Reactive oxygen species-related induction of multidrug resistance-associated protein 2 expression in primary hepatocytes exposed to sulforaphane

Sulforaphane Alters β-Naphthoflavone-Induced Changes in Activity and Expression of Drug-Metabolizing Enzymes in Rat Hepatocytes

Sulforaphane (SFN), an isothiocyanate found in cruciferous vegetables, exerts many beneficial effects on human health such as antioxidant, anti-inflammatory, and anticancer effects. The effect of SFN alone on drug-metabolizing enzymes (DMEs) has been investigated in numerous in vitro and in vivo models, but little is known about the effect of SFN in combination with cytochrome P450 (CYP) inducer. The aim of our study was to evaluate the effect of SFN on the activity and gene expression of selected DMEs in primary cultures of rat hepatocytes treated or non-treated with β-naphthoflavone (BNF), the model CYP1A inducer. In our study, SFN alone did not significantly alter the activity and expression of the studied DMEs, except for the glutathione S-transferase (GSTA1) mRNA level, which was significantly enhanced. Co-treatment of hepatocytes with SFN and BNF led to a substantial increase in sulfotransferase, aldoketoreductase 1C, carbonylreductase 1 and NAD(P)H:quinone oxidoreductase 1 activity and a marked decrease in cytochrome P450 (CYP) Cyp1a1, Cyp2b and Cyp3a4 expression in comparison to the treatment with BNF alone. Sulforaphane is able to modulate the activity and/or expression of DMEs, thus shifting the balance of carcinogen metabolism toward deactivation, which could represent an important mechanism of its chemopreventive activity.

In Vitro Antiproliferative Effects of Sulforaphane on Human Colon Cancer Cell Line SW620

The isothiocyanate sulforaphane (SF) has been reported to possess chemopreventive efficiency towards various malignancies including colon cancer. Here, we investigated the antiproliferative and pro-apoptotic effects of SF on colon cancer cell line SW620. We found that SF at concentrations of 10–50 μM inhibits cell viability and proliferation of SW620 cells in a time- and dose-dependent manner, with IC50 being 26 μM (24 h), 24.4 μM (48 h) and 18 μM (72 h). Also, in the same cells SF caused DNA damage and chromatin condensation after 24 h and 48 h as revealed by phospho-H2A.X western blot analysis and DAPI staining of nuclei. These changes were accompanied by the elevated activity of caspase 3, although after 20 μM SF concentration only. Together, these results indicate that SF suppresses growth of human metastacic colonocytes and induces apoptotic cell death.

Bardoxolone methyl modulates efflux transporter and detoxifying enzyme expression in cisplatin-induced kidney cell injury

Cisplatin is prescribed for the treatment of solid tumors and elicits toxicity to kidney tubules, which limits its clinical use. Nuclear factor erythroid 2-related factor 2 (Nrf2, NFE2L2) is a critical transcription factor that has been shown to protect against kidney injury through activation of antioxidant mechanisms. We aimed to evaluate the ability of short-term treatment with the Nrf2 activator bardoxolone methyl (CDDO-Me) to protect against cisplatin-induced kidney cell toxicity. Cell viability was assessed in human kidney proximal tubule epithelial cells (hPTCs) exposed to low, intermediate, and high cisplatin concentrations in the presence and absence of CDDO-Me, administered either prior to or after cisplatin. Treatment with cisplatin alone resulted in reductions in hPTC viability, while CDDO-Me administered prior to or after cisplatin exposure yielded significantly higher cell viability (17%-71%). Gene regulation (mRNA expression) studies revealed the ability of CDDO-Me to modify protective pathways including Nrf2 induced detoxifying genes [GCLC (increased 1.9-fold), NQO1 (increased 9.3-fold)], and an efflux transporter [SLC47A1 (increased 4.5-fold)] at 12h. Protein assessments were in agreement with gene expression. Immunofluorescence revealed localization of GCLC and NQO1 to the nucleus and cytosol, respectively, with CDDO-Me administered prior to or after cisplatin exposure. The findings of enhanced cell viability and increased expression of detoxifying enzymes (GCLC and NQO1) and the multidrug and toxin extrusion protein 1 (MATE1) efflux transporter (SLC47A1) in hPTCs exposed to CDDO-Me, suggest that intermittent treatment with CDDO-Me prior to or after cisplatin exposure may be a promising approach to mitigate acute kidney injury.

Fermented wheat powder induces the antioxidant and detoxifying system in primary rat hepatocytes

Many plants exhibit antioxidant properties which may be useful in the prevention of oxidative stress reactions, such as those mediated by the formation of free radical species in different pathological situations. In recent years a number of studies have shown that whole grain products in particular have strong antioxidant activity. Primary cultures of rat hepatocytes were used to investigate whether and how a fermented powder of wheat (Lisosan G) is able to modulate antioxidant and detoxifying enzymes, and whether or not it can activate Nrf2 transcription factor or inhibit NF-kB activation. All of the antioxidant and detoxifying enzymes studied were significantly up-regulated by 0.7 mg/ml Lisosan G treatment. In particular,

NAD(P)H

quinone oxidoreductase and heme oxygenase-1 were induced, although to different degrees, at the transcriptional, protein and/or activity levels by the treatment. As for the Nrf2 transcription factor, a partial translocation of its protein from the cytosol to the nucleus after 1 h of Lisosan G treatment was revealed by immunoblotting. Lisosan G was also observed to decrease H2O2-induced toxicity Taken together, these results show that this powder of wheat is an effective inducer of ARE/Nrf2-regulated antioxidant and detoxifying genes and has the potential to inhibit the translocation of NF-kB into the nucleus.

Exploring the effects of isothiocyanates on chemotherapeutic drugs

INTRODUCTION

Chemoprevention has emerged as a promising strategy to reduce the risk and to control cancer. In this context, isothiocyanates (ITCs), found in abundance in the form of glucosinolates in cruciferous vegetables, have gained increasing consideration for their chemopreventive activity. ITCs exert their effects mainly by inducing carcinogen metabolism or by inhibiting tumor cell proliferation.

AREAS COVERED

In recent years, novel combination treatments, by coupling chemopreventive agents and typical chemotherapeutics, have been exploited to increase the antitumor activities. The aim of this article is to examine the foremost studies carried out, so far, on the effects of dietary and synthetic ITCs on different signaling pathways involved in the pharmacokinetics and pharmacodynamics of chemotherapeutic agents, in order to enhance their effectiveness.

EXPERT OPINION

Undoubtedly, the beneficial anticarcinogenic potential of ITCs, both singly and in combination, has emerged in in vitro and in vivo studies. However, only a few clinical trials have been carried out so far with ITCs, which try to better define both the pharmacokinetic and pharmacodynamic impacts in humans. More toxicological evaluations after long-term administration of ITCs in different species are required for the clinical development of ITCs as anticarcinogenic agents.

