Modified ketogenic diet is associated with improved cerebrospinal fluid biomarker profile, cerebral perfusion, and cerebral ketone body uptake in older adults at risk for Alzheimer's disease: a pilot study

Exploratory Dual PET imaging of [18F] fluorodeoxyglucose and [11C]acetoacetate in type 2 diabetic nonhuman primates

Despite recent advancements in imaging (amyloid-PET & tau-PET) and fluid (Aβ42/Aβ40 & Aβ42/ptau) biomarkers, the current standard for in vivo assessment of AD, diagnosis and prediction of Alzheimer's disease (AD) remains challenging. We demonstrated in nonhuman primates (NHP) that increased plasma and cerebrospinal fluid (CSF) glucose correlated with decreased CSF Aβ42 and CSF Aβ40, a hallmark of plaque promoting pathogenesis. Together, our findings demonstrate that altered glucose homeostasis and insulin resistance are associated with Aβ and amyloid in rodent and NHP models. This warranted further exploration into the dynamics of altered brain metabolism in the NHP model of T2D, cross referenced with CSF and blood-based AD markers. Preliminary dual PET ([11C]acetoacetate ([11C]AcAc) and [18F]fluorodeoxyglucose ([18F]FDG) imaging studies were conducted in an aged cohort of NHPs classified as T2D (n = 5) and pre-diabetic (n = 1) along with corresponding plasma and CSF samples for metabolite analysis. [11C]AcAc and [18F]FDG PET brain standard uptake values (SUV) were highly positively associated (r = 0.88, p = 0.02) in the T2D and pre-diabetic NHPs. Age was not significantly associated with brain SUV (age range 16.5-23.5 years old). Metabolic measures were positively correlated with brain [18F]FDG and CSF Aβ42:40 was positively correlated to fasting glucose values. Although our findings suggest moderate correlations, this study further elucidates that peripheral insulin resistance and poor glycemia control alter AD-related pathology, illustrating how T2D is a risk factor for AD.

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.

Take the bull by the horns and tackle the potential downsides of the ketogenic diet

The ketogenic diet (KD) is a distinctive dietary regimen known for its low-carbohydrate and high-fat composition. Recently, it has garnered considerable interest from the scientific community and the general population because of its claimed efficacy in facilitating weight reduction, improving the management of glucose levels, and raising overall energy levels. The core principle of the KD is the substantial decrease in carbohydrate consumption, which is subsequently substituted by ingesting nourishing fats. While the KD has promising advantages and is gaining popularity, it must be acknowledged that this dietary method may not be appropriate for all individuals. The dietary regimen may give rise to adverse effects, including constipation, halitosis, and imbalances in electrolyte levels, which may pose a potential risk if not adequately supervised. Hence, thorough and meticulous inquiry is needed to better comprehend the possible hazards and advantages linked to the KD over prolonged durations. By obtaining a more comprehensive perspective, we can enhance our ability to make well-informed judgments and suggestions as to implementation of this specific dietary regimen.

Lower GLUT1 and unchanged MCT1 in Alzheimer's disease cerebrovasculature

The brain is a highly demanding organ, utilizing mainly glucose but also ketone bodies as sources of energy. Glucose transporter-1 (GLUT1) and monocarboxylates transporter-1 (MCT1) respectively transport glucose and ketone bodies across the blood-brain barrier. While reduced glucose uptake by the brain is one of the earliest signs of Alzheimer's disease (AD), no change in the uptake of ketone bodies has been evidenced yet. To probe for changes in GLUT1 and MCT1, we performed Western immunoblotting in microvessel extracts from the parietal cortex of 60 participants of the Religious Orders Study. Participants clinically diagnosed with AD had lower cerebrovascular levels of GLUT1, whereas MCT1 remained unchanged. GLUT1 reduction was associated with lower cognitive scores. No such association was found for MCT1. GLUT1 was inversely correlated with neuritic plaques and cerebrovascular β-secretase-derived fragment levels. No other significant associations were found between both transporters, markers of Aβ and tau pathologies, sex, age at death or apolipoprotein-ε4 genotype. These results suggest that, while a deficit of GLUT1 may underlie the reduced transport of glucose to the brain in AD, no such impairment occurs for MCT1. This study thus supports the exploration of ketone bodies as an alternative energy source for the aging brain.

Ketone body metabolism and the NLRP3 inflammasome in Alzheimer's disease

Alzheimer's disease (AD) is a degenerative brain disorder and the most common form of dementia. AD pathology is characterized by senile plaques and neurofibrillary tangles (NFTs) composed of amyloid-β (Aβ) and hyperphosphorylated tau, respectively. Neuroinflammation has been shown to drive Aβ and tau pathology, with evidence suggesting the nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome as a key pathway in AD pathogenesis. NLRP3 inflammasome activation in microglia, the primary immune effector cells of the brain, results in caspase-1 activation and secretion of IL-1β and IL-18. Recent studies have demonstrated a dramatic interplay between the metabolic state and effector functions of immune cells. Microglial metabolism in AD is of particular interest, as ketone bodies (acetone, acetoacetate (AcAc), and β-hydroxybutyrate (BHB)) serve as an alternative energy source when glucose utilization is compromised in the brain of patients with AD. Furthermore, reduced cerebral glucose metabolism concomitant with increased BHB levels has been demonstrated to inhibit NLRP3 inflammasome activation. Here, we review the role of the NLRP3 inflammasome and microglial ketone body metabolism in AD pathogenesis. We also highlight NLRP3 inflammasome inhibition by several ketone body therapies as a promising new treatment strategy for AD.

Association of diabetes mellitus with dementia- and non-dementia-related mortality amongst women: a secondary competing risks analysis of the California Teachers Study

BACKGROUND AND PURPOSE

The prevalence of dementia is rapidly increasing. Attempts to further understand modifiable risk factors such as diabetes mellitus (DM) are urgently needed to inform public health policies for prevention. Thus, the objective of the current study was to assess the relationship between DM and risk of dementia and non-dementia mortality amongst women in the California Teachers Study prospective cohort.

METHODS

Women (n = 124,509) aged 22-104 years at baseline were included. DM was ascertained from self-reported questionnaires and hospital-linked records. Dementia-related deaths were ascertained from state and national records. Competing risk regression models were used to estimate cause-specific hazard ratios and 95% confidence intervals for the association of DM with dementia- and non-dementia-related mortality.

RESULTS

There were 10,511 total DM cases and 3625 deaths due to dementia over a mean of 21.3 years of follow-up. Fully adjusted cause-specific hazard ratios of the association with DM were 2.26 (2.01, 2.55) for dementia-related and 1.97 (1.89, 2.05) for the competing risk of non-dementia-related mortality. This association was strongest amongst participants with incident DM, younger age at baseline and higher alcohol consumption or who were overweight.

CONCLUSIONS

In the California Teachers Study, women with DM had increased risk of mortality due to both dementia and non-dementia causes; however, the risk of mortality due to dementia was elevated compared to non-dementia causes only amongst participants with incident DM.

Adiposity, immunity, and inflammation: interrelationships in health and disease: a report from 24th Annual Harvard Nutrition Obesity Symposium, June 2023

The rapidly evolving field of immunometabolism explores how changes in local immune environments may affect key metabolic and cellular processes, including that of adipose tissue. Importantly, these changes may contribute to low-grade systemic inflammation. In turn, chronic low-grade inflammation affecting adipose tissue may exacerbate the outcome of metabolic diseases. Novel advances in our understanding of immunometabolic processes may critically lead to interventions to reduce disease severity and progression. An important example in this regard relates to obesity, which has a multifaceted effect on immunity, activating the proinflammatory pathways such as the inflammasome and disrupting cellular homeostasis. This multifaceted effect of obesity can be investigated through study of downstream conditions using cellular and systemic investigative techniques. To further explore this field, the National Institutes of Health P30 Nutrition Obesity Research Center at Harvard, in partnership with Harvard Medical School, assembled experts to present at its 24th Annual Symposium entitled "Adiposity, Immunity, and Inflammation: Interrelationships in Health and Disease" on 7 June, 2023. This manuscript seeks to synthesize and present key findings from the symposium, highlighting new research and novel disease-specific advances in the field. Better understanding the interaction between metabolism and immunity offers promising preventative and treatment therapies for obesity-related immunometabolic diseases.

