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

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.

Mendelian randomization supports causality between COVID-19 and glaucoma

To determine whether there is a causal relationship between Corona Virus Disease 2019 (COVID-19) and glaucoma, a 2-sample Mendelian Randomization (MR) design was applied with the main analysis method of inverse-variance-weighted. The reliability of the results was checked using the heterogeneity test, pleiotropy test, and leave-one-out method. Four sets of instrumental variables (IVs) were used to investigate the causality between COVID-19 and glaucoma risk according to data from the IEU Genome Wide Association Study (GWAS). The results showed that 2 sets of COVID-19(RELEASE) were significantly associated with the risk of glaucoma [ID: ebi-a-GCST011071, OR (95% CI) = 1.227 (1.076-1.400), P = .002259; ID: ebi-a-GCST011073: OR (95% CI) = 1.164 (1.022-1.327), P = .022450; 2 sets of COVID-19 hospitalizations were significantly associated with the risk of glaucoma (ID: ebi-a-GCST011081, OR (95% CI) = 1.156 (1.033-1.292), P = .011342; ID: ebi-a-GCST011082: OR (95% CI) = 1.097 (1.007-1.196), P = .034908)]. The sensitivity of the results was acceptable (P > .05) for the 3 test methods. In conclusion, this MR analysis provides preliminary evidence of a potential causal relationship between COVID-19 and glaucoma.

Diminazene aceturate-induced cytotoxicity is associated with the deregulation of cell cycle signaling and downregulation of oncogenes Furin, c-MYC, and FOXM1 in human cervical carcinoma Hela cells

Diminazene aceturate (DIZE) is an FDA-listed small molecule known for the treatment of African sleeping sickness. In vivo studies showed that DIZE may be beneficial for a range of human ailments. However, there is very limited information on the effects of DIZE on human cancer cells. The current study aimed to investigate the cytotoxic responses of DIZE, using the human carcinoma Hela cell line. WST-1 cell proliferation assay showed that DIZE inhibited the viability of Hela cells in a dose-dependent manner and the observed response was associated with the downregulation of Ki67 and PCNA cell proliferation markers. DIZE-treated cells stained with acridine orange-ethidium and JC-10 dye revealed cell death and loss of mitochondrial membrane potential (Ψm), compared with DMSO (vehicle) control, respectively. Cellular immunofluorescence staining of DIZE-treated cells showed upregulation of caspase 3 activities. DIZE-treated cells showed downregulation of mRNA for G1/S genes CCNA2 and CDC25A, S-phase genes MCM3 and PLK4, and G2/S phase transition/mitosis genes Aurka and PLK1. These effects were associated with decreased mRNA expression of Furin, c-Myc, and FOXM1 oncogenes. These results suggested that DIZE may be considered for its effects on other cancer types. To the best of our knowledge, this is the first study to evaluate the effect of DIZE on human cervical cancer cells.

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.

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.

Is Diminazene an Angiotensin-Converting Enzyme 2 (ACE2) Activator? Experimental Evidence and Implications

Antiprotozoal veterinary drug diminazene aceturate (DIZE) has been proposed to be an angiotensin-converting enzyme 2 (ACE2) activator. Since then, DIZE was used in dozens of experimental studies, but its mechanism of action attributed to ACE2 activation and enhanced formation of angiontensin-(1-7) [Ang-(1-7)] from Ang II was not carefully verified. The aim of this study was to confirm the effect of DIZE on catalytic activity of ACE2 and extend it to other peptidases involved in formation and degradation of Ang-(1-7). Concentration-dependent effect of DIZE on the initial rate of a fluorogenic substrate hydrolysis by human and mouse recombinant ACE2 was measured at assay conditions imitating that of the original report, but no activation of ACE2 was documented. Similar results were obtained with a more physiologically relevant assay buffer. In addition, DIZE did not affect activity of recombinant neprilysin, neurolysin, thimet oligopeptidase, and ACE. Efficiency of the fluorogenic substrate hydrolysis (Vmax/Km value) by ACE2 in response to different concentrations of DIZE was also measured, but no substantial effects were documented. Likewise, DIZE failed to enhance the hydrolysis of ACE2 endogenous substrate Ang II. Identity of the commercial recombinant ACE2 variants used in these experiments was confirmed by inhibition with two well characterized inhibitors (DX600 and MLN4760), activation by NaCl, and Western Blotting using validated antibodies. These observations challenge the widely accepted notion about the molecular mechanism of DIZE action and call for not ascribing this molecule as an ACE2 activator. SIGNIFICANCE STATEMENT: DIZE has been proposed and widely used in experimental studies as an ACE2 activator. The detailed in vitro pharmacological studies failed to confirm that DIZE is an ACE2 activator. In addition, DIZE did not substantially affect the activity of other peptidases involved in formation and degradation of angiotensin-(1-7). Researchers should refrain from calling DIZE an ACE2 activator. Other mechanisms are responsible for the therapeutic benefits attributed to DIZE.

