Response of [Ah] battery genes to compounds that protect against menadione toxicity

Indenoindoles and cyclopentacarbazoles as bioactive compounds: synthesis and biological applications

Indenoindoles and their isomers cyclopentacarbazoles represent a wide class of synthetic and natural compounds. The great interest of these structures in (bio)organic chemistry is due to the use of various building blocks to get the elemental four ring structure. Depending on the synthetic route chosen, the chemists can achieve a large number of regioisomers. Each regioisomer can be considered as a template for specific functionalizations. Therefore, this mini-review aims (i) to present an overview on how to access this large family of heterocyclic compounds and (ii) to discuss their various biological applications and drug development in oncology (e.g. kinases), in CNS disorders (e.g. Alzheimer's disease), in endocrinology (e.g. hormone replacement therapy) and oxidative stress (e.g. organ preservation). Past and present works will be presented through the systems 6-5-5-6 and 6-5-6-5 (combination of 6-membered and 5-membered rings).

C-Myc is a Nrf2-interacting protein that negatively regulates phase II genes through their electrophile responsive elements

c-Myc is a transcription factor that is implicated in many cellular processes including proliferation, apoptosis and cancers. Recently, c-Myc was shown to be involved in regulation of glutamate cysteine ligase through E-box sequences. This investigation examined whether c-Myc also regulates phase II genes through interaction with the electrophile response element (EpRE). Experiments were conducted in human bronchial epithelial cells using si-RNA to knock down c-Myc. RT-PCR and reporter assays were used to measure transcription and promoter activity. c-Myc downregulated transcription and promoter activity of phase II genes. Chromatin immunoprecipitation verified binding of c-Myc to EpRE while coimmunoprecipitation demonstrated interaction of c-Myc with Nrf2. c-Myc also forms a ternary complex with Nrf2 and p-c-Jun. Finally, c-Myc decreased Nrf2 stability. Thus, our results suggest regulation of the EpRE/Nrf2 signaling pathway by c-Myc through both interaction with the EpRE binding complex and increased degradation of Nrf2.

Glutathione: overview of its protective roles, measurement, and biosynthesis

This review is the introduction to a special issue concerning, glutathione (GSH), the most abundant low molecular weight thiol compound synthesized in cells. GSH plays critical roles in protecting cells from oxidative damage and the toxicity of xenobiotic electrophiles, and maintaining redox homeostasis. Here, the functions and GSH and the sources of oxidants and electrophiles, the elimination of oxidants by reduction and electrophiles by conjugation with GSH are briefly described. Methods of assessing GSH status in the cells are also described. GSH synthesis and its regulation are addressed along with therapeutic approaches for manipulating GSH content that have been proposed. The purpose here is to provide a brief overview of some of the important aspects of glutathione metabolism as part of this special issue that will provide a more comprehensive review of the state of knowledge regarding this essential molecule.

Arachidonic acid suppresses growth of human lung tumor A549 cells through down-regulation of ALDH3A1 expression

Expression of aldehyde dehydrogenase 3A1 (ALDH3A1) in certain normal and tumor cells is associated with protection against the growth inhibitory effect of reactive aldehydes generated during membrane lipid peroxidation. We found that human lung tumor (A549) cells, which express high levels of ALDH3A1 protein, were significantly less susceptible to the antiproliferative effects of 4-hydroxynonenal compared to human hepatoma HepG2 or SK-HEP-1 cells that lack ALDH3A1 expression. However, A549 cells became susceptible to lipid peroxidation products when they were treated with arachidonic acid. The growth suppression of A549 cells induced by arachidonic acid was associated with increased levels of lipid peroxidation and with reduced ALDH3A1 enzymatic activity, protein, and mRNA levels. Furthermore, arachidonic acid treatment of the A549 cells resulted in an increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma), whereas NF-kappaB binding activity was inhibited. Blocking PPARgamma using a selective antagonist, GW9662, prevented the arachidonic acid-mediated reduction of ALDH3A1 expression as well as the growth inhibition of A549 cells, suggesting the central role of PPARgamma in these phenomena. The increase in PPARgamma and the reduction in ALDH3A1 were also prevented by exposing cells to vitamin E concomitant with arachidonic acid treatment. In conclusion, our data show that the arachidonic acid-induced suppression of A549 cell growth is associated with increased lipid peroxidation and decreased ALDH3A1 expression, which may be due to activation of PPARgamma.

