Oculohypotensive effect of angiotensin-converting enzyme inhibitors in acute and chronic models of glaucoma

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.

Decreased choroidal vascularity index and subfoveal choroidal thickness in vitamin D insufficiency

BACKGROUND

To present the effects of vitamin D insufficiency on the choroidal vascularity index, central choroid and central macula.

METHODS

42 eyes of 42 patients with vitamin D insufficiency and 51 eyes of 51 age- and sex-matched healthy subjects were included in this retrospective, cross-sectional, and comparative study. The macular layer was examined using the retinal mapping mode of the spectral domain Optical coherence tomography (Optovue RTVue XR, Optovue Inc., Fremont, CA). Optical coherence tomography (OCT) images were taken in Enhanced Deep Imaging mode and transferred to Image J program. choroidal vascularity index (CVI) and subfoveal choroidal thickness (SFCT) measurements were evaluated.

RESULTS

The mean age of volunteers was 35.4 ± 7.2 years. There was a significant difference in CVI values 67.75±2.4 in the patients with vitamin D insufficiency and 69.22±1.75 in the control group. The SCFT of patients with vitamin D insufficiency and control group were 295.25±42.3 and 335.71±11.6 (p = 0.001, p<0.001 respectively).

CONCLUSION

OCT examination of patients with vitamin D insufficiency showed a decrease in CVI and SCFT values. These results are important in demonstrating the retinochoroidal effects of vitamin D insufficiency.

Advances in targeting the extracellular matrix for glaucoma therapy: current updates

INTRODUCTION

Elevated intraocular pressure (IOP) is a well-recognized risk factor for development of primary open angle glaucoma (POAG), a leading cause of irreversible blindness. Ocular hypertension is associated with excessive extracellular matrix (ECM) deposition in trabecular meshwork (TM) resulting in increased aqueous outflow resistance and elevated IOP. Hence, therapeutic options targeting ECM remodeling in TM to lower IOP in glaucomatous eyes are of considerable importance.

AREAS COVERED

This paper discusses the complex process of ECM regulation in TM and explores promising therapeutic targets. The role of Transforming Growth Factor-β as a central player in ECM deposition in TM is discussed. We elaborate the key regulatory processes involved in its activation, release, signaling, and cross talk with other signaling pathways including Rho GTPase, Wnt, integrin, cytokines, and renin-angiotensin-aldosterone. Further, we summarize the therapeutic agents that have been explored to target ECM dysregulation in TM.

EXPERT OPINION

Targeting molecular pathways to reduce ECM deposition and/or enhance its degradation are of considerable significance for IOP lowering. Challenges lie in pinpointing specific targets and designing drug delivery systems to precisely interact with pathologically active/inactive signaling. Recent advances in monoclonal antibodies, fusion molecules, and vectored nanotechnology offer potential solutions.

Identifying new drugs and targets to treat rapidly elevated intraocular pressure for angle closure and secondary glaucomas to curb visual impairment and prevent blindness

A multitude of pharmacological compounds have been shown to lower and control intraocular pressure (IOP) in numerous species of animals and human subjects after topical ocular dosing or via other routes of administration. Most researchers have been interested in finding drug candidates that exhibit a relatively long duration of action from a chronic therapeutic use perspective, for example to treat ocular hypertension (OHT), primary open-angle glaucoma and even normotensive glaucoma. However, it is equally important to seek and characterize treatment modalities which offer a rapid onset of action to help provide fast relief from quickly rising IOP that occurs in certain eye diseases. These include acute angle-closure glaucoma, primary angle-closure glaucoma, uveitic and inflammatory glaucoma, medication-induced OHT, and other secondary glaucomas induced by eye injury or infection which can cause partial or complete loss of eyesight. Such fast-acting agents can delay or prevent the need for ocular surgery which is often used to lower the dangerously raised IOP. This research survey was therefore directed at identifying agents from the literature that demonstrated ocular hypotensive activity, normalizing and unifying the data, determining their onset of action and rank ordering them on the basis of rapidity of action starting within 30-60 min and lasting up to at least 3-4 h post topical ocular dosing in different animal species. This research revealed a few health authority-approved drugs and some investigational compounds that appear to meet the necessary criteria of fast onset of action coupled with significant efficacy to reduce elevated IOP (by ≥ 20%, preferably by >30%). However, translation of the novel animal-based findings to the human conditions remains to be demonstrated but represent viable targets, especially EP2-receptor agonists (e.g. omidenepag isopropyl; AL-6598; butaprost), mixed activity serotonin/dopamine receptor agonists (e.g. cabergoline), rho kinase inhibitors (e.g. AMA0076, Y39983), CACNA2D1-gene product inhibitors (e.g. pregabalin), melatonin receptor agonists, and certain K+-channel openers (e.g. nicorandil, pinacidil). Other drug candidates and targets were also identified and will be discussed.

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.

