Biological effects of blocking blue and other visible light on the mouse retina

Violet Light Effects on the Circadian Rest-Activity Rhythm and the Visual System

BACKGROUND

Rooms illuminated by "black light" (<400 nm wavelength) has become popular, but there is not enough scientific evidence to support its implementation. This study aims to assess the effects of violet light (392 nm) on the circadian rest-activity rhythm and the visual system through animal experimentation.

MATERIALS AND RESULTS

Five groups of four mice were exposed to different white light, violet light, and dark periods, and their circadian rhythm was analyzed by measuring the circadian period using rest-activity cycles. Electroretinographic recordings and structural analysis of the retina were also performed on experimental animals.

RESULTS

Our study demonstrates that mice present normal circadian activity during exposure to violet light, taking rest not only under white light but under violet lighting periods. However, mice suffered a decrease in electrical retinal response after exposure to violet light as measured by electroretinography. Nevertheless, no structural changes were observed in the retinas of the animals under different lighting conditions.

CONCLUSIONS

Violet light elicits circadian rest-activity rhythm in mice but alters their visual function, although no structural changes are observed after short periods of violet light exposure.

Protective effect and mechanism of Lycium ruthenicum Murray anthocyanins against retinal damage induced by blue light exposure

Lycium ruthenicum Murray (LR) is a medicine and edible plant in Northwest China, and L. ruthenicum Murray anthocyanins (LRA) are green antioxidants with various pharmacological activities, such as antioxidant and anti-inflammatory activities. However, the protective effect and mechanism of LRA against retinal damage induced by blue light exposure are poorly understood. This study explored the protective effects and potential mechanisms of LRA on retinal damage induced by blue light exposure in vitro and in vivo. The results showed that LRA could ameliorate oxidative stress injury by activating the antioxidant stress nuclear factor-related factor 2 pathway, promoting the expression of phase II detoxification enzymes (HO-1, NQO1) and endogenous antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase), and reducing reactive oxygen species and malondialdehyde levels. Additionally, LRA could inhibit inflammatory response by decreasing the expression of blue light exposure-induced nuclear factor-κB (NF-κB) pathway-related proteins (NF-κB and p-IκBα), as well as interleukin (IL)-6, tumor necrosis factor-α, IL-1β pro-inflammatory factors and pro-inflammatory chemokine VEGF, and increasing the expression of anti-inflammatory factor IL-10. Furthermore, LRA could ameliorate oxidative stress-induced apoptosis by upregulating Bcl-2 and downregulating Bax and Caspase-3 protein expression. All these results indicate that LRA can be used as an antioxidant dietary supplement for the treatment or prevention of retinal diseases.

Artificial light and neurodegeneration: does light pollution impact the development of Alzheimer's disease?

Two multidimensional problems of recent times - Alzheimer's disease and light pollution - seem to be more interrelated than previously expected. A series of studies in years explore the pathogenesis and the course of Alzheimer's disease, yet the mechanisms underlying this pathology remain not fully discovered and understood. Artificial lights which accompany civilization on a daily basis appear to have more detrimental effects on both environment and human health than previously anticipated. Circadian rhythm is affected by inappropriate lighting conditions in particular. The consequences are dysregulation of the sleep-wake cycle, gene expression, neuronal restructuring, brain's electricity, blood flow, metabolites' turnover, and gut microbiota as well. All these phenomena may contribute to neurodegeneration and consequently Alzheimer's disease. There is an increasing number of research underlining the complexity of the correlation between light pollution and Alzheimer's disease; however, additional studies to enhance the key tenets are required for a better understanding of this relationship.

Retinal Pigment Epithelial Abnormality and Choroidal Large Vascular Flow Imbalance Are Associated with Choriocapillaris Flow Deficits in Age-Related Macular Degeneration in Fellow Eyes

Choriocapillaris flow deficits detected on optical coherence tomography angiographs were retrospectively analyzed. In 38 age-related macular degeneration (AMD) fellow eyes, without fundus findings (26 men, 71.7 ± 1.9 years old), and 22 control eyes (11 men, 69.4 ± 1.8), the choriocapillaris flow area (CCFA) ratio and coefficient of variation (CV) of the CCFA ratio (which represented the heterogeneity of the ratio), negatively and positively correlated with age (all p < 0.01), respectively. Moreover, the respective mean values were lower (p = 0.0031) and greater (p = 0.002) in AMD fellow eyes than in the control eyes. The high-risk condition of AMD fellow eyes was defined by a CCFA ratio <58.5%, and the CV of the CCFA ratio ≥0.165 (odds ratio (OR), 5.408; 95% confidence interval (CI): 1.117-21.118, p = 0.035, after adjusting for age and sex) was related to the presence of fundus autofluorescence abnormality (OR, 16.440; 95% CI, 1.262-214.240; p = 0.033) and asymmetrically dilated choroidal large vasculature (OR, 4.176; 95% CI, 1.057-16.503; p = 0.042), after adjusting for age and sex. The presence of fundus autofluorescence abnormality indicated a retinal pigment epithelium (RPE) abnormality. The RPE volume was reduced in the latter eye group, particularly in the thinner choroidal vasculature. In addition to aging, RPE abnormality and choroidal large vascular flow imbalances were associated with exacerbated heterogeneous choriocapillaris flow deficits in AMD fellow eyes without macular neovascularization.

