Dana Kim Reed

Degradation of the Alzheimer's amyloid beta peptide by endothelin-converting enzyme.

Deposition of β-amyloid (Aβ) peptides in the brain is an early and invariant feature of all forms of Alzheimers disease. As with any secreted protein, the extracellular concentration of Aβ is determined not only by its production but also by its catabolism. A major focus of Alzheimers research has been the elucidation of the mechanisms responsible for the generation of Aβ. Much less, however, is known about the mechanisms responsible for Aβ removal in the brain. In this report, we describe the identification of endothelin-converting enzyme-1 (ECE-1) as a novel Aβ-degrading enzyme. We show that treatment of endogenous ECE-expressing cell lines with the metalloprotease inhibitor phosphoramidon causes a 2–3-fold elevation in extracellular Aβ concentration that appears to be due to inhibition of intracellular Aβ degradation. Furthermore, we show that overexpression of ECE-1 in Chinese hamster ovary cells, which lack endogenous ECE activity, reduces extracellular Aβ concentration by up to 90% and that this effect is completely reversed by treatment of the cells with phosphoramidon. Finally, we show that recombinant soluble ECE-1 is capable of hydrolyzing synthetic Aβ40 and Aβ42 in vitro at multiple sites.

Insights into the mechanisms of action of anti-abeta antibodies in Alzheimer's disease mouse models

A number of hypotheses regarding how anti‐Aβ antibodies alter amyloid deposition have been postulated, yet there is no consensus as to how Aβ immunotherapy works. We have examined the in vivo binding properties, pharmacokinetics, brain penetrance, and alterations in Aβ levels after a single peripheral dose of anti‐Aβ antibodies to both wild‐type (WT) and young non‐Aβ depositing APP and BRI‐Aβ42 mice. The rapid rise in plasma Aβ observed after antibody (Ab) administration is attributable to prolongation of the half‐life of Aβ bound to the Ab. Only a miniscule fraction of Ab enters the brain, and despite dramatic increases in plasma Aβ, we find no evidence that total brain Aβ levels are significantly altered. Surprisingly, cerebral spinal fluid Aβ levels transiently rise, and when Ab:Aβ complex is directly injected into the lateral ventricles of mice, it is rapidly cleared from the brain into the plasma where it remains stable. When viewed in context of daily turnover of Aβ, these data provide a framework to evaluate proposed mechanisms of Aβ attenuation mediated by peripheral administration of an anti‐Aβ monoclonal antibody (mAb) effective in passive immunization paradigm. Such quantitative data suggest that the mAbs are either indirectly enhancing clearance of Aβ or targeting a low abundance aggregation intermediate.—Levites, Y., Smithson, L. A., Price, R. W., Dakin. R. S., Yuan, B., Sierks, M. R., Kim, J., McGowan, E., Reed, D. K., Rosenberry, T. L., Das, P., Golde, T. E. Insights into the mechanisms of action of anti‐Aβ antibodies in Alzheimers disease mouse models. FASEB J. 20, E2002–E2014 (2006)