Superparamagnetic Iron Oxide Nanoparticle Implantation and Magnetic Field Exposure Modulate Bone Microarchitecture Following Spinal Cord Injury in Adult Male Rats

Background: Osteoporosis is one of the detrimental effects of spinal cord injury (SCI), leading to bone loss. It has already been established that superparamagnetic nanoparticles when exposed to an external magnetic field (MF) show strong magnetisation and promote locomotor recovery. Purpose: The aim of the present study is to explore the role of magnetised nanoparticles in ameliorating SCI-induced osteoporosis. Methods: The rats were divided into Sham, SCI, SCI+MF, SCI+V, SCI+NP and SCI+NP+MF groups. A complete transection was performed at the T13 level, followed by iron oxide nanoparticle implantation along with MF exposure for 7 or 14 days. Results: A significant increase in locomotor score was evident at day 5 in all groups except in the SCI+V group, and at day 7, all groups showed a significant increase in Basso, Beattie and Bresnahan score as compared to the pre-surgery score at week 1 of the study period. A significant decrease in bone volume/total volume ratio and trabecular thickness and increase in trabecular separation were observed in all groups as compared to Sham. A significant increase in trabecular thickness in the SCI+NP+MF group as compared to the SCI+MF group was observed after one week. After two weeks, the SCI+MF group showed a significant increase in locomotor scores at days 5 and 13 as compared to the SCI, SCI+V and SCI+NP groups. Bone loss was significantly observed in all groups except SCI+MF, as compared to Sham. Cortical bone showed no significant change at both time points. On histopathological examination of the spinal cord, we observed significant improvement in lesion volume in SCI+MF and SCI+NP+MF groups after one week, whereas only the SCI+NP+MF group showed a significant decrease after two weeks. Conclusion: Electromagnetic field stimulation partially restored bone architecture after superparamagnetic nanoparticle implantation, which may be due to reduced lesion volume and improved locomotor behaviour.