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A Courtois

Publications and source records attributed to A Courtois.

At least 19 recordsLinked to original sources
PubMed2002

The drug efflux pump MRP2: regulation of expression in physiopathological situations and by endogenous and exogenous compounds.

The multidrug resistance-associated protein 2 (MRP2) is an ATP-binding cassette transporter involved in biliary, renal, and intestinal secretion of numerous organic anions, including endogenous compounds such as bilirubin and exogenous compounds such as drugs and toxic chemicals. Its expression can be modulated in various physiopathological situations, notably being markedly decreased during liver cholestasis and upregulated in some cancerous tissues. In addition, MRP2 levels are altered in hepatocytes in response to hormones such as glucocorticoids and to structurally unrelated drugs such as rifampicin, phenobarbital, ritonavir, and cisplatin. The chemical carcinogen 2-acetylaminofluorene and chemopreventive agents such as oltipraz and sulforaphane also markedly increased MRP2 expression in liver parenchymal cells. Interestingly, most of the chemical inducers of MRP2 act on drug-metabolizing enzymes, indicating a coordinated regulation of these detoxifying proteins; cellular mechanisms involved are, at least partly, common and may be related to nuclear hormone receptors such as the pregnane X receptor. Owing to the major role played by MRP2 in elimination of drugs and endogenous compounds, modulation of its expression may lead to adverse effects or to changes in drug pharmacokinetics.

Animals↗
PubMed2001

Regulation of biliary drug efflux pump expression by hormones and xenobiotics.

Biliary elimination of endogenous compounds and xenobiotics usually requires carrier-mediated systems allowing movement across the canalicular membrane of hepatocytes. The major systems implicated belong to the ATP binding cassette transporter family: P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2), principally mediate the passage into the bile of cationic and anionic compounds, respectively, whereas the bile salt export pump (BSEP) handles biliary acids and also some anticancer drugs. Expression of these canalicular proteins can be altered in response to various hormones and structurally unrelated xenobiotics. Indeed, glucocorticoids up-regulate expression of both MRP2 and BSEP in rat hepatocytes, whereas insulin induces P-gp. P-gp expression is also up-regulated by numerous chemical carcinogens, such as polycyclic aromatic hydrocarbons and 2-acetylaminofluorene and by some anticancer drugs, such as anthracyclins. 2-Acetylaminofluorene also induces MRP2; in addition, expression of this transporter in liver cells is increased in response to various drugs, such as the barbiturate phenobarbital, the chemopreventive agent, oltipraz and the anticancer drug, cisplatin. Most of the chemical inducers acting on canalicular transporter levels are well-known to up-regulate some hepatic drug metabolizing enzymes, suggesting a coordinate regulation of liver detoxifying proteins in response to these compounds.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2001

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

Expression of multidrug resistance-associated protein 2 (MRP2), an efflux pump contributing to biliary secretion of xenobiotics, was investigated in primary rat and human hepatocytes exposed to sulforaphane, a naturally-occurring chemopreventive agent. Northern blot indicated that sulforaphane increased MRP2 mRNA levels in primary rat hepatocytes; it also induced expression of drug metabolizing enzymes such as glutathione S-transferase A1/2 isoforms and NAD(P)H:quinone oxidoreductase in a dose-response and time-course manner similar to that observed for the upregulation of MRP2 transcripts. This sulforaphane-related increase of MRP2 mRNAs paralleled increased expression of 190 kD MRP2 protein as assessed by Western blotting; it was fully abolished by the transcription inhibitor actinomycin D. MRP2 induction was associated with increased cellular production of reactive oxygen species (ROS) and addition of dimethyl sulfoxide, that reduced sulforaphane-related formation of ROS, and also decreased MRP2 mRNA levels in sulforaphane-treated primary rat hepatocytes; this suggests that sulforaphane-mediated production of ROS may contribute to MRP2 induction. This link between ROS and MRP2 regulation was further supported by the increase of MRP2 expression occurring in response to t-butylhydroquinone, known to regulate drug metabolizing enzymes through ROS formation. In addition to rat cells, primary human hepatocytes exposed to sulforaphane also displayed induced MRP2 expression evidenced at both mRNA and protein levels. All these observations strongly support the conclusion that the export pump MRP2 can be classified among the detoxifying proteins that are regulated by sulforaphane and that are thought to contribute, at least in part, to its anticarcinogenic properties.

