Doris Rosenthal

Maternal Hypothyroxinemia Impairs Spatial Learning and Synaptic Nature and Function in the Offspring

Neurological deficits in the offspring caused by human maternal hypothyroxinemia are thought to be irreversible. To understand the mechanism responsible for these neurological alterations, we induced maternal hypothyroxinemia in pregnant rats. Behavior and synapse function were evaluated in the offspring of thyroid hormone-deficient rats. Our data indicate that, when compared with controls, hypothyroxinemic mothers bear litters that, in adulthood, show prolonged latencies during the learning process in the water maze test. Impaired learning capacity caused by hypothyroxinemia was consistent with cellular and molecular alterations, including: 1) lack of increase of phosphorylated c-fos on the second day of the water maze test; 2) impaired induction of long-term potentiation in response to theta-burst stimulation to the Schaffer collateral pathway in the area 1 of the hippocampus Ammons horn stratum radiatum, despite normal responses for input/output experiments; 3) increase of postsynaptic density protein 95 (PSD-95), N-methyl-D-aspartic acid receptor subunit 1, and tyrosine receptor kinase B levels in brain extracts; and 4) significant increase of PSD-95 at the PSDs and failure of this molecule to colocalize with N-methyl-D-aspartic acid receptor subunit 1, as it was shown by control rats. Our findings suggest that maternal hypothyroxinemia is a harmful condition for the offspring that can affect key molecular components for synaptic function and spatial learning.

Estrogen effects on thyroid iodide uptake and thyroperoxidase activity in normal and ovariectomized rats.

Sex steroids interfere with the pituitary-thyroid axis function, although the reports have been controversial and no conclusive data is available. Some previous reports indicate that estradiol might also regulate thyroid function through a direct action on the thyrocytes. In this report, we examined the effects of low and high doses of estradiol administered to control and ovariectomized adult female rats and to pre-pubertal females. We demonstrate that estradiol administration to both intact adult and pre-pubertal females causes a significant increase in the relative thyroid weight. Serum T3 is significantly decreased in ovariectomized rats, and is normalized by estrogen replacement. Neither doses of estrogen produced a significant change in serum TSH and total T4 in ovariectomized, adult intact and pre-pubertal rats. The highest, supraphysiological, estradiol dose produced a significant increase in thyroid iodide uptake in ovariectomized and in pre-pubertal rats, but not in control adult females. Thyroperoxidase activity was significantly higher in intact adult rats treated with both estradiol doses and in ovariectomized rats treated with the highest estradiol dose. Since serum TSH levels were not significantly changed, we suggest a direct action of estradiol on the thyroid gland, which depends on the age and on the previous gonad status of the animal.

The role of oxidative stress on breast cancer development and therapy

Reactive oxygen species (ROS) are produced by both enzymatic and non-enzymatic systems within eukaryotic cells and play important roles in cellular physiology and pathophysiology. Although physiological concentrations are crucial for ensuring cell survival, ROS overproduction is detrimental to cells, and considered key-factors for the development of several diseases, such as neurodegenerative diseases, cardiovascular disorders, and cancer. Cancer cells are usually submitted to higher ROS levels that further stimulate malignant phenotype through stimulus to sustained proliferation, death evasion, angiogenesis, invasiveness, and metastasis. The role of ROS on breast cancer etiology and progression is being progressively elucidated. However, less attention has been given to the development of redox system-targeted strategies for breast cancer therapy. In this review, we address the basic mechanisms of ROS production and scavenging in breast tumor cells, and the emerging possibilities of breast cancer therapies targeting ROS homeostasis.

The effect of acute exercise session on thyroid hormone economy in rats

The hypothalamic-pituitary-thyroid axis is affected by acute exercise, but the mechanisms underlying thyroid function changes after exercise remain to be defined. The aim of this study was to elucidate the effects of a session of acute exercise on the treadmill at 75% of maximum oxygen consumption on thyroid function of rats. Male Wistar rats were divided into five groups: control (without exercise), and killed immediately after (0 min) or 30, 60, and 120 min after the end of the exercise session. A significant increase in serum tri-iodothyronine (T(3)) occurred immediately after the exercise, with a gradual decrease thereafter, so that 120 min after the end of the exercise, serum T(3) was significantly lower than that in controls. Total thyroxine (T(4)) increased progressively reaching values significantly higher than that in the control group at 120 min. T(3)/T(4) ratio was significantly decreased 60 and 120 min after the exercise, indicating impaired T(4)-to-T(3) conversion. Liver type 1 deiodinase activity (D1) significantly decreased at 60 and 120 min, while pituitary D1 increased progressively from 30 to 120 min after the exercise, and thyroid D1 was increased only immediately after the end of the exercise. Brown adipose tissue (BAT) type 2 deiodinase activity (D2) was significantly lower at 30 min, but pituitary D2 remained unchanged. No change in serum thyrotropin was detected, while serum corticosterone was significantly higher 30 min after the exercise. Our results demonstrate that decreased liver D1 and BAT D2 might be involved in the decreased T(4)-to-T(3) conversion detected after an exercise session on the treadmill.

