Effect of Oral Captopril (SQ 14225) on Intraocular Pressure in Man

Toward structural-omics of the bovine retinal pigment epithelium

The use of an integrated systems biology approach to investigate tissues and organs has been thought to be impracticable in the field of structural biology, where the techniques mainly focus on determining the structure of a particular biomacromolecule of interest. Here, we report the use of cryoelectron microscopy (cryo-EM) to define the composition of a raw bovine retinal pigment epithelium (RPE) lysate. From this sample, we simultaneously identify and solve cryo-EM structures of seven different RPE enzymes whose functions affect neurotransmitter recycling, iron metabolism, gluconeogenesis, glycolysis, axonal development, and energy homeostasis. Interestingly, dysfunction of these important proteins has been directly linked to several neurodegenerative disorders, including Huntington's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, Alzheimer's disease, and schizophrenia. Our work underscores the importance of cryo-EM in facilitating tissue and organ proteomics at the atomic level.

Distribution of Pupil Size and Associated Factors: Results from the Population-Based Gutenberg Health Study

Results

18,335 eyes of 9,559 participants aged 40 to 80 years were included in the analysis. Median pupil diameter was 4.19 mm in right eyes and 4.12 mm in left eyes. A smaller pupil was associated with older age, hyperopic refractive error, previous cataract surgery, diabetes, obesity, and ACE inhibitor intake, whereas wider pupil was associated with female gender, arterial hypertension, intake of tricyclic antidepressants, and intake of SNRI and tetracyclic antidepressants. Socioeconomic status and smoking were not associated with pupil size.

Conclusion

Individuals of older age, after cataract surgery, under therapy with ACE inhibitors and with diabetes have a smaller pupil. This should be taken into account when planning nonmydriatic fundus photography-based screening programs, for instance, for diabetic retinopathy.

Physicochemical and Stability Evaluation of Topical Niosomal Encapsulating Fosinopril/γ-Cyclodextrin Complex for Ocular Delivery

This study aimed to develop a chemically stable niosomal eye drop containing fosinopril (FOS) for lowering intraocular pressure. The effects of cyclodextrin (CD), surfactant types and membrane stabilizer/charged inducers on physiochemical and chemical properties of niosome were evaluated. The pH value, average particle size, size distribution and zeta potentials were within the acceptable range. All niosomal formulations were shown to be slightly hypertonic with low viscosity. Span® 60/dicetyl phosphate niosomes in the presence and absence of γCD were selected as the optimum formulations according to their high %entrapment efficiency and negative zeta potential values as well as controlled release profile. According to ex vivo permeation study, the obtained lowest flux and apparent permeability coefficient values confirmed that FOS/γCD complex was encapsulated within the inner aqueous core of niosome and could be able to protect FOS from its hydrolytic degradation. The in vitro cytotoxicity revealed that niosome entrapped FOS or FOS/γCD formulations were moderate irritation to the eyes. Furthermore, FOS-loaded niosomal preparations exhibited good physical and chemical stabilities especially of those in the presence of γCD, for at least three months under the storage condition of 2–8 °C.

Mechanistic links between systemic hypertension and open angle glaucoma

Systemic hypertension or hypertension is a very common chronic age-related disease worldwide. It is typically characterised by a sustained elevation of blood pressure, particularly when the systolic blood pressure and/or diastolic blood pressure are of more than 140 mmHg and 90 mmHg, respectively. If hypertension is not well controlled, it may lead to an increased risk of stroke and heart attack. It has been shown that hypertension is linked to various ocular diseases, including cataract, diabetic retinopathy, age-related macular degeneration, and glaucoma. Glaucoma is the leading cause of irreversible blindness worldwide. Primary open angle glaucoma is the most common form of the disease and is usually characterised by an increase in intraocular pressure. This condition, together with normal tension glaucoma, constitutes open angle glaucoma. Systemic hypertension has been identified as a risk factor for open angle glaucoma. It is speculated that blood pressure is involved in the pathogenesis of open angle glaucoma by altering intraocular pressure or ocular blood flow, or both. Recent evidence has shown that both extremely high and low blood pressure are associated with increased risk of open angle glaucoma. Additional pathogenic mechanisms, including increased inflammation likely to be involved in the development and progression of these two diseases, are discussed.

