Nutrition, Gut Microbiota, and Alzheimer's Disease

Armillariella tabescens-derived polysaccharides alleviated Ɒ-Gal-induced neuroinflammation and cognitive injury through enterocerebral axis and activation of keap-1/Nrf2 pathway

The early symptoms of neurodegenerative diseases include oxidative stress disorder and accelerated inflammation levels. Edible fungi polysaccharides play essential roles in anti-neuroinflammation. We analyzed the regulatory mechanisms of polysaccharides from extracellular Armillariella tabescens (ATEP) in alleviating neuroinflammation in mice. Mice were induced with d-galactose and aluminum chloride to establish an animal model of Alzheimer's disease, then intragastrically treated with ATEP, which had been previously analyzed for its physicochemical properties. We assessed the critical characteristics of mice treated for neuroinflammation, including cognitive behavior, the anti-inflammatory potential of ATEP in hippocampal pathology and critical protein expression, and changes in fecal microbial composition and metabolites. ATEP intervened in oxidative stress by enhancing antioxidant enzyme activities and suppressing the Keap-1/Nrf2 signaling pathway. Changing the Nrf2 content in the nucleus led to changes in the downstream oxidation-related enzymes, HO-1, NQO-1, iNOS, and COX-2, and the neuronal morphology in CA3 region of the hippocampus. Microbiome analysis revealed that ATEP remodeled the gut microbiotas and regulated the short-chain fatty acids-producing bacteria. Early intervention with ATEP via active dietary supplementation may promote neuroprotection.

Exploring animal protein sources against prevent age-related short-term memory decline in mice: Dietary fish (Alaska Pollock) protein exhibits superior protective effects

Dietary factors, particularly proteins, have been extensively explored to combat cognitive impairment. We have previously reported that dietary fish (Alaska Pollock) protein (APP) is more effective than casein (CAS) or fish oil in maintaining short-term memory in senescence-accelerated mice prone 10 (SAMP10). To examine the specificity of the protective effect of APP intakes against short-term memory decline, we assessed the impact of various dietary animal proteins, including APP, CAS, chicken breast protein (CP), and whey protein (WP), against age-related cognitive function in SAMP10 mice. After feeding the experimental diets for 5 months, memory was assessed using the Y-maze. The APP group exhibited a significant increase in spontaneous alternation behavior as an indicator of working memory when group compared with groups fed with other protein source. Additionally, the APP group displayed significantly higher neurofilament heavy chain positivity than the CAS and CP groups, as evidenced immunohistochemical analysis. Gut microbiota analysis indicated that dietary APP significantly enhanced the relative abundance of Lactobacillus, which positively correlated with spontaneous alternation behavior. Collectively, these findings suggest that dietary APP is more effective than CAS, CP, or WP in preventing age-related short-term memory decline and morphological abnormalities in the hippocampal axons of SAMP10 mice. Moreover, APP-mediated improvements in cognitive deficits may be associated with changes in microbiota diversity. PRACTICAL APPLICATION: This research suggests that dietary fish protein from Alaska Pollock may be more efficient in prevention short-term memory decline in mice, compared to other animal proteins. This finding has practical implications for nutritional optimization, developing the new health food products, and elucidating the relationship between the impact of specific proteins on gut microbiota and prevention of age-related cognitive decline.

The microbiota-gut-brain-immune interface in the pathogenesis of neuroinflammatory diseases: a narrative review of the emerging literature

Importance

Research is beginning to elucidate the sophisticated mechanisms underlying the microbiota-gut-brain-immune interface, moving from primarily animal models to human studies. Findings support the dynamic relationships between the gut microbiota as an ecosystem (microbiome) within an ecosystem (host) and its intersection with the host immune and nervous systems. Adding this to the effects on epigenetic regulation of gene expression further complicates and strengthens the response. At the heart is inflammation, which manifests in a variety of pathologies including neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Multiple Sclerosis (MS).

