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Biomedical subjects

G J Juvenal

Publications and source records attributed to G J Juvenal.

At least 19 recordsLinked to original sources
PubMed2007

Inhibition of peroxidase and catalase activities and modulation of hydrogen peroxide level by inositol phosphoglycan-like compounds.

Inositol phosphoglycan-like compounds are produced by the hydrolysis of the membrane bound glycosyl phosphoinositides. Besides being short term mediators of insulin action, they inhibit peroxidases and catalase, increasing the concentration of cellular hydrogen peroxide. Although high concentrations of hydrogen peroxide are toxic, moderate increases of its basal level are signals for different metabolic pathways. The inhibitor, localized in the cytosol of the cell, acts on peroxidases and catalase of the same tissue (homologous action) and of other tissues or organisms (heterologous action). The inositol phosphoglycan-like compound inhibits peroxidases with different prosthetic groups, i.e. containing iron such as: thyroid peroxidase, lactoperoxidase, horseradish peroxidase, soy bean peroxidase; and containing selenium such as glutathione peroxidase and 2-cys peroxiredoxin with no prosthetic group. Besides peroxidases, the inositol phosphoglycan-like compound inhibits catalase, another heme enzyme. The inhibition kinetics demonstrates a noncompetitive effect. The site of action is not the prosthetic group, given that the inhibitor does not produce any effect on the peak in the Soret region in the presence or absence of hydrogen peroxide. In conclusion, the inositol phosphoglycan-like compound is the general inhibitor of peroxidases and catalase involved in the modulation of hydrogen peroxide level that acts in different metabolic pathways as a signal transducer.

Animals↗
PubMed2006

Nicotinamide increases thyroid radiosensitivity by stimulating nitric oxide synthase expression and the generation of organic peroxides.

Differentiated thyroid cancer and hyperthyroidism are treated with radioiodine. However, when the radioisotope dose exceeds certain limits, the patient must be hospitalized to avoid contact with people that would otherwise be exposed to radiation. It would be desirable to obtain a similar therapeutic effect using lower radioiodine doses. Radiosensitizers can be utilized for this purpose. Nicotinamide (NA) increases thyroid radiosensitivity to 131I in both normal and goitrous glands. NA causes a significant increase in thyroid blood flow, which would increase tissue oxygenation and tissue damage via free radicals. Wistar rats were treated with either nicotinamide (NA), 131I or both. The expression of the three isoforms of nitric oxide synthase (NOS) in the thyroid (Western blot) and the activities of SOD, GPx, catalase and organic peroxides were determined. Treatment with NA or 131I increased the expression of eNOS and the generation of organic peroxides. When administered jointly, they showed a synergistic effect. No changes were observed in the other NOS isoforms or in the activities of catalase, glutathione peroxidase and superoxide dismutase. NA potentiates the effect of 131I by increasing eNOS, which would in turn stimulate NO production, increasing thyroid blood flow and tissue damage via organic peroxides.

Animals↗
PubMed2005

Long-term effect of norepinephrine on thyroglobulin gene expression in FRTL-5 cells.

Many types of evidence support a role of the sympathetic nervous system in the regulation of thyroid function, although there is no general consensus on the type of influence that catecholamines exert. Depending on the experimental approach, epinephrine and norepinephrine (NE) can stimulate, inhibit, or fail to act on thyroid function. The aim of this study was to determine the effect of NE on thyroglobulin (Tg) synthesis and gene expression in FRTL-5 cells. Tg content, measured by immunoprecipitation with a specific antibody, showed that NE caused a 45% inhibition of thyrotropin (TSH) effect. The content of Tg mRNA was analyzed by Northern blot, the relative inhibition in total Tg mRNA levels from NE-treated cells, compared to TSH alone, ran parallel with inhibition in Tg content, while total RNA did not change after incubation with NE. There was no alteration in Tg mRNA stability by NE. When plasmids harboring different sequences of Tg promoter fused to the CAT reporter gene were transfected into FRTL-5 cells, TSH treatment stimulated promoter activity while NE diminished this effect by 43%-55%. Northern blots were performed to analyze mRNA for thyroid transcription factors (TTF1, TTF2, Pax8), and no significant changes were observed with the different treatments. In conclusion these results suggest that NE inhibits Tg synthesis at the transcriptional level.

Animals↗
PubMed2004

Boron neutron capture therapy for undifferentiated thyroid carcinoma: preliminary results with the combined use of BPA and BOPP.

