The excess accumulation of amyloid-beta (A beta) peptides derived from the sequential cleavage of amyloid precursor protein (APP) by secretases, is one of the toxic key events leading to neuronal loss in Alzheimer's disease (AD). Studies have shown that cholinergic activity may also be involved in the regulation of APP metabolism. In the current study, we have investigated the roles of toluidine blue O (TBO) and thionine (TH), newly recognized phenothiazine-derived cholinesterase inhibitors, on the metabolism of APP in Chinese hamster ovary cells stably expressing human APP751 and presenilin 1 (PS70 cells). We assessed the effects of both compounds on the levels of A beta, soluble APP-alpha (sAPP alpha), intracellular APP and (beta-site APP-cleaving enzyme 1 (BACE1). After treatment of PS70 cells with TBO or TH without any side effect on cell viability, the levels of secreted A beta 40, A beta 42 and sAPP alpha were assayed by specific sandwich ELISAs while APP and BACE1 in cell lysates were analyzed using Western blot. The secreted A beta 40, A beta 42 and sAPP alpha in TBO- and TH-treated cells were found to be reduced in a dose-dependent manner compared to vehicle-treated cells. Results suggest that TH mitigated the A beta pathology by lowering APP levels whereas reduced A beta caused by TBO treatment seems to be the outcome of both less substrate availability and amyloidogenic APP processing. Taken together, our results represent the first report demonstrating that TBO and TH can affect amyloid metabolism in vitro. (C) 2017 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.