Binding Of Angiotensin Research Articles

Untangling the Uncertain Role of Overactivation of the Renin-Angiotensin-Aldosterone System with the Aging Process Based on Sodium Wasting Human Models.

Every individual at some point encounters the progressive biological process of aging, which is considered one of the major risk factors for common diseases. The main drivers of aging are oxidative stress, senescence, and reactive oxygen species (ROS). The renin-angiotensin-aldosterone system (RAAS) includes several systematic processes for the regulation of blood pressure, which is caused by an imbalance of electrolytes. During activation of the RAAS, binding of angiotensin II (ANG II) to angiotensin II type 1 receptor (AGTR1) activates intracellular nicotinamide adenine dinucleotide phosphate (NADPH) oxidase to generate superoxide anions and promote uncoupling of endothelial nitric oxide (NO) synthase, which in turn decreases NO availability and increases ROS production. Promoting oxidative stress and DNA damage mediated by ANG II is tightly regulated. Individuals with sodium deficiency-associated diseases such as Gitelman syndrome (GS) and Bartter syndrome (BS) show downregulation of inflammation-related processes and have reduced oxidative stress and ROS. Additionally, the histone deacetylase sirtuin-1 (SIRT1) has a significant impact on the aging process, with reduced activity with age. However, GS/BS patients generally sustain higher levels of sirtuin-1 (SIRT1) activity than age-matched healthy individuals. SIRT1 expression in GS/BS patients tends to be higher than in healthy age-matched individuals; therefore, it can be assumed that there will be a trend towards healthy aging in these patients. In this review, we highlight the importance of the hallmarks of aging, inflammation, and the RAAS system in GS/BS patients and how this might impact healthy aging. We further propose future research directions for studying the etiology of GS/BS at the molecular level using patient-derived renal stem cells and induced pluripotent stem cells.

Novel Insights in the Hypertension Treatment & Type 2 Diabetics Induced by Angiotensin Receptor Blockers: MD Simulation Studies & Molecular Docking of Some Promising Natural Therapies.

Angiotensin receptor blockers (ARBs) are commonly used to treat hypertension that target the hormonal system (renin-angiotensin system (RAS)), which regulates various physiological functions in the body. ARBs work by blocking the binding of angiotensin II to its receptor, thereby preventing a rise in blood pressure. These drugs not only normalize the overactivation of RAS but also provide protective effects against cardiovascular, renal, and type 2 diabetic patients. Inappropriate RAS activity has been linked to insulin resistance of type 2 diabetes. Olmesartan, as an ARB, was found to have a beneficial role in reducing postprandial glucose levels in type 2 diabetes. However, ARBs can cause side effects, prompting a search for new compounds that have fewer adverse effects. This study explores the potential of natural metabolites, specifically eugenol, gallic acid, myricetin, p-cymene, quercetin, and kaempferol, as ARB inhibitors compared to the current standard, olmesartan. Using in silico studies, the binding affinity of these natural substances to the ARB receptor was evaluated. The results showed that myricetin and kaempferol had affinities higher than those of olmesartan, suggesting that they could serve as promising ARB inhibitors for hypertension treatment. These natural compounds could provide an alternative approach to conventional antihypertensive drugs, which may have fewer side effects. However, more research is needed to validate the efficacy and safety of these natural compounds as antihypertensive drugs. Further in vitro and in vivo studies are needed to confirm their effectiveness and safety. This study provides a promising starting point for future investigations into the potential of natural metabolites as alternative treatments for hypertension. The findings also highlight the importance of exploring natural alternative treatments for hypertension and the protective effects of ARBs on early stage type-2 diabetics.

Target Reserve and Turnover Parameters Determine Rightward Shift of Enalaprilat Potency From its Binding Affinity to the Angiotensin Converting Enzyme

