Kenya Yuki

Neurodegenerative influence of oxidative stress in the retina of a murine model of diabetes

Aims/hypothesisDiabetic retinopathy is a progressive neurodegenerative disease, but the underlying mechanism is still obscure. Here, we focused on oxidative stress in the retina, and analysed its influence on retinal neurodegeneration, using an antioxidant, lutein.MethodsC57BL/6 mice with streptozotocin-induced diabetes were constantly fed either a lutein-supplemented diet or a control diet from the onset of diabetes, and their metabolic data were recorded. In 1-month-diabetic mice, reactive oxygen species (ROS) in the retina were measured using dihydroethidium and visual function was evaluated by electroretinograms. Levels of activated extracellular signal-regulated kinase (ERK), synaptophysin and brain-derived neurotrophic factor (BDNF) were also measured by immunoblotting in the retina of 1-month-diabetic mice. In the retinal sections of 4-month-diabetic mice, histological changes, cleaved caspase-3 and TUNEL staining were analysed.ResultsLutein did not affect the metabolic status of the diabetic mice, but it prevented ROS generation in the retina and the visual impairment induced by diabetes. ERK activation, the subsequent synaptophysin reduction, and the BDNF depletion in the diabetic retina were all prevented by lutein. Later, in 4-month-diabetic mice, a decrease in the thickness of the inner plexiform and nuclear layers, and ganglion cell number, together with increase in cleaved caspase-3- and TUNEL-positive cells, were avoided in the retina of lutein-fed mice.Conclusions/interpretationThe results indicated that local oxidative stress that has a neurodegenerative influence in the diabetic retina is prevented by constant intake of a lutein-supplemented diet. The antioxidant, lutein may be a potential therapeutic approach to protect visual function in diabetes.

Resveratrol Prevents Light-Induced Retinal Degeneration via Suppressing Activator Protein-1 Activation

Light damage to the retina accelerates retinal degeneration in human diseases and rodent models. Recently, the polyphenolic phytoalexin resveratrol has been shown to exert various bioactivities in addition to its classical antioxidant property. In the present study, we investigated the effect of resveratrol on light-induced retinal degeneration together with its underlying molecular mechanisms. BALB/c mice with light exposure (5000-lux white light for 3 hours) were orally pretreated with resveratrol at a dose of 50 mg/kg for 5 days. Retinal damage was evaluated by TdT-mediated dUTP nick-end labeling, outer nuclear layer morphometry, and electroretinography. Administration of resveratrol to mice with light exposure led to a significant suppression of light-induced pathological parameters, including TdT-mediated dUTP nick-end labeling-positive retinal cells, outer nuclear layer thinning, and electroretinography changes. To clarify the underlying molecular mechanisms, the nuclear translocation of activator protein-1 subunit c-fos was evaluated by enzyme-linked immunosorbent assay, and the retinal activity of sirtuin 1 was measured by deacetylase fluorometric assay. Retinal activator protein-1 activation, up-regulated following light exposure, was significantly reduced by application of resveratrol. In parallel, retinal sirtuin 1 activity, reduced in animals with light damage, was significantly augmented by resveratrol treatment. Our data suggest the potential use of resveratrol as a therapeutic agent to prevent retinal degeneration related to light damage.

Neural Degeneration in the Retina of the Streptozotocin-Induced Type 1 Diabetes Model

Diabetic retinopathy, a vision-threatening disease, has been regarded as a vascular disorder. However, impaired oscillatory potentials (OPs) in the electroretinogram (ERG) and visual dysfunction are recorded before severe vascular lesions appear. Here, we review the molecular mechanisms underlying the retinal neural degeneration observed in the streptozotocin-(STZ-) induced type 1 diabetes model. The renin-angiotensin system (RAS) and reactive oxygen species (ROS) both cause OP impairment and reduced levels of synaptophysin, a synaptic vesicle protein for neurotransmitter release, most likely through excessive protein degradation by the ubiquitin-proteasome system. ROS also decrease brain-derived neurotrophic factor (BDNF) and inner retinal neuronal cells. The influence of both RAS and ROS on synaptophysin suggests that RAS-ROS crosstalk occurs in the diabetic retina. Therefore, suppressors of RAS or ROS, such as angiotensin II type 1 receptor blockers or the antioxidant lutein, respectively, are potential candidates for neuroprotective and preventive therapies to improve the visual prognosis.

Roles of AMP-activated protein kinase in diabetes-induced retinal inflammation.

