An Investigation Into Physical Frailty as a Link Between the Gut Microbiome and Cognitive Health

The Association of the Oral Microbiota with Cognitive Functioning in Adolescence

Background: A growing body of research supports the role of the microbial communities residing in the digestive system in the host's cognitive functioning. Most of these studies have been focused on the gut microbiome and its association with clinical phenotypes in middle-aged and older adults. There is an insufficiency of population-based research exploring the association of normative cognitive functioning with the microbiome particularly with the oral microbiota. Methods: In this study, using metagenomics and metabolomics, we characterized the salivary microbiome diversity in a sample of 51 males of Hispanic and African American origin aged 12-18 years and explored the associations between the microbiome and the youths' cognitive performance captured with the Kaufman Assessment Battery for Children II (KABC-II). Results: Several bacterial species of the oral microbiota and related metabolic pathways were associated with cognitive function. In particular, we found negative associations between indicators of general intelligence and the relative abundance of Bacteroidetes and Lachnospiraceae and positive associations with Bifidobacteriaceae and Prevotella histicola sp. Among metabolic pathways, the super pathways related to bacterial cell division and GABA metabolism were linked to cognitive function. Conclusions: The results of our work are consistent with the literature reporting on the association between microbiota and cognitive function and support further population work to elucidate the potential for a healthy oral microbiome to improve cognitive health.

Unlocking the mind-gut connection: Impact of human microbiome on cognition

This perspective explores the current understanding of the gut microbiota's impact on cognitive function in apparently healthy humans and in individuals with metabolic disease. We discuss how alterations in gut microbiota can influence cognitive processes, focusing not only on bacterial composition but also on often overlooked components of the gut microbiota, such as bacteriophages and eukaryotes, as well as microbial functionality. We examine the mechanisms through which gut microbes might communicate with the central nervous system, highlighting the complexity of these interactions. We provide a comprehensive overview of the emerging field of microbiota-gut-brain interactions and its significance for cognitive health. Additionally, we summarize novel therapeutic strategies designed to promote cognitive resilience and reduce the risk of cognitive disorders, focusing on interventions that target the gut microbiota. An in-depth understanding of the microbiome-brain axis is imperative for developing innovative treatments aimed at improving cognitive health.

UV aging may enhance adsorption capacity of Poly (butylene adipate-co-terephthalate) (PBAT) to heavy metals and toxicity to zebrafish

Compared with the fossil-based plastics, biodegradable plastics are more easily decomposed into small-sized particles (e.g., microplastics). However, the role of aged biodegradable plastics in being vector of co-existed pollutants and potential toxicological effects remain to be elucidated. The present study selected micro-sized biodegradable polymer Poly (butylene adipate-co-terephthalate) (PBAT) as the object, aiming to explore its aging process, environmental behavior with heavy metals (Cu and Pb), and the toxic effects on zebrafish. The results showed that distinct changes such as cracks and severe deformation can be observed on the surface of PBAT after 60 days of UV aging, and the functional groups changed consequently. The maximum adsorption capacity of aged PBAT for Cu and Pb reached 0.967 and 0.939 mg·g-1, which increased by 1.32 and 1.46 times, respectively. The results of 7-day acute toxicology experiments suggested that the adsorption behavior of aged PBAT may alleviate the toxic effects of heavy metals Cu and Pb on zebrafish in short-term exposure, however it could simultaneously cause a serious imbalance of intestinal microorganisms in zebrafish. As demonstrated, the coexistence of aged PBAT and heavy metals (Cu, Pb) can seriously reduce the intestinal microbial diversity and richness of zebrafish, which may induce more serious toxicity and disease in long-term exposure to pollutants. This study could provide fundamental data for better understanding on the adsorption behavior and ecological risk of aged biodegradable plastics with coexisted pollutants.

Changes of faecal bacterial communities and microbial fibrolytic activity in horses aged from 6 to 30 years old

Horse owners and veterinarians report that from the age of 15, their horses can lose body condition and be more susceptible to diseases. Large intestinal microbiome changes may be involved. Indeed, microbiota is crucial for maintaining the condition and health of herbivores by converting fibres into nutrients. This study aimed to compare the faecal microbiome in horses aged from 6 to 30 years old (yo), living in the same environment and consuming the same diet, in order to assess whether the parameters changed linearly with age and whether there was a pivotal age category. Fifty horses were selected from the same environment and distributed across four age categories: 6-10 (n = 12), 11-15 (n = 11), 16-20 (n = 13), and 21-30 (n = 14) yo. All horses had no digestive problems, had teeth suitable for consuming their feed, and were up to date with their vaccination and deworming programmes. After three weeks of constant diet (ad libitum hay and 860 g of concentrate per day), one faecal sample per horse was collected on the same day. The bacterial communities' richness and intra-sample diversity were negatively correlated with age. There was a new distribution of non-beneficial and beneficial taxa, particularly in the 21-30 yo category. Although the faecal concentration of short-chain fatty acids remained stable, the acetate proportion was negatively correlated with age while it was the opposite for the proportions of butyrate, valerate, and iso-valerate. Additionally, the faecal pH was negatively correlated with age. Differences were more pronounced when comparing the 6-10 yo and 21-30 yo categories. The values of the parameters studied became more dispersed from the 16-20 yo category onwards, which appeared as a transitional moment, as it did not differ significantly from the younger and older categories for most of these parameters. Our data suggest that the microbiome changes with age. By highlighting the pivotal age of 16-20, this gives the opportunity to intervene before individuals reach extremes that could lead to pathological conditions.

Gut Microbiome Multi-Omics and Cognitive Function in the Hispanic Community Health Study/Study of Latinos- Investigation of Neurocognitive Aging

INTRODUCTION

We conducted a study within the Hispanic Community Health Study/Study of Latinos- Investigation of Neurocognitive Aging (HCHS/SOL-INCA) cohort to examine the association between gut microbiome and cognitive function.

METHODS

We analyzed the fecal metagenomes of 2,471 HCHS/SOL-INCA participants to, cross-sectionally, identify microbial taxonomic and functional features associated with global cognitive function. Omnibus (PERMANOVA) and feature-wise analyses (MaAsLin2) were conducted to identify microbiome-cognition associations, and specific microbial species and pathways (Kyoto Encyclopedia of Genes and Genomes (KEGG modules) associated with cognition.

RESULTS

Eubacterium species( E. siraeum and E. eligens ), were associated with better cognition. Several KEGG modules, most strongly Ornithine, Serine biosynthesis and Urea Cycle, were associated with worse cognition.

DISCUSSION

In a large Hispanic/Latino cohort, we identified several microbial taxa and KEGG pathways associated with cognition.

The Interplay between Gut Microbiota and Cognitive Functioning in the Healthy Aging Population: A Systematic Review

BACKGROUND

The gut microbiota in healthy older individuals typically show a decrease in beneficial bacteria like Bifidobacterium and Lactobacillus, alongside an increase in pro-inflammatory microbes such as Enterobacteriaceae and Clostridia. These changes contrast with younger and middle-aged individuals and appear to correlate with cognitive status. Although there is extensive research on gut microbiota and cognitive functions in cognitively impaired elderly individuals, its impact on cognitively healthy elderly populations has not been extensively studied.

METHOD

A comprehensive literature search was conducted across PubMed, EBSCO, Web of Science, and Scopus databases to identify studies exploring the relationship between gut microbiota composition and cognitive functioning in healthy older adults. During the literature screening process, each record was initially assessed by its title, abstract, and keywords to exclude articles that did not align with the scope of this review. Three authors independently screened and retrieved the records. The inclusion criteria included: (1) publication in peer-reviewed journals; (2) studies involving neurologically, cognitively, and medically healthy populations; (3) participants identified as older adults, defined for this review as individuals aged 45 years and older due to the limited number of records; (4) analysis of gut microbiota; and (5) assessment of cognitive function. Subsequently, full texts were analyzed to determine eligibility. The exclusion criteria encompassed: (1) incorrect publication type; (2) inappropriate sample population; (3) unsuitable study design; (4) absence of one or more inclusion criteria; and (5) studies based on animal research. A risk of bias assessment was performed for each included study using the Joanna Briggs Institute (JBI) checklist, ensuring all selected studies met established quality standards.

