A case for neuroprotection in ophthalmology: developments in translational research

Abstract

Cellular aging occurs by the lifelong accumulation of oxidative damage leading to neuronal apoptosis, termed 'neurodegeneration', and the functional deficits of aging. Loss of visual function is one of the most important quality of life measures for older adults. We discuss recent clinical and laboratory advances in the neuroprotective treatment of the aging eye with particular emphasis on the three major ocular neurodegenerative conditions: glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR).

Figure 1. NAE 16:0 is neuroprotective against ischemic tissue damage and improves neurological outcome following I/R

(A) Representative TTC-stained sections of rat brain following 90 min. MCAO/24 h reperfusion (ischemia/reperfusion; I/R), treated with vehicle or NAE 16:0 at various time points. Viable tissue stains red, whereas damaged ischemic brain tissue appears unstained/white. (B) Quantification of the volume of the ischemic lesion (infarct volume) revealed that NAE 16:0 was neuroprotective when administered from 30 min. before MCAO (pretreatment), up to two h after occlusion. Administration of NAE 16:0 at 3 h post-MCAO had no effect on the size of the ischemic lesion. (C) I/R causes a moderate to severe neurological phenotype, as determined by the standardized neurological deficit score. NAE 16:0 reduced I/R-induced neurological deficits significantly (none to mild neurological phenotype) when administered before or at the time of occlusion. Data are shown as mean s.e.m. * p<0.05, ** p<0.01, *** p<0.001, compared with vehicle treated control group as determined using one-way ANOVA with Newman Keuls multiple comparison post-hoc test. Reprinted from reference , Garg P, Duncan RS, Kaja S, Zabaneh A, Chapman KD, Koulen P. Lauroylethanolamide and linoleoylethanolamide improve functional outcome in a rodent model for stroke. Neurosci Lett. Apr 4 2011;492(3):134–138, with permission from Elsevier Ltd.; permission conveyed through Copyright Clearance Center, Inc. Further reproduction prohibited without permission.

Figure 2. NAE 16:0 protects from I/R-induced apoptosis

(A) Representative photomicrographs of hematoxilin/eosin (HE) staining within the ischemic area of the cortex in sham-operated and ischemic-reperfusion rats with or without NAE 16:0 treatment. Yellow arrows indicate pyknotic nuclei, indicative of cells undergoing apoptosis. Fewer pyknotic nuclei were observed following I/R in the presence of NAE 16:0. Scale bar: 100 μm. (B) TUNEL labeling revealed a substantially reduced number of TUNEL-positive cells in the presence of NAE 16:0. In sham-operated animals, almost no TUNEL-positive cells were identified (data not shown). Scale bar: 50 μm. (C) For quantification of pyknotic nuclei and TUNEL-positive cells, five areas in each section were analyzed. Areas are indicated here on a TTC-stained section of a vehicle-treated rat following I/R. Areas 1–3 are cortical and lie in the ischemic core and penumbral zone, whereas areas 4–5 represent subcortical areas mainly falling in the ischemic penumbral zone. (D) Treatment with NAE 16:0 reduced the number of pyknotic nuclei following MCAO/reperfusion significantly by 53%, compared with vehicle-treated control. (E) Similarly, the number of TUNEL-positive cells was 60% lower in NAE 16:0 treated brain sections, compared with vehicle control, indicating that NAE 16:0 treatment protects from induction of apoptosis and cell-death pathways. Data are presented as mean ± s.e.m. for each group. * p<0.05, *** p<0.001, using one-way ANOVA with Newman Keuls multiple comparison post-hoc test. Reprinted from reference , Garg P, Duncan RS, Kaja S, Zabaneh A, Chapman KD, Koulen P. Lauroylethanolamide and linoleoylethanolamide improve functional outcome in a rodent model for stroke. Neurosci Lett. Apr 4 2011;492(3):134–138, with permission from Elsevier Ltd.; permission conveyed through Copyright Clearance Center, Inc. Further reproduction prohibited without permission.

Figure 3. NAE 18:2 protects RGC layer neurons from glutamate excitotoxicity

A) Exposure of retinas to 100 μM glutamate resulted in a dramatic increase in RGC layer neuron death (red arrows). Preincubation of retinas with NAE 18:2 for 6 hours prior to glutamate exposure resulted in a dose-dependent decrease in the number apoptotic, TUNEL-positive RGC layer neurons, with high physiological concentrations reducing the number of apoptotic RGCs. B) Quantitative summary data for the NAE 18:2-mediated neuroprotection from glutamate toxicity as measured by TUNEL histochemistry. Notes * denotes P < 0.05 as determined by a one-way analysis of variance test. Scale bar: 50μm. Abbreviations DIC, differential interference contrast; NAE, N-acylethanolamide; RGC, retinal ganglion cell; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP (2′-deoxyuridine 5′-triphosphate) nick-end labeling – green fluorescence. Republished with permission of Dove Medical Press Limited, from reference , Duncan RS, Xin H, Goad DL, Chapman KD, Koulen P. Protection of neurons in the retinal ganglion cell layer against excitotoxicity by the N-acylethanolamine, N-linoleoylethanolamine. Clin Ophthalmol. 2011;5:543–548; permission conveyed through Copyright Clearance Center, Inc. Further reproduction prohibited without permission.

Figure 4. NAE 18:2 preincubation is required for protection of RGC layer neurons against glutamate excitotoxicity. NAE 18:2 preincubation is critical for its neuroprotective effect

A) Retina explants were either pretreated for 24 hours (overnight, ON) with 40 μM NAE 18:2 prior to and during glutamate exposure or at the onset of glutamate exposure (no pretreatment). All glutamate exposures were for 24 hours and NAE 18:2 was present during the glutamate exposure period. Note the lack of protection without pretreatment (red arrows). B) Quantitative summary data revealing the requirement for NAE 18:2 protection of RGC layer neurons against glutamate. Notes * denotes P < 0.05 as determined by a one-way analysis of variance test. Scale bar: 50μm. Abbreviations DIC, differential interference contrast; NAE, N-acylethanolamide; RGC, retinal ganglion cell; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP (2′-deoxyuridine 5′-triphosphate) nick-end labeling – green fluorescence. Republished with permission of Dove Medical Press Limited, from reference , Duncan RS, Xin H, Goad DL, Chapman KD, Koulen P. Protection of neurons in the retinal ganglion cell layer against excitotoxicity by the N-acylethanolamine, N-linoleoylethanolamine. Clin Ophthalmol. 2011;5:543–548; permission conveyed through Copyright Clearance Center, Inc. Further reproduction prohibited without permission.