Effect of tunicamycin and monensin on secretion of thyroxine-binding globulin by cultured human hepatoma (Hep G2) cells

We have reported in the preceding paper that human hepatoma (Hep G2) cells synthesize thyroxine-binding globulin (TBG). In this paper, we evaluated the kinetics of secretion of the protein and the effects produced by the ionophore monensin and the glycosylation inhibitor tunicamycin. Cells were pulse labeled with [35S]methionine and then chased after addition of excess unlabeled methionine. TBG appeared in the medium after 10 min, and 50% of the protein was secreted after 45 min. After 2 h, more than 85% of TBG had been released. The rate of secretion of TBG was much slower than that of albumin, 50% of which was secreted after 20 min. Monensin, 1 microM, caused a marked delay in TBG secretion, with 50% released after 80 min. After 2 h, less than 60% had been released and a plateau was approached. Endoglycosidase H (endo H) treatment of intracellular and secreted TBG showed no alteration in the rate of conversion of TBG oligosaccharide units from high-mannose type (endo H-sensitive) to complex type (endo H-resistant), thus suggesting that monensin impeded the exit of TBG from the Golgi apparatus without affecting the terminal glycosylation of the protein. Tunicamycin, 5 micrograms/ml, completely blocked glycosylation and markedly affected TBG secretion, almost doubling the time required for the secretion of 50% of the protein. The effect was specific for TBG, since it was not observed in the case of albumin. After 2 h, only 56% of the protein had been released. Analysis of intracellular and extracellular immunoprecipitated products revealed the presence of aggregates (Mr greater than 100,000). The lack of carbohydrates, although not preventing TBG secretion, had marked quantitative effects, and increased the susceptibility to aggregation.

Acoustic reflex characteristics in hypo- and hyperthyroid patients

The various parameters of the stapedial reflex, evoked by acoustic stimuli and recorded using an impedance meter, were evaluated in untreated hyperthyroid and hypothyroid patients and in normal controls. In hyperthyroid patients neither the threshold nor the latency time, the rise time, the recovery time and the maximal amplitude of the reflex were different from normal subjects. On the contrary, hypothyroid patients showed a longer recovery time and a reduced maximal amplitude, suggesting, in the absence of alterations of middle ear structures, a weaker contractile activity of the stapedial muscle.

Polymorphism of human thyroxine-binding globulin

T4-binding globulin (TBG) consists of a single polypeptide chain containing 4 oligosaccharide units with an average of 10 terminal sialic acid residues. Isoelectric focusing (IEF) of TBG purified from pooled human plasma showed 4 main bands isoelectric at pH 4.2, 4.3, 4.5, and 4.6. Removal of 85% of carbohydrates by treatment with mixed glycosidases reduced these bands to 2, at pH 5.4 and 5.7. This residual microheterogeneity was not related to protein-ampholyte complexes, since it was still present in 8 M urea. It also did not represent an equilibrium mixture of interchangeable conformations, since each band obtained in the first dimension IEF gave a single spot when rerun in a second dimension. Therefore, the residual microheterogeneity of TBG after removal of carbohydrates can be attributed to variation in amino acid composition. Since genetic polymorphism of TBG was recently demonstrated, we further investigated whether the residual microheterogeneity was genetically determined. Plasma samples from 20 white donors and 17 black donors were labeled with [125I]T4 and submitted to IEF, followed by autoradiography. TBG-1, found in white donors and most black donors, showed the same 4 bands as TBG purified from pooled plasma. Two less frequent phenotypes were found in black individuals: TBG-2, with 4 bands at approximately pH 4.25, 4.45, 4.55, and 4.7; and TBG-1,2, having all of the bands present in TBG-1 and TBG-2. Electrophoretically homogeneous preparations of TBG of each type were obtained from 100 ml plasma; after deglycosylation, TBG-1 revealed 2 bands isoelectric at pH 5.4 and 5.7, TBG-2 had 2 bands at pH 5.7 and 5.9, and TBG-1,2 had 3 bands at pH 5.4, 5.7, and 5.9. The same TBG bands were found after neuraminidase treatment of whole plasma from the same donors. These data demonstrate two kinds of TBG polymorphism. The first is found in deglycosylated TBG from individual donors and is probably due to variation in amino acid composition. The second, also unrelated to the carbohydrate moiety, is a genetic polymorphism found in blacks.

