Unoprostone isopropyl rescues retinal progenitor cells from apoptosisin vitro

Neuroaxonal and cellular damage/protection by prostanoid receptor ligands, fatty acid derivatives and associated enzyme inhibitors

Cellular and mitochondrial membrane phospholipids provide the substrate for synthesis and release of prostaglandins in response to certain chemical, mechanical, noxious and other stimuli. Prostaglandin D₂, prostaglandin E₂, prostaglandin F_2α, prostaglandin I₂ and thromboxane-A₂ interact with five major receptors (and their sub-types) to elicit specific downstream cellular and tissue actions. In general, prostaglandins have been associated with pain, inflammation, and edema when they are present at high local concentrations and involved on a chronic basis. However, in acute settings, certain endogenous and exogenous prostaglandins have beneficial effects ranging from mediating muscle contraction/relaxation, providing cellular protection, regulating sleep, and enhancing blood flow, to lowering intraocular pressure to prevent the development of glaucoma, a blinding disease. Several classes of prostaglandins are implicated (or are considered beneficial) in certain central nervous system dysfunctions (e.g., Alzheimer’s, Parkinson’s, and Huntington’s diseases; amyotrophic lateral sclerosis and multiple sclerosis; stroke, traumatic brain injuries and pain) and in ocular disorders (e.g., ocular hypertension and glaucoma; allergy and inflammation; edematous retinal disorders). This review endeavors to address the physiological/pathological roles of prostaglandins in the central nervous system and ocular function in health and disease, and provides insights towards the therapeutic utility of some prostaglandin agonists and antagonists, polyunsaturated fatty acids, and cyclooxygenase inhibitors.

Looking into the Eyes—In Vitro Models for Ocular Research

Animal research undoubtedly provides scientists with virtually unlimited data but inflicts pain and suffering on animals. Currently, legislators and scientists alike are promoting alternative in vitro approaches allowing for an accurate evaluation of processes occurring in the body without animal sacrifice. Historically, one of the most infamous animal tests is the Draize test, mainly performed on rabbits. Even though this test was considered the gold standard for around 50 years, the Draize test fails to mimic human response mainly due to human and rabbit eye physiological differences. Therefore, many alternative assays were developed to evaluate ocular toxicity and drug effectiveness accurately. Here we review recent achievements in tissue engineering of in vitro 2D, 2.5D, 3D, organoid and organ-on-chip ocular models, as well as in vivo and ex vivo models in terms of their advantages and limitations.

Effect of topical isopropyl unoprostone on macular atrophy progression in eyes with exudative age-related macular degeneration

BACKGROUND

To evaluate the efficacy and safety of topical isopropyl unoprostone (IU) in treating macular atrophy in age-related macular degeneration (AMD) patients.

METHODS

Fifty-two AMD patients with macular atrophy were included and randomly assigned (1:1) to the treatment (topical 0.15% IU) or placebo group. Subjects used study eye drops 3 times a day for 54 weeks. The macular atrophy was documented on fundus autofluorescence photographs and measured using RegionFinder. The enlargement rate of macular atrophy and the changes in visual acuity were examined statistically between baseline and 54 weeks.

RESULTS

Forty-eight subjects were included in the analyses because 4 subjects withdrew from the study. The differences between the IU and placebo groups in mean and median area of macular atrophy were not statistically significant at baseline. The baseline median lesion size of macular atrophy was 2.33 mm in the IU group and 1.63 mm in the placebo group (P = 0.51). The intergroup difference in the enlargement ratio of macular atrophy (21 ± 15% in the IU group and 111 ± 96% in the placebo group) was statistically significant (P < 0.001). Additionally, visual acuity tended to improve over baseline in the IU group. No serious adverse events were observed.

CONCLUSIONS

Topical IU therapy is safe and effective for treating macular atrophy in AMD patients.

Natural compounds and retinal ganglion cell neuroprotection

Glaucoma, the second leading cause of blindness in the world, is a chronic optic neuropathy often associated with increased intraocular pressure and characterized by progressive retinal ganglion cell (RGC) axons degeneration and death leading to typical optic nerve head damage and distinctive visual field defects. Although the pathogenesis of glaucoma is still largely unknown, it is hypothesized that RCGs become damaged through various insults/mechanisms, including ischemia, oxidative stress, excitotoxicity, defective axonal transport, trophic factor withdrawal, and neuroinflammation. In this review, we summarize the potential benefits of several natural compounds for RGCs neuroprotection.

