Absence of circulating desialylated thyroxine-binding globulin in patients with hepatobiliary disease

Abstract

Thyroxine-binding globulin (TBG) is the major thyroid hormone carrier protein. The molecule contains approximately 10 sialic acid residues which play a key role in the peripheral metabolism of TBG. Since the serum of patients with liver disease often contains large amounts of several desialylated glycoproteins, the aim of the present studies was to characterize circulating TBG and to examine the possible presence of desialylated TBG (dTBG) in 24 patients with a variety of hepatobiliary diseases and selected on the basis of elevated serum levels of desialylated glycoproteins. Using 4 immunochemical techniques applied for the measurement of TBG, for the detection of dTBG and for the characterization of TBG microheterogeneity, the results indicated: a) a wide scatter of serum TBG levels between 4 and 23 mg/l; b) the absence of detectable amounts of dTBG in any of the sera tested; and c) a close similarity between the microheterogeneity of TBG in patients with liver disease with that of control sera or of purified TBG. In conclusion, in patients with acute and chronic liver disease, TBG, although quantitatively modified, remains qualitatively unaltered, suggesting that diseased liver produces fully sialylated TBG and that its catabolism is not impaired.Requests for reprints:

Mechanisms behind the non-thyroidal illness syndrome: an update

“…The acute fall in these plasma binding proteins may thus account for much of the changes in plasma total T 3 and total T 4 seen in acute illness. In some, but not all patients with chronic illness, a desialylated form of TBG is synthesised by the liver, and this protein appears to have an affinity for thyroid hormone of approximately one-tenth of that of normal TBG (also known as slow TBG because of altered electrophoretic mobility); this also gives rise to a fall in the circulating levels of total thyroid hormone as a consequence of the diminished thyroid hormone binding capacity (Reilly & Wellby 1983, Costante et al 1985. In rodents, inflammation and fasting leads to a marked decrease in transthyretin, the major plasma thyroid hormone-binding protein in this species (Dickson et al 1982, Wade et al 1988.…”