Adaptation and maladaptation of the heart in diabetes: Part II: potential mechanisms

Mechanisms responsible for enhanced fatty acid utilization by perfused hearts from type 2 diabetic db/db mice

The aim of this study was to determine the biochemical mechanism(s) responsible for enhanced FA utilization (oxidation and esterification) by perfused hearts from type 2 diabetic db/db mice. The plasma membrane content of fatty acid transporters FAT/CD36 and FABPpm was elevated in db/db hearts. Mitochondrial mechanisms that could contribute to elevated rates of FA oxidation were also examined. Carnitine palmitoyl transferase-1 activity was unchanged in mitochondria from db/db hearts, and sensitivity to inhibition by malonyl-CoA was unchanged. Malonyl-CoA content was elevated and AMP kinase activity was decreased in db/db hearts, opposite to what would be expected in hearts exhibiting elevated rates of FA oxidation. Uncoupling protein-3 expression was unchanged in mitochondria from db/db hearts. Therefore, enhanced FA utilization in db/db hearts is most likely due to increased FA uptake caused by increased plasma membrane content of FA transporters; the mitochondrial mechanisms examined do not contribute to elevated FA oxidation observed in db/db hearts.

Potential role for peripheral circadian clock dyssynchrony in the pathogenesis of cardiovascular dysfunction

Circadian clocks are intracellular molecular mechanisms designed to allow the cell, organ, and organism to prepare for an anticipated stimulus prior to its onset. In order for circadian clocks to maintain their selective advantage, they must be entrained to the environment. Light, sound, temperature, physical activity (including sleep/wake transitions), and food intake are among the strongest environmental factors influencing mammalian circadian clocks. Normal circadian rhythmicities in these environmental factors have become severely disrupted in our modern day society, concomitant with increased incidence of type 2 diabetes mellitus, obesity, and cardiovascular disease. Here, we review our current knowledge regarding the roles of peripheral circadian clocks, concentrating on those found within tissues directly involved in metabolic homeostasis and cardiovascular function. We propose that both inter- and intra-organ dyssynchronization, through alteration/impairment of peripheral circadian clocks, accelerates the development of cardiovascular disease risk factors associated with cardiometabolic syndrome.

Glucose levels predict hospitalization for congestive heart failure in patients at high cardiovascular risk

BACKGROUND

Patients with diabetes mellitus (DM) are at high risk of developing congestive heart failure (CHF). However, the relationships between glucose levels and CHF in people with or without a history of DM have not been well characterized.

METHODS AND RESULTS

We evaluated the associations between fasting plasma glucose and risk of hospitalization for CHF during follow-up in patients at high cardiovascular risk and without CHF enrolled in a large-scale clinical trials program. Baseline fasting plasma glucose levels were assessed in 31,546 high-risk subjects with > or = 1 coronary, peripheral, or cerebrovascular disease or DM with end-organ damage who are participating in 2 ongoing parallel trials evaluating the effects of telmisartan, ramipril, or their combination (Ongoing Telmisartan Alone and in Combination With Ramipril Global Endpoint Trial [ONTARGET]; n=25,620) and the effects of telmisartan against placebo in angiotensin-converting enzyme-intolerant patients (Telmisartan Randomized Assessment Study in ACE Intolerant Subjects With Cardiovascular Disease [TRANSCEND]; n=5926). Interim analyses blinded for randomized treatment were performed to compare baseline fasting plasma glucose with the adjusted CHF event rate at a mean follow-up of 886 days. Multivariable Cox regression models were performed, and associations were reported as hazard ratios and 95% confidence intervals. Among all subjects (mean age, 67 years; 69% men), of whom 11,708 (37%) had known DM and 1006 (3.2%) had newly diagnosed DM at baseline, 668 patients were hospitalized for CHF during follow-up. After adjustment for age and sex, a 1-mmol/L-higher fasting plasma glucose was associated with a 1.10-fold-increased risk of CHF hospitalization (95% confidence interval, 1.08 to 1.12; P<0.0001). The association persisted after adjustment for age, sex, smoking, previous myocardial infarction, hypertension, waist-to-hip ratio, creatinine, DM, and use of aspirin, beta-blockers, or statins (hazard ratio, 1.05; 95% confidence interval, 1.02 to 1.08; P<0.001).

CONCLUSIONS

Fasting plasma glucose is an independent predictor of hospitalization for CHF in high-risk subjects. These data provide theoretical support for potential direct beneficial effects of glucose lowering in reducing the risk of CHF and suggests the need for specific studies targeted at this issue.

Diabetes and heart failure in the post-myocardial infarction patient

Diabetes mellitus, a disease which is increasing in prevalence, is a major risk factor for coronary heart disease. In patients following acute myocardial infarction, the presence of diabetes is a powerful risk factor for the development of heart failure, and this intersection of heart failure and diabetes following myocardial infarction carries substantial risk. The poor prognosis associated with heart failure in diabetic patients following myocardial infarction is likely multifactorial. Aggressive strategies for prevention and treatment of heart failure are crucial to reducing the risk associated with diabetes and heart failure following myocardial infarction. This review summarizes epidemiologic, pathophysiologic, and therapeutic data related to diabetes and heart failure in the post-myocardial infarction setting.

Diabetes mellitus and heart failure: epidemiology, mechanisms, and pharmacotherapy

Diabetes mellitus and heart failure (HF), both of which are associated with high rates of adverse cardiovascular outcomes, commonly coexist. Given the marked increases in diabetes prevalence in developed countries, the proportion of the population with both conditions is likely to increase substantially. This article reviews the epidemiology of HF and diabetes, the mechanisms whereby diabetes causes HF, and the pharmacotherapy of both HF and diabetes. Specific challenges in treating patients with both HF and diabetes are also addressed.

Green tea extract impedes dyslipidaemia and development of cardiac dysfunction in streptozotocin-diabetic rats

1. The efficacy of green tea extract (GTE) on serum and cardiac lipids was investigated in streptozotocin (STZ)-diabetic rats. 2. Diabetes was induced in rats by a single intraperitoneal injection of STZ (60 mg/kg bodyweight). Six weeks after the induction of diabetes, GTE was administered orally for 4 weeks (300 mg/kg bodyweight daily). Bodyweight, heart weight, heart weight : bodyweight ratio, blood glucose, serum and cardiac lipids were determined in experimental rats. 3. In diabetic rats, there was a significant decrease in bodyweight with an increase in heart weight : bodyweight ratio and blood glucose. Diabetic rats had significantly increased serum levels of cholesterol, triglycerides, free fatty acids and low-density lipoprotein-cholesterol (LDL-C) and decreased levels of high-density lipoprotein-cholesterol (HDL-C). In the hearts of diabetic rats, there was a significant increase in cholesterol, triglycerides and free fatty acids levels, with an increase in lipoprotein lipase activity. 4. The administration of GTE to diabetic rats resulted in significant recovery in bodyweight, heart weight : bodyweight ratio and blood glucose levels. The administration of GTE reduced cholesterol, triglyceride, free fatty acid and LDL-C levels, and increased HDL-C levels, in the serum of diabetic rats. In addition, GTE decreased cholesterol, triglyceride, free fatty acids levels and lipoprotein lipase activity in the myocardium of diabetic rats. These beneficial effects of GTE are ascribed to its antihyperglycaemic and hypolipidaemic activity. In conclusion, green tea can reduce the risk of cardiovascular disease in diabetes with a significant improvement in lipid metabolism.