RESULTS

A total of 6 eligible research articles from a possible 1752 published until March 2024 were identified and included. We categorized the included studies into two groups based on their focus: the taxonomic composition of gut microbiota and the alpha diversity, which is the variety of organisms within a sample. Additionally, two methods were identified for assessing cognition: neuropsychological tests and physiological measurements, notably electroencephalography (EEG). The studies show varying results regarding the abundance of specific bacterial taxa and their cognitive associations. Notably, the relationship between certain bacteria and cognition may vary when analyzed at different taxonomic levels, such as phylum versus family.

CONCLUSIONS

Changes in gut microbiota composition in the elderly, even without a cognitive impairment diagnosis, could potentially serve as early biological markers for Alzheimer's disease or other dementias before mild cognitive impairment appears.

The human gut microbiome and aging

The composition of the human gut microbiome has been observed to change over the course of an individual's life. From birth, it is shaped by mode of delivery, diet, environmental exposures, geographic location, exposures to medications, and by aging itself. Here, we present a narrative review of the gut microbiome across the lifespan with a focus on its impacts on aging and age-related diseases in humans. We will describe how it is shaped, and features of the gut microbiome that have been associated with diseases at different phases of life and how this can adversely affect healthy aging. Across the lifespan, and especially in old age, a diverse microbiome that includes organisms suspected to produce anti-inflammatory metabolites such as short-chain fatty acids, has been reported to be associated with healthy aging. These findings have been remarkably consistent across geographic regions of the world suggesting that they could be universal features of healthy aging across all cultures and genetic backgrounds. Exactly how these features of the microbiome affect biologic processes associated with aging thus promoting healthy aging will be crucial to targeting the gut microbiome for interventions that will support health and longevity.

Dietary Marine Hydrolysate Improves Memory Performance and Social Behavior through Gut Microbiota Remodeling during Aging

Aging is characterized by a decline in social behavior and cognitive functions leading to a decrease in life quality. In a previous study, we show that a fish hydrolysate supplementation prevents age-related decline in spatial short-term memory and long-term memory and anxiety-like behavior and improves the stress response in aged mice. The aim of this study was to determine the effects of a fish hydrolysate enriched with EPA/DHA or not on the cognitive ability and social interaction during aging and the biological mechanisms involved. We showed for the first time that a fish hydrolysate enriched with EPA/DHA or not improved memory performance and preference for social novelty that were diminished by aging. These changes were associated with the modulation of the gut microbiota, normalization of corticosterone, and modulation of the expression of genes involved in the mitochondrial respiratory chain, circadian clock, neuroprotection, and antioxidant activity. Thus, these changes may contribute to the observed improvements in social behavior and memory and reinforced the innovative character of fish hydrolysate in the prevention of age-related impairments.

Gut microbiota in muscular atrophy development, progression, and treatment: New therapeutic targets and opportunities

Skeletal muscle atrophy is a debilitating condition that significantly affects quality of life and often lacks effective treatment options. Muscle atrophy can have various causes, including myogenic, neurogenic, and other factors. Recent investigation has underscored a compelling link between the gut microbiota and skeletal muscle. Discerning the potential differences in the gut microbiota associated with muscle atrophy-related diseases, understanding their influence on disease development, and recognizing their potential as intervention targets are of paramount importance. This review aims to provide a comprehensive overview of the role of the gut microbiota in muscle atrophy-related diseases. We summarize clinical and pre-clinical studies that investigate the potential for gut microbiota modulation to enhance muscle performance and promote disease recovery. Furthermore, we delve into the intricate interplay between the gut microbiota and muscle atrophy-related diseases, drawing from an array of studies. Emerging evidence suggests significant differences in gut microbiota composition in individuals with muscle atrophy-related diseases compared with healthy individuals. It is conceivable that these alterations in the microbiota contribute to the pathogenesis of these disorders through bacterium-related metabolites or inflammatory signals. Additionally, interventions targeting the gut microbiota have demonstrated promising results for mitigating disease progression in animal models, underscoring the therapeutic potential of modulating the gut microbiota in these conditions. By analyzing the available literature, this review sheds light on the involvement of the gut microbiota in muscle atrophy-related diseases. The findings contribute to our understanding of the underlying mechanisms and open avenues for development of novel therapeutic strategies targeting the gut-muscle axis.

INFLAMMATORY BOWEL DISEASE AND SARCOPENIA: A FOCUS ON MUSCLE STRENGTH - NARRATIVE REVIEW

•Muscle strength decline is a crucial factor for the course of sarcopenia in inflammatory bowel disease (IBD) patients. •There is a need to discuss the association between IBD and sarcopenia focusing not only on changes of muscle mass, but also on muscle strength. •A narrative review was conducted in order to present the set of factors with impact in both muscle strength and IBD. •Inflammation, reduced nutrient intake and malabsorption, changes in body composition and gut microbiota dysbiosis are most likely the main factors with impact on muscle strength in IBD patients. Inflammation, changes in nutrient absorption and gut dysbiosis are common conditions in patients with inflammatory bowel disease. These factors may lead to variations in macro- and micronutrients and, particularly, to an imbalance of protein metabolism, loss of muscle mass and development of sarcopenia. This narrative review aims to present the set of factors with impact in muscle strength and physical performance that may potentially mediate the relation between inflammatory bowel disease and sarcopenia. Studies that associated changes in muscle strength, sarcopenia and inflammatory bowel disease were selected through a literature search in databases Medline, Pubmed and Scielo using relevant keywords: muscle strength, physical performance, sarcopenia and inflammatory bowel disease. Chronic inflammation is currently reported as a determinant factor in the development of muscle atrophy in inflammatory bowel disease. In addition, strength decline in inflammatory bowel disease patients may be also influenced by changes in body composition and by gut dysbiosis. Measures of muscle strength and physical performance should be considered in the initial identification of sarcopenia, particularly in patients with inflammatory bowel disease, for a timely intervention can be provided. Presence of proinflammatory cytokines, high adiposity, malabsorption and consequent deficits of macro and micronutrients, loss of muscle mass, and gut dysbiosis may be the main factors with impact in muscle strength, that probably mediate the relation between inflammatory bowel disease and sarcopenia.

The possible role of gut microbiota dysbiosis in the pathophysiology of delirium in older persons

Delirium is a clinical syndrome characterized by an acute change in attention, awareness and cognition with fluctuating course, frequently observed in older patients during hospitalization for acute medical illness or after surgery. Its pathogenesis is multifactorial and still not completely understood, but there is general consensus on the fact that it results from the interaction between an underlying predisposition, such as neurodegenerative diseases, and an acute stressor acting as a trigger, such as infection or anesthesia. Alterations in brain insulin sensitivity and metabolic function, increased blood-brain barrier permeability, neurotransmitter imbalances, abnormal microglial activation and neuroinflammation have all been involved in the pathophysiology of delirium. Interestingly, all these mechanisms can be regulated by the gut microbiota, as demonstrated in experimental studies investigating the microbiota-gut-brain axis in dementia. Aging is also associated with profound changes in gut microbiota composition and functions, which can influence several aspects of disease pathophysiology in the host. This review provides an overview of the emerging evidence linking age-related gut microbiota dysbiosis with delirium, opening new perspectives for the microbiota as a possible target of interventions aimed at delirium prevention and treatment.

Longevity-Associated Core Gut Microbiota Mining and Effect of Mediated Probiotic Combinations on Aging Mice: Case Study of a Long-Lived Population in Guangxi, China

With an ageing population, healthy longevity is becoming an important scientific concern. The longevity phenomenon is closely related to the intestinal microflora and is highly complicated; it is challenging to identify and define the core gut microbiota associated with longevity. Therefore, in this study, 16S rRNA sequencing data were obtained from a total of 135 faecal samples collected as part of the latest sampling and pre-collection initiative in the Guangxi longevity area, and weighted gene co-expression network analysis (WGCNA) was used to find a mediumpurple3 network module significantly associated with the Guangxi longevity phenomenon. Five core genera, namely, Alistipes, Bacteroides, Blautia, Lachnospiraceae NK4A136 group, and Lactobacillus, were identified via network analysis and random forest (RF) in this module. Two potential probiotic strains, Lactobacillus fermentum and Bacteroides fragilis, were further isolated and screened from the above five core genera, and then combined and used as an intervention in naturally ageing mice. The results show a change in the key longevity gut microbiota in mice toward a healthy longevity state after the intervention. In addition, the results show that the probiotic combination effectively ameliorated anxiety and necrosis of hippocampal neuronal cells in senescent mice, improving their antioxidant capacity and reducing their inflammation levels. In conclusion, this longer-term study provides a new approach to the search for longevity hub microbiota. These results may also provide an important theoretical reference for the healthification of the intestinal microflora in the general population, and even the remodelling of the structure of the longevity-state intestinal microflora.

