Retinal Capillary Density Reduction Contributes to Dysthyroid Optic Neuropathy via an L-Arginine-NO Pathway: A Metabonomics and Clinical Trial Study

Abstract

Dysthyroid optic neuropathy (DON) is the most severe complication of thyroid-associated ophthalmopathy (TAO). Although recent evidence indicates that reduced retinal capillary density (RCD) may increase DON risk independently of orbital apex crowding, the underlying mechanisms and associated metabolic reprogramming remain unclear. In a retrospective analysis of TAO patients with and without DON, those with DON demonstrated elevated pulse pressure (PP), decreased RCD, and higher incidences of dyslipidemia, hyperglycemia, and internal carotid artery calcification. To explore the metabolic basis of these findings, untargeted and targeted metabolomic profiling of plasma from TAO patients and healthy controls was conducted, identifying DON-associated abnormalities in the L-arginine metabolic pathway (registration number: ChiCTR2000035598). Integrating these results with existing literature suggests that oxidative stress drives dysregulated L-arginine–nitric oxide (NO) metabolism, contributing to progressive RCD loss. In early-stage DON patients treated with oral L-arginine, improvements in RCD, PP, and visual function were observed (registration number: ChiCTR2300076962). Further analyses implicated reduced NO bioavailability, due to L-arginine depletion and endothelial NO synthase (eNOS) uncoupling, as a key contributor to declining RCD. Given that oral L-arginine can improve PP via NO-mediated pathways in cardiovascular disease, our findings offer a promising new therapeutic direction for DON management.

Keywords

dysthyroid optic neuropathy / L-arginine / nitric oxide / retinal capillary density / thyroid-associated ophthalmopathy

References

[1] K. A. Ponto, H. Binder, T. Diana, et al., “Prevalence, Phenotype, and Psychosocial Well-Being in Euthyroid/Hypothyroid Thyroid-Associated Orbitopathy,” Thyroid: Official Journal of the American Thyroid Association 25, no. 8 (2015): 942–948.

[2] J. H. Lazarus, “Epidemiology of Graves' Orbitopathy (GO) and Relationship With Thyroid Disease,” Best Practice & Research Clinical Endocrinology & Metabolism 26, no. 3 (2012): 273–279.

[3] G. B. Bartley, V. Fatourechi, E. F. Kadrmas, et al., “Long-Term Follow-Up of Graves Ophthalmopathy in an Incidence Cohort,” Ophthalmology 103, no. 6 (1996): 958–962.

[4] R. Gupta, R. Thomas, F. Almukhtar, and A. Kiran, “Visual Morbidity in Thyroid Eye Disease in Asian Indian Patients,” Indian Journal of Ophthalmology 68, no. 8 (2020): 1622–1627.

[5] N. Currò, C. Guastella, G. Pirola, et al., “Clinical and Visual Outcomes of Dysthyroid Optic Neuropathy After Surgical Orbital Decompression,” Thyroid: Official Journal of the American Thyroid Association 33, no. 6 (2023): 743–751.

[6] D. McKeag, C. Lane, J. H. Lazarus, et al., “Clinical Features of Dysthyroid Optic Neuropathy: A European Group on Graves' Orbitopathy (EUGOGO) Survey,” British Journal of Ophthalmology 91, no. 4 (2007): 455–458.

[7] H. Jin, X. Yu, S. Cao, et al., “Selective Deficits of S-Cone in Thyroid-Associated Ophthalmopathy Patients Without Clinical Signs of Dysthyroid Optic Neuropathy,” Frontiers in Neuroscience 16 (2022): 990425.

[8] Y. Tu, H. Jin, M. Xu, et al., “Reduced Contrast Sensitivity Function Correlated With Superficial Retinal Capillary Plexus Impairment in Early Stage of Dysthyroid Optic Neuropathy,” Eye and Vision 10, no. 1 (2023): 11.

[9] J. J. Khong, S. Finch, C. De Silva, et al., “Risk Factors for Graves' Orbitopathy; the Australian Thyroid-Associated Orbitopathy Research (ATOR) Study,” Journal of Clinical Endocrinology and Metabolism 101, no. 7 (2016): 2711–2720.

[10] S. Rath, M. Pattnaik, D. Tripathy, S. Mohapatra, B. Panigrahy, and M. H. Ali, “Sight-Threatening Thyroid Eye Disease: Role of Diabetes Mellitus and Interaction With Other Risk Factors,” Ophthalmic Plastic and Reconstructive Surgery 37, no. 4 (2021): 352–360.

[11] N. S. Poonam, M. S. Alam, P. Oberoi, and B. Mukherjee, “Dysthyroid Optic Neuropathy: Demographics, Risk Factors, Investigations, and Management Outcomes,” Indian Journal of Ophthalmology 70, no. 12 (2022): 4419–4426.

[12] Y. Wu, Y. Tu, L. Bao, et al., “Reduced Retinal Microvascular Density Related to Activity Status and Serum Antibodies in Patients With Graves' Ophthalmopathy,” Current Eye Research 45, no. 5 (2020): 576–584.

