Chronicin vitroketosis is neuroprotective but not anti-convulsant

Oral beta-hydroxybutyrate alleviates COVID-19 related acute respiratory distress syndrome: A randomized, single-blind, placebo-controlled trial

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a lung complication of COVID-19 that requires intensive care and ventilation. Beta-hydroxybutyrate (BHB) is a ketone body that can modulate metabolism and inflammation in immune cells and lung tissues. We hypothesized that oral BHB could alleviate COVID-19 related ARDS by reducing pro-inflammatory cytokines and increasing anti-inflammatory cytokines.

METHODS

We randomized 75 patients with mild (as per Berlin criteria) ARDS symptoms to receive oral 25 g twice daily or placebo for five days. The primary outcome was the change in pro-inflammatory cytokines (Interleukin-1β, Interleukin-6, interleukin-18, tumour necrosis factor-alpha) and anti-inflammatory cytokine (interleukin-10) from baseline to day 5. The secondary outcomes were the change in BHB levels from baseline to day 5, the number of hospitalization days, and the occurrence of adverse events.

RESULTS

Treatment with formulated BHB resulted in a significant decrease in pro-inflammatory cytokines; Interleukin-1β (p = 0.0204), Interleukin-6 (p = 0.0309), interleukin-18 (p = 0.0116), tumour necrosis factor-alpha (p = 0.0489) and increase in interleukin-10 (p = 0.0246) compared treatment with placebo. Importantly, higher BHB levels (p = 0.0001) were observed after supplementation; additionally, patients who underwent this approach were hospitalized for fewer days. No serious adverse events were reported.

CONCLUSION

Beta-hydroxybutyrate, an oral adjunct therapy, has shown promising results in ameliorating symptoms of ARDS. This includes reduced inflammation, oxidative stress, and decreased patient fatigue levels. Further study with a large sample size is warranted to assess the potential of BHB therapy's effectiveness in reducing the development of severe illness.

CLINICAL TRIAL REGISTRATION

(http://ctri.nic.in/CTRI/2021/03/031790).

Regional differences in the reduction in cerebral FDG uptake induced by the ketogenic diet

BACKGROUND

The postulated benefits of the ketogenic diet in the management of multiple medical conditions have seen more patients who are in therapeutic ketosis attending 18F-FDG PET scans. This study aimed to investigate the effect of ketosis on cerebral glucose metabolism in a clinical PET scanning environment using 18F-FDG uptake as a surrogate marker.

METHODS

A retrospective audit was conducted of the brain 18F-FDG uptake in 52 patients who underwent PET scans for possible cardiac sarcoidosis or suspected intracardiac infection, following a ketogenic diet and prolonged fasting. SUVbw for whole brain and separate brain regions was compared with serum glucose and serum ketone body (beta-hydroxybutyrate) levels.

RESULTS

The expected negative association between serum glucose levels and whole brain 18F-FDG uptake was confirmed. A reduction in SUVbw due to increasing serum ketones levels was also observed that was independent of and in addition to the effects of glucose. The magnitude of the reduction in SUVbw related to serum glucose level and serum ketone level was found to be greater in the precuneus than in the cerebellum or whole brain.

CONCLUSION

In a real-world clinical PET setting, cerebral 18F-FDG uptake appears to be affected by glycaemia and ketonaemia. This means when assessing the brain, both serum glucose and ketone levels need to be considered when SUVs are used to distinguish between pathologic and physiologic states. The magnitude of this effect appears to vary between different brain regions. This regional difference should be taken into consideration when selecting the appropriate brain region for SUV normalisation, particularly when undertaking database comparison in the assessment of dementia.

Expanding Indications for a Ketogenic Diet as an Adjuvant Therapy in Adult Refractory Status Epilepticus: an Exploratory Study Using Moderation Analysis

Refractory status epilepticus (RSE) requires multimodal treatment approaches to achieve rapid seizure cessation and neuroprotection. A ketogenic diet (KD) has demonstrated efficacy as a nutritional therapeutic option for adult RSE. However, the group of adult RSE patients who would benefit from adopting a KD needs to be determined to appropriately select the patients indicated for a KD. Therefore, we conducted a nonrandomized retrospective cohort study to explore the therapeutic efficacy of a KD by investigating the moderation effect of a KD on the association between the clinical characteristics of RSE patients and their functional outcomes. This study investigated 140 RSE patients, including 32 patients treated with a KD; among these patients, 28 (81%) achieved seizure cessation. We found that KD moderated the reduction in the modified Rankin scale (mRS) score at discharge among patients who were older, had higher seizure severity scores, were under continuous intravenous anesthetic therapy (CIVAD), and had super-RSE. Age and seizure severity scores, but not CIVAD or super-RSE, were associated with a KD-moderated change in mRS score at 3 months. Thus, we consider that our study provides evidence of a neuroprotective effect of KD in the most severe RSE patients with very few remaining therapeutic options, but future randomized controlled trials in these subgroups of KD patients are necessary.

KetoCycle mobile app for ketogenic diet: a retrospective study of weight loss and engagement

BACKGROUND

The ketogenic diet is one of the oldest diets that has been used for more than a centennial in the clinical setting, and it is gaining popularity as a measure to fight obesity, which is a major predisposing factor for many diseases to manifest, including diabetes mellitus, chronic heart disease, cancer, and others. Thus, we designed this retrospective investigation to determine if users of the mobile application KetoCycle achieved statistically significant weight loss outcomes.

METHODS

The initial study cohort comprised 12,965 consecutive users who started using KetoCycle between January 2020 and December 2020. The final cohort comprised 10,269 users. The main parameters obtained from the database containing all self-reported data were gender, number of active days (AD), total time of use (TT), height, initial weight, and last recorded weight. The primary outcome of the study was weight loss. Statistical analyses were performed using IBM SPSS Statistics, version 26 (IBM Corp., Armonk, NY, USA). In addition, a standard multiple regression model was created to predict weight loss from significant actions.

RESULTS

A retrospective analysis of KetoCycle user data showed that 87.3% of KetoCycle users lost some of their initial weight. Of those, 1645 users (18.3%) lost more than 10% of their initial body weight, 3528 (39.3%) users lost between 5 and 10% of their initial body weight, and 3796 (42.3%) users lost less than 5% of their body weight. When user activity was taken into account, it was found that active users lost statistically significantly more weight than non-active users (p < 0.05). App engagement was also associated with losing > 5% of initial weight. Using water tracking, weight tracking, and creation of a meals list within KetoCycle statistically significantly predicted weight loss in a multiple regression model.

