Radiation-induced differentiation of human skin fibroblasts: relationship with cell survival and collagen production.

The aim of this study was to determine whether significant inter-individual differences exist between skin fibroblast strains obtained from radiotherapy patients in both radiation-induced differentiation and collagen production in vitro, for use as potential parameters for a predictive assay for fibrosis following radiotherapy in patients. Morphological cell differentiation was determined 7 days after irradiation in seven early-passage primary human fibroblast cell strains and correlated with cell survival. Collagen production was measured in two cell strains by flow cytometry and incorporation of 3H-proline. There was a wide variation in the extent of radiation-induced differentiation for the seven cell strains, each showing a dose-related increase. The correlation between induced differentiation and cell survival was poor (r = 0.64) but statistically significant (p < 0.01). Collagen synthesis increased 7 days after irradiation for one cell strain (HF-48), as measured by incorporation of 3H-proline, but not in radiation sensitive AT-1 cells. The collagen I content of the two cell strains was assessed by flow cytometry but no significant differences were observed between the strains tested or with increasing dose. In conclusion, marked variations in radiation-induced fibroblast differentiation were observed between patients, this being an important criterion for a predictive assay.