Counteraction between angiotensin II and angiotensin-(1-7) via activating angiotensin type I and Mas receptor on rat renal mesangial cells.

In the updated concept of renin-angiotensin system (RAS), it contains the angiotensin converting enzyme (ACE)-angiotensin (Ang) II-angtiogensin type 1 receptor (AT1) axis and the angiotensin-converting enzyme-related carboxypeptidase (ACE2)-Ang-(1-7)-Mas axis. The former axis has been well demonstrated performing the vasoconstrictive, proliferative and pro-inflammatory functions by activation of AT1 receptors, while the later new identified axis is considered counterbalancing the effects of the former. The present study is aimed at observing the interaction between Ang-(1-7) and Ang II on cultured rat renal mesangial cells (MCs). RT-PCR, Western blot and immunofluorescent staining and confocal microscopy results showed that both AT1 and Mas receptor were co-distributed in rat renal MCs. Ang-(1-7) showed similar effects on Ang II in cultured MCs that stimulated phosphorylated extracellular signal-regulated kinase (ERK)1/2 phosphorylation and transforms growth factor-ß1 synthesis, and cell proliferation and extracellular matrix synthesis. Co-treatment of the cell with Ang-(1-7) and Ang II, Ang-(1-7) counteracted AngII-induced effects in a concentration dependent manner, but failed to alter the changes induced by endothelin-1. The stimulating effect of Ang II was mediated by AT1 receptor while all the effects of Ang-(1-7) were blocked by Mas receptor antagonist A-779, but not by AT1 receptor antagonist losartan or AT2 receptor antagonist PD123319. These results suggest that Ang-(1-7) and Ang II specifically interact with each other on rat renal MCs via activation of their specific receptors, Mas and AT1 receptor respectively.

Angiotensin-(3-4) counteracts the Angiotensin II inhibitory action on renal Ca2+-ATPase through a cAMP/PKA pathway.

We recently demonstrated that Angiotensin-(3-4) [Ang-(3-4)], an Ang II-derived dipeptide, overcomes inhibition of plasma membrane Ca(2+)-ATPase promoted by nanomolar concentrations of Ang II in basolateral membranes of renal proximal tubule cells, with involvement of a so far unknown AT(2)R-dependent and NO-independent mechanism. The present study investigates the signaling pathway triggered by Ang-(3-4) that is responsible for counteracting the inhibitory effect of Ang II, and attempts to elucidate the functional interaction of the dipeptide with Ang II at the level of AT(2)R. Stimulation by cholera toxin of G(s)α protein structurally linked to AT(2)R--as revealed by their co-immunoprecipitation--mimicked the effect of Ang-(3-4) on Ca(2+)-ATPase activity. Furthermore, addition of dibutyril-cAMP (db-cAMP) mimicked Ang-(3-4), whereas the specific PKA inhibitor, PKAi(5-24) peptide, suppressed the counter-regulatory effect of Ang-(3-4) and the AT(2)R agonist, CGP42112A. Membrane-associated PKA activity was stimulated by Ang-(3-4) or CGP42112A to comparable levels as db-cAMP, and the Ang-(3-4) effect was abrogated by the AT(2)R antagonist PD123319, whereas the AT(1)R antagonist Losartan had no effect. Ang-(3-4) stimulated PKA-mediated phosphorylation of Ca(2+)-ATPase and activated PKA to comparable levels. Binding assays demonstrated that Ang-(3-4) could not displace (3)H-Ang II from HEK 293T cells expressing AT(2)R, but 10(-10) mol/L Ang-(3-4) resulted in the appearance of a probable higher-affinity site (picomolar range) for Ang II. The results presented herein demonstrate that Ang-(3-4), acting as an allosteric enhancer, suppresses Ang II-mediated inhibition of Ca(2+)-ATPase through an AT(2)R/cAMP/PKA pathway, after inducing conformational changes in AT(2)R that results in generation of higher-affinity sites for Ang II.

Activation of PPARδ counteracts angiotensin II-induced ROS generation by inhibiting rac1 translocation in vascular smooth muscle cells.

