Cardiac function and metabolism in Type 2 diabetic mice after treatment with BM 17.0744, a novel PPAR-alpha activator

Indirect comparison of efficacy and safety of chiglitazar and thiazolidinedione in patients with type 2 diabetes: A meta-analysis

BACKGROUND

Chiglitazar is an emerging pan-agonist of all peroxisome proliferator activated receptors (PPAR)-α, δ and γ, and has therapeutic potential for type 2 diabetes (T2D). However, to date, no clinical studies or meta-analyses have compared the efficacy and safety of chiglitazar and traditional PPAR-γ agonist thiazolidinediones (TZDs). A meta-analysis concerning this topic is therefore required.

AIM

To compare the efficacy and safety of chiglitazar and TZD in patients with T2D.

METHODS

PubMed, Medline, Embase, the Cochrane Central Register of Controlled Trials, Reference Citation Analysis and Clinicaltrial.gov websites were searched from August 1994 to March 2022. Randomized controlled trials (RCTs) of chiglitazar or TZD vs placebo in patients with T2D were included. Indirect comparisons and sensitivity analyses were implemented to evaluate multiple efficacy and safety endpoints of interest.

RESULTS

We included 93 RCTs that compared TZD with placebo and one that compared chiglitazar with placebo. For efficacy endpoints, the augmented dose of chig-litazar resulted in greater reductions in hemoglobin (Hb)A1c [weighted mean difference (WMD) = -0.15%, 95% confidence interval (CI): -0.27 to -0.04%], triglycerides (WMD = -0.17 mmol/L, 95%CI: -0.24 to -0.11 mmol/L) and alanine aminotransferase (WMD = -5.25 U/L, 95%CI: -8.50 to -1.99 U/L), and a greater increase in homeostasis model assessment-β (HOMA-β) (WMD = 17.75, 95%CI: 10.73-24.77) when compared with TZD treatment. For safety endpoints, the risks of hypoglycemia, edema, bone fractures, upper respiratory tract infection, urinary tract infection, and weight gain were all comparable between the augmented dose of chiglitazar and TZD. In patients with baseline HbA1c ≥ 8.5%, body mass index ≥ 30 kg/m2 or diabetes duration < 10 years, the HbA1c reduction and HOMA-β increase were more conspicuous for the augmented dose of chiglitazar compared with TZD.

CONCLUSION

Augmented dose of chiglitazar, a pan-activator of PPARs, may serve as an antidiabetic agent with preferable glycemic and lipid control, better β-cell function preserving capacity, and does not increase the risk of safety concerns when compared with TZD.

The effect of pomegranate extract on anthropometric indices, serum lipids, glycemic indicators, and blood pressure in patients with nonalcoholic fatty liver disease: A randomized double-blind clinical trial

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease. The beneficial effects of pomegranate have been shown on insulin resistance and obesity, which are linked to NAFLD pathogenesis. The aim of this study was to investigate the efficacy of pomegranate extract in patients with NAFLD. Forty-four NAFLD patients were randomly assigned to receive two pomegranate extract tablets or placebo for 12 weeks. Anthropometric measurements, serum lipids, glycemic indicators, and blood pressure were assessed at baseline and the end of the study. Pomegranate was associated with a reduction in the total cholesterol (p ˂ .001), triglyceride (p ˂ .001), low-density lipoprotein cholesterol (LDL-C)-to-high-density lipoprotein cholesterol (HDL-C) ratio (p ˂ .003), fasting blood sugar (p ˂ .001), homeostatic model assessment of insulin resistance (p = .02), diastolic blood pressure (p = .04), weight (p ˂ .001), body mass index (p ˂ .001), and waist circumference (p = .002), as compared to placebo. A significant increase was observed in serum HDL-C (p ˂ .001) after intervention with the pomegranate extract. However, no significant difference was shown between the two groups in serum insulin and LDL-C. The pomegranate extract supplement could be used as a complementary therapy along with existing therapies to improve glycemic indicators, serum lipids, anthropometric indices, and blood pressure in patients with nonalcoholic fatty liver.

Label-free and noninvasive method for assessing the metabolic status in type 2 diabetic rats with myocardium diastolic dysfunction

This study assesses the metabolic status of rat diabetic cardiomyopathy (DCM) models. Echocardiography is used to detect the diastolic dysfunction in type 2 diabetic rats, and a lower threshold for inducible atrial fibrillation is found in type 2 diabetic rats with diastolic dysfunction compared to the control. Metabolic abnormalities are detected by status changes of reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H), which is an essential coenzyme in cells or tissues. Fluorescence lifetime imaging microscopy (FLIM) is used to monitor changes in NAD(P)H in both myocardial tissues and blood. FLIM reveals that the protein-bound proportion of NAD(P)H in rat myocardium in the DCM group is smaller than the control group, which indicates the oxidative phosphorylation rate of the DCM group decreased. Similar results are found for blood plasma of DCM rats by the FLIM study. FLIM exhibits high potential for screening DCM as a label-free, sensitive, and noninvasive method.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

Impact of Obesity-Related Inflammation on Cardiac Metabolism and Function

This review focuses on the role of adipose tissue in obese individuals in the development of metabolic diseases, and their consequences for metabolic and functional derangements in the heart. The general idea is that the expansion of adipocytes during the development of obesity gives rise to unhealthy adipose tissue, characterized by low-grade inflammation and the release of proinflammatory adipokines and fatty acids (FAs). This condition, in turn, causes systemic inflammation and elevated FA concentrations in the circulation, which links obesity to several pathologies, including impaired insulin signaling in cardiac muscle and a subsequent shift in myocardial substrate oxidation in favor of FAs and reduced cardiac efficiency. This review also argues that efforts to prevent obesity-related cardiometabolic disease should focus on anti-obesogenic strategies to restore normal adipose tissue metabolism.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Long-chain free fatty acids inhibit ischaemic preconditioning of the isolated rat heart

We recently reported that non-preconditioned hearts from diet-induced obese rats showed, compared to controls, a significant reduction in infarct size after ischaemia/reperfusion, whilst ischaemic preconditioning was without effect. In view of the high circulating FFA concentration in diet rats, the aims of the present study were to: (i) compare the effect of palmitate on the preconditioning potential of hearts from age-matched controls and diet rats (ii) elucidate the effects of substrate manipulation on ischaemic preconditioning. Substrate manipulation was done with dichloroacetate (DCA), which enhances glucose oxidation and decreases fatty acid oxidation. Isolated hearts from diet rats, age-matched controls or young rats, were perfused in the working mode using the following substrates: glucose (10 mM); palmitate (1.2 mM)/3% albumin) + glucose (10 mM) (HiFA + G); palmitate (1.2 mM/3% albumin) (HiFA); palmitate (0.4 mM/3% albumin) + glucose(10 mM) (LoFA + G); palmitate (0.4 mM/3% albumin) (LoFA). Hearts were preconditioned with 3 × 5 min ischaemia/reperfusion, followed by 35 min coronary ligation and 60 min reperfusion for infarct size determination (tetrazolium method) or 20 min global ischaemia/10 or 30 min reperfusion for Western blotting (ERKp44/42, PKB/Akt). Preconditioning of glucose-perfused hearts from age-matched control (but not diet) rats reduced infarct size, activated ERKp44/42 and PKB/Akt and improved functional recovery during reperfusion (ii) perfusion with HiFA + G abolished preconditioning and activation of ERKp44/42 (iii) DCA pretreatment largely reversed the harmful effects of HiFA. Hearts from non-preconditioned diet rats exhibited smaller infarcts, but could not be preconditioned, regardless of the substrate. Similar results were obtained upon substrate manipulation of hearts from young rats. Abolishment of preconditioning in diet rats may be due to altered myocardial metabolic patterns resulting from changes in circulating FA. The harmful effects of HiFA were attenuated by stimulation of glycolysis and inhibition of FA oxidation.