Observations

Generally, the research to date is limited and has focused on bacteria, likely due to the simplicity and cost-effectiveness of 16s rRNA sequencing, despite its lower resolution and inability to determine functional ability/alterations. However, this omits all other microbiota including fungi, viruses, and phages, which are emerging as key members of the human microbiome. Much of the research has been done in pre-clinical models and/or in small human studies in more developed parts of the world. The relationships observed are promising but cannot be considered reliable or generalizable at this time. Specifically, causal relationships cannot be determined currently. More research has been done in Alzheimer's disease, followed by Parkinson's disease, and then little in MS. The data for MS is encouraging despite this.

Conclusions and relevance

While the research is still nascent, the microbiota-gut-brain-immune interface may be a missing link, which has hampered our progress on understanding, let alone preventing, managing, or putting into remission neurodegenerative diseases. Relationships must first be established in humans, as animal models have been shown to poorly translate to complex human physiology and environments, especially when investigating the human gut microbiome and its relationships where animal models are often overly simplistic. Only then can robust research be conducted in humans and using mechanistic model systems.

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.

A review of dairy food intake for improving health among black geriatrics in the US

The transition to older adulthood is generally marked by progressive declines in body composition, metabolism, cognitive function, and immunity. For socially disadvantaged geriatric populations such as Black Americans, this life stage may also include additional stressors, including dealing with discrimination, poor access to healthcare, and food insecurity. These types of chronic stressors are linked to a higher allostatic load, which is associated with accelerated biological aging, higher rates of adverse health outcomes, and an overall lower quality of life. Of the numerous factors involved in healthy aging, a growing body of research indicates that consuming a higher quality diet that is rich in fruits, vegetables, whole grains, protein foods, and dairy foods, is one of the most potent factors for helping to protect against age-related disease progression. Among the food groups listed above that are recommended by the 2020-2025 Dietary Guidelines for Americans dairy foods are unique in their ability to provide several of the essential nutrients (e.g., high-quality protein, calcium, potassium, vitamin B12, and vitamin D in fortified products) that are most often inadequately consumed by older Black Americans. However, dairy is the most inadequately consumed food group in the US, with older Black adults consuming fewer than half of the 3 daily recommended servings. Therefore, this review examines the current body of evidence exploring the links between dairy intake and age-related disease risk, with a special focus on health and disparities among older Black Americans. Overall, the evidence from most systematic reviews and/or meta-analyses focused on dairy intake and musculoskeletal health suggest that higher dairy intake across the life span, and especially from fermented and fortified products, is associated with better bone and muscle health outcomes in older adults. The evidence on dairy intake and neurocognitive and immune outcomes among older adults holds significant promise for potential benefits, but most of these results are sourced from individual studies or narrative reviews and are not currently corroborated in systematic reviews or meta-analyses. Additionally, most of the research on dairy intake and age-related disease risk has been performed in White populations and can only be extrapolated to Black populations. Nonetheless, older Black populations who do not meet the DGA recommended 3 servings of dairy per day due to lactose intolerance, restrictive dietary patterns, or for other reasons, are likely falling short of several of the nutritional requirements necessary to support healthy aging.

Antineoplastics for treating Alzheimer's disease and dementia: Evidence from preclinical and observational studies

As the world population ages, there will be an increasing need for effective therapies for aging-associated neurodegenerative disorders, which remain untreatable. Dementia due to Alzheimer's disease (AD) is one of the leading neurological diseases in the aging population. Current therapeutic approaches to treat this disorder are solely symptomatic, making the need for new molecular entities acting on the causes of the disease extremely urgent. One of the potential solutions is to use compounds that are already in the market. The structures have known pharmacokinetics, pharmacodynamics, toxicity profiles, and patient data available in several countries. Several drugs have been used successfully to treat diseases different from their original purposes, such as autoimmunity and peripheral inflammation. Herein, we divulge the repurposing of drugs in the area of neurodegenerative diseases, focusing on the therapeutic potential of antineoplastics to treat dementia due to AD and dementia. We briefly touch upon the shared pathological mechanism between AD and cancer and drug repurposing strategies, with a focus on artificial intelligence. Next, we bring out the current status of research on the development of drugs, provide supporting evidence from retrospective, clinical, and preclinical studies on antineoplastic use, and bring in new areas, such as repurposing drugs for the prion-like spreading of pathologies in treating AD.

