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

Effect of Dapagliflozin on Myocardial Insulin Sensitivity and Perfusion: Rationale and Design of The DAPAHEART Trial

INTRODUCTION

Sodium-glucose co-transporter-2 (SGLT-2) inhibitors have been shown to have beneficial effects on various cardiovascular (CV) outcomes in patients with type 2 diabetes (T2D) in primary prevention and in those with a high CV risk profile. However, the mechanism(s) responsible for these CV benefits remain elusive and unexplained. The aim of the DAPAHEART study will be to demonstrate that treatment with SGLT-2 inhibitors is associated with greater myocardial insulin sensitivity in patients with T2D, and to determine whether this improvement can be attributed to a decrease in whole-body (and tissue-specific) insulin resistance and to increased myocardial perfusion and/or glucose uptake. We will also determine whether there is an appreciable degree of improvement in myocardial-wall conditions subtended by affected and non-affected coronary vessels, and if this relates to changes in left ventricular function.

METHODS

The DAPAHEART trial will be a phase III, single-center, randomized, two-arm, parallel-group, double-blind, placebo-controlled study. A cohort of 52 T2D patients with stable coronary artery disease (without any previous history of myocardial infarction, with or without previous percutaneous coronary intervention), with suboptimal glycemic control (glycated hemoglobin [HbA1c] 7-8.5%) on their current standard of care anti-hyperglycemic regimen, will be randomized in a 1:1 ratio to dapagliflozin or placebo. The primary outcome is to detect changes in myocardial glucose uptake from baseline to 4 weeks after treatment initiation. The main secondary outcome will be changes in myocardial blood flow, as measured by 13N-ammonia positron emission tomography/computed tomography (PET/CT). Other outcomes include cardiac function, glucose uptake in skeletal muscle, adipose tissue, liver, brain and kidney, as assessed by fluorodeoxyglucose (FDG) PET-CT imaging during hyperinsulinemic-euglycemic clamp; pericardial, subcutaneous and visceral fat, and browning as observed on CT images during FDG PET-CT studies; systemic insulin sensitivity, as assessed by hyperinsulinemic-euglycemic clamp, glycemic control, urinary glucose output; and microbiota modification.

DISCUSSION

SGLT-2 inhibitors, in addition to their insulin-independent plasma glucose-lowering effect, are able to directly (substrate availability, fuel utilization, insulin sensitivity) as well as indirectly (cardiac after-load reduction, decreased risk factors for heart failure) affect myocardial functions. Our study will provide novel insights into how these drugs exert CV protection in a diabetic population.

TRIAL REGISTRATION

EudraCT No. 2016-003614-27; ClinicalTrials.gov Identifier: NCT03313752.

Run for your life: can exercise be used to effectively target GLUT4 in diabetic cardiac disease?

The global incidence, associated mortality rates and economic burden of diabetes are now such that it is considered one of the most pressing worldwide public health challenges. Considerable research is now devoted to better understanding the mechanisms underlying the onset and progression of this disease, with an ultimate aim of improving the array of available preventive and therapeutic interventions. One area of particular unmet clinical need is the significantly elevated rate of cardiomyopathy in diabetic patients, which in part contributes to cardiovascular disease being the primary cause of premature death in this population. This review will first consider the role of metabolism and more specifically the insulin sensitive glucose transporter GLUT4 in diabetic cardiac disease, before addressing how we may use exercise to intervene in order to beneficially impact key functional clinical outcomes.

The role of glucose, insulin and NEFA in regulating tissue triglyceride accumulation: Substrate cooperation in adipose tissue versus substrate competition in skeletal muscle

BACKGROUND AND AIMS

Metabolic factors initiating adipose tissue expansion and ectopic triglyceride accumulation are not completely understood. We aimed to investigate the independent role of circulating glucose, NEFA and insulin on glucose and NEFA uptake, and lipogenesis in skeletal muscle and subcutaneous adipose tissue (SCAT).

METHODS AND RESULTS

Twenty-two pigs were stratified according to four protocols: 1) and 2) low NEFA + high insulin ± high glucose (hyperinsulinaemia-hyperglycaemia or hyperinsulinaemia-euglycaemia), 3) high NEFA + low insulin (fasting), 4) low NEFA + low insulin (nicotinic acid). Positron emission tomography with [¹⁸F]fluoro-2-deoxyglucose and [¹¹C]acetate, was combined with [¹⁴C]acetate and [U-¹³C]palmitate enrichment techniques to assess glucose and lipid metabolism. Hyperinsulinaemia increased glucose extraction, whilst hyperglycaemia enhanced glucose uptake in skeletal muscle and SCAT. In SCAT, during hyperglycaemia, elevated glucose uptake was accompanied by greater [U-¹³C]palmitate-TG enrichment compared to the other groups, and by a 39% increase in de novo lipogenesis (DNL) compared to baseline, consistent with a 70% increment in plasma lipogenic index. Conversely, in skeletal muscle, [U-¹³C]palmitate-TG enrichment was higher after prolonged fasting.