Animals↗
PubMed2001

Unaltered expression of multidrug resistance transporters in polycyclic aromatic hydrocarbon-resistant rat liver cells.

Rat liver epithelial cells resistant to the chemical carcinogen 3MC, termed F258/3MC cells and generated by long-term exposure of parental F258 cells to the PAH, were characterized, especially with respect to expression of multidrug resistance transporters such as P-glycoprotein, MRP1 and MRP2. F258/3MC cells were found to be cross-resistant to other PAHs such as BP and dimethylbenz(a)anthracene but remained sensitive to known substrates of multidrug resistance efflux pumps such as doxorubicin and vincristine. They did not display either decreased cellular PAH accumulation or increased PAH efflux. In addition, P-glycoprotein and MRP2 mRNA levels were not, or only barely detected, in F258/3MC cells and in their parental counterparts whereas these PAH-resistant and sensitive cells showed closed levels of MRP1 mRNAs and activity. Moreover, P-gp- and MRP1-overexpressing cells were shown to display similar accumulation and efflux of BP than those found in P-gp- and MRP1-negative control cells. These data therefore suggest that multidrug resistance transporters do not contribute to PAH resistance in PAH-selected liver cells.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

The sulphonylurea glibenclamide inhibits multidrug resistance protein (MRP1) activity in human lung cancer cells.

1. Glibenclamide, a sulphonylurea widely used for the treatment of non-insulin-dependent diabetes mellitus, has been shown to inhibit the activities of various ATP-binding cassette (ABC) transporters. In the present study, its effects towards multidrug resistance protein 1 (MRP1), an ABC efflux pump conferring multidrug resistance and handling organic anions, were investigated. 2. Intracellular accumulation of calcein, an anionic dye substrate for MRP1, was strongly increased by glibenclamide in a dose-dependent manner in MRP1-overexpressing lung tumour GLC4/Sb30 cells through inhibition of MRP1-related calcein efflux. By contrast, glibenclamide did not alter calcein levels in parental control GLC4 cells. Another sulphonylurea, tolbutamide, was however without effect on calcein accumulation in both GLC4/Sb30 and GLC4 cells. 3. Glibenclamide used at 12.5 microM was, moreover, found to strongly enhance the sensitivity of GLC4/Sb30 cells towards vincristine, an anticancer drug handled by MRP1. 4. Efflux of carboxy-2',7'-dichlorofluorescein, an anionic dye handled by the ABC transporter MRP2 sharing numerous substrates with MRP1 and expressed at high levels in liver, was also strongly inhibited by glibenclamide in isolated rat hepatocytes. 5. In summary, glibenclamide reversed MRP1-mediated drug resistance likely through inhibiting MRP1 activity and blocked organic anion efflux from MRP2-expressing hepatocytes. Such effects associated with the known inhibitory properties of glibenclamide towards various others ABC proteins suggest that this sulphonylurea is a general inhibitor of ABC transporters.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Differential effects of oltipraz on CYP1A and CYP2B in rat lung.