We have shown the selective uptake of borophenylalanine (BPA) by undifferentiated human thyroid cancer (UTC) ARO cells both in vitro and in vivo. Moreover, a 50% histologic cure of mice bearing the tumor was observed when the complete boron neutron capture therapy was applied. More recently we have analyzed the biodistribution of BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha,beta-dihydroxyethyl)-deutero-porphyrin IX) and showed that when BOPP was injected 5 days before BPA, and the animals were sacrificed 60 min after the i.p. injection of BPA, a significant increase in boron uptake by the tumor was found (38-45 ppm with both compounds vs. 20 ppm with BPA alone). Five days post the i.p BOPP injection and 1h after BPA the ratios were: tumor/blood 3.75; tumor/distal skin 2. Other important ratios were tumor/thyroid 6.65 and tumor/lung 3.8. The present studies were performed in mice transplanted with ARO cells and injected with BOPP and BPA. Only in mice treated with the neutron beam and injected with the boronated compounds we observed a 100% control of tumor growth. Two groups of mice received different total absorbed doses: 3.00 and 6.01 Gy, but no further improvement in the outcome was found compared to the previous results using BPA alone (4.3 Gy).

Animals↗
PubMed2004

Biodistribution of p-borophenylalanine (BPA) in dogs with spontaneous undifferentiated thyroid carcinoma (UTC).

Human undifferentiated thyroid carcinoma (UTC) is a very aggressive tumor which lacks an adequate treatment. The UTC human cell line ARO has a selective uptake of BPA in vitro and after transplanting into nude mice. Applications of boron neutron capture therapy (BNCT) to mice showed a 100% control of growth and a 50% histological cure of tumors with an initial volume of 50 mm(3) or less. As a further step towards the potential application in humans we have performed the present studies. Four dogs with diagnosis of spontaneous UTC were studied. A BPA-fructose solution was infused during 60 min and dogs were submitted to thyroidectomy. Samples of blood and from different areas of the tumors (and in one dog from normal thyroid) were obtained and the boron was determined by ICP-OES. Selective BPA uptake by the tumor was found in all animals, the tumor/blood ratios ranged between 2.02 and 3.76, while the tumor/normal thyroid ratio was 6.78. Individual samples had tumor/blood ratios between 8.36 and 0.33. These ratios were related to the two histological patterns observed: homogeneous and heterogeneous tumors. We confirm the selective uptake of BPA by spontaneous UTC in dogs and plan to apply BNCT in the future.

Animals↗
PubMed2002

Selective uptake of p-borophenylalanine by undifferentiated thyroid carcinoma for boron neutron capture therapy.

Undifferentiated thyroid carcinoma (UTC) lacks an effective treatment. Boron neutron capture therapy (BNCT) is based on the selective uptake of 10B-boronated compounds by some tumors, followed by irradiation with an appropriate neutron beam. The radioactive boron originated (11B) decays releasing 7Li, gamma rays and alpha particles, and these latter will destroy the tumor. In order to explore the possibility of applying BNCT to UTC we have studied the biodistribution of BPA. In in vitro studies, the uptake of p-10borophenylalanine (BPA) by the UTC cell line ARO, primary cultures of normal bovine thyroid cells (BT), and human follicular adenoma (FA) thyroid was studied. No difference in BPA uptake was observed between proliferating and quiescent ARO cells. The uptake by quiescent ARO, BT, and FA showed that the ARO/BT and ARO/FA ratios were 4 and 5, respectively (p < 0.001). In in vivo studies, ARO cells were transplanted into the scapular region of NIH nude mice, and after 2 weeks BPA (350 or 600 mg/kg body weight) was injected intraperitoneally. The animals were sacrificed between 30 and 150 minutes after the injection. With 350 mg, tumor uptake was highest after 60 minutes and the tumor/normal thyroid and tumor/blood ratios were 3 and 5, respectively. When 600 mg/kg body weight BPA were administered, after 90 minutes the tumor/blood, tumor/normal thyroid, and tumor/distal skin ratios for 10B concentrations per gram of tissue were approximately 3, showing a selective uptake by the tumor. The present experimental results open the possibility of applying BNCT for the treatment of UTC.

Adenoma↗
PubMed2001

The protein kinase C pathway inhibits iodide uptake by calf thyroid cells via sodium potassium-adenosine triphosphatase.

