Chromosomal instability in various generations of human mesenchymal stem cells following the therapeutic radiation doses

Background: Radiotherapy is thecrucial treatment for most malignancies, however; it has short and long-term side effects. The occurrence of secondary cancer following radiation-induced genomic instability in stem cells is an important long-term side effect of radiation therapy. The radiation response of human mesenchymal stromal cells (hMSCs) is critical in cancer patients who are treated with radiotherapy for hMSCs lifetime proliferative potential. Evaluation of genomic instability in human mesenchymal stem cells at different radiation doses and times, and examining the relative expression of some effective genes, have been the objectives of this study. Methods: After extraction, characterization, and expansion of hMSCs, they were irradiated for 0, 0.5, 2, and 6 Grays. Nuclear alterations were evaluated at 2, 10, and 15 days after irradiation using the cytokinesis-block micronucleus assay. As well as TP53, Bax, Bcl2, and KRAS gene expressions were analyzed 48 hours post-irradiation for genomic response evaluation. Results: The mean incidence of micronucleus, nucleoplasmic bridges, and nuclear buds incidences were 4.8±1.6, 47.6±6, and 18±2.6, respectively, 48 hours after the fourth passage in the non-irradiated (control) group for one thousand binucleated cells. Micronuclei incidences in 0.5, 2, and 6 grays radiation groups were 14.3±4.9, 32.3±6.5 and 55±9.1 respectively in 48 hours after irradiation and 12.6±1.5, 19±5.5, and 22.3±5.2, respectively ten days post-irradiations. Conclusion: Low levels of nuclear alterations as genomic instability markers were seen in various cell generations of control groups, which must be considered for cell therapy and regenerative medicine applications. In the irradiated groups, chromosomal aberration increased significantly with the dose, 2days post-irradiation due to a disproportionate increase in the Bax/Bcl2 ratio and high expression of the KRAS gene. significant nuclear alterations were seen in the tenth to fifteenth generations of irradiated hMSCs due to radiation-induced genomic instability which may persuade secondary malignancies in the following years after the radiotherapy treatment of patients.