Chitosan-Covered Calcium Phosphate Particles Co-Loaded with Superoxide Dismutase 1 and ACE Inhibitor: Development, Characterization and Effect on Intraocular Pressure

Improvement of the efficiency of drug penetration into the eye tissues is still an actual problem in ophthalmology. One of the most promising solutions is drug encapsulation in carriers capable of overcoming the cornea/sclera tissue barrier. Formulations on the base of antioxidant enzyme, superoxide dismutase 1 (SOD1), and an inhibitor of angiotensin-converting enzyme, enalaprilat, were prepared by simultaneous inclusion of both drugs into calcium phosphate (CaP) particles in situ with subsequent covering of the particles with 5 kDa chitosan. The formulations obtained were characterized by dynamic light scattering and scanning electron microscopy. Hybrid CaP-chitosan particles co-loaded with SOD1 and enalaprilat had a mean hydrodynamic diameter of 120-160 nm and ζ-potential +20 ± 1 mV. The percentage of the inclusion of SOD1 and enalaprilat in hybrid particles was 30% and 56%, respectively. The ability of SOD1 and enalaprilat to reduce intraocular pressure (IOP) was examined in vivo in normotensive Chinchilla rabbits. It was shown that topical instillations of SOD1/enalaprilat co-loaded hybrid particles were much more effective in decreasing IOP compared to free enzyme or free enalaprilat and even to the same particles that contained a single drug. Thus, the proposed formulations demonstrate potential as prospective therapeutic agents for the treatment of glaucoma.

Co-occurrence of chronic kidney disease and glaucoma: Epidemiology and etiological mechanisms

As the histology, physiology, and pathophysiology of eyes and kidneys show substantial overlap, it has been suggested that eye and kidney diseases, such as glaucoma and chronic kidney disease (CKD), may be closely interlinked. We review the relationship between CKD and various subtypes of glaucoma, including primary open-angle glaucoma, primary angle- closure glaucoma, normal tension glaucoma, pseudoexfoliation syndrome, and several glaucoma endophenotypes. We also discuss the underlying pathogenic mechanisms and common risk factors for CKD and glaucoma, including atherosclerosis, the renin-angiotensin system, genes and genetic polymorphisms, vitamin D deficiency, and erythropoietin. The prevalence of glaucoma appears elevated in CKD patients, and vice versa, and the literature points to many intriguing associations; however, the associations are not always confirmed, and sometimes apparently opposite observations are reported. Glaucoma and CKD are complex diseases, and their mutual influence is only partially understood.

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

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

Chitosan-covered calcium phosphate particles as a drug vehicle for delivery to the eye

Formulations on the base of an inhibitor of angiotensin-converting enzyme, enalaprilat, were prepared by the inclusion of the drug into calcium phosphate (CaP)-particles in situ, followed by the covering of the particles with 5 kDa chitosan or 72 kDa glycol chitosan and cross-linking with sodium tripolyphosphate. Physicochemical characterization of the resulted hybrid particles was conducted using dynamic light scattering, as well as scanning and transmission electron microscopy. Enalaprilat-containing particles had a mean hydrodynamic diameter 180 nm and 260 nm and ζ-potential +7 mV and +16 mV for 5 kDa and 72 kDa chitosans, respectively. In vivo studies showed that enalaprilat within particles stayed longer in the tear fluid after single instillation and caused a significantly pronounced and prolonged decrease of intraocular pressure in rabbits, especially in the case of CaP-particles, covered by glycol chitosan. Thus, such formulations demonstrate potential as prospective therapeutic agents for the treatment of eye diseases.

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.

Deconstructing aqueous humor outflow - The last 50 years

Herein partially summarizes one scientist-clinician's wanderings through the jungles of primate aqueous humor outflow over the past ~45 years. Totally removing the iris has no effect on outflow facility or its response to pilocarpine, whereas disinserting the ciliary muscle (CM) from the scleral spur/trabecular meshwork (TM) completely abolishes pilocarpine's effect. Epinephrine increases facility in CM disinserted eyes. Cytochalasins and latrunculins increase outflow facility, subthreshold doses of cytochalasins and epinephrine given together increase facility, and phalloidin, which has no effect on facility, partially blocks the effect of both cytochalasins and epinephrine. H-7, ML7, Y27632 and nitric oxide - donating compounds all increase facility, consistent with a mechanosensitive TM/SC. Adenosine A1 agonists increase and angiotensin II decrease facility. OCT and optical imaging techniques now permit visualization and digital recording of the distal outflow pathways in real time. Prostaglandin (PG) F2α analogues increase the synthesis and release of matrix metalloproteinases by the CM cells, causing remodeling and thinning of the interbundle extracellular matrix (ECM), thereby increasing uveoscleral outflow and reducing IOP. Combination molecules (one molecule, two or more effects) and fixed combination products (two molecules in one bottle) simplify drug regimens for patients. Gene and stem cell therapies to enhance aqueous outflow have been successful in laboratory models and may fill an unmet need in terms of patient compliance, taking the patient out of the delivery system. Functional transfer of genes inhibiting the rho cascade or decoupling actin from myosin increase facility, while genes preferentially expressed in the glaucomatous TM decrease facility. In live NHP, reporter genes are expressed for 2+ years in the TM after a single intracameral injection, with no adverse reaction. However, except for one recent report, injection of facility-effective genes in monkey organ cultured anterior segments (MOCAS) have no effect in live NHP. While intracameral injection of an FIV. BOVPGFS-myc.GFP PGF synthase vector construct reproducibly induces an ~2 mmHg reduction in IOP, the effect is much less than that of topical PGF2⍺ analogue eyedrops, and dissipates after 5 months. The turnoff mechanism has yet to be defeated, although proteasome inhibition enhances reporter gene expression in MOCAS. Intracanalicular injection might minimize off-target effects that activate turn-off mechanisms. An AD-P21 vector injected sub-tenon is effective in 'right-timing' wound healing after trabeculectomy in live laser-induced glaucomatous monkeys. In human (H)OCAS, depletion of TM cells by saponification eliminates the aqueous flow response to pressure elevation, which can be restored by either cultured TM cells or by IPSC-derived TM cells. There were many other steps along the way, but much was accomplished, biologically and therapeutically over the past half century of research and development focused on one very small but complex ocular apparatus. I am deeply grateful for this award, named for a giant in our field that none of us can live up to.

