Transitory gliosis in the CA3 hippocampal region in rats fed on a ketogenic diet

Intermittent fasting reduces interictal epileptiform discharges and hippocampal reactive astrogliosis during electrical kindling epileptogenesis

It has been proposed that interictal epileptiform discharges observed in epilepsy-related structures, such as the hippocampus contributes to epileptogenesis. Intermittent fasting (IF) produces anticonvulsant effects protecting against experimentally induced seizures. It has been suggested that protective effects could be associated with astrocytic metabolic changes. However, it is unknown whether IF modifies the epileptogenic process. Therefore, this work aimed to analyze the impact of IF on interictal epileptiform discharges in the rat hippocampus and their possible correlation with astrocytic activation. Male Wistar rats were divided into two groups: one group had free access to food, while the other group was subjected to IF (food was provided for 2 h a day). Both groups underwent a hippocampal electrical kindling protocol with 36 stimulations. Our results showed that IF inhibited the incidence of generalized seizures induced by kindling and significantly reduced the total spectral power of interictal epileptiform discharges in the hippocampus. Furthermore, IF prevented the rise in fasting blood glucose and reduced seizure-induced astrogliosis by preventing the GFAP expression and the morphological complexity of astrocytes in the hippocampal CA3 region. These results support the notion that IF modifies epileptogenesis by modulating hippocampal hyperexcitability during the interictal stage, which could be associated with reductions in glucose metabolism and astrogliosis.

Ketogenic diet and behavior: insights from experimental studies

As a journal page for full details. The ketogenic diet (KD) has been established as a treatment for epilepsy, but more recently it has been explored as an alternative or add-on therapy for many other diseases ranging from weight loss to neurological disorders. Animal models are widely used in studies investigating the therapeutic effects of the KD as well as underlying mechanisms. Especially in the context of neurological, psychiatric, and neurodevelopmental disorders essential endpoints are assessed by behavioral and motor tests. Here we summarized research evaluating the influence of the KD on cognition, depressive and anxiety-related behaviors, and social and nutritional behaviors of laboratory rodents. Each section contains a brief description of commonly used behavioral tests highlighting their limitations. Ninety original research articles, written in English, performed on mice or rats, providing measurement of blood beta-hydroxybutyrate (BHB) levels and behavioral evaluation were selected for the review. The majority of research performed in various disease models shows that the KD positively impacts cognition. Almost an equal number of studies report a reduction or no effect of the KD on depressive-related behaviors. For anxiety-related behaviors, the majority of studies show no effect. Despite the increasing use of the KD in weight loss and its appetite-reducing properties the behavioral evaluation of appetite regulation has not been addressed in preclinical studies. This review provides an overview of the behavioral effects of nutritional ketosis addressed to a broad audience of scientists interested in the KD field but not necessarily specializing in behavioral tests.

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.

The Role of Ketogenic Diet in the Treatment of Neurological Diseases

Over a hundred years of study on the favourable effect of ketogenic diets in the treatment of epilepsy have contributed to a long-lasting discussion on its potential influence on other neurological diseases. A significant increase in the number of scientific studies in that field has been currently observed. The aim of this paper is a widespread, thorough analysis of the available scientific evidence in respect of the role of the ketogenic diet in the therapy of neurological diseases such as: epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A wide range of the mechanisms of action of the ketogenic diet has been demonstrated in neurological diseases, including, among other effects, its influence on the reduction in inflammatory conditions and the amount of reactive oxygen species (ROS), the restoration of the myelin sheath of the neurons, the formation and regeneration of mitochondria, neuronal metabolism, the provision of an alternative source of energy for neurons (ketone bodies), the reduction in glucose and insulin concentrations, the reduction in amyloid plaques, the induction of autophagy, the alleviation of microglia activation, the reduction in excessive neuronal activation, the modulation of intestinal microbiota, the expression of genes, dopamine production and the increase in glutamine conversion into GABA. The studies discussed (including randomised controlled studies), conducted in neurological patients, have stressed the effectiveness of the ketogenic diet in the treatment of epilepsy and have demonstrated its promising therapeutic potential in Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis (MS) and migraine. A frequent advantage of the diet was demonstrated over non-ketogenic diets (in the control groups) in the therapy of neurological diseases, with simultaneous safety and feasibility when conducting the nutritional model.