[13] T. Zhang, W. Xiao, H. Ye, R. Chen, Y. Mao, and H. Yang, “Peripapillary and Macular Vessel Density in Dysthyroid Optic Neuropathy: An Optical Coherence Tomography Angiography Study,” Investigative Ophthalmology & Visual Science 60, no. 6 (2019): 1863–1869.

[14] Y. Wu, Y. Tu, C. Wu, et al., “Reduced Macular Inner Retinal Thickness and Microvascular Density in the Early Stage of Patients With Dysthyroid Optic Neuropathy,” Eye and Vision 7 (2020): 16.

[15] Y. Wu, Q. Yang, L. Ding, et al., “Peripapillary Structural and Microvascular Alterations in Early Dysthyroid Optic Neuropathy,” Eye and Vision 9, no. 1 (2022): 30.

[16] K. T. Lewis, J. R. Bullock, R. T. Drumright, M. J. Olsen, and A. D. Penman, “Changes in Peripapillary Blood Vessel Density in Graves' Orbitopathy After Orbital Decompression Surgery as Measured by Optical Coherence Tomography Angiography,” Orbit 38, no. 2 (2019): 87–94.

[17] J. H. Wu, L. Y. Luo, H. Zhou, Y. Wu, J. Zhang, and J. W. Cheng, “Reduced Choroidal Peripapillary Capillaries in Thyroid-Associated Ophthalmopathy With Early Stage of Dysthyroid Optic Neuropathy,” International Journal of Ophthalmology 15, no. 7 (2022): 1135–1141.

[18] J. Ye, W. Liu, X. Hu, et al., “Elevated Pulse Pressure Correlated With Reduced Retinal Peripapillary Capillary in Thyroid-Associated Ophthalmology With Visual Field Defect,” Frontiers in Endocrinology 13 (2022): 941051.

[19] Z. Li, M. Wang, J. Tan, et al., “Single-Cell RNA Sequencing Depicts the Local Cell Landscape in Thyroid-Associated Ophthalmopathy,” Cell Reports Medicine 3, no. 8 (2022): 100699.

[20] K. De Bock, M. Georgiadou, S. Schoors, et al., “Role of PFKFB3-Driven Glycolysis in Vessel Sprouting,” Cell 154, no. 3 (2013): 651–663.

[21] Z. Dagher, N. Ruderman, K. Tornheim, and Y. Ido, “Acute Regulation of Fatty Acid Oxidation and Amp-Activated Protein Kinase in Human Umbilical Vein Endothelial Cells,” Circulation Research 88, no. 12 (2001): 1276–1282.

[22] H. Huang, S. Vandekeere, J. Kalucka, et al., “Role of Glutamine and Interlinked Asparagine Metabolism in Vessel Formation,” Embo Journal 36, no. 16 (2017): 2334–2352.

[23] S. Xu, I. Ilyas, P. J. Little, et al., “Endothelial Dysfunction in Atherosclerotic Cardiovascular Diseases and Beyond: From Mechanism to Pharmacotherapies,” Pharmacological Reviews 73, no. 3 (2021): 924–967.

[24] N. Froger, L. Moutsimilli, L. Cadetti, et al., “Taurine: The Comeback of a Neutraceutical in the Prevention of Retinal Degenerations,” Progress in Retinal and Eye Research 41 (2014): 44–63.

[25] H. Jian, Y. Wang, L. Ou, and W. He, “Altered Peripapillary Vessel Density and Nerve Fiber Layer Thickness in Thyroid-Associated Ophthalmopathy Using Optical Coherence Tomography Angiography,” International Ophthalmology 42, no. 3 (2022): 855–862.

[26] H. Sener, F. Ozer, M. Unlu, and D. Gulmez Sevim, “Automated Evaluation of Parapapillary Choroidal Microvasculature in Thyroid Eye Disease,” International Ophthalmology 43, no. 11 (2023): 4323–4331.

[27] X. Wang, S. Yang, H. Ye, et al., “Disulfiram Exerts Antiadipogenic, Anti-Inflammatory, and Antifibrotic Therapeutic Effects in an in Vitro Model of Graves' Orbitopathy,” Thyroid: Official Journal of the American Thyroid Association 32, no. 3 (2022): 294–305.

[28] L. Bartalena, G. J. Kahaly, L. Baldeschi, et al., “The 2021 European Group on Graves' Orbitopathy (EUGOGO) Clinical Practice Guidelines for the Medical Management of Graves' Orbitopathy,” European Journal of Endocrinology 185, no. 4 (2021): G43–G67.

[29] M. Liang, Z. Wang, H. Li, et al., “l-Arginine Induces Antioxidant Response to Prevent Oxidative Stress via Stimulation of Glutathione Synthesis and Activation of Nrf2 Pathway,” Food and Chemical Toxicology 115 (2018): 315–328.