Drug effects are often assumed to be directly proportional to the fraction of occupied targets. However, for a number of antagonists that exhibit target-mediated drug disposition (TMDD), such as angiotensin-converting enzyme (ACE) inhibitors, drug binding to the target at low concentrations may be significant enough to influence pharmacokinetics but insufficient to elicit a drug response (i.e., differences in drug-target binding affinity and potency). In this study, a pharmacokinetic/pharmacodynamic model for enalaprilat was developed in humans to provide a theoretical framework for assessing the relationship between ex vivo drug potency (IC50) and in vivo target-binding affinity (KD). The model includes competitive binding of angiotensin I and enalaprilat to ACE and accounts for the circulating target pool. Data were obtained from the literature, and model fitting and parameter estimation were conducted using maximum likelihood in ADAPT5. The model adequately characterized time-courses of enalaprilat concentrations and four biomarkers in the renin-angiotensin system and provided estimates for in vivo KD (0.646 nM) and system-specific parameters, such as total target density (32.0 nM) and fraction of circulating target (19.8%), which were in agreement with previous reports. Model simulations were used to predict the concentration-effect curve of enalaprilat, revealing a 6.3-fold increase in IC50 from KD. Additional simulations demonstrated that target reserve and degradation parameters are key factors determining the extent of shift of enalaprilat ex vivo potency from its in vivo binding affinity. This may be a common phenomenon for drugs exhibiting TMDD and has implications for translating binding affinity to potency in drug development.

Abstract P323: Direct Vascular Endothelial Actions Of Angiotensin II Via At 1 R And No Signaling Revealed By Intravital Multiphoton Microscopy.

The renin-angiotensin system (RAS) controls blood pressure and body fluid balance. The classic vasoactive effects of RAS are mediated by the binding of angiotensin II (ANGII) to ANGII type 1 receptors (AT 1 R) in vascular smooth muscle cells leading to vasoconstriction, or to opposing ANGII type 2 receptors (AT 2 R). However, only few studies investigated the direct effects of ANGII on vascular endothelial cells (VEC) in vivo and the mechanisms how VECs may mitigate ANGII-mediated vasoconstriction. The present study aimed to explore the molecular mechanisms and pathophysiological relevance of the direct actions of ANGII on VEC in the kidney. VEC calcium dynamics and NO synthesis were visualized by using intravital multiphoton microscopy (MPM) of Cdh5-G6 mice that selectively express the ratiometric Ca 2+ reporter GCaMP6f/tdTomato in VECs, or the endothelial uptake of iv injected nitric oxide (NO) sensitive dye DAF-FM, respectively. Bolus injection of ANGII (400 ng/kg, ia.) triggered a >4-fold increase in VEC calcium in afferent (AA) arterioles and glomerular capillaries, but not in peritubular capillaries. These responses were blocked by pretreatment with the AT 1 R inhibitor Losartan (60mg/kg ip.), but not by the AT 2 R inhibitor PD123319 (25mg/kg ip.)(1.2+/-0.4 p<0.001 and 5.6+/-0.9-fold, p=0.3, respectively). VEC responded to acute ANGII by increased NO synthesis as indicated by >1.5-fold increase in DAF-FM fluorescence intensity as compared to baseline (p<0.0001). In mice with unilateral ureteral obstruction (UUO), a well-known high ANGII and vasoconstrictor state associated with endothelial dysfunction, the ANGII induced calcium increase in VECs was significantly reduced (2.8+/-0.3-fold) as compared to control (4.6+/-0.4-fold, p<0.01). These results correlated with the significantly reduced AA diameter in UUO compared to control (8.2+/-0.4 and 10.43+/-0.3 μm, respectively, p<0.001). In summary, ANGII has major direct effects on VECs NO production that counterbalances agonist-induced vasoconstriction. These effects are diminished in conditions with endothelial dysfunction leading to increased vascular contractility. Cell-specific targeting of ANGII actions may represent exciting future therapeutic opportunities.

Thermal analysis of protein stability and ligand binding in complex media

Screening of ligands that can bind to biologic products of in vitro expression systems typically requires some purification of the expressed biologic target. Such purification is often laborious and time consuming as well as a limiting challenge. What is required, representing an enormous advantage, is the ability to screen expressed proteins in the crude lysate stage without purification. For that purpose, we explore here, the utility of differential scanning calorimetry (DSC) measurements for detecting the presence of specific proteins and their interactions with ligands in the complex media where they were prepared, i.e. crude lysates. Model systems were designed to mimic analogous conditions comparable to those that may be encountered in actual in vitro expression systems. Results are reported for several examples where DSC measurements distinctly showed differences in the thermal denaturation behaviors of the crude lysate alone, proteins and proteins plus binding ligands added to the crude lysate. Results were obtained for Streptavidin/Biotin binding in E. coli lysate, and binding of Angiotensin Converting Enzyme 2 (ACE2) by captopril or lisinopril in the lysate supernatant derived from cultured Human Kidney cells (HEK293). ACE2 binding by the receptor binding domain (RBD) of SARS-CoV-2 was also examined. Binding of ACE2 by RBD and lisinopril were similar and consistent with the reported ACE2 inhibitory activity of lisinopril.

