APP/Aß structural diversity and Alzheimer's disease pathogenesis.

The amyloid cascade hypothesis of Alzheimer's disease (AD) proposes amyloid- ß (Aß) is a chief pathological element of dementia. AD therapies have targeted monomeric and oligomeric Aß 1-40 and 1-42 peptides. However, alternative APP proteolytic processing produces a complex roster of Aß species. In addition, Aß peptides are subject to extensive posttranslational modification (PTM). We propose that amplified production of some APP/Aß species, perhaps exacerbated by differential gene expression and reduced peptide degradation, creates a diverse spectrum of modified species which disrupt brain homeostasis and accelerate AD neurodegeneration. We surveyed the literature to catalog Aß PTM including species with isoAsp at positions 7 and 23 which may phenocopy the Tottori and Iowa Aß mutations that result in early onset AD. We speculate that accumulation of these alterations induce changes in secondary and tertiary structure of Aß that favor increased toxicity, and seeding and propagation in sporadic AD. Additionally, amyloid-ß peptides with a pyroglutamate modification at position 3 and oxidation of Met35 make up a substantial portion of sporadic AD amyloid deposits. The intrinsic physical properties of these species, including resistance to degradation, an enhanced aggregation rate, increased neurotoxicity, and association with behavioral deficits, suggest their emergence is linked to dementia. The generation of specific 3D-molecular conformations of Aß impart unique biophysical properties and a capacity to seed the prion-like global transmission of amyloid through the brain. The accumulation of rogue Aß ultimately contributes to the destruction of vascular walls, neurons and glial cells culminating in dementia. A systematic examination of Aß PTM and the analysis of the toxicity that they induced may help create essential biomarkers to more precisely stage AD pathology, design countermeasures and gauge the impacts of interventions.

Chemical and neuropathological analyses of an Alzheimer's disease patient treated with solanezumab.

INTRODUCTION: Based on the amyloid cascade hypothesis of Alzheimer's disease (AD) pathogenesis, a series of clinical trials involving immunotherapies have been undertaken including infusion with the IgG1 monoclonal anti-Aß antibody solanezumab directed against the middle of the soluble Aß peptide. In this report, we give an account of the clinical history, psychometric testing, gross and microscopic neuropathology as well as immunochemical quantitation of soluble and insoluble Aß peptides and other proteins of interest related to AD pathophysiology in a patient treated with solanezumab. MATERIALS AND METHODS: The solanezumab-treated AD case (SOLA-AD) was compared to non-demented control (NDC, n = 5) and non-immunized AD (NI-AD, n = 5) subjects. Brain sections were stained with H&E, Thioflavine-S, Campbell-Switzer and Gallyas methods. ELISA and Western blots were used for quantification of proteins of interest. RESULTS: The SOLA-AD subject's neuropathology and biochemistry differed sharply from the NDC and NI-AD groups. The SOLA-AD case had copious numbers of amyloid laden blood vessels in all areas of the cerebral cortex, from leptomeningeal perforating arteries to arteriolar deposits which attained the cerebral amyloid angiopathy (CAA) maximum score of 12. In contrast, the maximum CAA for the NI-AD cases averaged a total of 3.6, while the NDC cases only reached 0.75. The SOLA-AD subject had 4.4-fold more soluble Aß40 and 5.6-fold more insoluble Aß40 in the frontal lobe compared to NI-AD cases. In the temporal lobe of the SOLA-AD case, the soluble Aß40 was 80-fold increased, and the insoluble Aß40 was 13-fold more abundant compared to the non-immunized AD cases. Both soluble and insoluble Aß42 levels were not dramatically different between the SOLA-AD and NI-AD cohort. DISCUSSION: Solanezumab immunotherapy provided no apparent relief in the clinical evolution of dementia in this particular AD patient, since there was a continuous cognitive deterioration and full expression of amyloid deposition and neuropathology.

Familial Presenilin Mutations and Sporadic Alzheimer's Disease Pathology: Is the Assumption of Biochemical Equivalence Justified?