More light components and less light damage on rats’ eyes: evidence for the photobiomodulation and spectral opponency

The blue-light hazard (BLH) has raised concerns with the increasing applications of white light-emitting diodes (LEDs). Many researchers believed that the shorter wavelength or more light components generally resulted in more severe retinal damage. In this study, based on the conventional phosphor-coated white LED, we added azure (484 nm), cyan (511 nm), and red (664 nm) light to fabricate the low-hazard light source. The low-hazard light sources and conventional white LED illuminated 68 Sprague-Dawley (SD) rats for 7 days. Before and after light exposure, we measured the retinal function, thickness of retinal layers, and fundus photographs. The expression levels of autophagy-related proteins and the activities of oxidation-related biochemical indicators were also measured to investigate the mechanisms of damaging or protecting the retina. With the same correlated color temperature (CCT), the low-hazard light source results in significantly less damage on the retinal function and photoreceptors, even if it has two times illuminance and blue-light hazard-weighted irradiance ([Formula: see text]) than conventional white LED. The results illustrated that [Formula: see text] proposed by IEC 62471 could not exactly evaluate the light damage on rats' retinas. We also figured out that more light components could result in less light damage, which provided evidence for the photobiomodulation (PBM) and spectral opponency on light damage.

Selective blue-filtering spectacle lens protected primary porcine RPE cells against light emitting diode-induced cell damage

This study aimed to investigate whether use of a selective-blue-filtering (S-BF) lens can protect cultured primary porcine RPE cells against photo-irradiation. Transmittance of S-BF and UV-filtering (UVF) lenses was characterised spectrophotometrically. RPE cells were exposed to 1700 lux of white (peak λ at 443 and 533 nm; 0.44 mW/cm²) or blue (peak λ at 448 and 523 nm; 0.85 mW/cm²) LED light for 16 h to evaluate the influence of light source on the culture. The effect of the S-BF and UVF ophthalmic lenses on RPE cell cultures under blue light irradiation was then investigated. Cell viability was compared using trypan blue and MTT assays. Intracellular ROS production was detected by a fluorescein probe CM-H2DCFDA. Expression levels of catalase and Prdx3 were analysed by western blot. Trypan blue staining showed blue light caused more cell death than no light (p = 0.001) or white light (p = 0.005). MTT assay supported the hypothesis that exposure to blue light damaged RPE cells more severely than no light (p = 0.002) or white light (p = 0.014). Under blue light, use of the S-BF lens, which blocked 17% more blue light than the UVF lens, resulted in higher cellular viability (S-BF: 93.4±1.4% vs UVF: 90.6±1.4%; p = 0.022; MTT: 1.2-fold; p = 0.029). Blue and white light both significantly increased ROS production. The S-BF lens protected cells, resulting in lower levels of ROS and higher expression of catalase and Prdx3. To conclude, blue LED light exposure resulted in significant cytotoxicity to RPE cells. Partial blockage of blue light by an S-BF lens led to protective effects against retinal phototoxicity, which were mediated by reduction of ROS and increased levels of antioxidant enzymes.

Effects of Epigenetic Modification of PGC-1α by a Chemical Chaperon on Mitochondria Biogenesis and Visual Function in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a hereditary blinding disease characterized by gradual photoreceptor death, which lacks a definitive treatment. Here, we demonstrated the effect of 4-phenylbutyric acid (PBA), a chemical chaperon that can suppress endoplasmic reticulum (ER) stress, in P23H mutant rhodopsin knock-in RP models. In the RP models, constant PBA treatment led to the retention of a greater number of photoreceptors, preserving the inner segment (IS), a mitochondrial- and ER-rich part of the photoreceptors. Electroretinography showed that PBA treatment preserved photoreceptor function. At the early point, ER-associated degradation markers, xbp1s, vcp, and derl1, mitochondrial kinetic-related markers, fis1, lc3, and mfn1 and mfn2, as well as key mitochondrial regulators, pgc-1α and tfam, were upregulated in the retina of the models treated with PBA. In vitro analyses showed that PBA upregulated pgc-1α and tfam transcription, leading to an increase in the mitochondrial membrane potential, cytochrome c oxidase activity, and ATP levels. Histone acetylation of the PGC-1α promoter was increased by PBA, indicating that PBA affected the mitochondrial condition through epigenetic changes. Our findings constituted proof of concept for the treatment of ER stress-related RP using PBA and revealed PBA’s neuroprotective effects, paving the way for its future clinical application.

