Induction of apoptosis in human lung fibroblasts and peripheral lymphocytes in vitro by Shosaiko-to derived phenolic metabolites

Shosaiko-to is a Kampo medicine used for the treatment of chronic hepatitis in Japan. Lately, over 200 cases of interstitial pneumonia have been reported resulting from Shosaiko-to therapy, and the number of cases increased when patients were administrated interferon (IFN)-alpha at the same time. However, the mechanisms of this Shosaiko-to implicated interstitial pneumonia are not fully understood. In this study, we examined by flow cytometry analysis the in vitro effects of 7 phenolic compounds (lignans and flavonoids), which were detected from human urine after administration of Shosaiko-to, and IFN-alpha on inducing apoptosis in human lung fibroblasts and peripheral blood mononuclear cells (PBMCs). Among the 7 compounds, baicalein and medicarpin (10 mug/ml) showed significant apoptosis-inducing effects on human PBMCs. In human lung fibroblasts, medicarpin exhibited a significantly higher activity to induce apoptosis compared to the control, and the percentage of cells undergoing apoptosis showed time- and dose-dependent increases. Baicalein (0.1 and 1 mug/ml), liquiritigenin (10 mug/ml) and davidigenin (10 mug/ml) also showed significant effects after 96h treatment. Whereas, baicalin, oroxylin A and wogonin did not show any effect on inducing apoptosis in PBMCs and fibroblasts. Baicalein and medicarpin significantly inhibited the growth and reduced the viability of lung fibroblasts. I FN-alpha had no apoptosis-inducing effect, and it did not show synergistic interaction with any of the compounds derived from Shosaikoto on inducing apoptosis in both human lung fibroblasts and PBMCs. These results suggested that phenolic compounds found in human post-administrative urine of Shosaiko-to, especially baicalein and medicarpin, exhibited a direct effect on human lung fibroblasts and immune cells to induce apoptosis.