Red light of the visual spectrum attenuates cell death in culture and retinal ganglion cell death in situ

Electrical, Electromagnetic, Ultrasound Wave Therapies, and Electronic Implants for Neuronal Rejuvenation, Neuroprotection, Axonal Regeneration, and IOP Reduction

The peripheral nervous system (PNS) of mammals and nervous systems of lower organisms possess significant regenerative potential. In contrast, although neural plasticity can provide some compensation, the central nervous system (CNS) neurons and nerves of adult mammals generally fail to regenerate after an injury or damage. However, use of diverse electrical, electromagnetic and sonographic energy waves are illuminating novel ways to stimulate neuronal differentiation, proliferation, neurite growth, and axonal elongation/regeneration leading to various levels of functional recovery in animals and humans afflicted with disorders of the CNS, PNS, retina, and optic nerve. Tools such as acupuncture, electroacupuncture, electroshock therapy, electrical stimulation, transcranial magnetic stimulation, red light therapy, and low-intensity pulsed ultrasound therapy are demonstrating efficacy in treating many different maladies. These include wound healing, partial recovery from motor dysfunctions, recovery from ischemic/reperfusion insults and CNS and ocular remyelination, retinal ganglion cell (RGC) rejuvenation, and RGC axonal regeneration. Neural rejuvenation and axonal growth/regeneration processes involve activation or intensifying of the intrinsic bioelectric waves (action potentials) that exist in every neuronal circuit of the body. In addition, reparative factors released at the nerve terminals and via neuronal dendrites (transmitter substances), extracellular vesicles containing microRNAs and neurotrophins, and intercellular communication occurring via nanotubes aid in reestablishing lost or damaged connections between the traumatized tissues and the PNS and CNS. Many other beneficial effects of the aforementioned treatment paradigms are mediated via gene expression alterations such as downregulation of inflammatory and death-signal genes and upregulation of neuroprotective and cytoprotective genes. These varied techniques and technologies will be described and discussed covering cell-based and animal model-based studies. Data from clinical applications and linkage to human ocular diseases will also be discussed where relevant translational research has been reported.

Inhibition of mitochondrial VDAC1 oligomerization alleviates apoptosis and necroptosis of retinal neurons following OGD/R injury

Ischemia-reperfusion (I/R) injury is a common pathological mechanism in many retinal diseases, which can lead to cell death via mitochondrial dysfunction. Voltage-dependent anion channel 1 (VDAC1), which is mainly located in the outer mitochondrial membrane, is the gatekeeper of mitochondria. The permeability of mitochondrial membrane can be regulated by controlling the oligomerization of VDAC1. However, the functional mechanism of VDAC1 in retinal I/R injury was unclear. Our results demonstrate that oxygen-glucose deprivation and re-oxygenation (OGD/R) injury leads to apoptosis, necroptosis, and mitochondrial dysfunction of R28 cells. The OGD/R injury increases the levels of VDAC1 oligomerization. Inhibition of VDAC1 oligomerization by VBIT-12 rescued mitochondrial dysfunction by OGD/R and also reduced apoptosis/necroptosis of R28 cells. In vivo, the use of VBIT-12 significantly reduced aHIOP-induced neuronal death (apoptosis/necroptosis) in the rat retina. Our findings indicate that VDAC1 oligomers may open and enlarge mitochondrial membrane pores during OGD/R injury, leading to the release of death-related factors in mitochondria, resulting in apoptosis and necroptosis. This study provides a potential therapeutic strategy against ocular diseases caused by I/R injury.

