A polyphenol, pyrogallol changes the acidic pH of the digestive vacuole of Plasmodium falciparum

Pyrogallol has a capability of generating free radicals like other antimalarial drugs such as artemisinin, which is thought to inhibit the proton pump located in the membrane of the Plasmodium falciparum digestive vacuole, thus alkalinising this acidic organelle. This study aimed to determine pH changes of the malaria parasite’s digestive vacuole following treatment with pyrogallol. The antimalarial activity of this compound was evaluated by a malarial SYBR Green 1 fluorescence-based assay to determine the 50% inhibitory concentration (IC50). Based on the IC50 value, different concentrations of pyrogallol were selected to ensure changes of the digestive vacuole pH were not due to parasite death. This was measured by flow cytometry after 4-hour pyrogallol treatment on the fluorescein isothiocyanate-dextran-accumulated digestive vacuole of the mid-trophozoite stage parasites. Pyrogallol showed a moderate antimalarial activity with the IC50 of 2.84 ± 9.40 µM. The treatment of 1.42, 2.84 and 5.67 µM pyrogallol increased 2.9, 3.0 and 3.1 units of the digestive vacuole pH, respectively as compared with the untreated parasite (pH 5.6 ± 0.78). The proton pump, V-type H+-ATPase might be inhibited by pyrogallol, hence causing the digestive vacuole pH alteration, which is similar with the result shown by a standard V-type H+-ATPase inhibitor, concanamycin A. This study provides a fundamental understanding on the antimalarial activity and mechanism of action of pyrogallol that has a potential to be the antimalarial drug candidate.