Feasibility Study of New Calibrators for Thyroid-Stimulating Hormone (TSH) Immunoprocedures Based on Remodeling of Recombinant TSH to Mimic Glycoforms Circulating in Patients with Thyroid Disorders

Abstract

Background: Differences between the glycosylation patterns of a pituitary thyroid-stimulating hormone calibrator (pitTSH) and serum samples have been shown to be responsible for nonidentical epitope expression and for introducing discrepancies in TSH measurements. We studied the feasibility of developing new candidate reference materials by remodeling recombinant TSH (recTSH) to generate potential mimics of serum TSH.

New Immunoassays of Bioactive TSH Improve Detection of Thyroid Disorders

“…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. The lack of immunological similarity between immunoreactive TSH present in the calibrator and in clinical samples has been shown to impact TSH measurements [16].…”

“…The lack of immunological similarity between immunoreactive TSH present in the calibrator and in clinical samples has been shown to impact TSH measurements [16]. Highly sialylated recombinant TSH however proved to display immunological identity with serum TSH, especially from hypothyroid patients [17]. Recently, we could demonstrate that combining a defined selection of TSH epitopes to a calibration based on glycoengineered TSH is able to abolish discrepancies among assays and achieve harmonization of TSH values as now requested by regulatory bodies [28].…”

“…In earlier studies, we have investigated various calibrators of TSH assays [17] including the use of a recombinant glycoengineered calibrator to measure bioactive TSH [28]. To achieve similar immunological behavior between this preparation and serum TSH, we designed new sandwich assays based on defined selection of epitopes.…”

“…The new assays also bind a remote cluster which is not necessarily targeted in routine tests [28]. Such assays were found to display enhanced binding to serum TSH over the whole range of TSH level [28], indicating that they were able to bind all forms of TSH, more preferably sialylated TSH as it raises upon hypothyroidism [16,17,28]. Interestingly, these assays identified individuals with elevated TSH (>97.5 th centile) who show an increased number of hCS and decreased FT4 levels compared to the routine assay.…”

N-Terminal Pro–Atrial Natriuretic Peptide Measurement in Plasma Suggests Covalent Modification

“…The problem is well known for other hormones. For instance, the measurement of thyroid-stimulating hormone is complicated by altered glycosylation as a function of the state of the thyroid (12 ), and gastrin is affected by disease-dependent molecular heterogeneity in the plasma (13,14 ).…”