Cardiac and metabolic changes in long-term high fructose-fat fed rats with severe obesity and extensive intramyocardial lipid accumulation

High-intensity interval training improves cardiomyocyte contractile function and myofilament sensitivity to intracellular Ca2+ in obese rats

High-intensity interval training (HIIT) has shown significant results in addressing adiposity and risk factors associated with obesity. However, there are no studies that investigate the effects of HIIT on contractility and intracellular Ca2+ handling. The purpose of this study was to explore the impact of HIIT on cardiomyocyte contractile function and intracellular Ca2+ handling in rats in which obesity was induced by a saturated high-fat diet (HFD). Male Wistar rats were initially randomized into a standard diet and a HFD group. The experimental protocol spanned 23 weeks, comprising the induction and maintenance of obesity (15 weeks) followed by HIIT treatment (8 weeks). Performance was assessed using the maximum oxygen consumption test (V ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ ). Evaluation encompassed cardiac, adipose and skeletal muscle histology, as well as contractility and intracellular Ca2+ handling. HIIT resulted in a reduction in visceral area, an increase inV ̇ O 2 max ${{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}{\mathrm{max}}}}$ , and an augmentation of gastrocnemius fibre diameter in obese subjects. Additionally, HIIT led to a decrease in collagen fraction, an increase in percentage shortening, and a reduction in systolic Ca2+/percentage shortening and systolic Ca2+/maximum shortening rates. HIIT induces physiological cardiac remodelling, enhancing the contractile function of cardiomyocytes and improving myofilament sensitivity to Ca2+ in the context of obesity. This approach not only enhances cardiorespiratory and physical performance but also reduces visceral area and prevents interstitial fibrosis.

Exercise-Induced Antisenescence and Autophagy Restoration Mitigate Metabolic Disorder-Induced Cardiac Disruption in Mice

INTRODUCTION

Metabolic disorder promotes premature senescence and poses more severe cardiac dysfunction in females than males. Although endurance exercise (EXE) has been known to confer cardioprotection against metabolic diseases, whether EXE-induced cardioprotection is associated with mitigating senescence in females remains unknown. Thus, the aim of the present study was to examine metabolic disorder-induced cardiac anomalies (cellular senescence, metabolic signaling, and autophagy) using a mouse model of obese/type 2 diabetes induced by a high-fat/high-fructose (HFD/HF) diet.

METHODS

Female C57BL/6 mice (10 wk old) were assigned to three groups ( n = 11/group): normal diet group (CON), HFD/HF group, and HFD/HF diet + endurance exercise (HFD/HF + EXE) group. Upon confirmation of hyperglycemia and overweight after 12 wk of HFD/HF diet, mice assigned to HFD/HF + EXE group started treadmill running exercise (60 min·d -1 , 5 d·wk -1 for 12 wk), with HFD/HF diet continued.

RESULTS

EXE ameliorated HFD/HF-induced body weight gain and hyperglycemia, improved insulin signaling and glucose transporter 4 (GLUT4) levels, and counteracted cardiac disruption. EXE reversed HFD/HF-induced myocyte premature senescence (e.g., prevention of p53, p21, p16, and lipofuscin accumulation), resulting in suppression of a senescence-associated secretory phenotype such as inflammation (tumor necrosis factor α and interleukin-1β) and oxidative stress (protein carbonylation). Moreover, EXE restored HFD/HF-induced autophagy flux deficiency, evidenced by increased LC3-II concomitant with p62 reduction and restoration of lysosome function-related proteins (LAMP2, CATHEPSIN L, TFEB, and SIRT1). More importantly, EXE retrieved HFD/HF-induced apoptosis arrest (e.g., increased cleaved CASPASE3, PARP, and TUNEL-positive cells).

CONCLUSIONS

Our study demonstrated that EXE-induced antisenescence phenotypes, autophagy restoration, and promotion of propitiatory cell removal by apoptosis play a crucial role in cardiac protection against metabolic distress-induced cardiac disruption.

Perindopril prevents development of obesity and hypertension in middle aged diet-induced obese rat models of metabolic syndrome

AIMS

The therapeutic properties of anti-hypertensive medications that extend beyond blood pressure lowering have started to become important clinical targets in recent years. This study aimed to assess the cardioprotective effects of perindopril in attenuating complications associated with metabolic syndrome in diet induced obese rats.

MAIN METHODS

Male Wistar-Kyoto (WKY) rats aged 16 weeks were fed either standard rat chow (SC) or given a high-fat-high-carbohydrate (HFHC) diet for 20 weeks. Perindopril treatment (1 mg/kg/day) was administered to a subset of WKY rats commencing at week 8 of the 20 week HFHC feeding period. Body weights, food, water and energy intakes, blood pressure, heart rate and glucose tolerance were measured throughout the treatment period. Oxidative stress and inflammatory markers, lipid levels, cardiac collagen deposition, vascular function, aortic and cardiac electrical function were examined after the treatment.

KEY FINDINGS

WKY rats developed metabolic syndrome after 20 weeks of HFHC feeding, evidenced by the presence of abdominal obesity, dyslipidaemia, glucose intolerance and hypertension. Perindopril treatment prevented the development of obesity and hypertension in WKY-HFHC. Perindopril improved blood lipid profiles in HFHC rats with decreases in LDL cholesterol, triglycerides and total cholesterol. Type I collagen levels were decreased in WKY-HFHC rats along with decreases in left ventricle mass. Perindopril treated rats also showed improved cardiac electrical function indicated by decreases in action potential at 90 % of repolarisation in WKY-HFHC rats.

SIGNIFICANCE

These results show that perindopril has a profound effect on preventing the development of metabolic syndrome in animals fed a HFHC diet.

Modelling Diabetic Cardiomyopathy: Using Human Stem Cell-Derived Cardiomyocytes to Complement Animal Models

Diabetes is a global epidemic, with cardiovascular disease being the leading cause of death in diabetic patients. There is a pressing need for an in vitro model to aid understanding of the mechanisms driving diabetic heart disease, and to provide an accurate, reliable tool for drug testing. Human induced-pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have potential as a disease modelling tool. There are several factors that drive molecular changes inside cardiomyocytes contributing to diabetic cardiomyopathy, including hyperglycaemia, lipotoxicity and hyperinsulinemia. Here we discuss these factors and how they can be seen in animal models and utilised in cell culture to mimic the diabetic heart. The use of human iPSC-CMs will allow for a greater understanding of disease pathogenesis and open up new avenues for drug testing.

Excessive Sodium Intake Leads to Cardiovascular Disease by Promoting Sex-Specific Dysfunction of Murine Heart

Background

Globally, a high-salt diet (HSD) has become a threat to human health as it can lead to a high risk of cardiac damage. Although some studies investigating HSD have been carried out, the majority has been conducted in males, and there are few female-specific studies, thereby ignoring any effects of sex-specific damage on the heart. In this study, we determined how HSD induces different pathways of cardiovascular diseases through sex-specific effects on cardiac damage in mice.

Methods

An HSD murine model of male and female C57BL/6J mice was fed with sodium-rich chow (4% NaCl). After 8 weeks, cardiac tissues were collected, and the whole gene transcriptome of the hearts of male and female mice was characterized and analyzed using high-throughput RNA sequencing. Immunohistochemistry staining was used to further assess the harmful effects of HSD on protein expression of genes associated with immunity, fibrosis, and apoptosis in male and female mice.

Results

HSD drastically altered the cardiac transcriptome compared to that of the normal heart in both male and female mice and had a sex-specific effect on the cardiac composition in the transcriptome. HSD produced various differentially expressed genes and affected different KEGG pathways of the transcriptome in male and female mice. Furthermore, we found that HSD induced different pathways of cardiovascular disease in the male mice and female mice. The pathway of hypertrophic cardiomyopathy is significantly enriched in HSD-treated male mice, while the pathway of dilated cardiomyopathy is significantly enriched in HSD-treated female mice. Finally, metabolism, immunity, fibrosis, and apoptosis in the mouse heart showed sex-specific changes predicting cardiac damage.

Conclusion

Our results demonstrate that HSD adversely impacts cardiac structure and function by affecting the metabolism, immunity, fibrosis, and apoptosis in the murine heart and induces the mouse to suffer from sex-specific cardiovascular disease. This study provides a new perspective and basis for the differences in the pharmacology and interventional treatment of sex-specific cardiovascular diseases induced by HSD in men and women.

