IN-VITRO GROWTH-INHIBITION OF PLASMODIUM-FALCIPARUM BY RETINOL AT CONCENTRATIONS PRESENT IN NORMAL HUMAN SERUM

To assess the in vitro effect of retinol on Plasmodium falciparum, the standard isolates 3D7, D10, W2 and K1 in continuous culture were expo sed to retinol added in concentrations ranging from 10(-7) to 0.1 mu m ol/l. Parasite growth inhibition was assessed from H-3-hypoxanthine in corporation. Triplicate experiments were performed at physiological pH and in the case of D10, additional experiments were performed at pH 7 .2 and 7.6. Final media retinol concentrations were assayed using high performance liquid chromatography. Retinol inhibited growth of both a synchronous and synchronous cultures of 3D7 and D10 and asynchronous c ultures of W2 and K1. IC50 values determined from assayed media concen trations ranged from 0.2 to 3.9 mu mol/l and were comparable to concen trations in normal human serum (1.0-3.0 mu mol/l). IC50 values for asy chronous D10 cultures at pH 7.2 were lower than at pH 7.4 or 7.6 (0.5, 3.9 and 5.0 mu mol/l, respectively); results from synchronous culture s were similar. These data suggest that P. falciparum is a retinol-sen sitive parasite, especially at pH levels equivalent to those in an aci dotic patient. Adjunctive retinol therapy may have a role in clinical management of malaria. (C) 1998 Elsevier Science B.V. All rights reser ved.