Anti-Inflammatory CeO(2) Nanoparticles Prevented Cytotoxicity Due to Exogenous Nitric Oxide Donors via Induction Rather Than Inhibition of Superoxide/Nitric Oxide in HUVE Cells

The mechanism behind the cytoprotective potential of cerium oxide nanoparticles (CeO(2) NPs) against cytotoxic nitric oxide (NO) donors and H(2)O(2) is still not clear. Synthesized and characterized CeO(2) NPs significantly ameliorated the lipopolysaccharide (LPS)-induced cytokines IL-1β and TNF-α. The main goal of this study was to determine the capacities of NPs regarding signaling effects that could have occurred due to reactive oxygen species (ROS) and/or NO, since NP-induced ROS/NO did not lead to toxicity in HUVE cells. Concentrations that induced 50% cell death (i.e., IC50s) of two NO donors (DETA-NO; 1250 ± 110 µM and sodium nitroprusside (SNP); 950 ± 89 µM) along with the IC50 of H(2)O(2) (120 ± 7 µM) were utilized to evaluate cytoprotective potential and its underlying mechanism. We determined total ROS (as a collective marker of hydrogen peroxide, superoxide radical (O(2)(•−)), hydroxyl radical, etc.) by DCFH-DA and used a O(2)(•−) specific probe DHE to decipher prominent ROS. The findings revealed that signaling effects mediated mainly by O(2)(•−) and/or NO are responsible for the amelioration of toxicity by CeO(2) NPs at 100 µg/mL. The unaltered effect on mitochondrial membrane potential (MMP) due to NP exposure and, again, CeO(2) NPs-mediated recovery in the loss of MMP due to exogenous NO donors and H(2)O(2) suggested that NP-mediated O(2)(•−) production might be extra-mitochondrial. Data on activated glutathione reductase (GR) and unaffected glutathione peroxidase (GPx) activities partially explain the mechanism behind the NP-induced gain in GSH and persistent cytoplasmic ROS. The promoted antioxidant capacity due to non-cytotoxic ROS and/or NO production, rather than inhibition, by CeO(2) NP treatment may allow cells to develop the capacity to tolerate exogenously induced toxicity.