Oltipraz (OPZ) is a potent chemopreventive agent against chemically-induced carcinogenesis in several animal models. It affects the expression and/or activity of xenobiotic-metabolizing enzymes and its effects are altered in the course of inflammation in liver. The present study was undertaken to analyse the effect of OPZ alone or in combination with Escherichia coli lipopolysaccharide (LPS) on the expression and activities of glutathione S-transferases (GSTs) and cytochrome P450 (CYPs) in rat lung and kidney. Male Wistar rats were fed a diet containing OPZ for 1-5 days. LPS was injected 24 h before the end of OPZ treatment (from 48 to 72 h). Total GST activity, measured using 1-chloro-2,4-dinitrobenzene as a substrate, increased slightly in both lung and kidney during OPZ treatment. As previously demonstrated in the liver, OPZ induced rat GSTP1 in both kidney and lung and this effect was totally (kidney) or partially (lung) inhibited by co-treatment with LPS. CYP1A expression and activity were strongly increased in both tissues 24 h after starting OPZ treatment and maintained for 5 days. This increase was suppressed during the acute-phase response to endotoxin. OPZ has no effect on CYP2B1 mRNA expression in the lung, but it dramatically decreased the amount and activity of the corresponding apoprotein. The OPZ-dependent decrease in the CYP2B1 apoprotein was abolished and its corresponding activity partially reversed during LPS treatment. In reconstitution experiments using cytosol from OPZ-treated or control rat lungs and microsomal fractions, CYP2B1 apoprotein was rapidly degraded in the presence of cytosol from treated rats. This effect was partially reversed in the presence of MG132, a proteasome inhibitor. These observations support the conclusion that the decrease of CYP2B1 by OPZ involves proteasome-dependent degradation and represents a new mechanism of regulation by this compound.

Animals↗
PubMed2001

[Positron emission tomography in head and neck oncology: five cases].

FDG-PET (18-fluoro-desoxyglucose positron emission tomography) is a fonctionnal imaging method based on the high rate of glycolysis in different types of cancer-cells. We report the first five cases where FDG-PET was used in France for head and neck cancers. The results were analyzed on the basis of data reported to date in the literature, leading to a proposal for rational use of this diagnostic available in only a few centers in France. For primary assessment of cervicofacial carcinomas, different imaging techniques such as CT and MRI have improved tumor staging. Although 18-FDG-PET cannot replace these techniques used to monitor size and structural changes in tumors and lymph nodes, it will be helpful in following their metabolic activity. This diagnostic tool consequently is greatly helpful for detection and post-therapeutic evaluation of head and neck carcinomas and their recurrence. 18-FDG-PET is currently under evaluation as a tool for detecting cervical lymph nodes and early assessment of response to chemotherapy.

Fluorodeoxyglucose F18↗
PubMed2000

Characterization and inhibition by a wide range of xenobiotics of organic anion excretion by primary human hepatocytes.

Organic anion secretion by human hepatocytes was characterized using primary liver parenchymal cell cultures and the anionic fluorescent dye carboxy-2',7'-dichlorofluorescein (CF). Probenecid, a well-known common blocker of the membrane transport process for anions, was shown to increase CF accumulation in primary human hepatocytes by inhibiting cellular CF efflux in a dose-dependent manner, thereby establishing the presence of an efflux system for organic anions in cultured hepatocytes. Outwardly directed transport of CF from hepatocytes was found to be temperature-dependent; it was not altered by changes in the ionic composition of the incubation medium used in efflux experiments. In addition to probenecid, various structurally and functionally unrelated xenobiotics such as glibenclamide, rifampicin, vinblastine, MK-571, indomethacin, and cyclosporin A were shown to inhibit secretion of CF by primary human hepatocytes, thus suggesting that organic anion excretion by human liver may be impaired by various drugs. Northern blot and Western blot analyses of the expression of multidrug resistance proteins (MRP), such as MRP1 and MRP2, which are known to mediate cellular outwardly directed transport of organic anions indicated that MRP2 was present at substantial levels in cultured human hepatocytes as well as in their in vivo counterparts, whereas MRP1 expression was only barely detectable. These results therefore suggest that MRP2, unlike MRP1, may contribute to the organic anion efflux system displayed by primary human hepatocytes and inhibited by a wide range of xenobiotics.

