Damage In Rat Retina Research Articles

Effect of hydrogen-rich saline on melanopsin after acute blue light-induced retinal damage in rats.

Excessive exposure to blue light can cause retinal damage. Hydrogen-rich saline (HRS), one of the hydrogen therapies, has been demonstrated to be effective in eye photodamage, but the effect on the expression of melanopsin in intrinsically photosensitive retinal ganglion cells (ipRGCs) is unknown. In this study, we used a rat model of light-induced retinal injury to observe the expression of melanopsin after HRS treatment and to determine the effect of HRS on retinal ganglion cell protection. Adult SD rats were exposed to blue light (48 h) and treated with HRS for 0, 3, 7, and 14 days. Real-time polymerase chain reaction (qRT-PCR) and Western blotting (WB) were performed to find the expression of genes and proteins, respectively. The function of retinal ipRGCs was measured by pattern-evoked electroretinography (pERG). The number and morphological changes of melanopsin-positive ganglion cells in the retina were observed by immunofluorescence (IF). Acute blue light exposure caused a decrease in ipRGC function, decreased expression of melanopsin protein and the melanopsin-positive RGCs, and diminished immunoreactivity in dendrites. However, over time, melanopsin showed a tendency to self-recovery, with an increase in melanopsin protein expression and the number of melanopsin-positive RGCs, with incomplete recovery of function within two weeks. HRS treatment accelerated the recovery process, with a significant increase in melanopsin expression and the number of melanopsin-positive RGCs, and an improvement in the pERG waveform within two weeks.

English

It has been established that peroxidation, inflammatory processes, and organ damage are involved in the pathogenesis of methanol intoxication. Research has shown that using hyperbaric oxygen reduces oxidative stress, inflammation, and tissue damage. In this research, it was investigated how hyperbaric oxygen therapy affected methanol-induced peroxidation and retinal damage in rats. The animals were classified into six categories (n = 8): control group (C), nitrous oxide (N2O) treated group, hyperbaric oxygen (HBO) treated group, methanol (MeOH) treated group, N2O+methanol treated group (N2O+MeOH) and N2O+methanol+hyperbaric oxygen (N2O+MeOH+HBO) treated group. Folate deficiency was started with N2O, four hours before the starting dose (4g/kg) of methanol. The rats were given a methanol maintenance dose (2g/kg, i.p) 24h and 48h after the starting dose. After each methanol administration, rats were given HBO (2 ATA) for 1 hour. Methanol intoxication decreased plasma folic acid levels while increasing formate levels and oxidative stress index and it caused a decrease in the amount of the retinal ganglion cells and thinned the total retinal thickness in folate-deficient mice. HBO treatment reduced the oxidative stress index but did not adequately improve retinal healing. Our findings indicate that the HBO treatment used to treat retinal damage in methanol poisoning was ineffective. However, increasing the duration of HBO therapy may be effective in preventing methanol-induced retinal damage

Calpain-2 Facilitates Autophagic/Lysosomal Defects and Apoptosis in ARPE-19 Cells and Rats Induced by Exosomes from RPE Cells under NaIO3 Stimulation.

Although accumulated evidence supports the notion that calpain contributes to eye disease, the mechanisms by which calpain promotes RPE injury are not defined. The present study is aimed at investigating whether the effect of NaIO3-exos (exosomes derived from RPE cells under NaIO3 stimulation) on the dysfunction of the autophagy-lysosomal pathway (ALP) and apoptosis is based on its regulation of calpain activation in ARPE-19 cells and rats. The results showed that calpain-2 activation, ALP dysfunction, and apoptosis were induced by NaIO3-exos in ARPE-19 cells. NaIO3-exo significantly increased autophagic substrates by activating lysosomal dysfunction. ALP dysfunction and apoptosis in vitro could be eliminated by knocking down calpain-2 (si-C2) or the inhibitor calpain-2-IN-1. Further studies indicated that NaIO3-exo enhanced calpain-2 expression, ALP dysfunction, apoptosis, and retinal damage in rats. In summary, these results demonstrate for the first time that calpain-2 is one of the key players in the NaIO3-exo-mediated ALP dysfunction, apoptosis, and retinal damage and identify calpain-2 as a promising target for therapies aimed at age-related macular degeneration (AMD).

