Antinutritional factors in pearl millet grains: Phytate and goitrogens content variability and molecular characterization of genes involved in their pathways.

Pearl millet [Pennisetum glaucum (L.) R. Br.] is an important "orphan" cereal and the most widely grown of all the millet species worldwide. It is also the sixth most important cereal in the world after wheat, rice, maize, barley, and sorghum, being largely grown and used in West Africa as well as in India and Pakistan. The present study was carried out in the frame of a program designed to increase benefits and reduce potential health problems deriving from the consumption of pearl millet. The specific goal was to provide a database of information on the variability existing in pearl millet germplasm as to the amounts of phytate, the most relevant antinutrient compound, and the goitrogenic compounds C-glycosylflavones (C-GFs) accumulated in the grain.Results we obtained clearly show that, as indicated by the range in values, a substantial variability subsists across the investigated pearl millet inbred lines as regards the grain level of phytic acid phosphate, while the amount of C-GFs shows a very high variation. Suitable potential parents to be used in breeding programs can be therefore chosen from the surveyed material in order to create new germplasm with increased nutritional quality and food safety. Moreover, we report novel molecular data showing which genes are more relevant for phytic acid biosynthesis in the seeds as well as a preliminary analysis of a pearl millet orthologous gene for C-GFs biosynthesis. These results open the way to dissect the genetic determinants controlling key seed nutritional phenotypes and to the characterization of their impact on grain nutritional value in pearl millet.

Antithyroid Drugs Inactivate TSH Binding to the TSH Receptor by their Reducing Action.

Backgroud and Objective: Antithyroid drugs (ATDs) [methylmercaptoimidazole (MMI) and propylthiouracil (PTU) ] are used to treat hyperthyroidism in Graves' disease. The effect of ATDs and reducing agents (mercaptoethanol, dithiothreitol and cysteine) on bovine (b) TSH binding to human (h) and porcine (p) TSH receptor (R) was examined. METHODS AND RESULTS: (1) ATDs was pre-incubated with hTSHR coated tube for 1- 4 h, washed free of ATDs, and then 125I-bTSH binding to hTSHR after 1 h incubation was examined. MMI (10-40 mM) decreased 125I-bTSH binding in a dose-dependent manner and binding decreased proportionally as preincubation time increased from 1 to 4 h. PTU (10mM) slightly decreased binding, When reducing agents were pre-incubated with hTSHR for 2 h, 125I-bTSH binding similarly decreased. (2) Porcine thyroid membrane was pre-incubated with both agents for 2 h. Then, the washed or unwashed membrane was incubated with 125I-bTSH for 1 h. 125I-bTSH binding in both methods decreased. (3) When the effect of ATDs or reducing agents on the biological activity of 125I-bTSH and thyroid stimulating antibody (TSAb) was examined after gel-filtration of 125I-bTSH- and TSAb- treated with both reagents for 1 h, no inactivation was observed. (4) ATDs showed similar reducing action as reducing agents because iodine (I+) was reduced to I- by ATDs. CONCLUSION: ATDs inactivate the TSH-binding site of TSHR by reduction, although ATDs do not inactivate bTSH and TSAb activity. This suggests that TSAb would not stimulate the thyroid due to the inactivation of the TSHR when ATDs are administered to patients with Graves' disease.

In vitro metabolic conversion of the organic breakdown products of glucosinolate to goitrogenic thiocyanate anion.

