The Brain-Gut Axis Contributes to Neuroprogression in Stress-Related Disorders

Adaptive remodeling of the stimulus-secretion coupling: Lessons from the 'stressed' adrenal medulla

Stress is part of our daily lives and good health in the modern world is offset by unhealthy lifestyle factors, including the deleterious consequences of stress and associated pathologies. Repeated and/or prolonged stress may disrupt the body homeostasis and thus threatens our lives. Adaptive processes that allow the organism to adapt to new environmental conditions and maintain its homeostasis are therefore crucial. The adrenal glands are major endocrine/neuroendocrine organs involved in the adaptive response of the body facing stressful situations. Upon stress episodes and in response to activation of the sympathetic nervous system, the first adrenal cells to be activated are the neuroendocrine chromaffin cells located in the medullary tissue of the adrenal gland. By releasing catecholamines (mainly epinephrine and to a lesser extent norepinephrine), adrenal chromaffin cells actively contribute to the development of adaptive mechanisms, in particular targeting the cardiovascular system and leading to appropriate adjustments of blood pressure and heart rate, as well as energy metabolism. Specifically, this chapter covers the current knowledge as to how the adrenal medullary tissue remodels in response to stress episodes, with special attention paid to chromaffin cell stimulus-secretion coupling. Adrenal stimulus-secretion coupling encompasses various elements taking place at both the molecular/cellular and tissular levels. Here, I focus on stress-driven changes in catecholamine biosynthesis, chromaffin cell excitability, synaptic neurotransmission and gap junctional communication. These signaling pathways undergo a collective and finely-tuned remodeling, contributing to appropriate catecholamine secretion and maintenance of body homeostasis in response to stress.

The role of microRNAs in depression

Major depressive disorder (MDD) is a psychiatric disorder with increasing prevalence worldwide. It is a leading cause of disability and suicide, severely affecting physical and mental health. However, the study of depression remains at an exploratory stage in terms of diagnostics and treatment due to the complexity of its pathogenesis. MicroRNAs are endogenous short-stranded non-coding RNAs capable of binding to the 3’untranslated region of mRNAs. Because of their ability to repress translation process of genes and are found at high levels in brain tissues, investigation of their role in depression has gradually increased recently. This article summarizes recent research progress on the relationship between microRNAs and depression. The microRNAs play a regulatory role in the pathophysiology of depression, involving dysregulation of monoamines, abnormalities in neuroplasticity and neurogenesis, hyperactivity of the HPA axis, and dysregulation of inflammatory responses. These microRNAs might provide new clue for the diagnosis and treatment of MDD, and the development of antidepressant drugs.

Childhood stress and midlife depression in women: the influence of diet quality

OBJECTIVE

How does diet quality (DQ) moderate associations between serious childhood stress exposures and adult depression?

METHODS

We analyzed a cohort of Californian women at midlife (N=382; age 36-42). Serious childhood stress was defined as high perceived stress during childhood or adverse childhood experiences (ACEs) of physical abuse, sexual abuse, and/or household substance abuse. Women were dichotomized by current depression risk (high/low). The Healthy Eating Index (HEI)-2015 and Alternate Healthy Eating Index (AHEI)-2010 measured current DQ from 3-day food records. Interactions between childhood stress exposures and DQ indices were tested one-by-one in multivariable Poisson regression models.

RESULTS

Depression risks associated with endorsing all 3 ACEs differed by HEI and AHEI scores, as did risks associated with endorsing high perceived stress, physical abuse, and sexual abuse by AHEI. Where DQ moderated stress-depression associations, predicted prevalences of high depression risk did not vary with DQ among women endorsing the particular childhood stressors. However, among non-endorsing women, predicted high depression risk prevalences were significantly lower with higher DQ compared to in their stress-exposed counterparts - e.g. at the 90th AHEI percentile, depression prevalences were ∼20% among 'non-childhood-stressed' women versus 48.8% (high perceived stress, sexual abuse), 52.0% (physical abuse), and 73.0% (3 ACEs) in 'childhood-stressed' women.

CONCLUSIONS

Higher current DQ, particularly as aligned with chronic disease prevention guidelines, predicts lower depression risk in women with low childhood adversity. DQ did not buffer depression risk in women with high childhood stress. Further research is warranted to examine persistent pathways of depression risk and diet's role within.

