Evidence for estrogen receptor independent neuroprotection afforded by 17?-estradiol (E2) in a model of acute angle closure glaucoma in rat

Nucci C.1, Tartaglione R.2, Morrone L.A.2, Rombola’ L. 2, Pelle C. 2, Fazzi E.3 and Bagetta G. 2,1Department of Biopathology, University of Rome Tor Vergata, Rome; 2 Department of Pharmaco-Biology, University of Calabria, Cosenza, Italy; 3IRCCS Fondazione Istituto Neurologico “C. Mondino”, Pavia, Italy.

High acute rise of intraocular pressure (IOP) is a model for retinal ischemia and may represent a model of acute angle closure glaucoma (Osborne et al., 2004). Recently, using high IOP experimental model associated with microdialysis technique we demonstrate a role for excessive glutamate in the mechanisms of retinal damage (Nucci et al., 2005). Using the above described experimental model, here we report on the neuroprotective effect of E 2, a steroid hormone that has neurotrophic and neuroprotective properties (Yu et al., 2004). Male Sprague-Dawley rats (250-300 g) were used. Control animals (n=6) received injections of saline (1 mgkg-1, given i.p. twice daily) whereas test group received (i.p.) E2 (0.2 mgkg-1; n=3) or the estrogen receptor antagonist, ICI 182-780 (0.2 mgkg-1; n=3) 1h before injection of E2 (0.2 mgkg-1). Under general anaesthesia (cloral hydrate 400 mgkg-1) the anterior chamber of the right eye was cannulated with a 27gauge infusion needle connected to a bottle containing saline, and 1h after treatment, the IOP was raised to 120 mmHg for 45 min by elevating the saline reservoir. Sham-procedure was performed without the elevation of the bottle in control rats. Retinal ischemia was confirmed by observing a whitening of the iris and loss of the red reflex of the retina. After 24 h reperfusion, the animals were sacrificed and sections, cut along the vertical meridian of the eye passing through the optic nerve head, were stained with haematoxylin and eosin (H&E). The number of retinal ganglion cells (RGC) was counted in 6 areas (1 mm length) of each section (n= 6 per eye) at 300 μm from the optic nerve head on the superior and inferior hemisphere, using light microscopy. The data are expressed as means + SEM per area, and evaluated statistically for differences using the Student’s “t” test. The results are shown in the table below.

* p<0.001 vs. control, ** p<0.001 vs.ischemia, § p=0.8 vs. 17 β -estradiol + Ischemia

Our data demonstrate that systemic administration of E2 significantly reduces RGC loss induced by high IOP in rat. The latter effect does not appear to be mediated by the activation of the estrogen receptor, since a pre-treatment with a specific estrogen receptor antagonist, e.g. ICI 182-780, failed to abrogate the neuroprotection afforded by E2.

Nucci et al., (2005) NeuroToxicology, 26; 935-941
Osborne et al. (2004) Prog. Ret. Eye Res. 23;91-147.
Yu et al. (2004) J. Biol Chem. 279;13086-94.

Financial support from The Italian Ministry of Health ( Rome) is acknowledged