Psychobiotics: a novel class of psychotropic

Harnessing Gut Microbes for Mental Health: Getting From Here to There

There has been an explosion of interest in the study of microorganisms inhabiting the gastrointestinal tract (gut microbiota) and their impact on host health and physiology. Accumulating data suggest that altered communication between gut microbiota and host systems could participate in disorders such as obesity, diabetes mellitus, and autoimmune disorders as well as neuropsychiatric disorders, including autism, anxiety, and major depressive disorders. The conceptual development of the microbiome-gut-brain axis has facilitated understanding of the complex and bidirectional networks between gastrointestinal microbiota and their host, highlighting potential mechanisms through which this environment influences central nervous system physiology. Communication pathways between gut microbiota and the central nervous system could include autonomic, neuroendocrine, enteric, and immune systems, with pathology resulting in disruption to neurotransmitter balance, increases in chronic inflammation, or exacerbated hypothalamic-pituitary-adrenal axis activity. However, uncertainty remains regarding the generalizability of controlled animal studies to the more multifaceted pattern of human pathophysiology, especially with regard to the therapeutic potential for neuropsychiatric health. This narrative review summarizes current understanding of gut microbial influence over physiological function, with an emphasis on neurobehavioral and neurological impairment based on growing understanding of the gut-brain axis. Experimental and clinical data regarding means of therapeutic manipulation of gut microbiota as a novel treatment option for mental health are described, and important knowledge gaps are identified and discussed.

The third tier in treatment: Attending to the growing connection between gut health and emotional well-being

The microbial environment of the human gut has powerful influence on immunity, metabolism, and obesity. There is now emerging evidence that the microbiome of our gastrointestinal system may also be a key factor impacting our emotional and behavioral health. The purpose of this article is to elucidate how this emerging area of science can further educate and encourage mental health professionals to explore an additional means to treatment. Since much of this research is found in the biological and neuroscientific literature, it can be quite cumbersome for clinicians to digest and apply, who would critically benefit from a concise discussion of the gut–brain connection.

Finding the needle in the haystack: systematic identification of psychobiotics

The brain-gut-microbiota axis is increasingly viewed as a novel paradigm in neuroscience with the capacity to generate innovative therapies for patients with psychiatric illnesses. Psychobiotics, defined as live bacteria, which when ingested in adequate amounts, confer mental health benefits, are increasingly of interest, as preclinical trials continue to show promising results. Particularly in stress-related, anxiety and depressive disorders, there is potential for psychobiotics to deliver new therapies. The question of which microbes may prove to be the most promising psychobiotic in delivering such therapies at a clinical level is of great importance. Here we look at the characteristics of psychobiotics, in an attempt to present an outline from which the identification of potential new psychobiotics may be possible. LINKED ARTICLES: This article is part of a themed section on When Pharmacology Meets the Microbiome: New Targets for Therapeutics? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.24/issuetoc.

The microbiota-gut-brain axis as a key regulator of neural function and the stress response: Implications for human and animal health

The brain-gut-microbiota axis comprises an extensive communication network between the brain, the gut, and the microbiota residing there. Development of a diverse gut microbiota is vital for multiple features of behavior and physiology, as well as many fundamental aspects of brain structure and function. Appropriate early-life assembly of the gut microbiota is also believed to play a role in subsequent emotional and cognitive development. If the composition, diversity, or assembly of the gut microbiota is impaired, this impairment can have a negative impact on host health and lead to disorders such as obesity, diabetes, inflammatory diseases, and even potentially neuropsychiatric illnesses, including anxiety and depression. Therefore, much research effort in recent years has focused on understanding the potential of targeting the intestinal microbiota to prevent and treat such disorders. This review aims to explore the influence of the gut microbiota on host neural function and behavior, particularly those of relevance to stress-related disorders. The involvement of microbiota in diverse neural functions such as myelination, microglia function, neuronal morphology, and blood-brain barrier integrity across the life span, from early life to adolescence to old age, will also be discussed. Nurturing an optimal gut microbiome may also prove beneficial in animal science as a means to manage stressful situations and to increase productivity of farm animals. The implications of these observations are manifold, and researchers are hopeful that this promising body of preclinical work can be successfully translated to the clinic and beyond.

Vagus Nerve as Modulator of the Brain-Gut Axis in Psychiatric and Inflammatory Disorders

The vagus nerve represents the main component of the parasympathetic nervous system, which oversees a vast array of crucial bodily functions, including control of mood, immune response, digestion, and heart rate. It establishes one of the connections between the brain and the gastrointestinal tract and sends information about the state of the inner organs to the brain via afferent fibers. In this review article, we discuss various functions of the vagus nerve which make it an attractive target in treating psychiatric and gastrointestinal disorders. There is preliminary evidence that vagus nerve stimulation is a promising add-on treatment for treatment-refractory depression, posttraumatic stress disorder, and inflammatory bowel disease. Treatments that target the vagus nerve increase the vagal tone and inhibit cytokine production. Both are important mechanism of resiliency. The stimulation of vagal afferent fibers in the gut influences monoaminergic brain systems in the brain stem that play crucial roles in major psychiatric conditions, such as mood and anxiety disorders. In line, there is preliminary evidence for gut bacteria to have beneficial effect on mood and anxiety, partly by affecting the activity of the vagus nerve. Since, the vagal tone is correlated with capacity to regulate stress responses and can be influenced by breathing, its increase through meditation and yoga likely contribute to resilience and the mitigation of mood and anxiety symptoms.

