The cardiac renin-angiotensin system is responsible for high-salt diet-induced left ventricular hypertrophy in mice

Deleterious effect in endothelin receptor-mediated coronary artery smooth muscle contractility in high-salt diet rats

BACKGROUND AND AIMS

High-salt diet has been suggested to increase the risk of heart disease. However, the mechanisms underlying coronary artery tension dysfunction caused by high-salt diet are unclear. Previous studies have shown that coronary artery spasm is often induced by endothelin-1 (ET-1) and thromboxane, leading to myocardial ischemia, while the store-operated Ca²⁺ entry (SOCE) function of coronary smooth muscle is very important in this process.

METHODS AND RESULTS

Tension measurements of endothelium-denuded coronary artery ring segments showed that vasocontraction induced by U46619, ET-1, orSTIM1/Orai1-mediated SOCE was significantly lower in 4% high-salt diet rats than in control rats fed a regular diet. The results of western blotting and immunohistochemistry assays showed lower expression levels of endothelial receptors ET_A and ET_B, STIM1 and Orai1 in coronary artery of high-salt intake rats compared with control rats. Fibrosis was observed by using Masson's trichrome staining and picrosirius red staining. The plasma ET-1 concentration in high-salt diet rats was significantly higher than that of controls. The interventricular septum and posterior wall of high-salt diet rats were significantly thickened.

CONCLUSION

Our findings indicated that coronary artery tension was significantly decreased in 4% high-salt diet rats and that this decrease may be due to the change of endothelin receptor and its downstream pathway SOCE related protein expression in coronary artery. Coronary fibrosis was observed in rats fed with high-salt diet. This study provides potential mechanistic insights into high-salt intake-induced heart disease.

Association between AT1 receptor gene polymorphism and left ventricular hypertrophy and arterial stiffness in essential hypertension patients: a prospective cohort study

BACKGROUND

AT1 receptor gene (AGTR1) is related to essential hypertension (EH), and left ventricular hypertrophy (LVH) and arterial stiffness are common complications of EH. This study aimed to explore the association between AGTR1 genotype and LVH and arterial stiffness in EH patients.

METHODS

A total of 179 EH patients were recruited in this study. Oral exfoliated cells were collected from each patient, and the genetic polymorphism of AGTR1(rs4524238) was assessed using a gene sequencing platform. The outcomes were LVH and arterial stiffness.

RESULTS

Among 179 patients, 114 were with AGTR1 genotype of GG (57 males, aged 59.54 ± 13.49 years) and 65 were with AGTR1 genotype of GA or AA (36 males, aged 61.28 ± 12.79 years). Patients with AGTR1 genotype of GG were more likely to have LVH (47 [41.23%] vs. 14 [21.54%], P = 0.006) and arterial stiffness (30 [26.32%] vs. 8 [12.31%], P = 0.036). The AGTR1 polymorphism frequency was in accordance with Hardy-Weinberg equilibrium (P = 0.291). The multivariate logistic regression showed that AGTR1 genotype of GA or AA was independently associated with lower risk of LVH (OR = 0.344, 95%CI 160~0.696, P = 0.003) and arterial stiffness (OR = 0.371, 95%CI 0.155~0.885, P = 0.025) after adjusting for gender, age, and diabetes.

CONCLUSION

EH patients with the AGTR1 genotype of GA or AA were at lower risk for LVH and arterial stiffness than those with the GG genotype.

Preclinical rodent models of cardiac fibrosis

Cardiac fibrosis (scarring), characterised by an increased deposition of extracellular matrix (ECM) proteins, is a hallmark of most types of cardiovascular disease and plays an essential role in heart failure progression. Inhibition of cardiac fibrosis could improve outcomes in patients with cardiovascular diseases and particularly heart failure. However, pharmacological treatment of the ECM build-up is still lacking. In this context, preclinical models of heart disease are important tools for understanding the complex pathogenesis involved in the development of cardiac fibrosis which in turn could identify new therapeutic targets and the facilitation of antifibrotic drug discovery. Many preclinical models have been used to study cardiac fibrosis and each model provides mechanistic insights into the many factors that contribute to cardiac fibrosis. This review discusses the most frequently used rodent models of cardiac fibrosis and also provides context for the use of particular models of heart failure.

