Development and characterization of P-glycoprotein 1 (Pgp1, ABCB1)-mediated doxorubicin-resistant PLHC-1 hepatoma fish cell line

Potency and mechanism of p-glycoprotein chemosensitizers in rainbow trout (Oncorhynchus mykiss) hepatocytes

The membrane efflux transporter P-glycoprotein (P-gp, [ABCB1, MDR1]) exports a wide range of xenobiotic compounds, resulting in a continuous first line of defense against toxicant accumulation at basal expression levels, and contributing to the multixenobiotic resistance (MXR) phenotype at elevated expression levels. Relatively little information exists on P-gp inhibition in fish by chemosensitizers, compounds which lower toxicity thresholds for harmful P-gp substrates in complex mixtures. The effects of four known mammalian chemosensitizers (cyclosporin A [CsA], quinidine, valspodar [PSC833], and verapamil) on the P-gp-mediated transport of rhodamine 123 (R123) and cortisol in primary cultures of rainbow trout (Oncorhynchus mykiss) hepatocytes were examined. Competitive accumulation assays using 25 µM R123 or cortisol and varying concentrations of chemosensitizers (0-500 µM) were used. CsA, quinidine, and verapamil inhibited R123 export (IC50 values ± SE: 132 ± 60, 83.3 ± 27.2, and 43.2 ± 13.6 µM, respectively). CsA and valspodar inhibited cortisol export (IC50 values: 294 ± 106 and 92.2 ± 34.9 µM, respectively). In an ATP depletion assay, hepatocytes incubated with all four chemosensitizers resulted in lower free ATP concentrations, suggesting that they act via competitive inhibition. Chemosensitizers that inhibit MXR transporters are an important class of environmental pollutant, and these results show that rainbow trout transporters are inhibited by similar chemosensitizers (and mostly at similar concentrations) as seen in mammals and other fish species.

The effects of P-glycoprotein induction on ivermectin-induced behavioural alterations in zebrafish (Danio rerio) under varying diets

The neuroprotective effects of inducing the blood-brain barrier ATP-binding cassette protein transporter P-glycoprotein (P-gp) with clotrimazole (CTZ) in both fed and fasted zebrafish (Danio rerio) against the CNS-toxicant ivermectin (IVM, 22,23-dihydro avermectin B1a + 22,23-dihydro avermectin B1b) were examined. Zebrafish were administered 2 μmol/kg IVM intraperitoneally, and various behavioural assays (swimming performance, exploratory behaviour, olfactory responses, motor coordination, and escape responses) were used to measure neurological dysfunction. IVM administration alone caused a decrease in mean swim speed (91 % of controls), maximal speed (71 %), passage rate (81 %), 90° turns (81 %), and response to food stimulus (39 %). IVM exposure also increased the percent time that fish spent immobile (45 % increase over controls) and the percent of lethargic fish (40 % increase). Fish administered 30 μmol/kg of the P-gp inducer CTZ intraperitoneally 3 d prior to IVM exposure exhibited a change in only the % time spent immobile. These data indicate that P-gp induction may be limited in protecting the zebrafish CNS from IVM over baseline. Fasted fish did not differ from fed fish in the effects of IVM on behaviour, and no differences were seen following P-gp induction with CTZ. These results suggest that this chemical defence system is not downregulated when fish are challenged with limited energy availability.

P-glycoprotein inhibition affects ivermectin-induced behavioural alterations in fed and fasted zebrafish (Danio rerio)

The role of the blood-brain barrier ATP-binding cassette protein transporter P-glycoprotein (P-gp) in protecting zebrafish (Danio rerio) from the central nervous system neurotoxicant ivermectin (IVM, 22,23-dihydroavermectin B1a + 22,23-dihydroavermectin B1b) was examined in the absence and presence of the competitive inhibitor cyclosporin A (CsA). Zebrafish injected intraperitoneally with 1, 2, 5, or 10 µmol/kg IVM exhibited mortality 30 min following administration at the highest dose. At sublethal doses > 1 µmol/kg, IVM altered the swimming performance, exploratory behaviour, motor coordination, escape response and olfactory response in exposed fish. When fish were exposed to IVM in the presence of CsA, alterations in swimming and behaviours increased significantly and at the highest IVM/CsA ratio resulted in a complete lack of exploratory and olfactory behaviours. In separate experiments, fish were either fed or fasted, and the effects of IVM and CsA administration were examined. The effects of IVM administration and the exacerbated effects seen with CsA co-administration were not affected by fasting. This study provides evidence that P-gp provides a protective role in the BBB of fish against environmental neurotoxicants. The results also show that P-gp activity is maintained even under conditions of food deprivation, suggesting that this chemical defence system is prioritized over other energy expenditures during diet limitation.