TSH-displacing activity versus TSH-binding inhibiting activity of immunoglobulins from patients with Graves' disease

Inhibition of binding of TSH to thyroid plasma membranes by immunoglobulins G (IgG) from patients with Graves' disease has been interpreted as evidence of an interaction with the TSH receptor, but other explanations may account for this phenomenon. Displacement of receptor-bound TSH might be a more direct index of such an interaction. The aim of the present study was to assess TSH-displacing activity (TDA) of Graves' IgG by a newly developed assay and compare TDA to TSH-binding inhibiting activity (TBIA) and thyroid-stimulating antibody (TSAb) activity. TDA was assessed by preincubating 125I-TSH with thyroid plasma membranes and by measuring residual bound 125I-TSH after addition of IgG. TBIA was evaluated by determining binding of 125I-TSH to thyroid plasma membranes preincubated with IgG. Results were expressed as % TSH-displacing or binding inhibition activities of test IgG with respect to normal control IgG. The percent of TDA positive Graves' IgG preparations (72.7%) was greater than that of TBIA positive (48.5%). There was no correlation between TDA and TBIA results, since 11 Graves' IgG preparations were TDA positive but TBIA negative, and 6 were TDA negative but TBIA positive. Hashimoto's or idiopathic myxedema IgG preparations were positive in 2/7 in the TDA and in 1/7 in the TBIA assays, respectively. Neither TDA nor TBIA correlated with TSAb determined by cAMP accumulation in thyroid plasma membrane. The TDA assay developed in this study appeared to be more sensitive than the more widely used TBIA assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Orbital cobalt irradiation combined with systemic corticosteroids for Graves' ophthalmopathy: comparison with systemic corticosteroids alone

The effects of different methods of treatment of Graves' ophthalmopathy were evaluated in a series of 48 patients. Thirty-six patients were given combined treatment with orbital cobalt irradiation and systemic 6 alpha-methylprednisolone (methylprednisolone). Included in this group were 12 of 24 consecutive patients who were randomly assigned to either combined therapy or systemic methylprednisolone alone. The degree of ocular involvement and responses to treatment were evaluated by numerical scoring (ophthalmopathy index) and clinical assessment. Of the 36 patients treated by combined therapy, 12 (33%) showed excellent responses, 14 (39%) showed good responses, 9 (25%) showed slight responses, and 1 (3%) had no response. Treatment was more effective for soft tissue involvement, newly developed ophthalmoplegia, and optic neuropathy, while proptosis and longstanding ophthalmoplegia were less responsive. There was an inverse relationship between the duration of ophthalmopathy and the efficacy of treatment, more favorable results being observed when symptoms had been present for less than 2 yr. Treatment with systemic methylprednisolone alone was also effective, but, in general, responses were less satisfactory; 4 of the 12 patients of this group (33%) had good responses, 6 (50%) had slight responses, and 2 (17%) had no response. The results obtained in the 24 patients randomly assigned to combined therapy or steroid treatment alone were compared by evaluating changes in the ophthalmopathy index. Mean initial ophthalmopathy indices (6.4 vs. 6.2, respectively) showed no significant differences between the 2 groups, whereas the mean decrease in the group receiving combined therapy (4.8) was significantly greater (P less than 0.05) than that in the other group (3.2). In conclusion, the present study indicates that both orbital cobalt irradiation combined with systemic methylprednisolone treatment and systemic methylprednisolone therapy alone are valuable methods of treatment for Graves' ophthalmopathy, but the combined therapy proved to be more effective.