The Identikit of Patient at Risk for Severe COVID-19 and Death: The Dysregulation of Renin-Angiotensin System as the Common Theme.

Since the first months of the coronavirus disease 2019 (COVID-19) pandemic, several specific physiologic traits, such as male sex and older age, or health conditions, such as overweight/obesity, arterial hypertension, metabolic syndrome, and type 2 diabetes mellitus, have been found to be highly prevalent and associated with increased risk of adverse outcomes in hospitalized patients. All these cardiovascular morbidities are widespread in the population and often coexist, thus identifying a common patient phenotype, characterized by a hyper-activation of the “classic” renin-angiotensin system (RAS) and mediated by the binding of angiotensin II (Ang II) to the type 1-receptor. At the same time, the RAS imbalance was proved to be crucial in the genesis of lung injury after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, where angiotensin-converting-enzyme-2 (ACE2) is not only the receptor for SARS-CoV-2, but its down-regulation through internalization and shedding, caused by the virus binding, leads to a further dysregulation of RAS by reducing angiotensin 1-7 (Ang 1-7) production. This focused narrative review will discuss the main available evidence on the role played by cardiovascular and metabolic conditions in severe COVID-19, providing a possible pathophysiological link based on the disequilibrium between the two opposite arms of RAS.

Receptor Interactions of Angiotensin II and Angiotensin Receptor Blockers-Relevance to COVID-19.

Angiotensin II (Ang II) may contain a charge relay system (CRS) involving Tyr/His/carboxylate, which creates a tyrosinate anion for receptor activation. Energy calculations were carried out to determine the preferred geometry for the CRS in the presence and absence of the Arg guanidino group occupying position 2 of Ang II. These findings suggest that Tyr is preferred over His for bearing the negative charge and that the CRS is stabilized by the guanidino group. Recent crystallography studies provided details of the binding of nonpeptide angiotensin receptor blockers (ARBs) to the Ang II type 1 (AT1) receptor, and these insights were applied to Ang II. A model of binding and receptor activation that explains the surmountable and insurmountable effects of Ang II analogues sarmesin and sarilesin, respectively, was developed and enabled the discovery of a new generation of ARBs called bisartans. Finally, we determined the ability of the bisartan BV6(TFA) to act as a potential ARB, demonstrating similar effects to candesartan, by reducing vasoconstriction of rabbit iliac arteries in response to cumulative doses of Ang II. Recent clinical studies have shown that Ang II receptor blockers have protective effects in hypertensive patients infected with SARS-CoV-2. Therefore, the usage of ARBS to block the AT1 receptor preventing the binding of toxic angiotensin implicated in the storm of cytokines in SARS-CoV-2 is a target treatment and opens new avenues for disease therapy.

Inhibitory Binding of Angiotensin Converting Enzyme Inhibitors with Carbonic Anhydrase III

Both angiotensin converting enzyme (ACE) and carbonic anhydrase III (CAIII) are zinc-containing enzymes. Interestingly, blocking of the both enzymes is attributed with clinically significant outcomes against hyperlipidemia and obesity. An optimized in-vitro screening approach based on HPLC–size exclusion chromatography was adopted to study the angiotensin converting enzyme inhibitors (ACEIs) affinity against CAIII enzyme. Series of concentrations of the enzyme were injected in the column with a mobile phase containing one of ACEIs in each time. The affinity of the ACEIs toward CAIII was characterized by vacancy (negative) peak whose intensity representing the fraction of the drug bound with CAIII. To explore whether the binding is within the binding site or just a promiscuous binding, exact procedure was repeated with apo-protein part of CAIII. Furthermore, an esterase activity of CAIII was performed to determine if the binding with ACEIs is excitatory or inhibitory. It has been found that ACEIs have real in-vitro inhibitory effects against CAIII at a micro-molar level. The chromatographic study revealed that the ionized carboxylate groups are essential for binding with Zn+2 ion in the enzyme active site. Among the four tested ACEIs, captopril, ramipril, enalapril, and lisinopril, captopril was found to be the most potent inhibitor with Ki = 12.1 μM, while lisinopril is the least potent one with Ki = 25.3 μM. This finding might open the door for further investigation to optimize ACEIs as lead compounds for the discovery and development of selective and potent CAIII inhibitors.

