Antioxidant Activity and Antiproliferative Effects of Acmella alba, Acmella oleracea, and Acmella calirrhiza
Authors: Weintraub Lindsey , Naftzger Trisha , Parr Tyler , Henning Shelby , Soendergaard Mette 
Published: April 2020

Plants of the genus Acmella are found in subtropical parts of the southern hemisphere. A few species are utilized as medicinal herbs to treat various illnesses such as stomatitis, snake bites, and tuberculosis. However, there is little research documenting antiproliferative and antioxidant properties of the plants.

Plants of the genus Acmella are found in subtropical parts of the southern hemisphere. A few species are utilized as medicinal herbs to treat various illnesses such as stomatitis, snake bites, and tuberculosis. However, there is little research documenting antiproliferative and antioxidant properties of the plants.

In order to investigate the antiproliferative and antioxidant activities of plants of the Acmella genus, Acmella alba, Acmella oleracea, and Acmella calirrhiza were separated into leaves, roots, stems, and flowers, freeze‐dried, and ground into a fine powder. For antioxidant activity assays and determination of phenolic content, plant powders were extracted using 1% HCl in 90% aqueous methanol for 2 h. The antioxidant capacity of extracts was then analyzed using 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH), and 2,2'‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) assays. The radical scavenging of each extract was compared to a 6‐hydroxy‐2,5,7,8‐tetramethylchroman‐2‐carboxylic acid (trolox) standard and was calculated as trolox equivalents (TE; μmol/g dry weight). Both assays revealed that the roots of all three plants contained the lowest antioxidant capacity compared to the leaves, stems, and flowers (Table
1).

The phenolic content was determined using the Folin‐Ciocalteu assay. In correlation with the DPPH and ABTS assays, the roots showed the lowest phenolic content for all three plants. For Acmella alba, and Acmella oleracea, the leaves exhibited the highest phenolic content. Acmella calirrhiza demonstrated the highest phenolic content in the flowers (Table
1).

For analysis of cell viability, plant materials were extracted thrice using ethanol for 24 h. Extracts were then evaporated overnight at 50°C, and then resuspended in DMSO to a final concentration of 20 mg/mL. Human ovarian adenocarcinoma (SKOV‐3) cells were treated with 0.2 mg/mL of each extract, 100 μM paclitaxel, or dimethyl sulfoxide (DMSO; vehicle) for 48 h at 37°C, 5% CO2. Cell viability was then determined using a tetrazolium reduction assay. In brief, 0.45 mg/mL 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) was incubated with the cells for 4 h, after which formed formazan crystals were dissolved using DMSO. The absorbance at 570 nm was then measured spectrophotometrically. As expected, paclitaxel showed a significant decrease in cell viability. Additionally, the leaves, roots, and stems of Acmella alba, the leaves, and roots of Acmella oleracea, and the leaves, stems, and flowers of Acmella calirrhiza resulted in a significant decrease in the cell viability of SKOV‐3 cells compared to DMSO.

Antioxidant capacity and phenolic content of Acmella, Acmella oleracea, and Acmella.

DPPH (TE: μmol/g dry weight)
mean±SEM

ABTS (TE: μmol/g dry weight)
mean±SEM

DPPH (GAE: μmol/g dry weight)
mean±SEM

Acmella alba

 Leaves

8.07±0.45

6.90±0.66

11.34±0.22

 Roots

10.91±0.30

13.97±0.39

24.61±0.73

 Stems

10.58±0.18

15.98±0.23

51.24±0.91

 Flowers

10.99±0.13

11.97±0.19

31.80±0.59

Acmella oleracea

 Leaves

8.60±0.36

4.53±0.21

8.15±0.12

 Roots

10.25±0.38

12.20±0.33

18.94±0.34

 Stems

10.44±0.14

16.74±0.11

63.13±1.00

 Flowers

10.75±0.10

13.93±0.16

37.93±0.68

Acmella calirrhiza

 Leaves

8.52±1.08

6.34±0.37

18.52±0.14

 Roots

10.34±0.39

11.77±0.56

21.74±0.29

 Stems

11.08±0.05

15.03±0.23

43.25±0.66

 Flowers

11.18±0.04

15.20±0.29

49.00±0.44