Abstract
Survival rate of mice are dramatically increased by the administration of radioprotectors such as heat-killed Lactobacillus casei (LBC) approx. 1 day before exposure of lethal dose of ionizing radiation. To reveal the mechanism, blood parameters that reflect the survival rate were examined. We found the relationship between the survival rate and blood interleukin-1beta (IL1b) level.
Strong radioprotective effect of LBC was reconfirmed by the following experiments: All the C3H/He mice exposed at supralethal dose (8.0Gy) of X-ray were died within 19 days following the radiation. When the LBC was injected 16∼48 hours before the radiation, survival rate of the mice was 80% at Day-28. To reveal the systemic effects of the LBC-injection, we quantified the levels of cytokines in the circulation and found that IL1b level was drastically increased. Plasma IL1b level was increased at 4 hours, and reached to the maximal levels between 8 and 16 hours, then decreased to undetectable level (<10 ng/ml) at 48 hours. When glucocorticoids and their stimulator were injected with LBC, LBC-induced increases in the plasma IL1b level as well as survival rate were abolished. Co-administration of non-steroidal anti-inflammatory drugs with LBC have no effect on the IL1b levels and the survival rates. In contrast, administration of mineral corticoids with LBC enhanced the blood IL1b levels and survival rate. The data show that radioprotection by the stimulator of inflammation such as LBC are mediated by the elevation of blood IL1b.
