Plasma selenoproteins concentrations in type 2 diabetes mellitus--a pilot study

Serum selenium and fasting blood glucose: a cross-sectional study in women of different menopause status

BACKGROUND

This cross-sectional study aims to explore whether there exists an interaction between selenium and menopause concerning type 2 diabetes (T2D) prevalence and its related indicators such as fasting blood glucose (FBG) and homeostasis model assessment of insulin resistance (HOMA-IR).

METHODS

150 women aged 35-60 years old were finally analyzed in this study. Multivariate linear or logistic regression modeling was conducted to explore the association of selenium and the prevalence of T2D besides its related indicators. Subgroup analyses were conducted based on menopause status to assess the potential impact on the relationship.

RESULTS

In the fully adjusted model, serum selenium was positively associated with FBG (β: 0.03, CI: 0.01-0.05) and the prevalence of T2D (OR: 1.04, CI: 1.00-1.08). After stratifying the data by menopause status, compared with the postmenopausal women group, as the serum selenium concentrations increased, the FBG concentrations were significantly higher in the premenopausal women group (p for interaction = 0.0020).

CONCLUSIONS

The present study found serum selenium was positively associated with FBG and the prevalence of T2D. Furthermore, the relationship between serum selenium and FBG was different in the premenopausal and postmenopausal women. More studies are still needed in the future to verify the relationship as well as to explore the specific mechanisms.

Human serum albumin-bound selenium (Se-HSA) in serum and its correlation with other selenium species

INTRODUCTION

Selenium (Se) is a trace element with different toxicological and nutritional properties according to its chemical forms. Among the wide range of selenium species, human serum albumin-bound selenium (Se-HSA) has still uncertain composition in terms of organic or inorganic selenium species. This study aimed at investigating the relation between Se-HSA levels with total selenium and the specific organic and inorganic selenium species.

METHODS

We determined levels of total selenium and selenium species in serum of participants enrolled in two populations of the Emilia-Romagna region, in Northern Italy. Anion exchange chromatography coupled with inductively coupled plasma dynamic reaction cell mass spectrometry was used as quantification method. Correlations between Se-HSA and the other selenium compounds were analyzed using linear regression and restricted cubic spline regression models, adjusted for potential confounders.

RESULTS

The first cohort comprised 50 participants (men/women: 26/24) with median (interquartile range, IQR) age 50 (55-62) years, while the second was composed of 104 participants (M/W: 50/54), median (IQR) age 48 (44-53) years. Median (IQR) levels of total selenium were 118.5 (109-136) µg/L and 116.5 (106-128) µg/L, respectively, while Se-HSA was 25.5 µg/L (16.2-51.5) and 1.1 (0.03-3.1) µg/L, respectively. In both populations, Se-HSA was positively associated with inorganic selenium species. Conversely, Se-HSA was inversely associated with organic selenium, especially with selenoprotein P-bound-Se (Se-SELENOP) and less strongly with selenomethionine-bound-Se (Se-Met), while the relation was null or even positive with other organic species. Evaluation of non-linear trends showed a substantially positive association with inorganic selenium, particularly selenite, until a concentration of 30 µg/L, above which a plateau was reached. The association with Se-SELENOP was inverse and strong until 100 µg/L, while it was almost null at higher levels.

CONCLUSIONS

Our findings seem to indicate that Se-HSA incorporates more selenium when circulating levels of inorganic compounds are higher, thus supporting its mainly inorganic nature, particularly at high circulating levels of selenite.

Selenium, Selenoproteins and 10-year Cardiovascular Risk: Results from the ATTICA Study

BACKGROUND

Selenium (Se) is an essential trace element that is involved in several pathophysiological functions. The relationship of Se with cardiovascular disease remains inconclusive, especially regarding the role of different selenospecies.

OBJECTIVE

The present study assessed the levels of Se distribution in plasma selenoproteins, namely glutathione peroxidase 3 (GPx3), selenoprotein P (SelP) and selenoalbumin (SeAlb) and total Se in selenoproteins in relation to 10-year cardiovascular risk in the ATTICA prospective study.

METHODS

A sub-sample from the ATTICA Study's database, consisting of 278 subjects (114 women and 164 men) with data on Se and selenoproteins levels, was considered. SeGPx3, SelP, and SeAlb in human plasma were simultaneously determined by high-performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) at baseline. The duration of the follow-up was 8.74 ±2.36 years (mean± standard deviation) and cardiovascular outcomes were recorded. Cox proportional hazards models were applied with total Se or selenoprotein Se as independent variables adjusted for several covariates.

