Selenium status parameters in patients with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of reproductive age. To date, no systematic study of interactions between selenium status parameters (SSPs: serum selenium concentration, plasma glutathione peroxidase, GPX3, plasma selenoprotein P, SELENOP), sex hormones, thyroid function parameters, and other laboratory parameters in patients with PCOS has been undertaken. Therefore we aimed to compare such parameters in women with PCOS and in the control groups, and to investigate the multidimensional interactions between various parameters in PCOS patients and in controls. The subjects were diagnosed either with PCOS (n=28, 25.4±5.2 y) or with PCOS+Hashimoto disease (n=13, 27.3±5.6 y). Female patients having normal menses were recruited into the first control group (n=70, 26.8±7.3 y) or to the second control group comprising women only with Hashimoto disease (n=10, 26.2±6.9 y). No apparent differences in SSPs between control subjects and patients with PCOS, also complicated with Hashimoto disease, were identified, though such differences were noticeable for total testosterone (tT), sex hormone binding globulin, free androgen index, dehydroepiandrosterone sulfate (DHEAS), and insulin profile. The correlation between tT and DHEAS was found the strongest. The other group of mutually highly and positively correlated parameters consisted of GPX3, follicle stimulating hormone, free triiodothyronine and free thyroxine. All the latter parameters correlated negatively with vitamin D3. SSPs took part in interactions with thyroid hormones, sex hormones and some other parameters, but only for GPX3 such interactions were statistically significant. The significance of these findings remains open for further investigation, particularly in patients with PCOS and/or Hashimoto disease.

The long-term outcome of uncemented Low Contact Stress total knee replacement in patients with rheumatoid arthritis

We reviewed the long-term clinical and radiological results of 63 uncemented Low Contact Stress (LCS) total knee replacements (TKRs) in 47 patients with rheumatoid arthritis. The mean age of the patients at the time of surgery was 69 years (53 to 81). At a mean follow-up of 22 years (20 to 25), 12 patients were alive (17 TKRs), 27 had died (36 TKRs), and eight (ten TKRs) were lost to follow-up.

Revision was necessary in seven patients (seven TKRs, 11.1%) at a mean of 12.1 years (0 to 19) after surgery. In the surviving ten patients who had not undergone revision (15 TKRs), the mean Oxford knee score was 30.2 (16 to 41) at a mean follow-up of 19.5 years (15 to 24.7) and mean active flexion was 105° (90° to 150°). The survival rate was 88.9% at 20 years (56 of 63) and the Kaplan–Meier survival estimate, without revision, was 80.2% (95% confidence interval 37 to 100) at 25 years.

Cite this article: Bone Joint J 2013;95-B:1497–9.

Expression of selenium-containing proteins in human colon carcinoma tissue

Selenium may be beneficial in reducing the risk of cancer incidence and mortality in many cancer types such as liver, prostate, colorectal and lung. However, despite the extensive recent research on selenium and selenium-containing proteins, there are still open questions concerning their expression in certain human cancer types, including colorectal carcinoma. Therefore, the expression level of the selenoproteins thioredoxin reductases 1 and 2 (TRXR-1 and TRXR-2) and glutathione peroxidases 1 and 4 (GPX1 and GPX4) in human colon carcinoma tissues was investigated. Up-regulation of TRXR-1 in the colon carcinoma specimens was found both in disease stage-dependent and independent analyses. No differences were found for TRXR-2 expression levels. GPX1 was up-regulated in carcinoma tissues at both the protein and mRNA levels. GPX4 was also up-regulated at the protein level, except for the samples derived from stage III patients. The expression of TRXR-1, GPX1 and GPX4, but not TRXR-2 is differently regulated in cancer as compared to healthy colonic tissue.

Differential regulation of expression of cytosolic and mitochondrial thioredoxin reductase in rat liver and kidney

Adequate supply of selenium (Se) is critical for synthesis of selenoproteins through selenocysteine insertion mechanism. To explore this process we investigated the expression of the cytosolic and mitochondrial isoenzymes of thioredoxin reductase (TrxR1 and TrxR2) in response to altered Se supply. Rats were fed diets containing different quantities of selenium and the levels of TrxR1 and TrxR2 protein and their corresponding mRNAs were determined in liver and kidney. Expression of the two isoenzymes was differentially affected, with TrxR1 being more sensitive to Se depletion than TrxR2 and greater changes in liver than kidney. In order to determine if the selenocysteine incorporation sequence (SECIS) element was critical in this response liver and kidney cell lines (H4 and NRK-52E) were transfected with reporter constructs in which expression of luciferase required read-through at a UGA codon and which contained either the TrxR1 or TrxR2 3'UTR, or a combination of the TrxR1 5' and 3'UTRs. Cell lines expressing constructs with the TrxR1 3'UTR demonstrated no response to restricted Se supply. In comparison the Se-deficient cells expressing constructs with the TrxR2 3'UTR showed considerably less luciferase activity than the Se-adequate cells. No disparity of response to Se supply was observed in the constructs containing the different TrxR1 5'UTR variants. The data show that there is a prioritisation of TrxR2 over TrxR1 during Se deficiency such that TrxR1 expression is more sensitive to Se supply than TrxR2 but this sensitivity of TrxR1 was not fully accounted for by TrxR1 5' or 3'UTR sequences when assessed using luciferase reporter constructs.

Long-term results of the uncemented Low Contact Stress total knee replacement in patients with rheumatoid arthritis

We analysed the long-term clinical and radiological results of 63 uncemented Low Contact Stress total knee replacements in 47 patients with rheumatoid arthritis. At a mean follow-up of 12.9 years (10 to 16), 36 patients (49 knees) were still alive; three patients (five knees) were lost to follow-up. Revision was necessary in three knees (4.8%) and the rate of infection was 3.2%. The mean clinical and functional Knee Society scores were 90 (30 to 98) and 59 (25 to 90), respectively, at final follow-up and the mean active range of movement was 104° (55° to 120°). The survival rate was 94% at 16 years but 85.5% of patients lost to follow-up were considered as failures. Radiological evidence of impending failure was noted in one knee.

Selenoprotein expression in endothelial cells from different human vasculature and species

Selenium (Se) can protect endothelial cells (EC) from oxidative damage by altering the expression of selenoproteins with antioxidant function such as cytoplasmic glutathione peroxidase (cyGPX), phospholipid hydroperoxide glutathione peroxidase (PHGPX) and thioredoxin reductase (TR). If the role of Se on EC function is to be studied, it is essential that a model system be chosen which reflects selenoprotein expression in human EC derived from vessels prone to developing atheroma. We have used [75Se]-selenite labelling and selenoenzyme measurements to compare the selenoproteins expressed by cultures of EC isolated from different human vasculature with EC bovine and porcine aorta. Only small differences were observed in selenoprotein expression and activity in EC originating from human coronary artery, human umbilical vein (HUVEC), human umbilical artery and the human EC line EAhy926. The selenoprotein profile in HUVEC was consistent over eight passages and HUVEC isolated from four cords also showed little variability. In contrast, EC isolated from pig and bovine aorta showed marked differences in selenoprotein expression when compared to human cells. This study firmly establishes the suitability and consistency of using HUVEC (and possibly the human cell line EAhy926) as a model to study the effects of Se on EC function in relation to atheroma development in the coronary artery. Bovine or porcine EC appear to be an inappropriate model.

