Poly-l-lysine-coated magnetic nanoparticles as intracellular actuators for neural guidance

Abstract

Purpose: It has been proposed in the literature that Fe 3 O 4 magnetic nanoparticles (MNPs) could be exploited to enhance or accelerate nerve regeneration and to provide guidance for regenerating axons. MNPs could create mechanical tension that stimulates the growth and elongation of axons. Particles suitable for this purpose should possess (1) high saturation magnetization, (2) a negligible cytotoxic profile, and (3) a high capacity to magnetize mammalian cells. Unfortunately, the materials currently available on the market do not satisfy these criteria; therefore, this work attempts to overcome these deficiencies. Methods: Magnetite particles were synthesized by an oxidative hydrolysis method and characterized based on their external morphology and size distribution (high-resolution transmission electron microscopy [HR-TEM]) as well as their colloidal (Z potential) and magnetic properties (Superconducting QUantum Interference Devices [SQUID]). Cell viability was assessed via Trypan blue dye exclusion assay, cell doubling time, and MTT cell proliferation assay and reactive oxygen species production. Particle uptake was monitored via Prussian blue staining, intracellular iron content quantification via a ferrozine-based assay, and direct visualization by dual-beam (focused ion beam/scanning electron microscopy [FIB/SEM]) analysis. Experiments were performed on human neuroblastoma SH-SY5Y cell line and primary Schwann cell cultures of the peripheral nervous system. Results: This paper reports on the synthesis and characterization of polymer-coated magnetic Fe 3 O 4 nanoparticles with an average diameter of 73 ± 6 nm that are designed as magnetic actuators for neural guidance. The cells were able to incorporate quantities of iron up to 2 pg/cell. The intracellular distribution of MNPs obtained by optical and electronic microscopy showed large structures of MNPs crossing the cell membrane into the cytoplasm, thus rendering them suitable for magnetic manipulation by external magnetic fields. Specifically, migration experiments under external magnetic fields confirmed that these MNPs can effectively actuate the cells, thus inducing measurable migration towards predefined directions more effectively than commercial nanoparticles (fluidMAG-ARA supplied by Chemicell). There were no observable toxic effects from MNPs on cell viability for working concentrations of 10 µg/mL (EC 25 of 20.8 µg/mL, compared to 12 µg/ mL in fluidMAG-ARA). Cell proliferation assays performed with primary cell cultures of the peripheral nervous system confirmed moderate cytotoxicity (EC 25 of 10.35 µg/mL). Conclusion: These results indicate that loading neural cells with the proposed MNPs is likely to be an effective strategy for promoting non-invasive neural regeneration through cell magnetic actuation.

Superparamagnetic Iron Oxide Nanoparticle-Mediated Forces Enhance the Migration of Schwann Cells Across the Astrocyte-Schwann Cell Boundary In vitro

“…In the present study, PLL was used to modify SPIONs via electrostatic interactions. PLL-SPIONs showed positive charges as reported previously (Riggio et al, 2012). In addition, it has been reported that no detectable uptake of iron was found for dextran-coated SPIONs with concentrations <0.5 mg/ml after 48 h incubation, and approximately half of the cells were abundantly labeled at 2 mg/ml (Dunning et al, 2004).…”

High-resolution analytical imaging and electron holography of magnetite particles in amyloid cores of Alzheimer’s disease

“…The Fe nanoparticles tested were coated with inorganic surfactants; bio-compatible compounds (proteins, peptides, carbohydrates or zwitterionic agents) can effectively reduce their toxicity. Like in the case of poly-lysine coated magnetite particles, they show no observable toxic effects after 24 h dose on primary Schwann cells of the peripheral nervous system and human neuroblastoma cells (SH-SY5Y) 56 . Some cytotoxic effects of magnetic nanoparticles can be attributed to chemical coating and by-products and not directly to the metal core, although long term effects in neurons and brain are unknown.…”

Growth factor choice is critical for successful functionalization of nanoparticles

“…One idea is to facilitate the uptake of magnetic NPs in regenerating neurons and their axons and to pull the axon along an external magnetic field. Therefore, the guidance of sprouting axons is promoted and the specificity of reinnervation is enhanced (Halpern, 2000 ; Riggio et al, 2012 ; Calatayud et al, 2013 ; Goya et al, 2014 ; Riggio et al, 2014 ). Previous studies showed initial success.…”

“…Human neuroblastoma (SH-SY5Y) cells were effectively influenced by an external magnetic field after magnetic NPs uptake. Also primary Schwann cells and olfactory ensheating cells showed satisfying uptake of NPs and could be moved along a magnetic field (Riggio et al, 2012 , 2013 ). Neurite orientation was shown to be directed toward a magnetic force after uptake of magnetic NPs into differentiated PC12 cells (Riggio et al, 2014 ).…”