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Large numbers of neuritic plaques surrounded by reactive astrocytes are characteristic of Alzheimer's disease (AD). There is a large body of research supporting a causal role for the amyloid beta peptide (Abeta), a main constituent of these plaques, in the neuropathology of AD. Several hypotheses have been proposed to explain the toxicity of Abeta including free radical injury and excitotoxicity. It has been reported that treatment of neuronal/astrocytic cultures with Abeta increases the vulnerability of neurons to glutamate-induced cell death. One mechanism that may explain this finding is inhibition of the astrocyte glutamate transporter by Abeta. The aim of the current study was to determine if Abetas inhibit astrocyte glutamate uptake and if this inhibition involves free radical damage to the transporter/astrocytes. We have previously reported that Abeta can generate free radicals, and this radical production was correlated with the oxidation of neurons in culture and inhibition of astrocyte glutamate uptake. In the present study, Abeta (25-35) significantly inhibited L-glutamate uptake in rat hippocampal astrocyte cultures and this inhibition was prevented by the antioxidant Trolox. Decreases in astrocyte function, in particular L-glutamate uptake, may contribute to neuronal degeneration such as that seen in AD. These results lead to a revised excitotoxicity/free radical hypothesis of Abeta toxicity involving astrocytes.
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