Baicalin ameliorates ulcerative colitis by regulating macrophage polarization through the JAK1/STAT1/SOCS1 pathway

Scutellaria baicalensis, a traditional Chinese medicine herb, has been classically used to treat diarrhea and dysentery caused by damp heat in Traditional Chinese Medicine. And it has been demonstrated to alleviate colonic mucosal inflammation in ulcerative colitis. However, the mechanism through which its main active ingredient, baicalin, alleviates ulcerative colitis remains unclear.

This study investigated whether baicalin regulates macrophages to ameliorate ulcerative colitis through the JAK1/STAT1/SOCS1 pathway.

LPS-induced RAW264.7 cells were used to investigate the anti-inflammatory and regulatory effects of baicalin on macrophage polarization. The NO content was assessed by a Griess assay, and label-free optical diffraction tomography for live-cell imaging and confocal imaging were conducted to observe macrophage polarization and analyze the expression of CD86 and CD206. The protective effect of baicalin on DSS-induced colitis mice was evaluated through the Disease Activity Index (DAI) system, endoscopy, enzyme-linked immunosorbent assay (ELISA), hematoxylin and eosin (HE) staining, Alcian Blue periodic acid Schiff (AB-PAS) staining, and immunofluorescence. Macrophages in the lamina propria of the colon were analyzed by tiling light sheet microscopy imaging and flow cytometry. Western blotting (WB) was used to evaluate the expression of JAK1/STAT1/SOCS1 pathway members, and the expression of the downstream transcription factors were quantified through qPCR.

Baicalin markedly inhibited NO levels induced by LPS and delayed the timing and quantity of macrophage polarization toward the M1 phenotype. Furthermore, baicalin ameliorated the symptoms of colitis in mice, such as diarrhea, hematochezia, weight loss, colon shortening, decreased spleen weight, pathological changes, intestinal mucosal barrier dysfunction, and decreased DAI and inflammatory factor levels. Moreover, baicalin promoted macrophage polarization toward the M2 phenotype and inhibited the polarization of M1 macrophages in the intestinal lamina propria. Mechanistically, baicalin inhibited the phosphorylation of JAK1 and STAT1 and restored the negative feedback inhibition of JAK1/STAT1 by upregulating SOCS1. In addition, baicalin reduced the mRNA levels of downstream genes.

Baicalin can alleviate intestinal inflammation, ameliorate intestinal barrier damage, and regulate macrophage polarization by inhibiting M1 macrophage polarization in an ulcerative colitis model. This protective effect was achieved through the JAK1/STAT1/SOCS1 pathway.