Update on the mechanism of action of bimatoprost: a review and discussion of new evidence

Analysis of the Responsiveness of Latanoprost, Travoprost, Bimatoprost, and Tafluprost in the Treatment of OAG/OHT Patients

Aim

Within the clinical setting, some patients have been identified as lacking in response to PGAs. This meta-analysis study aimed to evaluate the responsiveness of latanoprost, travoprost, bimatoprost, and tafluprost in OAG/OHT patients, latanoprost nonresponders (LNRs), and the IOP-reducing efficacy and safety.

Methods

A literature search was conducted on PubMed, Embase, and the Cochrane Controlled Trials Register. The primary clinical endpoint was the number of responders at the end of the study. The secondary clinical endpoint was the IOP reduction at the endpoint from baseline. Safety evaluation included five common adverse events: conjunctival hyperemia, hypertrichosis, ocular burning, ocular itching, and foreign-body sensation.

Results

Eleven articles containing ten RCTs were included in this meta-analysis study. The results highlighted that, in the OAG/OHT population, there was no statistically significant difference in the responsiveness of the four PGAs. Bimatoprost had a better IOP-reducing efficacy than latanoprost. There was no significant difference in the IOP-reducing efficacy of travoprost, latanoprost, and tafluprost. In LNRs, the responsiveness of bimatoprost, travoprost, and latanoprost did not show statistical differences. Bimatoprost reduced IOP with a greater extent than latanoprost and travoprost in LNRs, while there was no significant difference in the IOP-reducing efficacy of travoprost and latanoprost. No serious adverse events occurred with the treatment of the four PGAs. The prevalence of conjunctival hyperemia due to bimatoprost or tafluprost was significantly higher than that of latanoprost. Other adverse events had no significant difference between the four drugs.

Conclusion

The existing studies cannot prove that latanoprost, travoprost, bimatoprost, and tafluprost have different responsiveness in OAG/OHT patients. Switching to bimatoprost or travoprost cannot achieve a significant improvement in responsiveness in LNRs. Bimatoprost has a better IOP-reducing efficacy than latanoprost and travoprost. No serious adverse events occurred during treatment with any medication we studied.

The human endogenous metabolome as a pharmacology baseline for drug discovery

We have limited understanding of the variation in in vitro affinities of drugs for their targets. An analysis of a highly curated set of 815 interactions between 566 drugs and 129 primary targets reveals that 71% of drug-target affinities have values above that of the corresponding endogenous ligand, 96% of them fitting within a range of two orders of magnitude. Our findings suggest that the evolutionary optimised affinity of endogenous ligands for their native proteins can serve as a baseline for the primary pharmacology of drugs. We show that the degree of off-target selectivity and safety risks of drugs derived from their secondary pharmacology depend very much on that baseline. Thus, we propose a new approach for estimating safety margins.

[Hypotensive efficacy of bimatoprost in monotherapy of primary open-angle glaucoma]

PURPOSE

To study the effectiveness of monotherapy with bimatoprost in patients with decompensated intraocular pressure (IOP).

MATERIAL AND METHODS

90 patients (132 eyes) with stage I-II glaucoma and decompensated IOP previously treated with timolol, latanoprost and travoprost were included in the study. Average IOP at the beginning of the study was 25.4±2.5 mmHg. All patients had their hypotensive medications substituted by bimatoprost. The patients were examined during the initial appointment, as well as after 4 and 12 weeks.

RESULTS

IOP decrease was highest in the group of patients who had been treated with timolol: initially IOP was 26.2±1.8 mmHg, after 4 weeks - 21.0±2.2 mmHg, after 12 weeks - 20.8±1.9 mmHg (p<0.001). The initial IOP of patients who had been treated with latanoprost was 24.8±2.9 mmHg, 21.8±2.4 mmHg after 4 weeks, and 21.6±2.3 mmHg after 12 weeks (p<0.001). Patients who had been treated with travoprost had 25.6±2.2 mmHg initially, 23.0±2.5 mmHg after 4 weeks, and 23.2±2.6 mmHg after 12 weeks (p<0.001). By the end of the study IOP has decreased by 5.4, 3.2 and 2.4 mmHg in the groups of patients who had been treated with timolol, latanoprost and travoprost, respectively.

