LPS-stimulated inflammation and apoptosis in corneal injury models

To evaluate and compare the proinflammatory and apoptotic effects of lipopolysaccharide (LPS) in three rabbit corneal injury models using a new in vivo confocal microscope (IVCM) and immunohistological techniques.

Adult male New Zealand albino rabbits were used in this study. Three corneal models were tested: corneal incision, corneal epithelium scraping, and corneal suture. Ten rabbits were used in each model and these three groups were subdivided into two subgroups: with or without LPS instillation (with saline used as control) for eight days. Rabbit corneas were analyzed in vivo by using the Rostock Cornea Module (RCM) of the Heidelberg Retina Tomograph (HRT)-II. Immunohistology was used to evaluate inflammatory, proliferating, and apoptotic cells in the different injury models following saline or LPS instillations.

Clinically, LPS induced earlier and higher levels of inflammation and corneal neovascularization in eyes subjected to scraping and suturing compared to saline. The RCM/HRT successfully presented high-quality images allowing analysis of all pathological corneal layers. Compared to groups receiving saline, LPS caused earlier and greater surface and stromal inflammatory infiltration as well as neovascularization. Immunohistology was correlated with in vivo findings and confirmed these results by showing greater infiltration of KI 67+ proliferating cells, TUNEL+ apoptotic cells, and TNF-alpha+, TNFR1+, TLR4/MD2+, ICAM-1+, RLA-DR+, CD11b+, and CD11c+ inflammatory cells, in eyes receiving LPS compared to those receiving saline.

These results indicate that in various models of corneal injury, LPS is a potent proinflammatory stimulus and its exposure has major effects on determinants of inflammation, angiogenesis, and apoptosis.