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.

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.

Peripapillary choroidal thickness in patients with vitamin D deficiency

AIM

To investigate the effects of vitamin D deficiency on peripapillary choroidal thickness and retinal nerve fiber layer thickness.

MATERIALS AND METHODS

Patients diagnosed with vitamin D deficiency but not yet treated for it (Group 1) and patients with normal vitamin D levels (Group 2) were included in this study. Subjects with any kind of eye disease and/or systemic disease were excluded from this study. Demographic characteristics of the patients were collected, and the subfoveal choroidal thickness, central foveal thickness, retinal nerve fiber layer thickness, and peripapillary choroidal thickness were measured using optical coherence tomography.

RESULTS

The mean ages in Groups 1 and 2 were 30.5 ± 6.7 and 28 ± 5.78 years (p = 0.12), respectively, and female to male ratios were 19/11 and 17/13, respectively (p = 0.59). The mean vitamin D levels were 8.2 ± 2.5 and 28 ± 4.9 ng/mL in Groups 1 and 2, respectively (p <0.001). In Group 1, subfoveal choroidal thickness and nasal and inferior peripapillary choroidal thicknesses at 500 µm were 327.5 ± 81.4, 142.9 ± 40, and 140.66 ± 38.74 µm, respectively. For Group 2, these values were 407.1 ± 85.5, 189.3 0 ± 57.18, and 195.93 ± 67.58 µm, respectively (p <0.001, p = 0.001, and p <0.001, respectively). In addition, a positive correlation was found between vitamin D levels and the subfoveal choroidal thickness and nasal and inferior peripapillary choroidal thicknesses in all patients (r = 0.365, p = 0.005; r = 0.341, p = 0.008; and r = 0.370, p = 0.004, respectively).

CONCLUSION

Subfoveal choroidal thickness and inferior and nasal peripapillary choroidal thicknesses decreased in patients with vitamin D deficiency.

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.

Trabecular meshwork ECM remodeling in glaucoma: could RAS be a target?

INTRODUCTION

Disturbances of extracellular matrix (ECM) homeostasis in trabecular meshwork (TM) cause increased aqueous outflow resistance leading to elevated intraocular pressure (IOP) in glaucomatous eyes. Therefore, restoration of ECM homeostasis is a rational approach to prevent disease progression. Since renin-angiotensin system (RAS) inhibition positively alters ECM homeostasis in cardiovascular pathologies involving pressure and volume overload, it is likely that RAS inhibitors reduce IOP primarily by restoring ECM homeostasis. Areas covered: Current evidence showing the presence of RAS components in ocular tissue and its role in regulating aqueous humor dynamics is briefly summarized. The role of RAS in ECM remodeling is discussed both in terms of its effects on ECM synthesis and its breakdown. The mechanisms of ECM remodeling involving interactions of RAS with transforming growth factor-β, Wnt/β-catenin signaling, bone morphogenic proteins, connective tissue growth factor, and matrix metalloproteinases in ocular tissue are discussed. Expert opinion: Current literature strongly indicates a significant role of RAS in ECM remodeling in TM of hypertensive eyes. Hence, IOP-lowering effect of RAS inhibitors may primarily be attributed to restoration of ECM homeostasis in aqueous outflow pathways rather than its vascular effects. However, the mechanistic targets for RAS inhibitors have much wider distribution and consequences, which remain relatively unexplored in TM.

A common humoral background of intraocular and arterial blood pressure dysregulation

BACKGROUND

It has been postulated that intraocular pressure, an important glaucoma risk factor, correlates positively with arterial blood pressure (blood pressure). However, results of experimental and clinical studies are often contradictory. It is hypothesized that, in some hypertensive patients, disturbances in intraocular pressure regulation may depend on biological effects of blood borne hormones underlying a particular type of hypertension, rather than on blood pressure level itself.

