EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY Selim Doganay, MD¹; Cem Cankaya, MD¹; Alpay Alkan, MD² Inonu University School of Medicine, Malatya-Turkey ¹ Department of Ophthalmology, ² Department of Radiology Authors have no financial or proprietary interest in any instrument or products used in this study

Purpose  To determine whether metabolite changes in cellular level occur in vitreous fluid and corpus geniculatum laterale (CGL) in patients with glaucoma by magnetic resonance spectroscopy (MRS). EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY

Introduction  Glutamate is an important transmitter existing widely in central nervous system (CNS) and responsible for excitatory transmission. 1  Under the light of the apoptosis theory indicated as a factor in glaucoma pathophysiology, an increase in the level of glutamate, which has known neurotoxic effects on optic disc, vitreous fluid and corpus geniculatum laterale, is expected. 2-7  Magnetic Resonance Spectroscopy (MRS) is a diagnostic method which is able to evaluate biochemical structure and metabolites of tissues non- invasively and to show them in single spectrum. 8 EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY

Materials and methods  29 eyes of 29 patients with glaucoma, no existing ocular pathology and systemic disease (group 1) and 13 eyes of 13 healthy individuals whose routine ophthalmologic examinations were normal (group 2) were included in the study.  Single voxel MRS examination was performed by placing ROI (Region of interest) in vitreous fluid and corpus geniculatum laterale (CGL). Glutamate-glutamine (Glx)/Creatin (Cr) ratios and lactate peaks in the vitreous fluid, and the Glx/Cr, N-acetyl aspartate (NAA)/Cr, Choline (Cho)/Cr ratios in the ipsilateral area of CGL were evaluated. EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY

 Patients who had conditions such as previous ocular surgery, laser therapy, trauma history, corneal and lens pathologies preventing perform ocular fundus examination, uveitis, posterior segment pathologies, neurodegenerative diseases of central nervous system, and systemic diseases like diabetes and hypertension that may predispose to these situations were excluded from the study. EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY

MRS Technique  Single voxel MRS examination was performed by placing ROI (region of interest) in corpus vitreous and corpus geniculatum laterale (CGL) on the same side.  During placing ROI, it was avoided to contact to bone, vessel, air and fat.  A 13x13 mm (TE: 31 ms) ROI in vitreous fluid and a 12x12 mm (TE: 136 ms) ROI in CGL were placed using PRESS (Point Resolved Spectroscopy) technique.  ROI was placed by localizing CGL anatomically with 3 plane thin section MRI views. EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY

SD: Standard deviation, Min: Minimum, Max: Maximum, Glx: Glutamate-glutamine, Cr: Creatine, NAA: N-acetylaspartate, Cho: Choline; Group1: Patients with glaucoma, Group 2: Healthy individuals EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY The mean Glx/Cr, NAA/Cr, and Cho/Cr ratios in both vitreous body and corpus geniculatum laterale region in Groups. Vitreous fluid Corpus geniculatum laterale Glx/Cr (Mean±SD) (min-max) Glx/Cr (Mean±SD) (min-max) NAA/Cr (Mean±SD) (min-max) Cho/Cr (Mean±SD) (min-max) Group ±8.58 ( ) 1.29±1.21 ( ) 1.15±0.56 ( ) 1.36±1.30 ( ) Group ±1.51 ( ) 0.38±0.35 ( ) 1.44±0.57 ( ) 0.79±0.32 ( ) Results

EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY *p<0.05, VF: Vitreous fluid, CGL: Corpus geniculatum laterale, Glx: Glutamate-glutamine, Cr: Creatine, NAA: N-acetylaspartate, Cho: Choline, 1: Patients with glaucoma (Group 1), 2: Healthy individuals (Group 2)

Glx: Glutamate-glutamine EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY Increased Glx/Cr ratio was detected between ppm in a glaucoma patient’s vitreous fluid by MRS

NAA: N-acetylaspartate, Glx: Glutamate-glutamine, Cr: Creatine, Cho: Choline EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY NAA peaks were detected at 2,0 ppm, Glx peaks were detected at 2,1-2,5 ppm, Cr peaks were detected at 3,02 ppm, and Cho peaks were detected at 3,2 ppm in the corpus geniculatum laterale region of a patient with glaucoma by MRS.

Lactate peak EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY A lactate peak was detected at 1.32 ppm in 11 glaucoma patients ‘ vitreous fluid by MRS.

Discussion  Studies show that glaucoma leads to neuronal loss in optic nerve and CGL region. It is a natural consequence that these changes occurred in CGL alter some metabolites. 2-5,7 Our study has demonstrated that MRS method reveals these changes.  We think that MRS method, which is able to measure biochemical structure and metabolites of tissues non- invasively, would move the diagnosis of glaucoma one- step forward and open new horizons in understanding and diagnosing of glaucoma at cellular level. EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY

References 1.Honkanen RA, Baruah S, Zimmerman MB, et al. Vitreous aminoasid concentrations in patients with glaucoma undergoing vitrectomy. Arch Ophthalmol 2003; 121: Gupta N, Greenberg G, Tilly NL, et al. Atrophy of the lateral geniculate nucleus in human glaucoma detected by magnetic resonance imaging. Br J Ophthalmol 2009; 93: Yucel YH, Zhang Q, Weinreb RN, et al. Atrophy of Relay Neurons in Magno- and Parvocellular Layers in the Lateral Geniculate Nucleus in Experimental Glaucoma. Invest Ophthalmol Vis Sci 2001; 42: RJ Casson. Possible role of excitotoxicity in the pathogenesis of glaucoma. Clin Exp Ophthalmol 2006; 34: Okuno T, Oku H, Sugiyama T, et al. Glutamate level in optic nevre head is increased by artificial elevation of intraocular pressure in rabbits. Exp Eye Res 2006; 82: Dreyer EB, Zurakowski D, Schumer RA, et al. Elevated glutamate levels in vitreous body of humans and monkeys with glaucoma. Arch Ophthalmol 1996; 114: Gupta N, Ang LC, Tilly NL, et al. Human glaucoma and neural degeneration in intracranial optic nevre, lateral geniculate nucleus and visual cortex. Br J Ophthalmol 2006; 90: Castillo M, Kwock L, Mukherji SK. Clinical applications of proton MR spectroscopy. Am J Neuroradiol 1996; 17:1-15. EVALUATION OF GLUTAMATE AND OTHER AMINO ACID LEVELS IN GLAUCOMA PATIENT WITH MR SPECTROSCOPY: PRELIMINARY STUDY