Robson As Santos

Angiotensin-(1-7) and the renin-angiotensin system.

Purpose of reviewIn this review we will focus on the recent findings related to angiotensin-(1–7) as an angiotensin II counter-regulatory peptide within the renin–angiotensin system. Recent findingsThe identification of the angiotensin-converting enzyme homologue ACE2 as an angiotensin peptide processing enzyme and of Mas as a receptor for angiotensin-(1–7) has contributed to establishing this heptapeptide as a biologically active member of the renin–angiotensin system cascade. SummaryThe previously unsuspected complexity of the renin–angiotensin system, unmasked by novel findings, has revealed new possibilities for exploring its physiological and pathophysiological roles. In addition, the ACE2–angiotensin-(1–7)–Mas axis may be seriously considered as a putative target for the development of new cardiovascular drugs.

Angiotensin-(1-7) and its receptor as a potential targets for new cardiovascular drugs.

The identification of novel biochemical components of the renin–angiotensin system (RAS) has added a further layer of complexity to the classical concept of this cardiovascular regulatory system. It is now clear that there is a counter-regulatory arm within the RAS that is mainly formed by the angiotensin-converting enzyme 2–angiotensin (1-7)–receptor Mas axis. The functions of this axis are often opposite to those attributed to the major component of the RAS, angiotensin II. This review will highlight the current knowledge concerning the cardiovascular effects of angiotensin-(1-7) through a direct interaction with its receptor Mas or through an indirect interplay with the kallikrein–kinin system. In addition, there will be a discussion of its role in the beneficial effects of angiotensin-converting enzyme inhibitors and angio-tensin receptor type 1 (AT1) antagonists, and the potential of this peptide and its receptor as a novel targets for new cardiovascular drugs.

Opposing actions of angiotensins on angiogenesis.

Using the murine sponge model of angiogenesis, associated to functional and morphological parameters we have demonstrated opposing actions of angiotensin II (Ang II) and angiotensin-(1-7;Ang-1-7) in modulating fibrovascular tissue growth. Angiogenesis in the implants was assessed at day 7 postimplantation by extracting the hemoglobin content, by determining the outflow rate of sodium fluorescein applied intraimplant and by histological analysis. Furthermore, the proliferative activity of control and angiotensin-treated implants was established using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2(4 -sulfonyl)2H-tetrazolium)assay. The hemoglobin content in the control implants was 2.4 +/- 0.14 (microg/mg wet weight) versus 3.6 +/- 0.27(Ang II;100 ng) and 0.86 +/- 0.07 Ang-(1-7); 20 ng. Blood flow in the implants as determined by t1/2 values (time taken for the fluorescence to reach 50% of the peak in the systemic circulation) showed that Ang II stimulated angiogenesis, whereas Ang-(1-7) inhibited it. The proliferative activity of the sponge-induced fibrovascular tissue was enhanced by Ang II and diminished by Ang-(1-7). These results show the pro-versus anti-angiogenic effects of these angiotensin molecules, providing evidence for their opposing effects on vascular tissue growth and wound healing in vivo.

Angiotensin-(1-7)/Mas axis integrity is required for the expression of object recognition memory

It has been shown that the brain has its own intrinsic renin-angiotensin system (RAS) and angiotensin-(1-7) (Ang-(1-7)) is particularly interesting, because it appears to counterbalance most of the Ang II effects. Ang-(1-7) exerts its biological function through activation of the G-protein-coupled receptor Mas. Interestingly, hippocampus is one of the regions with higher expression of Mas. However, the role of Ang-(1-7)/Mas axis in hippocampus-dependent memories is still poorly understood. Here we demonstrated that Mas ablation, as well as the blockade of Mas in the CA1-hippocampus, impaired object recognition memory (ORM). We also demonstrated that the blockade of Ang II receptors AT1, but not AT2, recovers ORM impairment of Mas-deficient mice. Considering that high concentrations of Ang-(1-7) may activate AT1 receptors, nonspecifically, we evaluate the levels of Ang-(1-7) and its main precursors Ang I and Ang II in the hippocampus of Mas-deficient mice. The Ang I and Ang II levels are unaltered in the whole hipocampus of MasKo. However, Ang-(1-7) concentration is increased in the whole hippocampus of MasKo mice, as well as in the CA1 area. Taken together, our findings suggest that the functionality of the Ang-(1-7)/Mas axis is essential for normal ORM processing.

