The double face of licorice-kansui herb pair: cure or curse, depending on the combining ratio and mediated by hydrogen sulfide

Background The safety and efficacy of herbal medicines including traditional Chinese medicine (TCM) has been one of the major scientific problems in the medical field. In TCM prescriptions, reasonable herbal combinations bring stronger efficacy and low risk of toxicity. However, the rules and mechanisms for herbal combinations are far from complete understood yet. Purpose: In this study, we investigated the efficacy-toxicity transformation of the licorice-kansui herbal combination under clinical equivalent doses, and study the inside mechanisms. Study design Licorice-kansui or glycyrrhetinic acid-kansuinine A combinations of different combining ratio were given to malignant pleural effusion mice as well as the IEC-6 and S-180 cells. Methods The therapeutic and toxic effects were characterized by various indicators; the chemical changes were analyzed by LC-MS method; the role of H2S was also studied through its inhibitors Results Low-proportion of licorice combined with kansui exerted comparable therapeutic effects to cisplatin, by reducing pleural effusion, promoting respiration, increasing urine volume, protecting lung tissue, and inhibiting tumor cells by inducing oxidative stress and apoptosis. On the other hand, high-proportion of licorice combined with kansui had poor therapeutic effect but induced oxidative stress, inflammation and tissue damages, especially to the small intestine. This efficacy-toxicity transformation was also reproduced by the glycyrrhetinic acid-kansuinine A combination on IEC-6 epithelial cells and S-180 tumor cells. The transformation was not simply caused by the in-solution solubilization effects of licorice during co-decocted with kansui. Furthermore, the therapeutic and toxic effects were both highly related to the hydrogen sulfide level and its anabolic enzymes, cystathionine-gamma-lyase (CSE) or cystathionine beta-synthase (CBS), either in tissues or in-vitro cells. By inhibiting CSE or CBS, all the therapeutic or toxic effects were abolished both in-vivo and in-vitro. Moreover, the intestinal sulfide-reducing bacteria Desulfovibrio and body drug-metabolism were also important variants influencing the efficacy-toxicity transformation of licorice-fkansui herbal combination. Conclusion This study comprehensively uncovered the rules of licorice-kansui herbal combination, and for the first time confirmed that H2S plays a crucial role in mediating its efficacy-toxicity transformation. Our study not only supports the reasonable clinical usage of these two herbs but also provide ideas and methods for the study of other herb pairs in TCM prescriptions.