Previous work showed that rats that were exposed to a high-fat, low-carbohydrate/protein ketogenic diet (KD) exhibited elevated blood alcohol levels following alcohol exposure compared with rats fed regular chow. Additionally, the administration of a KD prior to alcohol exposure (i.e., a history of KD) reduced alcohol consumption in alcohol-dependent rats that were no longer on the diet. In the present study, we investigated the mechanisms by which a KD alters alcohol metabolism and tested whether ongoing KD exposure reduces alcohol consumption in rats. We hypothesized that chronic KD exposure alters hepatic alcohol-metabolizing enzymes, slows alcohol metabolism, and reduces alcohol self-administration in alcohol-dependent rats. We found that male and female rats maintained on a KD had higher blood alcohol levels, lower hepatic alcohol dehydrogenase 1 protein levels, and a higher nicotinamide adenine dinucleotide [NAD+]/[NADH] ratio in the liver cytoplasm compared with chow-fed control rats. Furthermore, KD-fed rats demonstrated lower brain glucose uptake relative to chow-fed control rats. In a model of alcohol dependence, the KD reduced alcohol consumption in male, but not female, rats compared with chow-fed rats. These findings suggest that a KD alters brain energetics and alcohol metabolism, which may contribute to reduced alcohol consumption in male rats.

Alzheimer disease is a neurodegenerative pathology-modifying mitochondrial metabolism with energy impairments where the effects of biological sex and DNA repair deficiencies are unclear. We investigated the therapeutic potential of dietary ketosis alone or with supplemental nicotinamide riboside (NR) on hippocampal intermediary metabolism and mitochondrial bioenergetics in older male and female wild-type (Wt) and 3xTgAD-DNA polymerase-beta-deficient (3xTg/POL beta+/-) (AD) mice. DNA polymerase-beta is a key enzyme in DNA base excision repair (BER) of oxidative damage that may also contribute to mitochondrial DNA repair. Metabolic alterations imparted by ketosis and/or NR were assessed in 16 male and female groups, 4 Wt and 4 AD. At 73 weeks of age, mice were divided into: (A) carbohydrate diet (Carb); (B) Carb diet with NR (Carb-NR); (C) Ket diet (Ket); and (D) Ket diet with NR (Ket-NR) groups and remained on their respective treatments for 12 weeks. Mice were euthanized and hippocampi were rapidly removed and frozen. Glycolytic and TCA cycle intermediates were determined by quantitative GC-MS and the ratios of the mitochondrial free [NADox]/[NADHred] and coenzyme ubiquinone (CoQ/CoQH2) couples and the Gibbs free energy of the Complex I-II system of the electron transport chain (ETC) (triangle Gmitochondrial ComplexI-II '$$ \Delta {G}_{\mathrm{mitochondrial}\ \mathrm{Complex}\ \mathrm{I}-\mathrm{II}}<^>{\prime } $$) were calculated from selected metabolites. Mice in Groups C and D had elevated blood ketones (1-2 mM). In most groupings, male mice had higher concentrations of TCA cycle intermediates than females. Moreover, higher concentrations of fumarate in Wt males were associated with elevations in the Delta G ' of Complex I-II compared to females. In Wt males, NR treatments were associated with elevated concentrations of alpha-ketoglutarate and malate and linked to increased energy of Complex I-II. In AD males, both NR treatment and dietary ketosis restored the Delta G ' of Complex I-II, where the ratio of the CoQ/CoQH2 couple was oxidized and the [NADox]/[NADHred] couple was reduced. In AD females, only mice in the Ket diet group had a sufficiently reduced [NADox]/[NADHred] couple to restore the free energy profile. image

