On the interdependence of ketone body oxidation, glycogen content, glycolysis and energy metabolism in the heart.

In heart, glucose and glycolysis are important for anaplerosis and potentially therefore for d-ß-hydroxybutyrate (ßHB) oxidation. As a glucose store, glycogen may also furnish anaplerosis. We determined the effects of glycogen content on ßHB oxidation and glycolytic rates, and their downstream effects on energetics, in the isolated rat heart. High glycogen (HG) and low glycogen (LG) containing hearts were perfused with 11 mM [5-3 H]glucose and/or 4 mM [14 C]ßHB to measure glycolytic rates or ßHB oxidation, respectively, then freeze-clamped for glycogen and metabolomic analyses. Free cytosolic [NAD+ ]/[NADH] and mitochondrial [Q+ ]/[QH2 ] ratios were estimated using the lactate dehydrogenase and succinate dehydrogenase reaction, respectively. Phosphocreatine (PCr) and inorganic phosphate (Pi ) concentrations were measured using 31 P-nuclear magnetic resonance spectroscopy. Rates of ßHB oxidation in LG hearts were half that in HG hearts, with ßHB oxidation directly proportional to glycogen content. ßHB oxidation decreased glycolysis in all hearts. Glycogenolysis in glycogen-replete hearts perfused with ßHB alone was twice that of hearts perfused with ßHB and glucose, which had significantly higher levels of the glycolytic intermediates fructose 1,6-bisphosphate and 3-phosphoglycerate, and higher free cytosolic [NAD+ ]/[NADH]. ßHB oxidation increased the Krebs cycle intermediates citrate, 2-oxoglutarate and succinate, the total NADP/H pool, reduced mitochondrial [Q+ ]/[QH2 ], and increased the calculated free energy of ATP hydrolysis (∆GATP ). Although ßHB oxidation inhibited glycolysis, glycolytic intermediates were not depleted, and cytosolic free NAD remained oxidised. ßHB oxidation alone increased Krebs cycle intermediates, reduced mitochondrial Q and increased ∆GATP . We conclude that glycogen facilitates cardiac ßHB oxidation by anaplerosis. KEY POINTS: Ketone bodies (d-ß-hydroxybutyrate, acetoacetate) are increasingly recognised as important cardiac energetic substrates, in both healthy and diseased hearts. As 2-carbon equivalents they are cataplerotic, causing depletion of Krebs cycle intermediates; therefore their utilisation requires anaplerotic supplementation, and intra-myocardial glycogen has been suggested as a potential anaplerotic source during ketone oxidation. It is demonstrated here that cardiac glycogen does indeed provide anaplerotic substrate to facilitate ß-hydroxybutyrate oxidation in isolated perfused rat heart, and this contribution was quantified using a novel pulse-chase metabolic approach. Further, using metabolomics and 31 P-MR, it was shown that glycolytic flux from myocardial glycogen increased the heart's ability to oxidise ßHB, and ßHB oxidation increased the mitochondrial redox potential, ultimately increasing the free energy of ATP hydrolysis.

The effects of endogenously- and exogenously-induced hyperketonemia on exercise performance and adaptation.

Elevating blood ketones may enhance exercise capacity and modulate adaptations to exercise training; however, these effects may depend on whether hyperketonemia is induced endogenously through dietary carbohydrate restriction, or exogenously through ketone supplementation. To determine this, we compared the effects of endogenously- and exogenously-induced hyperketonemia on exercise capacity and adaptation. Trained endurance athletes undertook 6 days of laboratory based cycling ("race") whilst following either: a carbohydrate-rich control diet (n = 7; CHO); a carbohydrate-rich diet + ketone drink four-times daily (n = 7; Ex Ket); or a ketogenic diet (n = 7; End Ket). Exercise capacity was measured daily, and adaptations in exercise metabolism, exercise physiology and postprandial insulin sensitivity (via an oral glucose tolerance test) were measured before and after dietary interventions. Urinary ß-hydroxybutyrate increased by ⁓150-fold and ⁓650-fold versus CHO with Ex Ket and End Ket, respectively. Exercise capacity was increased versus pre-intervention by ~5% on race day 1 with CHO (p < 0.05), by 6%-8% on days 1, 4, and 6 (all p < 0.05) with Ex Ket and decreased by 48%-57% on all race days (all p > 0.05) with End Ket. There was an ⁓3-fold increase in fat oxidation from pre- to post-intervention (p < 0.05) with End Ket and increased perceived exercise exertion (p < 0.05). No changes in exercise substrate metabolism occurred with Ex Ket, but participants had blunted postprandial insulin sensitivity (p < 0.05). Dietary carbohydrate restriction and ketone supplementation both induce hyperketonemia; however, these are distinct physiological conditions with contrasting effects on exercise capacity and adaptation to exercise training.