Mechanisms linking obesity with cardiovascular disease

Obesity increases the risk of cardiovascular disease and premature death. Adipose tissue releases a large number of bioactive mediators that influence not only body weight homeostasis but also insulin resistance - the core feature of type 2 diabetes - as well as alterations in lipids, blood pressure, coagulation, fibrinolysis and inflammation, leading to endothelial dysfunction and atherosclerosis. We are now beginning to understand the underlying mechanisms as well as the ways in which smoking and dyslipidaemia increase, and physical activity attenuates, the adverse effects of obesity on cardiovascular health.

Improvements in systemic metabolism, anthropometrics, and left ventricular geometry 3 months after bariatric surgery

BACKGROUND

Several lines of evidence have suggested a link between obesity and heart failure, including chronic inflammation, increased sympathetic tone, and insulin resistance. The goal of this study was to evaluate the changes in systemic metabolism, anthropometrics, and left ventricular (LV) contraction, as well as geometry, in clinically severe obese women after bariatric surgery.

METHODS

Enrollment was offered consecutively to 22 women with clinically severe obesity. Participants underwent abdominal magnetic resonance imaging to quantify the visceral adipose tissue (VAT) area and tissue Doppler imaging echocardiography to measure the LV contractile function. Fasting blood chemistries were drawn to measure inflammatory markers and to calculate insulin sensitivity. All tests were performed before surgery and 3 months postoperatively.

RESULTS

Three months after surgery, a significant increase in insulin sensitivity (mean change +/- SEM 34.0 +/- 10.4, P < .0001) was present. The VAT area had significantly decreased (-66.1 +/- 17.8 cm2, P = .002) and was associated with decreases in body mass index, serum glucose concentrations, and high-sensitivity C-reactive protein levels (r = .61 and P = .005, r = .48 and P = .033, and r = .53 and P = .016, respectively). The LV mass decreased significantly (-3.8 +/- 1.7 g/m(2.7), P = .037), and this decrease was associated with a decrease in glucose concentration (r = .46, P = .041). The LV systolic and diastolic contractile function were normal at baseline, and no change occurred after surgery.

CONCLUSION

The early phase of weight loss after bariatric surgery produces favorable changes in LV geometry, and these are associated with normalization in the glucose metabolism.

Predictors of in-hospital mortality difference between male and female patients with acute myocardial infarction

Many studies have demonstrated that, compared with men, women have increased long- and short-term mortality after acute myocardial infarction (AMI). The reasons for this mortality difference remain in dispute. We analyzed baseline characteristics, in-hospital management, and short-term outcomes of 1,246 men and 537 women with AMI to identify clinical variables that can predict the in-hospital mortality difference between genders. A higher in-hospital mortality was found in women with AMI than in men (11.9% vs 6.9%, p <0.001). Women were generally older, had a higher incidence of hypertension, diabetes mellitus, and hyperlipidemia, and had a higher Killip class of cardiac function compared with men. Reperfusion therapy and beta-receptor blockers were underused in women. Using a multivariate logistic regression model, we identified age, history of hypertension and diabetes mellitus, Killip class of cardiac function, and administration of reperfusion therapy and beta-receptor blockers as significant predictors of in-hospital mortality in patients with AMI, with odds ratios of 1.05 (95% confidence interval [CI] approximately 1.03 to 1.07), 1.65 (95% CI 1.12 to 2.41), 1.92 (95% CI 1.27 to 2.90), 3.62 (95% CI 2.88 to 4.56), 0.39 (95% CI 0.24 to 0.66), and 0.63 (95% CI 0.43 to 0.93), respectively. In conclusion, women with AMI had a higher in-hospital mortality rate than did men, probably due to older age, higher incidence of hypertension, diabetes mellitus, and hyperlipidemia, a higher Killip class of cardiac function, and less utilization of reperfusion therapy and beta-receptor blockers.

Impact of physiological variables and genetic background on myocardial frequency-resistivity relations in the intact beating murine heart

Conductance measurements for generation of an instantaneous left ventricular (LV) volume signal in the mouse are limited, because the volume signal is a combination of blood and LV muscle, and only the blood signal is desired. We have developed a conductance system that operates at two simultaneous frequencies to identify and remove the myocardial contribution to the instantaneous volume signal. This system is based on the observation that myocardial resistivity varies with frequency, whereas blood resistivity does not. For calculation of LV blood volume with the dual-frequency conductance system in mice, in vivo murine myocardial resistivity was measured and combined with an analytic approach. The goals of the present study were to identify and minimize the sources of error in the measurement of myocardial resistivity to enhance the accuracy of the dual-frequency conductance system. We extended these findings to a gene-altered mouse model to determine the impact of measured myocardial resistivity on the calculation of LV pressure-volume relations. We examined the impact of temperature, timing of the measurement during the cardiac cycle, breeding strain, anisotropy, and intrameasurement and interanimal variability on the measurement of intact murine myocardial resistivity. Applying this knowledge to diabetic and nondiabetic 11- and 20- to 24-wk-old mice, we demonstrated differences in myocardial resistivity at low frequencies, enhancement of LV systolic function at 11 wk and LV dilation at 20–24 wk, and histological and electron-microscopic studies demonstrating greater glycogen deposition in the diabetic mice. This study demonstrated the accurate technique of measuring myocardial resistivity and its impact on the determination of LV pressure-volume relations in gene-altered mice.

Suppression of nitrative damage by metallothionein in diabetic heart contributes to the prevention of cardiomyopathy

Diabetic cardiomyopathy has become a major contributor to the increased mortality of diabetic patients. Although the development and progression of diabetic cardiomyopathy are considered to be associated with diabetes-derived oxidative stress, the precise mechanisms for and effectively preventive approaches to diabetic cardiomyopathy remain to be explored. Recent studies showed that reactive oxygen or nitrogen species (ROS/RNS) not only play a critical role in the initiation of diabetic cardiomyopathy, but also play an important role in physiological signaling. Therefore, this review will first discuss the dual roles of ROS/RNS in the physiological signaling and pathogenic remodeling leading to cardiomyopathy under diabetic conditions. The significant prevention of diabetic cardiomyopathy by metallothionein (MT) as a potent and nonspecific antioxidant will be also summarized. It is clearly revealed that although dual roles of peroxynitrite-nitrated proteins have been indicated under both physiological and pathogenic conditions, suppression of nitrative damage by MT in the diabetic heart is the major mechanism responsible for its prevention of diabetic cardiomyopathy. Finally the potential for clinical enhancement of the cardiac MT expression to prevent or delay the occurrence of cardiomyopathy in diabetic patients will also be addressed.

Diabetic cardiomyopathy

This article focuses on advances in the understanding of the pathogenesis and treatment of diabetic cardiomyopathy. Patients with diabetes are at an elevated risk for heart failure, and comorbid heart failure confers an increased risk of morbidity and mortality. Diabetic cardiomyopathy and to apply proven lifesaving therapies in all heart failure patients, including those with diabetes, in the absence of contraindications or intolerance.

