Heart failure progression is accelerated following myocardial infarction in type 2 diabetic rats

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Cardiovascular Characteristics of Zucker Fatty Diabetes Mellitus Rats, an Animal Model for Obesity and Type 2 Diabetes

Zucker fatty diabetes mellitus (ZFDM) rats harboring the missense mutation (fa) in a leptin receptor gene have been recently established as a novel animal model of obesity and type 2 diabetes (T2D). Here, we explored changes in cardiovascular dynamics including blood pressure and heart rate (HR) associated with the progression of obesity and T2D, as well as pathological changes in adipose tissue and kidney. There was no significant difference in systolic blood pressure (SBP) in ZFDM-Lepr^fa/fa (Homo) compared with ZFDM-Lepr^fa/+ (Hetero) rats, while HR and plasma adrenaline in Homo were significantly lower than Hetero. The mRNA expression of monocyte chemotactic protein-1 in perirenal white adipose tissue (WAT) from Homo was significantly higher than Hetero. Interscapular brown adipose tissue (BAT) in Homo was degenerated and whitened. The plasma blood urea nitrogen in Homo was significantly higher than Hetero. In summary, we demonstrated for the first time that HR and plasma adrenaline concentration but not SBP in Homo decrease with obesity and T2D. In addition, inflammation occurs in WAT from Homo, while whitening occurs in BAT. Further, renal function is impaired in Homo. In the future, ZFDM rats will be useful for investigating metabolic changes associated with the progression of obesity and T2D.

Bioenergetic functions in subpopulations of heart mitochondria are preserved in a non-obese type 2 diabetes rat model (Goto-Kakizaki)

A distinct bioenergetic impairment of heart mitochondrial subpopulations in diabetic cardiomyopathy is associated with obesity; however, many type 2 diabetic (T2DM) patients with high-risk for cardiovascular disease are not obese. In the absence of obesity, it is unclear whether bioenergetic function in the subpopulations of mitochondria is affected in heart with T2DM. To address this issue, a rat model of non-obese T2DM was used to study heart mitochondrial energy metabolism, measuring bioenergetics and enzyme activities of the electron transport chain (ETC). Oxidative phosphorylation in the presence of substrates for ETC and ETC activities in both populations of heart mitochondria in T2DM rats were unchanged. Despite the preservation of mitochondrial function, aconitase activity in T2DM heart was reduced, suggesting oxidative stress in mitochondria. Our study indicate that metabolic function of heart mitochondria is unchanged in the face of oxidative stress and point to a critical role of obesity in T2DM cardiomyopathy.

Shenfu Formula reduces cardiomyocyte apoptosis in heart failure rats by regulating microRNAs

ETHNOPHARMACOLOGICAL RELEVANCE

Shenfu decoction consists of the water extract from the dried root or rootstalk of Panax ginseng C. A. Mey (Asian ginseng) and the lateral root of Aconitum carmichaeli Debx (Fuzi, Heishunpian in Chinese). Shenfu Formula has been used as a folk Chinese medicine for thousands of years. Recent studies have shown that Shenfu injection can enhance cardiac function and regulate arrhythmia.

AIM OF THE STUDY

Shenfu Formula plays an important role in the treatment of heart failure. However, its microRNA-mediated mechanisms are still not fully understood. Thus, we established a heart failure model in rats to investigate the microRNA mechanism of Shenfu Formula in cardiac function and apoptosis.

MATERIALS AND METHODS

The heart failure animal model was established via left-anterior descending coronary artery ligation in rats. Seven days after surgery, Shenfu Formula was given to the heart failure rats, which were selected by echocardiography with an LVEF< 45%. After Shenfu Formula was given intragastrically for 30 days, blood samples were drawn, the heart was excised after echocardiography, and echocardiographic parameters and apoptosis-related proteins were further examined. Fas/Fas-L and Bcl-2/Bax proteins were analyzed by Western blot, and microRNAs were evaluated using Affymetrix GeneChip miRNA arrays.

RESULTS

Shenfu Formula increased the left ventricular ejection fraction, improved the hemodynamic index of heart failure rats, and decreased serum brain natriuretic peptide (BNP) levels. Shenfu Formula also decreased the positive rate of myocardial cells as detected by the TUNEL method and significantly suppressed caspase 3 expression. Moreover, we found that Shenfu Formula can regulate the initiative factors Fas/Fas-L in the intrinsic pathway and Bcl-2/Bax in the extrinsic apoptosis pathway to suppress apoptosis in heart failure rats. Finally, Shenfu Formula potentially alters the balance of microRNAs involved in activating and inhibiting apoptosis, ultimately suppressing apoptosis; this leads to changes in the gene expression profiles of microRNAs targets.

