Influence of insulin and free fatty acids on contractile function in patients with chronically stunned and hibernating myocardium

Hemodynamic Effects of Ketone Bodies in Patients With Pulmonary Hypertension

Background Pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) are debilitating diseases with a high mortality. Despite emerging treatments, pulmonary vascular resistance frequently remains elevated. However, the ketone body 3-hydroxybutyrate (3-OHB) may reduce pulmonary vascular resistance in these patients. Hence, the aim was to assess the hemodynamic effects of 3-OHB in patients with PAH or CTEPH. Methods and Results We enrolled patients with PAH (n=10) or CTEPH (n=10) and residual pulmonary hypertension. They received 3-OHB infusion and placebo (saline) for 2 hours in a randomized crossover study. Invasive hemodynamic and echocardiography measurements were performed. Furthermore, we investigated the effects of 3-OHB on the right ventricle of isolated hearts and isolated pulmonary arteries from Sprague-Dawley rats. Ketone body infusion increased circulating 3-OHB levels from 0.5±0.5 to 3.4±0.7 mmol/L (P<0.001). Cardiac output improved by 1.2±0.1 L/min (27±3%, P<0.001), and right ventricular annular systolic velocity increased by 1.4±0.4 cm/s (13±4%, P=0.002). Pulmonary vascular resistance decreased by 1.3±0.3 Wood units (18%±4%, P<0.001) with no significant difference in response between patients with PAH and CTEPH. In the rat studies, 3-OHB administration was associated with decreased pulmonary arterial tension compared with saline administration (maximal relative tension difference: 12±2%, P<0.001) and had no effect on right ventricular systolic pressures (P=0.63), whereas pressures rose at a slower pace (dP/dtmax, P=0.02). Conclusions In patients with PAH or CTEPH, ketone body infusion improves cardiac output and decreases pulmonary vascular resistance. Experimental rat studies support that ketone bodies relax pulmonary arteries. Long-term studies are warranted to assess the clinical role of hyperketonemia. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT04615754.

Enhancing Glycolysis Protects against Ischemia-Reperfusion Injury by Reducing ROS Production

After myocardial ischemia-reperfusion, fatty acid oxidation shows fast recovery while glucose oxidation rates remain depressed. A metabolic shift aimed at increasing glucose oxidation has shown to be beneficial in models of myocardial ischemia-reperfusion. However, strategies aimed at increasing glucose consumption in the clinic have provided mixed results and have not yet reached routine clinical practice. A better understanding of the mechanisms underlying the protection afforded by increased glucose oxidation may facilitate the transfer to the clinic. The purpose of this study was to evaluate if the modulation of reactive oxygen species (ROS) was involved in the protection afforded by increased glucose oxidation. Firstly, we characterized an H9C2 cellular model in which the use of glucose or galactose as substrates can modulate glycolysis and oxidative phosphorylation pathways. In this model, there were no differences in morphology, cell number, or ATP and PCr levels. However, galactose-grown cells consumed more oxygen and had an increased Krebs cycle turnover, while cells grown in glucose had increased aerobic glycolysis rate as demonstrated by higher lactate and alanine production. Increased aerobic glycolysis was associated with reduced ROS levels and protected the cells against simulated ischemia-reperfusion injury. Furthermore, ROS scavenger N-acetyl cysteine (NAC) was able to reduce the amount of ROS and to prevent cell death. Lastly, cells grown in galactose showed higher activation of mTOR/Akt signaling pathways. In conclusion, our results provide evidence indicating that metabolic shift towards increased glycolysis reduces mitochondrial ROS production and prevents cell death during ischemia-reperfusion injury.