Angiotensin Receptor Blockers in cyclodextrin nanoparticle eye drops: Ocular pharmacokinetics and pharmacologic effect on intraocular pressure

PURPOSE

Orally administered angiotensin II receptor blockers (ARBs) decrease intraocular pressure (IOP). Topical administration may reduce systemic side effects and result in a useful glaucoma drug. The aim of this study is to test the ocular delivery and pharmacologic effect of nanoparticle eye drops containing ARBs (e.g. irbesartan and candesartan).

METHODS

1.5% irbesartan and 0.15% candesartan eye drops were applied to rabbits. The pharmacokinetics in cornea and aqueous humour after single eye drop application were studied in 49 rabbits. The effect of the eye drops on IOP was studied in 10 rabbits using an iCare (® TonoVet Plus, iCare, Finland) tonometer and compared with 0.5% timolol eye drops.

RESULTS

Candesartan lowered IOP from 24.6 ± 5.1 mmHg at baseline to 19.0 ± 2.9 mmHg (mean ± SD, p = 0.030, n = 10) 4 hr after application. Irbesartan lowered IOP from 24.2 ± 1.7 mmHg to 20.2 ± 0.9 mmHg (p = 0.14, n = 10). Timolol decreased the IOP from 24.9 ± 4.2 mmHg to 20.4 ± 4.8 mmHg (mean ± SD, p = 0.036, n = 10). The pharmacokinetics data show that both formulations deliver effective amounts of drug into the intraocular tissues, with irbesartan and candesartan reaching concentrations of 121 ± 69 and 30.43 ± 13.93 ng/g (mean ± SD), respectively, in the aqueous humour 3 hr after a single-dose administration.

CONCLUSIONS

Topical application of irbesartan and candesartan eye drops delivers effective drug concentrations to the anterior segment of the eye in rabbits, achieving drug concentrations 100 times above the IC50 for angiotensin II receptor and showing an IOP-lowering effect. Angiotensin receptor blocker (ARB) eye drops have potential as a new class of glaucoma drugs.

Endocrine Dysfunction in Open Angle Glaucoma

The eye, like all organs, is exposed to the effects of the body's endocrine system. In addition, however, local branches of the endocrine system control important organ-specific functions, such as the production and drainage of aqueous humour. Similarly, the eye as a sensory organ acts back on endocrine controlled functions of the body, for example the day-night rhythm. This article aims to illustrate the physiological and pathological interactions of the eye and the endocrine functions of the body in the context of glaucoma. 1. The renin-angiotensin-aldosterone system, which as a local system is involved in the control of aqueous humour production and outflow. 2. The hormone endothelin, which as a strong vasoconstrictor plays a role in the dysregulated perfusion of the optic nerve and retina, and 3. the disruption of the day-night rhythm in advanced glaucoma, which is thought to be caused by damage to light-sensitive ganglion cells.

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.

Low systemic vitamin D as a potential risk factor in primary open-angle glaucoma: a review of current evidence

Currently, intraocular pressure is the only modifiable risk factor for glaucoma; thus, identifying other modifiable determinants may have far-reaching outcomes. There has been increasing interest in vitamin D status and glaucoma pathogenesis as low vitamin D has been identified by some studies as an independent risk factor for glaucoma. Although the exact mechanism of vitamin D in glaucoma remains uncertain, there is sufficient evidence to continue research in this area. There is a potential physiological role for vitamin D as an anti-inflammatory agent in the oxidative stress-driven pathogenesis of primary open-angle glaucoma, and further studies are required to evaluate the temporal and causal relationship. Ocular vitamin D status in the tear, aqueous and vitreous fluid is a prospective gap in research.

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.

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.

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.

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.

The expression of Mas-receptor of the renin-angiotensin system in the human eye

PURPOSE

The local renin-angiotensin system has been held to be expressed in many organs, including the eye. It has an important role in the regulation of local fluid homeostasis, cell proliferation, fibrosis, and vascular tone. Mas-receptor (Mas-R) is a potential receptor acting mainly opposite to the well-known angiotensin II receptor type 1. The aim of this study was to determine if Mas-R is expressed in the human eye.

METHODS

Seven enucleated human eyes were used in immunohistochemical detection of Mas-R and its endogenous ligand angiotensin (1-7) [Ang(1-7)]. Both light microscopy and immunofluorescent detection methods were used. A human kidney preparation sample was used as control.

