Changes in retinal N-acylethanolamines and their oxylipin derivatives during the development of visual impairment in a mouse model for glaucoma

Abstract

Purpose : Damage to retinal neurons due to oxidative stress has been implicated in glaucoma pathogenesis and N-acylethanolamines (NAEs) were shown to protect CNS and retinal neurons from oxidative stress. The purpose of our study was to quantify changes in N-acylethanolamine species and their oxylipin derivatives in the retina of a mouse model for glaucoma and to identify relationships among changes of these signaling molecules and of parameters of glaucoma disease development.

Methods : Levels of five N-acylethanolamine species and three NAE oxylipin derivatives were quantified in the retinae of 1.5 (healthy) and 8.5 month-old (glaucomatous) DBA/2Crl mice and correlated with intraocular pressure (IOP) measured by rebound tonometry, visual acuity and contrast sensitivity determined behaviorally assessing optomotor responses to stimuli of varying contrast or spatial frequency. N-Acylethanolamines and NAE-oxylipins in retinal extracts were separated by reverse phase HPLC and derivatized with N,O-Bis(trimethylsilyl)trifluoroacetamide. Resulting trimethylsilyl-derivatives were quantified against deuterated standards by isotope dilution gas chromatography–mass spectrometry.

Results : Levels (in nmol/g dry weight) of N-arachidonoylethanolamine (anandamide) were significantly decreased in glaucomatous (2.88 ± 0.67) compared to young animals (5.18 ± 0.97). Conversely, the anandamide oxylipin, 15(S)-hydroxy-N-(2-hydroxyethyl)-5Z,8Z,11Z,13E-eicosatetraenamide, was significantly increased in aged (0.06 ± 0.01) compared to young animals (0.04 ± 0.01). Levels of N-stearoylethanolamine and N-linoleoylethanolamine correlated strongly (r = -0.74 and 0.75, respectively) and significantly (P = 0.03 and 0.03, respectively) with intraocular pressure. Anandamide levels correlated strongly and significantly with visual acuity (r=0.87, P=0.01) and contrast sensitivity (r = -0.79, P = 0.02), while levels of its oxylipin were strongly and significantly but negatively associated with visual acuity (r = -0.85, P = 0.03).

Conclusions : Enzymatic depletion of the anandamide pool by 15-lipoxygenase and consequent accumulation of 15(S)-HETE ethanolamine may contribute to decreased visual function in glaucomatous mice. Since NAEs effectively attenuate glaucoma pathogenesis and associated visual impairment, our data provides additional rationale and novel targets for glaucoma therapies.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.