Genetic and immunological characterisation of a multixenobiotic resistance system in the turbot (Scophthalmus maximus)

Unraveling cellular and molecular mechanisms of acid stress tolerance and resistance in marine species: New frontiers in the study of adaptation to ocean acidification

Since the industrial revolution, fossil fuel combustion has led to a 30 %-increase of the atmospheric CO₂ concentration, also increasing the ocean partial CO₂ pressure. The consequent lowered surface seawater pH is termed ocean acidification (OA) and severely affects marine life on a global scale. Cellular and molecular responses of marine species to lowered seawater pH have been studied but information on the mechanisms driving the tolerance of adapted species to comparatively low seawater pH is limited. Such information may be obtained from species inhabiting sites with naturally low water pH that have evolved remarkable abilities to tolerate such conditions. This review gathers information on current knowledge about species naturally facing low water pH conditions and on cellular and molecular adaptive mechanisms enabling the species to survive under, and even benefit from, adverse pH conditions. Evidences derived from case studies on naturally acidified systems and on resistance mechanisms will guide predictions on the consequences of future adverse OA scenarios for marine biodiversity.

Expression and Function of ABC Proteins in Fish Intestine

In fish, the intestine is fundamental for digestion, nutrient absorption, and other functions like osmoregulation, acid-base balance, and excretion of some metabolic products. These functions require a large exchange surface area, which, in turn, favors the absorption of natural and anthropogenic foreign substances (xenobiotics) either dissolved in water or contained in the food. According to their chemical nature, nutrients, ions, and water may cross the intestine epithelium cells' apical and basolateral membranes by passive diffusion or through a wide array of transport proteins and also through endocytosis and exocytosis. In the same way, xenobiotics can cross this barrier by passive diffusion or taking advantage of proteins that transport physiological substrates. The entry of toxic substances is counterbalanced by an active efflux transport mediated by diverse membrane proteins, including the ATP binding cassette (ABC) proteins. Recent advances in structure, molecular properties, and functional studies have shed light on the importance of these proteins in cellular and organismal homeostasis. There is abundant literature on mammalian ABC proteins, while the studies on ABC functions in fish have mainly focused on the liver and, to a minor degree, on the kidney and other organs. Despite their critical importance in normal physiology and as a barrier to prevent xenobiotics incorporation, fish intestine's ABC transporters have received much less attention. All the ABC subfamilies are present in the fish intestine, although their functionality is still scarcely studied. For example, there are few studies of ABC-mediated transport made with polarized intestinal preparations. Thus, only a few works discriminate apical from basolateral transport activity. We briefly describe the main functions of each ABC subfamily reported for mammals and other fish organs to help understand their roles in the fish intestine. Our study considers immunohistochemical, histological, biochemical, molecular, physiological, and toxicological aspects of fish intestinal ABC proteins. We focus on the most extensively studied fish ABC proteins (subfamilies ABCB, ABCC, and ABCG), considering their apical or basolateral location and distribution along the intestine. We also discuss the implication of fish intestinal ABC proteins in the transport of physiological substrates and aquatic pollutants, such as pesticides, cyanotoxins, metals, hydrocarbons, and pharmaceutical products.

Multixenobiotic resistance mechanism: Organ-specific characteristics in the fish Prochilodus lineatus and its role as a protection against genotoxic agents

The multixenobiotic resistance mechanism (MXR) can decrease intracellular genotoxic pressure through the efflux of compounds out of the cell. Thus, this work presents a temporal approach to evaluate the MXR activity and the occurrence of genotoxic damage in different organs of the fish Prochilodus lineatus after an intraperitoneal injection of benzo[a]pyrene (B[a]P). Although the liver and brain demonstrated rapid MXR induction (6 h), the occurrence of DNA damage was not prevented. However, these organs presented some return to DNA integrity after MXR activity. The kidney demonstrated the slowest response in the MXR induction (24 h), which may be related to the preferential excretion of B[a]P metabolites by this route. Moreover, the kidney MXR reduction at 96 h may be related to its role in the excretion of metabolites from all other metabolizing organs. The gills did not appear to play an essential role in xenobiotics efflux; however, their participation in biotransformation is exhibited through the occurrence of DNA damage. The integrated response of the organs in the dynamics for the maintenance of the organism integrity could be promoted by the circulation of the xenobiotic through the bloodstream, which corroborates the increase in the DNA damage in the erythrocytes at 6 h. Therefore, the ability to induce MXR was linked to the preservation of DNA integrity in the presence of B[a]P, since MXR acts to avoid the accumulation of xenobiotics inside the cell.

