Identification, functional analysis, prevalence and treatment of monocarboxylate transporter 8 (MCT8) mutations in a cohort of adult patients with mental retardation.

OBJECTIVE: Monocarboxylate transporter 8 (MCT8) is an essential thyroid hormone (TH) transporter as humans with MCT8 mutations have severe neurological and endocrine abnormalities. The objectives are (i) to identify novel MCT8 mutations and (ii) to assess their functional relevance; (iii) to describe the effects of block-and-replace treatment in an MCT8 patient. DESIGN: The TOP-R study is a cross-sectional nation-wide multicentre study. PATIENTS: Subjects with unexplained mental retardation (MR) were screened for MCT8 mutations. RESULTS: We identified three mutations: p.F501del (previously described), p.L492P and p.T162T. The F501del and L492P mutants, but not the T162T mutant, showed diminished T3, T4 and rT3 transport in transfected cells. TH transport in T162T fibroblasts was also not affected. One patient was treated with block-and-replace therapy to normalize serum TH levels. The results indicated a slow onset of the decrease in serum T4 and T3 by successive treatment with methimazole and PTU, and eventually their complete normalization by administration of LT4 with PTU but not with methimazole. The frequency of MCT8 mutations in males with X-linked MR approximately 3·9%. CONCLUSIONS: We identified several MCT8 mutations in a cohort of subjects with unexplained MR. We demonstrated the pathogenicity of two missense mutations. The synonymous variant did not affect TH transport. Block-and-replace therapy of one patient reversed the TH abnormalities. Our data suggest a decreased TH secretion rate and an increased T4 to T3 conversion by the type I deiodinase in patients with MCT8 mutations. Our study indicates that MCT8 mutations are a relatively frequent cause of X-linked MR.

Impact of Thyroglobulin and Thyroglobulin Antibody Assay Performance on the Differential Classification of DTC Patients.

CONTEXT: Measurements of thyroglobulin (Tg) and Tg antibodies are crucial in the follow-up of treated differentiated thyroid cancer (DTC) patients. Interassay differences may significantly impact follow-up. OBJECTIVE: The aim of this multicenter study was to explore the impact of Tg and Tg antibody assay performance on the differential classification of DTC patients, as described in national and international guidelines. DESIGN: Four commonly used Tg and Tg antibody assays were technically compared to reflect possible effects on patients with DTC follow-up. Storage stability at different storage temperatures was also investigated for LIAISON® and Kryptor assays, as this is an underexposed topic in current literature. RESULTS: B.R.A.H.M.S. assays yield approximately 50% lower Tg values over the whole range compared to the DiaSorin and Roche assays investigated. These differences between assays may result in potential misclassification in up to 7% of patients if fixed cutoffs (eg, 1 ng/mL) are applied. Poor correlation was also observed between the Tg antibody assays when the method-specific upper limits of normal are used as cutoffs. Storage of Tg and Tg antibodies was possible for 3 to 4 weeks at -20°C and -80°C. Calibration of the assays, however, was found to be crucial for stable results over time. CONCLUSIONS: Technical aspects of Tg and Tg antibody assays, including interassay differences, calibration and standardization, and cutoff values, may have a significant clinical impact on the follow-up of DTC patients.

Mutations in the iodotyrosine deiodinase gene and hypothyroidism.

DEHAL1 has been identified as the gene encoding iodotyrosine deiodinase in the thyroid, where it controls the reuse of iodide for thyroid hormone synthesis. We screened patients with hypothyroidism who had features suggestive of an iodotyrosine deiodinase defect for mutations in DEHAL1. Two missense mutations and a deletion of three base pairs were identified in four patients from three unrelated families; all the patients had a dramatic reduction of in vitro activity of iodotyrosine deiodinase. Patients had severe goitrous hypothyroidism, which was evident in infancy and childhood. Two patients had cognitive deficits due to late diagnosis and treatment. Thus, mutations in DEHAL1 led to a deficiency in iodotyrosine deiodinase in these patients. Because infants with DEHAL1 defects may have normal thyroid function at birth, they may be missed by neonatal screening programs for congenital hypothyroidism.