Neuroprotective Effect of 4-Phenylbutyric Acid against Photo-Stress in the Retina

Exposure to excessive visible light causes retinal degeneration and may influence the progression of retinal blinding diseases. However, there are currently no applied treatments. Here, we focused on endoplasmic reticulum (ER) stress, which can cause cellular degeneration and apoptosis in response to stress. We analyzed functional, histological, and molecular changes in the light-exposed retina and the effects of administering an ER-stress inhibitor, 4-phenylbutyric acid (4-PBA), in mice. We found that light-induced visual function impairment related to photoreceptor cell loss and outer segment degeneration were substantially suppressed by 4-PBA administration, following attenuated photoreceptor apoptosis. Induction of retinal ER stress soon after light exposure, represented by upregulation of the immunoglobulin heavy chain binding protein (BiP) and C/EBP-Homologous Protein (CHOP), were suppressed by 4-PBA. Concurrently, light-induced oxidative stress markers, Nuclear factor erythroid 2-related factor 2 (Nrf2) and Heme Oxygenase 1 (HO-1), and mitochondrial apoptotic markers, B-cell lymphoma 2 apoptosis regulator (Bcl-2)-associated death promoter (Bad), and Bcl-2-associated X protein (Bax), were suppressed by 4-PBA administration. Increased expression of glial fibrillary acidic protein denoted retinal neuroinflammation, and inflammatory cytokines were induced after light exposure; however, 4-PBA acted as an anti-inflammatory. Suppression of ER stress by 4-PBA may be a new therapeutic approach to suppress the progression of retinal neurodegeneration and protect visual function against photo-stress.

Visual stimulation with blue wavelength light drives V1 effectively eliminating stray light contamination during two-photon calcium imaging

BACKGROUND

Brain visual circuits are often studied in vivo by imaging Ca²⁺ indicators with green-shifted emission spectra. Polychromatic white visual stimuli have a spectrum that partially overlaps indicators´ emission spectra, resulting in significant contamination of calcium signals.

NEW METHOD

To overcome light contamination problems we choose blue visual stimuli, having a spectral composition not overlapping with Ca²⁺ indicator´s emission spectrum. To compare visual responsiveness to blue and white stimuli we used electrophysiology (visual evoked potentials -VEPs) and 3D acousto-optic two-photon (2P) population Ca²⁺ imaging in mouse primary visual cortex (V1).

RESULTS

VEPs in response to blue and white stimuli had comparable peak amplitudes and latencies. Ca²⁺ imaging in a Thy1 GP4.3 line revealed that the populations of neurons responding to blue and white stimuli were largely overlapping, that their responses had similar amplitudes, and that functional response properties such as orientation and direction selectivities were also comparable.

COMPARISON WITH EXISTING METHODS

Masking or shielding the microscope are often used to minimize the contamination of Ca²⁺ signal by white light, but they are time consuming, bulky and thus can limit experimental design, particularly in the more and more frequently used awake set-up. Blue stimuli not interfering with imaging allow to omit shielding.

CONCLUSIONS

Together, our results show that the selected blue light stimuli evoke responses comparable to those evoked by white stimuli in mouse V1. This will make complex designs of imaging experiments in behavioral set-ups easier, and facilitate the combination of Ca²⁺ imaging with electrophysiology and optogenetics.

Blue light filtering ophthalmic lenses: A systematic review

Background: Blue blocking (BB) lenses, including spectacles and intraocular lenses, work by attenuating short-wavelength light. BB glasses are being marketed with the aim to reduce eye fatigue symptoms when using digital devices, improve sleep quality and potentially confer protection from retinal phototoxicity. BB intraocular lenses following cataract surgery may be implanted because they are thought to prevent age-related macular degeneration (AMD) progression.Methods: The present study is a systematic review aiming to analyze BB lenses clinical efficacy in preventing blue light-related ocular disorders, including AMD progression, eye fatigue, and their impact on sleep quality. We searched Medline, PubMed, Web of Science and the Cochrane Library until May 2020.Results:Although several studies have been performed investigating BB lenses, clinical efficacy for preventing or attenuating the above-mentioned ocular disorders is often theorical or based on laboratory or animal experiments. Conclusions: To date, there is a lack of consistent evidence for a larger-sclale introduction of BB lenses in the routine clinical practice.

Whole transcriptome analysis on blue light-induced eye damage

AIM

To analyze abnormal gene expressions of mice eyes exposed to blue light using RNA-seq and analyze the related signaling pathways.

