Response of isolated working hearts to fatty acids and carnitine palmitoyltransferase I inhibition during reduction of coronary flow in acutely and chronically diabetic rats

Metabolic rewiring induced by ranolazine improves melanoma responses to targeted therapy and immunotherapy

Resistance of melanoma to targeted therapy and immunotherapy is linked to metabolic rewiring. Here, we show that increased fatty acid oxidation (FAO) during prolonged BRAF inhibitor (BRAFi) treatment contributes to acquired therapy resistance in mice. Targeting FAO using the US Food and Drug Administration-approved and European Medicines Agency-approved anti-anginal drug ranolazine (RANO) delays tumour recurrence with acquired BRAFi resistance. Single-cell RNA-sequencing analysis reveals that RANO diminishes the abundance of the therapy-resistant NGFRhi neural crest stem cell subpopulation. Moreover, by rewiring the methionine salvage pathway, RANO enhances melanoma immunogenicity through increased antigen presentation and interferon signalling. Combination of RANO with anti-PD-L1 antibodies strongly improves survival by increasing antitumour immune responses. Altogether, we show that RANO increases the efficacy of targeted melanoma therapy through its effects on FAO and the methionine salvage pathway. Importantly, our study suggests that RANO could sensitize BRAFi-resistant tumours to immunotherapy. Since RANO has very mild side-effects, it might constitute a therapeutic option to improve the two main strategies currently used to treat metastatic melanoma.

The Role of Mitochondria in Metabolic Syndrome–Associated Cardiomyopathy

With the rapid development of society, the incidence of metabolic syndrome (MS) is increasing rapidly. Evidence indicated that patients diagnosed with MS usually suffered from cardiomyopathy, called metabolic syndrome–associated cardiomyopathy (MSC). The clinical characteristics of MSC included cardiac hypertrophy and diastolic dysfunction, followed by heart failure. Despite many studies on this topic, the detailed mechanisms are not clear yet. As the center of cellular metabolism, mitochondria are crucial for maintaining heart function, while mitochondria dysfunction plays a vital role through mechanisms such as mitochondrial energy deprivation, calcium disorder, and ROS (reactive oxygen species) imbalance during the development of MSC. Accordingly, in this review, we will summarize the characteristics of MSC and especially focus on the mechanisms related to mitochondria. In addition, we will update new therapeutic strategies in this field.

Metabolic, structural and biochemical changes in diabetes and the development of heart failure

Diabetes contributes to the development of heart failure through various metabolic, structural and biochemical changes. The presence of diabetes increases the risk for the development of cardiovascular disease (CVD), and since the introduction of cardiovascular outcome trials to test diabetic drugs, the importance of improving our understanding of the mechanisms by which diabetes increases the risk for heart failure has come under the spotlight. In addition to the coronary vasculature changes that predispose individuals with diabetes to coronary artery disease, diabetes can also lead to cardiac dysfunction independent of ischaemic heart disease. The hyperlipidaemic, hyperglycaemic and insulin resistant state of diabetes contributes to a perturbed energy metabolic milieu, whereby the heart increases its reliance on fatty acids and decreases glucose oxidative rates. In addition to changes in cardiac energy metabolism, extracellular matrix remodelling contributes to the development of cardiac fibrosis, and impairments in calcium handling result in cardiac contractile dysfunction. Lipotoxicity and glucotoxicity also contribute to impairments in vascular function, cardiac contractility, calcium signalling, oxidative stress, cardiac efficiency and lipoapoptosis. Lastly, changes in protein acetylation, protein methylation and DNA methylation contribute to a myriad of gene expression and protein activity changes. Altogether, these changes lead to decreased cardiac efficiency, increased vulnerability to an ischaemic insult and increased risk for the development of heart failure. This review explores the above mechanisms and the way in which they contribute to cardiac dysfunction in diabetes.

The Contribution of Cardiac Fatty Acid Oxidation to Diabetic Cardiomyopathy Severity

Diabetes is a major risk factor for the development of cardiovascular disease via contributing and/or triggering significant cellular signaling and metabolic and structural alterations at the level of the heart and the whole body. The main cause of mortality and morbidity in diabetic patients is cardiovascular disease including diabetic cardiomyopathy. Therefore, understanding how diabetes increases the incidence of diabetic cardiomyopathy and how it mediates the major perturbations in cell signaling and energy metabolism should help in the development of therapeutics to prevent these perturbations. One of the significant metabolic alterations in diabetes is a marked increase in cardiac fatty acid oxidation rates and the domination of fatty acids as the major energy source in the heart. This increased reliance of the heart on fatty acids in the diabetic has a negative impact on cardiac function and structure through a number of mechanisms. It also has a detrimental effect on cardiac efficiency and worsens the energy status in diabetes, mainly through inhibiting cardiac glucose oxidation. Furthermore, accelerated cardiac fatty acid oxidation rates in diabetes also make the heart more vulnerable to ischemic injury. In this review, we discuss how cardiac energy metabolism is altered in diabetic cardiomyopathy and the impact of cardiac insulin resistance on the contribution of glucose and fatty acid to overall cardiac ATP production and cardiac efficiency. Furthermore, how diabetes influences the susceptibility of the myocardium to ischemia/reperfusion injury and the role of the changes in glucose and fatty acid oxidation in mediating these effects are also discussed.

Concurrent diabetes and heart failure: interplay and novel therapeutic approaches

Diabetes mellitus increases the risk of developing heart failure, and the co-existence of both diseases worsens cardiovascular outcomes, hospitalization and the progression of heart failure. Despite current advancements on therapeutic strategies to manage hyperglycemia, the likelihood of developing diabetes-induced heart failure is still significant, especially with the accelerating global prevalence of diabetes and an ageing population. This raises the likelihood of other contributing mechanisms beyond hyperglycemia in predisposing diabetic patients to cardiovascular disease risk. There has been considerable interest in understanding the alterations in cardiac structure and function in the diabetic patients, collectively termed as "diabetic cardiomyopathy". However, the factors that contribute to the development of diabetic cardiomyopathies is not fully understood. This review summarizes the main characteristics of diabetic cardiomyopathies, and the basic mechanisms that contribute to its occurrence. This includes perturbations in insulin resistance, fuel preference, reactive oxygen species generation, inflammation, cell death pathways, neurohormonal mechanisms, advanced glycated end-products accumulation, lipotoxicity, glucotoxicity, and posttranslational modifications in the heart of the diabetic. This review also discusses the impact of antihyperglycemic therapies on the development of heart failure, as well as how current heart failure therapies influence glycemic control in diabetic patients. We also highlight the current knowledge gaps in understanding how diabetes induces heart failure.

Reduction of Carnitine Content by Inhibition of Its Biosynthesis Results in Protection of Isolated Guinea Pig Hearts against Hypoxic Damage

Background

3-(2,2,2-trimethylhydrazinium) propionate (THP or mildronate) is an inhibitor of carnitine biosynthesis. This study was carried out to determine whether feeding of guinea pigs with THP results in decreased myocardial-free carnitine content and, as a result, attenuates hypoxic damage in isolated and paced work-performing hearts.

Methods and Results

Guinea pigs were administered either distilled water or 100 mg THP/kg/day orally for 10 days. The treatment resulted in about a 50% decline in myocardial-free carnitine content, from 11.1 ± 0.2 (n = 5) to 5.6 ± 0.2 (n = 5) μM/g dry weight of the heart. The left ventricular contractile function of the hearts was measured during normoxic perfusion (PO2= 590 mmHg), hypoxic perfusion (PO2= 149 mmHg), and reperfusion (PO2= 590 mmHg). In both untreated and THP-treated groups, the rate of development of intraventricular pressure (+dP/dt) under normoxic perfusion was similar; however, +dP/dt declined to about 10% of the initial rate within 20 minutes of hypoxic perfusion. In the THP-treated group of hearts, the initial decline was slower than that of the untreated animal hearts. After 20 minutes of normoxic reperfusion following 60 minutes of hypoxic perfusion, the recovery of +dP/dt and -dP/dt was greater in the THP-treated group than in the untreated group. The elevation of end-diastolic pressure during hypoxia was completely reversed by normoxic reperfusion of the THP-treated group but not in the untreated group. Mitochondria isolated from hearts from the THP-treated group after normoxic reperfusion following hypoxic perfusion exhibited better respiratory function than those from untreated hearts.

