Impairment of cardiac insulin signaling and myocardial contractile performance in high-cholesterol/fructose-fed rats

Qingda granule prevents obesity-induced hypertension and cardiac dysfunction by inhibiting adverse Akt signaling activation

Obesity rates have rapidly increased worldwide and obesity-related diseases such as hypertension and cardiovascular diseases have become leading factors for global morbidity and mortality. Currently, there are no effective treatments that can prevent or reverse obesity long-term, and hence the prevention of obesity-related adverse effects such as hypertension is critical. Qingda granule (QDG) is a condensed Traditional Chinese Medicine (TCM) formula that has been used clinically for treating hypertension, however, its effectiveness in obesity-induced hypertension and cardiac dysfunction remains explored. Mouse models of obesity via long-term feeding of high-fat high-fructose diet (HFFD) were established to examine the effect and mechanism of QDG in protecting against obesity-induced hypertension and cardiac dysfunction. C57BL/6 mice were fed with either normal diet or HFFD over a period of 16 weeks and administered with either saline or QDG for assessment of obesity-induced blood pressure and cardiac function. QDG administration demonstrated robust anti-hypertensive effects and significantly attenuated HFFD-induced elevations in blood pressures. Moreover, QDG treatment also demonstrated robust cardioprotective effects during obesity-induced hypertension by markedly improving cardiac function and preventing cardiac hypertrophy. QDG protected against obesity-induced hypertension and cardiac dysfunction was due to its ability to prevent adverse chronic activation of Akt signaling pathway during long-term feeding of HFFD. Long-term usage of QDG treatments exhibited no observable side effects and also completely prevented obesity-induced organ damage, demonstrating the feasibility and safety of prolonged use. Our findings thus elucidated the role of QDG in preventing obesity-induced hypertension and cardiac hypertrophy via inhibiting adverse activation of Akt signaling activation. Therefore, our study provides the theoretical basis for the utilization of QDG as both a safe and effective drug in the therapeutic treatment of metabolic diseases such as obesity-induced hypertension.

Maternal Fructose Intake Exacerbates Cardiac Remodeling in Offspring with Ventricular Pressure Overload

Recent studies demonstrated that metabolic syndrome and cardiovascular diseases could be elicited by developmental programming, which is regulated by prenatal nutritional and environmental stress. In this study, we utilized a rat model to examine the effect of excessive maternal fructose intake during pregnancy and lactation on cardiac development and progression of pressure overload-induced cardiac hypertrophy in offspring. Transverse aortic constriction (TAC) was performed on 3-month-old male offspring to induce ventricular pressure overload. Four weeks post-TAC, echocardiographic assessment as well as histopathological and biochemical examinations were performed on the myocardium of the offspring. Echocardiographic and gross examinations showed that heart weight, interventricular septal thickness in diastole (IVD; d), and left ventricular posterior wall thickness in diastole (LVPW; d) were elevated in offspring with TAC and further increased by maternal fructose exposure (MFE). However, the left ventricular ejection function was not significantly affected. Myocardial histopathological examination revealed that the indices of fibrosis and oxidative stress were higher in offspring with MFE and TAC than those in animals receiving either treatment. Molecular examinations on the myocardium demonstrated an MFE-induced upregulation of p38-MAPK signaling. Next generation sequence (NGS) analysis indicated a modulation of the expression levels of several cardiac hypertrophy-associated genes, including GPR22, Myh7, Nppa, P2RX4, and Npy by MFE. Subsequent RT-PCR indicated that MFE regulated the expression levels of genes responsive to cardiac hypertrophy (i.e., Myh-7, ANP) and oxidative stress (i.e., GR, GPx, and NQO-1). In conclusion, MFE during pregnancy and lactation modulated myocardial gene expression, increased oxidative stress, and exacerbated ventricular pressure overload-induced cardiac remodeling in rat offspring.

Run for your life: can exercise be used to effectively target GLUT4 in diabetic cardiac disease?

The global incidence, associated mortality rates and economic burden of diabetes are now such that it is considered one of the most pressing worldwide public health challenges. Considerable research is now devoted to better understanding the mechanisms underlying the onset and progression of this disease, with an ultimate aim of improving the array of available preventive and therapeutic interventions. One area of particular unmet clinical need is the significantly elevated rate of cardiomyopathy in diabetic patients, which in part contributes to cardiovascular disease being the primary cause of premature death in this population. This review will first consider the role of metabolism and more specifically the insulin sensitive glucose transporter GLUT4 in diabetic cardiac disease, before addressing how we may use exercise to intervene in order to beneficially impact key functional clinical outcomes.

Obesity cardiomyopathy: evidence, mechanisms, and therapeutic implications

The prevalence of heart failure is on the rise and imposes a major health threat, in part, due to the rapidly increased prevalence of overweight and obesity. To this point, epidemiological, clinical, and experimental evidence supports the existence of a unique disease entity termed “obesity cardiomyopathy,” which develops independent of hypertension, coronary heart disease, and other heart diseases. Our contemporary review evaluates the evidence for this pathological condition, examines putative responsible mechanisms, and discusses therapeutic options for this disorder. Clinical findings have consolidated the presence of left ventricular dysfunction in obesity. Experimental investigations have uncovered pathophysiological changes in myocardial structure and function in genetically predisposed and diet-induced obesity. Indeed, contemporary evidence consolidates a wide array of cellular and molecular mechanisms underlying the etiology of obesity cardiomyopathy including adipose tissue dysfunction, systemic inflammation, metabolic disturbances (insulin resistance, abnormal glucose transport, spillover of free fatty acids, lipotoxicity, and amino acid derangement), altered intracellular especially mitochondrial Ca²⁺ homeostasis, oxidative stress, autophagy/mitophagy defect, myocardial fibrosis, dampened coronary flow reserve, coronary microvascular disease (microangiopathy), and endothelial impairment. Given the important role of obesity in the increased risk of heart failure, especially that with preserved systolic function and the recent rises in COVID-19-associated cardiovascular mortality, this review should provide compelling evidence for the presence of obesity cardiomyopathy, independent of various comorbid conditions, underlying mechanisms, and offer new insights into potential therapeutic approaches (pharmacological and lifestyle modification) for the clinical management of obesity cardiomyopathy.

