Abstract: Objective To investigate the protective effect of indole- 3- carbinol (I3C) on radiation- induced mouse bone marrow hematopoietic cell injury and the involved mechanisms. Methods (1) The bone marrow nuclear cells (BMNCs) from CD45.1 subtype of C57BL/6J mice were collected by a density gradient centrifugation method. The BMNCs were pretreated with a series doses of I3C (0 mol/L, 10- 8 mol/L-10- 3 mol/L) and then exposed with radiation of 137Cs γ-ray (doses of irradiation were 0 Gy, 1 Gy and 4 Gy). After 18-hour culturing, the bioluminescence method was used to detect the cell viability. (2) These cells were divided into control group and 10- 6 mol/L I3C group. Both groups were received the irradiation (0 Gy, 1 Gy and 4 Gy) and inoculated into the methylcellulose semi-solid culture medium to incubate 7 days, the colony forming unit-granulocyte monocytes (CFU-GM) were observed. (3) Twenty-four CD45.2 subtype mice used as the receptor were exposed with 8 Gy radiation. The CD45.1 BMNCs were divided into control group, 4 Gy irradiation group, 4 Gy irradiation and 10- 6 mol/L I3C group. Donor cells were harvested from C57BL/6J (CD45.1) mice after they received various treatments, and were then mixed with competitive BMNCs from C57BL/6J (CD45.2) mice. The mixed cells were transplanted into recipient mice (8 mice/group). Flow cytometry was used to analyze the proportion of donor cells in peripheral blood of receptor. (4) The cells were divided into control group, 10- 6 mol/L I3C group, 1 Gy irradiation group, 1 Gy irradiation with 10-6 mol/L I3C group. After 24-hour culturing, Western blot assay was used to detect the expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and hemeoxygenase-1 (HO-1). Results (1) I3C showed a significant cytotoxic effect on the BMNCs when its concentration was above 10- 4 mol/L. 10- 7-10- 6 mol/L I3C could reduce the radiation injury of BMNCs under the same dose of irradiation. Therefore, 10-6 mol/L I3C was chosen for subsequent experiments. (2) The CFU-GM was significantly higher in 10-6 mol/L I3C group than that of control group (P < 0.05). (3) Results of flow cytometry showed that the proportion of donor cells in receptor was significantly higher in 4 Gy irradiation group than that of control group, which decreased the engraftment capability of irradiated HSCs (P < 0.05), although the engraftment capability of irradiated HSCs improved after 10-6 mol/L I3C treatment. (4) I3C significantly enhanced the increased protein expression of Nrf2 and HO-1 caused by radiation (P < 0.05). Conclusion I3C has a protective effect on hematopoietic cells following radiation-induced injury, which may be related with activating the Nrf2/HO-1 signal pathway.

Key words: myeloid progenitor cells, radiation injuries, radiation protection, hematopoietic stem cells, hematopoietic progenitor cells, indole-3-carbinol