The connection between epigenetics and gut microbiota-current perspective

Both the epigenetic changes and gut microbiota (GM) have attracted a growing interest in establishing effective diagnostics and potential therapeutic strategies for a number of diseases. These disorders include metabolic, central nervous system-related diseases, autoimmune, and gastrointestinal infections (GI). Despite the number of studies, there is no extensive review that connects the epigenetics modifications and GM as biomarkers that could confer effective diagnostics and confer treatment options. To this end, this review hopes to give detailed information on connecting the modifications in epigenetic and GM. An updated and detailed information on the connection between the epigenetics factors and GM that influence diseases are given. In addition, the review showed some associations between the epigenetics to the maternal GM and offspring health. Finally, the limitations of the concept and prospects into this new emerging discipline were also looked into. Although this review elucidated on the maternal diet and response to offspring health with respect to GM and epigenetic modifications, there still exist various limitations to this newly emerging discipline. In addition to integrating complementary multi-omics data, longitudinal sampling will aid with the identification of functional mechanisms that may serve as therapeutic targets. To this end, this review gave a detailed perspective into harnessing disease diagnostics, prevention and treatment options through epigenetics and GM.

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.

Alzheimer's disease and microorganisms: the non-coding RNAs crosstalk

Alzheimer's disease (AD) is a complex, multifactorial disorder, influenced by a multitude of variables ranging from genetic factors, age, and head injuries to vascular diseases, infections, and various other environmental and demographic determinants. Among the environmental factors, the role of the microbiome in the genesis of neurodegenerative disorders (NDs) is gaining increased recognition. This paradigm shift is substantiated by an extensive body of scientific literature, which underscores the significant contributions of microorganisms, encompassing viruses and gut-derived bacteria, to the pathogenesis of AD. The mechanism by which microbial infection exerts its influence on AD hinges primarily on inflammation. Neuroinflammation, activated in response to microbial infections, acts as a defense mechanism for the brain but can inadvertently lead to unexpected neuropathological perturbations, ultimately contributing to NDs. Given the ongoing uncertainty surrounding the genetic factors underpinning ND, comprehensive investigations into environmental factors, particularly the microbiome and viral agents, are imperative. Recent advances in neuroscientific research have unveiled the pivotal role of non-coding RNAs (ncRNAs) in orchestrating various pathways integral to neurodegenerative pathologies. While the upstream regulators governing the pathological manifestations of microorganisms remain elusive, an in-depth exploration of the nuanced role of ncRNAs holds promise for the development of prospective therapeutic interventions. This review aims to elucidate the pivotal role of ncRNAs as master modulators in the realm of neurodegenerative conditions, with a specific focus on Alzheimer's disease.

Thirty Risk Factors for Alzheimer's Disease Unified by a Common Neuroimmune-Neuroinflammation Mechanism

One of the major obstacles confronting the formulation of a mechanistic understanding for Alzheimer's disease (AD) is its immense complexity-a complexity that traverses the full structural and phenomenological spectrum, including molecular, macromolecular, cellular, neurological and behavioural processes. This complexity is reflected by the equally complex diversity of risk factors associated with AD. However, more than merely mirroring disease complexity, risk factors also provide fundamental insights into the aetiology and pathogenesis of AD as a neurodegenerative disorder since they are central to disease initiation and subsequent propagation. Based on a systematic literature assessment, this review identified 30 risk factors for AD and then extended the analysis to further identify neuroinflammation as a unifying mechanism present in all 30 risk factors. Although other mechanisms (e.g., vasculopathy, proteopathy) were present in multiple risk factors, dysfunction of the neuroimmune-neuroinflammation axis was uniquely central to all 30 identified risk factors. Though the nature of the neuroinflammatory involvement varied, the activation of microglia and the release of pro-inflammatory cytokines were a common pathway shared by all risk factors. This observation provides further evidence for the importance of immunopathic mechanisms in the aetiopathogenesis of AD.

