The Carotenoid Biosynthesis Pathway In The Asexual Intraerythrocytic Stages Of Plasmodium Falciparum: In Vitro Inhibiton Assays, HPLC Profiling Of Carotenoids And Bioinformatics Analysis

ABSTRACT

Plasmodium falciparum, like other Apicomplexans, has retained a relict plastid known as the apicoplast. This organelle represents a new and exciting target for the chemotherapeutic management of malaria because it houses metabolic pathways that are unique to the parasite such as isoprenoid biosynthesis. The phytoene synthase (PSY) gene, has been demonstrated to be very important in carotenogenesis, however, little is known about the evolutionary relatedness of this gene in P. falciparum and other Apicomplexans. This study therefore aimed at profiling the carotenoids synthesized in the asexual intraerythrocytic stages of P. falciparum and to determine the evolutionary history and relatedness of the PSY gene in Apicomplexans and other organisms. In vitro inhibition assays were performed on the asexual intraerythrocytic stages of P. falciparum using fluridone to determine its IC50 and effect on parasite population. HPLC was used to profile carotenoids synthesized at the asexual stages and to determine the evolutionary history and relatedness of the PSY gene in Apicomplexans and other organisms, an unrooted phylogenetic tree was generated using MEGA 6. A dose-dependent inhibition of parasite population was observed with fluridone treatment on all the asexual stages, with the ring stages being the most susceptible. The carotenoid profiles showed that synthesis of carotenoids in P. falciparum is cumulative through the asexual intraerythrocytic stages with carotenoids such lycopene, α-, β-carotene among others being synthesized. An exciting novel finding of this study was the discovery of relatively high amounts of abscisic acid (ABA) in the schizont stages and not in the other stages. This is the first time ABA has been demonstrated to be synthesized by P. falciparum and it would be pioneering to further investigate the specific role of ABA in P. falciparum schizont stages. The phylogenetic analysis showed that the P. falciparum PSY was most related to P. xii reichenowi, the chimpanzee strain of the malaria causing parasites further lending support to the proposed origin of malaria species in humans.