Sodium restriction modulates innate immunity and prevents cardiac remodeling in a rat model of metabolic syndrome

Cardiac remodeling associated with chronic kidney disease is enhanced in a rat model of metabolic syndrome: Preparation of mesenchymal transition

Cardiac alteration due to chronic kidney disease is described by tissue fibrosis. This remodeling involves myofibroblasts of various origins, including epithelial or endothelial to mesenchymal transitions. In addition, obesity and insulin resistance together or separately seem to exacerbate cardiovascular risk in chronic kidney disease (CKD). The main objective of this study was to assess if pre-existing metabolic disease exacerbates CKD-induced cardiac alterations. In addition, we hypothesised that endothelial to mesenchymal transition participates in this enhancement of cardiac fibrosis. Rats fed cafeteria type diet for 6 months underwent a subtotal nephrectomy at 4 months. Cardiac fibrosis was evaluated by histology and qRT-PCR. Collagens and macrophages were quantified by immunohistochemistry. Endothelial to mesenchymal transitions were assessed by qRT-PCR (CD31, VE-cadherin, α-SMA, nestin) and also by CD31 immunofluorescence staining. Rats fed with cafeteria type regimen were obese, hypertensive and insulin resistant. Cardiac fibrosis was predominant in CKD rats and was highly majored by cafeteria regimen. Collagen-1 and nestin expressions were higher in CKD rats, independently of regimen. Interestingly, in rats with CKD and cafeteria diet we found an increase of CD31 and α-SMA co-staining with suggest an implication of endothelial to mesenchymal transition during heart fibrosis. We showed that rats already obese and insulin resistant had an enhanced cardiac alteration to a subsequent renal injury. Cardiac fibrosis process could be supported by a involvement of the endothelial to mesenchymal transition phenomenon.

A low-salt diet with candesartan administration is associated with acute kidney injury in nephritis by increasing nitric oxide

A low-salt diet may activate the renin-angiotensin-aldosterone system (RAAS) and is often applied simultaneously with RAAS inhibitors, especially for treatment of proteinuric nephritis. To explore the effect of a low-salt diet combined with angiotensin receptor blockers (ARB) on kidney function, the proteinuric nephritis model was induced by single intravenous injection of doxorubicin, and then the SD rats were administrated with candesartan intraperitoneal injection and fed with different salt diets. Rats with low-salt plus candesartan, not either alone, experienced acute kidney injury (AKI) at day 7 and could not self-restore when extending the experiment time from 7 days to 21 days, unless switching low-salt to normal-salt. Among three nitric oxide synthetases (NOS), endothelial NOS (eNOS) was obviously elevated and PI3K-Akt-eNOS signal pathway was activated. N^G-Nitro-L-Arginine Methyl Ester (L-NAME), an eNOS inhibitor, reversed the decreased blood pressure and recovered the kidney dysfunction induced by low-salt with candesartan. The increased TUNEL-positive cells, Bax/Bcl-2 and cleaved-caspase3 protein abundance was ameliorated by L-NAME in vivo. In vitro, sodium nitroprusside, a nitric oxide donor, can also increase Bax/Bcl-2 and cleaved-caspase3 protein level in HK-2 cell. Thus, low-salt diet combined with candesartan in nephritis rats led to AKI, and the mechanism involved the increase of eNOS/NO, which linked to the decrease of blood pressure and the increase of apoptosis. This study provides practical guidance for salt intake in cases of RAS inhibitor usage clinically.

Excessive dietary salt promotes neuroinflammation to worsen retinopathy in mice with streptozotocin-induced diabetes

OBJECTIVE

Diabetic retinopathy (DR) includes vascular and neural tissue injury. Persistent low-grade inflammation may contribute to DR. Increased salt intake has been shown to promote autoimmunity in the brain. This study determined the role of salt intake in DR development.

