High levels of myocardial antioxidant defense in aging nondiabetic normotensive Zucker obese rats

Phenolic Compounds from Cherries and Berries for Chronic Disease Management and Cardiovascular Risk Reduction

Cardiovascular diseases (CVDs) are a leading cause of mortality worldwide. Therefore, there is increasing interest in dietary interventions to reduce risk factors associated with these conditions. Cherries and berries are rich sources of bioactive compounds and have attracted attention for their potential cardiovascular benefits. This review summarises the current research on the effects of cherry and berry consumption on cardiovascular health, including in vivo studies and clinical trials. These red fruits are rich in phenolic compounds, such as anthocyanins and flavonoids, which have multiple bioactive properties. These properties include antioxidant, anti-inflammatory, and vasodilatory effects. Studies suggest that regular consumption of these fruits may reduce inflammation and oxidative stress, leading to lower blood pressure, improved lipid profiles, and enhanced endothelial function. However, interpreting findings and establishing optimal dosages is a challenge due to the variability in fruit composition, processing methods, and study design. Despite these limitations, the evidence highlights the potential of cherries and berries as components of preventive strategies against CVD. Further research is needed to maximise their health benefits and improve clinical practice.

The interplay of inflammation, exosomes and Ca2+ dynamics in diabetic cardiomyopathy

Diabetes mellitus is one of the prime risk factors for cardiovascular complications and is linked with high morbidity and mortality. Diabetic cardiomyopathy (DCM) often manifests as reduced cardiac contractility, myocardial fibrosis, diastolic dysfunction, and chronic heart failure. Inflammation, changes in calcium (Ca²⁺) handling and cardiomyocyte loss are often implicated in the development and progression of DCM. Although the existence of DCM was established nearly four decades ago, the exact mechanisms underlying this disease pathophysiology is constantly evolving. Furthermore, the complex pathophysiology of DCM is linked with exosomes, which has recently shown to facilitate intercellular (cell-to-cell) communication through biomolecules such as micro RNA (miRNA), proteins, enzymes, cell surface receptors, growth factors, cytokines, and lipids. Inflammatory response and Ca²⁺ signaling are interrelated and DCM  has been known to adversely affect many of these signaling molecules either qualitatively and/or quantitatively. In this literature review, we have demonstrated that Ca²⁺ regulators are tightly controlled at different molecular and cellular levels during various biological processes in the heart. Inflammatory mediators, miRNA and exosomes are shown to interact with these regulators, however how these mediators are linked to Ca²⁺ handling during DCM pathogenesis remains elusive. Thus, further investigations are needed to understand the mechanisms to restore cardiac Ca²⁺ homeostasis and function, and to serve as potential therapeutic targets in the treatment of DCM.

Animal models and animal-free innovations for cardiovascular research: current status and routes to be explored. Consensus document of the ESC Working Group on Myocardial Function and the ESC Working Group on Cellular Biology of the Heart

Cardiovascular diseases represent a major cause of morbidity and mortality, necessitating research to improve diagnostics, and to discover and test novel preventive and curative therapies, all of which warrant experimental models that recapitulate human disease. The translation of basic science results to clinical practice is a challenging task, in particular for complex conditions such as cardiovascular diseases, which often result from multiple risk factors and comorbidities. This difficulty might lead some individuals to question the value of animal research, citing the translational 'valley of death', which largely reflects the fact that studies in rodents are difficult to translate to humans. This is also influenced by the fact that new, human-derived in vitro models can recapitulate aspects of disease processes. However, it would be a mistake to think that animal models do not represent a vital step in the translational pathway as they do provide important pathophysiological insights into disease mechanisms particularly on an organ and systemic level. While stem cell-derived human models have the potential to become key in testing toxicity and effectiveness of new drugs, we need to be realistic, and carefully validate all new human-like disease models. In this position paper, we highlight recent advances in trying to reduce the number of animals for cardiovascular research ranging from stem cell-derived models to in situ modelling of heart properties, bioinformatic models based on large datasets, and state-of-the-art animal models, which show clinically relevant characteristics observed in patients with a cardiovascular disease. We aim to provide a guide to help researchers in their experimental design to translate bench findings to clinical routine taking the replacement, reduction, and refinement (3R) as a guiding concept.