Involvement of Heparanase in Endothelial Cell-Cardiomyocyte Crosstalk

Traditionally, the management of diabetes has focused mainly on controlling high blood glucose levels. Unfortunately, despite valiant efforts to normalize this blood glucose, poor medication management predisposes these patients to heart failure. Following diabetes, how the heart utilizes different sources of fuel for energy is key to the development of heart failure. The diabetic heart switches from using both glucose and fats, to predominately using fats as an energy resource for maintaining its activities. This transformation to using fats as an exclusive source of energy is helpful in the initial stages of the disease and is tightly controlled. However, over the progression of diabetes, there is a loss of this controlled supply and use of fats, which ultimately has terrible consequences since the uncontrolled use of fats produces toxic by-products which weaken heart function and cause heart disease. Heparanase is a key player that directs how much fats are provided to the heart and does so in association with several partners like LPL and VEGFs. Together, they regulate the amount of fats supplied, and their subsequent breakdown to provide energy. Following diabetes, there is a disruption in this network resulting in fat oversupply and cell death. Understanding how the heparanase-LPL-VEGFs "ensemble" cooperates, and its dysfunction in the diabetic heart would be useful in restoring metabolic equilibrium and limiting diabetes-related cardiac damage.

Immunometabolic cross-talk in the inflamed heart

Inflammatory processes underlie many diseases associated with injury of the heart muscle, including conditions without an obvious inflammatory pathogenic component such as hypertensive and diabetic cardiomyopathy. Persistence of cardiac inflammation can cause irreversible structural and functional deficits. Some are induced by direct damage of the heart muscle by cellular and soluble mediators but also by metabolic adaptations sustained by the inflammatory microenvironment. It is well established that both cardiomyocytes and immune cells undergo metabolic reprogramming in the site of inflammation, which allow them to deal with decreased availability of nutrients and oxygen. However, like in cancer, competition for nutrients and increased production of signalling metabolites such as lactate initiate a metabolic cross-talk between immune cells and cardiomyocytes which, we propose, might tip the balance between resolution of the inflammation versus adverse cardiac remodeling. Here we review our current understanding of the metabolic reprogramming of both heart tissue and immune cells during inflammation, and we discuss potential key mechanisms by which these metabolic responses intersect and influence each other and ultimately define the prognosis of the inflammatory process in the heart.

Glucagon Receptor Antagonism Improves Glucose Metabolism and Cardiac Function by Promoting AMP-Mediated Protein Kinase in Diabetic Mice

The antidiabetic potential of glucagon receptor antagonism presents an opportunity for use in an insulin-centric clinical environment. To investigate the metabolic effects of glucagon receptor antagonism in type 2 diabetes, we treated Lepr^db/db and Lep^ob/ob mice with REMD 2.59, a human monoclonal antibody and competitive antagonist of the glucagon receptor. As expected, REMD 2.59 suppresses hepatic glucose production and improves glycemia. Surprisingly, it also enhances insulin action in both liver and skeletal muscle, coinciding with an increase in AMP-activated protein kinase (AMPK)-mediated lipid oxidation. Furthermore, weekly REMD 2.59 treatment over a period of months protects against diabetic cardiomyopathy. These functional improvements are not derived simply from correcting the systemic milieu; nondiabetic mice with cardiac-specific overexpression of lipoprotein lipase also show improvements in contractile function after REMD 2.59 treatment. These observations suggest that hyperglucagonemia enables lipotoxic conditions, allowing the development of insulin resistance and cardiac dysfunction during disease progression.

Targeting mitochondrial dynamics by regulating Mfn2 for therapeutic intervention in diabetic cardiomyopathy

Increasing evidence has implicated the important role of mitochondrial pathology in diabetic cardiomyopathy (DCM), while the underlying mechanism remains largely unclear. The aim of this study was to investigate the role of mitochondrial dynamics in the pathogenesis of DCM and its underlying mechanisms.

Methods: Obese diabetic (db/db) and lean control (db/+) mice were used in this study. Mitochondrial dynamics were analyzed by transmission electron microscopy in vivo and by confocal microscopy in vitro.

Results: Diabetic hearts from 12-week-old db/db mice showed excessive mitochondrial fission and significant reduced expression of Mfn2, while there was no significant alteration or slight change in the expression of other dynamic-related proteins. Reconstitution of Mfn2 in diabetic hearts inhibited mitochondrial fission and prevented the progression of DCM. In an in-vitro study, cardiomyocytes cultured in high-glucose and high-fat (HG/HF) medium showed excessive mitochondrial fission and decreased Mfn2 expression. Reconstitution of Mfn2 restored mitochondrial membrane potential, suppressed mitochondrial oxidative stress and improved mitochondrial function in HG/HF-treated cardiomyocytes through promoting mitochondrial fusion. In addition, the down-regulation of Mfn2 expression in HG/HF-treated cardiomyocytes was induced by reduced expression of PPARα, which positively regulated the expression of Mfn2 by directly binding to its promoter.

Conclusion: Our study provides the first evidence that imbalanced mitochondrial dynamics induced by down-regulated Mfn2 contributes to the development of DCM. Targeting mitochondrial dynamics by regulating Mfn2 might be a potential therapeutic strategy for DCM.

An Intermediary Role of Adenine Nucleotides on Free Fatty Acids-Induced Hyperglycemia in Obese Mice

Increased plasma free fatty acids (FFA) level plays a central role in the development of type 2 diabetes. Our previous studies have shown that plasma 5'-adenosine monophosphate (5'-AMP) elevates and acts as a potential upstream regulator of hyperglycemia in diabetic db/db mice. The relationship between FFA and plasma adenosine nucleotides in type 2 diabetes remains unclear. Here we found that plasma 5'-AMP level was also increased in diabetic mice induced by a high-fat diet and streptozotocin (HFD-STZ), as observed in diabetic db/db mice. The metabolites of adenosine nucleotides in plasma were increased in obese mice compared to lean mice. An acute oil gavage to lean mice increased both FFA and plasma purine metabolites, accompanying with glucose intolerance. 5'-AMP administration resulted in an increase in dose-dependent purine metabolites and different levels of glucose intolerance. FFA induced a release of adenine nucleotides from cultural human umbilical vein endothelial cells (HUVECs) prior to induction of their apoptosis. FFA also reduced red blood cells (RBCs) resistance to reactive oxygen species (ROS), leading to hemolysis, thereby increasing plasma nucleotides. Our results suggest that plasma adenine nucleotides play an intermediary role in FFA-induced glucose intolerance and hyperglycemia in obese mice.

Of mice and men: models and mechanisms of diabetic cardiomyopathy

Diabetes mellitus increases the risk of heart failure independent of co-existing hypertension and coronary artery disease. Although several molecular mechanisms for the development of diabetic cardiomyopathy have been identified, they are incompletely understood. The pathomechanisms are multifactorial and as a consequence, no causative treatment exists at this time to modulate or reverse the molecular changes contributing to accelerated cardiac dysfunction in diabetic patients. Numerous animal models have been generated, which serve as powerful tools to study the impact of type 1 and type 2 diabetes on the heart. Despite specific limitations of the models generated, they mimic various perturbations observed in the diabetic myocardium and continue to provide important mechanistic insight into the pathogenesis underlying diabetic cardiomyopathy. This article reviews recent studies in both diabetic patients and in these animal models, and discusses novel hypotheses to delineate the increased incidence of heart failure in diabetic patients.

Notoginsenoside R1 Protects Against Diabetic Cardiomyopathy Through Activating Estrogen Receptor α and Its Downstream Signaling

Diabetic cardiomyopathy (DCM) leads to heart failure and death in diabetic patients, no effective treatment is available. Notoginsenoside R1 (NGR1) is a novel saponin that is derived from Panax notoginseng and our previous studies have showed cardioprotective and neuroprotective effects of NGR1. However, its role in protecting against DCM remains unexplored. Herein, we examine potential effects of NGR1 on cardiac function of diabetic db/db mice and H9c2 cardiomyocytes treated by advanced glycation end products (AGEs). In vitro experiments revealed that pretreatment with NGR1 significantly decreased AGEs-induced mitochondria injury, limited an increase in ROS, and reduced apoptosis in H9c2 cells. NGR1 eliminated ROS by promoting estrogen receptor α expression, which subsequently activated Akt and Nrf2-mediated anti-oxidant enzymes. In vivo investigation demonstrated that NGR1 significantly reduced serum lipid levels, insulin resistance, the expression of enzymes related to cardiomyopathy, and the expression of apoptotic proteins. Finally, NGR1 improved cardiac dysfunction and attenuated histological abnormalities, as evidenced by elevating ejection fraction and fractional shortening, and reducing cardiac fibrosis. Mechanistically, NGR1 promoted ERα expression, which led to the activation of Akt-Nrf2 signaling and the inhibition of the TGFβ pathway. Collectively, these results strongly indicate that NGR1 exerts cardioprotective effects against DCM through its inhibition of oxidative stress and apoptosis, and eventually suppresses cardiac fibrosis and hypertrophy, which suggests that NGR1 is a potential therapeutic medicine for the treatment of DCM.

