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

Diminazene protects corpus cavernosum against hypercholesterolemia-induced injury

INTRODUCTION

Angiotensin-converting enzyme 2 (ACE2) is a key enzyme of the renin angiotensin system, which breaks down angiotensin II and forms angiotensin-(1-7). In erectile tissues, it has been documented that angiotensin II contributes to the development of erectile dysfunction (ED), while treatment with angiotensin-(1-7) improves penile erection. However, the expression and function of ACE2 in erectile tissues have never been investigated.

AIM

Here, we examined the expression of ACE2 in erectile tissues and its actions against hypercholesterolemia-induced corpus cavernosum (CC) injury.

METHODS

Hypercholesterolemic apolipoprotein E knockout (ApoE(-/-) ) mice, a well-known model of ED, were treated with diminazene aceturate (DIZE), an ACE2 activator compound, or vehicle for 3 weeks. Reactive oxygen species (ROS), collagen content, and protein expression of ACE2, neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) subunits were evaluated in the penis of DIZE-treated and untreated ApoE(-/-) mice. Functional studies were performed in CC strips.

MAIN OUTCOME MEASURES

ACE2 expression and its role in modulating nitric oxide (NO)/ROS production and fibrosis within the CC of hypercholesterolemic mice were the main outcome measures.

RESULTS

ACE2 was expressed in smooth muscle and endothelial cells of mouse CC. Interestingly, ACE2 was downregulated in penis of hypercholesterolemic mice with ED, suggesting a protective role of ACE2 on the CC homeostasis. In accordance with that, pharmacological ACE2 activation by DIZE treatment reduced ROS production and NADPH oxidase expression, and elevated nNOS and eNOS expression and NO bioavailability in the penis of ApoE(-/-) mice. Additionally, DIZE decreased collagen content within the CC. These beneficial actions of DIZE on the CC were not accompanied by improvements in atherosclerotic plaque size or serum lipid profile.

CONCLUSION

ACE2 is expressed in erectile tissue and its reduction is associated with hypercholesterolemia-induced ED. Additionally, treatment with DIZE improved hypercholesterolemia-induced CC injury, suggesting ACE2 as a potential target for treating ED. .

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.

Angiotensin-converting enzyme 2 decreases formation and severity of angiotensin II-induced abdominal aortic aneurysms

OBJECTIVE

Angiotensin-converting enzyme 2 (ACE2) cleaves angiotensin II (AngII) to form angiotensin-(1-7) (Ang-(1-7)), which generally opposes effects of AngII. AngII infusion into hypercholesterolemic male mice induces formation of abdominal aortic aneurysms (AAAs). This study tests the hypothesis that deficiency of ACE2 promotes AngII-induced AAAs, whereas ACE2 activation suppresses aneurysm formation.

APPROACH AND RESULTS

ACE2 protein was detectable by immunostaining in mice and human AAAs. Whole-body deficiency of ACE2 significantly increased aortic lumen diameters and external diameters of suprarenal aortas from AngII-infused mice. Conversely, ACE2 deficiency in bone marrow-derived cells had no effect on AngII-induced AAAs. In contrast to AngII-induced AAAs, ACE2 deficiency had no significant effect on external aortic diameters of elastase-induced AAAs. Because ACE2 deficiency promoted AAA formation in AngII-infused mice, we determined whether ACE2 activation suppressed AAAs. ACE2 activation by administration of diminazene aceturate (30 mg/kg per day) to Ldlr(-/-) mice increased kidney ACE2 mRNA abundance and activity and elevated plasma Ang-(1-7) concentrations. Unexpectedly, administration of diminazene aceturate significantly reduced total sera cholesterol and very low-density lipoprotein-cholesterol concentrations. Notably, diminazene aceturate significantly decreased aortic lumen diameters and aortic external diameters of AngII-infused mice resulting in a marked reduction in AAA incidence (from 73% to 29%). None of these effects of diminazene aceturate were observed in the Ace2(-/y) mice.

CONCLUSIONS

These results demonstrate that ACE2 exerts a modulatory role in AngII-induced AAA formation, and that therapeutic stimulation of ACE2 could be a benefit to reduce AAA expansion and rupture in patients with an activated renin-angiotensin system.

Angiotensin-converting enzyme 2 (ACE2) activator diminazene aceturate ameliorates endotoxin-induced uveitis in mice

PURPOSE

Uveitis is a common cause of vision loss. The renin angiotensin system (RAS), which plays a vital role in cardiovascular system, is a potent mediator of inflammation and has been implicated in the pathogenesis of uveitis. A newly identified axis of RAS, ACE2/Ang-(1-7)/Mas, has emerged as a novel target because it counteracts the deleterious effect of angiotensin II. The purpose of this study was to investigate the effect of endogenous ACE2 activation in preventing endotoxin-induced uveitis (EIU) in mice.

