In vitro analyses of Artemisia extracts on Plasmodium falciparum suggest a complex antimalarial effect

Abstract

Dried-leaf Artemisia annua L. (DLA) antimalarial therapy was shown effective in prior animal and human studies, but little is known about its mechanism of action. Here IC50s and ring-stage assays (RSAs) were used to compare extracts of A. annua (DLAe) to artemisinin (ART) and its derivatives in their ability to inhibit and kill Plasmodium falciparum strains 3D7, MRA1252, MRA1240, Cam3.11 and Cam3.11rev in vitro. Strains were sorbitol and Percoll synchronized to enrich for ring-stage parasites that were treated with hot water, methanol and dichloromethane extracts of DLA, artemisinin, CoArtem™, and dihydroartemisinin. Extracts of A. afra SEN were also tested. There was a correlation between ART concentration and inhibition of parasite growth. Although at 6 hr drug incubation, the RSAs for Cam3.11rev showed DLA and ART were less effective than high dose CoArtem™, 8 and 24 hr incubations yielded equivalent antiparasitic results. For Cam3.11, drug incubation time had no effect. DLAe was more effective on resistant MRA-1240 than on the sensitive MRA-1252 strain. Because results were not as robust as observed in animal and human studies, a host interaction was suspected, so sera collected from adult and pediatric Kenyan malaria patients was used in RSA inhibition experiments and compared to sera from adults naïve to the disease. The sera from both age groups of malaria patients inhibited parasite growth ≥ 70% after treatment with DLAe and compared to malaria naïve subjects suggesting some host interaction with DLA. The discrepancy between these data and in-vivo reports suggested that DLA’s effects require an interaction with the host to unlock their potential as an antimalarial therapy. Although we showed there are serum-based host effects that can kill up to 95% of parasites in vitro, it remains unclear how or if they play a role in vivo. These results further our understanding of how DLAe works against the malaria parasite in vitro.

Artemisinin as a therapeutic vs. its more complex Artemisia source material

“…The sexual stage includes male and female gametocytes that can reside in the blood for some time acting as a parasite reservoir and are responsible for asymptomatic malaria. A. annua and A. afra tea infusions kill both blood asexual 5,6,84 and gametocyte stages 5,6 in vitro , results that corroborate clinical observations. 65,85,86 Recently, Ashraf et al 5 showed that tea infusions of the artemisinin-deficient species, A. afra , were more effective than artemisinin-containing A. annua against both rings and schizonts, and even more effective than dihydroartemisinin (DHA).…”

“…While artemisinin is well-established as a potent bioactive molecule with significant antimalarial activity, a growing number of studies have shown that there is considerable antimalarial activity from the plant that extends beyond artemisinin. For example, the studies already described in Section 4.1 on malaria 5,6,65,84–86 clearly demonstrate that artemisinin is not the sole antimalarial molecule in A. annua . In fact, Ashraf et al , 2022 showed that artemisinin-free A. afra has potent antimalarial activity.…”

“…Furthermore, A. annua proved effective at eliminating artemisinin-resistant parasites in another rodent model, in contrast to pure artemisinin. 4 Indeed, there are many phytochemicals in the plant that have antimalarial activity, albeit weaker than artemisinin as summarized in Gruessner and Weathers 84 and that may explain the observed in vitro antimalarial effects of artemisinin-free Artemisia sp. 5,6 Although the WHO argues that use of A. annua causes artemisinin resistance, they have not offered any direct evidence to support that stance.…”

Nanoparticles: Synthesis and Their Role as Potential Drug Candidates for the Treatment of Parasitic Diseases

“…This kit, based on AuNPs, indicates the presence of the protein by the formation of a ring that can be analyzed visually. Hence, this kit can be used to detect malarial parasites [ 58 ].…”

Green synthesis and characterization of zinc oxide nanoparticles using extracts of Artemisia annua l. grown in Togo

“…The present study concerns ZnONPs biosynthesized from plant extracts (Artemisia annua L.) used as a bio-reducer. Artemisia annua L. is known for its medical value and the extracts from its leaves are believed to have organic molecules that have antioxidant activities to help reducing zinc to nanoparticles [31,32].…”