METHODS

Kunming mice were divided into an experimental group that was exposed to blue light and a control group that was exposed to natural light. After 14d, the mice were euthanized and their eyeballs were collected. Whole transcriptome analysis was attempted to analyze the gene expression of the eyeballs using RNA-seq to reconstruct genetic networks. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used to reveal the related signaling pathways.

RESULTS

The 737 differentially expressed genes were identified, including 430 up and 307 down regulated genes, by calculating the gene FPKM in each sample and conducting differential gene analysis. GO and KEGG pathway enrichment analysis showed that blue light damage may associated with the visual perception, sensory perception of light stimulus, phototransduction, and JAK-STAT signaling pathways. Differential lncRNA, circRNA and miRNA analysis showed that blue light exposure affected pathways for retinal cone cell development and phototransduction, among others.

CONCLUSION

Exposure to blue light can cause a certain degree of abnormal gene expression and modulate signaling pathways in the eye.

Loss of Concentration May Occur by Blink Inhibition in DED Simulation Models

Purpose: Patients with dry eye disease (DED) often suffer productivity loss and distress due to bothersome symptoms. The aim of this study was to objectively quantify and compare productivity-related emotional states obtained from brain waveforms in natural and simulated DED conditions. Method: 25 healthy adults (6 females and 19 males; mean age ± standard deviation, 22.6 ± 8.3 years) were recruited for the study, which included an electroencephalogram (EEG), measurements of interblinking time, and questionnaires. DED was simulated by suppressing blinking, while spontaneous blinking served as a control. Elements of concentration, stress, and alertness were extracted from the raw EEG waveforms and the values were compared during spontaneous and suppressed blinking. The relation with DED-related parameters was then explored. Written informed consent was obtained from all participants. Results: All participants successfully completed the experimental protocol. Concentration significantly decreased during suppressed blinking in 20 participants (80%), when compared with spontaneous blinking, whereas there were no or small differences in stress or alertness between spontaneous and suppressed blinking. The change in concentration was correlated with interblinking time (β = −0.515, p = 0.011). Conclusion: Loss of concentration was successfully captured in an objective manner using the EEG. The present study may enable us to understand how concentration is affected during blink suppression, which may happen in office work, particularly during computer tasks. Further study using detailed ocular evaluation is warranted to explore the effect of different interventions.

Neuroprotective and vision-protective effect of preserving ATP levels by AMPK activator

Progression of blinding diseases, such as age-related macular degeneration, is accelerated by light exposure. However, no particular intervention is applied to the photostress. Here, we report neuroprotective effects of the adenosine monophosphate (AMP)-activated protein kinase (AMPK) activator, 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR), on light-induced visual function impairment, photoreceptor disorders and death in mice. Increase in retinal ATP levels in response to photostress was transient, because oxygen consumption rate (OCR) and cytochrome c oxidase (CcO) activity were reduced under photostress. However, AICAR treatment preserved OCR, CcO activity, and high levels of retinal ATP after light exposure. AMPK knockdown in the photoreceptor-derived cell line revealed that AMPK targeted CcO activity. Further, our data indicated that photostress reduced mitochondrial respiratory function and ATP levels, while AICAR treatment promoted neuronal survival and retained visual function, stabilizing ATP levels through preserved CcO activity. The current study has provided proof of concept for providing cells with sufficient energy to promote cell survival in the presence of cellular stress. This is in contrast to the previous reports which primarily investigated therapeutic approaches to suppress stress signals. Hence, stabilization of the ATP supply may serve as a novel therapeutic approach to support tissue survival under stress and prevent neurodegeneration.

Suppression of Blue Light at Night Ameliorates Metabolic Abnormalities by Controlling Circadian Rhythms

Purpose

Light-emitting diodes that emit high-intensity blue light are associated with blue-light hazard. Here, we report that blue light disturbs circadian rhythms by interfering with the clock gene in the suprachiasmatic nucleus (SCN) and that suppression of blue light at night ameliorates metabolic abnormalities by controlling circadian rhythms.

Methods

C57BL/6J mice were exposed to 10-lux light for 30 minutes at Zeitgeber time 14 for light pulse with blue light or blue-light cut light to induce phase shift of circadian rhythms. Phase shift, clock gene expression in SCN, and metabolic parameters were analyzed. In the clinical study, healthy participants wore blue-light shield eyewear for 2 to 3 hours before bed. Anthropometric data analyses, laboratory tests, and sleep quality questionnaires were performed before and after the study.

Results

In mice, phase shift induced with a blue-light cut light pulse was significantly shorter than that induced with a white light pulse. The phase of Per2 expression in the SCN was also delayed after a white light pulse. Moreover, blood glucose levels 48 hours after the white light pulse were higher than those after the blue-cut light pulse. Irs2 expression in the liver was decreased with white light but significantly recovered with the blue-cut light pulse. In a clinical study, after 1 month of wearing blue-light shield eyeglasses, there were improvements in fasting plasma glucose levels, insulin resistance, and sleep quality.

