorylated epithelial growth factor receptor (pEGFR) and phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) were assessed by immunofluorescence staining.

Results

Levobunolol and ICI 118, 551 impaired corneal wound healing, decreased the expressions of CK3, CK14, and CK19 after limbal region scraping in vivo and reduced the migration and proliferation of TKE2 in vitro, whereas atenolol had no significant effect. Moreover, levobunolol and ICI 118, 551 inhibited corneal wound healing by mediating the expression of Ki67, and the phosphorylation of EGFR and ERK1/2 in the limbal and regenerated corneal epithelium.

Conclusion

β-blocker eye drops impaired corneal wound healing by inhibiting the β2AR of limbal stem cells, which decreased corneal epithelial regeneration-related signaling. Therefore, a selective β1AR antagonist might be a good choice for glaucoma treatment to avoid ocular surface damage.

Inhibitory and Agonistic Autoantibodies Directed Against the β2-Adrenergic Receptor in Pseudoexfoliation Syndrome and Glaucoma

Pseudoexfoliation syndrome (PEXS) and glaucoma (PEXG) are assumed to be caused by a generalized elastosis leading to the accumulation of PEX material in ocular as well as in extraocular tissues. The exact pathophysiology of PEXS is still elusive. PEXG, the most common type of secondary open-angle glaucoma (OAG), is characterized by large peaks of intraocular pressure (IOP) with a progressive loss of the visual field. Agonistic autoantibodies (agAAbs) against the β₂-adrenergic receptor (AR) have been shown to be present in sera of patients with primary and secondary OAG and ocular hypertension and are seemingly linked to IOP. In the present study, we investigated the autoantibodies directed against the β₂-AR in sera of patients with PEXS and PEXG. We recruited 15, 10, and 15 patients with PEXG, PEXS, and primary OAG, respectively. Ten healthy individuals served as controls. All patients underwent standard ophthalmological examination with Octopus G1 perimetry. agAAbs prepared from serum samples were analyzed in a rat cardiomyocyte-based bioassay for the presence of agAAbs. We identified the interacting loop of the β₂-AR and the immunoglobulin G (IgG) subclasses using synthetic peptides corresponding to the extracellular loops of the receptors and enzyme-linked immunosorbent assay, respectively. None of the controls were β₂-agAAb-positive (0.2 ± 0.5 U). No β₂-agAAbs (0.2 ± 0.4 U), but inhibitory β₂-AAbs were observed in 80% of the patients that partially blocked the drug-induced β₂-adrenergic stimulation; 5.8 ± 1.7 U vs. 11.1 ± 0.9 U for clenbuterol in the absence and the presence of sera from patients with PEXS, respectively. Epitope analyses identified the third extracellular loop of the β₂-AR as the target of the inhibitory β₂-AAbs, being of IgG3 subtype in PEXS patients. In contrast, patients with PEXG showed β₂-agAAbs (5.6 ± 0.9 U), but no inhibitory ones. The β₂-agAAbs levels of patients with PEXG and primary OAG patients (3.9 ± 2.8 U; p > 0.05) were at a similar level. In two cases of PEXG, the β₂-agAAbs exert synergistic effects with clenbuterol. The activity increased from 11.5 ± 0.3 (clenbuterol only) to 16.3 ± 0.9 U. As autoimmune mechanisms were reportedly involved in the pathogenesis of glaucoma, agonistic and inhibitory β₂-AAbs seem to be a part of this multifactorial interplay.

Agonistic autoantibodies against ß2-adrenergic receptor influence retinal microcirculation in glaucoma suspects and patients

PURPOSE

Agonistic β2-adrenergic receptor autoantibodies (β2-agAAb) have been observed in sera of patients with ocular hypertension and open-angle glaucoma (OAG). They target the β2-receptors on trabecular meshwork, ciliary body and pericytes (Junemann et al. 2018; Hohberger et al. 2019). In addition to their influence on the intraocular pressure, an association to retinal microcirculation is discussed. This study aimed to investigate foveal avascular zone (FAZ) characteristics by en face OCT angiography (OCT-A) in glaucoma suspects and its relationship to β2-agAAb status in patients with OAG.

MATERIAL AND METHODS

Thirty-four patients (28 OAG, 6 glaucoma suspects) underwent standardized, clinical examination including sensory testing as white-on-white perimetry (Octopus G1, mean defect, MD) and structural measures as retinal nerve fibre layer (RNFL) thickness, neuroretinal rim width (BMO-MRW), retinal ganglion cell layer (RGCL) thickness, and inner nuclear layer (INL) thickness with high-resolution OCT. FAZ characteristics were measured by OCT-A scans of superficial vascular plexus (SVP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP). FAZ-R was calculated (area FAZ (SVP)/area FAZ (ICP)). Using cardiomyocyte bioassays we analysed serum samples for the presence of β2-agAAb.