First characterization of multixenobiotic activity in Collembola: An approach on cadmium-induced response

ATP-binding cassette (ABC) efflux pumps mediate the activity of the Multixenobiotic Resistance (MXR) mechanism and have been proposed as a biomarker of environmental pollution mainly in aquatic invertebrates. MXR activity was never investigated in Collembola and represents a potential tool for soil biomonitoring. This study aimed to characterize for the first time the activity of ABC efflux pumps in the gut of collembolan species, and investigate its responsiveness to cadmium (Cd), a common stressor found in polluted soils. We performed in vitro rhodamine-B accumulation assays in the presence of model inhibitors of ABC efflux pumps: verapamil hydrochloride as P-gp (P-glycoprotein) inhibitor, and MK571, as MRPs (multidrug resistance-related proteins) inhibitor. We also performed rhodamine-B accumulation assays under Cd-exposure (209 μg/L;1 μM). Our results showed that all species presented basal (noninduced) level of MXR activity in their gut. Efflux pumps P-gp and/or MRPs activity were confirmed in Cyphoderus innominatus, Cyphoderus similis, and Folsomia candida, the standard species. The rhodamine-B accumulation assays performed with Cd, applied as soil pollutant, showed that the gut of non-standard species C. similis and Trogolaphysa sp. presented an increase of MXR activity for both P-gp and MRP transporters, indicating the potential of these species as test organisms for soil ecotoxicology studies in Neotropical region. Our findings suggest a functional role of ABC transporters in the collembolan gut and their cellular involvement in Cd defense response, corroborating that MXR phenotype in Collembola can be a promising tool for bioindication of soil contamination.

ABC transporters in gills of rainbow trout (Oncorhynchus mykiss)

Fish gills are a structurally and functionally complex organ at the interface between the organism and the aquatic environment. Gill functions include the transfer of organic molecules, both natural ones and xenobiotic compounds. Whether the branchial exchange of organic molecules involves active transporters is currently not known. Here, we investigated the presence, diversity and functional activity of ATP-binding cassette (ABC) transporters in gills of juvenile rainbow trout. By means of RT-qPCR, gene transcripts of members from the abcb, abcc and abcg subfamilies were identified. Comparisons with mRNA profiles from trout liver and kidney revealed that ABC transporters known to have an apical localization in polarized epithelia, especially abcc2 and abcb1, were under-represented in the gills. In contrast, ABC transporters with mainly basolateral localization showed comparable gene transcript levels in the three organs. The most prominent ABC transporter in gills was an abcb subfamily member, which was annotated as abcb5 based on the synteny and phylogeny. Functional in vivo assays pointed to a role of branchial ABC transporters in branchial solute exchange. We further assessed the utility of primary gill cell cultures to characterize transporter-mediated branchial exchange of organic molecules, by examining ABC transporter gene transcript patterns and functional activity in primary cultures. The gill cultures displayed functional transport activity, but the ABC mRNA expression patterns were different to those of the intact gills. Overall, the findings of this study provide evidence for the presence of functional ABC transporter activity in gills of fish.

Tumorigenesis, diagnosis, and therapeutic potential of exosomes in liver cancer

Hepatocellular carcinoma (HCC, also called primary liver cancer) is one of the most fatal cancers in the world. Due to the insidiousness of the onset of HCC and the lack of effective treatment methods, the prognosis of HCC is extremely poor, and the 5-year average survival rate is less than 10%. Exosomes are nano-sized microvesicle and contain various components such as nucleic acids, proteins, and lipids. Exosomes are important carriers for signal transmission or transportation of material from cell to cell or between cells and tissues. In recent years, exosomes have been considered as potential therapeutic targets of HCC. A large number of reports indicate that exosomes play a key role in the establishment of an HCC microenvironment, as well as the development, progression, invasion, metastasis, and even the diagnosis, treatment, and prognosis of HCC. However, the exact molecular mechanisms and roles of exosomes in these processes remain unclear. We believe that elucidation of the regulatory mechanism of HCC-related exosomes and its signaling pathway and analysis of its clinical applications in the diagnosis and treatment of HCC can provide useful clues for future treatment regimens for HCC. This article discusses and summarizes the research progress of HCC-related exosomes and their potential clinical applications.

Tumorigenesis, diagnosis, and therapeutic potential of exosomes in liver cancer

Hepatocellular carcinoma (HCC, also called primary liver cancer) is one of the most fatal cancers in the world. Due to the insidiousness of the onset of HCC and the lack of effective treatment methods, the prognosis of HCC is extremely poor, and the 5-year average survival rate is less than 10%. Exosomes are nano-sized microvesicle and contain various components such as nucleic acids, proteins, and lipids. Exosomes are important carriers for signal transmission or transportation of material from cell to cell or between cells and tissues. In recent years, exosomes have been considered as potential therapeutic targets of HCC. A large number of reports indicate that exosomes play a key role in the establishment of an HCC microenvironment, as well as the development, progression, invasion, metastasis, and even the diagnosis, treatment, and prognosis of HCC. However, the exact molecular mechanisms and roles of exosomes in these processes remain unclear. We believe that elucidation of the regulatory mechanism of HCC-related exosomes and its signaling pathway and analysis of its clinical applications in the diagnosis and treatment of HCC can provide useful clues for future treatment regimens for HCC. This article discusses and summarizes the research progress of HCC-related exosomes and their potential clinical applications.