CONCLUSION

Bimatoprost can be used as monotherapy if another hypotensive drug in monotherapy is insufficient for IOP compensation.

Investigational drugs targeting prostaglandin receptors for the treatment of glaucoma

INTRODUCTION

Prostaglandin F2α analogs were the first prostaglandin agonists introduced for glaucoma treatment. Thanks to their efficacy and favorable tolerability they set a high bar in competition, with a resultant paucity in new hypotensive drug development for many years. However, the scientific community has shown recently a new interest in exploring new options for glaucoma treatment, generating a remarkable incentive in the marketplace for new drugs.

AREAS COVERED

This article reviews agents targeting prostaglandin receptors that are currently being investigated for glaucoma treatment. We searched published literature for agonists targeting all subtypes of prostaglandin receptors found in ocular tissues. EP and FP receptor agonists are currently in the spotlight of clinical research, while less attention is paid in DP receptor agonists.

EXPERT OPINION

Prostaglandin analogs, targeting different and combinations of receptor subtypes and compounds that exhibit additivity to commonly prescribed medications seem to be highly promising options. New treatments need to be safe, more effective, superior to existing therapies, tolerable and cost-effective. New generation compounds with multiple mechanisms of action or multiagent formulations are vigorously being investigated and generated in laboratories around the world.

Treatment merits of Latanoprost/Thymoquinone - Encapsulated liposome for glaucomatus rabbits

Elevation of the intraocular pressure (IOP) is recognized as a risk factor for glaucoma development. Latanoprost (LAT) is a prostaglandin analog used to reduce the (IOP). Thymoquinone (TQ) is a major bioactive ingredient of Nigella sativa. The aim of this study was to develop novel liposomal drug carriers for ocular delivery of LAT, TQ and a mixture of them to investigate their IOP lowering efficacy upon subconjunctival injection in glaucoma-induced rabbit's eye. The aim of the present work extends also to study the effect of the different liposome formulations on the aqueous humor oxidative stress. Liposome samples were prepared using thin film hydration method. The physiochemical properties of the prepared drugs were characterized. The IOP was recorded for 70 rabbits using Schiotz-tonometer. Malondialdehyde (MDA), reduced glutathione (GSH), catalase (CAT) activities and total antioxidant activity of the aqueous humor were estimated. Fourier transform infrared and differential scanning calorimetric studies confirmed the interaction between the drug and the vesicles, which resulted in high drug encapsulation efficiency ≥88%. The size of the prepared liposomes was less than 10 μm which make them suitable in ophthalmic applications. The sustained effect was achieved by liposome samples of Lip (LAT) and Lip (LAT + TQ) which were able to reduce the IOP significantly up to 84 h. Morever, the treatment of glaucomatous rabbits with liposome formulations containing TQ in their preparation [Lip (TQ) and Lip (LAT + TQ)] greatly improved the ocular tissue-induced histopathological lesions. None of the prepared liposome formulations succeeded to improve the glaucoma-induced oxidative stress damage.

Patient considerations in ocular hypertension: role of bimatoprost ophthalmic solution

Glaucoma is a leading cause of irreversible blindness worldwide. The reduction of intraocular pressure has been well established as an effective treatment to prevent both the development and the progression of all forms of glaucoma. Bimatoprost 0.03% ophthalmic solution, introduced in 2001, is a synthetic prostamide with the unique mechanism of improving both uveoscleral and trabecular outflow. Comparative studies with other pharmacotherapies have shown favorable results for bimatoprost as a potent ocular hypotensive agent that is generally well tolerated. Common side effects include conjunctival hyperemia, eyelash growth, iris pigmentation and periorbital changes. Hyperemia rates were reduced following the introduction of bimatoprost 0.01%. Bimatoprost should be used with caution in those with higher risk of developing ocular inflammation and macular edema. However, the perceived risk of bimatoprost in these patient populations is likely greater than the actual risk observed in practice. Bimatoprost is currently in the center of several clinical trials including its use for dermatologic applications and sustained-release therapies for the treatment of ocular hypertension and glaucoma.

