Insa M. A. Ernst

Sulforaphane but not ascorbigen, indole-3-carbinole and ascorbic acid activates the transcription factor Nrf2 and induces phase-2 and antioxidant enzymes in human keratinocytes in culture

Please cite this paper as: Sulforaphane but not ascorbigen, indole‐3‐carbinole, and ascorbic acid activates the transcription factor Nrf2 and induces phase‐2 and antioxidant enzymes in human keratinocytes in culture. Experimental Dermatology 2010; 19: 137–144.

A diet rich in olive oil phenolics reduces oxidative stress in the heart of SAMP8 mice by induction of Nrf2-dependent gene expression.

A Mediterranean diet rich in olive oil has been associated with health benefits in humans. It is unclear if and to what extent olive oil phenolics may mediate these health benefits. In this study, we fed senescence-accelerated mouse-prone 8 (SAMP8, n=11 per group) semisynthetic diets with 10% olive oil containing either high (HP) or low amounts of olive oil phenolics (LP) for 4.5 months. Mice consuming the HP diet had significantly lower concentrations of the oxidative damage markers thiobarbituric acid-reactive substances and protein carbonyls in the heart, whereas proteasomal activity was similar in both groups. Nrf2-dependent gene expression may be impaired during the aging process. Therefore, we measured Nrf2 and its target genes glutathione-S-transferase (GST), γ-glutamyl cysteine synthetase (γ-GCS), nicotinamide adenine dinucleotide phosphate [NAD(P)H]:quinone oxidoreductase (NQO1), and paraoxonase-2 (PON2) in the hearts of these mice. Nrf2 as well as GST, γ-GCS, NQO1, and PON2 mRNA levels were significantly higher in heart tissue of the HP as compared to the LP group. The HP-fed mice had significantly higher PON1 activity in serum compared to those receiving the LP diet. Furthermore, HP feeding increased relative SIRT1 mRNA levels. Additional mechanistic cell culture experiments were performed, and they suggest that the olive oil phenolic hydroxytyrosol present in the HP oil may be responsible for the induction of Nrf2-dependent gene expression and the increase in PON activity. In conclusion, a diet rich in olive oil phenolics may prevent oxidative stress in the heart of SAMP8 mice by modulating Nrf2-dependent gene expression.

Allyl-, butyl- and phenylethyl-isothiocyanate activate Nrf2 in cultured fibroblasts

The isothiocyanate sulforaphane (SFN) has been shown to induce phase 2 and antioxidant enzymes in cultured cells and in vivo via a Nrf2 dependent signal transduction pathway. However, little is known regarding the effect of structurally related compounds such as allyl isothiocyanate (AITC), butyl isothiocyanate (BITC) and phenylethyl isothiocyanate (PEITC) on Nrf2 target gene expression. In this study AITC, BITC and PEITC significantly increased phosphorylation of ERK1/2, an upstream target of Nrf2 in NIH3T3 fibroblasts. EKR1/2 phosphorylation was accompanied by an increased nuclear translocation and transactivation of Nrf2. AITC, BITC and PEITC significantly enhanced mRNA and protein levels of the Nrf2 targets γ-glutamyl cysteine synthetase (γGCS), heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase (NQO1). HO-1 and γGCS both contain CpG islands within their promoter region. However, analysis of DNA methylation status in NIH3T3 cells indicated that expression of these genes may not be dependant on promoter methylation. Current data indicate that not only SFN but also other aliphatic and aromatic isothiocyanates such as AITC, BITC and PEITC induce phase 2 and antioxidant enzymes in cultured fibroblasts.

Sulforaphane and phenylethyl isothiocyanate protect human skin against UVR-induced oxidative stress and apoptosis: Role of Nrf2-dependent gene expression and antioxidant enzymes