RESULTS

The Mas-R was found to have nuclear localization, and localized in the retinal nuclear layers and in the structures of the anterior segment of the eye. A cytoplasmic immunostaining pattern of Ang(1-7) was found in the inner and outer nuclear and plexiform layers of the retina and in the ciliary body.

CONCLUSION

To the best of our knowledge, this is the first report showing Mas-R expression in the human eye. Its localization suggests that it may have a role in physiological and pathological processes in the anterior part of the eye and in the retina.

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.

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.

Insights into substrate specificity and metal activation of mammalian tetrahedral aspartyl aminopeptidase

Aminopeptidases are key enzymes involved in the regulation of signaling peptide activity. Here, we present a detailed biochemical and structural analysis of an evolutionary highly conserved aspartyl aminopeptidase called DNPEP. We show that this peptidase can cleave multiple physiologically relevant substrates, including angiotensins, and thus may play a key role in regulating neuron function. Using a combination of x-ray crystallography, x-ray absorption spectroscopy, and single particle electron microscopy analysis, we provide the first detailed structural analysis of DNPEP. We show that this enzyme possesses a binuclear zinc-active site in which one of the zinc ions is readily exchangeable with other divalent cations such as manganese, which strongly stimulates the enzymatic activity of the protein. The plasticity of this metal-binding site suggests a mechanism for regulation of DNPEP activity. We also demonstrate that DNPEP assembles into a functionally relevant tetrahedral complex that restricts access of peptide substrates to the active site. These structural data allow rationalization of the enzyme's preference for short peptide substrates with N-terminal acidic residues. This study provides a structural basis for understanding the physiology and bioinorganic chemistry of DNPEP and other M18 family aminopeptidases.

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.

1α,25-Dihydroxyvitamin D(3) and its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), suppress intraocular pressure in non-human primates

Ocular hypertension is the greatest known risk factor for glaucoma that affects an estimated 70 million people worldwide. Lowering intraocular pressure (IOP) remains the mainstay of therapy in the management of glaucoma. By means of microarray analysis, we have discovered that 1α,25-dihydroxyvitamin D(3) (1α,25-(OH)(2)D(3)) regulates genes that are known to be involved in the determination of intraocular pressure (IOP). Topical administration of 1α,25-(OH)(2)D(3) or its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), markedly reduces IOP in non-human primates. The reduction in IOP is not the result of reduced aqueous humor formation, while a 35% increase in aqueous humor drainage by 1α,25-(OH)(2)D(3) was found but this increase did not achieve significance. Nevertheless, our results suggest that 1α,25-(OH)(2)D(3), or an analog thereof, may present a new approach to the treatment of glaucoma.

Local ocular renin-angiotensin system - a target for glaucoma therapy?

An active local intraocular renin-angiotensin system (RAS) has recently been shown to exist in the human eye, and evidence is now accumulating that antihypertensive drugs acting on RAS can also lower intraocular pressure. They seem also to work as neuroprotective agents against retinal ganglion cell loss in vivo; though no compounds are in ophthalmological use at present. Classically, the highly vasoconstrictive angiotensin II (Ang II) is the key peptide in the circulatory RAS. However, the final 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.

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.

Glaucoma and systemic diseases

Glaucoma management may be extremely challenging, especially in elderly patients who have a variety of systemic diseases and take multiple medications. We obtained a comprehensive medical history in patients with primary open-angle glaucoma to determine which systemic diseases are most prevalent and which systemic medications are most commonly used. We have also reviewed the literature that addresses how these concomitant diseases and medical treatments influence the management of glaucoma. Knowledge of systemic diseases and potential drug interactions, especially between various systemic and glaucoma medications, is important for the safe management of glaucoma patients.

Activities of angiotensin-converting enzymes ACE1 and ACE2 and inhibition by bioactive peptides in porcine ocular tissues

PURPOSE

An active local renin-angiotensin system (RAS) has recently been found in the human eye. The aim of the present study was to compare the activities of central RAS enzymes (ACE1 and 2) in porcine ocular tissues, morphologically and physiologically close to the human eye. In addition, the effects of three ACE-inhibitory tripeptides on these enzymes were evaluated.

