Association between acetylcholinesterase and beta-amyloid peptide in Alzheimer's cerebrospinal fluid

The altered expression of acetylcholinesterase (AChE) in the brains of patients with Alzheimer's disease (AD) has raised much interest of late. Despite an overall decrease in the AD brain, the activity of AChE increases around beta-amyloid plaques and indeed, the beta-amyloid peptide (Abeta) can influence AChE levels. Such evidence stimulated our interest in the possibility that the levels of AChE and amyloid might vary together in AD. We previously found that the different AChE forms present in both the brain and in the cerebrospinal fluid (CSF) of AD patients varied in conjunction with abnormal glycosylation. Thus, the alterations in glycosylation are correlated with the accumulation of a minor subspecies of AChE monomers. We also recently analysed whether long-term exposure to the cholinesterase inhibitor (ChE-I) donepezil influences the AChE species found in AD CSF. The marked increase in CSF-AChE activity in AD patients following long-term treatment with donepezil was not paralleled by a rise in this subset of light variants. Hence, the correlation with the levels of CSF-Abeta is unique to these AChE species in patients receiving such treatment. The aim of this report is to review the links between AChE and beta-amyloid, and to discuss the significance of the responses of the distinct AChE species to ChE-I during the treatment of AD.     

Cerebrospinal fluid acetylcholinesterase changes after treatment with donepezil in patients with Alzheimer's disease

We analyzed whether donepezil differently influences acetylcholinesterase (AChE) variants from cerebrospinal fluid (CSF) in patients with Alzheimer's disease (AD) after long-term treatment. Overall CSF-AChE activity in AD patients before treatment was not different from controls, but the ratio between the major tetrameric form, G(4), and the smaller G(1) and G(2) species was significantly lower. AChE levels at study outset were found to correlate positively with beta-amyloid (1-42) (Abeta42). When patients were re-examined after 12 months treatment with donepezil, there was a remarkable increase in both the G(4) and the lighter species of CSF AChE. As compared with placebo, donepezil caused decreases in the percentage of AChE that failed to bind to the lectin concanavalin A and the antibody AE1. These non-binding species comprised primarily a small subset of G(1) and G(2) forms. In treated patients, these light variants were the only subset of CSF AChE that correlated with CSF-Abeta42 levels. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed that a 77-kDa band, attributed in part to inactive AChE, was lower in AD patients than in controls. Unlike enzyme activity, the intensity of this band did not increase after donepezil treatment. The varying responses of different AChE species to ChE-I treatment suggest different modes of regulation, which may have therapeutic implications.     

Cerebrospinal Fluid (CSF) 25-Hydroxyvitamin D Concentration and CSF Acetylcholinesterase Activity Are Reduced in Patients with Alzheimer's Disease

Background

Little is known of vitamin D concentration in cerebrospinal fluid (CSF) in Alzheimer´s disease (AD) and its relation with CSF acetylcholinesterase (AChE) activity, a marker of cholinergic function.

Methods

A cross-sectional study of 52 consecutive patients under primary evaluation of cognitive impairment and 17 healthy controls. The patients had AD dementia or mild cognitive impairment (MCI) diagnosed with AD dementia upon follow-up (n = 28), other dementias (n = 12), and stable MCI (SMCI, n = 12). We determined serum and CSF concentrations of calcium, parathyroid hormone (PTH), 25-hydroxyvitamin D (25OHD), and CSF activities of AChE and butyrylcholinesterase (BuChE).

Findings

CSF 25OHD level was reduced in AD patients (P < 0.05), and CSF AChE activity was decreased both in patients with AD (P < 0.05) and other dementias (P < 0.01) compared to healthy controls. None of the measured variables differed between BuChE K-variant genotypes whereas the participants that were homozygous in terms of the apolipoprotein E (APOE) ε4 allele had decreased CSF AChE activity compared to subjects lacking the APOE ε4 allele (P = 0.01). In AD patients (n=28), CSF AChE activity correlated positively with CSF levels of total tau (T-tau) (r = 0.44, P < 0.05) and phosphorylated tau protein (P-tau) (r = 0.50, P < 0.01), but CSF activities of AChE or BuChE did not correlate with serum or CSF levels of 25OHD.

Conclusions

In this pilot study, both CSF 25OHD level and CSF AChE activity were reduced in AD patients. However, the lack of correlations between 25OHD levels and CSF activities of AChE or BuChE might suggest different mechanisms of action, which could have implications for treatment trials.     

