Cu(II) enhances the effect of Alzheimer's amyloid-β peptide on microglial activation

Background: Aggregated forms of amyloid-beta (A beta) peptides are important triggers for microglial activation, which is an important pathological component in the brains of Alzheimer's patients. Cu(II) ions are reported to be coordinated to monomeric A beta, drive A beta aggregation, and potentiate A beta neurotoxicity. Here we investigated whether Cu(II) binding modulates the effect of A beta on microglial activation and the subsequent neurotoxicity. Methods: A beta peptides were incubated with Cu(II) at an equimolar ratio to obtain the Cu(II)-A beta complex. Primary and BV-2 microglial cells were treated with Cu(II)-A beta, A beta, or Cu(II). The tumor necrosis factor-alpha (TNF-alpha) and nitric oxide levels in the media were determined. Extracellular hydrogen peroxide was quantified by a fluorometric assay with Amplex Red. Mitochondrial superoxide was detected by MitoSOX oxidation. Results: Incubation of Cu(II) with A beta confers different chemical properties on the resulting complex. At the subneurotoxic concentrations, Cu(II)-A beta (but not A beta or Cu(II) alone) treatment induced an activating morphological phenotype of microglia and induced the microglial release of TNF-alpha and nitric oxide as well as microglia-mediated neuronal damage. Cu(II)-A beta-triggered microglial activation was blocked by nuclear factor (NF)-kappa B inhibitors and was accompanied with NF-kappa B activation. Moreover, Cu(II)-A beta induced hydrogen peroxide release, which was not affected by NADPH oxidase inhibitors. Mitochondrial superoxide production was increased after Cu(II)-A beta stimulation. N-acetyl-cysteine, a scavenger of reactive oxygen species (ROS), inhibited Cu(II)-A beta-elicited microglial release of TNF-alpha and nitric oxide as well as the microglia-mediated neurotoxic effect. Conclusion: Our observations suggest that Cu(II) enhances the effect of A beta on microglial activation and the subsequent neurotoxicity. The Cu(II)-A beta-triggered microglial activation involves NF-kappa B activation and mitochondrial ROS production.