Comparison of the efficacy of different boswellic acids. Caco-2 cells were treated with 50 μM BA, ABA, KBA, or AKBA for 24 h. Acid SMase activities in cell lysate were determined. The activities in control group were taken as 100%. Results are mean ± standard error from 3 separated experiments. The statistic significance was analyzed by one-way ANOVA followed by Tukey test. The statistic significances were indicated in the figure. * P < 0.05, ** P < 0.01, and *** P < 0.001.