Biomedical subjects

Maria Luiza M Barreto-Chaves

Publications and source records attributed to Maria Luiza M Barreto-Chaves.

12 recordsLinked to original sources

PubMed2006

Activity and expression of ecto-5'-nucleotidase/CD73 are increased by thyroid hormones in vascular smooth muscle cells.

Extracellular nucleotides ATP, ADP, AMP and adenosine are well known signaling molecules of the cardiovascular system that are involved in several physiological processes: cell proliferation, platelet aggregation, inflammatory processes and vascular tonus. The levels of these molecules are controlled by ecto-NTPDases and ecto-5'-nucleotidase/CD73 (ecto-5'-NT/CD73) actions, which are responsible for the complete ATP degradation to adenosine. The thyroid hormones, thyroxine (T(4)) and triiodothyronine (T(3)), play important roles in the vascular system promoting vasodilatation. Here we investigated the influence of thyroid hormones on the enzyme cascade that catalyzes the interconversion of purine nucleotides in vascular smooth muscle cells (VSMC). Exposure of VSMCs to 50nM T(3) or T(4) did not change ATP and ADP hydrolysis significantly. However, the same treatment caused an increase of 75% in AMP hydrolysis, which was time-dependent but dose-independent. Moreover, T(3) treatment significantly increased ecto-5'-NT/CD73 mRNA expression, which suggests a genomic effect of this hormone upon ecto-5'-NT/CD73. In addition to the importance of the ecto-5'-NT in cell proliferation and differentiation, its overexpression could result in higher extracellular levels of adenosine, an important local vasodilatator molecule.

5'-Nucleotidase↗

PubMed2006

Neonatal hypothyroidism affects the adenine nucleotides metabolism in astrocyte cultures from rat brain.

Neonatal hypothyroidism is associated with multiple and severe brain alterations. We recently demonstrated a significant increase in hydrolysis of AMP to adenosine in brain of hypothyroid rats at different ages. However, the origin of this effect was unclear. Considering the effects of adenine nucleotides to brain functions and the harmful effects of neonatal hypothyroidism to normal development of the central nervous system, in this study we investigated the metabolism of adenine nucleotides in hippocampal, cortical and cerebellar astrocyte cultures from rats submitted to neonatal hypothyroidism. ATP and AMP hydrolysis were enhanced by 52 and 210%, respectively, in cerebellar astrocytes from hypothyroid rats. In hippocampus of hypothyroid rats, the 47% increase in AMP hydrolysis was significantly reverted when the astrocytes were treated with T3. Therefore, the imbalance in the ATP and adenosine levels in astrocytes, during brain development, may contribute to some of the effects described in neonatal hypothyroidism.

Adenine Nucleotides↗

PubMed2006

E-NTPDase 3 (ATP diphosphohydrolase) from cardiomyocytes, activity and expression are modulated by thyroid hormone.

Degradation of adenine nucleotides by myocardial cells occurs, in part, by a cascade of surface-located enzymes converting ATP into adenosine that has important implications for the regulation of the nucleotide/nucleoside ratio modulating the cardiac functions. Thyroid hormones have profound effects on cardiovascular system, as observed in hypo- and hyperthyroidism. Combined biochemical parameters and gene expression analysis approaches were used to investigate the influence of tri-iodothyronine (T3) on ATP and ADP hydrolysis by isolated myocytes. Cultures of cardiomyocytes were submitted to increasing doses of T3 for 24h. Enzymatic activity and expression were evaluated. T3 (0.1 nM) caused an increase in ATP and ADP hydrolysis. Experiments with specific inhibitors suggest the involvement of an NTPDase, which was confirmed by an increase in NTPDase 3 messenger RNA (mRNA) levels. Since T3 promotes an increase in the contractile protein, leading to cardiac hypertrophy, it is tempting to postulate that the increase in ATP hydrolysis and the decrease in the extracellular levels signify an important factor for prevention of excessive contractility.

Adenosine Diphosphate↗

PubMed2005

Activation of adenosine A(1) receptors alters behavioral and biochemical parameters in hyperthyroid rats.

