Association between polymorphisms of the GPX1 gene and second primary tumours after index squamous cell cancer of the head and neck

Current Understanding of Human Polymorphism in Selenoprotein Genes: A Review of Its Significance as a Risk Biomarker

Selenium has been proven to influence several biological functions, showing to be an essential micronutrient. The functional studies demonstrated the benefits of a balanced selenium diet and how its deficiency is associated with diverse diseases, especially cancer and viral diseases. Selenium is an antioxidant, protecting the cells from damage, enhancing the immune system response, preventing cardiovascular diseases, and decreasing inflammation. Selenium can be found in its inorganic and organic forms, and its main form in the cells is the selenocysteine incorporated into selenoproteins. Twenty-five selenoproteins are currently known in the human genome: glutathione peroxidases, iodothyronine deiodinases, thioredoxin reductases, selenophosphate synthetase, and other selenoproteins. These proteins lead to the transport of selenium in the tissues, protect against oxidative damage, contribute to the stress of the endoplasmic reticulum, and control inflammation. Due to these functions, there has been growing interest in the influence of polymorphisms in selenoproteins in the last two decades. Selenoproteins' gene polymorphisms may influence protein structure and selenium concentration in plasma and its absorption and even impact the development and progression of certain diseases. This review aims to elucidate the role of selenoproteins and understand how their gene polymorphisms can influence the balance of physiological conditions. In this polymorphism review, we focused on the PubMed database, with only articles published in English between 2003 and 2023. The keywords used were "selenoprotein" and "polymorphism". Articles that did not approach the theme subject were excluded. Selenium and selenoproteins still have a long way to go in molecular studies, and several works demonstrated the importance of their polymorphisms as a risk biomarker for some diseases, especially cardiovascular and thyroid diseases, diabetes, and cancer.

Glutathione Peroxidase GPX1 and Its Dichotomous Roles in Cancer

As the first identified selenoprotein, glutathione peroxidase 1 (GPX1) is a widely and abundantly expressed antioxidant enzyme. GPX1 utilizes glutathione as a substrate to catalyze hydrogen peroxide, lipid peroxide, and peroxynitrite, thereby reducing intracellular oxidative stress. The GPX1 gene is regulated at transcriptional, post-transcriptional, and translational levels. Numerous case-control studies and meta-analyses have assessed the association between a functional genetic polymorphism of the GPX1 gene, named Pro198Leu (rs1050450 C>T), and cancer susceptibility in different populations. GPX1 polymorphism has type-specific effects as a candidate marker for cancer risk, but the association between GPX1 variants and cancer susceptibility remains controversial in different studies. GPX1 is abnormally elevated in most types of cancer but has complex dichotomous roles as tumor suppressor and promoter in different cancers. GPX1 can participate in various signaling pathways to regulate tumor biological behaviors, including cell proliferation, apoptosis, invasion, immune response, and chemoresistance. In this review, we comprehensively summarize the controversial associations between GPX1 polymorphism and cancer risks and further discuss the relationships between the aberrant expressions of GPX1 and tumorigenesis. Further studies are needed to elucidate the clinical significance of GPX1 as a potential prognostic biomarker and novel therapeutic target in various malignancies.

Contribution of glutathione peroxidase 1 (Pro200Leu) single nucleotide polymorphism and serum homocysteine levels in the risk of acute myocardial infarction in Egyptians

Background

Oxidative stress is among the most common risk factors in the pathogenesis of acute myocardial infarction (AMI). Glutathione peroxidase 1 enzyme coded by the GPX1 gene plays an essential role in reducing oxidative stress. Previous studies correlated the GPX1 (Pro200Leu) single nucleotide polymorphism (SNP) with AMI incidence. Elevated homocysteine (Hcy) levels induce oxidative stress and are considered an independent risk factor for AMI. Evidence showed a complex relationship between Hcy and GPx-1 activity. This study examined the association of the common (Pro200Leu) SNP in GPX1 with AMI incidence in an Egyptian population. This study is the first to check this association in an Egyptian population. Moreover, the association between serum Hcy and the incidence of AMI was checked, and the novelty was to statistically correlate GPX1 Pro200Leu genotypes with serum Hcy levels in patients and control subjects. Hundred control subjects and hundred and twenty AMI patients were genotyped using PCR-RFLP analysis. An ELISA was used to measure serum Hcy levels.