Conclusions

Our results suggest that suppression of blue light at night effectively maintains circadian rhythms and metabolism.

Dietary Spirulina Supplementation Protects Visual Function From Photostress by Suppressing Retinal Neurodegeneration in Mice

PURPOSE

We investigated whether daily consumption of Spirulina, an antioxidant generating cyanobacterial nutritional supplement, would suppress photostress-induced retinal damage and prevent vision loss in mice.

METHODS

Six-week-old male BALB/cAJcl mice were allowed constant access to either a standard or Spirulina-supplemented diet (20% Spirulina) that included the antioxidants, β-carotene and zeaxanthin, and proteins for 4 weeks. Following dark adaptation, mice were exposed to 3000-lux white light for 1 hour and returned to their cages. Visual function was analyzed by electroretinogram, and retinal histology by hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated, deoxyuridine triphosphate nick-end labeling (TUNEL) assay, and immunohistochemistry. Retinal expression of proteins, reactive oxygen species (ROS), and mRNAs were measured using immunoblot analysis, enzyme-linked immunosorbent assay (ELISA), 2',7'-dichlorofluorescein-diacetate, or ROS Brite 700 Dyes, and real-time reverse-transcription polymerase chain reaction, respectively.

RESULTS

Light-induced visual function impairment was suppressed by constant Spirulina intake. Thinning of the photoreceptor layer and outer segments, photoreceptor cell death, decreased rhodopsin protein, and induction of glial fibrillary acidic protein were ameliorated in the Spirulina-intake group. Increased retinal ROS levels after light exposure were reduced by Spirulina supplementation. Light-induced superoxide dismutase 2 and heme oxygenase-1 mRNAs in the retina, and Nrf2 activation in the photoreceptor cells, were preserved with Spirulina supplementation, despite reduced ROS levels, suggesting two pathways for suppressing ROS, scavenging and induction of endogenous antioxidative enzymes. Light-induced MCP-1 retinal mRNA and proteins were also suppressed by Spirulina.

CONCLUSIONS

Spirulina ingestion protected retinal photoreceptors from photostress in the retina.

TRANSLATIONAL RELEVANCE

Spirulina has potential as a nutrient supplement to prevent vision loss related to oxidative damage in the future.

Effects of light on aging and longevity

Increasing evidence suggests an important role for light in regulation of aging and longevity. UV radiation is a mutagen that can promote aging and decrease longevity. In contrast, NIR light has shown protective effects in animal disease models. In invertebrates, visible light can shorten or extend lifespan, depending on the intensity and wavelength composition. Visible light also impacts human health, including retina function, sleep, cancer and psychiatric disorders. Possible mechanisms of visible light include: controlling circadian rhythms, inducing oxidative stress, and acting through the retina to affect neuronal circuits and systems. Changes in artificial lighting (e.g., LEDs) may have implications for human health. It will be important to further explore the mechanisms of how light affects aging and longevity, and how light affects human health.

Protective effects of blue light-blocking shades on phototoxicity in human ocular surface cells

Objective

Blue light hazards for retina and ocular surface have been repeatedly described and many protective methods are introduced for retina; however, no study has been conducted on ocular surface protection. The purpose of this in vitro study was to examine phototoxicity and shade protection after blue light irradiation in primary human cells of corneal surface origin.

Methods and analysis

Primary human cells of corneal surface origin were obtained from eye bank eyes. After blue light irradiation (405 nm) of these cells for 3 min, and a further 24 hours’ incubation, surviving viable cells were assessed by the methyl thiazolyl tetrazolium assay. Simultaneously, cell viability was determined in wells covered by ultraviolet and blue light shades.

Results

Under subconfluent conditions, viable cells decreased by around 50% after blue light irradiation, compared with control cells without irradiation. The blue light phototoxicity was not blocked by the control shade, but the ultraviolet-blocking and blue light-blocking shades protected the cells from phototoxicity, producing a 30%–40% reduction (ultraviolet) and 15%–30% reduction (blue light) in viable cells.

Conclusion

These results indicate that blue light injures ocular surface cells and the cells are protected from damage by a shade. We recommend blue light protection to maintain ocular health, especially in high-risk populations, such as people with dry eye, contact lens users, the malnourished and the elderly.

The Protective Effects of Blue Light-Blocking Films With Different Shielding Rates: A Rat Model Study

Purpose

To examine light emitting diode (LED)-induced retinal photochemical damage and assess the protective performance of blue light-shielding films with different shielding rates in Sprague-Dawley rats (SD rats).

Methods

SD rats were randomly divided into five groups: blank control (group I), white LED illumination (group II), and white LED illumination combined with shielding of blue light of wavelength 440 nm at 40%, 60%, and 80% (groups III, IV, and V). The illumination was 200 lux. All animals underwent electroretinography (ERG), hematoxylin-eosin (H&E) staining, immunohistochemical (IHC) staining, and transmission electron microscopy (TEM) observation after 14 days of dark-adaptation before illumination, after 14 days of cyclic illumination, and after 14 days of darkness for recovery following illumination.