Studies of presenilin (PSEN) gene mutations producing early onset Alzheimer's disease (AD) have helped elucidate the pathogenic mechanisms of dementia and guided clinical trials of potential therapeutic interventions. Although familial and sporadic forms of AD share features, it is unclear if the two are precisely equivalent. In addition, PSEN mutations do not all produce a single phenotype, but exhibit substantial variability in clinical manifestations, which are related to the position and chemical nature of their amino acid substitutions as well as ratios of critical molecules such as Aß40 and Aß42. These differences complicate the interpretation of critical clinical trial results and their desired extrapolation to sporadic AD treatment. In this perspective, we examine differences between familial AD and sporadic AD as well as attributes shared by these uniquely arising disturbances in brain biochemical homeostasis that culminate in dementia.

Biochemical assessment of precuneus and posterior cingulate gyrus in the context of brain aging and Alzheimer's disease.

Defining the biochemical alterations that occur in the brain during "normal" aging is an important part of understanding the pathophysiology of neurodegenerative diseases and of distinguishing pathological conditions from aging-associated changes. Three groups were selected based on age and on having no evidence of neurological or significant neurodegenerative disease: 1) young adult individuals, average age 26 years (n = 9); 2) middle-aged subjects, average age 59 years (n = 5); 3) oldest-old individuals, average age 93 years (n = 6). Using ELISA and Western blotting methods, we quantified and compared the levels of several key molecules associated with neurodegenerative disease in the precuneus and posterior cingulate gyrus, two brain regions known to exhibit early imaging alterations during the course of Alzheimer's disease. Our experiments revealed that the bioindicators of emerging brain pathology remained steady or decreased with advancing age. One exception was S100B, which significantly increased with age. Along the process of aging, neurofibrillary tangle deposition increased, even in the absence of amyloid deposition, suggesting the presence of amyloid plaques is not obligatory for their development and that limited tangle density is a part of normal aging. Our study complements a previous assessment of neuropathology in oldest-old subjects, and within the limitations of the small number of individuals involved in the present investigation, it adds valuable information to the molecular and structural heterogeneity observed along the course of aging and dementia. This work underscores the need to examine through direct observation how the processes of amyloid deposition unfold or change prior to the earliest phases of dementia emergence.

Neuropathological and biochemical assessments of an Alzheimer's disease patient treated with the γ-secretase inhibitor semagacestat.

Amyloid deposition has been implicated as the key determinant of Alzheimer's disease (AD) pathogenesis. Interventions to antagonize amyloid accumulation and mitigate dementia are now under active investigation. We conducted a combined clinical, biochemical and neuropathological assessment of a participant in a clinical trial of the γ-secretase inhibitor, semagacestat. This patient received a daily oral dose of 140 mg of semagacestat for approximately 76 weeks. Levels of brain amyloid-ß (Aß) peptides were quantified using enzyme-linked immunosorbent assays (ELISA). Western blot/scanning densitometry was performed to reveal BACE1, presenilin1, amyloid precursor protein (APP) and its proteolysis-produced C-terminal peptides APP-CT99 and APP-CT83 as well as several γ-secretase substrates. To serve as a frame of reference, the ELISA and Western analyses were performed in parallel on samples from neuropathologically confirmed non-demented control (NDC) and AD subjects who did not receive semagacestat. Neuropathology findings confirmed a diagnosis of AD with frequent amyloid deposits and neurofibrillary tangles in most areas of the cortex and subcortical nuclei as well as cerebellar amyloid plaques. Mean levels of Tris-soluble Aß40 and glass-distilled formic acid (GDFA)/guanidine hydrochloride (GHCl)-extractable Aß40 in the frontal lobe and GDFA/GHCl-soluble Aß40 in the temporal lobe were increased 4.2, 9.5 and 7.7-fold, respectively, in the semagacestat-treated subject compared to those observed in the non-treated AD group. In addition, GDFA/GHCl-extracted Aß42 was increased 2-fold in the temporal lobe relative to non-treated AD cases. No major changes in APP, ß- and γ-secretase and CT99/CT83 were observed between the semagacestat-treated subject compared to either NDC or AD cases. Furthermore, the levels of γ-secretase substrates in the semagacestat-treated subject and the reference groups were also similar. Interestingly, there were significant alterations in the levels of several γ-secretase substrates between the NDC and non-treated AD subjects. This is the first reported case study of an individual enrolled in the semagacestat clinical trial. The subject of this study remained alive for ~7 months after treatment termination, therefore it is difficult to conclude whether the outcomes observed represent a consequence of semagacestat therapy. Additional evaluations of trial participants, including several who expired during the course of treatment, may provide vital clarification regarding the impacts and aftermath of γ-secretase inhibition.