Low-carbohydrate diet versus euglycemic hyperinsulinemic clamp for the assessment of myocardial viability with 18F-fluorodeoxyglucose-PET: a pilot study

Positron emission tomography with (18)F-fluorodeoxyglucose (FDG-PET) is considered the gold standard for myocardial viability. A pilot study was undertaken to compare FDG-PET using euglycemic hyperinsulinemic clamp before (18)F-fluorodeoxyglucose ((18)F-FDG) administration (PET-CLAMP) with a new proposed technique consisting of a 24-h low-carbohydrate diet before (18)F-FDG injection (PET-DIET), for the assessment of hypoperfused but viable myocardium (hibernating myocardium). Thirty patients with previous myocardial infarction were subjected to rest (99m)Tc-sestamibi-SPECT and two (18)F-FDG studies (PET-CLAMP and PET-DIET). Myocardial tracer uptake was visually scored using a 5-point scale in a 17-segment model. Hibernating myocardium was defined as normal or mildly reduced metabolism ((18)F-FDG uptake) in areas with reduced perfusion ((99m)Tc-sestamibi uptake) since (18)F-FDG uptake was higher than the degree of hypoperfusion-perfusion/metabolism mismatch indicating a larger flow defect. PET-DIET identified 79 segments and PET-CLAMP 71 as hibernating myocardium. Both methods agreed in 61 segments (agreement = 94.5 %, κ = 0.78). PET-DIET identified 230 segments and PET-CLAMP 238 as nonviable. None of the patients had hypoglycemia after DIET, while 20 % had it during CLAMP. PET-DIET compared with PET-CLAMP had a good correlation for the assessment of hibernating myocardium. To our knowledge, these data provide the first evidence of the possibility of myocardial viability assessment with this technique.

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.

Effect of acute hyperglycemia on left ventricular contractile function in diabetic patients with and without heart failure: two randomized cross-over studies

BACKGROUND

It is unknown whether changes in circulating glucose levels due to short-term insulin discontinuation affect left ventricular contractile function in type 2 diabetic patients with (T2D-HF) and without (T2D-nonHF) heart failure.

MATERIALS AND METHODS

In two randomized cross-over-designed trials, 18 insulin-treated type 2 diabetic patients with (Ejection Fraction (EF) 36 ± 6%, n = 10) (trial 2) and without systolic heart failure (EF 60 ± 3%, n = 8) (trial 1) were subjected to hyper- and normoglycemia for 9-12 hours on two different occasions. Advanced echocardiography, bicycle exercise tests and 6-minute hall walk distance were applied.

RESULTS

Plasma glucose levels differed between study arms (6.5 ± 0.8 mM vs 14.1 ± 2.6 mM (T2D-HF), 5.8 ± 0.4 mM vs 9.9 ± 2.1 mM (T2D-nonHF), p<0.001). Hyperglycemia was associated with an increase in several parameters: maximal global systolic tissue velocity (Vmax) (p<0.001), maximal mitral annulus velocity (S'max) (p<0.001), strain rate (p = 0.02) and strain (p = 0.05). Indices of increased myocardial systolic contractile function were significant in both T2D-HF (Vmax: 14%, p = 0.02; S'max: 10%, p = 0.04), T2D-nonHF (Vmax: 12%, p<0.01; S'max: 9%, p<0.001) and in post exercise S'max (7%, p = 0.049) during hyperglycemia as opposed to normoglycemia. LVEF did not differ between normo- and hyperglycemia (p = 0.17), and neither did peak exercise capacity nor catecholamine levels. Type 2 diabetic heart failure patients' 6-minute hall walk distance improved by 7% (p = 0.02) during hyperglycemia as compared with normoglycemia.

CONCLUSIONS

Short-term hyperglycemia by insulin discontinuation is associated with an increase in myocardial systolic contractile function in type 2 diabetic patients with and without heart failure and with a slightly prolonged walking distance in type 2 diabetic heart failure patients. (Clinicaltrials.gov identifier NCT00653510).

Metabolic remodelling in human heart failure

In addition to the typical abnormalities in myocardial structure and function, it is well established that the cardiac metabolism is abnormal in patients with heart failure (HF). Insulin resistance is a common co-morbidity in HF patients and also modulates cardiac metabolism in HF. The notion that an altered myocardial metabolism may contribute to the disease pathogenesis and optimizing it may serve therapeutic purposes underscores the importance of identifying the metabolic characteristics of HF patients. In this paper, the literature on the metabolic changes in human HF is reviewed, and the effects of metabolic modulators on patients with HF are discussed.