Effect of serum estradiol and leptin levels on thyroid function, food intake and body weight gain in female Wistar rats.

We evaluated the interplay among estrogen, leptin and thyroid function in the regulation of body mass in female rats. Adult female rats were divided into four groups: control (C, sham-operated), ovariectomized (OVX), ovariectomized treated with estradiol benzoate (Eb) 0.7 or 14microg/100gbw per day, during 21 days. OVX led to an increase in body mass, food intake and food efficiency (change in body mass as function of the amount of food ingested) which were normalized by the lower Eb dose, and decreased significantly when the higher dose was given. Serum leptin levels were increased more than two-fold in all ovariectomized groups. Serum T4 levels of the Eb treated OVX were significantly lower than in the controls. Serum T3 and TSH were unaffected by OVX or by Eb treatment. Uterine type 2 iodothyronine deiodinase (D2) activity changed in parallel with serum estradiol: decreased after OVX, returned to control levels after the lower E2 treatment, and increased significantly after the high Eb dosage. The hypothalamic D2 activity was reduced around 30% in all castrated groups, treated or not with estrogen, whereas in the brown adipose tissue the enzyme was not changed. Interestingly, although estrogen-treated OVX rats had lower body weight, serum leptin was high, suggesting that estrogen increases leptin secretion. Our results show that estradiol is necessary for the hypothalamic action of leptin, since the increase in leptin levels observed in all ovariectomized rats was associated with a decrease in food intake and food efficiency only in the rats treated with estrogen.

Hypothyroidism in the Adult Rat Causes Incremental Changes in Brain-Derived Neurotrophic Factor, Neuronal and Astrocyte Apoptosis, Gliosis, and Deterioration of Postsynaptic Density

BACKGROUND Adult hypothyroidism is a highly prevalent condition that impairs processes, such as learning and memory. Even though tetra-iodothyronine (T(4)) treatment can overcome the hypothyroidism in the majority of cases, it cannot fully recover the patients learning capacity and memory. In this work, we analyzed the cellular and molecular changes in the adult brain occurring with the development of experimental hypothyroidism. METHODS Adult male Sprague-Dawley rats were treated with 6-propyl-2-thiouracil (PTU) for 20 days to induce hypothyroidism. Neuronal and astrocyte apoptosis were analyzed in the hippocampus of control and hypothyroid adult rats by confocal microscopy. The content of brain-derived neurotrophic factor (BDNF) was analyzed using enzyme-linked immunosorbent assay (ELISA) and in situ hybridization. The glutamatergic synapse and the postsynaptic density (PSD) were analyzed by electron microscopy. The content of PSD proteins like tyrosine receptor kinase B (TrkB), p75, and N-methyl-D-aspartate receptor (NMDAr) were analyzed by immunoblot. RESULTS We observed that the hippocampus of hypothyroid adult rats displayed increased apoptosis levels in neurons and astrocyte and reactive gliosis compared with controls. Moreover, we found that the amount of BDNF mRNA was higher in the hippocampus of hypothyroid rats and the content of TrkB, the receptor for BDNF, was reduced at the PSD of the CA3 region of hypothyroid rats, compared with controls. We also observed that the glutamatergic synapses from the stratum radiatum of CA3 from hypothyroid rats, contained thinner PSDs than control rats. This observation was in agreement with a reduced content of NMDAr subunits at the PSD in hypothyroid animals. CONCLUSIONS Our data suggest that adult hypothyroidism affects the hippocampus by a mechanism that alters the composition of PSD, reduces neuronal and astrocyte survival, and alters the content of the signaling neurotrophic factors, such as BDNF.

