Effect of CS-088, an angiotensin AT1 receptor antagonist, on intraocular pressure in glaucomatous monkey eyes

Glaucoma and the ocular renin-angiotensin-aldosterone system: Update on molecular signalling and treatment perspectives

Glaucoma, a leading cause of blindness worldwide, encompasses a group of pathological conditions affecting the optic nerve and is characterized by progressive retinal ganglion cell loss, cupping of the optic nerve head, and distinct visual field defects. While elevated intraocular pressure (IOP) is the main risk factor for glaucoma, many patients do not have elevated IOP. Consequently, other risk factors, such as ocular blood flow abnormalities and immunological factors, have been implicated in its pathophysiology. Traditional therapeutic strategies primarily aim to reduce IOP, but there is growing interest in developing novel treatment approaches to improve disease management and reduce the high rates of severe visual impairment. In this context, targeting the ocular renin-angiotensin-aldosterone system (RAAS) has been found as a potential curative strategy. The RAAS contributes to glaucoma development through key effectors such as prorenin, angiotensin II, and aldosterone. Recent evidence has highlighted the potential of using RAAS modulators to combat glaucoma, yielding encouraging results. Our study aims to explore the molecular pathways linking the ocular RAAS and glaucoma, summarizing recent advances that elucidate the role of the RAAS in triggering oxidative stress, inflammation, and remodelling in the pathogenesis of glaucoma. Additionally, we will present emerging therapeutic approaches that utilize RAAS modulators and antioxidants to slow the progression of glaucoma.

A Cross Talk between the Endocannabinoid System and Different Systems Involved in the Pathogenesis of Hypertensive Retinopathy

The prognosis of hypertension leads to organ damage by causing nephropathy, stroke, retinopathy, and cardiomegaly. Retinopathy and blood pressure have been extensively discussed in relation to catecholamines of the autonomic nervous system (ANS) and angiotensin II of the renin–angiotensin aldosterone system (RAAS) but very little research has been conducted on the role of the ECS in the regulation of retinopathy and blood pressure. The endocannabinoid system (ECS) is a unique system in the body that can be considered as a master regulator of body functions. It encompasses the endogenous production of its cannabinoids, its degrading enzymes, and functional receptors which innervate and perform various functions in different organs of the body. Hypertensive retinopathy pathologies arise normally due to oxidative stress, ischemia, endothelium dysfunction, inflammation, and an activated renin–angiotensin system (RAS) and catecholamine which are vasoconstrictors in their biological nature. The question arises of which system or agent counterbalances the vasoconstrictors effect of noradrenaline and angiotensin II (Ang II) in normal individuals? In this review article, we discuss the role of the ECS and its contribution to the pathogenesis of hypertensive retinopathy. This review article will also examine the involvement of the RAS and the ANS in the pathogenesis of hypertensive retinopathy and the crosstalk between these three systems in hypertensive retinopathy. This review will also explain that the ECS, which is a vasodilator in its action, either independently counteracts the effect produced with the vasoconstriction of the ANS and Ang II or blocks some of the common pathways shared by the ECS, ANS, and Ang II in the regulation of eye functions and blood pressure. This article concludes that persistent control of blood pressure and normal functions of the eye are maintained either by decreasing systemic catecholamine, ang II, or by upregulation of the ECS which results in the regression of retinopathy induced by hypertension.

Medical therapy for glaucoma: A review

A number of pharmacological targets are exploited to modify the parameters in the Goldmann equation and reduce the intraocular pressure (IOP). This strategy constitutes the foundation for the medical management of glaucoma, the evolution of which, until only recently, has been in relative stagnation. A burst of innovation has produced new ocular hypotensive drugs and long-acting delivery methods, including intracameral delivery, which are expanding the clinician's medical armamentarium. A number of IOP-independent neuroprotection strategies have shown strong potential in animal models of glaucoma, but translational attempts have been surprisingly limited. However, while pharmacological options are expanding, the traditional role of topical medical therapy is being challenged by selective laser trabeculoplasty, micro-invasive glaucoma surgery, and sustained delivery methods. A scientifically rigorous assessment of new treatments will be critical to empower clinicians with evidence-based information to optimise vision preservation and quality of life outcomes for their patients.

Angiotensin II and Angiotensin Receptors 1 and 2-Multifunctional System in Cells Biology, What Do We Know?

For years, the renin-angiotensin system (RAS) has been perceived as a system whose role is to primarily modulate the functioning of the cardiovascular system. Years of research into the role of RAS have provided the necessary data to confirm that the role of RAS is very complex and not limited to the cardiovascular system. The presence of individual elements of the renin-angiotensin (RA) system allows to control many processes, ranging from the memorization to pro-cancer processes. Maintaining the proportions between the individual axes of the RA system allows for achieving a balance, often called homeostasis. Thus, any disturbance in the expression or activity of individual RAS elements leads to pathophysiological processes.

Telmisartan Reduces Axon Degeneration in Mice With Experimental Glaucoma

Purpose

The purpose of this study was to determine if treatment with telmisartan, an angiotensin II type 1 receptor blocker (ARB), protects against retinal ganglion cell (RGC) degeneration in a mouse glaucoma model with induced elevation of intraocular pressure (IOP).

