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.

Reduced clinical and postmortem measures of cardiac pathology in subjects with advanced Alzheimer's Disease.

BACKGROUND: Epidemiological studies indicate a statistical linkage between atherosclerotic vascular disease (ATH) and Alzheimer's disease (AD). Autopsy studies of cardiac disease in AD have been few and inconclusive. In this report, clinical and gross anatomic measures of cardiac disease were compared in deceased human subjects with and without AD. METHODS: Clinically documented cardiovascular conditions from AD (n = 35) and elderly non-demented control subjects (n = 22) were obtained by review of medical records. Coronary artery stenosis and other gross anatomical measures, including heart weight, ventricular wall thickness, valvular circumferences, valvular calcifications and myocardial infarct number and volume were determined at autopsy. RESULTS: Compared to non-demented age-similar control subjects, those with AD had significantly fewer total diagnosed clinical conditions (2.91 vs 4.18), decreased coronary artery stenosis (70.8 vs 74.8%), heart weight (402 vs 489 g for males; 319 vs 412 g for females) and valvular circumferences. Carriage of the Apolipoprotein E-ε4 allele did not influence the degree of coronary stenosis. Group differences in heart weight remained significant after adjustment for age, gender, body mass index and apolipoprotein E genotype while differences in coronary artery stenosis were significantly associated with body mass index alone. CONCLUSIONS: The results are in agreement with an emerging understanding that, while midlife risk factors for ATH increase the risk for the later development of AD, once dementia begins, both risk factors and manifest disease diminish, possibly due to progressive weight loss with increasing dementia as well as disease involvement of the brain's vasomotor centers.

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.

Tg-SwDI transgenic mice exhibit novel alterations in AbetaPP processing, Abeta degradation, and resilient amyloid angiopathy.

Alzheimer's disease (AD) is characterized by the accumulation of extracellular insoluble amyloid, primarily derived from polymerized amyloid-beta (Abeta) peptides. We characterized the chemical composition of the Abeta peptides deposited in the brain parenchyma and cerebrovascular walls of triple transgenic Tg-SwDI mice that produce a rapid and profuse Abeta accumulation. The processing of the N- and C-terminal regions of mutant AbetaPP differs substantially from humans because the brain parenchyma accumulates numerous, diffuse, nonfibrillar plaques, whereas the thalamic microvessels harbor overwhelming amounts of compact, fibrillar, thioflavine-S- and apolipoprotein E-positive amyloid deposits. The abundant accretion of vascular amyloid, despite low AbetaPP transgene expression levels, suggests that inefficient Abeta proteolysis because of conformational changes and dimerization may be key pathogenic factors in this animal model. The disruption of amyloid plaque cores by immunotherapy is accompanied by increased perivascular deposition in both humans and transgenic mice. This analogous susceptibility and response to the disruption of amyloid deposits suggests that Tg-SwDI mice provide an excellent model in which to study the functional aftermath of immunotherapeutic interventions. These mice might also reveal new avenues to promote amyloidogenic AbetaPP processing and fundamental insights into the faulty degradation and clearance of Abeta in AD, pivotal issues in understanding AD pathophysiology and the assessment of new therapeutic agents.

Amyloid beta peptides in human plasma and tissues and their significance for Alzheimer's disease.

BACKGROUND: We evaluated the amounts of amyloid beta (Abeta)) peptides in the central nervous system (CNS) and in reservoirs outside the CNS and their potential impact on Abeta plasma levels and Alzheimer's disease (AD) pathology. METHODS: Amyloid beta levels were measured in (1) the plasma of AD and nondemented (ND) controls in a longitudinal study, (2) the plasma of a cohort of AD patients receiving a cholinesterase inhibitor, and (3) the skeletal muscle, liver, aorta, platelets, leptomeningeal arteries, and in gray and white matter of AD and ND control subjects. RESULTS: Plasma Abeta levels fluctuated over time and among individuals, suggesting continuous contributions from brain and peripheral tissues and associations with reactive circulating proteins. Arteries with atherosclerosis had larger amounts of Abeta40 than disease-free vessels. Inactivated platelets contained more Abeta peptides than activated ones. Substantially more Abeta was present in liver samples from ND patients. Overall, AD brain and skeletal muscle contained increased levels of Abeta. CONCLUSIONS: Efforts to use plasma levels of Abeta peptides as AD biomarkers or disease-staging scales have failed. Peripheral tissues might contribute to both the circulating amyloid pool and AD pathology within the brain and its vasculature. The wide spread of plasma Abeta values is also due in part to the ability of Abeta to bind to a variety of plasma and membrane proteins. Sources outside the CNS must be accounted for because pharmacologic interventions to reduce cerebral amyloid are assessed by monitoring Abeta plasma levels. Furthermore, the long-range impact of Abeta immunotherapy on peripheral Abeta sources should also be considered.

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.

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.

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.

Neuropathology and amyloid-ß spectrum in a bapineuzumab immunotherapy recipient.