Chronic UVR-exposure may impair the stress response and antioxidant defense mechanisms of human skin. The transcription factor nuclear factor erythroid-2 related factor 2 (Nrf2) orchestrates the expression of genes coding for the stress response and antioxidant proteins. Here, we tested sulforaphane (SFN) and phenylethyl isothiocyanate (PEITC) for their ability to counteract UVR-induced oxidative stress and apoptosis in ex vivo human full-thickness skin combined with in vitro HaCaT keratinocytes. Investigation of Nrf2 transactivation and induction of genes coding for Nrf2-dependent phase II antioxidative enzymes (γ-glutamylcysteine-synthetase (γGCS), heme oxygenase 1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO1)) was performed in HaCaT keratinocytes. Comparative investigations in human ex vivo skin were conducted for analysis of gene expression of above mentioned phase II enzymes and catalase (CAT) as well as hematoxylin/eosin (H&E) and immunofluorescence (catalase, cleaved Casp-3). UVR exposure of human skin (300mJ/cm(2)) resulted in a significant time-dependent increase of the number of sunburn cells and caspase-3 activation as biomarkers of apoptosis for up to 48h (p<0.001) and induced a significant decrease of the antioxidant enzyme catalase (p<0.001). This was significantly counteracted by the pre-treatment of human skin with SFN and PEITC (5μM and 10μM). Mechanistic cell culture studies revealed SFN and PEITC to increase Nrf2 activity and Nrf2-dependent gene expression (γGCS, HO-1, NQO1); this was paralleled in human full skin mRNA. In conclusion, the induction of Nrf2-dependent antioxidant pathways seems to be a potential mechanism by which SFN and PEITC protect against UVR-induced oxidative stress and apoptosis in human skin.

Gene Expression and Physiological Changes of Different Populations of the Long-Lived Bivalve Arctica islandica under Low Oxygen Conditions

The bivalve Arctica islandica is extremely long lived (>400 years) and can tolerate long periods of hypoxia and anoxia. European populations differ in maximum life spans (MLSP) from 40 years in the Baltic to >400 years around Iceland. Characteristic behavior of A. islandica involves phases of metabolic rate depression (MRD) during which the animals burry into the sediment for several days. During these phases the shell water oxygen concentrations reaches hypoxic to anoxic levels, which possibly support the long life span of some populations. We investigated gene regulation in A. islandica from a long-lived (MLSP 150 years) German Bight population and the short-lived Baltic Sea population, experimentally exposed to different oxygen levels. A new A. islandica transcriptome enabled the identification of genes important during hypoxia/anoxia events and, more generally, gene mining for putative stress response and (anti-) aging genes. Expression changes of a) antioxidant defense: Catalase, Glutathione peroxidase, manganese and copper-zinc Superoxide dismutase; b) oxygen sensing and general stress response: Hypoxia inducible factor alpha, Prolyl hydroxylase and Heat-shock protein 70; and c) anaerobic capacity: Malate dehydrogenase and Octopine dehydrogenase, related transcripts were investigated. Exposed to low oxygen, German Bight individuals suppressed transcription of all investigated genes, whereas Baltic Sea bivalves enhanced gene transcription under anoxic incubation (0 kPa) and, further, decreased these transcription levels again during 6 h of re-oxygenation. Hypoxic and anoxic exposure and subsequent re-oxygenation in Baltic Sea animals did not lead to increased protein oxidation or induction of apoptosis, emphasizing considerable hypoxia/re-oxygenation tolerance in this species. The data suggest that the energy saving effect of MRD may not be an attribute of Baltic Sea A. islandica chronically exposed to high environmental variability (oxygenation, temperature, salinity). Contrary, higher physiological flexibility and stress hardening may predispose these animals to perform a pronounced stress response at the expense of life span.

Cellular uptake, stability, visualization by ‘Naturstoff reagent A’, and multidrug resistance protein 1 gene-regulatory activity of cyanidin in human keratinocytes

There is increasing interest in the role of anthocyanidins as potential skin protective phytochemicals. However, little is known if and to what extent anthocyanidins are taken up by the human skin. In the present study cellular uptake (as determined by HPLC), stability, and gene-regulatory activity of cyanidin were determined in human HaCaT keratinocytes in culture. Using the fluorescent dye Naturstoff reagent A cyanidin was visualized in order to determine its cellular accumulation via flow cytometry and fluorescence microscopy. Cyanidin was rapidly taken up by HaCaT cells at relatively low concentrations. Following incubation, cellular cyanidin levels decreased time-dependently most likely due to degradation into protocatechuic acid and phloroglucinol aldehyde. Confocal laser scanning microscopy data demonstrated that cyanidin was mainly present in the cytoplasm. Cellular uptake of cyanidin was accompanied by an inhibition of multidrug resistance protein 1 (involved in cellular efflux of flavonoids) mRNA-levels indicating its gene-regulatory activity. Naturstoff reagent A seems to be a promising fluorescent dye to visualize cyanidin in keratinocytes.

