title: On the pro-oxidant effects of haemozoin.
abstract: Haemozoin (Hz) is a haem aggregate produced in some blood-feeding organisms. There is a general belief that Hz formation would be a protective mechanism against haem toxicity. Here we show that when aggregated into Hz, haem is less deleterious than its free form. When haem was added to phosphatidylcholine (PC) liposomes, there was an intense stimulation of oxygen consumption, which did not occur when Hz was incubated with the same preparation. Evaluation of oxygen radical attack to lipids, by measurement of thiobarbituric acid reactive substances (TBARS), showed significantly lower levels of lipid peroxidation in samples containing PC liposomes incubated with Hz than with haem. However, TBARS production induced by Hz was much higher when using 2-deoxyribose (2-DR) as substrate, than with PC liposomes. Spin-trapping analysis by electron paramagnetic resonance (EPR) of Hz and tert-butylhydroperoxide (tert-BuOOH) showed that production of methoxyl and tert-butoxyl radicals was only slightly reduced compared to what was observed with haem. Interestingly, when large Hz crystals were used in 2-DR TBARS assays and tert-BuOOH EPR experiments, the pro-oxidant effects of Hz were strongly reduced. Moreover, increasing concentrations of Hz did not induce erythrocyte lysis, as occurred with haem. Thus, the reduced capacity of Hz to impose radical damage seems to result from steric hindrance of substrates to access the aggregated haem, that becomes less available to participate in redox reactions.
authors.affiliation: Departamento de Bioquímica Médica, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro, Av. Brigadeiro Trompowsky, s/n, Cidade Universitária, Ilha do Fundão, 21941-590, Rio de Janeiro, RJ, Brazil. maroli@bioqmed.ufrj.br
authors.forename: Marcus F
authors.initials: MF
authors.lastname: Oliveira
authors.forename: Bruno L
authors.initials: BL
authors.lastname: Timm
authors.forename: Ednildo A
authors.initials: EA
authors.lastname: Machado
authors.forename: Kildare
authors.initials: K
authors.lastname: Miranda
authors.forename: Márcia
authors.initials: M
authors.lastname: Attias
authors.forename: José R
authors.initials: JR
authors.lastname: Silva
authors.forename: Marílvia
authors.initials: M
authors.lastname: Dansa-Petretski
authors.forename: Marco A
authors.initials: MA
authors.lastname: de Oliveira
authors.forename: Wanderley
authors.initials: W
authors.lastname: de Souza
authors.forename: Nelson M
authors.initials: NM
authors.lastname: Pinhal
authors.forename: Joo J F
authors.initials: JJ
authors.lastname: Sousa
authors.forename: Ney V
authors.initials: NV
authors.lastname: Vugman
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Oliveira
mesh_terms: D000818:Animals; D005609:Free Radicals / Q000032:analysis; D006418:Heme / Q000633:toxicity*; D006420:Hemeproteins / Q000633:toxicity*; D006461:Hemolysis; D015227:Lipid Peroxidation; D017382:Reactive Oxygen Species / Q000633:toxicity*; D012239:Rhodnius; D017392:Thiobarbituric Acid Reactive Substances / Q000032:analysis
chemical_list: D005609:Free Radicals; D006420:Hemeproteins; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; C020753:hemozoin; D006418:Heme