Pharmacotherapy and Adherence Issues in Treating Elderly Patients with Glaucoma

Glaucoma is a leading cause of visual morbidity throughout the world and is an age-related condition, the prevalence of which rises significantly with increasing age. Glaucoma, a condition affecting the optic nerve, has a variety of subtypes with multiple aetiological factors, the most important of which are intraocular pressure (IOP) and increasing age. Treatment by lowering of IOP is the only current method, for which there is evidence, by which the rate of progressive visual deterioration can be slowed or halted. Although there are surgical and laser treatments that are efficacious in lowering IOP, the most common manner in which patients with glaucoma control their IOP is with administration of daily topical ocular hypotensive drugs (eye drops). The variety of topical drugs utilised in the management of glaucoma all have the potential to have adverse effects and/or interactions with concomitant medications, many of which may be used for other age-related conditions. Adherence with appropriate medicines has a major effect on the outcome of medical conditions and this aspect applies to the management of glaucoma. There are certain specific issues that relate to the administration of topical agents, with respect to both adverse effects and adherence. Although many suspect poor adherence in elderly patients with glaucoma, relative to younger patients, adequate evidence for this is lacking. Furthermore, the manner by which adherence issues could be improved remains inadequately understood and poorly addressed. The aims of this article were to review, from a clinical perspective, the medical therapies currently used for glaucoma and discuss adherence issues with respect to the population of patients with glaucoma, who tend to be relatively elderly.

Management of hypotrichosis of the eyelashes: focus on bimatoprost

Prominent eyelashes are generally recognized as enhancing beauty and are often desired by women. Until recently, the options available to augment the prominence of eyelashes were limited to makeup, over-the-counter products, artificial eyelashes, and eyelash transplantation. Originally approved for the treatment of ocular hypertension, the prostamide, bimatoprost, is now approved for the treatment of hypotrichosis of the eyelashes. Bimatoprost ophthalmic solution 0.03%, applied once daily to the skin of the upper eyelid margin using sterile single-use-per-eye applicators, increases eyelash growth, including length, thickness, and darkness. The effectiveness of bimatoprost for eyelash growth has been demonstrated by clinician ratings, digital image analysis, and patient-reported measures of satisfaction. The effects of bimatoprost treatment on eyelash length, thickness, and darkness are believed to result from longer anagen duration, increased hair bulb thickness, and increased melanogenesis, respectively. Dermally applied bimatoprost appears to be associated with a lower incidence of adverse events than administration of the medication as an eyedrop. This more favorable safety and tolerability profile is likely mediated by decreased exposure of ocular tissues to bimatoprost when applied dermally. Taken together, available data suggest that cutaneous application of bimatoprost ophthalmic solution 0.03% safely and effectively enhances upper eyelash growth.

Topical prostaglandin analogue drugs inhibit adipocyte differentiation

Purpose

To investigate the effects of topical prostaglandin analogue drugs on the differentiation of adipocytes.

Methods

Differentiation of 3T3-L1 preadipocytes was induced with isobutylmethylxanthine, dexamethasone, and insulin. 3T3-L1 cells were exposed to 0.008, 0.08, 0.2 µM of latanoprost and travoprost. Reverse transcription polymerase chain reaction for mRNA expression of lipoprotein lipase and peroxisome proliferator-activated receptor γ 2 (PPARγ2), and glycerol-3-phosphate dehydrogenase (G3PDH) assays were performed to examine the effects on early and late differentiation, respectively. Also, glycerol assays were done to evaluate the effect of prostaglandin analogues on lipolysis after differentiation.

Results

Both prostaglandin analogues inhibited differentiation of preadipocytes. Topical prostaglandin analogues significantly decreased G3PDH activity, a marker of late differentiation. However, topical prostaglandin analogues did not change mRNA expressions of lipoprotein lipase and PPARγ2, markers of early differentiation. The activities of the early markers of differentiation were not changed significantly before and after growth arrest. Compared to latanoprost, travoprost decreased G3PDH activity more significantly (p < 0.05). Both prostaglandin analogues did not affect the lipolysis of differentiated adipocytes (p > 0.05).