PCSK9 inhibitor effectively attenuates cardiometabolic impairment in obese-insulin resistant rats

Long-term high-fat diet consumption causes obese-insulin resistance and cardiac mitochondrial dysfunction, leading to impaired left ventricular (LV) function. Atorvastatin effectively improved lipid profiles in obese patients. However, inadequate reduction in low density lipoprotein cholesterol (LDL-C) level was found. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor effectively reduced LDL-C levels. We hypothesized that this PCSK9 inhibitor has a greater efficacy in attenuating cardiometabolic impairments than atorvastatin in obese-insulin resistant rats. Female rats were fed with either a high fat or normal diet for 12 weeks. High fat diet fed rats (HFD) were then divided into 3 groups and were given vehicle, atorvastatin (40 mg/kg/day; s.c.), or PCSK9 inhibitor (4 mg/kg/day; s.c.) for additional 3 weeks. The metabolic parameters, cardiac and mitochondrial function and [Ca²⁺]_i transients were determined. HFD rats developed obese-insulin resistance as indicated by increased plasma insulin and HOMA index. Although high-fat diet fed rats treated with vehicle (HFV) rats had markedly impaired LV function as indicated by reduced %LVFS, impaired cardiac mitochondrial function, and [Ca²⁺]_i transient regulation, these impairments were attenuated in high-fat diet fed rats treated with atorvastatin (HFA) and high-fat diet fed rats treated with PCSK9 inhibitor (HFP) rats. However, these improvements were greater in HFP rats than HFA rats. Our findings indicated that the PCSK9 inhibitor exerted greater cardioprotection than atorvastatin through improved mitochondrial function in obese-insulin resistant rats.

The Impact of Maternal Fructose Exposure on Angiogenic Activity of Endothelial Progenitor Cells and Blood Flow Recovery After Critical Limb Ischemia in Rat Offspring

Adult metabolic syndrome is considered to be elicited by the developmental programming which is regulated by the prenatal environment. The maternal excess intake of fructose, a wildly used food additive, is found to be associated with developmental programing-associated cardiovascular diseases. To investigate the effect of maternal fructose exposure (MFE) on endothelial function and repair, which participate in the initiation and progress of cardiovascular disease, we applied a rat model with maternal fructose excess intake during gestational and lactational stage and examined the number and function of endothelial progenitor cells (EPCs) in 3-month-old male offspring with induction of critical limb ischemia (CLI). Results showed that the circulating levels of c-Kit+/CD31+ and Sca-1+/KDR+ EPC were reduced by MFE. In vitro angiogenesis analysis indicated the angiogenic activity of bone marrow-derived EPC, including tube formation and cellular migration, was reduced by MFE. Western blots further indicated the phosphorylated levels of ERK1/2, p38-MAPK, and JNK in circulating peripheral blood mononuclear cells were up-regulated by MFE. Fourteen days after CLI, the reduced blood flow recovery, lowered capillary density, and increased fibrotic area in quadriceps were observed in offspring with MFE. Moreover, the aortic endothelium-mediated vasorelaxant response in offspring was impaired by MFE. In conclusion, maternal fructose intake during gestational and lactational stage modulates the number and angiogenic activity of EPCs and results in poor blood flow recovery after ischemic injury.

Cardiac SNARE Expression in Health and Disease

SNARE proteins are integral to intracellular vesicular trafficking, which in turn is the process underlying the regulated expression of substrate transporters such as the glucose transporter GLUT4 at the cell surface of insulin target tissues. Impaired insulin stimulated GLUT4 trafficking is associated with reduced cardiac function in many disease states, most notably diabetes. Despite this, our understanding of the expression and regulation of SNARE proteins in cardiac tissue and how these may change in diabetes is limited. Here we characterize the array of SNARE proteins expressed in cardiac tissue, and quantify the levels of expression of VAMP2, SNAP23, and Syntaxin4-key proteins involved in insulin-stimulated GLUT4 translocation. We examined SNARE protein levels in cardiac tissue from two rodent models of insulin resistance, db/db mice and high-fat fed mice, and show alterations in patterns of expression are evident. Such changes may have implications for cardiac function.

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.

Dietary soya protein improves intra-myocardial lipid deposition and altered glucose metabolism in a hypertensive, dyslipidaemic, insulin-resistant rat model

This study investigates the effects of replacing dietary casein by soya protein on the underlying mechanisms involved in the impaired metabolic fate of glucose and lipid metabolisms in the heart of dyslipidaemic rats chronically fed (8 months) a sucrose-rich (62·5 %) diet (SRD). To test this hypothesis, Wistar rats were fed an SRD for 4 months. From months 4 to 8, half the animals continued with the SRD and the other half were fed an SRD in which casein was substituted by soya. The control group received a diet with maize starch as the carbohydrate source. Compared with the SRD-fed group, the following results were obtained. First, soya protein significantly (P<0·001) reduced the plasma NEFA levels and normalised dyslipidaemia and glucose homoeostasis, improving insulin resistance. The protein levels of fatty acid translocase at basal state and under insulin stimulation and the protein levels and activity of muscle-type carnitine palmitoyltransferase 1 were normalised. Second, a significant (P<0·001) reduction of TAG, long-chain acyl CoA and diacylglycerol levels was observed in the heart muscle. Third, soya protein significantly increased (P<0·01) GLUT4 protein level under insulin stimulation and normalised glucose phosphorylation and oxidation. A reduction of phosphorylated AMP protein kinase protein level was recorded without changes in uncoupling protein 2 and PPARα. Fourth, hydroxyproline concentration decreased in the left ventricle and hypertension was normalised. The new information provided shows the beneficial effects of soya protein upon the altered pathways of glucose and lipid metabolism in the heart muscle of this rat model.