Cisplatin-induced chemoresistance in colon cancer cells involves FXR-dependent and FXR-independent up-regulation of ABC proteins

Export pumps often limit the usefulness of anticancer drugs. Here we investigated the effect of cisplatin on the expression of ABC proteins in human colon cancer cells. Short-term incubation of Caco-2 and LS174T cells with cisplatin resulted in up-regulation of several ABC pumps, in particular MRP2 and BCRP. In partially cisplatin-resistant cells (LS174T/R) obtained by long-term exposure to cisplatin, MRP2 and BCRP up-regulation was more marked. This was further enhanced when these cells were cultured under maintained stimulation with cisplatin. The MRP2 promoter (MRP2pr) was cloned, and partially deleted constructs linked to reporter genes were generated. Transfection of LS174T and LS174T/R cells with these constructs revealed the ability of cisplatin to activate MRP2pr. The intensity of this response was dependent on the conserved MRP2pr region. Basal MRP2pr activity was higher in LS174T/R cells, in which the expression of the transcription factors c/EBPβ, HNF1α, HNF3β, and HNF4α, but not PXR, p53, c-Myc, AP1, YB-1, NRF2, and RARα was enhanced. Up-regulation was particularly high for FXR (200-fold) and SHP (50-fold). In LS174T/R cells, GW4064 induced the expression of FGF19, SHP, OSTα/β, but not MRP2 and BCRP, although the sensitivity of these cells to cisplatin was further reduced. In LS174T cells, GW4064-induced chemoresistance was seen only after being transfected with FXR+RXR, when BCRP, but not MRP2, was up-regulated. Protection of LS174T cells against cisplatin was mimicked by transfection with BCRP. In conclusion, in colon cancer cells, cisplatin treatment enhances chemoresistance through FXR-dependent and FXR-independent mechanisms involving the expression of BCRP and MRP2, respectively.

Structural influence of isothiocyanates on expression of cytochrome P450, phase II enzymes, and activation of Nrf2 in primary rat hepatocytes

Primary cultures of rat hepatocytes were used to investigate whether and how eight isothiocynates (ITCs) with different chemical structures (the aromatic benzyl, 4-hydroxybenzyl, phenethyl isothiocyanates and the aliphatic allyl, napin, iberin, raphasatin isothiocyanates and sulforaphane) derived from hydrolyzed glucosinolates, were able to modulate cytochrome P450 (CYP) and antioxidant/detoxifying enzymes and to activate the Nrf2 transcription factor. The aromatic ITCs at 40 μM markedly increased the transcription of CYP1A1 and 1A2 mRNA and increased the associated ethoxyresorufin O-deethylase (EROD) activity after 24 h of treatment. By contrast, the aliphatic ITCs (40 μM) decreased CYP1A1 and 1A2 transcription, together with the corresponding EROD activity. The same treatment also caused a striking and similar transcriptional repression of CYP3A2, and the corresponding benzyloxyquinoline debenzylase activity in response to all the ITCs tested. In the same culture conditions, most of the antioxidant/detoxifying enzymes were significantly up-regulated by 40μM ITCs. In particular, NAD(P)H:quinone oxidoreductase and heme oxygenase-1 were induced, although to different levels, at transcriptional, protein and/or activity levels by all the ITCs. However, glutathione S-transferase activity was not induced by the allyl, benzyl, and 4-hydroxybenzyl ITCs, glutathione reductase activity was not induced by benzyl, and 4-hydroxybenzyl ITCs and catalase activity was not induced by allyl ITC. As for the Nrf2 transcription factor, a partial translocation of its protein from the cytosol to the nucleus was revealed by immunoblotting after 1h of treatment for all the ITCs tested. The ability of ITCs to induce the antioxidant and phase II enzymes did not appear to be affected by their hydrophilicity or other structural factors. Taken together, these results show that these ITCs are effective inducers of ARE/Nrf2-regulated antioxidant/detoxifying genes and have the potential to inhibit, at least in rat liver, the bioactivation of carcinogens dependent on CYP3A2 catalysis.

Effect of 5-fluorouracil treatment on SN-38 absorption from intestine in rats

5-Fluorouracil (5-FU)-based chemotherapies with irinotecan have been applied for the treatment of cancers, and a common dose-limiting toxicity is neutropenia and diarrhea. In this study, we investigated the effect of 5-FU treatment on expression levels of drug transporters for SN-38 transportation and SN-38 absorption from the intestine following 5-FU treatment. Expression levels of several drug transporters and nuclear receptors in rats after 5-FU treatment were evaluated. SN-38 absorption from the intestine was evaluated by SN-38 concentration levels in serum following SN-38 injection into the intestine of 5-FU treated rats. The levels of renal multidrug resistance protein 2 (Mrp2) on day 4 after treatment (400 mg/kg) showed significant upregulation, 359.2 ± 33.2% (mean ± S.E.) of control. Mrp2 levels in the intestine were downregulated to 26.2 ± 8.4% of control. 5-FU treatment (400 mg/kg) also significantly downregurated expression levels of P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) to 41.2 ± 14.7%, 15.7 ± 4.3% of control, respectively. To evaluate SN-38 absorption from the intestine, SN-38 was loaded in to the intestine on day 4 after 5-FU treatment. Pretreatment with 5-FU significantly increased SN-38 concentration in the blood 30, 60 and 90 min after SN-38 administration. The area under the curve for SN-38 in the 5-FU group was significantly higher than in vehicle groups. 5-FU treatment decreased expression levels of P-glycoprotein and Bcrp in intestine. The present study suggests that combination chemotherapy of 5-FU with irinotecan (CPT-11) may elevate SN-38 absorption from intestine.

Increased expression of the multidrug resistance-associated protein 1 (MRP1) in kidney glomeruli of streptozotocin-induced diabetic rats

Oxidative stress has been linked to the podocytopathy, mes-angial expansion and progression of diabetic nephropathy. The major cell defence mechanism against oxidative stress is reduced glutathione (GSH). Some ABC transporters have been shown to extrude GSH, oxidised glutathione or their conjugates out of the cell, thus implying a role for these transporters in GSH homeostasis. We found a remarkable expression of mRNA for multidrug resistance-associated proteins (MRP/ABCC) 1, 3, 4 and 5 in rat glomeruli. Three weeks after induction of diabetes in glomeruli of streptozotocin-treated rats, we observed a decline in reduced GSH levels and an increase in the expression and activity of MRP1 (ABCC1). These lower GSH levels were improved by ex vivo treatment with pharmacological inhibitors of MRP1 activity (MK571). We conclude that increased activity of MRP1 in diabetic glomeruli is correlated with an inadequate adaptive response to oxidative stress.

Molecular characterization and functions of zebrafish ABCC2 in cellular efflux of heavy metals

Multidrug-resistance associated protein 2 (MRP2/ABCC2) plays crucial roles in bile formation and detoxification by transporting a wide variety of endogenous compounds and xenobiotics, but its functions in zebrafish (Danio rerio) remain to be characterized. In this study, we obtained the full-length cDNA of zebrafish abcc2, analyzed its expression in developing embryos and adult tissues, investigated its transcriptional response to heavy metals, and evaluated its roles in efflux of heavy metals including cadmium, mercury and lead. Zebrafish abcc2 gene is located on chromosome 13 and composed of 32 exons. The deduced polypeptide of zebrafish ABCC2 consists of 1567 amino acids and possesses most of functional domains and critical residues defined in human ABCC2. Zebrafish abcc2 gene is not maternally expressed and its earliest expression was detected in embryos at 72hpf. In larval zebrafish, abcc2 gene was found to be exclusively expressed in liver, intestine and pronephric tubules. In adult zebrafish, the highest expression of abcc2 gene was found in intestine followed by those in liver and kidney, while relative low expression was detected in brain and muscle. Expression of abcc2 in excretory organs including kidney, liver and intestine of zebrafish larvae was induced by exposure to 0.5μM mercury or 5μM lead. Moreover, exposure to 0.125-1μM of mercury or lead also significantly induced abcc2 expression in these excretory organs of adult zebrafish. Furthermore, overexpression of zebrafish ABCC2 in ZF4 cells and zebrafish embryos decreased the cellular accumulation of heavy metals including cadmium, mercury and lead as determined by MRE (metal responsive element)- or EPRE (electrophile response element)-driven luciferase reporters and atomic absorption spectrometry. These results suggest that zebrafish ABCC2/MRP2 is capable of effluxing heavy metals from cells and may play important roles in the detoxification of toxic metals.