CCAAT/enhancer binding protein activation by PD98059 contributes to the inhibition of AhR-mediated 3-methylcholanthrene induction of CYP1A1

2'-Amino-3'-methoxyflavone (PD98059), an MKK1 inhibitor, negatively regulates the induction of the CYP1A1 gene by polycyclic aromatic hydrocarbons. In view of the observations that PD98059 inhibits AhR-mediated CYP1A1 induction and has the capability to activate C/EBPbeta, the study investigated whether the inhibition by PD98059 of 3-MC induction of CYP1A1 results from C/EBP activation. 3-MC induction of the CYP1A1 and the CYP1A1 promoter-luciferase gene were inhibited by treatment of H4IIE cells with PD98059. PD98059 treatment inhibited 3-MC-induced AhR binding to the XRE, but increased protein binding to the CYP1A1 C/EBP binding site. PD98059 inhibited 3-MC induction of CYP1A1 in cells stably transfected with a dominant negative mutant of MKK1, indicating that PD98059 represses CYP1A1 induction by 3-MC irrespective of its MKK1 inhibition. The role of C/EBP activation by PD98059 in repressing CYP1A1 induction was supported by the observation that a dominant-negative mutant C/EBP abolished the ability of PD98059 to suppress 3-MC induction of CYP1A1.

Molecular mechanism of nrf2 activation by oxidative stress

The capacity of cells to maintain homeostasis during oxidative stress resides in activation or induction of protective enzymes. Nuclear-factor-E2-related factor (Nrf)-2 as a member of bZIP transcription factors is expressed in a variety of tissues. Transcriptional activation of antioxidant genes through an antioxidant response element (ARE) is largely dependent upon Nrf2. The genes that contain a functional ARE include those encoding GSTA1, GSTA2, NAD(P)H:quinone reductase, and gamma-glutamylcysteine synthetase heavy and light subunits that play a role in defense against oxidative stress. Previously, we showed that phosphatidylinositol 3-kinase (PI3-kinase) controls nuclear translocation of Nrf2 in response to oxidative stress, which involves rearrangement of actin microfilaments. Now, we report that PI3-kinase is responsible for the rise of cellular Ca(2+), which is requisite for nuclear translocation of Nrf2. Immunocytochemistry and subcellular fractionation analyses revealed that Nrf2 relocated from the cytoplasm to the plasma membrane prior to its nuclear translocation. We further found that CCAAT/enhancer binding protein-beta (C/EBPbeta), peroxisome proliferatoractivated receptor-gamma (PPARgamma), and retinoid X receptor (RXR) heterodimer serve as the activating transcription factors for the phase II gene induction. Hence, PI3-kinase-mediated Nrf2 activation in combination with activating PPARgamma-RXR and C/EBPbeta contributes to antioxidant phase II enzyme induction via coordinate gene transactivation.

Role of human aldehyde dehydrogenases in endobiotic and xenobiotic metabolism

The human genome contains at least 17 genes that are members of the aldehyde dehydrogenase (ALDH) superfamily. These genes encode NAD(P)(+)-dependent enzymes that oxidize a wide range of aldehydes to their corresponding carboxylic acids. Aldehydes are highly reactive molecules that are intermediates or products involved in a broad spectrum of physiologic, biologic, and pharmacologic processes. Aldehydes are generated during retinoic acid biosynthesis and the metabolism of amino acids, lipids, carbohydrates, and drugs. Mutations in several ALDH genes are the molecular basis of inborn errors of metabolism and contribute to environmentally induced diseases.