METHODS

ACE2 activator diminazene aceturate (DIZE) was administered both systemically and locally. For systemic administration, female BALB/c mice received intraperitoneal injection of DIZE (60 mg/kg body weight [BW]) for 2 days prior to lipopolysaccharide (LPS) intravitreal injection (125 ng) to induce uveitis. For local study, DIZE was given at 0.5, 0.1, and 0 mg/mL as eyedrops six times per day for 2 days before LPS injection. The anterior segment of the mice was examined at 12, 24, 48, and 72 hours after LPS injection, and clinical scores were determined at the same time. Morphology and infiltrating inflammatory cells were evaluated after 24 hours. The mRNA levels of inflammatory cytokines were analyzed by real-time RT-PCR. ACE2 activity was determined using a self-quenching fluorescent substrate.

RESULTS

At 24 hours, the clinical score of mice treated with DIZE systemically was significantly lower (mean, ∼1.75) than the saline vehicle group (mean, ∼4) (P < 0.001). Histological examination showed 63.4% reduction of infiltrating inflammatory cells in the anterior segment and 57.4% reduction in the posterior segment of DIZE-treated eyes. The number of CD45(+) inflammatory cells in the vitreous of the DIZE-treated group was decreased (43.3%) compared to the vehicle group (P < 0.01). The mRNA levels of inflammatory cytokines were significantly reduced in the DIZE-treated group (P < 0.01, P < 0.001). The number of infiltrating inflammatory cells was also significantly reduced in eyes that received topical administration of DIZE: 73.8% reduction in the 0.5 mg/mL group and 51.7% reduction in the 0.1mg/mL group compared to the control group. DIZE treatment resulted in significantly increased ACE2 activity in the retina (P < 0.001).

CONCLUSIONS

Endogenous ACE2 activation by DIZE has a preventive effect on LPS-induced ocular inflammation in the EIU mouse model. These results support the notions that RAS plays a role in modulating ocular immune response and that enhancing ACE2 provides a novel therapeutic strategy for uveitis.

Activation of angiotensin-converting enzyme 2 improves cardiac electrical changes in ventricular repolarization in streptozotocin-induced hyperglycaemic rats

AIMS

Diabetic patients present a high level of cardiac arrhythmias and risk of cardiac sudden death. The renin-angiotensin system (RAS) plays a key role in diabetes and cardiac diseases. The present study aimed to evaluate whether an angiotensin-converting enzyme 2 (ACE2) activator, diminazene aceturate (DIZE), could improve the streptozotocin (STZ)-induced electrical changes in ventricular repolarization in hyperglycaemic rats.

METHODS AND RESULTS

Hyperglycaemia was induced in Wistar male rats with STZ (60 mg/kg/iv). After 4 weeks of STZ injection, rats were daily treated with saline (control) or DIZE (1 mg/kg/gavage) for four consecutive weeks. The cardiac electrical function was evaluated in vivo by electrocardiogram and in vitro by cardiac action potential records in different pacing frequencies. Treatment with DIZE was not able to reverse hyperglycaemia nor body weight loss. However, DIZE reversed hyperglycaemia-induced cardiac electrical changes in ventricular repolarization. Specifically, animals treated with DIZE showed shorter QT and QTc intervals. In addition, ACE2 activation was capable to shorten the cardiac action potential and also reverse the arrhythmic markers. Diminazene aceturate treatment did not induce arrhythmic events in normal, as well as in hyperglycaemic animals.

CONCLUSION

Our data indicate that activation of ACE2 has a beneficial effect in hyperglycaemic rats, improving the cardiac electrical function. Thus, DIZE represents a promising new therapeutic agent to treat hyperglycaemia-induced cardiac electrical changes in ventricular repolarization.

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

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

Angiotensin-converting enzyme 2-independent action of presumed angiotensin-converting enzyme 2 activators: studies in vivo, ex vivo, and in vitro

Angiotensin (Ang)-converting enzyme 2 (ACE2) is a key enzyme in the metabolism of Ang II. XNT (1-[(2-dimethylamino)ethylamino]-4-(hydroxymethyl)-7-[(4-methylphenyl) sulfonyl oxy]-9H-xanthene-9-one) and diminazene have been reported to exert various organ-protective effects, which are attributed to the activation of ACE2. To test the effect of these compounds, we studied Ang II degradation in vivo and in vitro as well as their effect on ACE2 activity in vivo and in vitro. In a model of Ang II-induced acute hypertension, blood pressure (BP) recovery was markedly enhanced by XNT (slope with XNT, -3.26±0.2 versus -1.6±0.2 mm Hg/min without XNT; P<0.01). After Ang II infusion, neither plasma nor kidney ACE2 activity was affected by XNT. Plasma Ang II and Ang (1-7) levels also were not significantly affected by XNT. The BP-lowering effect of XNT seen in wild-type animals was also observed in ACE2 knockout mice (slope with XNT, -3.09±0.30 versus -1.28±0.22 mm Hg/min without XNT; P<0.001). These findings show that the BP-lowering effect of XNT in Ang II-induced hypertension cannot be because of the activation of ACE2. In vitro and ex vivo experiments in both mice and rat kidney confirmed a lack of enhancement of ACE2 enzymatic activity by XNT and diminazene. Moreover, Ang II degradation in vitro and ex vivo was unaffected by XNT and diminazene. We conclude that the biological effects of these compounds are ACE2-independent and should not be attributed to the activation of this enzyme.