The effect of the phorbol esther phorbol myristate acetate (PMA) on iodide uptake was studied in primary cultures of calf thyroid cells. PMA caused a dose- and time-dependent inhibition of thyrotropin (TSH), forskolin, and db-cAMP stimulation, indicating an effect distal to both TSH receptor and cAMP generation. No action was found on iodide efflux, indicating a selective inhibition of iodide uptake. This inhibition was observed even after 5 minutes of incubation, thus excluding a possible genomic action. Bisindolmaleimide (BS), a specific inhibitor of the protein kinase C (PKC) pathway, reverted the effect of PMA. A similar degree of inhibition of the Na+/K+ adenosine triphosphatase (ATPase) and iodide uptake by PMA was found, thus suggesting a link between both parameters. These results indicate that the PKC pathway inhibits thyroid iodide uptake by an action distal to cAMP generation and probably because of a decrease in Na+/K+-ATPase activity.

Animals↗
PubMed2001

Influence of nicotinamide on the radiosensitivity of normal and goitrous thyroid in the rat.

Radioiodine is used to treat thyroid cancer and hyperthyroidism. In order to reduce radiation hazard to the patient and to people in contact with the patient it would be desirable to obtain the same therapeutic effect with lower activities of the radioisotope. This could be achieved by the simultaneous administration of a compound that increases tissue radiosensitivity. In this study we analyzed the use of nicotinamide (NA) as a radiosensitizer to radioiodine, to increase 131I efficacy. NA administered during 30 days to Wistar rats failed to alter thyroid weight. The influence of NA on radiothyroidectomy induced by increasing doses of 131I was examined in otherwise nontreated rats. NA produced a significant increase in the ablation caused by radioiodine. Goiter was then induced by the administration of methylmercaptoimidazol (MMI) to rats, followed by the treatment with radioiodine with and without simultaneous administration of NA. Thyroid weight per 100 g of body weight ratio was not changed by NA alone; 131I administration caused a 25% decrease in goiter size, while 131I plus NA produced a reduction of the ratio of 46% (p < 0.01 vs. NA). No changes were observed in adenosine diphosphate (ADP)-ribosilation of thyroid nuclear protein in NA-treated rats. Thyroid blood flow (determined by 86Rb uptake) was increased by 84% by NA. In conclusion, nicotinamide has a significant radiosensitizing effect to 131I both in normal and goitrous rats. This action is because of an increase in thyroid blood flow, which probably enhances tissue oxgenation.

Adenosine Diphosphate Ribose↗
PubMed1999

Presence of a soluble inhibitor of thyroid iodination in primary cultures of thyroid cells.

Monolayer cultures of thyroid cells lose their iodide organification capacity a few days before the disappearance of thyroid peroxidase (TPO) activity. The present studies were performed in order to clarify this point. The above mentioned difference was due to the presence of an inhibitor in the monolayer thyroid cells culture, given that total homogenate prepared from confluent cells caused a significant inhibition of activity of TPO from fresh tissue. The inhibitor was localized in the 105000g supernatant of the homogenate of the cell culture, but not in a similar preparation obtained from fresh thyroid. It is thermostable, dialyzable and has a molecular weight of less than 2 kDa. Addition of the inhibitor at the end of the reaction of tyrosine iodination failed to alter the results. This fact suggests that the compound does not destroy the iodinated product. The presence of the cytosolic inhibitor was observed in monolayer thyroid cell cultures of different species (bovine, porcine, rat and human) but not in free follicles cultures.

Animals↗
PubMed1997

Long-term effect of norepinephrine on iodide uptake in FRTL-5 cells.

The sympathetic nervous system plays a role in the regulation of thyroid function. In FRTL-5 rat thyroid cells, norepinephrine (NE) acutely depresses intracellular I- by increasing I- efflux. The present study was undertaken to determine the effect of NE on iodide transport after a longer time period. NE inhibited the ability of thyrotropin (TSH) to induce iodide uptake by FRTL-5 cells after 48 or 72 hours, but not after 24 hours. The effect of NE was more evident with increasing concentrations of TSH. NE did not modify the rate of I- efflux. Inhibition was associated with a decrease in the Vmax and no change in the Km for iodide influx. To determine if this was a generalized effect of NE on thyroid cell membrane, the uptake of alpha-aminoisobutyric acid (a nonmetabolizable aminoacid) and of 2-deoxyglucose was measured. NE did not inhibit TSH stimulation of the uptake of the two compounds. NE inhibited the action of dibutyryl cAMP (dbcAMP) on iodide uptake in a similar manner to TSH, but did not alter the cyclic adenosine monophosphate (cAMP) levels increased by TSH. The effects of different adrenoreceptor agonists and antagonists demonstrated that norepinephrine acts through an alpha1-adrenergic receptor.

