Bimatoprost, prostamide activity, and conventional drainage

Preservative-Free Bimatoprost 0.01% Ophthalmic Gel for Glaucoma Therapy: A Phase III Randomized Controlled Trial

PRCIS

Noninferiority of efficacy was demonstrated for a preservative-free bimatoprost 0.01% compared with BAK-containing bimatoprost 0.01% following a 12-week treatment period in patients with open angle glaucoma or ocular hypertension. Improved tolerability, in particular conjunctival hyperemia, was also observed.

PURPOSE

To evaluate the intraocular pressure (IOP)-lowering efficacy and safety of a preservative-free bimatoprost 0.01% ophthalmic gel (PFB 0.01% gel) compared with preserved bimatoprost 0.01% (PB 0.01%).

DESIGN

Phase III, international, multicenter, randomized, 2-parallel group, investigator-masked, 3-month treatment duration.

METHODS

Patients with glaucoma or ocular hypertension were randomized after a 7-week run-in/washout period to receive once-daily PFB 0.01% gel (n=236) or PB 0.01% (n=249) for 3 months. The primary efficacy measure was changed from baseline in IOP at week 12. Safety measures included adverse events (AEs) and assessment of conjunctival hyperemia.

RESULTS

The mean changes from baseline in IOP at week 12 in the PFB 0.01% gel and PB 0.01% were -9.72±2.97 and -9.47±3.06 mm Hg, respectively, at 8 am , -9.41±3.03 and -9.19±3.12 mm Hg at 10 am , and -8.99±3.36 and -8.54±3.44 mm Hg at 4 pm . Noninferiority of PFB 0.01% gel to PB 0.01% was demonstrated at week 12 based on predetermined criteria (upper 95% CI margin of 1.5 mmHg at all time points). The most frequently reported AE was conjunctival hyperemia; 13 (5.5%) patients with PFB 0.01% gel and 17 (6.8%) patients with PB 0.01%. The percentage of patients experiencing a worsening from baseline in conjunctival hyperemia score was lower with PFB 0.01% gel compared to PB 0.01% at week 6 (20.1% vs. 29.3%, respectively) and week 12 (18.3% vs. 30.4%, respectively).

CONCLUSIONS

PFB 0.01% ophthalmic gel has the same efficacy in lowering IOP as PB 0.01% and demonstrated less aggravation of conjunctival hyperemia at weeks 6 and 12.

Chemical Insights into Topical Agents in Intraocular Pressure Management: From Glaucoma Etiopathology to Therapeutic Approaches

Glaucoma encompasses a group of optic neuropathies characterized by complex and often elusive etiopathology, involvihttng neurodegeneration of the optic nerve in conjunction with abnormal intraocular pressure (IOP). Currently, there is no cure for glaucoma, and treatment strategies primarily aim to halt disease progression by managing IOP. This review delves into the etiopathology, diagnostic methods, and treatment approaches for glaucoma, with a special focus on IOP management. We discuss a range of active pharmaceutical ingredients used in glaucoma therapy, emphasizing their chemical structure, pharmacological action, therapeutic effectiveness, and safety/tolerability profiles. Notably, most of these therapeutic agents are administered as topical formulations, a critical aspect considering patient compliance and drug delivery efficiency. The classes of glaucoma therapeutics covered in this review include prostaglandin analogs, beta blockers, alpha agonists, carbonic anhydrase inhibitors, Rho kinase inhibitors, and miotic (cholinergic) agents. This comprehensive overview highlights the importance of topical administration in glaucoma treatment, offering insights into the current state and future directions of pharmacological management in glaucoma.

Is fat the future for saving sight? Bioactive lipids and their impact on glaucoma

Glaucoma is characterized by a continuous loss of retinal ganglion cells. The cause of glaucoma is associated with an increase in intraocular pressure (IOP), but the underlying pathophysiology is diverse and, in most cases, unknown. There is an indisputable unmet need to identify new pathways involved in glaucoma pathogenesis. Increasing evidence suggests that bioactive lipids may be critical in the development and progression of glaucoma. Preclinical and clinical bioactive lipid targets exist and are being developed. In this review, we aim to shed light on the potential of bioactive lipids for the prevention, diagnosis, prognosis, and treatment of glaucoma by asking the question "is fat the future for saving sight".

Bimatoprost Implant Biodegradation in the Phase 3, Randomized, 20-Month ARTEMIS Studies

Purpose: To evaluate the time course of biodegradation of an intracameral, biodegradable, sustained-release bimatoprost implant that lowers intraocular pressure without the need for daily eye drops. Methods: In 2 identically designed, randomized, phase 3 clinical trials, adults with open-angle glaucoma or ocular hypertension and open iridocorneal angles inferiorly in the study eye were administered 10- or 15-μg bimatoprost implant (day 1 and weeks 16 and 32) or twice-daily topical timolol 0.5%. Implants were assessed on gonioscopy throughout the studies. Investigators reported whether implants were visible, estimated the size of visible implants relative to their initial size at implantation, and reported the implant location. Data for 10-μg implant placed on day 1 were pooled from both studies for analysis. Results: A total of 372 patients received the 10-μg bimatoprost implant. The degree of implant biodegradation at each follow-up time point was variable among patients. The implant frequently swelled during the initial phase of biodegradation from 6 to 28 weeks. Accelerated biodegradation occurred between 31 and 52 weeks, resulting in 82% of implants absent or ≤25% of initial size by 52 weeks. By month 20, 95% of implants had biodegraded to absent or ≤25% of initial size. The implant was predominantly located inferiorly in the iridocorneal angle. Conclusions: Bimatoprost implant biodegradation in phase 3 studies showed some degree of variability among patients. Clinically significant implant biodegradation was observed in the majority of patients by 12 months. Clinical studies are in progress to further understand implant biodegradation and the ideal timing for implant re-administration. ClinicalTrials.gov NCT02247804; ClinicalTrials.gov NCT02250651.

Clinical pharmacology and pharmacogenetics of prostaglandin analogues in glaucoma

Glaucoma is the main cause of irreversible visual loss worldwide, and comprises a group of progressive, age-related, and chronic optic neuropathies. Prostaglandin analogs are considered a first-line treatment in the management of glaucoma and have the best efficacy in reducing intraocular pressure. When comparing these therapeutic agents between them, long-term therapy with 0.03% bimatoprost is the most effective followed by treatment with 0.005% latanoprost and 0.004% travoprost. The prevalence of adverse events is lower for latanoprost than for other prostaglandin analogs. However, some patients do not respond to the treatment with prostaglandin analogs (non-responders). Intraocular pressure-lowering efficacy differs significantly between individuals partly owing to genetic factors. Rs1045642 in ABCB1, rs4241366 in SLCO2A1, rs9503012 in GMDS, rs10306114 in PTGS1, rs11568658 in MRP4, rs10786455 and rs6686438 in PTGFR were reported to be positive with the response to prostaglandin analogs in patients with glaucoma. A negative association was found between single nucleotide polymorphisms of PTGFR (rs11578155 and rs6672484) and the response to prostaglandin analogs in patients with glaucoma. The current review is an analysis of the information relevant to prostaglandin analog treatments based on previous literatures. It describes in detail the clinical pharmacology and pharmacogenetics of drugs belonging to this therapeutical class to provide a sound pharmacological basis for their proper use in ophthalmological clinical practice.

Long-term Effects of Latanoprost with Different Excipient Compositions on Intraocular Pressure, Hyperemia and Discomfort

Purpose: To compare the long-term effects of two preservative-free 0.005% latanoprost ophthalmic solutions with different excipient compositions on intraocular pressure (IOP), conjunctival hyperemia, and subjective ocular discomfort.Methods: The medical records of patients newly diagnosed with normal tension glaucoma or primary open angle glaucoma who started treatment using Xalost S® or Monoprost® were reviewed. IOP was measured with Goldmann applanation tonometry. Conjunctival hyperemia was measured with a Keratograph® 5M and subjective ocular discomfort was surveyed using a visual analog scale. Routine examinations were scheduled 1 week and 1, 3, 6, and 12 months after treatment. A generalized estimating equation was used to evaluate the changes of these parameters with time.Results: Xalost S® was used in 31 patients (60 eyes) and Monoprost® in 27 patients (50 eyes). The baseline characteristics were generally similar in the two groups with no significant differences. In the Xalost S® group, the IOP difference from baseline was significant at all time points (p < 0.001). However, in the Monoprost® group, after 1 month of treatment, the IOP difference decreased significantly (p = 0.054 at 1 week; p = 0.005 at 1 month; p < 0.001 after 1 month). Conjunctival hyperemia and subjective ocular discomfort did not differ significantly from baseline in either group.Conclusions: There was no significant difference in the frequency of side effects between the two drugs. The effect on the IOP drop was similar over time, but the initial IOP drop was greater in the Xalost S® group. This difference is presumed to be due to the different excipient compositions of the two drugs.