Toxicological responses of Carassius auratus induced by benzophenone-3 exposure and the association with alteration of gut microbiota

Gut microbiota plays a fundamental role in host's physiology. However, the effect of organic UV filters, an emerging contaminant on gut microbiota is poorly understood. Here, fish (Carassius auratus) were exposed to 2, 20 and 200 μg/L of benzophenone-3 (BP3) for 28 days to explore the toxicological effects and its association with the changes in the gut microbiota. The BP3 accumulation is time and dose dependent in the liver and intestine. Under BP3 subchronic exposure, fish's body and intestinal weights, reactive oxygen species (ROS), immunoglobulin M (IgM) and vitellogenin (VTG) levels, as well as 7-benzyloxy-4-trifluoromethylcoumarin-O-debenzyloxylase (BFCOD) activities, were decreased. BP3 exposure has increased the abundance of Bacteroidetes phylum and Mycobacterium genus. Bioinformatic analysis revealed that the levels of ROS, IgM, estrogen receptor and VTG, activities of lysozyme, BFCOD and 7-ethoxyresorufin-O-deethylase were significantly correlated with the relative abundance of intestinal microbial genus (p < 0.05). These results highlight for the first time the association between the effects of organic UV filters on the antioxidant, immune, endocrine, and metabolic systems of the fish and changes in the gut microbiota, which extend knowledge of the role of gut microbiota in ecotoxicology.

Effects of emodin on ABC transporter gene expression in grass carp (Ctenopharyngodon idellus) exposed to diazinon

This study aimed to investigate the function of ATP-binding cassette (ABC) transporter genes in grass carp treated with emodin combined with diazinon (DZN) exposure. The transcription levels of five ABC transporter genes in different tissues of grass carp and at different time points were measured by real-time quantitative PCR (qRT-PCR). The analysis of different tissues showed higher ABCB1 expression in the skin (26-fold) and gill (2-fold) than in the liver. In addition, ABCB11 expression was higher in the skin (109-fold) and gill (57-fold) than in the liver, ABCC1 was more highly expressed in the gill (50-fold) than in the liver, and ABCG2 was expressed at higher levels in the skin (659-fold, p < 0.01), gill (628-fold, p < 0.01) and liver (659-fold, p < 0.01) than in brain tissue. The analysis of different time points revealed that the ABCB1, ABCB11, ABCC1, ABCC2 and ABCG2 genes were highly expressed at 24 h in the liver in the experimental group. However, analysis of the intestinal tissue of the experimental group showed that the expression of ABCB1 and ABCB11 peaked at 6 h, the expression of ABCC1 and ABCC2 peaked at 5 d, and the expression of ABCG2 peaked at 3 d. Furthermore, the emodin concentrations in the liver and intestine reached their peak levels (50.18 and 117.24 μg·ml⁻¹, respectively) after 48 and 1 h of treatment with emodin combined with DZN, respectively. The peak DZN concentrations in the liver (1.42 ng·ml⁻¹) and intestine (0.2 ng·ml⁻¹) were detected 3 and 6 h after emodin treatment combined with DZN, respectively. In conclusion, this study shows that the transcript levels of ABC transporters respond to the presence of emodin, which indicates their potential involvement in and contribution with the metabolic process in grass carp.

