Three Major Causes of Metabolic Retinal Degenerations and Three Ways to Avoid Them.

An imbalance of homeostasis in the retina leads to neuron loss and this eventually results in a deterioration of vision. If the stress threshold is exceeded, different protective/survival mechanisms are activated. Numerous key molecular actors contribute to prevalent metabolically induced retinal diseases-the three major challenges are age-related alterations, diabetic retinopathy and glaucoma. These diseases have complex dysregulation of glucose-, lipid-, amino acid or purine metabolism. In this review, we summarize current knowledge on possible ways of preventing or circumventing retinal degeneration by available methods. We intend to provide a unified background, common prevention and treatment rationale for these disorders and identify the mechanisms through which these actions protect the retina. We suggest a role for herbal medicines, internal neuroprotective substances and synthetic drugs targeting four processes: parainflammation and/or glial cell activation, ischemia and related reactive oxygen species and vascular endothelial growth factor accumulation, apoptosis and/or autophagy of nerve cells and an elevation of ocular perfusion pressure and/or intraocular pressure. We conclude that in order to achieve substantial preventive or therapeutic effects, at least two of the mentioned pathways should be targeted synergistically. A repositioning of some drugs is considered to use them for the cure of the other related conditions.

Retinal Toxicity Induced by Chemical Agents.

Vision is an important sense for humans, and visual impairment/blindness has a huge impact in daily life. The retina is a nervous tissue that is essential for visual processing since it possesses light sensors (photoreceptors) and performs a pre-processing of visual information. Thus, retinal cell dysfunction or degeneration affects visual ability and several general aspects of the day-to-day of a person's lives. The retina has a blood-retinal barrier, which protects the tissue from a wide range of molecules or microorganisms. However, several agents, coming from systemic pathways, reach the retina and influence its function and survival. Pesticides are still used worldwide for agriculture, contaminating food with substances that could reach the retina. Natural products have also been used for therapeutic purposes and are another group of substances that can get to the retina. Finally, a wide number of medicines administered for different diseases can also affect the retina. The present review aimed to gather recent information about the hazard of these products to the retina, which could be used to encourage the search for more healthy, suitable, or less risky agents.

Roots of Lithospermum erythrorhizon promotes retinal cell survival in optic nerve crush-induced retinal degeneration.

Lithospermum erythrorhizon (L. erythrorhizon), used in traditional medicine, is a potent wound healing, anti-inflammatory and antioxidant plant. However, the effects of L. erythrorhizon on retinal degenerative diseases remain unknown. Here, we explored the protective effects of L. erythrorhizon in in vitro and in vivo retinal degeneration. We found that ethanol extract of L. erythrorhizon (EELE) and the dichloromethane fraction of L. erythrorhizon (MCLE) significantly increased cell viability under glutamate/BSO-induced excitotoxicity/oxidative stress in R28 cells. Treatment with EELE and MCLE reduced the intracellular reactive oxygen species (ROS) and the levels of apoptotic proteins, such as cleaved PARP and cleaved caspase-3. Furthermore, oral administration of EELE and MCLE in an in vivo optic nerve crush mouse model decreased RGC cell death and increased retinal thickness. The major compound between EELE and MCLE was found to be lithospermic acid A (LAA), which has been shown to prevent the elevation of ROS in R28. Therefore, EELE and MCLE have protective effects against the death of retinal cells in vitro and in vivo, and the major compound, LAA, has an antioxidant effect on retinal cells, suggesting that EELE and MCLE could be beneficial agents for retinal degenerative diseases, including glaucoma.

Photobiomodulation preserves mitochondrial redox state and is retinoprotective in a rodent model of retinitis pigmentosa.

