Hyperoside protects the blood-brain barrier from neurotoxicity of amyloid beta 1-42

Mounting evidence indicates that amyloid beta protein (A beta) exerts neurotoxicity by disrupting the blood-brain barrier (BBB) in Alzheimer's disease. Hyperoside has neuroprotective effects both in vitro and in vivo against A beta. Our previous study found that hyperoside suppressed A beta(1-42)-induced leakage of the BBB, however, the mechanism remains unclear. In this study, bEnd.3 cells were pretreated with 50, 200, or 500 mu M hyperoside for 2 hours, and then exposed to A beta(1-42) for 24 hours. Cell viability was determined using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide assay. Flow cytometry and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay were used to analyze cell apoptosis. Western blot assay was carried out to analyze expression levels of Bax, Bcl-2, cytochrome c, caspase-3, caspse-8, caspase-9, caspase-12, occludin, claudin-5, zonula occludens-1, matrix metalloproteinase-2 (MMP-2), and MMP-9. Exposure to A beta(1-42 )alone remarkably induced bEnd.3 cell apoptosis; increased ratios of cleaved caspase-9/caspase-9, Bax/Bcl-2, cleaved caspase-8/caspase-8, and cleaved caspase-12/caspase-12; increased expression of cytochrome c and activity of caspase-3; diminished levels of zonula occludens-1, claudin-5, and occludin; and increased levels of MMP-2 and MMP-9. However, hyperoside pretreatment reversed these changes in a dose-dependent manner. Our findings confirm that hyperoside alleviates fibrillar A beta(1-42)-induced BBB disruption, thus offering a feasible therapeutic application in Alzheimer's disease.