The human IgG repertoire contains endogenous antibodies against beta amyloid (Aβ) that may be relevant to the pathogenesis and treatment of Alzheimer's disease. There have been widely disparate estimates of the levels of these antibodies in human plasma. We identify factors that have contributed to these disparities and describe improved methods for measuring anti-Aβ antibodies in blood. These methods include isolating immunoglobulin by thiophilic chromatography and using chaotropic salts to dislodge weakly bound antibodies without significantly reducing the binding of specific anti-Aβ antibodies. Using these methods, we show that human blood contains polyvalent IgG antibodies that bind to Aβ with relatively low avidity and specificity, as well as IgG antibodies that bind to linear and conformational epitopes on amyloid monomers and aggregates with moderate to high avidity.

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formation and disrupt pre-formed beta-amyloid protein fibrils. In addition, these 2 peptides following daily i.p. injections (50 mg/kg/day) significantly reduced fibrillar beta-amyloid protein load in brains of APP transgenic mice (containing the Swedish and London mutations) by 38-63% (as assessed by image analysis quantitation of Thioflavin S fluorescence and Congo red staining). One of these peptides, DP-74 also caused a marked and significant improvement (by 52%) in hippocampus-dependent memory determined by Morris water maze testing. Methods: In the present study, DP-74 was radiolabelled with tritium and the blood-brain-barrier (BBB) permeability and kinetics were determined. Results: Using capillary depletion analysis following 10 minutes of an i.v. injection of 3H-DP-74, the results demonstrated the apparent uptake was composed mainly of brain parenchymal permeation (with minimal capillary entrapment) indicating that the peptide crossed the BBB and entered the brain parenchyma. Stability studies indicated that 1 hour following i.v. administration intact 3H-DP-74 (analyzed by HPLC and mass spectroscopy) was completely stable in the circulation, and represented 45% of the radioactivity recovered in the brain homogenate. Following intranasal administration, 3H-DP-74 was identified in olfactory bulb, hypothalamus, cortex, subcortical regions, brainstem, cerebellum and spinal cord in a time and dose-dependent matter suggesting that intranasal delivery might be a viable option for administration using this peptide. Conclusions: Together, these results indicated the identification of a novel disease-modifying small peptide (DP-74) that crosses the BBB, and has the ability to reduce brain amyloid load and improve memory in APP transgenic animals. These studies suggest that small novel peptides show promise for the development of disease-modifying therapeutics for the prevention and treatment of AD and related disorders. Funded by ProteoTech and a SBIR Phase II Award (AG017787).

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