Phase 3, Randomized, 20-Month Study of the Efficacy and Safety of Bimatoprost Implant in Patients with Open-Angle Glaucoma and Ocular Hypertension (ARTEMIS 2)

Objective

To evaluate the intraocular pressure (IOP)-lowering efficacy and safety of 10 and 15 µg bimatoprost implant in patients with open-angle glaucoma (OAG) or ocular hypertension (OHT).

Methods

This randomized, 20-month, multicenter, masked, parallel-group, phase 3 trial enrolled 528 patients with OAG or OHT and an open iridocorneal angle inferiorly in the study eye. Study eyes were administered 10 or 15 µg bimatoprost implant on day 1, week 16, and week 32, or twice-daily topical timolol maleate 0.5%. Primary endpoints were IOP and IOP change from baseline through week 12. Safety measures included treatment-emergent adverse events (TEAEs) and corneal endothelial cell density (CECD).

Results

Both 10 and 15 µg bimatoprost implant met the primary endpoint of noninferiority to timolol in IOP lowering through 12 weeks. Mean IOP reductions from baseline ranged from 6.2–7.4, 6.5–7.8, and 6.1–6.7 mmHg through week 12 in the 10 µg implant, 15 µg implant, and timolol groups, respectively. IOP lowering was similar after the second and third implant administrations. Probabilities of requiring no IOP-lowering treatment for 1 year after the third administration were 77.5% (10 µg implant) and 79.0% (15 µg implant). The most common TEAE was conjunctival hyperemia, typically temporally associated with the administration procedure. Corneal TEAEs of interest (primarily corneal endothelial cell loss, corneal edema, and corneal touch) were more frequent with the 15 than the 10 µg implant and generally were reported after repeated administrations. Loss in mean CECD from baseline to month 20 was ~ 5% in 10 µg implant-treated eyes and ~ 1% in topical timolol-treated eyes. Visual field progression (change in the mean deviation from baseline) was reduced in the 10 µg implant group compared with the timolol group.

Conclusions

The results corroborated the previous phase 3 study of the bimatoprost implant. The bimatoprost implant met the primary endpoint and effectively lowered IOP. The majority of patients required no additional treatment for 12 months after the third administration. The benefit-risk assessment favored the 10 over the 15 µg implant. Studies evaluating other administration regimens with reduced risk of corneal events are ongoing. The bimatoprost implant has the potential to improve adherence and reduce treatment burden in glaucoma.

Clinicaltrials.gov Identifier

NCT02250651.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40265-021-01624-9.

The effect of topical bimatoprost on corneal clarity in primary open-angle glaucoma: a longitudinal prospective assessment

PURPOSE

To study the effect of topical bimatoprost on the corneal optical density values using a dual Scheimpflug Placido analysis system.

METHODS

This longitudinal case-control study included 18 patients with newly diagnosed primary open-angle glaucoma who received topical bimatoprost as a first-line treatment and 20 healthy individuals (age and sex-matched controls). Corneal densitometry data were obtained using the dual Scheimpflug analyzer at pre-treatment and 1st, 6th, 12th, 18th months of post-treatment. Repeated measures of ANOVA and Pearson correlation tests were used for statistical analysis.

RESULTS

There were statistically significant differences between pre-treatment and post-treatment 1st and 6th months corneal densitometry values (p < 0.001, p = 0.007, respectively). However, there was no statistically significant difference between the post-treatment 12th and 18th months (p > 0.05). Corneal densitometry values decreased during the 1st month. Intraocular pressure (IOP) differences were statistically significant between baseline and 1 month after treatment (P < 0.001), however not statistically significant between the 1st and 6th, 6th and 12th, 12th and 18th months after treatment (p > 0.05, for all). Corneal densitometry was not correlated with IOP (r = - 0.037, p = 0.44). In the control group, there was no statistically significant difference between baseline and post-baseline 18th-month corneal densitometry measurements (p > 0.05).

CONCLUSIONS

Topical bimatoprost administration might result in a decrease in corneal densitometry measurement. It is of clinical importance that topical bimatoprost administration can affect corneal transparency and cause a possible alteration in corneal properties.

Anti-fibrotic activity of a rho-kinase inhibitor restores outflow function and intraocular pressure homeostasis

Glucocorticoids are widely used as an ophthalmic medication. A common, sight-threatening adverse event of glucocorticoid usage is ocular hypertension, caused by dysfunction of the conventional outflow pathway. We report that netarsudil, a rho-kinase inhibitor, decreased glucocorticoid-induced ocular hypertension in patients whose intraocular pressures were poorly controlled by standard medications. Mechanistic studies in our established mouse model of glucocorticoid-induced ocular hypertension show that netarsudil both prevented and reduced intraocular pressure elevation. Further, netarsudil attenuated characteristic steroid-induced pathologies as assessed by quantification of outflow function and tissue stiffness, and morphological and immunohistochemical indicators of tissue fibrosis. Thus, rho-kinase inhibitors act directly on conventional outflow cells to prevent or attenuate fibrotic disease processes in glucocorticoid-induced ocular hypertension in an immune-privileged environment. Moreover, these data motivate the need for a randomized prospective clinical study to determine whether netarsudil is indeed superior to first-line anti-glaucoma drugs in lowering steroid-induced ocular hypertension.

Neuroinflammation in Primary Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is the second leading cause of irreversible blindness worldwide. Increasing evidence suggests oxidative damage and immune response defects are key factors contributing to glaucoma onset. Indeed, both the failure of the trabecular meshwork tissue in the conventional outflow pathway and the neuroinflammation process, which drives the neurodegeneration, seem to be linked to the age-related over-production of free radicals (i.e., mitochondrial dysfunction) and to oxidative stress-linked immunostimulatory signaling. Several previous studies have described a wide range of oxidative stress-related makers which are found in glaucomatous patients, including low levels of antioxidant defences, dysfunction/activation of glial cells, the activation of the NF-κB pathway and the up-regulation of pro-inflammatory cytokines, and so on. However, the intraocular pressure is still currently the only risk factor modifiable by medication or glaucoma surgery. This present review aims to summarize the multiple cellular processes, which promote different risk factors in glaucoma including aging, oxidative stress, trabecular meshwork defects, glial activation response, neurodegenerative insults, and the altered regulation of immune response.

Phase 3, Randomized, 20-Month Study of Bimatoprost Implant in Open-Angle Glaucoma and Ocular Hypertension (ARTEMIS 1)

PURPOSE

To evaluate the intraocular pressure (IOP)-lowering efficacy and safety of 10- and 15-μg bimatoprost implant in subjects with open-angle glaucoma (OAG) and ocular hypertension (OHT) after initial and repeated administrations.

DESIGN

Randomized, 20-month, multicenter, subject- and efficacy evaluator-masked, parallel-group, phase 3 clinical study.

PARTICIPANTS

Adults with OAG or OHT in each eye, open iridocorneal angle inferiorly in the study eye, and study eye baseline IOP (hour 0; 8 am) of 22-32 mmHg after washout.

METHODS

Study eyes received bimatoprost implant 10 μg (n = 198) or 15 μg (n = 198) on day 1 with readministration at weeks 16 and 32, or twice-daily topical timolol maleate 0.5% (n = 198). Intraocular pressure was measured at hours 0 and 2 at each visit.

MAIN OUTCOME MEASURES

Primary end points were IOP and change from baseline IOP through week 12. Safety measures included treatment-emergent adverse events (TEAEs) and corneal endothelial cell density (CECD).

