Local cardiac renin-angiotensin system: hypertension and cardiac failure

Research hotspots and trends regarding microRNAs in hypertension: a bibliometric analysis

To investigate the research levels, hotspots, and development trends regarding microRNAs in hypertension, this study conducted a visual analysis of studies on miRNA in hypertension based on the Web of Science core collection database using CiteSpace and VOSviewer analysis software along with literature from 2005-2023 as information data. Using citation frequency, centrality, and starting year as metrics, this study analyzed the research objects. It revealed the main research bodies and hotspots and evaluated the sources of literature and the distribution of knowledge from journals and authors. Finally, the potential research directions for miRNAs in hypertension are discussed. The results showed that the research field is in a period of vigorous development, and scholars worldwide have shown strong interest in this research field. A comprehensive summary and analysis of the current research status and application trends will prove beneficial for the advancement of this field.

Metformin induction of heat shock factor 1 activation and the mitochondrial unfolded protein response alleviate cardiac remodeling in spontaneously hypertensive rats

Heart failure and cardiac remodeling are both characterized by mitochondrial dysfunction. Healthy mitochondria are required for adequate contractile activity and appropriate regulation of cell survival. In the mammalian heart, enhancement of the mitochondrial unfolded protein response (UPRmt) is cardioprotective under pressure overload conditions. We explored the UPRmt and the underlying regulatory mechanism in terms of hypertension-induced cardiac remodeling and the cardioprotective effect of metformin. Male spontaneously hypertensive rats and angiotensin II-treated neonatal rat cardiomyocytes were used to induce cardiac hypertrophy. The results showed that hypertension induced the formation of aberrant mitochondria, characterized by a reduced mtDNA/nDNA ratio and swelling, as well as lower levels of mitochondrial complexes I to V and inhibition of the expression of one protein subunit of each of complexes I to IV. Such changes eventually enlarged cardiomyocytes and increased cardiac fibrosis. Metformin treatment increased the mtDNA/nDNA ratio and regulated the UPRmt, as indicated by increased expression of activating transcription factor 5, Lon protease 1, and heat shock protein 60, and decreased expression of C/EBP homologous protein. Thus, metformin improved mitochondrial ultrastructure and function in spontaneously hypertensive rats. In vitro analyses revealed that metformin reduced the high levels of angiotensin II-induced mitochondrial reactive oxygen species in such animals and stimulated nuclear translocation of heat shock factor 1 (HSF1). Moreover, HSF1 small-interfering RNA reduced the metformin-mediated improvements in mitochondrial morphology and the UPRmt by suppressing hypertrophic signals and cardiomyocyte apoptosis. These results suggest that HSF1/UPRmt signaling contributes to the beneficial effects of metformin. Metformin-mediated targeting of mitochondrial protein homeostasis and modulation of HSF1 levels have potential therapeutic implications in terms of cardiac remodeling.

Anti-hypertension effect of Wuwei Jiangya decoction via ACE2/Ang1-7/MAS signaling pathway in SHR based on network degree-distribution analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Wuwei Jiangya decoction (WJD) is a traditional Chinese medicinal formula (Fangji) composed of Gastrodiae Rhizoma, Chuanxiong Rhizoma, Puerariae Lobatae Radix, Cyathulae Radix, and Achyranthis Bidentatae Radix, all of which have been verified to combat hypertension. However, the integrative "shot-gun" mechanism of WJD and its primary active ingredients are still unclear.

AIM OF THE STUDY

To investigate the anti-hypertensive effects of WJD and its originating ingredients.

METHODS

Network-based degree distribution analysis combined with in vivo experiments were performed.

RESULTS

A total of 144 active ingredients in WJD were identified to regulate 84 hypertension-related targets, which are mainly involved in blood pressure and blood vessel diameter regulation. However, for the anti-hypertension effects, "more does not mean better". The majority (76%) of the hubs in the H-network were regulated by no more than four ingredients. We identified 16 primary ingredients that accounted for the therapeutic action against hypertension. For compatibility, the five herbs consistently focused on blood pressure, vascular diameter, and angiogenesis, with the renin-angiotensin system as a primary target. The characteristics of each herb were involved in processes such as lipid localization and oxidative stress, which interact to constitute the regulatory network targeting hypertension, its risk factors, and organ damage. In vivo, WJD significantly reduced systolic blood pressure (SBP), improved left ventricular mass index, and ameliorated cardiac hypertrophy and vascular injury by moderating the renin-angiotensin system via activating the ACE2/Ang-(1-7)/Mas signaling pathway.

CONCLUSION

WJD can lower SBP and ameliorate cardiac hypertrophy and vascular injury through the ACE2/Ang-(1-7)/Mas pathway, thus providing new insights into the development of traditional Chinese medicine as a therapeutic agent for hypertension.

Stem cell‐derived extracellular vesicles reduce the expression of molecules involved in cardiac hypertrophy—In a model of human-induced pluripotent stem cell-derived cardiomyocytes

Cardiac pathological hypertrophy is the major risk factor that usually progresses to heart failure. We hypothesized that extracellular vesicles (EVs), known to act as important mediators in regulating physiological and pathological functions, could have the potential to reduce the cardiac hypertrophy and the ensuing cardiovascular diseases. Herein, the effects of mesenchymal stem cell-derived extracellular vesicles (EV-MSCs) on cardiac hypertrophy were investigated. EVs were isolated from the secretome of human adipose tissue-derived stem cells (EV-ADSCs) or bone marrow-derived stem cells (EV-BMMSCs). Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were stimulated with AngII and TGF-β1, in absence or presence of EVs. The results showed that exposure of hiPSC-CMs to AngII and TGF-β1 generated in vitro model of hypertrophic cardiomyocytes characterized by increases in surface area, reactive oxygen species production, protein expression of cardiac-specific biomarkers atrial natriuretic factor, migration inhibitory factor, cTnI, COL1A1, Cx43, α-SMA and signalling molecules SMAD2 and NF-kBp50. The presence of EV-ADSCs or EV-BMMSCs in the hiPSC-CM culture along with hypertrophic stimuli reduced the protein expressions of hypertrophic specific markers (ANF, MIF, cTnI, COL1A1) and the gene expressions of IL-6 molecule involved in inflammatory process associated with cardiac hypertrophy and transcription factors SMAD2, SMAD3, cJUN, cFOS with role in cardiomyocyte hypertrophic response induced by AngII and TGF-β1. The EV-ADSCs were more effective in reducing the protein expressions of hypertrophic and inflammatory markers, while EV-BMMSCs in reducing the gene expressions of transcription factors. Notably, neither EV-ADSCs nor EV-BMMSCs induced significant changes in cardiac biomarkers Cx43, α-SMA and fibronectin. These different effects of stem cell-derived EVs could be attributed to their miRNA content: some miRNAs (miR-126-3p, miR-222-3p, miR-30e-5p, miR-181b-5p, miR-124-3p, miR-155-5p, miR-210-3p hsa-miR-221-3p) were expressed in both types of EVs and others only in EV-ADSCs (miR-181a-5p, miR-185-5p, miR-21-5p) or in EV-BMMSCs (miR-143-3p, miR-146a-5p, miR-93-5p), some of these attenuating the cardiac hypertrophy while others enhance it. In conclusion, in hiPSC-CMs the stem cell-derived EVs through their cargo reduced the expression of hypertrophic specific markers and molecules involved in inflammatory process associated with cardiac hypertrophy. The data suggest the EV potential to act as therapeutic mediators to reduce cardiac hypertrophy and possibly the subsequent cardiovascular events.

Action Potential Prolongation, β-Adrenergic Stimulation, and Angiotensin II as Co-factors in Sarcoplasmic Reticulum Instability

Introduction: Increases in action potential duration (APD), genetic or acquired, and arrhythmias are often associated; nonetheless, the relationship between the two phenomena is inconstant, suggesting coexisting factors. β-adrenergic activation increases sarcoplasmic reticulum (SR) Ca²⁺-content; angiotensin II (ATII) may increase cytosolic Ca²⁺ and ROS production, all actions stimulating RyRs opening. Here we test how APD interacts with β-adrenergic and AT-receptor stimulation in facilitating spontaneous Ca²⁺ release events (SCR).