Effect of Losartan on Different Biochemical Parameters in Essential Hypertensive Patients

The renin–angiotensin system (RAS) provides the most powerful regulation of blood pressure and angiotensin II is the primary mediator in this system. The binding of angiotensin II to AT1 receptors produces a number of potentially harmful effects that include increase in blood pressure, progression of atherosclerosis, myocardial and vascular hypertrophy. Losartan was the first ARB and found to reduce the risk of stroke, new onset of diabetes and to have a proven benefit in stroke. The present study was designed to evaluate the effect of losartan on different biochemical parameters viz; blood sugar, lipid profile, uric acid and serum electrolytes. 29 newly diagnosed patients of either gender with essential hypertension were included in the study. Baseline readings of lipid profile, serum electrolytes, fasting blood sugar and uric acid were recorded before starting losartan monotherapy and were repeated after six months. After comparing the means, it was revealed that there was a significant increase in HDL cholesterol and a significant decrease in serum uric acid levels after six months of losartan therapy. No significant difference was found in blood sugar and electrolyte levels. These findings suggest that losartan can be an attractive option for the treatment of hypertension and for metabolic syndrome.

Computational approaches to understanding ARB resistance: a route to personalized ARB therapy

The binding of Angiotensin II to the Angiotensin II type 1 receptor (AT1Rs) plays a pivotal role in the regulation of blood pressure and other physiological processes. AT1R blockers (ARBs) are commonly prescribed anti‐hypertensive drugs; however, not all patients respond equally to ARBs and some patients are ARB resistant. One documented reason behind these clinical observations is non‐synonymous polymorphisms within the AT1R that alter ARB affinity. There are 103 known polymorphisms within the crystallized AT1R structure that we utilized for computational approaches to predict which polymorphisms contribute to ARB resistance. To accomplish this, a 150 ns molecular dynamic (MD) simulation was performed to create a stable‐empty AT1R in an 87% POPC and 13% cholesterol membrane. Each polymorphism was made in the MD generated AT1R via MOE and minimized prior to docking performed with autodock4. Each ARB, including the active metabolite of Losartan, was docked using an experimentally derived grid that produced affinities in the wild‐type AT1R comparable to published reports. In total, 93,600 drug‐receptor complexes were analyzed and the data indicates that polymorphisms fall into two general categories: ARB specific resistance and total ARB resistance. Polymorphic AT1Rs displaying ARB specific resistance display wild‐type affinities for a subset of ARBs and in some cases, such as C101Y, G196V, and F313C, not the common ARBs valsartan and losartan; whereas, total ARB resistance, such as W84C, V108I, H132Y, and C289W, indicates that all ARBs are likely ineffective. In conclusion, patients that appear ARB resistant should have their AT1R sequenced and the sequence could be used to determine which ARB may be effective or suggest discontinuing ARB therapy.Support or Funding InformationThis project is funded by internal WesternU funds.

Angiotensin II receptor blockers induce autophagy in prostate cancer cells.

Angiotensin II receptor blockers (ARBs) are anti-hypertensive drugs that competitively inhibit the binding of angiotensin II to its receptor, resulting in blood vessel dilation and the reduction of blood pressure. These antagonists are also known as sartans, and are a group of pharmaceuticals that possess tetrazole or imidazole groups. In the present study, the anticancer and antimetastatic effects of the ARBs fimasartan, losartan, eprosartan and valsartan on the human prostate cancer PC-3, DU-145 and LNCap-LN3 cell lines were investigated in vitro. The proliferation of the prostate cancer cells was inhibited following treatment with 100 µM ARB. In particular, treatment with fimasartan resulted in marked anti-proliferative activity compared with the other ARBs. With respect to the molecular mechanism of the growth inhibition exhibited by the ARBs, 3-methyladenin (3-MA), an autophagy inhibitor, was revealed to increase the survival rate of PC-3 cells when cell death inhibitors were pretreated with fimasartan. In addition, the ARBs induced autophagy with increased expression levels of autophagy protein (Atg) 5–12, Atg 16-like-1, beclin-1 and microtubule-associated protein 1A/1B-light chain 3 (LC3). Notably, the enhanced expression of LC3-II (a 6.7-fold increase at 72 h) was observed in PC3 cells treated with fimasartan. This was supported by the observation of the time-dependent accumulation of LC3-positive foci in PC-3. In addition, a migration assay indicated that the ARBs induced anti-metastatic effects in PC-3 and DU-145 cells. The aforementioned results suggest that ARBs may induce autophagy-associated cell death and anti-metastatic activity in prostate cancer cells. Thus, ARBs may be a potential medication for patients with prostate cancer and hypertension.