RESULTS

(I) Total mean FAZ area [mm2]: 0.34±0.16 (SVP), 0.24±0.12 (ICP), and 0.49±0.24 (DCP); mean FAZ-R 1.58±0.94. No correlation was seen for FAZ-R with MD, RNFL, BMO-MRW, RGCL thickness and INL thickness (p>0.05). (II) ß2-agAAb have been observed in 91% patients and showed no correlation with MD, RNFL, BMO-MRW, RGCL thickness and INL thickness (p>0.05). (III) FAZ-R correlated significantly with the β2-agAAb-induced increase of the beat rate of cardiomyocyte (p = 0.028).

CONCLUSION

FAZ characteristics did not correlate with any glaucoma associated functional and morphometric follow-up parameter in the present cohort. However, level of β2-agAAb showed a significantly correlation with FAZ-ratio. We conclude that β2-agAAb might be a novel biomarker in glaucoma pathogenesis showing association to FAZ-ratio with OCT-A.

Agonistic β2-Adrenergic Receptor Autoantibodies Characterize the Aqueous Humor of Patients With Primary and Secondary Open-Angle Glaucoma

Purpose

Agonistic β2-adrenergic receptor autoantibodies (β2-agAAbs) were recently observed in sera of patients with ocular hypertension (OHT), primary (POAG), and secondary open-angle glaucoma (SOAG), yet not in healthy controls (HCs). It was the aim of the present study to investigate the presence of β2-agAAb in aqueous humor (AH) samples of OAG patients and to correlate these with the corresponding β2-agAAb serum data.

Material and Methods

Thirty-nine patients (21 male, 18 female) were recruited from the Department of Ophthalmology, University of Erlangen-Nürnberg: twenty-one POAG, 18 SOAG. Aqueous humor samples were collected during minimal invasive glaucoma surgery. Serum and AH samples were analyzed for β2-agAAb by a bioassay quantifying the beating rate of cultured cardiomyocyte (cut-off: 2 U).

Results

Thirty-six of 39 (92.3%) and 34 of 39 (87.2%) of OAG patients showed a β2-agAAb in their sera and AH samples, respectively. All β2-agAAb AH-positive OAG patients were also seropositive. We also observed a β2-agAAb seropositivity in 95 and 89% of patients with POAG and SOAG, respectively. Beta2-agAAbs were seen in 86% (POAG) and 78% (SOAG) of AH samples. The β2-agAAb adrenergic activity was increased in the AH of patients with POAG (6.5 ± 1.5 U) when compared with those with SOAG (4.1 ± 1.1 U; p = 0.004). Serum β2-agAAb adrenergic activity did not differ between the cohorts [POAG (4.5 ± 1.5 U); SOAG (4.6 ± 2.1 U; p=0.458)]. No correlation of the beating rates were observed between serum and AH samples for group and subgroup analyses.

Conclusion

The detection of β2-agAAb in systemic and local circulations supports the hypothesis of a direct functional impact of these agAAbs on ocular G-protein coupled receptors. The high prevalence of β2-agAAb in serum and AH samples of patients with POAG or SOAG suggests a common role of these AAbs in the etiopathogenesis of glaucoma, independent of open-angle glaucoma subtype.

Discovery to Launch of Anti-allergy (Emadine; Patanol/Pataday/Pazeo) and Anti-glaucoma (Travatan; Simbrinza) Ocular Drugs, and Generation of Novel Pharmacological Tools Such as AL-8810

The eye and eyesight are exquistly designed and are precious, and yet we often take them for granted. Good vision is critical for our long-term survival and for humanity's enduring progress. Unfortunately, since ocular diseases do not culminate in life-and-death scenarios, awareness of the plight of millions of people suffering from such eye ailments is not publicized as other diseases. However, losing eyesight or falling victim to visual impairment is a frightening outlook for most people. Glaucoma, a collection of chronic optic neuropathies, of which the most prevalent form, primary open-angle glaucoma (POAG), is the second leading cause of irreversible blindness. POAG currently afflicts >70 million people worldwide and is an insidious, progressive, silent thief of sight that is asymptomatic. On the other hand, allergic conjunctivitis (AC), and the associated rhinitis ("hay-fever"), frequently victimizes a huge number of people worldwide, especially during seasonal changes. While not life-threatening, sufferers of AC soon learn the value of drugs to treat their signs and symptoms of AC as they desire rapid relief to overcome the ocular itching/pain, redness, and tearing AC causes. Herein, I will describe the collective efforts of many researchers whose industrious, diligent, and dedicated team work resulted in the discovery, biochemical/pharmacological characterization, development and eventual launch of drugs to treat AC (e.g., olopatadine [Patanol/Pataday/Pazeo] and emedastine [Emedine]), and for treating ocular hypertension and POAG (e.g., travoprost [Travatan ] and Simbrinza). This represents a personal perspective.