Frailty status and risk of irritable bowel syndrome in middle-aged and older adults: A large-scale prospective cohort study

BACKGROUND

Frailty is a public health problem for ageing society, however, evidence is lacking regarding its impact on intestinal functions. We aimed to examine prospective relationships of frailty and pre-frailty in middle-aged and older adults with incident irritable bowel syndrome (IBS) in a large-scale population-based cohort.

METHODS

Participants (aged 37-73 years) free of IBS, coeliac disease, inflammatory bowel disease and any cancer at baseline were included, using data from the UK Biobank (collected 2006-2010, 22 assessment centres). Participants without available primary care data were excluded. Frailty status was assessed using Fried phenotype including five criteria (weight loss, exhaustion, low grip strength, low physical activity, slow walking pace). Participants who met at least three criteria were defined as frail, and those who fulfilled one or two criteria were defined as pre-frail. Primary outcome was incident IBS. Cox proportional hazard model was conducted to examine the associated risk of incident IBS.

FINDINGS

Among 176,423 participants (mean age 56.19 years), 7994 (4.5%) and 78,957 (44.8%) were frail and pre-frail at baseline. During a median of 13.2-year follow-up, 4155 cases of incident IBS were identified. Compared with non-frail individuals, those with frail (HR = 1.80, 95% CI: 1.59-2.04) and pre-frail (HR = 1.21, 1.14-1.30) showed significantly higher risk of developing IBS after multivariable adjustment (P_trend < 0.001). Specifically, the positive association was not only observed in older adults (HR = 1.69, 1.37-2.08 for frail; 1.24, 1.12-1.39 for pre-frail), but also in middle-aged adults (HR = 1.90, 1.62-2.22 for frail; 1.19, 1.10-1.30 for pre-frail), both with P_trend < 0.001. Further sensitivity analysis and subgroup analysis indicated similar results.

INTERPRETATION

Frailty and pre-frailty in middle-aged and older adults are associated with increased risk of incident clinical diagnosis of IBS.

FUNDING

National Natural Science Foundation of China (No. 82070550) & National Key Research and Development Program of China (2022YFC2504002, 2022YFC2504003).

Relation Between Dietary Protein Intake and Gut Microbiome Composition in Community-Dwelling Older Men: Findings from the Osteoporotic Fractures in Men Study (MrOS)

BACKGROUND

Little is known about the association of specific nutrients, especially proteins, on age-related gut dysbiosis.

OBJECTIVES

To determine the associations between the quantity and sources (vegetable and animal) of dietary protein intake and gut microbiome composition in community-dwelling older men.

METHODS

We performed a cross-sectional analysis on 775 older men from the Osteoporotic Fractures in Men Study (MrOS) (age 84.2 ± 4.0 y) with available dietary information and stool samples at visit 4 (2014-2016). Protein intake was estimated from a brief FFQ and adjusted to total energy intake. The gut microbiome composition was determined by 16S (v4) sequencing (processed by DADA2 and SILVA). A total of 11,534 amplicon sequence variants (ASVs) were identified and assigned to 21 phyla with dominance of Firmicutes (45%) and Bacteroidetes (43%). We performed α-diversity, β-diversity, and taxa abundance (by Analysis of Compositions of Microbiomes with Bias Correction [ANCOM-BC]) to determine the associations between protein intake and the gut microbiome.

RESULTS

Median protein intake was 0.7 g/(kg body weight · d). Participants with higher energy-adjusted protein intakes had higher Shannon and Chao1 α-diversity indices (P < 0.05). For β-diversity analysis, participants with higher protein intakes had a different center in weighted and unweighted UniFrac Principal Co-ordinates Analysis (PCoA) compared with those with lower intake (P < 0.05), adjusted for age, race, education, clinical center, batch number, fiber and energy intake, weight, height, and medications. Similarly, higher protein consumptions from either animal or vegetable sources were associated with higher gut microbiome diversity. Several genus-level ASVs, including Christensenellaceae, Veillonella, Haemophilus, and Klebsiella were more abundant in participants with higher protein intakes, whereas Clostridiales bacterium DTU089 and Desulfovibrio were more abundant in participants with lower protein intake (Bonferroni corrected P < 0.05).

CONCLUSIONS

We observed significant associations between protein intake and gut microbiome diversity in community-living older men. Further studies are needed to elucidate the mediation role of the gut microbiome on the relation between protein intake and health outcomes in older adults.

Mixed Tree Nuts, Cognition, and Gut Microbiota: A 4-Week, Placebo-Controlled, Randomized Crossover Trial in Healthy Nonelderly Adults

BACKGROUND

Beneficial effects of nut supplementation on cognitive function have previously been demonstrated in young and older adults. Alterations to gut microbiota have also been shown following tree nut consumption. However, no data exists on the effects of nuts on cognition and intestinal microbial communities assessed within the same study.

OBJECTIVES

The study aimed to examine the effects of daily consumption of tree nuts for 4 wk on cognitive function (primary outcome), mood, metabolomics, and gut microbial species (secondary outcomes) in healthy, nonelderly adults.

METHODS

This randomized, placebo-controlled, double-blind, counterbalanced crossover study assessed the effects of 4 wk of supplementation with 30 g/d mixed tree nuts versus placebo on cognition and mood in 79 healthy adults aged 18-49 y. Metabolic responses, gut bacterial community structure, and the potential for these to impact cognition were explored using a multi-omic approach. Bacterial community analysis was conducted in Quantitative Insights Into Microbial Ecology 2 (QIIME2).

RESULTS

Mixed model analysis indicated that nut consumption led to significant improvements to accuracy (placebo M = 92.2% compared with NUTS M = 94.5%; P = 0.019) and speed of response (placebo M = 788 ms compared with NUTS M = 757 ms; P = 0.004) on a picture recognition task. No significant changes to bacterial community α or β diversity were observed when comparing nut consumption to the placebo arm. However, an unclassified Lachnospiraceae amplicon sequence variant (ASV) was significantly enriched in participants when supplemented with nuts (P = 0.015). No correlations were observed between the changes to picture recognition and the changes to the unclassified Lachnospiraceae ASV. There were no significant changes to the urinary metabolome.

CONCLUSIONS

These findings indicate a positive effect of nut on cognition following only 4 wk of consumption in a healthy nonelderly sample, as well as upregulation of a microbial taxa associated with gut health. The effects appear to be independent of one another, but further exploration is required in those experiencing cognitive decline and/or gut dysbiosis.

The gut microbiome as a modulator of healthy ageing

The gut microbiome is a contributory factor in ageing-related health loss and in several non-communicable diseases in all age groups. Some age-linked and disease-linked compositional and functional changes overlap, while others are distinct. In this Review, we explore targeted studies of the gut microbiome of older individuals and general cohort studies across geographically distinct populations. We also address the promise of the targeted restoration of microorganisms associated with healthier ageing.

The effect of young blood plasma administration on gut microbiota in middle-aged rats

Numerous in-depth studies continue to reveal the many benefits of gut microbiota and young blood plasma administration. Dysbiosis, which occurs in the intestinal microbiota, especially in the aging process, is associated with many metabolic and cognitive disorders. Therefore, many studies aim to reverse the dysbiosis that occurs. There are also studies showing that young blood plasma application reverses the effects of aging at the level of many tissues and organs. Today, while research continues to reveal all the benefits of young blood plasma application in terms of health, blood plasma centers are also being established. In this study, we aimed to reveal the impact of young blood plasma, administered for 1 month, on the intestinal microbiota of middle-aged rats. After detailed metagenome analysis, alpha diversity indices demonstrated greater bacterial richness in the microbiota of plasma-administered rats compared with control rats. In addition, the Firmicutes/Bacteroidetes ratio was significantly diminished in plasma group microbiota, confirming possible rejuvenation properties of young plasma. Furthermore, increased counts of Bifidobacterium longum, Coprococcus catus, and Romboutsia ilealis species were measured in plasma-administered rats. The study revealed many fluctuations in different bacterial taxonomic units of the microbiota that could be valuable in future research on blood-based anti-aging treatments.