Conclusion

The data suggest that feeding guinea pigs with THP results in reduced myocardial-free carnitine content and attenuation of hypoxic and reperfusion injury in isolated hearts.

Diabetic animal fed with high-fat diet prevents the protective effect of myocardial ischemic preconditioning effect in isolated rat heart perfusion model

Diabetic heart (diabetes mellitus [DM]) has been shown to attenuate the beneficial effect of ischemic preconditioning (IPC) in rat heart. But the effect of IPC on diabetic rat heart that develops myopathy remains unclear. This study was designed to test the impact of IPC on diabetic cardiomyopathy (DCM) rat heart. Male Wistar rats were grouped as (a) normal, (b) DM (streptozotocin: 65 mg/kg; fed with normal diet), and (c) DCM (streptozotocin: 65 mg/kg; fed with high-fat diet). Isolated rat hearts from each group were randomly subjected to (a) normal perfusion, (b) ischemia-reperfusion (I/R), and (c) IPC procedure. At the end of the perfusion experiments, hearts were analyzed for injury, contractile function, mitochondrial activity, and oxidative stress. The results obtained from hemodynamics, cardiac injury markers, and caspase-3 activity showed that DCM rat displayed prominent I/R-associated cardiac abnormalities than DM rat heart. But the deteriorated physiological performance and cardiac injury were not recovered in both DM and DCM heart by IPC procedure. Unlike normal rat heart, IPC did not reverse mitochondrial dysfunction (determined by electron transport chain enzymes activity, ATP level, and membrane integrity, expression levels of genes like PGC-1ɑ, GSK3β, complex I, II, and V) in DCM and DM rat heart. The present study demonstrated that IPC failed to protect I/R-challenged DCM rat heart, and the underlying pathology was associated with deteriorated mitochondrial function.

miR-21-5p regulates mitochondrial respiration and lipid content in H9C2 cells

Cardiovascular-related pathologies are the single leading cause of death in patients with chronic kidney disease (CKD). Previously, we found that a 5/6th nephrectomy model of CKD leads to an upregulation of miR-21-5p in the left ventricle, targeting peroxisome proliferator-activated receptor-α and altering the expression of numerous transcripts involved with fatty acid oxidation and glycolysis. In the present study, we evaluated the potential for knockdown or overexpression of miR-21-5p to regulate lipid content, lipid peroxidation, and mitochondrial respiration in H9C2 cells. Cells were transfected with anti-miR-21-5p (40 nM), pre-miR-21-5p (20 nM), or the appropriate scrambled oligonucleotide controls before lipid treatment in culture or as part of the Agilent Seahorse XF fatty acid oxidation assay. Overexpression of miR-21-5p attenuated the lipid-induced increase in cellular lipid content, whereas suppression of miR-21-5p augmented it. The abundance of malondialdehyde, a product of lipid peroxidation, was significantly increased with lipid treatment in control cells but attenuated in pre-miR-21-5p-transfected cells. This suggests that miR-21-5p reduces oxidative stress. The cellular oxygen consumption rate (OCR) was increased in both pre-miR-21-5p- and anti-miR-21-5p-transfected cells. Levels of intracellular ATP were significantly higher in anti-mR-21-5p-transfected cells. Pre-miR-21-5p blocked additional increases in OCR in response to etomoxir and palmitic acid. Conversely, anti-miR-21-5p-transfected cells exhibited reduced OCR with both etomoxir and palmitic acid, and the glycolytic capacity was concomitantly reduced. Together, these results indicate that overexpression of miR-21-5p attenuates both lipid content and lipid peroxidation in H9C2 cells. This likely occurs by reducing cellular lipid uptake and utilization, shifting cellular metabolism toward reliance on the glycolytic pathway. NEW & NOTEWORTHY Both overexpression and suppression of miR-21-5p augment basal and maximal mitochondrial respiration. Our data suggest that reliance on glycolytic and fatty acid oxidation pathways can be modulated by the abundance of miR-21-5p within the cell. miR-21-5p regulation of mitochondrial respiration can be modulated by extracellular lipids.

Mitochondrial oxidative stress and cardiac ageing

According with different international organizations, cardiovascular diseases are becoming the first cause of death in western countries. Although exposure to different risk factors, particularly those related to lifestyle, contribute to the etiopathogenesis of cardiac disorders, the increase in average lifespan and aging are considered major determinants of cardiac diseases events. Mitochondria and oxidative stress have been pointed out as relevant factors both in heart aging and in the development of cardiac diseases such as heart failure, cardiac hypertrophy and diabetic cardiomyopathy. During aging, cellular processes related with mitochondrial function, such as bioenergetics, apoptosis and inflammation are altered leading to cardiac dysfunction. Increasing our knowledge about the mitochondrial mechanisms related with the aging process, will provide new strategies in order to improve this process, particularly the cardiovascular ones.

Platelet functional and transcriptional changes induced by intralipid infusion

Multiple studies have shown the effects of long-term exposure to high-fat or western diets on the vascular system. There is limited knowledge on the acute effects of high circulating fat levels, specifically on platelets, which have a role in many processes, including thrombosis and inflammation. This study investigated the effects of acute, high-fat exposure on platelet function and transcript profile. Twenty healthy participants were given an intravenous infusion of 20% Intralipid emulsion and heparin over 6 hours. Blood samples were taken prior to and the day after infusion to measure platelet function and transcript expression levels. Platelet aggregation was not significantly affected by Intralipid infusion, but, when mitochondria function was inhibited by carbonyl cyanide 3-chlorophenylhydrazone (CCCP) or oligomycin, platelet aggregation was higher in the post-infusion state compared to baseline. Through RNA sequencing, and verified by RT-qPCR, 902 miRNAs and 617 mRNAs were affected by Intralipid infusion. MicroRNAs increased include miR-4259 and miR-346, while miR-517b and miR-517c are both decreased. Pathway analysis identified two clusters significantly enriched, including cell motility. In conclusion, acute exposure to high fat affects mitochondrial-dependent platelet function, as well as the transcript profile.

Mitochondria and oxidative stress in heart aging

As average lifespan of humans increases in western countries, cardiac diseases become the first cause of death. Aging is among the most important risk factors that increase susceptibility for developing cardiovascular diseases. The heart has very aerobic metabolism, and is highly dependent on mitochondrial function, since mitochondria generate more than 90 % of the intracellular ATP consumed by cardiomyocytes. In the last few decades, several investigations have supported the relevance of mitochondria and oxidative stress both in heart aging and in the development of cardiac diseases such as heart failure, cardiac hypertrophy, and diabetic cardiomyopathy. In the current review, we compile different studies corroborating this role. Increased mitochondria DNA instability, impaired bioenergetic efficiency, enhanced apoptosis, and inflammation processes are some of the events related to mitochondria that occur in aging heart, leading to reduced cellular survival and cardiac dysfunction. Knowing the mitochondrial mechanisms involved in the aging process will provide a better understanding of them and allow finding approaches to more efficiently improve this process.

Impaired fatty acid oxidation as a cause for lipotoxicity in cardiomyocytes

A major cause for diabetic cardiomyopathy is excess lipid accumulation. To elucidate mechanisms of lipotoxicity mediated diabetic heart disease we need to further our understanding of how lipid metabolism is altered in the diabetic heart. Here we investigated the role of lipid clearance by oxidation as a regulator of lipid-mediated toxicity (lipotoxicity). We evaluated the effect of pre-treating rat neonatal cardiomyocytes (NCMs) with either oleate (mono-unsaturated fatty acid) or palmitate (saturated fatty acid) on fatty acid oxidation (FAO) by measuring (14)C-CO2 production. We evaluated carnitine palmitoyltransferase (Cpt1b) expression by western blotting and mitochondrial membrane potential by quantitative and qualitative fluorescence analyses using the JC-1 dye. We inhibited the Cpt1b pharmacologically using etomoxir and genetically by knocking down its expression using LentiVector mediated transduction of siRNAs targeting the Cpt1b gene. We found that palmitate had a slower clearance rate from NCMs than oleate, and this was associated with a significant decrease in FAO. This impairment in FAO was not the result of either loss of Cpt1b protein or mitochondrial integrity. Enhancing FAO with either oleate or carnitine was associated with a significant attenuation of palmitate mediated lipotoxicity. In contrast impairing FAO in oleate treated NCMs caused lipotoxicity. Here we demonstrate that a major difference between non-toxic unsaturated fatty acids and toxic saturated fatty acids is there ability to stimulate or inhibit fatty acid oxidation, respectively. This has important implications for diabetic cardiomyopathy since diabetic hearts consistently exhibit elevated lipid accumulation.

