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The characteristic insoluble, senile (neuritic) plaques found extracellularly in brains of patients with Alzheimer's disease (AD) contain the fibrillar form of beta-amyloid (Abeta42). A substantial proportion of autopsied elderly brains have demonstrated DNA evidence of herpes simplex virus type 1 (HSV-1) infiltration. HSV-1-infected cells produce significant quantities of non-infectious, non-DNA-containing light particles (L-particles) comprised of viral envelope and tegument proteins. HSV-induced L-particles can be exocytosed out of their host cells. This report advances the hypothesis that (1) Abeta binds to L-particles; (2) Abeta permeabilizes L-particles, destroying the integrity of the envelope and allowing the contained tegument proteins to spill into the extracellular space; and (3) these events are followed by a conformational shift of Abeta into its fibrillar form, physically trapping the L-particle-derived substances and resulting in the plaques characteristic of AD. These hypotheses are supported by reports of biomolecular changes and pathophysiologies which have been simultaneously observed in both AD- and HSV-infected brains.

In the absence of any naturally occurring animal model of Alzheimer's disease (AD), the British conviction in the 1970's that clinicopathological investigations of human cases offered the best approach to unraveling the pathogenesis of AD rapidly influenced clinical neuroscientists, neuropathologists and funding agencies in Canada and the USA. But as with my confreres, years of our quantifying AD lesions in autopsy brains have yet to yield definitive conclusions about what is the most important neuronal abnormality. However, during my elusive search, evidence has been slowly gathered that reactivation of latent Herpes simplex virus, traveling from trigeminal ganglia into neighbouring mesial temporal cortex, might best explain the limbic predilection for and earliest site of neurofibrillary tangle formation. This maturing hypothesis may serendipitously prove to have been a more essential byproduct of generating the voluminous data than all the publications from our laboratory that reflected endless hours of quantitative morphometry.

Herpes simplex virus type 1 (HSV-1) is latent in the nervous system of most humans. Ball [Can J Neurol Sci 9 (1982) 303] first suggested the hypothesis that HSV-1 could be involved in the pathogenesis of Alzheimer's Disease (AD) by noting that regions of the brain particularly and earliest affected in AD were the same as those most damaged during HSV encephalitis. Data from Itzhaki's research suggests that HSV-1 in the brain and the carriage of an apolipoprotein E allele 4 (ApoE e4) together confer risk for AD [J Pathol 97 (2002) 395], [Mol Chem Neuropathol 28 (1996) 135], [Alzheimer's Rep 1 (1998) 173], [Biochem Soc Trans 26 (1998) 273]. Of the two other studies based on Itzhaki's findings, one showed similar results [Lancet 349 (1997) 1102], and the other showed a similar trend [Lancet 351 (1998) 1330], [Lancet 352 (1998) 1312]. To further examine the role of HSV-1 in the etiology of AD, we have formulated a Neuroinvasive Score that quantifies the presence and viral load of HSV-1 in eight brain regions. These regions are: entorhinal cortex, hippocampus, pons, cerebellum, and neocortex (temporal, parietal, occipital, and frontal). We hypothesize that the Neuroinvasive Score that encompasses the presence, amount, and extent of HSV-1 spreading (neuroinvasiveness), will correlate with the genetic risk factor, ApoE e4, in the assessment of autopsy samples from AD patients. If the neuroinvasive score can be directly correlated to the different stages of AD (mild, moderate, severe), this will strengthen the hypothesis that HSV-1 is involved in AD and that ApoE e4 also confers risk for the development and progression of AD.

