The renin-angiotensin system in the human eye

Revisiting the renin-angiotensin-aldosterone system in the eye: Mechanistic insights and pharmacological targets

The renin-angiotensin-aldosterone system (RAAS) plays a fundamental role in regulating blood pressure and fluid homeostasis through key effectors such as angiotensin II and aldosterone. These agents and their receptors have become crucial molecular targets in several cardiovascular and renal diseases. Over the past few decades, a growing body of evidence has revealed the presence of RAAS components in ocular structures, suggesting a tissue-specific RAAS within the eye. Building on this knowledge, studies have indicated that the ocular RAAS plays a significant role in the pathogenesis of various eye diseases. An impaired and overactivated RAAS contributes to the development of severe and widespread disorders affecting both the anterior and posterior segments of the eye. In this context, the current work aims to delve into the pivotal molecular pathways involving the RAAS, with an in-depth exploration of the ocular pathophysiology. It focuses on the relationship between overactivation of the RAAS and oxidative stress, as well as the exacerbation of neovascularization and inflammatory processes. The objective is to provide an updated and comprehensive understanding of the role of the RAAS in ophthalmological diseases, highlighting the therapeutic potential of RAAS modulators and discussing the controversies and challenges in this area of research.

Citation metrics and scientometrics

I read the article "Scientometrics and academia" by Dr. Zerem and colleagues. My perspective on citation metrics and scientometrics is more cautious. Therefore, in this article, I present my viewpoint on this subject. Read more in the PDF.

Association of GNB3, ACE polymorphisms with POAG and NTG

PURPOSE

Primary open-angle glaucoma (POAG) represents the most prevalent form of glaucoma and stands as a foremost contributor to irreversible vision impairment on a global scale. Despite notable strides made in comprehending the genetic underpinnings of POAG, investigations within the context of Russia remain constrained.

METHODS

The study cohort comprised a total of 235 individuals, with 135 of them exhibiting various forms of glaucoma encompassing both POAG and (NTG, while the remaining 100 individuals served as control subjects. Each participant underwent a comprehensive ocular examination to ascertain their ocular health status. Genotyping of the relevant single nucleotide polymorphisms (SNPs) was carried out using the Taq Man genotyping assay. Specifically, the two SNPs under scrutiny were GNB3 rs5443 gene and ACE rs4646994. Statistical analysis was performed to evaluate the association of these SNPs with glaucoma risk.

RESULTS

The presence of the T allele of rs5443 was found to be associated with NTG (p = .004). However, no statistically significant correlation was identified between this SNP and POAG (p = .88).

CONCLUSION

This study provides evidence of an association between the T allele of rs5443 and a reduced susceptibility NTG within the Russian population. These observations augment the comprehension of the genetic underpinnings of glaucoma and hold potential implications for the prospective development of targeted therapeutic interventions.

Effect of Soluplus® on γ-cyclodextrin solubilization of irbesartan and candesartan and their nanoaggregates formation

The poor aqueous solubility of irbesartan (IRB) and candesartan cilexetil (CAC) may hamper their bioavailability when orally or topically administered. Among several attempts, the promising nanoaggregate formation by γ-cyclodextrin (γCD) complexation of drugs in aqueous solution with or without water-soluble polymers was investigated. According to phase solubility studies, Soluplus® showed the highest complexation efficiency (CE) of drug/γCD complexes among the polymers tested. The aqueous solubility of IRB and CAC was markedly increased as a function of Soluplus^® concentrations. The binary drug/γCD and ternary drug/γCD/Soluplus^® complex formations were supported and confirmed by solid-state characterizations, including differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and Fourier transform infrared (FT-IR) spectroscopy. The true inclusion mode was also proved by proton nuclear magnetic resonance (¹H-NMR) spectroscopy. The nanoaggregate size and morphology of binary and ternary systems were observed using dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques. The size of these nanocarriers depends on the concentration of Soluplus^®. The use of Soluplus^® could significantly enhance drug solubility and stabilize complex nanoaggregates, which could be a prospective platform for drug delivery systems.

