Effect of LXR/RXR agonism on brain and CSF Aβ40 levels in rats.

Alzheimer's disease (AD) is characterized pathologically by the presence of amyloid plaques and neurofibrillary tangles.  The amyloid hypothesis contends that the abnormal accumulation of Aβ, the principal component of amyloid plaques, plays an essential role in initiating the disease.  Impaired clearance of soluble Aβ from the brain, a process facilitated by apolipoprotein E (APOE), is believed to be a contributing factor in plaque formation.  APOE expression is transcriptionally regulated through the action of a family of nuclear receptors including the peroxisome proliferator-activated receptor gamma and liver X receptors (LXRs) in coordination with retinoid X receptors (RXRs).  It has been previously reported that various agonists of this receptor family can influence brain Aβ levels in rodents.  In this study we investigated the effects of LXR/RXR agonism on brain and cerebrospinal fluid (CSF) levels of Aβ40 in naïve rats.  Treatment of rats for 3 days or 7 days with the LXR agonist, TO901317 or the RXR agonist, Bexarotene did not result in significant changes in brain or CSF Aβ40 levels.