Methods

IOP elevation was induced by injection of polystyrene microbeads into the anterior chamber of the right eye of 3-month-old C57BL/6J mice, with the left eye serving as contralateral control. Starting the day of microbead injection, mice were maintained on solid food pellets with or without incorporated telmisartan. IOP was measured by Tono Lab tonometry prior to and weekly after microbead injection. Twelve weeks postinjection, mice were euthanized to obtain optic nerves for analysis of RGC axons. The total numbers of optic nerve axons were determined manually and automatedly using AxonJ. Degenerating axons were counted manually.

Results

IOP elevation induced by microbead injection was similar in magnitude and duration in vehicle and telmisartan-fed mice, although IOP was reduced 5.8% in uninjected mice treated with telmisartan (P = 0.0027). Axon loss determined by manual and automated methods was greater in vehicle compared to telmisartan-treated mice (manual: 9.5% vs. 1.8%, P = 0.044; automated: 14.2% vs. 2.9%, P = 0.0375). An increase in the percent of axons undergoing degeneration was observed in nerves from microbead-injected eyes that was greater in vehicle-treated compared to telmisartan-treated mice (49.0% vs. –0.58%, P = 0.0019).

Conclusions

Elevation of IOP by microbead injection led to loss of RGC axons in vehicle-treated mice that was largely prevented by telmisartan treatment, suggesting a neuroprotective effect of telmisartan.

Local ocular renin-angiotensin-aldosterone system: any connection with intraocular pressure? A comprehensive review

The renin-angiotensin system (RAS) is one of the oldest and most extensively studied human peptide cascades, well-known for its role in regulating blood pressure. When aldosterone is included, RAAS is involved also in fluid and electrolyte homeostasis. There are two main axes of RAAS: (1) Angiotensin (1-7), angiotensin converting enzyme 2 and Mas receptor (ACE2-Ang(1-7)-MasR), (2) Angiotensin II, angiotensin converting enzyme 1 and angiotensin II type 1 receptor (ACE1-AngII-AT1R). In its entirety, RAAS comprises dozens of angiotensin peptides, peptidases and seven receptors. The first mentioned axis is known to counterbalance the deleterious effects of the latter axis. In addition to the systemic RAAS, tissue-specific regulatory systems have been described in various organs, evidence that RAAS is both an endocrine and an autocrine system. These local regulatory systems, such as the one present in the vascular endothelium, are responsible for long-term regional changes. A local RAAS and its components have been detected in many structures of the human eye. This review focuses on the local ocular RAAS in the anterior part of the eye, its possible role in aqueous humour dynamics and intraocular pressure as well as RAAS as a potential target for anti-glaucomatous drugs.KEY MESSAGESComponents of renin-angiotensin-aldosterone system have been detected in different structures of the human eye, introducing the concept of a local intraocular renin-angiotensin-aldosterone system (RAAS).Evidence is accumulating that the local ocular RAAS is involved in aqueous humour dynamics, regulation of intraocular pressure, neuroprotection and ocular pathology making components of RAAS attractive candidates when developing new effective ways to treat glaucoma.

Receptor-Associated Prorenin System in the Trabecular Meshwork of Patients with Primary Open-Angle Glaucoma and Neovascular Glaucoma

The receptor-associated prorenin system (RAPS) is associated with several pathologic conditions, including diabetic retinopathy, age-related macular degeneration, and uveitis. Here, we show the involvement of RAPS in the trabecular meshwork (TM) from patients with primary open-angle glaucoma (POAG) and neovascular glaucoma (NVG) due to proliferative diabetic retinopathy. Anterior chamber (AC) levels of prorenin significantly increased in both POAG and NVG, as did those of angiotensin II in NVG alone, compared to cataract. In surgically excised TM tissues, (pro)renin receptor ((P)RR) and angiotensin II type 1 receptor (AT1R) co-localized with prorenin and angiotensinogen, respectively. In screening for various genes related to glaucoma, prorenin stimulation to human TM cells exclusively upregulated cell junction constituents connexin 43 and zona occludens 1, while downregulating an extracellular matrix-degrading enzyme tissue plasminogen activator, all of which were reversed by (P)RR blockade. In contrast, angiotensin II application upregulated a pro-angiogenic factor placental growth factor alone, which was abolished by AT1R blockade. Consistently, (P)RR and AT1R co-localized with these corresponding proteins in patient TM tissues. Oxidative stress, a known etiology for glaucoma, induced the expression of prorenin and angiotensinogen in human TM cells. These data suggest the contribution of RAPS to the molecular pathogenesis of POAG and NVG through TM tissue remodeling and AC angle angiogenesis.

Continuous intraocular pressure monitoring in patients with obstructive sleep apnea syndrome using a contact lens sensor

Purpose

To analyse nocturnal intraocular pressure (IOP) fluctuations in patients with obstructive sleep apnea syndrome (OSAS) using a contact lens sensor (CLS) and to identify associations between the OSAS parameters determined by polysomnographic study (PSG) and IOP changes.

Method

Prospective, observational study. Twenty participants suspected of having OSAS were recruited. During PSG study, IOP was monitored using a CLS placed in the eye of the patient. The patients were classified according to the apnea-hypopnea index (AHI) in two categories, severe (>30) or mild/moderate (<30) OSAS. We evaluated several parameters determined by the IOP curves, including nocturnal elevations (acrophase) and plateau times in acrophase (PTs) defined by mathematical and visual methods.

