Mechanisms of cardiac hypertrophy

Atrial Fibrillation in Chronic Kidney Disease: An Overview

Chronic kidney disease (CKD) is a condition that can be caused due to any etiology leading to structural damage to the kidney, which can be measured by a decrease in estimated glomerular filtration rate (eGFR) and the presence of damage biomarkers for more than three months. This article has discussed the causal relationship between atrial fibrillation (AF) and CKD, a few of them being inflammation, renin-angiotensin-aldosterone system (RAAS) activation, anemia, and uremia associated with CKD. This review mentioned the clinical impact of the presence of AF in CKD patients. The presence of AF in CKD patients aggravates the renal dysfunction, which in turn adds to the generation of AF. This article explores the various pharmacological and interventional treatment modalities, including antiarrhythmics, anticoagulants, and cardiac ablation, and their complications, leading to restricted usage in CKD patients.

Hypothalamic Norepinephrine Concentration and Heart Mass in Hypertensive ISIAH Rats Are Associated with a Genetic Locus on Chromosome 18

The relationship between activation of the sympathetic nervous system and cardiac hypertrophy has long been known. However, the molecular genetic basis of this association is poorly understood. Given the known role of hypothalamic norepinephrine in the activation of the sympathetic nervous system, the aim of the work was to carry out genetic mapping using Quantitative Trait Loci (QTL) analysis and determine the loci associated both with an increase in the concentration of norepinephrine in the hypothalamus and with an increase in heart mass in Inherited Stress-Induced Arterial Hypertension (ISIAH) rats simulating the stress-sensitive form of arterial hypertension. The work describes a genetic locus on chromosome 18, in which there are genes that control the development of cardiac hypertrophy associated with an increase in the concentration of norepinephrine in the hypothalamus, i.e., genes involved in enhanced sympathetic myocardial stimulation. No association of this locus with the blood pressure was found. Taking into consideration previously obtained results, it was concluded that the contribution to the development of heart hypertrophy in the ISIAH rats is controlled by different genetic loci, one of which is associated with the concentration of norepinephrine in the hypothalamus (on chromosome 18) and the other is associated with high blood pressure (on chromosome 1). Nucleotide substitutions that may be involved in the formation or absence of association with blood pressure in different rat strains are discussed.

Mechanistic insights to the cardioprotective effect of blueberry nutraceutical extract in isoprenaline-induced cardiac hypertrophy

BACKGROUND

Lowbush blueberry extract (Vaccinium angustifolium) is abundant with polyphenols (such as chlorogenic acid) with high antioxidant profile. It has received great interest due to its protective role in many disorders such as heart diseases and neurological disorders.

HYPOTHESIS

We hypothesized that blueberry leaf extract might have a protective effect against cardiac hypertrophy via suppressing oxidative stress, inflammation and fibrosis.

METHOD

Blueberry leaf nutraceutical extract was administered orally to male albino rats at three different doses (25, 50 and 100 mg/kg/day of the extract, equivalent to 3.4, 6.8 and 13.6 mg of chlorogenic acid, respectively) once daily for 28 consecutive days against a dose of isoprenaline (ISO) (5 mg/kg) for 14 days.

RESULTS

The results indicated that isoprenaline induced significant myocardial damage, characterized by conduction abnormalities, increased heart-to-body weight ratio, increased serum CKMB, AST, c-TnI and LDH. Pretreatment with blueberry extract at a dose of 50 mg/kg/day (equivalent to 6.8 mg chlorogenic acid) protected against ISO-induced ECG changes, leakage of cardiac enzymes and histopathological changes. Also, ISO caused significant glutathione depletion, lipid peroxidation and reduction in activities of antioxidant catalase enzyme. These effects were prevented by pretreatment with blueberry extract. Additionally, ISO elicited inflammatory effects by increasing the expression of NF-κB, COX-2, TNF-α and IL-6 while pretreatment with blueberry extract significantly inhibited these inflammatory responses. Furthermore, ISO induced fibrosis by increasing the level of TGF-β while pretreatment with blueberry extract significantly reduced it.

CONCLUSION

These findings indicate that blueberry leaf extract possessed a potent protective effect against ISO-induced cardiac hypertrophy via suppressing oxidative stress, inflammation and fibrosis.

