The effect of TiO₂ nanoparticles on ocular surface in normal and experimental dry eye rat model

Abstract

Purpose: Titanium dioxide (TiO₂) nanoparticles, one of the particulate matter 10 (PM10) components, is widely utilized in the nanoindustry for manufacturing and processing of various commercial products. The aim of this study was to evaluate the effect of TiO₂ nanoparticles on ocular surface in normal and experimental dry eye rat model.

Methods: Male Lewis rats were subcutaneously injected with scopolamine hydrobromide and placed in a controlled environment chamber for 3 days to induce dry eye disease (DED). Control rats received no treatment. 10㎍ of TiO₂ nanoparticles challenged topically in the conjunctival sac of right eye of normal and DED rat model. After 24 hours, corneal clarities were compared with scoring of Fantes’ classification and tear volume was measured with cotton thread test. Tear samples were collected for quantification of LDH, MUC5AC and TNF-α concentration. Corneal and conjunctival tissues were used for western blot analysis of TNF-α and, and the entire eyeball, including eyelids and conjunctiva, was surgically enucleated for evaluation of ocular surface inflammatory cell infiltration and detection of apoptotic cells using TUNEL assay.

Results: Rats were divided into 4 groups for this study; N, left eye of normal rat; T, TiO₂ challenged right eye of normal rat; D, left eye of DED model; DT, TiO₂ challenged right eye of DED model. Corneal clarity score was higher in TiO₂ challenge (T, DT) group than non-challenge (N, D) group (p=0.024, p=0.026, respectively), and the score in DED model was greater than normal rat (p<0.001). LDH and inflammatory cell infiltration were significantly higher in DED model than normal rat (p<0.001, p<0.001, respectively), and these results had increasing tendency after TiO₂ challenge. TNF-α level in tears, expression of western blot and TUNEL assay were also higher in DED model. However, MUC5AC level in DED model was significantly lower than normal rat (p<0.001). And tear volume of DED model was also significantly lower than normal rat (p<0.001), but that was not influenced by TiO₂ challenge.

Conclusions: The adverse effects of TiO₂ nanoparticles exposure to ocular surface were more prominent in DED model than normal rat. Ocular surface of DED seems to be more vulnerable to the fine dusts of air pollution.