Subjects harboring presenilin familial Alzheimer's disease mutations exhibit diverse white matter biochemistry alterations.

Alzheimer's disease (AD) dementia impacts all facets of higher order cognitive function and is characterized by the presence of distinctive pathological lesions in the gray matter (GM). The profound alterations in GM structure and function have fostered the view that AD impacts are primarily a consequence of GM damage. However, the white matter (WM) represents about 50% of the cerebrum and this area of the brain is substantially atrophied and profoundly abnormal in both sporadic AD (SAD) and familial AD (FAD). We examined the WM biochemistry by ELISA and Western blot analyses of key proteins in 10 FAD cases harboring mutations in the presenilin genes PSEN1 and PSEN2 as well as in 4 non-demented control (NDC) individuals and 4 subjects with SAD. The molecules examined were direct substrates of PSEN1 such as Notch-1 and amyloid precursor protein (APP). In addition, apolipoproteins, axonal transport molecules, cytoskeletal and structural proteins, neurotrophic factors and synaptic proteins were examined. PSEN-FAD subjects had, on average, higher amounts of WM amyloid-beta (Aß) peptides compared to SAD, which may play a role in the devastating dysfunction of the brain. However, the PSEN-FAD mutations we examined did not produce uniform increases in the relative proportions of Aß42 and exhibited substantial variability in total Aß levels. These observations suggest that neurodegeneration and dementia do not depend solely on enhanced Aß42 levels. Our data revealed additional complexities in PSEN-FAD individuals. Some direct substrates of γ-secretase, such as Notch, N-cadherin, Erb-B4 and APP, deviated substantially from the NDC group baseline for some, but not all, mutation types. Proteins that were not direct γ-secretase substrates, but play key structural and functional roles in the WM, likewise exhibited varied concentrations in the distinct PSEN mutation backgrounds. Detailing the diverse biochemical pathology spectrum of PSEN mutations may offer valuable insights into dementia progression and the design of effective therapeutic interventions for both SAD and FAD.

Bapineuzumab alters aß composition: implications for the amyloid cascade hypothesis and anti-amyloid immunotherapy.

The characteristic neuropathological changes associated with Alzheimer's disease (AD) and other lines of evidence support the amyloid cascade hypothesis. Viewing amyloid deposits as the prime instigator of dementia has now led to clinical trials of multiple strategies to remove or prevent their formation. We performed neuropathological and biochemical assessments of 3 subjects treated with bapineuzumab infusions. Histological analyses were conducted to quantify amyloid plaque densities, Braak stages and the extent of cerebral amyloid angiopathy (CAA). Amyloid-ß (Aß) species in frontal and temporal lobe samples were quantified by ELISA. Western blots of amyloid-ß precursor protein (AßPP) and its C-terminal (CT) fragments as well as tau species were performed. Bapineuzumab-treated (Bapi-AD) subjects were compared to non-immunized age-matched subjects with AD (NI-AD) and non-demented control (NDC) cases. Our study revealed that Bapi-AD subjects exhibited overall amyloid plaque densities similar to those of NI-AD cases. In addition, CAA was moderate to severe in NI-AD and Bapi-AD patients. Although histologically-demonstrable leptomeningeal, cerebrovascular and neuroparenchymal-amyloid densities all appeared unaffected by treatment, Aß peptide profiles were significantly altered in Bapi-AD subjects. There was a trend for reduction in total Aß42 levels as well as an increase in Aß40 which led to a corresponding significant decrease in Aß42:Aß40 ratio in comparison to NI-AD subjects. There were no differences in the levels of AßPP, CT99 and CT83 or tau species between Bapi-AD and NI-AD subjects. The remarkable alteration in Aß profiles reveals a dynamic amyloid production in which removal and depositional processes were apparently perturbed by bapineuzumab therapy. Despite the alteration in biochemical composition, all 3 immunized subjects exhibited continued cognitive decline.