Molecular Imaging on ACE2-dependent Transocular Infection of Coronavirus

A transocular infection has been proved as one of the main approaches that severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) invades the body, and angiotensin‐converting enzyme 2 (ACE2) plays a key role in this procedure. Dynamic and quantitative details on virus distribution are lacking for virus prevention and drug design. In this study, a radiotraceable pseudovirus packed with an enhanced green fluorescent protein (EGFP) gene, ¹²⁵I‐CoV, was prepared and inoculated in the unilateral eye of humanized ACE2 (hACE2) mice or ACE2‐knockout (ACE2‐KO) mice. Single‐photon emission computed tomography/computed tomography images were acquired at multiple time points to exhibit ACE2‐dependent procedures from invasion to clearance. Positron emission tomography (PET) and western blot were performed to quantify ACE2 expression and verify the factors affecting transocular infection. For the transocular infection of coronavirus (CoV), the renin–angiotensin–aldosterone system (RAAS), lungs, intestines, and genital glands were the main targeted organs. Due to the specific anchor to ACE2‐expressed host cells, virus concentrations in genital glands, liver, and lungs ranked the top three most and stabilized at 3.75 ± 0.55, 3.30 ± 0.25, and 2.10 ± 0.55% inoculated dose (ID)/mL at 48 h post treatment. Meanwhile, ACE2‐KO mice had already completed the in vivo clearance. In consideration of organ volumes, lungs (14.50 ± 3.75%ID) and liver (10.94 ± 0.71%ID) were the main in‐store reservoirs of CoV. However, the inoculated eye (5.52 ± 1.85%ID for hACE2, 5.24 ± 1.45%ID for ACE2‐KO, p > 0.05) and the adjacent brain exhibited ACE2‐independent virus infection at the end of 72 h observation, and absolute amount of virus played a key role in host cell infection. These observations on CoV infection were further manifested by infection‐driven intracellular EGFP expression. ACE2 PET revealed an infection‐related systematic upregulation of ACE2 expression in the organs involved in RAAS (e.g., brain, lung, heart, liver, and kidney) and the organ that was of own local renin–angiotensin system (e.g., eye). Transocular infection of CoV is ACE2‐dependent and constitutes the cause of disturbed ACE2 expression in the host. The brain, genital glands, and intestines were of the highest unit uptake, potentially accounting for the sequelae. Lungs and liver were of the highest absolute amount, closely related to the respiratory diffusion and in vivo duplication. ACE2 expression was upregulated in the short term after infection with CoV. These visual and quantitative results are helpful to fully understanding the transocular path of SARS‐CoV‐2 and other CoVs.

Therapeutic Drugs and Devices for Tackling Ocular Hypertension and Glaucoma, and Need for Neuroprotection and Cytoprotective Therapies

Damage to the optic nerve and the death of associated retinal ganglion cells (RGCs) by elevated intraocular pressure (IOP), also known as glaucoma, is responsible for visual impairment and blindness in millions of people worldwide. The ocular hypertension (OHT) and the deleterious mechanical forces it exerts at the back of the eye, at the level of the optic nerve head/optic disc and lamina cribosa, is the only modifiable risk factor associated with glaucoma that can be treated. The elevated IOP occurs due to the inability of accumulated aqueous humor (AQH) to egress from the anterior chamber of the eye due to occlusion of the major outflow pathway, the trabecular meshwork (TM) and Schlemm’s canal (SC). Several different classes of pharmaceutical agents, surgical techniques and implantable devices have been developed to lower and control IOP. First-line drugs to promote AQH outflow via the uveoscleral outflow pathway include FP-receptor prostaglandin (PG) agonists (e.g., latanoprost, travoprost and tafluprost) and a novel non-PG EP2-receptor agonist (omidenepag isopropyl, Eybelis^®). TM/SC outflow enhancing drugs are also effective ocular hypotensive agents (e.g., rho kinase inhibitors like ripasudil and netarsudil; and latanoprostene bunod, a conjugate of a nitric oxide donor and latanoprost). One of the most effective anterior chamber AQH microshunt devices is the Preserflo^® microshunt which can lower IOP down to 10–13 mmHg. Other IOP-lowering drugs and devices on the horizon will be also discussed. Additionally, since elevated IOP is only one of many risk factors for development of glaucomatous optic neuropathy, a treatise of the role of inflammatory neurodegeneration of the optic nerve and retinal ganglion cells and appropriate neuroprotective strategies to mitigate this disease will also be reviewed and discussed.

SARS-CoV-2 on the ocular surface: is it truly a novel transmission route?

Since December 2019, the novel COVID-19 outbreak has spread rapidly around the globe and infected millions of people. Although the major transmission route of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is considered to be airborne droplets and close contact, the ocular transmission route has been reported with great concern. The current work summarises the characteristics of SARS-CoV-2, the ocular distribution of the major SARS-CoV-2 binding protein, and the experimental and clinical evidence of the ocular transmission route. Although it seems that the likelihood of the ocular surface being an infection gateway is low, SARS-CoV-2 infection or transmission via the ocular surface may cause conjunctivitis and other ocular discomfort. Therefore, good eye protection is an essential safeguard procedure, especially for medical staff.

Emerging importance of ACE2 in external stratified epithelial tissues

Angiotensin converting enzyme 2 (ACE2), a component of the renin-angiotensin system (RAS), has been identified as the receptor for the SARS-CoV-2. Several RAS components including ACE2 and its substrate Ang II are present in both eye and skin, two stratified squamous epithelial tissues that isolate organisms from external environment. Our recent findings in cornea and others in both skin and eye suggest contribution of this system, and specifically of ACE2 in variety of physiological and pathological responses of these organ systems. This review will focus on the role RAS system plays in both skin and cornea, and will specifically discuss our recent findings on ACE2 in corneal epithelial inflammation, as well as potential implications of ACE2 in patients with COVID-19.

