Ketogenic Diet as a potential treatment for traumatic brain injury in mice

New insights into metabolism dysregulation after TBI

Traumatic brain injury (TBI) remains a leading cause of death and disability that places a great physical, social, and financial burden on individuals and the health system. In this review, we summarize new research into the metabolic changes described in clinical TBI trials, some of which have already shown promise for informing injury classification and staging. We focus our discussion on derangements in glucose metabolism, cell respiration/mitochondrial function and changes to ketone and lipid metabolism/oxidation to emphasize potentially novel biomarkers for clinical outcome prediction and intervention and offer new insights into possible underlying mechanisms from preclinical research of TBI pathology. Finally, we discuss nutrition supplementation studies that aim to harness the gut/microbiome-brain connection and manipulate systemic/cellular metabolism to improve post-TBI recovery. Taken together, this narrative review summarizes published TBI-associated changes in glucose and lipid metabolism, highlighting potential metabolite biomarkers for clinical use, the cellular processes linking these markers to TBI pathology as well as the limitations and future considerations for TBI "omics" work.

Non-pharmacological interventions for traumatic brain injury

Heterogeneity and variability of symptoms due to the type, site, age, sex, and severity of injury make each case of traumatic brain injury (TBI) unique. Considering this, a universal treatment strategy may not be fruitful in managing outcomes after TBI. Most of the pharmacological therapies for TBI aim at modifying a particular pathway or molecular process in the sequelae of secondary injury rather than a holistic approach. On the other hand, non-pharmacological interventions such as hypothermia, hyperbaric oxygen, preconditioning with dietary adaptations, exercise, environmental enrichment, deep brain stimulation, decompressive craniectomy, probiotic use, gene therapy, music therapy, and stem cell therapy can promote healing by modulating multiple neuroprotective mechanisms. In this review, we discussed the major non-pharmacological interventions that are being tested in animal models of TBI as well as in clinical trials. We evaluated the functional outcomes of various interventions with an emphasis on the links between molecular mechanisms and outcomes after TBI.

Sex-specific effects of ketogenic diet on anxiety-like behavior and neuroimmune response in C57Bl/6J mice

The ketogenic diet (KD) has been shown to reduce anxiety and enhance cognitive functions in neurological diseases. However, the sex-specific effects of KD on anxiety-like behavior in healthy individuals and the underlying molecular mechanisms contributing to these effects, including neuroinflammation, are unelucidated. This study investigated the sex-specific effects of KD on anxiety-like behavior and the neuroimmune response in the prefrontal cortex (PFC) and hippocampus of healthy C57BL/6J male and female mice. Animals were fed either a control diet (CD- 17% fat, 65% carb, 18% protein) or a KD (80% fat, 5% carb, 15% protein) for 4 weeks. KD increased the levels of circulating β-hydroxybutyrate (BHB) both in males and females. However, PFC BHB levels were found to be elevated only in KD males. Moreover, KD did not affect the behavior of females but improved motor abilities and reduced anxiety levels in males. KD suppressed the mRNA expression of the pan microglial markers (Cd68, P2ry12) and induced morphological changes in the male PFC microglia. A sex-specific decrease in IL1β and an increase in IL-10 levels was found in the PFC of KD males. A similar trend was observed in the hippocampus of males where KD reduced the mRNA expression of P2ry12, Il1β, and cFos. Additionally, BHB increased the production of IL-10 whereas it decreased the production of IL1β from human microglia in in-vitro conditions. In summary, these results demonstrate that the anxiolytic and motor function enhancement abilities of KD are male-specific. Reduced pro-inflammatory and improved anti-inflammatory factors in the male PFC and hippocampus may underlie these effects.

Modulation of beta-hydroxybutyrate in traumatic brain injury

PURPOSE OF REVIEW

Traumatic brain injury (TBI) is a significant public health concern with substantial morbidity and mortality rates in the United States. Current management strategies primarily focus on symptomatic approaches and prevention of secondary complications. However, recent research highlights the potential role of ketone bodies, particularly beta-hydroxybutyrate (BHB), in modulating cellular processes involved in TBI. This article reviews the metabolism of BHB, its effect in TBI, and its potential therapeutic impact in TBI.