Metabolic and Microbiota Measures as Peripheral Biomarkers in Major Depressive Disorder

Advances in understanding the role of the microbiome in physical and mental health are at the forefront of medical research and hold potential to have a direct impact on precision medicine approaches. In the past 7 years, we have studied the role of microbiota-brain communication on behavior in mouse models using germ-free mice, mice exposed to antibiotics, and healthy specific pathogen free mice. Through our work and that of others, we have seen an amazing increase in our knowledge of how bacteria signal to the brain and the implications this has for psychiatry. Gut microbiota composition and function are influenced both by genetics, age, sex, diet, life experiences, and many other factors of psychiatric and bodily disorders and thus may act as potential biomarkers of the gut-brain axis that could be used in psychiatry and co-morbid conditions. There is a particular need in major depressive disorder and other mental illness to identify biomarkers that can stratify patients into more homogeneous groups to provide better treatment and for development of new therapeutic approaches. Peripheral outcome measures of host-microbe bidirectional communication have significant translational value as biomarkers. Enabling stratification of clinical populations, based on individual biological differences, to predict treatment response to pharmacological and non-pharmacological interventions. Here we consider the links between co-morbid metabolic syndrome and depression, focusing on biomarkers including leptin and ghrelin in combination with assessing gut microbiota composition, as a potential tool to help identify individual differences in depressed population.

Gut-Brain Axis and Mood Disorder

Humans have over 100 trillion bacteria, highly abundant in the intestinal tract. Evidence suggests that intestinal microbiota is associated with the neuro-endocrine-immune pathways and can be associated with various mood disorders. This review summarizes findings from studies looking into neurobiochemical, neuroendocrine, and neuroimmune system mechanisms of the gut-brain axis to determine the relationship between intestinal microbiota and mood disorders. The effect of prebiotics, probiotics and antibiotics on mood disorders are also discussed, with the aim to propose some new therapeutic strategies for mood disorders.

Anxiety, Depression, and the Microbiome: A Role for Gut Peptides

The complex bidirectional communication between the gut and the brain is finely orchestrated by different systems, including the endocrine, immune, autonomic, and enteric nervous systems. Moreover, increasing evidence supports the role of the microbiome and microbiota-derived molecules in regulating such interactions; however, the mechanisms underpinning such effects are only beginning to be resolved. Microbiota-gut peptide interactions are poised to be of great significance in the regulation of gut-brain signaling. Given the emerging role of the gut-brain axis in a variety of brain disorders, such as anxiety and depression, it is important to understand the contribution of bidirectional interactions between peptide hormones released from the gut and intestinal bacteria in the context of this axis. Indeed, the gastrointestinal tract is the largest endocrine organ in mammals, secreting dozens of different signaling molecules, including peptides. Gut peptides in the systemic circulation can bind cognate receptors on immune cells and vagus nerve terminals thereby enabling indirect gut-brain communication. Gut peptide concentrations are not only modulated by enteric microbiota signals, but also vary according to the composition of the intestinal microbiota. In this review, we will discuss the gut microbiota as a regulator of anxiety and depression, and explore the role of gut-derived peptides as signaling molecules in microbiome-gut-brain communication. Here, we summarize the potential interactions of the microbiota with gut hormones and endocrine peptides, including neuropeptide Y, peptide YY, pancreatic polypeptide, cholecystokinin, glucagon-like peptide, corticotropin-releasing factor, oxytocin, and ghrelin in microbiome-to-brain signaling. Together, gut peptides are important regulators of microbiota-gut-brain signaling in health and stress-related psychiatric illnesses.

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

The gut microbiota (GM) is a complex, evolutionarily molded ecological system, which contributes to a variety of physiological functions. The GM is highly dynamic, being sensitive to environmental stimuli, and its composition changes over the host's entire lifespan. However, the basic question of how much these changes may be ascribed to variables such as population, diet, genetics and gender, and/or to the aging process per se is still largely unanswered. We argue that comparison among studies on centenarians-the best model of healthy aging and longevity-recruited from different geographical areas/populations (different genetics and dietary habits) can help to disentangle the contribution of aging and non-aging-related variables to GM remodeling with age. The current review focuses on the role of population, gender and host genetics as possible drivers of GM modification along the human aging process. The feedback impact of age-associated GM variation on the GM-brain axis and GM metabolomics is also discussed. We likewise address the role of GM in neurodegenerative diseases such as Parkinson's and Alzheimer's, and its possible therapeutic use, taking advantage of the fact that centenarians are characterized by an extreme (healthy) phenotype versus patients suffering from age-related pathologies. Finally, it is argued that longitudinal studies combining metagenomics sequencing and in-depth phylogenetic analysis with a comprehensive phenotypic characterization of centenarians and patients using up-to-date omics (metabolomics, transcriptomics and meta-transcriptomics) are urgently needed.

Principles of plasticity in the developing brain

The developing brain is especially sensitive to a wide range of experiences, showing a remarkable capacity for plastic changes that influence behavioural outcomes throughout the lifetime. We review the principles that regulate this plasticity in development and consider the factors that modulate the developing brain. These include early sensory, motor, and language experience, early stress, caregiver interactions, peer interactions, psychoactive drugs, diet, microbiome, and the immune system. Emphasis is given to changes in behaviour, epigenetics, and neuronal morphology.

WHAT THIS PAPER ADDS

A discussion of the surprising range of factors influencing brain development Life experiences interact resulting in a phenomenon called metaplasticity.

Psychobiotics: A new approach for treating mental illness?

Gut microbiomes may have a significant impact on mood and cognition, which is leading experts towards a new frontier in neuroscience. Studies have shown that increase in the amount of good bacteria in the gut can curb inflammation and cortisol level, reduces symptoms of depression and anxiety, lowers stress reactivity, improves memory and even lessens neuroticism and social anxiety. This shows that, probably the beneficial gut bacteria or probiotics function mechanistically as delivery vehicles for neuroactive compounds. Thus, a psychobiotic is a live organism, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness. Study of these novel class of probiotics may open up the possibility of rearrangement of intestinal microbiota for effective management of various psychiatric disorders.

Probiotic, Prebiotic, and Brain Development

Recently, a number of studies have demonstrated the existence of a link between the emotional and cognitive centres of the brain and peripheral functions through the bi-directional interaction between the central nervous system and the enteric nervous system. Therefore, the use of bacteria as therapeutics has attracted much interest. Recent research has found that there are a variety of mechanisms by which bacteria can signal to the brain and influence several processes in relation to neurotransmission, neurogenesis, and behaviour. Data derived from both in vitro experiments and in vivo clinical trials have supported some of these new health implications. While recent molecular advancement has provided strong indications to support and justify the role of the gut microbiota on the gut-brain axis, it is still not clear whether manipulations through probiotics and prebiotics administration could be beneficial in the treatment of neurological problems. The understanding of the gut microbiota and its activities is essential for the generation of future personalized healthcare strategies. Here, we explore and summarize the potential beneficial effects of probiotics and prebiotics in the neurodevelopmental process and in the prevention and treatment of certain neurological human diseases, highlighting current and future perspectives in this topic.