Therapeutic targeting of the angiotensin-converting enzyme 2/Angiotensin-(1-7)/Mas cascade in the renin-angiotensin system: a patent review.

Introduction: The renin–angiotensin system (RAS) is a main therapeutic target for cardiovascular diseases. Within the last two decades, novel components of the RAS have been discovered, opening new opportunities to interfere with its activity. Angiotensin(Ang)-(1-7) is synthesized by angiotensin-converting enzyme 2 (ACE2), and interacts with the G-protein-coupled receptor Mas. The axis formed by ACE2/Ang-(1-7)/Mas represents an endogenous counter regulatory pathway within the RAS. Areas covered: In this review, the authors discuss patents and recent initiatives to develop therapeutic strategies based on the ACE2/Ang-(1-7)/Mas axis. Expert opinion: Many publications and patents support a strategy to interfere with the activity of the RAS by stimulating its counter-regulatory axis mainly in two different ways: i) To increase the activity of ACE2, which will impact the system by increasing the inactivation of Ang II and the production of Ang-(1-7); ii) To stimulate Mas, taking advantage of nanostructured formulations of the natural peptide or analogues of Ang-(1-7). Although the preclinical studies are compelling, the possible impact of these novel therapeutic tools for the treatment of cardiometabolic diseases will only be known after completion of the ongoing clinical studies.

Molecular characterization and regulation of the angiotensin-converting enzyme type 2/Angiotensin-(1-7)/MAS receptor axis during the ovulation process in cattle:

The objective of this study was to characterize the profiles of Ang-(1-7), MAS receptor, ACE2, NEP and PEP during the ovulatory process in cattle. For this study, 40 synchronized cows with follicular diameter ≥ 12 mm were ovariectomized at different time-points (0, 3, 6, 12 and 24 h) after i.m. application of gonadotropin-releasing hormone (GnRH) to induce a luteinizing hormone surge. Follicular fluid was collected for measuring Ang-(1-7) by radioimmunoassay. Theca and granulosa cells were isolated from the preovulatory follicles to evaluate the gene expression of MAS receptor, ACE2, NEP and PEP by qRT-PCR assay. Cross-contamination between theca and granulosa cells was tested by RT-PCR to detect cytochrome P450 aromatase (CYP19A1) and 17α-hydroxylase (CYP17A1) mRNA. Ang-(1-7) levels were constant until 12 h and then increased (p < 0.05) at 24 h after GnRH. Messenger RNA expression of MAS, ACE2, NEP and PEP was detected in theca and granulosa cells at all time-points after GnRH. In granulosa cells, ACE2, NEP and PEP were differentially expressed after GnRH treatment (p < 0.05). In conclusion, the Ang-(1-7), MAS receptor, ACE2, NEP and PEP profiles in preovulatory follicles indicate that Ang-(1-7) plays a role in the regulation of the ovulatory process in cattle.

Angiotensin II profile and mRNA encoding RAS proteins during bovine follicular wave

Angiotensin II (AngII) has a role in ovarian follicle development, ovulation, and oocyte meiotic resumption. The objective of the present study was to characterise the AngII profile and the mRNA encoding RAS proteins in a bovine follicular wave. Cows were ovariectomised when the size between the largest (F1) and the second largest follicle (F2) was not statistically different (day 2), slightly different (day 3), or markedly different (day 4). AngII was measured in the follicular fluid and the mRNA abundance of genes encoding angiotensin-converting enzyme (ACE), (pro)renin receptor, and renin-binding protein (RnBP) was evaluated in the follicular cells from F1 and F2. The AngII levels increased at the expected time of the follicular deviation in F1 but did not change in F2. However, the expression of the genes encoding ACE, (pro)renin receptor, and RnBP was not regulated in F1 but was upregulated during or after the follicular deviation in F2. Moreover, RnBP gene expression increased when the F1 was treated with the oestrogen receptor-antagonist in vivo. In conclusion, the AngII concentration increased in the follicular fluid of the dominant follicle during and after deviation and further supports our finding that RAS is present in the ovary regulating follicular dominance.