RECENT FINDINGS

BHB can be produced endogenously through fasting or administered exogenously through ketogenic diets, and oral or intravenous supplements. Studies suggest that BHB may offer several benefits in TBI, including reducing oxidative stress, inflammation, controlling excitotoxicity, promoting mitochondrial respiration, and supporting brain regeneration. Various strategies to modulate BHB levels are discussed, with exogenous ketone preparations emerging as a rapid and effective option.

SUMMARY

BHB offers potential therapeutic advantages in the comprehensive approach to improve outcomes for TBI patients. However, careful consideration of safety and efficacy is essential when incorporating it into TBI treatment protocols. The timing, dosage, and long-term effects of ketone use in TBI patients require further investigation to fully understand its potential benefits and limitations.

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.

Metabolic Messengers: ketone bodies

Prospective molecular targets and therapeutic applications for ketone body metabolism have increased exponentially in the past decade. Initially considered to be restricted in scope as liver-derived alternative fuel sources during periods of carbohydrate restriction or as toxic mediators during diabetic ketotic states, ketogenesis and ketone bodies modulate cellular homeostasis in multiple physiological states through a diversity of mechanisms. Selective signalling functions also complement the metabolic fates of the ketone bodies acetoacetate and D-β-hydroxybutyrate. Here we discuss recent discoveries revealing the pleiotropic roles of ketone bodies, their endogenous sourcing, signalling mechanisms and impact on target organs, and considerations for when they are either stimulated for endogenous production by diets or pharmacological agents or administered as exogenous wellness-promoting agents.

Ketone bodies mediate alterations in brain energy metabolism and biomarkers of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. AD is a progressive neurodegenerative disorder characterized by cognitive dysfunction, including learning and memory deficits, and behavioral changes. Neuropathology hallmarks of AD such as amyloid beta (Aβ) plaques and neurofibrillary tangles containing the neuron-specific protein tau is associated with changes in fluid biomarkers including Aβ, phosphorylated tau (p-tau)-181, p-tau 231, p-tau 217, glial fibrillary acidic protein (GFAP), and neurofilament light (NFL). Another pathological feature of AD is neural damage and hyperactivation of astrocytes, that can cause increased pro-inflammatory mediators and oxidative stress. In addition, reduced brain glucose metabolism and mitochondrial dysfunction appears up to 15 years before the onset of clinical AD symptoms. As glucose utilization is compromised in the brain of patients with AD, ketone bodies (KBs) may serve as an alternative source of energy. KBs are generated from the β-oxidation of fatty acids, which are enhanced following consumption of ketogenic diets with high fat, moderate protein, and low carbohydrate. KBs have been shown to cross the blood brain barrier to improve brain energy metabolism. This review comprehensively summarizes the current literature on how increasing KBs support brain energy metabolism. In addition, for the first time, this review discusses the effects of ketogenic diet on the putative AD biomarkers such as Aβ, tau (mainly p-tau 181), GFAP, and NFL, and discusses the role of KBs on neuroinflammation, oxidative stress, and mitochondrial metabolism.

Combined effects of lead and manganese on locomotor activity and microbiota in zebrafish

