Memantine lowers amyloid-beta peptide levels in neuronal cultures and in APP/PS1 transgenic mice.

Memantine is a moderate-affinity, uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist that stabilizes cognitive, functional, and behavioral decline in patients with moderate to severe Alzheimer's disease (AD). In AD, the extracellular deposition of fibrillogenic amyloid-beta peptides (Abeta) occurs as a result of aberrant processing of the full-length Abeta precursor protein (APP). Memantine protects neurons from the neurotoxic effects of Abeta and improves cognition in transgenic mice with high brain levels of Abeta. However, it is unknown how memantine protects cells against neurodegeneration and affects APP processing and Abeta production. We report the effects of memantine in three different systems. In human neuroblastoma cells, memantine, at therapeutically relevant concentrations (1-4 muM), decreased levels of secreted APP and Abeta(1-40). Levels of the potentially amylodogenic Abeta(1-42) were undetectable in these cells. In primary rat cortical neuronal cultures, memantine treatment lowered Abeta(1-42) secretion. At the concentrations used, memantine treatment was not toxic to neuroblastoma or primary cultures and increased cell viability and/or metabolic activity under certain conditions. In APP/presenilin-1 (PS1) transgenic mice exhibiting high brain levels of Abeta(1-42), oral dosing of memantine (20 mg/kg/day for 8 days) produced a plasma drug concentration of 0.96 microM and significantly reduced the cortical levels of soluble Abeta(1-42). The ratio of Abeta(1-40)/Abeta(1-42) increased in treated mice, suggesting effects on the gamma-secretase complex. Thus, memantine reduces the levels of Abeta peptides at therapeutic concentrations and may inhibit the accumulation of fibrillogenic Abeta in mammalian brains. Memantine's ability to preserve neuronal cells against neurodegeneration, to increase metabolic activity, and to lower Abeta level has therapeutic implications for neurodegenerative disorders.

Important differences between human and mouse APOE gene promoters: limitation of mouse APOE model in studying Alzheimer's disease.

Apolipoprotein E (ApoE), encoded by the apolipoprotein E gene (APOE), plays an important role in the pathogenesis of Alzheimer's disease (AD). The APOE epsilon4 variant is strongly associated with AD. APOE promoter polymorphisms have also been reported to associate with higher AD risk. Mouse models of APOE expression have long been used to study the pathogenesis of AD. Elucidating the role of the APOE gene in AD requires understanding of how its regulation differs between mouse and human APOE genes, and how the differences influence AD risk. We compared the structure and function of both the human APOE gene promoter (hAPOEP) and mouse APOE gene promoter (mAPOEP) regions. Homology is less than 40% at 180 bp or more upstream of the two species' transcription start site (TSS, +1). Functional analysis revealed both similarities and important differences between the two sequences, significantly affected by human versus rodent cell line origin. We likewise probed nuclear extracts from several cell lines of different origins (astrocytic, glial, and neuronal) and mouse brain with specific hAPOEP and mAPOEP fragments. Each fragment shared DNA-protein interactions with the other but, notably, also bound distinct factors, demonstrated by gel shift and southwestern analyses. We determined possible identities for these distinct factors. These results suggest that regulation of mouse and human APOE genes may be sufficiently unique to justify the use of both the human APOE promoter sequence in transgenic rodent models and non-rodent AD models for studying factors involved in AD pathogenesis.

Differential effects of two hexahydropyrroloindole carbamate-based anticholinesterase drugs on the amyloid beta protein pathway involved in Alzheimer's disease.

One of the main hallmarks of Alzheimer's disease (AD) is the brain deposition of senile plaques made up of toxic amyloid beta-peptide (Abeta), which is derived from a larger protein called the beta-amyloid precursor protein (APP). Both APP processing and cholinesterase activity are affected in the AD brain, but, yet, cholinesterase inhibitors (ChEI) remain the primary Food and Drug Administration approved drugs for AD within the United States. Herein, we evaluated the effects of two clinically relevant drugs on the APP pathway, which is presumably involved in AD pathogenesis. Specifically, we compared the actions of the classical ChEI physostigmine (PHY) and its analog phenserine (PHE) on neuronal cell viability, on IC50 and on levels of different amyloid proteins. Interestingly, these drugs share the same chemical backbone, inhibit acetylcholinesterase with similar potency, but differentially affect APP processing. PHE treatment decreased levels of APP in the human neuroblastoma cells (p=0.009) whereas PHY showed a similar but less-pronounced trend, which did not attain statistical significance. PHE treatment significantly decreased levels of Abeta in human neuroblastoma cells (p=0.02) whereas PHY showed no significant change under the same conditions. The divergent actions of these two structurally related drugs on the amyloid pathway indicate that the mechanisms underpinning the cholinergic and the amyloid-lowering properties for this class of drugs are independent of each other.

Novel anticholinesterases based on the molecular skeletons of furobenzofuran and methanobenzodioxepine.

Reductive cyclization of 5-hydroxy-3-methyl-3-methoxycarbonylmethylenebenzofuran-2(3H)-one (4) gave 5-hydroxy-3a-methyl-2,3,3a,8a-tatrahydrofuro[2,3-b]benzofuran (5) and the rearrangement product 7-hydroxy-4,5-dihydro-2,5-methano-1,3-benzodioxepine (6). Reaction of compounds 5 and 6 with different isocyanates provided two series novel carbamates (7-12) whose structures were confirmed by X-ray crystallography. These were assessed for anticholinesterase action against freshly prepared human enzyme and proved to be potent inhibitors of either acetyl- (AChE) or butyrylcholinesterase (BChE) with specific compounds exhibiting remarkable selectivity. Because the two series of carbamates (7-12) differ in their phenolic moieties, their respective potency and selectivity for AChE versus BChE was governed by their N-substituted groups. This same characteristic was also present in a series of physovenine analogues (1, 13, 15, 17) and physostigmine analogues (2, 14, 16, 18). These structure-activity relations proved valuable in elucidating the mechanisms underpinning the interaction between carbamate-based cholinesterase inhibitors and their enzyme target. In addition, because physostigmine analogues have demonstrated activity in lowering the Alzheimer's disease protein, amyloid precursor protein (APP), examples of the two new series of carbamates were characterized in culture assays of quantifying cell viability and synthesis of APP.