Gut microbiota changes in the extreme decades of human life: a focus on centenarians

Immunosenescence is both functional/adaptive and dysfunctional/maladaptive

Alterations in the immune system with aging are considered to underlie many age-related diseases. However, many elderly individuals remain healthy until even a very advanced age. There is also an increase in numbers of centenarians and their apparent fitness. We should therefore change our unilaterally detrimental consideration of age-related immune changes. Recent data taking into consideration the immunobiography concept may allow for meaningful distinctions among various aging trajectories. This implies that the aging immune system has a homeodynamic characteristic balanced between adaptive and maladaptive aspects. The survival and health of an individual depends from the equilibrium of this balance. In this article, we highlight which parts of the aging of the immune system may be considered adaptive in contrast to those that may be maladaptive.

Pro-Aging Effects of Xanthine Oxidoreductase Products

The senescence process is the result of a series of factors that start from the genetic constitution interacting with epigenetic modifications induced by endogenous and environmental causes and that lead to a progressive deterioration at the cellular and functional levels. One of the main causes of aging is oxidative stress deriving from the imbalance between the production of reactive oxygen (ROS) and nitrogen (RNS) species and their scavenging through antioxidants. Xanthine oxidoreductase (XOR) activities produce uric acid, as well as reactive oxygen and nitrogen species, which all may be relevant to such equilibrium. This review analyzes XOR activity through in vitro experiments, animal studies and clinical reports, which highlight the pro-aging effects of XOR products. However, XOR activity contributes to a regular level of ROS and RNS, which appears essential for the proper functioning of many physiological pathways. This discourages the use of therapies with XOR inhibitors, unless symptomatic hyperuricemia is present.

The gut microbiome and antipsychotic treatment response

Patients with psychosis usually respond to one antipsychotic drug and not to another; one third fail to respond to any. Some patients, who initially do well, stop responding. Some develop serious side effects even at low doses. While several of the reasons for this variability are known, many are not. The aim of this review is to explore the potential role of intestinal organisms in response/non-response to antipsychotics. Much of the literature in this field is relatively new and still, for the most part, theoretical. A growing number of animal experiments and clinical trials are starting to point, however, to substantial effects of antipsychotics on the composition of gut bacteria and, reciprocally, to the effects of microbiota on the pharmacokinetics of antipsychotic medication. Because so many factors influence the constituents of the human intestine, it is difficult, at present, to sort out how much one or more either enhance or dampen the benefits of antipsychotics or the character/severity of the adverse effects they induce. Dietary and other therapies are being devised to reverse dysbiosis. If successful, such therapies plus the modification of factors that, together, are known to determine the composition of microbiota could help to maximize the effectiveness of currently available antipsychotic therapy.

Nutrition and the ageing brain: Moving towards clinical applications

The global increases in life expectancy and population have resulted in a growing ageing population and with it a growing number of people living with age-related neurodegenerative conditions and dementia, shifting focus towards methods of prevention, with lifestyle approaches such as nutrition representing a promising avenue for further development. This overview summarises the main themes discussed during the 3^rd Symposium on "Nutrition for the Ageing Brain: Moving Towards Clinical Applications" held in Madrid in August 2018, enlarged with the current state of knowledge on how nutrition influences healthy ageing and gives recommendations regarding how the critical field of nutrition and neurodegeneration research should move forward into the future. Specific nutrients are discussed as well as the impact of multi-nutrient and whole diet approaches, showing particular promise to combatting the growing burden of age-related cognitive decline. The emergence of new avenues for exploring the role of diet in healthy ageing, such as the impact of the gut microbiome and development of new techniques (imaging measures of brain metabolism, metabolomics, biomarkers) are enabling researchers to approach finding answers to these questions. But the translation of these findings into clinical and public health contexts remains an obstacle due to significant shortcomings in nutrition research or pressure on the scientific community to communicate recommendations to the general public in a convincing and accessible way. Some promising programs exist but further investigation to improve our understanding of the mechanisms by which nutrition can improve brain health across the human lifespan is still required.

Efficacy of probiotics on stress in healthy volunteers: A systematic review and meta-analysis based on randomized controlled trials

BACKGROUND

Probiotics seems to play a beneficial role in stressed populations; thus, a systematic review and meta-analysis to assess the effects of probiotics on stress in healthy subjects were conducted.

METHODS

Randomized controlled trials on the effects of probiotics on stress in healthy subjects were retrieved from five databases. The effects of probiotics on subjective stress level, stress-related subthreshold anxiety/depression level, cortisol level, and adverse reactions were analyzed. Separate subgroup analyses were conducted on single-strain probiotics versus multi-strain probiotics, and short-term administration versus long-term administration.

RESULTS

Seven studies were included, involving a total of 1,146 subjects. All the studies were rated as low or moderate risk of bias. Our research found that probiotic administration can generally reduce the subjective stress level of healthy volunteers and may improve their stress-related subthreshold anxiety/depression level, but no significant effect was observed in the subgroup analysis. The effect of probiotics on cortisol level was not significant. Adverse reactions were reported in only one of seven studies, but left undescribed.

CONCLUSION

Current evidence suggests that probiotics can reduce subjective stress level in healthy volunteers and may alleviate stress-related subthreshold anxiety/depression level, without significant effect on cortisol level, and there is not enough support to draw conclusions about adverse effects; thus, more reliable evidence from clinical trials is needed.

