Flavonoids from Selaginella doederleinii Hieron and Their Antioxidant and Antiproliferative Activities

Abstract

Selaginella doederleinii Hieron. (S. doederleinii) is a traditional herb that is widely used in China to treat several ailments, but mainly cancer. Studies have been carried out to determine the phytochemicals ascribed to its pharmacological activity. However, both phytochemical and pharmacological profiles have not been fully explored as few compounds have been reported. This study evaluated the flavonoid content of the ethanol extract and its four fractions (petroleum ether, dichloromethane, ethyl acetate, and n-butanol) together with their antioxidant activity (DPPH and FRAP assays). Further, the antiproliferative activity was evaluated. Two new secondary metabolites (1 and 3) were isolated from S. doederleinii, which comprised of an apigenin skeleton with a phenyl attached at C-8 of ring A and an acetyl group. Additionally, other known metabolites 2 and 4-16 were isolated, whereby compounds 2, 4, 5, 8, 12, 15, and 16 were reported for the first time in this species. These compounds were evaluated for their antioxidative potentials by both DPPH and FRAP assays, and for their antiproliferative activities by the MTT assay on three human cancer cell lines: colon cancer (HT-29), cervical cancer (HeLa), and lung cancer (A549). Compound 7 exhibited the best activity on the three cancer cell lines (HT-29, HeLa, A549) by inhibiting the rate of growth of the cancer cells in a dose-dependent manner with IC₅₀ values of 27.97, 35.47, and 20.71 µM, respectively. The structure-activity relationship of the pure compounds was highlighted in this study. Hence, the study enriched both the phytochemical and pharmacological profiles of S. doederleinii.

Keywords: Selaginella doederleinii Hieron; antioxidant; antiproliferative; apigenin derivative; flavonoid.

Figure 1

The total flavonoids content (TFC) of the ethanol extract and its fractions of S. doederleinii expressed rutin equivalents (RE) of dry weight sample. EE, ethanol extract; PE, petroleum ether; DCM, dichloromethane; EA, ethyl acetate; n-BuOH, n-butanol. All the data were expressed as mean ± standard deviation (n = 3). The letters ^(a–e) denote that the means are significantly different at a level of p < 0.05 (n = 3) by one-way ANOVA DMRT.

Figure 2

The radical scavenging percentage of ethanol extract and its PE (petroleum ether) fraction. DCM (dichloromethane), EA (ethyl acetate), and n-BuOH (n-butanol) of S. doederleinii by DPPH assay.

Figure 3

Antiproliferative activity in inhibition rate (%) at different concentrations of DCM (dichloromethane) and EA (ethyl acetate) fractions, respectively, against cancer cell lines HT-29, Hela, and A549 by the MTT assay. The cell growth inhibition rate of the ethanol extract, petroleum ether, and n-butanol could be expressed at a higher concentration than 200 µg/mL. The solvent’s inhibition rate was near zero value on all the cell lines. The data were expressed as mean ± SD (n = 3).

Figure 4

Chemical structures of isolated compounds (1–16) from DCM fraction of S. doederleinii.

Figure 5

Main ¹H-¹H COSY and HMBC correlations of compounds 1, 3, 4 and 5.

Figure 6

Free radical scavenging rates of isolated compounds from S. doederleinii by DPPH assay. The positive control used was Vitamin C (VC). Letters ^(a–f) indicate that the values are significantly different at a level of p < 0.05 (n = 3) by one-way ANOVA DMRT.

Figure 7

Antioxidant activities of isolated compounds from S. doederleinii evaluated by FRAP assay. The data were expressed as means ± SD (n = 3). The mean values denoted with letters ^(a–e) are significantly different at a level of p < 0.05 (n = 3) by one-way ANOVA DMRT.