Health risk of Licorice-Yuanhua combination through induction of colonic H2S metabolism

Abstract Ethnopharmacological relevance Licorice and Yuanhua are both famous herbs in Traditional Chinese Medicine (TCM), and their combination is used by some TCM doctors to treat renal and gastrointestinal diseases as well as tumors. On the other hand, the compatibility theory of TCM warns that toxic effects might be triggered by Licorice-Yuanhua combination. The usability of Licorice-Yuanhua combination has long been controversial due to lack of evidence and mechanism illustration. Colonic hydrogen sulfide (H 2 S) metabolism imbalance is closely related with colonic inflammation, tumor promotion and many other diseases. Aim of the study This study was carried out to investigate if licorice-Yuanhua combination could induce potential toxic effects in the aspect of colonic H 2 S metabolism. Materials and methods Normal mice were treated with high or low doses of Licorice, Yuanhua and Licorice-Yuanhua combination. Fecal H 2 S concentration was measured by colorimetric method, colon sulfomucin production was compared through tissue staining, fecal microbiota and microbial metagenomes were analyzed by 16S rDNA sequencing and data mining. Results Data shows that although licorice cannot change colonic H 2 S concentration, it can exacerbate Yuanhua induced H 2 S rising. Licorice or Yuanhua increases colon sulfomucin production, and their combination further enhances this effect. 16S rDNA sequencing analysis revealed that licorice or Yuanhua has little influence on gut microbiota, however, licorice-Yuanhua combination can impact gut microbiota structural balance and increase the abundance of Desulfovibrio genus and other related genera. Moreover, the combination extensively changes microbial metagenomes, influencing 1172 genes that cannot be changed by individual licorice or Yuanhua. By searching in KEGG database, ten genes are annotated with H 2 S producing gene, and these genes are remarkably increased by licorice-Yuanhua combination, more significantly than licorice or Yuanhua. Conclusions This study provides evidences and mechanisms for licorice induced risks, which is related with colonic H 2 S metabolism disturbance, gut microbiota and microbial metagenomes. More risk assessment should be evaluated when licorice was used in combination with foods, herbs or drugs. The study provides an example where healthy risks can be induced by combination of food additive, herbs or drugs, through regulating gut microbiota and its metagenomes.