Adenosine acting on A(1) receptors has been related with neuroprotective and neuromodulatory actions, protection against oxidative stress and decrease of anxiety and nociceptive signaling. Previous studies demonstrated an inhibition of the enzymes that hydrolyze ATP to adenosine in the rat central nervous system after hyperthyroidism induction. Manifestations of hyperthyroidism include increased anxiety, nervousness, high O(2) consumption and physical hyperactivity. Here, we investigated the effects of administration of a specific agonist of adenosine A(1) receptor (N(6)-cyclopentyladenosine; CPA) on nociception, anxiety, exploratory response, locomotion and brain oxidative stress of hyperthyroid rats. Hyperthyroidism was induced by daily intraperitoneal injections of l-thyroxine (T4) for 14 days. Nociception was assessed with a tail-flick apparatus and exploratory behavior, locomotion and anxiety were analyzed by open-field and plus-maze tests. We verified the total antioxidant reactivity (TAR), lipid peroxide levels by the thiobarbituric acid reactive species (TBARS) reaction and the free radicals content by the DCF test. Our results demonstrated that CPA reverted the hyperalgesia induced by hyperthyroidism and decreased the exploratory behavior, locomotion and anxiety in hyperthyroid rats. Furthermore, CPA decreased lipid peroxidation in hippocampus and cerebral cortex of control rats and in cerebral cortex of hyperthyroid rats. CPA also increased the total antioxidant reactivity in hippocampus and cerebral cortex of control and hyperthyroid rats, but the production of free radicals verified by the DCF test was changed only in cerebral cortex. These results suggest that some of the hyperthyroidism effects are subjected to regulation by adenosine A(1) receptor, demonstrating the involvement of the adenosinergic system in this pathology.

Adenosine↗

PubMed2005

Nociceptive response and adenine nucleotide hydrolysis in synaptosomes isolated from spinal cord of hypothyroid rats.

Purinergic system exerts a significant influence on the modulation of pain pathways at the spinal site. Adenosine has antinociceptive properties in experimental and clinical situations, while ATP exerts pronociceptive actions in different pain models. In this study we investigated the hydrolysis of ATP to adenosine in synaptosomes from spinal cord in parallel with the nociceptive response of rats at different ages after hypothyroidism induction. Hypothyroidism elicited a significant increase in AMP hydrolysis to adenosine in synaptosomes from spinal cord of rats subjected to neonatal hypothyroidism and in 420-day-old rats submitted to thyroidectomy. Accordingly, these rats presented an analgesic response as a consequence of hypothyroidism. In contrast, the ATP hydrolysis was decreased in the spinal cord of 60-day-old hypothyroid rats in parallel with a significant increase in nociceptive response. These results indicate the involvement of adenine nucleotides in the control of the hypothyroidism-induced nociceptive response during development.

Adenine Nucleotides↗

PubMed2005

Hyperthyroidism changes nociceptive response and ecto-nucleotidase activities in synaptosomes from spinal cord of rats in different phases of development.

Changes in transport, receptors and production of extracellular adenosine have been observed after induction of hyperthyroidism. Adenosine is associated with inhibitory actions such as reduction in release of excitatory neurotransmitters and antinociception at spinal site. In contrast, ATP acts as an excitatory neurotransmitter and produces pronociceptive actions. ATP may be completely hydrolyzed to adenosine by an enzyme chain constituted by an ATP diphosphohydrolase and an ecto-5'-nucleotidase, as previously described in the spinal cord. Thus, we now investigated the effects of the hyperthyroidism on adenine nucleotide hydrolysis in the spinal cord and verified the nociceptive response in this pathology during different phases of development. Hyperthyroidism was induced in male Wistar rats, aged 5, 60 and 330 days by daily intraperitoneal injections of L-thyroxine (T4) for 14 days. Nociception was assessed with a tail-flick apparatus. Rats starting the treatment aged 5 days demonstrated a significant increase in ADP and AMP hydrolysis and increased tail-flick latency (TFL). In contrast, in the spinal cord from hyperthyroid rats aged 60 and 330 days old, the hydrolysis of ATP, ADP and AMP were significantly decreased. Accordingly, the tail-flick latency was decreased, indicating a hyperalgesic response. These results suggest the involvement of ecto-nucleotidases in the control of the hyperthyroidism-induced nociceptive response in rats at distinct developmental stages.

Adenosine Triphosphatases↗

PubMed2005

Hypothyroidism changes adenine nucleotide hydrolysis in synaptosomes from hippocampus and cerebral cortex of rats in different phases of development.