Distinct effects of short- and long-term leptin treatment on glucose and fatty acid uptake and metabolism in HL-1 cardiomyocytes

Alterations in cardiac glucose and fatty acid metabolism are possible contributors to the pathogenesis of heart failure in obesity. Here we examined the effect of leptin, the product of the obese (ob) gene, on metabolism in murine cardiomyocytes. Neither short-term (1 hour) nor long-term (24 hours) treatment with leptin (60 nmol/L) altered basal or insulin-stimulated glucose uptake and oxidation, glycogen synthesis, insulin receptor substrate 1 tyrosine, Akt, or glycogen synthase kinase 3beta phosphorylation. Extracellular lactate levels were also unaffected by leptin. However, leptin increased basal and insulin-stimulated palmitate uptake at both short and long exposure times and this corresponded with increased cell surface CD36 levels and elevated fatty acid transport protein 1 (FATP1) and CD36 protein content. Whereas short-term leptin treatment increased fatty acid oxidation, there was a decrease in oxidation after 24 hours. The former corresponded with increased acetyl coenzyme A carboxylase phosphorylation and the latter with increased expression of this enzyme. The discrepancy between uptake and oxidation of fatty acids led to a transient decrease in intracellular lipid content with lipid accumulation ensuing after 24 hours. In summary, we demonstrate that leptin did not alter glucose uptake or metabolism in murine cardiomyocytes. However, fatty acid uptake increased while oxidation decreased over time leading to intracellular lipid accumulation, which may lead to lipotoxic damage in heart failure.

Liver steatosis coexists with myocardial insulin resistance and coronary dysfunction in patients with type 2 diabetes

Nonalcoholic fatty liver (NAFL) is a common comorbidity in patients with type 2 diabetes and links to the risk of coronary syndromes. The aim was to determine the manifestations of metabolic syndrome in different organs in patients with liver steatosis. We studied 55 type 2 diabetic patients with coronary artery disease using positron emission tomography. Myocardial perfusion was measured with [15O]H2O and myocardial and skeletal muscle glucose uptake with 2-deoxy-2-[18F]fluoro-D-glucose during hyperinsulinemic euglycemia. Liver fat content was determined by magnetic resonance proton spectroscopy. Patients were divided on the basis of their median (8%) into two groups with low (4.6 +/- 2.0%) and high (17.4 +/- 8.0%) liver fat content. The groups were well matched for age, BMI, and fasting plasma glucose. In addition to insulin resistance at the whole body level (P = 0.012) and muscle (P = 0.002), the high liver fat group had lower insulin-stimulated myocardial glucose uptake (P = 0.040) and glucose extraction rate (P = 0.0006) compared with the low liver fat group. In multiple regression analysis, liver fat content was the most significant explanatory variable for myocardial insulin resistance. In addition, the high liver fat group had increased concentrations of high sensitivity C-reactive protein, soluble forms of E-selectin, vascular adhesion protein-1, and intercellular adhesion molecule-1 (P < 0.05) and lower coronary flow reserve (P = 0.02) compared with the low liver fat group. In conclusion, in patients with type 2 diabetes and coronary artery disease, liver fat content is a novel independent indicator of myocardial insulin resistance and reduced coronary functional capacity. Further studies will reveal the effect of hepatic fat reduction on myocardial metabolism and coronary function.

Overexpression of glutathione peroxidase attenuates myocardial remodeling and preserves diastolic function in diabetic heart

Oxidative stress plays an important role in the structural and functional abnormalities of diabetic heart. Glutathione peroxidase (GSHPx) is a critical antioxidant enzyme that removes H(2)O(2) in both the cytosol and mitochondia. We hypothesized that the overexpression of GSHPx gene could attenuate left ventricular (LV) remodeling in diabetes mellitus (DM). We induced DM by injection of streptozotocin (160 mg/kg ip) in male GSHPx transgenic mice (TG+DM) and nontransgenic wildtype littermates (WT+DM). GSHPx activity was higher in the hearts of TG mice compared with WT mice, with no significant changes in other antioxidant enzymes. LV thiobarbituric acid-reactive substances measured in TG+DM at 8 wk were significantly lower than those in WT+DM (58 +/- 3 vs. 71 +/- 5 nmol/g, P < 0.05). Heart rate and aortic blood pressure were comparable between groups. Systolic function was preserved normal in WT+DM and TG+DM mice. In contrast, diastolic function was impaired in WT+DM and was improved in TG+DM as assessed by the deceleration time of peak velocity of transmitral diastolic flow and the time needed for relaxation of 50% maximal LV pressure to baseline value (tau; 13.5 +/- 1.2 vs. 8.9 +/- 0.7 ms, P < 0.01). The TG+DM values were comparable with those of WT+Control (tau; 7.8 +/- 0.2 ms). Improvement of LV diastolic function was accompanied by the attenuation of myocyte hypertrophy, interstitial fibrosis, and apoptosis. Overexpression of GSHPx gene ameliorated LV remodeling and diastolic dysfunction in DM. Therapies designed to interfere with oxidative stress might be beneficial to prevent cardiac abnormalities in DM.

The circadian clock within the cardiomyocyte is essential for responsiveness of the heart to fatty acids

Cells/organs must respond both rapidly and appropriately to increased fatty acid availability; failure to do so is associated with the development of skeletal muscle and hepatic insulin resistance, pancreatic beta-cell dysfunction, and myocardial contractile dysfunction. Here we tested the hypothesis that the intrinsic circadian clock within the cardiomyocytes of the heart allows rapid and appropriate adaptation of this organ to fatty acids by investigating the following: 1) whether circadian rhythms in fatty acid responsiveness persist in isolated adult rat cardiomyocytes, and 2) whether manipulation of the circadian clock within the heart, either through light/dark (L/D) cycle or genetic disruptions, impairs responsiveness of the heart to fasting in vivo. We report that both the intramyocellular circadian clock and diurnal variations in fatty acid responsiveness observed in the intact rat heart in vivo persist in adult rat cardiomyocytes. Reversal of the 12-h/12-h L/D cycle was associated with a re-entrainment of the circadian clock within the rat heart, which required 5-8 days for completion. Fasting rats resulted in the induction of fatty acid-responsive genes, an effect that was dramatically attenuated 2 days after L/D cycle reversal. Similarly, a targeted disruption of the circadian clock within the heart, through overexpression of a dominant negative CLOCK mutant, severely attenuated induction of myocardial fatty acid-responsive genes during fasting. These studies expose a causal relationship between the circadian clock within the cardiomyocyte with responsiveness of the heart to fatty acids and myocardial triglyceride metabolism.

Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

In patients with diabetes, an increased risk of symptomatic heart failure usually develops in the presence of hypertension or ischemic heart disease. However, a predisposition to heart failure might also reflect the effects of underlying abnormalities in diastolic function that can occur in asymptomatic patients with diabetes alone (termed diabetic cardiomyopathy). Evidence of cardiomyopathy has also been demonstrated in animal models of both Type 1 (streptozotocin-induced diabetes) and Type 2 diabetes (Zucker diabetic fatty rats and ob/ob or db/db mice). During insulin resistance or diabetes, the heart rapidly modifies its energy metabolism, resulting in augmented fatty acid and decreased glucose consumption. Accumulating evidence suggests that this alteration of cardiac metabolism plays an important role in the development of cardiomyopathy. Hence, a better understanding of this dysregulation in cardiac substrate utilization during insulin resistance and diabetes could provide information as to potential targets for the treatment of cardiomyopathy. This review is focused on evaluating the acute and chronic regulation and dysregulation of cardiac metabolism in normal and insulin-resistant/diabetic hearts and how these changes could contribute toward the development of cardiomyopathy.

Distinct transcriptional regulation of long-chain acyl-CoA synthetase isoforms and cytosolic thioesterase 1 in the rodent heart by fatty acids and insulin

The molecular mechanism(s) responsible for channeling long-chain fatty acids (LCFAs) into oxidative versus nonoxidative pathways is (are) poorly understood in the heart. Intracellular LCFAs are converted to long-chain fatty acyl-CoAs (LCFA-CoAs) by a family of long-chain acyl-CoA synthetases (ACSLs). Cytosolic thioesterase 1 (CTE1) hydrolyzes cytosolic LCFA-CoAs to LCFAs, generating a potential futile cycle at the expense of ATP utilization. We hypothesized that ACSL isoforms and CTE1 are differentially regulated in the heart during physiological and pathophysiological conditions. Using quantitative RT-PCR, we report that the five known acsl isoforms ( acsl1, acsl3, acsl4, acsl5, and acsl6) and cte1 are expressed in whole rat and mouse hearts, as well as adult rat cardiomyocytes (ARCs). Streptozotocin-induced insulin-dependent diabetes (4 wk) and fasting (≤24 h) both dramatically induced cte1 and repressed acsl6 mRNA, with no significant effects on the other acsl isoforms. In contrast, high-fat feeding (4 wk) induced cte1 without affecting expression of the acsl isoforms in the heart. Investigation into the mechanism(s) responsible for these transcriptional changes uncovered roles for peroxisome proliferator-activated receptor-α (PPARα) and insulin as regulators of specific acsl isoforms and cte1 in the heart. Culturing ARCs with oleate (0.1–0.4 mM) or the PPARα agonists WY-14643 (1 μM) and fenofibrate (10 μM) consistently induced acsl1 and cte1. Conversely, PPARα null mouse hearts exhibited decreased acsl1 and cte1 expression. Culturing ARCs with insulin (10 nM) induced acsl6, whereas specific loss of insulin signaling within the heart (cardiac-specific insulin receptor knockout mice) caused decreased acsl6 expression. Our data expose differential regulation of acsl isoforms and cte1 in the heart, where acsl1 and cte1 are PPARα-regulated genes, whereas acsl6 is an insulin-regulated gene.

Size of myocardial infarction induced by ischaemia/reperfusion is unaltered in rats with metabolic syndrome

Obesity is associated with metabolic syndrome and increased incidence of and mortality from myocardial infarction. The aim of the present study was to develop an animal model with metabolic syndrome and examine how that influences size of myocardial infarcts induced by occlusion and reperfusion of the left anterior descending coronary artery. Sprague–Dawley rats (n=105) were fed either LF (low-fat) or MHF (moderately high-fat) diets for 13 weeks before coronary occlusion for 45 min, followed by reperfusion for 60 min. Compared with LF-fed and lean MHF-fed rats, obese MHF-fed rats developed metabolic disturbances similar to those seen in the metabolic syndrome, including being overweight by 24% (compared with lean MHF-fed rats), having 74% more visceral fat (compared with LF-fed rats), 15% higher blood pressure (compared with LF-fed rats), 116% higher plasma insulin (compared with lean MHF-fed rats), 10% higher fasting plasma glucose (compared with LF-fed rats), 35% higher non-fasting plasma glucose (compared with lean MHF-fed rats), 36% higher plasma leptin (compared with lean MHF-fed rats) and a tendency to lower plasma adiponectin and higher plasma non-esterified fatty acids. Infarct size was similar in the three groups of rats (36±14, 42±18 and 41±14% in obese MHF-fed, lean MHF-fed and LF-fed rats respectively). In conclusion, rats fed a MHF diet developed metabolic syndrome, but this did not influence myocardial infarct size.

Perfused hearts from Type 2 diabetic (db/db) mice show metabolic responsiveness to insulin

Diabetic ( db/db) mice provide an animal model of Type 2 diabetes characterized by marked in vivo insulin resistance. The effect of insulin on myocardial metabolism has not been fully elucidated in this diabetic model. In the present study we tested the hypothesis that the metabolic response to insulin in db/db hearts will be diminished due to cardiac insulin resistance. Insulin-induced changes in glucose oxidation (GLUox) and fatty acid (FA) oxidation (FAox) were measured in isolated hearts from control and diabetic mice, perfused with both low as well as high concentration of glucose and FA: 10 mM glucose/0.5 mM palmitate and 28 mM glucose/1.1 mM palmitate. Both in the absence and presence of insulin, diabetic hearts showed decreased rates of GLUox and elevated rates of FAox. However, the insulin-induced increment in GLUox, as well as the insulin-induced decrement in FAox, was similar or even more pronounced in diabetic that in control hearts. During elevated FA and glucose supply, however, the effect of insulin was blunted in db/db hearts with respect to both FAox and GLUox. Finally, insulin-stimulated deoxyglucose uptake was markedly reduced in isolated cardiomyocytes from db/db mice, whereas glucose uptake in isolated perfused db/db hearts was clearly responsive to insulin. These results show that, despite reduced insulin-stimulated glucose uptake in isolated cardiomyocytes, isolated perfused db/db hearts are responsive to metabolic actions of insulin. These results should advocate the use of insulin therapy (glucose-insulin-potassium) in diabetic patients undergoing cardiac surgery or during reperfusion after an ischemic insult.

Cardiac metabolism in mice: tracer method developments and in vivo application revealing profound metabolic inflexibility in diabetes

Studies of cardiac fuel metabolism in mice have been almost exclusively conducted ex vivo. The major aim of this study was to assess in vivo plasma FFA and glucose utilization by the hearts of healthy control (db/+) and diabetic (db/db) mice, based on cardiac uptake of (R)-2-[9,10-(3)H]bromopalmitate ([3H]R-BrP) and 2-deoxy-D-[U-14C]glucose tracers. To obtain quantitative information about the evaluation of cardiac FFA utilization with [3H]R-BrP, simultaneous comparisons of [3H]R-BrP and [14C]palmitate ([14C]P) uptake were first made in isolated perfused working hearts from db/+ mice. It was found that [3H]R-BrP uptake was closely correlated with [14C]P oxidation (r2 = 0.94, P < 0.001). Then, methods for in vivo application of [3H]R-BrP and [14C]2-DG previously developed for application in the rat were specially adapted for use in the mouse. The method yields indexes of cardiac FFA utilization (R(f)*) and clearance (K(f)*), as well as glucose utilization (R(g)'). Finally, in the main part of the study, the ability of the heart to switch between FFA and glucose fuels (metabolic flexibility) was investigated by studying anesthetized, 8-h-fasted control and db/db mice in either the basal state or during glucose infusion. In control mice, glucose infusion raised plasma levels of glucose and insulin, raised R(g)' (+58%), and lowered plasma FFA level (-48%), K(f)* (-45%), and R(f)* (-70%). This apparent reciprocal regulation of glucose and FFA utilization by control hearts illustrates metabolic flexibility for substrate use. By contrast, in the db/db mice, glucose infusion raised glucose levels with no apparent influence on cardiac FFA or glucose utilization. In conclusion, tracer methodology for assessing in vivo tissue-specific plasma FFA and glucose utilization has been adapted for use in mice and reveals a profound loss of metabolic flexibility in the diabetic db/db heart, suggesting a fixed level of FFA oxidation in fasted and glucose-infused states.