No correlation between time-linked plasma and CSF Aβ levels

Plasma β-amyloid protein (Aβ) isoforms are considered potential biomarkers for Alzheimer's disease (AD) and dementia. The relation between plasma and cerebrospinal fluid (CSF) levels of Aβ isoforms remains unclear. In order to identify possible correlations between Aβ levels in plasma and CSF we determined Aβ levels in time-linked plasma and CSF samples. Aβ concentrations in plasma (Aβ_1–42 and Aβ_N–42) and CSF (Aβ_1–42) samples from 49 AD patients, 47 non-Alzheimer's disease dementia (NONAD) patients, 39 MCI patients and 29 controls were determined using a multi-parameter fluorimetric bead-based immunoassay using xMAP^® technology (for plasma) and a conventional single-parameter ELISA (for CSF). Plasma Aβ_1–42 concentrations did not correlate with CSF Aβ_1–42 concentrations in the total study population, or in the different diagnostic groups. No correlations between plasma Aβ_N–42 and CSF Aβ_1–42 levels were found either. The CSF/serum albumin index did not show any significant differences between AD, NONAD, MCI and controls.These results suggest that the Aβ levels in plasma are independent of the Aβ levels in CSF both in dementia and controls. The fact that CSF and plasma Aβ do not correlate in patients as well as controls and no significant differences in plasma Aβ_1–42 or Aβ_N–42 between patients and controls can be detected hampers the diagnostic utility of the plasma Aβ levels as biomarkers for dementia.     

Lowering β-Amyloid Levels Rescues Learning and Memory in a Down Syndrome Mouse Model

β-amyloid levels are elevated in Down syndrome (DS) patients throughout life and are believed to cause Alzheimer''s disease (AD) in adult members of this population. However, it is not known if β-amyloid contributes to intellectual disability in younger individuals. We used a γ-secretase inhibitor to lower β-amyloid levels in young mice that model DS. This treatment corrected learning deficits characteristic of these mice, suggesting that β-amyloid-lowering therapies might improve cognitive function in young DS patients.     

Altered Levels of Acetylcholinesterase in Alzheimer Plasma

Background

Many studies have been conducted in an extensive effort to identify alterations in blood cholinesterase levels as a consequence of disease, including the analysis of acetylcholinesterase (AChE) in plasma. Conventional assays using selective cholinesterase inhibitors have not been particularly successful as excess amounts of butyrylcholinesterase (BuChE) pose a major problem.

Principal Findings

Here we have estimated the levels of AChE activity in human plasma by first immunoprecipitating BuChE and measuring AChE activity in the immunodepleted plasma. Human plasma AChE activity levels were ∼20 nmol/min/mL, about 160 times lower than BuChE. The majority of AChE species are the light G₁+G₂ forms and not G₄ tetramers. The levels and pattern of the molecular forms are similar to that observed in individuals with silent BuChE. We have also compared plasma AChE with the enzyme pattern obtained from human liver, red blood cells, cerebrospinal fluid (CSF) and brain, by sedimentation analysis, Western blotting and lectin-binding analysis. Finally, a selective increase of AChE activity was detected in plasma from Alzheimer''s disease (AD) patients compared to age and gender-matched controls. This increase correlates with an increase in the G₁+G₂ forms, the subset of AChE species which are increased in Alzheimer''s brain. Western blot analysis demonstrated that a 78 kDa immunoreactive AChE protein band was also increased in Alzheimer''s plasma, attributed in part to AChE-T subunits common in brain and CSF.

Conclusion

Plasma AChE might have potential as an indicator of disease progress and prognosis in AD and warrants further investigation.     

Molecular isoform distribution and glycosylation of acetylcholinesterase are altered in brain and cerebrospinal fluid of patients with Alzheimer's disease

The glycosylation of acetylcholinesterase (AChE) in CSF was analyzed by lectin binding. AChE from Alzheimer's disease (AD) patients was found to bind differently to two lectins, concanavalin A and wheat germ agglutinin, than AChE from controls. As multiple isoforms of AChE are present in both CSF and brain, we examined whether the abnormal glycosylation of AD AChE was due to changes in a specific molecular isoform. Globular amphiphilic dimeric (G2a) and monomeric (G1a) isoforms of AChE were found to be differentially glycosylated in AD CSF. Glycosylation of AChE was also altered in AD frontal cortex but not in cerebellum and was also associated with an increase in the proportion of light (G2 and G1) isoforms. This study demonstrates that the glycosylation of AChE is altered in the AD brain and that changes in AChE glycosylation in AD CSF may reflect changes in the distribution of brain isoforms. The study also suggests that glycosylation of AChE may be a useful diagnostic marker for AD.     