Impact of Nutritional Interventions on Alzheimer's Disease: A Systematic Review and Meta-Analysis

The most prevalent type of dementia, especially in older persons, is Alzheimer's disease (AD), which has clinical signs of progressive cognitive decline and functional impairment. However, new research indicates that AD patients' dietary patterns and nutritional intake could hold the key to staving off some of the complications. Therefore, the primary aim of this investigation was to analyze various dietary patterns and the subsequent impact of the resulting nutritional intake on AD patients. Various online databases (PubMed, Scopus, Web of Science, and Google Scholar) were searched using appropriate keywords, reference searches, and citation searches. The databases were accessed using the search phrases "Alzheimer's disease," "dietary habits," "minerals," "nutritional profile," and "vitamins." Fifteen of the 21 investigations that we selected for our systematic review and subsequent meta-analysis revealed that micronutrient supplementation and some dietary patterns were helpful in alleviating a few of the symptoms of AD, especially with regard to the progression of dementia in the assessed patients. It was shown that dietary interventions and nutritional adjustments can considerably delay the onset of AD and the varying degrees of dementia that often accompany it. However, there were some areas of ambiguity in our findings because a few of the chosen studies did not document any noticeable improvements in the patient's conditions.

Unleashing nature's potential and limitations: Exploring molecular targeted pathways and safe alternatives for the treatment of multiple sclerosis (Review)

Driven by the limitations and obstacles of the available approaches and medications for multiple sclerosis (MS) that still cannot treat the disease, but only aid in accelerating the recovery from its attacks, the use of naturally occurring molecules as a potentially safe and effective treatment for MS is being explored in model organisms. MS is a devastating disease involving the brain and spinal cord, and its symptoms vary widely. Multiple molecular pathways are involved in the pathogenesis of the disease. The present review showcases the recent advancements in harnessing nature's resources to combat MS. By deciphering the molecular pathways involved in the pathogenesis of the disease, a wealth of potential therapeutic agents is uncovered that may revolutionize the treatment of MS. Thus, a new hope can be envisioned in the future, aiming at paving the way toward identifying novel safe alternatives to improve the lives of patients with MS.

Gut Microbial Metabolome and Dysbiosis in Neurodegenerative Diseases: Psychobiotics and Fecal Microbiota Transplantation as a Therapeutic Approach-A Comprehensive Narrative Review

The comprehensive narrative review conducted in this study delves into the mechanisms of communication and action at the molecular level in the human organism. The review addresses the complex mechanism involved in the microbiota-gut-brain axis as well as the implications of alterations in the microbial composition of patients with neurodegenerative diseases. The pathophysiology of neurodegenerative diseases with neuronal loss or death is analyzed, as well as the mechanisms of action of the main metabolites involved in the bidirectional communication through the microbiota-gut-brain axis. In addition, interventions targeting gut microbiota restructuring through fecal microbiota transplantation and the use of psychobiotics-pre- and pro-biotics-are evaluated as an opportunity to reduce the symptomatology associated with neurodegeneration in these pathologies. This review provides valuable information and facilitates a better understanding of the neurobiological mechanisms to be addressed in the treatment of neurodegenerative diseases.

Host insulin resistance caused by Porphyromonas gingivalis-review of recent progresses

Porphyromonas gingivalis (P. gingivalis) is a Gram-negative oral anaerobic bacterium that plays a key role in the pathogenesis of periodontitis. P. gingivalis expresses a variety of virulence factors that disrupt innate and adaptive immunity, allowing P. gingivalis to survive and multiply in the host and destroy periodontal tissue. In addition to periodontal disease, P.gingivalis is also associated with systemic diseases, of which insulin resistance is an important pathological basis. P. gingivalis causes a systemic inflammatory response, disrupts insulin signaling pathways, induces pancreatic β-cell hypofunction and reduced numbers, and causes decreased insulin sensitivity leading to insulin resistance (IR). In this paper, we systematically review the studies on the mechanism of insulin resistance induced by P. gingivalis, discuss the association between P. gingivalis and systemic diseases based on insulin resistance, and finally propose relevant therapeutic approaches. Overall, through a systematic review of the mechanisms related to systemic diseases caused by P. gingivalis through insulin resistance, we hope to provide new insights for future basic research and clinical interventions for related systemic diseases.