Methods: Under “action potential (AP) clamp”, guinea-pig cardiomyocytes (CMs) were driven with long (200 ms), normal (150 ms), and short (100 ms) AP waveforms at a CL of 500 ms; in a subset of CMs, all the 3 waveforms could be tested within the same cell. SCR were detected as inward current transients (I_TI) following repolarization; I_TI incidence and repetition within the same cycle were measured under increasing isoprenaline concentration ([ISO]) alone, or plus 100 nM ATII (30 min incubation+superfusion).

Results: I_TI incidence and repetition increased with [ISO]; at longer APs the [ISO]-response curve was shifted upward and I_TI coupling interval was reduced. ATII increased I_TI incidence more at low [ISO] and under normal (as compared to long) APs. Efficacy of AP shortening in suppressing I_TI decreased in ATII-treated myocytes and at higher [ISO].

Conclusions: AP prolongation sensitized the SR to the destabilizing actions of ISO and ATII. Summation of ISO, ATII and AP duration effects had a “saturating” effect on SCR incidence, thus suggesting convergence on a common factor (RyRs stability) “reset” by the occurrence of spontaneous Ca²⁺ release events.

Paeoniflorin improves pressure overload-induced cardiac remodeling by modulating the MAPK signaling pathway in spontaneously hypertensive rats

Paeoniflorin (PF) is a main bioactive component of the root of Paeonia lactiflora Pal, and previous investigations suggest that it may impact cardiac remodeling in spontaneous hypertensive rats (SHR) via the MAPK signaling pathway. Thus, the purpose of this investigation was to examine the impacts of paeoniflorin cardiac function in SHR rats. Cardiac function and blood pressure were observed using echocardiography and non-invasive tail pressure gauge. Heart histopathology was assessed by histological staining and transmission electron microscopy. Genomic sequencing was performed and signaling pathway enrichment analyzed the function of differentially expressed genes(DEGs). Biochemical kits were used to analyze the serum level of proinflammatory cytokines including TNF-α, IL-6 and MCP-1. qRT-PCR proved the mRNA expression of Ngfr, Grin2b, and Ntf4. MAPK pathways were determined via western blot. Paeoniflorin decreased blood pressure and increased hemodynamic indexes. 131 DEGs were identified (SHR vs. PF), and mainly enriched on the MAPK signaling pathway. Paeoniflorin reduced IL-6, MCP-1, Ngfr, Grin2b, and Ntf4, and also decreased p-JNK, p-Erk1/2, and p-p38 proteins compared with the SHR group. Paeoniflorin attenuated cardiac hypertrophy, cardiac fibrosis, and inflammation, and subsequently improved LV function. In conclusion, the cardioprotective role of paeoniflorin was associated with the inhibition of MAPK signaling pathway.

Gestational Protein Restriction Increases Cardiac Connexin 43 mRNA levels in male adult rat offspring

Background

The dietary limitation during pregnancy influences the growth and development of the fetus and offspring and their health into adult life. The mechanisms underlying the adverse effects of gestational protein restriction (GPR) in the development of the offspring hearts are not well understood.

Objectives

The aim of this study was to evaluate the effects of GPR on cardiac structure in male rat offspring at day 60 after birth (d60).

Methods

Pregnant Wistar rats were fed a normal-protein (NP, 17% casein) or low-protein (LP, 6% casein) diet. Blood pressure (BP) values from 60-day-old male offspring were measured by an indirect tail-cuff method using an electro sphygmomanometer. Hearts (d60) were collected for assessment of connexin 43 (Cx43) mRNA expression and morphological and morphometric analysis.

Results

LP offspring showed no difference in body weight, although they were born lighter than NP offspring. BP levels were significantly higher in the LP group. We observed a significant increase in the area occupied by collagen fibers, a decrease in the number of cardiomyocytes by 10⁴µm², and an increase in cardiomyocyte area associated with an increased Cx43 expression.

Conclusion

GPR changes myocardial levels of Cx43 mRNA in male young adult rats, suggesting that this mechanism aims to compensate the fibrotic process by the accumulation of collagen fibers in the heart interstitium.

ROS and endothelial nitric oxide synthase (eNOS)-dependent trafficking of angiotensin II type 2 receptor begets neuronal NOS in cardiac myocytes

Angiotensin II (Ang II), a potent precursor of hypertrophy and heart failure, upregulates neuronal nitric oxide synthase (nNOS or NOS1) in the myocardium. Here, we investigate the involvement of type 1 and 2 angiotensin receptors (AT1R and AT2R) and molecular mechanisms mediating Ang II-upregulation of nNOS. Our results showed that pre-treatment of left ventricular (LV) myocytes with antagonists of AT1R or AT2R (losartan, PD123319) and ROS scavengers (apocynin, tiron or PEG-catalase) blocked Ang II-upregulation of nNOS. Surface biotinylation or immunocytochemistry experiments demonstrated that AT1R expression in plasma membrane was progressively decreased (internalization), whereas AT2R was increased (membrane trafficking) by Ang II. Inhibition of AT1R or ROS scavengers prevented Ang II-induced translocation of AT2R to plasma membrane, suggesting an alignment of AT1R-ROS-AT2R. Furthermore, Ang II increased eNOS-Ser(1177) but decreased eNOS-Thr(495), indicating concomitant activation of eNOS. Intriguingly, ROS scavengers but not AT2R antagonist prevented Ang II-activation of eNOS. NOS inhibitor (L-NG-Nitroarginine Methyl Ester, L-NAME) or eNOS gene deletion (eNOS(-/-)) abolished Ang II-induced membrane trafficking of AT2R, nNOS protein expression and activity. Mechanistically, S-nitrosation of AT2R was increased by sodium nitroprusside (SNP), a NO donor. Site-specific mutagenesis analysis reveals that C-terminal cysteine 349 in AT2R is essential in AT2R translocation to plasma membrane. Taken together, we demonstrate, for the first time, that Ang II upregulates nNOS protein expression and activity via AT1R/ROS/eNOS-dependent S-nitrosation and membrane translocation of AT2R. Our results suggest a novel crosstalk between AT1R and AT2R in regulating nNOS via eNOS in the myocardium under pathogenic stimuli.

Endothelin A receptor antagonist, atrasentan, attenuates renal and cardiac dysfunction in Dahl salt-hypertensive rats in a blood pressure independent manner

Proteinuria is a hallmark of chronic kidney disease (CKD) and cardiovascular disease (CVD), and a good predictor of clinical outcome. Selective endothelin A (ET_A) receptor antagonist used with renin-angiotensin system (RAS) inhibitors prevents development of proteinuria in CKD. However, whether the improvement in proteinuria would have beneficial effects on CVD, independent of RAS inhibition, is not well understood. In this study, we investigated whether atrasentan, an ET_A receptor antagonist, has renal and cardiovascular effects independent of RAS inhibition. Male Dahl salt sensitive (DSS) rats, at six weeks of age, received water with or without different doses of atrasentan and/or enalapril under high salt (HS) diet or normal diet (ND) for 6 weeks. At the end of 12th week, atrasentan at a moderate dose significantly attenuated proteinuria and serum creatinine without reducing mean arterial pressure (MAP), thereby preventing cardiac hypertrophy and improving cardiac function. ACE inhibitor enalapril at a dose that did not significantly lowered BP, attenuated cardiac hypertrophy while moderately improving cardiac function without reducing proteinuria and serum creatinine level. Nonetheless, combined therapy of atrasentan and enalapril that does not altering BP exerted additional cardioprotective effect. Based on these findings, we conclude that BP independent monotherapy of ET_A receptor antagonist attenuates the progression of CKD and significantly mitigates CVD independent of RAS inhibition.

