AT1 Receptor Blockade Research Articles

Mental stress induces endothelial dysfunction by AT1R-mediated redox imbalance in overweight/obese men

The main goal of this study was to determine whether oxidative imbalance mediated by AT1 receptor (AT1R) is responsible for deleterious endothelial responses to mental stress (MS) in overweight/obese class I men. Fifteen overweight/obese men (27±7 years old; 29.8±2.6 kg/m2) participated in three randomized experimental sessions with oral administration of the AT1R blocker olmesartan (40 mg; AT1R blockade) or ascorbic acid (AA; 3g) infusion or placebo [both intravenously (0.9% NaCl) and orally]. After two hours, endothelial function was determined by flow-mediated dilation (FMD) before (baseline), 30 min (30MS), and 60 min (60MS) after a five-minute acute MS session (Stroop Color Word Test). Blood was collected before (baseline), during MS, and 60 min after MS for redox homeostasis profiling: lipid peroxidation (TBARS; thiobarbituric acid reactive species), protein carbonylation, and catalase activity by colorimetry and superoxide dismutase (SOD) activity by an ELISA kit. At the placebo session, FMD significantly decreased 30MS (P=0.05). When compared to baseline, TBARS (P<0.02), protein carbonylation (P<0.01), catalase (P<0.01), and SOD (P<0.01) increased during the placebo session. During AT1R blockade, FMD increased 30 min after MS (P=0.01 vs baseline; P<0.01 vs placebo), while AA infusion increased FMD only 60 min after MS. No differences were observed during MS with the AT1R blockade and AA regarding TBARS, protein carbonylation, catalase, and SOD. AT1R-mediated redox imbalances played an important role in endothelial dysfunction to mental stress.

AT1R blocker prevents mental stress induced retrograde blood flow in overweight/obese men.

The main goal was to determine the impact of mental stress (MS) on blood flow regulation in overweight/obese men. Fourteen overweight/obese men (27 ± 7 years; 29.8 ± 2.6kg/m2 ) participated in two randomized experimental sessions with oral administration of the AT1R blocker Olmesartan (40 mg; AT1RB) or placebo (PL). After 2 h, a 5-min acute MS session (Stroop Color Word Test) was administered. Blood flow was assessed at baseline and during the first 3 min of MS by vascular ultrasound in the brachial artery. Blood was collected before (baseline) and during mental stress (MS) for measurement of nitrite (chemiluminescence) and endothelin-1 (ELISA kit). The AT1R blocker was able to reverse the MS responses observed in the placebo session for retrograde flow (p < 0.01), retrograde SR (p < 0.01) and oscillatory shear index (p=0.01). Regarding vasoactive substances, no differences were observed in ET-1 (p > 0.05) responses to MS between experimental sessions. However, for nitrite responses, the administration of the AT1R blocker was able to increase circulating levels of NO (p=0.03) Blockade of AT1R appears to prevent the decrease in endothelial function by reducing low shear stress and maintaining the vasoactive substances balance after MS in overweight/obese men.

S-39-4: PLASMA FROM SARS-COV-2 PATIENTS INDUCES OXIDATIVE STRESS AND ENDOTHELIAL DYSFUNCTION VIA ANGIOTENSIN II TYPE 1 RECEPTOR (AT1R)/P38 MAPK PATHWAY

Background: Acute respiratory distress syndrome (ARDS) is a distinctive feature of severe COVID-19 infections that occurs mainly in patients with coexisting health problems, such as hypertension, atherosclerosis, and diabetes. Endothelial dysfunction is a major contributing factor during ARDS development in COVID-19 patients with pre-existing comorbidities. Objective: Studying the mechanism by which endothelial activation and dysfunction could provide a therapeutic target for COVID-19 treatment. Design and method: The current study measured endothelial dysfunction and oxidative stress by incubating human umbilical vein endothelial cells (HUVECs) with plasma from patients with mild, moderate, severe and extremely severe COVID-19. Using flow cytometry, wound-healing assays and phosphokinase arrays, Results: We detected increases in cell apoptosis; reactive oxygen species (ROS) formation; hypoxia-inducible factor-1 alpha (HIF-1 alpha), vascular cell adhesion molecule-1 (VCAM-1), and vascular endothelial growth factor receptor-1 (VEGFR-1) expression; viral entry; and inflammatory-related protein activity. We also found an impairment in the wound-healing process. Moreover, we found that AT1R blockade and P38 MAPK inhibition reversed all of these effects, especially in the severe group. Conclusions: These findings indicate that AT1R/P38 MAPK-mediated oxidative stress and endothelial dysfunction occur during COVID-19 infection.

