Background: An altered gastrointestinal barrier function is reportedly associated with the pathogenesis of functional dyspepsia (FD); however, the pathogenesis of FD has not yet been fully elucidated. Aims: The objective of the present study was to determine whether the mucosal barrier function is impaired in patients with FD and to investigate the mechanisms underlying FD. Methods: The present study included patients with FD (FD group, n = 24), non-FD patients with abdominal symptoms (symptomatic control group, n = 14), and patients with no abdominal symptoms (asymptomatic control group, n = 20). The groups were compared regarding the mucosal electrical impedance (MI) values of the stomach and duodenum, which were measured using a tissue conductance meter during esophagogastroduodenoscopy. Results: There were no significant differences between the three groups in the MI of the stomach. In contrast, the duodenal MI of the FD group (17.8 ± 4.3 Ω) was significantly lower than those of the symptomatic control group (27.2 ± 6.4 Ω, p < 0.0001) and asymptomatic control group (23.0 ± 7.4 Ω, p = 0.016). The expression of zonula occludens-1 (ZO-1) was significantly lower in the FD group than in the symptomatic control group (p = 0.011), where ZO-1 was positively correlated with the duodenal MI (β = 0.513, p = 0.017). The interleukin (IL)-1β expression was significantly higher in the FD group than in the symptomatic control group (p = 0.041), where IL-1β was inversely correlated with the duodenal MI (β = − 0.600, p = 0.004). Conclusions: The mucosal barrier function of the duodenum was altered in patients with FD. Both a decreased ZO-1 and increased IL-1β may play a role in the pathogenesis of FD.
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