Molecular characterization of ABC transporters in marine ciliate, Euplotes crassus: Identification and response to cadmium and benzo[a]pyrene

ATP-binding cassette (ABC) transporters participate in transporting various substances, including xenobiotics, in or out of cells. However, their genetic information and function in ciliates remain still unclear. In this study, we sequenced and characterized two ABC transporter genes (EcABCB and EcABCC), and investigated the effect of cadmium (Cd) and benzo[a]pyrene (B[a]P) on their function and gene expression, using efflux assay and real-time reverse transcription-polymerase chain reaction (qRT-PCR), respectively, in the marine ciliate, Euplotes crassus. Sequencing analysis and efflux assay showed that EcABCB and EcABCC are typical ABC transporters, possessing conserved function. Exposure to Cd (≥5mg/L) and B[a]P (≥50.5μg/L) enhanced accumulation of a substrate. A significant increase in the expression of EcABCB and EcABC mRNA was observed at lower concentration in response to Cd and B[a]P. Our findings indicate that Cd and B[a]P could inhibit the efflux function of ABC transporters, leading to cellular toxicity in the ciliate.

Organic UV filters inhibit multixenobiotic resistance (MXR) activity in Tetrahymena thermophila: investigations by the Rhodamine 123 accumulation assay and molecular docking

Multixenobiotic resistance (MXR) transporters, which belong to ATP-binding cassette (ABC) family proteins, are present in living organisms as a first line of defense system against xenobiotics and environmental contaminants. The effects of six organic UV filters (4-methyl -benzylidene camphor, 4-MBC; benzophenone-3, BP-3; butyl methoxydibenzoyl-methane, BM-DBM; ethylhexyl methoxy cinnamate, EHMC; octocrylene, OC and homosalate, HMS) on multixenobiotic resistance (MXR) in Tetrahymena thermophila were investigated in this study. It was found that 4-MBC, BP-3 and BM-DBM could significantly inhibit activity of the MXR system, causing concentration dependent accumulation of rhodamine 123; while EHMC, OC and HMS had weak MXR inhibition. The IC50 (50 % inhibition concentration) values of 4-MBC, BP-3 and BM-DBM were 23.54, 40.59 and 26.37 μM, respectively, with inhibitory potentials of 23.1, 13.4 and 20.6 % relative to verapamil (VER, a model inhibitor of P-glycoprotein). Our results firstly provide the evidence for UV filters inhibition effect on MXR in aquatic organisms. In addition, it was revealed by molecular docking analysis that the selected six UV filters can occupy the same binding site on T. thermophila P-gp as VER does; and form H-bonds with residues Ser 328 and/or Asn 281. This study raises the awareness of aquatic ecological risk from the organic UV filters exposure, as they would be involved in potentiating toxic effects by chemosensitizing.

An isocorydine derivative (d-ICD) inhibits drug resistance by downregulating IGF2BP3 expression in hepatocellular carcinoma

In our previous studies, we reported that CD133⁺ cancer stem cells (CSCs) were chemoresistant in hepatocellular carcinoma (HCC) and that isocorydine treatment decreased the percentage of CD133⁺ CSCs. Here, we found that a derivative of isocorydine (d-ICD) inhibited HCC cell growth, particularly among the CD133⁺ subpopulation, and rendered HCC cells more sensitive to sorafenib treatment. d-ICD inhibited IGF2BP3 expression in a time-dependent manner, and IGF2BP3 expression negatively correlated with d-ICD-induced growth suppression. IGF2BP3 overexpression enriched the CD133⁺ CSC subpopulation in HCC, enhanced tumor sphere formation and suppressed the cytotoxic effects of sorafenib and doxorubicin. The expression of drug resistance-related genes, including ABCB1 and ABCG2, and the CSC marker CD133 expression was increased after IGF2BP3 overexpression. The significance of these observations was underscored by our findings that high IGF2BP3 expression predicted poor survival in a cohort of 236 patients with HCC and positively correlated with ABCG2 and CD133 expression in vivo. These results suggested that the d-ICD may inhibit HCC cells growth by IGF2BP3 decrease and that IGF2BP3 may serve as a therapeutic target for HCC.

Induction of multixenobiotic defense mechanisms in resistant Daphnia magna clones as a general cellular response to stress

Multixenobiotic resistance mechanisms (MXR) were recently identified in Daphnia magna. Previous results characterized gene transcripts of genes encoding and efflux activities of four putative ABCB1 and ABCC transporters that were chemically induced but showed low specificity against model transporter substrates and inhibitors, thus preventing us from distinguishing between activities of different efflux transporter types. In this study we report on the specificity of induction of ABC transporters and of the stress protein hsp70 in clones selected to be genetically resistant to ABCB1 chemical substrates. Clones resistant to mitoxantrone, ivermectin and pentachlorophenol showed distinctive transcriptional responses of transporter protein coding genes and of putative transporter dye activities. Expression of hsp70 proteins also varied across resistant clones. Clones resistant to mitoxantrone and pentachlorophenol showed high constitutive levels of hsp70. Transcriptional levels of the abcb1 gene transporter and of putative dye transporter activity were also induced to a greater extent in the pentachlorophenol resistant clone. Observed higher dye transporter activities in individuals from clones resistant to mitoxantrone and ivermectin were unrelated with transcriptional levels of the studied four abcc and abcb1 transporter genes. These findings suggest that Abcb1 induction in D. magna may be a part of a general cellular stress response.

