Anti-Malignancy and Anti-Inflammation Properties of Emodin, an Essential Constituent in Popular Laxative Botanicals

The rhubarb root and the senna leaf are two commonly used laxative herbs for functional constipation, containing dianthrones and free anthraquinones. As a free anthraquinone, emodin is a crucial constituent isolated from laxative botanicals, and it is particularly abundant in the rhubarb root, a key ingredient in the classic Chinese medicine formula MaZiRenWan (or herbal medicine CDD-2101). This study explored emodin’s anti-malignancy, anti-inflammation, and underlying mechanisms. We examined emodin and other anthraquinones on human colorectal cancer cell proliferation, then used ApcMin/+ mice to assess effects on animal lifespan, intestinal tumor multiplicity, inflammatory cytokines, and adaptive immunity. Results showed MaZiRenWan extract inhibited HCT-116/HT-29 human cancer cells. However, two primary dianthrone sennosides, sennoside A and sennoside B, did not demonstrate such pronounced effects. Three free anthraquinones, emodin, aloe-emodin, and rhein, displayed antiproliferative effects on cancer cells, which were observed to be significantly concentration- and time-dependent, with emodin demonstrating the strongest action. Emodin was found to induce cell cycle arrest during the S-G2/M phases and trigger apoptosis. In vivo, emodin extended ApcMin/+ mice lifespan, reduced gut tumors, downregulated gut tissue levels of key pro-inflammatory cytokines such as IL-1α, IL-1β, IL-6, IL-17A, IL-8, G-CSF, and GM-CSF; this result was supported by the IL-8 secretion test. Emodin had no inhibitory effect on regulatory Treg cell differentiation, yet it effectively suppressed the Th1 and the Th17 cell differentiation. In conclusion, emodin prevents colorectal cancer via inhibiting cell growth, anti-inflammation, and adaptive immunity modulation, highlighting its potential in inflammation-associated colorectal cancer prevention.