Comprehensive investigation on the metabolism of emodin both in vivo and in vitro

Emodin is a natural anthraquinone, which displays numerous pharmacological activities, including anti-tumor, anti-inflammation and immunosuppression. However, there was no comprehensive study on its absorption, metabolism, distribution, and excretion. In order to further evaluation on the possibility of drug development of emodin, both in vivo and in vitro experiments were fulfilled in this study. The results showed that the absolute bioavailability of emodin is approximately 3.2%. Furthermore, about 56% of emodin was unabsorbed and mainly excreted into feces as prototype. The absorb constituent could be rapidly metabolized as hydroxylated and glucuronidated metabolites. Both prototype and metabolites of emodin absorbed into the body circulation were predominantly distributed in kidney. Hydroxyed metabolites were predominantly excreted via urine and feces and glucuronidated metabolites were predominantly excreted via urine and bile. CYP1A2, CYP2E1, UGT1A1, UGT1A9, and UGT2B7 played a key role in the metabolism of emodin in liver microsomes of rats. To the best of our knowledge, this is the first comprehensive study on the absorption, metabolism, distribution, and excretion of emodin, and our results could help to understand both pharmaceutical and toxicological effects of emodin greatly.