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Biomedical subjects

Regina Brigelius-Flohé

Publications and source records attributed to Regina Brigelius-Flohé.

At least 19 recordsLinked to original sources
PubMed2006

Modulation of pregnane X receptor- and electrophile responsive element-mediated gene expression by dietary polyphenolic compounds.

Based on animal models, dietary polyphenols are predicted to be promising chemopreventive agents in humans. Allspice, clove, and thyme extracts as well as defined dietary polyphenolic compounds were, therefore, tested for their ability to activate mechanisms related to phase 1 enzymes, i.e., the PXR-regulated CYP3A4 promoter, and phase 2 enzymes, i.e. the EpRE-regulated promoters of gastrointestinal glutathione peroxidase (GI-GPx) and heme oxygenase-1 (HO-1), examples of Nrf2-regulated genes. From the compounds tested, clove and thyme extracts as well as curcumin and resveratrol activated the PXR. PXR activation correlated with the activation of the CYP3A4 promoter in the case of thyme extract, curcumin, and resveratrol, but not in the case of clove extract. Allspice extract, EGCG, and quercetin did not activate PXR but enhanced CYP3A4 promoter activity. Thyme extract and quercetin activated the EpRE of HO-1. Both significantly activated the GI-GPx promoter, effects that depended on a functional EpRE. Resveratrol did not activate the isolated EpRE but enhanced the GI-GPx promoter activity, whereas clove extract even inhibited it. It is concluded that individual polyphenols as well as polyphenol-rich plant extracts may affect phase 1 and 2 enzyme expression by distinct mechanisms that must be elucidated, before potential health effects can reliably be predicted.

Catechin↗
PubMed2006

Glutathione peroxidase 2, the major cigarette smoke-inducible isoform of GPX in lungs, is regulated by Nrf2.

Disruption of NF-E2-related factor (Nrf2), a redox-sensitive basic leucine zipper transcription factor, causes early-onset and more severe emphysema due to chronic cigarette smoke. Nrf2 determines the susceptibility of lungs to cigarette smoke-induced emphysema in mice through the transcriptional induction of numerous antioxidant genes. The lungs of Nrf2-/- mice have higher oxidative stress as evident from the increased levels of lipid peroxidation (4-hydroxy-2-nonenal) and oxidative DNA damage (7,8-dihydro-8-Oxo-2'deoxyguanosine) in response to cigarette smoke. Glutathione peroxidases (GPX) are the primary antioxidant enzymes that scavenge hydrogen peroxide and organic hydroperoxides. Among the five GPX isoforms, expression of GPX2 was significantly induced at both mRNA and protein levels in the lungs of Nrf2+/+ mice, in response to cigarette smoke. Activation of Nrf2 by specific knock down of the cytosolic inhibitor of Nrf2, Keap1, by small inhibitory RNA (siRNA) upregulated the expression of GPx2, whereas Nrf2 siRNA down-regulated the expression of GPX2 in lung epithelial cells. An ARE sequence located in the 5' promoter-flanking region of exon 1 that is highly conserved between mouse, rat, and human was identified. Mutation of this ARE core sequence completely abolished the activity of promoter-reporter gene construct. The binding of Nrf2 to the GPX2 antioxidant response element was confirmed by chromatin immunoprecipation, electrophoretic mobility shift assays, and site-directed mutagenesis. This study shows that GPX2 is the major oxidative stress-inducible cellular GPX isoform in the lungs, and that its basal as well as inducible expression is dependent on Nrf2.

Animals↗
PubMed2006

Part of the series: from dietary antioxidants to regulators in cellular signaling and gene regulation. Sulforaphane and selenium, partners in adaptive response and prevention of cancer.

