Effects of hyperthyroidism on binding proteins for steroid hormones

Reductions in serum levels of LDL cholesterol, apolipoprotein B, triglycerides and lipoprotein(a) in hypercholesterolaemic patients treated with the liver-selective thyroid hormone receptor agonist eprotirome

BACKGROUND

Liver-selective thyromimetic agents could provide a new approach for treating dyslipidaemia.

METHODS

We performed a multicentre, randomized, placebo-controlled, double-blind study to evaluate the efficacy and safety of eprotirome, a liver-selective thyroid hormone receptor agonist, in 98 patients with primary hypercholesterolaemia. After previous drug wash-out and dietary run-in, patients received 100 or 200 μg day(-1) eprotirome or placebo for 12 weeks. The primary end-point was change in serum LDL cholesterol; secondary end-points included changes in other lipid parameters and safety measures.

RESULTS

Eprotirome treatment at 100 and 200 μg daily reduced serum LDL cholesterol levels by 23 ± 5% and 31 ± 4%, respectively, compared with 2 ± 6% for placebo (P < 0.0001). Similar reductions were seen in non-HDL cholesterol and apolipoprotein (apo) B, whereas serum levels of HDL cholesterol and apo A-I were unchanged. There were also considerable reductions in serum triglycerides and lipoprotein(a), in particular in patients with elevated levels at baseline. There was no evidence of adverse effects on heart or bone and no changes in serum thyrotropin or triiodothyronine, although the thyroxine level decreased. Low-grade increases in liver enzymes were evident in most patients.

CONCLUSION

In hypercholesterolaemic patients, the liver-selective thyromimetic eprotirome decreased serum levels of atherogenic lipoproteins without signs of extra-hepatic side effects. Selective stimulation of hepatic thyroid hormone receptors may be an attractive way to modulate lipid metabolism in hyperlipidaemia.

Adrenocortical reserves in hyperthyroidism

Explicit data regarding the changes in adrenocortical reserves during hyperthyroidism do not exist. We aimed to document the capability (response) of adrenal gland to secrete cortisol and DHEA-S during hyperthyroidism compared to euthyroidism, and to describe factors associated with these responses. A standard-dose (0.25 mg/i.v.) ACTH stimulation test was performed to the same patients before hyperthyroidism treatment, and after attainment of euthyroidism. Baseline cortisol (Cor(0)), DHEA-S (DHEA-S(0)), cortisol binding globulin (CBG), ACTH, calculated free cortisol (by Coolen's equation = CFC), free cortisol index (FCI), 60-min cortisol (Cor(60)), and DHEA-S (DHEA-S(60)), delta cortisol (ΔCor), delta DHEA-S (ΔDHEA-S) responses were evaluated. Forty-one patients [22 females, 49.5 ± 15.2 years old, 32 Graves disease, nine toxic nodular goiter] had similar Cor(0), DHEA-S(0), CFC, FCI, and DHEA-S(60) in hyperthyroid and euthyroid states. Cor(60), ΔCor, and ΔDHEA-S were lower in hyperthyroidism. In four (10 %) patients the peak ACTH-stimulated cortisol values were lower than 18 μg/dL. When the test repeated after attainment of euthyroidism, all of the patients had normal cortisol response. Regression analysis demonstrated an independent association of Cor(60) with free T3 in hyperthyroidism. However, the predictors of CFC, FCI, and DHEA-S levels were serum creatinine levels in hyperthyroidism, and both creatinine and transaminase levels in euthyroidism. ACTH-stimulated peak cortisol, delta cortisol, and delta DHEA-S levels are decreased during hyperthyroidism, probably due to increased turnover. Since about 10 % of the subjects with hyperthyroidism are at risk for adrenal insufficiency, clinicians dealing with Graves' disease should be alert to the possibility of adrenal insufficiency during hyperthyroid stage.

Regulation of cortisol bioavailability--effects on hormone measurement and action

Routine assessment of the hypothalamic-pituitary-adrenal axis relies on the measurement of total serum cortisol levels. However, most cortisol in serum is bound to corticosteroid-binding globulin (CBG) and albumin, and changes in the structure or circulating levels of binding proteins markedly affect measured total serum cortisol levels. Furthermore, high-affinity binding to CBG is predicted to affect the availability of cortisol for the glucocorticoid receptor. CBG is a substrate for activated neutrophil elastase, which cleaves the binding protein and results in the release of cortisol at sites of inflammation, enhancing its tissue-specific anti-inflammatory effects. Further tissue-specific modulation of cortisol availability is conferred by corticosteroid 11β-dehydrogenase. Direct assessment of tissue levels of bioavailable cortisol is not clinically practicable and measurement of total serum cortisol levels is of limited value in clinical conditions that alter prereceptor glucocorticoid bioavailability. Bioavailable cortisol can, however, be measured indirectly at systemic, extracellular tissue and cell levels, using novel techniques that have provided new insight into the transport, metabolism and biological action of glucocorticoids. A more physiologically informative approach is, therefore, now possible in the assessment of the hypothalamic-pituitary-adrenal axis, which could prove useful in clinical practice.