Isolated perfused working hearts provide valuable additional information during phenotypic assessment of the diabetic mouse heart

Although murine models for studying the development of cardiac dysfunction in diabetes mellitus are well established, their reported cardiac phenotypes vary. These reported divergences may, in addition to the severity of different models, also be linked to the methods used for cardiac functional assessment. In the present study, we examined the functional changes using conventional transthoracic echocardiography (in vivo) and isolated heart perfusion techniques (ex vivo), in hearts from two mouse models; one with an overt type 2 diabetes (the db/db mouse) and one with a prediabetic state, where obesity was induced by a high-fat diet (HFD). Analysis of left ventricular function in the isolated working hearts from HFD-fed mice, suggested that these hearts develop diastolic dysfunction with preserved systolic function. Accordingly, in vivo examination demonstrated maintained systolic function, but we did not find parameters of diastolic function to be altered. In db/db mice, ex vivo working hearts showed both diastolic and systolic dysfunction. Although in vivo functional assessment revealed signs of diastolic dysfunction, the hearts did not display reduced systolic function. The contrasting results between ex vivo and in vivo function could be due to systemic changes that may sustain in vivo function, or a lack of sensitivity using conventional transthoracic echocardiography. Thus, this study demonstrates that the isolated perfused working heart preparation provides unique additional information related to the development of cardiomyopathy, which might otherwise go unnoticed when only using conventional echocardiographic assessment.

Secondary Metabolites, Dietary Fiber and Conjugated Fatty Acids as Functional Food Ingredients against Overweight and Obesity

Obesity is a common serious health problem leading to many serious health disorders. This phenomenon is defined as the over-storage of lipids in adipose tissue that occurs when there is an imbalance between the energy intake and energy used. During obesity, many metabolic alterations occur that can damage several organs, such as vascular or skeletal muscle resulting in the dysfunction of these tissues. In this review, we will discuss molecular genetics and causes of obesity, some of the disorders related to human obesity as well as anti-obesity tool. An interesting solution to the obesity problem is natural substances, revealing anti-obesity activity, as well as functional food enriched with aforementioned substances. Functional foods are products exhibiting a potentially positive effect on health beyond basic nutrition. They contain well-known biologically active natural compounds, which promote optimal health and reduce the risk of many diseases, including obesity.

Diabetic db/db mice do not develop heart failure upon pressure overload: a longitudinal in vivo PET, MRI, and MRS study on cardiac metabolic, structural, and functional adaptations

Aims

Heart failure is associated with altered myocardial substrate metabolism and impaired cardiac energetics. Comorbidities like diabetes may influence the metabolic adaptations during heart failure development. We quantified to what extent changes in substrate preference, lipid accumulation, and energy status predict the longitudinal development of hypertrophy and failure in the non-diabetic and the diabetic heart.

Methods and results

Transverse aortic constriction (TAC) was performed in non-diabetic (db/+) and diabetic (db/db) mice to induce pressure overload. Magnetic resonance imaging, 31P magnetic resonance spectroscopy (MRS), 1H MRS, and 18F-fluorodeoxyglucose-positron emission tomography (PET) were applied to measure cardiac function, energy status, lipid content, and glucose uptake, respectively. In vivo measurements were complemented with ex vivo techniques of high-resolution respirometry, proteomics, and western blotting to elucidate the underlying molecular pathways. In non-diabetic mice, TAC induced progressive cardiac hypertrophy and dysfunction, which correlated with increased protein kinase D-1 (PKD1) phosphorylation and increased glucose uptake. These changes in glucose utilization preceded a reduction in cardiac energy status. At baseline, compared with non-diabetic mice, diabetic mice showed normal cardiac function, higher lipid content and mitochondrial capacity for fatty acid oxidation, and lower PKD1 phosphorylation, glucose uptake, and energetics. Interestingly, TAC affected cardiac function only mildly in diabetic mice, which was accompanied by normalization of phosphorylated PKD1, glucose uptake, and cardiac energy status.

Conclusion

The cardiac metabolic adaptations in diabetic mice seem to prevent the heart from failing upon pressure overload, suggesting that restoring the balance between glucose and fatty acid utilization is beneficial for cardiac function.

Modeling heart failure risk in diabetes and kidney disease: limitations and potential applications of transverse aortic constriction in high-fat-fed mice

There is an increased incidence of heart failure in individuals with diabetes mellitus (DM). The coexistence of kidney disease in DM exacerbates the cardiovascular prognosis. Researchers have attempted to combine the critical features of heart failure, using transverse aortic constriction, with DM in mice, but variable findings have been reported. Furthermore, kidney outcomes have not been assessed in this setting; thus its utility as a model of heart failure in DM and kidney disease is unknown. We generated a mouse model of obesity, hyperglycemia, and mild kidney pathology by feeding male C57BL/6J mice a high-fat diet (HFD). Cardiac pressure overload was surgically induced using transverse aortic constriction (TAC). Normal diet (ND) and sham controls were included. Heart failure risk factors were evident at 8-wk post-TAC, including increased left ventricular mass (+49% in ND and +35% in HFD), cardiomyocyte hypertrophy (+40% in ND and +28% in HFD), and interstitial and perivascular fibrosis (Masson's trichrome and picrosirius red positivity). High-fat feeding did not exacerbate the TAC-induced cardiac outcomes. At 11 wk post-TAC in a separate mouse cohort, echocardiography revealed reduced left ventricular size and increased left ventricular wall thickness, the latter being evident in ND mice only. Systolic function was preserved in the TAC mice and was similar between ND and HFD. Thus combined high-fat feeding and TAC in mice did not model the increased incidence of heart failure in DM patients. This model, however, may mimic the better cardiovascular prognosis seen in overweight and obese heart failure patients.

Molecular mechanisms of cardiac pathology in diabetes - Experimental insights

Diabetic cardiomyopathy is a distinct pathology independent of co-morbidities such as coronary artery disease and hypertension. Diminished glucose uptake due to impaired insulin signaling and decreased expression of glucose transporters is associated with a shift towards increased reliance on fatty acid oxidation and reduced cardiac efficiency in diabetic hearts. The cardiac metabolic profile in diabetes is influenced by disturbances in circulating glucose, insulin and fatty acids, and alterations in cardiomyocyte signaling. In this review, we focus on recent preclinical advances in understanding the molecular mechanisms of diabetic cardiomyopathy. Genetic manipulation of cardiomyocyte insulin signaling intermediates has demonstrated that partial cardiac functional rescue can be achieved by upregulation of the insulin signaling pathway in diabetic hearts. Inconsistent findings have been reported relating to the role of cardiac AMPK and β-adrenergic signaling in diabetes, and systemic administration of agents targeting these pathways appear to elicit some cardiac benefit, but whether these effects are related to direct cardiac actions is uncertain. Overload of cardiomyocyte fuel storage is evident in the diabetic heart, with accumulation of glycogen and lipid droplets. Cardiac metabolic dysregulation in diabetes has been linked with oxidative stress and autophagy disturbance, which may lead to cell death induction, fibrotic 'backfill' and cardiac dysfunction. This review examines the weight of evidence relating to the molecular mechanisms of diabetic cardiomyopathy, with a particular focus on metabolic and signaling pathways. Areas of uncertainty in the field are highlighted and important knowledge gaps for further investigation are identified. This article is part of a Special issue entitled Cardiac adaptations to obesity, diabetes and insulin resistance, edited by Professors Jan F.C. Glatz, Jason R.B. Dyck and Christine Des Rosiers.