Results

The GPX1 (Pro200Leu) genotype distribution and allele frequency were not significantly different between patients and control subjects (P = 0.60 and P = 0.62, respectively). Serum levels of Hcy were significantly elevated in patients compared to control subjects (P ≤ 0.0001). However, no significant difference was observed in serum Hcy levels among different GPX1 genotypes in neither patients nor control subjects.

Conclusions

The minor T allele of GPX1 Pro200Leu is not associated with AMI risk in this Egyptian population. However, high homocysteine serum levels might contribute independently to the risk of AMI. Finally, Hcy levels were not significantly different in homozygous minor TT compared to homozygous wild CC.

The ALA5/ALA6/ALA7 repeat polymorphisms of the glutathione peroxidase-1 (GPx1) gene and autism spectrum disorder

Autism is a severe neurodevelopmental disorder leading to deficits in social interaction, communication, and several activities. An increasing number of evidence suggests a role of oxidative stress in the etiology of autism spectrum disorder (ASD). Indeed, impaired antioxidant mechanisms may lead to the inadequate removal of H₂O₂ with a consequent increase in highly active hydroxyl radicals and other reactive oxygen species causing cellular damages. The GPx1 is one of the most important enzymes counteracting oxidative stress. In this work, we investigated a possible correlation between the GCG repeat polymorphism present in the first exon of GPx1 gene encoding a tract of five to seven alanine residues (ALA5, ALA6, and ALA7) and ASD. Our findings highlighted a high frequency of ALA5 allele in ASD subjects. Moreover, proteins corresponding to the three GPx1 variants were produced in vitro, and the evaluation of their activity showed a lower values for GPx1 having ALA5 polymorphism. The comparison of the secondary and tertiary structure predictions revealed an alpha‐helix in correspondence of alanine stretch only in the case of GPx1‐ALA7 variant. Finally, to better investigate protein structure, steady‐state fluorescence measurements of GPx1 intrinsic tryptophan were carried out and the three tested proteins exhibited a different stability under denaturing conditions. This work demonstrates the importance in adopting a multidisciplinary strategy to comprehend the role of GPx1 in ASD.

Results here obtained suggest a possible role of ALA5 GPx1 variant in ASD. However, given the multifactorial nature of autism, this evidence might be a piece of a more complex puzzle being the GPx1 enzyme part of a complex pathway in which several proteins are involved.

Single nucleotide polymorphisms and the risk of developing a second primary cancer among head and neck cancer patients: a systematic literature review and meta-analysis

BACKGROUND

Head and Neck Cancer (HNC) survivors are at increased risk of developing a second primary cancer (SPC). Along with the environmental risk factors, genetic factors have been associated with a potential increased susceptibility to SPC development. We aim to identify the Single Nucleotide Polymorphisms (SNPs) that contribute to SPC development among HNC survivors through a systematic review and meta-analysis.

METHODS

We searched PubMed, Scopus and ISI Web of Science for eligible studies published in English until January 31st, 2020. We included studies reporting primary data that evaluated the association between SNPs and SPC risk in HNC patients. Data were pooled in a random-effect meta-analyses, when at least two studies on the same SNP evaluated the same genotype model. Heterogeneity was assessed using the χ2-based Q-statistics and the I2 statistics. Quality of the included studies was assessed using the Q-Genie tool.

RESULTS

Twenty-one studies, of moderate to good quality, were included in the systematic review. Fifty-one genes were reported across the included studies to have significant associations with an increased SPC risk. Overall, 81 out of 122 investigated SNPs were significantly associated with the SPC risk. Seven studies were included in the meta-analysis, which showed five SNPs associated with an increased risk of SPC: p21C70T, CT + TT (HR = 1.76; 95% CI: 1.28-2.43); FASLG -844C > T, CT + TT (HR = 1.82; 95% CI: 1.35-2.46), P21 C98A, CA + AA (HR = 1.75; 95% CI: 1.28-2.38); FAS -670A > G (HR = 1.84; 95% CI: 1.28-2.66) and GST-M1, Null genotype (HR = 1.54; 95% CI: 1.13-2.10).

CONCLUSIONS

The identified SNPs in our systematic review and meta-analysis might serve as potential markers for identification of patients at high risk of developing SPC after primary HNC.

PROSPERO REGISTRATION NUMBER

CRD42019135612 .