Effects of Camellia sinensis crude saponin on survival and biochemical markers of oxidative stress and multixenobiotic resistance of the Mediterranean mussel, Mytilus galloprovincialis

The Ebro Delta (NE Spain), formed by two bays, northern and southern hemidelta, is an area mainly devoted to rice farming. As a result shellfish species inhabiting or cultured in nearby bays may become increasingly threatened by exposure to pollutants associated to agriculture. The latest product applied in the rice fields is a plant based molluscicide called saponin, used to control populations of the giant apple snail (GAS). Saponins are known to also affect other organisms, hence research of its toxicity towards non target species is needed. In this study, mussels (Mytilus galloprovincialis) were exposed to three concentrations of suspended solid pellets containing saponin extracts from the plant species Camellia sinensis. Effects across a large set of biochemical markers were investigated in the digestive gland and gill tissue of exposed mussels to saponin for 1 and 7days. In addition, crude saponin was extracted from solid pellets to confirm its correct concentration. Results obtained from this study, showed that the concentration of crude saponin in dry pellets was of 5.5%. Lethal levels of saponin were 3.2 fold higher than the maximal predicted field concentration, and activated respiratory metabolism and expression of transmembrane protein transporters. Mussels, exposed to sub lethal concentrations of saponin showed increase of antioxidant defenses.

Tissue-specific bioconcentration and biotransformation of cypermethrin and chlorpyrifos in a native fish (Jenynsia multidentata) exposed to these insecticides singly and in mixtures

The aim of the present study was to evaluate the accumulation of cypermethrin and chlorpyrifos when the fish Jenynsia multidentata was exposed to these pesticides singly and in technical and commercial mixtures. Adult female fish were exposed over 96 h to 0.04 μg/L of cypermethrin; 0.4 μg/L of chlorpyrifos; 0.04 μg/L of cypermethrin + 0.4 μg/L of chlorpyrifos in a technical mixture; and 0.04 μg/L of cypermethrin + 0.4 μg/L of chlorpyrifos in a mixture of commercial products. Fish exposed to cypermethrin accumulated this compound only in muscle, probably because of the low biotransformation capacity of this organ and the induction of cytochrome P4501A1 (CYP1A1) expression in the liver. The accumulation of chlorpyrifos occurred in fish exposed to the insecticide (intestine > liver > gills) even when these fish had higher gluthatione-S-transferase (GST) activity in gills and P-glycoprotein (P-gp) expression in the liver, compared with the control. Fish exposed to the technical mixture showed cypermethrin accumulation (liver > intestine > gills) with higher levels than those measured in fish after only cypermethrin exposure. Higher expression levels of CYP1A1 in the liver were also observed compared with the Control. Fish exposed to the commercial mixture accumulated both insecticides (cypermethrin: intestine > gills and chlorpyrifos: liver > intestine > gills > muscle). In the organs where accumulation occurred, biotransformation enzymes were inhibited. Consequently, the commercial formulation exposure provoked the highest accumulation of cypermethrin and chlorpyrifos in J. multidentata, possibly associated with the biotransformation system inhibition. Environ Toxicol Chem 2017;36:1764-1774. © 2016 SETAC.

ABC transporters and xenobiotic defense systems in early life stages of rainbow trout (Oncorhynchus mykiss)

Embryos of oviparous fish, in contrast to (ovo) viviparous species, develop in the aquatic environment, and therefore need solute transport systems at their body surfaces for maintaining internal homeostasis and defending against potentially harmful substances. We hypothesized that solute transporters undergo changes in tissue distribution from the embryo to the larval stage. We therefore studied the mRNA profiles of eight ABC transporters (abcb1a, abcb1b, abcc1, abcc2, abcc3, abcc4, abcc5, abcg2) and three solute carriers (oatp1d, putative oatp2 putative, mate1) in different body regions (head, yolk sac epithelium, abdominal viscera, skin/muscles) of developing rainbow trout. Additionally, we investigated mRNA levels of phase I (cyp1a, cyp3a) and phase II (gstp, putative ugt1, putative ugt2) biotransformation enzymes. The study covered the developmental period from the eleuthero-embryo stage to the first-feeding larval stage (1-20days post-hatch, dph). At 1dph, transcripts of abcc2, abcc4, abcg2, cyp3a, gstp, putative mate1, and putative oatp2 occurred primarily in the yolk sac epithelium, whereas at later stages expression of these genes was predominantly observed in the abdominal viscera. The functional activity of ABC transporters in fish early life stages was assessed by rhodamine B accumulation assays. Finally, we investigated the potential impact of xenobiotics (clotrimazole, clofibric acid) on the ABC and biotransformation systems of trout early life stages. While clofibric acid had no effect, clotrimazole lead to an increased rhodamine B accumulation. The results provide evidence that the transition from the eleuthero-embryo to the larval stage is accompanied by a major alteration in tissue expression of ABC transporters.