Angiotensin II (Ang II)-mediated modification of the redox milieu of vascular smooth muscle cells (VSMCs) has been implicated in several pathophysiological processes, including cell proliferation, migration and differentiation. In this study, we demonstrate that the peroxisome proliferator-activated receptor (PPAR) δ counteracts Ang II-induced production of reactive oxygen species (ROS) in VSMCs. Activation of PPARδ by GW501516, a specific ligand for PPARδ, significantly reduced Ang II-induced ROS generation in VSMCs. This effect was, however, reversed in the presence of small interfering (si)RNA against PPARδ. The marked increase in ROS levels induced by Ang II was also eliminated by the inhibition of phosphatidylinositol 3-kinase (PI3K) but not of protein kinase C, suggesting the involvement of the PI3K/Akt signalling pathway in this process. Accordingly, ablation of Akt with siRNA further enhanced the inhibitory effects of GW501516 in Ang II-induced superoxide production. Ligand-activated PPARδ also blocked Ang II-induced translocation of Rac1 to the cell membrane, inhibiting the activation of NADPH oxidases and consequently ROS generation. These results indicate that ligand-activated PPARδ plays an important role in the cellular response to oxidative stress by decreasing ROS generated by Ang II in vascular cells.

Effects of proangiotensin-12 infused continuously over 14 days in conscious rats.

The carboxyl terminal-extended form of angiotensin I, proangotensin-12, was recently identified in rat tissues including the small intestine, cardiac ventricles, and kidneys. Single administration of proangiotensin-12 exerts vasoconstrictor and pressor effects, probably by conversion to angiotensin II; however, there are currently no data available about the subacute effects of proangiotensin-12. In the present study, we examined the effects of prolonged infusion of proangiotensin-12 in conscious rats. Continuous, subcutaneous infusion of 240 pmol/kg/min of proangiotensin-12 gradually elevated blood pressure over 14 days, as did the same dose of angiotensin II. The pressor effects of proangiotensin-12 were abolished by oral administration of losartan, an angiotensin II type 1 receptor blocker, or perindopril, an angiotensin converting enzyme (ACE) inhibitor. Meanwhile, angiotensin II-induced elevation of blood pressure was inhibited by losartan but not by perindopril. Both the plasma aldosterone level and heart weight/body weight ratio were increased by the prolonged infusion of proangiotensin-12, but these increases were attenuated by losartan and perindopril. The present results suggest that proangiotensin-12 infused continuously over 14 days exerts pressor effects accompanied with the elevation of plasma aldosterone and cardiac hypertrophy in an ACE- and angiotensin II type 1 receptor-dependent manner.

Angiotensin II receptor type 1 blockers suppress the cell proliferation effects of angiotensin II in breast cancer cells by inhibiting AT1R signaling.

Chronic stress and a high-fat diet are well-documented risk factors associated with the renin-angiotensin system in the development of breast cancer. The angiotensin II type 1 receptor (AT1R) is a novel component of the renin-angiotensin system. Several recent studies have focused on the function of AT1R in cell proliferation during cancer development. Thus, we hypothesized that angiotensin II (Ang Ⅱ) can promote proliferation of breast cancer via activated AT1R; the activation of AT1R may play an important role in promoting breast cancer growth, and AT1R blocker (ARB) may suppress the promotional effect on proliferation by antagonizing AT1R. The expression level of AT1R was found to be significantly upregulated in breast cancer cells by immunohistochemistry, but no correlation between AT1R expression and ER/PR/Her-2 expression was observed. The AT1R(+)-MCF-7 cell line exhibited high expression of AT1R protein, and we generated the AT1R(-)-MCF-7 cell line using RNA interference. ARBs, and in particular irbesartan, effectively inhibited the effects of Ang II on cell proliferation, cell cycle development and downstream AT1R signaling events, including the activation of the Ras-Raf-MAPK pathway and the transcription factors NF-κB and CREB. Irbesartan also significantly altered p53, PCNA and cyclin D1 expression, which was also influenced by activated AT1R in AT1R(+)-MCF-7 cells. These results suggest that ARBs may be useful as a novel preventive and therapeutic strategy for treating breast cancer.