Nitric Oxide Alleviated High Salt-Induced Cardiomyocyte Apoptosis and Autophagy Independent of Blood Pressure in Rats

The present study aimed to explore whether high-salt diet (HSD) could cause cardiac damage independent of blood pressure, and whether nitric oxide (NO) could alleviate high-salt–induced cardiomyocyte apoptosis and autophagy in rats. The rats received 8% HSD in vivo. H9C2 cells or primary neonatal rat cardiomyocytes (NRCM) were treated with sodium chloride (NaCl) in vitro. The levels of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1 and autophagy related 7 (ATG7) were increased in the heart of HSD rats with hypertension (HTN), and in hypertension-prone (HP) and hypertension-resistant (HR) rats. Middle and high doses (50 and 100 mM) of NaCl increased the level of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in H9C2 cells and NRCM. The endothelial NO synthase (eNOS) level was increased, but p-eNOS level was reduced in the heart of HSD rats and H9C2 cells treated with 100 mM NaCl. The level of NO was reduced in the serum and heart of HSD rats. NO donor sodium nitroprusside (SNP) reversed the increases of cleaved-caspase 3/caspase 3, cleaved-caspase 8/caspase 8, Bax/Bcl2 induced by NaCl (100 mM) in H9C2 cells and NRCM. SNP treatment attenuated the increases of cleaved-caspase 3/caspase 3, Bax/Bcl2, LC3 II/LC3 I, Beclin-1, and ATG7 in the heart, but had no effect on the blood pressure of HSD rats with HR. These results demonstrated that HSD enhanced cardiac damage independently of blood pressure. Exogenous NO supplementarity could alleviate the high salt–induced apoptosis and autophagy in cardiomyocytes.

Left Ventricular Mass Reduction by a Low-Sodium Diet in Treated Hypertensive Patients

Objective: To evaluate the left ventricular mass (LVM) reduction induced by dietary sodium restriction. Patients and Methods: A simple sodium-restricted diet was advised in 138 treated hypertensives. They had to avoid common salt loads, such as cheese and salt-preserved meat, and were switched from regular to salt-free bread. Blood pressure (BP), 24-h urinary sodium (UNaV) and LVM were recorded at baseline, after 2 months. and after 2years. Results: In 76 patients UNaV decreased in the recommended range after 2 months and remained low at 2 years. In 62 patients UNaV levels decreased after 2 months and then increased back to baseline at 2 years. Initially the two groups did not differ in terms of BP (134.3 ± 16.10/80.84 ± 12.23 vs. 134.2 ± 16.67/81.55 ± 11.18 mmHg, mean ± SD), body weight (72.64 ± 15.17 vs. 73.79 ± 12.69 kg), UNaV (161.0 ± 42.22 vs. 158.2 ± 48.66 mEq/24 h), and LVM index (LVMI; 97.09 ± 20.42 vs. 97.31 ± 18.91 g/m²). After 2years. they did not differ in terms of BP (125.3 ± 10.69/74.97 ± 7.67 vs. 124.5 ± 9.95/75.21 ± 7.64 mmHg) and body weight (71.14 ± 14.29 vs. 71.50 ± 11.87 kg). Significant differences were seen for UNaV (97.3 ± 23.01 vs. 152.6 ± 49.96 mEq/24 h) and LVMI (86.38 ± 18.17 vs. 103.1 ± 21.06 g/m²). Multiple regression analysis: UNaV directly and independently predicted LVMI variations, either as absolute values (R² = 0.369; β = 0.611; p < 0.001), or changes from baseline to +2years. (R² = 0.454; β = 0.677; p < 0.001). Systolic BP was a weaker predictor of LVMI (R² = 0.369; β = 0.168; p = 0.027; R² = 0.454; β = 0.012; p = 0.890), whereas diastolic BP was not correlated with LVMI. The prevalence of left ventricular hypertrophy decreased (29/76 to 15/76) in the first group while it increased in the less compliant patients (25/62 to 36/62; Chi²p = 0.002). Conclusion: LVM seems linked to sodium consumption in patients already under proper BP control by medications.

Increased O-GlcNAcylation induces myocardial hypertrophy

Myocardial hypertrophy is a common precursor of many diseases, and it can lead to myocardial ischemia and weaken cardiac contractility. High-sugar diets and diabetes are high risk factors for cardiac hypertrophy. O-GlcNAcylation, a dynamic and ubiquitous post-translational glycosylation of proteins on serine/threonine residues, has been usually considered as a nutrient sensor. Hyperglycemia, hyperlipidemia, and hyperinsulinemia lead to an enhancement of protein O-GlcNAcylation; however, whether excessive O-linked β-N-acetylglucosamine (O-GlcNAc) glycosylation of proteins in cardiomyocytes causes cardiac hypertrophy remains unclear. In this study, we treated cultured primary cardiomyocytes or mice with streptozotocin (STZ) or PUGNAc, two inhibitors of O-GlcNAcase (OGA) to elevate cellular O-GlcNAcylation. We found that increased O-GlcNAcylation induced hypertrophy-like changes by detecting cardiomyocyte morphology or measuring the thickness of mice left ventricular wall with HE staining. The mRNA levels of cardiac hypertrophy-related genes, atrial natriuretic peptide (ANP) and β-myosin heavy chain (β-MHC), are increased in drug treatment groups. We further found that the increase of O-GlcNAcylation upregulated the activity of cAMP response element-binding protein (CREB) in cultured primary cells and in vivo by detecting the phosphorylation level of CREB by Western blot and the mRNA levels of CREB downstream targets C-fos and C-jun by RT-qPCR. These results suggest that the increased O-GlcNAcylation in cardiomyocytes is associated with cardiac hypertrophy both in cultured cells and in vivo, which provides possible intervention targets and approaches for the clinical treatment of myocardial hypertrophy triggered by high carbohydrate diets.

