The neuroprotective effects of β-hydroxybutyrate on Aβ-injected rat hippocampus in vivo and in Aβ-treated PC-12 cells in vitro

Therapeutic potential of the ketogenic diet: A metabolic switch with implications for neurological disorders, the gut-brain axis, and cardiovascular diseases

The Ketogenic Diet (KD) is a dietary regimen that is low in carbohydrates, high in fats, and contains adequate protein. It is designed to mimic the metabolic state of fasting. This diet triggers the production of ketone bodies through a process known as ketosis. The primary objective of KD is to induce and sustain ketosis, which has been associated with numerous health benefits. Recent research has uncovered promising therapeutic potential for KD in the treatment of various diseases. This includes evidence of its effectiveness as a dietary strategy for managing intractable epilepsy, a form of epilepsy that is resistant to medication. We are currently assessing the efficacy and safety of KD through laboratory and clinical studies. This review focuses on the anti-inflammatory properties of the KD and its potential benefits for neurological disorders and the gut-brain axis. We also explore the existing literature on the potential effects of KD on cardiac health. Our aim is to provide a comprehensive overview of the current knowledge in these areas. Given the encouraging preliminary evidence of its therapeutic effects and the growing understanding of its mechanisms of action, randomized controlled trials are warranted to further explore the rationale behind the clinical use of KD. These trials will ultimately enhance our understanding of how KD functions and its potential benefits for various health conditions. We hope that our research will contribute to the body of knowledge in this field and provide valuable insights for future studies.

[Beneficial effects of ketogenic diet for Alzheimer's disease management]

Alzheimer's disease (AD) is a neurodegenerative disease that affects almost 1 million people in France and 55 million in the world. This pathology is a global health preoccupation because of the lack of efficient curative treatment and the increase of its prevalence. During the last decade, the comprehension of pathophysiological mechanisms involved in AD have been improved. Amyloid plaques and neurofibrillary tangles accumulation are characteristic of Alzheimer's brain patients, accompanied by increased brain inflammation and oxidative stress, impaired cerebral metabolism of glucose and mitochondrial function. Treatment of AD includes different approaches, as pharmacology, psychology support, physiotherapy, and speech therapy. However, these interventions do not have a curative effect, but only compensatory on the disease. Ketogenic diet (KD), a low-carbohydrates and high-fat diet, associated with a medium-chain triglycerides intake (MCTs) might induce benefices for Alzheimer disease patients. Carbohydrate restriction and MCTs promotes the production of ketone bodies from fatty acid degradation. These metabolites replacing glucose, serve the brain as energetic substrates, and induce neuroprotective effects. Such a nutritional support might slow down the disease progression and improve cognitive abilities of patients. This review aims to examine the neuroprotective mechanisms of KD in AD progression and describes the advantages and limitations of KD as a therapeutic strategy.

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.

Insulin Resistance and Hypertension: Mechanisms Involved and Modifying Factors for Effective Glucose Control

Factors such as aging, an unhealthy lifestyle with decreased physical activity, snacking, a standard Western diet, and smoking contribute to raising blood pressure to a dangerous level, increasing the risk of coronary artery disease and heart failure. Atherosclerosis, or aging of the blood vessels, is a physiological process that has accelerated in the last decades by the overconsumption of carbohydrates as the primary sources of caloric intake, resulting in increased triglycerides and VLDL-cholesterol and insulin spikes. Classically, medications ranging from beta blockers to angiotensin II blockers and even calcium channel blockers were used alone or in combination with lifestyle modifications as management tools in modern medicine to control arterial blood pressure. However, it is not easy to control blood pressure or the associated complications. A low-carbohydrate, high-fat (LCHF) diet can reduce glucose and insulin spikes, improve insulin sensitivity, and lessen atherosclerosis risk factors. We reviewed articles describing the etiology of insulin resistance (IR) and its impact on arterial blood pressure from databases including PubMed, PubMed Central, and Google Scholar. We discuss how the LCHF diet is beneficial to maintaining arterial blood pressure at normal levels, slowing down the progression of atherosclerosis, and reducing the use of antihypertensive medications. The mechanisms involved in IR associated with hypertension are also highlighted.

Minocycline effects on memory and learning impairment in the beta-amyloid-induced Alzheimer's disease model in male rats using behavioral, biochemical, and histological methods

Alzheimer's disease (AD), as an advanced neurodegenerative disease, is characterized by the everlasting impairment of memory, which is determined by hyperphosphorylation of intracellular Tau protein and accumulation of beta-amyloid (Aβ) in the extracellular space. Minocycline is an antioxidant with neuroprotective effects that can freely cross the blood-brain barrier (BBB). This study investigated the effect of minocycline on the changes in learning and memory functions, activities of blood serum antioxidant enzymes, neuronal loss, and the number of Aβ plaques after AD induced by Aβ in male rats. Healthy adult male Wistar rats (200-220g) were divided randomly into 11 groups (n = 10). The rats received minocycline (50 and 100 mg/kg/day; per os (P.O.)) before, after, and before/after AD induction for 30 days. At the end of the treatment course, behavioral performance was measured by standardized behavioral paradigms. Subsequently, brain samples and blood serum were collected for histological and biochemical analysis. The results indicated that Aβ injection impaired learning and memory performances in the Morris water maze test, reduced exploratory/locomotor activities in the open field test, and enhanced anxiety-like behavior in the elevated plus maze. The behavioral deficits were accompanied by hippocampal oxidative stress (decreased glutathione (GSH) peroxidase enzyme activity and increased malondialdehyde (MDA) levels in the brain (hippocampus) tissue), increased number of Aβ plaques, and neuronal loss in the hippocampus evidenced by Thioflavin S and H&E staining, respectively. Minocycline improved anxiety-like behavior, recovered Aβ-induced learning and memory deficits, increased GSH and decreased MDA levels, and prevented neuronal loss and the accumulation of Aβ plaques. Our results demonstrated that minocycline has neuroprotective effects and can reduce memory dysfunction, which are due to its antioxidant and anti-apoptotic effects.

