Evaluation of Serum Zonulin and Occludin Levels in Bipolar Disorder

OBJECTIVE: The etiology of bipolar disorder (BD) is still not fully understood. Little is currently known about the relationship between the interaction the gastrointestinal system and brain function and BD. Zonulin is the only known physiological modulator of tight junctions and is a biomarker for intestinal permeability (IP). Occludin is an integral transmembrane tight junction protein involved in the maintenance and assembly of such junctions. The current study aims to determine whether zonulin and occludin levels are altered in BD and whether they can serve as clinical biomarkers of disease. METHODS: Forty-four patients with BD and 44 healthy controls were included in this study. The Young Mania Rating Scale (YMRS) was used to determine the severity of manic symptoms, while the Hamilton Depression Rating Scale (HDRS) was used to determine the severity of depressive symptoms, and the Brief Functioning Rating Scale (FAST) to assess functionality. Venous blood samples were taken from all participants and serum zonulin and occludin levels were measured. RESULTS: The mean serum zonulin and occludin levels of the patients were significantly higher compared to the healthy control group. There was no difference between manic, depressive, and euthymic patients in terms of zonulin and occludin levels. There was no correlation between the total number of attacks, duration of disease, YMRS, HDRS, FAST scores, and zonulin and occludin levels in the patient group. The groups were divided into three according to body mass index as normal, overweight, and obese. Zonulin and occludin levels increased as body mass index increased and were highest in the obese group. CONCLUSION: The study shows that zonulin and occludin levels in BD increase independently of the disease stage. Consideration of the role of IP in the pathogenesis of BD may be helpful in determining the appropriate treatment modality.