Exploring the erythrocyte invasion–blocking effect of modified heparin and heparin mimetics in the human malaria parasite Plasmodium falciparum

Hmoud, Muqdad Kareem

Abstract

Despite the efforts in malaria eradication and elimination, malaria still poses a global challenge to health that, through the spread of antimalarial resistance, highlights an urgent need for new approaches for malaria treatment. Heparin and sulphated glycosaminoglycans (GAGs) have been reported to have inhibition activity against intraerythrocytic stages of P.falciparum in vitro by (i) disrupting rosette formation, (ii) reversing cytoadhesion to human endothelial cell lines and (iii) blocking merozoite invasion. The extracellular form merozoites are the target of sulphated GAG inhibitors and, given relative ease of access to this stage and its essential activity in propagating an infection, an attractive target of drug development. However, due to the anticoagulation property and potential risk of heparin-induced thrombocytopaenia, heparin’s development as a potential adjunct therapy was halted.
A rapid and scalable in vitro evaluation of the inhibitory activity of sulphated GAGs is a challenge using standard fluorescent assays of parasite growth as the dyes interact with the large negatively charged sulphated GAGs. In this study, we report the development of a robust and scalable luciferase-based assay, including the preparation of a new transgenic P.falciparum parasite strain, to determine whether sulphated GAGs have potential growth inhibition activity. Two distinct P.flaciparum strains (Dd2luc & NF54luc) were also used to explore the staging of the inhibition activity during the reinvasion process. This study uses GAGs from a range of sources; chemically modified heparins, low molecular weight heparins, and GAGs from animal, plant, marine and microbial sources.
Sulphated GAGs inhibitors with good invasion-blocking potency (EC50 ranging between 2-10µg/ml) have been identified and their anticoagulation activity was shown to be reduced compared with unfractionated heparin. The staging of the effect of these compounds shows that they appear to have a profound effect on merozoite egress from an infected erythrocyte- inducing what is called here a clustered merozoite phenotype. This inhibitory effect hasn’t been recognized in previous studies for these GAGs, with only one other report of merozoite egress inhibition by unfractionated heparin available. This thesis highlight routes forward towards developing potent GAG inhibitors of merozoite release and the potential of a number of GAGs identified in this study as chemical tools to study the biology of merozoite egress from the erythrocyte. This study also discusses the implications in developing heparin mimetic with low or no anticoagulation activity, to be used as an adjunct therapy for the treatment of severe malaria.

Citation

Hmoud, M. K. (2019). Exploring the erythrocyte invasion–blocking effect of modified heparin and heparin mimetics in the human malaria parasite Plasmodium falciparum. (Thesis). Keele University. Retrieved from https://keele-repository.worktribe.com/output/414945

• Thesis Type: Thesis
• Publicly Available Date: May 26, 2023
• Public URL: https://keele-repository.worktribe.com/output/414945
• Award Date: 2019-10