The utility of vaccine strategies to treat neurodegenerative diseases such as Alzheimer's disease (AD) may still hold promise. Both active and passive immunization strategies reduced AD-like pathology and restored cognitive deficits in transgenic mice. These results were initially met with considerable optimism; however, phase IIa clinical trials were halted because of a small but significant occurrence of meningoencephalitis. Knowledge gained from studies on amyloid-␤ peptide (A␤) immunotherapy will allow optimization of new-generation vaccines, targeting highly specific epitopes while reducing undesired side effects. In harnessing and steering the immune system, an effective response can be generated against A␤. If this proves successful, A␤ vaccination could provide the first definitive treatment for AD. Alzheimer's disease (AD) is the most common cause of age-related cognitive decline, affecting Ͼ12 million people worldwide (1). The disease is characterized in its earlier stages by progressive memory impairment and cognitive decline, altered behavior, and language deficits. Later, patients present with global amnesia and slowing of motor functions, with death typically occurring within 9 years after diagnosis (2). Current drug therapy aims at slowing cognitive decline and ameliorating the affective and behavioral symptoms associated with disease progression. However, these drugs provide limited symptomatic treatment, without targeting the underlying cause of AD. Immunization of AD patients provides a novel means of specifically targeting the neurotoxic effects of amyloid-␤ peptide (A␤) and thereby targeting disease progression. The Amyloid Cascade HypothesisThe main constituent of amyloid consists of a 40-to 43-aa peptide, A␤, and is derived from the proteolytic cleavage of a family of ubiquitously expressed membrane-spanning proteins, termed the amyloid precursor proteins (APP) (3). Under normal conditions, the most abundant species in the brain is the A␤ (1-40) peptide (A␤ 40 ); however, much of the fibrillar A␤ is composed of the longer, more fibrillogenic A␤ (1-42) peptide (A␤ 42 ) (3). These normally soluble peptides undergo conformational change and polymerize into an aggregated and toxic form, rich in ␤-structure (4). Initially, A␤ 42 is deposited in an immature, diffuse (nonfibrillar) plaque, with little or no detectable neuritic dystrophy.Early studies have shown that synthetic fibrillar forms of A␤ are toxic to cultured neurons (5-7). Several mechanisms of A␤-induced neurotoxicity have been proposed, including oxidative stress, free-radical formation, disrupted calcium homeostasis, induction of apoptosis, chronic inflammation, and activation of complement (8). Although it has been shown that increased levels of A␤ in the brain correlate with cognitive decline (9), relatively weak correlations exist between fibrillar amyloid plaque density and severity of dementia (10-12). Recent studies point to other forms of A␤, namely, small oligomers as the neurotoxic species (13,14).Recent reports using antibo...

Inositol is a simple polyol with eight naturally occurring stereoisomers. myo-Inositol, D-chiro- and epi-inositol have been examined as potential therapeutic agents for various diseases, with favorable results, but treatment with scyllo-inositol has not been previously investigated. Our laboratory has shown that scyllo-inositol inhibits cognitive deficits in TgCRND8 mice and significantly ameliorates disease pathology, suggesting it might be effective in treating Alzheimer's disease (AD). In this paper, we show that scyllo-inositol has a sustained ability to treat animals at advanced stages of AD-like pathology. Significant decreases in insoluble Abeta40, Abeta42, and plaque accumulation were observed in the brains of treated versus untreated TgCRND8 mice. The growth of plaques of all sizes was inhibited by scyllo-inositol administration. To demonstrate that the scyllo-inositol effects were within the CNS, gas chromatography/mass spectrometry was used to examine myo- and scyllo-inositol concentrations after oral administration. Further, we examined how closely scyllo- and myo-inositol are inter-regulated in the CNS and whether scyllo-inositol, if elevated within the CNS, would incorporate into phosphatidylinositol lipids. Cerebral spinal fluid levels of scyllo-inositol increased after scyllo-inositol treatment but not myo-inositol treatment. scyllo-Inositol treatment also caused increased levels of scyllo-inositol in the brain. We further show that scyllo-inositol, even at elevated levels, does not incorporate into the phosphatidylinositol family of lipids. These combined results demonstrate that scyllo-inositol accumulates within the CNS up to tenfold endogenous levels and does not interfere with phosphatidylinositol lipid production.

