Clinical efficacy of selenium supplementation in patients with Hashimoto thyroiditis: A systematic review and meta-analysis

BACKGROUND

Evidence suggests that selenium supplementation could be useful in the treatment of Hashimoto thyroiditis (HT), but the available trials are heterogeneous. This study investigates clinically relevant effects of selenium supplementation in patients with HT.

METHODS

A systematic search was performed in PubMed, Web of Science, EMBASE, Scopus, and the Cochrane Library. The latest update was performed on December 3, 2022. We investigated the changes in thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb) after selenium supplementation. The effect sizes were expressed as weighted mean difference (WMD) with 95% confidence intervals (CIs).

RESULTS

After screening and full-text assessment, 7 controlled trials comprising 342 patients were included in the systematic review. The results showed that there was no significant change in TPOAb levels (WMD = -124.28 [95% CI: -631.08 to 382.52], P = .631, I2 = 94.5%) after 3 months of treatment. But there was a significant decrease in TPOAb levels (WMD = -284.00 [95% CI: -553.41 to -14.60], P < .05, I2 = 93.9%) and TgAb levels (WMD = -159.86 [95% CI: -293.48 to -26.24], P < .05, I2 = 85.3%) after 6 months of treatment.

CONCLUSIONS

Selenium supplementation reduces serum TPOAb and TgAb levels after 6 months of treatment in patients with HT, but future studies are warranted to evaluate health-related quality or disease progression.

Propranolol inhibits myocardial infarction-induced brown adipose tissue D2 activation and maintains a low thyroid hormone state in rats

Considering the recognized role of thyroid hormones on the cardiovascular system during health and disease, we hypothesized that type 2 deiodinase (D2) activity, the main activation pathway of thyroxine (T4)-to-triiodothyronine (T3), could be an important site to modulate thyroid hormone status, which would then constitute a possible target for β-adrenergic blocking agents in a myocardial infarction (MI) model induced by left coronary occlusion in rats. Despite a sustained and dramatic fall in serum T4 concentrations (60-70%), the serum T3 concentration fell only transiently in the first week post-infarction (53%) and returned to control levels at 8 and 12 weeks after surgery compared to the Sham group (P<0.05). Brown adipose tissue (BAT) D2 activity (fmol T4·min-1·mg ptn-1) was significantly increased by approximately 77% in the 8th week and approximately 100% in the 12th week in the MI group compared to that of the Sham group (P<0.05). Beta-blocker treatment (0.5 g/L propranolol given in the drinking water) maintained a low T3 state in MI animals, dampening both BAT D2 activity (44% reduction) and serum T3 (66% reduction in serum T3) compared to that of the non-treated MI group 12 weeks after surgery (P<0.05). Propranolol improved cardiac function (assessed by echocardiogram) in the MI group compared to the non-treated MI group by 40 and 57%, 1 and 12 weeks after treatment, respectively (P<0.05). Our data suggested that the beta-adrenergic pathway may contribute to BAT D2 hyperactivity and T3 normalization after MI in rats. Propranolol treatment maintained low T3 state and improved cardiac function additionally.

Interaction between deca-BDE and hepatic deiodinase in a highly PBDE-exposed bird

Studies have shown that debromination of the major component in the deca-brominated diphenyl ether mixture (deca-BDE), BDE-209, occurs in vivo in birds. Recent work from our laboratory on breeding ring-billed gulls (Larus delawarensis) exposed to elevated PBDE concentrations in the densely-populated metropolis of Montreal (Canada) further suggests that BDE-209 debromination is potentially catalyzed by deiodinases in liver microsomes. The first objective of this study was to determine if type 1 deiodinase (D1) was involved in the in vitro debromination of BDE-209 in liver microsomes of ring-billed gulls. The second objective was to determine if there was an interaction between D1 and BDE-209 using an in vitro D1 activity assay. No depletion of BDE-209 was observed in gull liver microsomes. A significant 42% increase in total D1 activity was found in gull liver microsomes at the medium BDE-209 concentration (1.0 nM), although not at the low (0.5 nM) or high (2.5 nM) concentrations, suggesting potential non-dose related interaction with D1. Moreover, no correlation was found between total D1 activity in liver microsomes and plasma thyroid hormone levels, although there was a negative relationship between plasma BDE-209 concentrations and FT₃ levels. Results from this study suggest that debromination of BDE-209 did not occur using present in vitro assay conditions, although indicated potential interaction with D1 that may have implication on circulating thyroid hormone status.

Regulation of Gene Expression by Thyroid Hormone in Primary Astrocytes: Factors Influencing the Genomic Response

Astrocytes mediate the action of thyroid hormone in the brain on other neural cells through the production of the active hormone triiodothyronine (T3) from its precursor thyroxine. T3 has also many effects on the astrocytes in vivo and in culture, but whether these actions are directly mediated by transcriptional regulation is not clear. In this work, we have analyzed the genomic response to T3 of cultured astrocytes isolated from the postnatal mouse cerebral cortex using RNA sequencing. Cultured astrocytes express relevant genes of thyroid hormone metabolism and action encoding type 2 deiodinase (Dio2), Mct8 transporter (Slc16a2), T3 receptors (Thra1 and Thrb), and nuclear corepressor (Ncor1) and coactivator (Ncoa1). T3 changed the expression of 668 genes (4.5% of expressed genes), of which 117 were responsive to T3 in the presence of cycloheximide. The Wnt and Notch pathways were downregulated at the posttranscriptional level. Comparison with the effect of T3 on astrocyte-enriched genes in mixed cerebrocortical cultures isolated from fetal cortex revealed that the response to T3 is influenced by the degree of astrocyte maturation and that, in agreement with its physiological effects, T3 promotes the transition between the fetal and adult patterns of gene expression.

Impacts of Unregulated Novel Brominated Flame Retardants on Human Liver Thyroid Deiodination and Sulfotransferation

The inhibitory effects of five novel brominated flame retardants, 1,2-bis(2,4,5-tribromophenoxy)ethane (BTBPE), decabromodiphenylethane (DBDPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), bis(2-ethylhexyl)tetrabromophthalate (BEH-TEBP), and β-tetrabromoethylcyclohexane (β-TBECH), on thyroid hormone deiodinase (DIO) and sulfotransferase (SULT) activity were investigated using human in vitro liver microsomal and cytosolic bioassays. Enzymatic activity was measured by incubating active human liver subcellular fractions with thyroid hormones (T4 and rT3 separately) and measuring changes in thyroid hormone (T4, T3, rT3, and 3,3'-T2) concentrations. Only DBDPE showed inhibition of both outer and inner ring deiodination (O and IRD) of T3 and 3,3'-T2 formation from T4, respectively, with an estimated IC₅₀ of 160 nM; no statistically significant inhibition of SULT activity was observed. ORD inhibition of 3,3'-T2 formation from rT3 was also observed (IC₅₀ ∼ 100 nM). The kinetics of T4 O and IRD were also investigated, although a definitive mechanism could not be identified as the Michaelis-Menten parameters and maximal rate constants were not significantly different. Concentrations tested were intentionally above expected environmental levels, and this study suggests that these NBFRs are not potent human liver DIO and SULT inhibitors. To our knowledge, DBDPE is the first example of a nonhydroxylated contaminant inhibiting DIO activity, and further study of the mechanism of action is warranted.

