Lack of Association between Selenium Status and Disease Severity and Activity in Patients with Graves' Ophthalmopathy.

BACKGROUND: Selenium (Se) is of importance for regular functioning of the immune system and thyroid gland, and may have a health effect in mild Graves' ophthalmopathy (GO). OBJECTIVE: As the Se status declines in inflammation, we analyzed whether GO activity or severity affects the Se status of patients. METHODS: Serum Se and selenoprotein P (SePP) concentrations were retrospectively determined in 84 consecutive GO patients before treatment and compared to their clinical activity score (CAS) and severity of eye changes (NOSPECS) status, and to the concentrations of autoantibodies targeting the TSH receptor (TRAK) or the IGF1 receptor (IGF1R-aAB). RESULTS: Serum Se and SePP were linearly associated, indicating a suboptimal Se status of our patients. In comparison to data from other European cohorts, the majority of GO patients had a relatively poor Se status ([Se] ± SD; 70.0 ± 23.8 µg/l), below the threshold needed for full expression of selenoproteins. TRAK were inversely associated with Se concentrations, while IGF1R-aAB titers were not associated with Se. Neither Se nor SePP concentrations differed between GO patients with severe versus mild or active versus inactive disease, or showed significant associations with the CAS or NOSPECS values. CONCLUSION: GO patients are at risk of a low Se status, yet disease severity or activity does not seem to affect Se or SePP concentrations directly. However, as the retrospective nature of the analysis does not allow conclusions on a potential causative role of Se on Graves' disease or GO risk, these results neither support nor discourage adjuvant Se supplementation attempts.

Factors impacting the aminoglycoside-induced UGA stop codon readthrough in selenoprotein translation.

Aminoglycosides (AG) are oligosaccharide antibiotics that interfere with the small ribosomal subunit in aerobic, Gram-negative bacteria, causing pathogen-destructing error rates in their protein biosynthesis. Aminoglycosides also induce mRNA misinterpretation in eukaryotic cells, especially of the UGA (Opal)-stop codon, albeit to a lower extent. UGA recoding is essentially required for the incorporation of selenocysteine (Sec) into growing selenoproteins during translation. Selenocysteine incorporation requires the presence of a selenoprotein-specific stem-loop structure within the 3'-untranslated region of the mRNA, the so-called Sec-insertion sequence (SECIS) element. Interestingly, selenoprotein genes differ in their SECIS-element sequence and in their UGA base context. We hypothesized that the SECIS-element and the specific codon context synergize in controlling the effects of AG on stop codon readthrough. To this end, the SECIS-elements of glutathione peroxidase 1, glutathione peroxidase 4 and selenoprotein P transcripts were cloned into a reporter system and analyzed in combination with different UGA codon contexts. Our results indicate that a cytosine in position 4 (directly downstream of UGA) confers strongest effects on both the Se- and AG-dependent readthrough. Overall selenoprotein biosynthesis rate depends on the Se-status, AG concentration and the specific SECIS-element present in the transcript. These findings help to get a better understanding for the susceptibility of different transcripts towards AG-mediated interference with the biosynthesis of functional Se-containing selenoproteins, and highlight the importance of the Se-status for successful selenoprotein biosynthesis under antibiotic therapy.

Identification of thyroid hormone response elements in vivo using mice expressing a tagged thyroid hormone receptor α1.

TRα1 (thyroid hormone receptor α1) is well recognized for its importance in brain development. However, due to the difficulties in predicting TREs (thyroid hormone response elements) in silico and the lack of suitable antibodies against TRα1 for ChIP (chromatin immunoprecipitation), only a few direct TRα1 target genes have been identified in the brain. Here we demonstrate that mice expressing a TRα1-GFP (green fluorescent protein) fusion protein from the endogenous TRα locus provide a valuable animal model to identify TRα1 target genes. To this end, we analysed DNA-TRα1 interactions in vivo using ChIP with an anti-GFP antibody. We validated our system using established TREs from neurogranin and hairless, and by verifying additional TREs from known TRα1 target genes in brain and heart. Moreover, our model system enabled the identification of novel TRα1 target genes such as RNF166 (ring finger protein 166). Our results demonstrate that transgenic mice expressing a tagged nuclear receptor constitute a feasible approach to study receptor-DNA interactions in vivo, circumventing the need for specific antibodies. Models like the TRα1-GFP mice may thus pave the way for genome-wide mapping of nuclear receptor-binding sites, and advance the identification of novel target genes in vivo.

