The protective role of multixenobiotic resistance (MXR)-mediated ATP-binding cassette (ABC) transporters in biocides-exposed rotifer Brachionus koreanus

Synergistic toxic mechanisms of microplastics and triclosan via multixenobiotic resistance (MXR) inhibition-mediated autophagy in the freshwater water flea Daphnia magna

Since a mixed state of environmental contaminants, including microplastics (MPs), heavy metals, pharmaceuticals, and personal care products (PPCPs), exists in aquatic ecosystems, it is necessary to evaluate not only the adverse effects of exposure to a single stressor but to combined stressors. In this study, we exposed the freshwater water flea Daphnia magna to 2 μm MPs and triclosan (TCS), one of PPCPs, for 48 h to investigate the synergistic toxic consequences of simultaneous exposure to both pollutants. We measured in vivo endpoints, antioxidant responses, multixenobiotic resistance (MXR) activity, and autophagy-related protein expression via the PI3K/Akt/mTOR and MAPK signaling pathways. While MPs single exposure did not show toxic effects in water fleas, simultaneous exposure to TCS and MPs was associated with significantly greater deleterious effects in the form of increased mortality and alterations in antioxidant enzymatic activities compared with water fleas exposed to TCS alone. In addition, MXR inhibition was confirmed by measurement of the expression of P-glycoproteins and multidrug-resistance proteins in MPs-exposed groups, which led to the accumulation of TCS. Overall, these results suggest that simultaneous exposure to MPs and TCS resulted in higher TCS accumulation via MXR inhibition, leading to synergistic toxic effects such as autophagy in D. magna.

Physiological effects and molecular response in the marine rotifer Brachionus plicatilis after combined exposure to nanoplastics and copper

Because nanoplastics (NPs) can transport pollutants, the absorption of surrounding pollutants into NPs and their effects are important environmental issues. This study shows a combined effect of high concentrations of NPs and copper (Cu) in the marine rotifer Brachionus plicatilis. Co-exposure decreased the growth rate, reproduction, and lifespan. The highest level of NP ingestion was detected in the co-treated group, but the Cu concentration was higher in the Cu single-exposure group. ERK activation played a key role in the downstream cell signaling pathway activated by the interaction of NPs and Cu. The increased sensitivity of B. plicatilis to Cu could be due to the impairment of MXR function caused by a high concentration of NPs, which supports our in vivo experiment results. Our results show that exposure to NPs could induce the dysfunction of several critical molecular responses, weakening resistance to Cu and thereby increasing its physiological toxicity in B. plicatilis.

Short- and long-term single and combined effects of microplastics and chromium on the freshwater water flea Daphnia magna

In this study, we investigated the individual and combined effects of microplastics (MPs) and chromium (Cr) on the freshwater water flea Daphnia magna by measuring mortality, bioaccumulation, antioxidative response, multixenobiotic resistance activity, and sestrin-related mitochondrial biogenesis in short-term assays and in vivo endpoints including reproduction and adult survival rate in long-term assays. Exposure to MPs, Cr, and their combination caused significant deleterious effects and acute toxicity in D. magna. Alterations in oxidative stress occurred in the groups treated with MPs and Cr alone and together. However, upon co-exposure to MPs, the Cr concentration, measured by inductively coupled plasma optical emission spectroscopy, decreased, suggesting that MPs and Cr interact with each other. Based on enzymatic activities, we noted a decrease in MP egestion via inhibition of P-glycoprotein activity in the MP-exposed groups, and multidrug resistance-associated protein activity increased in some of the MP-exposed animals depending on Cr concentration. On the other hand, MP exposure seemed to lead to mitochondrial transcription dysfunction induced by Cr via sestrin-related mitochondrial biogenesis. Overall, these results indicate that co-exposure to MPs and Cr causes acute toxicity in D. magna but lacks the chronic toxicity (21 days) and mitochondrial dysfunction caused by Cr exposure alone.