Differences in tolerance to anthropogenic stress between invasive and native bivalves

Tolerance towards environmental stress has been frequently considered as one of the key determinants of invasion success. However, empirical evidence supporting the assumption that invasive species can better endure unfavorable conditions compared with native species is limited and has yielded opposing results. In this study, we examined the tolerance to different stress conditions (thermal stress and trace metal zinc pollution stress) in two phylogenetically related and functionally similar freshwater bivalve species, the native Anodonta anatina and the invasive Sinanodonta woodiana. We assessed potential differences in response to stress conditions using several cellular response assays: efficiency of the multixenobiotic resistance mechanism, respiration estimate (INT reduction capacity), and enzymatic biomarkers. Our results demonstrated that the invasive species overall coped much better with unfavorable conditions. The higher tolerance of S. woodiana was evident from (i) significantly decreased Rhodamine B accumulation indicating more efficient multixenobiotic resistance mechanism; (ii) significantly higher INT reduction capacity and (iii) less pronounced alterations in the activity of stress-related enzymes (glutathione-S-transferase, catalase) and of a neurotoxicity biomarker (cholinesterase) in the majority of treatment conditions in both stress trials. Higher tolerance to thermal extremes may provide physiological benefit for further invasion success of S. woodiana in European freshwaters, especially in the context of climate change.

Effects of triclosan and triclocarban on the growth inhibition, cell viability, genotoxicity and multixenobiotic resistance responses of Tetrahymena thermophila

The information about adverse effects of emerging contaminants on aquatic protozoa is very scarce. The growth inhibition effect, cell viability, genotoxicity and multixenobiotic resistance (MXR) responses of two commonly used antimicrobial agents, triclosan (TCS) and triclocarban (TCC) to protozoan Tetrahymena thermophila were investigated in this study. The results revealed that TCS and TCC can inhibit the growth of T. thermophila with 24h EC50 values of 1063 and 295μgL(-1), respectively. The impairment of plasma membrane was observed after 2h exposure of TCS or TCC at the level of mg/L. Furthermore, it is noticeable that at environmentally relevant concentration (1.0μgL(-1)), both TCS and TCC can lead to statistically significant DNA damage in T. thermophila, while the inhibition of growth and change of cell viability cannot be observed. Our results firstly provide the evidence for genotoxic effects of TCS and TCC on the freshwater protozoan. Additionally, both TCS and TCC were found to inhibit the efflux transporter activities, with the inhibitory potencies of 39% and 40% (using verapamil as a model inhibitor), respectively. Particularly, TCC could significantly down-regulate the expression of MXR related gene Abcb15, which encodes the membrane efflux protein that acting as P-gp in T. thermophila. The results raise the awareness of potential aquatic ecological and human health risks from the exposure of TCS and TCC, as they might potentiate the toxic effects by chemosensitizing with co-existing toxicants.

Functional xenobiotic metabolism and efflux transporters in trout hepatocyte spheroid cultures

Prediction of xenobiotic fate in fish is important for the regulatory assessment of chemicals under current legislation. Trout hepatocyte spheroids are a promising in vitro model for this assessment. In this investigation, the gene expression and function for xenobiotic metabolism and cellular efflux were characterised. Using fluorescence, transport and real time PCR analysis, the expression and functionality of a variety of genes related to xenobiotic metabolism and drug efflux were assessed in a range of trout hepatocyte culture preparations. Significantly greater levels of expression of genes involved in xenobiotic metabolism and efflux were measured in spheroids (which have been shown to remain viable in excess of 30 days), compared to hepatocytes cultured using conventional suspension and monolayer culture techniques. A transient decline in the expression of genes related to both xenobiotic metabolism and transport was determined during spheroid development, with a subsequent recovery in older spheroids. The most mature spheroids also exhibited an expression profile most comparable to that reported in vivo. Functionality of efflux transporters in spheroids was also demonstrated using fluorescent markers and specific inhibitors. In conclusion, the more physiologically relevant architecture in spheroid cultures provides a high functional integrity in relation to xenobiotic metabolism and efflux. Together with the enhanced gene expression and longevity of the model, hepatocytes in spheroid culture may prove to be an accurate alternative model to study the mechanisms of these processes in fish liver and provide an assay to determine the bioaccumulation potential of environmental contaminants.

Current advances on ABC drug transporters in fish

Most members of the large ATP-binding cassette (ABC) gene family are transporters involved in substrate translocation across biological membranes. In eukaryotes, ABC proteins functioning as drug transporters are located in the plasma membrane and mediate the cellular efflux of a wide range of organic chemicals, with some transporters also transporting certain metals. As the enhanced expression of ABC drug transporters can confer multidrug resistance (MDR) to cancers and multixenobiotic resistance (MXR) to organisms from polluted habitats, these ABC family members are also referred to as MDR or MXR proteins. In mammals, ABC drug transporters show predominant expression in tissues involved in excretion or constituting internal or external body boundaries, where they facilitate the excretion of chemicals and their metabolites, and limit chemical uptake and penetration into "sanctuary" sites of the body. Available knowledge about ABC proteins is still limited in teleost fish, a large vertebrate group of high ecological and economic importance. Using transport activity measurements and immunochemical approaches, early studies demonstrated similarities in the tissue distribution of ABC drug transporters between teleosts and mammals, suggesting conserved roles of the transporters in the biochemical defence against toxicants. Recently, the availability of teleost genome assemblies has stimulated studies of the ABC family in this taxon. This review summarises the current knowledge regarding the genetics, functional properties, physiological function, and ecotoxicological relevance of teleostean ABC transporters. The available literature is reviewed with emphasis on recent studies addressing the tissue distribution, substrate spectrum, regulation, physiological function and phylogenetic origin of teleostean ABC transporters.

