The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

A gut (microbiome) feeling about addiction: Interactions with stress and social systems

In recent years, an increasing attention has given to the intricate and diverse connection of microorganisms residing in our gut and their impact on brain health and central nervous system disease. There has been a shift in mindset to understand that drug addiction is not merely a condition that affects the brain, it is now being recognized as a disorder that also involves external factors such as the intestinal microbiota, which could influence vulnerability and the development of addictive behaviors. Furthermore, stress and social interactions, which are closely linked to the intestinal microbiota, are powerful modulators of addiction. This review delves into the mechanisms through which the microbiota-stress-immune axis may shape drug addiction and social behaviors. This work integrates preclinical and clinical evidence that demonstrate the bidirectional communication between stress, social behaviors, substance use disorders and the gut microbiota, suggesting that gut microbes might modulate social stress having a significance in drug addiction.

The microbiota drives diurnal rhythms in tryptophan metabolism in the stressed gut

Chronic stress disrupts microbiota-gut-brain axis function and is associated with altered tryptophan metabolism, impaired gut barrier function, and disrupted diurnal rhythms. However, little is known about the effects of acute stress on the gut and how it is influenced by diurnal physiology. Here, we used germ-free and antibiotic-depleted mice to understand how microbiota-dependent oscillations in tryptophan metabolism would alter gut barrier function at baseline and in response to an acute stressor. Cecal metabolomics identified tryptophan metabolism as most responsive to a 15-min acute stressor, while shotgun metagenomics revealed that most bacterial species exhibiting rhythmicity metabolize tryptophan. Our findings highlight that the gastrointestinal response to acute stress is dependent on the time of day and the microbiome, with a signature of stress-induced functional alterations in the ileum and altered tryptophan metabolism in the colon.

Antidiarrheal effect of Psidium guajava L. extract in acute diarrhea: a systematic review

Acute diarrheal diseases are a leading cause of childhood mortality and morbidity worldwide. Psidium guajava has been globally used for its antidiarrheal potential. We conducted a systematic review of scientific articles published up to the year 2021, which included in vivo pre-clinical tests and clinical trials involving patients with acute infectious diarrhea to verify the antidiarrheal, antibacterial and antispasmodic effects of galenic preparations or phytopharmaceuticals from P. guajava. PRISMA and Rayyan were used as tools for the selection of studies collected in four databases (Pubmed, Scopus, Web of Science and Science Direct). The keywords used to carry out the search were: 'Psidium guajava', 'guava', 'antidiarrhe*' and 'diarrhe*', joined by Boolean operators 'OR' or 'AND'. The characteristics of studies in animal models of acute diarrhea induction, as well as in vivo and in vitro motility and microbiological tests linked with its main pathophysiological mechanisms, were collected. Twenty-three articles were included. Twenty (87%) of these reported heterogenic preclinical studies, predominating pharmacological studies of efficacy against conventional antidiarrheal agents, which utilized relevant outcomes and models of infectious diarrhea from the top pathogens in the clinic along with classical castor oil-induced diarrhea associated with motility tests. Only three articles (13%) corresponded to clinical trials investigating the efficacy, dose and safety of these preparations. Most studies reported positive results and significant mechanistic evidence from antibacterial, anti-motility, anti-secretory and protective/anti-inflammatory perspectives. However, further studies are needed to define the clinical significance and safety treatment with P. guajava extracts. © 2024 Society of Chemical Industry.

Unmet needs of drugs for irritable bowel syndrome and inflammatory bowel diseases: interest of vagus nerve stimulation and hypnosis

The gut and the brain communicate bidirectionally through the autonomic nervous system. The vagus nerve is a key component of this gut-brain axis, and has numerous properties such as anti-inflammatory, antinociceptive, anti-depressive effects. A perturbation of this gut-brain communication is involved in the pathogeny of functional digestive disorders, such as irritable bowel syndrome, and inflammatory bowel diseases. Stress plays a role in the pathogeny of these diseases, which are biopsychosocial models. There are presently unmet needs of pharmacological treatments of these chronic debilitating diseases. Treatments are not devoid of side effects, cost-effective, do not cure the diseases, can lose effects over time, thus explaining the poor satisfaction of patients, their lack of compliance, and their interest for non-drug therapies. The gut-brain axis can be targeted for therapeutic purposes in irritable bowel syndrome and inflammatory bowel disease through non-drug therapies, such as hypnosis and vagus nerve stimulation, opening up possibilities for responding to patient expectations.

