Intestinal permeability and its significance in psychiatric disorders – A narrative review and future perspectives

The topic of increased intestinal permeability and its impact on the human body is increasingly being addressed by researchers. It is associated with disruption of the intestinal barrier, leading to the "leaky gut" syndrome. This can be assessed by classical methods, determining the concentration of orally administered tracer molecules in urine or by using biomarkers such as LPS, LBP or zonulin in blood plasma. The presence of bacterial endotoxins in the body causes inflammation. In this article, we review research on increased intestinal permeability in psychiatric illness: mood disorders, schizophrenia, alcohol dependence, anxiety disorders, neurodegenerative and neurodevelopmental disorders. The results of the studies used to assess intestinal permeability in different disease entities are presented. Possible mechanisms for these interactions are the effects of chronic, low-grade inflammation on the human brain, causing interruption of the brain blood barrier and dysfunction of astrocytes and microglia. This affects brain function by reducing the number of dopaminergic neurons, disrupting tryptophan metabolism and altering the amount of GABA and glutamate. The links and mechanisms found may, in the future, allow earlier detection of diseases and their targeted treatment.