Poly-L-glutamate, an anionic polymer, enhances transgene expression for plasmids delivered by intramuscular injection with in vivo electroporation

Intramuscular (i.m.) injection of plasmids followed by electropermeabilization is an efficient process to deliver genes into skeletal myofibers that permits proteins to be produced and secreted at therapeutically relevant levels. To further improve skeletal muscle as a bioreactor, we identified a formulation that elevates transgene expression in myofibers after i.m. injection and electroporation. With secreted placental alkaline phosphate (SEAP) as reporter gene, plasmid formulated with poly-L-glutamate produced two- to eight-fold higher levels of SEAP in mouse serum than plasmid in saline. Various concentrations and molecular weights of poly-L-glutamate were similarly effective, but 6 mg/ml of 15-50 kDa poly-L-glutamate consistently yielded the highest expression levels. The poly-L-glutamate formulation was effective in two different muscle groups in mice at various plasmid doses for several transgenes, including an erythropoietin (EPO) gene, for which expression was elevated four- to 12-fold in comparison to animals that received EPO plasmid in saline. Transgene expression was localized to myofibers. Poly-L-glutamate may improve transgene expression in part by increasing plasmid retention in skeletal muscle. Poly-L-glutamate did not enhance gene transfer in the absence of electroporation. Therefore, the polymer is a novel formulation that specifically enhances the transfer and expression of genes delivered with electroporation.

Thioredoxin reductase and cytoplasmic glutathione peroxidase activity in human foetal and neonatal liver

Cytosolic thioredoxin reductase (TR) is an FAD-containing homodimeric selenoenzyme which, together with thioredoxin (Trx) and NADPH, forms a powerful oxidoreductase system. Cytoplasmic glutathione peroxidase (GPX-1) is a selenoprotein with antioxidant activity. The TR/Trx system has been associated with cellular processes including regulation of cell growth, and modification of activity of transcription factors. TR may also act as an antioxidant. We have measured TR activity, TR concentration, and GPX-1 activity in human hepatic cytosols from foetuses and neonates. The concentration of TR was significantly greater (P<0.05) in foetal (43.6, 37.9-50.8 microg/g protein, median, interquartile range) than in neonatal liver (11.6, 8.70-15.0 microg/g). This was also true of TR activity which was 2.1, 1.8-2.5 U/g protein in foetal, and 0.65, 0.44-0.74 U/g protein in neonatal liver (P<0.0005). Similarly, GPX-1 activity was significantly higher (P<0.005) in the foetal (199.7, 144.0-227.9 U/g protein) than in neonatal (77.0, 58.4-110.3 U/g protein) hepatic cytosol. Overall, foetal liver expressed approx. 3-fold higher activities of TR and GPX-1 than neonatal liver.

Selenium status of cats in four regions of the world and comparison with reported incidence of hyperthyroidism in cats in those regions

OBJECTIVE

To assess selenium (Se) status of cats in 4 regions of the world and to compare results for Se status with reported incidence of hyperthyroidism in cats in those regions.

ANIMALS

50 cats (30 from 2 regions with an allegedly high incidence of hyperthyroidism and 20 from 2 regions in which the disease is less commonly reported).

PROCEDURE

Hematologic samples (heparinized whole blood, plasma, and RBC fractions) were obtained from 43 healthy euthyroid cats and 7 hyperthyroid cats. Plasma concentration of Se and activity of glutathione peroxidase (GPX) in whole blood and plasma were determined.

RESULTS

Plasma concentration of Se and GPX activity in whole blood or plasma did not differ significantly among cats from the 4 regions. However, cats had a plasma concentration of Se that was approximately 5 times the concentration reported in rats and humans. The GPX activity in whole blood or plasma in cats generally was higher than values reported in rats or humans.

CONCLUSIONS AND CLINICAL RELEVANCE

Cats have higher Se concentrations in plasma, compared with values for other species. However, Se status alone does not appear to affect the incidence of hyperthyroidism in cats. High Se concentrations may have implications for health of cats if such concentrations are influenced by the amount of that micronutrient included in diets.

Selenite protects human endothelial cells from oxidative damage and induces thioredoxin reductase

The ability of selenium to protect cultured human coronary artery endothelial cells (HCAEC), human umbilical vein endothelial cells (HUVEC) and bovine aortic endothelial cells (BAEC) from oxidative damage induced by 100 microM t-butyl hydroperoxide (t-BuOOH) was compared. Preincubation of human endothelial cells for 24 h with sodium selenite at concentrations as low as 5 nM provided significant protection against the harmful effects of 100 microM t-BuOOH, with complete protection being achieved with 40 nM selenite. The preincubation period was required for selenite to exert this protective effect on endothelial cells. When compared with selenium-deficient cells, the activities of cytoplasmic glutathione peroxidase (GPX-1), phospholipid hydroperoxide glutathione peroxidase (GPX-4) and thioredoxin reductase (TR) were each induced approx. 3--4-fold by 40 nM selenite. HCAEC and HUVEC showed great similarity in their relative abilities to resist oxidative damage in the presence and absence of selenite, and the activities of TR and the GPXs were also similar in these cell types. BAEC were more susceptible to damage by 100 microM t-BuOOH than were human endothelial cells, and could not be protected completely by incubation with selenite at concentrations up to 160 nM. The activity of TR in human endothelial cells was approx. 25-fold greater than that in BAEC of a similar selenium status, but GPX-1 and GPX-4 activities were not significantly different between the human and bovine cells. These studies, although performed with a small number of cultures, show for the first time that selenium at low doses can provide significant protection of the human coronary artery endothelium against damage by oxidative stress. TR may be an important antioxidant selenoprotein in this regard, in addition to the GPXs. The data also suggest that HUVEC, but not BAEC, represent a suitable model system in which to study the effects of selenium on the endothelium of human coronary arteries.

Gene therapy for the treatment of hemophilia B using PINC-formulated plasmid delivered to muscle with electroporation

Gene therapy, as a safe and efficacious treatment or prevention of diseases, is one of the next fundamental medical innovations. Direct injection of plasmid into skeletal muscle is still a relatively inefficient and highly variable method of gene transfer. However, published reports have shown that application of an electric field to the muscle immediately after plasmid injection increases gene expression at least 2 orders of magnitude. Using this methodology, we have achieved potentially therapeutic circulating levels of human factor IX (hF.IX) in mice and dogs. A plasmid encoding hF.IX formulated with a protective, interactive, noncondensing (PINC) polymer was injected into the skeletal muscle followed by administration of multiple electrical pulses (electroporation). In mice long-term expression was achieved and the ability to readminister formulated plasmid was demonstrated. In normal dogs, expression of hF.IX reached 0.5-1.0% of normal levels. The transient response in dogs was due to the development of antibodies against hF.IX. Elevated circulating creatine kinase levels and histological examination indicated transient minor trauma associated with the procedure. These data show that gene delivery using a plasmid formulated with a PINC polymer augmented with electroporation is scalable into large animal models and represents a promising approach for treating patients with hemophilia B.

Muscle-specific enhancement of gene expression by incorporation of SV40 enhancer in the expression plasmid

Skeletal muscle is established as an ideal tissue for gene delivery to treat systemic diseases. However, the relatively low levels of gene expression obtained from using naturally occurring promoters, including the strong cytomegalovirus (CMV) enhancer/promoter (E/P), have limited the use of muscle as a target tissue. The relatively weak simian virus 40 (SV40) enhancer is known to have dual functions promoting localization of DNA to the nucleus and activating transcription. An SV40 enhancer incorporated either at the 5' end of CMV E/P or the 3' end of the polyadenylation site gave as much as a 20-fold increase in the level of exogenous gene expression in muscle in vivo, compared with expression observed with CMV E/P alone. The minimum requirement for this enhancement is a single copy of a 72-bp element of the SV40 enhancer, in combination with either the CMV E/P or skeletal actin (SkA) promoter. Enhancement of gene expression in muscle by this SV40 enhancer was also observed by using the powerful electroporation delivery. However, the SV40 enhancer does not increase the level of CMV E/P driven reporter gene expression in dividing tumor cells in vivo and in the dividing myoblast cell C2C12 in vitro. The data suggest that including this enhancer in the plasmid will enhance the level of gene production for muscle-based gene therapy.