S-13-4: INHIBITORY IMPACTS OF CHLOROGENIC ACID ON ADRENAL CATECHOLAMINE SECRETION

(Objective) Chlorogenic acid (CGA) is one of the most available phenolic acid compounds in foods, such as coffee and tea. Thus, the present study was aimed to determine the characteristics of CGA on secretion of catecholamines (CA) in the perfused model of the rat adrenal medulla, and also to validify its mechanism of action. (Design and Methods) The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. (Results) CGA (30∼300 μM), administered into an adrenal vein for 90 min, reduced ACh-induced CA secretion in a dose- and time-dependent manner. CGA also time-dependently depressed the CA secretion induced by McN-A-343 (a selective muscarinic M1 receptor agonist), DMPP (a selective neuronal nicotinic receptor agonist), and angiotensin II. CGA itself failed to influence spontaneous CA secretion. Also, During the perfusion of CGA for 90 min, the CA secretory responses induced by high K+ (56 mM, a direct membrane depolarizer), veratridine (a voltage-dependent Na+ channel activator, cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor, Bay-K-8644 (an L-type dihydropyridine Ca2+ channel activator were suppressed. However, in the simultaneous presence of CGA and L-NAME (an inhibitor of NO synthase), the CA secretory responses induced by ACh, Ang II, Bay-K-8644 and veratridine was restored nearly to the control level compared to those of the inhibitory effects of CGA-treatment alone. Virtually, the adrenal NO release was significantly enhanced by CGA-treatment. Also, in the coexistence of CGA and olmesartan, ACh-induced CA secretion was markedly reduced compared to that of olmesartan-treatment alone. (Conclusion) Taken together, we present the first evidence that CGA suppresses the CA secretion induced by activation of cholinergic receptors as well as AT1-receptors. This CGA-induced inhibitory effect seems to be exerted by reducing both the influx of Na+ and Ca2+ through their ionic channels into the adrenomedullary chromaffin cells as well as by suppressing the Ca2+ release from the cytoplasmic calcium store, at least through the elevated NO release by the activation of NO synthase, which is associated to the blockade of neuronal cholinergic receptors and AT1-receptors. Based on these results, the ingestion of CGA may be helpful to alleviate or prevent the cardiovascular diseases, via reduction of adrenal CA secretion and consequent decreased CA level in the circulation. Co-administration of CGA and Olmesartan (ARB) may be clinically beneficial for treatment of cardiovascular diseases, including hypertension and angina pectoris.

PS-B10-8: BLOCKADE OF AT1 RECEPTORS RESTORE P2/P1 WITHOUT CHANGING INTRACRANIAL PRESSURE IN RENOVASCULAR HYPERTENSIVE RATS WITH 0.3 M NACL AD LIBITUM

Objective: Renovascular hypertension is characterized by activation of the renin angiotensin aldosterone system, elevated sympathetic nerve activity and sodium appetite behavior. The association of increased sodium intake and hypertension can worsen the injury to end organs. We tested the effects of AT1 receptors blockade (losartan, 10 mg/kg iv) on mean arterial pressure (MAP), intracranial pressure (ICP) and P2/P1 ratio (index of brain compliance) in 2K1C rats with 0.3 M NaCl ad libitum. Design and Methods: Male Holtzman rats (150 tp 180 g) with water and food ad libitum received a silver clip around the left renal artery to induce 2K1C or no clip (SHAM surgery) resulting 3 groups: SHAM (n = 9), 2K1C (n = 9) and 2K1C/Na (n = 7), which had an additional bottle of 0.3 M NaCl ad libitum. Six weeks after the renal surgery, MAP and ICP were recorded under urethane anesthesia (1.2 g/kg iv) and the P2/P1 was calculated offline from the waveform. Saline (0.2 ml/rat) was used as control injection before losartan. Results: In SHAM rats, ICP and P2/P1 were not changed by losartan (7.8 ± 1.1 and 0.88 ± 0.02; vs. saline: 7.9 ± 1.1 and 0.83 ± 0.01 mmHg, respectively), while MAP was decreased (104 ± 5, vs. saline: 120 ± 3 mmHg, p &lt; 0.05). In 2K1C, MAP, ICP and P2/P1 values were greater than SHAM (respectively, 196 ± 6, 14.7 ± 2.7 and 1.1 ± 0.03 mmHg, vs. SHAM; p &lt; 0.05) and all of them were decreased by losartan pre-treatment (137 ± 6, 8.6 ± 1.3 and 0.87 ± 0.05 mmHg, vs. saline, respectively). In 2K1C-Na MAP and P2/P1 were greater than in SHAM (186 ± 7 and 1.15 ± 0.06 mmHg, vs sham p &lt; 0.05) and were decreased by losartan (162 ± 8 and 0.87 ± 0.02 mmHg, vs. saline; p &lt; 0.05), although the decrease in MAP after losartan was lesser than the observed in 2K1C rats (p &lt; 0.05). In 2K1C-Na rats, ICP was not different from SHAM (10.8 ± 1.2, vs. SHAM: 7.8 ± 1.1 mmHg, p &gt; 0.05) and losartan had no effect on ICP (10.3 ± 1.7, vs. saline: 10.8 ± 1.2 mmHg, p &gt; 0.05). Conclusion: Even without a change in ICP, AT1 blockade in 2K1C-Na was effective in restoring P2/P1 ratio, suggesting a beneficial effect on brain compliance in this situation.