Metagenomics Study Reveals Changes in Gut Microbiota in Centenarians: A Cohort Study of Hainan Centenarians

Several studies based on 16SrDNA analysis have revealed certain unique characteristics of gut microbiome in centenarians. We established a prospective cohort of fecal microbiota and conducted the first metagenomics-based study among centenarians. The objective was to explore the dynamic changes of gut microbiota in healthy centenarians and centenarians approaching end of life and to unravel the characteristics of aging-associated microbiome. Seventy-five healthy centenarians residing in three regions of Hainan participated in follow-up surveys and collection of fecal samples at intervals of 3 months. Data pertaining to dietary status, health status scores, cause of disease and death, and fecal specimens were collected for 15 months. Twenty participants died within 20 months during the follow-up period. The median survival time was 8-9 months (range, 1-17) and the mortality rate was 14.7% per year. The health status scores before death were significantly lower than those at 3 months before the end of the follow-up period [median score: 3 (range, 1-5), P < 0.05]. At this time, the participants mainly exhibited symptoms of anorexia and reduced dietary intake and physical activity. Metagenomics sequencing and analysis were carried out to characterize the gut microbiota changes in the centenarians during their transition from healthy status to death. Anosim analysis showed a significant change in gut microbiota from 7 months prior to death (R = 0.10, P = 0.02). All participants were grouped with 7 months before death as cut-off; no significant difference in α diversity was found between the two groups (P = 0.45). Semi-supervised monitoring and log rank sum analysis revealed significant changes in the abundance of ten bacterial species before death; of these, eight species were significantly reduced (Akkermansia muciniphila, Alistipes finegoldii, Alistipes shahii, Bacteroides faecis, Bacteroides intestinalis, Butyrivibrio crossotus, Bacteroides stercoris, and Prevotella stercorea) while two were significantly increased before death (Bifidobacterium longum and Ruminococcus bromii). Compared to centenarians in northern Italy, Hainan centenarians exhibited unique characteristics of gut microbiome. The abundance of ten bacterial species showed significant changes starting from 7 months before death. We speculate that these changes might occur before the clinical symptoms of deterioration in health status.

Unveiling the Role of Inflammation and Oxidative Stress on Age-Related Cardiovascular Diseases

The global population above 60 years has been growing exponentially in the last decades, which is accompanied by an increase in the prevalence of age-related chronic diseases, highlighting cardiovascular diseases (CVDs), such as hypertension, atherosclerosis, and heart failure. Aging is the main risk factor for these diseases. Such susceptibility to disease is explained, at least in part, by the increase of oxidative stress, in which it damages cellular components such as proteins, DNA, and lipids. In addition, the chronic inflammatory process in aging “inflammaging” also contributes to cell damage, creating a stressful environment which drives to the development of CVDs. Taken together, it is possible to identify the molecular connection between oxidative stress and the inflammatory process, especially by the crosstalk between the transcription factors Nrf-2 and NF-κB which are mediated by redox signalling and are involved in aging. Therapies that control this process are key targets in the prevention/combat of age-related CVDs. In this review, we show the basics of inflammation and oxidative stress, including the crosstalk between them, and the implications on age-related CVDs.

Antimicrobial Resistance Gene Prevalence in a Population of Patients with Advanced Dementia Is Related to Specific Pathobionts

Long-term care facilities are significant reservoirs of antimicrobial-resistant organisms, and patients with advanced dementia are particularly vulnerable to multidrug-resistant organism (MDRO) acquisition and antimicrobial overuse. In this study, we longitudinally examined a group of patients with advanced dementia using metagenomic sequencing. We found significant inter- and intra-subject heterogeneity in microbiota composition, suggesting temporal instability. We also observed a link between the antimicrobial resistance gene density in a sample and the relative abundances of several pathobionts, particularly Escherichia coli, Proteus mirabilis, and Enterococcus faecalis, and used this relationship to predict resistance gene density in samples from additional subjects. Furthermore, we used metagenomic assembly to demonstrate that these pathobionts had higher resistance gene content than many gut commensals. Given the frequency and abundances at which these pathobionts were found in this population and the underlying vulnerability to MDRO of patients with advanced dementia, attention to microbial blooms of these species may be warranted.

Shotgun Metagenomics of Gut Microbiota in Humans with up to Extreme Longevity and the Increasing Role of Xenobiotic Degradation

The gut microbiome of long-lived people display an increasing abundance of subdominant species, as well as a rearrangement in health-associated bacteria, but less is known about microbiome functions. In order to disentangle the contribution of the gut microbiome to the complex trait of human longevity, we here describe the metagenomic change of the human gut microbiome along with aging in subjects with up to extreme longevity, including centenarians (aged 99 to 104 years) and semisupercentenarians (aged 105 to 109 years), i.e., demographically very uncommon subjects who reach the extreme limit of the human life span. According to our findings, the gut microbiome of centenarians and semisupercentenarians is more suited for xenobiotic degradation and shows a rearrangement in metabolic pathways related to carbohydrate, amino acid, and lipid metabolism. Collectively, our data go beyond the relationship between intestinal bacteria and physiological changes that occur with aging by detailing the shifts in the potential metagenomic functions of the gut microbiome of centenarians and semisupercentenarians as a response to progressive dietary and lifestyle modifications.IMPORTANCE The study of longevity may help us understand how human beings can delay or survive the most frequent age-related diseases and morbidities. In this scenario, the gut microbiome has been proposed as one of the variables to monitor and possibly support healthy aging. Indeed, the disruption of host-gut microbiome homeostasis has been associated with inflammation and intestinal permeability as well as a general decline in bone and cognitive health. Here, we performed a metagenomic assessment of fecal samples from semisupercentenarians, i.e., 105 to 109 years old, in comparison to young adults, the elderly, and centenarians, shedding light on the longest compositional and functional trajectory of the human gut microbiome with aging. In addition to providing a fine taxonomic resolution down to the species level, our study emphasizes the progressive age-related increase in degradation pathways of pervasive xenobiotics in Western societies, possibly as a result of a supportive process within the molecular continuum characterizing aging.