Shared mechanisms among probiotic taxa: implications for general probiotic claims

Strain-specificity of probiotic effects has been a cornerstone principle of probiotic science for decades. Certainly, some important mechanisms are present in only a few probiotic strains. But scientific advances now reveal commonalities among members of certain taxonomic groups of probiotic microbes. Some clinical benefits likely derive from these shared mechanisms, suggesting that sub-species-specific, species-specific or genus-specific probiotic effects exist. Human trials are necessary to confirm specific health benefits. However, a strain that has not been tested in human efficacy trials may meet the minimum definition of the term 'probiotic' if it is a member of a well-studied probiotic species expressing underlying core mechanisms and it is delivered at an effective dose.

Links of gut microbiota composition with alcohol dependence syndrome and alcoholic liver disease

BACKGROUND

Alcohol abuse has deleterious effects on human health by disrupting the functions of many organs and systems. Gut microbiota has been implicated in the pathogenesis of alcohol-related liver diseases, with its composition manifesting expressed dysbiosis in patients suffering from alcoholic dependence. Due to its inherent plasticity, gut microbiota is an important target for prevention and treatment of these diseases. Identification of the impact of alcohol abuse with associated psychiatric symptoms on the gut community structure is confounded by the liver dysfunction. In order to differentiate the effects of these two factors, we conducted a comparative "shotgun" metagenomic survey of 99 patients with the alcohol dependence syndrome represented by two cohorts-with and without liver cirrhosis. The taxonomic and functional composition of the gut microbiota was subjected to a multifactor analysis including comparison with the external control group.

RESULTS

Alcoholic dependence and liver cirrhosis were associated with profound shifts in gut community structures and metabolic potential across the patients. The specific effects on species-level community composition were remarkably different between cohorts with and without liver cirrhosis. In both cases, the commensal microbiota was found to be depleted. Alcoholic dependence was inversely associated with the levels of butyrate-producing species from the Clostridiales order, while the cirrhosis-with multiple members of the Bacteroidales order. The opportunist pathogens linked to alcoholic dependence included pro-inflammatory Enterobacteriaceae, while the hallmarks of cirrhosis included an increase of oral microbes in the gut and more frequent occurrence of abnormal community structures. Interestingly, each of the two factors was associated with the expressed enrichment in many Bifidobacterium and Lactobacillus-but the exact set of the species was different between alcoholic dependence and liver cirrhosis. At the level of functional potential, the patients showed different patterns of increase in functions related to alcohol metabolism and virulence factors, as well as pathways related to inflammation.

CONCLUSIONS

Multiple shifts in the community structure and metabolic potential suggest strong negative influence of alcohol dependence and associated liver dysfunction on gut microbiota. The identified differences in patterns of impact between these two factors are important for planning of personalized treatment and prevention of these pathologies via microbiota modulation. Particularly, the expansion of Bifidobacterium and Lactobacillus suggests that probiotic interventions for patients with alcohol-related disorders using representatives of the same taxa should be considered with caution. Taxonomic and functional analysis shows an increased propensity of the gut microbiota to synthesis of the toxic acetaldehyde, suggesting higher risk of colorectal cancer and other pathologies in alcoholics.

Brain-Gut-Microbiota Axis and Mental Health

OBJECTIVE

The brain-gut-microbiota axis has been put forward as a new paradigm in neuroscience, which may be of relevance to mental illness. The mechanisms of signal transmission in the brain-gut-microbiota axis are complex and involve bidirectional communications that enable gut microbes to communicate with the brain and the brain to communicate with the microbes. This review assesses the potential usefulness and limitations of the paradigm.

METHODS

A selective literature review was conducted to evaluate the current knowledge in clinical and preclinical brain-gut-microbiota interactions as related to psychiatric disorders.

RESULTS

Most published studies in the field are preclinical, and there is so far a lack of clinical studies. Preliminary studies in psychiatric populations support the view of a dysbiosis in some conditions, but studies are often small scale and marred by potential confounding variables. Preclinical studies support the view that psychobiotics ("bacteria which when ingested in adequate amounts have a positive mental health benefit") might be of use in treating some patients with mental health difficulties. To date, we have no well-conducted studies in clinical populations, although there are some studies in healthy volunteers. A cocktail of probiotics has been shown to alter brain activity as monitored by functional magnetic resonance imaging, and Bifidobacterium longum was reported to alter brain electrical activity.

CONCLUSIONS

It has yet to be convincingly demonstrated that the exciting findings of psychobiotic efficacy demonstrated in preclinical models of psychiatric illness will translate to patients.

A Perspective on Brain-Gut Communication: The American Gastroenterology Association and American Psychosomatic Society Joint Symposium on Brain-Gut Interactions and the Intestinal Microenvironment

BACKGROUND

Alterations in brain-gut communication and the intestinal microenvironment have been implicated in a variety of medical and neuropsychiatric diseases. Three central areas require basic and clinical research: (1) how the intestinal microenvironment interacts with the host immune system, central nervous system, and enteric nervous system; (2) the role of the intestinal microenvironment in the pathogenesis of medical and neuropsychiatric disease; and (3) the effects of diet, prebiotics, probiotics, and fecal microbiota transplantation on the intestinal microenvironment and the treatment of disease.

METHODS

This review article is based on a symposium convened by the American Gastroenterology Association and the American Psychosomatic Society to foster interest in the role of the intestinal microenvironment in brain-gut communication and pathogenesis of neuropsychiatric and biopsychosocial disorders. The aims were to define the state of the art of the current scientific knowledge base and to identify guidelines and future directions for new research in this area.