Troxerutin abrogates mitochondrial oxidative stress and myocardial apoptosis in mice fed calorie-rich diet

Mitochondrial oxidative stress plays a major role in the pathogenesis of myocardial apoptosis in metabolic syndrome (MS) patients. In this study, we investigated the effect of troxerutin (TX), an antioxidant on mitochondrial oxidative stress and apoptotic markers in heart of mice fed fat and fructose-rich diet. Adult male Mus musculus mice were fed either control diet or high fat, high fructose diet (HFFD) for 60 days to induce MS. Mice from each dietary group were divided into two on the 16th day and were either treated or untreated with TX (150 mg/kg bw, p.o) for the next 45 days. At the end of the study, mitochondrial reactive oxygen species (ROS) generation, oxidative stress markers, levels of intracellular calcium, cardiolipin content, cytochrome c release and apoptotic markers were examined in the myocardium. HFFD-feeding resulted in diminution of antioxidants and increased ROS production, lipid peroxidation and oxidatively modified adducts of 8-OHG, 4-HNE and 3-NT. Further increase in Ca²⁺ levels, low levels of calcium transporters and decrease in cardiolipin content were noted. Changes in the mitochondrial structure were observed by electron microscopy. Furthermore, cytochrome c release, increase in proapoptotic proteins (APAF-1, BAX, caspases-9 and-3) and decrease in antiapoptotic protein (BCL-2) in HFFD-fed mice suggest myocardial apoptosis. These changes were significantly restored by TX supplementation. TX administration effectively attenuated cardiac apoptosis and exerted a protective role by increasing antioxidant potential and by improving mitochondrial function. Thus, TX could be a promising therapeutic candidate for treating cardiac disease in MS patients.

Troxerutin attenuates diet-induced oxidative stress, impairment of mitochondrial biogenesis and respiratory chain complexes in mice heart

Mitochondrial abnormality is thought to play a key role in cardiac disease originating from the metabolic syndrome (MS). We evaluated the effect of troxerutin (TX), a semi-synthetic derivative of the natural bioflavanoid rutin, on the respiratory chain complex activity, oxidative stress, mitochondrial biogenesis and dynamics in heart of high fat, high fructose diet (HFFD) -induced mouse model of MS. Adult male Mus musculus mice of body weight 25-30 g were fed either control diet or HFFD for 60 days. Mice from each dietary regimen were divided into two groups on the 16th day and were treated or untreated with TX (150 mg/kg body weight [bw], per oral) for the next 45 days. At the end of experimental period, respiratory chain complex activity, uncoupling proteins (UCP)-2 and -3, mtDNA content, mitochondrial biogenesis and dynamics, oxidative stress markers and reactive oxygen species (ROS) generation were analyzed. Reduced mtDNA abundance with alterations in the expression of genes related to mitochondrial biogenesis and fission and fusion processes were observed in HFFD-fed mice. Disorganized and smaller mitochondria, reduction in complexes I, III and IV activities (by about 55%) and protein levels of UCP-2 (52%) and UCP-3 (46%) were noted in these mice. TX administration suppressed oxidative stress, improved the oxidative capacity and biogenesis and restored fission/fusion imbalance in the cardiac mitochondria of HFFD-fed mice. TX protects the myocardium by modulating the putative molecules of mitochondrial biogenesis and dynamics and by its anti-oxidant function in a mouse model of MS.

The Higher the Insulin Resistance the Lower the Cardiac Output in Men with Type 1 Diabetes During the Maximal Exercise Test

BACKGROUND

The aim of this study was to assess the hemodynamic parameters analyzed in bioimpedance cardiography during maximal exercise in patients with type 1 diabetes differing in insulin resistance.

METHODS

The study group consisted of 40 men with type 1 diabetes. Tissue sensitivity to insulin was assessed on the basis of the glucose disposal rate (GDR) analyzed during hyperinsulinemic-euglycemic clamp. Patients were divided into groups with GDR <4.5 mg/kg/min (G1 group-lower insulin sensitivity) and GDR ≥4.5 mg/kg/min (G2 group-higher insulin sensitivity). During the exercise test, the heart rate, systolic volume, cardiac output, cardiac index were measured by the impedance meter (PhysioFlow).

RESULTS

Compared with the G2 group, the G1 group had a lower cardiac output (CO): during exercise 8.6 (IQR 7.7-10.0) versus 12.8 (IQR 10.8-13.7) L/min; P < 0.0001, at the maximal effort 13.1 (IQR 12.2-16.7) versus 18.6 (IQR 16.9-20.2) L/min; P = 0.001, and during observation after exercise 8.4 (IQR 6.3-9.6) versus 11.9 (IQR 10.1-13.1) L/min; P < 0.0001. We noticed a positive correlation of GDR and cardiac output: during the exercise test (r = 0.63, P = 0.0002), at the maximal effort (Rs 0.56, P = 0.001), and during observation after the exercise test (r = 0.72, P < 0.0001). In multivariate logistic regression, cardiac output during exercise and during observation was associated with high GDR, regardless of the age and duration of diabetes [OR: 1.98 (95% CI 1.10-3.56), P = 0.02 and OR: 1.91 (95% CI 1.05-3.48), P = 0.03; respectively].

CONCLUSION

In nonobese subjects with type 1 diabetes, with good metabolic control, insulin resistance is associated with cardiac hemodynamic parameters assessed during and after exercise. The higher the insulin resistance the lower the cardiac output during maximal exercise in men with type 1 diabetes.

Diabetic Cardiomyopathy: An Immunometabolic Perspective

The heart possesses a remarkable inherent capability to adapt itself to a wide array of genetic and extrinsic factors to maintain contractile function. Failure to sustain its compensatory responses results in cardiac dysfunction, leading to cardiomyopathy. Diabetic cardiomyopathy (DCM) is characterized by left ventricular hypertrophy and reduced diastolic function, with or without concurrent systolic dysfunction in the absence of hypertension and coronary artery disease. Changes in substrate metabolism, oxidative stress, endoplasmic reticulum stress, formation of extracellular matrix proteins, and advanced glycation end products constitute the early stage in DCM. These early events are followed by steatosis (accumulation of lipid droplets) in cardiomyocytes, which is followed by apoptosis, changes in immune responses with a consequent increase in fibrosis, remodeling of cardiomyocytes, and the resultant decrease in cardiac function. The heart is an omnivore, metabolically flexible, and consumes the highest amount of ATP in the body. Altered myocardial substrate and energy metabolism initiate the development of DCM. Diabetic hearts shift away from the utilization of glucose, rely almost completely on fatty acids (FAs) as the energy source, and become metabolically inflexible. Oxidation of FAs is metabolically inefficient as it consumes more energy. In addition to metabolic inflexibility and energy inefficiency, the diabetic heart suffers from impaired calcium handling with consequent alteration of relaxation-contraction dynamics leading to diastolic and systolic dysfunction. Sarcoplasmic reticulum (SR) plays a key role in excitation-contraction coupling as Ca²⁺ is transported into the SR by the SERCA2a (sarcoplasmic/endoplasmic reticulum calcium-ATPase 2a) during cardiac relaxation. Diabetic cardiomyocytes display decreased SERCA2a activity and leaky Ca²⁺ release channel resulting in reduced SR calcium load. The diabetic heart also suffers from marked downregulation of novel cardioprotective microRNAs (miRNAs) discovered recently. Since immune responses and substrate energy metabolism are critically altered in diabetes, the present review will focus on immunometabolism and miRNAs.

