A cDNA microarray analysis of gene expression profiles in rat hippocampus following a ketogenic diet

Ketogenic Diet-Induced Alterations in Neuronal Signaling-Related Proteins are Not Due to Differences in Synaptosome Protein Levels

Impaired cognitive function is a hallmark of advancing age, and the potential to reverse or delay these cognitive deficits through dietary intervention holds promise for improving quality of life for older adults. Specifically, ketogenic diets (KDs) have now been widely used for the treatment of several neurological and peripheral disorders, including diseases profoundly affecting cognitive health, of which advanced age is the single greatest risk factor. However, the precise mechanisms of the efficacy of KD-based interventions to reverse age-related cognitive and neurobiological declines are not fully elucidated. We have previously demonstrated that a KD improves cognitive function, with concurrent increases in global levels of proteins related to synaptic signaling in the aging hippocampus (HPC) and prefrontal cortex (PFC). Despite these advances, it remains unclear as to whether these changes reflect biochemical modifications specifically localized to synaptic terminals. To address this important, unanswered question, we purified synaptosomes from the HPC and PFC of aging rats fed a KD or control diet (CD) for a minimum of 4 months and quantified 10 proteins related to synaptic transmission. In contrast to previous studies of global protein expression, the signaling proteins measured did not show significant differences between diet groups in synaptosomes isolated from either region. When pre-mortem performance on an Object-Place Paired Association task was considered, we found a significant correlation between several proteins within the HPC and PFC synaptosomes of CD-fed rats, more pronounced in CD-fed aged rats, that are conspicuously absent in KD-fed rats from both age groups. Moreover, there is a significant alteration in the ratio of VGAT/VGluT1, markers of excitatory and inhibitory synaptic vesicles, in the PFC with dietary intervention that is absent in the HPC, confirming prior reports of regionally specific alterations in excitatory and inhibitory signaling post KD. These new and extended findings reveal important, naturally occurring associations between protein levels localized to synaptic terminals, while clarifying that effects KD likely increase synaptic abundance without altering the biochemical composition of isolated synapses.

Ketogenic diet, adenosine, and dopamine in addiction and psychiatry

Adhering to the ketogenic diet can reduce or stop seizures, even when other treatments fail, via mechanism(s) distinct from other available therapies. These results have led to interest in the diet for treating conditions such as Alzheimer's disease, depression and schizophrenia. Evidence points to the neuromodulator adenosine as a key mechanism underlying therapeutic benefits of a ketogenic diet. Adenosine represents a unique and direct link among cell energy, neuronal activity, and gene expression, and adenosine receptors form functional heteromers with dopamine receptors. The importance of the dopaminergic system is established in addiction, as are the challenges of modulating the dopamine system directly. A mediator that could antagonize dopamine's effects would be useful, and adenosine is such a mediator due to its function and location. Studies report that the ketogenic diet improves cognition, sociability, and perseverative behaviors, and might improve depression. Many of the translational opportunities based on the ketogenic diet/adenosine link have come to the fore, including addiction, autism spectrum disorder, painful conditions, and a range of hyperdopaminergic disorders.

Ketogenic diet alleviates cognitive dysfunction and neuroinflammation in APP/PS1 mice via the Nrf2/HO-1 and NF-κB signaling pathways

Alzheimer's disease is a progressive neurological disorder characterized by cognitive decline and chronic inflammation within the brain. The ketogenic diet, a widely recognized therapeutic intervention for refractory epilepsy, has recently been proposed as a potential treatment for a variety of neurological diseases, including Alzheimer's disease. However, the efficacy of ketogenic diet in treating Alzheimer's disease and the underlying mechanism remains unclear. The current investigation aimed to explore the effect of ketogenic diet on cognitive function and the underlying biological mechanisms in a mouse model of Alzheimer's disease. Male amyloid precursor protein/presenilin 1 (APP/PS1) mice were randomly assigned to either a ketogenic diet or control diet group, and received their respective diets for a duration of 3 months. The findings show that ketogenic diet administration enhanced cognitive function, attenuated amyloid plaque formation and proinflammatory cytokine levels in APP/PS1 mice, and augmented the nuclear factor-erythroid 2-p45 derived factor 2/heme oxygenase-1 signaling pathway while suppressing the nuclear factor-kappa B pathway. Collectively, these data suggest that ketogenic diet may have a therapeutic potential in treating Alzheimer's disease by ameliorating the neurotoxicity associated with Aβ-induced inflammation. This study highlights the urgent need for further research into the use of ketogenic diet as a potential therapy for Alzheimer's disease.

Dynamic regulation of the extracellular matrix in reward memory processes: a question of time

Substance use disorders are a global health problem with increasing prevalence resulting in significant socioeconomic burden and increased mortality. Converging lines of evidence point to a critical role of brain extracellular matrix (ECM) molecules in the pathophysiology of substance use disorders. An increasing number of preclinical studies highlight the ECM as a promising target for development of novel cessation pharmacotherapies. The brain ECM is dynamically regulated during learning and memory processes, thus the time course of ECM alterations in substance use disorders is a critical factor that may impact interpretation of the current studies and development of pharmacological therapies. This review highlights the evidence for the involvement of ECM molecules in reward learning, including drug reward and natural reward such as food, as well as evidence regarding the pathophysiological state of the brain's ECM in substance use disorders and metabolic disorders. We focus on the information regarding time-course and substance specific changes in ECM molecules and how this information can be leveraged for the development of therapeutic strategies.

Epilepsy and Autism Spectrum Disorder (ASD): The Underlying Mechanisms and Therapy Targets Related to Adenosine

Epilepsy and autism spectrum disorder (ASD) are highly mutually comorbid, suggesting potential overlaps in genetic etiology, pathophysiology, and neurodevelopmental abnormalities. Adenosine, an endogenous anticonvulsant and neuroprotective neuromodulator of the brain, has been proved to affect the process of epilepsy and ASD. On the one hand, adenosine plays a crucial role in preventing the progression and development of epilepsy through adenosine receptordependent and -independent ways. On the other hand, adenosine signaling can not only regulate core symptoms but also improve comorbid disorders in ASD. Given the important role of adenosine in epilepsy and ASD, therapeutic strategies related to adenosine, including the ketogenic diet, neuromodulation therapy, and adenosine augmentation therapy, have been suggested for the arrangement of epilepsy and ASD. There are several proposals in this review. Firstly, it is necessary to further discuss the relationship between both diseases based on the comorbid symptoms and mechanisms of epilepsy and ASD. Secondly, it is important to explore the role of adenosine involved in epilepsy and ASD. Lastly, potential therapeutic value and clinical approaches of adenosine-related therapies in treating epilepsy and ASD need to be emphasized.

Ketogenic diets and the nervous system: a scoping review of neurological outcomes from nutritional ketosis in animal studies

OBJECTIVES

Ketogenic diets have reported efficacy for neurological dysfunctions; however, there are limited published human clinical trials elucidating the mechanisms by which nutritional ketosis produces therapeutic effects. The purpose of this present study was to investigate animal models that report variations in nervous system function by changing from a standard animal diet to a ketogenic diet, synthesise these into broad themes, and compare these with mechanisms reported as targets in pain neuroscience to inform human chronic pain trials.

METHODS

An electronic search of seven databases was conducted in July 2020. Two independent reviewers screened studies for eligibility, and descriptive outcomes relating to nervous system function were extracted for a thematic analysis, then synthesised into broad themes.