Increased myocardial oxygen consumption reduces cardiac efficiency in diabetic mice

Altered cardiac metabolism and function (diabetic cardiomyopathy) has been observed in diabetes. We hypothesize that cardiac efficiency, the ratio of cardiac work (pressure-volume area [PVA]) and myocardial oxygen consumption (MVo(2)), is reduced in diabetic hearts. Experiments used ex vivo working hearts from control db/+, db/db (type 2 diabetes), and db/+ mice given streptozotocin (STZ; type 1 diabetes). PVA and ventricular function were assessed with a 1.4-F pressure-volume catheter at low (0.3 mmol/l) and high (1.4 mmol/l) fatty acid concentrations with simultaneous measurements of MVo(2). Substrate oxidation and mitochondrial respiration were measured in separate experiments. Diabetic hearts showed decreased cardiac efficiency, revealed as an 86 and 57% increase in unloaded MVo(2) in db/db and STZ-administered hearts, respectively. The slope of the PVA-MVo(2) regression line was increased for db/db hearts after elevation of fatty acids, suggesting that contractile inefficiency could also contribute to the overall reduction in cardiac efficiency. The end-diastolic and end-systolic pressure-volume relationships in db/db hearts were shifted to the left with elevated end-diastolic pressure, suggesting left ventricular remodeling and/or myocardial stiffness. Thus, by means of pressure-volume technology, we have for the first time documented decreased cardiac efficiency in diabetic hearts caused by oxygen waste for noncontractile purposes.

Aldose Reductase and AGE-RAGE Pathways: Key Players in Myocardial Ischemic Injury

Cardiovascular disease represents the major cause of morbidity and mortality in patients with diabetes mellitus. The impact of cardiac disease includes increased sensitivity of diabetic myocardium to ischemic episodes and diabetic cardiomyopathy, manifested as a subnormal functional response of the diabetic heart independent of coronary artery disease. In this context, we were to our knowledge the first to demonstrate that diabetes increases glucose flux via the first and key enzyme, aldose reductase, of the polyol pathway, resulting in impaired glycolysis under normoxic and ischemic conditions in diabetic myocardium. Our laboratory has been investigating the role of the polyol pathway in mediating myocardial ischemic injury in diabetics. Furthermore, the influence of the aldose reductase pathway in facilitating generation of key potent glycating compounds has led us to investigate the impact of advanced glycation end products (AGEs) in myocardial ischemic injury in diabetics. The potent impact of increased flux via the aldose reductase pathway and the increased AGE interactions with its receptor (RAGE) resulting in cardiac dysfunction will be discussed in this chapter.

Metabolic and endothelial effects of trimetazidine on forearm skeletal muscle in patients with type 2 diabetes and ischemic cardiomyopathy

The aim of the present study was to evaluate the effect of prolonged inhibition of beta-oxidation on glucose and lipid muscle forearm metabolism and cGMP and endothelin-1 forearm release in patients with type 2 diabetes mellitus and ischemic cardiomyopathy. Fifteen patients were randomly allocated in a double-blind cross-over parallel study with trimetazidine (20 mg tid) or placebo lasting 15 days. At the end of each period, all patients underwent euglycemic hyperinsulinemic clamps with forearm indirect calorimetry and endothelial balance of vasodilator and vasoconstricor factors. Compared with placebo, trimetazidine induced 1) an increase in insulin-induced forearm glucose uptake and glucose oxidation accompanied by a reduction in forearm lipid oxidation and citrate release and 2) a decrease of endothelin-1 release paralleled by a significant increase in forearm cGMP release. Forearm glucose oxidation significantly correlated with cGMP release (r=0.37, P<0.04), whereas forearm lipid oxidation positively correlated with endothelin-1 release (r=0.40, P<0.03). In conclusion, for the first time, we demonstrated that insulin-induced forearm glucose oxidation and forearm cGMP release were increased whereas forearm endothelin-1 release was decreased during trimetazidine treatment. Muscle's metabolic and vascular effects of trimetazidine add new interest in the use of trimetazidine in type 2 diabetic patients with cardiovascular disease.

The circadian clock within the heart: potential influence on myocardial gene expression, metabolism, and function

It is becoming increasingly clear that the intrinsic properties of both the heart and vasculature exhibit dramatic oscillations over the course of the day. Diurnal variations in the responsiveness of the cardiovascular system to environmental stimuli are mediated by a complex interplay between extracellular (i.e., neurohumoral factors) and intracellular (i.e., circadian clock) influences. The intracellular circadian clock is composed of a series of transcriptional modulators that together allow the cell to perceive the time of day, thereby enabling preparation for an anticipated stimulus. These molecular timepieces have been characterized recently within both vascular smooth muscle cells and cardiomyocytes, giving rise to a multitude of hypotheses relating to the potential role(s) of the circadian clock as a modulator of physiological and pathophysiological cardiovascular events. For example, evidence strongly supports the hypothesis that the circadian clock within the heart modulates myocardial metabolism, which in turn facilitates anticipation of diurnal variations in workload, substrate availability, and/or the energy supply-to-demand ratio. The purpose of this review is therefore to summarize our current understanding of the molecular events governing diurnal variations in the intrinsic properties of the heart, with special emphasis on the intramyocardial circadian clock. Whether impairment of this molecular mechanism contributes toward cardiovascular disease associated with hypertension, diabetes mellitus, shift work, sleep apnea, and/or obesity will be discussed.

The Cardiometabolic Syndrome and Cardiovascular Disease

The cardiometabolic syndrome is a prevalent metabolic disorder. Epidemiologic studies correlate the cardiometabolic syndrome with an increased risk of coronary heart disease, ischemic stroke, cardiovascular mortality, and total mortality. There is also evidence that the cardiometabolic syndrome is a risk factor for abnormalities in myocardial metabolism, cardiac dysfunction, and arrhythmias such as atrial fibrillation. Multiple imaging modalities, both invasive and noninvasive, may help physicians better define the presence or risk of cardiovascular disease in their patients with the cardiometabolic syndrome.