Parkinson's disease (PD) is a progressive, neurodegenerative disease characterized by motor dysfunction and dopamine deficits. The MitoPark (MP) mouse model of PD recapitulates several facets of Parkinson's disease, including gradual development of motor deficits, which enables the study of potential therapeutic interventions. One therapeutic strategy involves decreasing the mitochondrial metabolic load by inducing ketosis and providing an alternative energy source for neurons, leading to decreased neuronal oxidative stress. Thus, we hypothesized that administration of a ketone ester-enriched diet (KEED) would improve motor and dopamine release deficits in MP mice. Motor function (rotarod and open field tests), dopamine release (fast-scan cyclic voltammetry), tissue dopamine levels (gas chromatography-mass spectrometry) and dopamine neurons and axons (immunofluorescence) were assessed in MP, and control mice fed either the standard or a KEED. When started on the ketone diet before motor dysfunction onset, MP mice had improved motor function relative to standard diet (SD) MP mice. While the KEED did not preserve dopamine neurons or striatal dopamine axons, dopamine release in ketone diet MP mice was greater than SD MP mice but less than control mice. In a follow-up experiment, we began the ketone diet after motor dysfunction onset and observed a modest preservation of motor function in ketone diet MP mice relative to SD MP mice. The improvement in motor dysfunction indicates that a KEED or ketone supplement may have a beneficial effect on delaying motor deficit progression in Parkinson's disease.

OPINION article Front. Physiol., 09 May 2023Sec. Metabolic Physiology Volume 14 - 2023 | https://doi.org/10.3389/fphys.2023.1197768

Background Heart failure is responsible for approximately 65% of deaths in patients with type 2 diabetes mellitus. However, existing therapeutics for type 2 diabetes mellitus have limited success on the prevention of diabetic cardiomyopathy. The aim of this study was to determine whether moderate elevation in D‐β‐hydroxybutyrate improves cardiac function in animals with type 2 diabetes mellitus. Methods and Results Type 2 diabetic (db/db) and their corresponding wild‐type mice were fed a control diet or a diet where carbohydrates were equicalorically replaced by D‐β‐hydroxybutyrate‐(R)‐1,3 butanediol monoester (ketone ester [KE]). After 4 weeks, echocardiography demonstrated that a KE diet improved systolic and diastolic function in db/db mice. A KE diet increased expression of mitochondrial succinyl‐CoA:3‐oxoacid‐CoA transferase and restored decreased expression of mitochondrial β‐hydroxybutyrate dehydrogenase, key enzymes in cardiac ketone metabolism. A KE diet significantly enhanced both basal and ADP‐mediated oxygen consumption in cardiac mitochondria from both wild‐type and db/db animals; however, it did not result in the increased mitochondrial respiratory control ratio. Additionally, db/db mice on a KE diet had increased resistance to oxidative and redox stress, with evidence of restoration of decreased expression of thioredoxin and glutathione peroxidase 4 and less permeability transition pore activity in mitochondria. Mitochondrial biogenesis, quality control, and elimination of dysfunctional mitochondria via mitophagy were significantly increased in cardiomyocytes from db/db mice on a KE diet. The increase in mitophagy was correlated with restoration of mitofusin 2 expression, which contributed to improved coupling between cytosolic E3 ubiquitin ligase translocation into mitochondria and microtubule‐associated protein 1 light chain 3–mediated autophagosome formation. Conclusions Moderate elevation in circulating D‐β‐hydroxybutyrate levels via KE supplementation enhances mitochondrial biogenesis, quality control, and oxygen consumption and increases resistance to oxidative/redox stress and mPTP opening, thus resulting in improvement of cardiac function in animals with type 2 diabetes mellitus.

Alcohol use disorder (AUD) is a chronic, relapsing brain disorder, characterized by compulsive alcohol seeking and disrupted brain function. In individuals with AUD, abstinence from alcohol often precipitates withdrawal symptoms than can be life threatening. Here, we review evidence for nutritional ketosis as a potential means to reduce withdrawal and alcohol craving. We also review the underlying mechanisms of action of ketosis. Several findings suggest that during alcohol intoxication there is a shift from glucose to acetate metabolism that is enhanced in individuals with AUD. During withdrawal, there is a decline in acetate levels that can result in an energy deficit and could contribute to neurotoxicity. A ketogenic diet or ingestion of a ketone ester elevates ketone bodies (acetoacetate, β-hydroxybutyrate and acetone) in plasma and brain, resulting in nutritional ketosis. These effects have been shown to reduce alcohol withdrawal symptoms, alcohol craving, and alcohol consumption in both preclinical and clinical studies. Thus, nutritional ketosis may represent a unique treatment option for AUD: namely, a nutritional intervention that could be used alone or to augment the effects of medications.