Altered pectin composition in primary cell walls of korrigan, a dwarf mutant of Arabidopsis deficient in a membrane-bound endo-1,4-beta-glucanase

Korrigan (kor) is a dwarf mutant of Arabidopsis thaliana (L.) Heynh. that is deficient in a membrane-bound endo-1,4-beta-glucanase. The effect of the mutation on the pectin network has been studied in kor by microscopical techniques associated with various probes specific for different classes of pectic polysaccharides. The localisation of native crystalline cellulose was also examined using the cellobiohydrolase I-gold probe. The investigations were focused on the external cell walls of the epidermis, a cell layer that, in a number of plant species, has been shown to be growth limiting. Anionic sites associated with pectic polymers were quantified using the cationic gold probe. Homogalacturonans were quantified using polyclonal anti-polygalacturonic acid/rhamnogalacturonan I antibodies recognising polygalacturonic acid, and monoclonal JIM7 and JIM5 antibodies recognising homogalacturonans with a high or low degree of methyl-esterification, respectively. Rhamnogalacturonans were quantified with two monoclonal antibodies, LM5, recognising beta-1,4 galactan side chains of rhamnogalacturonan I, and CCRCM2. Our results show a marked increase in homogalacturonan epitopes and a decrease in rhamnogalacturonan epitopes in kor compared to the wild type. A substantial decrease in cellobiohydrolase I-gold labelling was also observed in the mutant cell walls. These findings demonstrate that a deficiency in an endo-1,4-beta-glucanase, which is in principle not directly implicated in pectin metabolism, can induce important changes in pectin composition in the primary cell wall. The changes indicate the existence of feedback mechanisms controlling the synthesis and/or deposition of pectic polysaccharides in primary cell walls.

Selenoproteins in human thyroid tissues

The aim of the present work was to clarify whether the activities of selenoenzymes can serve as markers for different tumors or goiters, as classified by histological criteria. The following parameters were determined: 1) selenium content of plasma (Se), 2) activities of the selenoenzymes: plasma glutathione peroxidase (plGSHPx), cytosolic glutathione peroxidase (cGSHPx), type I and type II iodothyronine deiodinases (ID-I, ID-II), thioredoxin reductase (THRR) in human thyroid tissues. The material came from follicular neoplasm, papillary carcinoma, struma nodosa, struma lymphomatosis Hashimoto, other thyroid surgery specimens, and normal tissues. There was no difference in Se nor in plGSHPx between patients and healthy volunteers. No significant differences were found for any parameter in thyroid carcinoma versus normal or goitrous thyroid tissue. In the whole group of thyroid surgery specimens the statistically significant correlations were found between ID-I and ID-II and between THRR and selenoperoxidases. Principal components analysis confirmed the above correlation and moreover revealed correlation between Se and plGSHPx, but did not detect any clear distinction between patients with the different diagnoses.

Effects of organic and inorganic selenium supplementation on selenoenzyme activity in blood lymphocytes, granulocytes, platelets and erythrocytes

The blood selenium (Se) concentration in the U.K. population has declined by approx. 50% between 1974 and 1991, reflecting a large decrease in dietary Se supply, with intakes only half the reference nutrient intake of 1 microg/kg body weight. Tissue levels of Se are readily influenced by dietary intake. Therefore selenoprotein activity may be sub-optimal due to low Se status, and thus compromise normal cell function. To examine the effects of changing Se intake on selenoproteins, we have determined the relative effectiveness of organic selenomethionine and inorganic sodium selenite (50 microg of Se daily for 28 days) in modulating glutathione peroxidase activities in blood cells from 45 healthy men and women, from a U.K. population. Transient and acute changes in lymphocyte, granulocyte and platelet phospholipid-hydroperoxide glutathione peroxidase (GPx4) activity occurred by day 7 or 14 of sodium selenite treatment and by day 7 in lymphocytes from selenomethionine-treated subjects compared with controls taking a placebo. In contrast, GPx4 activity in granulocytes and platelets in the selenomethionine group increased gradually over the 28 days. Cytosolic glutathione peroxidase (GPx1) activity in these blood cells from both treatment groups increased gradually over the 28 days. For each cellular selenoenzyme activity a significant inter-individual difference (P<0.001) in the extent of the response to Se supplementation was observed, but this was not related to blood Se concentrations either before or after treatments. Significant inverse correlations were evident between baseline enzyme activities and percentage change in activity after 28 days of supplementation [e.g. lymphocyte GPx4, r=-0.695 (P<0.001)], indicating that pre-treatment activity may be sub-optimal as a result of poor Se status. The different and contrasting effects that Se supplementation had on blood selenoenzyme activities may be indicative of a difference in metabolic need for Se regulated at the level of Se-dependent cell function.

Type II and type III monodeiodinase activities in the skin of untreated and propylthiouracil-treated cashmere goats

The presence or absence of types I, II and III iodothyronine monodeiodinase enzymes (MDI, MDII and MDIII) and their levels of activity in the skin of goats, which were orally dosed for 60 days with 0, 1.1, 2.2, 4.4, 8.8, 17.5, or 35 mg(-1)kg liveweight day(-1)of the anti-thyroid, enzyme-inhibiting drug, propylthiouracil (PTU), were determined. Contrary to our earlier report that PTU did not influence skin MDII activity, the currect more thorough investigation (in terms of numbers of observations and the efficiency of the enzyme extraction procedure) indicated that doses of 1.1.to 17.5 mg kg(-1)liveweight induced a 2 to 3 fold increase (P = 0.01) in MDII activity. However, in three of the four goats treated with 35 mg kg(-1)group, activity was similar to that of control animals. There were no significant differences between treatments in MDIII activity but there was a trend towards lower levels of activity in the goats dosed with 17.5 and 35 mg kg(-1). It is concluded that there is significant MDII and MDIII activity in the skin of goats and that although there is none of the PTU -sensitive MDI enzyme, synthesis of T3 within the skin could nevertheless be modified through increases in MDII activity induced by lower T4 concentrations in the circulation caused by PTU. Changes in pattern of fibre moult induced by treatment with low doses of MD-inhibiting drugs may therefore be achieved through this effect. Since MDII and MDIII enzyme activity may be reduced by high doses of PTU, prolonged treatment with high doses of PTU may have adverse effects on skin tissue.