Brain-immune axis regulation is responsive to cognitive behavioral therapy and mindfulness intervention: Observations from a randomized controlled trial in patients with Crohn's disease

Background and aims

Crohn's disease (CD) is a chronic inflammatory bowel disease associated with psychological stress that is regulated primarily by the hypothalamus-pituitary-adrenal (HPA) axis. Here, we determined whether the psychological characteristics of CD patients associate with their inflammatory state, and whether a 3-month trial of cognitive-behavioral and mindfulness-based stress reduction (COBMINDEX) impacts their inflammatory process.

Methods

Circulating inflammatory markers and a wide range of psychological parameters related to stress and well-being were measured in CD patients before and after COBMINDEX. Inflammatory markers in CD patients were also compared to age- and sex-matched healthy controls (HCs).

Results

CD patients exhibited increased peripheral low-grade inflammation compared with HCs, demonstrated by interconnected inflammatory modules represented by IL-6, TNFα, IL-17, MCP-1 and IL-18. Notably, higher IL-18 levels correlated with higher score of stress and a lower score of wellbeing in CD patients. COBMINDEX was accompanied by changes in inflammatory markers that coincided with changes in cortisol: changes in serum levels of cortisol correlated positively with those of IL-10 and IFNα and negatively with those of MCP-1. Furthermore, inflammatory markers of CD patients at baseline predicted COBMINDEX efficacy, as higher levels of distinct cytokines and cortisol at baseline, correlated negatively with changes in disease activity (by Harvey-Bradshaw Index) and psychological distress (global severity index measure) following COBMINDEX.

Conclusion

CD patients have a characteristic immunological profile that correlates with psychological stress, and disease severity. We suggest that COBMINDEX induces stress resilience in CD patients, which impacts their well-being, and their disease-associated inflammatory process.

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Patients with Crohn's disease exhibit distinct inflammatory and psychological modules.

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IL-18 correlates with clinical and psychological features of patients with Crohn's disease.

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COBMINDEX treatment strengthens resilience and recovers stress-induced inflammation among Crohn's disease patients.

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Both inflammatory and psychological measures predict COBMINDEX efficacy.

Extra-skeletal effects of dietary calcium: Impact on the cardiovascular system, obesity, and cancer

Calcium is well known to be integral to bone and muscle health, with deleterious effects such as osteoporosis associated with inadequate calcium intake. Recent studies have also highlighted the significant effects of calcium in extra-musculoskeletal functioning, including the cardiovascular system, obesity, and cancer. Calcium impacts the cardiovascular system as an antagonist associated with a reduction in hypertension, increase vasodilation, and improvement in blood vessel function when obtained in the diet as an organic source, through food. However, the inorganic source of calcium, found in supplements, may be negatively associated with the cardiovascular system due to plaque deposits and atherogenesis when taken in excess. Some studies suggest that calcium intake may impact obesity by regulation of adipogenesis and reducing fat deposits with resulting weight loss. The pathogenesis of calcium for reducing obesity is thought to be related in part to its impact on gut microbiota profile, with the suggestion that calcium may have prebiotic properties. Animal and some human studies propose that calcium may also have a role in cancer prevention and/or treatment due to its function in the cell proliferation process and the impact on hormonal regulation, and thus warrants more investigations in the human population. Some prospective and small clinical studies suggest that calcium may be beneficial for colorectal cancer. Overall, emerging research in various areas continues to highlight the essentiality of dietary calcium for functioning at the molecular and biochemical level toward improvement in health and some chronic disease conditions.

Impact of Microbial Metabolites on Microbiota-Gut-Brain Axis in Inflammatory Bowel Disease

