The Mongolian rhubarb-Rheum undulatum L. (RU)-and Rumex crispus L. (RC)-a Taiwanese local rhubarb belonging to the family of Polygonaceae-are principal therapeutic materials in integrative medicine due to their rich quantities of bioactive compounds; however, their
phytochemical and
antioxidant properties, and anti-
cancer activity is poorly investigated. Furthermore, the
phytochemical characteristics of both species may be affected by their different geographical distribution and climatic variance. The current study aimed to compare RU with RC extracts in different polarity
solvents (
n-hexane,
ethyl acetate,
acetone,
ethanol, and water) for their
phytochemical contents including the total phenolic content (TPC), total
anthraquinone content (TAC), total
flavonoid content (TFC),
antioxidant and
free radical scavenging capacities, and anticancer ability on the HepG2 cell. Except for the
n-hexane extract, all of the RU extracts had considerably higher TPCs than RC extracts, ranging from 8.39 to 11.16 mg
gallic acid equivalent (GAE) per gram of dry weight, and the TPCs of each extract were also significantly correlated with their
antioxidant capacities by
ABTS, DPPH, and FRAP assays (p < 0.05). Moreover, there was no remarkable association between the
antioxidant capacities and either TACs or TFCs in both the RU and RC extracts. Besides, high-performance liquid chromatography (HPLC) analysis revealed that both the RU and RC extracts contained
chrysophanol,
emodin, and
physcion, and those bioactive compounds were relatively higher in the
n-hexane solvent extracts. Additionally, we observed different levels of dose-dependent cytotoxic effects in all the extracts by cell viability assay. Notably, the
ethanol extract of RU had a compelling cytotoxic effect with the lowest half-maximum inhibition concentration (IC50-171.94 ± 6.56 µg/mL at 48 h) among the RU extracts than the
ethanol extract of RC. Interestingly, the
ethanol extract of RU but not RC significantly induced apoptosis in the human
liver cancer cell line, HepG2, with a distinct pattern in
caspase-3 activation, resulting in increased PARP cleavage and DNA damage. In summary, Mongolian Rhubarb, RU, showed more
phytochemical contents, as well as a higher
antioxidant capacity and apoptotic effect to HepG2 than RC; thus, it can be exploited for the proper source of natural
antioxidants and
liver cancer treatment in further investigation.