The effect of idebenone and corticosteroid treatment on methanol-induced toxic optic nerve and retinal damage in rats: biochemical and histopathological examination

ABSTRACT Purpose To evaluate the therapeutic effects of methylprednisolone, the CoenzymeQ10 (CoQ10) structural analogue idebenone, and both together on the optic nerve (ON) and retinal layers following methanol intoxication in rats with histopathological and biochemical methods. Materials and methods This experimental study was conducted with 30 male Wistar rats. The rats were divided into five equal groups depending on the treatment protocol:healthy controls (HC), methanol (M), methanol + methylprednisolone (MM), methanol + idebenone (MI), and methanol + methylprednisolone + idebenone (MMI).Distilled water was provided orally to the HC group, while 20% methanol was administered orally at a dose of 3 g/kg with a nasogastric tube to all rats in groups except the HC group. Four hours later, group MM received 1 mg/kg of intraperitoneal methylprednisolone for 10 days using an insulin syringe, and group MI received 20 mg/kg idebenone by nasogastric catheter for 28 days. MMI group was administered oral idebenone and intraperitoneal methylprednisolone at the same dose. Serum samples were obtained on the 28th day for biochemical analysis and afterwards the rats were euthanized for histopathological examination and eyes were enucleated. ON was evaluated for circumference thickness, vascularization and number of astrocytes, also retinal layers were examined for structural changes by histopathological examination. Results Comparison of the antioxidant and oxidative stress biomarkers between the groups revealed no statistically significant difference (p > 0.05). By histopathological evaluation the most marked results were obtained by MMI group with an improvement of all parameters mentioned. There was no statistically significant difference between MM group and M group for RD score (p = 0.123). In addition, ON vacuolization in MI group (p < 0.001) and ON astrocyte increase in both MI and MMI groups were statistically significantly lower than in M group (p = 0.001, p = 0.001, respectively). Conclusions The early use (within hours) of idebenone and short-term methylprednisolone treatment together may protect against the retinal and ON damage developing after methanol ingestion in rats as guided by the histopathological data.

Allyl isothiocyanate attenuates LED light-induced retinal damage in rats: exploration for the potential molecular mechanisms

Purpose Environmental light pollution due to artificial light may increase the rate and severity of retinal diseases, and plant-based nutritional interventions with antioxidant properties have the potential to reverse this phenomenon. We aimed to investigate the potential effects of allyl isothiocyanate (AITC) against white light-emitting diode (LED)-induced retinal degeneration (RD) in the rats. Methods Twenty-eight male rats were allocated as: (i) Control, (ii) LED, (iii) LED + AITC (10 mg/kg BW), (iv) LED + AITC (20 mg/kg BW). Rats were administered with AITC for 28 days, followed by two days of intense environmental LED light (750 Lux) exposure to the eyes. Animals were sacrificed immediately at the end of the study, then the blood and eyeballs were taken for the biochemical, western blotting, and histopathology examinations. Results AITC lowered the serum and retina malondialdehyde (MDA) levels while significantly (p < 0.05) improving the retinal antioxidant enzyme activities in a dose-dependent manner. AITC improved retinal and outer nuclear layer (ONL) thickness as compared to the LED group (p < 0.05). AITC increased the levels of Bax, caspase-3, HO-1, GAP43, and VEGF, while decreasing IL-1β, IL-6, NF-κB, Bcl-2, GFAP, Grp78, activating ATF4 and ATF6 as compared to the LED group (p < 0.05). Conclusion In conclusion, four weeks of AITC administration to the rats showed specific protective effects against two days of intense LED light-induced retinal damage; through antiinflammatory, antioxidant, anti-apoptotic, and modulating mitochondrial metabolic pathways.