BACKGROUND: Glucosinolates are abundant in Brassicaceae vegetables, and they are degraded into various organic breakdown products (BPs) (R-CN, -NCS and -SCN) by myrosinase when plant tissues are damaged. This study was designed to investigate whether these BPs could be broken further into goitrogenic thiocyanate anions (SCN(-) ) metabolically and/or spontaneously. Ten glucosinolates were chosen for this study based on the various structures of their side chains. SCN(-) and cyanide anions (CN(-) ) liberated from the BPs of these glucosinolates were quantified after incubation with human liver S9 and rhodanese. RESULTS: Upon treatment with metabolic enzymes, CN(-) was produced from all organic thiocyanates, aliphatic and benzyl nitriles, then a substantial amount of produced CN(-) was further metabolized to SCN(-) by rhodanese. All organic thiocyanates and allyl isothiocyanate were metabolized to produce SCN(-), without involving CN(-) production. Spontaneous degradation to SCN(-) in an aqueous environment was observed only in 4-(methylthio)butyl thiocyanate, though the enzymatic reaction rate exceeded the spontaneous one. Among these BPs, the major source of SCN(-) was organic thiocyanates. CONCLUSION: The results show that some organic nitriles, organic thiocyanates and allyl isothiocyanate may be regarded as potential sources of SCN(-) through metabolism when people ingest glucosinolate-containing vegetables.

Atom-based 3D-QSAR, molecular docking and molecular dynamics simulation assessment of inhibitors for thyroid hormone receptor α and ß.

The three-dimensional quantitative structure-activity relationship (3D-QSAR) for inhibitors of thyroid hormone receptors (TR) α and (TR) ß was studied. The training set of the TRα model generated a correlation coefficient (R(2)) = 0.9535, with standard deviation (SD) = 0.3016. From the test set of the TRα model, a Q(2) value for the predicted activities (= 0.4303), squared correlation (random selection R(2)-CV = 0.6929), Pearson-R (= 0.7294) and root mean square error (RMSE = 0.6342) were calculated. The P-value for TRα (= 1.411e-96) and TRß (= 2.108e-165) models indicate a high degree of self-reliance. For the TRß model, the training set yielded R(2) = 0.9424 with SD = 0.3719. From the test set of TRß, Q(2) value (= 0.5336), the squared correlation (R(2)-CV = 0.7201), the Pearson-R (= 0.7852) and RMSE for test set predictions (= 0.8630) all strengthen the good predictive competence of the QSAR model derived. Examination of internal as well as external validation supports the rationality and good predictive ability of the best model. Molecular docking explained the conformations of molecules and important amino acid residues at the docking pocket, and a molecular dynamics simulation study further uncovered the binding process and validated the rationality of docking results. The findings not only lead to a better understanding of interactions between these antagonists and thyroid hormone receptors α and ß, but also provide valuable information about the impact of structure on activity that will be very beneficial in the design of novel antagonists with preferred activity.

The pharmacokinetics of methimazole in a novel lipophilic formulation administered transdermally to healthy cats.

AIM: To determine the pharmacokinetics of a novel lipophilic formulation of transdermal methimazole compared to oral carbimazole. METHODS: Healthy cats received 5 mg carbimazole orally every 12 hours for 13 treatments (n=6), then received transdermal methimazole (n=5) at a dose of 5 mg, then 10 mg, once daily on the pinna for 7 days, with 21 days between treatments. Concentrations of methimazole in serum over 24 hours and at 148 hours were determined by high performance liquid chromatography. RESULTS: Concentrations of methimazole in serum for the first 24 hours were not reliably detected in all cats treated with 5 mg methimazole transdermally, while for those receiving 5 mg carbimazole orally and 10 mg methimazole transdermally all cats had detectable concentrations of methimazole in serum. The maximum concentration and area under the curve were lower in cats receiving 10 mg methimazole transdermally (108 (SD 25) ng/mL and 2544 (SD 216) mg-hour/mL, respectively) than those receiving 5 mg oral carbimazole (355 (SD 113) ng/mL and 31,866 (SD 439) ng-hour/mL, respectively) (p<0.05). The time at maximal concentration and elimination half-life were longer for 10 mg transdermal methimazole (5.2 (SD 1.1) hours and 13 (SD 3) hours, respectively) compared to 5 mg oral carbimazole (2.1 (SD 1.6) hours and 5.1 (SD 1.2) hours, respectively). At 148 hours, mean concentrations of methimazole in serum were higher in cats receiving 10 mg methimazole transdermally (506 (SD 165) ng/mL) than for 5 mg oral carbimazole (255 (SD 28) ng/mL) or 5 mg transdermally (204 (SD 76) ng/mL). The mean relative bioavailability of 10 mg transdermal methimazole compared to oral carbimazole was 48 (min 43, max 55)%. CONCLUSION: Transdermal methimazole at a dose of 10 mg administered to the pinnae of healthy cats once daily in a novel lipophilic formulation has half the relative bioavailablity compared to 5 mg oral carbimazole. CLINICAL RELEVANCE: Transdermal methimazole can be absorbed from the skin of healthy cats.