Conclusions

Prostaglandin analogues display an inhibitory effect on the differentiation of adipocytes when the cells start to differentiate especially in the late stage of differentiation. Thus, commercial topical prostaglandin analogues may decrease the fat contents of eyelids.

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.

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 Patents on Emerging Therapeutics for the Treatment of Glaucoma, Age Related Macular Degeneration and Uveitis

Advancements in the field and rising interest among pharmaceutical researchers have led to the development of new molecules with enhanced therapeutic activity. Design of new drugs which can target a particular pathway and/or explore novel targets is of immense interest to ocular pharmacologists worldwide. Delivery of suitable pharmacologically active agents at proper dose (within the therapeutic window) to the target tissues without any toxicity to the healthy ocular tissues still remain an elusive task. Moreover, the presence of static and dynamic barriers to drug absorption including the corneal epithelium (lipophilic), corneal and scleral stroma (hydrophilic), conjunctival lymphatics, choroidal vasculature and the blood-ocular barriers also pose a significant challenge for achieving therapeutic drug concentrations at the target site. Although many agents are currently available, new compounds are being introduced for treating various ocular diseases. Deeper understanding of the etiology and complex mechanisms associated with the disease condition would aid in the development of potential therapeutic candidates. Novel small molecules as well as complex biotechnology derived macromolecules with superior efficacy, safety and tolerability are being developed. Therefore, this review article provides an overview of existing drugs, treatment options, advances in emerging therapeutics and related recent patents for the treatment of ocular disorders such as glaucoma, age related macular degeneration (AMD) and uveitis.

The use of prostaglandin analogs in the uveitic patient

Glaucoma is a disease process characterized by progressive optic nerve damage and corresponding visual field loss. It may be further categorized into either primary open-angle glaucoma or secondary glaucoma. These secondary glaucomas include glaucomas associated with uveitis and inflammation. Prostaglandin analogs (PGA) have been used to help lower intraocular pressure (IOP) in these often difficult to manage eyes. However, controversy exists concerning their use in uveitic patients due to the theoretically higher risk of anterior uveitis, development of cystoid macular edema (CME), and reactivation of herpes simplex keratitis (HSK). There is little evidence that PGA disrupt the blood-aqueous barrier and only anecdotal evidence suggesting an increased risk of these rare findings. PGA may be used in uveitic glaucoma when other topical treatments have not lowered IOP to the patient's target range.

Changes to upper eyelid orbital fat from use of topical bimatoprost, travoprost, and latanoprost

PURPOSE

To confirm the possible mechanism by which topical prostaglandin antiglaucoma drugs cause a deep superior sulcus.

METHODS

Among patients who used bimatoprost (Lumigan), latanoprost (Xalatan), or travoprost (Travatan) and who developed a deep upper lid sulcus, 18 eyes of 11 patients (mean age, 58.2 ± 8.9 years) were studied. Seven patients were binocular users of one of the eye drops and four were monocular users. Preaponeurotic orbital fat was obtained, and the mean adipocyte density compared.

RESULTS

In the four monocular users, mean adipocyte density of treated eyes was 1758.21 ± 158.15 cells/mm(2), and that of untreated eyes was 1258.73 ± 127.54 cells/mm(2). This difference was statistically significant (P = 0.04), suggesting that the adipocytes were atrophied in the treated eyes. The mean adipocyte density of the bimatoprost group was 2073.35 ± 184.89 cells/mm(2), that of the travoprost group was 1623.46 ± 218.99 cells/mm(2), and that of the latanoprost group was 1468.20 ± 113.44 cells/mm(2). The densities of the bimatoprost and travoprost groups, but not of the latanoprost group (P = 0.75), were significantly different from that of the untreated group (P < 0.001).

CONCLUSIONS

Fat atrophy can be considered a mechanism of upper eyelid sulcus deepening in patients using topical prostaglandin analogs.

