Degraded Products of Stem Bromelain Destabilize Aggregates of β-Amyloid Peptides Involved in Alzheimer’s Disease

Deposition of fibrils originating from monomeric β- amyloid (Aβ) peptide in brain cells is responsible for progressive neuronal damages in Alzheimer’s disease. Peptides from bromelain, a cysteine protease from Ananas comosus (pineapple), were generated after digestion with proteases under conditions similar to human gastrointestinal tract. These peptides not only inhibit the growth of Aβ-amyloid aggregates, but also irreversibly destabilize the preformed aggregates. Gel filtration followed by mass spectrometric analysis identified a pool of peptides of <700 Da in the digest. Probable composition of the peptides interacting with Aβ-peptide was predicted from homology alignment between Aβ-peptide and bromelain using bioinformatics tools. Corresponding synthetic peptides can also destabilize the preformed aggregates as observed from thioflavin T assay, transmission electron microscopy and atomic force microscopy. Aβ aggregates that were preincubated with the bromelain-derived peptides did not exert appreciable toxicity on human neuroblastoma cells (SH-SY5Y) cultured in vitro.