TAZ Induction Directs Differentiation of Thyroid Follicular Cells from Human Embryonic Stem Cells

OBJECTIVE

The differentiation program for human thyroid follicular cells (TFCs) relies on the interplay between sequence-specific transcription factors and transcriptional co-regulators. Transcriptional co-activator with PDZ-binding motif (TAZ) is a co-activator that regulates several transcription factors, including PAX8 and NKX2-1, which play a central role in thyroid-specific gene transcription. TAZ and PAX8/NKX2-1 are co-expressed in the nuclei of thyroid cells, and TAZ interacts directly with both PAX8 and NKX2-1, leading to their enhanced transcriptional activity on the thyroglobulin (TG) promoter and additional genes.

METHODS

The use of a small molecule, ethacridine, recently identified as a TAZ activator, in the differentiation of thyroid cells from human embryonic stem (hES) cells was studied. First, endodermal cells were derived from hES cells using Activin A, followed by induction of differentiation into thyroid cells directed by ethacridine and thyrotropin (TSH).

RESULTS

The expression of TAZ was increased in the Activin A-derived endodermal cells by ethacridine in a dose-dependent manner and followed by increases in PAX8 and NKX2-1 when assessed by both quantitative polymerase chain reaction and immunostaining. Following further differentiation with the combination of ethacridine and TSH, the thyroid-specific genes TG, TPO, TSHR, and NIS were all induced in the differentiated hES cells. When these cells were cultured with extracellular matrix-coated dishes, thyroid follicle formation and abundant TG protein expression were observed. Furthermore, such hES cell-derived thyroid follicles showed a marked TSH-induced and dose-dependent increase in radioiodine uptake and protein-bound iodine accumulation.

CONCLUSION

These data show that fully functional human thyroid cells can be derived from hES cells using ethacridine, a TAZ activator, which induces thyroid-specific gene expression and promotes thyroid cell differentiation from the hES cells. These studies again demonstrate the importance of transcriptional regulation in thyroid cell development. This approach also yields functional human thyrocytes, without any gene transfection or complex culture conditions, by directly manipulating the transcriptional machinery without interfering with intermediate signaling events.

Effects of Long-Term In Vivo Exposure to Di-2-Ethylhexylphthalate on Thyroid Hormones and the TSH/TSHR Signaling Pathways in Wistar Rats

Di-(2-ethylhexyl)phthalate (DEHP) was a widely used chemical with human toxicity. Recent in vivo and in vitro studies suggested that DEHP-exposure may be associated with altered serum thyroid hormones (THs) levels, but the underlying molecular mechanisms were largely unknown. To explore the possible molecular mechanisms, 128 Wistar rats were dosed with DEHP by gavage at 0, 150, 300, and 600 mg/kg/day for 3 months (M) and 6 M, respectively. After exposure, expression of genes and proteins in the thyroid, pituitary, and hypothalamus tissues of rats were analyzed by Q-PCR and western blot, while the sera and urine samples were assayed by radioimmunoassay and ELISA. Results showed that serum THs levels were suppressed by DEHP on the whole. DEHP treatment influenced the levels of rats’ thyrotropin releasing hormone receptor (TRHr), Deiodinases 1 (D1), thyroid stimulating hormone beta (TSHβ), sodium iodide symporter (NIS), thyroid stimulating hormone receptor (TSHr), thyroperoxidase (TPO), thyroid transcription factor 1 (TTF-1), and thyroglobulin (TG) mRNA/protein expression in the hypothalamus-pituitary-thyroid (HPT) axis and decreased urine iodine. Taken together, observed findings indicate that DEHP could reduce thyroid hormones via disturbing the HPT axis, and the activated TSH/TSHR pathway is required to regulate thyroid function via altering TRHr, TSHβ, NIS, TSHr, TPO, TTF-1 and TG mRNA/protein expression of the HPT axis.

Increased Thyroid Hormone Activation Accompanies the Formation of Thyroid Hormone-Dependent Negative Feedback in Developing Chicken Hypothalamus

The hypothalamic-pituitary-thyroid axis is governed by hypophysiotropic TRH-synthesizing neurons located in the hypothalamic paraventricular nucleus under control of the negative feedback of thyroid hormones. The mechanisms underlying the ontogeny of this phenomenon are poorly understood. We aimed to determine the onset of thyroid hormone-mediated hypothalamic-negative feedback and studied how local hypothalamic metabolism of thyroid hormones could contribute to this process in developing chicken. In situ hybridization revealed that whereas exogenous T4 did not induce a statistically significant inhibition of TRH expression in the paraventricular nucleus at embryonic day (E)19, T4 treatment was effective at 2 days after hatching (P2). In contrast, TRH expression responded to T3 treatment in both age groups. TSHβ mRNA expression in the pituitary responded to T4 in a similar age-dependent manner. Type 2 deiodinase (D2) was expressed from E13 in tanycytes of the mediobasal hypothalamus, and its activity increased between E15 and P2 both in the mediobasal hypothalamus and in tanycyte-lacking hypothalamic regions. Nkx2.1 was coexpressed with D2 in E13 and P2 tanycytes and transcription of the cdio2 gene responded to Nkx2.1 in U87 glioma cells, indicating its potential role in the developmental regulation of D2 activity. The T3-degrading D3 enzyme was also detected in tanycytes, but its level was not markedly changed before and after the period of negative feedback acquisition. These findings suggest that increasing the D2-mediated T3 generation during E18-P2 could provide the sufficient local T3 concentration required for the onset of T3-dependent negative feedback in the developing chicken hypothalamus.

Bile acids induce uncoupling protein 1-dependent thermogenesis and stimulate energy expenditure at thermoneutrality in mice

It has been proposed that diet-induced obesity at thermoneutrality (TN; 29°C) is reduced by a UCP1-dependent thermogenesis; however, it has not been shown how UCP1-dependent thermogenesis can be activated in the absence of sympathetic activity. A recent study provides such a mechanism by showing that dietary bile acids (BAs) suppress obesity in mice fed a high-fat diet (HFD) by a mechanism dependent on type 2 deiodinase (DIO2); however, neither a role for UCP1 nor the influence of sympathetic activity was properly assessed. To test whether the effects of BAs on adiposity are independent of Ucp1 and cold-activated thermogenesis, obesity phenotypes were determined in C57BL6/J.(+)/(+) (WT) and C57BL6/J.Ucp1.(-)/(-) mice (Ucp1-KO) housed at TN and fed a HFD with or without 0.5% (wt/wt) cholic acid (CA) for 9 wk. CA in a HFD reduced adiposity and hepatic lipogenesis and improved glucose tolerance in WT but not in Ucp1-KO mice and was accompanied by increases in food intake and energy expenditure (EE). In iBAT, CA increased Ucp1 mRNA and protein levels 1.5- and twofold, respectively, and increased DIO2 and TGR5 protein levels in WT mice. Despite enhanced Dio2 expression in Ucp1-KO and Ucp1-KO-CA treated mice, this did not enhance the ability of BAs to reduce obesity. By comparing the effects of BAs on WT and Ucp1-KO mice at TN, our study showed that BAs suppress diet-induced obesity by increasing EE through a mechanism dependent on Ucp1 expression, which is likely independent of adrenergic signaling.

