We have reported previously that growth hormone (GH) therapy increases cell radiosensitivity; in this study we tested whether GH itself or IGFs induce chromosome aberrations and investigated the expression of p53 protein in response to DNA damage.
Human peripheral blood lymphocytes were incubated with GH (100 and 1000 μg L−1), insulin-like growth factor I (IGF-I; 150 and 1000 μg L−1) and IGF-II (600 and 1200 μg L−1) for 24 h. The radiomimetic agent bleomycin (BLM; 5 μg mL−1) was added in the last 3 h. Cytogenetic analysis was performed by assessing the percentages of damaged cells (%DC) and chromosome aberrations (%CA). The expression of p53 was investigated by flow cytometric assay using the monoclonal antibody DO-7, and expressed as percentage positive cells and mean fluorescence intensity.
BLM significantly increased both percentage DC and percentage CA and p53 expression (P < 0.01). The %DC was unaffected by the tested peptides. IGF-I (150 μg L−1) increased spontaneous percentage CA (P < 0.01). All peptides further increased the BLM-induced chromosome breakage: GH 100 and 1000 μg L−1 by 30% and 73% respectively, IGF-I 150 and 1000 μg L−1 by 41% and 96% respectively and IGF-II 600 and 1200 μg L−1 by 89% and 45% respectively. The spontaneous and BLM-induced expression of p53 was unaffected by GH, whereas it was significantly increased by IGFs (P < 0.001).
These results indicate that the DNA-damaging effect of BLM is amplified by GH and, more markedly, IGF-I and -II. IGF-I and -II also stimulate p53 protein expression that, taking part in DNA repair, may counteract the IGF action on genome stability.