Cardiomyocyte apoptosis in animal models of obesity

High fat diet altered cardiac metabolic gene profile in Psammomys obesus gerbils

Background

In metabolic disorders, myocardial fatty infiltration is critically associated with lipotoxic cardiomyopathy.

Methods

Twenty Psammomys obesus gerbils were randomly assigned to normal plant or high fat diet. Sixteen weeks later, myocardium was sampled for pathobiological evaluation.

Results

A sixteen-week high fat diet resulted in myocardial structure disorganization, with collagen deposits, lipid accumulation, cardiomyocyte apoptosis and inflammatory cell infiltration. Myocardial expressions of glucose transporter GLUT1 and pyruvate dehydrogenase (PDH) inhibitor, PDH kinase (PDK)4 increased, while insulin-regulated GLUT4 expression remained unchanged. Myocardial expressions of molecules regulating fatty acid transport, CD36 and fatty acid binding protein (FABP)3, were increased, while expression of rate-controlling fatty acid β-oxidation, carnitine palmitoyl transferase (CPT)1B decreased. Myocardial expression of AMP-activated protein kinase (AMPK), decreased, while expression of peroxisome proliferator activated receptors (PPAR)-α and -γ did not change.

Conclusion

In high fat diet fed Psammomys obesus, an original experimental model of nutritionally induced metabolic syndrome mixing genetic predisposition and environment interactions, a short period of high fat feeding was sufficient to induce myocardial structural alterations, associated with altered myocardial metabolic gene expression in favor of lipid accumulation.

High Fat Diet Upregulates Fatty Acid Oxidation and Ketogenesis via Intervention of PPAR-γ

Background/Aims:

Systemic hyperlipidemia and intracellular lipid accumulation induced by chronic high fat diet (HFD) leads to enhanced fatty acid oxidation (FAO) and ketogenesis. The present study was aimed to determine whether activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) by surplus free fatty acids (FA) in hyperlipidemic condition, has a positive feedback regulation over FAO and ketogenic enzymes controlling lipotoxicity and cardiac apoptosis.

Methods:

8 weeks old C57BL/6 wild type (WT) or PPAR-γ^−/− mice were challenged with 16 weeks 60% HFD to induce obesity mediated type 2 diabetes mellitus (T2DM) and diabetic cardiomyopathy. Treatment course was followed by echocardiographic measurements, glycemic and lipid profiling, immunoblot, qPCR and immunohistochemistry (IHC) analysis of PPAR-γ and following mitochondrial metabolic enzymes 3-hydroxy-3- methylglutaryl-CoA synthase (HMGCS2), mitochondrial β-hydroxy butyrate dehydrogenase (BDH1) and pyruvate dehydrogenase kinase isoform 4 (PDK4). In vivo model was translated in vitro, with neonatal rat cardiomyocytes (NRCM) treated with PPAR-γ agonist/antagonist and PPAR-γ overexpression adenovirus in presence of palmitic acid (PA). Apoptosis was determined in vivo from left ventricular heart by TUNEL assay and immunoblot analysis.

Results:

We found exaggerated circulating ketone bodies production and expressions of the related mitochondrial enzymes HMGCS2, BDH1 and PDK4 in HFD-induced diabetic hearts and in PA-treated NRCM. As a mechanistic approach we found HFD mediated activation of PPAR-03B3 is associated with the above-mentioned mitochondrial enzymes. HFD-fed PPAR-γ^−/− mice display decreased hyperglycemia, hyperlipidemia associated with increased insulin responsiveness as compared to HFD-fed WT mice PPAR-γ^−/−−HFD mice demonstrated a more robust functional recovery after diabetes induction, as well as significantly reduced myocyte apoptosis and improved cardiac function.

Conclusions:

PPAR-γ has been described previously to regulate lipid metabolism and adipogenesis. The present study suggests for the first time that increased PPAR-γ expression by HFD is responsible for cardiac dysfunction via upregulation of mitochondrial enzymes HMGCS2, BDH1 and PDK4. Targeting PPAR-γ and its downstream mitochondrial enzymes will provide novel strategies in preventing metabolic and myocardial dysfunction in diabetes mellitus.

