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Glycation and microglial reaction in lesions of Alzheimer's disease.

Single, double, and triple immunostaining of cryostat sections of elderly normal and Alzheimer disease (AD) brain was performed with monoclonal and polyclonal antibodies to advanced glycation end products (AGE). The sections were counterstained with thioflavin-S or with immunocytochemistry for A beta and also stained with markers for microglia. AGE-immunoreactivity was detected in senile plaques and neurofibrillary tangles (NFT). AGE immunoreactivity was most intense in dense or reticular amyloid deposits and extracellular NFT, while intracellular NFT and diffuse amyloid had less AGE immunoreactivity. This pattern of immunoreactivity was similar to that noted in previous studies with antibodies to apolipoprotein-E (apo-E). Therefore, double labeling with antibodies to apo-E and AGE was performed. AGE immunoreactivity colocalized to a very high degree with apo-E immunoreactivity, except that relatively more intense apo-E immunoreactivity was detected in amyloid deposits and more intense AGE immunoreactivity in NFT. The lesions that were immunostained with antibodies to AGE and apo-E were often, but not always, associated with a local microglial reaction. The results raise the possibility that apo-E or a fragment of apo-E may be glycated. Biochemical studies are needed to determine the extent of possible apo-E glycation in AD. The present results raise the possibility that glycation may serve as one of the signals for activation of microglia associated with amyloid deposits and extracellular NFT.

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PubMedDate not supplied

Role of advanced glycosylation products in complications of diabetes.

Glucose and other reducing sugars can react with proteins and nucleic acids, without the aid of enzymes, to form stable covalent adduct. These reactions, although studied by food chemists, have recently been found to occur in vivo. This has led to studies on the accumulation of these advanced glycosylation end products (AGE) and the role it plays in the aging of long-lived proteins and nucleic acids. In contrast to the Amadori product, which is in equilibrium with glucose, AGE is irreversibly attached to the proteins. The AGE moieties are brown, fluorescent chromophores that can cross-link proteins. We have identified and characterized two specific AGE glucose-derived cross-links in proteins 2-furoyl-4(5)-(2-furanyl)-1H-imidazole (FFI) and 1-alkyl-2-formyl-3,4-diglycosylpyrrole (AFGP). By use of a radioimmunoassay for FFI identification, it has been possible to demonstrate the presence of FFI in situ in proteins that had been exposed to glucose in vitro and in vivo. Recently, we found that reducing sugars react with amino groups on DNA nucleotides in a manner analogous to the nonenzymatic glycosylation of amino groups on proteins. The AGE-DNA formed in this manner has spectral and fluorescent properties similar to those of AGE-proteins. We have observed that formation of AGE on DNA decreases the ability of the single-stranded virus f1 to transfect Escherichia coli. When the plasmid pBR322 containing ampicillin- and tetracycline-resistant genes is incubated with reducing sugars, specific mutations are observed. These mutations have been found to be caused by insertions and deletions of the DNA. Further studies are needed for measuring the amounts of AGE-DNA and proteins linked to DNA by AGE. Potential mechanisms for repair of AGE-DNA also needs to be explored further.(ABSTRACT TRUNCATED AT 250 WORDS)

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