Molecular cloning, characterization, and tissue distribution of c-Myc from blood clam Tegillarca granosa and its role in cadmium-induced stress response

Cadmium (Cd) pollution threatens the cultivation of the blood clam Tegillarca granosa (T. granosa) in coastal regions of the East China Sea. The molecular mechanisms regulating Cd stress response and detoxification in blood clams are largely unclear. In the present study, the full-length T. granosa c-Myc (Tgc-Myc) cDNA was cloned for the first time. The 3063-bp cDNA consisted of a 129-bp 5' untranslated region (UTR), a 1746-bp 3' UTR, and a 1188-bp open reading frame encoding a predicted protein of 395 amino acid residues. The predicted protein had a calculated molecular weight of 44.9 kDa and an estimated isoelectric point of 6.82. The predicted protein contained an N-terminal transactivation domain and a C-terminal basic helix-loop-helix leucine zipper domain, which are conserved functional domains of c-Myc proteins. Tgc-Myc showed broad tissue distribution in blood clams, with the highest expression detected in the gill and hepatopancreas. Exposure to Cd, a major heavy metal pollutant in coastal regions of the East China Sea, induced Tgc-Myc expression in gill tissues. Tgc-Myc knockdown led to reduced expression of a variety of stress response/detoxification genes in blood clams cultivated in Cd-contaminated seawater. Tgc-Myc knockdown also led to decreased expression of IGF1R, a proto-oncogene that promotes cell proliferation. These findings indicated that Tgc-Myc regulates Cd-induced stress response and detoxification in blood clams. The upregulation of Tgc-Myc may serve as an approach to generate strains with an enhanced detoxification response and consequently a low heavy metal buildup.

Effects of atrazine and diuron on life parameters, antioxidant response, and multixenobiotic resistance in non-targeted marine zooplankton

Atrazine and diuron are among the most widely used antifoulant biocides in the world. Due to their persistence in the environment, they can induce adverse effects on non-targeted organisms. In this study, we investigated the chronic in vivo toxicity of atrazine and diuron with further assessments on oxidative stress responses (e.g., oxidative stress, antioxidant) and multixenobiotic resistance (MXR) function in the rotifer Brachionus koreanus, a non-targeted microzooplanktonic grazer at the primary level of the marine food chain. Although similar oxidative response was shown by both biocides, diuron induced stronger retardation on reproduction and population growth rates of B. koreanus while moderate effects were observed by atrazine. This higher toxicity of diuron was shown to be associated with its stronger inhibition of MXR conferred by P-glycoprotein and multidrug resistance proteins which play as a first line of defense by transporting various toxicants out of a cell. Our study provides new insight into non-targeted effects of biocides on marine zooplankton and mechanisms beyond their different degrees of toxicity.

Comparative genome analysis of the monogonont marine rotifer Brachionus manjavacas Australian strain: Potential application for ecotoxicology and environmental genomics

This is the first study to analyze the whole-genome sequence of B. manjavacas Australian (Aus.) strain through combination of Oxford Nanopore long-read seq, resulting in a total length of 108.1 Mb and 75 contigs. Genome-wide detoxification related gene families in B. manjavacas Aus. strain were comparatively analyzed with those previously identified in other Brachionus spp., including B. manjavacas German (Ger.) strain. Most of the subfamilies in detoxification related families (CYPs, GSTs, and ABCs) were highly conserved and confirmed orthologous relationship with Brachionus spp., and with accumulation of genome data, clear differences between genomic repertoires were demonstrated the marine and the freshwater species. Furthermore, strain-specific genetic variations were present between the Aus. and Ger. strains of B. manjavacas. This whole-genome analysis provides in-depth review on the genomic structural differences for detoxification-related gene families and further provides useful information for comparative ecotoxicological studies and evolution of detoxification mechanisms in Brachionus spp.

