Jacob Marthinsen Seefeldt

By investigating the effects of oral versus IV lactate administration, we find that oral lactate elevates plasma l-lactate and strongly increases circulating l-Lac-Phe and l-Lac-Val, potentially via an alternative mechanism than exercise-induced formation. Furthermore, we find that GLP-1 secretion is not directly induced by lactate but may be mediated via increased bile acids and SCFAs in the gut.

Cardiogenic shock (CS) is characterized by reduced cardiac output (CO), reduced end-organ perfusion, and high mortality. Medical therapies have failed to improve survival. The ketone body 3-hydroxybutyrate (3-OHB) enhances cardiac function in heart failure and CS. We aimed to elucidate the cardiovascular and cardiometabolic effects of 3-OHB treatment during CS. In a randomized, assessor-blinded crossover design, we studied 16 female pigs (60 kg, 5 months of age). CS was induced by left main coronary artery microsphere injections. Predefined criteria for CS were a 30% reduction in CO or mixed venous saturation (SvO₂). Intravenous 3-OHB infusion and a matching control solution were administered for 120 min in random order. Hemodynamic measurements were obtained by pulmonary artery catheterization and a left ventricular (LV) pressure–volume catheter. Myocardial mitochondrial function was assessed using high resolution respirometry. During CS, infusion with 3-OHB increased CO by 0.9 L/min (95%CI 0.4–1.3 L/min) compared with control infusion. SvO₂ (P = 0.026) and heart rate (P < 0.001) increased. Stroke volume (P = 0.6) was not altered. LV contractile function as determined by LV end-systolic elastance improved during 3-OHB infusion compared with control infusion (P = 0.004). Systemic and pulmonary vascular resistance decreased, and diuresis increased. LV mitochondrial function was higher after 3-OHB infusion compared with control. We conclude that 3-OHB infusion enhances cardiac function by increasing contractility and reducing vascular resistance, while also preserving myocardial mitochondrial respiratory function in a large animal model of ischemic CS. These novel findings support the therapeutic potential of exogenous ketone supplementation in CS management. Graphical abstract

Background: Wild‐type transthyretin amyloid (ATTRwt) cardiomyopathy is increasingly recognized in the development of heart failure. The link between cardiac performance, hemodynamics, and mitochondrial function in disease stages of ATTRwt has not previously been studied but may provide new insights into the pathophysiology and clinical performance of the patients. Methods and Results: The study investigated 47 patients diagnosed with ATTRwt at Aarhus University Hospital, Denmark. Patients were stratified according to the disease stages of the National Amyloidosis Centre (NAC) as NAC I with low levels of NT‐proBNP (N‐terminal pro‐B‐type natriuretic peptide) (NAC I‐L, n=14), NAC I with high levels NT‐proBNP (NAC I‐H, n=20), and NAC II‐III (n=13). Exercise testing with simultaneous right heart catheterization was performed in all patients. Endomyocardial biopsies were collected from the patients and the mitochondrial oxidative phosphorylation capacity was assessed. All NAC disease groups, even in the NAC I‐L group, a significant abnormal increase in biventricular filling pressures were noted during exercise while the filling pressures was normal or near normal at rest. The inotropic response to exercise was reduced with diminished increase in cardiac output which was significantly more pronounced in the NAC I‐H (Diff. ‐2.4, 95% CI (−4.2: −0.7), P =0.00) and the NAC II‐III group (Diff: −3.1 L/min, 95% CI (−5.2: −1.1), P =0.00) compared with the NAC I‐L group. The pulmonary artery wedge pressure to cardiac output ratio at peak exercise was significantly different between NAC I‐L and NAC II‐III (Diff: 1.6 mm Hg*min/L, 95% CI (0.01:3.3, P =0.04)). Patients with ATTRwt had a reduced oxidative phosphorylation capacity which correlated to left ventricular mass but not to cardiac output capacity. Conclusions: An abnormal restrictive left ventricle and right ventricle response to exercise was demonstrated, even present in patients with early‐stage ATTRwt. In more advanced disease stages a progressive impairment of the pressure‐flow relationship was noted. The myocyte energetics is deranged but not associated to the contractile reserve or restrictive filling characteristics in ATTRwt.