Fructose Metabolism and Cardiac Metabolic Stress

Cardiovascular disease is one of the leading causes of mortality in diabetes. High fructose consumption has been linked with the development of diabetes and cardiovascular disease. Serum and cardiac tissue fructose levels are elevated in diabetic patients, and cardiac production of fructose via the intracellular polyol pathway is upregulated. The question of whether direct myocardial fructose exposure and upregulated fructose metabolism have potential to induce cardiac fructose toxicity in metabolic stress settings arises. Unlike tightly-regulated glucose metabolism, fructose bypasses the rate-limiting glycolytic enzyme, phosphofructokinase, and proceeds through glycolysis in an unregulated manner. In vivo rodent studies have shown that high dietary fructose induces cardiac metabolic stress and functional disturbance. In vitro, studies have demonstrated that cardiomyocytes cultured in high fructose exhibit lipid accumulation, inflammation, hypertrophy and low viability. Intracellular fructose mediates post-translational modification of proteins, and this activity provides an important mechanistic pathway for fructose-related cardiomyocyte signaling and functional effect. Additionally, fructose has been shown to provide a fuel source for the stressed myocardium. Elucidating the mechanisms of fructose toxicity in the heart may have important implications for understanding cardiac pathology in metabolic stress settings.

The effects of two types of Western diet on the induction of metabolic syndrome and cardiac remodeling in obese rats

Metabolic syndrome (MetS) include obesity as a critical feature and is strongly associated with risk of cardiovascular disease (CVD). Insights into mechanisms involved in the pathophysiology of these clinical manifestations are essential for the development of therapeutic strategies. Thus, Western diets (WD) have been widely employed in diet-induced obesity (DIO) model. However, there are variations in fat and sugar proportions of such diets, making comparisons challenging. We aimed to assess the impact of two types of the WD on metabolic status and cardiac remodeling, to achieve a DIO model that better mimics the human pathogenesis of MetS-induced CVD. Male Wistar rats were distributed into three groups: control diet, Western diet fat (WDF), and Western diet sugar (WDS) for 41 weeks. Metabolic and inflammatory parameters and cardiac changes were characterized. WDF and WDS feeding promoted higher serum triglycerides, glucose intolerance, and insulin resistance, while just WDF presented inflammation in adipose tissue. WDF-fed rats showed increased catalase activity and malondialdehyde (MDA) and carbonyl protein levels, suggesting cardiac oxidative stress, while WDS-fed rats only raised MDA. Both WD equally elevated protein expressions involved in lipid metabolism, but only WDF downregulated the glycolysis pathway. Furthermore, the mechanical myocardial function was impaired in obese rats, being more relevant in WDF. In conclusion, both WD effectively triggered MetS features, although inflammation was detected just on the WDF-fed animals. Moreover, the WDF promoted a more pronounced functional, metabolic, and oxidative cardiac disorder, suggesting to be an adequate model for studying CVD in the scenario of MetS.

Molecular Mechanisms of Obesity-Linked Cardiac Dysfunction: An Up-Date on Current Knowledge

Obesity is defined as excessive body fat accumulation, and worldwide obesity has nearly tripled since 1975. Excess of free fatty acids (FFAs) and triglycerides in obese individuals promote ectopic lipid accumulation in the liver, skeletal muscle tissue, and heart, among others, inducing insulin resistance, hypertension, metabolic syndrome, type 2 diabetes (T2D), atherosclerosis, and cardiovascular disease (CVD). These diseases are promoted by visceral white adipocyte tissue (WAT) dysfunction through an increase in pro-inflammatory adipokines, oxidative stress, activation of the renin-angiotensin-aldosterone system (RAAS), and adverse changes in the gut microbiome. In the heart, obesity and T2D induce changes in substrate utilization, tissue metabolism, oxidative stress, and inflammation, leading to myocardial fibrosis and ultimately cardiac dysfunction. Peroxisome proliferator-activated receptors (PPARs) are involved in the regulation of carbohydrate and lipid metabolism, also improve insulin sensitivity, triglyceride levels, inflammation, and oxidative stress. The purpose of this review is to provide an update on the molecular mechanisms involved in obesity-linked CVD pathophysiology, considering pro-inflammatory cytokines, adipokines, and hormones, as well as the role of oxidative stress, inflammation, and PPARs. In addition, cell lines and animal models, biomarkers, gut microbiota dysbiosis, epigenetic modifications, and current therapeutic treatments in CVD associated with obesity are outlined in this paper.

Basic Mechanisms of Diabetic Heart Disease

Diabetes mellitus predisposes affected individuals to a significant spectrum of cardiovascular complications, one of the most debilitating in terms of prognosis is heart failure. Indeed, the increasing global prevalence of diabetes mellitus and an aging population has given rise to an epidemic of diabetes mellitus-induced heart failure. Despite the significant research attention this phenomenon, termed diabetic cardiomyopathy, has received over several decades, understanding of the full spectrum of potential contributing mechanisms, and their relative contribution to this heart failure phenotype in the specific context of diabetes mellitus, has not yet been fully resolved. Key recent preclinical discoveries that comprise the current state-of-the-art understanding of the basic mechanisms of the complex phenotype, that is, the diabetic heart, form the basis of this review. Abnormalities in each of cardiac metabolism, physiological and pathophysiological signaling, and the mitochondrial compartment, in addition to oxidative stress, inflammation, myocardial cell death pathways, and neurohumoral mechanisms, are addressed. Further, the interactions between each of these contributing mechanisms and how they align to the functional, morphological, and structural impairments that characterize the diabetic heart are considered in light of the clinical context: from the disease burden, its current management in the clinic, and where the knowledge gaps remain. The need for continued interrogation of these mechanisms (both known and those yet to be identified) is essential to not only decipher the how and why of diabetes mellitus-induced heart failure but also to facilitate improved inroads into the clinical management of this pervasive clinical challenge.

Protective effect of Hedansanqi Tiaozhi Tang against non-alcoholic fatty liver disease in vitro and in vivo through activating Nrf2/HO-1 antioxidant signaling pathway

BACKGROUND

Hedansanqi Tiaozhi Tang extract (HTT) consists of Notoginseng, Danshen, Hawthorn and Lotus leaf from traditional Chinese medicine, which has significant therapeutic effects on hyperlipidemia in patients with non-alcoholic fatty liver disease (NAFLD).

PURPOSE

This study sought to evaluate the pharmacological effects and molecular mechanism of HTT for the treatment of hyperlipidemia in adipocytes and animal model with NAFLD.

METHODS

Quantitative phytochemical analysis of HTT was performed by HPLC. Antioxidant activity and the adipogenesis in 3T3-L1 cells were assessed. In the rat model induced by high-fat diet, lipid-related and antioxidant markers in serum and liver were detected. Moreover, the organ weights, non-alcoholic steatohepatitis (NASH) score and the levels of Nrf2 and HO-1 in liver sections were analyzed by tissue pathological techniques.

RESULTS

8 constituents were identified in HTT including saponins, flavonoids, alkaloids and others. HTT treatment enhanced antioxidant activities and promoted lipolysis in 3T3-L1 adipocytes. We also found that HTT inhibited weight gain, reduced the lipid profiles and improved the liver function and pathological characteristics induced by high-fat diet. In addition, HTT activated the Nrf2/HO-1 antioxidant pathway in the liver.

CONCLUSION

HTT has protective effect against NAFLD in vitro and in vivo by activating the Nrf2/HO-1 antioxidant pathway.

Prediabetes Induced by Fructose-Enriched Diet Influences Cardiac Lipidome and Proteome and Leads to Deterioration of Cardiac Function prior to the Development of Excessive Oxidative Stress and Cell Damage

Prediabetes is a condition affecting more than 35% of the population. In some forms, excessive carbohydrate intake (primarily refined sugar) plays a prominent role. Prediabetes is a symptomless, mostly unrecognized disease which increases cardiovascular risk. In our work, we examined the effect of a fructose-enriched diet on cardiac function and lipidome as well as proteome of cardiac muscle. Male Wistar rats were divided into two groups. The control group received a normal diet while the fructose-fed group received 60% fructose-supplemented chow for 24 weeks. Fasting blood glucose measurement and oral glucose tolerance test (OGTT) showed slightly but significantly elevated values due to fructose feeding indicating development of a prediabetic condition. Both echocardiography and isolated working heart perfusion performed at the end of the feeding protocol demonstrated diastolic cardiac dysfunction in the fructose-fed group. Mass spectrometry-based, high-performance lipidomic and proteomic analyses were executed from cardiac tissue. The lipidomic analysis revealed complex rearrangement of the whole lipidome with special emphasis on defects in cardiolipin remodeling. The proteomic analysis showed significant changes in 75 cardiac proteins due to fructose feeding including mitochondria-, apoptosis-, and oxidative stress-related proteins. Nevertheless, just very weak or no signs of apoptosis induction and oxidative stress were detected in the hearts of fructose-fed rats. Our results suggest that fructose feeding induces marked alterations in the cardiac lipidome, especially in cardiolipin remodeling, which leads to mitochondrial dysfunction and impaired cardiac function. However, at the same time, several adaptive responses are induced at the proteome level in order to maintain a homeostatic balance. These findings demonstrate that even very early stages of prediabetes can impair cardiac function and can result in significant changes in the lipidome and proteome of the heart prior to the development of excessive oxidative stress and cell damage.

