Short-term hyperinsulinemia and hyperglycemia increase myocardial lipid content in normal subjects

Myocardial steatosis across the spectrum of human health and disease

Preclinical data strongly suggest that myocardial steatosis leads to adverse cardiac remodelling and left ventricular dysfunction. Using 1 H cardiac magnetic resonance spectroscopy, similar observations have been made across the spectrum of health and disease. The purpose of this brief review is to summarize these recent observations. We provide a brief overview of the determinants of myocardial triglyceride accumulation, summarize the current evidence that myocardial steatosis contributes to cardiac dysfunction, and identify opportunities for further research.

Insulin resistance and metabolic flexibility as drivers of liver and cardiac disease in T2DM

Metabolic flexibility refers to the ability of tissues to adapt their use of energy sources according to substrate availability and energy demands. This review aims to disentangle the emerging mechanisms through which altered metabolic flexibility and insulin resistance promote NAFLD and heart disease progression. Insulin resistance and metabolic inflexibility are central drivers of hepatic and cardiac diseases in individuals with type 2 diabetes. Both play a critical role in the complex interaction between glucose and lipid metabolism. Disruption of metabolic flexibility results in hyperglycemia and abnormal lipid metabolism, leading to increased accumulation of fat in the liver, contributing to the development and progression of NAFLD. Similarly, insulin resistance affects cardiac glucose metabolism, leading to altered utilization of energy substrates and impaired cardiac function, and influence cardiac lipid metabolism, further exacerbating the progression of heart failure. Regular physical activity promotes metabolic flexibility by increasing energy expenditure and enabling efficient switching between different energy substrates. On the contrary, weight loss achieved through calorie restriction ameliorates insulin sensitivity without improving flexibility. Strategies that mimic the effects of physical exercise, such as pharmacological interventions or targeted lifestyle modifications, show promise in effectively treating both diabetes and NAFLD, finally reducing the risk of advanced liver disease.

Osteoblast-intrinsic defect in glucose metabolism impairs bone formation in type II diabetic male mice

Skeletal fragility is associated with type 2 diabetes mellitus (T2D), but the underlying mechanism is not well understood. Here, in a mouse model for youth-onset T2D, we show that both trabecular and cortical bone mass is reduced due to diminished osteoblast activity. Stable isotope tracing in vivo with 13C-glucose demonstrates that both glycolysis and glucose fueling of the TCA cycle are impaired in diabetic bones. Similarly, Seahorse assays show suppression of both glycolysis and oxidative phosphorylation by diabetes in bone marrow mesenchymal cells as a whole, whereas single-cell RNA sequencing reveals distinct modes of metabolic dysregulation among the subpopulations. Metformin not only promotes glycolysis and osteoblast differentiation in vitro, but also improves bone mass in diabetic mice. Finally, osteoblast-specific overexpression of either Hif1a, a general inducer of glycolysis, or Pfkfb3 which stimulates a specific step in glycolysis, averts bone loss in T2D mice. The study identifies osteoblast-intrinsic defects in glucose metabolism as an underlying cause of diabetic osteopenia, which may be targeted therapeutically.

DPP4 Activity, Hyperinsulinemia, and Atherosclerosis

CONTEXT

Obesity and type 2 diabetes are associated with chronic hyperinsulinemia, elevated plasma levels of dipeptidyl peptidase-4 (DPP4), and a pro-atherosclerotic milieu.

EVIDENCE ACQUISITION

PubMed search of the term "insulin and atherosclerosis," "hyperinsulinemia," "atherosclerosis," or "cardiovascular outcomes" cross-referenced with "DPP4." Relevant research and review articles were reviewed.

EVIDENCE SYNTHESIS

Hyperinsulinemia in the setting of insulin resistance promotes vascular inflammation, vascular smooth muscle cell growth, pathological cholesterol profile, hypertension, and recruitment of immune cells to the endothelium, all contributing to atherosclerosis. DPP4 has pleiotropic functions and its activity is elevated in obese humans. DPP4 mirrors hyperinsulinemia's atherogenic actions in the insulin resistant state, and genetic deletion of DPP4 protects rodents from developing insulin resistance and improves cardiovascular outcomes. DPP4 inhibition in pro-atherosclerotic preclinical models results in reduced inflammation and oxidative stress, improved endothelial function, and decreased atherosclerosis. Increased incretin levels may have contributed to but do not completely account for these benefits. Small clinical studies with DPP4 inhibitors demonstrate reduced carotid intimal thickening, improved endothelial function, and reduced arterial stiffness. To date, this has not been translated to cardiovascular risk reduction for individuals with type 2 diabetes with prior or exaggerated risk of cardiovascular disease.

CONCLUSION

DPP4 may represent a key link between central obesity, insulin resistance, and atherosclerosis. The gaps in knowledge in DPP4 function and discrepancy in cardiovascular outcomes observed in preclinical and large-scale randomized controlled studies with DPP4 inhibitors warrant additional research.

Trace element, immune and opioid biomarkers of unstable angina, increased atherogenicity and insulin resistance: Results of machine learning

BACKGROUND

Aberrations in endothelial cells, immune and oxidative pathways are associated with atherosclerosis (ATS) and unstable angina (UA). The role of trace elements, minerals, and the endogenous opioid system (EOS) in UA are less well established.

METHODS

We measured lipid, insulin resistance (IR), and immune, trace element (copper and zinc), mineral (magnesium, calcium), EOS (β-endorphin and mu-opioid receptor (MOR)) and antioxidant (vitamin D3) biomarkers in patients with ATS (n = 60) and UA (n = 60) and healthy controls (n = 58).

RESULTS

ATS patients showed increased atherogenic and IR indices, IL-6, IL-10, β-endorphin, copper and magnesium, and lower zinc than healthy controls. Logistic regression showed that UA was significantly discriminated from ATS without UA with an accuracy of 85.5 % using calcium, IL-10, β-endorphin, MOR, triglycerides, IR (all positively), and copper and vitamin D3 (inversely). Neural networks showed that UA was discriminated from ATS without UA with an area under the ROC curve of 0.942 using MOR, β-endorphin, calcium, insulin resistance, vitamin D3 and copper as input variables. We found that 50.0 % of the variance in IR was explained by the regression on copper, IL-10, IL-6 (all positively), and zinc (inversely), while 32.9 % of the variance in the atherogenic index of plasma was explained by copper, IL-10 (both positively), and magnesium (inversely).

CONCLUSION

UA is not only mediated by insulin resistance, atherogenicity, and immune disorders, but also by aberrations in the endogenous opioid system and trace elements as well as lowered antioxidant levels. Copper appears to play a key role in IR and atherogenicity.

