(255af) Counteracting the Formation of β-Protein Fibrils By Natural Polysaccharides

Neurodegenerative diseases such as Alzheimerâ??s disease (AD) and Parkinsonâ??s disease (PD) are characterized by aggregation and precipitation of normally soluble proteins: amyloid beta for Alzheimerâ??s disease and α-synuclein for Parkinsonâ??s disease. Therefore, alteration of the aggregation pathways of these proteins is a promising therapeutic approach for neurodegenerative diseases. This research is focused on using the mucilage extracted from Opuntia ficus indica to inhibit aggregation of disease-related proteins.

Mucilage is a neutral pectin polysaccharide with a backbone of α-D-galacturonic acid and β-L-rhamnose and a branch of either arabinose or xylose extracted from cactus plants. Polysaccharides extracted from the mucilage are water-soluble, have a flexible backbone, and are amphiphilic in nature. Two different fractions of mucilage can be extracted from the cactus pads: pectin gelling extraction (GE) and non-gelling extraction (NE). We have previously demonstrated that both GE and NE fractions can be utilized to disperse heavy aliphatic and aromatic molecules. In this work, the effectiveness of mucilage in disturbing the formation of Aβ and α-synuclein fibrils was evaluated.

Aggregation kinetics was monitored by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and time-resolved thioflavine-T (ThT) fluorescence spectroscopy. Transmission electron microscopy (TEM) was used to visually inspect the fibril morphology. We found that both extracts could significantly disturb the kinetics of amyloid proteins aggregation. Aggregation process was completely inhibited at approximately 1:20 mass ratios of GE extract/protein and 1:10 mass ratios of NE extract/protein. These represent much lower ratios than found with other natural inhibitors. Below these critical ratios, aggregation kinetics were dependent on the extract concentrations. TEM data confirmed that both extracts promoted formation of oligomeric protein aggregates instead of fibrils. FTIR data showed loss of β-structure for aggregates formed in the presence of extracts.

These experimental results show the effectiveness of cactus mucilage as an inhibitor of amyloid formation and suggest that it could be used for further drug development.