Effect of phospholipid composition on an amphipathic peptide-mediated pore formation in bilayer vesicles

To better understand the influence of phospholipid acyl-chain composition on the formation of pores by cytotoxic amphipathic helices in biological membranes, the leakage of aqueous contents induced by the synthetic peptide GALA (WEAALAEALAE ALAEHLAEALAEALEALAA) from large unilamellar phospholipid vesicles of various compositions has been studied. Peptide-mediated leakage was examined at pH 5.0 from vesicles made of phosphatidylcholine (PC) and phosphatidylglycerol (PG) with the following acyl-chain compositions: 1-palmitoyl-2-oleoyl (PO), 1,2-dioleoyl (DO), 1, 2-dielaidoyl (DE), and 1,2-dipetroselinoyl (DPe). A mathematical model predicts and simulates the final extents of GALA-mediated leakage of 1-aminonaphthalene-3,6,8-trisulfonic acid (ANTS) and p-xylene-bis-pyridinium bromide (DPX) from 1-palmitoyl-2-oleoyl-phosphatidylcholine/1-palmitoyl-2-oleoyl-phospha tidylglycerol (POPC/POPG) and 1, 2-dielaidoyl-sn-glycero-3-phosphocholine/1, 2-dielaidoyl-phosphatidylglycerol (DEPC/DEPG) liposomes at pH 5.0 as a function of peptide concentration in the bilayer, by considering that GALA pores responsible for this leakage have a minimum size of 10 +/- 2 monomers and are formed by quasiirreversible aggregation of the peptide. With the phospholipid acyl-chain compositions tested, GALA-induced ANTS/DPX leakage follows the rank order POPC/POPG approximately DEPC/DEPG > DPePC/DPePG > DOPC/DOPG. Results from binding experiments reveal that this reduced leakage from DOPC/DOPG vesicles cannot be explained by a reduced binding affinity of the peptide to these membranes. As shown by monitoring the leakage of a fluorescent dextran, an increase in the minimum pore size also does not explain the reduction in ANTS/DPX leakage. The data suggest that surface-associated GALA monomers or aggregates are stabilized in bilayers composed of phospholipids containing a cis unsaturation per acyl chain (DO and DPe), while transbilayer peptide insertion is reduced. GALA-induced ANTS/DPX leakage is also decreased when the vesicles contain phosphatidylethanolamine (PE). This lends further support to the suggestion that factors stabilizing the surface state of the peptide reduce its insertion and subsequent pore formation in the bilayer.

Thioredoxin reductase is the major selenoprotein expressed in human umbilical-vein endothelial cells and is regulated by protein kinase C

Damage to the endothelium by reactive oxygen species favours atherogenesis. Such damage can be prevented by selenium, which is thought to exert its actions through the expression of selenoproteins. The family of glutathione peroxidases (GPXs) may have antioxidant roles in the endothelium but other intracellular and extracellular selenoproteins with antioxidant actions may also be important. The selenoproteins expressed by cultured human umbilical-vein endothelial cells (HUVECs) were labelled with [(75)Se]selenite and separated using SDS/PAGE. HUVECs secreted no extracellular selenoproteins. There were distinct differences between the intracellular selenoprotein profile of (75)Se-labelled HUVECs and those of other tissues. A single selenoprotein with a molecular mass of 58 kDa accounted for approx. 43% of the intracellular (75)Se-labelled proteins in HUVECs. This protein was identified by Western blotting as the redox-active lipid-hydroperoxide-detoxifying selenoprotein, thioredoxin reductase (TR). TR expression in HUVECs was down-regulated by transiently exposing cells to the phorbol ester PMA for periods as short as 1 min. However, there was a delay of 48 h after PMA exposure before maximal down-regulation of TR was observed. The protein kinase C (PKC) inhibitor bisindolylmaleimide I hydrochloride had no effect on TR expression when added alone, but the agent prevented the down-regulation of TR expression seen with PMA. The calcium ionophore A23187 increased TR expression in HUVECs after a 12-h exposure, but the maximal effect was only observed after a 35-h exposure. These findings suggest that TR may be an important factor in the known ability of Se to protect HUVECs from peroxidative damage. Furthermore, the results also suggest that TR expression can be negatively regulated through PKC. It is possible that TR expression may be positively regulated by the calcium-signalling cascade, although TR induction by A23187 may be due to toxicity.

Does formal approval of educational courses guarantee quality?

OBJECTIVES

To assess whether organizers of continuing medical education for general practitioners used principles of adult learning when designing their meetings.

DESIGN

A questionnaire study of organizers of approved educational meetings for general medical practitioners (GPs).

SETTING

South East Scotland.

SUBJECTS

Organizers of educational meetings.

RESULTS

Organizers often failed to use principles of adult learning in the construction of their meetings. Organizers with prior training in medical education were, however, significantly more likely to adopt these principles.

CONCLUSIONS

Given concern about the quality of educational meetings as assessed by their educational impact, formal approval is not an indicator of quality. Postgraduate bodies should use explicit criteria both in the development and approval of continuing educational meetings.

Orientation of the pore-forming peptide GALA in POPC vesicles determined by a BODIPY-avidin/biotin binding assay

We determined the orientation of a biotinylated version of the pore-forming peptide GALA (WEAALAEALAEALAEHLAEALAEALEALAA) at pH 5.0 in large unilamellar phosphatidylcholine vesicles, using the enhancement of BODIPY-avidin fluorescence subsequent to its irreversible binding to a biotin moiety. GALA and its variants were biotinylated at the N- or C-terminus. BODIPY-avidin was either added externally or was pre-encapsulated in vesicles to assess the fraction of liposome-bound biotinylated GALA that exposed its labeled terminus to the external or internal side of the bilayer, respectively. Under conditions where most of the membrane-bound peptides were involved in transmembrane aggregates and formed aqueous pores (at a lipid/bound peptide molar ratio of 2500/1), the head-to-tail (N- to C-terminus) orientation of the membrane-inserted peptides was such that 3/4 of the peptides exposed their N-terminus on the inside of the vesicle and their C-terminus on the outside. Under conditions resulting in reduced pore formation (at higher lipid/peptide molar ratios), we observed an increase in the fraction of GALA termini exposed to the outside of the vesicle. These results are consistent with a model (Parente et al., Biochemistry, 29:8720, 1990) that requires a critical number of peptides (M) in an aggregate to form a transbilayer structure. When the peptides form an aggregate of size i, with i < M = 4 to 6, the orientation of the peptides is mostly parallel to the membrane surface, such that both termini of the biotinylated peptide are exposed to external BODIPY-avidin. This BODIPY-avidin/biotin binding assay should be useful to determine the orientation of other membrane-interacting molecules.

Surface aggregation and membrane penetration by peptides: relation to pore formation and fusion

The peptide GALA undergoes a conformational change to an amphipathic alpha-helix when the pH is reduced, inducing leakage of contents from vesicles. Leakage from neutral or negatively-charged vesicles at pH 5.0 was similar and could be adequately explained by a mathematical model which assumed that GALA becomes incorporated into the vesicle bilayer and irreversibly aggregates to form a pore consisting of M = 10 +/- 2 peptides. Increasing cholesterol content in the membranes resulted in reduced leakage, and increased reversibility of surface aggregation of the peptide. Employing fluorescently labelled peptides confirmed that the degree of reversibility of surface aggregation of GALA was significantly larger in cholesterol containing liposomes. Orientation of the peptide GALA in bilayers was determined by a bodipy-avidin/biotin binding assay. The peptide was labelled by biotin at the N- or C-terminus and bodipy-avidin molecules were added externally or were preencapsulated in the vesicles. The peptides are arranged in the pore perpendicularly to the membrane, such that 3/4 of the N-termini are on the internal side of the membrane. The pores are stable and persist for at least 10 min. When the peptides form an aggregate of size smaller than M, the orientation of the peptide is mostly parallel to the surface and the biotinylated peptide does not translocate. When a critical size of the aggregate is attained, a rearrangement of the peptide occurs, which amounts to rapid penetration and formation of a pore structure. Induction of fusion by peptides may be antagonistic to pore formation, the outcome being dependent on vesicle aggregation.