Exercise of obese mice induces cardioprotection and oxygen sparing in hearts exposed to high-fat load

Exercise training is a potent therapeutic approach in obesity and diabetes that exerts protective effects against the development of diabetic cardiomyopathy and ischemic injury. Acute increases in circulating fatty acids (FAs) during an ischemic insult can challenge the heart, since high FA load is considered to have adverse cardiac effects. In the present study, we tested the hypothesis that exercise-induced cardiac effects in diet-induced obese mice are abrogated by an acute high FA load. Diet-induced obese mice were fed a high-fat diet (HFD) for 20 wk. They were exercised using moderate- and/or high-intensity exercise training (MIT and HIT, respectively) for 10 or 3 wk, and isolated perfused hearts from these mice were exposed to a high FA load. Sedentary HFD mice served as controls. Ventricular function and myocardial O2 consumption were assessed after 10 wk of HIT and MIT, and postischemic functional recovery and infarct size were examined after 3 wk of HIT. In addition to improving aerobic capacity and reducing obesity and insulin resistance, long-term exercise ameliorated the development of diet-induced cardiac dysfunction. This was associated with improved mechanical efficiency because of reduced myocardial oxygen consumption. Although to a lesser extent, 3-wk HIT also increased aerobic capacity and decreased obesity and insulin resistance. HIT also improved postischemic functional recovery and reduced infarct size. Event upon the exposure to a high FA load, short-term exercise induced an oxygen-sparing effect. This study therefore shows that exercise-induced cardioprotective effects are present under hyperlipidemic conditions and highlights the important role of myocardial energetics during ischemic stress.

NEW & NOTEWORTHY The exercise-induced cardioprotective effects in obese hearts are present under hyperlipidemic conditions, comparable to circulating levels of FA occurring with an ischemic insult. Myocardial oxygen sparing is associated with this effect, despite the general notion that high fat can decrease cardiac efficiency. This highlights the role of myocardial energetics during ischemic stress.

Longitudinal evaluation of myocardial glucose metabolism and contractile function in obese type 2 diabetic db/db mice using small-animal dynamic 18F-FDG PET and echocardiography

The aim was to evaluate sequential changes of myocardial glucose utilization and LV systolic function in db/db mice.

Eight db/db and eight wild-type mice underwent plasma substrate analysis and dynamic ¹⁸F-FDG PET at week 8 (W8), W10, W12, W14, and W16. ¹⁸F-FDG uptake constant Ki and the rate of myocardial glucose uptake (MRGlu) were derived via Patlak graphic analysis. Another 8 db/db and 8 wild-type mice received echocardiography at W8, W12, and W16 and LV structure and function were measured.

The db/db mice showed increased weights and glucose levels as they aged. The index of homeostasis model assessment-estimated insulin resistance, insulin, and free fatty acid concentrations were higher in db/db mice compared with wild-type. MRGlu of db/db mice across all time points was markedly higher than that of wild-type. An age-dependent elevation of MRGlu was observed in db/db mice. Ki and MRGlu of db/db mice showed negative correlation with triglyceride levels. When two groups were pooled together, Ki and MRGlu were significantly proportional to glucose levels. No significant difference in LV structure and function was noted between db/db and control mice.

In conclusion, we demonstrated altered myocardial glucose utilization preceding the onset of LV systolic dysfunction in db/db mice.

Metabolic Remodeling in Diabetic Cardiomyopathy

Diabetes is a risk factor for heart failure and cardiovascular mortality with specific changes to myocardial metabolism, energetics, structure, and function. The gradual impairment of insulin production and signalling in diabetes is associated with elevated plasma fatty acids and increased myocardial free fatty acid uptake and activation of the transcription factor PPARα. The increased free fatty acid uptake results in accumulation of toxic metabolites, such as ceramide and diacylglycerol, activation of protein kinase C, and elevation of uncoupling protein-3. Insulin signalling and glucose uptake/oxidation become further impaired, and mitochondrial function and ATP production become compromised. Increased oxidative stress also impairs mitochondrial function and disrupts metabolic pathways. The diabetic heart relies on free fatty acids (FFA) as the major substrate for oxidative phosphorylation and is unable to increase glucose oxidation during ischaemia or hypoxia, thereby increasing myocardial injury, especially in ageing female diabetic animals. Pharmacological activation of PPARγ in adipose tissue may lower plasma FFA and improve recovery from myocardial ischaemic injury in diabetes. Not only is the diabetic heart energetically-impaired, it also has early diastolic dysfunction and concentric remodelling. The contractile function of the diabetic myocardium negatively correlates with epicardial adipose tissue, which secretes proinflammatory cytokines, resulting in interstitial fibrosis. Novel pharmacological strategies targeting oxidative stress seem promising in preventing progression of diabetic cardiomyopathy, although clinical evidence is lacking. Metabolic agents that lower plasma FFA or glucose, including PPARγ agonism and SGLT2 inhibition, may therefore be promising options.

Short-term caloric restriction in db/db mice improves myocardial function and increases high molecular weight (HMW) adiponectin

BACKGROUND

Obesity and metabolic syndrome lead to the development of metabolic heart disease (MHD) that is characterized by left ventricular hypertrophy (LVH), diastolic dysfunction, and increased mitochondrial ROS. Caloric restriction (CR) is a nutritional intervention that protects against obesity, diabetes, and cardiovascular disease. Healthy adipose tissue is cardioprotective via releasing adipokines such as adiponectin. We tested the hypothesis that CR can ameliorate MHD and it is associated with improved adipose tissue function as reflected by increased circulating levels of high molecular weight (HMW) adiponectin and AMP-activated protein kinase (AMPK) in db/db mice.

METHODS

Genetically obese db/db and lean db/+ male mice were fed either ad libitum or subjected to 30% CR for 5 weeks. At the end of the study period, echocardiography was carried out to assess diastolic function. Blood, heart, and epididymal fat pads were harvested for mitochondrial study, ELISA, and Western blot analyses.

RESULTS

CR reversed the development of LVH, prevented diastolic dysfunction, and decreased cardiac mitochondrial H₂O₂ in db/db (vs. ad lib) mice. These beneficial effects on the heart were associated with increased circulating level of HMW adiponectin. Furthermore, CR increased AMPK and eNOS activation in white adipose tissue of db/db mice, but not in the heart.

CONCLUSIONS

These findings indicate that even short-term CR protects the heart from MHD. Whether the beneficial effects of CR on the heart could be related to the improved adipose tissue function warrants future investigation.

Comprehensive metabolic modeling of multiple 13C-isotopomer data sets to study metabolism in perfused working hearts

In many forms of cardiomyopathy, alterations in energy substrate metabolism play a key role in disease pathogenesis. Stable isotope tracing in rodent heart perfusion systems can be used to determine cardiac metabolic fluxes, namely those relative fluxes that contribute to pyruvate, the acetyl-CoA pool, and pyruvate anaplerosis, which are critical to cardiac homeostasis. Methods have previously been developed to interrogate these relative fluxes using isotopomer enrichments of measured metabolites and algebraic equations to determine a predefined metabolic flux model. However, this approach is exquisitely sensitive to measurement error, thus precluding accurate relative flux parameter determination. In this study, we applied a novel mathematical approach to determine relative cardiac metabolic fluxes using ¹³C-metabolic flux analysis (¹³C-MFA) aided by multiple tracer experiments and integrated data analysis. Using ¹³C-MFA, we validated a metabolic network model to explain myocardial energy substrate metabolism. Four different ¹³C-labeled substrates were queried (i.e., glucose, lactate, pyruvate, and oleate) based on a previously published study. We integrated the analysis of the complete set of isotopomer data gathered from these mouse heart perfusion experiments into a single comprehensive network model that delineates substrate contributions to both pyruvate and acetyl-CoA pools at a greater resolution than that offered by traditional methods using algebraic equations. To our knowledge, this is the first rigorous application of ¹³C-MFA to interrogate data from multiple tracer experiments in the perfused heart. We anticipate that this approach can be used widely to study energy substrate metabolism in this and other similar biological systems.

