AD-related Neuropathology Research Articles

Effect of Chronic hCG Administration on Alzheimer’s-Related Cognition and Aβ Accumulation in PS1KI Mice

Age-associated changes in the reproductive hormones-the gonadal steroid hormones and the gonadotropins-have been identified as potential risk factors for Alzheimer's disease (AD). However, levels of gonadotropins and estrogens are closely linked in vivo, and it has proven difficult to separate the effects of gonadotropins from the well-documented estrogenic effects on AD-related neuropathology in experimental models of menopause. To assess the effects of gonadotropins on cognition and AD biochemical markers independent of estrogenic effects, a potent analog of luteinizing hormone [human chorionic gonadotropin (hCG)] was administered to ovariectomized presenilin1 knock-in mice (PS1KI). Gonadotropin administration was found to induce hyperactivity and anxiety (Open Field Maze and Taste Neophobia Task) and working memory dysfunction, without altering reference memory (Morris Water Maze). Although gonadotropin administration modestly altered β amyloid (Aβ40) levels, levels of the longer more toxic form (Aβ42) were unaffected. Furthermore, altered Aβ40 levels were not associated with observed behavioral and cognitive impairments. These findings provide proof, in principle, that the gonadotropin hormones play a role in the modulation of AD-related behavior, cognition, and neuropathology.

Effect of Huprine X on β-Amyloid, Synaptophysin and α7 Neuronal Nicotinic Acetylcholine Receptors in the Brain of 3xTg-AD and APPswe Transgenic Mice

Background: Several studies implicate acetylcholinesterase (AChE) in the pathogenesis of Alzheimer’s disease (AD), raising the question of whether inhibitors of AChE also might act in a disease-modifying manner. Huprine X (HX), a reversible AChE inhibitor hybrid of tacrine and huperzine A, has shown to affect the amyloidogenic process in vitro. In this study, the aim was to investigate whether HX could affect the AD-related neuropathology in vivoin two mouse models. Methods:Tg2576 (K670M/N671L) (APPswe) and 3xTg-AD (K670M/N671L, PS1M146V, tauP301L) mice were treated with HX (0.12 µmol/kg, i.p., 21 days) or saline at 6–7 months. Human β-amyloid (Aβ) was measured by ELISA, synaptophysin by Western blot and α7 neuronal nicotinic acetylcholine receptors (nAChRs) were analyzed by [¹²⁵I]α-bungarotoxin autoradiography. Results: Treatment with HX reduced insoluble Aβ1–40 (about 40%) in the hippocampus of 3xTg-AD mice, while showing no effect in APPswe mice. Additionally, HX markedly increased cortical synaptophysin levels (about 140%) and decreased (about 30%) the levels of α7 nAChRs in the caudate nucleus of 3xTg-AD mice, while increasing (about 10%) hippocampal α7 nAChRs in APPswe mice. Conclusion: The two mouse models react differently to HX treatment, possibly due to their differences in brain neuropathology. The modulation of Aβ and synaptophysin by HX in 3xTg-AD mice might be due to its suggested interaction with the peripheral anionic site on AChE, and/or via cholinergic mechanisms involving activation of cholinergic receptors. Our results provide further evidence that drugs targeting AChE affect some of the fundamental processes that contribute to neurodegeneration, but whether HX might act in a disease-modifying manner in AD patients remains to be proven.

Grape seed polyphenolic extract specifically decreases Aβ∗56 in the brains of Tg2576 mice

Amyloid- (A) oligomers, found in the brains of Alzheimer's disease (AD) patients and transgenic mouse models of AD, cause synaptotoxicity and memory impairment. Grape seed polyphenolic extract (GSPE) inhibits A oligomerization in vitro and attenuates cognitive impairment and AD-related neuropathology in the brains of transgenic mice. In the current study, GSPE was administered to Tg2576 mice for a period of five months. Treatment significantly decreased brain levels of A*56, a 56-kDa A oligomer previously shown to induce memory dysfunction in rodents, without changing the levels of transgenic amyloid- protein precursor, monomeric A, or other A oligomers. These results thus provide the first demonstration that a safe and affordable intervention can lower the levels of a memory-impairing A oligomer in vivo and strongly suggest that GSPE should be further tested as a potential prevention and/or therapy for AD.

