Antioxidant capacity contributes to protection of ketone bodies against oxidative damage induced during hypoglycemic conditions

Investigating Ketone Bodies as Immunometabolic Countermeasures against Respiratory Viral Infections

Respiratory viral infections remain a scourge, with seasonal influenza infecting millions and killing many thousands annually and viral pandemics, such as COVID-19, recurring every decade. Age, cardiovascular disease, and diabetes mellitus are risk factors for severe disease and death from viral infection. Immunometabolic therapies for these populations hold promise to reduce the risks of death and disability. Such interventions have pleiotropic effects that might not only target the virus itself but also enhance supportive care to reduce cardiopulmonary complications, improve cognitive resilience, and facilitate functional recovery. Ketone bodies are endogenous metabolites that maintain cellular energy but also feature drug-like signaling activities that affect immune activity, metabolism, and epigenetics. Here, we provide an overview of ketone body biology relevant to respiratory viral infection, focusing on influenza A and severe acute respiratory syndrome (SARS)-CoV-2, and discuss the opportunities, risks, and research gaps in the study of exogenous ketone bodies as novel immunometabolic interventions in these diseases.

Exogenous Ketones as Therapeutic Signaling Molecules in High-Stress Occupations: Implications for Mitigating Oxidative Stress and Mitochondrial Dysfunction in Future Research

High-stress occupations (ie, firefighters, military personnel, police officers, etc.) are often plagued by cardiometabolic diseases induced by exposure to chronic stressors. Interrupted sleep cycles, poor dietary patterns, lack of physical activity, and smoke exposure along with simultaneous psychological stressors promote chronic low-grade inflammation and excessive oxidative stress. Collectively, these data suggest that practical interventions which might mitigate the underlying pathologies of these cardiometabolic diseases are warranted. Ketones, specifically R-βHB, modulates intracellular signaling cascades such as the cellular redox ratios of NAD+/NADH, the activity of NAD dependent deacetylases SIRT1 and SIRT3, and promotes a robust mitochondrial environment which favors reductions in oxidative stress and inflammation. To date, the literature examining R-βHB as a signaling metabolite has mostly been performed from endogenous R-βHB production achieved through nutritional ketosis or cell culture and mouse models using exogenous R-βHB. To the authors knowledge, only 1 study has attempted to report on the effects of exogenous ketones and the mitigation of oxidative stress/inflammation. Therefore, the scope of this review is to detail the mechanisms of R-βHB as a signaling metabolite and the role that exogenous ketones might play in mitigating diseases in individuals serving in high-stress occupations.

Effects of Ketone Bodies on Brain Metabolism and Function in Neurodegenerative Diseases

Under normal physiological conditions the brain primarily utilizes glucose for ATP generation. However, in situations where glucose is sparse, e.g., during prolonged fasting, ketone bodies become an important energy source for the brain. The brain’s utilization of ketones seems to depend mainly on the concentration in the blood, thus many dietary approaches such as ketogenic diets, ingestion of ketogenic medium-chain fatty acids or exogenous ketones, facilitate significant changes in the brain’s metabolism. Therefore, these approaches may ameliorate the energy crisis in neurodegenerative diseases, which are characterized by a deterioration of the brain’s glucose metabolism, providing a therapeutic advantage in these diseases. Most clinical studies examining the neuroprotective role of ketone bodies have been conducted in patients with Alzheimer’s disease, where brain imaging studies support the notion of enhancing brain energy metabolism with ketones. Likewise, a few studies show modest functional improvements in patients with Parkinson’s disease and cognitive benefits in patients with—or at risk of—Alzheimer’s disease after ketogenic interventions. Here, we summarize current knowledge on how ketogenic interventions support brain metabolism and discuss the therapeutic role of ketones in neurodegenerative disease, emphasizing clinical data.

Treatment with the Ketone Body D-β-hydroxybutyrate Attenuates Autophagy Activated by NMDA and Reduces Excitotoxic Neuronal Damage in the Rat Striatum In Vivo

BACKGROUND

The ketone bodies (KB), β-hydroxybutyrate (BHB) and acetoacetate, have been proposed for the treatment of acute and chronic neurological disorders, however, the molecular mechanisms involved in KB protection are not well understood. KB can substitute for glucose and support mitochondrial metabolism increasing cell survival. We have reported that the D-isomer of BHB (D-BHB) stimulates autophagic degradation during glucose deprivation in cultured neurons increasing cell viability. Autophagy is a lysosomal degradation process of damaged proteins and organelles activated during nutrient deprivation to obtain building blocks and energy. However, impaired or excessive autophagy can contribute to neuronal death.

OBJECTIVE

The aim of the present study was to test whether D-BHB can preserve autophagic function in an in vivo model of excitotoxic damage induced by the administration of the glutamate receptor agonist, N-methyl-Daspartate (NMDA), in the rat striatum.

METHODS

D-BHB was administered through an intravenous injection followed by either an intraperitoneal injection (i.v+i.p) or a continuous epidural infusion (i.v+pump), or through a continuous infusion of D-BHB alone. Changes in the autophagy proteins ATG7, ATG5, BECLIN 1 (BECN1), LC3, Sequestrosome1/p62 (SQSTM1/ p62) and the lysosomal membrane protein LAMP2, were evaluated by immunoblot. The lesion volume was measured in cresyl violet-stained brain sections.

RESULTS

Autophagy is activated early after NMDA injection but autophagic degradation is impaired due to the cleavage of LAMP2. Twenty-four h after NMDA intrastriatal injection, the autophagic flux is re-established, but LAMP2 cleavage is still observed. The administration of D-BHB through the i.v+pump protocol reduced the content of autophagic proteins and the cleavage of LAMP2, suggesting decreased autophagosome formation and lysosomal membrane preservation, improving autophagic degradation. D-BHB also reduced brain injury. The i.v+i.p administration protocol and the infusion of D-BHB alone showed no effect on autophagy activation or degradation.

The Ketogenic Diet in the Treatment of Post-concussion Syndrome-A Feasibility Study

Concussion is the most common form of mild traumatic brain injury (mTBI). Although most patients' symptoms resolve within a month, patients with post-concussion syndrome (PCS) may continue to experience symptoms for years and have limited treatment options. This pilot study assessed the feasibility and symptom-related effects of a ketogenic diet (KD) in patients with PCS symptoms. The Ketogenic Diet in Post-Concussion Syndrome (KD-PCS) was a single-arm trial of a 2-month KD high in non-starchy vegetables and supplemented with medium-chain triglyceride (MCT) oil. Macronutrient targets were ≥70% fat, ≤10% carbohydrate, and the remainder as protein as energy. We assessed feasibility by daily self-reported measure of urine acetoacetate and collection of 3-day food records and serum beta-hydroxybutyrate at multiple timepoints. We assessed symptoms by administering the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) and Modified Balance Error Scoring System (M-BESS) at baseline and month 2 and the Post-Concussion Symptom Scale (PCSS) at baseline, month 1, and month 2. Fourteen participants enrolled in the KD-PCS. Twelve participants completed the study and 11 implemented the KD (73% fat, 9% carbohydrate, and 18% protein) and achieved ketosis. One participant complained of MCT-related diarrhea that resolved and another reported nausea and fatigue that resulted in withdrawal from the study. Among compliant participants, the visual memory domain of the ImPACT improved by 12 points (p = 0.02) and PCSS scores improved by 9 points, although not statistically significant. This pilot trial suggests that the KD is a feasible experimental treatment for PCS and justifies further study of its efficacy.

