The enzymatic activity of type 1 iodothyronine deiodinase (D1) is low in liver hemangioma: a preliminary study

Current concepts and challenges to unravel the role of iodothyronine deiodinases in human neoplasias

Thyroid hormones (THs) are essential for the regulation of several metabolic processes and the energy consumption of the organism. Their action is exerted primarily through interaction with nuclear receptors controlling the transcription of thyroid hormone-responsive genes. Proper regulation of TH levels in different tissues is extremely important for the equilibrium between normal cellular proliferation and differentiation. The iodothyronine deiodinases types 1, 2 and 3 are key enzymes that perform activation and inactivation of THs, thus controlling TH homeostasis in a cell-specific manner. As THs seem to exert their effects in all hallmarks of the neoplastic process, dysregulation of deiodinases in the tumoral context can be critical to the neoplastic development. Here, we aim at reviewing the deiodinases expression in different neoplasias and exploit the mechanisms by which they play an essential role in human carcinogenesis. TH modulation by deiodinases and other classical pathways may represent important targets with the potential to oppose the neoplastic process.

Contribution of mammalian selenocysteine-containing proteins to carcinogenesis

Oxidative stress caused by a sharp growth of free radicals in the organism is a major cause underlying the occurrence of all kinds of malignant formations. Selenium is an important essential trace element found in selenoproteins in the form of selenocysteine, an amino acid differing from cysteine for the presence of selenium instead of sulfur and making such proteins highly active. To date the role of selenium has been extensively investigated through studying the functions of selenoproteins in carcinogenesis. Analysis of the obtained results clearly demonstrates that selenoproteins can act as oncosuppressors, but can also, on the contrary, favor the formation of malignant tumors.

Enzymatic activity of type 1 iodothyronine deiodinase in selected liver tumors

INTRODUCTION

Type 1 iodothyronine deiodinase (D1) converts thyroxin (T4) into tri-iodothyronine (T3). Strong evidence indicates that thyroid hormone metabolism is disturbed in neoplasms such as thyroid and breast cancer. However, there is limited data concerning the function of the D1 enzyme in liver tumors. We aimed to estimate the enzymatic activity of D1 in two different common liver tumors.

MATERIAL AND METHODS

We obtained 20 tumor samples from patients who had undergone a liver resection. Of the tissue samples, there were 13 benign lesions of focal nodular hyperplasia (FNH) and 7 malignant lesions of hepatocellular carcinomas (HCC). The D1 activity was assessed by measuring the amount of radioactive iodine released in reaction to D1-catalysed deiodination. Groups were compared by the Mann-Whitney non-parametrical test for independent trials, and the Kruskal Wallis test.

RESULTS

The enzymatic activity of D1 was not significantly altered in the FNH group (median = 536 fmol/mg of protein/min; p = 0.972) and HCC group (367 fmol/mg; p = 0.128) when compared to matched normal liver parenchyma controls (546 fmol/mg and 556 fmol/mg, respectively).

CONCLUSIONS

Liver parenchyma expresses high levels of D1. The results clearly revealed that D1 activity was not significantly different between benign and malignant tumors (FNH and HCC) compared to healthy liver parenchyma cells.

Iodothyronine deiodinases and cancer

Thyroid hormones (TH) regulate key cellular processes, including proliferation, differentiation, and apoptosis in virtually all human cells. Disturbances in TH pathway and the resulting deregulation of these processes have been linked with neoplasia. The concentrations of TH in peripheral tissues are regulated via the activity of iodothyronine deiodinases. There are 3 types of these enzymes: type 1 and type 2 deiodinases are involved in TH activation while type 3 deiodinase inactivates TH. Expression and activity of iodothyronine deiodinases are disturbed in different types of neoplasia. According to the limited number of studies in cancer cell lines and mouse models changes in intratumoral and extratumoral T3 concentrations may influence proliferation rate and metastatic progression. Recent findings showing that increased expression of type 3 deiodinases may lead to enhanced tumoral proliferation support the idea that deiodinating enzymes have the potential to influence cancer progression. This review summarizes the observations of impaired expression and activity in different cancer types, published to date, and the mechanisms behind these alterations, including impaired regulation via TH receptors, transforming growth factor-β, and Sonic-hedgehog pathway. Possible roles of deiodinases as cancer markers and potential modulators of tumor progression are also discussed.

β-blockers for infantile hemangiomas: a single-institution experience

Propranolol has become first-line therapy for the treatment of infantile hemangiomas in many centers. Of 302 children with hemangiomas seen at the University of North Carolina from 2008 through 2010, 15.6% were treated with oral propranolol alone, 5.6% with topical timolol (a propranolol derivative) alone, and 2.3% with both. The use of these agents increased over time from 7% of patients seen in 2008 to 54% of patients first seen in 2010. Starting doses of propranolol ranged from 0.25 to 1 mg/kg/d, with target doses of 1 to 4 mg/kg/d. Serious side effects, noted in 6/54 (10.9%) patients, included somnolence, bradycardia, hypotension, hypoglycemia, and mottling of extremities.The authors confirm the variation in use of propranolol for vascular lesions and extend experience with timolol. They suggest daily home monitoring of patients for the first 2 weeks of initiating or increasing doses. Frequent feeding of infants and young children on this drug is recommended.