Change in retinal vessel diameter and choroidal thickness in patients with severe COVID-19: Change In Retinal Parameters In Patients With Severe COVID-19

Purpose

: To compare the differences in retinal vascular structure and choroidal thickness between the active disease and post-recovery periods in COVID-19 patients and healthy controls.

Material and Methods

: This prospective, cross-sectional study included 30 eyes from 30 patients with severe COVID-19 and 30 eyes of 30 sex-matched healthy controls. Central macular thickness (CMT), subfoveal choroidal thickness (CT) and retinal vascular changes of patients were measured after positive polymerase chain reaction (PCR) (where the patient had COVID-19-related symptoms) and then three months after two negative PCRs. Laboratory parameters, including C-reactive protein and d-dimer levels, were also recorded.

Results

: The mean age of the patients was 47.90 ± 9.06 years in patients group, 49.07 ± 8.41 years in control goups (p = 0.467). In terms of choroidal thicknesses subfoveal, nasal and temporal region were significantly higher in the active disease period than control group (p = 0.019, p = 0.036, p = 0.003, respectively). When the after recovery period was compared with the control group in terms of choroidal thickness, although the choroidal thickness was higher in all regions, this difference was not found statistically significant. There was no statistically significant difference in CMT between groups (p = 0.506).The mean venous and arterial wall thicknesses were significantly higher in the active period than after recovery (p = 0.023, p = 0.013, respectively) but there were no differences between after recovery and control groups in the pairwise comparison (p = 0.851, p = 0.715, respectively).

Conclusion

: In patients with severe COVID-19, there are changes in thickness of the choroid and retinal vessel walls. While vascular wall thickness increases due to inflammation, the absence of lumen changes may be associated with hemodynamic variables.

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.

The (pro)renin receptor ((P)RR) and soluble (pro)renin receptor (s(P)RR) in pregnancy

The (pro)renin receptor ((P)RR) is a multi-functional protein that can be proteolytically cleaved and released in a soluble form (s(P)RR). Recently, the (P)RR and s(P)RR have become of interest in pregnancy and its associated pathologies. This is because the (P)RR not only activates tissue renin angiotensin systems, but it is also an integral component of vacuolar-ATPase, activates the wingless/integrated (Wnt)/β-catenin and extracellular signal regulated kinases 1 and 2/mitogen-activated protein kinase signalling pathways, and stabilises the β subunit of pyruvate dehydrogenase. Additionally, s(P)RR is detected in plasma and urine, and maternal plasma levels are elevated in pregnancy complications including fetal growth restriction, preeclampsia and gestational diabetes mellitus. Therefore, s(P)RR has potential as a biomarker for these pregnancy pathologies. Preliminary functional findings suggest that s(P)RR may be important for regulating fluid balance, inflammation and blood pressure, all of which contribute to a successful pregnancy. The (P)RR and s(P)RR regulate pathways that are known to be important in maintaining pregnancy, however their role in the physiological context of pregnancy is poorly characterised. This review summarises the known and potential functions of the (P)RR and s(P)RR in pregnancy, and how their dysregulation may contribute to pregnancy complications. It also highlights the need for further research into the source and function of s(P)RR in pregnancy. Soluble (P)RR levels could be indicative of placental, kidney or liver dysfunction and therefore be a novel clinical biomarker, or therapeutic target, to improve the detection and treatment of pregnancy pathologies.

Therapeutic effects of various renin angiotensin modulators on hyperglycemia-induced cataract formation in Sprague Dawley rats

Objects:

Our previous research work reported the beneficial effects of angiotensin receptor blockers (ARBs) for the treatment of diabetes associated cataract which was induced by streptozotocin (STZ). The current study, evaluated the effects of topical administration of various renin angiotensin modulators on STZ-induced cataracts in rats.

Methods:

Single dose of STZ (60 mg/kg, i.p.) was administered in the rats to induce diabetes. Animals were divided into normal and diabetic rats. Normal rats were administered with single dose of sodium citrate buffer (0.1 M, 10ml/kg, i.p.). Diabetic animals were divided into various treatment groups, each group contains six animals and received aliskiren, olmesartan, enalapril, and angiotensin 1–7 at a dose of 0.5% w/v topically on the cornea of the eye for a period of 8 weeks. During experimental protocol morphology of the eyes and lenticular opacity were monitored. Animals were sacrificed after 8 weeks of drug treatment, and various cataractogenic biochemical parameters were assessed.