PS-B03-5: HIGH-DOSES OF LOSARTAN RATHER ENHANCE CATECHOLAMINE SECRETION FROM THE PERFUSED ADRENAL GLAND

Objective: Previously, we have found that Losartan (5∼50 μM), an AT1 receptor blocker, dose-dependently inhibits secretion of catecholamines (CA) evoked by cholinergic and angiotensin II (Ang II) receptor stimulation from the perfused rat adrenal medulla. The aim of the present study was to examine the characteristic effects of high-dose losartan on the CA secretion from the isolated perfused rat adrenal gland, and also to establish its mechanism of action. Design and Methods: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: The perfusion of high-dose losartan (150 ∼ 600 μM) into an adrenal vein for 90 min resulted in great increases in CA secretions evoked by acetylcholine in a dose-dependent fashion. Also, losartan (300 μM) enhanced the CA release evoked by Ang II, high K+ and DMPP (a selective nicotinic receptor agonist), McN-A-343 (a selective muscarinic M1 receptor agonist). Also, in the presence of losartan (300 μM), the CA secretory responses to veratridine (a selective Na+ channel activator), Bay-K-8644 (a Ca2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor) were significantly potentiated, respectively. The facilitatory CA-releasing effect of Ach evoked by high-dose losartan (300 μM) was time-dependently depressed by pretreatment with nifedipine (Ca2+ channel blocker), while not by pretreatment with sodium nitroprusside (an NO donor). High-dose olmesartan (150 ∼ 600 μM), one of ARBs, also potentiated Ach-evoked CA release in time-dependent fashion. However, in the simultaneous presence of losartan (300 μM) and CGP42112 (an AT2 receptor agonist), the facilitatory responses of losartan on the CA secretion evoked by ACh were rather significantly reduced in comparison with that of losartan-treatment alone. Conclusion: Conclusively, these results demonstrate that high-dose losartan can potentiate the adrenomedullary CA secretion in a calcium-dependent fashion. It seems that this facilitatory effect of high-dose losartan may be mediated by activation of the Ca2+ influx through L-type Ca2+ channels into adrenomedullary cells without inhibition of NO synthesis, which seems to be relevant to AT2 receptor blockade. It also suggests that high-dose ARBs may be a risk factor in causing hypertensive response.

The Angiotensin Antagonist Losartan Modulates Social Reward Motivation and Punishment Sensitivity via Modulating Midbrain-Striato-Frontal Circuits.

Social deficits and dysregulations in dopaminergic midbrain-striato-frontal circuits represent transdiagnostic symptoms across psychiatric disorders. Animal models suggest that interactions between the dopamine (DA) and renin-angiotensin system (RAS) may modulate learning and reward-related processes. The present study therefore examined the behavioral and neural effects of the Angiotensin II type 1 receptor (AT1R) antagonist losartan on social reward and punishment processing in humans. A preregistered randomized double-blind placebo-controlled between-subject pharmacological design was combined with a social incentive delay (SID) functional MRI (fMRI) paradigm during which subjects could avoid social punishment or gain social reward. Healthy volunteers received a single-dose of losartan (50 mg, n = 43, female = 17) or placebo (n = 44, female = 20). We evaluated reaction times (RTs) and emotional ratings as behavioral and activation and functional connectivity as neural outcomes. Relative to placebo, losartan modulated the reaction time and arousal differences between social punishment and social reward. On the neural level the losartan-enhanced motivational salience of social rewards was accompanied by stronger ventral striatum-prefrontal connectivity during reward anticipation. Losartan increased the reward-neutral difference in the ventral tegmental area (VTA) and attenuated VTA associated connectivity with the bilateral insula in response to punishment during the outcome phase. Thus, losartan modulated approach-avoidance motivation and emotional salience during social punishment versus social reward via modulating distinct core nodes of the midbrain-striato-frontal circuits. The findings document a modulatory role of the renin-angiotensin system in these circuits and associated social processes, suggesting a promising treatment target to alleviate social dysregulations.SIGNIFICANCE STATEMENT Social deficits and anhedonia characterize several mental disorders and have been linked to the midbrain-striato-frontal circuits of the brain. Based on initial findings from animal models we here combine the pharmacological blockade of the Angiotensin II type 1 receptor (AT1R) via losartan with functional MRI (fMRI) to demonstrate that AT1R blockade enhances the motivational salience of social rewards and attenuates the negative impact of social punishment via modulating the communication in the midbrain-striato-frontal circuits in humans. The findings demonstrate for the first time an important role of the AT1R in social reward processing in humans and render the AT1R as promising novel treatment target for social and motivational deficits in mental disorders.

