Effects of Nerve Growth Factor (NGF) Treatment in an Animal Model of Herpes Simplex Virus 1 Keratitis

Abstract

Purpose: : Herpes simplex virus type 1 keratitis is a common condition, and despite antiviral treatment, recurrent HSV–1 infection continues to be the leading cause of corneal blindness in industrialized nations. HSV latency can be influenced by a variety of factors, among them NGF exerts antiviral activity and modulate HSV–1 reactivation, as demonstrated by in vitro and in vivo studies. We evaluated the antiviral efficacy of NGF eye drop treatment, comparing it with acyclovir.

Methods: : 40 rabbits’ corneas were inoculated with HSV–1 virus, randomly divided in 4 groups and then treated 5 times daily with the following different treatments starting 3 days after the infection: 1) one drop of BSS 5 (control) 2) one drop of NGF (200 µg/ml) 3) one drop of antibody neutralizing NGF (1000 µg/ml) 4) 3% Acyclovir ointment (Zovirax®) Clinical course of HSV keratitis was daily evaluated by slit–lamp examination, and severity of conjunctival hyperemia, secretion, and corneal lesions were graded from 0 to 3. After 15 days animals were sacrificed and corneas removed for biochemical (immunohistochemestry for glycoprotein D) and molecular analysis (Real time PCR for HSV 1 Thymidine kinase) to evaluate the viral replicative activity. Statistical analysis on the course of the disease was performed using ANOVA repeated measure.

Results: : Rabbits treated with NGF had significant less severe course of HSV keratitis and a faster resolution of the infective process compared with both control group and acyclovir treated animals. On the contrary, the neutralization of the NGF by neutralizing antibody administration resulted in a significant more severe infection associated with the development of viral encephalitis in 2 animals (20%). The antiviral efficacy of NGF was confirmed by immunohystochemistry and molecular analysis that demonstrated reduced presence of HSV and decreased expression of Thymidine kinase in the corneas of rabbits treated with NGF when compared to both controls and acyclovir treated animals. The corneas of rabbits treated with antibody neutralizing NGF showed an increased expression of both viral protein and RNAm.

Conclusions: : This study demonstrated in vivo an antiviral activity of NGF treatment, confirming previous in vitro data, suggesting a potential use of NGF for the treatment of herpetic keratitis.

Keywords: herpes simplex virus • keratitis • growth factors/growth factor receptors