title: Clotrimazole binds to heme and enhances heme-dependent hemolysis: proposed antimalarial mechanism of clotrimazole.
abstract: Two recent studies have demonstrated that clotrimazole, a potent antifungal agent, inhibits the growth of chloroquine-resistant strains of the malaria parasite, Plasmodium falciparum, in vitro. We explored the mechanism of antimalarial activity of clotrimazole in relation to hemoglobin catabolism in the malaria parasite. Because free heme produced from hemoglobin catabolism is highly toxic to the malaria parasite, the parasite protects itself by polymerizing heme into insoluble nontoxic hemozoin or by decomposing heme coupled to reduced glutathione. We have shown that clotrimazole has a high binding affinity for heme in aqueous 40% dimethyl sulfoxide solution (association equilibrium constant: K(a) = 6.54 x 10(8) m(-2)). Even in water, clotrimazole formed a stable and soluble complex with heme and suppressed its aggregation. The results of optical absorption spectroscopy and electron spin resonance spectroscopy revealed that the heme-clotrimazole complex assumes a ferric low spin state (S = 1/2), having two nitrogenous ligands derived from the imidazole moieties of two clotrimazole molecules. Furthermore, we found that the formation of heme-clotrimazole complexes protects heme from degradation by reduced glutathione, and the complex damages the cell membrane more than free heme. The results described herein indicate that the antimalarial activity of clotrimazole might be due to a disturbance of hemoglobin catabolism in the malaria parasite.
authors.affiliation: Department of Applied Biology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
authors.forename: Nguyen Tien
authors.initials: NT
authors.lastname: Huy
authors.forename: Kaeko
authors.initials: K
authors.lastname: Kamei
authors.forename: Takushi
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Kondo
authors.forename: Kenji
authors.initials: K
authors.lastname: Kanaori
authors.forename: Ryo
authors.initials: R
authors.lastname: Takano
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Tajima
authors.forename: Saburo
authors.initials: S
authors.lastname: Hara
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000378:metabolism* / Q000494:pharmacology*; D003022:Clotrimazole / Q000378:metabolism* / Q000494:pharmacology*; D005978:Glutathione / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006461:Hemolysis; D006801:Humans; D010963:Plasmodium falciparum / Q000187:drug effects; D011485:Protein Binding; D013057:Spectrum Analysis
chemical_list: D000962:Antimalarials; D006418:Heme; D003022:Clotrimazole; D005978:Glutathione