The myocardium is metabolically flexible and can use fatty acids, glucose, lactate/pyruvate, ketones, or amino acids to fuel mechanical work. However, impaired metabolic flexibility is associated with cardiac dysfunction in conditions including diabetes and heart failure. The mitochondrial pyruvate carrier (MPC) is required for pyruvate metabolism and is composed of a hetero-oligomer of two proteins known as MPC1 and MPC2. Interestingly, MPC1 and MPC2 expression is downregulated in failing human hearts and in a mouse model of heart failure. Mice with cardiac-specific deletion of MPC2 (CS-MPC2-/-) exhibited loss of both MPC2 and MPC1 proteins and reduced pyruvate-stimulated mitochondrial respiration. CS-MPC2-/- mice exhibited normal cardiac size and function at 6-weeks old, but progressively developed cardiac dilation and contractile dysfunction thereafter. Feeding CS-MPC2-/- mice a ketogenic diet (KD) completely prevented or reversed the cardiac remodeling and dysfunction. Other diets with higher fat content and enough carbohydrate to limit ketosis also improved heart failure in CS-MPC2-/- mice, but direct ketone body provisioning provided only minor improvements in cardiac remodeling. Finally, KD was also able to prevent further remodeling in an ischemic, pressure-overload mouse model of heart failure. In conclusion, loss of mitochondrial pyruvate utilization leads to dilated cardiomyopathy that can be corrected by a ketogenic diet.

Because of a decreased sensitivity toward insulin, a key regulator of pyruvate dehydrogenase (PDH), Alzheimer’s patients have lower brain glucose utilization with reductions in Tricarboxylic Acid (TCA) cycle metabolites such as citrate, a precursor to n-acetyl-aspartate. In the 3xTgAd mouse model of Alzheimer’s disease (AD), aging mice also demonstrate low brain glucose metabolism. Ketone metabolism can overcome PDH inhibition and restore TCA cycle metabolites, thereby enhancing amino acid biosynthesis. A ketone ester of d-β-hydroxybutyrate was incorporated into a diet (Ket) and fed to 3xTgAd mice. A control group was fed a calorically matched diet (Cho). At 15 months of age, the exploratory and avoidance-related behavior patterns of the mice were evaluated. At 16.5 months of age, the animals were euthanized, and their hippocampi were analyzed for citrate, α-ketoglutarate, and amino acids. In the hippocampi of the Ket-fed mice, there were higher concentrations of citrate and α-ketoglutarate as well as higher concentrations of glutamate, aspartate and n-acetyl-aspartate compared with controls. There were positive associations between (1) concentrations of aspartate and n-acetyl-aspartate (n = 14, R = 0.9327), and (2) α-ketoglutarate and glutamate (n = 14, R = 0.8521) in animals maintained on either diet. Hippocampal n-acetyl-aspartate predicted the outcome of several exploratory and avoidance-related behaviors. Ketosis restored citrate and α-ketoglutarate in the hippocampi of aging mice. Higher concentrations of n-acetyl-aspartate corresponded with greater exploratory activity and reduced avoidance-related behavior.

The myocardium is metabolically flexible; however, impaired flexibility is associated with cardiac dysfunction in conditions including diabetes and heart failure. The mitochondrial pyruvate carrier (MPC) complex, composed of MPC1 and MPC2, is required for pyruvate import into the mitochondria. Here we show that MPC1 and MPC2 expression is downregulated in failing human and mouse hearts. Mice with cardiac-specific deletion of Mpc2 (CS-MPC2−/−) exhibited normal cardiac size and function at 6 weeks old, but progressively developed cardiac dilation and contractile dysfunction, which was completely reversed by a high-fat, low-carbohydrate ketogenic diet. Diets with higher fat content, but enough carbohydrate to limit ketosis, also improved heart failure, while direct ketone body provisioning provided only minor improvements in cardiac remodelling in CS-MPC2−/− mice. An acute fast also improved cardiac remodelling. Together, our results reveal a critical role for mitochondrial pyruvate use in cardiac function, and highlight the potential of dietary interventions to enhance cardiac fat metabolism to prevent or reverse cardiac dysfunction and remodelling in the setting of MPC deficiency. Impaired myocardial metabolic flexibility is associated with cardiac dysfunction in diabetes and heart failure. McCommis et al. reveal a critical role for mitochondrial pyruvate use in cardiac function, and use dietary interventions to enhance cardiac fat metabolism in dilated cardiomyopathy.