Targeting glucose metabolism in chondrosarcoma cells enhances the sensitivity to doxorubicin through the inhibition of lactate dehydrogenase-A

Chondrosarcoma is a malignant cartilage-forming cancer composed of cells derived from transformed cells that produce cartilage. Conventional chemotherapy and radiotherapy have very limited efficacy in patients with advanced chondrosarcoma. In the present study, we reported a novel therapeutic approach in the treatment of chondrosarcoma cells. We detected that lactate dehydrogenase-A (LDHA) is highly active in chondrosarcoma cells and chondrosarcoma patient samples compared with normal chondrocyte cell lines and primary human chondrocyte. Moreover, chondrosarcoma cells exhibited elevated levels of LDHA expression under doxorubicin treatment. To further explore the mechanisms, we generated doxorubicin-resistant cells from SW1353 chondrosarcoma cell line. Notably, the activity and expression of LDHA are upregulated in doxorubicin-resistant cells. Moreover, our data showed a strong correlation between glucose metabolism and doxorubicin resistance in chondrosarcoma cells; doxorubicin-resistant cells displayed highly activated glucose metabolism and depended more on glucose supply. Finally, we reported a synergistic effect produced by incorporating doxorubicin with glycolysis inhibitors-oxamate in the combined treatment of chondrosarcoma cells in vitro and in vivo. In summary, the present study may aid in the development of new approaches using the combination of chemotherapeutic agents for the treatment of chondrosarcoma patients.

Differential ABCB and ABCC gene expression and efflux activities in gills and hemocytes of Mytilus galloprovincialis and their involvement in cadmium response

The aim of the study was to characterize ABC transport proteins gene expression and efflux activities in gills and hemocytes of the Mediterranean mussel and to evaluate their response to Cd. At basal level a higher expression of abcb-like gene was observed in gills than in hemocytes while abcc-like gene showed similar levels. Both P-gp and MRPs inhibitors (cyclosporine and MK571) blocked efflux activities in gills; hemocytes were sensitive only to MK571. After 120 min in vitro pre-exposure to CdCl2, the efflux activity increased significantly in gills and hemocytes. In vivo exposure to CdCl2 (0.4 μM) increased abcb-like gene expression in gills without affecting efflux activity. In hemocytes abcc-like gene resulted up-regulated and Ca-AM efflux resulted enhanced. An increased uptake of Cd in gills biopsies was observed in the presence of both P-gp and MRPs inhibitors. Our results indicate that ABC transporters seem involved in the first protective response to Cd and this response is tissue-specific.

Identification of P-glycoprotein inhibitors in contaminated freshwater sediments

P-glycoprotein (P-gp, ABCB1) is an important part of the multixenobiotic resistance (MXR) defense system in aquatic organisms. The main goal of this study was identification of P-gp inhibitors in contaminated sediments using the effect-directed analysis (EDA) approach. The samples were collected from the Gorjak creek (Zagreb, Croatia), a recipient of wastewater effluents from the pharmaceutical industry. Sediment samples were extracted and fractionated using a two-tiered approach. Resulting nonpolar, medium polar, and polar fractions were tested on the inhibition of P-gp activity using P-gp overexpressing PLHC-1/dox cells and calcein-AM as model substrate. The obtained EC50 values (up to 757 μg/g, expressed in toxicity equivalents of model P-gp inhibitor cyclosporine A) revealed high inhibitory potential of polar fractions of investigated sediments and clearly reflected the impact of pharmaceutical wastewater. P-gp specific ATPase assay and the cytotoxicity modulation experiments with colchicine indicated that most of the observed P-gp inhibition was due to the presence of noncompetitive inhibitors. A detailed chemical analysis by ultrahigh-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (UPLC-QTOFMS) revealed nonionic surfactants, including alcohol polyethoxylates (LAEOs) and polypropylene glycols (PPGs), as the major components of the most active subfractions. Testing of several LAEO and PPG commercial mixtures confirmed their potential to inhibit the fish P-glycoprotein and modulate toxicity of other xenobiotics present in complex environmental samples.

