Strain specific stress-modulating effects of candidate probiotics: A systematic screening in a mouse model of chronic restraint stress

Metabolic Status Influences Probiotic Efficacy for Depression-PRO-DEMET Randomized Clinical Trial Results

Probiotics may represent a safe and easy-to-use treatment option for depression or its metabolic comorbidities. However, it is not known whether metabolic features can influence the efficacy of probiotics treatments for depression. This trial involved a parallel-group, prospective, randomized, double-blind, controlled design. In total, 116 participants with depression received a probiotic preparation containing Lactobacillus helveticus Rosell®-52 and Bifidobacterium longum Rosell®-175 or placebo over 60 days. The psychometric data were assessed longitudinally at five time-points. Data for blood pressure, body weight, waist circumference, complete blood count, serum levels of C-reactive protein, cholesterol, triglycerides, and fasting glucose were measured at the beginning of the intervention period. There was no advantage of probiotics usage over placebo in the depression score overall (PRO vs. PLC: F(1.92) = 0.58; p = 0.45). However, we found a higher rate of minimum clinically important differences in patients supplemented with probiotics than those allocated to placebo generally (74.5 vs. 53.5%; X2(1,n = 94) = 4.53; p = 0.03; NNT = 4.03), as well as in the antidepressant-treated subgroup. Moreover, we found that the more advanced the pre-intervention metabolic abnormalities (such as overweight, excessive central adipose tissue, and liver steatosis), the lower the improvements in psychometric scores. A higher baseline stress level was correlated with better improvements. The current probiotic formulations may only be used as complementary treatments for depressive disorders. Metabolic abnormalities may require more complex treatments. ClinicalTrials.gov identifier: NCT04756544.

Lactobacillus plantarum LLY-606 Supplementation Ameliorates the Cognitive Impairment of Natural Aging in Mice: The Potential Role of Gut Microbiota Homeostasis

This work explored the effects of Lactobacillus plantarum LLY-606 (LLY-606) on cognitive function in aging mice. Our findings demonstrated that LLY-606 effectively prolonged the lifespan of mice and improved age-related cognitive impairments. Additionally, our study revealed that supplementation with LLY-606 resulted in the downregulation of inflammatory cytokine levels and the upregulation of antioxidant capacity. Furthermore, probiotic supplementation effectively mitigated the deterioration of the intestinal barrier function in aging mice. Amplicon analysis indicated the successful colonization of probiotics, facilitating the regulation of age-induced gut microbiota dysbiosis. Notably, the functional abundance prediction of microbiota indicated that tryptophan metabolism pathways, glutamatergic synapse pathways, propanoate metabolism pathways, and arginine and proline metabolism pathways were enriched after the LLY-606 intervention. In summary, LLY-606 emerged as a potential functional probiotic capable of influencing cognitive function in aging mice. This effect was achieved through the modulation of gut microbiota, the regulation of synaptic plasticity, and the enhancement of neurotrophic factor levels.

The adolescent and young adult microbiome and its association with substance use: a scoping review

AIMS

The microbiome is a critical factor in health throughout human development. The aims of this scoping review are to (i) elucidate the differences between the youth (post-natal day 21-65 for rodents, 2-7 years for non-human primates, and 10-25 years for humans) microbiome with other life stages and (ii) identify youth-specific microbial changes associated with substance use.

METHODS

Peer-reviewed studies published up to May 2023 were identified in PubMed and SCOPUS and included gut and oral microbiome studies from rodents, non-human primates, and humans (N = 1733). Twenty-six articles were determined eligible based on inclusion criteria (aim 1: n = 19, aim 2: n = 7).

RESULTS

The adolescent and young adult oral and gut microbiomes are distinct compared to other life stages, within both non-human and human models. While there is limited research in this area, the microbiome appears to be vulnerable to substance use exposure earlier in life, including substances commonly initiated and escalated during adolescence and young adulthood (i.e. alcohol, cannabis, and tobacco).

CONCLUSIONS

Studies across the lifespan indicate that adolescence and young adulthood are distinct periods of development, where the microbiome is sensitive to exposures, including substance use. There is a need for more studies focused on the adolescent and young adult microbiome and substance use, as well as focused on the oral microbiome during this developmental period. Understanding the gut and oral microbiome during adolescence and young adulthood may provide insight into the pathophysiology of substance use disorders.

Butterflies in the gut: the interplay between intestinal microbiota and stress

Psychological stress is a global issue that affects at least one-third of the population worldwide and increases the risk of numerous psychiatric disorders. Accumulating evidence suggests that the gut and its inhabiting microbes may regulate stress and stress-associated behavioral abnormalities. Hence, the objective of this review is to explore the causal relationships between the gut microbiota, stress, and behavior. Dysbiosis of the microbiome after stress exposure indicated microbial adaption to stressors. Strikingly, the hyperactivated stress signaling found in microbiota-deficient rodents can be normalized by microbiota-based treatments, suggesting that gut microbiota can actively modify the stress response. Microbiota can regulate stress response via intestinal glucocorticoids or autonomic nervous system. Several studies suggest that gut bacteria are involved in the direct modulation of steroid synthesis and metabolism. This review provides recent discoveries on the pathways by which gut microbes affect stress signaling and brain circuits and ultimately impact the host's complex behavior.

Protective Effects of Lacticaseibacillus rhamnosus IDCC3201 on Motor Functions and Anxiety Levels in a Chronic Stress Mouse Model

Growing evidence indicates a crucial role of the gut microbiota in physiological functions. Gut-brain axis imbalance has also been associated with neuropsychiatric and neurodegenerative disorders. Studies have suggested that probiotics regulate the stress response and alleviate mood-related symptoms. In this study, we investigated the effects of the probiotic Lacticaseibacillus rhamnosus IDCC3201 (L3201) on the behavioral response and fecal metabolite content in an unpredictable chronic mild stress (UCMS) mouse model. Our study shows that chronic stress in mice for three weeks resulted in significant changes in behavior, including lower locomotor activity, higher levels of anxiety, and depressive-like symptoms, compared to the control group. Metabolomic analysis demonstrated that disrupted fecal metabolites associated with aminoacyl-tRNA biosynthesis and valine, leucine, and isoleucine biosynthesis by UCMS were restored with the administration of L3201. Oral administration of the L3201 ameliorated the observed changes and improved the behavioral alterations along with fecal metabolites, suggesting that probiotics play a neuroprotective role.