Evaluation of Acute Supplementation With the Ketone Ester (R)-3-Hydroxybutyl-(R)-3-Hydroxybutyrate (deltaG) in Healthy Volunteers by Cardiac and Skeletal Muscle 31P Magnetic Resonance Spectroscopy.

In this acute intervention study, we investigated the potential benefit of ketone supplementation in humans by studying cardiac phosphocreatine to adenosine-triphosphate ratios (PCr/ATP) and skeletal muscle PCr recovery using phosphorus magnetic resonance spectroscopy (31P-MRS) before and after ingestion of a ketone ester drink. We recruited 28 healthy individuals: 12 aged 23-70 years for cardiac 31P-MRS, and 16 aged 60-75 years for skeletal muscle 31P-MRS. Baseline and post-intervention resting cardiac and dynamic skeletal muscle 31P-MRS scans were performed in one visit, where 25 g of the ketone monoester, deltaG®, was administered after the baseline scan. Administration was timed so that post-intervention 31P-MRS would take place 30 min after deltaG® ingestion. The deltaG® ketone drink was well-tolerated by all participants. In participants who provided blood samples, post-intervention blood glucose, lactate and non-esterified fatty acid concentrations decreased significantly (-28.8%, p ≪ 0.001; -28.2%, p = 0.02; and -49.1%, p ≪ 0.001, respectively), while levels of the ketone body D-beta-hydroxybutyrate significantly increased from mean (standard deviation) 0.7 (0.3) to 4.0 (1.1) mmol/L after 30 min (p ≪ 0.001). There were no significant changes in cardiac PCr/ATP or skeletal muscle metabolic parameters between baseline and post-intervention. Acute ketone supplementation caused mild ketosis in blood, with drops in glucose, lactate, and free fatty acids; however, such changes were not associated with changes in 31P-MRS measures in the heart or in skeletal muscle. Future work may focus on the effect of longer-term ketone supplementation on tissue energetics in groups with compromised mitochondrial function.

Abnormal whole-body energy metabolism in iron-deficient humans despite preserved skeletal muscle oxidative phosphorylation.

Iron deficiency impairs skeletal muscle metabolism. The underlying mechanisms are incompletely characterised, but animal and human experiments suggest the involvement of signalling pathways co-dependent upon oxygen and iron availability, including the pathway associated with hypoxia-inducible factor (HIF). We performed a prospective, case-control, clinical physiology study to explore the effects of iron deficiency on human metabolism, using exercise as a stressor. Thirteen iron-deficient (ID) individuals and thirteen iron-replete (IR) control participants each underwent 31P-magnetic resonance spectroscopy of exercising calf muscle to investigate differences in oxidative phosphorylation, followed by whole-body cardiopulmonary exercise testing. Thereafter, individuals were given an intravenous (IV) infusion, randomised to either iron or saline, and the assessments repeated ~ 1 week later. Neither baseline iron status nor IV iron significantly influenced high-energy phosphate metabolism. During submaximal cardiopulmonary exercise, the rate of decline in blood lactate concentration was diminished in the ID group (P = 0.005). Intravenous iron corrected this abnormality. Furthermore, IV iron increased lactate threshold during maximal cardiopulmonary exercise by ~ 10%, regardless of baseline iron status. These findings demonstrate abnormal whole-body energy metabolism in iron-deficient but otherwise healthy humans. Iron deficiency promotes a more glycolytic phenotype without having a detectable effect on mitochondrial bioenergetics.

Exogenous d-ß-hydroxybutyrate lowers blood glucose in part by decreasing the availability of L-alanine for gluconeogenesis.

