Update on the angiotensin AT(2) receptor

Systematic-Narrative Hybrid Literature Review: Crosstalk between Gastrointestinal Renin-Angiotensin and Dopaminergic Systems in the Regulation of Intestinal Permeability by Tight Junctions

In the first part of this article, the role of intestinal epithelial tight junctions (TJs), together with gastrointestinal dopaminergic and renin-angiotensin systems, are narratively reviewed to provide sufficient background. In the second part, the current experimental data on the interplay between gastrointestinal (GI) dopaminergic and renin-angiotensin systems in the regulation of intestinal epithelial permeability are reviewed in a systematic manner using the PRISMA methodology. Experimental data confirmed the copresence of DOPA decarboxylase (DDC) and angiotensin converting enzyme 2 (ACE2) in human and rodent enterocytes. The intestinal barrier structure and integrity can be altered by angiotensin (1-7) and dopamine (DA). Both renin-angiotensin and dopaminergic systems influence intestinal Na+/K+-ATPase activity, thus maintaining electrolyte and nutritional homeostasis. The colocalization of B0AT1 and ACE2 indicates the direct role of the renin-angiotensin system in amino acid absorption. Yet, more studies are needed to thoroughly define the structural and functional interaction between TJ-associated proteins and GI renin-angiotensin and dopaminergic systems.

The role of the brain renin-angiotensin system in Parkinson´s disease

The renin-angiotensin system (RAS) was classically considered a circulating hormonal system that regulates blood pressure. However, different tissues and organs, including the brain, have a local paracrine RAS. Mutual regulation between the dopaminergic system and RAS has been observed in several tissues. Dysregulation of these interactions leads to renal and cardiovascular diseases, as well as progression of dopaminergic neuron degeneration in a major brain center of dopamine/angiotensin interaction such as the nigrostriatal system. A decrease in the dopaminergic function induces upregulation of the angiotensin type-1 (AT1) receptor activity, leading to recovery of dopamine levels. However, AT1 receptor overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH-oxidase-superoxide axis and Ca2+ release, which mediate several key events in oxidative stress, neuroinflammation, and α-synuclein aggregation, involved in Parkinson's disease (PD) pathogenesis. An intraneuronal antioxidative/anti-inflammatory RAS counteracts the effects of the pro-oxidative AT1 receptor overactivity. Consistent with this, an imbalance in RAS activity towards the pro-oxidative/pro-inflammatory AT1 receptor axis has been observed in the substantia nigra and striatum of several animal models of high vulnerability to dopaminergic degeneration. Interestingly, autoantibodies against angiotensin-converting enzyme 2 and AT1 receptors are increased in PD models and PD patients and contribute to blood-brain barrier (BBB) dysregulation and nigrostriatal pro-inflammatory RAS upregulation. Therapeutic strategies addressed to the modulation of brain RAS, by AT1 receptor blockers (ARBs) and/or activation of the antioxidative axis (AT2, Mas receptors), may be neuroprotective for individuals with a high risk of developing PD or in prodromal stages of PD to reduce progression of the disease.

Exploring the Role of ACE2 as a Connecting Link between COVID-19 and Parkinson's Disease

Coronavirus disease 2019 (COVID-19) is frequently accompanied by neurological manifestations such as headache, delirium, and epileptic seizures, whereas ageusia and anosmia may appear before respiratory symptoms. Among the various neurological COVID-19-related comorbidities, Parkinson's disease (PD) has gained increasing attention. Some cases of PD disease have been linked to COVID-19, and both motor and non-motor symptoms in Parkinson's disease patients frequently worsen following SARS-CoV-2 infection. Although it is still unclear whether PD increases the susceptibility to SARS-CoV-2 infection or whether COVID-19 increases the risk of or unmasks future cases of PD, emerging evidence sheds more light on the molecular mechanisms underlying the relationship between these two diseases. Among them, angiotensin-converting enzyme 2 (ACE2), a significant component of the renin-angiotensin system (RAS), seems to play a pivotal role. ACE2 is required for the entry of SARS-CoV-2 to the human host cells, and ACE2 dysregulation is implicated in the severity of COVID-19-related acute respiratory distress syndrome (ARDS). ACE2 imbalance is implicated in core shared pathophysiological mechanisms between PD and COVID-19, including aberrant inflammatory responses, oxidative stress, mitochondrial dysfunction, and immune dysregulation. ACE2 may also be implicated in alpha-synuclein-induced dopaminergic degeneration, gut-brain axis dysregulation, blood-brain axis disruption, autonomic dysfunction, depression, anxiety, and hyposmia, which are key features of PD.

Association of Early and Supernormal Vascular Aging categories with cardiovascular disease in the Chinese population

Background

Early Vascular Aging and Supernormal Vascular Aging are two extreme phenotypes of vascular aging, and people in the two categories demonstrate distinct clinical characteristics and cardiovascular prognosis. However, the clinical implication of vascular aging categories in the Asian or Chinese population has not been investigated. We aimed to investigate the association between vascular aging categories and cardiovascular events in a Chinese cohort.

Methods

We explored the association of vascular aging categories with incident cardiovascular disease in a community cohort in Shanghai, China, which included 10,375 participants following up for 4.5 years. Vascular age was predicted by a multivariable linear regression model including classical risk factors and brachial-ankle pulse wave velocity. Early and Supernormal vascular aging groups were defined by 10% and 90% percentiles of Δ-age, which was calculated as chronological minus vascular age.

Results

We found that cardiovascular risk significantly increased in Early [hazard ratio (HR), 1.597 (95% CI, 1.043–2.445)] and decreased in Supernormal [HR, 0.729 (95% CI, 0.539–0.986)] vascular aging individuals, comparing with normal vascular aging subjects. The associations were independent of the Framingham risk score. Early vascular aging individuals also showed an elevated risk of total mortality [HR, 2.614 (95% CI, 1.302–5.249)]. Further, the associations of vascular aging categories with cardiovascular risk were much stronger in females than in males. Vascular aging categories with different cutoff levels expressed as percentiles (10th, 20th, and 25th) of Δ-age showed similar associations with cardiovascular risk.

Conclusions

In conclusion, the vascular aging categories could identify people with different levels of cardiovascular risk in the Chinese population, particularly in women.