Pathological cardiac remodeling occurs early in CKD mice from unilateral urinary obstruction, and is attenuated by Enalapril

Cardiovascular disease constitutes the leading cause of mortality in patients with chronic kidney disease (CKD) and end-stage renal disease. Despite increasing recognition of a close interplay between kidney dysfunction and cardiovascular disease, termed cardiorenal syndrome (CRS), the underlying mechanisms of CRS remain poorly understood. Here we report the development of pathological cardiac hypertrophy and fibrosis in early stage non-uremic CKD. Moderate kidney failure was induced three weeks after unilateral urinary obstruction (UUO) in mice. We observed pathological cardiac hypertrophy and increased fibrosis in UUO-induced CKD (UUO/CKD) animals. Further analysis indicated that this cardiac fibrosis was associated with increased expression of transforming growth factor β (TGF-β) along with significant upregulation of Smad 2/3 signaling in the heart. Moreover early treatment of UUO/CKD animals with an angiotensin-converting-enzyme inhibitor (ACE I), Enalapril, significantly attenuated cardiac fibrosis. Enalapril antagonized activation of the TGF-β signaling pathway in the UUO/CKD heart. In summary our study demonstrates the presence of pathological cardiac hypertrophy and fibrosis in mice early in UUO-induced CKD, in association with early activation of the TGF-β/Smad signaling pathway. We also demonstrate the beneficial effect of ACE I in alleviating this early fibrogenic process in the heart in UUO/CKD animals.

Hypertension regulating angiotensin peptides in the pathobiology of cardiovascular disease

Renin angiotensin system (RAS) is an endogenous hormone system involved in the control of blood pressure and fluid volume. Dysregulation of RAS has a pathological role in causing cardiovascular diseases through hypertension. Among several key components of RAS, angiotensin peptides, varying in amino acid length and biological function, have important roles in preventing or promoting hypertension, cardiovascular diseases, stroke, vascular remodeling etc. These peptides are generated by the metabolism of inactive angiotensinogen or its derived peptides by hydrolyzing action of certain enzymes. Angiotensin II, angiotensin (1-12), angiotensin A and angiotensin III bind primarily to angiotensin II type 1 receptor and cause vasoconstriction, accumulation of inflammatory markers to sub-endothelial region of blood vessels and activate smooth muscle cell proliferation. Moreover, when bound to angiotensin II type 2 receptor, angiotensin II works as cardio-protective peptide and halt pathological cell signals. Other peptides like angiotensin (1-9), angiotensin (1-7), alamandine and angiotensin IV also help in protecting from cardiovascular diseases by binding to their respective receptors.

Extracellular Vesicles in Cardiovascular Theranostics

Extracellular vesicles (EVs) are small bilayer lipid membrane vesicles that can be released by most cell types and detected in most body fluids. EVs exert key functions for intercellular communication via transferring their bioactive cargos to recipient cells or activating signaling pathways in target cells. Increasing evidence has shown the important regulatory effects of EVs in cardiovascular diseases (CVDs). EVs secreted by cardiomyocytes, endothelial cells, fibroblasts, and stem cells play essential roles in pathophysiological processes such as cardiac hypertrophy, cardiomyocyte survival and apoptosis, cardiac fibrosis, and angiogenesis in relation to CVDs. In this review, we will first outline the current knowledge about the physical characteristics, biological contents, and isolation methods of EVs. We will then focus on the functional roles of cardiovascular EVs and their pathophysiological effects in CVDs, as well as summarize the potential of EVs as therapeutic agents and biomarkers for CVDs. Finally, we will discuss the specific application of EVs as a novel drug delivery system and the utility of EVs in the field of regenerative medicine.

Non-proliferative and Proliferative Lesions of the Cardiovascular System of the Rat and Mouse

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Japan (JSTP), Europe (ESTP), Great Britain (BSTP) and North America (STP) to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory animals. The primary purpose of this publication is to provide a standardized nomenclature for characterizing lesions observed in the cardiovascular (CV) system of rats and mice commonly used in drug or chemical safety assessment. The standardized nomenclature presented in this document is also available electronically for society members on the internet (http://goreni.org). Accurate and precise morphologic descriptions of changes in the CV system are important for understanding the mechanisms and pathogenesis of those changes, differentiation of natural and induced injuries and their ultimate functional consequence. Challenges in nomenclature are associated with lesions or pathologic processes that may present as a temporal or pathogenic spectrum or when natural and induced injuries share indistinguishable features. Specific nomenclature recommendations are offered to provide a consistent approach.