Brain angiotensin converting enzyme-2 in central cardiovascular regulation

The brain renin-angiotensin system (RAS) plays an important role in the regulation of autonomic and neuroendocrine functions, and maintains cardiovascular homeostasis. Ang-II is the major effector molecule of RAS and exerts most of its physiological functions, including blood pressure (BP) regulation, via activation of AT1 receptors. Dysregulation of brain RAS in the central nervous system results in increased Ang-II synthesis that leads to sympathetic outflow and hypertension. Brain angiotensin (Ang) converting enzyme-2 (ACE2) was discovered two decades ago as an RAS component, exhibiting a counter-regulatory role and opposing the adverse cardiovascular effects produced by Ang-II. Studies using synthetic compounds that can sustain the elevation of ACE2 activity or genetically overexpressed ACE2 in specific brain regions found various beneficial effects on cardiovascular function. More recently, ACE2 has been shown to play critical roles in neuro-inflammation, gut dysbiosis and the regulation of stress and anxiety-like behaviors. In the present review, we aim to highlight the anatomical locations and functional implication of brain ACE2 related to its BP regulation via modulation of the sympathetic nervous system and discuss the recent developments and future directions in the ACE2-mediated central cardiovascular regulation.

Evaluation of the non-clinical toxicity of an antiparasitic agent: diminazene aceturate

The diminazene aceturate (C₁₄H₁₅N₇.2C₄H₇NO₃) is a chemotherapeutic agent with more than six decades of use, however more studies regarding its toxicity still need to be performed. Thus, the present study determined the acute toxicity (14 days) of diminazene acetate (DIZE) in male and female swiss mice by changes in body mass, food consumption, biochemical and hematological parameters, locomotor activity and motor coordination. DIZE was administered at a single dose (1000 and 2000 mg/kg) orally. In addition, in vitro antioxidant capacity, hemolytic activity, toxicity in Artemia salina and in silico evaluation were also performed. The results obtained include several signs of toxicity (hypoactivity, loss of the straightening reflex and tachycardia), reduction of behavioral activity (locomotor activity and motor coordination) and significant changes (p < 0.05) in biochemical and hematological parameters. According to the in silico study, the DIZE can be classified based on the mean lethal dose (LD₅₀) in category 4 (300 mg/kg < LD₅₀ ≤ 2000 mg/kg, ProTox-II) or 3 (50 mg/kg < LD₅₀ ≤ 300 mg/kg, AdmetSAR 1.0). Additionally, DIZE (30.3-969.9 nM) was not toxic to A. salina in the first 48 hours of treatment and was not cytotoxic to rat red blood cells after induced hemolysis. In vitro results indicated low antioxidant capacity against DPPH^• and ABTS^•+ radicals. Therefore, DIZE induces several adverse effects with influence on the central nervous system, changes in hematological and biochemical parameters and even mortality at the highest dose. However, absence of toxicity was observed in A. salina and rats red blood cells.

Update on New Aspects of the Renin-Angiotensin System in Hepatic Fibrosis and Portal Hypertension: Implications for Novel Therapeutic Options

There is considerable experimental evidence that the renin angiotensin system (RAS) plays a central role in both hepatic fibrogenesis and portal hypertension. Angiotensin converting enzyme (ACE), a key enzyme of the classical RAS, converts angiotensin I (Ang I) to angiotensin II (Ang II), which acts via the Ang II type 1 receptor (AT1R) to stimulate hepatic fibrosis and increase intrahepatic vascular tone and portal pressure. Inhibitors of the classical RAS, drugs which are widely used in clinical practice in patients with hypertension, have been shown to inhibit liver fibrosis in animal models but their efficacy in human liver disease is yet to be tested in adequately powered clinical trials. Small trials in cirrhotic patients have demonstrated that these drugs may lower portal pressure but produce off-target complications such as systemic hypotension and renal failure. More recently, the alternate RAS, comprising its key enzyme, ACE2, the effector peptide angiotensin-(1–7) (Ang-(1–7)) which mediates its effects via the putative receptor Mas (MasR), has also been implicated in the pathogenesis of liver fibrosis and portal hypertension. This system is activated in both preclinical animal models and human chronic liver disease and it is now well established that the alternate RAS counter-regulates many of the deleterious effects of the ACE-dependent classical RAS. Work from our laboratory has demonstrated that liver-specific ACE2 overexpression reduces hepatic fibrosis and liver perfusion pressure without producing off-target effects. In addition, recent studies suggest that the blockers of the receptors of alternate RAS, such as the MasR and Mas related G protein-coupled receptor type-D (MrgD), increase splanchnic vascular resistance in cirrhotic animals, and thus drugs targeting the alternate RAS may be useful in the treatment of portal hypertension. This review outlines the role of the RAS in liver fibrosis and portal hypertension with a special emphasis on the possible new therapeutic approaches targeting the ACE2-driven alternate RAS.

An update on ACE2 amplification and its therapeutic potential

The renin angiotensin system (RAS) plays an important role in the pathogenesis of variety of diseases. Targeting the formation and action of angiotensin II (Ang II), the main RAS peptide, has been the key therapeutic target for last three decades. ACE‐related carboxypeptidase (ACE2), a monocarboxypeptidase that had been discovered 20 years ago, is one of the catalytically most potent enzymes known to degrade Ang II to Ang‐(1‐7), a peptide that is increasingly accepted to have organ‐protective properties that oppose and counterbalance those of Ang II. In addition to its role as a RAS enzyme ACE2 is the main receptor for SARS‐CoV‐2. In this review, we discuss various strategies that have been used to achieve amplification of ACE2 activity including the potential therapeutic potential of soluble recombinant ACE2 protein and novel shorter ACE2 variants.

Current Evidence of 2019 Novel Coronavirus Disease (COVID-19) Ocular Transmission: A Systematic Review and Meta-Analysis

OBJECTIVE

To estimate the prevalence rate of ocular symptoms and the positive rate of conjunctival swab samples of patients diagnosed with 2019 Novel Coronavirus Disease (COVID-19).

METHODS

We performed a systematic review and meta-analysis. A comprehensive literature search was done based on PubMed, Embase, MedRxiv, and the Cochrane Library. The primary outcomes are the prevalence rate of conjunctivitis/conjunctival congestion and the positive rate of conjunctival swab samples. Rates were expressed as proportions with 95% confidence intervals (CIs).

