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Allison Loiselle, Aruna Rikkers, Nomdo M Jansonius; Biomarkers in glaucoma and tinnitus suggest low nitric oxide bioavailability and excitotoxicity. Invest. Ophthalmol. Vis. Sci. 2020;61(7):989.
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Low nitric oxide (NO) bioavailability and oxidative stress may be common mechanisms behind glaucoma and tinnitus. NO itself diffuses quickly and is difficult to measure, however, certain metabolites can be measured as biomarkers of NO production. The aim of this study was to test these biomarkers of NO in glaucoma patients both with and without tinnitus.
Serum levels of asymmetric dimethylarginine (ADMA), L-arginine (ARG), L-ornithine (ORN), L-citrulline (CIT), L-glutamate (GLU), and L-glutamine (GLN) were assessed in 51 patients with primary open angle glaucoma. Of these, 25 patients had tinnitus and 26 did not; the groups were gender and age similar, and had a similar proton pump inhibitor intake. A Wilcoxon test was used to determine differences between the groups. In addition, patients were compared to reference values of the metabolites of interest in healthy people.
Both GLN, GLU, and the GLN/GLU ratio were higher in those with tinnitus compared to those without tinnitus (P=0.001, P=0.039, P=0.027, respectively). Additionally, median ARG, ORN, and GLU for the 51 patients were outside the reference ranges for healthy people in the expected directions [ARG: 20 μmol/L, ref (20-95), ORN: 231 μmol/L, ref (39-151), GLU: 292 μmol/L, ref (13-113)].
Low ARG and high ORN suggest a decrease in NO bioavailability in all patients. The high GLU in all patients and relatively high GLN in tinnitus patients suggest an increase in excitotoxicity and oxidative stress. Low NO and high excitatory amino acids may be a common underlying mechanism between glaucoma and tinnitus.
This is a 2020 ARVO Annual Meeting abstract.
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