title: Haemozoin formation in the midgut of the blood-sucking insect Rhodnius prolixus.
abstract: Malaria parasites digest haemoglobin and detoxify the free haem by its sequestration into an insoluble dark-brown pigment known as haemozoin (Hz). Until recently, this pigment could be found only in Plasmodium parasites. However, we have shown that Hz is also present in the midgut of the blood-sucking insect Rhodnius prolixus [Oliveira et al. (1999) Nature 400, 517-518]. Here we show that Hz synthesis in the midgut of this insect is promoted by a particulate fraction from intestine lumen. Haem aggregation activity is heat-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 peroxidation. 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 against haem toxicity.
authors.affiliation: Departamento de Bioquimica Médica, Universidaade Federal do Rio de Janeiro, Cidade Universitária Ilha do Fundão, Centro de Ciências de Saúde, Av. Brigadeiro Trompowsky, sln, Rio de Janeiro, Brazil. maroli@bioqmed.ufrj.br
authors.forename: M F
authors.initials: MF
authors.lastname: Oliveira
authors.forename: J R
authors.initials: JR
authors.lastname: Silva
authors.forename: M
authors.initials: M
authors.lastname: Dansa-Petretski
authors.forename: W
authors.initials: W
authors.lastname: de Souza
authors.forename: C M
authors.initials: CM
authors.lastname: Braga
authors.forename: H
authors.initials: H
authors.lastname: Masuda
authors.forename: P L
authors.initials: PL
authors.lastname: Oliveira
mesh_terms: D000818:Animals; D001685:Biological Factors / Q000032:analysis / Q000494:pharmacology; D002738:Chloroquine / Q000494:pharmacology; D003460:Crystallization; D005260:Female; D006418:Heme / Q000378:metabolism* / Q000633:toxicity; D006420:Hemeproteins / Q000096:biosynthesis* / Q000378:metabolism; D006458:Hemolymph / Q000378:metabolism; D006358:Hot Temperature; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000737:chemistry; D015227:Lipid Peroxidation / Q000187:drug effects; D008854:Microscopy, Electron; D010860:Pigments, Biological / Q000096:biosynthesis / Q000378:metabolism; D011803:Quinine / Q000494:pharmacology; D012239:Rhodnius / Q000033:anatomy & histology* / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D001685:Biological Factors; D006420:Hemeproteins; D010860:Pigments, Biological; C020753:hemozoin; D006418:Heme; D002738:Chloroquine; D011803:Quinine