Quantitative appraisal of ventricular cerebrospinal fluid biomarkers in neuropathologically diagnosed Parkinson's disease cases lacking Alzheimer's disease pathology.

Identifying biomarkers that distinguish Parkinson's disease (PD) from normal control (NC) individuals has the potential to increase diagnostic sensitivity for the detection of early-stage PD. A previous proteomic study identified potential biomarkers in postmortem ventricular cerebrospinal fluid (V-CSF) from neuropathologically diagnosed PD subjects lacking Alzheimer's disease (AD) neuropathology. In the present study, we assessed these biomarkers as well as p-tau(181), Aß42, and S100B by ELISA in PD (n = 43) and NC (n = 49) cases. The p-tau(181)/Aß42 ratio and ApoA-1 showed statistically significant differences between groups. Multiple regression analysis demonstrated that p-tau(181)/Aß42 had a significant odds ratio: OR = 1.42 (95% confidence interval [CI], 1.12-1.84), P = 0.006. Among the molecules investigated, intriguing correlations were observed that require further investigation. Our results suggest coexistent AD CSF biomarkers within the PD group notwithstanding that it was selected to minimize AD neuropathological lesions.

Molecular Differences and Similarities Between Alzheimer's Disease and the 5XFAD Transgenic Mouse Model of Amyloidosis.

Transgenic (Tg) mouse models of Alzheimer's disease (AD) have been extensively used to study the pathophysiology of this dementia and to test the efficacy of drugs to treat AD. The 5XFAD Tg mouse, which contains two presenilin-1 and three amyloid precursor protein (APP) mutations, was designed to rapidly recapitulate a portion of the pathologic alterations present in human AD. APP and its proteolytic peptides, as well as apolipoprotein E and endogenous mouse tau, were investigated in the 5XFAD mice at 3 months, 6 months, and 9 months. AD and nondemented subjects were used as a frame of reference. APP, amyloid-beta (Aß) peptides, APP C-terminal fragments (CT99, CT83, AICD), ß-site APP-cleaving enzyme, and APLP1 substantially increased with age in the brains of 5XFAD mice. Endogenous mouse tau did not show age-related differences. The rapid synthesis of Aß and its impact on neuronal loss and neuroinflammation make the 5XFAD mice a desirable paradigm to model AD.

Neurochemical profile of dementia pugilistica.

Dementia pugilistica (DP), a suite of neuropathological and cognitive function declines after chronic traumatic brain injury (TBI), is present in approximately 20% of retired boxers. Epidemiological studies indicate TBI is a risk factor for neurodegenerative disorders including Alzheimer disease (AD) and Parkinson disease (PD). Some biochemical alterations observed in AD and PD may be recapitulated in DP and other TBI persons. In this report, we investigate long-term biochemical changes in the brains of former boxers with neuropathologically confirmed DP. Our experiments revealed biochemical and cellular alterations in DP that are complementary to and extend information already provided by histological methods. ELISA and one-dimensional and two dimensional Western blot techniques revealed differential expression of select molecules between three patients with DP and three age-matched non-demented control (NDC) persons without a history of TBI. Structural changes such as disturbances in the expression and processing of glial fibrillary acidic protein, tau, and α-synuclein were evident. The levels of the Aß-degrading enzyme neprilysin were reduced in the patients with DP. Amyloid-ß levels were elevated in the DP participant with the concomitant diagnosis of AD. In addition, the levels of brain-derived neurotrophic factor and the axonal transport proteins kinesin and dynein were substantially decreased in DP relative to NDC participants. Traumatic brain injury is a risk factor for dementia development, and our findings are consistent with permanent structural and functional damage in the cerebral cortex and white matter of boxers. Understanding the precise threshold of damage needed for the induction of pathology in DP and TBI is vital.