What is the collective effect of aging and HIV on the gut microbiome?

PURPOSE OF REVIEW

Aging and HIV share features of intestinal damage and alterations in the communities of enteric bacteria, termed dysbiosis. The purpose of this review is to highlight the various features of the gut microbiome in aging and in people with HIV (PWH) and to discuss how aging and HIV converge to impact the gut microbiome. The term microbiome reflects the combined genetic material of micro-organisms present including bacteria, viruses, bacteriophages, and fungi. To date, the majority of studies investigating the impact of aging and HIV on the gut microbiome have focused on bacteria, and therefore, for the purposes of this review, the term 'microbiome' is used to reflect enteric bacterial communities.

RECENT FINDINGS

Aging is associated with alterations in the gut bacterial microbiome. Although changes vary by the age of the population, lifestyle (diet, physical activity) and geographic location, the age-associated dysbiosis is typically characterized by an increase in facultative anaerobes with inflammatory properties and a decrease in obligate anaerobes that play critical roles in maintaining intestinal homeostasis and in regulating host immunity. PWH also have dysbiotic gut microbiomes, many features of which reflect those observed in elderly persons. In one study, the age effect on the gut microbiome differed based on HIV serostatus in older adults.

SUMMARY

HIV and age may interact to shape the gut microbiome. Future studies should investigate relationships between the gut microbiome and age-associated comorbidities in older PWH populations. Identifying these links will provide new avenues for treatments and interventions to improve the healthspan and lifespan of older PWH.

Gut-Joint Axis: The Role of Physical Exercise on Gut Microbiota Modulation in Older People with Osteoarthritis

Osteoarthritis (OA) is considered one of the most common joint disorders worldwide and its prevalence is constantly increasing due to the global longevity and changes in eating habits and lifestyle. In this context, the role of gut microbiota (GM) in the pathogenesis of OA is still unclear. Perturbation of GM biodiversity and function, defined as ‘gut dysbiosis’, might be involved in the development of inflammaging, one of the main risk factors of OA development. It is well known that physical exercise could play a key role in the prevention and treatment of several chronic diseases including OA, and it is recommended by several guidelines as a first line intervention. Several studies have shown that physical exercise could modulate GM composition, boosting intestinal mucosal immunity, increasing the Bacteroidetes–Firmicutes ratio, modifying the bile acid profile, and improving the production of short chain fatty acids. Moreover, it has been shown that low intensity exercise might reduce the risk of gastrointestinal diseases, confirming the hypothesis of a strict correlation between skeletal muscle and GM. However, up to date, there is still a lack of clinical trials focusing on this research field. Therefore, in this narrative, we aimed to summarize the state-of-the-art of the literature regarding the correlation between these conditions, supporting the hypothesis of a ‘gut–joint axis’ and highlighting the role of physical exercise combined with adequate diet and probiotic supplements in rebalancing microbial dysbiosis.

Food Allergies and Ageing

All over the world, there is an increase in the overall survival of the population and the number of elderly people. The incidence of allergic reactions is also rising worldwide. Until recently, allergies, and in particular food allergies (FAs), was regarded as a pediatric problem, since some of them start in early childhood and may spontaneously disappear in adulthood. It is being discovered that, on the contrary, these problems are increasingly affecting even the elderly. Along with other diseases that are considered characteristics of advanced age, such as cardiovascular, dysmetabolic, autoimmune, neurodegenerative, and oncological diseases, even FAs are increasingly frequent in the elderly. An FA is a pleiomorphic and multifactorial disease, characterized by an abnormal immune response and an impaired gut barrier function. The elderly exhibit distinct FA phenotypes, and diagnosis is difficult due to frequent co-morbidities and uncertainty in the interpretation of in vitro and in vivo tests. Several factors render the elderly susceptible to FAs, including the physiological changes of aging, a decline in gut barrier function, the skewing of adaptive immunity to a Th2 response, dysregulation of innate immune cells, and age-related changes of gut microbiota. Aging is accompanied by a progressive remodeling of immune system functions, leading to an increased pro-inflammatory status where type 1 cytokines are quantitatively dominant. However, serum Immunoglobulin E (IgE) levels and T helper type 2 (Th2 cytokine production have also been found to be increased in the elderly, suggesting that the type 2 cytokine pattern is not necessarily defective in older age. Dysfunctional dendritic cells in the gut, defects in secretory IgA, and decreased T regulatory function in the elderly also play important roles in FA development. We address herein the main immunologic aspects of aging according to the presence of FAs.