Increased Levels of Antigen-Bound β-Amyloid Autoantibodies in Serum and Cerebrospinal Fluid of Alzheimer’s Disease Patients

Recent studies have suggested a protective role of physiological β-amyloid autoantibodies (Aβ-autoantibodies) in Alzheimer’s disease (AD). However, the determination of both free and dissociated Aβ-autoantibodies in serum hitherto has yielded inconsistent results regarding their function and possible biomarker value. Here we report the application of a new sandwich enzyme-linked immunosorbent assay (ELISA) for the determination of antigen-bound Aβ-autoantibodies (intact Aβ-IgG immune complexes) in serum and cerebrospinal fluid (CSF) of a total number of 112 AD patients and age- and gender-matched control subjects. Both serum and CSF levels of Aβ-IgG immune complexes were found to be significantly higher in AD patients compared to control subjects. Moreover, the levels of Aβ-IgG complexes were negatively correlated with the cognitive status across the groups, increasing with declining cognitive test performance of the subjects. Our results suggest a contribution of IgG-type autoantibodies to Aβ clearance in vivo and an increased immune response in AD, which may be associated with deficient Aβ-IgG removal. These findings may contribute to elucidating the role of Aβ-autoantibodies in AD pathophysiology and their potential application in AD diagnosis.     

Longitudinal Study of CSF Biomarkers in Patients with Alzheimer's Disease

Background

The CSF biomarkers tau and Aβ42 can identify patients with AD, even during the preclinical stages. However, previous studies on longitudinal changes of tau and Aβ42 in individual patients with AD and elderly controls report somewhat inconsistent results.

Methodology/Principal Findings

We investigated the levels of tau and Aβ42 at baseline and after 1 year in 100 patients with AD. In a second cohort of 45 AD patients we measured the CSF biomarkers at baseline and after 2 years. Moreover, in 34 healthy elderly controls the CSF biomarkers were followed for 4 years. The baseline levels of tau were increased with >60% in AD patients compared to controls (p<0.001), while baseline Aβ42 levels were decreased with >50% (p<0.001). In the AD group followed for 2 years, tau increased with 16% compared to the baseline levels (p<0.05). However, the levels of tau were stable over 4 years in the controls. The levels of Aβ42 did not change significantly over time in any of the groups. In the patients with AD, tau was moderately associated with worse cognitive performance already at baseline (p<0.05).

Conclusions/Significance

Tau and Aβ42 in CSF seem to reflect the underlying disease state in both early and late stages of AD. The slight increase in tau over time observed in the patients with AD is modest when compared to the relatively large difference in absolute tau levels between AD patients and controls. Therefore, these markers maintain their usefulness as state markers over time and might serve as surrogate markers for treatment efficacy in clinical trials.     

Effects of Baseline CSF α-Synuclein on Regional Brain Atrophy Rates in Healthy Elders,Mild Cognitive Impairment and Alzheimer’s Disease

Background

Cerebrospinal fluid (CSF) α-synuclein is reduced in synucleinopathies, including dementia with Lewy bodies, and some studies have found increased CSF α-synuclein in Alzheimer’s disease (AD). No study has explored effects of CSF α-synuclein on brain atrophy. Here we tested if baseline CSF α-synuclein affects brain atrophy rates and if these effects vary across brain regions, and across the cognitive spectrum from healthy elders (NL), to patients with mild cognitive impairment (MCI) and AD.

Methods

Baseline CSF α-synuclein measurements and longitudinal structural brain magnetic resonance imaging was performed in 74 NL, 118 MCI patients and 55 AD patients. Effects of baseline CSF α-synuclein on regional atrophy rates were tested in 1) four pre-hoc defined regions possibly associated with Lewy body and/or AD pathology (amygdala, caudate, hippocampus, brainstem), and 2) all available regions of interest. Differences across diagnoses were tested by assessing the interaction of CSF α-synuclein and diagnosis (testing NL versus MCI, and NL versus AD).

Results

The effects of CSF α-synuclein on longitudinal atrophy rates were not significant after correction for multiple comparisons. There were tendencies for effects in AD in caudate (higher atrophy rates in subjects with higher CSF α-synuclein, P=0.046) and brainstem (higher atrophy rates in subjects with lower CSF α-synuclein, P=0.063). CSF α-synuclein had significantly different effects on atrophy rates in NL and AD in brainstem (P=0.037) and caudate (P=0.006). Discussion: With the possible exception of caudate and brainstem, the overall weak effects of CSF α-synuclein on atrophy rates in NL, MCI and AD argues against CSF α-synuclein as a biomarker related to longitudinal brain atrophy in these diagnostic groups. Any effects of CSF α-synuclein may be attenuated by possible simultaneous occurrence of AD-related neuronal injury and concomitant Lewy body pathology, which may elevate and reduce CSF α-synuclein levels, respectively.     