Background: The heart can metabolize the microbiota‐derived short‐chain fatty acid butyrate. Butyrate may have beneficial effects in heart failure, but the underlying mechanisms are unknown. We tested the hypothesis that butyrate elevates cardiac output by mechanisms involving direct stimulation of cardiac contractility and vasorelaxation in rats. Methods and Results: We examined the effects of butyrate on (1) in vivo hemodynamics using parallel echocardiographic and invasive blood pressure measurements, (2) isolated perfused hearts in Langendorff systems under physiological conditions and after ischemia and reperfusion, and (3) isolated coronary arteries mounted in isometric wire myographs. We tested Na‐butyrate added to injection solutions or physiological buffers and compared its effects with equimolar doses of NaCl. Butyrate at plasma concentrations of 0.56 mM increased cardiac output by 48.8±14.9%, stroke volume by 38.5±12.1%, and left ventricular ejection fraction by 39.6±6.2%, and lowered systemic vascular resistance by 33.5±6.4% without affecting blood pressure or heart rate in vivo. In the range between 0.1 and 5 mM, butyrate increased left ventricular systolic pressure by up to 23.7±3.4% in isolated perfused hearts and by 9.4±2.9% following ischemia and reperfusion, while reducing myocardial infarct size by 81.7±16.9%. Butyrate relaxed isolated coronary septal arteries concentration dependently with an EC ₅₀ =0.57 mM (95% CI, 0.23–1.44). Conclusions: We conclude that butyrate elevates cardiac output through mechanisms involving increased cardiac contractility and vasorelaxation. This effect of butyrate was not associated with adverse myocardial injury in damaged hearts exposed to ischemia and reperfusion.

Background: The ketone body 3‐hydroxybutyrate (3‐OHB) increases cardiac output (CO) by 35% to 40% in healthy people and people with heart failure. The mechanisms underlying the effects of 3‐OHB on myocardial contractility and loading conditions as well as the cardiovascular effects of its enantiomeric forms, D‐3‐OHB and L‐3‐OHB, remain undetermined. Methods and Results: Three groups of 8 pigs each underwent a randomized, crossover study. The groups received 3‐hour infusions of either D/L‐3‐OHB (racemic mixture), 100% L‐3‐OHB, 100% D‐3‐OHB, versus an isovolumic control. The animals were monitored with pulmonary artery catheter, left ventricle pressure‐volume catheter, and arterial and coronary sinus blood samples. Myocardial biopsies were evaluated with high‐resolution respirometry, coronary arteries with isometric myography, and myocardial kinetics with D‐[ ¹¹ C]3‐OHB and L‐[ ¹¹ C]3‐OHB positron emission tomography. All three 3‐OHB infusions increased 3‐OHB levels ( P P P =0.2). Circulating 3‐OHB levels correlated with CO for both enantiomers ( P 11 C]3‐OHB showed rapid cardiac uptake and metabolism, whereas L‐[ ¹¹ C]3‐OHB demonstrated much slower pharmacokinetics. Conclusions: 3‐OHB increased CO by reducing afterload. L‐3‐OHB exerted a stronger hemodynamic response than D‐3‐OHB due to higher circulating 3‐OHB levels. There was a dissocitation between the myocardial metabolism and hemodynamic effects of the enantiomers, highlighting L‐3‐OHB as a potent cardiovascular agent with strong hemodynamic effects.

Normothermic regional perfusion (NRP) allows assessment of therapeutic interventions prior to donation after circulatory death transplantation. Sodium-3-hydroxybutyrate (3-OHB) increases cardiac output in heart failure patients and diminishes ischemia–reperfusion injury, presumably by improving mitochondrial metabolism. We investigated effects of 3-OHB on cardiac and mitochondrial function in transplanted hearts and in cardiac organoids. Donor pigs (n = 14) underwent circulatory death followed by NRP. Following static cold storage, hearts were transplanted into recipient pigs. 3-OHB or Ringer’s acetate infusions were initiated during NRP and after transplantation. We evaluated hemodynamics and mitochondrial function. 3-OHB mediated effects on contractility, relaxation, calcium, and conduction were tested in cardiac organoids from human pluripotent stem cells. Following NRP, 3-OHB increased cardiac output (P < 0.0001) by increasing stroke volume (P = 0.006), dP/dt (P = 0.02) and reducing arterial elastance (P = 0.02). Following transplantation, infusion of 3-OHB maintained mitochondrial respiration (P = 0.009) but caused inotropy-resistant vasoplegia that prevented weaning. In cardiac organoids, 3-OHB increased contraction amplitude (P = 0.002) and shortened contraction duration (P = 0.013) without affecting calcium handling or conduction velocity. 3-OHB had beneficial cardiac effects and may have a potential to secure cardiac function during heart transplantation. Further studies are needed to optimize administration practice in donors and recipients and to validate the effect on mitochondrial function.