The JAK-STAT pathway in hypertrophic stress signaling and genomic stress response

The JAK-STAT signaling pathway plays a central role in transducing stress and growth signals in the hypertrophic heart. Unlike most signal transducers, JAKs and STATs signal in a number of different ways, both within the JAK-STAT pathway and in collaboration with other signaling pathways. In this review, we discuss how IL-6 activates cells lacking IL-6 receptors through trans-signaling and examine JAK-STAT pathway interaction with GPCR-linked pathways both within and between cells. Finally, we discuss recent studies showing how the JAK-STAT pathway can intersect with a general transcriptional regulatory mechanism to effect transcription of STAT-dependent stress response genes.

Histamine H4-receptors inhibit mast cell renin release in ischemia/reperfusion via protein kinase C ε-dependent aldehyde dehydrogenase type-2 activation

Renin released by ischemia/reperfusion (I/R) from cardiac mast cells (MCs) activates a local renin-angiotensin system (RAS) causing arrhythmic dysfunction. Ischemic preconditioning (IPC) inhibits MC renin release and consequent activation of this local RAS. We postulated that MC histamine H4-receptors (H4Rs), being Gαi/o-coupled, might activate a protein kinase C isotype-ε (PKCε)-aldehyde dehydrogenase type-2 (ALDH2) cascade, ultimately eliminating MC-degranulating and renin-releasing effects of aldehydes formed in I/R and associated arrhythmias. We tested this hypothesis in ex vivo hearts, human mastocytoma cells, and bone marrow-derived MCs from wild-type and H4R knockout mice. We found that activation of MC H4Rs mimics the cardioprotective anti-RAS effects of IPC and that protection depends on the sequential activation of PKCε and ALDH2 in MCs, reducing aldehyde-induced MC degranulation and renin release and alleviating reperfusion arrhythmias. These cardioprotective effects are mimicked by selective H4R agonists and disappear when H4Rs are pharmacologically blocked or genetically deleted. Our results uncover a novel cardioprotective pathway in I/R, whereby activation of H4Rs on the MC membrane, possibly by MC-derived histamine, leads sequentially to PKCε and ALDH2 activation, reduction of toxic aldehyde-induced MC renin release, prevention of RAS activation, reduction of norepinephrine release, and ultimately to alleviation of reperfusion arrhythmias. This newly discovered protective pathway suggests that MC H4Rs may represent a new pharmacologic and therapeutic target for the direct alleviation of RAS-induced cardiac dysfunctions, including ischemic heart disease and congestive heart failure.

Modulation of the cardiac sodium/bicarbonate cotransporter by the renin angiotensin aldosterone system: pathophysiological consequences

The sodium/bicarbonate cotransporter (NBC) is one of the major alkalinizing mechanisms in the cardiomyocytes. It has been demonstrated the existence of at least two functional isoforms, one that promotes the co-influx of 1 molecule of Na⁺ per 1 molecule of HCO⁻₃ (electroneutral isoform; NBCn1) and the other one that generates the co-influx of 1 molecule of Na⁺ per 2 molecules of HCO⁻₃ (electrogenic isoform; NBCe1). Both isoforms are important to maintain intracellular pH (pH_i) and sodium concentration ([Na⁺]_i). In addition, NBCe1 generates an anionic repolarizing current that modulates the action potential duration (APD). The renin-angiotensin-aldosterone system (RAAS) is implicated in the modulation of almost all physiological cardiac functions and is also involved in the development and progression of cardiac diseases. It was reported that angiotensin II (Ang II) exhibits an opposite effect on NBC isoforms: it activates NBCn1 and inhibits NBCe1. The activation of NBCn1 leads to an increase in pH_i and [Na⁺]_i, which indirectly, due to the stimulation of reverse mode of the Na⁺/Ca²⁺ exchanger (NCX), conduces to an increase in the intracellular Ca²⁺ concentration. On the other hand, the inhibition of NBCe1 generates an APD prolongation, potentially representing a risk of arrhythmias. In the last years, the potentially altered NBC function in pathological scenarios, as cardiac hypertrophy and ischemia-reperfusion, has raised increasing interest among investigators. This review attempts to draw the attention on the relevant regulation of NBC activity by RAAS, since it modulates pH_i and [Na⁺]_i, which are involved in the development of cardiac hypertrophy, the damage produced by ischemia-reperfusion and the generation of arrhythmic events, suggesting a potential role of NBC in cardiac diseases.

Regulation of the cardiac sodium/bicarbonate cotransporter by angiotensin II: potential Contribution to structural, ionic and electrophysiological myocardial remodelling

The sodium/ bicarbonate cotransporter (NBC) is, with the Na⁺/H⁺ exchanger (NHE), an important alkalinizing mechanism that maintains cellular intracellular pH (pHi). In the heart exists at least three isoforms of NBC, one that promotes the co-influx of 1 molecule of Na⁺ per 1molecule of HCO₃^-(electroneutral isoform; nNBC) and two others that generates the co-influx of 1 molecule of Na⁺ per 2 molecules of HCO₃^- (electrogenic isoforms; eNBC). In addition, the eNBC generates an anionic repolarizing current that modulate the cardiac action potential (CAP), adding to such isoforms the relevance to modulate the electrophysiological function of the heart. Angiotensin II (Ang II) is one of the main hormones that regulate cardiac physiology. The alkalinizing mechanisms (NHE and NBC) are stimulated by Ang II, increasing pHi and intracellular Na⁺ concentration, which indirectly, due to the stimulation of the Na⁺/Ca²⁺ exchanger (NCX) operating in the reverse form, leads to an increase in the intracellular Ca²⁺ concentration. Interestingly, it has been shown that Ang II exhibits an opposite effect on NBC isoforms: it activates the nNBC and inhibits the eNBC. This inhibition generates a CAP prolongation, which could directly increase the intracellular Ca²⁺ concentration. The regulation of the intracellular Na⁺ and Ca²⁺ concentrations is crucial for the cardiac cellular physiology, but these ions are also involved in the development of cardiac hypertrophy and the damage produced by ischemia-reperfusion, suggesting a potential role of NBC in cardiac diseases.

Mitochondrial reactive oxygen species (ROS) as signaling molecules of intracellular pathways triggered by the cardiac renin-angiotensin II-aldosterone system (RAAS)

Mitochondria represent major sources of basal reactive oxygen species (ROS) production of the cardiomyocyte. The role of ROS as signaling molecules that mediate different intracellular pathways has gained increasing interest among physiologists in the last years. In our lab, we have been studying the participation of mitochondrial ROS in the intracellular pathways triggered by the renin-angiotensin II-aldosterone system (RAAS) in the myocardium during the past few years. We have demonstrated that acute activation of cardiac RAAS induces mitochondrial ATP-dependent potassium channel (mitoK_ATP) opening with the consequent enhanced production of mitochondrial ROS. These oxidant molecules, in turn, activate membrane transporters, as sodium/hydrogen exchanger (NHE-1) and sodium/bicarbonate cotransporter (NBC) via the stimulation of the ROS-sensitive MAPK cascade. The stimulation of such effectors leads to an increase in cardiac contractility. In addition, it is feasible to suggest that a sustained enhanced production of mitochondrial ROS induced by chronic cardiac RAAS, and hence, chronic NHE-1 and NBC stimulation, would also result in the development of cardiac hypertrophy.

Early apoptosis in different models of cardiac hypertrophy induced by high renin-angiotensin system activity involves CaMKII

The objective of this study was to establish whether 1) hyperactivity of renin-angiotensin-aldosterone system (RAAS) produces apoptosis in early stages of cardiac disease; and 2) Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is involved in these apoptotic events. Two models of hypertrophy were used at an early stage of cardiac disease: spontaneously hypertensive rats (SHR) and isoproterenol-treated rats (Iso-rats). At 4 mo, SHR showed blood pressure, aldosterone serum levels, used as RAAS activity index, and left ventricular mass index, used as hypertrophy index, above control values by 84.2 ± 2.6 mmHg, 211.2 ± 25.8%, and 8.6 ± 1.1 mg/mm, respectively. There was also an increase in apoptotis (Bax-to-Bcl-2 ratio and terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling positive cells) associated with an enhancement of CaMKII activity with respect to age-matched controls (phosphorylated-CaMKII, 98.7 ± 14.1 above control). Similar results were observed in 4-mo-old Iso-rats. Cardiac function studied by echocardiography remained unaltered in all groups. Enalapril treatment significantly prevented hypertrophy, apoptosis, and CaMKII activity. Moreover, intracellular Ca(2+) handling in isolated myocytes was similar between SHR, Iso-rats, and their aged-matched controls. However, SHR and Iso-rats showed a significant increase in superoxide anion generation (lucigenin) and lipid peroxidation (thiobarbituric acid reactive substance). In transgenic mice with targeted cardiomyocyte expression of a CaMKII inhibitory peptide (AC3-I) or a scrambled control peptide (AC3-C), Iso treatment increased thiobarbituric acid reactive substance in both strains, whereas it increased CaMKII activity and apoptosis only in AC3-C mice. Endogenous increases in RAAS activity induce ROS and CaMKII-dependent apoptosis in vivo. CaMKII activation could not be associated with intracellular Ca(2+) increments and was directly related to the increase in oxidative stress.

