The role of probiotics and prebiotics in modulating of the gut-brain axis

Abstract

Pro-and prebiotics have been indicated to modulate the gut-brain axis, which have supportive impacts on central nervous systems, and decrease or control the incidence of some mental disorders such as depression, anxiety, autism, Schizophrenia, and Alzheimer's. In this review, complex communications among microbiota, gut, and the brain, and also recent scientific findings of the impacts and possible action mechanisms of pro-and prebiotics on mental disorders have been discussed. The results have shown that pro-and prebiotics can improve the function of central nervous system and play an important role in the prevention and treatment of some brain disorders; however, in order to prove these effects conclusively and firmly and to use these compounds in a therapeutic and supportive way, more studies are needed, especially human studies/clinical trials.

Keywords: Alzheimer’s; anxiety; depression; gut microbiome; gut-brain axis; mental disorders; prebiotics; probiotics.

Figure 1

The connection among the microbiome, enteric nervous system/ENS, and central nervous system/CNS. Intestinal bacteria are transmitted from the intestinal lumen to the lamina propria by microfold cells and dendritic cells. Intestinal microbiome secretions like exopolysaccharides/EPS and short-chain fatty acids/SCFAs pass through the intestinal epithelium and directly affect the CNS. Intestinal bacteria and their metabolites can interact with certain receptors such as G-protein coupled receptors/GPCRs and Toll-like receptors/TLRs. The intestinal microbiome can adjust ENS function through TLRs, inspire the expression of glial cell line-derived neurotrophic factor/GDNF, and enhance the number of glial cells and enteric neurons. On the other hand, SCFAs adjust colonic regulatory T cell/cTreg homeostasis via affecting on GPCRs.

Figure 2

The effect of probiotics on the central nervous system/CNS through the effect on the microbiome-gut-brain axis. Probiotics affect brain function both directly and indirectly. Probiotic microorganisms affect the hypothalamic–pituitary–adrenal/HPA axis, through fluctuating corticosteroid/CORT and adrenocorticotropic hormone/ACTH ranges. The immune system is impacted by limited pro-inflammatory cytokine creation and inflammation and has stimuluses on the CNS. Probiotics can moreover straightly modify CNS biochemistry, for example by fluctuating 5-hydroxytryptamine/5-HT, brain-derived neurotrophic factor/BDNF, g-aminobutyric acid/GABA, Dopamine/DA, and c-Fos ranges, subsequently compelling mind and manners. The vagus and enteric nerves are also involved in gut-brain communications and are impacted by certain probiotic strains. Also, probiotic microorganisms regulate the gut microbiota by expanding microbiota variety and beneficial bacteria configuration. At that point, gut microbiota can adjust metabolites, such as, short-chain fatty acids/SCFAs, exopolysaccharides/EPS, and tryptophan, afterward, progresses CNS function indirectly. Also, the gut microbiota collaborates with the immune system, endocrine, and neural system.