The Potential Effects of Light Irradiance in Glaucoma and Photobiomodulation Therapy

Human vision is mediated by the retina, one of the most critical tissues in the central nervous system. Glaucoma is a complex retinal disease attributed to environmental, genetic, and stochastic factors, all of which contribute to its pathogenesis. Historically, glaucoma had been thought of primarily as a disease of the elderly; however, it is now becoming more problematic as the incidence rate increases among young individuals. In recent years, excessive light exposure has been suggested as contributing to the rise in glaucoma among the younger generation. Blue light induces mitochondrial apoptosis in retinal ganglion cells, causing optic damage; red light increases cytochrome c oxidase activity in the electron transport system, reducing inflammation and increasing antioxidant reactions to promote cell regeneration. In conclusion, the minimization of blue light exposure and the general application of red light treatment strategies are anticipated to show synergistic effects with existing treatments for retinal disease and glaucoma and should be considered a necessary prospect for the future. This review introduces the recent studies that support the relationship between light exposure and the onset of glaucoma and discusses new treatments, such as photobiomodulation therapy.

Potential Neuroprotective Role of Calretinin-N18 and Calbindin-D28k in the Retina of Adult Zebrafish Exposed to Different Wavelength Lights

The incidence rates of light-induced retinopathies have increased significantly in the last decades because of continuous exposure to light from different electronic devices. Recent studies showed that exposure to blue light had been related to the pathogenesis of light-induced retinopathies. However, the pathophysiological mechanisms underlying changes induced by light exposure are not fully known yet. In the present study, the effects of exposure to light at different wavelengths with emission peaks in the blue light range (400-500 nm) on the localization of Calretinin-N18 (CaR-N18) and Calbindin-D28K (CaB-D28K) in adult zebrafish retina are studied using double immunofluorescence with confocal laser microscopy. CaB-D28K and CaR-N18 are two homologous cytosolic calcium-binding proteins (CaBPs) implicated in essential process regulation in central and peripheral nervous systems. CaB-D28K and CaR-N18 distributions are investigated to elucidate their potential role in maintaining retinal homeostasis under distinct light conditions and darkness. The results showed that light influences CaB-D28K and CaR-N18 distribution in the retina of adult zebrafish, suggesting that these CaBPs could be involved in the pathophysiology of retinal damage induced by the short-wavelength visible light spectrum.

Protector role of intraocular lenses under artificial light conditions

INTRODUCTION

The aim of this work is to analyse, in an in vitro model, the possible protective effects of ultraviolet- (UV-) or UV/ blue-filtering intraocular lens (IOLs) under LED lighting conditions.

METHODS

10 models of IOLs were evaluated. Light transmission spectrum was recorded from 300 to 800 nm, in steps of 1 nm. Photodamage in vitro model was induced in ARPE-19 cells by blue LED light (465-475 nm). Changes in cell viability and oxidative stress variables were studied to assess the protective effect of IOLs.

RESULTS

UV/blue-filtering IOLs models block blue light spectrum in different proportion and UV-filtering IOLs blocking wavelength below 400 nm. However, in vitro study under blue LED light exposure does not show protective effects related with mitochondrial dysfunction and oxidative stress of UV/blue-filtering IOLs.

CONCLUSIONS

The current in vitro study suggest that UV/blue filtering IOLs are not useful in terms of photoprotection in artificial light conditions. The results obtained indicate that it is needed to give attention to other IOLs parameters besides the type of filter, as it seems they could have influence also protective role.

Tolerance to Light of Patients Suffering From Infectious Keratitis

PURPOSE

With very photophobic patients, the advantages of red or near infrared light to develop new ophthalmology imaging devices seem obvious: no or little glare, possibility of long signal integration, no phototoxicity, and lesser autofluorescence of ocular tissues. Nevertheless, in this range, the shortest possible wavelength facilitates signal detection. The aim of this study was, thus, to determine the maximal irradiance tolerated with 6 wavelengths: 2 red, 2 far red, and 1 near infrared lights to determine the shortest wavelength well tolerated by patients, in comparison with the standard cobalt blue light of ophthalmology slitlamp.

METHODS

An interventional, monocentric, single-group assignment study was conducted on 30 eyes of 30 patients with infectious keratitis. Thanks to a customized machine, the photophobic eye was exposed to the 6 lights with increasing intensity. The patients switched off the light when the discomfort was too elevated. The maximal cumulative irradiance possible at 482, 650, 675, 700, 750, and 800 nm were 171, 689, 759, 862, 920, and 889 mW/cm, respectively.