The association of decreased cancer risk with intake of cruciferous vegetables and selenium is stronger than that reported for fruits and vegetables in general. An active constituent in cruciferae is sulforaphane. Chemopreventive effects of both, sulforaphane and selenium have been attributed to an antioxidant action which certainly is too simplicistic. Sulforaphane induces via activation of the Nrf2/Keap1 system phase 2 enzymes that protect against carcinogens and oxidants. Induced enzymes comprise the selenoproteins thioredoxin reductase-1 (TrxR1) and gastrointestinal glutathione peroxidase (GI-GPx, GPx2), which contain antioxidant response elements (ARE) in their promoter regions. Translational realisation of the enhanced transcripts depends on adequate selenium supply, which explains the synergism of Nrf2 activators and selenium. Regarding tumorigenesis the role of TrxR1 is ambiguous: it is essential for fast tumor cell growth but also diminishes vascularisation of tumors. The anticarcinogenic role of GI-GPx is evident from enhanced gastrointestinal tumor formation in gpx2/gpx1 double KO mice.

Animals↗
PubMed2005

Blocking tumor cell eicosanoid synthesis by GP x 4 impedes tumor growth and malignancy.

Using tumor cell-restricted overexpression of glutathione peroxidase 4 (GP x 4), we investigated the contribution of tumor cell eicosanoids to solid tumor growth and malignant progression in two tumor models differing in tumorigenic potential. By lowering cellular lipid hydroperoxide levels, GP x 4 inhibits cyclooxygenase (COX) and lipoxygenase (LOX) activities. GP x 4 overexpression drastically impeded solid tumor growth of weakly tumorigenic L929 fibrosarcoma cells, whereas B16BL6 melanoma solid tumor growth was unaffected. Yet, GP x 4 overexpression did markedly increase the sensitivity of B16BL6 tumors to angio-destructive TNF-alpha therapy and abolished the metastatic lung colonizing capacity of B16BL6 cells. Furthermore, the GP x 4-mediated suppression of tumor cell prostaglandin E(2) (PGE(2)) production impeded the induction of COX-2 expression by the tumor stress conditions hypoxia and inflammation. Thus, our results reflect a PGE(2)-driven positive feedback loop for COX-2 expression in tumor cells. This was further supported by the restoration of COX-2 induction capacity of GP x 4-overexpressing L929 tumor cells when cultured in the presence of exogenous PGE(2). Thus, although COX-2 expression and eicosanoid production may be enabled by PGE(2) from the tumor microenvironment, our results demonstrate the predominant tumor cell origin of protumoral eicosanoids, promoting solid tumor growth of weakly tumorigenic tumors and malignant progression of strongly tumorigenic tumors.

Animals↗
PubMed2005

Cellular trafficking of the IL-1RI-associated kinase-1 requires intact kinase activity.

Upon stimulation of cells with interleukin-1 (IL-1) the IL-1 receptor type I (IL-1RI) associated kinase-1 (IRAK-1) transiently associates to and dissociates from the IL-1RI and thereafter translocates into the nucleus. Here we show that nuclear translocation of IRAK-1 depends on its kinase activity since translocation was not observed in EL-4 cells overexpressing a kinase negative IRAK-1 mutant (EL-4(IRAK-1-K239S)). IRAK-1 itself, an endogenous substrate with an apparent molecular weight of 24kDa (p24), and exogenous substrates like histone and myelin basic protein are phosphorylated by nuclear located IRAK-1. Phosphorylation of p24 cannot be detected in EL-4(IRAK-1-K239S) cells. IL-1-dependent recruitment of IRAK-1 to the IL-1RI and subsequent phosphorylation of IRAK-1 is a prerequisite for nuclear translocation of IRAK-1. It is therefore concluded that intracellular localization of IRAK-1 depends on its kinase activity and that IRAK-1 may also function as a kinase in the nucleus as shown by a new putative endogenous substrate.

Active Transport, Cell Nucleus↗
PubMed2005

Modulation of Cyp3a11 mRNA expression by alpha-tocopherol but not gamma-tocotrienol in mice.