Role of the receptor Mas in macrophage-mediated inflammation in vivo

Recently, an alternative renin-angiotensin system pathway has been described, which involves binding of angiotensin-(1-7) to its receptor Mas. The Mas axis may counterbalance angiotensin-II-mediated proinflammatory effects, likely by affecting macrophage function. Here we investigate the role of Mas in murine models of autoimmune neuroinflammation and atherosclerosis, which both involve macrophage-driven pathomechanisms. Mas signaling affected macrophage polarization, migration, and macrophage-mediated T-cell activation. Mas deficiency exacerbated the course of experimental autoimmune encephalomyelitis and increased macrophage infiltration as well as proinflammatory gene expression in the spleen and spinal cord. Furthermore, Mas deficiency promoted atherosclerosis by affecting macrophage infiltration and migration and led to increased oxidative stress as well as impaired endothelial function in ApoE-deficient mice. In summary, we identified the Mas axis as an important factor in macrophage function during inflammation of the central nervous and vascular system in vivo. Modulating the Mas axis may constitute an interesting therapeutic target in multiple sclerosis and/or atherosclerosis.

Deletion of proton-sensing receptor GPR4 associates with lower blood pressure and lower binding of angiotensin II receptor in SFO.

Diets rich in grains and meat and low in fruits and vegetables (acid-producing diets) associate with incident hypertension, whereas vegetarian diets associate with lower blood pressure (BP). However, the pathways that sense and mediate the effects of acid-producing diets on BP are unknown. Here, we examined the impact of the deletion of an acid sensor GPR4 on BP. GPR4 is a proton-sensing G protein-coupled receptor and an acid sensor in brain, kidney, and blood vessels. We found that GPR4 mRNA was higher in subfornical organ (SFO) than other brain regions. GPR4 protein was abundant in SFO and present in capillaries throughout the brain. Since SFO partakes in BP regulation through the renin-angiotensin system (RAS), we measured BP in GPR4-/- and GPR4+/+ mice and found that GPR4 deletion associated with lower systolic BP: 87 ± 1 mmHg in GPR4-/- (n = 35) vs. 99 ± 2 mmHg (n = 29) in GPR4+/+; P < 0.0001, irrespective of age and sex. Angiotensin II receptors detected by 125I-Sarthran binding were lower in GPR4-/- than GPR4+/+ mice in SFO and in paraventricular nucleus of hypothalamus. Circulating angiotensin peptides were comparable in GPR4-/- and GPR4+/+ mice, as were water intake and excretion, serum and urine osmolality, and fractional excretion of sodium, potassium, or chloride. A mild metabolic acidosis present in GPR4-/- mice did not associate with elevated BP, implying that deficiency of GPR4 may preclude the effect of chronic acidosis on BP. Collectively, these results posit the acid sensor GPR4 as a novel component of central BP control through interactions with the RAS.

Angiotensin II counteracts the effects of cAMP/PKA on NHE3 activity and phosphorylation in proximal tubule cells.

Binding of angiotensin II (ANG II) to the AT1 receptor (AT1R) in the proximal tubule stimulates Na+/H+ exchanger isoform 3 (NHE3) activity through multiple signaling pathways. However, the effects of ANG II/AT1R-induced inihibitory G protein (Gi) activation and subsequent decrease in cAMP accumulation on NHE3 regulation are not well established. We therefore tested the hypothesis that ANG II reduces cAMP/PKA-mediated phosphorylation of NHE3 on serine 552 and, in doing so, stimulates NHE3 activity. Under basal conditions, ANG II stimulated NHE3 activity but did not affect PKA-mediated NHE3 phosphorylation at serine 552 in opossum kidney (OKP) cells. However, in the presence of the cAMP-elevating agent forskolin (FSK), ANG II blocked FSK-induced NHE3 inhibition, reduced intracellular cAMP concentrations, lowered PKA activity, and prevented the FSK-mediated increase in NHE3 serine 552 phosphorylation. All effects of ANG II were blocked by pretreating OKP cells with the AT1R antagonist losartan, highlighting the contribution of the AT1R/Gi pathway in ANG II-mediated NHE3 upregulation under cAMP-elevating conditions. Accordingly, Gi inhibition by pertussis toxin treatment decreased NHE3 activity both in vitro and in vivo and, more importantly, prevented the stimulatory effect of ANG II on NHE3 activity in rat proximal tubules. Collectively, our results suggest that ANG II counteracts the effects of cAMP/PKA on NHE3 phosphorylation and inhibition by activating the AT1R/Gi pathway. Moreover, these findings support the notion that NHE3 dephosphorylation at serine 552 may represent a key event in the regulation of renal proximal tubule sodium handling by ANG II in the presence of natriuretic hormones that promote cAMP accumulation and transporter phosphorylation.