Adrenergic alpha-Agonists↗
PubMed1997

Role of cyclic 3'5' guanosine monophosphate and nitric oxide in the regulation of iodide uptake in calf thyroid cells.

Sodium nitroprusside (SNP) spontaneously produces nitric oxide (NO). In many cell types, this activates the soluble form of the enzyme guanylyl cyclase (GC), resulting in the elevation of cGMP. We herein report the role of NO and cGMP on iodide uptake in primary cultures of calf thyroid cells. Iodide uptake is the limiting step in thyroid hormone biosynthesis and a typical functional parameter. The effect of SNP on this parameter was thus determined. In cells treated with TSH for 72 h, addition of 5 mM SNP for the last 2 h caused a significant inhibition on iodide uptake, with no change in cells not treated with TSH. This action was mimicked by an analogue of cGMP, 8Br-cGMP, and blocked by reduced hemoglobin, thus suggesting that it is mediated by the GC-cGMP pathway. SNP also inhibited the stimulation caused by forskolin or analogues of cAMP, indicating that the effect takes place in this pathway, which would be distal to cAMP generation. The accumulation of radioiodine by thyroid cells is a consequence of the balance between influx and efflux. The studies demonstrate that SNP does not affect iodide efflux, thus revealing that it inhibits the influx.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Studies on the goiter inhibiting action of iodolactones.

The thyroid gland synthesizes 6-delta-iodolactone, a compound shown to inhibit goiter growth in vivo and cell proliferation in culture. The present studies were performed to characterize this effect further with the aim of exploring the possible therapeutic action of iodolactones. Prevention assay: rats were treated simultaneously with a goitrogen, methylmercaptoimidazole, and either 6-delta-iodo-lactone or 14-iodo-omega-lactone, a synthetic derivative, given either i.p. or p. o. Both compounds caused a significant decrease in thyroid weight irrespective of the route of administration, but oral administration was less effective. A dose-response relationship was observed, the minimal effective dose (i.p.) being 3 micrograms/day. Involution assay: goiter was first induced with methylmercaptoimidazole and then the iodolactones were injected. Both compounds caused a significant involution, which was dose-related. Acute (10 days) administration of the iodolactones did not produce significant changes in several serum parameters (total T3 and T4, cholesterol, total protein, urea and acetylcholinesterase). These results give further support to the potential therapeutic application of iodolactones.

Administration, Oral↗
PubMed1992

Effect of iodoarachidonates on thyroid FRTL-5 cells growth.

Excess iodide inhibits several thyroid parameters, by a putative organic iodocompound. Different iodolipids, including iodinated derivatives of arachidonic acid (IAs), are produced by rat, calf and pig thyroid. The action of two iodolactones, one bearing the iodine atom at the position 6 (IL-d) and the other at position 14 (IL-w) on growth of FRTL-5 cells was studied. KI, IL-w and IL-d exert a dose-related inhibition on FRTL-5 cell proliferation. The first two compounds caused inhibition at 1 microM while IL-d was effective at 10 microM. This inhibitory action of iodolactones (ILs) was not altered by 1 mM methyl-mercaptoimidazol (MMI), indicating that they exert their effect per se. The action of ILw on cell growth was reversible. The growth-stimulating effect of 10 microM forskolin was inhibited by IAs, showing that one possible site of action lies at the cAMP pathway. The present results give further support to our hypothesis about the role of IAs in thyroid growth autoregulation.

Animals↗
PubMed1992

Further studies on the antigoitrogenic action of iodoarachidonates.

Previous studies have shown that iodoarachidonates (IAs) prevent goiter production in rats. In the present studies we show that both IL-d and IL-w (IAs bearing the iodine atom at the positions 6 and 14, respectively), cause a significant involution of preformed goiter. This effect was evident when IAs were administered either orally or via i.p., although the first one required larger doses to obtain the same degree of inhibition. No changes were observed in serum protein, urea, cholesterol, cholinesterase, T3 or T4. In vitro studies with FRTL-5 cells showed that both IAs inhibit iodide and alpha-AIB uptake, as well as ATPase activity.

Adenosine Triphosphatases↗