A Technique for Serial Collection of Cerebrospinal Fluid from the Cisterna Magna in Mouse

Alzheimer''s disease (AD) is a progressive neurodegenerative disease that is pathologically characterized by extracellular deposition of β-amyloid peptide (Aβ) and intraneuronal accumulation of hyperphosphorylated tau protein. Because cerebrospinal fluid (CSF) is in direct contact with the extracellular space of the brain, it provides a reflection of the biochemical changes in the brain in response to pathological processes. CSF from AD patients shows a decrease in the 42 amino-acid form of Aβ (Aβ42), and increases in total tau and hyperphosphorylated tau, though the mechanisms responsible for these changes are still not fully understood. Transgenic (Tg) mouse models of AD provide an excellent opportunity to investigate how and why Aβ or tau levels in CSF change as the disease progresses. Here, we demonstrate a refined cisterna magna puncture technique for CSF sampling from the mouse. This extremely gentle sampling technique allows serial CSF samples to be obtained from the same mouse at 2-3 month intervals which greatly minimizes the confounding effect of between-mouse variability in Aβ or tau levels, making it possible to detect subtle alterations over time. In combination with Aβ and tau ELISA, this technique will be useful for studies designed to investigate the relationship between the levels of CSF Aβ42 and tau, and their metabolism in the brain in AD mouse models. Studies in Tg mice could provide important validation as to the potential of CSF Aβ or tau levels to be used as biological markers for monitoring disease progression, and to monitor the effect of therapeutic interventions. As the mice can be sacrificed and the brains can be examined for biochemical or histological changes, the mechanisms underlying the CSF changes can be better assessed. These data are likely to be informative for interpretation of human AD CSF changes.Open in a separate windowClick here to view.^{(49M, flv)}     

Methylene Blue Modulates β-Secretase,Reverses Cerebral Amyloidosis,and Improves Cognition in Transgenic Mice

Amyloid precursor protein (APP) proteolysis is required for production of amyloid-β (Aβ) peptides that comprise β-amyloid plaques in the brains of patients with Alzheimer disease (AD). Here, we tested whether the experimental agent methylene blue (MB), used for treatment of methemoglobinemia, might improve AD-like pathology and behavioral deficits. We orally administered MB to the aged transgenic PSAPP mouse model of cerebral amyloidosis and evaluated cognitive function and cerebral amyloid pathology. Beginning at 15 months of age, animals were gavaged with MB (3 mg/kg) or vehicle once daily for 3 months. MB treatment significantly prevented transgene-associated behavioral impairment, including hyperactivity, decreased object recognition, and defective spatial working and reference memory, but it did not alter nontransgenic mouse behavior. Moreover, brain parenchymal and cerebral vascular β-amyloid deposits as well as levels of various Aβ species, including oligomers, were mitigated in MB-treated PSAPP mice. These effects occurred with inhibition of amyloidogenic APP proteolysis. Specifically, β-carboxyl-terminal APP fragment and β-site APP cleaving enzyme 1 protein expression and activity were attenuated. Additionally, treatment of Chinese hamster ovary cells overexpressing human wild-type APP with MB significantly decreased Aβ production and amyloidogenic APP proteolysis. These results underscore the potential for oral MB treatment against AD-related cerebral amyloidosis by modulating the amyloidogenic pathway.     

Cerebral β-Amyloidosis in Mice Investigated by Ultramicroscopy

Alzheimer´s disease (AD) is the most common neurodegenerative disorder. AD neuropathology is characterized by intracellular neurofibrillary tangles and extracellular β-amyloid deposits in the brain. To elucidate the complexity of AD pathogenesis a variety of transgenic mouse models have been generated. An ideal imaging system for monitoring β-amyloid plaque deposition in the brain of these animals should allow 3D-reconstructions of β-amyloid plaques via a single scan of an uncropped brain. Ultramicroscopy makes this possible by replacing mechanical slicing in standard histology by optical sectioning. It allows a time efficient analysis of the amyloid plaque distribution in the entire mouse brain with 3D cellular resolution. We herein labeled β-amyloid deposits in a transgenic mouse model of cerebral β-amyloidosis (APPPS1 transgenic mice) with two intraperitoneal injections of the amyloid-binding fluorescent dye methoxy-X04. Upon postmortem analysis the total number of β-amyloid plaques, the β-amyloid load (volume percent) and the amyloid plaque size distributions were measured in the frontal cortex of two age groups (2.5 versus 7-8.5 month old mice). Applying ultramicroscopy we found in a proof-of-principle study that the number of β-amyloid plaques increases with age. In our experiments we further observed an increase of large plaques in the older age group of mice. We demonstrate that ultramicroscopy is a fast, and accurate analysis technique for studying β-amyloid lesions in transgenic mice allowing the 3D staging of β-amyloid plaque development. This in turn is the basis to study neural network degeneration upon cerebral β-amyloidosis and to assess Aβ -targeting therapeutics.     