Effect of β-Hydroxybutyrate on Autophagy Dynamics During Severe Hypoglycemia and the Hypoglycemic Coma

Glucose supply from blood is mandatory for brain functioning and its interruption during acute hypoglycemia or cerebral ischemia leads to brain injury. Alternative substrates to glucose such as the ketone bodies (KB), acetoacetate (AcAc), and β-hydroxybutyrate (BHB), can be used as energy fuels in the brain during hypoglycemia and prevent neuronal death, but the mechanisms involved are still not well understood. During glucose deprivation adaptive cell responses can be activated such as autophagy, a lysosomal-dependent degradation process, to support cell survival. However, impaired or excessive autophagy can lead to cell dysfunction. We have previously shown that impaired autophagy contributes to neuronal death induced by glucose deprivation in cortical neurons and that D isomer of BHB (D-BHB) reestablishes the autophagic flux increasing viability. Here, we aimed to investigate autophagy dynamics in the brain of rats subjected to severe hypoglycemia (SH) without glucose infusion (GI), severe hypoglycemia followed by GI (SH + GI), and a brief period of hypoglycemic coma followed by GI (Coma). The effect of D-BHB administration after the coma was also tested (Coma + BHB). The transformation of LC3-I to LC3-II and the abundance of autophagy proteins, Beclin 1 (BECN1), ATG7, and ATG12–ATG5 conjugate, were analyzed as an index of autophagosome formation, and the levels of sequestrosome1/p62 (SQSTM1/p62) were determined as a hallmark of autophagic degradation. Data suggest that autophagosomes accumulate in the cortex and the hippocampus of rats after SH, likely due to impaired autophagic degradation. In the cortex, autophagosome accumulation persisted at 6 h after GI in animals exposed to SH but recovered basal levels at 24 h, while in the hippocampus no significant effect was observed. In animals subjected to coma, autophagosome accumulation was observed at 24 h after GI in both regions. D-BHB treatment reduced LC3-II and SQSTM1/p62 content and reduced ULK1 phosphorylation by AMPK, suggesting it stimulates the autophagic flux and decreases AMPK activity reducing autophagy initiation. D-BHB also reduced the number of degenerating cells. Together, data suggest different autophagy dynamics after GI in rats subjected to SH or the hypoglycemic coma and support that D-BHB treatment can modulate autophagy dynamics favoring the autophagic flux.

Sodium-glucose cotransporter 2 inhibitors’ mechanisms of action in heart failure

Three major cardiovascular outcome trials (CVOTs) with a new class of antidiabetic drugs - sodium-glucose cotransporter 2 (SGLT2) inhibitors (EMPA-REG OUTCOME trial with empagliflozin, CANVAS Program with canagliflozin, DECLARE-TIMI 58 with dapagliflozin) unexpectedly showed that cardiovascular outcomes could be improved possibly due to a reduction in heart failure risk, which seems to be the most sensitive outcome of SGLT2 inhibition. No other CVOT to date has shown any significant benefit on heart failure events. Even more impressive findings came recently from the DAPA-HF trial in patients with confirmed and well-treated heart failure: Dapagliflozin was shown to reduce heart failure risk for patients with heart failure with reduced ejection fraction regardless of diabetes status. Nevertheless, despite their possible wide clinical implications, there is much doubt about the mechanisms of action and a lot of questions to unravel, especially now when their benefits translated to non-diabetic patients, rising doubts about the validity of some current mechanistic assumptions.The time frame of their cardiovascular benefits excludes glucose-lowering and antiatherosclerotic-mediated effects and multiple other mechanisms, direct cardiac as well as systemic, are suggested to explain their early cardiorenal benefits. These are: Anti-inflammatory, antifibrotic, antioxidative, antiapoptotic properties, then renoprotective and hemodynamic effects, attenuation of glucotoxicity, reduction of uric acid levels and epicardial adipose tissue, modification of neurohumoral system and cardiac fuel energetics, sodium-hydrogen exchange inhibition. The most logic explanation seems that SGLT2 inhibitors timely target various mechanisms underpinning heart failure pathogenesis. All the proposed mechanisms of their action could interfere with evolution of heart failure and are discussed separately within the main text.

β-Hydroxybutyrate Increases Exercise Capacity Associated with Changes in Mitochondrial Function in Skeletal Muscle

β-hydroxybutyrate is the main ketone body generated by the liver under starvation. Under these conditions, it can sustain ATP levels by its oxidation in mitochondria. As mitochondria can modify its shape and function under different nutritional challenges, we study the chronic effects of β-hydroxybutyrate supplementation on mitochondrial morphology and function, and its relation to exercise capacity. Male C57BL/6 mice were supplemented with β-hydroxybutyrate mineral salt (3.2%) or control (CT, NaCl/KCl) for six weeks and submitted to a weekly exercise performance test. We found an increase in distance, maximal speed, and time to exhaustion at two weeks of supplementation. Fatty acid metabolism and OXPHOS subunit proteins declined at two weeks in soleus but not in tibialis anterior muscles. Oxygen consumption rate on permeabilized fibers indicated a decrease in the presence of pyruvate in the short-term treatment. Both the tibialis anterior and soleus showed decreased levels of Mitofusin 2, while electron microscopy assessment revealed a significant reduction in mitochondrial cristae shape in the tibialis anterior, while a reduction in the mitochondrial number was observed only in soleus. These results suggest that short, but not long-term, β-hydroxybutyrate supplementation increases exercise capacity, associated with modifications in mitochondrial morphology and function in mouse skeletal muscle.

Selenium and antioxidant levels in children with intractable epilepsy receiving ketogenic diet

Ketogenic diet is a high-fat, low-carbohydrate, and adequate-protein diet. It is well-established as a treatment option for drug-resistant childhood epilepsies. Our study aimed to evaluate Selenium levels and oxidative stress in children receiving ketogenic diet for intractable seizures for 6 months. This is a comparative case-control study included 90 children under 6 years age. They were subdivided into three groups. Group I: Thirty patients with drug-resistant epilepsy under antiepileptic drugs only. Group II: Thirty patients with drug-resistant epilepsy under treatment with ketogenic diet for 6 months and antiepileptic drugs. Group III: Thirty age and sex-matched healthy children as controls. Full history taking with special emphasis on severity and frequency of seizures, neurological examination, anthropometric measurements and laboratory analysis for serum Malonaldehyde, and total antioxidant capacity and Selenium were done for all participants. The frequency and severity of seizures were significantly lower in group II receiving ketogenic diet than group I on antiepileptic drugs only. Selenium levels were significantly lower in epileptic patients in comparison to controls. However, it was markedly lower in the ketogenic diet group. Malonaldehyde levels were significantly higher in epileptic children in comparison to controls, with lower values among ketogenic diet group when compared to patients on antiepileptic drugs only. Total antioxidant capacity levels were significantly lower in epileptic patients in comparison to controls, with higher values among ketogenic diet group as compared to epileptic patients on pharmacological treatment. Ketogenic diet is an effective treatment for refractory epilepsy for its anti-epileptic mechanism. It also may exert antioxidant effects. The nutrient content of the ketogenic diet may not meet the recommended daily allowance for selenium. So, this should be taken into consideration for supplementation of minerals in adequate amounts for patients receiving this diet.

Induced Ketosis as a Treatment for Neuroprogressive Disorders: Food for Thought?

Induced ketosis (or ketone body ingestion) can ameliorate several changes associated with neuroprogressive disorders, including schizophrenia, bipolar disorder, and major depressive disorder. Thus, the effects of glucose hypometabolism can be bypassed through the entry of beta-hydroxybutyrate, providing an alternative source of energy to glucose. The weight of evidence suggests that induced ketosis reduces levels of oxidative stress, mitochondrial dysfunction, and inflammation-core features of the above disorders. There are also data to suggest that induced ketosis may be able to target other molecules and signaling pathways whose levels and/or activity are also known to be abnormal in at least some patients suffering from these illnesses such as peroxisome proliferator-activated receptors, increased activity of the Kelch-like ECH-associated protein/nuclear factor erythroid 2-related factor 2, Sirtuin-1 nuclear factor-κB p65, and nicotinamide adenine dinucleotide (NAD). This review explains the mechanisms by which induced ketosis might reduce mitochondrial dysfunction, inflammation, and oxidative stress in neuropsychiatric disorders and ameliorate abnormal levels of molecules and signaling pathways that also appear to contribute to the pathophysiology of these illnesses. This review also examines safety data relating to induced ketosis over the long term and discusses the design of future studies.

