The choroid plexus removes β-amyloid from brain cerebrospinal fluid

beta-Amyloid (A beta) concentration in the cerebrospinal fluid (CSF) of the brain may be regulated by the choroid plexus, which forms a barrier between blood and brain CSF. A beta uptake from CSF was determined as its volume of distribution (VD) into isolated rat choroid plexus tissue. The VD Of [I-125]A beta(1-40) was corrected by subtraction of the VD Of [C-14]sucrose, a marker for extracellular space and diffusion. A beta uptake into choroid plexus was time and temperature dependent. Uptake of [I-125]A beta was saturable. A beta uptake was not affected by addition of transthyretin or apolipoprotein E3. In studies with primary culture monolayers of choroidal epithelial cells in Transwells, All permeability across cells, corrected by [C-14]sucrose, was greater from the CSF-facing membrane than from the blood-facing membrane. Similarly, cellular accumulation of [I-125]A beta was concentrative from both directions and was greater from the CSF-facing membrane, suggesting a bias for efflux. Overall, these results suggest the choroid plexus selectively cleanses A beta from the CSF by an undetermined mechanism(s), potentially reducing A beta from normal brains and the brains of Alzheimer's disease patients.