Pathophysiology of cognitive dysfunction in older people with type 2 diabetes: vascular changes or neurodegeneration?

Recent studies have revealed that type 2 diabetes mellitus (T2DM) is a risk factor for cognitive dysfunction or dementia, especially those related to Alzheimer's disease (AD). Basic research suggests that insulin accelerates Alzheimer-related pathology through its effects on the amyloid beta (Abeta). Several pathological studies with autopsy samples have demonstrated, however, that dementia subjects with diabetes have less AD-related neuropathology than subjects without diabetes. We and others have reported that small vessel diseases affect cognitive function in older diabetics. Asymptomatic ischemic lesions in T2DM subjects may lower the threshold for the development of dementia and this may explain the inconsistency between the basic research and clinicopathological studies. Longitudinal follow-up of T2DM subjects without overt dementia using both amyloid imaging and magnetic resonance imaging may elucidate these issues. Following up until the development of overt dementia would make it possible to compare both amyloid load and ischemic lesions before and after the development of dementia. Moreover, amyloid imaging in non-demented older people with or without insulin resistance would verify the role of insulin in the processing and deposition of Abeta. Vascular risk factors may represent a therapeutic target, while neurodegenerative pathologies have not yet been amenable to treatment. It remains to be investigated whether medical interventions on vascular risk factors have protective effects against the development and progress of dementia.

Cortical neuritic plaques and hippocampal neurofibrillary tangles are related to dementia severity in elderly schizophrenia patients

Cognitive decline has been described in elderly patients with schizophrenia, but the underlying pathology remains unknown. Some studies report increases in plaques and neurofibrillary tangles, but there is no evidence for an increased risk for Alzheimer's disease (AD) in elderly schizophrenics. Models of a decreased cerebral reserve suggest that increases in AD-related neuropathology below the threshold for a neuropathological diagnosis could be related to dementia severity in elderly schizophrenia patients. We tested this hypothesis in 110 autopsy specimens of schizophrenia patients, without a neuropathological diagnosis of AD or other neurodegenerative disorders. Furthermore, we assessed the effects of apolipoprotein E (ApoE) status, a known genetic risk factor for AD. Measures of density of neuritic plaques were obtained in five cortical regions, and the degree of hippocampal neurofibrillary tangles was rated. Dementia severity was measured prior to postmortem using the Clinical Dementia Rating (CDR) scale. multivariate analyses of variance were conducted with the factors dementia severity, by ApoE4 carrier status. Hippocampal neurofibrillary tangles correlated with increased dementia severity ( p < .05). Neuritic plaque density increased with greater dementia severity ( p < .005), and ApoE4 carrier status ( p < .005), and these differences were magnified by the ApoE4 carrier status ( p < .01). Even below the threshold for a neuropathological diagnosis of AD, neuritic plaques and hippocampal neurofibrillary tangles are associated with dementia severity in schizophrenia patients, even more so in the presence of genetic risk factors, suggesting that a decreased cerebral reserve in elderly schizophrenics may increase susceptibility for dementia.

Neural stem cells improve cognition via BDNF in a transgenic model of Alzheimer disease

Neural stem cell (NSC) transplantation represents an unexplored approach for treating neurodegenerative disorders associated with cognitive decline such as Alzheimer disease (AD). Here, we used aged triple transgenic mice (3xTg-AD) that express pathogenic forms of amyloid precursor protein, presenilin, and tau to investigate the effect of neural stem cell transplantation on AD-related neuropathology and cognitive dysfunction. Interestingly, despite widespread and established Ass plaque and neurofibrillary tangle pathology, hippocampal neural stem cell transplantation rescues the spatial learning and memory deficits in aged 3xTg-AD mice. Remarkably, cognitive function is improved without altering Ass or tau pathology. Instead, the mechanism underlying the improved cognition involves a robust enhancement of hippocampal synaptic density, mediated by brain-derived neurotrophic factor (BDNF). Gain-of-function studies show that recombinant BDNF mimics the beneficial effects of NSC transplantation. Furthermore, loss-of-function studies show that depletion of NSC-derived BDNF fails to improve cognition or restore hippocampal synaptic density. Taken together, our findings demonstrate that neural stem cells can ameliorate complex behavioral deficits associated with widespread Alzheimer disease pathology via BDNF.

