MICHAEL P. VITEK, KESHAB BHATTACHARYA, J. MICHAEL GLENDENING, EDWARD STOPA, HELEN VLASSARA, RICHARD BUCALA, KIRK MANOGUE, AND ANTHONY CERAMI
Alzheimer disease (AD) is characterized by deposits of an aggregated 42-amino-acid β-amyloid peptide (βAP)in the brain and cerebrovasculature. After a concentration dependent lag period during invitro incubations, soluble preparations of synthetic βAP slowly form fibrilar aggregates that resemble natural amyloid and are measurable by sedimentation and thioflavin T-based fluorescence. Aggregation of soluble βAP in these in vitro assays is enhanced by addition of small amounts of pre-aggregated β-amyloid “seed” material. We also have prepared these seeds by using a naturally occurring reaction between glucose and protein amino groups resulting in the formation of advanced “glycosylation” end products (AGEs) which chemically crosslink proteins. AGE-modified βAP-nucleation seeds further accelerated aggregation of soluble βAP compared to non-modiflied “seed” material. Over time, nonenzymatic advanced glycation also results in the gradual accumulation of a set of post translational covalent adducts on long-lived proteins in vivo. In a standardized competitive ELISA, plaque fractions of AD brains were found to contain about 3-fold more AGE adducts per mg of protein than preparations from healthy,age-matched controls. These results suggest that the in vivo half-life of β-amyloid is prolonged in AD,resulting in greater accumultion of AGE modification swhich in turn may act to promote accumulation of additional amyloid.