Environmental particulate matter of different sizes leads to differential damage of the ocular surface

Abstract

Purpose : Environmental particulate matter (PM) is a known trigger for development of ocular surface disease. The purpose of this study was to compare the toxic effects of small and large PM in rabbit corneal epithelial cells (SIRC) in vitro and ocular surface damage in rabbits in vivo.

Methods : Standard Reference Material consisting of atmospheric PM of diameter under 4 µM (PM4; SRM® 2786) and under 10 µM (PM10; SRM® 2787) were obtained from NIST. SIRC cells were exposed to a dose range of PM4 or PM10 up to 300 µg/ml for 24 h. MTT and LDH assays for viability, mitochondrial oxidative stress (MitoSox^TM) assay, and scratch assay for motility were performed. For in vivo studies, male and female New Zealand White rabbits received topical instillation of PM (5 mg/ml, TID, 35 µl) for 10 days. Ophthalmic exams were performed by a veterinary ophthalmologist in awake animals and scored using SPOTS system. Corneal fluorescein staining was performed under isoflurane anesthesia. Images were acquired with a Spectralis HRT system. Images were scored using the NEI scoring system (0 – 4 scale per quadrant with a maximum score of 16).

Results : Cell viability assays revealed that PM4 is more toxic than PM10; 300 µg/mL PM4 caused nearly 75% cell death (p<0.001), while 300 µg/mL PM10 caused only 50% cell death (p<0.001). PM10 caused significant induction of mitochondrial oxidative stress at concentrations greater than 100 µg/ml. Both PM4 (p<0.001) and PM10 (p<0.001) induced a similar ~20% reduction of cellular motility. In rabbits, exposure to PM4 for 7 days caused hyperemia and increased corneal fluorescein scores. Discontinuation of PM exposure did not improve ocular surface health for 10 days. In contrast, PM10 did not result in significant ocular surface pathology. Notably, PM10 caused scratches on the cornea, especially in the area covered by the third eyelid.

Conclusions : The ocular surface phenotype induced by PM4 in vivo is reminiscent of allergic conjunctivitis. In contrast, PM10 caused minimal ocular surface damage, consistent with lesser in vitro cytotoxicity of PM10. PM4 and PM10 exert differential toxic effects, likely attributable to their different physiochemical properties and chemical composition. Future optimization and standardization of the experimental paradigms presented herein will aid drug discovery efforts for PM-mediated ocular surface pathologies.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.