Targeting soluble Abeta peptide with Tramiprosate for the treatment of brain amyloidosis.

Amyloid beta-peptide (Abeta) is a major constituent of senile plaques in Alzheimer's disease (AD). Neurotoxicity results from the conformational transition of Abeta from random-coil to beta-sheet and its oligomerization. Among a series of ionic compounds able to interact with soluble Abeta, Tramiprosate (3-amino-1-propanesulfonic acid; 3APS; Alzhemedtrade mark) was found to maintain Abeta in a non-fibrillar form, to decrease Abeta(42)-induced cell death in neuronal cell cultures, and to inhibit amyloid deposition. Tramiprosate crosses the murine blood-brain barrier (BBB) to exert its activity. Treatment of TgCRND8 mice with Tramiprosate resulted in significant reduction (approximately 30%) in the brain amyloid plaque load and a significant decrease in the cerebral levels of soluble and insoluble Abeta(40) and Abeta(42) (approximately 20-30%). A dose-dependent reduction (up to 60%) of plasma Abeta levels was also observed, suggesting that Tramiprosate influences the central pool of Abeta, changing either its efflux or its metabolism in the brain. We propose that Tramiprosate, which targets soluble Abeta, represents a new and promising therapeutic class of drugs for the treatment of AD.

Mapping genetic modulators of amyloid plaque deposition in TgCRND8 transgenic mice.

Alzheimer's disease (AD) is a complex disorder for which various in vivo models exist. The TgCRND8 mouse, transgenic for the human amyloid precursor protein, is an aggressive early onset model of brain amyloid deposition. Preliminary studies revealed that when the transgene is expressed on an A/J genetic background, these mice not only survive longer but also deposit less parenchymal amyloid-beta (Abeta) peptides as compared to those on a C57BL/6 background. We performed a genome-wide study of an F2 intercross between TgCRND8 on an A/J background and C57BL/6 mice, to identify genetic modulators of amyloid accumulation and deposition. We identified four highly significant QTLs that together account for 55% of the phenotypic variance in the number of plaques (Thioflavin S). QTLs were found on the distal part of chromosome 4 with an LOD score of 8.1 at D4Mit251, on chromosome 11 with an LOD score of 5.5 at D11Mit242, on chromosome 9 with an LOD score of 5.0 at D9Mit336 and on the proximal part of chromosome 8 with an LOD score of 4.5 at D8Mit223. A/J alleles at these loci are protective and all decreased the amount of Abeta deposition. Interestingly, the QTL on chromosome 11 is also significantly linked to the levels of brain Abeta(42) and Abeta(40). Although these QTLs do not control the levels of plasmatic Abeta, other regions on chromosomes 1 and 6 show significant linkage. Further characterization of these QTL regions may lead to the identification of genes involved in the pathogenesis of AD.

The cAMP-specific phosphodiesterase 4B mediates Abeta-induced microglial activation.

Microglial activation is a key player in the degenerative process that accompanies the deposition of amyloid-beta (Abeta) peptide into senile plaques in Alzheimer's disease (AD) patients. The goal of this study is to identify novel genes involved in microglial activation in response to Abeta peptide. Prompted by the fact that soluble Abeta(1-42) (sAbeta(1-42))-stimulated primary rat microglia produce more tumor necrosis factor-alpha (TNF-alpha) than fibrillar Abeta(1-42) (fAbeta(1-42))-stimulated microglia, we examined gene expression in these cells following stimulation using cDNA arrays. This analysis confirms the upregulation caused by both sAbeta(1-42) and fAbeta(1-42) of pro-inflammatory molecules such as TNF-alpha, interleukin-1beta and macrophage inflammatory protein-1alpha. In addition, other transcripts not previously described in the context of Abeta-induced microglial activation were identified. The modulation of some of these genes within microglial cells seems to be specific to sAbeta(1-42) as compared to fAbeta(1-42) suggesting that different forms of Abeta may activate distinct pathways during the progression of AD. Importantly, we demonstrate that Pde4B, a cAMP-specific phosphodiesterase, is upregulated by Abeta and results in an increased production of TNF-alpha. Inhibition of Pde4B reduces by up to 70% the release of TNF-alpha from sAbeta-stimulated microglial cells, implicating cAMP as an important mediator of Abeta-induced microglial activation.