REVIEW

This review compares the effects of hormones on blood pressure and intraocular pressure, in order to identify a hormonal profile of hypertensive patients with an increased risk of intraocular pressure surge. The PUBMED database was searched to identify pre-clinical and clinical studies investigating the role of angiotensin II, vasopressin, adrenaline, noradrenaline, prostaglandins, and gaseous transmitters in the regulation of blood pressure and intraocular pressure.

RESULTS

Studies included in the review suggest that intraocular and blood pressures often follow a different pattern of response to the same hormone. For example, vasopressin increases blood pressure, but decreases intraocular pressure. In contrast, high level of nitric oxide decreases blood pressure, but increases intraocular pressure.

CONCLUSIONS

Arterial hypertension is associated with altered levels of blood borne hormones. Contradicting results of studies on the relationship between arterial hypertension and intraocular pressure might be partially explained by diverse effects of hormones on arterial and intraocular pressures. Further studies are needed to evaluate if hormonal profiling may help to identify glaucoma-prone patients.

Co-instillation of nano-solid magnesium hydroxide enhances corneal permeability of dissolved timolol

We prepared magnesium hydroxide (MH) nanoparticles by a bead mill method, and investigated whether the co-instillation of MH nanoparticles improves the low transcorneal penetration of water-soluble drugs, such as the anti-glaucoma eye drug timolol maleate (TM). MH particle size was decreased by the bead mill treatment to a mean particle size of 71 nm. In addition, the MH nanoparticles were highly stable. Next, we demonstrated the effect of MH nanoparticles on the corneal surface. MH shows only slight solubility in lacrimal fluid, and the instillation of MH nanoparticles for 14 days did not affect the behavior (balance of secretion and excretion) of the lacrimal fluid in rabbit corneas. Moreover, there was no observable corneal toxicity of MH nanoparticles, and treatment with MH nanoparticles enhanced the intercellular space ratio in the eyes of rats. MH alone did not permeate into the cornea; however, the co-instillation of MH nanoparticles and dissolved TM (nMTFC) enhanced the corneal penetration of TM. In addition, the intraocular pressure (IOP)-reducing effect of nMTFC was significantly higher than those of the TM solution or the co-instillation of MH microparticles and TM. In conclusion, we found that MH nanoparticles enhance the corneal penetration of dissolved TM with no observable corneal stimulation or obstruction of the nasolacrimal duct by the MH nanoparticles. It is possible that the co-instillation of MH nanoparticles may provide a useful way to improve the bioavailability of water-soluble drugs in the ophthalmic field. These findings provide significant information that can be used to design further studies aimed at developing anti-glaucoma eye drugs.

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.

Pathogenesis of Uveitic Glaucoma

Uveitic glaucoma consists one of the most serious complications of intraocular inflammation and, despite its rarity, is considered as one of the leading causes of preventable loss of vision worldwide. It has been associated with a wide spectrum of inflammatory diseases, but its pathogenesis is still not fully comprehended. It appears that the type of inflammation, the steroid-response and the anatomical alterations of the anterior chamber play a pivotal role. To our knowledge, the mechanisms may be both acute and chronic. The main targets of the treatment are to control the inflammation and reduce the intraocular pressure (IOP). The management of glaucoma associated with uveitis remains an extremely challenging condition for ophthalmologists. The successful treatment of uveitic glaucoma is inextricably correlated with prompt and immediate therapeutic decisions. Very often a solid collaboration between clinicians from different specialties may be required for treating the underlying disease.

Further understanding of its pathogenesis can indicate therapeutic targets and may lead to the development of new and more efficient therapeutic approaches. New glaucoma surgical modalities may ameliorate the prognosis after surgical intervention, but this calls for further evaluation. This study aims to highlight the complexity of uveitic glaucoma analyzing the main pathogenetic mechanisms and the correlations with the inflammatory response.

The Relationship between Vitamin D and Glaucoma: A Kangbuk Samsung Health Study

PURPOSE

To investigate the relationship between vitamin D and glaucoma.

METHODS

This retrospective, cross-sectional study included subjects who underwent a health screening at the Health Screening Center of Kangbuk Samsung Hospital from August 2012 to July 2013. All fundus photographs were reviewed by ophthalmologists. The ophthalmologists determined if an eye was glaucomatous based on the criteria set forth by the International Society of Geographical and Epidemiological Ophthalmology and by the appearance of the retinal nerve fiber layer and optic disc. If the subjects previously underwent an ophthalmologic examination, they were enrolled based on the documented history. In addition to fundus photographs, each participant underwent a systemic examination including blood sampling and sociodemographic and behavioral questionnaires. The subjects were divided into five groups according to serum 25-hydroxyvitamin D (25(OH)D) level. Multivariate logistic regression models were constructed to assess possible associations between elevated glaucoma risk and systemic factors with a p < 0.2 on univariate analysis.

