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Prooxidant effects of ascorbate in rat brain slices

Ascorbate is a well‐known reducing agent, but it can generate oxidative potential under appropriate condition. In rat cerebral cortex homogenate, 1 mM ascorbate decreased thiobarbituric acid‐reactive substances (TBARS) content to 86% ± 4% of control values, confirming that ascorbate is a reducing agent. However, ascorbate increased TBARS, in a dose‐related manner, in slices prepared from cerebral cortex. Ferrous ion (Fe2+) had little effect on ascorbate‐induced lipid oxidation in cortical slices, and EDTA did not have an influence on the ascorbate‐induced oxidative action. Conversely, ascorbate plus Fe2+ elevated TBARS content to more than threefold over ascorbate alone in tissue homogenates. In summary, ascorbate is a reducing agent in the brain tissue homogenate but has an oxidizing effect in brain slices. A hypothesis is proposed to explain the oxidative effects of ascorbate in cortical slices, wherein extracellular ascorbate is oxidized to dehydroascorbate, which is rapidly carried into the cells via a glucose transporter (GLUT). The dehydroascorbate in cytosol is then reduced back to ascorbate, and, during the reduction process, cellular components are oxidized. J. Neurosci. Res. 58:328–336, 1999. © 1999 Wiley‐Liss, Inc.