Fisetin protects against streptozotocin-induced diabetic cardiomyopathy in rats by suppressing fatty acid oxidation and inhibiting protein kinase R

This study examined if the Fisetin against streptozotocin-induced diabetic cardiomyopathy (DC) in rats involves regulating cardiac metabolism and suppressing protein kinase R (PKR). Male rats were divided (12/groups) as control (non-diabetic), control + Fisetin, T1DM, and T1DM + Fisetin. Fisetin was administered orally at a final dose of 2.5 mg/kg for 12 weeks. In T1DM1-induced rats, Fisetin prevented heart and final body weights loss, lowered circulatory levels troponin I and creatinine kinase-MB (CK-MB), increased fasting insulin levels, and improved ventricular systolic and diastolic functions. It also preserved the structure of the cardiomyocytes and reduced oxidative stress, fibrosis, protein levels of transforming growth factor-β1 (TGF-β1), collagenase 1A, caspase-3, and the activation of JNK, p53, and p38 MAPK. In the control and diabetic rats, Fisetin attenuated fasting hyperglycaemia, the increases in glucose levels after the oral and insulin tolerance tests, and HOMA-IR. It also increased cardiac glucose oxidation by increasing the activity of private dehydrogenase (PDH), phosphofructokinase (PFK), protein levels of PPAR-α and suppressed cardiac inflammation by inhibiting NF-κB. These effects were associated with a reduction in the activity of PKR and subsequent increase in the activity of eeukaryotic initiation factor 2 (eIF2) with a parallel increase in protein levels of p67, a cellular inhibitor of PKR. In cultured cardiomyocytes, Fisetin, prevented high glucose (HG)-induced activation of PKR and reduction in p67, in a dose-dependent manner. However, the effect of Fisetin on PKR was diminished in LG and HG-treated cardiomyocytes with p67-siRNA. In conclusion, Fisetin protects against DC in rats by improving cardiac glucose metabolism and suppressing PKR.

Asymptomatic type 2 diabetes mellitus display a reduced myocardial deformation but adequate response during exercise

BACKGROUND AND PURPOSE

The development of myocardial fibrosis is a major complication of Type 2 diabetes mellitus (T2DM), impairing myocardial deformation and, therefore, cardiac performance. It remains to be established whether abnormalities in longitudinal strain (LS) exaggerate or only occur in well-controlled T2DM, when exposed to exercise and, therefore, cardiac stress. We therefore studied left ventricular LS at rest and during exercise in T2DM patients vs. healthy controls.

METHODS AND RESULTS

Exercise echocardiography was applied with combined breath-by-breath gas exchange analyses in asymptomatic, well-controlled (HbA1c: 6.9 ± 0.7%) T2DM patients (n = 36) and healthy controls (HC, n = 23). Left ventricular LS was assessed at rest and at peak exercise. Peak oxygen uptake (V̇O_2peak) and workload (W_peak) were similar between groups (p > 0.05). Diastolic (E, e'_s, E/e') and systolic function (left ventricular ejection fraction) were similar at rest and during exercise between groups (p > 0.05). LS (absolute values) was significantly lower at rest and during exercise in T2DM vs. HC (17.0 ± 2.9% vs. 19.8 ± 2% and 20.8 ± 4.0% vs. 23.3 ± 3.3%, respectively, p < 0.05). The response in myocardial deformation (the change in LS from rest up to peak exercise) was similar between groups (+ 3.8 ± 0.6% vs. + 3.6 ± 0.6%, in T2DM vs. HC, respectively, p > 0.05). Multiple regression revealed that HDL-cholesterol, fasted insulin levels and exercise tolerance accounted for 30.5% of the variance in response of myocardial deformation in the T2DM group (p = 0.002).

CONCLUSION

Myocardial deformation is reduced in well-controlled T2DM and despite adequate responses, such differences persist during exercise.

TRIAL REGISTRATION

NCT03299790, initially released 09/12/2017.

Insulin Resistance and Atherosclerosis: Implications for Insulin-Sensitizing Agents

Patients with type 2 diabetes mellitus (T2DM) are at high risk for macrovascular complications, which represent the major cause of mortality. Despite effective treatment of established cardiovascular (CV) risk factors (dyslipidemia, hypertension, procoagulant state), there remains a significant amount of unexplained CV risk. Insulin resistance is associated with a cluster of cardiometabolic risk factors known collectively as the insulin resistance (metabolic) syndrome (IRS). Considerable evidence, reviewed herein, suggests that insulin resistance and the IRS contribute to this unexplained CV risk in patients with T2DM. Accordingly, CV outcome trials with pioglitazone have demonstrated that this insulin-sensitizing thiazolidinedione reduces CV events in high-risk patients with T2DM. In this review the roles of insulin resistance and the IRS in the development of atherosclerotic CV disease and the impact of the insulin-sensitizing agents and of other antihyperglycemic medications on CV outcomes are discussed.

Nuclear miR-320 Mediates Diabetes-Induced Cardiac Dysfunction by Activating Transcription of Fatty Acid Metabolic Genes to Cause Lipotoxicity in the Heart

Supplemental Digital Content is available in the text.

Diabetes mellitus is often associated with cardiovascular complications, which is the leading cause of morbidity and mortality among patients with diabetes mellitus, but little is known about the mechanism that connects diabetes mellitus to the development of cardiovascular dysfunction.

Reduced hepatocellular lipid accumulation and energy metabolism in patients with long standing type 1 diabetes mellitus

The prevalence of obesity and metabolic syndrome increases in patients with type 1 diabetes mellitus (T1DM). In the general population this is linked with ectopic lipid accumulation in liver (HCL) and skeletal muscle (IMCL), representing hallmarks in the development of insulin resistance. Moreover, hepatic mitochondrial activity is lower in newly diagnosed patients with T1DM. If this precedes later development of diabetes related fatty liver disease is currently not known. This study aims to investigate energy metabolism in liver (k_ATP) and skeletal muscle (k_CK) and its impact on HCL, IMCL, cardiac fat depots and heart function in 10 patients with long standing T1DM compared to 11 well-matched controls by ³¹P/¹H magnetic resonance spectroscopy. HCL was almost 70% lower in T1DM compared to controls (6.9 ± 5% vs 2.1 ± 1.3%; p = 0.030). Also k_ATP was significantly reduced (0.33 ± 0.1 s^-1 vs 0.17 ± 0.1 s^-1; p = 0.018). In T1DM, dose of basal insulin strongly correlated with BMI (r = 0.676, p = 0.032) and HCL (r = 0.643, p = 0.045), but not with k_ATP. In the whole cohort, HCL was significantly associated with BMI (r = 0.615, p = 0.005). In skeletal muscle k_CK was lower in patients with T1DM (0.25 ± 0.05 s^-1 vs 0.31 ± 0-04 s^-1; p = 0.039). No significant differences were found in IMCL. Cardiac fat depots as well as heart function were not different. Our results in patients with long standing T1DM show that HCL is lower compared to matched controls, despite reduced energy metabolism in liver and skeletal muscle.

Gliptin therapy reduces hepatic and myocardial fat in type 2 diabetic patients

BACKGROUND

Increased hepatic fat and cardiac fat are common in patients with type 2 diabetes mellitus (T2DM) and are associated with a greater risk of liver fibrosis and cardiovascular (CV) events. Sex-specific differences of dipeptidyl peptidase-four (DPP-4) inhibitor effects on hepatic (HCL) and myocardial fat content (MYCL) have not yet been evaluated.