A Novel Function of Hepatic FOG2 in Insulin Sensitivity and Lipid Metabolism Through PPARα

Friend of GATA 2 (FOG2) is a transcriptional cofactor involved mostly in cardiac function. The aim of this study was to investigate the role of hepatic FOG2 in insulin sensitivity and lipid accumulation. FOG2 overexpression by adenovirus-expressing FOG2 (Ad-FOG2) significantly attenuates insulin signaling in hepatocytes in vitro. Opposite effects were observed when FOG2 was knocked down through adenovirus-expressing small hairpin RNA for FOG2 (Ad-shFOG2). Furthermore, FOG2 knockdown by Ad-shFOG2 ameliorated insulin resistance in leptin receptor-mutated (db/db) mice, and FOG2 overexpression by Ad-FOG2 attenuated insulin sensitivity in C57BL/6J wild-type (WT) mice. In addition, Ad-FOG2 reduced, whereas Ad-shFOG2 promoted, hepatic triglyceride (TG) accumulation in WT mice under fed or fasted conditions, which was associated with increased or decreased hepatic peroxisome proliferator-activated receptor α (PPARα) expression, respectively. Moreover, the improved insulin sensitivity and increased hepatic TG accumulation by Ad-shFOG2 were largely reversed by adenovirus-expressing PPARα (Ad-PPARα) in WT mice. Finally, we generated FOG2 liver-specific knockout mice and found that they exhibit enhanced insulin sensitivity and elevated hepatic TG accumulation, which were also reversed by Ad-PPARα. Taken together, the results demonstrate a novel function of hepatic FOG2 in insulin sensitivity and lipid metabolism through PPARα.

Endothelial cell-cardiomyocyte crosstalk in diabetic cardiomyopathy

The incidence of diabetes is increasing globally, with cardiovascular disease accounting for a substantial number of diabetes-related deaths. Although atherosclerotic vascular disease is a primary reason for this cardiovascular dysfunction, heart failure in patients with diabetes might also be an outcome of an intrinsic heart muscle malfunction, labelled diabetic cardiomyopathy. Changes in cardiomyocyte metabolism, which encompasses a shift to exclusive fatty acid utilization, are considered a leading stimulus for this cardiomyopathy. In addition to cardiomyocytes, endothelial cells (ECs) make up a significant proportion of the heart, with the majority of ATP generation in these cells provided by glucose. In this review, we will discuss the metabolic machinery that drives energy metabolism in the cardiomyocyte and EC, its breakdown following diabetes, and the research direction necessary to assist in devising novel therapeutic strategies to prevent or delay diabetic heart disease.

Triacylglycerol turnover in the failing heart

No longer regarded as physiologically inert the endogenous triacylglyceride (TAG) pool within the cardiomyocyte is now recognized to play a dynamic role in metabolic regulation. Beyond static measures of content, the relative rates of interconversion among acyl intermediates are more closely linked to dynamic processes of physiological function in normal and diseased hearts, with the potential for both adaptive and maladaptive contributions. Indeed, multiple inefficiencies in cardiac metabolism have been identified in the decompensated, hypertrophied and failing heart. Among the intracellular responses to physiological, metabolic and pathological stresses, TAG plays a central role in the balance of lipid handling and signaling mechanisms. TAG dynamics are profoundly altered from normal in both diabetic and pathologically stressed hearts. More than just expansion or contraction of the stored lipid pool, the turnover rates of TAG are sensitive to and compete against other enzymatic pathways, anabolic and catabolic, for reactive acyl-CoA units. The rates of TAG synthesis and lipolysis thusly affect multiple components of cardiomyocyte function, including energy metabolism, cell signaling, and enzyme activation, as well as the regulation of gene expression in both normal and diseased states. This review examines the multiple etiologies and metabolic consequences of the failing heart and the central role of lipid storage dynamics in the pathogenic process. This article is part of a Special Issue entitled: Heart Lipid Metabolism edited by G.D. Lopaschuk.

Individuals with Metabolically Healthy Overweight/Obesity Have Higher Fat Utilization than Metabolically Unhealthy Individuals

The mechanisms underlying the change in phenotype from metabolically healthy to metabolically unhealthy obesity are still unclear. The aim of this study is to investigate whether a difference in fasting fat utilization exists between overweight/obese individuals with a favorable cardiovascular risk profile and those with Metabolic Syndrome and Type 2 diabetes. Furthermore, we sought to explore whether there is an association between fasting fat utilization and insulin resistance. In this cross-sectional study, 172 overweight/obese individuals underwent a nutritional assessment. Those with fasting glucose ≥ 126 mg/dL or antidiabetic treatment were considered to be diabetics. If at least three of the NCEP criteria were present, they had Metabolic Syndrome, while those with less criteria were considered to be healthy overweight/obese. An indirect calorimetry was performed to estimate Respiratory Quotient, an index of nutrient utilization. A lower Respiratory Quotient (i.e., higher fat utilization) was found in healthy overweight/obese individuals than in those with Metabolic Syndrome and Type 2 diabetes (0.85 ± 0.05; 0.87 ± 0.06; 0.88 ± 0.05 respectively, p = 0.04). The univariate and multivariable analysis showed a positive association between the Respiratory Quotient and HOMA-IR (slope in statistic (B) = 0.004; β = 0.42; p = 0.005; 95% Confidence interval = 0.001-0.006). In this study, we find, for the first time, that the fasting Respiratory Quotient is significantly lower (fat utilization is higher) in individuals who are metabolically healthy overweight/obese than in those with metabolically unhealthy obesity. In addition, we demonstrated the association between fat utilization and HOMA-IR, an insulin resistance index.

Myocardial metabolism in diabetic cardiomyopathy: potential therapeutic targets

SIGNIFICANCE

Cardiovascular complications in diabetes are particularly serious and represent the primary cause of morbidity and mortality in diabetic patients. Despite early observations of cardiac dysfunction in diabetic humans, cardiomyopathy unique to diabetes has only recently been recognized.

RECENT ADVANCES

Research has focused on understanding the pathogenic mechanisms underlying the initiation and development of diabetic cardiomyopathy. Emerging data highlight the importance of altered mitochondrial function as a major contributor to cardiac dysfunction in diabetes. Mitochondrial dysfunction occurs by several mechanisms involving altered cardiac substrate metabolism, lipotoxicity, impaired cardiac insulin and glucose homeostasis, impaired cellular and mitochondrial calcium handling, oxidative stress, and mitochondrial uncoupling.

CRITICAL ISSUES

Currently, treatment is not specifically tailored for diabetic patients with cardiac dysfunction. Given the multifactorial development and progression of diabetic cardiomyopathy, traditional treatments such as anti-diabetic agents, as well as cellular and mitochondrial fatty acid uptake inhibitors aimed at shifting the balance of cardiac metabolism from utilizing fat to glucose may not adequately target all aspects of this condition. Thus, an alternative treatment such as resveratrol, which targets multiple facets of diabetes, may represent a safe and promising supplement to currently recommended clinical therapy and lifestyle changes.

FUTURE DIRECTIONS

Elucidation of the mechanisms underlying the initiation and progression of diabetic cardiomyopathy is essential for development of effective and targeted treatment strategies. Of particular interest is the investigation of alternative therapies such as resveratrol, which can function as both preventative and mitigating agents in the management of diabetic cardiomyopathy.

Myosin Activator Omecamtiv Mecarbil Increases Myocardial Oxygen Consumption and Impairs Cardiac Efficiency Mediated by Resting Myosin ATPase Activity

BACKGROUND

Omecamtiv mecarbil (OM) is a novel inotropic agent that prolongs systolic ejection time and increases ejection fraction through myosin ATPase activation. We hypothesized that a potentially favorable energetic effect of unloading the left ventricle, and thus reduction of wall stress, could be counteracted by the prolonged contraction time and ATP-consumption.