Neuronal nitric oxide synthase is up-regulated by angiotensin II and attenuates NADPH oxidase activity and facilitates relaxation in murine left ventricular myocytes

Angiotensin II (Ang II) is critical in myocardial pathogenesis, mostly via stimulating NADPH oxidase. Neuronal nitric oxide synthase (nNOS) has recently been shown to play important roles in modulating myocardial oxidative stress and contractility. Here, we examine whether nNOS is regulated by Ang II and affects NADPH oxidase production of intracellular reactive oxygen species (ROS(i)) and contractile function in left ventricular (LV) myocytes. Our results showed that Ang II induced biphasic effects on ROS(i) and LV myocyte relaxation (TR(50)) without affecting the amplitude of sarcomere shortening and L-type Ca(2+) current density: TR(50) was prolonged at 30 min but was shortened after 3h (or after Ang II treatment in vivo). Correspondingly, ROS(i) was increased, followed by a reduction to control level. Quantitative RT-PCR and immunoblotting experiments showed that Ang II (3h) increased the mRNA and protein expression of nNOS and increased NO production (nitrite assay) in LV myocyte homogenates, suggesting that nNOS activity may be enhanced and involved in mediating the effects of Ang II. Indeed, n(omega)-nitro-l-arginine methyl ester (l-NAME) or a selective nNOS inhibitor, S-methyl-l-thiocitrulline (SMTC) increased NADPH oxidase production of superoxide/ROS(i) and abolished faster myocyte relaxation induced by Ang II. The positive lusitropic effect of Ang II was not mediated by PKA-, CaMKII-dependent signaling or peroxynitrite. Conversely, inhibition of cGMP/PKG pathway abolished the Ang II-induced faster relaxation by reducing phospholamban (PLN) Ser(16) phosphorylation. Taken together, these results clearly demonstrate that myocardial nNOS is up-regulated by Ang II and functions as an early adaptive mechanism to attenuate NADPH oxidase activity and facilitate myocardial relaxation.

The Relationship between Reactive Oxygen Species and Cardiac Fibrosis in the Dahl Salt-Sensitive Rat under ACEI Administration

Enalapril maleate, the oldest and most widely distributed ACEI, and alacepril, the newest and antioxidant ACEI, were compared in the point of cardioprotective effect for Dahl salt-sensitive rat. In order to evaluate the correlation between the three factors, cardiac fibrosis and blood pressure/oxidative-stress marker (tissue TBARS), index of correlation was calculated. The results showed a significant difference in cardiac fibrosis between high-dose alacepril (30 mg/kg/day, group H) and enalapril maleate (10 mg/kg/day, group E). There was significant correlation between cardiac fibrosis and oxidative-stress marker, although there was no correlation between cardiac fibrosis and blood pressure. Fibrosis was more influenced by oxidative stress not by blood pressure, we should not select ACEI only by blood pressure-lowering effect and should more consider cardioprotective effects of ACEI.

Long-term use of low-dose spironolactone in spontaneously hypertensive rats: effects on left ventricular hypertrophy and stiffness

The aim of the present study was to evaluate the effect of low-dose spironolactone initiated during the early stages of hypertension development and to assess the effects of chronic pressure overload on ventricular remodeling in rats. Male spontaneously hypertensive rats (SHRs) (4 weeks) were randomized to receive daily spironolactone (20 mg/kg) or vehicle (mineral oil) from 4 weeks to 8 months of age. Systolic blood pressure was measured non-invasively by tail-cuff pletysmography at baseline, 4 and 8 months. Hemodynamic assessment was performed at the end of treatment by arterial and ventricular catheterization. An in situ left ventricular pressure-volume curve was created to evaluate dilatation and wall stiffness. Systolic blood pressure at 1 month of age was higher in SHRs than in the Wistar group; it increased throughout the follow-up period and remained elevated with treatment (Wistar: 136 ± 2, SHR: 197 ± 6.8, SHR-Spiro: 207 ± 7.1 mmHg; p < 0.05). Spironolactone reduced cardiac hypertrophy (Wistar: 1.25 ± 0.03 SHR: 1.00 ± 0.03, SHR-Spiro: 0.86 ± 0.02 g; p < 0.05) and left ventricular mass normalized to body weight (Wistar: 2.51 ± 0.06, SHR: 2.70 ± 0.08, 2.53 ± 0.07 mg/g; p < 0.05). Moreover, the left ventricular wall stiffness that was higher in SHRs was partially reduced by spironolactone treatment (Wistar: 0.370 ± 0.032; SHR: 0.825 ± 0.058; SHR-Spiro: 0.650 ± 0.023 mmHg/ml; p < 0.05). Our results show that long-term spironolactone treatment initiated at the early stage of hypertension development reduces left ventricular hypertrophy and wall stiffness in SHRs.

Identifying the regulatory element for human angiotensin-converting enzyme 2 (ACE2) expression in human cardiofibroblasts

Angiotensin-converting enzyme 2 (ACE2) has been proposed as a potential target for cardioprotection in regulating cardiovascular functions, owing to its key role in the formation of the vasoprotective peptides angiotensin-(1-7) from angiotensin II (Ang II). The regulatory mechanism of ace2 expression, however, remains to be explored. In this study, we investigated the regulatory element within the upstream of ace2. The human ace2 promoter region, from position -2069 to +20, was cloned and a series of upstream deletion mutants were constructed and cloned into a luciferase reporter vector. The reporter luciferase activity was analyzed by transient transfection of the constructs into human cardiofibroblasts (HCFs) and an activating domain was identified in the -516/-481 region. Deletion or reversal of this domain within ace2 resulted in a significant decrease in promoter activity. The nuclear proteins isolated from the HCFs formed a DNA-protein complex with double stranded oligonucleotides of the -516/-481 domain, as detected by electrophoretic mobility shift assay. Site-directed mutagenesis of this region identified a putative protein binding domain and a potential binding site, ATTTGGA, homologous to that of an Ikaros binding domain. This regulatory element was responsible for Ang II stimulation via the Ang II-Ang II type-1 receptor (AT1R) signaling pathway, but was not responsible for pro-inflammatory cytokines TGF-β1 and TNF-α. Our results suggest that the nucleotide sequences -516/-481 of human ace2 may be a binding domain for an as yet unidentified regulatory factor(s) that regulates ace2 expression and is associated with Ang II stimulation.

An update on the islet renin-angiotensin system

The traditional renin-angiotensin system (RAS) components have been studied extensively since the rate-limiting component of RAS, renin, was first characterized. The ongoing identification of various novel RAS components and signaling pathways continues to elaborate the complexity of this system. Regulation of RAS according to the conventional and contemporary views of its functions in various tissues under pathophysiological conditions is a main treatment strategy for many metabolic diseases. The local pancreatic RAS, first proposed to exist in pancreatic islets two decades ago, could regulate islet function and glycemic control via influences on islet cell mass, inflammation, and ion channels. Insulin secretion, the major function of pancreatic islets, is controlled by numerous factors. Among these factors and of particular interest are glucagon-like peptide-1 (GLP-1) and vitamin D, which may regulate islet function by directly binding receptors on islet beta cells. These factors may work with local RAS signaling in islets to protect and maintain islet function under diabetic and hyperglycemic conditions. In this concise review, the local islet RAS will be discussed with particular attention being paid to recent notable findings.

