The antioxidant xanthorrhizol prevents amyloid-β-induced oxidative modification and inactivation of neprilysin

Activity of neprilysin (NEP), the major protease which cleaves amyloid-β peptide (Aβ), is reportedly reduced in the brains of patients with Alzheimer's disease (AD). Accumulation of Aβ generates reactive oxygen species (ROS) such as 4-hydroxynonenal (HNE), and then reduces activities of Aβ-degrading enzymes including NEP. Xanthorrhizol (Xan), a natural sesquiterpenoid, has been reported to possess antioxidant and anti-inflammatory properties. The present study examined the effects of Xan on HNE- or oligomeric Aβ 42 -induced oxidative modification of NEP protein. Xan was added to the HNE- or oligomeric Aβ 42 -treated SK-N-SH human neuroblastoma cells and then levels, oxidative modification and enzymatic activities of NEP protein were measured. Increased HNE levels on NEP proteins and reduced enzymatic activities of NEP were observed in the HNE- or oligomeric Aβ 42 -treated cells. Xan reduced HNE levels on NEP proteins and preserved enzymatic activities of NEP in HNE- or oligomeric Aβ 42 -treated cells. Xan reduced Aβ 42 accumulation and protected neurones against oligomeric Aβ 42 -induced neurotoxicity through preservation of NEP activities. These findings indicate that Xan possesses therapeutic potential for the treatment of neurodegenerative diseases, including AD, and suggest a potential mechanism for the neuroprotective effects of antioxidants for the prevention of AD.