Impact of di-ethylhexylphthalate exposure on metabolic programming in P19 ECC-derived cardiomyocytes

Di(2-ethylhexyl)phthalate (DEHP) is the most common plasticizer in plastic devices of everyday use. It is a ubiquitous environmental contaminant and primarily known to impair male gonadal development and fertility. Studies concerning the long-term effects of prenatal DEHP exposure on certain diseases [The Developmental Origins of Health and Disease paradigm (DOHaD) hypothesis] are scarce although it is proven that DEHP crosses the placenta. Rising environmental pollution during the last centuries coincides with an increasing prevalence of cardiovascular and metabolic diseases. We have investigated the effects of an early embryonic DEHP exposure at different developmental stages on cardiomyogenesis. We used an in-vitro model, the murine P19 embryonic carcinoma cell line (P19 ECC), mimicking early embryonic stages up to differentiated beating cardiomyocytes. P19 ECC were exposed to DEHP (5, 50, 100 µg ml(-1)) at the undifferentiated stage for 5 days and subsequently differentiated to beating cardiomyocytes. We analyzed the expression of metabolic (Pparg1, Fabp4 and Glut4), cardiac (Myh6, Gja1) and methylation (Dnmt1, Dnmt3a) marker genes by quantitative real-time PCR (qRT-PCR), beating rate and the differentiation velocity of the cells. The methylation status of Pparg1, Ppara and Glut4 was investigated by pyrosequencing. DEHP significantly altered the expression of all investigated genes. The beating rate and differentiation velocity were accelerated. Exposure to DEHP led to small but statistically significant increases in methylation of specific CpGs within Ppara and Pparg1, which otherwise were generally hypomethylated, but methylation of Glut4 was unaltered. Early DEHP exposure of P19 ECC alters the expression of genes associated with cellular metabolism and the functional features of cardiomyocytes.

Treatment with a copper-selective chelator causes substantive improvement in cardiac function of diabetic rats with left-ventricular impairment

BACKGROUND

Defective copper regulation is implicated as a causative mechanism of organ damage in diabetes. Treatment with trientine, a divalent-copper-selective chelator, improves arterial and renal structure/function in diabetes, wherein it also ameliorates left-ventricular (LV) hypertrophy. However, direct in vivo evidence that trientine can improve cardiac function in heart failure has hitherto been lacking.

METHODS

To determine whether trientine treatment could improve in vivo outcome, we measured cardiac function in groups of trientine-treated diabetic (TETA-DIA), non-drug-treated diabetic (DIA) and sham-treated control (SHAM) rats, by using in vivo high-field cardiac magnetic-resonance imaging (cMRI) and an ex vivo isolated-perfused working heart method. Forty age-matched animals underwent a cMRI scan after which 12 were randomized to the SHAM group and 28 underwent streptozotocin-injection; of these, 25 developed stable diabetes, and 12 were then randomized to receive no treatment for 16 weeks (DIA) and the other 13 to undergo 8-weeks' untreated diabetes followed by 8-weeks' drug treatment (TETA-DIA). Animals were studied again by cMRI at 8 and 16 weeks following disease induction, and finally by measurement of ex vivo cardiac function.

RESULTS

After eight weeks diabetes, rats (DIA/TETA-DIA) had developed significant impairment of LV function, as judged by impairment of ejection fraction (LVEF), cardiac output (CO), and LV mass (LVM)/body-mass (all P < 0.001), as well as other functional indexes. LVEF, CO (both P < 0.001) and the other indexes deteriorated further at 16 weeks in DIA, whereas trientine (TETA-DIA) improved cardiac function by elevating LVEF and CO (both P < 0.001), and also partially reversed the increase in LVM/body-mass (P < 0.05). In ex vivo hearts from DIA, the CO response to increasing preload pressure was deficient compared with SHAM (P < 0.001) whereas the preload-CO relationship was significantly improved in TETA-DIA animals (P < 0.001).

CONCLUSIONS

Trientine treatment significantly improved cardiac function in diabetic rats with substantive LV impairment. These results implicate impaired copper regulation in the pathogenesis of impaired cardiac function caused by diabetic cardiomyopathy, and support ongoing studies of trientine treatment in patients with heart failure.

NADPH oxidase-dependent and -independent mechanisms of reported inhibitors of reactive oxygen generation

NADPH oxidase isoform-2 (NOX2) generates reactive oxygen species (ROS) that contribute to neurodegenerative and cardiovascular pathologies. However, validation of NOX2 as a pharmacotherapeutic target has been hampered by a lack of mechanistically-defined inhibitors. Using cellular and biochemical assays, we explored previously reported inhibitors of ROS production (perhexiline, suramin, VAS2870 and two Shionogi patent compounds) as direct NOX2 inhibitors. All but suramin, which presumably lacks cell penetrance, inhibit cellular ROS production. However, only perhexiline and suramin inhibit biochemical NOX2 activity. Indeed, our data suggest that NOX2 inhibition by perhexiline may contribute significantly to its demonstrated cardioprotective effects. Inhibition of protein kinase CβII explains the cellular activity of the Shionogi compounds, whereas VAS2870 inhibits by an as-yet unidentified mechanism unrelated to direct NOX2 function or subunit assembly. These data delineate the mechanisms of action of these compounds and highlight their strengths and limitations for use in future target validation studies.

Cardiac remodeling rather than disturbed myocardial energy metabolism is associated with cardiac dysfunction in diabetic rats

BACKGROUND

Diabetes mellitus (DM) alters the energy substrate metabolism in the heart and the early sign of diabetic cardiomyopathy is the diastolic dysfunction. Although it is known that the extracellular matrix must be altered in the presence of diabetes, its local regulation has not been fully elucidated. Our aim was to evaluate in vivo left ventricular (LV) structure; function and bioenergetics in streptozotocin (STZ) induced diabetes mellitus.

METHODS

Cardiac function was evaluated using echocardiography in anesthetized Sprague–Dawley rats 12 weeks after injection of STZ and in age-matched control rats before and after atrial pacing. In vivo ³¹P magnetic resonance spectroscopy was done to measure the phosphocreatine (PCr) to ATP ratio. Myocardial protein expression of metalloproteinases MMP-2, -9, tissue inhibitor TIMP-1, -2 and collagen was measured using Western blot.

RESULTS

Bodyweight (BW) was decreased in diabetic rats. Heart weight/BW and LV mass/BW ratios were higher in diabetic animals compared to controls (2.3 ± 08 vs 2.1 ± 08 mg/g p <0.05). Heart rate was lower in diabetic rats (293 ± 20 vs 394 ± 36 bpm p <0.05). The velocity of circumferential shortening and peak aortic velocity were lower in diabetic animals and were more pronounced during atrial pacing. The basal PCr/ATP ratio was not different in the two groups. Total collagen was higher in diabetic rats (3.8 ± 0.3 vs 2.9 ± 01 mg/g, p <0.05). Protein expression of MMP-2 was significantly diminished in diabetic rats by ≈ 60%, while MMP-9, TIMP-1 and -2 were unchanged.

CONCLUSION

Streptozotocin induced diabetes led to increased LV/bodyweight, increased collagen content, and diminished MMP-2 with no change in PCr/ATP. Therefore, remodeling rather than disturbed energetics may underlie diabetic cardiomyopathy.

