Reduction of HDL- and LDL-associated cholesterylester and phospholipid hydroperoxides by phospholipid hydroperoxide glutathione peroxidase and Ebselen (PZ 51)

GPX4 regulates cellular necrosis and host resistance in Mycobacterium tuberculosis infection

Cellular necrosis during Mycobacterium tuberculosis (Mtb) infection promotes both immunopathology and bacterial dissemination. Glutathione peroxidase-4 (Gpx4) is an enzyme that plays a critical role in preventing iron-dependent lipid peroxidation-mediated cell death (ferroptosis), a process previously implicated in the necrotic pathology seen in Mtb-infected mice. Here, we document altered GPX4 expression, glutathione levels, and lipid peroxidation in patients with active tuberculosis and assess the role of this pathway in mice genetically deficient in or overexpressing Gpx4. We found that Gpx4-deficient mice infected with Mtb display substantially increased lung necrosis and bacterial burdens, while transgenic mice overexpressing the enzyme show decreased bacterial loads and necrosis. Moreover, Gpx4-deficient macrophages exhibited enhanced necrosis upon Mtb infection in vitro, an outcome suppressed by the lipid peroxidation inhibitor, ferrostatin-1. These findings provide support for the role of ferroptosis in Mtb-induced necrosis and implicate the Gpx4/GSH axis as a target for host-directed therapy of tuberculosis.

HMGB1 mediates lipopolysaccharide-induced inflammation via interacting with GPX4 in colon cancer cells

Background

Inflammation is one of a main reason for colon cancer progression and poor prognosis. The high-mobility group box-1 (HMGB1) and glutathione peroxidase 4 (GPX4) are responsible for inflammation, but the relationship between HMGB1 and GPX4 remains unknown about inflammation in colon cancer.

Methods

RT-qPCR was carried out to investigate the expression of IL1β, IL6 and TNFα in colon cancer cells stimulated with LPS or siHMGB1. To observe the relationship between HMGB1, GPX4 and inflammation or ROS, Western blot assays were adopted. Pull-down, CoIP and immunohistochemistry assays were performed to further investigate the molecular mechanisms of HMGB1 and GPX4 in colon cancer.

Results

We report that HMGB1 mediates lipopolysaccharide (LPS)-induced inflammation in colon cancer cells. Mechanistically, acetylated HMGB1 interacts with GPX4, negatively regulating GPX4 activity. Furthermore, by utilizing siHMGB1 and its inhibitor, our discoveries demonstrate that HMGB1 knockdown can inhibit inflammation and reactive oxygen species (ROS) accumulation via NF-kB.

Conclusion

Collectively, our findings first demonstrate that acetylated HMGB1 can interact with GPX4, leading to inflammation, and providing therapeutic strategies targeting HMGB1 and GPX4 for colon cancer.

Activation of Glutathione Peroxidase 4 as a Novel Anti-inflammatory Strategy

The anti-oxidative enzyme, glutathione peroxidase 4 (GPX4), helps to promote inflammation resolution by eliminating oxidative species produced by the arachidonic acid (AA) metabolic network. Up-regulating its activity has been proposed as a promising strategy for inflammation intervention. In the present study, we aimed to study the effect of GPX4 activator on the AA metabolic network and inflammation related pathways. Using combined computational and experimental screen, we identified a novel compound that can activate the enzyme activity of GPX4 by more than two folds. We further assessed its potential in a series of cellular assays where GPX4 was demonstrated to play a regulatory role. We are able to show that GPX4 activation suppressed inflammatory conditions such as oxidation of AA and NF-κB pathway activation. We further demonstrated that this GPX4 activator can decrease the intracellular ROS level and suppress ferroptosis. Our study suggests that GPX4 activators can be developed as anti-inflammatory or cyto-protective agent in lipid-peroxidation-mediated diseases.

Topical delivery of ebselen encapsulated in biopolymeric nanocapsules: drug repurposing enhanced antifungal activity

Aim: Ebselen (Eb) is an example of a repurposed drug with poor aqueous solubility which requires sophisticated delivery system such as nanoencapsulation in nanocapsules for topical application. Materials & methods: Eb-nanocapsules were examined for morphology, activity against Candida spp., cytotoxicity and skin permeation. Results: Eb-nanocapsules were active against skin-infecting Candida tropicalis, Candida albicans and Candida parapsilosis yeasts (minimal inhibitory concentration values were about 4-, 2- and 1.25-times lower vs free Eb, respectively) and able to suppress induced lipid oxidation in the oil/water emulsion. Moreover, demonstrated minimal toxicity in normal human dermal fibroblast cell line, whereas ex vivo skin permeation studies showed no transdermal passage and strong interactions with stratum corneum. Conclusion: Eb-nanocapsules represent a promising, safe and complementary alternative to the treatment of cutaneous candidiasis.

Toenail selenium levels and prevalence of dyslipidaemia among Korean adults

Multiple studies have elucidated the antioxidant properties of Se, which are now well known among the nutrition and biomedical science communities. Recently, considerable interest has been focused on the possible association between Se exposure and risk of metabolic disease, such as lipid dysregulation; however, there is limited epidemiological data on this topic. The present study aimed to investigate associations between toenail Se levels and dyslipidaemia or individual lipid levels, and to examine the effect of dietary supplement use on these associations. We analysed baseline data from a cohort in the Yeungnam area, including 232 men and 269 women. Information on demographic, dietary and lifestyle characteristics was obtained through a self-reported questionnaire. Se levels in toenail specimens were measured using neutron activation analysis. Fasting blood lipid levels were measured during medical examinations. After adjusting for multiple confounding variables, we observed no association between toenail Se levels and dyslipidaemia or individual lipid profiles. However, the association was modified by dietary supplement use. Among the supplement users, higher toenail Se levels were associated with a higher prevalence of lipid dysregulation, whereas non-users exhibited a lower prevalence of lipid dysregulation. Associations between toenail Se levels, lipid levels and dyslipidaemia may be influenced by taking dietary supplements. Future large-scale, prospective cohort studies should be conducted to further evaluate the association between Se levels in the body and metabolic health effects in light of increasing rates of dietary supplement use.

Crystal and solution structural studies of mouse phospholipid hydroperoxide glutathione peroxidase 4

The mammalian glutathione peroxidase (GPx) family is a key component of the cellular antioxidative defence system. Within this family, GPx4 has unique features as it accepts a large class of hydroperoxy lipid substrates and has a plethora of biological functions, including sperm maturation, regulation of apoptosis and cerebral embryogenesis. In this paper, the structure of the cytoplasmic isoform of mouse phospholipid hydroperoxide glutathione peroxidase (O70325-2 GPx4) with selenocysteine 46 mutated to cysteine is reported solved at 1.8 Å resolution using X-ray crystallography. Furthermore, solution data of an isotope-labelled GPx protein are presented.