Biological profile of erucin: a new promising anticancer agent from cruciferous vegetables

Consumption of cruciferous vegetables has been associated with a reduced risk in the development of various types of cancer. This has been attributed to the bioactive hydrolysis products that are derived from these vegetables, namely isothiocyanates. Erucin is one such product derived from rocket salads, which is structurally related to sulforaphane, a well-studied broccoli-derived isothiocyanate. In this review, we present current knowledge on mechanisms of action of erucin in chemoprevention obtained from cell and animal models and relate it to other isothiocyanates. These mechanisms include modulation of phase I, II and III detoxification, regulation of cell growth by induction of apoptosis and cell cycle arrest, induction of ROS-mechanisms and regulation androgen receptor pathways.

Antioxidant and pro-oxidant capacities of ITCs

Isothiocyanates (ITCs) are breakdown products of glucosinolates contained in cruciciferous vegetables. This heterogeneous family of molecules has the -N=C=S group as its common structural feature and possesses important cytoprotective properties. Their biological interactions are strongly related to modulation of cellular redox status, and a number of studies have documented their indirect antioxidant properties, particularly related to induction of phase-2 enzymes. On the other hand, some direct antioxidant behavior has also been observed for a limited number of ITCs. Paradoxically relevant pro-oxidant properties have also been documented, possibly related to the simultaneous induction of phase-1 enzymes. In this review, we will summarize and discuss the prevailing mechanisms for the antioxidant and pro-oxidant activity of ITCs, both in vivo and in vitro.

Prospective type 1 and type 2 disulfides of Keap1 protein

Experiments were carried out to detect cysteine residues on human Keap1 protein that may be sensors of oxidative stress that gives rise to changes in the GSH/GSSG redox couple. Human Keap1 protein, at a final concentration of 6 microM, was incubated for two hours in aqueous buffer containing 0.010 M GSH, pH 8, in an argon atmosphere. Subsequently, excess iodoacetamide and trypsin were added to generate a peptide map effected by LCMS analysis. Peptides containing all 27 carboxamidomethylated cysteines were identified. Replacement of GSH by 0.010 M GSSG yielded a map in which 13 of the original carboxamidomethylated peptides were unperturbed, while other caboxamidomethylated cysteine-containing peptides were undetected, and a number of new cysteine-containing peptide peaks were observed. By mass analysis, and in some cases, by isolation, reduction, carboxamidomethylation, and reanalysis, these were identified as S-glutathionylated (Type 1) or Cys-Cys (Type 2) disulfides. Such peptides derived from the N-terminal, dimerization, central linker, Kelch repeat and C-terminal domains of Keap1. Experiments were carried out in which Keap1 was incubated similarly but in the presence of various GSH/GSSG ratios between 100 and 1 ([GSH + GSSG] = 0.010 M), with subsequent caraboxamidomethylation and trypsinolysis to determine differences in sensitivities of the different cysteines to the type 1 and type 2 modifications. Cysteines most sensitive to S-glutathionylation include Cys77, Cys297, Cys319, Cys368, and Cys434, while cysteine disulfides most readily formed are Cys23-Cys38 and Cys257-Cys297. The most reducing conditions at which these modifications are at GSH/GSSG = 10, which computes to an oxidation potential of E h = -268.5 mV, a physiologically relevant value. Under somewhat more oxidizing, but still physiologically relevant, conditions, GSH/GSSG = 1 ( E h = -231.1 mV), a Cys319-Cys319 disulfide is detected far from the dimerization domain of the Keap1 homodimer. The potential impact on protein structure of the glutathionylation of Cys434 and Cys368, the two modified residues in the Kelch repeat domain, was analyzed by docking and energy minimizations of glutathione residues attached to the Kelch repeat domain, whose coordinates are known. The energy minimizations indicated marked alterations in structure with a substantial constriction of Neh2 binding domain of the Keap1 Kelch repeat domain. This alteration appears to be enforced by an extended hydrogen-bonding network between residues on the glutathione moiety attached to Cys434 and amino acid side chains that have been shown to be essential for repression of Nrf2 by Keap1. The modifications of Keap1 detected in the present study are discussed in the context of previous work of others who have examined the sensitivity of cysteines on Keap1 to electrophile assault.

Sulforaphane and erucin increase MRP1 and MRP2 in human carcinoma cell lines

Multidrug resistance (MDR) transporters have been termed the Phase III detoxification system because they not only export endogenous metabolites but provide protection from xenobiotic insult by actively secreting foreign compounds and their metabolites from tissues. However, MDR overexpression in tumors can lead to drug resistance, a major obstacle in the treatment of many cancers, including lung cancer. Isothiocyanates from cruciferous vegetables, such as sulforaphane (SF) and erucin (ER), are known to enhance the expression of Phase II detoxification enzymes. Here we evaluated the ability of SF and ER to modulate MDR mRNA and protein expressions, as well as transporter activity. The expression of P-glycoprotein (P-gp), multidrug resistance protein 1 (MRP1) and multidrug resistance protein 2 (MRP2) in liver (HepG2), colon (Caco-2) and lung (A549) cancer cells treated with ER or SF was analyzed by Western blotting. Neither SF nor ER affected P-gp expression in any of the cell lines tested. Both SF and ER increased the protein levels of MRP1 and MRP2 in HepG2 cells and of MRP2 in Caco-2 cells in a dose-dependent manner. In A549 lung cancer cells, SF increased MRP1 and MRP2 mRNA and protein levels; ER caused a similar yet smaller increase in MRP1 and MRP2 mRNA. In addition, SF and ER increased MRP1-dependent efflux of 5-carboxyfluorescein diacetate in A549 cells, although again the effect of SF was substantially greater than that of ER. The implication of these findings is that dietary components that modulate detoxification systems should be studied carefully before being recommended for use during chemotherapy, as these compounds may have additional influences on the disposition of chemotherapeutic drugs.

Discovery and development of sulforaphane as a cancer chemopreventive phytochemical

Sulforaphane (SF) is a phytochemical that displays both anticarcinogenic and anticancer activity. SF modulates many cancer-related events, including susceptibility to carcinogens, cell death, cell cycle, angiogenesis, invasion and metastasis. We review its discovery and development as a cancer chemopreventive agent with the intention of encouraging further research on this important compound and facilitating the identification and development of new phytochemicals for cancer prevention.

Isothiocyanate E-4IB induces MAPK activation, delayed cell cycle transition and apoptosis

INTRODUCTION

Epidemiologic studies point towards a significant correlation between the dietary intake of isothiocyanate-containing foods and the reduced risk for cancer.

METHODS AND RESULTS

In the current investigation, we examined the consequence of activating of signalling pathways during the release the cells from the block at G(1)/S boundary by synthetic isothiocyanate E-4IB. Using synchronized leukaemic HL60 cells, we show that activation of mitogen-activated protein kinases ERK1/2, c-Jun N-terminal kinase and p38 signalling pathways by E-4IB are coupled with delayed transition through the cell cycle and rapid cell cycle arrest resulted in diminished mitochondrial membrane potential culminating in apoptosis. These events were accompanied by histone deacetylase inhibition, increase of double strand DNA breaks detected by histone H2AX phosphorylation and up-regulation of cell cycle regulatory protein p21 and phosphorylation of CDC25C phosphatase.