Chronotropic, Inotropic and Dromotropic Parameters of the Heart and Oxidative Stress in Rats Receiving High Doses of Fructose

Background:

Many risk factors, including nutritional ones, contribute to cardiovascular diseases (CVDs). Increased fructose consumption, for example, can lead to an increase in CVD risk factors, i.e. an increase in blood lipids and the development of insulin resistance.

Materials and Methods:

In the present study, Sprague Dawley rats were divided into two groups: control group (free access to tap drinking water for seven weeks), and a group that received fructose 10% in drinking water for seven weeks, (n═8 per each group). In all groups, before starting the test period and seven weeks after it, electrocardiogram was recorded by Power lab system. Unpaired t-test and two-way ANOVA were used for data analysis. Also, oxidative stress parameters were measured.

Results:

In the group received high doses of fructose, a significant reduction (P <0.05) was observed in the PR interval (P<0.001) and a significant increase (P<0.05) in the QTc interval. However, there was no significant change in the RR interval and the voltage of the QRS complex. A significant decrease in catalase, superoxide dismutase and glutathione peroxidase (P<0.05) and a significant increase (P<0.05) in malondialdehyde and lactate dehydrogenase were observed in the group that received fructose in comparison with the control group at the end of the experiment.

Conclusion:

According to our results, the chance of arrhythmias in the rats receiving high doses of fructose was possibly due to the increased oxidative stress in the healthy rats.

Acute intramyocardial lipid accumulation in rats does not slow cardiac conduction per se

Diabetic patients suffer from both cardiac lipid accumulation and an increased risk of arrhythmias and sudden cardiac death. This correlation suggests a link between diabetes induced cardiac steatosis and electrical abnormalities, however, the underlying mechanism remains unknown. We previously showed that cardiac conduction velocity slows in Zucker diabetic fatty rats and in fructose-fat fed rats, models that both exhibit prominent cardiac steatosis. The aim of this study was to investigate whether acute cardiac lipid accumulation reduces conduction velocity per se. Cardiac lipid accumulation was induced acutely by perfusing isolated rat hearts with palmitate-glucose buffer, or subacutely by fasting rats overnight. Subsequently, longitudinal cardiac conduction velocity was measured in right ventricular tissue strips, and intramyocardial triglyceride and lipid droplet content was determined by thin layer chromatography and BODIPY staining, respectively. Perfusion with palmitate-glucose buffer significantly increased intramyocardial triglyceride levels compared to perfusion with glucose (2.16 ± 0.17 (n = 10) vs. 0.92 ± 0.33 nmol/mg WW (n = 9), P < 0.01), but the number of lipid droplets was very low in both groups. Fasting of rats, however, resulted in both significantly elevated intramyocardial triglyceride levels compared to fed rats (3.27 ± 0.43 (n = 10) vs. 1.45 ± 0.24 nmol/mg WW (n = 10)), as well as a larger volume of lipid droplets (0.60 ± 0.13 (n = 10) vs. 0.21 ± 0.06% (n = 10), P < 0.05). There was no significant difference in longitudinal conduction velocity between palmitate-glucose perfused and control hearts (0.77 ± 0.025 (n = 10) vs. 0.75 m/sec ± 0.029 (n = 9)), or between fed and fasted rats (0.75 ± 0.042 m/sec (n = 10) vs. 0.79 ± 0.047 (n = 10)). In conclusion, intramyocardial lipid accumulation does not slow cardiac longitudinal conduction velocity per se. This is true for both increased intramyocardial triglyceride content, induced by palmitate-glucose perfusion, and increased intramyocardial triglyceride and lipid droplet content, generated by fasting.

Pterostilbene Decreases Cardiac Oxidative Stress and Inflammation via Activation of AMPK/Nrf2/HO-1 Pathway in Fructose-Fed Diabetic Rats

PURPOSE

Oxidative stress has a pivotal role in the pathogenesis of diabetes-associated cardiovascular problems, which has remained a primary cause of the increased morbidity and mortality in diabetic patients. It is of paramount importance to prevent the diabetes-associated cardiac complications by reducing oxidative stress with the help of nutritional or pharmacological agents. Pterostilbene (PT), the primary antioxidant in blueberries, has recently gained attention for its promising health benefits in metabolic and cardiac diseases. However, the mechanism whereby PT reduces diabetic cardiac complications is currently unknown.

METHODS

Sprague-Dawley rats were fed with 65% fructose diet with or without PT (20 mg kg^-1 day^-1) for 8 weeks. Heart rate and blood pressure were measured by tail-cuff apparatus. Real-time PCR and western blot experiments were executed to quantify the expression levels of mRNA and protein, respectively.

RESULTS

Fructose-fed rats demonstrated cardiac hypertrophy, hypertension, enhanced myocardial oxidative stress, inflammation and increased NF-κB expression. Administration of PT significantly decreased cardiac hypertrophy, hypertension, oxidative stress, inflammation, NF-κB expression and NLRP3 inflammasome. We demonstrated that PT improved mitochondrial biogenesis as evidenced by increased protein expression of PGC-1α, complex III and complex V in fructose-fed diabetic rats. Further, PT increased protein expressions of AMPK, Nrf2, HO-1 in cardiac tissues, which may account for the prevention of cardiac oxidative stress and inflammation in fructose-fed rats.

CONCLUSIONS

Collectively, PT reduced cardiac oxidative stress and inflammation in diabetic rats through stimulation of AMPK/Nrf2/HO-1 signalling.

Treatment with a fixed dose combination antiretroviral therapy drug containing tenofovir, emtricitabine and efavirenz is associated with cardioprotection in high calorie diet-induced obese rats

HIV-infection, certain antiretroviral drug classes, especially protease inhibitors (PI), and obesity are associated with increased ischaemic heart disease (IHD) risk. However, the effect of PI-free fixed dose combination (FDC) antiretroviral therapy (ART) on hearts exposed to ischaemia-reperfusion injury (I/R) is unknown, particularly in obesity. This is becoming relevant as World Health Organisation guidelines recommend a FDC ART containing (non-) nucleoside reverse transcriptase inhibitors (tenofovir (TDF), emtricitabine (FTC) and efavirenz (EFV)) as first-line HIV treatment. Additionally, obesity rates are rising in HIV-infected populations, not only in ART-experienced individuals, but also at the time of ART initiation, which may further increase the risk of IHD. Therefore, we investigated the effects of PI-free FDC ART in myocardial I/R-exposed hearts from obese rats. Obesity was induced in male wistar rats via a 16-week high calorie diet. At week 10, treatment with a FDC ART drug containing TDF/FTC/EFV was initiated. Biometric and metabolic parameters, as well as myocardial functional recovery and infract size (IS), and myocardial signalling proteins following I/R were assessed after 16 weeks. Obese rats presented with increased body and intraperitoneal fat mass, elevated triglyceride and TBARS levels, whilst the hearts responded to I/R with impaired functional performance and increased IS. The FDC ART treatment did not alter biometric and metabolic parameters in obese rats. In a novel finding, ART protected obese hearts against I/R as shown by improved functional performance and smaller IS vs. untreated obese hearts. Cardioprotection was underscored by increased myocardial phosphorylated endothelial nitric oxide synthase (eNOS) and reduced AMP-kinase levels. In conclusion, these results demonstrate for the first time, that 6-weeks treatment of obese rats with a FDC ART drug specifically containing TDF/FTC/EFV conferred cardioprotection against I/R. The FDC ART-induced cardioprotection was seemingly unrelated to metabolic changes, but rather due to direct cardiac mechanisms including the up-regulation of myocardial eNOS.

Amelioration of High Fructose-Induced Cardiac Hypertrophy by Naringin

Heart failure is a frequent unfavorable outcome of pathological cardiac hypertrophy. Recent increase in dietary fructose consumption mirrors the rise in prevalence of cardiovascular diseases such as cardiac hypertrophy leading to concerns raised by public health experts. Mitochondria, comprising 30% of cardiomyocyte volume, play a central role in modulating redox-dependent cellular processes such as metabolism and apoptosis. Furthermore, mitochondrial dysfunction is a key cause of pathogenesis of fructose-induced cardiac hypertrophy. Naringin, a major flavanone glycoside in citrus species, has displayed strong antioxidant potential in models of oxidative stress. In this study, we evaluated protective effects of naringin against fructose-induced cardiac hypertrophy and associated mechanisms of action, using in vitro and in vivo models. We found that naringin suppressed mitochondrial ROS production and mitochondrial dysfunction in cardiomyocytes exposed to fructose and consequently reduced cardiomyocyte hypertrophy by regulating AMPK-mTOR signaling axis. Furthermore, naringin counteracted fructose-induced cardiomyocyte apoptosis, and this function of naringin was linked to its ability to inhibit ROS-dependent ATM-mediated p53 signaling. This result was supported by observations in in vivo mouse model of cardiac hypertrophy. These findings indicate a novel role for naringin in protecting against fructose-induced cardiac hypertrophy and suggest unique therapeutic strategies for prevention of cardiovascular diseases.