Randomised controlled trial of the effect of long-term selenium supplementation on plasma cholesterol in an elderly Danish population

Although cross-sectional studies have shown a positive association between Se and cholesterol concentrations, a recent randomised controlled trial in 501 elderly UK individuals of relatively low-Se status found that Se supplementation for 6 months lowered total plasma cholesterol. The Danish PRECISE (PREvention of Cancer by Intervention with Selenium) pilot study (ClinicalTrials.gov ID: NCT01819649) was a 5-year randomised, double-blinded, placebo-controlled trial with four groups (allocation ratio 1:1:1:1). Men and women aged 60-74 years (n 491) were randomised to 100 (n 124), 200 (n 122) or 300 (n 119) μg Se-enriched yeast or matching placebo-yeast tablets (n 126) daily for 5 years. A total of 468 participants continued the study for 6 months and 361 participants, equally distributed across treatment groups, continued for 5 years. Plasma samples were analysed for total and HDL-cholesterol and for total Se concentrations at baseline, 6 months and 5 years. The effect of different doses of Se supplementation on plasma lipid and Se concentrations was estimated by using linear mixed models. Plasma Se concentration increased significantly and dose-dependently in the intervention groups after 6 months and 5 years. Total cholesterol decreased significantly both in the intervention groups and in the placebo group after 6 months and 5 years, with small and nonsignificant differences in changes in plasma concentration of total cholesterol, HDL-cholesterol, non-HDL-cholesterol and total:HDL-cholesterol ratio between intervention and placebo groups. The effect of long-term supplementation with Se on plasma cholesterol concentrations or its sub-fractions did not differ significantly from placebo in this elderly population.

Spatial and temporal expression of zebrafish glutathione peroxidase 4 a and b genes during early embryo development

Antioxidant cellular mechanisms are essential for cell redox homeostasis during animal development and in adult life. Previous in situ hybridization analyses of antioxidant enzymes in zebrafish have indicated that they are ubiquitously expressed. However, spatial information about the protein distribution of these enzymes is not available. Zebrafish embryos are particularly suitable for this type of analysis due to their small size, transparency and fast development. The main objective of the present work was to analyze the spatial and temporal gene expression pattern of the two reported zebrafish glutathione peroxidase 4 (GPx4) genes during the first day of zebrafish embryo development. We found that the gpx4b gene shows maternal and zygotic gene expression in the embryo proper compared to gpx4a that showed zygotic gene expression in the periderm covering the yolk cell only. Following, we performed a GPx4 protein immunolocalization analysis during the first 24-h of development. The detection of this protein suggests that the antibody recognizes GPx4b in the embryo proper during the first 24 h of development and GPx4a at the periderm covering the yolk cell after 14-somite stage. Throughout early cleavages, GPx4 was located in blastomeres and was less abundant at the cleavage furrow. Later, from the 128-cell to 512-cell stages, GPx4 remained in the cytoplasm but gradually increased in the nuclei, beginning in marginal blastomeres and extending the nuclear localization to all blastomeres. During epiboly progression, GPx4b was found in blastoderm cells and was excluded from the yolk cell. After 24 h of development, GPx4b was present in the myotomes particularly in the slow muscle fibers, and was excluded from the myosepta. These results highlight the dynamics of the GPx4 localization pattern and suggest its potential participation in fundamental developmental processes.

T cell lipid peroxidation induces ferroptosis and prevents immunity to infection

Matsushita et al. investigated the role of the selenoenzyme glutathione peroxidae 4 (Gpx4) in T cell responses and found that loss of Gpx4 results in an intrinsic T cell developmental defect in the periphery, which leads to a failure to expand and protect from acute viral and parasitic infection.The defects were rescued with dietary supplementation of vitamin E. The Gp4^−/− T cells accumulate membrane lipid peroxides and undergo cell death by ferroptosis.

The selenoenzyme glutathione peroxidase 4 (Gpx4) is a major scavenger of phospholipid hydroperoxides. Although Gpx4 represents a key component of the reactive oxygen species-scavenging network, its relevance in the immune system is yet to be defined. Here, we investigated the importance of Gpx4 for physiological T cell responses by using T cell–specific Gpx4-deficient mice. Our results revealed that, despite normal thymic T cell development, CD8⁺ T cells from T^{ΔGpx4/ΔGpx4} mice had an intrinsic defect in maintaining homeostatic balance in the periphery. Moreover, both antigen-specific CD8⁺ and CD4⁺ T cells lacking Gpx4 failed to expand and to protect from acute lymphocytic choriomeningitis virus and Leishmania major parasite infections, which were rescued with diet supplementation of high dosage of vitamin E. Notably, depletion of the Gpx4 gene in the memory phase of viral infection did not affect T cell recall responses upon secondary infection. Ex vivo, Gpx4-deficient T cells rapidly accumulated membrane lipid peroxides and concomitantly underwent cell death driven by ferroptosis but not necroptosis. These studies unveil an essential role of Gpx4 for T cell immunity.

Characterization and structural analysis of human selenium-dependent glutathione peroxidase 4 mutant expressed in Escherichia coli

Glutathione peroxidase 4 (GPx4) is a monomeric selenium-dependent glutathione peroxidase highly expressed in mammalian cells, which can reduce phospholipid hydroperoxides. However, it has been difficult to express recombinant mammalian GPx4 in Escherichia coli because of the differences in the selenocysteine (Sec) incorporation machinery between eukaryotes and prokaryotes. In this study, an E. coli BL21(DE3)cys auxotrophic strain was used to express GPx4 mutants. We found that untargeted substitution of Cys-2, Cys-37, Cys-75, Cys-107, and Cys-148 with Sec led to loss of activity, suggesting that mutation of any of these Cys residues in GPx4 could result in a structural change. Additionally, we found that the catalytic activity of GPx4 mutants increased as the number of noncatalytic Sec residues decreased, indicating that the negative effects could be mitigated by replacing these Cys residues with Ser residues. A GPx4 mutant with all Cys residues converted to Ser exhibited a "Ping-Pong" mechanism and structure similar to that of native GPx4, indicating that it could act as a substitute for GPx4, when heterologously expressing the protein in E. coli. This research provides an important foundation for biosynthesis of selenium-dependent GPx4 mutants in E. coli.

Combined deficiency in glutathione peroxidase 4 and vitamin E causes multiorgan thrombus formation and early death in mice

RATIONALE

Growing evidence indicates that oxidative stress contributes markedly to endothelial dysfunction. The selenoenzyme glutathione peroxidase 4 (Gpx4) is an intracellular antioxidant enzyme important for the protection of membranes by its unique activity to reduce complex hydroperoxides in membrane bilayers and lipoprotein particles. Yet a role of Gpx4 in endothelial cell function has remained enigmatic.

OBJECTIVE

To investigate the role of Gpx4 ablation and subsequent lipid peroxidation in the vascular compartment in vivo.

METHODS AND RESULTS

Endothelium-specific deletion of Gpx4 had no obvious impact on normal vascular homeostasis, nor did it impair tumor-derived angiogenesis in mice maintained on a normal diet. In stark contrast, aortic explants from endothelium-specific Gpx4 knockout mice showed a markedly reduced number of endothelial branches in sprouting assays. To shed light onto this apparent discrepancy between the in vivo and ex vivo results, we depleted mice of a second antioxidant, vitamin E, which is normally absent under ex vivo conditions. Therefore, mice were fed a vitamin E-depleted diet for 6 weeks before endothelial deletion of Gpx4 was induced by 4-hydroxytamoxifen. Surprisingly, ≈80% of the knockout mice died. Histopathological analysis revealed detachment of endothelial cells from the basement membrane and endothelial cell death in multiple organs, which triggered thrombus formation. Thromboembolic events were the likely cause of various clinical pathologies, including heart failure, renal and splenic microinfarctions, and paraplegia.

CONCLUSIONS

Here, we show for the first time that in the absence of Gpx4, sufficient vitamin E supplementation is crucial for endothelial viability.

Selenium supplementation for the primary prevention of cardiovascular disease

BACKGROUND

Selenium is a key component of a number of selenoproteins which protect against oxidative stress and have the potential to prevent chronic diseases including cardiovascular disease (CVD). However, observational studies have shown inconsistent associations between selenium intake and CVD risk; in addition, there is concern around a possible increased risk of type 2 diabetes with high selenium exposure.

