The influence of extremely low frequency magnetic field and magnetic nanoparticle on Aβ1-40 aggregation in vitro

Summary form only given. The magnetic nanoparticle had been found in the brain of the aging population especially Alzheimer´s disease (AD) patients. Base on the existing researches, it has been speculated that the magnetic nanoparticles may coexist with senile plaque, a hallmark of AD which consists of excessive accumulation of β-Amyloid (Aβ). Epidemiological investigation had presented possible correlation between extremely low frequency magnetic field (ELF MF) and AD. Therefore a hypothesis was presented that the magnetic nanoparticles might be taken as a media between ELF MF and AD to have an effect on the organism and affect the process of diseases. In this study we try to investigate the role of magnetic nanoparticle and ELF MF (50 Hz, 400 μT) exposure in the process of Aβ_1-40 aggregation in vitro with a magnetic nanoparticle (Fe₃O₄) coated with SiO₂ (MNP-SiO₂). Aβ_1-40 was treated to be monomers by HFIP, and then mixed with MNP-SiO₂ followed by incubation at 37 for 48 h with or without MF exposure. Tricine-SDS-PAGE was used to identify the molecular weight (MW) of Aβ_1-40 aggregates. The results showed that Aβ_1-40 monomer was ~5 kDa by HFIP treatment (0 h) and a small amount of dimer (~10 kDa) appeared. After incubation at 37 for 48 h, evident dimer bands emerged in the Aβ_1-40 samples incubation alone (Aβ-sham group and Aβ-MF group) in addition to the monomer band; Meanwhile, the dimer bands and significant high MW bands (~70 kDa and ~90 kDa)appeared in the Aβ_1-40 co-incubation samples with MNP-SiO₂ with or without magnetic field exposure (i.e. Aβ-MNP-MF group and Aβ-MNP-sham group respectively). The atomic force microscope (AFM) was used to observe the 3D morphology of Aβ_1-40 aggregates . In the sample of 0h - Aβ-0h), a loose pseudo spherical structure can be observed . After incubation at 37 for 48 h, Aβ aggregates appeared in both Aβ-sham and Aβ-MF samples . In the sham group, the pseudo spherical structure still exists with a smaller size in the Aβ-sham sample and some short aggregates were visible; in the sample of Aβ-MNP-sham, most pseudo spherical structure disappeared and protofibrils/fibers-like aggregates came into appear with a loosely structure . In MF group, the morphology of Aβ-MF sample was similar to Aβ-MNP-sham sample where short fibrillike aggregates appeared with a loose structure; in the Aβ-MNP-MF sample, the longer fibril-like aggregates formed with a compact structure . In comparison with Aβ_1-40 aggregation without MF exposure, it seemed Aβ_1-40 aggregated more significantly under MF exposure; compared with Aβ incubation alone, MNP-SiO₂ made Aβ aggregation more easily since there were more longer protofibrils/fibrils . Roughness analysis revealed that Z values, Ra and Rq were higher in the Aβ-0h sample . After incubation for 48 h, that in the Aβ-sham and Aβ-MNP-sham samples had the lowest roughness, and the roughness of Aβ-MF and Aβ-MNP-MF samples exceeded that of the Aβ-0h, Aβ-sham and Aβ-MNP-sham samples which showed significances (P<;0 .01) . After incubation for 48 h, the order of the roughness is as follows: Aβ-sham <; Aβ-MNP-sham <; Aβ-MF <; Aβ-MNP-MF . Combined with image analysis, it was presumed that Aβ aggregation began with the larger and uneven pseudo spherical structure followed with the pseudo spherical structure collapsing and unfolding . And then the polypeptide elongated and bundled accompanied with protofibrils/fibrils maturation . In this process, the MF exposure and magnetic part