Impact of High-Dose Perindopril on Cardiac Function and Angiotensin Converting Enzyme 2/Ang-(1-9)/Ang-(1-7) in Rabbits with Ischemic Cardiac Dysfunction

Aim: To investigate the impact of high-dose of perindopril on cardiac function and ACE2/AT2R pathway in rabbits with ischemic cardiac dysfunction. Methods: The thirty rabbits with ischemic cardiac dysfunction were divided into high-dose group (Perindopril, 2 mg/kg/d), low-dose group (Perindopril, 0.66 mg/kg/d), and control groups (Saline, 2 ml/kg/d) by a random number table. After four weeks, we measured the cardiac function, The level of Ang-(1-7) and Ang-(1-9), mRNA expression level of ACE2 and AT2R. Results: The results showed that high dose and low dose of perindopril could improve cardiac function (p < 0.001), and high-dose perindopril had more significant improvement (p = 0.041). After treatment, in high-dose group, mRNA level of ACE2, AT2R in myocardium (p < 0.001) and Ang-(1-9) level in serum (p = 0.012) were higher than low-dose group, while Ang-(1-7) levels in serum didn’t show a significant difference (p = 0.829). LVEF and serum Ang-(1-9) were significantly correlated (p = 0.002), LVEF and ACE2 (p = 0.001), LVEF and AT2R (p = 0.007); however, it was no correlation between LVEF and serum Ang-(1-7) (p = 0.067). Conclusion: A high-dose of perindopril could improve ischemic cardiac dysfunction by ACE2/Ang-(1-9)/Ang-(1-7) pathway.

S-nitrosylation of c-Jun N-terminal kinase mediates pressure overload-induced cardiac dysfunction and fibrosis

Cardiac fibrosis (CF) is an irreversible pathological process that occurs in almost all kinds of cardiovascular diseases. Phosphorylation-dependent activation of c-Jun N-terminal kinase (JNK) induces cardiac fibrosis. However, whether S-nitrosylation of JNK mediates cardiac fibrosis remains an open question. A biotin-switch assay confirmed that S-nitrosylation of JNK (SNO-JNK) increased significantly in the heart tissues of hypertrophic patients, transverse aortic constriction (TAC) mice, spontaneously hypertensive rats (SHRs), and neonatal rat cardiac fibroblasts (NRCFs) stimulated with angiotensin II (Ang II). Site to site substitution of alanine for cysteine in JNK was applied to determine the S-nitrosylated site. S-Nitrosylation occurred at both Cys116 and Cys163 and substitution of alanine for cysteine 116 and cysteine 163 (C116/163A) inhibited Ang II-induced myofibroblast transformation. We further confirmed that the source of S-nitrosylation was inducible nitric oxide synthase (iNOS). 1400 W, an inhibitor of iNOS, abrogated the profibrotic effects of Ang II in NRCFs. Mechanistically, SNO-JNK facilitated the nuclear translocation of JNK, increased the phosphorylation of c-Jun, and induced the transcriptional activity of AP-1 as determined by chromatin immunoprecipitation and EMSA. Finally, WT and iNOS^-/- mice were subjected to TAC and iNOS knockout reduced SNO-JNK and alleviated cardiac fibrosis. Our findings demonstrate an alternative mechanism by which iNOS-induced SNO-JNK increases JNK pathway activity and accelerates cardiac fibrosis. Targeting SNO-JNK might be a novel therapeutic strategy against cardiac fibrosis.

Drugs Modulating Renin-Angiotensin System in COVID-19 Treatment

A massive worldwide vaccination campaign constitutes the main tool against the COVID-19 pandemic. However, drug treatments are also necessary. Antivirals are the most frequently considered treatments. However, strategies targeting mechanisms involved in disease aggravation may also be effective. A major role of the tissue renin-angiotensin system (RAS) in the pathophysiology and severity of COVID-19 has been suggested. The main link between RAS and COVID-19 is angiotensin-converting enzyme 2 (ACE2), a central RAS component and the primary binding site for SARS-CoV-2 that facilitates the virus entry into host cells. An initial suggestion that the susceptibility to infection and disease severity may be enhanced by angiotensin type-1 receptor blockers (ARBs) and ACE inhibitors (ACEIs) because they increase ACE2 levels, led to the consideration of discontinuing treatments in thousands of patients. More recent experimental and clinical data indicate that ACEIs and, particularly, ARBs can be beneficial for COVID-19 outcome, both by reducing inflammatory responses and by triggering mechanisms (such as ADAM17 inhibition) counteracting viral entry. Strategies directly activating RAS anti-inflammatory components such as soluble ACE2, Angiotensin 1-7 analogues, and Mas or AT2 receptor agonists may also be beneficial. However, while ACEIs and ARBs are cheap and widely used, the second type of strategies are currently under study.

The intracellular renin-angiotensin system: Friend or foe. Some light from the dopaminergic neurons

The renin-angiotensin system (RAS) is one of the oldest hormone systems in vertebrate phylogeny. RAS was initially related to regulation of blood pressure and sodium and water homeostasis. However, local or paracrine RAS were later identified in many tissues, including brain, and play a major role in their physiology and pathophysiology. In addition, a major component, ACE2, is the entry receptor for SARS-CoV-2. Overactivation of tissue RAS leads several oxidative stress and inflammatory processes involved in aging-related degenerative changes. In addition, a third level of RAS, the intracellular or intracrine RAS (iRAS), with still unclear functions, has been observed. The possible interaction between the intracellular and extracellular RAS, and particularly the possible deleterious or beneficial effects of the iRAS activation are controversial. The dopaminergic system is particularly interesting to investigate the RAS as important functional interactions between dopamine and RAS have been observed in the brain and several peripheral tissues. Our recent observations in mitochondria and nucleus of dopaminergic neurons may clarify the role of the iRAS. This may be important for the developing of new therapeutic strategies, since the effects on both extracellular and intracellular RAS must be taken into account, and perhaps better understanding of COVID-19 cell mechanisms.

Brain Angiotensin Type-1 and Type-2 Receptors in Physiological and Hypertensive Conditions: Focus on Neuroinflammation

PURPOSE OF REVIEW

To review recent data that suggest opposing effects of brain angiotensin type-1 (AT1R) and type-2 (AT2R) receptors on blood pressure (BP). Here, we discuss recent studies that suggest pro-hypertensive and pro-inflammatory actions of AT1R and anti-hypertensive and anti-inflammatory actions of AT2R. Further, we propose mechanisms for the interplay between brain angiotensin receptors and neuroinflammation in hypertension.