CONCLUSION

Shenfu Granule can effectively improve cardiac function in heart failure rats, and the anti-apoptosis effects of Shenfu Formula are potential mechanisms for inhibiting heart failure.

Voltage dependence of the Ca2+ transient in endocardial and epicardial myocytes from the left ventricle of Goto-Kakizaki type 2 diabetic rats

Diabetes mellitus is a major global health disorder and, currently, over 450 million people have diabetes with 90% suffering from type 2 diabetes. Left untreated, diabetes may lead to cardiovascular diseases which are a leading cause of death in diabetic patients. Calcium is the trigger and regulator of cardiac muscle contraction and derangement in cellular Ca²⁺ homeostasis, which can result in heart failure and sudden cardiac death. It is of paramount importance to investigate the regional involvement of Ca²⁺ in diabetes-induced cardiomyopathy. Therefore, the aim of this study was to investigate the voltage dependence of the Ca²⁺ transients in endocardial (ENDO) and epicardial (EPI) myocytes from the left ventricle of the Goto-Kakizaki (GK) rats, an experimental model of type 2 diabetes mellitus. Simultaneous measurement of L-type Ca²⁺ currents and Ca²⁺ transients was performed by whole-cell patch clamp techniques. GK rats displayed significantly increased heart weight, heart weight/body weight ratio, and non-fasting and fasting blood glucose compared to controls (CON). Although the voltage dependence of L-type Ca²⁺ current was unaltered, the voltage dependence of the Ca²⁺ transients was reduced to similar extents in EPI-GK and ENDO-GK compared to EPI-CON and ENDO-CON myocytes. TPK L-type Ca²⁺ current and Ca²⁺ transient were unaltered. THALF decay of L-type Ca²⁺ current was unaltered; however, THALF decay of the Ca²⁺ transient was shortened in ENDO and EPI myocytes from GK compared to CON rat hearts. In conclusion, the amplitude of L-type Ca²⁺ current was unaltered; however, the voltage dependence of the Ca²⁺ transient was reduced to similar extents in EPI and ENDO myocytes from GK rats compared to their respective controls, suggesting the possibility of dysfunctional sarcoplasmic reticulum Ca²⁺ transport in the GK diabetic rat hearts.

Calcium Signaling in the Ventricular Myocardium of the Goto-Kakizaki Type 2 Diabetic Rat

The association between diabetes mellitus (DM) and high mortality linked to cardiovascular disease (CVD) is a major concern worldwide. Clinical and preclinical studies have demonstrated a variety of diastolic and systolic dysfunctions in patients with type 2 diabetes mellitus (T2DM) with the severity of abnormalities depending on the patients' age and duration of diabetes. The cellular basis of hemodynamic dysfunction in a type 2 diabetic heart is still not well understood. The aim of this review is to evaluate our current understanding of contractile dysfunction and disturbances of Ca²⁺ transport in the Goto-Kakizaki (GK) diabetic rat heart. The GK rat is a widely used nonobese, nonhypertensive genetic model of T2DM which is characterized by insulin resistance, elevated blood glucose, alterations in blood lipid profile, and cardiac dysfunction.

Obesity and Cardiometabolic Defects in Heart Failure Pathology

Obesity is a major global epidemic that sets the stage for diverse multiple pathologies, including cardiovascular disease. The obesity-related low-grade chronic inflamed milieu is more pronounced in aging and responsive to cardiac dysfunction in heart failure pathology. Metabolic dysregulation of obesity integrates with immune reservoir in spleen and kidney network. Therefore, an integrative systems biology approach is necessary to delay progressive cardiac alternations. The purpose of this comprehensive review is to largely discuss the impact of obesity on the cardiovascular pathobiology in the context of problems and challenges, with major emphasis on the diversified models, and to study cardiac remodeling in obesity. The information in this article is immensely helpful in teaching advanced undergraduate, graduate, and medical students about the advancement and impact of obesity on cardiovascular health. © 2017 American Physiological Society. Compr Physiol 7:1463-1477, 2017.

Transcriptomic alterations in the heart of non-obese type 2 diabetic Goto-Kakizaki rats

Background

There is a spectacular rise in the global prevalence of type 2 diabetes mellitus (T2DM) due to the worldwide obesity epidemic. However, a significant proportion of T2DM patients are non-obese and they also have an increased risk of cardiovascular diseases. As the Goto-Kakizaki (GK) rat is a well-known model of non-obese T2DM, the goal of this study was to investigate the effect of non-obese T2DM on cardiac alterations of the transcriptome in GK rats.

