Purpose: This investigation is aimed to determine the role of low LET (linear energy transfer, gamma-rays) and high LET (alpha-particles) radiations on bystander effect of using the same type of cells and its implications on colony-forming efficiency from a single cell.
Materials and methods: Normal human fetal lung (MRC-5), immortalized repair deficient ataxia telangiectasia mutated (ATM) (GM5,849C) and normal (GM637H) fibroblast cells were used. Colony-forming efficiency in bystander cells (GM637H) was studied using the medium transfer technique from the two donor (MRC-5 and GM5,849C) cells and the procedure followed for bystander treatment is presented schematically in Figure 1. Evidence of change in colony formation in bystander cells, was assessed by scavenging nitric oxide (NO).
Results: Enhancement of 10 - 30% in colony-forming efficiency was observed in bystander GM637H cells treated with irradiated conditioned medium (ICM) from MRC-5 cells collected 1 h after different doses of either gamma-rays (1, 2.5, 5 and 10 Gy) or alpha particles (0.25, 0.5, 1 and 2.5 Gy) irradiation. Similar results were obtained when ICM derived from the ATM (GM5,849C) cells. However, the stimulation was not dose dependent. Furthermore, we also show that the increase in dilutions of ICM (1:1, 1:5 and 1:10) showed an inverse correlation with cloning efficiency. Treatment of MRC-5 cells with PTIO (2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide) a NO scavenger, 1 h prior to irradiation reduced the enhancement of ICM mediated cell survival.
Conclusions: In the present study, though both the low and high LET radiations enhanced the clonogenic potential of the bystander recipient cells, medium from the ATM defective (GM5,849C) cells after gamma-irradiation showed less stimulating effect than the medium from the normal (MRC-5) cells. However, after alpha-irradiation an inverse effect was seen. NO may play an important role in enhancing the growth potential in these bystander cells.