Shinji Yoneda

Vitreous fluid levels of β-amyloid(1–42) and tau in patients with retinal diseases

PurposeA decrease in β-amyloid1–42 (Aβ42) and an increase in tau in the cerebrospinal fluid are reported to be characteristic phenomena in Alzheimer’s disease patients. To test the idea that Aβ42 and tau contribute to the development of retinal diseases, we measured Aβ42 and tau concentrations in the vitreous fluid from patients with macular hole (n = 13), diabetic retinopathy (n = 15), or glaucoma concurrent with other ocular diseases (n = 8).MethodsVitreous samples were collected from patients who underwent vitrectomy, and sensitive and specific enzyme-linked immunosorbent assays were used to determine the concentrations of Aβ42 and tau.ResultsBy comparison with the levels in the control macular-hole patients (33.9 ± 7.1 pg/ml for Aβ42; 3.3 ± 3.2 pg/ml for tau), there was a significant decrease in the Aβ42 level and a significant increase in the tau level in patients with diabetic retinopathy (1.8 ± 1.9 pg/ml for Aβ42, P = 0.002; 153.7 ± 71.6 pg/ml for tau, P = 0.041) or glaucoma concurrent with other ocular diseases (2.8 ± 1.8 pg/ml for Aβ42, P = 0.006; 113.6 ± 43.1 pg/ml for tau, P = 0.023).ConclusionsOur findings indicate the possibility of a role for Aβ42 and tau in the pathogenesis of some retinal diseases.

Topiramate reduces excitotoxic and ischemic injury in the rat retina.

The effects of topiramate, a drug used clinically as an anti-epileptic, were investigated in excitotoxin-induced neurotoxicity models involving two different retinal primary cultures and in a rat model of retinal ischemic injury. For the in vitro studies, we used retinal-neuron cultures from rat embryos and purified retinal ganglion cells (RGCs) from newborn rats. In the retinal-neuron cultures, neurotoxicity was induced by a 10-min exposure to 1 mM glutamate or (+/-)-a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). In RGCs, neurotoxicity was induced by incubation for 3 days in a culture medium containing 25 microM glutamate. For the in vivo study, retinal ischemia was induced by elevating intraocular pressure to 130 mmHg for 45 min, and topiramate was administered intraperitoneally before and after the ischemia. Retinal damage was evaluated by measuring the number of cells in the ganglion cell layer (GCL) and the thickness of the inner plexiform layer (IPL), and by examining the a- and b-waves of the electroretinogram (ERG). Topiramate (> or =1 microM) markedly reduced the neuronal cell death induced by each of the excitotoxins in rat retinal-neuron cultures and in RGCs. Ischemia caused a decrease in GCL cells and in IPL thickness, and a diminution of the ERG waves. Histopathologic and functional analyses indicated that systemic treatment with topiramate prevented ischemia-induced damage in a dose-dependent manner. In conclusion, topiramate was protective against excitotoxic and ischemic retinal-neuron damage in vitro and in vivo, respectively. Therefore, it may be useful for treatment of the retina-related diseases such as central retinal artery occlusion, diabetic retinopathy, and glaucoma.

Neuroprotective effects of β-secretase inhibitors against rat retinal ganglion cell death

Beta-secretase, an enzyme participating in amyloid beta-peptide generation, is thought to be involved in the pathogenesis of Alzheimers disease. We examined the effects of beta-secretase inhibitors such as N-benzyloxycarbonyl-Val-Leu-leucinal (Z-VLL-CHO) and H-EVNstatineVAEF-NH2 (GL-189) on glutamate-induced retinal ganglion cell (RGC) death in vitro. In cultures of purified RGCs from neonatal rats, 2-day exposure to 25 microM glutamate induced RGC death, and Z-VLL-CHO (100 nM) and GL-189 (1 microM) had neuroprotective effects. We also found out that Z-VLL-CHO showed a neuroprotective effect on retinal damage induced by optic nerve crush in vivo. Thus, beta-secretase could be a potential target for therapy of neurodegenerative retinal diseases.