Signalling cognition: the gut microbiota and hypothalamic-pituitary-adrenal axis

Cognitive function in humans depends on the complex and interplay between multiple body systems, including the hypothalamic-pituitary-adrenal (HPA) axis. The gut microbiota, which vastly outnumbers human cells and has a genetic potential that exceeds that of the human genome, plays a crucial role in this interplay. The microbiota-gut-brain (MGB) axis is a bidirectional signalling pathway that operates through neural, endocrine, immune, and metabolic pathways. One of the major neuroendocrine systems responding to stress is the HPA axis which produces glucocorticoids such as cortisol in humans and corticosterone in rodents. Appropriate concentrations of cortisol are essential for normal neurodevelopment and function, as well as cognitive processes such as learning and memory, and studies have shown that microbes modulate the HPA axis throughout life. Stress can significantly impact the MGB axis via the HPA axis and other pathways. Animal research has advanced our understanding of these mechanisms and pathways, leading to a paradigm shift in conceptual thinking about the influence of the microbiota on human health and disease. Preclinical and human trials are currently underway to determine how these animal models translate to humans. In this review article, we summarize the current knowledge of the relationship between the gut microbiota, HPA axis, and cognition, and provide an overview of the main findings and conclusions in this broad field.

Peripheral metabolism of lipoprotein-amyloid beta as a risk factor for Alzheimer's disease: potential interactive effects of APOE genotype with dietary fats

Alzheimer's disease (AD) is a progressive neurodegenerative disorder pathologically characterized by brain parenchymal abundance of amyloid-beta (Aβ) and the accumulation of lipofuscin material that is rich in neutral lipids. However, the mechanisms for aetiology of AD are presently not established. There is increasing evidence that metabolism of lipoprotein-Aβ in blood is associated with AD risk, via a microvascular axis that features breakdown of the blood-brain barrier, extravasation of lipoprotein-Aβ to brain parenchyme and thereafter heightened inflammation. A peripheral lipoprotein-Aβ/capillary axis for AD reconciles alternate hypotheses for a vascular, or amyloid origin of disease, with amyloidosis being probably consequential. Dietary fats may markedly influence the plasma abundance of lipoprotein-Aβ and by extension AD risk. Similarly, apolipoprotein E (Apo E) serves as the primary ligand by which lipoproteins are cleared from plasma via high-affinity receptors, for binding to extracellular matrices and thereafter for uptake of lipoprotein-Aβ via resident inflammatory cells. The epsilon APOE ε4 isoform, a major risk factor for AD, is associated with delayed catabolism of lipoproteins and by extension may increase AD risk due to increased exposure to circulating lipoprotein-Aβ and microvascular corruption.

The gut microbiome in Alzheimer's disease: what we know and what remains to be explored

Alzheimer's disease (AD), the most common cause of dementia, results in a sustained decline in cognition. There are currently few effective disease modifying therapies for AD, but insights into the mechanisms that mediate the onset and progression of disease may lead to new, effective therapeutic strategies. Amyloid beta oligomers and plaques, tau aggregates, and neuroinflammation play a critical role in neurodegeneration and impact clinical AD progression. The upstream modulators of these pathological features have not been fully clarified, but recent evidence indicates that the gut microbiome (GMB) may have an influence on these features and therefore may influence AD progression in human patients. In this review, we summarize studies that have identified alterations in the GMB that correlate with pathophysiology in AD patients and AD mouse models. Additionally, we discuss findings with GMB manipulations in AD models and potential GMB-targeted therapeutics for AD. Lastly, we discuss diet, sleep, and exercise as potential modifiers of the relationship between the GMB and AD and conclude with future directions and recommendations for further studies of this topic.