RESULTS

This review provides a characterization of the intestinal microbial composition and function. We also provide evidence for the interactions between the intestinal microbiome, the host, and the environment. The role of the intestinal microbiome in medical and neuropsychiatric diseases is reviewed as well as the treatment effects of manipulation of the intestinal microbiome.

CONCLUSIONS

Based on this review, opportunities and challenges for conducting research in the field are described, leading to potential avenues for future research.

Toward a Biopsychosocial Ecology of the Human Microbiome, Brain-Gut Axis, and Health

OBJECTIVE

Rapidly expanding insights into the human microbiome and health suggest that Western medicine is poised for significant evolution, or perhaps revolution-this while medicine continues on a trajectory from reductionism to a biopsychosocial (BPS) paradigm recognizing biological, psychological, and social influences on health. The apparent sensitivity of the microbiota to perturbations across BPS domains suggests that a broad and inclusive framework is needed to develop applicable knowledge in this emerging area. We outline an ecological framework of the human microbiome by extending the BPS concept to better incorporate environmental and human factors as members of a global, dynamic set of systems that interact over time.

METHODS

We conducted a selective literature review across disciplines to integrate microbiome research into a BPS framework.

RESULTS

The microbiome can be understood in terms of ecological systems encompassing BPS domains at four levels: (a) immediate (molecular, genetic, and neural processes), (b) proximal (physiology, emotion, social integration), (c) intermediate (built environments, behaviors, societal practices), and (d) distal (physical environments, attitudes, and broad cultural, economic, and political factors). The microbiota and host are thus understood in terms of their immediate interactions and the more distal physical and social arenas in which they participate.

CONCLUSIONS

A BPS ecological paradigm encourages replicable, generalizable, and interdisciplinary/transdisciplinary research and practices that take into account the vast influences on the human microbiome that may otherwise be overlooked or understood out of context. It also underscores the importance of sustainable bioenvironmental, psychological, and social systems that broadly support microbial, neural, and general health.

Food and the gut: relevance to some of the autisms

Complex, diverse and rarely appearing without comorbidity, the autism spectrum disorders continue to be a source of research interest. With core symptoms variably impacting on social communication skills, the traditional focus of many research efforts has centred on the brain and how genetic and environmental processes impact on brain structure, function and/or connectivity to account for various behavioural presentations. Alongside emerging ideas on autistic traits being present in various clinical states, the autisms, and the overrepresentation of several comorbid conditions impacting on quality of life, other research avenues have opened up. The central role of the brain in relation to autism may be at least partially influenced by the functions of other organs. The gastrointestinal (GI) tract represents an important biological system pertinent to at least some autism. The notion of a gut-brain-behaviour axis has garnered support from various findings: an overrepresentation of functional and pathological bowel states, bowel and behavioural findings showing bidirectional associations, a possible relationship between diet, GI function and autism and recently, greater focus on aspects of the GI tract such as the collected gut microbiota in relation to autism. Gaps remain in our knowledge of the functions of the GI tract linked to autism, specifically regarding mechanisms of action onward to behavioural presentation. Set however within the context of diversity in the presentation of autism, science appears to be moving towards defining important GI-related autism phenotypes with the possibility of promising dietary and other related intervention options onward to improving quality of life.

MicroRNAs-Based Inter-Domain Communication between the Host and Members of the Gut Microbiome

The gut microbiome is an important modulator of host gene expression, impacting important functions such as the innate immune response. Recent evidence suggests that the inter-domain communication between the gut microbiome and host may in part occur via microRNAs (small, non-coding RNA molecules) which are often differentially expressed in the presence of bacteria and can even be released and taken up by bacteria. The role of microRNAs in microbiome–host communication in intestinal diseases is not fully understood, particularly in diseases impacted by exposure to environmental toxicants. Here, we review the present knowledge in the areas of microbiome and microRNA expression-based communication, microbiome and intestinal disease relationships, and microRNA expression responses to intestinal diseases. We also examine potential links between host microRNA–microbiota communication and exposure to environmental toxicants by reviewing connections between (i) toxicants and microRNA expression, (ii) toxicants and gut diseases, and (iii) toxicants and the gut microbiome. Future multidisciplinary research in this area is needed to uncover these interactions with the potential to impact how gut-microbiome associated diseases [e.g., inflammatory bowel disease (IBD) and many others] are managed.

Evidences of a New Psychobiotic Formulation on Body Composition and Anxiety

Background

Gut microbiota is implied in obesity, because of its ability to harvest energy from diet, and in the regulation of behavior. Given the link between gut microbiota, body composition, obesity, and anxiety, the aim of this study was to evaluate the effects of a new psychobiotic formulation.

Methods

Eligible patients were randomly divided into three groups: psychobiotics oral suspension group (POSG); dietary treatment group (DTG); combined treatment group (CTG). All subjects underwent body composition and psychological profile evaluation.

Results

Significant changes in body composition parameters in each group were relieved after all treatments. Hamilton anxiety rating scale (HAM-A) highlighted a significant reduction of the total score for all study population after treatments in POSG (p = 0.01) and CTG (p = 0.04). A reduction of HAM-A total score in anxious subjects in POSG or CTG and a significant reduction of positive subjects for HAM-A in POSG (p = 0.03) and in CDG (p = 0.01) were shown.

Discussion

Three-week intake of selected POS represents a good approach to solve problems related to obesity and behavior disorders. However, new clinical trials need to be performed on a larger population and for a longer period of treatment before definitive conclusions can be made. This trial is registered with NCT01890070.

Cross Talk: The Microbiota and Neurodevelopmental Disorders

Humans evolved within a microbial ecosystem resulting in an interlinked physiology. The gut microbiota can signal to the brain via the immune system, the vagus nerve or other host-microbe interactions facilitated by gut hormones, regulation of tryptophan metabolism and microbial metabolites such as short chain fatty acids (SCFA), to influence brain development, function and behavior. Emerging evidence suggests that the gut microbiota may play a role in shaping cognitive networks encompassing emotional and social domains in neurodevelopmental disorders. Drawing upon pre-clinical and clinical evidence, we review the potential role of the gut microbiota in the origins and development of social and emotional domains related to Autism spectrum disorders (ASD) and schizophrenia. Small preliminary clinical studies have demonstrated gut microbiota alterations in both ASD and schizophrenia compared to healthy controls. However, we await the further development of mechanistic insights, together with large scale longitudinal clinical trials, that encompass a systems level dimensional approach, to investigate whether promising pre-clinical and initial clinical findings lead to clinical relevance.