OBJECTIVES

To determine the effectiveness of selenium only supplementation for the primary prevention of CVD and examine the potential adverse effect of type 2 diabetes.

SEARCH METHODS

The following electronic databases were searched: the Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 10 of 12, October 2012) on The Cochrane Library; MEDLINE (Ovid) (1946 to week 2 October 2012); EMBASE Classic + EMBASE (Ovid) (1947 to 2012 Week 42); CINAHL (EBSCO) (to 24 October 2012); ISI Web of Science (1970 to 24 October 2012); PsycINFO (Ovid) (1806 to week 3 October 2012); Database of Abstracts of Reviews of Effects (DARE), Health Technology Assessment Database and Health Economics Evaluations Database (Issue 4 of 4, October 2012) on The Cochrane Library. Trial registers and reference lists of reviews and articles were searched and experts in the field were approached. No language restrictions were applied.

SELECTION CRITERIA

Randomised controlled trials on the effects of selenium only supplementation on major CVD end-points, mortality, changes in CVD risk factors, and type 2 diabetes were included both in adults of all ages from the general population and in those at high risk of CVD. Trials were only considered where the comparison group was placebo or no intervention. Only studies with at least three months follow-up were included in the meta-analyses, shorter term studies were dealt with descriptively.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. Study authors were contacted for additional information.

MAIN RESULTS

Twelve trials (seven with duration of at least three months) met the inclusion criteria, with 19,715 participants randomised. The two largest trials that were conducted in the USA (SELECT and NPC) reported clinical events. There were no statistically significant effects of selenium supplementation on all cause mortality (RR 0.97, 95% CI 0.88 to 1.08), CVD mortality (RR 0.97, 95% CI 0.79 to 1.2), non-fatal CVD events (RR 0.96, 95% CI 0.89 to 1.04) or all CVD events (fatal and non-fatal) (RR 1.03, 95% CI 0.95 to 1.11). There was a small increased risk of type 2 diabetes with selenium supplementation but this did not reach statistical significance (RR 1.06, 95% CI 0.97 to 1.15). Other adverse effects that increased with selenium supplementation, as reported in the SELECT trial, included alopecia (RR 1.28, 95% CI 1.01 to 1.62) and dermatitis grade 1 to 2 (RR 1.17, 95% CI 1.0 to 1.35). Selenium supplementation reduced total cholesterol but this did not reach statistical significance (WMD - 0.11 mmol/L, 95% CI - 0.3 to 0.07). Mean high density lipoprotein (HDL) levels were unchanged. There was a statistically significant reduction in non-HDL cholesterol (WMD - 0.2 mmol/L, 95% CI - 0.41 to 0.00) in one trial of varying selenium dosage. None of the longer term trials examined effects on blood pressure. Overall, the included studies were regarded as at low risk of bias.

AUTHORS' CONCLUSIONS

The limited trial evidence that is available to date does not support the use of selenium supplements in the primary prevention of CVD.

Targeted disruption of glutathione peroxidase 4 in mouse skin epithelial cells impairs postnatal hair follicle morphogenesis that is partially rescued through inhibition of COX-2

Selenoproteins are essential molecules for the mammalian antioxidant network. We previously demonstrated that targeted loss of all selenoproteins in mouse epidermis disrupted skin and hair development and caused premature death. In the current study we targeted specific selenoproteins for epidermal deletion to determine whether similar phenotypes developed. Keratinocyte-specific knockout mice lacking either the glutathione peroxidase 4 (GPx4) or thioredoxin reductase 1 (TR1) gene were generated by cre-lox technology using K14-cre. TR1 knockout mice had a normal phenotype in resting skin while GPx4 loss in epidermis caused epidermal hyperplasia, dermal inflammatory infiltrate, dysmorphic hair follicles and alopecia in perinatal mice. Unlike epidermal ablation of all selenoproteins, mice ablated for GPx4 recovered after 5 weeks and had a normal lifespan. GPx1 and TR1 were upregulated in the skin and keratinocytes of GPx4 knockout mice. GPx4 deletion reduces keratinocyte adhesion in culture and increases lipid peroxidation and COX-2 levels in cultured keratinocytes and whole skin. Feeding a COX-2 inhibitor to nursing mothers partially prevents development of the abnormal skin phenotype in knockout pups. These data link the activity of cutaneous GPx4 to the regulation of COX-2 and hair follicle morphogenesis and provide insight into the function of individual selenoprotein activity in maintaining cutaneous homeostasis.

Detection and characterization of cholesteryl ester hydroperoxides in oxidized LDL and oxidized HDL by use of an Orbitrap mass spectrometer

Oxidation of cholesteryl esters in lipoproteins by reactive oxygen species yields cholesteryl ester hydroperoxides (CEOOH). In this study, we developed a novel method for identification and characterization of CEOOH molecules in human lipoproteins by use of reversed-phase liquid chromatography with an hybrid linear ion trap-Orbitrap mass spectrometer (LC-LTQ Orbitrap). Electrospray ionization tandem mass spectrometric analysis was performed in both positive-ion and negative-ion modes. Identification of CEOOH molecules was completed by use of high-mass-accuracy (MA) mass spectrometric data obtained by using the spectrometer in Fourier-transform (FT) mode. Native low-density lipoproteins (nLDL) and native high-density lipoproteins (nHDL) from a healthy donor were oxidized by CuSO(4), furnishing oxidized LDL (oxLDL) and oxidized HDL (oxHDL). No CEOOH molecules were detected in the nLDL and the nHDL, whereas six CEOOH molecules were detected in the oxLDL and the oxHDL. In positive-ion mode, CEOOH was detected as [M + NH(4)](+) and [M + Na](+) ions. In negative-ion mode, CEOOH was detected as [M + CH(3)COO](-) ions. CEOOH were more easily ionized in positive-ion mode than in negative-ion mode. The LC-LTQ Orbitrap method was applied to human plasma and six species of CEOOH were detected. The limit of detection was 0.1 pmol (S/N = 5:1) for synthesized CEOOH.

Selenium supplementation for the primary prevention of cardiovascular disease

This is the protocol for a review and there is no abstract. The objectives are as follows: The primary objective is to determine the effectiveness of selenium only supplementation for the primary prevention of CVD. We will also determine potential adverse effects of selenium only supplementation on major CVD risk factors, such as blood pressure, blood lipids and type 2 diabetes. Results will be stratified by baseline selenium status and country where possible, as well as by selenium dosage.

The Roles of Glutathione Peroxidases during Embryo Development

Embryo development relies on the complex interplay of the basic cellular processes including proliferation, differentiation, and apoptotic cell death. Precise regulation of these events is the basis for the establishment of embryonic structures and the organ development. Beginning with fertilization of the oocyte until delivery the developing embryo encounters changing environmental conditions such as varying levels of oxygen, which can give rise to reactive oxygen species (ROS). These challenges are met by the embryo with metabolic adaptations and by an array of anti-oxidative mechanisms. ROS can be deleterious by modifying biological molecules including lipids, proteins, and nucleic acids and may induce abnormal development or even embryonic lethality. On the other hand ROS are vital players of various signaling cascades that affect the balance between cell growth, differentiation, and death. An imbalance or dysregulation of these biological processes may generate cells with abnormal growth and is therefore potentially teratogenic and tumorigenic. Thus, a precise balance between processes generating ROS and those decomposing ROS is critical for normal embryo development. One tier of the cellular protective system against ROS constitutes the family of selenium-dependent glutathione peroxidases (GPx). These enzymes reduce hydroperoxides to the corresponding alcohols at the expense of reduced glutathione. Of special interest within this protein family is the moonlighting enzyme glutathione peroxidase 4 (Gpx4). This enzyme is a scavenger of lipophilic hydroperoxides on one hand, but on the other hand can be transformed into an enzymatically inactive cellular structural component. GPx4 deficiency - in contrast to all other GPx family members - leads to abnormal embryo development and finally produces a lethal phenotype in mice. This review is aimed at summarizing the current knowledge on GPx isoforms during embryo development and tumor development with an emphasis on GPx4.