PURPOSE AMP-activated protein kinase (AMPK) is a sensor of cellular energy status. The purpose of the present study was to elucidate the roles of AMPK in the pathogenesis of diabetic retinopathy using the known AMPK activators resveratrol and AICAR (5-aminoimidazole-4-carboxamide ribonucleoside) in a mouse model. METHODS C57BL/6 mice with streptozotocin-induced diabetes were treated with resveratrol orally at 50 mg/kg for 7 days or with AICAR intraperitoneally at 100 mg/kg 24 hours before death. Retinal protein levels of phosphorylated and total AMPK, phosphorylated nuclear factor (NF)-κB p65, intercellular adhesion molecule (ICAM)-1, and vascular endothelial growth factor (VEGF) were evaluated by Western blot analysis or enzyme-linked immunosorbent assay. Retinal activity of sirtuin (SIRT)1 was measured by deacetylase fluorometric assay. Leukocyte adhesion to the retinal vasculature was examined with a concanavalin A lectin perfusion-labeling technique. RESULTS Induction of diabetes in mice led to retinal AMPK dephosphorylation, which was significantly reversed by either resveratrol or AICAR. Either resveratrol or AICAR significantly reversed SIRT1 deactivation and NF-κB phosphorylation, both of which were induced in the diabetic retina. Administration of resveratrol to diabetic mice significantly reduced diabetes-induced retinal leukocyte adhesion, together with retinal expression of ICAM-1 and VEGF. CONCLUSIONS The present findings reveal that diabetes-induced retinal inflammation stems from downregulation of the AMPK pathway, leading subsequently to SIRT1 deactivation and NF-κB activation. The data also suggest the potential use of the AMPK activator resveratrol as a therapeutic agent for diabetic retinopathy.

Retinal Ganglion Cell Loss in Superoxide Dismutase 1 Deficiency

PURPOSE To investigate the influence of deficiency in superoxide dismutase (SOD) 1, a major antioxidative enzyme, on retinal ganglion cells (RGCs). METHODS In the SOD1 total knockout (SOD1-deficient) mice, the level of superoxide anion was measured using dihydroethidium. The number of RGCs was counted in both the retinal sections and the flat-mount retinas after retrograde labeling. Thickness of nerve fiber layer (NFL) was measured in the sections, and the amount of neurofilament protein was measured by immunoblot analysis. Pattern electroretinogram (ERG), which reflects the function of retinal ganglion cells, dark-adapted ERG, and cone ERG were performed. The intraocular pressure (IOP) was measured with an induction-impact tonometer. The levels of SOD-1 and -2 were measured by ELISA, in the serum of 47 newly diagnosed consecutive normal tension glaucoma (NTG) patients and 44 consecutive control subjects. RESULTS The level of superoxide anion in the RGC layer was significantly higher in 24-week-old SOD1-deficient mice than in wild-type mice. The RGC number was significantly reduced in 24-week-old SOD1-deficient mice, although they were not in 8-week-old mice. The NFL thickness and neurofilament protein were reduced in 24-week-old SOD1-deficient mice. The amplitude of pattern ERG was significantly reduced, although dark-adapted and cone ERGs showed no impairment, in 24-week-old SOD1-deficient mice. The IOP level was not changed in the SOD1-deficient mice. The serum level of SOD1, but not SOD2, was significantly lower in the NTG patients than in the healthy controls. CONCLUSIONS SOD1 deficiency causes RGC vulnerability, which may be involved in the underlying condition of NTG.

Predictive factors for non-response to intravitreal ranibizumab treatment in age-related macular degeneration

Background/aims To study the initial characteristics and response to intravitreal ranibizumab (IVR) treatment of age-related macular degeneration (AMD). Methods We reviewed the clinical records of 141 eyes in 141 AMD patients who received monthly IVR for 3 months and thereafter pro re nata (PRN) injections for 9 months as the first treatment for AMD. Patients whose best corrected visual acuity (BCVA) worsened at month 12, and those with increased exudative fundus findings after IVR or an increased central retinal thickness of more than 100 μm at month 12, were considered to be non-responders as judged by BCVA and fundus findings, respectively. Non-responders’ initial characteristics were analysed using logistic regression models. Results 14.9% of eyes were non-responders as judged by BCVA, and 17.0% were non-responders as judged by fundus findings. Initial fibrovascular pigment epithelial detachment (PED) (OR 22.9, 95% CI 2.61 to 201) and serous PED (OR 4.12, 95% CI 1.08 to 15.8) were associated with non-response as judged by BCVA. Initial fibrovascular PED (OR 33.5, 95% CI 2.95 to 381) and type 1 choroidal neovascularization (OR 6.46, 95% CI 1.39 to 30.0) were associated with non-response, as judged by fundus findings. Conclusions Although most AMD responded to IVR, non-responders had initial clinical characteristics that might be informative for managing their treatment.