Aqueous humor concentrations of bimatoprost free acid, bimatoprost and travoprost free acid in cataract surgical patients administered multiple topical ocular doses of LUMIGAN or TRAVATAN

PURPOSE

To quantify the aqueous humor (AH) concentrations of bimatoprost (amide), travoprost (isopropyl ester), and their hydrolysis products, bimatoprost free acid (BFA) and travoprost free acid (TFA), after multiple topical ocular doses of LUMIGAN and TRAVATAN, respectively, in patients awaiting cataract surgery.

METHODS

In 2 separate open-label, sparse-sampling trials, glaucoma patients with cataracts received LUMIGAN (bimatoprost ophthalmic solution, 0.03%) or TRAVATAN (travoprost ophthalmic solution, 0.004%) bilaterally once daily for at least 21 days prior to cataract surgery. Anterior chamber paracentesis was performed at selected times up to 5 h after the last dose and an AH sample was collected. AH samples were assayed by an independent bioanalytical laboratory using a sensitive and validated tandem LC-MS/MS method. The assay lower limits of quantitation were 0.59 nM for bimatoprost, 0.29 nM for BFA, and 0.44 nM for TFA.

RESULTS

AH concentrations of BFA (17-phenyl-trinor PGF(2alpha)) were quantifiable in all but one sample at 0.5 h. The maximum concentration achieved (C(max)) of BFA was 30.9 + or - 16.41 nM (n =5), observed at 2 h postdose. AH concentrations of bimatoprost amide were lower than BFA at all time points, with a C(max) of 6.81 + or - 1.36 nM (n = 7) at 1 h postdose. For TFA, measurable AH concentrations were obtained at all time points with a TFA C(max) of 3.91 + or - 2.27 nM (n = 5), which was observed at 3 h after the dose (all data are mean + or - SEM).

CONCLUSIONS

Once daily topical ocular administration of LUMIGAN or TRAVATAN for 3 weeks resulted in significant concentrations of BFA and TFA in the AH. Quantifiable levels of bimatoprost amide were also measured. Maximum concentrations of BFA (30.9 nM) and TFA (3.91 nM) in the anterior chamber are sufficient to fully activate the FP prostanoid receptors in the target cells of the ciliary muscle and trabecular meshwork. Both bimatoprost in LUMIGAN and travoprost in TRAVATAN are essentially prodrugs that are rapidly hydrolyzed to their respective free acids that induce the IOP-lowering effect observed with both drugs in vivo.

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.

Management of hypotrichosis of the eyelashes: Focus on bimatoprost

Prominent eyelashes are generally recognized as enhancing beauty and are often desired by women. Until recently, the options available to augment the prominence of eyelashes were limited to makeup, over-the-counter products, artificial eyelashes, and eyelash transplantation. Originally approved for the treatment of ocular hypertension, the prostamide, bimatoprost, is now approved for the treatment of hypotrichosis of the eyelashes. Bimatoprost ophthalmic solution 0.03%, applied once daily to the skin of the upper eyelid margin using sterile single-use-per-eye applicators, increases eyelash growth, including length, thickness, and darkness. The effectiveness of bimatoprost for eyelash growth has been demonstrated by clinician ratings, digital image analysis, and patient-reported measures of satisfaction. The effects of bimatoprost treatment on eyelash length, thickness, and darkness are believed to result from longer anagen duration, increased hair bulb thickness, and increased melanogenesis, respectively. Dermally applied bimatoprost appears to be associated with a lower incidence of adverse events than administration of the medication as an eyedrop. This more favorable safety and tolerability profile is likely mediated by decreased exposure of ocular tissues to bimatoprost when applied dermally. Taken together, available data suggest that cutaneous application of bimatoprost ophthalmic solution 0.03% safely and effectively enhances upper eyelash growth.

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.

Bilateral deepening of upper lid sulcus from topical bimatoprost therapy

PURPOSE

To report a new adverse effect related to treatment with bimatoprost.

METHOD

Case report. A 43-year-old Asian female with bilateral glaucoma was noticed to have bilateral deepening of upper lid sulcus 3 months after beginning treatment with bimatoprost 0.03%.

RESULTS

Bimatoprost was discontinued due to cosmetic reasons, and there was improvement of the lid sulcus deepening bilaterally 4 weeks after stopping the drug.

