Metallothionein induction: a measure of radioprotective action

Mice treated to induce metallothionein (MT) synthesis in the liver prior to irradiation were resistant to radiation; this also was true of mice that had a portion of skin surgically removed or an immunomodulator administered. Mice given Mn, Cd or Zn subcutaneously prior to irradiation showed increased tolerance to an LD50 level (6-8 Gy) of x rays compared with controls that received no pretreatments (p less than 0.01). All the mice were evaluated during a 30-d postirradiation period. Weight loss in control mice peaked two weeks after irradiation, whereas body weight in mice pretreated with Mn continued to increase after irradiation with x rays. The normal level of MT in mouse liver (25 micrograms g-1 tissue) increased to 70 micrograms g-1 liver tissue in mice irradiated with 6.3-Gy x rays. However, following subcutaneous injection of Cd, Mn or Zn, or intraperitoneal injection of OK-432 (Picibanil, a killed streptococcal preparation, obtained from Chugai Pharmaceutical Co., Ltd., Tokyo, Japan), MT levels in liver increased by a factor of 2-8 compared to irradiated that were not treated with the reagents listed above. The mortality rate of mice with a surgically excised 2 X 2-cm2 portion of dorsal skin or of those administered OK-432 was lower than that of controls, and MT levels in liver (150-400 micrograms g-1 tissue) were higher than those of irradiated mice that were not surgically treated. These results suggest that the body's protective action against radiation correlates with the biosynthesis of MT, or that MT acts as a scavenger of radiation-induced peroxides.