Taihung Duong

Immunodetection of the amyloid P component in Alzheimer's disease

SummaryAmyloid P component (AP), a plasma constituent normally not found in brain arenchyma, has been immunohistochemically determined in brains from patients with Alzheimers disease (AD). Tissue came from 11 clinically diagnosed and neuropathologically verified AD patients and from 6 normal aged controls. Positive labeling for AP was observed in amyloidotic blood vessels, senile plaques (SP) and neurofibrillary tangles (NFT). The immunoreactivity was specific for these AD-associated lesions and clearly revealed their morphological appearance. Affected blood vessels appeared to be mainly of the arteriolar types and were labeled abluminally in short segments. SP constituents such as amyloid fibrils, anyloid core and degenerative axonal and dendritic processes were positive for AP antiserum; the morphology and distribution of immunoreactive SP corresponded to previous descriptions. Labeling of NFT revealed the morphology of paired helical and straight filaments. In all cerebral areas studied, tangle-bearing neurons were immunoreactive to AP antiserum, suggesting that AP is involved in early cellular development of NFT. Given the large molecular weight of AP (about 220,000), these results point to a potential impairment of the blood-brain barrier in AD. Since AP is always present in systemic amyloidosis, its detection in cerebral amyloidosis associated with AD may suggest mechanisms common to the two disorders.

C-reactive protein-like immunoreactivity in the neurofibrillary tangles of Alzheimer's disease.

C-reactive protein (CRP) is a plasma acute-phase protein, normally not found in the brain. Previous studies have demonstrated the presence of CRP in the senile plaques of Alzheimers disease (AD). In this study, the presence of CRP-like immunoreactivity in AD neurofibrillary tangles (NFT) was demonstrated following pre-treatment of tissue sections with formic acid. CRP-like immunoreactivity was observed in both extracellular and intracellular NFT and was co-localized with the NFT marker PHF-1 and the amyloid P component (AP). The CRP-like immunoreactive NFT were less numerous and more limited in their distribution than PHF-1 or AP-immunoreactive NFT. The present results further support an involvement of inflammatory processes in the etiology of AD.

Neuronal cytoskeletal abnormalities in human cerebral cortical dysplasia

The cytoskeletal abnormalities of cortical neurons in human cerebral cortical dysplasia were compared by immunohistochemical methods to the neurofibrillary tangles of Alzheimers disease (AD). Surgical specimens from cortical resections performed for the treatment of intractable childhood seizures as well as autopsied samples from AD patients were analyzed with different antibodies directed against high- or medium-molecular mass neurofilament epitopes, phosphorylated or non-phosphorylated forms of neurofilaments, ubiquitin, the microtubule-associated protein tau, and paired helical filaments (PHF), a defining feature of AD tangles. A strong abnormal increase in immunoreactivity to the high and medium molecular mass neurofilament epitopes was seen in hypertrophic neurons of cortical dysplasia. These neurofilamentous accumulations of cortical dysplasia as well as AD tangles also displayed immunoreactivity with antibodies also displayed immunoreactivity with antibodies against phosphorylated and non-phosphorylated neurofilament epitopes, tau and ubiquitin. Only the AD tangles, however, were immunoreactive to the antiserum to PHF. These results replicate and extend our previous findings that the neurofibrillary accumulations in cerebral cortical dysplasia share some common antigens with the neurofibrillary tangles of AD but do not demonstrate immunoreactivity to PHF antiserum. The results also suggest that the cytoskeletal abnormalities observed in neurons of cortical dysplasia may result in part from alterations in the level of expression, in phosphorylation state or in transport of cytoskeletal components.

A Reexamination of Aluminum in Alzheimer's Disease: Analysis by Energy Dispersive X-ray Microprobe and Flameless Atomic Absorption Spectrophotometry

We have attempted to verify the presence of increased aluminum (Al) levels in Alzheimers disease (AD) brains by energy dispersive X-ray microanalysis (EDX) and flameless atomic absorption spectrophotometry (AAS). Tissue from seven AD brains, mounted on carbon polymerized coverslips, were stained with Congo-red or treated immunohistochemically to allow optical localization of AD-associated lesions during EDX. Despite a demonstrated sensitivity of 20-25 ppm, we were unable to detect Al in either plaque cores or neurons containing neurofibrillary tangles. For AAS, wet weight samples (ranging from 48-144 mg) from six of the seven AD brains and four controls were selected from regions similar to those studied under EDX, i.e., Brodmann areas 9, 11, 28, 46, 47, and the hippocampus. The tissue surrounding each sample site was sectioned and stained for thioflavin S. Both controls and AD samples revealed similar levels of Al ranging from undetectable to 1.80 ng/mg wet wt. (mean AD: 0.28 +/- 0.39 (SD), control: 0.54 +/- 0.58 (SD], independent of degree of histopathology or age of the case. We conclude that the combined strengths of these two techniques on similar tissue specimens demonstrate that abnormal Al levels are not required to produce the histologic findings of AD and that this element may not accumulate in the aging brain. It is unlikely, therefore, that Al is essential in the etiology of pathogenesis of plaques and tangles in AD. Als role as a primary or secondarily associated event, when present, needs further delineation.