Sodium orthovanadate suppresses palmitate-induced cardiomyocyte apoptosis by regulation of the JAK2/STAT3 signaling pathway

Elevated circulatory free fatty acids (FFAs) especially saturated FFAs, such as palmitate (PA), are detrimental to the heart. However, mechanisms responsible for this phenomenon remain unknown. Here, the role of JAK2/STAT3 in PA-induced cytotoxicity was investigated in cardiomyocytes. We demonstrate that PA suppressed the JAK2/STAT3 pathway by dephosphorylation of JAK2 (Y1007/1008) and STAT3 (Y705), and thus blocked the translocation of STAT3 into the nucleus. Conversely, phosphorylation of S727, another phosphorylated site of STAT3, was increased in response to PA treatment. Pretreatment of JNK inhibitor, but not p38 MAPK inhibitor, inhibited STAT3 (S727) activation induced by PA and rescued the phosphorylation of STAT3 (Y705). The data suggested that JNK may be another upstream factor regulating STAT3, and verified the important function of P-STAT3 (Y705) in PA-induced cardiomyocyte apoptosis. Sodium orthovanadate (SOV), a protein tyrosine phosphatase inhibitor, obviously inhibited PA-induced apoptosis by restoring JAK2/STAT3 pathways. This effect was diminished by STAT3 inhibitor Stattic. Collectively, our data suggested a novel mechanism that the inhibition of JAK2/STAT3 activation was responsible for palmitic lipotoxicity and SOV may act as a potential therapeutic agent by targeting JAK2/STAT3 in lipotoxic cardiomyopathy treatment.

Cardiac-specific down-regulation of carnitine palmitoyltransferase-1b (CPT-1b) prevents cardiac remodeling in obese mice

OBJECTIVE

To determine whether inhibiting cardiac carnitine palmitoyltransferase-1b (CPT-1b) improves obesity-related cardiomyopathy.

METHODS

Four-week-old male C57BL/6J mice were fed with high-fat diet (HFD) for 12 weeks to induce obesity. At 6 weeks of age, mice were subjected to intramyocardial injection with lentivirus to down-regulate the expression of either cardiac CPT-1b or green fluorescent protein. Morphological, biochemical, functional, histological, and ultrastructural profiles were assessed at 16 weeks of age.

RESULTS

HFD administration elicited obesity, cardiac hypertrophy, and systolic dysfunction accompanied with altered biochemical parameters. In addition, HFD consumption promoted lipid accumulation and reactive oxygen species generation in cardiomyocytes and damaged myocardial ultrastructure. Cardiac CPT-1b silencing protected against HFD-induced cardiac remodeling by decreasing heart weight/tibial length ratio and increasing left ventricular ejection fraction and fractional shortening, as well as normalizing left ventricular diameter. Meanwhile, CPT-1b inhibition mitigated the changes in biochemical parameters, aggravated myocardial lipid accumulation, reduced intramyocardial reactive oxygen species production, and partly amended myocardial ultrastructural alterations in obese mice.

CONCLUSIONS

Cardiac CPT-1b suppression protects against the aggravation of cardiac morphology and function associated with HFD feeding. CPT-1b represents a potential therapeutic target for the treatment of cardiac dysfunction related to metabolic diseases such as obesity and diabetes.

The number of cardiac myocytes in the hypertrophic and hypotrophic left ventricle of the obese and calorie-restricted mouse heart

Changes in body mass due to varying amounts of calorie intake occur frequently with obesity and anorexia/cachexia being at opposite sides of the scale. Here, we tested whether a high-fat diet or calorie restriction (CR) decreases the number of cardiac myocytes and affects their volume. Ten 6-8-week-old mice were randomly assigned to a normal (control group, n = 5) or high-fat diet (obesity group, n = 5) for 28 weeks. Ten 8-week-old mice were randomly assigned to a normal (control group, n = 5) or CR diet (CR group, n = 5) for 7 days. The left ventricles of the hearts were prepared for light and electron microscopy, and analysed by design-based stereology. In CR, neither the number of cardiac myocytes, the relationship between one- and multinucleate myocytes nor their mean volume were significantly different between the groups. In contrast, in the obese mice we observed a significant increase in cell size combined with a lower number of cardiomyocytes (P < 0.05 in the one-sided U-test) and an increase in the mean number of nuclei per myocyte. The mean volume of myofibrils and mitochondria per cardiac myocyte reflected the hypertrophic and hypotrophic remodelling in obesity and CR, respectively, but were only significant in the obese mice, indicating a more profound effect of the obesity protocol than in the CR experiments. Taken together, our data indicate that long-lasting obesity is associated with a loss of cardiomyocytes of the left ventricle, but that short-term CR does not alter the number of cardiomyocytes.

20 years of leptin: Role of leptin in cardiomyocyte physiology and physiopathology

Since the discovery of leptin in 1994 by Zhang et al., there have been a number of reports showing its implication in the development of a wide range of cardiovascular diseases. However, there exists some controversy about how leptin can induce or preserve cardiovascular function, as different authors have found contradictory results about leptin beneficial or detrimental effects in leptin deficient/resistant murine models and in wild type tissue and cardiomyocytes. Here, we will focus on the main discoveries about the leptin functions at cardiac level within the last two decades, focusing on its role in cardiac metabolism, remodeling and contractile function.