Defining the immunoreactive epitope for the monoclonal anti-human glutathione peroxidase-4 antibody anti-hGPx4 Mab63-1

Glutathione peroxidases (GPx) form a heterogeneous enzyme family and GPx4-isoforms have been implicated in anti-oxidative defense, brain development, neuroinjury and sperm maturation. In humans seven GPx isoforms (GPx1-GPx7) can be separated. To selectively quantify the expression of GPx4-isoforms we have raised a monoclonal antibody (anti-hGPx4 Mab63-1) against the pure recombinant Sec46Cys mutant of human cytosolic GPx4 and used it for immunoblotting, immunoprecipitation and immunohistochemistry. The antibody recognizes human GPx4, its mouse ortholog but neither reacted with rat GPx4 nor other human GPx-isoforms. Sequence alignment of human and rat GPx4 proteins indicated three different amino acids (S18, F35, K99 in humans, A18, C35, R99 in rats) and a S18A exchange in the human enzyme completely abolished immunoreactivity. To further characterize the immunological epitope we synthesized a set of 12-mer peptides flanking S18* of human GPx4 and found that the sequence SMHEFS*AKDIDG exhibited strongest immunoreactivity. Substitution analysis and peptide length variation narrowed down the essential epitope to FS*AKDI and indicated that most mutations in this region strongly impaired immunoreactivity. In silico blast searches of public protein databases failed to identify proteins with potential immunoreactivity suggesting that the antibody exhibits a high specificity for human and mouse GPx4 and may not cross-react with unrelated proteins.

Delineating the role of glutathione peroxidase 4 in protecting cells against lipid hydroperoxide damage and in Alzheimer's disease

Numerous studies characterizing the function of glutathione peroxidase 4 (GPx4) have demonstrated that this selenoenzyme is protective against oxidative stress. Herein, we characterized the function of this protein by targeting GPx4 downregulation using RNA interference. Partial knockdown of GPx4 levels resulted in growth retardation and morphological changes. Surprisingly, GPx4 knockdown cells showed virtually unchanged levels of intracellular ROS, yet highly increased levels of oxidized lipid by-products. GPx1, another glutathione peroxidase and a major cellular peroxide scavenging enzyme, did not rescue GPx4-deficient cells and did not reduce lipid peroxide levels. The data established an essential role of GPx4 in protecting cells against lipid hydroperoxide damage, yet a limited role as a general antioxidant enzyme. As oxidized lipid hydroperoxides are a characteristic of neurodegenerative diseases, we analyzed brain tissues of mice suffering from a model of Alzheimer's disease and found that oxidized lipid by-products were enriched, and expression of both GPx4 and guanine-rich sequence-binding factor, which is known to control GPx4 synthesis, was downregulated. Brain tissue from an Alzheimer's diseased human also manifested enhanced levels of one of the oxidized lipid by-products, 4-hydroxynonenal. These data suggest a role of GPx4 in neurodegenerative diseases through its function in removal of lipid hydroperoxides.

Multiple actions of high-density lipoprotein

PURPOSE OF REVIEW

The most accepted property of high-density lipoprotein is reverse cholesterol transport. However, other beneficial actions may contribute to the antiatherogenic role of high-density lipoprotein. This review addresses the action of high-density lipoprotein beyond reverse cholesterol transport.

RECENT FINDINGS

High-density lipoprotein cholesterol levels are inversely associated with coronary heart disease and other forms of vascular disease. Apart from transferring excess cholesterol to the liver, high-density lipoprotein exhibits favorable effects on oxidation, inflammation, thrombosis and endothelial function. Some of these actions are at least in part attributed to high-density lipoprotein-associated enzymes, such as paraoxonase and platelet-activating factor acetylhydrolase. However, high-density lipoprotein can become dysfunctional and proatherogenic under certain circumstances.

SUMMARY

Current data suggest that high-density lipoprotein possesses various properties beyond reverse cholesterol transport. However, many issues on the exact role of high-density lipoprotein remain unknown. Future research is needed.

Molecular biology of glutathione peroxidase 4: from genomic structure to developmental expression and neural function

Selenoproteins have been recognized as modulators of brain function and signaling. Phospholipid hydroperoxide glutathione peroxidase (GPx4/PHGPx) is a unique member of the selenium-dependent glutathione peroxidases in mammals with a pivotal role in brain development and function. GPx4 exists as a cytosolic, mitochondrial, and nuclear isoform derived from a single gene. In mice, the GPx4 gene is located on chromosome 10 in close proximity to a functional retrotransposome that is expressed under the control of captured regulatory elements. Elucidation of crystallographic data uncovered structural peculiarities of GPx4 that provide the molecular basis for its unique enzymatic properties and substrate specificity. Monomeric GPx4 is multifunctional: it acts as a reducing enzyme of peroxidized phospholipids and thiols and as a structural protein. Transcriptional regulation of the different GPx4 isoforms requires several isoform-specific cis-regulatory sequences and trans-activating factors. Cytosolic and mitochondrial GPx4 are the major isoforms exclusively expressed by neurons in the developing brain. In stark contrast, following brain trauma, GPx4 is specifically upregulated in non-neuronal cells, i.e., reactive astrocytes. Molecular approaches to genetic modification in mice have revealed an essential and isoform-specific function for GPx4 in development and disease. Here we review recent findings on GPx4 with emphasis on its molecular structure and function and consider potential mechanisms that underlie neural development and neuropathological conditions.

The roles of selenium and mercury in the pathogenesis of viral cardiomyopathy

Research on the pathogenesis of nonischemic dilated cardiomyopathy (DCM) has largely been focused on the role of viral pathogens and altered immunity. Trace elements have only rarely been considered; however, clinical observations that trace elements influence cardiovascular disease have been made in populations with extreme dietary deficiency or occupational exposure. Recently, animal models of DCM have been used to explore interactions among trace elements, viral pathogens, and the immune system. Discovery of interactions of trace elements with causes for DCM has heightened awareness of potential contributions of environmental variables to DCM pathogenesis. This article reviews the present knowledge regarding trace elements, in particular selenium and mercury, in the pathogenesis of viral and immune-mediated DCM. Based on recent studies, the authors propose a novel paradigm for the pathogenesis of viral DCM that incorporates trace element imbalance and its interactions with the cellular physiology of viral-induced cardiomyocyte dysfunction.