Anion Transport Proteins↗
PubMed2000

Expression and regulation of hepatic drug and bile acid transporters.

Transport across hepatocyte plasma membranes is a key parameter in hepatic clearance and usually occurs through different carrier-mediated systems. Sinusoidal uptake of compounds is thus mediated by distinct transporters, such as Na(+)-dependent or Na(+)-independent anionic transporters and by some cationic transporters. Similarly, several membrane proteins located at the apical pole of hepatocytes have been incriminated in the excretion of compounds into the bile. Indeed, biliary elimination of anionic compounds, including glutathione S-conjugates, is mediated by MRP2, whereas bile salts are excreted by a bile salt export pump (BSEP) and Class I-P-glycoprotein (P-gp) is involved in the secretion of amphiphilic cationic drugs, whereas class II-P-gp is a phospholipid transporter. The expression of hepatic transporters and their activity are regulated in various situations, such as ontogenesis, carcinogenesis, cholestasis, cellular stress and after treatment by hormones and xenobiotics. Moreover, a direct correlation between a defect and the absence of transporter with hepatic disease has been demonstrated for BSEP, MDR3-P-gp and MRP2.

Animals↗
PubMed1999

Up-regulation of multidrug resistance-associated protein 2 (MRP2) expression in rat hepatocytes by dexamethasone.

Regulation of multidrug resistance-associated protein (MRP2) expression in response to dexamethasone (DEX) was analyzed using mainly primary rat hepatocytes. Enhanced levels of MRP2 mRNAs associated with increased amounts of a 190 kDa MRP2 were found in cultured DEX-treated hepatocytes; similarly, administration of DEX to rats (100 mg/kg, i.p.) led to a marked increase of hepatic amounts of MRP2 mRNAs. Maximal induction of MRP2 expression in DEX-treated primary hepatocytes was reached with 10(-5) M DEX, a concentration higher than that (10(-7) M) required for maximal up-regulation of tyrosine aminotransferase (TAT), a typical glucocorticoid receptor-regulated enzyme. In addition, the anti-glucocorticoid compound RU486 failed to inhibit MRP2 induction caused by DEX whereas it fully blocked that of TAT. These findings therefore demonstrate that DEX is a potent inducer of MRP2 expression in rat hepatocytes through a mechanism that seems not to involve the classical glucocorticoid receptor pathway.

Animals↗
PubMed1999

Reversal of MRP-mediated multidrug resistance in human lung cancer cells by the antiprogestatin drug RU486.

Multidrug resistance-associated protein (MRP) and P-glycoprotein (P-gp) are drug efflux pumps conferring multidrug resistance to tumor cells. RU486, an antiprogestatin drug known to inhibit P-gp function, was examined for its effect on MRP activity in MRP-overexpressing lung tumor GLC4/Sb30 cells. In such cells, the antihormone compound was found to increase intracellular accumulation of calcein, a fluorescent compound transported by MRP, in a dose-dependent manner, through inhibition of cellular export of the dye; in contrast, it did not alter calcein levels in parental GLC4 cells. RU486, when used at 10 microM, a concentration close to plasma concentrations achievable in humans, strongly enhanced the sensitivity of GLC4/Sb30 cells towards two known cytotoxic substrates of MRP, the anticancer drug vincristine and the heavy metal salt potassium antimonyl tartrate. Vincristine accumulation levels were moreover up-regulated in RU486-treated GLC4/Sb30 cells. In addition, such cells were demonstrated to display reduced cellular levels of glutathione which is required for MRP-mediated transport of some anticancer drugs. These findings therefore demonstrate that RU486 can down-modulate MRP-mediated drug resistance, in addition to that linked to P-gp, through inhibition of MRP function.

ATP-Binding Cassette Transporters↗
PubMed1999

The multidrug resistance-associated protein (MRP) is over-expressed and functional in rat hepatoma cells.

