P4-332: γ-glutamylcysteine (GGC)-mediated upregulation of glutathione levels can ameliorate toxicity of natural beta-amyloid oligomers in primary adult human neurons

Soluble amyloid-β (Aβ) oligomers can induce oxidative stress, synaptic dysfunction and memory deficits which are present in Alzheimer's disease (AD). Exogenous Aβ(1–42) has been previously shown to induce oxidative stress and deplete the levels of the important endogenous antioxidant glutathione (GSH). However, the effect of Aβ oligomers isolated from natural sources such as AD brain extracts and cerebrospinal fluid, on GSH levels in primary adult human neurons has not been previously investigated. Moreover, administration of γ-glutamylcysteine (GGC) can increase intracellular levels of GSH, by circumventing the regulation of GSH biosynthesis by providing the limiting substrate. Using isolated pure cultures of primary adult human neurons, we examined the neuroprotective effects of increased GSH levels by GGC against the oxidative and cytotoxic effects of soluble Aβ oligomers extracted from post-mortem AD brains. More specifically, we assessed protein oxidation and lipid peroxidation in vitro using standard spectrophotometric assay kits. The conformation structure of Aβ oligomers in the presence of GGC was assessed using immunoflourescence microscopy. GGC treatment to neurons led to a significant upregulation of GSH levels compared to non-treated control cells, and protected neurons against protein, and lipid oxidation, and impaired mitochondrial respiration. Moreover, GGC was able to remodel the fibrillar conformation of Aβ oligomers to non-toxic forms. These data provide renewed insight on the beneficial effects of increased GSH levels by GGC in human neurons, and identify additional targets to attenuate the neurotoxic effects of Aβ oligomers in AD.