Thyroid status in a large cohort of patients with mental retardation: the TOP-R (Thyroid Origin of Psychomotor Retardation) study.

OBJECTIVE: Abnormalities in thyroid state may affect development and function of the brain and result in mental retardation (MR). Thyroid parameters have not been systematically investigated in institutionalized MR subjects. The objective is to measure thyroid parameters in a novel cohort of 946 institutionalized subjects. DESIGN: The TOP-R (Thyroid Origin of Psychomotor Retardation) study is a cross-sectional nation-wide multicentre study. PATIENTS: Subjects with unexplained MR. RESULTS: The majority of the MR subjects had thyroid parameters within the reference range used in our laboratory. Antiepileptic drugs (AEDs) use affected thyroid hormones (T4: 102·1 ± 1·2 vs 83·9 ± 1·2 nmol/l, P < 1 × 10(-24) ; FT4: 18·0 ± 0·2 vs 16·1 ± 0·2 pmol/l, P < 1 × 10(-9) ; T3: 1·72 ± 0·02 vs 1·57 ± 0·02 nmol/l, P < 1 × 10(-9) ; and rT3: 0·37 ± 0·01 vs 0·27 ± 0·01 nmol/l, P < 1 × 10(-28) in subjects without vs with AEDs). The prevalence of unrecognized primary hypothyroidism and hyperthyroidism was 5·2% and 2·8%, respectively. CONCLUSIONS: We report thyroid parameters in a cohort of institutionalized subjects with MR. Our findings substantiate the fact that AEDs affect thyroid hormone levels. Future studies will be employed to investigate genetic causes of MR related to abnormalities in thyroid hormone homeostasis.

Tissue-Specific Suppression of Thyroid Hormone Signaling in Various Mouse Models of Aging.

DNA damage contributes to the process of aging, as underscored by premature aging syndromes caused by defective DNA repair. Thyroid state changes during aging, but underlying mechanisms remain elusive. Since thyroid hormone (TH) is a key regulator of metabolism, changes in TH signaling have widespread effects. Here, we reveal a significant common transcriptomic signature in livers from hypothyroid mice, DNA repair-deficient mice with severe (Csbm/m/Xpa-/-) or intermediate (Ercc1-/Δ-7) progeria and naturally aged mice. A strong induction of TH-inactivating deiodinase D3 and decrease of TH-activating D1 activities are observed in Csbm/m/Xpa-/- livers. Similar findings are noticed in Ercc1-/Δ-7, in naturally aged animals and in wild-type mice exposed to a chronic subtoxic dose of DNA-damaging agents. In contrast, TH signaling in muscle, heart and brain appears unaltered. These data show a strong suppression of TH signaling in specific peripheral organs in premature and normal aging, probably lowering metabolism, while other tissues appear to preserve metabolism. D3-mediated TH inactivation is unexpected, given its expression mainly in fetal tissues. Our studies highlight the importance of DNA damage as the underlying mechanism of changes in thyroid state. Tissue-specific regulation of deiodinase activities, ensuring diminished TH signaling, may contribute importantly to the protective metabolic response in aging.

Serum thyroid hormones in preterm infants: associations with postnatal illnesses and drug usage.