Serum and CSF metabolomics analysis shows Mediterranean Ketogenic Diet mitigates risk factors of Alzheimer's disease

Alzheimer's disease (AD) is influenced by a variety of modifiable risk factors, including a person's dietary habits. While the ketogenic diet (KD) holds promise in reducing metabolic risks and potentially affecting AD progression, only a few studies have explored KD's metabolic impact, especially on blood and cerebrospinal fluid (CSF). Our study involved participants at risk for AD, either cognitively normal or with mild cognitive impairment. The participants consumed both a modified Mediterranean Ketogenic Diet (MMKD) and the American Heart Association diet (AHAD) for 6 weeks each, separated by a 6-week washout period. We employed nuclear magnetic resonance (NMR)-based metabolomics to profile serum and CSF and metagenomics profiling on fecal samples. While the AHAD induced no notable metabolic changes, MMKD led to significant alterations in both serum and CSF. These changes included improved modifiable risk factors, like increased HDL-C and reduced BMI, reversed serum metabolic disturbances linked to AD such as a microbiome-mediated increase in valine levels, and a reduction in systemic inflammation. Additionally, the MMKD was linked to increased amino acid levels in the CSF, a breakdown of branched-chain amino acids (BCAAs), and decreased valine levels. Importantly, we observed a strong correlation between metabolic changes in the CSF and serum, suggesting a systemic regulation of metabolism. Our findings highlight that MMKD can improve AD-related risk factors, reverse some metabolic disturbances associated with AD, and align metabolic changes across the blood-CSF barrier.

Polyphenols and Diets as Current and Potential Nutrition Senotherapeutics in Alzheimer's Disease: Findings from Clinical Trials

Cellular senescence, a hallmark of aging, plays an important role in age-related conditions among older adults. Targeting senescent cells and its phenotype may provide a promising strategy to delay the onset or progression of Alzheimer's disease (AD). In this review article, we investigated efficacy and safety of nutrition senotherapy in AD, with a focus on the role of polyphenols as current and potential nutrition senotherapeutic agents, as well as relevant dietary patterns. Promising results with neuroprotective effects of senotherapeutic agents such as quercetin, resveratrol, Epigallocatechin-gallate, curcumin and fisetin were reported from preclinical studies. However, in-human trials remain limited, and findings were inconclusive. In future, nutrition senotherapeutic agents should be studied both individually and within dietary patterns, through the perspective of cellular senescence and AD. Further studies are warranted to investigate bioavailability, dosing regimen, long term effects of nutrition senotherapy and provide better understanding of the underlying mechanisms. Collaboration between researchers needs to be established, and methodological limitations of current studies should be addressed.

Enhancing of cerebral Abeta clearance by modulation of ABC transporter expression: a review of experimental approaches

Clearance of amyloid-beta (Aβ) from the brain is impaired in both early-onset and late-onset Alzheimer's disease (AD). Mechanisms for clearing cerebral Aβ include proteolytic degradation, antibody-mediated clearance, blood brain barrier and blood cerebrospinal fluid barrier efflux, glymphatic drainage, and perivascular drainage. ATP-binding cassette (ABC) transporters are membrane efflux pumps driven by ATP hydrolysis. Their functions include maintenance of brain homeostasis by removing toxic peptides and compounds, and transport of bioactive molecules including cholesterol. Some ABC transporters contribute to lowering of cerebral Aβ. Mechanisms suggested for ABC transporter-mediated lowering of brain Aβ, in addition to exporting of Aβ across the blood brain and blood cerebrospinal fluid barriers, include apolipoprotein E lipidation, microglial activation, decreased amyloidogenic processing of amyloid precursor protein, and restricting the entrance of Aβ into the brain. The ABC transporter superfamily in humans includes 49 proteins, eight of which have been suggested to reduce cerebral Aβ levels. This review discusses experimental approaches for increasing the expression of these ABC transporters, clinical applications of these approaches, changes in the expression and/or activity of these transporters in AD and transgenic mouse models of AD, and findings in the few clinical trials which have examined the effects of these approaches in patients with AD or mild cognitive impairment. The possibility that therapeutic upregulation of ABC transporters which promote clearance of cerebral Aβ may slow the clinical progression of AD merits further consideration.

Nutrient-epigenome interactions: Implications for personalized nutrition against aging-associated diseases

Aging is a multifaceted process involving genetic and environmental interactions often resulting in epigenetic changes, potentially leading to aging-related diseases. Various strategies, like dietary interventions and calorie restrictions, have been employed to modify these epigenetic landscapes. A burgeoning field of interest focuses on the role of microbiota in human health, emphasizing system biology and computational approaches. These methods help decipher the intricate interplay between diet and gut microbiota, facilitating the creation of personalized nutrition strategies. In this review, we analysed the mechanisms related to nutritional interventions while highlighting the influence of dietary strategies, like calorie restriction and intermittent fasting, on microbial composition and function. We explore how gut microbiota affects the efficacy of interventions using tools like multi-omics data integration, network analysis, and machine learning. These tools enable us to pinpoint critical regulatory elements and generate individualized models for dietary responses. Lastly, we emphasize the need for a deeper comprehension of nutrient-epigenome interactions and the potential of personalized nutrition informed by individual genetic and epigenetic profiles. As knowledge and technology advance, dietary epigenetics stands on the cusp of reshaping our strategy against aging and related diseases.

The interaction between Mediterranean diet and intestinal microbiome: relevance for preventive strategies against frailty in older individuals

Age-related changes in intestinal microbiome composition and function are increasingly recognized as pivotal in the pathophysiology of aging and are associated with the aging phenotype. Diet is a major determinant of gut-microbiota composition throughout the entire lifespan, and several of the benefits of a healthy diet in aging could be mediated by the microbiome. Mediterranean diet (MD) is a traditional dietary pattern regarded as the healthy diet paradigm, and a large number of studies have demonstrated its benefits in promoting healthy aging. MD has also a positive modulatory effect on intestinal microbiome, favoring bacterial taxa involved in the synthesis of several bioactive compounds, such as short-chain fatty acids (SCFAs), that counteract inflammation, anabolic resistance, and tissue degeneration. Intervention studies conducted in older populations have suggested that the individual response of older subjects to MD, in terms of reduction of frailty scores and amelioration of cognitive function, is significantly mediated by the gut-microbiota composition and functionality. In this context, the pathophysiology of intestinal microbiome in aging should be considered when designing MD-based interventions tailored to the needs of geriatric patients.

A randomized feasibility trial of the modified Atkins diet in older adults with mild cognitive impairment due to Alzheimer's disease

Background

Alzheimer's disease (AD) is increasing in prevalence, but effective treatments for its cognitive impairment remain severely limited. This study investigates the impact of ketone body production through dietary manipulation on memory in persons with mild cognitive impairment due to early AD and explores potential mechanisms of action.

Methods

We conducted a 12-week, parallel-group, controlled feasibility trial of a ketogenic diet, the modified Atkins diet (MAD), compared to a control diet in patients with cognitive impairments attributed to AD. We administered neuropsychological assessments, including memory tests, and collected blood samples at baseline and after 12 weeks of intervention. We performed untargeted lipidomic and targeted metabolomic analyses on plasma samples to detect changes over time.

Results

A total of 839 individuals were screened to yield 38 randomized participants, with 20 assigned to receive MAD and 18 assigned to receive a control diet. Due to attrition, only 13 in the MAD arm and nine in the control arm were assessed for the primary endpoint, with two participants meeting ketosis levels used to define MAD adherence criteria. The average change from baseline in the Memory Composite Score was 1.37 (95% CI: -0.87, 4.90) points higher in the MAD group compared to the control group. The effect size of the intervention on baseline MAD change was moderate (Cohen's D = 0.57, 95% CI: -0.67, 1.33). In the 15 participants (nine MAD, six control) assessed for lipidomic and metabolomic-lipidomics and metabolomics, 13 metabolites and 10 lipids showed significant changes from baseline to 12 weeks, including triacylglycerols (TAGs, 50:5, 52:5, and 52:6), sphingomyelins (SM, 44:3, 46:0, 46:3, and 48:1), acetoacetate, fatty acylcarnitines, glycerol-3-phosphate, and hydroxy fatty acids.

Conclusions

Attrition was greatest between baseline and week 6. All participants retained at week 6 completed the study. Despite low rates of adherence by criteria defined a priori, lipidomic and metabolomic analyses indicate significant changes from baseline in circulating lipids and metabolites between MAD and control participants at 12-week postrandomization, and MAD participants showed greater, albeit nonsignificant, improvement in memory.