3,3′-Diindolylmethane but not indole-3-carbinol activates Nrf2 and induces Nrf2 target gene expression in cultured murine fibroblasts

Abstract There is increasing interest in the gene-regulatory activity of Brassica vegetable derived phytochemicals such as 3,3′-diindolylmethane (DIM) and indole-3-carbinol (I3C). DIM is formed under acidic conditions by dimerization of I3C. This study compared the Nrf2 activating potential of DIM and I3C in murine fibroblasts (NIH3T3). In contrast to its precursor I3C, DIM induces the transactivation of Nrf2. Furthermore, Nrf2 targets such as HO-1, γGCS and NQO1 were increased on the mRNA and protein levels following DIM treatment. DIM was less potent than sulforaphane (used as positive control) in inducing Nrf2-dependent gene expression. The present data suggest that the dimerization of I3C to DIM increases its Nrf2 inducing activity.

Genistein as a potential inducer of the anti-atherogenic enzyme paraoxonase-1: studies in cultured hepatocytes in vitro and in rat liver in vivo

A number of cardioprotective effects, including the reduced oxidation of the low‐density lipoprotein (LDL) particles, have been attributed to dietary soy isoflavones. Paraoxonase 1 (PON1), an enzyme mainly synthesized in the liver, may exhibit anti‐atherogenic activity by protecting LDL from oxidation. Thus, dietary and pharmacological inducers of PON1 may decrease cardiovascular disease risk. Using a luciferase reporter gene assay we screened different flavonoids for their ability to induce PON1 in Huh7 hepatocytes in culture. Genistein was the most potent flavonoid with regard to its PON1‐inducing activity, followed by daidzein, luteolin, isorhamnetin and quercetin. Other flavonoids such as naringenin, cyanidin, malvidin and catechin showed only little or no PON1‐inducing activity. Genistein‐mediated PON1 transactivation was partly inhibited by the oestrogen‐receptor antagonist fulvestrant as well as by the aryl hydrocarbon receptor antagonist 7‐ketocholesterol. In contrast to genistein, the conjugated genistein metabolites genistein‐7‐glucuronide, genistein‐7‐sulfate and genistein‐7,4′‐disulfate were only weak inducers of PON1 transactivation. Accordingly, dietary genistein supplementation (2 g/kg diet over three weeks) in growing rats did not increase hepatic PON1 mRNA and protein levels as well as plasma PON1 activity. Thus, genistein may be a PON1 inducer in cultured hepatocytes in vitro, but not in rats in vivo.

Synthesis and Nrf2-inducing activity of the isothiocyanates iberverin, iberin and cheirolin

Numerous studies have reported a potent induction of Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-dependent gene expression by the isothiocyanate sulforaphane. However, little is known regarding the Nrf2-inducing activities of the lower structure-related sulforaphane homologues, such as iberverin, iberin and cheirolin, which exhibit different sulfur oxidation states. Therefore, in this study we synthesized the isothiocyanates iberverin, iberin and cheirolin with a high yield and purity and determined their Nrf2-inducing activity in NIH3T3 fibroblasts. Iberverin, iberin and cheirolin significantly induced Nrf2 nuclear translocation. The increase in nuclear Nrf2 levels was accompanied by a significant increase in heme oxygenase 1 (HO-1) and γ-glutamylcysteine synthetase (γGCS) mRNA and protein levels. Overall, iberverin, iberin and cheirolin exhibited a similar potency to sulforaphane in inducing Nrf2-dependent gene-expression. Furthermore, our data suggest that the induction of Nrf2 by iberverin, iberin and cheirolin may have occurred via an extracellular signal-related kinase (ERK)-dependent signal-transduction pathway.

Cyanidin does not affect sulforaphane-mediated Nrf2 induction in cultured human keratinocytes

There is increasing interest in the gene-regulatory activities of isothiocyanates and flavonoids in human skin. Nrf2 agonists, such as isothiocyanate sulforaphane (SFN), have been shown to promote chemopreventive effects in skin both in vitro and in vivo. Recent data indicate that different secondary plant compounds may either antagonise or enhance SFN-induced Nrf2 activation. We therefore studied the interactions of a flavonoid, cyanidin and the potent Nrf2 inductor SFN in cultured human keratinocytes (HaCaT cells). We observed that cyanidin does not induce the activation of Nrf2 and its target genes, γ-glutamylcysteine synthetase (γGCS), NAD(P)H:quinone oxidoreductase 1 and haem oxygenase-1 in HaCaT cells. Furthermore, SFN-mediated Nrf2 activation and its target gene expression were not further enhanced by the co-application of SFN with cyanidin.