Ketogenic Diet Alleviates Brain Iron Deposition and Cognitive Dysfunction via Nrf2-mediated Ferroptosis pathway in APP/PS1 Mouse

Progressive cognitive decline and increased brain iron deposition with age are important features of Alzheimer's disease. Previous studies have found that the short-term ketogenic diet has neuroprotective effects in a variety of neurodegenerative diseases, but the effects of an early and long-term ketogenic diet on brain iron content and cognition of Alzheimer's disease have not been reported. In our study, 8-week-old APP/PS1 mice were given a 12-month ketogenic or standard diet, while C57BL/6 mice matched with the age and genetic background of APP/PS1 mice were used as normal controls to be given a standard diet for the same length of time. We found that 12 months of an early ketogenic diet improved the impaired learning and memory ability of APP/PS1 mice. The improvement of cognitive function may be related to the reduction of amyloid-beta deposition and neuronal ferroptosis. The mechanism was achieved by the regulation of ferroptosis-related pathways after activation of nuclear factor erythroid 2-related factor 2 by ketogenic diet-induced elevated β-hydroxybutyrate. In addition, blood biochemical results showed that compared with the standard diet group of the disease, although the early and long-term ketogenic diet increased blood lipids to some extent, it seemed to reduce liver, renal, and myocardial damage caused by genetic differences. This will provide a piece of positive evidence for the early and long-term use of ketogenic diets in people at risk of Alzheimer's disease.

Short-Chain Fatty Acids in the Microbiota-Gut-Brain Axis: Role in Neurodegenerative Disorders and Viral Infections

The gut-brain axis (GBA) is the umbrella term to include all bidirectional communication between the brain and gastrointestinal (GI) tract in the mammalian body. Evidence from over two centuries describes a significant role of GI microbiome in health and disease states of the host organism. Short-chain fatty acids (SCFAs), mainly acetate, butyrate, and propionate that are the physiological forms of acetic acid, butyric acid, and propionic acid respectively, are GI bacteria derived metabolites. SCFAs have been reported to influence cellular function in multiple neurodegenerative diseases (NDDs). In addition, the inflammation modulating properties of SCFAs make them suitable therapeutic candidates in neuroinflammatory conditions. This review provides a historical background of the GBA and current knowledge of the GI microbiome and role of individual SCFAs in central nervous system (CNS) disorders. Recently, a few reports have also identified the effects of GI metabolites in the case of viral infections. Among these viruses, the flaviviridae family is associated with neuroinflammation and deterioration of CNS functions. In this context, we additionally introduce SCFA based mechanisms in different viral pathogenesis to understand the former's potential as agents against flaviviral disease.

Ketogenic Diet as a Promising Non-Drug Intervention for Alzheimer’s Disease: Mechanisms and Clinical Implications

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder that is mainly characterized by cognitive deficits. Although many studies have been devoted to developing disease-modifying therapies, there has been no effective therapy until now. However, dietary interventions may be a potential strategy to treat AD. The ketogenic diet (KD) is a high-fat and low-carbohydrate diet with adequate protein. KD increases the levels of ketone bodies, providing an alternative energy source when there is not sufficient energy supply because of impaired glucose metabolism. Accumulating preclinical and clinical studies have shown that a KD is beneficial to AD. The potential underlying mechanisms include improved mitochondrial function, optimization of gut microbiota composition, and reduced neuroinflammation and oxidative stress. The review provides an update on clinical and preclinical research on the effects of KD or medium-chain triglyceride supplementation on symptoms and pathophysiology in AD. We also detail the potential mechanisms of KD, involving amyloid and tau proteins, neuroinflammation, gut microbiota, oxidative stress, and brain metabolism. We aimed to determine the function of the KD in AD and outline important aspects of the mechanism, providing a reference for the implementation of the KD as a potential therapeutic strategy for AD.

Low-Carbohydrate High-Fat Diet: A SWOC Analysis

Insulin resistance (IR) plays a role in the pathogenesis of many diseases, such as type 2 diabetes mellitus, cardiovascular disease, non-alcoholic fatty liver disease, obesity, and neurodegenerative diseases, including Alzheimer's disease. The ketogenic diet (KD) is a low-carbohydrate/high-fat diet that arose in the 1920s as an effective treatment for seizure control. Since then, the KD has been studied as a therapeutic approach for various IR-related disorders with successful results. To date, the use of the KD is still debatable regarding its safety. Some studies have acknowledged its usefulness, while others do not recommend its long-term implementation. In this review, we applied a SWOC (Strengths, Weaknesses, Opportunities, and Challenges) analysis that revealed the positive, constructive strengths of the KD, its potential complications, different conditions that can make used for it, and the challenges faced by both physicians and subjects throughout a KD. This SWOC analysis showed that the KD works on the pathophysiological mechanism of IR-related disorders such as chronic inflammation, oxidative stress and mitochondrial stress. Furthermore, the implementation of the KD as a potential adjuvant therapy for many diseases, including cancer, neurodegenerative disorders, polycystic ovary syndrome, and pain management was proven. On the other hand, the short and long-term possible undesirable KD-related effects, including nutritional deficiencies, growth retardation and nephrolithiasis, should be considered and strictly monitored. Conclusively, this review provides a context for decision-makers, physicians, researchers, and the general population to focus on this dietary intervention in preventing and treating diseases. Moreover, it draws the attention of scientists and physicians towards the opportunities and challenges associated with the KD that requires attention before KD initiation.