Methods

Fasting blood glucose, serum insulin and cholesterol levels were measured at 7, 11, and 15 weeks of age in male GK and control rats. Oral glucose tolerance test and pancreatic insulin level measurements were performed at 11 weeks of age. At week 15, total RNA was isolated from the myocardium and assayed by rat oligonucleotide microarray for 41,012 genes, and then expression of selected genes was confirmed by qRT-PCR. Gene ontology and protein–protein network analyses were performed to demonstrate potentially characteristic gene alterations and key genes in non-obese T2DM.

Results

Fasting blood glucose, serum insulin and cholesterol levels were significantly increased, glucose tolerance and insulin sensitivity were significantly impaired in GK rats as compared to controls. In hearts of GK rats, 204 genes showed significant up-regulation and 303 genes showed down-regulation as compared to controls according to microarray analysis. Genes with significantly altered expression in the heart due to non-obese T2DM includes functional clusters of metabolism (e.g. Cyp2e1, Akr1b10), signal transduction (e.g. Dpp4, Stat3), receptors and ion channels (e.g. Sln, Chrng), membrane and structural proteins (e.g. Tnni1, Mylk2, Col8a1, Adam33), cell growth and differentiation (e.g. Gpc3, Jund), immune response (e.g. C3, C4a), and others (e.g. Lrp8, Msln, Klkc1, Epn3). Gene ontology analysis revealed several significantly enriched functional inter-relationships between genes influenced by non-obese T2DM. Protein–protein interaction analysis demonstrated that Stat is a potential key gene influenced by non-obese T2DM.

Conclusions

Non-obese T2DM alters cardiac gene expression profile. The altered genes may be involved in the development of cardiac pathologies and could be potential therapeutic targets in non-obese T2DM.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0424-3) contains supplementary material, which is available to authorized users.

Sexual dimorphism in myocardial acylcarnitine and triglyceride metabolism

Background

Cardiovascular disease is the leading cause of death among diabetic patients. Importantly, recent data highlight the apparent sexual dimorphism in the pathogenesis of cardiovascular disease in diabetics with respect to both frequency- and age-related risk factors. The disposition to cardiovascular disease among diabetic patients has been attributed, at least in part, to excess lipid supply to the heart culminating in lipotoxicity of the heart and downstream derangements. A confounding factor in obese animal models of diabetes is that increased peripheral lipid availability to the heart can induce cardio-metabolic remodeling independent of the underlying pathophysiology of diabetes, thus masking the diabetic phenotype. To that end, we hypothesized that the use of non-obese diabetic (NOD) animal models will reveal metabolic signatures of diabetes in a sex-specific manner.

Methods

To test this hypothesis, male and female NOD Goto-Kakizaki (GK) rats were used to assess the expression profile of 84 genes involved in lipid metabolism. In parallel, targeted lipidomics analysis was performed to characterize sex differences in homeostasis of non-esterified fatty acids (NEFA), acylcarnitines (AC), and triglycerides (TG).

Results

Our analysis revealed significant sex differences in the expression of a broad range of genes involved in transport, activation, and utilization of lipids. Furthermore, NOD male rats exhibited enhanced oxidative metabolism and accumulation of TG, whereas female NOD rats exhibited reduced TG content coupled with accumulation of AC species. Multi-dimensional statistical analysis identified saturated AC16:0, AC18:0, and AC20:0 as dominant metabolites in mediating sex differences in AC metabolism. Confocal microscopy of rat cardiomyocytes exposed to AC14:0, AC16:0, and AC18:0 confirmed induction of ROS with AC18:0 being more potent followed by AC14:0.

Conclusion

Overall, we demonstrate sex differences in myocardial AC and TG metabolism with implications for therapy and diagnosis of diabetic cardiovascular disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-016-0077-7) contains supplementary material, which is available to authorized users.

Contractile apparatus dysfunction early in the pathophysiology of diabetic cardiomyopathy

Diabetes mellitus significantly increases the risk of cardiovascular disease and heart failure in patients. Independent of hypertension and coronary artery disease, diabetes is associated with a specific cardiomyopathy, known as diabetic cardiomyopathy (DCM). Four decades of research in experimental animal models and advances in clinical imaging techniques suggest that DCM is a progressive disease, beginning early after the onset of type 1 and type 2 diabetes, ahead of left ventricular remodeling and overt diastolic dysfunction. Although the molecular pathogenesis of early DCM still remains largely unclear, activation of protein kinase C appears to be central in driving the oxidative stress dependent and independent pathways in the development of contractile dysfunction. Multiple subcellular alterations to the cardiomyocyte are now being highlighted as critical events in the early changes to the rate of force development, relaxation and stability under pathophysiological stresses. These changes include perturbed calcium handling, suppressed activity of aerobic energy producing enzymes, altered transcriptional and posttranslational modification of membrane and sarcomeric cytoskeletal proteins, reduced actin-myosin cross-bridge cycling and dynamics, and changed myofilament calcium sensitivity. In this review, we will present and discuss novel aspects of the molecular pathogenesis of early DCM, with a special focus on the sarcomeric contractile apparatus.