Do bacteria shape our development? Crosstalk between intestinal microbiota and HPA axis

The human body contains as many bacteria in the intestine as the total number of human body cells. These bacteria have a central position in human health and disease, and would also play a role in the regulation of emotions, behavior, and even higher cognitive functions. The Hypothalamic-Pituitary-Adrenal axis (HPA axis) is a major physiological stress system that produces cortisol. This hormone is involved in responding to environmental stress and also shapes many aspects of brain development. Both the HPA axis and the intestinal microbiota show rapid and profound developmental changes during the first years of life. Early environmental disturbances can affect the development of both systems. Early adversity, for example, is known to lead to later unbalances in both, as well as to psychopathological behavior and emotions. The goal of this theoretical review is to summarize current knowledge on the developmental crosstalk between the intestinal microbiota and the HPA axis, providing a basis for understanding the development and bidirectional communication between these two essential systems in human functioning.

Gut microbiota and attention deficit hyperactivity disorder: new perspectives for a challenging condition

A bidirectional communication between the gut and the brain (gut-brain axis) is well recognized with the gut microbiota viewed as a key regulator of this cross-talk. Currently, a body of preclinical and to a lesser extent epidemiological evidence supports the notion that host-microbe interactions play a key role in brain development and function and in the etiology of neurodevelopmental disorders. Early life events and shifts away from traditional lifestyles are known to impact gut microbiota composition and function and, thereby, may increase the risk of developing neurodevelopmental disorders. Attention deficit hyperactivity disorder (ADHD) is nowadays the most prevalent neurodevelopmental disorder. Despite many years of research its etiology is unclear and its diagnosis and treatment are still challenging. Different factors reported to be associated with the risk of developing ADHD and/or linked to different ADHD manifestations have also been linked to shifts in gut microbiota composition, suggesting a link between the microbiota and the disorder. Evidence from preliminary human studies also suggests that dietary components that modulate gut microbiota may also influence ADHD development or symptoms, although further studies are warranted to confirm this hypothesis. Here, we firstly review the potential mechanisms by which the gut microbiota may regulate the brain-gut axis and influence behavior and neurodevelopmental disorders. Secondly, we discuss the current knowledge about the different factors and dietary components reported to be associated with the risk of developing ADHD or its manifestations and with shifts in gut microbiota composition. Finally, we briefly highlight the need to progress our understanding regarding the role of the gut microbiota in ADHD, since this could open new avenues for early intervention and improved management of the disease.

Habitual yoghurt consumption and depressive symptoms in a general population study of 19,596 adults

PURPOSE

Epidemiological studies directly examining the association between habitual yoghurt consumption and mental health remain scarce. The aim of this study is to investigate the association of yoghurt consumption with depressive symptoms in adults.

METHODS

This is a cross-sectional study of 19,596 Chinese adults (mean age 41.2, standard deviation 11.8 years; males, 54.3%). Depressive symptoms were assessed using the Self-Rating Depression Scale (SDS). Dietary intake was obtained through a valid food frequency questionnaire. Multiple logistic regression analysis was conducted to assess the association between yoghurt consumption and depressive symptoms. A number of potential confounders were adjusted in the model.

RESULTS

The prevalence of elevated depressive symptoms was 17.1% (SDS ≥45). The multivariable adjusted odds ratios (95% CI) of having elevated depressive symptoms by increasing levels of yoghurt consumption (1-3 times/week, 4-7 times/week, and  ≥twice/day) were 1.05 (0.96, 1.15), 1.02 (0.91, 1.15), and 2.10 (1.61, 2.73) in comparison with lowest consumption group (<once/week or hardly ever).

CONCLUSIONS

These findings suggest no significant association between habitual yoghurt consumption and self-reported depressive symptoms, while the relatively high frequency of yoghurt consumption (≥twice/day), which was seen in a small subset of subjects, was associated with increased depressive symptoms. These results need to be interpreted with caution because of the cross-sectional nature of the data.

Influence of gut microbiota on neuropsychiatric disorders

The last decade has witnessed a growing appreciation of the fundamental role played by an early assembly of a diverse and balanced gut microbiota and its subsequent maintenance for future health of the host. Gut microbiota is currently viewed as a key regulator of a fluent bidirectional dialogue between the gut and the brain (gut-brain axis). A number of preclinical studies have suggested that the microbiota and its genome (microbiome) may play a key role in neurodevelopmental and neurodegenerative disorders. Furthermore, alterations in the gut microbiota composition in humans have also been linked to a variety of neuropsychiatric conditions, including depression, autism and Parkinson's disease. However, it is not yet clear whether these changes in the microbiome are causally related to such diseases or are secondary effects thereof. In this respect, recent studies in animals have indicated that gut microbiota transplantation can transfer a behavioral phenotype, suggesting that the gut microbiota may be a modifiable factor modulating the development or pathogenesis of neuropsychiatric conditions. Further studies are warranted to establish whether or not the findings of preclinical animal experiments can be generalized to humans. Moreover, although different communication routes between the microbiota and brain have been identified, further studies must elucidate all the underlying mechanisms involved. Such research is expected to contribute to the design of strategies to modulate the gut microbiota and its functions with a view to improving mental health, and thus provide opportunities to improve the management of psychiatric diseases. Here, we review the evidence supporting a role of the gut microbiota in neuropsychiatric disorders and the state of the art regarding the mechanisms underlying its contribution to mental illness and health. We also consider the stages of life where the gut microbiota is more susceptible to the effects of environmental stressors, and the possible microbiota-targeted intervention strategies that could improve health status and prevent psychiatric disorders in the near future.