CONCLUSIONS

We concluded that KetoCycle appeared as a promising mobile application suited for weight loss and weight control.

TRIAL REGISTRATION

This retrospective chart review study was approved by BRANY IRB in January 2022 (registration ID.: 21-08-564-939).

Using Dictyostelium to Advance Our Understanding of the Role of Medium Chain Fatty Acids in Health and Disease

Ketogenic diets have been utilized for many years to improve health, and as a dietary approach for the treatment of a range of diseases, where the mechanism of these low carbohydrate and high fat diets is widely considered to be through the production of metabolic products of fat breakdown, called ketones. One of these diets, the medium chain triglyceride ketogenic diet, involves high fat dietary intake in the form of medium chain fatty acids (MCFAs), decanoic and octanoic acid, and is commonly used in endurance and high intensity exercises but has also demonstrated beneficial effects in the treatment of numerous pathologies including drug resistant epilepsy, cancer, and diabetes. Recent advances, using Dictyostelium discoideum as a model, have controversially proposed several direct molecular mechanisms for decanoic acid in this diet, independent of ketone generation. Studies in this model have identified that decanoic acid reduces phosphoinositide turnover, diacylglycerol kinase (DGK) activity, and also inhibits the mechanistic target of rapamycin complex 1 (mTORC1). These discoveries could potentially impact the treatment of a range of disorders including epilepsy, cancer and bipolar disorder. In this review, we summarize the newly proposed mechanisms for decanoic acid, identified using D. discoideum, and highlight potential roles in health and disease treatment.

Potential Roles of Exercise-Induced Plasma Metabolites Linking Exercise to Health Benefits

Regular exercise has a myriad of health benefits. An increase in circulating exercise factors following exercise is a critical physiological response. Numerous studies have shown that exercise factors released from tissues during physical activity may contribute to health benefits via autocrine, paracrine, and endocrine mechanisms. Myokines, classified as proteins secreted from skeletal muscle, are representative exercise factors. The roles of myokines have been demonstrated in a variety of exercise-related functions linked to health benefits. In addition to myokines, metabolites are also exercise factors. Exercise changes the levels of various metabolites via metabolic reactions. Several studies have identified exercise-induced metabolites that positively influence organ functions. Here, we provide an overview of selected metabolites secreted into the circulation upon exercise.

Antiepileptic effects of exogenous β-hydroxybutyrate on kainic acid-induced epilepsy

The aim of the present study was to explore the potential anticonvulsant effects of β-hydroxybutyrate (BHB) in a kainic acid (KA)-induced rat epilepsy model. The KA-induced rat seizure model was established and BHB was administrated intraperitoneally at a dose of 4 mmol/kg 30 min prior to KA injection. Hippocampal tissues were then obtained 1, 3 and 7 days following KA administration, following which the expression levels of neuron-specific enolase (NSE) and glial fibrillary acidic protein (GFAP) were measured using a double immunofluorescence labeling method. In addition, the contents of glutathione (GSH), γ-aminobutyric acid (GABA) and ATP were measured using ELISA. Pretreatment with BHB markedly increased the expression of NSE after KA injection compared with that in the normal saline (NS) + KA group, suggesting that the application of BHB could alleviate neuronal damage in rats. The protective effect of BHB may be associated with suppressed inflammatory responses, which was indicated by the observed inhibition of GFAP expression in rats in the BHB + KA group compared with that in the NS + KA group. It was also found that GSH and GABA contents were notably increased after the rats were pretreated with BHB compared with those in the NS + KA group. To conclude, the application of exogenous BHB can serve as a novel therapeutic agent for epilepsy.

Therapeutic Potential of Exogenous Ketone Supplement Induced Ketosis in the Treatment of Psychiatric Disorders: Review of Current Literature

Globally, psychiatric disorders, such as anxiety disorder, bipolar disorder, schizophrenia, depression, autism spectrum disorder, and attention-deficit/hyperactivity disorder (ADHD) are becoming more prevalent. Although the exact pathological alterations are not yet clear, recent studies have demonstrated that widespread changes of very complex metabolic pathways may partially underlie the pathophysiology of many psychiatric diseases. Thus, more attention should be directed to metabolic-based therapeutic interventions in the treatment of psychiatric disorders. Emerging evidence from numerous studies suggests that administration of exogenous ketone supplements, such as ketone salts or ketone esters, generates rapid and sustained nutritional ketosis and metabolic changes, which may evoke potential therapeutic effects in cases of central nervous system (CNS) disorders, including psychiatric diseases. Therefore, the aim of this review is to summarize the current information on ketone supplementation as a potential therapeutic tool for psychiatric disorders. Ketone supplementation elevates blood levels of the ketone bodies: D-β-hydroxybutyrate (βHB), acetoacetate (AcAc), and acetone. These compounds, either directly or indirectly, beneficially affect the mitochondria, glycolysis, neurotransmitter levels, activity of free fatty acid receptor 3 (FFAR3), hydroxycarboxylic acid receptor 2 (HCAR2), and histone deacetylase, as well as functioning of NOD-like receptor pyrin domain 3 (NLRP3) inflammasome and mitochondrial uncoupling protein (UCP) expression. The result of downstream cellular and molecular changes is a reduction in the pathophysiology associated with various psychiatric disorders. We conclude that supplement-induced nutritional ketosis leads to metabolic changes and improvements, for example, in mitochondrial function and inflammatory processes, and suggest that development of specific adjunctive ketogenic protocols for psychiatric diseases should be actively pursued.

