Transformation of beta-amyloid (Aβ) (1-42) tyrosine to L-Dopa as the result of in vitro hydroxyl radical attack

Abstract

A form of beta-amyloid peptide Aβ ending at amino acid 42 (Aβ42) is the major component of senile amyloid plaques in Alzheimer's Disease (AD). The Aβ-peptide earliest modifications are extremely important since they constitute the key events in the progression towards further changes finally leading to fibril formation and to Aβ deposits which constitute the core pathological change in AD. Chemical and conformational early modifications of the beta-amyloid peptide are critical steps in AD pathogenesis and have been widely investigated. We now show that a Fenton-type OH-generating system is capable of generating L-Dopa (3, 4-dihydroxyphenylalanine) in the tyrosine residue of Aβ-peptide via aromatic ring hydroxylation, as the result of hydroxyl radical attack on proteins. Since L-Dopa is not a constituent of mammalian proteins and peptides, the formation of L-Dopa in Aβ in vitro constitutes a possible important modification caused by hydroxyl radical attack These results lay the groundwork for further studies on modification and damage associated with the degenerative disorder in AD where oxidative stress and inflammation are known to occur.

Key Words:

• beta-amyloid hydroxylation
• reactive oxygen species
• hydroxyl radical
• tyrosine
• L-Dopa