Eating Disorders and the Intestinal Microbiota: Mechanisms of Energy Homeostasis and Behavioral Influence

PURPOSE OF REVIEW

We reviewed and evaluated recently published scientific studies that explored the role of the intestinal microbiota in eating disorders.

RECENT FINDINGS

Studies have demonstrated that the intestinal microbiota is a contributing factor to both host energy homeostasis and behavior-two traits commonly disrupted in patients with eating disorders. To date, intestinal microbiota research in eating disorders has focused solely on anorexia nervosa (AN). Initial studies have reported an atypical intestinal microbial composition in patients with AN compared to healthy controls. However, the impact of these AN-associated microbial communities on host metabolism and behavior remains unknown. The intriguing pattern of findings in patients with AN encourages further investigation of the intestinal microbiota in eating disorders. Elucidating the specific role(s) of these microbial communities may yield novel ideas for augmenting current clinical therapies to promote weight gain, decrease gastrointestinal distress, and even reduce psychological symptomatology.

Prenatal stress affects placental cytokines and neurotrophins, commensal microbes, and anxiety-like behavior in adult female offspring

Recent studies demonstrate that exposure to stress changes the composition of the intestinal microbiota, which is associated with development of stress-induced changes to social behavior, anxiety, and depression. Stress during pregnancy has also been related to the emergence of these disorders; whether commensal microbes are part of a maternal intrauterine environment during prenatal stress is not known. Here, we demonstrate that microbiome changes are manifested in the mother, and also found in female offspring in adulthood, with a correlation between stressed mothers and female offspring. Alterations in the microbiome have been shown to alter immune responses, thus we examined cytokines in utero. IL-1β was increased in placenta and fetal brain from offspring exposed to the prenatal stressor. Because IL-1β has been shown to prevent induction of brain derived neurotrophic factor (BDNF), we examined BDNF and found a reduction in female placenta and adult amygdala, suggesting in utero impact on neurodevelopment extending into adulthood. Furthermore, gastrointestinal microbial communities were different in adult females born from stressed vs. non-stressed pregnancies. Adult female offspring also demonstrated increased anxiety-like behavior and alterations in cognition, suggesting a critical window where stress is able to influence the microbiome and the intrauterine environment in a deleterious manner with lasting behavioral consequences. The microbiome may be a key link between the intrauterine environment and adult behavioral changes.

A double-blind, randomized, placebo-controlled trial of Lactobacillus helveticus and Bifidobacterium longum for the symptoms of depression

OBJECTIVES

This trial investigated whether probiotics improved mood, stress and anxiety in a sample selected for low mood. We also tested whether the presence or severity of irritable bowel syndrome symptoms, and levels of proinflammatory cytokines, brain-derived neurotrophic factor and other blood markers, would predict or impact treatment response.

METHOD

Seventy-nine participants (10 dropouts) not currently taking psychotropic medications with at least moderate scores on self-report mood measures were randomly allocated to receive either a probiotic preparation (containing Lactobacillus helveticus and Bifidobacterium longum) or a matched placebo, in a double-blind trial for 8 weeks. Data were analysed as intent-to-treat.

RESULTS

No significant difference was found between the probiotic and placebo groups on any psychological outcome measure (Cohen's d range = 0.07-0.16) or any blood-based biomarker. At end-point, 9 (23%) of those in the probiotic group showed a ⩾60% change on the Montgomery-Åsberg Depression Rating Scale (responders), compared to 10 (26%) of those in the placebo group ([Formula: see text], p = ns). Baseline vitamin D level was found to moderate treatment effect on several outcome measures. Dry mouth and sleep disruption were reported more frequently in the placebo group.

CONCLUSIONS

This study found no evidence that the probiotic formulation is effective in treating low mood, or in moderating the levels of inflammatory and other biomarkers. The lack of observed effect on mood symptoms may be due to the severity, chronicity or treatment resistance of the sample; recruiting an antidepressant-naive sample experiencing mild, acute symptoms of low mood, may well yield a different result. Future studies taking a preventative approach or using probiotics as an adjuvant treatment may also be more effective. Vitamin D levels should be monitored in future studies in the area. The results of this trial are preliminary; future studies in the area should not be discouraged.

Human Gut Microbiota: Toward an Ecology of Disease

Composed of trillions of individual microbes, the human gut microbiota has adapted to the uniquely diverse environments found in the human intestine. Quickly responding to the variances in the ingested food, the microbiota interacts with the host via reciprocal biochemical signaling to coordinate the exchange of nutrients and proper immune function. Host and microbiota function as a unit which guards its balance against invasion by potential pathogens and which undergoes natural selection. Disturbance of the microbiota composition, or dysbiosis, is often associated with human disease, indicating that, while there seems to be no unique optimal composition of the gut microbiota, a balanced community is crucial for human health. Emerging knowledge of the ecology of the microbiota-host synergy will have an impact on how we implement antibiotic treatment in therapeutics and prophylaxis and how we will consider alternative strategies of global remodeling of the microbiota such as fecal transplants. Here we examine the microbiota-human host relationship from the perspective of the microbial community dynamics.

Investigating the link between drug-naive first episode psychoses (FEPs), weight gain abnormalities and brain structural damages: Relevance and implications for therapy

Evidence suggests that obesity and overweight may be associated with severe brain structural abnormalities and poor cognitive and functional outcomes in the general population. Despite these observations and the high prevalence of weight gain abnormalities in patients with psychosis spectrum disorders (PSDs), no studies have investigated the impact that these metabolic disturbances may have on brain structures and development in the earliest stages of PSDs. In the present review we shed light on the association between weight gain and brain structural abnormalities that may affect the course of illness in drug-naïve FEPs. Given the lack of studies directly investigating this issue, we firstly identified and critically evaluated the literature assessing weight gain abnormalities and gray or white matter (GM, WM) volumes (either globally or in specific regions of interest) in otherwise healthy obese/overweight adolescents and young adults. We then compared the results of this systematic review with those of two recent meta-analysis investigating GM and WM abnormalities in drug-naïve FEPs. Weight gain in otherwise healthy subjects was consistently associated with frontal and temporal GM atrophy and with reduced integrity of WM in the corpus callosum. Of relevance, all these brain regions are affected in drug-naïve FEPs, and their integrity is associated with clinical, cognitive and functional outcomes. The underlying mechanisms that may explain the association between weight gain, adiposity, and brain damage in both healthy subjects and drug-naïve FEPs are widely discussed. On the basis of this knowledge, we tried: a) to deduce an integrative model for the development of obesity in psychosis spectrum disorders; b) to identify the key vulnerability factors underlying the association between weight gain and psychosis; c) to provide information on new potential targets of intervention.