RESULTS

In total, 170 studies from eighteen different disease models were identified and grouped into fourteen broad themes: alterations in cellular energetics and metabolism, biochemical, cortical excitability, epigenetic regulation, mitochondrial function, neuroinflammation, neuroplasticity, neuroprotection, neurotransmitter function, nociception, redox balance, signalling pathways, synaptic transmission and vascular supply.

DISCUSSION

The mechanisms presented centred around the reduction of inflammation and oxidative stress as well as a reduction in nervous system excitability. Given the multiple potential mechanisms presented, it is likely that many of these are involved synergistically and undergo adaptive processes within the human body, and controlled animal models that limit the investigation to a particular pathway in isolation may reach differing conclusions. Attention is required when translating this information to human chronic pain populations owing to the limitations outlined from the animal research.

Ketogenesis controls mitochondrial gene expression and rescues mitochondrial bioenergetics after cervical spinal cord injury in rats

A better understanding of the secondary injury mechanisms that occur after traumatic spinal cord injury (SCI) is essential for the development of novel neuroprotective strategies linked to the restoration of metabolic deficits. We and others have shown that Ketogenic diet (KD), a high fat, moderate in proteins and low in carbohydrates is neuroprotective and improves behavioural outcomes in rats with acute SCI. Ketones are alternative fuels for mitochondrial ATP generation, and can modulate signaling pathways via targeting specific receptors. Here, we demonstrate that ad libitum administration of KD for 7 days after SCI rescued mitochondrial respiratory capacity, increased parameters of mitochondrial biogenesis, affected the regulation of mitochondrial-related genes, and activated the NRF2-dependent antioxidant pathway. This study demonstrates that KD improves post-SCI metabolism by rescuing mitochondrial function and supports the potential of KD for treatment of acute SCI in humans.

Targeting Diet and Exercise for Neuroprotection and Neurorecovery in Glaucoma

Glaucoma is a leading cause of blindness worldwide. In glaucoma, a progressive dysfunction and death of retinal ganglion cells occurs, eliminating transfer of visual information to the brain. Currently, the only available therapies target the lowering of intraocular pressure, but many patients continue to lose vision. Emerging pre-clinical and clinical evidence suggests that metabolic deficiencies and defects may play an important role in glaucoma pathophysiology. While pre-clinical studies in animal models have begun to mechanistically uncover these metabolic changes, some existing clinical evidence already points to potential benefits in maintaining metabolic fitness. Modifying diet and exercise can be implemented by patients as an adjunct to intraocular pressure lowering, which may be of therapeutic benefit to retinal ganglion cells in glaucoma.

Ketogenic Diet for the Treatment and Prevention of Dementia: A Review

Dementia (major neurocognitive disorder) is an increasingly common syndrome with a significant burden on patients, caregivers, the health-care system, and the society. The prevalence of dementia will certainly continue to grow as the US population ages. Current treatments for dementia, though, are limited. One proposed nonpharmacologic approach for the delay or prevention of dementia is the use of a ketogenic diet. The ketogenic diet was originally employed to treat refractory epilepsy and has shown promise in many neurologic diseases. It has also gained recent popularity for its weight loss effects. Several preclinical studies have confirmed a benefit of ketosis on cognition and systemic inflammation. Given the renewed emphasis on neuroinflammation as a pathogenic contributor to cognitive decline, and the decreased systemic inflammation observed with the ketogenic diet, it is plausible that this diet may delay, ameliorate, or prevent progression of cognitive decline. Several small human studies have shown benefit on cognition in dementia with a ketogenic diet intervention. Future, large controlled studies are needed to confirm this benefit; however, the ketogenic diet has shown promise in regard to delay or mitigation of symptoms of cognitive decline.

Proteomic profile differentiating between mesial temporal lobe epilepsy with and without hippocampal sclerosis

Hippocampal sclerosis (HS) is the most common neuropathological condition in adults with drug-resistant epilepsy and represents a critical feature in mesial temporal lobe epilepsy (MTLE) syndrome. Although epileptogenic brain tissue is associated with glutamate excitotoxicity leading to oxidative stress, the proteins that are targets of oxidative damage remain to be determined. In the present study we designed comprehensive analyses of changes in protein expression level and protein oxidation status in the hippocampus or neocortex to highlight proteins associated with excitotoxicity by comparing MTLE patients with relatively mild excitotoxicity (MTLE patients without HS, MTLE-non-HS) and those with severe excitotoxicity (MTLE patients with HS, MTLE-HS). We performed 2-dimensional fluorescence difference gel electrophoresis, 2D-oxyblot analysis, and mass spectrometric amino acid sequencing. We identified 16 proteins at 18 spots in which the protein expression levels differed between sclerotic and non-sclerotic hippocampi. In the sclerotic hippocampus, the expression levels of several synaptic proteins were decreased, and those of some glia-associated proteins increased. We confirmed histologically that all MTLE-HS cases examined exhibited severe neuronal cell loss and remarkable astrocytic gliosis in the hippocampi. In all MTLE-non-HS cases examined, neurons were spared and gliosis was unremarkable. Therefore, we consider that decreased synaptic proteins are a manifestation of loss of neuronal cell bodies and dendrites, whereas increased glia-associated proteins are a manifestation of proliferation and hypertrophy of astrocytes. These are considered to be the result of hippocampal sclerosis. In contrast, the expression level of d-3-phosphoglycerate dehydrogenase (PHGDH), an l-serine synthetic enzyme expressed exclusively by astrocytes, was decreased, and that of stathmin 1, a neurite extension-related protein expressed by neurons, was increased in the sclerotic hippocampus. These findings cannot be explained solely as the result of hippocampal sclerosis. Rather, these changes can be involved in the continuation of seizure disorders in MTLE-HS. In addition, the protein carbonylation detection, an indicator of protein oxidation caused by excitotoxicity of multiple seizures and/or status epilepticus, revealed that the carbonyl level of collapsin response mediator protein 2 (CRMP2) increased significantly in the sclerotic hippocampus. In conclusion, protein identification following profiling of protein expression levels and detection of oxidative proteins indicated potential pathognomonic protein changes. The decreased expression of PHGDH, increased expression of stathmin 1, and carbonylation of CRMP2 differentiate between MTLE with and without HS. Therefore, further investigations of PHGDH, stathmin 1 and CRMP2 are promising to study more detailed effects of excitotoxicity on epileptogenic hippocampal tissue.

Caloric Restriction and Ketogenic Diet Therapy for Epilepsy: A Molecular Approach Involving Wnt Pathway and KATP Channels

Epilepsy is a neurological disorder in which, in many cases, there is poor pharmacological control of seizures. Nevertheless, it may respond beneficially to alternative treatments such as dietary therapy, like the ketogenic diet or caloric restriction. One of the mechanisms of these diets is to produce a hyperpolarization mediated by the adenosine triphosphate (ATP)-sensitive potassium (KATP) channels (KATP channels). An extracellular increase of K+ prevents the release of Ca2+ by inhibiting the signaling of the Wnt pathway and the translocation of β-catenin to the cell nucleus. Wnt ligands hyperpolarize the cells by activating K+ current by Ca2+. Each of the diets described in this paper has in common a lower use of carbohydrates, which leads to biochemical, genetic processes presumed to be involved in the reduction of epileptic seizures. Currently, there is not much information about the genetic processes implicated as well as the possible beneficial effects of diet therapy on epilepsy. In this review, we aim to describe some of the possible genes involved in Wnt pathways, their regulation through the KATP channels which are implicated in each one of the diets, and how they can reduce epileptic seizures at the molecular level.