Objective: To assess whether changes in antemortem MRI brain volume measurements are valid predictors of subsequent Alzheimer disease (AD) pathology., Methods: Thirty-nine subjects, 15 nondemented and 24 with cognitive impairment, were followed until death. Regional postmortem measures of senile plaque (SP) and neurofibrillary tangle (NFT) severity were examined in relationship to cross-sectional and longitudinal volumetric measurements obtained from antemortem MRI., Results: Total brain volume change over time was related to the accumulation of cortical NFT. The rate of ventricular CSF volume increase was related to both cortical NFT and SP. The last hippocampal volume prior to death was related to hippocampal NFT burden; the rate of hippocampal volume atrophy was not related to hippocampal NFT pathology. These significant relationships continue to exist when all nondemented subjects are excluded from analysis. In subjects with cognitive impairment, the best predictor of cortical NFT and SP is the rate of ventricular volume increase. Excluding subjects with long duration between MRI and death did not appreciably alter results., Conclusions: MRI volumes measured over time are valid biomarkers of pathologic progression of AD across a range of antemortem clinical states. The rate of ventricular volume enlargement can be used to monitor disease progression or response to treatment in future clinical trials that are targeted at NFT and SP pathology.

Objective: To describe the relationship between neuropathologic aging and longitudinal measures of cognitive function in healthy oldest old individuals., Methods: Nondemented individuals without cardiovascular or other age-associated diseases of age > or =85 years were followed until death. Regional postmortem measures of senile plaque (SP) and neurofibrillary tangle (NFT) severity were examined in relationship to clinical status, cognitive measures, and rate of cognitive change., Results: Among 19 healthy individuals, 10 became demented or had incipient dementia develop. Clinical status and rate of change in cognitive scores correlated with increasing brain lesion burden, particularly in neocortical regions. Compared to demented individuals, nondemented individuals had few or no neocortical NFT (p = 0.009) or SP (p = 0.001). There was a strong correlation between rate of cognitive change on Mini-Mental State Examination (MMSE) and neocortical NFT (r = 0.859, p = 0.001). The few NFT and SP in nondemented patients had a predilection for limbic areas., Conclusions: These results support a continuum in which AD is infrequent in the healthy, cognitively stable, oldest old. The minimal abnormalities in cognitively stable individuals are consistent with the notion that preclinical pathologic AD precedes obvious cognitive impairment. Longitudinal cognitive testing shows an increased burden of neuropathologic changes in those who have cognitive decline but are not functionally impaired and do not meet criteria for the diagnosis of dementia. The strong relationship between cumulative pathologic changes and rate of cognitive decline suggests that these lesions may have clinical consequences at any age and are not likely to be benign senescent changes.

The specific diagnosis of AD as a particular dementia from which a patient suffered assumes, debatably, a reasonably pure clinicopathological entity in which the same concatenation of lesions will not be encountered in others dying with a similar clinical disorder. Statistically complex computations such as multivariate analyses of morphometric data from our laboratory and similar attempts in Swedish and British series may not prove pragmatic for pathological confirmation. The Braaks' schema posits six stages in the evolution of AD. Unfortunately, application of this model to 50 British autopsies cannot reliably identify those cases clinically diagnosed as demented. Furthermore, lack of universal definition for each of the probable lesional subtypes augments the difficulty devising a quantitative consensus. Disease stage refers to a progressive increase in anatomical (geographic) extent of involvement, whereas, grade refers to a progressive increase in severity of affliction within any one site. There is only a tendency for stage and grade to progress in parallel. Nor is it obligatory that either always does progress. More energies should be concentrated upon determining which histopathological abnormality is most injurious to neuronal integrity. Dutch workers opine that in both normal aging and AD, claims of massive, neocortical nerve cell loss may have been based on inadequate morphometry and/or a loss of markers. Requiring urgent resolution is whether cellular changes seen in brains of aging normals represent merely the earliest phase of typical AD (and therefore a good model for Alzheimer pathogenesis), or rather reflect a totally different aging syndrome distinct from AD. We have proposed that abnormalities in the hippocampal formation (with or without neocortical neuronal lesions) may underlie a decline of all higher cognitive functions in senile dementia Alzheimer type. West and colleagues optical disector approach likewise shows that neurodegeneration associated within aging individuals' hippocampi is quantitatively and qualitatively distinct from the neuronal loss in AD. Clinical confreres' imprecision whether or when to term subtle cognitive loss "incipient AD" is understandably mirrored by residual neuropathological struggles to dichotomize such brains as "normative aging" distinct from "putative AD."

