Differential activation of NF-κB and nitric oxide in lymphocytes regulates in vitro and in vivo radiosensitivity.
Lymphocytes are more sensitive to radiation in vivo than in vitro. However, the mechanism of this differential response is poorly understood. In the present study, it was found that the lipid peroxidation and cell death were significantly higher in lymphocytes following whole body irradiation (WBI) as compared to lymphocytes exposed to radiation in vitro. EL-4 cells transplanted in mice were also more sensitive to radiation than EL-4 cells irradiated in vitro. DNA repair, as assessed by comet assay, was significantly faster in lymphocytes exposed to 4Gy radiation in vitro as compared to that in lymphocytes obtained from whole body irradiated mice exposed to the same dose of radiation. This was associated with increased NF-κB activation in response to genotoxic stress and lesser activation of caspase in lymphocytes in vitro compared to in vivo. To explain the differential radiosensitivity, we postulated a role of nitric oxide, an extrinsic diffusible mediator of radiosensitivity that has also been implicated in DNA repair inhibition. Nitric oxide levels were significantly elevated in the plasma of whole body irradiated mice but not in the supernatant of cells irradiated in vitro. Addition of sodium nitroprusside (SNP), a nitric oxide donor to cells irradiated in vitro inhibited the repair of DNA damage and enhanced apoptosis (increased Bax to Bcl-2 ratio). Administration of l-NAME, a nitric oxide synthase inhibitor, to mice significantly protected lymphocytes against WBI-induced DNA damage and inhibited in vivo radiation-induced production of nitric oxide. These results confirm that the observed differential radiosensitivity of lymphocytes was due to slow repair of DNA due to nitric oxide production in vivo.
Sharma
Deepak
D
Radiation Biology & Health Sciences Division, Bio-Medical Group, Bhabha Atomic Research Centre, Modular Laboratories, Trombay, Mumbai, Maharashtra 400 085, India.
Sandur
Santosh K
SK
Rashmi
R
R
Maurya
D K
DK
Suryavanshi
Shweta
S
Checker
Rahul
R
Krishnan
Sunil
S
Sainis
K B
KB
D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D002478:Cells, Cultured; D004249:DNA Damage / Q000528:radiation effects; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation / Q000528:radiation effects; D015227:Lipid Peroxidation / Q000528:radiation effects; D008214:Lymphocytes / Q000378:metabolism / Q000528:radiation effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000378:metabolism / Q000493:pharmacokinetics*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism / Q000528:radiation effects*; D009599:Nitroprusside / Q000494:pharmacology; D011836:Radiation Tolerance
D016328:NF-kappa B; D009599:Nitroprusside; D009569:Nitric Oxide; D003907:Dexamethasone; D019331:NG-Nitroarginine Methyl Ester