Novel Effects of the Gastrointestinal Hormone Secretin on Cardiac Metabolism and Renal Function

The cardiac benefits of gastrointestinal hormones have been of interest in recent years. The aim of this study was to explore the myocardial and renal effects of the gastrointestinal hormone secretin in the GUTBAT trial (NCT03290846). A placebo-controlled crossover study was conducted on 15 healthy males in fasting conditions, where subjects were blinded to the intervention. Myocardial glucose uptake was measured with [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG) positron emission tomography. Kidney function was measured with [18F]FDG renal clearance and estimated glomerular filtration rate (eGFR). Secretin increased myocardial glucose uptake compared to placebo (secretin vs. placebo, mean + standard deviation, 15.5 + 7.4 vs. 9.7 + 4.9 μmol/100g/min, 95% confidence interval (CI) [2.2, 9.4], p=0.004). Secretin also increased [18F]FDG renal clearance (44.5 + 5.4 vs. 39.5 + 8.5 ml/min, 95%CI[1.9, 8.1], p=0.004) and eGFR was significantly increased from baseline after secretin, compared to placebo (17.8 + 9.8 vs. 6.0 + 5.2 Δml/min/1.73m2, 95%CI[6.0, 17.6], p=0.001). Our results implicate that secretin increases heart work and renal filtration, making it an interesting drug candidate for future studies in heart and kidney failure.

Sleeve Gastrectomy Ameliorates Diabetes-Induced Cardiac Hypertrophy Correlates With the MAPK Signaling Pathway

Background: Cardiac hypertrophy as a main pathological manifestation of diabetic cardiomyopathy (DCM), is a significant complication of diabetes. Bariatric surgery has been proven to relieve DCM; however, whether it can alleviate diabetes-induced cardiac hypertrophy is undefined.Methods: Diabetic and obese rats were performed sleeve gastrectomy (SG) after having diabetes for 16weeks. The rats were euthanized 8weeks after SG. Metabolic parameters, heart function parameters, myocardial glucose uptake, morphometric and histological changes, and the expression level of mitogen-activated protein kinases (MAPKs) were determined and compared among the control group (CON group), diabetes mellitus group (DM group), sham operation group (SHAM group), and SG group.Results: Compared with the SHAM group, the blood glucose, body weight, insulin resistance, and other metabolic parameters were significantly improved in the SG group. There was also a marked improvement in myocardial morphometric and histological parameters after SG. Furthermore, the myocardial glucose uptake and heart function were reversed after SG. Additionally, the phosphorylation of MAPKs was inhibited after SG, including p38 MAPKs, c-Jun N-terminal kinases (JNKs), and extracellular signal-regulated kinases 1/2 (ERK1/2). The expression of DUSP6, which dephosphorylates ERK1/2, was upregulated after SG. These findings suggest that SG ameliorated diabetes-induced cardiac hypertrophy correlates with the MAPK signaling pathway.Conclusion: These results showed that diabetes-induced cardiac hypertrophy was ameliorated after SG was closely related to the inhibition of the MAPK signaling pathway and upregulation of DUSP6. Therefore, this study provides a novel strategy for treating diabetes-induced cardiac hypertrophy.

BH4 Increases nNOS Activity and Preserves Left Ventricular Function in Diabetes

Rationale: In diabetic patients, heart failure with predominant left ventricular (LV) diastolic dysfunction is a common complication for which there is no effective treatment. Oxidation of the nitric oxide synthase (NOS) co-factor tetrahydrobiopterin (BH4) and dysfunctional NOS activity have been implicated in the pathogenesis of the diabetic vascular and cardiomyopathic phenotype. Objective: Using mice models and human myocardial samples, we evaluated whether and by which mechanism increasing myocardial BH4 availability prevented or reversed LV dysfunction induced by diabetes. Methods and Results: In contrast to the vascular endothelium, BH4 levels, superoxide production and NOS activity (by liquid chromatography) did not differ in the LV myocardium of diabetic mice or in atrial tissue from diabetic patients. Nevertheless, the impairment in both cardiomyocyte relaxation and [Ca2+]i decay and in vivo LV function (echocardiography and tissue Doppler) that developed in wild type mice (WT) 12 weeks post-DM induction (streptozotocin, 42-45mg/kg) was prevented in mice with elevated myocardial BH4 content secondary to overexpression of GTP-cyclohydrolase 1 (mGCH1-Tg) and reversed in WT mice receiving oral BH4 supplementation from the 12th to the 18th week after DM induction. The protective effect of BH4 was abolished by CRISPR/Cas9-mediated knockout of neuronal NOS (nNOS) in mGCH1-Tg. In HEK cells, S-nitrosoglutathione led to a PKG-dependent increase in plasmalemmal density of the insulin-independent glucose transporter, GLUT-1. In cardiomyocytes, mGCH1 overexpression induced a NO/sGC/PKG-dependent increase in glucose uptake via GLUT-1, which was instrumental in preserving mitochondrial creatine kinase activity, oxygen consumption rate, LV energetics (by 31P MRS) and myocardial function. Conclusions: We uncovered a novel mechanism whereby myocardial BH4 prevents and reverses LV diastolic and systolic dysfunction associated with diabetes via a nNOS-mediated increase in non-insulin dependent myocardial glucose uptake and utilization. These findings highlight the potential of GCH1/BH4-based therapeutics in human diabetic cardiomyopathy.

