title: The roles of TGF-β3 and peroxynitrite in removal of hyper-radiosensitivity by priming irradiation.
abstract: OBJECTIVE
  To investigate the mechanisms inducing and maintaining the permanent elimination of low dose hyper-radiosensitivity (HRS) in cells given a dose of 0.3 Gy at low dose-rate (LDR) (0.3 Gy/h).
  
  
  METHODS
  Two human HRS-positive cell lines (T-47D, T98G) were used. The effects of pretreatments with transforming growth factor beta (TGF-β) neutralizers, TGF-β3 or peroxynitrite scavenger on HRS were investigated using the colony assay. Cytoplasmic levels of TGF-β3 were measured using post-embedding immunogold electron microscopic analysis.
  
  
  RESULTS
  TGF-β3 neutralizer inhibited the removal of HRS by LDR irradiation. Adding 0.001 ng/ml TGF-β3 to cells removed HRS in T98G cells while 0.01 ng/ml additionally induced resistance to higher doses. Cytoplasmic levels of TGF-β3 were higher in LDR-primed cells than in unirradiated cells. The presence of the peroxynitrite scavenger uric acid inhibited the effect of LDR irradiation. Furthermore, the permanent elimination of HRS in LDR-primed cells was reversed by treatment with uric acid. The removal of HRS by medium from hypoxic cells was inhibited by adding TGF-β3 neutralizer to the medium before transfer or by adding hypoxia inducible factor 1 (HIF-1) inhibitor chetomin to the cell medium during hypoxia.
  
  
  CONCLUSIONS
  TGF-β3 is involved in the regulation of cellular responses to small doses of acute irradiation. TGF-β3 activation seems to be induced by low dose-rate irradiation by a mechanism involving inducible nitric oxide (iNOS) and peroxynitrite, or during cycling hypoxia by a mechanism most likely involving HIF-1. The study suggests methods to turn resistance to doses in the HRS-range on (by TGF-β3) or off (by TGF-β3 neutralizer or by peroxynitrite inhibition).
authors.affiliation: Department of Physics, University of Oslo , Norway.
authors.forename: Nina Jeppesen
authors.initials: NJ
authors.lastname: Edin
authors.forename: Joe Alexander
authors.initials: JA
authors.lastname: Sandvik
authors.forename: Chang
authors.initials: C
authors.lastname: Cheng
authors.forename: Linda
authors.initials: L
authors.lastname: Bergersen
authors.forename: Erik Olai
authors.initials: EO
authors.lastname: Pettersen
mesh_terms: D015687:Cell Hypoxia / Q000187:drug effects / Q000528:radiation effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D003593:Cytoplasm / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000494:pharmacology*; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000187:drug effects* / Q000528:radiation effects; D013997:Time Factors; D053782:Transforming Growth Factor beta3 / Q000494:pharmacology*
chemical_list: D053782:Transforming Growth Factor beta3; D030421:Peroxynitrous Acid; D052247:Nitric Oxide Synthase Type II
keywords: TGF-β3; low dose hyper-radiosensitivity; low dose-rate irradiation; peroxynitrite