RECENT FINDINGS

The renin-angiotensin system (RAS) plays an important role in regulating cardiovascular physiology. This includes brain AT1R and AT2R, both of which are expressed in or adjacent to brain regions that control BP. Activation of AT1R within those brain regions mediate increases in BP and cause neuroinflammation, which augments the BP increase in hypertension. The fact that AT1R and AT2R have opposing actions on BP suggests that AT1R and AT2R may have similar opposing actions on neuroinflammation. However, the mechanisms by which brain AT1R and AT2R mediate neuroinflammatory responses remain unclear. The interplay between brain angiotensin receptor subtypes and neuroinflammation exacerbates or protects against hypertension.

Maternal high-fat diet alters angiotensin II receptors and causes changes in fetal and neonatal rats†

Maternal high-fat diet (HFD) during pregnancy is linked to cardiovascular diseases in postnatal life. The current study tested the hypothesis that maternal HFD causes myocardial changes through angiotensin II receptor (AGTR) expression modulation in fetal and neonatal rat hearts. The control group of pregnant rats was fed a normal diet and the treatment group of pregnant rats was on a HFD (60% kcal fat). Hearts were isolated from embryonic day 21 fetuses (E21) and postnatal day 7 pups (PD7). Maternal HFD decreased the body weight of the offspring in both E21 and PD7. The ratio of heart weight to body weight was increased in E21, but not PD7, when compared to the control group. Transmission electron microscopy revealed disorganized myofibrils and effacement of mitochondria cristae in the treatment group. Maternal HFD decreased S-phase and increased G1-phase of the cellular cycle for fetal and neonatal cardiac cells. Molecular markers of cardiac hypertrophy, such as Nppa and Myh7, were found to be increased in the treatment group. There was an associated increase in Agtr2 mRNA and protein, whereas Agtr1a mRNA and AGTR1 protein were decreased in HFD fetal and neonatal hearts. Furthermore, maternal HFD decreased glucocorticoid receptors (GRs) binding to glucocorticoid response elements at the Agtr1a and Agtr2 promoter, which correlated with downregulation of GR in fetal and neonatal hearts. These findings suggest that maternal HFD may promote premature termination of fetal and neonatal cardiomyocyte proliferation and compensatory hypertrophy through intrauterine modulation of AGTR1 and AGTR2 expression via GR dependent mechanism.

Sex differences in mechanisms of arterial stiffness

Arterial stiffness progressively increases with aging and is an independent predictor of cardiovascular disease (CVD) risk. Evidence supports that there are sex differences in the time course of aging-related arterial stiffness and the associated CVD risk, which increases disproportionately in postmenopausal women. The association between arterial stiffness and mortality is almost twofold higher in women versus men. The differential clinical characteristics of the development of arterial stiffness between men and women indicate the involvement of sex-specific mechanisms. This review summarizes the current literature on sex differences in vascular stiffness induced by aging, obesity, hypertension, and sex-specific risk factors as well as the impact of hormonal status, diet, and exercise on vascular stiffness in males and females. An understanding of the mechanisms driving sex differences in vascular stiffness has the potential to identify novel sex-specific therapies to lessen CVD risk, the leading cause of death in males and females. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Activation of angiotensin type 2 (AT2) receptors prevents myocardial hypertrophy in Zucker diabetic fatty rats

AIMS

Compound 21 (C21), selective AT2 receptor agonist, has cardioprotective effects in experimental models of hypertension and myocardial infarction. The aims of the study was to evaluate the effect of C21, losartan, or both in Zucker diabetic fatty (ZDF) rats (type 2 diabetes) on (1) the prevention of myocardial hypertrophy; (2) myocardial expression of phosphatase and tensin homolog (PTEN), a target gene of miR-30a-3p, involved in myocardial remodelling.

METHODS

Experiments were performed in ZDF (n = 33) and in control Lean (8) rats. From the 6th to the 20th week of age, we administered C21 (0.3 mg/kg/day) to 8 ZDF rats. 8 ZDF rats were treated with losartan (10 mg/kg/day), 8 rats underwent combination treatment, C21+ losartan, and 9 ZDF rats were left untreated. Blood glucose and blood pressure were measured every 4 weeks. At the end of the study the hearts were removed, the apex was cut for the quantification of PTEN mRNA and miR-30a-3p expression (realtime-PCR). Myocardial hypertrophy was evaluated by histomorphometric analysis, and nitrotyrosine expression (as marker of oxidative stress) by immunohistochemistry.

RESULTS

ZDF rats had higher blood glucose (p < 0.0001) with respect to control Lean rats, while blood pressure did not change. Both parameters were not modified by C21 treatment, while losartan and losartan + C21 reduced blood pressure in ZDF rats (p < 0.05). miR-30a-3p expression was increased in ZDF rats (p < 0.01) and PTEN mRNA expression was decreased (p < 0.05). ZDF rats developed myocardial hypertrophy (p < 0.01) and increased oxidative stress (p < 0.01), both were prevented by C21 or losartan, or combination treatment. C21 or losartan normalized the expression of miR-30a-3p and PTEN.

CONCLUSIONS

Activation of AT2 receptors or AT1 receptor blockade prevents the development of myocardial hypertrophy in ZDF rats. This occurs through the modulation of the miR-30a-3p/PTEN interaction.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Bidirectional Neural Interaction Between Central Dopaminergic and Gut Lesions in Parkinson's Disease Models

The exact mechanism of gut dysfunction in Parkinson's disease and, conversely, the role of gut pathology in brain dopaminergic degeneration are controversial. We investigated the effects of nigral lesions on the colonic neurotransmission, the effect of gut inflammation on the nigrostriatal dopaminergic function, and the possible involvement of the vagus nerve and the local renin-angiotensin system (RAS). Nigrostriatal dopamine depletion was performed by bilateral injection 6-hydroxydopamine, and gut inflammation was induced by dextran sulfate sodium salt treatment in rats and mice, respectively, with or without vagal disruption. A decrease in central dopamine levels induced a decrease in colonic dopamine types 1 and 2 receptor expression together with an increase in the colonic levels of dopamine and a decrease in the levels of acetylcholine, which may explain a decrease in gut motility. Central dopaminergic depletion also induced an increase in the colonic levels of inflammatory and oxidative stress markers together with activation of the pro-inflammatory arm of the local RAS. Mice with acute (1 week) or subchronic (3 weeks) gut inflammation did not show a significant increase in colonic α-synuclein and phosphorylated α-synuclein expression during this relatively short survival period. Interestingly, we observed early changes in the nigrostriatal dopaminergic homeostasis, dopaminergic neuron death, and increased levels of nigral pro-inflammatory markers and RAS pro-inflammatory activity. The present results show that a dysregulation of the neural bidirectional gut-brain interaction may explain the early gut disturbances observed in parkinsonian patients, and also the increase in vulnerability of nigral dopaminergic neurons after gut inflammation.