Semi-quantitative neuropathological analysis and morphometric evaluations of the brains of 5 elderly people (63-85 years old) dying following a 5-27-year history of dementia reveal that, despite exhaustive survey of all major brain regions, 4 of these cases show virtually no histopathological lesions of Alzheimer's disease. Instead their CNS manifests a severe, bilateral, neuronal depletion, and astrogliosis afflicting the lateral temporal neocortex, highly compatible with a previous herpetic viral encephalitis. In the fifth case unilateral neocortical temporal lobe sclerosis is accompanied by Alzheimer's disease, but with much more dense Alzheimer lesions throughout the contralateral cerebral hemisphere. Three of these 5 individuals had a history either of herpes zoster of the skin or of a single episode of viral meningoencephalitis, roughly concomitant with the onset of memory loss. This clinical and pathological evidence that a remote herpes virus encephalopathy (when bilateral) "protects" that brain against Alzheimer's disease strengthens our growing suspicion that incomplete replication cycles of herpes simplex or zoster virus, following repeated reactivation within neurons of the trigeminal ganglia, may link these viruses to the pathogenetic cascade underlying dementia of the Alzheimer type.

Protein kinase C (PKC) is an important intracellular signalling enzyme. Numerous studies have suggested that alterations in this enzyme occur in aging and dementia. The objective of this study was to examine PKC in the cerebral microcirculation in aging and Alzheimer's disease. PKC activity, amount, and isoform distribution were analyzed in microvessels from adult and aged rodents as well as from Alzheimer patients and nondemented elderly controls. PKC activity was lower in Alzheimer vessels than in vessels from control brains, despite the presence of similar levels of PKC enzyme. In contrast, both activity and enzyme levels in young and aged rats were comparable. The beta-isoform was present in both rat and human microvessels and there were no age- or disease-related alterations. The loss in activity in cerebromicrovascular PKC in Alzheimer's suggest that perturbations in phosphorylation signalling cascades may exist at the Alzheimer blood-brain barrier.

Despite the close morphological association of beta-amyloid and vascular cells, the functional effects of amyloid in cerebral endothelial cells in Alzheimer's disease have not been assessed. In this study, effects of amyloid fractions purified from senile plaques of AD brains were compared to synthetic amyloid peptides for their ability to affect brain endothelial cells in vitro. Our results indicate that plaque-derived amyloid inhibit brain endothelial cell proliferation in vitro by 40%. This inhibition was specific for plaque-derived amyloid, was not evoked by synthetic A beta 1-40, and was not mediated by alterations in intracellular calcium levels. Amyloid fractions from AD brains, although not directly toxic to brain endothelial cells, inhibit endothelial replication in vitro and therefore could alter the ability of vessels to repair and regenerate after injury.

It has been recently reported that the 72 kDa proteolytic enzyme gelatinase A/type IV collagenase/matrix metalloproteinase 2 (MMP2) hydrolyzed the Lys 16-Leu 17 peptide bond of a synthetic decapeptide (YEVHHQKLVFF) representing the soluble A beta sequence of amino acid residues 10-20. Our aim was to test if this enzyme could also degrade the insoluble 40-42 residues long A beta peptides purified from Alzheimer Disease brain. Our results indicate that MMP2 hydrolyzes A beta 1-40 and A beta 1-42 peptides at Lys 16-Leu 17, at Leu 34-Met 35, and Met 35-Val 36 peptide bonds. These results suggest that MMP2 has the ability of degrading A beta of AD in vitro. If this hydrolysis also occurs in the brain's extracellular matrix, the enzymatic action of gelatinase a could prevent the generation of amyloidogenic A beta 1-40(42).