A plasma membrane-bound putative endo-1,4-beta-D-glucanase is required for normal wall assembly and cell elongation in Arabidopsis

Endo-1,4-beta-D-glucanases (EGases) form a large family of hydrolytic enzymes in prokaryotes and eukaryotes. In higher plants, potential substrates in vivo are xyloglucan and non-crystalline cellulose in the cell wall. Gene expression patterns suggest a role for EGases in various developmental processes such as leaf abscission, fruit ripening and cell expansion. Using Arabidopsis thaliana genetics, we demonstrate the requirement of a specialized member of the EGase family for the correct assembly of the walls of elongating cells. KORRIGAN (KOR) is identified by an extreme dwarf mutant with pronounced architectural alterations in the primary cell wall. The KOR gene was isolated and encodes a membrane-anchored member of the EGase family, which is highly conserved between mono- and dicotyledonous plants. KOR is located primarily in the plasma membrane and presumably acts at the plasma membrane-cell wall interface. KOR mRNA was found in all organs examined, and in the developing dark-grown hypocotyl, mRNA levels were correlated with rapid cell elongation. Among plant growth factors involved in the control of hypocotyl elongation (auxin, gibberellins and ethylene) none significantly influenced KOR-mRNA levels. However, reduced KOR-mRNA levels were observed in det2, a mutant deficient for brassinosteroids. Although the in vivo substrate remains to be determined, the mutant phenotype is consistent with a central role for KOR in the assembly of the cellulose-hemicellulose network in the expanding cell wall.

Identification of a 57-kilodalton selenoprotein in human thyrocytes as thioredoxin reductase and evidence that its expression is regulated through the calcium-phosphoinositol signaling pathway

Human thyrocytes incubated with the phorbol ester, phorbol 12-myristate 13-acetate (PMA; 10(-5)-10(-8) mol/L) and the calcium ionophore A23187 (10(-5)-10(-8) mol/L) showed a marked increase in the expression of a 57-kDa selenoprotein identified as thioredoxin reductase (TR). After the addition of A23187 with PMA, a significant induction in TR expression was observed after 6 h, with maximal induction occurring by 24 h. The addition of 8-bromo-cAMP (10(-4) mol/L) or TSH (10 U/L) alone had no effect on TR expression, nor did these agents influence the induction of TR brought about by the addition of A23187 and PMA. These data show that the calcium-phosphoinositol second messenger cascade that controls hydrogen peroxide generation in the human thyrocyte is also an important stimulator of TR expression. The role of TR in the thyrocyte is unclear, but the selenoenzyme has a high capacity to detoxify compounds, such as hydrogen peroxide and lipid hydroperoxides, that are produced in high concentration during thyroid hormone synthesis.

Differential expression of selenoproteins by human skin cells and protection by selenium from UVB-radiation-induced cell death

The generation of reactive oxygen species has been implicated as part of the mechanism responsible for UVB-radiation-induced skin damage. In mice, evidence suggests that increased dietary selenium intake may protect skin from many of the harmful effects of UVB radiation. We sought to determine the selenoprotein profile of cultured human skin cells and whether selenium supplementation could protect keratinocytes and melanocytes from the lethal effects of UVB radiation. Labelling experiments using [75Se]selenite showed qualitative and quantitative differences in selenoprotein expression by human fibroblasts, keratinocytes and melanocytes. This was most noticeable for thioredoxin reductase (60 kDa) and phospholipid glutathione peroxidase (21 kDa); these proteins were identified by Western blotting. Despite these differences, we found that a 24 h preincubation with sodium selenite or selenomethionine protected both cultured human keratinocytes and melanocytes from UVB-induced cell death. With primary keratinocytes, the greatest reduction in cell death was found with 10 nM sodium selenite (79% cell death reduced to 21.7%; P<0.01) and with 50 nM selenomethionine (79% cell death reduced to 13.2%; P<0.01). Protection could be obtained with concentrations as low as 1 nM with sodium selenite and 10 nM with selenomethionine. When selenium was added after UVB radiation, little protection could be achieved, with cell death only being reduced from 88.5% to about 50% with both compounds. In all of the experiments sodium selenite was more potent than selenomethionine at providing protection from UVB radiation.

Iodine deficiency in cattle: compensatory changes in thyroidal selenoenzymes

The trace elements selenium and iodine are both essential for normal thyroid hormone metabolism. To investigate the relationships between these functions, heifers were maintained on iodine-deficient or iodine-sufficient diets from mid pregnancy to term. In these heifers and their offspring the interrelationship between iodine and selenium was apparent with the preferential 10- to 12-fold induction of the selenoenzyme, thyroidal type I, selenium-containing iodothyronine deiodinase activity by iodine deficiency. This was accompanied by two- to four-fold increases in cytosolic glutathione peroxidase activity, probably reflecting increased oxidative activity and metabolism in the thyroid gland in response to iodine deficiency. The above selenoenzyme activities were not affected in liver, kidney, pituitary and brain by iodine deficiency. The results are consistent with a critical role for selenium in both the normal function of cattle thyroid and key enzymes to compensate for the effects of iodine deficiency.

Selenoprotein expression and brain development in preweanling selenium- and iodine-deficient rats

Selenium deficiency causes further impairment of thyroid hormone metabolism in iodine-deficient rats and therefore could have a role in the aetiology of both myxoedematous and neurological cretinism in humans. Thyroidal type I iodothyronine deiodinase (ID-I), cytosolic glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase activities were increased in iodine-deficient adult rats and their offspring at 11 days of age. Thyroidal ID-I activity was unchanged and thyroidal cytosolic glutathione peroxidase activity was decreased by more than 75% by combined selenium and iodine deficiency in 11-day-old rats, indicating that, while the thyroid retained an ability to produce 3,3',5-triiodothyronine (T3), the gland was probably more susceptible to peroxidative damage caused by increased hydrogen peroxide concentrations driven by increased thyrotrophin. Thyroidal atrophy, common in myxoedematous cretinism, did not occur in iodine- or selenium and iodine-deficient rat pups. Iodine deficiency increased brain type II iodothyronine deiodinase activity 1.5-fold in 4-day-old rats and 3-fold in 11-day-old rats, regardless of selenium status. Thus rats were able to activate compensatory mechanisms in brain that would maintain T3 concentrations in selenium and iodine deficiencies. Surprisingly, however, selenium deficiency had a greater effect than iodine deficiency on markers of brain development in rat pups. Expression of the brain-derived neurotrophic factor (BDNF) mRNA was decreased in selenium deficiency in 4- and 11-day-old pups and in combined selenium and iodine deficiency in 4-day-old pups. Iodine deficiency caused an increase in BDNF expression in 11-day-old pups but had no effect on 4-day-old pups. Myelin basic protein mRNA expression in brain was decreased by combined selenium and iodine deficiency in 11-day-old rats.

Plant cell expansion: scaling the wall

The regulation of plant cell size and shape is poorly understood at the molecular level. Recently, two loci required for normal cell expansion in Arabidopsis were cloned. They both encode enzymes involved in the construction of the cell wall. These studies are the first promising examples of the use of Arabidopsis molecular genetics for the study of wall synthesis and assembly during plant cell elongation.