METHODS AND RESULTS

Postischemic left ventricular dysfunction was created by repetitive left coronary occlusions in 7 pigs (7 healthy pigs also included). In both groups, systolic ejection time and ejection fraction increased after OM (0.75 mg/kg loading for 10 minutes, followed by 0.5 mg/kg/min continuous infusion). Cardiac efficiency was assessed by relating myocardial oxygen consumption to the cardiac work indices, stroke work, and pressure-volume area. To circumvent potential neurohumoral reflexes, cardiac efficiency was additionally assessed in ex vivo mouse hearts and isolated myocardial mitochondria. OM impaired cardiac efficiency; there was a 31% and 23% increase in unloaded myocardial oxygen consumption in healthy and postischemic pigs, respectively. Also, the oxygen cost of the contractile function was increased by 63% and 46% in healthy and postischemic pigs, respectively. The increased unloaded myocardial oxygen consumption was confirmed in OM-treated mouse hearts and explained by an increased basal metabolic rate. Adding the myosin ATPase inhibitor, 2,3-butanedione monoxide abolished all surplus myocardial oxygen consumption in the OM-treated hearts.

CONCLUSIONS

Omecamtiv mecarbil, in a clinically relevant model, led to a significant myocardial oxygen wastage related to both the contractile and noncontractile function. This was mediated by that OM induces a continuous activation in resting myosin ATPase.

Targeting metabolic disturbance in the diabetic heart

Diabetic cardiomyopathy is defined as ventricular dysfunction initiated by alterations in cardiac energy substrates in the absence of coronary artery disease and hypertension. In addition to the demonstrated burden of cardiovascular events associated with diabetes, diabetic cardiomyopathy partly explains why diabetic patients are subject to a greater risk of heart failure and a worse outcome after myocardial ischemia. The raising prevalence and accumulating costs of cardiovascular disease in diabetic patients underscore the deficiencies of tertiary prevention and call for a shift in medical treatment. It is becoming increasingly clearer that the effective prevention and treatment of diabetic cardiomyopathy require measures to regulate the metabolic derangement occurring in the heart rather than merely restoring suitable systemic parameters. Recent research has provided deeper insight into the metabolic etiology of diabetic cardiomyopathy and numerous heart-specific targets that may substitute or reinforce current strategies. From both experimental and translational perspectives, in this review we first discuss the progress made with conventional therapies, and then focus on the need for prospective metabolic targets that may avert myocardial vulnerability and functional decline in next-generation diabetic care.

Speckle tracking echocardiography in the diagnosis of early left ventricular systolic dysfunction in type II diabetic mice

Background

The leptin receptor-deficient db/db mouse is a well-established type II diabetes animal model used to investigate diabetic cardiomyopathy. Previous reports have documented diabetic cardiomyopathy is accompanied by cardiac structural and functional abnormalities. To better elucidate early or subtle changes in cardiac performance in db/db mice, we used speckle tracking echocardiography to assess systolic myocardial strain in vivo with diabetic db/db mice in order to study early changes of left ventricle contractile function in type II diabetes model.

Methods

Male diabetic db/db mice and age-matched control mice from C57BL/6J strain at 8,12 and 16 weeks of age were subjected to echocardiography. At the midpapillary level in the parasternal left ventricular short-axis view, end diastolic and systolic left ventricular diameter, interventricular septal thickness and posterior wall thicknesses, ejection fraction, fractional shortening were determined by M-mode echocardiography. Using speckle-tracking based strain analysis of two-dimensional echocardiographic images acquired from the parasternal short-axis views at the mid-papillary level, systolic global radial and circumferential strain values were analyzed.

Results

There was no significant difference in interventricular septal thickness, posterior wall thicknesses, end diastolic and systolic left ventricular diameter, ejection fraction and fractional shortening between db/db and age-matched control mice at 8,12 or 16 weeks of age (P > 0.05). At 8 and 12 weeks of age, there was no significant difference in left ventricular radial strain and circumferential strain between db/db mice and age-matched controls (P > 0.05). But at 16 weeks of age, the left ventricular radial strain and circumferential strain in db/db mice were lower than in control mice (P < 0.01).

Conclusion

The present study shows that speckle tracking echocardiography can be used to evaluate cardiac functional alterations in mouse models of cardiovascular disease. Radial and circumferential strain are more sensitive and can be used for detection of early left ventricular contractile dysfunction in db/db type II diabetic mice.

Mitochondrial inefficiencies and anoxic ATP hydrolysis capacities in diabetic rat heart

As ~80% of diabetic patients die from heart failure, an understanding of diabetic cardiomyopathy is crucial. Mitochondria occupy 35-40% of the mammalian cardiomyocyte volume and supply 95% of the heart's ATP, and diabetic heart mitochondria show impaired structure, arrangement, and function. We predict that bioenergetic inefficiencies are present in diabetic heart mitochondria; therefore, we explored mitochondrial proton and electron handling by linking oxygen flux to steady-state ATP synthesis, reactive oxygen species (ROS) production, and mitochondrial membrane potential (ΔΨ) within rat heart tissues. Sprague-Dawley rats were injected with streptozotocin (STZ, 55 mg/kg) to induce type 1 diabetes or an equivalent volume of saline (control, n = 12) and fed standard rat chow for 8 wk. By coupling high-resolution respirometers with purpose-built fluorometers, we followed Magnesium Green (ATP synthesis), Amplex UltraRed (ROS production), and safranin-O (ΔΨ). Relative to control rats, the mass-specific respiration of STZ-diabetic hearts was depressed in oxidative phosphorylation (OXPHOS) states. Steady-state ATP synthesis capacity was almost one-third lower in STZ-diabetic heart, which, relative to oxygen flux, equates to an estimated 12% depression in OXPHOS efficiency. However, with anoxic transition, STZ-diabetic and control heart tissues showed similar ATP hydrolysis capacities through reversal of the F1F0-ATP synthase. STZ-diabetic cardiac mitochondria also produced more net ROS relative to oxygen flux (ROS/O) in OXPHOS. While ΔΨ did not differ between groups, the time to develop ΔΨ with the onset of OXPHOS was protracted in STZ-diabetic mitochondria. ROS/O is higher in lifelike OXPHOS states, and potential delays in the time to develop ΔΨ may delay ATP synthesis with interbeat fluctuations in ADP concentrations. Whereas diabetic cardiac mitochondria produce less ATP in normoxia, they consume as much ATP in anoxic infarct-like states.

Peroxisome proliferator-activated receptor targets for the treatment of metabolic diseases

Metabolic syndrome is estimated to affect more than one in five adults, and its prevalence is growing in the adult and pediatric populations. The most widely recognized metabolic risk factors are atherogenic dyslipidemia, elevated blood pressure, and elevated plasma glucose. Individuals with these characteristics commonly manifest a prothrombotic state and a proinflammatory state as well. Peroxisome proliferator-activated receptors (PPARs) may serve as potential therapeutic targets for treating the metabolic syndrome and its related risk factors. The PPARs are transcriptional factors belonging to the ligand-activated nuclear receptor superfamily. So far, three isoforms of PPARs have been identified, namely, PPAR- α, PPAR-β/δ, and PPAR-γ. Various endogenous and exogenous ligands of PPARs have been identified. PPAR- α and PPAR- γ are mainly involved in regulating lipid metabolism, insulin sensitivity, and glucose homeostasis, and their agonists are used in the treatment of hyperlipidemia and T2DM. Whereas PPAR- β / δ function is to regulate lipid metabolism, glucose homeostasis, anti-inflammation, and fatty acid oxidation and its agonists are used in the treatment of metabolic syndrome and cardiovascular diseases. This review mainly focuses on the biological role of PPARs in gene regulation and metabolic diseases, with particular focus on the therapeutic potential of PPAR modulators in the treatment of thrombosis.

Preventive and prophylactic mechanisms of action of pomegranate bioactive constituents

Pomegranate fruit presents strong anti-inflammatory, antioxidant, antiobesity, and antitumoral properties, thus leading to an increased popularity as a functional food and nutraceutical source since ancient times. It can be divided into three parts: seeds, peel, and juice, all of which seem to have medicinal benefits. Several studies investigate its bioactive components as a means to associate them with a specific beneficial effect and develop future products and therapeutic applications. Many beneficial effects are related to the presence of ellagic acid, ellagitannins (including punicalagins), punicic acid and other fatty acids, flavonoids, anthocyanidins, anthocyanins, estrogenic flavonols, and flavones, which seem to be its most therapeutically beneficial components. However, the synergistic action of the pomegranate constituents appears to be superior when compared to individual constituents. Promising results have been obtained for the treatment of certain diseases including obesity, insulin resistance, intestinal inflammation, and cancer. Although moderate consumption of pomegranate does not result in adverse effects, future studies are needed to assess safety and potential interactions with drugs that may alter the bioavailability of bioactive constituents of pomegranate as well as drugs. The aim of this review is to summarize the health effects and mechanisms of action of pomegranate extracts in chronic inflammatory diseases.