Hipotiroidismo y síndrome de Down / Hypothyroidism and Down’s syndrome

Introducción: el hipotiroidismo subclínico es frecuente en los primeros años de vida de los niños con síndrome de Down (SD). El objetivo del estudio fue analizar la evolución natural de esta patología identificando los factores que predicen su remisión espontánea. Material y métodos: estudio observacional retrospectivo sobre pacientes con SD e hipotiroidismo diagnosticado antes de los 5 años de edad, atendidos en un centro médico de referencia para SD. Resultados: se identificó a 53 pacientes con hipotiroidismo subclínico, 28 niños y 25 niñas, con una media de edad de 2,4 ± 1,1 años. El hipotiroidismo se resolvió espontáneamente en 39 casos (73,6%), en un tiempo medio de 13,2 ± 11,1 meses, y la tasa de resolución fue significativamente superior en los pacientes sin bocio: 94,9% (intervalo de confianza [IC] del 95%: 81,2-99,3%) frente a 28,6% (IC del 95%: 4,4-37,7%), p < 0,05, y con anticuerpos antitiroideos negativos: 89,7% (IC del 95%: 74,6-96,2%) frente a 42,9% (IC del 95%: 20,7-56%), p < 0,05. Un total de 15 pacientes (28,3%) fueron tratados con levotiroxina. Conclusiones: el hipotiroidismo subclínico que aparece en la primera infancia en el SD suele ser transitorio. La ausencia de bocio y anticuerpos se asocia a una mayor tasa de resolución espontánea (AU)

Introduction: Subclinical hypothyroidism is common in the first years of life of children with Down’s syndrome (DS). The aim of this study was to analyse the natural evolution of this disease and to identify the factors that predict its spontaneous remission. Material and methods: A retrospective, observational study conducted on patients with DS and hypothyroidism diagnosed before 5 years of age, who were seen in a DS reference medical centre. Results: A total of 53 patients, 28 boys and 25 girls, with a mean age 2.4 ± 1.1 years, were identified with subclinical hypothyroidism. The hypothyroidism resolve spontaneously in 39 cases (73.6%), in a mean time of 13.2 ± 11.1 months, this resolution rate being significantly higher in the patients without goitre: 94.9% (95% confidence interval [CI]: 81.2-99.3%) vs 28.6% (95% CI: 4.4-37.7%), p < .05, and with negative antithyroid antibodies: 89.7% (95% CI: 74.6-96.2%), vs 42.9% (95% CI: 20.7–56%), p < .05). Fifteen patients (28.3%) were treated with levothyroxine. Conclusions: The subclinical hypothyroidism that appears in early infancy in DS is usually transient. The absence of goitre and antibodies is associated with a higher spontaneous resolution rate (AU)

Maternal transfer of methimazole and effects on thyroid hormone availability in embryonic tissues.