Treatment of glaucoma by prostaglandin agonists and beta-blockers in combination directly reduces pro-fibrotic gene expression in trabecular meshwork

Prostaglandin analogues (PG), beta-blockers (BB) or their combination (PG+BB) are used primarily to reduce the intraocular pressure (IOP) pathologically associated with glaucoma. Since, fibrosis of the trabecular meshwork (TM) is a major aetiological factor in glaucoma, we studied the effect of these drugs on fibrosis-associated gene expression in TM of primary glaucoma patients. In the present study, TM and iris of primary open-angle (n = 32) and angle-closure (n = 37) glaucoma patients were obtained surgically during trabeculectomy and categorized based on the type of IOP-lowering medications use as PG, BB or PG+BB. mRNA expression of pro-fibrotic and anti-fibrotic genes was quantified using qPCR in these tissues. The gene expression levels of pro-fibrotic genes were significantly lower in PG+BB as compared to other groups. These observations and underlying signalling validated in vitro in human TM cells also showed reduced fibrotic gene and protein expression levels following PG+BB treatment. In conclusion, it is observed that PG+BB combination rather than their lone use renders a reduced fibrotic status in TM. This further suggests that IOP-lowering medications, in combination, would also modulate fibrosis-associated molecular changes in the TM, which may be beneficial for maintaining aqueous out-flow mechanisms over the clinical treatment duration.

Autoantibodies Activating the β2-Adrenergic Receptor Characterize Patients With Primary and Secondary Glaucoma

Recently, agonistic autoantibodies (agAAb) activating the β2-adrenergic receptor were detected in primary open-angle glaucoma (POAG) or ocular hypertension (OHT) patients and were linked to intraocular pressure (IOP) (1). The aim of the present study was to quantify β2-agAAb in the sera of glaucoma suspects and patients with primary and secondary glaucoma. Patients with OHT (n = 33), pre-perimetric POAG (pre-POAG; n = 11), POAG (n = 28), and 11 secondary OAG (SOAG) underwent ophthalmological examinations including examinations with Octopus G1 perimetry and morphometry. Twenty-five healthy individuals served as controls. Serum-derived IgG samples were analyzed for β2-agAAb using a functional bioassay. The beat-rate-increase of spontaneously beating cultured neonatal rat cardiomyocytes was monitored with 1.6 beats/15 s as cut-off. None of the sera of normal subjects showed β2-agAAb. In POAG or OHT patients increased beating rates of 4.1 ± 2.2 beats/15 s, and 3.7 ± 2.8 beats/15 s were detected (p > 0.05). Glaucoma patients with (POAG) and without perimetric (pre-POAG) defects did not differ (pre-POAG 4.4 ± 2.6 beats/15 s, POAG 4.1 ± 2.0 beats/15 s, p > 0.05). Patients with SOAG yielded mean beating rates of 4.7 ± 1.7 beats/15 s (p > 0.05). β2-agAAb were seen in 73% of OHT, 82% of pre-POAG, 82% of POAG, and 91% SOAG patients (p < 0.001). Clinical data did not correlate with beating rate (p > 0.05). The robust β2-agAAb seropositivity in patients with OHT, pre-POAG, POAG, and SOAG suggest a primary common role for β2-agAAb starting early in glaucoma pathophysiology and turned out to be a novel marker identifying all patients with increased IOP independent of glaucoma stage and entity.

GPR158 in the Visual System: Homeostatic Role in Regulation of Intraocular Pressure

Purpose: GPR158 is a newly characterized family C G-protein-coupled receptor, previously identified in functional screens linked with biological stress, including one for susceptibility to ocular hypertension/glaucoma induced by glucocorticoid stress hormones. In this study, we investigated GPR158 function in the visual system. Methods: Gene expression and protein immunolocalization analyses were performed in mouse and human brain and eye to identify tissues where GPR158 might function. Gene expression was perturbed in mice, and in cultures of human trabecular meshwork cells of the aqueous outflow pathway, to investigate function and mechanism. Results: GPR158 is highly expressed in the brain, and in this study, we show prominent expression specifically in the visual center of the cerebral cortex. Expression was also observed in the eye, including photoreceptors, ganglion cells, and trabecular meshwork. Protein was also localized to the outer plexiform layer of the neural retina. Gpr158 deficiency in knockout (KO) mice conferred short-term protection against the intraocular pressure increase that occurred with aging, but this was reversed over time. Most strikingly, the pressure lowering effect of the acute stress hormone, epinephrine, was negated in KO mice. In contrast, no disruption of the electroretinogram was observed. Gene overexpression in cell cultures enhanced cAMP production in response to epinephrine, suggesting a mechanism for intraocular pressure regulation. Overexpression also increased survival of cells subjected to oxidative stress linked to ocular hypertension, associated with TP53 pathway activation. Conclusions: These findings implicate GPR158 as a homeostatic regulator of intraocular pressure and suggest GPR158 could be a pharmacological target for managing ocular hypertension.