Gastrointestinal and brain barriers: unlocking gates of communication across the microbiota-gut-brain axis

Crosstalk between gut and brain has long been appreciated in health and disease, and the gut microbiota is a key player in communication between these two distant organs. Yet, the mechanisms through which the microbiota influences development and function of the gut-brain axis remain largely unknown. Barriers present in the gut and brain are specialized cellular interfaces that maintain strict homeostasis of different compartments across this axis. These barriers include the gut epithelial barrier, the blood-brain barrier and the blood-cerebrospinal fluid barrier. Barriers are ideally positioned to receive and communicate gut microbial signals constituting a gateway for gut-microbiota-brain communication. In this Review, we focus on how modulation of these barriers by the gut microbiota can constitute an important channel of communication across the gut-brain axis. Moreover, barrier malfunction upon alterations in gut microbial composition could form the basis of various conditions, including often comorbid neurological and gastrointestinal disorders. Thus, we should focus on unravelling the molecular and cellular basis of this communication and move from simplistic framing as 'leaky gut'. A mechanistic understanding of gut microbiota modulation of barriers, especially during critical windows of development, could be key to understanding the aetiology of gastrointestinal and neurological disorders.

The Impact of Chronic Stress Related to COVID-19 on Eating Behaviors and the Risk of Obesity in Children and Adolescents

During the COVID-19 pandemic, an increase in the incidence of overweight and obesity in children was observed. It appears that unhealthy food choices, an unbalanced diet, and a sedentary lifestyle, as well as experiencing stress related to the pandemic, may be contributing to this disturbing trend. Chronic stress is a significant factor contributing to eating disorders and obesity in youngsters, involving medical, molecular, and psychological elements. Individuals under chronic stress often focus on appearance and weight, leading to negative body image and disrupted relationships with food, resulting in unhealthy eating behaviors. Chronic stress also impacts hormonal balance, reducing the satiety hormone leptin and elevating the appetite-stimulating hormone ghrelin, fostering increased hunger and uncontrolled snacking. Two systems, the hypothalamic-pituitary-adrenal axis and the sympathetic system with the adrenal medulla, are activated in response to stress, causing impaired secretion of noradrenaline and cortisol. Stress-related obesity mechanisms encompass oxidative stress, neuroinflammation, insulin resistance, and neurohormonal and neurotransmission disorders. Stress induces insulin resistance, elevating obesity risk by disrupting blood sugar regulation and fat storage. Stress also affects the gut microbiome, potentially influencing chronic inflammation and metabolic processes linked to obesity. In conclusion, chronic stress is a multifaceted risk factor for eating disorders and obesity in children, necessitating a comprehensive understanding of effective preventive and intervention strategies amid the escalating prevalence of childhood overweight and obesity.

Psychosocial stress-induced intestinal permeability in healthy humans: What is the evidence?

An impaired intestinal barrier function can be detrimental to the host as it may allow the translocation of luminal antigens and toxins into the subepithelial tissue and bloodstream. In turn, this may cause local and systemic immune responses and lead to the development of pathologies. In vitro and animal studies strongly suggest that psychosocial stress is one of the factors that can increase intestinal permeability via mast-cell dependent mechanisms. Remarkably, studies have not been able to yield unequivocal evidence that such relation between stress and intestinal permeability also exists in (healthy) humans. In the current Review, we discuss the mechanisms that are involved in stress-induced intestinal permeability changes and postulate factors that influence these alterations and that may explain the translational difficulties from in vitro and animal to human studies. As human research differs highly from animal research in the extent to which stress can be applied and intestinal permeability can be measured, it remains difficult to draw conclusions about the presence of a relation between stress and intestinal permeability in (healthy) humans. Future studies should bear in mind these difficulties, and more research into in vivo methods to assess intestinal permeability are warranted.