Deiodinase 2 upregulation demonstrated in osteoarthritis patients cartilage causes cartilage destruction in tissue-specific transgenic rats

OBJECTIVE

Chondrocyte hypertrophy followed by cartilage destruction is a crucial step for osteoarthritis (OA) development, however, the underlying mechanism remains largely unknown. The objectives of this study are to identify the gene that may cause cartilage hypertrophy and to elucidate its role on OA pathogenesis.

DESIGN

Gene expression profiles of cartilages from OA patients and normal subjects were examined by microarray analysis. Expression of deiodinases, enzymes for regulation of triiodothyronine (T3) biosynthesis, in human and rat articular cartilage (AC) were examined by real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). Rat ACs and chondrocytes were treated with T3 to investigate its role on chondrocyte hypertrophy and inflammatory reaction. Cartilage-specific Type II deiodinase (DIO2) transgenic rats were generated using bacterial artificial chromosome harboring the entire rat Col2a1 and human DIO2 gene. An experimental OA model was created in the animal to examine the role of DIO2 on cartilage degeneration.

RESULTS

DIO2 is highly expressed in OA patient AC compared to normal control. In rat AC, DIO2 is specifically expressed among deiodinases and dominantly expressed the same as in brown adipose tissue. T3 induces hypertrophic markers in articular chondrocyte and cartilage explant culture, and enhances the effect of IL-1α on induction of cartilage degrading enzymes. Importantly, cartilage-specific DIO2 transgenic rats are more susceptible to knee joint destabilization and develop severe AC destruction.

CONCLUSION

Our findings demonstrate that upregulated expression of DIO2 in OA patient cartilage might be responsible for OA pathogenesis by enhancing the chondrocyte hypertrophy and inflammatory response.

Soy content of basal diets determines the effects of supplemental selenium in male mice

The effects of supplemental Se in rodent models may depend upon composition of the basal diet to which it is added. Wild-type male littermates of Transgenic Adenocarcinoma of Mouse Prostate mice were fed until 18 wk of age 1 of 2 Se-adequate stock diets high in soy (HS) or low in phytoestrogens (LP) or the same diets supplemented with 3.0 mg Se/kg diet as seleno-methylselenocysteine. Body and abdominal fat pad weights were lower (P < 0.01) in mice fed the HS diet. Supplemental Se reduced fat pad weights in mice receiving the LP diet but increased body and fat pad weights in mice consuming the HS formulation (P-interaction < 0.005). Serum free triiodothyronine concentrations were unaffected by supplemental Se in mice fed the LP diet but were decreased by Se supplementation of mice given the HS feed (P-interaction < 0.02). Free thyroxine concentrations were higher in mice consuming the HS diet regardless of Se intake (P < 0.001). Hepatic mRNA for iodothyronine deiodinase I was lower (P < 0.001) in mice fed the HS diet. Supplementation of Se increased this mRNA (P < 0.001) in both diet groups. Results from this study show a significant interaction between the composition of basal diets and the effects of supplemental Se with respect to body composition. These findings have important implications for future studies in rodent models of the effects of supplemental Se on heart disease, cancer, diabetes, and other conditions related to body weight and composition.

[Effects of nano-selenium on the capability of learning memory and the activity of Se-protein of mice]

OBJECTIVE

To investigate the effects of Nano-Selenium on learning memory capability and activity of two kinds of Se-protein in brain and liver of mice, Na, SeO3 as the controls.

METHODS

The mice were administred two kinds of origin (doses of 1 microgSe/d, 2 microgSe/d, 4 microgSe/d) Se by intra-gastric injection respectively. The learning memory ability of the mice was measured by Y-type maze test. Activities of glutathione peroxidase (GSH-Px) and iodothyronine deiodinase (ID) in brain and liver were also measured.

RESULTS

In comparison with the control groups of Na2 Se03, learning memory abilities were improved and activities of ID and GSH-Px (P < 0.01 or P < 0.05) of brain and liver were increased in Nano-Se treatment groups.

CONCLUSION

Nano-Se could improve learning memory ability of mice, and enhance ID and GSH-Px activities of brain and liver in mice.

Synthesis and evaluation of novel pyridine based PLG tripeptidomimetics

Analogues of the pyridine based PLG (Pro-Leu-Gly-NH(2)) peptidomimetic were synthesized and evaluated as dopamine modulating agents. Modifications in the position corresponding to the leucine side chain in PLG afforded derivatives , and , substituted with H, Me and Bn instead of the isobutyl group, respectively. Changes in the proline residue produced derivative , substituted with a symmetrical piperidine ring instead of the pyrrolidine ring and , in which the pyrrolidine ring is connected to the pyridine ring via a hydroxymethyl group instead of a keto function. The peptidomimetics were tested for their ability to enhance the maximal effect of N-propylapomorphine (NPA) at dopamine D2 receptors in the functional cell-based R-SAT assay. Compounds , , and , produced a statistically significant increase in the maximal NPA response at 10 nM (117 +/- 6%, 118 +/- 6%, and 116 +/- 3%, respectively), which is similar to the effect of PLG in this assay, whereas was able to potentiate the response to a similar extent at 1 nM concentration (115 +/- 5%). All derivatives produced a bell-shaped dose-response curve and none of the compounds were active at the D2 receptor alone, which indicates that the mechanism behind the activity of both the pyridine based mimetics and PLG is the same. Interestingly, l-Pro-d-Leu-Gly-NH(2) was found to be more potent than PLG and produced a 119 +/- 1% increase in the NPA response at 1 nM.

Endocrine disruptors and the thyroid gland--a combined in vitro and in vivo analysis of potential new biomarkers

BACKGROUND

There is growing evidence that, in addition to the reproductive system, the hypothalamic-pituitary-thyroid axis is a target of endocrine-disrupting compounds (EDCs). However, this is not reflected adequately in current screening and assessment procedures for endocrine activity that to date determine only general parameters of thyroid function.

OBJECTIVE AND METHODS

We used several in vitro and ex vivo assays in an attempt to identify suitable biomarkers for antithyroid action testing a selected panel of putative EDCs.

RESULTS

In vitro we detected stimulation or inhibition of iodide uptake into FRTL-5 rat thyroid cells, inhibition of thyroid hormone binding to transthyretin, agonistic or antagonistic effects in a thyroid hormone receptor-dependent reporter assay, and inhibition of thyroid peroxidase using a novel assay system based on human recombinant thyroperoxidase that might be suitable for routine screening for potential EDCs. In rats, chronic application of several EDCs led to changes in thyroid morphology, alterations of thyrotropin and thyroid hormone serum levels as well as alterations in peripheral thyroid hormone-regulated end points such as malic enzyme and type I 5'-deiodinase activity.

CONCLUSIONS

As the effects of EDCs do not reflect classic mechanisms of hormone-dependent regulation and feedback, we believe multitarget and multimodal actions of EDCs affect the hypothalamic-pituitary-thyroid axis. These complex effects require a diverse approach for screening, evaluation, and risk assessment of potential antithyroid compounds. This approach involves novel in vitro or cell-based screening assays in order to assess thyroid hormone synthesis, transport, metabolism, and action as well as in vivo assays to measure thyroid hormone-regulated tissue-specific and developmental end points in animals.