Synthesis and Excretion of Atrial Natriuretic Peptide in Secretory Cardiomyocytes in Experimental Hypertension

The intensity of accumulation and excretion of atrial natriuretic peptide in myocytes of the right atrium in rat models of renovascular hypertension and salt loading was studied by immunocytochemical analysis and transmission electron microscopy. The data suggest that high BP is not the decisive factor affecting secretion of atrial natriuretic peptide in atrial cardiomyocytes. The regulatory mechanisms of the accumulation and release of the peptide from myocyte granules can vary and depend on the pathogenesis of hypertension.

Sodium Intake and Target Organ Damage in Hypertension-An Update about the Role of a Real Villain

Salt intake is too high for safety nowadays. The main active ion in salt is sodium. The vast majority of scientific evidence points out the importance of sodium restriction for decreasing cardiovascular risk. International Guidelines recommend a large reduction in sodium consumption to help reduce blood pressure, organ damage, and cardiovascular risk. Regulatory authorities across the globe suggest a general restriction of sodium intake to prevent cardiovascular diseases. In spite of this seemingly unanimous consensus, some researchers claim to have evidence of the unhealthy effects of a reduction of sodium intake, and have data to support their claims. Evidence is against dissenting scientists, because prospective, observational, and basic research studies indicate that sodium is the real villain: actual sodium consumption around the globe is far higher than the safe range. Sodium intake is directly related to increased blood pressure, and independently to the enlargement of cardiac mass, with a possible independent role in inducing left ventricular hypertrophy. This may represent the basis of myocardial ischemia, congestive heart failure, and cardiac mortality. Although debated, a high sodium intake may induce initial renal damage and progression in both hypertensive and normotensive subjects. Conversely, there is general agreement about the adverse role of sodium in cerebrovascular disease. These factors point to the possible main role of sodium intake in target organ damage and cardiovascular events including mortality. This review will endeavor to outline the existing evidence.

Serelaxin and the AT2 Receptor Agonist CGP42112 Evoked a Similar, Nonadditive, Cardiac Antifibrotic Effect in High Salt-Fed Mice That Were Refractory to Candesartan Cilexetil

Fibrosis is involved in the majority of cardiovascular diseases and is a key contributor to end-organ dysfunction. In the current study, the antifibrotic effects of recombinant human relaxin-2 (serelaxin; RLX) and/or the AT₂R agonist CGP42112 (CGP) were compared with those of the established AT₁R antagonist, candesartan cilexetil (CAND), in a high salt-induced cardiac fibrosis model. High salt (HS; 5%) for 8 weeks did not increase systolic blood pressure in male FVB/N mice, but CAND treatment alone significantly reduced systolic blood pressure from HS-induced levels. HS significantly increased cardiac interstitial fibrosis, which was reduced by either RLX and/or CGP, which were not additive under the current experimental conditions, while CAND failed to reduce HS-induced cardiac fibrosis. The antifibrotic effects induced by RLX and/or CGP were associated with reduced myofibroblast differentiation. Additionally, all treatments inhibited the HS-induced elevation in tissue inhibitor of matrix metalloproteinases-1, together with trends for increased MMP-13 expression, that collectively would favor collagen degradation. Furthermore, these antifibrotic effects were associated with reduced cardiac inflammation. Collectively, these results highlight that either RXFP1 or AT₂R stimulation represents novel therapeutic strategies to target fibrotic conditions, particularly in HS states that may be refractory to AT₁R blockade.

Imbalance of angiotensin-converting enzymes affects myocardial apoptosis during cardiac arrest induced by acute pulmonary embolism in a porcine model

Acute pulmonary embolism (APE) with cardiac arrest (CA) is associated with a high mortality rate. Even upon return of the spontaneous circulation (ROSC), APE‑CA survivors are prone to myocardial cell apoptosis, a key cellular mechanism that induces heart failure. A recent study by our group discovered a post‑resuscitation imbalance in the serum angiotensin‑converting enzyme (ACE)2/ACE axis of the renin‑angiotensin system (RAS), as well as regressive cardiac function in a porcine model of APE‑CA. However, it has remained elusive how this imbalance in the ACE2/ACE axis affects myocardial cell apoptosis. In the present study, western blot and immunohistochemical analyses demonstrated that the RAS was only activated in the left myocardium, as evidenced by a decreased ACE2/ACE ratio following APE‑CA and ROSC, but not the right myocardium. Ultrastructural analysis confirmed myocardial apoptosis in the left and right myocardium. Furthermore, B‑cell lymphoma 2 (Bcl‑2)‑associated X protein (Bax) and caspase‑3 levels were elevated and Bcl‑2 levels were decreased in the left myocardium following APE‑CA and ROSC. Treatment with the ACE inhibitor captopril for 30 min after initiation of ROSC prevented the increase in Bax and the decrease in Bcl‑2 in the left myocardium compared with that in saline‑treated pigs. Captopril also inhibited the activation of extracellular signal‑regulated kinase (ERK)1/2 in the left myocardium. The results of the present study suggest that an imbalance in the ACE2/ACE axis has an important role in myocardial apoptosis following APE‑CA, which may be attributed to decreased ERK1/2 activation. In addition, it was indicated that captopril prevents apoptosis in the left myocardium after ROSC.

