Increased radioiodine uptake of thyroid cell cultures after external irradiation.
BACKGROUND
Radioiodine uptake (RIU) is one of the main prognostic factors for curative results of radioiodine therapy in patients with differentiated thyroid cancer. Some days after application of (131)I, the uptake of a subsequent administration of radioiodine was found to be reduced. In contrast, early after irradiation with high-energy photons glucose and amino acid uptake were observed to be increased. Effects of external irradiation on RIU of thyrocytes using high-energy photons have not been investigated so far.


METHODS
Two different cell lines (FRTL-5 and ML-1 cells) derived from thyroid tissue were studied in vitro. Cell lines were either incubated with (131)I only (controls) or additionally irradiated with single doses of 6 or 10 Gy of high-energy photons using a linear accelerator. Cell number and RIU were determined 24-96 h after (131)I application. RIU measurements were repeated after application of sodium perchlorate in excess to investigate specificity of the uptake. Statistical analyses were performed using non-parametric tests.


RESULTS
Incubation with radioiodine as well as irradiation with high-energy photons slowed down proliferation in investigated cell lines significantly. Irradiation with solely (131)I resulted in stable or slightly decreased iodide uptake. Compared to those cells, the RIU increased significantly in externally irradiated cells, i. e., additional irradiation with 10 Gy resulted in an almost threefold increase of RIU in FRTL-5 after 72 h. The increase of RIU after irradiation was dose-dependent in both cell lines and could be blocked by perchlorate excess.


CONCLUSIONS
It could be demonstrated that external irradiation increases RIU in thyroid cell cultures early after irradiation. The increase was dose-dependent and specific, as it could be blocked by perchlorate. This effect appears to be similar to the increase of other actively transported substances after irradiation with high-energy photons. Therefore, the results of this study may contribute to the knowledge of a generalized irradiation-induced mechanism which causes the activation of different cellular transporters. The clinical impact of these findings on combined therapy concepts has to be investigated in further experiments.
Meller
Birgit
B
Clinic of Radiotherapy and Nuclear Medicine, University of Luebeck, Germany. meller@nuk.uni-luebeck.de
Deisting
Wibke
W
Wenzel
Björn E
BE
Pethe
Annette
A
Nadrowitz
Roger
R
Meller
Johannes
J
Richter
Eckart
E
Baehre
Manfred
M
D000818:Animals; D002452:Cell Count; D002460:Cell Line; D003627:Data Interpretation, Statistical; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007454:Iodides / Q000378:metabolism; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics*; D010472:Perchlorates / Q000494:pharmacology; D017785:Photons; D011829:Radiation Dosage; D051381:Rats; D017670:Sodium Compounds / Q000494:pharmacology; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D013997:Time Factors
D007454:Iodides; D007457:Iodine Radioisotopes; D010472:Perchlorates; D017670:Sodium Compounds; C031068:sodium perchlorate