Agonistic Autoantibodies to the β2-Adrenergic Receptor Involved in the Pathogenesis of Open-Angle Glaucoma

Glaucoma is a frequent ocular disease that may lead to blindness. Primary open-angle glaucoma (POAG) and ocular hypertension (OHT) are common diseases with increased intraocular pressure (IOP), which are mainly responsible for these disorders. Their pathogenesis is widely unknown. We screened the sera of patients with POAG and OHT for the prevalence of autoantibodies (AAb) against G protein-coupled receptors (GPCRs) in comparison to controls. Employing frequency modulation of spontaneously contracting neonatal rat cardiomyocytes in vitro, agonistic GPCR AAb were to be detected in roughly 75% of the patients with POAG and OHT, however, not in controls. Using inhibitory peptides the AAb’ target was identified as β2 adrenergic receptor (β2AR). The AAb interact with the second extracellular loop of β2AR. The peptides 181–187 and 186–192 were identified as binding sites of the AAb within the extracellular loop II. The binding of the AAb to β2ARs was verified by surface-plasmon-resonance analysis. The isotype of the AAb was (immunoglobulin) IgG3. In an additional pilot principal-of-proof study, including four patients with POAG, the removal of the AAb against the β2AR and other immunoglobulins G by immunoadsorption resulted in a transient reduction of IOP. These findings might indicate a possible role of agonistic AAb directed against β2ARs in the dynamics of aqueous humor and might support a contribution of adaptive autoimmunity in the etiopathogenesis of POAG and OHT.

Melatonin and its analog 5-methoxycarbonylamino-N-acetyltryptamine potentiate adrenergic receptor-mediated ocular hypotensive effects in rabbits: significance for combination therapy in glaucoma

Melatonin is currently considered a promising drug for glaucoma treatment because of its ocular hypotensive and neuroprotective effects. We have investigated the effect of melatonin and its analog 5-methoxycarbonylamino-N-acetyltryptamine, 5-MCA-NAT, on β₂/α(2A)-adrenergic receptor mRNA as well as protein expression in cultured rabbit nonpigmented ciliary epithelial cells. Quantitative polymerase chain reaction and immunocytochemical assays revealed a significant β₂-adrenergic receptor downregulation as well as α(2A)-adrenergic receptor up-regulation of treated cells (P < 0.001, maximal significant effect). In addition, we have studied the effect of these drugs upon the ocular hypotensive action of a nonselective β-adrenergic receptor (timolol) and a selective α₂-adrenergic receptor agonist (brimonidine) in normotensive rabbits. Intraocular pressure (IOP) experiments showed that the administration of timolol in rabbits pretreated with melatonin or 5-MCA-NAT evoked an additional IOP reduction of 14.02% ± 5.8% or 16.75% ± 5.48% (P < 0.01) in comparison with rabbits treated with timolol alone for 24 hours. Concerning brimonidine hypotensive action, an additional IOP reduction of 29.26% ± 5.21% or 39.07% ± 5.81% (P < 0.001) was observed in rabbits pretreated with melatonin or 5-MCA-NAT when compared with animals treated with brimonidine alone for 24 hours. Additionally, a sustained potentiating effect of a single dose of 5-MCA-NAT was seen in rabbits treated with brimonidine once daily for up 4 days (extra IOP decrease of 15.57% ± 5.15%, P < 0.05, compared with brimonidine alone). These data confirm the indirect action of melatoninergic compounds on adrenergic receptors and their remarkable effect upon the ocular hypotensive action mainly of α₂-adrenergic receptor agonists but also of β-adrenergic antagonists.

Indirect sympatholytic actions at β-adrenoceptors account for the ocular hypotensive actions of cannabinoid receptor agonists