Treatment with enalapril and not diltiazem ameliorated progression of chronic kidney disease in rats, and normalized renal AT1 receptor expression as measured with PET imaging

ACE inhibitors are considered first line of treatment in patients with many forms of chronic kidney disease (CKD). Other antihypertensives such as calcium channel blockers achieve similar therapeutic effectiveness in attenuating hypertension-related renal damage progression. Our objective was to explore the value of positron emission tomography (PET) imaging of renal AT1 receptor (AT1R) to guide therapy in the 5/6 subtotal-nephrectomy (Nx) rat model of CKD. Ten weeks after Nx, Sprague-Dawley rats were administered 10mg/kg/d enalapril (NxE), 30mg/kg/d diltiazem (NxD) or left untreated (Nx) for an additional 8-10 weeks. Kidney AT1R expression was assessed using in vivo [18F]fluoropyridine-losartan PET and in vitro autoradiography. Compared to shams, Nx rats exhibited higher systolic blood pressure that was reduced by both enalapril and diltiazem. At 18-20 weeks, plasma creatinine and albuminuria were significantly increased in Nx, reduced to sham levels in NxE, but enhanced in NxD rats. Enalapril treatment decreased kidney angiotensin II whereas diltiazem induced significant elevations in plasma and kidney levels. Reduced PET renal AT1R levels in Nx were normalized by enalapril but not diltiazem, and results were supported by autoradiography. Reduction of renal blood flow in Nx was restored by enalapril, while no difference was observed in myocardial blood flow amongst groups. Enhanced left ventricle mass in Nx was not reversed by enalapril but was augmented with diltiazem. Stroke volume was diminished in untreated Nx compared to shams and restored with both therapies. [18F]Fluoropyridine-Losartan PET allowed in vivo quantification of kidney AT1R changes associated with progression of CKD and with various pharmacotherapies.

High-salt intake negatively regulates fat deposition in mouse

High-salt (HS) intake contributes to hypertension and cardiopathy, but the effect of HS on fat deposition is controversial. Feed intake, fat mass, the percentage of abdominal fat, heat production, rate of oxygen consumption and the respiratory exchange ratio of mice on a HS diet were significantly decreased (P < 0.01 or 0.05) compared with mice on a normal-salt (NS) diet. An in vitro experiment with differentiating pre-adipocytes showed reduced fat deposition in the presence of high concentrations of NaCl (>0.05 M). Abdominal fat mRNA profiles and protein measurements showed that 5 known genes involved in lipolysis were up-regulated significantly and 9 genes related to lipogenesis were down-regulated in HS mice. Abundant genes and some proteins (ATP2a1, AGT, and ANGPTL4) related to calcium ion metabolism or the renin-angiotensin system (RAS) were differentially expressed between HS and NS mice. Of special interest, CREB1 phosphorylation (S133 and S142), a key factor involved in calcium signaling and other pathways, was up-regulated in HS mice. By IPA analysis, a network mediated by calcium was established providing the molecular mechanisms underlying the negative effect of HS on fat deposition.

Hydrogen Sulfide Inhibits High-Salt Diet-Induced Myocardial Oxidative Stress and Myocardial Hypertrophy in Dahl Rats