CONTEXT: Transient hypothyroxinemia is common in infants less than 30 wk gestation and is associated with neurodevelopmental deficits. Reductions in T4 and T3 levels with TSH unchanged are the key features of severe illness using surrogate indices of overall severity of illness, but these do not inform the impact of individual disease conditions or drug use. OBJECTIVE: Our objective was to investigate the contribution of postnatal factors to the variations in serum levels of iodothyronines, thyroid-binding globulin, and TSH. DESIGN: We recruited a cohort of infants (23-34 wk gestation; n = 780) between January 1998 and September 2001. SETTING AND PATIENTS: The study involved 11 level III Scottish neonatal intensive care units and included cohorts of infants delivered at 23-34 wk gestation. MAIN OUTCOME: We assessed serum levels of iodothyronines, thyroid-binding globulin, and TSH at 7, 14, and 28 d adjusted for the potentially significant postnatal influences (n = 31). RESULTS: Serum levels of TSH, free T4, T3, and T4 are variably but significantly associated with bacteremia, endotracheal bacterial cultures, persistent ductus arteriosus, necrotizing enterocolitis, cerebral ultrasonography changes, oxygen dependence at 28 d, and the use of aminophylline, caffeine, dexamethasone, diamorphine, and dopamine. CONCLUSIONS: There are many more associations of postnatal factors with transient hypothyroxinemia than had previously been considered in preterm infants. Alternative strategies should be considered for correction of hypothyroxinemia rather than sole reliance on the direct therapy of hormone replacement. A more oblique preventative approach may be necessary through reduction in the incidence or severity of individual illness(es). Similarly, alternatives to those drugs that interfere with the hypothalamic-pituitary-thyroid axis should be evaluated (e.g. other inotropics instead of dopamine).

Increased thyroxine sulfate levels in critically ill patients as a result of a decreased hepatic type I deiodinase activity.

INTRODUCTION: Marked changes in peripheral thyroid hormone metabolism occur in critical illness, resulting in low serum T3 and high rT3 levels. In this study, we investigated whether T4S levels are increased in patients who died after intensive care and whether T4S levels are correlated with liver type I deiodinase (D1) or sulfotransferase (SULT) activity. METHODS: A total of 64 blood samples and 65 liver biopsies were obtained within minutes after death from 79 intensive care patients, randomized for intensive or conventional insulin treatment. Serum T4S and the activities of hepatic D1 and 3,3'-diiodothyronine (T2)-SULT and estrogen-SULT were determined. RESULTS: No differences in T4S or hepatic SULT activities were found between patients treated with intensive or with conventional insulin therapy. T4S levels were significantly elevated compared with healthy references. Furthermore, hepatic D1, but not SULT activity, showed a strong correlation with serum T4S (R = -0.53; P < 0.001) and T4S/T4 ratio (R = -0.62; P < 0.001). Cause of death was significantly correlated with hepatic T2- and estrogen-SULT activities (P < 0.01), with SULT activities being highest in the patients who died of severe brain damage and lowest in the patients who died of a cardiovascular collapse. A longer period of intensive care was associated with higher levels of T4S (P = 0.005), and high levels of bilirubin were associated with low T2-SULT (P = 0.04) activities and high levels of T4S (P < 0.001). CONCLUSION: Serum T4S levels were clearly elevated compared with healthy references, and the decreased deiodination by liver D1 during critical illness appears to play a role in this increase in serum T4S levels.

Serum thyroid hormones in preterm infants and relationships to indices of severity of intercurrent illness.

The purpose of this study was to relate severity of illness at 1, 7, 14, and 28 postnatal days in preterm infants groups, 23-27 (n = 73), 28-30 (n = 160), and 31-34 (n = 208) wk gestation, to the corresponding sera levels of T(4), free T(4), T(4)-binding globulin, TSH, T(3), rT(3), and T(4) sulfate. The British Association of Perinatal Medicine and Neonatal Nurses Association 1992 scoring categories (published elsewhere) were used as an index of illness severity: level 1 (maximal intensive care) was compared with level 2 (high-dependency intensive care) combined with level 3 (special care); infants were scored on 1, 7, 14, and 28 postnatal days. In level 1 infants, there were significant reductions in T(3) at 7 d (28-30 wk), 14, and 28 d (23-27 and 28-30 wk); T(4) at 7, 14, and 28 d (23-27 wk); at 14 and 28 d (28-30 wk); and at 7 d (31-34 wk); and free T(4) at 14 d (23-27 wk). TSH was unchanged in all groups at all ages and with reductions in T(4) and T(3) being the key features of severe illness in extreme preterm infants.

Serum 3,3',5'-triiodothyronine (rT3) and 3,5,3'-triiodothyronine/rT3 are prognostic markers in critically ill patients and are associated with postmortem tissue deiodinase activities.