Cardiovascular effects of angiotensin A: a novel peptide of the renin-angiotensin system.

Introduction: Angiotensin (Ang) A was first identified in human plasma and it differs from Ang II in Ala1 instead of Asp1. Here, we hypothesized that the actions of this peptide might explain, at least partially, the limited effects of AT1R antagonists in certain cardiovascular diseases. Materials and methods: The effects of Ang A and Ang II on blood pressure (BP) and heart function were compared. Importantly, participation of AT1R in these effects was evaluated. Furthermore, the effects of these two peptides on ischemia/reperfusion arrhythmias and involvement of calcium in these effects were investigated. Results: Administration of increasing doses of these peptides caused elevations in BP at comparable magnitude. AT1R blockade completely abolished these effects. The actions of these peptides in cardiac function were quite similar although the effects of Ang A were only partially blocked by losartan. Interestingly, Ang II elicited an increase in the duration of ischemia/reperfusion arrhythmias while Ang A had no effect on cardiac rhythm during reperfusion. In accordance, differently to Ang II, Ang A did not induce any significant effect on calcium transient during baseline and ischemic stress conditions. Conclusions: These data suggest that the existence of alternative peptides of the renin–angiotensin system (RAS) might contribute to the limited effects of angiotensin receptor blockers (ARBs) in certain pathophysiological circumstances.

Age-related changes in vascular responses to angiotensin-(1-7) in female mice

The vasodilatory effect of angiotensin-(1-7) seems to vary between sexes, and estradiol (E2) can modulate the magnitude of the Ang-(1-7) vasodilatory response in female rats. However, there are few studies addressing the influence of sex on the age-related vasodilatory effect of Ang-(1-7). Here, we evaluated the vasodilatory response to Ang-(1-7) on vascular ageing. Ang-(1-7) dose–response curves were determined in mice aortic rings from males (old and young) and females (E2 treated/non-treated old and young) mounted in an isolated organ chamber. Abdominal aortic rings were used for protein expression analysis and determination of reactive oxygen species (ROS) and nitric oxide (NO) production. Our results showed that the Ang-(1-7) vasodilatory effect was absent in aorta from old females, contrasting with a full response in vessels from young females. The Ang-(1-7) vasodilatory effect was restored by E2 replacement in old females. A robust increase in Mas receptor, SOD2, NRF-2 and NOX2 expression was observed in aorta from old females, which was normalized by E2. This effect of E2 was also associated with lower production of ROS and normal levels of NO. In conclusion, our data demonstrated that pathways involved in the Ang-(1-7) vasodilatory response in female mice is affected by hormonal changes in ageing and rescued by E2.

Angiotensin-converting enzyme inhibition increases glucose-induced insulin secretion in response to acute restraint.

There is increasing evidence suggesting involvement of the renin–angiotensin system (RAS) in carbohydrate metabolism and its response to stress. Thus, the aim of the present study was to evaluate the effects of chronic inhibition of the RAS on glucose and insulin levels during acute restraint stress. Male Holtzman rats were treated with 10 mg/kg per day enalapril solution or vehicle for 14 days. After 14 days, rats were divided into three experimental groups: enalapril + restraint (ER), vehicle + restraint (VR) and enalapril + saline (ES). Rats in the restraint groups were subjected to 30 min restraint stress, whereas rats in the ES groups were given saline infusion instead. Blood samples were collected at baseline and after 5, 10, 20 and 30 min restraint stress or saline infusion. After restraint, a hyperglycaemic response was observed in the ER and VR groups that peaked at 20 and 10 min, respectively (P < 0.05 compared with baseline). The area under the glucose curve was markedly increased in the ER and VR groups compared with that in the ES group (P < 0.05 for both). Importantly, restraint induced a marked increase in insulin secretion in the ER group compared with only a mild elevation in the VR group; insulin secretion in both groups peaked at 20 min (P < 0.05 compared with baseline). Analysis of the area under the insulin curve confirmed an increase in insulin secretion in the ER compared with the VR and ES groups (P < 0.05 for both). The results of the present study reinforce that the RAS is involved in modulating responses to stress and suggest that RAS inhibition with enalapril may increase glucose‐induced insulin secretion in response to acute restraint.