Inositol stereoisomers, myo- and scyllo-inositol, are known to enter the brain and are significantly elevated following oral administration. Elevations in brain inositol levels occur across a concentration gradient as a result of active transport from the periphery. There are two sodium/myo-inositol transporters (SMIT1, SMIT2) that may be responsible for regulating brain inositol levels. The goals of this study were to determine the effects of aging and Alzheimer's disease (AD)-like amyloid pathology on transporter expression, to compare regional expression and to analyze substrate requirements of the inositol transporters. QPCR was used to examine expression of the two transporters in the cortex, hippocampus and cerebellum of TgCRND8 mice, a mouse model of amyloid pathology, in comparison to non-transgenic littermates. In addition, we examined the structural features of inositol required for active transport, utilizing a cell-based competitive uptake assay. Disease pathology did not alter transporter expression in the cortex or hippocampus (p>0.005), with only minimal effects of aging observed in the cerebellum (SMIT1: F2,26 = 12.62; p = 0.0002; SMIT2: F2,26 = 8.71; p = 0.0015). Overall, brain SMIT1 levels were higher than SMIT2, however, regional differences were observed. For SMIT1, at 4 and 6 months cerebellar SMIT1 levels were significantly higher than cortical and hippocampal levels (p<0.05). For SMIT2, at all three ages both cortical and cerebellar SMIT2 levels were significantly higher than hippocampal levels (p<0.05) and at 4 and 6 months of age, cerebellar SMIT2 levels were also significantly higher than cortical levels (p<0.05). Inositol transporter levels are stably expressed as a function of age, and expression is unaltered with disease pathology in the TgCRND8 mouse. Given the fact that scyllo-inositol is currently in clinical trials for the treatment of AD, the stable expression of inositol transporters regardless of disease pathology is an important finding.

Inositol is a simple polyol with eight naturally occurring stereoisomers, the most common of which are myo-inositol, chiro-inositol, epi-inositol, and scyllo-inositol [1]. myo-Inositol is the most abundant isomer and is a ubiquitous component of all eukaryotic cells. We have shown that scyllo-inositol may represent a potential therapeutic agent for amyloid disorders such as Alzheimer's disease (AD) [2,3]. We showed that myoinositol complexes with amyloid-b (Ab)42 in vitro to form a small, stable micelle [4]. The ability of inositol stereoisomers to interact with and stabilize small Ab complexes was subsequently addressed [5]. CD spectroscopy demonstrated that epi-inositol and scylloinositol, but not chiro-inositol, were able to induce a structural transition from a random to a b-structure in Ab42. Furthermore, electron microscopy demonstrated that scyllo-inositol stabilizes small aggregates of Ab42 that are nontoxic to nerve growth factor (NGF)-differentiated PC-12 cells and primary human neuronal cultures.We then examined the in vivo effects of the inositol stereoisomers. myo-Inositol, epi-inositol and scyllo-inositol were administered to the TgCRND8 mouse model of AD, which demonstrates age-associated cognitive deficits and AD-like pathology [2,6]. myo-Inositol was effective in vitro but was ineffective in vivo [2,5]. epiInositol had some initial positive results as a prophylactic treatment, but these positive effects were not sustained with disease advancement [2]. scyllo-Inositol treatment, however, resulted in a significant improvement in cognitive function, synaptic function, and lifespan. Significant decreases in Ab40 and Ab42 levels, vascular amyloid levels, plaque size and area were also observed [2]. Therefore, scyllo-inositol is effective at Amyloid-b (Ab) aggregation and amyloid formation are key pathological features of Alzheimer's disease, and are considered to be two of the major contributing factors to neurodegeneration and dementia. Identification of small molecule inhibitors that are orally available, have low toxicity and high central nervous system bioavailability is one approach to the potential development of a disease-modifying treatment for Alzheimer's disease. We have previously identified inositol stereoisomers as exhibiting stereospecific inhibition of Ab aggregation and toxicity in vitro and in vivo. We report here the effects of inosose versus inositol stereoisomers on Ab fibrillogenesis as determined using CD and fluorescence spectroscopy and negativestain electron microscopy. The inososes differ from inositols by the oxidation of one of the hydroxyl groups to a ketone. These molecules help in the further elucidation of the structure-activity relationships of inositolAb interactions and identify both allo-inositol and epi-2-inosose as in vitro inhibitors of Ab aggregation.Abbreviations AD, Alzheimer's disease; Ab, amyloid-b; HMIT, hydrogen myo-inositol transporter; NGF, nerve growth factor; SMIT, sodium myo-inositol transporter; TFE, trifluoroethanol.