Roles of obese-insulin resistance and anti-diabetic drugs on the heart with ischemia-reperfusion injury

The incidence of obesity with insulin resistance is increasing worldwide. This condition is also known as a risk factor of coronary artery disease and associated with increased arrhythmias, impaired left ventricular function, and increased infarct size during cardiac ischemia-reperfusion (I/R) injury. The proposed mechanisms are due to impaired glucose utilization and pro-survival signaling molecules, and increased inflammatory cytokines, which have been demonstrated in the I/R hearts in various models of obese-insulin resistance. However, the cardiac effects of diets in the I/R heart are still unsettled since several studies reported that high-caloric diet consumption might protect the heart from I/R injury. Although several therapeutic strategies such as anti-diabetic drugs, natural compounds as well as treadmill exercise have been proposed to exert cardioprotection in the I/R heart in obese-insulin resistant animals, some interventions including ischemic post-conditioning failed to protect the heart from I/R injury. In this comprehensive review, reports from both genetic deletion and dietary-induced obese-insulin resistant animal models regarding the effects of obese-insulin resistance on metabolic parameters, cardiac function, infarct size, and molecular mechanisms under I/R injury are summarized. Moreover, the effects of anti-diabetic drugs and other pharmacological interventions on these parameters in an obese-insulin resistant model under I/R injury are also comprehensively summarized and discussed.

Involvement of peroxisome proliferator-activated receptors in cardiac and vascular remodeling in a novel minipig model of insulin resistance and atherosclerosis induced by consumption of a high-fat/cholesterol diet

Background

A long-term high-fat/cholesterol (HFC) diet leads to insulin resistance (IR), which is associated with inflammation, atherosclerosis (AS), cardiac sympathovagal imbalance, and cardiac dysfunction. Peroxisome proliferator-activated receptors (PPARs) and nuclear factor ĸB (NF-κB) are involved in the development of IR-AS. Thus, we elucidated the pathological molecular mechanism of IR-AS by feeding an HFC diet to Tibetan minipigs to induce IR and AS.

Methods

Male Tibetan minipigs were fed either a normal diet or an HFC diet for 24 weeks. Thereafter, the minipigs were tested for physiological and biochemical blood indices, blood pressure, cardiac function, glucose tolerance, heart rate variability (HRV), and PPAR-associated gene and protein expression levels.

Results

HFC-fed minipigs exhibited IR through increased body weight, fasting blood glucose levels, plasma cholesterol and its composition, and insulin and free fatty acid (FFA) levels; decreased insulin sensitivity; impaired glucose tolerance; and hypertension. Increased C-reactive protein (CRP) levels, cardiac dysfunction, depressed HRV, and the up-regulation of PPAR expression in the abdominal aorta concomitant with down-regulation in the heart tissue were observed in HFC-fed minipigs. Furthermore, the levels of NF-κBp65, IL-1β, TNF-α, MCP-1, VCAM-1, ICAM-1, MMP-9, and CRP proteins were also significantly increased.

Conclusions

These data suggest that HFC-fed Tibetan minipigs develop IR and AS and that PPARs are involved in cardiovascular remodeling and impaired function.

Ca(2+) mishandling and cardiac dysfunction in obesity and insulin resistance: role of oxidative stress

Obesity and insulin resistance (IR) are strongly connected to the development of subclinical cardiac dysfunction and eventually can lead to heart failure, which is the main cause of morbidity and death in patients having these metabolic diseases. It has been considered that excessive fat tissue may play a critical role in producing systemic IR and enhancing reactive oxygen species (ROS) generation. This oxidative stress (OS) may elicit or exacerbate IR. On the other hand, evidence suggests that some of the cellular mechanisms involved in the pathophysiology of obesity and IR-related cardiomyopathy are excessive myocardial ROS production and abnormal Ca(2+) homeostasis. In addition, emerging evidence suggests that augmented ROS production may contribute to Ca(2+) mishandling by affecting the redox state of key proteins implicated in this process. In this review, we focus on the role of Ca(2+) mishandling in the development of cardiac dysfunction in obesity and IR and address the evidence suggesting that OS might also contribute to cardiac dysfunction by affecting Ca(2+) handling.

Interplay of oxidative, nitrosative/nitrative stress, inflammation, cell death and autophagy in diabetic cardiomyopathy

Diabetes is a recognized risk factor for cardiovascular diseases and heart failure. Diabetic cardiovascular dysfunction also underscores the development of diabetic retinopathy, nephropathy and neuropathy. Despite the broad availability of antidiabetic therapy, glycemic control still remains a major challenge in the management of diabetic patients. Hyperglycemia triggers formation of advanced glycosylation end products (AGEs), activates protein kinase C, enhances polyol pathway, glucose autoxidation, which coupled with elevated levels of free fatty acids, and leptin have been implicated in increased generation of superoxide anion by mitochondria, NADPH oxidases and xanthine oxidoreductase in diabetic vasculature and myocardium. Superoxide anion interacts with nitric oxide forming the potent toxin peroxynitrite via diffusion limited reaction, which in concert with other oxidants triggers activation of stress kinases, endoplasmic reticulum stress, mitochondrial and poly(ADP-ribose) polymerase 1-dependent cell death, dysregulates autophagy/mitophagy, inactivates key proteins involved in myocardial calcium handling/contractility and antioxidant defense, activates matrix metalloproteinases and redox-dependent pro-inflammatory transcription factors (e.g. nuclear factor kappaB) promoting inflammation, AGEs formation, eventually culminating in myocardial dysfunction, remodeling and heart failure. Understanding the complex interplay of oxidative/nitrosative stress with pro-inflammatory, metabolic and cell death pathways is critical to devise novel targeted therapies for diabetic cardiomyopathy, which will be overviewed in this brief synopsis. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Chronic intermittent hypobaric hypoxia prevents cardiac dysfunction through enhancing antioxidation in fructose-fed rats