Exposure to lead (Pb) and manganese (Mn) during early life influences neurodevelopment and increases the risk of neurodegenerative disorders. However, the level of developmental neurotoxicity due to combined exposure to the two metals remains unclear. Although the microbiota plays an essential part in the development of the nervous system via the gut-brain axis, there is a paucity of information regarding the interactions between exposure to Pb and Mn, the destruction of the microbiome, and neurodevelopmental impacts. To fill in this knowledge gap, we investigated the developmental neurotoxicity and effects on the microbiota of Pb (0.05 mg·L-1) alone and in combination with Mn (0.3 mg·L-1) in zebrafish larvae. Our results revealed that combined exposure precipitated higher malformation rates and lower locomotor activity levels than exposure to either Pb or Mn alone. Additionally, when we separated the combined exposure group from the other groups by applying unsupervised principal coordinates analysis (PCoA) and linear discriminant analysis (LEfSe) of microflora sequencing results, we observed extensive alterations in microbial abundances under combined-exposure conditions. Functional prediction analysis showed that combined exposure contributed to altered amino acid and lipid metabolism, and also that combined exposure to Pb and Mn reflected the greatest number of differentially activated biological pathways compared to the other three groups. ATP-binding cassette G (ABCG) genes and genes related to serotonin signaling and metabolism were altered following combined Pb and Mn exposure and exhibited disparate trends vis-à-vis Pb or Mn exposure alone. According to the results, the combined exposure to Pb and Mn led to more severe effects on both zebrafish locomotor activity and gut microbial composition. We suggest that the microbiota contributes to the combined neurotoxicity by increasing ABCG5 and ABCG8 gene expression.

Progress in research on the role of clinical nutrition in treating traumatic brain injury affecting the neurovascular unit

The neurovascular unit (NVU) is composed of neurons, glial cells, and blood vessels. NVU dysfunction involves the processes of neuroinflammation, and microcirculatory disturbances, as well as neuronal injury after traumatic brain injury (TBI). Traditional anti-inflammatory drugs have limited efficacy in improving the prognosis of TBI. Thus, treatments that target NVU dysfunction may provide a breakthrough. A large number of clinical studies have shown that the nutritional status of patients with TBI was closely related to their conditions and prognoses. Nutrient complexes and complementary therapies for the treatment of TBI are therefore being implemented in many preclinical studies. Importantly, the mechanism of action for this treatment may be related to repair of NVU dysfunction by ensuring adequate omega-3 fatty acids, curcumin, resveratrol, apigenin, vitamins, and minerals. These nutritional supplements hold promise for translation to clinical therapy. In addition, dietary habits also play an important role in the rehabilitation of TBI. Poor dietary habits may worsen the pathology and prognosis of TBI. Adjusting dietary habits, especially with a ketogenic diet, may improve outcomes in patients with TBI. This article discusses the impact of clinical nutrition on NVU dysfunction after TBI, focusing on nutritional complexes and dietary habits.

Cognitive and Cellular Effects of Combined Organophosphate Toxicity and Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is considered the most common neurological disorder among people under the age of 50. In modern combat zones, a combination of TBI and organophosphates (OP) can cause both fatal and long-term effects on the brain. We utilized a mouse closed-head TBI model induced by a weight drop device, along with OP exposure to paraoxon. Spatial and visual memory as well as neuron loss and reactive astrocytosis were measured 30 days after exposure to mild TBI (mTBI) and/or paraoxon. Molecular and cellular changes were assessed in the temporal cortex and hippocampus. Cognitive and behavioral deficits were most pronounced in animals that received a combination of paraoxon exposure and mTBI, suggesting an additive effect of the insults. Neuron survival was reduced in proximity to the injury site after exposure to paraoxon with or without mTBI, whereas in the dentate gyrus hilus, cell survival was only reduced in mice exposed to paraoxon prior to sustaining a mTBI. Neuroinflammation was increased in the dentate gyrus in all groups exposed to mTBI and/or to paraoxon. Astrocyte morphology was significantly changed in mice exposed to paraoxon prior to sustaining an mTBI. These results provide further support for assumptions concerning the effects of OP exposure following the Gulf War. This study reveals additional insights into the potentially additive effects of OP exposure and mTBI, which may result in more severe brain damage on the modern battlefield.