CONCLUSIONS

Our data show the necessary role of hyperglycaemia-hyperinsulinaemia vs euglycaemia-hyperinsulinaemia in promoting expansion of TG stores in SCAT, by the consensual elevation in plasma NEFA and glucose uptake and DNL. In contrast, skeletal muscle NEFA uptake for TG synthesis is primarily driven by circulating NEFA levels. These results suggest that a) prolonged fasting or dietary regimens enhancing lipolysis might promote muscle steatosis, and b) the control of glucose levels, in association with adequate energy balance, might contribute to weight loss.

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.

Biomarkers and prediction of myocardial triglyceride content in non-diabetic men

BACKGROUND AND AIMS

Lipid oversupply to cardiomyocytes or decreased utilization of lipids leads to cardiac steatosis. We aimed to examine the role of different circulating metabolic biomarkers as predictors of myocardial triglyceride (TG) content in non-diabetic men.

METHODS AND RESULTS

Myocardial and hepatic TG contents were measured with 1.5 T magnetic resonance (MR) spectroscopy, and LV function, visceral adipose tissue (VAT), abdominal subcutaneous tissue (SAT), epicardial and pericardial fat by MR imaging in 76 non-diabetic men. Serum concentration of circulating metabolic biomarkers [adiponectin, leptin, adipocyte-fatty acid binding protein 4 (A-FABP 4), resistin, and lipocalin-2] including β-hydroxybuturate (β-OHB) were measured. Subjects were stratified by tertiles of myocardial TG into low, moderate, and high myocardial TG content groups. Concentrations of β-OHB were lower (p = 0.003) and serum levels of A-FABP 4 were higher (p < 0.001) in the group with high myocardial TG content compared with the group with low myocardial TG content. β-OHB was negatively correlated with myocardial TG content (r = -0.316, p = 0.006), whereas A-FABP 4 was not correlated with myocardial TG content (r = 0.192, p = 0.103). In multivariable analyses β-OHB and plasma glucose levels were the best predictors of myocardial TG content independently of VAT and hepatic TG content. The model explained 58.8% of the variance in myocardial TG content.

CONCLUSION

Our data showed that β-OHB and fasting glucose were the best predictors of myocardial TG content in non-diabetic men. These data suggest that hyperglycemia and alterations in lipid oxidation may be associated with cardiac steatosis in humans.

Seven-Day Caloric and Saturated Fat Restriction Increases Myocardial Dietary Fatty Acid Partitioning in Impaired Glucose-Tolerant Subjects

Subjects with impaired glucose tolerance (IGT) have increased myocardial partitioning of dietary fatty acids (DFAs) with left ventricular dysfunction, both of which are improved by modest weight loss over 1 year induced by lifestyle changes. Here, we determined the effects of a 7-day hypocaloric diet (-500 kcal/day) low in saturated fat (<7% of energy) (LOWCAL study) versus isocaloric with the usual amount saturated fat (∼10% of energy) diet (ISOCAL) on DFA metabolism in subjects with IGT. Organ-specific DFA partitioning and cardiac and hepatic DFA fractional uptake rates were measured in 15 IGT subjects (7 males/8 females) using the oral 14(R,S)-[18F]-fluoro-6-thia-heptadecanoic acid positron emission tomography method after 7 days of an ISOCAL diet versus a LOWCAL diet using a randomized crossover design. The LOWCAL diet led to reductions in weight and postprandial insulin area under the curve. Myocardial DFA partitioning over 6 h was increased after the LOWCAL diet (2.3 ± 0.1 vs. 1.9 ± 0.2 mean standard uptake value, P < 0.04). However, the early (90-120 min) myocardial DFA fractional uptake was unchanged after the LOWCAL diet (0.055 ± 0.025 vs. 0.046 ± 0.009 min(-1), P = 0.7). Liver DFA partitioning was unchanged, but liver fractional uptake of DFA tended to be increased. Very short-term caloric and saturated fat dietary restrictions do not lead to the same changes in organ-specific DFA metabolism as those associated with weight loss in subjects with IGT.