Anti-Inflammatory and Antioxidant Properties of Tart Cherry Consumption in the Heart of Obese Rats

Obesity is a risk factor for cardiovascular diseases, frequently related to oxidative stress and inflammation. Dietary antioxidant compounds improve heart health. Here, we estimate the oxidative grade and inflammation in the heart of dietary-induced obese (DIO) rats after exposure to a high-fat diet compared to a standard diet. The effects of tart cherry seed powder and seed powder plus tart cherries juice were explored. Morphological analysis and protein expressions were performed in the heart. The oxidative status was assessed by the measurement of protein oxidation and 4-hydroxynonenal in samples. Immunochemical and Western blot assays were performed to elucidate the involved inflammatory markers as proinflammatory cytokines and cellular adhesion molecules. In the obese rats, cardiomyocyte hypertrophy was accompanied by an increase in oxidative state proteins and lipid peroxidation. However, the intake of tart cherries significantly changed these parameters. An anti-inflammatory effect was raised from tart cherry consumption, as shown by the downregulation of analyzed endothelial cell adhesion molecules and cytokines compared to controls. Tart cherry intake should be recommended as a dietary supplement to prevent or counteract heart injury in obese conditions.

Reciprocal organ interactions during heart failure: a position paper from the ESC Working Group on Myocardial Function

Heart failure-either with reduced or preserved ejection fraction (HFrEF/HFpEF)-is a clinical syndrome of multifactorial and gender-dependent aetiology, indicating the insufficiency of the heart to pump blood adequately to maintain blood flow to meet the body's needs. Typical symptoms commonly include shortness of breath, excessive fatigue with impaired exercise capacity, and peripheral oedema, thereby alluding to the fact that heart failure is a syndrome that affects multiple organ systems. Patients suffering from progressed heart failure have a very limited life expectancy, lower than that of numerous cancer types. In this position paper, we provide an overview regarding interactions between the heart and other organ systems, the clinical evidence, underlying mechanisms, potential available or yet-to-establish animal models to study such interactions and finally discuss potential new drug interventions to be developed in the future. Our working group suggests that more experimental research is required to understand the individual molecular mechanisms underlying heart failure and reinforces the urgency for tailored therapeutic interventions that target not only the heart but also other related affected organ systems to effectively treat heart failure as a clinical syndrome that affects and involves multiple organs.

Therapeutic potential of targeting oxidative stress in diabetic cardiomyopathy

Even in the absence of coronary artery disease and hypertension, diabetes mellitus (DM) may increase the risk for heart failure development. This risk evolves from functional and structural alterations induced by diabetes in the heart, a cardiac entity termed diabetic cardiomyopathy (DbCM). Oxidative stress, defined as the imbalance of reactive oxygen species (ROS) has been increasingly proposed to contribute to the development of DbCM. There are several sources of ROS production including the mitochondria, NAD(P)H oxidase, xanthine oxidase, and uncoupled nitric oxide synthase. Overproduction of ROS in DbCM is thought to be counterbalanced by elevated antioxidant defense enzymes such as catalase and superoxide dismutase. Excess ROS in the cardiomyocyte results in further ROS production, mitochondrial DNA damage, lipid peroxidation, post-translational modifications of proteins and ultimately cell death and cardiac dysfunction. Furthermore, ROS modulates transcription factors responsible for expression of antioxidant enzymes. Lastly, evidence exists that several pharmacological agents may convey cardiovascular benefit by antioxidant mechanisms. As such, increasing our understanding of the pathways that lead to increased ROS production and impaired antioxidant defense may enable the development of therapeutic strategies against the progression of DbCM. Herein, we review the current knowledge about causes and consequences of ROS in DbCM, as well as the therapeutic potential and strategies of targeting oxidative stress in the diabetic heart.