Measuring anxiety-like behavior in a mouse model of mTBI: Assessment in standard and home cage assays

Traumatic brain injury (TBI) is a primary global health concern and one of the most common causes of neurological impairments in people under 50. Mild TBI (mTBI) accounts for the majority of TBI cases. Anxiety is the most common complaint after mTBI in humans. This study aims to evaluate behavioral tests designed to assess anxiety-like phenotypes in a mice model of mTBI. ICR mice underwent mTBI using the weight-drop model. Seven days post-injury, mice were subjected to one of five different behavioral tests: Elevated Plus Maze (EPM), Open Field apparatus (OF), Marble Burying test (MBT), Light Dark Box (LDB), and the Light Spot test within the PhenoTyper home cage (LS). In the EPM and OF tests, there were no significant differences between the groups. During the 30-min test period of the MBT, mTBI mice buried significantly more marbles than control mice. In the LDB, mTBI mice spent significantly less time on the far side of the arena than control mice. In addition, the time it took for mTBI mice to get to the far side of the arena was significantly longer compared to controls. Results of LS show significant within-group mean differences for total distance traveled for mTBI mice but not for the control. Furthermore, injured mice moved significantly more than control mice. According to the results, the anxiety traits exhibited by mTBI mice depend upon the time of exposure to the aversive stimulus, the apparatus, and the properties of the stressors used. Therefore, the characterization of anxiety-like behavior in mTBI mice is more complicated than was initially suggested. Based on our findings, we recommend incorporating a variety of stressors and test session lengths when assessing anxiety-like behavior in experimental models of mTBI.

Neuroprotective mechanisms of OXCT1 via the SIRT3-SOD2 pathway after traumatic brain injury

BACKGROUND

Ketones are not only utilized to produce energy but also play a neuroprotective role in many neurodegenerative diseases. However, whether this process has an impact on secondary brain damage after traumatic brain injury (TBI) remains unknown. OXCT1 (3-Oxoacid CoA-Transferase 1) is the rate-limiting enzyme in the intra-neuronal utilization of ketones. In this study, we investigated whether reduced expression of OXCT1 after TBI could impact neuroprotective mechanisms and exacerbate neurological dysfunction.

MATERIALS AND METHODS

Experimental TBI was induced by a modified version of the weight drop model, it is a model of severe head trauma. Expression of OXCT1 in the injured hippocampus of mice was measured at different time points using immunoblotting assays. The release of abnormal mitochondrial cytochrome c from neurons of the mouse injured lateral hippocampus was measured 1 week after TBI using immunoblotting assays. Neuronal death was assessed by Nissl staining and the level of reactive oxygen species (ROS) within the neurons of the injured lateral hippocampus was assessed by Dihydroethidium staining. Results OXCT1 was overexpressed in hippocampal neurons by injection of adeno-associated virus into the lateral ventricle. OXCT1 expression levels decreased significantly 1 week post-TBI. After comparing the data obtained from different groups of mice, OXCT1 was found to significantly increase the expression of SIRT3 and reduce the proportion of acetylated SOD2, thus decreasing the production of ROS in the injured hippocampal neurons, reducing neuronal death, and improving cognitive function. Conclusions OXCT1 has a critical previously unappreciated protective role in neurological impairment following TBI via the SIR3-SOD2 pathway. These findings highlight the potential of OXCT1 as a simple treatment for patients with TBI.

High fat diet exacerbates long-term metabolic, neuropathological, and behavioral derangements in an experimental mouse model of traumatic brain injury

AIMS

Traumatic brain injury (TBI) constitutes a serious public health concern. Although TBI targets the brain, it can exert several systemic effects which can worsen the complications observed in TBI subjects. Currently, there is no FDA-approved therapy available for its treatment. Thus, there has been an increasing need to understand other factors that could modulate TBI outcomes. Among the factors involved are diet and lifestyle. High-fat diets (HFD), rich in saturated fat, have been associated with adverse effects on brain health.

MAIN METHODS

To study this phenomenon, an experimental mouse model of open head injury, induced by the controlled cortical impact was used along with high-fat feeding to evaluate the impact of HFD on brain injury outcomes. Mice were fed HFD for a period of two months where several neurological, behavioral, and molecular outcomes were assessed to investigate the impact on chronic consequences of the injury 30 days post-TBI.