A Luminex Assay Detects Amyloid β Oligomers in Alzheimer’s Disease Cerebrospinal Fluid

Amyloid beta (aβ) protein assembles into larger protein aggregates during the pathogenesis of Alzheimer’s disease (AD) and there is increasing evidence that soluble aβ oligomers are a critical pathologic species. Diagnostic evaluations rely on the measurement of increased tau and decreased aβ42 in the cerebrospinal fluid (CSF) from AD patients and evidence for oligomeric aβ in patient CSF is conflicting. In this study, we have adapted a monoclonal single antibody sandwich ELISA assay to a Luminex platform and found that this assay can detect oligomerized aβ42 and sAPPα fragments. We evaluated oligomeric aβ reactivity in 20 patients with AD relative to 19 age matched controls and compared these values with a commercially available Alzbio3 kit that detects tau, phosphorylated tau and aβ42 on the same diagnostic platform. We found that CSF samples of patients with AD had elevated aβ oligomers compared to control subjects (p < 0.05) and the ratio of aβ oligomers to aβ42 was also significantly elevated (p < 0.0001). Further research to develop high sensitivity analytical platforms and rigorous methods of developing stable assay standards will be needed before the analysis of oligomeric aβ becomes a routine diagnostic assay for the evaluation of late onset AD patients.     