The study aimed to examine the protective effect of hydrogen sulfide (H₂S) on high-salt-induced oxidative stress and myocardial hypertrophy in salt-sensitive (Dahl) rats. Thirty male Dahl rats and 40 SD rats were included in the study. They were randomly divided into Dahl control (Dahl + NS), Dahl high salt (Dahl + HS), Dahl + HS + NaHS, SD + NS, SD + HS, SD + HS + NaHS, and SD + HS + hydroxylamine (HA). Rats in Dahl + NS and SD + NS groups were given chow with 0.5% NaCl and 0.9% normal saline intraperitoneally daily. Myocardial structure, α-myosin heavy chain (α-MHC) and β-myosin heavy chain (β-MHC) expressions were determined. Endogenous myocardial H₂S pathway and oxidative stress in myocardial tissues were tested. Myocardial H₂S pathway was downregulated with myocardial hypertrophy featured by increased heart weight/body weight and cardiomyocytes cross-sectional area, decreased α-MHC and increased β-MHC expressions in Dahl rats with high-salt diet (all P < 0.01), and oxidative stress in myocardial tissues was significantly activated, demonstrated by the increased contents of hydroxyl radical, malondialdehyde and oxidized glutathione and decreased total antioxidant capacity, carbon monoxide, catalase, glutathione, glutathione peroxidase, superoxide dismutase (SOD) activities and decreased SOD1 and SOD2 protein expressions (P < 0.05, P < 0.01). However, H₂S reduced myocardial hypertrophy with decreased heart weight/body weight and cardiomyocytes cross-sectional area, increased α-MHC, decreased β-MHC expressions and inhibited oxidative stress in myocardial tissues of Dahl rats with high-salt diet. However, no significant difference was found in H₂S pathway, myocardial structure, α-MHC and β-MHC protein and oxidative status in myocardial tissues among SD + NS, SD + HS, and SD + HS + NaHS groups. HA, an inhibitor of cystathionine β-synthase, inhibited myocardial H₂S pathway (P < 0.01), and stimulated myocardial hypertrophy and oxidative stress in SD rats with high-salt diet. Hence, H₂S inhibited myocardial hypertrophy in high salt-stimulated Dahl rats in association with the enhancement of antioxidant capacity, thereby inhibiting oxidative stress in myocardial tissues.

Irbesartan ameliorates hyperlipidemia and liver steatosis in type 2 diabetic db/db mice via stimulating PPAR-γ, AMPK/Akt/mTOR signaling and autophagy

Irbesartan (Irb), a unique subset of angiotensin II receptor blockers (ARBs) with PPAR-γ activation function, has been reported to play a role in renal dysfunction, glucose metabolism, and abnormal lipid profile in diabetic animal models and humans. However, the underlying mechanisms that improve hyperlipidemia and liver steatosis are unclear. This study investigated the effects of Irb on lipid metabolism and hepatic steatosis using the spontaneous type 2 diabetic db/db mouse model. The results demonstrated body and liver weight, food consumption, lipid content in serum and liver tissue, and liver dysfunction as well as hepatic steatosis were increased in db/db mice compared with db/m mice, whereas the increases were reversed by Irb treatment. Moreover, Irb administration resulted in an increase in LC3BII as well as the LC3BII/I ratio through activating PPAR-γ and p-AMPK and inhibiting p-Akt and p-mTOR, thereby inducing autophagy in the db/db mouse liver. Therefore, our findings suggest that Irb can ameliorate hyperlipidemia and liver steatosis by upregulating the expression of PPAR-γ, activating the AMPK/Akt/mTOR signaling pathway and inducing liver autophagy.

High salt intake as a multifaceted cardiovascular disease: new support from cellular and molecular evidence

Scientists worldwide have disseminated the idea that increased dietary salt increases blood pressure. Currently, salt intake in the general population is ten times higher than that consumed in the past and at least two times higher than the current recommendation. Indeed, a salt-rich diet increases cardiovascular morbidity and mortality. For a long time, however, the deleterious effects associated with high salt consumption were only related to the effect of salt on blood pressure. Currently, several other effects have been reported. In some cases, the deleterious effects of high salt consumption are independently associated with other common risk factors. In this article, we gather data on the effects of increased salt intake on the cardiovascular system, from infancy to adulthood, to describe the route by which increased salt intake leads to cardiovascular diseases. We have reviewed the cellular and molecular mechanisms through which a high intake of salt acts on the cardiovascular system to lead to the progressive failure of a healthy heart.

Activation of TRPV1 attenuates high salt-induced cardiac hypertrophy through improvement of mitochondrial function

BACKGROUND AND PURPOSE

High-salt diet induces cardiac remodelling and leads to heart failure, which is closely related to cardiac mitochondrial dysfunction. Transient receptor potential (TRP) channels are implicated in the pathogenesis of cardiac dysfunction. We investigated whether activation of TRP vanilloid (subtype 1) (TRPV1) channels by dietary capsaicin can, by ameliorating cardiac mitochondrial dysfunction, prevent high-salt diet-induced cardiac hypertrophy.

EXPERIMENTAL APPROACH

Male wild-type (WT) and TRPV1(-/-) mice were fed a normal or high-salt diet with or without capsaicin for 6 months. Their cardiac parameters and endurance capacity were assessed. Mitochondrial respiration and oxygen consumption were measured using high-resolution respirometry. The expression levels of TRPV1, sirtuin 3 and NDUFA9 were detected in cardiac cells and tissues.

KEY RESULTS

Chronic high-salt diet caused cardiac hypertrophy and reduced physical activity in mice; both effects were ameliorated by capsaicin intake in WT but not in TRPV1(-/-) mice. TRPV1 knockout or high-salt diet significantly jeopardized the proficiency of mitochondrial Complex I oxidative phosphorylation (OXPHOS) and reduced Complex I enzyme activity. Chronic dietary capsaicin increased cardiac mitochondrial sirtuin 3 expression, the proficiency of Complex I OXPHOS, ATP production and Complex I enzyme activity in a TRPV1-dependent manner.

