When used in very small doses the tannin content in rhubarb has a constipating effect. At higher doses, however, the hydrolyzed metabolites of emodin and sennidin stimulate the gastrointestinal tract and produce a laxative effect (4); in vitro tests show suppression of TNF, IL-1, and IL-6 production. The actions of anthraquinones on rheinanthrone that is transformed from sennoside A may promote the purgative effects of sennoside A (16).The anti-inflammatory activity of emodin may mediate rhubarb's hepatoprotective effects in rats with cholestatic hepatitis (11).
Lindeyin, a phenolic gallylglucoside exhibits analgesic and anti-inflammatory activity in animal models. Catechin, epicatechin, procyanidins, and gallylglucose inhibit hyaluronidase in vitro (10) (12).
Aloe-emodin also possesses anti-proliferative activity, inducing cell cycle arrest in cancer cell lines (6). Anthraquinone extracts of rhubarb were shown to induce cytotoxicity in cancer cell lines (5) and tumor necrosis in mice (sarcoma 37, mammary, and Ehrlich) (1), although this has not been demonstrated in humans.
Another study showed that emodin inhibits human cancer cell invasiveness by specifically antagonizing the adenosine 5'-triphosphate (ATP)-gated Ca(2+)-permeable channel P2X7 receptor (P2X7R) (17).