Lead exposure activates the Nrf2/Keap1 pathway, aggravates oxidative stress, and induces reproductive damage in female mice

Lead, a common metallic contaminant, is widespread in the living environment, and has deleterious effects on the reproductive systems of humans and animals. Although numerous toxic effects of lead have been reported, the effects and underlying mechanisms of the impacts of lead exposure on the female reproductive system, especially oocyte maturation and fertility, remain unknown. In this study, mice were treated by gavage for seven days to evaluate the reproductive damage and role of Nrf2-mediated defense responses during lead exposure. Lead exposure significantly reduced the maturation and fertilization of oocytes in vivo. Additionally, lead exposure triggered oxidative stress with a decreased glutathione level, increased amount of reactive oxygen species, and abnormal mitochondrial distribution. Moreover, lead exposure caused histopathological and ultrastructural changes in oocytes and ovaries, along with decreases in the activities of catalase, glutathione peroxidase, total superoxide dismutase, and glutathione-S transferase, and increases in the levels of malonaldehyde in mouse ovaries. Further experiments demonstrated that lead exposure activated the Nrf2 signaling pathway to protect oocytes against oxidative stress by enhancing the transcription levels of antioxidant enzymes. In conclusion, our study demonstrates that lead activates the Nrf2/Keap1 pathway and impairs oocyte maturation and fertilization by inducing oxidative stress, leading to a decrease in the fertility of female mice.

Susceptibility of Multiple Primary Cancers in Patients With Head and Neck Cancer: Nature or Nurture?

Multiple primary cancers (MPCs) are major obstacles to long-term survival in head and neck cancer (HNSCC), however, the molecular mechanism underlying multiple carcinogenesis remains unclear. “Field cancerization” is a classical theory to elaborate the malignant progression of MPCs. Apart from environmental and immune factors, genetic factors may have great potential as molecular markers for MPCs risk prediction. This review focuses on inherited and acquired gene mutations in MPCs, including germ-line mutation, single-nucleotide polymorphism, chromosomal instability, microsatellite instability and DNA methylation. And definition and prognosis of MPCs have also been discussed. These may pave the way for the early detection, prevention and effective treatment of MPCs in HNSCC.

Zearalenone induced oxidative stress in the jejunum in postweaning gilts through modulation of the Keap1-Nrf2 signaling pathway and relevant genes1

Researches have shown that dietary zearalenone (ZEA) caused oxidative stress in the liver and reproductive organs of postweaning gilts. However, information on the effects of ZEA on oxidative stress of the small intestine in the piglets is limited. The objective of this study was to determine the effects of ZEA exposure on oxidative stress, the Kelch-like erythroid cell-derived protein with CNC homology (ECH)-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway and on immunohistochemistry of the jejunum in postweaning gilts. A 35-d feeding experiment using 40 postweaning gilts (Landrace × Yorkshire × Duroc) with an average BW of 14.01 ± 0.86 kg in 4 groups fed corn-soybean meal-based diets containing 0, 0.5, 1.0, and 1.5 mg ZEA/kg was conducted. The jejunum was obtained at the end of the experiment and used for analyses. The results showed that the activities of total superoxide dismutase and glutathione peroxidase and the relative expressions of Keap1 mRNA and protein in the jejunum linearly and quadratically decreased (P < 0.05) with increasing concentrations of ZEA in the diets. The malondialdehyde content, the integrated optical density of Nrf2 and glutathione peroxidase 1 (GPX1), and the relative expressions of Nrf2, GPX1, quinone oxidoreductase 1 (NQO1), and modifier subunit of glutamate-cysteine ligase (GCLM) mRNA and proteins linearly and quadratically increased (P < 0.05) with increasing levels of ZEA. Immunohistochemical analysis showed that Nrf2 and GPX1 immunoreactivity was enhanced by the ZEA treatments, and block localization of yellow and brown immunoreactive substances in the jejunum was observed with increasing levels of ZEA. The results suggest that ingested ZEA induced oxidative stress in the jejunum in postweaning gilts through upregulation of the Keap1-Nrf2 signaling pathway and downstream target genes NQO1, HO1, and GCLM, indicating the important role of the Keap1-Nrf2 signaling pathway in oxidative stress induced by ZEA in the jejunum of the postweaning piglets.

