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 μmol/L of Se from dl-selenomethionine (Se-Met), sodium selenite (Na₂SeO₃) or Kappa-selenocarrageenan (Se-Car). Compared with controls, a significantly lower level of release of lactic dehydrogenase (LDH) was observed at 0.5–5 μmol/L of Se-Met, 0.5–1 μmol/L of Na₂SeO₃ and 0.5 μmol/L of Se-Car, but significantly higher LDH release was observed at 2–5 μmol/L of Na₂SeO₃ and 3–5 μmol/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 μmol/L of Se-Met, 1.5 μmol/L of Na₂SeO₃ and 2 μmol/L of Se-Car, respectively. Furthermore, 3 μmol/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, Na₂SeO₃ and Se-Car are 3, 1.5 and 2 μmol/L, respectively.