Results:

Topical administrations with aliskiren, enalapril, olmesartan, and angiotensin 1–7 showed non-significant alterations in the blood glucose level, but significantly decreased lenticular opacity, restored antioxidant level, restored MDA level and Nitrite content, and decreased the onset of cataract formation.

Conclusion:

Overall, our findings suggest that topical treatment with renin angiotensin modulators delayed the onset of diabetes-induced cataract formation.

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.

Structural and Molecular Tear Film Changes in Glaucoma

The Tear Film (TF) is a trilaminar and dynamic fluid covering the entire Ocular Surface (OS), consisting of a mucus, aqueous, and lipid layer deeply interacting between them. Because of its structure and functions, TF plays a pivotal role in the preservation of the OS integrity and the quality of vision. Medical therapy for glaucoma is recognized to profoundly disturb the OS homeostasis by altering all components of the ocular surface unit, including TF. The presence of preservatives, the number of daily eye drops instillations, and the duration of therapy are the main contributors to TF changes. From the physio-pathological side, TF alterations are induced by toxic and allergic mechanisms and result from goblet cell and Meibomian gland loss, dysfunction of accessory lacrimal glands, and epithelial disruption. In detail, TF changes are represented by mucus layer thinning, reduced mucin concentration, aqueous layer volume reduction, and lipid layer thinning with increased tear evaporation. Hyper- osmolarity and instability represent the main hallmarks of these changes and are an expression of a iatrogenic form of dry eye. TF undergoes also molecular modifications that primarily reflect a therapy- or disease-induced inflammatory status of the OS. Over the last years, this field of research aimed a progressively growing interest since molecular variations may be considered as potential candidate biomarkers of glaucoma. The aim of this review is to report the main TF changes occurring during glaucoma, exploring the relationship they may have with the glaucoma-related ocular surface disease and the patient quality of life, and their utility as potential biomarkers of disease.

An exploration of bioactive peptides: My collaboration with Ervin G. Erdös

This paper provides a brief historical sketch of the science of biologically active peptides. It also offers the story of how Ervin G. Erdös, a pioneer in the study of metabolism of various peptides, influenced me through collaborations that span many years. I worked in Dr. Erdös's research laboratories in Oklahoma City, Dallas, and Chicago, and we shared research interests through visits across the Atlantic between the former Yugoslavia and the United States. Among other findings, we discovered angiotensin-converting enzyme in the retina, which opened up a new research direction for many scientists interested in serious ocular diseases. This tribute to my mentor paints a portrait of a man who, in addition to his dedication to science and his seminal discoveries about the metabolism of peptides, took the time to invest in training many young scientists. His fine personal qualities explain why all of those who worked with him hold him in such high regard.

Role of Tissue Renin-angiotensin System and the Chymase/angiotensin-( 1-12) Axis in the Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy (DR) is a major diabetes complication and the leading cause for vision loss and blindness in the adult human population. Diabetes, being an endocrinological disorder dysregulates a number of hormonal systems including the renin angiotensin system (RAS), which thereby may damage both vascular and neuronal cells in the retina. Angiotensin II (Ang II), an active component of the RAS is increased in diabetic retina, and may play a significant role in neurovascular damage leading to the progression of DR. In this review article, we highlight the role of Ang II in the pathogenesis of retinal damage in diabetes and discuss a newly identified mechanism involving tissue chymase and angiotensin-(1-12) [Ang-(1-12)] pathways. We also discuss the therapeutic effects of potential RAS inhibitors targeting blockade of cellular Ang II formation to prevent/ protect the retinal damage. Thus, a better understanding of Ang II formation pathways in the diabetic retina will elucidate early molecular mechanism of vision loss. These concepts may provide a novel strategy for preventing and/or treating diabetic retinopathy, a leading cause of blindness worldwide.