Egg white hydrolysates improve vascular damage in obese Zucker rats by its antioxidant properties

Metabolic Syndrome (MS) is related to increased risk of early death due to cardiovascular complications, among others. Dietary intervention has been suggested as the safest and most cost-effective alternative for treatment of those alterations in patients with MS. The aim of this study was to investigate the effects of different egg white hydrolysates (HEW1 and HEW2) in obese Zucker rats, focus on the development of cardiovascular complications. Blood pressure, heart rate, basal cardiac function and vascular reactivity in aorta and mesenteric resistance arteries were evaluated. Reactive oxygen species production by dihydroethidium-emitted fluorescence, NOX-1 mRNA levels by qRT-PCR, angiotensin-converting enzyme activity by fluorimetry and kidney histopathology were also analysed. Both hydrolysates improve the endothelial dysfunction occurring in resistance arteries. Additionally, HEW2 reduced vascular oxidative stress. PRACTICAL APPLICATIONS: Egg white is a good source of bioactive peptides, some of them with high antioxidant activity. They may be used as functional foods ingredients and could serve as an alternative therapeutic option to decrease some Metabolic Syndrome-related complications. This study suggests that these hydrolysates could be an interesting non-pharmacological tool to control cardiovascular complications related to Metabolic Syndrome.

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.

Murine Models of Heart Failure with Preserved Ejection Fraction: a "Fishing Expedition"

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of HF in the presence of a normal left ventricular (LV) ejection fraction (EF). Despite accounting for up to 50% of all clinical presentations of HF, the mechanisms implicated in HFpEF are poorly understood, thus precluding effective therapy. The pathophysiological heterogeneity in the HFpEF phenotype also contributes to this disease and likely to the absence of evidence-based therapies. Limited access to human samples and imperfect animal models that completely recapitulate the human HFpEF phenotype have impeded our understanding of the mechanistic underpinnings that exist in this disease. Aging and comorbidities such as atrial fibrillation, hypertension, diabetes and obesity, pulmonary hypertension and renal dysfunction are highly associated with HFpEF. Yet, the relationship and contribution between them remains ill-defined. This review discusses some of the distinctive clinical features of HFpEF in association with these comorbidities and highlights the advantages and disadvantage of commonly used murine models, used to study the HFpEF phenotype.

Extrapancreatic effects of incretin hormones: evidence for weight-independent changes in morphological aspects and oxidative status in insulin-sensitive organs of the obese nondiabetic Zucker rat (ZFR)

Incretin‐based therapies are widely used to treat type 2 diabetes. Although hypoglycemic actions of incretins are mostly due to their insulinotropic/glucagonostatic effects, they may also influence extrapancreatic metabolism. We administered exendin‐4 (Ex‐4), a long‐acting glucagon‐like peptide receptor agonist, at low dose (0.1 nmol/kg/day) for a short period (10 days), in obese nondiabetic fa/fa Zucker rats (ZFRs). Ex‐4‐treated ZFRs were compared to vehicle (saline)‐treated ZFRs and vehicle‐ and Ex‐4‐treated lean rats (LRs). Blood glucose levels were measured at days 0, 9, and 10. Ingested food and animal weight were recorded daily. On the day of sacrifice (d10), blood was sampled along with liver, epididymal, subcutaneous, brown adipose, and skeletal muscle tissues from animals fasted for 24 h. Plasma insulin and blood glucose levels, food intake, and body and epididymal fat weight were unchanged, but gross morphological changes were observed in insulin‐sensitive tissues. The average size of hepatocytes was significantly lower in Ex‐4‐treated ZFRs, associated with decreased number and size of lipid droplets and 4‐hydroxy‐2‐nonenal (HNE) staining, a marker of oxidative stress (OS). Myocytes, which were smaller in ZFRs than in LRs, were significantly enlarged and depleted of lipid droplets in Ex‐4‐treated ZFRs. Weak HNE staining was increased by Ex‐4. A similar observation was made in brown adipose tissue, whereas the elevated HNE staining observed in epididymal adipocytes of ZFRs, suggestive of strong OS, was decreased by Ex‐4. These results suggest that incretins by acting on OS in insulin‐sensitive tissues may contribute to weight‐independent improvement in insulin sensitivity.