Results

ERG showed retinal functional loss after LED light exposure. However, retinal cell function was partly recovered after a further 2 weeks of dark adaptation. H&E staining and TEM revealed increases in photoreceptor cell death after illumination. IHC staining demonstrated that oxidative stress was associated with retinal injury. Although retinal light injury was discovered in the LED light-exposure groups, shielding 60% of blue light of wavelength 440 nm (bandwidth 20 nm) protected retinas.

Conclusions

Cyclic illumination of low light intensity (200 lux) for 14 days produced retinal degeneration; shielding 60% of blue light may protect retinas from light damage.

Translational Relevance

This study found the effective shielding rate that could protect retinas from light damage when shielding specific narrow-band harmful blue light; thus providing a more normative method for protecting eyes from blue light hazard.

Retinal Neuron Is More Sensitive to Blue Light-Induced Damage than Glia Cell Due to DNA Double-Strand Breaks

Blue light is a major component of visible light and digital displays. Over-exposure to blue light could cause retinal damage. However, the mechanism of its damage is not well defined. Here, we demonstrate that blue light (900 lux) impairs cell viability and induces cell apoptosis in retinal neurocytes in vitro. A DNA electrophoresis assay shows severe DNA damage in retinal neurocytes at 2 h after blue light treatment. γ-H2AX foci, a specific marker of DNA double-strand breaks (DSBs), is mainly located in the Map2-posotive neuron other than the glia cell. After assaying the expression level of proteins related to DNA repair, Mre11, Ligase IV and Ku80, we find that Ku80 is up-regulated in retinal neurocytes after blue light treatment. Interestingly, Ku80 is mainly expressed in glia fibrillary acidic protein (GFAP)-positive glia cells. Moreover, following blue light exposure in vivo, DNA DSBs are shown in the ganglion cell layer and only observed in Map2-positive cells. Furthermore, long-term blue light exposure significantly thinned the retina in vivo. Our findings demonstrate that blue light induces DNA DSBs in retinal neurons, and the damage is more pronounced compared to glia cells. Thus, this study provides new insights into the mechanisms of the effect of blue light on the retina.

Lactobacillus paracasei KW3110 Prevents Blue Light-Induced Inflammation and Degeneration in the Retina

Age-related macular degeneration and retinitis pigmentosa are leading causes of blindness and share a pathological feature, which is photoreceptor degeneration. To date, the lack of a potential treatment to prevent such diseases has raised great concern. Photoreceptor degeneration can be accelerated by excessive light exposure via an inflammatory response; therefore, anti-inflammatory agents would be candidates to prevent the progress of photoreceptor degeneration. We previously reported that a lactic acid bacterium, Lactobacillus paracasei KW3110 (L. paracasei KW3110), activated macrophages suppressing inflammation in mice and humans. Recently, we also showed that intake of L. paracasei KW3110 could mitigate visual display terminal (VDT) load-induced ocular disorders in humans. However, the biological mechanism of L. paracasei KW3110 to retain visual function remains unclear. In this study, we found that L. paracasei KW3110 activated M2 macrophages inducing anti-inflammatory cytokine interleukin-10 (IL-10) production in vitro using bone marrow-derived M2 macrophages. We also show that IL-10 gene expression was significantly increased in the intestinal immune tissues 6 h after oral administration of L. paracasei KW3110 in vivo. Furthermore, we demonstrated that intake of L. paracasei KW3110 suppressed inflammation and photoreceptor degeneration in a murine model of light-induced retinopathy. These results suggest that L. paracasei KW3110 may have a preventive effect against degrative retinal diseases.

Removal of the blue component of light significantly decreases retinal damage after high intensity exposure

Light causes damage to the retina (phototoxicity) and decreases photoreceptor responses to light. The most harmful component of visible light is the blue wavelength (400–500 nm). Different filters have been tested, but so far all of them allow passing a lot of this wavelength (70%). The aim of this work has been to prove that a filter that removes 94% of the blue component may protect the function and morphology of the retina significantly. Three experimental groups were designed. The first group was unexposed to light, the second one was exposed and the third one was exposed and protected by a blue-blocking filter. Light damage was induced in young albino mice (p30) by exposing them to white light of high intensity (5,000 lux) continuously for 7 days. Short wavelength light filters were used for light protection. The blue component was removed (94%) from the light source by our filter. Electroretinographical recordings were performed before and after light damage. Changes in retinal structure were studied using immunohistochemistry, and TUNEL labeling. Also, cells in the outer nuclear layer were counted and compared among the three different groups. Functional visual responses were significantly more conserved in protected animals (with the blue-blocking filter) than in unprotected animals. Also, retinal structure was better kept and photoreceptor survival was greater in protected animals, these differences were significant in central areas of the retina. Still, functional and morphological responses were significantly lower in protected than in unexposed groups. In conclusion, this blue-blocking filter decreases significantly photoreceptor damage after exposure to high intensity light. Actually, our eyes are exposed for a very long time to high levels of blue light (screens, artificial light LED, neons…). The potential damage caused by blue light can be palliated.

Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies

Mammals receive light information through the eyes, which perform two major functions: image forming vision to see objects and non-image forming adaptation of physiology and behavior to light. Cone and rod photoreceptors form images and send the information via retinal ganglion cells to the brain for image reconstruction. In contrast, nonimage-forming photoresponses vary widely from adjustment of pupil diameter to adaptation of the circadian clock. nonimage-forming responses are mediated by retinal ganglion cells expressing the photopigment melanopsin. Melanopsin-expressing cells constitute 1–2% of retinal ganglion cells in the adult mammalian retina, are intrinsically photosensitive, and integrate photic information from rods and cones to control nonimage-forming adaptation. Action spectra of ipRGCs and of melanopsin photopigment peak around 480 nm blue light. Understanding melanopsin function lets us recognize considerable physiological effects of blue light, which is increasingly important in our modern society that uses light-emitting diode. Misalignment of circadian rhythmicity is observed in numerous conditions, including aging, and is thought to be involved in the development of age-related disorders, such as depression, diabetes, hypertension, obesity, and cancer. The appropriate regulation of circadian rhythmicity by proper lighting is therefore essential. This perspective introduces the potential risks of excessive blue light for human health through circadian rhythm disruption and sleep deprivation. Knowing the positive and negative aspects, this study claims the importance of being exposed to light at optimal times and intensities during the day, based on the concept of the circadian clock, ultimately to improve quality of life to have a healthy and longer life.

Neuroprotective effect of bilberry extract in a murine model of photo-stressed retina

Excessive exposure to light promotes degenerative and blinding retinal diseases such as age-related macular degeneration and retinitis pigmentosa. However, the underlying mechanisms of photo-induced retinal degeneration are not fully understood, and a generalizable preventive intervention has not been proposed. Bilberry extract is an antioxidant-rich supplement that ameliorates ocular symptoms. However, its effects on photo-stressed retinas have not been clarified. In this study, we examined the neuroprotective effects of bilberry extract against photo-stress in murine retinas. Light-induced visual function impairment recorded by scotopic and phototopic electroretinograms showing respective rod and cone photoreceptor function was attenuated by oral administration of bilberry extract through a stomach tube in Balb/c mice (750 mg/kg body weight). Bilberry extract also suppressed photo-induced apoptosis in the photoreceptor cell layer and shortening of the outer segments of rod and cone photoreceptors. Levels of photo-induced reactive oxygen species (ROS), oxidative and endoplasmic reticulum (ER) stress markers, as measured by real-time reverse transcriptase polymerase chain reaction, were reduced by bilberry extract treatment. Reduction of ROS by N-acetyl-L-cysteine, a well-known antioxidant also suppressed ER stress. Immunohistochemical analysis of activating transcription factor 4 expression showed the presence of ER stress in the retina, and at least in part, in Müller glial cells. The photo-induced disruption of tight junctions in the retinal pigment epithelium was also attenuated by bilberry extract, repressing an oxidative stress marker, although ER stress markers were not repressed. Our results suggest that bilberry extract attenuates photo-induced apoptosis and visual dysfunction most likely, and at least in part, through ROS reduction, and subsequent ER stress attenuation in the retina. This study can help understand the mechanisms of photo-stress and contribute to developing a new, potentially useful therapeutic approach using bilberry extract for preventing retinal photo-damage.

Lutein acts via multiple antioxidant pathways in the photo-stressed retina

Lutein slows the progression of age-related macular degeneration (AMD), a leading cause of blindness in ageing societies. However, the underlying mechanisms remain elusive. Here, we evaluated lutein's effects on light-induced AMD-related pathological events. Balb/c mice exposed to light (2000 lux, 3 h) showed tight junction disruption in the retinal pigment epithelium (RPE) at 12 h, as detected by zona occludens-1 immunostaining. Substantial disruption remained 48 h after light exposure in the vehicle-treated group; however, this was ameliorated in the mice treated with intraperitoneal lutein at 12 h, suggesting that lutein promoted tight junction repair. In the photo-stressed RPE and the neighbouring choroid tissue, lutein suppressed reactive oxygen species and increased superoxide dismutase (SOD) activity at 24 h, and produced sustained increases in sod1 and sod2 mRNA levels at 48 h. SOD activity was induced by lutein in an RPE cell line, ARPE19. We also found that lutein suppressed upregulation of macrophage-related markers, f4/80 and mcp-1, in the RPE-choroid tissue at 18 h. In ARPE19, lutein reduced mcp-1 mRNA levels. These findings indicated that lutein promoted tight junction repair and suppressed inflammation in photo-stressed mice, reducing local oxidative stress by direct scavenging and most likely by induction of endogenous antioxidant enzymes.