Methimazole (MMI) is an anti-thyroid drug used in the treatment of chronic hyperthyroidism. There is, however, some debate about its use during pregnancy as MMI is known to cross the mammalian placenta and reach the developing foetus. A similar problem occurs in birds, where MMI is deposited in the egg and taken up by the developing embryo. To investigate whether maternally derived MMI can have detrimental effects on embryonic development, we treated laying hens with MMI (0.03% in drinking water) and measured total and reduced MMI contents in the tissues of hens and embryos at different stages of development. In hens, MMI was selectively increased in the thyroid gland, while its levels in the liver and especially brain remained relatively low. Long-term MMI treatment induced a pronounced goitre with a decrease in thyroxine (T4) content but an increase in thyroidal 3,5,3'-triiodothyronine (T3) content. This resulted in normal T3 levels in tissues except in the brain. In chicken embryos, MMI levels were similar in the liver and brain. They gradually decreased during development but always remained above those in the corresponding maternal tissues. Contrary to the situation in hens, T4 availability was only moderately affected in embryos. Peripheral T3 levels were reduced in 14-day-old embryos but normal in 18-day-old embryos, while brain T3 content was decreased at all embryonic stages tested. We conclude that all embryonic tissues are exposed to relatively high doses of MMI and its oxidised metabolites. The effect of maternal MMI treatment on embryonic thyroid hormone availability is most pronounced for brain T3 content, which is reduced throughout the embryonic development period.

Parallel biotransformation of tetrabromobisphenol A in Xenopus laevis and mammals: Xenopus as a model for endocrine perturbation studies.

The flame retardant tetrabromobisphenol A (TBBPA) is a high production flame retardant that interferes with thyroid hormone (TH) signaling. Despite its rapid metabolism in mammals, TBBPA is found in significant amounts in different tissues. Such findings highlight first a need to better understand the effects of TBBPA and its metabolites and second the need to develop models to address these questions experimentally. We used Xenopus laevis tadpoles to follow radiolabeled (14)C-TBBPA uptake and metabolism. Extensive and rapid uptake of radioactivity was observed, tadpoles metabolizing > 94% of (14)C-TBBPA within 8 h. Four metabolites were identified in water and tadpole extracts: TBBPA-glucuronide, TBBPA-glucuronide-sulfate, TBBPA-sulfate, and TBBPA-disulfate. These metabolites are identical to the TBBPA conjugates characterized in mammals, including humans. Most radioactivity (> 75%) was associated with sulfated conjugates. The antithyroid effects of TBBPA and the metabolites were compared using two in vivo measures: tadpole morphology and an in vivo tadpole TH reporter gene assay. Only TBBPA, and not the sulfated metabolites, disrupted thyroid signaling. Moreover, TBBPA treatment did not affect expression of phase II enzymes involved in TH metabolism, suggesting that the antithyroid effects of TBBPA are not due to indirect effects on TH metabolism. Finally, we show that only the parent TBBPA inhibits T3-induced transactivation in cells expressing human, zebrafish, or X. laevis TH receptor, TRα. We conclude, first, that perturbation of thyroid signaling by TBBPA is likely due to rapid direct action of the parent compound, and second, that Xenopus is an excellent vertebrate model for biotransformation studies, displaying homologous pathways to mammals.

Postnatal testis development, Sertoli cell proliferation and number of different spermatogonial types in C57BL/6J mice made transiently hypo- and hyperthyroidic during the neonatal period.

The role of thyroid hormones in testis structure and function has been fairly well studied in laboratory rodents. However, there are no comprehensive data in the literature for mice regarding the effects of transiently induced neonatal hypo- and hyperthyroidism on testis and spermatogonial cell development from birth to adulthood. Our goals were to evaluate the effects of propylthiouracil (PTU) and triidothyronine (T3) on Sertoli cell proliferation/differentiation and to correlate these events with the evolution of the spermatogenic process, tubular lumen formation, blood vessel volume density, and size and number of different spermatogonial types. Although Sertoli cell maturation was accelerated or delayed, respectively, in T3- and PTU-treated mice, the pace of the germ cell maturation was only slightly altered before puberty and the period of Sertoli cell proliferation was apparently not affected by the treatments. However, compared with controls, the total number of Sertoli cells per testis from 10 days of age to adulthood was significantly increased and decreased in PTU- and T3-treated mice, respectively. In comparison to all other spermatogonia, type A(2) was the largest cell in all ages and groups investigated. The PTU-treated mice had a significantly increased total number of undifferentiated spermatogonia as well as volume and percentage of vessels/capillaries, probably due to the higher number of Sertoli cells, particularly at 10 days of age. Taken together, our results suggest that neonatal hypothyroidism may be a valuable tool for studying spermatogonial biology as well as a means for providing more spermatogonial stem cells that could potentially be used for spermatogonial transplantation, thereby optimizing the efficiency of this technique when young mice are used as donors.