HNF4alpha dysfunction as a molecular rational for cyclosporine induced hypertension

Induction of tolerance against grafted organs is achieved by the immunosuppressive agent cyclosporine, a prominent member of the calcineurin inhibitors. Unfortunately, its lifetime use is associated with hypertension and nephrotoxicity. Several mechanism for cyclosporine induced hypertension have been proposed, i.e. activation of the sympathetic nervous system, endothelin-mediated systemic vasoconstriction, impaired vasodilatation secondary to reduction in prostaglandin and nitric oxide, altered cytosolic calcium translocation, and activation of the renin-angiotensin system (RAS). In this regard the molecular basis for undue RAS activation and an increased signaling of the vasoactive oligopeptide angiotensin II (AngII) remain elusive. Notably, angiotensinogen (AGT) is the precursor of AngII and transcriptional regulation of AGT is controlled by the hepatic nuclear factor HNF4alpha. To better understand the molecular events associated with cyclosporine induced hypertension, we investigated the effect of cyclosporine on HNF4alpha expression and activity and searched for novel HNF4alpha target genes among members of the RAS cascade. Using bioinformatic algorithm and EMSA bandshift assays we identified angiotensin II receptor type 1 (AGTR1), angiotensin I converting enzyme (ACE), and angiotensin I converting enzyme 2 (ACE2) as genes targeted by HNF4alpha. Notably, cyclosporine represses HNF4alpha gene and protein expression and its DNA-binding activity at consensus sequences to AGT, AGTR1, ACE, and ACE2. Consequently, the gene expression of AGT, AGTR1, and ACE2 was significantly reduced as evidenced by quantitative real-time RT-PCR. While RAS is composed of a sophisticated interplay between multiple factors we propose a decrease of ACE2 to enforce AngII signaling via AGTR1 to ultimately result in vasoconstriction and hypertension. Taken collectively we demonstrate cyclosporine to repress HNF4alpha activity through calcineurin inhibitor mediated inhibition of nuclear factor of activation of T-cells (NFAT) which in turn represses HNF4alpha that leads to a disturbed balance of RAS.

Regulation of angiotensin converting enzyme II by angiotensin peptides in human cardiofibroblasts

Numerous studies have suggested that angiotensin peptides modulate the expression of angiotensin converting enzyme II (ACE2) in the cardiovascular system, but the molecular mechanisms remain poorly understood. In the present study, human cardiac fibroblasts (HCF) were used to test the regulatory effects of angiotensin II (Ang II) and angiotensin-(1-7) [Ang-(1-7)] on ACE2 expression. The results show that Ang II upregulates ACE2 expression. This action is modulated through activation of Ang II type 1 receptor (AT1R). Ang II-mediated ACE2 upregulation was blocked by antagonists of AT1R and ERK-MAPK signaling pathways. Additionally, Ang-(1-7) increased ACE2 expression, and this upregulation was inhibited by Ang-(1-7) Mas receptor blockade. Our results further reveal that the activation of p-ERK1/2 proteins plays a critical role in upregulating ACE2 in Ang-(1-7)-stimulated HCF cells. This effect occurs independently of the Ang II-AT1R signaling pathway. In conclusion, we propose that Ang II-upregulated ACE2 may increase Ang-(1-7) formation from Ang II, and that ACE2 expression is further enhanced by Ang-(1-7) in a positive feedback loop.

Thyroid Hormone Increases TGF-beta1 in Cardiomyocytes Cultures Independently of Angiotensin II Type 1 and Type 2 Receptors

TH-induced cardiac hypertrophy in vivo is accompanied by increased cardiac Transforming Growth Factor-beta1 (TGF-beta1) levels, which is mediated by Angiotensin II type 1 receptors (AT1R) and type 2 receptors (AT2R). However, the possible involvement of this factor in TH-induced cardiac hypertrophy is unknown. In this study we evaluated whether TH is able to modulate TGF-beta1 in isolated cardiac, as well as the possible contribution of AT1R and AT2R in this response. The cardiac fibroblasts treated with T(3) did not show alteration on TGF-beta1 expression. However, cardiomyocytes treated with T(3) presented an increase in TGF-beta1 expression, as well as an increase in protein synthesis. The AT1R blockade prevented the T(3)-induced cardiomyocyte hypertrophy, while the AT2R blockage attenuated this response. The T(3)-induced increase on TGF-beta1 expression in cardiomyocytes was not changed by the use of AT1R and AT2R blockers. These results indicate that Angiotensin II receptors are not implicated in T(3)-induced increase on TGF-beta expression and suggest that the trophic effects exerted by T(3) on cardiomyocytes are not dependent on the higher TGF-beta1 levels, since the AT1R and AT2R blockers were able to attenuate the T(3)-induced cardiomyocyte hypertrophy but were not able to attenuate the increase on TGF-beta1 levels promoted by T(3).

Angiotensin type 1 receptor mediates thyroid hormone-induced cardiomyocyte hypertrophy through the Akt/GSK-3beta/mTOR signaling pathway

Several studies have implicated the renin angiotensin system in the cardiac hypertrophy induced by thyroid hormone. However, whether Angiotensin type 1 receptor (AT1R) is critically required to the development of T3-induced cardiomyocyte hypertrophy as well as whether the intracellular mechanisms that are triggered by AT1R are able to contribute to this hypertrophy model is unknown. To address these questions, we employed a selective small interfering RNA (siRNA, 50 nM) or an AT1R blocker (Losartan, 1 microM) to evaluate the specific role of this receptor in primary cultures of neonatal cardiomyocytes submitted to T3 (10 nM) treatment. The cardiomyocytes transfected with the AT1R siRNA presented reduced mRNA (90%, P < 0.001) and protein (70%, P < 0.001) expression of AT1R. The AT1R silencing and the AT1R blockade totally prevented the T3-induced cardiomyocyte hypertrophy, as evidenced by lower mRNA expression of atrial natriuretic factor (66%, P < 0.01) and skeletal alpha-actin (170%, P < 0.01) as well as by reduction in protein synthesis (85%, P < 0.001). The cardiomyocytes treated with T3 demonstrated a rapid activation of Akt/GSK-3beta/mTOR signaling pathway, which was completely inhibited by the use of PI3K inhibitors (LY294002, 10 microM and Wortmannin, 200 nM). In addition, we demonstrated that the AT1R mediated the T3-induced activation of Akt/GSK-3beta/mTOR signaling pathway, since the AT1R silencing and the AT1R blockade attenuated or totally prevented the activation of this signaling pathway. We also reported that local Angiotensin I/II (Ang I/II) levels (120%, P < 0.05) and the AT1R expression (180%, P < 0.05) were rapidly increased by T3 treatment. These data demonstrate for the first time that the AT1R is a critical mediator to the T3-induced cardiomyocyte hypertrophy as well as to the activation of Akt/GSK-3beta/mTOR signaling pathway. These results represent a new insight into the mechanism of T3-induced cardiomyocyte hypertrophy, indicating that the Ang I/II-AT1R-Akt/GSK-3beta/mTOR pathway corresponds to a potential mediator of the trophic effect exerted by T3 in cardiomyocytes.

High-Expression of Transforming Growth Factor β1and Phosphorylation of Extracellular Signal-Regulated Protein Kinase in Vascular Smooth Muscle Cells from Aorta and Renal Arterioles of Spontaneous Hypertension Rats

To further elucidate the molecular mechanisms involved in hypertensive vascular remodeling, an immunohistochemical technique and Western blot were applied to study phospho-extracellular signal-regulated kinase (ERK1/2) and transforming growth factor beta1 (TGF-beta1) expression in endothelial and vascular smooth muscle cell (VSMC) of the thoracic aorta and renal arterioles from SHR of different ages. Results of both the immunohistochemistry and Western blot assays showed that either the phospho-ERK1/2 at endothelium or VSMC of renal small arteries from SHR8, SHR16, and SHR20 groups and of the aorta from SHR16 and SHR20 were higher than that from control group. Comparing with that in the small arteries of the kidney, the phospho-ERK1/2 in the endothelium and in VSMC was markedly increased in the aorta, and high expression of TGF-beta1 was detected in the aorta and kidney from SHR16 and SHR20 by Western blot. These results suggested that ERK 1/2 could be activated by phosphorylation with over-expression of TGF-beta1 in the endothelium and in VSMC of aorta and renal arterioles from SHR, which might play an important role in VSMC proliferation under hypertension.

