Strong associations of serum selenoprotein P with all-cause mortality and mortality due to cancer, cardiovascular, respiratory and gastrointestinal diseases in older German adults.

BACKGROUND: Selenium is an essential trace mineral. The main function of selenoprotein P (SELENOP) is to transport selenium but it has also been ascribed anti-oxidative effects. METHODS: To assess the association of repeated measurements of serum SELENOP concentration with all-cause and cause-specific mortality serum SELENOP was measured at baseline and 5-year follow-up in 7,186 and 4,164 participants of the ESTHER study, a German population-based cohort aged 50-74 years at baseline. RESULTS: During 17.3 years of follow-up, 2,126 study participants (30%) died. The relationship of serum SELENOP concentration with all-cause mortality was L-shaped, with mortality being significantly higher at SELENOP concentrations < 4.1 mg/L, which is near the bottom tertile's cut-off (4.2 mg/L). All-cause mortality of participants in the bottom SELENOP tertile was significantly increased compared to subjects in the top tertile (hazard ratio [95% confidence interval]: 1.35 [1.21-1.50]). SELENOP in the bottom tertile was further associated with increased cardiovascular mortality (1.24 [1.04-1.49]), cancer mortality (1.31 [1.09-1.58]), respiratory disease mortality (2.06 [1.28-3.32]) and gastrointestinal disease mortality (2.04 [1.25-3.32]). The excess risk of all-cause mortality for those in the bottom SELENOP tertile was more than twice as strong in men as in women (interaction of SELENOP and sex; p = 0.008). CONCLUSIONS: In this large cohort study, serum SELENOP concentration was inversely associated with all-cause and cause-specific mortality. Consistent inverse associations with multiple mortality outcomes might be explained by an impaired selenium transport and selenium deficiency in multiple organs. Trials testing the efficacy of selenium supplements in subjects with low baseline SELENOP concentration are needed. TRIAL REGISTRATION: Retrospectively registered in the German Clinical Trials Register on Feb 14, 2018 (ID: DRKS00014028).

Sex-specific associations of serum selenium and selenoprotein P with type 2 diabetes mellitus and hypertension in the Berlin Aging Study II.

BACKGROUND: Selenium is essential for expression and proper function of a set of redox active selenoproteins implicated in aging-relevant diseases, e.g. type 2 diabetes mellitus (T2D) and hypertension. However, data in cohorts of older adults, particularly with respect to different Se biomarkers and sex-specific analyses are sparse. OBJECTIVE: To assess associations of serum Se and selenoprotein P (SELENOP) concentrations with T2D and hypertension in a cohort of older females and males. METHODS: This study included 1500 participants from the Berlin Aging Study II. Diagnosis of T2D was made in case of antidiabetic medication, self-reported T2D, or laboratory parameters. Diagnosis of hypertension was based on self-report, blood pressure measurement, or anti-hypertensive medication. Se was measured by spectroscopy, and SELENOP by ELISA. Multiple adjusted regression models quantified dose-dependent associations. RESULTS: Participants had a median(IQR) age of 68 (65,71) years, and 767 (51%) were women. 191 (13%) participants had T2D and 1126 (75%) had hypertension. Se and SELENOP correlated significantly (r = 0.59, p < 0.001), and were elevated in those with self-reported Se supplementation. Serum Se and SELENOP were not associated with T2D in the whole cohort. In men, SELENOP was positively associated with T2D, OR (95%CI) for one mg/L increase in SELENOP was 1.22 (1.00,1.48). Se was non-linearly associated with hypertension, comparing to the lowest quartile (Q1), and participants with higher Se levels (Q3) had a lower OR (95%CI) of 0.66 (0.45,0.96), which was specific for men. SELENOP positively associated with hypertension, and OR (95%CI) per one mg/L increase was 1.15 (1.01,1.32). CONCLUSIONS: The data suggest a sex-specific interrelationship of Se status with T2D and hypertension, with apparent biomarker-specific associations.

Association of Selenoprotein and Selenium Pathway Genotypes with Risk of Colorectal Cancer and Interaction with Selenium Status.