Non-Equilibrium Molecular Dynamics to Simulate Shear Stress on Angiotensin II Type 1 (AT1) Receptor

AT1 is a G protein-coupled receptor responsible for controlling blood pressure in the cardiovascular system. The binding of angiotensin II (AngII) causes Gq recruitment, while shear stress (SS) activates AT1 and causes ERK1/2 phosphorylation independently of Gαq. In order to investigate the latter, atomistic non-equilibrium molecular dynamics simulations explored AT1 conformational changes under SS. The complete structure of AT1 inserted in a POPC bilayer and solvated in water, was simulated for 1 μs at 1 bar and 310 K. SS was applied deforming the simulation box separately in the x and y directions for 100 ns, at a rate of 1 pm/ps. AT1 without SS presents increased flexibility in the intracellular loop (ICL) 2, ICL 3, and helix 8. The root mean square fluctuation of the C-terminal (Leu317-Glu359) is higher without SS (0.61-1.64 nm) versus SS (0.32-0.76 nm). The radius of gyration of the C-terminal is smaller without SS (1.04-1.19 nm) compared to SS (1.36-1.40 nm), suggesting this region is more extended under SS. C-terminal is also more exposed to water in SS, as the average solvent accessible surface area is higher (44.5± 2.2 nm²) compared to AT1 without SS (38.5±1.6 nm²), including the residues prone to phosporylation by GRK (Thr332-Ser338). Collectively, the findings suggest SS exposes and makes the C-terminal more stable to GRK binding, leading to β-arrestin recruitment and, ultimately, ERK1/2 phosphorylation.

Structural Basis for Ligand Recognition and Functional Selectivity at Angiotensin Receptor

Angiotensin II type 1 receptor (AT1R) is the primary blood pressure regulator. AT1R blockers (ARBs) have been widely used in clinical settings as anti-hypertensive drugs and share a similar chemical scaffold, although even minor variations can lead to distinct therapeutic efficacies toward cardiovascular etiologies. The structural basis for AT1R modulation by different peptide and non-peptide ligands has remained elusive. Here, we report the crystal structure of the human AT1R in complex with an inverse agonist olmesartan (Benicar(TM)), a highly potent anti-hypertensive drug. Olmesartan is anchored to the receptor primarily by the residues Tyr-35(1.39), Trp-84(2.60), and Arg-167(ECL2), similar to the antagonist ZD7155, corroborating a common binding mode of different ARBs. Using docking simulations and site-directed mutagenesis, we identified specific interactions between AT1R and different ARBs, including olmesartan derivatives with inverse agonist, neutral antagonist, or agonist activities. We further observed that the mutation N111(3.35)A in the putative sodium-binding site affects binding of the endogenous peptide agonist angiotensin II but not the β-arrestin-biased peptide TRV120027.

Blockade of renin angiotensin system in heart failure post-myocardial infarction: what is the best therapy?

Heart Failure (HF) is a progressive and fatal disorder, which ranks among the major public health problems in Brazil and worldwide. However, survival for patients who developed the syndrome after myocardial infarction (MI) enhanced significantly, as a result of an improvement of pharmacological therapies. A medical breakthrough was the discovery that remodelling of the left ventricle (LV) may be limited by the blockade of the renin-angiotensin system (RAS), at the level of angiotensin converting enzyme (ACE) and binding of angiotensin (Ang) II to its AT1 receptor. This review shows that the therapeutic effects of both ACE inhibitors and the angiotensin receptor blockers (ARB) go beyond the interference in the biochemical pathway ACE-Ang II AT1-receptor. Such effects are also related to the potentiation of bradykinin and increased beneficial effects mediated by the AT2 receptor. Therefore, the results of five randomized trials were presented, which evaluated the use of losartan, valsartan or candesartan, considering their effects on survival and risk of clinical deterioration in patients with symptomatic HF after MI. These studies confirmed the advantage of ARBs over inhibitors in case of cough, rashes and angioneurotic edema, despite similar adverse effects, such as hyperkalemia, renal failure and hypotension. Thus, in this article we have discussed with patents that ACE inhibitors also appear as the first option as RAS inhibitors in search of relevant results for the patient, allowing the alternative use of ARBs to those patients with intolerance.