Role of ketogenic diet in neurodegenerative diseases focusing on Alzheimer diseases: The guardian angle

The ketogenic diet (KD) is a low-carbohydrate, adequate protein and high-fat diet. KD is primarily used to treat refractory epilepsy. KD was shown to be effective in treating different neurodegenerative diseases. Alzheimer disease (AD) is the first common neurodegenerative disease in the world characterized by memory and cognitive impairment. However, the underlying mechanism of KD in controlling of AD and other neurodegenerative diseases are not discussed widely. Therefore, this review aims to revise the fundamental mechanism of KD in different neurodegenerative diseases focusing on the AD. KD induces a fasting-like which modulates the central and peripheral metabolism by regulating mitochondrial dysfunction, oxidative stress, inflammation, gut-flora, and autophagy in different neurodegenerative diseases. Different studies highlighted that KD improves AD neuropathology by regulating synaptic neurotransmission and inhibiting of neuroinflammation and oxidative stress. In conclusion, KD improves cognitive function and attenuates the progression of AD neuropathology by reducing oxidative stress, mitochondrial dysfunction, and enhancing neuronal autophagy and brain BDNF.

Existing and Future Strategies to Manipulate the Gut Microbiota With Diet as a Potential Adjuvant Treatment for Psychiatric Disorders

Nutrition and diet quality play key roles in preventing and slowing cognitive decline and have been linked to multiple brain disorders. This review compiles available evidence from preclinical studies and clinical trials on the impact of nutrition and interventions regarding major psychiatric conditions and some neurological disorders. We emphasize the potential role of diet-related microbiome alterations in these effects and highlight commonalities between various brain disorders related to the microbiome. Despite numerous studies shedding light on these findings, there are still gaps in our understanding due to the limited availability of definitive human trial data firmly establishing a causal link between a specific diet and microbially mediated brain functions and symptoms. The positive impact of certain diets on the microbiome and cognitive function is frequently ascribed with the anti-inflammatory effects of certain microbial metabolites or a reduction of proinflammatory microbial products. We also critically review recent research on pro- and prebiotics and nondietary interventions, particularly fecal microbiota transplantation. The recent focus on diet in relation to brain disorders could lead to improved treatment outcomes with combined dietary, pharmacological, and behavioral interventions.

Emergence of Extracellular Vesicles as "Liquid Biopsy" for Neurological Disorders: Boom or Bust

Extracellular vesicles (EVs) have emerged as an attractive liquid biopsy approach in the diagnosis and prognosis of multiple diseases and disorders. The feasibility of enriching specific subpopulations of EVs from biofluids based on their unique surface markers has opened novel opportunities to gain molecular insight from various tissues and organs, including the brain. Over the past decade, EVs in bodily fluids have been extensively studied for biomarkers associated with various neurological disorders, such as Alzheimer's disease, Parkinson's disease, schizophrenia, bipolar disorder, major depressive disorders, substance use disorders, human immunodeficiency virus-associated neurocognitive disorder, and cancer/treatment-induced neurodegeneration. These studies have focused on the isolation and cargo characterization of either total EVs or brain cells, such as neuron-, astrocyte-, microglia-, oligodendrocyte-, pericyte-, and endothelial-derived EVs from biofluids to achieve early diagnosis and molecular characterization and to predict the treatment and intervention outcomes. The findings of these studies have demonstrated that EVs could serve as a repetitive and less invasive source of valuable molecular information for these neurological disorders, supplementing existing costly neuroimaging techniques and relatively invasive measures, like lumbar puncture. However, the initial excitement surrounding blood-based biomarkers for brain-related diseases has been tempered by challenges, such as lack of central nervous system specificity in EV markers, lengthy protocols, and the absence of standardized procedures for biological sample collection, EV isolation, and characterization. Nevertheless, with rapid advancements in the EV field, supported by improved isolation methods and sensitive assays for cargo characterization, brain cell-derived EVs continue to offer unparallel opportunities with significant translational implications for various neurological disorders. SIGNIFICANCE STATEMENT: Extracellular vesicles present a less invasive liquid biopsy approach in the diagnosis and prognosis of various neurological disorders. Characterizing these vesicles in biofluids holds the potential to yield valuable molecular information, thereby significantly impacting the development of novel biomarkers for various neurological disorders. This paper has reviewed the methodology employed to isolate extracellular vesicles derived from various brain cells in biofluids, their utility in enhancing the molecular understanding of neurodegeneration, and the potential challenges in this research field.

Novel insights into brain lipid metabolism in Alzheimer's disease: Oligodendrocytes and white matter abnormalities

Alzheimer's disease (AD) is the most common cause of dementia. A genome-wide association study has shown that several AD risk genes are involved in lipid metabolism. Additionally, epidemiological studies have indicated that the levels of several lipid species are altered in the AD brain. Therefore, lipid metabolism is likely changed in the AD brain, and these alterations might be associated with an exacerbation of AD pathology. Oligodendrocytes are glial cells that produce the myelin sheath, which is a lipid-rich insulator. Dysfunctions of the myelin sheath have been linked to white matter abnormalities observed in the AD brain. Here, we review the lipid composition and metabolism in the brain and myelin and the association between lipidic alterations and AD pathology. We also present the abnormalities in oligodendrocyte lineage cells and white matter observed in AD. Additionally, we discuss metabolic disorders, including obesity, as AD risk factors and the effects of obesity and dietary intake of lipids on the brain.

The Role of Diet and Gut Microbiota in Alzheimer's Disease

Alzheimer's disease (AD), the most prevalent form of dementia, is characterized by the accumulation of amyloid-beta (Aβ) plaques and hyperphosphorylated tau tangles. Currently, Alzheimer's disease (AD) impacts 50 million individuals, with projections anticipating an increase to 152 million by the year 2050. Despite the increasing global prevalence of AD, its underlying pathology remains poorly understood, posing challenges for early diagnosis and treatment. Recent research suggests a link between gut dysbiosis and the aggregation of Aβ, the development of tau proteins, and the occurrence of neuroinflammation and oxidative stress are associated with AD. However, investigations into the gut-brain axis (GBA) in the context of AD progression and pathology have yielded inconsistent findings. This review aims to enhance our understanding of microbial diversity at the species level and the role of these species in AD pathology. Additionally, this review addresses the influence of confounding elements, including diet, probiotics, and prebiotics, on AD throughout different stages (preclinical, mild cognitive impairment (MCI), and AD) of its progression.

New Insights into the Relationship between Nutrition and Neuroinflammation in Alzheimer's Disease: Preventive and Therapeutic Perspectives

Neurodegenerative diseases are progressive brain disorders characterized by inexorable synaptic dysfunction and neuronal loss. Since the most consistent risk factor for developing neurodegenerative diseases is aging, the prevalence of these disorders is intended to increase with increasing life expectancy. Alzheimer's disease is the most common cause of neurodegenerative dementia, representing a significant medical, social, and economic burden worldwide. Despite growing research to reach an early diagnosis and optimal patient management, no disease-modifying therapies are currently available. Chronic neuroinflammation has been recognized as a crucial player in sustaining neurodegenerative processes, along with pathological deposition of misfolded proteins, including amyloid-β and tau protein. Modulating neuroinflammatory responses may be a promising therapeutic strategy in future clinical trials. Among factors that are able to regulate neuroinflammatory mechanisms, diet, and nutrients represent easily accessible and modifiable lifestyle components. Mediterranean diet and several nutrients, including polyphenols, vitamins, and omega-3 polyunsaturated fatty acids, can exert antioxidant and anti-inflammatory properties, impacting clinical manifestations, cognitive decline, and dementia. This review aims to provide an updated overview of the relationship between neuroinflammation, nutrition, gut microbiota, and neurodegeneration. We summarize the major studies exploring the effects of diet regimes on cognitive decline, primarily focusing on Alzheimer's disease dementia and the impact of these results on the design of ongoing clinical trials.