The complex bidirectional communication system existing between the gastrointestinal tract and the brain initially termed the "gut-brain axis" and renamed the "microbiota-gut-brain axis", considering the pivotal role of gut microbiota in sustaining local and systemic homeostasis, has a fundamental role in the pathogenesis of Inflammatory Bowel Disease (IBD). The integration of signals deriving from the host neuronal, immune, and endocrine systems with signals deriving from the microbiota may influence the development of the local inflammatory injury and impacts also more distal brain regions, underlying the psychophysiological vulnerability of IBD patients. Mood disorders and increased response to stress are frequently associated with IBD and may affect the disease recurrence and severity, thus requiring an appropriate therapeutic approach in addition to conventional anti-inflammatory treatments. This review highlights the more recent evidence suggesting that alterations of the microbiota-gut-brain bidirectional communication axis may concur to IBD pathogenesis and sustain the development of both local and CNS symptoms. The participation of the main microbial-derived metabolites, also defined as "postbiotics", such as bile acids, short-chain fatty acids, and tryptophan metabolites in the development of IBD-associated gut and brain dysfunction will be discussed. The last section covers a critical evaluation of the main clinical evidence pointing to the microbiome-based therapeutic approaches for the treatment of IBD-related gastrointestinal and neuropsychiatric symptoms.

Stress and the gut microbiota-brain axis

Stress is a nonspecific response of the body to any demand imposed upon it, disrupting the body homoeostasis and manifested with symptoms such as anxiety, depression or even headache. These responses are quite frequent in the present competitive world. The aim of this review is to explore the effect of stress on gut microbiota. First, we summarize evidence of where the microbiota composition has changed as a response to a stressful situation, and thereby the effect of the stress response. Likewise, we review different interventions that can modulate microbiota and could modulate the stress according to the underlying mechanisms whereby the gut-brain axis influences stress. Finally, we review both preclinical and clinical studies that provide evidence of the effect of gut modulation on stress. In conclusion, the influence of stress on gut microbiota and gut microbiota on stress modulation is clear for different stressors, but although the preclinical evidence is so extensive, the clinical evidence is more limited. A better understanding of the mechanism underlying stress modulation through the microbiota may open new avenues for the design of therapeutics that could boost the pursued clinical benefits. These new designs should not only focus on stress but also on stress-related disorders such as anxiety and depression, in both healthy individuals and different populations.

Microbiota and organophosphates

Organophosphates (OPs) are important toxic compounds commonly used for a variety of purposes in agriculture, industry and household settings. Consumption of these compounds affects several central nervous system functions. Some of the most recognised consequences of organophosphate pesticide exposure in humans include neonatal developmental abnormalities, endocrine disruption, neurodegeneration, neuroinflammation and cancer. In addition, neurobehavioral and emotional deficits following OP exposure have been reported. It would be of great value to discover a therapeutic strategy which produces a protective effect against these neurotoxic compounds. Moreover, a growing body of preclinical data suggests that the microbiota may affect metabolism and neurotoxic outcomes through exposure to OPs. The human gut is colonised by a broad variety of microorganisms. This huge number of bacteria and other microorganisms which survive by colonising the gastrointestinal tract is defined as "gut microbiota". The gut microbiome plays a profound role in metabolic processing, energy production, immune and cognitive development and homeostasis. The effects are not only localized in the gut, but also influence many other organs, such as the brain through the microbiome-gut-brain axis. Therefore, given the gut microbiota's key role in host homeostasis, this microbiota may be altered or modified temporarily by factors such as antibiotics, diet and toxins such as pesticides. The aim of this review is to examine scientific articles concerning the impact of microbiota in OP toxicity. Studies focussed on the possible contribution the microbiota has on variable host pharmacokinetic responses such as absorption and biotransformation of xenobiotics will be evaluated. Microbiome manipulation by antibiotic or probiotic administration and faecal transplantation are experimental approaches recently proposed as treatments for several diseases. Finally, microbiota manipulation as a possible therapeutic strategy in order to reduce OP toxicity will be discussed.

Blood CRP levels are elevated in children and adolescents with functional neurological symptom disorder

There is accumulating evidence that patients with functional neurological symptom disorder (FND) show activation of multiple components of the stress system-the hypothalamic-pituitary-adrenal axis, autonomic nervous system, and brain regions involved in arousal- and emotion-processing. This study aims to examine whether the immune-inflammatory component of the stress system is also activated. C-reactive protein (CRP) blood titre levels were measured in 79 children and adolescents with FND. CRP values ≥ 2 mg/L suggest low-grade inflammation. CRP values > 10 mg/L suggest a disease process. Sixty-six percent of subjects (n = 52) had CRP titres ≥ 2 mg/L. The upward shift in the distribution of CRP levels suggested low-grade inflammation (median CRP concentration was 4.60 mg/L, with 75th and 90th percentiles of 6.1 and 10.3 mg/L, respectively). Elevated CRP titres were not explained by sex, pubertal status, BMI, or medical factors. Confounder analyses suggested that history of maltreatment (χ² = 2.802, df = 1, p = 0.094, φ = 0.190; β = 2.823, p = 0.04) and a diagnosis of anxiety (χ² = 2.731, df = 1, p = 0.098, φ = 0.187; β = 4.520, p = 0.061) contributed to elevated CRP levels. Future research will need to identify the origins and locations of immune cell activation and the pathways and systems contributing to their activation and modulation. Because functional activity in neurons and glial cells-the brain's innate effector immune cells-is tightly coupled, our finding of elevated CRP titres suggests activation of the immune-inflammatory component of the brain's stress system. A more direct examination of inflammation-related molecules in the brain will help clarify the role of immune-inflammatory processes in FND.