Use of the thyroid hormone analogue eprotirome in statin-treated dyslipidemia

BACKGROUND

Dyslipidemia increases the risk of atherosclerotic cardiovascular disease and is incompletely reversed by statin therapy alone in many patients. Thyroid hormone lowers levels of serum low-density lipoprotein (LDL) cholesterol and has other potentially favorable actions on lipoprotein metabolism. Consequently, thyromimetic drugs hold promise as lipid-lowering agents if adverse effects can be avoided.

METHODS

We performed a randomized, placebo-controlled, double-blind, multicenter trial to assess the safety and efficacy of the thyromimetic compound eprotirome (KB2115) in lowering the level of serum LDL cholesterol in patients with hypercholesterolemia who were already receiving simvastatin or atorvastatin. In addition to statin treatment, patients received either eprotirome (at a dose of 25, 50, or 100 microg per day) or placebo. Secondary outcomes were changes in levels of serum apolipoprotein B, triglycerides, and Lp(a) lipoprotein. Patients were monitored for potential adverse thyromimetic effects on the heart, bone, and pituitary.

RESULTS

The addition of placebo or eprotirome at a dose of 25, 50, or 100 microg daily to statin treatment for 12 weeks reduced the mean level of serum LDL cholesterol from 141 mg per deciliter (3.6 mmol per liter) to 127, 113, 99, and 94 mg per deciliter (3.3, 2.9, 2.6, and 2.4 mmol per liter), respectively, (mean reduction from baseline, 7%, 22%, 28%, and 32%). Similar reductions were seen in levels of serum apolipoprotein B, triglycerides, and Lp(a) lipoprotein. Eprotirome therapy was not associated with adverse effects on the heart or bone. No change in levels of serum thyrotropin or triiodothyronine was detected, although the thyroxine level decreased in patients receiving eprotirome.

CONCLUSIONS

In this 12-week trial, the thyroid hormone analogue eprotirome was associated with decreases in levels of atherogenic lipoproteins in patients receiving treatment with statins. (ClinicalTrials.gov number, NCT00593047.)

Effects of the thyromimetic agent diiodothyropropionic acid on body weight, body mass index, and serum lipoproteins: a pilot prospective, randomized, controlled study

CONTEXT

Widespread thyroid hormone actions offer the possibility of developing selective thyromimetic analogs with salutary metabolic properties. Consequently, effects of diiodothyropropionic acid (DITPA) on body weight, serum lipoproteins, and bone metabolism markers were studied in a prospective, controlled, double-blind 24-wk trial, which was primarily designed to assess treatment of stable chronic heart failure.

DESIGN

Eighty-six patients (aged 66 +/- 11 yr, mean +/- sd) were randomized (1:2) to placebo or an escalating DITPA dose (90 to 180, 270, and 360 mg/d) over 8 wk until serum TSH was less than 0.02 mU/liter. Patients were studied at 2, 4, 6, 8, 16, and 24 wk and after 4 wk off study drug. Only 21 DITPA-treated and 27 placebo patients completed the full 24 wk of therapy.

RESULTS

DITPA therapy lowered serum TSH levels and, to a lesser extent, serum T(3) and T(4), but there were no differences in clinical manifestations of thyrotoxicosis or hypothyroidism. Serum total and low-density lipoprotein cholesterol levels both decreased on DITPA; there was a transient decrease in triglycerides and no change in high-density lipoprotein cholesterol. DITPA therapy was associated with significant reduction in body weight, 12.5 lb at 24 wk. Increases in serum osteocalcin, N-telopeptide, and deoxypyridinoline levels were consistent with increased bone turnover on DITPA.

CONCLUSION

This investigation of DITPA actions demonstrated its efficacy in reducing body weight and lowering total and low-density lipoprotein cholesterol levels. However, DITPA's adverse effects at doses used resulted in a high dropout rate and potentially dangerous skeletal actions were observed.

Plasma adrenocorticotropin (ACTH) values and cortisol response to 250 and 1 microg ACTH stimulation in patients with hyperthyroidism before and after carbimazole therapy: case-control comparative study

CONTEXT

Although the production and metabolic clearance rate of cortisol is increased during thyrotoxic state, the net effect on adrenocortical reserves is not clear.

OBJECTIVE

We assessed circulating ACTH levels, cortisol binding globulin (CBG), and adrenocortical reserves in hyperthyroid patients (before and after carbimazole therapy) and healthy controls.