Therapeutic efficacy of topical unoprostone isopropyl in retinitis pigmentosa

PURPOSE

To evaluate the therapeutic effect of topical unoprostone isopropyl (unoprostone) on patients with retinitis pigmentosa (RP).

METHODS

Forty patients with typical forms of RP were included in the study.Seventeen of 40 patients were treated with 0.12% topical unoprostone twice daily in a randomly selected eye. Patients underwent follow-up examinations every 3 months after treatment. The efficacy of the treatment was monitored by visual acuity and visual field measurement testing using the Humphrey Field Analyzer (HFA: the central 10-2 programme). Moreover, 12 RP patients who were included this study and 12 normal subjects were evaluated in terms of their macular blood flow of both eyes after instillation of unoprostone using the laser speckle method.

RESULTS

One year after treatment, the 'macular sensitivity', calculated by HFA as the average sensitivity of the central 12 points, was preserved in the fellow eyes as well as the unoprostone-treated eyes. On the other hand, that in the eyes of the control RP patient was significantly decreased. Moreover, there were significantly greater improvements of the 'macular sensitivity' in the unoprostone-treated eyes than the fellow eyes. The change ratios of macular blood flow obtained from both RP patients and normal subjects were significantly increased in both the treated and the fellow eyes. No severe side-effects were observed.

CONCLUSIONS

These results demonstrate that topical unoprostone might have a therapeutic efficacy in patients with RP as a consequence of the macular bloodflow improvement as well as its direct neuroprotective effect.

An evidence-based review of unoprostone isopropyl ophthalmic solution 0.15% for glaucoma: place in therapy

Glaucoma is a progressive, neurodegenerative optic nerve disease that can cause significant visual morbidity and affects over 60 million people worldwide. The only known modifiable risk factor for glaucoma at this time is elevated intraocular pressure (IOP), which may be treated with medications, laser therapy, and/or incisional surgery. Topical ocular medications are commonly used as first-line therapy for glaucoma, although side effects may limit their use. Unoprostone is a novel 22-carbon ocular hypotensive agent that may be advantageous in treating some patients with open angle glaucoma or ocular hypertension. Unlike the 20-carbon prostanoids, such as latanoprost, that lower IOP primarily through an increase in uveoscleral outflow, unoprostone may lower IOP through increased aqueous outflow via the conventional trabecular meshwork pathway. Although not as efficacious as other prostanoids, unoprostone is effective for IOP reduction both as monotherapy and adjunctive therapy with timolol. Unoprostone has decreased affinity for the prostaglandin F2α receptor, which may explain its well tolerated ocular and systemic side effect profile compared with other prostanoids.

Regeneration of optic nerve fibers with unoprostone, a prostaglandin-related antiglaucoma drug, in adult cats

PURPOSE

We investigated the effects of unoprostone on neurite extension of cultured retinal pieces and axonal regeneration of retinal ganglion cells in the crushed optic nerve of adult cats.

METHODS

The retinal pieces were cultured with unoprostone or its primary metabolite, M1, dissolved in DMSO or polysorbate for 14 days, and the number and length of Tau-1-positive neurites and glial processes labeled with anti-glial fibrillary acidic protein antibodies were examined. After the optic nerve was crushed, unoprostone was injected into the vitreous body and the crushed site. On day 12, wheat germ agglutinin-conjugated horseradish peroxidase was injected into the vitreous body to anterogradely label the regenerated axons. On day 14, the optic nerve was excised and longitudinally sectioned. After peroxidase reaction, the number of axons regenerating beyond the crush site was examined.

RESULTS

The greatest number of neurites protruded from the cultured retinal pieces in 3 μM unoprostone and 3 μM M1. The neurite length was also the longest at 3 μM unoprostone and 3 μM M1, in which no glial processes were detected. After injections of 3 μM unoprostone, the final concentration in the vitreous humor, into the vitreous body and the crush site, the optic nerve fibers regenerated and extended beyond the crush site. In contrast, almost no fibers extended beyond the crush site after injection of phosphate-buffered saline.

CONCLUSIONS

The results indicate that intravitreal injection of unoprostone promotes regeneration of crushed optic nerve fibers in adult cats.