BACKGROUND: Interventions that induce ketosis simultaneously lower blood glucose and the explanation for this phenomenon is unknown. Additionally, the glucose-lowering effect of acute ketosis is greater in people with type 2 diabetes (T2D). On the contrary, L-alanine is a gluconeogenic substrate secreted by skeletal muscle at higher levels in people with T2D and infusing of ketones lower circulating L-alanine blood levels. In this study, we sought to determine whether supplementation with L-alanine would attenuate the glucose-lowering effect of exogenous ketosis using a ketone ester (KE). METHODS: This crossover study involved 10 healthy human volunteers who fasted for 24 h prior to the ingestion of 25 g of d-ß-hydroxybutyrate (ßHB) in the form of a KE drink (ΔG® ) on two separate visits. During one of the visits, participants additionally ingested 2 g of L-alanine to see whether L-alanine supplementation would attenuate the glucose-lowering effect of the KE drink. Blood L-alanine, L-glutamine, glucose, ßHB, free fatty acids (FFA), lactate and C-peptide were measured for 120 min after ingestion of the KE, with or without L-alanine. FINDINGS: The KE drinks elevated blood ßHB concentrations from negligible levels to 4.52 ± 1.23 mmol/L, lowered glucose from 4.97 ± SD 0.39 to 3.77 ± SD 0.40 mmol/L, and lowered and L-alanine from 0.56 ± SD 0.88 to 0.41 ± SD 0.91 mmol/L. L-alanine in the KE drink elevated blood L-Alanine by 0.68 ± SD 0.15 mmol/L, but had no significant effect on blood ßHB, L-glutamine, FFA, lactate, nor C-peptide concentrations. By contrast, L-alanine supplementation significantly attenuated the ketosis-induced drop in glucose from 28% ± SD 8% to 16% ± SD 7% (p < .01). CONCLUSIONS: The glucose-lowering effect of acutely elevated ßHB is partially due to ßHB decreasing L-alanine availability as a substrate for gluconeogenesis.

The ketone ester, 3-hydroxybutyl-3-hydroxybutyrate, attenuates neurobehavioral deficits and improves neuropathology following controlled cortical impact in male rats.

Traumatic brain injury (TBI) is a leading cause of human death and disability with no effective therapy to fully prevent long-term neurological deficits in surviving patients. Ketone ester supplementation is protective in animal models of neurodegeneration, but its efficacy against TBI pathophysiology is unknown. Here, we assessed the neuroprotective effect of the ketone monoester, 3-hydroxybutyl-3-hydroxybutyrate, (KE) in male Sprague Dawley rats (n=32). TBI was induced using the controlled cortical impact (CCI) with Sham animals not receiving the brain impact. KE was administered daily by oral gavage (0.5 ml/kg/day) and provided ad libitum at 0.3% (v/v) in the drinking water. KE supplementation started immediately after TBI and lasted for the duration of the study. Motor and sensory deficits were assessed using the Neurobehavioral Severity Scale-Revised (NSS-R) at four weeks post-injury. The NSS-R total score in CCI + KE (1.2 ± 0.4) was significantly lower than in CCI + water (4.4 ± 0.5). Similarly, the NSS-R motor scores in CCI + KE (0.6 ± 0.7) were significantly lower than CCI + water (2.9 ± 1.5). Although the NSS-R sensory score in the CCI + KE group (0.5 ± 0.2) was significantly lower compared to CCI + water (1.8 ± 0.4), no difference was observed between CCI + water and Sham + water (1.0 ± 0.2) groups. The lesion volume was smaller in the CCI + KE (10 ± 3 mm3) compared to CCI + water (47 ± 11 mm3; p < 0.001). KE significantly decreased Iba1+ stained areas in the cortex and hippocampus, and GFAP+ stained areas in all brain regions analyzed - prefrontal cortex, hippocampus, cortex, amygdala (p < 0.01). In summary, our results indicate that KE can protect against TBI-induced morphological and functional deficits when administered immediately after an insult.

ß-Hydroxybutyrate Oxidation in Exercise Is Impaired by Low-Carbohydrate and High-Fat Availability.

