Background This study aimed to confirm the cytotoxicity of zymosan in vitro and in vivo and determine the appropriate treatment time and the dose of zymosan. Methods AHH-1 cells and HIECs were administered by 0, 20, 40, 80 or 160 μg/mL zymosan. The CCK-8 assay and flow cytometry were used to evaluate the cell viability and apoptosis 24 h, 48 h, and 72 h after administration. Furthermore, 12 h before irradiation, the cells were treated with 0, 5, 10, or 20 μg/mL zymosan and then irradiated with 4 Gy X-rays. Cell viability and apoptosis were measured by the CCK-8 assay and flow cytometry at 24 h. In addition, the protective effect of zymosan against radiation in vitro was compared to that of 20 μg/mL LPS. In vivo, weight, the spleen index, and the thymus index were measured to evaluate the toxicity of 0, 5, 10, 20, and 10 mg/kg zymosan. In addition, rats were treated with 0, 2, 4, 8, or 10 mg/kg zymosan and then irradiated with 7 Gy X-rays. The survival rate, organ index were evaluated. The protective effect of zymosan against radiation in vivo was compared to that of 10 mg/kg LPS a positive control. Results The viability and apoptosis of cells treated with different doses and treatment times of zymosan were not different from those of control cells (p < 0.05). Furthermore, cell viability and apoptosis were clearly improved after zymosan preadministration (p < 0.05). The radioprotective effect of zymosan was dose-dependent. In addition, the viability of cells pretreated with zymosan was higher than that of cells pretreated with LPS, and the apoptosis rate of zymosan-treated cells was lower than that of cells pretreated with LPS (p < 0.05). In vivo, weight, the spleen index and the thymus index were significantly decreased by zymosan at a concentration of 20 mg/kg (p < 0.05). Further experiments showed that the concentration at which zymosan exerted radioprotective effects was 10 mg/kg. The survival curves in the irradiated rats were barely separated between the LPS treatment and zymosan treatment. Conclusion Zymosan administration before radiation exposure significantly increased cell viability and the survival rates of rats.

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Background: This study was to confirm the radiation protective effect of different doses of zymosan on AHH-1 and HIEC cells irradiated at different times and different doses, and further to explore whether zymosan exerts a radiation protection mechanism by targeting TLR2/4.Methods: AHH-1 and HIEC cells were respectively administered to Zymosan at 0, 20, 40, 80 and 160 μg/ml. CCK-8 and cell flow cytometry were used to detect the cell activity and apoptosis at 24 h, 48 h, and 72 h after administration to determine the dose-limiting toxicities of zymosan. Twelve hours before irradiation, cells were treated with zymosan at 0, 5, 10, and 20 μg/ml, and then irradiated with 4Gy X-rays. The cell activity and apoptosis were measured by CCK-8 and cell flow cytometry at 24 h to determine the optimal dose of zymosan. LPS was used as a positive control to compare the protective effect of zymosan. The cells were treated with MyD88 inhibitors to explore the protective mechanism of zymosan.Results: The activity of AHH-1 and HIEC cells treated with different concentration of zymosan at different time was not affected and the apoptosis of cells was not promoted. The radiation protection effect of Zymosan pretreated cells on cells is dose-dependent. After zymosan pre-treated the cells, its radiation protection effect on the cells was dose-dependent. The higher zymosan’s concentration was, the stronger the activities of AHH-1 cells and HIEC cells were, and the lower the apoptosis rate was. The activity of cells pretreated with zymosan was higher than that pretreated with LPS at the same dose (20 μg/ml), and the cell apoptosis rate was lower than that pretreated with LPS. After zymosan pretreated AHH-1 and HIEC cells, TLR2/4-MyD88-G-CSF/GM-CSF/IL-12/IL-6 pathway was activated.Conclusion: Zymosan is nontoxic to cells and has better radiation protection effect than LPS. Its mechanism of action is related to the activation of the TLR2/4-MyD88/G-CSF/GM-CSF/IL-12/IL-6 pathway.