Estimated Glomerular Filtration Rate and Systolic Time Intervals in Risk Stratification for Increased Left Ventricular Mass Index and Left Ventricular Hypertrophy

Either decreased renal function or increased systolic time interval is associated with cardiac hypertrophy and poor cardiac outcome. The aim of this study was to evaluate combination of renal function and brachial systolic time intervals were associated with increased left ventricular mass index (LVMI) and left ventricular hypertrophy (LVH).In total of 990 patients were consecutively included in this study from January 2011 to December 2012. All study participants were further classified into 4 groups by the values of estimated glomerular filtration rate (eGFR) and ratio of brachial preejection period (bPEP) to brachial ejection time (bET). The classification of 4 groups were eGFR ≥ 45 mL/min/1.73 m and bPEP/bET < 0.38 (group 1), eGFR ≥ 45 ml/min/1.73 m and bPEP/bET ≥ 0.38 (group 2), eGFR < 45 mL/min/1.73 m and bPEP/bET < 0.38 (group 3), and eGFR < 45 mL/min/1.73 m and bPEP/bET ≥ 0.38 (group 4), respectively. Patients in groups 1 and 4 had the lowest and highest LVMI among 4 groups, respectively (P < 0.001). In multivariable analyses, increased LVMI and LVH were significantly associated with patients in groups 2, 3 and 4 (vs group 1) (P ≤ 0.019).Our study demonstrated that joined parameter of renal function and systolic time intervals, in terms of eGFR and bPEP/bET, might be an alternative method in risk stratification for increased LVMI and LVH.

Volume overload and adverse outcomes in chronic kidney disease: clinical observational and animal studies

BACKGROUND

Volume overload is frequently encountered and is associated with cardiovascular risk factors in patients with chronic kidney disease (CKD). However, the relationship between volume overload and adverse outcomes in CKD is not fully understood.

METHODS AND RESULTS

A prospective cohort of 338 patients with stage 3 to 5 CKD was followed for a median of 2.1 years. The study participants were stratified by the presence or absence of volume overload, defined as an overhydration index assessed by bioimpedance spectroscopy exceeding 7%, the 90th percentile for the healthy population. The primary outcome was the composite of estimated glomerular filtration rate decline ≥50% or end-stage renal disease. The secondary outcome included a composite of morbidity and mortality from cardiovascular causes. Animal models were used to simulate fluid retention observed in human CKD. We found that patients with volume overload were at a higher risk of the primary and secondary end points in the adjusted Cox models. Furthermore, overhydration appears to be more important than hypertension in predicting an elevated risk. In rats subjected to unilateral nephrectomy and a high-salt diet, the extracellular water significantly increased. This fluid retention was associated with an increase in blood pressure, proteinuria, renal inflammation with macrophage infiltration and tumor necrosis factor-α overexpression, glomerular sclerosis, and cardiac fibrosis. Diuretic treatment with indapamide attenuated these changes, suggesting that fluid retention might play a role in the development of adverse outcomes.

CONCLUSIONS

Volume overload contributes to CKD progression and cardiovascular diseases. Further research is warranted to clarify whether the correction of volume overload would improve outcomes for CKD patients.