CONCLUSION

These findings suggest that the activation of mitogen-activated protein kinases signalling pathways, followed by the induction cell cycle arrest and apoptosis, might be responsible for anticancer activities of E-4IB.

Emodin Induces Growth Arrest and Death of Human Vascular Smooth Muscle Cells Through Reactive Oxygen Species and p53

Percutaneous coronary intervention is the main therapy for revascularization of occluded coronary arteries. However, a progressive artery restenosis caused by abnormal proliferation and migration of vascular smooth muscle cells (VSMC) hinders the effective treatment. In this study, we examined the effect of emodin, a natural anthraquinoid compound, on cultured VSMC. Lower doses of emodin suppressed cell proliferation and induced unscheduled DNA synthesis. Higher doses of emodin increased lumpy chromatin condensation and lysosomes in VSMC, suggesting the occurrence of apoptosis and autophagy. Emodin increased production of reactive oxygen species (ROS), which was abolished by an NADPH oxidase inhibitor diphenylene iodonium (DPI). DPI could also decrease the number of apoptosis induced by emodin, suggesting the involvement of ROS in emodin-induced apoptosis. Emodin upregulated the protein levels of p53 in a dose-dependent manner. Laser confocal microscope showed most of emodin scattering in the cytoplasms and a little within the nuclei. These findings collectively indicated that emodin induces both growth arrest and death of human VSMCs in 2 independent manners, implying it as a promising therapy for preventing restenosis.

Antioxidant and choleretic properties of Raphanus sativus L. sprout (Kaiware Daikon) extract

Brassica vegetables and glucosinolates contained therein are supposed to reduce the risk of cancer and to possess health-promoting properties. The benefits of a Brassica-based diet may be particularly expressed by eating sprouts, in which the glucosinolate content is higher than in mature vegetables. With this in mind, a first objective of this study was to evaluate the antioxidant properties of radish (Raphanus sativus L.) sprouts (Kaiware Daikon) extract (KDE), in which the glucosinolate glucoraphasatin (GRH), showing some antioxidant activity, is present at 10.5% w/w. The contribution of GRH to KDE's antioxidant activity was considered in two chemical assays (Trolox equivalent antioxidant capacity and Briggs-Rauscher methods). The total phenol assay by Folin-Ciocalteu reagent was performed to quantify the reducing capacity of KDE. Finally, on the basis of the putative choleretic properties of antioxidant plant extracts, the effect on the bile flow of KDE administration was investigated in an animal experimental model. The findings showed that KDE has antioxidant properties and significantly induced bile flow in rats administered 1.5 g/kg of body weight for 4 consecutive days.

The apical conjugate efflux pump ABCC2 (MRP2)

ABCC2 is a member of the multidrug resistance protein subfamily localized exclusively to the apical membrane domain of polarized cells, such as hepatocytes, renal proximal tubule epithelia, and intestinal epithelia. This localization supports the function of ABCC2 in the terminal excretion and detoxification of endogenous and xenobiotic organic anions, particularly in the unidirectional efflux of substances conjugated with glutathione, glucuronate, or sulfate, as exemplified by leukotriene C(4), bilirubin glucuronosides, and some steroid sulfates. The hepatic ABCC2 pump contributes to the driving forces of bile flow. Acquired or hereditary deficiency of ABCC2, the latter known as Dubin-Johnson syndrome in humans, causes an increased concentration of bilirubin glucuronosides in blood because of their efflux from hepatocytes via the basolateral ABCC3, which compensates for the deficiency in ABCC2-mediated apical efflux. In this article we provide an overview on the molecular characteristics of ABCC2 and its expression in various tissues and species. We discuss the transcriptional and posttranscriptional regulation of ABCC2 and review approaches to the functional analysis providing information on its substrate specificity. A comprehensive list of sequence variants in the human ABCC2 gene summarizes predicted and proven functional consequences, including variants leading to Dubin-Johnson syndrome.

Vegetable-derived isothiocyanates: anti-proliferative activity and mechanism of action

Many isothiocyanates (ITC), which are available to human subjects mainly through consumption of cruciferous vegetables, demonstrate strong cancer-preventive activity in animal models. Human studies also show an inverse association between consumption of ITC and risk of cancer in several organs. Whereas earlier studies primarily focused on the ability of ITC to inhibit carcinogen-activating enzymes and induce carcinogen-detoxifying enzymes, more recent investigations have shown that ITC inhibit the proliferation of tumour cells both in vitro and in vivo by inducing apoptosis and arresting cell cycle progression. ITC cause acute cellular stress, which may be the initiating event for these effects. These findings shed new light on the mechanism of action of ITC and indicate that ITC may be useful both as cancer-preventive and therapeutic agents. ITC activate caspase 9-mediated apoptosis, apparently resulting from mitochondrial damage, and also activate caspase 8, but the mechanism remains to be defined. Cell cycle arrest caused by ITC occurs mainly in the G2/M phase, and both the G2 and M phases are targetted; critical G2-phase regulators, including cyclin B1, cell division cycle (Cdc) 2 and Cdc25C, are down regulated or inhibited, and tubulin polymerization and spindle assembly are disrupted. Moreover, ITC are metabolized in vivo through the mercapturic acid pathway, giving rise to thiol conjugates (dithiocarbamates). Studies show that these dithiocarbamates are similar to their parent ITC in exerting anti-proliferative activity. Taken together, dietary ITC are highly-promising anti-cancer agents, capable of targetting multiple cellular components that are important for tumour cell survival and proliferation.

Role of Nrf2 in the regulation of the Mrp2 (ABCC2) gene

The Nrf2 (nuclear factor-erythroid 2 p45-related factor 2) transcription factor regulates gene expression of the GCLC (glutamate-cysteine ligase catalytic subunit), which is a key enzyme in glutathione synthesis, and GSTs (glutathione S-transferases) via the ARE (antioxidant-response element). The Mrp2 (multidrug-resistance protein 2) pump mediates the excretion of GSH and GSSG excretion as well as endo- and xeno-biotics that are conjugated with GSH, glucuronate or sulphate. Considering that Mrp2 acts synergistically with these enzymes, we hypothesized that the regulation of Mrp2 gene expression is also dependent on Nrf2. Using BHA (butylated hydroxyanisole), which is a classical activator of the ARE-Nrf2 pathway, we observed an increase in the transcriptional activity of Mrp2, GCLC and Gsta1/Gsta2 genes in the mouse liver. A similar pattern of co-induction of Mrp2 and GCLC genes was also observed in mouse (Hepa 1-6) and human (HepG2) hepatoma cells treated with BHA, beta-NF (beta-naphthoflavone), 2,4,5-T (trichlorophenoxyacetic acid) or 2AAF (2-acetylaminofluorene), suggesting that these genes share common mechanism(s) of transcriptional activation in response to exposure to xenobiotics. To define the mechanism of Mrp2 gene induction, the 5'-flanking region of the mouse Mrp2 gene (2.0 kb) was isolated, and two ARE-like sequences were found: ARE-2 (-1391 to -1381) and ARE-1 (-95 to -85). Deletion analyses demonstrated that the proximal region (-185 to +99) contains the elements for the basal expression and xenobiotic-mediated induction of the Mrp2 gene. Gel-shift and supershift assays indicated that Nrf2-protein complexes bind ARE sequences of the Mrp2 promoter, preferentially to the ARE-1 sequence. Overexpression of Nrf2 increased ARE-1-mediated CAT (chloramphenicol acetyltransferase) gene activity, while overexpression of mutant Nrf2 protein repressed the activity. Thus Nrf2 appears to regulate Mrp2 gene expression via an ARE element located at the proximal region of its promoter in response to exposure to xenobiotics.