INTRODUCTION AND METHODS: Critical illness is associated with reduced TSH and thyroid hormone secretion, and with changes in peripheral thyroid hormone metabolism, resulting in low serum T3 and high rT3. In 451 critically ill patients who received intensive care for more than 5 d, serum thyroid parameters were determined on d 1, 5, 15, and last day (LD). All patients had been randomized for intensive or conventional insulin treatment. Seventy-one patients died, and postmortem liver and skeletal muscle biopsies were obtained from 50 of them for analysis of deiodinase (D1-3) activities. RESULTS: Insulin treatment did not affect thyroid parameters. On d 1, rT3 was higher and T3/rT3 was lower in nonsurvivors as compared with survivors (P = 0.001). Odds ratio for survival of the highest vs. the lowest quartile was 0.3 for rT3 and 2.9 for T3/rT3. TSH, T4, and T3 were lower in nonsurvivors from d 5 until LD (P < 0.001). TSH, T4, T3, and T3/rT3 increased over time in survivors, but decreased or remained unaltered in nonsurvivors. Liver D1 activity was positively correlated with LD serum T3/rT3 (R = 0.83, P < 0.001) and negatively correlated with rT3 (R = -0.69, P < 0.001). Both liver and skeletal muscle D3 activity were positively correlated with LD serum rT3 (R = 0.32, P = 0.02 and R = 0.31, P = 0.03). CONCLUSION: In critically ill patients who required more than 5 d of intensive care, rT3 and T3/rT3 were already prognostic for survival on d 1. On d 5, T4, T3, but also TSH levels are higher in patients who will survive. Serum rT3 and T3/rT3 were correlated with postmortem tissue deiodinase activities.

Transient hypothyroxinemia in preterm infants: the role of cord sera thyroid hormone levels adjusted for prenatal and intrapartum factors.

CONTEXT: Transient hypothyroxinemia is common in infants less than 30 wk gestation and is associated with neurodevelopmental deficits; it has no consensus definition. We previously suggested that appropriate ranges for postnatal serum T4 values are at least cord levels corrected to an equivalent gestational age if the fetuses had remained in utero. OBJECTIVE: The study objective is to investigate the contribution of prenatal and intrapartum factors (n = 27) to the variations in cord levels of iodothyronines, T4-binding globulin, and TSH, and to provide an appropriate definition of transient hypothyroxinemia. DESIGN: The study design is a cohort study (n = 620) in 11 Scottish neonatal intensive care units. PATIENTS: Infants were delivered at 23- to 42-wk gestation and recruited between January 1998 and September 2001. RESULTS: Using -2 SD of adjusted T4 cord levels applied to postnatal d-7 values of equivalent gestational age, 14% of the 23- to 27-wk group, 1% of the 28- to 30-wk group, and 3% of the 31- to 34-wk group are hypothyroxinemic; using -1 SD, the respective figures are 41, 23, and 12%. CONCLUSIONS: In the absence of neurodevelopmental follow-up studies to quantify transient hypothyroxinemia, a pragmatic criterion is necessary for selection of extreme preterm infants into clinical trials of T4 supplementation. We suggest the use of serum T4 levels on postnatal d 7 that are below -1 SD of adjusted cord T4 levels of equivalent gestational age. This criterion avoids over-recruitment of the more mature infants in whom universal T4 supplementation is detrimental to neurodevelopmental outcome, but still allows selection of the least mature entrants on whom universal T4 supplementation is beneficial.

Tissue thyroid hormone levels in critical illness.

