Psychobiotics and Microbial Therapies for Mental Health

Researchers examined the use of psychobiotics to treat depression by microbially balancing the microbiome, gut, and brain (MGB) axis and restoring microbiological equilibrium in a recent review published in the journal Nutrients.

Suicide risk is elevated, pain is experienced, productivity is lost, and healthcare costs are increased due to depression, a worldwide health concern. The gut-brain axis (GBA) can be impacted by dysbiosis, a disturbance in the equilibrium of the gut microbiome, which can lead to microbial changes. Psychobiotics may be utilized as a supportive treatment for depression, especially in cases of treatment-recalcitrant depression (TRD), as they have positive effects on the gastrointestinal barrier, immunological responses, cortisol expression, and the hypothalamic-pituitary-adrenal (HPA) axis.

Concerning the review

Through their impact on the gut-brain connection, the researchers in this review provided clinical data and clarified the underlying processes of psychobiotic therapy for depression.

Relationship between depression disorders and the gut-brain axis

A multitude of molecular mechanisms, including a reduction in neurotransmitters, a drop in brain-derived neurotrophic factor (BDNF), an abnormally stressed HPA axis, an increase in pro-inflammatory gut microbial responses, and vagus nerve interaction between the gut microbiota and brain, influence depression, a complex biological disorder. Intestinal bacteria and GBA are closely related, as MGB affects neurobehavioral outcomes through immunological, neuronal, and endocrine processes. An alteration in the intestinal microbiome due to dysbiosis, or a disruption in the GBA axis, can impact immunology, gut inflammation, and neuronal function.

Prolonged stress disrupts intestinal balance and modifies the makeup of gut microbes, with an increase in Faecalibaculum and Clostridium and a decrease in Lactobacillus and Bifidobacterium in people. Recent animal studies have linked the gut-brain axis and stress sensitivity and resilience. Psychiatric disorders like major depressive disorder, bipolar disorder, psychosis, schizophrenia, anorexia nervosa, anxiety disorders, obsessive-compulsive disorder, post-traumatic stress disorder, and attention deficit hyperactivity disorder (ADHD) are linked to the gut microbiome, which also affects inflammatory reactions and brain states. 

Metabolites produced by gut microbes that have antidepressant effects

The gut microbiome is an essential source of metabolites that promote communication between the gut and the central nervous system. Tryptophan, serotonin, histamine, 5-hydroxytryptamine (5-HT), short-chain fatty acids (SCFAs), acetylcholine, and dopamine (DA) are the components of these metabolites. Microbial metabolites affect several processes critical to mental health, including the development of the immune and neuroendocrine systems, control of nutrition metabolism, and xenobiotic transformation. Additionally, they support the integrity of the intestinal mucosa, preserve the integrity of the gut barrier, and prevent the spread of toxins and harmful infections. SCFAs act on G-protein-coupled receptors in the host’s brain to influence emotional and cognitive states. They preserve the intestinal barrier, control inflammatory reactions, control hunger hormones, and provide energy to colonocytes.

Increasing the amount of SCFAs can improve brain adaptability by reducing neuroinflammation and increasing BDNF production.

Probiotic gut bacteria’ effect on depression

Probiotic bacteria known as “psychobiotics” improve the intestinal barrier and alter the immune response in the gut-associated lymphoid tissue (GALT), which contributes to the development of inflammation. Because it controls inflammatory processes, the gut microbiota plays a critical role in the pathophysiology of depression. Increased BDNF, decreased TNF-alpha (TNF-α) and interleukin-6 (IL-60) levels, and improved cognitive function are all brought about by Bifidobacterium breve.

Tight junction (TJ) expression is increased, neuroinflammation is decreased, and kynurenine levels are lowered by lactic acid bacteria (LAB). Lactobacillus plantarum 299v reduces kynurenine levels and improves cognitive function by increasing dopamine levels and supporting selective serotonin reuptake inhibitor (SSRI) therapy. By inhibiting inflammatory cytokines in microglial cells, Akkermansia muciniphila reduces depressive-like behavior. 

Clinical data demonstrating the psychobiotic qualities of certain bacterial strains

Postbiotics like Bifidobacterium longum 1714 and Bacillus coagulans MTCC 5856 can aid with depression and symptoms of irritable bowel syndrome (IBS). Probiotics that improve cognition and reduce stress include Bifidobacterium longum 1714 and NCC 3001. TRD can be successfully treated with these probiotics in conjunction with antidepressants. Probiotics that improve overall health and reduce mood problems include Lactobacillus casei Shirota and Lactobacillus gasseri CP2305, both of which have 2.5 × 109 CFU/g. Additionally, taking a multi-strain probiotic supplement improves overall health, lessens feelings of anxiety, and lowers inflammation. A fermented black soybean beverage made with Lactobacillus gasseri improves sleep quality and reduces stress in healthy persons. For those with Alzheimer’s disease and mild cognitive impairment, probiotic milk beverages and fermented soybean seed paste enhance cognitive function.

The review emphasizes the significance of probiotics for mental health and their role in reducing depressed symptoms. The gut microbiota has a critical role in food absorption, digestion, and mental health issues like anxiety and stress management. As the focus of medical attention has shifted from infectious diseases to more prevalent mental health conditions like depression, probiotics and healthy eating practices are essential for mental health.

For more information: The Power of Psychobiotics in Depression: A Modern Approach through the Microbiota–Gut–Brain Axis: A Literature Review, Nutrients, https://doi.org/10.3390/nu16071054