A Potential Role for the Ketogenic Diet in Alzheimer's Disease Treatment: Exploring Pre-Clinical and Clinical Evidence

Given the remarkable progress in global health and overall quality of life, the significant rise in life expectancy has become intertwined with the surging occurrence of neurodegenerative disorders (NDs). This emerging trend is poised to pose a substantial challenge to the fields of medicine and public health in the years ahead. In this context, Alzheimer's disease (AD) is regarded as an ND that causes recent memory loss, motor impairment and cognitive deficits. AD is the most common cause of dementia in the elderly and its development is linked to multifactorial interactions between the environment, genetics, aging and lifestyle. The pathological hallmarks in AD are the accumulation of β-amyloid peptide (Aβ), the hyperphosphorylation of tau protein, neurotoxic events and impaired glucose metabolism. Due to pharmacological limitations and in view of the prevailing glycemic hypometabolism, the ketogenic diet (KD) emerges as a promising non-pharmacological possibility for managing AD, an approach that has already demonstrated efficacy in addressing other disorders, notably epilepsy. The KD consists of a food regimen in which carbohydrate intake is discouraged at the expense of increased lipid consumption, inducing metabolic ketosis whereby the main source of energy becomes ketone bodies instead of glucose. Thus, under these dietary conditions, neuronal death via lack of energy would be decreased, inasmuch as the metabolism of lipids is not impaired in AD. In this way, the clinical picture of patients with AD would potentially improve via the slowing down of symptoms and delaying of the progression of the disease. Hence, this review aims to explore the rationale behind utilizing the KD in AD treatment while emphasizing the metabolic interplay between the KD and the improvement of AD indicators, drawing insights from both preclinical and clinical investigations. Via a comprehensive examination of the studies detailed in this review, it is evident that the KD emerges as a promising alternative for managing AD. Moreover, its efficacy is notably enhanced when dietary composition is modified, thereby opening up innovative avenues for decreasing the progression of AD.

Molecular Mechanisms of Neuroprotection by Ketone Bodies and Ketogenic Diet in Cerebral Ischemia and Neurodegenerative Diseases

Ketone bodies (KBs), such as acetoacetate and β-hydroxybutyrate, serve as crucial alternative energy sources during glucose deficiency. KBs, generated through ketogenesis in the liver, are metabolized into acetyl-CoA in extrahepatic tissues, entering the tricarboxylic acid cycle and electron transport chain for ATP production. Reduced glucose metabolism and mitochondrial dysfunction correlate with increased neuronal death and brain damage during cerebral ischemia and neurodegeneration. Both KBs and the ketogenic diet (KD) demonstrate neuroprotective effects by orchestrating various cellular processes through metabolic and signaling functions. They enhance mitochondrial function, mitigate oxidative stress and apoptosis, and regulate epigenetic and post-translational modifications of histones and non-histone proteins. Additionally, KBs and KD contribute to reducing neuroinflammation and modulating autophagy, neurotransmission systems, and gut microbiome. This review aims to explore the current understanding of the molecular mechanisms underpinning the neuroprotective effects of KBs and KD against brain damage in cerebral ischemia and neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease.

Low-carbohydrate and ketogenic diets: a scoping review of neurological and inflammatory outcomes in human studies and their relevance to chronic pain

Dietary restriction of carbohydrate has been demonstrated to be beneficial for nervous system dysfunction in animal models and may be beneficial for human chronic pain. The purpose of this review is to assess the impact of a low-carbohydrate/ketogenic diet on the adult nervous system function and inflammatory biomarkers to inform nutritional research for chronic pain. An electronic database search was carried out in May 2021. Publications were screened for prospective research with dietary carbohydrate intake <130 g per day and duration of ≥2 weeks. Studies were categorised into those reporting adult neurological outcomes to be extracted for analysis and those reporting other adult research outcomes. Both groups were screened again for reported inflammatory biomarkers. From 1548 studies, there were 847 studies included. Sixty-four reported neurological outcomes with 83% showing improvement. Five hundred and twenty-three studies had a different research focus (metabolic n = 394, sport/performance n = 51, cancer n = 33, general n = 30, neurological with non-neuro outcomes n = 12, or gastrointestinal n = 4). The second screen identified sixty-three studies reporting on inflammatory biomarkers, with 71% reporting a reduction in inflammation. The overall results suggest a favourable outcome on the nervous system and inflammatory biomarkers from a reduction in dietary carbohydrates. Both nervous system sensitisation and inflammation occur in chronic pain, and the results from this review indicate it may be improved by low-carbohydrate nutritional therapy. More clinical trials within this population are required to build on the few human trials that have been done.

Effects of the ketogenic diet on cognition: a systematic review

INTRODUCTION

Ketogenic diet (KD) therapy has been used as a dietary intervention in drug-resistant epilepsy for several years. Research currently suggests that KD therapy may carry neuroprotective and cognition enhancing effects for individuals with non-epileptic conditions as well as for healthy individuals. Therefore, KD may have potential as a non-invasive, nutritional treatment approach for difficult to manage conditions such as neurodegenerative illnesses or mood disorders. The aim of this review is to summarize the available evidence on ketogenic interventions and the resulting cognitive outcomes.

MATERIALS AND METHODS

The paper was based on PRISMA 2020 guidelines. The search was conducted in June 2021 on the following databases: CENTRAL, PubMed, EMBASE, PsycInfo, Web of Science. The search yielded 2014 studies, of which 49 were included.

RESULTS

There were 22 animal studies assessing murine models and 27 studies on humans. The primary indications in these studies were epileptic conditions, neurodegenerative disorders, cognitive impairment, and healthy populations.

DISCUSSION

Administration of KD seems to confer cognitive-enhancing effects in areas such as working memory, reference memory and attention. Studies found that KD treatment in animals has the potential to alleviate age-related cognitive decline. Over 80% of the 27 human studies reported a favourable effect of intervention, and none reported a detrimental effect of KD. While these findings suggest that KD may improve the functioning of certain cognitive domains, definitive conclusions were limited by studies with small sample sizes, the absence of controls and randomization, and the lack of objective measures of cognition.

Ketogenic therapies in Parkinson's disease, Alzheimer's disease, and mild cognitive impairment: An integrative review

BACKGROUND

Ketogenic therapies have shown benefit for seizure reduction in epilepsy but their impact on other neurologic conditions is less known. In this literature review, the efficacy of ketogenic therapies were assessed in Parkinson's disease (PD), Alzheimer's disease (AD), and mild cognitive impairment (MCI).

METHODS

A literature search was conducted using PubMed, Scopus, and Google Scholar focusing on ketogenic therapies in PD, AD, and MCI.

RESULTS

A total of 2565 records were identified with a total of 15 studies (3 for PD and 12 for MCI/AD) meeting criteria for analysis. The ketogenic diet was used in all the PD studies and did show significant improvement in motor function either through vocal quality, gait, freezing, tremor, and/or balance. A variety of ketogenic therapies were utilized in the MCI and AD groups including a ketogenic diet, low-carbohydrate diet, modified Adkins diet, Mediterranean diet with coconut oil supplementation, a ketogenic diet with a ketogenic medium chain triglyceride (kMCT) supplement, as well as ketogenic supplements including a ketogenic drink with kMCT, oral ketogenic compounds (Axona and AC-1202), and MCT oil or emulsion. The ketogenic diet independently showed a non-significant trend towards improvement in cognition. The Mediterranean diet, modified Adkins diet, and low-carbohydrate diet showed statistically significant improvements in some, although not all, of their cognitive measures. Use of ketogenic supplements, drinks, or compounds showed variable results in the AD and MCI groups. The Axona and AC-1202 compounds showed no significant improvement in cognition at the end of their respective 90-day trials. Most MCT supplements did show cognitive improvements, although only after 6 months of adherence. Adherence to the intervention was problematic in most of the diet studies.

CONCLUSION

Ketogenic therapies have promise in PD, AD, and MCI for symptom improvement although larger studies are needed to support their implementation in clinical practice.

APOE-Genotype and Insulin Modulate Estimated Effect of Dietary Macronutrients on Cognitive Performance: Panel Analyses in Nondiabetic Older Adults at Risk of Dementia

BACKGROUND

The apolipoprotein E gene (APOE ε-2/3/4, combined as 6 different genotypes: ε-22/23/24/33/34/44) and insulin status modulate dementia risk and play a role in the metabolism of macronutrients.

OBJECTIVES

We aimed to examine APOE-genotype and fasting insulin as effect modifiers of the slopes between dietary macronutrients and cognitive performance among older adults at risk of dementia.

