Infectious keratitis is common blinding eye disease in China. Inflammatory runaway reaction often occurs in infectious keratitis, and its mechanism and treating approach are worthy of research.

This study was to investigate the clinical manifestation, mechanism and treatment outcome of doxycycline in overwhelming inflammation induced by Pseudomonas aeruginosa keratitis.

Pseudomonas aeruginosa suspension was intrastromal injected in 60 right eyes of 60 New Zealand white rabbits, and gatifloxacin eye drops was frequent instilled for consecutive 3 days to establish corneal inflammatory runaway reaction models, and 42 eyes with worse keratitis were defined as overwhelming inflammation. Then the models were randomly divided into gatifloxacin treatment group (15 rabbits), combined treatment group (gatifloxacin with doxycycline treatment, 15 rabbits) and balance salt solution (BSS) control group (12 rabbits), and corresponding eye drops was topically administered in the rabbits 8 times per day for 14 days. The symptoms of the models were observed under the slit lamp microscope on day 1, 3, 7 and 14 after treatment, and the corneal infiltration area was calculated. The corneal morphology was examined by using hematoxylin-eosin staining. The expressions of matrix metalloproteinase-2 (MMP-2) and MMP-9 in the corneal tissue were examined by immunohistochemistry. The contents of tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β) in corneal homogenate were detected by ELISA. The use and care of the animals complied with the ARVO Statement.

The inflammatory scores were lower and infiltration area of cornea was smaller 7 days after treatment than those before treatment in the combined treatment group and gatifloxacin treatment group (both at P<0.05). Hematoxylin-eosin staining result showed that the inflammation response of cornea subsided 14 days in comparison with 5 days after treatment in the combined treatment group, with the proliferation and rearrangement of fiberal tissue. The MMP-2 and MMP-9 were strongly expressed in corneal tissue with overwhelming inflammation in day 5 after treatment, however, the expression intensity weakened in 14 days after treatment in the combined treatment, showing significant differences in the absorbance between them (all at P<0.05). ELISA assay showed that the contents of TNF-α and IL-1β in corneal tissue were significantly lower in the combined treatment group than those in the BSS group (P=0.00, 0.03). In addition, contents of TNF-α and IL-1β in corneal tissue were significantly declined at day 14 in comparison with day 5 and day 7 after treatment in the combined treatment group (all at P<0.05).

Overwhelming inflammatory keratitis models can be successfully established by corneal intrastromal injection of Pseudomonas aeruginosa suspension and immediately frequent 3-day instillation of gatifloxacin eye drops in rabbits. The topical application of doxycycline plays treating effect on overwhelming inflammatory keratitis by inhibiting the release of pro-inflammatory cytokines and MMPs.

[Key words] Infectious eye disease, corneal; Bacteria; Pseudomonas aeruginosa; Antibacterial agents; Overwhelming inflammation; Keratitis/drug therapy; Doxycycline; Disease models, animal; Rabbits