Selenoprotein genetic variations and suboptimal selenium (Se) levels may contribute to the risk of colorectal cancer (CRC) development. We examined the association between CRC risk and genotype for single nucleotide polymorphisms (SNPs) in selenoprotein and Se metabolic pathway genes. Illumina Goldengate assays were designed and resulted in the genotyping of 1040 variants in 154 genes from 1420 cases and 1421 controls within the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Multivariable logistic regression revealed an association of 144 individual SNPs from 63 Se pathway genes with CRC risk. However, regarding the selenoprotein genes, only TXNRD1 rs11111979 retained borderline statistical significance after adjustment for correlated tests (PACT = 0.10; PACT significance threshold was P < 0.1). SNPs in Wingless/Integrated (Wnt) and Transforming growth factor (TGF) beta-signaling genes (FRZB, SMAD3, SMAD7) from pathways affected by Se intake were also associated with CRC risk after multiple testing adjustments. Interactions with Se status (using existing serum Se and Selenoprotein P data) were tested at the SNP, gene, and pathway levels. Pathway analyses using the modified Adaptive Rank Truncated Product method suggested that genes and gene x Se status interactions in antioxidant, apoptosis, and TGF-beta signaling pathways may be associated with CRC risk. This study suggests that SNPs in the Se pathway alone or in combination with suboptimal Se status may contribute to CRC development.

Severe selenium deficits in pregnant women irrespective of autoimmune thyroid disease in an area with marginal selenium intake.

OBJECTIVES: Selenium (Se) deficiency is related to an increased risk of preterm labor, miscarriage, preeclampsia, gestational diabetes, and other obstetric complications. As the Se status declines during pregnancy, we hypothesized that the decline may be exacerbated in women with autoimmune thyroid disease (AITD). MATERIAL AND METHODS: Pregnant women (n=74; 30 [23-38] years) were consecutively recruited from the district of Warsaw, Poland, and divided into healthy subjects (HS, n=45), and women with a diagnosis of AITD (AITD, n=29). Thyroglobulin antibodies (TG-aAb), thyroid peroxidase antibodies (TPO-aAb), TSH, free T3, free T4, total T3, and total T4, as well as urine iodine excretion were determined. Se status was assessed by serum Se and selenoprotein P (SELENOP) concentrations. Thyroid volume was evaluated by ultrasonography. RESULTS: Serum Se and SELENOP concentrations were relatively low in both control and AITD women. A Se deficit according to WHO definition (<45µg/l) was observed in 0%, 3.4%, 28.6% and 4.5%, 18.2%, 35.5% of women in the AITD and HS group, respectively, during the 1st, 2nd, and 3rd trimester. From first to third trimester, TPO-aAb and TG-aAb declined in AITD by 71% and 60%, respectively. The decline in TPO- and TG-aAb was unrelated to the Se status. CONCLUSIONS: In this area of habitual low Se intake, a high proportion of women developed a severe Se deficit during pregnancy, irrespective of AITD status. This decline must be considered as a preventable risk factor for pregnancy complications of relevance to both the unborn child and the pregnant mother.

Aminoglycoside-driven biosynthesis of selenium-deficient Selenoprotein P.

Selenoprotein biosynthesis relies on the co-translational insertion of selenocysteine in response to UGA codons. Aminoglycoside antibiotics interfere with ribosomal function and may cause codon misreading. We hypothesized that biosynthesis of the selenium (Se) transporter selenoprotein P (SELENOP) is particularly sensitive to antibiotics due to its ten in frame UGA codons. As liver regulates Se metabolism, we tested the aminoglycosides G418 and gentamicin in hepatoma cell lines (HepG2, Hep3B and Hepa1-6) and in experimental mice. In vitro, SELENOP levels increased strongly in response to G418, whereas expression of the glutathione peroxidases GPX1 and GPX2 was marginally affected. Se content of G418-induced SELENOP was dependent on Se availability, and was completely suppressed by G418 under Se-poor conditions. Selenocysteine residues were replaced mainly by cysteine, tryptophan and arginine in a codon-specific manner. Interestingly, in young healthy mice, antibiotic treatment failed to affect Selenop biosynthesis to a detectable degree. These findings suggest that the interfering activity of aminoglycosides on selenoprotein biosynthesis can be severe, but depend on the Se status, and other parameters likely including age and general health. Focused analyses with aminoglycoside-treated patients are needed next to evaluate a possible interference of selenoprotein biosynthesis by the antibiotics and elucidate potential side effects.