METHOD

Forty-one T2DM patients (20 male, 21 female) received a gliptin add-on therapy if HbA1c goals were not reached under metformin monotherapy. They underwent cardiac and liver magnetic resonance tomography and spectroscopy before and 6 months after therapy initiation. Plasma samples were analysed for the growth differentiation factor 15 (GDF-15), a novel marker for cardiovascular risk.

RESULTS

Thirty-eight patients on gliptin therapy completed the study. We observed a positive correlation between MYCL and HCL before therapy (R = 0·41, P = 0·05). After 6 months of therapy, we noticed a significant weight reduction in women only (P = 0·02) whereas waist circumference decreased similarly in both sexes. HbA1c sunk significantly in both sexes (P = 0·002). HCL decreased significantly (P = 0·0004), with women featuring higher basal HCL (P < 0·05). MYCL decreased in women only (P = 0·01) and GDF-15 comparably in both sexes (P < 0·05).

CONCLUSIONS

6 months of DPP-4-therapy led to a significant overall decrease in HCL and body weight such as a reduction of MYCL only in women. This preliminary data set could implicate that gliptin may be a feasible therapy option in fatty liver patients with diabetes potentially including positive effects on cardiovascular function particularly in women.

Lipotoxicity in Obesity: Benefit of Olive Oil

The clinical implication of Lipotoxicity in obesity derives primarily from its potential to progress to insulin resistance, endothelial dysfunction and atherosclerosis. Olive oil rich diet decrease accumulation of triglyceride in the liver, improved postprandial triglyceride levels, improve glucose and GLP-1 response in insulin resistant subjects, and up regulate GLUT-2 expression in the liver. The exact molecular mechanism is unknown but, decreasing NFkB activation, decreasing LDL oxidation and improving insulin resistance by less production of inflammatory cytokines (TNF-a, IL-6) and improvement of kinases JNK-mediated phosphorylation of IRS-1 are the principle mechanisms. The beneficial effect of the Mediterranean diet derived from monounsaturated fatty acids (MUFA), mainly from olive oil. In this review we document lipotoxicity in obesity and the benefit of olive oil.

Association of pulse pressure with left ventricular geometry and function in elderly nonhypertensive patients with diabetes: A 3D speckle tracking echocardiography study

PURPOSE

The aims of this study were to investigate and compare the left ventricular (LV) geometry and function in elderly nonhypertensive type 2 diabetic patients with normal (NPP, <60 mm Hg) and with high (HPP, ≥60 mmHg) 24-hour pulse pressure, and to explore the independent predictors of LV strain values in these patients.

METHODS

A total of 76 elderly nonhypertensive type 2 diabetic patients with normal (≥55%) LV ejection fraction (LVEF) were included, 36 of whom had HPP. The control group included 40 age- and sex-matched healthy volunteers with normal NPP. Conventional echocardiography and three-dimensional speckle-tracking echocardiography (3DSTE) were performed and LV global longitudinal strain (GLS), global circumferential strain (GCS), global area strain (GAS), and global radial strain (GRS) were measured.

RESULTS

Significant differences in the two-dimensional LV geometry were found among the three groups (p = 0.015), and concentric geometry was most prevalent in the diabetic patients with HPP. The diabetic patients with NPP only showed significantly lower GLS than the controls (p < 0.05). However, the diabetic patients with HPP showed significantly lower LVEF and severely lower strain values in all directions than the controls and the diabetic patients with NPP (p < 0.01or p < 0.05 or p < 0.001). Fasting plasma glucose, HPP, and body mass index were independently associated with all strain parameters in diabetic patients.

CONCLUSIONS

The combination of conventional echocardiography and 3DSTE could detect LV subclinical abnormalities in nonhypertensive type 2 diabetic patients with NPP and HPP. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:416-425, 2017.

Heart, lipids and hormones

Cardiovascular disease is the leading cause of death in general population. Besides well-known risk factors such as hypertension, impaired glucose tolerance and dyslipidemia, growing evidence suggests that hormonal changes in various endocrine diseases also impact the cardiac morphology and function. Recent studies highlight the importance of ectopic intracellular myocardial and pericardial lipid deposition, since even slight changes of these fat depots are associated with alterations in cardiac performance. In this review, we overview the effects of hormones, including insulin, thyroid hormones, growth hormone and cortisol, on heart function, focusing on their impact on myocardial lipid metabolism, cardiac substrate utilization and ectopic lipid deposition, in order to highlight the important role of even subtle hormonal changes for heart function in various endocrine and metabolic diseases.

Saturated palmitic acid induces myocardial inflammatory injuries through direct binding to TLR4 accessory protein MD2

Obesity increases the risk for a number of diseases including cardiovascular diseases and type 2 diabetes. Excess saturated fatty acids (SFAs) in obesity play a significant role in cardiovascular diseases by activating innate immunity responses. However, the mechanisms by which SFAs activate the innate immune system are not fully known. Here we report that palmitic acid (PA), the most abundant circulating SFA, induces myocardial inflammatory injury through the Toll-like receptor 4 (TLR4) accessory protein MD2 in mouse and cell culture experimental models. Md2 knockout mice are protected against PA- and high-fat diet-induced myocardial injury. Studies of cell surface binding, cell-free protein–protein interactions and molecular docking simulations indicate that PA directly binds to MD2, supporting a mechanism by which PA activates TLR4 and downstream inflammatory responses. We conclude that PA is a crucial contributor to obesity-associated myocardial injury, which is likely regulated via its direct binding to MD2.

The free fatty acid-mediated inflammatory activities are regulated through TLR4. Here the authors show that palmitic acid binds to MD2, initiating complex formation with TLR4, recruitment of MyD88, and subsequent activation of pro-inflammatory molecules, and that MD2 blockade protects against diet-induced cardiac dysfunction.

Suppression of plasma free fatty acids reduces myocardial lipid content and systolic function in type 2 diabetes

BACKGROUND AND AIM

Type 2 diabetes (T2DM) is closely associated with the development of heart failure, which might be related with impaired substrate metabolism and accumulation of myocardial lipids (MYCL). The aim of this study was to investigate the impact of an acute pharmacological inhibition of adipose tissue lipolysis leading to reduced availability of circulating FFA on MYCL and heart function in T2DM.

METHODS AND RESULTS

8 patients with T2DM (Age: 56 ± 11; BMI: 28 ± 3.5 kg/m(2); HbA1c: 7.29 ± 0.88%) were investigated on two study days in random order. Following administration of Acipimox or Placebo MYCL and heart function were measured by (1)H-magnetic-resonance-spectroscopy and tomography at baseline, at 2 and at 6 h. Acipimox reduced circulating FFA by -69% (p < 0.001), MYCL by -39 ± 41% (p < 0.001) as well as systolic heart function (Ejection Fraction (EF): -13 ± 8%, p = 0.025; Cardiac Index: -16 ± 15%, p = 0.063 compared to baseline). Changes in plasma FFA concentrations strongly correlated with changes in MYCL (r = 0.707; p = 0.002) and EF (r = 0.651; p = 0.006). Diastolic heart function remained unchanged.