RESULTS

The maximal cumulative irradiance tolerated by patients increased significantly with wavelength (P < 0.001), but the difference was not significant between each increment: red at 675 nm gave a significantly higher cumulative irradiance than blue at 482 nm; red at 700 nm did not provide significant gain compared with 675 nm; and far red at 750 nm still provided additional gain compared with 700 nm, but no significant gain was observed between 750 and 800 nm. The shortest wavelengths were stopped more quickly, and more than 50% of patients reached the maximum irradiance delivered by the source at 750 and 800 nm.

CONCLUSIONS

We demonstrate that a light source at 750 and 800 nm can be used for ophthalmic imaging with good tolerance in photophobic patients.

CLINICAL TRIAL REGISTRATION

NCT03586505.

Quantitative visual tests in primary open-angle glaucoma patients according to three different lights with different color-rendering index

Purpose

To compare quantitative visual tests, such as visual acuity, contrast sensitivity, and color vision tests in patients with primary open-angle glaucoma (POAG) patients according to three different light systems with different color-rendering index (CRI).

Methods

This was a cross-sectional study of 36 eyes in 36 patients with POAG. Three different light systems consisting of a 3-band fluorescent lamp (CRI 80), a white LED (CRI 75), and a quantum dot LED (CRI > 95) were used. All lights had the same illuminance of 230 lx to exclude illuminance effects. The visual testing included best-corrected visual acuity (BCVA) using an ETDRS chart, a CSV-1000E contrast test, and a color test performed by the Farnsworth Munsell 100-hue test.

Results

There was no significant difference in BCVA (p = 0.86). There were no significant differences in the detail contrast tests according to the three light systems (p = 0.95, p = 0.94, p = 0.94, respectively, p = 0.64). There was significant difference between the three light systems in color test (p = 0.042). The color test scores with a quantum dot LED were significantly lower than those of the white LED and 3-band fluorescent lamp (p = 0.03 and 0.047, respectively).

Conclusions

POAG patients did not show significant differences in visual acuity scores and contrast test scores, expressed as black and white symbols, according to the different light systems. However, POAG patients tested under a quantum dot LED (CRI > 95) could distinguish color differences better than in the other light systems.

Near Infrared (NIR) Light Therapy of Eye Diseases: A Review

Near infrared (NIR) light therapy, or photobiomodulation therapy (PBMT), has gained persistent worldwide attention in recent years as a new novel scientific approach for therapeutic applications in ophthalmology. This ongoing therapeutic adoption of NIR therapy is largely propelled by significant advances in the fields of photobiology and bioenergetics, such as the discovery of photoneuromodulation by cytochrome c oxidase and the elucidation of therapeutic biochemical processes. Upon transcranial delivery, NIR light has been shown to significantly increase cytochrome oxidase and superoxide dismutase activities which suggests its role in inducing metabolic and antioxidant beneficial effects. Furthermore, NIR light may also boost cerebral blood flow and cognitive functions in humans without adverse effects. In this review, we highlight the value of NIR therapy as a novel paradigm for treatment of visual and neurological conditions, and provide scientific evidence to support the use of NIR therapy with emphasis on molecular and cellular mechanisms in eye diseases.

Photobiomodulation Mediates Neuroprotection against Blue Light Induced Retinal Photoreceptor Degeneration