SGLT2 Inhibition Does Not Affect Myocardial Fatty Acid Oxidation or Uptake, But Reduces Myocardial Glucose Uptake and Blood Flow in Individuals With Type 2 Diabetes– a Randomized Double-Blind, Placebo-Controlled Crossover Trial

Sodium-glucose cotransporter 2 (SGLT2) inhibition reduces cardiovascular morbidity and mortality in individuals with type 2 diabetes. Beneficial effects have been attributed to increased ketogenesis, reduced cardiac fatty acid oxidation and diminished cardiac oxygen consumption. We therefore studied whether SGLT2 inhibition altered cardiac oxidative substrate consumption, efficiency, and perfusion. <p>13 individuals with type 2 diabetes were studied after four weeks treatment with empagliflozin and placebo in a randomized, double-blind, placebo-controlled crossover study. Myocardial palmitate and glucose uptake were measured with ¹¹C-palmitate and ¹⁸F-FDG PET/CT. Oxygen consumption and myocardial external efficiency (MEE) were measured with ¹¹C-acetate PET/CT. Resting and adenosine stress myocardial blood flow (MBF) and myocardial flow reserve (MFR) were measured using ¹⁵O-H₂O PET/CT. </p> <p>Empagliflozin did not affect myocardial FFA uptake but reduced myocardial glucose uptake by 57% (p<0.001). Empagliflozin did not change myocardial oxygen consumption or MEE. Empagliflozin reduced resting MBF by 13% (p<0.01), but did not significantly affect stress MBF or MFR.</p> <p>In conclusion, SGLT2 inhibition did not affect myocardial FFA uptake, but channeled myocardial substrate utilization from glucose towards other sources and reduced resting MBF. However, the observed metabolic and hemodynamic changes were modest and most likely contribute only partially to the cardioprotective effect of SGLT2 inhibition. </p>

SGLT2 Inhibition Does Not Affect Myocardial Fatty Acid Oxidation or Uptake, But Reduces Myocardial Glucose Uptake and Blood Flow in Individuals With Type 2 Diabetes– a Randomized Double-Blind, Placebo-Controlled Crossover Trial

Sodium-glucose cotransporter 2 (SGLT2) inhibition reduces cardiovascular morbidity and mortality in individuals with type 2 diabetes. Beneficial effects have been attributed to increased ketogenesis, reduced cardiac fatty acid oxidation and diminished cardiac oxygen consumption. We therefore studied whether SGLT2 inhibition altered cardiac oxidative substrate consumption, efficiency, and perfusion. <p>13 individuals with type 2 diabetes were studied after four weeks treatment with empagliflozin and placebo in a randomized, double-blind, placebo-controlled crossover study. Myocardial palmitate and glucose uptake were measured with ¹¹C-palmitate and ¹⁸F-FDG PET/CT. Oxygen consumption and myocardial external efficiency (MEE) were measured with ¹¹C-acetate PET/CT. Resting and adenosine stress myocardial blood flow (MBF) and myocardial flow reserve (MFR) were measured using ¹⁵O-H₂O PET/CT. </p> <p>Empagliflozin did not affect myocardial FFA uptake but reduced myocardial glucose uptake by 57% (p<0.001). Empagliflozin did not change myocardial oxygen consumption or MEE. Empagliflozin reduced resting MBF by 13% (p<0.01), but did not significantly affect stress MBF or MFR.</p> <p>In conclusion, SGLT2 inhibition did not affect myocardial FFA uptake, but channeled myocardial substrate utilization from glucose towards other sources and reduced resting MBF. However, the observed metabolic and hemodynamic changes were modest and most likely contribute only partially to the cardioprotective effect of SGLT2 inhibition. </p>

SGLT2 Inhibition Does Not Affect Myocardial Fatty Acid Oxidation or Uptake, But Reduces Myocardial Glucose Uptake and Blood Flow in Individuals With Type 2 Diabetes– a Randomized Double-Blind, Placebo-Controlled Crossover Trial