Gut microbiota and osteoarthritis management: An expert consensus of the European society for clinical and economic aspects of osteoporosis, osteoarthritis and musculoskeletal diseases (ESCEO)

The prevalence of osteoarthritis (OA) increases not only because of longer life expectancy but also because of the modern lifestyle, in particular physical inactivity and diets low in fiber and rich in sugar and saturated fats, which promote chronic low-grade inflammation and obesity. Adverse alterations of the gut microbiota (GMB) composition, called microbial dysbiosis, may favor metabolic syndrome and inflammaging, two important components of OA onset and evolution. Considering the burden of OA and the need to define preventive and therapeutic interventions targeting the modifiable components of OA, an expert working group was convened by the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) to review the potential contribution of GMB to OA. Such a contribution is supported by observational or dietary intervention studies in animal models of OA and in humans. In addition, several well-recognized risk factors of OA interact with GMB. Lastly, GMB is a critical determinant of drug metabolism and bioavailability and may influence the response to OA medications. Further research targeting GMB or its metabolites is needed to move the field of OA from symptomatic management to individualized interventions targeting its pathogenesis.

Neuroinflammation and the Gut Microbiota: Possible Alternative Therapeutic Targets to Counteract Alzheimer's Disease?

Alzheimer's disease (AD) is a complex, multi-factorial disease affecting various brain systems. This complexity implies that successful therapies must be directed against several core neuropathological targets rather than single ones. The scientific community has made great efforts to identify the right AD targets beside the historic amyloid-β (Aβ). Neuroinflammation is re-emerging as determinant in the neuropathological process of AD. A new theory, still in its infancy, highlights the role of gut microbiota (GM) in the control of brain development, but also in the onset and progression of neurodegenerative diseases. Bidirectional communication between the central and the enteric nervous systems, called gut-brain axes, is largely influenced by GM and the immune system is a potential key mediator of this interaction. Growing evidence points to the role of GM in the maturation and activation of host microglia and peripheral immune cells. Several recent studies have found abnormalities in GM (dysbiosis) in AD populations. These observations raise the intriguing question whether and how GM dysbiosis could contribute to AD development through action on the immune system and whether, in a therapeutic prospective, the development of strategies preserving a healthy GM might become a valuable approach to prevent AD. Here, we review the evidence from animal models and humans of the role of GM in neuroinflammation and AD.

Aryl hydrocarbon receptor activation mediates kidney disease and renal cell carcinoma

The aryl hydrocarbon receptor (AhR) is a well-known ligand-activated cytoplasmic transcription factor that contributes to cellular responses against environmental toxins and carcinogens. AhR is activated by a range of structurally diverse compounds from the environment, microbiome, natural products, and host metabolism, suggesting that AhR possesses a rather promiscuous ligand binding site. Increasing studies have indicated that AhR can be activated by a variety of endogenous ligands and induce the expression of a battery of genes. AhR regulates a variety of physiopathological events, including cell proliferation, differentiation, apoptosis, adhesion and migration. These new roles have expanded our understanding of the AhR signalling pathways and endogenous metabolites interacting with AhR under homeostatic and pathological conditions. Recent studies have demonstrated that AhR is linked to cardiovascular disease (CVD), chronic kidney disease (CKD) and renal cell carcinoma (RCC). In this review, we summarize gut microbiota-derived ligands inducing AhR activity in patients with CKD, CVD, diabetic nephropathy and RCC that may provide a new diagnostic and prognostic approach for complex renal damage. We further highlight polyphenols from natural products as AhR agonists or antagonists that regulate AhR activity. A better understanding of structurally diverse polyphenols and AhR biological activities would allow us to illuminate their molecular mechanism and discover potential therapeutic strategies targeting AhR activation.

Nutrients in the Prevention of Alzheimer's Disease

Alzheimer's disease (AD) is a disease caused by the complex interaction of multiple mechanisms, some of which are still not fully understood. To date, pharmacological treatments and supplementation of individual nutrients have been poorly effective in terms of the prevention and treatment of AD, while alternative strategies based on multimodal approaches (diet, exercise, and cognitive training) seem to be more promising. In this context, the focus on dietary patterns rather than on single food components could be more useful in preventing or counteracting the pathological processes typical of AD, thanks to the potential synergistic effects of various nutrients (neuronutrients). The aim of this narrative review is to summarize the currently existing preclinical and clinical evidence regarding the Mediterranean diet (MeDi), the Dietary Approaches to Stop Hypertension (DASH) diet, and the Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet, which are three dietary patterns with well-known anti-inflammatory and antioxidant properties. Recently, they have been related to brain protection and AD prevention, perhaps thanks to their high content of neuroprotective bioactive compounds. Similarly, intermittent fasting (IF) or calorie restriction (CR) is emerging as interesting approaches that seem to promote hippocampal neurogenesis, activate adaptive stress response systems, and enhance neuronal plasticity, thus leading to motor and cognitive improvements in animal models of AD and hopefully also in human beings.

