title: Protective effects of melatonin against low- and high-LET irradiation.
abstract: To investigate the protective effects of melatonin against high-LET ionizing radiation, V79 Chinese hamster cells were irradiated with 100 keV/microm carbon beam. Parallel experiments were performed with 200 kV X-rays. To avoid the impact from extra solvents, melatonin was dissolved directly in culture medium. Cells were cultured in melatonin medium for 1 hr before irradiation. Cell inactivation was measured with conventional colony forming assay, medium containing 6-thioguanine was used for the selection of mutants at hprt locus, and the cell cycle was monitored by flow cytometry. Both carbon beam and X-rays induced cell inactivation, hprt gene mutation and cell cycle G2 block dose-dependently. But carbon beam showed stronger effects as indicated by all three endpoints and the relative biological effectiveness (RBE) was 3.5 for cell killing (at 10% survival level) and 2.9 for mutation induction (at 5 x 10(-5) mutants/cell level). Melatonin showed protective effects against ionizing radiation in a dose-dependent manner. In terms of cell killing, melatonin only increased the survival level of those samples exposed to 8Gy or larger of X-rays or 6 Gy or larger of carbon beam. In the induction of hprt mutation and G2 block, melatonin reduced such effects induced by carbon beam but not by X-rays. The results suggest that melatonin reduces the direct interaction of particles with cells rather than an indirect interaction. Further studies are required to disclose the underlying mechanisms.
authors.affiliation: Radiobiology Group, Institute of Modern Physics, Chinese Academy of Sciences, China.
authors.forename: Guangming
authors.initials: G
authors.lastname: Zhou
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Kawata
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.forename: Mizuho
authors.initials: M
authors.lastname: Aoki
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Hirayama
authors.forename: Koichi
authors.initials: K
authors.lastname: Ando
authors.forename: Hisao
authors.initials: H
authors.lastname: Ito
mesh_terms: D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects* / Q000528:radiation effects*; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000528:radiation effects*; D020450:Heavy Ions; D018499:Linear Energy Transfer; D008550:Melatonin / Q000008:administration & dosage*; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000187:drug effects; D011837:Radiation-Protective Agents / Q000008:administration & dosage; D014965:X-Rays
chemical_list: D011837:Radiation-Protective Agents; D008550:Melatonin