CONTEXT: Pronounced alterations in serum thyroid hormone levels occur during critical illness. T3 decreases and rT3 increases, the magnitudes of which are related to the severity of disease. It is unclear whether these changes are associated with decreased tissue T3 concentrations and, thus, reduced thyroid hormone bioactivity. PATIENTS AND STUDY QUESTIONS: We therefore investigated, in 79 patients who died after intensive care and who did or did not receive thyroid hormone treatment, whether total serum thyroid hormone levels correspond to tissue levels in liver and muscle. Furthermore, we investigated the relationship between tissue thyroid hormone levels, deiodinase activities, and monocarboxylate transporter 8 expression. RESULTS: Tissue iodothyronine levels were positively correlated with serum levels, indicating that the decrease in serum T3 during illness is associated with decreased levels of tissue T3. Higher serum T3 levels in patients who received thyroid hormone treatment were accompanied by higher levels of liver and muscle T3, with evidence for tissue-specific regulation. Tissue rT3 and the T3/rT3 ratio were correlated with tissue deiodinase activities. Monocarboxylate transporter 8 expression was not related to the ratio of the serum over tissue concentration of the different iodothyronines. CONCLUSION: Our results suggest that, in addition to changes in the hypothalamus-pituitary-thyroid axis, tissue-specific mechanisms are involved in the reduced supply of bioactive thyroid hormone in critical illness.

A polymorphism in type I deiodinase is associated with circulating free insulin-like growth factor I levels and body composition in humans.

The interaction between the GH-IGF-I axis and thyroid hormone metabolism is complex and not fully understood. T(4) stimulates IGF-I activity in animals in the absence of GH. On the other hand, GH replacement therapy results in an increase in serum T(3) and a decrease in T(4) and rT(3) levels, suggesting a stimulation of type I deiodinase (D1) activity. Recently, we demonstrated the association of two polymorphisms in D1 (D1a-C/T; T = 34%, and D1b-A/G; G = 10%) with serum iodothyronine levels. Haplotype alleles were constructed, suggesting a lower activity of the D1 haplotype 2 allele (aT-bA) and a higher activity of the haplotype allele 3 (aC-bG). In this study, we investigated whether genetic variations in D1 are associated with the IGF-I system. In 156 blood donors and 350 elderly men, the association of the D1 haplotype alleles with circulating IGF-I and free IGF-I levels was studied. In addition, potential associations with muscle strength and body composition were investigated in the elderly population. Finally, the relation between serum iodothyronine levels and IGF-I levels was studied. In blood donors, haplotype allele 2 was associated with higher levels of free IGF-I (302.9 +/- 22.9 vs. 376.3 +/- 19.1 pg/ml, P = 0.02). In elderly men, haplotype allele 2 also showed an allele dose increase in free IGF-I levels (P(trend) = 0.01) and an allele dose decrease in serum T(3) levels (P(trend) = 0.01), independent of age. Carriers of the D1a-T variant also had a higher isometric grip strength (P = 0.047) and maximum leg extensor strength (P = 0.07) as well as a higher lean body mass (P = 0.03). In blood donors, T(4) and free T(4) were negatively correlated with total IGF-I levels (R = -0.18, P = 0.03 and R = -0.24, P = 0.003), whereas T(3) to T(4) and T(3) to reverse T(3) ratios were positively correlated with total IGF-I (R = 0.31, P < 0.001 and R = 0.18, P = 0.03). Free IGF-I showed a negative correlation with T(4) (R = -0.26, P = 0.001) and T(4)-binding globulin (R = -0.31, P < 0.001) and a positive correlation with T(3) to T(4) ratio (R = 0.21, P = 0.01). In conclusion, a polymorphism that results in a decreased D1 activity is associated with an increase in free IGF-I levels. The pathophysiological significance of this association with IGF-I is supported by an increased muscle strength and muscle mass in carriers of the D1 haplotype 2 allele in a population of elderly men. The association of D1 haplotype allele 2 with serum T(3) levels in the elderly population suggests a relative increase in its contribution to circulating T(3) in old age.

Molecular basis for the substrate selectivity of cat type I iodothyronine deiodinase.