Effects of a Lacticaseibacillus Mix on Behavioural, Biochemical, and Gut Microbial Outcomes of Male Mice following Chronic Restraint Stress

The effect of supplementation with Lactobacillus strains to prevent the consequences of chronic stress on anxiety in mouse strains sensitive to stress and the consequences on gut microbiota have been relatively unexplored. Thus, we administered a Lacticaseibacillus casei LA205 and Lacticaseibacillus paracasei LA903 mix to male BALB/cByJrj mice two weeks before and during 21-day chronic restraint stress (CRS) (non-stressed/solvent (NS-PBS), non-stressed/probiotics (NS-Probio), CRS/solvent (S-PBS), CRS/probiotics (S-Probio)). CRS resulted in lower body weight and coat state alteration, which were attenuated by the probiotic mix. S-Probio mice showed less stress-associated anxiety-like behaviours than their NS counterpart, while no difference was seen in PBS mice. Serum corticosterone levels were significantly higher in the S-Probio group than in other groups. In the hippocampus, mRNA expression of dopamine and serotonin transporters was lower in S-Probio than in S-PBS mice. Few differences in bacterial genera proportions were detected, with a lower relative abundance of Alistipes in S-Probio vs. S-PBS. CRS was accompanied by a decrease in the proportion of caecal acetate in S-PBS mice vs. NS-PBS, but not in the intervention groups. These data show that the probiotic mix could contribute to better coping with chronic stress, although the precise bacterial mechanism is still under investigation.

Efficacy and safety of Lacticaseibacillus paracasei Lpc-37® in students facing examination stress: A randomized, triple-blind, placebo-controlled clinical trial (the ChillEx study)

Lacticaseibacillus paracasei Lpc-37 (Lpc-37) has previously shown to reduce perceived stress in healthy adults. The ChillEx study investigated whether Lpc-37 reduces stress in a model of chronic examination stress in healthy students. One hundred ninety university students (18-40 y) were randomized to take 1.56 × 1010 colony-forming units of Lpc-37 or placebo (1:1) each day for 10 weeks, in a triple-blind, parallel, multicenter clinical trial consisting of six visits: two screening visits, a baseline visit, and visits at 4, 8, and 10 weeks after baseline. The primary objective was to demonstrate that Lpc-37 reduces stress, as measured by the change in state anxiety from baseline to just before the first examination, after 8 weeks using the State Trait Anxiety Inventory (STAI-state). Secondary objectives aimed to demonstrate that Lpc-37 modulates psychological stress-induced symptoms and biomarkers related to mood and sleep. An exploratory analysis of fecal microbiota composition was also conducted. There was no difference between Lpc-37 and placebo groups in the change of STAI-state score (estimate 1.03; 95% confidence interval [CI]: -1.62, 3.67; p = 0.446). None of the secondary outcomes resulted in significant results when corrected for multiplicity, but exploratory results were notable. Results showed an improvement in sleep-disturbance scores (odds ratio 0.30; 95% CI: 0.11, 0.82; p = 0.020) and reduction in duration of sleep (odds ratio 3.52; 95% CI: 1.46, 8.54; p = 0.005) on the Pittsburgh Sleep Quality Index questionnaire after 8 weeks in the Lpc-37 group compared to placebo. A reduction in Bond Lader VAS-alertness was also demonstrated in the Lpc-37 group compared to placebo (estimate -3.97; 95% CI: -7.78, -0.15; p = 0.042) just prior to the examination. Analysis of fecal microbiota found no differences between study groups for alpha and beta diversity or microbiota abundance. Adverse events were similar between groups. Vital signs, safety-related laboratory measures, and gastrointestinal parameters were stable during the trial. In conclusion, probiotic Lpc-37 was safe but had no effect on stress, mood, or anxiety in healthy university students in this model of chronic academic stress. ClinicalTrials.gov: NCT04125810.

Lactobacillus salivarius and Lactobacillus gasseri supplementation reduces stress-induced sugar craving in mice

OBJECTIVE

Increased intake of sweets or sugar craving may occur in response to chronic stress representing a risk factor for development of eating disorders and obesity. However, no safe treatment of stress-induced sugar craving is available. In this study we analysed effects of two Lactobacillus strains on food and sucrose intake in mice before and during their exposure to a chronic mild stress (CMS).

RESEARCH METHODS & PROCEDURES

C57Bl6 mice were gavaged daily for 27 days with a mix of L. salivarius (LS) LS7892 and L. gasseri (LG) LG6410 strains or with 0.9% NaCl as a control. Following 10 days of gavage, mice were individually placed into the Modular Phenotypic cages, and after 7 days of acclimation were exposed to a CMS model for 10 days. Food, water and 2% sucrose intakes as well as meal pattern were monitored. Anxiety and depressive-like behaviour were analysed by standard tests.

RESULTS

Exposure of mice to CMS was accompanied by increased size of sucrose intake in the control group likely reflecting the stress-induced sugar craving. A consistent, about 20% lower total sucrose intake, was observed in the Lactobacilli-treated group during stress which was mainly due to a reduced number of intakes. Lactobacilli treatment also modified the meal pattern before and during the CMS, showing a decrease of meal number and an increase of meal size with a tendency of reduced total daily food intake. Mild anti-depressive behavioural effects of the Lactobacilli mix were also present.

CONCLUSION

Supplementation of mice with LS LS7892 and LG LG6410 decreases sugar consumption suggesting a potential utility of these strains against stress-induced sugar craving.