Antihypertensive Medication Postpones the Onset of Glaucoma: Evidence From a Nationwide Study

The aim was to investigate the impact of antihypertensive medication on the onset of glaucoma. Data from the complete Danish population between 40 and 95 years of age were used in the period from 1996 to 2012, covering >2.6 million individuals. The National Danish Registry of Medicinal Products Statistics was used to identify all claimed prescriptions for glaucoma medication and antihypertensive drugs. We first investigated basic correlations in the data and found that patients treated with antihypertensive medication, at any time during the study period, had a significantly higher overall relative risk (RR) of glaucoma, even when controlling for age and sex (with a RR of 1.31 and P<0.0001). Furthermore, our data confirm the well-known positive association between age and glaucoma. To investigate the causal effect of antihypertensive treatment on the onset of treatment for glaucoma, we used a regression discontinuity study design. This analysis provides our main finding, namely that prescription of antihypertensive medication leads to a significant reduction in the risk of developing glaucoma. Therefore, although hypertension-as indicated by the use of antihypertensive medication-is positively correlated with glaucoma, our study indicates that antihypertensive medication itself may have a preventive effect on the development of glaucoma.

Danish Nationwide Data Reveal a Link between Diabetes Mellitus, Diabetic Retinopathy, and Glaucoma

Aims. To determine the association between treatment against diabetes mellitus (DM) and treatment with antiglaucomatous drugs in the entire Danish population and to investigate the comorbidity between DM and its complications with antiglaucomatous treatment. Methods. Retrospective nationwide cohort study with data over a 16-year follow-up period. The National Danish Registry of Medicinal Products Statistics was used to identify all claimed prescriptions for antiglaucomatous medication and DM drugs. ICD-10 classifications were furthermore used to identify comorbidities between antiglaucomatous medication and the DM complications, diabetic retinopathy (DR), and nephropathy. Results. A total of 6,343,747 individuals in the period between 1996 and 2012 were analyzed. The overall incidence rate of new-onset glaucoma patients was 0.07 per 1000 person-years for the reference population compared to 36 per 1000 person-years for all diagnosed DM cases. Patients treated with DM drugs had about two times higher relative risk of glaucoma, when adjusting for a range of factors. The presence of DR alone or in combination with nephropathy increased the risk of glaucoma. Conclusions. The present study reports a strong association between DM and onset of glaucoma treatment in the entire Danish population.

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.

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.

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.

Renin-angiotensin system expression and secretory function in cultured human ciliary body non-pigmented epithelium

BACKGROUND

Renin-angiotensin system (RAS) components have been identified in human ciliary body and aqueous humour, pointing to a role for the RAS in the regulation of aqueous humour dynamics. Here, the authors examine the functional expression of a RAS and the effects of angiotensin II (AII) on a signal transduction pathway and ion secretion mechanism in cultured human ciliary body non-pigmented epithelium (HNPE).

METHODS

RAS expression was examined in cultured HNPE cells using polymerase chain reaction (PCR) analysis. Secretory function was determined using spectrofluorescence imaging microscopy to measure cell calcium (Ca(2+)(I)) and volume responses. Single channel patch clamp techniques were employed to investigate ion channel activity.

RESULTS

PCR analysis demonstrated the expression of angiotensinogen and the AT(1b) receptor in HNPE cells. A large conductance potassium (BK) channel (mean 190 (SEM 5.6) pS, n = 22 cells), was observed in plasma membrane patches. This channel was calcium sensitive with channel open probability (Po) increasing with increasing Ca(2+)(I) (K(0.5) 10.79 (0.44) microM Ca(2+), Hill coefficient of 1.04 (0.04)). AII (100 nM) increased the number (N) of active BK channels in HNPE cells and also the probability of channel opening (Po). N.P(o) increased from 0.008 (0.002) to 1.38 (0.4) following the addition of AII (p=0.0064). AII also induced a rapid rise in Ca(2+)(I) from resting values of 112 (14) nM to a peak of 992 (106) nM (p<10(-4)). A simultaneous cell volume reduction of 24.70% (3.34%) (p<10(-4)) occurred during this calcium signal. Losartan (1 microM) significantly blocked the AII induced BK channel activation (p=0.0131), the Ca(2+)(I) response (p<10(-4)), and the AII induced volume effect (p=0.0046).