Current status of unoprostone for the management of glaucoma and the future of its use in the treatment of retinal disease

INTRODUCTION

Optic nerve and retinal diseases such as glaucoma, age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are significant public health concerns and have a momentous impact on patients' functional status and quality of life. These diseases are among the most common causes of visual impairment worldwide and account for billions of dollars in healthcare expenditures and lost productivity. The importance of adequate treatment of these conditions and the need for efficacious therapeutic drugs cannot be overstated. Unoprostone continues to be developed as a potential treatment for these debilitating diseases.

AREAS COVERED

This review provides background information on unoprostone isopropyl (unoprostone), a prostanoid and synthetic docosanoid approved for the treatment of open-angle glaucoma and ocular hypertension, and recapitulates safety and efficacy data as it relates to this indication. Additionally, this review describes potential new uses of unoprostone as therapy for dry AMD and RP. A literature search of peer-reviewed publications was performed utilizing PubMed. Searches were last updated on 10 September 2012.

EXPERT OPINION

Current data indicate that unoprostone does significantly lower intraocular pressure (IOP) and has a favorable safety and tolerability profile. However, the IOP-lowering effects of unoprostone do not compare with other commercially available prostanoids and it has the disadvantage of a twice-daily rather than once-daily dosing regimen. Nonetheless, recent data suggest that unoprostone may improve neuronal survival and increase ocular blood flow, indicating that it may have some value as a therapy for glaucoma, RP and dry AMD. Further studies are needed to confirm whether unoprostone provides any clinically significant advantage over the other commercially available prostanoids.

Topical isopropyl unoprostone for retinitis pigmentosa: microperimetric results of the phase 2 clinical study

Introduction

The purpose of this study was to determine whether topical 0.15% isopropyl unoprostone (IU), a BK-channel activator, could improve or maintain the central retinal sensitivity in patients with middle- to late-stage retinitis pigmentosa (RP). IU was approved for glaucoma and ocular hypertension in 1994. The drug re-profiling strategy is one of the effective ways to develop safe drugs for patients with RP.

Methods

A randomized, double-blind, and placebo-controlled phase II safety/efficacy trial was conducted. One hundred and nine patients with middle- to late-stage RP having a visual acuity of ≥0.5 were studied at six ophthalmological centers in Japan. The treatments of IU/day were divided into three groups: placebo group; two-drop group; and four-drop group for 24 weeks. The primary outcome measure was changes in the retinal sensitivity from baseline in the central 2° determined by MP-1 microperimetry (MP-1, Nidek, Japan). The secondary outcomes were changes in best-correct visual acuity, contrast sensitivity, retinal sensitivity of the central 10° by MP-1, mean deviation (MD) by a Humphrey field analyzer (HFA; Carl Zeiss Meditec, Dublin, CA, USA) 10-2, and the Visual Functioning Questionnaire 25 (VFQ-25) questionnaire scores.

Results

There was a tendency for a dose-dependent responsiveness in retinal sensitivity in the central 2°, MD, and total VFQ-25 score after 24 weeks of IU instillation by a simple linear regression analysis. A stratified analysis showed a significant dose-dependent responsiveness of the 2° central retinal sensitivity in more advanced patients (P = 0.028). The number of patients having a ≥4 dB decrease in the primary outcome measure was significantly fewer in the four-drop group than in the placebo group (P = 0.02). No adverse reactions were observed.

Conclusions

A higher dose of IU can delay progression of the central retinal sensitivity decrease through an improvement of retinal sensitivity.

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.

Tafluprost protects rat retinal ganglion cells from apoptosis in vitro and in vivo

BACKGROUND

To investigate whether tafluprost, which is a prostaglandin-related compound and an anti-glaucoma drug, has a direct anti-apoptotic effect in cultured retinal ganglion cells (RGCs) and rat RGCs in retinas with optic nerve crush (ONC).

METHODS

RGC-5 cells were induced to undergo apoptosis by a serum deprivation and by exogenous glutamate. The level of cell death with or without tafluprost was monitored by an XTT assay and by immunocytochemistry with activated caspase-3. Changes in intracellular calcium ([Ca(2+)]i) levels were measured with fluo-4 fluorescence. Rat RGCs were degenerated by ONC. After topical instillation of tafluprost for 7 and 14 days, the numbers of retrograde-labeled RGCs were counted. Retinal flatmounts were subjected to terminal dUTP nick end labeling (TUNEL) staining to detect apoptotic cells.