Copper(II) complexes of methimazole, an anti Grave's disease drug. Synthesis, characterization and its potential biological behavior as alkaline phosphatase inhibitor.

Methimazole (MeimzH) is an anti-thyroid drug and the first choice for patients with Grave's disease. Two new copper(II) complexes of this drug: [Cu(MeimzH)(2)(NO(3))(2)]*0.5H(2)O and [Cu(MeimzH)(2)(H(2)O)(2)](NO(3))(2)*H(2)O were synthesized and characterized by elemental analysis, dissolution behavior, thermogravimetric analysis and UV-vis, diffuse reflectance, FTIR and EPR spectroscopies. As it is known that copper(II) cation can act as an inhibitor of alkaline phosphatase (ALP), the inhibitory effect of methimazole and its copper(II) complexes on ALP activity has also been investigated.

Binding of 6-propyl-2-thiouracil to human serum albumin destabilized by chemical denaturants.

We compared the binding affinity of 6-propyl-2-thiouracil (PTU) with native and destabilized human serum albumin (HSA) as a model to assess the binding ability of albumin in patients suffering from chronic liver or renal diseases. Urea (U) and guanidine hydrochloride (Gu.HCl) at a concentration of 3.0M were used as denaturation agents. Increasing the concentration of PTU from 0.8x10(-5) to 1.20x10(-4)M in the systems with HSA causes a decrease in fluorescence intensity of the protein excited with both 280 and 295nm wavelengths. The results indicate that urea and Gu.HCl bind to the carbonyl group and then to the NH-group. To determine binding constants we used the Scatchard plots. The presence of two classes of HSA-PTU binding sites was observed. The binding constants (K(b)) are equal to 1.99x10(4)M(-1) and 1.50x10(4)M(-1) at lambda(ex)=280nm, 5.20x10(4)M(-1) and 1.65x10(4)M(-1) at lambda(ex)=295nm. At lambda(ex)=280nm the number of drug molecules per protein molecule is a(I)=1.45 and a(II)=1.32 for I and II binding sites, respectively. At lambda(ex)=295nm they are a(I)=0.63 and a(II)=1.54 for the I and II binding sites. The estimation of the binding ability of changed albumin in the uremic and diabetic patients suffering from chronic liver or renal diseases is very important for safety and effective therapy.

Thyroid peroxidase forms thionamide-sensitive homodimers: relevance for immunomodulation of thyroid autoimmunity.

Thyroid peroxidase (TPO) is the key enzyme in thyroid hormone production and a universal autoantigen in Graves' and other autoimmune thyroid diseases. We wished to explore the expression of TPO and whether it was affected by thionamide antithyroid drugs. We studied recombinant TPO, stably expressed by a Chinese hamster ovary cell line (CHO-TPO) and transiently expressed TPO-enhanced green fluorescent protein (eGFP) and -FLAG fusion proteins. Immunoblotting of CHO-TPO cell extracts showed high-molecular weight (HMW) TPO isoforms that were resistant to reduction, as well as 110 kDa monomeric TPO. Co-immunoprecipitation and enzyme-linked-immunosorbent assay (ELISA) binding studies of FLAG- and eGFP-tagged TPO demonstrated TPO dimerisation. CHO-TPO cells cultured in methimazole (MMI) for 10 days showed a significant reduction in HMW-TPO isoforms at MMI concentrations of 1 microM and above (p < 0.01), whereas monomeric TPO expression was unchanged. We observed a similar reduction in HMW-TPO in CHO-TPO cells cultured in propylthiouracil (10 microM and above). Binding of Graves' disease patient sera and TPO-Fabs to enzymatically active TPO that was captured onto solid phase was not abrogated by MMI. The cellular localisation of TPO in CHO-TPO cells was unchanged by MMI treatment. Our demonstration of homodimeric TPO and the reduction in HMW-TPO isoforms during thionamide treatment of CHO-TPO cells shows, for the first time, an effect of thionamides on TPO structure. This suggests a structural correlate to the effect of thionamides on TPO enzymatic activity and opens up a novel potential mechanism for thionamide immunomodulation of autoimmune thyroid disease.