tert-Butylhydroquinone is a novel aryl hydrocarbon receptor ligand

In contrast to the beneficial effects of tert-butylhydroquinone (tBHQ) as a food antioxidant, a number of studies have shown that chronic exposure to tBHQ may induce carcinogenicity. Therefore, we examined the ability of tBHQ to induce the cytochrome P450 1a1 (Cyp1a1), an enzyme known to play an important role in the chemical activation of xenobiotics to carcinogenic derivatives. A significant concentration-dependent increase in Cyp1a1 mRNA, protein, and activity occurred after treatment of murine hepatoma Hepa 1c1c7 cells with tBHQ. The increase in mRNA was apparent 3 h after treatment. The RNA polymerase inhibitor, actinomycin D, completely blocked the Cyp1a1 induction by tBHQ, indicating a requirement of de novo RNA synthesis through transcriptional activation. The protein synthesis inhibitor cycloheximide superinduced the tBHQ-mediated induction of Cyp1a1 mRNA and completely prevented the increase in Cyp1a1 activity, indicating that the induction of enzyme activity by tBHQ is dependent on de novo protein synthesis. In addition, the aryl hydrocarbon receptor (AHR) antagonist, resveratrol, inhibited the increase in Cyp1a1 activity by tBHQ. Gel electrophoretic mobility shift assays showed that tBHQ causes activation or transformation of the AHR in nuclear extracts, indicating that AHR-dependent mechanisms contributed to the Cyp1a1 induction. Similar to murine Hepa 1c1c7 cells, tBHQ caused a concentration-dependent increase in CYP1A1 at the mRNA and activity levels in human HepG2 cells. This is the first demonstration that the phenolic antioxidant, tBHQ, can directly induce Cyp1a1 gene expression in an AHR-dependent manner and may represent a novel mechanism by which tBHQ promotes carcinogenicity.

Oltipraz inhibits 3-methylcholanthrene induction of CYP1A1 by CCAAT/enhancer-binding protein activation

Oltipraz, a cancer chemopreventive agent, induces CYP1A1 to a certain extent by transactivation of the gene via the Ah receptor (AhR)-xenobiotic response element (XRE) pathway. Previously, we showed that oltipraz promoted CCAAT/enhancer binding proteinbeta (C/EBPbeta) activation, which leads to the induction of glutathione S-transferase. Given that oltipraz activates C/EBPbeta for gene transactivation and that the putative C/EBP binding site is located in the CYP1A1 promoter region, this study investigated the effect of oltipraz on CYP1A1 induction by 3-methylcholanthrene (3-MC). 3-MC induced CYP1A1 in H4IIE cells in a time- and concentration-dependent manner. Gel shift analysis showed that 3-MC increased the band intensity of protein binding to the XRE. Immunocompetition analysis verified the specificity of AhR-XRE binding. Oltipraz (30 microM) induced CYP1A1 and the CYP1A1 promoter-luciferase gene and increased AhR DNA binding activity, which was 10-20% of those in 3-MC (100 nM)-treated cells. However, AhR-XRE binding was not increased after 10 microM oltipraz treatment. Oltipraz (10 microM) significantly inhibited CYP1A1 and CYP1A1-luciferase gene induction by 3-MC with no increase in AhR DNA binding. Oltipraz enhanced protein binding to the C/EBP binding site in the gene promoter and the binding complex comprised of C/EBPbeta and partly C/EBPdelta. Overexpression of dominant-negative mutant C/EBP significantly abolished the ability of oltipraz to suppress 3-MC-inducible CYP1A1 and the CYP1A1 reporter gene expression. Consistently, C/EBPbeta overexpression blocked CYP1A1 reporter gene induction by 3-MC. These results provide evidence that oltipraz suppresses 3-MC induction of CYP1A1 gene expression and that activation of C/EBPbeta by oltipraz contributes to suppression of 3-MC-inducible AhR-mediated CYP1A1 expression.

Involvement of the electrophile responsive element and p53 in the activation of hepatic stellate cells as a response to electrophile menadione