Nutritional ketosis as an intervention to relieve astrogliosis: Possible therapeutic applications in the treatment of neurodegenerative and neuroprogressive disorders

Nutritional ketosis, induced via either the classical ketogenic diet or the use of emulsified medium-chain triglycerides, is an established treatment for pharmaceutical resistant epilepsy in children and more recently in adults. In addition, the use of oral ketogenic compounds, fractionated coconut oil, very low carbohydrate intake, or ketone monoester supplementation has been reported to be potentially helpful in mild cognitive impairment, Parkinson’s disease, schizophrenia, bipolar disorder, and autistic spectrum disorder. In these and other neurodegenerative and neuroprogressive disorders, there are detrimental effects of oxidative stress, mitochondrial dysfunction, and neuroinflammation on neuronal function. However, they also adversely impact on neurone–glia interactions, disrupting the role of microglia and astrocytes in central nervous system (CNS) homeostasis. Astrocytes are the main site of CNS fatty acid oxidation; the resulting ketone bodies constitute an important source of oxidative fuel for neurones in an environment of glucose restriction. Importantly, the lactate shuttle between astrocytes and neurones is dependent on glycogenolysis and glycolysis, resulting from the fact that the astrocytic filopodia responsible for lactate release are too narrow to accommodate mitochondria. The entry into the CNS of ketone bodies and fatty acids, as a result of nutritional ketosis, has effects on the astrocytic glutamate–glutamine cycle, glutamate synthase activity, and on the function of vesicular glutamate transporters, EAAT, Na⁺, K⁺-ATPase, K_ir4.1, aquaporin-4, Cx34 and K_ATP channels, as well as on astrogliosis. These mechanisms are detailed and it is suggested that they would tend to mitigate the changes seen in many neurodegenerative and neuroprogressive disorders. Hence, it is hypothesized that nutritional ketosis may have therapeutic applications in such disorders.

Metabolic and Immunological Effects of Intermittent Fasting on a Ketogenic Diet Containing Medium-Chain Triglycerides in Healthy Dogs

In several species, intermittent fasting (IF) has been shown to have beneficial effects, including delayed aging, increased lifespan, increased insulin sensitivity, reduced ischemic tissue damage, delayed onset of neurodegenerative disease and improved neuronal repair following injury. However, the metabolic and immunological effects of IF have not been well-established in dogs. The aim of this study was to examine the effects of a 48 h IF regimen using a low fat and a high fat diet in healthy dogs by quantifying the metabolic, hormonal, and immunological changes. We hypothesized that IF dogs would have higher blood ketone and ghrelin concentrations, lower blood leptin, insulin and glucose concentrations, and signs of immunosuppression compared to dogs eating daily. Ten healthy adult dogs were randomized into three group and underwent three feeding regimes in a 3 × 3 Latin square design: twice a day feeding on a low fat (23% energy from fat; LF) diet, 48 h fasting on a low fat diet, and 48 h fasting on a high fat enriched with medium-chain triglycerides (68% energy from fat; HF) diet. Body weight, food intake, activity, blood glucose, β-hydroxybutyrate, leptin, ghrelin, and insulin were measured. Lymphocyte proliferation and neutrophil/macrophage phagocytosis and respiratory burst were measured as markers of immune function. Nuclear magnetic resonance spectroscopy was used to relatively quantify plasma metabolites. When the dogs were IF on a HF diet, they had the highest concentration of blood ketones (mean 0.061 mmol/L, SD 0.024), whereas they had the lowest concentration (mean 0.018 mmol/L, SD 0.004) when fed daily. Blood glucose and insulin concentrations were lower in IF dogs on a HF diet compared to daily feeding or IF on a LF diet. There was an increase in plasma β-hydroxybutyrate concentrations, and a reduction in glucose and insulin concentrations when dogs were IF on a HF diet. There was only a decline in the immune parameters studied when the dogs were IF on a LF diet, which was not seen when on the HF diet. The results of this study indicate the potential of IF to be further investigated as a potential beneficial feeding regime for dogs.

Ketone bodies, stress response, and redox homeostasis

The ketone body β-hydroxybutyrate is no longer viewed simply as a metabolic intermediate, as it regulates a broad range of physiological processes at cellular and systemic levels. Particularly, β-hydroxybutyrate functions as a stress response molecule and orchestrates an antioxidant defense program to maintain redox homeostasis in response to environmental and metabolic challenges, such as ischemia. This property of β-hydroxybutyrate might be key for the beneficial effect of calorie restriction on stress response and disease processes.

Therapeutic strategies for ketosis induction and their potential efficacy for the treatment of acute brain injury and neurodegenerative diseases

The therapeutic use of ketone bodies (KB) against acute brain injury and neurodegenerative disorders has lately been suggested by many studies. Several mechanisms responsible for the protective action of KB have been described, including metabolic, anti-inflammatory and epigenetic. However, it is still not clear whether a specific mechanism of action can be associated with a particular neurological disorder. Different strategies to induce ketosis including the ketogenic diet (KD), caloric restriction (CR), intermittent fasting (IF), as well as the administration of medium chain triglycerides (MCTs), exogenous ketones or KB derivatives, have been used in animal models of brain injury and in humans. They have shown different degrees of success to prevent neuronal damage, motor alterations and cognitive decline. However, more investigation is needed in order to establish safe protocols for clinical application. Throughout the present review, we describe the different approaches that have been used to elevate blood KB and discuss their effectiveness considering their advantages and limitations, as tested in models of brain injury, neurodegeneration and clinical research. We also describe the mechanisms of action of KB in non-pathologic conditions and in association with their protective effect against neuronal damage in acute neurological disorders and neurodegenerative diseases.

Ketone Bodies in Neurological Diseases: Focus on Neuroprotection and Underlying Mechanisms

There is growing evidence that ketone bodies, which are derived from fatty acid oxidation and usually produced in fasting state or on high-fat diets have broad neuroprotective effects. Although the mechanisms underlying the neuroprotective effects of ketone bodies have not yet been fully elucidated, studies in recent years provided abundant shreds of evidence that ketone bodies exert neuroprotective effects through possible mechanisms of anti-oxidative stress, maintaining energy supply, modulating the activity of deacetylation and inflammatory responses. Based on the neuroprotective effects, the ketogenic diet has been used in the treatment of several neurological diseases such as refractory epilepsy, Parkinson's disease, Alzheimer's disease, and traumatic brain injury. The ketogenic diet has great potential clinically, which should be further explored in future studies. It is necessary to specify the roles of components in ketone bodies and their therapeutic targets and related pathways to optimize the strategy and efficacy of ketogenic diet therapy in the future.

Exogenous Ketone Bodies as Promising Neuroprotective Agents for Developmental Brain Injury

Ketone bodies are a promising area of neuroprotection research that may be ideally suited to the injured newborn. During normal development, the human infant is in significant ketosis for at least the first week of life. Ketone uptake and metabolism is upregulated in the both the fetus and neonate, with ketone bodies providing at least 10% of cerebral metabolic energy requirements, as well as being the preferred precursors for the synthesis of fatty acids and cholesterol. At the same time, ketone bodies have been shown to have multiple neuroprotective effects, including being anticonvulsant, decreasing oxidative stress and inflammation, and epigenetically upregulating the production of neurotrophic factors. While ketogenic diets and exogenous ketosis are largely being investigated in the setting of adult brain injury, the adaptation of the neonate to ketosis suggests that developmental brain injury may be the area most suited to the use of ketones for neuroprotection. Here, we describe the mechanisms by which ketone bodies exert their neuroprotective effects, and how these may translate to benefits within each of the phases of neonatal asphyxial brain injury.

Potential Protective Mechanisms of Ketone Bodies in Migraine Prevention

An increasing amount of evidence suggests that migraines are a response to a cerebral energy deficiency or oxidative stress levels that exceed antioxidant capacity. The ketogenic diet (KD), a diet mimicking fasting that leads to the elevation of ketone bodies (KBs), is a therapeutic intervention targeting cerebral metabolism that has recently shown great promise in the prevention of migraines. KBs are an alternative fuel source for the brain, and are thus likely able to circumvent some of the abnormalities in glucose metabolism and transport found in migraines. Recent research has shown that KBs-D-β-hydroxybutyrate in particular-are more than metabolites. As signalling molecules, they have the potential to positively influence other pathways commonly believed to be part of migraine pathophysiology, namely: mitochondrial functioning, oxidative stress, cerebral excitability, inflammation and the gut microbiome. This review will describe the mechanisms by which the presence of KBs, D-BHB in particular, could influence those migraine pathophysiological mechanisms. To this end, common abnormalities in migraines are summarised with a particular focus on clinical data, including phenotypic, biochemical, genetic and therapeutic studies. Experimental animal data will be discussed to elaborate on the potential therapeutic mechanisms of elevated KBs in migraine pathophysiology, with a particular focus on the actions of D-BHB. In complex diseases such as migraines, a therapy that can target multiple possible pathogenic pathways seems advantageous. Further research is needed to establish whether the absence/restriction of dietary carbohydrates, the presence of KBs, or both, are of primary importance for the migraine protective effects of the KD.

