Abstract
The rich source of heme within malarial parasites has been considered to underly the action specificity of artemisinin. We reasoned that increasing intraparasitic free heme levels might further sensitize the parasites to artemisinin. Various means, such as modulating heme synthesis, degradation, polymerization, or hemoglobin digestion, were tried to boost intracellular heme levels, and under several scenarios, free heme levels were significantly augmented. Interestingly, all results arrived at the same conclusion, i.e., elevating heme acted in a strongly negative way, impacting the antimalarial action of artemisinin, but exerted no effect on several other antimalarial drugs. Suppression of the elevated free heme level by introducing heme oxygenase expression effectively restored artemisinin potency. Consistently, zinc protoporphyrin IX/zinc mesoporphyrin, as analogues of heme, drastically increased free heme levels and, concomitantly, the EC50 values of artemisinin. We were unable to effectively mitigate free heme levels, possibly due to an unknown compensating heme uptake pathway, as evidenced by our observation of efficient uptake of a fluorescent heme homologue by the parasite. Our results thus indicate the existence of an effective and mutually compensating heme homeostasis network in the parasites, including an uncharacterized heme uptake pathway, to maintain a certain level of free heme and that augmentation of the free heme level negatively impacts the antimalarial action of artemisinin. Importance: It is commonly believed that heme is critical in activating the antimalarial action of artemisinins. In this work, we show that elevating free heme levels in the malarial parasites surprisingly negatively impacts the action of artemisinin. We tried to boost free heme levels with various means, such as by modulating heme synthesis, heme polymerization, hemoglobin degradation and using heme analogues. Whenever we saw elevation of free heme levels, reduction in artemisinin potency was also observed. The homeostasis of heme appears to be complex, as there exists an unidentified heme uptake pathway in the parasites, nullifying our attempts to effectively reduce intraparasitic free heme levels. Our results thus indicate that too much heme is not good for the antimalarial action of artemisinins. This research can help us better understand the biological properties of this mysterious drug.
Highlights
Malaria remains one of the major threats to global public health; it is estimated to have caused 241 million cases and 627,000 deaths worldwide in 2020 [1]
To study the interaction of heme and artemisinin in Plasmodium falciparum, we first tried to investigate whether exogenous heme could affect the antimalarial effect of artemisinin
The addition of hemin to the medium decreased the sensitivity of P. falciparum to artemisinin (Figure 1), whereas the addition of the corresponding solvent (0.1 M NaOH) had little effect (Supplementary Figure S1D)
Summary
Malaria remains one of the major threats to global public health; it is estimated to have caused 241 million cases and 627,000 deaths worldwide in 2020 [1]. Malaria is caused by parasites of the genus Plasmodium, especially by Plasmodium falciparum, which is transmitted by the Anopheles mosquito. Artemisia annua [5,6], and a number of derivatives, such as dihydroartemisinin, artemether and artesunate, have been synthesized. These semisynthetic compounds (Artemisinins) exhibit improvement over artemisinin in solubility and efficacy [7]. K13, were discovered to be connected to the reduced artemisinin sensitivity in some patients [11]. These mutations led to corresponding in vitro change in the ring-stage survival assay (RSA0–3 h ) of artemisinins [10,12]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