RESULTS

Both dose strengths of bimatoprost implant were noninferior to timolol in IOP lowering after each administration. Mean diurnal IOP was 24.0, 24.2, and 23.9 mmHg at baseline and from 16.5-17.2, 16.5-17.0, and 17.1-17.5 mmHg through week 12 in the 10-μg implant, 15-μg implant, and timolol groups, respectively. The incidence of corneal and inflammatory TEAEs of interest (e.g., corneal endothelial cell loss, iritis) was higher with bimatoprost implant than timolol and highest with the 15-μg dose strength. Incidence of corneal TEAEs increased after repeated treatment; with 3 administrations at fixed 16-week intervals, incidence of ≥20% CECD loss was 10.2% (10-μg implant) and 21.8% (15-μg implant). Mean best-corrected visual acuity (BCVA) was stable; 3 implant-treated subjects with corneal TEAEs had >2-line BCVA loss at their last visit.

CONCLUSIONS

Both dose strengths of bimatoprost implant met the primary end point of noninferiority to timolol through week 12. One year after 3 administrations, IOP was controlled in most subjects without additional treatment. The risk-benefit assessment favored the 10-μg implant over the 15-μg implant. Ongoing studies are evaluating other administration regimens to reduce the potential for CECD loss. The bimatoprost implant has potential to improve adherence and reduce treatment burden in glaucoma.

Matrix Metalloproteinases and Glaucoma Treatment

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that degrade extracellular matrix (ECM) components such as collagen and have important roles in multiple biological processes, including development and tissue remodeling, both in health and disease. The activity of MMPs is influenced by the expression of MMPs and tissue inhibitors of metalloproteinase (TIMPs). In the eye, MMP-mediated ECM turnover in the juxtacanalicular region of the trabecular meshwork (TM) reduces outflow resistance in the conventional outflow pathway and helps maintain intraocular pressure (IOP) homeostasis. An imbalance in the MMP/TIMP ratio may be involved in the elevated IOP often associated with glaucoma. The prostaglandin analog/prostamide (PGA) class of topical ocular hypotensive medications used in glaucoma treatment reduces IOP by increasing outflow through both conventional and unconventional (uveoscleral) outflow pathways. Evidence from in vivo and in vitro studies using animal models and anterior segment explant and cell cultures indicates that the mechanism of IOP lowering by PGAs involves increased MMP expression in the TM and ciliary body, leading to tissue remodeling that enhances conventional and unconventional outflow. PGA effects on MMP expression are dependent on the identity and concentration of the PGA. An intracameral sustained-release PGA implant (Bimatoprost SR) in development for glaucoma treatment can reduce IOP for many months after expected intraocular drug bioavailability. We hypothesize that the higher concentrations of bimatoprost achieved in ocular outflow tissues with the implant produce greater MMP upregulation and more extensive, sustained MMP-mediated target tissue remodeling, providing an extended duration of effect.

How many aqueous humor outflow pathways are there?

The aqueous humor (AH) outflow pathways definition is still matter of intense debate. To date, the differentiation between conventional (trabecular meshwork) and unconventional (uveoscleral) pathways is widely accepted, distinguishing the different impact of the intraocular pressure on the AH outflow rate. Although the conventional route is recognized to host the main sites for intraocular pressure regulation, the unconventional pathway, with its great potential for AH resorption, seems to act as a sort of relief valve, especially when the trabecular resistance rises. Recent evidence demonstrates the presence of lymphatic channels in the eye and proposes that they may participate in the overall AH drainage and intraocular pressure regulation, in a presumably adaptive fashion. For this reason, the uveolymphatic route is increasingly thought to play an important role in the ocular hydrodynamic system physiology. As a result of the unconventional pathway characteristics, hydrodynamic disorders do not develop until the adaptive routes cannot successfully counterbalance the increased AH outflow resistance. When their adaptive mechanisms fail, glaucoma occurs. Our review deals with the standard and newly discovered AH outflow routes, with particular attention to the importance they may have in opening new therapeutic strategies in the treatment of ocular hypertension and glaucoma.

Prostaglandin receptor agonists as antiglaucoma agents (a patent review 2013 - 2018)

Introduction: Elevated intraocular pressure (IOP) is the most prevalent risk factor for glaucoma. Prostaglandin analogs are a first-line therapy for glaucoma due to their ability to reduce IOP, once-daily dosing, efficacy, and minimal side-effect profile. Many compounds targeting different PG receptors have been developed in the last years, some of them being in clinical use. Latanoprost, Bimatoprost, Travoprost, and Tafluprost are clinically used as antiglaucoma drugs and act as agonists of the PGF2α receptor. The inability to fully understand the mechanism of action of clinically used PGF2α analogs is thus a strong driver for additional research into the mechanism of action of ocular hypotensive drugs belonging to this class of pharmacological agents. Areas covered: This review explores the last 5 years (2013-2018), where many patents describing new compounds acting on different prostaglandin receptors, and mainly targeting EP1-4 and FP receptors, were released. Expert opinion: To date, there has been a growing awareness over recent years of the therapeutic use of novel derivatives as new antiglaucoma pharmaceutical products. Patents involved in discovering new approaches and new molecules for the treatment of glaucoma diseases encouraged the scientific community to increase the variety of drugs available for the treatment of ocular diseases.

Intraocular Pressure Effects and Mechanism of Action of Topical Versus Sustained-Release Bimatoprost

Purpose

To assess the intraocular pressure (IOP)-lowering effects of bimatoprost sustained-release implant (BimSR) in normotensive monkeys receiving topical bimatoprost.

Methods

Six eyes from six female, normotensive, cynomolgus monkeys were treated with once-daily topical latanoprost 0.005% plus twice-daily fixed-combination dorzolamide 2%/timolol 0.5%. At week 5, topical latanoprost was switched to once-daily topical bimatoprost 0.03% and twice-daily dorzolamide 2%/timolol 0.5% was continued. At week 8, BimSR 20 μg was administered intracamerally to three eyes and topical therapy was continued in all eyes. At week 12, all topical therapy was discontinued and animals were monitored for another 4 weeks. IOP was measured with a TonoVet rebound tonometer in nonsedated animals weekly for 16 weeks.

Results

Average mean (standard deviation) IOP was 19.8 (1.6) mm Hg at baseline, 15.7 (0.9) mm Hg during treatment with topical latanoprost/dorzolamide/timolol from weeks 1 to 5, and 14.2 (0.5) mm Hg during weeks 6 to 8 after topical latanoprost was switched to topical bimatoprost. After BimSR was added, average mean IOP during weeks 9 to 12 was 10.8 (1.3) mm Hg, a decrease of 3.9 mm Hg compared with the topical-only arm. When topical therapy was discontinued, IOP in BimSR-treated eyes remained below that in unmedicated eyes (15.8 [0.9] vs. 20.2 [0.2] mm Hg at weeks 14–16).

Conclusions

Intracameral BimSR has IOP-lowering effects additive to those of topical bimatoprost, suggesting an additional mechanism of action with intracameral drug delivery.

Translational Relevance

Compared with topical bimatoprost, intracameral BimSR may have an additional mechanism of action of IOP lowering.

Age-related changes in eye morphology and aqueous humor dynamics in DBA/2J mice using contrast-enhanced ocular MRI

PURPOSE

Here, we are testing the hypothesis that dynamic contrast enhanced MRI (DCE-MRI) is a useful approach for non-invasively evaluating age-related changes in aqueous humor outflow and its contribution to elevated intraocular pressure in the DBA/2J model of pigmentary glaucoma.

METHODS

A rodent-specific 7 T MRI was used to assess eye anatomy (anterior chamber (AC) and vitreous body (VB) morphology, eye size, lens size) and aqueous humor dynamics (via intravenous administration of Gd-DTPA and Gd-BOPTA contrast agents) in C57BL/6 and DBA/2J mice at 3 and 9 months of age.

RESULTS

Gd-MRI was used to demonstrate an anterior solute pathway into the mouse AC. Topical latanoprost treatment in C57BL/6J mice reduced Gd-BOPTA accumulation in the AC. Age-related increases in AC area, AC depth and eye size were observed in DBA/2J mice compared to C57BL/6J mice. The rate of Gd-DTPA accumulation and peak Gd-DTPA intensity was lowest in 9-month old DBA/2J mice compared to 3-month old DBA/2J mice and C57BL/6J mice at both ages. Leakage of Gd-DTPA posteriorly into the VB was also observed in 9-month old DBA/2J mice.