Assessment of the environmental fate and effects of azilsartan, a selective antagonist of angiotensin II type 1.

In this paper the results of a thorough evaluation of the environmental fate and effects of azilsartan are presented. Azilsartan medoxomil is administered as a pro-drug for the treatment of patients with essential hypertension. The pro-drug is converted by hydrolysis to the active pharmaceutical ingredient azilsartan. Laboratory tests to evaluate the environmental fate and effects of azilsartan medoxomil were conducted with azilsartan and performed in accordance with OECD test guidelines. The predicted environmental concentration (PEC) in surface water was estimated at 0.32 µg L(-1) (above the action limit of 0.01 µg L(-1)), triggering a Phase II assessment. Azilsartan is not readily biodegradable. Results of the water sediment study demonstrated significant shifting of azilsartan metabolites to sediment. Based on the equilibrium partitioning method, metabolites are unlikely to pose a risk to sediment-dwelling organisms. Ratios of the predicted environmental concentrations (PECs) to the predicted-no-effect concentrations (PNECs) did not exceed the relevant triggers, and the risk to aquatic, sewage treatment plant (STP), groundwater and sediment compartments was concluded acceptable. A terrestrial assessment was not triggered. Azilsartan poses an acceptable risk to the environment.

Role of angiotensin II-mediated AMPK inactivation on obesity-related salt-sensitive hypertension.

Salt-sensitive hypertension is a characteristic of the metabolic syndrome. Given the links to cardiovascular events, the mechanisms underlying sodium metabolism may represent an important therapeutic target for this disorder. Angiotensin II (AII) is a key peptide underlying sodium retention. However, 5'AMP-activated protein kinase (AMPK) has also been reported to participate in the regulation of ion transport. In this study we examined the relationship between AII and AMPK on the development of hypertension in two salt-sensitive mouse models. In the first model, the mice were maintained on a high-fat diet (HFD) for 12 weeks, in order to develop features similar to the metabolic syndrome, including salt-sensitive hypertension. HFD-induced obese mice showed elevated systolic blood pressure and lower sodium excretion in response to salt loading, along with an increase in AII contents and inactivation of AMPK in the kidney, which were significantly improved by the treatment of an angiotensin II antagonist, losartan, for 2 weeks. To clarify the effects of AII, a second group of mice was infused with AII via an osmotic pump, which led to higher systolic blood pressure, and decreases in urinary sodium excretion and the expression of AMPK, in a manner similar to those observed in the HFD mice. However, treatment with an AMPK activator, metformin, improved the changes induced by the AII, suggesting that AII induced sodium retention works by acting on AMPK activity. Finally, we evaluated the changes in salt-sensitivity by performing 2-week salt loading experiments with or without metformin. AII infusion elevated blood pressure by salt loading but metformin prevented it. These findings indicate that AII suppresses AMPK activity in the kidney, leading to sodium retention and enhanced salt-sensitivity, and that AMPK activation may represent a new therapeutic target for obesity-related salt-sensitive hypertension.

Angiotensin II-aldosterone interaction in human coronary microarteries involves GPR30, EGFR, and endothelial NO synthase.

AIMS: The aim of this study was to investigate the aldosterone-angiotensin (Ang) II interaction in human coronary microarteries (HCMAs). METHODS AND RESULTS: HCMAs, obtained from 75 heart-beating organ donors, were mounted in myographs and exposed to Ang II, either directly or following a 30-min pre-incubation with aldosterone, 17ß-oestradiol, hydrocortisone, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580, the extracellular regulated kinase 1/2 (ERK1/2) inhibitor PD98059, the GPR30 antagonist G15, or the epidermal growth factor receptor (EGFR) antagonist AG1478. Ang II constricted HCMAs in a concentration-dependent manner. All steroids, at nanomolar levels, potentiated Ang II and G15 prevented this effect. The potentiation disappeared or was reversed into Ang II antagonism at micromolar steroid levels. NO synthase (NOS) inhibition prevented the latter antagonism in the case of 17ß-oestradiol, whereas both aldosterone and 17ß-oestradiol at micro- (but not nano-) molar levels induced endothelial NOS phosphorylation in human umbilical vein endothelial cells. AG1478, but not SB203580 or PD98059, abolished the Ang II-induced contraction in the presence of aldosterone or 17ß-oestradiol, and none of these drugs affected Ang II alone. CONCLUSION: Steroids including aldosterone affect Ang II-induced vasoconstriction in a biphasic manner. Potentiation occurs at nanomolar steroid levels and depends on GPR30 and EGFR transactivation. At micromolar steroid levels, this potentiation either disappears (aldosterone and hydrocortisone) or is reversed into an inhibition (17ß-oestradiol), and this is due to the endothelial NOS activation that occurs at such concentrations.