Modulation of hepatic inflammation and energy-sensing pathways in the rat liver by high-fructose diet and chronic stress

PURPOSE

High-fructose consumption and chronic stress are both associated with metabolic inflammation and insulin resistance. Recently, disturbed activity of energy sensor AMP-activated protein kinase (AMPK) was recognized as mediator between nutrient-induced stress and inflammation. Thus, we analyzed the effects of high-fructose diet, alone or in combination with chronic stress, on glucose homeostasis, inflammation and expression of energy sensing proteins in the rat liver.

METHODS

In male Wistar rats exposed to 9-week 20% fructose diet and/or 4-week chronic unpredictable stress we measured plasma and hepatic corticosterone level, indicators of glucose homeostasis and lipid metabolism, hepatic inflammation (pro- and anti-inflammatory cytokine levels, Toll-like receptor 4, NLRP3, activation of NFκB, JNK and ERK pathways) and levels of energy-sensing proteins AMPK, SIRT1 and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α).

RESULTS

High-fructose diet led to glucose intolerance, activation of NFκB and JNK pathways and increased intrahepatic IL-1β, TNFα and inhibitory phosphorylation of insulin receptor substrate 1 on Ser³⁰⁷. It also decreased phospho-AMPK/AMPK ratio and increased SIRT1 expression. Stress alone increased plasma and hepatic corticosterone but did not influence glucose tolerance, nor hepatic inflammatory or energy-sensing proteins. After the combined treatment, hepatic corticosterone was increased, glucose tolerance remained preserved, while hepatic inflammation was partially prevented despite decreased AMPK activity.

CONCLUSION

High-fructose diet resulted in glucose intolerance, hepatic inflammation, decreased AMPK activity and reduced insulin sensitivity. Chronic stress alone did not exert such effects, but when applied together with high-fructose diet it could partially prevent fructose-induced inflammation, presumably due to increased hepatic glucocorticoids.

Long-term diet-induced hypertension in rats is associated with reduced expression and function of small artery SKCa, IKCa, and Kir2.1 channels

Abdominal obesity and/or a high intake of fructose may cause hypertension. K+ channels, Na/K-ATPase, and voltage-gated Ca2+ channels are crucial determinants of resistance artery tone and thus the control of blood pressure. Limited information is available on the role of K+ transporters in long-term diet-induced hypertension in rats. We hypothesized that a 28-week diet rich in fat, fructose, or both, will lead to changes in K+ transporter expression and function, which is associated with increased blood pressure and decreased arterial function. Male Sprague–Dawley (SD) rats received a diet containing normal chow (Control), high-fat chow (High Fat), high-fructose in drinking water (High Fructose), or a combination of high-fat and high-fructose diet (High Fat/Fruc) for 28 weeks from the age of 4 weeks. Measurements included body weight (BW), systolic blood pressure (SBP), mRNA expression of vascular K+ transporters, and vessel myography in small mesenteric arteries (SMAs). BW was increased in the High Fat and High Fat/Fruc groups, and SBP was increased in the High Fat/Fruc group. mRNA expression of small conductance calcium-activated K+ channel (SKCa), intermediate conductance calcium-activated K+ (IKCa), and Kir2.1 inward rectifier K+ channels were reduced in the High Fat/Fruc group. Reduced endothelium-derived hyperpolarization (EDH)-type relaxation to acetylcholine (ACh) was seen in the High Fat and High Fat/Fruc groups. Ba2+-sensitive dilatation to extracellular K+ was impaired in all the experimental diet groups. In conclusion, reduced expression and function of SKCa, IKCa, and Kir2.1 channels are associated with elevated blood pressure in rats fed a long-term High Fat/Fruc. Rats fed a 28-week High Fat/Fruc provide a relevant model of diet-induced hypertension.

UP601, a standardized botanical composition composed of Morus alba, Yerba mate and Magnolia officinalis for weight loss

Background

The prevalence of obesity is surging in an alarming rate all over the world. Pharmaceutical drugs are considered potential adjunctive therapy to lifestyle modification. However, for most, besides being too expensive, their long term usages are hindered by their severe adverse effects. Here we describe the effect of UP601, a standardized blend of extracts from Morus alba, Yerba mate and Magnolia officinalis, in modulating a number of obesity-related phenotypic and biochemical markers in a high-fat high-fructose (HFF)-induced C57BL/6J mouse model of obesity.

Method

Adipogenesis activity of the composition was assessed in 3T3-L1 cells in vitro. Effects of UP601 on body weight and metabolic markers were evaluated. It was administered at oral doses of 300 mg/kg, 450 mg/kg and 600 mg/kg for 7 weeks. Orlistat (40 mg/kg/day) was used as a positive control. Body compositions of mice were assessed using dual energy X-ray absorptiometry (DEXA). Serum biomarkers were measured for liver function and lipid profiling. Relative organ weights were determined. Histopathological analysis was performed for non-alcoholic steatohepatitis (NASH) scoring.

Results

UP601 at 250 μg/ml resulted in 1.8-fold increase in lipolysis. Statistically significant changes in body weight (decreased by 9.1, 19.6 and 25.6% compared to the HFF group at week-7) were observed for mice treated with UP601 at 300, 450 and 600 mg/kg, respectively. Reductions of 9.1, 16.9, and 18.6% in total cholesterol; 45.0, 55.0, 63.6% in triglyceride; 34.8, 37.1 and 41.6% in LDL; 3.2, 21.6 (P = 0.03) and 33.7% (P = 0.005) in serum glucose were observed for UP601 at 300, 450 and 600 mg/kg, respectively. Body fat distribution was found reduced by 31.6 and 17.2% for the 450 mg/kg UP601 and orlistat, respectively, from the DEXA scan analysis. Up to an 89.1% reduction in mesenteric fat deposit was observed for UP601 in relative organ weight. Statistically significant improvements in NASH scores were observed for mice treated with UP601.

Conclusion

UP601, a standardized botanical composition from Morus alba, Yerba mate and Magnolia officinalis could potentially be used for achieving healthy weight loss and maintenance.

Metabolic syndrome and the hepatorenal reflex

Insufficient hepatic O₂ in animal and human studies has been shown to elicit a hepatorenal reflex in response to increased hepatic adenosine, resulting in the stimulation of renal as well as muscle sympathetic nerve activity and activating the renin angiotensin system. Low hepatic ATP, hyperuricemia, and hepatic lipid accumulation reported in metabolic syndrome (MetS) patients may reflect insufficient hepatic O₂ delivery, potentially accounting for the sympathetic overdrive associated with MetS. This theoretical concept is supported by experimental results in animals fed a high fructose diet to induce MetS. Hepatic fructose metabolism rapidly consumes ATP resulting in increased adenosine production and hyperuricemia as well as elevated renin release and sympathetic activity. This review makes the case for the hepatorenal reflex causing sympathetic overdrive and metabolic syndrome in response to exaggerated splanchnic oxygen consumption from excessive eating. This is strongly reinforced by the fact that MetS is cured in a matter of days in a significant percentage of patients by diet, bariatric surgery, or endoluminal sleeve, all of which would decrease splanchnic oxygen demand by limiting nutrient contact with the mucosa and reducing the nutrient load due to loss of appetite or dietary restriction.

Metabolic syndrome and the hepatorenal reflex

Insufficient hepatic O₂ in animal and human studies has been shown to elicit a hepatorenal reflex in response to increased hepatic adenosine, resulting in stimulation of renal as well as muscle sympathetic nerve activity and activating the renin angiotensin system. Low hepatic ATP, hyperuricemia, and hepatic lipid accumulation reported in metabolic syndrome (MetS) patients may reflect insufficient hepatic O₂ delivery, potentially accounting for the sympathetic overdrive associated with MetS. This theoretical concept is supported by experimental results in animals fed a high fructose diet to induce MetS. Hepatic fructose metabolism rapidly consumes ATP resulting in increased adenosine production and hyperuricemia as well as elevated renin release and sympathetic activity. This review makes the case for the hepatorenal reflex causing sympathetic overdrive and metabolic syndrome in response to exaggerated splanchnic oxygen consumption from excessive eating. This is strongly reinforced by the fact that MetS is cured in a matter of days in a significant percentage of patients by diet, bariatric surgery, or endoluminal sleeve, all of which would decrease splanchnic oxygen demand by limiting nutrient contact with the mucosa and reducing the nutrient load due to the loss of appetite or dietary restriction.

