Early phase of amyloid β42-induced cytotoxicity in neuronal cells is associated with vacuole formation and enhancement of exocytosis

Amyloid beta (A beta) neurotoxicity is believed to play a critical role in the pathogenesis of Alzheimer's disease (AD) mainly because of its deposition in AD brain and its neuronal toxicity. However, there have been discrepancies in A beta-induced cytotoxicity studies, depending on the assay methods. Comparative analysis of A beta 42-induced in vitro cytotoxicity might be useful to elucidate the etiological role of A beta in the pathogenesis of AD. In this study, MTT, CCK-8, calcein-AM/EthD-1 assays as well as thorough microscopic examinations were comparatively performed after A beta 42 treatment in a neuronal precursor cells (NT2) and a somatic cells (EcR293). Extensive formation of vacuoles was observed at the very early stage of A beta 42 treatment in both cells. Early observation of A beta 42 toxicity as seen in vacuole formation was also shown in MTT assay, but not in CCK-8 and calcein-AM/EthD-1 assays. In addition, A beta 42 treatment dramatically accelerated MTT formazan exocytosis, implying its effect on the extensive formation of cytoplasmic vacuoles. A beta 42 seems to cause indirect inhibition on the intracellular MTT reduction as well as vacuole formation and exocytosis enhancement. Following the acute cellular dysfunction induced by A beta 42, the prolonged treatment of micromolar concentration of A beta 42 resulted in slight inhibition on redox and esterase activity. The early A beta 42-induced vacuolated morphology and later chronic cytotoxic effect in neuronal cell might be linked to the chronic neurode-generation caused by the accumulation of A beta 42 in AD patients' brain.