The role of reactive oxygen species in the modulation of the contraction induced by angiotensin II in carotid artery from diabetic rat.

The modulation played by reactive oxygen species on the angiotensin II-induced contraction in type I-diabetic rat carotid was investigated. Concentration-response curves for angiotensin II were obtained in endothelium-intact or endothelium-denuded carotid from control or streptozotocin-induced diabetic rats, pre-treated with tiron (superoxide scavenger), PEG-catalase (hydrogen peroxide scavenger), dimethylthiourea (hydroxyl scavenger), apocynin [NAD(P)H oxidase inhibitor], SC560 (cyclooxygenase-1 inhibitor), SC236 (cyclooxygenase-2 inhibitor) or Y-27632 (Rho-kinase inhibitor). Reactive oxygen species were measured by flow cytometry in dihydroethidium (DHE)-loaded endothelial cells. Cyclooxygenase and AT(1)-receptor expression was assessed by immunohistochemistry. Diabetes increased the angiotensin II-induced contraction but reduced the agonist potency in rat carotid. Endothelium removal, tiron or apocynin restored the angiotensin II-induced contraction in diabetic rat carotid to control levels. PEG-catalase, DMTU or SC560 reduced the angiotensin II-induced contraction in diabetic rat carotid at the same extent. SC236 restored the angiotensin II potency in diabetic rat carotid. Y-27632 reduced the angiotensin II-induced contraction in endothelium-intact or -denuded diabetic rat carotid. Diabetes increased the DHE-fluorescence of carotid endothelial cells. Apocynin reduced the DHE-fluorescence of endothelial cells from diabetic rat carotid to control levels. Diabetes increased the muscular cyclooxygenase-2 expression but reduced the muscular AT(1)-receptor expression in rat carotid. In summary, hydroxyl radical, hydrogen peroxide and superoxide anion-derived from endothelial NAD(P)H oxidase mediate the hyperreactivity to angiotensin II in type I-diabetic rat carotid, involving the participation of cyclooxygenase-1 and Rho-kinase. Moreover, increased muscular cyclooxygenase-2 expression in type I-diabetic rat carotid seems to be related to the local reduced AT(1)-receptor expression and the reduced angiotensin II potency.

Losartan inhibits STAT1 activation and protects human glomerular mesangial cells from angiotensin II induced premature senescence.

Human glomerular mesangial cells (HMCs) have a finite lifespan, and eventually enter irreversible growth arrest known as cellular senescence, which is thought to contribute to kidney ageing and age-related kidney disorders, such as chronic kidney disease. The signal transducer and activator of transcription 1 (STAT1) is a latent transcription factor involved in a variety of signal transduction pathways, including cell proliferation, apoptosis, and differentiation, but whether it could regulate HMC senescence still remains to be explored. In our study, the induction of angiotensin II (Ang II)-accelerated HMC senescence, as judged by increased senescence-associated ß-galactosidase (SA-ß-gal)-positive staining cells, morphological changes, and G0/G1 cell cycle arrest. STAT1 activity and the expression of p53 and p21(Cip1) were increased after Ang II treatment. STAT1 knockdown using RNA interference significantly inhibited the progression of HMC senescence and decreased the elevated expression of p53 and p21(Cip1). Pretreating HMCs with Ang II receptor blocker losartan also inhibited the progression of HMC senescence and STAT1 activity. Our results indicate that STAT1 is implicated in the mediation of Ang II-induced HMC senescence through p53/ p21(Cip1) pathway, and that losartan could attenuate HMC senescence by regulating STAT1. The antioxidant N-acetyl-L-cysteine reduced ROS production and STAT1 activity induced by Ang II, indicating that Ang II uses ROS as a second messenger to regulate STAT1 activity.