Dual effects of interleukin-1β on N-methyl-d-aspartate-induced retinal neuronal death in rat eyes

In this study we determine if interleukin-1beta (IL-1beta) modulates N-methyl-D-aspartate (NMDA)-induced retinal damage. Sprague-Dawley rats were anesthetized with inhalation of halothane, after which a single injection of 5 microl of IL-1beta (0.1 to 10 ng/eye) (and/or IL-1 receptor antagonist (IL-1ra)) for experimental eyes was administered. Two days later (or simultaneously), NMDA (20 nmol) was injected into the vitreous space. One week later, each eye was enucleated and transverse sections were subjected to morphometric analysis. Enzyme-linked immunosorbent assay (ELISA) was conducted for the determination of IL-1beta levels in retina. Immunohistochemical and immunoblot studies were also performed. In eyes that received an intravitreal injection of IL-1beta (0.1 to 10 ng/eye), significant thinning of the inner plexiform layer (IPL) was observed (P<0.05). Immunohistochemical and ELISA studies demonstrated upregulated expression of IL-1beta in retinas that had undergone NMDA injection. Treatment with 10 ng of IL-1ra induced a protective effect against NMDA-induced retinal damage. Pretreatment with IL-1beta induced a significant protective effect on NMDA-induced retinal damage. Our studies suggest that IL-1beta induces neuronal cell death directly, as shown by the protective effects of IL-1ra, but has a protective effect on NMDA-induced retinal damage indirectly after an incubation time of at least 2 days.

Adenosine protects cultured retinal neurons against NMDA-induced cell death through A1 receptors.

Purpose. To determine whether adenosine can protect cultured retinal neurons, consisting mainly of amacrine cells, from N-methyl-D-aspartate (NMDA)-induced neurotoxicity, and to determine whether agonists and antagonists of adenosine receptors also have a protective effect. Methods. Cultured retinal neurons obtained from fetal Wistar rats (gestational age 18–19 days) were maintained for 10–11 days. Neurons were exposed to NMDA (1.0 mM) for 10 min with or without adenosine or to NMDA with adenosine receptor agonists or antagonists. Neuronal death was assessed by the trypan-blue exclusion method 24 hr after the exposure. Results. Adenosine at doses of 0.01 μM and higher significantly protected (p < 0.05, Dunnett) primary cultured fetal rat retinal neurons from apoptotic and/or necrotic death induced by NMDA (1.0 mM). The protective effect of adenosine (10 μM) against NMDA-induced neuronal death was lost by simultaneous exposure to selective A1 receptor antagonist but not to A2a receptor antagonist. Selective A1 receptor agonists had similar effects as adenosine, but A2a receptor agonists and 8-Br-cyclic AMP had no effect on cell viability. Conclusions. Adenosine can protect cultured retinal neurons against NMDA-induced cell death via the A1 receptor.

Effects of poly(ADP-ribose) polymerase inhibitor on NMDA-induced retinal injury.

Purpose. Excessive activation of poly(ADP-ribose) polymerase (PARP), a nuclear enzyme that is activated by DNA damage, leads to neuronal cell death through depletion of ATP. The purpose of this study was to determine whether inhibition of PARP has some neuroprotective effects on the N-methyl-D-aspartate (NMDA)-induced functional and morphological injury to the rabbit retina. Methods. Visually evoked potentials (VEPs) were recorded at different times after an intravitreal injection of NMDA (200, 660, and 2000 nmol) alone, or NMDA with 3-aminobenzamide (ABA, 200 nmol), a PARP inhibitor, or with MK-801 (200 nmol), an NMDA antagonist. The physiological changes were followed for 2 weeks, after which the eyes were enuculeated and prepared for histological examinations. Results. Intravitreal injections of NMDA reduced the amplitudes of rabbit VEPs and the number of cells in the retinal ganglion cell layer in a dose-dependent manner. No significant changes could be detected in the bright-flash electroretinograms (ERGs). Simultaneous injection of MK-801 (200 nmol) significantly diminished the changes induced by intravitreal NMDA. 3-Aminobenzamide (ABA) (200 nmol) also suppressed these changes, but its effects were less than those of MK-801. Conclusions. NMDA-induced retinal damage can be detected by VEPs, and PARP inhibition has some neuroprotective effects on the NMDA-induced retinal damage.