title: The radioprotective properties of fungal melanin are a function of its chemical composition, stable radical presence and spatial arrangement.
abstract: Melanized microorganisms are often found in environments with very high background radiation levels such as in nuclear reactor cooling pools and the destroyed reactor in Chernobyl. These findings and the laboratory observations of the resistance of melanized fungi to ionizing radiation suggest a role for this pigment in radioprotection. We hypothesized that the radioprotective properties of melanin in microorganisms result from a combination of physical shielding and quenching of cytotoxic free radicals. We have investigated the radioprotective properties of melanin by subjecting the human pathogenic fungi Cryptococcus neoformans and Histoplasma capsulatum in their melanized and non-melanized forms to sublethal and lethal doses of radiation of up to 8 kGy. The contribution of chemical composition, free radical presence, spatial arrangement, and Compton scattering to the radioprotective properties of melanin was investigated by high-performance liquid chromatography, electron spin resonance, transmission electron microscopy, and autoradiographic techniques. Melanin protected fungi against ionizing radiation and its radioprotective properties were a function of its chemical composition, free radical quenching, and spherical spatial arrangement.
authors.affiliation: Department of Nuclear Medicine, Albert Einstein College of Medicine, Bronx, NY, USA. edadacho@aecom.yu.edu
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Dadachova
authors.forename: Ruth A
authors.initials: RA
authors.lastname: Bryan
authors.forename: Robertha C
authors.initials: RC
authors.lastname: Howell
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Schweitzer
authors.forename: Philip
authors.initials: P
authors.lastname: Aisen
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Nosanchuk
authors.forename: Arturo
authors.initials: A
authors.lastname: Casadevall
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003455:Cryptococcus neoformans / Q000737:chemistry* / Q000528:radiation effects* / Q000648:ultrastructure; D004307:Dose-Response Relationship, Radiation; D016166:Free Radical Scavengers; D005720:Gamma Rays; D008543:Melanins / Q000737:chemistry* / Q000502:physiology*; D046529:Microscopy, Electron, Transmission; D015394:Molecular Structure; D011836:Radiation Tolerance
chemical_list: D016166:Free Radical Scavengers; D008543:Melanins