Intraocular pressure (IOP) is the primary risk factor for glaucoma, a blinding eye disease. Cannabinoid agonists have long been known to decrease IOP, suggesting they may be useful in glaucoma treatment. However, the specific mechanism by which cannabinoids generate this ocular hypotensive effect remains unknown. The current evidence suggests the cannabinoids reduce IOP through actions at cannabinoid 1 (CB(1)) receptors within the eye, and adrenergic receptors (ARs) may also contribute to this action of cannabinoids. Considering this, the present study aimed to elucidate the mechanism behind the ocular hypotensive properties of cannabinoids through the use of mice genetically lacking either cannabinoid receptors or βARs. Cannabinoid agonists, βAR antagonists, and βAR agonists decreased IOP in wild-type mice and CB(2)(-/-) mice. In contrast, none of these compounds were found to reduce IOP in βAR(-/-) or CB(1)(-/-) mice. Desensitization of the βARs and depletion of catecholamines in wild-type mice also eliminated the ability of the cannabinoid agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate (WIN 55,212-2) to reduce IOP, strongly implicating a role for both βARs and catecholamines in the ocular hypotensive properties of cannabinoids. Finally, CB(1) receptors were shown to colocalize with tyrosine hydroxylase, a marker for adrenergic neurons. Taken together, these findings suggest that βARs are required for the ocular hypotensive properties of cannabinoids, and cannabinoids reduce IOP by acting as indirect sympatholytics and inhibiting norepinephrine release within the eye.

Intracellular signaling in human iridial fibroblasts and iridial melanocytes in response to prostaglandins, endothelin, isoproterenol, and other pharmacological agents

PURPOSE

The receptor-coupled signal transduction systems present in isolated human iridial fibroblasts (HIF) and in human iridial melanocytes (HIM) were investigated. Cell responsiveness to numerous prostaglandins (PGs), and other compounds of interest, was profiled in order to better understand their involvement in the iridial hyper-pigmentation process observed during treatment of elevated intraocular pressure with FP-receptor against PG analogs.

METHODS

[(3)H]-inositol phosphates ([(3)H]-IPs) generated in the cells were measured by ion-exchange chromatography followed by liquid scintillation spectroscopy. cAMP generated in the cells was quantified using an enzyme immunoassay.

RESULTS

HIF cells exhibited a robust phosphoinositide (PI) hydrolysis response to FP-class PG analogs, such as cloprostenol (potency, EC(50) = 2.4 ± 0.5 nM, n = 5), fluprostenol (EC(50) = 5.3 ± 0.6 nM, n = 3), PGF(2α) (EC(50) = 54 ± 18 nM, n = 5), and latanoprost acid (EC(50) = 121 ± 17 nM, n = 4). Other PGs exhibited the following potencies (EC(50)) for stimulating [(3)H]-IPs accumulation in HIF cells: PGD(2) EC(50) = 327 ± 195 nM, n =3; PGE(2) EC(50) = 550 ± 50 nM, n = 3; and two TP-receptor agonists (I-BOP, EC(50) = 23 ± 8 nM, n = 3; U-46619 EC(50) = 1.1 ± 0.4 µM, n = 3). Endothelin-1 (ET-1) and histamine increased [(3)H]-IPs production in HIF and HIM cells. HIM cells exhibited minimal PI turnover response to cloprostenol, latanoprost acid, latanoprost, PGF(2α), PGE(2), and histamine, but there were robust responses to ET-1 (EC(50) = 4.6 nM, n = 2) and an ET(B)-receptor agonist (BQ-3020, EC(50) = 5 nM, n = 2) that were blocked by an ET(B)-antagonist (BQ-788, IC(50) = 21 ± 6 nM, n = 3). In the adenylyl cyclase activation assay, numerous PGs (1 and 10 µM) stimulated cAMP production in HIF cells yielding the following rank order of efficacy: PGI(2) > PGE(2) > misoprostil > isoproterenol = BW245C > PGD(2) = PGF(2α) = fluprostenol. In HIM cells, PGE(2) (EC(50) = 1.3 ± 0.3 nM) and isoproterenol (β-agonist; EC(50) = 89 ± 13 nM) potently and efficaciously stimulated cAMP production and ICI-118851 (β(2)-antagonist) attenuated the effects of isoproterenol. However, latanoprost acid, latanoprost, ET-1, and BW245C (DP-receptor agonist) were relatively less efficacious than isoproterenol and PGE(2) in HIM cells at stimulating cAMP production.

CONCLUSIONS

These studies have shown that while HIF cells express FP prostaglandin and histamine receptors coupled to phospholipase C to produce [(3)H]-IPs, the HIM cells lack such functionally active FP-receptors. In contrast, HIF and HIM cells express functional ET-1 receptors coupled to [(3)H]-IPs production and both cell-types respond to PGE(2), BW245C, and isoproterenol by generating cAMP. It is concluded that human iridial fibroblasts and melanocytes respond differently to PGs and histamine, but in the same manner to ET-1, isoproterenol and BW245C. This may have relevance to the intercellular communication within the iris relative to the melanogenic processes.

