Haemozoin formation in the midgut of the blood-sucking insect Rhodnius prolixus

Malaria parasites digest haemoglobin and detoxify the free haem by its sequ estration into an insoluble dark-brown pigment known as haemozoin (Hz). Unt il recently, this pigment could be found only in Plasmodium parasites. Howe ver, we have shown that Hz is also present in the midgut of the blood-sucki ng insect Rhodnius prolixus [Oliveira et al. (1999) Nature 400, 517-518]. H ere we show that Hz synthesis in the midgut of this insect is promoted by a particulate fraction from intestine lumen. Haem aggregation activity is he at-labile and is inhibited in vitro by chloroquine (CLQ), Inhibition of Hz formation in vivo by feeding insects with CLQ leads to increased levels of haem in the haemolymph of the insect, which resulted in increased lipid per oxidation, Taken together, these results indicate that a factor capable of promoting Hz crystallisation is present in R. prolixus midgut and that this activity represents an important physiological defence of this insect agai nst haem toxicity. (C) 2000 Federation of European Biochemical Societies. P ublished by Elsevier Science B.V. All rights reserved.