Effects of Aroclor 1254 on oxidative stress in developing Xenopus laevis tadpoles.

Over the last decades, amphibians decline has been reported worldwide. Exposure to polychlorinated biphenyls (PCBs) is one of the possible causes in addition to climate changes, UV-radiation or habitat destruction. In the present study, we tested the hypothesis that PCBs could induce oxidative stress in young tadpoles. Developing Xenopus laevis were exposed from 2- to 5-d postfertilization (pf) to 0.1 or 1 mg/l of Aroclor 1254. Lipid peroxidation and antioxidant systems (SOD, CAT, GST, GPx, GR activities and t-GSH level) were investigated in whole organisms. Exposure to both concentrations did not impact on the survival and development whereas the average body weight decreased. Exposure to 1 mg/l of Aroclor 1254 induced a significant (p<0.05) increase of GST activity when compared to controls 0 and DMSO. The other antioxidant enzymes and LPO evaluation remained unchanged. Our results demonstrate that exposure of X. laevis tadpoles to environmental concentrations of Aroclor 1254 interfere with normal growth. They also highlight that very young X. laevis tadpoles express antioxidant systems.

Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats.

Carbimazole, a prodrug of methimazole, is used in the treatment of hyperthyroidism in cats. The pharmacokinetics of methimazole was investigated in healthy cats following oral administration of 15 mg of carbimazole as a controlled-release tablet (Vidalta), Intervet). The controlled-release tablet did not produce a pronounced concentration peak and methimazole was present in the circulation for a sustained period, compared with a conventional tablet formulation. The time to reach peak concentrations after carbimazole administration was quite long (t(max) 6 h). The absolute bioavailability of carbimazole was around 88 +/- 11%. Repeated oral administration daily for 13 consecutive days did not lead to accumulation of methimazole in plasma. The extent of absorption of carbimazole was about 40% higher when administered to cats that had been fed compared to fasted cats. The relative oral bioavailability of methimazole following administration of the controlled-release tablets was similar to that of a conventional release formulation (83 +/- 21%). The pharmacokinetics of this controlled-release formulation of carbimazole supports its use as a once daily treatment (both as a starting dose and for maintenance therapy) for cats with hyperthyroidism.

Calorimetric and spectroscopic studies on the interaction of methimazole with bovine serum albumin.

The potential binding interaction(s) of the anti-thyroid drug methimazole (MMZ) with the protein bovine serum albumin (BSA) has been studied using isothermal titration calorimetry (ITC) and UV-Visible, fluorescence and circular dichroism (CD) spectroscopic techniques. The binding of MMZ to BSA has been studied in both the presence and absence of added surfactants. Since, the ITC thermograms show the molar enthalpy of binding of MMZ and BSA to be zero within experimental error, either the enthalpy change of the binding interaction is zero or there is no binding occurring. The CD and the intrinsic fluorescence and life time spectra of BSA were unchanged by the addition of MMZ. This is also indicative of the absence of any significant interaction of MMZ with BSA.

An in vivo multiwell-based fluorescent screen for monitoring vertebrate thyroid hormone disruption.