C1q-TNF-related protein-9, a novel cardioprotetcive cardiokine, requires proteolytic cleavage to generate a biologically active globular domain isoform

Prevalence and severity of postmyocardial infarction heart failure continually escalate in type 2 diabetes via incompletely understood mechanisms. The discovery of the cardiac secretomes, collectively known as "cardiokines", has significantly enhanced appreciation of the local microenvironment's influence on disease development. Recent studies demonstrated that C1q-TNF-related protein-9 (CTRP9), a newly discovered adiponectin (APN) paralog, is highly expressed in the heart. However, its relationship with APN (concerning diabetic cardiovascular injury in particular) remains unknown. Plasma CTRP9 levels are elevated in APN knockout and reduced in diabetic mice. In contrast to APN, which circulates as full-length multimers, CTRP9 circulates in the plasma primarily in the globular domain isoform (gCTRP9). Recombinant full-length CTRP9 (fCTRP9) was cleaved when incubated with cardiac tissue extracts, generating gCTRP9, a process inhibited by protease inhibitor cocktail. gCTRP9 rapidly activates cardiac survival kinases, including AMPK, Akt, and endothelial NOS. However, fCTRP9-mediated kinase activation is much less potent and significantly delayed. Kinase activation by fCTRP9, but not gCTRP9, is inhibited by protease inhibitor cocktail. These results demonstrate for the first time that the novel cardiokine CTRP9 undergoes proteolytic cleavage to generate gCTRP9, the dominant circulatory and actively cardioprotective isoform. Enhancing cardiac CTRP9 production and/or its proteolytic posttranslational modification are of therapeutic potential, attenuating diabetic cardiac injury.

Genomic and metabolic disposition of non-obese type 2 diabetic rats to increased myocardial fatty acid metabolism

Lipotoxicity of the heart has been implicated as a leading cause of morbidity in Type 2 Diabetes Mellitus (T2DM). While numerous reports have demonstrated increased myocardial fatty acid (FA) utilization in obese T2DM animal models, this diabetic phenotype has yet to be demonstrated in non-obese animal models of T2DM. Therefore, the present study investigates functional, metabolic, and genomic differences in myocardial FA metabolism in non-obese type 2 diabetic rats. The study utilized Goto-Kakizaki (GK) rats at the age of 24 weeks. Each rat was imaged with small animal positron emission tomography (PET) to estimate myocardial blood flow (MBF) and myocardial FA metabolism. Echocardiograms (ECHOs) were performed to assess cardiac function. Levels of triglycerides (TG) and non-esterified fatty acids (NEFA) were measured in both plasma and cardiac tissues. Finally, expression profiles for 168 genes that have been implicated in diabetes and FA metabolism were measured using quantitative PCR (qPCR) arrays. GK rats exhibited increased NEFA and TG in both plasma and cardiac tissue. Quantitative PET imaging suggests that GK rats have increased FA metabolism. ECHO data indicates that GK rats have a significant increase in left ventricle mass index (LVMI) and decrease in peak early diastolic mitral annular velocity (E’) compared to Wistar rats, suggesting structural remodeling and impaired diastolic function. Of the 84 genes in each the diabetes and FA metabolism arrays, 17 genes in the diabetes array and 41 genes in the FA metabolism array were significantly up-regulated in GK rats. Our data suggest that GK rats’ exhibit increased genomic disposition to FA and TG metabolism independent of obesity.

Sex, sex steroids, and diabetic cardiomyopathy: making the case for experimental focus