Probiotics as functional foods: How probiotics can alleviate the symptoms of neurological disabilities

Neurological disorders are diseases of the central nervous system with progressive loss of nervous tissue. One of the most difficult problems associated with neurological disorders is that there is no clear treatment for these diseases. In this review, the physiopathology of some neurodegenerative diseases, etiological causes, drugs used and their side effects, and finally the role of probiotics in controlling the symptoms of these neurodegenerative diseases are presented. Recently, researchers have focused more on the microbiome and the gut-brain axis, which may play a critical role in maintaining brain health. Probiotics are among the most important bacteria that have positive effects on the balance of homeostasis via influencing the microbiome. Other important functions of probiotics in alleviating symptoms of neurological disorders include anti-inflammatory properties, short-chain fatty acid production, and the production of various neurotransmitters. The effects of probiotics on the control of abnormalities seen in neurological disorders led to probiotics being referred to as "psychobiotic. Given the important role of the gut-brain axis and the imbalance of the gut microbiome in the etiology and symptoms of neurological disorders, probiotics could be considered safe agents that positively affect the balance of the microbiome as complementary treatment options for neurological disorders.

Restorative effects of probiotics on memory impairment in sleep-deprived mice

BACKGROUND

Insufficient sleep is a serious public health epidemic in modern society, impairing memory and other cognitive functions. In this study, partial sleep deprivation (SD) was used to induce cognitive impairment in mice to determine the effects of probiotics on subsequent cognitive deficits.

METHODS

Lactiplantibacillus plantarum Lp-115 (Lp-115), Lacticaseibacillus paracasei Lpc-37 (Lpc-37), Bifidobacterium animalis subsp. lactis 420 (B420) and their combination were administered to mice subjected to partial SD and compared with non-SD and SD vehicle groups. Mice were administered a daily oral gavage containing either 1 × 10⁹ colony forming units (CFU) of single-strain, 1.5 × 10⁹ CFU of multi-strain (5 × 10⁸ CFU/strain), or vehicle for thirty days prior to and for nine days during a behavioural test paradigm. The novel object recognition (NOR) test, spontaneous alternation Y-maze (Y-maze), and the step-through passive avoidance (STPA) task were applied to evaluate learning and memory performance following partial SD.

RESULTS

Partial SD had a significant impact on cognitive function in vehicle mice. Intervention with Lpc-37 significantly improved recognition memory deficits in the NOR test, spatial working memory deficits in the Y-maze, and contextual long-term memory impairments in the STPA task, in mice subjected to partial SD compared to the SD vehicle group. The multi-strain significantly improved recognition memory deficits in the NOR test and spatial working memory deficits in the Y-maze in mice subjected to partial SD compared to the SD vehicle group.

CONCLUSIONS

These findings demonstrate that Lpc-37 and the multi-strain may play a role in alleviating memory impairments and improve cognitive function in partially sleep-deprived mice.

The microbiota-gut-brain axis in pathogenesis of depression: A narrative review

The microbiota-gut-brain axis is a bidirectional regulatory pathway between the brain and the gastrointestinal tract, which plays an important role in maintain homeostasis. Gut microbiota could influence the behavior, cognition, stress response and others via the axis. Depression is a complex psychiatric disease, giving rise to heavy social health and economic burden. In recent years, studies have shown that the gut microbiota are closely linked to the pathophysiological processes of depression. In this article, the interaction and its underlying mechanisms between depression and gut microbiota were summarized.

Silent information regulator 1 mediates H 2 S-inhibited chronic restraint stress-induced depressive-like behaviors by regulating hippocampal autophagy

OBJECTIVES

Our previous study has demonstrated that hydrogen sulfide (H 2 S), a novel gasotransmitter, attenuates excessive autophagy and depressive-like behaviors in chronic restraint stress (CRS)-exposed rats, but the underlying molecular mechanism remains to be elucidated. Silent information regulator 1 (SIRT1), a deacetylase at the consumption of NAD+ plays an important regulatory role in depression. Hence, this study aimed to investigate whether SIRT1 mediates the protective effect of H 2 S on CRS-induced depressive-like behaviors by regulating hippocampal autophagy.

METHODS

Adult male Sprague-Dawley (SD) rats were subjected to CRS (6 h × 28 days) to induce depression-like behavior. Rats were injected with sodium hydrosulfate (NaHS, 100 μmol/kg/d, i.p.), as a donor of H 2 S, alone or in combination with Sirtinol (a SIRT1 inhibitor; 10 nmol, i.c.v.) during CRS process. The depression-like characteristics of rats were assessed by the novelty-suppressed feeding test (NSFT), tail suspension test (TST), forced swimming test (FST) and open field test (OFT). The number of hippocampal autophagosomes was detected by transmission electron microscopy. The expressions of hippocampal autophagy-related proteins were measured by western blotting analysis.

RESULTS

Sirtinol blocked the inhibitory effect of H 2 S on depressive-like behaviors in CRS-exposed rats according to NSFT, TST, FST and OFT. In addition, sirtinol reversed the protective response of H 2 S to CRS-induced excessive autophagy, as proved by the increases in the number of autophagosomes and the expression of Beclin-1 as well as a decrease in the expression of P62 in the hippocampus.

CONCLUSION

These results indicated that SIRT1 contributes to the antidepressant-like function of H 2 S during CRS via reducing hippocampal autophagy.

Psychobiotic Lactobacillus plantarum JYLP-326 relieves anxiety, depression, and insomnia symptoms in test anxious college via modulating the gut microbiota and its metabolism

Introduction

Test anxiety is a common issue among college students, which can affect their physical and psychological health. However, effective interventions or therapeutic strategies are still lacking. This study aims to evaluate the potential effects of Lactobacillus plantarum JYLP-326 on test anxious college students.

Methods

Sixty anxious students were enrolled and randomly allocated to the placebo group and the probiotic group. Both groups were instructed to take placebo and JYLP-326 products twice per day for three weeks, respectively. Thirty unanxious students with no treatments were assigned to a regular control group. The anxiety, depression, and insomnia questionnaires were used to measure students' mental states at the baseline and the end of this study. 16S rRNA sequencing and untargeted metabolomics were performed to analyze the changes in the gut microbiota and fecal metabolism.