Mitochondrial dysfunction caused by saturated fatty acid loading induces myocardial insulin-resistance in differentiated H9c2 myocytes: a novel ex vivo myocardial insulin-resistance model

Heart failure (HF) is often accompanied with metabolic disorders and insufficient energy production. Some previous studies have suggested an elevated serum free fatty acid (FA) due to chronic adrenergic stimulation induces myocardial insulin-resistance, which further impairs myocardial energy production. Because little is known about the pathogenesis of FA-induced cardiac insulin-resistance, we established an ex vivo cardiac insulin-resistant model and investigated the relationship between insulin-resistance and mitochondrial dysfunction. The ex vivo insulin-resistant myocytes, which was produced by treating differentiated H9c2 myocytes with palmitate (saturated FA; 0.2mM) for 24h, exhibited insulin-signaling deficiency and attenuated 2-deoxy-d-glucose (2-DG) uptake. When myocytes were pretreated with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (TMPyP, a ROS scavenger; 200 μM), the insulin-signaling deficiency by palmitate was restored, whereas the attenuated 2-DG uptake was remained. In contrast to TMPyP, the pretreatment with perhexiline (a mitochondrial FA uptake inhibitor; 2 μM) restored the insulin-signaling deficiency and the attenuated 2-DG uptake by palmitate. Perhexiline restored the depolarized mitochondrial membrane potential (ΔΨm) and the reduced intracellular ATP by palmitate, and thereby improved the impaired GLUT4 recruitment to plasma membrane after insulin, whereas TMPyP failed to do so. These results suggested that the mitochondrial dysfunction by saturated FA loading and consequent intracellular energy shortage induced myocardial insulin-resistance in our ex vivo insulin-resistant model.

Diabetes mellitus and myocardial mitochondrial dysfunction: bench to bedside

In diabetics, the risk for development of heart failure is increased even after adjusting for coronary artery disease and hypertension. Although the cause of this increased heart failure risk is multifactorial, increasing evidence suggests that dysfunction of myocardial mitochondria represents an important pathogenetic factor. To date, no specific therapy exists to treat mitochondrial function in any cardiac disease. This article presents underlying mechanisms of mitochondrial dysfunction in the diabetic heart and discusses potential therapeutic options that may attenuate these mitochondrial derangements.

Obesity: the preventive role of the pomegranate (Punica granatum)

Obesity represents a rapidly growing threat to the health of populations in an increasing number of countries. Diet intervention has been proposed as one of the strategies for weight loss and weight maintenance. Traditionally, the pomegranate, including its roots, tree bark, fruit juice, leaves, and flowers, has been used to treat some conditions such as diarrhea, hemorrhage, acidosis, and microbial infections. Pomegranate extracts have been found to have strong anti-inflammatory, antioxidant, and even antitumor properties in vivo and in vitro. More recently, positive effects on fat reduction have been shown using the pomegranate and its extracts. Many of the beneficial effects are related to the presence of anthocyanins, tannins, and very high levels of antioxidants, including polyphenols and flavonoids. Many studies have explored the effects of the pomegranate in obesity, and various mechanisms have been proposed as to how these different extracts help in fat reduction. This article provides an overview of the work done addressing the potential benefits of the pomegranate on obesity and assesses the efficacy of intervention by means of the pomegranate and its extracts. Human studies in this field are still limited and need more attention that would help in understanding the preventive and protective roles pomegranate extracts have on obesity.

The plasma 5'-AMP acts as a potential upstream regulator of hyperglycemia in type 2 diabetic mice

Increased plasma free fatty acid (FFA) level is a hallmark of type 2 diabetes. However, the underlying molecular basis for FFA-caused hyperglycemia remains unclear. Here we identified plasma 5'-adenosine monophosphate (pAMP) markedly elevated in the plasma of type 2 diabetic mice. High levels of FFAs induced damage in vein endothelial cells and contributed to an increase in pAMP. Administration of synthetic 5'-AMP caused hyperglycemia and impaired insulin action in lean wild-type mice. 5'-AMP elevated blood glucose in mice deficient in adenosine receptors with equal efficiency as wild-type mice. The function of pAMP was initiated by the elevation of cellular adenosine levels, directly stimulating G-6-Pase enzyme activity, attenuating insulin-dependent GLUT4 translocation in skeletal muscle, and displaying a rapid and steep increase in blood glucose and a decrease in hepatic glycogen level. It was followed by an increase in the gene expression of hepatic Foxo1 and its targeting gene Pepck and G6Pase, which was similar to diabetic phenotype in db/db mice. Our results suggest that pAMP is a potential upstream regulator of hyperglycemia in type 2 diabetes.

High fat diet induced diabetic cardiomyopathy

In response to a chronic high plasma concentration of long-chain fatty acids (FAs), the heart is forced to increase the uptake of FA at the cost of glucose. This switch in metabolic substrate uptake is accompanied by an increased presence of the FA transporter CD36 at the cardiac plasma membrane and over time results in the development of cardiac insulin resistance and ultimately diabetic cardiomyopathy. FA can interact with peroxisome proliferator-activated receptors (PPARs), which induce upregulation of the expression of enzymes necessary for their disposal through mitochondrial β-oxidation, but also stimulate FA uptake. This then leads to a further increase in FA concentration in the cytoplasm of cardiomyocytes. These metabolic changes are supposed to play an important role in the development of cardiomyopathy. Although the onset of this pathology is an increased FA utilization by the heart, the subsequent lipid overload results in an increased production of reactive oxygen species (ROS) and accumulation of lipid intermediates such as diacylglycerols (DAG) and ceramide. These compounds have a profound impact on signaling pathways, in particular insulin signaling. Over time the metabolic changes will introduce structural changes that affect cardiac contractile characteristics. The present mini-review will focus on the lipid-induced changes that link metabolic perturbation, characteristic for type 2 diabetes, with cardiac remodeling and dysfunction.

Role of Peroxisome Proliferator-Activated Receptor α in Diabetic Nephropathy

With a developing worldwide epidemic of diabetes mellitus, the renal complications associated with diabetes have become a serious health concern. Primary therapy for treating diabetic nephropathy is a multifactorial process. Peroxisome proliferator-activated receptor alpha (PPARα) agonists have been used primarily in clinical practice for the treatment of dyslipidemia and insulin resistance. Given that PPARα expression and regulation of metabolic pathways are involved in oxidative stress, inflammation, blood pressure regulation, and the renin-angiotensin aldosterone system, PPARα likely influences the development and pathogenesis of diabetic nephropathy via indirect effects on glucose and lipid homeostasis and also by direct action on the kidneys. These findings suggest that PPARα may become an important therapeutic target for treating diabetic renal complications.

The PPARalpha-PGC-1alpha Axis Controls Cardiac Energy Metabolism in Healthy and Diseased Myocardium

The mammalian myocardium is an omnivorous organ that relies on multiple substrates in order to fulfill its tremendous energy demands. Cardiac energy metabolism preference is regulated at several critical points, including at the level of gene transcription. Emerging evidence indicates that the nuclear receptor PPARα and its cardiac-enriched coactivator protein, PGC-1α, play important roles in the transcriptional control of myocardial energy metabolism. The PPARα-PGC-1α complex controls the expression of genes encoding enzymes involved in cardiac fatty acid and glucose metabolism as well as mitochondrial biogenesis. Also, evidence has emerged that the activity of the PPARα-PGC-1α complex is perturbed in several pathophysiologic conditions and that altered activity of this pathway may play a role in cardiomyopathic remodeling. In this review, we detail the current understanding of the effects of the PPARα-PGC-1α axis in regulating mitochondrial energy metabolism and cardiac function in response to physiologic and pathophysiologic stimuli.

