A High Content Drug Screen Identifies Ursolic Acid as an Inhibitor of Amyloid β Protein Interactions with Its Receptor CD36

A pathological hallmark of Alzheimer disease (AD) is deposition of amyloid beta (A beta) in the brain. A beta binds to microglia via a receptor complex that includes CD36 leading to production of proinflammatory cytokines and neurotoxic reactive oxygen species and subsequent neurodegeneration. Interruption of A beta binding to CD36 is a potential therapeutic strategy for AD. To identify pharmacologic inhibitors of A beta binding to CD36, we developed a 384-well plate assay for binding of fluorescently labeled A beta to Chinese hamster ovary cells stably expressing human CD36 (CHO-CD36) and screened an Food and Drug Administration-approved compound library. The assay was optimized based on the cells' tolerance to dimethyl sulfoxide, A beta concentration, time required for A beta binding, reproducibility, and signal-to-background ratio. Using this assay, we identified four compounds as potential inhibitors of A beta binding to CD36. These compounds were ursolic acid, ellipticine, zoxazolamine, and homomoschatoline. Of these compounds, only ursolic acid, a naturally occurring pentacyclic triterpenoid, successfully inhibited binding of A beta to CHO-CD36 cells in a dose-dependent manner. The ursolic acid effect reached a plateau at similar to 20 mu M, with a maximal inhibition of 64%. Ursolic acid also blocked binding of A beta to microglial cells and subsequent ROS production. Our data indicate that cell-based high-content screening of small molecule libraries for their ability to block binding of A beta to its receptors is a useful tool to identify novel inhibitors of receptors involved in AD pathogenesis. Our data also suggest that ursolic acid is a potential therapeutic agent for AD via its ability to block A beta-CD36 interactions.