Impaired mitochondrial function and aberrant neuronal network activity are believed to be early events in the pathogenesis of Alzheimer's disease (AD), but how mitochondrial alterations contribute to aberrant activity in neuronal circuits is unknown. In this study, we examined the function of mitochondrial protein deacetylase sirtuin 3 (SIRT3) in the pathogenesis of AD. Compared with AppPs1 mice, Sirt3-haploinsufficient AppPs1 mice (Sirt3+/−AppPs1) exhibit early epileptiform EEG activity and seizure. Both male and female Sirt3+/−AppPs1 mice were observed to die prematurely before 5 months of age. When comparing male mice among different genotypes, Sirt3 haploinsufficiency renders GABAergic interneurons in the cerebral cortex vulnerable to degeneration and associated neuronal network hyperexcitability. Feeding Sirt3+/−AppPs1 AD mice with a ketone ester-rich diet increases SIRT3 expression and prevents seizure-related death and the degeneration of GABAergic neurons, indicating that the aggravated GABAergic neuron loss and neuronal network hyperexcitability in Sirt3+/−AppPs1 mice are caused by SIRT3 reduction and can be rescued by increase of SIRT3 expression. Consistent with a protective role in AD, SIRT3 levels are reduced in association with cerebral cortical Aβ pathology in AD patients. In summary, SIRT3 preserves GABAergic interneurons and protects cerebral circuits against hyperexcitability, and this neuroprotective mechanism can be bolstered by dietary ketone esters. SIGNIFICANCE STATEMENT GABAergic neurons provide the main inhibitory control of neuronal activity in the brain. By preserving mitochondrial function, SIRT3 protects parvalbumin and calretinin interneurons against Aβ-associated dysfunction and degeneration in AppPs1 Alzheimer's disease mice, thus restraining neuronal network hyperactivity. The neuronal network dysfunction that occurs in Alzheimer's disease can be partially reversed by physiological, dietary, and pharmacological interventions to increase SIRT3 expression and enhance the functionality of GABAergic interneurons.

Heart failure (HF) accounts for ∼65% of deaths in patients with type 2 diabetes (T2D). However, existing therapeutics for T2D have limited impact on the prevention of diabetic cardiomyopathy. Since ketone bodies can be a more efficient energy substrate in diabetics, we examined whether moderate elevation of the ketone body beta-hydroxybutyrate would improve cardiac performance in hearts of T2D animals. Here, 10-wk-old male control (WT) and diabetic (db/db) mice were fed a ketogenic diet containing D-beta-hydroxybutyrate-(R)-1,3 butanediol monoester (ketone ester, KE replacing equicaloric amounts of carbohydrate) for 4 weeks and several parameters of cardiac function were measured in vivo. Diets contained equal amounts of fat, protein, and micronutrients. The KE groups were fed ad libitum, whereas the control diet groups were pair-fed to the KE group. We found that the KE diet prevented a gradual decline in both diastolic and systolic cardiac function and restored heart dimensions in diabetic animals. Accordingly, we observed an almost 2-fold increase in succinyl-CoA:3-oxoacid-CoA transferase (SCOT) expression, a key enzyme in KB metabolism. Using novel genetically-encoded oxidative stress and redox sensors, we determined that diabetic mice on KE diet had increased resistance to oxidative stress. Furthermore, there was significant improvement in mitochondrial electron coupling and energetics with KE diet. In contrast, WT mice on the KE diet, when subjected to ascending aortic constriction (AAC) to induce HF, had a decreased survival rate compared to AAC animals on control diet, and corresponding sham controls. We determined that HF myocytes had decreased expression of SCOT and enhanced formation of the ketone body polymer, poly-beta-hydroxybutyrate, leading to enhanced mPTP formation. Therefore, high KE diets may have radically different mechanistic effects on cardiac function in control, diabetic and HF animals.