Protective Angiotensin Type 2 Receptors in the Brain and Hypertension

PURPOSE OF REVIEW

The goal of this review is to assess the evidence that activation of angiotensin type 2 receptors (AT2R) in the brain can lower blood pressure and possibly constitute an endogenous anti-hypertensive mechanism.

RECENT FINDINGS

Recent studies that detail the location of AT2R in the brain, particularly within or near cardiovascular control centers, mesh well with findings from pharmacological and gene transfer studies which demonstrate that activation of central AT2R can influence cardiovascular regulation. Collectively, these studies indicate that selective activation of brain AT2R causes moderate decreases in blood pressure in normal animals and more profound anti-hypertensive effects, along with restoration of baroreflex function, in rodent models of neurogenic hypertension. These findings have opened the door to studies that can (i) assess the role of specific AT2R neuron populations in depressing blood pressure, (ii) determine the relevance of such mechanisms, and (iii) investigate interactions between AT2R and depressor angiotensin-(1-7)/Mas mechanisms in the brain.

Crosstalk between insulin-like growth factor-1 and angiotensin-II in dopaminergic neurons and glial cells: role in neuroinflammation and aging

The local renin-angiotensin system (RAS) and insulin-like growth factor 1 (IGF-1) have been involved in longevity, neurodegeneration and aging-related dopaminergic degeneration. However, it is not known whether IGF-1 and angiotensin-II (AII) activate each other. In the present study, AII, via type 1 (AT1) receptors, exacerbated neuroinflammation and dopaminergic cell death. AII, via AT1 receptors, also increased the levels of IGF-1 and IGF-1 receptors in microglial cells. IGF-1 inhibited RAS activity in dopaminergic neurons and glial cells, and also inhibited the AII-induced increase in markers of the M1 microglial phenotype. Consistent with this, IGF-1 decreased dopaminergic neuron death induced by the neurotoxin MPP⁺ both in the presence and in the absence of glia. Intraventricular administration of AII to young rats induced a significant increase in IGF-1 expression in the nigral region. However, aged rats showed decreased levels of IGF-1 relative to young controls, even though RAS activity is known to be enhanced in aged animals. The study findings show that IGF-1 and the local RAS interact to inhibit or activate neuroinflammation (i.e. transition from the M1 to the M2 phenotype), oxidative stress and dopaminergic degeneration. The findings also show that this mechanism is impaired in aged animals.

Hypertension regulating angiotensin peptides in the pathobiology of cardiovascular disease

Renin angiotensin system (RAS) is an endogenous hormone system involved in the control of blood pressure and fluid volume. Dysregulation of RAS has a pathological role in causing cardiovascular diseases through hypertension. Among several key components of RAS, angiotensin peptides, varying in amino acid length and biological function, have important roles in preventing or promoting hypertension, cardiovascular diseases, stroke, vascular remodeling etc. These peptides are generated by the metabolism of inactive angiotensinogen or its derived peptides by hydrolyzing action of certain enzymes. Angiotensin II, angiotensin (1-12), angiotensin A and angiotensin III bind primarily to angiotensin II type 1 receptor and cause vasoconstriction, accumulation of inflammatory markers to sub-endothelial region of blood vessels and activate smooth muscle cell proliferation. Moreover, when bound to angiotensin II type 2 receptor, angiotensin II works as cardio-protective peptide and halt pathological cell signals. Other peptides like angiotensin (1-9), angiotensin (1-7), alamandine and angiotensin IV also help in protecting from cardiovascular diseases by binding to their respective receptors.

A convenient transesterification method for synthesis of AT2 receptor ligands with improved stability in human liver microsomes

A series of AT₂R ligands have been synthesized applying a quick, simple, and safe transesterification-type reaction whereby the sulfonyl carbamate alkyl tail of the selective AT₂R antagonist C38 was varied. Furthermore, a limited number of compounds where acyl sulfonamides and sulfonyl ureas served as carboxylic acid bioisosteres were synthesized and evaluated. By reducing the size of the alkyl chain of the sulfonyl carbamates, ligands 7a and 7b were identified with significantly improved in vitro metabolic stability in both human and mouse liver microsomes as compared to C38 while retaining the AT₂R binding affinity and AT₂R/AT₁R selectivity. Eight of the compounds synthesized exhibit an improved stability in human microsomes as compared to C38.

Insulin-Like Growth Factor-1 and Neuroinflammation

Insulin-like growth factor-1 (IGF-1) effects on aging and neurodegeneration is still controversial. However, it is widely admitted that IGF-1 is involved in the neuroinflammatory response. In peripheral tissues, several studies showed that IGF-1 inhibited the expression of inflammatory markers, although other studies concluded that IGF-1 has proinflammatory functions. Furthermore, proinflammatory cytokines such as TNF-α impaired IGF-1 signaling. In the brain, there are controversial results on effects of IGF-1 in neuroinflammation. In addition to direct protective effects on neurons, several studies revealed anti-inflammatory effects of IGF-1 acting on astrocytes and microglia, and that IGF-1 may also inhibit blood brain barrier permeability. Altogether suggests that the aging-related decrease in IGF-1 levels may contribute to the aging-related pro-inflammatory state. IGF-1 inhibits the astrocytic response to inflammatory stimuli, and modulates microglial phenotype (IGF-1 promotes the microglial M2 and inhibits of M1 phenotype). Furthermore, IGF-1 is mitogenic for microglia. IGF-1 and estrogen interact to modulate the neuroinflammatory response and microglial and astrocytic phenotypes. Brain renin-angiotensin and IGF-1 systems also interact to modulate neuroinflammation. Induction of microglial IGF-1 by angiotensin, and possibly by other pro-inflammatory inducers, plays a major role in the repression of the M1 microglial neurotoxic phenotype and the enhancement of the transition to an M2 microglial repair/regenerative phenotype. This mechanism is impaired in aged brains. Aging-related decrease in IGF-1 may contribute to the loss of capacity of microglia to undergo M2 activation. Fine tuning of IGF-1 levels may be critical for regulating the neuroinflammatory response, and IGF-1 may be involved in inflammation in a context-dependent mode.