A unifying mechanism of ketogenic diet action: The multiple roles of nicotinamide adenine dinucleotide

The ability of a ketogenic diet to treat seizures and render a neuronal network more resistant to strong electrical activity has been observed for a century in clinics and for decades in research laboratories. Alongside ongoing efforts to understand how this therapy works to stop seizures, metabolic health is increasingly appreciated as critical buffer to resisting and recovering from acute and chronic disease. Accordingly, links between metabolism and health, and the broader emerging impact of the ketogenic diet in improving diverse metabolic, immunological and neurological conditions, have served to intensify the search for its key and/or common mechanisms. Here we review diverse evidence for increased levels of NAD⁺, and thus an altered ratio of NAD⁺/NADH, during metabolic therapy with a ketogenic diet. We propose this as a potential unifying mechanism, and highlight some of the evidence linking altered NAD⁺/NADH with reduced seizures and with a range of short and long-term changes associated with the beneficial effects of a ketogenic diet. An increase in NAD⁺/NADH is consistent with multiple lines of evidence and hypotheses, and therefore we suggest that increased NAD⁺ may be a common mechanism underlying beneficial effects of ketogenic diet therapy.

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.

Age and Ketogenic Diet Have Dissociable Effects on Synapse-Related Gene Expression Between Hippocampal Subregions

As the number of individuals living beyond the age of 65 is rapidly increasing, so is the need to develop strategies to combat the age-related cognitive decline that may threaten independent living. Although the link between altered neuronal signaling and age-related cognitive impairments is not completely understood, it is evident that declining cognitive abilities are at least partially due to synaptic dysfunction. Aging is accompanied by well-documented changes in both excitatory and inhibitory synaptic signaling across species. Age-related synaptic alterations are not uniform across the brain, however, with different regions showing unique patterns of vulnerability in advanced age. In the hippocampus, increased activity within the CA3 subregion has been observed across species, and this can be reversed with anti-epileptic medication. In contrast to CA3, the dentate gyrus shows reduced activity with age and declining metabolic activity. Ketogenic diets have been shown to decrease seizure incidence and severity in epilepsy, improve metabolic function in diabetes type II, and improve cognitive function in aged rats. This link between neuronal activity and metabolism suggests that metabolic interventions may be able to ameliorate synaptic signaling deficits accompanying advanced age. We therefore investigated the ability of a dietary regimen capable of inducing nutritional ketosis and improving cognition to alter synapse-related gene expression across the dentate gyrus, CA3 and CA1 subregions of the hippocampus. Following 12 weeks of a ketogenic or calorie-matched standard diet, RTq-PCR was used to quantify expression levels of excitatory and inhibitory synaptic signaling genes within CA1, CA3 and dentate gyrus. While there were no age or diet-related changes in CA1 gene expression, expression levels were significantly altered within CA3 by age and within the dentate gyrus by diet for several genes involved in presynaptic glutamate regulation and postsynaptic excitation and plasticity. These data demonstrate subregion-specific alterations in synaptic signaling with age and the potential for a ketogenic diet to alter these processes in dissociable ways across different brain structures that are uniquely vulnerable in older animals.

Ketogenic diets attenuate cyclooxygenase and lipoxygenase gene expression in multiple sclerosis

BACKGROUND

Adapted ketogenic diet (AKD) and caloric restriction (CR) have been suggested as alternative therapeutic strategies for inflammatory, hyperproliferative and neurodegenerative diseases. Pro-inflammatory eicosanoids have been implicated in the pathogenesis of multiple sclerosis since they augment vascular permeability and induce leukocyte migration into the brain. We explored the impact of ketogenic diets on gene expression of biosynthetic enzymes for pro- (ALOX5, COX1, COX2) and anti-inflammatory (ALOX15) eicosanoids in patients with relapsing-remitting multiple sclerosis.

METHODS

60 adults were prospectively recruited for this six months randomized controlled trial and the impact of dietary treatment on the Multiple Sclerosis Quality of Life-54 index (ClinicalTrials.gov (NCT01538355) has previously been published. Here we explored 24 patients (8 controls, 5 on CR and 11 on AKD). For statistical analysis we combined the two diet groups to a single pooled treatment group.

FINDINGS

Inter-group comparison indicated that expression of the pro-inflammatory ALOX5 in the pooled treatment group was significantly (p < 0.05) reduced when compared with the control group. Moreover, intra-group comparison (same individuals before and after dietary treatment) suggested significantly impaired expression of other pro-inflammatory enzymes, such as COX1 (p < 0.001) and COX2 (p < 0.05). Finally, pretreatment cross-group analysis revealed a significant positive correlation between expression of pro-inflammatory ALOX5 and COX2 and an inverse correlation of ALOX5 and COX1 expression with the MSQoL-54 index.

INTERPRETATION

Ketogenic diets can reduce the expression of enzymes involved in the biosynthesis of pro-inflammatory eicosanoids. Pharmacological interference with eicosanoid biosynthesis might constitute a strategy supplementing current therapeutic approaches for MS.

Genome-wide association study: Exploring the genetic basis for responsiveness to ketogenic dietary therapies for drug-resistant epilepsy

OBJECTIVE

With the exception of specific metabolic disorders, predictors of response to ketogenic dietary therapies (KDTs) are unknown. We aimed to determine whether common variation across the genome influences the response to KDT for epilepsy.

METHODS

We genotyped individuals who were negative for glucose transporter type 1 deficiency syndrome or other metabolic disorders, who received KDT for epilepsy. Genotyping was performed with the Infinium HumanOmniExpressExome Beadchip. Hospital records were used to obtain demographic and clinical data. KDT response (≥50% seizure reduction) at 3-month follow-up was used to dissect out nonresponders and responders. We then performed a genome-wide association study (GWAS) in nonresponders vs responders, using a linear mixed model and correcting for population stratification. Variants with minor allele frequency <0.05 and those that did not pass quality control filtering were excluded.

RESULTS

After quality control filtering, the GWAS of 112 nonresponders vs 123 responders revealed an association locus at 6p25.1, 61 kb upstream of CDYL (rs12204701, P = 3.83 × 10-8 , odds ratio [A] = 13.5, 95% confidence interval [CI] 4.07-44.8). Although analysis of regional linkage disequilibrium around rs12204701 did not strengthen the likelihood of CDYL being the candidate gene, additional bioinformatic analyses suggest it is the most likely candidate.

SIGNIFICANCE

CDYL deficiency has been shown to disrupt neuronal migration and to influence susceptibility to epilepsy in mice. Further exploration with a larger replication cohort is warranted to clarify whether CDYL is the causal gene underlying the association signal.

Feasibility and efficacy data from a ketogenic diet intervention in Alzheimer's disease

Introduction

We assessed the feasibility and cognitive effects of a ketogenic diet (KD) in participants with Alzheimer's disease.

Methods

The Ketogenic Diet Retention and Feasibility Trial featured a 3-month, medium-chain triglyceride-supplemented KD followed by a 1-month washout in clinical dementia rating (CDR) 0.5, 1, and 2 participants. We obtained urine acetoacetate, serum β-hydroxybutyrate, food record, and safety data. We administered the Alzheimer's Disease Assessment Scale-cognitive subscale and Mini-Mental State Examination before the KD, and following the intervention and washout.