Alzheimer disease periventricular white matter lesions exhibit specific proteomic profile alterations.

The white matter (WM) represents approximately half the cerebrum volume and is profoundly affected in Alzheimer's disease (AD). However, both the WM responses to AD as well as potential influences of this compartment to dementia pathogenesis remain comparatively neglected. Neuroimaging studies have revealed WM alterations are commonly associated with AD and renewed interest in examining the pathologic basis and importance of these changes. In AD subjects, immunohistochemistry and electron microscopy revealed changes in astrocyte morphology and myelin loss as well as up to 30% axonal loss in areas of WM rarefaction when measured against non-demented control (NDC) tissue. Comparative proteomic analyses were performed on pooled samples of periventricular WM (PVWM) obtained from AD (n=4) and NDC (n=5) subjects with both groups having a mean age of death of 86 years. All subjects had an apolipoprotein E ε3/3 genotype with the exception of one NDC subject who was ε2/3. Urea-detergent homogenates were analyzed using two different separation techniques: 2-dimensional isoelectric focusing/reverse-phase chromatography and 2-dimensional difference gel electrophoresis (2D-DIGE). Proteins with different expression levels between the 2 diagnostic groups were identified using MALDI-Tof/Tof mass spectrometry. In addition, Western blots were used to quantify proteins of interest in individual AD and NDC cases. Our proteomic studies revealed that when WM protein pools were loaded at equal amounts of total protein for comparative analyses, there were quantitative differences between the 2 groups. Molecules related to cytoskeleton maintenance, calcium metabolism and cellular survival such as glial fibrillary acidic protein, vimentin, tropomyosin, collapsin response mediator protein-2, calmodulin, S100-P, annexin A1, α-internexin, α- and ß-synuclein, α-B-crystalline, fascin-1, ubiquitin carboxyl-terminal esterase and thymosine were altered between AD and NDC pools. Our experiments suggest that WM activities become globally impaired during the course of AD with significant morphological, biochemical and functional consequential implications for gray matter function and cognitive deficits. These observations may endorse the hypothesis that WM dysfunction is not only a consequence of AD pathology, but that it may precipitate and/or potentiate AD dementia.

Cerebral blood flow in Alzheimer's disease.

BACKGROUND: Alzheimer's disease (AD) dementia is a consequence of heterogeneous and complex interactions of age-related neurodegeneration and vascular-associated pathologies. Evidence has accumulated that there is increased atherosclerosis/arteriosclerosis of the intracranial arteries in AD and that this may be additive or synergistic with respect to the generation of hypoxia/ischemia and cognitive dysfunction. The effectiveness of pharmacologic therapies and lifestyle modification in reducing cardiovascular disease has prompted a reconsideration of the roles that cardiovascular disease and cerebrovascular function play in the pathogenesis of dementia. METHODS: Using two-dimensional phase-contrast magnetic resonance imaging, we quantified cerebral blood flow within the internal carotid, basilar, and middle cerebral arteries in a group of individuals with mild to moderate AD (n = 8) and compared the results with those from a group of age-matched nondemented control (NDC) subjects (n = 9). Clinical and psychometric testing was performed on all individuals, as well as obtaining their magnetic resonance imaging-based hippocampal volumes. RESULTS: Our experiments reveal that total cerebral blood flow was 20% lower in the AD group than in the NDC group, and that these values were directly correlated with pulse pressure and cognitive measures. The AD group had a significantly lower pulse pressure (mean AD 48, mean NDC 71; P = 0.0004). A significant group difference was also observed in their hippocampal volumes. Composite z-scores for clinical, psychometric, hippocampal volume, and hemodynamic data differed between the AD and NDC subjects, with values in the former being significantly lower (t = 12.00, df = 1, P = 0.001) than in the latter. CONCLUSION: These results indicate an association between brain hypoperfusion and the dementia of AD. Cardiovascular disease combined with brain hypoperfusion may participate in the pathogenesis/pathophysiology of neurodegenerative diseases. Future longitudinal and larger-scale confirmatory investigations measuring multidomain parameters are warranted.