AT2 receptor agonist Compound 21: A silver lining for diabetic nephropathy

The currently available therapies for diabetic nephropathy, one of the leading causes of renal failure globally are based on inhibition of renin angiotensin system. However, recently, the focus has shifted towards activation of its protective arm rather than the inhibition of deteriorative axis, using specific agonists. Compound 21 (C21), a novel non-peptide Angiotensin II type 2 receptor (AT₂) agonist, recently granted orphan drug status for the treatment of a rare disease, idiopathic pulmonary fibrosis has also shown a potent anti-inflammatory, anti-fibrotic, antioxidant and anti-apoptotic potential in various diseases including heart failure, myocardial infarction, chronic inflammatory diseases, and neurological diseases such as ischemic stroke. A pool of evidences suggest that C21, either alone or in combination with angiotensin receptor blockers could be extremely beneficial in the treatment of diabetic nephropathy, a chronic inflammatory condition sharing its pathogenesis with aforementioned diseases. The review analyses the new therapeutic tool, C21, its mechanisms of action for renoprotection in diabetic nephropathy, and its future perspectives and thereby provides an insight into the potential application of C21 as a novel therapeutic tool in the eradication of diabetic nephropathy.

Anti-fibrotic Potential of AT2 Receptor Agonists

There are a number of therapeutic targets to treat organ fibrosis that are under investigation in preclinical models. There is increasing evidence that stimulation of the angiotensin II type 2 receptor (AT₂R) is a novel anti-fibrotic strategy and we have reviewed the published in vivo preclinical data relating to the effects of compound 21 (C21), which is the only nonpeptide AT₂R agonist that is currently available for use in chronic preclinical studies. In particular, the differential influence of AT₂R on extracellular matrix status in various preclinical fibrotic models is discussed. Collectively, these studies demonstrate that pharmacological AT₂R stimulation using C21 decreases organ fibrosis, which has been most studied in the setting of cardiovascular and renal disease. In addition, AT₂R-mediated anti-inflammatory effects may contribute to the beneficial AT₂R-mediated anti-fibrotic effects seen in preclinical models.

Angiotensin II type 2 receptor (AT2R) in renal and cardiovascular disease

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin-angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water-electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

Dopamine modulates astroglial and microglial activity via glial renin-angiotensin system in cultures

Dopamine is an immunomodulatory molecule that acts on immune effector cells both in the CNS and peripheral tissues. However, the role of changes in dopamine levels in the neuroinflammatory response is controversial. The local/paracrine renin-angiotensin system (RAS) plays a major role in inflammatory processes in peripheral tissues and brain. In the present study, we investigated the possible role of the brain RAS in the effects of dopamine on the glial inflammatory responses. Astrocytes are the major source of the precursor protein angiotensinogen and angiotensin II (AII) in the brain. Neurotoxins such as MPP⁺ (1-methyl-4-phenylpyridinium) can act directly on astrocytes to increase levels of angiotensinogen and AII. Conversely, dopamine, via type-2 (D2) receptors, inhibited production of angiotensinogen, decreased expression of angiotensin type-1 (AT1) receptors and increased expression of AT2 receptors. In microglia, dopamine and dopamine agonists also regulated RAS activity. First, indirectly, via downregulation of the astrocyte-derived AII. Second, via dopamine-induced regulation of microglial angiotensin receptors. Dopamine decreased the microglial AT1/AT2 ratio leading to inhibition of the pro-inflammatory AT1/NADPH-oxidase/superoxide axis. D2 receptors were particularly responsible for microglial RAS inhibition in basal culture conditions. However, both D1 and D2 agonists inhibited the AT1/NADPH-oxidase axis in lipopolysaccharide-treated (LPS; i.e. activated) microglia. The results indicate that the decrease in dopamine levels observed in early stages of Parkinson's disease and aging may promote neuroinflammation and disease progression via glial RAS exacerbation.

Epochs in the depressor/pressor balance of the renin-angiotensin system

The renin-angiotensin system (RAS) plays a commanding role in the regulation of extracellular fluid homoeostasis. Tigerstadt and Bergman first identified the RAS more than two centuries ago. By the 1980s a voyage of research and discovery into the mechanisms and actions of this system led to the development of drugs that block the RAS, which have become the mainstay for the treatment of cardiovascular and renal disease. In the last 25 years new components of the RAS have come to light, including the angiotensin type 2 receptor (AT2R) and the angiotensin-converting enzyme 2 (ACE2)/angiotensin-(1-7) [Ang(1-7)]/Mas receptor (MasR) axis. These have been shown to counter the classical actions of angiotensin II (AngII) at the predominant angiotensin type 1 receptor (AT1R). Our studies, and those of others, have demonstrated that targeting these depressor RAS pathways may be therapeutically beneficial. It is apparent that the evolution of both the pressor and depressor RAS pathways is distinct throughout life and that the depressor/pressor balance of the RAS vary between the sexes. These temporal patterns of expression suggest that therapies targeting the RAS could be optimized for discrete epochs in life.

Novel approaches for treating hypertension

Hypertension, or high blood pressure, is a prevalent yet modifiable risk factor for cardiovascular disease. While there are many effective treatments available to combat hypertension, patients often require at least two to three medications to control blood pressure, although there are patients who are resistant to such therapies. This short review will briefly update on recent clinical advances and potential emerging therapies and is intended for a cross-disciplinary readership.

Angiotensin type-2 (AT-2)-receptor activation reduces renal fibrosis in cyclosporine nephropathy: evidence for blood pressure independent effect

Compound 21 (C21), selective agonist of angiotensin type-2 (AT-2) receptors, shows anti-inflammatory effects in experimental models of hypertension and nephroprotection in diabetes. The aim of the present study was to evaluate the effects of C21 in cyclosporine nephropathy, which is characterized mainly by tubulo-interstitial fibrosis. Ten days before and during the experimental periods, low-salt diet was administered to Sprague–Dawley rats. Cyclosporine-A (CsA; 15 mg/kg per day, intraperitoneal injection) and CsA plus C21 (0.3 mg/kg per day, intraperitoneal injection) were administered for 1 and 4 weeks. Control groups were left without any treatment. Blood pressure (plethysmographic method) and 24 h urinary albumin excretion were measured once a week. At the end of the experimental protocols, the kidneys were excised for histomorphometric analysis of renal fibrosis and for immunohistochemical evaluation of inflammatory infiltrates and type I and type IV collagen expression. After 1 and 4 weeks, the rats treated with CsA showed a significant increase (P<0.01) in blood pressure, no significant changes in urinary albumin excretion and a significant increase (P<0.01) in glomerular and tubulo-interstitial fibrosis and inflammatory infiltrates as compared with the control rats. Treatment with C21 did not modify the CsA dependent increase of blood pressure, which was higher than in control rats, but after 4 weeks of treatment significantly reduced (P<0.01) glomerular and tubulo-interstitial fibrosis, type 1 collagen expression and macrophage infiltration, as compared with rats treated with cyclosporine. The administration of C21 showed a protective effect on cyclosporine nephropathy, decreasing renal fibrosis and macrophage infiltration. These data suggest that C21 may counteract tubulo-interstitial fibrosis, the most potent predictor of the progression of renal diseases.