Renin dynamics in adipose tissue: adipose tissue control of local renin concentrations

The renin-angiotensin system (RAS) has been implicated in a variety of adipose tissue functions, including tissue growth, differentiation, metabolism, and inflammation. Although expression of all components necessary for a locally derived adipose tissue RAS has been demonstrated within adipose tissue, independence of local adipose RAS component concentrations from corresponding plasma RAS fluctuations has not been addressed. To analyze this, we varied in vivo rat plasma concentrations of two RAS components, renin and angiotensinogen (AGT), to determine the influence of their plasma concentrations on adipose and cardiac tissue levels in both perfused (plasma removed) and nonperfused samples. Variation of plasma RAS components was accomplished by four treatment groups: normal, DOCA salt, bilateral nephrectomy, and losartan. Adipose and cardiac tissue AGT concentrations correlated positively with plasma values. Perfusion of adipose tissue decreased AGT concentrations by 11.1%, indicating that adipose tissue AGT was in equilibrium with plasma. Cardiac tissue renin levels positively correlated with plasma renin concentration for all treatments. In contrast, adipose tissue renin levels did not correlate with plasma renin, with the exception of extremely high plasma renin concentrations achieved in the losartan-treated group. These results suggest that adipose tissue may control its own local renin concentration independently of plasma renin as a potential mechanism for maintaining a functional local adipose RAS.

Candesartan-induced gene expression in five organs of stroke-prone spontaneously hypertensive rats

To test the functional consequences of blocking the local renin-angiotensin system (RAS), we investigated the effects of an angiotensin II type 1 receptor blocker (ARB), candesartan, on the systemic gene expression profile of five important organs (brain, heart, kidney, liver and adipose tissues) in the stroke-prone spontaneously hypertensive rat (SHRSP), an established model of essential hypertension and cardiovascular disorders, and its normotensive control, the Wistar Kyoto (WKY) rat. Rats were treated with candesartan (5 mg/kg/d) for 4 weeks from 12 to 16 weeks of age. DNA microarray technology was used to identify changes in gene expression. Four weeks of treatment with candesartan significantly lowered systolic blood pressure in male rats of both the SHRSP and the WKY strains (p<0.0005). Candesartan differentially modulated the gene expression profile in an organ-specific manner in male SHRSP; of the five organs tested, gene expression was most prominently altered in the hearts of SHRSP. In contrast, candesartan treatment exerted minimal or no significant effects on the gene expression profile of the corresponding organs of male WKY rats. The inter-strain differences in gene expression changes induced by candesartan were considered to be associated with both blood pressure-dependent and independent mechanisms. These results help to delineate the mechanisms that underlie the organ or tissue protection conferred by ARB at the levels of cellular biology and genomics in the context of the local RAS. Further studies are warranted to investigate not only individual genes of interest but also genetic "networks" that involve differential organ- or tissue-specific gene expression induced by the blockade of RAS in essential hypertension. Tokyo, Japan

Cytokines and renin-angiotensin system signaling in hepatic fibrosis

Hepatic fibrosis is the result of a complex interplay between resident hepatic cells, infiltrating inflammatory cells, and a number of locally acting peptides called cytokines. Key mediators include transforming growth factor b1, vasoactive substances, adipokines, inflammatory cytokines and chemokines. Angiotensin II, the main effector of the renin-angiotensin system, is a true cytokine that plays a major role in liver fibrosis. Angiotensin II is locally synthesized in the injured liver and induces profibrogenic actions in hepatic stellate cells. Drugs blocking the renin-angiotensin system are promising antifibrotic agents. There are multiple signal transduction pathways involved in cytokine signaling. Drugs interfering intracellular pathways involved in increased collagen production are potential therapies for liver fibrosis.

Oxidative stress mediates cardiac fibrosis by enhancing transforming growth factor-beta1 in hypertensive rats

Cardiac fibrosis represented as perivascular/interstial fibrosis occurs in patients with hypertension. Oxidative stress has been demonstrated to contribute to such structural remodeling. The underlying mechanisms, however, remain to be elucidated. Herein, we tested the hypothesis that oxidative stress mediates cardiac fibrogenesis by stimulating transforming growth factor (TGF)-beta1 expression, which in turn triggers a series of fibrogenic responses. Sprague-Dawley rats were treated with angiotensin (Ang)II (9 microg/h s) for 4 weeks with/without co-treatment of combined antioxidants, apocynin, and tempol (120 mg/kg/day each, oral). Untreated rats served as controls. Appearance of cardiac oxidative stress and its potential effect on the expression of TGF-beta1, population of myofibroblasts, collagen synthesis/degradation, and fibrosis in hearts were examined. Chronic AngII infusion elevated systemic blood pressure (210 +/- 5 mmHg). Extensive perivascular and interstitial fibrosis was found in both ventricles, which were co-localized with oxidative stress represented as upregulated NADPH oxidase (gp91(phox) subunit) expression. Co-treatment with antioxidants led to: (1) markedly decreased cardiac gp91(phox); (2) significantly attenuated gene expression of TGF-beta1, type-I collagen, and tissue inhibitors of matrix metalloproteinase (TIMP)-I/II in the heart; (3) largely reduced population of myofibroblasts at sites of fibrosis; (4) significantly reduced cardiac collagen volume; (5) and partially suppressed blood pressure (190 +/- 4 mmHg). Thus, cardiac oxidative stress promotes the development of cardiac fibrosis by upregulating TGF-beta1 expression, which subsequently enhances cardiac collagen synthesis and suppresses collagen degradation in hypertensive rats.

Angiotensin II type 1 receptor blocker preserves tolerance to ischemia-reperfusion injury in Dahl salt-sensitive rat heart

Oxidative stress is involved in the tolerance to ischemia-reperfusion (I/R) injury. Because angiotensin II type 1 receptor blockers (ARBs) inhibit oxidative stress, there is concern that ARBs abolish the tolerance to I/R injury. Dahl salt-sensitive (DS) hypertensive and salt-resistant (DR) normotensive rats received an antioxidant, 2-mercaptopropionylglycine (MPG), or an ARB, losartan, for 7 days. Losartan and MPG significantly inhibited oxidative stress as determined by tissue malondialdehyde + 4-hydroxynoneal and increased expression of inducible nitric oxide synthase (iNOS) in the DS rat heart. However, losartan but not MPG activated endothelial nitric oxide synthase (eNOS) as assessed by phosphorylation of eNOS on Ser1177. Infarct size after 30-min left coronary artery occlusion followed by 2-h reperfusion was comparable between DS and DR rat hearts. Although MPG and losartan had no effect on infarct size in the DR rat heart, MPG but not losartan significantly increased infarct size in the DS rat heart. A selective iNOS inhibitor, 1400W, increased infarct size in the DS rat heart, but it had no effect on infarct size in the losartan-treated DS rat heart. However, a nonselective NOS inhibitor, Nω-nitro-l-arginine methyl ester, increased infarct size in the losartan-treated DS rat heart. These results suggest that losartan preserves the tolerance to I/R injury by activating eNOS despite elimination of redox-sensitive upregulation of iNOS and iNOS-dependent cardioprotection in the DS rat heart.