METHODS

Panel analyses-with diet and cognition measured at baseline and follow-up at years 1 and 2-were performed in a sub-sample from the FINGER (Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability) trial (n = 676, 60-77 y, 46% females, all nondiabetics). The associations between macronutrients (3-d food records, z-scores) and global cognition (modified Neuropsychological Test Battery, z-score) were analyzed in mixed regression models adjusted for confounders selected a priori. After a gradient was implied by the point estimates in categorical APOE analyses, we investigated a continuous APOE variable [APOE-gradient, coded -1 (for ε-23), -0.5 (ε-24), 0 (ε-33), 1 (ε-34), 2 (ε-44)] as an effect-modifier.

RESULTS

At increasing levels of the APOE-gradient, a relatively more favorable slope between diet and cognition was observed for a lower carbohydrate/fat ratio [β = -0.040, 95% confidence interval (CI): -0.074, -0.006; P = 0.020 for interaction diet × APOE-gradient), and higher protein (β = 0.075, 95% CI: 0.042, 0.109; P = 9.4 × 10-6). Insulin concentration (log-linear) modulated the association between the carbohydrate/fat ratio and cognition by a quadratic interaction (β = -0.016, P = 0.039). Coherent findings for exploratory predictors (fiber, fat subtypes, composite score, metabolic biomarkers) were compatible with published hypotheses of differential dietary adaptation by APOE, with cognition among ε-33 being relatively independent of dietary parameters-implying "metabolic flexibility." Antagonistic slopes to cognition for ε-23 (positive) compared with ε-34 and ε-44 (negative) were found for a Higher-carbohydrates-fiber-Lower-fat-protein composite score, even as within-subjects effects.

CONCLUSIONS

APOE-based precision nutrition appears conceptually promising, but replications in wider samples are warranted, as well as support from trials. Both relative hyper- and hypoinsulinemia might modulate the effect of diet on cognition.

A Modified Mediterranean Ketogenic Diet mitigates modifiable risk factors of Alzheimer's Disease: a serum and CSF-based metabolic analysis

Alzheimer's disease (AD) is influenced by a variety of modifiable risk factors, including a person's dietary habits. While the ketogenic diet (KD) holds promise in reducing metabolic risks and potentially affecting AD progression, only a few studies have explored KD's metabolic impact, especially on blood and cerebrospinal fluid (CSF). Our study involved participants at risk for AD, either cognitively normal or with mild cognitive impairment. The participants consumed both a modified Mediterranean-ketogenic diet (MMKD) and the American Heart Association diet (AHAD) for 6 weeks each, separated by a 6-week washout period. We employed nuclear magnetic resonance (NMR)-based metabolomics to profile serum and CSF and metagenomics profiling on fecal samples. While the AHAD induced no notable metabolic changes, MMKD led to significant alterations in both serum and CSF. These changes included improved modifiable risk factors, like increased HDL-C and reduced BMI, reversed serum metabolic disturbances linked to AD such as a microbiome-mediated increase in valine levels, and a reduction in systemic inflammation. Additionally, the MMKD was linked to increased amino acid levels in the CSF, a breakdown of branched-chain amino acids (BCAAs), and decreased valine levels. Importantly, we observed a strong correlation between metabolic changes in the CSF and serum, suggesting a systemic regulation of metabolism. Our findings highlight that MMKD can improve AD-related risk factors, reverse some metabolic disturbances associated with AD, and align metabolic changes across the blood-CSF barrier.

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.

Effects of a ketogenic and low-fat diet on the human metabolome, microbiome, and foodome in adults at risk for Alzheimer's disease

INTRODUCTION

The ketogenic diet (KD) is an intriguing therapeutic candidate for Alzheimer's disease (AD) given its protective effects against metabolic dysregulation and seizures. Gut microbiota are essential for KD-mediated neuroprotection against seizures as well as modulation of bile acids, which play a major role in cholesterol metabolism. These relationships motivated our analysis of gut microbiota and metabolites related to cognitive status following a controlled KD intervention compared with a low-fat-diet intervention.

METHODS

Prediabetic adults, either with mild cognitive impairment (MCI) or cognitively normal (CN), were placed on either a low-fat American Heart Association diet or high-fat modified Mediterranean KD (MMKD) for 6 weeks; then, after a 6-week washout period, they crossed over to the alternate diet. We collected stool samples for shotgun metagenomics and untargeted metabolomics at five time points to investigate individuals' microbiome and metabolome throughout the dietary interventions.

RESULTS

Participants with MCI on the MMKD had lower levels of GABA-producing microbes Alistipes sp. CAG:514 and GABA, and higher levels of GABA-regulating microbes Akkermansia muciniphila. MCI individuals with curcumin in their diet had lower levels of bile salt hydrolase-containing microbes and an altered bile acid pool, suggesting reduced gut motility.

DISCUSSION

Our results suggest that the MMKD may benefit adults with MCI through modulation of GABA levels and gut-transit time.

Preliminary PET Imaging of Microtubule-Based PET Radioligand [11C]MPC-6827 in a Nonhuman Primate Model of Alzheimer's Disease

The microtubule (MT) instability observed in Alzheimer's disease (AD) is commonly attributed to hyperphosphorylation of the MT-associated protein, tau. In vivo PET imaging offers an opportunity to gain critical information about MT changes with the onset and development of AD and related dementia. We developed the first brain-penetrant MT PET ligand, [11C]MPC-6827, and evaluated its in vivo imaging utility in vervet monkeys. Consistent with our previous in vitro cell uptake and in vivo rodent imaging experiments, [11C]MPC-6827 uptake increased with MT destabilization. Radioactive uptake was inversely related to (cerebrospinal fluid) CSF Aβ42 levels and directly related to age in a nonhuman primate (NHP) model of AD. Additionally, in vitro autoradiography studies also corroborated PET imaging results. Here, we report the preliminary results of PET imaging with [11C]MPC-6827 in four female vervet monkeys with high or low CSF Aβ42 levels, which have been shown to correlate with the Aβ plaque burden, similar to humans.

Targeting immunometabolic pathways for combination therapy in Alzheimer's disease

The recent success of disease-modifying anti-amyloid monoclonal antibodies in slowing Alzheimer's disease (AD) symptoms has been an exciting step forward for the field. Despite successfully clearing amyloid from the brain, however, only modest symptomatic improvement has been demonstrated, and treatment-related side effects such as amyloid-related imaging abnormalities (ARIA) limit use for some. These limitations suggest that fully efficacious AD treatment may require combination therapy regimens, as are used in other complex disorders such as cancer and HIV. One reasonable strategy may be to use agents that address the biological changes that predict future amyloid accumulation, or accompany amyloid accumulation in preclinical disease states. Immunometabolic pathways, including the insulin signaling pathway, are dysregulated at the earliest stages of AD, concomitant with amyloid accumulation. It is plausible that agents that target these pathways may work synergistically with anti-amyloid therapies to halt AD progression. Insulin signaling is integrally involved in innate and adaptive immune systems, with pleiotropic effects that moderate pro- and anti-inflammatory responses. Metabolic modulators that enhance insulin sensitivity and function, such as GLP-1 receptor agonists, SGLT2 inhibitors, and insulin itself have been shown to improve immune function and reduce chronic inflammation. Additional effects of insulin and metabolic modulators demonstrated in preclinical and clinical studies of AD include increased clearance of amyloid-β, slowed tau progression, improved vascular function and lipid metabolism, reduced synaptotoxicity, and improved cognitive and functional outcomes. A large number of compounds that treat metabolic disorders have been extensively characterized with respect to mechanism of action and safety, and thus are readily available to be repurposed for combination therapy protocols. Determining the most successful combination regimens of these agents together with disease-modifying therapies, and the appropriate timing of treatment, are promising next steps in the quest to treat and prevent AD.

Metabolic Reprogramming toward Aerobic Glycolysis and the Gut Microbiota Involved in the Brain Amyloid Pathology

Alzheimer's disease (AD) is characterized by the formation of senile plaques consisting of fibrillated amyloid-β (Aβ), dystrophic neurites, and the neurofibrillary tangles of tau. The oligomers/fibrillar Aβ damages the neurons or initiates an intracellular signaling cascade for neuronal cell death leading to Aβ toxicity. The Aβ is a 4 kDa molecular weight peptide originating from the C-terminal region of the amyloid precursor protein via proteolytic cleavage. Apart from the typical AD hallmarks, certain deficits in metabolic alterations have been identified. This study describes the emerging features of AD from the aspect of metabolic reprogramming in the main pathway of carbohydrate metabolism in the human brain. Particularly, the neurons in patients with AD favor glycolysis despite a normal mitochondrial function indicating a Warburg-like effect. In addition, certain dietary patterns are well known for their properties in preventing AD. Among those, a ketogenic diet may substantially improve the symptoms of AD. An effective therapeutic method for the treatment, mitigation, and prevention of AD has not yet been established. Therefore, the researchers pursue the development and establishment of novel therapies effective in suppressing AD symptoms and the elucidation of their underlying protective mechanisms against neurodegeneration aiming for AD therapy in the near future.

