The effect of MIF inhibitor ISO-1 on apoptosis in chick retinal damage model

Abstract

Purpose : Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine which may play a role in neuronal apoptosis after retinal damage. In this study we evaluated the retinal expression and localization of MIF after excitotoxic retinal injury in the chick. We also tested if the intraocular injections of the MIF inhibitor ISO-1 will affect retinal apoptosis.

Methods : Under an IACUC-approved protocol P7 Leghorn chicks (Gallus gallus domesticus) were treated with intravitreal injection of NMDA 500 nmol or vehicle and evaluated for MIF expression with immunohistochemistry (IHC) (n=6). Apoptosis was detected with TUNEL assay. A dose-finding study (n= 4-6/group) was conducted in order to determine the maximum effective dose of ISO-1 which would significantly decrease NMDA-induced apoptosis. Chicks received a pre-treating dose of vehicle or ISO-1 (250 μmol) 24 hours before intraocular NMDA injection and a second dose of different doses of ISO-1 (25 μmol - 20 mmol) on day 0. Eyes were enucleated; retinal TUNEL was evaluated on day 1 and images were analyzed via Image J. Paired t-test was used for statistical analysis.

Results : IHC demonstrated a markedly increased elevation of MIF expression in the cytoplasm of inner retinal neurons after NMDA damage compared to non-damaged control eyes. The dose finding study showed that the intravitreal injection of 10 mmol ISO-1 produced the most statistically significant decrease in TUNEL positive cells in the inner nuclear layer (INL) 24 hours after NMDA injection (9756.4 ± 1646.7 cells/mm² retina vehicle vs 4566.3 ± 1443.8 cells/mm² retina ISO-1, p=0.02).

Conclusions : The neuronal upregulation of MIF in the damaged chick retina suggests this model can be a valid tool for evaluating how MIF impacts neuronal survival after excitotoxic retinal injury. The significant reduction in apoptosis by intravitreal injection of ISO-1 at day 1, suggests ISO-1 as a potential neuroprotective agent against retinal damage.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.