Potent neuroprotective effects of photobiomodulation with 670 nm red light (RL) have been demonstrated in several models of retinal disease. RL improves mitochondrial metabolism, reduces retinal inflammation and oxidative cell stress, showing its ability to enhance visual function. However, the current knowledge is limited to the main hypothesis that the respiratory chain complex IV, cytochrome c oxidase, serves as the primary target of RL. Here, we demonstrate a comprehensive cellular, molecular, and functional characterization of neuroprotective effects of 670 nm RL and 810 nm near-infrared light (NIRL) on blue light damaged murine primary photoreceptors. We show that respiratory chain complexes I and II are additional PBM targets, besides complex IV, leading to enhanced mitochondrial energy metabolism. Accordingly, our study identified mitochondria related RL- and NIRL-triggered defense mechanisms promoting photoreceptor neuroprotection. The observed improvement of mitochondrial and extramitochondrial respiration in both inner and outer segments is linked with reduced oxidative stress including its cellular consequences and reduced mitochondria-induced apoptosis. Analysis of regulatory mechanisms using gene expression analysis identified upregulation α-crystallins that indicate enhanced production of proteins with protective functions that point to the rescued mitochondrial function. The results support the hypothesis that energy metabolism is a major target for retinal light therapy.

Light-Induced Retinal Ganglion Cell Damage and the Relevant Mechanisms

While light is the basic element for inducing vision and modulating circadian rhythms, excessive light has been reported to have a negative effect on the survival of various types of retinal cells. Among them photoreceptors and retinal pigment epithelial (RPE) cells degeneration after light exposure is widely observed, but light-induced retinal ganglion cell (RGC) damage achieves relatively little attention. The purpose of this article is to summarize the experimental evidence for the possible negative effects of excessive light on RGCs. By searching the database, twenty-six related articles have been included. Taken together, excessive light may insult RGCs through the three main ways: (i) directly action on RGC mitochondria, as well as DNA, resulting in an upregulation of reactive oxygen species (ROS) and subsequently caspase-dependent or -independent cell death; (ii) mediation in gliotransmitters or relevant receptors of retinal glial cells; and (iii) a secondary event to photoreceptors and RPE cells degeneration and subsequent retinal remodeling. So RGCs can certainly be injured by excessive light, especially when they are already energetically compromised in some diseases. And more attentions should be paid to this topic to take timely measures to protect these frail RGCs from being damaged by excessive light.

Neuroprotective Effect of Ginkgo Biloba Extract Against Hypoxic Retinal Ganglion Cell Degeneration In Vitro and In Vivo

Hypoxia-induced oxidative stress and disturbed microvascular circulation are both associated with pathogenesis of glaucoma. Ginkgo biloba extract (GBE) has been reported to have positive pharmacological effects on oxidative stress and impaired vascular circulation. This study aimed to investigate the neuroprotective effect of GBE against hypoxic injury to retinal ganglion cells (RGCs) both in vitro and in vivo. The rat RGC line was used, and oxidative stress was induced by hydrogen peroxide (H₂O₂) in vitro. EGb 761, a standardized GBE, or vehicle was applied to RGCs. Hypoxic optic nerve injury in vivo was induced by clamping the optic nerve of rats with a "microserrefine clip" with an applicator, which was applied without crushing the optic nerve. This method is different from "optic nerve crush model" and does not involve elevation of intraocular pressure, and may serve as a possible normal tension glaucoma animal model. EGb 761 at various concentrations or vehicle was administered intraperitoneally. RGC density was measured to estimate the survival both in vitro and in vivo. The survival of RGCs was significantly (P < .001) higher upon treatment with 1 or 5 μg/mL of EGb 761 compared with vehicle after oxidative stress in vitro. RGC density upon treatment with EGb 761 of 100 mg/kg (1465.6 ± 175 cells/mm²) or 250 mg/kg (1307.6 ± 213 cells/mm²) was significantly higher (P < .01, P < .05, respectively) than that obtained with vehicle (876.3 ± 136 cells/mm²) in vivo. Our results suggest that GBE has neuroprotective effect on RGCs against hypoxic injury both in vitro and in vivo.