Supplementation of Regular Diet With Medium-Chain Triglycerides for Procognitive Effects: A Narrative Review

It is now widely accepted that ketosis (a physiological state characterized by elevated plasma ketone body levels) possesses a wide range of neuroprotective effects. There is a growing interest in the use of ketogenic supplements, including medium-chain triglycerides (MCT), to achieve intermittent ketosis without adhering to a strict ketogenic diet. MCT supplementation is an inexpensive and simple ketogenic intervention, proven to benefit both individuals with normal cognition and those suffering from mild cognitive impairment, Alzheimer's disease, and other cognitive disorders. The commonly accepted paradigm underlying MCT supplementation trials is that the benefits stem from ketogenesis and that MCT supplementation is safe. However, medium-chain fatty acids (MCFAs) may also exert effects in the brain directly. Moreover, MCFAs, long-chain fatty acids, and glucose participate in mutually intertwined metabolic pathways. Therefore, the metabolic effects must be considered if the desired procognitive effects require administering MCT in doses larger than 1 g/kg. This review summarizes currently available research on the procognitive effects of using MCTs as a supplement to regular feed/diet without concomitant reduction of carbohydrate intake and focuses on the revealed mechanisms linked to particular MCT metabolites (ketone bodies, MCFAs), highlighting open questions and potential considerations.

MEF2C ameliorates learning, memory, and molecular pathological changes in Alzheimer’s disease in vivo and in vitro

Myocyte enhancer factor 2C (MEF2C) is highly expressed in the nervous system, and regulates neuro-development, synaptic plasticity, and inflammation. However, its mechanism in Alzheimer's disease (AD) is underestimated. In this study, the role and mechanism of MEF2C were investigated in the brain tissue specimens from patients with AD, APPswe/PSEN1dE9 double transgenic (APP/PS1_DT) mice, and SH-SY5Y cells treated with β-amyloid peptide (Aβ). The results indicated that the expression of MEF2C is significantly reduced, and the expression of MEF2C/Aβ in different parts of brain is negatively correlated in patients with AD. Knockdown of MEF2C promotes cell apoptosis and the level of β-amyloid precursor protein cleaving enzyme 1 (BACE) but reduces BACE2 expression. In addition, knockdown of enhances the generation and aggregation of Aβ in the cortex of APP/PS1_DT mice, reduces the expression of synaptic proteins, exacerbates the ability of learning and memory of APP/PS1_DT mice, damages the structure of mitochondria, increases the oxidative stress (OS) level, and inhibits the expression levels of members of the Nrf2-ARE signal pathway. In summary, inhibition of MEF2C exacerbates the toxic effect of Aβ and , damages synaptic plasticity, reduces the ability of learning and memory of APP/PS1 mice, and increases the level of OS via the Nrf2-ARE signal pathway.

β-hydroxybutyrate Alleviates Learning and Memory Impairment Through the SIRT1 Pathway in D-Galactose-Injured Mice

Learning and memory impairment is a common clinical symptom of aging and nervous system injuries, and seriously affects quality of life. Memory impairment is associated with increased oxidative stress (OS) and inflammatory response. β-hydroxybutyrate (BHBA) is a water-soluble endogenous small-molecule ketone body that easily crosses the blood-brain barrier and has shown neuroprotection activities. In this study, we investigated the effects and mechanisms of BHBA on D-galactose (D-gal)-induced memory impairment in mice by in vitro and in vivo experiments. BHBA was administered intragastrically to D-gal-injured C57BL/6 mice for 42 days. Water maze performance, the morphology of the hippocampus with Nissl staining, the ACh content, OS, and inflammation status were examined. To further investigate the mechanism, hippocampal neuronal cells (HT22) were treated with BHBA with or without the SIRT1 inhibitor or small interfering RNAs against sirt1 (si-SIRT1) before incubation with D-gal. BHBA significantly improved water maze performance; increased the ACh content, SOD activity, and SIRT1 expression; and decreased AChE and LDH activity, ROS, MDA, IL-1β, TNF-α contents, and NLRP3 expression. Further studies with the SIRT inhibitor or siRNAs against sirt1 reversed the above effects of BHBA. Collectively, BHBA inhibited hippocampal OS and the inflammation process to alleviate learning and memory impairment through activating the SIRT1 pathway in D-gal-injured mice, suggesting that BHBA could be a potential option for drug development of learning and memory impairment induced by nervous system injuries.

The potential pharmacological mechanisms of β-hydroxybutyrate for improving cognitive functions

β-Hydroxybutyl acid (βOHB), the most prevalent type of ketone in the human body, is involved in the pathogenesis of cognitive disorders, especially Alzheimer's dementia (AD), through a variety of mechanisms, such as enhancing mitochondrial metabolism, regulating signaling molecule, increasing histone acetylation, affecting the metabolism of Aβ and Tau proteins, inhibiting inflammation and lipid metabolism, and regulating intestinal microbes. Based on the above findings, clinical drug development in AD has begun to focus on βOHB.