Effect of the renin-angiotensin system on the exacerbation of adrenal glucocorticoid steroidogenesis in diabetic mice: Role of angiotensin-II type 2 receptor.

Prior investigation shows an increase in the activity of both hypothalamus-pituitary-adrenal (HPA) axis and the renin-angiotensin system (RAS) in diabetic patients. Moreover, activation of angiotensin-II type 1 receptor (AT1) has been associated with adrenal steroidogenesis. This study investigates the role of RAS on the overproduction of corticosterone in diabetic mice. Diabetes was induced by intravenous injection of alloxan into fasted Swiss-webster mice. Captopril (angiotensin-converting enzyme inhibitor), Olmesartan (AT1 receptor antagonist), CGP42112A (AT2 receptor agonist) or PD123319 (AT2 receptor antagonist) were administered daily for 14 consecutive days, starting 7 days post-alloxan. Plasma corticosterone was evaluated by ELISA, while adrenal gland expressions of AT1 receptor, AT2 receptor, adrenocorticotropic hormone receptor MC2R, pro-steroidogenic enzymes steroidogenic acute regulatory protein (StAR), and 11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) were assessed using immunohistochemistry or western blot. Diabetic mice showed adrenal gland overexpression of AT1 receptor, MC2R, StAR, and 11βHSD1 without altering AT2 receptor levels, all of which were sensitive to Captopril or Olmesartan treatment. In addition, PD123319 blocked the ability of Olmesartan to reduce plasma corticosterone levels in diabetic mice. Furthermore, CGP42112A significantly decreased circulating corticosterone levels in diabetic mice, without altering the overexpression of MC2R and StAR in the adrenal glands. Our findings revealed that inhibition of both angiotensin synthesis and AT1 receptor activity reduced the high production of corticosterone in diabetic mice via the reduction of MC2R signaling expression in the adrenal gland. Furthermore, the protective effect of Olmesartan on the overproduction of corticosterone by adrenals in diabetic mice depends on both AT1 receptor blockade and AT2 receptor activation.

Angiotensin II Modulates Calcium/Phosphate Excretion in Experimental Model of Hypertension: Focus on Bone.

A link between hypertension and long-term bone health has been suggested. The aim of this study was to investigate the effects of chronic angiotensin II administration on urinary calcium/phosphate excretion, bone mineral density, bone remodeling and osteoblast population in a well-established experimental model of hypertension, in the absence of possible confounding factors that could affect bone metabolism. Male Sprague-Dawley rats, divided in the following groups: (a) Angiotensin II (Ang II, 200 ng/kg/min, osmotic minipumps, sub cutis, n = 8); (b) Ang II+losartan (Los, 50 mg/kg/day, per os, n = 6); (c) control group (physiological saline, sub cutis, n = 9); and (d) control+losartan (n = 6) were treated for four weeks. During the experimental period, 24-hour diuresis, urinary calcium, phosphate and sodium excretion were measured prior to the treatment, at two weeks of treatment, and at the end of the treatment. Systolic blood pressure was measured by plethysmography technique (tail cuff method). At the end of the experimental protocol, the rats were euthanized and peripheral quantitative computed tomography at the proximal metaphysis and at the diaphysis of the tibiae and quantitative bone histomorphometry on distal femora were performed. Angiotensin II-dependent hypertension is associated with increased calcium and phosphate excretion. AT1 receptor blockade prevented the increase of blood pressure and phosphate excretion but did not affect the increase of calcium excretion. These changes took place without significantly affecting bone density, bone histology or osteoblast population. In conclusion, in our experimental conditions, angiotensin II-dependent hypertension gave rise to an increased urinary excretion of calcium and phosphate without affecting bone density.