METHODS

Enucleated fresh porcine eyes were used. Activities of ACE1 and ACE2 and their inhibition by bioactive tripeptides (Ile-Pro-Pro, Val-Pro-Pro, Leu-Pro-Pro) as well as by a standard ACE-inhibitor captopril were assayed in the vitreous body, the retina and the ciliary body using fluorometric detection methods.

RESULTS

Activity of ACE1 as well as ACE2 was found in all tissues evaluated. ACE1 activity was markedly higher in the ciliary body (3.7 +/- 0.7 mU/mg protein) than in retina (0.2 +/- 0.02 mU/mg), whereas ACE2 activities in the ciliary body (0.2 +/- 0.02 mU/mg) and retina (0.2 +/- 0.01 mU/mg) were at the same level. In the vitreous body ACE1 activity (8.2 +/- 0.31 nmol/min/mL) was manifold compared to that of ACE2 (0.1 +/- 0.02 nmol/min/mL). The tripeptides inhibited ACE1 at one-thousandth of the concentration needed to inhibit ACE2. All peptides studied evinced about equal inhibitory activities.

CONCLUSION

To our knowledge the present findings constitute the first evidence of ACE2 activity in the ciliary and vitreous bodies, in addition to previously described activity in the retina. The known favorable effects of ACE2 products vs. those of ACE1 suggest a counterbalancing interaction of these two enzyme homologues in physiological regulation of ocular circulation and pressure and possible protective role in certain ophthalmic disorders such as glaucoma and diabetic retinopathy.

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.

No relation between angiotensin-converting enzyme gene polymorphism and pseudoexfoliation

AIMS

To determine the association between the angiotensin-converting enzyme insertion/deletion (I/D) polymorphism and pseudoexfoliation (PEX) in Turkish patients.

METHODS

This prospective study consisted of 89 patients with PEX, and 120 controls. The I/D polymorphism of the angiotensin-converting enzyme gene was measured with the use of the polymerase chain reaction method.

RESULTS

The distribution of the polymorphism was not significantly different in cases with PEX and controls. The frequencies of the I and D alleles were not significantly different between the groups.

CONCLUSION

According to our findings, I/D polymorphism in the angiotensin-converting enzyme gene does not play any role in the pathogenesis of PEX.

Immunohistochemical localization of angiotensin-converting enzyme, angiotensin II and AT1 receptor in human ocular tissues

We investigated the immunohistochemical distribution of 3 components of the renin-angiotensin system (RAS), angiotensin-converting enzyme (ACE), angiotensin II (AngII) and AT1 receptor (AT1), in the human eye. ACE and AngII were localized to nonpigmented epithelial cells of the ciliary body, to endothelial and epithelial cells of the cornea, to epithelial cells of the conjunctiva and to trabecular meshwork cells in the anterior part of the eye. In the posterior part of the eye, ACE and AngII were localized to ganglion cells, some cells in the inner nuclear layer, photoreceptor cells and to endothelial cells of the retinal and choroidal vessels. The overall intensity of AT1 immunoreactivity was weak in all ocular tissues, but the main localization was in ganglion cells. As a preliminary investigation, we were able to include 2 Alzheimer's disease (AD) cases. In AD, no differences from controls were found in the cellular distribution and staining intensity of all 3 antigens. The manifold localization sites of the observed antigens point to rather generalized functions of the RAS in human ocular tissues, such as regulatory effects on neuronal cells, vessels and vitreous humor homeostasis.

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

To evaluate the effect of CS-088, an angiotensin AT1 receptor antagonist, on intraocular pressure (IOP) in monkey eyes with unilateral laser-induced glaucoma. A multiple-dose study was performed in 8 glaucomatous monkey eyes. One 50 microl drop of CS-088, 2% or 4%, was topically applied to the glaucomatous eye at 9:30 a.m. and 3:30 p.m. for 5 consecutive days. IOP was measured hourly for 6 hours beginning at 9:30 a.m. for one baseline day, one vehicle-treated day, and daily for 5 days of treatment with CS-088. The washout period between the two drug concentrations was at least 2 weeks. Twice daily administration of 2 % CS-088 for 5 days did not reduce the IOP until the third dose on day 2 of the treatment regimen. A significant (p<0.02) reduction in IOP began 1 hour after the third dose, and lasted for 3 hours. The maximum reduction in IOP was 5.3+/- 0.8 (mean+/-SEM) mmHg (15%) (p<0.001), with the longest duration of IOP reduction of at least 6 hours after dosing on day 5. The 4% dose of CS-088 reduced (p<0.05) IOP from 1 to 5 hours after the first dose. The maximum reduction in IOP was 6.9+/-1.0 mmHg (20%), with the longest duration of IOP reduction of at least 18 hours after administration on day 5. Both 2% and 4% CS-088 showed enhancement of the ocular hypotensive effect with repeated dosing. 4% CS-088 produced greater (p<0.05) IOP reduction with longer duration of action than 2%. Topically applied CS-088, a new antagonist drug at the angiotensin AT1 receptor, reduced IOP in glaucomatous monkey eyes in a dose-dependent manner.