Animal models of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) constitutes a clinical syndrome in which the diagnostic criteria of heart failure are not accompanied by gross disturbances of systolic function, as assessed by ejection fraction. In turn, under most circumstances, diastolic function is impaired. Although it now represents over 50 % of all patients with heart failure, the mechanisms of HFpEF remain understood, precluding effective therapy. Understanding the pathophysiology of HFpEF has been restricted by both limited access to human myocardial biopsies and by the lack of animal models that fully mimic human pathology. Animal models are valuable research tools to clarify subcellular and molecular mechanisms under conditions where the comorbidities and other confounding factors can be precisely controlled. Although most of the heart failure animal models currently available represent heart failure with reduced ejection fraction, several HFpEF animal models have been proposed. However, few of these fulfil all the features present in human disease. In this review we will provide an overview of the currently available models to study HFpEF from rodents to large animals as well as present advantages and disadvantages of these models.

Hydrogen peroxide activates store-operated Ca(2+) entry in coronary arteries

BACKGROUND AND PURPOSE

Abnormal Ca(2+) metabolism has been involved in the pathogenesis of vascular dysfunction associated with oxidative stress. Here, we have investigated the actions of H2 O2 on store-operated Ca(2+) (SOC) entry in coronary arteries and assessed whether it is impaired in arteries from a rat model of metabolic syndrome.

EXPERIMENTAL APPROACH

Simultaneous measurements of intracellular Ca(2+) concentration and contractile responses were made in coronary arteries from Wistar and obese Zucker rats, mounted in microvascular myographs, and the effects of H2 O2 were assessed.

KEY RESULTS

H2 O2 raised intracellular Ca(2+) concentrations, accompanied by simultaneous vasoconstriction that was markedly reduced in a Ca(2+) -free medium. Upon Ca(2+) re-addition, a nifedipine-resistant sustained Ca(2+) entry, not coupled to contraction, was obtained in endothelium-denuded coronary arteries. The effect of H2 O2 on this voltage-independent Ca(2+) influx was concentration-dependent, and high micromolar H2 O2 concentrations were inhibitory and reduced SOC entry evoked by inhibition of the sarcoplasmic reticulum ATPase (SERCA). H2 O2 -induced increases in Fura signals were mimicked by Ba(2+) and reduced by heparin, Gd(3+) ions and by Pyr6, a selective inhibitor of the Orai1-mediated Ca(2+) entry,. In coronary arteries from obese Zucker rats, intracellular Ca(2+) mobilization and SOC entry activated by acute exposure to H2 O2 were augmented and associated with local oxidative stress.

CONCLUSION AND IMPLICATIONS

H2 O2 exerted dual concentration-dependent stimulatory/inhibitory effects on store-operated, IP3 receptor-mediated and Orai1-mediated Ca(2+) entry, not coupled to vasoconstriction in coronary vascular smooth muscle. SOC entry activated by H2 O2 was enhanced and associated with vascular oxidative stress in coronary arteries in metabolic syndrome.

Updating experimental models of diabetic cardiomyopathy

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

Murine models of diastolic dysfunction and heart failure with preserved ejection fraction

Left ventricular diastolic dysfunction leads to heart failure with preserved ejection fraction, an increasingly prevalent condition largely driven by modern day lifestyle risk factors. As heart failure with preserved ejection fraction accounts for almost one-half of all patients with heart failure, appropriate nonhuman animal models are required to improve our understanding of the pathophysiology of this syndrome and to provide a platform for preclinical investigation of potential therapies. Hypertension, obesity, and diabetes are major risk factors for diastolic dysfunction and heart failure with preserved ejection fraction. This review focuses on murine models reflecting this disease continuum driven by the aforementioned common risk factors. We describe various models of diastolic dysfunction and highlight models of heart failure with preserved ejection fraction reported in the literature. Strengths and weaknesses of the different models are discussed to provide an aid to translational scientists when selecting an appropriate model. We also bring attention to the fact that heart failure with preserved ejection fraction is difficult to diagnose in animal models and that, therefore, there is a paucity of well described animal models of this increasingly important condition.