Purpose: In this study, we determined ketone oxidation rates in athletes under metabolic conditions of high and low carbohydrate (CHO) and fat availability. Methods: Six healthy male athletes completed 1 h of bicycle ergometer exercise at 75% maximal power (WMax) on three occasions. Prior to exercise, participants consumed 573 mg·kg bw-1 of a ketone ester (KE) containing a 13C label. To manipulate CHO availability, athletes undertook glycogen depleting exercise followed by isocaloric high-CHO or very-low-CHO diets. To manipulate fat availability, participants were given a continuous infusion of lipid during two visits. Using stable isotope methodology, ß-hydroxybutyrate (ßHB) oxidation rates were therefore investigated under the following metabolic conditions: (i) high CHO + normal fat (KE+CHO); (ii) high CHO + high fat KE+CHO+FAT); and (iii) low CHO + high fat (KE+FAT). Results: Pre-exercise intramuscular glycogen (IMGLY) was approximately halved in the KE+FAT vs. KE+CHO and KE+CHO+FAT conditions (both p < 0.05). Blood free fatty acids (FFA) and intramuscular long-chain acylcarnitines were significantly greater in the KE+FAT vs. other conditions and in the KE+CHO+FAT vs. KE+CHO conditions before exercise. Following ingestion of the 13C labeled KE, blood ßHB levels increased to ≈4.5 mM before exercise in all conditions. ßHB oxidation was modestly greater in the KE+CHO vs. KE+FAT conditions (mean diff. = 0.09 g·min-1, p = 0.03; d = 0.3), tended to be greater in the KE+CHO+FAT vs. KE+FAT conditions (mean diff. = 0.07 g·min-1; p = 0.1; d = 0.3) and were the same in the KE+CHO vs. KE+CHO+FAT conditions (p < 0.05; d < 0.1). A moderate positive correlation between pre-exercise IMGLY and ßHB oxidation rates during exercise was present (p = 0.04; r = 0.5). Post-exercise intramuscular ßHB abundance was markedly elevated in the KE+FAT vs. KE+CHO and KE+CHO+FAT conditions (both, p < 0.001; d = 2.3). Conclusion: ßHB oxidation rates during exercise are modestly impaired by low CHO availability, independent of circulating ßHB levels.

Exogenous ketosis in patients with type 2 diabetes: Safety, tolerability and effect on glycaemic control.

INTRODUCTION: Ketogenic diets have shown to improve glycaemic control in patients with type 2 diabetes. This study investigated the safety, tolerability, and effects on glycaemic control in patients with type 2 diabetes of an exogenous ketone monoester (KE) capable of inducing fasting-like elevations in serum ß-hydroxybutyrate (ßHB) without the need for caloric or carbohydrate restriction. METHODS: Twenty one participants (14 men and 7 women, aged 45 ± 11 years) with insulin-independent type 2 diabetes, and unchanged hypoglycaemic medication for the previous 6 months, were recruited for this non-randomised interventional study. Participants wore intermittent scanning glucose monitors (IS-GM) for a total of 6 weeks and were given 25 ml of KE 3 times daily for 4 weeks. Serum electrolytes, acid-base status, and ßHB concentrations were measured weekly and cardiovascular risk markers were measured before and after the intervention. The primary endpoints were safety and tolerability, with the secondary endpoint being glycaemic control. RESULTS: The 21 participants consumed a total of 1,588 drinks (39.7 litres) of KE over the course of the intervention. Adverse reactions were mild and infrequent, including mild nausea, headache, and gastric discomfort following fewer than 0.5% of the drinks. Serum electrolyte concentrations, acid-base status, and renal function remained normal throughout the study. Compared to baseline, exogenous ketosis induced a significant decrease in all glycaemic control markers, including fructosamine (335 ± 60 µmol/L to 290 ± 49 µmol/L, p < .01), HbA1c (61 ± 10 mmol/mol to 55 ± 9 mmol/mol [7.7 ± 0.9% to 7.2 ± 0.9%], p < .01), mean daily glucose (7.8 ± 1.4 mM to 7.4 ± 1.3 mM [140 ± 23 mg/dl to 133 ± 25 mg/dl], p < .01) and time in range (67 ± 11% to 69 ± 10%, p < .01). CONCLUSIONS: Constant ketone monoester consumption over 1 month was safe, well tolerated, and improved glycaemic control in patients with type 2 diabetes.

The Use of Reactive Oxygen Species Production by Succinate-Driven Reverse Electron Flow as an Index of Complex 1 Activity in Isolated Brown Adipose Tissue Mitochondria.

