[Changes in plasma concentrations of osteoprotegerin before and after levothyroxine replacement therapy in...

To investigate the alteration of plasma osteoprotegerin (OPG) concentration before and after levothyroxine (L-T4) replacement therapy and its association with endothelium-dependent arterial dilation in patients with overt hypothyroidism (oHT) and subclinical hypothyroidism (sHT).

L-T4 therapy was given to 20 oHT patients and 20 sHT patients, all female, till the free serum triiodothyronine (FT3), free thyroxin (FT4), and thyroid-stimulating hormone (TSH) were near or within the respective normal ranges. Twenty healthy women were used as controls. Sandwich ELISA was used to measure the plasma OPG concentration before and after treatment.

The plasma OPG levels before treatment of the oHT and sHT patients were 3.13 ng/L +/- 0.27 ng/L and 2.95 ng/L +/- 0.24 ng/L respectively, both significantly higher than that of the controls (2.42 ng/L +/- 0.26 ng/L, both P = 0.000). Multivariate analysis showed that OPG was significantly associated with TSH (r = 0.306, P < 0.05) and endothelium-dependent arterial dilation (r = -0.675, P < 0.01) at baseline. After the normalization of thyroid function the OPG levels of the oHT and sHT patients decreased markedly to 2.53 ng/L +/- 0.28 ng/L and 2.54 ng/L +/- 0.21 ng/L respectively (both P = 0.000), very close to that in the controls. The absolute changes of OPG was significantly positively correlated with the changes of TSH (P < 0.05), negatively correlated with the changes of endothelium-dependent arterial dilation (P < 0.01), and not significantly correlated with other parameters in the hypothyroid patients during the course of treatment.

OPG may act as an important regulatory molecule in the vasculature and, particularly, may be involved in the development of vascular dysfunction in hypothyroid patients.