Intervertebral disk regeneration in a rat model by allopurinol-loaded chitosan/alginate hydrogel

Intervertebral disk degeneration remains one of the most challenging health problems. In the current study, allopurinol was loaded into the chitosan nanoparticles and then incorporated into chitosan/alginate hydrogels and then further studied for its disk regeneration potential in a rat model. In vitro studies were performed to characterize the hydrogel system, including scanning electron microscopy, cell viability assay, cytoprotection assay, cell migration assay, swelling assay, and drug release assay. In vivo study was performed in a rat model of the intervertebral disk injury. Animal studies showed that allopurinol-loaded hydrogels had significantly higher disk regeneration potential compared with other experimental groups. The gene expression studies showed that the animals treated with allopurinol-loaded hydrogel had significantly higher tissue expression levels of type I and type II collagen genes than other groups. Furthermore, the tissue expression levels of nuclear factor κB (NF-κB) and glutathione peroxidase (GPx) genes were significantly lower in this group. The relative expression levels of type I collagen, type II collagen, NF-κB, and GPx genes in the allopurinol-loaded hydrogel group were 2.77 ± 0.2%, 2.86 ± 0.25%, 0.58 ± 0.03%, and 0.45 ± 0.02%, respectively. We showed for the first time that allopurinol-loaded hydrogel promoted intervertebral disk repair, which could be due to its potential to modulate oxidative stress, reduce inflammation, and improve matrix synthesis.