The genome of the freshwater monogonont rotifer Brachionus rubens: Identification of phase I, II, and III detoxification genes

Monogonont rotifers are common species in aquatic environments and make model species for ecotoxicology studies. Whole genomes of several species of the genus Brachionus have been assembled, but no information on the freshwater rotifer Brachionus rubens has been reported. In this study, the whole-genome sequence of B. rubens was successfully assembled using NextDenovo. The total length of the genome was 132.7 Mb (N50 = 2.51 Mb), including 122 contigs. The GC contents accounted for 29.96% of the genome. Aquatic organisms are always exposed to various external stresses, and a comprehensive genomic analysis is needed to better understand the adverse effects on organisms. This paper focuses on the ecotoxicological aspect and conducted genome analysis of representative gene families involved in detoxification mechanisms against environmental stressors. Specifically, we identified cytochrome P450 genes (CYPs) of phase I, glutathione S-transferase genes (GSTs) of phase II, and ATP-binding cassette transporter genes (ABCs) of phase III in the genome of B. rubens. Gene duplications were found in CYP, GST, and ABC genes, as is the case for other Brachionus rotifers. Our results suggest that these detoxification-related gene families have evolved in a species-specific and/or lineage-specific manner. This paper improves our understanding of how the freshwater Brachionus rotifers respond to environmental stressors in a molecular ecotoxicology context.

Alleviation of Tris(2-chloroethyl) Phosphate Toxicity on the Marine Rotifer Brachionus plicatilis by Polystyrene Microplastics: Features and Molecular Evidence

As emerging pollutants, microplastics (MPs) and organophosphorus esters (OPEs) coexist in the aquatic environment, posing a potential threat to organisms. Although toxicological studies have been conducted individually, the effects of combined exposure are unknown since MPs can interact with OPEs acting as carriers. In this study, we assessed the response of marine rotifer, Brachionus plicatilis, to co-exposure to polystyrene MPs and tris(2-chloroethyl) phosphate (TCEP) at different concentrations, including population growth, oxidative status, and transcriptomics. Results indicated that 0.1 μm and 1 μm MPs were accumulated in the digestive system, and, even at up to 2000 μg/L, they did not exert obvious damage to the stomach morphology, survival, and reproduction of B. plicatilis. The presence of 1 μm MPs reversed the low population growth rate and high oxidative stress induced by TCEP to the normal level. Some genes involved in metabolic detoxification and stress response were upregulated, such as ABC and Hsp. Subsequent validation showed that P-glycoprotein efflux ability was activated by combined exposure, indicating its important role in the reversal of population growth inhibition. Such results challenge the common perception that MPs aggravate the toxicity of coexisting pollutants and elucidate the molecular mechanism of the limited toxic effects induced by MPs and TCEP.

A review of physiological resistance to insecticide stress in Nilaparvata lugens

Insecticides are widely used in agriculture as effective means to control pests. However, pests have not been completely mitigated with the increased use of insecticides. Instead, many side effects have arisen, especially the '3Rs' (resistance, resurgence, and residue). The brown planthopper, Nilaparvata lugens, is one of the most threatening rice pests. The main insecticides for controlling N. lugens belong to organochlorine, organophosphorus, carbamate, neonicotinoid and pyrethroid groups. However, metabolic enzymes, including cytochrome P450s, esterases, glutathione-S-transferases, and ATP-binding cassette transporters, effectively promote the detoxification of insecticides. Besides, mutations of neurological target sites, such as acetylcholinesterase, nicotinic acetylcholine, γ-aminobutyric acid receptor, and ryanodine receptor, result in insensitivity to insecticides. Here, we review the physiological metabolic resistance in N. lugens under insecticide stress to provide a theoretical basis for identifying and developing more effective and harmless insecticides.