The Association between Primary Open-Angle Glaucoma and Motor Vehicle Collisions

PURPOSE To investigate and compare the prevalence of motor vehicle collisions (MVCs) in individuals with or without primary open-angle glaucoma (POAG). METHODS A total of 265 subjects were consecutively enrolled: 121 (79 men, 42 women; age, 62.1 ± 8.0 years) with POAG; and 144 (95 men, 49 women; age, 61.2 ± 7.9 years) who were free of ocular disease. Participants answered a questionnaire on MVC experience during the previous 10 years, past driving experience, and daily driving habits. The POAG group was subdivided into three groups according to disease severity (mild, moderate, or severe), to assess the relationship between POAG severity and MVC. RESULTS A statistically significant association between POAG severity and MVC frequency was observed; 3.5% of the controls, 0.0% of the mild POAG group, 3.9% of the moderate POAG group, and 25.0% of the severe POAG group had experienced MVCs (P = 0.007, Cochran-Armitage trend test). The severe POAG group had experienced a much higher frequency of MVCs during the surveyed period than had the control group (P < 0.010; Fishers exact test). Logistic regression analyses to account for confounding factors (age, presence of diabetes mellitus, driving history, time spent driving per day, and best corrected visual acuity in the better or worse eye) produced consistent results. CONCLUSIONS Advanced POAG with marked visual field defects may be a risk factor for MVCs.

Retinal Aging and Sirtuins

The process of aging involves the accumulating changes in the microenvironment that lead to cell senescence or apoptosis, and subsequent tissue or organ dysfunction. Multiple extrinsic and intrinsic events that cause DNA instability are associated with aging. Cells containing unstable DNA are biologically vulnerable, and if the DNA damage is too great for the cell to repair, it becomes senescent or dies by apoptosis. Thus, the cell’s capacity to repair its DNA determines the progress of aging, at least in part. Here, we focus on the sirtuins, the mammalian homologs of the yeast life-span-extending molecule, Sir2. Among the sirtuin family proteins in mammals, the one most similar to yeast Sir2 is SIRT1, which is involved in multiple pathways, including the repair of DNA double-strand breaks. Although the role of SIRT1 in mammalian longevity is not clear, it is expressed throughout the retina, where it may suppress aging. In fact, a mutant mouse model of retinal degeneration shows an abnormal subcellular localization of SIRT1 protein and accelerated retinal cell apoptosis. Further analyses are required to elucidate the mechanism of DNA damage and repair, including the contributions of the sirtuins, in the aged or diseased retinas, which will help us understand the mechanisms of retinal aging.

Increased serum total antioxidant status and decreased urinary 8-hydroxy-2'-deoxyguanosine levels in patients with normal-tension glaucoma.

Acta Ophthalmol. 2010: 88: e259–e264

Lead Accumulation as Possible Risk Factor for Primary Open-Angle Glaucoma

We evaluated the association between hair lead concentrations and primary open-angle glaucoma. Ninety-eight Japanese patients (40 males, 58 females; average age 57.6±10.8 years) with primary open-angle glaucoma and control subjects (131 males, 114 females; average age 56.0±12.8 years) were recruited in this study. Hair lead levels were measured by inductively coupled plasma mass spectrometry. Hair lead concentrations between primary open-angle glaucoma and control groups were compared using Mann–Whitney U test. As a subgroup analysis, we compared hair lead concentrations between low-tension glaucoma, high-tension glaucoma, and control groups using one-factor analysis of variance. Lead accumulation levels were significantly higher in the female subjects with primary open-angle glaucoma compared to the control group (P=0.03). Lead accumulation levels were significantly higher in female patients with low intraocular pressure compared to control group 2 (P=0.02). A higher hair lead level, which reflects the total body burden of lead, was observed to be associated with primary open-angle glaucoma in females especially with low-tension glaucoma. Accumulation of lead may be an unrecognized risk factor of non-pressure-dependent glaucomatous optic neuropathy.