RESULTS

Total Se in selenoproteins was positively related to 10-year relative risk of cardiovascular disease (Hazard Ratios of 3rd vs 2nd tertile 10.02, 95% CI:1.15, 92.34). Subjects with high Se but low SeGPx3, as identified by discordant percentiles in the distribution of SeGPx3 and Se, had a higher cardiovascular risk.

CONCLUSION

The differentiated effects of circulating selenoproteins on cardiovascular disease risk in the present study, suggest the importance of redox regulation by specific selenoproteins.

Selenium status and type 2 diabetes risk

Optimal selenium (Se) status is necessary for overall health. That status can be affected by food intake pattern, age, sex, and health status. At nutritional levels of intake, Se functions metabolically as an essential constituent of some two dozen selenoproteins, most, if not all, of which have redox functions. Insufficient dietary intake of Se reduces, to varying degrees, the expression of these selenoproteins. Recent clinical and animal studies have indicated that both insufficient and excessive Se intakes may increase risk of type 2 diabetes mellitus (T2D), perhaps by way of selenoprotein actions. In this review, we discuss the current evidence linking Se status and T2D risk, and the roles of 14 selenoproteins and other proteins involved in selenoprotein biosynthesis. Understanding such results can inform the setting of safe and adequate Se intakes.

Associations between Circulating SELENOP Level and Disorders of Glucose and Lipid Metabolism: A Meta-Analysis

Selenoprotein P (SELENOP) is an extracellular antioxidant, selenium transporter, and hepatokine interfering with glucose and lipid metabolism. To study the association between the circulating SELENOP concentration and glucose and lipid metabolic diseases (GLMDs), including gestational diabetes (GD), metabolic syndrome (MetS), non-alcoholic fatty liver disease, obesity, and type 2 diabetes, as well as the individual markers, a meta-analysis was conducted by searching multiple databases from their establishment through March 2022 and including 27 articles published between October 2010 and May 2021, involving 4033 participants. Participants with GLMDs had higher levels of SELENOP than those without GLMDs (standardized mean difference = 0.84, 95% CI: 0.16 to 1.51), and the SELENOP levels were positively correlated with the markers of GLMDs (pooled effect size = 0.09, 95% CI: 0.02 to 0.15). Subgroup analyses showed that the SELENOP concentrations were higher in women with GD and lower in individuals with MetS than their counterparts, respectively. Moreover, SELENOP was positively correlated with low-density lipoprotein cholesterol, but not with the other markers of GLMDs. Thus, the heterogenicity derived from diseases or disease markers should be carefully considered while interpreting the overall positive association between SELENOP and GLMDs. Studies with a larger sample size and advanced design are warranted to confirm these findings.

Selenomethionine modulates insulin secretion in the MIN6-K8 mouse insulinoma cell line

Selenium is an essential trace element of interest for its potential role in glucose homeostasis. The present study investigated the impact of selenium supplementation as selenomethionine (SeMet) on insulin secretion in MIN6-K8 cells, a pancreatic β-cell model. We found that SeMet enhanced percent glucose-induced insulin secretion, while also increasing tolbutamide- and KCl-induced percent insulin secretion. RNA-sequencing showed that SeMet supplementation altered expression of several selenoproteins, including glutathione peroxidase 3 (Gpx3) and selenoprotein P (SelP). Targeted knockdown of Gpx3 increased both percent and total insulin release, while SelP knockdown increased insulin content and insulin release. Collectively, these studies support a putative role for selenium and selenoproteins in the regulation of insulin secretion, glucose homeostasis, and diabetes risk.

Characterization and Quantification of Selenoprotein P: Challenges to Mass Spectrometry

Selenoprotein P (SELENOP) is an emerging marker of the nutritional status of selenium and of various diseases, however, its chemical characteristics still need to be investigated and methods for its accurate quantitation improved. SELENOP is unique among selenoproteins, as it contains multiple genetically encoded SeCys residues, whereas all the other characterized selenoproteins contain just one. SELENOP occurs in the form of multiple isoforms, truncated species and post-translationally modified variants which are relatively poorly characterized. The accurate quantification of SELENOP is contingent on the availability of specific primary standards and reference methods. Before recombinant SELENOP becomes available to be used as a primary standard, careful investigation of the characteristics of the SELENOP measured by electrospray MS and strict control of the recoveries at the various steps of the analytical procedures are strongly recommended. This review critically discusses the state-of-the-art of analytical approaches to the characterization and quantification of SELENOP. While immunoassays remain the standard for the determination of human and animal health status, because of their speed and simplicity, mass spectrometry techniques offer many attractive and complementary features that are highlighted and critically evaluated.

