Total flavonoids of Sophora flavescens and kurarinone ameliorated ulcerative colitis by regulating Th17/Treg cell homeostasis

Ethnopharmacological relevance: Ulcerative colitis (UC) is relevant to dysregulation of inflammation and immune processes. Sophora flavescens Aiton is a classic medicine widely used in the treatment of UC in ancient and modern China, alkaloids and flavonoids are the main components. Previous studies reveal that Sophora flavescens Aiton total flavonoids extracts (SFE) exert an anti-UC effect by regulating the intestinal microbe structure and restoring the balance of the "host-microbe" co-metabolic network in UC mice. However, whether SFE influences immune inflammation remains unclear, which is the core link to UC disease. It also remains to be verified flavonoids are the material basis that plays a role in SFE. Aim of the study: To identify the action mechanism of the immune-inflammatory regulation of SFE and its main active component Kurarinone against UC. Methods: This study constructed UC mice and abnormal immune RAW 264.7 cell models, and subsequently used western blotting and flow cytometry (FCM) to evaluate the effects of SFE on the NF-kappa B pathway and the regulation of immunity in UC mice. Kurarinone was screened from flavonoid compounds of SFE by lipopolysaccharide (LPS)-induced RAW 264.7 cells, and its effect was subsequently investigated in UC mice. Western blotting, ELISA, FCM, and RT-PCR were used to determine the regulation of Kurarinone on the Th17/Treg differentiation and the JAK2/STAT3 signaling pathway. Results: SFE regulated the differentiation of Th17/Treg in peripheral blood and inhibited immune-inflammatory response to treat UC. Various flavonoid components in SFE inhibited the synthesis of IL-6 and TNF-alpha in RAW 264.7 cells, among which Kurarinone had better effect. This study revealed the therapeutic effects of Kurarinone in UC mice for the first time. Kurarinone promoted the secretion of SIgA to improve the regulation of the intestinal mucosal barrier and resistance to pathogens. It also regulated the transcription level of ROR gamma t and Foxp3 in colon, decreased the expression of pro-inflammatory factor IL-17A and up-regulated the expression of immunosuppressive factors TGF-beta 1 and IL-10 in colon. Furthermore, Kurarinone restored intestinal immune system homeostasis by down-regulating the JAK2/STAT3 signaling pathway and regulating the balance of Th17/Treg cell differentiation in UC. Conclusions: SFE, especially the flavonoid ingredients represented by Kurarinone, has significant effects on immunoregulation against UC. And their mechanism of effect is related to inhibiting the activation of JAK2/STAT3 signaling pathway and regulating differentiation of Th17/Treg cells.