Results

We enrolled seven CDR 0.5, four CDR 1, and four CDR 2 participants. One CDR 0.5 and all CDR 2 participants withdrew citing caregiver burden. The 10 completers achieved ketosis. Most adverse events were medium-chain triglyceride-related. Among the completers, the mean of the Alzheimer's Disease Assessment Scale-cognitive subscale score improved by 4.1 points during the diet (P = .02) and reverted to baseline after the washout.

Discussion

This pilot trial justifies KD studies in mild Alzheimer's disease.

Reduction of epileptiform activity in ketogenic mice: The role of monocarboxylate transporters

Epilepsy is a chronic neurological disorder that affects approximately 50 million people worldwide. Ketogenic diet (KD) can be a very effective treatment for intractable epilepsy. Potential mechanisms of action for KD have been proposed, including the re-balance among excitatory and inhibitory neurotransmission and decrease in the glycolytic rate in brain cells. KD has been shown to have an effect on the expression pattern of monocarboxylate transporters (MCT), however, it is unknown whether MCT transport activity is affected by KD and linked to the reduction of seizures during KD. Therefore, we studied the influence of KD on MCT transport activity and the role of MCTs during epileptiform activity. Our results showed a decrease in the epileptiform activity in cortical slices from mice fed on KD and in the presence of beta-hydroxybutyrate. KD increased transport capacity for ketone bodies and lactate in cortical astrocytes by raising the MCT1 expression level. Inhibition of MCT1 and MCT2 in control conditions decreases epileptiform activity, while in KD it induced an increase in epileptiform activity. Our results suggest that MCTs not only play an important role in the transport of ketone bodies, but also in the modulation of brain energy metabolism under normal and ketogenic conditions.

The ketogenic diet affects the social behavior of young male rats

The positive effects of the ketogenic diet (KD) on social behavior have been recently reported in patients and rodent models of autism spectrum disorder (ASD). Given the beneficial effects of the KD on epilepsy, mitochondrial function, carbohydrate metabolism, and inflammation, treatment based on the KD has the potential to reduce some of the ASD-associated symptoms, including abnormal social interactions. It is not known whether the KD influences sociability by reducing the pathological processes underlying ASD or through some independent mechanism. The aim of the present study was to evaluate the influence of the KD on the social behavior of rats. Four-week-old Long-Evans males were treated with the KD for 4 subsequent weeks. Afterwards, behavioral tests were performed in order to evaluate sociability, locomotor activity, working memory, and anxiety-related behaviors. Additionally we performed the social interaction test in animals that were receiving β-hydroxybutyrate or acetone. We have observed that rats fed with the KD showed increased social exploration in three different experimental settings. We did not observe any changes in the level of social interactions in animals treated with exogenous ketone bodies. The results did not show any difference in mobility or anxiety-related behaviors or working memory between the animals fed with the KD or standard rodent chow. In conclusion, we showed that the KD affects the social behavior of wild-type young adult male rats, which was not associated with other behavioral changes.

Improved cerebral energetics and ketone body metabolism in db/db mice

It is becoming evident that type 2 diabetes mellitus is affecting brain energy metabolism. The importance of alternative substrates for the brain in type 2 diabetes mellitus is poorly understood. The aim of this study was to investigate whether ketone bodies are relevant candidates to compensate for cerebral glucose hypometabolism and unravel the functionality of cerebral mitochondria in type 2 diabetes mellitus. Acutely isolated cerebral cortical and hippocampal slices of db/db mice were incubated in media containing [U-¹³C]glucose, [1,2-¹³C]acetate or [U-¹³C]β-hydroxybutyrate and tissue extracts were analysed by mass spectrometry. Oxygen consumption and ATP synthesis of brain mitochondria of db/db mice were assessed by Seahorse XFe96 and luciferin-luciferase assay, respectively. Glucose hypometabolism was observed for both cerebral cortical and hippocampal slices of db/db mice. Significant increased metabolism of [1,2-¹³C]acetate and [U-¹³C]β-hydroxybutyrate was observed for hippocampal slices of db/db mice. Furthermore, brain mitochondria of db/db mice exhibited elevated oxygen consumption and ATP synthesis rate. This study provides evidence of several changes in brain energy metabolism in type 2 diabetes mellitus. The increased hippocampal ketone body utilization and improved mitochondrial function in db/db mice, may act as adaptive mechanisms in order to maintain cerebral energetics during hampered glucose metabolism.

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.

Rapid adaptation of rat brain and liver metabolism to a ketogenic diet: an integrated study using (1)H- and (13)C-NMR spectroscopy

The ketogenic diet (KD) is an effective alternative treatment for refractory epilepsy in children, but the mechanisms by which it reduces seizures are poorly understood. To investigate how the KD modifies brain metabolism, we infused control (CT) and 7-day KD rats with either [1-(13)C]glucose (Glc) or [2,4-(13)C2]β-hydroxybutyrate (β-HB). Specific enrichments of amino acids (AAs) measured by (1)H- and (13)C-NMR in total brain perchloric acid extracts were similar between CT and KD rats after [1-(13)C]Glc infusion whereas they were higher in KD rats after [2,4-(13)C2]β-HB infusion. This suggests better metabolic efficiency of ketone body utilization on the KD. The relative rapid metabolic adaptation to the KD included (1) 11%-higher brain γ-amino butyric acid (GABA)/glutamate (Glu) ratio versus CT, (2) liver accumulation of the ketogenic branched-chain AAs (BCAAs) leucine (Leu) and isoleucine (ILeu), which were never detected in CT, and (3) higher brain Leu and ILeu contents. Since Glu and GABA are excitatory and inhibitory neurotransmitters, respectively, higher brain GABA/Glu ratio could contribute to the mechanism by which the KD reduces seizures in epilepsy. Increased BCAA on the KD may also contribute to better seizure control.

Effect of one month duration ketogenic and non-ketogenic high fat diets on mouse brain bioenergetic infrastructure

Diet composition may affect energy metabolism in a tissue-specific manner. Using C57Bl/6J mice, we tested the effect of ketosis-inducing and non-inducing high fat diets on genes relevant to brain bioenergetic infrastructures, and on proteins that constitute and regulate that infrastructure. At the end of a one-month study period the two high fat diets appeared to differentially affect peripheral insulin signaling, but brain insulin signaling was not obviously altered. Some bioenergetic infrastructure parameters were similarly impacted by both high fat diets, while other parameters were only impacted by the ketogenic diet. For both diets, mRNA levels for CREB, PGC1α, and NRF2 increased while NRF1, TFAM, and COX4I1 mRNA levels decreased. PGC1β mRNA increased and TNFα mRNA decreased only with the ketogenic diet. Brain mtDNA levels fell in both the ketogenic and non-ketogenic high fat diet groups, although TOMM20 and COX4I1 protein levels were maintained, and mRNA and protein levels of the mtDNA-encoded COX2 subunit were also preserved. Overall, the pattern of changes observed in mice fed ketogenic and non-ketogenic high fat diets over a one month time period suggests these interventions enhance some aspects of the brain's aerobic infrastructure, and may enhance mtDNA transcription efficiency. Further studies to determine which diet effects are due to changes in brain ketone body levels, fatty acid levels, glucose levels, altered brain insulin signaling, or other factors such as adipose tissue-associated hormones are indicated.

