The insulin-like growth axis in patients with autoimmune thyrotoxicosis: effect of antithyroid drug treatment

Insulin-like Growth Factor-I Receptor and Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a complex disease process presumed to emerge from autoimmunity occurring in the thyroid gland, most frequently in Graves disease (GD). It is disfiguring and potentially blinding, culminating in orbital tissue remodeling and disruption of function of structures adjacent to the eye. There are currently no medical therapies proven capable of altering the clinical outcome of TAO in randomized, placebo-controlled multicenter trials. The orbital fibroblast represents the central target for immune reactivity. Recent identification of fibroblasts that putatively originate in the bone marrow as monocyte progenitors provides a plausible explanation for why antigens, the expressions of which were once considered restricted to the thyroid, are detected in the TAO orbit. These cells, known as fibrocytes, express relatively high levels of functional TSH receptor (TSHR) through which they can be activated by TSH and the GD-specific pathogenic antibodies that underpin thyroid overactivity. Fibrocytes also express insulin-like growth factor I receptor (IGF-IR) with which TSHR forms a physical and functional signaling complex. Notably, inhibition of IGF-IR activity results in the attenuation of signaling initiated at either receptor. Some studies suggest that IGF-IR-activating antibodies are generated in GD, whereas others refute this concept. These observations served as the rationale for implementing a recently completed therapeutic trial of teprotumumab, a monoclonal inhibitory antibody targeting IGF-IR in TAO. Results of that trial in active, moderate to severe disease revealed dramatic and rapid reductions in disease activity and severity. The targeting of IGF-IR with specific biologic agents may represent a paradigm shift in the therapy of TAO.

Association of insulin-like growth factor-1 with thyroid nodules

The aim of the present study was to investigate the relationship between insulin-like growth factor-1 (IGF-1) and thyroid nodules. A total of 56 patients with thyroid nodules confirmed by physical examination and ultrasound screening were randomly selected. The patients were divided into three groups by radionuclide scan: the hot nodule group (group 1, n=18); the cold and solid nodule group (group 2, n=18); and the cold and cystic nodule group (group 3, n=20). Cystic fluid samples from patients with cystic cold thyroid nodules were defined as group 4. A control group of 18 healthy adults matched for age, gender and body mass index (group 0) was also included. For all participants, levels of the thyroid hormones, TT3, TT4, TSH and IGF-1, were determined by radioimmunoassay. The measurement data were expressed as the mean ± standard deviation (SD). The analysis of variance was performed by the t-test and the correlation analysis was performed by linear regression. The serum levels of IGF-1 in the solid cold nodule group were significantly higher than those in the hot nodule group (P<0.05). Serum levels of IGF-1 in the cystic cold nodule group were significantly lower than those in the control group (P<0.05). The serum IGF-1 levels in the cystic fluid were significantly lower than those in the cystic cold nodule (P<0.05) and the control groups (P<0.05). Additionally, the mean serum IGF-1 level in patients with thyroid adenoma was significantly higher than that in the control group (P<0.05). The serum IGF-1 level may not be involved in the pathogenesis of hot thyroid nodules and cold and cystic thyroid nodules; however, it may play a significant role in the pathogenesis of certain solid cold thyroid nodules.

Autoimmune polyglandular syndrome Type 3 and growth hormone deficiency

The simultaneous occurrence of prepubertal Graves' disease, type 1 Diabetes Mellitus (DM), and Growth hormone deficiency (GHD) is uncommon. GHD has been reported in Autoimmune Polyglandular Syndrome (APS) Type 1 and Type 2 but not in APS Type 3. We report a 3-yr-old boy who presented simultaneously with type 1 DM and Graves' disease. After he developed urticarial rash to Propylthiouracil and Methimazole with persistent thyrotoxicosis, he received 8 millicuries of (131)I at 5 yr of age. We diagnosed GHD at age 8 yr 8 months because of growth deceleration (from 95 to 25%) and abnormal growth rate (3 cm/yr) despite euthyroidism, fair glycemic control, and normal weight gain. Both insulin-like growth factor (IGF) 1 (90 ng/mL; normal 113-261 ng/mL) and IGFBP3 (1.3 mcg/mL; normal 2.1-4.2 mcg/mL) levels were low and peak growth hormone level measured by RIA was 5.2 ng/mL after L-Dopa and insulin tolerance test. The rest of his pituitary functions and magnetic resonance imaging of the pituitary gland were normal. Growth hormone treatment (0.3 mg/kg/wk) was administered at 8 yr 9 months until near final adult height (FAH). Near FAH (172 cm) was close to midparental target height of 180 cm. GHD may be a component of all APS even though it is rare. Growth in treated children with Graves' disease should be followed closely as catch down growth below genetic height potential may be a harbinger of underlying GHD.

Growth hormone/insulin-like growth factor axis in patients with subclinical thyroid dysfunction

OBJECTIVE

Our aim was to evaluate serum concentrations of GH, IGF-I, and insulin-like growth factor-binding protein-3 (IGFBP-3) in patients with subclinical thyroid dysfunction before and after normalization of thyroid function.