We compared the activity of complex 1, complex 2, and the expression of the complex 1 subunit, NDUFA9, in isolated brown adipose tissue mitochondria from wild type and mitochondrial uncoupling protein 1 (UCP1) knockout mice. Direct spectrophotometric measurement revealed that complex 2 activity was similar, but complex 1 activity was greater (~2.7 fold) in isolated mitochondria from wild-type mice compared to UCP1 knockout mice, an observation endorsed by greater complex 1 subunit expression (NDUFA9) in mitochondria of wild-type mice. We also measured reactive oxygen species (ROS) production by isolated brown adipose mitochondria respiring on succinate, without rotenone, thus facilitating reverse electron flow through complex 1. We observed that reverse electron flow in isolated mitochondria from wild-type mice, with UCP1 inhibited, produced significantly greater (~1.6 fold) ROS when compared with isolated brown adipose mitochondria from UCP1 knockout mice. In summary, we demonstrate that ROS production by succinate-driven reverse electron flow can occur in brown adipose tissue mitochondria and is a good index of complex 1 activity.

Metabolic maturation of differentiating cardiosphere-derived cells.

Cardiosphere-derived cells (CDCs) can be expanded in vitro and induced to differentiate along the cardiac lineage. To recapitulate the phenotype of an adult cardiomyocyte, differentiating progenitors need to upregulate mitochondrial glucose and fatty acid oxidation. Here we cultured and differentiated CDCs using protocols aimed to maintain stemness or to promote differentiation, including triggering fatty acid oxidation using an agonist of peroxisome proliferator-activated receptor alpha (PPARα). Metabolic changes were characterised in undifferentiated CDCs and during differentiation towards a cardiac phenotype. CDCs from rat atria were expanded on fibronectin or collagen IV via cardiosphere formation. Differentiation was assessed using flow cytometry and qPCR and substrate metabolism was quantified using radiolabelled substrates. Collagen IV promoted proliferation of CDCs whereas fibronectin primed cells for differentiation towards a cardiac phenotype. In both populations, treatment with 5-Azacytidine induced a switch towards oxidative metabolism, as shown by changes in gene expression, decreased glycolytic flux and increased oxidation of glucose and palmitate. Addition of a PPARα agonist during differentiation increased both glucose and fatty acid oxidation and expression of cardiac genes. We conclude that oxidative metabolism and cell differentiation act in partnership with increases in one driving an increase in the other.

Effects of acute nutritional ketosis during exercise in adults with glycogen storage disease type IIIa are phenotype-specific: An investigator-initiated, randomized, crossover study.

Glycogen storage disease type IIIa (GSDIIIa) is an inborn error of carbohydrate metabolism caused by a debranching enzyme deficiency. A subgroup of GSDIIIa patients develops severe myopathy. The purpose of this study was to investigate whether acute nutritional ketosis (ANK) in response to ketone-ester (KE) ingestion is effective to deliver oxidative substrate to exercising muscle in GSDIIIa patients. This was an investigator-initiated, researcher-blinded, randomized, crossover study in six adult GSDIIIa patients. Prior to exercise subjects ingested a carbohydrate drink (~66 g, CHO) or a ketone-ester (395 mg/kg, KE) + carbohydrate drink (30 g, KE + CHO). Subjects performed 15-minute cycling exercise on an upright ergometer followed by 10-minute supine cycling in a magnetic resonance (MR) scanner at two submaximal workloads (30% and 60% of individual maximum, respectively). Blood metabolites, indirect calorimetry data, and in vivo 31 P-MR spectra from quadriceps muscle were collected during exercise. KE + CHO induced ANK in all six subjects with median peak ßHB concentration of 2.6 mmol/L (range: 1.6-3.1). Subjects remained normoglycemic in both study arms, but delta glucose concentration was 2-fold lower in the KE + CHO arm. The respiratory exchange ratio did not increase in the KE + CHO arm when workload was doubled in subjects with overt myopathy. In vivo 31 P MR spectra showed a favorable change in quadriceps energetic state during exercise in the KE + CHO arm compared to CHO in subjects with overt myopathy. Effects of ANK during exercise are phenotype-specific in adult GSDIIIa patients. ANK presents a promising therapy in GSDIIIa patients with a severe myopathic phenotype. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier: NCT03011203.