Coenzyme Q10 effect on cisplatin-induced oxidative retinal injury in rats

Aim In this study, it was aimed to investigate the effect of coenzyme Q10 (CoQ10) on cisplatin-induced oxidative retinal damage in rats biochemically and histopathologically. Materials and methods Thirty male Wistar albino rats were divided into 3 groups randomly: untreated control (C group), only 2.5 mg/kg cisplatin daily administrated group for 2 weeks (CP group), 2.5 mg/kg cisplatin + 20 mg/kg orally CoQ10 daily administrated group for 2 weeks (CoQC group). At the end of experimental period, blood samples obtained before sacrification for the biochemical examination of serum malondialdehyde (MDA), total glutathione (tGSH), total oxidant system (TOS), total antioxidant systemic (TAS) levels and after eyes were removed for examined histopathology. Results As a result of our study, severe histopathological damage was detected in the retinal tissue of the cisplatin group with serum malondialdehyde (MDA) and total oxidant system (TOS) levels were high and total glutathione (tGSH) and total antioxidant systemic (TAS) levels were low. However, it was observed that the histopathological damage associated with cisplatin was decreased in the retinal tissue of the CoQ10 group, which inhibited the increase in blood serum MDA/TOS levels and decrease in tGSH/TAS levels. Conclusion The biochemical and histopathological results of our study were compatible with each other, so we concluded that the damage to the rat retinal tissue caused by cisplatin may be reversible with coenzyme.

Metformin Protects against NMDA-Induced Retinal Injury through the MEK/ERK Signaling Pathway in Rats.

Metformin, an anti-hyperglycemic drug of the biguanide class, exerts positive effects in several non-diabetes-related diseases. In this study, we aimed to examine the protective effects of metformin against N-methyl-D-aspartic acid (NMDA)-induced excitotoxic retinal damage in rats and determine the mechanisms of its protective effects. Male Sprague–Dawley rats (7 to 9 weeks old) were used in this study. Following intravitreal injection of NMDA (200 nmol/eye), the number of neuronal cells in the ganglion cell layer and parvalbumin-positive amacrine cells decreased, whereas the number of CD45-positive leukocytes and Iba1-positive microglia increased. Metformin attenuated these NMDA-induced responses. The neuroprotective effect of metformin was abolished by compound C, an inhibitor of AMP-activated protein kinase (AMPK). The AMPK activator, AICAR, exerted a neuroprotective effect in NMDA-induced retinal injury. The MEK1/2 inhibitor, U0126, reduced the neuroprotective effect of metformin. These results suggest that metformin protects against NMDA-induced retinal neurotoxicity through activation of the AMPK and MEK/extracellular signal-regulated kinase (ERK) signaling pathways. This neuroprotective effect could be partially attributable to the inhibitory effects on inflammatory responses.

Different Doses of β-Cryptoxanthin May Secure the Retina from Photooxidative Injury Resulted from Common LED Sources.

Retinal damage associated with loss of photoreceptors is a hallmark of eye diseases such as age-related macular degeneration (AMD) and diabetic retinopathy. Potent nutritional antioxidants were previously shown to abate the degenerative process in AMD. β-Cryptoxanthin (BCX) is an essential dietary carotenoid with antioxidant, anti-inflammatory, and provitamin A activity. It is a potential candidate for developing intervention strategies to delay the development/progression of AMD. In the current study, the effect of a novel, highly purified BCX oral formulation on the rat retinal damage model was evaluated. Rats were fed with BCX for four weeks at the doses of 2 and 4 mg/kg body weight in the form of highly bioavailable oil suspension, followed by retinal damage by exposing to the bright light-emitting diode (LED) light (750 lux) for 48 hrs. Animals were sacrificed after 48 hours, and eyes and blood samples were collected and analyzed. BCX supplementations (2 and 4 mg/kg) showed improvements in the visual condition as demonstrated by histopathology of the retina and measured parameters such as total retinal thickness and outer nuclear layer thickness. BCX supplementation helped reduce the burden of oxidative stress as seen by decreased serum and retinal tissue levels of malondialdehyde (MDA) and restored the antioxidant enzyme activities in BCX groups. Further, BCX supplementation modulated inflammatory markers (IL-1β, IL-6, and NF-κB), apoptotic proteins (Bax, Bcl-2, caspase 3), growth proteins and factors (GAP43, VEGF), glial and neuronal proteins (GFAP, NCAM), and heme oxygenase-1 (HO-1), along with the mitochondrial stress markers (ATF4, ATF6, Grp78, Grp94) in the rat retinal tissue. This study indicates that oral supplementation of BCX exerts a protective effect on light-induced retinal damage in the rats via reducing oxidative stress and inflammation, also protected against mitochondrial DNA damage and cellular death.