The Effect of APOE-ε4 on Dementia is Mediated by Alzheimer Neuropathology

The degree to which the association of epsilon4 with dementia is mediated by AD lesions in comparison with vascular lesions is controversial. The present study was undertaken to determine the roles of Alzheimer disease (AD) and vascular pathology in mediating the effect of apolipoprotein E (APOE)-epsilon4 alleles on dementia. Clinicopathologic correlations were studied in 267 Catholic sisters participating in the Nun Study. The extent to which AD and vascular pathologies mediated the effect of APOEepsilon4 on dementia was investigated using multiple logistic regression. Adjusted for age at death and education, possession of 1 or more epsilon4 alleles was an important risk factor for dementia (odds ratio=2.98; 95% confidence interval, 1.62-5.48). This association was lost (odds ratio=1.38; 95% confidence interval, 0.68-2.80) when an index of the severity of AD-related neuropathology was added to the model, but changed little when measures of the severity of vascular pathology were added. The findings suggest that the effect of epsilon4 on dementia is mediated by the severity of AD pathology. Although infarcts and atherosclerosis contribute to the occurrence of dementia, this contribution seems unrelated to APOE genotype.

Detergent‐Insoluble EAAC1/EAAT3 Aberrantly Accumulates in Hippocampal Neurons of Alzheimer's Disease Patients

Disturbed glutamate homeostasis may contribute to the pathological processes involved in Alzheimer's disease (AD). Once glutamate is released from synapses or from other intracellular sources, it is rapidly cleared by glutamate transporters. EAAC1 (also called EAAT3 or SLC1A1) is the primary glutamate transporter in forebrain neurons. In addition to transporting glutamate, EAAC1 plays other roles in regulating GABA synthesis, reducing oxidative stress in neurons, and is important in supporting neuron viability. Currently, little is known about EAAC1 in AD. To address whether EAAC1 is disturbed in AD, immunohistochemistry was performed on tissue from hippocampus and frontal cortex of AD and normal control subjects matched for age and gender. While EAAC1 immunostaining in cortex appeared comparable to controls, in the hippocampus, EAAC1 aberrantly accumulated in the cell bodies and proximal neuritic processes of CA2-CA3 pyramidal neurons in AD patients. Biochemical analyses showed that Triton X-100-insoluble EAAC1 was significantly increased in the hippocampus of AD patients compared to both controls and Parkinson's disease patients. These findings suggest that aberrant glutamate transporter expression is associated with AD-related neuropathology and that intracellular accumulation of detergent-insoluble EAAC1 is a feature of the complex biochemical lesions in AD that include altered protein solubility.

Reduced hippocampal activation during episodic encoding in middle-aged individuals at genetic risk of Alzheimer's Disease: a cross-sectional study

BackgroundThe presence of the apolipoprotein E (APOE) ε4 allele is a major risk factor for the development of Alzheimer's disease (AD), and has been associated with metabolic brain changes several years before the onset of typical AD symptoms. Functional MRI (fMRI) is a brain imaging technique that has been used to demonstrate hippocampal activation during measurement of episodic encoding, but the effect of the ε4 allele on hippocampal activation has not been firmly established.MethodsThe present study examined the effects of APOE genotype on brain activation patterns in the medial temporal lobe (MTL) during an episodic encoding task using a well-characterized novel item versus familiar item contrast in cognitively normal, middle-aged (mean = 54 years) individuals who had at least one parent with AD.ResultsWe found that ε3/4 heterozygotes displayed reduced activation in the hippocampus and MTL compared to ε3/3 homozygotes. There were no significant differences between the groups in age, education or neuropsychological functioning, suggesting that the altered brain activation seen in ε3/4 heterozygotes was not associated with impaired cognitive function. We also found that participants' ability to encode information on a neuropsychological measure of learning was associated with greater activation in the anterior MTL in the ε3/3 homozygotes, but not in the ε3/4 heterozygotes.ConclusionTogether with previous studies reporting reduced glucose metabolism and AD-related neuropathology, this study provides convergent validity for the idea that the MTL exhibits functional decline associated with the APOE ε4 allele. Importantly, these changes were detected in the absence of meaningful neuropsychological differences between the groups. A focus of ongoing work in this laboratory is to determine if these findings are predictive of subsequent cognitive decline.

