heparitin-sulfate and Graves-Disease

Qualitative and quantitative analyses of glycosaminoglycans (GAGs) in serum obtained from Graves' disease (GD) patients without extrathyroidal complications were carried out to provide a clearer understanding of the role of these macromolecules in the disease pathogenesis.. GAGs were isolated from-SIMEL (Italian Society of Laboratory Medicine) Inter-associative Study Group on Diabetes Mellitus serum of 17 GD patients before treatment and after attainment of the euthyroid state, as well as from 20 healthy individuals. GAGs were quantified using the hexuronic acid assay and subjected to electrophoretic fractionation.. Increased amounts of total GAGs were found in GD patients. Attainment of euthyroidism led to a decrease in, but not normalization of, total serum GAGs level. Electrophoretic analyses of GAGs before and after treatment identified the presence of chondroitin sulfate (CS), heparan sulfate/heparin (HS/H) and dermatan sulfate (DS) in serum from healthy subjects and GD patients. CS was the predominant serum GAG constituent in all subjects investigated. Enhanced CS levels in both GD patient groups were accompanied by increased structural heterogeneity of these compounds. Normalization of thyroid function did not change CS levels. DS levels in serum of untreated GD patients were elevated in comparison to healthy subjects. Anti-thyroid treatment led to a significant decrease in DS to levels below those in controls. DS in all serum samples investigated displayed a similar structure. HS/H levels in serum of untreated GD patients was seven-fold higher than in healthy subjects. In addition, HS/H in untreated GD patients were characterized by higher structural heterogeneity than those isolated from control subjects and euthyroid GD patients. Anti-thyroid therapy led to a decrease in HS/H concentrations towards normal values.. Our results indicate that in the course of GD, the metabolism of particular types of GAGs is regulated by different mechanisms, including a hyperthyroid state and immunological abnormalities. Furthermore, qualitative and quantitative changes in serum GAGs seem to reflect GD-associated systemic changes in extracellular matrix properties.

Topics: Adult; Case-Control Studies; Chemistry, Clinical; Chondroitin Sulfates; Dermatan Sulfate; Extracellular Matrix; Female; Glycosaminoglycans; Graves Disease; Heparin; Heparitin Sulfate; Humans; Male; Middle Aged; Nitrous Acid

Hormone secretion by thyrocytes occurs by fluid phase uptake and lysosomal degradation of the prohormone thyroglobulin (Tg). However, some Tg internalized by megalin bypasses lysosomes and is transcytosed across cells and released into the bloodstream. Because the hormone content of Tg is variable, we investigated whether this affects transcytosis. We found that rat Tg with a low hormone content [low-hormonogenic rat Tg (low-horm-rTg)] is transcytosed by megalin across thyroid FRTL-5 cells to a greater extent than rat Tg with a high hormone content [hormonogenic rat Tg (horm-rTg)]. In immunoprecipitation experiments, the Tg sequence Arg-2489-Lys-2503 (required for binding to megalin and heparan sulfate proteoglycans) was found to be more exposed in low-horm-rTg, which accounted for its preferential transcytosis. Thus, removal of surface heparan sulfate proteoglycans from FRTL-5 cells or blocking of 2489-2503 reduced transcytosis of low-horm-rTg to a greater extent than that of horm-rTg. Preferential transcytosis of low-horm-rTg affected hormone release. Thus, the increase in hormone release from horm-rTg in FRTL-5 cells determined by megalin blocking (due to reduced transcytosis and enhanced Tg degradation) was rescued by low-horm-rTg, suggesting that megalin is required for effective hormone release. This finding was confirmed in a small number of megalin-deficient mice, which had serological features resembling mild hypothyroidism. Reduced hormone formation within Tg in vivo, due to treatment of rats with aminotriazole or of patients with Graves' disease with methimazole, resulted in increased Tg transcytosis via megalin, in confirmation of results with FRTL-5 cells. Our study points to a major role of megalin in thyroid homeostasis with possible implications in thyroid diseases.

Topics: Adult; Amitrole; Animals; Dose-Response Relationship, Drug; Endocytosis; Enzyme-Linked Immunosorbent Assay; Female; Graves Disease; Heparitin Sulfate; Homozygote; Hormones; Humans; Hypothyroidism; Low Density Lipoprotein Receptor-Related Protein-2; Male; Methimazole; Mice; Mice, Transgenic; Middle Aged; Models, Biological; Precipitin Tests; Rats; Rats, Inbred Lew; Thyroglobulin; Thyroid Gland; Thyroid Hormones

From three patients with pretibial myxedema (PTM) of Graves' disease, a portion of the skin involved was biopsied, analyzed for proteoglycans and the results were compared with those obtained with euthyroid and hyperthyroid subjects without PTM. The tissue specimen was extracted with 4 M guanidine HCl and subjected to subsequent CsCl density gradient centrifugation. Glycosaminoglycan and protein were recovered in the heaviest density fraction in the three specimens obtained from patients with PTM and not from subjects without PTM. From the analysis by Sepharose CL-6B column, glycosaminoglycan was present as a form of proteoglycan because alkaline borohydride treatment released single chain glycosaminoglycan with a molecular weight of 77,000 or 66,000. The digestion with chondroitin ABC lyase revealed that the majority of proteoglycan in the skin tissue was chondroitin sulfate or dermatan sulfate, and heparan sulfate comprised the minor component (14-34%). The rate of proteoglycan biosynthesis was examined by 35S incorporation into glycosaminoglycan's by cultured fibroblasts from PTM and normal skin. Incorporation of 35S into both proteoglycan and single chain glycosaminoglycan was observed in the fibroblasts of PTM patients as well as of those of subjects without PTM, although the rate of synthesis was more pronounced in the former. The rate of synthesis was influenced neither by normal serum or serum from a pretibial myxedema patient. Since proteoglycan accumulation was detected only in the affected skin of PTM patients, the impairment of local degradation and the proteoglycan clearance mechanism may also be involved.

Topics: Centrifugation, Isopycnic; Chondroitin Sulfates; Graves Disease; Heparitin Sulfate; Humans; Molecular Weight; Myxedema; Proteoglycans; Skin Diseases