Weight loss, improved physical performance, cognitive function, eating behavior, and metabolic profile in a 12-week ketogenic diet in obese adults

The ketogenic diet (KD) is being increasingly promoted as a strategy to fight obesity. Although the KD is effective for weight loss and weight control, comprehensive determination of its relationship with biochemical, physiological and psychological changes is still largely unexplored. We hypothesized that a 12-week KD (12KD) would significantly affect body weight, physical performance, cognitive function, eating behaviors, the metabolic and hormonal profile in obese adults, although differently in men and women. In an uncontrolled intervention, 35 sedentary obese adults (13 men, 25 women), aged 37 ± 7 years with a BMI 36.1 ± 5.6 kg/m² underwent a 12KD between March 2017 and June 2017 at the University of Primorska. The 12KD resulted in decreased appetite, significant weight loss of participants (-18 ± 9 kg men vs. -11 ± 3 kg women; P < .001), decreased emotional and external eating (P < .001 for both), increased body image satisfaction (P < .001) and improved physical performance (P < .001). Biochemically, a significant drop in glucose (P = .026), and a significant increase in LDL-cholesterol (P = .031), CRP (P = .007), and BDNF (P = .035) were observed in the first 2 weeks; then, all listed parameters returned to baseline. On the other hand, a significant reduction in insulin (P < .001) and leptin levels (P < .001), and a significant increase in adiponectin (P = .008) and NPY (P = .009) were detected throughout the duration of the 12KD. Our results show the efficacy of the 12KD on weight loss, physical performance, cognitive function, eating behaviors and metabolic profile. However, the long-term effects of a KD on these outcomes needs to be further studied before general recommendations can be made.

Bioenergetic Mechanisms of Seizure Control

Epilepsy is characterized by the regular occurrence of seizures, which follow a stereotypical sequence of alterations in the electroencephalogram. Seizures are typically a self limiting phenomenon, concluding finally in the cessation of hypersynchronous activity and followed by a state of decreased neuronal excitability which might underlie the cognitive and psychological symptoms the patients experience in the wake of seizures. Many efforts have been devoted to understand how seizures spontaneously stop in hope to exploit this knowledge in anticonvulsant or neuroprotective therapies. Besides the alterations in ion-channels, transmitters and neuromodulators, the successive build up of disturbances in energy metabolism have been suggested as a mechanism for seizure termination. Energy metabolism and substrate supply of the brain are tightly regulated by different mechanisms called neurometabolic and neurovascular coupling. Here we summarize the current knowledge whether these mechanisms are sufficient to cover the energy demand of hypersynchronous activity and whether a mismatch between energy need and supply could contribute to seizure control.

Ketogenic diet, a potentially valuable therapeutic option for the management of refractory epilepsy in classical neonatal nonketotic hyperglycinemia: a case report

Nonketotic hyperglycinemia (NKH) is a devastating inborn error of glycine metabolism caused by deficient activity of the glycine cleavage enzyme. Classically, patients present with lethargy, hypotonia, myoclonic jerks, transient respiratory depression in the first week of life and often progress to death. Surviving infants have profound psychomotor retardation, refractory epilepsy and poor quality of life. Currently, no effective therapeutic avenues exist for severe NKH. Ketogenic diet (KD) has been trialled only in a small group of patients with neonatal NKH and early myoclonic encephalopathy, in whom significant improvements in seizure control were reported. We describe an infant with classical neonatal NKH who presented on the third day of life with hypotonia, poor feeding, respiratory insufficiency resulting in ventilatory support and seizures with burst-suppression pattern on electroencephalogram (EEG). KD initiated at age 6 months for intractable seizures, lead to a dramatic decrease in seizure frequency, EEG improvements, normalisation of plasma glycine levels, reduced spasticity and improved quality of life. KD may be a valuable treatment modality for refractory seizure control in classical NKH.

Do ketone bodies mediate the anti-seizure effects of the ketogenic diet?

Although the mechanisms underlying the anti-seizure effects of the high-fat ketogenic diet (KD) remain unclear, a long-standing question has been whether ketone bodies (i.e., β-hydroxybutyrate, acetoacetate and acetone), either alone or in combination, contribute mechanistically. The traditional belief has been that while ketone bodies reflect enhanced fatty acid oxidation and a general shift toward intermediary metabolism, they are not likely to be the key mediators of the KD's clinical effects, as blood levels of β-hydroxybutyrate do not correlate consistently with improved seizure control. Against this unresolved backdrop, new data support ketone bodies as having anti-seizure actions. Specifically, β-hydroxybutyrate has been shown to interact with multiple novel molecular targets such as histone deacetylases, hydroxycarboxylic acid receptors on immune cells, and the NLRP3 inflammasome. Clearly, as a diet-based therapy is expected to render a broad array of biochemical, molecular, and cellular changes, no single mechanism can explain how the KD works. Specific metabolic substrates or enzymes are only a few of many important factors influenced by the KD that can collectively influence brain hyperexcitability and hypersynchrony. This review summarizes recent novel experimental findings supporting the anti-seizure and neuroprotective properties of ketone bodies.

Anticonvulsant effect of exogenous β-hydroxybutyrate on kainic acid-induced epilepsy

The present study aimed to investigate the anticonvulsant effects of β-hydroxybutyrate (BHB) in a kainic acid (KA)-induced rat seizure model. The concentrations of BHB and glucose were detected in the blood prior to exogenous BHB administration. Three different doses of BHB (2, 4 and 8 mmol/kg) were then injected into male Wistar rats intraperitoneally, and the concentrations of BHB and glucose in the blood were detected. Rats received 0.9% normal saline intraperitoneally at a dose of 4 ml/kg as a control. Subsequently, a KA-induced rat seizure model was established and the anticonvulsant effects of BHB were investigated. The onset time of seizure and the degree of seizure behavior were recorded. Nissl and Timm staining were used to evaluate neuronal loss and mossy fiber sprouting, respectively. The present study demonstrated that exogenous BHB administration could significantly increase BHB concentration in the blood and this concentration was maintained for 90 min without affecting blood glucose levels. Furthermore, it was determined that a dose of 4 mmol/kg BHB is optimal for exogenous administration. The onset time of seizure was significantly prolonged in BHB-pretreated rats (63.31±4.050 min) compared with the control group (37.08±1.958 min; P=0.039). In addition, neuronal loss and mossy fiber sprouting were both alleviated in the BHB-pretreated model group. Exogenous BHB administration at a dose of 4 mmol/kg may be an alternative to a ketogenic diet to exert a protective effect in the epileptic model induced by KA. The results of the present study may allow novel therapeutic strategies to be developed to treat epilepsy.