METHODS

Eight-week-old C57BL/6 J male mice received streptozotocin to induce diabetes. Diabetic or non-diabetic mice were fed a diet containing normal, low and high amounts of salt. The retinal function, structure and inflammatory response were determined 8 weeks after the establishment of diabetes. Interleukin (IL)-1β or a NLR family pyrin domain containing 3 (NLRP3) inhibitor was injected intravitreally and the retinal changes were evaluated.

RESULTS

A high salt diet worsened the functional and structural damage of retinal cells and increased IL-1β in the retina of diabetic mice. IL-1β injection impaired the function of photoreceptors and retinal structure in the diabetic mice. Blocking NLRP3 inhibited IL-1β increase in the mouse bone marrow macrophages cultured in high sodium medium. NLRP3 inhibition attenuated retinal injury of diabetic mice on high salt diet. A low-salt diet also triggered inflammation and cell damage in the retina of diabetic mice but at a lower grade than those induced by high salt diet. A low or high salt diet for 8 weeks did not induce inflammation or cell injury in the retina of mice without diabetes.

CONCLUSION

These results indicate that high salt intake has deleterious effects in DR development through NLRP3 inflammasome activation and the subsequent production of IL-1β. Limiting salt intake may not attenuate DR development.

Diagnostic Criteria for Metabolic Syndrome in Diet-Induced Rodent Models: A Systematic Review

BACKGROUND

Thousands of publications in recent years have addressed the induction of metabolic syndrome (MetS) in rodents. However, the criteria and the reference values for diagnosing this disease have not been defined.

OBJECTIVE

Our main objective was to carry out a systematic review to gather evidence about the criteria for biochemical and anthropometric parameters in which scientific studies have relied on to report that rats developed MetS from a previous dietary manipulation.

METHODS

We compiled characteristics and findings of diet-induced MetS with high-fat, high-carbohydrate, high-fat/high-carbohydrates, and cafeteria diet from PubMed and Science Direct databases published in the last 5 years.

RESULTS

The results on the principal determinants for the syndrome, published in the reviewed articles, were chosen to propose reference values in the rat models of food induction.

CONCLUSION

The values obtained will serve as reference cut-of points in the development of the disease; in addition, the compilation of data will be useful in planning and executing research protocols in animal models.

The effect of venlafaxine on blood pressure and ECG in rats fed with high-fat-fructose diet

Metabolic syndrome represents one of the major health, social and economic issues nowadays, and affects more than 25% people worldwide. Being a multifactorial health problem, metabolic syndrome clusters various features, such as obesity, dyslipidemia, hyperglycemia and hypertension. Each of these disturbances represents a risk factor for developing cardiovascular disease. Moreover, patients with metabolic syndrome are more likely to suffer from depression, thus treatment with antidepressants (e.g. venlafaxine) is often neccessary. However, many of the antidepressants themselves may contribute to worsening or even development of the metabolic syndrome, thus creating a “vicious circle”. The aim of this work was to investigate on the animal model of metabolic syndrome, i.e. on hypertriacylglycerolemic rats fed high-fat-fructose diet (HFFD): 1) the effect of a change in diet from HFFD to a standard diet (SD) and the effect of venlafaxine treatment, 2) during HFFD, 3) as well as during a changed diet to SD. We focused on biometric parameters, blood pressure and selected ECG parameters. We observed the reversibility of the present metabolic and cardiovascular changes by switching the HFFD to SD in the last 3 weeks of the experiment. Switch to the standard diet led to decrease of body weight, even in the presence of venlafaxine. Administration of venlafaxine caused the decrease of heart weight/body weight index in rats fed with HFFD compared to the untreated group fed with HFFD for 8 weeks. Blood pressure, which was increased in the HFFD group showed a tendency to decrease to control values after switching to the standard diet . Administration of venlafaxine led to significant increase in all parameters of blood pressure when rats were fed with HFFD throughout the whole experiment. In untreated rats fed with HFFD for 8 weeks, we observed a shorter PQ interval and prolonged QRS complex as well as QTc interval compared to untreated rats with diet switched to SD. This effect was potentiated by venlafaxine administered not only during HFFD but even after switch to SD. Our results point to the fact that metabolic syndrome is clearly affecting the function of the cardiovascular system by modifying blood pressure and electrical activity of the heart. Moreover, administration of venlafaxine may lead to worsening of the observed changes, especially in the presence of high-fat-fructose diet.