RESULTS

Of the 169,208 subjects older than 20 years, 123,331 were eligible for the study. There was no difference in the prevalence of glaucoma according to quintile of serum 25(OH)D level based on sex (p = 0.412 for males, p = 0.169 for females). According to the multivariable-adjusted logistic analysis, the odds ratio of glaucoma for the fourth quintile was significantly lower than that of the first quintile in females (odds ratio, 0.713; 95% confidence interval, 0.520 to 0.979).

CONCLUSIONS

Lower 25(OH)D level was significantly associated with an elevated risk of glaucoma in females compared with higher 25(OH)D level. Further evaluation is needed to investigate the relationship between glaucoma and vitamin D.

Long-Term Subconjunctival Delivery of Brimonidine Tartrate for Glaucoma Treatment Using a Microspheres/Carrier System

Core-shell polymer microspheres with poly(d,l-lactic-co-glycolic acid) core and poly(l-lactic acid) (PLLA) shell are developed for the long-term subconjunctival release of brimonidine tartrate (BT) in order to reduce intraocular pressure (IOP) in the treatment of glaucoma. The PLLA-rich shell acts as a diffusion barrier, enabling linear release of BT over an extended period of 40 d. The microspheres are encased in a porous non-degradable methacrylate-based carrier for ease of subconjunctival implantation in a glaucoma-induced rabbit model. In vivo release of BT from the microspheres/carrier system has enabled a significant, immediate IOP reduction of 20 mmHg, which is sustained for 55 d. Long-term IOP reduction may be maintained by periodic replacement of the microspheres/carrier system.

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.

Effect of potassium channel openers in acute and chronic models of glaucoma

PURPOSE

Glaucoma is characterized by increased intraocular pressure (IOP). The effect of nicorandil and pinacidil on IOP in experimentally induced acute and chronic models of glaucoma and the mechanism of action involved were studied.

METHODS

New Zealand white rabbits were used for the study. After the measurement of IOP, nicorandil (1%), pinacidil (1%), and pilocarpine as standard (1%) were instilled topically into the left eye. The other eye served as control. Dextrose (5%) was used to induce acute glaucoma. IOP changes were recorded every 15 minutes until the pressure became normal. Freshly prepared α-chymotrypsin solution was introduced in the posterior chamber to induce chronic glaucoma. Rabbits with ocular hypertension were selected for the study. Similar drug solutions were used to study the effect on IOP. Glibenclamide, pilocarpine, and indomethacin (1%) were used to study the mechanism of action of both drugs. The IOPs were measured just prior to drug instillation and at suitable time intervals using a tonometer.

RESULTS

Pretreatment with topical nicorandil and pinacidil significantly lowered the rise in IOP in the acute model. Nicorandil and pinacidil initially caused rise in IOP for 15-30 minutes in chronic glaucoma. This was followed by reduction in IOP. Pretreatment with indomethacin and pilocarpine did not modify the effect of nicorandil and pinacidil on IOP. Pretreatment with glibenclamide blocked IOP from the lowering effect of nicorandil and pinacidil.

CONCLUSION

The oculohypotensive effect shown by these drugs appears to be attributable to enhancement of the aqueous humor outflow. This effect is perhaps mediated through potassium channels.

Anti-glaucoma potential of Heliotropium indicum Linn in experimentally-induced glaucoma

Background

Heliotropium indicum is used as a traditional remedy for hypertension in Ghana. The aim of the study was to evaluate the anti-glaucoma potential of an aqueous whole plant extract of H. indicum to manage experimentally-induced glaucoma.

Methods

The percentage change in intraocular pressure (IOP), after inducing acute glaucoma (15 mLkg⁻¹ of 5 % dextrose, i.v.), in New Zealand White rabbits pretreated with Heliotropium indicum aqueous extract (HIE) (30–300 mgkg⁻¹), acetazolamide (5 mgkg⁻¹), and normal saline (10 mLkg⁻¹) per os were measured. IOPs were also monitored in chronic glaucoma in rabbits (induced by 1 % prednisolone acetate drops, 12 hourly for 21 days) after treatments with the same doses of HIE, acetazolamide, and normal saline for 2 weeks. The anti-oxidant property of the extract was assessed by assaying for glutathione levels in the aqueous humour. Glutamate concentration in the vitreous humour was also determined using ELISA technique. Histopathological assessment of the ciliary bodies was made.

Results

The extract significantly reduced intraocular pressure (p ≤ 0.05–0.001) in acute and chronic glaucoma, preserved glutathione levels and glutamate concentration (p ≤ 0.01–0.001). Histological assessment of the ciliary body showed a decrease in inflammatory infiltration in the extract and acetazolamide-treated group compared with the normal saline-treated group.

Conclusion

The aqueous whole plant extract of Heliotropium indicum has ocular hypotensive, anti-oxidant and possible neuro-protective effects, which therefore underscore its plausible utility as an anti-glaucoma drug with further investigation.

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.

The Pathogenesis of Raised Intraocular Pressure in Uveitis

AIM

To analyze current understanding of the factors that contribute to raised intraocular pressure (IOP) in patients with uveitis.