Pharmacological characterization of alpha1- and beta-adrenergic synergism of 5'DII activity in rat brown adipocytes

The role of adrenoceptor subtypes was studied in rat brown adipose tissue (BAT). The type II 5'-deiodinase (5'DII) was activated in response to simultaneous stimulation by beta3- and alpha1-adrenergic agonists, BRL 37344 or CGP 12177, and cirazoline, in brown adipocytes. Inhibition of the alpha1- and beta-adrenergic phenylephrine-stimulated 5'DII activity was obtained by the alpha1-adrenergic antagonists in the order of prazosin >/= wb 4101 > 5-methylurapidil. In comparison, the binding of [3H]prazosin to rat BAT plasma membranes was inhibited by alpha1-adrenergic antagonists in the order of prazosin > WB 4101 = benoxathian > 5-methylurapidil. Although the order of the alpha1-adrenergic competition seemed to be rather typical for the alpha1B-adrenergic receptors, a molecular analysis on adrenoceptor mRNAs should be made to confirm the exact alpha1-adrenergic subtypes at the level of brown adipocytes, since the possibility of a mixture of different receptor subtypes in brown fat cells and/or tissue may interact with the pharmacological characterization. Thus, specific alpha1- and beta-adrenoceptor subtypes participate in the regulation of 5'DII activity in the rat brown adipocytes, and therefore, an impaired alpha1- and beta-adrenergic co-work may be involved in a defective BAT function, e.g., in obese Zucker rats, too. An interesting possibility is that the decreased number of alpha1-adrenoceptors in the BAT of obese Zucker rats is due to the decrease in the alpha1B-adrenoceptor subtype which would further be involved especially in the regulation of BAT 5'DII activity.

Development of invasive follicular cell carcinomas in a rat thyroid carcinogenesis model: Biological impact of capsular inflammation and reduced cyclooxygenase-2 expression

We have previously reported that thyroid capsular inflammation induced by sulfadimethoxine (SDM), a goitrogen, might play a role in development of invasive follicular cell adenocarcinomas in rats initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). The present study was designed to examine the role of cyclooxygenase (COX)-2, widely known to be up-regulated in inflammatory states, during chemically induced rat thyroid carcinogenesis. Male F344 rats received a subcutaneous DHPN (2800 mg/kg) injection, and 1 week later were allowed free access to drinking water containing antithyroidal propylthiouracil (PTU, 0.003%) or SDM (0.1%) for 4 or 10 weeks. Control groups receiving goitrogen alone and no treatment were also included. At week 4, diffuse follicular cell hyperplasia was induced in all PTU- and SDM-treated groups, along with fibrous capsular thickening and capsular thickening with inflammation, respectively. Additionally, multiple focal follicular cell hyperplasias and adenomas were observed in the DHPN + PTU and DHPN + SDM cases. At week 10, adenocarcinomas invasive to the capsule and restricted to the capsular adjacent region, were frequent in the DHPN + SDM group, but not observed in the animals given DHPN + PTU. Western blots and immunohistochemistry revealed constitutive COX-2 expression in non-neoplastic follicular cells of the control and all of the PTU- and SDM-treated rats. However, COX-2 reactivity was significantly reduced or negative in the preneoplastic/neoplastic lesions in the DHPN-treated groups. In fibrous or inflamed thickened capsules, only a few component cells with inflammatory elements were positive for COX-2, and there was no significant difference in this regard between the PTU and SDM treatments. The present results suggest that capsular inflammation could play a role in development of invasive carcinomas, but COX-2 expression does not make a major contribution.

Piperine lowers the serum concentrations of thyroid hormones, glucose and hepatic 5'D activity in adult male mice

Piperine, the main alkaloid of Piper nigrum fruits, was evaluated for its thyroid hormone and glucose regulatory efficacy in adult male Swiss albino mice. Its daily oral administration (2.50 mg/kg) for 15 days lowered the serum levels of both the thyroid hormones, thyroxin (T (4)) and triiodothyronine (T (3)) as well as glucose concentrations with a concomitant decrease in hepatic 5'D enzyme and glucose-6-phospatase (G-6-Pase) activity. However, no significant alterations were observed in animals treated with 0.25 mg/kg of piperine in any of the activities studied except an inhibition in serum T (3) concentration. The decrease in T (4), T (3) concentrations and in G-6-Pase were comparable to that of a standard antithyroid drug, Proylthiouracil (PTU). The hepatic lipid-peroxidation (LPO) and the activity of endogenous antioxidants, superoxide dismutase (SOD), and catalase (CAT) were not significantly altered in either of the doses. It appears that the action of P. nigrum on thyroid functions is mediated through its active alkaloid, piperine. We also suggest that a higher dose of piperine may inhibit thyroid function and serum glucose concentration in euthyroid individuals.

Selenium in the treatment of autoimmune thyroiditis

We recently conducted a prospective, placebo-controlled clinical study, where we could demonstrate, that a substitution of 200 microg sodium selenite for three months in patients with autoimmune thyroiditis reduced thyroid peroxidase antibody (TPO-Ab) concentrations significantly. Forty-seven patients from the initially 70 patients agreed to participate in a follow-up cross-over study for further six months. One group (n = 13), which initially received selenium continued to take 200 microg sodium selenite (Se-Se), one group stopped taking selenium (Se-0) ( n = 9), another group which received placebo started to take 200 microg selenium (n = 14) (Plac-Se) and the last group was without selenium substitution (Plac-0) (n = 11). TPO-Ab concentrations were measured at beginning and the end of the study. In the Se-Se group, the TPO-Ab concentrations further significantly p = 0.004) decreased from 625 +/- 470 U/ml to 354 +/- 321 U/ml, in the Se-0 group the TPO-Ab concentrations increased significantly p = 0.017) from 450 +/- 335 to 708 +/- 313 U/ml. In the placebo group, the TPO-Ab concentrations in those patients who were followed without selenium substitution were unchanged (1351 +/- 940 vs. 1724 +/- 1112 U/ml, p = 0.555). In contrast, the patients who received 200 microg sodium selenite after placebo, the TPO-Ab concentrations decreased significantly (p = 0.029) from 1182 +/- 723 to 643 +/- 477 U/ml.

Tissue-specific regulation of type III iodothyronine 5-deiodinase gene expression mediates the effects of prolactin and growth hormone in Xenopus metamorphosis

Prolactin (PRL) and growth hormone (GH) are known to be able to act as antimetamorphic hormones. From investigations of how PRL inhibits Xenopus tail regression in vitro, it was found that the both hormones could, in addition to their known antimetamorphic actions, upregulate mRNA expression of type III iodothyronine 5-deiodinase (5D), an enzyme that inactivates thyroid hormones (TH). Conversely, both PRL and GH were found to downregulate 5D mRNA expression in the liver. Blockage by PRL of TH-induced tail regression in organ culture was released by treatment with iopanoic acid (IOP, an inhibitor of 5D activity). The IOP-released tail regression displayed a unique morphology of the larger fins retained on the regressing tails, consistent with the finding that mRNA for both PRL receptor and 5D were enriched in the fin. The results suggest that the metamorphosis-modulating actions of PRL and GH are mediated, at least partially, by tissue-specific regulation of 5D mRNA expression.