Cerebrospinal fluid biomarkers of neuropathologically diagnosed Parkinson's disease subjects.

OBJECTIVES: Parkinson's disease (PD) afflicts approximately 1-2% of the population over 50 years of age. No cures or effective modifying treatments exist and clinical diagnosis is currently confounded by a lack of definitive biomarkers. We sought to discover potential biomarkers in the cerebrospinal fluid (CSF) of neuropathologically confirmed PD cases. METHODS: We compared postmortem ventricular CSF (V-CSF) from PD and normal control (NC) subjects using two-dimensional difference gel electrophoresis (2D-DIGE). Spots exhibiting a 1·5-fold or greater difference in volume between PD patients and controls were excised from the two-dimensional gels, subjected to tryptic digestion and identification of peptides assigned using mass spectrometric/data bank correlation methods. RESULTS: Employing this strategy six molecules: fibrinogen, transthyretin, apolipoprotein E, clusterin, apolipoprotein A-1, and glutathione-S-transferase-Pi, were found to be different between PD and NC populations. DISCUSSION: These molecules have been implicated in PD pathogenesis. Combining biomarker data from multiple laboratories may create a consensus panel of proteins that may serve as a diagnostic tool for this neurodegenerative disorder.

Morphological and pathological evolution of the brain microcirculation in aging and Alzheimer's disease.

Key pathological hallmarks of Alzheimer's disease (AD), including amyloid plaques, cerebral amyloid angiopathy (CAA) and neurofibrillary tangles do not completely account for cognitive impairment, therefore other factors such as cardiovascular and cerebrovascular pathologies, may contribute to AD. In order to elucidate the microvascular changes that contribute to aging and disease, direct neuropathological staining and immunohistochemistry, were used to quantify the structural integrity of the microvasculature and its innervation in three oldest-old cohorts: 1) nonagenarians with AD and a high amyloid plaque load; 2) nonagenarians with no dementia and a high amyloid plaque load; 3) nonagenarians without dementia or amyloid plaques. In addition, a non-demented (ND) group (average age 71 years) with no amyloid plaques was included for comparison. While gray matter thickness and overall brain mass were reduced in AD compared to ND control groups, overall capillary density was not different. However, degenerated string capillaries were elevated in AD, potentially suggesting greater microvascular "dysfunction" compared to ND groups. Intriguingly, apolipoprotein ε4 carriers had significantly higher string vessel counts relative to non-ε4 carriers. Taken together, these data suggest a concomitant loss of functional capillaries and brain volume in AD subjects. We also demonstrated a trend of decreasing vesicular acetylcholine transporter staining, a marker of cortical cholinergic afferents that contribute to arteriolar vasoregulation, in AD compared to ND control groups, suggesting impaired control of vasodilation in AD subjects. In addition, tyrosine hydroxylase, a marker of noradrenergic vascular innervation, was reduced which may also contribute to a loss of control of vasoconstriction. The data highlight the importance of the brain microcirculation in the pathogenesis and evolution of AD.

Is Alzheimer's disease amyloidosis the result of a repair mechanism gone astray?

Here, we synthesize several lines of evidence supporting the hypothesis that at least one function of amyloid-ß is to serve as a part of the acute response to brain hemodynamic disturbances intended to seal vascular leakage. Given the resilient and adhesive physicochemical properties of amyloid, an abluminal hemostatic repair system might be highly advantageous, if deployed on a limited and short-term basis, in young individuals. However, in the aged, inevitable cardiovascular dysfunction combined with brain microvascular lesions may yield global chronic hypoperfusion that may lead to continuous amyloid deposition and consequential negative effects on neuronal viability. A large body of experimental evidence supports the hypothesis of an amyloid-ß rescue function gone astray. Preventing or inducing the removal of amyloid in Alzheimer's disease (AD) has been simultaneously successful and disappointing. Amyloid deposits clearly play major roles in AD, but they may not represent the preeminent factor in dementia pathogenesis. Successful application of AD preventative approaches may hinge on an accurate and comprehensive view of comorbidities, including cardiovascular disease, diabetes, and head trauma.