Lipotoxicity in type 2 diabetic cardiomyopathy

As obesity and type 2 diabetes are becoming an epidemic in westernized countries, the incidence and prevalence of obesity- and diabetes-related co-morbidities are increasing. In type 2 diabetes ectopic lipid accumulation in the heart has been associated with cardiac dysfunction and apoptosis, a process termed lipotoxicity. Since cardiovascular diseases are the main cause of death in diabetic patients, diagnosis and treatment become increasingly important. Although ischaemic heart disease is a major problem in diabetes, non-ischaemic heart disease (better known as diabetic cardiomyopathy) becomes increasingly important with respect to the impairment of cardiac function and mortality in type 2 diabetes. The underlying aetiology of diabetic cardiomyopathy is incompletely understood but is beginning to be elucidated. Various mechanisms have been proposed that may lead to lipotoxicity. Therefore, this review will focus on the mechanisms of cardiac lipid accumulation and its relation to the development of cardiomyopathy.

Protein-mediated Fatty Acid Uptake in the Heart

Long chain fatty acids (LCFAs) provide 70-80% of the energy for cardiac contractile activity. LCFAs are also essential for many other cellular functions, such as transcriptional regulation of proteins involved in lipid metabolism, modulation of intracellular signalling pathways, and as substrates for membrane constituents. When LCFA uptake exceeds the capacity for their cardiac utilization, the intracellular lipids accumulate and are thought to contribute to contractile dysfunction, arrhythmias, cardiac myocyte apoptosis and congestive heart failure. Moreover, increased cardiac myocyte triacylglycerol, diacylglycerol and ceramide depots are cardinal features associated with obesity and type 2 diabetes. In recent years considerable evidence has accumulated to suggest that, the rate of entry of long chain fatty acids (LCFAs) into the cardiac myocyte is a key factor contributing to a) regulating cardiac LCFA metabolism and b) lipotoxicity in the obese and diabetic heart. In the present review we i) examine the evidence indicating that LCFA transport into the heart involves a protein-mediated mechanism, ii) discuss the proteins involved in this process, including FAT/CD36, FABPpm and FATP1, iii) discuss the mechanisms involved in regulating LCFA transport by some of these proteins (including signaling pathways), as well as iv) the possible interactions of these proteins in regulating LCFA transport into the heart. In addition, v) we discuss how LCFA transport and transporters are altered in the obese/diabetic heart.

Mitochondrial biogenesis in the metabolic syndrome and cardiovascular disease

The metabolic syndrome is a constellation of metabolic disorders including obesity, hypertension, and insulin resistance, components which are risk factors for the development of diabetes, hypertension, cardiovascular, and renal disease. Pathophysiological abnormalities that contribute to the development of the metabolic syndrome include impaired mitochondrial oxidative phosphorylation and mitochondrial biogenesis, dampened insulin metabolic signaling, endothelial dysfunction, and associated myocardial functional abnormalities. Recent evidence suggests that impaired myocardial mitochondrial biogenesis, fatty acid metabolism, and antioxidant defense mechanisms lead to diminished cardiac substrate flexibility, decreased cardiac energetic efficiency, and diastolic dysfunction. In addition, enhanced activation of the renin-angiotensin-aldosterone system and associated increases in oxidative stress can lead to mitochondrial apoptosis and degradation, altered bioenergetics, and accumulation of lipids in the heart. In addition to impairments in metabolic signaling and oxidative stress, genetic and environmental factors, aging, and hyperglycemia all contribute to reduced mitochondrial biogenesis and mitochondrial dysfunction. These mitochondrial abnormalities can predispose a metabolic cardiomyopathy characterized by diastolic dysfunction. Mitochondrial dysfunction and resulting lipid accumulation in skeletal muscle, liver, and pancreas also impede insulin metabolic signaling and glucose metabolism, ultimately leading to a further increase in mitochondrial dysfunction. Interventions to improve mitochondrial function have been shown to correct insulin metabolic signaling and other metabolic and cardiovascular abnormalities. This review explores mechanisms of mitochondrial dysfunction with a focus on impaired oxidative phosphorylation and mitochondrial biogenesis in the pathophysiology of metabolic heart disease.

The effect of insulin in combination with selenium on blood glucose and GLUT4 expression in the cardiac muscle of streptozotocin-induced diabetic rats

We evaluated the effect of a combination of low doses of insulin (1 U/kg/day) and selenium (180 microg/kg/day) on general physiological parameters and the level of glucose transporter (GLUT4) in the cardiac muscle of streptozotocin-induced diabetic rats. Diabetic rats were treated with insulin, selenium and a combination of insulin and selenium for 4 weeks. The levels of blood glucose and hemoglobin A1c were estimated; the level of the GLUT4 in the cardiac muscle was examined by immunoblotting and immunohistochemistry. Insulin in combination with selenium could significantly lower blood glucose and HbA1c levels and could restore disturbances in GLUT4 level in the cardiac muscle. The treatment with insulin was only partially effective in the restoration of diabetic alterations. We conclude that there was cooperation between insulin and selenium, and that the treatment of diabetic rats with combined doses of insulin and selenium was effective in the control of blood glucose and correction of altered GLUT4 distribution in diabetic rat hearts.

Myocardial ischemic-reperfusion injury in a rat model of metabolic syndrome

Hearts of NaCl-induced hypertensive-glucose intolerant (HGI) rats develop reduced infarcts after ischemia-reperfusion injury (IRI) than their hypertensive (H) counterparts. Because high intake of saturated fat is a major risk factor for ischemic heart disease, we tested the hypothesis that chronic (18 weeks) consumption of a high saturated fat diet increases susceptibility to IRI, an effect more marked in the HGI rats than in the H rats. The fat-fed H (HFAT) rat displayed significantly higher body weight and plasma leptin content compared to the H, HGI, or fat-fed HGI (HGIFAT) rats which all showed similar values. In contrast, plasma triglyceride concentration was significantly higher in the HGIFAT rat than in the other three groups. Plasma insulin concentration was similar in the two H groups but higher than that of the two HGI groups. Compared to the H rat, the HGI rat was markedly glucose intolerant, with fat feeding causing comparable worsening of glucose intolerance in each group. The HGIFAT rats displayed a reduction in baseline myocardial contractility and relaxation and a higher end-diastolic pressure compared to the other three groups. Infarct size was significantly lower in the HGI rats than in the H rats. Although fat feeding did not affect infarct size of the H rat, it worsened that of the HGIFAT rat thereby abrogating the differential that existed between the H and HGI rats. In conclusion, excess fat feeding impairs myocardial function of HGI rats and increases their susceptibility to IRI. These findings are of relevance to the metabolic syndrome that manifests as a cluster of insulin resistance, dyslipidemia, and systemic hypertension.

Potential of metabolic agents as adjunct therapies in heart failure

Heart failure continues to have a significant morbidity and mortality rate despite several recent advances in treatment such as additional neurohumoral blockades and cardiac resynchronisation therapy. There is emerging evidence that, irrespective of etiology, heart failure is associated with an energetic disorder and that this may contribute to the pathogenesis of the syndrome. Recently, a number of studies have suggested that some metabolic agents may have potential as adjunctive therapy in patients with heart failure. These agents cause a shift of myocardial-substrate utilization away from free fatty acids toward glucose. Free fatty acid utilization consumes more oxygen to generate an equivalent amount of energy compared with glucose. Some of these agents are also effective antianginals, presumably by reducing the myocardial oxygen requirement. In this review we will discuss some of the current issues and progresses relating to metabolic manipulation in heart failure.

Renin-angiotensin-aldosterone system and oxidative stress in cardiovascular insulin resistance

Hypertension commonly occurs in conjunction with insulin resistance and other components of the cardiometabolic syndrome. Insulin resistance plays a significant role in the relationship between hypertension, Type 2 diabetes mellitus, chronic kidney disease, and cardiovascular disease. There is accumulating evidence that insulin resistance occurs in cardiovascular and renal tissue as well as in classical metabolic tissues (i.e., skeletal muscle, liver, and adipose tissue). Activation of the renin-angiotensin-aldosterone system and subsequent elevations in angiotensin II and aldosterone, as seen in cardiometabolic syndrome, contribute to altered insulin/IGF-1 signaling pathways and reactive oxygen species formation to induce endothelial dysfunction and cardiovascular disease. This review examines currently understood mechanisms underlying the development of resistance to the metabolic actions of insulin in cardiovascular as well as skeletal muscle tissue.