Hepatocyte nuclear factor (HNF) 1 and HNF4 mediate hepatic multidrug resistance protein 2 up-regulation during hepatitis C virus gene expression

Hepatitis C virus (HCV) is known to induce hepatic oxidative stress that is implicated in the up-regulation of multidrug resistance proteins (MRPs). The relationship between increased prooxidant production, MRPs, and HCV has not been investigated. Here, we report that a homeodomain-containing transcription factor, hepatocyte nuclear factor (HNF) 1, plays a central role in liver gene regulation during HCV gene expression and/or subgenome replication. MRP2 protein and mRNA expression were increased and MRP2 promoter activity was increased 7-fold. Mutations within the putative HNF1 binding site of the human MRP2 promoter abrogated HCV-induced activation, implicating HNF1 in the induction of MRP2 by HCV. The mechanism by which HNF1-mediated activation occurs seems to be transcriptional, because the regulated expression of HNF4, which is known to control HNF1 expression, was also increased. Consistent with this finding, HNF1 mRNA was increased 10-fold. A promoter-luciferase construct of the human HNF1 gene was activated in an HNF4-dependent manner, and a mutant construct lacking the HNF4 binding site was not activated in HCV-positive cells. Consistent with this hypothesis, HNF4 protein and mRNA levels as well as HNF4 promoter activity and DNA binding activity were increased. The expression of HNF1 seems to play a critical role in the induction of hepatic MRP2 secondary to HCV subgenomic replication. The ability of HCV to induce HNF1 and HNF4 is attributed to 1) increased oxidative stress and 2) direct protein-protein interactions between HCV nonstructural component (NS) 5A and HNF1, leading to enhanced HNF1 DNA binding. In conclusion, we describe a novel mechanism by which HCV gene expression may induce adaptive responses involving MRP2 via HNF1 activation. This may constitute, in part, the cellular detoxification task force during HCV infection.

Interaction of arsenic trioxide As2O3 with DNA and RNA

Arsenic salts have been used for centuries to treat a variety of medical conditions ranging from infectious disease to cancer. More recently, trivalent arsenic trioxide was found to exhibit high antitumor activity towards hematological malignancies. Even though much is known about antitumor activity and DNA damage by As2O3, there has been no report on the interaction of arsenic trioxide with isolated DNA or RNA. Therefore, it was of interest to examine the interaction of As2O3 with DNA and RNA in aqueous solution at physiological pH. FTIR and UV-visible difference spectroscopic methods were used to characterize the nature of drug-DNA and drug-RNA interactions and to determine the As binding site, the binding constant, the sequence selectivity, the helix stability, and the biopolymer secondary structure in the As2O3-polynucleotide complexes in vitro. The FTIR spectroscopic studies were conducted with As2O3-polynucleotide (phosphate) ratios of 1/40, 1/20, 1/10, and 1/5, with a final DNA (P) or RNA (P) concentration of 6.25 mmol/l. Spectroscopic results showed As2O3 binds to DNA and RNA at G-C, A-T, and A-U bases, and no interaction with the backbone PO2 group. As2O3-DNA and -RNA adducts showed one type of binding with overall binding constant of K(As2O3-DNA) = 1.24 x 10(5) M(-1) and K(As2O3-RNA) = 2.60 x 10(5) M(-1). The As2O3-polynucleotide complexation is associated with a partial biopolymer aggregation and no major alterations of B-DNA or A-RNA structure.

Time-dependent modulation of thioredoxin reductase activity might contribute to sulforaphane-mediated inhibition of NF-kappaB binding to DNA

The chemopreventive agent sulforaphane (SFN) exerts anti-inflammatory activity by thiol-dependent inhibition of nuclear factor kappaB (NF-kappaB) DNA binding. To further analyze the underlying mechanisms, we focused on the thioredoxin/thioredoxin reductase (TrxR) system as a key redox mechanism regulating NF-kappaB DNA binding. Using cultured Raw 264.7 mouse macrophages as a model, 1-chloro-2,4-dinitrobenzene (CDNB), a known inhibitor of TrxR, was identified as an inhibitor of lipopolysaccharide (LPS)-mediated nitric oxide (NO) production and of NF-kappaB DNA binding. CDNB and SFN acted synergistically with respect to inhibition of LPS-induced NO release, and we consequently identified SFN as a novel inhibitor of TrxR enzymatic activity in vitro. Short-term treatment of Raw macrophages with SFN or CDNB resulted in the inhibition of TrxR activity in vivo with half-maximal inhibitory concentration of 25.0 +/- 3.5 microM and 9.4 +/- 3.7 microM, respectively, whereas after a 24-h treatment with 25 microM SFN, TrxR activity was >1.5-fold elevated. In additional experiments, we could exclude that inhibition of trans-activating activity of NF-kappaB contributed to the reduced expression of pro-inflammatory proteins by SFN, based on transient transfection experiments with a (kappaB)(2)- chloramphenicol acetyltransferase construct and a lack of inhibition of protein kinase A activity. These findings further emphasize the importance of redox modulation or thiol reactivity for the regulation of NF-kappaB-dependent transcription by SFN. Antioxid. Redox Signal. 7, 1601-1611.

p53-independent G1 cell cycle arrest of human colon carcinoma cells HT-29 by sulforaphane is associated with induction of p21CIP1 and inhibition of expression of cyclin D1

Isothiocyanate sulforaphane (SFN) is a potent cancer chemopreventive agent. We investigated the mechanisms underlying the anti-proliferative effects of SFN in the human colon carcinoma cell line, HT-29. We demonstrate that SFN inhibits the growth of HT-29 cells in a dose- and time-dependent manner. Treatment of serum-stimulated HT-29 cells with SFN suppressed the re-initiation of cell cycle by inducing a G(1) phase cell cycle arrest. At high doses (>25 microM), SFN dramatically induces the expression of p21(CIP1) while significantly inhibits the expression of the G(1) phase cell cycle regulatory genes such as cyclin D1, cyclin A, and c-myc. This regulation can be detected at both the mRNA and protein levels as early as 4 h post-treatment of SFN at 50 microM. Additionally, SFN activates MAPKs pathways, including ERK, JNK and p38. Exposure of HT-29 cells with both SFN and an antioxidant, either NAC or GSH, completely blocked the SFN-mediated activation of these MAPK signaling cascades, regulation of cyclin D1and p21(CIP1) gene expression, and G(1)phase cell cycle arrest. This finding suggests that SFN-induced oxidative stress plays a role in these observed effects. Furthermore, the activation of the ERK and p38 pathways by SFN is involved in the upregulation of p21(CIP1) and cyclin D1, whereas the activation of the JNK pathway plays a contradictory role and may be partially involved in the downregulation of cyclin D1. Because cyclin D1 and p21(CIP1) play opposing roles in G(1) phase cell cycle progression regulation, blocking the activation of each MAPK pathway with specific MAPK inhibitors, is unable to rescue the SFN-induced G(1) phase cell cycle arrest in HT-29 cells.

