Noriko Himori

Critical role of Nrf2 in oxidative stress-induced retinal ganglion cell death

NF‐E2 related factor 2 (Nrf2) is a key transcription factor that plays a pivotal role in endogenous protection against oxidative stress. However, the role of Nrf2 in visual disorders remains unclear. It has been reported that oxidative stress is thought of as one of the causes of glaucoma. Here, we investigate whether the function of Nrf2 in oxidative stress‐induced retinal ganglion cell (RGC) death. This study used adult male Nrf2 deficient mice (Nrf2 KO) and age‐ and sex‐matched wild‐type (WT) mice. We dissociated and purified N‐4‐[4‐didecylaminostryryl]‐N‐methyl‐pyridinium iodide‐labeled RGCs with fluorescence‐activated cell sorting, and tried to detect the Nrf2 and Keap1 genes. In the absence of nerve crush (NC), the number of RGCs in Nrf2 KO mice was almost same as that in WT mice. 1‐(2‐cyano‐3‐, 12‐dioxooleana‐1, 9 (11)‐dien‐28‐oyl) imidazole (CDDO‐Im), an Nrf2 activator, prevented NC‐induced loss of RGCs in WT mice. Seven days after NC, without treatment, the number of RGCs in Nrf2 KO mice was significantly lower than in WT mice. In addition, after CDDO‐Im treatment, quantitative RT‐PCR showed increased expression of antioxidant and phase II detoxifying enzymes. These results suggest that up‐regulation of Nrf2 signaling after CDDO‐Im treatment may be a novel therapeutic strategy for the protection of RGCs, especially in glaucoma.

The novel Rho kinase (ROCK) inhibitor K-115: a new candidate drug for neuroprotective treatment in glaucoma.

PURPOSE To investigate the effect of K-115, a novel Rho kinase (ROCK) inhibitor, on retinal ganglion cell (RGC) survival in an optic nerve crush (NC) model. Additionally, to determine the details of the mechanism of K-115s neuroprotective effect in vivo and in vitro. METHODS ROCK inhibitors, including K-115 and fasudil (1 mg/kg/d), or vehicle were administered orally to C57BL/6 mice. Retinal ganglion cell death was then induced with NC. Retinal ganglion cell survival was evaluated by counting surviving retrogradely labeled cells and measuring RGC marker expression with quantitative real-time polymerase chain reaction (qRT-PCR). Total oxidized lipid levels were assessed with a thiobarbituric acid-reactive substances (TBARS) assay. Reactive oxygen species (ROS) levels were assessed by co-labeling with CellROX and Fluorogold. Expression of the NADPH oxidase (Nox) family of genes was evaluated with qRT-PCR. RESULTS The survival of RGCs after NC was increased 34 ± 3% with K-115, a significantly protective effect. Moreover, a similar effect was revealed by the qRT-PCR analysis of Thy-1.2 and Brn3a, RGC markers. Levels of oxidized lipids and ROS also increased with time after NC. NC-induced oxidative stress, including oxidation of lipids and production of ROS, was significantly attenuated by K-115. Furthermore, expression of the Nox gene family, especially Nox1, which is involved in the NC-induced ROS production pathway, was dramatically reduced by K-115. CONCLUSIONS The results indicated that oral K-115 administration delayed RGC death. Although K-115 may be mediated through Nox1 downregulation, we found that it did not suppress ROS production directly. Our findings show that K-115 has a potential use in neuroprotective treatment for glaucoma and other neurodegenerative diseases.