Intracerebroventricular leptin administration differentially alters cardiac energy metabolism in mice fed a low-fat and high-fat diet

Leptin directly acts on peripheral tissues and alters energy metabolism in obese mice. It also has acute beneficial effects on these tissues via its hypothalamic action. However, it is not clear what effect chronic intracerebroventrical (ICV) leptin administration has on cardiac energy metabolism. We examined the effects of chronic ICV leptin on glucose and fatty acid metabolism in isolated working hearts from high-fat-fed and low-fat-fed mice. Mice were fed a high-fat (60% calories from fat) or low-fat (10% calories from fat) diet for 8 weeks before ICV leptin (5 [mu]g/d) for 7 days. In low-fat-fed mice, leptin increased glucose oxidation rates in isolated working hearts when compared with control [203 +/- 21 vs. 793 +/- 93 nmol[middle dot](g dry weight)-1[middle dot]min-1]. In high-fat-fed mice leptin inhibited fatty acid oxidation [476 +/- 73 vs. 251 +/- 38 nmol[middle dot](g[middle dot]dry[middle dot]wt)-1[middle dot]min-1]. The increase in glucose oxidation in low-fat-fed mice was accompanied by increased pyruvate dehydrogenase activity. In high-fat-fed mice, leptin increased cardiac malonyl coenzyme A levels, secondary to a decrease in malonyl coenzyme A decarboxylase expression. These results suggest that ICV leptin alters cardiac energy metabolism opposite to its peripheral effects and that these effects differ depending on energy substrate supply to the mice.

Cardioprotective effect of the PPAR ligand tetradecylthioacetic acid in type 2 diabetic mice

Tetradecylthioacetic acid (TTA) is a novel peroxisome proliferator-activated receptor (PPAR) ligand with marked hypolipidemic and insulin-sensitizing effects in obese models. TTA has recently been shown to attenuate dyslipidemia in patients with type 2 diabetes, corroborating the potential for TTA in antidiabetic therapy. In a recent study on normal mice, we showed that TTA increased myocardial fatty acid (FA) oxidation, which was associated with decreased cardiac efficiency and impaired postischemic functional recovery. The aim of the present study was, therefore, to elucidate the effects of TTA treatment (0.5%, 8 days) on cardiac metabolism and function in a hyperlipidemic type 2 diabetic model. We found that TTA treatment increased myocardial FA oxidation, not only in nondiabetic ( db/+) mice but also in diabetic ( db/db) mice, despite a clear lipid-lowering effect. Although TTA had deleterious effects in hearts from nondiabetic mice (decreased efficiency and impaired mitochondrial respiratory capacity), these effects were not observed in db/db hearts. In db/db hearts, TTA improved ischemic tolerance, an effect that is most likely related to the antioxidant property of TTA. The present study strongly advocates the need for investigation of the cardiac effects of PPAR ligands used in antidiabetic/hypolipidemic therapy, because of their pleiotropic properties.

A high-fat diet impairs cardiac high-energy phosphate metabolism and cognitive function in healthy human subjects

BACKGROUND

High-fat, low-carbohydrate diets are widely used for weight reduction, but they may also have detrimental effects via increased circulating free fatty acid concentrations.

OBJECTIVE

We tested whether raising plasma free fatty acids by using a high-fat, low-carbohydrate diet results in alterations in heart and brain in healthy subjects.

DESIGN

Men (n = 16) aged 22 ± 1 y (mean ± SE) were randomly assigned to 5 d of a high-fat, low-carbohydrate diet containing 75 ± 1% of calorie intake through fat consumption or to an isocaloric standard diet providing 23 ± 1% of calorie intake as fat. In a crossover design, subjects undertook the alternate diet after a 2-wk washout period, with results compared after the diet periods. Cardiac (31)P magnetic resonance (MR) spectroscopy and MR imaging, echocardiography, and computerized cognitive tests were used to assess cardiac phosphocreatine (PCr)/ATP, cardiac function, and cognitive function, respectively.

RESULTS

Compared with the standard diet, subjects who consumed the high-fat, low-carbohydrate diet had 44% higher plasma free fatty acids (P < 0.05), 9% lower cardiac PCr/ATP (P < 0.01), and no change in cardiac function. Cognitive tests showed impaired attention (P < 0.01), speed (P < 0.001), and mood (P < 0.01) after the high-fat, low-carbohydrate diet.

CONCLUSION

Raising plasma free fatty acids decreased myocardial PCr/ATP and reduced cognition, which suggests that a high-fat diet is detrimental to heart and brain in healthy subjects.

Mechanical function, glycolysis, and ultrastructure of perfused working mouse hearts following thoracic aortic constriction

BACKGROUND

Glycolytic flux in the mouse heart during the progression of left ventricular hypertrophy (LVH) and mechanical dysfunction has not been described.

METHODS

The main objectives of this study were to characterize the effects of thoracic aortic banding, of 3- and 6-week duration, on: (1) left ventricular (LV) systolic and diastolic function of perfused working hearts quantified by analysis of pressure-volume loops; (2) glycolytic flux in working hearts expressed as the rate of conversion of (3)H-glucose to (3)H(2)O, and (3) ultrastructure of LV biopsies assessed by quantitative and qualitative analysis of light and electron micrographs.

RESULTS

Results revealed that (1) indexes of systolic function, including LV end-systolic pressure, cardiac output, and rate of LV pressure development and decline, were depressed to similar degrees at 3 and 6 weeks post-banding; (2) diastolic dysfunction, represented by elevated LV end-diastolic pressure and volume, was more severe at 6 than at 3 weeks, consistent with a transition to failure; (3) a progressive decline in glycolytic flux that was roughly half the control rate by 6 weeks post-banding; and (4) structural derangements, manifested by increases in interstitial collagen content and myocyte Z-band disruption, that were more marked at 3 weeks than at 6 weeks.

CONCLUSION

The results are consistent with the view that myocyte damage, fibrosis, and suppressed glycolytic flux represent maladaptive structural and metabolic remodeling that contribute to the development of failure in high pressure load-induced LVH in the mouse.

Targeting fatty acid and carbohydrate oxidation--a novel therapeutic intervention in the ischemic and failing heart

Cardiac ischemia and its consequences including heart failure, which itself has emerged as the leading cause of morbidity and mortality in developed countries are accompanied by complex alterations in myocardial energy substrate metabolism. In contrast to the normal heart, where fatty acid and glucose metabolism are tightly regulated, the dynamic relationship between fatty acid β-oxidation and glucose oxidation is perturbed in ischemic and ischemic-reperfused hearts, as well as in the failing heart. These metabolic alterations negatively impact both cardiac efficiency and function. Specifically there is an increased reliance on glycolysis during ischemia and fatty acid β-oxidation during reperfusion following ischemia as sources of adenosine triphosphate (ATP) production. Depending on the severity of heart failure, the contribution of overall myocardial oxidative metabolism (fatty acid β-oxidation and glucose oxidation) to adenosine triphosphate production can be depressed, while that of glycolysis can be increased. Nonetheless, the balance between fatty acid β-oxidation and glucose oxidation is amenable to pharmacological intervention at multiple levels of each metabolic pathway. This review will focus on the pathways of cardiac fatty acid and glucose metabolism, and the metabolic phenotypes of ischemic and ischemic/reperfused hearts, as well as the metabolic phenotype of the failing heart. Furthermore, as energy substrate metabolism has emerged as a novel therapeutic intervention in these cardiac pathologies, this review will describe the mechanistic bases and rationale for the use of pharmacological agents that modify energy substrate metabolism to improve cardiac function in the ischemic and failing heart. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.

Mitochondrial dysfunction in diabetic cardiomyopathy

Cardiovascular disease is common in patients with diabetes and is a significant contributor to the high mortality rates associated with diabetes. Heart failure is common in diabetic patients, even in the absence of coronary artery disease or hypertension, an entity known as diabetic cardiomyopathy. Evidence indicates that myocardial metabolism is altered in diabetes, which likely contributes to contractile dysfunction and ventricular failure. The mitochondria are the center of metabolism, and recent data suggests that mitochondrial dysfunction may play a critical role in the pathogenesis of diabetic cardiomyopathy. This review summarizes many of the potential mechanisms that lead to mitochondrial dysfunction in the diabetic heart. This article is part of a Special Issue entitled: Mitochondria and Cardioprotection.