DESIGN AND SETTING

This was a case-control investigative study in a tertiary care setting.

PATIENTS AND METHODS

Plasma ACTH and free cortisol index (FCI; serum cortisol/CBG) were measured in 49 consecutive patients with hyperthyroidism and 50 controls. ACTH(1-24) stimulation tests (250 and 1 microg) were carried out in the first 29 patients and 15 controls. Peak FCI less than the mean -3 sd of healthy controls was considered subnormal. ACTH(1-24) stimulation tests were repeated in 24 patients in the euthyroid state.

RESULTS

The mean basal plasma ACTH and FCI were higher and CBG was lower in thyrotoxic patients in comparison with controls. The peak cortisol was less than 18 microg/dl in 10 of 29 and 14 of 29 on 250 and 1 microg ACTH(1-24) stimulation. Peak FCI was subnormal only in three of 27 (11.1%) and two of 21 (7.4%) on 250 and 1 microg ACTH(1-24) stimulation, respectively. The mean plasma ACTH, basal FCI, and subnormal peak FCI (two of the three) normalized after euthyroidism. Plasma ACTH and FCI did not correlate with severity of thyrotoxicosis.

CONCLUSIONS

Up to 11% of thyrotoxics have subnormal peak FCI on ACTH(1-24) stimulation. Such changes occur despite high basal plasma ACTH and FCI. Use of FCI, rather than total cortisol, is required for the interpretation of cortisol values in thyrotoxicosis due to the variation in CBG.

Hormonal effects on the secretion and glycoform profile of corticosteroid-binding globulin

Corticosteroid-binding globulin (CBG) is a plasma glycoprotein that is primarily synthesized in the liver and binds cortisol and progesterone with high affinity. In this study, a CBG secreting hepatocellular carcinoma derived cell line (HepG2) was used to investigate the hormonal regulation of hepatic CBG synthesis. HepG2 cells were grown for 72 h in 30, 300 and 3000 nM concentrations of estradiol (E2), testosterone (T), insulin, thyroxin (T4) and dexamethasone (DMZ) and the secreted CBG quantified by a novel enzyme-linked immunosorbent assay (ELISA). Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) was carried out to determine the effects of these hormones on the relative distribution of CBG glycoforms. Insulin, T4 and high concentrations of E2 decreased the secretion of CBG by HepG2 cells (p<0.05). Ethanol, the solvent used for E2, T and DMZ, also significantly attenuated CBG secretion. 2D-PAGE resolved 13-14 glycoforms of CBG produced by HepG2 cells. Insulin caused a reduction in the synthesis of more acidic, while T4 and DMZ decreased the production of more basic CBG glycoforms. Stimulation with E2 resulted in the synthesis of additional isoforms of increased acidity, which may represent a type of CBG only seen during pregnancy in vivo. Possible physiological implications of these findings are discussed.

Growth hormone treatment in hypopituitary GH deficient adults reduces circulating cortisol levels during hydrocortisone replacement therapy

OBJECTIVES

Patients with GH deficiency frequently have multiple hormone deficiencies and require hydrocortisone replacement. We have investigated whether GH treatment alters circulating cortisol levels in hypopituitary patients receiving stable replacement therapy.

DESIGN

Subjects were studied during 6 or 12 months of s.c. GH at a dose of 0.25 IU/kg/week (0.125 IU/kg/week for the first 4 weeks), and after a wash-out period of at least 2 months off GH (range 2-5 months).

PATIENTS

Fourteen hypopituitary patients (2F:12M) receiving stable hydrocortisone replacement and thyroxine, gonadal steroids and bromocriptine therapy as required.

MEASUREMENTS

Serum cortisol values were measured throughout the day over 10.5 hours. Thyroid hormones and cortisol binding globulin (CBG) were measured in the baseline sample. Comparisons of the serum cortisol peak after receiving the first dose of hydrocortisone, the time when the serum cortisol peak was obtained, the area under the curve (AUC) for the cortisol values and the levels of unbound cortisol on and off GH therapy were made. The results are expressed as mean +/- SEM. Comparisons were carried out within individuals, using the Wilcoxon signed rank test. A P-value less than 0.05 was considered statistically significant.