The effects of chronic trimetazidine treatment on mechanical function and fatty acid oxidation in diabetic rat hearts

Clinical and experimental evidence suggest that increased rates of fatty acid oxidation in the myocardium result in impaired contractile function in both normal and diabetic hearts. Glucose utilization is decreased in type 1 diabetes, and fatty acid oxidation dominates for energy production at the expense of an increase in oxygen requirement. The objective of this study was to examine the effect of chronic treatment with trimetazidine (TMZ) on cardiac mechanical function and fatty acid oxidation in streptozocin (STZ)-diabetic rats. Spontaneously beating hearts from male Sprague–Dawley rats were subjected to a 60-minute aerobic perfusion period with a recirculating Krebs–Henseleit solution containing 11 mmol/L glucose, 100 μU/mL insulin, and 0.8 mmol/L palmitate prebound to 3% bovine serum albumin (BSA). Mechanical function of the hearts, as cardiac output × heart rate (in (mL/min)·(beats/min)·10–2), was deteriorated in diabetic (73 ± 4) and TMZ-treated diabetic (61 ± 7) groups compared with control (119 ± 3) and TMZ-treated controls (131 ± 6). TMZ treatment increased coronary flow in TMZ-treated control (23 ± 1 mL/min) hearts compared with untreated controls (18 ± 1 mL/min). The mRNA expression of 3-ketoacyl-CoA thiolase (3-KAT) was increased in diabetic hearts. The inhibitory effect of TMZ on fatty acid oxidation was not detected at 0.8 mmol/L palmitate in the perfusate. Addition of 1 μmol/L TMZ 30 min into the perfusion did not affect fatty acid oxidation rates, cardiac work, or coronary flow. Our results suggest that higher expression of 3-KAT in diabetic rats might require increased concentrations of TMZ for the inhibitory effect on fatty acid oxidation. A detailed kinetic analysis of 3-KAT using different concentrations of fatty acid will determine the fatty acid inhibitory concentration of TMZ in diabetic state where plasma fatty acid levels are increased.

Modification of myocardial substrate use as a therapy for heart failure

Despite advances in treatment, chronic heart failure is still associated with significant morbidity and a poor prognosis. The scope for further advances based on additional neurohumoral blockade is small. Effective adjunctive therapies acting via a different cellular mechanism would, therefore, be attractive. Energetic impairment seems to contribute to the pathogenesis of heart failure. The findings from several studies have shown that the so-called metabolic agents could have potential as adjunctive therapies in heart failure. These agents cause a shift in the substrate used by the heart away from free fatty acids, the oxidation of which normally provides around 70% of the energy needed, towards glucose. The oxygen cost of energy generation is lessened when glucose is used as the substrate. In this review we aim to draw attention to the metabolic alteration in heart failure and we present evidence supporting the use of metabolic therapy in heart failure.

Aldose reductase inhibitors improve myocardial reperfusion injury in mice by a dual mechanism

Aldose reductase (AR) has been implicated in the pathogenesis of diabetic complications, although the clinical efficacy of AR inhibitors has not been clearly proven. To clarify the pathophysiological role of AR in the heart, we investigated effects of AR inhibitors applied either during the pre-ischemic phase, or during the post-ischemic reperfusion phase on ischemia-reperfusion injury in isolated heart from transgenic mice overexpressing human AR. On reperfusion following global ischemia, transgenic mouse hearts exhibited lower left developed pressure, increased release of creatine kinase, and lower ATP content compared with their littermates. When inhibitors of AR were applied during the pre-ischemic phase, they significantly improved deranged cardiac function, creatine kinase release, and ATP content. On the other hand, inhibition of AR during the post-ischemic reperfusion phase did not affect cardiac performance and ATP content, but it significantly attenuated creatine kinase release and the level of thiobarbiturate-reactive substances in transgenic mouse hearts. These results suggest a dual role of AR in ischemia-reperfusion injury. Inhibition of AR during ischemia preserved generation of ATP via glycolysis, whereas inhibition during the reperfusion phase reduced myocardial injury by attenuating oxidative stress elicited by ischemic insult and reoxygenation.

Hypoxia-induced fatty acid transporter translocation increases fatty acid transport and contributes to lipid accumulation in the heart

Protein-mediated LCFA transport across plasma membranes is highly regulated by the fatty acid transporters FAT/CD36 and FABPpm. Physiologic stimuli (insulin stimulation, AMP kinase activation) induce the translocation of one or both transporters to the plasma membrane and increase the rate of LCFA transport. In the hypoxic/ischemic heart, intramyocardial lipid accumulation has been attributed to a reduced rate of fatty acid oxidation. However, since acute hypoxia (15 min) activates AMPK, we examined whether an increased accumulation of intramyocardial lipid during hypoxia was also attributable to an increased rate of LCFA uptake as a result AMPK-induced translocation of FAT/CD36 and FABPpm. In cardiac myocytes, hypoxia (15 min) induced the redistribution of FAT/CD36 from an intracellular pool (LDM) (-25%, P<0.05) to the plasma membranes (PM) (+54%, P<0.05). Hypoxia also induced an increase in FABPpm at the PM (+56%, P<0.05) and a concomitant FABPpm reduction in the LDM (-24%, P<0.05). Similarly, in intact, Langendorff perfused hearts, hypoxia induced the translocation of a both FAT/CD36 and FABPpm to the PM (+66% and +61%, respectively, P<0.05), with a concomitant decline in FAT/CD36 and FABPpm in the LDM (-24% and -23%, respectively, P<0.05). Importantly, the increased plasmalemmal content of these transporters was associated with increases in the initial rates of palmitate uptake into cardiac myocytes (+40%, P<0.05). Acute hypoxia also redirected palmitate into intracellular lipid pools, mainly to PL and TG (+48% and +28%, respectively, P<0.05), while fatty acid oxidation was reduced (-35%, P<0.05). Thus, our data indicate that the increased intracellular lipid accumulation in hypoxic hearts is attributable to both: (a) a reduced rate of fatty acid oxidation and (b) an increased rate of fatty acid transport into the heart, the latter being attributable to a hypoxia-induced translocation of fatty acid transporters.

Increased myocardial fatty acid metabolism in patients with type 1 diabetes mellitus

OBJECTIVES

The purpose of this study was to determine if myocardial fatty acid utilization (MFAU) and myocardial fatty acid oxidation (MFAO) are increased in diabetic patients.

BACKGROUND

Experimental models of diabetes mellitus demonstrate that MFAU and MFAO are increased, and that this dependence on myocardial fatty acid metabolism may be detrimental to cardiac function. Whether similar metabolic changes occur in humans with diabetes mellitus is unclear.

METHODS

Eleven healthy non-diabetic control patients (5 women, ages 25 +/- 5 years) and 11 otherwise healthy patients with type 1 diabetes mellitus (T1DM) (8 women, ages 36 +/- 10 years, HbA1c 8.4 +/- 1.9%) underwent positron emission tomography for the determination of myocardial blood flow (MBF); myocardial oxygen consumption (MVO2); myocardial glucose utilization (MGU); and MFAU, MFAO, and %MFAO.

RESULTS

Plasma lactate, insulin, and MBF levels were similar between the two groups. However, plasma glucose (5.71 +/- 0.98 mumol/ml vs. 5.28 +/- 0.65 mumol/ml, p = 0.04), free fatty acid levels (0.60 +/- 0.24 mumol/ml vs. 0.19 +/- 0.07 mumol/ml, p < 0.0001), and MVO2 (6.64 +/- 2.21 vs. 4.51 +/- 1.39 mumol/g/min, p = 0.007) levels were higher in the T1DM subjects. Furthermore, compared with control patients, T1DM subjects exhibited higher MFAU (213 +/- 135 nmol/g/min vs. 57 +/- 28 nmol/g/min, p = 0.0004), MFAO (206 +/- 131 nmol/g/min s. 50 +/- 26 nmol/g/min, p = 0.0002), and %MFAO (94 +/- 6% vs. 81 +/- 19%, respectively, p = 0.04). In contrast, MGU was lower in T1DM subjects than in controls (207 +/- 108 nmol/g/min vs. 403 +/- 191 nmol/g/min, p = 0.0008).

CONCLUSIONS

Humans with diabetes mellitus exhibit increased MFAU and MFAO and reduced MGU consistent with observations obtained in experimental models of diabetes.