Expression of multidrug-resistance-associated protein (MRP), a drug efflux pump transporting a wide range of xenobiotics, including anti-cancer drugs and chemical carcinogens, and present at low levels in normal hepatocytes, was investigated in rat hepatoma cells. Northern-blot analysis allowed detection of high levels of MRP mRNA in rat diethylnitrosamine-induced hepatocarcinomas when compared with normal liver. Similarly, elevated expression of MRP transcripts were evidenced in 6 rat hepatoma cell lines of different origins, especially in HTC cells, that, in contrast, failed to express mRNA of the canalicular multispecific organic anion transporter (cMOAT), an efflux pump sharing numerous substrates with MRP. HTC cells were also found by Western blotting to display much higher amounts of MRP than those observed in normal hepatocytes. In contrast, the MRP gene copy number was similar both in hepatoma HTC cells and in hepatocytes, as assessed by Southern blotting. Analysis of MRP-related transport using 3 types of MRP substrates, namely, the fluorescent glutathione-bimane, the anionic dye calcein and the cationic anti-cancer drug vincristine, demonstrated that HTC cells displayed cellular efflux of these 3 compounds, an efflux strongly inhibited by MRP modulators such as indomethacin. These results indicate that MRP is over-expressed and functional in rat hepatoma cells and may therefore be included in the de-toxifying pathways that are altered during hepatocarcinogenesis and are thus thought to contribute to the known multidrug resistance of liver tumors.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Inhibition of multidrug resistance-associated protein (MRP) activity by rifampicin in human multidrug-resistant lung tumor cells.

The multidrug resistance-associated protein (MRP) is a drug efflux membrane pump conferring multidrug resistance on tumor cells. In order to look for compounds that can lead to reversal of such a resistance, the antituberculosis compound rifampicin, belonging to the chemical class of rifamycins, was examined for its effect on MRP activity in human multidrug resistant lung cancer GLC4/ADR cells. Rifampicin was shown to increase accumulation of the MRP substrate calcein in GLC4/ADR cells in a dose-dependent manner by inhibiting its MRP-mediated efflux from the cells; it also enhanced intracellular retention of another substrate of MRP such as the anticancer drug vincristine in the resistant cells. By contrast, the antituberculosis drug did not alter cellular levels of accumulation of either calcein or vincristine in parental drug-sensitive GLC4 cells. Other rifamycins such as rifamycin B and rifamycin SV were also demonstrated to increase intracellular accumulation of calcein in GLC4/ADR cells. These results therefore indicate that rifamycins, including rifampicin, probably constitute a new chemical class of modulators down-regulating MRP-mediated drug transport.

ATP-Binding Cassette Transporters↗
PubMed1999

Overexpression of the multidrug resistance-associated protein (MRP1) in human heavy metal-selected tumor cells.

Cellular and molecular mechanisms involved in the resistance to cytotoxic heavy metals remain largely to be characterized in mammalian cells. To this end, we have analyzed a metal-resistant variant of the human lung cancer GLC4 cell line that we have selected by a step-wise procedure in potassium antimony tartrate. Antimony-selected cells, termed GLC4/Sb30 cells, poorly accumulated antimony through an enhanced cellular efflux of metal, thus suggesting up-regulation of a membrane export system in these cells. Indeed, GLC4/Sb30 cells were found to display a functional overexpression of the multidrug resistance-associated protein MRP1, a drug export pump, as demonstrated by Western blotting, reverse transcriptase-polymerase chain reaction and calcein accumulation assays. Moreover, MK571, a potent inhibitor of MRP1 activity, was found to markedly down-modulate resistance of GLC4/Sb30 cells to antimony and to decrease cellular export of the metal. Taken together, our data support the conclusion that overexpression of functional MRP1 likely represents one major mechanism by which human cells can escape the cytotoxic effects of heavy metals.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Evidence for a multidrug resistance-associated protein 1 (MRP1)-related transport system in cultured rat liver biliary epithelial cells.

