Stress is a pivotal factor for inflammation, reactive oxygen species (ROS) production and formation of visceral hypersensitivity (VH) in the process of gastroesophageal reflux disease (GERD). In the present study, the effects of stress on esophageal inflammation, oxidative stress and VH were investigated in a chronic restraint stress mouse model. c57Bl/6J male mice were subjected to 2 weeks of intermittent restraint stress, and histopathological analysis revealed that stress induced esophageal inflammation and fibrosis, while no distinct changes were detected in non-stressed control mice. In addition, increased NADPH oxidase 4 expression was observed in the plasma and esophagus of stressed mice, indicating accumulation of ROS. The expression levels of antioxidants, including Mn-superoxide dismutase (MnSOD), cu/Zn-Sod, catalase and glutathione peroxidase, were also analyzed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). In addition, transient receptor potential vanilloid 1 (TrPV-1) and protease-activated receptor 2 (Par-2), which are crucial receptors for VH, were measured by immunohistochemistry and RT-qPCR. The results demonstrated that stress markedly reduced antioxidant expression, while it significantly upregulated TRPV-1 and PAR-2 expression levels in the mouse esophagus. Finally, 2 weeks of restraint stress significantly increased the esophageal and plasma levels of inflammatory cytokines, including interleukin (IL)-6, IL-8, interferon-γ and tumor necrosis factor-α. Taken together, the present study results indicated that stress-induced esophageal inflammation and ROS generation involves VH.

Although the underlying mechanism of stress remains unknown, it has been associated with the pathophysiology of gastroesophageal reflux diseases, the development of which appear to be accelerated by oxidative stress and fibrosis. The aim of the current study was to investigate the effect of chronic restraint stress on esophageal oxidative stress and fibrosis, as well as the impact of oxidative stress in a murine model whereby 8-week old C57BL/6J male mice were subjected to intermittent chronic restraint stress for a two-week period. The current study demonstrated that chronic restraint stress significantly reduced the body weight of mice compared with the control group. Although chronic restraint stress did not significantly alter the levels of triglycerides or cholesterol, free fatty acid concentration was significantly increased compared with the control group. Furthermore, chronic restraint stress significantly upregulated the expression levels of several fibrotic biomarkers including collagen type I, transforming growth factor β-1, α-smooth muscle actin and SMAD-3 compared with the control group. In addition, the expression levels of the reactive oxygen species (ROS) NADPH oxidase-4 and malondialdehyde were significantly increased, while the expression levels of nuclear factor erythroid 2-related factor 2 and heme oxygenase-1 were significantly decreased in esophageal tissue from mice in the chronic restraint stress group compared with the control group. In conclusion, chronic restraint stress may induce esophageal fibrosis by accumulating ROS and increasing fibrotic gene expression in a murine model.

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