Age-related diseases, therapies and gut microbiome: A new frontier for healthy aging

The gut microbiome is undoubtedly a key modulator of human health, which can promote or impair homeostasis throughout life. This is even more relevant in old age, when there is a gradual loss of function in multiple organ systems, related to growth, metabolism, and immunity. Several studies have described changes in the gut microbiome across age groups up to the extreme limits of lifespan, including maladaptations that occur in the context of age-related conditions, such as frailty, neurodegenerative diseases, and cardiometabolic diseases. The gut microbiome can also interact bi-directionally with anti-age-related disease therapies, being affected and in turn influencing their efficacy. In this framework, the development of integrated microbiome-based intervention strategies, aimed at favoring a eubiotic configuration and trajectory, could therefore represent an innovative approach for the promotion of healthy aging and the achievement of longevity.

Gut Microbiota Markers and Dietary Habits Associated with Extreme Longevity in Healthy Sardinian Centenarians

This study was aimed at characterizing the gut microbiota (GM) and its functional profile in two groups of Sardinian subjects with a long healthy life expectancy, overall named Long-Lived Subjects (LLS) [17 centenarians (CENT) and 29 nonagenarians (NON)] by comparing them to 46 healthy younger controls (CTLs). In addition, the contribution of genetics and environmental factors to the GM phenotype was assessed by comparing a subgroup of seven centenarian parents (CPAR) with a paired cohort of centenarians’ offspring (COFF). The analysis was performed through Next Generation Sequencing (NGS) of the V3 and V4 hypervariable region of the 16S rRNA gene on the MiSeq Illumina platform. The Verrucomicrobia phylum was identified as the main biomarker in CENT, together with its members Verrucomicrobiaceae, Akkermansia and Akkermansia muciniphila. In NON, the strongest associations concern Actinobacteria phylum, Bifidobacteriaceae and Bifidobacterium, while in CTLs were related to the Bacteroidetes phylum, Bacteroidaceae, Bacteroides and Bacteroides spp. Intestinal microbiota of CPAR and COFF did not differ significantly from each other. Significant correlations between bacterial taxa and clinical and lifestyle data, especially with Mediterranean diet adherence, were observed. We observed a harmonically balanced intestinal community structure in which the increase in taxa associated with intestinal health would limit and counteract the action of potentially pathogenic bacterial species in centenarians. The GM of long-lived individuals showed an intrinsic ability to adapt to changing environmental conditions, as confirmed by functional analysis. The GM analysis of centenarians’ offspring suggest that genetics and environmental factors act synergistically as a multifactorial cause in the modulation of GM towards a phenotype similar to that of centenarians, although these findings need to be confirmed by larger study cohorts and by prospective studies.

A prospective investigation into the association between the gut microbiome composition and cognitive performance among healthy young adults

Background

There is emerging evidence that the gut microbiome composition is associated with several human health outcomes, which include cognitive performance. However, only a few prospective epidemiological studies exist and none among young adults. Here we address the gap in the literature by investigating whether the gut microbiome composition is prospectively linked to fluid intelligence among healthy young adults.

Methods

Forty individuals (65% females, 26 years) from the DOrtmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study provided a fecal sample for gut microbiome composition and subsequently (average of 166 days) completed a cognitive functioning test using the Cattell’s Culture Fair Intelligence Test, revised German version (CFT 20-R). The assessment of the gut microbiome at the genera level was by 16S rRNA V3-V4 Illumina sequencing. The relative abundance of 158 genera was summarized into bacterial communities using a novel data-driven dimension reduction, amalgamation. The fluid intelligence score was regressed on the relative abundance of the bacterial communities and adjusted for selected covariates.

Results

The 158 genera were amalgamated into 12 amalgams (bacterial communities), which were composed of 18, 6, 10, 14, 8, 10, 16, 13, 12, 12, 3, and 11 genera. Only the 14-genera bacterial community, named the “Ruminococcaceae- and Coriobacteriaceae-dominant community” was positively associated with fluid intelligence score (β = 7.8; 95% CI: 0.62, 15.65, P = 0.04).

Conclusion

Among healthy young adults, the abundance of a gut bacterial community was associated with fluid intelligence score. This study suggests that cognitive performance may potentially benefit from gut microbiome-based intervention.

Gut environment changes due to androgen deprivation therapy in patients with prostate cancer

BACKGROUND

It is estimated that by 2040 there will be 1,017,712 new cases of prostate cancer worldwide. Androgen deprivation therapy (ADT) is widely used as a treatment option for all disease stages. ADT, and the resulting decline in androgen levels, may indirectly affect gut microbiota. Factors affecting gut microbiota are wide-ranging; however, literature is scarce on the effects of ADT on gut microbiota and metabolome profiles in patients with prostate cancer.

METHODS

To study the changes of gut microbiome by ADT, this 24-week observational study investigated the relationship between testosterone levels and changes in gut microbiota in Japanese patients with prostate cancer undergoing ADT. Sequential faecal samples were collected 1 and 2 weeks before ADT, and 1, 4, 12, and 24 weeks after ADT. Blood samples were collected at almost the same times. Bacterial 16 S rRNA gene-based microbiome analyses and capillary electrophoresis-time-of-flight mass spectrometry-based metabolome analyses were performed.

RESULTS

In total, 23 patients completed the study. The α- and ß-diversity of gut microbiota decreased significantly at 24 weeks after ADT (p = 0.017, p < 0.001, respectively). Relative abundances of Proteobacteria, Gammaproteobacteria, Pseudomonadales, Pseudomonas, and concentrations of urea, lactate, butyrate, 2-hydroxyisobutyrate and S-adenosylmethionine changed significantly after ADT (p < 0.05). There was a significant positive correlation between the abundance of Proteobacteria, a known indicator of dysbiosis, and the concentration of lactate (R = 0.49, p < 0.01).

CONCLUSIONS

The decline in testosterone levels resulted in detrimental changes in gut microbiota. This dysbiosis may contribute to an increase in frailty and an increased risk of adverse outcomes in patients with prostate cancer.

Distinct Serum and Fecal Metabolite Profiles Linking With Gut Microbiome in Older Adults With Frailty

Frailty is a critical aging-related syndrome but the underlying metabolic mechanism remains poorly understood. The aim of this study was to identify novel biomarkers and reveal potential mechanisms of frailty based on the integrated analysis of metabolome and gut microbiome. In this study, twenty subjects consisted of five middle-aged adults and fifteen older adults, of which fifteen older subjects were divided into three groups: non-frail, pre-frail, and frail, with five subjects in each group. The presence of frailty, pre-frailty, or non-frailty was established according to the physical frailty phenotype (PFP). We applied non-targeted metabolomics to serum and feces samples and used 16S rDNA gene sequencing to detect the fecal microbiome. The associations between metabolites and gut microbiota were analyzed by the Spearman’s correlation analysis. Serum metabolic shifts in frailty mainly included fatty acids and derivatives, carbohydrates, and monosaccharides. Most of the metabolites belonging to these classes increased in the serum of frail older adults. Propylparaben was found to gradually decrease in non-frail, pre-frail, and frail older adults. Distinct changes in fecal metabolite profiles and gut microbiota were also found among middle-aged adults, non-frail and frail older subjects. The relative abundance of Faecalibacteriu, Roseburia, and Fusicatenibacter decreased while the abundance of Parabacteroides and Bacteroides increased in frailty. The above altered microbes were associated with the changed serum metabolites in frailty, which included dodecanedioic acid, D-ribose, D-(-)-mannitol, creatine and indole, and their related fecal metabolites. The changed microbiome and related metabolites may be used as the biomarkers of frailty and is worthy of further mechanistic studies.

Interactions between dietary polyphenols and aging gut microbiota: A review

Aging induces significant shifts in the composition of gut microbiota associated with decreased microbial diversity. Age-related changes in gut microbiota include a loss of commensals and an increase in disease-associated pathobionts. These alterations are accelerated by lifestyle factors, such as poor nutritional habits, physical inactivity, and medications. Given that diet is one of the main drivers shaping the gut microbiota, nutritional interventions for restoring gut homeostasis are of great importance to the overall health of older adults. Polyphenols, ubiquitously present in fruits and vegetables, have emerged as promising anti-aging candidates because of their ability to modulate some of the common denominators of aging, including gut dysbiosis. These compounds can influence the composition of the gut microbiota, and gut bacteria metabolize polyphenols into bioactive compounds that produce relevant health effects. Although the role of polyphenols on the aging gut has not been fully characterized, accumulating evidence suggests that these compounds exert selective effects on the gut microbial community. Here, we discuss the reciprocal interactions between polyphenols and gut microbiota and summarize the latest findings on the effects of polyphenols on modulating intestinal bacteria during aging.