The potential for mitochondrial therapeutics in the treatment of primary open-angle glaucoma: a review

Glaucoma, an age-related neurodegenerative disease, is characterized by the death of retinal ganglion cells (RGCs) and the corresponding loss of visual fields. This disease is the leading cause of irreversible blindness worldwide, making early diagnosis and effective treatment paramount. The pathophysiology of primary open-angle glaucoma (POAG), the most common form of the disease, remains poorly understood. Current available treatments, which target elevated intraocular pressure (IOP), are not effective at slowing disease progression in approximately 30% of patients. There is a great need to identify and study treatment options that target other disease mechanisms and aid in neuroprotection for POAG. Increasingly, the role of mitochondrial injury in the development of POAG has become an emphasized area of research interest. Disruption in the function of mitochondria has been linked to problems with neurodevelopment and systemic diseases. Recent studies have shown an association between RGC death and damage to the cells' mitochondria. In particular, oxidative stress and disrupted oxidative phosphorylation dynamics have been linked to increased susceptibility of RGC mitochondria to secondary mechanical injury. Several mitochondria-targeted treatments for POAG have been suggested, including physical exercise, diet and nutrition, antioxidant supplementation, stem cell therapy, hypoxia exposure, gene therapy, mitochondrial transplantation, and light therapy. Studies have shown that mitochondrial therapeutics may have the potential to slow the progression of POAG by protecting against mitochondrial decline associated with age, genetic susceptibility, and other pathology. Further, these therapeutics may potentially target already present neuronal damage and symptom manifestations. In this review, the authors outline potential mitochondria-targeted treatment strategies and discuss their utility for use in POAG.

Dietary Patterns and Alzheimer's Disease: An Updated Review Linking Nutrition to Neuroscience

Alzheimer's disease (AD) is a growing concern for the aging population worldwide. With no current cure or reliable treatments available for AD, prevention is an important and growing area of research. A range of lifestyle and dietary patterns have been studied to identify the most effective preventive lifestyle changes against AD and related dementia (ADRD) pathology. Of these, the most studied dietary patterns are the Mediterranean, DASH, MIND, ketogenic, and modified Mediterranean-ketogenic diets. However, there are discrepancies in the reported benefits among studies examining these dietary patterns. We herein compile a narrative/literature review of existing clinical evidence on the association of these patterns with ADRD symptomology and contemplate their preventive/ameliorative effects on ADRD neuropathology in various clinical milieus. By and large, plant-based dietary patterns have been found to be relatively consistently and positively correlated with preventing and reducing the odds of ADRD. These impacts stem not only from the direct impact of specific dietary components within these patterns on the brain but also from indirect effects through decreasing the deleterious effects of ADRD risk factors, such as diabetes, obesity, and cardiovascular diseases. Importantly, other psychosocial factors influence dietary intake, such as the social connection, which may directly influence diet and lifestyle, thereby also impacting ADRD risk. To this end, prospective research on ADRD should include a holistic approach, including psychosocial considerations.

Molecular Aspects of a Diet as a New Pathway in the Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia in the world. Lack of an established pathology makes it difficult to develop suitable approaches and treatment for the disease. Besides known hallmarks, including amyloid β peptides cumulating in plaques and hyperphosphorylated tau forming NFTs, inflammation also plays an important role, with known connections to the diet. In AD, adhering to reasonable nutrition according to age-related principles is recommended. The diet should be high in neuroprotective foods, such as polyunsaturated fatty acids, antioxidants, and B vitamins. In addition, foods capable of rising BDNF should be considered because of the known profitable results of this molecule in AD. Adhering to beneficial diets might result in improvements in memory, cognition, and biomarkers and might even reduce the risk of developing AD. In this review, we discuss the effects of various diets, foods, and nutrients on brain health and possible connections to Alzheimer's disease.

Potential of Akkermansia muciniphila and its outer membrane proteins as therapeutic targets for neuropsychological diseases

The gut microbiota varies dramatically among individuals, and changes over time within the same individual, due to diversities in genetic backgrounds, diet, nutrient supplementations and use of antibiotics. Up until now, studies on dysbiosis of microbiota have expanded to a wider range of diseases, with Akkermansia muciniphila at the cross spot of many of these diseases. A. muciniphila is a Gram-negative bacterium that produces short-chain fatty acids (SCFAs), and Amuc_1100 is one of its most highly expressed outer membrane proteins. This review aims to summarize current knowledge on correlations between A. muciniphila and involved neuropsychological diseases published in the last decade, with a focus on the potential of this bacterium and its outer membrane proteins as therapeutic targets for these diseases, on the basis of evidence accumulated from animal and clinical studies, as well as mechanisms of action from peripheral to central nervous system (CNS).

Neurotrophic effects of intermittent fasting, calorie restriction and exercise: a review and annotated bibliography

In the last decades, important progress has been achieved in the understanding of the neurotrophic effects of intermittent fasting (IF), calorie restriction (CR) and exercise. Improved neuroprotection, synaptic plasticity and adult neurogenesis (NSPAN) are essential examples of these neurotrophic effects. The importance in this respect of the metabolic switch from glucose to ketone bodies as cellular fuel has been highlighted. More recently, calorie restriction mimetics (CRMs; resveratrol and other polyphenols in particular) have been investigated thoroughly in relation to NSPAN. In the narrative review sections of this manuscript, recent findings on these essential functions are synthesized and the most important molecules involved are presented. The most researched signaling pathways (PI3K, Akt, mTOR, AMPK, GSK3β, ULK, MAPK, PGC-1α, NF-κB, sirtuins, Notch, Sonic hedgehog and Wnt) and processes (e.g., anti-inflammation, autophagy, apoptosis) that support or thwart neuroprotection, synaptic plasticity and neurogenesis are then briefly presented. This provides an accessible entry point to the literature. In the annotated bibliography section of this contribution, brief summaries are provided of about 30 literature reviews relating to the neurotrophic effects of interest in relation to IF, CR, CRMs and exercise. Most of the selected reviews address these essential functions from the perspective of healthier aging (sometimes discussing epigenetic factors) and the reduction of the risk for neurodegenerative diseases (Alzheimer's disease, Huntington's disease, Parkinson's disease) and depression or the improvement of cognitive function.

Effects of risk factors on longitudinal changes in brain structure and function in the progression of AD

INTRODUCTION

Past research on Alzheimer's disease (AD) has focused on biomarkers, cognition, and neuroimaging as primary predictors of its progression, albeit additional ones have recently gained attention. When turning to the prediction of the progression from one stage to another, one could benefit from the joint assessment of imaging-based biomarkers and risk/protective factors.

METHODS

We included 86 studies that fulfilled our inclusion criteria.

RESULTS

Our review summarizes and discusses the results of 30 years of longitudinal research on brain changes assessed with neuroimaging and the risk/protective factors and their effect on AD progression. We group results into four sections: genetic, demographic, cognitive and cardiovascular, and lifestyle factors.

DISCUSSION

Given the complex nature of AD, including risk factors could prove invaluable for a better understanding of AD progression. Some of these risk factors are modifiable and could be targeted by potential future treatments.

The Dietary Carbohydrate/Fat-Ratio and Cognitive Performance: Panel Analyses in Older Adults at Risk for Dementia

Background

Roughly 80% of total energy intake (TEI) in most human diets originates from digestible carbohydrates (eCarb) and fat (eFat), but the impact of their proportions on cognitive performance is poorly understood.

Objectives

Our primary aim was to investigate estimates of global cognition in relation to macronutrient intake, with the log-ratio eCarb/eFat (CFr) as the primary predictor variable of interest. Secondary predictors were protein and the saturated/total fat ratio. Exploratory comparisons of CFr with eCarb and eFat as separate predictors were an additional aim.

