The use of mass spectrometry to study the covalent modification of amyloid beta protein due to oxidative stress: insights into the pathophysiology of AD

Aβ peptides are associated in various ways with metal ions and with mediating oxidative stress in Alzheimer's disease (AD). That oxidative stress, acting on ω-6 and ω-3 polyunsaturated fatty acyl chains, produces 4-hydroxy-2-nonenal (HNE) and 4-hydroxy-hexanal (HHE) respectively, which can covalently modify the Aβ peptides that helped producing it. To examine possible feedback pathways involving Aβ peptides, metal ions and HNE, the interactions were examined by mass spectrometry and fluorescence spectroscopy. Results indicate that metal ions, particularly copper(II), interfere with the modification of His side chains by HNE, but that once modified, metal ions can still bind to Aβ with high affinity. Moreover, a first attempt to monitor the relative amounts of unmodified Aβ and HNE/HHE modified Aβ in vivo is also reported. These results provide insight into a network of biochemical reactions that may be operating as a consequence of oxidative stress in AD, or as part of the pathogenic process.