Angiotensin II Regulates the Neural Expression of Subjective Fear in Humans: A Precision Pharmaco-Neuroimaging Approach

BackgroundRodent models and pharmacological neuroimaging studies in humans have been used to test novel pharmacological agents to reduce fear. However, these strategies are limited with respect to determining process-specific effects on the actual subjective experience of fear, which represents the key symptom that motivates patients to seek treatment. In this study, we used a novel precision pharmacological functional magnetic resonance imaging approach based on process-specific neuroaffective signatures to determine effects of the selective angiotensin II type 1 receptor (AT1R) antagonist losartan on the subjective experience of fear. MethodsIn a double-blind, placebo-controlled, randomized pharmacological functional magnetic resonance imaging design, healthy participants (N = 87) were administered 50 mg losartan or placebo before they underwent an oddball paradigm that included neutral, novel, and fear oddballs. Effects of losartan on brain activity and connectivity as well as on process-specific multivariate neural signatures were examined. ResultsAT1R blockade selectively reduced neurofunctional reactivity to fear-inducing visual oddballs in terms of attenuating dorsolateral prefrontal activity and amygdala-ventral anterior cingulate communication. Neurofunctional decoding further demonstrated fear-specific effects in that AT1R blockade reduced the neural expression of subjective fear but not of threat or nonspecific negative affect and did not influence reactivity to novel oddballs. ConclusionsThese results show a specific role of the AT1R in regulating the subjective fear experience and demonstrate the feasibility of a precision pharmacological functional magnetic resonance imaging approach to the affective characterization of novel receptor targets for fear in humans.

Formulation and Characterization of Novel Transfersomes Gel for Enhance TDDS of Losartan Potassium

A transferosome is the first generation of an elastic liposome prepared from phospholipids and edge activators. An edge activator is often a single-chain surfactant with a high radius of curvature that destabilizes the lipid bilayers of vesicles and increases the deformability of the bilayers, thereby making the vehicle ultra-deformable. Losartan potassium is an orally active angiotensin-II receptor antagonist used in the treatment of hypertension due to mainly blockade of AT1 receptor. It is freely soluble in water, slightly soluble in acetonitrile, and soluble in isopropyl alcohol. The aim of the present study was to investigate the potential of transfersomal gel formulations for transdermal delivery of losartan potassium by reverse phase evaporation method. Characterization of transfersomes gel performed by vesicle size, pH measurements, drug content, entrapment efficiency, in vitro drug diffusion study, spreadability and stability study. In the formulations pH is found to be around 6.8 to 6.9, pH is found in the range of 6 which is compatible with skin. In the formulations spreadability is found to be around 6.75 to 10.11 g m cm/sec. The prepared gel containing losartan potassium-loaded transfersomal formulation was optimized and can be use for topical preparation. The results were obtained which showed that transfersomal gel was a promising candidate for transdermal delivery with targeted and prolonged release of a drug. It also enhances skin permeation of many drugs.&#x0D; Keywords: Transferosome gel, Losartan potassium, Antihypertensives, Reverse phase evaporation method

Improved lipogenesis gene expression in liver is associated with elevated plasma angiotensin 1-7 after AT1 receptor blockade in insulin-resistant OLETF rats

Increased angiotensin II (Ang II) signaling contributes to insulin resistance and liver steatosis. In addition to ameliorating hypertension, angiotensin receptor blockers (ARBs) improve lipid metabolism and hepatic steatosis, which are impaired with metabolic syndrome (MetS). Chronic blockade of the Ang II receptor type 1 (AT1) increases plasma angiotensin 1-7 (Ang 1–7), which mediates mechanisms counterregulatory to AT1 signaling. Elevated plasma Ang 1–7 is associated with decreased plasma triacylglycerol (TAG), cholesterol, glucose, and insulin; however, the benefits of RAS modulation to prevent non-alcoholic fatty liver disease (NAFLD) are not fully investigated. To better address the relationships among chronic ARB treatment, plasma Ang 1–7, and hepatic steatosis, three groups of 10-week-old-rats were studied: (1) untreated lean Long Evans Tokushima Otsuka (LETO), (2) untreated Otsuka Long Evans Tokushima Fatty (OLETF), and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/d × 6 weeks). Following overnight fasting, rats underwent an acute glucose load to better understand the dynamic metabolic responses during hepatic steatosis and early MetS. Tissues were collected at baseline (pre-load; T0) and 1 and 2 h post-glucose load. AT1 blockade increased plasma Ang 1–7 and decreased liver lipids, which was associated with decreased fatty acid transporter 5 (FATP5) and fatty acid synthase (FASN) expression. AT1 blockade decreased liver glucose and increased glucokinase (GCK) expression. These results demonstrate that during MetS, overactivation of AT1 promotes hepatic lipid deposition that is stimulated by an acute glucose load and lipogenesis genes, suggesting that the chronic hyperglycemia associated with MetS contributes to fatty liver pathologies via an AT1-mediated mechanism.