Studies on thyroid cell surface antigens using cultured human thyroid cells

Human thyroid cells in primary culture were used for studies of thyroid cell surface antibodies in patients with thyroid autoimmune disorders. Radioiodinated IgG preparations containing thyroid microsomal antibody (TMAb), thyroid stimulating antibody (TSAb) and/or thyroglobulin antibody (TgAb) were tested for binding to thyroid cells. Binding was observed with radioiodinated IgG from patients with Graves' disease, Hashimoto's thyroiditis and idiopathic myxoedema containing TMAb, irrespective of the presence of TSAb and TgAb, while negative results were obtained with normal IgG. A dose-dependent inhibition of binding to thyroid cells was produced by the addition of the corresponding unlabelled IgG preparations. Evidence for tissue specificity was provided by the absence of binding to human skin fibroblasts used as controls. Preabsorption with human thyroid microsomes completely abolished the binding to thyroid cells of a radioiodinated TMAb positive IgG preparation, while only incomplete removal of the reactivity to thyroid microsomes was produced by preabsorption with thyroid cells. These data suggest that some but not all microsomal antigenic determinants are expressed on the thyroid cell surface. Binding to thyroid cells was also observed with purified TgAb, indicating that thyroglobulin antigenic determinants are present on the surface of thyroid cells. No evidence of binding was obtained with a TSAb positive Graves' IgG preparation with undetectable TMAb and TgAb. Unlabelled IgG preparations containing TMAb from patients with either Hashimoto's thyroiditis or idiopathic myxoedema were shown to inhibit the binding to thyroid cells of radioiodinated TMAb positive Graves' IgG and vice versa. These data indicate that antibodies present in these thyroid autoimmune disorders share common thyroid cell surface antigens. However, the binding of radioiodinated IgG from a patient with idiopathic myxoedema was only partially inhibited by Graves' or Hashimoto's IgG, suggesting that some of the thyroid cell surface antibodies of idiopathic myxoedema may not be detectable in other thyroid autoimmune disorders.

Thyroid-stimulating immunoglobulins

The presence of thyroid-stimulating immunoglobulins in patients with Graves' disease is well established. Considerable evidence has accumulated that these immunoglobulins are antibodies to a thyroid plasma membrane antigen whose precise nature remains to be identified. The question whether the antigen is related to the TSH receptor is still debated. The causative role of thyroid-stimulating immunoglobulins in the hyperthyroidism of Graves' disease is widely recognized. The use of human specific stimulation assays has circumvented the objection of the relatively low frequency of long-acting-thyroid-stimulator-(LATS)-positive patients. Individual variations in the thyroid response may account for the lack of correlation between the levels of thyroid-stimulating immunoglobulins and most parameters of thyroid function. In this respect, the interference of nonstimulatory thyroid antibodies and of other autoimmune mechanisms may be of importance. An important clinical implication of thyroid-stimulating immunoglobulin determinations is their value in predicting the relapse of hyperthyroidism in treated patients. This clinical application has been so far limited by the technical difficulties of the assays. This emphasizes the need for a simple and reliable test, which can be used for routine measurements of thyroid-stimulating immunoglobulins.

Measurement of thyroid cell surface antibodies by radioassay using human cultured thyroid cells

The present report describes a sensitive and quantitative binding radioassay for measurement of thyroid cell surface antibodies (TCSAb). Enzyme-dispersed thyroid cells from surgical specimens of human normal thyroid tissue were used after 7 days of culture. 125I-labelled Graves' IgG was shown to bind to cultured thyroid cells. The binding was time-and temperature-dependent and increased linearly with the number of thyroid cells. Evidence for specificity was provided by the lack of binding of radioiodinated Graves' IgG to human fibroblasts and by the negligible binding of 125I-labelled normal IgG to thyroid cells. A dose-dependent inhibition of binding of 125I-labelled Graves' igG to thyroid cells was produced by the addition of graded amounts of the unlabelled original Graves' IgG preparation, but not by normal IgG. Assays for TCSAb were performed on IgG preparations from patients with and without thyroid autoimmune disorders using the original Graves' IgG preparation as reference standard. Results were expressed in terms of arbitrary units/100 microgram IgG, 1 unit corresponding to the minimum amount of the standard IgG producing a significant inhibition of binding. Negative tests were found in most normal subjects (15/18) while low TCSAb levels (less than or equal to 1.8 U/100 microgram IgG) were detected in 3 cases. Increased TCSAb levels were found in the majority of the patients wit Graves' disease (14/21), in most of the patients with idiopathic myxedema (9/10) and in all of those with Hashimoto's thyroiditis (10/10).