Alzheimer's Disease and Diabetes: Role of Diet, Microbiota and Inflammation in Preclinical Models

Alzheimer's disease (AD) is the most common cause of dementia. Epidemiological studies show the association between AD and type 2 diabetes (T2DM), although the mechanisms are not fully understood. Dietary habits and lifestyle, that are risk factors in both diseases, strongly modulate gut microbiota composition. Also, the brain-gut axis plays a relevant role in AD, diabetes and inflammation, through products of bacterial metabolism, like short-chain fatty acids. We provide a comprehensive review of current literature on the relation between dysbiosis, altered inflammatory cytokines profile and microglia in preclinical models of AD, T2DM and models that reproduce both diseases as commonly observed in the clinic. Increased proinflammatory cytokines, such as IL-1β and TNF-α, are widely detected. Microbiome analysis shows alterations in Actinobacteria, Bacteroidetes or Firmicutes phyla, among others. Altered α- and β-diversity is observed in mice depending on genotype, gender and age; therefore, alterations in bacteria taxa highly depend on the models and approaches. We also review the use of pre- and probiotic supplements, that by favoring a healthy microbiome ameliorate AD and T2DM pathologies. Whereas extensive studies have been carried out, further research would be necessary to fully understand the relation between diet, microbiome and inflammation in AD and T2DM.

Ketone Metabolite β-Hydroxybutyrate Ameliorates Inflammation After Spinal Cord Injury by Inhibiting the NLRP3 Inflammasome

Ketogenic diet (KD) has been shown to be beneficial in a range of neurological disorders, with ketone metabolite β-hydroxybutyrate (βOHB) reported to block the nucleotide oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome in bone marrow-derived macrophages. In this study, we show that pretreatment with KD or in situ βOHB suppressed macrophages/microglia activation and the overproduction of inflammatory cytokines, while KD downregulated the expression of NLRP3 inflammasome. Moreover, KD promoted macrophages/microglia transformation from the M1 phenotype to the M2a phenotype following spinal cord injury (SCI) in the in vivo study. Rats in the KD group demonstrated improved behavioral and electrophysiological recovery after SCI when compared to those rats in the standard diet group. The in vitro study performed on BV2 cells indicated that βOHB inhibited an LPS+ATP-induced inflammatory response and decreased NLRP3 protein levels. Our data demonstrated that pretreatment with KD attenuated neuroinflammation following SCI, probably by inhibiting NLRP3 inflammasome and shifting the activation state of macrophages/microglia from the M1 to the M2a phenotype. Therefore, the ketone metabolite βOHB might provide a potential future therapeutic strategy for SCI.

Nutritional Ketosis as a Potential Treatment for Alcohol Use Disorder

Alcohol use disorder (AUD) is a chronic, relapsing brain disorder, characterized by compulsive alcohol seeking and disrupted brain function. In individuals with AUD, abstinence from alcohol often precipitates withdrawal symptoms than can be life threatening. Here, we review evidence for nutritional ketosis as a potential means to reduce withdrawal and alcohol craving. We also review the underlying mechanisms of action of ketosis. Several findings suggest that during alcohol intoxication there is a shift from glucose to acetate metabolism that is enhanced in individuals with AUD. During withdrawal, there is a decline in acetate levels that can result in an energy deficit and could contribute to neurotoxicity. A ketogenic diet or ingestion of a ketone ester elevates ketone bodies (acetoacetate, β-hydroxybutyrate and acetone) in plasma and brain, resulting in nutritional ketosis. These effects have been shown to reduce alcohol withdrawal symptoms, alcohol craving, and alcohol consumption in both preclinical and clinical studies. Thus, nutritional ketosis may represent a unique treatment option for AUD: namely, a nutritional intervention that could be used alone or to augment the effects of medications.

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

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

Neuroinflammation Mediated by NLRP3 Inflammasome After Intracerebral Hemorrhage and Potential Therapeutic Targets

Intracerebral hemorrhage (ICH) is the most fatal subtype of stroke; there is still a lack of effective treatment. Microglia are a major component of the innate immune system, and they respond to acute brain injury by activating and forming classic M1-like (pro-inflammatory) or alternative M2-like (anti-inflammatory) phenotype. The existence of the polarization indicates that the role of microglia in disease's progression and recovery after ICH is still unclear, perhaps involving microglial secretion of anti-inflammatory or pro-inflammatory cytokines and chemokines. The NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome is considered to be the main participant in neuroinflammation. Recent evidence has shown that NLRP3 inflammasome can be activated after ICH, resulting in inflammatory cascade reactions and aggravating brain injury. Furthermore, previous studies have reported that NLRP3 inflammasome is mainly present in microglia, so we speculate that its activation may be strongly associated with microglial polarization. Many scholars have investigated the role of brain injury caused by NLRP3 inflammasome after ICH, but the precise operating mechanisms remain uncertain. This review summarized the activation mechanism of NLRP3 inflammasome after ICH and the possible mechanism of NLRP3 inflammasome promoting neuroinflammation and aggravating nerve injury and discussed the relevant potential therapeutic targets.

Restoration of metabolic tempo through time-restricted eating (TRE) as the preventive measure for metabolic diseases

The characteristics of healthy bioenergetics are the overall balance of energy intake and expenditure, the alternate switching for different metabolic fuels, and the temporal rhythm of eating and fasting. These three bioenergetic attributes, herein, are termed as the metabolic tempo. Cumulative studies revealed the beneficial health effects of fasting. Most of the fasting regimens harness their innate mechanisms of enhancing metabolic fuel switching, thus improving metabolic flexibility. The emerging time-restricted eating (TRE) regimen includes the restoration of diurnal eating and fasting rhythms, improve the metabolic flexibility, while spontaneously reduces the food intake despite the ad-libitum eating. TRE thus simultaneously improves all three bioenergetic-tempo attributes when compared to the energy balance control in general obesity control. We reviewed fifteen human studies of TRE and TRE-liked interventions from 2007 to 2019. These studies reported promising beneficial metabolic effects on body weight, glycemic, and lipid controls while demonstrating most of the fasting-related metabolic and epigenetic responses in overweight and obese individuals. TRE is practically possible for long-termed implementation. Despite its potentials to restore the underlying dysregulated bioenergetics., there is no study confirming that TRE could prevent the development of common metabolic diseases in healthy subjects after long-term implementation. This gap of knowledge warrants future investigation.