Mitochondria are the primary target in isothiocyanate-induced apoptosis in human bladder cancer cells

Many isothiocysanates (ITC) are promising cancer-preventive agents, and induction of apoptosis is one of their underlying mechanisms of action. We recently found that caspase-9 was preferentially activated over other initiator caspases in human bladder cancer UM-UC-3 cells. We report here that caspase-9 activation is the major step leading to ITC-induced apoptosis in this cell line. More importantly, our results show that caspase-9 activation by the ITCs may result primarily from mitochondrial damage. Four common naturally occurring ITCs were studied, including allyl ITC, benzyl ITC (BITC), phenethyl ITC (PEITC), and sulforaphane. BITC and PEITC showed more potent mitochondria-damaging ability than the other two ITCs, correlating well with their stronger apoptosis-inducing potentials. Furthermore, BITC and PEITC damaged both the outer and inner mitochondrial membranes. Use of isolated mitochondria allowed us to establish that ITCs, and more importantly their major intracellular derivatives (glutathione conjugates) at concentrations that are readily achievable in cells, damage mitochondria, leading to the collapse of mitochondrial trans-membrane potential and release of cytochrome c. The mitochondria-damaging potencies of the ITCs correlate well with their lipophilicities. Bcl-2 family members are known to influence the stability of mitochondrial membrane. Our results show that the ITCs caused phosphorylation of Bcl-2, induced mitochondrial translocation of Bak, and disrupted the association of Bcl-xl with both Bak and Bax in mitochondrial membrane, indicating that ITC-induced mitochondrial damage results at least in part from modulation of select Bcl-2 family members.

Role of PI3K/Akt and MEK/ERK signaling pathways in sulforaphane- and erucin-induced phase II enzymes and MRP2 transcription, G2/M arrest and cell death in Caco-2 cells

Isothiocyanate sulforaphane is an extensively studied cancer chemopreventive agent in human diet. In this study, the effects of sulforaphane (SFN) and its sulfide analog, erucin (ERN), have been examined on the induction of the phase II enzymes, quinine oxidoreductase (NQO1) and UDP-glucuronosyl transferase (UGT1A1), multidrug transporter (MRP2), cell cycle arrest and cell death in human colon adenocarcinoma Caco-2 cells. Additionally, the roles of PI3K/Akt and MEK/ERK signaling pathways have been assessed in these sulforaphane- and erucin-induced events. Although erucin and sulforaphane have similar IC50 values (21 and 23 microM after 72 h treatment), erucin was more effective in the induction of G2/M accumulation, depletion of mitochondrial potential, induction of cell death and mRNA induction of phase II enzymes and MRP2. Erucin (20 microM) induced the mRNAs of NQO1, UGT1A1 and MRP2 by 11.1-, 11.6- and 6.7-fold, whereas sulforaphane (20 microM) induced 3.3-, 5.3- and 2.2-fold, respectively. Both erucin and sulforaphane induced activation (phosphorylation) of ERK1/2 and Akt kinases but had no effect on JNK and p38 activation. Erucin-induced phase II enzyme transcriptions were decreased by PI3K and MEK1 inhibitors (LY294002 and PD98059), but the decreases in sulforaphane-induced transcription were less marked. Erucin induced a large increase in G2/M cell number than sulforaphane. The ability of kinase inhibitors to overcome G2/M block was low with the exception of PD98059 in sulforaphane-treated cells. Both, sulforaphane and erucin at high concentrations induced accumulation of sub-G1 cells, cell death and dissipation of mitochondrial membrane potential. Taken together, these results demonstrate that PI3K/Akt and MEK/ERK signals are important intracellular mediators in erucin- and sulforaphane-mediated phase II enzyme transcription and cell cycle arrest in Caco-2 cells.

Physiological, pharmacological and clinical features of the multidrug resistance protein 2

Multidrug resistance protein 2 (MRP2, ABCC2) is a drug efflux pump belonging to the ATP-binding cassette (ABC) transporter superfamily. MRP2 is present predominantly at the biliary pole of hepatocytes and is also expressed in the kidney and intestine. It plays a major role in hepato-biliary elimination of many structurally diverse xenobiotics, including organic anions and drug conjugates, and therefore most likely contributes to pharmacokinetic parameters of these compounds. MRP2 also handles endogenous molecules such as bilirubin, and its overexpression has been shown to confer a multidrug resistance phenotype to tumoral cells. MRP2 expression can be regulated by endogenous substances such as inflammatory cytokines and biliary acids. The MRP2 levels and activity can also be affected by a large panel of xenobiotics, including chemopreventive agents and ligands of the pregnane X receptor, which may be a potential source of drug-drug interactions and drug adverse effects. MRP2 appears therefore as one of the major drug efflux pumps of the organism, whose functional and regulatory features are important to consider, notably for drug disposition.

Micronucleus formation and induction of apoptosis by different isothiocyanates and a mixture of isothiocyanates in human lymphocyte cultures

Isothiocyanates (ITCs) are the main sulfur-containing metabolites found in cruciferous vegetables. There is evidence that some ITCs may act as chemopreventive agents against different tumor types and induce apoptosis and modulate cell-cycle progression of highly proliferative cancer cells. However, there are also studies reporting genotoxic or co-carcinogenic effects for some ITCs, such as benzyl ITC and phenyl ITC. Since selectivity for transformed cells and absence of genotoxicity for healthy cells are important pre-requisites for new chemopreventive agents, we investigated micronucleus formation and induction of apoptosis by 4-(methylthio)butylisothiocyanate (MTBITC), sulforaphane and a mixture of ITCs in human T-lymphocyte cultures. We demonstrate that MTBITC, sulforaphane and the mixture of ITCs did not induce micronuclei. Moreover, sulforaphane induced a dose-dependent increase in the number of apoptotic cells, which was significant at the highest concentration tested (30 microM) (41% versus 18% in the untreated samples, P<0.05). The mixture of ITCs presented a trend similar to that found for sulforaphane. In fact, the mixture of ITCs was able to induce a dose-dependent increase in the percentage of apoptotic cells, which reached a maximum value at the concentration of 13 microg/ml (46% versus 19% in control samples, P<0.05). Induction of apoptosis was not observed in cultures treated with MTBITC. Our results suggest that different ITCs can have different effects. Moreover, although the mixture of glucosinolates (GLs) used in the present study does not reflect the exact composition of broccoli, our findings demonstrate that the quantitative effects of a single, specific ITC can be significantly different from those of an ITC mixture, where other ITCs of the mixture contribute to the outcome observed.

Cancer-preventive isothiocyanates: dichotomous modulators of oxidative stress

Isothiocyanates (ITCs), a class of phytochemicals with promising cancer-preventive potential, are double-edged swords in the modulation of cellular oxidative stress. While ITCs transcriptionally stimulate many antioxidative enzymes and nonenzyme proteins, leading to enhanced protection against oxidative stressors, they also directly alkylate and deplete cellular thiols, damage mitochondria, and elevate reactive oxygen species, leading to cellular stress. These paradoxical effects appear to occur in tandem: exposure of cells to an ITC rapidly leads to an acute increase in stress, which is followed by a delayed but lasting increase in cellular protection against oxidants and carcinogens. Ironically, although ITC-induced stress may lead to oxidative damage, it has become increasingly clear that much of the chemoprotective activity of ITCs stems from the response of cells to the stress induced by these compounds.