Angiotensin II type 1 receptor blockade attenuates gefitinib-induced cardiac hypertrophy via adjusting angiotensin II-mediated oxidative stress and JNK/P38 MAPK pathway in a rat model

Gefitinib is a tyrosine kinase inhibitor (TKI) of the epidermal growth factor receptor (EGFR), used for the treatment of advanced or metastatic non-small cell lung cancer. Recently, studies proved that Gefitinib-induced cardiotoxicity through induction of oxidative stress leads to cardiac hypertrophy. The current study was conducted to understand the mechanisms underlying gefitinib-induced cardiac hypertrophy through studying the roles of angiotensin II (AngII), oxidative stress, and mitogen-activated protein kinase (MAPK) pathway. Male Wistar albino rats were treated with valsartan, gefitinib, or both for four weeks. Blood samples were collected for AngII and cardiac markers measurement, and hearts were harvested for histological study and biochemical analysis. Gefitinib caused histological changes in the cardiac tissues and increased levels of cardiac hypertrophy markers, AngII and its receptors. Blocking of AngII type 1 receptor (AT1R) via valsartan protected hearts and normalized cardiac markers, AngII levels, and the expression of its receptors during gefitinib treatment. valsartan attenuated gefitinib-induced NADPH oxidase and oxidative stress leading to down-regulation of JNK/p38-MAPK pathway. Collectively, AT1R blockade adjusted AngII-induced NADPH oxidase and JNK/p38-MAPK leading to attenuation of gefitinib-induced cardiac hypertrophy. This study found a pivotal role of AngII/AT1R signaling in gefitinib-induced cardiac hypertrophy, which may provide novel approaches in the management of EGFRIs-induced cardiotoxicity.

Клинико-фармакологические особенности и место ирбесартана в лечении сердечно-сосудистых заболеваний

Irbesartan belongs to a group of angiotensin II receptor blockers that are used worldwide for the treatment of patients with hypertension, type 2 diabetes, and impaired renal function. Irbesartan can be administered alone or in combination with other antihypertensive drugs (for example, hydrochlorothiazide), if blood pressure control cannot be achieved with monotherapy. The mechanism of action of Irbesartan is mainly due to the selective blockade of AT1 receptors and, as a consequence, a decrease in the vasopressor effect of angiotensin II. The review article summarizes pharmacokinetic and pharmacodynamic properties and clinical data on the tolerability and safety of Irbesartan.

PERMISSIVE ROLE OF ANGIOTENSIN II IN MANTENANCE OF ENDOTHELIUM-DEPENDENT VASODILATION IN CEREBRAL MICROCIRCULATION

Objective: A number of data suggest, rather controversial, permissive role of angiotensin II (ANGII) in maintaining vasodilator responses in microcirculation, via its interaction with AT1 receptors (AT1R). This study aimed to determine the role of ANGII and AT1R in the mechanisms of flow-induced dilation (FID) in middle cerebral arteries (MCA) and incidence of oxidative stress at the functional, cellular and molecular level in the cerebral vasculature and in the serum of Sprague-Dawley (SD) rats fed high salt diet (HS). Design and method: Eleven-week old, male SD rats were randomly assigned to control group (CTRL, 0.4% NaCl in rat chow); Losartan group (rats on a standard diet given the AT1R blocker losartan (1 mg/mL) in drinking water); HS group (7 days 4% NaCl in rat chow) or HS+ANGII group (7 days HS with 3 days ANGII administration via osmotic minipumps (100 ng/kg/min on days 4–7)). FID of MCA was determined in absence/presence of the NOS inhibitor L-NAME, the non-selective cyclooxygenases inhibitor indomethacin, and the superoxide dismutase mimetic TEMPOL. Gene and protein expression of antioxidative enzymes and enzymes involved in FID mechanisms were determined by RT-qPCR and western blot. Vascular NO and superoxide/ROS levels were assessed by direct fluorescence. Serum systemic oxidative stress parameters was measured by spectrophotometry. All experimental procedures conformed to the EU Directive 2010/63/EU. Results: HS or AT1R blockade impaired FID and increased oxidative stress. Supplementation of ANGII restored the mechanisms of FID in MCA of rats fed HS diet to the ones present in CTRL rats without affecting arterial blood pressure by decreasing systemic oxidative stress and decreasing superoxide/ROS levels and increased NO bioavailability in the vascular wall of HS treated rats. The AT1R blockade resulted in significantly attenuated endothelium-dependent dilation, changed mechanisms of FID, increased vascular and systemic oxidative stress and decreased expression/ activity of antioxidative enzymes. Conclusions: ANGII is crucial in the preservation of vascular oxidative stress-antioxidant system balance and via AT1R, in maintenance of physiological vasodilation mechanisms of MCA. Suppression of ANGII is a key link between HS intake and development of endothelial dysfunction, and impaired regulation of cerebral blood flow.