Results

The IOP curves exhibited a nocturnal acrophase followed by PTs of varying extents at which the IOP remained higher than daytime measurement with small variations. We found significant differences in the length of the PTs in patients with severe OSAS compared to those with mild/moderate disease (P = 0.032/P = 0.028). We found a positive correlation between PTs and OSAS severity measured by the total number of apneic events (r = 0.681/0.751 P = 0.004/0.001) and AHI (r = 0.674/0.710, P = 0.004/0.002). Respiratory-related arousal and oxygen saturation also were associated significantly with the IOP PT length.

Conclusions

Periods of nocturnal IOP elevation lasted longer in severe OSAS patients than those with mild/moderate OSAS and correlate with the severity of the disease. The length of the nocturnal PT is also associated to respiratory parameters altered in patients with OSAS.

Differential effects of angiotensin II type I receptor blockers on reducing intraocular pressure and TGFβ signaling in the mouse retina

PURPOSE

Angiotensin II type 1 receptor blockers (ARBs) have been investigated for their neuroprotective and intraocular pressure (IOP) lowering effects in treating glaucoma, but the reports have been inconsistent possibly because different compounds and models have been used. Here we selected three ARBs for head-to-head comparisons of their effects on IOP and transforming growth factor β (TGFβ) signaling, which is believed to play an important role in glaucoma pathogenesis.

METHODS

Three ARBs (losartan, irbesartan or telmisartan) or vehicle controls were administered via chow to C57BL/6J mice for up to 7 days. Drug concentrations in the eye, brain, and plasma were evaluated by liquid chromatography mass spectrometry. Cohorts of mice were randomly assigned to different treatments. IOP and blood pressure were measured before and after ARB treatment. Effects of ARBs on TGFβ signaling in the retina were evaluated by phosphorylated Smad2 (pSmad2) immunohistochemistry.

RESULTS

Physiologically relevant concentrations of losartan, irbesartan and telmisartan were detected in eye, brain and plasma after drug administration (n = 11 mice/treatment). Blood pressure was significantly reduced by all ARBs compared to vehicle-fed controls (all p-values < 0.001, n = 8-15 mice/treatment). Compared to vehicle control, IOP was significantly reduced by irbesartan (p = 0.030) and telmisartan (p = 0.019), but not by losartan (n = 14-17 mice/treatment). Constitutive pSmad2 fluorescence observed in retinal ganglion cells was significantly reduced by telmisartan (p = 0.034), but not by losartan or irbesartan (n = 3-4 mice/treatment).

CONCLUSIONS

Administration via chow is an effective delivery method for ARBs, as evidenced by lowered blood pressure. ARBs vary in their abilities to lower IOP or reduce TGFβ signaling. Considering the significant roles of IOP and TGFβ in glaucoma pathogenesis, specific ARBs with dual effects, such as telmisartan, may be more effective than other ARBs for treating glaucoma.

iDrugs and iDevices Discovery Research: Preclinical Assays, Techniques, and Animal Model Studies for Ocular Hypotensives and Neuroprotectants

Discovery ophthalmic research is centered around delineating the molecular and cellular basis of ocular diseases and finding and exploiting molecular and genetic pathways associated with them. From such studies it is possible to determine suitable intervention points to address the disease process and hopefully to discover therapeutics to treat them. An investigational new drug (IND) filing for a new small-molecule drug, peptide, antibody, genetic treatment, or a device with global health authorities requires a number of preclinical studies to provide necessary safety and efficacy data. Specific regulatory elements needed for such IND-enabling studies are beyond the scope of this article. However, to enhance the overall data packages for such entities and permit high-quality foundation-building publications for medical affairs, additional research and development studies are always desirable. This review aims to provide examples of some target localization/verification, ocular drug discovery processes, and mechanistic and portfolio-enhancing exploratory investigations for candidate drugs and devices for the treatment of ocular hypertension and glaucomatous optic neuropathy (neurodegeneration of retinal ganglion cells and their axons). Examples of compound screening assays, use of various technologies and techniques, deployment of animal models, and data obtained from such studies are also presented.

Many Faces of Renin-angiotensin System - Focus on Eye

The renin-angiotensin system (RAS), that is known for its role in the regulation of blood pressure as well as in fluid and electrolyte homeostasis, comprises dozens of angiotensin peptides and peptidases and at least six receptors. Six central components constitute the two main axes of the RAS cascade. Angiotensin (1-7), an angiotensin converting enzyme 2 and Mas receptor axis (ACE2-Ang(1-7)-MasR) counterbalances the harmful effects of the angiotensin II, angiotensin converting enzyme 1 and angiotensin II type 1 receptor axis (ACE1-AngII-AT1R) Whereas systemic RAS is an important factor in blood pressure regulation, tissue-specific regulatory system, responsible for long term regional changes, that has been found in various organs. In other words, RAS is not only endocrine but also complicated autocrine system. The human eye has its own intraocular RAS that is present e.g. in the structures involved in aqueous humor dynamics. Local RAS may thus be a target in the development of new anti-glaucomatous drugs. In this review, we first describe the systemic RAS cascade and then the local ocular RAS especially in the anterior part of the eye.