Kidney fibrosis in hypertensive rats: role of oxidative stress

Fibrosis of the glomerulus and the tubulointerstitium occurs in patients with hypertension. Studies have shown that renal oxidative stress appears in hypertensive kidney disease. The potential role of oxidative stress in renal fibrogenesis remains to be elucidated. Herein, we tested the hypothesis that oxidative stress contributes to the development of renal fibrosis during hypertension.Sprague-Dawley rats received angiotensin II (AngII; 9 microg/h s.c.) for 4 weeks with/without co-treatment of antioxidants, apocynin and tempol (120 mg/kg/day each, p.o.). Untreated rats served as controls. Appearance of renal oxidative stress and its effect on the expression of transforming growth factor (TGF)-beta(1), population of myofibroblasts, collagen synthesis/degradation and fibrosis in kidneys were examined. Chronic AngII infusion elevated systemic blood pressure (228 +/- 6 mm Hg), which was accompanied with extensive renal fibrosis and oxidative stress represented as upregulated NADPH oxidase and suppressed superoxide dismutase (SOD). Co-treatment with antioxidants led to: (1) markedly decreased renal NADPH oxidase; (2) significantly attenuated gene expression of TGF-beta(1), type I collagen, and tissue inhibitors of matrix metalloproteinase (TIMP)-I/-II in the kidney; (3) largely reduced population of myofibroblasts in both the cortex and medulla; (4) significantly reduced renal collagen volume, and (5) partially suppressed blood pressure (190 +/- 8 mm Hg). Thus, prolonged AngII administration promotes renal oxidative stress, which is associated with hypertensive renal disease. AngII induces renal oxidative stress by increasing NADPH oxidase and reducing SOD in the kidney, which, in turn, upregulates collagen synthesis, while suppressing collagen degradation, thereby promoting the development of fibrosis in kidneys of hypertensive rats.

Ischemic preconditioning: from molecular mechanisms to therapeutic opportunities

Ischemia/reperfusion (I/R) injury is a major contributory factor to cardiac dysfunction and infarct size that determines patient prognosis after acute myocardial infarction. Considerable interest exists in harnessing the heart's endogenous capacity to resist I/R injury, known as ischemic preconditioning (IPC). The IPC research has contributed to uncovering the pathophysiology of I/R injury on a molecular and cellular basis and to invent potential therapeutic means to combat such damage. However, the translation of basic research findings learned from IPC into clinical practice has often been inadequate because the majority of basic research findings have stemmed from young and healthy animals. Few if any successful implementations of IPC have occurred in the diseased hearts that are the primary target of viable therapies activating cardioprotective mechanisms to limit cardiac dysfunction and infarct size. Therefore, the first purpose of this review is to facilitate understanding of pathophysiology of I/R injury and the mechanisms of cardioprotection afforded by IPC in the normal heart. Then I focus on the problems and opportunities for successful bench-to-bedside translation of IPC in the diseased hearts.

Immunopathogenesis of hepatitis C virus infection and hepatic fibrosis: New insights into antifibrotic therapy in chronic hepatitis C

Fibrosis and cirrhosis represent the consequences of a sustained wound-healing response to chronic liver injury of any cause. Chronic hepatitis C virus (HCV) has emerged as a leading cause of cirrhosis in the USA and throughout the world. HCV may induce fibrogenesis directly by hepatic stellate cell activation or indirectly by promoting oxidative stress and apoptosis of infected cells. The ultimate result of chronic HCV injury is the accumulation of extracellular matrix with high density type I collagen within the subendothelial space of Disse, culminating in cirrhosis with hepatocellular dysfunction. The treatment of hepatitis C with the combination of pegylated interferon and ribavirin is still both problematic and costly, has suboptimal efficacy, serious side effects and a high level of intolerance, and is contraindicated in many patients. Hence, new approaches have assumed greater importance, for which there is an urgent need. The sustained progress in understanding the pathophysiology of hepatic fibrosis in the past two decades has increased the possibility of developing drugs specifically targeting the fibrogenic process. Future efforts should identify genetic markers associated with fibrosis risk in order to tailor the treatment of HCV infection based on genetically regulated pathways of injury and/or fibrosis. Such advances will expand the arsenal to overcome liver fibrosis, particularly in patients with hepatic diseases who have limited treatment options, such as those patients with chronic hepatitis C who have a high risk of fibrosis progression and recurrent HCV disease after liver transplantation.

The intracellular renin-angiotensin system: a new paradigm

More than a century after its discovery, the physiological implications of the renin-angiotensin system (RAS) continue to expand, with the identification of new components, functions and subsystems. These advancements have led to better management and understanding of a broad range of cardiovascular and metabolic disorders. The RAS has traditionally been viewed as a circulatory system, involved in the short-term regulation of volume and blood pressure homeostasis. Recently, local RASs have been described as regulators of chronic tissue effects. Most recently, studies have provided evidence of a complete, functional RAS within cells, described as an 'intracrine' or intracellular system. A more comprehensive understanding of the intracellular RAS provides for new strategies in system regulation and a more efficacious approach to the management of RAS-related diseases.

Undernutrition in utero augments systolic blood pressure and cardiac remodeling in adult mouse offspring: possible involvement of local cardiac angiotensin system in developmental origins of cardiovascular disease

Evidence has emerged that undernutrition in utero is a risk factor for cardiovascular disorders in adulthood, along with genetic and environmental factors. Recently, the local expression of angiotensinogen and related bioactive substances has been demonstrated to play a pivotal role in cardiac remodeling, i.e. fibrosis and hypertrophy. The aim of the present study was to clarify the possible involvement of the local cardiac angiotensin system in fetal undernutrition-induced cardiovascular disorders. We developed a mouse model of undernutrition in utero by maternal food restriction, in which offspring (UN offspring) showed an increase in systolic blood pressure (8 wk of age, P < 0.05; and 16 wk, P < 0.01), perivascular fibrosis of the coronary artery (16 wk, P < 0.05) and cardiac cardiomegaly (16 wk, P < 0.01), and cardiomyocyte enlargement, concomitant with a significant augmentation of angiotensinogen (P < 0.05) and endothelin-1 (P < 0.01) mRNA expression and a tendency to increase in immunostaining for both angiotensin II and endothelin-1 in the left ventricles (16 wk). These findings suggest that fetal undernutrition activated the local cardiac angiotensin system-associated bioactive substances, which contributed, at least partly, to the development of cardiac remodeling in later life, in concert with the effects of increase in blood pressure.

Molecular Signaling Mediated by Angiotensin II Type 1A Receptor Blockade Leading to Attenuation of Renal Dysfunction-Associated Heart Failure

BACKGROUND

In patients with end-stage renal disease, angiotensin II type 1A receptor (AT1) blockade attenuates the associated cardiac dysfunction. We investigated the molecular signaling mediating that effect.

METHODS AND RESULTS

We used 5/6 nephrectomy to induce significant renal dysfunction in AT1 knockout (AT1KO) and wild-type mice (WT). Twelve weeks after nephrectomy, WT showed significant left ventricular dilation and dysfunction that were accompanied by cardiomyocyte hypertrophy, fibrosis, and reduced capillary density. All of these effects were significantly mitigated in AT1KO. Nephrectomy led to upregulation of myocardial expression of AT1, transforming growth factor-beta1 (TGF-beta1), matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and phosphorylated Akt (p-Akt), and also led to increased oxidative damage in cardiomyocytes. In AT1KO, TGF-beta1, TIMP-1, oxidative damage levels were lower, whereas MMPs and p-Akt levels were higher. Treating nephrectomized WT mice with valsartan (an AT1 blocker), but not hydralazine, improved cardiac function and altered molecular signaling in a manner similar to that seen in AT1KO mice. Notably, AT1 expression was downregulated in valsartan-treated but not hydralazine-treated hearts.

CONCLUSIONS

These findings provide novel insight into the mechanism underlying the beneficial effects of AT1 blockade on cardiac function in a model of renal dysfunction-associated heart failure.

Left Ventricular Structural Adaptations to Obstructive Sleep Apnea in Dilated Cardiomyopathy

RATIONALE AND OBJECTIVES

Obstructive sleep apnea is common among patients with heart failure and exposes the left ventricle to trophic mechanical and adrenergic stimuli. We hypothesized that in heart failure patients with nonischemic dilated cardiomyopathy (a condition characterized by eccentric hypertrophy), those with obstructive sleep apnea would have a higher prevalence of left ventricular hypertrophy by wall thickness criteria (> or = 12 mm), and greater septal thickness than those without obstructive sleep apnea.