Emerging Evidence on the Use of Probiotics and Prebiotics to Improve the Gut Microbiota of Older Adults with Frailty Syndrome: A Narrative Review

BACKGROUND

The gut microbiota can impact older adults' health, especially in patients with frailty syndrome. Understanding the association between the gut microbiota and frailty syndrome will help to explain the etiology of age-related diseases. Low-grade systemic inflammation is a factor leading to geriatric disorders, which is known as "inflammaging". Intestinal dysbiosis has a direct relationship with low-grade systemic inflammation because when the natural gut barrier is altered by age or other factors, some microorganisms or their metabolites can cross this barrier and reach the systemic circulation.

OBJECTIVES

This review had two general goals: first, to describe the characteristics of the gut microbiota associated with age-related diseases, specifically frailty syndrome. The second aim was to identify potential interventions to improve the composition and function of intestinal microbiota, consequently lessening the burden of patients with frailty syndrome.

METHODS

A search of scientific evidence was performed in PubMed, Science Direct, and Redalyc using keywords such as "frailty", "elderly", "nutrient interventions", "probiotics", and "prebiotics". We included studies reporting the effects of nutrient supplementation on frailty syndrome and older adults. These studies were analyzed to identify novel therapeutic alternatives to improve gut microbiota characteristics as well as subclinical signs related to this condition.

RESULTS

The gut microbiota participates in many metabolic processes that have an impact on the brain, muscles, and other organs. These processes integrate feedback mechanisms, comprising their respective axis with the intestine and the gut microbiota. Alterations in these associations can lead to frailty. We report a few interventions that demonstrate that prebiotics and probiotics could modulate the gut microbiota in humans. Furthermore, other nutritional interventions could be used in patients with frailty syndrome.

CONCLUSION

Probiotics and prebiotics may potentially prevent frailty syndrome or improve the quality of life of patients with this disorder. However, there is not enough information about their appropriate doses and periods of administration. Therefore, further investigations are required to determine these factors and improve their efficacy as therapeutic approaches for frailty syndrome.

Gut Microbiota and Subjective Memory Complaints in Older Women

BACKGROUND

Epidemiological studies that investigate alterations in gut microbial composition associated with cognitive dysfunction are limited.

OBJECTIVE

To examine the association between the gut microbiota and subjective memory complaints (SMCs), a self-reported, validated indicator of cognitive dysfunction.

METHODS

In this cross-sectional study of 95 older women selected from the New York University Women's Health Study (NYUWHS), we characterized the gut microbial composition using 16S rRNA gene sequencing. We estimated odds ratio (OR) from beta regression which approximates the ratio of mean relative abundances of individual bacterial taxon from phylum to genus levels by binary (2+ versus < 2) and continuous SMCs.

RESULTS

Women reporting 2 or more SMCs had higher relative abundances of genus Holdemania and family Desulfovibrionaceae compared with those reporting one or no complaint. Compared with women with < 2 SMCs, the relative abundances of Holdemania and family Desulfovibrionaceae were 2.09 times (OR: 2.09, 95% confidence interval [CI]: 1.38-3.17) and 2.10 times (OR: 2.10, 95% CI: 1.43-3.09) higher in women with 2+ SMCs, respectively (false discovery rate (FDR)-adjusted p = 0.038 and 0.010, respectively). A dose-response association was observed for genus Sutterella and family Desulfovibrionaceae. Every one-unit increase in SMCs was associated with 25% and 27% higher relative abundances of Sutterella (OR: 1.25; 95% CI: 1.11-1.40) and Desulfovibrionaceae (OR: 1.27; 95% CI: 1.13-1.42), respectively (FDR-adjusted p = 0.018 and 0.006, respectively).

CONCLUSION

Our findings support an association between alterations in the gut bacterial composition and cognitive dysfunction.

The Relationship between Gut Microbiome and Cognition in Older Australians

Ageing is associated with changes in biological processes, including reductions in cognitive functions and gut microbiome diversity. However, not much is known about the relationship between cognition and the microbiome with increasing age. Therefore, we examined the relationship between the gut microbiome and cognition in 69 healthy participants aged 60–75 years. The gut microbiome was analysed with the 16S rRNA sequencing method. The cognitive assessment included the Cognitive Drug Research computerised assessment battery, which produced five cognitive factors corresponding to ‘Quality of Episodic Secondary Memory’, ‘Quality of Working Memory’, ‘Continuity of Attention, ‘Speed of Memory’ and ‘Power of Concentration’. Multiple linear regression showed that the bacterial family Carnobacteriaceae explained 9% of the variance in predicting Quality of Episodic Secondary Memory. Alcaligenaceae and Clostridiaceae explained 15% of the variance in predicting Quality of Working Memory; Bacteroidaceae, Barnesiellaceae, Rikenellaceae and Gemellaceae explained 11% of the variance in Power of Concentration. The present study provides specific evidence of a relationship between specific families of bacteria and different domains of cognition.

Gut Microbiota and Mycobiota Evolution Is Linked to Memory Improvement after Bariatric Surgery in Obese Patients: A Pilot Study

Patients with obesity are known to exhibit gut microbiota dysbiosis and memory deficits. Bariatric surgery (BS) is currently the most efficient anti-obesity treatment and may improve both gut dysbiosis and cognition. However, no study has investigated association between changes of gut microbiota and cognitive function after BS. We prospectively evaluated 13 obese patients on anthropometric data, memory functions, and gut microbiota-mycobiota before and six months after BS. The Rey Auditory Verbal Learning Test (AVLT) and the symbol span (SS) of the Weschler Memory Scale were used to assess verbal and working memory, respectively. Fecal microbiota and mycobiota were longitudinally analyzed by 16S and ITS2 rRNA sequencing respectively. AVLT and SS scores were significantly improved after BS (AVLT scores: 9.7 ± 1.7 vs. 11.2 ± 1.9, p = 0.02, and SS scores: 9.7 ± 23.0 vs. 11.6 ± 2.9, p = 0.05). An increase in bacterial alpha-diversity, and Ruminococcaceae, Prevotella, Agaricus, Rhodotorula, Dipodascus, Malassezia, and Mucor were significantly associated with AVLT score improvement after BS, while an increase in Prevotella and a decrease in Clostridium, Akkermansia,&nbsp;Dipodascus and Candida were linked to SS scores improvement. We identified several changes in the microbial communities that differ according to the improvement of either the verbal or working memories, suggesting a complex gut-brain-axis that evolves after BS.

Research progress of gut microbiota and frailty syndrome

Frailty is a clinical syndrome caused by homeostasis imbalance. It is characterized by marked vulnerability to endogenous or exogenous stressors, reduced self-care ability, and increased mortality risk. This aging-related syndrome is common in individuals older than 65 years and carries an increased risk for poor health outcomes. These include falls, incident disability, incapacity, and mortality. In addition, it can result in a poor prognosis for other comorbidities. With the aging population, frailty increases the burden of adverse health outcomes. Studies on frailty are at their infancy. In addition, there is a lack of thorough understanding of its pathogenesis. Several studies have suggested that frailty is caused by chronic inflammation due to enhanced intestinal permeability following gut microbiota imbalance as well as pathogen-related antibodies entering the circulation system. These result in musculoskeletal system disorders and neurodegenerative diseases. However, this assumption has not been validated in large cohort-based studies. Several studies have suggested that inflammation is not the only cause of frailty. Hence, further studies are necessary to extend our understanding of its pathogenesis. This review summarizes the research findings in the field and expands on the possible role of the gut microbiota in frailty syndrome.