Alzheimer's disease and non-demented high pathology control nonagenarians: comparing and contrasting the biochemistry of cognitively successful aging.

The amyloid cascade hypothesis provides an economical mechanistic explanation for Alzheimer's disease (AD) dementia and correlated neuropathology. However, some nonagenarian individuals (high pathology controls, HPC) remain cognitively intact while enduring high amyloid plaque loads for decades. If amyloid accumulation is the prime instigator of neurotoxicity and dementia, specific protective mechanisms must enable these HPC to evade cognitive decline. We evaluated the neuropathological and biochemical differences existing between non-demented (ND)-HPC and an age-matched cohort with AD dementia. The ND-HPC selected for our study were clinically assessed as ND and possessed high amyloid plaque burdens. ELISA and Western blot analyses were used to quantify a group of proteins related to APP/Aß/tau metabolism and other neurotrophic and inflammation-related molecules that have been found to be altered in neurodegenerative disorders and are pivotal to brain homeostasis and mental health. The molecules assumed to be critical in AD dementia, such as soluble or insoluble Aß40, Aß42 and tau were quantified by ELISA. Interestingly, only Aß42 demonstrated a significant increase in ND-HPC when compared to the AD group. The vascular amyloid load which was not used in the selection of cases, was on the average almost 2-fold greater in AD than the ND-HPC, suggesting that a higher degree of microvascular dysfunction and perfusion compromise was present in the demented cohort. Neurofibrillary tangles were less frequent in the frontal cortices of ND-HPC. Biochemical findings included elevated vascular endothelial growth factor, apolipoprotein E and the neuroprotective factor S100B in ND-HPC, while anti-angiogenic pigment epithelium derived factor levels were lower. The lack of clear Aß-related pathological/biochemical demarcation between AD and ND-HPC suggests that in addition to amyloid plaques other factors, such as neurofibrillary tangle density and vascular integrity, must play important roles in cognitive failure.

Biochemical and morphological characterization of the AßPP/PS/tau triple transgenic mouse model and its relevance to sporadic Alzheimer's disease.

Transgenic (Tg) mouse models of Alzheimer's disease (AD) have been genetically altered with human familial AD genes driven by powerful promoters. However, a Tg model must accurately mirror the pathogenesis of the human disease, not merely the signature amyloid and/or tau pathology, as such hallmarks can arise via multiple convergent or even by pathogenic mechanisms unrelated to human sporadic AD. The 3 × Tg-AD mouse simultaneously expresses 3 rare familial mutant genes that in humans independently produce devastating amyloid-ß protein precursor (AßPP), presenilin-1, and frontotemporal dementias; hence, technically speaking, these mice are not a model of sporadic AD, but are informative in assessing co-evolving amyloid and tau pathologies. While end-stage amyloid and tau pathologies in 3 × Tg-AD mice are similar to those observed in sporadic AD, the pathophysiological mechanisms leading to these lesions are quite different. Comprehensive biochemical and morphological characterizations are important to gauge the predictive value of Tg mice. Investigation of AßPP, amyloid-ß (Aß), and tau in the 3 × Tg-AD model demonstrates AD-like pathology with some key differences compared to human sporadic AD. The biochemical dissection of AßPP reveals different cleavage patterns of the C-terminus of AßPP when compared to human AD, suggesting divergent pathogenic mechanisms. Human tau is concomitantly expressed with AßPP/Aß from an early age while abundant extracellular amyloid plaques and paired helical filaments are manifested from 18 months on. Understanding the strengths and limitations of Tg mouse AD models through rigorous biochemical, pathological, and functional analyses will facilitate the derivation of models that better approximate human sporadic AD.

Chemical characterization of pro-inflammatory amyloid-beta peptides in human atherosclerotic lesions and platelets.