Ketogenic diet improves the spatial memory impairment caused by exposure to hypobaric hypoxia through increased acetylation of histones in rats

Exposure to hypobaric hypoxia causes neuron cell damage, resulting in impaired cognitive function. Effective interventions to antagonize hypobaric hypoxia-induced memory impairment are in urgent need. Ketogenic diet (KD) has been successfully used to treat drug-resistant epilepsy and improves cognitive behaviors in epilepsy patients and other pathophysiological animal models. In the present study, we aimed to explore the potential beneficial effects of a KD on memory impairment caused by hypobaric hypoxia and the underlying possible mechanisms. We showed that the KD recipe used was ketogenic and increased plasma levels of ketone bodies, especially β-hydroxybutyrate. The results of the behavior tests showed that the KD did not affect general locomotor activity but obviously promoted spatial learning. Moreover, the KD significantly improved the spatial memory impairment caused by hypobaric hypoxia (simulated altitude of 6000 m, 24 h). In addition, the improving-effect of KD was mimicked by intraperitoneal injection of BHB. The western blot and immunohistochemistry results showed that KD treatment not only increased the acetylated levels of histone H3 and histone H4 compared to that of the control group but also antagonized the decrease in the acetylated histone H3 and H4 when exposed to hypobaric hypoxia. Furthermore, KD-hypoxia treatment also promoted PKA/CREB activation and BDNF protein expression compared to the effects of hypoxia alone. These results demonstrated that KD is a promising strategy to improve spatial memory impairment caused by hypobaric hypoxia, in which increased modification of histone acetylation plays an important role.

Energy and the Alzheimer brain

The high energy demands of the poorly myelinated long axon hippocampal and cortical neurons render these neurons selectively vulnerable to degeneration in Alzheimer's disease. However, pathology engages all of the major elements of the neurovascular unit of the mature Alzheimer brain, the neurons, glia and blood vessels. Neurons present with retrograde degeneration of the axodendritic tree, capillaries with string vessels and markedly reduced densities and glia with signs of inflammatory activation. The neurons, capillaries and astrocytes of the mature Alzheimer brain harbor structurally defective mitochondria. Clinically, reduced glucose utilization, decades before cognitive deterioration, betrays ongoing energy insufficiency. β-hydroxybutyrate and γ-hydroxybutyrate can both provide energy to the brain when glucose utilization is blocked. Early work in mouse models of Alzheimer's disease demonstrate their ability to reverse the pathological changes in the Alzheimer brain and initial clinical trials reveal their ability to improve cognition and every day function. Supplying the brain with energy holds great promise for delaying the onset of Alzheimer's disease and slowing its progress.

Metabolic Therapy for Temporal Lobe Epilepsy in a Dish: Investigating Mechanisms of Ketogenic Diet using Electrophysiological Recordings in Hippocampal Slices

The hippocampus is prone to epileptic seizures and is a key brain region and experimental platform for investigating mechanisms associated with the abnormal neuronal excitability that characterizes a seizure. Accordingly, the hippocampal slice is a common in vitro model to study treatments that may prevent or reduce seizure activity. The ketogenic diet is a metabolic therapy used to treat epilepsy in adults and children for nearly 100 years; it can reduce or eliminate even severe or refractory seizures. New insights into its underlying mechanisms have been revealed by diverse types of electrophysiological recordings in hippocampal slices. Here we review these reports and their relevant mechanistic findings. We acknowledge that a major difficulty in using hippocampal slices is the inability to reproduce precisely the in vivo condition of ketogenic diet feeding in any in vitro preparation, and progress has been made in this in vivo/in vitro transition. Thus far at least three different approaches are reported to reproduce relevant diet effects in the hippocampal slices: (1) direct application of ketone bodies; (2) mimicking the ketogenic diet condition during a whole-cell patch-clamp technique; and (3) reduced glucose incubation of hippocampal slices from ketogenic diet–fed animals. Significant results have been found with each of these methods and provide options for further study into short- and long-term mechanisms including Adenosine triphosphate (ATP)-sensitive potassium (K_ATP) channels, vesicular glutamate transporter (VGLUT), pannexin channels and adenosine receptors underlying ketogenic diet and other forms of metabolic therapy.

Unified theory of Alzheimer's disease (UTAD): implications for prevention and curative therapy

The aim of this review is to propose a Unified Theory of Alzheimer's disease (UTAD) that integrates all key behavioural, genetic and environmental risk factors in a causal chain of etiological and pathogenetic events. It is based on three concepts that emanate from human's evolutionary history: (1) The grandmother-hypothesis (GMH), which explains human longevity due to an evolutionary advantage in reproduction by trans-generational transfer of acquired knowledge. Consequently it is argued that mental health at old-age must be the default pathway of humans' genetic program and not development of AD. (2) Therefore, mechanism like neuronal rejuvenation (NRJ) and adult hippocampal neurogenesis (AHN) that still function efficiently even at old age provide the required lifelong ability to memorize personal experiences important for survival. Cumulative evidence from a multitude of experimental and epidemiological studies indicate that behavioural and environmental risk factors, which impair productive AHN, result in reduced episodic memory performance and in reduced psychological resilience. This leads to avoidance of novelty, dysregulation of the hypothalamic-pituitary-adrenal (HPA)-axis and cortisol hypersecretion, which drives key pathogenic mechanisms of AD like the accumulation and oligomerization of synaptotoxic amyloid beta, chronic neuroinflammation and neuronal insulin resistance. (3) By applying to AHN the law of the minimum (LOM), which defines the basic requirements of biological growth processes, the UTAD explains why and how different lifestyle deficiencies initiate the AD process by impairing AHN and causing dysregulation of the HPA-axis, and how environmental and genetic risk factors such as toxins or ApoE4, respectively, turn into disease accelerators under these unnatural conditions. Consequently, the UTAD provides a rational strategy for the prevention of mental decline and a system-biological approach for the causal treatment of AD, which might even be curative if the systemic intervention is initiated early enough in the disease process. Hence an individualized system-biological treatment of patients with early AD is proposed as a test for the validity of UTAD and outlined in this review.

Ketogenic Diet, but Not Polyunsaturated Fatty Acid Diet, Reduces Spontaneous Seizures in Juvenile Rats with Kainic Acid-induced Epilepsy

Background and Purpose:

The high-fat, low-carbohydrate ketogenic diet (KD) is effective in many cases of drug-resistant epilepsy, particularly in children. In the classic KD, fats consist primarily of long-chain saturated triglycerides. Polyunsaturated fatty acids (PUFAs), especially the n-3 type, decrease neuronal excitability and provide neuroprotection; pilot human studies have raised the possibility of using PUFAs to control seizures in patients.