Management of glaucoma as a neurodegenerative disease

Glaucoma is a neurodegenerative disease with an estimated prevalence of 60 million people, and the most common cause of irreversible blindness worldwide. The mainstay of treatment has been aimed at lowering intraocular pressure, currently the only modifiable risk factor. Unfortunately, despite adequate pressure control, many patients go on to suffer irreversible visual loss. We first briefly examine currently established intraocular pressure lowering-treatments, with a discussion of their roles in neuroprotection as demonstrated by both animal and clinical studies. The review then examines currently available intraocular pressure independent agents that have shown promise for possessing neuroprotective effects in the management of glaucoma. Finally, we explore potential future treatments such as immune-modulation, stem cell therapy and neural regeneration as they may provide further protection against the neurodegenerative processes involved in glaucomatous optic neuropathy.

Therapeutic targets of renin-angiotensin system in ocular disorders

Purpose

To review current literature on the renin-angiotensin system (RAS)-mediated pathogenic mechanisms and therapeutic targets in ocular diseases.

Methods

A comprehensive literature survey was performed on PubMed, Scopus, and Google Scholar databases published from 1977 to 2016. The search terms were a RAS, angiotensin, angiotensin receptor, prorenin, pro (renin) receptor, angiotensin converting enzyme inhibitor, angiotensin receptor blocker associated with ocular disorders like cataract, glaucoma, diabetic retinopathy (DR), macular degeneration, and uveitis. Articles were reviewed on the basis of the association between ocular disorders and RAS and relevant articles were discussed.

Results

The literature revealed that the individual RAS components including renin, angiotensins, angiotensin converting enzymes, and RAS receptors have been expressed in the specific ocular tissues like retina, choroid, and ciliary body. The activation of both circulatory and local RAS potentiate the various inflammatory and angiogenic signaling molecules, including vascular endothelial growth factor (VEGF), extracellular signal-regulated kinase, and advanced glycation end products (AGE) in the ocular tissues and leads to several blinding disorders like DR, glaucoma, and macular degeneration. The classical and newer RAS inhibitors have illustrated protective effects on blinding disorders, including DR, glaucoma, macular degeneration, uveitis, and cataract.

Conclusions

The RAS components are present in the extrarenal tissues including ocular tissue and have an imperative role in the ocular pathophysiology. The clinical studies are needed to show the role of therapeutic modalities targeting RAS in the treatment of different ocular disorders.

Losartan Treatment Protects Retinal Ganglion Cells and Alters Scleral Remodeling in Experimental Glaucoma

Purpose

To determine if oral losartan treatment decreases the retinal ganglion cell (RGC) death caused by experimental intraocular pressure (IOP) elevation in mice.

Methods

We produced IOP increase in CD1 mice and performed unilateral optic nerve crush. Mice received oral losartan, spironolactone, enalapril, or no drug to test effects of inhibiting angiotensin receptors. IOP was monitored by Tonolab, and blood pressure was monitored by tail cuff device. RGC loss was measured in masked axon counts and RGC bodies by β-tubulin labeling. Scleral changes that could modulate RGC injury were measured including axial length, scleral thickness, and retinal layer thicknesses, pressure-strain behavior in inflation testing, and study of angiotensin receptors and pathways by reverse transcription polymerase chain reaction, Western blot, and immunohistochemistry.

Results

Losartan treatment prevented significant RGC loss (median loss = 2.5%, p = 0.13), while median loss with water, spironolactone, and enalapril treatments were 26%, 28% and 43%; p < 0.0001). The lower RGC loss with losartan was significantly less than the loss with spironolactone or enalapril (regression model p = 0.001; drug treatment group term p = 0.01). Both losartan and enalapril significantly lowered blood pressure (p< 0.001), but losartan was protective, while enalapril led to worse than water-treated RGC loss. RGC loss after crush injury was unaffected by losartan treatment (difference from control p = 0.9). Survival of RGC in cell culture was not prolonged by sartan treatment. Axonal transport blockade after 3 day IOP elevations was less in losartan-treated than in control glaucoma eyes (p = 0.007). Losartan inhibited effects of glaucoma, including reduction in extracellular signal-related kinase activity and modification of glaucoma-related changes in scleral thickness and creep under controlled IOP.

Conclusions

The neuroprotective effect of losartan in mouse glaucoma is associated with adaptive changes in the sclera expressed at the optic nerve head.

Ocular renin-angiotensin system with special reference in the anterior part of the eye

The renin-angiotensin system (RAS) regulates blood pressure (BP) homeostasis, systemic fluid volume and electrolyte balance. The RAS cascade includes over twenty peptidases, close to twenty angiotensin peptides and at least six receptors. Out of these, angiotensin II, angiotensin converting enzyme 1 and angiotensin II type 1 receptor (AngII-ACE1-AT1R) together with angiotensin (1-7), angiotensin converting enzyme 2 and Mas receptor (Ang(1-7)-ACE2-MasR) are regarded as the main components of RAS. In addition to circulating RAS, local RA-system exists in various organs. Local RA-systems are regarded as tissue-specific regulatory systems accounting for local effects and long term changes in different organs. Many of the central components such as the two main axes of RAS: AngII-ACE1-AT1R and Ang(1-7)-ACE2-MasR, have been identified in the human eye. Furthermore, it has been shown that systemic antihypertensive RAS- inhibiting medications lower intraocular pressure (IOP). These findings suggest the crucial role of RAS not only in the regulation of BP but also in the regulation of IOP, and RAS potentially plays a role in the development of glaucoma and antiglaucomatous drugs.