Structure- and cell-specific effects of imidoselenocarbamates on selenoprotein expression and activity in liver cells in culture.

The essential micronutrient selenium (Se) exerts its biological effects mainly through selenoproteins thereby affecting a number of physiological pathways including intracellular redox control, stress response and cancer cell proliferation. Besides affecting selenoprotein expression, some selenocompounds have been synthesized and analyzed in order to serve as chemotherapeutic substances preferentially targeting cancer cells. This promising chemotherapeutic potential has recently been verified for a particular imidoselenocarbamate in a mouse tumor model. In the present study we tested the effects of this and a number of related Se-methyl- and Se-benzyl-imidoselenocarbamates on selenoprotein expression in nontransformed and hepatic carcinoma cells in culture. Most of the Se-benzyl-imidoselenocarbamates strongly stimulated selenoprotein P (SePP) secretion while the Se-methyl-imidoselenocarbamates elicited less pronounced effects in hepatocarcinoma HepG2 cells. However, most of the Se-methyl-imidoselenocarbamates increased glutathione peroxidase (GPx) activity and decreased thioredoxin reductase (TXNRD) activity in parallel, while the majority of the Se-benzyl-imidoselenocarbamates were without a respective effect in HepG2 cells. Performing inhibitor assays in vitro, GPx activity was unaffected by the imidoselenocarbamates. In contrast, most of the Se-methyl-imidoselenocarbamates inhibited TXNRD activity in vitro in line with the results in HepG2 cells. Both classes of imidoselenocarbamates strongly induced selenoprotein S (SELS) expression without a respective increase in ER stress or unfolded protein response which are known inducers of SELS biosynthesis. Notably, many of these effects were cancer cell-specific, and not observed in nontransformed AML12 hepatocytes. Our results indicate that these novel selenocompounds affect expression and activity of crucial selenoenzymes in a compound- and cell-specific way in hepatocytes. Especially the Se-methyl-imidoselenocarbamates elicit a unique spectrum of activities by stimulating GPx activity, SELS expression and SePP secretion while inhibiting TXNRD activity in hepatocarcinoma cells. These effects represent a promising finding with respect to the identification of therapeutic selenocompounds, as cancer-cell specificity is combined with desired effects on selenoprotein expression and activity.

Interference of endocrine disrupters with thyroid hormone receptor-dependent transactivation.

Thyroid hormones regulate critical developmental processes and key metabolic pathways. A number of natural and synthetic substances have been identified which adversely interfere with the endocrine system. These so-called endocrine disrupters (ED) have mainly been studied for their impact on the gonadal hormone axis. The aim of this work was to develop a novel sensitive and convenient in vitro screening assay for the detection and characterization of potential ED of thyroid hormone (TH)-dependent transactivation of gene transcription and to apply this tool to test relevant environmental and nutritive ED compounds. We constructed a TH-responsive luciferase-based reporter plasmid and established a reporter gene assay in a 96 well microplate format using the human hepatocarcinoma cell line HepG2 as host system. Both the synthetic TH receptor (TR) agonist GC-1 and the antagonist NH-3 were used to evaluate the assay. Concentration-response data of test compounds (food constituents, isoflavones, ultraviolet-absorbers, pesticides, industrial chemicals) were recorded in activation assays. In addition, interference with TH-mediated transactivation was tested by coincubation of the ED with triiodothyronine (T(3)) in competition assays. Most ED tested affected T(3) reporter gene activity at concentrations of 1 microM or higher and displayed either agonistic or mixed agonistic/antagonistic activities. Effects of relevant ED occurred only at relatively high concentrations compared with the endogenous TR ligand T(3). However, on basis of their high production volumes and potential bioaccumulation of some fat-soluble ED our data indicate the need to carefully monitor certain ED for potential disruption of the TH system in intact organisms and humans.