METHODS

A pubmed literature review was carried out using words including "uveitic glaucoma", "IOP AND uveitis", "ocular hypertension AND uveitis", "inflammation AND glaucoma", "aqueous dynamics" AND "glaucoma/uveitis".

RESULTS

Of the two studies looking at the aqueous dynamics in experimentally induced uveitis, both found aqueous flow decreased acutely, and one found that uveoscleral outflow increased. This is likely to reflect the types of uveitis that present acutely with hypotony. A study examining patients with Fuch's heterochromic cyclitis found no difference in aqueous flow or uveoscleral outflow. No studies have examined aqueous dynamics in types of uveitis that present with acutely raised IOP. Levels of prostaglandins rise in acute uveitis, which has been shown to increase uveoscleral and trabecular outflow, without affecting aqueous flow. Studies have demonstrated that raised levels of trabecular protein reduce trabecular outflow. Steroid treatment, inflammatory cells, free radicals and enzymes are also likely to contribute to the development of raised pressure. When considering the impact of the pathogenesis of raised pressure in uveitis on its treatment, prostaglandins may provide good intraocular pressure control, but there are concerns regarding their theoretical ability to worsen the inflammatory response in uveitis. Studies have not conclusively proven this to be the case. Surgical success rates vary, but trabeculectomy plus an antimetabolite, deep sclerectomy plus an antimetabolite, and Ahmed valve surgery have been used.

CONCLUSIONS

Uveitic glaucoma is caused by a number of different diseases, some of which present with acute hypotony, others with acutely raised IOP, and others which demonstrate an increase in IOP over time. Further studies should be carried out to examine the differing pathogenesis in these types of diseases, and to establish the best treatment options.

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.

Discovery of novel inhibitors for the treatment of glaucoma

INTRODUCTION

Glaucoma is a neurodegenerative disease with heterogeneous causes that result in retinal ganglionic cell (RGC) death. The discovery of ocular antihypertensives has shifted glaucoma therapy, largely, from surgery to medical intervention. Indeed, several intraocular pressure (IOP)-lowering drugs, with different mechanisms of action and RGC protective property, have been developed.

AREAS COVERED

In this review, the authors discuss the main new class of kinase inhibitors used as glaucoma treatments, which lower IOP by enhancing drainage and/or lowering production of aqueous humor. The authors include novel inhibitors under preclinical evaluation and investigation for their anti-glaucoma treatment. Additionally, the authors look at treatments that are in clinics now and which may be available in the near future.

EXPERT OPINION

Treatment of glaucoma remains challenging because the exact cause is yet to be delineated. Neuroprotection to the optic nerve head is undisputable. The novel Rho-associated kinase inhibitors have the capacity to lower IOP and provide optic nerve and RGC protection. In particular, the S-isomer of roscovitine has the capacity to lower IOP and provide neuroprotection. Combinations of selected drugs, which can provide maximal and sustained IOP-lowering effects as well as neuroprotection, are paramount to the prevention of glaucoma progression. In the near future, microRNA intervention may be considered as a potential therapeutic target.

Effect of Eye Drops Containing Disulfiram and Low-Substituted Methylcellulose in Reducing Intraocular Pressure in Rabbit Models

PURPOSE

We attempted to develop anti-glaucoma eye drops using 0.5% disulfiram (DSF), 5% 2-hydroxypropyl-β-cyclodextrin, 0.1% hydroxypropylmethylcellulose, and 2% methylcellulose (MC) (DSF eye drops with MC), and tested the ability of a DSF eye drops with MC to reduce intraocular pressure (IOP) in rabbit models.

METHODS

Elevated IOP was induced by the rapid infusion of 5% glucose solution (15 ml/kg of body weight) through the marginal ear vein or by keeping rabbits in the dark for 5 h. IOP and the nitric oxide (NO) level in the aqueous humor were measured with an electronic tonometer and by a microdialysis method, respectively. ΔIOP and ΔNO values were analyzed as the differences in IOP and NO in rabbits instilled with saline or eye drops, respectively.

RESULTS

Increased IOP in rabbit models was reduced by the instillation of DSF eye drops with or without MC, and a close relationship was observed between IOP and NO levels in rabbit receiving a rapid infusion of isotonic glucose. We present kinetic parameters [secondary AUC (prolonged drug effect) and secondary MRT (prolonged effective time)] analyzed as the area under the curve (AUC) of ΔIOP or ΔNO versus time using rabbits instilled with eye drops 10, 50, or 90 min prior to the infusion of the isotonic glucose solution. The elevations in IOP and NO level were reduced by the instillation of DSF eye drops with or without MC; the addition of MC increased the secondary AUC and MRT of DSF eye drops.

CONCLUSIONS

The present study demonstrates that 0.5% DSF eye drops suppress increased IOP in rabbit models, probably by inhibiting the elevation in NO levels. In addition, we propose a kinetic analysis method to predict drug effects and effective time. These findings suggest that a low-substituted MC-based drug delivery system promotes drug effectiveness and effective time.