Silibinin attenuates cardiac hypertrophy and fibrosis through blocking EGFR-dependent signaling

Cardiac hypertrophy is a major determinant of heart failure. The epidermal growth factor receptor (EGFR) plays an important role in cardiac hypertrophy. Since silibinin suppresses EGFR in vitro and in vivo, we hypothesized that silibinin would attenuate cardiac hypertrophy through disrupting EGFR signaling. In this study, we examined this hypothesis using neonatal cardiac myocytes and fibroblasts induced by angiotensin II (Ang II) and animal model by aortic banding (AB) mice. Our data revealed that silibinin obviously blocked cardiac hypertrophic responses induced by pressure overload. Meanwhile, silibinin markedly reduced the increased generation of EGFR. Moreover, these beneficial effects were associated with attenuation of the EGFR-dependent ERK1/2, PI3K/Akt signaling cascade. We further demonstrated silibinin decreased inflammation and fibrosis by blocking the activation of NF-kappaB and TGF-beta1/Smad signaling pathways in vitro and in vivo. Our results indicate that silibinin has the potential to protect against cardiac hypertrophy, inflammation, and fibrosis through blocking EGFR activity and EGFR-dependent different intracellular signaling pathways.

Effect of intermedin1-53 on angiotensin II-induced hypertrophy in neonatal rat ventricular myocytes

OBJECTIVES

Intermedin (IMD) is coexpressed in the heart with its receptor, which suggests that it may have localized actions as a modulator of cardiac function. The present study was designed to observe the interaction between IMD and cardiac hypertrophy and the possible mechanism involved in the antihypertrophic effects of IMD1-53 in cultured neonatal ventricular myocytes.

METHODS

Myocyte hypertrophy was induced by treating the cells with angiotensin II, and the hypertrophic response was characterized by a significant increase in cell surface area, protein synthesis, and BNP mRNA expression.

RESULTS

Our results showed that angiotensin II led to an obvious decrease in the production, secretion, and mRNA expression of IMD and increase receptor activity modifying proteins 1, 3 mRNA expression. Moreover, IMD1-53 inhibited the angiotensin II-induced hypertrophic response and the effects of IMD1-53 were similar to those of equivalent-dose adrenomedullin and could been blocked by H89. Otherwise, in our study, IMD1-53 resulted in dose-dependent increases of cAMP production in cardiomyocytes.

CONCLUSIONS

Thus, IMD and its receptor system are involved in cardiac hypertrophy, and like adrenomedullin, IMD1-53 exerts an antihypertrophic effect on neonatal cardiomyocytes and the effect can be mediated by the cAMP/PKA pathway.

The effects of intra-cage aspen tube on cardiac morphology and gene expression

According to the European recommendations rodents should be provided with a nest box if there is insufficient nesting material to build a complete, covered nest. Rats are generally poor nest builders; hence an additional structure is needed. Optimally, housing refinement may be combined with better science; at least it should not detract from the scientific integrity. In order to evaluate these options, there is a need to assess the items used in individual research projects. Studies investigating molecular mechanisms of cardiac hypertrophy and heart failure are typically long-lasting studies; therefore, refinement of the housing of rats in these studies is important. The aim of this study was to evaluate in rats whether a wooden tube has any impact on cardiac morphology or on basal gene expression of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP); known markers of cardiac overload, hypertrophy and heart failure. The experimental protocol simulated cardiovascular studies, but without any surgical operations. A total of 42 male Hsd:SD rats were used in an eight-week experiment. After weaning, the experimental group was provided with a rectangular aspen tube and nesting material, and the control group with only nesting material. ANP and BNP gene expression were measured from the left ventricles with Northern blot analysis postmortem along with the absolute weights of the whole heart, left and right atria and left and right chambers. The weights of the whole heart and left chamber were also analysed in relation to body weight. No statistically significant differences were observed in any of these variables. The inter-individual variation was also unchanged by the cage item. In conclusion, the aspen tube does not disrupt research results or alter the number of animals needed and can therefore be recommended for enrichment purposes in cardiovascular studies.