Low intensity exercise prevents disturbances in rat cardiac insulin signaling and endothelial nitric oxide synthase induced by high fructose diet

Increase in fructose consumption together with decrease in physical activity contributes to the development of metabolic syndrome and consequently cardiovascular diseases. The current study examined the preventive role of exercise on defects in cardiac insulin signaling and function of endothelial nitric oxide synthase (eNOS) in fructose fed rats. Male Wistar rats were divided into control, sedentary fructose (received 10% fructose for 9 weeks) and exercise fructose (additionally exposed to low intensity exercise) groups. Concentration of triglycerides, glucose, insulin and visceral adipose tissue weight were determined to estimate metabolic syndrome development. Expression and/or phosphorylation of cardiac insulin receptor (IR), insulin receptor substrate 1 (IRS1), tyrosine-specific protein phosphatase 1B (PTP1B), Akt, extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) and eNOS were evaluated. Fructose overload increased visceral adipose tissue, insulin concentration and homeostasis model assessment index. Exercise managed to decrease visceral adiposity and insulin level and to increase insulin sensitivity. Fructose diet increased level of cardiac PTP1B and pIRS1 (Ser307), while levels of IR and ERK1/2, as well as pIRS1 (Tyr 632), pAkt (Ser473, Thr308) and pERK1/2 were decreased. These disturbances were accompanied by reduced phosphorylation of eNOS at Ser1177. Exercise managed to prevent most of the disturbances in insulin signaling caused by fructose diet (except phosphorylation of IRS1 at Tyr 632 and phosphorylation and protein expression of ERK1/2) and consequently restored function of eNOS. Low intensity exercise could be considered as efficient treatment of cardiac insulin resistance induced by fructose diet.

Potential link between excess added sugar intake and ectopic fat: a systematic review of randomized controlled trials

CONTEXT

The effect of added sugar intake on ectopic fat accumulation is a subject of debate.

OBJECTIVE

A systematic review and meta-analysis of randomized controlled trials (RCTs) was conducted to examine the potential effect of added sugar intake on ectopic fat depots.

DATA SOURCES

MEDLINE, CAB Abstracts, CAB Global Health, and EBM (Evidence-Based Medicine) Reviews - Cochrane Central Register of Controlled Trials databases were searched for studies published from 1973 to September 2014.

DATA EXTRACTION

RCTs with a minimum of 6 days' duration of added sugar exposure in the intervention group were selected. The dosage of added sugar intake as a percentage of total energy was extracted or calculated. Means and standard deviations of pre- and post-test measurements or changes in ectopic fat depots were collected.

DATA SYNTHESIS

Fourteen RCTs were included. Most of the studies had a medium to high risk of bias. Meta-analysis showed that, compared with eucaloric controls, subjects who consumed added sugar under hypercaloric conditions likely increased ectopic fat, particularly in the liver (pooled standardized mean difference = 0.9 [95%CI, 0.6-1.2], n = 6) and muscles (pooled SMD = 0.6 [95%CI, 0.2-1.0], n = 4). No significant difference was observed in liver fat, visceral adipose tissue, or muscle fat when isocaloric intakes of different sources of added sugars were compared.

CONCLUSIONS

Data from a limited number of RCTs suggest that excess added sugar intake under hypercaloric diet conditions likely increases ectopic fat depots, particularly in the liver and in muscle fat. There are insufficient data to compare the effect of different sources of added sugars on ectopic fat deposition or to compare intake of added sugar with intakes of other macronutrients. Future well-designed RCTs with sufficient power and duration are needed to address the role of sugars on ectopic fat deposition.

Early inflammation-associated factors blunt sterol regulatory element-binding proteins-1-mediated lipogenesis in high-fat diet-fed APPSWE /PSEN1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) patients have an increased incidence of Type 2 diabetes (T2D); however, the underlying mechanisms are not well understood. Since AD is considered a multifactorial disease that affects both the central nerves system and periphery and the dysregulation of hepatic lipid and glucose metabolism play critical roles in T2D, we, therefore, aim to explore the influence of AD genotype on the liver during the progress of high-fat diet (HFD)-induced T2D. Fourteen-week-old female APP_SWE /PSEN1dE9 (AD) mice and age-, gender-matched wild-type controls C57BL/6J (WT) mice were fed a HFD (45% kcal fat content) or a standard chow diet (chow, 12% kcal fat content) for 22 weeks. The effects of diet and genotype were analyzed. Mouse primary hepatocytes were used to decipher the underlying mechanisms. HFD induced significantly higher body weight gain, more severe hyperglycemia, glucose intolerance and hepatic insulin resistance in AD mice than in WT mice. However, AD mice showed reduced HFD-induced hepatic steatosis, and SREBP-1-mediated lipogenic signaling was activated by HFD in WT mice but not in AD mice. In addition, 14-week-old AD mice exhibited higher expression of NF-κB p65, p-JNK and p-p38MAPK, as well as higher hepatic and serum contents of IL-6 and TNFα. In mouse primary hepatocyte cultures, IL-6 and TNFα inhibited high-glucose plus insulin-induced activation of SREBP-1-mediated lipogenic signaling and biosynthesis of non-esterified fatty acid and triglyceride. Early inflammation-associated factors most likely diminish HFD-induced hepatic lipid deposition by inhibiting SREBP-1-mediated de novo lipogenesis, thus driving substrate flux to glucose production for hyperglycemia and hepatic insulin resistance in T2D development. Alzheimer's disease (AD) is a multifactorial disease affecting both central nerves system and periphery organs. Therefore, we explored the hepatic susceptibility to high-fat diet (HFD) in AD mice. We found that AD mice were resistant to HFD-induced hepatic fat accumulation in spite of more severe obesity, hyperglycemia, glucose intolerance and hepatic insulin resistance. Mechanistically, AD mice exhibited hepatic inflammation at an early stage, which inhibited sterol regulatory element-binding proteins-1 (SREBP-1)-mediated de novo lipogenesis, and most likely drive substrate flux to glucose production for hyperglycemia and hepatic insulin resistance. Cover Image for this issue: doi: 10.1111/jnc.13306.

Effects of high-fat feeding on ectopic fat storage and postprandial lipid metabolism in mouse offspring

OBJECTIVE

Parental high-fat feeding was proposed to negatively impact metabolic health in offspring. Here, the ectopic fat storage in heart and liver in offspring was investigated, and the effects on mitochondrial function, de novo lipogenesis, and postprandial lipid metabolism were explored in detail.

METHODS

Male and female mice received either a high-fat (HF) or standard chow (LF) diet during mating, gestation and lactation. All offspring animals received the HF diet.

RESULTS

Abdominal visceral adipose tissue tended to be higher in HF/HF mice. Cardiac lipid content was also higher in the HF/HF mice (LF/HF vs.

HF/HF

1.03% ± 0.08% vs. 1.33% ± 0.07% of water signal, P = 0.01). In contrast, hepatic lipid content tended to be lower in HF/HF mice compared to LF/HF mice. A severely disturbed postprandial lipid clearance was revealed in HF/HF mice by the results from the triglyceride (TG) tolerance tests (LF/HF vs.

HF/HF

6,753 ± 2,213 vs. 14,367 ± 1,978 mmol l(-1)  min(-1) , P = 0.01) and (13) C-fatty acid retention test (LF/HF vs.

HF/HF

2.73% ± 0.85% vs. 0.89% ± 0.26% retention from bolus, P = 0.04), which may underlie the lower hepatic lipid content.

CONCLUSIONS

Here it is shown that HF diet negatively impacts postprandial TG clearance in offspring and results in an overall metabolic unfavorable phenotype and ectopic lipid deposition in the heart and in visceral storage sites.

Diet-induced pre-diabetes slows cardiac conductance and promotes arrhythmogenesis

Background

Type 2 diabetes is associated with abnormal electrical conduction and sudden cardiac death, but the pathogenic mechanism remains unknown. This study describes electrophysiological alterations in a diet-induced pre-diabetic rat model and examines the underlying mechanism.

Methods

Sprague–Dawley rats were fed either high-fat diet and fructose water or normal chow and water for 6 weeks. The electrophysiological properties of the whole heart was analyzed by in vivo surface ECG recordings, as wells as ex vivo in Langendorff perfused hearts during baseline, ischemia and re-perfussion. Conduction velocity was examined in isolated tissue strips. Ion channel and gap junction conductances were analyzed by patch-clamp studies in isolated cardiomyocytes. Fibrosis was examined by Masson’s Trichrome staining and thin-layer chromatography was used to analyze cardiac lipid content. Connexin43 (Cx43) expression and distribution was examined by western blotting and immunofluorescence respectively.

Results

Following 6 weeks of feeding, fructose-fat fed rats (FFFRs) showed QRS prolongation compared to controls (16.1 ± 0.51 (n = 6) vs. 14.7 ± 0.32 ms (n = 4), p < 0.05). Conduction velocity was slowed in FFFRs vs. controls (0.62 ± 0.02 (n = 13) vs. 0.79 ± 0.06 m/s (n = 11), p < 0.05) and Langendorff perfused FFFR hearts were more prone to ventricular fibrillation during reperfusion following ischemia (p < 0.05). The patch-clamp studies revealed no changes in Na⁺ or K⁺ currents, cell capacitance or gap junctional coupling. Cx43 expression was also unaltered in FFFRs, but immunofluorescence demonstrated an increased fraction of Cx43 localized at the intercalated discs in FFFRs compared to controls (78 ± 3.3 (n = 5) vs. 60 ± 4.2 % (n = 6), p < 0.01). No fibrosis was detected but FFFRs showed a significant increase in cardiac triglyceride content (1.93 ± 0.19 (n = 12) vs. 0.77 ± 0.13 nmol/mg (n = 12), p < 0.0001).