Gut-derived β-amyloid: Likely a centerpiece of the gut-brain axis contributing to Alzheimer's pathogenesis

Peripheral β-amyloid (Aβ), including those contained in the gut, may contribute to the formation of Aβ plaques in the brain, and gut microbiota appears to exert an impact on Alzheimer's disease (AD) via the gut-brain axis, although detailed mechanisms are not clearly defined. The current study focused on uncovering the potential interactions among gut-derived Aβ in aging, gut microbiota, and AD pathogenesis. To achieve this goal, the expression levels of Aβ and several key proteins involved in Aβ metabolism were initially assessed in mouse gut, with key results confirmed in human tissue. The results demonstrated that a high level of Aβ was detected throughout the gut in both mice and human, and gut Aβ42 increased with age in wild type and mutant amyloid precursor protein/presenilin 1 (APP/PS1) mice. Next, the gut microbiome of mice was characterized by 16S rRNA sequencing, and we found the gut microbiome altered significantly in aged APP/PS1 mice and fecal microbiota transplantation (FMT) of aged APP/PS1 mice increased gut BACE1 and Aβ42 levels. Intra-intestinal injection of isotope or fluorescence labeled Aβ combined with vagotomy was also performed to investigate the transmission of Aβ from gut to brain. The data showed that, in aged mice, the gut Aβ42 was transported to the brain mainly via blood rather than the vagal nerve. Furthermore, FMT of APP/PS1 mice induced neuroinflammation, a phenotype that mimics early AD pathology. Taken together, this study suggests that the gut is likely a critical source of Aβ in the brain, and gut microbiota can further upregulate gut Aβ production, thereby potentially contributing to AD pathogenesis.

Central and peripheral regulations mediated by short-chain fatty acids on energy homeostasis

The human gut microbiota influences obesity, insulin resistance, and the subsequent development of type 2 diabetes (T2D). The gut microbiota digests and ferments nutrients resulting in the production of short-chain fatty acids (SCFAs), which generate various beneficial metabolic effects on energy and glucose homeostasis. However, their roles in the central nervous system (CNS)-mediated outputs on the metabolism have only been minimally studied. Here, we explore what is known and future directions that may be worth exploring in this emerging area. Specifically, we searched studies or data in English by using PubMed, Google Scholar, and the Human Metabolome Database. Studies were filtered by time from 1978 to March 2022. As a result, 195 studies, 53 reviews, 1 website, and 1 book were included. One hundred and sixty-five of 195 studies describe the production and metabolism of SCFAs or the effects of SCFAs on energy homeostasis, glucose balance, and mental diseases through the gut-brain axis or directly by a central pathway. Thirty of 195 studies show that inappropriate metabolism and excessive of SCFAs are metabolically detrimental. Most studies suggest that SCFAs exert beneficial metabolic effects by acting as the energy substrate in the TCA cycle, regulating the hormones related to satiety regulation and insulin secretion, and modulating immune cells and microglia. These functions have been linked with AMPK signaling, GPCRs-dependent pathways, and inhibition of histone deacetylases (HDACs). However, the studies focusing on the central effects of SCFAs are still limited. The mechanisms by which central SCFAs regulate appetite, energy expenditure, and blood glucose during different physiological conditions warrant further investigation.

Periodontal health, cognitive decline, and dementia: A systematic review and meta-analysis of longitudinal studies

BACKGROUND

Emerging evidence indicates that poor periodontal health adversely impacts cognition. This review examined the available longitudinal evidence concerning the effect of poor periodontal health on cognitive decline and dementia.

METHODS

Comprehensive literature search was conducted on five electronic databases for relevant studies published until April 2022. Longitudinal studies having periodontal health as exposure and cognitive decline and/or dementia as outcomes were considered. Random effects pooled estimates and 95% confidence intervals were generated (pooled odds ratio for cognitive decline and hazards ratio for dementia) to assess whether poor periodontal health increases the risk of cognitive decline and dementia. Heterogeneity between studies was estimated by I2 and the quality of available evidence was assessed through quality assessment criteria.

