Cellular basis for bimatoprost effects on human conventional outflow

From Eye Care to Hair Growth: Bimatoprost

BACKGROUND

Bimatoprost has emerged as a significant medication in the field of medicine over the past several decades, with diverse applications in ophthalmology, dermatology, and beyond. Originally developed as an ocular hypotensive agent, it has proven highly effective in treating glaucoma and ocular hypertension. Its ability to reduce intraocular pressure has established it as a first-line treatment option, improving management and preventing vision loss. In dermatology, bimatoprost has shown promising results in the promotion of hair growth, particularly in the treatment of alopecia and hypotrichosis. Its mechanism of action, stimulating the hair cycle and prolonging the growth phase, has led to the development of bimatoprost-containing solutions for enhancing eyelash growth.

AIM

The aim of our review is to provide a brief description, overview, and studies in the current literature regarding the versatile clinical use of bimatoprost in recent years. This can help clinicians determine the most suitable individualized therapy to meet the needs of each patient.

METHODS

Our methods involve a comprehensive review of the latest advancements reported in the literature in bimatoprost formulations, which range from traditional eye drops to sustained-release implants. These innovations offer extended drug delivery, enhance patient compliance, and minimize side effects.

RESULTS

The vast literature published on PubMed has confirmed the clinical usefulness of bimatoprost in lowering intraocular pressure and in managing patients with glaucoma. Numerous studies have shown promising results in dermatology and esthetics in promoting hair growth, particularly in treating alopecia and hypotrichosis. Its mechanism of action involves stimulating the hair cycle and prolonging the growth phase, leading to the development of solutions that enhance eyelash growth. The global use of bimatoprost has expanded significantly, with applications growing beyond its initial indications. Ongoing research is exploring its potential in glaucoma surgery, neuroprotection, and cosmetic procedures.

CONCLUSIONS

Bimatoprost has shown immense potential for addressing a wide range of therapeutic needs through various formulations and advancements. Promising future perspectives include the exploration of novel delivery systems such as contact lenses and microneedles to further enhance drug efficacy and patient comfort. Ongoing research and future perspectives continue to shape its role in medicine, promising further advancements and improved patient outcomes.

Next generation therapeutics for retinal neurodegenerative diseases

Neurodegenerative diseases affecting the visual system encompass glaucoma, macular degeneration, retinopathies, and inherited genetic disorders such as retinitis pigmentosa. These ocular pathologies pose a serious burden of visual impairment and blindness worldwide. Current treatment modalities include small molecule drugs, biologics, or gene therapies, most of which are administered topically as eye drops or as injectables. However, the topical route of administration faces challenges in effectively reaching the posterior segment and achieving desired concentrations at the target site, while injections and implants risk severe complications, such as retinal detachment and endophthalmitis. This necessitates the development of innovative therapeutic strategies that can prolong drug release, deliver effective concentrations to the back of the eye with minimal systemic exposure, and improve patient compliance and safety. In this review, we introduce retinal degenerative diseases, followed by a discussion of the existing clinical standard of care. We then delve into detail about drug and gene delivery systems currently in preclinical and clinical development, including formulation and delivery advantages/drawbacks, with a special emphasis on potential for clinical translation.

FP and EP2 prostanoid receptor agonist drugs and aqueous humor outflow devices for treating ocular hypertension and glaucoma

Prostaglandin (PG) receptors represent important druggable targets due to the many diverse actions of PGs in the body. From an ocular perspective, the discovery, development, and health agency approvals of prostaglandin F (FP) receptor agonists (FPAs) have revolutionized the medical treatment of ocular hypertension (OHT) and glaucoma. FPAs, such as latanoprost, travoprost, bimatoprost, and tafluprost, powerfully lower and control intraocular pressure (IOP), and became first-line therapeutics to treat this leading cause of blindness in the late 1990s to early 2000s. More recently, a latanoprost-nitric oxide (NO) donor conjugate, latanoprostene bunod, and a novel FP/EP3 receptor dual agonist, sepetaprost (ONO-9054 or DE-126), have also demonstrated robust IOP-reducing activity. Moreover, a selective non-PG prostanoid EP2 receptor agonist, omidenepag isopropyl (OMDI), was discovered, characterized, and has been approved in the United States, Japan and several other Asian countries for treating OHT/glaucoma. FPAs primarily enhance uveoscleral (UVSC) outflow of aqueous humor (AQH) to reduce IOP, but cause darkening of the iris and periorbital skin, uneven thickening and elongation of eyelashes, and deepening of the upper eyelid sulcus during chronic treatment. In contrast, OMDI lowers and controls IOP by activation of both the UVSC and trabecular meshwork outflow pathways, and it has a lower propensity to induce the aforementioned FPA-induced ocular side effects. Another means to address OHT is to physically promote the drainage of the AQH from the anterior chamber of the eye of patients with OHT/glaucoma. This has successfully been achieved by the recent approval and introduction of miniature devices into the anterior chamber by minimally invasive glaucoma surgeries. This review covers the three major aspects mentioned above to highlight the etiology of OHT/glaucoma, and the pharmacotherapeutics and devices that can be used to combat this blinding ocular disease.