Photobiomodulation (PBM) by far-red (FR) to near-infrared (NIR) light has been demonstrated to restore the function of damaged mitochondria, increase the production of cytoprotective factors and prevent cell death. Our laboratory has shown that FR PBM improves functional and structural outcomes in animal models of retinal injury and retinal degenerative disease. The current study tested the hypothesis that a brief course of NIR (830 nm) PBM would preserve mitochondrial metabolic state and attenuate photoreceptor loss in a model of retinitis pigmentosa, the P23H transgenic rat. P23H rat pups were treated with 830 nm light (180 s; 25 mW/cm2; 4.5 J/cm2) using a light-emitting diode array (Quantum Devices, Barneveld, WI) from postnatal day (p) 10 to p25. Sham-treated rats were restrained, but not treated with 830 nm light. Retinal metabolic state, function and morphology were assessed at p30 by measurement of mitochondrial redox (NADH/FAD) state by 3D optical cryo-imaging, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), and histomorphometry. PBM preserved retinal metabolic state, retinal function, and retinal morphology in PBM-treated animals compared to the sham-treated group. PBM protected against the disruption of the oxidation state of the mitochondrial respiratory chain observed in sham-treated animals. Scotopic ERG responses over a range of flash intensities were significantly greater in PBM-treated rats compared to sham controls. SD-OCT studies and histological assessment showed that PBM preserved the structural integrity of the retina. These findings demonstrate for the first time a direct effect of NIR PBM on retinal mitochondrial redox status in a well-established model of retinal disease. They show that chronic proteotoxic stress disrupts retinal bioenergetics resulting in mitochondrial dysfunction, and retinal degeneration and that therapies normalizing mitochondrial metabolism have considerable potential for the treatment of retinal degenerative disease.

Neuroprotective effects of Acer palmatum thumb. leaf extract (KIOM-2015E) against ischemia/reperfusion-induced injury in the rat retina.

Purpose: The present study aimed to determine whether the administration of Acer palmatum thumb. leaf extract (KIOM-2015E) protects against the degeneration of rat retinal ganglion cells after ischemia/reperfusion (I/R) induced by midbrain cerebral artery occlusion (MCAO). Methods: Sprague-Dawley rats were subjected to 90 min of MCAO, which produces transient ischemia in both the retina and brain due to the use of an intraluminal filament that blocks the ophthalmic and middle cerebral arteries. This was followed by reperfusion under anesthesia with isoflurane. The day after surgery, the eyes were treated three times (eye drop) or one time (oral administration) daily with KIOM-2015E for five days. Retinal histology was assessed in flat mounts and vertical sections to determine the effect of KIOM-2015E on I/R injury. Results: A significant loss of brain-specific homeobox/POU domain protein 3A (Brn3a) and neuron-specific class III beta-tubulin (Tuj-1) fluorescence and a marked increase in glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) expression were observed after five days in the PBS-treated MCAO group compared to the sham-operated control group. However, KIOM-2015E treatment reduced (1) MCAO-induced upregulation of GFAP and GS, (2) retinal ganglion cell loss, (3) nerve fiber degeneration, and (4) the number of TUNEL-positive cells. KIOM-2015E application also increased staining for parvalbumin (a marker of horizontal cell associated calcium-binding protein and amacrine cells) and recoverin (a marker of photoreceptor expression) in rats subjected to MCAO-induced retinal damage. Conclusions: Our findings indicated that KIOM-2015E treatment exerted protective effects against retinal damage following MCAO injury and that this extract may aid in the development of novel therapeutic strategies for retinal diseases, such as glaucoma and age-related macular disease.

Metabolite therapy guided by liquid biopsy proteomics delays retinal neurodegeneration.

BACKGROUND: Neurodegenerative diseases are incurable disorders caused by progressive neuronal cell death. Retinitis pigmentosa (RP) is a blinding neurodegenerative disease that results in photoreceptor death and progresses to the loss of the entire retinal network. We previously found that proteomic analysis of the adjacent vitreous served as way to indirectly biopsy the retina and identify changes in the retinal proteome. METHODS: We analyzed protein expression in liquid vitreous biopsies from autosomal recessive (ar)RP patients with PDE6A mutations and arRP mice with Pde6ɑ mutations. Proteomic analysis of retina and vitreous samples identified molecular pathways affected at the onset of photoreceptor death. Based on affected molecular pathways, arRP mice were treated with a ketogenic diet or metabolites involved in fatty-acid synthesis, oxidative phosphorylation, and the tricarboxylic acid (TCA) cycle. FINDINGS: Dietary supplementation of a single metabolite, ɑ-ketoglutarate, increased docosahexaeonic acid levels, provided neuroprotection, and enhanced visual function in arRP mice. A ketogenic diet delayed photoreceptor cell loss, while vitamin B supplementation had a limited effect. Finally, desorption electrospray ionization mass spectrometry imaging (DESI-MSI) on ɑ-ketoglutarate-treated mice revealed restoration of metabolites that correlated with our proteomic findings: uridine, dihydrouridine, and thymidine (pyrimidine and purine metabolism), glutamine and glutamate (glutamine/glutamate conversion), and succinic and aconitic acid (TCA cycle). INTERPRETATION: This study demonstrates that replenishing TCA cycle metabolites via oral supplementation prolongs retinal function and provides a neuroprotective effect on the photoreceptor cells and inner retinal network. FUNDING: NIH grants [R01EY026682, R01EY024665, R01EY025225, R01EY024698, R21AG050437, P30EY026877, 5P30EY019007, R01EY018213, F30EYE027986, T32GM007337, 5P30CA013696], NSF grant CHE-1734082.

Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency.

In a consanguineous Pakistani family with two affected individuals, a homozygous variant Gly399Val in the eighth transmembrane domain of the taurine transporter SLC6A6 was identified resulting in a hypomorph transporting capacity of ~15% compared with normal. Three-dimensional modeling of this variant has indicated that it likely causes displacement of the Tyr138 (TM3) side chain, important for transport of taurine. The affected individuals presented with rapidly progressive childhood retinal degeneration, cardiomyopathy and almost undetectable plasma taurine levels. Oral taurine supplementation of 100 mg/kg/day resulted in maintenance of normal blood taurine levels. Following approval by the ethics committee, a long-term supplementation treatment was introduced. Remarkably, after 24-months, the cardiomyopathy was corrected in both affected siblings, and in the 6-years-old, the retinal degeneration was arrested, and the vision was clinically improved. Similar therapeutic approaches could be employed in Mendelian phenotypes caused by the dysfunction of the hundreds of other molecular transporters.

Creatine is Neuroprotective to Retinal Neurons In Vitro But Not In Vivo.

Purpose: To investigate the neuroprotective properties of creatine in the retina using in vitro and in vivo models of injury. Methods: Two different rat retinal culture systems (one containing retinal ganglion cells [RGC] and one not) were subjected to either metabolic stress, via treatments with the mitochondrial complex IV inhibitor sodium azide, or excitotoxic stress, via treatment with N-methyl-D-aspartate for 24 hours, in the presence or absence of creatine (0.5, 1.0, and 5.0 mM). Neuronal survival was assessed by immunolabeling for cell-specific antigens. Putative mechanisms of creatine action were investigated in vitro. Expression of creatine kinase (CK) isoenzymes in the rat retina was examined using Western blotting and immunohistochemistry. The effect of oral creatine supplementation (2%, wt/wt) on retinal and blood creatine levels was determined as well as RGC survival in rats treated with N-methyl-D-aspartate (NMDA; 10 nmol) or high IOP-induced ischemia reperfusion. Results: Creatine significantly prevented neuronal death induced by sodium azide and NMDA in both culture systems. Creatine administration did not alter cellular adenosine triphosphate (ATP). Inhibition of CK blocked the protective effect of creatine. Retinal neurons, including RGCs, expressed predominantly mitochondrial CK isoforms, while glial cells expressed exclusively cytoplasmic CKs. In vivo, NMDA and ischemia reperfusion caused substantial loss of RGCs. Creatine supplementation led to elevated blood and retinal levels of this compound but did not significantly augment RGC survival in either model. Conclusions: Creatine increased neuronal survival in retinal cultures; however, no significant protection of RGCs was evident in vivo, despite elevated levels of this compound being present in the retina after oral supplementation.

ß-alanine supplementation induces taurine depletion and causes alterations of the retinal nerve fiber layer and axonal transport by retinal ganglion cells.

To study the effect of taurine depletion induced by ß-alanine supplementation in the retinal nerve fiber layer (RNFL), and retinal ganglion cell (RGC) survival and axonal transport. Albino Sprague-Dawley rats were divided into two groups: one group received ß-alanine supplementation (3%) in the drinking water during 2 months to induce taurine depletion, and the other group received regular water. After one month, half of the rats from each group were exposed to light. Retinas were analyzed in-vivo using Spectral-Domain Optical Coherence Tomography (SD-OCT). Prior to processing, RGCs were retrogradely traced with fluorogold (FG) applied to both superior colliculi, to assess the state of their retrograde axonal transport. Retinas were dissected as wholemounts, surviving RGCs were immunoidentified with Brn3a, and the RNFL with phosphorylated high-molecular-weight subunit of the neurofilament triplet (pNFH) antibodies. ß-alanine supplementation decreases significantly taurine plasma levels and causes a significant reduction of the RNFL thickness that is increased after light exposure. An abnormal pNFH immunoreactivity in some RGC bodies, their proximal dendrites and axons, and a further diminution of the mean number of FG-traced RGCs compared with Brn3a+RGCs, indicate that their retrograde axonal transport is affected. In conclusion, taurine depletion causes RGC loss and axonal transport impairment. Finally, our results suggest that care should be taken when ingesting ß-alanine supplements due to the limited understanding of their potential adverse effects.