Critical role of calpain in axonal damage-induced retinal ganglion cell death

Calpain, an intracellular cysteine protease, has been widely reported to be involved in neuronal cell death. The purpose of this study is to investigate the role of calpain activation in axonal damage‐induced retinal ganglion cell (RGC) death. Twelve‐week‐old male calpstatin (an endogenous calpain inhibitor) knockout mice (CAST KO) and wild‐type (WT) mice were used in this study. Axonal damage was induced by optic nerve crush (NC) or tubulin destruction induced by leaving a gelatin sponge soaked with vinblastine (VB), a microtubule disassembly chemical, around the optic nerve. Calpain activation was assessed by immunoblot analysis, which indirectly quantified the cleaved α‐fodrin, a substrate of calpain. RGCs were retrogradely labeled by injecting a fluorescent tracer, Fluoro‐Gold (FG), and the retinas were harvested and flat‐mounted retinas prepared. The densities of FG‐labeled RGCs harvested from the WT and CAST KO groups were assessed and compared. Additionally, a calpain inhibitor (SNJ‐1945, 100 mg/kg/day) was administered orally, and the density of surviving RGCs was compared with that of the vehicle control group. The mean density of surviving RGCs in the CAST KO group was significantly lower than that observed in the WT group, both in NC and in VB. The mean density of surviving RGCs in the SNJ‐1945‐treated group was significantly higher than that of the control group. The calpain inhibitor SNJ‐1945 has a neuroprotective effect against axonal damage‐induced RGC death. This pathway may be an important therapeutic target for preventing this axonal damage‐induced RGC death, including glaucoma and diabetic optic neuropathy and other CNS diseases that share a common etiology.

Metabolic stress response implicated in diabetic retinopathy: The role of calpain, and the therapeutic impact of calpain inhibitor

To describe how a high fat diet (HFD) and hyperglycemia initiate a sequence of calpain activation and oxidative stress associated with neuro-degenerative changes in diabetic retinopathy (DR), hyperglycemia was induced with streptozotocin in mice lacking the gene for calpastatin (CAST KO), and in mice lacking the gene for the transcription factor NF-E2 related factor 2 (Nrf2 KO). All animals were fed a HFD. Retinal ganglion cell (RGC) density was estimated by labeling with fluorogold and immunohistochemistry. A potent calpain inhibitor, SNJ-1945, was administered daily until the animals were sacrificed. In vitro, oxidative stress-induced RGC loss was evaluated in a high glucose culture medium with and without SNJ-1945. Retinal mRNA of calpain-1 and calpain-2 was measured by quantitative RT-PCR. Pre-apoptotic substrates of cleaved α-fodrin and synaptophysin protein were quantified by immunoblot analysis. Axonal damage was examined in transverse sections of the optic nerve. A HFD and hyperglycemia significantly increased RGC and axonal degeneration 3 weeks into the experiment. Levels of cleaved α-fodrin were increased. In the CAST KO mice, the neurotoxicity was augmented significantly. Gene manipulation of CAST and orally administered SNJ-1945 successfully modified calpain levels in the retina and prevented RGC death. In vitro, a high-glucose culture of retinal cells without antioxidants showed more RGC death than that with antioxidant treatment. The expression of synaptophysin was significantly suppressed by SNJ-1945 treatment. These results suggest that calpain plays a crucial role in metabolic-induced RGC degeneration caused by hyperglycemia and oxidative stress. Antioxidant and calpain inhibition offers important opportunities for future neuroprotective treatment against RGC death in various metabolic stress-induced diseases including DR.

Progression of Visual Field Defects in Eyes With Different Optic Disc Appearances in Patients With Normal Tension Glaucoma

Purpose:To investigate the relationship between the optic disc appearance and the progression of visual field defects in eyes with normal tension glaucoma (NTG). Methods:Two hundred nine patients with NTG, who were being treated with topical antiglaucoma drugs and had been followed for at least 3 years, were studied. The baseline optic disc appearance was classified into 4 types: focal ischemic (FI), myopic glaucomatous (MY), senile sclerotic (SS), and generalized cup enlargement (GE). The progression of the NTG was assessed by the slope of the mean deviations (MDs) obtained from the visual field results collected during the follow-up examinations. The baseline and mean intraocular pressures (IOPs) were also followed. Results:Twenty-seven patients were placed in the FI group, 63 into the MY group, 24 into the SS group, and 43 into the GE group. Fifty-two patients (24.9%) could not be classified. There were no significant differences in the percentage reduction of the IOP among the 4 groups. The MD slope in the GE group (−0.51±0.74 dB/y) was significantly steeper than that in the other groups. Regression analyses showed that the factors most associated with the MD slope were the age in the FI (r, −0.495) and the GE (r=0.496) groups, and the relative reduction of the IOP (r=0.413) in the SS group. None of the factors in the MY group was significantly associated with the MD slope. Conclusions:The rate of progression of the field defects, the MD slope, in patients with NTG is possibly dependent on the baseline optic disc appearance. Thus, the optic disc appearance may be useful for the management of patients with NTG.