Amyloid-ß (Aß) peptides are intimately involved in the inflammatory pathology of atherosclerotic vascular disease (AVD) and Alzheimer's disease (AD). Although substantial amounts of these peptides are produced in the periphery, their role and significance to vascular disease outside the brain requires further investigation. Amyloid-ß peptides present in the walls of human aorta atherosclerotic lesions as well as activated and non-activated human platelets were isolated using sequential size-exclusion columns and HPLC reverse-phase methods. The Aß peptide isolates were quantified by ELISA and structurally analyzed using MALDI-TOF mass spectrometry procedures. Our experiments revealed that both aorta and platelets contained Aß peptides, predominately Aß40. The source of the Aß pool in aortic atherosclerosis lesions is probably the activated platelets and/or vascular wall cells expressing APP/PN2. Significant levels of Aß42 are present in the plasma, suggesting that this reservoir makes a minor contribution to atherosclerotic plaques. Our data reveal that although aortic atherosclerosis and AD cerebrovascular amyloidosis exhibit clearly divergent end-stage manifestations, both vascular diseases share some key pathophysiological promoting elements and pathways. Whether they happen to be deposited in vessels of the central nervous system or atherosclerotic plaques in the periphery, Aß peptides may promote and perhaps synergize chronic inflammatory processes which culminate in the degeneration, malfunction and ultimate destruction of arterial walls.

Transcranial doppler ultrasound blood flow velocity and pulsatility index as systemic indicators for Alzheimer's disease.

BACKGROUND: Multiple lines of evidence suggest that cardiovascular co-morbidities hasten the onset of Alzheimer's disease (AD) or accelerate its course. METHODS: To evaluate the utility of cerebral vascular physical function and/or condition parameters as potential systemic indicators of AD, transcranial Doppler (TCD) ultrasound was used to assess cerebral blood flow and vascular resistance of the 16 arterial segments comprising the circle of Willis and its major tributaries. RESULTS: Our study showed that decreased arterial mean flow velocity and increased pulsatility index are associated with a clinical diagnosis of presumptive AD. Cerebral blood flow impairment shown by these parameters reflects the global hemodynamic and structural consequences of a multifaceted disease process yielding diffuse congestive microvascular pathology, increased arterial rigidity, and decreased arterial compliance, combined with putative age-associated cardiovascular output declines. CONCLUSIONS: TCD evaluation offers direct physical confirmation of brain perfusion impairment and might ultimately provide a convenient and a noninvasive means to assess the efficacy of medical interventions on cerebral blood flow or reveal incipient AD. In the near term, TCD-based direct assessments of brain perfusion might offer the prospect of preventing or mitigating AD simply by revealing patients who would benefit from interventions to improve circulatory system function.

Intracranial atherosclerosis as a contributing factor to Alzheimer's disease dementia.

BACKGROUND: A substantial body of evidence collected from epidemiologic, correlative, and experimental studies strongly associates atherosclerotic vascular disease (AVD) with Alzheimer's disease (AD). Depending on the precise interrelationship between AVD and AD, systematic application of interventions used to maintain vascular health and function as a component of standard AD therapy offers the prospect of mitigating the presently inexorable course of dementia. To assess this hypothesis, it is vital to rigorously establish the measures of AVD that are most strongly associated with an AD diagnosis. METHODS: A precise neuropathological diagnosis was established for all subjects, using a battery of genetic, clinical, and histological methods. The severity of atherosclerosis in the circle of Willis was quantified by direct digitized measurement of arterial occlusion in postmortem specimens and was compared between AD and nondemented control groups by calculating a corresponding index of occlusion. RESULTS: Atherosclerotic occlusion of the circle of Willis arteries was more extensive in the AD group than in the nondemented control group. Statistically significant differences were also observed between control and AD groups with regard to Braak stage, total plaque score, total neurofibrillary tangle score, total white matter rarefaction score, brain weight, Mini-Mental State Examination scores, and apolipoprotein E allelic frequencies. CONCLUSIONS: Our results, combined with a consideration of the multifaceted effects of impaired cerebral circulation, suggest an immediate need for prospective clinical trials to assess the efficacy of AD prevention using antiatherosclerotic agents.