CONCLUSIONS

Deepening of upper lid sulcus is one of the adverse effects related to treatment with bimatoprost. This effect may be more prominent in Asians who have relatively full upper lid sulcus.

Commercially available prostaglandin analogs for the reduction of intraocular pressure: similarities and differences

Over the last 12 years, the pharmacological management of glaucoma and ocular hypertension has significantly changed with the introduction of the prostaglandin analogs, specifically, latanoprost, bimatoprost, and travoprost. Their ability to effectively reduce intraocular pressure with once-per-day dosing, their comparable ocular tolerability with timolol, and their general lack of systemic side effects have made them the mainstay of pharmacological therapy for glaucoma and ocular hypertension in most parts of the world. A review of their pharmacology reveals that they are all prodrugs that are converted to their respective free acids within the eye to activate the prostanoid FP receptor and to reduce intraocular pressure by enhancing the uveoscleral and the trabecular meshwork outflow pathways. A review of numerous prospective, randomized comparative studies indicates that no clinically significant differences exist among these agents regarding their ability to lower intraocular pressure.

Influence of topical bimatoprost on macular thickness and volume in glaucoma patients with phakic eyes

BACKGROUND

In light of concern about the possible relation between the extensive clinical use of prostaglandin analogues and the development of retinal disorders such as cystoid macular edema, this study investigated the influence of topical application of bimatoprost 0.03% on macular thickness and volume in glaucoma patients with phakic eyes.

METHODS

A total of 40 eyes in 22 patients with primary open-angle glaucoma or normal-tension glaucoma were evaluated in this study. Optical coherence tomography images were taken before initiation of bimatoprost application and after 1, 2, and 3 months of treatment. In addition, best-corrected visual acuity (BCVA) and intraocular pressure (IOP) were measured, and contrast sensitivity tests and fundus examinations were performed. Changes in various parameters, including macular thickness and volume, were analyzed.

RESULTS

BCVA and contrast sensitivity did not change from baseline over the treatment period. IOP declined by 20% to 25% from baseline for 1 month before stabilizing. Macular thickness and volume did not increase significantly during the 3 months.

INTERPRETATION

Topical application of bimatoprost does not induce clinical or structural changes in the macula, at least in glaucoma patients with phakic eyes. Moreover, bimatoprost effectively lowered IOP without causing macular disorders such as cystoid macular edema.

Cat iris sphincter smooth-muscle contraction: comparison of FP-class prostaglandin analog agonist activities

The pharmacologic characteristics of a number of FP-class prostaglandin (PG) analogs were determined by using the cat iris sphincter smooth-muscle-contraction assay. Cumulative concentration-response curves were generated for each compound. The relative agonist potencies (EC(50)) of the compounds were: cloprostenol (0.0012 +/- 0.0004 nM) >> travoprost acid (0.46 +/- 0.13 nM) = bimatoprost acid (0.99 +/- 0.19 nM) > (+/-)-fluprostenol (15.8 +/- 2.6 nM) = PGF(2alpha) (18.6 +/- 1.8 nM) > latanoprost acid (29.9 +/- 1.6 nM) > bimatoprost (140 +/- 45 nM) > S-1033 (588 +/- 39 nM) > unoprostone (UF-021; 1280 +/- 50 nM; n = 4-14). The maximum response induced by travoprost acid (122% +/- 2.3% maximum response relative to PGF(2alpha)) was significantly greater than that induced by all the other PG compounds (P < 0.001 - P < 0.02). Interestingly, the FP-receptor antagonist, AL-8810, behaved as a moderate efficacy partial agonist (EC(50) = 2140 +/- 190 nM; 63 +/- 4.3% maximum response relative to PGF(2alpha)), indicating that the cat iris contains an extremely well-coupled FP-receptor population, and/or the tissue contains an extremely high density of the FP-receptor and/or spare receptors. The cat iris contraction data were well correlated with other FP-receptor-mediated signal-transduction processes, including FP-receptor binding in bovine corpus luteum (r = 0.86), FP-receptor binding in human iris (r = 0.61), phosphoinositide (PI) hydrolysis in human ciliary muscle and trabecular meshwork cells (r = 0.77 - 0.86), PI turnover in rat and mouse cells (r = 0.73 - 0.76) and via cloned human FP-receptor (r = 0.9), and rat uterus contraction (r = 0.84). These data confirm the presence of functional FP-receptors in the cat iris sphincter, which are exquisitely well coupled and which respond to a variety of FP-class PG analogs with differing potencies.