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.

Central Infusion of Angiotensin II Type 2 Receptor Agonist Compound 21 Attenuates DOCA/NaCl-Induced Hypertension in Female Rats

The present study investigated whether central activation of angiotensin II type 2 receptor (AT2-R) attenuates deoxycorticosterone acetate (DOCA)/NaCl-induced hypertension in intact and ovariectomized (OVX) female rats and whether female sex hormone status has influence on the effects of AT2-R activation. DOCA/NaCl elicited a greater increase in blood pressure in OVX females than that in intact females. Central infusion of compound 21, a specific AT2-R agonist, abolished DOCA/NaCl pressor effect in intact females, whereas same treatment in OVX females produced an inhibitory effect. Real-time RT-PCR analysis revealed that DOCA/NaCl enhanced the mRNA expression of hypertensive components including AT1-R, ACE-1, and TNF-α in the paraventricular nucleus of hypothalamus in both intact and OVX females. However, the mRNA expressions of antihypertensive components such as AT2-R, ACE-2, and IL-10 were increased only in intact females. Central AT2-R agonist reversed the changes in the hypertensive components in all females, while this agonist further upregulated the expression of ACE2 and IL-10 in intact females, but only IL-10 in OVX females. These results indicate that brain AT2-R activation plays an inhibitory role in the development of DOCA/NaCl-induced hypertension in females. This beneficial effect of AT2-R activation involves regulation of renin-angiotensin system and proinflammatory cytokines.

High-Dose Estradiol-Replacement Therapy Enhances the Renal Vascular Response to Angiotensin II via an AT2-Receptor Dependent Mechanism

Physiological levels of estrogen appear to enhance angiotensin type 2 receptor- (AT₂R-) mediated vasodilatation. However, the effects of supraphysiological levels of estrogen, analogous to those achieved with high-dose estrogen replacement therapy in postmenopausal women, remain unknown. Therefore, we pretreated ovariectomized rats with a relatively high dose of estrogen (0.5 mg/kg/week) for two weeks. Subsequently, renal hemodynamic responses to intravenous angiotensin II (Ang II, 30–300 ng/kg/min) were tested under anesthesia, while renal perfusion pressure was held constant. The role of AT₂R was examined by pretreating groups of rats with PD123319 or its vehicle. Renal blood flow (RBF) decreased in a dose-related manner in response to Ang II. Responses to Ang II were enhanced by pretreatment with estradiol. For example, at 300 ng kg⁻¹ min⁻¹, Ang II reduced RBF by 45.7 ± 1.9% in estradiol-treated rats but only by 27.3 ± 5.1% in vehicle-treated rats. Pretreatment with PD123319 blunted the response of RBF to Ang II in estradiol-treated rats, so that reductions in RBF were similar to those in rats not treated with estradiol. We conclude that supraphysiological levels of estrogen promote AT₂R-mediated renal vasoconstriction. This mechanism could potentially contribute to the increased risk of cardiovascular disease associated with hormone replacement therapy using high-dose estrogen.

Reciprocal regulation between sirtuin-1 and angiotensin-II in the substantia nigra: implications for aging and neurodegeneration

Local angiotensin II (AII) and sirtuin 1 (SIRT1) play a major role in the modulation of neuroinflammation, oxidative stress and aging-related dopaminergic vulnerability to damage. However, it is not known whether the modulation is related to reciprocal regulation between SIRT1 and AII. In the present study, a single intraventricular injection of AII increased nigral SIRT1 levels in young adult rats. Although AII activity is known to be increased in aged rats, levels of SIRT1 were significantly lower than in young controls. Treatment with the SIRT1-activating compound resveratrol increased nigral SIRT1 levels in aged rats. Levels of SIRT1 were significantly higher in aged wild type mice than in AII type-1 receptor (AT1) deficient mice. In cell culture studies, treatment with AII also induced a transitory increase in levels of SIRT1 in the MES 23.5 dopaminergic neuron and the N9 microglial cell lines. In aged rats, treatment with resveratrol induced a significant decrease in the expression of AT1 receptors and markers of NADPH-oxidase activation (p47phox). In aged transgenic mice over-expressing SIRT1, levels of AT1 and p47 phox were lower than in aged wild type controls. In vitro, the inhibitory effects of resveratrol on AII/AT1/NADPH-oxidase activity were confirmed in primary mesencephalic cultures, the N9 microglial cell line, and the dopaminergic neuron cell line MES 23.5, and they were blocked by the SIRT1 specific inhibitor EX527. The present findings show that SIRT1 and the axis AII/AT1/NADPH-oxidase regulate each other. This is impaired in aged animals and may be mitigated with sirtuin-activating compounds.

Summertime dosage-dependent hypersensitivity to an angiotensin II receptor blocker

Background

Summertime dips in blood pressure (BP), both in normotensive and hypertensive subjects, are well known. However, the dips are small and are not related to particular forms or doses of antihypertensive medication. Nevertheless it is the practice in some quarters to decrease antihypertensive medication in summer, and/or to increase in winter. Large scale studies being inconclusive, there are calls for long-term examination of the relationship between environmental temperature and blood pressure in single individuals under medication.

Case presentation

While analyzing data from a subject whose BP had been controlled for a decade with the angiotensin-II receptor blocker losartan, an extreme, dosage-dependent, summertime dip came to light. Downward dosage adjustment appeared essential and may have prevented hypotension-related pathology.

Conclusion

The benefits of aggressive medication (the “J curve” phenomenon) being debated, the possibility of seasonal hypersensitivity, perhaps explicable in terms of differential signaling by countervailing receptors, should be taken into account when considering dosage adjustments in hypertensive subjects.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Brain endogenous angiotensin II receptor type 2 (AT2-R) protects against DOCA/salt-induced hypertension in female rats

Background

Recent studies demonstrate that there are sex differences in the expression of angiotensin receptor type 2 (AT2-R) in the kidney and that AT2-R plays an enhanced role in regulating blood pressure (BP) in females. Also, brain AT2-R activation has been reported to negatively modulate BP and sympathetic outflow. The present study investigated whether the central blockade of endogenous AT2-R augments deoxycorticosterone acetate (DOCA)/salt-induced hypertension in both male and female rats.