Identification and Structural Characterisation of Carboxy-Terminal Polypeptides and Antibody Epitopes of Alzheimer's Amyloid Precursor Protein Using High-Resolution Mass Spectrometry

Alzheimer's disease (AD) is the most common cause for human age-related dementia, characterised by formation of diffuse plaques in brain that are directly involved in AD pathogenesis. The major component of AD plaques is beta-amyloid, a 40 to 42 amino acid polypeptide derived from the amyloid precursor protein (APP) by proteolytic degradation involving the specific proteases, beta-and gamma-secretase acting at the N- and C- terminal cleavage site, respectively. In this study we have prepared polypeptides comprising the carboxy-terminal and transmembrane sequences of APP, by bacterial expression and chemical synthesis, as substrates for studying the C-terminal processing of APP and its interaction with the gamma-secretase complex. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used as a major tool for structure analysis. Immunisation of transgenic mouse models of AD with Abeta42 has been recently shown to be effective to inhibit and disaggregate Abeta-fibrils, and to reduce AD-related neuropathology and memory impairments. However, the mechanism underlying these therapeutic effects has been as yet unclear. Using proteolytic epitope excision from immune complexes in combination with FT-ICR-MS, we identified the epitope recognised by the therapeutically active antibody as the N-terminal Abeta(4-10) sequence; this soluble, nontoxic epitope opens new lead structures for AD vaccine development. A monoclonal antibody (Jonas; JmAb) directed against the cytosolic APP domain was used in studies of APP biochemistry and metabolism. Here we report the identification of the epitope recognised by the JmAb, using the combination of epitope excision and peptide mapping by FT-ICR-MS. The epitope was determined to be located at the C-terminal APP(740-747) sequence; it was confirmed by ELISA binding assays and authentic synthetic peptides and will be an efficient tool in the development of new specific vaccines. These results demonstrate high-resolution FT-ICR-MS as a powerful method for characterising biochemical pathways and molecular recognition structures of APP.

Medicare Drug Beneficiaries and Cost-Lowering Strategies

In Reply: Dr Daniell raises possible confounders of the results of our study that demonstrated an inverse relationship between brain levels of testosterone and development of AD. Although we were unable to directly control for obesity, we believe that the contribution of an association with low testosterone to our observations is minimal. Obesity is also associated with elevated estradiol levels and we observed no significant relationship between brain levels of estradiolandneuropathologicalstatus.Wealsodonotthink that expectant care and opioid use as features of the agonal state explain our results. While it is likely that agonal state may significantly differ between individuals with and without AD, our design indirectly controlled for this possibility with the use of a third group, men with mild neuropathological changes who also showed low levels of testosterone. We reason that because death in this group was unrelatedtoneurologicaldisease,agonalstateinthecontrolgroup and the mild neuropathological changes group should be similar. Moreover, our findings are consistent with the recent results of Moffat et al, 1 who reported that serum levels of testosterone are negatively associated with clinical measures of AD. In their longitudinal study, agonal state was not a relevant factor, and the relationship between testosterone and AD was unaffected by variables such as obesity. Dr Bowen and colleagues discuss the possibility that development of AD may be associated with elevated gonadotropins, particularly luteinizing hormone, rather than low testosterone. However, as argued by Hogervorst et al, 2 any relationshipbetweenelevatedserumgonadotropinsandAD would appear to be most relevant in patients older than 80 years, the age when luteinizing hormone normally shows modest but significant elevations in men. 3 In our study, we comparedADneuropathologicalstatusinmenyoungerthan 80 years. We do not think that the actions of elevated luteinizing hormone rather than reduced androgens as an explanation of the finding of significantly increased brain levels of -amyloid following castration of male rodents 4 is a likely possibility in our paradigm. -Amyloid levels in castratedrodentsarereducedbyandrogenbutnotestradioltreatment 4 ; however, estradiol treatment reverses elevations in luteinizing hormone caused by castration of male rodents. 5 Thus, our human data, as well as rodent data, implicate androgens in regulation of AD-related neuropathology. However, we agree with the need to understand the broader role of normal, age-related disruption of the hypothalamicpituitary-gonadal axis in AD pathogenesis.