Direct effects of adipokines on the heart: focus on adiponectin

Cardiovascular disease, including heart failure, is a principal cause of death in individuals with obesity and diabetes. However, the mechanisms of obesity- and diabetes-induced heart disease are multifaceted and remain to be clearly defined. Of relevance to this review, there is currently great research and clinical interest in the endocrine effects of adipokines on the myocardium and their role in heart failure. We will discuss the potential significance of adipokines in the pathogenesis of heart failure via their ability to regulate remodeling events including metabolism, hypertrophy, fibrosis, and cell death. As an excellent example, we will first focus on adiponectin which is best known to confer numerous cardioprotective effects. However, we comprehensively discuss the existing literature that highlights it would be naive to assume that this was always the case. We also focus on lipocalin-2 which mediates pro-inflammatory and pro-apoptotic effects. It is important when studying actions of adipokines to integrate cellular and mechanistic analyses and translate these to physiologically relevant in vivo models and clinical studies. However, assimilating studies on numerous cardiac remodeling events which ultimately dictate cardiac dysfunction into a unifying conclusion is challenging. Nevertheless, there is undoubted potential for the use of adipokines as robust biomarkers and appropriate therapeutic targets in heart failure.

The role of echocardiography in the evaluation of cardiac damage in hypertensive obese patient

Obesity rates are rising worldwide. Often obesity is associated with hypertension leading to an increased cardiovascular risk. Both obesity and hypertension induce several modifications in cardiac structure and function, particularly atrial and ventricular remodeling is a common finding shared by these two conditions. It has been demonstrated obesity leads to: left ventricular (LV) mass increase, LV systolic and diastolic dysfunction, left atrium (LA) size increase, LA function alterations and pericardial fat accumulation. Nowadays, the development of cardiac imaging techniques allows to early identifying any preclinical damage related to hypertension and obesity. This could be very important in order to improve patient management and medical therapy.

Evaluation of antiobesity and cardioprotective effect of Gymnema sylvestre extract in murine model

OBJECTIVE

Obesity plays a central role in the insulin resistance syndrome, which is associated with hyperinsulinemia, hypertension, hyperlipidemia, type 2 diabetes mellitus, and an increased risk of atherosclerotic cardiovascular disease. The present study was done to assess the effect of Gymnema sylvestre extract (GSE) in the high fat diet (HFD)-induced cellular obesity and cardiac damage in Wistar rats.

MATERIALS AND METHODS

Adult male Wistar rats (150-200 g body weight) were used in this study. HFD was used to induce obesity. Body mass index, hemodynamic parameters, serum leptin, insulin, glucose, lipids, apolipoprotein levels, myocardial apoptosis, and antioxidant enzymes were assessed. Organ and visceral fat pad weights and histopathological studies were also carried out.

RESULTS

Oral feeding of HFD (20 g/day) for a period of 28 days resulted in a significant increase in body mass index, organ weights, visceral fat pad weight, cardiac caspase-3, cardiac DNA laddering (indicating apoptotic inter-nucleosomal DNA fragment), and lipid peroxide levels of cardiac tissues of rats. Further, mean arterial blood pressure, heart rate, serum leptin, insulin, LDH, LDL-C, total cholesterol, triglycerides, and apolipoprotein-B levels were enhanced significantly, whereas serum HDL-C, apoliporotein-A1 levels, and cardiac Na(+) K(+) ATPase, antioxidant enzymes levels were significantly decreased. Furthermore, treatment with standardized ethanolic GSE (200 m/kg/p.o.) for a period of 28 days resulted in significant reversal of above mentioned changes in the obese Wistar rats.

CONCLUSION

The present study has demonstrated the significant antiobesity potential of GSE in murine model of obesity.

Long-term effects of early overnutrition in the heart of male adult rats: role of the renin-angiotensin system

To analyze the long-term effects of early overfeeding on the heart and coronary circulation, the effect of ischemia-reperfusion (I/R) and the role of the renin-angiotensin system (RAS) was studied in isolated hearts from control and overfed rats during lactation. On the day of birth litters were adjusted to twelve pups per mother (controls) or to three pups per mother (overfed). At 5 months of age, the rats from reduced litters showed higher body weight and body fat than the controls. The hearts from these rats were perfused in a Langendorff system and subjected to 30 min of ischemia followed by 15 min of reperfusion (I/R). The myocardial contractility (dP/dt) and the coronary vasoconstriction to angiotensin II were lower, and the expression of the apoptotic marker was higher, in the hearts from overfed rats compared to controls. I/R reduced the myocardial contractily, the coronary vasoconstriction to angiotensin II and the vasodilatation to bradykinin, and increased the expression of (pro)renin receptor and of apoptotic and antiapoptotic markers, in both experimental groups. I/R also increased the expression of angiotensinogen in control but not in overfed rats. In summary, the results of this study suggest that early overnutrition induces reduced activity of the RAS and impairment of myocardial and coronary function in adult life, due to increased apoptosis. Ischemia-reperfusion produced myocardial and coronary impairment and apoptosis, which may be related to activation of RAS in control but not in overfed rats, and there may be protective mechanisms in both experimental groups.