METHODS AND RESULTS

We performed echocardiography and polysomnography in 47 patients with nonischemic dilated cardiomyopathy. Obstructive sleep apnea was present in 45% of these patients. The prevalence of left ventricular hypertrophy was greater in those with than in those without obstructive sleep apnea (47.6 vs. 15.4%, p = 0.016). Interventricular septal thickness (p < 0.001) and relative wall thickness (p = 0.011) were significantly greater in those with than in those without obstructive sleep apnea. However, there was no significant difference in posterior wall thickness between the groups. The frequency of obstructive apneas and hypopneas during sleep was the only significant independent correlate of septal thickness (p = 0.001).

CONCLUSIONS

In patients with nonischemic dilated cardiomyopathy, the presence of obstructive sleep apnea is associated with an increased prevalence of left ventricular hypertrophy. The higher relative wall thickness and interventricular septal thickness in patients with obstructive sleep apnea indicate that the left ventricle is relatively less eccentric than in patients without obstructive sleep apnea, and that such remodeling affects mainly the septum. These structural adaptations may reflect unique nocturnal mechanical and adrenergic stimuli associated with obstructive sleep apnea.

The Antagonism of Aldosterone Receptor Prevents the Development of Hypertensive Heart Failure Induced by Chronic Inhibition of Nitric Oxide Synthesis in Rats

Aldosterone promotes cardiovascular inflammation and remodeling, both of which are characteristic changes in hypertensive and failing hearts. Since chronic inhibition of nitric oxide (NO) synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME) induces systemic hypertension associated with cardiovascular inflammation and remodeling, we examined the potential role of aldosterone in this process using eplerenone, a selective aldosterone receptor antagonist. Ten-week-old male Wistar-Kyoto rats were randomly divided into 3 groups: the control group (no treatment), the L-NAME group (received L-NAME 1 g/L in drinking water), and the L-NAME+Eplerenone group (L-NAME plus eplerenone at 100 mg/kg/day). After 8 weeks of the treatment, the L-NAME group showed significantly higher systolic blood pressure than the control group (198 +/- 7 vs. 141 +/- 3 mmHg, P < 0.05). Eplerenone did not affect the increase in blood pressure caused by L-NAME (189 +/- 12 mmHg). Chronic inhibition of NO synthesis increased the plasma aldosterone concentration and CYP11B2 mRNA in adrenal glands. Cardiac inflammation and fibrosis were detected in the L-NAME group, while both changes were completely prevented by eplerenone. Cardiac hypertrophy was induced in L-NAME group, but was partially prevented by eplerenone. In the L-NAME group, left ventricular fractional shortening (LVFS: 27 +/- 2 vs. 38 +/- 1%) and E/A ratio (1.7 +/- 0.1 vs. 2.1 +/- 0.1) were significantly lower and LV end-diastolic pressure (LVEDP) was higher (4.9 +/- 0.6 vs. 13.9 +/- 0.5 mmHg) without LV enlargement, compared with those in the control group (P < 0.05). Eplerenone completely normalized LVFS (36 +/- 2%), E/A ratio (2.2 +/- 0.1), and LVEDP (6.2 +/- 0.7 mmHg). These results suggest that chronic inhibition of NO synthesis induces cardiac inflammation and dysfunction via an aldosterone receptor-dependent mechanism.

Identification of differentially expressed genes induced by angiotensin II in rat cardiac fibroblasts

1. Cardiac fibroblasts play an important regulatory role in cardiac remodelling by undergoing proliferation, differentiation and upregulating various gene products, including some cytokines and extracellular matrix (ECM) proteins. A highly potent mediator of cardiac remodelling is angiotensin (Ang) II. 2. In the present study, the suppression subtractive hybridization method was used to identify differentially expressed cDNAs in adult rat cardiac fibroblasts induced by AngII. 3. Following mRNA isolation of non-stimulated and AngII-stimulated cells, cDNAs of both populations were prepared and subtracted by suppression polymerase chain reaction. Sequencing of the partially enriched cDNAs identified 36 genes differentially expressed, including ECM proteins (pro-alpha(1) collagen type III, fibronectin), structural protein (spectrin), enzyme (GTP-specific succinyl-CoA synthetase), transcriptional regulators (glucocorticoid-induced leucine zipper, inhibitor of DNA binding 3) and proteins involved in cell division control (cdc2) or cell signalling (insulin-like growth factor binding protein-3, mutant p53-binding protein, grp75, CGI-121, protein phosphatase type 2A, tspan-2 and Sam68). 4. The diversity of genes identified in the present study further emphasises the central role of AngII in the regulation of cardiac remodelling.

The effect of neurohormonal antagonists in reducing heart failure hospitalizations

OBJECTIVE

Heart failure (HF) is a major health problem facing the US and studies suggest that the incidence of this condition will rise significantly over the next 10 years. Limiting the incidence or duration of HF hospitalizations would, therefore, have a major impact on healthcare costs. The purpose of this review is to establish and discuss the proposed neurohormonal mechanisms by which HF can occur along with pharmacologic treatments designed to antagonize these pathological states in order to aid in the reduction of HF hospitalization.

METHODS

A Medline search (to December 200) was performed to compile published literature and assess numerous large-scale studies regarding the use of neurohormonal antagonists in the treatment of HF. In addition, evaluation of statistics and figures from various organizations dedicated to the improvement of HF care was utilized as aids in understanding the impact of these therapies on hospitalization and healthcare.

RESULTS

Heart failure is the most costly cardiovascular disease in the United States, with an estimated annual expenditure in excess of $20 billion. The frequency and duration of HF-associated hospitalizations are the key contributors to this pronounced economic burden. Use of pharmacologic interventions designed to specifically antagonize the renin-angiotensin-aldosterone system and the adrenergic system has had a significant impact on limiting hospitalization with regard to HF. However, the ever burdensome level of re-hospitalization rates for these patients is still problematic and appears to be based on a disconnect between established procedures to effectively treat these patients and the inability to accurately measure performance standards by managed care organization and hospital accreditation bodies. As a consequence, these antagonists, beta-blockers in particular, are still underutilized in the treatment of HF. Studies have shown that many of these hospitalizations could have been avoided had healthcare providers followed effective HF management programs.

CONCLUSIONS

Current evidence supports the benefits of neurohormonal blockade in decreasing hospital admissions due to HF. Appropriate use of these agents plus agreed-upon guidelines for treatment can continue to significantly decrease total HF-related hospitalizations and costs. Inclusion of beta-blockers as a performance measure in quality-of-care HF indicators should be considered as an important instrument to increase their utilization and to improve overall HF care.

The lord of the ring: mandatory role of the kidney in drug therapy of hypertension

Strong evidence supports the idea that total peripheral resistance (TPR) is increased in all forms of human and experimental hypertension. Although the etiological participation of TPR in the origin and long-term maintenance of hypertension has been extensively debated, it now seems clear that the renal, nonadaptive, infinite gain-working, pressure-sensitive natriuresis and diuresis is the main mechanism of blood pressure control in the long term. The tissue, cellular, biochemical, and genetic sensors and executors of this process have not been fully identified yet, but the role of the renal medulla has gained growing attention as the physiopathological scenario in which the key regulatory elements reside. Specifically, the functionality of the renomedullary vasculature seems to be highly responsible for blood pressure control. The vasculature of the renal medulla becomes a new and more specific target for the therapeutic intervention of hypertension. Recent data on the effect of baroreceptor-controlled renal sympathetic activity on the long-term regulation of blood pressure are integrated. The renomedullary effects of the main antihypertensive drugs are discussed, and new perspectives for the therapeutic intervention of hypertension are outlined. Comparison of the genetic program of the renal medulla before and after the development of hypertension in spontaneously hypertensive and experimentally induced animal models might provide a mechanism for identifying the key genes that become activated or suppressed in the development of high blood pressure. These genes, their encoded proteins, or other elements related to their signalling and genetic pathways might serve as new and more specific targets for the pharmacological treatment of abnormally elevated blood pressure. Besides, proteins specifically located to the luminal side of the renomedullary vascular endothelium may serve as potential targets for site-directed drug and gene therapy.