Reed, Dana Kim

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 Alzheimer's disease mouse models. FASEB J. 20, E2002–E2014 (2006)

Previously, using a synthetic peptide strategy, we determined that the region of the common glycoprotein hormone alpha subunit between residues 26 and 46 is a site of interaction of the hormone with the thyroid membrane-bound receptor for thyroid-stimulating hormone (TSH). We have undertaken to identify further the specific residues within this 21-amino acid span that are critical in hormone receptor binding. We synthesized three nested sets of peptide, two in which we systematically truncated the amino-terminal region of the sequence and another in which we truncated the carboxyl-terminal region, and we synthesized a fourth nested set in which we systematically substituted alanine for the native residues from the region of highest activity. Each peptide was tested in a TSH radioreceptor assay for its ability to inhibit binding of 125I-labeled bovine TSH to porcine thyroid membranes. Removal either by truncation or alanine substitution, of several specific residues resulted in a significant reduction in the ability of the sequence to interact with receptor; these residues included Cys31, Cys32, Phe33, Arg35, Arg42, Lys44, and Lys45, suggesting that they are crucial for binding activity. Loss of activity also occurred with substitution for Gly30 and Ser34, but the reduction was less pronounced. Amino-terminal truncation of the sequence through Arg35 (leaving the alpha-subunit peptide 36-46) resulted in greater than 98% loss of activity of the sequence. We conclude that two distinct receptor binding regions lie within the alpha-subunit 26-46 sequence. The first lies between residues Gly30 and Arg35 and includes Cys31, Cys32, and Phe33 as important constituents, and the second region lies between residues Arg42 and Lys45 and includes Lys44 as an important residue and Ser43 as a less important component.