Ketogenic diets, mitochondria, and neurological diseases

The ketogenic diet (KD) is a broad-spectrum therapy for medically intractable epilepsy and is receiving growing attention as a potential treatment for neurological disorders arising in part from bioenergetic dysregulation. The high-fat/low-carbohydrate "classic KD", as well as dietary variations such as the medium-chain triglyceride diet, the modified Atkins diet, the low-glycemic index treatment, and caloric restriction, enhance cellular metabolic and mitochondrial function. Hence, the broad neuroprotective properties of such therapies may stem from improved cellular metabolism. Data from clinical and preclinical studies indicate that these diets restrict glycolysis and increase fatty acid oxidation, actions which result in ketosis, replenishment of the TCA cycle (i.e., anaplerosis), restoration of neurotransmitter and ion channel function, and enhanced mitochondrial respiration. Further, there is mounting evidence that the KD and its variants can impact key signaling pathways that evolved to sense the energetic state of the cell, and that help maintain cellular homeostasis. These pathways, which include PPARs, AMP-activated kinase, mammalian target of rapamycin, and the sirtuins, have all been recently implicated in the neuroprotective effects of the KD. Further research in this area may lead to future therapeutic strategies aimed at mimicking the pleiotropic neuroprotective effects of the KD.

Combinatorial treatment of acute spinal cord injury with ghrelin, ibuprofen, C16, and ketogenic diet does not result in improved histologic or functional outcome

Because of the complex, multifaceted nature of spinal cord injury (SCI), it is widely believed that a combination of approaches will be superior to individual treatments. Therefore, we employed a rat model of cervical SCI to evaluate the combination of four noninvasive treatments that individually have been reported to be effective for acute SCI during clinically relevant therapeutic time windows. These treatments included ghrelin, ibuprofen, C16, and ketogenic diet (KD). These were selected not only because of their previously reported efficacy in SCI models but also for their potentially different mechanisms of action. The administration of ghrelin, ibuprofen, C16, and KD several hours to days postinjury was based on previous observations by others that each treatment had profound effects on the pathophysiology and functional outcome following SCI. Here we showed that, with the exception of a modest improvement in performance on the Montoya staircase test at 8-10 weeks postinjury, the combinatorial treatment with ghrelin, ibuprofen, C16, and KD did not result in any significant improvements in the rearing test, grooming test, or horizontal ladder. Histologic analysis of the spinal cords did not reveal any significant differences in tissue sparing between treatment and control groups. Although single approaches of ghrelin, ibuprofen, C16, and KD have been reported to be beneficial after SCI, our results show that the combination of the four interventions did not confer significant functional or histological improvements in a cervical model of SCI. Possible interactions among the treatments may have negated their beneficial effects, emphasizing the challenges that have to be addressed when considering combinatorial drug therapies for SCI.

A novel variant in the 3' UTR of human SCN1A gene from a patient with Dravet syndrome decreases mRNA stability mediated by GAPDH's binding

Mutations in the SCN1A gene-encoding voltage-gated sodium channel α-I subunit (Nav1.1) cause various spectrum of epilepsies including Dravet syndrome (DS), a severe and intractable form. A large number of SCN1A mutations identified from the DS patients lead to the loss of function or truncation of Nav1.1 that result in a haploinsufficiency effects, indicating that the exact expression level of SCN1A should be essential to maintain normal brain function. In this study, we have identified five variants c.*1025T>C, c.*1031A>T, c.*1739C>T, c.*1794C>T and c.*1961C>T in the SCN1A 3' UTR in the patients with DS. The c.*1025T>C, c.*1031A>T and c.*1794C>T are conserved among different species. Of all the five variants, only c.*1794C>T is a novel variant and alters the predicted secondary structure of the 3' UTR. We also show that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) only binds to the 3' UTR sequence containing the mutation allele 1794U but not the wild-type allele 1794C, indicating that the mutation allele forms a new GAPDH-binding site. Functional analyses show that the variant negatively regulates the reporter gene expression by affecting the mRNA stability that is mediated by GAPDH's binding, and this phenomenon could be reversed by shRNA-induced GAPDH knockdown. These findings suggest that GAPDH and the 3'-UTR variant are involved in regulating SCN1A expression at post-transcriptional level, which may provide an important clue for further investigating on the relationship between 3'-UTR variants and SCN1A-related diseases.

Adenosine receptors and epilepsy: current evidence and future potential

Adenosine receptors are a powerful therapeutic target for regulating epileptic seizures. As a homeostatic bioenergetic network regulator, adenosine is perfectly suited to establish or restore an ongoing balance between excitation and inhibition, and its anticonvulsant efficacy is well established. There is evidence for the involvement of multiple adenosine receptor subtypes in epilepsy, but in particular the adenosine A1 receptor subtype can powerfully and bidirectionally regulate seizure activity. Mechanisms that regulate adenosine itself are increasingly appreciated as targets to thus influence receptor activity and seizure propensity. Taken together, established evidence for the powerful potential of adenosine-based epilepsy therapies and new strategies to influence receptor activity can combine to capitalize on this endogenous homeostatic neuromodulator.

Potential therapeutic use of the ketogenic diet in autism spectrum disorders

The ketogenic diet (KGD) has been recognized as an effective treatment for individuals with glucose transporter 1 (GLUT1) and pyruvate dehydrogenase (PDH) deficiencies as well as with epilepsy. More recently, its use has been advocated in a number of neurological disorders prompting a newfound interest in its possible therapeutic use in autism spectrum disorders (ASD). One study and one case report indicated that children with ASD treated with a KGD showed decreased seizure frequencies and exhibited behavioral improvements (i.e., improved learning abilities and social skills). The KGD could benefit individuals with ASD affected with epileptic episodes as well as those with either PDH or mild respiratory chain (RC) complex deficiencies. Given that the mechanism of action of the KGD is not fully understood, caution should be exercised in ASD cases lacking a careful biochemical and metabolic characterization to avoid deleterious side effects or refractory outcomes.

Ketogenic diet improves forelimb motor function after spinal cord injury in rodents

High fat, low carbohydrate ketogenic diets (KD) are validated non-pharmacological treatments for some forms of drug-resistant epilepsy. Ketones reduce neuronal excitation and promote neuroprotection. Here, we investigated the efficacy of KD as a treatment for acute cervical spinal cord injury (SCI) in rats. Starting 4 hours following C5 hemi-contusion injury animals were fed either a standard carbohydrate based diet or a KD formulation with lipid to carbohydrate plus protein ratio of 3:1. The forelimb functional recovery was evaluated for 14 weeks, followed by quantitative histopathology. Post-injury 3:1 KD treatment resulted in increased usage and range of motion of the affected forepaw. Furthermore, KD improved pellet retrieval with recovery of wrist and digit movements. Importantly, after returning to a standard diet after 12 weeks of KD treatment, the improved forelimb function remained stable. Histologically, the spinal cords of KD treated animals displayed smaller lesion areas and more grey matter sparing. In addition, KD treatment increased the number of glucose transporter-1 positive blood vessels in the lesion penumbra and monocarboxylate transporter-1 (MCT1) expression. Pharmacological inhibition of MCTs with 4-CIN (α-cyano-4-hydroxycinnamate) prevented the KD-induced neuroprotection after SCI, In conclusion, post-injury KD effectively promotes functional recovery and is neuroprotective after cervical SCI. These beneficial effects require the function of monocarboxylate transporters responsible for ketone uptake and link the observed neuroprotection directly to the function of ketones, which are known to exert neuroprotection by multiple mechanisms. Our data suggest that current clinical nutritional guidelines, which include relatively high carbohydrate contents, should be revisited.