Protein kinase Cθ is required for cardiomyocyte survival and cardiac remodeling

Protein kinase Cs (PKCs) constitute a family of serine/threonine kinases, which has distinguished and specific roles in regulating cardiac responses, including those associated with heart failure. We found that the PKCθ isoform is expressed at considerable levels in the cardiac muscle in mouse, and that it is rapidly activated after pressure overload. To investigate the role of PKCθ in cardiac remodeling, we used PKCθ^−/− mice. In vivo analyses of PKCθ^−/− hearts showed that the lack of PKCθ expression leads to left ventricular dilation and reduced function. Histological analyses showed a reduction in the number of cardiomyocytes, combined with hypertrophy of the remaining cardiomyocytes, cardiac fibrosis, myofibroblast hyper-proliferation and matrix deposition. We also observed p38 and JunK activation, known to promote cell death in response to stress, combined with upregulation of the fetal pattern of gene expression, considered to be a feature of the hemodynamically or metabolically stressed heart. In keeping with these observations, cultured PKCθ^−/− cardiomyocytes were less viable than wild-type cardiomyocytes, and, unlike wild-type cardiomyocytes, underwent programmed cell death upon stimulation with α1-adrenergic agonists and hypoxia. Taken together, these results show that PKCθ maintains the correct structure and function of the heart by preventing cardiomyocyte cell death in response to work demand and to neuro-hormonal signals, to which heart cells are continuously exposed.

Sensitivity of cardiac carnitine palmitoyltransferase to malonyl-CoA is regulated by leptin: similarities with a model of endogenous hyperleptinemia

Acute leptin increase as well as endogenous hyperleptinemia evoked by high-fat diets (HF) activate fatty acid metabolism in nonadipose tissues. This supports the notion that hyperleptinemia is pivotal to prevent/delay steatosis during periods of positive energy balance. We have previously shown that long-term HF spares ectopic accumulation of lipids specifically in the miocardium. Because carnitine palmitoyltransferase I (CPT-I) allows mitochondrial uptake/oxidation of fatty acids, we have hypothesized that leptin drives cardiac CPT-I activity. In the current study, hyperleptinemia was induced in C57BL/6J mice either by exogenous leptin administration or by means of HF, and the ability of malonyl-coenzyme A (malonyl-CoA) (the main endogenous inhibitor of CPT-I) to inhibit cardiac CPT was analyzed. IC(50) values of malonyl-CoA were 8.1 +/- 1.5 micromol/liter in controls vs. 69.3 +/- 5.2 micromol/liter (P < 0.01) in leptin-treated mice. This effect was also observed in cardiac explants incubated with leptin and was blocked by triciribine, a compound shown to inhibit protein kinase B (Akt) phosphorylation (pAkt). In accordance, acute leptin evoked an increase of cardiac pAkt levels, which correlated with CPT sensitivity to malonyl-CoA. Otherwise, the inhibitory effect of malonyl-CoA was hindered in HF hyperleptinemic mice, and in this case, pAkt levels also correlated with CPT sensitivity to malonyl-CoA. Our data show that leptin reduces the sensitivity of cardiac CPT-I to malonyl-CoA and suggest the involvement of an Akt-related signaling pathway in this effect. This mechanism appears to be sensitive to both acute and chronic hyperleptinemia. We conclude that this action of leptin is pivotal to drive cardiac metabolism under situations associated to hyperleptinemia.

Left ventricular geometry predicts cardiovascular outcomes associated with anemia correction in CKD

Partial correction of anemia in patients with chronic kidney disease (CKD) reduces left ventricular hypertrophy (LVH), which is a risk factor for cardiovascular (CV) morbidity, but complete correction of anemia does not improve CV outcomes. Whether LV geometry associates with CV events in patients who are treated to different hemoglobin (Hb) targets is unknown. One of the larger trials to study the effects of complete correction of anemia in stages 3 to 4 CKD was the Cardiovascular Risk Reduction by Early Anemia Treatment with Epoetin Beta (CREATE) trial. Here, we analyzed echocardiographic data from CREATE to determine the prevalence, dynamics, and prognostic implications of abnormal LV geometry in patients who were treated to different Hb targets. The prevalence of LVH at baseline was 47%, with eccentric LVH more frequent than concentric. During the study, LVH prevalence and mean left ventricular mass index did not change significantly, but LV geometry fluctuated considerably within 2 yr in both groups. CV event-free survival was significantly worse in the presence of concentric LVH and eccentric LVH compared with the absence of LVH (P = 0.0009 and P < or = 0.0001, respectively). Treatment to the higher Hb target associated with reduced event-free survival in the subgroup with eccentric LVH at baseline (P = 0.034). In conclusion, LVH is common and associates with poor outcomes among patients with stages 3 to 4 CKD, although both progression and regression of abnormal LV geometry occur. Complete anemia correction may aggravate the adverse prognosis of eccentric LVH.