Denervation microangiopathy in senile dementia, Alzheimer type.

Structural analysis of the capillary plexus in the brains of 5 patients with clinical and neuropathological diagnosis of Senile Dementia, Alzheimer Type, revealed a group of striking physical alterations compared with tissue specimens from 5 age-matched controls. Capillary walls were thickened with irregular lumpy, nodulated contours which appeared due, in part, to infiltration of the vascular wall with rounded cell-like bodies. In some cases, these resembled the perikarya of pericytes or monocytes, or their protoplasmic extensions, which were often filled with lipids. In each case, there was no trace of the perivascular neural plexus which regularly invests the microvasculature of the brain parenchyma. The loss of this neural plexus, believed to originate largely from locus ceruleus and the basal forebrain, may be related to the changes in capillary wall structure, and these, in turn, may lead to profound alterations in blood-brain barrier function. We suggest that this subcortically induced denervation microangiopathy may serve as a pathogenic factor in the development of SDAT.

The in vitro neuronal toxicity of pentraxins associated with Alzheimer's disease brain lesions

Serum amyloid P component (AP) and C-reactive protein (CRP) are normal serum components which belong to the pentraxin family of proteins. These proteins have been previously localized by immunohistochemical method to the brain lesions of Alzheimers disease (AD). AP is a constant constituent of amyloid deposits including those found in AD. Both AP and CRP have been localized to AD neurofibrillary tangles. An indirect role for these proteins has been previously suggested in the etiology of AD. We studied the effects of serum AP and CRP on a human-derived neuronal cell line (hNT). In treated cell cultures, AP and CRP were detected immunohistochemically within hNT neurons, indicating cellular uptake of these proteins. Serum AP at the lowest serum physiological concentration (8 microgram/ml) showed a marked toxicity to hNT neurons. CRP also displayed toxicity to the hNT neurons but at a level compatible with inflammatory states (50 microgram/ml). These results suggest a more direct role for serum AP and CRP in the pathogenesis of AD.

Microtubule-associated proteins tau and amyloid P component in Alzheimer's disease

The localization of the intracerebral microtubule-associated proteins tau (MAP-tau) has been compared to that of amyloid P component (AP), an extracerebral protein, by single- and double-antigen immunohistochemistry in neurofibrillary tangles of Alzheimers brains. The results show that, individually, MAP-tau and AP may be observed in all stages of neurofibrillary tangle (NFT) formation. However, NFT labeled by MAP-tau and those labeled by AP largely do not overlap in their distribution. Furthermore, within the few NFT double-labeled by MAP-tau and AP, there was an inverse relationship between the immunoreactivity to MAP-tau and to AP. It is suggested that MAP-tau and AP are incorporated at different times into NFT and that this difference in the timing of NFT expression of these 2 proteins may be useful in the study of progressive NFT formation.

On the possible relationship of cortical microvascular pathology to blood brain barrier changes in Alzheimer's disease

A group of alterations in the structure of cortical microvessels is described in the brain tissue of neuropathologically confirmed patients with Alzheimers disease. These changes include irregular thickening of the vessel walls, infiltration with amyloid and the serum P component of amyloid, loss of the perivascular neural plexus and the frequent occurrence of pits and lacunae in vessel walls. The possibility that these alterations may be related to blood brain barrier defects is suggested.

Immunohistochemical analysis of the basal forebrain in Alzheimer's disease.

An immunohistochemical analysis utilizing antibodies to glial fibrillary acid protein (GFAP), microglia, beta-amyloid, amyloid P-component, neurofibrillary tangles (NFT), and microtubule associated protein-tau (MAP-tau) was performed on the cholinergic basal forebrain in Alzheimers disease (AD). This severely compromised system, which includes the nucleus basalis of Meynert, is largely responsible for the massive loss of cortical and subcortical cholinergic innervation in the diseased state. Our study juxtaposes the basal forebrain immunohistopathology to the hippocampus, amygdala, and entorhinal cortex in AD. Key findings include a progressive degeneration of these cholinergic neurons characterized by the formation of immunoreactively atypical NFT, the loss of intraneuronal lipofuscin, a lack of senile plaque and beta-amyloid deposition within the basal forebrain, and end-stage gliosis without residual extracellular NFT. These structural and compositional differences suggest a unique pathogenesis of the basal forebrain separate from other cortical regions in AD.

Immunoreactivity patterns in neurofibrillary tangles of the inferior temporal cortex in Alzheimer disease

The distributions of various immunohistochemical markers of neurofibrillary tangles (NFT) were compared to that of a normal nerve cell cytoskeletal marker, SMI32, in the inferior temporal cortex of Alzheimer brains and normal aged controls. NFT markers included antibodies to the microtubule-associated proteins tau, ubiquitin, or amyloid P component (AP). The results showed that, in our group of patients, the decrease of SMI32 immunoreactivity in the Alzheimer temporal cortex is paralleled by an increase in AP immunoreactivity in neurons and neurofibrillary tangles. This suggests that AP may play an important role in NFT formation or evolution in Alzheimer disease.