Angiotensin converting anzyme (ACE) activity in porcine ocular tissue: effects of diet and ACE inhibitors

The aim of the present experiments was to determine angiotensin converting enzyme (ACE) activity in different parts of the porcine eye, and to examine whether an atherogenic diet influenced ACE activity. Female mini-pigs were fed a standard diet or a diet with high cholesterol to produce atherosclerosis. The animals were killed by an overdose of pentobarbital, and the eyes were enucleated and dissected into iris, ciliary body, retina, and choroid. Crude tissue homogenates were used for determination of ACE activity, which was done with a radioenzymatic assay. In pigs fed a normal diet, basal ACE activity was 18.1 +/- 1.6, 13.6 +/- 1.9, 4.4 +/- 0.6, and 44.7 +/- 8.5 units/mg for iris, ciliary body, retina, and choroid, respectively. The ACE activities in ocular tissues from the pigs that had been fed an atherogenic diet were not significantly different. Nor was the ACE activity in the abdominal aorta and serum significantly different between the two groups. In both groups, the ACE inhibitors captopril and enalaprilat, caused a significant inhibition of the ACE activity in the choroid and ciliary body, with enalaprilat being more potent. In the retina, ACE activity was inhibited significantly only in the group fed a normal diet, whereas ACE activity in the iris was not significantly inhibited in either group. We did not find any differences in ACE activity between pigs fed a normal diet and pigs fed an atherogenic diet, which is in disagreement with previous studies that showed an increased ACE activity in aorta from atherosclerotic mini-pigs. The reason for this discrepancy is not clear, but lower cholesterol levels are one possibility.

Angiotensin-Converting Enzyme Insertion-Deletion Polymorphism in Primary Open-Angle Glaucoma

PURPOSE

To investigate the hypothesis that primary open-angle glaucoma (POAG) is associated with a common insertion-deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene.

METHODS

ACE I/D polymorphism was investigated in a control group of healthy subjects (n = 101) and in a group of patients diagnosed with POAG (n = 104). Polymerase chain reaction detection of I/D polymorphism was used to determine the presence of the two ACE alleles in the groups.

RESULTS

Neither the I/D genotype distributions nor the allele frequencies differed significantly between POAG and control subjects (DD genotype 34.6 vs. 39.6%; ID genotype 53.9 vs. 40.6%; II genotype 11.5 vs. 19.8%, p = 0.1; D allele 61.5 vs. 60%; I allele 38.5 vs. 40%, p = 0.8).

CONCLUSION

We could not identify a possible association of the I/D polymorphism in the ACE gene with POAG, however further studies with larger patient numbers in different populations are required to clarify the role of ACE gene in susceptibility to POAG.

Associations between the deletion polymorphism of the angiotensin 1-converting enzyme gene and ocular signs of primary open-angle glaucoma

BACKGROUND

Primary open-angle glaucoma (POAG) is a leading cause of blindness. High intraocular pressure (IOP) has been shown to be a key risk factor for POAG. Topical application of angiotensin 1-converting enzyme (ACE) inhibitors has been shown to lower IOP, and angiotensin-induced increase in vascular tone has been implicated as a pathogenetic mechanism in glaucomatous cupping and damage to the optic nerve. The objective of this study was to investigate the association between the deletion polymorphism in the ACE gene and ocular signs of POAG.

METHODS

Baseline data from the Rotterdam Study was used. The ACE genotype was determined in 6,462 subjects. We used univariate and multiple variable statistical techniques to examine associations between ACE genotype and each of ocular hypertension, glaucomatous optic neuropathy, glaucomatous visual field defects and POAG diagnosis.