Immunotherapy for Alzheimer disease

Immunotherapy approaches for Alzheimer disease currently are among the leading therapeutic directions for the disease. Active and passive immunotherapy against the β-amyloid peptides that aggregate and accumulate in the brain of those afflicted by the disease have been shown by numerous groups to reduce plaque pathology and improve behavior in transgenic mouse models of the disease. Several ongoing immunotherapy clinical trials for Alzheimer disease are in progress. The background and ongoing challenges for these immunological approaches for the treatment of Alzheimer disease are discussed.Key words: Alzheimer disease, amyloid, tau, immunotherapy, vaccineThe publication in Nature on a vaccine approach for Alzheimer disease (AD) by Schenk and colleagues in 1999 initiated a push for treatment for this major disease of aging. AD neuropathology is characterized by the progressive loss of synapses and neurons, and the aberrant accumulation in the brain of β-amyloid peptides in plaques and the microtubule associated protein tau in neurofibrillary tangles. Mutations in familial forms of AD have been associated with elevated β-amyloid levels, whereas mutations in tau have been linked to familial forms of frontotemporal dementia. Remarkably, injection of β-amyloid peptides with Freund''s adjuvant into transgenic mice harboring a human AD mutation that develop AD-like neuropathology and progressive cognitive decline led to reduced β-amyloid plaque pathology.¹ This study was subsequently confirmed and extended by multiple groups to show also behavioral improvement in AD transgenic mice with active β-amyloid immunization.^2,3 Passive immunotherapy with antibodies directed at β-amyloid were similarly effective in reducing plaques and improving behavior in AD transgenic mice.⁴ A temporary setback occurred when the first clinical trial with β-amyloid vaccination was halted after 6% of patients developed an inflammatory reaction in the brain (chemical meningoencephalitis). A subsequent study supported clinical benefits among patients in this active vaccination trial.⁵ A more recent postmortem study on a subset of patients who had participated in the aborted trial supported active removal of β-amyloid plaques by inflammatory cells, but also indicated that 7 of the 8 patients who were studied at autopsy continued to have progressive cognitive decline despite the removal of amyloid plaques.⁶The critical mechanisms whereby active or passive vaccination against β-amyloid can affect the disease process remain uncertain. Recruitment and activation of microglia, the macrophage of the central nervous system, by β-amyloid antibodies is thought to lead to β-amyloid plaque removal. At the same time, fibrillar β-amyloid containing plaques, formerly viewed as the major toxic entities in AD, are increasingly viewed as potentially only pathological remnants of the disease. Smaller assemblies, particularly of two to twelve β-amyloid peptides (oligomers), are considered pathogenic, although the site of pathogenesis remains controversial. Secreted, extracellular β-amyloid oligomers have been shown to damage synapses.⁷ Some groups stress the aberrant accumulation of β-amyloid within neurons and synapses leading to subsequent extracellular localization following destruction of neurites and synapses.⁸ Evidence has been presented that antibodies targeting β-amyloid peptides up to 42–43 amino acids can block the toxic effects of extracellular β-amyloid oligomers on synapses.⁷ Interestingly, β-amyloid immunotherapy was also shown to clear intraneuronal β-amyloid in an AD transgenic mouse; the intraneuronal variety is a pool of β-amyloid that correlates with the onset of cognitive decline prior to plaques and tangles in these mice.⁹ Intriguingly, antibodies directed at the β-amyloid domain exposed to the extracellular space within the amyloid precursor protein (APP) were shown to be internalized by neurons, where they reduced the intraneuronal pool of β-amyloid and protected against synaptic damage in neurons cultured from AD transgenic mice.^10,11 It is possible that inefficient clearance of the intracellular pool of β-amyloid played a role in the continued cognitive decline in the seven of eight patients in the aborted active vaccination clinical trial studied at autopsy who showed clearance of β-amyloid plaques.Work on β-amyloid immunotherapy in AD contributed to a reevaluation of the role of the immune system in the brain. Previously, it was considered that the brain was immune privileged, and that antibodies entered the brain only with the breakdown of the blood brain barrier. Rare neuroimmunological disorders had suggested more complex interactions. Pathological antibodies directed at neuronal proteins could be found localizing to specific types of neurons in paraneoplastic diseases linked to diverse systemic cancers^12,13 or collagen-vascular diseases such as lupus.¹⁴ Such pathological antibodies can be directed at synaptic or even intracellular proteins in selective neurons in the brain, leading to localized neurological symptoms. For paraneoplastic diseases it is hypothesized that antibodies directed at the cancer cells cross-react with neuronal antigens. Since titers of antibodies can be higher in brain than in the blood, intrathecal synthesis of antibodies from sequestration of B cells has been proposed to occur in the brain.¹⁵ The interaction between the immune system and the brain is therefore viewed as increasingly complex, with antibodies not only gaining access to the brain but also nerve cells, where they can even alter intracellular biology.¹⁰ These findings open up new possibilities for antibody-directed therapies for diseases of the nervous system.Currently, leading concerns for β-amyloid immunotherapy are the potential development of chemical meningoencephalitis and micro-hemorrhages in the brain. Involvement of T cells in damage to the brain vasculature is considered to contribute to these potential side effects. In addition, the β-amyloid released upon antibody-induced removal of plaques may damage blood vessels as β-amyloid is cleared from the brain via the vasculature.¹⁶ Recently, a phase 2 Elan/Wyeth study using passive β-amyloid immunotherapy with a humanized monoclonal antibody described (at the 2008 International Conference on Alzheimer''s disease) significant benefits in patients not harboring the apolipoprotein E4 (apoE4) allele genetic risk factor for late onset AD. In contrast, no clear therapeutic benefit and more cases with brain inflammation occurred in those with the apoE4 allele linked with an increased risk for AD. Why apoE4 carriers did not benefit in this β-amyloid immunotherapy trial is unknown, but has prompted separation of patients into E4 negative and positive groups in subsequent clinical trials. The less robust than hoped for effects even in the apoE4 negative patients has further dampened expectations. The reason for why the human studies are not showing the protection seen in the transgenic mouse studies could relate to β-amyloid playing less of a role in the more typical late onset AD than it does in the rare autosomal dominant familial forms used to generate the AD transgenic mice. It is also not clear which β-amyloid epitope(s) should be targeted by antibodies to maximize potential benefits while minimizing side effects in AD patients. Optimizing antibody specificity for immunotherapy is further complicating by the varied conformations of different β-amyloid aggregation states. In addition, β-amyloid immunotherapy may be more challenging in patients with AD because it is not effective in reducing tau tangle pathology.⁶ Most immunotherapy studies were done on transgenic AD mouse models that deposit β-amyloid plaques, but not tau tangles. In the more recently generated triple transgenic AD mouse that develops both plaques and tangles, β-amyloid antibodies reversed β-amyloid pathology and early pre-tangle tau pathology, but not hyperphosphorylated tau aggregates.⁸ Recent evidence supports that β-amyloid neurotoxicity acts synergistic with tau,¹⁷ and that both pathologies begin at synapses.¹⁸ Interestingly, tau immunotherapy was reported to protect against tau pathology in transgenic mice harboring mutant tau.¹⁹ Thus, dual immunotherapy targeting of both β-amyloid and tau can be considered. Finally, immunotherapy at earlier stages of the disease process may be more effective.In summary, the β-amyloid vaccine heralded a new era of therapeutic research for AD and despite some setbacks is actively being pursued in several ongoing clinical trials. It continues to be among the leading hopes in the AD research community. Another major effort to specifically block the generation of β-amyloid is also progressing, although not without setbacks along the way. For example, the protease involved in the final cleavage to liberate β-amyloid was found to be involved in multiple other important activities, such as cleavage of Notch. Antibody approaches are also being applied in efforts to block secretase cleavage to generate β-amyloid.²⁰ Finally, there remains some worry that β-amyloid peptides have an as yet unknown normal biological function, although cumulative immunotherapy and other therapeutic studies in animal models have provided sufficient support for the continued pursuit of β-amyloid lowering as a treatment for AD.     