Results

The questionnaire results suggested that JYLP-326 administration could relieve the symptoms of anxiety, depression, and insomnia in test anxious students. The gut microbiomes of the placebo group showed a significantly greater diversity index than the control group (p < 0.05). An increased abundance of Bacteroides and Roseburia at the genus level was observed in the placebo group, and the relative abundance of Prevotella and Bifidobacterium decreased. Whereas, JYLP-326 administration could partly restore the disturbed gut microbiota. Additionally, test anxiety was correlated with disordered fecal metabolomics such as a higher Ethyl sulfate and a lower Cyclohexylamine, which could be reversed after taking JYLP-326. Furthermore, the changed microbiota and fecal metabolites were significantly associated with anxiety-related symptoms.

Conclusion

The results indicate that the intervention of L. plantarum JYLP-326 could be an effective strategy to alleviate anxiety, depression, and insomnia in test anxious college students. The potential mechanism underlying this effect could be related to the regulation of gut microbiota and fecal metabolites.

Antidepressant and Anxiolytic Effects of Fermented Huauzontle, a Prehispanic Mexican Pseudocereal

This study aimed to assess the potential antidepressant- and anxiolytic-like effects of huauzontle fermented by Lactiplantibacillus plantarum Lp22. The possible association between oxidative stress/inflammation biomarkers and unconditional behavioural tests was also evaluated. Red light-induced stress mice C57Bl/6 (n = 5 per group) received orally either fermented or unfermented huauzontle, diazepam or fluoxetine. A non-stressed group which received saline solution was also included. Then, anxiety-related and depression-related behaviour tests were performed; after that, blood and tissues samples were collected to determine oxidative stress/inflammation biomarkers. The mice receiving both fermented and unfermented huauzontle spent more time (94 s) in open arms in the elevated plus maze test p < 0.05; besides, travelled longer distance (p < 0.05) and increased by more than 50% the exploration time for the open field, as well as the time spent in the illuminated zone (197 s) in the light/dark test. Furthermore, reduced immobility time in the tail suspension and forced swim tests (23.1 and 15.85, respectively), and anhedonia was no detected in the sucrose preference test. The oxidative stress index was lower in the liver of fermented huauzontle-treated mice, while enhanced levels of IL-10, MCP-1 and BDNF in plasma, and lipoxygenase (LOX) activity in the hippocampus were found. Finally, PCA revealed a positive correlation among LOX and BDNF and parameters determined in the anxiety tests, as between catalase activity and immobility time in the depression test. These findings indicate the novel potential therapeutic applications of fermented huauzontle on depression and anxiety-like behaviours possibly mediated by antioxidant and anti-inflammatory mechanisms.

Viability droplet digital polymerase chain reaction accurately enumerates probiotics and provides insight into damage experienced during storage

Probiotics are typically enumerated by agar plate counting (PC) techniques. PC has several limitations including poor specificity, high variability, inability to enumerate dead cells, viable but non-culturable cells and cells in complex matrices. Viability droplet digital polymerase chain reaction (v-ddPCR) is an emerging enumeration technique with improved specificity, precision, and the ability to enumerate cells in varying states of culturability or in complex matrices. Good correlation and agreement between v-ddPCR and PC is well documented, but not much research has been published on the comparison when enumerating freeze-dried (FD) probiotics during storage. In this study, v-ddPCR utilizing PE51 (PE51-ddPCR), a combination of propidium monoazide (PMA) and ethidium monoazide (EMA), was evaluated as alternative enumeration technique to PC on blends of four FD probiotic strains over the course of a 3-month storage study with accelerated conditions. When PMA and EMA are combined (PE51), this study demonstrates agreement (bias = 7.63e+9, LOA = 4.38e+10 to 5.9e+10) and association (r = 0.762) between PC and v-ddPCR, at or above levels of an accepted alternative method. Additionally, v-ddPCR with individual dyes PMA and EMA provide insight into how they individually contribute to the viable counts obtained by PE51-ddPCR and provide a more specific physiological understanding of how probiotics cope with or experience damage during storage.

Beneficial effects of Lactococcus lactis subsp. cremoris LL95 treatment in an LPS-induced depression-like model in mice

Clinical evidence suggests that neuroinflammation, activation of the immune system, and the composition of the intestinal microbiota are involved in the pathology of depression. This study evaluated the effectiveness of a probiotic intervention using Lactococcus lactis subsp. cremoris LL95 in ameliorating mood disorders in a lipopolysaccharide (LPS)-induced depression-like mouse model. C57BL/6 mice were randomly divided into four groups and treated with 5 mg/kg LPS via intraperitoneal injection to induce depression-like symptoms, followed by oral administration of LL95 for one week (1 × 109 CFU/mouse). The animals were then subjected to a series of behavioral assessments, including open field, sucrose preference, and forced swimming tests. In addition, we evaluated the levels of reactive oxygen species, tumor necrosis factor-α, and interleukin-1β in the hippocampal tissues of these animals, and also determined their fecal lactic acid bacteria (LAB) content. LL95 intervention improved LPS-induced depression-like behaviors in mice, including decreased sucrose preference and increased immobility time in the forced swim test. LL95 treatment reversed the LPS-induced increase in hippocampal levels of reactive oxygen species and tumor necrosis factor-α, and of interleukin-1β to a lesser extent. Furthermore, LL95 intervention increased the fecal LAB content in these animals, suggesting changes in the gut microbiota. These findings suggest that LL95 exerts antidepressant-like effects in LPS-induced depression, which may be attributed to modulation of the oxidative status and pro-inflammatory cytokine expression in the hippocampus and alteration in the LAB content of the gut microbiota.

Stressful events induce long-term gut microbiota dysbiosis and associated post-traumatic stress symptoms in healthcare workers fighting against COVID-19

OBJECTIVE

The microbiota-gut-brain axis is a key pathway perturbed by prolonged stressors to produce brain and behavioral disorders. Frontline healthcare workers (FHWs) fighting against COVID-19 typically experience stressful event sequences and manifest some mental symptoms; however, the role of gut microbiota in such stress-induced mental problems remains unclear. We investigated the association between the psychological stress of FHW and gut microbiota.