Sodium-glucose cotransporter 2 (SGLT2) inhibition reduces cardiovascular morbidity and mortality in individuals with type 2 diabetes. Beneficial effects have been attributed to increased ketogenesis, reduced cardiac fatty acid oxidation and diminished cardiac oxygen consumption. We therefore studied whether SGLT2 inhibition altered cardiac oxidative substrate consumption, efficiency, and perfusion. <p>13 individuals with type 2 diabetes were studied after four weeks treatment with empagliflozin and placebo in a randomized, double-blind, placebo-controlled crossover study. Myocardial palmitate and glucose uptake were measured with ¹¹C-palmitate and ¹⁸F-FDG PET/CT. Oxygen consumption and myocardial external efficiency (MEE) were measured with ¹¹C-acetate PET/CT. Resting and adenosine stress myocardial blood flow (MBF) and myocardial flow reserve (MFR) were measured using ¹⁵O-H₂O PET/CT. </p> <p>Empagliflozin did not affect myocardial FFA uptake but reduced myocardial glucose uptake by 57% (p<0.001). Empagliflozin did not change myocardial oxygen consumption or MEE. Empagliflozin reduced resting MBF by 13% (p<0.01), but did not significantly affect stress MBF or MFR.</p> <p>In conclusion, SGLT2 inhibition did not affect myocardial FFA uptake, but channeled myocardial substrate utilization from glucose towards other sources and reduced resting MBF. However, the observed metabolic and hemodynamic changes were modest and most likely contribute only partially to the cardioprotective effect of SGLT2 inhibition. </p>

Abstract 15820: Differential Myocardial Gene Expression of Glucose Transporters in Heart Transplant Recipients With and Without Diabetes Mellitus

Introduction: The Sodium Glucose cotransporter (SGLT) and glucose transporters(GLUTs) play a crucial role in cellular glucose transport. Although experimental data have shown differential regulation of GLUT4 and SGLT in diabetic cardiomyopathy, the impact of diabetes mellitus (DM) upon myocardial glucose transporters in humans remains undetermined. Aim: To better understand the impact of elevated glucose levels upon myocardial expression of glucose transporters, the endomyocardial gene expression of GLUT1, GLUT4 and SGLT1 was investigated in heart transplant(HTx) recipients, with and without DM, who received a heart from a DM- donor. Methods: At baseline(BL), immediately after HTx and 12 ± 2 months(FU) later, serial endomyocardial biopsies were procured in 26 Htx pts, free of clinical or histological rejection, at time of routine surveillance biopsy. Patients were categorized in DM+ (n = 13pts) and DM- (n = 13 pts), according to the presence of diabetes mellitus (DM) at FU. Results: Despite similar hemodynamics and HbA1c levels at BL, DM+ pts had higher HbA1c levels (46,00 ± 13,79 vs 38,33 ± 4,88; p < 0,05) at FU. No differences were noted in BL GLUT1, GLUT4 and SGLT gene expression between both groups. In DM- pts SGLT1(0,081 ± 0,080 vs 0,188 ± 0,108; p = 0,0036) , GLUT4(0,076 ± 0,068 vs 0,137 ± 0,065; p = 0,0011 )and GLUT1(0,020 ± 0,021 vs 0,022 ± 0,009; p = 0,043) increased significantly at FU whereas no change was observed in DM+ pts. Conclusion: Similar to experimental data, differential endomyocardial regulation in SGLT1 and GLUT4 was noted between DM+ and DM-pts with a blunted upregulation of glucose transporters at 1 year in DM+ HTx pts. These observations are in line with experimental data and suggest that myocardial glucose uptake is differentially regulated in DM+ HTx pts.

Non-alcoholic fatty liver disease, diastolic dysfunction, and impaired myocardial glucose uptake in patients with type 2 diabetes

Background Non-alcoholic fatty liver disease (NAFLD) is highly prevalent in patients with type 2 diabetes and is associated with cardiovascular risk. We investigated whether the degree of NAFLD was associated with myocardial dysfunction related to impaired myocardial glucose uptake in patients with type 2 diabetes. Methods In total, 131 patients with type 2 diabetes from a tertiary care hospital were included. Myocardial glucose uptake was assessed using [18F]-fluorodeoxyglucose-positron emission tomography. Hepatic steatosis and fibrosis were determined using transient liver elastography. Echocardiography was performed to evaluate cardiac structure and function. Results Patients with NAFLD revealed cardiac diastolic dysfunction with higher left ventricular filling pressure (E/e’ ratio) and left atrial volume index (LAVI) than patients without NAFLD (all p < 0.05). Hepatic steatosis correlated with E/e’ ratio and LAVI, and hepatic fibrosis also correlated with E/e’ ratio (all p < 0.05). In linear regression analyses, a higher degree of hepatic steatosis (r2 = 0.409; p = 0.041) and a higher degree of fibrosis (r2 = 0.423; p = 0.009) were independent determinants for a higher E/e’ ratio even after adjusting for confounding factors. Decreased myocardial glucose uptake was associated with a higher degree of steatosis (p for trend = 0.084) and fibrosis (p for trend = 0.012). In addition, decreased myocardial glucose uptake was an independent determinant factor for a higher E/e’ ratio (r2 = 0.409; p = 0.04). Conclusions Hepatic steatosis and fibrosis are significantly associated with diastolic heart dysfunction in patients with type 2 diabetes coupled with impaired myocardial glucose uptake.