Methods

All rats were subcutaneously infused with DOCA combined with 1% NaCl solution as the sole drinking fluid. BP and heart rate (HR) were recorded by telemetric transmitters. To determine the effect of central AT2-R on DOCA/salt-induced hypertension, male and female rats were intracerebroventricularly (icv) infused with AT2-R antagonist, PD123,319, during DOCA/salt treatment. Subsequently, the paraventricular nucleus (PVN) of the hypothalamus, a key cardiovascular regulatory region of the brain, was analyzed by quantitative real-time PCR and Western blot.

Results

DOCA/salt treatment elicited a greater increase in BP in male rats than that in females. Icv infusions of the AT2-R antagonist significantly augmented DOCA/salt pressor effects in females. However, this same treatment had no enhanced effect on DOCA/salt-induced increase in the BP in males. Real-time PCR and Western blot analysis of the female brain revealed that DOCA/salt treatment enhanced the mRNA and protein expression for both antihypertensive components including AT2-R, angiotensin-converting enzyme (ACE)-2, and interleukin (IL)-10 and hypertensive components including angiotensin receptor type 1 (AT1-R), ACE-1, tumor necrosis factor (TNF)-α, and IL-1β, but decreased mRNA expression of renin in the PVN. The central blockade of AT2-R reversed the changes in mRNA and protein expressions of ACE-2, IL-10, and renin, further increased the expressions of TNF-α and IL-1β, and kept higher the expressions of AT1-R, ACE-1, and AT2-R.

Conclusions

These results indicate that endogenous AT2-R activation in the brain plays an important protective role in the development of DOCA/salt-induced hypertension in females, but not in males. The protective effect of AT2-R in females involves regulating the expression of brain renin-angiotensin system components and proinflammatory cytokines.

G-protein coupled receptors of the renin-angiotensin system: new targets against breast cancer?

G-protein coupled receptors (GPCRs) constitute the largest family of membrane receptors, with high potential for drug discovery. These receptors can be activated by a panel of different ligands including ions, hormones, small molecules, and vasoactive peptides. Among those, angiotensins [angiotensin II (AngII) and angiotensin 1–7] are the major biologically active products of the classical and alternative renin-angiotensin system (RAS). These peptides bind and activate three different subtypes of GPCRs, namely AT1, AT2, and Mas receptors, to regulate cardiovascular functions. Over the past decade, the contribution of several RAS components in tumorigenesis has emerged as a novel important concept, AngII being considered as harmful and Ang1–7 as protective against cancer. Development of selective ligands targeting each RAS receptor may provide novel and efficient targeted therapeutic strategies against cancer. In this review, we focus on breast cancer to summarize current knowledge on angiotensin receptors (AT1, AT2, and Mas), and discuss the potential use of angiotensin receptor agonists and antagonists in clinics.

Interconversion of Functional Activity by Minor Structural Alterations in Nonpeptide AT2 Receptor Ligands

Migration of the methylene imidazole side chain in the first reported selective drug-like AT2 receptor agonist C21/M024 (1) delivered the AT2 receptor antagonist C38/M132 (2). We now report that the AT2 receptor antagonist compound 4, a biphenyl derivative that is structurally related to 2, is transformed to the agonist 6 by migration of the isobutyl group. The importance of the relative position of the methylene imidazole and the isobutyl substituent is highlighted herein.

Prevention of diabetic nephropathy by compound 21, selective agonist of angiotensin type 2 receptors, in Zucker diabetic fatty rats

The aim of this study was to evaluate the effect of compound 21 (C21), a selective AT2 receptor agonist, on diabetic nephropathy and the potential additive effect of C21, when associated with losartan treatment, on the development of albuminuria and renal fibrosis in Zucker diabetic fatty (ZDF) rats. The experiments lasted 15 wk (from 5 to 20 wk of age) and were performed in 40 ZDF rats and 12 control lean rats. ZDF rats were divided into 4 groups: 1) 9 rats were treated with losartan; 2) 10 rats were treated with C21; 3) 9 rats were treated with losartan plus C21; and 4) 12 rats were maintained without any treatment. ZDF rats showed an increase in blood glucose level, albuminuria, renal fibrosis, macrophage infiltration, and TNF-α expression and a reduction of glomerular nephrin expression compared with control lean rats. C21 treatment reduced renal glomerular, tubulointerstitial, and perivascular fibrosis, and macrophage infiltration and TNF-α expression in ZDF rats. C21 treatment caused a decrease in albuminuria in ZDF rats up to 11 wk of age. Losartan decreased macrophage infiltration, TNF-α expression, and renal glomerular and perivascular fibrosis, restored glomerular nephrin expression, but did not affect tubulointerstitial fibrosis. Losartan treatment caused a decrease in albuminuria in ZDF rats up to 15 wk of age. At the end of the protocol, only the combination of C21 plus losartan significantly reduced albuminuria in ZDF rats. These data demonstrate that C21 has beneficial effects on diabetic nephropathy, suggesting the combination of C21 and losartan as a novel pharmacological tool to slow the progression of nephropathy in type II diabetes.

Angiotensin II type 2 receptor stimulation improves fatty acid ovarian uptake and hyperandrogenemia in an obese rat model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is mainly defined by hyperandrogenism but is also characterized by insulin resistance (IR). Studies showed that overexposure of nonadipose tissues to nonesterified fatty acids (NEFA) may explain both IR and hyperandrogenism. Recent studies indicate that treatment with an angiotensin II type 2 receptor (AT2R)-selective agonist improves diet-induced IR. We thus hypothesized that PCOS hyperandrogenism is triggered by ovarian NEFA overexposure and is improved after treatment with an AT2R agonist. Experiments were conducted in 12-week-old female JCR:LA-cp/cp rats, which are characterized by visceral obesity, IR, hyperandrogenism, and polycystic ovaries. Control JCR:LA +/? rats have a normal phenotype. Rats were treated for 8 days with saline or the selective AT2R agonist C21/M24 and then assessed for: 1) fasting testosterone, NEFA, and insulin levels; and 2) an iv 14(R,S)-[(18)F]fluoro-6-thia-heptadecanoic acid test to determine NEFA ovarian tissue uptake (Km). Compared with controls, saline-treated PCOS/cp rats displayed higher insulin (100 vs 5.6 μU/mL), testosterone (0.12 vs 0.04 nmol/L), NEFA (0.98 vs 0.48 mmol/L), and Km (20.7 vs 12.9 nmol/g·min) (all P < .0001). In PCOS/cp rats, C21/M24 did not significantly improve insulin or NEFA but normalized testosterone (P = .004) and Km (P = .009), which were strongly correlated together in all PCOS/cp rats (ρ = 0.74, P = .009). In conclusion, in an obese PCOS rat model, ovarian NEFA uptake and testosterone levels are strongly associated and are both significantly reduced after short-term C21/M24 therapy. These findings provide new information on the role of NEFA in PCOS hyperandrogenemia and suggest a potential role for AT2R agonists in the treatment of PCOS.