Impact of Hypoglycemia on Brain Metabolism During Diabetes

Diabetes is a metabolic disease afflicting millions of people worldwide. A substantial fraction of world's total healthcare expenditure is spent on treating diabetes. Hypoglycemia is a serious consequence of anti-diabetic drug therapy, because it induces metabolic alterations in the brain. Metabolic alterations are one of the central mechanisms mediating hypoglycemia-related functional changes in the brain. Acute, chronic, and/or recurrent hypoglycemia modulate multiple metabolic pathways, and exposure to hypoglycemia increases consumption of alternate respiratory substrates such as ketone bodies, glycogen, and monocarboxylates in the brain. The aim of this review is to discuss hypoglycemia-induced metabolic alterations in the brain in glucose counterregulation, uptake, utilization and metabolism, cellular respiration, amino acid and lipid metabolism, and the significance of other sources of energy. The present review summarizes information on hypoglycemia-induced metabolic changes in the brain of diabetic and non-diabetic subjects and the manner in which they may affect brain function.

Systemic redox status in lung cancer patients is related to altered glucose metabolism

Altered systemic redox status is often observed in lung cancer. However, detailed information on factors other, than smoking, which influence this perturbation is rather scarce. Elevated oxidative stress has been linked with disturbances in glucose metabolism before, but such associations have not been investigated in lung cancer. The aim of this study was to evaluate the relationship between systemic parameters of glucose metabolism and redox status in lung cancer patients (LC). Biochemical variables related to circulating glucose, i.e. glucose, insulin, c-peptide, fructosamine (FA), and glucose metabolism, i.e. β-hydroxybutyrate (BHB), lactate (LACT), non-esterified fatty acids (NEFAs), as well as redox status i.e. total antioxidant status (TAS) and total oxidant status (TOS) were determined for LC (n = 122) and control subjects (CS) (n = 84). HOMA-IR and the oxidative stress index (OSI) were calculated. LC patients had an altered redox status and glucose metabolism compared to CS. Positive correlations in LC were observed between TOS, OSI and circulating glucose as well as FA, while TAS positively correlated with BHB and NEFAs. In contrast, in metastatic LC, NEFAs and BHB positively correlated with OSI. Smoking status additionally stratified the observed relationships. In conclusion, we found that parameters related to circulating glucose or non-enzymatic glycation were correlated with oxidative stress (TOS and OSI), while metabolites such as BHB and NEFAs were correlated with antioxidant capacity (TAS). Metastasis prevalence and smoking seem to influence these correlations. However, the detailed mechanism of this relationship requires further research, in particular as regards the surprising positive correlation between NEFAs and TAS.

Nutritional Ketosis and Mitohormesis: Potential Implications for Mitochondrial Function and Human Health

Impaired mitochondrial function often results in excessive production of reactive oxygen species (ROS) and is involved in the etiology of many chronic diseases, including cardiovascular disease, diabetes, neurodegenerative disorders, and cancer. Moderate levels of mitochondrial ROS, however, can protect against chronic disease by inducing upregulation of mitochondrial capacity and endogenous antioxidant defense. This phenomenon, referred to as mitohormesis, is induced through increased reliance on mitochondrial respiration, which can occur through diet or exercise. Nutritional ketosis is a safe and physiological metabolic state induced through a ketogenic diet low in carbohydrate and moderate in protein. Such a diet increases reliance on mitochondrial respiration and may, therefore, induce mitohormesis. Furthermore, the ketone β-hydroxybutyrate (BHB), which is elevated during nutritional ketosis to levels no greater than those resulting from fasting, acts as a signaling molecule in addition to its traditionally known role as an energy substrate. BHB signaling induces adaptations similar to mitohormesis, thereby expanding the potential benefit of nutritional ketosis beyond carbohydrate restriction. This review describes the evidence supporting enhancement of mitochondrial function and endogenous antioxidant defense in response to nutritional ketosis, as well as the potential mechanisms leading to these adaptations.

On the Metabolism of Exogenous Ketones in Humans

Background and aims: Currently there is considerable interest in ketone metabolism owing to recently reported benefits of ketosis for human health. Traditionally, ketosis has been achieved by following a high-fat, low-carbohydrate "ketogenic" diet, but adherence to such diets can be difficult. An alternative way to increase blood D-β-hydroxybutyrate (D-βHB) concentrations is ketone drinks, but the metabolic effects of exogenous ketones are relatively unknown. Here, healthy human volunteers took part in three randomized metabolic studies of drinks containing a ketone ester (KE); (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, or ketone salts (KS); sodium plus potassium βHB. Methods and Results: In the first study, 15 participants consumed KE or KS drinks that delivered ~12 or ~24 g of βHB. Both drinks elevated blood D-βHB concentrations (D-βHB C_max: KE 2.8 mM, KS 1.0 mM, P < 0.001), which returned to baseline within 3-4 h. KS drinks were found to contain 50% of the L-βHB isoform, which remained elevated in blood for over 8 h, but was not detectable after 24 h. Urinary excretion of both D-βHB and L-βHB was <1.5% of the total βHB ingested and was in proportion to the blood AUC. D-βHB, but not L-βHB, was slowly converted to breath acetone. The KE drink decreased blood pH by 0.10 and the KS drink increased urinary pH from 5.7 to 8.5. In the second study, the effect of a meal before a KE drink on blood D-βHB concentrations was determined in 16 participants. Food lowered blood D-βHB C_max by 33% (Fed 2.2 mM, Fasted 3.3 mM, P < 0.001), but did not alter acetoacetate or breath acetone concentrations. All ketone drinks lowered blood glucose, free fatty acid and triglyceride concentrations, and had similar effects on blood electrolytes, which remained normal. In the final study, participants were given KE over 9 h as three drinks (n = 12) or a continuous nasogastric infusion (n = 4) to maintain blood D-βHB concentrations greater than 1 mM. Both drinks and infusions gave identical D-βHB AUC of 1.3-1.4 moles.min. Conclusion: We conclude that exogenous ketone drinks are a practical, efficacious way to achieve ketosis.

On the Metabolism of Exogenous Ketones in Humans

Background and aims: Currently there is considerable interest in ketone metabolism owing to recently reported benefits of ketosis for human health. Traditionally, ketosis has been achieved by following a high-fat, low-carbohydrate "ketogenic" diet, but adherence to such diets can be difficult. An alternative way to increase blood D-β-hydroxybutyrate (D-βHB) concentrations is ketone drinks, but the metabolic effects of exogenous ketones are relatively unknown. Here, healthy human volunteers took part in three randomized metabolic studies of drinks containing a ketone ester (KE); (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, or ketone salts (KS); sodium plus potassium βHB. Methods and Results: In the first study, 15 participants consumed KE or KS drinks that delivered ~12 or ~24 g of βHB. Both drinks elevated blood D-βHB concentrations (D-βHB C_max: KE 2.8 mM, KS 1.0 mM, P < 0.001), which returned to baseline within 3-4 h. KS drinks were found to contain 50% of the L-βHB isoform, which remained elevated in blood for over 8 h, but was not detectable after 24 h. Urinary excretion of both D-βHB and L-βHB was <1.5% of the total βHB ingested and was in proportion to the blood AUC. D-βHB, but not L-βHB, was slowly converted to breath acetone. The KE drink decreased blood pH by 0.10 and the KS drink increased urinary pH from 5.7 to 8.5. In the second study, the effect of a meal before a KE drink on blood D-βHB concentrations was determined in 16 participants. Food lowered blood D-βHB C_max by 33% (Fed 2.2 mM, Fasted 3.3 mM, P < 0.001), but did not alter acetoacetate or breath acetone concentrations. All ketone drinks lowered blood glucose, free fatty acid and triglyceride concentrations, and had similar effects on blood electrolytes, which remained normal. In the final study, participants were given KE over 9 h as three drinks (n = 12) or a continuous nasogastric infusion (n = 4) to maintain blood D-βHB concentrations greater than 1 mM. Both drinks and infusions gave identical D-βHB AUC of 1.3-1.4 moles.min. Conclusion: We conclude that exogenous ketone drinks are a practical, efficacious way to achieve ketosis.