Thyroid hormone activation in human vascular smooth muscle cells: expression of type II iodothyronine deiodinase

Thyroid hormone has been reported to have significant effects on the peripheral vascular system, including relaxation of vascular smooth muscle cells and antiatherosclerotic effects. To exert its biological activity, thyroxine, which is a major secretory product of thyroid gland, needs to be converted to 3,5,3'-triiodothyronine (T(3)) by iodothyronine deiodinase. Type I iodothyronine deiodinase (DI) is widely distributed and maintains circulating T(3) level, whereas type II iodothyronine deiodinase (DII) is present in a limited number of tissues to provide local intracellular T(3). In the present study, we have identified iodothyronine deiodinase in cultured human coronary artery smooth muscle cells (hCASMCs) and human aortic smooth muscle cells (hASMCs). All of the characteristics of the deiodinating activity in hCASMCs and hASMCs were compatible with DII. Northern analysis demonstrated that DII mRNA was expressed in both hCASMCs and hASMCs, and DII mRNA levels as well as DII activities were rapidly increased by dibutyryl-cAMP or forskolin. These data demonstrate, for the first time, the expression of DII in human vascular smooth muscle cells, which is regulated by a cAMP-mediated mechanism. The present results suggest a previously unrecognized role of local T(3) production by DII in the pathophysiology of human vascular smooth muscle cells.

Human natural tumor necrosis factor alpha induces multiple endocrine and hematologic disorders in rats

Slc:Wistar male rats treated with human natural tumor necrosis factor alpha (hn TNF-alpha, 3 X 10(5) Japan reference units/kg intravenously) for 3 months showed histologic vacuolation of basophils in the anterior pituitary, hyperplasia of the thyroidal follicular epithelium, and hyperplasia of the testicular interstitial cells. The vacuolated basophils were immunohistochemically shown to be thyrotrophs. In addition, there were decreases in plasma levels of triiodothyronine (T3), thyroxin (T4), and testosterone, and an increase in thyroid-stimulating hormone (TSH). The number of lymphocytes in the marginal zones of lymphoid follicles in spleen and lymph nodes and B-lymphocytes in the peripheral blood decreased. Hyperplasia of hematopoietic cells in the bone marrow and decreases in both leukocytes and erythrocytes in the peripheral blood were prominent. Hyperplasia of bile ductular epithelial cells with periportal mononuclear cell infiltration in the liver and increased cellularity in alveolar walls in the lung were also characteristic. In in vitro studies, hn TNF-alpha inhibited both proliferation and peroxidase activity of thyroid follicular epithelial cells. These findings demonstrate that hn TNF-alpha may induce histologic vacuolation of thyrotrophs by causing a decrease in plasma levels of T3 and T4; hyperplasia of the thyroid follicular epithelium, which may be attributed to the increased plasma level of TSH; hyperplasia of testicular interstitial cells, by lowering the plasma level of testosterone; hyperplasia of bile ductular epithelial cells; hyperplasia of hematopoietic cells in bone marrow; and the increase in cellularity in pulmonary alveolar walls. In addition, hn TNF-alpha may suppress the differentiation of B-lymphocytes.

TPA induces a block of differentiation and increases the susceptibility to neoplastic transformation of a rat thyroid epithelial cell line

The PC Cl 3 cell line is a well-characterized epithelial cell line of rat thyroid origin. This cell line retains in vitro the typical markers of thyroid differentiation: thyroglobulin (TG) synthesis and secretion, iodide uptake, thyroperoxidase (TPO) expression, and dependency on TSH for growth. Although the differentiated phenotype of thyroid cells has been relatively well described, the molecular mechanisms that regulate both differentiation and neoplastic transformation of thyroid cells still need to be investigated in detail. Protein kinase C (PKC), the target of tetradecanoylphorbol acetate (TPA), regulates growth and differentiation of several cell types. Here we show that treatment of PC Cl 3 cells with TPA induces an acute block of thyroid differentiation. TPA-treated PC Cl 3 cells are unable to trap iodide and the expression levels of thyroglobulin, TSH receptor, and TPO genes are drastically reduced by TPA treatment. This differentiation block is not caused by a reduced expression of one of the master genes of thyroid differentiation, the thyroid transcription factor 1 (TTF-1). TPA-treated PC Cl 3 cells display an increased growth rate indicating that, in addition to the differentiation block, TPA also significantly affects the growth regulation of thyroid cells. Finally, TPA treatment dramatically increases the number of transformation foci induced in PC Cl 3 cells by retroviruses carrying v-Ki-ras, v-Ha-ras, and v-mos oncogenes. These findings support the notion that the PKC pathway can influence proliferation, differentiation, and neoplastic transformation of thyroid cells in culture.

Induction of type 2 deiodinase activity by cyclic guanosine 3',5'-monophosphate in cultured rat glial cells

We investigated the effects of cyclic guanosine 3',5'-monophosphate (cGMP) on type 2 iodothyronine deiodinase (D2) in cultured rat glial cells. Rat glial cells were cultured in Dulbecco's modified Eagle's medium supplemented with 15% fetal bovine serum. When cells were cultured in the presence of 8-bromo cGMP (8-Br cGMP), an analogue of cGMP, D2 activity was increased in a time- and concentration-dependent manner. Lineweaver-Burk plots revealed that the stimulation of D2 activity by 8-Br cGMP (10(-3) M) was associated with fivefold increase in maximum velocity but without a significant change in Michaelis-Menten constant, suggesting that cGMP increases D2 activity via new enzyme synthesis. Both atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are well known to increase the intracellular cGMP level via their guanylate cyclase-linked receptors in rat glial cells. In the present study, ANP (10(-6) M) and CNP (10(-6) M) significantly increased the D2 activity in rat glial cells (1.9-fold [ANP] or 2.3-fold [CNP] compared with control activity, respectively). Northern blot analysis demonstrated that D2 mRNA level increased in the presence of 8-Br cGMP (10(-3) M), and reached a plateau (six-fold) after 4 hours of incubation. The increment of D2 mRNA level by 8-Br cGMP was comparable with the increase of the D2 activity by this agent. Our data suggest that cGMP induces rat D2 activity, at least in part, at the pretranslational level, and that ANP and CNP increase D2 activity most likely via their guanylate cyclase-linked receptors in rat glial cells.

Perchlorate and the thyroid gland

Perchlorate competitively blocks iodide from entering the thyroid by an effect on the Na+/I- symporter thus preventing the further synthesis of thyroid hormone but has no effect on the iodination process itself. It is concentrated by thyroid tissue in a manner similar to iodide but is not significantly metabolized in the gland or peripherally. What is not settled is whether there are additional perchlorate effects on iodide transport. Perchlorate has a fast turnover in the body and requires frequent daily doses for therapy of thyrotoxicosis. Perchlorate appears to be substantially more effective against large iodide loads than the thionamides, and, with long-term iodide contamination, combined therapy of perchlorate (with < or = 1 g/day) and thionamides is recommended for the more severe cases of thyrotoxicosis that may result from excess iodide or iodide-generating organic compounds, as for example with amiodarone. After approximately 30 days, the perchlorate dosage can be tapered or stopped, continuing with thionamides alone. This markedly increases its safe use. Despite serious side effects during its early use, lower dosages and shorter treatment periods appear to have prevented such reactions in its recent reintroduction, mostly for amiodarone-induced thyroid dysfunction. Perchlorate can also protect against inhibition of thyroid function and the resulting hypothyroidism caused by excess iodide, presumably by reducing the formation of an iodinated inhibitor. The reduction of the iodide pool by perchlorate thus has dual effects--reduction of excess hormone synthesis and hyperthyroidism, on the one hand, and reduction of thyroid inhibitor synthesis and hypothyroidism on the other. Perchlorate remains very useful also as a single dose application in tests measuring the discharge of radioiodide accumulated in the thyroid as a result of many different disruptions in the further metabolism of iodide in the thyroid gland.