The ketone body 3-hydroxybutyrate (3-OHB) increases cardiac output and myocardial perfusion without affecting blood pressure in humans, but the cardiovascular sites of action remain obscure. Here, we test the hypothesis in rats that 3-OHB acts directly on the heart to increase cardiac contractility and directly on blood vessels to lower systemic vascular resistance. We investigate effects of 3-OHB on (a) in vivo hemodynamics using echocardiography and invasive blood pressure measurements, (b) isolated perfused hearts in Langendorff systems, and (c) isolated arteries and veins in isometric myographs. We compare Na-3-OHB to equimolar NaCl added to physiological buffers or injection solutions. At plasma concentrations of 2–4 mM in vivo, 3-OHB increases cardiac output (by 28.3±7.8%), stroke volume (by 22.4±6.0%), left ventricular ejection fraction (by 13.3±4.6%), and arterial dP/dt_max (by 31.9±11.2%) and lowers systemic vascular resistance (by 30.6±11.2%) without substantially affecting heart rate or blood pressure. Applied to isolated perfused hearts at 3–10 mM, 3-OHB increases left ventricular developed pressure by up to 26.3±7.4 mmHg and coronary perfusion by up to 20.2±9.5%. Beginning at 1–3 mM, 3-OHB relaxes isolated coronary (EC₅₀=12.4 mM), cerebral, femoral, mesenteric, and renal arteries as well as brachial, femoral, and mesenteric veins by up to 60% of pre-contraction within the pathophysiological concentration range. Of the two enantiomers that constitute racemic 3-OHB, D-3-OHB dominates endogenously; but tested separately, the enantiomers induce similar vasorelaxation. We conclude that increased cardiac contractility and generalized systemic vasorelaxation can explain the elevated cardiac output during 3-OHB administration. These actions strengthen the therapeutic rationale for 3-OHB in heart failure management.

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 P P =0.002). Pulmonary vascular resistance decreased by 1.3±0.3 Wood units (18%±4%, P P 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.

The Sodium Glucose Co-Transporter-2 inhibitor, empagliflozin (EMPA), reduces mortality and hospitalisation for heart failure following myocardial infarction irrespective of diabetes status. While the findings suggest an inherent cardioprotective capacity, the mechanism remains unknown. We studied infarct size (IS) ex-vivo in isolated hearts exposed to global IR injury and in-vivo in rats subjected to regional myocardial ischemia reperfusion (IR) injury, in whom we followed left ventricular dysfunction for 28 days. We compared rats that were given EMPA orally for 7 days before, EMPA 1.5 h before IR injury and at onset of reperfusion and continued orally during the follow-up period. We used echocardiography, high resolution respirometry, microdialysis and plasma levels of β-hydroxybutyrate to assess myocardial performance, mitochondrial respiration and intermediary metabolism, respectively. Pretreatment with EMPA for 7 days reduced IS in-vivo (65 ± 7% vs. 46 ± 8%, p < 0.0001 while administration 1.5 h before IR, at onset of reperfusion or ex-vivo did not. EMPA alleviated LV dysfunction irrespective of the reduction in IS. EMPA improved mitochondrial respiration and modulated myocardial interstitial metabolism while the concentration of β-hydroxybutyric acid was only transiently increased without any association with IS reduction. EMPA reduces infarct size and yields cardioprotection in non-diabetic rats with ischemic LV dysfunction by an indirect, delayed intrinsic mechanism that also improves systolic function beyond infarct size reduction. The mechanism involves enhanced mitochondrial respiratory capacity and modulated myocardial metabolism but not hyperketonemia.

Introduction Aerobic capacity is a strong predictor of cardiovascular mortality. Whether aerobic capacity influences myocardial ischemia and reperfusion (IR) injury is unknown. Purpose To investigate the impact of intrinsic differences in aerobic capacity and the cardioprotective potential on IR injury. Methods We studied hearts from rats developed by selective breeding for high (HCR) or low (LCR) capacity for treadmill running. The rats were randomized to: (1) control, (2) local ischemic preconditioning (IPC) or (3) remote ischemic preconditioning (RIC) followed by 30 minutes of ischemia and 120 minutes of reperfusion in an isolated perfused heart model. The primary endpoint was infarct size. Secondary endpoints included uptake of labelled glucose, content of selected mitochondrial proteins in skeletal and cardiac muscle, and activation of AMP-activated kinase (AMPK). Results At baseline, running distance was 203 +/- 7 m in LCR vs 1905 +/- 51 m in HCR rats (p0.99, respectively). Phosphorylaion of AMPK did not differ between LCR and HCR controls. IPC did not modulate cardiac phosphorylation of AMPK. Glucose uptake during reperfusion was similar in LCR and HCR rats. IPC increased glucose uptake during reperfusion in LCR animals (p = 0.02). Mitochondrial protein content in skeletal muscle was lower in LCR than in HCR (0.77 +/- 0.10 arbitrary units (AU) vs 1.09 +/- 0.07 AU, p = 0.02), but not in cardiac muscle. Conclusion Aerobic capacity is associated with altered myocardial sensitivity to IR injury, but the cardioprotective effect of IPC is not. Glucose uptake, AMPK activation immediately prior to ischemia and basal mitochondrial protein content in the heart seem to be of minor importance as underlying mechanisms for the cardioprotective effects.