Multi-functional cerium oxide nanoparticles regulate inflammation and enhance osteogenesis

Oxidative stress increases bone loss and limits repair, in part, through immunoregulation and the formation and maintenance of low-grade chronic inflammation. The aim of this study was to investigate the effect of cerium oxide nanoparticles (CeONPs) on (i) macrophage phenotype and cytokine expression under normal and simulated acute and chronic inflammatory conditions and, (ii) human mesenchymal stem cell (hBMSCs) proliferation, osteoinduction and osteogenic differentiation. Spherical particles composed of 60% Ce³⁺ with a hydrodynamic size of ~35 nm and surface charge of 25.4 mV were internalized within cells. Under both acute and chronic conditions, inducible nitric oxide synthase (iNOS) activity decreased with a significant reduction seen in the 1 and 10 μg/mL groups (p < 0.001). A dose dependent and significant increase in anti-inflammatory cytokine gene expression was observed in all CeONP groups under chronic inflammatory condition. No increase in alkaline phosphatase (ALP) activity or mineral deposits were measured following hBMSCs cultured without osteogenic media in any of the CeONP groups, however, a significant increase in osteogenic-related gene expression, ALP activity and bone mineral deposits was measured when supplemented with both CeONPs and osteogenic media. CeONP activity was multifaceted and exhibited low toxicity. A therapeutic dose of 1 μg/mL delivered a disparate but protective effect when under both acute and chronic inflammatory conditions while at the same dose, potentiated osteogenesis.