Is triiodothyronine capable of ameliorating pyrethroid-induced thyroid dysfunction and lipid peroxidation?

A study on the effect of triiodothyronine (T3) in the regulation of pyrethroid (fenvalerate)-induced thyroid dysfunction and lipid peroxidation was carried out in male mice. Fenvalerate (120 mg kg(-1) body wt. daily for 15 days) administration led to a decrease in the serum concentration of thyroid hormones and the activity of hepatic type I iodothyronine 5'-monodeiodinase (5'D-I) and an increase in the level of lipid peroxidation. The decrease in the activity of hepatic 5'D-I due to the administration of fenvalerate was restored with the administration of T3 (7 microg kg[-1] body wt. on alternate days). The increased level of lipid peroxidation was also ameliorated by T3. However, T3 could not restore the serum concentration of thyroxine (T4), only that of T3. We suggest that the ameliorating role of T3 in the fenvalerate-intoxicated mice could be the result of the lipogenic action of the thyroid hormone, which in turn led to the restoration of 5'D-I activity.

Characterization of a propylthiouracil-insensitive type I iodothyronine deiodinase

Mammalian type I iodothyronine deiodinase (D1) activates and inactivates thyroid hormone by outer ring deiodination (ORD) and inner ring deiodination (IRD), respectively, and is potently inhibited by propylthiouracil (PTU). Here we describe the cloning and characterization of a complementary DNA encoding a PTU-insensitive D1 from teleost fish (Oreochromis niloticus, tilapia). This complementary DNA codes for a protein of 248 amino acids, including a putative selenocysteine (Sec) residue, encoded by a TGA triplet, at position 126. The 3' untranslated region contains two putative Sec insertion sequence (SECIS) elements. Recombinant enzyme expressed in COS-1 cells catalyzes both ORD of T4 and rT3 and IRD of T3 and T3 sulfate with the same substrate specificity as native tilapia D1 (tD1), i.e. rT3 >> T4 > T3 sulfate > T3. Native and recombinant tD1 show equally low sensitivities to inhibition by PTU, iodoacetate, and gold thioglucose compared with the potent inhibitions observed with mammalian D1s. Because the residue 2 positions downstream from Sec is Pro in tD1 and in all (PTU-insensitive) type II and type III iodothyronine deiodinases but Ser in all PTU-sensitive D1s, we prepared the Pro128Ser mutant of tD1. The mutant enzyme showed strongly decreased ORD and somewhat increased IRD activity, but was still insensitive to PTU. These results provide new information about the structure-activity relationship of D1 concerning two characteristic properties, i.e. catalysis of both ORD and IRD, and inhibition by PTU.

Effects of estradiol benzoate on 5'-iodothyronine deiodinase activities in female rat anterior pituitary gland, liver and thyroid gland

There is little information on the possible effects of estrogen on the activity of 5'-deiodinase (5'-ID), an enzyme responsible for the generation of T3, the biologically active thyroid hormone. In the present study, anterior pituitary sonicates or hepatic and thyroid microsomes from ovariectomized (OVX) rats treated or not with estradiol benzoate (EB, 0.7 or 14 micrograms/100 g body weight, s.c., for 10 days) were assayed for type I 5'-ID (5'-ID-I) and type II 5'-ID (5'-ID-II, only in pituitary) activities. The 5'-ID activity was evaluated by the release of 125I from deiodinated 125I rT3, using specific assay conditions for type I or type II. Serum TSH and free T3 and free T4 were measured by radioimmunoassay. OVX alone induced a reduction in pituitary 5'-ID-I (control = 723.7 +/- 67.9 vs OVX = 413.9 +/- 26.9; P < 0.05), while the EB-treated OVX group showed activity similar to that of the normal group. Thyroid 5'-ID-I showed the same pattern of changes, but these changes were not statistically significant. Pituitary and hepatic 5'-ID-II did not show major alterations. The treatment with the higher EB dose (14 micrograms), contrary to the results obtained with the lower dose, had no effect on the reduced pituitary 5'-ID-I of OVX rats. However, it induced an important increment of 5'-ID-I in the thyroid gland (0.8 times higher than that of the normal group: control = 131.9 +/- 23.7 vs OVX + EB 14 micrograms = 248.0 +/- 31.2; P < 0.05), which is associated with increased serum TSH (0.6-fold vs OVX, P < 0.05) but normal serum free T3 and free T4. The data suggest that estrogen is a physiological stimulator of anterior pituitary 5'-ID-I and a potent stimulator of the thyroid enzyme when employed at high doses.

Studies on rat thyroid after oral administration of mancozeb: morphological and biochemical evaluations

Mancozeb, an ethylenebisdithiocarbamate (EBDC), has been studied for its effects on rat thyroid. Single oral administration of mancozeb at different concentrations (9600, 12,000, 15,000 and 18,750 mg kg(-1) body wt) has derived the oral LD50 value as 15,000 mg kg(-1) body wt. in male rats. Mancozeb at repeated oral doses of 500, 1000 and 1500 mg kg(-1) day(-1) for periods of 30, 90, 180 and 360 days has produced dose-dependent signs of toxicity and death of animals. The fungicide caused a significant increase in thyroid/body weight ratio and histopathological changes. Reduced levels of thyroid radioiodine ([125]I) uptake, serum protein-bound iodine (PB[125]I), thyroxine (T4) and reduced activity of thyroid peroxidase (TPO) have also been observed after exposure to mancozeb. Thus, mancozeb has been shown to produce marked structural and functional changes in thyroid of rats.

Evidence of a thyrotropin-releasing activity of ovine corticotropin-releasing factor in the domestic fowl (Gallus domesticus)

Ovine corticotropin-releasing factor (oCRF) administered to 19-day-old chicken embryos (E19) increased plasma concentration of pituitary glycoprotein alpha-subunit concentrations within 15 min for at least 4 hr. Follicle stimulating hormone levels were unchanged, while plasma luteinizing hormone concentrations only began to increase 1 hr after the oCRF treatment. Calculation of circulating thyrotropin (TSH) indicator values revealed a rapid elevation in TSH plasma levels following oCRF. Concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), and corticosterone increased from 1 hr postinjection. Hypothalamic outer ring deiodinating type II increased and hepatic inner ring deiodinating type III fell after 2 and 4 hr, explaining at least in part the plasma T3 increase at the end of the experiment. In a second experiment, using E18 chicks, a comparison was made between the effects of a single injection of 2 micrograms oCRF and 20 mlU bovine TSH. Both hormones increased T4, T3, and rT3 plasma concentrations, supporting the hypothesis of a TSH-releasing activity for oCRF in the embryonic chicken. The proposed TSH-mediated effect of CRF on thyroid function was further confirmed in two in vitro experiments in which oCRF did not directly influence the thyroidal T4 secretion but, when applied to pituitaries, clearly increased the alpha-subunit release. In chickens CRF is concluded to not only control the adrenal axis, but also to participate in the coordination of avian TSH release.