Conclusion

Six weeks on a high fructose-fat diet cause electrophysiological changes, which leads to QRS prolongation, decreased conduction velocity and increased arrhythmogenesis during reperfusion. These alterations are not explained by altered gap junctional coupling, Na⁺, or K⁺ currents, differences in cell size or fibrosis.

Oestradiol Treatment Counteracts the Effect of Fructose-Rich Diet on Matrix Metalloproteinase 9 Expression and NFκB Activation

Fructose-rich diet induces metabolic changes similar to those observed in metabolic syndrome. Among other matrix metalloproteinases, MMP-9 has an important role in adverse cardiac remodelling and might have a role in the development of cardiovascular disorders associated with metabolic syndrome. The changes of MMP-9 expression could be mediated via the NFκB pathway. In this study we investigated the effect of fructose-rich diet on MMP-9 expression in the heart of male and female rats, along with the effect of fructose-rich diet and oestradiol on MMP-9 expression in ovariectomized females. We further assessed the effect of fructose-rich diet and oestradiol on NFκB activation, measured as the level of p65 phosphorylation at Ser 276. The results showed that the diet regime did not affect the heart mass. Higher MMP-9 gene expression was found in cardiac tissue of male rats fed the fructose-rich diet than in females on the same diet regime. In ovariectomized females, fructose-rich diet upregulated MMP-9 protein and mRNA expression in the heart, as well as phosphorylation of the p65 subunit of NFκB at Ser 276. Oestradiol replacement therapy reverted these changes in the heart of ovariectomized females. This study has shown that oestradiol could revert the early molecular changes in MMP-9 expression induced by fructose-rich diet that occurred before cardiac hypertrophy development by decreasing phosphorylation of the NFκB p65 subunit at Ser 276.

Updating experimental models of diabetic cardiomyopathy

Diabetic cardiomyopathy entails a serious cardiac dysfunction induced by alterations in structure and contractility of the myocardium. This pathology is initiated by changes in energy substrates and occurs in the absence of atherothrombosis, hypertension, or other cardiomyopathies. Inflammation, hypertrophy, fibrosis, steatosis, and apoptosis in the myocardium have been studied in numerous diabetic experimental models in animals, mostly rodents. Type I and type II diabetes were induced by genetic manipulation, pancreatic toxins, and fat and sweet diets, and animals recapitulate the main features of human diabetes and related cardiomyopathy. In this review we update and discuss the main experimental models of diabetic cardiomyopathy, analysing the associated metabolic, structural, and functional abnormalities, and including current tools for detection of these responses. Also, novel experimental models based on genetic modifications of specific related genes have been discussed. The study of specific pathways or factors responsible for cardiac failures may be useful to design new pharmacological strategies for diabetic patients.

Metabolic fate of fructose in human adipocytes: a targeted 13C tracer fate association study

The development of obesity is becoming an international problem and the role of fructose is unclear. Studies using liver tissue and hepatocytes have contributed to the understanding of fructose metabolism. Excess fructose consumption also affects extra hepatic tissues including adipose tissue. The effects of fructose on human adipocytes are not yet fully characterized, although in vivo studies have noted increased adiposity and weight gain in response to fructose sweetened-beverages. In order to understand and predict the metabolic responses of adipocytes to fructose, this study examined differentiating and differentiated human adipocytes in culture, exposed to a range of fructose concentrations equivalent to that reported in blood after consuming fructose. A stable isotope based dynamic profiling method using [U-¹³C₆]-d-fructose tracer was used to examine the metabolism and fate of fructose. A targeted stable isotope tracer fate association method was used to analyze metabolic fluxes and flux surrogates with exposure to escalating fructose concentration. This study demonstrated that fructose stimulates anabolic processes in adipocytes robustly, including glutamate and de novo fatty acid synthesis. Furthermore, fructose also augments the release of free palmitate from fully differentiated adipocytes. These results imply that in the presence of fructose, the metabolic response of adipocytes in culture is altered in a dose dependent manner, particularly favoring increased glutamate and fatty acid synthesis and release, warranting further in vivo studies.

Modulation of Diabetes and Dyslipidemia in Diabetic Insulin-Resistant Rats by Mangiferin: Role of Adiponectin and TNF-α

Mangiferin, present in Mangifera indica bark, was reported to produce hypoglycemic and antidiabetic activity in an animal model of genetic type 2 diabetes and in streptozotocin diabetic rats. Its effect on diabetic insulin-resistant animals has not been investigated. The current work aimed to explore the effect of mangiferin on diabetic insulin-resistant rat model. Diabetes was induced by high-fat/high fructose diet for eight weeks followed by a subdiabetogenic dose of streptozotocin (HFD-Fr-STZ). Rats were treated with mangiferin (20 mg/kg i.p.) for 28 days starting one week after STZ and its effects were compared to the standard insulin sensitizer, rosiglitazone. HFD-Fr-STZ, induced obesity, hyperglycemia and insulin resistance accompanied by depletion in liver glycogen and dyslipidemia. Moreover, there was an elevation in serum TNF-α and a reduction in adiponectin. Mangiferin ameliorated the consequences of HFD-Fr-STZ and its actions were comparable to the effects of the standard insulin sensitizer, rosiglitazone. The results obtained in this study provide evidence that mangiferin is a possible beneficial natural compound for type 2 diabetes and metabolic disorders associated with the metabolic syndrome. This effect is mediated through improving insulin sensitivity, modulating lipid profile and reverting adipokine levels to normal.

AMP-activated protein kinase suppresses urate crystal-induced inflammation and transduces colchicine effects in macrophages

OBJECTIVE

AMP-activated protein kinase (AMPK) is metabolic biosensor with anti-inflammatory activities. Gout is commonly associated with excesses in soluble urate and in nutrition, both of which suppress tissue AMPK activity. Gout is driven by macrophage-mediated inflammation transduced partly by NLRP3 inflammasome activation and interleukin (IL)-1β release. Hence, we tested the hypothesis that AMPK activation limits monosodium urate (MSU) crystal-induced inflammation.

METHODS

We studied bone marrow-derived macrophages (BMDMs) from AMPKα1 knockout and wild-type mice, and assessed the selective AMPK pharmacological activator A-769662 and a low concentration (10 nM) of colchicine. We examined phosphorylation (activation) of AMPKα Thr172, NLRP3 mRNA expression, and caspase-1 cleavage and IL-1β maturation using western blot and quantitative RT-PCR approaches. We also assessed subcutaneous murine air pouch inflammatory responses to MSU crystals in vivo.

RESULTS

MSU crystals suppressed phosphorylation of AMPKα in BMDMs. Knockout of AMPKα1 enhanced, and, conversely, A-769662-inhibited MSU crystal-induced inflammatory responses including IL-1β and CXCL1 release in vitro and in vivo. A-769662 promoted AMPK-dependent macrophage anti-inflammatory M2 polarisation and inhibited NLRP3 gene expression, activation of caspase-1 and IL-1β. Colchicine, at low concentration (10 nM) achieved in gout flare prophylaxis dosing, promoted phosphorylation of AMPKα and macrophage M2 polarisation, and reduced activation of caspase-1 and release of IL-1β and CXCL1 by MSU crystals in BMDMs in vitro.

CONCLUSIONS

AMPK activity limits MSU crystal inflammation in vitro and in vivo, and transduces multiple anti-inflammatory effects of colchicine in macrophages. Targeting increased and sustained AMPK activation in inflammatory cells merits further investigation for enhancing efficacy of prophylaxis and treatment of gouty inflammation.

Preventative effect of Zingiber officinale on insulin resistance in a high-fat high-carbohydrate diet-fed rat model and its mechanism of action

Insulin resistance is a core component of metabolic syndrome and usually precedes the development of type 2 diabetes mellitus. We have examined the preventative effect of an ethanol extract of ginger (Zingiber officinale, Zingiberaceae) on insulin resistance in a high-fat high-carbohydrate (HFHC) diet-fed rat model of metabolic syndrome. The HFHC control rats displayed severe insulin resistance, whilst rats treated with ginger extract (200 mg/kg) during HFHC diet feeding showed a significant improvement of insulin sensitivity using the homeostatic model assessment of insulin resistance (HOMA-IR) after 10 weeks (p < 0.01). An in vitro mechanistic study showed that (S)-[6]-gingerol, the major pungent phenolic principle in ginger, dose-dependently (from 50 to 150 μM) increased AMPK α-subunit phosphorylation in L6 skeletal muscle cells. This was accompanied by a time-dependent marked increment of PGC-1α mRNA expression and mitochondrial content in L6 skeletal muscle cells. These results suggest that the protection from HFHC diet-induced insulin resistance by ginger is likely associated with the increased capacity of energy metabolism by its major active component (S)-[6]-gingerol.