Metabolic fingerprint of ischaemic cardioprotection: importance of the malate-aspartate shuttle

The convergence of cardioprotective intracellular signalling pathways to modulate mitochondrial function as an end-target of cytoprotective stimuli is well described. However, our understanding of whether the complementary changes in mitochondrial energy metabolism are secondary responses or inherent mechanisms of ischaemic cardioprotection remains incomplete. In the heart, the malate-aspartate shuttle (MAS) constitutes the primary metabolic pathway for transfer of reducing equivalents from the cytosol into the mitochondria for oxidation. The flux of MAS is tightly linked to the flux of the tricarboxylic acid cycle and the electron transport chain, partly by the amino acid l-glutamate. In addition, emerging evidence suggests the MAS is an important regulator of cytosolic and mitochondrial calcium homeostasis. In the isolated rat heart, inhibition of MAS during ischaemia and early reperfusion by the aminotransferase inhibitor aminooxyacetate induces infarct limitation, improves haemodynamic responses, and modulates glucose metabolism, analogous to effects observed in classical ischaemic preconditioning. On the basis of these findings, the mechanisms through which MAS preserves mitochondrial function and cell survival are reviewed. We conclude that the available evidence is supportive of a down-regulation of mitochondrial respiration during lethal ischaemia with a gradual 'wake-up' during reperfusion as a pivotal feature of ischaemic cardioprotection. Finally, comments on modulating myocardial energy metabolism by the cardioprotective amino acids glutamate and glutamine are given.

Suppression of circulating free fatty acids with acipimox in chronic heart failure patients changes whole body metabolism but does not affect cardiac function

Circulating free fatty acids (FFAs) may worsen heart failure (HF) due to myocardial lipotoxicity and impaired energy generation. We studied cardiac and whole body effects of 28 days of suppression of circulating FFAs with acipimox in patients with chronic HF. In a randomized double-blind crossover design, 24 HF patients with ischemic heart disease [left ventricular ejection fraction: 26 ± 2%; New York Heart Association classes II ( n = 13) and III ( n = 5)] received 28 days of acipimox treatment (250 mg, 4 times/day) and placebo. Left ventricular ejection fraction, diastolic function, tissue-Doppler regional myocardial function, exercise capacity, noninvasive cardiac index, NH2-terminal pro-brain natriuretic peptide (NT-pro-BNP), and whole body metabolic parameters were measured. Eighteen patients were included for analysis. FFAs were reduced by 27% in the acipimox-treated group [acipimox vs. placebo ( day 28 − day 0): −0.10 ± 0.03 vs. +0.01 ± 0.03 mmol/l, P < 0.01]. Glucose and insulin levels did not change. Acipimox tended to increase glucose and decrease lipid utilization rates at the whole body level and significantly changed the effect of insulin on substrate utilization. The hyperinsulinemic euglycemic clamp M value did not differ. Global and regional myocardial function did not differ. Exercise capacity, cardiac index, systemic vascular resistance, and NT-pro-BNP were not affected by treatment. In conclusion, acipimox caused minor changes in whole body metabolism and decreased the FFA supply, but a long-term reduction in circulating FFAs with acipimox did not change systolic or diastolic cardiac function or exercise capacity in patients with HF.

Cardiovascular and metabolic effects of 48-h glucagon-like peptide-1 infusion in compensated chronic patients with heart failure