RESULTS

Tafluprost dose-dependently promoted RGC-5 cell viability with an optimum concentration of 3 microM (p = 0.006). Tafluprost significantly reduced caspase-3-positive cells and suppressed [Ca(+2)]i evoked by exogenous glutamate. The cGMP-dependent protein kinase inhibitor and KT-5823 partially blocked the rescue effect of tafluprost (p = 0.002). The survival rate of RGCs significantly increased in eyes treated with tafluprost (p = 0.01), and the prevalence of TUNEL-positive cells was significantly decreased 14 days after ONC (p < 0.001).

CONCLUSIONS

These data suggest that tafluprost has an anti-apoptotic effect in RGCs.

Nipradilol protects rat retinal ganglion cells from apoptosis induced by serum deprivation in vitro and by diabetes in vivo

PURPOSE

To investigate if nipradilol has an anti-apoptotic effect in serum-deprived RGC-5 cells and in the streptozotocin-induced diabetic rat retina.

METHODS

Apoptosis was quantified by activated caspase-3 immunohistochemistry or terminal dUTP nick end-labeling assay.

RESULTS

Nipradilol dose-dependently suppressed apoptosis in a protein kinase A- and G-dependent manner and counteracted glutamate-induced calcium entry in the RGC-5 cells and reduced apoptotic cells in the retinal ganglion cell layer of 4- and 12-week diabetic retinas compared to controls when instilled for 5 days. Removal of the nitric oxide moiety from nipradilol blocked these effects.

CONCLUSIONS

Nipradilol protects RGCs from apoptosis induced by serum-deprivation in vitro and by diabetes in vivo. The NO-related signaling pathway mediates the anti-apoptotic ability of nipradilol.

Effects of unoprostone on phosphorylated extracellular signal-regulated kinase expression in endothelin-1-induced retinal and optic nerve damage

Endothelin-1 (ET-1), a potent vasoconstrictor peptide, has been implicated in the development of normal- and high-tension glaucoma. We investigated the effects of unoprostone on extracellular signal-regulated kinase (ERK) in ET-1-induced retinal ganglion cell (RGC) death and optic nerve injury. Our morphometric study showed that intravitreal injection of ET-1 led to cell loss in the RGC layer (RGCL) in 28 days. Western blot analysis showed decreased neurofilament (NF) protein in the optic nerve 28 days after ET-1 injection. In this in vivo model, increased phosphorylated ERK (p-ERK) was observed in the retina on 1 day and subsequently in the optic nerve from 7 days after ET-1 injection. Simultaneous injection of M1, as a metabolite of unoprostone, showed further increased p-ERK levels compared with ET-1 injection alone. Our morphometric study of flat-mount preparations stained with cresyl violet or retrograde labeling with a neuro-tracer and Western blot analysis of NF showed that inhibition of ERK phosphorylation led to acceleration of ET-1-induced RGC death and optic nerve damage. In addition, M1 significantly attenuated both RGC loss and the decrease in NF protein induced by ET-1. The protective effects of M1 were significantly inhibited by U0126, an ERK inhibitor. These results suggest that unoprostone has neuroprotective effects against ET-1-induced neuronal injury through ERK phosphorylation.

Cellular and molecular effects of unoprostone as a BK channel activator

Effects of unoprostone isopropyl (unoprostone), a prostaglandin metabolite analog; latanoprost, a PGF(2alpha) analog; and PGF(2alpha) were examined in HCN-1A cells, a model system for studies of large conductance Ca(2+) activated K(+)(BK) channel activator-based neuroprotective agents. Unoprostone and latanoprost, both used as anti-glaucoma agents, have been suggested to act through FP receptors and have neuroprotective effects. Ion channel activation, plasma membrane polarization, [Ca(2+)](i) changes and protection against long-term irreversible glutamate-induced [Ca(2+)](i) increases were studied. Unoprostone activated iberiotoxin (IbTX)-sensitive BK channels in HCN-1A cells with an EC(50) of 0.6+/-0.2 nM and had no effect on Cl(-) currents. Unoprostone caused IbTX-sensitive plasma membrane hyperpolarization that was insensitive to AL8810, an FP receptor antagonist. In contrast, latanoprost and PGF(2alpha) activated a Cl(-) current sensitive to [Ca(2+)](i) chelation, tamoxifen and AL8810, and caused IbTX-insensitive, AL8810-sensitive membrane depolarization consistent with FP receptor-mediated Ca(2+) signaling Cl(-) current activation. Latanoprost and PGF(2alpha), but not unoprostone, increased [Ca(2+)](i). Unoprostone, PGF(2alpha) only partially, but not latanoprost protected HCN-1A cells against glutamate-induced Ca(2+) deregulation. These findings show that unoprostone has a distinctly different mechanism of action from latanoprost and PGF(2alpha). Whether unoprostone affects the BK channel directly or an unidentified signaling mechanism has not been determined.