Methods:

To determine the relative roles of the KD and PUFAs in an animal model, we induced epilepsy in juvenile rats (P29–35) using intraperitoneal kainic acid (KA). KA caused status epilepticus in all rats. Two days after KA, rats were randomized to one of 4 dietary groups: Control diet; PUFA diet; KD; or KD plus PUFA. All diets were administered isocalorically at 90% of the rat recommended daily calorie requirement. Spontaneous recurrent seizures (SRS) were assessed for 3 months after diet randomization.

Results:

Rats receiving the KD or KD-PUFA diet had significantly fewer SRS than those receiving the Control diet or PUFA diet. The PUFA diet did not reduce SRS compared to the Control diet.

Conclusions:

In the KA epilepsy model, the KD protects against SRS occurrence but dietary enhancement with PUFA does not afford additional protection against spontaneous seizures.

β-hydroxybutyrate: much more than a metabolite

The ketone body β-hydroxybutyrate (βOHB) is a convenient carrier of energy from adipocytes to peripheral tissues during fasting or exercise. However, βOHB is more than just a metabolite, having important cellular signaling roles as well. βOHB is an endogenous inhibitor of histone deacetylases (HDACs) and a ligand for at least two cell surface receptors. In addition, the downstream products of βOHB metabolism including acetyl-CoA, succinyl-CoA, and NAD+ (nicotinamide adenine dinucleotide) themselves have signaling activities. These regulatory functions of βOHB serve to link the outside environment to cellular function and gene expression, and have important implications for the pathogenesis and treatment of metabolic diseases including type 2 diabetes.

Ketogenic diet sensitizes glucose control of hippocampal excitability

A high-fat low-carbohydrate ketogenic diet (KD) is an effective treatment for refractory epilepsy, yet myriad metabolic effects in vivo have not been reconciled clearly with neuronal effects. A KD limits blood glucose and produces ketone bodies from β-oxidation of lipids. Studies have explored changes in ketone bodies and/or glucose in the effects of the KD, and glucose is increasingly implicated in neurological conditions. To examine the interaction between altered glucose and the neural effects of a KD, we fed rats and mice a KD and restricted glucose in vitro while examining the seizure-prone CA3 region of acute hippocampal slices. Slices from KD-fed animals were sensitive to small physiological changes in glucose, and showed reduced excitability and seizure propensity. Similar to clinical observations, reduced excitability depended on maintaining reduced glucose. Enhanced glucose sensitivity and reduced excitability were absent in slices obtained from KD-fed mice lacking adenosine A₁ receptors (A₁Rs); in slices from normal animals effects of the KD could be reversed with blockers of pannexin-1 channels, A₁Rs, or K_ATP channels. Overall, these studies reveal that a KD sensitizes glucose-based regulation of excitability via purinergic mechanisms in the hippocampus and thus link key metabolic and direct neural effects of the KD.

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.

Neuroactive peptides as putative mediators of antiepileptic ketogenic diets

Various ketogenic diet (KD) therapies, including classic KD, medium chain triglyceride administration, low glycemic index treatment, and a modified Atkins diet, have been suggested as useful in patients affected by pharmacoresistant epilepsy. A common goal of these approaches is to achieve an adequate decrease in the plasma glucose level combined with ketogenesis, in order to mimic the metabolic state of fasting. Although several metabolic hypotheses have been advanced to explain the anticonvulsant effect of KDs, including changes in the plasma levels of ketone bodies, polyunsaturated fatty acids, and brain pH, direct modulation of neurotransmitter release, especially purinergic (i.e., adenosine) and γ-aminobutyric acidergic neurotransmission, was also postulated. Neuropeptides and peptide hormones are potent modulators of synaptic activity, and their levels are regulated by metabolic states. This is the case for neuroactive peptides such as neuropeptide Y, galanin, cholecystokinin, and peptide hormones such as leptin, adiponectin, and growth hormone-releasing peptides (GHRPs). In particular, the GHRP ghrelin and its related peptide des-acyl ghrelin are well-known controllers of energy homeostasis, food intake, and lipid metabolism. Notably, ghrelin has also been shown to regulate the neuronal excitability and epileptic activation of neuronal networks. Several lines of evidence suggest that GHRPs are upregulated in response to starvation and, particularly, in patients affected by anorexia and cachexia, all conditions in which also ketone bodies are upregulated. Moreover, starvation and anorexia nervosa are accompanied by changes in other peptide hormones such as adiponectin, which has received less attention. Adipocytokines such as adiponectin have also been involved in modulating epileptic activity. Thus, neuroactive peptides whose plasma levels and activity change in the presence of ketogenesis might be potential candidates for elucidating the neurohormonal mechanisms involved in the beneficial effects of KDs. In this review, we summarize the current evidence for altered regulation of the synthesis of neuropeptides and peripheral hormones in response to KDs, and we try to define a possible role for specific neuroactive peptides in mediating the antiepileptic properties of diet-induced ketogenesis.

Ketone bodies as signaling metabolites

Traditionally, the ketone body β-hydroxybutyrate (βOHB) has been looked upon as a carrier of energy from liver to peripheral tissues during fasting or exercise. However, βOHB also signals via extracellular receptors and acts as an endogenous inhibitor of histone deacetylases (HDACs). These recent findings support a model in which βOHB functions to link the environment, in this case the diet, and gene expression via chromatin modifications. We review the regulation and functions of ketone bodies, the relationship between ketone bodies and calorie restriction, and the implications of HDAC inhibition by the ketone body βOHB in the modulation of metabolism and in diseases of aging.

