The metabolism of selenite and selenomethionine in mouse fibroblasts grown in tissue culture

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Abstract
Recent reports have provided evidence that selenium is an essential growth factor for cells grown in tissue culture. The aim of the work reported in this paper was to evaluate mouse fibroblasts as a model for the study of selenium metabolism in mammalian cells. The results showed that transformed mouse lung fibroblasts grown in media containing 9.1% bovine serum did not show a growth response to added selenium as selenite over the range of 10–1000 ng/mL. Uptake of selenium by cells was a direct function of the selenium concentration in the medium. The rate of uptake varied with the time of exposure of the cells to the selenium, and to the form of selenium in the medium. Experiments using radioactive selenium showed that75Se from selenite was rapidly absorbed into the cell wall, but slowly incorporated into the soluble protein fraction.75Se from selenomethionine was more slowly absorbed into the cells, but once inside, it became rapidly incorporated into soluble cytoplasmic proteins. Cell fractionation and gel filtration procedures established that75Se from selenite was rapidly incorporated into glutathione peroxidase (GSHpx), whereas75Se from selenomethionine was initially incorporated into a wide spectrum of proteins and only after a longer period did the75Se peak become associated with GSHpx. These findings suggest fundamental differences exist in the manner in which mammalian cells initially absorb and metabolize different selenium compounds.