METHODS

We used full-length 16S rRNA gene sequencing to characterize the longitudinal changes in gut microbiota and investigated the impact of microbial changes on FHWs' mental status.

RESULTS

Stressful events induced significant depression, anxiety, and stress in FHWs and disrupted the gut microbiome; gut dysbiosis persisted for at least half a year. Different microbes followed discrete trajectories during the half-year of follow-up. Microbes associated with mental health were mainly Faecalibacterium spp. and [Eubacterium] eligens group spp. with anti-inflammatory effects. Of note, the prediction model indicated that low abundance of [Eubacterium] hallii group uncultured bacterium and high abundance of Bacteroides eggerthii at Day 0 (immediately after the two-month frontline work) were significant determinants of the reappearance of post-traumatic stress symptoms in FHWs.

LIMITATIONS

The lack of metabolomic evidence and animal experiments result in the unclear mechanism of gut dysbiosis-related stress symptoms.

CONCLUSION

The stressful event sequences of fighting against COVID-19 induce characteristic longitudinal changes in gut microbiota, which underlies dynamic mental state changes.

Probiotic effects on anxiety-like behavior in animal models

Gut microbiota have been shown to be useful in treating gastrointestinal diseases, cancer, obesity, infections, and, more recently, neuropsychiatric conditions such as degenerative diseases and depression. There has also been recent expansion in testing probiotics and prebiotics on anxiety-like behaviors in animals. Current results indicate that probiotic substances of the Lactobacillus and Bifidobacterium type are effective in reducing anxiety-like behaviors in mice or rats evaluated in the elevated plus-maze, the open-field, the light-dark box, and conditioned defensive burying. Probiotics are also effective in reducing serum or plasma corticosterone levels after acute stress. It is hypothesized that probiotics cause anxiolytic-like effects via vagal influences on caudal solitary nucleus, periaqueductal gray, central nucleus of the amygdala, and bed nucleus of the stria terminalis. Further experimentation is needed to trace the neurochemical anatomy underlying anxiolytic-like behaviors of gut microbiata exerting effects via vagal or nonvagal pathways.

The Effects of Stress and Diet on the "Brain-Gut" and "Gut-Brain" Pathways in Animal Models of Stress and Depression

Compelling evidence is building for the involvement of the complex, bidirectional communication axis between the gastrointestinal tract and the brain in neuropsychiatric disorders such as depression. With depression projected to be the number one health concern by 2030 and its pathophysiology yet to be fully elucidated, a comprehensive understanding of the interactions between environmental factors, such as stress and diet, with the neurobiology of depression is needed. In this review, the latest research on the effects of stress on the bidirectional connections between the brain and the gut across the most widely used animal models of stress and depression is summarised, followed by comparisons of the diversity and composition of the gut microbiota across animal models of stress and depression with possible implications for the gut–brain axis and the impact of dietary changes on these. The composition of the gut microbiota was consistently altered across the animal models investigated, although differences between each of the studies and models existed. Chronic stressors appeared to have negative effects on both brain and gut health, while supplementation with prebiotics and/or probiotics show promise in alleviating depression pathophysiology.

One Giant Leap from Mouse to Man: The Microbiota-Gut-Brain Axis in Mood Disorders and Translational Challenges Moving towards Human Clinical Trials

The microbiota–gut–brain axis is a bidirectional communication pathway that enables the gut microbiota to communicate with the brain through direct and indirect signaling pathways to influence brain physiology, function, and even behavior. Research has shown that probiotics can improve several aspects of health by changing the environment within the gut, and several lines of evidence now indicate a beneficial effect of probiotics on mental and brain health. Such evidence has prompted the arrival of a new term to the world of biotics research: psychobiotics, defined as any exogenous influence whose effect on mental health is bacterially mediated. Several taxonomic changes in the gut microbiota have been reported in neurodevelopmental disorders, mood disorders such as anxiety and depression, and neurodegenerative disorders such as Alzheimer’s disease. While clinical evidence supporting the role of the gut microbiota in mental and brain health, and indeed demonstrating the beneficial effects of probiotics is rapidly accumulating, most of the evidence to date has emerged from preclinical studies employing different animal models. The purpose of this review is to focus on the role of probiotics and the microbiota–gut–brain axis in relation to mood disorders and to review the current translational challenges from preclinical to clinical research.

How Microbes Affect Depression: Underlying Mechanisms via the Gut-Brain Axis and the Modulating Role of Probiotics

Accumulating evidence suggests that the gut microbiome influences the brain functions and psychological state of its host via the gut-brain axis, and gut dysbiosis has been linked to several mental illnesses, including major depressive disorder (MDD). Animal experiments have shown that a depletion of the gut microbiota leads to behavioral changes, and is associated with pathological changes, including abnormal stress response and impaired adult neurogenesis. Short-chain fatty acids such as butyrate are known to contribute to the up-regulation of brain-derived neurotrophic factor (BDNF), and gut dysbiosis causes decreased levels of BDNF, which could affect neuronal development and synaptic plasticity. Increased gut permeability causes an influx of gut microbial components such as lipopolysaccharides, and the resultant systemic inflammation may lead to neuroinflammation in the central nervous system. In light of the fact that gut microbial factors contribute to the initiation and exacerbation of depressive symptoms, this review summarizes the current understanding of the molecular mechanisms involved in MDD onset, and discusses the therapeutic potential of probiotics, including butyrate-producing bacteria, which can mediate the microbiota-gut-brain axis.

Microbiota-targeted interventions for mental health

PURPOSE OF REVIEW

The gut microbiota has emerged as a key conduit in mental health and is a promising target for interventions. This review provides an update on recent advances in using microbiota-targeted approaches for the management of mental health.

RECENT FINDINGS

Approaches that have emerged as microbiota-targeted interventions in the management of mental health include probiotics, prebiotics, synbiotics, fecal microbiota transplant as well as diet. Among these approaches, probiotic supplementation has been investigated most prominently, providing promising evidence for its use in improving mood and anxiety. There is also growing interest in the use of multistrain probiotics, whole dietary interventions or combined approaches, with encouraging results emerging from recent studies.