Selenium and iodine deficiencies: effects on brain and brown adipose tissue selenoenzyme activity and expression

Adequate dietary iodine supplies and thyroid hormones are needed for the development of the central nervous system (CNS) and brown adipose tissue (BAT) function. Decreases in plasma thyroxine (T4) concentrations may increase the requirement for the selenoenzymes types I and II iodothyronine deiodinase (ID-I and ID-II) in the brain and ID-II in BAT to protect against any fall in intracellular 3,3',5 tri-iodothyronine (T3) concentrations in these organs. We have therefore investigated selenoenzyme activity and expression and some developmental markers in brain and BAT of second generation selenium- and iodine-deficient rats. Despite substantial alterations in plasma thyroid hormone concentrations and thyroidal and hepatic selenoprotein expression in selenium and iodine deficiencies, ID-I, cytosolic glutathione peroxidase (cGSHPx) and phospholipid hydroperoxide glutathione peroxidase (phGSHPx) activities and expression remained relatively constant in most brain regions studied. Additionally, brain and pituitary ID-II activities were increased in iodine deficiency regardless of selenium status. This can help maintain tissue T3 concentrations in hypothyroidism. Consistent with this, no significant effects of iodine or selenium deficiency on the development of the brain were observed, as assessed by the activities of marker enzymes. In contrast, BAT from selenium- and iodine deficient rats had impaired thyroid hormone metabolism and less uncoupling protein than in tissue from selenium- and iodine-supplemented animals. Thus, the effects of selenium and iodine deficiency on the brain are limited due to the activation of the compensatory mechanisms but these mechanisms are less effective in BAT.

Selenium and iodine deficiencies and selenoprotein function

This paper reviews some recent findings on the interactions between selenium deficiency and iodine deficiency. Both micronutrients can control the levels of selenoprotein mRNAs, particularly in the thyroid and brain. When selenium and iodine supplies are limiting the compensatory mechanisms work to minimise adverse effects on thyroid hormone metabolism and thus neurological development. The mechanisms for regulation of selenoproteins in selenium and iodine deficiency are however very tissue-specific. For example, unlike the brain and thyroid, brown adipose tissue is unable to retain selenoproteins in selenium and iodine deficiency and is therefore at greater risk from injurious effects of the deficiencies.

A technique for recording and analysis of postural changes associated with thermal comfort

The recording of posture has a long history in the study of ergonomics, but has generally been concerned with the assessment of mechanical strain on the human body. This paper extends the concern to the thermal implications of posture. A change in posture can change the effective body surface area available for heat exchange with the environment and therefore the metabolic rate per unit body surface area. This effect is systematised into a method of postural coding which reflects the extent of changes in effective body surface area available for heat exchange. The paper reports a brief assessment of the extent of the effect of posture in normal office work and the extent to which posture is temperature-related.

Selenium status of a group of Scottish adults

OBJECTIVE

To examine dietary selenium intake and indices of selenium status (plasma and red blood cell selenium and glutathione peroxidase activities) in apparently healthy Scottish individuals.

DESIGN AND SUBJECTS

One hundred subjects, aged between 40 and 60 y, completed a seven day weighed food intake and provided blood samples for selenium status analysis.

SETTING

Inverurie, Aberdeenshire, Scotland.

RESULTS

Average reported selenium intake was low (43 micrograms/d). A significant number of subjects had reported intakes below the RNI. Low levels of plasma selenium were also found but no subject had values below 40 micrograms/1. Red blood cell selenium was within the reference range established for a healthy UK population. Smoking status had no consistent effect on selenium status.

CONCLUSIONS

The results of the present study suggest that selenium status of certain Scottish individuals may be compromised and that further studies are warranted.

SPONSORSHIP

BASF, Germany; The Tobacco Products Research Trust, UK; Scottish Office Agriculture Environment and Fisheries Department.

Design, synthesis, and characterization of a cationic peptide that binds to nucleic acids and permeabilizes bilayers

We have designed a cationic amphipathic peptide, KALA (WEAKLAKALAKALAKHLAKALAKALKACEA), that binds to DNA, destabilizes membranes, and mediates DNA transfection. KALA undergoes a pH-dependent random coil to amphipathic alpha-helical conformational change as the pH is increased from 5.0 to 7.5. One face displays hydrophobic leucine residues, and the opposite face displays hydrophilic lysine residues. KALA-mediated release of entrapped aqueous contents from neutral and negatively charged liposomes increases with increasing helical content. KALA binds to oligonucleotides or plasmid DNA and retards their migration in gel electrophoresis. It displaces 50% of ethidium bromide from DNA at a charge ratio (+/-) of 0.9/1. In cultured cells, KALA assists oligonucleotide nuclear delivery when complexes are prepared at a 10/1 (+/-) charge ratio. KALA/DNA (10/1)(+/-) complexes mediate transfection of a variety of cell lines. The KALA sequence provides a starting point for a family of peptides that incorporate other functions to improve DNA delivery systems.

Effect of cholesterol and charge on pore formation in bilayer vesicles by a pH-sensitive peptide

The effect of cholesterol on the bilayer partitioning of the peptide GALA (WEAALAEALAEALAEHLAEALAEALEALAA) and its assembly into a pore in large unilamellar vesicles composed of neutral and negatively charged phospholipids has been determined. GALA undergoes a conformational change from a random coil to an amphipathic alpha-helix when the pH is reduced from 7.0 to 5.0, inducing at low pH leakage of contents from vesicles. Leakage from neutral or negatively charged vesicles at pH 5.0 was similar and could be adequately explained by the mathematical model (Parente, R. A., S. Nir, and F. C. Szoka, Jr., 1990. Mechanism of leakage of phospholipid vesicle contents induced by the peptide GALA. Biochemistry. 29:8720-8728) which assumed that GALA becomes incorporated into the vesicle bilayer and irreversibly aggregates to form a pore consisting of 10 +/- 2 peptides. Increasing cholesterol content in the membranes resulted in a reduced efficiency of the peptide to induce leakage. Part of the cholesterol effect was due to reduced binding of the peptide to cholesterol-containing membranes. An additional effect of cholesterol was to increase reversibility of surface aggregation of the peptide in the membrane. Results could be explained and predicted with a model that retains the same pore size, i.e., 10 +/- 2 peptides, but includes reversible aggregation of the monomers to form the pore. Resonance energy transfer experiments using fluorescently labeled peptides confirmed that the degree of reversibility of surface aggregation of GALA was significantly larger in cholesterol-containing liposomes, thus reducing the efficiency of pore formation.

Selenoenzyme expression in thyroid and liver of second generation selenium- and iodine-deficient rats

The stimulation of thyroid hormone synthesis in iodine deficiency may increase the requirement for the selenoproteins which are involved in thyroid hormone synthesis in the thyroid gland. Selenoenzyme activity and expression were investigated in the thyroid and liver of second generation selenium-and/or iodine-deficient rats. Selenium deficiency caused substantial decreases in hepatic selenium-containing type I iodothyronine deiodinase (ID-I) and cytosolic glutathione peroxidase (cGSHPx) activities and mRNA abundances, but phospholipid hydroperoxide glutathione peroxidase (phGSHPx) activity was only 55% of selenium-supplemented control levels, despite the absence of change in its mRNA abundance. Selenoenzyme mRNA concentrations were maintained at control levels in thyroid glands from the selenium-deficient rat pups. Despite this, a differential effect was observed in selenoenzyme activities: ID-I activity was decreased to 61%, cGSHPx activity to 45% and phGSHPx to 29% of that in selenium-adequate controls. In iodine-deficient thyroid glands, mRNA levels were increased 2.2, 5.0 and 2.8 times for ID-I, cGSHPx and phGSHPx respectively. ID-I and cGSHPx enzyme activities were also increased but the activity of phGSHPx was decreased despite the high mRNA abundance. Thyroid selenoprotein mRNA levels were also increased in combined selenium and iodine deficiency but again there were differential effects on enzyme activities, with ID-I activity increased, cGSHPx unchanged and phGSHPx decreased. Thus, iodine deficiency may produce an oxidant stress on the thyroid gland, increasing the requirement for selenium to maintain selenoenzyme activity. When dietary supplies of selenium are limiting, thyroid selenoprotein mRNA levels are increased to compensate for overall lack of the micronutrient. Furthermore, there is a preferential supply of available selenium to ID-I and cGSHPx to allow maintenance of thyroid function.