The Effect of Blood Ketone Concentration and Exercise Intensity on Exogenous Ketone Oxidation Rates in Athletes.

INTRODUCTION: Exogenous ketones potentially provide an alternative, energetically advantageous fuel to power exercising skeletal muscle. However, there is limited evidence regarding their relative contribution to energy expenditure during exercise. Furthermore, the effect of blood ketone concentration and exercise intensity on exogenous ketone oxidation rates is unknown. METHODS: Six athletes completed cycling ergometer exercise on three occasions within a single-blind, random-order controlled, crossover design study. Exercise duration was 60 min, consisting of 20-min intervals at 25%, 50%, and 75% maximal power output (WMax). Participants consumed (i) bitter flavored water (control), (ii) a low-dose ß-hydroxybutyrate (ßHB) ketone monoester (KME; 252 mg·kg BW-1, "low ketosis"), or (iii) a high-dose ßHB KME (752 mg·kg BW-1, "high ketosis"). The KME contained a 13C isotope label, allowing for the determination of whole-body exogenous ßHB oxidation rates through sampled respiratory gases. RESULTS: Despite an approximate doubling of blood ßHB concentrations between low- and high-ketosis conditions (~2 mM vs ~4.4 mM), exogenous ßHB oxidation rates were similar at rest and throughout exercise. The contribution of exogenous ßHB oxidation to energy expenditure peaked during the 25% WMax exercise intensity but was relatively low (4.46% ± 2.71%). Delta efficiency during cycling exercise was significantly greater in the low-ketosis (25.9% ± 2.1%) versus control condition (24.1% ± 1.9%; P = 0.027). CONCLUSIONS: Regardless of exercise intensity, exogenous ßHB oxidation contributes minimally to energy expenditure and is not increased by elevating circulating concentrations greater than ~2 mM. Despite low exogenous ßHB oxidation rates, exercise efficiency was significantly improved when blood ßHB concentration was raised to ~2 mM.

A Ketone Ester Drink Enhances Endurance Exercise Performance in Parkinson's Disease.

OBJECTIVES: Routine exercise is thought to be among the only disease-modifying treatments for Parkinson's disease; however, patients' progressive loss of physical ability limits its application. Therefore, we sought to investigate whether a ketone ester drink, which has previously been shown to enhance endurance exercise performance in elite athletes, could also improve performance in persons with Parkinson's disease. PARTICIPANTS: 14 patients, aged 40-80 years, with Hoehn and Yahr stage 1-2 Parkinson's disease. INTERVENTION: A randomized, placebo-controlled, crossover study in which each participant was administered a ketone ester drink or an isocaloric carbohydrate-based control drink on separate occasions prior to engaging in a steady state cycling test at 80 rpm to assess endurance exercise performance. OUTCOMES MEASURES: The primary outcome variable was length of time participants could sustain a therapeutic 80 rpm cadence. Secondary, metabolic outcomes measures included cardiorespiratory parameters as well as serum ß-hydroxybutyrate, glucose, and lactate. RESULTS: The ketone ester increased the time that participants were able to sustain an 80 rpm cycling cadence by 24 ± 9% (p = 0.027). Correspondingly, the ketone ester increased ß-hydroxybutyrate levels to >3 mmol/L and decreased respiratory exchange ratio, consistent with a shift away from carbohydrate-dependent metabolism. CONCLUSION: Ketone ester supplementation improved endurance exercise performance in persons with Parkinson's disease and may, therefore, be useful as an adjunctive therapy to enhance the effectiveness of exercise treatment for Parkinson's disease.

Nicotinic acid receptor agonists impair myocardial contractility by energy starvation.

