N-Truncated Aβ Starting at Position Four—Biochemical Features, Preclinical Models, and Potential as Drug Target in Alzheimer’s Disease

The discussion of whether amyloid plaque Aβ is a valid drug target to fight Alzheimer’s disease (AD) has been a matter of scientific dispute for decades. This question can only be settled by successful clinical trials and the approval of disease-modifying drugs. However, many clinical trials with antibodies against different regions of the amyloid Aβ peptide have been discontinued, as they did not meet the clinical endpoints required. Recently, passive immunization of AD patients with Donanemab, an antibody directed against the N-terminus of pyroglutamate Aβ, showed beneficial effects in a phase II trial, supporting the concept that N-truncated Aβ is a relevant target for AD therapy. There is long-standing evidence that N-truncated Aβ variants are the main variants found in amyloid plaques besides full-length Aβ(1–42), t, therefore their role in triggering AD pathology and as targets for drug development are of interest. While the contribution of pyroglutamate Aβ(3–42) to AD pathology has been well studied in the past, the potential role of Aβ(4–42) has been largely neglected. The present review will therefore focus on Aβ(4–42) as a possible drug target based on human and mouse pathology, in vitro and in vivo toxicity, and anti-Aβ(4-X) therapeutic effects in preclinical models.