Vasoconstrictor and Pressor Effects of Des-Aspartate-Angiotensin I in Rat.

This study investigated the vasoactive effects of des-aspartate-angiotensin-I (DAA-I) in male Wistar rats on whole body vascular bed, isolated perfused kidneys, and aortic rings. Dose–response curves to DAA-I were compared with those to angiotensin II (Ang II). The Ang II-type-1 (AT1) receptor blocker, losartan, was used to evaluate the role of AT1 receptors in the responses to DAA-I. Studies were also conducted of the responsiveness in aortic rings after endothelium removal, nitric oxide synthase inhibition, or AT2 receptor blockade. DAA-I induced a dose-related systemic pressor response that was shifted to the right compared with Ang II. Losartan markedly attenuated the responsiveness to DAA-I. DAA-I showed a similar pattern in renal vasculature and aortic rings. In aortic rings, removal of endothelium and nitric oxide inhibition increased the sensitivity and maximal response to DAA-I and Ang II. AT2 receptor blockade did not significantly affect the responsiveness to DAA-I. According to these findings, DAA-I increases the systemic blood pressure and vascular tone in conductance and resistance vessels via AT1 receptor activation. This vasoconstrictor effect of DAA-I participates in the homeostatic control of arterial pressure, which can also contribute to the pathogenesis of hypertension. DAA-I may therefore be a potential therapeutic target in cardiovascular disease.

AT1R blockade together with AT2R stimulation prevents aortic aneurysm in mice with progressively severe Marfan syndrome

Angiotensin II receptor signaling regulate vascular tone by stimulating either vasoconstriction (AT1R) or vasodilation (AT2R). AT1R antagonism (via losartan) has been shown to mitigate thoracic aortic aneurysm (TAA) progression in mouse models of Marfan syndrome (MFS). Here we monitored multiple pathological readouts of TAA in MFS mice chronically treated for 90 days with either losartan, the AT2R agonist C21, or both. While C21 had no apparent effects on arterial disease by itself, it significantly enhanced losartan’s efficacy by preventing death of MFS mice from ruptured TAA during the treatment period. Specifically, the combination therapy normalized the diameters of the aortic root and ascending aorta, the architecture of the vessel wall, endothelial‐dependent relaxation, and circumferential wall strength (a strong biomechanical indicator of aneurysmal vulnerability). Computational analyses of bulk RNASeq data predicted that the combination therapy largely decreased expression of abnormally upregulated genes, principally those associated with inflammatory pathways. By contrast, these in silico analyses predicted no modifications of signaling pathways associated with dysregulated mitochondrial energy metabolism. Ongoing investigations are using single cell RNASeq to identify the different cell types targeted by the two drugs used in combination therapy, as well as potential cell‐cell interactions that underlie the efficacy of the combination therapy.

Abstract 543: Inhibition Of Renin-angiotensin System Failed To Suppress Beta-aminopropionitrile-induced Thoracic Aortopathies In Mice

