Claudin is a promising biomarker of intestinal wall permeability

To date, sufficient information is available on changes in the levels of tight contact proteins (TCPs) in various diseases. Of greatest interest is the study of claudin due to numerous studies confirming the important role of this protein in the development of pathologies. Deafness, behavioural changes, and nerve conduction disorders occur due to insufficient claudin production. Claudin is involved in the maintenance of cell polarity due to its apical location in the cell. When pathological processes occur, claudin may undergo phosphorylation, leading to changes in cell polarity and impaired regulation of APC levels. Irritable bowel syndrome is one of the possible causes of impaired regulation of claudin levels. In this pathology there is adecrease in claudin-1 expression. In addition, claudins play different roles in different tumour tissues, and the same protein may be differentially expressed in different forms of cancer. Claudin-4 expression is upregulated as disease progresses in colorectal cancer (CRC), oesophageal squamous cell carcinoma, and its upregulation is associated with decreased invasiveness and metastatic potential, which is positively correlated with improved prognosis. In contrast, overexpression of CLDN 4 in breast cancer (BC) and pancreatic cancer (PC) is positively correlated with invasion, metastasis, angiogenesis and poor prognosis. Aim: systematisation of available data on the biological role and clinical significance of claudin. Materials: review of Russian and foreign literature from 2013-2023.