Weak Anti-inflammatory and Anti-cancer Properties of Saffron

Background and objectives: Positive role of saffron in human health promotion has been investigated in widespread researches. Anticancer property, neuroprotection, protection of cardiovascular system and several positive properties are reported for saffron customers. The aim of this study was assessment of saffron weakness against light damage in rat retina. Methods: Gene profiles of control samples (C group) and light damage (L) groups were extracted from Gene Expression Omnibus (GEO) and compared with similar samples in the presence of saffron. The unprotected differentially expressed genes (DEGs) were evaluated via network analysis and pathway investigation. The critical genes which were not protected by saffron were identified and discussed. Results: Numbers of 67 DEGs were investigated via protein-protein interaction (PPI) network analysis, pathway assessment, and action map investigation. Findings indicated that STAT1, JUN, FOS, and STAT3 were the crucial genes that were not protected by saffron against light damage in rat retina. Conclusion: It may be necessary that consumption of saffron require a suitable protocol to avoid from possible disadvantages; however, saffron is well known for its benefits in human nutrition.

Resveratrol ameliorates disorders of mitochondrial biogenesis and dynamics in a rat chronic ocular hypertension model

AimsTo explore the roles of mitochondrial biogenesis and dynamics in both RGC-5 cells apoptosis and rat retinal damage induced by elevated pressure and their involvement in resveratrol (RSV)-induced cell protection. Materials and methodsThe chronic ocular hypertension (COH) model was established in rats by injecting superparamagnetic iron oxide into anterior chamber. The RGC-5 cells were incubated under ambient and elevated pressure (70 mm Hg) respectively. The intraocular pressure (IOP) was measured using a handheld Tonolab tonometer; mitochondrial dysfunction was analyzed by membrane potential (MMP) depolarization, reactive oxygen species (ROS) level and transmission electron microscope (TEM) detection. Annexin V/PI staining and the terminal deoxynucleotidy transferase dUTP nick end labeling (TUNEL) staining assay were performed for apoptosis detection. Hematoxylin–Eosin staining was performed for retinal morphology detection. The expression of mitochondrial biogenesis and dynamics relating proteins were analyzed by western blot. Key findingsThe retinal morphology and mitochondrial function deteriorated in chronic ocular hypertension (COH) rats. The cells showed apoptosis and mitochondrial dysfunction under elevated pressure (70 mm Hg) incubation. Upregulating AMPK, NRF-1, Tfam, mfn-2, OPA1 expression with RSV-treatment could decrease the cell apoptosis, mitochondrial membrane potential depolarization, ROS generation both in in vitro and in vivo experiments, and normalized the retinal morphology in vivo. SignificanceBoth in vitro and in vivo experiments demonstrated that activated AMPK/PGC-1α signaling pathway and improved expression of proteins were related to mitochondrial dynamics could be the possible mechanism underlying in the RSV's mitochondrial protection.

Protective Effect of Highly Polymeric A-Type Proanthocyanidins from Seed Shells of Japanese Horse Chestnut (Aesculus turbinata BLUME) against Light-Induced Oxidative Damage in Rat Retina.

Retinal tissue is exposed to oxidative stress caused by visible light. Light-damaged rat used in age-related macular degeneration (AMD) studies clarified that antioxidants decrease retinal light damage. Albino rats were exposed to 5000 Lux light for 12 h with oral administration of the polyphenolic compounds fraction (PF) from the seed shells of Japanese horse chestnut (30 mg/kg, 100 mg/kg, and 300 mg/kg body weight: BW). To evaluate the protective effects against light damage, electroretinograms (ERGs), the outer nuclear layer (ONL) thickness, the antioxidant activity of plasma, oxidized retinal lipids, and the detection of apoptosis were examined. To reveal their active compounds, PF were separated into an A-type proanthocyanidin (PAF) and a flavonol O-glycosides fraction. The protective effects of these fractions against light damage were compared by measuring the thickness of the ERGs and ONL. Compared with the negative control, the PF group (100 mg/kg and 300 mg/kg BW) significantly suppressed the decrease of the ERG amplitudes and ONL thickness. PF (300 mg/kg BW) induced the elevation of in vivo antioxidant activity, and the suppression of retinal lipid oxidation. PF administration also suppressed apoptotic cell death. The protective effects against light damage were attributable to the antioxidant activity of PAF. The light-induced damage of retinas was protected by oral administration of PF and PAF. Taken together, these compounds are potentially useful for the prevention of the disease caused by light exposure. Highlights: The protective effects of retinal damage by light exposure were evaluated using polyphenolic compounds from the seed shells of Japanese horse chestnut (Aesculus turbinata BLUME) as an antioxidant. Decreases in the electroretinographic amplitude and outer nuclear layer thickness were suppressed by the polyphenolic compounds of the seed shells. Polyphenolic compounds from the seed shells of Japanese horse chestnut inhibited the oxidation of retinal lipids. Highly polymeric A-type proanthocyanidin from the seed shells protected the rat retina from light exposure damage by inhibiting oxidative stress and apoptotic mechanisms.