Neuroprogression: the hidden mechanism of depression

For many years, depressive disorder (DD) was considered a transient and natural disease of people's mood. Its etiology had been attributed mainly to biochemical alterations of the monoamines and their receptors. Nevertheless, its prevalence and considerable impact on the family and social environment of those afflicted by it have placed the disease as a global public health problem. Neuroprogression is the term used to describe the changes in several psychiatric conditions evidenced and observed in the clinical manifestations, biochemical markers, and cerebral structures of the patients with major depressive disorder (MDD), which frequently overlap with neurodegenerative disorders. DD is considered a potentially aggressive state of neuronal deterioration involving apoptosis, reduced neurogenesis, decreased neuronal plasticity, and increased immune response. Clinically, it encompasses a poor response to treatment and an increase in depressive episodes, both of which bring about vulnerability and decline of functions associated with structural changes in the brain. The interest of this work is to review the metabolic processes involved in the morphologic alterations in the limbic system reported in patients with MDD, as well as the neurologic bases of this complex pathology that include environmental stress, genetic vulnerability, alterations in the neurotransmission, and changes in the neuroplasticity, all of which today bring into limelight a mechanism of progressive neuronal damage.

A Microbial Signature of Psychological Distress in Irritable Bowel Syndrome

OBJECTIVE

Irritable bowel syndrome (IBS) is associated with alterations along the brain-gut-microbiota axis. Previous studies have suggested a parallel segregation of microbial features and psychological burden in IBS. This study aimed at exploring the microbial correlates of psychological distress in patients with IBS.

METHODS

Forty-eight patients with IBS (Rome III criteria, M (SD) age = 42 (15) years, 35 female, 25 diarrhea-dominant, 5 constipation-dominant, and 18 alternating-type IBS) were assessed for psychological and clinical variables with validated questionnaires, fecal samples underwent microbial 16S rRNA analyses (regions V1-2). Microbial analyses comprised examination of alpha and beta diversity, correlational analyses of bacterial abundance and comparisons among subgroups defined by thresholds of psychological and IBS symptom variables, and machine learning to identify bacterial patterns corresponding with psychological distress.

RESULTS

Thirty-one patients (65%) showed elevated psychological distress, 22 (31%) anxiety, and 10 depression (21%). Microbial beta diversity was significantly associated with distress and depression (q = .036 each, q values are p values false discovery rate-corrected for multiple testing). Depression was negatively associated with Lachnospiraceae abundance (Spearman's ρ = -0.58, q = .018). Patients exceeding thresholds of distress, anxiety, depression, and stress perception showed significantly higher abundances of Proteobacteria (q = .020-.036). Patients with anxiety were characterized by elevated Bacteroidaceae (q = .036). A signature of 148 unclassified species accounting for 3.9% of total bacterial abundance co-varied systematically with the presence of psychological distress.

CONCLUSIONS

Psychological variables significantly segregated gut microbial features, underscoring the role of brain-gut-microbiota interaction in IBS. A microbial signature corresponding with psychological distress was identified.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT02536131, retrospectively registered.

