Influence of the glutathione peroxidase 1 Pro200Leu polymorphism on the response of glutathione peroxidase activity to selenium supplementation: a randomized controlled trial

The role of glutathione peroxidase-1 in health and disease

Glutathione peroxidase 1 (GPx1) is an important cellular antioxidant enzyme that is found in the cytoplasm and mitochondria of mammalian cells. Like most selenoenzymes, it has a single redox-sensitive selenocysteine amino acid that is important for the enzymatic reduction of hydrogen peroxide and soluble lipid hydroperoxides. Glutathione provides the source of reducing equivalents for its function. As an antioxidant enzyme, GPx1 modulates the balance between necessary and harmful levels of reactive oxygen species. In this review, we discuss how selenium availability and modifiers of selenocysteine incorporation alter GPx1 expression to promote disease states. We review the role of GPx1 in cardiovascular and metabolic health, provide examples of how GPx1 modulates stroke and provides neuroprotection, and consider how GPx1 may contribute to cancer risk. Overall, GPx1 is protective against the development and progression of many chronic diseases; however, there are some situations in which increased expression of GPx1 may promote cellular dysfunction and disease owing to its removal of essential reactive oxygen species.

Association of genetic variants in the GPX1 and GPX4 genes with the activities of glutathione-dependent enzymes, their interaction with smoking and the risk of acute pancreatitis

Genetic factors and tobacco smoke exposure can be associated with an increased risk of acute pancreatitis (AP). The pathogenesis of AP is associated with intensive oxidative stress. Glutathione peroxidase (GPx) is one of many enzymes involved in the neutralization of free radicals. This study aimed to investigate the impact of SNP rs1050450 in the GPX1 gene and rs713041 in the GPX4 gene on the activity of total GPx in a group of AP patients and healthy subjects. It was found that AP can contribute to decreased GPx activity (in plasma and erythrocyte lysate) accompanied by an increased glutathione reductase (GR) activity and decreased glutathione (GSH) concentration in two groups, non-smokers and smokers. A decreased GPx activity in erythrocyte lysate of AP patients compared to healthy subjects was associated with the occurrence of the CC genotype for SNP rs1050450. It was noted an increased GPx activity and decreased GR activity in erythrocytes of non-smoking AP patients with the TT genotype compared to subjects with the CC and TC genotype for SNP rs713041. However, in the group of smoking AP patients with this genotype, GR activity was elevated compared to non-smokers, which was accompanied by increased GSH concentration. These results can indicate that smoking in the course of AP can change the involvement of antioxidants in dependence on the genotype for the examined SNPs. The CC genotype for SNP rs1050450 and the TT genotype for rs713041 increases the risk of AP recurrence, which may be associated with increased MDA concentration.

Plasma selenium and the risk of first stroke in adults with hypertension: a secondary analysis of the China Stroke Primary Prevention Trial

BACKGROUND

Previous studies have indicated that selenium (Se) may play an important role in cardio-cerebrovascular disease. However, the relation between circulating selenium and risk of first stroke remains inconclusive.

OBJECTIVES

We conducted a secondary analysis of the China Stroke Primary Prevention Trial (CSPPT), using a nested case-control design, and aimed to investigate the correlation between Se concentration and first stroke risk in adults with hypertension and examine the potential effect modifiers.

METHODS

In the CSPPT, a total of 20,702 adults with hypertension were randomly assigned to a double-blind daily treatment with either 10 mg enalapril and 0.8 mg folic acid or 10 mg enalapril alone. A total of 618 first stroke cases and 618 controls matched for age, sex, treatment group, and study site were included in this study.