Amyloid plaque cores were purified from Alzheimer disease brain tissue. Plaque core proteins were solubilized in formic acid which upon dialysis against guanidinium hydrochloride (GuHCl) partitioned into soluble (approximately 15%) and insoluble (approximately 85%) components. The GuHCl-soluble fraction contained beta-amyloid1-40, whereas the GuHCl-insoluble fraction was fractionated into six components by size exclusion HPLC: S1 (> 200 kDa), S2 (200 kDa), S3 (45 kDa), S4 (15 kDa), S5 (10 kDa), and S6 (5 kDa). Removal of the GuHCl reconstituted 10-nm filaments composed of two intertwined 5-nm strands. Fractions S5 and S6 also yielded filamentous structures when treated similarly, whereas fractions S1-S4 yielded amorphous aggregates. Chemical analysis identified S4-S6 as multimeric and monomeric beta-amyloid. Immunochemical analyses revealed alpha 1-antichymotrypsin and non-beta-amyloid segments of the beta-amyloid precursor protein within fractions S1 and S2. Several saccharide components were identified within plaque core protein preparations by fluorescence and electron microscopy, as seen with fluorescein isothiocyanate- and colloidal gold-conjugated lectins. We have shown previously that this plaque core protein complex is more toxic to neuronal cultures than beta-amyloid. The non-beta-amyloid components likely mediate this additional toxicity, imposing a significant influence on the pathophysiology of Alzheimer disease.

The structure of beta-amyloid (beta A) from Alzheimer disease brains was examined to determine if post-translational modifications might be linked to the abnormal deposition of this peptide in the diseased tissue. The beta A peptides were isolated from the compact amyloid cores of neuritic plaques and separated from minor glycoprotein components by size-exclusion high-pressure liquid chromatography (HPLC). This parenchymal beta A has a maximal length of 42 residues, but shorter forms with "ragged" NH2 termini are also present. Tryptic peptide analysis revealed heterogeneity in the beta A1-5 and beta A6-16 peptides, each of which eluted as four peaks on reverse phase HPLC. Amino acid composition and sequence analyses, mass spectrometry, enzymatic methylation, and stereoisomer determinations revealed that these multiple peptide forms resulted from structural rearrangements of the aspartyl residues at beta A positions 1 and 7. The L-isoaspartyl form predominates at each of these positions, whereas the D-isoaspartyl, L-aspartyl, and D-aspartyl forms are present in lesser amounts. beta A purified from the leptomeningeal microvasculature contains the same structural alterations as parenchymal beta A, but is 2 residues shorter at its COOH terminus. Using two different purification protocols, and using a synthetic beta A1-42 peptide as a control, we show that these modifications arose endogenously and were not caused by the experimental manipulations. The abundance of structurally altered aspartyl residues may profoundly affect the conformation of the beta A protein within plaque cores and thus significantly impact normal catabolic processes designed to limit its deposition. These alterations may therefore contribute to the production and stability of beta-amyloid deposits in Alzheimer brain tissue.

We examined patterns of cerebral glucose metabolism in 33 patients with dementia of the Alzheimer type by applying principal component analysis to identify subgroups. Four subgroups were identified: one with predominant parietotemporal hypometabolism (15 patients); one with paralimbic metabolic deficits (8 patients); one with left hemisphere neocortical abnormality (5 patients); and one with frontal and parietotemporal deficit (5 patients). Differences among the subgroups were found in neuropsychological impairments and prevalence of psychiatric symptoms. These metabolic subgroups could not be explained on the basis of dementia severity, illness duration, or age, but were most likely related to an underlying pathology with a variable regional distribution.

The paired helical filaments (PHFs) of Alzheimer's disease were purified by a strategy in which the neurons and amyloid plaque cores of protein (APCP) were initially isolated. This was achieved by several steps of isocratic sucrose centrifugations of increasing molarity and a discontinuous isotonic Percoll density gradient. After collagenase elimination of contaminating blood vessels, lysis of neurons was produced by SDS treatment. The released PHF cytoskeletons were separated from contaminating APCP and lipofuscin by sucrose density gradient. A final step consisted in the chemical purification of highly enriched PHFs and APCP components via a formic acid to guanidine hydrochloride transition. PHFs and APCPs were fractionated by size exclusion HPLC and further characterized and quantitated by automatic amino acid analysis. We also present some of the morphological and immunochemical characteristics of PHF polypeptides and APCP. Our studies indicate that apart from differences in localization and morphology, PHF and APCP significantly differ in (a) chemical structure (peptide and amino acid composition); (b) epitope specificity (antiubiquitin, antitau, antineurofilament); (c) physicochemical properties (structural conformation in guanidine hydrochloride); and (d) thioflavine T fluorescence emission. These parameters strongly suggest important differences in the composition and, probably, in the etiopathology of PHF and APCP of Alzheimer's disease.