Effect of Preconception Selenium Intake on the Risk for Gestational Diabetes: The Japan Environment and Children's Study

Selenium (Se) acts as a cofactor of antioxidant enzymes. Preconception care may reduce the risk of gestational diabetes mellitus (GDM). We examined the association between preconception Se intake and the risk of GDM in Japanese women. Using the Japan Environment and Children’s Study database, we identified 92,764 Japanese women recruited between January 2011 and March 2014. Participants were categorized into five groups according to preconception Se intake quintiles (Q1 and Q5 were the lowest and highest Se intake groups, respectively). GDM was categorized as early-onset (Eo-GDM) or late-onset (Lo-GDM) diagnosed before or after 24 weeks, respectively. Multiple logistic regressions were performed to identify the effect of preconception Se intake on GDM, Eo-GDM, and Lo-GDM. Using Q3 (the middle Se intake group) as the reference, a multiple logistic regression analysis showed that the highest (Q5) Se intake group demonstrated increased risks of GDM (adjusted odds ratio (aOR): 1.15, 95% confidence interval (CI): 1.01–1.30) and the lowest (Q1) Se intake group had increased risks of Lo-GDM (aOR: 1.19, 95% CI: 1.01–1.41). Thus, both high and low preconception Se intakes increase risks of glucose intolerance during pregnancy. This finding may indicate new recommendations for preconception Se intake to prevent GDM.

Selenium Levels in Community Dwellers with Type 2 Diabetes Mellitus

Selenium (Se) is an essential micronutrient required by the human body and exerts biological functions through selenoproteins. The relationship between Se and diabetes remains ambiguous. This study aimed at, through measurements of serum selenoprotein P (SelP), glutathione peroxidase (GPx3), and Se content in serum and hair, evaluating Se levels in community dwellers with type 2 diabetes mellitus (T2DM). A total of 336 subjects, including 176 T2DM patients (65.5 ± 8.7 years old) and 160 healthy residents (63.7 ± 9.8 years old, as controls), were recruited in this cross-sectional community-based study performed in Suzhou. Samples of fasting venous blood and hair were collected for measurements of Se levels, glycometabolism, and biochemistry parameters. We found that the serum Se level and SelP concentration in T2DM patients were substantially higher than those in healthy residents (p < 0.05). There was no significant difference in GPx3 activity and hair Se level between the two groups of subjects (p > 0.05). Serum Se was positively correlated with both GPx3 and hair Se in T2DM patients (r = 0.167 and 0.164, respectively, p < 0.05) and negatively correlated with SelP in healthy controls (r = - 0.293, p < 0.05). In conclusion, this study showed significantly higher levels of serum Se and SelP in community dwellers with T2DM than in matched healthy residents.

Total plasma magnesium, zinc, copper and selenium concentrations in type-I and type-II diabetes

Glycemia and insulin resistance are important regulators of multiple physiological processes and their dysregulation has wide-ranging consequences, including alterations in plasma concentrations of metal micronutrients. Here, magnesium, zinc, copper, selenium and glycated albumin (HbA1c) concentrations and quartile differences were examined in 45 subjects with type-I diabetes (T1DM), 54 subjects with type-II diabetes (T2DM) and 62 control subjects in order to assess potential differences between sexes and between T1DM and T2DM. Plasma magnesium concentration was decreased in T1DM subjects, with the second, third and fourth quartiles of magnesium concentrations associated with the absence of T1DM. This effect was observed in females but not males. In T2DM, the highest quartile of selenium concentrations and the third quartile of copper concentrations associated with the absence of diabetes in males. The highest quartile of magnesium concentrations was associated with the absence of T2DM in males but not females. HbA1c correlated with plasma concentrations of magnesium (negatively, in both sexes together in T1DM and T1DM males), copper (positively, in T1DM males and in both sexes together in T2DM), selenium (positively, in both sexes together in T1DM and T2DM, and T2DM females) and with zinc/copper ratio (negatively, in both sexes together in T1DM and T2DM). This study shows that plasma magnesium concentration is altered to the highest degree in T1DM, while in T2DM, plasma selenium and copper concentrations are significantly affected. This work increases our understanding of how T1DM and T2DM affects plasma metal concentrations and may have future implications for diabetes management.