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.

The first demonstration of CYP1A and the ABC protein(s) gene expression and activity in European seabass (Dicentrarchus labrax) primary hepatocytes

Primary hepatocytes are a model for studying various effects of different xenobiotics, including detoxification strategies. In this study we have isolated and cultured European seabass (Dicentrarchus labrax) primary hepatocytes and assessed gene transcription and activity of CYP1A (phase I of cellular detoxification) and ABCC1 and ABCC2 (phase III) transport proteins after exposure to benzo(a)pyrene (BaP). A dose dependent increase in Abcc2 and Cyp1a mRNA transcripts was observed in seabass primary hepatocytes upon exposure to BaP. The activity of ABC proteins, as key mediators of the multixenobiotic resistance (MXR), was further confirmed by assessing the accumulation of the model fluorescence substrate rhodamine 123 in the absence and presence of model inhibitors. A weak interaction between BaP and ABC proteins was observed. CYP1A dependent ethoxyresorufin-O-deeethylase (EROD) activity was significantly induced by the presence of BaP. After the 24h exposure period only 10% of the initial BaP was present in the incubation medium, clearly demonstrating biotransformation potential of primary seabass hepatocytes. Furthermore, the presence of the 3-hydroxybenzo(a)pyrene, a BaP metabolite, in the medium implies its active efflux. In conclusion, we showed that seabass primary hepatocytes do express important elements of the cellular detoxification machinery and may be a useful in vitro model for studying basic cellular detoxification mechanisms and their interaction with environmental contaminants.

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.

Presence of ecotoxicologically relevant Pgp and MRP transcripts and proteins in Cyprinid fish

One of the most intriguing defence strategies which aquatic organisms developed through evolution is multixenobiotic resistance (MXR). The key mediators of MXR activity are ATP-binding cassette (ABC) transport proteins. They provide resistance of aquatic organisms by binding xenobiotics and extruding them from cells in an energy-dependent manner. Since Cyprinid fish species are common target in freshwater biomonitoring programs, we have studied the presence of two main MDR/MXR efflux transporters P-glycoprotein (Pgp, Abcb1) and MRP-like protein(s) (Abcc) in the liver of five Cyprinid species: common carp, European chub, sneep, barbel, and silver prussian carp. Their presence was evaluated on the mRNA and protein level. Various pairs of primers were designed to clone homologous fragments of MXR-related genes. At the protein level, we used Western blotting with specific monoclonal antibodies against human Pgp (Abcb1, Ab C219), MRP1 (Abcc1; Ab MRPm6) or MRP2 (Abcc2; Ab M2I-4). Transcripts of both key types of MXR transporters were identified in all species examined and here we provide the phylogenetic analysis of new partial sequences. Immunochemical determinations with mammalian antibodies failed to identify the presence of MRP(s), but Pgp expression was found in all five Cyprinid species. These results support that MXR is a defence system mediated by both Pgp and MRP types of ABC transport proteins.

Gene expression analysis of the ABC efflux transporters in rainbow trout (Oncorhynchus mykiss)

In this study we examined gene expression of a series of ABC efflux transporters in various rainbow trout (Oncorhynchus mykiss) tissues. Based on their reported toxicological relevance, we have used quantitative real time PCR SYBR green quantification methodology, with combination of absolute and relative approach, to quantify RNA expression of eight ABC transporters from three different families: abcb1 and abcb11, abcc1-5 and abcg2. Level of mRNA transcripts was measured in seven tissues: liver, brain, gonads, kidney, gills, proximal intestine and distal intestine, and the obtained expression profiles were compared with data available for related mammalian tissues. Most of the analyzed genes showed similar gene expression pattern as the ones found in mammals, with some notable exceptions. E.g., gills were in our study characterized by extremely low expression of all analyzed ABC genes; and despite the pronounced role of ABCC1 (MRP1) in protection of mammalian cells from chemical toxins, we found low expression of this transporter in trout tissues. Taken together, our study offers the first thorough insight into distribution pattern of (eco)toxicologically relevant ABC transporters, serving as a necessary base for further studies directed to better understanding of physiological and/or protective role of ABC transporters in fish.