Ocular Inserts for Sustained Release of the Angiotensin-Converting Enzyme 2 Activator, Diminazene Aceturate, to Treat Glaucoma in Rats

The aim of this study was to develop and evaluate the effects of chitosan inserts for sustained release of the angiotensin-converting enzyme 2 (ACE2) activator, diminazene aceturate (DIZE), in experimental glaucoma. Monolayer DIZE loaded inserts (D+I) were prepared and characterized through swelling, attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC) and in vitro drug release. Functionally, the effects of D+I were tested in glaucomatous rats. Glaucoma was induced by weekly injections of hyaluronic acid (HA) into the anterior chamber and intraocular pressure (IOP) measurements were performed. Retinal ganglion cells (RGC) and optic nerve head cupping were evaluated in histological sections. Biodistribution of the drug was accessed by scintigraphic images and ex vivo radiation counting. We found that DIZE increased the swelling index of the inserts. Also, it was molecularly dispersed and interspersed in the polymeric matrix as a freebase. DIZE did not lose its chemical integrity and activity when loaded in the inserts. The functional evaluation demonstrated that D+I decreased the IOP and maintained the IOP lowered for up to one month (last week: 11.0±0.7 mmHg). This effect of D+I prevented the loss of RGC and degeneration of the optic nerve. No toxic effects in the eyes related to application of the inserts were observed. Moreover, biodistribution studies showed that D+I prolonged the retention of DIZE in the corneal site. We concluded that D+I provided sustained DIZE delivery in vivo, thereby evidencing the potential application of polymeric-based DIZE inserts for glaucoma management.

Angiotensin(1-7) and ACE2, "The Hot Spots" of Renin-Angiotensin System, Detected in the Human Aqueous Humor

Background:

The main purpose of the study was to establish whether essential components of the renin-angiotensin system (RAS) exist in the human aqueous humor.

Methods:

Forty-five patients ≥ 60 (74±7) years of age undergoing cataract surgery at Tampere University Hospital were randomly selected for the prospective study. The exclusion criterion was the use of oral antihypertensive medicine acting via renin-angiotensin system. Aqueous humor samples were taken at the beginning of normal cataract extraction. The samples were frozen and stored at -80 °C. The concentrations of intraocular endogenous RAS components Ang(1-7), ACE2, and ACE1 were measured using ELISA.

Results:

Concentration medians of Ang(1-7), ACE2, and ACE1 in the aqueous humor were: Ang(1-7) 4.08 ng/ml, ACE2 2.32 ng/ml and ACE1 0.35 ng/ml. The concentrations were significantly higher in glaucomatous than in non-glaucomatous eyes, ACE1 (p=0.014) and Ang(1-7) (p=0.026) vs non-glaucomatous eyes.

Conclusions:

Ang(1-7), ACE2 and ACE1 are found in the human aqueous humor. The observations are consistent with the conception that local tissue-RAS exists in the human eye and it might have a role in the control of intraocular pressure.

Novel potential treatment modalities for ocular hypertension: focus on angiotensin and bradykinin system axes

Despite the availability of modern surgical procedures, new drug delivery techniques, health authority-approved single topical ocular drugs, and combination products thereof, there continues to be an unmet medical need for novel treatment modalities for preserving vision. This is especially true for the treatment of glaucoma and the high risk factor often associated with this ocular disease, elevated intraocular pressure (IOP). Undesirable local or systemic side effects, frequency of dosing, lack of sustained IOP lowering, and lack of prevention of diurnal IOP spikes are among the greatest challenges. The very recent discovery, characterization, and publication of 2 novel IOP-lowering agents that pertain to the renin-angiotensin and kallikrein-kinin axes potentially offer novel means to treat and control ocular hypertension (OHT). Here, some contextual introductory information is provided first, followed by more detailed discussion of the properties and actions of diminazene aceturate (DIZE; a novel angiotensin-converting enzyme-2 activator) and FR-190997 (a nonpeptide bradykinin receptor-2 agonist) in relation to their anti-OHT activities in rodent and cynomolgus monkey eyes, respectively. It is anticipated that these compounds will pave the way for future discovery, development, and marketing of novel drugs to treat glaucoma and thus help save sight for millions of people afflicted with this slow progressive optic neuropathy.

The association of blood pressure and primary open-angle glaucoma: a meta-analysis

PURPOSE

To conduct a systematic review and meta-analysis of the association between blood pressure levels and hypertension with primary open-angle glaucoma and intraocular pressure endpoints.

DESIGN

Systematic review with quantitative meta-analysis.

METHODS

Studies were identified by searching the PubMed and EMBASE databases. Inverse-variance weighted random-effects models were used to summarize relative risks. Subgroup analyses and meta-regression were used to explore potential sources of heterogeneity across studies.