Role for glutathione peroxidase-4 in brain development and neuronal apoptosis: specific induction of enzyme expression in reactive astrocytes following brain injury

Glutathione peroxidase-4 (GPx4) is a multifunctional selenoprotein expressed as mitochondrial, cytosolic, or nuclear isoforms. As a catalytically active enzyme it has been implicated in antioxidative defense, but during sperm development it functions as a structural protein. GPx4 null mice die in utero at midgestation and knockdown of GPx4 during embryogenesis disturbs brain development. To explore the cerebral function of GPx4 we profiled cell-specific enzyme expression at various stages of perinatal brain maturation and investigated its regulation following brain injury by immunohistochemistry, in situ hybridization, and quantitative RT-PCR. Large amounts of GPx4 mRNA were detected in all neuronal layers during perinatal brain development but expression became restricted during postnatal maturation. In adult brain mitochondrial and cytosolic GPx4 isoforms were detected in neurons of cerebral cortex, hippocampus, and cerebellum whereas glial cells were devoid of GPx4. Following selective brain injury expression of the enzyme was upregulated in reactive astrocytes of lesioned areas and deafferented regions but not in neurons. Selective knockdown of GPx4 by small interfering RNA induced depletion of phosphatidylinositol-(4,5)-bisphosphate in the neuronal plasma membrane and subsequently apoptosis as indicated by caspase-3 activation. We hypothesize that astrocytic upregulation of GPx4 in response to injury is part of a protective cascade counteracting further cell damage.

Substrates of the methionine sulfoxide reductase system and their physiological relevance

Posttranslational modifications can change a protein's structure, function, and solubility. One specific modification caused by reactive oxygen species is the oxidation of the sulfur atom in the methionine (Met) side chain. This modified amino acid is denoted as methionine sulfoxide (MetO). MetOs in proteins are of considerable interest as they are involved in early posttranslational modification events. Thus, various organisms produce specific enzymes that can reverse these modifications. MetO reductases, known collectively as the methionine sulfoxide reductase (Msr) system, are the only known enzymes that can reduce MetOs. The current research field of Met redox cycles is consumed with elucidating its role in regulation, redox homeostasis, prevention of irreversible modifications, pathogenesis, and the aging process. Substrates of the Msr system can be loosely classified by the overall effect of the MetO on the protein. Regulated substrates utilize Met as a molecular switch to modulate activation; scavenging substrates use Mets to detoxify oxidants and protect important regions of the protein; and modified substrates are altered by Met oxidation resulting in various changes in their properties, including function, activity, structure, and degradation resistance.

Functionally defective high-density lipoprotein: a new therapeutic target at the crossroads of dyslipidemia, inflammation, and atherosclerosis

High-density lipoproteins (HDL) possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, and anti-oxidative and anti-inflammatory activities. Plasma HDL particles are highly heterogeneous in physicochemical properties, metabolism, and biological activity. Within the circulating HDL particle population, small, dense HDL particles display elevated cellular cholesterol efflux capacity, afford potent protection of atherogenic low-density lipoprotein against oxidative stress and attenuate inflammation. The antiatherogenic properties of HDL can, however be compromised in metabolic diseases associated with accelerated atherosclerosis. Indeed, metabolic syndrome and type 2 diabetes are characterized not only by elevated cardiovascular risk and by low HDL-cholesterol (HDL-C) levels but also by defective HDL function. Functional HDL deficiency is intimately associated with alterations in intravascular HDL metabolism and structure. Indeed, formation of HDL particles with attenuated antiatherogenic activity is mechanistically related to core lipid enrichment in triglycerides and cholesteryl ester depletion, altered apolipoprotein A-I (apoA-I) conformation, replacement of apoA-I by serum amyloid A, and covalent modification of HDL protein components by oxidation and glycation. Deficient HDL function and subnormal HDL-C levels may act synergistically to accelerate atherosclerosis in metabolic disease. Therapeutic normalization of attenuated antiatherogenic HDL function in terms of both particle number and quality of HDL particles is the target of innovative pharmacological approaches to HDL raising, including inhibition of cholesteryl ester transfer protein, enhanced lipidation of apoA-I with nicotinic acid and infusion of reconstituted HDL or apoA-I mimetics. A preferential increase in circulating concentrations of HDL particles possessing normalized antiatherogenic activity is therefore a promising therapeutic strategy for the treatment of common metabolic diseases featuring dyslipidemia, inflammation, and premature atherosclerosis.

The role of phospholipid hydroperoxide glutathione peroxidase isoforms in murine embryogenesis

Phospholipid hydroperoxide glutathione peroxidase (GPx4) is a selenocysteine-containing enzyme, and three different isoforms (cytosolic, mitochondrial, and nuclear) originate from the GPx4 gene. Homozygous GPx4-deficient mice die in utero at midgestation, since they fail to initiate gastrulation and do not develop embryonic cavities. To investigate the biological basis for embryonic lethality, we first explored expression of the GPx4 in adult murine brain and found expression of the protein in cerebral neurons. Next, we profiled mRNA expression during the time course of embryogenesis (embryonic days 6.5-17.5 (E6.5-17.5)) and detected mitochondrial and cytosolic mRNA species at high concentrations. In contrast, the nuclear isoform was only expressed in small amounts. Cytosolic GPx4 mRNA was present at constant levels (about 100 copies per 1000 copies of glyceraldehyde-3-phosphate dehydrogenase mRNA), whereas nuclear and mitochondrial isoforms were down-regulated between E14.5 and E17.5. In situ hybridization indicated expression of GPx4 isoforms in all developing germ layers during gastrulation and in the somite stage in the developing central nervous system and in the heart. When we silenced expression of GPx4 isoforms during in vitro embryogenesis using short interfering RNA technology, we observed that knockdown of mitochondrial GPx4 strongly impaired segmentation of rhombomeres 5 and 6 during hindbrain development and induced cerebral apoptosis. In contrast, silencing expression of the nuclear isoform led to retardations in atrium formation. Taken together, our data indicate specific expression of GPx4 isoforms in embryonic brain and heart and strongly suggest a role of this enzyme in organogenesis. These findings may explain in part intrauterine lethality of GPx4 knock-out mice.

Is there a future for antioxidants in atherogenesis?

Antioxidants, preferentially those of dietary origin, have for a long time been considered to help against diseases that are presumably aggravated by oxidative stress, such as cardiovascular diseases, cancer, and neurodegenerative disorders. The outcome of clinical trials undertaken to corroborate this hypothesis, however, remained largely inconclusive. Evidence is now emerging that some dietary "antioxidants" influence signaling pathways and the expression of genes relevant in atherosclerosis by mechanisms other than antioxidative ones. By concrete examples we show that (1) vitamin E has gene regulatory functions which might be more important than acting as an antioxidant in vivo, (2) selenium itself is not an antioxidant at all, and even not in general when incorporated into glutathione peroxidases, and (3) a moderate oxidative stress is beneficial rather than detrimental since it can induce defense mechanisms counteracting xenobiotic and oxidative stress. Thus, there is only a future for antioxidants in the prevention of any disease if their real mechanism of action is considered and suitable read-outs and biomarkers are established.

Omega-3 fatty acids and selenium as coronary heart disease risk modifying factors in Asian Indian and Chinese males

OBJECTIVE

Asian Indian men are reported to have a higher incidence of coronary heart disease than men of other ethnic groups worldwide. Among the many hypotheses, one possible risk factor may be related to their dietary habits. This study estimated the plasma concentrations of fatty acids, antioxidant vitamins, and selenium in Indians and Chinese of Singapore.

METHODS

The study population consisted of 145 Indian men and 147 Chinese men ages 26 to 79 y from a cross-sectional survey, the National University of Singapore Heart Study.