Insights into AT1 Receptor Activation through AngII Binding Studies

This study investigates the binding of angiotensin II (AngII) to the angiotensin II type 1 receptor (AT1R), taking into consideration several known activation elements that have been observed for G-protein-coupled receptors (GPCRs). In order to determine the crucial interactions of AngII upon binding, several MD simulations were implemented using AngII conformations derived from experimental data (NMR ROEs) and in silico flexible docking methodologies. An additional goal was to simulate the induced activation mechanism and examine the already known structural rearrangements of GPCRs upon activation. Performing MD simulations to the AT1R - AngII - lipids complex, a series of dynamic changes in the topology of AngII and the intracellular part of the receptor were observed. Overall, the present study proposes a complete binding profile of AngII to the AT1R, as well as the key transitional elements of the receptor and the agonist peptide upon activation through NMR and in silico studies.

Binding Affinity of Candesartan, Losartan, Telmisartan and Valsartan with Angiotensin II Receptor 1 Subtype

This study was designed to examine the interaction in the binding of selective angiotensin II receptor antagonists towards angiotensin II type 1 receptor. The AT1 antagonists used in this study were valsartan, candesartan and losartan. Wild type AT1 receptors were transiently expressed in COS-7 cells and the expressed protein was isolated. The binding affinities of agonist and these four AT1 antagonists were determined towards AT1 receptors with the help of radioligand binding studies. The binding affinity of candesartan has been found to be maximum having a pKi value of 8.61±0.21 whereas losartan showed lowest binding affinity among the antagonists (pKi=7.17±0.07). Telmisartan also showed high (pKi=8.19±0.04) and valsartan had moderate binding affinity (pKi=7.65±0.12) towards AT1 receptors. The results of the study suggested that candesartan interacts very strongly with the receptor which is consistent with the maximum number of binding sites of in the chemical structure of candesartan. On the other hand, losartan has lower number of binding sites with the amino acid residues of AT1 receptor and as a result it showed the minimum affinity towards the receptor. DOI: http://dx.doi.org/10.3329/bpj.v16i1.14484 Bangladesh Pharmaceutical Journal 16(1): 10-14, 2013

PP018. Does altitude affect the placental renin angiotensin system (RAS) in pre-eclampsia (PE)?

We have previously shown the activation of placental RAS in high altitude normotensive (NT) pregnancies [1], presumably related to hypoxia during placental development. PE incidence is increased at high altitude; hypoxia-reoxygenation injury contributes to the elevated oxidative stress seen in this condition. Binding of Angiotensin II to its type I receptor (AT1R) increases generation of reactive oxygen species and we have shown an increase in AT1R in PE [2]. Therefore we investigated whether the RAS is further augmented in PE at high altitudes. Biopsies were collected, with informed, written consent, from NT and PE women (ISSHP guidelines) at sea-level (UK) and high altitude, 3100m (Leadville, Colorado) immediately after vaginal delivery or elective non-laboured Caesarean section. mRNA expression of the RAS components (angiotensinogen (AGT), prorenin, prorenin receptor, AT1R and angiotensin type 2 receptor) was determined by qRT-PCR and normalised to 3 stably-expressed housekeeping genes using geNorm. Protein expression was semi-quantitatively assessed by immunohistochemistry (H score) and compared between groups (Mann Whitney U test). mRNA expression of all RAS components was unaffected by altitude in NT, but significantly lower for all in PE (P=0.026-<0.0001). However, in NT, protein expression of all components except AGT was significantly increased at altitude (P=0.037-<0.001). Protein expression of AGT and AT1R was also increased in altitude PE (P<0.004 for both). We have shown the placental RAS to be activated at altitude, with apparent differences in transcription/translation. Hypoxia-inducible transcription factors such as HIF-1 enhance transcription and translation of many genes encoding "rescue" proteins; this might explain the effects of altitude in NTs. HIF-1 is increased in PE, which might allow increased protein expression at altitude in spite of lower mRNA.