Angiotensin II-dependent persistent podocyte loss from destabilized glomeruli causes progression of end stage kidney disease.

Podocyte depletion is a major mechanism driving glomerulosclerosis. Progression is the process by which progressive glomerulosclerosis leads to end stage kidney disease (ESKD). In order to determine mechanisms contributing to persistent podocyte loss, we used a human diphtheria toxin transgenic rat model. After initial diphtheria toxin-induced podocyte injury (over 30% loss in 4 weeks), glomeruli became destabilized, resulting in continued autonomous podocyte loss causing global podocyte depletion (ESKD) by 13 weeks. This was monitored by urine mRNA analysis and by quantitating podocytes in glomeruli. Similar patterns of podocyte depletion were found in the puromycin aminonucleoside and 5/6 nephrectomy rat models of progressive end-stage disease. Angiotensin II blockade (combined enalapril and losartan) restabilized the glomeruli, and prevented continuous podocyte loss and progression to ESKD. Discontinuing angiotensin II blockade resulted in recurrent glomerular destabilization, podocyte loss, and progression to ESKD. Reduction in blood pressure alone did not reduce proteinuria or prevent podocyte loss from destabilized glomeruli. The protective effect of angiotensin II blockade was entirely accounted for by reduced podocyte loss. Thus, an initiating event resulting in a critical degree of podocyte depletion can destabilize glomeruli and initiate a superimposed angiotensin II-dependent podocyte loss process that accelerates progression resulting in eventual global podocyte depletion and ESKD. These events can be monitored noninvasively in real-time through urine mRNA assays.

Angiotensin-II induced nitric oxide production during buffalo sperm capacitation and acrosome reaction.

The present study was designed to see the effects of Angiotensin-II (Ang-II) on buffalo sperm capacitation, acrosome reaction (AR), and its relation to nitric oxide (NO()) production. The extent of capacitation or AR was determined by dual staining while the NO() production was determined by spectrophotometry. The results thus obtained revealed that Ang-II induced capacitation in a concentration and time dependent manner and 200 nM Ang-II was found to be optimal for capacitation as it was comparable to heparin treatment (50.7±2.45% vs. 51.66±2.33%). In capacitated cells the extent of AR induced by Ang-II was significantly higher than the untreated control (48.13±2.31% vs. 22.16±2.11%) and comparable to lysophosphatidyl Choline (LPC) treatment (51.56±1.94%). The NO() production during Ang-II induced capacitation and AR was gradual and time dependent. These levels were significantly higher when compared to control (3.65±0.53 nmoles/10(8)cells vs. 9.12±0.30 nmoles/10(8)cells). All the actions of Ang-II were inhibited in the presence of Losartan but not PD123319, indicating the role of AT1 receptors in these actions. Further the NO() production was also significantly inhibited in the presence of neomycin and trifluoperazine pointing towards the role of phosphoinositide pathway in this process. In conclusion, Ang-II has a concentration and time dependent effect on buffalo sperm capacitation and AR, mediated via the AT1 receptors. Its effect on NO() production may be indirect involving the phosphoinositide pathway.

Reno-protective effects of renin-angiotensin system blockade in type 2 diabetic patients: a systematic review and network meta-analysis.

