Elimination of Ascorbic Acid-Induced Membrane Lipid Peroxidation and Serotonin Receptor Loss by Trolox-c, A Water Soluble Analogue of Vitamin E

Abstract

Ascorbic acid is commonly used as an antioxidant to prevent the decomposition of ligands in neurotransmitter receptor studies, but may alter biological membranes by initiating lipid peroxidation in the presence of physiologic metal ions. The aim of the present study was to characterize the effect of ascorbic acid-induced lipid peroxidation on an applicable membrane receptor and to examine an appropriate antioxidant system. Ascorbic acid generated significant lipid peroxidation (5.5 to 45 fold increase in malonaldehyde levels) in three diverse tissues having different membrane properties: bovine brain, mouse teratoma, and rat kidney. In membranes from bovine cerebral cortex, ascorbate-induced lipid peroxidation was associated with a 26% decrease in [³HJ-serotonin receptor binding (^Bmax = 159 ± 11 from control of 216 ± 10 fmol / mg protein), with no significant change in K_D. Trolox-C, a water soluble analogue of vitamin E, completely blocked the ascorbate-induced loss of serotonin receptor binding in brain membranes, and the combination of Trolox-C and ascorbate prevented [³H]-serotonin decomposition in solution. Trolox-C also prevented ascorbate-induced lipid peroxidation in brain, teratoma, and kidney membranes. Lipid peroxidation may by a significant factor in the ascorbate-induced alteration of brain membranes as reflected by reduced binding to serotonin receptors. The combination of Trolox-C (200 μM) and ascorbic acid (1.0 mM) maintains a protective environment for oxygen sensitive neurotransmitters while blocking the deleterious effects of ascorbic acid on lipid membranes.