Left ventricular diastolic dysfunction in diabetic patients: pathophysiology and therapeutic implications

Patients with signs and symptoms of heart failure and a preserved left ventricular (LV) systolic function may have significant abnormalities in diastolic function. This condition is called diastolic heart failure (DHF) and is observed in about 40% of patients with chronic heart failure (CHF). Diabetes mellitus is one of the major risk factors for DHF. Diastolic dysfunction is observed in about 40% of patients with diabetes mellitus and correlates with poor glycemic control. Suggested mechanisms for diastolic dysfunction in the diabetic heart are: (i) abnormalities in high-energy phosphate metabolism; (ii) impaired calcium transport; (iii) interstitial accumulation of advanced glycosylation end products; (iv) imbalance in collagen synthesis and degradation; (v) abnormal microvascular function, (vi) activated cardiac renin-angiotensin system; (vii) decreased adiponectin levels; and (viii) alteration in the metabolism of free fatty acids and glucose. Because most large, randomized clinical trials in CHF have enrolled only patients with systolic dysfunction, the specific management of diastolic dysfunction is largely unknown. The CHARM-Preserved (Candesartan in Heart Failure: Assessment of Reduction in Mortality and Morbidity-Preserved) trial, the only mega trial specific for DHF (LV ejection fraction >40%), showed that the angiotensin II type 1 receptor antagonist (angiotensin receptor blocker [ARB]) candesartan cilexetil reduced hospital admissions for CHF but not cardiovascular death. Currently, the pharmacologic treatment used in systolic heart failure is also recommended in DHF and includes administration of diuretics and nitrates for pulmonary congestion, and long-term management with ACE inhibitors, ARBs, aldosterone antagonists, and beta-adrenoceptor antagonists. Poor glycemic control is associated with a high incidence of heart failure in diabetic patients, but the preferable antihyperglycemic regimen for DHF in patients with diabetes mellitus needs to be determined in further studies.

Cross-sectional assessment of the effect of kidney and kidney-pancreas transplantation on resting left ventricular energy metabolism in type 1 diabetic-uremic patients: a phosphorous-31 magnetic resonance spectroscopy study

OBJECTIVES

To test whether left ventricular (LV) dysfunction affecting type 1 diabetic-uremic patients was associated with abnormal heart high-energy phosphates (HEPs) and to ascertain whether these alterations were also present in recipients of kidney or kidney-pancreas transplantation.

BACKGROUND

Heart failure is the major determinant of mortality in patients with diabetic uremia. Both uremia and diabetes induce alterations of cardiac HEPs metabolism.

METHODS

Magnetic resonance imaging and phosphorous magnetic resonance spectroscopy of the LV were performed in the resting state by means of a 1.5-T clinical scanner. Eleven diabetic-uremic patients, 5 nondiabetic patients with uremia, 11 diabetic recipients of kidney transplantation, and 16 diabetic recipients of combined kidney-pancreas transplantation were studied in a cross-sectional fashion. Eleven nondiabetic recipients of kidney-only transplant and 13 healthy subjects served as control groups.

RESULTS

Uremic patients had higher LV mass, diastolic dysfunction, and lower phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio in comparison with recipients of kidney-pancreas or nondiabetic recipients of kidney transplant. In diabetic recipients of kidney transplant the PCr/ATP ratio was higher than in uremic patients but was lower than in the controls. Recipients of combined kidney-pancreas transplant had a higher ratio than uremic patients but no difference was found in comparison with controls.

CONCLUSIONS

Altered resting myocardial HEPs metabolism may contribute to LV dysfunction in diabetic-uremic patients. In diabetic recipients of kidney transplantation, a certain degree of LV metabolic and functional impairment was found. In combined kidney-pancreas recipients the resting LV metabolism and function were not different than in controls.

Reduced cardiac efficiency and altered substrate metabolism precedes the onset of hyperglycemia and contractile dysfunction in two mouse models of insulin resistance and obesity

Hyperglycemia is associated with altered myocardial substrate use, a condition that has been hypothesized to contribute to impaired cardiac performance. The goals of this study were to determine whether changes in cardiac metabolism, gene expression, and function precede or follow the onset of hyperglycemia in two mouse models of obesity, insulin resistance, and diabetes (ob/ob and db/db mice). Ob/ob and db/db mice were studied at 4, 8, and 15 wk of age. Four-week-old mice of both strains were normoglycemic but hyperinsulinemic. Hyperglycemia develops in db/db mice between 4 and 8 wk of age and in ob/ob mice between 8 and 15 wk. In isolated working hearts, rates of glucose oxidation were reduced by 28-37% at 4 wk and declined no further at 15 wk in both strains. Fatty acid oxidation rates and myocardial oxygen consumption were increased in 4-wk-old mice of both strains. Fatty acid oxidation rates progressively increased in db/db mice in parallel with the earlier onset and greater duration of hyperglycemia. In vivo, cardiac catheterization revealed significantly increased left ventricular contractility and relaxation (positive and negative dP/dt) in both strains at 4 wk of age. dP/dt declined over time in db/db mice but remained elevated in ob/ob mice at 15 wk of age. Increased beta-myosin heavy chain isoform expression was present in 4-wk-old mice and persisted in 15-wk-old mice. Increased expression of peroxisomal proliferator-activated receptor-alpha regulated genes was observed only at 15 wk in both strains. These data indicate that altered myocardial substrate use and reduced myocardial efficiency are early abnormalities in the hearts of obese mice and precede the onset of hyperglycemia. Obesity per se does not cause contractile dysfunction in vivo, but loss of the hypercontractile phenotype of obesity and up-regulation of peroxisomal proliferator-activated receptor-alpha regulated genes occur later and are most pronounced in the presence of longstanding hyperglycemia.

Upstream stimulatory factor 1 transactivates the human gene promoter of the cardiac isoform of acetyl-CoA carboxylase

E-box cis-elements act as binding sites for upstream stimulatory factors (USFs), putative glucose-responsive transcriptional modulators. Since four E-boxes were identified on the human ACCbeta promoter, we hypothesized that USF1 induces ACCbeta expression in a glucose-dependent manner. Here, murine cardiac ACCbeta expression was significantly increased in response to high carbohydrate re-feeding after fasting. However, transfection studies showed no difference in ACCbeta promoter activity in neonatal cardiomyocytes and CV-1 fibroblasts after low (5.5mM) and high (25 mM) glucose exposure. USF1 overexpression significantly increased ACCbeta promoter activity in both cell lines under low glucose conditions. With high glucose exposure, USF1 further induced ACCbeta promoter activity only in CV-1 fibroblasts. USF1-induced ACCbeta promoter responsiveness was markedly attenuated when co-transfecting cardiomyocytes with a -93/+65 or -38/+65 promoter deletion construct (lacking E-boxes 1-3). Thus, USF1 transactivates the human ACCbeta promoter in the heart, likely through an E-box cis-element located close to the transcription start site.

Therapy insight: heart disease and the insulin-resistant patient

Insulin-resistance syndromes are of pandemic proportions; 150 million people worldwide and an estimated 43 million people in the US are currently affected by type 2 diabetes mellitus or metabolic syndrome respectively. Treatment of heart disease in the context of type 2 diabetes requires multifactorial risk-factor management, including lifestyle modification and drug treatment for comorbidities. Management of coronary risk extends beyond simple cholesterol lowering. Early use of cardiac imaging and, where appropriate, revascularization should be considered in high-risk or symptomatic patients. Traditionally, patients with type 2 diabetes and coronary arterial disease have been treated surgically, but percutaneous revascularization of these patients is increasingly common. Indeed, revascularization by use of drug-eluting coronary stents combined with administration of novel antiplatelet agents has revolutionized percutaneous coronary intervention in patients with type 2 diabetes. Despite these advances, there is no consensus of opinion regarding revascularization strategies or risk-factor management in insulin-resistant patients with symptomatic or prognostically important coronary arterial disease. Furthermore, specific therapies and preventative strategies for diabetic cardiomyopathy and heart failure in patients with type 2 diabetes remain elusive. The identification of optimized approaches for the prevention and treatment of the metabolic syndrome and heart disease in insulin-resistant, nondiabetic patients remains a major global challenge.