7,3',4'-Trihydroxyisoflavone modulates multidrug resistance transporters and induces apoptosis via production of reactive oxygen species

The development of multidrug resistance (MDR) to conventional chemoradiation therapy usually leads to failure in treating cervical cancer. This study aims to explore the effects and mechanisms of 7,3',4'-trihydroxyisoflavone (7,3',4'-THIF), one of the major metabolites of daidzein, on potentiating cytotoxicity of epirubicin (Epi), an anticancer drug in human cervical cancer HeLa cells. The cytotoxicity of Epi remarkably increased when it was combined with 7,3',4'-THIF. The cotreatment increased the reactive oxygen species (ROS) levels, including hydrogen peroxide and superoxide free radicals. 7,3',4'-THIF was shown to down-regulate the MDR1 promoter region composed of the elements of AP1, GC-box, and Y-box, as demonstrated by a luciferase assay. A negative regulation of hMDR1 gene with multiple transcription factors by this isoflavone may provide a novel molecular mechanism for MDR modulation. The mRNA expressions of MDR1, MDR-associated protein (MRP) 1, and MRP2 for the combined treatment were significantly lower than those of the Epi treatment. This result implies that MDR transporter-mediated Epi resistance is inhibited at various degrees by the addition of 7,3',4'-THIF. This isoflavone significantly enhanced intracellular Epi accumulation in HeLa cells. 7,3',4'-THIF and/or Epi triggered apoptosis through the upregulation of p53, Bax, and caspase-9. Apoptosis induction was also confirmed by the reduced mitochondrial membrane potential, increased sub-G1 and G2/M phases, nuclear DNA fragmentation, and chromatin condensation. Our findings demonstrate for the first time that 7,3',4'-THIF causes cell death in human cervical cancer cells through the ROS-dependent suppression of MDR transporters and p53-mediated activation of the intrinsic mitochondrial pathway of apoptosis. Thus, 7,3',4'-THIF has the potential to enhance the activity of a broad range of cancer chemotherapeutics in the MDR spectrum with the advantage of reducing adverse effects.

Interaction of ABC transport proteins with toxic metals at the level of gene and transport activity in the PLHC-1 fish cell line

The aim of this study was to investigate the interaction of four toxic metals with ABC transport proteins in piscine cell line PLHC-1. Cells were exposed for 24 h to 0.01-1 μM of CdCl(2), HgCl(2), As(2)O(3), or K(2)Cr(2)O(7) and the expression of a series of ABC genes (abcb1, abcc1-4) was determined using qRT-PCR. Using the fluorescent model substrates calcein-AM and monochlorbimane we measured interaction of metals with the transport activity of ABC transporters. P-glycoprotein (P-gp) activity was measured in PLHC-1/dox (P-gp overexpressing cells) while activity and interactions of metals with MRPs was measured in PLHC-1/wt cells. After 24 h exposure, abcc2-4 genes were dose-dependently up-regulated by all metals, while abcb1 and abcc1 were less affected. Up-regulation of abcc2 was more pronounced, with up to 8-fold increase in expression. Abcc3 and abcc4 were moderately inducible by HgCl(2) with 3.3-fold and 2.2-fold, respectively. All metals caused a significant inhibition of both P-gp (2.9- to 4-fold vs. controls) and MRP (1.3- to 1.8-fold) transport activities. Modulation of ABC genes and transport activities was further investigated in PLHC-1/wt cells exposed to 1 μM HgCl(2) for 72 h and in Hg resistant cells selected by long term cultivation of PLHC-1/wt cells in increasing concentrations of HgCl(2). Exposure to HgCl(2) for 72 h induced MRP genes expression and efflux activity. The long term cultivation of PLHC-1/wt cells in HgCl(2), did not cause prolonged up-regulation of the tested abc genes but resulted in higher MRP transport activities as determined by the increased sensitivity of these cells to MK571 (MRP specific inhibitor). Results of the present study indicated specific interaction of metals with selected ABC transport proteins. Modulation of ABC transporters takes place at both transcriptional and functional level. An active involvement of efflux pumps in Hg clearance in fish is suggested.

Regulation of xenobiotic transporter genes in liver and brain of juvenile thicklip grey mullets (Chelon labrosus) after exposure to Prestige-like fuel oil and to perfluorooctane sulfonate

Xenobiotic transport proteins are involved in cellular defence against accumulation of xenobiotics participating in multixenobiotic resistance (MXR). In order to study the transcriptional regulation of MXR genes in fish exposed to common chemical pollutants we selected the thicklip grey mullet (Chelon labrosus), since mugilids are widespread in highly degraded estuarine environments where they have to survive through development and adulthood. Partial sequences belonging to genes coding for members of 3 different families of ATP binding cassette (ABC) transporter proteins (ABCB1; ABCB11; ABCC2; ABCC3; ABCG2) and a vault protein (major vault protein, MVP) were amplified and sequenced from mullet liver. Their liver and brain transcription levels were examined in juvenile mullets under exposure to perfluorooctane sulfonate (PFOS) and to fresh (F) and weathered (WF) Prestige-like heavy fuel oil for 2 and 16 days. In liver, PFOS significantly up-regulated transcription of abcb1, abcb11 and abcg2 while in brain only abcb11 was up-regulated. Both fuel treatments significantly down-regulated abcb11 in liver at day 2 while abcc2 was only down-regulated by WF. mvp was significantly up-regulated by F and down-regulated by WF at day 2 in the liver. At day 16 only a significant up-regulation of abcb1 in the F group was recorded. Brain abcc3 and abcg2 were down-regulated by both fuels at day 2, while abcb1 and abcc2 were only down-regulated by F exposure. After 16 days of exposure only abcb11 and abcg2 were regulated. In conclusion, exposure to organic xenobiotics significantly alters transcription levels of genes participating in xenobiotic efflux, especially after short periods of exposure. Efflux transporter gene transcription profiling could thus constitute a promising tool to assess exposure to common pollutants.

