Apple polysaccharide prevents from colitis-associated carcinogenesis through regulating macrophage polarization

Macrophages, an important component of inflammatory microenvironment and tumor microenvironment, are closely related to tumor development and progression. Our previous studies showed that apple polysaccharide (AP) could prevent from colitis associated colorectal carcinogenesis. Herein, we further our study to observe the effect of AP on the polarization of macrophages in Raw 264.7 cells and a colitis associated colorectal cancer mouse model, and to investigate the possible mechanisms. Forty male ICR mice were administered with azoxymethane (AOM) and dextran sodium sulfate (DSS). Twenty mice were given no further treatment as model mice, the rest twenty were fed basal diet mixed with 5% of AP. Raw 264.7 cells were treated with 0.5 mg/mL AP. AP could protect ICR mice against AOM/DSS-induced carcinogenesis, keep the colon of AOM/DSS-treated mice in a moderative inflammatory state, and shift macrophage polarization toward M1 phenotype. In vitro study showed that AP could upregulate TLR-4 signaling mildly and trigger M1 macrophage transition. Moreover, AP-induced transition of macrophage phenotype was suppressed by a TLR-4 antagonist, TAK-242. These data may provide a novel molecular basis for understanding how apples act to prevent colorectal cancer (CRC) and indicate that AP has a potential to prevent and treat CRC.