AIMS/HYPOTHESIS: This meta-analysis aimed to compare the renal outcomes between ACE inhibitor (ACEI)/angiotensin II receptor blocker (ARB) and other antihypertensive drugs or placebo in type 2 diabetes. METHODS: Publications were identified from Medline and Embase up to July 2011. Only randomised controlled trials comparing ACEI/ARB monotherapy with other active drugs or placebo were eligible. The outcome of end-stage renal disease, doubling of serum creatinine, microvascular complications, microalbuminuria, macroalbuminuria and albuminuria regression were extracted. Risk ratios were pooled using a random-effects model if heterogeneity was present; a fixed-effects model was used in the absence of heterogeneity. RESULTS: Of 673 studies identified, 28 were eligible (n = 13-4,912). In direct meta-analysis, ACEI/ARB had significantly lower risk of serum creatinine doubling (pooled RR = 0.66 [95% CI 0.52, 0.83]), macroalbuminuria (pooled RR = 0.70 [95% CI 0.50, 1.00]) and albuminuria regression (pooled RR 1.16 [95% CI 1.00, 1.39]) than other antihypertensive drugs, mainly calcium channel blockers (CCBs). Although the risks of end-stage renal disease and microalbuminuria were lower in the ACEI/ARB group (pooled RR 0.82 [95% CI 0.64, 1.05] and 0.84 [95% CI 0.61, 1.15], respectively), the differences were not statistically significant. The ACEI/ARB benefit over placebo was significant for all outcomes except microalbuminuria. A network meta-analysis detected significant treatment effects across all outcomes for both active drugs and placebo comparisons. CONCLUSIONS/INTERPRETATION: Our review suggests a consistent reno-protective effect of ACEI/ARB over other antihypertensive drugs, mainly CCBs, and placebo in type 2 diabetes. The lack of any differences in BP decrease between ACEI/ARB and active comparators suggest this benefit is not due simply to the antihypertensive effect.

Interference by o-phenanthroline in the radioimmunoassay of angiotensin II in small volume blood samples.

OBJECTIVES: To investigate the ratio of enzyme inhibitor volume to blood volume in angiotensin II (Ang II) blood collection tubes. DESIGN AND METHODS: Whole blood was mixed with known volumes of inhibitor prior to angiotensin II analysis. RESULTS: Imunoreactive Ang II levels increased at low blood volume to high inhibitor volume ratios, due to interference by o-phenanthroline. CONCLUSION: To prevent falsely elevated Ang II levels in low volume blood samples an appropriate volume of inhibitor solution must be used.

Angiotensinase and vasopressinase activities in hypothalamus, plasma, and kidney after inhibition of angiotensin-converting enzyme: basis for a new working hypothesis.

Reducing angiotensin II (Ang II) production via angiotensin-converting enzyme (ACE) inhibitors is a key approach for the treatment of hypertension. However, these inhibitors may also affect other enzymes, such as angiotensinases and vasopressinase, responsible for the metabolism of other peptides also involved in blood pressure control, such as Ang 2-10, Ang III, Ang IV, and vasopressin. We analyzed the activity of these enzymes in the hypothalamus, plasma, and kidney of normotensive adult male rats after inhibition of ACE with captopril. Aspartyl- (AspAP), glutamyl- (GluAP), alanyl- (AlaAP) and cystinyl-aminopeptidase (CysAP) activities were measured fluorimetrically using arylamides as substrates. Systolic blood pressure (SBP), water intake, and urine flow were also measured. Captopril reduced SBP and increased urine flow. In the hypothalamus, GluAP and AspAP increased, without significant changes in either AlaAP or CysAP. In contrast with effects in plasma, GluAP was unaffected, AspAP decreased, while AlaAP and CysAP increased. In the kidney, enzymatic activities did not change in the cortex, but decreased in the medulla. These data suggest that after ACE inhibition, the metabolism of Ang I in hypothalamus may lead mainly to Ang 2-10 formation. In plasma, the results suggest an increased formation of Ang IV together with increased vasopressinase activity. In the kidney, there is a reduction of vasopressinase activity in the medulla, suggesting a functional reduction of vasopressin in this location. The present data suggest the existence of alternative pathways in addition to ACE inhibition that might be involved in reducing BP after captopril treatment.

Regulation of alveolar fluid clearance and ENaC expression in lung by exogenous angiotensin II.