First characterization of fish P-glycoprotein (abcb1) substrate specificity using determinations of its ATPase activity and calcein-AM assay with PLHC-1/dox cell line

P-glycoprotein (P-gp; abcb1) is one of the major ABC transport proteins that mediates multixenobiotic resistance (MXR) defense in fish. In order to offer a sound evaluation of its ecotoxicological relevance it is critical to characterize substrate specificity of fish P-gp. Measurement of the ATPase activity is a reliable approach often used to discern type of interaction of various drugs with mammalian P-gp. A similar assay has never been used for characterization of P-gp in aquatic organisms and the main goal of this study was to develop a specific ATPase assay for characterization of fish P-gp. For this purpose we have used P-gp enriched membrane vesicles isolated from fish hepatoma PLHC-1/dox cells characterized by high overexpression of P-gp. As additional demonstration of a P-gp specific phenotype, we have quantified transcript expression of a series of eight ABC efflux transporter genes constitutively expressed in PLHC-1 wild type and PLHC-1/dox cells. Transcript expression analysis confirmed high and specific P-gp transcript overexpression in PLHC-1/dox cells. Provided that the transcript abundance is translated to protein, the development of ATPase assay is enabled. Using this model we determined Km(ATP) of 0.4mM, baseline ATPase activity from 35-50nmol/mg(PROT)/min, and maximal activation of ATPase activity obtained for fish P-gp in our system was 1.8-2.5-fold over baseline. All these values were in good agreement with data previously reported for mammalian P-gp. In order to perform a more detailed characterization of fish P-gp substrate specificity, in the next step of our study we used the developed ATPase assay to test 50 different compounds for their interaction with fish P-gp. The same set of compounds was also tested with calcein-AM (Ca-AM) transport activity assay both using PLHC-1/dox cells and NIH 3T3/MDR1 fibroblast cells overexpressing human P-gp. Our results showed that there is a clear difference for some substances-five compounds specifically interacted only with fish P-gp, while seven compounds exhibited interaction with human P-gp only. Most of the compounds tested in this study showed similar behavior in respect to fish or human P-gp and relatively high correlation in the interaction potency was found between fish and human P-gp. In summary, the described results represent the first in depth insight into substrate specificity of an important xenobiotic efflux transporter in fish. In addition, our study showed that combination of Ca-AM assay and the developed ATPase assay using inside/out vesicles isolated from PLHC-1/dox cells, offers a high-throughput and reliable approach for identification of environmentally relevant pollutants that interact with fish P-gp.

Assessment of toxicological profiles of the municipal wastewater effluents using chemical analyses and bioassays

The hazardous chemical contamination of untreated wastewater and secondary effluent from the wastewater treatment plant (WWTP) of the city of Zagreb, Croatia was comprehensively characterized using large-volume solid-phase extraction (SPE) and silica gel fractionation, followed by a detailed analysis of the resulting extracts by a combination of chemical and bioassay methods. Over 100 individual contaminants or closely related-contaminant groups were identified by high-resolution gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/quadrupole time-of-flight mass spectrometry (LC-QTOF). Ecotoxicity profiling of the investigated samples, including cytotoxicity, chronic toxicity and EROD activity; inhibition of the multixenobiotic resistance (MXR), genotoxicity and estrogenic potential, revealed the most significant contribution of toxic compounds to be present in polar fractions. Wastewater treatment using conventional activated sludge process reduced the initial toxicity of raw wastewater to various extents, ranging from 28% for algal toxicity to 73.2% for an estrogenic activity. The most efficient toxicity removal was observed for the polar compounds.

Constitutive mRNA expression and protein activity levels of nine ABC efflux transporters in seven permanent cell lines derived from different tissues of rainbow trout (Oncorhynchus mykiss)