CONCLUSION

It was demonstrated that AII activates a Ca(2+)(I) signalling system which subsequently increases potassium ion channel activity. These effects are accompanied simultaneously by cell volume loss, indicating that AII acts as receptor operated secretagogue in HNPE cells. The ability of an AT(1) receptor antagonist to inhibit these processes may thus offer a new family of pharmaceutical agents to the current armamentarium in the treatment of glaucoma.

Angiotensin II receptor subtype gene expression and cellular localization in the retina and non-neuronal ocular tissues of the rat

In addition to its function as a peripheral hormone, angiotensin II (AngII) has been shown to act as a neuromodulator in various brain regions. AngII effects are mediated by two major AngII receptor subtypes, AT1 and AT2, and different AT1 receptor isoforms AT1A and AT1B are described in rat brains. The purpose of the present study was to analyse the expression pattern of AT receptors in different parts of the rat eye with special emphasis on the retina. Specific primers were constructed and the gene expression of AngII receptor subtypes was investigated by means of reverse transcription-polymerase chain reaction (RT-PCR). An antibody was used for cellular localization of AT1 receptor in the retina. AT2 receptor mRNA was localized by in situ hybridization (ISH). We examined the retinas of different developmental stages as well as non-neuronal ocular tissues, e.g. choroid and anterior uveal tract of rats (Brown Norway and Wistar strain), for the gene expression of AT receptors. Our results show that AT1A and AT2 mRNAs are expressed in rat choroid, iris/ciliary body and retinas, whereas AT1B mRNA is not expressed in the retina but in all other ocular tissues under investigation. AT1 receptor immunohistochemistry of the retina showed strong labelling in the ganglion cell layer (GCL), and some cells in the inner nuclear layer (INL), suggesting putative ganglion cell but also amacrine cell labelling. In the retina, ISH for AT2 mRNA revealed labelling in the GCL and a faint labelling in the inner nuclear layer. No AT2 ISH-signal was found in the other ocular tissues. These data suggest that there is a specific distribution pattern of AT receptors in rat ocular tissues, especially in the retina. The expression of AT receptors on retinal ganglion cells confirms the AngII action on these cell types and supports the role of AngII as a retinal neurotransmitter or neuromodulator.

Serum total renin, an independent marker of the activity and severity of retinopathy in patients with IDDM

BACKGROUND/AIMS

Recent studies have demonstrated marked renin and prorenin concentration gradients between ocular tissues and blood, and local expression of the renin-angiotensin system (RAS) in the eye. The authors determined whether serum total renin, which mostly consists of prorenin, is a marker of the activity and severity of diabetic retinopathy independent of other microvascular complications.

METHODS

Total renin concentrations (TRC) were measured with a time resolved immunofluorometric assay in 38 patients with IDDM (age 34 (SD 7) years, duration of disease 22 (7) years, serum creatinine 95 (15) mumol/l, urinary albumin excretion rate (UAER) 207 (829) micrograms/min, HbA1c 8.5% (1.2%)), and in 13 matched normal subjects. All subjects were carefully characterised with respect to the presence and severity of retinopathy (RP score), nephropathy, and neuropathy using seven different tests of autonomic neuropathy.

RESULTS

Serum TRC was on average twofold higher in IDDM (396 (SE 211) ng/l) than in normal subjects (201 (88) ng/l, p < 0.001). It was nearly twofold higher in patients with preproliferative or active proliferative retinopathy requiring careful follow up or therapy (TRC 596 (268) ng/l, n = 11) compared with those with quiescent proliferative retinopathy after laser treatment (TRC 338 (183) ng/l, p < 0.01, n = 5); moderately severe non-proliferative retinopathy (337 (106) ng/l, p < 0.01, n = 13), no retinopathy, or only minimal non-proliferative retinopathy (270 (43) ng/l, p < 0.001, n = 9). In multiple linear regression analysis, RP score (p < 0.01), but not the UAER or any index of autonomic neuropathy, was an independent determinant of serum TRC, and explained 32% of its variation (R = 0.57, p < 0.005).

CONCLUSIONS

Serum TRC in patients with diabetic retinopathy is increased independent of renal function and autonomic neuropathy especially in those with severe active changes requiring careful follow up or treatment. These findings support the idea that diabetic retinopathy is the most important determinant of serum TRC in patients with IDDM, and that TRC is produced when retinopathy is active.