1B). characterized by the progressive cerebral accumulation of amyloid- (A) deposits in either dense-core senile plaques or diffuse amorphous plaques (1). In vivo imaging studies strongly support the amyloid hypothesis, which postulates that formation of senile plaques initiates a pathological cascade resulting in recruitment of microglia and induction of local neuritic changes near the plaques (2,3). A is composed primarily of 40- and 42-amino acid peptides generated from the amyloid precursor protein (APP) by sequential proteolytic cleavages mediated by – and -secretases (4). Many anti-amyloid therapies are currently in development but only a few have successfully reversed existing amyloid pathology (2,5). In regulatable APP transgenic mice, a conceptual model for therapies targeting A generation, plaque pathology could not be reversed by simply shutting down APP over-expression and A production (6). Thus, suppression of A generation may only be able to cease the progression of the disease without reversing existing amyloid pathology. Genetic, epidemiological and biochemical studies have suggested that cholesterol is an important risk factor for AD (7,8). We have previously CREB4 shown that pharmacological or genetic inhibition of acyl-coenzyme A:cholesterol acyltransferase (ACAT), an enzyme that controls cellular equilibrium between free cholesterol and cholesteryl esters, modulates proteolytic processing of APP in vitro (9,10). In a transgenic mouse model of AD, a 2-month treatment with the ACAT inhibitor CP-113,818 markedly reduced A generation and amyloid pathology, resulting in reversal of cognitive deficits (11). Recently, ACAT1 gene ablation in triple transgenic 3xTg-AD mice was shown to reduce brain levels of APP and its proteolytic fragments while improving cognitive function (12). CI-1011, a [(2,4,6-tris(1-methylethyl)phenyl) acetyl]sulfamic acid, 2,6-bis(1-methylethyl)phenyl ester, also known as avasimibe, Catharanthine hemitartrate is an ACAT inhibitor that is suitable for clinical use because of an improved pharmacological and safety profile (13). CI-1011 failed to improve coronary atherosclerosis in phase III clinical trials (14), but it may hold therapeutic potential for AD. Here, we tested the anti-amyloidogenic effects of CI-1011 in 2 age groups of hAPP transgenic mice. We show that CI-1011 partially protects from development of amyloid pathology in young mice and reduces amyloid burden in old animals with preexisting amyloid deposits. Intriguingly, our results suggest that by limiting further A generation, ACAT inhibition may be able to reverse neuronal damage caused by earlier accumulation of oligomeric deposits of A. == MATERIALS AND METHODS == == Mice == hAPP transgenic mice overexpress human APP751with the London (V717I) and Swedish (K670M/N671L) mutations under the regulatory control of the neuron-specific murine Thy-1 promoter (mThy-1-hAPP751; heterozygous with respect to the transgene, on a C57BL/6 F3 background) (15). Mice were handled and treated as previously described (11). CI-1011 was kindly provided by Dr. Lit-Fui Lau (Pfizer, Groton, Connecticut). The drug was compounded in biopolymer release pellets to provide continuous dosing for 60 days by Innovative Research of America (Sarasota, FL). For implantation of pellets, female mice were anesthetized with isofluorane. Sterile pellets containing either CI-1011 or placebo (containing only the biopolymer Catharanthine hemitartrate matrix) were then implanted subcutaneously along the anterolateral aspect of the shoulder with a special precision trocar in accordance with the suppliers instructions. A single pellet was inserted for placebo and 4.8 mg/kg/day dose of CI-1011. Two 7.2 mg/kg/day pellets were used to achieve the 14.4 mg/kg/day dose. == Tissue and Cerebrospinal Fluid Catharanthine hemitartrate Sampling == Cerebrospinal fluid (CSF) was obtained from anesthetized mice after exsanguination by blunt dissection and exposure of the foramen magnum. Upon exposure, a Pasteur pipette was inserted to the approximate depth of 0.3 to 1 1 mm into the cisterna magna. CSF was suctioned by capillary action until flow fully ceased. Animals were killed on day 56 of treatment. Brain, liver, kidney, adrenal gland and blood samples were collected. Brains were divided along the sagittal plane and then either.