Permanent fish cell lines have become common model systems for determining ecotoxicological effects of pollutants. For these cell lines little is known on the cellular active transport mechanisms that control the amount of a compound entering the cell, such as the MXR (multixenobiotic resistance) system mediated by ATP binding cassette (ABC) transport proteins. Therefore, for toxic evaluation of chemicals with those cells information on MXR is important. We here present data on constitutive mRNA expression and protein activity levels of a series of ABC efflux transporters in seven permanent cell lines derived from liver (RTL-W1; R1) and liver hepatoma (RTH-149), gill (RTgill-W1), gonad (RTG-2), gut (RTgutGC) and brain (RTbrain) of rainbow trout (Oncorhynchus mykiss). In addition to known transporters abcb1 (designated here abcb1a), abcb11, abcc1-3, abcc5 and abcg2, we quantified expression levels of a newly identified abcb1 isoform (abcb1b) and abcc4, previously unknown in trout. Quantitative real time PCR (qPCR) indicated that mRNA of the examined ABC transporters was constitutively expressed in all cell lines. Transporter mRNA expression patterns were similar in all cell lines, with expression levels of abcc transporters being 80 to over 1000 fold higher than for abcg2, abcb1a/b and abcb11 (abcc1-5>abcg2>abcb1a/b, 11). Transporter activity in the cell lines was determined by measuring uptake of transporter type specific fluorescent substrates in the presence of activity inhibitors. The combination of the ABCB1 and ABCC transporter substrate calcein-AM with inhibitors cyclosporine A, PSC833 and MK571 resulted in a concentration-dependent fluorescence increase of up to 3-fold, whereas reversin 205 caused a slight, but not concentration-dependent fluorescence increase. Accumulation of the dyes Hoechst 33342 and 2',7'-dichlorodihydrofluorescein diacetate was basically unchanged in the presence of Ko134 and taurocholate, respectively, indicating low Abcg2 and Abcb11 activities, in accordance with low abcg2 and abcb11 transcript levels. Our data indicate that transporter expression and activity patterns in the different trout cell lines are irrespective of the tissue of origin, but are determined by factors of cell cultivation.

Characterization of the multixenobiotic resistance (MXR) mechanism in embryos and larvae of the zebra mussel (Dreissena polymorpha) and studies on its role in tolerance to single and mixture combinations of toxicants

The study of the cellular mechanisms of tolerance of organisms to pollution is a key issue in aquatic environmental risk assessment. Recent evidence indicates that multixenobiotic resistance (MXR) mechanisms represent a general biological defense of many marine and freshwater organisms against environmental toxicants. In this work, toxicologically relevant xenobiotic efflux transporters were studied in early life stages of zebra mussels (Dreissena polymorpha). Expression of a P-gp1 (ABCB1) transporter gene and its associated efflux activities during development were studied, using qRT-PCR and the fluorescent transporter substrates rhodamine B and calcein-AM combined with specific transporter inhibitors (chemosensitizers). Toxicity bioassays with the model P-gp1 chemotherapeutic drug vinblastine applied singly and in combination with different chemosensitizers were performed to elucidate the tolerance role of the P-gp1 efflux transporter. Results evidenced that the gene expression and associated efflux activities of ABC transporters were low or absent in eggs and increased significantly in 1-3d old trochophora and veliger larvae. Specific inhibitors of Pgp1 and/or MRP transport activities including cyclosporine A, MK571, verapamil and reversin 205 and the musk celestolide resulted in a concentration dependent inhibition of related transport activities in zebra mussel veliger larvae, with IC50 values in the lower micromolar range and similar to those reported for mammals, fish and mussels. Binary mixtures of the tested transporter inhibitors except celestolide with the anticancer drug and P-gp1 substrate vinblastine increased the toxicity of the former compound more than additively. These results indicate that MXR transporter activity is high in early life-stages of the zebra mussel and that may play an important role in the tolerance to environmental contaminants.

Human pharmaceuticals modulate P-gp1 (ABCB1) transport activity in the fish cell line PLHC-1

The ubiquitous presence of pharmaceuticals in aquatic systems is a challenging problem as their potential chronic effects on aquatic organisms remain largely unknown. The ATP-binding cassette (ABC) transport proteins contributing to the multidrug/multixenobiotic resistance (MDR/MXR) phenomenon seem to have an important role in the elimination of xenobiotics in aquatic organisms. Modulation of their efflux activities by contaminants may lead to substantial increase in intracellular accumulation and toxic effects of other xenobiotics. The aim of our work was to analyse a series of pharmaceuticals for their potential to modulate the activity of xenobiotic efflux transporters from the ABCB and ABCC sub-family in the Poeciliopsis lucida hepatoma cell (PLHC-1) fish cell line (PLHC-1/wt) and a doxorubicin (DOX) resistant PLHC-1 subclone (PLHC-1/dox) characterized by an elevated expression of the P-glycoprotein (ABCB1). Cellular accumulation of the model fluorescent substrates calcein-AM and rhodamine123 were used to determine an inhibitory effect on P-gp1 and/or MRP-like efflux transporters. 18 out of 33 tested pharmaceuticals showed MXR inhibitory activity with IC50 values occurring in the lower micromolar to millimolar range. Further, cytotoxic effects of pharmaceuticals were evaluated in PLHC-1/dox cells. Co-exposure of resistant cells to model P-gp1 inhibitor cyclosporine A (CyA) resulted in up to five times increased cytotoxicity of pharmaceuticals. In addition, some pharmaceuticals lead to a marked increase in cytotoxicity of doxorubicin, a model P-gp1 substrate. The modulation of toxicity by MDR inhibitors indicates their role in influencing cellular toxicity. In conclusion, the results of our study revealed significant inhibitory effects of environmentally relevant pharmaceuticals on P-gp1 and MRP-like transporters in fish. Our findings correspond well with data from mammalian systems indicating that the specificity and roles of the related efflux transporters may be similar in fish. Furthermore, due to the presence of active and inducible ABC transport proteins, the PLHC-1 cells appear to be a reliable in vitro system for the investigation of MDR/MXR mechanisms in fish.