The influence of the thyroid hormones on the normal function of the mammalian central nervous system depends on the brain region and on the developmental stage. Adenine nucleotides and their products also affect the brain function; ATP is an excitatory neurotransmitter, and adenosine has inhibitory effects on neurotransmission. Thus, this study aimed to evaluate the effects of hypothyroidism on the hydrolysis of ATP to adenosine in hippocampal and cortical synaptosomes and blood serum of rats during different phases of development. Rats aged 60 and 420 days old were divided into three groups: control, sham-operated and hypothyroid. Hypothyroidism was induced in these rats by thyroidectomy and methimazole (0.05%) added to their drinking water for 14 days. Neonatal hypothyroidism was induced by adding 0.02% methimazole in the drinking water from day 9 of gestation, and continually until 14 days old. Hypothyroidism increased the AMP hydrolysis in both hippocampus and cerebral cortex synaptosomes of rats in all aged tested. In blood serum, thyroid hormones deficiency increased the AMP hydrolysis in 14-day-old rats and the hydrolysis of ATP, ADP and AMP in 60-day-old rats; however, no alteration was observed in 420-day-old rats. Thus, our results suggest the involvement of the 5'-nucleotidase in synaptic function control in hypothyroidism throughout brain development.

Adenine Nucleotides↗

PubMed2005

Hypo-and hyperthyroidism affect the ATP, ADP and AMP hydrolysis in rat hippocampal and cortical slices.

The presence of severe neurological symptoms in thyroid diseases has highlighted the importance of thyroid hormones in the normal functioning of the mature brain. Since, ATP is an important excitatory neurotransmitter and adenosine acts as a neuromodulatory structure inhibiting neurotransmitters release in the central nervous system (CNS), the ectonucleotidase cascade that hydrolyzes ATP to adenosine, is also involved in the control of brain functions. Thus, we investigated the influence of hyper-and hypothyroidism on the ATP, ADP and AMP hydrolysis in hippocampal and cortical slices from adult rats. Hyperthyroidism was induced by daily injections of l-thyroxine (T4) 25 microg/100 g body weight, for 14 days. Hypothyroidism was induced by thyroidectomy and methimazole (0.05%) added to their drinking water for 14 days. Hypothyroid rats were hormonally replaced by daily injections of T4 (5 microg/100 g body weight, i.p.) for 5 days. Hyperthyroidism significantly inhibited the ATP, ADP and AMP hydrolysis in hippocampal slices. In brain cortical slices, hyperthyroidism inhibited the AMP hydrolysis. In contrast, hypothyroidism increased the ATP, ADP and AMP hydrolysis in both hippocampal and cortical slices and these effects were reverted by T4 replacement. Furthermore, hypothyroidism increased the expression of NTPDase1 and 5'-nucleotidase, whereas hyperthyroidism decreased the expression of 5'-nucleotidase in hippocampus of adult rats. These findings demonstrate that thyroid disorders may influence the enzymes involved in the complete degradation of ATP to adenosine and possibly affects the responses mediated by adenine nucleotides in the CNS of adult rats.

5'-Nucleotidase↗

PubMed2005

5'-nucleotidase activity is altered by hypo- and hyperthyroidism in platelets from adult rats.

Thyroid disorders are associated to a number of vascular diseases that involve processes such as platelet aggregation and vascular tone control. Since, these processes can be also affected by ATP, ADP and adenosine levels, we investigate the hydrolysis of these nucleotides in platelets from hyperthyroid, hypothyroid, and hypothyroid with hormonal replacement rats. Hyperthyroidism was induced by daily injections of L-thyroxine (T4) 25 microg/100 g body weight for 14 days. Hypothyroidism was induced by thyroidectomy and methimazole (0.05%) for 14 days. In the hormonal replacement group, hypothyroid rats were injected with T4 (5 microg/100 g body weight, i.p.) for 5 days. The AMP hydrolysis by platelets was increased 49% in hyperthyroid rats and decreased 50% in response to hypothyroidism, while the ATP and ADP hydrolysis was not altered in both groups. Besides, the T4 replacement significantly reversed the inhibition of the AMP hydrolysis observed in hypothyroid rats. Our findings indicate that the thyroid disorders affect the 5'-nucleotidase activity and consequently can alter the adenosine levels in a reversible manner in platelet fraction. Since, adenosine is able to inhibit platelet aggregation and acts as a potent vasodilator, these results can contribute to a better comprehension of the vascular events described in thyroid disorders.

5'-Nucleotidase↗

PubMed2004

Effects of steroid hormones on synaptosomal ectonucleotidase activities from hippocampus and cortex of adult female rats.

