Forsythia suspensa polyphenols regulate macrophage M1 polarization to alleviate intestinal inflammation in mice

Inflammatory bowel disease (IBD) was a chronic intestinal disease related to autoimmunity, and its pathogenesis was complex. Forsythia suspensa (F. suspensa) had good anti-inflammatory and antioxidant effects. The active component polyphenols had significant effects in the treatment of intestinal inflammation. Researches had found that polarization, pyroptosis and apoptosis of macrophages can drive the occurrence and development of colitis. In this study, we examined whether F. suspensa polyphenols (FPP) mitigated DSS-induced colitis, and explored its potential mechanisms. The potential targets of F. suspensa in intestinal inflammation were predicted through network pharmacology. Using LPS and IFN-γ induced macrophage M1 polarization in J774A.1 cells. Macrophage polarization was detected through RT-qPCR, flow cytometry and ELISA. Ulcerative colitis (UC) in mice was induced by 2.5% DSS for 7 days, and then oral administrated different doses of FPP for another 7 days. Then we assessed the body weight, diarrhea, bleeding in stool, colon length, cytokines of serum and pathology of colon. The effects of FPP on the gut microbiota in mice also tested and evaluated. Our results showed that the main active ingredient of F. suspensa in protecting intestinal inflammation were polyphenols and F. suspensa was multi-targeted in the treatment of intestinal inflammation. FPP inhibited M1 polarization and polarizes towards M2 in J774A.1 cells. FPP inhibited pyroptosis and apoptosis to exert anti-inflammatory effects. FPP had a good protective effect on DSS induced UC in mice. In unison, FPP inhibited M1 polarization, apoptosis, and pyroptosis in UC mice. FPP regulated intestinal homeostasis in mice with UC by improving the gut microbiota and enhancing the intestinal metabolites short-chain fatty acid (SCFAs). These data indicated that FPP may alleviate UC by inhibiting M1 polarization in mice. Collectively, these findings suggest that the reduction of colitis by FPP may related to macrophage polarization, pyroptosis and apoptosis.