BACKGROUND:Conditioned medium from mesenchymal stem cels (MSC-CM) that contains abundant MSCs paracrine substances may represent a promising alternative to MSCs transplantation. However, normal MSC-CM with insufficient paracrine ability is not effective for tissue damage repair. OBJECTIVE:To investigate the effects of MSC-CM with (MSC-CMHyp) and without hypoxic activation (MSC-CMNor) on the proliferation and apoptosis of radiation-induced injured intestinal epithelial cels (IEC-6) and to further discuss the paracrine mechanisms. METHODS: IEC-6 cels were exposed to 10 Gy irradiation and cultured in MSC-CMHyp, MSC-CMNor, and DMEM-F12 medium, respectively. RESULTS AND CONCLUSION: Findings from trypan blue staining, flow cytometry and western blot assay showed that, compared with the DMEM-F12 medium group, treatment with MSC-CMHyp significantly enhanced IEC-6 viability proliferation after radiation-induced injury, as wel as significantly decreased cel apoptosis and expression of Caspases-3/8 (P < 0.05). However, there was no significant difference between the MSC-CMNor group and DMEM-F12 medium group (P > 0.05). On the other hand, the increased levels of vascular endothelial growth factor, basic fibroblast growth factor, insulin-like growth factor-1, and interleukin-10 were detected in the MSC-CMHyp group compared to the MSC-CMNor group (P < 0.05). These results suggest that the MSC-CMHyp improves the viability and proliferative capacity of IEC-6 cels after radiation-induced injuryvia up-regulating secretion of cytokines and down-regulating apoptotic signaling.