In order to improve the problems about poor water solubility of astaxanthin (ATX), Fe₃O₄ nanoparticles (NPs) were used to encapsulate ATX and evaluate its targeted aggregation by cortical cultured neurons in vitro.

The Fe₃O₄ nanoparticles were synthesized by a thermal decomposition method. For the formulation of astaxanthin nanoparticles (ATX-NPs), ATX was directly absorbed on the particle surfaces and encapsulated with polyethylene glycol (PEG) by hydrophobic interaction. In order to target neurons, transferrin was effectively conjugated with ATX-NPs by Carbodiimide method. Then, we used transmission electron microscopy (TEM) for observation and dynamic light scattering (DLS) for particle size and zeta-potential. In vitro experiment, primary neurons were cultured from the embryonic cortex of C57BL/6 mice aged 16-18 d of gestation. Lactate dehydrogenase (LDH) kit was used to study the toxic effect of ATX-NPs on neurons. Next, TEM, laser confocal fluorescence microscopy (LSCM) and flow cytometry were used to investigate the effect of ATX-NPs targeting neurons. The data was calculated by SPSS 25.0 software.

According to the TEM, the ATX-NPs were observed to be near-spherical. The constructed ATX-NPs were about 21 nm with Fe₃O₄ core and zeta potential of -28.8 mV, analyzed by DLS. After incubation with ATX-NPs for 24 h, LSCM showed that ATX-NPs gathered in the cytoplasm of neurons. TEM exhibited that the endosome formed by endocytosis of neurons through transferrin and flow cytometry also confirmed that ATX-NPs distributed in neurons. The LDH assay demonstrated that LDH in medium was not significantly changed by ATX-NPs at different concentrations (F=0.610, P>0.05).

The constructed ATX-NPs containing transferrin presented both favourable stability and biocompatibility. They were able to target neurons and aggregate as well.

Astaxanthin; Nanoparticles; Transferrin; Primary neurons; Targeting