The Ketone Metabolite β-Hydroxybutyrate Attenuates Oxidative Stress in Spinal Cord Injury by Suppression of Class I Histone Deacetylases

The ketone metabolite β-hydroxybutyrate (βOHB), is reported to be neuroprotective after spinal cord injury (SCI) in rats, but the underlying mechanism remains unknown. The present study aims to investigate effects of βOHB on suppression of oxidative stress and inhibition of class I histone deacetylases (HDACs) in in vivo and in vitro models. Rats were fed with ketogenic diet (KD) or standard diet (SD) for 3 weeks. A C5 hemi-contusion injury was applied to these animals on the 14th day of experiment, and spinal cord samples were harvested on the 1st, 3rd and 7th days after SCI, respectively. The blood ketone levels were significantly higher in the KD groups. KD reduced oxidative stress markers and reactive oxygen species (ROS) products, downregulated the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)2 and NOX4, and upregulated the expression of forkhead box group O (FOXO)3a, mitochondrial superoxide dismutase (MnSOD), and catalase after SCI. The in vitro study, performed on PC12 cells, indicated that βOHB inhibited H₂O₂-induced ROS production, decreased NOX2 and NOX4 protein levels, and upregulated FOXO3a, MnSOD, and catalase levels in a dose-dependent manner, which was consistent with the in vivo results. The ketone metabolite βOHB inhibited HDAC1, HDAC2, and HDAC3 activity, but not HDAC8 in SCI rats and PC12 cells. Depletion of HDAC1 or HDAC2 with small interfering RNA (siRNA) attenuated H₂O₂-induced ROS production and protein carbonylation and elevated FOXO3a protein levels, meanwhile reducing NOX2 and NOX4 protein expression in PC12 cells. Our results indicate that the ketone metabolite βOHB attenuates oxidative stress in SCI by inhibition of class I HDACs, and selected suppression of HDAC1 or HDAC2 regulates FOXO3a, NOX2, and NOX4 expression. Therefore, the ketone metabolite βOHB may be a novel promising therapeutic agent for SCI.

Cardiovascular Protection by Sodium Glucose Cotransporter 2 Inhibitors: Potential Mechanisms

The mechanism of action of empagliflozin in reducing the risk of adverse cardiovascular outcomes vs placebo in patients with type 2 diabetes mellitus and a high risk of cardiovascular disease in the Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients-Removing Excess Glucose (EMPA-REG OUTCOME) trial is currently unknown. An antiatherosclerotic effect is considered unlikely given the speed of the observed decrease in cardiovascular mortality. Hemodynamic effects, such as reductions in blood pressure and intravascular volume, and involving osmotic diuresis, may provide a more plausible explanation. Metabolic effects, such as cardiac fuel energetics, and hormonal effects, such as increased glucagon release, may also contribute to the results observed during EMPA-REG OUTCOME. This review discusses the main hypotheses suggested to date.

Cardiovascular Protection by Sodium Glucose Cotransporter 2 Inhibitors: Potential Mechanisms

The mechanism of action of empagliflozin in reducing the risk of adverse cardiovascular outcomes vs placebo in patients with type 2 diabetes mellitus and a high risk of cardiovascular disease in the Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients-Removing Excess Glucose (EMPA-REG OUTCOME) trial is currently unknown. An antiatherosclerotic effect is considered unlikely given the speed of the observed decrease in cardiovascular mortality. Hemodynamic effects, such as reductions in blood pressure and intravascular volume, and involving osmotic diuresis, may provide a more plausible explanation. Metabolic effects, such as cardiac fuel energetics, and hormonal effects, such as increased glucagon release, may also contribute to the results observed during EMPA-REG OUTCOME. This review discusses the main hypotheses suggested to date.

ROS Production and ERK Activity Are Involved in the Effects of d-β-Hydroxybutyrate and Metformin in a Glucose Deficient Condition

Hypoglycemia, a complication of insulin or sulfonylurea therapy in diabetic patients, leads to brain damage. Furthermore, glucose replenishment following hypoglycemic coma induces neuronal cell death. In this study, we investigated the molecular mechanism underlying glucose deficiency-induced cytotoxicity and the protective effect of d-β-hydroxybutyrate (D-BHB) using SH-SY5Y cells. The cytotoxic mechanism of metformin under glucose deficiency was also examined. Cell viability under 1 mM glucose (glucose deficiency) was significantly decreased which was accompanied by increased production of reactive oxygen species (ROS) and decreased phosphorylation of extracellular signal-regulated kinase (ERK) and glycogen synthase 3 (GSK3β). ROS inhibitor reversed the glucose deficiency-induced cytotoxicity and restored the reduced phosphorylation of ERK and GSK3β. While metformin did not alter cell viability in normal glucose media, it further increased cell death and ROS production under glucose deficiency. However, D-BHB reversed cytotoxicity, ROS production, and the decrease in phosphorylation of ERK and GSK3β induced by the glucose deficiency. ERK inhibitor reversed the D-BHB-induced increase in cell viability under glucose deficiency, whereas GSK3β inhibitor did not restore glucose deficiency-induced cytotoxicity. Finally, the protective effect of D-BHB against glucose deficiency was confirmed in primary neuronal cells. We demonstrate that glucose deficiency-induced cytotoxicity is mediated by ERK inhibition through ROS production, which is attenuated by D-BHB and intensified by metformin.

Inhibition of the mitochondrial pyruvate carrier protects from excitotoxic neuronal death

In cortical neurons and hippocampal slice cultures, blocking mitochondrial pyruvate uptake rewires metabolism to increase reliance on glutamate to fuel the TCA cycle. This diminishes the readily releasable pool of neuronal glutamate and minimizes the positive-feedback cascade of excitotoxic injury.

Glutamate is the dominant excitatory neurotransmitter in the brain, but under conditions of metabolic stress it can accumulate to excitotoxic levels. Although pharmacologic modulation of excitatory amino acid receptors is well studied, minimal consideration has been given to targeting mitochondrial glutamate metabolism to control neurotransmitter levels. Here we demonstrate that chemical inhibition of the mitochondrial pyruvate carrier (MPC) protects primary cortical neurons from excitotoxic death. Reductions in mitochondrial pyruvate uptake do not compromise cellular energy metabolism, suggesting neuronal metabolic flexibility. Rather, MPC inhibition rewires mitochondrial substrate metabolism to preferentially increase reliance on glutamate to fuel energetics and anaplerosis. Mobilizing the neuronal glutamate pool for oxidation decreases the quantity of glutamate released upon depolarization and, in turn, limits the positive-feedback cascade of excitotoxic neuronal injury. The finding links mitochondrial pyruvate metabolism to glutamatergic neurotransmission and establishes the MPC as a therapeutic target to treat neurodegenerative diseases characterized by excitotoxicity.

Multi-dimensional Roles of Ketone Bodies in Fuel Metabolism, Signaling, and Therapeutics

Ketone body metabolism is a central node in physiological homeostasis. In this review, we discuss how ketones serve discrete fine-tuning metabolic roles that optimize organ and organism performance in varying nutrient states and protect from inflammation and injury in multiple organ systems. Traditionally viewed as metabolic substrates enlisted only in carbohydrate restriction, observations underscore the importance of ketone bodies as vital metabolic and signaling mediators when carbohydrates are abundant. Complementing a repertoire of known therapeutic options for diseases of the nervous system, prospective roles for ketone bodies in cancer have arisen, as have intriguing protective roles in heart and liver, opening therapeutic options in obesity-related and cardiovascular disease. Controversies in ketone metabolism and signaling are discussed to reconcile classical dogma with contemporary observations.