Near infra-red light attenuates corneal endothelial cell dysfunction in situ and in vitro

In the present study mechanical damage to the corneal endothelium was induced by elevation of intraocular pressure (IOP, 140 mmHg, 60 min) to one eye of rats, delivered either in complete darkness or in the presence of red light (16.5 W/m², 3000 lx, 625-635 nm). IOP raised in the dark revealed the endothelium to be damaged as staining for the gap junction protein ZO-1 was irregular in appearance with some cells displaced in position or lost to leave gaps or holes. This damage was clearly attenuated when red light was focused through the pupil during the insult of raised IOP. Moreover, staining of endothelium with JC-1 dye showed mitochondria to be activated by both elevated IOP and red light but the activation of mitochondria persisted longer for red light. We interpret this finding to suggest that raised IOP causes apoptosis of endothelial cells and that their mitochondria are activated in the initial stages of the process. In contrast, red light activates mitochondria to induce a protective mechanism to counteract the negative influence of raised IOP on endothelial cells. Evidence is provided to support this notion by the finding that red light stimulates mitochondrial cytochrome oxidase IV (COX IV). Moreover, mitochondria in corneal endothelial cell cultures are activated by red light, revealed by staining with JC-1, that results in an increased rate of proliferation and are also able to counteract toxic insults (sodium azide or cobalt chloride) to the cultures. The present studies therefore show that a non-toxic level of red light attenuates damage to the corneal endothelium both in situ and in vitro through action on COX IV located in mitochondria that results in an enhancement of a cell's survival mechanisms. The study provides proof of principle for the non-invasive use of red-light therapy to attenuate any dysfunctions associated with the corneal endothelium and so preserve maximum visual acuity.

Visual light effects on mitochondria: The potential implications in relation to glaucoma

Light of different wave-lengths have the potential to interact with four major mitochondrial protein complexes that are involved in the generation of ATP. Neurones of the central nervous system have an absolute dependence on mitochondrial generated ATP. Laboratory studies show that short-wave or blue light (400-480nm) that impinges on the retina affect flavin and cytochrome constituents associated with mitochondria to decrease the rate of ATP formation, stimulate ROS and results in cell death. This suggests that blue light could potentially have a negative influence on retinal ganglion cell (RGC) mitochondria that are abundant and not shielded by macular pigments as occurs for photoreceptor mitochondria. This might be of significance in glaucoma where it is likely that RGC mitochondria are already affected and therefore be more susceptible to blue light. Thus simply filtering out some natural blue light from entering the eye might be beneficial for the treatment of glaucoma. Long-wave or red light (650-800nm) affects mitochondrial complex IV or cytochrome oxidase to increase the rate of formation of ATP and ROS causing the generation of a number of beneficial factors. Significantly, laboratory studies show that increasing the normal amount of natural red light reaching rat RGC mitochondria in situ, subjected to ischemia, proved to be beneficial. A challenge now is to test whether extra red light delivered to the human retina can slow-down RGC loss in glaucoma. Such a methodology has also the advantage of being non-invasive. One very exciting possibility might be in the production of a lens where solar UV light is convertes to add to the amount of natural red light entering the eye.

Glaucoma: Focus on mitochondria in relation to pathogenesis and neuroprotection

Primary open-angle glaucoma (POAG) is a common form of glaucoma in which retinal ganglion cells (RGCs) die at varying intervals. Primary open-angle glaucoma is often associated with an increased intraocular pressure (IOP), which when reduced, can slow down the progression of the disease. However, it is essential to develop better modes of treatments for glaucoma patients. In this overview, we discuss the hypothesis that RGC mitochondria are affected during the initiation of POAG, by becoming gradually weakened, but at different rates because of their specific receptor profiles. With this in mind, we argue that neuroprotection in the context of glaucoma should focus on preserving RGC mitochondrial function and suggest a number of ways by which this can theoretically be achieved. Since POAG is a chronic disease, any neuroprotective treatment strategy must be tolerated over many years. Theoretically, topically applied substances should have the fewest side effects, but it is questionable whether sufficient compounds can reach RGC mitochondria to be effective. Therefore, other delivery procedures that might result in greater concentrations of neuroprotectants reaching RGC mitochondria are being developed. Red-light therapy represents another therapeutic alternative for enhancing RGC mitochondrial functions and has the advantage of being both non-toxic and non-invasive.