Animal Models of LED-Induced Phototoxicity. Short- and Long-Term In Vivo and Ex Vivo Retinal Alterations

Abstract

Phototoxicity animal models have been largely studied due to their degenerative communalities with human pathologies, e.g., age-related macular degeneration (AMD). Studies have documented not only the effects of white light exposure, but also other wavelengths using LEDs, such as blue or green light. Recently, a blue LED-induced phototoxicity (LIP) model has been developed that causes focal damage in the outer layers of the superior-temporal region of the retina in rodents. In vivo studies described a progressive reduction in retinal thickness that affected the most extensively the photoreceptor layer. Functionally, a transient reduction in a- and b-wave amplitude of the ERG response was observed. Ex vivo studies showed a progressive reduction of cones and an involvement of retinal pigment epithelium cells in the area of the lesion and, in parallel, an activation of microglial cells that perfectly circumscribe the damage in the outer retinal layer. The use of neuroprotective strategies such as intravitreal administration of trophic factors, e.g., basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) or pigment epithelium-derived factor (PEDF) and topical administration of the selective alpha-2 agonist (Brimonidine) have demonstrated to increase the survival of the cone population after LIP.

Keywords: LED induced phototoxicity; cone photoreceptor; microglia activation; neuroprotection; retinal pigment epithelium.

Figure 1

Iba-1⁺ cells in outer segment layer (OSL) after LIP. Wholemount retina of a retina photo-exposed 3 days after LIP with an Iba-1⁺ reaction in the OSL after LIP (green) in the centre of the lesion in an albino rat retina (A). Confocal magnification of a right eye retina (RE) without microglial cells in OSL (red; B) and of a damage retina at 3 days after LIP where Iba-1⁺ cells (green) were observed in the center of the lesion and localised in OSL (red; C). Magnifications of Iba-1⁺ cells located in OSL at 1, 3, 7, 14 and 30 days after LIP in which morphological changes were observed from a dendritic shape at 1 day to an ameboid shape at 3 days after LIP and progressively returning to an elongated morphology (D–H). Bar scale in A = 1 mm; in D-H = 50 µm.

Figure 2

RPE analysis ex vivo by labelling zonulas occludens (A–D,G,H) and in vivo by blue autofluorescence (BAF; F,I). In the right eyes (RE) RPE showed a hexagonal and regular morphology (A,B). Intravitreal bFGF-treated retinas (C) showed less pleomorphism at 3 days after LIP than vehicle retinas (treated intravitreally with saline; D). However, these differences disappeared 7 days after LIP with similar RPE morphology in the bFGF group and vehicles (G,H). In addition, RPE alterations were observed by BAF one day after LIP with a hypo-autofluorescent circle in the lesion area leading to a hyper-autofluorescent spot in the circular lesion area at 7 days (F,I). Bar scale in (A) = 250 µm; in (B–D,G,H) = 100 µ; in (F,I) = 600 µm.