Control of seizures by ketogenic diet-induced modulation of metabolic pathways

Epilepsy is too complex to be considered as a disease; it is more of a syndrome, characterized by seizures, which can be caused by a diverse array of afflictions. As such, drug interventions that target a single biological pathway will only help the specific individuals where that drug's mechanism of action is relevant to their disorder. Most likely, this will not alleviate all forms of epilepsy nor the potential biological pathways causing the seizures, such as glucose/amino acid transport, mitochondrial dysfunction, or neuronal myelination. Considering our current inability to test every individual effectively for the true causes of their epilepsy and the alarming number of misdiagnoses observed, we propose the use of the ketogenic diet (KD) as an effective and efficient preliminary/long-term treatment. The KD mimics fasting by altering substrate metabolism from carbohydrates to fatty acids and ketone bodies (KBs). Here, we underscore the need to understand the underlying cellular mechanisms governing the KD's modulation of various forms of epilepsy and how a diverse array of metabolites including soluble fibers, specific fatty acids, and functional amino acids (e.g., leucine, D-serine, glycine, arginine metabolites, and N-acetyl-cysteine) may potentially enhance the KD's ability to treat and reverse, not mask, these neurological disorders that lead to epilepsy.

Ketogenic diet decreases oxidative stress and improves mitochondrial respiratory complex activity

Cerebral metabolism of ketones after traumatic brain injury (TBI) improves neuropathology and behavior in an age-dependent manner. Neuroprotection is attributed to improved cellular energetics, although other properties contribute to the beneficial effects. Oxidative stress is responsible for mitochondrial dysfunction after TBI. Ketones decrease oxidative stress, increase antioxidants and scavenge free radicals. It is hypothesized that ketogenic diet (KD) will decrease post-TBI oxidative stress and improve mitochondria. Postnatal day 35 (PND35) male rats were given sham or controlled cortical impact (CCI) injury and placed on standard (STD) or KD. Ipsilateral cortex homogenates and mitochondria were assayed for markers of oxidative stress, antioxidant expression and mitochondrial function. Oxidative stress was significantly increased at 6 and 24 h post-injury and attenuated by KD while inducing protein expression of antioxidants, NAD(P)H dehydrogenase quinone 1 (NQO1) and superoxide dismutase (SOD1/2). Complex I activity was inhibited in STD and KD groups at 6 h and normalized by 24 h. KD significantly improved Complex II-III activity that was reduced in STD at 6 h. Activity remained reduced at 24 h in STD and unchanged in KD animals. These results strongly suggest that ketones improve post-TBI cerebral metabolism by providing alternative substrates and through antioxidant properties, preventing oxidative stress-mediated mitochondrial dysfunction.

Regulation of brain PPARgamma2 contributes to ketogenic diet anti-seizure efficacy

The ketogenic diet (KD) is an effective therapy primarily used in pediatric patients whom are refractory to current anti-seizure medications. The mechanism of the KD is not completely understood, but is thought to involve anti-inflammatory and anti-oxidant processes. The nutritionally-regulated transcription factor peroxisome proliferator activated receptor gamma, PPARγ, regulates genes involved in anti-inflammatory and anti-oxidant pathways. Moreover, endogenous ligands of PPARγ include fatty acids suggesting a potential role in the effects of the KD. Here, we tested the hypothesis that PPARγ contributes to the anti-seizure efficacy of the KD. We found that the KD increased nuclear protein content of the PPARγ2 splice variant by 2-4 fold (P<0.05) in brain homogenates from wild-type (WT) and epileptic Kv1.1 knockout (KO) mice, while not affecting PPARγ1. The KD reduced the frequency of seizures in Kv1.1KO mice by ~70% (P<0.01). GW9662, a PPARγ antagonist, prevented KD-mediated changes in PPARγ2 expression and prevented the anti-seizure efficacy of the KD in Kv1.1KO mice. Further supporting the association of PPARγ2 in mediating KD actions, the KD significantly prolonged the latency to flurothyl-induced seizure in WT mice by ~20-35% (P<0.01), but was ineffective in PPARγ2KO mice and neuron-specific PPARγKO mice. Finally, administering the PPARγ agonist pioglitazone increased PPARγ2 expression by 2-fold (P<0.01) and reduced seizures in Kv1.1KO mice by ~80% (P<0.01). Our findings implicate brain PPARγ2 among the mechanisms by which the KD reduces seizures and strongly support the development of PPARγ2 as a therapeutic target for severe, refractory epilepsy.

Hyperketonemia and ketosis increase the risk of complications in type 1 diabetes

Diets that boost ketone production are increasingly used for treating several neurological disorders. Elevation in ketones in most cases is considered favorable, as they provide energy and are efficient in fueling the body's energy needs. Despite all the benefits from ketones, the above normal elevation in the concentration of ketones in the circulation tend to illicit various pathological complications by activating injurious pathways leading to cellular damage. Recent literature demonstrates a plausible link between elevated levels of circulating ketones and oxidative stress, linking hyperketonemia to innumerable morbid conditions. Ketone bodies are produced by the oxidation of fatty acids in the liver as a source of alternative energy that generally occurs in glucose limiting conditions. Regulation of ketogenesis and ketolysis plays an important role in dictating ketone concentrations in the blood. Hyperketonemia is a condition with elevated blood levels of acetoacetate, 3-β-hydroxybutyrate, and acetone. Several physiological and pathological triggers, such as fasting, ketogenic diet, and diabetes cause an accumulation and elevation of circulating ketones. Complications of the brain, kidney, liver, and microvasculature were found to be elevated in diabetic patients who had elevated ketones compared to those diabetics with normal ketone levels. This review summarizes the mechanisms by which hyperketonemia and ketoacidosis cause an increase in redox imbalance and thereby increase the risk of morbidity and mortality in patients.

β-Hydroxybutyrate: A signaling metabolite in starvation response?

Ketone bodies β-hydroxybutyrate (BHB) and acetoacetate are important metabolic substrates for energy production during prolonged fasting. However, BHB also has signaling functions. Through several metabolic pathways or processes, BHB modulates nutrient utilization and energy expenditure. These findings suggest that BHB is not solely a metabolic intermediate, but also acts as a signal to regulate metabolism and maintain energy homeostasis during nutrient deprivation. We briefly summarize the metabolism and emerging physiological functions of ketone bodies and highlight the potential role for BHB as a signaling molecule in starvation response.

Methyl-esterified 3-hydroxybutyrate oligomers protect bacteria from hydroxyl radicals

Bacteria rely mainly on enzymes, glutathione and other low-molecular weight thiols to overcome oxidative stress. However, hydroxyl radicals are the most cytotoxic reactive oxygen species, and no known enzymatic system exists for their detoxification. We now show that methyl-esterified dimers and trimers of 3-hydroxybutyrate (ME-3HB), produced by bacteria capable of polyhydroxybutyrate biosynthesis, have 3-fold greater hydroxyl radical-scavenging activity than glutathione and 11-fold higher activity than vitamin C or the monomer 3-hydroxybutyric acid. We found that ME-3HB oligomers protect hypersensitive yeast deletion mutants lacking oxidative stress-response genes from hydroxyl radical stress. Our results show that phaC and phaZ, encoding polymerase and depolymerase, respectively, are activated and polyhydroxybutyrate reserves are degraded for production of ME-3HB oligomers in bacteria infecting plant cells and exposed to hydroxyl radical stress. We found that ME-3HB oligomer production is widespread, especially in bacteria adapted to stressful environments. We discuss how ME-3HB oligomers could provide opportunities for numerous applications in human health.

Ketogenic diet in a patient with congenital hyperinsulinism: a novel approach to prevent brain damage

Background

Congenital hyperinsulinism (CHI) is the most frequent cause of hypoglycemia in children. In addition to increased peripheral glucose utilization, dysregulated insulin secretion induces profound hypoglycemia and neuroglycopenia by inhibiting glycogenolysis, gluconeogenesis and lipolysis. This results in the shortage of all cerebral energy substrates (glucose, lactate and ketones), and can lead to severe neurological sequelae. Patients with CHI unresponsive to medical treatment can be subjected to near-total pancreatectomy with increased risk of secondary diabetes. Ketogenic diet (KD), by reproducing a fasting-like condition in which body fuel mainly derives from beta-oxidation, is intended to provide alternative cerebral substrates such ketone bodies. We took advantage of known protective effect of KD on neuronal damage associated with GLUT1 deficiency, a disorder of impaired glucose transport across the blood-brain barrier, and administered KD in a patient with drug-unresponsive CHI, with the aim of providing to neurons an energy source alternative to glucose.