Green Tea Extract Ameliorates Ischemia-Induced Retinal Ganglion Cell Degeneration in Rats.

PURPOSE: Oxidative stress induced by reduced blood circulation is a critical pathological damage to retinal ganglion cells (RGCs) in glaucoma. We previously showed that green tea extract (GTE) and its catechin constituents alleviate sodium iodate-induced retinal degeneration in rats. Here, we investigated the therapeutic effect of GTE on ischemia-induced RGC degeneration in rats. METHODS: RGC degeneration was induced by ischemic reperfusion in adult Fischer F344 rats. Green tea extract (Theaphenon E) was intragastrically administered 4 times within 48 hours after ischemia. RGC survival, pupillary light reflex, expressions of cell apoptosis, oxidative stress, and inflammation-related proteins were studied. RESULTS: Ischemic reperfusion significantly induced apoptotic RGCs, RGC loss, and larger constricted pupil area compared to the untreated normal rats. Expressions of activated caspase-3 and caspase-8, Sod2, and inflammation-related proteins as well as p38 phosphorylation were significantly upregulated in the ischemia-injured rats. Compared to the saline-fed ischemic rats, significantly higher number of surviving RGCs, less apoptotic RGCs, and smaller constricted pupil area were observed in the GTE-fed ischemic rats. GTE also reduced the increased protein expressions caused by ischemic injury but enhanced the Jak phosphorylation in the retina. Notably, green tea extract did not affect the survival of RGCs in the uninjured normal rats. CONCLUSIONS: In summary, GTE offers neuroprotection to RGCs under ischemic challenge, suggesting a potential therapeutic strategy for glaucoma and optic neuropathies.

Liver-Specific, but Not Retina-Specific, Hepcidin Knockout Causes Retinal Iron Accumulation and Degeneration.

The liver secretes hepcidin (Hepc) into the bloodstream to reduce blood iron levels. Hepc accomplishes this by triggering degradation of the only known cellular iron exporter ferroportin in the gut, macrophages, and liver. We previously demonstrated that systemic Hepc knockout (HepcKO) mice, which have high serum iron, develop retinal iron overload and degeneration. However, it was unclear whether this is caused by high blood iron levels or, alternatively, retinal iron influx that would normally be regulated by retina-produced Hepc. To address this question, retinas of liver-specific and retina-specific HepcKO mice were studied. Liver-specific HepcKO mice had elevated blood and retinal pigment epithelium (RPE) iron levels and increased free (labile) iron levels in the retina, despite an intact blood-retinal barrier. This led to RPE hypertrophy associated with lipofuscin-laden lysosome accumulation. Photoreceptors also degenerated focally. In contrast, there was no change in retinal or RPE iron levels or degeneration in the retina-specific HepcKO mice. These data indicate that high blood iron levels can lead to retinal iron accumulation and degeneration. High blood iron levels can occur in patients with hereditary hemochromatosis or result from use of iron supplements or multiple blood transfusions. Our results suggest that high blood iron levels may cause or exacerbate retinal disease.

(3R, 3'R)-zeaxanthin protects the retina from photo-oxidative damage via modulating the inflammation and visual health molecular markers.

