Endocrine Abstracts

Objective: Detecting recurrence of differentiated thyroid cancer is performed by serial measurements of serum thyroglobulin (Tg) levels, however, in the presence of anti-Tg antibodies, this measurement is unreliable. Extracellular vesicles (EVs) are small membrane-enclosed structures, with a prominent role in cell-to-cell communication. All cell types release EVs and they can be isolated from various biofluids, while their cargo reflects the content of the cell of origin. Previous studies showed that EVs from bovine serum, FRTL-6 rat thyroid cell line conditioned medium and human urine all contain thyroglobulin. EVs isolated from human serum were not previously investigated for the presence of Tg. We performed a qualitative study to determine whether Tg can be detected in the EVs isolated from human plasma or serum of patients with thyroid diseases, in order to test a novel approach for measuring Tg segregated from anti-Tg antibodies.

Methods: We employed 4 samples for this analysis: one plasma sample from a healthy donor, 2 plasma samples from patients with thyroid nodules and one serum sample of a patient positive for thyroglobulin antibodies. Extracellular vesicles were isolated by differential ultracentrifugation. The size and the number of vesicles were determined with nanoparticle tracking analysis (NTA) and the characterisation of EVs surface markers as well as thyroglobulin detection was performed by means of Western blot.

Results: NTA analysis showed that the median size of particles in the extracellular vesicle-enriched preparations isolated from plasma or serum samples fell in the range of 90 – 110 nm, corresponding to the size of EVs. EVs-enriched preparation isolated from the plasma of thyroid nodule patients and serum of a patient with thyroglobulin antibodies were positive for the presence of thyroglobulin, while this protein was not detected in the sample from the healthy donor.

Conclusions: Thyroglobulin can be detected in the EVs-enriched preparation isolated from serum and plasma samples of patients suffering from thyroid gland pathophysiologies. Although preliminary, these results point out the possibility of efficiently bypassing the obstacles caused by Tg antibodies in serum Tg detection. Detecting thyroglobulin enclosed in vesicles that are actively secreted from the thyroid follicular cells holds promise as an innovative concept in diagnosing differentiated thyroid cancer recurrence. Quantitative studies on a large sample cohort are in progress.