Management of patients with type 2 diabetes after acute coronary syndromes

Acute coronary syndromes are associated with a high risk for subsequent major cardiovascular events and with a risk for mortality that remains substantially increased for many months following the acute phase. Patients with type 2 diabetes mellitus are especially vulnerable and encounter excessive long-term mortality. Effective management of patients with type 2 diabetes following acute coronary syndromes requires aggressive multidisciplinary efforts for reduction of several risk factors, including meticulous control of blood glucose. The evidence for different medication and treatment strategies capable of improving the outcomes is reviewed and the currently available recommendations are summarised.

Myocardial substrate metabolism in the normal and failing heart

The alterations in myocardial energy substrate metabolism that occur in heart failure, and the causes and consequences of these abnormalities, are poorly understood. There is evidence to suggest that impaired substrate metabolism contributes to contractile dysfunction and to the progressive left ventricular remodeling that are characteristic of the heart failure state. The general concept that has recently emerged is that myocardial substrate selection is relatively normal during the early stages of heart failure; however, in the advanced stages there is a downregulation in fatty acid oxidation, increased glycolysis and glucose oxidation, reduced respiratory chain activity, and an impaired reserve for mitochondrial oxidative flux. This review discusses 1) the metabolic changes that occur in chronic heart failure, with emphasis on the mechanisms that regulate the changes in the expression of metabolic genes and the function of metabolic pathways; 2) the consequences of these metabolic changes on cardiac function; 3) the role of changes in myocardial substrate metabolism on ventricular remodeling and disease progression; and 4) the therapeutic potential of acute and long-term manipulation of cardiac substrate metabolism in heart failure.

Fatty acid metabolism is enhanced in type 2 diabetic hearts

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

The association between glucose abnormalities and heart failure in the population-based Reykjavik study

OBJECTIVE

Diabetes is an independent risk factor for heart failure, whereas the relation between heart failure and abnormal glucose regulation (AGR) needs further evaluation. We studied this combination in the Reykjavik Study.

RESEARCH DESIGN AND METHODS

The Reykjavik Study, a population-based cohort study during 1967-1997, recruited 19,381 participants aged 33-84 years who were followed until 2002. Oral glucose tolerance tests and chest X-rays were obtained from all participants. Cases were defined in accordance with World Health Organization criteria for type 2 diabetes or AGR (impaired glucose tolerance or impaired fasting glucose) and European Society of Cardiology guidelines for heart failure.

RESULTS

The overall prevalence of type 2 diabetes and heart failure was 0.5% in men and 0.4% in women, while AGR and heart failure were found in 0.7% of men and 0.6% of women. Among participants with normal glucose regulation, heart failure was diagnosed in 3.2% compared with 6.0 and 11.8% among those with AGR and type 2 diabetes, respectively. The prevalence of type 2 diabetes in the age-group 45-65 years increased in both sexes during the period (P for trend = 0.007). The odds ratio was 2.8 (95% CI 2.2-3.6) for the association between type 2 diabetes and heart failure and 1.7 (1.4-2.1) between AGR and heart failure.

CONCLUSIONS

There is a strong association between any form of glucometabolic perturbation and heart failure. Future studies in this field should focus on all types of glucose abnormalities rather than previously diagnosed diabetes only.

Diabetic cardiomyopathy: mechanisms, diagnosis and treatment

Independent of the severity of coronary artery disease, diabetic patients have an increased risk of developing heart failure. This clinical entity has been considered to be a distinct disease process referred to as 'diabetic cardiomyopathy'. Experimental studies suggest that extensive metabolic perturbations may underlie both functional and structural alterations of the diabetic myocardium. Translational studies are, however, limited and only partly explain why diabetic patients are at increased risk of cardiomyopathy and heart failure. Although a range of diagnostic methods may help to characterize alterations in cardiac function in general, none are specific for the alterations in diabetes. Treatment paradigms are very much limited to interpretation and translation from the results of interventions in non-diabetic patients with heart failure. This suggests that there is an urgent need to conduct pathogenetic, diagnostic and therapeutic studies specifically in diabetic patients with cardiomyopathy to better understand the factors which initiate and progress diabetic cardiomyopathy and to develop more effective treatments.

Insulin resistance and inflammatory activation in older patients with systolic and diastolic heart failure

OBJECTIVE

To evaluate insulin resistance and systemic inflammation in older patients with systolic (SHF) or diastolic heart failure (DHF).

PATIENTS

52 non-diabetic patients (> 70 and < 90 years old) with chronic heart failure (CHF) and hospitalised within the previous six months for heart failure were studied, together with a control group of older healthy volunteers (n = 26). On the basis of Doppler echocardiographic criteria patients were classed as having SHF (n = 27) or DHF (n = 25).

MAIN OUTCOME MEASURES

Fasting glucose, insulin, C reactive protein, interleukin 6, and tumour necrosis factor alpha soluble receptor II (TNF-alphaSRII) concentrations were determined. Insulin resistance was estimated by the homeostasis model assessment (HOMA).

RESULTS

HOMA index (median, interquartile range) was higher in patients with DHF (1.77, 1.06-2.26) than in patients with SHF (0.97, 0.81-1.85) or healthy volunteers (1.04, 0.76-1.44; p = 0.01). After adjustment for body mass index, age, and use of angiotensin converting enzyme inhibitors, both groups of patients with CHF were more insulin resistant than were healthy volunteers (p = 0.02). C reactive protein, interleukin 6, and TNF-alphaSRII were all significantly (p < 0.001) higher in patients with DHF and SHF than in healthy volunteers. All markers of systemic inflammation were independently associated with the presence of clinical CHF.

CONCLUSION

Insulin resistance and inflammatory activation are present in older patients with SHF and DHF.

Cellular mechanisms of insulin resistance, lipodystrophy and atherosclerosis induced by HIV protease inhibitors

Accumulating clinical evidence now links HIV protease inhibitors (HPIs) to the pathogenesis of insulin resistance, dyslipidaemia, lipodystrophy and atherosclerosis associated with highly active anti-retroviral therapy. Here we briefly describe the evidence for a distinct causative role for HPIs, and explore the cellular mechanisms proposed to underlie these side-effects. Acute inhibition of GLUT4-mediated glucose transport, and defective insulin signalling induced by chronic exposure to nelfinavir, are described as cellular mechanisms of insulin resistance. Interference with adipogenesis and adipocyte apoptosis and nelfinavir-induced activation of lipolysis are discussed as potential mechanisms of HPI-induced lipodystrophy. HPI-induced free radical production, apoptosis and increased glucose utilization in vascular smooth muscle cells are presented as possible novel mechanisms for atherosclerosis. Common pathways and cause-effect relationships between the various cellular mechanisms presented are then discussed, with emphasis on the role of insulin resistance, free radical production and enhanced lipolysis. Understanding the cellular mechanisms of HPI-induced side-effects will enhance the search for improved anti-retroviral therapy, and may also shed light on the pathogenesis of common forms of insulin resistance, dyslipidaemia and atherosclerosis.

