Proliferative response of bystander cells adjacent to cells with incorporated radioactivity.
BACKGROUND
In a recent study, we showed that cells irradiated with gamma-rays stimulate cell growth of unirradiated (bystander) cells, when the two populations are co-cultured as a mixture. Direct cell-to-cell contact appears to be a prerequisite for the proliferative response of the bystander cells. The aim of the current work is to investigate the possible proliferative bystander effects caused by intracellular irradiation with incorporated radionuclides, specifically the short-range beta particle emitter, tritium ((3)H).


METHODS
Subconfluent monolayers of rat liver epithelial cells (WB-F344) were incubated in the presence of (methyl-(3)H)thymidine ((3)HTdR) at concentrations ranging between 5.2 kBq/ml and 57.8 kBq/ml for 18 h. Radiolabeled cells, containing between 0.7 x 10(-3) Bq/cell and 8.8 x 10(-3) Bq/cell were mixed with unlabeled (i.e., bystander) cells in a ratio of 1:1 and cultured together for 24 h followed by an flow cytometry (FCM) study of their proliferation. In order to discriminate the two populations of co-cultured cells, one cell population (unlabeled bystander cells) was stained with carboxyfluorescein diacetate, succinimidyl ester (CFDA SE), which metabolizes intracellularly. The absorbed doses received by the radiolabeled cells that contained 0.7 x 10(-3), 2.5 x 10(-3), and 8.8 x 10(-3) Bq/cell were 0.14, 0.49, and 1.7 Gy, respectively.


RESULTS
Cells that were not treated with tritiated thymidine (unlabeled cells), in the presence of radiolabeled cells that received absorbed doses from 0.14-1.7 Gy, showed enhanced cell growth by approximately 9 to 10%.


CONCLUSIONS
Cells labeled with (3)HTdR can induce increased proliferation in neighboring unlabeled bystander cells. FCM provides an excellent basis for characterization of proliferative bystander effects in co-culture systems.
Gerashchenko
Bogdan I
BI
Department of Radiology, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA.
Howell
Roger W
RW
D000818:Animals; D024201:Bystander Effect / Q000528:radiation effects*; D002460:Cell Line; D049109:Cell Proliferation / Q000528:radiation effects*; D002469:Cell Separation; D018920:Coculture Techniques; D003470:Culture Media / Q000737:chemistry; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D005434:Flow Cytometry; D008099:Liver / Q000166:cytology; D051381:Rats; D013936:Thymidine / Q000737:chemistry / Q000378:metabolism; D014316:Tritium / Q000378:metabolism*
D003470:Culture Media; D014316:Tritium; D013936:Thymidine