Inter-relationships among diet, obesity and hippocampal-dependent cognitive function

Intake of a Western diet (WD), which is high in saturated fat and sugar, is associated with deficits in hippocampal-dependent learning and memory processes as well as with markers of hippocampal pathology. In the present study, rats were trained to asymptote on hippocampal-dependent serial feature negative (FN) and hippocampal-independent simple discrimination problems. Performance was then assessed following 7 days on ad libitum chow and after 10, 24, 40, 60, and 90 days of maintenance on WD, on ketogenic (KETO) diet, which is high in saturated fat and low in sugar and other carbohydrates, or continued maintenance on chow (CHOW). Confirming and extending previous findings, diet-induced obese (DIO) rats fed WD showed impaired FN performance, increased blood-brain barrier (BBB) permeability, and increased fasting blood glucose levels compared to CHOW controls and to diet-resistant (DR) rats that did not become obese when maintained on WD. For rats fed the KETO diet, FN performance and BBB integrity were more closely associated with level of circulating ketone bodies than with obesity phenotype (DR or DIO), with higher levels of ketones appearing to provide a protective effect. The evidence also indicated that FN deficits preceded and predicted increased body weight and adiposity. This research (a) further substantiates previous findings of WD-induced deficits in hippocampal-dependent FN discriminations, (b) suggests that ketones may be protective against diet-induced cognitive impairment, and (c) provides evidence that diet-induced cognitive impairment precedes weight gain and obesity.

GPR109A and vascular inflammation

GPR109A has generated expanding interest since its discovery as the receptor for niacin a decade ago, along with deorphanisation as the receptor for endogenous ligand 3-hydroxy-butyrate shortly after. This interest is generated especially because of the continuing exploration of niacin's "pleiotropic" mechanisms of action and its potential in the "cross-talk" between metabolic and inflammatory pathways. As GPR109A's primary pharmacological ligand in clinical use, niacin has been used for over 50 years in the treatment of cardiovascular disease, mainly due to its favourable effects on plasma lipoproteins. However, it has become apparent that niacin also possesses lipoprotein-independent effects that influence inflammatory pathways mediated through GPR109A. In addition to its G-protein-mediated effects, recent evidence has emerged to support alternative GPR109A signalling via adaptive protein β-arrestins. In this article, we consider the role of GPR109A and its downstream effects in the context of atherosclerosis and vascular inflammation, along with insights into strategy for future drug development.

Augmentation of normal and glutamate-impaired neuronal respiratory capacity by exogenous alternative biofuels

Mitochondrial respiratory capacity is critical for responding to changes in neuronal energy demand. One approach toward neuroprotection is the administration of alternative energy substrates ("biofuels") to overcome brain injury-induced inhibition of glucose-based aerobic energy metabolism. This study tested the hypothesis that exogenous pyruvate, lactate, β-hydroxybutyrate, and acetyl-L-carnitine each increase neuronal respiratory capacity in vitro either in the absence of or following transient excitotoxic glutamate receptor stimulation. Compared to the presence of 5 mM glucose alone, the addition of pyruvate, lactate, or β-hydroxybutyrate (1.0-10.0 mM) to either day in vitro (DIV) 14 or 7 rat cortical neurons resulted in significant, dose-dependent stimulation of respiratory capacity, measured by cell respirometry as the maximal O2 consumption rate in the presence of the respiratory uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. A 30-min exposure to 100 μM glutamate impaired respiratory capacity for DIV 14, but not DIV 7, neurons. Glutamate reduced the respiratory capacity for DIV 14 neurons with glucose alone by 25 % and also reduced respiratory capacity with glucose plus pyruvate, lactate, or β-hydroxybutyrate. However, respiratory capacity in glutamate-exposed neurons following pyruvate or β-hydroxybutyrate addition was still, at least, as high as that obtained with glucose alone in the absence of glutamate exposure. These results support the interpretation that previously observed neuroprotection by exogenous pyruvate, lactate, or β-hydroxybutyrate is at least partially mediated by their preservation of neuronal respiratory capacity.

Nicotinic acid receptor GPR109A is down-regulated in human macrophage-derived foam cells

Nicotinic acid (NA) regresses atherosclerosis in human imaging studies and reduces atherosclerosis in mice, mediated by myeloid cells, independent of lipoproteins. Since GPR109A is expressed by human monocytes, we hypothesized that NA may drive cholesterol efflux from foam cells. In THP-1 cells NA suppressed LPS-induced mRNA transcription of MCP-1 by 76.6±12.2% (P<0.01) and TNFα by 56.1±11.5% (P<0.01), yet restored LPS-induced suppression of PPARγ transcription by 536.5±46.4% (P<0.001) and its downstream effector CD36 by 116.8±19.8% (P<0.01). Whilst direct PPARγ-agonism promoted cholesterol efflux from THP-1 derived foam cells by 37.7±3.1% (P<0.01) and stimulated transcription of LXRα by 87.9±9.5% (P<0.001) and ABCG1 by 101.2±15.5% (P<0.01), NA showed no effect in foam cells on either cholesterol efflux or key RCT genes transcription. Upon foam cell induction, NA lost its effect on PPARγ and cAMP pathways, since its receptor, GPR109A, was down-regulated by foam cell transformation. This observation was confirmed in explanted human carotid plaques. In conclusion, despite NA's anti-inflammatory effect on human macrophages, it has no effect on foam cells in reverse cholesterol transport; due to GPR109A down-regulation.

The ketogenic diet: metabolic influences on brain excitability and epilepsy

A dietary therapy for pediatric epilepsy known as the ketogenic diet has seen a revival in its clinical use during the past decade. Although the underlying mechanism of the diet remains unknown, modern scientific approaches, such as the genetic disruption of glucose metabolism, are allowing for more detailed questions to be addressed. Recent work indicates that several mechanisms may exist for the ketogenic diet, including disruption of glutamatergic synaptic transmission, inhibition of glycolysis, and activation of ATP-sensitive potassium channels. Here, we describe on-going work in these areas that is providing a better understanding of metabolic influences on brain excitability and epilepsy.

Ketogenic diet in early myoclonic encephalopathy due to non ketotic hyperglycinemia

Non ketotic hyperglycinemia is a rare inborn error of glycine metabolism due to deficient activity of glycine cleavage system, a multienzymatic complex consisting of four protein subunits: the P-protein, the H-protein, the T-protein and the L-protein. The neonatal form of non ketotic hyperglycinemia presents in the first days of life with encephalopathy, seizures, multifocal myoclonus and characteristic "hiccups". Rapid progression may lead to intractable seizures, coma and respiratory failure requiring mechanical ventilation. Clinical trial with scavenges drugs decreasing glycine levels such as sodium benzoate, and with drugs reducing NMDA receptors excitatory properties, such as ketamine and dextromethorphan, have been tried but the outcome is usually poor; antiepileptic therapy, moreover, is unable to control epileptic seizures. Ketogenic diet has been successfully tried for refractory epilepsy in pediatric patients. We report three cases affected by neonatal non ketotic hyperglycinemia and early myoclonic encephalopathy treated with ketogenic diet. In our patients ketogenic diet, in association with standard pharmacological therapy, determined dramatic reduction of seizures and improved quality of life.