The precursor cells for metabolically beneficial beige adipocytes can alternatively become fibrogenic and contribute to adipose fibrosis. We found that cold exposure or β3-adrenergic agonist treatment of mice decreased the fibrogenic profile of precursor cells and stimulated beige adipocyte differentiation. This fibrogenic-to-adipogenic transition was impaired in aged animals, correlating with reduced adipocyte expression of the transcription factor PRDM16. Genetic loss of Prdm16 mimicked the effect of aging in promoting fibrosis, whereas increasing PRDM16 in aged mice decreased fibrosis and restored beige adipose development. PRDM16-expressing adipose cells secreted the metabolite β-hydroxybutyrate (BHB), which blocked precursor fibrogenesis and facilitated beige adipogenesis. BHB catabolism in precursor cells, mediated by BDH1, was required for beige fat differentiation in vivo. Finally, dietary BHB supplementation in aged animals reduced adipose fibrosis and promoted beige fat formation. Together, our results demonstrate that adipocytes secrete a metabolite signal that controls beige fat remodeling.

Cell membrane potential and inorganic ion distributions are currently viewed from a kinetic electric paradigm, which ignores thermodynamics. The resting membrane potential is viewed as a diffusion potential. The 9 major inorganic ions found in blood plasma (Ca2+, Na+, Mg2+, K+, H+, Cl-, HCO3-, H2PO4-, and HPO42-) are distributed unequally across the plasma membrane. This unequal distribution requires the energy of ATP hydrolysis through the action of the Na+-K+ ATPase. The cell resting membrane potential in each of 3 different tissues with widely different resting membrane potentials has been shown to be equal to the Nernst equilibrium potential of the most permeant inorganic ion. The energy of the measured distribution of the 9 major inorganic ions between extra- and intracellular phases was essentially equal to the independently measured energy of ATP hydrolysis, showing that the distribution of these 9 major ions was in near-equilibrium with the ΔG' of ATP. Therefore, thermodynamics does appear to play an essential role in the determination of the cell resting membrane potential and the inorganic ion distribution across the plasma membrane.-Veech, R. L., King, M. T., Pawlosky, R., Bradshaw, P. C., Curtis, W. Relationship between inorganic ion distribution, resting membrane potential, and the ΔG' of ATP hydrolysis: a new paradigm.

The extension of life span by caloric restriction has been studied across species from yeast and C aenorhabditis elegans to primates. No generally accepted theory has been proposed to explain these observations. Here, we propose that the life span extension produced by caloric restriction can be duplicated by the metabolic changes induced by ketosis. From nematodes to mice, extension of life span results from decreased signaling through the insulin/insulin‐like growth factor receptor signaling (IIS) pathway. Decreased IIS diminishes phosphatidylinositol (3,4,5) triphosphate (PIP 3 ) production, leading to reduced PI3K and AKT kinase activity and decreased forkhead box O transcription factor (FOXO) phosphorylation, allowing FOXO proteins to remain in the nucleus. In the nucleus, FOXO proteins increase the transcription of genes encoding antioxidant enzymes, including superoxide dismutase 2, catalase, glutathione peroxidase, and hundreds of other genes. An effective method for combating free radical damage occurs through the metabolism of ketone bodies, ketosis being the characteristic physiological change brought about by caloric restriction from fruit flies to primates. A dietary ketone ester also decreases circulating glucose and insulin leading to decreased IIS. The ketone body, d ‐β‐hydroxybutyrate ( d ‐βHB), is a natural inhibitor of class I and IIa histone deacetylases that repress transcription of the FOXO3a gene. Therefore, ketosis results in transcription of the enzymes of the antioxidant pathways. In addition, the metabolism of ketone bodies results in a more negative redox potential of the NADP antioxidant system, which is a terminal destructor of oxygen free radicals. Addition of d ‐βHB to cultures of C. elegans extends life span. We hypothesize that increasing the levels of ketone bodies will also extend the life span of humans and that calorie restriction extends life span at least in part through increasing the levels of ketone bodies. An exogenous ketone ester provides a new tool for mimicking the effects of caloric restriction that can be used in future research. The ability to power mitochondria in aged individuals that have limited ability to oxidize glucose metabolites due to pyruvate dehydrogenase inhibition suggests new lines of research for preventative measures and treatments for aging and aging‐related disorders. © 2017 The Authors IUBMB Life published by Wiley Periodicals, Inc. on behalf of International Union of Biochemistry and Molecular Biology, 69(5):305–314, 2017

