Early epidermal response after a single dose of gamma-rays in organotypic culture of human breast skin

BACKGROUND: Skin reaction is the most common side-effect of radiation therapy. Radiation-induced dermal fibrosis has been characterized histologically, but little is known about the epidermis overlying fibronecrotic lesions. OBJECTIVES: To characterize the epidermal response 24 h after a single clinically relevant dose of gamma-rays in cultured human breast skin. METHODS: Biopsies obtained from cosmetic surgery (n = 7) were placed epidermis upwards in a Transwell system, and were exposed to a single dose of gamma-irradiation (2 Gy). A parallel set of nonirradiated skin fragments was incubated under the same conditions. Both irradiated and nonirradiated fragments were harvested 24 h after irradiation and processed for light microscopy and molecular biology analysis. A quantitative analysis of cell proliferation was performed after 5-bromo-2'-deoxyuridine incorporation. Cytokeratin 10 (CK10) and desmocollin 1 (Dsc1) expression was evaluated by immunofluorescence. Dsc1 and transforming growth factor (TGF)-beta1 gene expression was measured by reverse transcriptase-polymerase chain reaction analysis. RESULTS: The mean percentage inhibition of epidermal proliferation in irradiated samples was 53.7% (P < 0.01, paired Student's t-test). The inhibition of cell proliferation was significant in five of seven samples (P < 0.05, unpaired Student's t-test). Normal cell architecture was found in irradiated samples. Throughout the epithelial compartment, the distribution patterns of CK10 and Dsc1 were comparable in nonirradiated and irradiated fragments. Condensation of CK10 filaments suggested a cytoskeletal rearrangement in irradiated samples. Dsc1 and TGF-beta1 mRNA levels were, respectively, reduced and unmodified 24 h after irradiation. CONCLUSIONS: A perturbation of epidermal homeostasis occurs as early as 24 h after a single dose of gamma-rays. Our immunofluorescence observations indicate that keratinocyte terminal differentiation is not yet affected at the protein level 24 h after exposure to gamma-rays. The lack of an inverse relationship between TGF-beta1 gene expression and epidermal proliferation, together with decreased Dsc1 gene expression, may represent the early molecular basis for the development of the late effects of radiotherapy observed many months/years after radiotherapy. Our findings set the stage for further investigation of the best time to begin topical treatment at the start of radiation therapy.