Identification and Characterization of Neuroprotective Properties of Thaumatin-like Protein 1a from Annurca Apple Flesh Polyphenol Extract

Background: Alzheimer’s disease (AD) and Parkinson’s disease (PD) are multifactorial neurodegenerative disorders that are mostly treated with drugs inhibiting key enzymes of choliner- gic and aminergic neurotransmission, such as acetyl and butyryl cholinesterase (AChE, BuChE) or monoamine oxidases (MAO)-A/B, and of Aβ 1–40 aggregation. Diet plant components with multitar- get functions are promising compounds in the prevention of AD and PD. Our aim was to identify neuroprotective compounds from Annurca apple polyphenol extract (AFPE). Methods: AFPE was fractionated by gel filtration, and the eluted peaks were subjected to chemical analyses (i.e., RP-HPLC and mass spectrometry), determination of inhibitory enzyme activity and cell effects by MTT, and morphology assays. Results: In AFPE, we identified thaumatin-like protein 1a, belonging to the pathogenesis-related protein (PR) family. This protein showed the best inhibitory activity on AChE, MAO-A (IC50 = 5.53 μM and 1.71 μM, respectively), and Aβ 1–40 fibril aggregation (IC50 = 9.16 μM), compared to AFPE and other polyphenol-containing fractions. Among the latter, Peak 4 reverted Aβ fibril formation (IC50 = 104.87 μM). Moreover, thaumatin-like protein 1a protected AGS and MKN-28 cells from serum-deprivation-induced stress conditions. Conclusions: We showed that AFPE exerted neuroprotective functions not only through its polyphenols but also through thaumatin-like protein 1a, which acted like a multitarget molecule.