CONCLUSIONS AND IMPLICATIONS

TRPV1 activation by dietary capsaicin can antagonize high-salt diet-mediated cardiac lesions by ameliorating its deleterious effect on the proficiency of Complex I OXPHOS. TRPV1-mediated amendment of mitochondrial dysfunction may represent a novel target for management of early cardiac dysfunction.

A1H NMR-based metabonomic investigation of time-dependent metabolic trajectories in a high salt-induced hypertension rat model

The time-dependent metabolic profiles in urine, plasma and feces of salt-fed hypertensive rats were systematically investigated using NMR-based metabonomics.

Cardiovascular effects of dietary salt intake in aged healthy cats: a 2-year prospective randomized, blinded, and controlled study

High salt dry expanded diets are commercially available for cats to increase water intake and urine volume, as part of the prevention or treatment of naturally occurring urinary stone formation (calcium oxalates and struvites). However, chronic high salt intake may have potential cardiovascular adverse effects in both humans, especially in aging individuals, and several animal models. The objective of this prospective, randomized, blinded, and controlled study was to assess the long-term cardiovascular effects of high salt intake in healthy aged cats. Twenty healthy neutered cats (10.1±2.4 years) were randomly allocated into 2 matched groups. One group was fed a high salt diet (3.1 g/Mcal sodium, 5.5 g/Mcal chloride) and the other group a control diet of same composition except for salt content (1.0 g/Mcal sodium, 2.2 g/Mcal chloride). Clinical examination, systolic and diastolic arterial blood pressure measurements, standard transthoracic echocardiography and conventional Doppler examinations were repeatedly performed on non-sedated cats by trained observers before and over 24 months after diet implementation. Radial and longitudinal velocities of the left ventricular free wall and the interventricular septum were also assessed in systole and diastole using 2-dimensional color tissue Doppler imaging. Statistics were performed using a general linear model. No significant effect of dietary salt intake was observed on systolic and diastolic arterial blood pressure values. Out of the 33 tested imaging variables, the only one affected by dietary salt intake was the radial early on late diastolic velocity ratio assessed in the endocardium of the left ventricular free wall, statistically lower in the high salt diet group at 12 months only (P = 0.044). In conclusion, in this study involving healthy aged cats, chronic high dietary salt intake was not associated with an increased risk of systemic arterial hypertension and myocardial dysfunction, as observed in some elderly people, salt-sensitive patients and animal models.

Enhanced angiotensin-converting enzyme activity and systemic reactivity to angiotensin II in normotensive rats exposed to a high-sodium diet

A high salt diet is associated with reduced activity of the renin-angiotensin-aldosterone system (RAAS). However, normotensive rats exposed to high sodium do not show changes in systemic arterial pressure. We hypothesized that, despite the reduced circulating amounts of angiotensin II induced by a high salt diet, the cardiovascular system's reactivity to angiotensin II is increased in vivo, contributing to maintain arterial pressure at normal levels. Male Wistar rats received chow containing 0.27% (control), 2%, 4%, or 8% NaCl for six weeks. The high-sodium diet did not lead to changes in arterial pressure, although plasma levels of angiotensin II and aldosterone were reduced in the 4% and 8% NaCl groups. The 4% and 8% NaCl groups showed enhanced pressor responses to angiotensin I and II, accompanied by unchanged and increased angiotensin-converting enzyme activity, respectively. The 4% NaCl group showed increased expression of angiotensin II type 1 receptors and reduced expression of angiotensin II type 2 receptors in the aorta. In addition, the hypotensive effect of losartan was reduced in both 4% and 8% NaCl groups. In conclusion these results explain, at least in part, why the systemic arterial pressure is maintained at normal levels in non-salt sensitive and healthy rats exposed to a high salt diet, when the functionality of RAAS appears to be blunted, as well as suggest that angiotensin II has a crucial role in the vascular dysfunction associated with high salt intake, even in the absence of hypertension.

AT1 blockade abolishes left ventricular hypertrophy in heterozygous cMyBP-C null mice: role of FHL1