Cellular accumulation and efflux of the anionic fluorescent dye carboxy-2',7'-dichlorofluorescein (CF) were studied in rat liver SDVI cells thought to derive from primitive bile ductules, in order to characterize carrier-related membrane transport of organic anions in epithelial cells. Probenecid, a common blocker of anion transport, was found to strongly enhance CF levels in SDVI cells in a dose-dependent manner through inhibition of dye efflux. Such an outwardly-directed transport was demonstrated to be temperature-dependent and down-regulated by various metabolic inhibitors, therefore outlining its requirement for energy; it was shown to be Na+- and membrane potential-independent and inhibited by anionic drugs such as indomethacin, indoprofen and rifamycin B. These functional features are closed to those described for multidrug resistance-associated protein 1 (MRP1) that was furthermore demonstrated, in contrast to P-glycoprotein, to be expressed in SDVI cells and to lower CF accumulation in MRP1-overexpressing drug-resistant tumor cells. These data therefore suggest that active membrane transport of organic anions such as CF occurs in epithelial cells like cultured liver biliary SDVI cells through a MRP1-related efflux system.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Differential regulation of canalicular multispecific organic anion transporter (cMOAT) expression by the chemopreventive agent oltipraz in primary rat hepatocytes and in rat liver.

Expression of the canalicular multispecific organic anion transporter (cMOAT), an efflux pump involved in biliary secretion of xenobiotics, was investigated in rat hepatocytes exposed to the chemopreventive agent oltipraz. Northern blotting indicated that this compound increased cMOAT mRNA levels in primary cultured hepatocytes. Such an induction of cMOAT transcripts was demonstrated to be dose-dependent and started as early as 4 h treatment; in addition, western blotting showed increased levels of 190 kDa cMOAT in oltipraz-treated primary rat hepatocytes when compared with their untreated counterparts. In contrast, administration of oltipraz to rats failed to enhance hepatic cMOAT mRNA and protein amounts whereas it was found to induce liver expression of glutathione S-transferase P1, a well-known oltipraz-regulated drug metabolizing enzyme. These data therefore suggest that cMOAT up-regulation occurring in rat hepatocytes in response to oltipraz may be restricted to in vitro situations and is therefore unlikely to be directly involved in the in vivo chemopreventive properties of oltipraz.

Animals↗
PubMed1999

Use of the anionic dye carboxy-2',7'-dichlorofluorescein for sensitive flow cytometric detection of multidrug resistance-associated protein activity.

Multidrug resistance-associated protein (MRP) and P-glycoprotein are drug efflux pumps conferring multidrug resistance to tumor cells and sharing numerous substrates. In order to determine a flow cytometric assay allowing to analyse MRP activity in cancerous cells in a sensitive and specific manner, cellular accumulation and efflux of the anionic fluorescent dye carboxy-2',7'-dichlorofluorescein (CDF) were studied by flow cytometry using mainly MRP-overexpressing lung GLC4/Sb30 cells and parental GLC4 cells. GLC4/Sb30 cells were found to display reduced accumulation and enhanced efflux of the dye when compared to their parental counterparts. Probenecid, a well known blocker of MRP, strongly enhanced CDF accumulation in GLC4/Sb30 cells through inhibiting efflux of the dye; it also increased CDF levels in GLC4 cells, although to a lesser extent, which may likely be linked to the low, but detectable, expression of MRP in these cells. Comparison of CDF retention with that of calcein demonstrated that the former dye was the most efficiently effluxed by GLC4/Sb30 cells. In contrast to MRP overexpression, that of P-glycoprotein was not found to alter cellular CDF labelling whereas it strongly impaired calcein staining. These results indicate that CDF is a substrate for MRP, but not for P-gp, which may likely be useful for sensitive and specific flow cytometric determination of MRP activity in clinical samples.

ATP Binding Cassette Transporter, Subfamily B, Mem↗