Effect of Magnesium Acetyltaurate and Taurine on Endothelin1-Induced Retinal Nitrosative Stress in Rats

ABSTRACTPurpose: Retinal ganglion cell apoptosis in glaucoma is associated with elevated levels of endothelin-1 (ET1), a potent vasoconstrictor. ET1-induced retinal ischemia leads to altered expression of nitric oxide synthase (NOS) isoforms leading to increased formation of nitric oxide (NO) and retinal nitrosative stress. Since magnesium (Mg) is known to improve endothelial functions and reduce oxidative stress and taurine (TAU) possesses potent antioxidant properties, we investigated the protective effects of magnesium acetyltaurate (MgAT) against ET1-induced nitrosative stress and retinal damage in rats. We also compared the effects of MgAT with that of TAU alone.Methods: Sprague Dawley rats were intravitreally injected with ET1. MgAT and TAU were administered as pre-, co-, or posttreatment. Subsequently, the expression of NOS isoforms was detected in retina by immunohistochemistry, retinal nitrotyrosine level was estimated using ELISA, and retinal cell apoptosis was detected by TUNEL staining.Results: Intravitreal ET1 caused a significant increase in the expressions of nNOS and iNOS while eNOS expression was significantly reduced compared to vehicle treated group. Administration of both MgAT and TAU restored the altered levels of NOS isoform expression, reduced retinal nitrosative stress and retinal cell apoptosis. The effect of MgAT, however, was greater than that of TAU alone.Conclusions: MgAT and TAU prevent ET1-induced retinal cell apoptosis by reducing retinal nitrosative stress in Sprague Dawley rats. Addition of TAU to Mg seems to enhance the efficacy of TAU compared to when given alone. Moreover, the pretreatment with MgAT/TAU showed higher efficacy compared to co- or posttreatment.

The protective effect of erythropoietin on the experimental light-induced retinal degeneration of rat

Objective To investigate the protective effect of erythropoietin(EPO) on the structure and function of light-induced damage in rat retina. Methods The animal model of light-induced retinal degeneration was made. Thirty-six SD rats were randomly divided into experimental group, peritoneal injection with EPO and control group, peritoneal injection with the same amount of normal saline. The EPO and EPOR expression were observed in two groups. The structure and thickness of the retina and ERG before and after light explosure were observed. Results The gray value of EPO and EPOR expression in any layer of the retina reached peak value at 24 hours after light explosure.EPO and EPOR expression at 6, 24 and 72 hours were higher than that of before light explosure. The difference were statistically significant(P=0.002, 0.000, 0.000; P=0.001, 0.000, 0.000). Seven days after light explosure, the outer retina thickness of two groups markedly reduced(P=0.000), but the reduction of outer retina thickness in experimental group was less than that in control group(P=0.000). The amplitude of a-wave and b-wave in two groups decreased remarkably at 1 day, 1 week and 2 weeks after light explosure, but the amplitude of a-wave and b-wave in experimental group was higher than those in control group(P=0.013-0.039). Conclusion Endogenous EPO and EPOR express increasingly after light damage. Systemic exogenous EPO plays a protective role in light-induced damage in retina. Key words: Erythropoietin; Animal model; Retina; Light-induced damage

Editor's Highlight: Periodic Exposure to Smartphone-Mimic Low-Luminance Blue Light Induces Retina Damage Through Bcl-2/BAX-Dependent Apoptosis.

Blue light-induced phototoxicity plays an important role in retinal degeneration and might cause damage as a consequence of smartphone dependency. Here, we investigated the effects of periodic exposure to blue light-emitting diode in a cell model and a rat retinal damage model. Retinal pigment epithelium (RPE) cells were subjected to blue light in vitro and the effects of blue light on activation of key apoptotic pathways were examined by measuring the levels of Bcl-2, Bax, Fas ligand (FasL), Fas-associated protein with death domain (FADD), and caspase-3 protein. Blue light treatment of RPE cells increased Bax, cleaved caspase-3, FasL, and FADD expression, inhibited Bcl-2 and Bcl-xL accumulation, and inhibited Bcl-2/Bax association. A rat model of retinal damage was developed with or without continuous or periodic exposure to blue light for 28 days. In this rat model of retinal damage, periodic blue light exposure caused fundus damage, decreased total retinal thickness, caused atrophy of photoreceptors, and injured neuron transduction in the retina.