Age-Associated Changes in Gut Microbiota and Dietary Components Related with the Immune System in Adulthood and Old Age: A Cross-Sectional Study

The fecal microbiota plays an important role in human health, and alterations in the microbiota–host interaction seem to be involved in the ageing process. Therefore, it is of interest to develop strategies for promoting a balanced microbiota in old age in order to prevent the physiological and immune decline associated with age. However, the specific microbiota changes in the transition from adulthood to senescence are not yet well understood. Here we assessed the levels of some intestinal microorganisms and short chain fatty acids (SCFAs) across different age-groups. In total, 153 adults from four age groups (<50, 50–65, 66–80, and >80 years-old) were recruited; the levels of different bacterial groups in fecal samples were determined by quantitative polymerase chain reaction (qPCR), and those of SCFA by gas chromatography. Dietary information was collected by using a Food Frequency Questionnaire. The presence of the Bifidobacterium, Faecalibacterium, Bacteroides group, and Clostridium cluster XIVa decreased with age up to 66–80 years of age, with differences reaching statistical significance for the latter group. Interestingly, the levels of some of these microorganisms recovered in the very old age group (>80 years), with these older individuals presenting significantly higher counts of Akkermansia and Lactobacillus group than adults and the younger elderly. In addition, ageing was associated with a progressively and statistically significant reduction in the fecal concentrations of SCFAs. Dietary intakes also showed some statistically significant differences among the groups for some macro- and micronutrients. Moreover, associations of some microorganisms with age and macronutrients were also evidenced. Considering the role that fecal microbiota alterations may have in terms of impairing homeostasis and resilience, our results underline the importance of understanding the ageing and immunosenescence processes by including the microbiota perspective.

The peculiar aging of human liver: A geroscience perspective within transplant context

An appraisal of recent data highlighting aspects inspired by the new Geroscience perspective are here discussed. The main findings are summarized as follows: i) liver has to be considered an immunological organ, and new studies suggest a role for the recently described cells named telocytes; ii) the liver-gut axis represents a crucial connection with environment and life style habits and may influence liver diseases onset; iii) the physiological aging of liver shows relatively modest alterations. Nevertheless, several molecular changes appear to be relevant: a) an increase of microRNA-31-5p; -141-3p; -200c-3p expressions after 60 years of age; b) a remodeling of genome-wide DNA methylation profile evident until 60 years of age and then plateauing; c) changes in transcriptome including the metabolic zones of hepatocyte lobules; d) liver undergoes an accelerated aging in presence of chronic inflammation/liver diseases in a sort of continuum, largely as a consequence of unhealthy life styles and exposure to environmental noxious agents. We argue that chronic liver inflammation has all the major characteristics of "inflammaging" and likely sustains the onset and progression of liver diseases. Finally, we propose to use a combination of parameters, mostly obtained by omics such as transcriptomics and epigenomics, to evaluate in deep both the biological age of liver (in comparison with the chronological age) and the effects of donor-recipient age-mismatches in the context of liver transplant.

An in vitro exploratory study of dietary strategies based on polyphenol-rich beverages, fruit juices and oils to control trimethylamine production in the colon

Trimethylamine-N-oxide (TMAO) has been described as a new biomarker of cardiovascular disease (CVD), derived from gut microbial biotransformation of dietary choline and l-carnitine into trimethylamine (TMA) and subsequent hepatic oxidation. (Poly)phenols are among the dietary factors able to interfere with microbial enzymatic activity, possibly modulating TMA biotransformation at the gut level. The aim of this work was to investigate the in vitro biotransformation of choline and carnitine using faecal starters obtained from omnivorous and vegetarian subjects and the effect of (poly)phenol-rich foods on TMA production. Choline and l-carnitine were fermented with vegetarian or omnivorous faecal slurries, alone or in combination with 10 (poly)phenol-rich food items. TMA production from carnitine, but not from choline, was significantly lower when vegetarian faecal starters were used and, among the tested food items, blonde orange juice significantly reduced TMA formation during faecal biotransformation. Consequently, the main compounds of orange juice, namely phenolic compounds, terpenes, limonoids, organic acids and sugars, were tested individually. Sugars exerted the highest inhibitory effect on TMA production. Despite some limitations deriving from the applied in vitro model, this is the first work describing a possible role of some (poly)phenol-rich dietary products on the modulation of TMA colonic production. Free sugars were the main factor responsible for TMA inhibition, suggesting a potential beneficial role of colonic fermentation of carbohydrates in reducing TMA formation from its precursor molecules. This work opens new research directions to evaluate the effect of dietary fermentable fibre on TMA production and, potentially, on circulating TMAO levels.

Common miRNA Patterns of Alzheimer's Disease and Parkinson's Disease and Their Putative Impact on Commensal Gut Microbiota

With the rise of Next-Generation-Sequencing (NGS) methods, Micro-RNAs (miRNAs) have achieved an important position in the research landscape and have been found to present valuable diagnostic tools in various diseases such as multiple sclerosis or lung cancer. There is also emerging evidence that miRNAs play an important role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD) or Parkinson's disease (PD). Apparently, these diseases come along with changes in miRNA expression patterns which led to attempts from researchers to use these small RNA species from several body fluids for a better diagnosis and in order to observe disease progression. Additionally, it became evident that microbial commensals might play an important role for pathology development and were shown to have a significantly different composition in patients suffering from neurodegeneration compared with healthy controls. As it could recently be shown that secreted miRNAs are able to enter microbial organisms, it is conceivable that the host's miRNA might affect the gut microbial ecosystem. As such, miRNAs may inherit a central role in shaping the "diseased microbiome" and thereby mutually act on the characteristics of these neurodegenerative diseases. We have therefore (1) compiled a list of miRNAs known to be associated with AD and/or PD, (2) performed an in silico target screen for binding sites of these miRNA on human gut metagenome sequences and (3) evaluated the hit list for interesting matches potentially relevant to the etiology of AD and or PD. The examination of protein identifiers connected to bacterial secretion system, lipopolysaccharide biosynthesis and biofilm formation revealed an overlap of 37 bacterial proteins that were targeted by human miRNAs. The identified links of miRNAs to the biological processes of bacteria connected to AD and PD have yet to be validated via in vivo experiments. However, our results show a promising new approach for understanding aspects of these neurodegenerative diseases in light of the regulation of the microbiome.