Circulating copper and zinc levels and risk of hepatobiliary cancers in Europeans.

BACKGROUND: Copper and zinc are essential micronutrients and cofactors of many enzymatic reactions that may be involved in liver-cancer development. We aimed to assess pre-diagnostic circulating levels of copper, zinc and their ratio (Cu/Zn) in relation to hepatocellular carcinoma (HCC), intrahepatic bile duct (IHBD) and gall bladder and biliary tract (GBTC) cancers. METHODS: A nested case-control study was conducted within the European Prospective Investigation into Cancer and Nutrition cohort. Serum zinc and copper levels were measured in baseline blood samples by total reflection X-ray fluorescence in cancer cases (HCC n=106, IHDB n=34, GBTC n=96) and their matched controls (1:1). The Cu/Zn ratio, an indicator of the balance between the micronutrients, was computed. Multivariable adjusted odds ratios and 95% confidence intervals (OR; 95% CI) were used to estimate cancer risk. RESULTS: For HCC, the highest vs lowest tertile showed a strong inverse association for zinc (OR=0.36; 95% CI: 0.13-0.98, Ptrend=0.0123), but no association for copper (OR=1.06; 95% CI: 0.45-2.46, Ptrend=0.8878) in multivariable models. The calculated Cu/Zn ratio showed a positive association for HCC (OR=4.63; 95% CI: 1.41-15.27, Ptrend=0.0135). For IHBC and GBTC, no significant associations were observed. CONCLUSIONS: Zinc may have a role in preventing liver-cancer development, but this finding requires further investigation in other settings.

Sex-specific and inter-individual differences in biomarkers of selenium status identified by a calibrated ELISA for selenoprotein P.

Selenoprotein P (SELENOP) is a liver-derived transporter of selenium (Se) in blood, and a meaningful biomarker of Se status. Se is an essential trace element for the biosynthesis of enzymatically-active selenoproteins, protecting the organism from oxidative damage. The usage of uncalibrated assays hinders the comparability of SELENOP concentrations and their pathophysiological interpretation across different clinical studies. On this account, we established a new sandwich SELENOP-ELISA and calibrated against a standard reference material (SRM1950). The ELISA displays a wide working range (11.6-538.4µg/L), high accuracy (2.9%) and good precision (9.3%). To verify whether SELENOP correlates to total Se and to SELENOP-bound Se, serum samples from healthy subjects and age-selected participants from the Berlin Aging Study II were analyzed by SELENOP-ELISA and Se quantification. SELENOP was affinity-purified and its Se content was determined from a subset of samples. There was a high correlation of total Se and SELENOP concentrations in young and elderly men, and in elderly women, but not in young women, indicating a specific sexual dimorphism in these biomarkers of Se status in young subjects. The Se content of isolated SELENOP was independent of sex and age (mean±SD: 5.4±0.5). By using this calibrated SELENOP-ELISA, prior reports on pathological SELENOP concentrations in diabetes and obesity are challenged as the reported values are outside reasonable limits. Biomarkers of Se status in clinical research need to be measured by validated assays in order to avoid erroneous data and incorrect interpretations, especially when analyzing young women. The Se content of circulating SELENOP differs between individuals and may provide some important diagnostic information on Se metabolism and status.

Prediagnostic selenium status and hepatobiliary cancer risk in the European Prospective Investigation into Cancer and Nutrition cohort.