RESULTS

We found no consistent evidence between ACE genotype and ocular signs of POAG. We did, however, find evidence of an association between ACE genotype and optic disc area, subjects homozygous for the deletion allele tending to have fractionally smaller optic disc areas than those with a single deletion allele subjects, who in turn tended to have fractionally smaller optic discs than those with no deletion alleles (P=0.01).

CONCLUSIONS

The data provided little evidence of any association between ocular signs of POAG and the deletion polymorphism of ACE. There was, however, evidence that ACE may be associated with optic disc size-this was an unexpected finding.

The effects of antiglaucoma and systemic medications on ocular blood flow

Based on the body of evidence implicating ocular blood flow disturbances in the pathogenesis of glaucoma, there is great interest in the investigation of the effects of antiglaucoma drugs and systemic medications on the various ocular vascular beds. The primary aim of this article was to review the current data available on the effects of antiglaucoma drugs and systemic medications on ocular blood flow. We performed a literature search in November 2002, which consisted of a textword search in MEDLINE for the years 1968-2002. The results of this review suggest that there is a severe lack of well-designed long-term studies investigating the effects of antiglaucoma and systemic medications on ocular blood flow in glaucomatous patients. However, among the 136 articles dealing with the effect of antiglaucoma drugs on ocular blood flow, only 36 (26.5%) investigated the effects of medications on glaucoma patients. Among these 36 articles, only 3 (8.3%) were long-term studies, and only 16 (44.4%) were double-masked, randomized, prospective trials. Among the 33 articles describing the effects of systemic medications on ocular blood flow, only 11 (33.3%) investigated glaucoma patients, of which only one (9.1%) was a double-masked, randomized, prospective trial. Based on this preliminary data, we would intimate that few antiglaucoma medications have the potential to directly improve ocular blood flow. Unoprostone appears to have a reproducible antiendothelin-1 effect, betaxolol may exert a calcium-channel blocker action, apraclonidine consistently leads to anterior segment vasoconstriction, and carbonic anhydrase inhibitors seem to accelerate the retinal circulation. Longitudinal, prospective, randomized trials are needed to investigate the effects of vasoactive substances with no hypotensive effect on the progression of glaucoma.

Nitric oxide and cyclic GMP enhance aqueous humor outflow facility in rabbits

PURPOSE

Nitric oxide (NO) may control intraocular pressure (IOP)-regulating mechanisms physiologically and in ocular diseases such as glaucoma. The aim of the present study was to clarify whether an increase in aqueous humor outflow facility could explain the IOP-lowering effect of the NO/cyclic GMP pathway we recently described.

METHODS

Test compounds were administered to anesthetized rabbits (New Zealand White, n = 6) intracamerally (5 microl) in the following doses: nitrosocaptopril 12.3 microg, captopril 10.9 microg, sodium nitroprusside (SNP) 13.1 microg and 8-Br-cGMP 22.3 microg. Outflow facility (C) was determined by the two-level constant pressure infusion method. Outflow facility, C( 1) and C(2), was measured at lower and higher pressure levels, respectively.

RESULTS

Outflow facility was increased after treatment with SNP (increase in C in the experimental eye as compared to the control eye C( 1) 80% and C(2) 74%), nitrosocaptopril (C(1) 69% and C(2) 64%) and 8-Br-cGMP (C(1) 35% and C(2) 33%). Captopril had no effect on outflow facility (C(1) -12% and C(2) 2%). Blood pressure was not affected by the drugs.

CONCLUSIONS

We conclude that enhancement of outflow facility by nitrosocaptopril, SNP and 8-Br-cGMP, their second messenger derivative, at least partly explains the IOP-lowering effect of NO releasing compounds.