The type I iodothyronine deiodinase (D1) catalyzes the activation of T4 to T3 as well as the degradation of T3 (rT3) and sulfated iodothyronines. A comparison of the catalytic activities of D1 in liver microsomal preparations from several species revealed a remarkable difference between cat D1 on one hand and rat/human D1 on the other hand. The Michaelis constant (Km) of cat D1 for rT3 (11 microm) is 30-fold higher than that of rat and human D1 (0.2-0.5 microm). Deiodination of rT3 by cat D1 is facilitated by sulfation [maximal velocity (Vmax)/Km rT3 = 3 and Vmax/Km rT3S = 81]. To understand the molecular basis for the difference in substrate interaction the cat D1 cDNA was cloned, and the deduced amino acid sequence was compared with rat/human D1 protein. In the region between amino acid residues 40 and 70 of cat D1, various differences with rat/human D1 are concentrated. By site-directed mutagenesis of cat D1 it was found that a combination of mutations was necessary to improve the deiodination of rT3 by cat D1 enzyme. For efficient rT3 deiodination, a Phe at position 65 and the insertion of the Thr-Gly-Met-Thr-Arg48-52 sequence as well as the amino acids Gly and Glu at position 45-46 are essential. Either of these changes alone resulted in only a limited improvement of rT3 deiodination. At the same time the combination of the described mutations did not affect the already quite efficient outer ring deiodination of rT3S nor the inner ring deiodination of T3S, whereas each of the described changes alone did affect rT3S deiodination. Our findings suggest great flexibility of the active site in D1 that adapts to its various substrates. The active site of wild-type cat D1 is less flexible than the active site of rat/human D1 and favors sulfated iodothyronines.

Human fetal and cord serum thyroid hormones: developmental trends and interrelationships.

Thyroid hormone is essential for fetal and neonatal development in particular of the brain, but little is known about regulation of fetal thyroid hormone levels throughout human gestation. The purpose of this study was to clarify developmental trends and interrelationships among T(4), free T(4) (FT4), thyroxine-binding globulin (TBG), TSH, T(3), rT(3), and T(4) sulfate (T4S) levels in cord and fetal blood sera (n = 639, 15-42 wk gestation) and correlate infant levels (23-42 wk gestation) to maternal values (n = 428, 16-45 yr) and those of nonpregnant women (n = 233, 16-46 yr). In cord and fetal serum, T(4), T(3), and TBG levels increase with gestation until term; TSH, FT4, T4S, and rT(3) levels increase and peak in the late second/early third trimester and then decline to term; T(4)/TBG ratios increase until late second trimester and plateau to term. Term cord sera TSH, TBG, and all iodothyronine levels, except T(3), are higher than nonpregnant women. In the third trimester, cord serum FT4, TSH, rT(3), and T4S levels are also higher than corresponding maternal levels, but T(4), T(3), and TBG levels are lower than maternal values. The late second/early third trimester is a critical transition period in fetal thyroid hormone metabolism, which may be interrupted by preterm birth and contribute to postnatal thyroid dysfunction.

The hypothalamic-pituitary-thyroid axis in preterm infants; changes in the first 24 hours of postnatal life.

The purpose of this study was to measure serum T4, free T4, TSH, T3, rT3, T4 sulfate, and thyroxine binding globulin at four time points within the first 24 h of life (cord and 1, 7, and 24 h) in infants between 24 and 34 wk gestation. The infants were subdivided into gestational age groups: 24-27 wk (n = 22); 28-30 wk (n = 26); and 31-34 wk (n = 24). The TSH surge in the first hour of postnatal life was markedly attenuated in infants of 24-27 wk gestation [8 compared with 20 (28-30 wk) and 23 mU/liter (31-34 wk)]. T4 levels in the most immature group declined over the first 24 h, whereas levels increased in the more mature groups [mean cord and 24-h levels: 65 and 59 (NS) vs. 70 and 84 (P < 0.002) vs. 98 and 125 (NS) nmol/liter]. Free T4 and T3 showed only small, transient increases in the most immature group and progressively larger and sustained increases in the other gestational groups. rT3 and T4 sulfate levels in cord serum were higher in the most immature infants, and in all groups levels decreased initially and then variably increased. The features of a severely attenuated or failed hypothalamic-pituitary-thyroid response to delivery critically define this 24- to 27-wk group as distinct from more mature preterm infants.

Polymorphisms in thyroid hormone pathway genes are associated with plasma TSH and iodothyronine levels in healthy subjects.