High-fructose intake induces metabolic syndrome and cardiac dysfunction. Chronic intermittent hypobaric hypoxia (CIHH) preserves cardiac function during ischemia. We hypothesized that CIHH restores the impaired cardiac function in fructose-fed rats. Sprague-Dawley rats were randomly subject to treatment with fructose (10% fructose in drinking water for 6 weeks), CIHH (simulated 5000 m altitude, 6 h/day for 6 weeks in a hypobaric chamber), and CIHH plus fructose groups. In addition to an increase in blood pressure, fructose feeding caused elevated serum levels of glucose, fasting insulin and insulin C peptide, triglyceride, cholesterol, and mass ratio of heart to body. CIHH treatment decreased the arterial blood pressure, serum levels of biochemical markers, and cardiac hypertrophy in fructose-fed rats. Furthermore, CIHH treatment improved the recovery of left ventricular function after ischemia-reperfusion procedure (30 min global no-flow ischemia followed by 60 min of reperfusion) in rats with or without fructose feeding. In addition, CIHH treatment caused a significant increase in superoxide dismutase (SOD) activity and decrease in malondialdehyde level in cardiac myocardium experiencing ischemia-reperfusion in control and fructose-fed rats. Collectively, these data suggest that CIHH improve impaired cardiac function in fructose-fed rats through enhancing antioxidation in the myocardium.

Autophagy, myocardial protection, and the metabolic syndrome

Autophagy is a housekeeping process that helps to maintain cellular energy homeostasis and remove damaged organelles. In the heart, autophagy is an adaptive process that is activated in response to stress including acute and chronic ischemia. Given the evidence that autophagy is suppressed in energy-rich conditions, the objective of this review is to examine autophagy and cardioprotection in the setting of the metabolic syndrome. Clinical approaches that involve the induction of cardiac autophagy pharmacologically to enhance the heart's tolerance to ischemia are also discussed.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Cardiovascular correlates of insulin resistance in normotensive and hypertensive African Americans

Insulin resistance (IR) is associated with obesity and predisposes to diabetes mellitus (DM) and cardiovascular disease. The purpose of this study is to determine if IR is related to cardiovascular function independent of DM or hypertension among African Americans (AA). Four hundred sixty-two nondiabetic AA (50% hypertensive and 51% women) were studied on an inpatient General Clinical Research Center. Measurements included anthropometrics and 24-hour blood pressure (BP), heart rate (HR), fasting blood glucose, plasma aldosterone, and insulin. Stroke volume (SV) and cardiac output (CO) were measured by impedance plethysmography; peripheral vascular resistance (PVRI) and vascular compliance indices (VCI) were computed. These measurements were also obtained in response to mental (computerized math testing) and pharmacologic (graded norepinephrine infusion) stress. Insulin resistance was calculated using the homeostasis model assessment (HOMA-IR). SV, CO, and VCI decreased with increasing HOMA-IR, whereas HR and PVRI increased. Overall, BP, HR, and PVRI were positively correlated with HOMA-IR (P < .01); and SV index, cardiac index, and VCI were negatively correlated with HOMA-IR (P < .0001). The correlations persisted after adjustment for BP, age, sex, plasma aldosterone, total cholesterol, or low-density lipoprotein and high-density lipoprotein cholesterol. In addition, multiple linear regression analyses showed that HOMA-IR contributes to the maximum variability of all the hemodynamic variables. Blood pressure responses to math stress and norepinephrine infusion did not correlate with HOMA-IR. Unrelated to DM and BP, IR is associated with increased PVRI and decreased CO in AA. These observations suggest that an exclusive focus on effects of IR on DM or BP may ignore independent pathophysiologic contributions of IR to cardiovascular disease.

Refined fructose and cancer

INTRODUCTION

Caloric excess, including increased refined carbohydrate intake, is associated with higher cancer risk emphasizing the importance of improved understanding of cancer cell metabolism in tumor survival and metastasis.

AREAS COVERED

This article reviews the relationship between increased dietary refined sugar and cancer risk, with specific emphasis on the monosaccharide fructose. Cancer cell metabolism is reviewed, and the potential mechanisms by which dietary sugars contribute to the tumor microenvironment are discussed. Recent observations indicate that cancer cells readily utilize fructose to support proliferation and preferentially use fructose for nucleic acid synthesis. This review discusses the potential role of how dietary fructose can promote cancer growth by a variety of mechanisms, including altered cellular metabolism, increased reactive oxygen species, DNA damage and inflammation. Preliminary insights into potential therapeutic strategies by which fructose-mediated cancer effects may be abrogated are presented.

EXPERT OPINION

Other sugars (particularly fructose, given its abundance in the modern diet) must be considered with reference to cancer cell metabolism. Cancer cells utilize similar sugars in distinct ways, which may present important new therapeutic avenues of targeting cancer.

Absence of meal-induced insulin sensitization (AMIS) in aging rats is associated with cardiac dysfunction that is protected by antioxidants

We have previously demonstrated that progressive development of absence of meal-induced insulin sensitization (AMIS) leads to postprandial hyperglycemia, compensatory hyperinsulinemia, resultant hyperlipidemia, increased oxidative stress, and obesity, progressing to syndrome X in aging rats. The present study tested the hypothesis that progressive development of AMIS in aging rats further resulted in deterioration in cardiac performance. Anesthetized male Sprague-Dawley rats were tested at 9, 26, and 52 wk to determine their dynamic response to insulin and cardiac function. Dynamic insulin sensitivity was determined before and after atropine to quantitate hepatic insulin sensitizing substance (HISS)-dependent and -independent insulin action. Cardiac performance was evaluated using a Millar pressure-volume conductance catheter system. AMIS developed with age, as demonstrated by significant decrease in HISS-dependent insulin action, and this syndrome was increased by sucrose supplementation and inhibited by the antioxidant treatment. Associated with progressive development of AMIS, aging rats showed impaired cardiac performance, including the reduction in cardiac index, heart rate, dP/dt(max), dP/dt(min), ejection fraction and decreased slope of left ventricular end-systolic pressure-volume relationship, and increased relaxation time constant of left ventricular pressure as well as increased left ventricular end-diastolic pressure. Total peripheral vascular resistance also increased with age. Sucrose supplementation and antioxidant treatment, respectively, potentiated and attenuated cardiac dysfunction associated with age. In addition, poor cardiac performance correlated closely with the development of AMIS. These results indicate that AMIS is the first metabolic defect that leads to homeostatic disturbances and dysfunctions, including cardiovascular diseases.