RESULTS

Sixty observational studies were included. The pooled relative risk for primary open-angle glaucoma comparing patients with hypertension to those without hypertension was 1.16 (95% CI = 1.05-1.28), with modest heterogeneity across studies (I(2) 34.5%). Virtually all studies reported a positive association between blood pressure and intraocular pressure (IOP). The pooled average increase in IOP associated with a 10 mm Hg increase in systolic blood pressure was 0.26 mm Hg (95% CI 0.23-0.28, I(2) 30.7%), and the average increase associated with a 5 mm Hg increase in diastolic blood pressure was 0.17 mm Hg (95% CI 0.11-0.23, I(2) 90.5%).

CONCLUSIONS

In this meta-analysis, hypertension was associated with increased intraocular pressure. The association between hypertension and primary open-angle glaucoma was stronger in cross-sectional compared with case-control and longitudinal studies. Our findings support a role of increased blood pressure in elevated intraocular pressure and possibly in the development of glaucoma.

Development of eye drops containing antihypertensive drugs: formulation of aqueous irbesartan/γCD eye drops

Aqueous nanoparticulated eye drop formulations based on γ-cyclodextrin (γCD) complexes were developed and tested in vitro. Three antihypertensive drugs, i.e. enalapril maleate, irbesartan and verapamil HCl, that have been shown to possess IOP-lowering activity were selected for this study. All three drugs displayed Bs-type phase-solubility diagrams in aqueous γCD solutions and had relatively low affinity for γCD. Irbesartan was selected for further formulation development. The drug was relatively stable at pH 4.5 but somewhat less stable at physiologic pH. However, presence of γCD in the aqueous media enhanced the chemical stability of irbesartan. Aqueous γCD-based eye drop formulations containing 1% and 2% (w/v) irbesartan were prepared and the effect of pH on the particles size distribution and drug release investigated. Only ∼2% of the drug was in solution in the pH 4.5 formulations but up to 45% in the pH 7 formulations. The pH 7 formulations, where larger fraction of the drug was in solution, displayed somewhat greater drug permeation flux but much lower drug permeation coefficients than the pH 4.5 formulations. Dynamic light scattering studies indicated the faster permeation was due to formation of smaller particles in presence tyloxapol.

The microfibril hypothesis of glaucoma: implications for treatment of elevated intraocular pressure

Microfibrils are macromolecular aggregates located in the extracellular matrix of both elastic and nonelastic tissues that have essential functions in formation of elastic fibers and control of signaling through the transforming growth factor beta (TGFβ) family of cytokines. Elevation of systemic TGFβ and chronic activation of TGFβ signal transduction are associated with diseases caused by mutations in microfibril-associated genes, including FBN1. A role for microfibrils in glaucoma is suggested by identification of risk alleles in LOXL1 for exfoliation glaucoma and mutations in LTBP2 for primary congenital glaucoma, both of which are microfibril-associated genes. Recent identification of a mutation in another microfibril-associated gene, ADAMTS10, in a dog model of primary open-angle glaucoma led us to form the microfibril hypothesis of glaucoma, which in general states that defective microfibrils may be an underlying cause of glaucoma. Microfibril defects could contribute to glaucoma through alterations in biomechanical properties of tissue and/or through effects on signaling through TGFβ, which is well established to be elevated in the aqueous humor of glaucoma patients. Recent work has shown that diseases caused by microfibril defects are associated with increased concentrations of TGFβ protein and chronic activation of TGFβ-mediated signal transduction. In analogy with other microfibril-related diseases, defective microfibrils could provide a mechanism for the elevation of TGFβ2 in glaucomatous aqueous humor. If glaucoma shares mechanisms with other diseases caused by defective microfibrils, such as Marfan syndrome, therapeutic interventions to inhibit chronic activation of TGFβ signaling used in those diseases may be applied to glaucoma.

[Is there a connection between intraocular pressure and blood pressure? Results of the Gutenberg Health Study and review of the current study situation]

Intraocular pressure (IOD) is the most important risk factor for the occurrence and progression of glaucoma because it is the only measurable risk factor. There is a positive connection between IOD and both systolic and diastolic blood pressure. The clinical relevance is, however, limited because the moderate alterations in IOD are less than the known measurement error and daily physiological oscillation.

The ocular renin-angiotensin system: a therapeutic target for the treatment of ocular disease

The renin-angiotensin system (RAS) is most well-known for its role in regulation and dysregulation of blood pressure as well as fluid and electrolyte homeostasis. Due to its ability to cause cardiovascular disease, the RAS is the target of a multitude of drugs that antagonize its pathophysiological effects. While the "classical" RAS is a systemic hormonal system, there is an increasing awareness of the existence and functional significance of local RASs in a number of organs, e.g., liver, kidney, heart, lungs, reproductive organs, adipose tissue and adrenal. The eye is one of these organs where a compelling body of evidence has demonstrated the presence of a local RAS. Individual components of the RAS have been shown to be present in many structures of the eye and their potential functional significance in ocular disease states is described. Because the eye is one of the most important and complex organs in the body, this review also discusses the implications of dysregulation of the systemic RAS on the pathogenesis of ocular diseases and how pharmacological manipulation of the RAS might lead to novel or adjunctive therapies for ocular disease states.

