Exposure of Normal Human Fibroblasts to Heavy-Ion Radiation Promotes Their Morphological Differentiation

Abstract

Here we investigated the potential impact of energetic heavy ions on fibroblast differentiation. The differentiation pattern was morphologically determined at days 3 and 5 after exposure to graded dose of γ-rays (0.2 keV/μm) or carbon ions (18.3 MeV/u, 108 keV/μm). The cells irradiated with higher doses progressed toward later differentiation stages as time goes postirradiation, but underwent fewer cell divisions. Thus, radiation exposure accelerated morphological differentiation, for which carbon ions were more effective than γ-rays. The relative biological effectiveness of carbon ions for differentiation was higher than that for the clonogenic survival, and this was the most case for terminally differentiated cells that may not divide any more. The results are suggestive of the distinct mechanism underlying inactivation of clonogenic potential between the radiation quality, such that the contribution of the differentiation to heavy ion-induced reductions in the survival is greater than to those induced by photons. Such accelerated differentiation could be a protective mechanism that minimizes further expansion of aberrant cells.