RESULTS

Our findings indicated that Indians had lower plasma concentrations of docosahexanoic acid (3.07% versus 3.54%, P < 0.001), alpha-linolenic acid (0.48% versus 0.57%, P < 0.001), and total omega-3 fatty acids (4.71% versus 5.27%, P < 0.001) than did the Chinese. Arachidonic acid was higher in Indians (4.83%) than in the Chinese (4.51%, P = 0.007). The ratio of omega-3 acid to omega-6 fatty acid was also lower in Indians (0.15) than in the Chinese (0.16, P = 0.007). There were no significant differences in the concentrations of monounsaturated fatty acids, but saturated fatty acids were higher in Indians (39.17%) than in the Chinese (38.28%, P < 0.001). Analysis of vitamins A, C, and E showed no significant differences between Indians (0.67, 5.72, and 13.04 mg/L, respectively) and Chinese (0.68, 6.48, and 12.71 mg/L, respectively); however, serum concentration of selenium in Indians (117.49 microg/L) was significantly lower than in the Chinese (126.72 microg/L, P < 0.001).

CONCLUSION

The results suggest that lower plasma concentrations of omega-3 fatty acids and selenium and higher concentrations of arachidonic acid and saturated fatty acids in Indians may reflect lower intakes of marine foods and, as a consequence, higher susceptibility to coronary heart disease.

Human macrophages limit oxidation products in low density lipoprotein

This study tested the hypothesis that human macrophages have the ability to modify oxidation products in LDL and oxidized LDL (oxLDL) via a cellular antioxidant defence system. While many studies have focused on macrophage LDL oxidation in atherosclerosis development, less attention has been given to the cellular antioxidant capacity of these cells.

Compared to cell-free controls (6.2 ± 0.7 nmol/mg LDL), macrophages reduced TBARS to 4.42 ± 0.4 nmol/mg LDL after 24 h incubation with LDL (P = 0.022). After 2 h incubation with oxLDL, TBARS were 3.69 ± 0.5 nmol/mg LDL in cell-free media, and 2.48 ± 0.9 nmol/mg LDL in the presence of macrophages (P = 0.034). A reduction of lipid peroxides in LDL (33.7 ± 6.6 nmol/mg LDL) was found in the presence of cells after 24 h compared to cell-free incubation (105.0 ± 14.1 nmol/mg LDL) (P = 0.005). The levels of lipid peroxides in oxLDL were 137.9 ± 59.9 nmol/mg LDL and in cell-free media 242 ± 60.0 nmol/mg LDL (P = 0.012). Similar results were obtained for hydrogen peroxide. Reactive oxygen species were detected in LDL, acetylated LDL, and oxLDL by isoluminol-enhanced chemiluminescence (CL). Interestingly, oxLDL alone gives a high CL signal. Macrophages reduced the CL response in oxLDL by 45% (P = 0.0016). The increased levels of glutathione in oxLDL-treated macrophages were accompanied by enhanced catalase and glutathione peroxidase activities.

Our results suggest that macrophages respond to oxidative stress by endogenous antioxidant activity, which is sufficient to decrease reactive oxygen species both in LDL and oxLDL. This may suggest that the antioxidant activity is insufficient during atherosclerosis development. Thus, macrophages may play a dual role in atherogenesis, i.e. both by promoting and limiting LDL-oxidation.

Identification and analysis of products formed from phospholipids in the free radical oxidation of human low density lipoproteins

Phospholipids reside in the surface layer of LDLs and constitute approximately 20-25% of the particle by weight. We report a study of the primary products generated from the most abundant molecular species of phosphatidylcholines present in LDL during in vitro free radical oxidations. The 13-hydroperoxides of 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (PLPC) and 1-stearoyl-2-linoleoyl-sn-glycero-phosphocholine (SLPC) and the 15-hydroperoxides of 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (PAPC) and 1-stearoyl-2-arachidonoyl-sn-glycero-phosphocholine (SAPC) were found to increase in a time-dependent manner and in significant amounts even in the presence of alpha-tocopherol. Phospholipid alcohols also formed during the course of the oxidations. Early in the LDL oxidations, while alpha-tocopherol was still present, the thermodynamically favored trans,trans products of PLPC and SLPC were found to form in significantly larger quantities than those formed from cholesteryl linoleate. Additionally, quantities of PAPC 11-hydroperoxide (11-OOH) decreased over time relative to PAPC 15-OOH, even while alpha-tocopherol was still present in the oxidation, presumably as a result of further oxidation of PAPC 11-OOH to form cyclic peroxide oxidation products. These results suggest that alpha-tocopherol is more closely associated with the inner cholesteryl ester-rich hydrophobic core of an LDL particle and is not as effective as an antioxidant in the outer phospholipid layer as it is in the lipid core.

Formation of methionine sulfoxide-containing specific forms of oxidized high-density lipoproteins

Atherosclerosis is characterized by the accumulation of both lipoprotein-derived lipids and inflammatory cells in the affected vascular wall that results in a state of heightened oxidative stress and that is reflected by the accumulation of oxidized lipoproteins. Circulating oxidized low-density lipoprotein (oxLDL) is used as a surrogate marker for coronary artery disease, although the 'escape' of oxLDL from the vessel wall is hindered by the large size of this lipoprotein and its specific retention by the extracellular matrix. Also, the oxidation of lipoproteins in human atherosclerotic lesions is not limited to LDL. In fact, the lipids of all classes of lipoproteins are oxidized to a comparable extent. Examining the fate of lipid hydroperoxides, the primary lipid peroxidation products, in high-density lipoproteins (HDL) undergoing oxidation, revealed that they become reduced to the corresponding alcohols by specific Met residues of apolipoprotein A-I (apoA-I) and apoA-II. As a consequence, Met residues in apoA-I and apoA-II become selectively and consecutively oxidized to their respective Met sulfoxide (MetO) forms that can be separated by HPLC. This review describes the characterization of specifically oxidized HDL with an emphasis on MetO formation, the structural and functional consequences of such oxidation, and the potential utility of specifically oxidized HDL as a surrogate marker of atherosclerosis.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Functional characterization of cis- and trans-regulatory elements involved in expression of phospholipid hydroperoxide glutathione peroxidase

Phospholipid hydroperoxide glutathione peroxidase (phGPx) is a member of the seleno glutathione peroxidase family that is comprised of five selenoproteins capable of reducing hydroperoxy lipids to the corresponding alcohols. The enzyme has been implicated in antioxidative defense, but its high expression level in testicular tissue suggests a more specific function during sperm maturation. The phGPx is encoded for by a joint sperm nucleus/phGPx gene (sn/phGPx) and can be expressed as a mitochondrial or cytosolic isoform. Although sn/phGPx genes have been cloned from various mammalian species expression regulation of the enzyme has not been studied in detail. We investigated the 5'-flanking region of the murine sn/phGPx gene and observed basic promoter activity in a 200 bp region localized immediately upstream of the translational initiation site of the cytosolic isoform (3'-ATG). DNase protection assays indicated the presence of five distinct protein-binding regions and electrophoretic mobility shift assays and supershift experiments revealed binding of stimulating protein 1 (SP1), nuclear factor Y (NF-Y) and members of the SMAD family. Site-directed mutagenesis of the consensus binding sequences abolished in vitro transcription factor binding. Expression of reporter genes was most effectively impaired when SP1/SP3 and NF-Y binding site-deficient constructs were tested. Chromatin immunoprecipitation suggested the in vivo relevance of these transcription factors. Our data indicate that the basic phGPx promoter constitutes a 200 bp oligonucleotide, which is localized immediately upstream of the 3'-ATG and involves functional SP1/SP3, NF-Y and SMAD binding sites. The corresponding trans-regulatory proteins may contribute to differential expression regulation of the mitochondrial and cytosolic phGPx isoforms.

