Amyloid precursor protein (APP) is a type I transmembrane protein found in many tissues, with high concentrations at neuronal synapses. It is proposed to regulate synapse formation and neural plasticity. APP can be processed through two distinct pathways. In one, it is cleaved by β- and γ-secretases to generate amyloid-β protein (Aβ), a key component of amyloid plaques and a major pathological feature of Alzheimer’s disease (AD). In the alternative pathway, α-secretase cleaves APP, producing a fragment that counteracts amyloid formation and prevents Aβ peptide generation. This fragment is considered antiamyloidogenic due to its non-toxic nature and its role in inhibiting Aβ peptide formation. Soluble APP containing the Kunitz protease inhibitor (KPI) domain, also known as protease nexin II, is a potent inhibitor of serine proteases and may possess additional functional roles.