Neuroprotective Effect of New Nanochelating-Based Nano Complex, ALZc3, Against Aβ (1-42)-Induced Toxicity in Rat: a Comparison with Memantine

PURPOSE

The current drugs for Alzheimer's disease (AD) are only used to slow or delay the progression of the pathology. So using a novel technology is a necessity to synthesize more effective medications to control this most common cause of dementia. In this study, using nanochelating technology, ALZc3 was synthesized and its therapeutic effects were evaluated in comparison with memantine on a well-known rat model of AD, which is based on Amyloid-βeta (Aβ) injection into the brain.

MATERIALS AND METHODS

Aβ (1-42) was injected bilaterally into the CA1 area of the hippocampus of male rats and then animals were treated daily by oral administration of Alz-C3, memantine or their vehicles. Activities of antioxidant enzymes catalase and superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) levels, as well as Bax/Bcl-2 ratio, caspase-3 activation, and TNF-α expression were evaluated 7 days after Aβ injection. Finally, learning and memory of the rats were assessed by Morris water maze test.

RESULTS

ALZc3 and memantine improved memory impairment and antioxidant activity and reduced TNF-α expression, caspase-3 activity and Bax/Bcl-2 ratio in the rat's hippocampus. The results showed a superiority of ALZC3 compared to memantine in reducing caspase-3, increasing CAT activity in Aβ (1-42)-injected groups and improving apoptosis factor in healthy mice.

CONCLUSION

These results indicated that ALZc3 could significantly prevent the memory impairment and Aβ (1-42) toxicity. Thus, ALZc3 could be a promising novel anti-AD agent.

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

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

Targeting the microglial NLRP3 inflammasome and its role in Parkinson's disease

Excessive activation of microglia and subsequent release of proinflammatory cytokines play a crucial role in neuroinflammation and neurodegeneration in Parkinson's disease (PD). Components of the nucleotide-binding oligomerization domain and leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome complex, leucine-rich-repeat- and pyrin-domain-containing 3, caspase-1, and apoptosis-associated speck-like protein containing a CARD, are highly expressed in activated microglia in PD patient brains. Findings suggest that neurotoxins, aggregation of α-synuclein, mitochondrial reactive oxygen species, and disrupted mitophagy are the key regulators of microglial leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome activation and release of interleukin-1β and interleukin-18 caspase-1-mediated pyroptotic cell death in the substantia nigra of the brain. Although this evidence suggests the leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome may be a potential drug target for treatment of PD, the exact mechanism of how the microglia sense these stimuli and initiate leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome signaling is unknown. Here, the molecular mechanism and regulation of microglial leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome activation and its role in the pathogenesis of PD are discussed. Moreover, the potential of both endogenous and synthetic leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome modulators, long noncoding RNA, microRNA to develop novel therapeutics to treat PD is presented. Overall, we recommend that the microglial leucine-rich-repeat- and pyrin-domain-containing 3 inflammasome can be a potential target for PD treatment. © 2019 International Parkinson and Movement Disorder Society.

Shaping the Nrf2-ARE-related pathways in Alzheimer's and Parkinson's diseases

A failure in redox homeostasis is a common hallmark of Alzheimer's Disease (AD) and Parkinson's Disease (PD), two age-dependent neurodegenerative disorders (NDD), causing increased oxidative stress, oxidized/damaged biomolecules, altered neuronal function and consequent cell death. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a redox-regulated transcription factor, results in upregulation of cytoprotective and antioxidant enzymes/proteins, protecting against oxidative stress. Nrf2 regulation is achieved by various proteins and pathways, at both cytoplasmatic and nuclear level; however, the elaborate network of mechanisms involved in Nrf2 regulation may restrain Nrf2 pathway normal activity. Indeed, altered Nrf2 activity is involved in aging and NDD, such as AD and PD. Therefore, understanding the diversity of Nrf2 control mechanisms and regulatory proteins is of high interest, since more effective NDD therapeutics can be identified. In this review, we first introduce Keap1-Nrf2-ARE structure, function and regulation, with a special focus on the several pathways involved in Nrf2 positive and negative modulation, namely p62, PKC, PI3K/Akt/GSK-3β, NF-kB and p38 MAPK. We then briefly describe the evidences for oxidative stress and Nrf2 pathway deregulation in different stages of NDDs. Finally, we discuss the potential of Nrf2-related pathways as potential therapeutic targets to possibly prevent or slowdown NDD progression.