Over the last few years, the effects of steroid hormones on the brain have been intensively discussed. It has been demonstrated that ATP (acting as a neurotransmitter) is hydrolyzed to adenosine in the synaptic cleft by the conjugated action of ectonucleotidases, which include an enzyme of the E-NTPDase family (NTPDase3, apyrase, EC 3.6.1.5) and a 5'-nucleotidase (EC 3.1.3.5). The 5'-nucleotidase enzyme is able to hydrolyze AMP as well as other monophosphate nucleotides. The importance of this enzyme in the central nervous system is to participate in the adenosine formation, a nucleoside with neuroprotective properties and modulatory effects. However, several questions have been raised about the mechanisms of steroid hormones and the possible neuroprotective effects of estrogen. Thus, we examined the effects of gonadal steroid hormone deprivation, induced by ovary removal (OVX) and estradiol replacement therapy, on the ectonucleotidase activities in synaptosomes from hippocampus and cerebral cortex of adult rats. ATP and ADP hydrolysis in synaptosomes from cerebral cortex and hippocampus did not change as a function of OVX and results demonstrated an increase in AMP hydrolysis (82%) in the animals submitted to OVX in cerebral cortex, but not in hippocampus, when compared to control and sham-operated groups. Estradiol replacement therapy reversed this effect. RT-PCR analysis showed that the enhancement of enzyme activity in cerebral cortex could be explained by the higher expression of 5'-nucleotidase, following OVX. The hormones 17beta-estradiol (cyclodextrin-encapsulated 17beta-estradiol), DHEAS, and pregnenolone (1.0, 2.5, and 5.0 microM) did not alter the nucleotide hydrolysis, in vitro, in synaptosomes from cortex and hippocampus of female adult rats. Results presented, herein, should be considered relevant for hormone replacement therapy, since much controversy exists surrounding this area and the relationship between adenosine and sex steroids is still poorly understood.

Adenosine Monophosphate↗

PubMed2004

Thyroid hormone stimulates 5'-ecto-nucleotidase of neonatal rat ventricular myocytes.

Degradation of adenine nucleotides in myocardial cells has important physiological implications associated with the regulation of the high-energy phosphate precursor pool and the production of adenosine. Adenosine may be released as from cells or, following adenine nucleotides release, they may be metabolized and rapidly converted to adenosine via the action of an ectoenzyme cascade formed by an ATP diphosphohydrolase and a 5'-nucleotidase. Thyroid hormones are known to have profound effects on the cardiovascular system, as demonstrated by the changes accompanying both hypothyroidism and hyperthyroidism. We previously reported that thyroid hormone significantly increases the ecto-5'-nucleotidase (CD73) activity and expression in C6 glioma cells culture. The object of the present study was to evaluate the extracellular adenosine production from AMP in cardiomyocytes and also the effect of (T3) on activity and expression of the enzyme, CD73. Primary cultures of rat ventricular neonatal cardiac myocytes were submitted to increasing doses of T3 for 24 h. Cell viability and purity were estimated by measuring the release of lactate dehydrogenase (LDH) activity and immunofluorescence cell staining, respectively. CD73 activity was measurement using a malachite green method and RT-PCR was used to analyze enzyme expression. T3 stimulated CD73 activity and expression of the cells, suggesting that this effect could promote an increase in adenosine formation and, therefore, has an important modulatory role in the elicitation of responses that serve to restore the tissue oxygen supply-to-demand ratio back to normal.

5'-Nucleotidase↗

PubMed2002

In vitro effects of thyroid hormones on ectonucleotidase activities in synaptosomes from hippocampus of rats.

1. Studies have shown that adenosine transport and adenosine A1 receptors in rat brain are subjected to regulation by thyroid hormone levels. Since the ectonucleotidase pathway is an important source of adenosine extracellular, in the present study the in vitro action of T3 and T4 hormones on ectonucleotidase activities in hippocampal synaptosomes was evaluated. 2. T3 (Triiodo-l-thyronine) significantly inhibited, in an uncompetitive manner, the ATP and ADP hydrolysis promoted by ATP diphosphohydrolase activity in hippocampal synaptosomes of adult rats. 3. In contrast, T4 (Thyroxine) only inhibited ATP hydrolysis in an uncompetitive mechanism, at the concentrations tested (100-500 microM), but at the same time did not affect ADP hydrolysis. 4. In the present study, we also investigate the in vitro effect of T3 and T4 on 5'-nucleotidase activity. However, there are no changes in the activity of this enzyme in the presence of T3 and T4 in the hippocampal synaptosomes of rats. 5. These results suggest that thyroid hormones could be involved in the regulation of ectonucleotidase activities, such as ecto-ATP diphosphohydrolase and ecto-ATPase, possibly exerting a modulatory role in extracellular adenosine levels.

Adenosine↗