Mechanisms Linking the Gut-Muscle Axis With Muscle Protein Metabolism and Anabolic Resistance: Implications for Older Adults at Risk of Sarcopenia

Aging is associated with a decline in skeletal muscle mass and function-termed sarcopenia-as mediated, in part, by muscle anabolic resistance. This metabolic phenomenon describes the impaired response of muscle protein synthesis (MPS) to the provision of dietary amino acids and practice of resistance-based exercise. Recent observations highlight the gut-muscle axis as a physiological target for combatting anabolic resistance and reducing risk of sarcopenia. Experimental studies, primarily conducted in animal models of aging, suggest a mechanistic link between the gut microbiota and muscle atrophy, mediated via the modulation of systemic amino acid availability and low-grade inflammation that are both physiological factors known to underpin anabolic resistance. Moreover, in vivo and in vitro studies demonstrate the action of specific gut bacteria (Lactobacillus and Bifidobacterium) to increase systemic amino acid availability and elicit an anti-inflammatory response in the intestinal lumen. Prospective lifestyle approaches that target the gut-muscle axis have recently been examined in the context of mitigating sarcopenia risk. These approaches include increasing dietary fiber intake that promotes the growth and development of gut bacteria, thus enhancing the production of short-chain fatty acids (SCFA) (acetate, propionate, and butyrate). Prebiotic/probiotic/symbiotic supplementation also generates SCFA and may mitigate low-grade inflammation in older adults via modulation of the gut microbiota. Preliminary evidence also highlights the role of exercise in increasing the production of SCFA. Accordingly, lifestyle approaches that combine diets rich in fiber and probiotic supplementation with exercise training may serve to produce SCFA and increase microbial diversity, and thus may target the gut-muscle axis in mitigating anabolic resistance in older adults. Future mechanistic studies are warranted to establish the direct physiological action of distinct gut microbiota phenotypes on amino acid utilization and the postprandial stimulation of muscle protein synthesis in older adults.

Microbiota's role in health and diseases

The microbiome is a term that usually refers to the community of various microorganisms that inhabit/live inside human/animal bodies or on their skin. It forms a complex ecosystem that includes trillions of commensals, symbiotics, and even pathogenic microorganisms. The external environment, diet, and lifestyle are the major determinants influencing the microbiome's composition and vitality. Recent studies have indicated the tremendous influence of the microbiome on health and disease. Their number, constitution, variation, and viability are dynamic. All these elements are responsible for the induction, development, and treatment of many health disorders. Serious diseases such as cancer, metabolic disorders, cardiovascular diseases, and even psychological disorders such as schizophrenia are influenced directly or indirectly by microbiota. In addition, in the last few weeks, accumulating data about the link between COVID-19 and the microbiota were published. In the present work, the role of the microbiome in health and disease is discussed. A deep understanding of the exact role of microbiota in disease induction enables the prevention of diseases and the development of new therapeutic concepts for most diseases through the correction of diet and lifestyle. The present review brings together evidence from the most recent works and discusses suggested nutraceutical approaches for the management of COVID-19 pandemic.

Targeting the Gut Microbiota to Improve Dietary Protein Efficacy to Mitigate Sarcopenia

Sarcopenia is characterised by the presence of diminished skeletal muscle mass and strength. It is relatively common in older adults as ageing is associated with anabolic resistance (a blunted muscle protein synthesis response to dietary protein consumption and resistance exercise). Therefore, interventions to counteract anabolic resistance may benefit sarcopenia prevention and are of utmost importance in the present ageing population. There is growing speculation that the gut microbiota may contribute to sarcopenia, as ageing is also associated with [1) dysbiosis, whereby the gut microbiota becomes less diverse, lacking in healthy butyrate-producing microorganisms and higher in pathogenic bacteria, and [2) loss of epithelial tight junction integrity in the lining of the gut, leading to increased gut permeability and higher metabolic endotoxemia. Animal data suggest that both elements may impact muscle physiology, but human data corroborating the causality of the association between gut microbiota and muscle mass and strength are lacking. Mechanisms wherein the gut microbiota may alter anabolic resistance include an attenuation of gut-derived low-grade inflammation and/or the increased digestibility of protein-containing foods and consequent higher aminoacidemia, both in favour of muscle protein synthesis. This review focuses on the putative links between the gut microbiota and skeletal muscle in the context of sarcopenia. We also address the issue of plant protein digestibility because plant proteins are increasingly important from an environmental sustainability perspective, yet they are less efficient at stimulating muscle protein synthesis than animal proteins.

The Effects of Lifestyle and Diet on Gut Microbiota Composition, Inflammation and Muscle Performance in Our Aging Society

Living longer is associated with an increased risk of chronic diseases, including impairments of the musculoskeletal and immune system as well as metabolic disorders and certain cancers, each of which can negatively affect the relationship between host and microbiota up to the occurrence of dysbiosis. On the other hand, lifestyle factors, including regular physical exercise and a healthy diet, can affect skeletal muscle and immune aging positively at all ages. Accordingly, health benefits could partly depend on the effect of such interventions that influence the biodiversity and functionality of intestinal microbiota. In the present review, we first discuss the physiological effects of aging on the gut microbiota, immune system, and skeletal muscle. Secondly, we describe human epidemiological evidence about the associations between physical activity and fitness and the gut microbiota composition in older adults. The third part highlights the relevance and restorative mechanisms of immune protection through physical activity and specific exercise interventions during aging. Fourth, we present important research findings on the effects of exercise and protein as well as other nutrients on skeletal muscle performance in older adults. Finally, we provide nutritional recommendations to prevent malnutrition and support healthy active aging with a focus on gut microbiota. Key nutrition-related concerns include the need for adequate energy and protein intake for preventing low muscle mass and a higher demand for specific nutrients (e.g., dietary fiber, polyphenols and polyunsaturated fatty acids) that can modify the composition, diversity, and metabolic capacity of the gut microbiota, and may thus provide a practical means of enhancing gut and systemic immune function.

Characterization of the gut-liver-muscle axis in cirrhotic patients with sarcopenia

BACKGROUND & AIM

Sarcopenia is frequent in cirrhosis and is associated with unfavourable outcomes. The role of the gut-liver-muscle axis in this setting has been poorly investigated. The aim of this study was to identify gut microbiota, metabolic and inflammatory signatures associated with sarcopenia in cirrhotic patients.

METHODS

Fifty cirrhotic patients assessed for the presence of sarcopenia by the quantification of muscle mass and strength were compared with age- and sex-matched controls. A multiomic analysis, including gut microbiota composition and metabolomics, serum myokines and systemic and intestinal inflammatory mediators, was performed.

RESULTS

The gut microbiota of sarcopenic cirrhotic patients was poor in bacteria associated with physical function (Methanobrevibacter, Prevotella and Akkermansia), and was enriched in Eggerthella, a gut microbial marker of frailty. The abundance of potentially pathogenic bacteria, such as Klebsiella, was also increased, to the detriment of autochthonous ones. Sarcopenia was associated with elevated serum levels of pro-inflammatory mediators and of fibroblast growth factor 21 (FGF21) in cirrhotic patients. Gut microbiota metabolic pathways involved in amino acid, protein and branched-chain amino acid metabolism were up-regulated, in addition to ethanol, trimethylamine and dimethylamine production. Correlation networks and clusters of variables associated with sarcopenia were identified, including one centred on Klebsiella/ethanol/FGF21/Eggerthella/Prevotella.

CONCLUSIONS

Alterations in the gut-liver-muscle axis are associated with sarcopenia in patients with cirrhosis. Detrimental but also compensatory functions are involved in this complex network.

Frailty in Patients With Inflammatory Bowel Disease

Older individuals comprise a growing proportion of patients with inflammatory bowel disease (IBD). Assessing older patients for frailty, defined as an age-related decline in multiple physiologic systems, is increasingly recognized as important for risk-stratifying patients with IBD. Mechanistically, both persistent chronic inflammation and common microbial perturbations may predispose patients with IBD to the development of frailty. In those with IBD, frailty is associated with an increased risk for mortality that is independent of age and comorbidity. Among hospitalized patients, frailty is associated with a higher risk for readmission and postoperative complications. In patients starting on immunomodulator or tumor necrosis factor-alpha antagonist therapy, frailty is also associated with an increased risk for infectious complications, including serious infections. For a beneficial effect on patient outcomes, it is important that clinicians familiarize themselves with the tools for assessing frailty and implement interventions aimed at mitigating the individual components of the frailty phenotype. This article examines the proposed mechanisms for an association between frailty and IBD, tools for assessment of frailty, and data involving the impact of frailty on outcomes in patients with IBD.

Mining microbes for mental health: Determining the role of microbial metabolic pathways in human brain health and disease

There is increasing knowledge regarding the role of the microbiome in modulating the brain and behaviour. Indeed, the actions of microbial metabolites are key for appropriate gut-brain communication in humans. Among these metabolites, short-chain fatty acids, tryptophan, and bile acid metabolites/pathways show strong preclinical evidence for involvement in various aspects of brain function and behaviour. With the identification of neuroactive gut-brain modules, new predictive tools can be applied to existing datasets. We identified 278 studies relating to the human microbiota-gut-brain axis which included sequencing data. This spanned across psychiatric and neurological disorders with a small number also focused on normal behavioural development. With a consistent bioinformatics pipeline, thirty-five of these datasets were reanalysed from publicly available raw sequencing files and the remainder summarised and collated. Among the reanalysed studies, we uncovered evidence of disease-related alterations in microbial metabolic pathways in Alzheimer's Disease, schizophrenia, anxiety and depression. Amongst studies that could not be reanalysed, many sequencing and technical limitations hindered the discovery of specific biomarkers of microbes or metabolites conserved across studies. Future studies are warranted to confirm our findings. We also propose guidelines for future human microbiome analysis to increase reproducibility and consistency within the field.