Cholesteryl ester oxidation products in atherosclerosis

Lipid oxidation products are formed at sites of increased oxidant stress and have been shown to accumulate in atherosclerotic lesions. Although recent studies have focused on the formation and metabolism of oxidized lipids, very little is known about their biological activities and possible (patho)physiological functions. Oxidation of cholesteryl esters containing unsaturated fatty acids leads to the formation of hydroperoxides that are either reduced to alcohols or degrade into biologically active "core-aldehydes". In this review, the mechanisms of formation and metabolic fate of oxidized cholesteryl esters, their occurrence, as well as possible biological activities are discussed. Based on the current knowledge, cholesteryl ester oxidation leads to the formation of biologically active substances, which could actively contribute to the progression of atherosclerotic lesions and their resulting complications.

Ascorbate does not act as a pro-oxidant towards lipids and proteins in human plasma exposed to redox-active transition metal ions and hydrogen peroxide

The combination of ascorbate, transition metal ions, and hydrogen peroxide (H(2)O(2)) is an efficient hydroxyl radical generating system called "the Udenfriend system." Although the pro-oxidant role of ascorbate in this system has been well characterized in vitro, it is uncertain whether ascorbate also acts as a pro-oxidant under physiological conditions. To address this question, human plasma, used as a representative biological fluid, was either depleted of endogenous ascorbate with ascorbate oxidase, left untreated, or supplemented with 25 microM-1 mM ascorbate. Subsequently, the plasma samples were incubated at 37 degrees C with 50 microM-1 mM iron (from ferrous ammonium sulfate), 60 or 100 microM copper (from cupric sulfate), and/or 200 microM or 1 mM H(2)O(2). Although endogenous and added ascorbate was depleted rapidly in the presence of transition metal ions and H(2)O(2), no cholesterol ester hydroperoxides or malondialdehyde were formed, i.e., ascorbate protected against, rather than promoted, lipid peroxidation. Conversely, depletion of endogenous ascorbate was sufficient to cause lipid peroxidation, the rate and extent of which were enhanced by the addition of metal ions but not H(2)O(2). Ascorbate also did not enhance protein oxidation in plasma exposed to metal ions and H(2)O(2), as assessed by protein carbonyl formation and depletion of reduced thiols. Interestingly, neither the rate nor the extent of endogenous alpha-tocopherol oxidation in plasma was affected by any of the treatments. Our data show that even in the presence of redox-active iron or copper and H(2)O(2), ascorbate acts as an antioxidant that prevents lipid peroxidation and does not promote protein oxidation in human plasma in vitro.

A comparative study on the hydroperoxide and thiol specificity of the glutathione peroxidase family and selenoprotein P

Glutathione peroxidase catalyzes the reduction of hydrogen peroxide and organic hydroperoxide by glutathione and functions in the protection of cells against oxidative damage. Glutathione peroxidase exists in several forms that differ in their primary structure and localization. We have also shown that selenoprotein P exhibits a glutathione peroxidase-like activity (Saito, Y., Hayashi, T., Tanaka, A., Watanabe, Y., Suzuki, M., Saito, E., and Takahashi, K. (1999) J. Biol. Chem. 274, 2866-2871). To understand the physiological significance of the diversity among these enzymes, a comparative study on the peroxide substrate specificity of three types of ubiquitous glutathione peroxidase (cellular glutathione peroxidase, phospholipid hydroperoxide glutathione peroxidase, and extracellular glutathione peroxidase) and of selenoprotein P purified from human origins was done. The specific activities and kinetic parameters against two hydroperoxides (hydrogen peroxide and phosphatidylcholine hydroperoxide) were determined. We next examined the thiol specificity and found that thioredoxin is the preferred electron donor for selenoprotein P. These four enzymes exhibit different peroxide and thiol specificities and collaborate to protect biological molecules from oxidative stress both inside and outside the cells.

Regulation of enzymatic lipid peroxidation: the interplay of peroxidizing and peroxide reducing enzymes

For a long time lipid peroxidation has only been considered a deleterious process leading to disruption of biomembranes and thus, to cellular dysfunction. However, when restricted to a certain cellular compartment and tightly regulated, lipid peroxidation may have beneficial effects. Early on during evolution of living organisms special lipid peroxidizing enzymes, called lipoxygenases, appeared and they have been conserved during phylogenesis of plants and animals. In fact, a diverse family of lipoxygenase isoforms has evolved starting from a putative ancient precursor. As with other enzymes, lipoxygenases are regulated on various levels of gene expression and there are endogenous antagonists controlling their cellular activity. Among the currently known mammalian lipoxygenase isoforms only 12/15-lipoxygenases are capable of directly oxygenating ester lipids even when they are bound to membranes and lipoproteins. Thus, these enzymes represent the pro-oxidative part in the cellular metabolism of complex hydroperoxy ester lipids. Its metabolic counterplayer, representing the antioxidative part, appears to be the phospholipid hydroperoxide glutathione peroxidase. This enzyme is unique among glutathione peroxidases because of its capability of reducing ester lipid hydroperoxides. Thus, 12/15-lipoxygenase and phospholipid hydroperoxide glutathione peroxidase constitute a pair of antagonizing enzymes in the metabolism of hydroperoxy ester lipids, and a balanced regulation of the two proteins appears to be of major cell physiological importance. This review is aimed at summarizing the recent developments in the enzymology and molecular biology of 12/15-lipoxygenase and phospholipid hydroperoxide glutathione peroxidase, with emphasis on cytokine-dependent regulation and their regulatory interplay.

The argument for increasing selenium intake

The essential trace mineral, Se, is of fundamental importance to human health. As a constituent of selenoproteins it plays both structural and enzymic roles, in the latter context being best known as an antioxidant and catalyst for the production of active thyroid hormone. While Se-deficiency diseases have been recognised for some time, evidence is mounting that less-overt deficiency can also cause adverse health effects and furthermore, that supra-nutritional levels of Se may give additional protection from disease. In the context of these effects, low or diminishing Se status in some parts of the world, notably in some European countries such as the UK, is giving cause for concern. While deficiency has an adverse effect on immunocompetence, Se supplementation appears to enhance the immune response. Se appears to be a key nutrient in counteracting certain viral infections; thus, in a Se-deficient host the benign coxsackie virus becomes virulent, causing heart damage, the influenza virus causes more serious lung pathology and HIV infection progresses more rapidly to AIDS. Long recognised as essential for successful animal reproduction, Se is required for human sperm maturation and sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking Se to cardiovascular disease risk, although other conditions involving oxidative stress and inflammation have shown some association with Se status. There is growing evidence that higher Se intakes are associated with reduced cancer risk. While persuasive evidence already exists to suggest that additional Se would be beneficial in some health conditions, results from intervention trials underway or planned have the potential to reinforce or refute the argument for increasing Se intake.