Biomonitoring of selenoprotein P in human serum by fast affinity chromatography coupled to ICP-MS

Most of the Se in human serum is bound to selenoprotein P (SEPP1) in which Se is present in form of selenocysteine. The SEPP1 is a new possible biomarker for the Se status and for this reason we developed a fast, simple and reliable method for the quantitative determination of SEPP1 in serum by affinity chromatography coupled to ICP-MS. It is possible to separate SEPP1 from other selenoproteins in serum in only 5 min, which allows high sample throughput in clinical laboratories. Measured and certified concentrations of total Se and Se(SEPP1) are in good agreement for the reference material SRM 1950. The SEPP1 concentration was stable in serum samples of 3 persons for a minimum of 2 weeks. Further results of method validation were described including internal and external quality assurance. The analytical method was applied for a biomonitoring study of the SEPP1 and total Se concentration in human serum of 50 occupationally non-exposed persons living in northern Germany. Concentration ranges and mean concentrations for Se(SEPP1) are 31.1-59.7 and 46.2 μg/L, respectively. The corresponding values for total Se are 62-120 and 83.5 μg/L. The mean percentage of total Se in serum present as SEPP1 is 58%.

Simultaneous Speciation of Selenoproteins and Selenometabolites in Plasma and Serum

Selenium is an essential element incorporated to different proteins with important biological functions in connection to antioxidant activity, cancer-protective properties, neurodegenerative pathologies, and prevention of effects of diabetes, among others. In addition, selenoamino acids play a basic role in the global equilibrium of key selenium-biomolecules synthesis, including selenoprotein P, selenoalbumin, and glutathione peroxidase. Homeostasis of these selenium-containing biomolecules involves different organs in living organisms including human, and bloodstream is the connection fluid in this process. Therefore, it is very important to have an analytical methodology suitable for selenium proteins and metabolites speciation in serum and plasma samples. For this purpose, a simultaneous speciation method for Se-containing biomolecules in serum/plasma is described on the basis of in series three-dimensional chromatography: size exclusion, affinity, and anion exchange high performance liquid chromatography (3D/SE-AF-AEC-HPLC), using different columns of each type and hyphenation to inductively coupled plasma-(quadrupole) mass spectrometry (ICP-MS). The method allows the quantitative simultaneous analysis of selenoprotein P (SeP), extracellular glutathione peroxidase (eGPx), selenoalbumin (SeAlb), selenite, and selenate in serum (from human and mouse) using species-unspecific isotope dilution (SUID). In addition, a simplified two-dimensional approach (2D/SE-AF-HPLC-SUID-ICP-MS) is described when selenium metabolites are globally analyzed. The method provides detection limits in the range 0.2-1.3 ng of Se g^-1 and avoids typical interferences in this matrix from chloride and bromide with a chromatographic runtime less than 35 min.

Effects of selenium supplementation on glucose homeostasis and free androgen index in women with polycystic ovary syndrome: A randomized, double blinded, placebo controlled clinical trial

BACKGROUND/OBJECTIVES

Insulin resistance (IR) is a main pathophysiologic feature in polycystic ovary syndrome (PCOS) patients which is triggered by elevated oxidative stress in these patients. Selenium, an essential micronutrient, is a major constituent of antioxidant enzymes such as glutathione peroxidase. Recently, decreased plasma selenium concentrations were reported in PCOS patients. So, the present study was carried out in order to assess whether selenium consumption can improve the metabolic response to insulin and reduce the insulin resistance in these women.

SUBJECTS/METHODS

A total of 53 PCOS patients (diagnosed by Rotterdam criteria), 18-42 years old, participated in this randomized, double-blind and placebo controlled trial for 12 weeks (selenium, n=26; placebo, n=27). The effects of daily administration of 200 μg selenium or placebo on serum glucose, total testosterone (tT), sex hormone binding globulin (SHBG) and free androgen index (FAI) in fasting state were evaluated.

RESULTS

At the end of the study, insulin resistance was significantly increased in selenium recipients when compared with the placebo group (2.05 ± 0.39 when compared with 1.81 ± 0.25, p=0.017). Also, selenium supplementation resulted in marginally significant increase (p=0.056) in insulin level when compared with the placebo group. There were no statistically significant changes in other study endpoints, when comparing the two groups.

CONCLUSION

This study showed that selenium supplementation in PCOS patients may worsen insulin resistance in them. Until the results of larger studies become available, indiscriminate consumption of selenium supplements in PCOS patients will warrant caution.

