Nanomolar Amyloid β Protein‐Induced Inhibition of Cellular Redox Activity in Cultured Astrocytes

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Abstract
It has been previously reported that Alzheimer's amyloid beta protein (A beta) induces reactive astrocytosis in culture. In the present study, we found that A beta potently inhibits cellular redox activity of cultured astrocytes, as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. The following comparative studies revealed several differences between these two actions of A beta on astrocytes. First, A beta-induced reactive morphological change was suppressed by the presence of serum or thrombin, and A beta inhibition of cellular redox activity was observed in either the presence or the absence of serum. Second, micromolar concentrations (10 microM or more) were required for A beta to induce reactive astrocytosis, whereas nanomolar concentrations (0.1-100 nM) were sufficient to inhibit cellular redox activity. Third, the effect of micromolar A beta was virtually irreversible, but nanomolar A beta-induced inhibition of cellular redox activity was reversed by washing out A beta. Furthermore, as it has been reported that A beta neurotoxicity is mediated by reactive oxygen species, we also examined if similar mechanisms are involved in astrocytic response to A beta. However, neither A beta-induced morphological change nor inhibition of redox activity was blocked by antioxidants, suggesting that these effects are not caused by oxidative stress.

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