New therapeutic targets for intraocular pressure lowering

Primary open-angle glaucoma (POAG) is a leading cause of irreversible and preventable blindness and ocular hypertension is the strongest known risk factor. With current classes of drugs, management of the disease focuses on lowering intraocular pressure (IOP). Despite of their use to modify the course of the disease, none of the current medications for POAG is able to reduce the IOP by more than 25%-30%. Also, some glaucoma patients show disease progression despite of the therapeutics. This paper examines the new described physiological targets for reducing the IOP. The main cause of elevated IOP in POAG is thought to be an increased outflow resistance via the pressure-dependent trabecular outflow system, so there is a crescent interest in increasing trabecular meshwork outflow by extracellular matrix remodeling and/or by modulation of contractility/TM cytoskeleton disruption. Modulation of new agents that act mainly on trabecular meshwork outflow may be the future hypotensive treatment for glaucoma patients. There are also other agents in which modulation may decrease aqueous humour production or increase uveoscleral outflow by different mechanisms from those drugs available for glaucoma treatment. Recently, a role for the ghrelin-GHSR system in the pathophysiology modulation of the anterior segment, particularly regarding glaucoma, has been proposed.

Ophthalmic drug discovery: novel targets and mechanisms for retinal diseases and glaucoma

Blindness affects 60 million people worldwide. The leading causes of irreversible blindness include age-related macular degeneration, retinal vascular diseases and glaucoma. The unique features of the eye provide both benefits and challenges for drug discovery and delivery. During the past decade, the landscape for ocular drug therapy has substantially changed and our knowledge of the pathogenesis of ophthalmic diseases has grown considerably. Anti-angiogenic drugs have emerged as the most effective form of therapy for age-related macular degeneration and retinal vascular diseases. Lowering intraocular pressure is still the mainstay for glaucoma treatment but neuroprotective drugs represent a promising next-generation therapy. This Review discusses the current state of ocular drug therapy and highlights future therapeutic opportunities.

Renin-Angiotensin system hyperactivation can induce inflammation and retinal neural dysfunction

The renin-angiotensin system (RAS) is a hormone system that has been classically known as a blood pressure regulator but is becoming well recognized as a proinflammatory mediator. In many diverse tissues, RAS pathway elements are also produced intrinsically, making it possible for tissues to respond more dynamically to systemic or local cues. While RAS is important for controlling normal inflammatory responses, hyperactivation of the pathway can cause neural dysfunction by inducing accelerated degradation of some neuronal proteins such as synaptophysin and by activating pathological glial responses. Chronic inflammation and oxidative stress are risk factors for high incidence vision-threatening diseases such as diabetic retinopathy (DR), age-related macular degeneration (AMD), and glaucoma. In fact, increasing evidence suggests that RAS inhibition may actually prevent progression of various ocular diseases including uveitis, DR, AMD, and glaucoma. Therefore, RAS inhibition may be a promising therapeutic approach to fine-tune inflammatory responses and to prevent or treat certain ocular and neurodegenerative diseases.

Effect of SPP 635, a renin inhibitor, on intraocular pressure in glaucomatous monkey eyes

The effect of topical application of SPP 635, a renin inhibitor, on intraocular pressure (IOP) was evaluated in the eyes of monkeys with laser induced unilateral glaucoma. A multiple-dose study was performed in 8 glaucomatous monkey eyes with 3 concentrations of SPP 635, 0.2%, 0.3% and 0.4%. IOP was measured hourly for 6 h on each day of the study beginning at 9:30 a.m. Following one baseline day (untreated) and one vehicle-treated day (50 μl drop of vehicle to the glaucomatous eye at 9:30 a.m.), a 50 μl drop (25 μl × 2) of SPP 635, 0.2%, 0.3% or 0.4%, was topically applied to the glaucomatous eye at 9:30 a.m. and 3:30 p.m. for 5 consecutive days. Twice daily administration of each of the 3 concentrations of SPP 635 for 5 days significantly (p < 0.05) reduced IOP. The maximum reduction in IOP occurred 3 or 4 h after morning dosing and was 4.3 ± 0.8 (mean ± SEM) mmHg (14%) for 0.2% SPP 635, 5.3 ± 1.0 mmHg, (19%) for 0.3% SPP 635, and 8.0 ± 1.3 mmHg (25%) for 0.4% SPP 635. The longest duration of IOP reduction was for 6 h with 0.2% or 0.3% SPP 635, and was for at least 18 h with 0.4% concentration. Compared to 0.2% or 0.3% concentrations, 0.4% SPP 635 produced a greater (p < 0.05) and longer duration of IOP reduction (18 vs. 6 h). Mild conjunctival discharge appeared in 2 of 8 eyes, and hyperemia appeared in 2 eyes with the 0.3% and 0.4% concentrations on treatment days 3 and 5. Topically applied SPP 635, a new renin inhibitor, reduces IOP in glaucomatous monkeys in a dose-dependent manner. Renin inhibitors, are a novel class of compounds which may have potential for the treatment of glaucoma.

Novel ocular antihypertensive compounds in clinical trials

Introduction:

Glaucoma is a multifactorial disease characterized by progressive optic nerve injury and visual field defects. Elevated intraocular pressure (IOP) is the most widely recognized risk factor for the onset and progression of open-angle glaucoma, and IOP-lowering medications comprise the primary treatment strategy. IOP elevation in glaucoma is associated with diminished or obstructed aqueous humor outflow. Pharmacotherapy reduces IOP by suppressing aqueous inflow and/or increasing aqueous outflow.