Angiotensin II (Ang II) has been demonstrated as a pro-inflammatory effect in acute lung injury, but studies of the effect of Ang II on the formation of pulmonary edema and alveolar filling remains unclear. Therefore, in this study the regulation of alveolar fluid clearance (AFC) and the expression of epithelial sodium channel (ENaC) by exogenous Ang II was verified. SD rats were anesthetized and were given Ang II with increasing doses (1, 10 and 100 µg/kg per min) via osmotic minipumps, whereas control rats received only saline vehicle. AT1 receptor antagonist ZD7155 (10 mg/kg) and inhibitor of cAMP degeneration rolipram (1 mg/kg) were injected intraperitoneally 30 min before administration of Ang II. The lungs were isolated for measurement of alveolar fluid clearance. The mRNA and protein expression of ENaC were detected by RT-PCR and Western blot. Exposure to higher doses of Ang II reduced AFC in a dose-dependent manner and resulted in a non-coordinate regulation of α-ENaC vs. the regulation of ß- and γ-ENaC, however Ang II type 1 (AT1) receptor antagonist ZD7155 prevented the Ang II-induced inhibition of fluid clearance and dysregulation of ENaC expression. In addition, exposure to inhibitor of cAMP degradation rolipram blunted the Ang II-induced inhibition of fluid clearance. These results indicate that through activation of AT(1) receptor, exogenous Ang II promotes pulmonary edema and alveolar filling by inhibition of alveolar fluid clearance via downregulation of cAMP level and dysregulation of ENaC expression.

Atenuação da remodelação ventricular após infarto agudo do miocárdio / Attenuation of ventricular remodeling after myocardial acute infarction

Após o infarto agudo do miocárdio podem ocorrer complexas alterações da arquitetura ventricular, envolvendo tanto a região infartada como a região não infartada. Há alguns anos, essas alterações passaram a ser designadas como remodelação ventricular pós-infarto. Do ponto de vista clínico, a remodelação está associada ao pior prognóstico após a oclusão coronária. Assim, a remodelação predispõe o coração infartado à ruptura ventricular e é o substrato fisiopatológico para a posterior formação do aneurisma ventricular. Cronicamente, a remodelação está associada com maior prevalência de arritmias malignas, principalmente a taquicardia ventricular sustentada e a fibrilação ventricular. O aspecto mais relevante da remodelação pós-infarto, no entanto, é que esse processo desempenha papel fundamental na fisiopatologia da disfunção ventricular. Aspecto a ser considerado refere-se ao fato de que a evolução do processo de remodelação pode ser modificado por meio de diversas intervenções terapêuticas. Entre as estratégias para atenuar a remodelação ventricular destacam-se: terapia de reperfusão, inibidores da enzima conversora da angiotensina e antagonistas da angiotensina II, betabloqueadores, antagonistas da aldosterona e dispositivos de assistência circulatória.

After acute myocardial infarction (AMI), complex changes in ventricular architecture may occur involving the infarcted and the non-infarcted region. This set of adaptations, which includes changes in the composition, mass, volume and geometry of the heart, is known as myocardial remodeling. In relation to clinical significance, the intensity of the ventricular remodeling process is directly associated with worse prognosis, due to the higher incidence of aneurysm formation, ventricular rupture and arrhythmia, and is also associated with the progression of ventricular dysfunction. A relevant aspect to be considered is that a number of strategies have been employed to prevent or mitigate the process of ventricular remodeling following AMI, for instance: reperfusion therapy, angiotensin converting enzyme inhibitors and angiotensin II antagonists, beta-adrenergic receptor blockade, aldosterone antagonists, and left ventricular assist devices.

Targeting cardiac mast cells: pharmacological modulation of the local renin-angiotensin system.