The nerve cell counts indicated that the neuronal population of the nucleus basalis of Meynert (nbM) was bilaterally symmetrical in both control and Alzheimer-diseased brains. In addition, the discussion deals with the possibility that a loss of neurons from rostral vs caudal parts of the nbM may occur during different stages of the disease.

Hippocampal capillary and arteriolar measurements showed a significant reduction in capacity with normal aging. Alzheimer's dementia was not associated with any further reduction; in fact regional variations suggested that the zones of Ammon's horn most severely affected by tangles and granulovacuoles retained the best vascular capacity. The arterial system supplying the hippocampus, from the posterior cerebral artery to the series of small hippocampal arteries, was also assessed. Its capacity, as judged by arterial diameters, was similarly found to decrease significantly with age; the arterial diameters of Alzheimer cases were (insignificantly) greater than those of the normal old. Calcarine capillary and arteriolar measurements also indicated a marked reduction of capacity with normal aging, and, as before, in Alzheimer's dementia there was no further significant change. All three phases of the study thus suggest that cerebrovascular capacity in Alzheimer's dementia is at least as good as in the normal old, if not better. Senile (neuritic) plaques with amyloid cores and their relationship to the microvasculature were examined in the calcarine cortex. In both normal old and Alzheimer cases the plaques tended to congregate where capillaries were densest. Their correlation with capillary density was however better in the normal old, raising the question of whether their pathogenesis might differ in the two conditions.

Seven members of a family succumbed to prolonged dementing illnesses. In two, those dementia lasted 10 years, spongiform encephalopathy was found at autopsy. This duration of illness has not been a feature in other instances of familial Creutzfeldt-Jakob disease.

Postmortem human brain samples were taken from non-neurological controls as well as demented subjects who died with Alzheimer's disease (AD), multi-infarct dementia (MID), or a combination of AD and MID dementia (MIXED). Choline acetyltransferase (ChAT) activity was measured radiometrically using [1-14C]acetyl-coenzyme A as the substrate, muscarinic binding was assayed with [3H]quinuclidinyl benzilate, and the proportion of binding associated with high affinity agonist sites was measured by carbamylcholine displacement of the radioligand. Relative to control, ChAT activity was significantly reduced (p less than or equal to 0.01) in samples taken from the temporal, frontal, and hippocampal areas of demented patients. A small elevation in Bmax was noted in the hippocampal endplate (p less than or equal to 0.01) (AD vs. control) and the H1-subiculum region (p less than or equal to 0.05) (AD vs. all other groups). In addition, the percentage of binding associated with high affinity agonist sites was greater in the frontal cortex of AD and MID samples (p less than or equal to 0.05). The results suggest a regionally specific upregulation of cerebral muscarinic receptors in dementia, especially in AD.

Although establishing that a patient is suffering from dementia of the Alzheimer type initially reflects a clinician's opinion, neuropathological study is for the present the most definitive examination to confirm the clinical diagnosis of Alzheimer disease. We review several comprehensive publications attempting on a quantitative basis to differentiate the changes occurring with normal aging of the human brain from those indicative of Alzheimer disease. New morphometric data on 5 histopathological lesions in the mesial temporal cortex of 42 subjects indicate that, when multivariate analyses are performed on such microscopic information, a diagnostic prediction about the brain of any unknown individual should indeed be possible with a statistically calculated degree of certainty.

Twelve regions of grey matter from the brains of 25 Beagle dogs, varying from one to over 16 years in age, were serially sectioned and sequentially scanned with a semi-automated sampling stage microscope, in a morphometric search for neuritic plaques, neurofibrillary tangles, and evidence of nerve cell loss. Examination of 227,776 light microscopic fields failed to reveal any senile plaques or neurofibrillary tangles. The neuronal densities, which ranged from 473 to 37,014 nucleolated neurons/mm3, showed no significant relationship with ageing. Neuronal lesions of Alzheimer type may be more typical of the human CNS; and physiological evidence for regionally reduced glucose metabolic rate in this animal model may require other structural alterations for its explanation.