Plasma thyroid hormone levels and iodothyronine deiodinase activity following an acute glucocorticoid challenge in embryonic compared with posthatch chickens

Embryonic chickens (Day 18 of incubation) and 8-day-old posthatch chicks were subjected to an acute glucocorticoid challenge by a single iv injection of corticosterone (B), dexamethasone, or porcine adrenocorticotropin. Plasma samples were analyzed for changes in T4, T3, rT3, alpha-subunit, LH, GH, and B levels; iodothyronine deiodinase activity was measured in liver, kidney, and hypothalamus at several time points after injection. The effects of the different treatments were broadly similar within one age group, but differed clearly between pre- and post-hatch animals. In 18-day-old embryos glucocorticoids increased plasma T3 and decreased plasma T4, rT3, and the calculated TSH index, within hours after injection. These changes were accompanied by an immediate (1-4-24 hr after injection) decrease in hepatic inner ring deiodinating type III enzyme (IRD-III) activity and a delayed (24-48 hr after injection) increase in hepatic outer ring deiodinating type I enzyme (ORD-1) activity. Glucocorticoid challenge in 8-day-old chicks similarly decreased plasma T4 and the TSH index but tended to also lower plasma T3. Hepatic ORD-I activity decreased within 1 hr after injection, while the already very low hepatic IRD-III activity was for the most part unaffected. Acute increases in glucocorticoids lower thyroidal T4 secretion in both pre- and posthatch chickens but have clearly different effects on peripheral thyroid hormone deiodination and hence on circulating T3 at both developmental stages.

Influence of recombinant chicken prolactin on thyroid hormone metabolism in the chick embryo

The influence of a recombinant chicken prolactin (rcPRL) preparation on thyroid function was studied in 18- and 19-day-old chicken embryos. Displacement studies on hepatic microsomes indicate that this preparation does not compete with radiolabeled chicken growth hormone (cGH) for hepatic GH-receptor binding. In a first series of experiments rcPRL or immunoaffinity-purified cGH was injected intravenously in 19-day-old chicken embryos. After 2 hr, cGH increased plasma T3 in a dose-dependent way by inhibiting hepatic inner ring type III deiodination (IRD-III) and consequently T3 degradation. Outer ring deiodination (ORD-I) was not influenced confirming previous results. The rcPRL preparation (2 and 10 microg) did not influence plasma T3, but depressed T4 and raised hepatic IRD-III activity simultaneously, whereas no influence on hepatic ORD-I activity could be found. In a second experiment on 18-day-old embryos, it could be demonstrated that the effect of 2.5 microg cGH on plasma T3 and liver IRD-III lasted up to 6 hr after injection, whereas 2.5 microg cPRL affected plasma T4 and liver IRD-III up to 2 hr. Both rcPRL and cGH depressed rT3 up to 6 hr, whereas an injection of rcPRL, but not of cGH, elevated plasma concentrations of corticosterone. These results indicate that prolactin may have a role, together with GH, in controlling peripheral thyroid hormone metabolism.

Sexual differences in 5'-deiodinase activity in the Harderian gland of Syrian hamsters and the effect of pinealectomy: regulation by androgens

Sexual differences on thyroxin 5'-deiodinase (5'-D) in the Harderian gland of Syrian hamsters were investigated. We compared the 24-h profile of 5'-D activity in male and female hamsters, observing a clear rhythm in males but not in females. Female values were always significantly higher than male ones. After pinealectomy day/night variations in male 5'-D activity at the time points studied were abolished, results that are in correlation with serum thyroid hormones. We also studied the regulation by androgen of the enzyme activity. Basal 5'-D activity increased in castrated males and levels fell when animals were implanted with testosterone or its product 5 alpha-dihydrotestosterone (DHT). Female 5'-D activity was also inhibited by androgens. As only the addition of DHT in the presence of epitestosterone, an inhibitor of the conversion of testosterone on DHT, in castrated males was able to decrease 5'-D activity to the control animal levels, we suggest a probable direct effect of DHT by itself.

Inhibition of thyroid peroxidase by dietary flavonoids

Flavonoids are widely distributed in plant-derived foods and possess a variety of biological activities including antithyroid effects in experimental animals and humans. A structure-activity study of 13 commonly consumed flavonoids was conducted to evaluate inhibition of thyroid peroxidase (TPO), the enzyme that catalyzes thyroid hormone biosynthesis. Most flavonoids tested were potent inhibitors of TPO, with IC50 values ranging from 0.6 to 41 microM. Inhibition by the more potent compounds, fisetin, kaempferol, naringenin, and quercetin, which contain a resorcinol moiety, was consistent with mechanism-based inactivation of TPO as previously observed for resorcinol and derivatives. Other flavonoids inhibited TPO by different mechanisms, such as myricetin and naringin, showed noncompetitive inhibition of tyrosine iodination with respect to iodine ion and linear mixed-type inhibition with respect to hydrogen peroxide. In contrast, biochanin A was found to be an alternate substrate for iodination. The major product, 6,8-diiodo-biochanin A, was characterized by electrospray mass spectrometry and 1H-NMR. These inhibitory mechanisms for flavonoids are consistent with the antithyroid effects observed in experimental animals and, further, predict differences in hazards for antithyroid effects in humans consuming dietary flavonoids. In vivo, suicide substrate inhibition, which could be reversed only by de novo protein synthesis, would be long-lasting. However, the effects of reversible binding inhibitors and alternate substrates would be temporary due to attenuation by metabolism and excretion. The central role of hormonal regulation in growth and proliferation of thyroid tissue suggests that chronic consumption of flavonoids, especially suicide substrates, could play a role in the etiology of thyroid cancer.

Evidence for a radical mechanism in peroxidase-catalyzed coupling. I. Steady-state experiments with various peroxidases

Biosynthesis of thyroxine in the thyroid gland involves a reaction between two diiodotyrosyl residues within the same molecule of thyroglobulin, a large, thyroid-specific glycoprotein. This reaction, generally referred to as the coupling reaction, is catalyzed in the thyroid by the heme-containing glycoprotein enzyme, thyroid peroxidase, also a thyroid-specific protein. The coupling reaction is, however, not specific for thyroid peroxidase; it is also efficiently catalyzed by other heme-containing peroxidases. Peroxidase-catalyzed coupling may also occur between a monoiodotyrosyl and a diiodotyrosyl residue in thyroglobulin to form the more potent thyroid hormone, 3',3,5-triiodothyronine. Under most conditions, thyroxine formation in the thyroid is greatly favored over that of 3',3,5-triiodothyronine. Two mechanisms have been proposed for the coupling reaction, a radical mechanism and an ionic mechanism. In this, and in the following paper, we present evidence favoring a radical mechanism. This view is bsed primarily on the observation that peroxidase-catalyzed coupling is markedly stimulated by substoichiometric concentrations of free diiodotyrosine (DIT). Evidence obtained in this and in the following paper leads us to conclude that the stimulatory effect of DIT on coupling involves peroxidase-catalyzed oxidation of the added DIT to a radical form. We propose that this stimulation involves a radical chain propagation mechanism. This implies that peroxidase-catalyzed coupling in the absence of DIT must also be a radical-mediated reaction.