Selenoprotein gene expression during selenium-repletion of selenium-deficient rats

Selenium repletion of selenium-deficient rats with 20 micrograms selenium / kg body weight as Na2SeO3 was used as a model to investigate the mechanisms that control the distribution of the trace element to specific selenoproteins in liver and thyroid. Cytosolic glutathione peroxidase (cGSHPx), phospholipid hydroperoxide glutathione peroxidase (PHGSHPx), and iodothyronine 5'-deiodinase (IDI) activities were all transiently increased in liver 16 to 32 h after ip injection with selenium. However, only cGSHPx and PHGSHPx activities increased in the thyroid where IDI activity was already increased by selenium deficiency. These responses were owing to synthesis of the seleoproteins on newly synthesised and/or existing mRNAs. The selenoprotein mRNAs in the thyroid gland were increased two- and threefold after the transitory increases in selenoprotein activity. In contrast, there were parallel changes in selenoprotein mRNAs and enzyme activities in the liver, with no prolonged rises in mRNA levels. The organ differences suggest that increased thryotrophin (TSH) concentrations, which are known to induce thyrodial IDI and mRNA, may control the mRNAs for all the thyroidal selenoproteins investigated and be a major mechanism for the preservation of thyroidal selenoproteins when selenium supplies are limited.

Tissue-specific regulation of selenoenzyme gene expression during selenium deficiency in rats

Regulation of synthesis of the selenoenzymes cytosolic glutathione peroxidase (GSH-Px), phospholipid hydroperoxide glutathione peroxidase (PHGSH-Px) and type-1 iodothyronine 5'-deiodinase (5'IDI) was investigated in liver, thyroid and heart of rats fed on diets containing 0.405, 0.104 (Se-adequate), 0.052, 0.024 or 0.003 mg of Se/kg. Severe Se deficiency (0.003 mg of Se/kg) caused almost total loss of GSH-Px activity and mRNA in liver and heart. 5'IDI activity decreased by 95% in liver and its mRNA by 50%; in the thyroid, activity increased by 15% and mRNA by 95%. PHGSH-Px activity was reduced by 75% in the liver and 60% in the heart but mRNA levels were unchanged; in the thyroid, PHGSH-Px activity was unaffected by Se depletion but its mRNA increased by 52%. Thus there is differential regulation of the three mRNAs and subsequent protein synthesis within and between organs, suggesting both that mechanisms exist to channel Se for synthesis of a particular enzyme and that there is tissue-specific regulation of selenoenzyme mRNAs. During Se depletion, the levels of selenoenzyme mRNA did not necessarily parallel the changes in enzyme activity, suggesting a distinct mechanism for regulating mRNA levels. Nuclear run-off assays with isolated liver nuclei showed severe Se deficiency to have no effect on transcription of the three genes, suggesting that there is post-transcriptional control of the three selenoenzymes, probably involving regulation of mRNA stability.

Making reaccreditation meaningful

Reaccreditation is a well-accepted fact for many doctors outside the United Kingdom and is likely to become a reality for British general practitioners. The author'sabbatical year in the United States of America studying reaccreditation and its relationship to continuing medical education has enabled a critical analysis of recent proposals in the UK to be carried out. The aim of reaccreditation must be understood by the profession and must be clearly stated. To be credible it will have to be mandatory and linked to continuing medical education. Current types of continuing medical education must be developed so that they are meaningful, influence doctors' behaviour and include research, audit, training, reading and medical writing. The profession must confront the need to penalize the small number of doctors who have an unacceptable standard of practice. The potential benefits of an appropriate form of reaccreditation may include improved quality of care and patient outcome, enhanced job satisfaction and reduced rates of burnout.

Effect of selenium depletion on thyroidal type-I iodothyronine deiodinase activity in isolated human thyrocytes and rat thyroid and liver

The effects of dietary selenium deficiency on hepatic and thyroidal type I iodothyronine deiodinase (ID-I) and selenium-dependent glutathione peroxidase (GPx) activities have been studied in weanling rats. In selenium-deficient animals hepatic ID-I activity was reduced to 11% of the activity found in the selenium-replete groups, whilst thyroidal ID-I activity increased by 42%. Hepatic and thyroidal GPx activities were also reduced by selenium deficiency to approximately 0.6 and 70%, respectively, of the values found in the selenium-replete animals. We have also studied the effects of thyrotropin (TSH), and selenium supply on the activity of IDI and GPx in human thyrocytes grown in primary culture. When thyrocytes were grown in selenium-deficient (< 1 nmol l-1 Se) medium in the absence of TSH, addition of sodium selenite up to 1000 nmol l-1 had little or no effect on ID-I activity. In the absence of added selenite, TSH addition produced a significant increase in ID-I activity and this stimulation was increased further when selenite was added at concentrations of 50-1000 nmol l-1 with an optimal effect on ID-I activity being observed at a 500 nmol l-1. Selenium content and GPx activity in human thyrocytes grown in selenium-free media (selenium content < 1 nmol l-1) were not significantly lower than the corresponding measurements made in cells grown in media containing selenium at a concentration of 5.4 nmol l-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization and postnatal development of 5'-deiodinase activity in goat perirenal fat

The capacity to generate the active thyroid hormone 3,3',5-triiodothyronine (T3) from thyroxine (T4) has been assessed in the major adipose tissue depot (perirenal) of newborn goats through measurements of iodothyronine 5'-deiodinase activity. High activity of the enzyme was found in the perirenal adipose tissue. Developmental studies demonstrated that there was a rise, then a fall, in iodothyronine 5'-deiodinase activity (per milligram of protein) over the first week of postnatal life, with a further decline between the second and third weeks. At 3 wk of age, the activity per gram of tissue was only 2% of that of the newborn; however, because of age-related increases in the lipid content of the perirenal adipose tissue, the activity per cell (per microgram of DNA) at 3 wk of age was approximately 10% of the activity in the newborn. Kinetic studies and inhibition characteristics with propylthiouracil, gold thioglucose, and T4 indicated that the iodothyronine 5'-deiodinase in goat perirenal adipose tissue is of the type I form; there was no evidence for the type II enzyme. Affinity labeling of the iodothyronine 5'-deiodinase with bromoacetyl-rT3 or bromoacetyl-T4 was consistent with this view. In contrast to goats, only the type II enzyme is evident in rats and mice. It is concluded that the perirenal (brown) adipose tissue is likely to be a significant source of T3 for other tissues in newborn goats and that there are major species variations in the form of iodothyronine 5'-deiodinase present in brown fat, with the goat exclusively exhibiting type I.

Presence of the brown fat-specific mitochondrial uncoupling protein and iodothyronine 5'-deiodinase activity in subcutaneous adipose tissue of neonatal lambs

Subcutaneous adipose tissue of neonatal lambs has been examined for the presence of markers diagnostic of thermogenic brown fat. Uncoupling protein, uncoupling protein mRNA, and iodothyronine 5'-deiodinase activity were each detected in subcutaneous adipose tissue, as well as in the major internal fat depot (perirenal), of newborn lambs. These brown fat markers were not present, however, in adipose tissue of adult sheep. It is concluded that subcutaneous fat in newborn lambs is functionally 'brown', and similar to the internal fat; subcutaneous and internal adipose tissues follow a similar developmental path--from 'brown' to 'white'.