From gene to protein-experimental and clinical studies of ACE2 in blood pressure control and arterial hypertension

Hypertension is a major risk factor for stroke, coronary events, heart and renal failure, and the renin-angiotensin system (RAS) plays a major role in its pathogenesis. Within the RAS, angiotensin converting enzyme (ACE) converts angiotensin (Ang) I into the vasoconstrictor Ang II. An “alternate” arm of the RAS now exists in which ACE2 counterbalances the effects of the classic RAS through degradation of Ang II, and generation of the vasodilator Ang 1-7. ACE2 is highly expressed in the heart, blood vessels, and kidney. The catalytically active ectodomain of ACE2 undergoes shedding, resulting in ACE2 in the circulation. The ACE2 gene maps to a quantitative trait locus on the X chromosome in three strains of genetically hypertensive rats, suggesting that ACE2 may be a candidate gene for hypertension. It is hypothesized that disruption of tissue ACE/ACE2 balance results in changes in blood pressure, with increased ACE2 expression protecting against increased blood pressure, and ACE2 deficiency contributing to hypertension. Experimental hypertension studies have measured ACE2 in either the heart or kidney and/or plasma, and have reported that deletion or inhibition of ACE2 leads to hypertension, whilst enhancing ACE2 protects against the development of hypertension, hence increasing ACE2 may be a therapeutic option for the management of high blood pressure in man. There have been relatively few studies of ACE2, either at the gene or the circulating level in patients with hypertension. Plasma ACE2 activity is low in healthy subjects, but elevated in patients with cardiovascular risk factors or cardiovascular disease. Genetic studies have investigated ACE2 gene polymorphisms with either hypertension or blood pressure, and have produced largely inconsistent findings. This review discusses the evidence regarding ACE2 in experimental hypertension models and the association between circulating ACE2 activity and ACE2 polymorphisms with blood pressure and arterial hypertension in man.

Differences in the clinical effects of angiotensin-converting enzyme inhibitors and Angiotensin receptor blockers: a critical review of the evidence

The renin-angiotensin-aldosterone system plays a major role in the pathophysiology of hypertension and closely related cardio- and cerebrovascular events. Although both angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor antagonists (angiotensin receptor blockers; ARBs) are equally important in the treatment of hypertension, according to the results of recent years, there might be substantial differences in their cardiovascular protective effects, and these differences might be explained by our increasing knowledge of their non-overlapping mechanisms of action. The number of studies investigating how ACE inhibitors and ARB agents differ will certainly be increasing in the future. ACE inhibitors are the safe therapeutic opportunity for hypertensive patients at high risk, with a cardiological comorbidity.

N-Aryl Isoleucine Derivatives as Angiotensin II AT2 Receptor Ligands

A novel series of ligands for the recombinant human AT2 receptor has been synthesized utilizing a fast and efficient palladium-catalyzed procedure for aminocarbonylation as the key reaction. Molybdenum hexacarbonyl [Mo(CO)6] was employed as the carbon monoxide source, and controlled microwave heating was applied. The prepared N-aryl isoleucine derivatives, encompassing a variety of amide groups attached to the aromatic system, exhibit binding affinities at best with K i values in the low micromolar range versus the recombinant human AT2 receptor. Some of the new nonpeptidic isoleucine derivatives may serve as starting points for further structural optimization. The presented data emphasize the importance of using human receptors in drug discovery programs.

Aging-related dysregulation of dopamine and angiotensin receptor interaction

It is not known whether the aging-related decrease in dopaminergic function leads to the aging-related higher vulnerability of dopaminergic neurons and risk for Parkinson's disease. The renin-angiotensin system (RAS) plays a major role in the inflammatory response, neuronal oxidative stress, and dopaminergic vulnerability via type 1 (AT1) receptors. In the present study, we observed a counterregulatory interaction between dopamine and angiotensin receptors. We observed overexpression of AT1 receptors in the striatum and substantia nigra of young adult dopamine D1 and D2 receptor-deficient mice and young dopamine-depleted rats, together with compensatory overexpression of AT2 receptors or compensatory downregulation of angiotensinogen and/or angiotensin. In aged rats, we observed downregulation of dopamine and dopamine receptors and overexpression of AT1 receptors in aged rats, without compensatory changes observed in young animals. L-Dopa therapy inhibited RAS overactivity in young dopamine-depleted rats, but was ineffective in aged rats. The results suggest that dopamine may play an important role in modulating oxidative stress and inflammation in the substantia nigra and striatum via the RAS, which is impaired by aging.

Synthesis and evaluation of isoleucine derived angiotensin II AT(2) receptor ligands

Sixteen new C-terminally modified analogues of 2, a previously described potent and selective AT2R ligand, were designed, synthesized and evaluated for their affinity to the AT2R receptor. The introduction of large, hydrophobic substituents was shown to be beneficial and the most active compound (17, Ki=8.5 μM) was over 12-times more potent than the lead compound 2.

The effects of angiotensin II signaling pathway in the systolic response to acute stretch in the normal and ischemic myocardium

Acute myocardial stretch elicits a biphasic increase in contractility: an immediate increase, known as Frank-Starling mechanism (FSM), followed by a progressive increase, regarded as slow force response (SFR). In this study, we characterized the contractile response to acute stretch from 92 to 100% Lmax in rabbit papillary muscles (n=86) under normoxic and ischemic conditions, and its modulation by angiotensin II signaling pathway. Under normoxia, the FSM was independent of Na(+)/H(+)-exchanger, reverse mode of Na(+)/Ca(2+)-exchanger (r-NCX), AT1 receptor, AT2 receptor and PKC. Regarding the SFR, it was mediated by AT1 receptor activation and its downstream effectors PKC, Na(+)/H(+)-exchanger and r-NCX. Ischemia negatively impacted on the FSM and abolished the SFR, with the muscles exhibiting a time-dependent decline in contractility. Under ischemic conditions, FSM was not influenced by AT1 and AT2 receptors or PKC activation. AT1 receptor antagonism rescued the progressive deterioration in contractility, an effect partially dependent on AT2 receptor activation.