Enrichment of selenium in allium vegetables for cancer prevention

We previously reported that garlic cultivated with selenium fertilization is superior to regular garlic in mammary cancer prevention in the rat 7,12-dimethylbenz[a]anthracene (DMBA) model (Nutr. Cancer, 17, 279-286, 1992). A new crop of high-selenium garlic was harvested in 1992 and was used in a dose-response study to confirm the reproducibility of the product and the bioassay. Supplementation of 1 or 2 p.p.m. Se in the diet from the high-selenium garlic produced a 56% or 75% reduction respectively in the total tumor yield. Since both garlic and onion belong to the same allium family of vegetables, we were also interested in finding out whether our experience with garlic could be similarly applied to onion. A high-selenium onion crop was grown in the same season and location and with the same schedule of selenium fertilization. Two distinct differences were noted with the high-selenium onion regarding its capacity to accumulate selenium and its efficacy in cancer prevention. First, the selenium concentration in onion was considerably lower (28 p.p.m. Se dry wt) as compared to that found in garlic (110-150 p.p.m. Se). Second, given the same levels of selenium supplementation, the high-selenium onion was apparently not as powerful as the high-selenium garlic in mammary cancer inhibition. Thus different plants, even those of the same genus, may respond in their unique way to selenium fertilization and the biological benefits of selenium enrichment may vary depending on the species. Additional information from our study indicated that the high-selenium garlic/onion might provide an ideal system for delivering selenium-substituted analogs in a food form for cancer prevention: (i) they expressed a good range of anticancer activity and could be easily adapted for human consumption on a regular basis; (ii) their ingestion did not result in an excessive accumulation of tissue selenium, a concern that is associated with the standard selenium compounds such as selenite and selenomethionine; (iii) no perturbation in the maintenance of functional selenoenzymes were observed even at high levels of supplementation.

Effect of the antioxidant TK 12627 (Irganox) on monodeiodination and on the levels of messenger ribonucleic acid of 5'-deiodinase type I and spot 14

Until now, most potent inhibitors of monodeiodination are iodinated, propylthiouracil being an exception. We report here studies on a new non-iodinated substance, triethylene glycol bis-3-(3-tert-butyl-4-hydroxy-5-methyl-phenyl) propionate (TK 12627 or Irganox), which is used as a very efficient antioxidant in the chemistry of plastics. The studies were performed with 23 hypothyroid rats that received Irganox in their daily food (8 mg.day-1 x (100 g body wt)-1) for 3 weeks. Thyroxine (T4) metabolism was studied by implanting minipumps delivering 2.3 nmol T4.day-1 x (100 g body wt)-1 for 1 week. On day 1 before sacrifice, another minipump containing [125I]-3,5,3'-triiodothyronine (T3, 2.6 microCi/day) and [131I]-3,3',5'-triiodothyronine (rT3, 2.1 microCi/day) was implanted. The results showed that with Irganox treatment serum T4 concentrations were higher (p < 0.05). Serum T3 concentrations markedly decreased (1.07 +/- 0.07 vs 0.65 +/- 0.04 nmol/l), accompanied by a decrease of free T3 concentrations (p < 0.001). Serum rT3 concentrations increased by 50% (p < 0.001). Serum thyrotropin levels were mostly unmeasurable. The plasma clearance rate decreased slightly for T4 (19%, p < 0.05) and remarkably for rT3 (46.7%, p < 0.001). The conversion rate of T4 to rT3 did not change. Deiodinase type I (5'D-I) activity decreased in both liver and kidney tissues by 54% and 52%, respectively, and correlated with T3 (r2 = 0.79 and 0.65, respectively). Brain deiodinase type III (5D-III) was unchanged and type II (5'D-II) was unmeasurable.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroxine 5'-monodeiodinase activity in microsomes from isolated hepatocytes of rainbow trout: effects of growth hormone and 3,5,3'-triiodo-L-thyronine

Rainbow trout hepatocytes isolated by collagenase perfusion were suspended in primary culture for up to 72 hr at 11 degrees and then the microsomal L-thyroxine (T4) 5'-monodeiodinase (5'D) activity was evaluated by 125I- generation from [125I]T4. The 5'D activity and Vmax (level of functional enzyme) and Km (Michaelis-Menten constant) values for microsomes obtained from incubated hepatocytes corresponded to those for microsomes obtained directly from intact livers. HPLC analysis revealed 3,5-[125I]3'-triiodo-L-thyronine (T3) as the only significant 125I-labeled organic product. Hepatocyte survival ( > 90%) and 5'D activity were unaltered by insulin (10(-9) M) in the incubate, but 5'D activity was inhibited by 10% fetal calf serum. Human growth hormone (hGH) at concentrations of 5-250 ng/ml did not increase 5'D activity. These results do not support previous in vivo studies demonstrating hGH-enhanced hepatic 5'D function in trout and indicate that either hGH acts indirectly on the liver to enhance 5'D activity or incubated hepatocytes lose GH responsiveness. However, coincubation of hepatocytes with T3 (15 or 30 nM) for 24 hr inhibited 5'D activity in a dose-dependent manner and induced the production of 3-[125I]3',5'-triiodo-L-thyronine (reverse T3). These data support previous in vivo studies in showing that T3 autoregulates its own hepatic production and show that T3 does so by acting directly on the hepatocyte to modify deiodination pathways.

Impairment of cold-induced increase in thyroxine 5'-deiodinase activity in mouse brown adipose tissue by the intracerebroventricular administration of bombesin

Effects of bombesin on brown adipose tissue (BAT) thyroxine (T4) 5'-deiodinase (5'D) activity and rectal temperature were examined in male mice. Immediately following an intracerebroventricular (ICV) or intravenous (IV) injection of bombesin (0.1-100 ng/animal) or vehicle (20 mM bacitracin dissolved in 0.9% saline), the mice were placed in a room at 4 degrees C or 22 degrees C for 30, 60, 120 or 240 min. The ICV injection of bombesin dose-dependently lessened cold-induced increase in BAT 5'D activity and increased hypothermia determined at 120 min of cold exposure, whereas the IV injection of bombesin was without effect. Bombesin (ICV)-induced hypothermia preceded the inhibition of BAT 5'D activity by at least 30 min at 4 degrees C. BAT 5'D activity was not affected by ICV injection of bombesin in mice kept at 22 degrees C, although the rectal temperature was significantly decreased. Bombesin thus appears to prevent cold-induced increase in T4 5'D activity in mouse BAT by its central effect. Bombesin-induced excessive hypothermia itself and/or the decrease in sympathetic tone of BAT by bombesin might decrease cold-induced increase in BAT 5'D activity.

The effect of dithiotreitol on thyroid peroxidase and microsomal antigen epitopes recognized by auto and monoclonal antibodies

The effect of disulphide bridges reduction of the microsomal antigen (Mic-Ag) and thyroid peroxidase (TPO) by dithiotreitol (DTT) has been investigated. The reaction of all 67 tested sera from untreated hyperthyroid Graves' and from 22 Hashimoto's patients with high microsomal antibodies (aAb) titer was diminished by 90-95% by DTT, at pH 9.6. The remaining 5-10% of the activity was not destroyed by DTT. The residual Mic-Ag after DTT reduction was able to inhibit the binding of all 45 Graves' and 22 Hashimoto's tested aAb's to the native microsomal antigen by 100% at high concentration. Reaction of affinity purified TPO with two monoclonal antibodies (mAb) were diminished by 80% to 95% by DTT pretreatment, while the reaction of one mAb with TPO was only slightly affected. The reaction of TPO and Mic-Ag with rabbit polyclonal anti-TPO serum (rabbit a TPO) was diminished by 60% by DTT pretreatment. The immunological reactivity of TPO with aAb's was diminished by 65% after DTT pretreatment. The microsomal antigen-aAb's complex was not destroyed by DTT. Results presented in this paper suggest conformational epitope structure of the Mic-Ag recognized by aAb's in patients with thyroid autoimmune disease (AITD).