Enhanced production of angiotensin II and excessive release of norepinephrine in the ischemic heart are major causes of arrhythmias and sudden cardiac death. Mast cell-dependent mechanisms are pivotal in the local formation of angiotensin II and modulation of norepinephrine release in cardiac pathophysiology. Cardiac mast cells increase in number in myocardial ischemia and are located in close proximity to sympathetic neurons expressing angiotensin AT1- and histamine H3-receptors. Once activated, cardiac mast cells release a host of potent pro-inflammatory and pro-fibrotic cytokines, chemokines, preformed mediators (e.g., histamine) and proteases (e.g., renin). In myocardial ischemia, angiotensin II (formed locally from mast cell-derived renin) and histamine (also released from local mast cells) respectively activate AT1- and H3-receptors on sympathetic nerve endings. Stimulation of angiotensin AT1-receptors is arrhythmogenic whereas H3-receptor activation is cardioprotective. It is likely that in ischemia/reperfusion the balance may be tipped toward the deleterious effects of mast cell renin, as demonstrated in mast cell-deficient mice, lacking mast cell renin and histamine in the heart. In these mice, no ventricular fibrillation occurs at reperfusion following ischemia, as opposed to wild-type hearts which all fibrillate. Preventing mast cell degranulation in the heart and inhibiting the activation of a local renin-angiotensin system, hence abolishing its detrimental effects on cardiac rhythmicity, appears to be more significant than the loss of histamine-induced cardioprotection. This suggests that therapeutic targets in the treatment of myocardial ischemia, and potentially congestive heart failure and hypertension, should include prevention of mast cell degranulation, mast cell renin inhibition, local ACE inhibition, ANG II antagonism and H3-receptor activation.

Propofol attenuates angiotensin II-induced apoptosis in human coronary artery endothelial cells.

BACKGROUND: Angiotensin II (Ang II) induces oxidative stress and apoptosis in vascular endothelial cells. We hypothesized that propofol may attenuate Ang II-induced apoptosis in human coronary artery endothelial cells (HCAECs) and aimed to identify the underlying mechanisms. METHODS: Endothelial cells were pre-treated with propofol and then stimulated with Ang II. Apoptosis was examined by TUNEL, DNA laddering, and caspase-3 activity assays. The effect of propofol on Ang II-modulated NADPH oxidase expression and activity, nitric oxide synthase III (NOSIII) expression and phosphorylation and activity, lipid peroxidation, superoxide anion generation, nitric oxide production, caspase activity, and protein expression of cytochrome c, Bcl-2, and C-IAP-1 were measured. RESULTS: Ang II induced apoptosis, which was attenuated by 50 µM propofol (P<0.05). Propofol ameliorated Ang II-induced NADPH oxidase expression and activation (P<0.01), lipid peroxidation (P<0.05), and superoxide anion generation (P<0.05), whereas restoring NOSIII phosphorylation and activity (P<0.01) were down-regulated by Ang II. Propofol attenuated Ang II-modulated cytochrome c release, and the expression of Bcl-2 and C-IAP-1. In addition, propofol inhibited Ang II-induced caspase-9 (P<0.01) and caspase-3 activity (P<0.01). CONCLUSIONS: Propofol protected HCAECs from Ang II-induced apoptosis by interfering with the generation of oxidative stress and redox-sensitive apoptotic pathways.

Angiotensin II as a morphogenic cytokine stimulating renal fibrogenesis.

Inhibitors of the renin-angiotensin-aldosterone system attenuate glomerulosclerosis and interstitial fibrosis. Although the mechanisms underlying their antifibrotic effects are complex, angiotensin II (Ang II) emerges as a major profibrogenic cytokine. Ang II modulates renal cell growth, extracellular matrix synthesis, and degradation by multiple fibrotic pathways. One of the main targets of Ang II in renal fibrosis is TGFß. Many, but not all, of the stimulatory effects of Ang II on fibrogenesis depend on the induction of TGFß and its downstream mediators of matrix accumulation, inflammation, and apoptosis. However because of the difficulty in targeting TGFß, connective tissue growth factor ß (CTGF), a downstream mediator of TGFß, has become a more promising antifibrotic target. Ang II can directly induce expression of renal CTGF and mediate epithelial-mesenchymal transition. Other profibrotic factors stimulated by Ang II include endothelin-1, plasminogen activator inhibitor-1, matrix metalloproteinase (MMP)-2, and a tissue inhibitor of metalloproteinase-2. Finally, connections among Ang II, hypoxia, and the induction of hypoxia-inducible factor-1α contribute to fibrogenesis. A better understanding of the multiple morphogenic effects of Ang II may be necessary to develop better strategies to halt the progression of renal disease.