UHPLC-QQQ-MS/MS assay for the quantification of dianthrones as potential toxic markers of Polygonum multiflorum Thunb: applications for the standardization of traditional Chinese medicines (TCMs) with endogenous toxicity
Authors: Yang Jian-Bo , Song Yun-Fei , Liu Yue , Gao Hui-Yu , Wang Qi , Wang Ying , Cheng Xian-Long , Zuo Tian-Tian , Hu Xiao-Wen , Wei Feng , Jin Hong-Tao , Wang Shu-Ting , Ma Shuang-Cheng 
Published: July 2021

Abstract
Background
The raw and processed roots of Polygonum multiflorum Thunb (PM) are commonly used in clinical practice to treat diverse diseases; however, reports of hepatotoxicity induced by Polygoni Multiflori Radix (PMR) and Polygoni Multiflori Radix Praeparata (PMRP) have emerged worldwide. Thus, it is necessary for researchers to explore methods to improve quality standards to ensure their quality and treatment effects.

Methods
In the present study, an ultra-high performance liquid chromatography triple quadrupole mass spectrometry (UHPLC-QQQ-MS/MS) method was optimized and validated for the determination of dianthrones in PMR and PMRP using bianthronyl as the internal standard. Chromatographic separation with a gradient mobile phase [A: acetonitrile and B: water containing 0.1% formic acid (v/v)] at a flow rate of 0.25 mL/min was achieved on an Agilent ZORBAX SB-C18 column (2.1 mm × 50 mm, 1.8 μm). The triple quadrupole mass spectrometer (TQMS) was operated in negative ionization mode with multiple reaction monitoring for the quantitative analysis of six dianthrones. Moreover, compounds 5 and 6 were further evaluated for their cytotoxicity in HepaRG cells by CCK-8 assay.

Results
The UHPLC-QQQ-MS/MS method was first developed to simultaneously determine six dianthrones in PMR and PMRP, namely, polygonumnolides C1–C4 (1–4), trans-emodin dianthrones (5), and cis-emodin dianthrones (6). The contents of 1–6 in 90 batches of PMR were in the ranges of 0.027–19.04, 0.022–13.86, 0.073–15.53, 0.034–23.35, 0.38–83.67 and 0.29–67.00 µg/g, respectively. The contents of 1–6 in 86 batches of commercial PMRP were in the ranges of 0.020–13.03, 0.051–8.94, 0.022–7.23, 0.030–12.75, 0.098–28.54 and 0.14–27.79 µg/g, respectively. Compounds 1–4 were almost completely eliminated after reasonable processing for 24 h and the contents of compounds 5 and 6 significantly decreased. Additionally, compounds 5 and 6 showed inhibitory activity in HepaRG cells with IC50 values of 10.98 and 15.45 μM, respectively. Furthermore, a systematic five-step strategy to standardize TCMs with endogenous toxicity was proposed for the first time, which involved the establishment of determination methods, the identification of potentially toxic markers, the standardization of processing methods, the development of limit standards and a risk–benefit assessment.

Conclusion
The results of the cytotoxicity evaluation of the dianthrones indicated that trans-emodin dianthrones (5) and cis-emodin dianthrones (6) could be selected as toxic markers of PMRP. Taking PMR and PMRP as examples, we hope this study provides insight into the standardization and internationalization of endogenous toxic TCMs, with the main purpose of improving public health by scientifically using TCMs to treat diverse complex diseases in the future.