Immunomodulatory activity of Dioscorea membranacea Pierre rhizomes and of its main active constituent Dioscorealide B

BACKGROUND The rhizomes of Dioscorea membranacea Pierre, also called Hua-Khao-Yen by Thai name, are used as ingredients in many Thai traditional medicines for the alternative or complementary treatment of cancer and AIDs. Preliminary in vitro studies have indicated that D. membranacea extracts exhibited high cytotoxic activity with several cancer cell lines, but the underlining mechanisms are far from clear. The aims of this study were to investigate the effects of ethanolic and aqueous crude extracts from D. membranacea Pierre, and pure compound from D. membranacea Pierre, Dioscorealide B, on natural killer cells activity and on lymphocyte proliferation. METHODS Immunomodulatory activity was investigated using PBMCs from healthy donors. NK cells activity was performed by the chromium release assay using PBMCs as effector cells, and K562 cells line labelled with chromium as target cells. Lymphocyte proliferation was determined by 3H-thymidine uptake. The degree of activation was expressed as the stimulation index. RESULTS The crude ethanolic extracts of D. membranacea Pierre significantly stimulated NK cells activity against K562 cells line at lower concentrations of 10 and 100 ng/ml, but not at higher concentrations. The ethanolic extracts showed no observable effect on lymphocyte proliferation. The crude water extracts significantly increased NK cell activity at concentrations of 10 ng/ml, 100 ng/ml, 1 μg/ml, 10 μg/ml and 100 μg/ml, and also activated lymphocyte proliferation at concentration of 1 ng/ml, 10 ng/ml, 100 ng/ml, 1 μg/ml, 5 μg/ml, 10 μg/ml and 100 μg/ml. However, Dioscorealide B had no significant effect at lower concentrations (0-1 μg/ml and 0-0.1 μg/ml, respectively) on NK cell activity and lymphocyte proliferation. In fact higher concentrations (>10 μg/ml and >0.5 μg/ml) of Dioscorealide B cause a significant decrease in NK cell activity and lymphocyte proliferation. CONCLUSIONS D. membranacea Pierre stimulated NK cells activity and lymphocyte proliferation, but Dioscorealide B either had no effect, and at higher concentrations decreased NK cell activity and lymphocyte proliferation. Our results suggest that both extracts of D. membranacea Pierre significantly increases immune function, but the underlining mechanism is not clearly understood.