CONCLUSIONS

These studies support the idea that age-related changes in aqueous humor outflow contribute to elevated intraocular pressure (IOP) in the DBA/2J model of pigmentary glaucoma. Gd-MRI is a valuable tool for better understanding of mechanisms and dynamics of aqueous humor circulation in normal and glaucomatous mouse eyes or following topical administration of medicines to reduce IOP.

Pharmacological regulation of outflow resistance distal to Schlemm's canal

The trabecular meshwork (TM) and Schlemm's canal generate the majority of outflow resistance; however, the distal regions of the conventional outflow pathway account for 25-50% of total resistance. Sections of distal vessels are surrounded by α-smooth muscle actin-containing cells, indicating that they may be vasoregulated. This study examined the effect of a potent vasodilator, nitric oxide (NO), and its physiological antagonist, endothelin-1 (ET-1), on the regulation of outflow resistance in the distal regions of the conventional outflow pathway. Using a physiological model of the conventional outflow pathway, human and porcine anterior segments were perfused in organ culture under constant flow conditions, while intrachamber pressure was continually monitored. For porcine anterior segments, a stable baseline outflow facility with TM intact was first achieved before anterior segments were removed and a trabeculotomy was performed. For human anterior segments, a trabeculotomy was immediately performed. In human anterior segments, 100 nM ET-1 significantly decreased distal outflow facility from 0.49 ± 0.26 to 0.31 ±  0.18 (mean ± SD) µl·min^-1·mmHg, P < 0.01. Perfusion with 100 µM diethylenetriamine-NO in the presence of 1 nM ET-1 immediately reversed ET-1 effects, significantly increasing distal outflow facility to 0.54 ± 0.35 µl·min^-1·mmHg, P = 0.01. Similar results were obtained in porcine anterior segment experiments. Therefore, data show a dynamic range of resistance generation by distal vessels in both the human and the porcine conventional outflow pathways. Interestingly, maximal contraction of vessels in the distal outflow tract of trabeculotomized eyes generated resistance very near physiological levels for both species having an intact TM.

Biomechanical, ultrastructural, and electrophysiological characterization of the non-human primate experimental glaucoma model

Laser-induced experimental glaucoma (ExGl) in non-human primates (NHPs) is a common animal model for ocular drug development. While many features of human hypertensive glaucoma are replicated in this model, structural and functional changes in the unlasered portions of trabecular meshwork (TM) of laser-treated primate eyes are understudied. We studied NHPs with ExGl of several years duration. As expected, ExGl eyes exhibited selective reductions of the retinal nerve fiber layer that correlate with electrophysiologic measures documenting a link between morphologic and elctrophysiologic endpoints. Softening of unlasered TM in ExGl eyes compared to untreated controls was observed. The degree of TM softening was consistent, regardless of pre-mortem clinical findings including severity of IOP elevation, retinal nerve fiber layer thinning, or electrodiagnostic findings. Importantly, this softening is contrary to TM stiffening reported in glaucomatous human eyes. Furthermore, microscopic analysis of unlasered TM from eyes with ExGl demonstrated TM thinning with collapse of Schlemm's canal; and proteomic analysis confirmed downregulation of metabolic and structural proteins. These data demonstrate unexpected and compensatory changes involving the TM in the NHP model of ExGl. The data suggest that compensatory mechanisms exist in normal animals and respond to elevated IOP through softening of the meshwork to increase outflow.

Open-angle glaucoma: therapeutically targeting the extracellular matrix of the conventional outflow pathway

INTRODUCTION

Ocular hypertension in open-angle glaucoma is caused by a reduced rate of removal of aqueous humour (AH) from the eye, with the majority of AH draining from the anterior chamber through the conventional outflow pathway, comprising the trabecular meshwork (TM) and Schlemm's Canal. Resistance to outflow is generated, in part, by the extracellular matrix (ECM) of the outflow tissues. Current pressure-lowering topical medications largely suppress AH production, or enhance its clearance through the unconventional pathway. However, therapies targeting the ECM of the conventional pathway in order to decrease intraocular pressure have become a recent focus of attention. Areas covered: We discuss the role of ECM of the TM in outflow homeostasis and its relevance as a target for glaucoma therapy, including progress in development of topical eye formulations, together with gene therapy approaches based on inducible, virally-mediated expression of matrix metalloproteinases to enhance aqueous outflow. Expert opinion: There remains a need for improved glaucoma medications that more specifically act upon sites causative to glaucoma pathogenesis. Emerging strategies targeting the ECM of the conventional outflow pathway, or associated components of the cytoskeleton of TM cells, involving new pharmacological formulations or genetically-based therapies, are promising avenues of future glaucoma treatment.

Efficacy and safety of bimatoprost in glaucoma and ocular hypertension in non-responder patients

AIM

To establish the efficacy and safety of bimatoprost 0.03% monotherapy in glaucoma and ocular hypertension (OHT) patients with inadequate intraocular pressure (IOP)on current therapy.

METHODS

Pre- and post-switch IOPs were analyzed for 59 consecutive patients who were switched from current therapy to bimatoprost monotherapy between 2011-2015. Demographic information, diagnosis, and any adverse events were recorded. Change in IOP post-pre switch was analyzed using a 2-sided Student's paired t-test at the 5% significance level.

RESULTS

There was a statistically significant mean reduction in IOP at the first follow up visit, which was maintained at subsequent follow up visits for patients regardless of diagnosis, or pre-switch treatment (P<0.001). Subgroup analysis also demonstrated a statistically significant mean reduction in IOP when looking at OHT patients only, as well as patients with any diagnosis switched from latanoprost monotherapy to bimatoprost monotherapy (P<0.001).

CONCLUSION

This is the largest independent data set which supports switching glaucoma patients with poor response to current treatment onto bimatoprost monotherapy before considering other adjuvant medical or more invasive therapy.

Evaluating intraocular pressure-lowering solutions for the treatment of open-angle glaucoma: comparison between bimatoprost 0.03% and bimatoprost 0.01% - an observational switch study

PURPOSE

The purpose of this study is to evaluate the intraocular pressure (IOP)-lowering efficacy of bimatoprost 0.01% solution in patients with primary open-angle glaucoma (POAG), who were switched from bimatoprost 0.03% solution, compared to patients with POAG who continued on bimatoprost 0.03% solution.

METHODS

A retrospective review evaluated 35 patients (35 right eyes [OD], 34 left eyes [OS]) who remained on bimatoprost 0.03% and 30 patients (27 OD, 30 OS) who were switched to bimatoprost 0.01% during the period January 8, 2010 to December 26, 2012. Mean IOP was measured 6 and 3 months before the switch, at switch, and 3, 6, and 12 months after the switch. Hyperemia scores were recorded before and after the switch and were compared to a picture scale.

RESULTS

Mean IOP in the group that switched was 16.96±5.03 mmHg in OD and 17.67±5.33 mmHg in OS at baseline. Mean IOP postswitch to bimatoprost 0.01% solution was 17.60±4.34 mmHg in OD and 17.00±3.37 mmHg in OS. IOP was not significantly reduced in either OD or OS postswitch to bimatoprost 0.01% (P₁=0.5 OD, P₂=0.2 OS). The hyperemia scores improved remarkably when bimatoprost 0.03% solution was switched to bimatoprost 0.01% solution (P<0.001).

CONCLUSION

To our knowledge, this is the first switch study evaluating the hypotensive efficacy and tolerability of bimatoprost in a group of patients with open-angle glaucoma. In this study comparing bimatoprost 0.03% and 0.01% solution, we found improved tolerability postswitch to 0.01% from 0.03% bimatoprost, similar efficacy between the two concentrations before and after switch in the same patient population, and similar IOPs comparable to nonswitch bimatoprost 0.03% solution.

Stanniocalcin-1 Is an Ocular Hypotensive Agent and a Downstream Effector Molecule That Is Necessary for the Intraocular Pressure-Lowering Effects of Latanoprost

Purpose

To identify downstream signaling molecules through which intraocular pressure (IOP) is lowered following treatment with the prostaglandin analog latanoprost.