Methods

A child with drug-resistant, long-standing CHI caused by a spontaneous GCK activating mutation (p.Val455Met) suffered from epilepsy and showed neurodevelopmental abnormalities. After attempting various therapeutic regimes without success, near-total pancreatectomy was suggested to parents, who asked for other options. Therefore, we proposed KD in combination with insulin-suppressing drugs.

Results

We administered KD for 2 years. Soon after the first six months, the patient was free of epileptic crises, presented normalization of EEG, and showed a marked recover in psychological development and quality of life.

Conclusions

KD could represent an effective treatment to support brain function in selected cases of CHI.

Hypothalamic-Pituitary-Adrenal Axis Programming after Recurrent Hypoglycemia during Development

Permanent brain injury is a complication of recurrent hypoglycemia during development. Recurrent hypoglycemia also has adverse consequences on the neuroendocrine system. Hypoglycemia-associated autonomic failure, characterized by ineffective glucose counterregulation during hypoglycemia, is well described in children and adults on insulin therapy for diabetes mellitus. Whether recurrent hypoglycemia also has a programming effect on the hypothalamus-pituitary-adrenal cortex (HPA) axis has not been well studied. Hypoglycemia is a potent stress that leads to increased glucocorticoid secretion in all age groups, including the perinatal period. Other conditions associated with exposure to excess glucocorticoid in the perinatal period have a programming effect on the HPA axis activity. Limited animal data suggest the possibility of similar programming effect after recurrent hypoglycemia in the postnatal period. The age at exposure to hypoglycemia likely determines the HPA axis response in adulthood. Recurrent hypoglycemia in the early postnatal period likely leads to a hyperresponsive HPA axis, whereas recurrent hypoglycemia in the late postnatal period lead to a hyporesponsive HPA axis in adulthood. The age-specific programming effects may determine the neuroendocrine response during hypoglycemia and other stressful events in individuals with history of recurrent hypoglycemia during development.

The Ketone Body, β-Hydroxybutyrate Stimulates the Autophagic Flux and Prevents Neuronal Death Induced by Glucose Deprivation in Cortical Cultured Neurons

Glucose is the major energy substrate in brain, however, during ketogenesis induced by starvation or prolonged hypoglycemia, the ketone bodies (KB), acetoacetate and β-hydroxybutyrate (BHB) can substitute for glucose. KB improve neuronal survival in diverse injury models, but the mechanisms by which KB prevent neuronal damage are still not well understood. In the present study we have investigated whether protection by the D isomer of BHB (D-BHB) against neuronal death induced by glucose deprivation (GD), is related to autophagy. Autophagy is a lysosomal-dependent degradation process activated during nutritional stress, which leads to the digestion of damaged proteins and organelles providing energy for cell survival. Results show that autophagy is activated in cortical cultured neurons during GD, as indicated by the increase in the levels of the lipidated form of the microtubule associated protein light chain 3 (LC3-II), and the number of autophagic vesicles. At early phases of glucose reintroduction (GR), the levels of p62 declined suggesting that the degradation of the autophagolysosomal content takes place at this time. In cultures exposed to GD and GR in the presence of D-BHB, the levels of LC3-II and p62 rapidly declined and remained low during GR, suggesting that the KB stimulates the autophagic flux preventing autophagosome accumulation and improving neuronal survival.

Ketogenic diet in epileptic children: impact on lipoproteins and oxidative stress

OBJECTIVES

Ketogenic diet (KD) is an important therapy used in the control of drug-refractory seizures. The major goal of this review is to update the knowledge about the adverse effects of KD on lipoproteins, lipid profile, and cardiometabolic risk.

METHODS

Articles on the effect of the KD on plasma lipoproteins of children and adolescents with refractory epilepsy, which were published in the past 15 years and indexed in the PubMed and MedLine databases, were included.

RESULTS

Dyslipidemia was recurrent in children, and adolescents treated with KD. Evidence suggests that hypercholesterolemia promotes structural modifications in low-density lipoprotein particles. Such modifications possibly favor oxidative processes and contribute to changes in the size of lipoproteins, particularly related to small and denser LDL. However, oxidative modifications in LDL of children on KD are not described in the literature.

DISCUSSION

The positive effects of KD on the health of children and adolescents with refractory epilepsy are unquestionable. Conversely, this positive role is associated with significant and negative changes in lipid metabolism. Moreover, the positive effects are possibly related to oxidative reactions and unbalance of antioxidants that can contribute to an increased cardiometabolic risk. Therefore, this review invites clinicians and researchers to investigate the lipid and oxidative metabolism in their clinical practice and trials, respectively.

Ketone Body Therapy Protects From Lipotoxicity and Acute Liver Failure Upon Pparα Deficiency

Acute liver failure (ALF) is a severe and rapid liver injury, often occurring without any preexisting liver disease, which may precipitate multiorgan failure and death. ALF is often associated with impaired β-oxidation and increased oxidative stress (OS), characterized by elevated levels of hepatic reactive oxygen species (ROS) and lipid peroxidation (LPO) products. Peroxisome proliferator-activated receptor (PPAR)α has been shown to confer hepatoprotection in acute and chronic liver injury, at least in part, related to its ability to control peroxisomal and mitochondrial β-oxidation. To study the pathophysiological role of PPARα in hepatic response to high OS, we induced a pronounced LPO by treating wild-type and Pparα-deficient mice with high doses of fish oil (FO), containing n-3 polyunsaturated fatty acids. FO feeding of Pparα-deficient mice, in contrast to control sunflower oil, surprisingly induced coma and death due to ALF as indicated by elevated serum alanine aminotransferase, aspartate aminotransferase, ammonia, and a liver-specific increase of ROS and LPO-derived malondialdehyde. Reconstitution of PPARα specifically in the liver using adeno-associated serotype 8 virus-PPARα in Pparα-deficient mice restored β-oxidation and ketogenesis and protected mice from FO-induced lipotoxicity and death. Interestingly, administration of the ketone body β-hydroxybutyrate prevented FO-induced ALF in Pparα-deficient mice, and normalized liver ROS and malondialdehyde levels. Therefore, PPARα protects the liver from FO-induced OS through its regulatory actions on ketone body levels. β-Hydroxybutyrate treatment could thus be an option to prevent LPO-induced liver damage.

Effects of Alda-1, an Aldehyde Dehydrogenase-2 Agonist, on Hypoglycemic Neuronal Death

Hypoglycemic encephalopathy (HE) is caused by a lack of glucose availability to neuronal cells, and no neuroprotective drugs have been developed as yet. Studies on the pathogenesis of HE and the development of new neuroprotective drugs have been conducted using animal models such as the hypoglycemic coma model and non-coma hypoglycemia model. However, both models have inherent problems, and establishment of animal models that mimic clinical situations is desirable. In this study, we first developed a short-term hypoglycemic coma model in which rats could be maintained in an isoelectric electroencephalogram (EEG) state for 2 min and subsequent hyperglycemia without requiring anti-seizure drugs and an artificial ventilation. This condition caused the production of 4-hydroxy-2-nonenal (4-HNE), a cytotoxic aldehyde, in neurons of the hippocampus and cerebral cortex, and a marked increase in neuronal death as evaluated by Fluoro-Jade B (FJB) staining. We also investigated whether N-(1,3-benzodioxole-5-ylmethyl)-2,6-dichlorobenzamide (Alda-1), a small-molecule agonist of aldehyde dehydrogenase-2, could attenuate 4-HNE levels and reduce hypoglycemic neuronal death. After confirming that EEG recordings remained isoelectric for 2 min, Alda-1 (8.5 mg/kg) or vehicle (dimethyl sulfoxide; DMSO) was administered intravenously with glucose to maintain a blood glucose level of 250 to 270 mg/dL. Fewer 4-HNE and FJB-positive cells were observed in the cerebral cortex of Alda-1-treated rats than in DMSO-treated rats 24 h after glucose administration (P = 0.002 and P = 0.020). Thus, activation of the ALDH2 pathway could be a molecular target for HE treatment, and Alda-1 is a potentially neuroprotective agent that exerts a beneficial effect on neurons when intravenously administered simultaneously with glucose.

