A few decades ago, researchers found emerging evidence showing that a number of sequential events lead to the pathological cascade of Alzheimer's disease (AD) which is caused by the accumulation of amyloid beta (A beta), a physiological peptide, in the brain. Therefore, regulation of A beta represents a crucial treatment approach for AD. Neprilysin (NEP), a membrane metallo-endopeptidase, is a rate-limiting peptidase which is known to degrade the amyloid beta peptide. This study investigated soluble NEP (sNEP) produced by recombinant mammalian cells stably transfected with a non-viral NEP expression vector to demonstrate its protective effect against A beta peptides in neuronal cells in vitro. Stably transfected HEK 293 cells were used to purify the soluble protein. sNEP and A beta peptide co-treated hippocampal cells had a decreased level of A beta peptides shown by an increase in cell viability and decrease in apoptosis measured by the CCK-8 and relative caspase-3 activity ratio assays, respectively. This study shows that stably transfected mammalian cells can produce soluble NEP proteins which could be used to protect against A beta accumulation in AD and subsequently neuronal toxicity. Additionally, approaches using protein therapy for potential targets could change the pathological cascade of Alzheimer's disease. (C) 2016 Elsevier Inc. All rights reserved.