Short-chain fatty acids: microbial metabolites that alleviate stress-induced brain-gut axis alterations

KEY POINTS

Chronic (psychosocial) stress changes gut microbiota composition, as well as inducing behavioural and physiological deficits. The microbial metabolites short-chain fatty acids (SCFAs) have been implicated in gastrointestinal functional, (neuro)immune regulation and host metabolism, but their role in stress-induced behavioural and physiological alterations is poorly understood. Administration of SCFAs to mice undergoing psychosocial stress alleviates enduring alterations in anhedonia and heightened stress-responsiveness, as well as stress-induced increases in intestinal permeability. In contrast, chronic stress-induced alterations in body weight gain, faecal SCFAs and the gene expression of the SCFA receptors FFAR2 and FFAR3 remained unaffected by SCFA supplementation. These results present novel insights into mechanisms underpinning the influence of the gut microbiota on brain homeostasis, behaviour and host metabolism, informing the development of microbiota-targeted therapies for stress-related disorders.

ABSTRACT

There is a growing recognition of the involvement of the gastrointestinal microbiota in the regulation of physiology and behaviour. Microbiota-derived metabolites play a central role in the communication between microbes and their host, with short-chain fatty acids (SCFAs) being perhaps the most studied. SCFAs are primarily derived from fermentation of dietary fibres and play a pivotal role in host gut, metabolic and immune function. All these factors have previously been demonstrated to be adversely affected by stress. Therefore, we sought to assess whether SCFA supplementation could counteract the enduring effects of chronic psychosocial stress. C57BL/6J male mice received oral supplementation of a mixture of the three principle SCFAs (acetate, propionate and butyrate). One week later, mice underwent 3 weeks of repeated psychosocial stress, followed by a comprehensive behavioural analysis. Finally, plasma corticosterone, faecal SCFAs and caecal microbiota composition were assessed. SCFA treatment alleviated psychosocial stress-induced alterations in reward-seeking behaviour, and increased responsiveness to an acute stressor and in vivo intestinal permeability. In addition, SCFAs exhibited behavioural test-specific antidepressant and anxiolytic effects, which were not present when mice had also undergone psychosocial stress. Stress-induced increases in body weight gain, faecal SCFAs and the colonic gene expression of the SCFA receptors free fatty acid receptors 2 and 3 remained unaffected by SCFA supplementation. Moreover, there were no collateral effects on caecal microbiota composition. Taken together, these data show that SCFA supplementation alleviates selective and enduring alterations induced by repeated psychosocial stress and these data may inform future research into microbiota-targeted therapies for stress-related disorders.

Cerebrovascular Injury After Serial Exposure to Chronic Stress and Abstinence from Methamphetamine Self-Administration

Cerebrovascular damage caused by either exposure to stress or the widely abused drug, methamphetamine (Meth) is known but stress and drug abuse frequently occur in tandem that may impact their individual cerebrovascular effects. This study examined their co-morbid cerebrovascular effects during abstinence from self-administered Meth after the exposure to chronic unpredictable stress (CUS). Exposure to CUS prior to unrestricted Meth self-administration had no effect on Meth intake in rats; however, the pro-inflammatory mediator cyclooxygenase-2 (COX-2) and the breakdown of cell-matrix adhesion protein β-dystroglycan in isolated cerebral cortical capillaries were increased after 3 days of abstinence and persisted for 7 days. These changes preceded decreases in occludin, a key structural protein component of the blood-brain barrier. The decrease in occludin was blocked by the COX-2 specific inhibitor nimesulide treatment during abstinence from Meth. The changes in COX-2, β-dystroglycan, and occludin were only evident following the serial exposure to stress and Meth but not after either one alone. These results suggest that stress and voluntary Meth intake can synergize and disrupt cerebrovasculature in a time-dependent manner during abstinence from chronic stress and Meth. Furthermore, COX-2 inhibition may be a viable pharmacological intervention to block vascular changes after Meth exposure.

A Review of Traumatic Brain Injury and the Gut Microbiome: Insights into Novel Mechanisms of Secondary Brain Injury and Promising Targets for Neuroprotection

The gut microbiome and its role in health and disease have recently been major focus areas of research. In this review, we summarize the different ways in which the gut microbiome interacts with the rest of the body, with focus areas on its relationships with immunity, the brain, and injury. The gut–brain axis, a communication network linking together the central and enteric nervous systems, represents a key bidirectional pathway with feed-forward and feedback mechanisms. The gut microbiota has a central role in this pathway and is significantly altered following injury, leading to a pro-inflammatory state within the central nervous system (CNS). Herein, we examine traumatic brain injury (TBI) in relation to this axis and explore potential interventions, which may serve as targets for improving clinical outcomes and preventing secondary brain injury.