Abstract
Plasmodium falciparum is the causative agent of malaria, a deadly infectious disease for which treatments are scarce and drug-resistant parasites are now increasingly found. A comprehensive method of identifying and quantifying metabolites of this intracellular parasite could expand the arsenal of tools to understand its biology, and be used to develop new treatments against the disease. Here, we present two methods based on liquid chromatography tandem mass spectrometry for reliable measurement of water-soluble metabolites involved in phospholipid biosynthesis, as well as several other metabolites that reflect the metabolic status of the parasite including amino acids, carboxylic acids, energy-related carbohydrates, and nucleotides. A total of 35 compounds was quantified. In the first method, polar compounds were retained by hydrophilic interaction chromatography (amino column) and detected in negative mode using succinic acid-13C4and fluorovaline as internal standards. In the second method, separations were carried out using reverse phase (C18) ion-pair liquid chromatography, with heptafluorobutyric acid as a volatile ion pairing reagent in positive detection mode, using d9-choline and 4-aminobutanol as internal standards. Standard curves were performed in P. falciparum-infected and uninfected red blood cells using standard addition method (r2> 0.99). The intra- and inter-day accuracy and precision as well as the extraction recovery of each compound were determined. The lower limit of quantitation varied from 50 pmol to 100 fmol/3 × 107cells. These methods were validated and successfully applied to determine intracellular concentrationsofmetabolitesfromuninfectedhostRBCsandisolatedPlasmodiumparasites.