Malaria is a disease that causes enormous human morbidity and mortality. One feature of mature Plasmodium falciparum-infected erythrocytes leading to the development of severe malaria is thought to be cytoadherence and blockage of the microvasculature. Therefore, an understanding of mechanisms that mediate parasite adhesion leading to malaria pathology is needed to yield new treatments for malaria. However, to date, cytoadherence-associated pathology is still under debate. Is cytoadherence needed to develop severe malaria? This review will discuss the available information on associations of cytoadherence with the development of severe malaria.
Chloroquine (CQ) and mefloquine (MQ) are no longer potent antimalarial drugs due to the emergence of resistant Plasmodium falciparum. Combination therapy has become the standard for many regimes in overcoming drug resistance. Roxithromycin (ROM), a known p-glycoprotein inhibitor, is reported to have antimalarial activity and it is hoped it will potentiate the effects of both CQ/MQ and reverse CQ/MQ-resistance. We assayed the effects of CQ and MQ individually and in combination with ROM on synchronized P. falciparum (Dd2 strain) cultures. The IC(50) values of CQ and MQ were 60.0+/-5.0 and 16.0+/-3.0 ng/ml; these were decreased substantially when combined with ROM. Isobolograms indicate that CQ-ROM combinations were relatively more synergistic (mean FICI 0.70) than MQ-ROM (mean FICI 0.85) with their synergistic effect at par with CQ-verapamil (VRP) (mean FICI 0.64) and MQ-VRP (mean FICI 0.60) combinations. We conclude that ROM potentiates the CQ/MQ response on multidrug-resistant P. falciparum.
Fluoxetine (FLX), a P-glycoprotein inhibitor with antimalarial activity, is promising candidate for reversing chloroquine/mefloquine (CQ/MQ) resistance. The Dd2 strain of CQ- and MQ-resistant Plasmodium falciparum was synchronized and assayed with various concentrations of CQ/MQ individually and in combination with FLX or verapamil (VPL). Our results indicated the 50% inhibitory concentration values of CQ and MQ were greatly lowered when FLX was used simultaneously. Isobolograms indicated that CQ-FLX combinations are more synergistic (mean fractional inhibitory concentration [FIC] index 0.55) than MQ-FLX (mean FIC index 0.64), and their synergistic effect was better than or at par with CQ-VPL (mean FIC index 0.88) and MQ-VPL (mean FIC index 0.60) combinations. We conclude that the FLX potentiates the CQ and MQ response on multidrug-resistant P. falciparum at clinically achievable concentrations.