P4-049 Genetic differences in young individuals with early amyloid or NFT-pathology

Background: Alzheimer's disease (AD) is histopathologically characterized by the presence of extracellular amyloid ~-protein (A[3) and intracellular neurofibrillary tangles (NFT). These hallmark pathological changes are early events that probably occur many years prior to clinical signs of AD. Whether NFT pathology precedes amyloid deposition or vice versa is still a matter of debate. It is also possible that A~ and NFI occur independently, indicating a difference with respect to pathophysiology, rates of progression, and genetic backgrotmd, Objective(s): The study aims to examine the neuropathological features of different subgroups of young individuals (age < 50 years) with regard to AD-related neuropathology and to identify genetic risk profiles useful in their delineation. Methods: More than 1,000 brains of non-selected consecutive autopsy cases (age range 21-49 years; mean and SD: 38 • 6.3 years) were assessed for AD-related neuropathology. Initial A[3 pathology without significant NFT pathology was apparent in 6% of all cases. Another 25% of the cases displayed NFT pathology devoid of AI3 pathology. The remaining vast majority was exempt from any AD pathology. In the present study, 245 cases were included (97 cases with NFT-only pathology, 21 cases with A~3-only pathology, and 127 age- and gender-matched controls without AD pathology). Polymorphisms of ApoE, A2M-D/I, A2M-GI000A, BCHE-K, IL-1A (-889), IL-1B (-511), IL-1B (+3954), and LRP-C766T were determined for each case. Results: Genotype frequencies [ApoE, BCHE-K, IL-1A (-889), IL-1B (+3954)] of the cases with NFT-only pathology differed significantly from those of the controls. Significant differences in genotype frequencies [ApoE, A2M-D/I, IL-1B (+3954)] were also apparent in cases with A[3-only pathology as compared to controls. Further analysis showed that cases with NFT-only pathology significantly differed from cases with AI3-only pathology in genetic background [ApoE, A2M-G1000A, BCHE-K, IL-1B (+3954)]. Conclusions: The present study, thus, reveals two subgroups of young individuals with different underlying nenropathology and genetic profiles. Therefore, the neuropathological phenotypes may strongly depend on genetic background that alters the neuropathological pattern of AD-related lesions, even in their earliest development.

Age-dependent association between butyrylcholinesterase K-variant and Alzheimer disease-related neuropathology in human brains

The association between the K-variant of the butyrylcholinesterase gene (BCHE-K) and Alzheimer disease (AD) or AD-related neuropathology has been reported to date with conflicting results. Here, we determined in a sample of 521 cases the severity of AD-related neuropathology and the polymorphisms of both BCHE-K and apolipoprotein E (ApoE). Histopathologically, all brains were classified according to procedures permitting differentiation of the evolutionary stages of neurofibrillary tangles (NFTs) and amyloid-β-protein deposition (Aβ-deposits). The results show that the association between BCHE-K and AD-related neuropathology only was limited to homozygotes for the K allele ( P=0.036 for NFTs, and P=0.045 for Aβ-deposits) at ages ≥70 years but not 50–69 years. Furthermore, no interaction was apparent between BCHE-K and ApoE.