RESULTS

A total of 12 studies with 1930 participants were included for meta-analysis. The pooled prevalence rate of conjunctivitis/conjunctival congestion was 8% (95% CI: 5%-12%). 1% (95% CI: 1%-4%) of COVID-19 patients were diagnosed with conjunctivitis/conjunctival congestion as the initial symptom. The pooled positive rate of conjunctival swab samples was 3% (95% CI: 2%-5%). We also assessed other ocular symptoms reported in the 12 studies, including foreign body sensation, increased secretion, and eye itching. The pooled prevalence rates were 6% (95% CI: 3%-10%), 10% (95% CI: 8%-12%), and 9% (95% CI: 7%-10%), respectively.

CONCLUSIONS

The evidence on the positive rate of conjunctival swab samples and the prevalence rates of ocular symptoms indicated that COVID-19 ocular transmission was possible but less likely.

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.

Potential neuroinvasive pathways of SARS-CoV-2: Deciphering the spectrum of neurological deficit seen in coronavirus disease-2019 (COVID-19)

Coronavirus disease-2019 (COVID-19) was declared a global pandemic on 11 March 2020. Scientists and clinicians must acknowledge that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has the potential to attack the human body in multiple ways simultaneously and exploit any weaknesses of its host. A multipronged attack could potentially explain the severity and extensive variety of signs and symptoms observed in patients with COVID-19. Understanding the diverse tactics of this virus to infect the human body is both critical and incredibly complex. Although patients diagnosed with COVID-19 have primarily presented with pulmonary involvement, viral invasion, and injury to diverse end organs is also prevalent and well documented in these patients, but has been largely unheeded. Human organs known for angiotensin-converting enzyme 2 (ACE2) expression including the gastrointestinal tract, kidneys, heart, adrenals, brain, and testicles are examples of extra pulmonary tissues with confirmed invasion by SARS-CoV-2. Initial multiple organ involvement may present with vague signs and symptoms to alert health care professionals early in the course of COVID-19. Another example of an ongoing, yet neglected element of the syndromic features of COVID-19, are the reported findings of loss of smell, altered taste, ataxia, headache, dizziness, and loss of consciousness, which suggest a potential for neural involvement. In this review, we further deliberate on the neuroinvasive potential of SARS-CoV-2, the neurologic symptomology observed in COVID-19, the host-virus interaction, possible routes of SARS-CoV-2 to invade the central nervous system, other neurologic considerations for patients with COVID-19, and a collective call to action.

Expression of SARS-CoV-2 receptor ACE2 and TMPRSS2 in human primary conjunctival and pterygium cell lines and in mouse cornea

PURPOSE

To determine the expressions of SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) and type II transmembrane serine protease (TMPRSS2) genes in human and mouse ocular cells and comparison to other tissue cells.

METHODS

Human conjunctiva and primary pterygium tissues were collected from pterygium patients who underwent surgery. The expression of ACE2 and TMPRSS2 genes was determined in human primary conjunctival and pterygium cells, human ocular and other tissue cell lines, mesenchymal stem cells as well as mouse ocular and other tissues by reverse transcription-polymerase chain reaction (RT-PCR) and SYBR green PCR.

RESULTS

RT-PCR analysis showed consistent expression by 2 ACE2 gene primers in 2 out of 3 human conjunctival cells and pterygium cell lines. Expression by 2 TMPRSS2 gene primers could only be found in 1 out of 3 pterygium cell lines, but not in any conjunctival cells. Compared with the lung A549 cells, similar expression was noted in conjunctival and pterygium cells. In addition, mouse cornea had comparable expression of Tmprss2 gene and lower but prominent Ace2 gene expression compared with the lung tissue.

CONCLUSION

Considering the necessity of both ACE2 and TMPRSS2 for SARS-CoV-2 infection, our results suggest that conjunctiva would be less likely to be infected by SARS-CoV-2, whereas pterygium possesses some possibility of SARS-CoV-2 infection. With high and consistent expression of Ace2 and Tmprss2 in cornea, cornea rather than conjunctiva has higher potential to be infected by SARS-CoV-2. Precaution is necessary to prevent possible SARS-CoV-2 infection through ocular surface in clinical practice.

New antiglaucomatous agent for the treatment of open angle glaucoma: Polymeric inserts for drug release and in vitro and in vivo study

A benzamidine derivative from diminazene was tested for a novel activity: treatment of primary open-angle glaucoma. This drug was incorporated into mucoadhesive polymeric inserts prepared using chitosan (Chs) and chondroitin sulfate (CS). Of current interest is the mucoadhesion, which increases the contact time with the ocular surface, resulting in improved bioavailability; also, the inserts are made to act as a prolonged release system. In the present work the inserts were prepared by the solvent casting method using different polymeric proportions (30:70, 50:50, 75:25% w/w Chs:CS and 100% Chs). Thermal analysis and infrared spectroscopy both demonstrated physical dispersion of the active drug. The most promising was the 50:50% Chs:CS which demonstrated that it was not fragile and has an in vitro release profile of up to 180 minutes. In addition, it presented greater adhesion strength in relation to the other formulations. These physicochemical results corroborate the in vivo tests performed. In this sense, we also demonstrated that the treatment with the 50:50% insert can control the intraocular pressure (IOP) for at least 3 weeks and prevents damage to the retinal ganglion cells (RGCs) compared to the placebo insert. Thus, this indicates thus that the new drug is quite viable and promising in glaucoma treatment.