This research investigated the impact of angiotensin AT1 receptor (Agtr1) blockade on left ventricular (LV) hypertrophy in a mouse model of human hypertrophic cardiomyopathy (HCM), which carries one functional allele of Mybpc3 gene coding cardiac myosin-binding protein C (cMyBP-C). Five-month-old heterozygous cMyBP-C knockout (Het-KO) and wild-type mice were treated with irbesartan (50 mg/kg/day) or vehicle for 8 weeks. Arterial blood pressure was measured by tail cuff plethysmography. LV dimension and function were accessed by echocardiography. Myocardial gene expression was evaluated using RT-qPCR. Compared with wild-type littermates, Het-KO mice had greater LV/body weight ratio (4.0 ± 0.1 vs. 3.3 ± 0.1 mg/g, P < 0.001), thicker interventricular septal wall (0.70 ± 0.02 vs. 0.65 ± 0.01 mm, P < 0.02), lower Mybpc3 mRNA level (-43%, P < 0.02), higher four-and-a-half LIM domains 1 (Fhl1, +110%, P < 0.01), and angiotensin-converting enzyme 1 (Ace1, +67%, P < 0.05), but unchanged Agtr1 mRNA levels in the septum. Treatment with irbesartan had no effect in wild-type mice but abolished septum-predominant LV hypertrophy and Fhl1 upregulation without changes in Ace1 but with an increased Agtr1 (+42%) in Het-KO mice. Thus, septum-predominant LV hypertrophy in Het-KO mice is combined with higher Fhl1 expression, which can be abolished by AT1 receptor blockade, indicating a role of the renin-angiotensin system and Fhl1 in cMyBP-C-related HCM.

Different cross-talk sites between the renin-angiotensin and the kallikrein-kinin systems

Targeting the renin-angiotensin system (RAS) constitutes a major advance in the treatment of cardiovascular diseases. Evidence indicates that angiotensin-converting enzyme inhibitors and angiotensin AT1 receptor blockers act on both the RAS and the kallikrein-kinin system (KKS). In addition to the interaction between the RAS and KKS at the level of angiotensin-converting enzyme catalyzing both angiotensin II generation and bradykinin degradation, the RAS and KKS also interact at other levels: 1) prolylcarboxypeptidase, an angiotensin II inactivating enzyme and a prekallikrein activator; 2) kallikrein, a kinin-generating and prorenin-activating enzyme; 3) angiotensin-(1-7) exerts kininlike effects and potentiates the effects of bradykinin; and 4) the angiotensin AT1 receptor forms heterodimers with the bradykinin B2 receptor. Moreover, angiotensin II enhances B1 and B2 receptor expression via transcriptional mechanisms. These cross-talks explain why both the RAS and KKS are up-regulated in some circumstances, whereas in other circumstances both systems change in the opposite manner, expressed as an activated RAS and a depressed KKS. As the cross-talks between the RAS and the KKS play an important role in response to different stimuli, taking these cross-talks between the two systems into account may help in the development of drugs targeting the two systems.

Ramipril attenuates lipid peroxidation and cardiac fibrosis in an experimental model of rheumatoid arthritis

INTRODUCTION

Recent studies revealed that co-morbidity and mortality due to cardiovascular disease are increased in patients with rheumatoid arthritis (RA) but little is known about factors involved in these manifestations. This study aimed at characterizing the impact of arthritis on oxidative stress status and tissue fibrosis in the heart of rats with adjuvant-induced arthritis (AIA).

METHODS

AIA was induced with complete Freund's adjuvant in female Lewis rats. Animals were treated by oral administration of vehicle or angiotensin-converting enzyme inhibitor ramipril (10 mg/kg/day) for 28 days, beginning 1 day after arthritis induction. Isolated adult cardiomyocytes were exposed to 10 μM 4-hydroxynonenal (HNE) for 24 hours in the presence or absence of 10 μM ramipril.

RESULTS

Compared to controls, AIA rats showed significant 55 and 30% increase of 4-HNE/protein adducts in serum and left ventricular (LV) tissues, respectively. Cardiac mitochondrial NADP+-isocitrate dehydrogenase (mNADP-ICDH) activity decreased by 25% in AIA rats without any changes in its protein and mRNA expression. The loss of mNADP-ICDH activity was correlated with enhanced accumulation of HNE/mNADP-ICDH adducts as well as with decrease of glutathione and NADPH. Angiotensin II type 1 receptor (AT1R) expression and tissue fibrosis were induced in LV tissues from AIA rats. In isolated cardiomyocytes, HNE significantly decreased mNADP-ICDH activity and enhanced type I collagen and connective tissue growth factor expression. The oral administration of ramipril significantly reduced HNE and AT1R levels and restored mNADP-ICDH activity and redox status in LV tissues of AIA rats. The protective effects of this drug were also evident from the decrease in arthritis scoring and inflammatory markers.

CONCLUSION

Collectively, our findings disclosed that AIA induced oxidative stress and fibrosis in the heart. The fact that ramipril attenuates inflammation, oxidative stress and tissue fibrosis may provide a novel strategy to prevent heart diseases in RA.