Dissociation Between Metabolic and Efficiency Effects of Perhexiline in Normoxic Rat Myocardium

The antianginal agent perhexiline inhibits rat cardiac carnitine palmitoyltransferase-1 (CPT-1) and CPT-2, key enzymes for mitochondrial transport of long-chain fatty acids. We tested the hypothesis that perhexiline, in therapeutic concentrations (2 microM), inhibits palmitate oxidation and enhances glucose oxidation in isolated rat cardiomyocytes and in the working rat heart, thereby increasing efficiency of oxygen utilization. In isolated cardiomyocytes, perhexiline (2 microM) exerted no acute effects on palmitate oxidation, but after 48 hours pre-exposure oxidation was inhibited by perhexiline (2 to 10 microM) by 15% to 35% (P < 0.0002). In non-ischemic working rat hearts (3%BSA, 0.4 mM palmitate, 11 mM glucose, 100 microU/mL insulin) perhexiline (2 microM) had no significant acute effect on cardiac efficiency, palmitate or glucose oxidation, but 24 hours pretreatment with transdermal perhexiline increased cardiac work (by 29%, P < 0.05) and cardiac efficiency (by 30%, P < 0.02) without significant effects on palmitate oxidation. The selective CPT-1 inhibitor oxfenicine (2 mM) inhibited palmitate oxidation and enhanced glucose oxidation, but failed to enhance cardiac efficiency. In conclusion, in the non-ischemic working rat heart, perhexiline increases myocardial efficiency by a mechanism(s) that is largely or entirely independent of its effects on CPT. Effects on cardiac efficiency during ischemia, and with changes in fatty acid oxidation after longer perhexiline pretreatment remain to be determined.

Dobutamine alters carnitine metabolism in the neonatal piglet heart

The use of inotropic agents to support the neonatal heart after sepsis or hypoxia increases cardiac energy demand. Carnitine plays a vital role in energy, fuel metabolism. To test the hypothesis that inotropic agents affect carnitine metabolism, hearts from sow-fed piglets were isolated and perfused with an oxygenated buffer containing glucose and palmitate. Increasing dosages of dobutamine (DOB 2.5–15 µg/Kg body wt per min, 0.007–0.044 µmol/kg per min) or saline vehicle (SAL) were administered. Heart rate (HR), left ventricular systolic (LVSP) and end diastolic pressures (LVEDP) were measured. Left ventricular developed pressure (LVDP = LVSP - LVEDP) and pressure-rate product (LVDP × HR) were calculated. Coronary effluent was collected to measure flow and metabolites. Heart tissue samples were collected for metabolite analysis. Results: DOB increased HR, LVEDP and the pressure-rate product [LVDP × HR]. Mean lactate production increased in DOB, but not in SAL control hearts, and was correlated with heart acylcarnitine, but not with coronary flow. Tissue acylcarnitine levels were higher in the DOB than in the SAL group. Plasma total carnitine was correlated with [LVDP × HR] and LVDP, but not with HR. The findings demonstrate that DOB alters myocardial carnitine metabolism and suggest that carnitine status may affect cardiac response to inotropic agents.Key words: carnitine, dobutamine, neonate, swine, isolated perfused heart.

Acyl coenzyme A esters differentially activate cardiac and beta-cell adenosine triphosphate-sensitive potassium channels in a side-chain length-specific manner

Recent evidence demonstrates that long-chain acyl coenzyme A esters (CoAs) activate cardiac and beta-cell plasma-membrane (pmK(ATP)) adenosine triphosphate (ATP)-sensitive potassium channels. In this study, we have investigated the differential effects of acyl CoAs of short and medium side-chain length on cardiac and beta-cell pmK(ATP) isoforms. At the single-channel level, the addition of acyl CoAs of differing side-chain length (2 to 16 carbons) to the inside face of membrane patches from ventricular myocytes caused varying increases in pmK(ATP) channel open probability proportional to increases in acyl side-chain length (20 mumol/L acetyl CoA: 310% +/- 90%, 20 mumol/L decanoyl CoA: 570% +/- 150%). A similar dependence of activation on side-chain length was observed in recombinant pmK(ATP) channels (SUR2A/Kir6.2) with full activation of current requiring both the acyl and CoA moieties in the esterified form. We found the recombinant beta-cell K(ATP) channel (SUR1/Kir6.2) to be much less sensitive to medium-chain acyl CoAs (decanoyl CoA: 124% +/- 15% v 231% +/- 25% in SUR2A/Kir6.2), suggesting a role for the cardiac sulfonylurea receptor, SUR2A, in the molecular mechanism of activation by these compounds. We propose that fatty acid metabolism, and the resultant generation of acyl CoAs of varying side-chain length, may be an important regulator of cellular excitability via interactions with the K(ATP) channel.

Effect of ischaemic preconditioning on genomic response to cerebral ischaemia: similarity to neuroprotective strategies in hibernation and hypoxia-tolerant states

BACKGROUND

Molecular mechanisms of neuroprotection that lead to ischaemic tolerance are incompletely understood. Identification of genes involved in the process would provide insight into cell survival and therapeutic approaches for stroke. We developed a mouse model of neuroprotection in stroke and did gene expression profiling to identify potential neuroprotective genes and their associated pathways.

METHODS

Eight mice per condition were subjected to occlusion of the middle cerebral artery for 15 min (preconditioning), 60 min (injurious ischaemia), or preconditioning followed 72 h later by injurious ischaemia. RNA was extracted from the cortical regions of the ischaemic and non-ischaemic hemispheres. Three pools per condition were generated, and RNA was hybridised to oligonucleotide microarrays for comparison of ischaemic and non-ischaemic hemispheres. Real-time PCR and western blots were used to validate results. Follow-up experiments were done to address the biological relevance of findings.

FINDINGS

Microarray analysis revealed changes in gene expression with little overlap among the conditions of injurious ischaemia, ischaemic preconditioning, or both. Injurious ischaemia induced upregulation of gene expression; 49 (86%) of 57 genes regulated showed increased expression in the ischaemic hemisphere. By contrast, preconditioning followed by injurious ischaemia resulted in pronounced downregulation; 47 (77%) of 61 regulated genes showed lower expression. Preconditioning resulted in transcriptional changes involved in suppression of metabolic pathways and immune responses, reduction of ion-channel activity, and decreased blood coagulation.

INTERPRETATION

Preconditioning reprogrammes the response to ischaemic injury. Similar changes reported by others support an evolutionarily conserved endogenous response to decreased blood flow and oxygen limitation such as seen during hibernation.

Prevention of ischemic heart failure by exercise in spontaneously diabetic BB Wor rats subjected to insulin withdrawal

Poor metabolic control resulting from insulin withdrawal in chronic type 1 diabetic rats results in ischemic heart failure. In the present study, we determined whether heart failure occurs in acute type 1 diabetic rats following insulin withdrawal and if prior exercise training can prevent this dysfunction. Four-week-old diabetic prone BB Wor rats were either sedentary or moderately exercised by daily treadmill running. Training was discontinued at the onset of diabetes. Isolated working rat heart function was then assessed in the following groups: diabetic resistant, uncontrolled sedentary diabetic (USD), controlled sedentary diabetic (CSD), uncontrolled trained diabetic (UTD), and controlled trained diabetic (CTD) rats. To induce an uncontrolled state, insulin treatment was withheld for 24 hours. During increased metabolic demand and reperfusion following ischemia, heart rate, contractility, and cardiac output were depressed in hearts from USD animals. Treatment with insulin prevented the depressions in cardiac performance from occurring. Hearts from UTD rats perfused under these conditions showed comparable cardiac function to that seen in the controlled state. This occurred despite poor metabolic control, reflected by elevated levels of plasma glucose and free fatty acids. Our results indicate that metabolic deteriorations in acute diabetes result in ischemic heart failure. However, this cardiac dysfunction can be prevented with exercise training.