Relationships Between Neurodegeneration and Vascular Damage in Diabetic Retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes and constitutes a major cause of vision impairment and blindness in the world. DR has long been described exclusively as a microvascular disease of the eye. However, in recent years, a growing interest has been focused on the contribution of neuroretinal degeneration to the pathogenesis of the disease, and there are observations suggesting that neuronal death in the early phases of DR may favor the development of microvascular abnormalities, followed by the full manifestation of the disease. However, the mediators that are involved in the crosslink between neurodegeneration and vascular changes have not yet been identified. According to our hypothesis, vascular endothelial growth factor (VEGF) could probably be the most important connecting link between the death of retinal neurons and the occurrence of microvascular lesions. Indeed, VEGF is known to play important neuroprotective actions; therefore, in the early phases of DR, it may be released in response to neuronal suffering, and it would act as a double-edged weapon inducing both neuroprotective and vasoactive effects. If this hypothesis is correct, then any retinal stress causing neuronal damage should be accompanied by VEGF upregulation and by vascular changes. Similarly, any compound with neuroprotective properties should also induce VEGF downregulation and amelioration of the vascular lesions. In this review, we searched for a correlation between neurodegeneration and vasculopathy in animal models of retinal diseases, examining the effects of different neuroprotective substances, ranging from nutraceuticals to antioxidants to neuropeptides and others and showing that reducing neuronal suffering also prevents overexpression of VEGF and vascular complications. Taken together, the reviewed evidence highlights the crucial role played by mediators such as VEGF in the relationship between retinal neuronal damage and vascular alterations and suggests that the use of neuroprotective substances could be an efficient strategy to prevent the onset or to retard the development of DR.

Angiotensin II and aldosterone in retinal vasculopathy and inflammation

Angiotensin II and aldosterone are the main effectors of the renin-angiotensin aldosterone system (RAAS) and have a central role in hypertension as well as cardiovascular and renal disease. The localization of RAAS components within the retina has led to studies investigating the roles of angiotensin II, aldosterone and the counter regulatory arm of the pathway in vision-threatening retinopathies. This review will provide a brief overview of RAAS components as well as the vascular pathology that develops in the retinal diseases, retinopathy of prematurity, diabetic retinopathy and neovascular age-related macular degeneration. The review will discuss pre-clinical and clinical evidence that modulation of the RAAS alters the development of vasculopathy and inflammation in the aforementioned retinopathies, as well as the emerging role of aldosterone and the mineralocorticoid receptor in central serous chorioretinopathy.

Neuroprotective Peptides in Retinal Disease

In the pathogenesis of many disorders, neuronal death plays a key role. It is now assumed that neurodegeneration is caused by multiple and somewhat converging/overlapping death mechanisms, and that neurons are sensitive to unique death styles. In this respect, major advances in the knowledge of different types, mechanisms, and roles of neurodegeneration are crucial to restore the neuronal functions involved in neuroprotection. Several novel concepts have emerged recently, suggesting that the modulation of the neuropeptide system may provide an entirely new set of pharmacological approaches. Neuropeptides and their receptors are expressed widely in mammalian retinas, where they exert neuromodulatory functions including the processing of visual information. In multiple models of retinal diseases, different peptidergic substances play neuroprotective actions. Herein, we describe the novel advances on the protective roles of neuropeptides in the retina. In particular, we focus on the mechanisms by which peptides affect neuronal death/survival and the vascular lesions commonly associated with retinal neurodegenerative pathologies. The goal is to highlight the therapeutic potential of neuropeptide systems as neuroprotectants in retinal diseases.

β-Cyclodextrin as a Functional Excipient Used for Enhancing the Diminazene Aceturate Bioavailability

In this study, we proposed formulations of diminazene aceturate (DA) designed to improve its bioavailability and to maximize the therapeutic index in animals by overcoming the rapid degradation under the acidic pH of the stomach. An important consequence is the fact that its amount in the bloodstream is close to the administered dose. This was made possible by incorporating DA into the β-cyclodextrin’s (βCD) cavity in a molar ratio of 1:1. The structure of the resulted inclusion complex was established by Raman, DSC, and Wide-Angle X ray Diffraction (WAXD) in solid state and by ¹H-NMR and H-H ROESY in aqueous solutions. The stoichiometry of the DA:βCD inclusion complex was obtained by using the continuous variation method (Job’s plot), considering the chemical shifts variations of protons from both DA and βCD compounds in ¹H-NMR spectra. The biological activity was estimated in vitro by antioxidant activity and in vivo by comparing the bioavailability of parent DA and its inclusion complexes after a single dose administration in Wistar rats by using the HPLC method on their blood plasma. In vitro tests showed an improved antioxidant activity. In vivo tests have shown that the DA concentration is always much higher in blood plasma of rats when DA:βCD inclusion complex of 1:1 molar ratio was administered (i.e., at 60 min, DA is around 11 and 3 times higher when DA:βCD inclusion complex of 1:1 molar ratio was administered than the parent DA one and DA:βCD lyophilized mixture of 1:2 molar ratio, respectively).

Therapeutic treatment of Zika virus infection using a brain-penetrating antiviral peptide

Zika virus is a mosquito-borne virus that is associated with neurodegenerative diseases, including Guillain-Barré syndrome¹ and congenital Zika syndrome². As Zika virus targets the nervous system, there is an urgent need to develop therapeutic strategies that inhibit Zika virus infection in the brain. Here, we have engineered a brain-penetrating peptide that works against Zika virus and other mosquito-borne viruses. We evaluated the therapeutic efficacy of the peptide in a lethal Zika virus mouse model exhibiting systemic and brain infection. Therapeutic treatment protected against mortality and markedly reduced clinical symptoms, viral loads and neuroinflammation, as well as mitigated microgliosis, neurodegeneration and brain damage. In addition to controlling systemic infection, the peptide crossed the blood-brain barrier to reduce viral loads in the brain and protected against Zika-virus-induced blood-brain barrier injury. Our findings demonstrate how engineering strategies can be applied to develop peptide therapeutics and support the potential of a brain-penetrating peptide to treat neurotropic viral infections.