Protection of hypoglycemia-induced neuronal death by β-hydroxybutyrate involves the preservation of energy levels and decreased production of reactive oxygen species

Glucose is the main energy substrate in brain but in certain circumstances such as prolonged fasting and the suckling period alternative substrates can be used such as the ketone bodies (KB), beta-hydroxybutyrate (BHB), and acetoacetate. It has been shown that KB prevent neuronal death induced during energy limiting conditions and excitotoxicity. The protective effect of KB has been mainly attributed to the improvement of mitochondrial function. In the present study, we have investigated the protective effect of D-BHB against neuronal death induced by severe noncoma hypoglycemia in the rat in vivo and by glucose deprivation (GD) in cortical cultures. Results show that systemic administration of D-BHB reduces reactive oxygen species (ROS) production in distinct cortical areas and subregions of the hippocampus and efficiently prevents neuronal death in the cortex of hypoglycemic animals. In vitro results show that D-BHB stimulates ATP production and reduces ROS levels, while the nonphysiologic isomer of BHB, L-BHB, has no effect on energy production but reduces ROS levels. Data suggest that protection by BHB, not only results from its metabolic action but is also related to its capability to reduce ROS, rendering this KB as a suitable candidate for the treatment of ischemic and traumatic injury.

Age-related changes in the diurnal variation of ketogenesis in patients with type 2 diabetes and relevance to hypoglycemic medications

To assess the significance of ketogenesis in the management of diabetes mellitus, we analyzed the factors associated with the diurnal variation of the plasma ketone body levels. The subjects consisted of 220 patients with type 2 diabetes, aged 60 ± 15 years, without advanced complications. They ate a standardized, low-fat meal at 8:00, 12:00, and 18:00. The plasma levels of 3-hydroxybutyrate (3HB) and free fatty acid (FFA) were increased before breakfast and before dinner. The plasma glucose concentration was almost the same at any blood sampling time point among age quartiles. However, the 3HB levels were significantly decreased with age, which was most obvious before dinner. The FFA levels also decreased with age, but the decline was mild. A multiple regression analysis with stepwise selection revealed that age was an independent, negative contributor and that the pre-breakfast FFA concentration was an independent, positive contributor to the pre-breakfast 3HB levels. Regarding the pre-dinner 3HB levels, in addition to age and the pre-dinner FFA concentration, the uses of sulfonylurea and dipeptidyl peptidase-4 inhibitors were independent negative contributors. The metabolism of ketone bodies is an alternative energy source for the brain under conditions of starvation. While excessive ketogenesis leads to critical ketoacidosis, inadequate ketone body production could be associated with a propensity to develop neurohypoglycemia in elderly patients treated with insulin secretagogues. Because age-related changes in ketogenesis were the most significant before dinner, attention should be paid not only to fasting but also to the pre-dinner levels of 3HB.

Hyperglycemia accentuates and ketonemia attenuates hypoglycemia-induced neuronal injury in the developing rat brain

BACKGROUND

Prolonged hypoglycemia leads to brain injury, despite treatment with 10% dextrose. Whether induction of hyperglycemia or ketonemia achieves better neuroprotection is unknown. Hyperglycemia is neuroprotective in other brain injuries during development; however, it worsens hypoglycemia-induced injury in the adult brain via poly(ADP-ribose)polymerase-1 (PARP-1) overactivation.

METHODS

Three-week-old rats were subjected to insulin-induced hypoglycemia and treated with 10% dextrose or 50% dextrose. Neuronal injury, PARP-1, and brain-derived neurotrophic factor (BDNF) III/TrkB/p75(NTR) expressions were determined. In the second experiment, ketonemia was induced by administering β-hydroxybutyrate during hypoglycemia and its effect on neuronal injury was compared with those conventionally treated using 10% dextrose.

RESULTS

Both 10 and 50% dextrose administration led to hyperglycemia (50% dextrose > 10% dextrose). Compared with the 10% dextrose group, neuronal injury was greater in the 50% dextrose group and was accompanied by PARP-1 overactivation. BDNF III and p75(NTR), but not TrkBFL, mRNA expressions were upregulated. Neuronal injury was less severe in the rats subjected to ketonemia, compared with those conventionally treated using 10% dextrose.

CONCLUSION

Hyperglycemia accentuated hypoglycemia-induced neuronal injury, likely via PARP-1 overactivation. Although BDNF was upregulated, it was not neuroprotective and potentially exaggerated injury by binding to p75(NTR) receptor. Conversely, ketonemia during hypoglycemia attenuated neuronal injury.

Estrogen regulates energy metabolic pathway and upstream adenosine 5'-monophosphate-activated protein kinase and phosphatase enzyme expression in dorsal vagal complex metabolosensory neurons during glucostasis and hypoglycemia

The ability of estrogen to shield the brain from the bioenergetic insult hypoglycemia is unclear. Estradiol (E) prevents hypoglycemic activation of the energy deficit sensor adenosine 5'-monophosphate-activated protein kinase (AMPK) in hindbrain metabolosensory A2 noradrenergic neurons. This study investigates the hypothesis that estrogen regulates A2 AMPK through control of fuel metabolism and/or upstream protein kinase/phosphatase enzyme expression. A2 cells were harvested by laser microdissection after insulin or vehicle (V) injection of E- or oil (O)-implanted ovariectomized female rats. Cell lysates were evaluated by immunoblot for glycolytic, tricarboxylic acid cycle, respiratory chain, and acetyl-CoA-malonyl-CoA pathway enzymes. A2 phosphofructokinase (PFKL), isocitrate dehydrogenase, pyruvate dehydrogenase, and ATP synthase subunit profiles were elevated in E/V vs. O/V; hypoglycemia augmented PFKL and α-ketoglutarate dehydrogenase expression in E only. Hypoglycemia increased A2 Ca(2+) /calmodulin-dependent protein kinase-β in O and reduced protein phosphatase in both groups. A2 phospho-AMPK levels were equivalent in O/V vs. E/V but elevated during hypoglycemia in O only. These results implicate E in compensatory upregulation of substrate catabolism and corresponding maintenance of energy stability of A2 metabolosensory neurons during hypoglycemia, outcomes that support the potential viability of molecular substrates for hormone action as targets for therapies alleviating hypoglycemic brain injury.

Energy substrates protect hippocampus against endogenous glutamate-mediated neurodegeneration in awake rats

Excitotoxicity due to excessive glutamatergic neurotransmission is a well-studied phenomenon that has been related to the mechanisms of neuronal death occurring in some disorders of the CNS. We have previously shown that the intrahippocampal perfusion by microdialysis of 4-aminopyridine (4-AP) in rats stimulates endogenous glutamate release from nerve endings and this results in excitotoxic effects such as immediate seizures and delayed neuronal death, due to the overactivation of N-methyl-D-aspartate (NMDA) receptors. To study whether mitochondrial energy dysfunction and oxidative stress could be involved in this 4-AP-induced excitotoxicity, we evaluated in awake rats the protective effect of several energy substrates and antioxidant compounds, using microdialysis, electroencephalographic (EEG) recording and histological analysis. The 4-AP-induced behavioral and EEG seizures, which progressed to status epilepticus in about 30 min, were prevented by the NMDA receptor antagonist MK-801, whereas acetoacetate, DL- and L-β-hydroxybutyrate did not protect against seizures but increased the latency to the onset of status epilepticus; pyruvate, α-ketoglutarate and glutathione ethyl ester did not show any protective effect. 4-AP also produced nearly complete loss of pyramidal neurons in CA1 and CA3 regions of the ipsilateral hippocampus 24 h after the experiment. MK-801 totally prevented this neuronal death and the energy substrates tested protected by about 50%, whereas the antioxidants showed only a weak protection. We conclude that ketone bodies possess weak anticonvulsant effects and that energy metabolism impairment plays a more important role than oxidative stress in the delayed hippocampal neurodegeneration resulting from the excitotoxic action of 4-AP mediated by endogenous glutamate.

Ketogenic diets and pain

Ketogenic diets are well established as a successful anticonvulsant therapy. Based on overlap between mechanisms postulated to underlie pain and inflammation, and mechanisms postulated to underlie therapeutic effects of ketogenic diets, recent studies have explored the ability for ketogenic diets to reduce pain. Here we review clinical and basic research thus far exploring the impact of a ketogenic diet on thermal pain, inflammation, and neuropathic pain.