CONCLUSIONS

Our results indicate, that inhibition of adipose tissue lipolysis is associated with a rapid depletion of MYCL-stores and reduced systolic heart function in T2DM. These changes were comparable to those previously found in insulin sensitive controls. MYCL thus likely serve as a readily available energy source to cope with short-time changes in FFA availability.

Pericardial- Rather than Intramyocardial Fat Is Independently Associated with Left Ventricular Systolic Heart Function in Metabolically Healthy Humans

Background

Obesity is a major risk factor to develop heart failure, in part due to possible lipotoxic effects of increased intramyocardial (MYCL) and/or local or paracrine effects of pericardial (PERI) lipid accumulation. Recent evidence suggests that MYCL is highly dynamic and might rather be a surrogate marker for disturbed energy metabolism than the underlying cause of cardiac dysfunction. On the other hand, PERI might contribute directly by mechanic and paracrine effects. Therefore, we hypothesized that PERI rather than MYCL is associated with myocardial function.

Methods

To avoid potential confounding of metabolic disease 31 metabolically healthy subjects (age: 29±10yrs; BMI: 23±3kg/m²) were investigated using ¹H-magnetic resonance spectroscopy and imaging. MYCL and PERI, as well as systolic and diastolic left ventricular heart function were assessed. Additionally, anthropometric data and parameters of glucose and lipid metabolism were analyzed. Correlation analysis was performed using Pearson’s correlation coefficient. Linear regression model was used to show individual effects of PERI and MYCL on myocardial functional parameters.

Results

Correlation analysis with parameters of systolic heart function revealed significant associations for PERI (Stroke Volume (SV): R = -0.513 p = 0.001; CardiacIndex (CI): R = -0.442 p = 0.014), but not for MYCL (SV: R = -0.233; p = 0.207; CI: R = -0.130; p = 0.484). No significant correlations were found for E/A ratio as a parameter of diastolic heart function. In multiple regression analysis CI was negatively predicted by PERI, whereas no impact of MYCL was observed in direct comparison.

Conclusions

Cardiac fat depots impact left ventricular heart function in a metabolically healthy population. Direct comparison of different lipid stores revealed that PERI is a more important predictor than MYCL for altered myocardial function.

Influence of breathing on the measurement of lipids in the myocardium by ¹H MR spectroscopy

The myocardium examination by MR spectroscopy is very challenging due to movements caused by the cardiac rhythm and breathing. The aim of the study was to investigate the influence of breathing on the quantitative measurement of lipid/water ratios in different groups of volunteers and different measuring protocols. We examined the lipid content of myocardium at 3T using the proton single voxel spectroscopy. Three protocols (free breathing, breath hold and the use of respiratory navigator) controlled by ECG were used for the examination of 42 adult volunteers including 14 free divers. Spectra were evaluated using jMRUI software. An average content of lipids in the healthy interventricular septum, gained by all protocols was equal to 0.6 %, which is in agreement with other published data. Based on the quality of examinations and the highest technical success, the best protocol seems to be the one containing a respiratory navigator since it is more acceptable by patients. Based on our results and the literature data we can conclude that MR spectroscopy is able to distinguish patients from controls only if their myocardial lipid content is higher than 1.6 % (mean value of lipids plus two standard deviations).

Myocardial Fat Accumulation Is Independent of Measures of Insulin Sensitivity

BACKGROUND

Myocardial steatosis, an independent predictor of diastolic dysfunction, is frequently present in type 2 diabetes mellitus. High free fatty acid flux, hyperglycemia, and hyperinsulinemia may play a role in myocardial steatosis. There are no prior studies examining the relationship between insulin sensitivity (antilipolytic and glucose disposal actions of insulin) and cardiac steatosis.

OBJECTIVE

Using a cross-sectional study design of individuals with and without metabolic syndrome (MetSyn), we examined the relationships between cardiac steatosis and the sensitivity of the antilipolytic and glucose disposal actions of insulin.

METHODS

Pericardial fat (PF) volume, intramyocardial and hepatic fat (MF and HF) content, visceral fat (VF) and sc fat content were assessed by magnetic resonance imaging in 77 subjects (49 without MetSyn and 28 with MetSyn). In a subset of the larger cohort (n = 52), peripheral insulin sensitivity index (SI) and adipocyte insulin sensitivity (Adipo-SI) were determined from an insulin-modified frequently sampled iv glucose tolerance test. The Quantitative Insulin Sensitivity Check Index was used as a surrogate for hepatic insulin sensitivity.

RESULTS

Individuals with the MetSyn had significantly higher body mass index, total body fat, and MF, PF, HF, and VF content. HF and VF, but not MF, were negatively correlated with the Quantitative Insulin Sensitivity Check Index, Adipo-SI, and SI. Stepwise regression revealed that waist circumference and serum triglyceride levels independently predicted MF and PF, respectively. Adipo-SI and serum triglyceride levels independently predict HF.

CONCLUSION

Myocardial steatosis is unrelated to hepatic, adipocyte, or peripheral insulin sensitivity. Although it is frequently observed in insulin-resistant subjects, further studies are necessary to identify and delineate pathogenic mechanisms that differentially affect cardiac and hepatic steatosis.

The Use of SGLT-2 Inhibitors in Type 2 Diabetes and Heart Failure

The concurrent management of type 2 diabetes mellitus (T2DM) and chronic congestive heart failure presents several therapeutic challenges. Of concern is that insulin and insulin-sensitizing medications detrimentally "flood" the heart with energy-providing substrates, including fats and glucose. In this population, treatment of T2DM should focus on the reduction of increased substrate supply. Sodium glucose cotransporter-2 (SGLT-2) inhibitors, a new class of antidiabetic medication, operate via this principle by blocking the reabsorption of glucose in the kidney and subsequently releasing glucose through the urine. In this review, we begin with an examination of the mechanisms of glucotoxicity and lipotoxicity in the heart. Then we analyze the potential role of SGLT-2 inhibitor therapy in patients with concurrent T2DM and chronic heart failure. Based on the available evidence, SGLT-2 inhibitors are safe and can be recommended to treat T2DM in patients with chronic heart failure and intact renal function. Further studies are in progress to assess long-term survival benefits.

Abnormal Myocardial Function Is Related to Myocardial Steatosis and Diffuse Myocardial Fibrosis in HIV-Infected Adults

BACKGROUND

Impaired cardiac function persists in the era of effective human immunodeficiency virus (HIV) therapy, although the etiology is unclear. We used magnetic resonance imaging (MRI) to measure intramyocardial lipid levels and fibrosis as possible contributors to HIV-associated myocardial dysfunction.

METHODS

A cross-sectional study of 95 HIV-infected and 30 matched-healthy adults, without known cardiovascular disease (CVD) was completed. Intramyocardial lipid levels, myocardial fibrosis, and cardiac function (measured on the basis of strain) were quantified by MRI.

