A study on the compatibility mechanism of Dahuang-Gancao decoction based on liquid-phase state and biopharmaceutics

Dahuang-Gancao decoction (DGD), from the Synopsis of Golden Chamber, consists of Rhubarb and Licorice. It clears heat, unblocks the bowels, and alleviates nausea. Rhubarb is potent, and clinical evidence shows that Licorice can alleviate the adverse reactions of Rhubarb, thereby enhancing its purgative action while mitigating its side effects. Nevertheless, the intricacies of the detoxification mechanism remain obscure.

This study explores the compatibility mechanism of DGD, focusing on its liquid-phase state and biopharmaceutical properties.

This study validated the regulatory effect of Licorice on the toxicity of Rhubarb through a zebrafish lethality assay. Zebrafish larvae, at 72 h post-fertilization, were subjected to a gradient of Rhubarb decoction (RD) and DGD concentrations ranging from 50 to 5000 μg/mL. Mortality rates were assessed after 24 h, and the half-maximal lethal concentration (IC50) was determined. Subsequently, phase separation of DGD and RD was performed via centrifugation (8000 rpm, 10 min) to isolate the precipitate phases of DGD (DGD-P) and RD (RD-P). Further dialysis and repeated high-speed centrifugation (12000 rpm, 30 min) were employed to separate the nanoparticle phases of DGD (DGD-N) and RD (RD-N) from their true solution phases. The physicochemical properties of RD, Licorice decoction (LD), and DGD-including salinity, conductivity, particle size, polydispersity index (PDI), and zeta potential-were analyzed using a salinometer, conductivity meter, and dynamic light scattering at 20 °C, 40 °C, and 60 °C. A validated high-performance liquid chromatography (HPLC) method was employed to quantify key constituents in each phase, including sennosides A/B, rhein, emodin, and aloe-emodin. The in vitro release profiles of these compounds were evaluated using dialysis bag experiments in simulated gastric fluid (pH 1.2), intestinal fluid (pH 6.8), and colonic fluid (pH 8.3). Release kinetics were modeled using zero-order, first-order, and Higuchi equations.

Licorice significantly reduced the toxicity of Rhubarb, as evidenced by a 2.5-fold increase in the zebrafish IC50 (from 938.46 μg/mL for RD to 2392.03 μg/mL for DGD). Mechanistically, Licorice altered the physicochemical properties of DGD, increasing particle size and promoting phase transition of key constituents into the precipitate phase. This redistribution diminished their stimulatory effects on the body, thereby reducing adverse reactions. In the simulated gastrointestinal environment, the precipitate phase acted as a natural slow-release matrix, while the nanoparticle phase exhibited a pattern of rapid initial release followed by sustained release. These phase-dependent release behaviors, regulated by Licorice-induced supramolecular interactions, alleviated the liver toxicity and gastrointestinal irritation caused by Rhubarb, while preserving its therapeutic efficacy.

Licorice mitigates Rhubarb's toxicity by influencing the distribution and release of key ingredients across phases. This finding offers new insights into the efficacy and safety of traditional Chinese medicine formulations.