SUMMARY

Although the current literature preliminarily supports targeting the microbiota to manage mental health and use as adjuvant therapies for certain brain disorders, large gaps remain and especially data including clinical cohorts remains scarce. Research studies including larger cohorts, well-characterized clinical populations and defined duration and dosage of the intervention are required to develop evidence-based guidelines for microbiota-targeted strategies.

Transcriptomics reveal different metabolic strategies for acid resistance and gamma-aminobutyric acid (GABA) production in select Levilactobacillus brevis strains

BACKGROUND

Of the many neurotransmitters in humans, gamma-aminobutyric acid (GABA) shows potential for improving several mental health indications such as stress and anxiety. The microbiota-gut-brain axis is an important pathway for GABAergic effects, as microbially-secreted GABA within the gut can affect host mental health outcomes. Understanding the molecular characteristics of GABA production by microbes within the gut can offer insight to novel therapies for mental health.

RESULTS

Three strains of Levilactobacillus brevis with syntenous glutamate decarboxylase (GAD) operons were evaluated for overall growth, glutamate utilization, and GABA production in typical synthetic growth media supplemented with monosodium glutamate (MSG). Levilactobacillus brevis Lbr-6108™ (Lbr-6108), formerly known as L. brevis DPC 6108, and Levilactobacillus brevis Lbr-35 ™ (Lbr-35) had similar growth profiles but differed significantly in GABA secretion and acid resistance. Lbr-6108 produced GABA early within the growth phase and produced significantly more GABA than Lbr-35 and the type strain Levilactobacillus brevis ATCC 14869 after the stationary phase. The global gene expression during GABA production at several timepoints was determined by RNA sequencing. The GAD operon, responsible for GABA production and secretion, activated in Lbr-6108 after only 6 h of fermentation and continued throughout the stationary phase. Furthermore, Lbr-6108 activated many different acid resistance mechanisms concurrently, which contribute to acid tolerance and energy production. In contrast, Lbr-35, which has a genetically similar GAD operon, including two copies of the GAD gene, showed no upregulation of the GAD operon, even when cultured with MSG.

CONCLUSIONS

This study is the first to evaluate whole transcriptome changes in Levilactobacillus brevis during GABA production in different growth phases. The concurrent expression of multiple acid-resistance mechanisms reveals niche-specific metabolic functionality between common human commensals and highlights the complex regulation of GABA metabolism in this important microbial species. Furthermore, the increased and rapid GABA production of Lbr-6108 highlights the strain's potential as a therapeutic and the overall value of screening microbes for effector molecule output.

Effect of Multi-strain Probiotic Formulation on Students Facing Examination Stress: a Double-Blind, Placebo-Controlled Study

In this placebo-controlled, double-blind clinical trial, we have investigated the effect of multi-strain probiotic (Bacillus coagulans Unique IS2, Lactobacillus rhamnosus UBLR58, Bifidobacterium lactis UBBLa70, Lactobacillus plantarum UBLP40 (each of 2 billion CFU); Bifidobacterium breve UBBr01, Bifidobacterium infantis UBBI01 (each of 1 billion CFU)) capsule with glutamine (250 mg) on students facing examination stress. A total of 80 students (18-24 years) were enrolled and randomised to receive multi-strain probiotic or placebo capsules twice a day for 28 days (i.e. pre- and during examination). The stress was analysed at the baseline and the end of the treatment by using the perceived stress scale (PSS), depression anxiety stress scale (DASS), and state-trait anxiety inventory (STAI) questionnaire. The serum cortisol levels were also determined. As a result, at the end of the trial, a total of 74 students completed the study, and those who consumed probiotic capsules showed a significant reduction in PSS, DASS, and STAI scores, and serum cortisol levels from the baseline as compared with placebo. No adverse events were reported during the study. In conclusion, the multi-strain probiotic is effective in reducing stress associated with examination. CTRI/2019/03/018178.

Lactobacillus-Based Probiotics Reduce the Adverse Effects of Stress in Rodents: A Meta-analysis

Lactobacillus species play a critical role in the bidirectional communication between the gut and the brain. Consequently, they have the potential to aid in the treatment of psychological disorders. The impact of Lactobacillus supplementation on the stress responses triggering psychological disorders has not been systematically reviewed. Therefore, the aim of this meta-analysis is to summarize the body of research assessing the effects of Lactobacillus-based probiotics in rodents that underwent an experimental stress treatment or not. The duration of immobility in a Forced Swim Test (FST) was the outcome used to measure changes induced by various treatments. Four online databases were systematically searched for relevant studies published in English. Fourteen studies meeting the criteria were included in the meta-analysis. The effects of probiotic supplementation and stress treatment on the duration of immobility in the FST were analyzed using a generalized linear mixed model. Publication bias was evaluated by funnel plots. Our analysis shows that Lactobacillus-based probiotic supplements significantly reduce immobility in the FST (P < 0.001) in stressed rodents. However, probiotics did not affect the rodents that did not undergo the stress treatment (P = 0.168). These findings provide a better understanding of the potential of Lactobacillus-based probiotics for the management of stress-induced behavior.

Immune-Enhancing Effects of Lactobacillus plantarum 200655 Isolated from Korean Kimchi in a Cyclophosphamide-Induced Immunocompromised Mouse Model

In this study, we evaluated the immune-enhancing activity of kimchi-derived Lactobacillus plantarum 200655 on immune suppression by cyclophosphamide (CP) in ICR mice. Animals were fed distilled water or 1×10⁹ colony-forming unit/kg B.W. 200655 or Lactobacillus rhamnosus GG as a positive control for 14 days. An in vivo model of immunosuppression was induced using CP 150 and 100 mg/kg B.W. at 7 and 10 days, respectively. Body weight, spleen index, spleen weight, and gene expression were measured to estimate the immune-enhancing effects. The dead 200655 (D-200655) group showed an increased spleen weight compared to the sham control (SC) group. Similarly, the spleen index was significantly higher than that in the CP-treated group. The live 200655 (L-200655) group showed an increased mRNA expression of tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6 in splenocytes. Also, the iNOS and COX-2 mRNA expression was upregulated in the L-200655 group compared to the CP-only (SC) group. The phosphorylation of ERK and MAPK was also upmodulated in the L-200655 group. These results indicate that L. plantarum 200655 ameliorated CP-induced immune suppression, suggesting that L. plantarum 200655 may have the potential to enhance the immune system.