RESULTS

Systolic function was significantly decreased in HIV-infected subjects as compared to controls (mean radial strain [±SD], 21.7 ± 8.6% vs 30.5 ± 14.2%; P = .004). Intramyocardial lipid level and fibrosis index were both increased in HIV-infected subjects as compared to controls (P ≤ .04 for both) and correlated with the degree of myocardial dysfunction measured by strain parameters. Intramyocardial lipid levels correlated positively with antiretroviral therapy duration and visceral adiposity. Further, impaired myocardial function was strongly correlated with increased monocyte chemoattractant protein 1 levels (r = 0.396, P = .0002) and lipopolysaccharide binding protein levels (r = 0.25, P = .02).

CONCLUSIONS

HIV-infected adults have reduced myocardial function as compared to controls in the absence of known CVD. Decreased cardiac function was associated with abnormal myocardial tissue composition characterized by increased lipid levels and diffuse myocardial fibrosis. Metabolic alterations related to antiretroviral therapy and chronic inflammation may be important targets for optimizing long-term cardiovascular health in HIV-infected individuals.

Free fatty acid availability is closely related to myocardial lipid storage and cardiac function in hypoglycemia counterregulation

Hypoglycemia, a major side effect of intensive glucose-lowering therapy, was recently linked to increased cardiovascular risk in patients with diabetes. Whether increased circulating free fatty acids (FFA) owing to catecholamine-induced lipolysis affect myocardial energy metabolism and thus link hypoglycemia to cardiac vulnerability is unclear. Therefore, this study investigated the impact of hypoglycemia counterregulation (± inhibition of lipolysis) on myocardial lipid content (MYCL) and left ventricular function in healthy subjects. Nine healthy men were studied in randomized order: 1) insulin/hypoglycemia test (IHT; ins+/aci-), 2) IHT during inhibition of adipose tissue lipolysis by acipimox (ins+/aci+), 3) normoglycemia with acipimox (ins-/aci+), and 4) normoglycemia with placebo (ins-/aci-). MYCL and cardiac function were assessed by employing magnetic resonance spectroscopy/imaging at baseline and at 2 and 6 h. In response to acute hypoglycemia, plasma FFA (P<0.0001) and ejection fraction (EF; from 63.2±5.5 to 69.6±6.3%, P=0.0001) increased significantly and were tightly correlated with each other (r=0.68, P=0.0002); this response was completely blunted by inhibition of adipose tissue lipolysis. In the presence of normoglycemia, inhibition of lipolysis was associated with a drop in EF (from 59.2±5.5 to 53.9±6.9%,P=0.005) and a significant decrease in plasma FFA, triglycerides, and MYCL (by 48.5%, P=0.0001). The present data indicate that an intact interorgan cross-talk between adipose tissue and the heart is a prerequisite for catecholamine-mediated myocardial contractility and preservation of myocardial lipid stores in response to acute hypoglycemia.

Insulin resistance as a physiological defense against metabolic stress: implications for the management of subsets of type 2 diabetes

Stratifying the management of type 2 diabetes (T2D) has to take into account marked variability in patient phenotype due to heterogeneity in its pathophysiology, different stages of the disease process, and multiple other patient factors including comorbidities. The focus here is on the very challenging subgroup of patients with T2D who are overweight or obese with insulin resistance (IR) and the most refractory hyperglycemia due to an inability to change lifestyle to reverse positive energy balance. For this subgroup of patients with T2D, we question the dogma that IR is primarily harmful to the body and should be counteracted at any cost. Instead we propose that IR, particularly in this high-risk subgroup, is a defense mechanism that protects critical tissues of the cardiovascular system from nutrient-induced injury. Overriding IR in an effort to lower plasma glucose levels, particularly with intensive insulin therapy, could therefore be harmful. Treatments that nutrient off-load to lower glucose are more likely to be beneficial. The concepts of "IR as an adaptive defense mechanism" and "insulin-induced metabolic stress" may provide explanation for some of the unexpected outcomes of recent major clinical trials in T2D. Potential molecular mechanisms underlying these concepts; their clinical implications for stratification of T2D management, particularly in overweight and obese patients with difficult glycemic control; and future research requirements are discussed.

Clustering effects on postprandial insulin secretion and sensitivity in response to meals with different fatty acid compositions

Dietary fatty acids play a role in glucose homeostasis. The aim of this study was to assess the individual relationship between dietary saturated (SFA), monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids with postprandial β-cell function and insulin sensitivity in subjects with normal and high fasting triglycerides. We assessed postprandial β-cell function (by the insulinogenic index and the ratio of the insulin to glucose areas under the time-concentration curve) and insulin sensitivity (by the oral glucose and the minimal model insulin sensitivity indices) over four nonconsecutive, randomly assigned, high-fat meals containing a panel of SFA (palmitic and stearic acids), MUFA (palmitoleic and oleic acids) and PUFA (linoleic and α-linolenic acids) in 14 subjects with normal and in 14 subjects with high fasting triglycerides. The proportions of each fatty acid in the meals and the values for surrogate measures of postprandial β-cell function and insulin sensitivity were subjected to a Pearson correlation and hierarchical cluster analysis, which revealed two classes of dietary fatty acids for regulating postprandial glucose homeostasis. We successfully discriminated the adverse effects of SFA palmitic acid from the beneficial effects of MUFA oleic acid on postprandial β-cell function (r ≥ 0.84 for SFA palmitic acid and r ≥ -0.71 for MUFA oleic acid; P < 0.05) and insulin sensitivity (r ≥ -0.92 for SFA palmitic acid and r ≥ 0.89 for MUFA oleic acid; P < 0.001) both in subjects with normal and high fasting triglycerides. In conclusion, dietary MUFA oleic acid, in contrast to SFA palmitic acid, favours the tuning towards better postprandial glycaemic control in subjects with normal and high fasting triglycerides.

No evidence of ectopic lipid accumulation in the pathophysiology of the acromegalic cardiomyopathy

CONTEXT

PATIENTS with acromegaly frequently display disturbances of glucose and lipid metabolism, which might contribute to their increased cardiovascular risk. Because insulin resistance and increased lipolysis have been linked to ectopic lipid deposition, altered lipid accumulation in the liver and the myocardium might contribute to metabolic and cardiac complications in these patients.

OBJECTIVE

The aim of this study was to investigate myocardial (MYCL) and hepatic lipid content (HCL), insulin sensitivity, and cardiac function in active acromegaly and after control of GH excess through transsphenoidal surgery.

PATIENTS

Ten patients with newly diagnosed acromegaly (ACRO_active) were compared with 12 healthy controls (CON), matched for age, body mass index, and gender. In seven patients GH excess was controlled, and they were compared with their active state.

METHODS

MYCL and HCL were assessed by (1)H-magnetic resonance spectroscopy, pericardial fat and cardiac function by (1)H-magnetic resonance imaging, and insulin sensitivity and secretion by an oral glucose tolerance test.