Close association between circulating high-sensitivity cardiac troponin I and metabolic syndrome in the general population

Individuals with metabolic syndrome reportedly have an increased risk of cardiovascular disease, although the association between asymptomatic myocardial damage and metabolic syndrome has not been sufficiently investigated. The present study investigated possible associations between circulating cardiac troponin and metabolic syndrome or related factors. Subjects undergoing their annual health checkups were enrolled in the study (n = 1242). Laboratory measurements included serum high-sensitivity cardiac troponin I (hs-cTnI) and plasma B-type natriuretic peptide (BNP). Individual salt intake was estimated by calculating 24-h urinary sodium excretion from spot urine. Subjects whose electrocardiograms revealed ST-T segment abnormalities or who had renal insufficiency or a history of cardiovascular events were excluded. Subjects with metabolic syndrome had higher hs-cTnI levels than those without, but their BNP levels were equivalent. hs-cTnI levels were significantly associated with the presence and components of metabolic syndrome. Logistic regression analysis with the endpoint of hs-cTnI levels higher than the median value identified metabolic syndrome as an independent determinant of increased hs-cTnI levels. Additionally, urinary salt excretion levels were increased in subjects with metabolic syndrome or any of its components. Logistic regression analysis with the endpoint of metabolic syndrome revealed that hs-cTnI levels were independently associated with the presence of metabolic syndrome. A close association between hs-cTnI levels and the presence of metabolic syndrome, at least partially mediated by increased salt intake, was confirmed to exist in the general population. The findings support the idea that patients with metabolic syndrome develop asymptomatic myocardial damage without obvious ischaemic findings, which leads to increased cardiovascular risk.

New Noonan syndrome model mice with RIT1 mutation exhibit cardiac hypertrophy and susceptibility to β-adrenergic stimulation-induced cardiac fibrosis

BACKGROUND

Noonan syndrome (NS) is a genetic disorder characterized by short stature, a distinctive facial appearance, and heart defects. We recently discovered a novel NS gene, RIT1, which is a member of the RAS subfamily of small GTPases. NS patients with RIT1 mutations have a high incidence of hypertrophic cardiomyopathy and edematous phenotype, but the specific role of RIT1 remains unclear.

METHODS

To investigate how germline RIT1 mutations cause NS, we generated knock-in mice that carried a NS-associated Rit1 A57G mutation (Rit1^A57G/+). We investigated the phenotypes of Rit1^A57G/+ mice in fetal and adult stages as well as the effects of isoproterenol on cardiac function in Rit1^A57G/+ mice.

FINDINGS

Rit1^A57G/+ embryos exhibited decreased viability, edema, subcutaneous hemorrhage and AKT activation. Surviving Rit1^A57G/+ mice had a short stature, craniofacial abnormalities and splenomegaly. Cardiac hypertrophy and cardiac fibrosis with increased expression of S100A4, vimentin and periostin were observed in Rit1^A57G/+ mice compared to Rit1^+/+ mice. Upon isoproterenol stimulation, cardiac fibrosis was drastically increased in Rit1^A57G/+ mice. Phosphorylated (at Thr308) AKT levels were also elevated in isoproterenol-treated Rit1^A57G/+ hearts.

INTERPRETATION

The A57G mutation in Rit1 causes cardiac hypertrophy, fibrosis and other NS-associated features. Biochemical analysis indicates that the AKT signaling pathway might be related to downstream signaling in the RIT1 A57G mutant at a developmental stage and under β-adrenergic stimulation in the heart. FUND: The Grants-in-Aid were provided by the Practical Research Project for Rare/Intractable Diseases from the Japan Agency for Medical Research and Development, the Japan Society for the Promotion of Science KAKENHI Grant.