The Putative Antidepressant Mechanisms of Probiotic Bacteria: Relevant Genes and Proteins

Probiotic bacteria are widely accepted as therapeutic agents against inflammatory bowel diseases for their immunostimulating effects. In the last decade, more evidence has emerged supporting the positive effects of probiotics on the course of neurodegenerative and psychiatric diseases. This brief review summarizes the data from clinical studies of probiotics possessing antidepressant properties and focuses on the potential genes and proteins underlying these mechanisms. Data from small-sample placebo-controlled pilot studies indicate that certain strains of bacteria can significantly reduce the symptoms of depression, especially in depressed patients. Despite the disparity between studies attempting to pinpoint the bacterial putative genes and proteins accounting for these mechanisms, they ultimately show that bacteria are a potential source of metabiotics—microbial metabolites or structural components. Since the constituents of cells—namely, secreted proteins, peptides and cell wall components—are most likely to be entangled in the gut–brain axis, they can serve as starting point in the search for probiotics with concrete properties.

Gut microbiota in mental health and depression: role of pre/pro/synbiotics in their modulation

The microbiome residing in the human gut performs a wide range of biological functions. Recently, it has been elucidated that a change in dietary habits is associated with alteration in the gut microflora which results in increased health risks and vulnerability towards various diseases. Falling in line with the same concept, depression has also been shown to increase its prevalence around the globe, especially in the western world. Various research studies have suggested that changes in the gut microbiome profile further result in decreased tolerance of stress. Although currently available medications help in relieving the symptoms of depressive disorders briefly, these drugs are not able to completely reverse the multifactorial pathology of depression. The discovery of the communication pathway between gut microbes and the brain, i.e. the Gut-Brain Axis, has led to new areas of research to find more effective and safer alternatives to current antidepressants. The use of probiotics and prebiotics has been suggested as being effective in various preclinical studies and clinical trials for depression. Therefore, in the present review, we address the new antidepressant mechanisms via gut microbe alterations and provide insight into how these can provide an alternative to antidepressant therapy without the side effects and risk of adverse drug reactions.

Probiotics as a Treatment for "Metabolic Depression"? A Rationale for Future Studies

Depression and metabolic diseases often coexist, having several features in common, e.g., chronic low-grade inflammation and intestinal dysbiosis. Different microbiota interventions have been proposed to be used as a treatment for these disorders. In the paper, we review the efficacy of probiotics in depressive disorders, obesity, metabolic syndrome and its liver equivalent based on the published experimental studies, clinical trials and meta-analyses. Probiotics seem to be effective in reducing depressive symptoms when administered in addition to antidepressants. Additionally, probiotics intake may ameliorate some of the clinical components of metabolic diseases. However, standardized methodology regarding probiotics use in clinical trials has not been established yet. In this narrative review, we discuss current knowledge on the recently used methodology with its strengths and limitations and propose criteria that may be implemented to create a new study of the effectiveness of probiotics in depressive disorders comorbid with metabolic abnormalities. We put across our choice on type of study population, probiotics genus, strains, dosages and formulations, intervention period, as well as primary and secondary outcome measures.

Interplay of Good Bacteria and Central Nervous System: Cognitive Aspects and Mechanistic Considerations

The human gastrointestinal tract hosts trillions of microorganisms that is called “gut microbiota.” The gut microbiota is involved in a wide variety of physiological features and functions of the body. Thus, it is not surprising that any damage to the gut microbiota is associated with disorders in different body systems. Probiotics, defined as living microorganisms with health benefits for the host, can support or restore the composition of the gut microbiota. Numerous investigations have proved a relationship between the gut microbiota with normal brain function as well as many brain diseases, in which cognitive dysfunction is a common clinical problem. On the other hand, increasing evidence suggests that the existence of a healthy gut microbiota is crucial for normal cognitive processing. In this regard, interplay of the gut microbiota and cognition has been under focus of recent researches. In the present paper, I review findings of the studies considering beneficial effects of either gut microbiota or probiotic bacteria on the brain cognitive function in the healthy and disease statuses.

A diet-microbial metabolism feedforward loop modulates intestinal stem cell renewal in the stressed gut

Dietary patterns and psychosocial factors, ubiquitous part of modern lifestyle, critically shape the gut microbiota and human health. However, it remains obscure how dietary and psychosocial inputs coordinately modulate the gut microbiota and host impact. Here, we show that dietary raffinose metabolism to fructose couples stress-induced gut microbial remodeling to intestinal stem cells (ISC) renewal and epithelial homeostasis. Chow diet (CD) and purified diet (PD) confer distinct vulnerability to gut epithelial injury, microbial alternation and ISC dysfunction in chronically restrained mice. CD preferably enriches Lactobacillus reuteri, and its colonization is sufficient to rescue stress-triggered epithelial injury. Mechanistically, dietary raffinose sustains Lactobacillus reuteri growth, which in turn metabolizes raffinose to fructose and thereby constituting a feedforward metabolic loop favoring ISC maintenance during stress. Fructose augments and engages glycolysis to fuel ISC proliferation. Our data reveal a diet-stress interplay that dictates microbial metabolism-shaped ISC turnover and is exploitable for alleviating gut disorders.