RESULTS

Although MYCL tended to be lower, HCL was significantly lower in ACRO_active compared with CON (HCL: 1.2% ± 1.2% vs 4.3% ± 3.5% of (1)H-magnetic resonance spectroscopy signal, P < .02). Parameters of systolic function and hypertrophy were significantly increased in ACRO_active compared with CON, as were insulin secretion and resistance. After the control of GH excess, HCL and MYCL remained unchanged, but pericardial fat was increased in the patients in whom GH excess was controlled (from 11.6 ± 5.5 to 14.7 ± 6.2 cm(2), P = .02).

CONCLUSION

Acromegaly represents a unique condition characterized by low myocardial and hepatic lipid content despite decreased insulin sensitivity, hyperinsulinemia, and hyperglycemia. Hence, ectopic lipid accumulation does not appear to contribute to cardiac morbidity, and increased lipid oxidation might counteract ectopic lipid accumulation in GH excess.

Independent effects of circulating glucose, insulin and NEFA on cardiac triacylglycerol accumulation and myocardial insulin resistance in a swine model

AIMS/HYPOTHESIS

Cardiac steatosis and myocardial insulin resistance elevate the risk of cardiac complications in obesity and diabetes. We aimed to disentangle the effects of circulating glucose, insulin and NEFA on myocardial triacylglycerol (TG) content and myocardial glucose uptake.

METHODS

Twenty-two pigs were stratified according to four protocols: low NEFA + low insulin (nicotinic acid), high NEFA + low insulin (fasting) and high insulin + low NEFA ± high glucose (hyperinsulinaemia-hyperglycaemia or hyperinsulinaemia-euglycaemia). Positron emission tomography, [U-(13)C]palmitate enrichment techniques and tissue biopsies were used to assess myocardial metabolism. Heart rate and rate-pressure product (RPP) were monitored.

RESULTS

Myocardial glucose extraction was increased by NEFA suppression and was similar in the hyperinsulinaemia-hypergylcaemia, hyperinsulinaemia-euglycaemia and nicotinic acid groups. Hyperglycaemia enhanced myocardial glucose uptake due to a mass action. Myocardial TG content was greatest in the fasting group, whereas hyperinsulinaemia had a mild effect. Heart rate and RPP increased in hyperinsulinaemia-euglycaemia, in which cardiac glycogen content was reduced. Heart rate correlated with myocardial TG and glycogen content.

CONCLUSIONS/INTERPRETATION

Elevated NEFA levels represent a powerful, self-sufficient promoter of cardiac TG accumulation and are a downregulator of myocardial glucose uptake, indicating that the focus of treatment should be to 'normalise' adipose tissue function to lower the risk of cardiac TG accumulation and myocardial insulin resistance. The observation that hyperinsulinaemia and nicotinic acid led to myocardial fuel deprivation provides a potential explanation for the cardiovascular outcomes reported in recent intensive glucose-lowering and NEFA-lowering clinical trials.

Cardiometabolic phenotyping of patients with familial hypocalcuric hypercalcemia

CONTEXT

Heterozygous inactivating mutations of the calcium-sensing receptor (CaSR) gene cause alterations in calcium metabolism [familial hypocalciuric hypercalcemia (FHH)]. In addition, calcium-sensing receptor is expressed in the myocardium and endocrine cells including pancreatic islets, enteroendocrine cells, and adipose tissue.

OBJECTIVE

To discern whether FHH is associated with cardiometabolic alterations of clinical significance, endocrine responses to systemic calcium stimulation and oral glucose tolerance tests were performed. Ectopic lipid deposition and heart function were assessed using magnetic resonance spectroscopy/imaging.

PARTICIPANTS

Eight FHH patients and nine controls matched for anthropometric characteristics (age 45 ± 18 y; body mass index 29 ± 4 vs 29 ± 6 kg/m(2)) were studied to determine cardiac function, ectopic and visceral lipid content, and insulin sensitivity and secretion.

RESULTS

Insulin sensitivity (clamp-like index: 4.5 ± 0.6 vs 4.3 ± 0.4 mg/kg · min), basal (insulin secretion rate: 266 ± 33 vs 218 ± 25 pmol/min), and glucose-stimulated β-cell function (adaptation index: 180.2 ± 12.2 vs 176.2 ± 17.4) as well as calcium-stimulated insulin secretion were comparable between FHH and controls, respectively. Ectopic lipid content in liver [3.75% (1.4%; 34%) vs 4.18% (0.9%; 28%)], soleus muscle (1.07% ± 0.38% vs 1.02% ± 0.56 %), and myocardium (0.39% ± 0.3% vs 0.32% ± 0.1 %), visceral and sc adipose tissue distribution (0.51 ± 0.16 vs 0.47 ± 0.17) as well as heart function (ejection fraction: 71.5% ± 8% vs 72.8% ± 8 %; E to A ratio: 1.4% ± 0.6% vs 1.3% ± 0.7%) were not different between the groups.

CONCLUSION

Despite comprehensive cardiometabolic phenotyping, no alterations in myocardial function, lipid distribution, or glucose metabolism were observed in FHH. Thus, FHH might reflect a laboratory finding without any relevant cardiometabolic alterations.

The effect of a single 2 h bout of aerobic exercise on ectopic lipids in skeletal muscle, liver and the myocardium

AIMS/HYPOTHESIS

Ectopic lipids are fuel stores in non-adipose tissues (skeletal muscle [intramyocellular lipids; IMCL], liver [intrahepatocellular lipids; IHCL] and heart [intracardiomyocellular lipids; ICCL]). IMCL can be depleted by physical activity. Preliminary data suggest that aerobic exercise increases IHCL. Data on exercise-induced changes on ICCL is scarce. Increased IMCL and IHCL have been related to insulin resistance in skeletal muscles and liver, whereas this has not been documented in the heart. The aim of this study was to assess the acute effect of aerobic exercise on the flexibility of IMCL, IHCL and ICCL in insulin-sensitive participants in relation to fat availability, insulin sensitivity and exercise capacity.

METHODS

Healthy physically active men were included. VO(2max) was assessed by spiroergometry and insulin sensitivity was calculated using the HOMA index. Visceral and subcutaneous fat were separately quantified by MRI. Following a standardised dietary fat load over 3 days, IMCL, IHCL and ICCL were measured using MR spectroscopy before and after a 2 h exercise session at 50-60% of VO(2max). Metabolites were measured during exercise.

RESULTS

Ten men (age 28.9 ± 6.4 years, mean ± SD; VO(2max) 56.3 ± 6.4 ml kg(-1) min(-1); BMI 22.75 ± 1.4 kg/m(2)) were recruited. A 2 h exercise session resulted in a significant decrease in IMCL (-17 ± 22%, p = 0.008) and ICCL (-17 ± 14%, p = 0.002) and increase in IHCL (42 ± 29%, p = 0.004). No significant correlations were found between the relative changes in ectopic lipids, fat availability, insulin sensitivity, exercise capacity or changes of metabolites during exercise.

CONCLUSIONS/INTERPRETATION

In this group, physical exercise decreased ICCL and IMCL but increased IHCL. Fat availability, insulin sensitivity, exercise capacity and metabolites during exercise are not the only factors affecting ectopic lipids during exercise.