Comparison between thyroid stimulating and tsh-binding inhibiting immunoglobulins of Graves' disease

In the sera of patients with Graves' disease abnormal thyroid 'stimulating' immunoglobulins have been demonstrated by in vivo and in vitro assay systems. Conflicting results have been reported when thyroid stimulating and thyrotrophin (TSH)-binding inhibiting activities have been compared. The present study was performed in forty-nine hyperthyroid Graves' patients to ascertain the relationships among TsH-binding inhibiting immunoglobulins (TBII), measured by a radio-receptor assay, thyroid stimulating antibody(TSAb), assayed by stimulation of adenylate cyclase-cAMP system in human thyroid plasma membranes, and LATS, measured by McKenzie's mouse bioassay.TBII was detected in twenty-one of forty-nine (42.9%), TSAb in thirty-five of forty-nine (71.4%) and LATS in nineteen of forty-nine (38.8%).TBII was also present in four of sixteen (25%) patients with other thyroid autoimmune disorders. When the results obtained with the different techniques were compared, correlation was found between LATS response and TSAb activity ( =0.53, P less than 0.001), while there was no correlation between TSAb and TBII activities and between LATS response and TBII activity. These data conform that TSAb is specific and sensitive marker of Graves' disease and suggest that TBII activity is not necessarily synonymous with thyroid stimulation, and could reflect a different phenomenon concomitantly produced.

Graves' disease and Turner's syndrome

A case of a 17-year-old female with Turner's syndrome and Graves' disease is reported. The karyotype analyzed in peripheral blood lymphocytes showed a 45,X0 pattern without mosaicism. The diagnosis of Graves' disease was based on the presence of diffuse goiter and appropriate laboratory data, including elevated thyroid radioiodine uptake, increased serum thyroxine and free thyroxine index, detectable thyroid-stimulating antibody and elevated thyroid microsomal antibody titer. Hyperthyroidism was first recognized when the patient was 13-year-old and treatment wih carbimazole was instituted for 18 months. Relapse of hyperthyroidism occurred 9 months after withdrawal of therapy, and a second course of antithyroid drug treatment was given for two yr. Ovarian dysgenesis has been described with a relatively high frequency in patients with Hashimoto's thyroiditis, while the association with Graves' disease has been only occasionally encountered. This finding is surprising in view of the etiopathogenetic and genetic relationships between these two thyroid autoimmune disorders. Some possible explanations are offered to clarify this problem.

Dissociation of responsiveness to thyrotropin-releasing hormone and thyroid suppressibility following antithyroid drug therapy of hyperthyroidism

Responsiveness to synthetic thyrotropin-releasing hormone (TRH), thyroid suppressibility by triiodothyronine (T3) and the outcome of hyperthyroidism following prolonged therapy with thionamides were studied in a group of 35 patients with toxic diffuse goiter. TRH and T3 suppression tests were performed 10 days to 24 months (mean 4 months) after withdrawal of antithyroid drugs. Nineteen patients were euthyroid and had a normal thyrotropin (TSH) response to TRH, while 4 were recovering from mild hypothyroidism due to overtreatment and had an exaggerated response. No response was observed in 12 patients with recurrent hyperthyroidism. Positive T3 suppression tests were found only in 10 of the 30 cases examined. Peak and net 2 h secretion responses of TSH to TRH exhibited a significant inverse correlation with the levels of serum thyroxine and serum triiodothyronine, but were unrelated to the degree of thyroid suppressibility. Relapse or recurrence of thyrotoxicosis occurred in at least 9 of the 23 patients having no evidence of hyperthyroidism at the time of TRH test. Each of them was found to be responsive to TRH, while the T3 suppression test was negative in 8 and had to be discontinued in one because of thyrotoxic symptoms. The present data indicate that during the early period after completion of a prolonged course of antithyroid drug therapy responsiveness to TRH in toxic diffuse goiter is: a) correlated with circulating thyroid hormones, b) unrelated to the degree of thyroid suppressibility by T3 and c) of little value in predicting the long-term results of treatment.