Detection and Physicochemical Characterization of Membrane Vesicles (MVs) of Lactobacillus reuteri DSM 17938

Membrane vesicles (MVs) are bilayer structures which bleb from bacteria, and are important in trafficking biomolecules to other bacteria or host cells. There are few data about MVs produced by the Gram-positive commensal-derived probiotic Lactobacillus reuteri; however, MVs from this species may have potential therapeutic benefit. The aim of this study was to detect and characterize MVs produced from biofilm (bMVs), and planktonic (pMVs) phenotypes of L. reuteri DSM 17938. MVs were analyzed for structure and physicochemical characterization by Scanning Electron Microscope (SEM) and Dynamic Light Scattering (DLS). Their composition was interrogated using various digestive enzyme treatments and subsequent Transmission Electron Microscopy (TEM) analysis. eDNA (extracellular DNA) was detected and quantified using PicoGreen. We found that planktonic and biofilm of L. reuteri cultures generated MVs with a broad size distribution. Our data also showed that eDNA was associated with pMVs and bMVs (e_MVsDNA). DNase I treatment demonstrated no modifications of MVs, suggesting that an eDNA-MVs complex protected the e_MVsDNA. Proteinase K and Phospholipase C treatments modified the structure of MVs, showing that lipids and proteins are important structural components of L. reuteri MVs. The biological composition and the physicochemical characterization of MVs generated by the probiotic L. reuteri may represent a starting point for future applications in the development of vesicles-based therapeutic systems.

Can psychobiotics intake modulate psychological profile and body composition of women affected by normal weight obese syndrome and obesity? A double blind randomized clinical trial

Background

Evidence of probiotics effects on gut function, brain activity and emotional behaviour were provided. Probiotics can have dramatic effects on behaviour through the microbiome–gut–brain axis, through vagus nerve. We investigated whether chronic probiotic intake could modulate psychological state, eating behaviour and body composition of normal weight obese (NWO) and preobese–obese (PreOB/OB) compared to normal weight lean women (NWL).

Methods

60 women were enrolled. At baseline and after a 3-week probiotic oral suspension (POS) intake, all subjects underwent evaluation of body composition by anthropometry and dual X-ray absorptiometry, and psychological profile assessment by self-report questionnaires (i.e. EDI-2, SCL90R and BUT). Statistical analysis was carried out using paired t test or a non-parametric Wilcoxon test to evaluate differences between baseline and after POS intake, one-way ANOVA to compare all three groups and, where applicable, Chi square or t test were used to assess symptoms.

Results

Of the 48 women that concluded the study, 24% were NWO, 26% were NWL and 50% were PreOB/OB. Significant differences in body composition were highlighted among groups both at baseline and after a POS (p < 0.05). After POS intake, a significant reduction of BMI, resistance, FM (kg and %) (p < 0.05), and a significant increase of FFM (kg and  %) (p < 0.05) were observed in all subjects in NOW and PreOB/OB. After POS intake, reduction of bacterial overgrowth syndrome (p < 0.05) and lower psychopathological scores (p < 0.05) were observed in NWO and PreOB/OB women. At baseline and after POS intake, all subjects tested were negative to SCL90R_GSI scale, but after treatment subjects positive to BUT_GSI scale were significantly reduced (8.33%) (p < 0.05) compared to the baseline (33.30%). In NWO and PreOB/OB groups significant differences (p < 0.05) in response to the subscales of the EDI-2 were observed. Significant improvement of the orocecal transit time was observed (p < 0.05) after POS intake. Furthermore, significant differences were observed for meteorism (p < 0.05) and defecation frequency (p < 0.05).

Conclusions

A 3-week intake of selected psychobiotics modulated body composition, bacterial contamination, psychopathological scores of NWO and PreOB/OB women. Further research is needed on a larger population and for a longer period of treatment before definitive conclusions can be made.

Trial registration ClinicalTrials.gov Id: NCT01890070

The Microbiome and Cancer: Implications for Oncology Nursing Science

BACKGROUND

Approximately 1.6 million Americans were diagnosed with cancer in 2014. To combat their disease, many individuals received either curative or palliative treatments that produced undesired symptoms. These symptoms, which often cause significant distress for individuals coping with cancer, may share biologic underpinnings such as epigenetic changes and immune dysregulation. Alterations in the normal flora of the gut may also influence cancer symptoms.

OBJECTIVE

The aim of this review is to describe the emerging role for the gut microbiome in cancer research, especially the potential relationship between the gut microbiome and cancer symptoms.

METHODS

Extant literature was reviewed and synthesized.

RESULTS

The majority of studies linking the gut microbiota and cancer are animal models and focus on the relationship between dysbiosis and colorectal cancer. Emerging evidence supports that the "gut-brain" connection is a plausible mechanism for "psychoneurological" cancer symptoms such as depression, pain, and fatigue.

CONCLUSIONS

There is compelling evidence that the gut microbiota affects cancer via several mechanisms, including microbial diversity and number, metabolism, and/or immune initiation. However, more research is necessary to elucidate these mechanisms, particularly among a variety of cancers and cancer-related symptoms.

IMPLICATIONS FOR PRACTICE

A better understanding of the role of the gut microbiota in cancer symptoms may lead to the development of targeted individualized interventions affecting the gut microbiota that prevent or ameliorate dysbiosis, thereby reducing symptoms. These interventions may emphasize self-care management strategies essential for wellness, such as diet, nutrition, and stress reduction.