Hyperglycemia induces embryopathy, even in the absence of systemic maternal diabetes: an in vivo test of the fuel mediated teratogenesis hypothesis

Embryonic exposure to excess circulating fuels is proposed to underlie diabetic embryopathy. To isolate the effects of hyperglycemia from the many systemic anomalies of diabetes, we infused 4 mg/min glucose into the left uterine artery of non-diabetic pregnant rats on gestation days (GD) 7-9. Right-sided embryos and dams exhibited no glucose elevation. Embryos were assessed on GD13, comparing the left versus right uterine horns. Hyperglycemic exposure increased rates of embryopathy, resorptions, and worsened embryopathy severity. By contrast, saline infusion did not affect any of these parameters. To assess for possible embryopathy susceptibility bias between uterine horns, separate dams were given retinoic acid (25mg/kg, a mildly embryopathic dose) systemically on GD7.5. The resultant embryopathy rates were equivalent between uterine horns. We conclude that hyperglycemia, even in the absence of systemic maternal diabetes, is sufficient to produce in vivo embryopathy during organogenesis.

Hepatic rather than cardiac steatosis relates to glucose intolerance in women with prior gestational diabetes

Background

Increased myocardial lipid accumulation has been described in patients with pre- and overt type 2 diabetes and could underlie the development of left-ventricular dysfunction in metabolic diseases (diabetic cardiomyopathy). Since women with prior gestational diabetes (pGDM) display a generally young population at high risk of developing diabetes and associated cardiovascular complications, we aimed to assess whether myocardial lipid accumulation can be detected at early stages of glucose intolerance and relates to markers of hepatic steatosis (Fatty Liver Index), cardiac function, insulin sensitivity and secretion.

Methods

Myocardial lipid content (MYCL), left-ventricular function (¹H-magnetic-resonance-spectroscopy and -imaging), insulin sensitivity/secretion (oral glucose tolerance test) and the fatty liver index (FLI) were assessed in 35 pGDM (45.6±7.0 years, 28.3±4.8 kg/m²) and 14 healthy control females (CON; 44.7±9.8 years, 26.1±2.5 kg/m²), matching for age and body-mass-index (each p>0.1).

Results

Of 35 pGDM, 9 displayed normal glucose tolerance (NGT), 6 impaired glucose regulation (IGR) and 20 had been already diagnosed with type 2 diabetes (T2DM). MYCL and cardiac function were comparable between pGDM and CON; in addition, no evidence of left-ventricular dysfunction was observed. MYCL was inversely correlated with the ejection fraction in T2DM (R = −0.45, p<0.05), while the FLI was tightly correlated with metabolic parameters (such as HbA1C, fasting plasma glucose and HDL-cholesterol) and rose along GT-groups.

Conclusions

There is no evidence of cardiac steatosis in middle-aged women with prior gestational diabetes, suggesting that cardiac complications might develop later in the time-course of diabetes and may be accelerated by the co-existence of further risk factors, whereas hepatic steatosis remains a valid biomarker for metabolic diseases even in this rather young female cohort.

Diabetic cardiomyopathy: Pathophysiology, diagnostic evaluation and management

Diabetes affects every organ in the body and cardiovascular disease accounts for two-thirds of the mortality in the diabetic population. Diabetes-related heart disease occurs in the form of coronary artery disease (CAD), cardiac autonomic neuropathy or diabetic cardiomyopathy (DbCM). The prevalence of cardiac failure is high in the diabetic population and DbCM is a common but underestimated cause of heart failure in diabetes. The pathogenesis of diabetic cardiomyopathy is yet to be clearly defined. Hyperglycemia, dyslipidemia and inflammation are thought to play key roles in the generation of reactive oxygen or nitrogen species which are in turn implicated. The myocardial interstitium undergoes alterations resulting in abnormal contractile function noted in DbCM. In the early stages of the disease diastolic dysfunction is the only abnormality, but systolic dysfunction supervenes in the later stages with impaired left ventricular ejection fraction. Transmitral Doppler echocardiography is usually used to assess diastolic dysfunction, but tissue Doppler Imaging and Cardiac Magnetic Resonance Imaging are being increasingly used recently for early detection of DbCM. The management of DbCM involves improvement in lifestyle, control of glucose and lipid abnormalities, and treatment of hypertension and CAD, if present. The role of vasoactive drugs and antioxidants is being explored. This review discusses the pathophysiology, diagnostic evaluation and management options of DbCM.

Combined acute hyperglycemic and hyperinsulinemic clamp induced profibrotic and proinflammatory responses in the kidney

Increase in matrix protein content in the kidney is a cardinal feature of diabetic kidney disease. While renal matrix protein content is increased by chronic hyperglycemia, whether it is regulated by acute elevation of glucose and insulin has not been addressed. In this study, we aimed to evaluate whether short duration of combined hyperglycemia and hyperinsulinemia, mimicking the metabolic environment of prediabetes and early type 2 diabetes, induces kidney injury. Normal rats were subjected to either saline infusion (control, n = 4) or 7 h of combined hyperglycemic-hyperinsulinemic clamp (HG+HI clamp; n = 6). During the clamp, plasma glucose and plasma insulin were maintained at about 350 mg/dl and 16 ng/ml, respectively. HG+HI clamp increased the expression of renal cortical transforming growth factor-β (TGF-β) and renal matrix proteins, laminin and fibronectin. This was associated with the activation of SMAD3, Akt, mammalian target of rapamycin (mTOR) complexes, and ERK signaling pathways and their downstream target events in the initiation and elongation phases of mRNA translation, an important step in protein synthesis. Additionally, HG+HI clamp provoked renal inflammation as shown by the activation of Toll-like receptor 4 (TLR4) and infiltration of CD68-positive monocytes. Urinary F2t isoprostane excretion, an index of renal oxidant stress, was increased in the HG+HI clamp rats. We conclude that even a short duration of hyperglycemia and hyperinsulinemia contributes to activation of pathways that regulate matrix protein synthesis, inflammation, and oxidative stress in the kidney. This finding could have implications for the control of short-term rises in blood glucose in diabetic individuals at risk of developing kidney disease.

Effects of short-term nutritional interventions on right ventricular function in healthy men

BACKGROUND

A physiological model of increased plasma nonesterified fatty acid (NEFA) levels result in myocardial triglyceride (TG) accumulation, which is related to cardiac dysfunction. A pathophysiological model of increased plasma NEFA levels result in hepatic steatosis, which has been linked to abnormal myocardial energy metabolism. Hepatic steatosis is accompanied by hepatic inflammation, reflected by plasma cholesteryl ester transfer protein (CETP) levels. The current study aimed to investigate effects of these models via different nutritional interventions on right ventricular (RV) function.

METHODS

Fifteen men (age 25.0±6.6 years) were included and underwent magnetic resonance imaging and spectroscopy in this prospective crossover intervention study. RV function, myocardial and hepatic TG content, and CETP levels were assessed on three occasions: after normal diet, very low-calorie diet (VLCD, physiological model) and high-fat high-energy (HFHE, pathophysiological model) diet (all 3-days diets, randomly ordered, washout phase at least 14 days).