RESULTS

During a median follow-up duration of 4.5 y (IQR: 4.2-4.6 y), there was a significant inverse association between plasma Se and the risk of first stroke (per SD increment; adjusted OR: 0.81; 95% CI: 0.68, 0.96) and ischemic stroke (per SD increment; adjusted OR: 0.76; 95% CI: 0.62, 0.93). Furthermore, a stronger inverse association between plasma Se and first stroke was observed in participants with higher folate concentrations at baseline [≥7.7 ng/mL (median), adjusted OR: 0.67; 95% CI: 0.54, 0.85, compared with <7.7 ng/mL, adjusted OR: 0.98; 95% CI: 0.80, 1.21; P-interaction = 0.008] and those with higher time-averaged systolic blood pressure (SBP) over the treatment period (≥140 mm Hg, adjusted OR: 0.71; 95% CI: 0.58, 0.86, compared with <140 mm Hg, adjusted OR: 0.96; 95% CI: 0.77, 1.20; P-interaction = 0.023).

CONCLUSIONS

There was a significant inverse association between plasma Se and risk of first stroke in Chinese adults with hypertension, especially among those with higher baseline folate concentrations and those with higher time-averaged SBP over the treatment period. This trial was registered at clinicaltrials.gov as NCT00794885.

Inflammation factors and element supplementation in cancer

The aim of the study was to evaluate the effect of dietary supplementation with chosen minerals (Zn, Se, Fe) on expression of selected cytokines (IL-1, IL-6, TNFα) in spleen of rats and on their concentrations in rat serum under inflammatory and pathological conditions obtained by implantation of prostate cancer cells (LnCaP). Serum levels of metabolites of arachidonic, eicosapentaenoic and linoleic acids (hydroxyeicosatetraenoic, hydroxyeicosapentaenoic and hydroxyoctadecadienoic acids, respectively), as compounds involved in inflammation and cancer development, were also investigated. Male rats were randomised into dietary groups supplemented with Zn, Se or Fe. Prostate cancer cells were implanted to some rats in each group. The study demonstrated that minerals supplemented with the diet may exert various effects on an organism. Selenium, zinc and iron influence pro-inflammatory cytokine expression, what leads to stimulation of inflammation. They also affect synthesis of arachidonic and linoleic acid metabolites that exert pro-inflammatory action and enable cancer development and metastasis.

Selenoproteins of the Human Prostate: Unusual Properties and Role in Cancer Etiology

The prostate is an important organ for the maintenance of sperm health with prostate cancer being a common disease for which there is a critical need to distinguish indolent from aggressive disease. Several selenium-containing proteins have been implicated in prostate cancer risk or outcome due to either enzyme function, the reduced levels of these proteins being associated with cancer recurrence after prostatectomy or their corresponding genes containing single-nucleotide polymorphisms associated with increased risk. Moreover, experimental data obtained from the manipulation of either cultured cells or animal models have indicated that some of these proteins are contributing mechanistically to prostate cancer incidence or progression. Among these are selenocysteine-containing proteins selenoprotein P (SELENOP), glutathione peroxidase (GPX1), and selenoprotein 15 (SELENOF); and the selenium-associated protein selenium-binding protein 1 (SBP1). Genotyping of some of the genes for these proteins has identified functional single-nucleotide polymorphisms that are associated with prostate cancer risk and the direct quantification of these proteins in human prostate tissues has not only revealed associations to clinical outcomes but have also identified unique properties that are different from what is observed in other tissue types. The location of GPX1 in the nucleus and SELENOF in the plasma membrane of prostate epithelial cells indicates that these proteins may have functions in normal prostate tissue that are distinct from that of the other tissue types.

The redox balance of healthy Brazilian adults is associated with GPX1 Pro198Leu and -602A/G polymorphisms, selenium status, and anthropometric and lifestyle parameters

PURPOSE

Considering that oxidative stress is implicated in the pathogenesis and progression of different health conditions, we aimed to evaluate whether the redox balance of a healthy Brazilian population is associated with GPX1 polymorphisms, selenium status, lipid profile, and anthropometric and lifestyle parameters.