The incretin hormone glucagon-like peptide-1 (GLP-1) and its analogs are currently emerging as antidiabetic medications. GLP-1 improves left ventricular ejection fraction (LVEF) in dogs with heart failure (HF) and in patients with acute myocardial infarction. We studied metabolic and cardiovascular effects of 48-h GLP-1 infusions in patients with congestive HF. In a randomized, double-blind crossover design, 20 patients without diabetes and with HF with ischemic heart disease, EF of 30 ± 2%, New York Heart Association II and III ( n = 14 and 6) received 48-h GLP-1 (0.7 pmol·kg−1·min−1) and placebo infusion. At 0 and 48 h, LVEF, diastolic function, tissue Doppler regional myocardial function, exercise testing, noninvasive cardiac output, and brain natriuretic peptide (BNP) were measured. Blood pressure, heart rate, and metabolic parameters were recorded. Fifteen patients completed the protocol. GLP-1 increased insulin (90 ± 17 pmol/l vs. 69 ± 12 pmol/l; P = 0.025) and lowered glucose levels (5.2 ± 0.1 mmol/l vs. 5.6 ± 0.1 mmol/l; P < 0.01). Heart rate (67 ± 2 beats/min vs. 65 ± 2 beats/min; P = 0.016) and diastolic blood pressure (71 ± 2 mmHg vs. 68 ± 2 mmHg; P = 0.008) increased during GLP-1 treatment. Cardiac index (1.5 ± 0.1 l·min−1·m−2 vs. 1.7 ± 0.2 l·min−1·m−2; P = 0.54) and LVEF (30 ± 2% vs. 30 ± 2%; P = 0.93), tissue Doppler indexes, body weight, and BNP remained unchanged. Hypoglycemic events related to GLP-1 treatment were observed in eight patients. GLP-1 infusion increased circulating insulin levels and reduced plasma glucose concentration but had no major cardiovascular effects in patients without diabetes but with compensated HF. The impact of minor increases in heart rate and diastolic blood pressure during GLP-1 infusion requires further studies. Hypoglycemia was frequent and calls for caution in patients without diabetes but with HF.

Myocardial fatty acid metabolism and cardiac performance in heart failure

It is well established that cardiac metabolism is abnormal in heart failure (HF). Experimental studies suggest that in severe HF, cardiac metabolism reverts to a more fetal-like substrate use characterized by enhanced glucose and downregulated free fatty acid (FFA) metabolism. Correspondingly, in humans, when FFA levels are similar, myocardial glucose metabolism is increased, and FFA metabolism is decreased. However, depression of left ventricular function and insulin resistance induces a shift back to greater FFA uptake and oxidation by increasing circulating FFA availability. Myocardial insulin resistance may further impair myocardial glucose uptake and lead to an energy depletion state. Experimental and preliminary clinical studies suggest that metabolic modulators enhancing myocardial glucose oxidation may improve cardiac function in patients with chronic HF. However, it has been found that acute FFA deprivation is harmful to the cardiac performance. Optimizing myocardial energy metabolism may serve as an additional approach for managing HF, but further studies are warranted.

Cardiovascular effects of intravenous ghrelin infusion in healthy young men

Ghrelin infusion improves cardiac function in patients suffering from cardiac failure, and bolus administration of ghrelin increases cardiac output in healthy subjects. The cardiovascular effects of more continuous intravenous ghrelin exposure remain to be studied. We therefore studied the cardiovascular effects of a constant infusion of human ghrelin at a rate of 5 pmol/kg per minute for 180 min. Fifteen healthy, young (aged 23.2 +/- 0.5 yr), normal-weight (23.0 +/- 0.4 kg/m(2)) men volunteered in a randomized double-blind, placebo-controlled crossover study. With the subjects remaining fasting, peak myocardial systolic velocity S', tissue tracking TT, left ventricular ejection fraction EF, and endothelium-dependent flow-mediated vasodilatation were measured. Ghrelin infusion increased S' 9% (P = 0.002) and TT 10% (P < 0.001), whereas EF, resting blood flow velocity, and endothelium-dependent flow-mediated vasodilatation did not change (P = 0.13). This was associated with a peak in serum growth hormone after 60 min of infusion (37.77 +/- 5.27 ng/ml, P < 0.001), a doubling of free fatty acid levels (P = 0.001), and a 1.6-fold increase in cortisol levels (P < 0.05), whereas glucose and catecholamine levels were constant. In conclusion, supraphysiological levels of ghrelin stimulate left ventricular function in terms of S' and TT in healthy young normal-weight men without changing resting blood flow velocity and endothelium-dependent flow-mediated vasodilatation. The effects did not translate into detectable increments in EF.