PURPOSE: Zeaxanthin protects the macula from ocular damage due to light or radiation by scavenging harmful reactive oxygen species. In the present study, zeaxanthin product (OmniXan®; OMX), derived from paprika pods (Capsicum annum; Family-Solanaceae), was tested for its efficacy in the rat retina against photooxidation. METHODS: Forty-two male 8-week-old Wistar rats exposed to 12L/12D, 16L/8D and 24L/0D hours of intense light conditions were orally administrated either 0 or 100 mg/kg BW of zeaxanthin concentration. Retinal morphology was analyzed by histopathology, and target gene expressions were detected with real-time polymerase chain reaction methods. RESULTS: OMX treatment significantly increased the serum zeaxanthin concentration (p < 0.001) and ameliorated oxidative damage by increasing the antioxidant enzyme activities in the retina induced by light (p < 0.001). OMX administration significantly upregulated the expression of genes, including Rhodopsin (Rho), Rod arrestin (SAG), Gα Transducin 1 (GNAT-1), neural cell adhesion molecule (NCAM), growth-associated protein 43 (GAP43), nuclear factor-(erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase (HO-1) and decreased the expression of nuclear factor-κB (NF- κB) and GFAP by OMX treatment rats. The histologic findings confirmed the antioxidant and gene expression data. CONCLUSIONS: This study suggests that OMX is a potent substance that can be used to protect photoreceptor cell degeneration in the retina exposed to intense light.

Bilberry extract and anthocyanins suppress unfolded protein response induced by exposure to blue LED light of cells in photoreceptor cell line.

Purpose: The purpose of this study was to investigate the effects of bilberry extract with its anthocyanins on retinal photoreceptor cell damage and on the endoplasmic reticulum (ER) stress induced by exposure to blue light-emitting diode (LED) light. Methods: Cultured murine photoreceptor cells (661W) were exposed to blue LED light with or without bilberry extract or its anthocyanins in the culture media. Aggregated short-wavelength opsin (S-opsin) in murine photoreceptor cells was observed with immunostaining. The expression of factors involved in the unfolded protein response was examined with immunoblot analysis and quantitative real-time reverse transcription (RT)-PCR. Furthermore, cell death was observed with double staining with Hoechst 33342 and propidium iodide after dithiothreitol (DTT) treatment. Results: Bilberry extract and anthocyanins suppressed the aggregation of S-opsin, activation of ATF4, and expression of the mRNA of the factors associated with the unfolded protein response (UPR). In addition, bilberry extract and the anthocyanins inhibited the death of photoreceptor cells induced by DTT, an ER stress inducer. Conclusions: These findings suggest that bilberry extract containing anthocyanins can alter the effects of blue LED light and DTT-induced retinal photoreceptor cell damage. These effects were achieved by modulating the activation of ATF4 and through the suppression of the abnormal aggregation of S-opsin.

Ubiquinol promotes retinal ganglion cell survival and blocks the apoptotic pathway in ischemic retinal degeneration.

Coenzyme Q10 (CoQ10) protects retinal ganglion cells (RGCs) in experimental retinal ischemia and glaucoma by scavenging reactive oxygen species. We tested whether a diet supplemented with ubiquinol, the reduced form of CoQ10, promotes RGC survival and blocks the apoptotic pathway in ischemic mouse retina induced by acute high intraocular pressure (IOP) elevation. Ubiquinol (1%) treatment significantly promoted RGC survival at 2 weeks after ischemia/reperfusion. The ubiquinol treatment significantly blocked activation of astroglial and microglial cells in the ischemic retina at 2 weeks. While the ubiquinol treatment significantly decreased active Bax protein expression in the ischemic retina, phosphorylation of Bad at serine 112 and Bcl-xL protein expression were preserved in the ubiquinol-treated ischemic retina at 12 h. Consistently, the ubiquinol treatment prevented apoptotic cell death by blocking caspase-3 cleavage. These results suggest that the ubiquinol enhances RGC survival by modulating the Bax/Bad/Bcl-xL-mediated apoptotic pathway in the ischemic retina. Ubiquinol has therapeutic potential for ameliorating elevated IOP-induced ischemic retinal degeneration.

The Neuroprotective and antioxidative effects of submicron and blended Lycium barbarum in experimental retinal degeneration in rats.