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.

Preserved insulin vasorelaxation and up-regulation of the Akt/eNOS pathway in coronary arteries from insulin resistant obese Zucker rats

Obesity is associated with insulin resistance in the peripheral vasculature and is an important risk factor for coronary artery disease. The current study assessed whether the vascular effects and the signaling pathways of insulin are impaired in coronary arteries from a rat model of genetic obesity. Intramyocardial arteries from obese Zucker rats (OZR) and lean Zucker rats (LZR) were mounted in microvascular myographs to assess insulin vasoactive effects and the proteins of the insulin pathway were determined by Western blotting. The endothelium-dependent and nitric oxide (NO)-mediated vasorelaxant effect of insulin was similar in arteries from LZR and OZR and blunted by inhibition of phosphatidylinositol 3-kinase (PI3K) and endothelial NO synthase (eNOS), but unaltered by either mitogen activated protein kinase (MAPK) or endothelin (ET) receptor blockade. Basal levels of phospho-eNOS Ser(1177) and phospho-Akt Ser(473) were up-regulated in OZR, and insulin increased phosphorylation of eNOS and Akt in both LZR and OZR. Moreover, insulin enhanced Akt expression in LZR. Basal and insulin-stimulated levels of phospho-MAPK p42/p44 were lower in OZR and palmitic acid reduced these levels in LZR. Coronary arteries are protected from vascular IR. The results underscore the fact that preservation of insulin-mediated vasorelaxation along with an up-regulation of the Akt/eNOS pathway and an impairment of the MAPK cascade account for this protection.

Experimental models of renal disease and the cardiovascular system

Cardiovascular disease is a leading cause of death among patients with end stage renal failure. Animal models have played a crucial role in teasing apart the complex pathological processes involved. This review discusses the principles of using animal models, the history of their use in the study of renal hypertension, the controversies arising from experimental models of non-hypertensive uraemic cardiomyopathy and the lessons learned from these models, and highlights important areas of future research in this field, including de novo cardiomyopathy secondary to renal transplantation.

Mitochondria in the diabetic heart

Diabetes mellitus increases the risk of developing cardiovascular diseases such as coronary artery disease and heart failure. Studies have shown that the heart failure risk is increased in diabetic patients even after adjusting for coronary artery disease and hypertension. Although the cause of this increased heart failure risk is multifactorial, increasing evidence suggests that derangements in cardiac energy metabolism play an important role. In particular, abnormalities in cardiomyocyte mitochondrial energetics appear to contribute substantially to the development of cardiac dysfunction in diabetes. This review will summarize these abnormalities in mitochondrial function and discuss potential underlying mechanisms.

Rodent models of diabetic cardiomyopathy

Diabetic cardiomyopathy increases the risk of heart failure in individuals with diabetes, independently of co-existing coronary artery disease and hypertension. The underlying mechanisms for this cardiac complication are incompletely understood. Research on rodent models of type 1 and type 2 diabetes, and the use of genetic engineering techniques in mice, have greatly advanced our understanding of the molecular mechanisms responsible for human diabetic cardiomyopathy. The adaptation of experimental techniques for the investigation of cardiac physiology in mice now allows comprehensive characterization of these models. The focus of the present review will be to discuss selected rodent models that have proven to be useful in studying the underlying mechanisms of human diabetic cardiomyopathy, and to provide an overview of the characteristics of these models for the growing number of investigators who seek to understand the pathology of diabetes-related heart disease.

Oral charcoal adsorbent (AST-120) prevents progression of cardiac damage in chronic kidney disease through suppression of oxidative stress

BACKGROUND

Chronic kidney disease (CKD) is an important risk factor for cardiovascular disease (CVD). Increased oxidative stress plays a role in the pathogenesis of CVD in CKD patients. The oral charcoal adsorbent AST-120 attenuates the progression of CKD possibly by removing uraemic toxins such as indoxyl sulfate (IS), and reduces oxidative stress. We investigated the relationship between oxidative stress and cardiac damage in CKD and its prevention by AST-120.