Impact of altered substrate utilization on cardiac function in isolated hearts from Zucker diabetic fatty rats

The goal of this study was to determine whether changes in cardiac metabolism in Type 2 diabetes are associated with contractile dysfunction or impaired response to ischemia. Hearts from Zucker diabetic fatty (ZDF) and lean control rats were isolated and perfused with glucose, lactate, pyruvate, and palmitate. The rates of glucose, lactate, pyruvate, and palmitate oxidation rates and glycolysis were determined during baseline perfusion and low-flow ischemia (LFI; 0.3 ml/min for 30 min) and after LFI and reperfusion. Under all conditions, ATP synthesis from palmitate was increased and synthesis from lactate was decreased in the ZDF group, whereas the contribution from glucose was unchanged. During baseline perfusion, the rate of glycolysis was lower in the ZDF group; however, during LFI and reperfusion, there were no differences between groups. Despite these metabolic shifts, there were no differences in oxygen consumption or ATP production rates between the groups under any perfusion conditions. Cardiac function was slightly depressed before LFI in the ZDF group, but during reperfusion, function was improved relative to the control group despite the increased dependence on fatty acids for energy production. These data suggest that in this model of diabetes, the shift from carbohydrates to fatty acids for oxidative energy production did not increase myocardial oxygen consumption and was not associated with impaired response to ischemia and reperfusion.

Diurnal variations in the responsiveness of cardiac and skeletal muscle to fatty acids

Cardiac and skeletal muscle both respond to elevated fatty acid availability by increasing fatty acid oxidation, an effect mediated in large part by peroxisome proliferator-activated receptor-alpha (PPAR alpha). We hypothesized that cardiac and skeletal muscle alter their responsiveness to fatty acids over the course of the day, allowing optimal adaptation when availability of this substrate increases. In the current study, pyruvate dehydrogenase kinase 4 (pdk4) was utilized as a representative PPAR alpha-regulated gene. Opposing diurnal variations in pdk4 expression were observed in cardiac and skeletal muscle isolated from the ad libitum-fed rat; pdk4 expression peaked in the middle of the dark and light phases, respectively. Elevation of circulating fatty acid levels by high-fat feeding, fasting, and streptozotocin-induced diabetes increased pdk4 expression in both heart and soleus muscle. Highest levels of induction were observed during the dark phase, regardless of muscle type or intervention. Specific activation of PPAR alpha with WY-14643 rapidly induced pdk4 expression in heart and soleus muscle. Highest levels of induction were again observed during the dark phase. The same pattern of induction was observed for the PPAR alpha-regulated genes malonyl-CoA decarboxylase and uncoupling protein 3. Investigation into the potential mechanism(s) for these observations exposed a coordinated upregulation of transcriptional activators of the PPAR alpha system during the night, with a concomitant downregulation of transcriptional repressors in both muscle types. In conclusion, responsiveness of cardiac and skeletal muscle to fatty acids exhibits a marked diurnal variation. These observations have important physiological and pathophysiological implications, ranging from experimental design to pharmacological treatment of patients.

Evidence for mitochondrial thioesterase 1 as a peroxisome proliferator-activated receptor-alpha-regulated gene in cardiac and skeletal muscle

The physiological role of mitochondrial thioesterase 1 (MTE1) is unknown. It was proposed that MTE1 promotes fatty acid (FA) oxidation (FAO) by acting in concert with uncoupling protein (UCP)3. We previously showed that ucp3 is a peroxisome proliferator-activated receptor-alpha (PPAR alpha)-regulated gene, allowing induction when FA availability increases. On the assumption that UCP3 and MTE1 act in partnership to increase FAO, we hypothesized that mte1 is also a PPAR alpha-regulated gene in cardiac and skeletal muscle. Using real-time RT-PCR, we characterized mte1 gene expression in rat heart and soleus muscles. Messenger RNA encoding for mte1 was 3.2-fold higher in heart than in soleus muscle. Cardiac mte1 mRNA exhibited modest diurnal variation, with 1.4-fold higher levels during dark phase. In contrast, skeletal muscle mte1 mRNA remained relatively constant over the course of the day. High-fat feeding, fasting, and streptozotocin-induced diabetes, interventions that increase FA availability, muscle PPAR alpha activity, and muscle FAO rates, increased mte1 mRNA in heart and soleus muscle. Conversely, pressure overload and hypoxia, interventions that decrease cardiac PPAR alpha activity and FAO rates, repressed cardiac mte1 expression. Specific activation of PPAR alpha in vivo through WY-14643 administration rapidly induced mte1 mRNA in cardiac and skeletal muscle. WY-14643 also induced mte1 mRNA in isolated adult rat cardiomyocytes dose dependently. Expression of mte1 was markedly lower in hearts and soleus muscles isolated from PPAR alpha-null mice. Alterations in cardiac and skeletal muscle ucp3 expression mirrored that of mte1 in all models investigated. In conclusion, mte1, like ucp3, is a PPAR alpha-regulated gene in cardiac and skeletal muscle.

Effects of diabetes mellitus and ischemic heart disease on the progression from asymptomatic left ventricular dysfunction to symptomatic heart failure: a retrospective analysis from the Studies of Left Ventricular Dysfunction (SOLVD) Prevention trial

BACKGROUND

Emerging data suggest that diabetes mellitus is a risk factor for the progression of established heart failure only in those patients with ischemic cardiomyopathy. Whether diabetes mellitus is a risk factor for the progression from asymptomatic left ventricular systolic dysfunction to symptomatic heart failure in patients with left ventricular dysfunction of an ischemic cause is not known.

METHODS

We performed a retrospective analysis of 2821 patients with asymptomatic left ventricular systolic dysfunction from the Studies of Left Ventricular Dysfunction (SOLVD) Prevention trial. We used adjusted survival analysis to examine the effects of ischemic heart disease and diabetes mellitus on 3 prespecified study end points: (1) development of heart failure (HF) symptoms, (2) HF hospitalization, and (3) death or development of symptoms.

RESULTS

There is a statistically significant interaction between the cause of left ventricular systolic dysfunction and diabetes mellitus on the risk of development of heart failure symptoms (P = .020). Patients with ischemic cardiomyopathy and diabetes had an increased risk of progression to symptomatic heart failure (HR = 1.56, P < .001), hospitalization for heart failure (HR = 2.16, P < .001), and death or development of symptoms (HR = 1.50, P < .001), compared with patients with ischemic cardiomyopathy without diabetes. In contrast, diabetes was not associated with an increased risk of reaching these end points in patients with nonischemic cardiomyopathy.

CONCLUSIONS

Diabetes mellitus is a risk factor for the progression from asymptomatic left ventricular systolic dysfunction to symptomatic heart failure, but this risk appears to be confined to those patients with ischemic cardiomyopathy.