Differences in the amyloid-beta-induced inflammatory response in microglia from C57BL/6 and A/J strains of mice.

The microglial inflammatory response to Abeta(1-42) stimulation with or without IFN-gamma priming was investigated in low and high responder strains of mice, A/J and C57BL/6, respectively. A/J microglia showed moderate morphological changes upon stimulation with IFN-gamma alone or with Abeta(1-42). Conversely, C57BL/6 microglia showed major changes in their cellular morphology, which were accompanied by a decrease in NO release and a marked increase in TNF-alpha production. These results indicate that the magnitude of the microglial inflammatory response to Abeta is strongly influenced by genetic factors. Individual differences in the regulation of the microglial response may be a key player in the rate of development of the neuropathology of AD.

Inflammation occurs early during the Abeta deposition process in TgCRND8 mice.

Alzheimer's disease (AD) is characterized by a progressive cognitive decline leading to dementia and involves the deposition of amyloid-beta (Abeta) peptides into senile plaques. Other neuropathological features that accompany progression of the disease include a decrease in synaptic density, neurofibrillary tangles, dystrophic neurites, inflammation, and neuronal cell loss. In this study, we report the early kinetics of brain amyloid deposition and its associated inflammation in an early onset transgenic mouse model of AD (TgCRND8) harboring the human amyloid precursor protein gene with the Indiana and Swedish mutations. Both diffuse and compact plaques were detected as early as 9-10 weeks of age. Abeta-immunoreactive (Abeta-IR) plaques (4G8-positive) appeared first in the neocortex and amygdala, then in the hippocampal formation, and lastly in the thalamus. Compact plaques (ThioS-positive) with an amyloid core were observed as early as diffuse plaques were detected, but in lower numbers. Amyloid deposition increased progressively with age. The formation of plaques was concurrent with the appearance of activated microglial cells and shortly followed by the clustering of activated astrocytes around plaques at 13-14 weeks of age. This TgCRND8 mouse model allows for a rapid, time-dependent study of the relationship between the fibrillogenic process and the inflammatory response during the brain amyloidogenic process.

Stereoselective interactions of peptide inhibitors with the beta-amyloid peptide.

Residues 16-20 of the beta-amyloid peptide (A beta) function as a self-recognition element during A beta assembly into fibers. Peptides containing this motif retain the ability to interact with A beta and, in some cases, potently inhibit its assembly. Replacing L- with D-amino acids could stabilize such peptides and permit their evaluation as therapeutic agents for Alzheimer's disease. Here we have assessed the effect that such a chiral reversal has on inhibitory potency. D-enantiomers of five peptides, KLVFFA, KKLVFFA, KFVFFA, KIVFFA, and KVVFFA, were unexpectedly more active as inhibitors in an in vitro fibrillogenesis assay. Circular dichroism showed that D-KLVFFA more effectively prevented A beta adopting the beta-sheet secondary structure correlated with fibrillogenesis. Electron microscopy showed that fiber formation was also more strongly inhibited by D-KLVFFA. Heterochiral inhibition was confirmed using D-A beta, on the principle that enantiomeric proteins exhibit reciprocal chiral biochemical interactions. With D-Abeta, L-KLVFFA was the more potent inhibitor, rather than d-KLVFFA. Most significantly, D-peptides were more potent at reducing the toxicity of both A beta1-40 and A beta 1-42 toward neuronal cells in culture. This unforeseen heterochiral stereoselectivity of A beta for D-peptide inhibitors should be considered during future design of peptide-based inhibitors of A beta neurotoxicity and fibrillogenesis.

STK receptor tyrosine kinase regulates susceptibility to infection with Listeria monocytogenes.

We have previously identified the STK receptor tyrosine kinase as a key regulator of macrophage activation and cell-mediated immune responses. Here we demonstrate that, although MSP activation of STK inhibits NO production by macrophages in response to heat-killed Listeria monocytogenes, STK-deficient mice exhibit increased susceptibility to infection with Listeria.