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.

The ketogenic diet for the treatment of glioma: insights from genetic profiling

Seizures, particularly first onset seizures in adults, are a diagnostic hallmark of brain tumors (Giglio and Villano, 2010). Unfortunately, malignant brain tumors are almost uniformly fatal due, in part, to the limitations of available therapies. Improvement in the survival of brain cancer patients requires the design of new therapeutic modalities including those that enhance currently available therapies. One potential strategy is to exploit differences in metabolic regulation between normal cells and tumor cells through dietary approaches. Previous studies have shown that a high-fat, low-carbohydrate ketogenic diet (KD) extends survival in animal models of glioma; however, the mechanism for this effect is not entirely known. We examined the effects of an experimental KD on a mouse model of glioma, and compared patterns of gene expression in tumors versus contralateral non-tumor containing brain from animals fed either a KD or a standard diet. We found that the KD reduced reactive oxygen species (ROS) production in tumor cells. Gene expression profiling demonstrated that the KD induces an overall reversion to expression patterns seen in non-tumor specimens, and a number of genes involved in modulating ROS levels and oxidative stress were altered in tumor cells. In addition, there was reduced expression of genes involved in signal transduction from growth factors known to be involved in glioma growth. These results suggest that the anti-tumor effect of the KD is multifactorial, and elucidation of genes whose expression is altered will help identify mechanisms through which ketones inhibit tumor growth, reduce seizure activity and provide neuroprotection.

Ketogenic diet-induced peroxisome proliferator-activated receptor-γ activation decreases neuroinflammation in the mouse hippocampus after kainic acid-induced seizures

Similar to fasting, the ketogenic diet (KD) has anti-inflammatory effects and protects against excitotoxicity-mediated neuronal cell death. Recent studies have shown that peroxisome proliferator-activated receptor (PPAR)γ has anti-inflammatory effects in seizure animal models. However, the exact mechanisms underlying the anti-inflammatory effects of the KD have not been determined for seizures. Here we investigated the effect of the KD and acetoacetate (AA) on neuroinflammation in a seizure animal model and glutamate-treated HT22 cells, respectively. Mice were fed the KD for 4 weeks and sacrificed 2 or 6h after KA injection. The KD reduced hippocampal tumor necrosis factor alpha (TNF-α) levels and nuclear factor (NF)-κB translocation into the nucleus 2h after KA treatment. KD-induced PPARγ activation was decreased by KA in neurons as assessed by western blotting and immunofluorescence. Finally, the KD inhibited cyclooxygenase (COX)-2 and microsomal prostaglandin E(2) synthase-1 (mPGES-1) expression in the hippocampus 6h after KA treatment. AA treatment also protected against glutamate-induced cell death in HT22 cells by reducing TNF-α and PPARγ-mediated COX-2 expression. Thus, the KD may inhibit neuroinflammation by suppressing a COX-2-dependent pathway via activation of PPARγ by the KD or AA.

A ketogenic diet delays weight loss and does not impair working memory or motor function in the R6/2 1J mouse model of Huntington's disease

Ketogenic diets are high in fat and low in carbohydrates, and have long been used as an anticonvulsant therapy for drug-intractable and pediatric epilepsy. Additionally, ketogenic diets have been shown to provide neuroprotective effects against acute and chronic brain injury, including beneficial effects in various rodent models of neurodegeneration. Huntington's disease is a progressive neurodegenerative disease characterized by neurological, behavioral and metabolic dysfunction, and ketogenic diets have been shown to increase energy molecules and mitochondrial function. We tested the effects of a ketogenic diet in a transgenic mouse model of Huntington's disease (R6/2 1J), with a focus on life-long behavioral and physiological effects. Matched male and female wild-type and transgenic mice were maintained on a control diet or were switched to a ketogenic diet fed ad libitum starting at six weeks of age. We found no negative effects of the ketogenic diet on any behavioral parameter tested (locomotor activity and coordination, working memory) and no significant change in lifespan. Progressive weight loss is a hallmark feature of Huntington's disease, yet we found that the ketogenic diet-which generally causes weight loss in normal animals-delayed the reduction in body weight of the transgenic mice. These results suggest that metabolic therapies could offer important benefits for Huntington's disease without negative behavioral or physiological consequences.

Quantitative targeted absolute proteomics of human blood-brain barrier transporters and receptors

We have obtained, for the first time, a quantitative protein expression profile of membrane transporters and receptors in human brain microvessels, that is, the blood-brain barrier (BBB). Brain microvessels were isolated from brain cortexes of seven males (16-77 years old) and protein expression of 114 membrane proteins was determined by means of a liquid chromatography-tandem mass spectrometric quantification method using recently established in-silico peptide selection criteria. Among drug transporters, breast cancer resistance protein showed the most abundant protein expression (8.14 fmol/μg protein), and its expression level was 1.85-fold greater in humans than in mice. By contrast, the expression level of P-glycoprotein in humans (6.06 fmol/μg protein) was 2.33-fold smaller than that of mdr1a in mice. The organic anion transporters reported in rodent BBB, that is, multidrug resistance-associated protein, organic anion transporter and organic anion-transporting polypeptide family members, were under limit of quantification in humans, except multidrug resistance-associated protein 4 (0.195 fmol/μg protein). Among detected transporters and receptors for endogenous substances, the glucose transporter 1 level was similar to that of mouse, while the L-type amino acid transporter 1 level was fivefold smaller than that of mouse. These findings should be useful for understanding human BBB function and its differences from that in mouse.

Gene expression changes in a rat model of oxygen-induced retinopathy

PURPOSE

To identify altered patterns of retinal mRNA expression in a rat model of oxygen-induced retinopathy (OIR).

METHODS

Sprague-Dawley rats from P2 to P14 were exposed to hyperoxia (80% oxygen) to induce OIR and then returned to normoxic conditions. Control rats were sustained in room air. Retinal gene expression between the rats of OIR and the controls was compared using cDNA microarray analysis. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to verify the microarray results.

RESULTS

Among a total of 12,731 cDNAs analyzed by microarray, 13 genes were strongly up- or down-regulated (>2-fold change over controls) in the OIR rats. We found a significant increase in expression of 10 genes (CaM-kinase II inhibitor; acidic nuclear phosphoprotein 32 family, member A; vascular endothelial growth factor; interferon α-inducible protein 27-like; similar to enthoprotin, epsin 4, clathrin interacting protein; nidogen [entactin]; tubulin, β5; fibrillin-1; spectrin β2; and stearoyl-coenzyme A desaturase 2) and a significant decrease in expression of 3 genes (myelin-associated oligodendrocytic basic protein, heat shock protein, and decorin) in OIR rats compared to controls.

CONCLUSIONS

We confirmed changes in expressions of various retinal genes in a rat model of OIR by microarray and RT-PCR. This study should contribute to the understanding of genetic indicators associated with OIR.

