A case of familial, atypical Alzheimer's disease: immunohistochemical study of amyloid P-component

Human neurons generate C-reactive protein and amyloid P: upregulation in Alzheimer's disease

C-reactive protein (CRP) and amyloid P (AP) are pentraxins which are associated with many pathological lesions, including the amyloid deposits and neurofibrillary tangles (NFTs) of Alzheimer disease (AD). It has always been assumed that they are generated by liver and delivered to their sites of action by serum. Here we report by in situ hydridization, reverse transcriptase-polymerase chain reaction analysis, Western blotting and immunohistochemistry that the mRNAs and proteins of both CRP and AP are concentrated in pyramidal neurons and are upregulated in affected areas of AD brain. Controlling pentraxin production at the tissue level may be important in reducing inflammatory damage in AD.

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 Alzheimer's 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.

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 Alzheimer's 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.

Serum amyloid P component prevents proteolysis of the amyloid fibrils of Alzheimer disease and systemic amyloidosis

Extracellular deposition of amyloid fibrils is responsible for the pathology in the systemic amyloidoses and probably also in Alzheimer disease [Haass, C. & Selkoe, D. J. (1993) Cell 75, 1039-1042] and type II diabetes mellitus [Lorenzo, A., Razzaboni, B., Weir, G. C. & Yankner, B. A. (1994) Nature (London) 368, 756-760]. The fibrils themselves are relatively resistant to proteolysis in vitro but amyloid deposits do regress in vivo, usually with clinical benefit, if new amyloid fibril formation can be halted. Serum amyloid P component (SAP) binds to all types of amyloid fibrils and is a universal constituent of amyloid deposits, including the plaques, amorphous amyloid beta protein deposits and neurofibrillary tangles of Alzheimer disease [Coria, F., Castano, E., Prelli, F., Larrondo-Lillo, M., van Duinen, S., Shelanski, M. L. & Frangione, B. (1988) Lab. Invest. 58, 454-458; Duong, T., Pommier, E. C. & Scheibel, A. B. (1989) Acta Neuropathol. 78, 429-437]. Here we show that SAP prevents proteolysis of the amyloid fibrils of Alzheimer disease, of systemic amyloid A amyloidosis and of systemic monoclonal light chain amyloidosis and may thereby contribute to their persistence in vivo. SAP is not an enzyme inhibitor and is protective only when bound to the fibrils. Interference with binding of SAP to amyloid fibrils in vivo is thus an attractive therapeutic objective, achievement of which should promote regression of the deposits.

Localization of amyloid P component in human brain: vascular staining patterns and association with Alzheimer's disease lesions

Amyloid P component is a normal serum protein that is highly conserved across phylogeny. Although it resembles the classic acute-phase reactant C-reactive protein, and is considered to be a normal extracellular matrix component, its physiologic role in humans is unknown. Amyloid P component is also colocalized with accumulations of all recognized forms of amyloid. The present study uses light and electron microscopy to compare the cerebral localization of amyloid P component in cases with (n = 19) and without (n = 15) Alzheimer's disease (AD). In non-AD cases, amyloid P component was predominantly localized to the cerebrovasculature. Perivascular staining was observed in most cases, more so in the white than in the gray matter. In AD cases, amyloid P component was localized to all three characteristics histopathologic lesions, namely, neurofibrillary tangles, senile plaques, and amyloid angiopathy. Furthermore, in cases with prominent staining of gray matter parenchymal lesions, intravascular staining was decreased. Given the fixation and processing methods used, amyloid P component was never seen to be localized to the cerebrovascular basement membrane. These data argue against amyloid P component's postulated role as the anchor for vascular beta-amyloid deposition. Because there is no evidence for intrinsic amyloid P component production in brain, its perivascular and parenchymal distributions suggest either compromise of the blood-brain barrier or transport across vascular endothelium.

Vascular basement membrane components and the lesions of Alzheimer's disease: light and electron microscopic analyses

Alzheimer's disease (AD) is one of several systemic and cerebral diseases that involve the abnormal deposition of fibrillar proteins called amyloids. All amyloids share conformational and staining characteristics, as well as an association with resident tissue macrophages and two extracellular matrix components [heparan sulfate proteoglycan (HSPG) and amyloid P component]. Vascular, glomerular, and Schwann cell basement membrane pathologies have been documented in many forms of amyloidosis, and often amyloid fibrils fuse to and project from the basement membrane in these diseases. The present report demonstrates the vascular basement membrane (VBM) alterations in AD autopsy samples, and details the methodologies used. Electron microscopy reveals the fusion of amyloid fibrils with the VBM and the alteration of the VBM in the absence of amyloid accumulation. Double-labelling and pre-embed immuno-electron microscopy techniques demonstrate the colocalization of amyloid P component and VBM components with amyloid, and also reveal that amyloid P component is not localized to the cerebral VBM. Finally, a novel correlative light/electron microscopy technique demonstrates the association between amyloid P component and cerebral resident tissue macrophages, the microglia. Taken together, these data suggest that the physicochemical processes of amyloid formation, rather than amyloid deposition, may be responsible for VBM pathology.