Methods

Total RNA and protein isolated from primary human Schlemm's canal cells (n = 3) treated with latanoprost (free acid; 100 nM) were processed for quantitative PCR and Western blot analysis. IOP was evaluated in stanniocalcin-1 (STC-1^−/−) and wild-type mice following treatment with latanoprost or Rho kinase inhibitor Y27632. Human anterior segment pairs (n = 8) were treated with recombinant STC-1 (5, 50, or 500 ng/mL) and pressure was recorded using custom-designed software. The effect of recombinant STC-1 (0.5 mg/mL) on IOP was evaluated in wild-type mice. Tissue morphology was evaluated by light and transmission electron microscopy.

Results

Increased STC-1 mRNA (4.0- to 25.2-fold) and protein expression (1.9- to 5.1-fold) was observed within 12 hours following latanoprost treatment. Latanoprost reduced IOP in wild-type mice (22.0% ± 1.9%), but had no effect on STC-1^−/− mice (0.5% ± 0.7%). In contrast, Y27632 reduced IOP in both wild-type (12.5% ± 1.2%) and in STC-1^−/− mice (13.1% ± 2.8%). Human anterior segments treated with STC-1 (500 ng/mL) showed an increase in outflow facility (0.15 ± 0.03 to 0.27 ± 0.09 μL/min/mm Hg) while no change was observed in paired vehicle-treated controls. Recombinant STC-1 reduced IOP in wild-type mice by 15.2% ± 3.0%. No observable morphologic changes were identified between treatment groups when evaluated by microscopy.

Conclusions

Latanoprost-induced reduction of IOP is mediated through the downstream signaling molecule STC-1. When used by itself, STC-1 exhibits ocular hypotensive properties.

Unconventional aqueous humor outflow: A review

Aqueous humor flows out of the eye primarily through the conventional outflow pathway that includes the trabecular meshwork and Schlemm's canal. However, a fraction of aqueous humor passes through an alternative or 'unconventional' route that includes the ciliary muscle, supraciliary and suprachoroidal spaces. From there, unconventional outflow may drain through two pathways: a uveoscleral pathway where aqueous drains across the sclera to be resorbed by orbital vessels, and a uveovortex pathway where aqueous humor enters the choroid to drain through the vortex veins. We review the anatomy, physiology and pharmacology of these pathways. We also discuss methods to determine unconventional outflow rate, including direct techniques that use radioactive or fluorescent tracers recovered from tissues in the unconventional pathway and indirect methods that estimate unconventional outflow based on total outflow over a range of pressures. Indirect methods are subject to a number of assumptions and generally give poor agreement with tracer measurements. We review the variety of animal models that have been used to study conventional and unconventional outflow. The mouse appears to be a promising model because it captures several aspects of conventional and unconventional outflow dynamics common to humans, although questions remain regarding the magnitude of unconventional outflow in mice. Finally, we review future directions. There is a clear need to develop improved methods for measuring unconventional outflow in both animals and humans.

The many faces of the trabecular meshwork cell

With the combined purpose of facilitating useful vision over a lifetime, a number of ocular cells have evolved specialized features not found elsewhere in the body. The trabecular meshwork (TM) cell at the irido-corneal angle, which is a key regulator of intraocular pressure, is no exception. Examination of cells in culture isolated from the human TM has shown that they are unique in many ways, displaying characteristic features of several different cell types. Thus, these neural crest derived cells display expression patterns and behaviors typical of endothelia, fibroblasts, smooth muscle and macrophages, owing to the multiple roles and two distinct environments where they operate to maintain intraocular pressure homeostasis. In most individuals, TM cells function normally over a lifetime in the face of persistent stressors, including phagocytic, oxidative, mechanical and metabolic stress. Study of TM cells isolated from ocular hypertensive eyes has shown a compromised ability to perform their daily duties. This review highlights the many responsibilities of the TM cell and its challenges, progress in our understanding of TM biology over the past 30 years, as well as discusses unanswered questions about TM dysfunction that results in IOP dysregulation and glaucoma.

The exit strategy: Pharmacological modulation of extracellular matrix production and deposition for better aqueous humor drainage

Primary open angle glaucoma (POAG) is an optic neuropathy and an irreversible blinding disease. The etiology of glaucoma is not known but numerous risk factors are associated with this disease including aging, elevated intraocular pressure (IOP), race, myopia, family history and use of steroids. In POAG, the resistance to the aqueous humor drainage is increased leading to elevated IOP. Lowering the resistance and ultimately the IOP has been the only way to slow disease progression and prevent vision loss. The primary drainage pathway comprising of the trabecular meshwork (TM) is made up of relatively large porous beams surrounded by extracellular matrix (ECM). Its juxtacanalicular tissue (JCT) or the cribriform meshwork is made up of cells embedded in dense ECM. The JCT is considered to offer the major resistance to the aqueous humor outflow. This layer is adjacent to the endothelial cells forming Schlemm's canal, which provides approximately 10% of the outflow resistance. The ECM in the TM and the JCT undergoes continual remodeling to maintain normal resistance to aqueous humor outflow. It is believed that the TM is a major contributor of ECM proteins and evidence points towards increased ECM deposition in the outflow pathway in POAG. It is not clear how and from where the ECM components emerge to hinder the normal aqueous humor drainage. This review focuses on the involvement of the ECM in ocular hypertension and glaucoma and the mechanisms by which various ocular hypotensive drugs, both current and emerging, target ECM production, remodeling, and deposition.

Effects of Latanoprost and Bimatoprost on the Expression of Molecules Relevant to Ocular Inflow and Outflow Pathways

BACKGROUND AND PURPOSE

The intraocular pressure (IOP)-lowering and side effects in response to different prostaglandin F2α analogues can be variable, but, the underlying basis for this difference remains unknown. This study investigated the differential changes of cellular proteins relevant to IOP-lowering effects of latanoprost and bimatoprost.

METHODS

The human T lymphoblast (MOLT-3) cell line and immortalized human trabecular meshwork (iHTM) cells were studied by quantitative PCR and by immunofluorescence after treatment with either latanoprost or bimatoprost. New Zealand white rabbit eyes were treated topically with each agent and, following euthanasia, anterior segment tissues were studied with immunostaining.

RESULTS

In cultured MOLT-3 cells, mRNA expression of both c-fos and matrix metalloproteinase 9 increased significantly in response to each agent. In addition, there was little change in tissue inhibitor of metalloproteinase (TIMP)-3 mRNA, but a significant decrease in TIMP-4. Fibronectin mRNA in MOLT-3 cells was down-regulated with bimatoprost, but was up-regulated with latanoprost. Immunofluorescence analysis of iHTM cells showed that intracellular fibronectin was significantly decreased by bimatoprost, but was increased by latanoprost. Both latanoprost and bimatoprost increased mRNA expression of NF-кB p65 and decreased that of IкBα. Aquaporin-1 mRNA expression was significantly down-regulated by bimatoprost. Immunostaining also revealed a significant decrease of aquaporin-1 in the ciliary epithelium of New Zealand white rabbits after bimatoprost treatment.

CONCLUSIONS

Similarities in protein expression produced by latanoprost and bimatoprost in vitro may be relevant to the mechanism for their IOP-lowering effects in vivo. Differences in fibronectin expression and in aquaporin-1 expression in response to each agent may contribute to variability in the IOP-lowering efficacy in some studies.

Efficacy and tolerability of prostaglandin-timolol fixed combinations: an updated systematic review and meta-analysis

BACKGROUND

Prostaglandin-timolol fixed combinations (PG-timolol FCs) are now widely used to reduce intraocular pressure in patients with glaucoma. The efficacy and tolerability of these drugs are worthy of further exploration. An updated systematic review and meta-analysis was performed to assess the clinical efficacy and tolerability of the three PG-timolol FCs.

METHODS

Pertinent randomized, controlled trials were identified through systematic searches of PubMed, Embase, the Cochrane central register of controlled trials and the Chinese Biomedicine Database. The main efficacy measures were the weighted mean differences (WMDs) for the reduction from baseline to end of treatment in IOP at 9 am, 12 pm and 4 pm and diurnal curve. The main tolerability measures were the odds ratios (ORs) for the incidence of conjunctival hyperemia.