Gender differences in the expression and cellular localization of lipin 1 in the hearts of fructose-fed rats

To give new insight to alterations of cardiac lipid metabolism accompanied by a fructose-rich diet (FRD), rats of both sexes were exposed to 10 % fructose in drinking water during 9 weeks. The protein level and subcellular localization of the main regulators of cardiac lipid metabolism, such as lipin 1, peroxisome proliferator-activated receptor α (PPARα), peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1α), carnitine palmitoyltransferase I (CPTI), and CD36 were studied. Caloric intake in fructose-fed rats (FFR) of both sexes was increased. Circulating triacylglyceroles (TAG) and non-esterified fatty acids were increased in male FFR, while females increased visceral adiposity and blood TAG. Total expression of lipin 1 in cardiac cell lysate and its cytosolic and microsomal level were increased in the hearts of male FFR. PPARα and PGC-1α content were decreased in the nuclear extract. In addition, cardiac deposition of TAG in male FFR was elevated, as well as inhibitory phosphorylation of insulin receptor substrate 1 (IRS-1). In contrast, in female FFR, lipin 1 level was increased in nuclear extract only, while overall CPTI expression and phosphorylation of IRS-1 at serine 307 were decreased. The results of our study suggest that fructose diet causes gender-dependent alterations in cardiac lipid metabolism. Potentially detrimental effects of FRD seem to be limited to male rats. Most of the observed changes might be a consequence of elevated expression and altered localization of lipin 1. Increased inhibitory phosphorylation of IRS-1 is possible link between cardiac lipid metabolism and insulin resistance in FFR.

Diabetic cardiomyopathy: mechanisms and new treatment strategies targeting antioxidant signaling pathways

Cardiovascular disease is the primary cause of morbidity and mortality among the diabetic population. Both experimental and clinical evidence suggest that diabetic subjects are predisposed to a distinct cardiomyopathy, independent of concomitant macro- and microvascular disorders. 'Diabetic cardiomyopathy' is characterized by early impairments in diastolic function, accompanied by the development of cardiomyocyte hypertrophy, myocardial fibrosis and cardiomyocyte apoptosis. The pathophysiology underlying diabetes-induced cardiac damage is complex and multifactorial, with elevated oxidative stress as a key contributor. We now review the current evidence of molecular disturbances present in the diabetic heart, and their role in the development of diabetes-induced impairments in myocardial function and structure. Our focus incorporates both the contribution of increased reactive oxygen species production and reduced antioxidant defenses to diabetic cardiomyopathy, together with modulation of protein signaling pathways and the emerging role of protein O-GlcNAcylation and miRNA dysregulation in the progression of diabetic heart disease. Lastly, we discuss both conventional and novel therapeutic approaches for the treatment of left ventricular dysfunction in diabetic patients, from inhibition of the renin-angiotensin-aldosterone-system, through recent evidence favoring supplementation of endogenous antioxidants for the treatment of diabetic cardiomyopathy. Novel therapeutic strategies, such as gene therapy targeting the phosphoinositide 3-kinase PI3K(p110α) signaling pathway, and miRNA dysregulation, are also reviewed. Targeting redox stress and protective protein signaling pathways may represent a future strategy for combating the ever-increasing incidence of heart failure in the diabetic population.

Long term metabolic syndrome induced by a high fat high fructose diet leads to minimal renal injury in C57BL/6 mice

Metabolic syndrome can induce chronic kidney disease in humans. Genetically engineered mice on a C57BL/6 background are highly used for mechanistic studies. Although it has been shown that metabolic syndrome induces cardiovascular lesions in C57BL/6 mice, in depth renal phenotyping has never been performed. Therefore in this study we characterized renal function and injury in C57BL/6 mice with long-term metabolic syndrome induced by a high fat and fructose diet (HFFD). C57BL/6 mice received an 8 months HFFD diet enriched with fat (45% energy from fat) and drinking water enriched with fructose (30%). Body weight, food/water consumption, energy intake, fat/lean mass ratio, plasma glucose, HDL, LDL, triglycerides and cholesterol levels were monitored. At 3, 6 and 8 months, renal function was determined by inulin clearance and measure of albuminuria. At sacrifice, kidneys and liver were collected. Metabolic syndrome in C57BL/6 mice fed a HFFD was observed as early 4 weeks with development of type 2 diabetes at 8 weeks after initiation of diet. However, detailed analysis of kidney structure and function showed only minimal renal injury after 8 months of HFFD. HFFD induced moderate glomerular hyperfiltration (436,4 µL/min vs 289,8 µL/min; p-value=0.0418) together with a 2-fold increase in albuminuria only after 8 months of HFFD. This was accompanied by a 2-fold increase in renal inflammation (p-value=0.0217) but without renal fibrosis or mesangial matrix expansion. In addition, electron microscopy did not show alterations in glomeruli such as basal membrane thickening and foot process effacement. Finally, comparison of the urinary peptidome of these mice with the urinary peptidome from humans with diabetic nephropathy also suggested absence of diabetic nephropathy in this model. This study provides evidence that the HFFD C57BL/6 model is not the optimal model to study the effects of metabolic syndrome on the development of diabetic kidney disease.

An overview of the crosstalk between inflammatory processes and metabolic dysregulation during diabetic cardiomyopathy

Metabolic disorders such as obesity, insulin resistance and type 2 diabetes mellitus are all linked to cardiovascular diseases such as cardiac hypertrophy and heart failure. Diabetic cardiomyopathy in particular, is characterized by structural and functional alterations in the heart muscle of people with diabetes that finally lead to heart failure, and which is not directly attributable to coronary artery disease or hypertension. Several mechanisms have been involved in the pathogenesis of diabetic cardiomyopathy, such as alterations in myocardial energy metabolism and calcium signaling. Metabolic disturbances during diabetic cardiomyopathy are characterized by increased lipid oxidation, intramyocardial triglyceride accumulation, and reduced glucose utilization. Overall changes result in enhanced oxidative stress, mitochondrial dysfunction and apoptosis of the cardiomyocytes. On the other hand, the progression of heart failure and cardiac hypertrophy usually entails a local rise in cytokines in cardiac cells and the activation of the proinflammatory transcription factor nuclear factor (NF)-κB. Interestingly, increasing evidences are arising in the recent years that point to a potential link between chronic low-grade inflammation in the heart and metabolic dysregulation. Therefore, in this review we summarize recent new insights into the crosstalk between inflammatory processes and metabolic dysregulation in the failing heart during diabetes, paying special attention to the role of NF-κB and peroxisome proliferator activated receptors (PPARs). In addition, we briefly describe the role of the AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1) and other pathways regulating cardiac energy metabolism, as well as their relationship with diabetic cardiomyopathy.

Non-alcoholic fatty liver disease (NAFLD): a tale of fat and sugar?

The global diffusion of the so-called Western diet, which is enriched in fat and carbohydrates, such as fructose, has been proposed to be an underlying cause of the increased prevalence of metabolic conditions, including non-alcoholic fatty liver disease (NAFLD). This Smart Card summarizes the main metabolic and hepatic histological features of rodent models fed with diets combining high fat and fructose.

RhoA mediates defective stem cell function and heterotopic ossification in dystrophic muscle of mice

Heterotopic ossification (HO) and fatty infiltration (FI) often occur in diseased skeletal muscle and have been previously described in various animal models of Duchenne muscular dystrophy (DMD); however, the pathological mechanisms remain largely unknown. Dystrophin-deficient mdx mice and dystrophin/utrophin double-knockout (dKO) mice are mouse models of DMD; however, mdx mice display a strong muscle regeneration capacity, while dKO mice exhibit a much more severe phenotype, which is similar to patients with DMD. Our results revealed that more extensive HO, but not FI, occurred in the skeletal muscle of dKO mice versus mdx mice, and RhoA activation specifically occurred at the sites of HO. Moreover, the gene expression of RhoA, BMPs, and several inflammatory factors were significantly up-regulated in muscle stem cells isolated from dKO mice; while inactivation of RhoA in the cells with RhoA/ROCK inhibitor Y-27632 led to reduced osteogenic potential and improved myogenic potential. Finally, inactivation of RhoA signaling in the dKO mice with Y-27632 improved muscle regeneration and reduced the expression of BMPs, inflammation, HO, and intramyocellular lipid accumulation in both skeletal and cardiac muscle. Our results revealed that RhoA represents a major molecular switch in the regulation of HO and muscle regeneration in dystrophic skeletal muscle of mice.