Medical Therapy and Scleral Windows for Uveal Effusion Syndrome: A Case Series and Literature Review

INTRODUCTION

Uveal effusion syndrome (UES) is a rare ocular disease causing idiopathic uveal effusion, often with associated ciliochoroidal and retinal detachment. UES diagnosis is challenging because of overlapping features with other ocular inflammatory, neoplastic, iatrogenic, and drug-induced causes of uveal effusion. While several successful surgical treatments have been described, such as full-thickness or partial-thickness sclerectomy, medical therapies may also have a therapeutic role.

OBJECTIVE

To provide an updated review of the published literature on the course of the disease, medical and surgical management strategies, as well as newer treatment modalities.

Remodeling of the Lamina Cribrosa: Mechanisms and Potential Therapeutic Approaches for Glaucoma

Glaucomatous optic neuropathy is the leading cause of irreversible blindness in the world. The chronic disease is characterized by optic nerve degeneration and vision field loss. The reduction of intraocular pressure remains the only proven glaucoma treatment, but it does not prevent further neurodegeneration. There are three major classes of cells in the human optic nerve head (ONH): lamina cribrosa (LC) cells, glial cells, and scleral fibroblasts. These cells provide support for the LC which is essential to maintain healthy retinal ganglion cell (RGC) axons. All these cells demonstrate responses to glaucomatous conditions through extracellular matrix remodeling. Therefore, investigations into alternative therapies that alter the characteristic remodeling response of the ONH to enhance the survival of RGC axons are prevalent. Understanding major remodeling pathways in the ONH may be key to developing targeted therapies that reduce deleterious remodeling.

The Latest Drugs in Development That Reduce Intraocular Pressure in Ocular Hypertension and Glaucoma

Glaucoma causes irreversible vision loss, with elevated intraocular pressure (IOP) being the only known modifiable risk factor. There are a variety of medical and interventional options for lowering IOP; however, despite these treatments, glaucoma continues to be a leading cause of visual impairment. Further research continues to strive for treatment options with improved side effect profiles, additional IOP-lowering effects, and ease of use. This review provides a brief summary of current IOP-lowering therapies and then outlines pipeline ocular hypotensive agents, their mechanisms of action, benefits, and side effect profiles. Advancements are seen within currently used eye drop classes such as prostaglandin analogues, Rho kinase inhibitors and nitric oxide donors, whilst there are also new drug classes, such as tyrosine protein kinase activators. Most developing drugs are topical drop formulations, with a number already having entered Phase III trials. Alternative drug delivery methods are also in development and will be briefly discussed. Pharmacological and drug delivery developments continue to provide glaucoma patients and clinicians with new options and the promise of better outcomes, particularly in terms of improved tolerance and reduced frequency of dosing.

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.

Application of Cell Impedance as a Screening Tool to Discover Modulators of Intraocular Pressure

