Hydrogen peroxide degradation and glutathione peroxidase activity in cultures of thyroid cells

Abstract

The degradation rate of H 2O 2, added to the incubation medium, and glutathione (GSH) peroxidase activity were measured in cultures of FRTL-5 cells and porcine thyroid cells. The H 2O 2 degradation rate increased proportionally to the H 2O 2 concentration and was in FRTL-5 cells, cultured with TSH, ∼50 nmol/min and mg DNA at 0.01 mM H 2O 2 and ∼3 × 10 4 nmol/min and mg DNA at 10 mH H 2O 2. The GSH peroxidase activity in the same cells was equivalent to an H 2O 2 degradation of ∼400 nmol/min and mg DNA. The involvement of enzymes in H 2O 2 degradation was studied by inhibiting catalase with aminotriazole (ATZ) and reducing GSH peroxidase by omitting glucose in the incubation medium. At 0.1 mM H 2O 2, ATZ or glucose omission alone did not measurably reduce H 2O 2 degradation but did so when combined. At 10 mM H 2O 2 ATZ caused a clear inhibition whereas glucose omission had no additive effect. These observations indicate that GSH peroxidase was involved in H 2O 2 degradation only at low H 2O 2 concentrations. The GSH peroxidase activity decreased by reduction of the selenite supply and increased after replenishment. The recovery of the enzyme activity required the presence of TSH in FRTL-5 cells but not in porcine thyrocytes.