Regulation of Mitochondrial Biogenesis as a Way for Active Longevity: Interaction Between the Nrf2 and PGC-1α Signaling Pathways

Aging is a general degenerative process related to deterioration of cell functions in the entire organism. Mitochondria, which play a key role in energy homeostasis and metabolism of reactive oxygen species (ROS), require lifetime control and constant renewal. This explains recently peaked interest in the processes of mitochondrial biogenesis and mitophagy. The principal event of mitochondrial metabolism is regulation of mitochondrial DNA (mtDNA) transcription and translation, which is a complex coordinated process that involves at least two systems of transcription factors. It is commonly believed that its major regulatory proteins are PGC-1α and PGC-1β, which act as key factors connecting several regulator cascades involved in the control of mitochondrial metabolism. In recent years, the number of publications on the essential role of Nrf2/ARE signaling in the regulation of mitochondrial biogenesis has grown exponentially. Nrf2 is induced by various xenobiotics and oxidants that oxidize some Nrf2 negative regulators. Thus, ROS, in particular H₂O₂, were found to be strong Nrf2 activators. At present, there are two major concepts of mitochondrial biogenesis. Some authors suggest direct involvement of Nrf2 in the regulation of this process. Others believe that Nrf2 regulates expression of the antioxidant genes, while the major and only regulator of mitochondrial biogenesis is PGC-1α. Several studies have demonstrated the existence of the regulatory loop involving both PGC-1α and Nrf2. In this review, we summarized recent data on the Nrf2 role in mitochondrial biogenesis and its interaction with PGC-1α in the context of extending longevity.

Beta-hydroxybutyric acid attenuates neuronal damage in epileptic mice

β-Hydroxybutyric acid (BHBA) reportedly has neuroprotective and anti-oxidation properties. The present study aimed to investigate the protective effects of BHBA against epilepsy. C57BL/6 J mice were exposed to lithium chloride and pilocarpine to induce epilepsy and then were administrated with 300 mg/kg/day BHBA for 30 days. The learning impairment was evaluated via Morris Water Maze. Neuron loss and cell apoptosis were detected through Nissl staining and TUNEL staining. The levels of oxidative stress-related factors were determined by commercial kits. The protein expression levels of AMP-activated protein kinase (AMPK), p-AMPK, peroxisome proliferator-activated receptor alpha (PPARα), anti-apoptotic Bcl-2, and pro-apoptotic Bax were measured through Western blots. It was found BHBA improved epilepsy- caused learning deficiency and attenuated epilepsy-mediated neuron loss and cell apoptosis in the hippocampus. BHBA ameliorated oxidative stress via decreasing the levels of reactive oxygen species and malondialdehyde plus strengthening the activities of glutathione peroxidase and superoxide dismutase. BHBA also promoted the phosphorylation of AMPK and upregulated PPARα in the epileptic hippocampus. In conclusion, BHBA attenuates neuronal damage in epileptic mice, which is associated with its anti-apoptotic and anti-oxidative effects as well as the activation of AMPK and PPARα.

β-Ecdysterone protects SH-SY5Y cells against β-amyloid-induced apoptosis via c-Jun N-terminal kinase- and Akt-associated complementary pathways

Recently, the significantly higher incidence of Alzheimer's disease (AD) in women than in men has been attributed to the loss of neuroprotective estrogen after menopause. Does phytoestrogen have the ability to protect against amyloid-β (Aβ) toxicity? The aim of this study was to evaluate hypothesis that β-ecdysterone (β-Ecd) protects SH-SY5Y cells from Aβ-induced apoptosis by separate signaling pathways involving protein kinase B (Akt) and c-Jun N-terminal kinase (JNK). Here, we demonstrate that phytoestrogen β-Ecd inhibits Aβ-triggered mitochondrial apoptotic pathway, as indicated by Bcl-2/Bax ratio elevation, cytochrome c (cyt c) release reduction, and caspase-9 inactivation. Interestingly, β-Ecd upregulates Bcl-2 expression in SH-SY5Y cells under both basal and Aβ-challenged conditions, but downregulates Bax expression only in Aβ-challenged conditions. Subsequently, Akt-dependent NF-κB activation is required for Bcl-2 upregulation, but not Bax downregulation, in response to β-Ecd, which was validated by the use of LY294002 and Bay11-7082. Notably, β-Ecd attenuates the Aβ-evoked reactive oxygen species (ROS) production, apoptosis signal-regulating kinase 1 (ASK1) phosphorylation and JNK activation without altering the basal ASK1 phosphorylation and JNK activation. ROS-scavenging by diphenyleneiodonium (DPI) abrogated the ability of β-Ecd to alter the activation of ASK1. Simultaneously, inhibition of JNK by SP600125 abolished β-Ecd-induced Bax downregulation in Aβ-challenged SH-SY5Y cells, whereas LY294002 failed to do so. Consequently, β-Ecd possesses neuroprotection by different and complementary pathways, which together promote a Bcl-2/Bax ratio. These data support our hypothesis and suggest that β-Ecd is a promising candidate for the treatment of AD.

Intermittent Fasting Alleviates the Increase of Lipoprotein Lipase Expression in Brain of a Mouse Model of Alzheimer's Disease: Possibly Mediated by β-hydroxybutyrate