Metabolism of vitamin E is initiated by cytochrome P450 (CYP) enzymes usually involved in the metabolism of xenobiotics. Like other CYP substrates, vitamin E induced a reporter gene under the control of the pregnane X receptor (PXR) which regulates the expression of CYPs including CYP3A4. gamma-Tocotrienol, the most effective PXR activator, also induced endogenous CYP3A4 mRNA in HepG2 cells. Since these findings imply an interference of vitamin E with drug metabolism it was deemed necessary to investigate their in vivo relevance. Therefore, mice were grown for 3 months with alpha-tocopherol-deficient, -adequate, and -supranutritional diet, i.e. 2, 20 and 200 mg RRR-alpha-tocopheryl acetate/kg diet, respectively. Half of them received 250 microg gamma-tocotrienol/day for the last 7 days. After 3 months, hepatic levels of Cyp3a11 mRNA, the murine homolog to human CYP3A4, were about 2.5-fold higher in the 20 and 200 mg alpha-tocopherol groups than in the 2 mg group. After feeding 200 mg alpha-tocopherol for 9 months, Cyp3a11 mRNA was 1.7-fold higher than after 3 months. In contrast, gamma-tocotrienol did not induce Cyp3a11 mRNA. This could be explained by its high metabolism as demonstrated by the 20- to 25-fold increase in the urinary excretion of gamma-CEHC, the final metabolite of gamma-tocotrienol degradation. In conclusion, alpha-tocopherol maintains an adequate level of xenobiotic-metabolizing enzymes. If fed in supranutritional dosages, especially for longer times, alpha-tocopherol induces Cyp3a11 to levels which might interfere with drug metabolism.

Animals↗
PubMed2005

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.

Antioxidants↗
PubMed2005

Induction of drug metabolizing enzymes by vitamin E.

Vitamin E is an essential micronutrient involved in various processes relevant to human health and disease. Although it has long been considered just as an antioxidant, it has now become clear that vitamin E has functions far exceeding that as an antioxidant. These include regulation of cellular signaling processes and gene expression. Expression control of enzymes involved in drug metabolism was recognized during the investigation of vitamin E degradation. Vitamin E is metabolized by side chain degradation initiated by an omega-hydroxylation, catalyzed by a cytochrome P450 enzyme (CYP). This mechanism is identical for all forms of vitamin E. The degree to which they are degraded, however, varies dramatically, and may, in part, explain their different biological activities. CYPs degrade various endogenous and exogenous compounds and many of them are induced by their substrates. Also, gamma-tocotrienol, identified as substrate of CYPs, increased endogenous CYP3A4 in human HepG2 cells. In two studies with mice undertaken independently, alpha-tocopherol induced Cyp3a11, the murine homolog to human CYP3A4, whereas neither gamma-tocopherol nor gamma-tocotrienol, due to rapid degradation, showed any effect. CYPs are induced via the activation of the pregnane-X-receptor (PXR), a member of the family of nuclear receptors. They are activated by a large number of lipophilic xenobiotics. Also, vitamin E induced a reporter gene driven by PXR. The induction was highest with alpha- and gamma-tocotrienol and low but significant with alpha-tocopherol. This roughly correlates with the in vitro binding of vitamin E to PXR. These findings reveal that, in principle, vitamin E is able to directly influence gene activity. They also raise the question of whether vitamin E may interfere with drug metabolism in humans. Related research is urgently deeded.

Animals↗
PubMed2005

Curcumin blocks interleukin-1 (IL-1) signaling by inhibiting the recruitment of the IL-1 receptor-associated kinase IRAK in murine thymoma EL-4 cells.

Curcumin is a dietary compound with diverse anti-inflammatory and anticarcinogenic effects in several experimental models. A mechanism by which curcumin exerts these actions might be the direct modification of protein thiols, thereby altering the activity of the affected proteins. An early event in inflammatory signaling cascades is the recruitment of the interleukin-1 (IL-1) receptor-associated kinase (IRAK) to the IL-1 receptor (IL-1RI) upon stimulation with IL-1. IRAK recruitment was shown recently to be inhibited by agents that modify thiols of IRAK. We asked, therefore, whether IRAK is also a target for curcumin. Curcumin indeed blocked IRAK thiols in a murine T-cell line stably overexpressing IRAK (EL-4(IRAK)), which resulted in the inhibition of IRAK recruitment to the IL-1RI and phosphorylation of IRAK and IL-1RI-associated proteins. Inhibitory effects were not reversible by thiol-reducing agents. Thus, modification by curcumin did not occur by oxidation but rather by alkylation, as is typical for electrophilic compounds reacting as Michael addition acceptors. The block in one of the earliest events in the IL-1 signaling cascade can explain the often observed inhibition of IL-1-mediated signaling steps by curcumin further downstream. Hence, thiol modification might be a crucial step in the anti-inflammatory functions of curcumin.