METHODS

Male Lewis rats were administered adriamycin at 8 weeks of age, and the right kidney was removed at 12 weeks of age. From 14 weeks of age, the rats were treated daily with AST-120 (n = 8) or were untreated (control group, n = 8). At 34 weeks of age, the rats were killed and urinary and blood biochemical tests as well as cardiac histological analyses were performed.

RESULTS

At 14 weeks of age, there were no significant differences in blood pressure, renal function (creatinine clearance: 1.54 +/- 0.28 mL/min versus 1.60 +/- 0.22 mL/min), oxidative stress markers or other biochemical data between the control and AST-120 groups. At 34 weeks, despite similar blood pressure and renal function (creatinine clearance: 0.78 +/- 0.46 mL/min versus 0.75 +/- 0.54 mL/min), serum concentrations of IS and urinary excretion of 8-hydroxydeoxyguanosine (8-OHdG), acrolein and IS were significantly lower in the AST-120 group than in the control group. Heart volume, left ventricular volume and cardiac fibrosis were significantly smaller in the experimental AST-120 group than in the control group. Immunohistological analysis revealed that the numbers of 8-OHdG- and acrolein-positive cardiomyocytes and the degrees of myocardial and perivascular fibrosis were ameliorated by AST-120 administration. The myocardial fibrosis score was significantly associated with the 8-OHdG- (r = 0.848, P < 0.001) and acrolein-positive (r = 0.812, P < 0.001) cell scores. The perivascular fibrosis score was also significantly associated with the 8-OHdG- (r = 0.906, P < 0.0001) and acrolein-positive (r = 0.789, P < 0.001) cell scores.

CONCLUSIONS

Oxidative stress is suggested to play a key role in the development of cardiac hypertrophy and fibrosis in CKD. AST-120 may suppress oxidative stress and reduce cardiac damage in CKD.

Molecular mechanisms for myocardial mitochondrial dysfunction in the metabolic syndrome

The metabolic syndrome represents a cluster of abnormalities, including obesity, insulin resistance, dyslipidaemia and Type 2 diabetes, that increases the risk of developing cardiovascular diseases, such as coronary artery disease and heart failure. The heart failure risk is increased even after adjusting for coronary artery disease and hypertension, and evidence is emerging that changes in cardiac energy metabolism might contribute to the development of contractile dysfunction. Recent findings suggest that myocardial mitochondrial dysfunction may play an important role in the pathogenesis of cardiac contractile dysfunction in obesity, insulin resistance and Type 2 diabetes. This review will discuss potential molecular mechanisms for these mitochondrial abnormalities.

Diabetic cardiomyopathy revisited

Diabetes mellitus increases the risk of heart failure independently of underlying coronary artery disease, and many believe that diabetes leads to cardiomyopathy. The underlying pathogenesis is partially understood. Several factors may contribute to the development of cardiac dysfunction in the absence of coronary artery disease in diabetes mellitus. This review discusses the latest findings in diabetic humans and in animal models and reviews emerging new mechanisms that may be involved in the development and progression of cardiac dysfunction in diabetes.

Adverse effects of reactive oxygen species on vascular reactivity in insulin resistance

Insulin resistance (IR) has adverse effects on the reactivity of arteries and arterioles and promotes arterial hypertension and vascular occlusive diseases. Altered reactivity of resistance vessels occurs at both the endothelium and smooth-muscle levels. One major mechanism of vascular dysfunction with IR involves the augmented generation, availability, and/or actions of reactive oxygen species (ROS). Scavengers of ROS are able immediately to restore normal dilator responsiveness in arteries from IR animals. Other factors, such as increased importance of constrictor agents such as endothelin, also restrict normal dilator responses. The basis of ROS-mediated vascular dysfunction in IR may be secondary to underlying inflammatory processes throughout the arterial wall. Although ROS scavengers may be beneficial in the short term, prolonged treatments involving behavioral approaches, such as changes in diet, weight loss, and regular exercise, and pharmacological approaches, involving the use of insulin-sensitizing agents, inhibitors of the renin-angiotensin system, or administration of statins, appear to offer benefits against the detrimental vascular effects of IR. Nonetheless, the most effective approach appears to involve prevention of IR via adoption of a healthy lifestyle by young people.