Influence of ANG II on cytoplasmic sodium in cultured rabbit nonpigmented ciliary epithelium

Angiotensin (ANG) II receptors have been reported in the nonpigmented ciliary epithelium (NPE) of the eye. In cultured NPE, we found ANG II caused a dose-dependent rise of cytoplasmic sodium. The sodium increase was inhibited by the AT(1)-AT(2) receptor antagonist saralasin (IC(50) = 3.7 nM) and the AT(1) antagonist losartan (IC(50) = 0.6 nM) but not by the AT(2) antagonist PD-123319. ANG II also caused a dose-dependent increase in the rate of ouabain-sensitive (86)Rb uptake. The ANG II-induced cell sodium increase and (86)Rb uptake increase were reduced by dimethylamiloride (DMA; 10 microM). On the basis of this finding, we propose that Na(+)/H(+) exchange is stimulated by ANG II. Simultaneously, ANG II appears to inhibit H(+)-ATPase-mediated proton export. Thus Ang II (10 nM) did not alter the baseline cytoplasmic pH (pH(i)) but reduced pH(i) in cells that were also exposed to 10 microM DMA. Consistent with the notion of H(+)-ATPase inhibition in ANG II-treated NPE, bafilomycin A(1) (100 nM) (BAF) and ANG II were both observed to suppress the pH(i) increase that occurs upon exposure to a mixture of epinephrine (1 microM) and acetylcholine (10 microM) and the pH(i) increase elicited by depolarization. In ATP hydrolysis measurements, H(+)-ATPase activity (bafilomycin A(1)-sensitive ATP hydrolysis) was reduced significantly in cells that had been pretreated 10 min with 10 nM ANG II. In summary, these studies suggest that ANG II causes H(+)-ATPase inhibition and an increase of cell sodium due to activation of Na(+)/H(+) exchange.

The effect of angiotensin II on uveoscleral outflow in rabbits

PURPOSE

In our previous study, we showed that the AT1 receptor antagonist increased uveoscleral outflow (USF) when topically applied to the rabbit eye. However this increase was too small to demonstrate a clear physiological role for ocular angiotensin II (AII). Hence, the purpose of this study was to determine whether ocular AII influenced USF regulation, and if so, how this occurred.

METHODS

USF was measured by the FITC-dextran perfusion method in albino rabbits. AII and its receptor antagonists were directly applied into the anterior chamber by adding into the perfusate and by perfusing with FITC-dextran. We also analyzed angiotensin receptors on the rabbit ciliary body membrane by a receptor binding assay with 125I-[Sar1), Ile8]-AII as a ligand.

RESULTS

CS-088 (1 microg/ml) increased USF by 24% while AII decreased USF in a concentration-dependent manner between 10 and 500 nM. Its maximum decrease of 19% occurred at 500 nM. At this AII concentration the USF reduction was antagonized by 1 microg/ml CS-088, an AT1-receptor antagonist, but not by the same concentration of PD-123,177, an AT2-receptor antagonist. Specific 125I-[Sar1, Ile8]-AII binding to the rabbit ciliary body membranes was inhibited by CS-088 with an inhibition constant of 7.05 nM, whereas inhibition by PD-123,177 was not observed.

CONCLUSIONS

Ocular AII was indicated to attenuate USF via AT1 receptors in rabbits, however its physiological effect was not critical in IOP regulation.

The effect of topical CS-088, an angiotensin AT1 receptor antagonist, on intraocular pressure and aqueous humor dynamics in rabbits

PURPOSE

To evaluate the ocular hypotensive effect of topical CS-088, an angiotensin AT1 receptor antagonist, and the effect of CS-088 on aqueous humor dynamics.

METHODS

The effects of CS-088 on intraocular pressure (IOP) were studied in 2 models of rabbit ocular hypertension. Experimental ocular hypertension was induced in albino rabbits by injecting alpha-chymotrypsin into the anterior chamber (alpha-chymotrypsin rabbit). The effects of the single application of CS-088 were examined. Additionally, CS-088 was repeatedly administered over a period of 3 weeks to hereditary ocular hypertensive rabbits (buphthalmic rabbits, JWHR bu/bu) and the IOPs were monitored throughout the experiment. The effects of CS-088 on aqueous humor dynamics were also examined in normal rabbits. In this study, the methods of IOP recovery rate, two-level constant pressure perfusion and fluorescein-dextran perfusion were used respectively to determine the aqueous inflow, outflow facility and uveoscleral outflow (USF).

RESULTS

CS-088 at 1% and 2% significantly lowered the IOP in the alpha-chymotrypsin rabbits with a maximum IOP reduction of 10.1 mmHg. The maximum effect obtained with 2% CS-088 was no greater than that with 1% CS-088. In the buphthalmic rabbits, 2% CS-088 also lowered IOP significantly. Timolol was effective in both models. In the study on aqueous humor dynamics, a slight increase in USF (17%) was seen after a topical application of CS-088 whereas changes in aqueous inflow or outflow facility were not observed.