Angiotensin converting enzyme 2 and diminazene: role in cardiovascular and blood pressure regulation

PURPOSE OF REVIEW

Angiotensin converting enzyme 2 (ACE2) is an important regulator of the renin-angiotensin system through actions to degrade angiotensin II. Loss of ACE2 can contribute to the development and progression of cardiovascular disease, and experimental studies have highlighted a beneficial role for novel therapeutic approaches that activate or replenish tissue ACE2. This review focuses on experimental studies that have used the off-target effects of the antitrypanosomal agent, diminazene aceturate (DIZE) to activate ACE2.

RECENT FINDINGS

In cardiovascular disease, activation of the classical renin-angiotensin system and depletion of ACE2 leads to pathophysiological changes. One approach to activate ACE2 involves the drug DIZE, which has been shown to have beneficial effects in experimental models of hypertension, pulmonary hypertension, myocardial infarction, stroke, atherosclerosis, type 1 diabetes, and eye disease. The precise mechanism of action of DIZE to activate ACE2 remains under scrutiny.

SUMMARY

Activation of ACE2 may represent an important therapeutic approach in cardiovascular disease. To date, most studies have focused on the off-target actions of DIZE, in experimental models of disease. More research is required to determine the exact mechanism of action of DIZE and evaluate its therapeutic potential in comparison with currently available clinical interventions. There are no clinical studies of DIZE, and its side-effects, and toxicity make such studies unlikely. Hence, new methods of selectively activating or replenishing ACE2 will be needed in the future if this approach is to be used in a clinical context.

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

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

The ACE2/Angiotensin-(1-7)/MAS Axis of the Renin-Angiotensin System: Focus on Angiotensin-(1-7)

The renin-angiotensin system (RAS) is a key player in the control of the cardiovascular system and hydroelectrolyte balance, with an influence on organs and functions throughout the body. The classical view of this system saw it as a sequence of many enzymatic steps that culminate in the production of a single biologically active metabolite, the octapeptide angiotensin (ANG) II, by the angiotensin converting enzyme (ACE). The past two decades have revealed new functions for some of the intermediate products, beyond their roles as substrates along the classical route. They may be processed in alternative ways by enzymes such as the ACE homolog ACE2. One effect is to establish a second axis through ACE2/ANG-(1-7)/MAS, whose end point is the metabolite ANG-(1-7). ACE2 and other enzymes can form ANG-(1-7) directly or indirectly from either the decapeptide ANG I or from ANG II. In many cases, this second axis appears to counteract or modulate the effects of the classical axis. ANG-(1-7) itself acts on the receptor MAS to influence a range of mechanisms in the heart, kidney, brain, and other tissues. This review highlights the current knowledge about the roles of ANG-(1-7) in physiology and disease, with particular emphasis on the brain.

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.

Significance of angiotensin 1-7 coupling with MAS1 receptor and other GPCRs to the renin-angiotensin system: IUPHAR Review 22

Angiotensins are a group of hormonal peptides and include angiotensin II and angiotensin 1-7 produced by the renin angiotensin system. The biology, pharmacology and biochemistry of the receptors for angiotensins were extensively reviewed recently. In the review, the receptor nomenclature committee was not emphatic on designating MAS1 as the angiotensin 1-7 receptor on the basis of lack of classical G protein signalling and desensitization in response to angiotensin 1-7, as well as a lack of consensus on confirmatory ligand pharmacological analyses. A review of recent publications (2013-2016) on the rapidly progressing research on angiotensin 1-7 revealed that MAS1 and two additional receptors can function as 'angiotensin 1-7 receptors', and this deserves further consideration. In this review we have summarized the information on angiotensin 1-7 receptors and their crosstalk with classical angiotensin II receptors in the context of the functions of the renin angiotensin system. It was concluded that the receptors for angiotensin II and angiotensin 1-7 make up a sophisticated cross-regulated signalling network that modulates the endogenous protective and pathogenic facets of the renin angiotensin system.

N-Methyl-d-Aspartate (NMDA) Receptor Blockade Prevents Neuronal Death Induced by Zika Virus Infection

Zika virus (ZIKV) infection is a global health emergency that causes significant neurodegeneration. Neurodegenerative processes may be exacerbated by N-methyl-d-aspartate receptor (NMDAR)-dependent neuronal excitoxicity. Here, we have exploited the hypothesis that ZIKV-induced neurodegeneration can be rescued by blocking NMDA overstimulation with memantine. Our results show that ZIKV actively replicates in primary neurons and that virus replication is directly associated with massive neuronal cell death. Interestingly, treatment with memantine or other NMDAR blockers, including dizocilpine (MK-801), agmatine sulfate, or ifenprodil, prevents neuronal death without interfering with the ability of ZIKV to replicate in these cells. Moreover, in vivo experiments demonstrate that therapeutic memantine treatment prevents the increase of intraocular pressure (IOP) induced by infection and massively reduces neurodegeneration and microgliosis in the brain of infected mice. Our results indicate that the blockade of NMDARs by memantine provides potent neuroprotective effects against ZIKV-induced neuronal damage, suggesting it could be a viable treatment for patients at risk for ZIKV infection-induced neurodegeneration.

Zika virus (ZIKV) infection is a global health emergency associated with serious neurological complications, including microcephaly and Guillain-Barré syndrome. Infection of experimental animals with ZIKV causes significant neuronal damage and microgliosis. Treatment with drugs that block NMDARs prevented neuronal damage both in vitro and in vivo. These results suggest that overactivation of NMDARs contributes significantly to the neuronal damage induced by ZIKV infection, and this is amenable to inhibition by drug treatment.

