The erythrocytic schizogony of two synchronized strains of Plasmodium berghei, NK65 and ANKA, in normocytes and reticulocytes

By a modified Percoll-glucose centrifugation technique the rings and young trophozoites of two strains of Plasmodium berghei, NK65 and ANKA, were separated from the other erythrocytic stages and inoculated into mice. The subsequent infection was followed for ANKA in normal mice and for NK65 in normal mice and in mice with high-grade reticulocytosis induced by injections of phenylhydrazine. The duration of the erythrocytic schizogony of the NK65 strain was shown to be independent of the age of the host cell, and the hour of inoculation did not influence the cycle of the ANKA strain

Biological activities of nitidine, a potential anti-malarial lead compound

International audienceAbstract Background Nitidine is thought to be the main active ingredient in several traditional anti-malarial remedies used in different parts of the world. The widespread use of these therapies stresses the importance of studying this molecule in the context of malaria control. However, little is known about its potential as an anti-plasmodial drug, as well as its mechanism of action. Methods In this study, the anti-malarial potential of nitidine was evaluated in vitro on CQ-sensitive and -resistant strains. The nitidine's selectivity index compared with cancerous and non-cancerous cell lines was then determined. In vivo assays were then performed, using the four-day Peter's test methodology. To gain information about nitidine's possible mode of action, its moment of action on the parasite cell cycle was studied, and its localization inside the parasite was determined using confocal microscopy. The in vitro abilities of nitidine to bind haem and to inhibit β-haematin formation were also demonstrated. Results Nitidine showed similar in vitro activity in CQ-sensitive and resistant strains, and also a satisfying selectivity index (> 10) when compared with a non-cancerous cells line. Its in vivo activity was moderate; however, no sign of acute toxicity was observed during treatment. Nitidine's moment of action on the parasite cycle showed that it could not interfere with DNA replication; this was consistent with the observation that nitidine did not localize in the nucleus, but rather in the cytoplasm of the parasite. Nitidine was able to form a 1-1 complex with haem in vitro and also inhibited β-haematin formation with the same potency as chloroquine. Conclusion Nitidine can be considered a potential anti-malarial lead compound. Its ability to complex haem and inhibit β-haematin formation suggests a mechanism of action similar to that of chloroquine. The anti-malarial activity of nitidine could therefore be improved by structural modification of this molecule to increase its penetration of the digestive vacuole in the parasite, where haemoglobin metabolization takes place

Effect of Inducers, Incubation Time and Heme Concentration on IC50 Value Variation in Anti-heme Crystallization Assay

Heme detoxification through crystallization into hemozoin has been suggested as a good target for the development of screening assays for new antimalarials. However, comparisons among the data obtained from different experiments are difficult, and the IC50 values (the concentrations of drug that are required to inhibit 50% of hemozoin formation) for the same drug vary widely. We studied the effects of changes in heme concentration (precursor of β-hematin), incubation time and three inducers (SDS, Tween 20 and linoleic acid) on the IC50 of some antimalarials (chloroquine, quinine, amodiaquine, and clotrimazole). The results showed that increasing both inducer concentration and incubation time raised the IC50 of selected antimalarials. Any change in those factors caused the IC50 value to vary. Standardization of assay conditions is, therefore, necessary to increase reproducibility and reduce discrepancies in assay performance. Considering all of the variables, the best choice of inducers is in the order of SDS > Tween 20 > linoleic acid