Effect of High Concentration of Ascorbate on Catalase Activity in Cultured Cells and Tissues of Guinea Pigs

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This study showed that the inhibition of cell growth in 3T6, induced by the supplementation of ascorbate at 0.5mM in cultured medium, was prevented by the addition of catalase in the range of 25-750 units/mL regardless of the degree of activity. However, cytotoxicity induced by concentrations of more than 2 mM ascorbate could not be prevented even when a high level of catalase (5, 000 units/mL) was added to the medium. Catalase activity in medium supplemented with ascorbate decreased with incubation time; the higher the concentration of ascorbate, the greater the decrease in catalase activity. These results indicate that even though catalase is present at a high concentration in the medium, it cannot prevent cytotoxicity by a high concentration of ascorbate because the oxygen radical derived from ascorbate inhibits its activity. We therefore investigated whether the inhibition of catalase activity by ascor-bate could be observed in animal tissues. The catalase activity in the tissues of guinea pigs 6 h after the administration of ascorbate was lower than that in non-administered animals. When guinea pigs were fed diets containing 5 mg or 100 mg ascorbate/d/animal over a 90 weeks period, a clear affect on catalase activity in the high-dose ascorbate group as compared to that in the low-dose ascorbate group was not observed.
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