RESULTS

VLCD induced a decrease in mean E deceleration by 27%. Myocardial TG content increased by 55%, whereas hepatic TG content decreased by 32%. Plasma CETP levels decreased by 14% (all P<0.05). HFHE diet induced a decrease in E/A by 19% (P<0.05). Myocardial TG content did not change, whereas hepatic TG content increased by 112% (P<0.01). Plasma CETP levels increased by 14% (P<0.05).

CONCLUSIONS

These findings show that RV diastolic function is impaired after short-term VLCD and HFHE diet in healthy men, respectively a physiological and a pathophysiological model of increased plasma NEFA levels. After short-term VLCD, myocardial lipotoxicity may be of importance in decreased RV diastolic function. RV diastolic dysfunction is accompanied by increased hepatic TG content and plasma CETP levels after short-term HFHE diet, suggesting that systemic inflammation reflecting local macrophage infiltration in the heart may be involved in RV dysfunction.

Failing heart of patients with type 2 diabetes mellitus can adapt to extreme short-term increases in circulating lipids and does not display features of acute myocardial lipotoxicity

BACKGROUND

Circulating lipid levels and myocardial lipid content (MyLC) is increased in type 2 diabetes mellitus. This may cause a state of lipotoxicity that compromises left ventricular function and aggravate heart failure. We investigated the relationship among circulating lipid levels, MyLC, and cardiac function together with the acute cardiac effects of high as opposed to low circulating free fatty acid (FFA) and triglyceride levels in patients with type 2 diabetes mellitus and heart failure.

METHODS AND RESULTS

Eighteen patients underwent 8-hour intralipid/heparin-infusion (high FFA) and hyperinsulinemic-euglycemic clamping (low FFA) in a randomized crossover-designed study. We applied magnetic resonance proton spectroscopy to measure MyLC. Cardiac function was assessed by advanced echocardiography, cardiopulmonary exercise, and MRI. MyLC correlated positively with circulating triglyceride (r=0.47; r(2)=0.22; P=0.003) and FFA (r=0.45; r(2)=0.20; P=0.001) levels and inversely with left ventricular ejection fraction (r=-0.54; r(2)=0.29; P=0.004). Circulating FFA concentrations differed between study arms (0.05 ± 0.04 mmol/L [low FFA] versus 1.04 ± 0.27 mmol/L [high FFA]; P<0.001) and MyLC increased from 0.78 ± 0.59% (low FFA) to 1.16 ± 0.73% (high FFA; P<0.01). Resting left ventricular ejection fraction and global strain did not differ between high and low FFA, whereas resting systolic mitral plane velocity (S'max) was highest during high FFA (3.6±0.8 cm/s [low FFA] versus 3.8±0.7 cm/s [high FFA]; P=0.02). Peak exercise capacity and oxygen consumption did not differ between the study arms, and neither did postexercise measurements of left ventricular ejection fraction, global strain, and S'max.

CONCLUSIONS

Our findings indicate that the failing heart of patients with type 2 diabetes mellitus can adapt to short-term extreme changes in circulating substrates and does not display features of acute myocardial lipotoxicity. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT01192373.

Mechanisms of lipotoxicity in the cardiovascular system

Cardiovascular diseases account for approximately one third of all deaths globally. Obese and diabetic patients have a high likelihood of dying from complications associated with cardiovascular dysfunction. Obesity and diabetes increase circulating lipids that upon tissue uptake, may be stored as triglyceride, or may be metabolized in other pathways, leading to the generation of toxic intermediates. Excess lipid utilization or activation of signaling pathways by lipid metabolites may disrupt cellular homeostasis and contribute to cell death, defining the concept of lipotoxicity. Lipotoxicity occurs in multiple organs, including cardiac and vascular tissues, and a number of specific mechanisms have been proposed to explain lipotoxic tissue injury. In addition, recent data suggests that increased tissue lipids may also be protective in certain contexts. This review will highlight recent progress toward elucidating the relationship between nutrient oversupply, lipotoxicity, and cardiovascular dysfunction. The review will focus in two sections on the vasculature and cardiomyocytes respectively.

Effects of insulin therapy on myocardial lipid content and cardiac geometry in patients with type-2 diabetes mellitus

Aims/Hypothesis

Recent evidence suggests a link between myocardial steatosis and diabetic cardiomyopathy. Insulin, as a lipogenic and growth-promoting hormone, might stimulate intramyocardial lipid (MYCL) deposition and hypertrophy. Therefore, the aim of the present study was to investigate the short-term effects of insulin therapy (IT) on myocardial lipid content and morphology in patients with T2DM.

Methods

Eighteen patients with T2DM were recruited (age 56±2 years; HbA1c: 10.5±0.4%). In 10 patients with insufficient glucose control under oral medication IT was initiated due to secondary failure of oral glucose lowering therapy (IT-group), while 8 individuals did not require additional insulin substitution (OT-group). In order to assess MYCL and intrahepatic lipid (IHLC) content as well as cardiac geometry and function magnetic resonance spectroscopy (MRS) and imaging (MRI) examinations were performed at baseline (IT and OT) and 10 days after initiation of IT. Follow up measurements took place 181±49 days after IT.

Results

Interestingly, basal MYCLs were 50% lower in IT- compared to OT-group (0.41±0.12 vs. 0.80±0.11% of water signal; p = 0.034). After 10 days of IT, an acute 80%-rise in MYCL (p = 0.008) was observed, while IHLC did not change. Likewise, myocardial mass (+13%; p = 0.004), wall thickness in end-diastole (+13%; p = 0.030) and concentricity, an index of cardiac remodeling, increased (+28%; p = 0.026). In the long-term MYCL returned to baseline, while IHCL significantly decreased (−31%; p = 0.000). No acute changes in systolic left ventricular function were observed.

Conclusions/Interpretation

The initiation of IT in patients with T2DM was followed by an acute rise in MYCL concentration and myocardial mass.

The role of cardiac fat in insulin resistance

PURPOSE OF REVIEW

To evaluate the relationship between cardiac fat accumulation and insulin resistance. We discuss the current knowledge regarding the different techniques for measuring, in vivo in humans, cardiac fat deposition, the effects of systemic and myocardial insulin resistance and the clinical relevance of the relation between atherosclerosis and cardiac fat in conditions of insulin resistance.

RECENT FINDINGS

In humans, fat accumulates mainly around the heart, as epicardial, perivascular and intrathoracic fat, but also inside the cardiomyocytes. All these cardiac fat depots have been shown to be markers of cardiac lipotoxicity, mitochondrial dysfunction, inflammation and local and systemic insulin resistance as well as of atherosclerosis and cardiac dysfunction.

SUMMARY

Although cardiac fat is associated with impairment in heart metabolism and cardiac dysfunction, the interplay among cardiac fat accumulation, insulin resistance and cardiac dysfunction remains to be fully established.