The Microbiome and Eating Disorders

Growing interest exists in the association of gut bacteria with diseases, such as diabetes, obesity, inflammatory bowel disease, and psychiatric disorders. Gut microbiota influence the fermentation of nutrients, body-weight regulation, gut permeability, hormones, inflammation, immunology, and behavior (gut-brain axis). Regarding anorexia nervosa (AN), altered microbial diversity and taxa abundance were found and associated with depressive, anxious, and eating disorder symptoms. Potential mechanisms involve increased gut permeability, low-grade inflammation, autoantibodies, and reduced brain cell neogenesis and learning. Gut microbiome is strongly influenced by refeeding practices. Microbiota-modulating strategies like nutritional interventions or psychobiotics application could become relevant additions to AN treatment.

Remitted affective disorders and high familial risk of affective disorders associate with aberrant intestinal microbiota

OBJECTIVE

Affective disorders seem associated with aberrant intestinal microbiota but whether this pattern also occurs in individuals at increased heritable risk is unknown. We investigated associations between gut microbiota profiles and affective disorders by comparing monozygotic (MZ) twins concordant (affected twins with unipolar or bipolar disorder in remission) and discordant to affective disorders (high-risk) with MZ twins without affective disorders (low-risk).

METHODS

Stool samples were collected from 128 MZ twins and the microbiome was profiled using 16S rDNA sequencing of the V3-V4 region.

RESULTS

Affected twins had a lower diversity and an absence of a specific operational taxonomical unit (OTU) in comparison with low-risk twins. The high-risk twins exhibited the same pattern although the lower diversity was only at a trend level. The OTU belonged to the family Christensenellaceae. The findings were not explained by lifestyle factors (smoking, alcohol consumption, body mass index, or psychotropic medication).

CONCLUSION

Affected twins in remission and high-risk twins presented aberrant gut microbiota with depletion of a specific OTU. If replicated, this reduced relative sequence absence may together with the globally altered microbiota composition act as a vulnerability marker by accentuating the effect of gene-environment interactions in individuals genetically disposed for an affective disorder.

The Impact of Starvation on the Microbiome and Gut-Brain Interaction in Anorexia Nervosa

Interactions between the gut microbiome and the brain are of increasing interest to both researchers and clinicians. Evidence is mounting on the causal role of an altered gut microbiome in inflammatory diseases such as arthritis, inflammatory bowel disease, obesity and diabetes, and psychiatric diseases like anxiety and depression. Mechanisms include altered energy harvest from food, hormonal changes, increased gut permeability, inflammation, immune response, and a direct influence on the brain and behavior. Anorexia nervosa (AN) is the third most common disease in adolescence and exacts a high burden on patients and caregivers. It often becomes chronic and has the highest mortality of all psychiatric diseases. As AN is characterized by nutritional restrictions, weight loss, and severe behavioral symptoms including weight phobia, comorbid anxiety and depression, accompanied by endocrine alterations, increased inflammation, and immune response, exploring the role of the gut microbiome is crucial. Here, we present an overview of the potential mechanisms of interaction between the gut microbiome, the host and particularly the brain in AN and summarize the initial findings of microbiome research on AN. We conclude by identifying future research directions and potential therapeutic approaches, including nutritional interventions, probiotics, prebiotics and food supplements, that could become important additions to current AN therapy.

Interaction between gut microbiota and ethnomedicine constituents

This highlight reviews the interaction processes between gut microbiota and ethnomedicine constituents, which may conceptualize future therapeutic strategies.

Aging, inflammation and cancer

Aging is a key aspect of neoplasia at the level of cells, individuals and populations. Unrestrained expression and production of inflammatory mediators is a key feature of aging at the cellular and organism level. Inflammatory cells and mediators are a key component of the tumor microenvironment and drive tumor progression. Non-resolving smoldering inflammation increases the risk of cancer (the extrinsic pathway connecting inflammation and cancer). In the intrinsic pathway, genetic events that cause neoplasia (oncogenes and oncosupressor genes) orchestrate the construction of cancer-related inflammation. We argue that uncontrolled smoldering inflammation drives carcinogenesis in aging and acts as a common denominator linking aging and cancer.

Aging and Alzheimer's disease: Comparison and associations from molecular to system level

Alzheimer's disease is the most prevalent cause of dementia, which is defined by the combined presence of amyloid and tau, but researchers are gradually moving away from the simple assumption of linear causality proposed by the original amyloid hypothesis. Aging is the main risk factor for Alzheimer's disease that cannot be explained by amyloid hypothesis. To evaluate how aging and Alzheimer's disease are intrinsically interwoven with each other, we review and summarize evidence from molecular, cellular, and system level. In particular, we focus on study designs, treatments, or interventions in Alzheimer's disease that could also be insightful in aging and vice versa.

