Concanavalin-A, Lentil, and Ricin Lectin Affinity Binding Characteristics of Human Thyrotropin: Differences in the Sialylation of Thyrotropin in Sera of Euthyroid, Primary, and Central Hypothyroid Patients*

Abstract

TSH from human serum was separated into classes by serial lectin affinity chromatography using Concanavalin-A (ConA), lentil, and ricin lectins. TSH from 10 euthyroid subjects, 40 patients with primary hypothyroidism, and 1 patient with central hypothyroidism was studied. The patterns of ConA and lentil affinity binding were similar for diverse patients; forms of TSH that bound firmly to ConA also tended to bind firmly to lentil. Differences in TSH-ricin binding suggested that there were differences in the sialylation of TSH in sera of euthyroid, primary, and central hypothyroidism patients. For euthyroid subjects, 16.1 +/- 5.4% (mean +/- SD) of the TSH bound to ricin, while after neuraminidase treatment, 38.4 +/- 5.4% bound. For patients with primary hypothyroidism, 23.5 +/- 6.0% of the TSH bound to the ricin, while after neuraminidase treatment, 65.7 +/- 8.8% bound. The increase in ricin binding induced by neuraminidase treatment was significantly higher for TSH from patients with primary hypothyroidism than in that from euthyroid subjects (42.3 +/- 7.6% vs. 22.3 +/- 4.4%; P less than 0.01) and was greater for long term than for short term hypothyroid patients (49.5 +/- 5.0% vs. 36.5 +/- 6.5%; P less than 0.01). While 30% of native TSH from the serum of the patient with central hypothyroidism bound to ricin, the amount bound increased only 17.6% after neuraminidase treatment. McKenzie bioassay of pituitary-derived TSH that was similarly fractionated using ricin failed to show detectable differences in bioactivity among the lectin column fractions. Thus, 1) circulating human TSH can be consistently separated into discrete classes using serial lectin affinity chromatography; 2) there is relatively more core fucosylation of the less processed high mannose and hybrid forms of TSH and less core fucosylation of more processed complex forms; 3) ConA and lentil binding of TSH in primary and central hypothyroidism is similar to that in the euthyroid state; 4) patients with primary hypothyroidism have more sialylated TSH than a patient with central hypothyroidism or euthyroid subjects; and 5) the degree of TSH sialylation increases with prolonged primary hypothyroidism.

Fatores Interferentes na Interpretação de Dosagens Laboratoriais no Diagnóstico de Hiper e Hipotireoidismo

“…A não elevação noturna do TSH ou uma resposta diminuída ou retardada do TSH ao TRH pode apontar para um hipotireoidismo central (18). A diminuição da bioatividade é parcialmente explicável por anormalidades na glicosilação do TSH, que se encontra sob o controle do TRH (19). Em pacientes com doença hipotalâmica ou hipofisária, o controle da reposição de T 4 deve ser feito unicamente pela medida dos hormônios livres, não existindo papel para o TSH sérico.…”

“…geração. Num estudo de 460 pacientes em uso supressivo de tiroxina, quase todos os pacientes com um TSH maior que 0,05mU/L tinham um nível sérico normal de T 4 livre (19). Apenas pacientes em terapia supressiva de TSH cujos níveis de TSH eram menores que 0,05mU/L foram beneficiados com uma dosagem simultânea de T 4 livre, uma vez que a detecção de uma hipertiroxinemia nesta situação deve sugerir redução na dose de T 4 (20).…”

New Immunoassays of Bioactive TSH Improve Detection of Thyroid Disorders

“…The current 3 rd IS 81/565 primary calibrator has been extracted from pituitaries and is mainly composed of GalNAc-sulfated glycoforms that are biosynthetic intermediates of low biopotency [16]. Indeed, such glycoforms are rapidly cleared from the circulation by a liver GalNAcsulfate lectin receptor [19] leaving in the circulation essentially longlived sialylated TSH forms [20][21][22] which escape hepatic clearance [23]. Previous studies of our laboratory [16,17,24,25] as well as those of others [26,27] have shown that the binding of anti-TSH antibodies may be altered by changes in TSH glycosylation.…”

Changes in the glycosylation pattern of circulating gonadotropins after acute administration of gonadotropin-releasing hormone in patients with anorexia nervosa

“…Similarly to thyrotropin-releasing hormone (19)(20)(21)(22)(23), a direct effect of GnRH on gonadotropin N-linked carbohydrate branching has been postulated to occur (17)(18). Qualitative changes in both circulating follicle-stimulating hormone (FSH) and LH occur in amenorrhoic AN patients, with evidence of circulating gonadotropin isoforms that are less sialylated (24).…”