Feeding the Brain: Effect of Nutrients on Cognition, Synaptic Function, and AMPA Receptors

In recent decades, traditional eating habits have been replaced by a more globalized diet, rich in saturated fatty acids and simple sugars. Extensive evidence shows that these dietary factors contribute to cognitive health impairment as well as increase the incidence of metabolic diseases such as obesity and diabetes. However, how these nutrients modulate synaptic function and neuroplasticity is poorly understood. We review the Western, ketogenic, and paleolithic diets for their effects on cognition and correlations with synaptic changes, focusing mainly (but not exclusively) on animal model studies aimed at tracing molecular alterations that may contribute to impaired human cognition. We observe that memory and learning deficits mediated by high-fat/high-sugar diets, even over short exposure times, are associated with reduced arborization, widened synaptic cleft, narrowed post-synaptic zone, and decreased activity-dependent synaptic plasticity in the hippocampus, and also observe that these alterations correlate with deregulation of the AMPA-type glutamate ionotropic receptors (AMPARs) that are crucial to neuroplasticity. Furthermore, we explored which diet-mediated mechanisms modulate synaptic AMPARs and whether certain supplements or nutritional interventions could reverse deleterious effects, contributing to improved learning and memory in older people and patients with Alzheimer’s disease.

Memory impairments and increased GFAP expression in hippocampal astrocytes following hypercaloric diet in rats

ABSTRACT Objective: Hypothalamic inflammation and glial fibrillary acidic protein (GFAP) overexpression in astrocytes are well described in obese animals, as are some cognitive and memory deficits. As the hippocampus plays important roles in the consolidation of information, this investigation aimed to observe the memory function and the astrocyte expression of GFAP in the hippocampus of rats that received either a hypercaloric or a normocaloric diet. Methods: Adult male Wistar rats received a high-fat (cafeteria) or a standard diet for 60 days. On the 61st day, the rats were submitted to the novel object recognition (NOR) test at three and 24 hours after the first contact with objects, to assess short-term and long-term memory, respectively. Thereafter, the rats were euthanized and their brains were collected for GFAP immunohistochemical investigation in the hippocampus (CA1, CA2, CA3 areas) and hypothalamus (periventricular and arcuate nuclei). Astrocytic reactivity was assessed by morphometry. Different white adipose tissue depots and brown adipose tissue were weighed to calculate the adiposity index. Results: The hypercaloric diet increased body weight gain, adiposity index, white adipose tissue weight (epididymal, subcutaneous and retroperitoneal) and brown adipose tissue weight. Rats fed with the hypercaloric diet showed short-term and long-term memory impairments in the NOR test, as well as increased GFAP expression in astrocytes from all analyzed hypothalamic and hippocampal areas. Conclusion: This astrogliosis suggests that the neuroinflammatory response also occurs in the hippocampus and may be involved in the memory losses observed in obese/overweight animals.

Evaluation of dietary and lifestyle changes as modifiers of S100β levels in Alzheimer's disease

There is a significant body of research undertaken in order to elucidate the mechanisms underlying the pathology of Alzheimer's disease (AD), as well as to discover early detection biomarkers and potential therapeutic strategies. One such proposed biomarker is the calcium binding protein S100β, which, depending on its local concentration, is known to exhibit both neurotrophic and neuroinflammatory properties in the central nervous system. At present, relatively little is known regarding the effect of chronic S100β disruption in AD. Dietary intake has been identified as a modifiable risk factor for AD. Preliminary in vitro and animal studies have demonstrated an association between S100β expression and dietary intake which links to AD pathophysiology. This review describes the association of S100β to fatty acids, ketone bodies, insulin, and botanicals as well as the potential impact of physical activity as a lifestyle factor. We also discuss the prospective implications of these findings, including support of the use of a Mediterranean dietary pattern and/or the ketogenic diet as an approach to modify AD risk.

Gestational ketogenic diet programs brain structure and susceptibility to depression & anxiety in the adult mouse offspring

INTRODUCTION

The ketogenic diet (KD) has seen an increase in popularity for clinical and non-clinical purposes, leading to rise in concern about the diet's impact on following generations. The KD is known to have a neurological effect, suggesting that exposure to it during prenatal brain development may alter neuro-anatomy. Studies have also indicated that the KD has an anti-depressant effect on the consumer. However, it is unclear whether any neuro-anatomical and/or behavioral changes would occur in the offspring and persist into adulthood.

METHODS

To fill this knowledge gap we assessed the brain morphology and behavior of 8-week-old young-adult CD-1 mice, who were exposed to the KD in utero, and were fed only a standard-diet (SD) in postnatal life. Standardized neuro-behavior tests included the Open-Field, Forced-Swim, and Exercise Wheel tests, and were followed by post-mortem Magnetic Resonance Imaging (MRI) to assess brain anatomy.

RESULTS

The adult KD offspring exhibit reduced susceptibility to anxiety and depression, and elevated physical activity level when compared with controls exposed to the SD both in utero and postnatally. Many neuro-anatomical differences exist between the KD offspring and controls, including, for example, a cerebellar volumetric enlargement by 4.8%, a hypothalamic reduction by 1.39%, and a corpus callosum reduction by 4.77%, as computed relative to total brain volume.