Inflammaging: a new immune-metabolic viewpoint for age-related diseases

Ageing and age-related diseases share some basic mechanistic pillars that largely converge on inflammation. During ageing, chronic, sterile, low-grade inflammation - called inflammaging - develops, which contributes to the pathogenesis of age-related diseases. From an evolutionary perspective, a variety of stimuli sustain inflammaging, including pathogens (non-self), endogenous cell debris and misplaced molecules (self) and nutrients and gut microbiota (quasi-self). A limited number of receptors, whose degeneracy allows them to recognize many signals and to activate the innate immune responses, sense these stimuli. In this situation, metaflammation (the metabolic inflammation accompanying metabolic diseases) is thought to be the form of chronic inflammation that is driven by nutrient excess or overnutrition; metaflammation is characterized by the same mechanisms underpinning inflammaging. The gut microbiota has a central role in both metaflammation and inflammaging owing to its ability to release inflammatory products, contribute to circadian rhythms and crosstalk with other organs and systems. We argue that chronic diseases are not only the result of ageing and inflammaging; these diseases also accelerate the ageing process and can be considered a manifestation of accelerated ageing. Finally, we propose the use of new biomarkers (DNA methylation, glycomics, metabolomics and lipidomics) that are capable of assessing biological versus chronological age in metabolic diseases.

Anti-senescence compounds: A potential nutraceutical approach to healthy aging

The desire of eternal youth seems to be as old as mankind. However, the increasing life expectancy experienced by populations in developed countries also involves a significantly increased incidence of the most common age-related diseases (ARDs). Senescent cells (SCs) have been identified as culprits of organismal aging. Their number rises with age and their senescence-associated secretory phenotype fuels the chronic, pro-inflammatory systemic state (inflammaging) that characterizes aging, impairing the regenerative ability of stem cells and increasing the risk of developing ARDs. A variegated class of molecules, including synthetic senolytic compounds and natural compounds contained in food, have been suggested to possess anti-senescence activity. Senolytics are attracting growing interest, and their safety and reliability as anti-senescence drugs are being assessed in human clinical trials. Notably, since SCs spread inflammation at the systemic level through pro-oxidant and pro-inflammatory signals, foods rich in polyphenols, which exert antioxidant and anti-inflammatory actions, have the potential to be harnessed as "anti-senescence foods" in a nutraceutical approach to healthier aging. We discuss the beneficial effects of polyphenol-rich foods in relation to the Mediterranean diet and the dietary habits of long-lived individuals, and examine their ability to modulate bacterial genera in the gut.

Identification of gut microbiome signatures associated with longevity provides a promising modulation target for healthy aging

The world population is aging, which poses a significant burden to the economy and health care system. As people age, so do their gut microbiomes. Age-related changes in gut microbiome have been reported, including decreased microbial diversity and increased Proteobacteria. Recently, we characterized the gut microbiome of a group of long-living (≥ 90 years old) Chinese people. Interestingly, the diversity of their gut microbiome was greater than that of a young adult control group. We also identified several potentially beneficial bacteria enriched in the long-living Chinese group. These results were validated using data from an independent Italian cohort that included a group of long-living individuals. Other recent studies have found similar results. Here, we provide a summary of these discoveries and discuss their implications in healthy aging.

Nutrition and Inflammation: Are Centenarians Similar to Individuals on Calorie-Restricted Diets?

Individuals capable of reaching the extreme limit of human life such as centenarians are characterized by an exceptionally healthy phenotype—that is, a low number of diseases, low blood pressure, optimal metabolic and endocrine parameters, and increased diversity in the gut microbiota—and they are epigenetically younger than their chronological age. We present data suggesting that such a remarkable phenotype is largely similar to that found in adults following a calorie-restricted diet. Interviews with centenarians and historical data on the nutritional and lifestyle habits of Italians during the twentieth century suggest that as children and into adulthood, centenarians lived in an environment that was nonobesogenic, but at the same time the environment did not produce malnutrition. Centenarians appear to be creatures of habit, and we argue that their habit of eating meals at the same time each day favored the maintenance of circadian rhythms, including their sleep cycle. Finally, we argue that centenarians’ chronic inflammatory status, which we dubbed inflammaging, is peculiar, likely adaptive, and less detrimental than in younger people.

Sex gap in aging and longevity: can sex chromosomes play a role?

It is well known that women live longer than men. This gap is observed in most human populations and can even reach 10-15 years. In addition, most of the known super centenarians (i.e., humans who lived for > 110 years) are women. The differences in life expectancy between men and women are often attributed to cultural differences in common thinking. However, sex hormones seem to influence differences in the prevalence of diseases, in the magnitude of aging, and in the longevity between men and women. Moreover, far from being human specific, the sex gap in longevity is extremely common in non-human animals, especially in mammals. Biological factors clearly contribute to such a sex gap in aging and longevity. Different hypotheses have been proposed to explain why males and females age and die differently. The cost of sexual selection and sexual dimorphism has long been considered the best explanation for the observed sex gap in aging/longevity. However, the way mitochondria are transmitted (i.e., through females in most species) could have an effect, called the mother's curse. Recent data suggest that sex chromosomes may also contribute to the sex gap in aging/longevity through several potential mechanisms, including the unguarded X/Z, the toxic Y/W and the loss of Y/W. We discuss future research directions to test these ideas.