Revealing the molecular relationship between type 2 diabetes and the metabolic changes induced by a very-low-carbohydrate low-fat ketogenic diet

Background

The prevalence of type 2 diabetes is increasing worldwide, accounting for 85-95% of all diagnosed cases of diabetes. Clinical trials provide evidence of benefits of low-carbohydrate ketogenic diets in terms of clinical outcomes on type 2 diabetes patients. However, the molecular events responsible for these improvements still remain unclear in spite of the high amount of knowledge on the primary mechanisms of both the diabetes and the metabolic state of ketosis. Molecular network analysis of conditions, diseases and treatments might provide new insights and help build a better understanding of clinical, metabolic and molecular relationships among physiological conditions. Accordingly, our aim is to reveal such a relationship between a ketogenic diet and type 2 diabetes through systems biology approaches.

Methods

Our systemic approach is based on the creation and analyses of the cell networks representing the metabolic state in a very-low-carbohydrate low-fat ketogenic diet. This global view might help identify unnoticed relationships often overlooked in molecule or process-centered studies.

Results

A strong relationship between the insulin resistance pathway and the ketosis main pathway was identified, providing a possible explanation for the improvement observed in clinical trials. Moreover, the map analyses permit the formulation of some hypothesis on functional relationships between the molecules involved in type 2 diabetes and induced ketosis, suggesting, for instance, a direct implication of glucose transporters or inflammatory processes. The molecular network analysis performed in the ketogenic-diet map, from the diabetes perspective, has provided insights on the potential mechanism of action, but also has opened new possibilities to study the applications of the ketogenic diet in other situations such as CNS or other metabolic dysfunctions.

Metabolic control of vesicular glutamate transport and release

Fasting has been used to control epilepsy since antiquity, but the mechanism of coupling between metabolic state and excitatory neurotransmission remains unknown. Previous work has shown that the vesicular glutamate transporters (VGLUTs) required for exocytotic release of glutamate undergo an unusual form of regulation by Cl(-). Using functional reconstitution of the purified VGLUTs into proteoliposomes, we now show that Cl(-) acts as an allosteric activator, and the ketone bodies that increase with fasting inhibit glutamate release by competing with Cl(-) at the site of allosteric regulation. Consistent with these observations, acetoacetate reduced quantal size at hippocampal synapses and suppresses glutamate release and seizures evoked with 4-aminopyridine in the brain. The results indicate an unsuspected link between metabolic state and excitatory neurotransmission through anion-dependent regulation of VGLUT activity.

The ketogenic diet reverses gene expression patterns and reduces reactive oxygen species levels when used as an adjuvant therapy for glioma

BACKGROUND

Malignant brain tumors affect people of all ages and are the second leading cause of cancer deaths in children. While current treatments are effective and improve survival, there remains a substantial need for more efficacious therapeutic modalities. The ketogenic diet (KD) - a high-fat, low-carbohydrate treatment for medically refractory epilepsy - has been suggested as an alternative strategy to inhibit tumor growth by altering intrinsic metabolism, especially by inducing glycopenia.

METHODS

Here, we examined the effects of an experimental KD on a mouse model of glioma, and compared patterns of gene expression in tumors vs. normal brain from animals fed either a KD or a standard diet.

RESULTS

Animals received intracranial injections of bioluminescent GL261-luc cells and tumor growth was followed in vivo. KD treatment significantly reduced the rate of tumor growth and prolonged survival. Further, the KD reduced reactive oxygen species (ROS) production in tumor cells. Gene expression profiling demonstrated that the KD induces an overall reversion to expression patterns seen in non-tumor specimens. Notably, genes involved in modulating ROS levels and oxidative stress were altered, including those encoding cyclooxygenase 2, glutathione peroxidases 3 and 7, and periredoxin 4.

CONCLUSIONS

Our data demonstrate that the KD improves survivability in our mouse model of glioma, and suggests that the mechanisms accounting for this protective effect likely involve complex alterations in cellular metabolism beyond simply a reduction in glucose.

Adenosine, ketogenic diet and epilepsy: the emerging therapeutic relationship between metabolism and brain activity

For many years the neuromodulator adenosine has been recognized as an endogenous anticonvulsant molecule and termed a “retaliatory metabolite.” As the core molecule of ATP, adenosine forms a unique link between cell energy and neuronal excitability. In parallel, a ketogenic (high-fat, low-carbohydrate) diet is a metabolic therapy that influences neuronal activity significantly, and ketogenic diets have been used successfully to treat medically-refractory epilepsy, particularly in children, for decades. To date the key neural mechanisms underlying the success of dietary therapy are unclear, hindering development of analogous pharmacological solutions. Similarly, adenosine receptor–based therapies for epilepsy and myriad other disorders remain elusive. In this review we explore the physiological regulation of adenosine as an anticonvulsant strategy and suggest a critical role for adenosine in the success of ketogenic diet therapy for epilepsy. While the current focus is on the regulation of adenosine, ketogenic metabolism and epilepsy, the therapeutic implications extend to acute and chronic neurological disorders as diverse as brain injury, inflammatory and neuropathic pain, autism and hyperdopaminergic disorders. Emerging evidence for broad clinical relevance of the metabolic regulation of adenosine will be discussed.

The ketogenic diet: stoking the powerhouse of the cell

Mitochondrial Biogenesis in the Anticonvulsant Mechanism of the Ketogenic Diet. Bough KJ, Wetherington J, Hassel B, Pare JF, Gawryluk JW, Greene JG, Shaw R, Smith Y, Geiger JD, Dingledine RJ. Ann Neurol 2006;60:223–235.

Objective

The full anticonvulsant effect of the ketogenic diet (KD) can require weeks to develop in rats, suggesting that altered gene expression is involved. The KD typically is used in pediatric epilepsies, but is effective also in adolescents and adults. Our goal was to use microarray and complementary technologies in adolescent rats to understand its anticonvulsant effect.

Methods

Microarrays were used to define patterns of gene expression in the hippocampus of rats fed a KD or control diet for 3 weeks. Hippocampi from control- and KD-fed rats were also compared for the number of mitochondrial profiles in electron micrographs, the levels of selected energy metabolites and enzyme activities, and the effect of low glucose on synaptic transmission.

Results

Most striking was a coordinated upregulation of all (n = 34) differentially regulated transcripts encoding energy metabolism enzymes and 39 of 42 transcripts encoding mitochondrial proteins, which was accompanied by an increased number of mitochondrial profiles, a higher phosphocreatine/creatine ratio, elevated glutamate levels, and decreased glycogen levels. Consistent with increased energy reserves, synaptic transmission in hippocampal slices from KD-fed animals was resistant to low glucose.

Conclusion

These data show that a calorie-restricted KD enhances brain metabolism. We propose an anticonvulsant mechanism of the KD involving mitochondrial biogenesis leading to enhanced alternative energy stores.

The ketogenic diet has no effect on the expression of spike-and-wave discharges and nutrient transporters in genetic absence epilepsy rats from Strasbourg

The genetic absence epilepsy rat from Strasbourg is considered an isomorphic, predictive, and homologous model of typical childhood absence epilepsy. It is characterized by the expression of spike-and-wave discharges (SWDs) in the thalamus and cortex. The ketogenic diet (KD) is successfully used in humans and animals with various types of seizures, but was not effective in children with intractable atypical absence epilepsy. Here, we studied its potential impact on the occurrence of SWDs in genetic absence epilepsy rat from Strasbourg. Rats were fed the KD for 3 weeks during which they were regularly subjected to the electroencephalographic recording of SWDs. The KD did not influence the number and duration of SWDs despite a 15-22% decrease in plasma glucose levels and a large increase in beta-hydroxybutyrate levels. Likewise, the KD did not affect the level of expression of the blood-brain barrier glucose transporter GLUT1 or of the monocarboxylate transporters, MCT1 and MCT2. This report extends the observation in humans that the KD does not appear to show effectiveness in intractable atypical absence epilepsy to this model of typical childhood absence epilepsy which responds to specific antiepileptic drugs.