Effects of microcystin-LR on the expression of P-glycoprotein in Jenynsia multidentata

The multixenobiotic resistance phenomenon (MXR) related to the P-glycoprotein multidrug transporter protein (P-gp) has been identified and characterized in several aquatic organisms. In the present work, we prove the presence of a P-gp in liver, gills and brain of Jenynsia multidentata by Western Blot and RT-PCR. A 170 kDa protein has been found in liver and gills while in brain a approximately 80 kDa protein has been detected. The partial nucleotide sequence obtained in this autochthonous fish showed high similarity ranging from 83% to 92% with other fishes. In addition, P-gp expression in this fish was evaluated after time and dose-dependent exposures to the cyanotoxin microcystin-LR. Individuals were exposed to MC-LR at concentrations of 2, 5 and 10 microg L(-1) for 24h and for 6, 12 and 24h at 2 microg L(-1) MC-LR. Changes in P-gp expression were observed in liver, gills and brain. However, this response was tissue specific. Only in gills of J. multidentata P-gp expression, measured either by real-time RT-PCR or Western Blot, was significantly higher compared to controls at most tested times and doses. A 3-fold increase with respect to controls was found at 12h by RT-PCR and after 24h by Western Blot. In dose-dependent experiments the maximum P-gp expression was observed at 2 microg L(-1) MC-LR, measured by both RT-PCR and Western Blot. In the liver, P-gp protein levels were significantly increased after 24h of exposure, at every toxin dose tested. Thus, probably longer exposures would show also significant increases in this tissue. Considering these results we can propose that P-gp belongs to the defence system involved in the response to MC-LR in J. multidentata.

Cloning and molecular characterization of apical efflux transporters (ABCB1, ABCB11 and ABCC2) in rainbow trout (Oncorhynchus mykiss) hepatocytes

Fish possess similar mechanisms of billiary excretion of xeno(endo)biotics and their metabolites as found in higher vertebrates and various types of ABC efflux proteins expressed in apical membranes of polarized cells appears to be key mediators of this vectorial transport. To test this hypothesis the main goals of this study were identification and cloning of genes coding for different types of ABC transport proteins, determination of the gene transcript (mRNA) levels, and characterization of the related protein transport activities in primary cultured rainbow trout (Oncorhynchus mykiss) hepatocytes. We have cloned one partial and two full gene sequences, which show high degree of identity with mammalian Pgp1 (ABCB1), BSEP (ABCB11) and MRP2 (ABCC2) efflux transporters. Using real-time RT-PCR expression levels of the mRNA of these genes were determined. Identical relative expression patterns of identified efflux transporters (BSEP>>MRP2>Pgp1) were observed for both liver and primary hepatocytes, with expression of all three transporter mRNAs approximately 3-4-fold lower in primary hepatocytes in comparison to intact liver. In addition, the presence of Pgp1-, BSEP- and MRP-like transport activities were indicated using putative specific fluorescent substrates (rhodamine 123, calcein-AM, bodipy-verapamil and dihydrofluorescein diacetat), model inhibitors (verapamil, cyclosporine A, MK571, reversine 205, taurocholate and taurochenodeoxycholate) and their combinations. Taken together the results of this study showed that primary trout hepatocytes express critical components of detoxification pathways-phase I and II enzymes, as well as the ABC proteins involved in transport of xenobiotics, affirming this in vitro model as a promising tool in (eco)toxicological research.

