High-dose wogonin exacerbates DSS-induced colitis by up-regulating effector T cell function and inhibiting Treg cell

Wogonin exerts anti-tumour activities via multiple mechanisms. We have identified that high-dose wogonin (50 or 100 mg/kg) could inhibit the growth of transplanted tumours by directly inducing tumour apoptosis and promoting DC, T and NK cell recruitment into tumour tissues to enhance immune surveillance. However, wogonin (20-50 μM) ex vivo prevents inflammation by inhibiting NF-κB and Erk signalling of macrophages and epithelial cells. It is elusive whether high-dose wogonin promotes or prevents inflammation. To investigate the effects of high-dose wogonin on murine colitis induced by dextran sodium sulphate (DSS), mice were co-treated with DSS and various doses of wogonin. Intraperitoneal administration of wogonin (100 mg/kg) exacerbated DSS-induced murine colitis. More CD4⁺ CD44⁺ and CD8⁺ CD44⁺ cells were located in the inflamed colons in the wogonin (100 mg/kg) treatment group than in the other groups. Frequencies of CD4⁺ CD25⁺ CD127^- and CD4⁺ CD25⁺ Foxp3⁺ cells in the colons and spleen respectively, were reduced by wogonin treatment. Ex vivo stimulations with high-dose wogonin (50-100 μg/ml equivalent to 176-352 μM) could synergize with IL-2 to promote the functions of CD4⁺ and CD8⁺ cells. However, regulatory T cell induction was inhibited. Wogonin stimulated the activation of NF-κB and Erk but down-regulated STAT3 phosphorylation in the CD4⁺ T cells. Wogonin down-regulated Erk and STAT3-Y705 phosphorylation in the regulatory T cells but promoted NF-κB and STAT3-S727 activation. Our study demonstrated that high-dose wogonin treatments would enhance immune activity by stimulating the effector T cells and by down-regulating regulatory T cells.