Ketogenic diet reduces Smac/Diablo and cytochrome c release and attenuates neuronal death in a mouse model of limbic epilepsy

The ketogenic diet (KD) is effective in the treatment of refractory epilepsy, yet the molecular mechanisms underlying its antiepileptic effects have not been determined. There is increasing evidence that neuronal cell death induced by seizures via mitochondrial pathway and seizures can lead to mitochondrial release of cytochrome c, and we have shown previously that translocation of Smac/DIABLO into the cytosol play a role in the brain damage in a model of limbic seizure. In the present study, we explored the neuroprotective effect of KD in C57BL/6 mice with seizures induced by kainic acid (KA). Status epilepticus triggered by intra-amygdaloid microinjection of KA lead to neuronal death in the selective ipsilateral CA3 subfield of the hippocampus and mitochondrial release of Smac/DIABLO and cytochrome c. We found that KD significantly decreased neuronal death in the ipsilateral CA3 at 24h after KA-induced seizures. Furthermore, KD reduced Smac/DIABLO and cytochrome c release from mitochondria, attenuated activation of casepase-9 and caspase-3 following seizures. These results demonstrate that the neuroprotective effect of KD against brain injury induced by limbic seizures, at least partially, is associated with inhibition of mitochondrial release of Smac/DIABLO and cytochrome c.

The nervous system and metabolic dysregulation: emerging evidence converges on ketogenic diet therapy

A link between metabolism and brain function is clear. Since ancient times, epileptic seizures were noted as treatable with fasting, and historical observations of the therapeutic benefits of fasting on epilepsy were confirmed nearly 100 years ago. Shortly thereafter a high fat, low-carbohydrate ketogenic diet (KD) debuted as a therapy to reduce seizures. This strict regimen could mimic the metabolic effects of fasting while allowing adequate caloric intake for ongoing energy demands. Today, KD therapy, which forces predominantly ketone-based rather than glucose-based metabolism, is now well-established as highly successful in reducing seizures. Cellular metabolic dysfunction in the nervous system has been recognized as existing side-by-side with nervous system disorders - although often with much less obvious cause-and-effect as the relationship between fasting and seizures. Rekindled interest in metabolic and dietary therapies for brain disorders complements new insight into their mechanisms and broader implications. Here we describe the emerging relationship between a KD and adenosine as a way to reset brain metabolism and neuronal activity and disrupt a cycle of dysfunction. We also provide an overview of the effects of a KD on cognition and recent data on the effects of a KD on pain, and explore the relative time course quantified among hallmark metabolic changes, altered neuron function and altered animal behavior assessed after diet administration. We predict continued applications of metabolic therapies in treating dysfunction including and beyond the nervous system.

β-Hydroxybutyrate increases the pilocarpine-induced seizure threshold in young mice

This study was designed to investigate the effects of β-hydroxybutyrate (BHB) on pilocarpine-induced seizures in young mice. Eighty-five male, postnatal day 21, ICR mice were used. All mice were pretreated with scopolamine methylbromide (1 mg/kg) 30 min prior to pilocarpine administration. Experimental mice (n=46) were injected intraperitoneally with BHB (20 mmol/kg), 15 min prior to pilocarpine administration; control animals (n=39) were administered normal saline. Pilocarpine (300 mg/kg) was then administered intraperitoneally to induce seizures. Mice were monitored for 2 h after pilocarpine injection, and seizure behavior grades were evaluated according to Racine's scale. All mice developed typical seizure behaviors of grade 3 or higher. Although the severity in terms of seizure behavior grade was not significantly different between groups, the mean (±SD) latency to the onset of seizure was significantly prolonged in BHB-treated mice (5.15±2.19 min) compared with controls (2.95±1.06 min; p<0.001). This study demonstrates that treatment with BHB significantly prolongs the latency to the onset of seizures induced by pilocarpine in mice and suggests that BHB, one of the ketone bodies, may be direct anticonvulsant.

Purines and neuronal excitability: links to the ketogenic diet

ATP and adenosine are purines that play dual roles in cell metabolism and neuronal signaling. Acting at the A(1) receptor (A(1)R) subtype, adenosine acts directly on neurons to inhibit excitability and is a powerful endogenous neuroprotective and anticonvulsant molecule. Previous research showed an increase in ATP and other cell energy parameters when an animal is administered a ketogenic diet, an established metabolic therapy to reduce epileptic seizures, but the relationship among purines, neuronal excitability and the ketogenic diet was unclear. Recent work in vivo and in vitro tested the specific hypothesis that adenosine acting at A(1)Rs is a key mechanism underlying the success of ketogenic diet therapy and yielded direct evidence linking A(1)Rs to the antiepileptic effects of a ketogenic diet. Specifically, an in vitro mimic of a ketogenic diet revealed an A(1)R-dependent metabolic autocrine hyperpolarization of hippocampal neurons. In parallel, applying the ketogenic diet in vivo to transgenic mouse models with spontaneous electrographic seizures revealed that intact A(1)Rs are necessary for the seizure-suppressing effects of the diet. This is the first direct in vivo evidence linking A(1)Rs to the antiepileptic effects of a ketogenic diet. Other predictions of the relationship between purines and the ketogenic diet are discussed. Taken together, recent research on the role of purines may offer new opportunities for metabolic therapy and insight into its underlying mechanisms.

Neuroprotection in metabolism-based therapy

Metabolism-based therapy has been used successfully in the treatment of seizures but study of its use in other neurodegenerative disorders is growing. Data demonstrating the use of different forms of metabolism-based therapy in human trials of Alzheimer disease and Parkinson disease are discussed. Animal and in vitro studies have shed light on metabolism-based therapy's mechanisms in these diseases, as well as ALS, aging, ischemia, trauma and mitochondrial cytopathies. Additional insights may be obtained by considering the role of metabolism-based therapy in cell disability and death (specifically apoptosis, excitotoxicity, and autophagy).