Animals↗
PubMed2005

The GI-GPx gene is a target for Nrf2.

The gastrointestinal glutathione peroxidase (GI-GPx, GPx2) is a selenoprotein that was suggested to act as barrier against hydroperoxide absorption but has also been implicated in the control of inflammation and malignant growth. In CaCo-2 cells, GI-GPx was induced by t-butyl hydroquinone (tBHQ) and sulforaphane (SFN), i.e., "antioxidants" known to activate the "antioxidant response element" (ARE) via electrophilic thiol modification of Keap1 in the Nrf2/Keap1 system. The functional significance of a putative ARE in the GI-GPx promoter was validated by transcriptional activation of reporter gene constructs upon exposure to electrophiles (tBHQ, SFN, and curcumin) or overexpression of Nrf2 and by reversal of these effects by mutation of the ARE in the promoter and by overexpressed Keap1. Binding of Nrf2 to the ARE sequence in authentic gpx2 was corroborated by chromatin immunoprecipitation. Thus, the presumed natural antioxidants sulforaphane and curcumin may exert their anti-inflammatory and anticarcinogenic effects not only by induction of phase 2 enzymes but also by the up-regulation of the selenoprotein GI-GPx.

Animals↗
PubMed2004

Redox events in interleukin-1 signaling.

There is increasing evidence that reactive oxygen species (ROS) are mediators in growth factor and cytokine signaling pathways. Mechanisms by which ROS can interfere with signaling cascades may include regulation of protein activities by the modification of essential cysteines. Modification can be performed chemically or enzyme-catalyzed. Enzymes catalyzing a reversible thiol modification within proteins are to be able to react with both, ROS and protein thiols. If hydroperoxides are involved, promising candidates are peroxiredoxins and glutathione peroxidases (GPx), especially the phospholipid hydroperoxide GPx. Interleukin-1, one of the key players in inflammatory response, stimulates the production of ROS itself, but its signaling cascade can also be influenced by ROS and by thiol modifying agents. Targets are located in early, intermediate, and late events in the signaling cascade. We here summarize what is known about the effects of thiol modifying agents, selenium and glutathione peroxidases, on the assembly of the IL-1 receptor signaling complex as an early event, on the activation of NF-kappa B as an intermediate event, and on the expression of cell adhesion molecules as a late event in IL-1 signaling.

Animals↗
PubMed2004

Inhibition of basal and interleukin-1-induced VCAM-1 expression by phospholipid hydroperoxide glutathione peroxidase and 15-lipoxygenase in rabbit aortic smooth muscle cells.

Cytokines or hydroperoxides upregulate cell adhesion molecules (CAM) in early stages of atherosclerosis. VCAM-1 expression was therefore investigated in rabbit aortic smooth muscle cells (SMC) stably transfected either with phospholipid hydroperoxide glutathione peroxidase (PHGPx; SMCPHGPx) as a hydroperoxide-reducing enzyme or with 15-lipoxygenase (15-LOX; SMCLOX) as a hydroperoxide-producing enzyme. Transfected cells showed up to 3-fold enhanced PHGPx and a marked LOX activity, respectively, that was absent in controls. Intracellular hydroperoxides were 6-fold higher in SMCLOX than in SMC or SMCPHGPx. Intracellular protein thiols were decreased by 50 and 90% in SMCPHGPx and SMCLOX, respectively. Glutathione mixed disulfides were tentatively increased from SMC via SMCPHGPx to SMCLOX, accordingly. Thiol reduction with tris(2-carboxyethyl)phosphine completely restored protein thiols in SMCPHGPx, whereas in SMCLOX only 60% of control values were recovered. Basal VCAM-1 mRNA levels were decreased by 50% in SMCPHGPx and 75% in SMCLOX. VCAM-1-inducibility was abrogated in SMCLOX but not in SMCPHGPx. Accordingly, NFkappaB-driven reporter gene activation by IL-1 was unaffected in SMCPHGPx but abolished in SMCLOX. The data confirm that PHGPx overexpression dampens CAM expression either by lowering stimulatory hydroperoxides or by using hydroperoxides for protein modification. But hydroperoxides, when constitutively overproduced as in SMCLOX, inhibit CAM expression and render cells refractory to IL-1 stimulation likely due to oxidation of protein thiols of the signaling system.