Cancer-preventive isothiocyanates: measurement of human exposure and mechanism of action

Numerous studies in rodents have documented the cancer-preventive activity of a significant number of isothiocyanates (ITCs), the majority of which occur in plants, especially in cruciferous vegetables. Dietary ITCs may play an important role in the prevention of human cancers. Several recent epidemiological studies have already shown that dietary consumption of ITCs inversely correlates with the risk of developing lung, breast and colon cancers. ITCs are principally metabolized through the mercapturic acid pathway in vivo, giving rise to N-acetylcysteine conjugates, which are excreted in the urine. Analytical methods have been developed to allow detection of ITCs and their metabolites formed in the mercapturic acid pathway. Studies show that total urinary level of ITC equivalent is an excellent biomarker of human exposure to ITCs. Moreover, these methods also have made it possible to learn the bioavailability of ITCs from cruciferous vegetables. ITCs possess multiple anticarcinogenic mechanisms, including inhibition of carcinogen-activating enzymes, induction of carcinogen-detoxifying enzymes, increase of apoptosis, arrest of cell cycle progression, as well as several other mechanisms that are not yet fully described. These mechanisms, which are discussed in detail in this review, illustrate the remarkable ability of ITCs to inhibit cancer development-effective against both developing and developed cancer cells.

Contribution of NAD(P)H:quinone oxidoreductase 1 to protection against carcinogenesis, and regulation of its gene by the Nrf2 basic-region leucine zipper and the arylhydrocarbon receptor basic helix-loop-helix transcription factors

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a key enzyme involved in defence against reactive forms of oxygen and inhibition of neoplasia. Under conditions of oxidative stress, expression of NQO1 is induced, and the resulting increase in oxidoreductase protein provides the cell with multiple layers of protection against environmental insults. Firstly, the catalytic activity of NQO1 is directed towards the complete reduction and detoxication of highly reactive quinones. Secondly, the oxidoreductase maintains the endogenous lipid-soluble antioxidants, alpha-tocopherol-hydroquinone and ubiquinol in their reduced and active forms. Thirdly, NQO1 is required for the stabilisation of p53 protein in response to DNA-damaging stimuli, and it thereby influences cell fate decisions. In view of the anticarcinogenic actions of NQO1, an understanding of the mechanisms that govern its expression is desirable. The redox sensitivity of NQO1 transcription occurs through a cis-acting antioxidant response element (ARE) located within the regulatory region of the mouse, rat and human genes. This element recruits the positively acting basic leucine zipper (bZip) transcription factor NF-E2 p45-related factor 2 (Nrf2). Under normal constitutive conditions, Nrf2 associates with the cytoskeletal-binding protein Keap1, which regulates the subcellular distribution of the bZip factor and also targets it for proteasome-dependent degradation. Oxidative stress inhibits the Nrf2-Keap1 interaction, thus promoting nuclear accumulation of the transcription factor and transactivation of NQO1 and other ARE-driven genes. Mouse, rat and human NQO1 can also be induced by planar aromatic hydrocarbons through a cis-acting xenobiotic response element (XRE) located in their gene promoters. The XRE recruits the arylhydrocarbon receptor (AhR) and AhR nuclear translocator. Cross-talk may occur between Nrf2 and AhR, but the details of this process remain to be elucidated.

Absorption/metabolism of sulforaphane and quercetin, and regulation of phase II enzymes, in human jejunum in vivo

For the first time the human intestinal effective permeability, estimated from the luminal disappearance and intestinal metabolism of phytochemicals, sulforaphane and quercetin-3,4'-glucoside, as well as the simultaneous changes in gene expression in vivo in enterocytes, has been studied in the human jejunum in vivo (Loc-I-Gut). Both compounds as components of an onion and broccoli extract could readily permeate the enterocytes in the perfused jejunal segment. At the physiologically relevant, dietary concentration tested, the average effective jejunal permeability (Peff) and percentage absorbed (+/- S.D.) were 18.7 +/- 12.6 x 10-4 cm/s and 74 +/- 29% for sulforaphane and 8.9 +/- 7.1 x 10-4 cm/s and 60 +/- 31% for quercetin-3,4'-diglucoside, respectively. Furthermore, a proportion of each compound was conjugated and excreted back into the lumen as sulforaphane-glutathione and quercetin-3'-glucuronide. The capacity of the isolated segment to deconjugate quercetin from quercetin-3,4'-diglucoside during the perfusion was much higher than the beta-glucosidase activity of the preperfusion jejunal contents, indicating that the majority (79-100%) of the beta-glucosidase capacity derives from the enterocytes in situ. Simultaneously, we determined short-term changes in gene expression in exfoliated enterocytes, which showed 2.0 +/- 0.4-fold induction of glutathione transferase A1 (GSTA1) mRNA (p < 0.002) and 2.4 +/- 1.2-fold induction of UDP-glucuronosyl transferase 1A1 (UGT1A1) mRNA (p < 0.02). The changes in gene expression were also seen in differentiated Caco-2 cells, where sulforaphane was responsible for induction of GSTA1 and quercetin for induction of UGT1A1. These results show that food components have the potential to modify drug metabolism in the human enterocyte in vivo very rapidly.

Blockage of multidrug resistance-associated proteins potentiates the inhibitory effects of arsenic trioxide on CYP1A1 induction by polycyclic aromatic hydrocarbons

Arsenic is a toxic metalloid known to interact with drug-metabolizing enzymes. In the present study, we investigated the effects of arsenic trioxide (As2O3), recently used as an anticancer drug, on the expression of human cytochrome P450 (P450) 1A1, which bioactivates polycyclic aromatic hydrocarbons into mutagenic metabolites. Clinically relevant concentrations (0.25-5 microM) of As2O3 were demonstrated to inhibit CYP1A activity in primary human hepatocytes and hepatoma Hep3B and HepG2 cells coexposed to 3-methylcholanthrene (3MC), benzo(a)pyrene, or dioxin and the metalloid for 24 h. Inhibition reached 50 and 90% in Hep3B cells treated with 1 and 5 microM As2O3, respectively, and was not due to direct interaction of the metalloid with CYP1A1. As2O3 (2.5-5 microM) was demonstrated to markedly reduce induction of CYP1A1 mRNA and apoprotein levels and gene promotor activity in 3MC-treated Hep3B cells, whereas lower concentrations (0.25-1 microM) were ineffective. These effects of As2O3 were abrogated by N-acetylcysteine. Surprisingly, this agent was found 1) to block cellular arsenic uptake when coincubated with the metalloid and 2) to increase arsenic efflux through multidrug resistance-associated proteins. In addition, blockade of these transporters was shown to enhance intracellular amounts of metalloid and to potentiate its effects on CYP1A1 gene. Finally, our results have demonstrated that As2O3, at low concentrations routinely reached in As2O3-treated patients, prevents induction of human CYP1A1 gene expression and that such an effect is increased by blocking multidrug resistance-associated proteins.

Single nucleotide polymorphisms in multidrug resistance associated protein 2 (MRP2/ABCC2): its impact on drug disposition

Multidrug resistance associated protein 2 (MRP2/ABCC2), expressed on the bile canalicular membrane, plays an important role in the biliary excretion of various kinds of substrates. In addition, MRP2 is also expressed on the apical membrane of epithelial cells such as enterocytes. It is possible that the inter-individual difference in the function of MRP2 affects the drug disposition. In the present article, we will summarize the physiological and pharmacological role of MRP2, particularly focusing on the factors affecting its transport function such as single nucleotide polymorphisms and/or the induction/down regulation of this transporter. Mutations found in patients suffering from the Dubin-Johnson syndrome, along with the amino acid residues which are involved in supporting the transport activity of MRP2, are also summarized.

