Chitosan-citric acid hydrogels loaded with catalpol: A novel therapeutic strategy for spinal cord injury

Spinal cord injury (SCI), which often results from traumatic incidents, leads to neural damage and impaired sensory and motor functions and may pose a serious threat to life. Secondary injury mechanisms caused by persistent inflammation disrupt the local microenvironment, causing neuronal cell death and hindering neural regeneration. This study used a chitosan-citric acid (CS-CA) hydrogel as a carrier for Catalpol (CAT-CS-CA), which was directly applied to the injury site to promote SCI repair.

CAT-CS-CA and CS-CA hydrogels were characterized and implanted into rat SCI models. Fifty-four male Sprague-Dawley rats (230–250 g) rats were involved in the experiment. Six rats were randomly divided into two groups (n = 3 per group) for in vivo degradation of hydrogels. Forty-eight rats were randomly assigned into four groups (n = 12) using a randomization protocol: sham operation group (laminectomy only), SCI group, CS-CA hydrogel group, and CAT-CS-CA hydrogel group. From each group, 3 rats were randomly selected for serum and spinal cord tissue extraction, followed by ELISA and RT-qPCR assays to determine the expression levels of various inflammatory factors (IL-1β, IL-6, TNF-α, and IL-10). Another 3 randomly selected rats were used for the evaluation of hindlimb motor function. The remaining 6 rats in each group were used to detect the expression of neuronal nuclei (NeuN), βⅢ-tubulin (Tuj1), glial fibrillary acidic protein (GFAP), and macrophage polarization (M1/M2 markers).

The CAT-CS-CA hydrogel retains CS-CA hydrogel's advantages and gains enhanced neuroprotective and anti-inflammatory abilities. The implantation of CAT-CS-CA into injured rat spinal cords enhanced neuronal survival, stimulated axonal regeneration, and significantly suppressed glial proliferation at the injury site. In addition, it promoted macrophage polarization to the M2 phenotype and substantially enhanced hindlimb motor function in rats with SCI.

CAT-CS-CA hydrogel promotes neuronal survival, suppresses glial scarring, and improves motor function, offering a promising strategy for SCI repair.