METHODS

343 healthy adults were assessed for redox balance markers [glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity; malondialdehyde (MDA) and oxygen radical absorption capacity (ORAC)]; genotyped for the polymorphisms GPX1 Pro198Leu (rs1050450), -602A/G (rs3811699) and Arg5Pro (rs8179169); evaluated for selenium biomarkers (plasma, erythrocyte, and urine) and intake; and assessed for lipid profile. Anthropometric (BMI) and lifestyle data (physical activity, current smoking habit and alcohol consumption) were collected. Multivariable regression models were applied to investigate the possible associations.

RESULTS

Although there were no differences in GPx activity according to GPX1 Pro198Leu and -602A/G polymorphisms, this redox balance marker was positively associated with erythrocyte selenium and negatively associated with the presence of a minor allele of Pro198Leu. SOD activity was positively associated with the presence of a minor allele for these polymorphisms. ORAC showed the same pattern among Leu and G carriers and was positively associated with Leu allele presence, BMI and alcohol intake. MDA was only associated negatively with the male sex and plasma selenium.

CONCLUSIONS

Our findings suggest that the redox balance of a Brazilian healthy population is associated with GPX1 polymorphisms (Pro198Leu and -602A/G), selenium status, BMI, sex, smoking habit and alcohol consumption.

Selenium-Rich Diet Induces Myocardial Structural and Functional Abnormalities by Activating Caspase-9 and Caspase-3 in Gpx-1P198L-Overexpression Transgenic Mice

Background

Selenium (Se) deficiency and supplementation result in multiple effects. GPx-1 (Pro198Leu) polymorphism is associated with Se deficiency. This study aimed to observe associations between Se-deficiency/supplement and GPx-1-198Leu overexpression in myocardial injuries.

Material/Methods

GPx-1P198L transgenic (Tg) mice and non-transgenic wild-type (WT) littermates were divided into Control (CON, 0.1–0.2 mg/kg), Se-deficiency (SD, <0.02 mg/kg), and Se-supplement (SS, 0.4 mg/kg) groups. Cardiac functions were observed with animal M-mode echocardiography. Se level was measured using 2,3-diamino Kenai fluorospectrophotometry. Total cardiac GPx activity was also measured. Myocardial histopathology was determined with HE and Masson’s trichrome staining. Caspase-9 and caspase-3 were measured with Western blot analysis.

Results

In WT Se-deficient mice, cardiac GPx activity was significantly decreased, and was not elevated by overexpression of GPx-1-198Leu gene. Increased GPx activity was observed in WT Se-supplemented mice and Tg Se-supplemented mice (much more). Se deficiency as well as supplementation resulted in cardiac systolic dysfunction, which was not affected by GPx-1-198Leu gene. Se deficiency led to myocardial fibrosis and pathological changes accompanied by increased activation of caspase-9 and caspase-3. Se supplementation significantly reduced pathological changes, as well as caspase-9 and caspase-3 levels in the presence of increased myocardial fibrosis. In Se-deficient mice, GPx-1-198Leu overexpression did not significantly decrease myocardial pathological injuries and fibrosis. In Se-supplemented Tg mice, myocardial fibrosis and caspase-9 level were increased, although pathological injuries and caspase-3 were similar to that in Se-supplemented WT mice.

Conclusions

Se deficiency as well as supplementation induced myocardial structural and functional abnormalities through activation of caspase-9 and caspase-3 in GPx-1P198L overexpression transgenic mice.

