N-Acetylcysteine Prevents 4-Hydroxynonenal- and Amyloid-beta-Induced Modification and Inactivation of Neprilysin in SH-SY5Y Cells

As one of the dominant amyloid-beta peptide (A beta) proteases, neprilysin (NEP) plays a crucial role in maintaining a physiologic balance between A beta production and catabolism. We have previously shown that NEP is modified by 4-hydroxynonenal (HNE) adducts, resulting in decreased activity in the brain of AD patients and cultured cells. In order to determine whether antioxidants can rescue NEP, SH-SY5Y cells were treated with HNE or A beta, together with N-acetylcysteine for 24 hours, prior to analysis of NEP protein levels, activity, and oxidative modifications. Intracellular NEP developed HNE adducts after 24 hours of HNE or A beta treatment as determined by immunoprecipitation, immunoblotting, and double immunofluorescence staining. N-acetylcysteine at 10 to 100 mu M alleviated HNE adduction after HNE or A beta treatment. In keeping with previous reports, HNE-modified NEP showed decreased catalytic activity. The present study demonstrates that antioxidants can be used to spare NEP from oxidative modification, suggesting a potential mechanism underlying the neuroprotective effects of antioxidants in aging or Alzheimer's disease.