Cytotoxicity comparison of different crystal forms of titanium dioxide nanoparticles following UVC activation of photocatalytic activity

To investigate whether ultraviolet-C band (UVC)-induced photocatalytic activation enhances the toxic effects of titanium dioxide nanoparticles (TNPs) in their rutile (TNPs-R) and anatase (TNPs-A) crystalline forms, human hepatocytes L-02 and QGY-7703 were exposed to 25 nm TNPs-R or TNPs-A (80 μg/mL) with or without UVC irradiation for 20 or 40 min. Rates of cell division, necrosis, and apoptosis were analyzed via Giemsa staining. Additionally, C57BL/6 mice received an oral gavage of TNPs-A pre-irradiated with UVC for 1 h over 21 days; organ coefficients were assessed to evaluate systemic toxicity, and bone marrow polychromatic erythrocyte micronucleus (MN) rates were measured to evaluate genotoxicity. Results showed that both TNPs-R and TNPs-A significantly increased cell death and inhibited cell division in both cell lines (p <0 .05). UVC irradiation for 20 min exacerbated TNPs-R-induced necrosis and inhibition of cell division in both cell lines (p <0 .05). When the UVC exposure duration was extended to 40 min, TNPs-A induced significantly higher cell death rates (p <0 .01) and proliferation inhibition (p <0 .001) in both cell lines compared to TNPs-R. In mice administered UVC-TNPs-A, no significant changes in organ coefficients were observed; nevertheless, both the TNPs-A and UVC-TNPs-A groups showed elevated MN rates (p <0 .05), with the latter exhibiting the highest values. Our findings suggest that photocatalytic activation enhances the toxicity of TNPs both in vitro and in vivo. Furthermore, this toxicity is dependent on crystal form and UVC exposure duration: TNPs-R display stronger toxicity under short-duration UVC exposure, whereas TNPs-A exhibit greater toxicity following prolonged UVC irradiation.