The Involvement ofβ-Catenin/COX-2/VEGF Axis in NMDA-Caused Retinopathy

NMDA, a molecule that is capable of producing the loss of retinal ganglia cells (RGCs), has been widely studied; however, the detailed mechanism is not yet clarified. Previously, Wnt/β-catenin signaling has been suggested to be involved in the NMDA-induced retinopathy. In addition, previous investigations in our group demonstrated the presence of a Wnt/β-catenin/COX-2 axis in dorsal root ganglions (DRGs). Therefore, here in this paper, we tested whether there is an association of such axis with NMDA-induced RGC loss. Rat retinal damage models generated by intravitreal injection of NMDA were used to measure the expression levels of β-catenin, COX-2, and VEGF in retinas, and the neuron numbers of the retinal GCL of rats were counted. Then, pharmacological tools (MK801, a NMDA receptor inhibitor; Dickkopf homolog 1, a specific inhibitor of the Wnt pathway; NS-398, a COX-2 inhibitor; and bevacizumab, IVB, a VEGF inhibitor) were introduced to evaluate the detailed roles of Wnt/β-catenin, COX-2, and VEGF in retinopathy of rats. Results demonstrated that all three factors in sequence are positively regulated neuronal loss induced by NMDA. These observations indicated that the Wnt pathway/COX-2/VEGF axis plays a pathogenic role in retinopathy and represented novel therapeutic targets.

Novel Tetrahydropyrido[4,3-d]pyrimidines as Potent Inhibitors of Chaperone Heat Shock Protein 90.

Heat shock protein 90 (Hsp90) is a potential target for oncology therapeutics. Some inhibitors have shown antitumor effects in clinical trials, spurring the discovery of small molecule Hsp90 inhibitors. Here, we describe the structural optimization studies of a hit compound, tetrahydropyrido[4,3-d]pyrimidine-based Hsp90 inhibitor 15, which exhibits inhibitory activity against Hsp90. A series of analogues were synthesized, and their structure-activity and structure-property relationships were analyzed. These explorations led to the discovery of compound 73, which exhibited potent in vitro activities, good physicochemical properties, favorable ADME properties, and a potent antitumor effect in an HCT116 xenograft model. Furthermore, 73 exhibited no ocular toxicity in a rat retinal damage model, suggesting it is a relatively safe Hsp90 inhibitor. As a promising antitumor agent, 73 was progressed for further preclinical evaluation.

Protective effects of PF-4708671 against N-methyl-d-aspartic acid-induced retinal damage in rats.

We previously demonstrated that rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), protects against N-methyl-d-aspartic acid (NMDA)-induced retinal damage in rats. Rapamycin inhibits mTOR activity, thereby preventing the phosphorylation of ribosomal protein S6, which is a downstream target of S6 kinase. Therefore, we aimed to determine whether PF-4708671, an inhibitor of S6 kinase, protects against NMDA-induced retinal injury. Intravitreal injection of NMDA (200 nmol/eye) caused cell loss in the ganglion cell layer and neuroinflammatory responses, such as an increase in the number of CD45-positive leukocytes and Iba1-positive microglia. Surprisingly, simultaneous injection of PF-4708671 (50 nmol/eye) with NMDA significantly attenuated these responses without affecting phosphorylated S6 levels. These results suggest that PF-4708671 and rapamycin likely protect against NMDA-induced retinal damage via distinct pathways. The neuroprotective effect of PF-4708671 is unlikely to be associated with inhibition of the S6 kinase, even though PF-4708671 is reported to be a S6 kinase inhibitor.