More than three decades ago, the Framingham study revealed that cardiovascular risk is elevated for all diabetics and that this jeopardy is substantially accentuated for women in particular. Numerous studies have subsequently documented worsened cardiac outcomes for women. Given that estrogen and insulin exert major regulatory effects through common intracellular signaling pathways prominent in maintenance of cardiomyocyte function, a sex-hormone:diabetic-disease interaction is plausible. Underlying aspects of female cardiovascular pathophysiology that exaggerate cardiovascular diabetic risk may be identified, including increased vulnerability to coronary microvascular disease, age-dependent impairment of insulin-sensitivity, and differential susceptibility to hyperglycemia. Since Framingham, considerable progress has been made in the development of experimental models of diabetic disease states, including a diversity of genetic rodent models. Ample evidence indicates that animal models of both type 1 and 2 diabetes variably recapitulate aspects of diabetic cardiomyopathy including diastolic and systolic dysfunction, and cardiac structural pathology including fibrosis, loss of compliance, and in some instances ventricular hypertrophy. Perplexingly, little of this work has explored the relevance and mechanisms of sexual dimorphism in diabetic cardiomyopathy. Only a small number of experimental studies have addressed this question, yet the prospects for gaining important mechanistic insights from further experimental enquiry are considerable. The case for experimental interrogation of sex differences, and of sex steroid influences in the aetiology of diabetic cardiomyopathy, is particularly compelling-providing incentive for future investigation with ultimate therapeutic potential.

Role of ER stress in ventricular contractile dysfunction in type 2 diabetes

Background

Diabetes mellitus (DM) is associated with an increased risk of ischemic heart disease and of adverse outcomes following myocardial infarction (MI). Here we assessed the role of endoplasmic reticulum (ER) stress in ventricular dysfunction and outcomes after MI in type 2 DM (T2DM).

Methodology and Principal Findings

In hearts of OLETF, a rat model of T2DM, at 25∼30 weeks of age, GRP78 and GRP94, markers of ER stress, were increased and sarcoplasmic reticulum calcium ATPase (SERCA)2a protein was reduced by 35% compared with those in LETO, a non-diabetic control. SERCA2a mRNA levels were similar, but SERCA2a protein was more ubiquitinated in OLETF than in LETO. Left ventricular (LV) end-diastolic elastance (Eed) was higher in OLETF than in LETO (53.9±5.2 vs. 20.2±5.6 mmHg/µl), whereas LV end-systolic elastance and positive inotropic responses to β-adrenergic stimulation were similar in OLETF and LETO. 4-Phenylbutyric acid (4-PBA), an ER stress modulator, suppressed both GRP up-regulation and SERCA2a ubiquitination and normalized SERCA2a protein level and Eed in OLETF. Sodium tauroursodeoxycholic acid, a structurally different ER stress modulator, also restored SERCA2a protein level in OLETF. Though LV dysfunction was modest, mortality within 48 h after coronary occlusion was markedly higher in OLETF than in LETO (61.3% vs. 7.7%). Telemetric recording showed that rapid progression of heart failure was responsible for the high mortality rate in OLETF. ER stress modulators failed to reduce the mortality rate after MI in OLETF.

Conclusions

ER stress reduces SERCA2a protein via its augmented ubiquitination and degradation, leading to LV diastolic dysfunction in T2DM. Even at a stage without systolic LV dysfunction, susceptibility to lethal heart failure after infarction is markedly increased, which cannot be explained by ER stress or change in myocardial response to sympathetic nerve activation.

The GK rat: a prototype for the study of non-overweight type 2 diabetes

Type 2 diabetes mellitus (T2D) arises when the endocrine pancreas fails to secrete sufficient insulin to cope with the metabolic demand because of β-cell secretory dysfunction and/or decreased β-cell mass. Defining the nature of the pancreatic islet defects present in T2D has been difficult, in part because human islets are inaccessible for direct study. This review is aimed to illustrate to what extent the Goto Kakizaki rat, one of the best characterized animal models of spontaneous T2D, has proved to be a valuable tool offering sufficient commonalities to study this aspect. A comprehensive compendium of the multiple functional GK abnormalities so far identified is proposed in this perspective, together with their time-course and interactions. A special focus is given toward the pathogenesis of defective β-cell number and function in the GK model. It is proposed that the development of T2D in the GK model results from the complex interaction of multiple events: (1) several susceptibility loci containing genes responsible for some diabetic traits; (2) gestational metabolic impairment inducing an epigenetic programming of the offspring pancreas and the major insulin target tissues; and (3) environmentally induced loss of β-cell differentiation due to chronic exposure to hyperglycemia/hyperlipidemia, inflammation, and oxidative stress.