Purpose: To identify new targets and compounds involved in mediating cellular contractility or relaxation in trabecular meshwork (TM) cells and test their efficacy in an ex vivo model measuring outflow facility. Methods: A low-molecular weight compound library composed of 3,957 compounds was screened for cytoskeletal changes using the Acea xCelligence impedance platform in immortalized human NTM5 TM cells. Hits were confirmed by 8-point concentration response and were subsequently evaluated for impedance changes in 2 primary human TM strains, as well as cross-reactivity in bovine primary cells. A recently described bovine whole eye perfusion system was used to evaluate effects of compounds on aqueous outflow facility. Results: The primary screen conducted was robust, with Z' values >0.5. Fifty-two compounds were identified in the primary screen and confirmed to have concentration-dependent effects on impedance in NTM5 cells. Of these, 9 compounds representing distinct drug classes were confirmed to modulate impedance in both human primary TM cells and bovine cells. One of these compounds, wortmannin, an inhibitor of phosphoinositide 3-kinase, increased outflow facility by 11%. Conclusions: A robust phenotypic assay was developed that enabled identification of contractility modulators in immortalized TM cells. The screening hits were translatable to primary TM cells and modulated outflow facility in an ex vivo perfusion assay.

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.

Label-Free Whole Cell Biosensing for High-Throughput Discovery of Activators and Inhibitors Targeting G Protein-Activated Inwardly Rectifying Potassium Channels

Dynamic mass redistribution (DMR) and cellular dielectric spectroscopy (CDS) are label-free biosensor technologies that capture real-time integrated cellular responses upon exposure to extra- and intracellular stimuli. They register signaling routes that are accompanied by cell shape changes and/or molecular movement of cells proximal to the biosensor to which they are attached. Here, we report the unexpected observation that robust DMR and CDS signatures are also elicited upon direct stimulation of G protein-activated inwardly rectifying potassium (GIRK) channels, which are involved in the regulation of excitability in the heart and brain. Using ML297, a small-molecule GIRK activator, along with channel blockers and cytoskeletal network inhibitors, we found that GIRK activation exerts its effects on cell shape by a mechanism which depends on actin but not the microtubule network. Because label-free real-time biosensing (i) quantitatively determines concentration dependency of GIRK activators, (ii) accurately assesses the impact of GIRK channel blockers, (iii) is high throughput-compatible, and (iv) visualizes previously unknown cellular consequences downstream of direct GIRK activation, we do not only provide a novel experimental strategy for identification of GIRK ligands but also an entirely new angle to probe GIRK (ligand) biology. We envision that DMR and CDS may add to the repertoire of technologies for systematic exploitation of ion channel function and, in turn, to the identification of novel GIRK ligands in order to treat cardiovascular and neurological disorders.

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.

Prostanoid Receptor Antagonist Effects on Intraocular Pressure, Supported by Ocular Biodisposition Experiments

PURPOSE

Since all prostanoid receptors affect intraocular pressure (IOP) and endogenous prostanoids are found in ocular tissues, the pressor effects of prostanoid antagonists were comprehensively evaluated. The absence of effects of most of these antagonists was not entirely anticipated. To ensure no false-negative results, ocular biodisposition studies were conducted.

METHODS

Monkeys with laser-induced ocular hypertension were used to study antagonist effects on IOP. Ocular biodisposition of each antagonist was assessed in rabbits, with LC/MS/MS analyses of tissue extracts and blood.

RESULTS

EP₁, EP₂, EP₃, EP₄, FP, IP, and TP prostanoid receptor antagonists did not affect IOP, even at a high 1% dose. These studies were followed by ocular biodisposition studies. Striking differences in ocular tissue bioavailability were observed, which were independent of solubility. Only the EP₁ antagonist SC-51322 failed to penetrate sufficiently to be bioavailable in the aqueous humor and ciliary body/iris. This obliged testing an alternative EP₁ antagonist, namely ONO-8713, to reliably conclude that an EP₁ antagonist does not alter IOP.

CONCLUSIONS

These antagonist studies provided no evidence for individual endogenous prostanoids exerting a meaningful role in regulating IOP. They do reaffirm the critical importance of studying ocular bioavailability for confirming negative data. Large differences among the antagonists in anterior segment and even ocular surface tissue biodisposition were observed in rabbits. It appears from these monkey studies, supported by rabbit ocular bioavailability data, that an absence of drug effect in the eye cannot be adequately substantiated without determination of ocular pharmacokinetics.

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.

