The apparent mechanical effect of isolated amyloid-β and α-synuclein aggregates revealed by multi-frequency MRE.

Several biological processes are involved in dementia, and fibrillar aggregation of misshaped endogenous proteins appears to be an early hallmark of neurodegenerative disease. A recently developed means of studying neurodegenerative diseases is magnetic resonance elastography (MRE), an imaging technique investigating the mechanical properties of tissues. Although mechanical changes associated with these diseases have been detected, the specific signal of fibrils has not yet been isolated in clinical or preclinical studies. The current study aims to exploit the fractal-like properties of fibrils to separate them from nonaggregated proteins using a multi-frequency MRE power law exponent in a phantom study. Two types of fibril, alpha-synuclein (alpha-Syn) and amyloid-beta (A beta), and a nonaggregated protein, bovine serum albumin, used as control, were incorporated in a dedicated nondispersive agarose phantom. Elastography was performed at multiple frequencies between 400 and 1200 Hz. After 3D-direct inversion, storage modulus (G'), phase angle (phi), wave speed and the power law exponent (y) were computed. No significant changes in G' and phi were detected. Both alpha-Syn and A beta inclusions showed significantly higher y values than control inclusions (P = 0.005) but did not differ between each other. The current phantom study highlighted a specific biomechanical effect of alpha-Syn and A beta aggregates, which was better captured with the power law exponent derived from multi-frequency MRE than with single frequency-derived parameters.