Effects of 3-month Probiotic Mix Supplementation (L. Helveticus R-0052, B. Longum R-0175) on Gut Microbiota and Metabolome, Endocannabinoid and Immune Systems Activation, Along With Symptoms of Fatigue in Professional Dancers

Professional dancers are often referred to as artistic athletes due to their high level of physical activity and competition. Training dance for over 11.5 hours a week increases the risk of injury (women - mostly bone injuries, men - mostly bruises and tendon injuries). One of the reasons for the increased susceptibility to injuries among dancers is psychological stress. The observations results indicate that dancers often decide to continue training despite feeling pain, which limits the smoothness of their movements and leads to a further increase of stress. Highly physically active groups of people are more exposed to functional dyspepsia (FD) and irritable bowel syndrome (IBS), which occurence is correlated to chronic stress. As a result of chronic stress and the activation of the hypothalamic pituitary-adrenal axis (HPA), inflammatory processes in the gastrointestinal mucosa are initiated. The presence of noradrenaline increases the adhesion of bacteria and viruses to the epithelium, which in turn modulates the immune system within the intestines and increases their inflammation. Systemically acting cortisol causes the leakage of tight junctions (TJ) cells and an increase in the permeability of the intestinal barrier. Inflammation stimulates the secretion of cortisol, which initiates the further cycle of inflammation and weakening of the intestinal barrier function. As a consequence, cytokines and inflammatory mediators released in the course of inflammation act directly on the nerve endings that transmit these afferent nerve signals to the brain, becoming an endogenous stressor.

When exogenous and endogenous stress factors overlap, the body's perception of stress increases, which ultimately leads to psychological, physiological and behavioral changes.

Pain and depression are common comorbidities of neuropsychiatric origin. One of the body's regulatory systems, which in both cases is dysfunctional, is the endocannabinoid system (ECS). It has been suggested that these diseases can be caused by intense and prolonged exercise, which disrupts the intestinal barrier, causing changes in the profile of metabolites and the function of the intestinal microbiota. Overtraining leads to an increase in the levels of cortisol, adrenaline and noradrenaline, and to the translocation of lipopolysaccharide (LPS) outside the gut, increasing the concentration of pro-inflammatory cytokines in the body. This results in dysregulation of the balance between serotonin (5-HT), dopamine (DA) and gamma-aminobutyric acid (GABA) and fatigue. These changes lead to further activation of the endocannabinoid system and, in the long-term, weakening of adaptive abilities.

The neuromodulatory properties of the cannabinoid system are manifested e.g. in short- and long-term synaptic plasticity and modulation of pain conduction. Research results indicate that the endocannabinoid system, in addition to its key role in regulating intestinal motility, also affects the secretory functions of the gastrointestinal tract and the integrity of the intestinal epithelium, which may be an alternative way to regulate the immune system and inflammation in the intestines.

Type 1 cannabinoid receptors (CB1) are located presynaptically in the cell membrane of central and peripheral nervous system neurons, and their activation inhibits the release of many neurotransmitters, i.e. acetylcholine, noradrenaline, dopamine, serotonin, glutamate and γ-aminobutyric acid. Type 2 cannabinoid receptors (CB2) are found mainly on the surface of cells of the immune system, especially B-lymphocytes, macrophages and monocytes. Their activation inhibits pro-inflammatory cytokines release and increases the release of anti-inflammatory cytokines.