Established amyloid-β pathology is unaffected by chronic treatment with the selective serotonin reuptake inhibitor paroxetine.

Introduction: Treatment with selective serotonin reuptake inhibitors has been suggested to mitigate amyloid-β (Aβ) pathology in Alzheimer's disease, in addition to an antidepressant mechanism of action.

Methods: We investigated whether chronic treatment with paroxetine, a selective serotonin reuptake inhibitor, mitigates Aβ pathology in plaque-bearing double-transgenic amyloid precursor protein (APP)/presenilin 1 (PS1) mutants. In addition, we addressed whether serotonin depletion affects Aβ pathology. Treatments were assessed by measurement of serotonin transporter occupancy and high-performance liquid chromatography. The effect of paroxetine on Aβ pathology was evaluated by stereological plaque load estimation and Aβ/Aβ ratio by enzyme-linked immunosorbent assay.

Results: Contrary to our hypothesis, paroxetine therapy did not mitigate Aβ pathology, and depletion of brain serotonin did not exacerbate Aβ pathology. However, chronic paroxetine therapy increased mortality in APP/PS1 transgenic mice.

Discussion: Our results question the ability of selective serotonin reuptake inhibitor therapy to ameliorate established Aβ pathology. The severe adverse effect of paroxetine may discourage its use for disease-modifying purposes in Alzheimer's disease.