Suppression of phagocytic cells in retinal disorders using amphiphilic poly(γ-glutamic acid) nanoparticles containing dexamethasone

To investigate the potential of nanoparticles (NPs) composed of poly(γ-glutamic acid) conjugated with l-phenylalanine (γ-PGA-Phe NPs) for the treatment of retinal diseases, γ-PGA-Phe NPs (200nm) were tested with macrophages and microglia in vitro or by intravitreal administration into normal or pathological rat eyes. The anti-inflammatory effects of the NPs containing dexamethasone (DEX-NPs) were examined using qRT-PCR in vitro by counting activated microglia and Fluorogold-labeled retinal ganglion cells in the retinas under excitotoxicity or by counting TUNEL (+) photoreceptors in the detached retinas. The NPs were taken up efficiently by cultured macrophages or microglia. At day 7, 60-80% of the diffuse signal remained in the cytoplasm of these cells. In normal rat eyes, the NPs did not accumulate in the retinas and no inflammatory cells were recruited. Conversely, under pathological conditions, the NPs were localized in activated CD11b-positive cells in the retina. DEX-NPs suppressed the expression of TNFα and MCP-1 in cultured macrophages or microglia, the activation of microglia, the loss of retinal ganglion cells (RGCs) in excitotoxic retinas, and the number of TUNEL (+) photoreceptors in detached retinas. These data suggest that γ-PGA-Phe NPs can be a powerful tool for suppressing inflammatory cells in pathological conditions in the retina.

Fiber-based polarization-sensitive OCT for birefringence imaging of the anterior eye segment

We demonstrate a prototype system of polarization-sensitive optical coherence tomography (PS-OCT) designed for clinical studies of the anterior eye segment imaging. The system can measure Jones matrices of the sample with depth-multiplexing of two orthogonal incident polarizations and polarization-sensitive detection. An optical clock is generated using a quadrature modulator and a logical circuit to double the clock frequency. Systematic artifacts in measured Jones matrices are theoretically analyzed and numerically compensated using signals at the surface of the sample. Local retardation images of filtering blebs after trabeculectomy show improved visualization of subconjunctival tissue, sclera, and scar tissue of the bleb wall in the anterior eye segment.

Simulated Visual Fields Produced from Macular RNFLT Data in Patients with Glaucoma

Abstract Purpose: We investigated in detail the correlation between structure and function in the macula, and whether optical coherence tomography (OCT)-measured macular structure could be used to simulate the visual field. Materials and methods: This study comprised 60 eyes of 34 patients with open angle glaucoma (Anderson-Patella classification). To assess macular function, reliable data from the Humphrey field analyzer (HFA, SITA-standard, 10-2 program) for threshold, total deviation (TD), and pattern deviation (PD) were used. To assess macular structure, thickness data for the retinal nerve fiber layer (RNFL), ganglion cell complex (GCC), and ganglion cell layer plus inner plexiform layer (GCL + IPL) from macular OCT maps (3D OCT-2000, Topcon) were analyzed. Spearman’s coefficient of correlation analysis was performed to determine the significance of the correlation, as well as the formula for simulation. The formula was used to calculate the simulated threshold, TD, and PD values. The simulation method was validated by comparing results for simulated and actual visual fields in a new data set of 29 eyes from glaucoma patients. Results: In most test points, macular function and the layer-by-layer structure were significantly correlated, however, the distribution of highly-correlated points varied. Simulated grayscale maps of the visual field based on the formula of regression line for RNFLT and thresholds were similar to actual visual fields. There was a significant correlation between simulated visual fields created from RNFLT, GCC and GCL + IPL data and actual average threshold values in all 68 test points (r = 0.63–0.87, p < 0.001) and TD (r = 0.62–0.86, p < 0.001). Conclusion: We found that there was a significant correlation between structure and function in the macular area, and that simulated visual fields from RNFLT data reflected actual visual fields. Such a simulation of macular function from OCT parameters may be useful in assessing glaucoma in patients who have difficulty undergoing actual visual field examinations.