Pro198Leu Polymorphism in the Glutathione Peroxidase 1 Gene Contributes to Diabetic Peripheral Neuropathy in Type 2 Diabetes Patients

Glutathione peroxidase 1 (Gpx1) is an endogenous antioxidant enzyme. The T allele of the Pro198Leu polymorphism in the Gpx1 (rs1050450, 198C > T) gene is associated with reduced enzyme activity. The aim of this study was to evaluate the association between Pro198Leu polymorphism and risk of diabetic peripheral neuropathy (DPN). We examined 1244 T2DM patients and 730 healthy controls. In the patient group, 33 % had diabetic peripheral neuropathy. All subjects were genotyped for the Gpx1 Pro198Leu polymorphism by polymerase chain reaction and restriction analysis. A significant increase in the T allele and TT genotype frequencies was observed in DPN patients compared to those without DPN (OR 1.55, 95 % CI 1.30-1.85 and 1.89, 95 % CI 1.30-2.74, respectively). The association remained significant after correction for age, disease duration, HbA1c and BMI. When distribution of T allele was compared between DPN+ and DPN- subgroups and controls, OR was 1.54 for DPN+ and 1.00 for DPN- patients. In conclusion, our findings suggest that Gpx1 Pro198Leu genotypes are significantly associated with the risk of diabetic peripheral neuropathy in patients with T2DM. The study provides new clinically relevant information regarding genetic determinants of susceptibility to diabetic neuropathy.

Genetic variant of glutathione peroxidase 1 in autism

Genetic factors can contribute to autistic disorder (AD). Abnormal genes of oxidative stress pathways and increased oxidative stress have been reported in autism spectrum disorders. Polymorphisms of genes involved in glutathione metabolism, e.g. GSTP1 and GSTM1 are reportedly associated with autistic disorder. We investigated a GCG repeat polymorphism of a human glutathione peroxidase (GPX1) polyalanine repeat (ALA5, ALA6 and ALA7) in 103 trios of AD (probands and parents) using the transmission disequilibrium test. Significant transmission disequilibrium (p=0.044) was found in the overall transmission of the three alleles. The ALA6 allele was under transmitted (p=0.017). These results suggest that possessing this ALA6 allele may be protective for AD. Future study of interaction of the GPX1 GCG repeat and other gene polymorphisms such as the MnSOD ALA16 or the GPX1 Pro198Leu polymorphism in this cohort of AD families may shed light in whether the combination of the ALA6 allele with another polymorphism of antioxidant allele contributes to the increased oxidative stress in autism.

Molecular consequences of genetic variations in the glutathione peroxidase 1 selenoenzyme

Accumulating data have implicated the selenium-containing cytosolic glutathione peroxidase, GPx-1, as a determinant of cancer risk and a mediator of the chemopreventive properties of selenium. Genetic variants of GPx-1 have been shown to be associated with cancer risk for several types of malignancies. To investigate the relationship between GPx-1 enzyme activity and genotype, we measured GPx-1 enzyme activity and protein levels in human lymphocytes as a function of the presence of two common variations: a leucine/proline polymorphism at codon 198 and a variable number of alanine-repeat codons. Differences in GPx activity among these cell lines, as well as in the response to the low-level supplementation of the media with selenium, indicated that factors other than just genotype are significant in determining activity. To restrict the study to genotypic effects, human MCF-7 cells were engineered to exclusively express allelic variants representing a combination of either a codon 198 leucine or proline and either 5 or 7 alanine-repeat codons following transfection of GPx-1 expression constructs. Transfectants were selected and analyzed for GPx-1 enzyme activity and protein levels. GPx-1 with 5 alanines and a leucine at codon 198 showed a significantly higher induction when cells were incubated with selenium and showed a distinct pattern of thermal denaturation as compared with GPx-1 encoded by the other examined alleles. The collective data obtained using both lymphocytes and MCF-7 indicate that both intrinsic and extrinsic factors cooperate to ultimately determine the levels of this enzyme available to protect cells against DNA damage and mutagenesis.

Molecular mechanisms by which selenoproteins affect cancer risk and progression

Selenoproteins comprise a unique class of proteins that contain selenium in the form of selenocysteine. Several selenoproteins have been implicated in the risk or development of cancers in humans by genetic data. These include Selenoprotein P, 3 members of the glutathione peroxidase family of anti-oxidant enzymes and Sep15. At-risk alleles in the germline indicate a likely role in determining susceptibility to cancer, while loss of heterozygosity or chromosomal epigenetic silencing indicate that the reduction in the levels of the corresponding proteins contribute to malignant progression. Lower levels of these proteins are likely to be detrimental due to the resulting cellular stress and perturbations in important regulatory signaling pathways. The genetic data indicating the involvement of these selenoproteins in cancer etiology are discussed, as are the possible mechanisms by which these genes might promote carcinogenesis.