RESULTS

Nine studies involving 991 patients were included in the meta-analysis. Latanoprost-timolol FC (LTFC) and travoprost-timolol FC (TTFC) were not significantly different in lowering IOP at diurnal mean, 9 am, 12 pm and 4 pm. Bimatoprost-timolol FC (BTFC) provided significantly greater efficacy in lowering IOP at the three measurement time points and over the mean diurnal curve than LTFC (diurnal curve: WMD = 0.88 mmHg [95% CI, 0.42 to 1.33]; 9 am: WMD = 1.27 mmHg [0.68 to 1.86]; 12 pm: WMD = 1.16 mmHg [0.85 to 1.46]; 4 pm: WMD = 0.61 mmHg [0.51 to 0.70]) and TTFC (diurnal curve: WMD = 1.94 mmHg [0.19 to 3.68]; 9 am: WMD = 0.68 mmHg [0.15 to 1.21]; 12 pm: WMD = 0.90 mmHg [0.41 to 1.39]; 4 pm: WMD = 1.06 mmHg [0.61 to 1.51]). The incidence of hyperemia was significantly higher with BTFC than LTFC (pooled ORs: 1.85 [1.09 to 3.13]). The incidence of hyperemia was not significantly higher with TTFC than LTFC (pooled ORs: 2.52 [0.85 to 7.46]), and was not significantly higher with BTFC than TTFC (pooled OR: 1.65 [0.48 to 5.70]).

CONCLUSIONS

BTFC provided significantly greater efficacy in lowering IOP at diurnal mean, 9 am, 12 pm and 4 pm than LTFC and TTFC. LTFC was as effective as TTFC in lowering IOP at the four measurement time points and BTFC caused conjunctival hyperemia in more patients than LTFC. Further clinical trials are needed because of the limited number of studies.

The prostaglandin f2α analog fluprostenol attenuates the fibrotic effects of connective tissue growth factor on human trabecular meshwork cells

Abstract Purpose: The trabecular meshwork (TM) outflow pathways of the aqueous humor show an increase in extracellular matrix in patients with primary open-angle glaucoma (POAG). The increase in TM extracellular matrix appears to be caused by transforming growth factor-β signaling and its downstream mediator connective-tissue growth factor (CTGF). Here we studied whether treatment with the prostaglandin F2α analog fluprostenol modulates the CTGF-mediated increase of the TM extracellular matrix.

METHODS

Human TM cells from 3 different donors were treated with CTGF (50 ng/mL) and/or fluprostenol (10(-6) M and 10(-7) M) and were analyzed by real-time reverse transcription polymerase chain reaction and Western blotting. Cell supernatants of the treated cells were analyzed by zymography.

RESULTS

Treatment with CTGF induced the expression and synthesis of CTGF, fibronectin, collagen type IV and VI, while treatment with fluprostenol alone had no effects. The effects of CTGF were blocked by 1-h pretreatment with fluprostenol in a dose-dependent manner. Treatment with fluprostenol or combined fluprostenol/CTGF induced the activity of matrix metalloproteinase 2 (MMP2) in TM cells, whereas treatment with CTGF alone had no effects on MMP2 activity.

CONCLUSIONS

Fluprostenol blocks the fibrotic effects of CTGF on human TM cells and increases the activity of MMP2. Both effects have the distinct potential to attenuate a CTGF-mediated increase in TM extracellular matrix in patients with POAG and any effects on TM outflow resistance that may result from that.

Endogenous Bioactive Lipids and the Regulation of Conventional Outflow Facility

Perturbation of paracrine signaling within the human conventional outflow pathway influences tissue homeostasis and outflow function. For example, exogenous introduction of the bioactive lipids, sphingosine-1-phosphate, anandamide or prostaglandin F(2α), to conventional outflow tissues alters the rate of drainage of aqueous humor through the trabecular meshwork, and into Schlemm's canal. This review summarizes recent data that characterizes endogenous bioactive lipids, their receptors and associated signaling partners in the conventional outflow tract. We also discuss the potential of targeting such signaling pathways as a strategy for the development of therapeutics to treat ocular hypertension and glaucoma.

Effects of prostaglandin analogues on aqueous humor outflow pathways

Elevated intraocular pressure (IOP) is the most prevalent risk factor for glaucoma. All treatments, whether surgical or pharmaceutical, are aimed at lowering IOP. Prostaglandin analogues are a first line therapy for glaucoma due to their ability to reduce IOP, once-daily dosing, efficacy, and minimal side-effect profile. Whereas prostaglandin analogues have been known to alter aqueous humor outflow through the unconventional (uveoscleral) pathway, more recent evidence suggests their action also occurs through the conventional (trabecular) pathway. Understanding how prostaglandin analogues successfully lower IOP is important, as this information may lead to the discovery of new molecular targets for future therapeutic intervention. This review explores the current understanding of prostaglandin analogue biology as it pertains to IOP reduction and improved aqueous humor outflow facility.

Ghrelin in ocular pathophysiology: from the anterior to the posterior segment

Ghrelin is a 28 amino acid acylated peptide produced in several organs that binds the growth hormone secretagogues receptor type 1a (GHSR-1a). It acts over a wide range of systems, e.g. the endocrine, cardiovascular, musculoskeletal and immune systems and the eye. The aim of this work is to review the physiologic and pathologic implications of the ghrelin-GHSR-1a in the eye. A systematic revision of studies published between 2000 and 2013 in English, Spanish or Portuguese in MEDLINE, EMBASE and Scopus was performed. Search words used included: ghrelin, GHSR-1a, ocular production, iris muscular kinetics, ciliary body, glaucoma, retinopathy and uvea. The production of ghrelin by the ocular tissue has been detected both in the anterior and posterior segments, as well as the presence of GHSR-1a. This peptide promotes the relaxation of the iris sphincter and dilator muscles, being this effect independent from GHSR-1a and dependent on prostaglandins release in the first case and dependent on GHSR-1a in the second. Regarding ocular pathology, ghrelin levels in the aqueous humor appear to be decreased in individuals with glaucoma. Moreover, ghrelin has been shown to decrease the intraocular pressure in animal models of ocular hypertension through GHSR-1a. In the posterior segment, the ghrelin-GHSR-1a system interferes with the development of oxygen-induced retinopathy, being protective in the vaso-obliterative phase and deleterious in the vaso-proliferative stage of the disease. Thus, the ghrelin-GHSR-1a system presents as a possible local regulatory mechanism in the eye, with pathophysiological implications, constituting a target for future clinical and therapeutic research and interventions.

Recent progress in prostaglandin F2α ethanolamide (prostamide F2α) research and therapeutics

Prostamide (prostaglandin ethanolamide) research emerged from two distinct lines of research: 1) the unique pharmacology of the antiglaucoma drug bimatoprost and 2) the discovery that endocannabinoid anandamide was converted by COX-2 to a series of electrochemically neutral prostaglandin (PG) ethanolamides. Bimatoprost pharmacology was found to be virtually identical to that of prostamide F2α. The earliest studies relied on comparison of agonist potencies compared with PGF2α and synthetic prostaglandin F2α (FP) receptor agonists. The subsequent discovery of selective and potent prostamide receptor antagonists (AGN 211334-6, as shown in Fig. 3) was critical for distinguishing between prostamide and FP receptor-mediated effects. The prostamide F2α receptor was then modeled by cotransfecting the wild-type FP receptor with an mRNA splicing variant (altFP4).Bimatoprost is now used therapeutically for treating both glaucoma and eyelash hypotrichosis. Bimatoprost also stimulates hair growth in isolated human scalp hair follicles. A strong effect is also seen in mouse pelage hair, where bimatoprost essentially halves the onset of hair regrowth and the time to achieve full hair regrowth in shaved mice. Beyond glaucoma and hair growth, bimatoprost has potential for reducing fat deposition. Studies to date suggest that preadipocytes are the cellular target for bimatoprost. The discovery of the enzyme prostamide/PGF synthase was invaluable in elucidating the anatomic distribution of prostamide F2α. High expression in the central nervous system provided the impetus for later studies that described prostamide F2α as a nociceptive mediator in the spinal cord. At the translational level, bimatoprost has already provided therapeutics in two distinct areas and the use of both prostamide agonists and antagonists may provide other useful medicaments.

