Presence of Phylloquinone in the Intraerythrocytic Stages of Plasmodium falciparum.

Malaria is one of the most widespread parasitic diseases, especially in Africa, Southeast Asia and South America. One of the greatest problems for control of the disease is the emergence of drug resistance, which leads to a need for the development of new antimalarial compounds. The biosynthesis of isoprenoids has been investigated as part of a strategy to identify new targets to obtain new antimalarial drugs. Several isoprenoid quinones, including menaquinone-4 (MK-4/vitamin K2), α- and γ-tocopherol and ubiquinone (UQ) homologs UQ-8 and UQ-9, were previously detected in in vitro cultures of Plasmodium falciparum in asexual stages. Herein, we described for the first time the presence of phylloquinone (PK/vitamin K1) in P. falciparum and discuss the possible origins of this prenylquinone. While our results in metabolic labeling experiments suggest a biosynthesis of PK prenylation via phytyl pyrophosphate (phytyl-PP) with phytol being phosphorylated, on the other hand, exogenous PK attenuated atovaquone effects on parasitic growth and respiration, showing that this metabolite can be transported from extracellular environment and that the mitochondrial electron transport system (ETS) of P. falciparum is capable to interact with PK. Although the natural role and origin of PK remains elusive, this work highlights the PK importance in plasmodial metabolism and future studies will be important to elucidate in seeking new targets for antimalarial drugs.

Antimalarial activity of the terpene nerolidol.

Malaria, an infectious disease that kills more than 438,000 people per year worldwide, is a major public health problem. The emergence of strains resistant to conventional therapeutic agents necessitates the discovery of new drugs. We previously demonstrated that various substances, including terpenes, have antimalarial activity in vitro and in vivo. Nerolidol is a sesquiterpene present as an essential oil in several plants that is used in scented products and has been approved by the US Food and Drug Administration as a food-flavouring agent. In this study, the antimalarial activity of nerolidol was investigated in a mouse model of malaria. Mice were infected with Plasmodium berghei ANKA and were treated with 1000 mg/kg/dose nerolidol in two doses delivered by the oral or inhalation route. In mice treated with nerolidol, parasitaemia was inhibited by >99% (oral) and >80% (inhalation) until 14 days after infection (P <0.0001). On Day 30 post-infection, the survival rate of orally treated mice was 90% compared with 16% in controls (P <0.0001). In contrast, inhalation-treated mice showed a survival rate of 50% vs. 42% in controls (P > 0.05). The toxicity of nerolidol administered by either route was not significant, whilst genotoxicity was observed only at the highest dose tested. These results indicate that combined use of nerolidol and other drugs targeting different points of the same isoprenoid pathway may be an effective treatment for malaria.