Pharmacological properties and discriminative stimulus effects of a novel and selective 5-HT2 receptor agonist AL-38022A [(S)-2-(8,9-dihydro-7H-pyrano[2,3-g]indazol-1-yl)-1-methylethylamine]

AL-38022A is a novel synthetic serotonergic (5-HT) ligand that exhibited high affinity for each of the 5-HT2 receptor subtypes (Ki100-fold less) affinity for other 5-HT receptors. In addition, AL-38022A displayed a very low affinity for a broad array of other receptors, neurotransmitter transport sites, ion channels, and second messenger elements, making it a relatively selective agent. AL-38022A potently stimulated functional responses via native and cloned rat (EC50 range: 1.9-22.5 nM) and human (EC50 range: 0.5-2.2 nM) 5-HT2 receptor subtypes including [Ca2+]i mobilization and tissue contractions with apparently similar potencies and intrinsic activities and was a full agonist at all 5-HT2 receptor subtypes. The CNS activity of AL-38022A was assessed by evaluating its discriminative stimulus effects in both a rat and a monkey drug discrimination paradigm using DOM as the training drug. AL-38022A fully generalized to the DOM stimulus in each of these studies; in monkeys MDL 100907 antagonized both DOM and AL-38022A. The pharmacological profile of AL-38022A suggests that it could be a useful tool in defining 5-HT2 receptor signaling and receptor characterization where 5-HT may function as a neurotransmitter.

A 6-week, double-masked, parallel-group study of the efficacy and safety of travoprost 0.004% compared with latanoprost 0:005%/timolol 0.5% in patients with primary open-angle glaucoma or ocular hypertension

OBJECTIVE

The objective of this study was to directly compare the intraocular pressure (IOP)-lowering efficacy and safety of travoprost 0.004% eyedrops with the fixed combination of latanoprost 0.005%/timolol 0.5% eyedrops in patients with primary open-angle glaucoma or ocular hypertension.

METHODS

This was a randomized, double-masked, multicenter, parallel-group, active-controlled study. Adult subjects with open-angle glaucoma (with or without pseudoexfoliation or pigment dispersion component) or ocular hypertension were eligible to participate if their IOP was inadequately controlled with > or =4 weeks of beta-blocker monotherapy, as indicated by IOP of 22 to 36 mm Hg at 9 AM at screening. Patients were randomly assigned in a 1:1 ratio to receive placebo + travoprost or latanoprost/timolol + placebo. Patients in the travoprost group administered travoprost at 9 PM and placebo at 9 AM; patients in the latanoprost/timolol group administered latanoprost/timolol at 9 AM and placebo at 9 PM. IOP measurements were performed using Goldmann applanation tonometry at 9 AM and 5 PM at the week-2 and week-6 visits. Both volunteered and elicited reports of adverse events were collected; all patients who were randomized and received > or =1 dose of study drug were included in the safety analysis.

RESULTS

One hundred ten patients were randomized, of whom 106 patients were evaluable (travoprost, n = 50; latanoprost/timolol, n = 56). There were no statistically significant differences at baseline between the treatment groups, based on age group, sex, race, iris color, or diagnosis. Mean IOP values were not statistically different between groups at baseline or during treatment. In the pooled results for 9 Am assessment at weeks 2 and 6, mean (SEM) IOP reductions for travoprost and latanoprost/timolol were 7.0 (0.5) and 6.4 (0.5) mm Hg, respectively (P = NS). Adverse events related to therapy were mild in nature, and there were no statistically significant differences between the 2 treatment groups. The most frequently experienced adverse events in the travoprost group were ocular hyperemia (9.3%), foreign body sensation (5.6%), abnormal vision (1.9%), allergic reaction (1.9%), conjunctivitis (1.9%), dacryocystitis (1.9%), eye discharge (1.9%), eye pruritus (1.9%), lid edema (1.9%), lid erythema (1.9%), and tearing (1.9%). In the latanoprost/timolol group, the most frequently experienced adverse events were cataract (1.8%), dry eyes (1.8%), eye pruritus (1.8%), foreign body sensation (1.8%), and ocular hyperemia (1.8%).

CONCLUSIONS

Mean IOP changes from baseline for travoprost 0.004% and latanoprost 0.005%/timolol 0.5% fixed combination were not significantly different at follow-up in these patients. Both medications were well tolerated.

1-((S)-2-Aminopropyl)-1H-indazol-6-ol: A Potent Peripherally Acting 5-HT2 Receptor Agonist with Ocular Hypotensive Activity

Serotonin 5-HT(2) receptor agonists have been identified as a potential new class of agents for the treatment of ocular hypertension and glaucoma. The initially reported tryptamine analogues displayed either poor solution stability, potent central nervous system activity, or both of these undesirable characteristics and were unacceptable for clinical evaluation. A series of 1-(2-aminopropyl)-1H-indazole analogues was synthesized and evaluated for their suitability for consideration as clinical candidates. 1-((S)-2-Aminopropyl)-1H-indazol-6-ol (9) was identified as a peripherally acting potent 5-HT(2) receptor agonist (EC(50) = 42.7 nM, E(max) = 89%) with high selectivity for the 5-HT(2) receptors relative to other serotonergic receptor subtypes and other families of receptors and has significantly greater solution stability than alpha-methyl-5-hydroxytryptamine. Additionally, 9 potently lowers intraocular pressure in conscious ocular hypertensive monkeys (-13 mmHg, 33%); this reduction appears to be through a local rather than a centrally mediated effect. Compound 9 appears to be an excellent 5-HT(2) receptor agonist for conducting further studies directed toward a clinical proof-of-concept study for this class of ocular hypotensive agents.