A critical role for PPARalpha-mediated lipotoxicity in the pathogenesis of diabetic cardiomyopathy: modulation by dietary fat content

To explore the role of peroxisome proliferator-activated receptor alpha (PPARalpha)-mediated derangements in myocardial metabolism in the pathogenesis of diabetic cardiomyopathy, insulinopenic mice with PPARalpha deficiency (PPARalpha(-/-)) or cardiac-restricted overexpression [myosin heavy chain (MHC)-PPAR] were characterized. Whereas PPARalpha(-/-) mice were protected from the development of diabetes-induced cardiac hypertrophy, the combination of diabetes and the MHC-PPAR genotype resulted in a more severe cardiomyopathic phenotype than either did alone. Cardiomyopathy in diabetic MHC-PPAR mice was accompanied by myocardial long-chain triglyceride accumulation. The cardiomyopathic phenotype was exacerbated in MHC-PPAR mice fed a diet enriched in triglyceride containing long-chain fatty acid, an effect that was reversed by discontinuing the high-fat diet and absent in mice given a medium-chain triglyceride-enriched diet. Reactive oxygen intermediates were identified as candidate mediators of cardiomyopathic effects in MHC-PPAR mice. These results link dysregulation of the PPARalpha gene regulatory pathway to cardiac dysfunction in the diabetic and provide a rationale for serum lipid-lowering strategies in the treatment of diabetic cardiomyopathy.

Effect of sodium selenite treatment on platelet aggregation of streptozotocin-induced diabetic rats

INTRODUCTION

There is a well-known association between diabetes and atherosclerosis. Platelets are involved in the development of atherosclerotic vascular diseases and play a key role in atherosclerotic complications. Diabetes mellitus is related to alteration in the homeostasis of selenium and the protective role of selenium against lipid peroxidation in diabetes is reported. In the present study, thrombin-induced platelet aggregation and thromboxane A2 (TxA2) formation in diabetes and the effect of sodium selenite were evaluated.

MATERIALS AND METHODS

Diabetes was induced by intraperitoneal injection of streptozotocin (STZ) in Wistar rats (n = 21). Thirty of them were used as control rats. A week after streptozotocin injection, 11 of the control rats and 12 of the diabetics were injected with 5 micromol/kg/day of sodium selenite for 4 weeks. Thrombin-induced aggregation of the platelets was evaluated by optical technique. Thromboxane B2 (TxB2), TxA2 metabolite, was measured by enzyme-linked immunoassay (EIA) in thrombin-induced platelets.

RESULTS AND CONCLUSION

The platelet aggregation and TxB2 level increased in diabetic rats. Sodium selenite reversed the increase in platelet aggregation and TxB2 and caused a small but significant (p < 0.05) decrease in the glucose level. The hyperaggregability of platelets in STZ-induced diabetic rats was thought to be related to the enhanced TxA2 formation of platelets. Increase in TxA2 formation implies lipid peroxidation. Sodium selenite decreased the TxA2 formation. Besides its antioxidative effect, further studies are needed to establish the insulin-like effect of selenite because of a small decrease in blood glucose.

Malonyl CoA control of fatty acid oxidation in the diabetic rat heart

Increased fatty acid metabolism can decrease cardiac function and efficiency, and may therefore contribute to the outcome of ischemic injury in the diabetic. Alterations in the control of myocardial malonyl CoA levels is an important contributing factor to these high fatty acid oxidation rates. This includes alterations in AMPK, ACC, and MCD activity in the diabetic rat heart. A further understanding of how malonyl CoA controls fatty acid oxidation in the diabetic heart should help identify new targets for pharmacological intervention which decreases the reliance of the heart on fatty acid oxidation, and ultimately improves heart function.

Metabolic abnormalities in the diabetic heart

Congestive heart failure is a major health problem in the diabetic. Diabetics have a high incidence of heart disease, including an increased incidence and severity of congestive heart failure than the non-diabetic. Progression to heart failure after an acute myocardial infarction is also more frequent in diabetics then non-diabetics. While atherosclerosis and ischemic injury are important contributing factors to this high in incidence of heart failure, another important factor is diabetes-induced changes within the heart itself. A prominent change that occurs in the diabetic is a switch in cardiac energy metabolism. Increases in fatty acid oxidation accompanied by decreases in glucose metabolism can result in the myocardium becoming almost entirely reliant on fatty acid oxidation as a source of energy. This switch in energy metabolism contributes to congestive heart failure by increasing the severity of injury following an acute myocardial infarction, and by having direct negative effects on contractile function. This paper will review the evidence linking alterations in energy metabolism to alterations in contractile function in the diabetic.

Magnetic resonance imaging analysis of cardiac cycle events in diabetic rats: the effect of angiotensin-converting enzyme inhibition

Non-invasive magnetic resonance imaging (MRI) was used to characterize changes in left and right ventricular cardiac cycles following induction of experimental, streptozotocin (STZ)-induced, diabetes in male Wistar rats at different ages. The effects of the angiotensin-converting enzyme (ACE) inhibitor captopril upon such chronic physiological changes were then evaluated, also for the first time. Diabetes was induced at the age of 7 weeks in two experimental groups, of which one group was subsequently maintained on captopril (2 g l(-1))-containing drinking water, and at 10 and 13 weeks in two further groups. The fifth group provided age-matched controls. All groups (each n = 4 animals) were scanned consistently at 16 weeks, in parallel with timings used in earlier studies that employed this experimental model. Cine magnetic resonance (MR) image acquisition provided transverse sections through both ventricles at twelve time points covering systole and most of diastole. These yielded reconstructions of cardiac anatomy used to derive critical functional indices and their dependence upon time following the triggering electrocardiographic R waves. The left and right ventricular end-diastolic (EDV), end-systolic (ESV) and stroke volumes (SV), and ejection fractions (EF) calculated from each, control and experimental, group showed matching values. This confirmed a necessary condition requiring balanced right and left ventricular outputs and further suggested that STZ-induced diabetes produced physiological changes in both ventricles. Absolute left and right ventricular SVs were significantly altered in all diabetic animals; EDVs and EFs significantly altered in animals diabetic from 7 and 10 but not 13 weeks. When normalized to body weight, left and right ventricular SVs had significantly altered in animals diabetic from 7 and 10 weeks but not 13 weeks. Normalized left ventricular EDVs were also significantly altered in animals diabetic from 7 and 10 weeks. However, normalized right ventricular EDVs were significantly altered only in animals made diabetic from 7 weeks. Diabetic hearts showed major kinetic changes in left and right ventricular contraction (ejection) and relaxation (filling). Both the initial rates of volume change (dV/dt) in both ventricles and the plots of dV/dt values through the cardiac cycle demonstrated more gradual developments of tension during systole and relaxation during diastole. Estimates of the derived left ventricular performance parameters of cardiac output, cardiac power output and stroke work in control animals were comparable with human values when normalized to both body (or cardiac) weight and heart rate. All deteriorated with diabetes. Comparisons of experimental groups diabetic from 7 weeks demonstrated that captopril treatment relieved the alterations in critical volumes, dependence of SV upon EDV, kinetics of systolic contraction and diastolic relaxation and in the derived indicators of ventricular performance. This study represents the first demonstration using non-invasive MRI of early, chronic changes in diastolic filling and systolic ejection in both the left and the right ventricles and of their amelioration by ACE inhibition following STZ-induction of diabetes in intact experimental animals.

Non-invasive magnetic resonance imaging assessment of myocardial changes and the effects of angiotensin-converting enzyme inhibition in diabetic rats

A non-invasive cine magnetic resonance imaging (MRI) technique was developed to allow, for the first time, detection and characterization of chronic changes in myocardial tissue volume and the effects upon these of treatment by the angiotensin-converting enzyme (ACE) inhibitor captopril in streptozotocin (STZ)-diabetic male Wistar rats. Animals that had been made diabetic at the ages of 7, 10 and 13 weeks and a captopril-treated group of animals made diabetic at the age of 7 weeks were scanned. The findings were compared with the results from age-matched controls. All animal groups (n = 4 animals in each) were consistently scanned at 16 weeks. Left and right ventricular myocardial volumes were reconstructed from complete data sets of left and right ventricular transverse sections which covered systole and most of diastole using twelve equally incremented time points through the cardiac cycle. The calculated volumes remained consistent through all twelve time points of the cardiac cycle in all five experimental groups and agreed with the corresponding post-mortem determinations. These gave consistent myocardial densities whose values could additionally be corroborated by previous reports, confirming the validity of the quantitative MRI results and analysis. The myocardial volumes were conserved in animals whose diabetes was induced at 13 weeks but were significantly increased relative to body weight in animals made diabetic at 7 and 10 weeks. Captopril treatment, which was started immediately after induction of diabetes, prevented the development of this relative hypertrophy in both the left and right ventricles. We have thus introduced and validated quantitative MRI methods in a demonstration, for the first time, of chronic myocardial changes in both the right and left ventricles of STZ-diabetic rats and their prevention by the ACE inhibitor captopril.

