Antioxidants significantly affect the formation of different classes of isoprostanes and neuroprostanes in rat cerebral synaptosomes

Abstract

Lipid peroxidation has been implicated in the pathogenesis of a number of diseases, including neurodegenerative disorders. Evidence that antioxidants can affect the clinical course of neurodegenerative diseases is limited. In the present study, we examined the ability of five common antioxidants or antioxidant combinations, α-tocopherol, γ-tocopherol, ascorbic acid, GSH ethyl ester, and a combination of ascorbate and α-tocopherol, to modulate lipid peroxidation in peroxidizing rat cerebral synaptosomes, a well-characterized model of oxidant injury. In these studies, we quantified isoprostanes (IsoPs) derived from arachidonic acid as an index of whole tissue oxidation and neuroprostanes (NeuroPs) formed from docosahexaenoic acid as a marker of selective neuronal peroxidation. We report that these various antioxidants displayed markedly different capacities to inhibit IsoP and NeuroP formation with the most potent effects on IsoPs observed for ascorbate, GSH ethyl ester, and the α-tocopherol–ascorbate combination. α-Tocopherol was slightly less potent and γ-tocopherol significantly less effective. The concentration–response relationships were significantly different for NeuroP formation with the antioxidants being significantly less potent than for IsoP generation. In particular, α-tocopherol did not inhibit NeuroP formation at concentrations up to 100 μM. We also determined that tocopherols, in particular α-tocopherol, act in vitro as reducing agents to convert IsoP and NeuroP endoperoxides to reduced F-ring compounds, a finding we have observed previously in vivo in brain. These studies are of importance because they have further defined the role of antioxidants to modulate the formation of lipid peroxidation products in peroxidizing brain tissue. In addition, they suggest that α-tocopherol may not be a particularly effective agent to inhibit oxidant stress in the terminal compartment of neurons in the central nervous system.