Efficacy and safety of a fixed combination of travoprost 0.004%/timolol 0.5% ophthalmic solution once daily for open-angle glaucoma or ocular hypertension

PURPOSE

To compare the efficacy of a fixed combination of travoprost 0.004%/timolol 0.5% every day in the morning with a concomitant regimen of timolol 0.5% every day in the morning, plus travoprost 0.004% every day in the evening; and timolol 0.5% twice daily on the intraocular pressure (IOP) of subjects with open-angle glaucoma or ocular hypertension over 3 months.

DESIGN

Prospective, randomized, double-masked, parallel-group, active-controlled, multicenter trial.

METHODS

Patients comprised adult subjects (n = 403) of either gender with open-angle glaucoma or ocular hypertension in at least one eye. To qualify, the IOP had to be between 22 to 36 mm Hg in the same eye at two consecutive eligibility visits. The primary outcome variable was IOP measured with a Goldmann applanation tonometer.

RESULTS

Mean IOP ranged from 16.2 to 17.4 mm Hg with the combination travoprost/timolol compared with 15.4 to 16.8 mm Hg in the concomitant travoprost + timolol group, from baselines of 23.1 to 25.6 mm Hg and 22.9 to 25.0 mm Hg, respectively. The fixed combination of travoprost/timolol significantly lowered IOP by 7 to 9 mm, similar to the IOP reductions observed with concomitant therapy. The most frequent ocular adverse event was hyperemia that occurred in 14.3% and 23.4% of subjects treated with travoprost/timolol combination and concomitant travoprost + timolol, respectively.

CONCLUSIONS

Travoprost/timolol combination produces greater IOP reductions than the positive control, timolol 0.5%, and reductions that were similar to concomitant travoprost + timolol. This study demonstrates that the fixed combination of travoprost/timolol produces significant and clinically relevant reductions of IOP in a once-daily dosing regimen.

Binding affinities of ocular hypotensive beta-blockers levobetaxolol, levobunolol, and timolol at endogenous guinea pig beta-adrenoceptors

The current study determined the relative affinities and selectivities of numerous beta-adrenoceptor antagonists at the endogenous beta(1)- and beta(2)-adrenoceptors in guinea pig heart and lung, respectively, using [(3)H]-CGP12177. Specific binding of [(3)H]-CGP12177 comprised 80 +/- 0.2% (n = 11) and 94 +/- 0.2% (n = 16) of the total binding in washed heart and lung homogenates, respectively. Concentration-dependent displacement of [(3)H]-CGP12177 binding from beta-adrenoceptors in both preparations was observed with nine different beta-adrenoceptor antagonists. Levobetaxolol, betaxolol, CGP-20712A, levobunolol, and timolol yielded bi-phasic (two-site-fit) competition curves in the heart, while CGP-20712A, ICI-118551 and levobunolol produced bi-phasic curves in the lung preparation. The high-affinity component of [(3)H]-CGP12177 binding in the heart and lung reflected binding to beta(1)-receptors and beta(2)-receptors, respectively. The binding inhibition parameters (IC(50)s) for displacement of [(3)H]-CGP12177 from these predominantly high-affinity sites were: levobetaxolol (24.9 +/- 1.6 nM heart, 4810 +/- 367 nM lung), racemic betaxolol (37.9 +/- 8.7 mM heart; 8840 +/- 424 mM lung), CGP-20712A (4.6 +/- 0.9 nM heart; 171,000 +/- 109,000 nM lung), ICI-118551 (9230 +/- 3240 nM heart; 2.9 +/- 0.6 nM lung), levobunolol (42 +/- 15 nM heart, 0.3 +/- 0.2 nM lung), (l)-timolol (3.1 nM heart, 2.9 +/- 1.5 nM lung), ICI-215001 (5840 +/- 114 nM heart; 26100 +/- 3200 nM lung), BRL-37344 (83,300 +/- 2660 nM heart; 13,200 +/- 1250 lung). These data indicated that while levobetaxolol and betaxolol possessed a 193-233-fold selectivity for beta(1)-receptors, levobunolol exhibited a 140-fold beta(2)-receptor selectivity and (l)-timolol was essentially nonselective.

