Increased Sulfatation of Orbital Glycosaminoglycans in Graves’ Ophthalmopathy¹

Abstract

Accumulation of interstitial glycosaminoglycans (GAG) in orbital tissue of patients with Graves' ophthalmopathy (GO) leads to edema, increased orbital pressure, and proptosis. In this study, a new, highly sensitive, high performance liquid chromatography method was developed to determine the altered concentration and biochemical composition of different GAG polymers in orbital connective tissue of 27 GO patients and 18 controls. GAG were isolated by tissue homogenization and digestion, followed by sequential enzymatic GAG hydrolysis and high performance liquid chromatographic analysis of the resulting alpha,beta-unsaturated disaccharides. High recovery rates of 78 +/- 6% (mean +/- SE) and a detection limit of 4.0 microg/L (0.01 micromol/L) were obtained. Total tissue GAG amounted to 254 +/- 16 microg/g wet tissue wt in patients and 150 +/- 13 microg/g (P < 0.0001) in controls. Regarding the GAG polymers, marked differences were detected between patients and controls (chondroitin sulfate, 127 +/- 13 vs. 47 +/- 5 microg/g; hyaluronic acid, 56 +/- 5 vs. 34 +/- 4 microg/g; both P < 0.0001; dermatan sulfate, 77 +/- 6 vs. 69 +/- 6 microg/g; P < 0.05). In patients, chondroitin sulfate was the major GAG component (48 +/- 6 vs. 31 +/- 5% of total GAG in controls), whereas dermatan sulfate was dominant in controls (46 +/- 8% vs. 30 +/- 5%). The sulfated disaccharide digestion products were markedly increased (P < 0.0001) in patients, and the ratio of sulfated vs. total disaccharide content was 85 +/- 6% vs. 65 +/- 5% (P < 0.05) in patients and controls, respectively. As accumulation of negatively charged sulfate residues in GAG disaccharides results in enhanced water-binding capacity, beside inflammation and increased volume of the orbital adipose tissue, the altered structure and nature of sulfated GAG units in the orbit may be responsible for the pathogenic changes in Graves' ophthalmopathy.

Thyrotropin receptor antibodies and Graves’ orbitopathy

“…Thyrotropin receptor stimulating antibodies (TSAb) bind to orbital fibroblasts and adipocytes in the orbital connective tissue. Binding of TSAb to the TSHR activates orbital fibroblasts hence causing increased synthesis of glycosaminoglycan (GAG) and in the long-term induction of adipogenesis to immunologically mediated activation of TSHR expressing fibroblasts in the extra ocular muscles and skin, proliferation of connective and adipose tissue with accumulation of glycosaminoglycans, leading to the trapping of water and edema [22][23][24][25][26][27][28][29]. Later, fibrosis becomes prominent.…”

New insights into the pathogenesis and nonsurgical management of Graves orbitopathy

“…The orbital fibroblast 2 is the target of a spectrum of autoimmune responses, which collectively promote proliferation, excess adipogenesis (formation of new fat cells by differentiation of fibroblasts) and over-production of extra-cellular matrix (ECM). The ECM comprises glycosaminoglycans (GAGs), such as chondroitin sulphate and hyaluronan, which is not sulphated but is able to absorb up to 1000 times its weight in water 12 .…”

Radiotherapy for thyroid-associated orbitopathy

“…Recent studies indicate that activated orbital T-lymphocytes secrete various cytokines, which in a paracrine manner are thought to induce glycosaminoglycan production by fibroblasts (Hansen et al 1996). Excessive secretion of the very hydrophilic glycosaminoglycan molecules (Hansen et al 1997(Hansen et al , 1999 results in tissue oedema, which, besides lymphocyte infiltration, causes the marked swelling of the extraocular eye muscles and connective/fat tissue in TAO.…”