Probiotic treatment reduces depressive-like behaviour in rats independently of diet

The gut microbiota has recently emerged as an important regulator of brain physiology and behaviour in animals, and ingestion of certain bacteria (probiotics) therefore appear to be a potential treatment for major depressive disorder (MDD). However, some conceptual and mechanistical aspects need further elucidation. We therefore aimed at investigating whether the habitual diet may interact with the effect of probiotics on depression-related behaviour and further examined some potentially involved mechanisms underlying the microbe-mediated behavioural effects. Forty male Sprague-Dawley rats were fed a control (CON) or high-fat diet (HFD) for ten weeks and treated with either a multi-species probiotic formulation or vehicle for the last five weeks. Independently of diet, probiotic treatment markedly reduced depressive-like behaviour in the forced swim test by 34% (95% CI: 22-44%). Furthermore, probiotic treatment skewed the cytokine production by stimulated blood mononuclear cells towards IFNγ, IL2 and IL4 at the expense of TNFα and IL6. In addition, probiotics lowered hippocampal transcript levels of factors involved in HPA axis regulation (Crh-r1, Crh-r2 and Mr), whereas HFD increased these levels. A non-targeted plasma metabolomics analysis revealed that probiotics raised the level of indole-3-propionic acid, a potential neuroprotective agent. Our findings clearly support probiotics as a potential treatment strategy in MDD. Importantly, the efficacy was not attenuated by intake of a "Western pattern" diet associated with MDD. Mechanistically, the HPA axis, immune system and microbial tryptophan metabolism could be important in this context. Importantly, our study lend inspiration to clinical trials on probiotics in depressed patients.

The Host Microbiome Regulates and Maintains Human Health: A Primer and Perspective for Non-Microbiologists

Humans consider themselves discrete autonomous organisms, but recent research is rapidly strengthening the appreciation that associated microorganisms make essential contributions to human health and well being. Each person is inhabited and also surrounded by his/her own signature microbial cloud. A low diversity of microorganisms is associated with a plethora of diseases, including allergy, diabetes, obesity, arthritis, inflammatory bowel diseases, and even neuropsychiatric disorders. Thus, an interaction of microorganisms with the host immune system is required for a healthy body. Exposure to microorganisms from the moment we are born and appropriate microbiome assembly during childhood are essential for establishing an active immune system necessary to prevent disease later in life. Exposure to microorganisms educates the immune system, induces adaptive immunity, and initiates memory B and T cells that are essential to combat various pathogens. The correct microbial-based education of immune cells may be critical in preventing the development of autoimmune diseases and cancer. This review provides a broad overview of the importance of the host microbiome and accumulating knowledge of how it regulates and maintains a healthy human system. Cancer Res; 77(8); 1783-812. ©2017 AACR.

Bifidobacterium in the gut microbiota confer resilience to chronic social defeat stress in mice

Accumulating evidence suggests that abnormalities in the composition of the gut microbiota may play a role in the pathogenesis of depression. Although approximately 30% mice are resilient to chronic social defeat stress (CSDS), the role of gut microbiota in this stress resilience is unknown. In this study, male C57BL/6 mice were exposed to a different CD1 aggressor mouse for 10 min on 10 consecutive days. A social interaction test was applied to distinguish between resilient and susceptible mice. Using 16S rRNA analysis, we examined the composition of gut microbiota in feces from control, resilient, and susceptible mice. The marked appearance of Bifidobacterium was detected in the resilient mice, whereas in the control and susceptible mice, Bifidobacterium were below the detection limit. Oral intake of Bifidobacterium significantly increased the number of resilient mice after CSDS compared with vehicle-treated mice. These findings suggest that Bifidobacterium may confer resilience to CSDS. Therefore, supplementation of Bifidobacterium may prevent the onset of depression from stress in humans. In addition, supplementation of Bifidobacterium may prevent or minimize relapse from remission induced by inflammation and/or stress in depressed patients.

A psychology of the human brain-gut-microbiome axis

In recent years, we have seen increasing research within neuroscience and biopsychology on the interactions between the brain, the gastrointestinal tract, the bacteria within the gastrointestinal tract, and the bidirectional relationship between these systems: the brain-gut-microbiome axis. Although research has demonstrated that the gut microbiota can impact upon cognition and a variety of stress-related behaviours, including those relevant to anxiety and depression, we still do not know how this occurs. A deeper understanding of how psychological development as well as social and cultural factors impact upon the brain-gut-microbiome axis will contextualise the role of the axis in humans and inform psychological interventions that improve health within the brain-gut-microbiome axis. Interventions ostensibly aimed at ameliorating disorders in one part of the brain-gut-microbiome axis (e.g., psychotherapy for depression) may nonetheless impact upon other parts of the axis (e.g., microbiome composition and function), and functional gastrointestinal disorders such as irritable bowel syndrome represent a disorder of the axis, rather than an isolated problem either of psychology or of gastrointestinal function. The discipline of psychology needs to be cognisant of these interactions and can help to inform the future research agenda in this emerging field of research. In this review, we outline the role psychology has to play in understanding the brain-gut-microbiome axis, with a focus on human psychology and the use of research in laboratory animals to model human psychology.

Intervention strategies for cesarean section-induced alterations in the microbiota-gut-brain axis

Microbial colonization of the gastrointestinal tract is an essential process that modulates host physiology and immunity. Recently, researchers have begun to understand how and when these microorganisms colonize the gut and the early-life factors that impact their natural ecological establishment. The vertical transmission of maternal microbes to the offspring is a critical factor for host immune and metabolic development. Increasing evidence also points to a role in the wiring of the gut-brain axis. This process may be altered by various factors such as mode of delivery, gestational age at birth, the use of antibiotics in early life, infant feeding, and hygiene practices. In fact, these early exposures that impact the intestinal microbiota have been associated with the development of diseases such as obesity, type 1 diabetes, asthma, allergies, and even neurodevelopmental disorders. The present review summarizes the impact of cesarean birth on the gut microbiome and the health status of the developing infant and discusses possible preventative and restorative strategies to compensate for early-life microbial perturbations.