Cerebrospinal Fluid PKR Level Predicts Cognitive Decline in Alzheimer’s Disease

The cerebrospinal fluid (CSF) levels of the proapoptotic kinase R (PKR) and its phosphorylated PKR (pPKR) are increased in Alzheimer’s disease (AD), but whether CSF PKR concentrations are associated with cognitive decline in AD patients remain unknown. In this study, 41 consecutive patients with AD and 11 patients with amnestic mild cognitive impairment (aMCI) from our Memory Clinic were included. A lumbar puncture was performed during the following month of the clinical diagnosis and Mini-Mental State Examination (MMSE) evaluations were repeated every 6 months during a mean follow-up of 2 years. In AD patients, linear mixed models adjusted for age and sex were used to assess the cross-sectional and longitudinal associations between MMSE scores and baseline CSF levels of Aβ peptide (Aβ 1-42), Tau, phosphorylated Tau (p-Tau 181), PKR and pPKR. The mean (SD) MMSE at baseline was 20.5 (6.1) and MMSE scores declined over the follow-up (-0.12 point/month, standard error [SE] = 0.03). A lower MMSE at baseline was associated with lower levels of CSF Aβ 1–42 and p-Tau 181/Tau ratio. pPKR level was associated with longitudinal MMSE changes over the follow-up, higher pPKR levels being related with an exacerbated cognitive deterioration. Other CSF biomarkers were not associated with MMSE changes over time. In aMCI patients, mean CSF biomarker levels were not different in patients who converted to AD from those who did not convert.These results suggest that at the time of AD diagnosis, a higher level of CSF pPKR can predict a faster rate of cognitive decline.     

Antiaggregation Potential of Padina gymnospora against the Toxic Alzheimer’s Beta-Amyloid Peptide 25–35 and Cholinesterase Inhibitory Property of Its Bioactive Compounds

Inhibition of β-amyloid (Aβ) aggregation in the cerebral cortex of the brain is a promising therapeutic and defensive strategy in identification of disease modifying agents for Alzheimer’s disease (AD). Since natural products are considered as the current alternative trend for the discovery of AD drugs, the present study aims at the evaluation of anti-amyloidogenic potential of the marine seaweed Padina gymnospora. Prevention of aggregation and disaggregation of the mature fibril formation of Aβ _25–35 by acetone extracts of P. gymnospora (ACTPG) was evaluated in two phases by Thioflavin T assay. The results were further confirmed by confocal laser scanning microscopy (CLSM) analysis and Fourier transform infrared (FTIR) spectroscopic analysis. The results of antiaggregation and disaggregation assay showed that the increase in fluorescence intensity of aggregated Aβ and the co-treatment of ACTPG (250 μg/ml) with Aβ _25–35, an extensive decrease in the fluorescence intensity was observed in both phases, which suggests that ACTPG prevents the oligomers formation and disaggregation of mature fibrils. In addition, ACTPG was subjected to column chromatography and the bioactivity was screened based on the cholinesterase inhibitory activity. Finally, the active fraction was subjected to LC-MS/MS analysis for the identification of bioactive compounds. Overall, the results suggest that the bioactive compound alpha bisabolol present in the alga might be responsible for the observed cholinesterase inhibition with the IC50 value < 10 μg/ml for both AChE and BuChE when compared to standard drug donepezil (IC50 value < 6 μg/ml) and support its use for the treatment of neurological disorders.     

