Pharmacokinetics, tissue distribution, and excretion of anthraquinones and their glucuronide metabolites from raw and steamed pieces of Rhei Radix et Rhizoma extract in constipation rats

Background: Rhei Radix et Rhizoma has been traditionally used as a potent laxative for centuries due to its remarkable efficacy. Raw pieces of Rhei Radix et Rhizoma (RP) are known for their strong laxative effects, often accompanied by side effects, while steamed Rhei Radix et Rhizoma pieces (SP) possess a milder laxative effect and are widely used clinically. However, there is a lack of comprehensive evidence examining the mechanisms underlying SP’s effectiveness, particularly from a bioavailability perspective. Objective: This study aimed to investigate the impact of the steaming process on the in vivo disposition of RP and SP through pharmacokinetics, tissue distribution, and excretion assays. Methods: An ultra-performance liquid chromatography-tandem mass spectrometry method was developed for the simultaneous quantitative analysis of prototype anthraquinones and their glucuronide metabolites. Pharmacokinetic, tissue distribution, and excretion assays were conducted in constipation rats following oral administration of RP and SP. Blood, tissue, urine, and fecal samples were collected and analyzed to compare the absorption, distribution, metabolism, and excretion profiles of anthraquinones, highlighting differences in bioavailability and safety between RP and SP. Results: Compared with the RP group, the SP group showed significantly reduced area under the plasma concentration–time curve, mean residence time, and half-life time values for rhein-8- O - β - D -glucopyranoside, rhein, emodin, aloe-emodin, and their glucuronide metabolites. The clearance values were significantly increased in the SP group. These results demonstrate that SP led to lower exposure levels and higher elimination rates of these components compared with RP. Additionally, these components were primarily distributed in the large intestine, where they exerted their laxative effects. Glucuronide metabolites were mainly excreted through urination, while prototype components were excreted in both urine and feces. Notably, the cumulative excretion of aloe-emodin, emodin, rhein, and their glucuronide metabolites was significantly higher in both urine and feces after SP administration, indicating that SP enhances the excretion of these components compared with RP. Conclusion: The findings suggest that SP reduced anthraquinone exposure levels while enhancing their excretion, demonstrating that the steaming process significantly promotes the elimination of key components. This study provides a comprehensive analysis of how steaming alters the in vivo disposition of Rhei Radix et Rhizoma, offering a scientific basis for the improved safety and clinical use of SP. These insights not only clarify the mechanistic differences between RP and SP but also contribute to a broader understanding of processing-induced modifications in Chinese medicines. This research paves the way for optimizing Chinese medicine processing techniques to enhance the safety and efficacy of herbal therapies.