Non-redundant functions of cyclooxygenases: oxygenation of endocannabinoids

The two cyclooxygenase (COX) enzymes catalyze the oxygenation of arachidonic acid to prostaglandin endoperoxides, which are the common intermediates in the biosynthesis of the bioactive lipids prostaglandins and thromboxane. COX-1 and COX-2 are approximately 60% identical in amino acid sequence, exhibit highly homologous three-dimensional structures, and appear functionally similar at the biochemical level. Recent work has uncovered a subtle functional difference between the two enzymes, namely the ability of COX-2 to efficiently utilize neutral derivatives (esters and amides) of arachidonic acid as substrates. Foremost among these neutral substrates are the endocannabinoids 2-arachidonoylglycerol and arachidonoylethanolamide. This raises the possibility that COX-2 oxygenation plays a role in a novel signaling pathway dependent on agonist-induced release of endocannabinoids and their selective oxygenation by COX-2. Among the products of COX-2 oxygenation of endocannabinoids are glyceryl prostaglandins, some of which (e.g. glyceryl prostaglandin E(2) and glyceryl prostaglandin I(2)) exhibit interesting biological activities in inflammatory, neurological, and vascular systems. These compounds are produced in intact cells stimulated with physiological agonists and have been isolated from in vivo sources. Important concepts relevant to the hypothesis of a COX-2-selective signaling pathway are presented.

Effects of latanoprost, timolol and GLC756, a novel dopamine D(2) agonist and D(1) antagonist on LTC(4) release after rat mast cell activation

PURPOSE

Mast cells participate in ocular allergic inflammation by releasing biologically active mediators. Leukotrienes are released from activated mast cells via an IgE-dependent mechanism, and play a crucial role in ocular allergic inflammation. In this study, the effect of three topical antiglaucoma drugs, that is, latanoprost, timolol and GLC756, a novel dopamine D(2) agonist and D(1) antagonist, on leukotriene C(4) (LTC(4)) release after rat mast cell activation was examined.

METHODS

A rat basophilic leukaemia RBL-2H3 mast cell line was activated via IgE/anti-IgE. Rat mast cells were incubated with latanoprost, timolol, or GLC756 at concentrations of 0.1, 1, 10 and 30 microM. LTC(4) concentration in supernatant was assessed 5 h post activation by EIA.

RESULTS

Compared with controls, timolol showed no relevant effect on LTC(4) release, 5 h after mast cell activation. Latanoprost and GLC756, in contrast, revealed an inhibitory effect on LTC(4) release, which was dose-related and statistically significant at the concentrations of 10 and 30 microM.

CONCLUSION

The results of this study suggest that timolol has no significant influence on LTC(4) release from activated mast cells. By contrast, latanoprost and GLC756 inhibited LTC(4) release, suggesting a possible anti-inflammatory effect on ocular allergic inflammatory processes in topical glaucoma medication.

Prostamides (prostaglandin-ethanolamides) and their pharmacology

The prostamides are part of a large and continually expanding series of pharmacologically unique neutral lipids. They are COX-2 derived oxidation products of the endocannabinoid/endovanniloid anandamide. Prostamide pharmacology is unique and, as in the case of the endocannabinoids anandamide and 2-arachidonylglycerol, bears little resemblance to that of the corresponding free acids. By virtue of its close relationship to the anti-glaucoma drug bimatoprost, prostamide F(2alpha) has received the greatest research attention. Prostamide F(2alpha) and bimatoprost effects appear independent of prostanoid FP receptor activation, according to a litany of agonist studies. Studies involving freshly isolated and separate feline iridial smooth muscle cells revealed that bimatoprost and FP receptor agonists stimulated different cells, without exception. This suggests the existence of receptors that preferentially recognize prostamide F(2alpha). The recent discovery of prostamide antagonists has provided further support for prostamide receptors as discrete entities. The prototypical prostamide antagonists, AGN 204396 and 7, blocked the effects of prostamide F(2alpha) and bimatoprost but not those of PGF(2alpha) and FP receptor agonists in the feline iris. Second generation more potent prostamide antagonists, such as AGN 211334, should allow the role of prostamides in health and disease to be elucidated. From the therapeutics standpoint, the prostamide F(2alpha) analogue bimatoprost is the most efficacious ocular hypotensive agent currently available for the treatment of glaucoma.