Neuropathy optic glaucomatosa induced by systemic hypertension through activation endothelin-1 signaling pathway in central retinal artery in rats

AIM

To evaluate effect of hypertension on retinal ganglion cell (RGC) apoptosis, intraocular pressure (IOP), and the activation of endothelin-1 (ET-1) signaling pathway in central retinal artery (CRA) in rats.

METHODS

The experimental study was performed on 20 male Sprague Dawley rats that were divided into control group, and hypertension groups. The hypertension was induced by subcutaneous deoxycorticoacetate (DOCA) 10 mg/kg twice a week and administered 0.9% NaCl solution daily for 2, 6, and 10wk. Blood pressure (BP) was measured using animal BP analyzer. IOP was measured by handheld tonometry. Retinal tissue preparations by paraffin blocks were made after enucleation. The expression of ET-1, eNOS, ET-1 receptor A (ETR_A), ET-1 receptor B (ETR_B), and phosphorylated myosin light chain kinase (MLCK), and caldesmon (CaD) in CRA and RGC apoptosis were evaluated through immunofluorescent staining method then observed using laser scanning confocal microscopy.

RESULTS

BP significantly increased in all of the hypertension groups compared to control (P=0.001). Peak IOP elevation (7.78±4.14 mm Hg) and RGC apoptosis (576.15±33.28 Au) occurred on 2wk of hypertension. ET-1 expression (1238.6±55.1 Au) and eNOS expression (2814.2±70.7 Au) were found highest in 2wk of hypertension, although the ratio of ET-1/eNOS decreased since 2wk. ETR_A reached peak expression in 10wk of hypertension (1219.4±6.3 Au), while ETR_B significantly increased only in 2 weeks group (1069.2±9.6 Au). The highest MLCK expression (1190.09±58.32 Au), CaD (1670.28±18.36 Au) were also found in 2wk of hypertension.

CONCLUSION

Hypertension effects to activation of ET-1 signaling pathway significantly in CRA, elevation of IOP, and RGC apoptosis. The highest value was achieved at 2wk, which is the development phase of hypertension.

One protein, multiple pathologies: multifaceted involvement of amyloid β in neurodegenerative disorders of the brain and retina

Accumulation of amyloid β (Aβ) and its aggregates in the ageing central nervous system is regarded synonymous to Alzheimer's disease (AD) pathology. Despite unquestionable advances in mechanistic and diagnostic aspects of the disease understanding, the primary cause of Aβ accumulation as well as its in vivo roles remains elusive; nonetheless, the majority of the efforts to address pathological mechanisms for therapeutic development are focused towards moderating Aβ accumulation in the brain. More recently, Aβ deposition has been identified in the eye and is linked with distinct age-related diseases including age-related macular degeneration, glaucoma as well as AD. Awareness of the Aβ accumulation in these markedly different degenerative disorders has led to an increasing body of work exploring overlapping mechanisms, a prospective biomarker role for Aβ and the potential to use retina as a model for brain related neurodegenerative disorders. Here, we present an integrated view of current understanding of the retinal Aβ deposition discussing the accumulation mechanisms, anticipated impacts and outlining ameliorative approaches that can be extrapolated to the retina for potential therapeutic benefits. Further longitudinal investigations in humans and animal models will determine retinal Aβ association as a potential pathognomonic, diagnostic or prognostic biomarker.

AAV8-Mediated Angiotensin-Converting Enzyme 2 Gene Delivery Prevents Experimental Autoimmune Uveitis by Regulating MAPK, NF-κB and STAT3 Pathways

Renin angiotensin system (RAS) is a key hormonal system which regulates the cardiovascular function and is implicated in several autoimmune diseases. With the discovery of the angiotensin-converting enzyme 2 (ACE2), a protective axis of RAS namely ACE2/Ang-(1-7)/Mas that counteracts the deleterious ACE/AngII/AT1R axis has been established. This axis is emerging as a novel target to attenuate ocular inflammation. However, the underlying molecular mechanisms remain unclear. We investigated the hypothesis that enhancing the activity of the protective axis of RAS by subretinal delivery of an AAV8 (Y733F)-ACE2 vector would protect against the ocular inflammation in experimental autoimmune uveitis (EAU) mice through regulating the local immune responses. Our studies demonstrated that increased ACE2 expression exerts protective effects on inflammation in EAU mouse by modulating ocular immune responses, including the differentiation of Th1/Th17 cells and the polarization of M1/M2 macrophages; whereas the systemic immune responses appeared not affected. These effects were mediated by activating the Ang-(1-7)/Mas and inhibiting the MAPK, NF-κB and STAT3 signaling pathways. This proof-of-concept study suggests that activation of ocular ACE2/Ang-(1-7)/Mas axis with AAV gene transfer modulates local immune responses and may be a promising, long-lasting therapeutic strategy for refractory and recurrent uveitis, as well as other inflammatory eye diseases.