The Gut Microbiome, Aging, and Longevity: A Systematic Review

Aging is determined by complex interactions among genetic and environmental factors. Increasing evidence suggests that the gut microbiome lies at the core of many age-associated changes, including immune system dysregulation and susceptibility to diseases. The gut microbiota undergoes extensive changes across the lifespan, and age-related processes may influence the gut microbiota and its related metabolic alterations. The aim of this systematic review was to summarize the current literature on aging-associated alterations in diversity, composition, and functional features of the gut microbiota. We identified 27 empirical human studies of normal and successful aging suitable for inclusion. Alpha diversity of microbial taxa, functional pathways, and metabolites was higher in older adults, particularly among the oldest-old adults, compared to younger individuals. Beta diversity distances significantly differed across various developmental stages and were different even between oldest-old and younger-old adults. Differences in taxonomic composition and functional potential varied across studies, but Akkermansia was most consistently reported to be relatively more abundant with aging, whereas Faecalibacterium, Bacteroidaceae, and Lachnospiraceae were relatively reduced. Older adults have reduced pathways related to carbohydrate metabolism and amino acid synthesis; however, oldest-old adults exhibited functional differences that distinguished their microbiota from that of young-old adults, such as greater potential for short-chain fatty acid production and increased butyrate derivatives. Although a definitive interpretation is limited by the cross-sectional design of published reports, we integrated findings of microbial composition and downstream functional pathways and metabolites, offering possible explanations regarding age-related processes.

Gut bacterial taxonomic abundances vary with cognition, personality, and mood in the Wisconsin Longitudinal Study

Animal studies have shown that the gut microbiome can influence memory, social behavior, and anxiety-like behavior. Several human studies show similar results where variation in the gut microbiome is associated with dementia, depression, and personality traits, though most of these studies are limited by small sample size and other biases. Here, we analyzed fecal samples from 313 participants in the Wisconsin Longitudinal Study, a randomly selected population-based cohort of older adults, with measured psycho-cognitive dimensions (cognition, mood, and personality) and key confounders. 16s V4 sequencing showed that Megamonas is associated with all measured psycho-cognitive traits, Fusobacterium is associated with cognitive and personality traits, Pseudoramibacter_Eubacterium is associated with mood and personality traits, Butyvibrio is associated with cognitive traits, and Cloacibacillus is associated with mood traits. These findings are robust to sensitivity analyses and provide novel evidence of shared relationships between the gut microbiome and multiple psycho-cognitive traits in older adults, confirming some of the animal literature, while also providing new insights. While we addressed some of the weaknesses in prior studies, further studies are necessary to elucidate temporal and causal relationships between the gut microbiome and multiple psycho-cognitive traits in well-phenotyped, randomly-selected population-based samples.

Characterization of the gut microbiota in frail elderly patients

BACKGROUND

The change in the composition of gut microbiota has been reported in the elderly and in the frail individuals; however, studies on gut microbiota in frail elderly are limited.

AIMS

This study aimed to investigate the gut microbiota of the frail elderly.

METHODS

From September 2017 to February 2018, 27 elderly patients hospitalized in the Department of Geriatrics of our hospital were enrolled and divided into the frailty group (n = 15) and the control group (n = 12) based on the cutoff of 0.25 for the frailty index. The fecal samples were collected for 16S rRNA-amplicon sequencing to analyze the composition and richness of gut microbiota. Operational taxonomic unit (OTU) clustering was performed using Usearch software. Intra-sample diversity (alpha-diversity) analysis and inter-sample diversity (beta-diversity) analyses were performed. The community richness was compared between the two groups at family and genus levels.

RESULTS

There were 1903 and 1880 OTUs identified in the control and frailty groups, respectively, with 1282 OTUs overlap between the two groups. The alpha diversity of microbiota community was similar between the two groups, whereas the frailty group had larger beta diversity than the control group. The top-10 taxonomy categories and abundances of gut microbiota between the two groups were similar. As for the gut microbiota composition, 4 families and 17 genera were significantly different between the two groups (p < 0.05).

CONCLUSION

These results suggested that frailty can affect gut microbiota diversity and compositions in late elderly hospitalized patients.

The microbiota-gut-brain axis: An emerging therapeutic target in chemotherapy-induced cognitive impairment

Chemotherapy-induced cognitive impairment (CICI) is an ill-defined complication of chemotherapy treatment that places a significant psychosocial burden on survivors of cancer and has a considerable impact on the activities of daily living. CICI pathophysiology has not been clearly defined, with candidate mechanisms relating to both the direct cytotoxicity of chemotherapy drugs on the central nervous system (CNS) and more global, indirect mechanisms such as neuroinflammation and blood brain barrier (BBB) damage. A growing body of research demonstrates that changes to the composition of the gastrointestinal microbiota is an initiating factor in numerous neurocognitive conditions, profoundly influencing both CNS immunity and BBB integrity. Importantly, chemotherapy causes significant disruption to the gastrointestinal microbiota. While microbial disruption is a well-established factor in the development of chemotherapy-induced gastrointestinal toxicities (largely diarrhoea), its role in CICI remains unknown, limiting microbial-based therapeutics or risk prediction strategies. Therefore, this review aims to synthesise and critically evaluate the evidence addressing the microbiota-gut-brain axis as a critical factor influencing the development of CICI.

The gut microbiome and frailty

The human microbiome is constituted by an extensive network of organisms that lie at the host/environment interface and transduce signals that play vital roles in human health and disease across the lifespan. Frailty is a critical aging-related syndrome marked by diminished physiological reserve and heightened vulnerability to stress, predictive of major adverse clinical outcomes including death. While recent studies suggest the microbiome may impact key pathways critical to frailty pathophysiology, direct evaluation of the microbiome-frailty relationship remains limited. In this article, we review the complex interplay of biological, behavioral, and environmental factors that may influence shifts in gut microbiome composition and function in aging populations and the putative implications of such shifts for progression to frailty. We discuss HIV infection as a key prototype for elucidating the complex pathways via which the microbiome may precipitate frailty. Finally, we review considerations for future research efforts.

Comparing Analytical Methods for the Gut Microbiome and Aging: Gut Microbial Communities and Body Weight in the Osteoporotic Fractures in Men (MrOS) Study

Determining the role of gut microbial communities in aging-related phenotypes, including weight loss, is an emerging gerontology research priority. Gut microbiome datasets comprise relative abundances of microbial taxa that necessarily sum to 1; analysis ignoring this feature may produce misleading results. Using data from the Osteoporotic Fractures in Men (MrOS) study (n = 530; mean [SD] age = 84.3 [4.1] years), we assessed 163 genera from stool samples and body weight. We compared conventional analysis, which does not address the sum-to-1 constraint, to compositional analysis, which does. Specifically, we compared elastic net regression (for variable selection) and conventional Bayesian linear regression (BLR) and network analysis to compositional BLR and network analysis; adjusting for past weight, height, and other covariates. Conventional BLR identified Roseburia and Dialister (higher weight) and Coprococcus-1 (lower weight) after multiple comparisons adjustment (p < .0125); plus Sutterella and Ruminococcus-1 (p < .05). No conventional network module was associated with weight. Using compositional BLR, Coprococcus-2 and Acidaminococcus were most strongly associated with higher adjusted weight; Coprococcus-1 and Ruminococcus-1 were most strongly associated with lower adjusted weight (p < .05), but nonsignificant after multiple comparisons adjustment. Two compositional network modules with respective hub taxa Blautia and Faecalibacterium were associated with adjusted weight (p < .01). Findings depended on analytical workflow. Compositional analysis is advocated to appropriately handle the sum-to-1 constraint.