Multixenobiotic resistance, acetyl-choline esterase activity and total oxyradical scavenging capacity of the Arctic spider crab, Hyasaraneus, following exposure to bisphenol A, tetra bromo diphenyl ether and diallyl phthalate

The Arctic has become a sink for persistent organic pollutants (POPs) originating from lower latitudes, and relatively high levels have been found in different biota. Recent studies have identified detrimental effects on wildlife including endocrine disruption, impairment of enzyme activity, and reduced immune function. The Arctic spider crab, Hyas araneus, shown interesting potential for its use as sentinel organism in polar ecosystems. This study investigated the effect of 2,2',4,4'-tetra bromo diphenyl ether (BPDE), bisphenol A (BPA), and diallyl phthalte (DPA) on H. araneus in a three weeks exposure study. Expression of multixenibiotic resistance (MXR) proteins has been studied using the C219 monoclonal antibody which allows identifying an immunoreactive protein of 40 kDa in the digestive gland while no such protein could be observed in the gills. Expression of this protein was increased by exposure to DPA (+75%; p<0.05, n=10). All compounds significantly affected muscle acetylcholine esterase (AChE) activity (p<0.05, n=10) with 50 microg/L DPA having the strongest effect by lowering the value to 37% of control. The total oxyradical scavenging capacity measured in the digestive gland toward peroxyl, hydroxyl and peroxynitrite was also significantly reduced indicating a decreased resistance to oxidative stress generated by DPA (p<0.05, n=5). These results thus suggest the potential detrimental effects of DPA even at concentration as low as 50 microg/L on H. araneus.

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

The development of the multidrug resistance (MDR) phenotype in mammals is often mediated by the overexpression of the P-glycoprotein1 (Pgp, ABCB1) or multidrug resistance-associated protein (MRP)-like ABC transport proteins. A similar phenomenon has also been observed and considered as an important part of the multixenobiotic resistance (MXR) defence system in aquatic organisms. We have recently demonstrated the presence of ABC transporters in the widely used in vitro fish model, the PLHC-1 hepatoma cell line. In the present study we were able to select a highly resistant PLHC-1 sub-clone (PLHC-1/dox) by culturing the wild-type cells in the presence of 1 microM doxorubicin. Using quantitative PCR a 42-fold higher expression of ABCB1 gene was determined in the PLHC-1/dox cells compared to non-selected wild-type cells (PLHC-1/wt). The efflux rates of model fluorescent Pgp1 substrates rhodamine 123 and calcein-AM were 3- to 4-fold higher in the PLHC-1/dox in comparison to the PLHC-1/wt cells. PLHC-1/dox were 45-fold more resistant to doxorubicin cytotoxicity than PLHC-1/wt. Similarly to mammalian cell lines, typical cross-resistance to cytotoxicity of other chemotherapeutics such as daunorubicin, vincristine, vinblastine, etoposide and colchicine, occurred. Furthermore, cyclosporine A, verapamil and PSC833, specific inhibitors of Pgp1 transport activity, completely reversed resistance of PLHC-1/dox cells to all tested drugs, resulting in EC50 values similar to the EC50 values found for PLHC-1/wt. In contrast, MK571, a specific inhibitor of MRP type of efflux transporters, sensitized PLHC-1/dox cells, neither to doxorubicin, nor to any other of the chemotherapeutics used in the study. These data demonstrate for the first time that a specific Pgp1-mediated doxorubicin resistance mechanism is present in the PLHC-1 fish hepatoma cell line. In addition, the fact that low micromolar concentrations of specific inhibitors may completely reverse a highly expressed doxorubicin resistance points to the fragility of Pgp1-mediated MXR defence mechanism in fish.

Increase in multidrug transport activity is associated with oocyte maturation in sea stars

In this study, we report on the presence of efflux transporter activity before oocyte maturation in sea stars and its upregulation after maturation. This activity is similar to the multidrug resistance (MDR) activity mediated by ATP binding cassette (ABC) efflux transporters. In sea star oocytes the efflux activity, as measured by exclusion of calcein-am, increased two-fold 3 h post-maturation. Experiments using specific and non-specific dyes and inhibitors demonstrated that the increase in transporter activity involves an ABCB protein, P-glycoprotein (P-gp), and an ABCC protein similar to the MDR-associated protein (MRP)-like transporters. Western blots using an antibody directed against mammalian P-gp recognized a 45 kDa protein in sea star oocytes that increased in abundance during maturation. An antibody directed against sea urchin ABCC proteins (MRP) recognized three proteins in immature oocytes and two in mature oocytes. Experiments using inhibitors suggest that translation and microtubule function are both required for post-maturation increases in transporter activity. Immunolabeling revealed translocation of stored ABCB proteins to the plasma cell membrane during maturation, and this translocation coincided with increased transport activity. These MDR transporters serve protective roles in oocytes and eggs, as demonstrated by sensitization of the oocytes to the maturation inhibitor, vinblastine, by MRP and PGP-specific transporter inhibitors.