CONCLUSIONS

These results suggest that prenatal exposure to the KD programs the offspring neuro-anatomy and influences their behavior in adulthood.

Effects of high-fat diet on neuronal damage, gliosis, inflammatory process and oxidative stress in the hippocampus induced by transient cerebral ischemia

In this study, we investigated the effects of a normal diet (ND) and high-fat diet (HFD) on delayed neuronal death in the gerbil hippocampal CA1 region after transient cerebral ischemia. In the HFD-fed gerbils, ischemia-induced hyperactivity was significantly increased and neuronal damage was represented more severely compared to the ND-fed gerbils. Ischemia-induced glial activation was accelerated in the HFD-fed gerbils. Cytokines including interleukin-2 and -4 were more sensitive in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. Additionally, we found that decreased 4-HNE and SODs immunoreactivity and protein levels in the hippocampal CA1 region of the HFD-fed gerbils after ischemia-reperfusion. These results indicate that HFD may lead to the exacerbated effects on ischemia-induced neuronal death in the hippocampal CA1 region after ischemia-reperfusion. These effects of HFD may be associated with more accelerated activations of glial cells and imbalance of pro- and anti-inflammatory cytokines and/or antioxidants after transient cerebral ischemia.

Green tea (-)epigallocatechin-3-gallate reverses oxidative stress and reduces acetylcholinesterase activity in a streptozotocin-induced model of dementia

Alzheimer's disease (AD) is the most prevalent form of dementia. Intracerebroventricular (ICV) infusion of streptozotocin (STZ) provides a relevant animal model of chronic brain dysfunction that is characterized by long-term and progressive deficits in learning, memory, and cognitive behavior, along with a permanent and ongoing cerebral energy deficit. Numerous studies on green tea epigallocatechin gallate (EGCG) demonstrate its beneficial effects on cognition and memory. As such, this study evaluated, for the first time, the effects of sub-chronic EGCG treatment in rats that were submitted to ICV infusion of STZ (3mg/kg). Male Wistar rats were divided into sham, STZ, sham+EGCG and STZ+EGCG groups. EGCG was administered at a dose of 10mg/kg/day for 4 weeks per gavage. Learning and memory was evaluated using Morris' Water Maze. Oxidative stress markers and involvement of the nitric oxide (NO) system, acetylcholinesterase activity (AChE) and glucose uptake were evaluated as well as glial parameters including S100B content and secretion and GFAP content. Our results show that EGCG was not able to modify glucose uptake and glutathione content, although cognitive deficit, S100B content and secretion, AChE activity, glutathione peroxidase activity, NO metabolites, and reactive oxygen species content were completely reversed by EGCG administration, confirming the neuroprotective potential of this compound. These findings contribute to the understanding of diseases accompanied by cognitive deficits and the STZ-model of dementia.

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 neuroprotective effect of two statins: simvastatin and pravastatin on a streptozotocin-induced model of Alzheimer's disease in rats

Astrocytes play a fundamental role in glutamate metabolism by regulating the extracellular levels of glutamate and intracellular levels of glutamine. They also participate in antioxidant defenses, due to the synthesis of glutathione, coupled to glutamate metabolism. Although the cause of Alzheimer's disease (AD) remains elusive, some changes in neurochemical parameters, such as glutamate uptake, glutamine synthetase activity and glutathione have been investigated in this disease. A possible neuroprotective effect of two statins, simvastatin and pravastatin (administered p.o.), was evaluated using a model of dementia, based on the intracerebroventricular (ICV) administration of streptozotocin (STZ), and astrocyte parameters were determined. We confirmed a cognitive deficit in rats submitted to ICV-STZ, and a prevention of this deficit by statin administration. Moreover, both statins were able to prevent the decrease in glutathione content and glutamine synthetase activity in this model of AD. Interestingly, simvastatin increased per se glutamate uptake activity, while both statins increased glutamine synthetase activity per se. These results support the idea that these drugs could be effective for the prevention of alterations observed in the STZ dementia model and may contribute to reduce the cognitive impairment and brain damage observed in AD patients.

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.

