AB4 ameliorates DSS-induced colitis symptoms
In order to seek the Pulsatilla saponins with anti-inflammatory activities in vitro, we screened a series of saponins AB4, Anemoside A3 (AA3), and 23-hydroxy botulinic acid (23-HA) (Fig. 1A) and tested their inhibitory activity against IL-1β in LPS-challenged differentiated THP-1 cells. Interestingly, AB4 showed the highest inhibitory activity against IL-1β (Fig. 1B and C). In parallel, the cell viability assay showed that AB4 was not cytotoxic at concentrations below 200μM (Supporting Information Fig. S1A-C). Therefore, we hypothesized that AB4 might be the main component of BTWT against colitis.
DSS-induced colitis is known to be a widely accepted model with clinical symptoms similar to human UC, including diarrhea, rectal bleeding and weight loss (Chassaing, Aitken, Malleshappa, & Vijay-Kumar, 2014; Clapper, Cooper, & Chang, 2007). To evaluate the effect of AB4 on colitis in mice, C57BL/6 (wild-type; WT) mice were challenged with 3.0% DSS for 7 days and then administered with AB4 (5 mg/kg) daily for 7 days or 14 days, as well as the 5-ASA (200 mg/kg) being the positive control (Supporting Information Fig. S2A). AB4 markedly decreased the disease activity indices characterized by diarrhea, bleeding, and weight loss compared to the DSS group (Fig. S2B and S2C). Decreased disease severity was also accompanied by a reduction of colon shortening, which was ameliorated by both AB4 treatment and pretreatment. There was no significant difference between AB4 (5mg/kg) alone group and the normal group (Fig. S2D). Notably, we found that the AB4 pretreatment group was more effective than the AB4 treatment group and the 5-ASA group (Fig. S2B-D). Therefore, we continued to investigate the effect of AB4 pretreatment on DSS-induced colitis in mice. We found AB4 (5, 10, and 15 mg/kg) markedly decreased the disease activity indices characterized by body weight loss, diarrhea, and bleeding in a dose-dependent manner compared with the DSS group (Fig. 1D and E). Colonic shortening (Fig. 1F), and splenomegaly (Fig. 1G) caused by the DSS challenge were also improved at the given doses. There was no significant difference between AB4 (15mg/kg) alone group and the normal group. At the same time, the survival experiment showed that AB4 improved the survival rate of mice compared with the DSS group (Fig. 1H). These data suggested that AB4 successfully ameliorated DSS-induced colitis in mice.