Thyroid peroxidase inhibition by Kalanchoe brasiliensis aqueous extract

Flavonoids are known inhibitors of thyroid peroxidase (TPO) and some are components of Kalanchoe brasiliensis, a plant used in popular medicine to treat tissue injuries, enlarged ganglia and peptic ulcer. As K. brasiliensis extract is currently used, the present study was designed to evaluate the effects of K. brasiliensis aqueous extract on TPO activity. We show here that TPO iodide-oxidation activity was significantly inhibited by K. brasiliensis aqueous extract and that TPO inhibition seems to be competitive, since the enzyme V(max) was unchanged and K(m) for iodide was significantly increased in the presence of the plant extract. Furthermore, TPO inhibitory activity produced by K. brasiliensis extract was unchanged after boiling or by incubation with hepatic enzymes (activated S9 fraction), suggesting that at least the antithyroid component of this plant infusion could probably reach systemic circulation. We also report that K. brasiliensis aqueous extract is able to scavenge H(2)O(2), in vitro. As H(2)O(2) is an essential TPO cofactor, it is possible that the H(2)O(2) trapping effect of K. brasiliensis may be responsible, at least in part, for the inhibition of the iodide-oxidation reaction catalysed by this enzyme. Thus, K. brasiliensis aqueous extract has antithyroid effects in vitro, suggesting that its chronic consumption could contribute to the development of goitre and hypothyroidism, mainly in areas of low iodine intake.

EFFECT OF AGING ON THYROIDAL AND PITUITARY T4-5'-DEIODINASE ACTIVITY IN FEMALE RATS

Some alterations in hypothalamo-pituitary-thyroid axis occur during aging. In this study we evaluated the changes induced by aging in pituitary and thyroid iodothyronine-deiodinase (DI) activities, and in serum T4, T3 and TSH. Groups of 6-18 female Dutch-Miranda rats aged 3-5 months (young adults) were studied in parallel with similar groups of old (10-12 months) and senescent (24-30 months) animals. DI activities were determined in the microsomal fraction of pooled pituitary or thyroid glands (6 glands per pool), using T4 as substrate and DTT as cofactor; the T3 formed was measured by specific radioimmunoassay. Serum T3, T4 and TSH were measured by specific radioimmunoassays. Serum T4 was significantly decreased in both groups of aged rats, but serum TSH was unaffected. Serum T3 was just slightly decreased in the senescent rats. Total pituitary DI activity was significantly decreased in the aged rats (10-12 and 24-30 months). Both type I and type II DI activities were affected, although the decrease in type I DI only became significant in the senescent rats. In contrast, to its effect in the pituitary, aging does not decrease, even slightly, the DI activity in the thyroid gland. The thyroid DI activity may contribute to the unaltered serum T3 levels found in aged rats in the present study.

Enzimas envolvidas na organificação tireoideana do iodo

Thyroid hormone biosynthesis depends on iodide uptake and its incorporation into the acceptor protein thyroglobulin (Tg), a high molecular weight protein secreted into the follicular lumen. The sodium-iodide symporter (NIS) is responsible for thyroid iodide uptake, the first step in thyroid hormonogenesis. Iodide is subsequently transported through the cellular membrane by pendrin (PDS) and then incorporated into Tg. Iodide oxidation and organification occur mainly in the thyrocyte apical surface and these reactions are catalyzed by thyroperoxidase (TPO) in the presence of hydrogen peroxide. Thus, thyroid iodide organification depends on TPO activity, which is modulated by the concentration of substrates (thyroglobulin and iodide) and cofactor (hydrogen peroxide). Hydrogen peroxide generation is catalyzed by the thyroid NADPH oxidase (ThOx), which is present in the apical pole of thyrocytes, is stimulated by thyrotropin and is inhibited by iodide. Hydrogen peroxide generation is the limiting step in thyroid hormone biosynthesis under iodine sufficiency conditions.

Effects of ageing and pharmacological hypothyroidism on pituitary–thyroid axis of Dutch-Miranda and Wistar rats

To evaluate the ability of the aged rat pituitary to increase TSH secretion in response to major decreases in serum thyroid hormones, hypothyroidism was induced by methimazole in young and old, male and female, Dutch-Miranda and Wistar rats. Before MMI-treatment there were no differences in serum TSH of young and old rats, but serum T(4) was significantly decreased in aged rats from both genders and strains, while serum T(3) was significantly decreased in aged male rats from both strains, and in old Wistar females. MMI treatment significantly decreased serum T(4) and T(3) in all treated animals, and progressively increased serum TSH in both male and female rats, but the increase was significantly smaller in the elder rats. The pituitary TSH content was higher in Wistar than in Dutch-Miranda rats, of both genders, and was not significantly affected by age. MMI treatment decreased the pituitary TSH in both young and old Dutch-Miranda rats, but in the Wistar strain only the old females had a significant decrease. Our results show that the ability of the pituitary thyrotrophs to increase hormonal secretion in response to decreased levels of thyroid hormones is impaired in the old rat, even when the thyroid hormone levels are dramatically reduced.