The association between systemic oxidative stress and ocular blood flow in patients with normal-tension glaucoma

PurposeTo evaluate the association between ocular blood flow and biomarkers of systemic oxidative stress, as well as the potential of these biomarkers to assess normal-tension glaucoma (NTG).MethodsThis study included 73 eyes of 73 patients with NTG. We assessed ocular blood flow by measuring mean blur rate (MBR) in the optic nerve head using laser speckle flowgraphy, both overall and separately in the vessel and tissue areas. We also measured urinary 8-hydroxy-2’-deoxyguanosine (8-OHdG) and skin autofluorescence (SAF), and lastly, determined correlations between these measurements and with other clinical parameters.ResultsSAF was correlated with age, circumpapillary retinal nerve fiber layer thickness (cpRNFLT), mean deviation (MD), and overall MBR (P = 0.003, P = 0.013, P = 0.015 and P = 0.006, respectively). SAF and 8-OHdG were both correlated with tissue-area MBR (P = 0.006 and P = 0.010, respectively). Visual acuity, cpRNFLT, mean deviation and tissue-area MBR had a significant tendency to change with NTG severity (P = 0.014, P < 0.001, P < 0.001 and P = 0.006, respectively). Multiple regression analysis revealed that cpRNFLT and 8-OHdG were independent contributing factors to MD (P < 0.001 and P = 0.040, respectively), and that cpRNFLT and 8-OHdG were independent contributing factors to tissue-area MBR (P = 0.005 and P = 0.028, respectively).ConclusionsWe found a close relationship between cpRNFLT, MD, tissue MBR, SAF and 8-OHdG, suggesting that systemic oxidative stress is associated with decreased ocular blood flow and may be involved in the pathogenesis of NTG.

The role of the Nrf2-mediated defense system in corneal epithelial wound healing.

The corneal epithelium exists at the surface of cornea and is easily damaged by external stresses such as UV radiation or physical injury. The Nrf2-mediated defense system plays a central role in protecting cells by activating genes against these types of stress. In this study, we investigated the role of the Nrf2-mediated defense system in corneal epithelial wound healing by using Nrf2-knockout (KO) mice. Nrf2 was expressed in the corneal epithelium of wild-type (WT) mice, but not in KO mice. Observation of wounds after 24h of healing revealed that healing of the corneal epithelium was significantly delayed in the Nrf2 KO mice, whereas Nrf2 was activated in the corneal epithelium of WT mice. Ki-67 staining revealed that the number of Ki-67-positive proliferating cells was significantly lower in the Nrf2 KO mice than in the WT mice at 24-36h after injury; however, these numbers were approximately equivalent by 48h. To clarify the role of Nrf2 during wound healing, we performed in vitro experiments with siRNA for Nrf2 and its suppressor Keap1. Nrf2 knockdown significantly delayed corneal epithelial cell migration, but did not affect cell proliferation. Conversely, Keap1 knockdown significantly accelerated cell migration. These results suggest that Nrf2 contributed to the corneal epithelial wound-healing process by accelerating cell migration, and Nrf2 would therefore be a good target for the treatment of corneal epithelial diseases such as dry eye or chronic corneal epithelial defect.