Comparison of the ocular hypotensive effects of bimatoprost and timolol-dorzolamide combination in patients with elevated intraocular pressure: a 6-month study

PURPOSE

To compare the ocular hypotensive efficacy and safety of topical bimatoprost and timolol-dorzolamide combination in patients with primary open-angle glaucoma (POAG) or ocular hypertension during 6 months of treatment.

METHODS

A sample of 65 patients with a diagnosis of POAG or ocular hypertension were randomized to receive either bimatoprost 0.03% once daily or timolol-dorzolamide combination twice daily. Study visits occurred at baseline and after 2 weeks and 1, 3 and 6 months of therapy. Intraocular pressure (IOP) measurements were performed at 12.00 hours at all study visits and also at 08.00 hours and 16.00 hours at baseline and 6-month visits. At each visit, local and systemic side-effects that occurred during the treatment period were recorded. Student's t-test was used to compare the differences between IOP values.

RESULTS

Differences in IOP between the bimatoprost and timolol-dorzolamide groups were statistically insignificant at all study visits (p > 0.05). In the bimatoprost-treated group, the IOP reduction was 6.2 +/- 1.8 mmHg, whereas it was 6.5 +/- 2.3 mmHg in the timolol-dorzolamide group after 6 months of treatment. The difference was not statistically significant (p = 0.48).

CONCLUSIONS

The IOP-lowering efficacies of bimatoprost and timolol-dorzolamide combination were similar over a 6-month follow-up. Both bimatoprost and the timolol-dorzolamide combination were well tolerated. Bimatoprost can be used as a longterm monotherapy agent in the treatment of POAG and ocular hypertension.

Drugs, their targets and the nature and number of drug targets

What is a drug target? And how many such targets are there? Here, we consider the nature of drug targets, and by classifying known drug substances on the basis of the discussed principles we provide an estimation of the total number of current drug targets.

Effect of GLC756, a novel mixed dopamine D1 receptor antagonist and dopamine D2 receptor agonist, on TNF-alpha release in vitro from activated rat mast cells

Tumor necrosis factor-alpha (TNF-alpha) is released from activated mast cells via an IgE-dependent mechanisms, and plays a crucial role in ocular allergic inflammation. This study examined the influence of three antiglaucoma drugs differing in their chemical structure and pharmacological profile (i.e. latanoprost, timolol, GLC756) on TNF-alpha release from activated rat mast cells. A rat basophilic leukemia mast cell line (RBL-2H3) was activated via IgE/anti-IgE. Rat mast cells were incubated with latanoprost, timolol, GLC756 or betamethasone (positive control) at concentrations of 0.1, 1, 10 and 30 microM. TNF-alpha concentration in supernatant was measured by ELISA 5 h post-activation. Compared to controls, the prostaglandin derivative latanoprost and the beta-blocker timolol in the concentration range 0.1-30 microM, had no significant effect on TNF-alpha release from rat mast cells measured 5h after activation. By contrast, the dopaminergic drug GLC756 compared to controls in the concentration range 1-30 microM significantly inhibited TNF-alpha release from activated rat mast cells in a concentration-dependent manner. The positive control betamethasone inhibited TNF-alpha release almost completely at all concentrations tested. In conclusion, the results of this study suggest that latanoprost and timolol do not reduce inflammation triggered by activated mast cells. By contrast, the dopaminergic drug GLC756 inhibited TNF-alpha release from activated mast cells, suggesting an palliative potential of dopaminergic compounds on allergic conjunctivitis in topical glaucoma medication.