Methods

The observations were made on panel data (years 0, 1, 2) from the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability, n = 1251; age 60-77 y; 47% females; selected by risk factors for dementia. Self-reported diet was assessed by 3-d food records. Global cognition was measured using a modified Neuropsychological Test Battery. A mixed linear regression model was used, adjusted for age, sex, education, body-mass index, cholesterol-lowering drugs, TEI, time, time × intervention/control group, with study site and subject as random factors. Estimates were standardized (mean = 0; SD = 1) with 95% CI.

Results

CFr had a negative estimate to global cognition (β = -0.022, CI: -0.039, -0.005; P = 0.011). The point estimate for protein was β = 0.013 (P = 0.41), and for the saturated/total fat ratio, associations with cognition were nonlinear. CFr correlated highly with eCarb (Pearson's r = 0.92) and eFat (r = -0.94). The point estimate for CFr fell between eCarb (β = -0.026, P < 0.001) and (inversely) eFat (β = 0.017, P = 0.090).

Conclusions

A lower CFr was associated with better global cognition among older adults at risk for dementia. Because this is an important target group for preventive interventions, clinical trials are warranted to further investigate the impact of macronutritional composition on cognitive health. The potential role of CFr as a predictor for cognitive health should be further studied.

Ketogenic Diet and Ketone Bodies as Clinical Support for the Treatment of SARS-CoV-2-Review of the Evidence

One of the proposed nutritional therapies to support drug therapy in COVID-19 is the use of a ketogenic diet (KD) or ketone bodies. In this review, we summarized the evidence from tissue, animal, and human models and looked at the mechanisms of action of KD/ketone bodies against COVID-19. KD/ketone bodies were shown to be effective at the stage of virus entry into the host cell. The use of β-hydroxybutyrate (BHB), by preventing the metabolic reprogramming associated with COVID-19 infection and improving mitochondrial function, reduced glycolysis in CD4+ lymphocytes and improved respiratory chain function, and could provide an alternative carbon source for oxidative phosphorylation (OXPHOS). Through multiple mechanisms, the use of KD/ketone bodies supported the host immune response. In animal models, KD resulted in protection against weight loss and hypoxemia, faster recovery, reduced lung injury, and resulted in better survival of young mice. In humans, KD increased survival, reduced the need for hospitalization for COVID-19, and showed a protective role against metabolic abnormalities after COVID-19. It appears that the use of KD and ketone bodies may be considered as a clinical nutritional intervention to assist in the treatment of COVID-19, despite the fact that numerous studies indicate that SARS-CoV-2 infection alone may induce ketoacidosis. However, the use of such an intervention requires strong scientific validation.

Improving Adherence to a Mediterranean Ketogenic Nutrition Program for High-Risk Older Adults: A Pilot Randomized Trial

(1) Background: Mediterranean ketogenic nutrition (MKN) may directly target multiple neurobiological mechanisms associated with dementia risk in older adults. Despite its promise, this type of nutrition can be challenging to learn and adhere to in a healthy manner. Our team used the National Institutes of Health Obesity Related Behavioral Intervention Trials (NIH ORBIT) model to develop and pilot a program to help older adults with memory concerns use MKN. (2) Methods: Using a two-arm, randomized design, we evaluated an MKN Adherence (MKNA) program compared to an MKN education (MKNE) program (N = 58). The primary difference between study arms involved the use of motivational interviewing (MI) strategies and behavior change techniques (BCT) only in the MKNA arm. Participants were included if they evidenced subjective memory concerns or objective memory impairment on the Montreal Cognitive Assessment (Score 19 ≤ 26). Primary outcomes examined included feasibility, acceptability, adherence, and clinical outcomes associated with the program. (3) Results: Overall, there was relatively high program completion in both groups, with 79% of participants completing the 6-week program. The recruitment protocol required adjustment but was successful in reaching the target sample size. Retention (82%) and session attendance (91%) were higher in the MKNA arm compared to the MKNE (retention = 72%; attendance = 77%). Overall, most participants in both groups rated the program as "excellent" using the client satisfaction questionnaire. Participants in the MKNA arm evidenced higher objective and self-reported adherence to MKN during the 6-week program. Further, there was some evidence of clinical benefits of the program, although these effects diminished as adherence decreased in the 3 months follow-up. (4) Discussion: This pilot trial demonstrated that the MKN program incorporating MI and BCT strategies may better engage and retain participants than a nutrition education program alone, although participants in both groups reported high satisfaction.

The Relationship of Ketogenic Diet with Neurodegenerative and Psychiatric Diseases: A Scoping Review from Basic Research to Clinical Practice

BACKGROUND

The ketogenic diet (KD) has become widespread for the therapy of epileptic pathology in childhood and adulthood. In the last few decades, the current re-emergence of its popularity has focused on the treatment of obesity and diabetes mellitus. KD also exerts anti-inflammatory and neuroprotective properties, which could be utilized for the therapy of neurodegenerative and psychiatric disorders.

PURPOSE

This is a thorough, scoping review that aims to summarize and scrutinize the currently available basic research performed in in vitro and in vivo settings, as well as the clinical evidence of the potential beneficial effects of KD against neurodegenerative and psychiatric diseases. This review was conducted to systematically map the research performed in this area as well as identify gaps in knowledge.

METHODS

We thoroughly explored the most accurate scientific web databases, e.g., PubMed, Scopus, Web of Science, and Google Scholar, to obtain the most recent in vitro and in vivo data from animal studies as well as clinical human surveys from the last twenty years, applying effective and characteristic keywords.

RESULTS

Basic research has revealed multiple molecular mechanisms through which KD can exert neuroprotective effects, such as neuroinflammation inhibition, decreased reactive oxygen species (ROS) production, decreased amyloid plaque deposition and microglial activation, protection in dopaminergic neurons, tau hyper-phosphorylation suppression, stimulating mitochondrial biogenesis, enhancing gut microbial diversity, restoration of histone acetylation, and neuron repair promotion. On the other hand, clinical evidence remains scarce. Most existing clinical studies are modest, frequently uncontrolled, and merely assess the short-term impacts of KD. Moreover, several clinical studies had large dropout rates and a considerable lack of compliance assessment, as well as an increased level of heterogeneity in the study design and methodology.

CONCLUSIONS

KD can exert substantial neuroprotective effects via multiple molecular mechanisms in various neurodegenerative and psychiatric pathological states. Large, long-term, randomized, double-blind, controlled clinical trials with a prospective design are strongly recommended to delineate whether KD may attenuate or even treat neurodegenerative and psychiatric disease development, progression, and symptomatology.

Levels of Soluble Interleukin 6 Receptor and Asp358Ala Are Associated With Cognitive Performance and Alzheimer Disease Biomarkers

BACKGROUND AND OBJECTIVES

Alzheimer disease (AD) is a neurodegenerative disease process manifesting clinically with cognitive impairment and dementia. AD pathology is complex, and in addition to plaques and tangles, neuroinflammation is a consistent feature. Interleukin (IL) 6 is a multifaceted cytokine involved in a plethora of cellular mechanisms including both anti-inflammatory and inflammatory processes. IL6 can signal classically through the membrane-bound receptor or by IL6 trans-signaling forming a complex with the soluble IL6 receptor (sIL6R) and activating membrane-bound glycoprotein 130 on cells not expressing IL6R. IL6 trans-signaling has been demonstrated as the primary mechanism of IL6-mediated events in neurodegenerative processes. In this study, we performed a cross-sectional analysis to investigate whether inheritance of a genetic variation in the IL6R gene and associated elevated sIL6R levels in plasma and CSF were associated with cognitive performance.

METHODS

We genotyped the IL6R rs2228145 nonsynonymous variant (Asp³⁵⁸Ala) and assayed IL6 and sIL6R concentrations in paired samples of plasma and CSF obtained from 120 participants with normal cognition, mild cognitive impairment, or probable AD enrolled in the Wake Forest Alzheimer's Disease Research Center's Clinical Core. IL6 rs2228145 genotype and measures of plasma IL6 and sIL6R were assessed for relationships with cognitive status and clinical data, including the Montreal Cognitive Assessment (MoCA), modified Preclinical Alzheimer's Cognitive Composite (mPACC), cognitive domain scores obtained from the Uniform Data Set, and CSF concentrations of phosphoTau^T181 (pTau181), β-amyloid (Aβ) Aβ40 and Aβ42 concentrations.

RESULTS

We found that inheritance of the IL6R Ala³⁵⁸ variant and elevated sIL6R levels in plasma and CSF were correlated with lower mPACC, MoCA and memory domain scores, increases in CSF pTau181, and decreases in the CSF Aβ42/40 ratio in both unadjusted and covariate-adjusted statistical models.