The cytotoxic effects of menadione and hydrogen peroxide were examined in two hepatic stellate cell lines derived from normal or cirrhotic rat liver. The cirrhotic fat-storing cells (CFSC) were found more resistant than the normal fat-storing cells (NFSC) to menadione cytotoxicity. No significant differences were observed in hydrogen peroxide toxicity in these two cell lines. Although protein levels and enzymatic activities of catalase, Cu,Zn-SOD, Mn-SOD, and NADPH cytochrome c reductase were similar in these cell lines, 20-fold increases of NAD(P)H:quinone oxidoreductase 1 (NQO1) enzymatic activity and protein levels were detected in CFSC compared to those of NFSC. Gel mobility shift assays and functional analysis using transient transfection experiments indicated the involvement of the electrophile responsive element (EPRE) in the up-regulation of the NQO1 expression. Antibody supershift analysis revealed that, although Nrf2 is a member of the EPRE-binding complex in both NFSC and CFSC, Nrf1 was identified as a part of the protein/DNA complex only in CFSC. Expression of p53 tumor suppressor gene was found in higher levels in CFSC than in NFSC. We conclude that activation of the EPRE-signaling pathway, which up-regulates several phase II genes and affects p53 stabilization, may offer resistance to hepatic stellate cells against oxidative damage during hepatic injury. This resistance may be a part of the activation process of the hepatic stellate cells and could contribute to their increased proliferation and production of extracellular matrix.

Role of aldehyde dehydrogenases in endogenous and xenobiotic metabolism

Aldehydes are highly reactive molecules that are intermediates or products involved in a broad spectrum of physiologic, biologic and pharmacologic processes. Aldehydes are generated from chemically diverse endogenous and exogenous precursors and aldehyde-mediated effects vary from homeostatic and therapeutic to cytotoxic, and genotoxic. One of the most important pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). Oxidation of the carbonyl functional group is considered a general detoxification process in that polymorphisms of several human ALDHs are associated a disease phenotypes or pathophysiologies. However, a number of ALDH-mediated oxidation form products that are known to possess significant biologic, therapeutic and/or toxic activities. These include the retinoic acid, an important element for vertebrate development, gamma-aminobutyric acid (GABA), an important neurotransmitter, and trichloroacetic acid, a potential toxicant. This review summarizes the ALDHs with an emphasis on catalytic properties and xenobiotic substrates of these enzymes.

Protective action of cardiac DT-diaphorase against menadione toxicity in guinea pig isolated atria

In myocardial preparations isolated from guinea pigs, 2-methyl-1, 4-naphthoquinone (menadione) causes an increase in contractility that is strictly related to the generation of reactive oxygen species (ROS) as a consequence of quinone metabolism. In heart, menadione undergoes one-electron reduction to semiquinone, a reaction mainly catalysed by mitochondrial NADH: ubiquinone oxidoreductase. It is also converted to hydroquinone by the soluble two-electron reductase, DT-diaphorase, and is conjugated with GSH by glutathione S-transferase. In order to assess the role of DT-diaphorase in cardiac responses to menadione, we examined the effects of both a specific inhibitor (dicoumarol) and an inducer (beta-naphthoflavone) of the enzyme on the inotropic action of the quinone. In electrically driven left atria of guinea pig, 4 microM dicoumarol significantly enhanced the positive inotropic effect of menadione, especially at the lower concentrations of the quinone. In myocardial preparations isolated from guinea pigs treated with beta-naphthoflavone (80 mg/kg i.p.for 2 days), DT-diaphorase activity was enhanced (+36% with respect to control animals, P < 0. 01), whereas the activities of the other enzymes involved in menadione metabolism were not modified. In these preparations, menadione caused a significantly lower increase in the force of contraction than in atria from untreated animals; moreover, pretreatment with beta-naphthoflavone caused a significant decrease in the menadione-induced oxidative stress, as evaluated from the GSH redox index. Taken together, these results demonstrate that cardiac DT-diaphorase does not contribute to ROS generation, but represents a detoxification system.

Inhibition of CYP1A1 enzyme activity in mouse hepatoma cell culture by soybean isoflavones