Obese and lean Zucker rats demonstrate differential sensitivity to rates of food reinforcement in a choice procedure

The obese Zucker rat carries two recessive fa alleles that result in the expression of an obese phenotype. Obese Zuckers have higher food intake than lean controls in free-feed studies in which rats have ready access to a large amount of one type of food. The present study examined differences in obese and lean Zucker rats using concurrent schedules of reinforcement, which more ecologically models food selection using two food choices that have limited, but generally predictable availability. Lever-pressing of ten lean (Fa/Fa or Fa/fa) and ten obese (fa/fa) Zucker rats was placed under three concurrent variable interval variable interval (conc VI VI) schedules of sucrose and carrot reinforcement, in which the programmed reinforcer ratios for 45-mg food pellets were 5:1, 1:1, and 1:5. Allocation of responses to the two food alternatives was characterized using the generalized matching equation, which allows sensitivity to reinforcer rates (a) and bias toward one alternative (log k) to be quantified. All rats showed a bias toward sucrose, though there were no differences between lean and obese Zucker rats. In addition, obese Zucker rats exhibited higher sensitivity to reinforcement rates than lean rats. This efficient pattern of responding was related to overall higher deliveries of food pellets. Effective matching for food, then, may be another behavioral pattern that contributes to an obese phenotype.

Modulation of the cardiovascular system by leptin

It is well established that individuals with the metabolic syndrome have a significantly increased risk of cardiovascular disease and much effort has been expended to elicit the underlying mechanisms. Various studies have proposed that excessive or deficient physiological effects mediated by leptin make an important contribution, yet many paradoxical observations often preclude a clear definition of the role of leptin. This review article will briefly discuss principal and most recent evidence on direct and indirect regulation of the cardiovascular system by leptin, focusing on cardiac structural and functional as well as vascular effects.

Lipocalin-2 induces cardiomyocyte apoptosis by increasing intracellular iron accumulation

Our objective was to determine whether lipocalin-2 (Lcn2) regulates cardiomyocyte apoptosis, the mechanisms involved, and the functional significance. Emerging evidence suggests that Lcn2 is a proinflammatory adipokine associated with insulin resistance and obesity-related complications, such as heart failure. Here, we used both primary neonatal rat cardiomyocytes and H9c2 cells and demonstrated for the first time that Lcn2 directly induced cardiomyocyte apoptosis, an important component of cardiac remodeling leading to heart failure. This was shown by detection of DNA fragmentation using TUNEL assay, phosphatidylserine exposure using flow cytometry to detect annexin V-positive cells, caspase-3 activity using enzymatic assay and immunofluorescence, and Western blotting for the detection of cleaved caspase-3. We also observed that Lcn2 caused translocation of the proapoptotic protein Bax to mitochondria and disruption of mitochondrial membrane potential. Using transient transfection of GFP-Bax, we confirmed that Lcn2 induced co-localization of Bax with MitoTracker® dye. Importantly, we used the fluorescent probe Phen Green SK to demonstrate an increase in intracellular iron in response to Lcn2, and depleting intracellular iron using an iron chelator prevented Lcn2-induced cardiomyocyte apoptosis. Administration of recombinant Lcn2 to mice for 14 days increased cardiomyocyte apoptosis as well as an acute inflammatory response with compensatory changes in cardiac functional parameters. In conclusion, Lcn2-induced cardiomyocyte apoptosis is of physiological significance and occurs via a mechanism involving elevated intracellular iron levels and Bax translocation.

Adipocytokines in atherothrombosis: focus on platelets and vascular smooth muscle cells

Visceral obesity is a relevant pathological condition closely associated with high risk of atherosclerotic vascular disease including myocardial infarction and stroke. The increased vascular risk is related also to peculiar dysfunction in the endocrine activity of adipose tissue responsible of vascular impairment (including endothelial dysfunction), prothrombotic tendency, and low-grade chronic inflammation. In particular, increased synthesis and release of different cytokines, including interleukins and tumor necrosis factor-α (TNF-α), and adipokines—such as leptin—have been reported as associated with future cardiovascular events. Since vascular cell dysfunction plays a major role in the atherothrombotic complications in central obesity, this paper aims at focusing, in particular, on the relationship between platelets and vascular smooth muscle cells, and the impaired secretory pattern of adipose tissue.