An important role of heparan sulfate proteoglycan (Perlecan) in a model system for the deposition and persistence of fibrillar A beta-amyloid in rat brain

A consistent rat model for the study of the consequences of congophilic and fibrillar A beta-amyloid in brain has been developed. One hundred percent of animals receiving infusions of synthetic beta-amyloid protein (A beta 1-40) plus a specific heparan sulfate proteoglycan (HSPG) for 1 week or 7 weeks (following 2 week infusions) demonstrated Congo red and thioflavin S-positive deposits adjacent to the infusion site. Extracellular amyloid fibrils were identified by electron microscopy and were immunogold decorated with A beta antibody. Significant increases in Congo red staining were observed in animals infused with A beta plus HSPG versus those infused with only A beta. Infusion of A beta alone was variable with respect to congophilic amyloid persistence, which occurred in 50% of animals and only when endogenous HSPGs accumulated at A beta deposition sites. By 7 weeks, only animals infused with A beta plus HSPG demonstrated compaction of the Congo red material from amorphous, wispy deposits (at 1 week) to stellate deposits resembling a Maltese cross. These spherical amyloid deposits were very similar to Congo red-stained amyloid plaques in human Alzheimer's disease brain, and in vitro data suggest that they were probably formed in vivo following interactions with endogenous brain components.

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 Alzheimer's 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.

Fibronectin and basement membrane components in renal amyloid deposits in patients with primary and secondary amyloidosis

Kidney biopsies from one patient with primary (AL) and three with secondary (AA) amyloidosis were used for an ultrastructural study of the collocalization of basement membrane proteins and the extracellular matrix protein fibronectin within amyloid deposits. Antibodies against amyloid P component, laminin, and heparan sulphate proteoglycan core protein all reacted with the basement membranes and the amyloid depositions in AA and AL amyloidosis. Monoclonal and polyclonal antibodies against collagen type IV reacted only with the basement membranes. Anti-fibronectin reaction was found in association with the basement membranes in all four cases, while labelling of amyloid depositions was found only in one of the AA amyloid cases and in the AL amyloid depositions. It is concluded that basement membrane components may be of importance for the formation of amyloid fibrils.

Widespread serum amyloid P immunoreactivity in cortical amyloid deposits and the neurofibrillary pathology of Alzheimer's disease and other degenerative disorders

Amyloid P (AP) component is present in all types of systemic amyloid deposits. Recently, it has been shown to be also present in cerebral amyloid lesions of Alzheimer's disease (AD). In this study, we used immunocytochemical methods to extend these findings at the electron microscope level and characterize the spectrum of AP immunoreactivity in neurofibrillary pathology (NFP) of AD and other neurodegenerative disorders including Down's syndrome (DS), Creutzfeldt-Jakob, Parkinson's, Pick's and diffuse Lewy body diseases and progressive supranuclear palsy. In AD and DS, AP immunoreaction product was evident in all the classical amyloid lesions and NFP in a large sample of all cortical areas examined. The distribution and relative intensity of immunostaining was similar to that of thioflavin S staining in serial sections. In many cases, however, plaques and vessels stained by anti-AP serum were not apparent with thioflavin S. Serial sections immunostained with antiserum to amyloid A, C-reactive protein or to other proteins involved in systemic amyloidoses and the acute phase response showed no evidence of staining in any of the cerebral lesions. Electron microscopy confirmed that AP immunoreactivity was associated with the abnormal filaments characteristic of NFP as well as amyloid fibrils found in plaques and vessels showing congophilic amyloid angiopathy. Plaques of Creutzfeldt-Jakob disease, Pick bodies of Pick's disease, tangles and Lewy bodies in Parkinson's disease and a subpopulation of Lewy bodies in the diffuse Lewy body disease coexistent with AD were also stained. With the exception of vessels in two of the five cases, AP was not detected in age-matched controls. Our observations indicate AP to be a consistent feature of cerebral NFP and amyloid deposits.

Antibodies to viral antigens, xenoantigens, and autoantigens in Alzheimer's disease

Sera from 19 patients with Alzheimer's disease (AD) and 21 control subjects were studied by immunofluorescence and enzyme immunoassay for antibody activity against various viruses and 12 self- and non-self-antigens. Total IgG mean level was significantly higher in the AD group; the IgG level was above 15 g/L in 52.8% of AD patients versus 14.3% of control subjects. Antiviral antibody titers showed no significant differences except for antibodies to herpes simplex virus-1, which were increased in control group. In contrast, autoantibodies were more frequently found in AD patients, and the prevalence of antibodies to spectrin, peroxidase, and thyroglobulin was significantly increased. Thus, in our series, autoimmune but not antiviral responses were heightened in at least 42% of AD patients (versus 9% of the control group) suggesting the existence of two subpopulations in the AD group.

Immunodetection of the amyloid P component in Alzheimer's disease

Amyloid P component (AP), a plasma constituent normally not found in brain parenchyma, has been immunohistochemically determined in brains from patients with Alzheimer's 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 type and were labeled abluminally in short segments. SP constituents such as amyloid fibrils, amyloid 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.

Diagnostic radionuclide imaging of amyloid: biological targeting by circulating human serum amyloid P component

The specific molecular affinity of the normal plasma protein, serum amyloid P component (SAP), for all known types of amyloid fibrils was used to develop a new general diagnostic method for in-vivo radionuclide imaging of amyloid deposits. After intravenous injection of 123I-labelled purified human SAP there was specific uptake into amyloid deposits in all affected patients, 7 with systemic AL amyloid, 5 with AA amyloid, and 2 with beta 2M amyloid, in contrast to the complete absence of any tissue localisation in 5 control subjects. Distinctive high-resolution scintigraphic images, even of minor deposits in the carpal regions, bone marrow, or adrenals, were obtained. This procedure should yield much information on the natural history and the management of amyloidosis, the presence of which has hitherto been confirmed only by biopsy. Clearance and metabolic studies indicated that, in the presence of extensive amyloidosis, the rate of synthesis of SAP was greatly increased despite maintenance of normal plasma levels. Furthermore, once localised to amyloid deposits the 123I-SAP persisted for long periods and was apparently protected from its normal rapid degradation. These findings shed new light on the pathophysiology of amyloid and may have implications for therapeutic strategies based upon specific molecular targeting with SAP.