The cardiac phenotype induced by PPARalpha overexpression mimics that caused by diabetes mellitus

Recent evidence has defined an important role for PPARalpha in the transcriptional control of cardiac energy metabolism. To investigate the role of PPARalpha in the genesis of the metabolic and functional derangements of diabetic cardiomyopathy, mice with cardiac-restricted overexpression of PPARalpha (MHC-PPAR) were produced and characterized. The expression of PPARalpha target genes involved in cardiac fatty acid uptake and oxidation pathways was increased in MHC-PPAR mice. Surprisingly, the expression of genes involved in glucose transport and utilization was reciprocally repressed in MHC-PPAR hearts. Consistent with the gene expression profile, myocardial fatty acid oxidation rates were increased and glucose uptake and oxidation decreased in MHC-PPAR mice, a metabolic phenotype strikingly similar to that of the diabetic heart. MHC-PPAR hearts exhibited signatures of diabetic cardiomyopathy including ventricular hypertrophy, activation of gene markers of pathologic hypertrophic growth, and transgene expression-dependent alteration in systolic ventricular dysfunction. These results demonstrate that (a) PPARalpha is a critical regulator of myocardial fatty acid uptake and utilization, (b) activation of cardiac PPARalpha regulatory pathways results in a reciprocal repression of glucose uptake and utilization pathways, and (c) derangements in myocardial energy metabolism typical of the diabetic heart can become maladaptive, leading to cardiomyopathy.

Short-term carnitine deficiency does not alter aerobic rat heart function but depresses reperfusion recovery after ischemia

Clinical and experimental studies have shown that long-term carnitine deficiency is often associated with cardiomyopathy and ischemic failure. The present study was designed to determine whether cardiac dysfunction is seen in an experimental model of short-term carnitine deficiency. Carnitine deficiency was induced in Sprague-Dawley rats by supplementing the drinking water with sodium pivalate for a period of 2 weeks. This resulted in a 25% depletion of total myocardial carnitine content. When isolated working hearts from these animals were paced and subjected to increments in left atrial filling pressure, there were no differences in mechanical function compared with control hearts. Following no-flow ischemia, however, recovery of cardiac output and relaxation parameters was depressed in hearts from pivalate-treated animals. Under these conditions, L-carnitine prevented the depressions of function from occurring. Our results show that short-term carnitine deficiency is not associated with cardiac dysfunction under normoxic conditions. However, hearts from pivalate-treated animals are more susceptible to ischemic injury and thus may prove to be useful for the study of metabolic and functional aspects of carnitine deficiency.Key words: pivalate, carnitine deficiency, cardiac, ischemia, reperfusion.

Altered susceptibility to ischemia-reperfusion injury in isolated-perfused hearts of short-term diabetic rats associated with changes in non-enzymatic antioxidants

The effects of short-term (2-week) diabetes on myocardial ischemia-reperfusion (I-R) injury and associated changes in myocardial non-enzymatic antioxidant level were examined. Isolated-perfused hearts prepared from control and diabetic rats were subjected to increasing periods of ischemia and reperfusion, and myocardial I-R injury was assessed by measuring the extent of lactate dehydrogenase (LDH) leakage and contractile force recovery. While a brief period (20 min) of post-ischemic reperfusion caused a smaller extent of LDH leakage, the prolonged period (40 min) of reperfusion produced a greater degree of I-R injury in diabetic hearts, as indicated by the impaired recovery of contractile force. The apparent protection against I-R injury in diabetic hearts during the early phase of post-ischemic reperfusion was associated with increases in myocardial reduced glutathione/ascorbic acid and a-tocopherol levels, with the effect on a-tocopherol being most prominent. Insulin treatment could reverse the diabetes-associated changes in susceptibility to myocardial I-R injury and antioxidant response. The ensemble of results indicates that the myocardium isolated from short-term diabetic rat can produce a beneficial antioxidant response to I-R challenge, which may, in turn, be attributable to the decreased susceptibility to I-R injury observable during the early phase of reperfusion.

Free fatty acids, but not ketone bodies, protect diabetic rat hearts during low-flow ischemia

To determine whether the effects of fatty acids on the diabetic heart during ischemia involve altered glycolytic ATP and proton production, we measured energetics and intracellular pH (pH(i)) by using (31)P NMR spectroscopy plus [2-(3)H]glucose uptake in isolated rat hearts. Hearts from 7-wk streptozotocin diabetic and control rats, perfused with buffer containing 11 mM glucose, with or without 1.2 mM palmitate or the ketone bodies, 4 mM beta-hydroxybutyrate plus 1 mM acetoacetate, were subjected to 32 min of low-flow (0.3 ml x g wet wt(-1) x min(-1)) ischemia, followed by 32 min of reperfusion. In control rat hearts, neither palmitate nor ketone bodies altered the recovery of contractile function. Diabetic rat hearts perfused with glucose alone or with ketone bodies, had functional recoveries 50% lower than those of the control hearts, but palmitate restored recovery to control levels. In a parallel group with the functional recoveries, palmitate prevented the 54% faster loss of ATP in the diabetic, glucose-perfused rat hearts during ischemia, but had no effect on the rate of ATP depletion in control hearts. Palmitate decreased total glucose uptake in control rat hearts during low-flow ischemia, from 106 +/- 17 to 52 +/- 12 micromol/g wet wt, but did not alter the total glucose uptake in the diabetic rat hearts, which was 42 +/- 5 micromol/g wet wt. Recovery of contractile function was unrelated to pH(i) during ischemia; the glucose-perfused control and palmitate-perfused diabetic hearts had end-ischemic pH(i) values that were significantly different at 6.36 +/- 0.04 and 6.60 +/- 0.02, respectively, but had similar functional recoveries, whereas the glucose-perfused diabetic hearts had significantly lower functional recoveries, but their pH(i) was 6.49 +/- 0.04. We conclude that fatty acids, but not ketone bodies, protect the diabetic heart by decreasing ATP depletion, with neither having detrimental effects on the normal rat heart during low-flow ischemia.

Effect of perhexiline and oxfenicine on myocardial function and metabolism during low-flow ischemia/reperfusion in the isolated rat heart

Perhexiline is a potent prophylactic anti-anginal agent that has been shown to inhibit myocardial utilization of long-chain fatty acids and to inhibit the mitochondrial enzyme carnitine palmitoyltransferase (CPT)-1. We compared the hemodynamic and biochemical effects of perhexiline (0.5 and 2.0 microM) and of another CPT-1 inhibitor, oxfenicine (0.5 mM), in Langendorff-perfused rat hearts subjected to 60 min of low-flow ischemia (95% flow reduction) followed by 30 min of reperfusion. Both perhexiline (2 microM only) and oxfenicine attenuated (p < 0.003, p < 0.0002, respectively) increases in diastolic tension during ischemia, without significant effects on developed tension, or on cardiac function during reperfusion. Myocardial concentrations of long-chain acylcarnitines (LCAC), products of CPT-1 action, were decreased (p < 0.05) by oxfenicine, unaffected by 2 microM perhexiline, and increased slightly by 0.5 microM perhexiline. Perhexiline, but not the active metabolite of oxfenicine, also inhibited cardiac CPT-2 with similar IC50 and Emax, although lower Hill slope, compared with CPT-1. Oxfenicine, but not perhexiline, reduced concentrations of the endogenous CPT-1 inhibitor, malonyl-CoA. Perhexiline, but not oxfenicine, inhibited myocardial release of lactate during normal flow. We conclude that (a) perhexiline protects against diastolic dysfunction during ischemia in this model, independent of major changes in LCAC accumulation and (b) this may result from simultaneous effects of perhexiline on myocardial CPT-1 and CPT-2.