[30] N. Toda and M. Nakanishitoda, “Nitric Oxide: Ocular Blood Flow, Glaucoma, and Diabetic Retinopathy,” Progress in Retinal and Eye Research 26, no. 3 (2007): 205–238.

[31] B. Poeggeler, S. K. Singh, K. Sambamurti, and M. A. Pappolla, “Nitric Oxide as a Determinant of Human Longevity and Health Span,” International Journal of Molecular Sciences 24, no. 19 (2023): 14533.

[32] Y. Oe, S. Mitsui, E. Sato, et al., “Lack of Endothelial Nitric Oxide Synthase Accelerates Ectopic Calcification in Uremic Mice Fed an Adenine and High Phosphorus Diet,” American Journal of Pathology 191, no. 2 (2021): 283–293.

[33] J. Richards, I. El-Hamamsy, S. Chen, et al., “Side-Specific Endothelial-Dependent Regulation of Aortic Valve Calcification,” American Journal of Pathology 182, no. 5 (2013): 1922–1931.

[34] Y. Wu, Y. Ding, T. Ramprasath, and M.-H. Zou, “Oxidative Stress, GTPCH1, and Endothelial Nitric Oxide Synthase Uncoupling in Hypertension,” Antioxid Redox Signaling 34, no. 9 (2021): 750–764.

[35] S. Karbach, P. Wenzel, A. Waisman, T. Munzel, and A. Daiber, “eNOS Uncoupling in Cardiovascular Diseases—The Role of Oxidative Stress and Inflammation,” Current Pharmaceutical Design 20, no. 22 (2014): 3579–3594.

[36] D. Khalaf, M. Krüger, M. Wehland, M. Infanger, and D. Grimm, “The Effects of Oral L-Arginine and L-Citrulline Supplementation on Blood Pressure,” Nutrients 11, no. 7 (2019): 1679.

[37] F. Leo, T. Suvorava, S. K. Heuser, et al., “Red Blood Cell and Endothelial eNOS Independently Regulate Circulating Nitric Oxide Metabolites and Blood Pressure,” Circulation 144, no. 11 (2021): 870–889.

[38] J. T. Mammedova, A. V. Sokolov, I. S. Freidlin, and E. A. Starikova, “The Mechanisms of L-Arginine Metabolism Disorder in Endothelial Cells,” Biochemistry 86, no. 2 (2021): 146–155.

[39] S. Hess, G. Baker, G. Gyenes, R. Tsuyuki, S. Newman, and J.-M. Le Melledo, “Decreased Serum L-Arginine and L-Citrulline Levels in Major Depression,” Psychopharmacology 234, no. 21 (2017): 3241–3247.

[40] D. G. Harrison, “Cellular and Molecular Mechanisms of Endothelial Cell Dysfunction,” Journal of Clinical Investigation 100, no. 9 (1997): 2153–2157.

[41] P. Vallance and N. Chan, “Endothelial Function and Nitric Oxide: Clinical Relevance,” Heart 85, no. 3 (2001): 342–350.

[42] W. C. Sessa, M. Hecker, J. A. Mitchell, and J. R. Vane, “The Metabolism of L-Arginine and Its Significance for the Biosynthesis of Endothelium-Derived Relaxing Factor: L-Glutamine Inhibits the Generation of L-Arginine by Cultured Endothelial Cells,” PNAS 87, no. 21 (1990): 8607–8611.

[43] R. H. Boger, “The Pharmacodynamics of L-Arginine,” Journal of Nutrition 137 (2007): 1650S–1655S.

[44] G. Wu, C. J. Meininger, D. A. Knabe, F. W. Baze, and J. M. Rhoads, “Arginine Nutrition in Development, Health and Disease,” Current Opinion in Clinical Nutrition and Metabolic Care 3, no. 1 (2000): 59–66.

[45] G. B. Bartley, “Evolution of Classification Systems for Graves' Ophthalmopathy,” Ophthalmic Plastic and Reconstructive Surgery 11, no. 4 (1995): 229–237.

[46] L. Bartalena, L. Baldeschi, A. J. Dickinson, et al., “Consensus Statement of the European Group on Graves' Orbitopathy (EUGOGO) on Management of Graves' Orbitopathy,” Thyroid: Official Journal of the American Thyroid Association 18, no. 3 (2008): 333–346.

[47] M. E. Safar, P. M. Nilsson, J. Blacher, and A. Mimran, “Pulse Pressure, Arterial Stiffness, and End-Organ Damage,” Current Hypertension Reports 14, no. 4 (2012): 339–344.

[48] M. Tölle, A. Reshetnik, M. Schuchardt, M. Höhne, and M. van der Giet, “Arteriosclerosis and Vascular Calcification: Causes, Clinical Assessment and Therapy,” European Journal of Clinical Investigation 45, no. 9 (2015): 976–985.

[49] R. J. Woodcock, J. H. Goldstein, D. F. Kallmes, H. J. Cloft, and C. D. Phillips, “Angiographic Correlation of CT Calcification in the Carotid Siphon,” Ajnr American Journal of Neuroradiology 20, no. 3 (1999): 495–499.

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