title: Bystander and delayed effects after fractionated radiation exposure.
abstract: Human immortalized keratinocytes were exposed to a range of single or fractionated doses of gamma rays from (60)Co, to medium harvested from donor cells exposed to these protocols, or to a combination of radiation and irradiated cell conditioned medium (ICCM). The surviving fractions after direct irradiation or exposure to ICCM were determined using a clonogenic assay. The results show that medium harvested from cultures receiving fractionated irradiation gave lower "recovery factors" than direct fractionated irradiation, where normal split-dose recovery occurred. The recovery factor is defined here as the surviving fraction of the cells receiving two doses (direct or ICCM) separated by an interval of 2 h divided by the surviving fraction of cells receiving the same dose in one exposure. After treatment with ICCM, the recovery factors were less than 1 over a range of total doses from 5 mGy-5 Gy. Varying the time between doses from 10 min to 180 min did not alter the effect of ICCM, suggesting that two exposures to ICCM are more toxic than one irrespective of the dose used to generate the response. In certain protocols using mixtures of direct irradiation and ICCM, it was possible to eliminate the bystander effect. If bystander factors are produced in vivo, then they may reduce the sparing effect of the dose fractionation.
authors.affiliation: Radiation and Environmental Science Centre, Dublin Institute of Technology, Fitzwilliam House, 30 Upper Pembroke Street, Dublin 2, Ireland. cmothersill@rsc.iol.ie
authors.forename: Carmel
authors.initials: C
authors.lastname: Mothersill
authors.forename: C B
authors.initials: CB
authors.lastname: Seymour
mesh_terms: D024201:Bystander Effect / Q000187:drug effects / Q000528:radiation effects*; D016923:Cell Death / Q000187:drug effects / Q000528:radiation effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D003470:Culture Media; D017077:Culture Media, Conditioned / Q000378:metabolism / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D005720:Gamma Rays / Q000009:adverse effects*; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D003470:Culture Media; D017077:Culture Media, Conditioned