Dual effects of Pepstatin A on Plasmodium falciparum asexual blood-stage and early gametocyte development

Background Plasmodium falciparum is the most important species of malaria parasites, capable of causing severe illness and mortality, especially in pregnant women and children under the age of 5. In the patient's blood, the asexual stage and gametocyte cause harmful manifestations, impacting the patients and contributing to the spread of the disease in the community, respectively. Unfortunately, most recent drugs targeting the asexual blood-stage do not affect the gametocyte. The discovery of a new drug with dual effects on both stages would be 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. Methods Pepstatin A, the representative of the board-spectrum aspartyl protease inhibitor, was utilized to investigate its inhibitory effects on parasite development. The experiments were separately performed in vitro for four different developmental stages of parasites, including the asexual blood-stage, early developmental stage of gametocytes, late developmental stage of gametocytes, and gamete formation. To demonstrate the effect 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. Moreover, morphological changes in pepstatin A-treated parasites were illustrated to observe alterations in parasite development. Results Pepstatin A (100 µM) inhibited the asexual stage and early-stage gametocyte development by 47% and 73%, respectively. Besides, the parasite also exhibited morphological defects, including 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. Conclusions Pepstatin A exhibited a dual effect by inhibiting both asexual blood-stage and early-stage gametocyte development, suggesting its potential for reducing the severity of the disease and minimizing transmission. However, for its practical application in treatment, further research and development are required, with a focus on identifying drug targets and modifying the drug to be more sensitive and effective. Graphical abstract