The role of thyroidal type-I iodothyronine deiodinase in tri-iodothyronine production by human and sheep thyrocytes in primary culture

We have studied the origin of tri-iodothyronine (T3) secreted by human and sheep thyrocytes in primary culture and also the expression of type-I thyroidal iodothyronine deiodinase (ID-I) in the thyroid and liver of man and various other animals. Inhibitors of ID-I reduced T3 secretion from human but not sheep thyrocytes. In contrast, inhibitors of de-novo thyroid hormone synthesis reduced both thyroxine (T4) and T3 production in sheep thyrocytes, but had no effect on the T3 secreted by human thyrocytes. Human thyrocytes did not produce T4 under the culture conditions used, although some endogenous T4 was present in the cells following their isolation. Although thyrotrophin (TSH) stimulated T3 production in both human and sheep thyrocytes, iodine in the form of potassium iodide was only essential for T3 and T4 production by the sheep cells. Although 125I from Na125I was incorporated into T3 and T4 in TSH-stimulated sheep thyrocytes, no 125I incorporation into T3 or T4 was detected in TSH-stimulated human thyrocytes. Using activity measurements and affinity labelling, ID-I was present in the livers of all species studied, but ID-I could not be detected in thyroid tissue from cattle, pigs, sheep, goats, rabbits, deer or llamas. In contrast, thyroid tissue from man, mice, guinea-pigs and rats had significant ID-I activity and expressed an affinity-labelled protein with a molecular mass of approximately 28.1 kDa on SDS-PAGE. These data show that under the culture conditions used, sheep thyrocytes produced T3 by de-novo synthesis, whilst human thyrocytes produced T3 by deiodination of endogenous T4. We conclude that thyroidal ID-I shows marked species difference in its expression and that, in those species which express the enzyme (man, mice, guinea-pigs and rats, in this study), it appears that it may make an important contribution to thyroidal T3 production.

Effects of combined iodine and selenium deficiency on thyroid hormone metabolism in rats

This paper compares the effects of combined iodine and selenium deficiency, of single deficiencies of these trace elements, and of no deficiency on thyroid hormone metabolism in rats. In rats deficient in both trace elements, thyroidal triiodothyronine (T3), thyroidal thyroxin (T4), thyroidal total iodine, hepatic T4, and plasma T4 were significantly lower, and plasma thyroid-stimulating hormone (TSH) and thyroid weight were significantly higher than in rats deficient in iodine alone. Plasma and hepatic T3 concentrations were similar in the dietary groups. Hepatic type I iodothyronine deiodinase (ID-I) activity was inhibited by selenium deficiency irrespective of the iodine status. Type II deiodinase (ID-II) activity in the brain was significantly higher and in pituitary, significantly lower in combined deficiency than in iodine deficiency alone. These data show that selenium can play an important role in determining the severity of the hypothyroidism associated with iodine deficiency.

Selenium deficiency, thyroid hormone metabolism, and thyroid hormone deiodinases

Much research into the functions of selenium in the cell has concentrated on its role in selenium-containing glutathione peroxidases. However, selenium was recently shown to be an essential component of type I iodothyronine 5'-deiodinase in rats, which converts thyroxin to the more biologically active hormone 3,5,3'-triiodothyronine. Thus, selenium-deficient rats have low tissue deiodinase activities and abnormal thyroid hormone metabolism. The discovery of this function for selenium in thyroid hormone metabolism has important implications for the interpretation of the effects of selenium deficiency, especially in individuals with an adequate vitamin E status.

The role of selenium in thyroid hormone metabolism and effects of selenium deficiency on thyroid hormone and iodine metabolism

Selenium deficiency impairs thyroid hormone metabolism by inhibiting the synthesis and activity of the iodothyronine deiodinases, which convert thyroxine (T4) to the more metabolically active 3,3'-5 triiodothyronine (T3). Hepatic type I iodothyronine deiodinase, identified in partially purified cell fractions using affinity labeling with [125I]N-bromoacetyl reverse triiodothyronine, is also labeled with 75Se by in vivo treatment of rats with 75Se-Na2SeO3. Thus, the type I iodothyronine 5'-deiodinase is a selenoenzyme. In rats, concurrent selenium and iodine deficiency produces greater increases in thyroid weight and plasma thyrotrophin than iodine deficiency alone. These results indicate that a concurrent selenium deficiency could be a major determinant of the severity of iodine deficiency.

The role of selenium in thyroid hormone metabolism and effects of selenium deficiency on thyroid hormone and iodine metabolism

Selenium deficiency impairs thyroid hormone metabolism by inhibiting the synthesis and activity of the iodothyronine deiodinases, which convert thyroxine (T4) to the more metabolically active 3,3'-5 triiodothyronine (T3). Hepatic type I iodothyronine deiodinase, identified in partially purified cell fractions using affinity labeling with [125I]N-bromoacetyl reverse triiodothyronine, is also labeled with 75Se by in vivo treatment of rats with 75Se-Na2SeO3. Thus, the type I iodothyronine 5'-deiodinase is a selenoenzyme. In rats, concurrent selenium and iodine deficiency produces greater increases in thyroid weight and plasma thyrotrophin than iodine deficiency alone. These results indicate that a concurrent selenium deficiency could be a major determinant of the severity of iodine deficiency.

Effect of selenium deficiency on hepatic type I 5-iodothyronine deiodinase activity and hepatic thyroid hormone levels in the rat

Selenium deficiency in rats for a period of up to 6 weeks inhibited both the production of 3,3',5-tri-iodothyronine (T3) from thyroxine (T4) (5'-deiodination) and also the catabolism of T3 to 3,3'-di-iodothyronine (5-deiodination) in liver homogenates. The hepatic stores of T3 were decreased by only 8% in selenium deficiency, despite the T3 production rate from T4 being only 7% of the rate found in selenium-supplemented rats. Hepatic glutathione S-transferase (GST) activity was increased in both hypothyroidism and selenium deficiency, but apparently by different mechanisms, since mRNA expression for this family of enzymes was lowered by hypothyroidism and increased in selenium deficiency. It is concluded that, since both T3 production and catabolism are inhibited by selenium deficiency, there is little change in hepatic T3 stores, and therefore the changes in the activity of certain hepatic enzymes, such as GST, that are found in selenium deficiency are not the result of tissue hypothyroidism.

Inter-relationships between selenium and thyroid hormone metabolism in the rat and man

Labelling of rat kidney microsomes in vitro with [125I]-bromoacetyl T4 produced two bands on SDS/PAGE with Mr of 55 kDa and 27.5 kDa representing protein disulphide isomerase and type I iodothyronine deiodinase (ID-I) respectively. The amount of the 55 kDa band was unchanged by selenium (Se) deficiency but the 27.5 kDa protein was markedly decreased in kidney microsomal fraction obtained from Se-deficient rats. Concurrent Se and iodine deficiency produced a significant increase in thyroid weight, plasma thyrotrophin (TSH) and a decrease in thyroidal iodine when compared with either single Se or iodine deficiency. These results suggest that ID-I is a selenoprotein and that Se deficiency can exacerbate the hypothyroidism observed in iodine deficiency. In man, blood glutathione peroxidase and blood Se levels were decreased in hyperthyroidism due to Graves' disease whilst normal levels of these analytes were found in patients treated for Graves' disease. These results suggest that thyroid status can affect Se balance rather than Se deficiency predisposes to Graves' disease.