The object is to determine the neuroprotective and antioxidative effects of submicron and blended Lycium barbarum (LB) on retinal degeneration as evaluated by ERG, retinal histopathology and assays of antioxidant (total GSH) and peroxidant (MDA) in the retina. A rat model of light-induced retinal degeneration was used to assess the protective effect of different forms of Lycium barbarum (LB) on retinal degeneration. Rats were divided into four experimental groups, normal control, light-induced untreated, submicron LB and blended LB treated. The rats of submicron and blended groups were treated with 250 mg/kg LB orally once daily for 54 days, followed by induction of retinal degeneration. Retinal function was assessed by electroretinography (ERG). Enzyme-linked immunosorbent assay of the retina lysates was measured for the levels of antioxidants, reduced glutathione and glutathione disulfide, and peroxidants, malondialdehyde, in the retina. The ERG results showed a protective effect in LB treated groups with a greater effect observed in submicron LB treated group than the blended LB treated group. There were higher levels of GSH plus GSSG and lower MDA in submicron LB treated group than other groups. In conclusion, LB provided protective and antioxidative effects on the rat retina with light-induced retinal degeneration. Submicron LB protected degenerative retina better than blended LB. LB is effective against oxidative stress in the degenerative retina.

Reduced Disc Shedding and Phagocytosis of Photoreceptor Outer Segment Contributes to Kava Kava Extract-induced Retinal Degeneration in F344/N Rats.

There was a significant increase in the incidence of retinal degeneration in F344/N rats chronically exposed to Kava kava extract (KKE) in National Toxicology Program (NTP) bioassay. A retrospective evaluation of these rat retinas indicated a similar spatial and morphological alteration as seen in light-induced retinal degeneration in albino rats. Therefore, it was hypothesized that KKE has a potential to exacerbate the light-induced retinal degeneration. To investigate the early mechanism of retinal degeneration, we conducted a 90-day F344/N rat KKE gavage study at doses of 0 and 1.0 g/kg (dose which induced retinal degeneration in the 2-year NTP rat KKE bioassay). The morphological evaluation indicated reduced number of phagosomes in the retinal pigment epithelium (RPE) of the superior retina. Transcriptomic alterations related to retinal epithelial homeostasis and melatoninergic signaling were observed in microarray analysis. Phagocytosis of photoreceptor outer segment by the underlying RPE is essential to maintain the homeostasis of the photoreceptor layer and is regulated by melatonin signaling. Therefore, reduced photoreceptor outer segment disc shedding and subsequent lower number of phagosomes in the RPE and alterations in the melatonin pathway may have contributed to the increased incidences of retinal degeneration observed in F344/N rats in the 2-year KKE bioassay.

Leaves of Acer palmatum thumb. Rescues N-ethyl-N-nitrosourea (ENU)-Induced retinal degeneration in mice.

BACKGROUND: In the East Asia, the genus Acer (Aceraceae) is a herbal medicine that is used to treat various diseases, including hemostasis, hepatic disorders, traumatic bleeding and poor eyesight. However, the effects of Acer palmatum thumb. on retinal degeneration are unknown. AIM: In this study, we investigated whether Acer palmatum thumb.ethanol extract (KIOM-2015E) can protect eyes from retinal degeneration. Our research investigated whether KIOM-2015E could have a protective effect in the retinal degenerating mouse model induced by N-ethyl-N-nitrosourea (ENU). MATERIALS AND METHODS: Retinal degeneration was induced by a single intraperitoneal injection of ENU in ICR mice. KIOM-2015E (100, 200 mg/kg) was orally administered once per day. The eyeballs were embedded and lysed after drug administration to examine the histological changed and protein expression levels. RESULTS: The ENU-induced retinal degeneration model exhibited increased photoreceptor cell death and a loss of the outer nuclear layer. Additionally, the expression of PKCα and OPN1SW was reduced, and that of GFAP and Nestin was increased in ENU-treated retinal tissues. CONCLUSION: KIOM-2015E treatment ameliorated the ENU-induced retinal degeneration. KIOM-2015E prevents ENU-induced retinal degeneration by modulating protein expression and the thickness of the outer nuclear layer in the retina.

Antioxidant effects of Lycium barbarum polysaccharides on photoreceptor degeneration in the light-exposed mouse retina.

