Alzheimer's disease is characterized by formation of neuritic plaque primarily composed of a small filamentous protein called amyloid-beta peptide . The rate-limiting step in the production of Abeta is the processing of Abeta precursor protein by beta-site APP-cleaving enzyme . Hence, BACE1 activity plausibly plays a rate-limiting role in the generation of potentially toxic Abeta within brain and the development of AD, thereby making it an interesting drug target. A phase II trial of the promising LY2886721 inhibitor of BACE1 was (...) suspended in June 2013 by Eli Lilly and Co., due to possible liver toxicity. This outcome was apparently a surprise to the study's team, particularly since BACE1 knockout mice and mice treated with the drug did not show such liver toxicity. Lilly proposed that the problem was not due to LY2886721 anti-BACE1 activity. We offer an alternative hypothesis, whereby anti-BACE1 activity may induce apparent hepatotoxicity through inhibiting BACE1's processing of beta-galactoside alpha-2,6-sialyltransferase I . In knockout mice, paralogues, such as BACE2 or cathepsin D, could partially compensate. Furthermore, the short duration of animal studies and short lifespan of study animals could mask effects that would require several decades to accumulate in humans. Inhibition of hepatic BACE1 activity in middle-aged humans would produce effects not detectable in mice. We present a testable model to explain the off-target effects of LY2886721 and highlight more broadly that so-called off-target drug effects might actually represent off-site effects that are not necessarily off-target. Consideration of this concept in forthcoming drug design, screening, and testing programs may prevent such failures in the future. (shrink)

Major hallmarks of Alzheimer's disease include brain deposition of the amyloid-beta peptide , which is proteolytically cleaved from a large Abeta precursor protein by beta and gamma- secretases. A transmembrane aspartyl protease, beta-APP cleaving enzyme , has been recognized as the beta-secretase. We review the structure and function of the BACE1 protein, and of 4129 bp of the 5'-flanking region sequence of the BACE1 gene and its interaction with various transcription factors involved in cell signaling. The promoter region and 5'-untranslated (...) region contain multiple transcription factor binding sites, such as AP-1, CREB and MEF2. A 91 bp fragment is the shortest region with significant reporter gene activity and constitutes the minimal promoter element for BACE1. The BACE1 promoter contains six unique functional domains and three structural domains of increasing sequence complexity as the "ATG" start codon is approached. Notably, the BACE1 gene promoter contains basal regulatory elements, inducible features and sites for regulation by various important transcription factors. Herein, we also discuss and speculate how the interaction of these transcription factors with the BACE1 promoter can modulate synaptic plasticity, neuronal apoptosis and oxidative stress, which are pertinent to the pathogenesis and progression of AD. (shrink)