RESULTS

During GH therapy, there was a significant reduction in the mean cortisol peak (662.2 +/- 61.1 vs 848.0 +/- 58.6 nmol/l; P = 0.001), and in the AUC for cortisol (185.3 +/- 18.3 vs 230 +/- 17.9 nmol/l/10.5h; P = 0.03), but there was no significant change in the time of the cortisol peak (55.7 +/- 7.6 vs 57.8 +/- 4.9 minutes; P = NS). During GH therapy there was a significant reduction in CBG levels (33.64 +/- 1.16 vs 40.86 +/- 1.34 mg/l; P = 0.001); however, no changes were found in the levels of calculated unbound cortisol on and off GH (2.87 +/- 0.38 vs 2.90 +/- 0.30 nmol/l; P = NS). During GH therapy, there was a significant increase in serum triiodothyronine (T3) (1.88 +/- 0.15 vs 1.44 +/- 0.11 nmol/l; P = 0.01), and a significant decrease in thyroxine (T4) levels (74.9 +/- 11.1 vs 97.6 +/- 10.9 nmol/l; P = 0.02) but levels remained within the normal range. No change was observed in serum TSH levels (0.29 +/- 0.13 vs 0.83 +/- 0.71 mU/l; P = NS).

CONCLUSIONS

These results suggest that GH therapy in GH deficient adults produces an alteration in the measured serum cortisol profile, with a reduction in concentration of total cortisol in blood after orally administered hydrocortisone. These changes in circulating cortisol probably depend primarily on the fall in CBG levels, as no changes were found in the levels of calculated unbound cortisol on and off GH. Our data show that when measuring circulating cortisol levels, the results should be interpreted with caution in GH deficient patients on GH replacement, and different criteria may have to be applied to the circulating cortisol profile of these patients. The results highlight the importance of ensuring adequate corticosteroid replacement in patients starting GH therapy.

Serum soluble interleukin-2 receptors as an index of the biological activity of thyroid hormones in hyperthyroidism

In order to examine whether serum soluble Interleukin-2 Receptors (sIL-2R) could be used as a marker of the biological effects of the thyroid hormones, we measured the sIL-2R, sex hormone binding globulin and beta-2 microglobulin levels in thirty-three hyperthyroid patients (14 with Graves' disease, 17 with Toxic Nodular Goiter and 2 with toxic adenoma) before and during treatment with antithyroid drugs. We found that serum sIL-2R concentrations of the patients, at diagnosis, were significantly higher compared with normal controls (2424 +/- 1447 vs 459 +/- 184 U/ml). All hyperthyroid patients had sIL-2R levels > mean + 2SD of normal controls, with 28 of the 33 patients having sIL-2R concentrations higher than 1011 U/ml (mean + 3SD of normal controls). Only 15 patients had SHBG levels higher than 3SD above the mean for the normal controls and 28 had SHBG levels 2SD above the mean for the normal controls. Three of the 5 hyperthyroid patients with normal SHBG levels at presentation had abnormally high sIL-2R levels. In all patients sIL-2R levels decreased gradually during therapy down to normal levels when euthyroidism was achieved. A strong positive correlation was found between sIL-2R, SHBG and T3 and T4 concentrations. Serum B2-microglobulin (B2-m) levels were higher than the upper normal limit only in 9 patients, but a significant decrement was observed in all patients when euthyroidism was achieved. The above results indicate that serum sIL-2R levels could be a useful marker of the in vivo biological effects of the thyroid hormones on lymphocytes in hyperthyroid patients.

Serum levels of free and bound testosterone in hyperthyroidism

OBJECTIVE

The aim of this study was to improve knowledge about the relationships between free and bound forms of testosterone in serum and the major testosterone-binding proteins during hyperthyroidism.

DESIGN

Nine men and 11 women were studied when hyperthyroid due to Graves' disease and again after at least 3 months of euthyroidism.

MEASUREMENTS

The serum concentrations of free T3, free T4, TSH, sex hormone-binding globulin (SHBG), LH, progesterone and free, non-SHBG bound and total testosterone were determined.

RESULTS

For both sexes, hyperthyroidism was associated with significant elevations of the mean total testosterone and sex hormone-binding globulin (SHBG) levels and significant depressions of the mean percentage and concentration of non-SHBG-bound testosterone and the mean percentage of free testosterone. For women, the mean free testosterone concentration was significantly lower during hyperthyroidism than during euthyroidism; no significant difference in mean free testosterone concentration was observed between hyperthyroid and euthyroid men. When the experimentally derived data were analysed according to a model based on the binding constants of testosterone with SHBG and albumin, the simulated results for each patient when hyperthyroid and euthyroid paralleled the actual results. However, the model consistently overestimated the actual amounts of non-SHBG-bound testosterone. There was a significant correlation between SHBG concentration and the severity of thyrotoxicosis as measured by the change in thyroid hormone levels between euthyroidism and hyperthyroidism.

CONCLUSIONS

Our results support the following pathogenetic sequence: thyrotoxicosis leads to a rise in serum SHBG concentration which is accompanied by an increase in testosterone concentration, a fall in the concentration of non-SHBG-bound testosterone and little or no change in the concentration of free testosterone.