DISCUSSION

These data suggest that IL6 trans-signaling and the inheritance of the IL6R Ala³⁵⁸ variant are related to reduced cognition and greater levels of biomarkers for AD disease pathology. Follow-up prospective studies are necessary, as patients who inherit IL6R Ala³⁵⁸ may be identified as ideally responsive to IL6 receptor-blocking therapies.

A Review of Ketogenic Dietary Therapies for Epilepsy and Neurological Diseases: A Proposal to Implement an Adapted Model to Include Healthy Mediterranean Products

Based on the growing evidence of the therapeutic role of high-fat ketogenic dietary therapies (KDTs) for neurological diseases and on the protective effect of the Mediterranean diet (MD), it could be important to delineate a Mediterranean version of KDTs in order to maintain a high ketogenic ratio, and thus avoid side effects, especially in patients requiring long-term treatment. This narrative review aims to explore the existing literature on this topic and to elaborate recommendations for a Mediterranean version of the KDTs. It presents practical suggestions based on MD principles, which consist of key elements for the selection of foods (both from quantitative and qualitative prospective), and indications of the relative proportions and consumption frequency of the main food groups that constitute the Mediterranean version of the KDTs. We suggest the adoption of a Mediterranean version of ketogenic diets in order to benefit from the multiple protective effects of the MD. This translates to: (i) a preferential use of olive oil and vegetable fat sources in general; (ii) the limitation of foods rich in saturated fatty acids; (iii) the encouragement of high biological value protein sources; (iv) inserting fruit and vegetables at every meal possible, varying their choices according to seasonality.

Cerebrospinal Fluid Metabolomics: Pilot Study of Using Metabolomics to Assess Diet and Metabolic Interventions in Alzheimer's Disease and Mild Cognitive Impairment

Brain glucose hypometabolism is an early sign of Alzheimer's disease (AD), and interventions which offset this deficit, such as ketogenic diets, show promise as AD therapeutics. Conversely, high-fat feeding may exacerbate AD risk. We analyzed the metabolomic profile of cerebrospinal fluid (CSF) in a pilot study of older adults who underwent saline and triglyceride (TG) infusions. Older adults (12 cognitively normal (CN), age 65.3 ± 8.1, and 9 with cognitive impairment (CI), age 70.9 ± 8.6) underwent a 5 h TG or saline infusion on different days using a random crossover design; CSF was collected at the end of infusion. Aqueous metabolites were measured using a targeted mass spectroscopy (MS) platform focusing on 215 metabolites from over 35 different metabolic pathways. Data were analyzed using MetaboAnalyst 4.0 and SAS. Of the 215 targeted metabolites, 99 were detectable in CSF. Only one metabolite significantly differed by treatment: the ketone body 3-hydroxybutyrate (HBA). Post hoc analyses showed that HBA levels were associated with age and markers of metabolic syndrome and demonstrated different correlation patterns for the two treatments. When analyzed by cognitive diagnosis group, TG-induced increases in HBA were over 3 times higher for those with cognitive impairment (change score CN +9.8 uM ± 8.3, CI +32.4 ± 7.4, p = 0.0191). Interestingly, individuals with cognitive impairment had higher HBA levels after TG infusion than those with normal cognition. These results suggest that interventions that increase plasma ketones may lead to higher brain ketones in groups at risk for AD and should be confirmed in larger intervention studies.

The association of dietary and nutrient patterns on neurocognitive decline: A systematic review of MRI and PET studies

BACKGROUND

As the global population ages, there has been a growing incidence of neurodegenerative diseases such as Alzheimer's. More recently, studies exploring the relationship between dietary patterns and neuroimaging outcomes have received particular attention. This systematic literature review provides a structured overview of the association between dietary and nutrient patterns on neuroimaging outcomes and cognitive markers in middle-aged to older adults. A comprehensive literature search was conducted to find relevant articles published from 1999 to date using the following databases Ovid MEDLINE, Embase, PubMed, Scopus and Web of Science. The inclusion criteria for the articles comprised studies reporting on the association between dietary patterns and neuroimaging outcomes, which includes both specific pathological hallmarks of neurodegenerative diseases such as Aβ and tau and nonspecific markers such as structural MRI and glucose metabolism. The risk of bias was evaluated using the Quality Assessment tool from the National Heart, Lung, and Blood Institute of the National Institutes of Health. The results were then organized into a summary of results table, collated based on synthesis without meta-analysis. After conducting the search, 6050 records were extracted and screened for eligibility, with 107 eligible for full-text screening and 42 articles ultimately being included in this review. The results of the systematic review indicate that there is some evidence suggesting that healthy dietary and nutrient patterns were associated with neuroimaging measures, indicative of a protective influence on neurodegeneration and brain ageing. Conversely, unhealthy dietary and nutrient patterns showed evidence pointing to decreased brain volumes, poorer cognition and increased Aβ deposition. Future research should focus on sensitive neuroimaging acquisition and analysis methods, to study early neurodegenerative changes and identify critical periods for interventions and prevention.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration no, CRD42020194444).

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.

The role of the probiotic Akkermansia muciniphila in brain functions: insights underpinning therapeutic potential

The role of Akkermansia muciniphila, one of the most abundant microorganisms of the intestinal microbiota, has been studied extensively in metabolic diseases, such as obesity and diabetes. It is considered a next-generation probiotic microorganism. Although its mechanism of action has not been fully elucidated, accumulating evidence indicates the important role of A. muciniphila in brain functions via the gut-brain axis and its potential as a therapeutic target in various neuropsychiatric disorders. However, only a limited number of studies, particularly clinical studies, have directly assessed the therapeutic effects of A. muciniphila interventions in these disorders. This is the first review to discuss the comprehensive mechanism of A. muciniphila in the gut-brain axis via the protection of the intestinal mucosal barrier and modulation of the immune system and metabolites, such as short-chain fatty acids, amino acids, and amino acid derivatives. Additionally, the role of A. muciniphila and its therapeutic potential in various neuropsychiatric disorders, including Alzheimer's disease and cognitive deficit, amyotrophic lateral sclerosis, Parkinson's disease, and multiple sclerosis, have been discussed. The review suggests the potential role of A. muciniphila in healthy brain functions.

Lipid metabolism and Alzheimer's disease: clinical evidence, mechanistic link and therapeutic promise

Alzheimer's disease (AD) is an age-associated neurodegenerative disorder with multifactorial etiology, intersecting genetic and environmental risk factors, and a lack of disease-modifying therapeutics. While the abnormal accumulation of lipids was described in the very first report of AD neuropathology, it was not until recent decades that lipid dyshomeostasis became a focus of AD research. Clinically, lipidomic and metabolomic studies have consistently shown alterations in the levels of various lipid classes emerging in early stages of AD brains. Mechanistically, decades of discovery research have revealed multifaceted interactions between lipid metabolism and key AD pathogenic mechanisms including amyloidogenesis, bioenergetic deficit, oxidative stress, neuroinflammation, and myelin degeneration. In the present review, converging evidence defining lipid dyshomeostasis in AD is summarized, followed by discussions on mechanisms by which lipid metabolism contributes to pathogenesis and modifies disease risk. Furthermore, lipid-targeting therapeutic strategies, and the modification of their efficacy by disease stage, ApoE status, and metabolic and vascular profiles, are reviewed.

Nutritional metabolism and cerebral bioenergetics in Alzheimer's disease and related dementias

Disturbances in the brain's capacity to meet its energy demand increase the risk of synaptic loss, neurodegeneration, and cognitive decline. Nutritional and metabolic interventions that target metabolic pathways combined with diagnostics to identify deficits in cerebral bioenergetics may therefore offer novel therapeutic potential for Alzheimer's disease (AD) prevention and management. Many diet-derived natural bioactive components can govern cellular energy metabolism but their effects on brain aging are not clear. This review examines how nutritional metabolism can regulate brain bioenergetics and mitigate AD risk. We focus on leading mechanisms of cerebral bioenergetic breakdown in the aging brain at the cellular level, as well as the putative causes and consequences of disturbed bioenergetics, particularly at the blood-brain barrier with implications for nutrient brain delivery and nutritional interventions. Novel therapeutic nutrition approaches including diet patterns are provided, integrating studies of the gut microbiome, neuroimaging, and other biomarkers to guide future personalized nutritional interventions.