Metabolism, hypoxia and the diabetic heart

The diabetic heart becomes metabolically remodelled as a consequence of exposure to abnormal circulating substrates and hormones. Fatty acid uptake and metabolism are increased in the type 2 diabetic heart, resulting in accumulation of intracellular lipid intermediates and an increased contribution of fatty acids towards energy generation. Cardiac glucose uptake and oxidation are decreased, predominantly due to increased fatty acid metabolism, which suppresses glucose utilisation via the Randle cycle. These metabolic changes decrease cardiac efficiency and energetics in both humans and animal models of diabetes. Diabetic hearts have decreased recovery following ischemia, indicating a reduced tolerance to oxygen-limited conditions. There is evidence that diabetic hearts have a compromised hypoxia signalling pathway, as hypoxia-inducible factor (HIF) and downstream signalling from HIF are reduced following ischemia. Failure to activate HIF under oxygen-limited conditions results in less angiogenesis, and an inability to upregulate glycolytic ATP generation. Given that glycolysis is already suppressed in the diabetic heart under normoxic conditions, the inability to upregulate glycolysis in response to hypoxia may have deleterious effects on ATP production. Thus, impaired HIF signalling may contribute to metabolic and energetic abnormalities, and impaired collateral vessel development following myocardial infarction in the type 2 diabetic heart.

Insulin and resveratrol act synergistically, preventing cardiac dysfunction in diabetes, but the advantage of resveratrol in diabetics with acute heart attack is antagonized by insulin

Resveratrol (RSV), a natural phenolic compound, has been found to display cardiovascular protective and insulin-sensitizing properties. In this study, the effects of RSV and its combination with insulin on mortality, hemodynamics, insulin signaling, and nitrosative stress were compared in streptozotocin (STZ)-induced diabetic rats with or without acute myocardial ischemia/reperfusion (I/R) injury. Under normoxic conditions, cardiac systolic and diastolic functions and insulin-mediated Akt/GLUT4 (glucose transporter 4) activation were impaired in STZ-diabetic rats. The combination of RSV and insulin significantly prevented the above diabetes-associated abnormalities. Notwithstanding that, the diabetic state rendered the animals more susceptible to myocardial I/R injury, and the mortality rate and inducible nitric oxide synthase (iNOS)/nitrotyrosine protein expression and superoxide anion production were also further increased in I/R-injured diabetic hearts. In contrast, RSV treatment alone resulted in a lower mortality rate (from 62.5 to 18%) and better cardiac systolic function than its combination with insulin. RSV also inhibited iNOS/nitrotyrosine protein overexpression and superoxide anion overproduction in I/R-injured diabetic myocardium. Hyperglycemia, impairment of insulin signaling, overexpression of iNOS/nitrotyrosine, and superoxide anion overproduction were markedly rescued by the combination treatment, which did not show an improvement in mortality rate (30%) or cardiac performance over RSV treatment alone. These results indicate that insulin and RSV synergistically prevented cardiac dysfunction in diabetes and this may be in parallel with activation of the insulin-mediated Akt/GLUT4 signaling pathway. Although activation of the protective signal (Akt/GLUT4) and suppression of the adverse markers (iNOS, nitrotyrosine, and superoxide anion) were simultaneously observed in insulin and RSV combination treatment, insulin counteracted the advantage of RSV in diabetics with acute heart attack.

Hepatic inflammation and insulin resistance in pre-diabetes - further evidence for the beneficial actions of PPAR-gamma agonists and a role for SOCS-3 modulation

Pre-diabetes is a condition affecting increasing numbers of the population who find themselves caught in the grey area between normal glucose regulation and diabetes mellitus and who experience impaired glucose tolerance or fasting glucose. The ability of thiozolidinediones (TZDs) to ameliorate the clinical signs of diabetes mellitus is well-known but there is also emerging evidence for the benefits of PPAR-gamma agonists in pre-diabetes. In this issue of the British Journal of Pharmacology, Collino and colleagues report that pioglitazone can reduce hepatic inflammation and insulin resistance in rats administered a high cholesterol and fructose diet. Furthermore, pioglitazone reduced the expression of suppressor of cytokine signalling (SOCS)-3 - considered to be a key link between inflammation and insulin resistance. Although much work remains to be performed in fully understanding how TZDs modulate the cellular mechanisms which underlie pre-diabetes, these findings provide preliminary evidence that administration of TZDs to pre-diabetics could be beneficial.

Green tea polyphenols improve cardiac muscle mRNA and protein levels of signal pathways related to insulin and lipid metabolism and inflammation in insulin-resistant rats

Epidemiological studies indicate that the consumption of green tea polyphenols (GTP) may reduce the risk of coronary artery disease. To explore the underlying mechanisms of action at the molecular level, we examined the effects of GTP on the cardiac mRNA and protein levels of genes involved in insulin and lipid metabolism and inflammation. In rats fed a high-fructose diet, supplementation with GTP (200 mg/kg BW daily dissolved in distilled water) for 6 wk, reduced systemic blood glucose, plasma insulin, retinol-binding protein 4, soluble CD36, cholesterol, triglycerides, free fatty acids and LDL-C levels, as well as the pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and IL-6. GTP did not affect food intake, bodyweight and heart weight. In the myocardium, GTP also increased the insulin receptor (Ir), insulin receptor substrate 1 and 2 (Irs1 and Irs2), phosphoinositide-3-kinase (Pi3k), v-akt murine thymoma viral oncogene homolog 1 (Akt1), glucose transporter 1 and 4 (Glut1 and Glut4) and glycogen synthase 1 (Gys1) expression but inhibited phosphatase and tensin homolog deleted on chromosome ten (Pten) expression and decreased glycogen synthase kinase 3beta (Gsk3beta) mRNA expression. The sterol regulatory element-binding protein-1c (Srebp1c) mRNA, microsomal triglyceride transfer protein (Mttp) mRNA and protein, Cd36 mRNA and cluster of differentiation 36 protein levels were decreased and peroxisome proliferator-activated receptor (Ppar)gamma mRNA levels were increased. GTP also decreased the inflammatory factors: Tnf, Il1b and Il6 mRNA levels, and enhanced the anti-inflammatory protein, zinc-finger protein, protein and mRNA expression. In summary, consumption of GTP ameliorated the detrimental effects of high-fructose diet on insulin signaling, lipid metabolism and inflammation in the cardiac muscle of rats.