There is a pressing need for high throughput methods to assess potential effects of endocrine disrupting chemicals (EDCs). released into the environment. Currently our ability to identify effects in vitro exceeds that for in vivo monitoring. However, only in vivo analysis provides the full spectrum of physiological impacts exerted by a given chemical. With the aim of finding a physiological system compatible with automatic plate reading we tested the capacity of early embryonic stage Xenopus laevis tadpoles to monitor thyroid hormone (TH) disruption. Fluorescent transgenic X. laevis embryos bearing a TH/bZIP-eGFP construct, placed in 96 well plates, were used for a physiological-based screen for potential TH signaling disruptors. Using stage NF-45 embryos (time of thyroid gland formation) allowed rapid detection of chemical interference with both peripheral TR signaling and production of endogenous TH. Nanomolar concentrations of TH receptor agonists could be detected within 72 h. Moreover, when testing against a 5nM T3 challenge, the effects of inhibitors of TH production were revealed, including inhibitors of TH synthesis, (methimazole: 1 mM or sodium perchlorate: 3.56 microM), as well as antagonists acting at the receptor level (NH3: 2 microM) and a deiodinase inhibitor (iopanoic acid: 10 microM). Finally, we show that the thyroid disrupting activities of BPA (10 microM) and TBBPA (1 microM) can also be detected in this rapid screening protocol. Finally, this noninvasive technology using an automatic reading system shows low variability (around 5%) and permits detection of subtle changes in signaling by EDCs that either inhibit or activate TH signaling in vivo.

Radioiodine treatment for malignant thyroid disease.

Radioiodine treatment for thyroid disease has been given for half a decade in Sweden. The most common indication for treatment is hyperthyroidism, when iodine uptake is high. The situation in which radioiodine treatment is used in thyroid cancer is less favourable and measures therefore have to be taken to optimize the treatment. Treatment should be performed early in the course of the disease to achieve the highest possible differentiation. Before treatment the iodine and goitrogen intake should be kept low. Stimulation of the thyrocytes by thyroid-stimulating hormone (TSH) should be high. It is conventionally achieved by thyroid hormone withdrawal rendering the patient hypothyroid, or by the recently available recombinant human TSH (rhTSH) which can be recommended for ablation of the thyroid remnant after thyroidectomy and for treatment of metastases in fragile patients unable to undergo hypothyroidism. Finally, stunning--the negative effect of a prior test dose from radioactive iodine--should be avoided.

Influência do hipotireoidismo induzido por propiltiouracil na mucosa gengival do rato / Influence of propilthiouracil-induced hypothyroidism on rat gingival mucosa / Influence of propilthiouracil-induced hypothyroidism on rat gingival mucosa

O objetivo foi verificar a influência da deficiência dos hormônios tireoideanos induzida por propiltiouracil (PTU) na mucosa gengival do rato, analisando bioquimicamente as proteínas totais, colágeno (hidroxiprolina) e população celular (DNA). Foram utilizados 50 ratos machos da cepa Sprague-Dawley, separados em 2 grupos: propiltiouracil (PTU) (10 mg/d i.p.), e controle (C), durante 10 semanas. As proteínas totais foram determinadas pelo método de Lowry, a hidroxiprolina pelo método de Newman e DNA pelo método de Burton. Observou-se diminuição das proteínas totais no grupo PTU (PTU= 41,23 ± 24,05; C= 63,36 ± 18,05); não houve diferença na hidroxiprolina e DNA (PTU= 2,18 ± 1,48; C= 2,29 ± 1,51) e (PTU= 0,33 ± 0,19; C= 0,46 ± 0,31). Conclui-se que o tratamento com PTU diminui o conteúdo de proteínas totais na mucosa gengival do rato, provavelmente pela diminuição da síntese protéica, sem alteração do colágeno e da população celular.