Single nucleotide polymorphisms (SNPs) in genes involved in thyroid hormone metabolism may affect thyroid hormone bioactivity. We investigated the occurrence and possible effects of SNPs in the deiodinases (D1-D3), the TSH receptor (TSHR), and the T(3) receptor beta (TR beta) genes. SNPs were identified in public databases or by sequencing of genomic DNA from 15 randomly selected subjects (30 alleles). Genotypes for the identified SNPs were determined in 156 healthy blood donors and related to plasma T(4), free T(4), T(3), rT(3), and TSH levels. Eight SNPs of interest were identified, four of which had not yet been published. Three are located in the 3'-untranslated region: D1a-C/T (allele frequencies, C = 66%, T = 34%), D1b-A/G (A = 89.7%, G = 10.3%), and D3-T/G (T = 85.5%, G = 14.2%). Four are missense SNPs: D2-A/G (Thr92Ala, Thr = 61.2%, Ala = 38.8%), TSHRa-G/C (Asp36His, Asp = 99.4%, His = 0.6%), TSHRb-C/A (Pro52Thr, Pro = 94.2%, Thr = 5.8%), and TSHRc-C/G (Asp727Glu, Asp = 90.7%, Glu = 9.3%). One is a silent SNP: TR beta-T/C (T = 96.8%, C = 3.2%). D1a-T was associated in a dose-dependent manner with a higher plasma rT(3) [CC, 0.29 +/- 0.01; CT, 0.32 +/- 0.01; and TT, 0.34 +/- 0.02 nmol/liter (mean +/- SE); P = 0.017], a higher plasma rT(3)/T(4) (P = 0.01), and a lower T(3)/rT(3) (P = 0.003) ratio. The D1b-G allele was associated with lower plasma rT(3)/T(4) (P = 0.024) and with higher T(3)/rT(3) (P = 0.08) ratios. TSHRc-G was associated with a lower plasma TSH (CC, 1.38 +/- 0.07, vs. GC, 1.06 +/- 0.14 mU/liter; P = 0.04), and with lower plasma TSH/free T(4) (P = 0.06), TSH/T(3) (P = 0.06), and TSH/T(4) (P = 0.08) ratios. No associations with TSH and iodothyronine levels were found for the other SNPs. We have analyzed eight SNPs in five thyroid hormone pathway genes and found significant associations of three SNPs in two genes (D1, TSHR) with plasma TSH or iodothyronine levels in a normal population.

Reduced activation and increased inactivation of thyroid hormone in tissues of critically ill patients.

Critical illness is often associated with reduced TSH and thyroid hormone secretion as well as marked changes in peripheral thyroid hormone metabolism, resulting in low serum T(3) and high rT(3) levels. To study the mechanism(s) of the latter changes, we determined serum thyroid hormone levels and the expression of the type 1, 2, and 3 iodothyronine deiodinases (D1, D2, and D3) in liver and skeletal muscle from deceased intensive care patients. To study mechanisms underlying these changes, 65 blood samples, 65 liver, and 66 skeletal muscle biopsies were obtained within minutes after death from 80 intensive care unit patients randomized for intensive or conventional insulin treatment. Serum thyroid parameters and the expression of tissue D1-D3 were determined. Serum TSH, T(4), T(3), and the T(3)/rT(3) ratio were lower, whereas serum rT(3) was higher than in normal subjects (P < 0.0001). Liver D1 activity was down-regulated and D3 activity was induced in liver and skeletal muscle. Serum T(3)/rT(3) ratio correlated positively with liver D1 activity (P < 0.001) and negatively with liver D3 activity (ns). These parameters were independent of the type of insulin treatment. Liver D1 and serum T(3)/rT(3) were highest in patients who died from severe brain damage, intermediate in those who died from sepsis or excessive inflammation, and lowest in patients who died from cardiovascular collapse (P < 0.01). Liver D3 showed an opposite relationship. Acute renal failure requiring dialysis and need of inotropes were associated with low liver D1 activity (P < 0.01 and P = 0.06) and high liver D3 (P < 0.01) and skeletal muscle D3 (P < 0.05) activity. Liver D1 activity was negatively correlated with plasma urea (P = 0.002), creatinine (P = 0.06), and bilirubin (P < 0.0001). D1 and D3 mRNA levels corresponded with enzyme activities (both P < 0.001), suggesting regulation of the expression of both deiodinases at the pretranslational level. This is the first study relating tissue deiodinase activities with serum thyroid hormone levels and clinical parameters in a large group of critically ill patients. Liver D1 is down-regulated and D3 (which is not present in liver and skeletal muscle of healthy individuals) is induced, particularly in disease states associated with poor tissue perfusion. These observed changes, in correlation with a low T(3)/rT(3) ratio, may represent tissue-specific ways to reduce thyroid hormone bioactivity during cellular hypoxia and contribute to the low T(3) syndrome of severe illness.