Prostaglandins in the eye: Function, expression, and roles in glaucoma

Prostaglandins are small pro-inflammatory molecules derived from arachidonic acid that play roles in a multitude of biological processes including, but not limited to, inflammation, pain modulation, allergies, and bone formation. Prostaglandin analogues are the front-line medications for the treatment of glaucoma, a condition resulting in blindness due to the death of retinal ganglion cells. These drugs act by lowering intraocular pressure (IOP), a major risk factor for glaucoma. The currently used prostaglandin analogues (latanoprost, bimatoprost, tafluprost, and travoprost) mimic PGF2 and target one of the prostaglandin receptors (FP), though research into harnessing the other receptors using compounds like Sulprostone (EP3 receptor), or Iloprost (IP receptor) are currently ongoing. In this review, we summarize the research into each of the prostaglandin molecules (PGD2, PGE2, PGF2, PGI2, TXA2) and their respective receptors (DP, EP1, 2, 3, 4, FP, IP). We examine the modes of action of each of these receptors, their expression, their role in aqueous humour production and outflow within the eye, as well as their roles as medications for the treatment of glaucoma.

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.

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.

Ocular pharmacokinetics of bimatoprost formulated in DuraSite compared to bimatoprost 0.03% ophthalmic solution in pigmented rabbit eyes

PURPOSE

To compare the aqueous humor (AH) and iris-ciliary body (ICB) concentration of bimatoprost in rabbit eyes treated with ISV-215 (0.03% bimatoprost formulated in DuraSite) with the marketed product bimatoprost 0.03% ophthalmic solution.

METHODS

The left eye of rabbits received a single topical instillation of either ISV-215 (n = 32 eyes) or bimatoprost 0.03% (n = 32 eyes). At predetermined time points, levels of bimatoprost and bimatoprost acid in the AH and the ICB were quantified by HPLC-MS/MS.

RESULTS

Both bimatoprost and bimatoprost acid were detected in the AH and the ICB within 15 minutes of dosing. Bimatoprost acid concentrations in both compartments were markedly higher than bimatoprost. There was a statistically significant (P < 0.01) increase in the concentration of the prodrug in the AH and its acid form in the ICB in animals treated with ISV-215 compared to bimatoprost 0.03%. In the ISV-215-treated rabbit eyes, the highest concentrations of bimatoprost and bimatoprost acid were in the ICB and AH, respectively, while in the bimatoprost 0.03%-treated eyes, no differences in the drug content of the selected ocular tissues were observed.

CONCLUSIONS

Bimatoprost 0.03% formulated in DuraSite has superior ocular distribution and area under the curve compared to bimatoprost 0.03% in rabbit eyes. This improvement in the pharmacokinetic parameters of ISV-215 may provide us with a better platform to optimize a bimatoprost formulation that offers the same degree of efficacy in lowering intraocular pressure and improved therapeutic index in glaucomatous patients by lessening the ocular side effects associated with long-term use of topical prostaglandin F2α analogs.

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.

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.

Protein markers and differentiation in culture for Schlemm's canal endothelial cells

The two cell types that populate the human conventional outflow pathway, Schlemm's canal (SC) and trabecular meshwork (TM) regulate intraocular pressure. In culture, SC and TM cells have been useful tools toward understanding their respective roles in conventional outflow homeostasis. Unfortunately, currently available protein markers that distinguish SC from TM cells are limited, motivating the present study. Antibodies that specifically recognize different vascular endothelial markers were used to probe lysates from mature cell monolayers subjected to SDS-PAGE followed by western blot analyses. Results show that SC and TM cells both expressed many of the endothelial candidate proteins investigated, such as Robo1/4, Tie2/TEK, VEGF-R1/R2, VCAM-1, eNOS and neuropilin-1. In contrast, all SC cell strains tested (n=11) expressed two proteins, fibulin-2 and vascular endothelial (VE) cadherin, not expressed by TM cells. To examine changes in VE-cadherin expression and cell-cell junction formation, indicated by transendothelial electrical resistance (TEER), SC cells were seeded onto filters at confluence and growth factors were withdrawn. Culturing cells in media containing adult bovine serum rather than fetal bovine serum resulted in a 75% mean increase in TEER and 67% corresponding average increase in VE-cadherin expression (p<0.05). While both TM and SC cells form monolayers, are contact inhibited, share some endothelial responsibilities and several endothelial protein markers, SC cells uniquely express at least two proteins which likely reflect a distinction in cellular responsibilities in vivo. One of these responsibilities, maintenance of the blood-aqueous barrier, can be modeled in culture upon withdrawal of growth factors from SC cell monolayers.