Ketogenic diets: evidence for short- and long-term efficacy

The use of dietary treatments for epilepsy (ketogenic, modified Atkins, and low glycemic index diets) has been in continuous use since 1921. These treatments have been well studied in the short term, with approximately half of children having at least a 50% reduction in seizures after 6 months. Approximately one third will attain >90% reduction in their seizures. Animal studies confirm these findings, with broad evidence demonstrating acute anticonvulsant effects of the diet. Furthermore, the diet appears to maintain its efficacy in humans when provided continuously for several years. Interestingly, benefits may be seen long term even when the diet is discontinued after only a few months of use, suggesting neuroprotective effects. This potential antiepileptogenic activity has been recently demonstrated in some animal studies as well. This review discusses the animal and human evidence for both short- and long-term benefits of dietary therapies.

The neuroprotective properties of calorie restriction, the ketogenic diet, and ketone bodies

Both calorie restriction and the ketogenic diet possess broad therapeutic potential in various clinical settings and in various animal models of neurological disease. Following calorie restriction or consumption of a ketogenic diet, there is notable improvement in mitochondrial function, a decrease in the expression of apoptotic and inflammatory mediators and an increase in the activity of neurotrophic factors. However, despite these intriguing observations, it is not yet clear which of these mechanisms account for the observed neuroprotective effects. Furthermore, limited compliance and concern for adverse effects hamper efforts at broader clinical application. Recent research aimed at identifying compounds that can reproduce, at least partially, the neuroprotective effects of the diets with less demanding changes to food intake suggests that ketone bodies might represent an appropriate candidate. Ketone bodies protect neurons against multiple types of neuronal injury and are associated with mitochondrial effects similar to those described during calorie restriction or ketogenic diet treatment. The present review summarizes the neuroprotective effects of calorie restriction, of the ketogenic diet and of ketone bodies, and compares their putative mechanisms of action.

Neuroprotective effects of the ketogenic diet

The ketogenic diet (KD) is an alternative treatment for medically refractory epilepsy. Despite numerous mechanistic hypotheses advanced to explain the anticonvulsant action of the KD, few studies to date have addressed the molecular changes in brain following KD treatment. Here, we present recent experimental results based on systemic administration of kainic acid (KA) in rodents. KA typically induces acute limbic seizures and results in cellular and molecular alterations, accompanied by neuronal death mainly in limbic structures, similar to what has been observed in surgically resected temporal lobe tissue in epileptic patients. We have reported that neuronal degeneration induced by KA is ameliorated by KD treatment via diverse protective mechanisms, including inhibition of caspase-3-mediated apoptosis in hippocampal neurons. Neuroprotective strategies such as the KD, if implemented early, might exert an antiepileptogenic effect, and could prevent associated learning and memory deficits.

Oxidative impairment of hippocampal long-term potentiation involves activation of protein phosphatase 2A and is prevented by ketone bodies

Previous studies have shown that ketone bodies (KB) exert antioxidant effects in experimental models of neurological disease. In the present study, we explored the effects of the KB acetoacetate (ACA) and beta-hydroxybutyrate (BHB) on impairment of hippocampal long-term potentiation (LTP) in rats by hydrogen peroxide (H(2)O(2)) using electrophysiological, fluorescence imaging, and enzyme assay techniques. We found that: 1) a combination of ACA and BHB (1 mM each) prevented impairment of LTP by H(2)O(2) (200 microM); 2) KB significantly lowered intracellular levels of reactive oxygen species (ROS)--measured with the fluorescent indicator carboxy-H(2)DCFDA (carboxy-2',7'-dichlorodihydrofluorescein diacetate)--in CA1 pyramidal neurons exposed to H(2)O(2); 3) the effect of KB on LTP was replicated by the protein phosphatase 2A (PP2A) inhibitor fostriecin; 4) KB prevented impairment of LTP by the PP2A activator C(6) ceramide; 5) fostriecin did not prevent the increase in ROS levels in CA1 pyramidal neurons exposed to H(2)O(2), and C(6) ceramide did not increase ROS levels; 6) PP2A activity was enhanced by both H(2)O(2) and rotenone (a mitochondrial complex I inhibitor that increases endogenous superoxide production); and 7) KB inhibited PP2A activity in protein extracts from brain tissue treated with either H(2)O(2) or ceramide. We propose that oxidative impairment of hippocampal LTP is associated with PP2A activation, and that KB prevent this impairment in part by inducing PP2A inhibition through an antioxidant mechanism.

The ketogenic diet in a pill: is this possible?

Over the past decade, much progress has been made in understanding the mechanisms of ketogenic diet (KD) action. From the complex systemic and metabolic changes induced by the KD have emerged innovative hypotheses attempting to link biochemical adaptations to its clinical effects. Despite such developments, the fundamental question of how the KD works remains as elusive as ever. At present, it is unclear which of the many potential mechanisms proposed thus far are directly relevant to the clinical effects of the KD. It is unlikely that these numerous hypotheses can be unified into a single mechanism (or a final common pathway). Nevertheless, it may be instructive to consider each of these putative mechanisms in turn and ask the following question: if the mechanism or target in question is a critical determinant of the anticonvulsant efficacy of the KD, then would a similar intervention known to be based on that mechanism yield a comparable effect? Perhaps answering this question for each mechanistic speculation might help substantiate (or invalidate) that particular hypothesis. Can the KD be packaged into a pill? At present, the answer is likely "no." We have yet to discover a "magic bullet" that completely mirrors the anticonvulsant (and potential neuroprotective) effects of the KD. However, without a clearer understanding of the mechanistic elements comprising the complex metabolic puzzle posed by the KD, we would be left only with empiric observations, and to wonder curiously how a high-fat diet can exert such profound clinical effects.

The ketogenic diet and epilepsy

PURPOSE OF REVIEW

The ketogenic diet has long been used to treat medically refractory epilepsy. The mechanisms underlying its clinical effects, however, have remained a mystery. The evidence to date suggests that a fundamental shift from glycolysis to intermediary metabolism induced by the ketogenic diet is necessary and sufficient for clinical efficacy. This notion is supported by a growing number of studies indicating that glucose restriction, ketone bodies and polyunsaturated fatty acids may all play mechanistic roles, possibly by enhancing mitochondrial respiration and ATP production, and decreasing reactive oxygen species production.

RECENT FINDINGS

Recent reports indicate that ketone bodies can reduce oxidative stress and that fatty acid-induced mitochondrial uncoupling may also yield similar protective effects. Ketone bodies may attenuate spontaneous firing of ATP-sensitive potassium channels in central neurons, and pharmacological inhibition of glycolysis has been shown to retard epileptogenesis in a rat kindling model.

SUMMARY

While the mechanisms underlying the broad clinical efficacy of the ketogenic diet remain unclear, there is growing evidence that the ketogenic diet alters the fundamental biochemistry of neurons in a manner that not only inhibits neuronal hyperexcitability but also induces a protective effect. Thus, the ketogenic diet may ultimately be useful in the treatment of a variety of neurological disorders.