Adaptation of nonrevascularized human hibernating and chronically stunned myocardium to long-term chronic myocardial ischemia

It is unknown whether human chronically ischemic dysfunctional myocardium degenerates over time or adapts to chronic ischemia. We studied whether perfusion, metabolism, and contractile function and reserve can be preserved in nonrevascularized human chronically stunned and hibernating myocardium. We studied 16 event-free, medically treated patients with ejection fractions of 31 +/- 2% and chronically stunned or hibernating myocardium in 56 +/- 5% of the left ventricle on technetium-99m sestamibi single-photon emission computed tomography/fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography. Patients underwent repeat single-photon emission computed tomography, positron emission tomography, and tissue Doppler echocardiography at rest and during stress at follow-up after 25 +/- 4 months, and we investigated whether measurements of myocardial viability remained stable over time. Patients were stable with respect to New York Heart Association class and global left ventricular function (30 +/- 2%, p = 0.81). Wall motion score was unaltered in hibernating myocardium and chronically stunned regions, and a contractile reserve by tissue Doppler stress echocardiography was preserved. Overall, 74% of hibernating myocardium and chronically stunned regions retained their initial perfusion/metabolism pattern at follow-up. In hibernating myocardium, initial and follow-up sestamibi uptakes (53 +/- 1% and 53 +/- 2%, p = 0.85) and FDG uptakes (76 +/- 1% and 74 +/- 1%, p = 0.21) did not differ. In chronically stunned regions, sestamibi uptake displayed a minor decrease at follow-up (70 +/- 1% vs 67 +/- 1%, p <0.01) and FDG uptake remained constant (68 +/- 2% and 67 +/- 1%, p = 0.21). In conclusion, myocardial perfusion, FDG uptake, and contractile function in nonrevascularized chronically stunned and hibernating myocardium adapt to chronic ischemia in patients who are free of events. In chronically stunned regions, adaptation may be less complete than in hibernating myocardium.

Free Fatty Acid Depletion Acutely Decreases Cardiac Work and Efficiency in Cardiomyopathic Heart Failure

Background— Metabolic modulators that enhance myocardial glucose metabolism by inhibiting free fatty acid (FFA) metabolism may improve cardiac function in heart failure patients. We studied the effect of acute FFA withdrawal on cardiac function in patients with heart failure caused by idiopathic dilated cardiomyopathy (IDCM).

Methods and Results— Eighteen fasting nondiabetic patients with IDCM (14 men, 4 women, aged 58.8±8.0 years, ejection fraction 33±8.8%) and 8 matched healthy controls underwent examination of myocardial perfusion and oxidative and FFA metabolism, before and after acute reduction of serum FFA concentrations by acipimox, an inhibitor of lipolysis. Metabolism was monitored by positron emission tomography and [ 15 O]H 2 O, [ 11 C]acetate, and [ 11 C]palmitate. Left ventricular function and myocardial work were echocardiographically measured, and efficiency of forward work was calculated. Acipimox decreased myocardial FFA uptake by >80% in both groups. Rate–pressure product and myocardial perfusion remained unchanged, whereas stroke volume decreased similarly in both groups. In the healthy controls, reduced cardiac work was accompanied by decreased oxidative metabolism (from 0.071±0.019 to 0.055±0.016 min −1 , P <0.01). In IDCM patients, cardiac work fell, whereas oxidative metabolism remained unchanged and efficiency fell (from 35.4±12.6 to 31.6±13.3 mm Hg · L · g −1 , P <0.05).

Conclusions— Acutely decreased serum FFA depresses cardiac work. In healthy hearts, this is accompanied by parallel decrease in oxidative metabolism, and myocardial efficiency is preserved. In failing hearts, FFA depletion did not downregulate oxidative metabolism, and myocardial efficiency deteriorated. Thus, failing hearts are unexpectedly more dependent than healthy hearts on FFA availability. We propose that both glucose and fatty acid oxidation are required for optimal function of the failing heart.