Black Carbon Induces Cytotoxicity and NLRP3 Inflammasome Activation in Human Corneal Epithelial Cells

Purpose: To investigate the cytotoxic effects of fresh black carbon (FBC) particles and ozone-oxidized BC (OBC) particles on human corneal epithelial cells (HCECs), and the role of the NLRP3 inflammasome signal pathway in the process.Methods: HCECs were treated with different doses of FBC and OBC particles, the cell inhibitory effect was observed by MTS assay and the inhibitory concentration 50 (IC50) was calculated; the effect of FBC and OBC particles on cell apoptosis was assessed using flow cytometry-based annexin V/7AAD assay; the mRNA levels of NLRP3 inflammasome signal pathway components (NLRP3, ASC, and Caspase-1) and downstream cytokine (IL-1 β) were detected in HCECs.Results: After treatment for 24 h, the IC50 of FBC and OBC particles in HCECs were 295.5 μg/ml and 224.6 μg/ml, respectively. The percentages of cells in total apoptosis after exposure to FBC and OBC were significantly higher than in untreated control cells (P < .001). Moreover, OBC exposed cells exhibited significantly more total apoptosis than FBC exposed cells (P < .001). Compared to the untreated control, there was enhanced mRNA expression of NLRP3, Caspased-1, ASC, and IL-1β in both FBC and OBC treated HCECs (all P < .01). In addition, OBC treated HCECs yielded higher levels of IL-1β mRNA compared to FBC treated cells (P < .05).Conclusion: Both FBC and OBC particles have a cytotoxic effect on HCECs, accompanied by NLRP3 inflammasome activation, indicating that the NLRP3 inflammasome signaling pathway may be involved in the pathogenesis of the BC cytotoxic process. OBC is more toxic than FBC particles.