This work aimed at verifying the influence of propilthiouracil (PTU)-induced thyroid hormone deficiency on gingival mucosa of young male rats, measuring total protein concentration, collagen content and DNA concentration as indices of cellular population. Fifty Sprague-Dawley rats were used. The animals were grouped in: PTU-treated (i.p. 10 mg/d) and control rats (C). The experience was maintained for a period of 10 weeks. Total protein content of gingival mucosa tissue was determined by the Lowry method; hydroxyprolin rate, as prototype aminoacid of collagen, was determined using the Newman method, and DNA concentration was measured by Burton's methodology. The results showed decreased amounts of PTU-treated rats gingival total protein content (PTU= 41.23 ± 24.05 vs. C= 63.36 ± 18.05); no alterations were seen in hydroxyprolin concentration neither in DNA content of PTU treated rats, respectively (PTU= 2.18 ± 1.48 vs. C= 2.29 ± 1.51) and (PTU= 0.33 ± 0.19 vs. C= 0.46 ± 0.41). Thus, PTU treatment promotes a decrease in total protein content of rat gingival mucosa that may be interpreted as a decrease in protein synthesis induced by the hypothyroid condition, but with no alteration either in collagen or nucleic acid rates.

Studies on the goitrogenic mechanism of action of N,N,N',N'-tetramethylthiourea.

N,N,N',N'-Tetramethylthiourea (TMTU) is a rat goitrogen inducing thyroid hyperplasia, hypertrophy, and tumor formation. Little is known about the exact underlying mechanism of action. As thyroid peroxidase (TPO) and type I iodothyronine deiodinase (ID-I) have been established as targets of goitrogenic thiourea derivatives, we investigated interactions of TMTU with target enzymes using a partially purified fraction from hog thyroids or solubilized hog thyroid microsomes and 10,000g supernatant from rat liver homogenate, respectively, as enzyme sources. For comparison, comprehensively characterized goitrogenic thiourea derivatives were studied as well. In contrast to propylthiouracil (PTU), and like ethylenethiourea (ETU), TMTU only marginally affected TPO-catalyzed oxidation of guaiacol. TMTU, like ETU, concentration-dependently suppressed TPO-catalyzed iodine formation with concomitant oxidative metabolism. Suppression ceased upon consumption of thiourea derivatives, the rate of the reappearing iodine formation was similar to that of controls. TMTU, like ETU, also suppressed non-enzymatic and TPO-catalyzed monoiodination of l-tyrosine with a stoichiometry of 2:1, i.e., one molecule of thiourea derivative suppressed two times monoiodination. TMTU and ETU were unable to irreversibly inhibit TPO. In contrast to PTU, TMTU did not inhibit ID-I. These findings provide evidence that TMTU interferes with thyroid hormone synthesis at the level of iodination and demonstrate a metabolic route for the oxidative detoxification of TMTU in the thyroid suggesting that low-level or intermittent exposure to TMTU would have only minimal effects on thyroid hormone synthesis. Finally, it can be concluded that meaningful toxicological studies on TPO inhibition can be performed without a need for highly purified TPO.

Short-term thyroxine administration leads to lipid peroxidation in renal and testicular tissues of rats with hypothyroidism.

Thyroid dysfunction brings about pathological changes in different organs of the body. The aim of the present study was to examine how experimental hypothyroidism and additional short-term high-dose thyroxine administration (one-week) affected lipid peroxidation in renal and testicular tissues of rats. The study was carried out on 30 male Spraque-Dawley rats. The experimental animals were divided into 3 groups as control, hypothyroidism and hypothyroidism + thyroxine administration. Both malondialdehyde (MDA) and glutathione (GSH) levels were lower in renal and testicular tissues of the hypothyroidism group than the control and hypothyroidism + thyroxine administration groups and the levels in hypothyroidism + thyroxine administration group were higher than those in the control and hypothyroidism groups (p < 0.001). Results of the study demonstrate that hypothyroidism reduced oxidant stress in kidney and testis tissues, but short-term, high-dose thyroxine administration in addition to hypothyroidism increased oxidant stress in the same tissues of rats.