BACKGROUND: Selenium status is suboptimal in many Europeans and may be a risk factor for the development of various cancers, including those of the liver and biliary tract. OBJECTIVE: We wished to examine whether selenium status in advance of cancer onset is associated with hepatobiliary cancers in the EPIC (European Prospective Investigation into Cancer and Nutrition) study. DESIGN: We assessed prediagnostic selenium status by measuring serum concentrations of selenium and selenoprotein P (SePP; the major circulating selenium transfer protein) and examined the association with hepatocellular carcinoma (HCC; n = 121), gallbladder and biliary tract cancers (GBTCs; n = 100), and intrahepatic bile duct cancer (IHBC; n = 40) risk in a nested case-control design within the EPIC study. Selenium was measured by total reflection X-ray fluorescence, and SePP was determined by a colorimetric sandwich ELISA. Multivariable ORs and 95% CIs were calculated by using conditional logistic regression. RESULTS: HCC and GBTC cases, but not IHBC cases, showed significantly lower circulating selenium and SePP concentrations than their matched controls. Higher circulating selenium was associated with a significantly lower HCC risk (OR per 20-µg/L increase: 0.41; 95% CI: 0.23, 0.72) but not with the risk of GBTC or IHBC. Similarly, higher SePP concentrations were associated with lowered HCC risk only in both the categorical and continuous analyses (HCC: P-trend ≤ 0.0001; OR per 1.5-mg/L increase: 0.37; 95% CI: 0.21, 0.63). CONCLUSION: These findings from a large prospective cohort provide evidence that suboptimal selenium status in Europeans may be associated with an appreciably increased risk of HCC development.

Selenium status in neonates with connatal infection.

Infectious diseases impair Se metabolism, and low Se status is associated with mortality risk in adults with critical disease. The Se status of neonates is poorly characterised, and a potential impact of connatal infection is unknown. We hypothesised that an infection negatively affects the Se status of neonates. We conducted an observational case-control study at three intensive care units at the Charité-Universitätsmedizin Berlin, Germany. Plasma samples were collected from forty-four neonates. On the basis of clinical signs for bacterial infection and concentrations of IL-6 or C-reactive protein, neonates were classified into control (n 23) and infected (n 21) groups. Plasma Se and selenoprotein P (SePP) concentrations were determined by X-ray fluorescence and ELISA, respectively, at day of birth (day 1) and 48 h later (day 3). Se and SePP showed a positive correlation in both groups of neonates. Se concentrations indicative of Se deficit in adults (500 ng/l). During antibiotic therapy, SePP increased significantly from day 1 (1·03 (sd 0·10) mg/l) to day 3 (1·34 (sd 0·10) mg/l), indicative of improved hepatic Se metabolism. We conclude that both Se and SePP are suitable biomarkers for assessing Se status in neonates and for identifying subjects at risk of deficiency.

Regulation of Selenocysteine Content of Human Selenoprotein P by Dietary Selenium and Insertion of Cysteine in Place of Selenocysteine.

Selenoproteins are a unique group of proteins that contain selenium in the form of selenocysteine (Sec) co-translationally inserted in response to a UGA codon with the help of cis- and trans-acting factors. Mammalian selenoproteins contain single Sec residues, with the exception of selenoprotein P (SelP) that has 7-15 Sec residues depending on species. Assessing an individual's selenium status is important under various pathological conditions, which requires a reliable selenium biomarker. Due to a key role in organismal selenium homeostasis, high Sec content, regulation by dietary selenium, and availability of robust assays in human plasma, SelP has emerged as a major biomarker of selenium status. Here, we found that Cys is present in various Sec positions in human SelP. Treatment of cells expressing SelP with thiophosphate, an analog of the selenium donor for Sec synthesis, led to a nearly complete replacement of Sec with Cys, whereas supplementation of cells with selenium supported Sec insertion. SelP isolated directly from human plasma had up to 8% Cys inserted in place of Sec, depending on the Sec position. These findings suggest that a change in selenium status may be reflected in both SelP concentration and its Sec content, and that availability of the SelP-derived selenium for selenoprotein synthesis may be overestimated under conditions of low selenium status due to replacement of Sec with Cys.

Selenium status is associated with colorectal cancer risk in the European prospective investigation of cancer and nutrition cohort.