Isothiocyanates: mechanism of cancer chemopreventive action

Dietary and synthetic isothiocyanates have cancer chemopreventive activity. Dietary isothiocyanates are formed from glucosinolate precursors of ingested green vegetables. Isothiocyanates are absorbed across intestinal cell membranes by passive diffusion and bind reversibly to plasma protein thiols by thiocarbamoylation. Free isothiocyanate enters cells and is converted to the glutathione conjugate by glutathione S-transferases (GSTs). The glutathione conjugate is exported from cells by multidrug resistance proteins (MRPs), and metabolized in the mercapturic acid pathway to the corresponding mercapturic acid. The isothiocyanate is reformed by fragmentation of mercapturic acid pathway metabolites; it is inactivated by slow hydrolysis to the corresponding amine that is inactive in chemoprevention. Depletion of cellular glutathione and protein thiocarbamoylation activates signal transduction for cancer chemoprevention. Isothiocyanates inhibited and inactivated cytochrome P450 isoforms. They induced increased expression of GST, NADPH: quinone oxidoreductase, aldo-keto reductase and gamma-glutamylcysteine synthetase. These responses were coordinated at the transcription level by nuclear factor-erythroid 2 p45-related factor-2 acting through the antioxidant/electrophile enhancer response element and stimulated by the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase-1 and c-Jun N-terminal kinase-1 (JNK1) pathway. Isothiocyanates also induced apoptosis of pre-cancerous cells and tumor cells activated by caspase-8 and potentiated by JNK1. The chemopreventive activity of isothiocyanates is influenced by the isothiocyanate bioavailability-as is toxicity, GST polymorphism, protein thiocarbamoylation and probably also by MRP expression. These features of isothiocyanate metabolism and chemoprevention deserve further investigation.

Acute cytotoxicity of the chemical carcinogen 2-acetylaminofluorene in cultured rat liver epithelial cells

Acute cytotoxic effects of 2-acetylaminofluorene (AAF), a powerful chemical carcinogen, were studied in cultured rat liver epithelial F258 cells. Acute treatment of these cells by AAF resulted in inhibition of cell proliferation, through an arrest in G0/G1 phase of the cell cycle, and a loss of cell viability. By contrast, AAF failed to trigger apoptosis as demonstrated by flow cytometric analysis of hypoploid sub-G1 cells. Cytochrome P4501A1 (CYP1A1), a drug metabolizing enzyme thought to play a major role in biotransformation of AAF, was induced in AAF-treated F258 cells as assessed by Northern blotting. AAF cytotoxic effects were however not blocked by the CYP1A1 inhibitor alpha-naphtoflavone, thus suggesting that they did not require CYP1A1 activity. They were also not prevented by the antioxidant N-acetylcysteine, making unlikely a major contribution of AAF-related reactive oxygen species. These data therefore indicate that AAF can exert acute cellular toxicity, including inhibition of cell growth and cell death, in rat liver epithelial cells without triggering an apoptotic process. Such an acute toxicity may contribute to the well-known promoting effects of AAF.

Differential regulation of multidrug resistance-associated protein 2 (MRP2) and cytochromes P450 2B1/2 and 3A1/2 in phenobarbital-treated hepatocytes

Multidrug resistance-associated protein 2 (MRP2) is a drug efflux pump found at the biliary pole of hepatocytes. In the present study, we have investigated its expression in response to phenobarbital, a liver tumor promoter known to up-regulate hepatic cytochromes P450 (CYPs), such as CYP2B1/2 and CYP3A1/2. MRP2 mRNA and protein levels were found to be markedly increased in both primary rat and human hepatocytes exposed to phenobarbital. However, features of this up-regulation, especially the dose-response, were different from those of the induction of CYP2B1/2 and CYP3A1/2. In addition, hepatic MRP2 expression remained unaltered in rats treated by phenobarbital that, by contrast, increased CYP2B1/2 and CYP3A1/2 gene expression in the liver. Therefore, MRP2 and CYPs appeared differently regulated in response to phenobarbital in both in vivo and in vitro situations, suggesting that cellular and molecular mechanisms underlying up-regulation of MRP2 are, at least in part, unrelated to those operating for CYPs. Phenobarbital-related MRP2 induction in primary rat hepatocytes was associated with some phenotypic effects of the barbiturate, such as prolonged cell survival and inhibition of cell proliferation. Phenobarbital also inhibited growth of human hepatoma HepG(2) cells and increased their level of MRP2 gene expression. Such results may favor a putative relationship between phenobarbital-mediated MRP2 regulation in cultured liver parenchymal cells and alteration of cell cycle and survival.

Neuroprotection for Parkinson's disease: a new approach for a new millennium

Parkinson's disease (PD) is the only neurodegenerative disorder in which pharmacological intervention has resulted in a marked decrease in morbidity and a significant delay in mortality. However, the medium to long-term efficacy of this pharmacotherapy, mainly consisting of dopaminomimetics like L -dopa and dopamine receptor agonists, suffers greatly from the unrelenting progression of the disease process underlying PD, i.e., the degeneration of neuromelanin-containing, dopaminergic neurones in the substantia nigra. Efforts concentrated on understanding the mechanisms of dopaminergic cell death in Parkinson's disease have led to identification of a large variety of pathogenetic factors, including excessive release of oxygen free radicals during enzymatic dopamine breakdown, impairment of mitochondrial function, production of inflammatory mediators, loss of trophic support, and apoptosis. Therapeutic approaches aimed at correcting these abnormalities are currently being evaluated on their efficacy as neuroprotectants for PD. Here, we focus on the process of dopamine auto-oxidation, the chain of reactions leading to the formation of neuromelanin, as an often overlooked, yet obvious pathogenetic factor. In particular, we discuss the option of drug-mediated stimulation of endogenous mechanisms responsible for the detoxification of dopamine auto-oxidation products as a novel means of neuroprotection in Parkinson's disease.

Expression of the multidrug resistance P glycoprotein (Pgp) and multidrug resistance associated protein (MRP1) in Down syndrome brains

Transport by ATP-dependent efflux pumps such as P glycoprotein (Pgp) and multidrug resistance associated protein (MRP), encoded by multidrug resistant (MDR) associated genes, is an increasingly recognized mechanism by which cells maintain substrate homeostasis and evade drug therapy. Pgp and MRP are members of the so-called ATP binding cassette (ABC) transporters superfamily, which are associated with many biological processes in both prokaryotes and eukaryotes, as well as clinical problems. The observation of upregulated sequences that are homologous to the Mycobacterium smegmatis phage resistance (mpr) gene and putative ABC transporters subunits in fetal Down syndrome (DS) using the gene hunting technique, subtractive hybridization formed the Rationale for this study. The expression of Pgp and MRP1 is therefore investigated in different brain regions of controls and adult DS patients with western blot technique. No apparent changes were observed between controls and DS in levels of Pgp in all brain regions examined. By contrast, MRP1 detection using the rat monoclonal antibody (MRPr1) produced a significant elevation in DS temporal cortex (P < 0.01) and parietal cortex (P < 0.05). Although MRP1 detected with the mouse monoclonal antibody (MRPm6) tended to increase in most of the regions of DS brain, it failed to reach significance level. Age or postmortem interval did not correlate with protein levels in both controls as well as DS. Taken together, the current data provide evidence for the presence of MDR related pumps in different regions of the human brain. In addition, overexpression of MRP1 in DS brain may have some relevance to the disorder either by deranging substrate homeostasis or limiting drug access.