Effects of organic and inorganic selenium supplementation on selenoenzyme activity in blood lymphoctyes, granulocytes, platelets and erythrocytes

The blood selenium (Se) concentration in the U.K. population has declined b y approx. 50% between 1974 and 1991, reflecting a large decrease in dietary Se supply, with intakes only half the reference nutrient intake of 1 mu g/ kg body weight. Tissue levels of Se are readily influenced by dietary intak e. Therefore selenoprotein activity may be sub-optimal due to low Se status , and thus compromise normal cell function. To examine the effects of chang ing Se intake on selenoproteins, we have determined the relative effectiven ess of organic selenomethionine and inorganic sodium selenite (50 mu g of S e daily for 28 days) in modulating glutathione peroxidase activities in blo od cells from 45 healthy men and women, from a U.K. population. Transient a nd acute changes in lymphocyte, granulocyte and platelet phospholipid-hydro peroxide glutathione peroxidase (GP x 4) activity occurred by day 7 or 14 o f sodium selenite treatment and by day 7 in lymphocytes from selenomethioni ne-treated subjects compared with controls taking a placebo. In contrast, G P x 4 activity in granulocytes and platelets in the selenomethionine group increased gradually over the 28 days. Cytosolic glutathione peroxidase (GP x 1) activity in these blood cells from both treatment groups increased gra dually over the 28 days. For each cellular selenoenzyme activity a signific ant inter-individual difference (P < 0.001) in the extent of the response t o Se supplementation was observed, but this was not related to blood Se con centrations either before or after treatments. Significant inverse correlat ions were evident between baseline enzyme activities and percentage change in activity after 28 days of supplementation [e.g. lymphocyte GPx4, r = -0. 695 (P < 0.001)], indicating that pretreatment activity may be sub-optimal as a result of poor Se status. The different and contrasting effects that S e supplementation had on blood selenoenzyme activities may be indicative of a difference in metabolic need for Se regulated at the level of Se-depende nt cell function.