Role of brainstem thyrotropin-releasing hormone-triggered sympathetic overactivation in cardiovascular mortality in type 2 diabetic Goto-Kakizaki rats

Sympathetic hyperactivity has an important role in cardiovascular mortality in patients with type 2 diabetes (T2D). Thyrotropin-releasing hormone (TRH)-containing fibers innervate autonomic motor and premotor nuclei of the brainstem and spinal cord that regulate cardiovascular functions. We compared cardiovascular responses to application of TRH-analog in the brainstem of Wistar and T2D Goto-Kakizaki (GK) rats. GK rats exhibited basal systolic hypertension (152±2 mm Hg) and had a significantly potentiated, dose-related hypertensive response to intracisternal (i.c.) injection of the TRH-analog RX77368 (10-60 ng). In GK rats only, i.c. RX77368 (30-60 ng) markedly increased heart rate (HR; +88 b.p.m.) and induced acute cardiac mortality (100%), concurrent with extreme hyperglycemia (>26 mmol l(-1)), increased plasma H(2)O(2) and 8-isoprostane, and enhanced heart expression of NADPH oxidase 4 and vascular cell adhesion molecule-1 mRNAs. GK rats also had elevated basal plasma epinephrine, higher adrenal gene expression of tyrosine hydroxylase and dopamine β-hydroxylase (DβH), and greater plasma catecholamine and adrenal DβH responses to i.c. TRH-analog, compared with Wistar rats. In GK rats, hexamethonium blocked i.c. RX77368-induced hypertensive and tachycardic responses, and reduced mortality by 86%, whereas phentolamine abolished the hypertensive response but enhanced tachycardia (+160 b.p.m.), and reduced mortality by 50%. The angiotensin II type 1 receptor antagonist irbesartan prevented i.c. RX77368-induced increases in blood pressure, HR and mortality. In conclusion, sympathetic overactivation triggered by brainstem TRH contributes to the mechanism of cardiovascular morbidity and mortality in T2D, which involves heightened cardiac inflammation and peripheral oxidative stress responses to sympathetic drive, and a mediating role of the renin-angiotensin system.

Single nucleotide polymorphisms of the purinergic 1 receptor are not associated with myocardial infarction in a Latvian population

The purinergic 1 receptor (P2RY1) has been implicated in development of heart disease and in individual pharmacodynamic response to anticoagulant therapies. However, the association of polymorphisms in the P2RY1 gene with myocardial infarction (MI), and its associated conditions, has yet to be reported in the literature. We evaluated seven known SNPs in P2RY1 for association with MI in a Latvian population. Seven independent parameters that are related to MI [body mass index (BMI), type 2 diabetes (T2D), angina pectoris, hypertension, hyperlipidemia, atrial fibrillation and heart failure] were investigated. No significant association with MI was observed for any of the polymorphisms. Those SNPs for which the P value was close to significance were located in coding or promoter regions. Intriguingly, carriers of the minor allele in the P2RY1 gene locus showed a tendency towards higher onset age for MI, suggesting a possible protective effect of these SNPs against MI or their contribution in progression as opposed to onset. Finally, a linkage disequilibrium (LD) plot was generated for these polymorphisms in the Latvian population. The results of this study suggest that the role of P2RY1 in individuals from Latvian population is likely to be principally involved in platelet aggregation and thromboembolic diseases, and not as a significant contributing factor to the global metabolic syndrome.

Stem cells in the diabetic infarcted heart

Diabetes mellitus is one of the leading causes of death, and the majority of these deaths are associated with cardiovascular diseases. Development and progression of myocardial infarction leading to heart failure is much more complex and multifactorial in diabetics compared with non-diabetics. Despite significant advances in pharmacological interventions and surgical techniques, the disease progression leading to diabetic end-stage heart failure remains very high. Recently, cell therapy has gained much attention as an alternative approach to treat various heart diseases. However, transplanted stem cell studies in diabetic animal models are very limited. In this review, we discuss the pathogenesis of the diabetic infarcted heart and the potential of stem cell therapy to repair and regenerate.

Oxidative stress in cardiac and skeletal muscle dysfunction associated with diabetes mellitus

Diabetes mellitus increases the risk of heart failure independently of underlying coronary artery disease. It also causes skeletal muscle dysfunction, which is responsible for reduced exercise capacity commonly seen in heart failure. The underlying pathogenesis is partially understood. Several factors may contribute to the development of cardiac and skeletal muscle dysfunction in heart failure and diabetes mellitus. Based on the findings in animal models, this review discusses the role of oxidative stress that may be involved in the development and progression of cardiac and skeletal dysfunction associated with diabetes.

