[Mechanism of total iridoids from Gardeniae Fructus in treating ulcerative colitis based on "bitterness drying...

This study aimed to explore the mechanism of total iridoids from Gardeniae Fructus in treating ulcerative colitis(UC) in rats from the perspective of the " bitterness drying dampness" theory in TCM. SD rats were randomly divided into a blank group, a model group, groups of high-and low-dose total iridoids from Gardeniae Fructus(200 and 100 mg·kg~(-1), respectively), and a positive drug group, with 10 rats per group. Except for the blank group, UC model was induced in all other groups via enema administration of 2,4, 6-trinitrobenzene sulfonic acid(TNBS) solution(100 mg·kg~(-1)). During the administration period, the appearance of the rats was observed and recorded daily, and the disease activity index(DAI) was scored. Colon length and spleen weight were measured, and the colon mucosal damage index(CMDI) was scored. Microscopic pathological damage in the colon was observed via HE staining and AB staining, and the histopathological index(HI) was scored. The levels of inflammatory cytokines tumor necrosis factor-α(TNF-α), interleukin-6(IL-6), interleukin-10(IL-10), and 3',5'-cyclicade-nosine monophosphate(cAMP) in colon tissue were detected by ELISA. The expression levels and distribution/damage of intercellular tight junction proteins E-cadherin, claudin-1, and occludin in the colon mucosal layer were detected using Western blot and immunofluorescence. The expression levels of bitter taste receptor 38(TAS2R38), phospholipase C β2( PLCβ2), inositol 1,4,5-trisphos-phate( IP3), and α-gustducin(GNAT3) were detected by Western blot and RT-qPCR. The results showed that compared with the blank group, rats in the model group exhibited a significant decrease in body weight and a significant increase in DAI score. Furthermore, colon length was significantly shortened, while the spleen index, CMDI, and HI scores were all significantly increased. Concomitantly, the levels of TNF-α and IL-6 in colon tissue were significantly elevated, while IL-10 levels were significantly decreased. Additionally, the protein expression levels of E-cadherin, claudin-1, and occludin were significantly reduced. The protein expression level of TAS2R38 was significantly downregulated, and the protein and mRNA expression levels of PLCβ2, IP3, GNAT3 in colon tissue were significantly downregulated, and the content of cAMP was significant reduced. Administration of total iridoids from Gardeniae Fructus significantly improved all the above indicators in UC rats. These treatments significantly enhanced TAS2R38 protein expression in colonic tissues, restored the protein and mRNA expression of PLCβ2, IP3 and GNAT3, and raised cAMP content. In conclusion, total iridoids from Gardeniae Fructus may alleviate colonic epithelial barrier damage and inflammatory responses by activating TAS2R38 and regulating the GNAT3/cAMP and PLCβ2/IP3 signaling pathways, thereby improving symptoms in UC rats.