We assessed the neuroprotective effects of Lycium barbarum Polysaccharides (LBP) on photoreceptor degeneration and the mechanisms involved in oxidative stress in light-exposed mouse retinas. Mice were given a gavage of LBP (150 mg/kg or 300 mg/kg) or phosphate buffered saline (PBS) for 7 days before exposure to light (5000 lx for 24 h). We found that LBP significantly improved the electroretinography (ERG) amplitudes of the a- and b-waves that had been attenuated by light exposure. In addition, changes caused by light exposure including photoreceptor cell loss, nuclear condensation, an increased number of mitochondria vacuoles, outer membrane disc swelling and cristae fractures were distinctly ameliorated by LBP. LBP treatment also significantly prevented the generation of reactive oxygen species (ROS) compared with PBS treatment. The levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and thioredoxin reductase (TrxR1) mRNA were decreased in PBS-treated mice compared with controls but increased remarkably in LBP-treated mice. The mRNA levels of the DNA repair gene Poly (ADP-ribose) polymerase (PARP14) was increased in PBS-treated mice but decreased significantly in the LBP-treated mice. Our findings indicate that pretreatment with LBP effectively protected photoreceptor cells against light-induced retinal damage probably through the up-regulation of the antioxidative genes Nrf2 and TrxR1, the elimination of oxygen free radicals, and the subsequent reduction in the mitochondrial reaction to oxidative stress and enhancement in antioxidant capacity. In addition, the decreased level of PARP14 mRNA in LBP-treated mice also indicated a protective effect of LBP on delaying photoreceptor in the light-damaged retina.

Taurine Depletion Causes ipRGC Loss and Increases Light-Induced Photoreceptor Degeneration.

Purpose: To examine if light exposure exacerbates retinal neuronal loss induced by taurine depletion. Methods: Albino rats received ß-alanine in the drinking water to induce taurine depletion. One month later, half of the animals were exposed to white light (3000 lux) continuously for 48 hours and the rest remained in normal environmental conditions. A control group of animals nontreated with ß-alanine also was prepared, and half of them were exposed to light using the same protocol. All the animals were processed 2 months after the beginning of the experiment. Retinas were dissected as wholemounts and immunodetected with antibodies against Brn3a, melanopsin, S-opsin, and L-opsin to label different retinal populations: Brn3a+ retinal ganglion cells (RGCs) (image-forming RGCs), m+RGCs (non-image-forming RGCs), and S- and L/M-cones, respectively. Results: Light exposure did not affect the numbers of Brn3a+RGCs or m+RGCs but diminished the numbers of S- and L/M-cones and caused the appearance of rings devoid of cones, mainly in an "arciform" area in the superotemporal retina. Taurine depletion caused a diminution of all the studied populations, with m+RGCs the most affected, followed by S-cones. Light exposure under taurine depletion increased photoreceptor degeneration but did not seem to increase Brn3a+RGCs or m+RGCs loss. Conclusions: Our results document that taurine is necessary for cell survival in the rat retina and even more under light-induced photoreceptor degeneration. Thus, taurine supplementation may help to prevent retinal degenerations, especially those that commence with S-cone degeneration or in which light may be an etiologic factor, such as inherited retinal degenerations, AMD, or glaucoma.

670nm light treatment following retinal injury modulates Müller cell gliosis: Evidence from in vivo and in vitro stress models.

Photobiomodulation (PBM) with 670 nm light has been shown to accelerate wound healing in soft tissue injuries, and also to protect neuronal tissues. However, little data exist on its effects on the non-neuronal components of the retina, such as Müller cells (MCs), which are the principal macroglia of the retina that play a role in maintaining retinal homeostasis. The aim of this study was to explore the effects of 670 nm light on activated MCs using in vivo and in vitro stress models. Adult Sprague-Dawley rats were exposed to photo-oxidative damage (PD) for 24 h and treated with 670 nm light at 0, 3 and 14 days after PD. Tissue was collected at 30 days post-PD for analysis. Using the in vitro scratch model with a human MC line (MIO-M1), area coverage and cellular stress were analysed following treatment with 670 nm light. We showed that early treatment with 670 nm light after PD reduced MC activation, lowering the retinal expression of GFAP and FGF-2. 670 nm light treatment mitigated the production of MC-related pro-inflammatory cytokines (including IL-1ß), and reduced microglia/macrophage (MG/MΦ) recruitment into the outer retina following PD. This subsequently decreased photoreceptor loss, slowing the progression of retinal degeneration. In vitro, we showed that 670 nm light directly modulated MC activation, reducing rates of area coverage by suppressing cellular proliferation and spreading. This study indicates that 670 nm light treatment post-injury may have therapeutic benefit when administered shortly after retinal damage, and could be useful for retinal degenerations where MC gliosis is a feature of disease progression.