A Comprehensive Assessment of Bioactive Metabolites, Antioxidant and Antiproliferative Activities of Cyclocarya paliurus (Batal.) Iljinskaja Leaves

Cyclocarya paliurus (Batal.) Iljinskaja is an indigenous and multifunction tree species in China, but it is mainly used in pharmaceutical and nutraceutical ingredients. To make a comprehensive evaluation on its bioactive metabolites, antioxidant and antitumor potentials of C. paliurus leaves, the leaf samples were collected from 15 geographic locations (natural populations) throughout its distribution areas. High-performance liquid chromatography (HPLC) and colorimetric methods were used to detect the contents of bioactive metabolites. The antioxidant activity was evaluated by 2,2′-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and reducing power assays. The antiproliferative activity on different cancer cell types was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Contents of bioactive metabolites, and antioxidant and antiproliferative activities in the extracts were significantly affected by solvent and population. In most cases, the contents of flavonoids and triterpenoids, and the antioxidant and antiproliferative activities in the ethanol extracts were higher than the water extracts. The best scavenging capacity of DPPH (IC50 = 0.34 mg/mL) and ABTS (IC50 = 0.50 mg/mL) radical occurred in the ethanol extracts of S15 and S7 population respectively, while the strongest reducing power (EC50 = 0.71 mg/mL) was achieved in the ethanol extracts of S14 population. The antiproliferation effects of C. paliurus extracts on cancer cells varied with different cell types. The HeLa cell was the most sensitive to C. paliurus extracts, and their IC50 values of the ethanol extracts varied from 0.13 to 0.42 mg/mL among C. paliurus populations. Redundancy analysis showed that total polyphenol had the greatest contribution to the antioxidant activity, but total flavonoid was mostly responsible for the antiproliferation effects. These results would provide important scientific evidences not only for developing C. paliurus as a potent antioxidant and antitumor reagent, but also for obtaining the higher yield of bioactive compounds in the C. paliurus plantation.