The etiology in bipolar disorder has not been fully understanding. There are limited data regarding the relationship between the permeability of intestinal and blood-brain barrier (BBB), and bipolar disorder etiology. Zonulin is regarded as a non-invasive biomarker for intestinal permeability. Claudin-5 is an important part of BBB permeability. In this study, we assumed that there may be a deterioration in serum zonulin and claudin-5 levels in patients with bipolar disorder and this may affect the severity of the disease.
Forty-one bipolar disorder patients (21 patients in remission and 20 patients with manic episodes) and 41 healthy controls were included in this study. The patients were administered Young Mania Rating Scale (YMRS) and Hamilton Depression Rating Scale (HDRS) to determine the severity of manic and depressive symptoms, respectively. Venous blood samples were collected, and serum zonulin and claudin-5 levels were measured.
The mean serum zonulin and claudin-5 levels in patients were significantly higher than healthy controls. There is no difference zonulin and claudın-5 levels between patients with manic episodes and patients in remission.
This study’s small sample size limits the generalization of these outcomes to a larger population. Also, a major limitation of our study is lack of evaluations of gut microbiota in patients with bipolar disorder and controls.
In conclusion, the current research indicates that zonulin and claudin-5 are increased in patients with bipolar disorder and this finding may contribute to the role of intestinal permeability or BBB in the pathogenesis of bipolar disorder.

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