Research paperEffects of phenothiazine-structured compounds on APP processing in Alzheimer's disease cellular model

- TBO and TH reduce the levels of secreted Aβ40, Aβ42, sAPPα and intracellular APP in PS70 cells.
- TBO decreases BACE1 levels whereas TH does not cause any change in BACE1.
- TBO might show its effect on Aβ pathology by reducing the levels of APP and BACE1.
- Effects of TH on amyloid metabolism might be related to the reduction of intracellular APP.
- TBO and TH may be potential drug candidates to prevent cognitive decline in AD.

The excess accumulation of amyloid-β (Aβ) 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 Aβ, soluble APP-α (sAPPα), intracellular APP and β-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 Aβ40, Aβ42 and sAPPα were assayed by specific sandwich ELISAs while APP and BACE1 in cell lysates were analyzed using Western blot. The secreted Aβ40, Aβ42 and sAPPα 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 Aβ pathology by lowering APP levels whereas reduced Aβ 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.