Sodium selenite inhibits deoxynivalenol-induced injury in GPX1-knockdown porcine splenic lymphocytes in culture

Deoxynivalenol (DON) is a cytotoxic mycotoxin that can cause cell damages. The main effect is to inhibit protein synthesis. Oxidative stress is one of the effects of DON. Selenium (Se) can ameliorate the cell damage caused by DON-induced oxidative stress, but it is unclear whether through selenoprotein glutathione peroxidase 1 (GPX1). We established GPX1-knockdown porcine spleen lymphocytes, and treated them with DON and Se. Untransfected porcine splenic lymphocytes (group P) and transfected cells (group M, GPX1 knockdown) were treated with or without DON (0.824, 0.412, 0.206, or 0.103 μg/mL, group D1-4), Se (Na₂SeO₃, 2 μM, group Se), or both (group SD1–4) for 6, 12, or 24 h. The cells were collected and the activities of SOD and CAT, levels of GSH, H₂O₂, malonaldehyde (MDA), total antioxidant capacity (T-AOC), and the inhibition of free hydroxyl radicals were determined. Levels of ROS were measured at 24 h. Compared with group P, the antioxidant capacity of group M was reduced. DON caused greater oxidative damage to the GPX1-knockdown porcine splenic lymphocytes than to the normal control cells. When Na₂SeO₃ was combined with DON, it reduced the damage in the GPX1-knockdown porcine splenic lymphocytes, but less effectively than in the normal porcine splenic lymphocytes.

Selenoproteins in human body: focus on thyroid pathophysiology

Selenium (Se) has a multilevel, complex and dynamic effect on the human body as a major component of selenocysteine, incorporated into selenoproteins, which include the selenocysteine-containing enzymes iodothyronine deiodinases. At the thyroid level, these proteins play an essential role in antioxidant protection and hormone metabolism. This is a narrative review based on PubMed/Medline database research regarding thyroid physiology and conditions with Se and Se-protein interferences. In humans, Se-dependent enzyme functions are best expressed through optimal Se intake, although there is gap in our knowledge concerning the precise mechanisms underlying the interrelation. There is a good level of evidence linking low serum Se to autoimmune thyroid diseases and, to a lesser extent, differentiated thyroid cancer. However, when it comes to routine supplementation, the results are heterogeneous, except in the case of mild Graves' orbitopathy. Autoimmune hypothyroidism is associated with a state of higher oxidative stress, but not all studies found an improvement of thyroid function after Se was introduced as antioxidant support. Meanwhile, no routine supplementation is recommended. Low Se intake is correlated with an increased risk of developing antithyroid antibodies, its supplementation decreasing their titres; there is also a potential reduction in levothyroxine replacement dose required for hypothyroidism and/or the possibility that it prevents progression of subclinical hypothyroidism, although not all studies agree. In thyroid-associated orbitopathy, euthyroidism is more rapidly achieved if the micronutrient is added to traditional drugs, while controls appear to benefit from the microelement only if they are deficient; thus, a basal assay of Se appears advisable to better select patients who need substitution. Clearly, further Se status biomarkers are required. Future introduction of individual supplementation algorithms based on baseline micronutrient levels, underlying or at-risk clinical conditions, and perhaps selenoprotein gene polymorphisms is envisaged.

The effect of selenium supplementation on coronary heart disease: A systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Selenium is a crucial mineral with antioxidant and immune functions, and selenium deficiency may increase the risk of coronary heart disease (CHD). However, the effect of selenium supplementation on CHD is still controversial according to numerous randomized controlled trials (RCTs). The aim of our meta-analysis study was to investigate the impact of selenium on CHD.

METHODS

PUBMED, EMBASE, MEDLINE, and the Cochrane Central Register of Controlled Trials databases were systematically searched to identify RCTs evaluating the effect of selenium supplementation on CHD mortality, blood lipid profile (high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and total cholesterol), serum C-reactive protein (CRP), and the level of glutathione peroxidase (GSH-PX) from inception until September 20, 2016. Odds ratio of CHD mortality and the associated 95% confidence intervals (CIs) were calculated using the fixed effect model. Weighted mean difference or standardized mean difference (SMD) and 95% confidence intervals (CIs) were calculated to determine the lipid profile, serum CRP, and GSH-PX using fixed effect or random effect models depending on the observed heterogeneity.