Suboptimal intakes of the micronutrient selenium (Se) are found in many parts of Europe. Low Se status may contribute to colorectal cancer (CRC) development. We assessed Se status by measuring serum levels of Se and Selenoprotein P (SePP) and examined the association with CRC risk in a nested case-control design (966 CRC cases; 966 matched controls) within the European Prospective Investigation into Cancer and Nutrition. Se was measured by total reflection X-ray fluorescence and SePP by immunoluminometric sandwich assay. Multivariable incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression. Respective mean Se and SePP levels were 84.0 µg/L and 4.3 mg/L in cases and 85.6 µg/L and 4.4 mg/L in controls. Higher Se concentrations were associated with a non-significant lower CRC risk (IRR = 0.92, 95% CI: 0.82-1.03 per 25 µg/L increase). However, sub-group analyses by sex showed a statistically significant association for women (p(trend) = 0.032; per 25 µg/L Se increase, IRR = 0.83, 95% CI: 0.70-0.97) but not for men. Higher SePP concentrations were inversely associated with CRC risk (p(trend) = 0.009; per 0.806 mg/L increase, IRR = 0.89, 95% CI: 0.82-0.98) with the association more apparent in women (p(trend) = 0.004; IRR = 0.82, 95% CI: 0.72-0.94 per 0.806 mg/L increase) than men (p(trend) = 0.485; IRR = 0.98, 95% CI: 0.86-1.12 per 0.806 mg/L increase). The findings indicate that Se status is suboptimal in many Europeans and suggest an inverse association between CRC risk and higher serum Se status, which is more evident in women.

Hypoxia reduces and redirects selenoprotein biosynthesis.

Selenium deficiency constitutes a risk factor for the incidence and negative course of severe diseases including sepsis, stroke, autoimmune diseases or cancer. In this study, hypoxia is identified as a powerful stimulus to redirect selenoprotein biosynthesis causing reduced selenoprotein P expression and diminished selenium export from hepatocytes in favour of increased biosynthesis of the essential protective intracellular phospholipid hydroperoxide glutathione peroxidase GPX4. Specifically, hypoxia decreases transcript concentrations of central factors controlling selenium and selenocysteine metabolism including selenophosphate synthetase-2, phosphoseryl-tRNA(SerSec) kinase and selenocysteine lyase, which are all proven to be rate-limiting enzymes in selenoprotein biosynthesis. These effects are paralleled by a general decline of selenoprotein expression; however, not all selenoproteins are affected to the same extent by hypoxia, and GPX4 constitutes an exception as its expression becomes slightly increased. Supplemental selenium is able to overcome the hypoxia-dependent down regulation of selenoprotein expression in our cell culture model system, supporting the concept of using selenium as an adjuvant treatment option in severe diseases. Although it remains to be tested whether these effects constitute a hepatocyte-specific response, the selenium-dependent decline of selenoprotein P biosynthesis under hypoxic conditions may explain the progressive selenium deficit developing in severe diseases.

Selenium status in patients with autoimmune and non-autoimmune thyroid diseases from four European countries.

CONTEXT: Selenium supplementation has been suggested for Hashimoto thyroiditis and Graves' ophthalmopathy. Objective, Design: Our aim is to measure selenium status (p-Se, p-SePP), urine iodine (UI) levels and urine iodine/creatinine ratio (UI/C) in different thyroid diseases (n = 416) from four European countries and to compare the results between patients with and without thyroid autoimmunity. RESULTS: p-Se and p-SePP showed positive correlation and did not correlate with UI/C. Also, these measurements were higher in patients from Italy in comparison with the other countries. Austria had the lowest UI/C ratios. Selenium deficiency exists in these four European countries. Selenium status was lower in patients with Hashimoto thyroiditis and Graves' disease in comparison with non-autoimmune thyroid disease patients and did not differ between autoimmune patients with or without thyroid peroxidase antibodies. The latter correlated positively with age. CONCLUSIONS: Our findings suggest that Se supplementation might have a beneficial effect in autoimmune thyroid patients.