Deficits in cerebral glucose utilization in Alzheimer’s disease (AD) arise decades before cognitive impairment and accumulation of amyloid plaques and neurofibrillary tangles in brain. Addressing this metabolic deficit has greater potential in treating AD than targeting later disease processes – an approach that has failed consistently in the clinic. Cerebral glucose utilization requires numerous enzymes, many of which have been shown to decline in AD. Perhaps the most important is pyruvate dehydrogenase (PDH), which links glycolysis with the Krebs cycle and aerobic metabolism, and whose activity is greatly suppressed in AD. The unique metabolism of ketone bodies allows them to bypass the block at pyruvate dehydrogenase and restore brain metabolism. Recent studies in mouse genetic models of AD and in a human Alzheimer’s patient showed the potential of ketones in maintaining brain energetics and function. Oral ketone bodies might be a promising avenue for treatment of Alzheimer’s disease.

Ketosis, the metabolic response to energy crisis, is a mechanism to sustain life by altering oxidative fuel selection. Often overlooked for its metabolic potential, ketosis is poorly understood outside of starvation or diabetic crisis. Thus, we studied the biochemical advantages of ketosis in humans using a ketone ester-based form of nutrition without the unwanted milieu of endogenous ketone body production by caloric or carbohydrate restriction. In five separate studies of 39 high-performance athletes, we show how this unique metabolic state improves physical endurance by altering fuel competition for oxidative respiration. Ketosis decreased muscle glycolysis and plasma lactate concentrations, while providing an alternative substrate for oxidative phosphorylation. Ketosis increased intramuscular triacylglycerol oxidation during exercise, even in the presence of normal muscle glycogen, co-ingested carbohydrate and elevated insulin. These findings may hold clues to greater human potential and a better understanding of fuel metabolism in health and disease.

Reactive oxygen and nitrogen species, ROS and RNS, are ubiquitous in living cells. They have beneficial effects but are also the cause of a wide variety of diseases. However adding excessive amounts of reducing agents has a long history of clinical failure. This problem can be overcome by providing a novel ester of D-beta-hydroxybutyrate–R-1,3-butanediol, which is rapidly hydrolyzed to ketone bodies, the metabolism of which leads to the production of NADPH. The free cytosolic [NADP+]/[NADPH] redox potential is the most negative in the cell and sets the potential of the glutathione and ascorbic acid couples. Ketone bodies also act by inhibiting histone deacetylases, activating the transcription factor FOXO3 and increasing the transcription of enzymes involved in the destruction of ROS. Ketone esters would be effective in the treatment of a variety of disparate diseases where ROS play a role, ranging from Parkinson’s disease to radiation sickness and aging.

Ketone bodies are the most energy-efficient fuel and yield more ATP per mole of substrate than pyruvate and increase the free energy released from ATP hydrolysis. Elevation of circulating ketones via high-fat, low carbohydrate diets has been used for the treatment of drug-refractory epilepsy and for neurodegenerative diseases, such as Parkinson's disease. Ketones may also be beneficial for muscle and brain in times of stress, such as endurance exercise. The challenge has been to raise circulating ketone levels by using a palatable diet without altering lipid levels. We found that blood ketone levels can be increased and cholesterol and triglycerides decreased by feeding rats a novel ketone ester diet: chow that is supplemented with (R)-3-hydroxybutyl (R)-3-hydroxybutyrate as 30% of calories. For 5 d, rats on the ketone diet ran 32% further on a treadmill than did control rats that ate an isocaloric diet that was supplemented with either corn starch or palm oil (P < 0.05). Ketone-fed rats completed an 8-arm radial maze test 38% faster than did those on the other diets, making more correct decisions before making a mistake (P < 0.05). Isolated, perfused hearts from rats that were fed the ketone diet had greater free energy available from ATP hydrolysis during increased work than did hearts from rats on the other diets as shown by using [P-31]-NMR spectroscopy. The novel ketone diet, therefore, improved physical performance and cognitive function in rats, and its energy-sparing properties suggest that it may help to treat a range of human conditions with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cole, M. A., Cochlin, L. E., Carter, E., Tchabanenko, K., Pichulik, T., Gulston, M. K., Atherton, H. J., Schroeder, M. A., Deacon, R. M. J., Kashiwaya, Y., King, M. T., Pawlosky, R., Rawlins, J. N. P., Tyler, D. J., Griffin, J. L., Robertson, J., Veech, R. L., Clarke, K. Novel ketone diet enhances physical and cognitive performance.