Differential effects of prostaglandin E2-sensitive receptors on contractility of human ocular cells that regulate conventional outflow

PURPOSE

The goal of this study was to functionally compare prostaglandin E2 (PGE2)-sensitive receptors in human primary cells involved in conventional outflow.

METHODS

The expression profile of prostaglandin (PG) receptors in primary cultures of human trabecular meshwork (TM) and Schlemm's canal (SC) cells were determined by quantitative-PCR. The functional activities of endogenous PGE2-sensitive receptors were evaluated using subtype-selective agonists and antagonists with cell impedance technology.

RESULTS

Agonist-sensitive EP1, EP2, and EP4 receptors were present in TM cells, all increasing cell stiffness (or contractility) in a dose-dependent manner. Rank order of efficacy (Emax) for agonists in TM cells were EP1 greater than EP2 greater than EP4 with EC50 1.1 μM, 0.56 μM, and 0.1 μM, respectively, and no functional EP3 receptors were found. Of the four EP receptor subtypes active in SC cells, EP1 and EP3 receptor activation increased cell stiffness, while EP2 and EP4 agonists dose-dependently decreased cell stiffness 47% and 23% with EC50 values of 170 nM and 69 nM, respectively. Consistent with these observations, the Rho kinase inhibitor Y-27632 decreased cell impedance (stiffness) of TM and SC cells (∼60%), while Rho GTPase activator thrombin caused cell impedance to increase in both cell types (168%-190%).

CONCLUSIONS

Cell impedance positively correlates with cellular stiffness/contractility. Because EP2/4 receptors caused decreased cell stiffness in SC, but not in TM cells, both receptors appear to mediate IOP lowering via changes in SC cell stiffness in the conventional outflow pathway.

Current understanding of conventional outflow dysfunction in glaucoma

PURPOSE OF REVIEW

Regulation of intraocular pressure by the conventional (trabecular) outflow pathway is complicated, involving a myriad of mechanical and chemical signals. In most, intraocular pressure is maintained within a tight range over a lifetime. Unfortunately in some, dysfunction results in ocular hypertension and open-angle glaucoma. In the context of established knowledge, this review summarizes recent investigations of conventional outflow function, with the goal of identifying areas for future inquiry and therapeutic targeting.

RECENT FINDINGS

Mechanical stimulation of conventional outflow cells due to intraocular pressure fluctuations impacts contractility, gene expression, pore formation, enzyme activity, and signaling. Numerous local signaling mediators in the conventional pathway such as bioactive lipids, cytokines, nitric oxide, and nucleotides participate in the regulation of outflow. Interestingly outflow through the conventional pathway is not uniform, but segmental, with passageways constantly changing due to focal protease activity of trabecular cells clearing extracellular matrix materials. The relationship between extracellular matrix expression and trabecular meshwork contractility appears to coordinately impact outflow resistance and is the target of a new class of drugs, the Rho kinase inhibitors.

SUMMARY

The conventional outflow pathway is a dynamic, pressure-sensitive tissue that is vulnerable to pathology on many fronts, each representing a therapeutic opportunity.

Unique response profile of trabecular meshwork cells to the novel selective glucocorticoid receptor agonist, GW870086X

PURPOSE

Glucocorticoid (GC)-induced glaucoma is an undesirable side effect of traditional GCs. Ocular hypertension responsible for GC-induced glaucoma is due to alterations in conventional outflow homeostasis. The present study evaluates a novel selective GC receptor agonist (SEGRA), GW870086X, in two different in vitro models of the human conventional outflow pathway.

METHODS

Primary cultures of human trabecular meshwork (TM) cell monolayers were treated with dexamethasone (DEX), prednisolone (PRED), or GW870086X for 5 days and then assayed for cellular expression and secretion of fibronectin, myocilin, tissue plasminogen activator (tPA), and/or matrix metalloproteinase-2 (MMP2). In parallel, TM cell monolayers on permeable filters treated for 5 days with GCs were assayed for changes in hydraulic conductivity.

RESULTS

All three GCs increased fibronectin and myocilin secretion in a concentration-dependent manner (P < 0.05). In addition, DEX increased cellular fibronectin and both DEX and PRED significantly increased cellular myocilin (P < 0.0001), while GW870086X did neither. Interestingly, DEX and PRED significantly decreased tPA expression (P ≤ 0.01), while GW870086X had the opposite effect and increased tPA expression in a concentration-dependent manner (P = 0.01). For MMP2, only DEX treatment consistently decreased secretion (P < 0.01). In a functional assay, only PRED treatment significantly decreased hydraulic conductivity of TM cell monolayers (P < 0.05).

CONCLUSIONS

All three GCs induced differential responses from TM cells. While the novel SEGRA GW870086X increases fibronectin and myocilin secretion similar to two traditional GCs, effects on the matrix degradation enzymes MMP2 and tPA differed significantly, suggesting that GW870086X favors matrix turnover. Consequently, effects on conventional outflow homeostasis may also be dissimilar.

Therapeutic uses of prostaglandin F(2α) analogues in ocular disease and novel synthetic strategies

The pharmacological management of glaucoma and ocular hypertension has significantly changed over the last 18 years with the introduction of PGF2α analogues, more specifically latanoprost (6), travoprost (8), bimatoprost (10) and tafluprost (12). Prostanoids are currently the first-line medicines among ocular antihypertensive drugs in terms of efficacy, safety, patient compliance and medical economy. Their ability to effectively reduce intraocular pressure with once-per-day dosing, ocular tolerability comparable to timolol and general lack of systemic adverse effects have made them the mainstay of pharmacological therapy for glaucoma and ocular hypertension all over the world. The present review reports a novel, convergent and highly diastereoselective method for the synthesis of PGF2α analogues from the structurally advanced prostaglandin phenylsulfone (5Z)-(+)-15 and new ω-chain synthons. The biochemistry, clinical efficacy and side effects of four commercially available PGF2α analogues, currently used as first-line agents for reducing intraocular pressure in patients with glaucoma or ocular hypertension, are also discussed.

The biodisposition and hypertrichotic effects of bimatoprost in mouse skin

Studies on bimatoprost were performed with two objectives: (i) to determine whether bimatoprost possesses hair growth-stimulating properties beyond eyelash hypertrichosis and (ii) to investigate the biodisposition of bimatoprost in skin for the first time. Bimatoprost, at the dose used clinically for eyelash growth (0.03%) and given once daily for 14 days, increased pelage hair growth in C57/black 6 mice. This occurred as a much earlier onset of new hair growth in shaved mice and the time taken to achieve complete hair regrowth, according to photographic documentation and visual assessment. Bimatoprost biodisposition in the skin was determined at three concentrations: 0.01%, 0.03% and 0.06%. Dose-dependent C_max values were obtained (3.41, 6.74, 12.3 μg/g tissue), and cutaneous bimatoprost was well maintained for 24 h following a single dose. Bimatoprost was recovered from the skin only as the intact molecule, with no detectable levels of metabolites. Thus, bimatoprost produces hypertrichosis as the intact molecule.

Clinical options for the reduction of elevated intraocular pressure

Elevated IOP in clinical practice is usually seen in glaucoma or ocular hypertension. Glaucoma affects 60 million people worldwide and 8.4 million are bilaterally blind from this chronic disease.1 Options for reducing IOP rely on pharmacological agents, laser treatments and surgery which may be penetrating or non-penetrating. The last twenty years has seen significant changes in all of these strategies. This review aims to cover these clinical options and introduce some of the new technologies currently in development for the clinical lowering of IOP.

Efficacy and safety of switching from topical latanoprost to bimatoprost in patients with normal-tension glaucoma

PURPOSE

The aim of this study was to evaluate the efficacy and safety of bimatoprost in Japanese patients with normal-tension glaucoma (NTG) who showed insufficient response to latanoprost.

METHODS

A prospective, nonrandomized study was conducted in patients with NTG, with ≤20% intraocular pressure (IOP) decrease from pretreatment baseline with latanoprost monotherapy who had been switched to bimatoprost. The IOP was measured at 4, 8, and 12 weeks after the switch to bimatoprost. In 12 weeks after the switch to bimatoprost, efficacy and safety were evaluated.