Hippocampal estrogen β-receptor immunoreactivity is increased in Alzheimer’s disease

Post-menopausal estrogen use reduces the risk and severity of Alzheimer’s disease (AD). The present study investigates the distribution of both estrogen receptors ERα and ERβ in the human hippocampus in aged controls and in AD cases with immunohistochemistry. No ERα immunoreactivity was observed both in controls and in AD cases. On the other hand, ERβ was observed in some neuronal cells in the hippocampal subfields CA1–4, in astrocytes and in extracellular deposits both in controls and AD cases. The ERβ immunoreactivity was distinctly increased in all AD cases in cellular and extracellular localizations indicating a role for ERβ-mediated estrogen effects in AD-related neuropathology. This study provides the first demonstration of ERβ in human hippocampus in aged controls compared to AD cases.

Gender and age modify the association between APOE and AD-related neuropathology.

To assess the impact of apolipoprotein E (APOE) polymorphism on AD-related neurofibrillary tangle (NFT) formation and senile plaques (SP). A sample of 729 routine autopsy brains (359 men, 370 women; age range, 60 to 99 years) was investigated. All brains were classified neuropathologically according to a procedure permitting differentiation of six NFT stages and three SP stages. APOE genotyping was performed on all cases. The epsilon4 allele of APOE was associated not only with SP (p < 0.0001) but also with NFT formation (p < 0.0001). The effect of the epsilon4 allele on NFT formation was noted at ages > or =80 years (p < 0.0001) but not between ages 60 and 79 years (p = 0.12). An association between the epsilon4 allele and SP for women was found at ages 60 to 79 years (p < 0.0001) but not at > or =80 years of age (p = 0.063). By comparison, men showed an association in both age categories (p = 0.001 and p = 0.001). The results confirm the association between the epsilon4 allele and both types of AD-related lesions and show that this association is differentially modified by age and gender.

Abnormalities in oxidative processes in non-neuronal tissues from patients with Alzheimer's disease*

Overwhelming evidence demonstrates that oxidative stress occurs in brains from patients with Alzheimer's Disease (AD). Whether the oxidative stress is secondary to neurodegeneration, or if it underlies the pathology is not clear. The persistence of AD-related abnormalities in oxidative processes in non-neuronal tissues, including cultured cells, infers that an imbalance in production and removal of reactive oxygen species is an inherent property of cells from AD patients. These results suggest that changes in oxidative processes in AD cells could precede and/or cause AD-related neuropathology. Abnormalities in oxidative processes may also cause changes in signal transduction systems such as calcium that occur in cells from AD patients. The ability to manipulate oxidative processes in peripheral tissues, especially cultured cells, from AD patients should facilitate a mechanistic understanding of the changes in oxidative processes in AD brain. The use of peripheral tissues has the potential to identify both state and trait dependent diagnostic markers, which could be used as endpoints for selecting treatments or monitoring therapeutic effectiveness.

Increased density of olfactory receptor neurons immunoreactive for apolipoprotein E in patients with Alzheimer's disease.

Immunolocalization of apolipoprotein E (apoE) was investigated in human olfactory mucosa in which olfactory receptor neurons (ORNs) were identified with antiserum to protein gene product (PGP) 9.5. Tissue was obtained at autopsy from 10 nondemented middle-aged or elderly subjects and 9 patients with Alzheimer's disease (AD). Double-labeling immunofluorescence established that apoE immunoreactivity was colocalized in a subpopulation of PGP 9.5-immunoreactive ORNs. The mean number of apoE-immunoreactive ORNs per unit epithelial length in AD patients was about 3.5 times greater than that in nondemented patients, although the mean number of PGP 9.5-immunoreactive ORNs was similar. The apoE-immunopositive Schwann cells in olfactory nerve bundles were the probable source of apoE in the ORNs. The increased numbers of apoE-immunoreactive ORNs in AD patients compared to nondemented subjects demonstrates another manifestation of AD-related neuropathology, in addition to cytoskeletal changes, beta-amyloid deposition, and changes in immunoreactivity for other neuroproteins, that parallels changes in neurons in the AD brain.