Transformation in vitro of Leishmania mexicana amastigotes to promastigotes: nutritional requirements and the effect of drugs

Abstract

An in vitro system is described in which over 85% of a population of Leishmania mexicana mexicana amastigotes transforms to promastigotes within 48 h. The differentiation process involves 3 morphologically and biochemically distinct intermediates, including a division stage. Cell division is shown to be necessary for complete development to promastigotes. Foetal calf serum (FCS) has been found to be an essential component of the medium for high percentage transformation to be achieved. One of the important components of the FCS has been identified as non-esterified fatty acids, and these support a relatively high percentage of amastigotes through transformation in the absence of FCS, possibly due to their use as energy substrates. Only small numbers of amastigotes transform to promastigotes if glucose or amino acids are the only energy substrates available. Transformation is inhibited by a number of metabolic inhibitors including anti-leishmanial and other anti-protozoal drugs. The stage at which inhibition is apparent varies with the inhibitor. It is suggested that the system described for the transformation in vitro of L. m. mexicana amastigotes to promastigotes may be the best method available at present for studying the metabolism and drug sensitivity of amastigotes free from possible interference by host macrophage components.