Upregulation of eNOS and unchanged energy metabolism in increased susceptibility of the aging type 2 diabetic GK rat heart to ischemic injury

We investigated the tolerance of the insulin-resistant diabetic heart to ischemic injury in the male Goto-Kakizaki (GK) rat, a model of type 2 diabetes. Changes in energy metabolism, nitric oxide (NO) pathway, and cardiac function were assessed in the presence of physiological substrates. Age-matched control Wistar (n = 19) and GK (n = 18) isolated rat hearts were perfused with 0.4 mM palmitate, 3% albumin, 11 mM glucose, 3 U/l insulin, 0.2 mM pyruvate, and 0.8 mM lactate for 24 min before switching to 1.2 mM palmitate (11 rats/group) during 32 min low-flow (0.5 ml·min(-1)·g wet wt(-1)) ischemia. Next, flow was restored with 0.4 mM palmitate buffer for 32 min. A subset of hearts from each group (n = 8 for control and n = 7 for GK groups) were freeze-clamped for determining baseline values after the initial perfusion of 24 min. ATP, phosphocreatine (PCr), and intracellular pH (pH(i)) were followed using (31)P magnetic resonance spectroscopy with simultaneous measurement of contractile function. The NO pathway was determined by nitric oxide synthase (NOS) isoform expression and total nitrate concentration (NOx) in hearts. We found that coronary flow was 26% lower (P < 0.05) during baseline conditions and 61% lower (P < 0.05) during reperfusion in GK vs. control rat hearts. Rate pressure product was lower during reperfusion in GK vs. control rat hearts (P < 0.05). ATP, PCr, and pH(i) during ischemia-reperfusion were similar in both groups. Endothelial NOS expression was increased in GK rat hearts during baseline conditions (P < 0.05). NOx was increased during baseline conditions (P < 0.05) and after reperfusion (P < 0.05) in GK rat hearts. We report increased susceptibility of type 2 diabetic GK rat heart to ischemic injury that is not associated with impaired energy metabolism. Reduced coronary flow, upregulation of eNOS expression, and increased total NOx levels confirm NO pathway modifications in this model, presumably related to increased oxidative stress. Modifications in the NO pathway may play a major role in ischemia-reperfusion injury of the type 2 diabetic GK rat heart.

Abnormal in vivo myocardial energy substrate uptake in diet-induced type 2 diabetic cardiomyopathy in rats

The purpose of this study was to determine in vivo myocardial energy metabolism and function in a nutritional model of type 2 diabetes. Wistar rats rendered insulin-resistant and mildly hyperglycemic, hyperinsulinemic, and hypertriglyceridemic with a high-fructose/high-fat diet over a 6-wk period with injection of a small dose of streptozotocin (HFHFS) and control rats were studied using micro-PET (microPET) without or with a euglycemic hyperinsulinemic clamp. During glucose clamp, myocardial metabolic rate of glucose measured with [(18)F]fluorodeoxyglucose ([(18)F]FDG) was reduced by approximately 81% (P < 0.05), whereas myocardial plasma nonesterified fatty acid (NEFA) uptake as determined by [(18)F]fluorothia-6-heptadecanoic acid ([(18)F]FTHA) was not significantly changed in HFHFS vs. control rats. Myocardial oxidative metabolism as assessed by [(11)C]acetate and myocardial perfusion index as assessed by [(13)N]ammonia were similar in both groups, whereas left ventricular ejection fraction as assessed by microPET was reduced by 26% in HFHFS rats (P < 0.05). Without glucose clamp, NEFA uptake was approximately 40% lower in HFHFS rats (P < 0.05). However, myocardial uptake of [(18)F]FTHA administered by gastric gavage was significantly higher in HFHFS rats (P < 0.05). These abnormalities were associated with reduced Glut4 mRNA expression and increased Cd36 mRNA expression and mitochondrial carnitine palmitoyltransferase 1 activity (P < 0.05). HFHFS rats display type 2 diabetes complicated by left ventricular contractile dysfunction with profound reduction in myocardial glucose utilization, activation of fatty acid metabolic pathways, and preserved myocardial oxidative metabolism, suggesting reduced myocardial metabolic efficiency. In this model, increased myocardial fatty acid exposure likely occurs from circulating triglyceride, but not from circulating plasma NEFA.

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

Metabolic syndrome and obesity-related diseases are affecting more and more people in the Western world. The basis for an effective treatment of these patients is a better understanding of the underlying pathophysiology. Here, we characterize fructose- and fat-fed rats (FFFRs) as a new animal model of metabolic syndrome. Sprague-Dawley rats were fed a 60 kcal/100 kcal fat diet with 10% fructose in the drinking water. After 6, 12, 18, 24, 36, and 48 wk of feeding, blood pressure, glucose tolerance, plasma insulin, glucose, and lipid levels were measured. Cardiac function was examined by in vivo pressure volume measurements, and intramyocardial lipid accumulation was analyzed by confocal microscopy. Cardiac AMP-activated kinase (AMPK) and hepatic phosphoenolpyruvate carboxykinase (PEPCK) levels were measured by Western blotting. Finally, an ischemia-reperfusion study was performed after 56 wk of feeding. FFFRs developed severe obesity, decreased glucose tolerance, increased serum insulin and triglyceride levels, and an initial increased fasting glucose, which returned to control levels after 24 wk of feeding. The diet had no effect on blood pressure but decreased hepatic PEPCK levels. FFFRs showed significant intramyocardial lipid accumulation, and cardiac hypertrophy became pronounced between 24 and 36 wk of feeding. FFFRs showed no signs of cardiac dysfunction during unstressed conditions, but their hearts were much more vulnerable to ischemia-reperfusion and had a decreased level of phosphorylated AMPK at 6 wk of feeding. This study characterizes a new animal model of the metabolic syndrome that could be beneficial in future studies of metabolic syndrome and cardiac complications.