cAMP-responsive element binding protein mediates a cGMP/protein kinase G-dependent anti-apoptotic signal induced by nitric oxide in retinal neuro-glial progenitor cells

Nitric oxide (NO) is cytoprotective to certain types of neuronal cells. The neuroprotective ability of NO in the retina was reportedly mediated by the cyclic GMP (cGMP) to protein kinase G (PKG) pathway. Cyclic AMP-responsive element binding protein (CREB) plays an essential role in the NO/cGMP/PKG-mediated survival of rat cerebellar granule cells. We tested whether CREB transduces the NO/cGMP/PKG anti-apoptotic cascade in R28 neuro-glial progenitor cells. Apoptosis was induced in R28 cells by serum deprivation for 24 h. Varying concentrations of two NO donors, sodium nitroprusside (SNP) and nipradilol, were added to medium with or without an NO scavenger, a soluble guanylyl cyclase inhibitor, or a PKG inhibitor. The cells were immunostained against activated caspase-3 and counterstained with Hoechst 33258. Apoptosis was quantified by counting activated caspase-3 positive or pyknotic cells. SNP and nipradilol rescued R28 cells from apoptosis in a dose-dependent manner, at an optimal concentration of 1.0 microM and 10 microM, respectively. Higher concentrations were cytotoxic. The NO scavenger and the inhibitors decreased the anti-apoptotic effect of the NO donors. Intracellular cGMP levels were increased after exposure to SNP and nipradilol. Western blotting showed that both NO donors increased CREB phosphorylation, which was blocked when pre-exposed to the inhibitors. Transfection with a dominant negative CREB construct defective of phosphorylation at Ser-133 interfered with the anti-apoptotic activity of SNP. These results indicate that CREB at least in part mediates the cGMP/PKG-dependent anti-apoptotic signal induced by NO in R28 cells.

Latanoprost rescues retinal neuro-glial cells from apoptosis by inhibiting caspase-3, which is mediated by p44/p42 mitogen-activated protein kinase

The purpose of this study was to investigate whether latanoprost, a prostaglandin F2alpha analogue, has a direct anti-apoptotic effect both in retinal neuro-glial cells in culture and in diabetic retina. R28 cells, immortalized retinal neuroglial progenitor cells, were induced apoptosis by 24h serum deprivation. Serum withdrawal made up to 15% of R28 cells pyknotic and activated caspase-3 immunoreactive, and latanoprost acid suppressed apoptosis with dose dependency at an optimum concentration of 1.0 microM (P<0.001). UO126, a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase (MEK) 1 and 2 inhibitor reversed this effect. Streptozotocin induced one- or three-month diabetic rats received balanced-salt-solution (BSS) in the left eye and latanoprost eye drops in the right for 5 days. Retinal wholemount was subjected to terminal dUTP nick end labeling (TUNEL) staining, whereas eyeballs were enucleated for cleaved caspase-3 immunofluorescence. Retinal homogenates were probed for phospho- or total p44/p42 MAPK and Akt. One- and three-month diabetic retina had 30.2+/-15.3 and 23.6+/-9.0 TUNEL positive cells per 0.5 cm(2), respectively, whereas control retina had few TUNEL positive cells. Latanoprost instillation significantly reduced these cells (10.0+/-3.1 and 11.3+/-3.1 cells per 0.5 cm(2) for 1M and 3M, respectively, P<0.01), whereas BSS did not. Latanoprost also significantly reduced cleaved caspase-3 immunoreactive cells in ganglion cell and inner nuclear layers (P<0.05). Latanoprost increased phosphorylated to total protein ratio of p44/p42 MAPK (P<0.05), but not of Akt. Taken together, the present findings suggest that latanoprost rescues retinal neurons and/or glial cells from apoptosis, which is probably mediated by p44/p42 MAPK through caspase-3 inhibition.