Antioxidant Properties of a Traditional Vine Tea, Ampelopsis grossedentata

Abstract

Ampelopsis grossedentata, also called vine tea, has been used as a traditional beverage in China for centuries. Vine tea contains rich polyphenols and shows benefit to human health, but the chemical and antioxidant properties of vine tea polyphenols from different locations remain unclear. This study aims to investigate the chemical and antioxidant properties of vine tea from three major production areas in China including Guizhou, Hunan, and Guangxi Provinces. The highest amount of polyphenol from vine tea was extracted by 70% ethanol at 70 °C for 40 min with ultrasonic treatment. The major compound in vine tea polyphenols (VTP) was determined as dihydromyricetin (DMY) by high-performance liquid chromatography (HPLC) and the content was estimated as 21.42%, 20.17%, and 16.47% of dry weight basis from Hunan, Guizhou, and Guangxi products, respectively. The antioxidant activities were investigated in vitro and in culture hepatic cells. VTP and DMY showed strong 1,1-Diphenyl-2-picrylhydrazyl free radical (DPPH) scavenging ability and high oxygen radical absorption capacity (ORAC) value in vitro. VTP and DMY also increased the level of nicotinamide adenine dinucleotide phosphate (NADPH):quinone oxidoreductase (NQO1) in HepG2 cells. Moreover, VTP and DMY enhanced the level of nuclear factor erythroid 2-related factor 2 (Nrf2) and reduced the level of Kelch-like ECH-associated protein 1 (Keap1). Taken together, our data demonstrated that the extraction of vine tea by 70% ethanol with ultrasonic treatment is a novel method to efficiently obtain components possessing stronger antioxidant activity. Furthermore, the results from the culture cells suggest that the bioactive component of vine tea might exert the antioxidant activity by activating the cellular Nrf2/Keap1 pathway.

Keywords: Ampelopsis grossedentata; Nrf2/Keap1; antioxidant ability; dihydromyricetin.

Figure 1

Diagram of vine tea polyphenol (VTP) extraction. All vine tea leaves from different locations were freeze-dried to ensure the same moisture content.

Figure 2

Conditions for extracting the vine tea polyphenols. (A) Polyphenol yield extracted by different solvents. (B) Polyphenol yield extracted by different concentrations of ethanol. (C) Polyphenol yield extracted by 70% ethanol with different times. (D) Polyphenol yield extracted by 70% ethanol at different temperatures. (E) Polyphenol yield extracted by 70% ethanol alone (control) and 70% ethanol plus ultrasonic treatment (ultrasonic). (F) Polyphenol yield of vine tea from different locations. The data represent mean ± SD with three repeats, and different letters in the same column indicate significant differences (p < 0.05).

Figure 3

Dihydromyricetin determination in vine tea polyphenols by high-performance liquid chromatography (HPLC). The HPLC profiles of vine tea polyphenols (VTP) from Hunan Province (A), Guizhou Province (B), Guangxi Province (C) as well as the VTP plus standard dihydromyricetin (DMY) (D). (E) DMY content in the vine tea dry powder (white bar) and in VTP (black bar) from the above three locations. (F) Chemical structure of DMY. The data represent mean ± SD from three repeats, different letters in the same column indicate significant differences (p < 0.05).

Figure 4

Antioxidant ability of VTP. (A) 2,2-diphenyl-1-picrylhydrazy (DPPH) free-radical scavenging rate of VTP from three locations and DMY. (B) IC₅₀ value of the DPPH free-radical scavenging of VTP from three locations and DMY. (C) Relative florescence intensity of oxygen radical absorbance capacity (ORAC) of VTP from three locations and DMY in 2 h. (D) ORAC value (Trolox equivalent/g sample) of VTP from three locations and DMY. The data represent mean ± SD with three repeats, different letters in the same bar indicate significant differences (p < 0.05).

Figure 5

Effects of DMY and VTP on the level of nicotinamide adenine dinucleotide phosphate (NADPH):quinone oxidoreductase (NQO1), nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associated protein 1 (Keap1) proteins. A time-effect of DMY (A) and VTP (B) on the level of NQO1, Nrf2 ,and Keap1 proteins. HepG2 cells were treated with DMY (40 μM) or VTP (equivalent to 40 μM DMY) for 0–12 h. A dose-effect of DMY (C) and VTP (D) on the level of NQO1, Nrf2, and Keap1 proteins. HepG2 cells were treated with DMY (20–120 μM) and VTP (equivalent to 20–120 μM DMY) for 9 h. The fold was normalized with the control protein, β-actin, and obtained from triplicate blot data.