Donepezil in a Narrow Concentration Range Augments Control and Impaired by Beta-Amyloid Peptide Hippocampal LTP in NMDAR-Independent Manner

Acetylcholinesterase (AChE) inhibitor donepezil is widely used for the treatment of Alzheimer’s disease (AD). The mechanisms of therapeutic effects of the drug are not well understood. The ability of donepezil to reverse a known pathogenic effect of β-amyloid peptide (Abeta), namely, the impairment of hippocampal long-term potentiation (LTP), was not studied yet. The goal of the present study was to study the influence of donepezil in 0.1–10 μM concentrations on control and Abeta-impaired hippocampal LTP. Possible involvement of N-methyl-d-aspartate receptors (NMDARs) into mechanisms of donepezil action was also studied. LTP of population spike (PS) was studied in the CA1 region of rat hippocampal slices. Change of LTP by donepezil treatment had a bell-shaped dose–response curve. The drug in concentrations of 0.1 and 1 μM did not change LTP while in concentration of 0.5 μM significantly increased it, and in concentration of 5 and 10 μM suppressed LTP partially or completely. Abeta (200 nM) markedly suppressed LTP. Addition of 0.1, 0.5 or 1 μM donepezil to Abeta solution caused a restoration of LTP. N-methyl-d-aspartate (NMDA) currents were studied in acutely isolated pyramidal neurons from CA1 region of rat hippocampus. Neither Abeta, nor 0.5 μM donepezil were found to change NMDA currents, while 10 μM donepezil rapidly and reversibly depressed it. Results suggest that donepezil augments control and impaired by Abeta hippocampal LTP in NMDAR-independent manner. In general, our findings extend the understanding of mechanisms of therapeutic action of donepezil, especially at an early stage of AD, and maybe taken into account while considering the possibility of donepezil overdose.     

Impact of Cerebrospinal Fluid Shunting for Idiopathic Normal Pressure Hydrocephalus on the Amyloid Cascade

The aim of this study was to determine whether the improvement of cerebrospinal fluid (CSF) flow dynamics by CSF shunting, can suppress the oligomerization of amyloid β-peptide (Aβ), by measuring the levels of Alzheimer’s disease (AD)-related proteins in the CSF before and after lumboperitoneal shunting. Lumbar CSF from 32 patients with idiopathic normal pressure hydrocephalus (iNPH) (samples were obtained before and 1 year after shunting), 15 patients with AD, and 12 normal controls was analyzed for AD-related proteins and APLP1-derived Aβ-like peptides (APL1β) (a surrogate marker for Aβ). We found that before shunting, individuals with iNPH had significantly lower levels of soluble amyloid precursor proteins (sAPP) and Aβ38 compared to patients with AD and normal controls. We divided the patients with iNPH into patients with favorable (improvement ≥ 1 on the modified Rankin Scale) and unfavorable (no improvement on the modified Rankin Scale) outcomes. Compared to the unfavorable outcome group, the favorable outcome group showed significant increases in Aβ38, 40, 42, and phosphorylated-tau levels after shunting. In contrast, there were no significant changes in the levels of APL1β25, 27, and 28 after shunting. After shunting, we observed positive correlations between sAPPα and sAPPβ, Aβ38 and 42, and APL1β25 and 28, with shifts from sAPPβ to sAPPα, from APL1β28 to 25, and from Aβ42 to 38 in all patients with iNPH. Our results suggest that Aβ production remained unchanged by the shunt procedure because the levels of sAPP and APL1β were unchanged. Moreover, the shift of Aβ from oligomer to monomer due to the shift of Aβ42 (easy to aggregate) to Aβ38 (difficult to aggregate), and the improvement of interstitial-fluid flow, could lead to increased Aβ levels in the CSF. Our findings suggest that the shunting procedure can delay intracerebral deposition of Aβ in patients with iNPH.     

Obesity and Hepatic Steatosis Are Associated with Elevated Serum Amyloid Beta in Metabolically Stressed APPswe/PS1dE9 Mice

Diabesity-associated metabolic stresses modulate the development of Alzheimer’s disease (AD). For further insights into the underlying mechanisms, we examine whether the genetic background of APPswe/PS1dE9 at the prodromal stage of AD affects peripheral metabolism in the context of diabesity. We characterized APPswe/PS1dE9 transgenic mice treated with a combination of high-fat diet with streptozotocin (HFSTZ) in the early stage of AD. HFSTZ-treated APPswe/PS1dE9 transgenic mice exhibited worse metabolic stresses related to diabesity, while serum β-amyloid levels were elevated and hepatic steatosis became apparent. Importantly, two-way analysis of variance shows a significant interaction between HFSTZ and genetic background of AD, indicating that APPswe/PS1dE9 transgenic mice are more vulnerable to HFSTZ treatment. In addition, body weight gain, high hepatic triglyceride, and hyperglycemia were positively associated with serum β-amyloid, as validated by Pearson’s correlation analysis. Our data suggests that the interplay between genetic background of AD and HFSTZ-induced metabolic stresses contributes to the development of obesity and hepatic steatosis. Alleviating metabolic stresses including dysglycemia, obesity, and hepatic steatosis could be critical to prevent peripheral β-amyloid accumulation at the early stage of AD.