Animals↗
PubMed2004

Localization of alpha-tocopherol transfer protein in trophoblast, fetal capillaries' endothelium and amnion epithelium of human term placenta.

Vitamin E has been linked to fertility since its discovery in 1922. However, the exact mechanism by which alpha-tocopherol allows pregnancy to continue until term has remained puzzling over the last 80 years. Alpha-tocopherol transfer protein (TTPA) is expressed in liver and in Purkinje cells of the cerebellum. TTPA is suggested to be responsible for the transfer of alpha-tocopherol across barrier membranes. Ttpa-knockout mice are infertile and show symptoms similar to those observed in severe vitamin E deficiency. We thus investigated TTPA expression in human placenta and whether clues from its localization in different parts of the placenta might be of functional significance. TTPA-mRNA transcripts were quantified with a fluorescent 5'-nuclease assay (TaqMan) in five different tissues. Placental expression ranged second behind that of liver. Immunohistochemistry identified TTPA in the cytosol but also in nuclei of the trophoblast and in the endothelium of the fetal capillaries. Expression in trophoblast and fetal capillaries' endothelium indicates a role of TTPA in the stereoselective transport of RRR-alpha-tocopherol from the maternal to the fetal plasma. In amnion epithelial cells, however, TTPA was predominantly located in the nuclei. Nuclear localization of the protein may represent a novel function of TTPA.

Amnion↗
PubMed2004

Vitamin E: underestimated as an antioxidant.

Some 80 years after its discovery, vitamin E has experienced a renaissance which is as surprising as it is trivial. Although vitamin E is essential for reproduction, in rats at least, and deficiency causes neurological disorders in humans, the main interest in the last decades has concentrated on its antioxidant functions. This focus has highly underestimated the biological importance of vitamin E, which by far exceeds the need for acting as a radical scavenger. Only recently has it become clear that vitamin E can regulate cellular signaling and gene expression. Out of the eight different tocols included in the term vitamin E, alpha-tocopherol often exerts specific functions, which is also reflected in its selective recognition by proteins such as the alpha-tocopherol transfer protein and alpha-tocopherol-associated proteins. Vitamin E forms other than alpha-tocopherol are very actively metabolised, which explains their low biopotency. In vivo, metabolism may also attenuate the novel functions of gamma-tocopherol and tocotrienols observed in vitro. On the other hand, metabolites derived from individual forms of vitamin E have been shown to exert effects by themselves. This article focuses on the metabolism and novel functions of vitamin E with special emphasis on differential biological activities of individual vitamin E forms.

Animals↗
PubMed2004

The effect of age on vitamin E status, metabolism, and function: metabolism as assessed by labeled tocopherols.

The effects of age on vitamin E metabolism were studied in 97 healthy 20-75-year-old male nonsmoking Austrian volunteers of the VITAGE project. After a single oral intake of 30 mg d(6)-RRR-alpha- and d(2)-RRR-gamma-tocopheryl acetate, blood and 24-hour urine was collected. Deuterated tocopherols in plasma and deuterated urinary metabolites were analyzed by GC-MS. A first evaluation revealed a similar uptake of d(6)-alpha- and d(2)-gamma-tocopherol during the first 6 hours, and then d(2)-gamma-tocopherol started to decrease. Urinary d(2)-gamma- carboxyethyl hydroxychroman metabolites (CEHCs) exceeded those of d(6)-alpha-CEHCs by about 10 times. There was no effect of age. Thus, there might be no need for a higher vitamin E intake for healthy elderly nonsmoking men.

Absorption↗