Cardiovascular Function in a Rat Model of Diet-Induced Obesity

The obesity-prone/obesity-resistant rat model has been used to study mechanisms responsible for obesity-related abnormalities in renal function and blood pressure, but whether this model exhibits cardiac dysfunction has not been determined. We tested the hypothesis that obesity-prone rats would display cardiovascular abnormalities seen in other diet-induced obese models (ie, hypertension, tachycardia, left ventricular hypertrophy, increased collagen deposition, reduced cardiac contractility, and increased end diastolic pressure). Male Sprague-Dawley rats were fed a control diet or a moderate fat diet containing 32% kcal as fat while hemodynamics were continuously monitored using telemetry. After 12 weeks, obesity-prone rats were significantly heavier and had greater body fat compared with obesity-resistant rats and controls, but daily (20 hours/d) averages and diurnal rhythms of blood pressure and heart rate did not differ among groups. Echocardiographic indices of cardiac structure and function, histological evidence of cardiac collagen, and directly measured heart weights did not differ among groups. Peak left ventricular pressure, end diastolic pressure, +dP/dt, and -dP/dt were also not significantly different among groups. Plasma cholesterol and hepatic cholesterol were significantly higher in obesity-prone rats compared with obesity-resistant rats and controls; hepatic triglycerides were higher in obesity-prone rats compared with controls (P< or =0.05). Leptin was significantly higher in obesity-prone rats compared with controls and across all groups was significantly correlated with body fat (P< or =0.05). These results suggest that 12 weeks of a moderate fat diet in the obesity-prone/obesity-resistant rat model induced lipid and endocrine abnormalities typical of obesity but was not sufficient to cause significant cardiac abnormalities.

Diabetic cardiomyopathy: the search for a unifying hypothesis

Although diabetes is recognized as a potent and prevalent risk factor for ischemic heart disease, less is known as to whether diabetes causes an altered cardiac phenotype independent of coronary atherosclerosis. Left ventricular systolic and diastolic dysfunction, left ventricular hypertrophy, and alterations in the coronary microcirculation have all been observed, although not consistently, in diabetic cardiomyopathy and are not fully explained by the cellular effects of hyperglycemia alone. The recent recognition that diabetes involves more than abnormal glucose homeostasis provides important new opportunities to examine and understand the impact of complex metabolic disturbances on cardiac structure and function.

Fatty acid metabolism is enhanced in type 2 diabetic hearts

The metabolic phenotype of hearts has been investigated using rodent models of type 2 diabetes which exhibit obesity and insulin resistance: db/db and ob/ob mice, and Zucker fatty and ZDF rats. In general, cardiac fatty acid (FA) utilization is enhanced in type 2 diabetic hearts, with increased rates of FA oxidation (db/db, ob/ob and ZDF models) and increased FA esterification into cellular triacylglycerols (db/db hearts). Hearts from db/db and ob/ob mice and ZDF rat hearts all have elevated levels of myocardial triacylglycerols, consistent with enhanced FA utilization. A number of mechanisms may be responsible for enhanced FA utilization in type 2 diabetic hearts: (i) increased FA uptake into cardiac myocytes and into mitochondria; (ii) altered mitochondrial function, with up-regulation of uncoupling proteins; and (iii) stimulation of peroxisome proliferator-activated receptor-alpha. Enhanced cardiac FA utilization in rodent type 2 diabetic models is associated with reduced cardiac contractile function, perhaps as a consequence of lipotoxicity and/or reduced cardiac efficiency. Similar results have been obtained with human type 2 diabetic hearts, suggesting that pharmacological interventions that can reduce cardiac FA utilization may have beneficial effects on contractile function.