The field of Alzheimer's disease (AD) research eagerly awaits the results of a large number of Phase III clinical trials that are underway to investigate the effectiveness of anti-amyloid-ß (Aß) immunotherapy for AD. In this case report, we review the pertinent clinical history, examine the neuropathology, and characterize the Aß profile of an AD patient who received bapineuzumab immunotherapy. The patient received four bapineuzumab infusions over a 39 week period. During the course of this treatment, there was no remarkable change in cognitive impairment as determined by MMSE scores. Forty-eight days after the fourth bapineuzumab infusion was given, MRI revealed that the patient had developed lacunar infarcts and possible vasogenic edema, probably related to immunotherapy, but a subsequent MRI scan 38 days later demonstrated resolution of vasogenic edema. The patient expired due to acute congestive heart failure complicated by progressive AD and cerebrovascular accident 378 days after the first bapineuzumab infusion and 107 days after the end of therapy. Neuropathological and biochemical analysis did not produce evidence of lasting plaque regression or clearance of Aß due to immunotherapy. The Aß species profile of this case was compared with non-immunized AD cases and non-demented controls and found to be similar to non-immunized AD cases. SELDI-TOF mass spectrometric analysis revealed the presence of full-length Aß1₋42 and truncated Aß peptides demonstrating species with and without bapineuzumab specific epitopes. These results suggest that, in this particular case, bapineuzumab immunotherapy neither resulted in detectable clearance of amyloid plaques nor prevented further cognitive impairment.

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.

The biochemical aftermath of anti-amyloid immunotherapy.

BACKGROUND: Active and passive immunotherapy in both amyloid-beta precursor protein (APP) transgenic mice and Alzheimer's Disease (AD) patients have resulted in remarkable reductions in amyloid plaque accumulation, although the degree of amyloid regression has been highly variable. Nine individuals with a clinical diagnosis of AD dementia were actively immunized with the Aß peptide 1-42 (AN-1792) and subjected to detailed postmortem biochemical analyses. These patients were compared to 6 non-immunized AD cases and 5 non-demented control (NDC) cases. RESULTS: All patients were assessed for the presence of AD pathology including amyloid plaques, neurofibrillary tangles and vascular amyloidosis. This effort revealed that two immunotherapy recipients had dementia as a consequence of diseases other than AD. Direct neuropathological examination consistently demonstrated small to extensive areas in which amyloid plaques apparently were disrupted. Characterization of Aß species remnants by ELISA suggested that total Aß levels may have been reduced, although because the amounts of Aß peptides among treated individuals were extremely variable, those data must be regarded as tentative. Chromatographic analysis and Western blots revealed abundant dimeric Aß peptides. SELDI-TOF mass spectrometry demonstrated a substantive number of Aß-related peptides, some of them with elongated C-terminal sequences. Pro-inflammatory TNF-α levels were significantly increased in the gray matter of immunized AD cases compared to the NDC and non-immunized AD groups. CONCLUSIONS: Immunotherapy responses were characterized by extreme variability. Considering the broad range of biological variation that characterizes aging and complicates the recognition of reliable AD biomarkers, such disparities will make the interpretation of outcomes derived from epidemiologic and therapeutic investigations challenging. Although in some cases the apparent removal of amyloid plaques by AN-1792 was impressive, proportionate alterations in the clinical progression of AD were not evident. The fact that plaque elimination did not alter the trajectory of decline into dementia suggests the likelihood that these deposits alone are not the underlying cause of dementia.

Histopathological and molecular heterogeneity among individuals with dementia associated with Presenilin mutations.

BACKGROUND: Mutations in the presenilin (PSEN) genes are associated with early-onset familial Alzheimer's disease (FAD). Biochemical characterizations and comparisons have revealed that many PSEN mutations alter gamma-secretase activity to promote accumulation of toxic Abeta42 peptides. In this study, we compared the histopathologic and biochemical profiles of ten FAD cases expressing independent PSEN mutations and determined the degradation patterns of amyloid-beta precursor protein (AbetaPP), Notch, N-cadherin and Erb-B4 by gamma-secretase. In addition, the levels of Abeta40/42 peptides were quantified by ELISA. RESULTS: We observed a wide variation in type, number and distribution of amyloid deposits and neurofibrillary tangles. Four of the ten cases examined exhibited a substantial enrichment in the relative proportions of Abeta40 over Abeta42. The AbetaPP N-terminal and C-terminal fragments and Tau species, assessed by Western blots and scanning densitometry, also demonstrated a wide variation. The Notch-1 intracellular domain was negligible by Western blotting in seven PSEN cases. There was significant N-cadherin and Erb-B4 peptide heterogeneity among the different PSEN mutations. CONCLUSION: These observations imply that missense mutations in PSEN genes can alter a range of key gamma-secretase activities to produce an array of subtly different biochemical, neuropathological and clinical manifestations. Beyond the broad common features of dementia, plaques and tangles, the various PSEN mutations resulted in a wide heterogeneity and complexity and differed from sporadic AD.