The chronic effects of neonatal alloxan-induced diabetes mellitus on ventricular myocyte shortening and cytosolic Ca2+

Diabetes mellitus is a serious global health problem, and cardiovascular complications are the major cause of morbidity and mortality in diabetic patients. The chronic effects of neonatal alloxan- (ALX) induced diabetes mellitus on ventricular myocyte contraction and intracellular Ca(2+) transport have been investigated. Ventricular myocyte shortening was measured with a video edge detection system and intracellular Ca(2+) was measured in fura-2 loaded cells by fluorescence photometry. Diabetes was induced in 5-day old male Wistar rats by a single intraperitoneal injection of ALX (200 mg/kg body weight). Experiments were performed 12 months after ALX treatment. Fasting blood glucose was elevated and blood glucose at 60, 120 and 180 min after a glucose challenge (2 g/kg body weight, intraperitoneal) was elevated in diabetic rats compared to age-matched controls. Amplitude of shortening was significantly (P < 0.05) reduced in electrically stimulated myocytes from diabetic hearts (5.70 ± 0.24%) compared to controls (6.48 ± 0.28%). Amplitude of electrically evoked Ca(2+) transients was also significantly (P < 0.05) reduced in myocytes from diabetic hearts (0.11 ± 0.01 fura-2 ratio units) compared to controls (0.15 ± 0.01 fura-2 ratio units). Fractional sarcoplasmic reticulum Ca(2+) release was not significantly (P > 0.05) altered in myocytes from diabetic heart (0.70 ± 0.03 fura-2 ratio units) compared to controls (0.72 ± 0.03 fura-2 ratio units). Amplitude of caffeine-stimulated Ca(2+) transients was significantly (P < 0.05) reduced in myocytes from diabetic hearts (0.43 ± 0.02 fura-2 ratio units) compared to controls (0.51 ± 0.03 fura-2 ratio units). Area under the caffeine-evoked Ca(2+) transient was significantly (P < 0.05) reduced in myocytes from diabetic heart (0.77 ± 0.06 Vsec) compared to controls (1.14 ± 0.12 Vsec). Intracellular Ca(2+) refilling rate during electrical stimulation following application of caffeine was significantly (P < 0.05) slower in myocytes from diabetic heart (0.013 ± 0.001 V/sec) compared to controls (0.031 ± 0.007 V/sec). Depressed shortening may be partly attributed to depressed sarcoplasmic reticulum Ca(2+) transport in myocytes from neonatal ALX-induced diabetic rat heart.

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

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

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.

Sirtuin1-p53, forkhead box O3a, p38 and post-infarct cardiac remodeling in the spontaneously diabetic Goto-Kakizaki rat

Background

Diabetes is associated with changes in myocardial stress-response pathways and is recognized as an independent risk factor for cardiac remodeling. Using spontaneously diabetic Goto Kakizaki rats as a model of type 2 DM we investigated whether post-translational modifications in the Akt - FOXO3a pathway, Sirt1 - p53 pathway and the mitogen activated protein kinase p38 regulator are involved in post-infarct cardiac remodeling

Methods

Experimental myocardial infarction (MI) was induced by left anterior descending coronary artery ligation in spontaneously diabetic Goto-Kakizaki rats and non-diabetic Wistar controls. Cardiac function was studied by echocardiography. Myocardial hypertrophy, cardiomyocyte apoptosis and cardiac fibrosis were determined histologically 12 weeks post MI or Sham operation. Western blotting was used to study Caspase-3, Bax, Sirt1, acetylation of p53 and phosphorylation of p38, Akt and FOXO3a. Electrophoretic mobility shift assay was used to assess FOXO3a activity and its nuclear localization.

Results

Post-infarct heart failure in diabetic GK rats was associated with pronounced cardiomyocyte hypertrophy, increased interstitial fibrosis and sustained cardiomyocyte apoptosis as compared with their non-diabetic Wistar controls. In the GK rat myocardium, Akt- and FOXO3a-phosphorylation was decreased and nuclear localization of FOXO3a was increased concomitantly with increased PTEN protein expression. Furthermore, increased Sirt1 protein expression was associated with decreased p53 acetylation, and phosphorylation of p38 was increased in diabetic rats with MI.

Conclusions

Post-infarct heart failure in diabetic GK rats was associated with more pronounced cardiac hypertrophy, interstitial fibrosis and sustained cardiomyocyte apoptosis as compared to their non-diabetic controls. The present study suggests important roles for Akt-FOXO3a, Sirt1 - p53 and p38 MAPK in the regulation of post-infarct cardiac remodeling in type 2 diabetes.

The accelerated post-infarction progression of cardiac remodelling is associated with genetic changes in an untreated streptozotocin-induced diabetic rat model

AIMS

The mechanism by which diabetes mellitus exacerbates myocardial injury and the incidence of heart failure after acute myocardial infarction (AMI), remains unclear. We studied the severity of cardiac dysfunction and time-dependent gene expression in a hyperglycaemic rat model with AMI.