Impaired contractile recovery after low-flow myocardial ischemia in a porcine model of metabolic syndrome

Clinical metabolic syndrome conveys a poor prognosis in patients with acute coronary syndrome, not fully accounted for by the extent of coronary atherosclerosis. To explain this observation, we determined whether postischemic myocardial contractile and metabolic function are impaired in a porcine dietary model of metabolic syndrome without atherosclerosis. Micropigs (n = 28) were assigned to a control diet (low fat, no added sugars) or an intervention diet (high saturated fat and simple sugars, no added cholesterol) for 7 mo. The intervention diet produced obesity, hypertension, dyslipidemia, and impaired glucose tolerance, but not atherosclerosis. Under open-chest, anesthetized conditions, pigs underwent 45 min of low-flow myocardial ischemia and 120 min of reperfusion. In both diet groups, contractile function was similar at baseline and declined similarly during ischemia. However, after 120 min of reperfusion, regional work recovered to 21 ± 12% of baseline in metabolic syndrome pigs compared with 61 ± 13% in control pigs (P = 0.01). Ischemia-reperfusion caused a progressive decline in mechanical/metabolic efficiency (regional work/O2 consumption) in metabolic syndrome hearts, but not in control hearts. Metabolic syndrome hearts demonstrated altered fatty acyl composition of cardiolipin and increased Akt phosphorylation in both ischemic and nonischemic regions, suggesting tonic activation. Metabolic syndrome hearts used more fatty acid than control hearts (P = 0.03). When fatty acid availability was restricted by prior insulin exposure, differences between groups in postischemic contractile recovery and mechanical/metabolic efficiency were eliminated. In conclusion, pigs with characteristics of metabolic syndrome demonstrate impaired contractile and metabolic recovery after low-flow myocardial ischemia. Contributory mechanisms may include remodeling of cardiolipin, abnormal activation of Akt, and excessive utilization of fatty acid substrates.

Does oestradiol attenuate the damaging effects of a fructose-rich diet on cardiac Akt/endothelial nitric oxide synthase signalling?

Fructose-rich diets (FRD) cause cardiac insulin resistance manifested by impairment of Akt/endothelial NO synthase (eNOS) signalling. In contrast, oestradiol (E2) activates this signalling pathway in the heart. To study the ability of E2 to revert the detrimental effect of fructose on cardiac Akt/eNOS, female rats were subjected to a FRD and ovariectomy followed with or without E2 replacement. We also analysed the effects of the FRD and E2 on cardiac extracellular signal-regulated kinase (Erk 1/2) signalling related to their role in cardiac hypertrophy development. Expression of Akt, eNOS and Erk 1/2, as well as regulatory phosphorylations of these molecules were determined. The protein expression of cardiac Akt and eNOS was not affected by the diet or E2 treatment. However, the FRD was accompanied by a decrease in Akt phosphorylation at Ser(473) and Thr(308), and eNOS at Ser(1177), while the phosphorylation of eNOS at Thr(495) was increased. E2 replacement in ovariectomised fructose-fed rats caused a reversion of the diet effect on Akt and eNOS serine phosphorylation, but mostly had no effect on threonine phosphorylation of the molecules. The FRD and E2 treatment did not influence Erk 1/2 expression and phosphorylation and heart mass as well. The data show that E2 selectively suppress the negative effects of a FRD on Akt/eNOS signalling and probably point to the different effects of E2 on kinase/phosphatase pathways responsible for phosphorylation/dephosphorylation of Akt and eNOS. Furthermore, the results suggest that the heart of females in the reproductive period is partially protected against the damaging effects of increasedfructose intake.

A high-fat diet decreases AMPK activity in multiple tissues in the absence of hyperglycemia or systemic inflammation in rats

Consumption of a high-fat diet (HFD) in experimental animal models initiates a series of molecular events and outcomes, including insulin resistance and obesity, that mimic the metabolic syndrome in humans. The relationship among, and order of, the molecular events linking a diet high in fat to pathologies is often unclear. In the present study, we provide several novel insights into the relationship between a HFD and AMP-activated protein kinase (AMPK), a key regulator of cellular metabolism and whole-body energy balance. HFD substantially decreased the activities of both isoforms of AMPK in white adipose tissue, heart, and liver. These decreases in AMPK activity occurred in the absence of decreased AMPK transcription, systemic inflammation, hyperglycemia, or elevated levels of free fatty acids. The HFD-induced decrease in AMPK activity was associated with systemic insulin resistance and hyperleptinemia. In blood, >98 % of AMPK activity was localized in agranulocytes as the α1 isoform. In contrast to the solid tissues studied, AMPK activities were not altered by HFD in granulocytes or agranulocytes. We conclude that HFD-induced obesity causes a broad, non-tissue, or isoform-specific lowering of AMPK activity. Given the central position AMPK plays in whole-body energy balance, this decreased AMPK activity may play a previously unrecognized role in obesity and its associated pathologies.

Review article: fructose in non-alcoholic fatty liver disease

BACKGROUND

The role of excess fructose intake in the pathogenesis of non-alcoholic fatty liver disease (NAFLD) has recently received increasing attention, but the pathophysiology of this relationship has been only partly elucidated.

AIM

To provide an overview of the potential role played by fructose in the pathogenesis of NAFLD by focusing on both indirect and direct harmful effects.

METHODS

Experimental and clinical studies which investigated the relation of fructose with NAFLD are reviewed.

RESULTS

Several factors may potentially contribute to fructose-induced NAFLD, including the induction of the metabolic syndrome, copper deficiency, bacterial translocation from the gut to the liver, the formation of advanced glycation endproducts and a direct dysmetabolic effect on liver enzymes.

CONCLUSIONS

Experimentally-increased fructose intake recapitulates many of the pathophysiological characteristics of the metabolic syndrome in humans, which may in turn lead to NAFLD. However, the majority of experimental studies tend to involve feeding excessively high levels of fructose (60-70% of total energy intake) which is not reflective of average human intake. Hopefully, the combination of in vivo, in vitro and genetic research will provide substantial mechanistic evidence into the role of fructose in NAFLD development and its complications.

Changes in glucose tolerance and leptin responsiveness of rats offered a choice of lard, sucrose, and chow

Rats offered chow, lard, and 30% sucrose solution (choice) rapidly become obese. We tested metabolic disturbances in rats offered choice, chow+lard, or chow+30% sucrose solution [chow+liquid sucrose (LS)] and compared them with rats fed a composite 60% kcal fat, 7% sucrose diet [high-fat diet (HFD)], or a 10% kcal fat, 35% sucrose diet [low-fat diet (LFD)]. Choice rats had the highest energy intake, but HFD rats gained the most weight. After 23 days carcass fat was the same for choice, HFD, chow+lard, and chow+LS groups. Glucose clearance was the same for all groups during an intraperitoneal glucose tolerance test (GTT) on day 12, but fasting insulin was increased in choice, LFD fed, and chow+LS rats. By contrast, only choice and chow+LS rats were resistant to an intraperitoneal injection of 2 mg leptin/kg on day 17. In experiment 2 choice rats were insulin insensitive during an intraperitoneal GTT, but this was corrected in an oral GTT due to GLP-1 release. UCP-1 protein was increased in brown fat and inguinal white fat in choice rats, and this was associated with a significant increase in energy expenditure of choice rats during the dark period whether expenditure was expressed on a per animal or a metabolic body size basis. The increase in expenditure obviously was not great enough to prevent development of obesity. Further studies are required to determine the mechanistic basis of the rapid onset of leptin resistance in choice rats and how consumption of sucrose solution drives this process.

Metformin prevents the development of chronic heart failure in the SHHF rat model

Insulin resistance is a recently identified mechanism involved in the pathophysiology of chronic heart failure (CHF). We investigated the effects of two insulin-sensitizing drugs (metformin and rosiglitazone) in a genetic model of spontaneously hypertensive, insulin-resistant rats (SHHF). Thirty SHHF rats were randomized into three treatment groups as follows: 1) metformin (100 mg/kg per day), 2) rosiglitazone (2 mg/kg per day), and 3) no drug. Ten Sprague-Dawley rats served as normal controls. At the end of the treatment period (12 months), the cardiac phenotype was characterized by histology, echocardiography, and isolated perfused heart studies. Metformin attenuated left ventricular (LV) remodeling, as shown by reduced LV volumes, wall stress, perivascular fibrosis, and cardiac lipid accumulation. Metformin improved both systolic and diastolic indices as well as myocardial mechanical efficiency, as shown by improved ability to convert metabolic energy into mechanical work. Metformin induced a marked activation of AMP-activated protein kinase, endothelial nitric oxide synthase, and vascular endothelial growth factor and reduced tumor necrosis factor-α expression and myocyte apoptosis. Rosiglitazone did not affect LV remodeling, increased perivascular fibrosis, and promoted further cardiac lipid accumulation. In conclusion, long-term treatment with metformin, but not with rosiglitazone, prevents the development of severe CHF in the SHHF model by a wide-spectrum interaction that involves molecular, structural, functional, and metabolic-energetic mechanisms.