Exposure of human corneal epithelial cells to microplastic particles induces a phase-specific cytokine response.

Microplastics have been identified in ophthalmic therapeutics and linked to dry eye disease and meibomian gland dysfunction. Inflammation is hypothesised to drive the resulting ocular surface damage. This in-vitro study investigates how varying concentrations of microplastics affect corneal cell viability and cytokine expression. Microplastic powder was produced by grinding polyethylene eyedrop vials and added to human corneal epithelial cells (HCE-T) at 1, 5, or 25 μg/mL, while microplastics were absent in controls. Cell proliferation and apoptosis were monitored for 28 days using the xCelligence real-time cell analyser, as well as TUNEL and EdU assays. Cytokine and chemokine expression were quantified via the Bio-Plex Pro Human 27-plex Assay. Scanning electron microscopy confirmed irregular microplastic particles (62-700 μm) consistent with those found in commercial tear solutions. No significant changes in proliferation and apoptosis were observed at day 7, 14, 21 or 28 (p > 0.05 for all days). A distinct two-phase temporal response was observed. The first phase was characterised by a transient dose-dependent rise in pro-inflammatory cytokines, including IL-5, IL-7, IL-8, IL-9, IP-10, MCP-1, MIP-1β, and VEGF, and a non-dose-dependent elevation of IL-1ra, IL-6, RANTES and TNF-α at day 14. By day 21, the expression of most cytokines returned to baseline, with IP-10 (p = 0.021) and RANTES (p = 0.010) decreasing below control levels. This was followed by a second phase, marked by a delayed and sustained induction of G-CSF, which demonstrated a dose-dependent increase at day 21 (p = 0.021) and 28 (p < 0.001). While trends suggested late-phase increases for IFN-γ and PDGF-BB, these were not statistically significant. In summary, exposure of human corneal epithelial cells to microplastics demonstrated an early pro-inflammatory wave that was followed by an increase in G-CSF and a reduction in pro-inflammatory cytokines. Findings from this study highlight the need to explore the long-term effects of microplastic exposure on inflammation and ocular surface disease.