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.

Is vitamin D status associated with open-angle glaucoma? A cross-sectional study from South Korea

OBJECTIVE

Open-angle glaucoma (OAG) is one of the major chronic diseases involving the optic nerve. However, little is known about the association between vitamin D and OAG. The present study was conducted to test the hypothesis that lower vitamin D status is associated with greater prevalence of OAG.

DESIGN

Cross-sectional study. Multivariable logistic regression was performed to examine the relationship between serum 25-hydroxyvitamin D (25(OH)D) and OAG after adjusting for traditional potential confounders. OAG was defined by the criteria of the International Society for Geographical and Epidemiological Ophthalmology.

SETTING

The Fifth Korean National Health and Nutrition Examination Survey conducted in 2010-2011.

SUBJECTS

Six thousand and ninety-four adult participants randomly selected from 192 surveys in 131 locations in South Korea.

RESULTS

Multivariable-adjusted odds ratios of OAG across quintiles of decreasing 25(OH)D were 1.26, 1.00 (reference), 1.31, 1.36 and 1.69 (P for quadratic trend <0.01). The odds ratio for the lowest 25(OH)D quintile was significantly higher than that for the second quintile (P < 0.01). In addition, we discovered that the predictors for worsening of OAG, such as intraocular pressure or vertical and horizontal cup-to-disc ratios, had a significant relationship with 25(OH)D level.

CONCLUSIONS

There was a reverse J-shaped association between 25(OH)D levels and the risk of OAG, with significantly elevated risk at lower 25(OH)D. The findings of this research suggest that vitamin D deficiency should be considered as a potential risk factor for the development of OAG. To our knowledge, the present study is the first one that shows an association between vitamin D status and OAG.

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.

Antiglaucomatous effects of the activation of intrinsic Angiotensin-converting enzyme 2

PURPOSE

To evaluate the effects of the activation of endogenous angiotensin-converting enzyme 2 (ACE2) using the compound diminazene aceturate (DIZE) in an experimental model of glaucoma in Wistar rats.

METHODS

DIZE (1 mg/kg) was administered daily, either systemically or topically, and the IOP was measured weekly. To examine the role of the Mas receptor in the effects of DIZE, the Ang-(1-7) antagonist A-779 was co-administered. Drainage of the aqueous humor was evaluated by using scintigraphy. The analysis of ACE2 expression by immunohistochemistry and the counting of retinal ganglion cells (RGCs) were performed in histologic sections. Additionally, the nerve fiber structure was evaluated by transmission electron microscopy.

RESULTS

The systemic administration and topical administration (in the form of eye drops) of DIZE increased the ACE2 expression in the eyes and significantly decreased the IOP of glaucomatous rats without changing the blood pressure. Importantly, this IOP-lowering action of DIZE was similar to the effects of dorzolamide. The antiglaucomatous effects of DIZE were blocked by A-779. Histologic analysis revealed that the reduction in the number of RGCs and the increase in the expression of caspase-3 in the RGC layer in glaucomatous animals were prevented by DIZE. This compound also prevented alterations in the cytoplasm of axons in glaucomatous rats. In addition to these neuroprotective effects, DIZE facilitated the drainage of the aqueous humor.

CONCLUSIONS

Our results evidence the pathophysiologic relevance of the ocular ACE2/Ang-(1-7)/Mas axis of the renin-angiotensin system and, importantly, indicate that the activation of intrinsic ACE2 is a potential therapeutic strategy to treat glaucoma.

Blood pressure, ocular perfusion pressure, and body mass index in glaucoma patients

PURPOSE

To investigate relationships between blood pressure (BP), ocular perfusion pressure (OPP), and intraocular pressure (IOP) in patients with open-angle glaucoma (OAG) of different body mass index (BMI) classes. 


METHODS

Data from participants of a prospective, longitudinal, single site, observational study were analyzed. Patients with a prior diagnosis of OAG completed 2 baseline visits (1 week apart) with follow-up visits every 6 months for 2 years. At each visit, BP, weight, height, and IOP were recorded for normal-weight (BMI 18.5-24.9; n = 38), overweight (BMI 25.0-29.9; n = 43), and obese (BMI ≥30; n = 34) patients: The BP was measured using automated ambulatory measurements after 5 minutes rest and IOP was measured using Goldmann applanation tonometry.


RESULTS

The IOP decreased from baseline to 2-year measurement in normal-weight (-1.5, 95% confidence interval [CI] -2.7 to -0.4), overweight (-1.9, 95% CI -3.4 to -0.4), and obese (-2.5, 95% CI -3.9 to -1.2) patients with OAG. Systolic BP (SBP) and OPP decreased from baseline to 2-year measurement in all 3 BMI categories, although not reaching statistical significance. In normal-weight patients, there was a significant, positive correlation between changes in IOP and SBP (r = 0.36, p = 0.0431). A significant, negative correlation was observed between changes in IOP and OPP in overweight 
(r = -0.56, p = 0.0002) and obese (r = -0.38, p = 0.0499) patients.