Intermittent fasting has been demonstrated to protect against Alzheimer's disease (AD), however, the mechanism is unclear. Histone acetylation and lipoprotein lipase (LPL) are involved in AD progression. Importantly, LPL has been documented to be regulated by histone deacetylases (HDACs) inhibitors (increase histone acetylation level) in adipocyte and mesenchymal stem cells, or by fasting in adipose and muscle tissues. In brain, however, whether histone acetylation or fasting regulates LPL expression is unknown. This study was designed to demonstrate intermittent fasting may protect against AD through increasing β-hydroxybutyrate, a HDACs inhibitor, to regulate LPL. We also investigated microRNA-29a expression associating with regulation of LPL and histone acetylation. The results showed LPL mRNA expression was increased and microRNA-29a expression was decreased in the cerebral cortex of AD model mice (APP/PS1), which were alleviated by intermittent fasting. No significant differences were found in the total expression of LPL protein (brain-derived and located in capillary endothelial cells from peripheral tissues) in the cerebral cortex of APP/PS1 mice. Further study indicated that LPL located in capillary endothelial cells was decreased in the cerebral cortex of APP/PS1 mice, which was alleviated by intermittent fasting. LPL and microRNA-29a expression were separately increased and down-regulated in 2 μM Aβ₂₅₋₃₅-exposed SH-SY5Y cells, but respectively decreased and up-regulated in 10 μM Aβ₂₅₋₃₅-exposed cells, which were all reversed by β-hydroxybutyrate. The increase of HDAC2/3 expression and the decrease of acetylated H3K9 and H4K12 levels were alleviated in APP/PS1 mice by intermittent fasting treatment, as well in 2 or 10 μM Aβ₂₅₋₃₅-exposed cells by β-hydroxybutyrate treatment. These findings above suggested the results from APP/PS1 mice were consistent with those from cells treated with 2 μM Aβ₂₅₋₃₅. Interestingly, LPL expression was reduced (0.2-folds) and microRNA-29a expression was up-regulated (1.7-folds) in HDAC2-silenced cells, but respectively increased (1.3-folds) and down-regulated (0.8-folds) in HDAC3-silenced cells. Furthermore, LPL expression was decreased in cells treated with microRNA-29a mimic and increased with inhibitor treatment. In conclusion, intermittent fasting inhibits the increase of brain-derived LPL expression in APP/PS1 mice partly through β-hydroxybutyrate-mediated down-regulation of microRNA-29a expression. HDAC2/3 may be implicated in the effect of β-hydroxybutyrate on microRNA-29a expression.

Intermittent Fasting Protects against Alzheimer's Disease Possible through Restoring Aquaporin-4 Polarity

The impairment of amyloid-β (Aβ) clearance in the brain plays a causative role in Alzheimer's disease (AD). Polarity distribution of aquaporin-4 (AQP4) is important to remove Aβ from brain. AQP4 polarity can be influenced by the ratio of two AQP4 isoforms M1 and M23 (AQP4-M1/M23), however, it is unknown whether the ratio of AQP4-M1/M23 changes in AD. Histone deacetylase 3 has been reported to be significantly increased in AD brain. Moreover, evidence indicated that microRNA-130a (miR-130a) possibly mediates the regulation of histone deacetylase 3 on AQP4-M1/M23 ratio by repressing the transcriptional activity of AQP4-M1 in AD. This study aimed to investigate whether intermittent fasting (IF), increasing the level of an endogenous histone deacetylases inhibitor β-hydroxybutyrate, restores AQP4 polarity via miR-130a mediated reduction of AQP4-M1/M23 ratio in protection against AD. The results showed that IF ameliorated cognitive dysfunction, prevented brain from Aβ deposition, and restored the AQP4 polarity in a mouse model of AD (APP/PS1 double-transgenic mice). Additionally, IF down-regulated the expression of AQP4-M1 and histone deacetylase 3, reduced AQP4-M1/M23 ratio, and increased miR-130a expression in the cerebral cortex of APP/PS1 mice. In vitro, β-hydroxybutyrate was found to down-regulate the expression of AQP4-M1 and histone deacetylase 3, reduce AQP4-M1/M23 ratio, and increase AQP4-M23 and miR-130a expression in 2 μM Aβ-treated U251 cells. Interestingly, on the contrary to the result observed in 2 μM Aβ-treated cells, AQP4 expression was obviously decreased in cells exposed to 10 μM Aβ. miR-130a mimic decreased the expression of AQP4-M1 and the ratio of AQP4-M1/M23, as well as silencing histone deacetylase 3 caused the up-regulation of AQP4 and miR-130a, and the reduction of AQP4-M1/M23 ratio in U251 cells. In conclusion, IF exhibits beneficial effects against AD. The mechanism may be associated with recovery of AQP4 polarity, resulting from the reduction of AQP4-M1/M23 ratio. Furthermore, β-hydroxybutyrate may partly mediate the effect of IF on the reduction of AQP4-M1/M23 ratio in AD, in which miR-130a and histone deacetylase 3 may be implicated.

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

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

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

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

D-β-hydroxybutyrate promotes functional recovery and relieves pain hypersensitivity in mice with spinal cord injury

BACKGROUND AND PURPOSE

Spinal cord injury (SCI) leads to severe motor and sensory dysfunction and significantly reduces the quality of life. The aim of the present work was to investigate the effect of administration of exogenous D-β-hydroxybutyrate (DBHB) on functional recovery and neuropathic pain in spinal cord-injured mice.

EXPERIMENTAL APPROACH

Mice were given a moderate-severe thoracic spinal contusion injury at the T_9-10 level and treated with exogenous DBHB.

KEY RESULTS

Treatment of SCI mice with DBHB markedly improved locomotor function and relieved SCI-induced hypersensitivities to mechanical and thermal stimulation. DBHB treatment partly prevented the SCI-induced loss of motor neurons and suppressed microglial and glial activation. DBHB treatment enhanced histone acetylation and up-regulated expression of the transcription factor FOXO3a, catalase and SOD2 in injured region of SCI mice. DBHB treatment suppressed SCI-induced NLRP3 inflammasome activation and reduced protein expression of IL-1β and IL-18. In addition, DBHB treatment improved mitochondrial function and abated oxidative stress following SCI.