Selenoprotein P is not elevated in gestational diabetes mellitus

Selenoprotein P concentrations have been found to be associated with insulin resistance and elevated in patients with type 2 diabetes mellitus (DM). The aim of the present study was to investigate circulating selenoprotein P level and its possible relationship with metabolic parameters in gestational diabetes mellitus (GDM). Plasma selenoprotein P concentrations were measured in 30 pregnant women with GDM, 35 pregnant women without GDM and 22 healthy nonpregnant women. No difference in selenoprotein P levels was observed among the groups [6.2 (4.5-8.2), 7.9 (4.5-10.7) and 6.7 (5.3-9.1) ng/ml, respectively, p = 0.69]. In pregnant women with and without GDM, selenoprotein P did not correlate with age, gestational age, prepregnancy body mass index (BMI), HbA1c, glucose concentrations at oral glucose tolerance test (OGTT), area under curve (AUC) glucose, total cholesterol, LDL cholesterol and triglycerides levels (p > 0.05). But, there were statistically significant correlations between selenoprotein P and current BMI (r = -0.28, p = 0.04) and HDL cholesterol levels (r = 0.43, p = 0.01). We found that selenoprotein P concentrations are not elevated in women with GDM but associated with BMI and HDL cholesterol.

Gender-specific distribution of selenium to serum selenoproteins: associations with total selenium levels, age, smoking, body mass index, and physical activity

The epidemiology of selenium (Se) is mainly based on the determination of total serum selenium levels (TSe) which by many aspects is an inadequate marker of Se status. In this study we applied a recently developed LC-ICP-MS method, for the determination of the selenium content of the three main serum selenium-containing proteins, in a subcohort of the ATTICA study. This enables us to investigate whether the selenium distribution to selenoproteins may correlate with demographic (age, gender) and lifestyle variables (smoking, physical activity) that are crucial for the development of chronic diseases. A sub-sample from the ATTICA Study, consisted of 236 males (40 ± 11 years) and 163 females (38 ± 12 years), was selected. The selenium content of glutathione peroxidase (GPx-3), selenoprotein P (SelP) and selenoalbumin (SeAlb) was determined in serum by LC-ICP/MS method. We found that 26% of TSe is found in GPx-3, 61% in SelP and 13% in SeAlb. We have assessed the different ratios of selenoproteins' selenium content (Se-GPX-3/Se-SelP, Se-GPX-3/Se-SeAlb, Se-SelP/Se-SeAlb), showing that people with similar TSe may have different distribution of this selenium to selenoproteins. Total selenium levels and gender are the variables that mostly affect selenium distribution to selenoproteins while age, smoking, physical activity and BMI do not significantly influence selenium distribution. In conclusion, the simultaneous determination of the selenium content of serum selenium-containing selenoproteins is necessary for a thorough estimation of selenium status. The ratio of the Se content between selenoproteins may be proven a novel, valid marker of selenium status.

Selenium and diabetes--evidence from animal studies

Whereas selenium was found to act as an insulin mimic and to be antidiabetic in earlier studies, recent animal experiments and human trials have shown an unexpected risk of prolonged high Se intake in potentiating insulin resistance and type 2 diabetes. Elevating dietary Se intake (0.4 to 3.0mg/kg of diet) above the nutrient requirements, similar to overproduction of selenoproteins, led to insulin resistance and/or diabetes-like phenotypes in mice, rats, and pigs. Although its diabetogenic mechanism remains unclear, high Se intake elevated activity or production of selenoproteins including GPx1, MsrB1, SelS, and SelP. This upregulation diminished intracellular reactive oxygen species and then dysregulated key regulators of β cells and insulin synthesis and secretion, leading to chronic hyperinsulinemia. Overscavenging intracellular H2O2 also attenuated oxidative inhibition of protein tyrosine phosphatases and suppressed insulin signaling. High Se intake might affect expression and/or function of key regulators of glycolysis, gluconeogenesis, and lipogenesis. Future research is needed to find out if certain forms of Se metabolites in addition to selenoproteins and if mechanisms other than intracellular redox control mediate the diabetogenic effects of high Se intake. Furthermore, a potential interactive role of high Se intake in the interphase of carcinogenesis and diabetogenesis should be explored to make optimal use of Se in human nutrition and health.

Selenium supranutrition: are the potential benefits of chemoprevention outweighed by the promotion of diabetes and insulin resistance?

Selenium was considered a toxin until 1957, when this mineral was shown to be essential in the prevention of necrotic liver damage in rats. The hypothesis of selenium chemoprevention is principally formulated by the observations that cancer incidence is inversely associated with selenium status. However, recent clinical and epidemiological studies demonstrate a role for some selenoproteins in exacerbating or promoting other disease states, specifically type 2 diabetes, although other data support a role of selenium in stimulating insulin sensitivity. Therefore, it is clear that our understanding in the role of selenium in glucose metabolism and chemoprevention is inadequate and incomplete. Research exploring the role of selenium in individual healthcare is of upmost importance and possibly will help explain how selenium is a double-edged sword in the pathologies of chronic diseases.