CONCLUSIONS

Topical CS-088 can decrease IOP in rabbits. Despite the USF change, the ocular hypotensive mechanism by CS-088 was not fully determined.

The impact of glaucoma medication on parameters of ocular perfusion

Whereas intraocular pressure is considered a major risk factor in glaucoma, growing evidence now indicates that ocular ischemia plays a major role too. By virtue of this and because many existing medications are able to interact with vasculature, altering ocular blood flow, it is essential that current and future medications for glaucoma be evaluated for their effect on ocular circulation. The authors review published papers examining the effect of topical and some systemic medications on ocular blood flow, focusing mostly on data from the human eye. The authors provide a comprehensive review on the effect of subclasses of medications (eg, carbonic anhydrase inhibitors, beta-blockers, alpha-adrenergic agonists, and prostaglandin analogues on optic nerve head, and on retinal, choroidal, and retrobulbar circulation. The various claims for enhancements or reduction of ocular circulation within each class of medication are reviewed and evaluated.

Expression of angiotensin-converting enzyme (ACE) in the developing chicken retina

Angiotensin-converting enzyme (ACE) performs two contrasting enzymatic effects: as part of the renin-angiotensin system it converts angiotensin I into physiologically active angiotensin II, and it inactivates a number of peptides, e.g. substance P. These peptides are well known neurotransmitters in the retina and recently angiotensin II was described in retinal neurons. We therefore investigated a possible involvement of ACE in retinal metabolism by determining the mRNA and protein expression of ACE in the developing and mature chicken retina. ACE-mRNA expression was investigated by RT-PCR in the iris/ciliary body, the choroid, the optic nerve head, pecten, and the retina. Levels of ACE-mRNA were quantified by competitive PCR with heterologous competitor fragments in the retina at different developmental stages. To localize protein expression of ACE in the mature chicken retina an antibody directed against ACE was used. ACE-mRNA was present in all ocular tissues examined. Quantification of ACE-mRNA in avascular retinas of developing chickens revealed small amounts (0.13 attomol microl(-1)) at embryonic day 7 and values of about 0.6 attomol microl(-1)during embryonic days 7-17. ACE-mRNA expression transiently increased ten-fold (7.3 attomol microl(-1)) on postnatal day 1, decreased again to about 1.4 attomol microl(-1)on postnatal day 6, and remained constant thereafter. ACE-immunohistochemistry revealed labeling of photoreceptors, bipolar cells, amacrine cells, and cells in the ganglion cell layer as well as of Müller glia. Our data show that ACE-mRNA is an intrinsic component of the retina and that ACE itself has a widespread but distinct cellular distribution. The transient high expression of ACE-mRNA directly after hatching indicate, that ACE may be involved in fine tuning the neuropeptidergic equipment of the retinal network during the initial phase of visual experience.

Effect of oral losartan potassium administration on intraocular pressure in normotensive and glaucomatous human subjects

The effects of the type 1 angiotensin II receptor antagonist Losartan potassium on intraocular pressure (IOP) were studied. Four groups of subjects were analysed: group A, ten controls; group B, ten patients with essential arterial hypertension and with IOP within the normal range; group C, ten patients with primary open angle glaucoma (POAG), but without essential arterial hypertension; group D, ten patients with arterial hypertension and POAG. The study design was held in a randomized crossover double-blind fashion. Systolic and diastolic arterial pressure, heart rate, pupil diameter, IOP and total outflow facility were recorded at baseline and at 1 hr intervals up to 6 hr, following the oral administration of 50 mg of Losartan potassium and/or placebo. The alternative treatment was given a week later. Drug administration significantly reduced IOP in all subjects. No variation in heart rate and pupil diameter was observed during the follow-up period. Blood pressure dropped only in arterial hypertensive patients (groups B and D). Total outflow facility increased significantly in all groups. Placebo did not induce any variation in all groups. These findings demonstrate that the mechanism by which Losartan potassium reduces intraocular pressure is not mediated by a decrease in blood pressure, but rather it is more specific, confirming the role of the renin-angiotensin system also in the regulation of intraocular pressure in man.