Modification of survival and hematopoiesis in mice by tocopherol injection following irradiation.

The LD50/30 of CD-1 female mice increased from 6.6 Gy to 7.0 Gy when 2.5 mg of dl-alpha-tocopherol was injected immediately post irradiation. Increased survival was associated with increased numbers of hematopoietic colony forming units (CFU). Endogenous spleen colonies were found in greater numbers in the tocopherol-treated mice after irradiation. The vitamin, however, must be injected within five hours following irradiation to have this effect. The increased numbers of CFU in tocopherol-treated mice may be due to a stimulation of recovery or repair processes. Split-dose studies suggest that most repair of sublethal damage in hematopoietic stem cells take place within seven and nine hours following irradiation. Tocopherol injection appears to enhance the recovery manifested in the split-dose assay. There is also evidence that tocopherol-treatment caused an earlier onset of mitotic activity in CFU after irradiation. The increased number of spleen colonies in tocopherol-injected mice is not due to an altered CFU seeding efficiency associated with an altered spleen microenvironment. Tocopherol injection did not affect the shoulder of the stem cell survival curve using exogenous spleen colony assays of bone marrow-derived or spleen-derived hematopoietic stem cells. There appears to be a decrease in Do in the higher dose region (4.3 Gy) of the bone marrow exogenous SCA survival curves for the vehicle-injected and the non-injected groups; however, the tocopherol-injected group showed no evidence of change in radiosensitivity up to the highest dose used (5.0 Gy). Data may be interpreted to suggest that the therapeutic effect of tocopherol may involve repair of hematopoietic stem cell damage in the higher dose range of bone marrow syndrome.