Nicotinic acid receptor agonists have previously been shown to cause acute reductions in cardiac contractility. We sought to uncover the changes in cardiac metabolism underlying these alterations in function. In nine humans, we recorded cardiac energetics and function before and after a single oral dose of nicotinic acid using cardiac MRI to demonstrate contractile function and Phosphorus-31 (31 P) magnetic resonance spectroscopy to demonstrate myocardial energetics. Nicotinic Acid 400 mg lowered ejection fraction by 4% (64 ± 8% to 60 ± 7%, P = .03), and was accompanied by a fall in phosphocreatine/ATP ratio by 0.4 (2.2 ± 0.4 to 1.8 ± 0.1, P = .04). In four groups of eight Wistar rats, we used pyruvate dehydrogenase (PDH) flux studies to demonstrate changes in carbohydrate metabolism induced by the nicotinic acid receptor agonist, Acipimox, using hyperpolarized Carbon-13 (13 C) magnetic resonance spectroscopy. In rats which had been starved overnight, Acipimox caused a fall in ejection fraction by 7.8% (67.5 ± 8.9 to 60 ± 3.1, P = .03) and a nearly threefold rise in flux through PDH (from 0.182 ± 0.114 to 0.486 ± 0.139, P = .002), though this rise did not match pyruvate dehydrogenase flux observed in rats fed carbohydrate rich chow (0.726 ± 0.201). In fed rats, Acipimox decreased pyruvate dehydrogenase flux (to 0.512 ± 0.13, P = .04). Concentration of plasma insulin fell by two-thirds in fed rats administered Acipimox (from 1695 ± 891 ng/L to 550 ± 222 ng/L, P = .005) in spite of glucose concentrations remaining the same. In conclusion, we demonstrate that nicotinic acid receptor agonists impair cardiac contractility associated with a decline in cardiac energetics and show that the mechanism is likely a combination of reduced fatty acid availability and a failure to upregulate carbohydrate metabolism, essentially starving the heart of fuel.

Ketotherapeutics for neurodegenerative diseases.

Alzheimer's disease (AD) and Parkinson's disease (PD) are, respectively, the most prevalent and fastest growing neurodegenerative diseases worldwide. The former is primarily characterized by memory loss and the latter by the motor symptoms of tremor and bradykinesia. Both AD and PD are progressive diseases that share several key underlying mitochondrial, inflammatory, and other metabolic pathologies. This review will detail how these pathologies intersect with ketone body metabolism and signaling, and how ketone bodies, particularly d-ß-hydroxybutyrate (ßHB), may serve as a potential adjunctive nutritional therapy for two of the world's most devastating conditions.

Male sex adversely affects the phenotypic expression of diabetic heart disease.

BACKGROUND: Type 2 diabetes (T2D) is associated with an increased risk of heart failure (HF) and cardiovascular mortality. A large-scale meta-analysis on HF found that diabetes was more frequent in women than men, and diabetes appeared to have attenuated the otherwise protective effect of female sex on progression of cardiomyopathy. The exact underlying mechanisms for this remain unclear. Here, we aimed to determine the effect of sex on the phenotypic expression of diabetic heart disease in patients with T2D. METHODS: A total of 62 male [mean age 44 ± 8 years, body mass index (BMI) 33 ± 5 kg/m2, mean HBA1c of 7.8 ± 1.8%] and 67 female (44 ± 10 years, BMI 35 ± 6 kg/m2, HBA1c 7.6 ± 1.2%) T2D patients on oral glucose-lowering treatment, and 16 male (48 ± 17 years, BMI 25 ± 3 kg/m2) and 14 female (50 ± 10 years, BMI 25 ± 4 kg/m2) controls were recruited. Left ventricular (LV) volumes, mass, function and deformation, and left atrial (LA) volumes and function were assessed using cardiac magnetic resonance imaging (CMR). RESULTS: Participants in all groups were of similar age, and there were no significant differences in blood pressure (BP), diabetes duration or metabolic profile between the two diabetes groups. Concentric remodeling was present in both sexes (p < 0.0001), with greater degree of concentric hypertrophy in males (12%, p = 0.0015). Biplane LA ejection fraction (LAEF) (p = 0.038), peak systolic circumferential strain (p < 0.0001) and diastolic strain rates (p = 0.001) were significantly reduced in men compared with women with T2D. There were no significant differences in biplane LAEF, peak systolic circumferential strain and diastolic strain rates in women with T2D compared with female controls. Whereas in women with T2D, glycaemic control was linked to LV contractile function, there was no such relationship in men with T2D. CONCLUSION: Male sex adversely affects the phenotypic expression of diabetic heart disease. The striking differences in the cardiac phenotype between male and female patients with T2D promote awareness of gender-specific risk factors in search of treatment and prevention of diabetes-associated HF. CONDENSED ABSTRACT: We aimed to determine the effect of sex on the phenotypic expression of diabetic heart disease in patients with T2D. While our findings support the notion that in T2D, male sex adversely affects the phenotypic expression of diabetic heart disease, this is in apparent conflict with the previous large-scale study showing diabetes attenuates the otherwise protective effect of female sex on progression of cardiomyopathy. Further longitudinal studies looking at gender differences in clinical outcomes in T2D patients are needed. These sex-related differences promote awareness of sex-specific risk factors in search of treatment and prevention of diabetes-associated HF.

