Regulation of expression and activity of selenoenzymes by different forms and concentrations of selenium in primary cultured chicken hepatocytes.

The expression and activity of selenoenzymes are regulated by Se. In the present study, the effects of different forms and concentrations of Se on the regulation of glutathione peroxidase (GPx) activity and phospholipid hydroperoxide GPx (GPx4) and type I deiodinase (D1) mRNA levels in chicken hepatocytes were evaluated. Primary cultured chicken hepatocyte monolayers derived from male White Leghorn chickens (aged 30-40 d) were incubated for 24 h with 0 (control), 0.5, 1, 1.5, 2, 3, 4 or 5 µmol/l of Se supplied as dl-selenomethionine (Se-Met), κ-selenocarrageenan (Se-Car) or sodium selenite (Na2SeO3). Compared with the control, Se significantly increased GPx activity in all the hepatocytes, but the activity was not increased in the hepatocytes treated with 5 µmol/l of Na2SeO3, with maximal effects being observed at 2 µmol/l of Se-Met or Se-Car and at 1.5 µmol/l of Na2SeO3, respectively. Significant decreases in GPx4 mRNA levels were observed in all the hepatocytes treated with Se (v. control). The D1 mRNA levels were significantly increased in all the groups treated with Se (v. control), with maximal effects being observed at 1.5 µmol/l of Se-Met and at 0.5 µmol/l of Se-Car or Na2SeO3, respectively. Se-Met at doses of 1.5-5 µmol/l had a greater effect on D1 mRNA than Se-Car and Na2SeO3 at equivalent doses. After resulting in a maximal effect, higher Se supplementation led to a dose-dependent reduction in GPx activity and D1 mRNA levels in all the hepatocytes treated with Se. These results suggest that in chicken hepatocytes, the regulations of GPx and D1 by different forms and concentrations of Se vary.

Regulation of cellular glutathione peroxidase by different forms and concentrations of selenium in primary cultured bovine hepatocytes.

The expression and activity of cellular glutathione peroxidase (GPx1) are regulated by selenium (Se). Generally speaking, organic forms of Se have less toxicity and greater bioavailability compared with inorganic forms. In this study, the effects of different forms and concentrations of Se on the regulation of mRNA level and activity of GPx1 in bovine hepatocytes were evaluated, and the optimal doses of different forms of Se that supported the full expression of GPx1 were determined. Primary cultured bovine hepatocyte monolayers derived from neonatal male Holstein calves (aged 1-2 days) were incubated for 24 h with 0 (control), 0.5, 1, 1.5, 2, 3, 4 or 5 micromol/L of Se from dl-selenomethionine (Se-Met), sodium selenite (Na(2)SeO(3)) or Kappa-selenocarrageenan (Se-Car). Compared with controls, a significantly lower level of release of lactic dehydrogenase (LDH) was observed at 0.5-5 micromol/L of Se-Met, 0.5-1 micromol/L of Na(2)SeO(3) and 0.5 micromol/L of Se-Car, but significantly higher LDH release was observed at 2-5 micromol/L of Na(2)SeO(3) and 3-5 micromol/L of Se-Car, and the response occurred in a dose-dependent manner. The intracellular content of reduced glutathione in all hepatocytes treated with Se was significantly lower than that of controls. Significant increases in GPx1 mRNA were obtained in all hepatocytes treated with Se, with maximal effects at 3 micromol/L of Se-Met, 1.5 micromol/L of Na(2)SeO(3) and 2 micromol/L of Se-Car, respectively. Furthermore, 3 micromol/L of Se from Se-Met resulted in peak levels of GPx1 mRNA. After reaching a maximal level, higher Se supplementation led to a reduction of GPx1 mRNA. The activity of GPx1 showed similar patterns but of lower magnitude. We conclude that (a) the regulation of mRNA level and activity of GPx1 in primary cultured bovine hepatocytes by different forms of Se varies and (b) the optimal doses of Se to support the full expression of GPx1 in bovine hepatocytes when supplied as Se-Met, Na(2)SeO(3) and Se-Car are 3, 1.5 and 2 micromol/L, respectively.