Comparing the effects of two different strains of mycobacteria, Mycobacterium vaccae NCTC 11659 and M. vaccae ATCC 15483, on stress-resilient behaviors and lipid-immune signaling in rats

Stress-related disorders, such as posttraumatic stress disorder (PTSD), are highly prevalent and often difficult to treat. In rodents, stress-related, anxiety-like defensive behavioral responses may be characterized by social avoidance, exacerbated inflammation, and altered metabolic states. We have previously shown that, in rodents, subcutaneous injections of a heat-killed preparation of the soil-derived bacterium Mycobacterium vaccae NCTC 11659 promotes stress resilience effects that are associated with immunoregulatory signaling in the periphery and the brain. In the current study, we sought to determine whether treatment with a heat-killed preparation of the closely related M. vaccae type strain, M. vaccae ATCC 15483, would also promote stress-resilience in adult male rats, likely due to biologically similar characteristics of the two strains. Here we show that immunization with either M. vaccae NCTC 11659 or M. vaccae ATCC 15483 prevents stress-induced increases in hippocampal interleukin 6 mRNA expression, consistent with previous studies showing that M. vaccae NCTC 11659 prevents stress-induced increases in peripheral IL-6 secretion, and prevents exaggeration of anxiety-like defensive behavioral responses assessed 24 h after exposure to inescapable tail shock stress (IS) in adult male rats. Analysis of mRNA expression, protein abundance, and flow cytometry data demonstrate overlapping but also unique effects of treatment with the two M. vaccae strains on immunological and metabolic signaling in the host. These data support the hypothesis that treatment with different M. vaccae strains may immunize the host against stress-induced dysregulation of physiology and behavior.

Lacticaseibacillus paracasei Lpc-37® improves psychological and physiological markers of stress and anxiety in healthy adults: a randomized, double-blind, placebo-controlled and parallel clinical trial (the Sisu study)

Chronic stress is a risk-factor for the development of mood and stress-related disorders. Clinical evidence indicates that probiotics can influence the stress response and mood. The Sisu study investigated whether Lacticaseibacillus paracasei Lpc-37® (Lpc-37®) could modulate stress, mood and well-being. Prior to a two-week run-in period, 120 healthy adults (18-45 y) were stratified for sex and chronic stress and randomized to either 1.75 × 1010 colony forming units (CFU) of Lpc-37 or placebo (1:1) per day for 5 weeks. The primary objective was the effect of Lpc-37 on heart rate (HR) in response to the Trier Social Stress Test (TSST). Secondary objectives were assessed by biomarkers and self-report scales over the study. The primary hypothesis was not met in either the Intention-to-Treat (ITT) or Per Protocol (PP) population, but Lpc-37 reduced the increase in HR in participants with low chronic stress (LCS) and increased HR in participants with high chronic stress (HCS) during the TSST. Supporting significant efficacy in the PP population (n = 113), Lpc-37 reduced perceived stress following intervention. More significant effects were identified within the subgroups where Lpc-37 reduced exhaustion during the TSST and normalized cortisol levels at 8pm in participants with LCS, reduced perceived stress also in females, and increased perceived health and sleep-related recovery in participants with HCS. Adverse events (AEs) were similar between groups, there were no severe AEs, and vital signs remained unchanged. Overall, Lpc-37 reduced perceived stress compared to placebo. Other beneficial effects within biomarkers related to stress indicate that the effects of Lpc-37 may be differentially dependent on sex and chronic stress. (ClinicalTrials.gov: NCT03494725).

Effects of a Psychobiotic Supplement on Serum Brain-derived Neurotrophic Factor Levels in Depressive Patients: A Post Hoc Analysis of a Randomized Clinical Trial

Background/Aims

Psychobiotics are probiotics or prebiotics that, upon ingestion in adequate amounts, yield positive influence on mental health via microbiota-gut-brain axis regulation to modulate the circulating cytokines, chemokines, neurotransmitters, or neurotrophins levels. We have recently shown that a psychobiotic combination (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175; CEREBIOME) significantly improved depression symptoms in patients with depression. Recent animal data suggest the influence of the gut microbiota on brain-derived neurotrophic factor (BDNF), which was shown to correlate with antidepressant response in depressive patients. Therefore, we conducted this exploratory post hoc analysis of BDNF levels to clarify the mechanism of action of this psychobiotic in our cohort.

Methods

Our study was a double-blind, randomized controlled trial of patients with low-to-moderate depression receiving either a probiotic combination, prebiotic or placebo. From the 110 patients randomized in the trial, 78 were included in this post hoc analysis (probiotic, n = 28; prebiotic and placebo, n = 25). We compared serum BDNF levels from participants at baseline and endpoint, and assessed the Pearson correlation between depression severity and BDNF levels for each intervention.

Results

We found that post-intervention BDNF levels were significantly different between groups (P < 0.001). Furthermore, BDNF levels increased significantly in the probiotic group compared to both the prebiotic (P < 0.001) and placebo groups (P = 0.021), which inversely correlated with depression severity compared to placebo (ANOVA/ANCOVA, P = 0.012; Pearson, r = -0.79, P < 0.001). In the prebiotic group, BDNF levels reduced but not significantly compared with placebo group (P > 0.05).

Conclusion

Eight-week supplementation with B. longum and L. helveticus in depressive patients improved depression symptoms, possibly by increasing BDNF levels.

GABAergic System in Stress: Implications of GABAergic Neuron Subpopulations and the Gut-Vagus-Brain Pathway

Stress can cause a variety of central nervous system disorders, which are critically mediated by the γ-aminobutyric acid (GABA) system in various brain structures. GABAergic neurons have different subsets, some of which coexpress certain neuropeptides that can be found in the digestive system. Accumulating evidence demonstrates that the gut-brain axis, which is primarily regulated by the vagus nerve, is involved in stress, suggesting a communication between the "gut-vagus-brain" pathway and the GABAergic neuronal system. Here, we first summarize the evidence that the GABAergic system plays an essential role in stress responses. In addition, we review the effects of stress on different brain regions and GABAergic neuron subpopulations, including somatostatin, parvalbumin, ionotropic serotonin receptor 5-HT3a, cholecystokinin, neuropeptide Y, and vasoactive intestinal peptide, with regard to signaling events, behavioral changes, and pathobiology of neuropsychiatric diseases. Finally, we discuss the gut-brain bidirectional communications and the connection of the GABAergic system and the gut-vagus-brain pathway.