Original Research: ACE2 activator associated with physical exercise potentiates the reduction of pulmonary fibrosis

The interstitial lung diseases are poorly understood and there are currently no studies evaluating the association of physical exercise with an ACE2 activator (DIZE) as a possible treatment for this group of diseases. We evaluate the effects of pharmacological treatment with an angiotensin-converting enzyme 2 activator drug, associated with exercise, on the pulmonary lesions induced by bleomycin. From the 96 male Balb/c mice used in the experiment, only 49 received 8 U/kg of bleomycin (BLM, intratracheally). The mice were divided into control (C) and bleomycin (BLM) groups, sedentary and trained (C-SED, C-EXE, BLM-SED, BLM-EXE), control and bleomycin and also sedentary and trained treated with diminazene (C-SED/E, C-EXE/E, BLM-SED/E, BLM-EXE/E). The animals were trained five days/week, 1 h/day with 60% of the maximum load obtained in a functional capacity test, for four weeks. Diminazene groups were treated (1 mg/kg, by gavage) daily until the end of the experiment. The lungs were collected 48 h after the training program, set in buffered formalin and investigated by Gomori's trichrome, immunohistochemistry of collagen type I, TGF-β₁, beta-prolyl-4-hydroxylase, MMP-1 and -2. The BLM-EXE/E group obtained a significant increase in functional capacity, reduced amount of fibrosis and type I collagen, decreased expression of TGF-β₁ and beta-prolyl-4-hydroxylase and an increase of metalloproteinase -1, -2 when compared with the other groups. The present research shows, for the first time, that exercise training associated with the activation of ACE2 potentially reduces pulmonary fibrosis.

Renin-angiotensin system as a potential therapeutic target in stroke and retinopathy: experimental and clinical evidence

As our knowledge expands, it is now clear that the renin-angiotensin (Ang) system (RAS) mediates functions other than regulating blood pressure (BP). The RAS plays a central role in the pathophysiology of different neurovascular unit disorders including stroke and retinopathy. Moreover, the beneficial actions of RAS modulation in brain and retina have been documented in experimental research, but not yet exploited clinically. The RAS is a complex system with distinct yet interconnected components. Understanding the different RAS components and their functions under brain and retinal pathological conditions is crucial to reap their benefits. The aim of the present review is to provide an experimental and clinical update on the role of RAS in the pathophysiology and treatment of stroke and retinopathy. Combining the evidence from both these disorders allows a unique opportunity to move both fields forward.

Therapeutic uses for Angiotensin-(1-7)

INTRODUCTION

Angiotensin-(1-7) is a key component of the Renin-Angiotensin System, which can counter-regulate several deleterious effects caused by angiotensin II. Due to the potential for therapeutic use, several of its actions are specifically described in patents.

AREAS COVERED

In this review, the authors describe a plethora of therapeutic uses for Angiotensin-(1-7), claimed and supported by experimental evidence in patent documents and applications.

EXPERT OPINION

The clinical potential of Angiotensin-(1-7) as a therapeutic agent to treat several pathologies is evidenced by the variety of patents and clinical trials involving this peptide. Cancer treatment is one of the most advanced therapeutic areas, but clinical studies are also available in several other areas, such as cardiovascular, hematological, transplantation, surgical and medical procedures.

Activation of endogenous angiotensin converting enzyme 2 prevents early injuries induced by hyperglycemia in rat retina

Diabetic retinopathy (DR) is a serious complication of diabetes mellitus that may result in blindness. We evaluated the effects of activation of endogenous angiotensin converting enzyme (ACE) 2 on the early stages of DR. Rats were administered an intravenous injection of streptozotocin to induce hyperglycemia. The ACE2 activator 1-[[2-(dimethylamino) ethyl] amino]-4-(hydroxymethyl)-7-[[(4-methylphenyl) sulfonyl] oxy]-9H-xanthone 9 (XNT) was administered by daily gavage. The death of retinal ganglion cells (RGC) was evaluated in histological sections, and retinal ACE2, caspase-3, and vascular endothelial growth factor (VEGF) expressions were analyzed by immunohistochemistry. XNT treatment increased ACE2 expression in retinas of hyperglycemic (HG) rats (control: 13.81±2.71 area%; HG: 14.29±4.30 area%; HG+XNT: 26.87±1.86 area%; P<0.05). Importantly, ACE2 activation significantly increased the RCG number in comparison with HG animals (control: 553.5±14.29; HG: 530.8±10.3 cells; HG+XNT: 575.3±16.5 cells; P<0.05). This effect was accompanied by a reduction in the expression of caspase-3 in RGC of the HG+XNT group when compared with untreated HG rats (control: 18.74±1.59; HG: 38.39±3.39 area%; HG+XNT: 27.83±2.80 area%; P<0.05). Treatment with XNT did not alter the VEGF expression in HG animals (P>0.05). Altogether, these findings indicate that activation of ACE2 reduced the death of retinal ganglion cells by apoptosis in HG rats.

Diminazene enhances stability of atherosclerotic plaques in ApoE-deficient mice

Angiotensin (Ang) II contributes to the development of atherosclerosis, while Ang-(1-7) has atheroprotective actions. Accordingly, angiotensin-converting enzyme 2 (ACE2), which breaks-down Ang II and forms Ang-(1-7), has been suggested as a target against atherosclerosis. Here we investigated the actions of diminazene, a recently developed ACE2 activator compound, in a model of vulnerable atherosclerotic plaque. Atherosclerotic plaque formation was induced in the carotid artery of ApoE-deficient mice by a shear stress (SS) modifier device. The animals were treated with diminazene (15mg/kg/day) or vehicle. ACE2 was strongly expressed in the aortic root and low SS-induced carotid plaques, but poorly expressed in the oscillatory SS-induced carotid plaques. Diminazene treatment did not change the lesion size, but ameliorated the composition of aortic root and low SS-induced carotid plaques by increasing collagen content and decreasing both MMP-9 expression and macrophage infiltration. Interestingly, these beneficial effects were not observed in the oscillatory SS-induced plaque. Additionally, diminazene treatment decreased intraplaque ICAM-1 and VCAM-1 expression, circulating cytokine and chemokine levels and serum triglycerides. In summary, ACE2 was distinctively expressed in atherosclerotic plaques, which depends on the local pattern of shear stress. Moreover, diminazene treatment enhances the stability of atherosclerotic plaques.

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

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

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

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

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.

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.