RESULTS

Adopted search strategy produced 2132 studies for cognitive decline and 2023 for dementia, from which 47 studies (24 for cognitive decline and 23 for dementia) were included in this review. Poor periodontal health (reflected by having periodontitis, tooth loss, deep periodontal pockets, or alveolar bone loss) was associated with both cognitive decline (OR = 1.23; 1.05-1.44) and dementia (HR = 1.21; 1.07-1.38). Further analysis, based on measures of periodontal assessment, found tooth loss to independently increase the risk of both cognitive decline (OR = 1.23; 1.09-1.39) and dementia (HR = 1.13; 1.04-1.23). Stratified analysis based on the extent of tooth loss indicated partial tooth loss to be important for cognitive decline (OR = 1.50; 1.02-2.23) and complete tooth loss for dementia (HR = 1.23; 1.05-1.45). However, the overall quality of evidence was low, and associations were at least partly due to reverse causality.

CONCLUSIONS

Poor periodontal health and tooth loss appear to increase the risk of both cognitive decline and dementia. However, the available evidence is limited (e.g., highly heterogenous, lacking robust methodology) to draw firm conclusions. Further well-designed studies involving standardized periodontal and cognitive health assessment and addressing reverse causality are highly warranted.

Polysaccharide Regulation of Intestinal Flora: A Viable Approach to Maintaining Normal Cognitive Performance and Treating Depression

The intestinal tract of a healthy body is home to a large variety and number of microorganisms that will affect every aspect of the host’s life. In recent years, polysaccharides have been found to be an important factor affecting intestinal flora. Polysaccharides are widely found in nature and play a key role in the life activities of living organisms. In the intestinal tract of living organisms, polysaccharides have many important functions, such as preventing the imbalance of intestinal flora and maintaining the integrity of the intestinal barrier. Moreover, recent studies suggest that gut microbes can influence brain health through the brain-gut axis. Therefore, maintaining brain health through polysaccharide modulation of gut flora deserves further study. In this review, we outline the mechanisms by which polysaccharides maintain normal intestinal flora structure, as well as improving cognitive function in the brain via the brain-gut axis by virtue of the intestinal flora. We also highlight the important role that gut microbes play in the pathogenesis of depression and the potential for treating depression through the use of polysaccharides to modulate the intestinal flora.

Influence of the Microbiota-Gut-Brain Axis on Cognition in Alzheimer’s Disease

The gut microbiota is made up of trillions of microbial cells including bacteria, viruses, fungi, and other microbial bodies and is greatly involved in the maintenance of proper health of the host body. In particular, the gut microbiota has been shown to not only be involved in brain development but also in the modulation of behavior, neuropsychiatric disorders, and neurodegenerative diseases including Alzheimer’s disease. The precise mechanism by which the gut microbiota can affect the development of Alzheimer’s disease is unknown, but the gut microbiota is thought to communicate with the brain directly via the vagus nerve or indirectly through signaling molecules such as cytokines, neuroendocrine hormones, bacterial components, neuroactive molecules, or microbial metabolites such as short-chain fatty acids. In particular, interventions such as probiotic supplementation, fecal microbiota transfer, and supplementation with microbial metabolites have been used not only to study the effects that the gut microbiota has on behavior and cognitive function, but also as potential therapeutics for Alzheimer’s disease. A few of these interventions, such as probiotics, are promising candidates for the improvement of cognition in Alzheimer ’s disease and are the focus of this review.

Infection and Immunometabolism in the Central Nervous System: A Possible Mechanistic Link Between Metabolic Imbalance and Dementia

