Pharmacokinetic alterations of rhubarb anthraquinones in experimental colitis induced by dextran sulfate sodium in the rat

Ethnopharmacological relevance: Rhubarb (Rhei Rhizoma et Radix) is used for the treatment of digestive diseases in traditional medicinal practice in China. Recent studies also support its beneficial activities in alleviating ulcerative colitis (UC). Aim of the study: This study aimed to characterize the oral pharmacokinetics of rhubarb anthraquinones, the main bioactive components of this herb, in the experimental chronic colitis rat model induced by dextran sulfate sodium (DSS) and to identify the factors causing the pharmacokinetic alterations. Materials and methods: Rats received drinking water (normal group) or 5% DSS for the first 7 days and 3% DSS for additional 14 days (UC group). On day 21 both groups received an oral dose of the rhubarb extract (equivalent to 5.0 g crude drug/kg body weight). Plasma anthraquinone aglycones levels were determined directly by an LC-MS/MS method and the total of each anthraquinone (aglycone+conjugates) was quantified after beta-glucuronidases hydrolysis. Results: Rhubarb anthraquinones predominantly existed as conjugates in plasma samples from both groups and only free aloe-emodin, rhein and emodin were detected. Compared to the normal rats, both Cm. and AUC of the three free anthraquinones were increased, while the systemic exposure (AUC) of the total (aglycone +conjugates) of most anthraquinones decreased by UC accompanied by the disappearance of multiple-peak phenomenon in the plasma concentration-time profiles. Gut bacteria from UC rats exhibited a decreased activity in hydrolyzing anthraquinone glycosides to form respective aglycone and there were significant decreases in microbial beta-glucosidases and beta-glucuronidases activities. Moreover, the intestinal microsomes from UC rats catalyzed glucuronidation of free anthraquinones with higher activities, while the activities of hepatic microsomes were comparable to normal rats. Conclusions: The decreases of beta-glucuronidases activity in DSS-induced chronic rat colitis should mainly account for the decreases in systemic exposure and abrogation of enterohepatic recirculation of most rhubarb anthraquinones after oral intake.