Detection and functional characterization of Pgp1 (ABCB1) and MRP3 (ABCC3) efflux transporters in the PLHC-1 fish hepatoma cell line

The PLHC-1 hepatoma cell line derived from topminnow (Poeciliopsis lucida) is one of the most frequently used fish cell lines in aquatic ecotoxicology. These cells have been well characterized regarding the presence of phase I and phase II enzymes involved in the metabolism of xenobiotics. However, the presence of the ABC transport proteins possibly involved in the MultiXenobiotic Resistance (MXR) mechanism as phase III of cellular detoxification has never been described in the PLHC-1 cells. The main goal of this study was the detection and functional characterization of toxicologically relevant xenobiotic efflux transporters from ABCB and ABCC subfamily in the PLHC-1 cells. Using specific primer pairs two PCR products 1769 and 1023bp in length were successfully cloned and sequenced. Subsequent multiple alignment and phylogenetic analysis showed that these sequences share a high degree of homology with the P-glycoprotein (Pgp1; ABCB1) and the MRP3 (ABCC3). Functional experiments with fluorescent model substrates and specific inhibitors were used to verify that transport activities of Pgp- and MRP-related proteins are indeed present in PLHC-1 cells. Accumulation or efflux/retention rates of rhodamine 123, calcein-AM or monochlorbimane were time- and concentration-dependent. Cyclosporine A, MK571, verapamil, reversine 205, indomethacine and probenecid were used as specific inhibitors of Pgp1 and/or MRPs transport activities, resulting in a dose dependent inhibition of related transport activities in PLHC-1 cells. Similar to mammalian systems, the obtained IC(50) values were in the lower micromolar range. Taken together these data demonstrate that: (1) the PLHC-1 cells do express a functional MXR mechanism mediated by toxicologically relevant ABC efflux transporters; and (2) the presence of all three critical phases of cellular detoxification additionally affirms the PLHC-1 cells as a reliable in vitro model in aquatic toxicology.

Identification of a multixenobiotic resistance mechanism in primary cultured epidermal cells from Oncorhynchus mykiss and the effects of environmental complex mixtures on its activity

Multixenobiotic resistance (MXR) is a mechanism analogous to the mammalian multidrug resistance (MDR) phenotype, whereby, simultaneous resistance is conferred against the intracellular accumulation of structurally and functionally diverse, natural, endogenous and environmental toxicants. Expression of P-glycoproteins (P-gp), ATP-dependent transporters encoded for by the mdr1 gene that have been implicated in this xenobiotic efflux mechanism, have previously been detected in normal teleost tissues involved in a secretory, absorption or a barrier function. The presence of these proteins in the epidermis of fish species has not to our knowledge previously been investigated. In the present study, primary cultures of epidermis from the rainbow trout Oncorhynchus mykiss were employed to investigate whether an MXR mechanism is functional in the epidermis of fish. The efflux of the fluorescent mdr1 substrate rhodamine 123 from the cells was significantly inhibited by verapamil, a compound known to interfere with P-gp mediated transport. The cultured epidermal cells were also observed to accumulate this fluorescent dye in a verapamil sensitive manner, thus indicating the presence of an mdr1-like mechanism. Immunocytochemical analysis, using a monoclonal antibody (JSB1) directed against a conserved cytoplasmic P-gp epitope, also demonstrated the presence of P-gp-like proteins. Sediment elutriate extracts were employed as models of environmental complex mixtures to evaluate the potential of the epidermal cultures to discriminate between samples of varying contaminant burden using MXR activity as an endpoint. The induction of P-gp expression was found to be in accordance with the level of contamination detected in the sediments from which the elutriates were extracted. The findings of the functional study also demonstrated that environmental pollutants, which interfere with P-gp function, could be identified using this model.