Shuganyin decoction improves the intestinal barrier function in a rat model of irritable bowel syndrome induced by water-avoidance stress

To determine the effect of Shuganyin decoction (SGD) on the intestinal barrier function in an irritable bowel syndrome (IBS) rat model induced by water-avoidance stress.

Forty male Wistar rats were divided into control, water-avoidance stress (WAS) group, WAS plus Shuganyin decoction (SGD) group and WAS plus dicetel (Dicetel) group. IBS was induced in rats by subjecting them to water-avoidance stress for 7 days. On day 4 of the WAS protocol, the rats were treated for 7 consecutive days (days 4–11) with SGD, dicetel or a negative control (saline). The number of feces granules, histopathological changes of the intestine and mast cell (MC) morphometry were determined. Intestinal permeability was approximated by measuring the absorption of FITC-dextran 4400 (FD-4) from the lumen into the bloodstream in vivo and in vitro experiments. Also, the expression of protease active receptor-2 (PAR-2) and tumor necrosis factor-α (TNF-α) was estimated using immunohistochemical staining and ELISA, respectively. Tight junction (TJ) protein abundance was measured following a quantitative immunofluorescent analysis of intestinal sections and western blotting.

In vivo, WAS elicited a significantly increase in the transfer of FD-4 from the intestine to blood about threefold in 30 min compared with control group. After treated with SGD, the intestinal permeability to FD-4 of WAS-induced rats was significantly attenuated (P < 0.05). In vitro, the permeability coefficient (Papp) values were measured for FD-4 absorption across the excised intestine. WAS was shown to increase the intestinal permeability to (4.695 ± 0.3629) × 10⁻⁷ cm/s in 120 min, which was 2.6-fold higher than the control group. Rats treated with SGD showed a significant decrease in Papp values of FD-4 as compared to WAS group (P < 0.05). Furthermore, by immunofluorescent detection we found that WAS elicited the irregular distribution of TJ proteins. Using the quantitative analysis software of the medical image, the average optical density and protein abundance of TJ proteins was shown to be lower in the WAS group as compared to control group, (P < 0.05). SGD could attenuate this response and improve TJ distribution (P < 0.05). Western blot analysis confirmed that TJ protein abundance was significantly decreased in WAS group and that they could be returned to control levels following an SGD treatment. WAS also induced an increase in number of MCs, their area and diameter as compared to controls. These observations were attenuated with an SGD or dicetel treatment. Similarly, the expression of PAR-2 and TNF-α exceeded control values in the WAS group and were shown to be successfully attenuated with an SGD treatment.

WAS-induced IBS rat model exhibited intestinal barrier dysfunction, which was manifested as tight junction damage and structural rearrangements that increased the intestinal permeability. Under these conditions, MCs were activated and degranulated in the intestinal mucosa leading to the activation of PAR-2. Our data showed that SGD could inhibit the activation of MCs and down-regulate the expression of both PAR-2 and TNF-α. In turn, this was shown to improve the expression and structural arrangement of TJ proteins in the intestinal mucosa, thereby regulating the intestinal permeability. It was concluded that Shuganyin could protect the intestinal barrier.