Comparison of human ocular distribution of bimatoprost and latanoprost

PURPOSE

This study investigated the ocular distribution of bimatoprost, latanoprost, and their acid hydrolysis products in the aqueous humor, cornea, sclera, iris, and ciliary body of patients treated with a single topical dose of 0.03% bimatoprost or 0.005% latanoprost for understanding concentration-activity relationships.

METHODS

Thirty-one patients undergoing enucleation for an intraocular tumor not affecting the anterior part of the globe were randomized to treatment with bimatoprost or latanoprost at 1, 3, 6 or 12 h prior to surgery. Concentrations of bimatoprost, bimatoprost acid, latanoprost, and latanoprost acid in the human aqueous and ocular tissues were measured using liquid chromatography tandem mass spectrometry.

RESULTS

Following topical administration, intact bimatoprost was distributed in human eyes with a rank order of cornea/sclera >iris/ciliary body >aqueous humor. Bimatoprost acid was also detected in these tissues, where its low levels in the cornea relative to that of latanoprost acid indicated that bimatoprost hydrolysis was limited. Latanoprost behaved as a prodrug that entered eyes predominantly via the corneal route. Levels of latanoprost acid were distributed as cornea >>aqueous humor>iris>sclera>ciliary body.

CONCLUSIONS

Our study provided experimental evidence that levels of bimatoprost in relevant ocular tissues, and not only aqueous humor, are needed to understand the mechanisms by which bimatoprost lowers intraocular pressure (IOP) in human subjects. The data suggest that bimatoprost reached the target tissues favoring the conjunctival/scleral absorption route. Findings of intact bimatoprost in the target ciliary body indicated its direct involvement in reducing IOP. However, bimatoprost acid may have only a limited contribution on the basis that bimatoprost has greater/similar IOP-lowering efficacy than latanoprost, yet bimatoprost acid levels were a fraction of latanoprost acid levels in the aqueous humor and cornea and only sporadically detectable in the ciliary body. In this report, human ocular tissues were examined concurrently with aqueous humor for the in vivo distribution of bimatoprost, bimatoprost acid, latanoprost, and latanoprost acid.

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.

A model of giant vacuole dynamics in human Schlemm's canal endothelial cells

Aqueous humour transport across the inner wall endothelium of Schlemm's canal likely involves flow through giant vacuoles and pores, but the mechanics of how these structures form and how they influence the regulation of intraocular pressure (IOP) are not well understood. In this study, we developed an in vitro model of giant vacuole formation in human Schlemm's canal endothelial cells (HSCECs) perfused in the basal-to-apical direction (i.e., the direction that flow crosses the inner wall in vivo) under controlled pressure drops (2 or 6 mmHg). The system was mounted on a confocal microscope for time-lapse en face imaging, and cells were stained with calcein, a fluorescent vital dye. At the onset of perfusion, elliptical void regions appeared within an otherwise uniformly stained cytoplasm, and 3-dimensional reconstructions revealed that these voids were dome-like outpouchings of the cell to form giant vacuole-like structures or GVLs that reproduced the classic "signet ring" appearance of true giant vacuoles. Increasing pressure drop from 2 to 6 mmHg increased GVL height (14 ± 4 vs. 21 ± 7 μm, p < 0.0001) and endothelial hydraulic conductivity (1.15 ± 0.04 vs. 2.11 ± 0.49 μl min⁻¹ mmHg⁻¹ cm⁻²; p < 0.001), but there was significant variability in the GVL response to pressure between cell lines isolated from different donors. During perfusion, GVLs were observed "migrating" and agglomerating about the cell layer and often collapsed despite maintaining the same pressure drop. GVL formation was also observed in human umbilical vein and porcine aortic endothelial cells, suggesting that giant vacuole formation is not a unique property of Schlemm's canal cells. However, in these other cell types, GVLs were rarely observed "migrating" or contracting during perfusion, suggesting that Schlemm's canal endothelial cells may be better adapted to withstand basal-to-apical directed pressure gradients. In conclusion, we have established an in vitro model system to study giant vacuole dynamics, and we have demonstrated that this system reproduces key aspects of giant vacuole morphology and behaviour. This model offers promising opportunities to investigate the role of endothelial cell biomechanics in the regulation of intraocular pressure in normal and glaucomatous eyes.