Alzheimer's disease (AD) is characterized by the accumulation of β-amyloid 
peptide (Aβ) in the brain because of an imbalance between Aβ production and 
clearance. Neprilysin (NEP) is the most important Aβ-degrading enzyme in the 
brain. Thus, researchers have explored virus-mediated NEP gene delivery. 
However, such strategies may entail unexpected risks, and thus exploration of a 
new possibility for NEP delivery is also required. Here, we show that human 
adipose tissue-derived mesenchymal stem cells (ADSCs) secrete exosomes carrying 
enzymatically active NEP. The NEP-specific activity level of 1 μg protein from 
ADSC-derived exosomes was equivalent to that of ~ 0.3 ng of recombinant human 
NEP. Of note, ADSC-derived exosomes were transferred into N2a cells, and were 
suggested to decrease both secreted and intracellular Aβ levels in the N2a 
cells. Importantly, these characteristics were more pronounced in ADSCs than 
bone marrow-derived mesenchymal stem cells, suggesting the therapeutic relevance 
of ADSC-derived exosomes for AD.