Differential utilization of ketone bodies by neurons and glioma cell lines: a rationale for ketogenic diet as experimental glioma therapy

Background

Even in the presence of oxygen, malignant cells often highly depend on glycolysis for energy generation, a phenomenon known as the Warburg effect. One strategy targeting this metabolic phenotype is glucose restriction by administration of a high-fat, low-carbohydrate (ketogenic) diet. Under these conditions, ketone bodies are generated serving as an important energy source at least for non-transformed cells.

Methods

To investigate whether a ketogenic diet might selectively impair energy metabolism in tumor cells, we characterized in vitro effects of the principle ketone body 3-hydroxybutyrate in rat hippocampal neurons and five glioma cell lines. In vivo, a non-calorie-restricted ketogenic diet was examined in an orthotopic xenograft glioma mouse model.

Results

The ketone body metabolizing enzymes 3-hydroxybutyrate dehydrogenase 1 and 2 (BDH1 and 2), 3-oxoacid-CoA transferase 1 (OXCT1) and acetyl-CoA acetyltransferase 1 (ACAT1) were expressed at the mRNA and protein level in all glioma cell lines. However, no activation of the hypoxia-inducible factor-1α (HIF-1α) pathway was observed in glioma cells, consistent with the absence of substantial 3-hydroxybutyrate metabolism and subsequent accumulation of succinate. Further, 3-hydroxybutyrate rescued hippocampal neurons from glucose withdrawal-induced cell death but did not protect glioma cell lines. In hypoxia, mRNA expression of OXCT1, ACAT1, BDH1 and 2 was downregulated. In vivo, the ketogenic diet led to a robust increase of blood 3-hydroxybutyrate, but did not alter blood glucose levels or improve survival.

Conclusion

In summary, glioma cells are incapable of compensating for glucose restriction by metabolizing ketone bodies in vitro, suggesting a potential disadvantage of tumor cells compared to normal cells under a carbohydrate-restricted ketogenic diet. Further investigations are necessary to identify co-treatment modalities, e.g. glycolysis inhibitors or antiangiogenic agents that efficiently target non-oxidative pathways.

Therapeutic role of mammalian target of rapamycin (mTOR) inhibition in preventing epileptogenesis

Traditionally, medical therapy for epilepsy has aimed to suppress seizure activity, but has been unable to alter the progression of the underlying disease. Recent advances in our understanding of mechanisms of epileptogenesis open the door for the development of new therapies which prevent the pathogenic changes in the brain that predispose to spontaneous seizures. In particular, the mammalian target of rapamycin (mTOR) signaling pathway has recently garnered interest as an important regulator of cellular changes involved in epileptogenesis, and mTOR inhibitors have generated excitement as potential antiepileptogenic agents. mTOR hyperactivation occurs in tuberous sclerosis complex (TSC), a common genetic cause of epilepsy, as a result of genetic mutations in upstream regulatory molecules. mTOR inhibition prevents epilepsy and brain pathology in animal models of TSC. mTOR dysregulation has also been demonstrated in a variety of other genetic and acquired epilepsies, including brain tumors, focal cortical dysplasias, and animal models of brain injury due to status epilepticus or trauma. Indeed, mTOR inhibitors appear to possess antiepileptogenic properties in animal models of acquired epilepsy as well. Thus, mTOR dysregulation may represent a final common pathway in epilepsies of various causes. Therefore, mTOR inhibition is an exciting potential antiepileptogenic strategy with broad applications for epilepsy and could be involved in a number of treatment modalities, including the ketogenic diet. Further research is necessary to determine the clinical utility of rapamycin and other mTOR inhibitors for antiepileptogenesis, and to devise new therapeutic targets by further elucidating the signaling molecules involved in epileptogenesis.

Does ketogenic diet alter seizure sensitivity and cell loss following fluid percussion injury?

Traumatic brain injury (TBI) frequently leads to epilepsy. The process of epileptogenesis - the development of that seizure state - is still poorly understood, and effective antiepileptogenic treatments have yet to be identified. The ketogenic diet (KD) has been shown to be effective as an antiepileptic therapy, but has not been extensively tested for its efficacy in preventing the development of the seizure state, and certainly not within the context of TBI-induced epileptogenesis. We have used a rat model of TBI - fluid percussion injury (FPI) - to test the hypothesis that KD treatment is antiepileptogenic and protects the brain from neuronal cell loss following TBI. Rats fed a KD had a higher seizure threshold (longer latency to flurothyl-induced seizure activity) than rats fed a standard diet (SD); this effect was seen when KD was in place at the time of seizure testing (3 and 6 weeks following FPI), but was absent when KD had been replaced by SD at time of testing. FPI caused significant hippocampal cell loss in both KD-fed and SD-fed rats; the degree of cell loss appeared to be reduced by KD treatment before FPI but not after FPI. These results are consistent with prior demonstrations that KD raises seizure threshold, but do not provide support for the hypothesis that KD administered for a limited time directly before or after FPI alters later seizure sensitivity; that is, within the limits of this model and protocol, there is no evidence for KD-induced antiepileptogenesis.

Neuroprotective effects of pyruvate following NMDA-mediated excitotoxic insults in hippocampal slices

The activation of N-methyl-D-aspartate (NMDA) receptors and subsequent release of nitric oxide (NO) are likely contributors to the delayed neuronal damage that accompanies ischemia and other neurodegenerative conditions. NMDA receptor antagonists and inhibitors of NO synthesis, however, are of limited benefit when administered following excitotoxic events, suggesting the importance of determining downstream events that result in neuronal degeneration. Inhibition of glyceraldehyde-3-phosphate-dehydrogenase (GAPDH), a key glycolytic enzyme, which may result in glycolytic impairment, is one of the biological targets of NO. This suggests that alternative energy substrates may prevent neuronal damage. Using rat hippocampal slices from juvenile rats, we examined the role of glycolytic impairment in NMDA-mediated excitotoxicity and whether pyruvate, an end product of glycolysis, prevents the excitotoxic neuronal injury. We observed that administration of NMDA acutely depresses ATP levels and result in a slowly developing inhibition of GAPDH. Unlike NMDA receptor antagonists or NO inhibitors, exogenously applied pyruvate is effective in restoring ATP levels and preventing delayed neuronal degeneration and synaptic deterioration when administered in the period following NMDA receptor activation. This raises the possibility that treatment with agents that maintain cellular energy function can prevent delayed excitotoxicity.