Assessment of Visual and Chromatic Functions in a Rodent Model of Retinal Degeneration

We evaluated the photoreceptor response of pigmented P23H and normal pigmented Long Evans (LE) rats over time using functional tests in variable lighting conditions. Pigmented P23H rats were studied by optomotor testing and electroretinogram (ERG) recordings at P30, P150, and P240. Pigmented LE rats were used as a normal wild-type control. Stimuli were modified with colored filters. Neutral density filters were used to reduce luminance. Age-related decreases in visual acuity (VA) and contrast sensitivity (CS) were observed in P23H rats. Good correlations in measurements without filter and with green filter were observed between LE and P23H P30 rat values. Differences between groups were smaller with red and purple filters. A strong relationship with luminance was observed in LE rats (VA and CS) and with P23H P30 rats (CS). A decline in the ERG responses of P23H rats was consistent with the gradual loss of photoreceptors. Differences in a- and b-wave amplitudes with different colored filters were negligible with the exception of the red filter, which resulted in smaller responses. Visual function parameters decreased with age in pigmented P23H rats. Irrespective of luminance, color filter, and retinal degeneration, minimum thresholds of VA and CS were found. Smaller differences than expected were found using color filters. Responses to functional tests at long wavelengths were observed, where there is very low photoreceptor spectral sensitivity. The use of filters with functional testing could minimize light-induced retinal damage in rats.

Application of clotrimazole via a novel controlled release device provides potent retinal protection.

Age-related macular degeneration is the leading cause of legal blindness among older individuals. Therefore, the development of new therapeutic agents and optimum drug delivery systems for its treatment are crucial. In this study, we investigate whether clotrimazole (CLT) is capable of protecting retinal cells against oxidative-induced injury and the possible inhibitory effect of a sustained CLT-release device against light-induced retinal damage in rats. In vitro results indicated pretreatment of immortalized retinal pigment epithelium cells (RPE-J cells) with 10–50 µM CLT before exposure to oxygen/glucose deprivation conditions for 48 h decreased the extent of cell death, attenuated the percentage of reactive oxygen species-positive cells, and decreased the levels of cleaved caspase-3. The device consists of a separately fabricated reservoir, a CLT formulation, and a controlled release cover, which are made of poly(ethyleneglycol) dimethacrylate (PEGDM) and tri(ethyleneglycol) dimethacrylate (TEGDM). The release rate of CLT was successfully tuned by changing the ratio of PEGDM/TEGDM in the cover. In vivo results showed that use of a CLT-loaded device lessened the reduction of electroretinographic amplitudes after light exposure. These findings indicate that the application of a polymeric CLT-loaded device may be a promising method for the treatment of some retinal disorders.

The effect of thiamine pyrophosphate on ethambutol-induced ocular toxicity

Context: Ethambutol-induced retinal oxidative damage in patients with tuberculosis is still not being adequately treated. The protective effect of thiamine pyrophosphate against oxidative damage in some tissues has been reported, but no information on the protective effects of thiamine pyrophosphate against ethambutol-induced oxidative retinal damage has been found in the medical literature.Objective: The objective is to investigate whether thiamine pyrophosphate has a protective effect against oxidative retinal damage in rats induced by ethambutol.Materials and methods: Experimental animals divided into four groups (n = 10): the healthy group (HG), the ethambutol control group (EMB), thiamine + ethambutol group (Thi–EMB) and thiamine pyrophosphate + ethambutol group (TPP–EMB). The rats in the TPP–EMB and Thi–EMB groups were administered thiamine pyrophosphate and thiamine, respectively, at doses of 20 mg/kg intraperitoneally. Distilled water was administered intraperitoneally to the HG and the EMB groups as a solvent in the same volumes. One hour after drug injection, 30 mg/kg ethambutol was administered via an oral gavage to the TPP–EMB, Thi–EMB and EMB groups. This procedure was repeated once a day for 90 days. At the end of this period, all rats were euthanized under high-dose thiopental sodium anesthesia, and biochemical and histopathological investigations of the retinal tissue were performed.Results: Malondialdehyde (MDA) and DNA damage product 8-hydroxyguanine levels were significantly lower in the retinal tissue of TPP–EMB and HG groups compared to those of the Thi–EMB and EMB groups, and total glutathione (tGSH) was also found to be higher. In addition, severe retinal tissue vascularization, edema and loss of ganglion cells were observed in the Thi–EMB and EMB groups, whereas histopathological findings for the TPP–EMB group were observed to be close to normal.Discussion and conclusion: These findings suggest that thiamine pyrophosphate protects retinal tissues from ethambutol-induced oxidative damage, and thiamine does not. This positive effect of thiamine pyrophosphate may be useful in the prevention of ocular toxicity that occurs during ethambutol use.