RESULTS

A total of 16 eligible RCTs with 43998 participants were included. Significant effects were observed for serum CRP (SMD=-0.48; 95% CI, -0.96 to 0; p=0.049) and GSH-PX (SMD=0.5; 95% CI, 0.36-0.64; p<0.001) after selenium supplementation. However, selenium supplementation was not statistically associated with CHD mortality and an aberrant lipid profile.

CONCLUSION

Selenium supplementation decreased serum CRP and increased the GSH-PX level, suggesting a positive effect on reducing oxidative stress and inflammation in CHD. However, selenium supplementation is not sufficient to reduce mortality and to improve the lipid status.

GPX1 Pro198Leu polymorphism and GSTM1 deletion do not affect selenium and mercury status in mildly exposed Amazonian women in an urban population

Mercury is potent toxicant element, but its toxicity can be reduced by forming a complex with selenium for safe excretion. Considering the impact of mercury exposure in the Amazon region and the possible interaction between these two elements, we aimed to assess the effects of Pro198Leu polymorphism to GPX1 and GSTM1 deletion, on mercury levels in a population from Porto Velho, an urban locality in the Brazilian Amazon region. Two hundred women from the capital city of Rondônia state were recruited for this study with 149 deemed suitable to participate. We assessed dietary intake using 24-hour recall. Selenium levels in plasma and erythrocytes were measured using hydride generation quartz tube atomic absorption spectroscopy and total hair mercury using cold vapor atomic absorption spectrometry. Oxidative stress parameters (GPx activity, oxygen radical absorbency capacity [ORAC] and malondialdehyde [MDA]) were also analyzed. All participants were genotyped for Pro198Leu polymorphism and GSTM1 deletion. We observed that this population presented high prevalence of selenium deficiency, and also low levels of mercury, likely due to food habits that did not include selenium-rich food sources or significant consumption of fish (mercury biomagnifiers) regularly. Univariate statistical analysis showed that Pro198Leu and GSTM1 genotypes did not affect selenium and mercury levels in this population. Pro198Leu polymorphism and GSTM1 deletion had no effect on mercury levels in mildly exposed people, suggesting these genetic variants impact mercury levels only in highly exposed populations.

DNA damage and oxidative stress response to selenium yeast in the non-smoking individuals: a short-term supplementation trial with respect to GPX1 and SEPP1 polymorphism

Purpose

Selenium, both essential and toxic element, is considered to protect against cancer, though human supplementation trials have generated many inconsistent data. Genetic background may partially explain a great variability of the studies related to selenium and human health. The aim of this study was to assess whether functional polymorphisms within two selenoprotein-encoding genes modify the response to selenium at the level of oxidative stress, DNA damage, and mRNA expression, especially in the individuals with a relatively low selenium status.

Methods

The trial involved 95 non-smoking individuals, stratified according to GPX1 rs1050450 and SEPP1 rs3877899 genotypes, and supplemented with selenium yeast (200 µg) for 6 weeks. Blood was collected at four time points, including 4 weeks of washout.

Results

After genotype stratification, the effect of GPX1 rs1050450 on lower GPx1 activity responsiveness was confirmed; however, in terms of DNA damage, we failed to indicate that individuals homozygous for variant allele may especially benefit from the increased selenium intake. Surprisingly, considering gene and time interaction, GPX1 polymorphism was observed to modify the level of DNA strand breaks during washout, showing a significant increase in GPX1 wild-type homozygotes. Regardless of the genotype, selenium supplementation was associated with a selectively suppressed selenoprotein mRNA expression and inconsistent changes in oxidative stress response, indicating for overlapped, antioxidant, and prooxidant effects. Intriguingly, DNA damage was not influenced by supplementation, but it was significantly increased during washout.

Conclusions

These results point to an unclear relationship between selenium, genotype, and DNA damage.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-015-1118-4) contains supplementary material, which is available to authorized users.