CONCLUSIONS

This study demonstrated that in normal-weight individuals with OAG, changes in SBP were positively correlated to changes in IOP. However, this relationship did not exist for overweight or obese patients. Instead, overweight and obese patients displayed a negative correlation between OPP and IOP.

Glaucomatous optic nerve head alterations in patients with chronic heart failure

Purpose

To evaluate the association between chronic heart failure (CHF) and optic nerve head alterations.

Methods

A cross-sectional study was performed. Heart failure patients with recent echocardiograms were subjected to ophthalmologic examinations, including intraocular pressure measurement, optic nerve head, and retinal nerve fiber layer evaluation using stereophotography, Heidelberg retinal tomography, and standard automated perimetry. The ocular findings were correlated with the cardiological evaluation, and compared with a control group without cardiopathy.

Results

A total of 30 patients with CHF and 30 individuals without cardiopathy were enrolled in this study. The mean (standard deviation [SD]) intraocular pressure was 12.3 (2.5) mmHg in the CHF group, and 14.7 (2.9) mmHg in the control group (P < 0.001). The mean (SD) arterial blood pressure was 86.9 (17.1) mmHg in the CHF group, and 103.6 (15.2) mmHg in the control group (P < 0.001). The mean (SD) ocular perfusion pressure was 45.6 (11.1) mmHg in the CHF group, and 54.4 (10.4) mmHg in the control group (P = 0.001). The mean (SD) rim area was 1.41 (0.3) mm² in the CHF group, and 1.60 (0.26) mm² in the control group (P = 0.003). The mean (SD) vertical cup/disc ratio was 0.51 (0.17) in the CHF group, and 0.41 (0.18) in the control group (P = 0.02). The Moorfields regression analysis was outside the normal limits in 16 out of 58 (27.6%) eyes of the CHF subjects, and in 4 out of 60 (6.7%) eyes of the control subjects (P = 0.01). The frequency of glaucoma was 10% in the CHF group, whereas none of the control subjects met the criteria for the diagnosis of glaucoma (P = 0.24).

Conclusion

CHF is associated with lower ocular perfusion pressure, and glaucomatous optic nerve head changes.

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.

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.

Oculohypotensive effect of perindopril in acute and chronic models of glaucoma in rabbits

We studied the effect of perindopril (1%) on intraocular pressure (IOP) and compared it with the effect of pilocarpine, a therapeutic agent used in experimentally induced acute and chronic models of glaucoma in rabbits. Acute glaucoma was induced by intravenous administration of 5% glucose. Pretreatment with topical perindopril (1%) and pilocarpine (1%) prevented acute rise in IOP induced by intravenous administration of 5% glucose. For inducing chronic ocular hypertension in rabbits, 50 units of freshly prepared α-chymotrypsin in 0.1 mL of sterile saline was injected in the posterior chamber of the eye. Perindopril (1%) (35 ± 1.38 mm Hg to 22.45 ± 1.42 mm Hg) and pilocarpine (1%) (34.4 ± 0.81 mm Hg to 20.15 ± 0.69 mm Hg) produced a significant fall in IOP in these rabbits; pretreatment with indomethacin (prostaglandin synthesis inhibitor) did not affect the IOP-lowering action of perindopril (1%). Perindopril (2.71 × 10−7 mol/L) and neostigmine (1.49 × 10−7mol/L) inhibited true cholinesterase and pseudocholinesterase enzyme activity in blood. The cholinesterase enzyme inhibition by perindopril was comparable with that by neostigmine. In conclusion, our data suggest that perindopril reduced IOP in experimentally induced acute and chronic glaucoma in rabbits. One of the possible mechanisms of perindopril, apart from the inhibition of angiotensin-converting enzyme, may be inhibition of the enzyme cholinesterase.

Diabetes, glycemic control and risk of medical glaucoma treatment: A population-based case-control study

Purpose:

To examine the association between diabetes and risk of medical glaucoma treatment and to assess the role of long-term glycemic control in the putative association.

Design:

Population-based case-control study.

Methods:

Cases of treated glaucoma were all persons filling at least three prescriptions for glaucoma medication for the first time within one year between 2001 and 2006 in Northern Jutland, Denmark. We used risk set sampling to select 10 gender- and age-matched general population controls per case using the Danish Civil Registration System. Data on diabetes, comorbidities, and laboratory tests, including glycosylated hemoglobin (as a measure of glycemic control) were obtained from population-based medical registries. We calculated odds ratio (OR) as an estimate of relative risk for treated glaucoma comparing patients with and without diabetes, adjusted for comorbid conditions and medication use.

Results:

We included 5,991 persons with incident medical glaucoma treatment and 59,910 population controls. The adjusted OR for treated glaucoma for patients with diabetes was 1.81 (95% confidence interval: 1.65–1.98). The strength of the association between diabetes and glaucoma risk did not vary by diabetes duration or by the level of glycemic control.

Conclusions:

Regardless of glycemic control, diabetes is associated with a substantially increased risk for medical glaucoma treatment.