METHODS AND RESULTS

The diabetic model was produced by injection of streptozotocin in Sprague-Dawley rats. Ten weeks after induction of diabetes, AMI was induced by ligation of the left anterior descending coronary artery. Cardiac function and left ventricular (LV) dimensions were evaluated using two-dimensional echocardiography. Structural changes were assessed by histological examination. Gene expression profile was documented by using affymetrix genechip U230 2.0 array and real time-PCR. During 56 days post-AMI, lower survival rates, worse LV function, more severe fibrosis, and larger LV diameters were identified in diabetic rats compared with non-diabetic rats. A total 1221 genes involved in processes, such as glucose metabolism, fatty acid metabolism, extracellular matrix, and apoptosis, were found to be differentially expressed between diabetic and non-diabetic rats, of these 770 were up-regulated and 451 down-regulated. Up-regulation of the genes was found 1-2 weeks earlier in diabetic rats than in non-diabetic rats.

CONCLUSION

The present data suggest that hyperglycaemia up-regulates remodelling-related genes, which may be responsible for the worse outcomes in diabetics than in non-diabetics after AMI.

Increased myocardial NAD(P)H oxidase-derived superoxide causes the exacerbation of postinfarct heart failure in type 2 diabetes

Type 2 diabetes adversely affects the outcomes in patients with myocardial infarction (MI), which is associated with the development of left ventricular (LV) failure. NAD(P)H oxidase-derived superoxide (O(2)(-)) production is increased in type 2 diabetes. However, its pathophysiological significance in advanced post-MI LV failure associated with type 2 diabetes remains unestablished. We thus hypothesized that an inhibitor of NAD(P)H oxidase activation, apocynin, could attenuate the exacerbated LV failure after MI in high-fat diet (HFD)-induced obese mice with type 2 diabetes. Male C57BL/6J mice were fed on either HFD or normal diet (ND) for 8 wk. At 4 wk of feeding, MI was created in mice by ligating the left coronary artery. HFD-fed MI mice were treated with either 10 mmol/l apocynin or vehicle. HFD + MI had significantly greater LV end-diastolic diameter (LVEDD; 5.7 +/- 0.1 vs. 5.3 +/- 0.2 mm), end-diastolic pressure (12 +/- 2 vs. 8 +/- 1 mmHg), and lung weight/tibial length (10.1 +/- 0.3 vs. 8.7 +/- 0.7 mg/mm) than ND + MI, which was accompanied by an increased interstitial fibrosis of noninfarcted LV. Treatment of HFD + MI with apocynin significantly decreased LVEDD (5.4 +/- 0.1 mm), LV end-diastolic pressure (9.7 +/- 0.8 mmHg), lung weight/tibial length (9.0 +/- 0.3 mg/mm), and concomitantly interstitial fibrosis of noninfarcted LV to the ND + MI level without affecting body weight, glucose metabolism, and infarct size. NAD(P)H oxidase activity and O(2)(-) production were increased in noninfarcted LV tissues from HFD + MI, both of which were attenuated by apocynin to the ND + MI level. Type 2 diabetes was associated with the exacerbation of LV failure after MI via increasing NAD(P)H oxidase-derived O(2)(-), which may be a novel important therapeutic target in advanced heart failure with diabetes.

Polyol pathway and modulation of ischemia-reperfusion injury in Type 2 diabetic BBZ rat hearts

We investigated the role of polyol pathway enzymes aldose reductase (AR) and sorbitol dehydrogenase (SDH) in mediating injury due to ischemia-reperfusion (IR) in Type 2 diabetic BBZ rat hearts. Specifically, we investigated, (a) changes in glucose flux via cardiac AR and SDH as a function of diabetes duration, (b) ischemic injury and function after IR, (c) the effect of inhibition of AR or SDH on ischemic injury and function. Hearts isolated from BBZ rats, after 12 weeks or 48 weeks diabetes duration, and their non-diabetic littermates, were subjected to IR protocol. Myocardial function, substrate flux via AR and SDH, and tissue lactate:pyruvate (L/P) ratio (a measure of cytosolic NADH/NAD+), and lactate dehydrogenase (LDH) release (a marker of IR injury) were measured. Zopolrestat, and CP-470,711 were used to inhibit AR and SDH, respectively. Myocardial sorbitol and fructose content, and associated changes in L/P ratios were significantly higher in BBZ rats compared to non-diabetics, and increased with disease duration. Induction of IR resulted in increased ischemic injury, reduced ATP levels, increases in L/P ratio, and poor cardiac function in BBZ rat hearts, while inhibition of AR or SDH attenuated these changes and protected hearts from IR injury. These data indicate that AR and SDH are key modulators of myocardial IR injury in BBZ rat hearts and that inhibition of polyol pathway could in principle be used as a therapeutic adjunct for protection of ischemic myocardium in Type 2 diabetic patients.