Selenium status and cardiovascular diseases: meta-analysis of prospective observational studies and randomized controlled trials

BACKGROUND/OBJECTIVES

Selenium was thought to have a role in cardiovascular disease (CVD) owing to its antioxidant properties; however, evidence from observational studies and randomized controlled trials (RCTs) has been inconsistent and controversial. We thus conducted a meta-analysis to assess the discrepancies between observational and randomized trial evidence.

SUBJECTS/METHODS

We searched MEDLINE and EMBASE for eligible prospective studies regarding the relationship between selenium and CVD up to 15 December 2013 and finally included 16 prospective observational studies and 16 RCTs. Random effects model was used to estimate the pooled relative risk (RR). Generalized least-squares trend test and restricted cubic spline model were performed to assess a linear and a nonlinear dose-response relationship.

RESULTS

Our meta-analysis of prospective studies showed a nonlinear relationship of CVD risk with blood selenium concentrations across a range of 30-165 μg/l and a significant benefit of CVD within a narrow selenium range of 55-145 μg/l. Our meta-analyses of RCTs showed that oral selenium supplements (median dose: 200 μg/day) for 2 weeks to 144 months significantly raised the blood selenium concentrations by 56.4 μg/l (95% confidence interval (CI): 40.9, 72.0 μg/l), whereas oral selenium supplements (median: 100 μg/day) for 6 to 114 months caused no effect on CVD (RR=0.91; 95% CI: 0.74, 1.10).

CONCLUSIONS

Our meta-analysis in prospective studies demonstrated a significant inverse association between selenium status and CVD risk within a narrow selenium range and a null effect of selenium supplementation on CVD was observed in RCTs. These findings indicate the importance of considering selenium status, dose and safety in health assessment and future study design.

Selenium-enriched foods are more effective at increasing glutathione peroxidase (GPx) activity compared with selenomethionine: a meta-analysis

Selenium may play a beneficial role in multi-factorial illnesses with genetic and environmental linkages via epigenetic regulation in part via glutathione peroxidase (GPx) activity. A meta-analysis was undertaken to quantify the effects of dietary selenium supplementation on the activity of overall GPx activity in different tissues and animal species and to compare the effectiveness of different forms of dietary selenium. GPx activity response was affected by both the dose and form of selenium (p < 0.001). There were differences between tissues on the effects of selenium supplementation on GPx activity (p < 0.001); however, there was no evidence in the data of differences between animal species (p = 0.95). The interactions between dose and tissue, animal species and form were significant (p < 0.001). Tissues particularly sensitive to changes in selenium supply include red blood cells, kidney and muscle. The meta-analysis identified that for animal species selenium-enriched foods were more effective than selenomethionine at increasing GPx activity.

Protective effects of meat from lambs on selenium nanoparticle supplemented diet in a mouse model of polycyclic aromatic hydrocarbon-induced immunotoxicity

Increased environmental oxidative stress caused primarily by chemicals like polycyclic aromatic hydrocarbons, plays significant role in human diseases. A representative compound, 7,12-dimethylbenz(a)anthracene (DMBA), was used for modeling oxidative damages including the significant decrease of the antioxidant capacity of the blood. Selenium has antioxidant effects but with a narrow therapeutic window. In our current studies to avoid accidental overdose and toxicity selenium was given to meat-producing animals. The standard rodent diet of mice was replaced by meat from lambs either on standard or selenium-enriched diet. Selenium concentration of lamb meat was enhanced three times by nano-selenium administration and an increase in the antioxidant capacity of the blood of mice was measured after the indirect selenium supplementation. Protective effects were also observed against DMBA-induced immunotoxicity. Twice the amount of white blood cells and among them three times more phagocytes survived. Similarly, in their renewal system in bone marrow twice the amount of cells survived and regenerative capacity of granulopoiesis was four times higher than in control DMBA-damaged mice. Our findings suggest functional dietary benefits of lamb meat enriched with selenium by feeding lambs with nanoparticle selenium supplements.