Moderate cardiac-selective overexpression of angiotensin II type 2 receptor protects cardiac functions from ischaemic injury

We hypothesized that moderate cardiac-selective overexpression of the angiotensin II type 2 receptor (AT2R) would protect the myocardium from ischaemic injury after a myocardial infarction (MI) induced by coronary artery ligation. For in vitro studies, adenoviral vector expressing genomic DNA of AT2R and enhanced green fluorescence protein (EGFP) was used to overexpress AT2R in rat neonatal cardiac myocytes. Expression of AT2R, measured by real-time PCR and immunostaining, demonstrated efficient transduction of AT2R in a dose-dependent pattern. The AT2R constitutively induced apoptosis in rat neonatal cardiac myocytes in dose-dependent patterns. For in vivo studies, 4 × 10(10) vector genomes (vg) of recombinant adeno-associated virus serotype 9 (rAAV9)-chicken β actin promoter-AT2R was injected into the left ventricle of 5-day-old Sprague-Dawley rats. At 6 weeks of age, hearts were harvested and expression of AT2R determined by real-time PCR and Western blotting. Expression was increased onefold over control hearts, and no apoptosis was detected. Two subsequent in vivo studies were performed. In a prevention study, 4 × 10(10) vg of rAAV9-CBA-AT2R was injected into the left ventricle of 5-day-old Sprague-Dawley rats and MI was induced at 6 weeks of age. For a post-treatment study, 4 × 10(10) vg of rAAV9-CBA-AT2R was administrated to the peri-infarcted myocardium area immediately after MI in 6-week-old animals. For both in vivo studies, cardiac functions were assessed using echocardiography and haemodynamic measurements 4 weeks after coronary artery ligation. In the in vivo studies, the rats subjected to MI showed significant decreases in fractional shortening and rate of change of left ventricular pressure, with increased left ventricular end-diastolic pressure and ventricular hypertrophy. For the prevention study, the moderate cardiac-selective overexpression of AT2R attenuated these MI-induced impairments and also caused a decrease in ventricular wall thinning. In the post-treatment study, the overexpression of AT2R partly reversed the MI-induced cardiac dysfunction. Myocardial infarction also induced the upregulation of angiotensin II type 1 receptor, angiotensin-converting enzyme and collagen I mRNA expression, all of which were attenuated by the overexpression of AT2R. It is concluded that moderate cardiac-selective overexpression of AT2R protects heart function from ischaemic injury, which may be mediated, at least in part, through modulation of components of the cardiac renin-angiotensin system and collagen levels in the myocardium.

Towards a re-definition of 'cardiac hypertrophy' through a rational characterization of left ventricular phenotypes: a position paper of the Working Group 'Myocardial Function' of the ESC

Many primary or secondary diseases of the myocardium are accompanied with complex remodelling of the cardiac tissue that results in increased heart mass, often identified as cardiac 'hypertrophy'. Although there have been numerous attempts at defining such 'hypertrophy', the present paper delineates the reasons as to why current definitions of cardiac hypertrophy remain unsatisfying. Based on a brief review of the underlying pathophysiology and tissue and cellular events driving myocardial remodelling with or without changes in heart dimensions, as well as current techniques to detect such changes, we propose to restrict the use of the currently popular term 'hypertrophy' to cardiac myocytes that may or may not accompany the more complex tissue rearrangements leading to changes in shape or size of the ventricles, more broadly referred to as 'remodelling'. We also discuss the great potential of genetically modified (mouse) models as tools to define the molecular pathways leading to the different forms of left ventricle remodelling. Finally, we present an algorithm for the stepwise assessment of myocardial phenotypes applicable to animal models using well-established imaging techniques and propose a list of parameters most suited for a critical evaluation of such pathophysiological phenomena in mouse models. We believe that this effort is the first step towards a much auspicated unification of the terminology between the experimental and the clinical cardiologists.

Diets rich in saturated fat and/or salt differentially modulate atrial natriuretic peptide and renin expression in C57BL/6 mice

PURPOSE

To study the effects of a diet rich in salt and/or saturated fat on atrial natriuretic peptide (ANP)-granules, hypertension, renin expression, and cardiac structure in C57Bl/6 mice.

METHODS

Young adult male mice were separated into four groups (n = 12) and fed one of the following for 9 weeks: standard chow/normal salt (SC-NS), high-fat chow/normal salt (HF-NS), standard chow/high salt (SC-HS) and high-fat chow/high salt (HF-HS). Alterations in the serum ANP, ultrastructural analysis of cardiomyocytes that produce ANP, structural analysis of the left ventricle, blood pressure, renin expression, glomerular filtration rate (GFR), feed efficiency, and lipid and glucose parameters were examined.

RESULTS

The HF-NS diet showed a small increase in ANP production and left ventricular hypertrophy, increased food efficiency, and abnormal lipid and glucose parameters. The SC-HS diet showed a large increase in ANP granules in myocytes and corresponding elevation in ANP serum levels, left ventricular hypertrophy, hypertension, decrease in renin levels, and increase in GFR. The combination of the two diets (HF-HS) had an additive effect.

CONCLUSION

The incorporation of a high-fat high-salt diet induced ultrastructural changes in cardiomyocytes, increased the production of ANP and increased its serum level, and reduced the amount of renin in the kidney.