Objective: Cross-linking of elastin and collagen fibers is a vital process in aortic development. Pharmacological inhibition of aortic cross-linking by β-aminopropionitrile (BAPN) leads to thoracic aortopathies, such as thoracic aortic aneurysm and dissection, in mice. Although the renin angiotensin system (RAS) contributes to several types of thoracic aortopathies, it remains unclear whether inhibition of the RAS protects against aortopathy formation caused by the impairment of elastin and collagen cross-linking in mice. Approach and Results: Either vehicle or losartan (15 mg/kg/d, AT1 receptor blocker) were administered through osmotic pumps for 4 weeks in male C57BL/6J mice (3-4-weeks-old, n=30/group). BAPN (0.5% wt/vol) was given through drinking water to induce aortopathies. Losartan increased plasma renin concentrations significantly compared to vehicle-infused mice, indicating effective blockade of at1 receptors. However, losartan did not suppress BAPN-induced aortic rupture and dilatation. Since losartan is a surmountable inhibitor, we also tested the effects of irbesartan, an insurmountable inhibitor of AT1 receptor blocker, on BAPN-induced aortopathy formation (50 mg/kg/day, diet, n=30/group). Despite the significant increase of plasma renin concentrations, irbesartan did not ameliorate aortic rupture and dilatation in BAPN-administered mice. Thus, BAPN-induced thoracic aortopathies were refractory to angiotensin receptor blockade. We next inhibited angiotensinogen, the unique substrate for angiotensin II, using an antisense oligonucleotide targeting angiotensinogen (AGT-ASO). AGT-ASO decreased plasma angiotensinogen concentrations, while aortic death and dilatations were not attenuated. Since hepatocytes are the major source of angiotensinogen, BAPN-induced thoracic aortopathy formation was also examined in mice with hepatocyte-specific angiotensinogen deletion. Although plasma angiotensinogen concentrations displayed 90% reduction compared to wild type littermates, aortic rupture and aneurysm formation were not suppressed. Conclusion: Inhibition of the RAS does not attenuate BAPN-induced thoracic aortopathy formation in mice.

Angiotensin Type-2 Receptors: Transducers of Natriuresis in the Renal Proximal Tubule.

Angiotensin II (Ang II) type-2 receptors (AT2R) are expressed in the adult kidney, prominently in renal proximal tubule cells (RPTCs), and play an important role in opposing renal sodium (Na+) retention induced by Ang II stimulation of Ang II type-1 receptor (AT1R). Natriuresis induced by AT1R blockade is due at least in part to AT2R activation and whole body deletion of AT2Rs reduces the natriuretic response to increased blood pressure (BP). The major endogenous AT2R agonist mediating the natriuretic response is Ang III, the Ang II heptapeptide metabolite generated by aminopeptidase A, and the principal nephron site mediating inhibition of Na+ reabsorption by the AT2R is the renal proximal tubule (RPT). AT2Rs induce natriuresis via a bradykinin, nitric oxide and cyclic GMP (cGMP) signaling cascade. Recent studies demonstrated a key role for protein phosphatase 2A (PP2A) in the AT2R-mediated natriuretic response upstream of cGMP. By inducing natriuresis, AT2Rs lower BP in the Ang II-infusion model of hypertension. PP2A activation and the natriuretic response to AT2R stimulation are defective in spontaneously hypertensive rats, a model of primary hypertension in humans. AT2R agonists are candidates for proximal tubule natriuretic agents in Na+ and fluid retention disorders.

Spectral analysis of cardiovascular oscillations in the 7-day regimen of losartan administration with and without cold stress.

Spectral analysis of heart rate (HR) and blood pressure (BP) variabilities (BPV and HRV) is widely available and utilized in understanding the dynamic cardiovascular autonomic regulation in a variety of pathophysiological conditions. In conscious cold-stressed (CS) rats, we examined the effect of a 7-day regimen administration of losartan, a selective nonpeptide angiotensin AT1 receptor blockade, on BPV and HRV at three frequency components: very-low frequency (VLF), low frequency (LF), and high frequency (HF). Key findings in changes of systolic BP (SBP), HR, and spectral power densities for cardiopulmonary oscillations (HF), sympathetic oscillations (LF), cardiovascular myogenic oscillations (VLF), and overall autonomic activity total power (TP) showed: (I) In the resting PreCS trial, compared with the saline, losartan increased HFBPV, TPHRV, all three HRV frequency powers, and the occurrence of the dicrotic notch (DN). However, it decreased SBP, HR, and the LFBPV frequency power. (II) In the CS trial, losartan significantly decreased SBP and DN occurrence and HR and LF/HFHRV but significantly increased HFHRV, TPBPV, and all three BPV frequency powers. In addition, similar to the saline, losartan showed positively correlated LFBPV and VLFBPV. Conversely, losartan converted the original inverse correlations between LFHRV and LFBPV of CS to a positive correlation. (III) Compared with saline in PreCS and CS trials, losartan detached the corresponding sympathetic oscillations between LFBPV and LFHRV. The overall result indicates that endogenous angiotensin II, through stimulation of the AT1 receptor, augments sympathetic tone but attenuates sympathetic oscillations in rats, particularly under the stressful cooling impacts.