Metabolic syndromes are frequently associated with dementia, suggesting that the dysregulation of energy metabolism can increase the risk of neurodegeneration and cognitive impairment. In addition, growing evidence suggests the link between infections and brain disorders, including Alzheimer's disease. The immune system and energy metabolism are in an intricate relationship. Infection triggers immune responses, which are accompanied by imbalance in cellular and organismal energy metabolism, while metabolic disorders can lead to immune dysregulation and higher infection susceptibility. In the brain, the activities of brain-resident immune cells, including microglia, are associated with their metabolic signatures, which may be affected by central nervous system (CNS) infection. Conversely, metabolic dysregulation can compromise innate immunity in the brain, leading to enhanced CNS infection susceptibility. Thus, infection and metabolic imbalance can be intertwined to each other in the etiology of brain disorders, including dementia. Insulin and leptin play pivotal roles in the regulation of immunometabolism in the CNS and periphery, and dysfunction of these signaling pathways are associated with cognitive impairment. Meanwhile, infectious complications are often comorbid with diabetes and obesity, which are characterized by insulin resistance and leptin signaling deficiency. Examples include human immunodeficiency virus (HIV) infection and periodontal disease caused by an oral pathogen Porphyromonas gingivalis. This review explores potential interactions between infectious agents and insulin and leptin signaling pathways, and discuss possible mechanisms underlying the relationship between infection, metabolic dysregulation, and brain disorders, particularly focusing on the roles of insulin and leptin.

Association between multiple sclerosis and dietary patterns based on the traditional concept of food nature: a case-control study in Iran

INTRODUCTION

It remains a matter of debate whether traditional concepts regarding the nature of food affect the development and progression of multiple sclerosis (MS).To date, there are limited studies that have investigated the association between MS and dietary patterns based on the categories of food nature (hot, cold, or balanced) defined in traditional medicine.

METHOD

This case-control study was conducted from October 2019 to February 2020. In total, 60 patients diagnosed with MS within the preceding 6 months and referred to our neurology outpatient clinic were included in our case group. The control group included 180 patients who were referred to the same center for general or orthopedic surgery. Dietary intake was assessed in both groups through a reliable and valid semi-quantitative food frequency questionnaire. Data were assessed using principal component analysis.

RESULTS

The mean age of the participants was 44.9 ± 17.33 years. The analysis showed that four food patterns were distinguished (eigenvalue > 1), namely "additives and cold-natured foods", "hot and balanced foods and nuts", "dairy and legumes", and "hot and balanced starches". These food patterns explained 57.8% of the total variance. After adjusting all confounding factors, individuals in the highest quartile and medium quartile of "additives and cold-natured foods" had an elevated MS risk compared with the lowest quartile (OR = 7.21, 95%CI = 2.01-12.38 and OR = 3.37, 95%CI = 1.02-11.35, respectively). Furthermore, individuals in the highest quartile of the "hot and balanced foods and nuts" group were protected against MS compared with its lowest quartile (OR = 0.28, 95%CI = 0.08-0.90). Moreover, a protective effect against MS was seen in the highest quartile of the "hot and balanced starches" group relative to its lowest quartile (OR = 0.34, 95%CI = 0.12-0.98). No significant association was found between "dairy and legumes" and the risk of MS.

CONCLUSION

This study revealed that dietary patterns based on the traditional concept of food nature might be associated with the risk of developing MS. This represents the first work in this area, so further research is recommended.

Effects of Nutrition on Cognitive Function in Adults with or without Cognitive Impairment: A Systematic Review of Randomized Controlled Clinical Trials

New dietary approaches for the prevention of cognitive impairment are being investigated. However, evidence from dietary interventions is mainly from food and nutrient supplement interventions, with inconsistent results and high heterogeneity between trials. We conducted a comprehensive systematic search of randomized controlled trials (RCTs) published in MEDLINE-PubMed, from January 2018 to July 2021, investigating the impact of dietary counseling, as well as food-based and dietary supplement interventions on cognitive function in adults with or without cognitive impairment. Based on the search strategy, 197 eligible publications were used for data abstraction. Finally, 61 articles were included in the analysis. There was reasonable evidence that dietary patterns, as well as food and dietary supplements improved cognitive domains or measures of brain integrity. The Mediterranean diet showed promising results, whereas the role of the DASH diet was not clear. Healthy food consumption improved cognitive function, although the quality of these studies was relatively low. The role of dietary supplements was mixed, with strong evidence of the benefits of polyphenols and combinations of nutrients, but with low evidence for PUFAs, vitamin D, specific protein, amino acids, and other types of supplements. Further well-designed RCTs are needed to guide the development of dietary approaches for the prevention of cognitive impairment.