Bacteria in the ageing gut: did the taming of fire promote a long human lifespan?

Unique among animals as they evolved towards Homo sapiens, hominins progressively cooked their food on a routine basis. Cooked products are characterized by singular chemical compounds, derived from the pervasive Maillard reaction. This same reaction is omnipresent in normal metabolism involving carbonyls and amines, and its products accumulate with age. The gut microbiota acts as a first line of defence against the toxicity of cooked Maillard compounds, that also selectively shape the microbial flora, letting specific metabolites to reach the blood stream. Positive selection of metabolic functions allowed the body of hominins who tamed fire to use and dispose of these age-related compounds. I propose here that, as a hopeful accidental consequence, this resulted in extending human lifespan far beyond that of our great ape cousins. The limited data exploring the role of taming fire on the human genetic setup and on its microbiota is discussed in relation with ageing.

The potential of non-myeloablative heterochronous autologous hematopoietic stem cell transplantation for extending a healthy life span

Aging is a complex multifactorial process, a prominent component being the senescence of the immune system. Consequently, immune-related diseases develop, including atherosclerosis, cancer, and life-threatening infections, which impact on health and longevity. Rejuvenating the aged immune system could mitigate these diseases, thereby contributing to longevity and health. Currently, an appealing option for rejuvenating the immune system is heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow/peripheral blood stem cells are collected during the youth of an individual, cryopreserved, and re-infused when he or she has reached an older age. After infusion, young hematopoietic stem cells can reconstitute the compromised immune system and improve immune function. Several studies using animal models have achieved substantial extension of the life span of animals treated with haHSCT. Therefore, haHSCT could be regarded as a potential procedure for preventing age-related immune defects and extending healthy longevity. In this review, the pros, cons, and future feasibility of this approach are discussed.

The Continuum of Aging and Age-Related Diseases: Common Mechanisms but Different Rates

Geroscience, the new interdisciplinary field that aims to understand the relationship between aging and chronic age-related diseases (ARDs) and geriatric syndromes (GSs), is based on epidemiological evidence and experimental data that aging is the major risk factor for such pathologies and assumes that aging and ARDs/GSs share a common set of basic biological mechanisms. A consequence is that the primary target of medicine is to combat aging instead of any single ARD/GSs one by one, as favored by the fragmentation into hundreds of specialties and sub-specialties. If the same molecular and cellular mechanisms underpin both aging and ARDs/GSs, a major question emerges: which is the difference, if any, between aging and ARDs/GSs? The hypothesis that ARDs and GSs such as frailty can be conceptualized as accelerated aging will be discussed by analyzing in particular frailty, sarcopenia, chronic obstructive pulmonary disease, cancer, neurodegenerative diseases such as Alzheimer and Parkinson as well as Down syndrome as an example of progeroid syndrome. According to this integrated view, aging and ARDs/GSs become part of a continuum where precise boundaries do not exist and the two extremes are represented by centenarians, who largely avoided or postponed most ARDs/GSs and are characterized by decelerated aging, and patients who suffered one or more severe ARDs in their 60s, 70s, and 80s and show signs of accelerated aging, respectively. In between these two extremes, there is a continuum of intermediate trajectories representing a sort of gray area. Thus, clinically different, classical ARDs/GSs are, indeed, the result of peculiar combinations of alterations regarding the same, limited set of basic mechanisms shared with the aging process. Whether an individual will follow a trajectory of accelerated or decelerated aging will depend on his/her genetic background interacting lifelong with environmental and lifestyle factors. If ARDs and GSs are manifestations of accelerated aging, it is urgent to identify markers capable of distinguishing between biological and chronological age to identify subjects at higher risk of developing ARDs and GSs. To this aim, we propose the use of DNA methylation, N-glycans profiling, and gut microbiota composition to complement the available disease-specific markers.

Immunosenescence and Inflamm-Aging As Two Sides of the Same Coin: Friends or Foes?

The immune system is the most important protective physiological system of the organism. It has many connections with other systems and is, in fact, often considered as part of the larger neuro-endocrine-immune axis. Most experimental data on immune changes with aging show a decline in many immune parameters when compared to young healthy subjects. The bulk of these changes is termed immunosenescence. Immunosenescence has been considered for some time as detrimental because it often leads to subclinical accumulation of pro-inflammatory factors and inflamm-aging. Together, immunosenescence and inflamm-aging are suggested to stand at the origin of most of the diseases of the elderly, such as infections, cancer, autoimmune disorders, and chronic inflammatory diseases. However, an increasing number of immune-gerontologists have challenged this negative interpretation of immunosenescence with respect to its significance in aging-related alterations of the immune system. If one considers these changes from an evolutionary perspective, they can be viewed preferably as adaptive or remodeling rather than solely detrimental. Whereas it is conceivable that global immune changes may lead to various diseases, it is also obvious that these changes may be needed for extended survival/longevity. Recent cumulative data suggest that, without the existence of the immunosenescence/inflamm-aging duo (representing two sides of the same phenomenon), human longevity would be greatly shortened. This review summarizes recent data on the dynamic reassessment of immune changes with aging. Accordingly, attempts to intervene on the aging immune system by targeting its rejuvenation, it may be more suitable to aim to maintain general homeostasis and function by appropriately improving immune-inflammatory-functions.