KEY FINDINGS

Two months of HFD feeding, together with TBI, led to a notable metabolic, neurological, and behavioral impairment. HFD was associated with increased blood glucose and fat-to-lean ratio. Spatial learning and memory, as well as motor coordination, were all significantly impaired. Notably, HFD aggravated neuroinflammation, oxidative stress, and neurodegeneration. Also, cell proliferation post-TBI was repressed by HFD, which was accompanied by an increased lesion volume.

SIGNIFICANCE

Our research indicated that chronic HFD feeding can worsen functional outcomes, predispose to neurodegeneration, and decrease brain recovery post-TBI. This sheds light on the clinical impact of HFD on TBI pathophysiology and rehabilitation as well.

Sirtuins functions in central nervous system cells under neurological disorders

The sirtuins (SIRTs), a class of NAD+ -dependent deacylases, contain seven SIRT family members in mammals, from SIRT1 to SIRT7. Extensive studies have revealed that SIRT proteins regulate virous cell functions. Central nervous system (CNS) decline resulted in progressive cognitive impairment, social and physical abilities dysfunction. Therefore, it is of vital importance to have a better understanding of potential target to promote homeostasis of CNS. SIRTs have merged as the underlying regulating factors of the process of neurological disorders. In this review, we profile multiple functions of SIRT proteins in different cells during brain function and under CNS injury.

Exogenous Ketones and Lactate as a Potential Therapeutic Intervention for Brain Injury and Neurodegenerative Conditions

Metabolic dysfunction is a ubiquitous underlying feature of many neurological conditions including acute traumatic brain injuries and chronic neurodegenerative conditions. A central problem in neurological patients, in particular those with traumatic brain injuries, is an impairment in the utilization of glucose, which is the predominant metabolic substrate in a normally functioning brain. In such patients, alternative substrates including ketone bodies and lactate become important metabolic candidates for maintaining brain function. While the potential neuroprotective benefits of ketosis have been recognized for up to almost a century, the majority of work has focused on the use of ketogenic diets to induce such a state, which is inappropriate in cases of acute disease due to the prolonged periods of time (i.e., weeks to months) required for the effects of a ketogenic diet to be seen. The following review seeks to explore the neuroprotective effects of exogenous ketone and lactate preparations, which have more recently become commercially available and are able to induce a deep ketogenic response in a fraction of the time. The rapid response of exogenous preparations makes their use as a therapeutic adjunct more feasible from a clinical perspective in both acute and chronic neurological conditions. Potentially, their ability to globally moderate long-term, occult brain dysfunction may also be relevant in reducing lifetime risks of certain neurodegenerative conditions. In particular, this review explores the association between traumatic brain injury and contusion-related dementia, assessing metabolic parallels and highlighting the potential role of exogenous ketone and lactate therapies.

Scientific Evidences of Calorie Restriction and Intermittent Fasting for Neuroprotection in Traumatic Brain Injury Animal Models: A Review of the Literature

It has widely been accepted that food restriction (FR) without malnutrition has multiple health benefits. Various calorie restriction (CR) and intermittent fasting (IF) regimens have recently been reported to exert neuroprotective effects in traumatic brain injury (TBI) through variable mechanisms. However, the evidence connecting CR or IF to neuroprotection in TBI as well as current issues remaining in this research field have yet to be reviewed in literature. The objective of our review was therefore to weigh the evidence that suggests the connection between CR/IF with recovery promotion following TBI. Medline, Google Scholar and Web of Science were searched from inception to 25 February 2022. An overwhelming number of results generated suggest that several types of CR/IF play a promising role in promoting post-TBI recovery. This recovery is believed to be achieved by alleviating mitochondrial dysfunction, promoting hippocampal neurogenesis, inhibiting glial cell responses, shaping neural cell plasticity, as well as targeting apoptosis and autophagy. Further, we represent our views on the current issues and provide thoughts on the future direction of this research field.