Impairment of insulin-stimulated Akt/GLUT4 signaling is associated with cardiac contractile dysfunction and aggravates I/R injury in STZ-diabetic rats

In this study, we established systemic in-vivo evidence from molecular to organism level to explain how diabetes can aggravate myocardial ischemia-reperfusion (I/R) injury and revealed the role of insulin signaling (with specific focus on Akt/GLUT4 signaling molecules). The myocardial I/R injury was induced by the left main coronary artery occlusion for 1 hr and then 3 hr reperfusion in control, streptozotocin (STZ)-induced insulinopenic diabetes, and insulin-treated diabetic rats. The diabetic rats showed a significant decrease in heart rate, and a prolonged isovolumic relaxation (tau) which lead to decrease in cardiac output (CO) without changing total peripheral resistance (TPR). The phosphorylated Akt and glucose transporter 4 (GLUT 4) protein levels were dramatically reduced in both I/R and non-I/R diabetic rat hearts. Insulin treatment in diabetes showed improvement of contractile function as well as partially increased Akt phosphorylation and GLUT 4 protein levels. In the animals subjected to I/R, the mortality rates were 25%, 65%, and 33% in the control, diabetic, and insulin-treated diabetic group respectively. The I/R-induced arrhythmias and myocardial infarction did not differ significantly between the control and the diabetic groups. Consistent with its anti-hyperglycemic effects, insulin significantly reduced I/R-induced arrhythmias but had no effect on I/R-induced infarctions. Diabetic rat with I/R exhibited the worse hemodynamic outcome, which included systolic and diastolic dysfunctions. Insulin treatment only partially improved diastolic functions and elevated P-Akt and GLUT 4 protein levels. Our results indicate that cardiac contractile dysfunction caused by a defect in insulin-stimulated Akt/GLUT4 may be a major reason for the high mortality rate in I/R injured diabetic rats.

Activation of estrogen receptor is crucial for resveratrol-stimulating muscular glucose uptake via both insulin-dependent and -independent pathways

OBJECTIVE

Estradiol (E(2)) is known to modulate insulin sensitivity and, consequently, glucose homeostasis. Resveratrol (RSV), an agonist of estrogen receptor (ER), has exerted antihyperglycemic effects in streptozotocin-induced type 1 diabetic rats in our previous study and was also shown to improve insulin resistance in other reports. However, it remains unknown whether activation of ER is involved in the metabolic effects of RSV via insulin-dependent and -independent mechanisms.

RESEARCH DESIGN AND METHODS

Male Sprague-Dawley rats were given a high cholesterol-fructose (HCF) diet for 15 weeks and were treated with RSV for either 15 days or 15 weeks.

RESULTS

Here, we show that RSV shifts the metabolic characteristics of rats on an HCF diet toward those of rats on a standard diet. RSV treatment increased insulin-stimulated whole-body glucose uptake and steady-state glucose uptake of soleus muscle and liver in HCF-fed rats as well as enhanced membrane trafficking activity of GLUT4 and increased phosphorylation of insulin receptor in insulin-resistant soleus muscles. Interestingly, the phosphorylated ER level in insulin-resistant soleus muscle was significantly elevated in rats with RSV treatment in both basal and euglycemic-hyperinsulinemic conditions. RSV exerted an insulin-like stimulatory effect on isolated soleus muscle, epididymal fat and hepatic tissue, and C2C12 myotubes. The RSV-stimulated glucose uptake in C2C12 myotubes was dependent on extracellular signal-related kinase/p38 (early phase, 1 h) and p38/phosphoinositide 3-kinase (late phase, 14 h) activation. Inhibition of ER abrogated RSV-induced glucose uptake in both early and late phases.

CONCLUSIONS

Collectively, these results indicate that ER is a key regulator in RSV-stimulating insulin-dependent and -independent glucose uptake, which might account for the protective effects of RSV on diet-induced insulin resistance syndrome.

Dietary fructose and the metabolic syndrome

PURPOSE OF REVIEW

Fructose, a naturally found sugar in many fruits, is now commonly used as an industrial sweetener and is excessively consumed in Western diets. High fructose intake is increasingly recognized as causative in development of prediabetes and metabolic syndrome. The mechanisms underlying fructose-induced metabolic disturbances are unclear but are beginning to be unravelled. This review presents recent findings in this field and an overall mechanistic insight into the metabolic effects of dietary fructose and its role in metabolic syndrome.

RECENT FINDINGS

Recent animal studies have confirmed the link between fructose feeding and increased plasma uric acid, a potentially causative factor in metabolic syndrome. Advanced glycation end products are also implicated because of their direct protein modifications and indirect effects on inflammation and oxidative stress. Human studies have demonstrated fructose's ability to change metabolic hormonal response, possibly contributing to decreased satiety.

SUMMARY

There is much evidence from both animal models and human studies supporting the notion that fructose is a highly lipogenic nutrient that, when consumed in high quantities, contributes to tissue insulin insensitivity, metabolic defects, and the development of a prediabetic state. Recently evidence has helped to decipher the mechanisms involved in these metabolic changes.

Deleterious effects of sugar and protective effects of starch on cardiac remodeling, contractile dysfunction, and mortality in response to pressure overload

Little is known about the effects of the composition of dietary carbohydrate on the development of left ventricular (LV) hypertrophy (LVH) and heart failure (HF) under conditions of pressure overload. The objective of this study was to determine the effect of carbohydrate composition on LVH, LV function, and mortality in a mouse model of chronic pressure overload. Male C57BL/6J mice of 6 wk of age ( n = 14–16 mice/group) underwent transverse aortic constriction (TAC) or sham surgery and were fed either standard chow (STD; 32% corn starch, 35% sucrose, 3% maltodextrin, and 10% fat expressed as a percent of the total energy), high-starch chow (58% corn starch, 12% maltodextrin, and 10% fat), or high-fructose chow (9% corn starch, 61% fructose, and 10% fat). After 16 wk of treatment, mice with TAC fed the STD or high-fructose diets exhibited increased LV mass, larger end-diastolic and end-systolic diameters, and decreased ejection fraction compared with sham. The high-starch diet, in contrast, prevented changes in LV dimensions and contractile function. Cardiac mRNA for myosin heavy chain-β was increased dramatically in the fructose-fed banded animals, as was mortality (54% compared with 8% and 29% in the starch and STD banded groups, respectively). In conclusion, a diet high in simple sugar was deleterious, resulting in the highest mortality and expression of molecular markers of cardiac dysfunction in TAC animals compared with sham, whereas a high-starch diet blunted mortality, increases in cardiac mass, and contractile dysfunction.