Relationship between dementia and gut microbiome-associated metabolites: a cross-sectional study in Japan

Dysregulation of the gut microbiome is associated with dementia. However, the relationship between microbiome-associated metabolites and dementia has yet to be identified. Outpatients visiting a memory clinic in Japan enrolled in this cross-sectional study; 107 subjects were eligible for the study, 25 of which had dementia. We collected demographics, activities of daily living, risk factors, cognitive function, and brain imaging data. The gut microbiome was assessed using terminal restriction fragment length polymorphism analysis. Concentrations of faecal metabolite were measured. We used multivariable logistic regression analyses to identify whether metabolites were independently related to dementia. The concentrations of metabolites were significantly different between subjects with and those without dementia. Every 1 standard deviation increment in faecal ammonia concentration was associated with around a 1.6-fold risk for the presence of dementia. A higher faecal lactic acid concentration was related to a lower risk of dementia, by around 60%. A combination of higher faecal ammonia and lactic acid concentrations was indicative of the presence of dementia, and had a similar predictive value as traditional biomarkers of dementia. Thus, faecal ammonia and lactic acid are related to dementia, independently of the other risk factors for dementia and dysregulation of the gut microbiome.

The gut microbiome and psycho-cognitive traits

The idea that trillions of bacteria inhabit our gut is somewhat unnerving, yet these bacteria may have a greater influence on our behavior than previously thought. Accumulating data strongly suggest that these gut commensal organisms have a strong inter-relationship with our brain and behavior, including cognitive function, mood, and personality. In this chapter, we discuss the role of the gut microbiome in the development of human personality, mood and mood disorders, and cognition, with a particular emphasis on the current consensus and controversies in the literature surrounding the behavioral effects of bioactive metabolites, microbial ratio shifts, and neurotransmitter synthesis facilitated by the microbiome.

Gut Microbial, Inflammatory and Metabolic Signatures in Older People with Physical Frailty and Sarcopenia: Results from the BIOSPHERE Study

Physical frailty and sarcopenia (PF&S) share multisystem derangements, including variations in circulating amino acids and chronic low-grade inflammation. Gut microbiota balances inflammatory responses in several conditions and according to nutritional status. Therefore, an altered gut-muscle crosstalk has been hypothesized in PF&S. We analyzed the gut microbial taxa, systemic inflammation, and metabolic characteristics of older adults with and without PF&S. An innovative multi-marker analytical approach was applied to explore the classification performance of potential biomarkers for PF&S. Thirty-five community dwellers aged 70+, 18 with PF&S, and 17 nonPF&S controls were enrolled. Sequential and Orthogonalized Covariance Selection (SO-CovSel), a multi-platform regression method developed to handle highly correlated variables, was applied. The SO-CovSel model with the best prediction ability using the smallest number of variables was built using seven mediators. The model correctly classified 91.7% participants with PF&S and 87.5% nonPF&S controls. Compared with the latter group, PF&S participants showed higher serum concentrations of aspartic acid, lower circulating levels of concentrations of threonine and macrophage inflammatory protein 1α, increased abundance of Oscillospira and Ruminococcus microbial taxa, and decreased abundance of Barnesiellaceae and Christensenellaceae. Future investigations are warranted to determine whether these biomediators are involved in PF&S pathophysiology and may, therefore, provide new targets for interventions.

Muscle strength is increased in mice that are colonized with microbiota from high-functioning older adults

Evidence in support of a gut-muscle axis has been reported in rodents, but studies in older adult humans are limited. Accordingly, the primary goals of the present study were to compare gut microbiome composition in older adults that differed in terms of the percentage of whole body lean mass and physical functioning (high-functioning, HF, n = 18; low-functioning, LF, n = 11), and to evaluate the causative role of the gut microbiome on these variables by transferring fecal samples from older adults into germ-free mice. Family-level Prevotellaceae, genus-level Prevotella and Barnesiella, and the bacterial species Barnesiella intestinihominis were higher in HF older adults at the initial study visit, at a 1-month follow-up visit, in HF human fecal donors, and in HF-colonized mice, when compared with their LF counterparts. Grip strength was significantly increased by 6.4% in HF-, when compared with LF-colonized mice. In contrast, despite significant differences for the percentage of whole body lean mass and physical functioning when comparing the human fecal donors, the percentage of whole body lean mass and treadmill endurance capacity were not different when comparing human microbiome-containing mice. In sum, these data suggest a role for gut bacteria on the maintenance of muscle strength, but argue against a role for gut bacteria on the maintenance of the percentage of whole body lean mass or endurance capacity, findings that collectively add to elucidation of the gut-muscle axis in older adults.

Gut Microbiota and Microbiota-Related Metabolites as Possible Biomarkers of Cognitive Aging

Gut microbiota composition and functionality can influence the pathophysiology of age-related cognitive impairment and dementia, according to a large number of animal studies. The translation of this concept to humans is still uncertain, due to the relatively low number of clinical studies focused on fecal microbiota and large number of environmental factors that influence the microbiota composition. However, the fecal microbiota composition of older patients with dementia is deeply different from that of healthy active controls, conditioning a different metabolic profile. The possible use of fecal microbiota-related parameters and microbiota-derived metabolites as biomarkers of cognitive performance and dementia is critically reviewed in this paper, focusing on the most promising areas of research for the future.

TwinsUK: The UK Adult Twin Registry Update

TwinsUK is the largest cohort of community-dwelling adult twins in the UK. The registry comprises over 14,000 volunteer twins (14,838 including mixed, single and triplets); it is predominantly female (82%) and middle-aged (mean age 59). In addition, over 1800 parents and siblings of twins are registered volunteers. During the last 27 years, TwinsUK has collected numerous questionnaire responses, physical/cognitive measures and biological measures on over 8500 subjects. Data were collected alongside four comprehensive phenotyping clinical visits to the Department of Twin Research and Genetic Epidemiology, King’s College London. Such collection methods have resulted in very detailed longitudinal clinical, biochemical, behavioral, dietary and socioeconomic cohort characterization; it provides a multidisciplinary platform for the study of complex disease during the adult life course, including the process of healthy aging. The major strength of TwinsUK is the availability of several ‘omic’ technologies for a range of sample types from participants, which includes genomewide scans of single-nucleotide variants, next-generation sequencing, metabolomic profiles, microbiomics, exome sequencing, epigenetic markers, gene expression arrays, RNA sequencing and telomere length measures. TwinsUK facilitates and actively encourages sharing the ‘TwinsUK’ resource with the scientific community — interested researchers may request data via the TwinsUK website (http://twinsuk.ac.uk/resources-for-researchers/access-our-data/) for their own use or future collaboration with the study team. In addition, further cohort data collection is planned via the Wellcome Open Research gateway (https://wellcomeopenresearch.org/gateways). The current article presents an up-to-date report on the application of technological advances, new study procedures in the cohort and future direction of TwinsUK.

Gut Microbiota, Muscle Mass and Function in Aging: A Focus on Physical Frailty and Sarcopenia

Human gut microbiota is able to influence the host physiology by regulating multiple processes, including nutrient absorption, inflammation, oxidative stress, immune function, and anabolic balance. Aging is associated with reduced microbiota biodiversity, increased inter-individual variability, and over-representation of pathobionts, and these phenomena may have great relevance for skeletal muscle mass and function. For this reason, the presence of a gut-muscle axis regulating the onset and progression of age-related physical frailty and sarcopenia has been recently hypothesized. In this narrative review, we summarize the studies supporting a possible association between gut microbiota-related parameters with measures of muscle mass, muscle function, and physical performance in animal models and humans. Reduced muscle mass has been associated with distinct microbiota composition and reduced fermentative capacity in mice, and the administration of probiotics or butyrate to mouse models of muscle wasting has been associated with improved muscle mass. However, no studies have targeted the human microbiome associated with sarcopenia. Limited evidence from human studies shows an association between microbiota composition, involving key taxa such as Faecalibacterium and Bifidobacterium, and grip strength. Similarly, few studies conducted on patients with parkinsonism showed a trend towards a different microbiota composition in those with reduced gait speed. No studies have assessed the association of fecal microbiota with other measures of physical performance. However, several studies, mainly with a cross-sectional design, suggest an association between microbiota composition and frailty, mostly assessed according to the deficit accumulation model. Namely, frailty was associated with reduced microbiota biodiversity, and lower representation of butyrate-producing bacteria. Therefore, we conclude that the causal link between microbiota and physical fitness is still uncertain due to the lack of targeted studies and the influence of a large number of covariates, including diet, exercise, multimorbidity, and polypharmacy, on both microbiota composition and physical function in older age. However, the relationship between gut microbiota and physical function remains a very promising area of research for the future.