Aspartyl protease inhibition interferes with Plasmodium falciparum asexual blood-stage and early gametocyte development

Background Plasmodium falciparum is the most influential species of malaria parasites, capable of causing severe illness and mortality, especially in pregnant women and children under the age of 5. Global distribution of disease impacted on billions of endemic people and travelers. Asexual stage and gametocyte cause harmful manifestations, impacting the patients and contributing to the spread of the disease in the community, respectively. Moreover, most recent therapeutic drugs did not affect the gametocyte. The discovery of a new drug with dual actions on both stages could elucidate a cost-effective way to combat malaria. Within a human host, the parasite possesses many activities for its survival, such as invasion, egress, hemoglobin degradation, and protein trafficking, many of which are related to aspartyl protease, revealing the potential for antimalarial drug targets. Methods Pepstatin A, the representative of the board-spectrum aspartyl protease inhibitor, was utilized to investigate the effects of aspartyl protease inhibition on parasite development. The experiments were separately performed in vitro for different developmental stages of parasites, including the asexual blood-stage, early gametocytes, late gametocytes, and gamete. To demonstrate the effects of pepstatin A, the number of intact parasites and their stage distribution were counted under the microscope and calculated as a percentage of inhibition compared to the control. Additionally, the morphology of pepstatin A-treated parasites was observed to identify cellular alterations in the parasites. Results Pepstatin A at 100 µM inhibited the asexual stage and early-stage gametocyte development by 47% and 73%, respectively. They exhibited morphological defects, including chromatin condensation, vacuolization and hemozoin clumping in both asexual blood-stage and early-stage gametocyte. However, it could not influence the late-stage gametocyte development and gamete formation. Conclusion The inhibition of aspartyl protease by pepstatin A moderately affected both asexual blood-stage and early-stage gametocyte development. Morphological changes on treated parasites implied the effect of pepstatin A on hemoglobin degradation process, suggesting its potential for reducing the severity of the disease and minimizing malaria transmission. However, further research and development are required to use aspartyl protease as a drug target, focusing on identifying and modifying the drug to be more sensitive and effective.