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Intraerythrocytic malaria parasite has evolved a unique pathway to detoxify hemoglobin-derived heme by forming a crystal of Ferri-protoporphyrin IX dimers, known as hemozoin or "malaria pigment." The prooxidant activity of beta-hematin (BH), the synthetic malaria pigment obtained from hematin at acidic pH, was studied in arachidonic acid micelles and phospholipid Large Unilamellar Vesicles (LUVs) and compared to that of alpha-hematin (AH, Ferri-protoporphyrin IX-hydroxide) and hemin (HE, Ferri-protoporphyrin-chloride). Lipid peroxidation was measured as production of thiobarbituric acid reactive substances (TBARS). The extent of peroxidation induced by either AH or BH was strongly dependent upon the content of pre-existing hydroperoxides and efficiently inhibited by triphenylphosphine, a deoxygenating agent able to reduce hydroperoxides to hydroxides and by lipophilic scavengers. BH prooxidant activity was linearly related to the material, whereas that of AH seemed dependent on the aggregation state of the porphyrin. Maximal activity was observed when AH was present in concentration lower than 2 microM. In this case a shift of spectra in the Soret region, leading to the increase of the O.D. 400/385 nm ratio, suggested a transition toward a less aggregated state. BH prooxidant activity was significantly lower than that of monomeric AH, yet higher than that of AH aggregates. Differently from AH aggregates, BH-induced peroxidation was unaffected by GSH and inhibited rather than enhanced by acidic pH (5.7) and chloroquine. UV/Vis spectroscopy of AH aggregates at acidic pH, low GSH concentrations and chloroquine suggests a shift of AH aggregates toward the less aggregated state, more active as peroxidation catalyst.

Original publication

DOI

10.1016/s0006-2952(01)00558-5

Type

Journal article

Journal

Biochemical pharmacology

Publication Date

04/2001

Volume

61

Pages

999 - 1009

Addresses

Institute of General Physiology and Biochemistry, University of Milan, Via Trentacoste 2, I-20134-, Milan, Italy.

Keywords

Erythrocytes, Cell Membrane, Humans, Heme, Hemin, Chloroquine, Arachidonic Acid, Phospholipids, Glutathione, Hemeproteins, Free Radical Scavengers, Oxidants, Spectrum Analysis, Lipid Peroxidation, Oxidative Stress, Drug Interactions, Micelles, Hydrogen-Ion Concentration, Statistics as Topic