A ketogenic diet reduces long-term potentiation in the dentate gyrus of freely behaving rats

Ketogenic diets are very low in carbohydrates and can reduce epileptic seizures significantly. This dietary therapy is particularly effective in pediatric and drug-resistant epilepsy. Hypothesized anticonvulsant mechanisms of ketogenic diets focus on increased inhibition and/or decreased excitability/excitation. Either of these consequences might not only reduce seizures, but also could affect normal brain function and synaptic plasticity. Here, we characterized effects of a ketogenic diet on hippocampal long-term potentiation, a widely studied form of synaptic plasticity. Adult male rats were placed on a control or ketogenic diet for 3 wk before recording. To maintain the most physiological conditions possible, we assessed synaptic transmission and plasticity using chronic in vivo recordings in freely behaving animals. Rats underwent stereotaxic surgery to chronically implant a recording electrode in the hippocampal dentate gyrus and a stimulating electrode in the perforant path; they recovered for 1 wk. After habituation and stable baseline recording, 5-Hz theta-burst stimulation was delivered to induce long-term potentiation. All animals showed successful plasticity, demonstrating that potentiation was not blocked by the ketogenic diet. Compared with rats fed a control diet, rats fed a ketogenic diet demonstrated significantly diminished long-term potentiation. This decreased potentiation lasted for at least 48 h. Reduced potentiation in ketogenic diet-fed rats is consistent with a general increase in neuronal inhibition (or decrease in excitability) and decreased seizure susceptibility. A better understanding of the effects of ketogenic diets on synaptic plasticity and learning is important, as diet-based therapy is often prescribed to children with epilepsy.

Cognitive impairment following high fat diet consumption is associated with brain inflammation

C57Bl/6 mice were administered a high fat, Western diet (WD, 41% fat) or a very high fat lard diet (HFL, 60% fat), and evaluated for cognitive ability using the Stone T-maze and for biochemical markers of brain inflammation. WD consumption resulted in significantly increased body weight and astrocyte reactivity, but not impaired cognition, microglial reactivity, or heightened cytokine levels. HFL increased body weight, and impaired cognition, increased brain inflammation, and decreased BDNF. Collectively, these data suggest that while different diet formulations can increase body weight, the ability of high fat diets to disrupt cognition is linked to brain inflammation.

Reduced pain and inflammation in juvenile and adult rats fed a ketogenic diet

The ketogenic diet is a high-fat, low-carbohydrate regimen that forces ketone-based rather than glucose-based cellular metabolism. Clinically, maintenance on a ketogenic diet has been proven effective in treating pediatric epilepsy and type II diabetes, and recent basic research provides evidence that ketogenic strategies offer promise in reducing brain injury. Cellular mechanisms hypothesized to be mobilized by ketone metabolism and underlying the success of ketogenic diet therapy, such as reduced reactive oxygen species and increased central adenosine, suggest that the ketolytic metabolism induced by the diet could reduce pain and inflammation. To test the effects of a ketone-based metabolism on pain and inflammation directly, we fed juvenile and adult rats a control diet (standard rodent chow) or ketogenic diet (79% fat) ad libitum for 3-4 weeks. We then quantified hindpaw thermal nociception as a pain measure and complete Freund's adjuvant-induced local hindpaw swelling and plasma extravasation (fluid movement from the vasculature) as inflammation measures. Independent of age, maintenance on a ketogenic diet reduced the peripheral inflammatory response significantly as measured by paw swelling and plasma extravasation. The ketogenic diet also induced significant thermal hypoalgesia independent of age, shown by increased hindpaw withdrawal latency in the hotplate nociception test. Anti-inflammatory and hypoalgesic diet effects were generally more robust in juveniles. The ketogenic diet elevated plasma ketones similarly in both age groups, but caused slowed body growth only in juveniles. These data suggest that applying a ketogenic diet or exploiting cellular mechanisms associated with ketone-based metabolism offers new therapeutic opportunities for controlling pain and peripheral inflammation, and that such a metabolic strategy may offer significant benefits for children and adults.

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.

Immunoassay for glial fibrillary acidic protein: antigen recognition is affected by its phosphorylation state

Glial fibrillary acid protein (GFAP) is used commonly as a marker of astrogliosis and astrocyte activation in several situations involving brain injury. Its content may be measured by immunocytochemistry, immunoblotting or enzyme-linked immunosorbent assay (ELISA), usually employing commercial antibodies. Two major post-translational modifications in GFAP (phosphorylation and proteolysis) may alter the interpretation of results or for immunoassay standardization. This study using a non-sandwich ELISA aimed to investigate the putative changes in the immunorecognition due to the phosphorylated state of the antigen by a routinely used polyclonal anti-GFAP antibody from DAKO. Results involving in vitro phosphorylation of purified GFAP or biological samples (brain tissue, cell culture and cerebrospinal fluid) mediated by protein kinase dependent on cAMP indicate that GFAP phosphorylation improves the recognition by the used antibody. These results provide support to the understanding of fast changes in the GFAP-immunoreactivity and suggest that caution is necessary in the interpretation of results using this antibody, as well as indicate that the effect of post-translational modifications must be considered during the standardization of immunoassays with other antibodies.