A novel and selective 5-HT2 receptor agonist with ocular hypotensive activity: (S)-(+)-1-(2-aminopropyl)-8,9-dihydropyrano[3,2-e]indole

Serotonin 5-HT2 receptor agonists have recently been shown to be effective in lowering intraocular pressure in nonhuman primates and represent a potential new class of antiglaucoma agents. As part of an effort to identify new selective agonists at this receptor, we have found that (S)-(+)-1-(2-aminopropyl)-8,9-dihydropyrano[3,2-e]indole (AL-37350A, 11) has high affinity and selectivity (>1000-fold) for the 5-HT(2) receptor relative to other 5-HT receptors. More specifically, 11 is a potent agonist at the 5-HT2A receptor (EC50 = 28.6 nM, E(max) = 103%) that is comparable to serotonin. Evaluation of 11 in conscious ocular hypertensive cynomolgus monkeys showed this compound to be efficacious in reducing intraocular pressure (13.1 mmHg, -37%). Thus, 11 is a potent full agonist with selectivity for the 5-HT2 receptor and is anticipated to serve as a useful tool in exploring the role of the 5-HT2 receptor and its effector system in controlling intraocular pressure.

A functional assay for G-protein-coupled receptors using stably transformed insect tissue culture cell lines

Insect cells are an underexplored resource for functional G-protein-coupled receptor (GPCR) assays, despite a strong record in biochemical (binding) assays. Here we describe the use of vectors capable of creating stably transformed insect cell lines to generate a cell-based functional GPCR assay. This assay employs the luminescent photoprotein aequorin and the promiscuous G-protein subunit Galpha16 and is broadly applicable to human GPCRs. We demonstrate that the assay can quantitate ligand concentration-activity relationships for seven different human GPCRs, can differentiate between partial and full agonists, and can determine rank order potencies for both agonists and antagonists that match those seen with other assay systems. Human Galpha16 improves signal strength but is not required for activity with some receptors. The coexpression of human and bovine betagamma subunits and/or phospholipase Cbeta makes no difference to agonist efficacy or potency. Two different receptors expressed in the same cell line respond to their specific agonists, and two different cell lines (Sf9 and High 5) are able to functionally detect the same expressed GPCR. Sf9 cells have the capability to produce fully functional human receptors, allied to a low background of endogenous receptors, and so are a valuable system for investigating orphan GPCRs and receptor dimerization.

A3 adenosine and CB1 receptors activate a PKC-sensitive Cl- current in human nonpigmented ciliary epithelial cells via a G beta gamma-coupled MAPK signaling pathway

(1) We examined A3 adenosine and CB1 cannabinoid receptor-coupled signaling pathways regulating Cl(-) current in a human nonpigmented ciliary epithelial (NPCE) cell line. (2) Whole-cell patch-clamp recordings demonstrated that the A3 receptor agonist, IB-MECA, activates an outwardly rectifying Cl(-)current (I(Cl,Aden)) in NPCE cells, which was inhibited by the adenosine receptor antagonist, CGS-15943 or by the protein kinase C (PKC) activator, phorbol 12,13 dibutyrate (PDBu). (3) Treatment of NPCE cells with pertussis-toxin (PTX), or transfection with the COOH-terminus of beta-adrenergic receptor kinase (ct-betaARK), inhibited I(Cl,Aden). The phosphatidyl inositol 3-kinase (PI3K) inhibitor, wortmannin, had no effect on I(Cl,Aden); however, the mitogen-activated protein kinase kinase (MEK) inhibitor, PD98059, inhibited I(Cl,Aden). (4) Reverse transcription-polymerase chain reaction experiments and immunocytochemistry confirmed mRNA and protein expression for the CB1 receptor in NPCE cells, and the CB1 receptor agonist, Win 55,212-2, activated a PDBu-sensitive Cl(-) current (I(Cl,Win)). (5) Transfection of NPCE cells with the human CB1 (hCB1) receptor, increased I(Cl,Win), consistent with increased receptor expression, and I(Cl,Win) in hCB1 receptor-transfected cells was decreased after application of a CB1 receptor inverse agonist, SR 141716. (6) Constitutive activity for CB1 receptors was not significant in NPCE cells as transfection with hCB1 receptors did not increase basal Cl(-) current, nor was basal current inhibited by SR 141716. (7) I(Cl,Win) was inhibited by PTX preincubation, by transfection with ct-betaARK and by the MEK inhibitor, PD98059, but unaffected by the PI3K inhibitor, wortmannin. (8) We conclude that both A3 and CB1 receptors activate a PKC-sensitive Cl(-) current in human NPCE cells via a G(i/o)/Gbetagamma signaling pathway, in a manner independent of PI3K but involving MAPK.