The mechanisms by which soybean- and soybean isoflavone-enriched diets inhibit carcinogenesis are not known. We found that the isoflavones genistin and daidzin, and their respective aglucone forms daidzein and genistein, block 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin)-induced CYP1A1 enzyme activity. This inhibition is correlated with the capacity of the isoflavones to prevent CYP1A1-mediated covalent binding of benzo[a]pyrene (BaP) metabolites to DNA. We further evaluated daidzein and genistein, believed to be the active forms of the isoflavones, for the mechanism of the inhibitory process. Although daidzein and genistein appear structurally similar to known aromatic hydrocarbon receptor (AHR) agonists and antagonists, gel mobility shift assays indicated that the isoflavones do not inhibit dioxin-induced activation of the AHR or the accumulation of CYP1A1 mRNA, suggesting that the isoflavones do not act at the transcriptional level. We therefore evaluated the isoflavones for direct effects on the CYP1A1 enzyme. Daidzein and genistein non-competitive with the CYP1A1 substrate BaP for microsomal BaP hydroxylation, with apparent Ki values of 325 microM and 140 microM, respectively. The extent of CYP1A1 inhibition increases with time of preincubation at 37 degrees C, but not at 4 degrees C, in the presence of isoflavone plus NADPH; after 60 min preincubation the inhibition remains non-competitive, with apparent Ki values of 55 microM and 50 microM, respectively. Inhibition is neither prevented nor reversed by the thiol antioxidant dithiothreitol, nor by the iron chelator deferoxamine. Repeated washing of the microsomes does not reverse the inhibition. The dependency on NADPH, temperature and time for inhibition of CYP1A1 suggests that metabolism of either isoflavone or molecular oxygen to reactive species is required. Isoflavone-mediated inhibition of CYP1A1 activity may contribute to the mechanism by which these soybean isoflavones protect against carcinogenesis.

A comparison of the individual and collective effects of four glucosinolate breakdown products from brussels sprouts on induction of detoxification enzymes

Four glucosinolate derivatives were evaluated individually and as a mixture for their effects on hepatic P4501A (CYP1A), glutathione S-transferase (GST), quinone reductase (QR), glutathione reductase (G-Rd), and GSH levels. Doses of the derivatives were chosen to represent their relative abundance in Brussels sprouts. Adult male F344 rats received either corn oil (vehicle); one of the agents: indole-3-carbinol (I3C, 56 mg/kg), iberin (38 mg/kg), phenylethylisothiocyanate (PEITC, 0.1 mg/kg), or cyanohydroxybutene (crambene, 50 mg/kg); or all of the agents at the doses shown (as a mixture) given by gavage daily for 7 days. The mixture and I3C caused an 11- and 9.4-fold induction of CYP1A, respectively. Crambene and I3C each caused a 1.4-fold increase in GST, while the mixture caused a 2.5-fold increase. Crambene and I3C caused a 2.5- and 1.9-fold increase in QR, respectively. The mixture caused a 6.2-fold increase. Crambene, PEITC, and the mixture caused a 1.8-, 1.6-, and 2.0-fold increase in hepatic GSH levels, respectively. Crambene, I3C, iberin, and the mixture caused 1.3-, 1.4-, 1.2-, and 1.7-fold increases in G-Rd, respectively. In a second study the mixture was given at 60 and 20% of the original dose. CYP 1A, QR, G-Rd, and GST elevations were dose-dependent; GSH levels were not elevated. It is concluded that I3C and crambene are responsible for the majority of enzyme increases seen. A synergistic effect of I3C and crambene was evident on induction of GST and QR, but not on GSH, G-Rd, or P4501A.

Characterization of the rat Class 3 aldehyde dehydrogenase gene promoter

The Class 3 aldehyde dehydrogenase gene (ALDH-3) is differentially expressed. Expression is either constitutive or xenobiotic inducible via an aromatic hydrocarbon (Ah) receptor-mediated pathway, depending upon the tissue. A series of studies were performed to examine the regulation of rat ALDH-3 basal expression. DNase I footprint analysis identified four DNA regions within the proximal 1 kb of the 5' flanking region of rat ALDH-3 which interact with regulatory proteins. Reporter gene and gel mobility shift assays indicate that Sp1-like proteins interact with two proximal DNase I footprinted sites to confer strong promoter activity. Two distal DNase I footprinted sites are found within a region that inhibits rat ALDH-3 promoter activity. This negative region is bound by NF1-like proteins and/or unique proteins. This 1 kb 5' flanking region of rat ALDH-3 may act constitutively in many cell types. In contrast with other Ah receptor regulated genes, no DNA elements or transcription factors acting within this region appear to be involved in regulating xenobiotic-inducible expression of rat ALDH-3.