DESIGN AND METHODS

The study included 51 patients (mean age 42.2+/-1.8 years) with subclinical hypothyroidism and 30 patients (mean age 44.3+/-2.4 years) with subclinical hyperthyroidism. A group of 37 euthyroid healthy subjects were studied as controls. Serum concentrations of TSH, FT4, FT3, GH, insulin, IGF-I, and IGFBP-3 were measured in all patients before starting therapy and after normalization of thyroid function. The dosage of levothyroxine (LT4) and antithyroid drugs was adjusted in attempt to keep the serum-free thyroxine (FT4) and thyrotropin (TSH) concentrations within the normal range.

MAIN OUTCOME

Baseline growth hormone levels were similar with hypothyroid group and hyperthyroid group in relation to euthyroid control subjects. Fasting serum IGF-I levels were significantly lower in the subclinical hypothyroid group compared with the control group. On the other hand, IGF-I levels of subclinical hyperthyroid patients and control group were similar. After normalization of thyroid function tests, IGF-I concentrations were increased in subclinical hypothyroid subjects, but unchanged in subclinical hyperthyroid subjects. Patients with subclinical hyperthyroidism showed slightly lower mean serum IGFBP-3 concentrations than those found in control group, but the difference was not statistically significant. Serum GH and IGFBP-3 levels were unaltered by treatment.

CONCLUSIONS

In this study, it was shown that GH-IGF axis was not affected in patients with subclinical hyperthyroidism, while it was affected in patients with subclinical hypothyroidism. That is, investigation of the axis in subclinical hyperthyroidism would not bring any extra advantages, but LT4 replacement therapy could prevent abnormalities related to GH-IGF axis in patients with subclinical hypothyroidism.

Insulin-like growth factor-I gene and insulin-like growth factor binding protein-3 polymorphism in patients with thyroid dysfunction

BACKGROUND AND AIMS

Thyroid hormones have important roles in normal growth and skeletal muscle development. IGF-I is one of the most important growth factors and is needed for the proliferation and development of thyroid cells. It stimulates fibroblasts, follicular and endothelia cells in thyroid gland. It has been shown that thyroid hormones play an important role in the regulation of IGF-I and IGFBP-3. In this study we proposed that IGF-I (CA)(19) and IGFBP-3-202 A/C gene polymorphism may affect thyroid functions. For this purpose, frequency of IGF-I (CA)(19) and IGFBP-3-202 A/C gene polymorphism in hypo- and hyperthyroid patients and possible role of these polymorphism in thyroid functions were investigated.

METHODS

This study was performed on 37 volunteer hyperthyroid and 76 hypothyroid patients as well as with 50 healthy subjects as controls. DNA isolation was applied in peripheral blood samples obtained from patients and controls. Required areas were amplified with PCR by using proper primers belonging to these gene areas from the isolated DNA samples. The products were evaluated with visualization by UV gel documentation system.

RESULTS

Frequency of IGF-I (CA)(19) gene polymorphism among hypothyroidism patients, hyperthyroidism patients and controls were statistically significant (chi(2) = 11.55, df = 4, p = 0.021). Genotypic variations between hyper- and hypothyroid patients were significant (chi(2) = 11.39, df = 2, p = 0.003), whereas there was no difference in IGF-I (CA)(19) gene polymorphism between the patients and controls. Differences in the IGFBP-3-202 A/C gene polymorphism between controls and hypo- as well as hyperthyroid patients were not significant. But IGFBP-3-202 A/C gene polymorphism genotype frequencies showed a significant difference between hypo- and hyperthyroid patients (chi(2) = 6.24, df = 2, p = 0.044).

CONCLUSIONS

These findings suggests that IGF-I (CA)(19) and IGFBP-3-202 A/C gene polymorphisms may be a risk factor for hypothyroidism.

Modulation of the growth hormone-insulin-like growth factor (GH-IGF) axis by pharmaceutical, nutraceutical and environmental xenobiotics: an emerging role for xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. A review

The growth hormone-insulin-like growth factor (GH-IGF) axis has gained considerable focus over recent years. One cause of this increased interest is due to a correlation of age-related decline in plasma GH/IGF levels with age-related degenerative processes, and it has led to the prescribing of GH replacement therapy by some practitioners. On the other hand, however, research has also focused on the pro-carcinogenic effects of high GH-IGF levels, providing strong impetus for finding regimes that reduce its activity. Whereas the effects of GH/IGF activity on the action of xenobiotic-metabolizing enzyme systems is reasonably well appreciated, the effects of xenobiotic exposure on the GH-IGF axis has not received substantial review. Relevant xenobiotics are derived from pharmaceutical, nutraceutical and environmental exposure, and many of the mechanisms involved are highly complex in nature, not easily predictable from existing in vitro tests and do not always predict well from in vivo animal models. After a review of the human and animal in vivo and in vitro literature, a framework for considering the different levels of direct and indirect modulation by xenobiotics is developed herein, and areas that still require further investigation are highlighted, i.e. the actions of common endocrine disruptors such as pesticides and phytoestrogens, as well as the role of xenobiotic-metabolizing enzymes and the transcription factors regulating their expression. It is anticipated that a fuller appreciation of the existing human paradigms for GH-IGF axis modulation gained through this review may help explain some of the variation in levels of plasma IGF-1 and its binding proteins in the population, aid in the prescription of particular dietary regimens to certain individuals such as those with particular medical conditions, guide the direction of long-term drug/nutraceutical safety trials, and stimulate ideas for future research. It also serves to warn athletes that using compounds touted as performance enhancing because they promote short-term GH release could in fact be detrimental to performance in the long-run.