CONCLUSIONS AND IMPLICATIONS

DBHB promoted functional recovery and relieved pain hypersensitivity in mice with SCI, possibly through inhibition of histone deacetylation and NLRP3 inflammasome activation and preservation of mitochondrial function. DBHB could thus be envisaged as a potential use of interventions for SCI but remains to be tested in humans.

NLRP3 Inflammasome in Neurological Diseases, from Functions to Therapies

Neuroinflammation has been identified as a causative factor of multiple neurological diseases. The nucleotide-binding oligomerization domain-, leucine-rich repeat- and pyrin domain-containing 3 (NLRP3) inflammasome, a subcellular multiprotein complex that is abundantly expressed in the central nervous system (CNS), can sense and be activated by a wide range of exogenous and endogenous stimuli such as microbes, aggregated and misfolded proteins, and adenosine triphosphate, which results in activation of caspase-1. Activated caspase-1 subsequently leads to the processing of interleukin-1β (IL-1β) and interleukin-18 (IL-18) pro-inflammatory cytokines and mediates rapid cell death. IL-1β and IL-18 drive inflammatory responses through diverse downstream signaling pathways, leading to neuronal damage. Thus, the NLRP3 inflammasome is considered a key contributor to the development of neuroinflammation. In this review article, we briefly discuss the structure and activation the NLRP3 inflammasome and address the involvement of the NLRP3 inflammasome in several neurological disorders, such as brain infection, acute brain injury and neurodegenerative diseases. In addition, we review a series of promising therapeutic approaches that target the NLRP3 inflammasome signaling including anti-IL-1 therapy, small molecule NLRP3 inhibitors and other compounds, however, these approaches are still experimental in neurological diseases. At present, it is plausible to generate cell-specific conditional NLRP3 knockout (KO) mice via the Cre system to investigate the role of the NLRP3 inflammasome, which may be instrumental in the development of novel pharmacologic investigations for neuroinflammation-associated diseases.

Scrutiny of the mechanism of small molecule inhibitor preventing conformational transition of amyloid-β42 monomer: insights from molecular dynamics simulations

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by loss of intellectual functioning of brain and memory loss. According to amyloid cascade hypothesis, aggregation of amyloid-β₄₂ (Aβ₄₂) peptide can generate toxic oligomers and their accumulation in the brain is responsible for the onset of AD. In spite of carrying out a large number of experimental studies on inhibition of Aβ₄₂ aggregation by small molecules, the detailed inhibitory mechanism remains elusive. In the present study, comparable molecular dynamics (MD) simulations were performed to elucidate the inhibitory mechanism of a sulfonamide inhibitor C1 (2,5-dichloro-N-(4-piperidinophenyl)-3-thiophenesulfonamide), reported for its in vitro and in vivo anti-aggregation activity against Aβ₄₂. MD simulations reveal that C1 stabilizes native α-helix conformation of Aβ₄₂ by interacting with key residues in the central helix region (13-26) with hydrogen bonds and π-π interactions. C1 lowers the solvent-accessible surface area of the central hydrophobic core (CHC), KLVFF (16-20), that confirms burial of hydrophobic residues leading to the dominance of helical conformation in the CHC region. The binding free energy analysis with MM-PBSA demonstrates that Ala2, Phe4, Tyr10, Gln15, Lys16, Leu17, Val18, Phe19, Phe20, Glu22, and Met35 contribute maximum to binding free energy (-43.1 kcal/mol) between C1 and Aβ₄₂ monomer. Overall, MD simulations reveal that C1 inhibits Aβ₄₂ aggregation by stabilizing native helical conformation and inhibiting the formation of aggregation-prone β-sheet conformation. The present results will shed light on the underlying inhibitory mechanism of small molecules that show potential in vitro anti-aggregation activity against Aβ₄₂.

Neuroprotective Strategies during Cardiac Surgery with Cardiopulmonary Bypass

Aortocoronary bypass or valve surgery usually require cardiac arrest using cardioplegic solutions. Although, in principle, in a number of cases beating heart surgery (so-called off-pump technique) is possible, aortic or valve surgery or correction of congenital heart diseases mostly require cardiopulmonary arrest. During this condition, the heart-lung machine also named cardiopulmonary bypass (CPB) has to take over the circulation. It is noteworthy that the invention of a machine bypassing the heart and lungs enabled complex cardiac operations, but possible negative effects of the CPB on other organs, especially the brain, cannot be neglected. Thus, neuroprotection during CPB is still a matter of great interest. In this review, we will describe the impact of CPB on the brain and focus on pharmacological and non-pharmacological strategies to protect the brain.

Ketogenic diet decreases oxidative stress and improves mitochondrial respiratory complex activity

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

Nrf2--a therapeutic target for the treatment of neurodegenerative diseases

The brain is very sensitive to changes in redox status; thus maintaining redox homeostasis in the brain is critical for the prevention of accumulating oxidative damage. Aging is the primary risk factor for developing neurodegenerative diseases. In addition to age, genetic and environmental risk factors have also been associated with disease development. The primary reactive insults associated with the aging process are a result of oxidative stress (OS) and nitrosative stress (NS). Markers of increased oxidative stress, protein and DNA modification, inflammation, and dysfunctional proteostasis have all been implicated in contributing to the progression of neurodegeneration. The ability of the cell to combat OS/NS and maintain a clearance mechanism for misfolded aggregating proteins determines whether or not it will survive. A critical pathway in this regard is the Nrf2 (nuclear factor erythroid 2-related factor 2)- antioxidant response element (ARE) pathway. Nrf2 activation has been shown to mitigate a number of pathologic mechanisms associated with Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis. This review will focus on the role of Nrf2 in these diseases and the potential for Nrf2 activation to attenuate disease progression.