Oxidative injury by peroxynitrite in neural and vascular tissue of the lateral geniculate nucleus in experimental glaucoma

doi:10.1016/j.exer.2004.08.016

Experimental Eye Research

Volume 80, Issue 1, January 2005, Pages 43-49

https://doi.org/10.1016/j.exer.2004.08.016 Get rights and content

Abstract

In glaucoma, recent studies show that neural degeneration extends beyond the retinal ganglion cells to include target neurons in the lateral geniculate nucleus of the brain. The pathobiology of LGN degeneration in glaucoma is as yet unknown. We investigated whether peroxynitrite-mediated oxidative stress plays a role in glaucomatous degeneration of the LGN.

Nitrotyrosine (NT), a marker for peroxynitrite-mediated oxidative injury, was studied in right LGN sections from monkeys with experimental unilateral glaucoma in the right eye and from normal controls. Immunoreactivity for NT was analyzed using bright-field microscopy. The density of NT profiles localized in neural tissue was determined for LGN layers (2,3,5) connected to the glaucoma eye and LGN layers (1,4,6) connected to the non-glaucoma eye. Density was calculated for each LGN layer by dividing the number of NT profiles by the cross-sectional area of each LGN layer. Blood vessels in each LGN were examined for NT formation.

NT formation was detected in LGN layers of all monkeys with glaucoma. Quantitative analysis revealed that compared to controls, the density of NT profiles was increased in monkeys with glaucoma in LGN layers connected to glaucoma and non-glaucoma eyes. The mean density of NT profiles (±sem) in neural tissue was significantly increased in glaucoma LGN layers compared to those of controls (2·30±0·56 vs. 0·29±0·12; P=0·016). Nitrotyrosine was readily apparent in LGN blood vessel endothelium in glaucoma, and not detected in blood vessels of control LGNs.

The presence of NT in neural and vascular tissue of the glaucomatous LGN implicates peroxynitrite-mediated oxidative cell injury in the pathobiology of central neural degeneration in glaucoma.

Introduction

In glaucoma, a leading cause of worldwide irreversible blindness, the pathological correlate of vision loss is the death of retinal ganglion cells (RGCs) (Garcia-Valenzuela et al., 1995, Quigley et al., 1995). Recent evidence suggests that glaucomatous damage is not confined to the RGCs, and that the neural degeneration extends to the lateral geniculate nucleus (LGN), their major target structure in the brain (Weber et al., 2000, Yücel et al., 2000, Gupta and Yücel, 2001, Yücel et al., 2001, Yücel et al., 2003). In experimental primate glaucoma monkeys with unilateral glaucoma, the degenerative changes of cell death and shrinkage are observed for LGN layers connected to the glaucoma eye, in addition to LGN layers connected to the fellow non-glaucoma eye (Weber et al., 2000, Yücel et al., 2003).

Several mechanisms have been proposed to contribute to glaucomatous RGC cell death including oxidative injury (Fechtner and Weinreb, 1994, Weinreb and Khaw, 2004). Although the pathological processes responsible for degenerative changes in the LGN in glaucoma are not yet known, oxidative damage may play a role. In experimental rat glaucoma (Neufeld, 1999, Shareef et al., 1999) and in naturally occurring human glaucoma (Neufeld et al., 1997, Neufeld, 1999, Liu and Neufeld, 2000), nitric oxide synthase-2 (NOS-2), an inducible enzyme responsible for nitric oxide (NO) synthesis, shows increased expression in the optic nerve head. The interaction of excessive NO with superoxide produces peroxynitrite, (Huie and Padmaja, 1993) a powerful oxidant causing damage to multiple cell components including proteins (Torreilles et al., 1999, Nucci et al., 2003). Peroxynitrite nitrates the tyrosine residue on proteins to form nitrotyrosine (NT), used as a footprint of peroxynitrite-mediated oxidative damage (Ischiropoulos et al., 1992). In the optic nerve head and blood vessels in human glaucoma, NT has been detected, implicating oxidative injury in glaucomatous optic nerve damage (Neufeld, 1999). Inhibitors of NOS appear protective against RGC loss in experimental glaucoma, supporting a role for oxidative damage in glaucoma (Neufeld et al., 1999, Neufeld et al., 2002). Oxidative injury by detection of NT has been described in neurodegenerative diseases such as Alzheimer's (Smith, 1997), and Parkinson's (Good et al., 1998) in neural tissue and blood vessels of relevant brain structures. The goal of this study was to determine, using NT as a marker, whether peroxynitrite-mediated oxidative cell damage is evident in glaucoma in the neural and/or vascular tissue of the LGN.