Purpose:

This review focuses on novel non-FDA approved ocular antihypertensive compounds being investigated for IOP reduction in ocular hypertensive and glaucoma patients in active clinical trials within approximately the past 2 years.

Methods:

The mode of IOP reduction, pharmacology, efficacy, and safety of these new agents were assessed. Relevant drug efficacy and safety trials were identified from searches of various scientific literature databases and clinical trial registries. Compounds with no specified drug class, insufficient background information, reformulations, and fixed-combinations of marketed drugs were not considered.

Results:

The investigational agents identified comprise those that act on the same targets of established drug classes approved by the FDA (ie, prostaglandin analogs and β-adrenergic blockers) as well as agents belonging to novel drug classes with unique mechanisms of action. Novel targets and compounds evaluated in clinical trials include an actin polymerization inhibitor (ie, latrunculin), Rho-associated protein kinase inhibitors, adenosine receptor analogs, an angiotensin II type 1 receptor antagonist, cannabinoid receptor agonists, and a serotonin receptor antagonist.

Conclusion:

The clinical value of novel compounds for the treatment of glaucoma will depend ultimately on demonstrating favorable efficacy and benefit-to-risk ratios relative to currently approved prostaglandin analogs and β-blockers and/or having complementary modes of action.

Medical treatment of glaucoma: present and future

INTRODUCTION

In the last decades, the therapy of glaucoma has largely shifted from surgery to medical treatment thanks to the introduction of strongly effective formulations, that is, prostaglandin analogs and fixed combinations. This clinical scenario may dramatically change in the future thanks to the progresses in biochemistry, genetics and drug delivery technology.

AREAS COVERED

This review covers the strategies currently used to achieve effective medical reduction of intraocular pressure in clinical practice; treatments that are currently been experimented in humans and that may be clinically available in the next few years; treatments at preclinical stages; and future goals of glaucoma treatment (gene therapy, ocular implants and neuroprotection).

EXPERT OPINION

Apart from an adequate reduction of intraocular pressure, effective glaucoma treatments should guarantee other characteristics: good tolerability, low problems of adherence and, possibly, multiple ways of action. From this viewpoint, a crucial clinical role may be played by drugs remodeling the trabecular meshwork (i.e., ROCK inhibitors, metalloproteinases). Other strategies such as the use of ocular implants for drug delivery, neuroprotection or gene therapy could renew glaucoma management in the future, but need long-term rigorous verification of safety and efficacy.

Angiotensin receptors in the eyes of arterial hypertensive rats

PURPOSE

The aim of the present study was to determine whether the eye tissues of arterial hypertensive rats evince expression of angiotensin receptors (AT(1) and AT(2)) as well as the novel Mas receptor, whose endogenous ligand is vasorelaxing Angiotensin (1-7) [Ang (1-7)].

METHODS

Enucleated eyes from spontaneously hypertensive rats (SHR) and double transgenic rats harbouring human renin and angiotensinogen genes (dTGR) and their normotensive controls were used. Half of the rats were pretreated orally with an Angiotensin II (Ang II) type 1 receptor blocker (ARB). The eyes were snap-frozen in isopentane at -40 degrees and stored at -70 degrees for subsequent reverse transcriptase polymerase chain reaction (RT-PCR) analysis or in vitro autoradiography.

RESULTS

The mRNA expression of AT(1a) and AT(2) as well as the novel Mas receptor was detected in all rat groups, being markedly higher in the retina than in the ciliary body. dTGR had significantly more receptors than SHR, but no direct relation to blood pressure level was seen. According to the autoradiography, treatment with ARB blocked a part of AT(1) receptors but had no clear effect on AT(2) receptors.

CONCLUSION

The novel Mas receptor was found by RT-PCR in eye tissue for the first time. Its specific ligand, Ang (1-7), may be involved in the regulation of intraocular pressure--as recently demonstrated by us--and in the pathogenesis of retinal diseases as a counter-regulatory component for the vascular and proliferative actions of Ang II. The results suggest that the density of AT(1) receptors in the eye is independent of the blood pressure level of the animal.

Does the renin-angiotensin system also regulate intra-ocular pressure?

The renin-angiotensin-aldosterone system is known to play an essential role in controlling sodium balance and body fluid volumes, and thus blood pressure. In addition to the circulating system which regulates urgent cardiovascular responses, a tissue-localized renin-angiotensin system (RAS) regulates long-term changes in various organs. Many recognized RAS components have also been identified in the human eye. The highly vasoconstrictive angiotensin II (Ang II) is considered the key peptide in the circulatory RAS. However, the ultimate effect of RAS activation at tissue level is more complex, being based not only on the biological activity of Ang II but also on the activities of other products of angiotensinogen metabolism, often exerting opposite effects to Ang II action. In recent studies, orally administered angiotensin II type 1 receptor blockers and angiotensin-converting enzyme inhibitors lower intra-ocular pressure (IOP), likewise topical application of these compounds, the effect being more prominent in ocular hypertensive eyes. Based on previous findings and our own experimental data, it can strongly be suggested that the RAS not only regulates blood pressure but is also involved in the regulation of IOP.