Assessment of the in vitro activity and selectivity of Artemisia afra and Artemisia annua aqueous extracts against artemisinin-resistant Plasmodium falciparum.

BACKGROUND

The recent emergence of artemisinin resistance in Africa is drawing scrutiny toward the use of alternative anti-malarial therapy based on Artemisia annua and Artemisia afra phytotherapies. This study aimed to determine if either A. annua and A. afra extracts are active against artemisinin-resistant Plasmodium falciparum isolates and determine the selectivity of inhibitory phytotherapies.

METHODS

Artemisia extracts were tested in vitro to mimic parasites exposure to extracts in population drinking Artemisia sp. teas. Artemisia extracts were tested in Ring Stage Survival Assays (RSA0-3 h) against Cambodian clinical isolates previously genetically and phenotypically characterized as artemisinin resistant or sensitive. Primary human hepatocytes and a human hepatoblastoma cell line (HepG2 cells) were used to assess the cytotoxicity of Artemisia extracts.

RESULTS

The study revealed a substantially decreased in vitro activity of A. annua extracts when tested on artemisinin-resistant parasites mutated in the Pfkelch13 gene (RSA50 0.137-2.56 g.L-1) compared to artemisinin-sensitive parasites (RSA50 0.080 g.L-1). Conversely, the A. afra extracts have a similar activity on the isolates tested whether they are sensitive or resistant to artemisinin (RSA50 0.537-0.758 g.L-1) However, the selectivity index for A. afra extracts was much lower than for A. annua extracts (A. afra: 4.628, 4.305 and 6.076 vs A. annua: 387.625, 226.350 and 12.099, respectively for WT, C580Y and R539T).

CONCLUSIONS

Artemisia annua activity is driven by artemisinin, implicating the same resistance profiles and concerns associated with semisynthetic artemisinin derivatives. Artemisia afra showed artemisinin-independent antiplasmodial activity. However, the molecular basis of this activity is unknown and may not present a sufficient selectivity, thus further characterization of A. afra is essential.