Potent inhibition of estrogen sulfotransferase by hydroxylated metabolites of polyhalogenated aromatic hydrocarbons reveals alternative mechanism for estrogenic activity of endocrine disrupters.

Polyhalogenated aromatic hydrocarbons (PHAHs), such as polychlorinated dibenzo-p-dioxins and dibenzofurans, polybrominated diphenylethers, and bisphenol A derivatives are persistent environmental pollutants, which are capable of interfering with reproductive and endocrine function in birds, fish, reptiles, and mammals. PHAHs exert estrogenic effects that may be mediated in part by their hydroxylated metabolites (PHAH-OHs), the mechanisms of which remain to be identified. PHAH-OHs show low affinity for the ER. Alternatively, they may exert their estrogenic effects by inhibiting E2 metabolism. As sulfation of E2 by estrogen sulfotransferase (SULT1E1) is an important pathway for E2 inactivation, inhibition of SULT1E1 may lead to an increased bioavailability of estrogens in tissues expressing this enzyme. Therefore, we studied the possible inhibition of human SULT1E1 by hydroxylated PHAH metabolites and the sulfation of the different compounds by SULT1E1. We found marked inhibition of SULT1E1 by various PHAH-OHs, in particular by compounds with two adjacent halogen substituents around the hydroxyl group that were effective at (sub)nanomolar concentrations. Depending on the structure, the inhibition is primarily competitive or noncompetitive. Most PHAH-OHs are also sulfated by SULT1E1. We also investigated the inhibitory effects of the various PHAH-OHs on E2 sulfation by human liver cytosol and found that the effects were strongly correlated with their inhibitions of recombinant SULT1E1 (r = 0.922). Based on these results, we hypothesize that hydroxylated PHAHs exert their estrogenic effects at least in part by inhibiting SULT1E1-catalyzed E2 sulfation.

Developmental trends in cord and postpartum serum thyroid hormones in preterm infants.

The purpose of this study was first to clarify postnatal trends in sera T(4), free T(4) (FT(4)), T(4)-binding globulin, TSH, T(3), rT(3), and T(4) sulfate levels in cord and at 7, 14, and 28 d in groups of preterm infants at 23-27 wk (n = 101), 28-30 wk (n = 196), and 31-34 (n = 253) wk gestation, and second to compare these trends to those of term infants and also with cord sera levels of equivalent gestational ages (n = 812; 23-42 wk gestation). In all preterm groups, TSH and rT(3) decrease to below, T(4)-binding globulin increases to within, and T(3) and T(4) sulfate increase to above cord levels of equivalent gestational age. Term infants are hyperthyroxinemic relative to cord and nonpregnant adult levels of T(4). Postnatal T(4) increases are attenuated in 31- to 34-wk infants, absent in 28- to 30-wk infants (although levels are equivalent to gestational age), and crucially reversed in 23- to 27-wk infants. This immature group is hypothyroxinemic relative to other groups and to cord levels of equivalent gestational age. Compared with term infants, postnatal FT(4) increases are lower in 31- to 34-wk infants, attenuated in 28- to 30-wk infants, and absent in 23- to 27-wk infants. The 23- to 27-wk group is distinctive; they are hypothyroxinemic on T(4) levels, yet FT(4) levels are within the cord levels of equivalent gestational age.