Influence of the origin and level of dietary protein on TBI-induced oxidative damage in mice.

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The influence of the origin and level of dietary protein on oxidative damage of lipid, protein, and DNA in mice after total body irradiation (TBI) was examined. Male mice were fed two types of dietary protein (casein and soybean protein) and different dietary protein levels (casein, 8% and 20%; soybean protein, 8% and 20%), and then treated with TBI with X-rays. The levels of lipid peroxides and chromosomal damage did not differ among the groups that did not receive TBI. However, the oxidative damage of lipid increased due to TBI only in the 8% protein group. The chromosomal damage in bone marrow increased due to TBI regardless of the different protein diets, and the damage was higher in the 8% protein group than that in the 20% protein group. Protein carbonyl levels were consistently higher in the 8% protein group than in the 20% protein group. In the 8% protein group, a greater decrease in the relative spleen weight was also observed. Concentrations of antioxidants [vitamins C, E, and glutathione (GSH)] in the liver were lower, and the concentration of non-heme iron in the liver was higher in the 8% protein group than in the 20% protein groups. Mice fed a low-protein diet became susceptible to TBI-induced oxidative damage regardless of the origin of protein. Vitamin C and E values of the soybean protein group were markedly lower than those of the casein group.