Diet modulates brain network stability, a biomarker for brain aging, in young adults.

Epidemiological studies suggest that insulin resistance accelerates progression of age-based cognitive impairment, which neuroimaging has linked to brain glucose hypometabolism. As cellular inputs, ketones increase Gibbs free energy change for ATP by 27% compared to glucose. Here we test whether dietary changes are capable of modulating sustained functional communication between brain regions (network stability) by changing their predominant dietary fuel from glucose to ketones. We first established network stability as a biomarker for brain aging using two large-scale (n = 292, ages 20 to 85 y; n = 636, ages 18 to 88 y) 3 T functional MRI (fMRI) datasets. To determine whether diet can influence brain network stability, we additionally scanned 42 adults, age < 50 y, using ultrahigh-field (7 T) ultrafast (802 ms) fMRI optimized for single-participant-level detection sensitivity. One cohort was scanned under standard diet, overnight fasting, and ketogenic diet conditions. To isolate the impact of fuel type, an independent overnight fasted cohort was scanned before and after administration of a calorie-matched glucose and exogenous ketone ester (d-ß-hydroxybutyrate) bolus. Across the life span, brain network destabilization correlated with decreased brain activity and cognitive acuity. Effects emerged at 47 y, with the most rapid degeneration occurring at 60 y. Networks were destabilized by glucose and stabilized by ketones, irrespective of whether ketosis was achieved with a ketogenic diet or exogenous ketone ester. Together, our results suggest that brain network destabilization may reflect early signs of hypometabolism, associated with dementia. Dietary interventions resulting in ketone utilization increase available energy and thus may show potential in protecting the aging brain.

Why a d-ß-hydroxybutyrate monoester?

Much of the world's prominent and burdensome chronic diseases, such as diabetes, Alzheimer's, and heart disease, are caused by impaired metabolism. By acting as both an efficient fuel and a powerful signalling molecule, the natural ketone body, d-ß-hydroxybutyrate (ßHB), may help circumvent the metabolic malfunctions that aggravate some diseases. Historically, dietary interventions that elevate ßHB production by the liver, such as high-fat diets and partial starvation, have been used to treat chronic disease with varying degrees of success, owing to the potential downsides of such diets. The recent development of an ingestible ßHB monoester provides a new tool to quickly and accurately raise blood ketone concentration, opening a myriad of potential health applications. The ßHB monoester is a salt-free ßHB precursor that yields only the biologically active d-isoform of the metabolite, the pharmacokinetics of which have been studied, as has safety for human consumption in athletes and healthy volunteers. This review describes fundamental concepts of endogenous and exogenous ketone body metabolism, the differences between the ßHB monoester and other exogenous ketones and summarises the disease-specific biochemical and physiological rationales behind its clinical use in diabetes, neurodegenerative diseases, heart failure, sepsis related muscle atrophy, migraine, and epilepsy. We also address the limitations of using the ßHB monoester as an adjunctive nutritional therapy and areas of uncertainty that could guide future research.

Cardiac ketone body metabolism.

The ketone bodies, d-ß-hydroxybutyrate and acetoacetate, are soluble 4-carbon compounds derived principally from fatty acids, that can be metabolised by many oxidative tissues, including heart, in carbohydrate-depleted conditions as glucose-sparing energy substrates. They also have important signalling functions, acting through G-protein coupled receptors and histone deacetylases to regulate metabolism and gene expression including that associated with anti-oxidant activity. Their concentration, and hence availability, increases in diabetes mellitus and heart failure. Whilst known to be substrates for ATP production, especially in starvation, their role(s) in the heart, and in heart disease, is uncertain. Recent evidence, reviewed here, indicates that increased ketone body metabolism is a feature of heart failure, and is accompanied by other changes in substrate selection. Whether the change in myocardial ketone body metabolism is adaptive or maladaptive is unknown, but it offers the possibility of using exogenous ketones to treat the failing heart.