Section snippets

Subjects

All studies were performed following the guidelines of the Statement on the Use of Animals in Ophthalmic and Visual Research. Five young adult monkeys (cynomolgus; Macaca fascicularis n=4 (V64, 91043, M35 and 93) and rhesus; Macaca mulatta n=1 (MK23)) with experimental glaucoma induced in the right eye by argon laser scarification of the trabecular meshwork (ALT) (Gaasterland and Kupfer, 1974), and four normal control young adult cynomologus monkeys were studied. In glaucoma monkeys, survival

Nitrotyrosine in the LGN in glaucoma. Neural LGN

In control monkeys, NT-immunoreactivity was generally absent in the LGN layers (Fig. 1A). In glaucoma monkeys, NT profiles were present in each of the LGN sections and appeared in layers connected to the glaucoma and non-glaucoma eyes (Fig. 1B–D). In some cases, dense NT staining was observed in both the nucleus and the cytoplasm (Fig. 1C,D).

Blood vessels of the LGN

In control monkeys, NT-immunoreactivity was absent in the blood vessels in all LGN sections (Fig. 2A). In contrast, for all glaucoma monkeys, blood vessel

Discussion

We present findings of increased NT formation in neural tissue and blood vessels of the LGN in monkeys with unilateral experimental glaucoma. In this model, cell death and shrinkage of LGN neurons has been previously described (Weber et al., 2000, Yücel et al., 2000, Yücel et al., 2001, Gupta and Yücel, 2003, Yücel et al., 2003). The observed increase in NT formation suggests that peroxynitrite-mediated oxidative damage contributes to LGN degeneration in glaucoma. Our findings of NT in the

Acknowledgements

This study was supported by the Vision Science Research Program, University of Toronto (AL) and Glaucoma Research Foundation, San Francisco (YHY). Supported also in part by Glaucoma Research Society of Canada (NG, YHY), National Eye Institute (EY02698, PLK) Research to Prevent Blindness (PLK), Ocular Physiology Research and Education Foundation (PLK), Sophie and Arthur Brody Fund (RNW), and Harry Newmann Foundation (NG).

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Oxidative injury by peroxynitrite in neural and vascular tissue of the lateral geniculate nucleus in experimental glaucoma

Abstract

Introduction

Section snippets

Subjects

Nitrotyrosine in the LGN in glaucoma. Neural LGN

Blood vessels of the LGN

Discussion

Acknowledgements

Surv. Ophthalmol.

Exp. Eye Res.

Brain Res.

Arch. Biochem. Biophys.

Brain Res.

Surv. Ophthalmol.

Toxicol. Lett.

Neurosci. Lett.

Brain Res. Brain Res. Rev.

Lancet

Prog. Retin. Eye Res.

Upregulation of protein-tyrosine nitration in the anterior horn cells of amyotrophic lateral sclerosis

Neurol. Res.

Glaucoma in primates: cytochrome oxidase reactivity in parvo- and magnocellular pathways

Invest. Ophthalmol. Vis. Sci.

Superoxide dismutase catalyzes nitration of tyrosines by peroxynitrite in the rod and head domains of neurofilament-L

J. Neurochem.

Peroxynitrite induces tryosine nitration and modulates tyrosine phosphorylation of synaptic proteins

J. Neurochem.

Experimental glaucoma in the rhesus monkey

Invest. Ophthalmol.

Protein nitration in Parkinson's disease

J. Neuropathol. Exp. Neurol.

Glaucoma and the brain

J. Glaucoma.