Retinoprotective Effects of Bilberry Anthocyanins via Antioxidant, Anti-Inflammatory, and Anti-Apoptotic Mechanisms in a Visible Light-Induced Retinal Degeneration Model in Pigmented Rabbits

Excessive visible light exposure can induce damage to retinal cells and contribute to the development or progression of age-related macular degeneration. In this study we created a model of phototoxicity in pigmented rabbits. Furthermore, we investigated the protective effect of bilberry anthocyanin extract (BAE, Table A1) and explored the possible mechanisms of action in this model. The model of light-induced retinal damage was established by the pigmented rabbits exposed to light at 18,000 lx for 2 h, and they were sacrificed on day 7. After administration of BAE at dosages of 250 and 500 mg/kg/day, retinal dysfunction was significantly inhibited in terms of electroretinograms, and the decreased thicknesses of retinal outer nuclear layer and lengths of the outer segments of the photoreceptor cells were suppressed in rabbits with retinal degeneration. BAE attenuated the changes caused by light to certain apoptotic proteins (Bax, Bcl-2, and caspase-3). The extract increased the levels of superoxide dismutase, glutathione peroxidase, and catalase, as well as the total antioxidant capacity, but decreased the malondialdehyde level in the retinal cells. BAE inhibited the light-induced elevation in the levels of proinflammatory cytokines and angiogenic parameters (IL-1β and VEGF). Results showed that visible light-induced retinal degeneration model in pigmented rabbits was successfully established and BAE exhibited protective effects by increasing the antioxidant defense mechanisms, suppressing lipid peroxidation and proinflammatory cytokines, and inhibiting retinal cells apoptosis.

Angiotensin II type 1 receptor blockade suppresses light-induced neural damage in the mouse retina

Exposure to light contributes to the development and progression of retinal degenerative diseases. However, the mechanisms underlying light-induced tissue damage are not fully understood. Here, we examined the role of angiotensin II type 1 receptor (AT1R) signaling, which is part of the renin-angiotensin system, in light-induced retinal damage. Light-exposed Balb/c mice that were treated with the AT1R blockers (angiotensin II receptor blockers; ARBs) valsartan, losartan, and candesartan before and after the light exposure exhibited attenuated visual function impairment, compared to vehicle-treated mice. This effect was dose-dependent and observed across the ARB class of inhibitors. Further evaluation of valsartan showed that it suppressed a number of light-induced retinal effects, including thinning of the photoreceptor cell layer caused by apoptosis, shortening of the photoreceptor cell outer segment, and increased levels of reactive oxygen species (ROS). The role of ROS in retinal pathogenesis was investigated further using the antioxidant N-acetyl-l-cysteine (NAC). Treatment of light-exposed mice with NAC before the light exposure suppressed the visual function impairment and photoreceptor cell histological changes due to apoptosis. Moreover, treatment with valsartan or NAC suppressed the induction of c-fos (a component of the AP-1 transcription factor) and the upregulation of fasl (a proapoptotic molecule whose transcript is regulated downstream of AP-1). Our results suggest that AT1R signaling mediates light-induced apoptosis, by increasing the levels of ROS and proapoptotic molecules in the retina. Thus, AT1R blockade may represent a new therapeutic approach for preventing light-induced retinal neural tissue damage.

Oxidative stress and histological changes in a model of retinal phototoxicity in rabbits

Photochemical damage occurs after an exposure to high energy radiation within the visible spectrum of light, causing morphological changes in the retina and the formation of superoxide anion. In this study we created a model of phototoxicity in rabbits. Animals were exposed to a light source for 120 minutes and were sacrificed immediately or one week after exposure. Outer nuclear layer and neurosensory retina thickness measurements and photoreceptor counting were performed. Caspase-1 and caspase-3 were assessed by immunohistochemistry. Dihydroethidium was used to evaluate in situ generation of superoxide and thiobarbituric acid reactive substances were measured in retinal homogenates as indicators of lipid peroxidation. The total antioxidant capacity and oxidative ratio were also determined. Retinas from rabbits exposed to light showed higher levels of lipid peroxidation than the unexposed animals and a decrease in outer nuclear layer and neurosensory retina thickness. Our study demonstrates that light damage produces an increase in retinal oxidative stress immediately after light exposure that decreases one week after exposure. However, some morphological alterations appear days after light exposure including apoptotic phenomena. This model may be useful in the future to study the protective effect of antioxidant substances or new intraocular lenses with yellow filters.