title: Chloroquine inhibits the intracellular multiplication of Legionella pneumophila by limiting the availability of iron. A potential new mechanism for the therapeutic effect of chloroquine against intracellular pathogens.
abstract: Chloroquine and ammonium chloride, by virtue of their basic properties, have been shown to raise endocytic and lysosomal pH and thereby interfere with normal iron metabolism in a variety of cell types, including mononuclear phagocytes. Cellular iron metabolism is of critical importance to Legionella pneumophila, an intracellular bacterial pathogen whose capacity to multiply in human mononuclear phagocytes is dependent upon the availability of intracellular iron. In view of this, we have studied the effects of chloroquine and ammonium chloride on L. pneumophila intracellular multiplication in human monocytes. Chloroquine, at a concentration of 20 microM, and ammonium chloride, at a concentration of 20 mM, inhibited L. pneumophila intracellular multiplication by 1.4 +/- 0.2 (SEM) logs and 1.5 +/- 0.2 logs, respectively. Chloroquine- and ammonium chloride-induced inhibition of L. pneumophila intracellular multiplication was completely reversed by iron nitrilotriacetate, an iron compound which is soluble in the neutral to alkaline pH range, but not by iron transferrin, which depends upon acidic intracellular conditions to release iron. Chloroquine had no major direct effect on L. pneumophila multiplication in artificial media except at extremely high concentrations (15,000-fold that which inhibited L. pneumophila multiplication in mononuclear phagocytes), and inhibition at such concentrations was not reversed by iron nitrilotriacetate. This study demonstrates that chloroquine and ammonium chloride inhibit the intracellular multiplication of L. pneumophila by limiting the availability of iron to the bacterium. It is possible that such a mechanism of action underlies chloroquine's antimicrobial effect against other intracellular pathogens, such as the agents of malaria and tuberculosis.
authors.affiliation: Department of Medicine, School of Medicine, University of California, Los Angeles 90026.
authors.forename: T F
authors.initials: TF
authors.lastname: Byrd
authors.forename: M A
authors.initials: MA
authors.lastname: Horwitz
mesh_terms: D000328:Adult; D000643:Ammonium Chloride / Q000494:pharmacology; D002738:Chloroquine / Q000494:pharmacology* / Q000627:therapeutic use; D004351:Drug Resistance; D005290:Ferric Compounds / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D007875:Legionella / Q000187:drug effects* / Q000502:physiology; D009000:Monocytes / Q000378:metabolism / Q000382:microbiology; D009571:Nitrilotriacetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D014168:Transferrin / Q000494:pharmacology
chemical_list: D005290:Ferric Compounds; D014168:Transferrin; D000643:Ammonium Chloride; D002738:Chloroquine; D007501:Iron; D009571:Nitrilotriacetic Acid; C020326:ferric nitrilotriacetate