RESULTS

Postswitch to bimatoprost, IOP was significantly reduced at every visit. Bimatoprost produced significantly greater mean% IOP reduction rate from pretreatment than that of latanoprost at week 12 (P<0.01). There was a significant correlation between% IOP reduction of bimatoprost and that of latanoprost (Pearson r(2)=0.374; P=0.007). No significant difference was observed in the mean scores of conjunctival hyperemia and corneal epithelial disorder between bimatoprost-treated eyes and latanoprost-treated eyes.

CONCLUSIONS

Significant additional IOP lowering was achieved by switching to bimatoprost in Japanese patients with NTG with insufficient response to latanoprost. Bimatoprost treatment was safe and well tolerated.

Recent advances in pharmacotherapy of glaucoma

Glaucoma is a slow progressive degeneration of the retinal ganglion cells (RGCs) and the optic nerve axons, leading to irreversible blindness if left undiagnosed and untreated. Although increased intraocular pressure is a major risk factor of glaucoma, other factors include increased glutamate levels, alterations in nitric oxide (NO) metabolism, vascular alterations and oxidative damage caused by reactive oxygen species. Glaucoma is the second leading cause of blindness globally, accounting for 12.3% of the total blindness. Glaucoma has been broadly classified as primary or secondary open-angle or angle-closure glaucoma. The primary goal in management of glaucoma is to prevent the risk factor, especially elevated intraocular pressure (IOP), using medications, laser therapy or conventional surgery. The first-line treatment of glaucoma usually begins with the use of a topical selective or nonselective blocker or a prostaglandin analog. Second-line drugs of choice include alpha-agonists and topical carbonic anhydrase inhibitors. Cholinergic agonists are considered third-line treatment options. When a single therapy is not sufficient to lower the IOP, a combination therapy is indicated. To enhance the patient compliance, drug delivery systems like electronic devices, ocular inserts, tansdermal and mechanical drug delivery systems have been developed. Use of viscoelastic agents in ophthalmic formulations, emulsions and soluble ophthalmic drug inserts (SODI) enhance patience compliance and ocular drug delivery in patients in long-term glaucoma therapy. For patients who do not respond to antiglaucoma medications, laser trabeculoplasty and incisional surgery are recommended. Several nutrients and botanicals hold promise for the treatment of glaucoma, but most studies are preliminary, and larger, controlled studies are required. Future directions for the development of a novel therapy glaucoma may target glutamate inhibition, NMDA receptor blockade, exogenously applied neurotrophins, open channel blockers, antioxidants, protease inhibitors and gene therapy.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Endothelin antagonism as an active principle for glaucoma therapy

Endothelin, the most potent vasoactive peptide known to date, has been suggested to play a potential role in the pathogenesis of open-angle glaucoma. Open-angle glaucoma is the most common optic nerve head neuropathy and is associated with a loss of retinal ganglion cells and visual field damage. Although an increased intraocular pressure is a major risk factor for glaucomatous optic neuropathy, other factors such as a reduced ocular blood flow play an important role for appearance of the disease. Thus, treatment of glaucoma is focused on lowering of intraocular pressure and preventing the occurrence or progression of glaucomatous optic neuropathy. Endothelin participates in the regulation of intraocular pressure by an effect on trabecular outflow, the main route for aqueous humour outflow from the eye. Trabecular outflow is modulated by trabecular meshwork contractility which is affected by endothelin. In addition to the effects of endothelin in the anterior part of the eye, the vasoconstrictor causes a decrease in ocular blood flow followed by pathological changes in the retina and the optic nerve head which is assumed to contribute to the degeneration of retinal ganglion cells. In sum, inhibition of endothelin signalling leads to lowering of intraocular pressure and exerts neuroprotective effects. Thus, endothelin antagonism in the eye represents a promising approach for pharmacological treatment of glaucoma.

Clinical utility and differential effects of prostaglandin analogs in the management of raised intraocular pressure and ocular hypertension

Prostaglandin analogs (PGA) are powerful topical ocular hypotensive agents available for the treatment of elevated intraocular pressure (IOP). Latanoprost 0.005% and travoprost 0.004% are prodrugs and analogs of prostaglandin F2α. Bimatoprost 0.03% is regarded as a prostamide, and debate continues as to whether it is a prodrug. The free acids of all 3 PGAs reduce IOP by enhancing uveoscleral and trabecular outflow via direct effects on ciliary muscle relaxation and remodeling of extracellular matrix. The vast majority of clinical trials demonstrate IOP-lowering superiority of latanoprost, bimatoprost and travoprost compared with timolol 0.5%, brimonidine 0.2%, or dorzolamide 2% monotherapy. Bimatoprost appears to be more efficacious in IOP-lowering compared with latanoprost, with weighted mean difference in IOP reduction documented in one meta-analysis of 2.59% to 5.60% from 1- to 6-months study duration. PGAs reduce IOP further when used as adjunctive therapy. Fixed combinations of latanoprost, bimatoprost or travoprost formulated with timolol 0.5% and administered once daily are superior to monotherapy of its constituent parts. PGA have near absence of systemic side effects, although do have other commonly encountered ocular adverse effects. The adverse effects of PGA, and also those found more frequently with bimatoprost use include ocular hyperemia, eyelash growth, and peri-ocular pigmentary changes. Iris pigmentary change is unique to PGA treatment. Once daily administration and near absence of systemic side effects enhances tolerance and compliance. PGAs are often prescribed as first-line treatment for ocular hypertension and open-angle glaucoma.

Cellular basis for bimatoprost effects on human conventional outflow

PURPOSE

Bimatoprost is a widely used ocular hypotensive agent to treat glaucoma. It lowers intraocular pressure in humans by increasing both pressure-independent (uveoscleral) and pressure-dependent (conventional) aqueous humor outflow. The present study specifically examines bimatoprost effects on the cells that populate human outflow tissues.

METHODS

The authors tested for prostamide receptor activation in primary cultures of human trabecular meshwork (TM), Schlemm's canal (SC), and ciliary smooth muscle (CSM) cells using cellular dielectric spectroscopy (CDS).

RESULTS

The authors observed that bimatoprost produced an immediate and concentration-dependent increase in cell monolayer impedance for TM, SC, and CSM cells with EC(50) values of 4.3, 1.2, and 1.7 nM, respectively; corresponding to decreased cell contractility. Notably, in TM, SC, and CSM cells, bimatoprost was approximately equipotent to the selective FP receptor agonists fluprostenol and 17-phenyl PGF(2α). Bimatoprost effects were insensitive to cholera toxin and pertussis toxin but were abolished by phorbol 12-myristate 13-acetate pretreatment, suggesting Gq-involvement in cell signaling. The effects of bimatoprost on TM and SC cells were inhibited by the prostamide receptor antagonist AGN211334, with IC(50) values of 1.2 and 3.3 μM, respectively. Interestingly, AGN211334 behaved as an apparent inverse agonist in CDS assays involving TM cells but as a neutral prostamide antagonist with SC cells.

CONCLUSIONS

Taken together, results suggest that bimatoprost specifically activates receptors in both cell types of the human conventional outflow pathway to modify intraocular pressure. However, only TM cell monolayers appear to have autocrine, or agonist-independent, receptor signaling that is sensitive to a prostamide receptor antagonist.

Bimatoprost - a review

Bimatoprost is a synthetic prostamide analog that is efficacious in the treatment of open-angle glaucoma, ocular hypertension and other forms of glaucoma. It reduces intraocular pressure (IOP) by increasing uveoscleral and trabecular outflow. When used as a 0.03% topical preparation once daily, it demonstrates sustained lowering of IOP of 7 - 8 mmHg over a 24-h period. The drug has been found to be more effective than timolol. In some studies it has shown greater ability to lower IOP when compared with other prostaglandin analogs; whereas in others all three clinically used prostaglandin analogs were found to be equally effective. It shows good IOP reduction when used in combination with other glaucoma medications. A common side effect includes mild conjunctival hyperemia, which is generally reversible. Other side effects include periorbital pigmentation, discomfort, ocular surface hyperemia and skin changes. Pharmacoeconomic data indicate that bimatoprost is cost effective in the treatment of open-angle glaucoma.