On the pro-oxidant effects of haemozoin.
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.
Oliveira
Marcus F
MF
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
Timm
Bruno L
BL
Machado
Ednildo A
EA
Miranda
Kildare
K
Attias
Márcia
M
Silva
José R
JR
Dansa-Petretski
Marílvia
M
de Oliveira
Marco A
MA
de Souza
Wanderley
W
Pinhal
Nelson M
NM
Sousa
Joo J F
JJ
Vugman
Ney V
NV
Oliveira
Pedro L
PL
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
D005609:Free Radicals; D006420:Hemeproteins; D017382:Reactive Oxygen Species; D017392:Thiobarbituric Acid Reactive Substances; C020753:hemozoin; D006418:Heme