Discovery of a functional retrotransposon of the murine phospholipid hydroperoxide glutathione peroxidase: chromosomal localization and tissue-specific expression pattern

Phospholipid hydroperoxide glutathione peroxidase (PHGPx), a selenoprotein capable of reducing toxic hydroperoxy ester lipids, has been implicated in antioxidative defense and spermatogenesis. Screening a murine genomic library, we isolated two recombinants (pseudogenes 1 and 2) containing retrotransposons for this enzyme. On comparison with the paralogous cDNA, pseudogene 1 contained only two silent nucleotide exchanges, and the 3'-untranslated region (3'-UTR) carrying the functionally important selenocysteine insertion sequence was free of mutations. This retrotransposon was found in various mouse strains and could be mapped to the region B2-B3 of chromosome 10. In vitro studies indicated significant promoter activity in the 5'-flanking region of pseudogene 1, and we observed a tissuespecific expression of this retrotransposon. In the submandibular gland. Most PHGPx transcripts originated from pseudogene 1. In contrast, pseudogene 2, containing numerous mutations in all parts of the retrotransposon, was not expressed in any tissue. It was mapped to region E3-E4 of chromosome 17, and we did not detect any promoter activity in its 5'-flanking region. These data indicate the existence of two retrotransposed PHGPx pseudogenes, one of which encodes a functional enzyme. This retrotransposon belongs to the rare group of pseudogenes that are tissue-specifically expressed under the control of captured regulatory elements, and it constitutes an example of evolutionarily acquired redundancy in gene expression. The results are important for the design of future knockout strategies aimed at investigating the biological role of this enzyme.

Unsaturated fatty acids selectively induce an inflammatory environment in human endothelial cells

BACKGROUND

Activation of the vascular endothelium by dietary fatty acids may be among the most critical early events in the development of atherosclerosis. However, the specific effects of fatty acids on inflammatory responses in endothelial cells are not fully understood.

OBJECTIVE

The present study focused on the induction of inflammatory genes in human endothelial cells exposed to individual dietary fatty acids. Because of the significance of nuclear factor kappaB (NF-kappaB) and activator protein 1 (AP-1) in the regulation of inflammatory gene expression, we also determined the effects of fatty acids on NF-kappaB and AP-1 transcriptional activation.

DESIGN

Human umbilical vein endothelial cells were exposed to dietary mono- and polyunsaturated 18-carbon fatty acids. Transcriptional activation of NF-kappaB and AP-1 was determined in human umbilical vein endothelial cells transfected with reporter constructs regulated by these transcription factors. Induction of the inflammatory genes was studied by use of reverse transcriptase-polymerase chain reaction.

RESULTS

Of the fatty acids studied, linoleic acid stimulated NF-kappaB and AP-1 transcriptional activation the most. In addition, treatment with this fatty acid markedly enhanced messenger RNA levels of tumor necrosis factor alpha, monocyte chemoattractant protein 1, vascular cell adhesion molecule 1, and intercellular adhesion molecule 1. Treatment with linolenic acid stimulated only a moderate induction of the genes encoding for these inflammatory mediators, and exposure to oleic acid either had no effect or resulted in decreased inflammatory gene messenger RNA. In addition, exposure to both linoleic and linolenic acids strongly stimulated induction of the phospholipid hydroperoxide glutathione peroxidase gene.

CONCLUSION

Specific unsaturated dietary fatty acids, particularly linoleic acid, can selectively stimulate the development of a proinflammatory environment within the vascular endothelium.

PHGPx and spermatogenesis

PHGPx of rat sperm mitochondrial capsule is cross-linked and inactive. The enzyme is in part released in an active form by mercaptoethanol. Treatment with H(2)O(2) of reduced and solubilised capsule proteins, in the absence of any added reductant, results in: i) H(2)O(2) consumption which depends on the presence of both, PHGPx activity and protein thiols; ii) protein thiol oxidation with a stoichiometry of 2 equivalents of thiol per mole of hydroperoxide and, iii) PHGPx inactivation and cross-linking. SDS-PAGE analysis of monobromobimane-labeled proteins, following incubation with H(2)O(2), shows that the oxidation takes place in specific bands in the area of 20~kDa. It is concluded that the protein thiol peroxidase activity of PHGPx is responsible for cross-linking proteins in the mammalian sperm capsule and accounts for the selenium dependency of spermatogenesis.

Overexpression of PHGPx inhibits hydroperoxide-induced oxidation, NFkappaB activation and apoptosis and affects oxLDL-mediated proliferation of rabbit aortic smooth muscle cells

Rabbit abdominal aortic smooth muscle cells (SMC) were stably transfected with the cDNA of porcine phospholipid hydroperoxide glutathione peroxidase (PHGPx) by means of a retroviral gene transfer technique, to create a model for studying cellular processes relevant to atherogenesis. The transfected cells (SMC/PHGPx) had approximately 4-fold higher PHGPx activity when cultured in the presence of selenite whereas the parental cells did not show any significant increase in PHGPx or total GPx activity upon selenium supplementation. In situ functionality of PHGPx was validated by inhibition of linoleic acid hydroperoxide-induced toxicity, dihydrorhodamine oxidation, NFkappaB activation and apoptosis. SMC grown in 1% FCS responded to oxidized LDL (oxLDL) with a marked proliferation, as measured by [3H]thymidine incorporation, irrespective of selenium supplementation. In SMC/PHGPx grown with or without selenite under control conditions or exposed to native LDL, thymidine incorporation was generally depressed. Also, oxLDL-induced proliferation was lower in SMC/PHGPx compared to untransfected SMC up to 24 h of incubation. After 40 h, however, selenite supplementation restored maximum proliferation response to oxLDL in SMC/PHGPx. The results suggest a proliferative effect of endogenous hydroperoxides in SMC. They further reveal that hydroperoxy lipids of oxLDL contribute to the induction of proliferation, but also suggest involvement of hydroxy lipids in the response to oxLDL.

Bacterial and nonbacterial expression of wild-type and mutant human phospholipid hydroperoxide glutathione peroxidase and purification of the mutant enzyme in the milligram scale

15-Lipoxygenases and phospholipid hydroperoxide glutathione peroxidases are counterparts in the metabolism of hydroperoxy lipids and a balanced regulation of both enzymes is essential for normal cell function. Glutathione peroxidases contain selenocysteine as catalytically active amino acid and this selenocysteine is encoded by a TGA stop codon. Detailed protein chemical investigations on phospholipid hydroperoxide glutathione peroxidases and crystal trials have been hampered in the past by limited protein supply. There is no efficient natural source for large-scale enzyme preparation and overexpression of the functional protein in recombinant systems has not been reported so far. To avoid problems with recognition of the selenocysteine stop codon we mutated the selenocysteine to a cysteine and expressed the Sec46Cys mutant in milligram amounts in the baculovirus/insect cell system and as His-tag fusion protein in Escherichia coli. The recombinant enzyme species were purified by conventional fast protein liquid chromatography (nonfusion protein) or by affinity chromatography on a nickel matrix (His-tag protein). Surprisingly, we found that both protein variants were functional although their specific activities were reduced when compared with the wild-type enzyme. Basic protein chemical and enzymatic properties of the purified enzyme species were determined and monoclonal antibodies which recognize the native phospholipid hydroperoxide glutathione peroxidases were raised using our enzyme preparations as antigen. The described strategies for overexpression of mutant phospholipid hydroperoxide glutathione peroxidase species and their purification from recombinant sources provide sufficient amounts of enzyme for future protein chemical investigations and detailed crystal trials.

The importance of selenium to human health

The essential trace mineral, selenium, is of fundamental importance to human health. As a constituent of selenoproteins, selenium has structural and enzymic roles, in the latter context being best-known as an antioxidant and catalyst for the production of active thyroid hormone. Selenium is needed for the proper functioning of the immune system, and appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression to AIDS. It is required for sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking selenium to cardiovascular disease risk although other conditions involving oxidative stress and inflammation have shown benefits of a higher selenium status. An elevated selenium intake may be associated with reduced cancer risk. Large clinical trials are now planned to confirm or refute this hypothesis. In the context of these health effects, low or diminishing selenium status in some parts of the world, notably in some European countries, is giving cause for concern.