Developmental toxicity assessment of 4-MBC in Danio rerio embryo-larval stages

Enormous production of cosmetic products and its indiscriminate use tends to discharge into the aquatic environment and might threaten non-target organisms inhabiting aquatic ecosystems. In the present study, developmental toxicity of 4-methylbenzylidene camphor (4-MBC), a widely used organic UV filter in personal care products has been evaluated using zebrafish embryo-larval stages. Waterborne exposure induced developmental toxicity and deduced 2.71 mg/L as 96 h LC₅₀ whereas embryos exposed to sub-lethal concentrations (50 and 500 μg/L) caused a significant delay in hatching rate, heart rate, reduced larval length, and restricted hatchlings motility besides the axial curvature. Chronic exposure to 10 dpf resulted in significant decrease in SOD activity at 500 μg/L with no changes in CAT level besides a significant increase in GST enzyme at 5 μg/L concentration in 5 dpf sampled larvae. However, all the three enzymes were significantly elevated in 10 dpf larvae indicating differential oxidative stress during the stages of development. Similar trend is noticed for acetylcholine esterase enzyme activity. A concentration dependent increase in malondialdehyde content was noted in larvae sampled at 5 and 10 dpf. In addition, multixenobiotic resistance (MXR) activity inhibition, and elevated oxidative tissue damage were noticed at 5 dpf with no significant changes in 10 dpf larvae. Furthermore, immunoblot analysis confirms 4-MBC induced apoptosis in zebrafish larvae with promoted cleaved Caspase-3, Bax and inhibited Bcl-2 proteins expression. Subsequently, docking studies revealed the binding potential of 4-MBC to zebrafish Abcb4 and CYP450 8A1 proteins with the binding energy of -8.1 and -8.5 kcal/mol representing target proteins interaction and toxicity potentiation. Our results showed that 4-MBC exposure triggers oxidative stress at sub-lethal concentrations leading to apoptosis, deformities and locomotion perturbations in developing zebrafish.This is first of its kind in systematically demonstrating developmental toxicity of 4-MBC and the information shall be used for aquatic toxicity risk assessment.

(Eco)toxicological tests for assessing impacts of chemical stress to aquatic ecosystems: Facts, challenges, and future

Monitoring of chemicals in the aquatic environment by chemical analysis alone cannot completely assess and predict the effects of chemicals on aquatic species and ecosystems. This is primarily because of the increasing number of (unknown) chemical stressors and mixture effects present in the environment. In addition, the ability of ecological indices to identify underlying stressors causing negative ecological effects is limited. Therefore, additional complementary methods are needed that can address the biological effects in a direct manner and provide a link to chemical exposure, i.e. (eco)toxicological tests. (Eco)toxicological tests are defined as test systems that expose biological components (cells, individuals, populations, communities) to (environmental mixtures of) chemicals to register biological effects. These tests measure responses at the sub-organismal (biomarkers and in vitro bioassays), whole-organismal, population, or community level. We performed a literature search to obtain a state-of-the-art overview of ecotoxicological tests available for assessing impacts of chemicals to aquatic biota and to reveal datagaps. In total, we included 509 biomarkers, 207 in vitro bioassays, 422 tests measuring biological effects at the whole-organismal level, and 78 tests at the population- community- and ecosystem-level. Tests at the whole-organismal level and biomarkers were most abundant for invertebrates and fish, whilst in vitro bioassays are mostly based on mammalian cell lines. Tests at the community- and ecosystem-level were almost missing for organisms other than microorganisms and algae. In addition, we provide an overview of the various extrapolation challenges faced in using data from these tests and suggest some forward looking perspectives. Although extrapolating the measured responses to relevant protection goals remains challenging, the combination of ecotoxicological experiments and models is key for a more comprehensive assessment of the effects of chemical stressors to aquatic ecosystems.

Multidrug Resistance in Mammals and Fungi-From MDR to PDR: A Rocky Road from Atomic Structures to Transport Mechanisms

Multidrug resistance (MDR) can be a serious complication for the treatment of cancer as well as for microbial and parasitic infections. Dysregulated overexpression of several members of the ATP-binding cassette transporter families have been intimately linked to MDR phenomena. Three paradigm ABC transporter members, ABCB1 (P-gp), ABCC1 (MRP1) and ABCG2 (BCRP) appear to act as brothers in arms in promoting or causing MDR in a variety of therapeutic cancer settings. However, their molecular mechanisms of action, the basis for their broad and overlapping substrate selectivity, remains ill-posed. The rapidly increasing numbers of high-resolution atomic structures from X-ray crystallography or cryo-EM of mammalian ABC multidrug transporters initiated a new era towards a better understanding of structure-function relationships, and for the dynamics and mechanisms driving their transport cycles. In addition, the atomic structures offered new evolutionary perspectives in cases where transport systems have been structurally conserved from bacteria to humans, including the pleiotropic drug resistance (PDR) family in fungal pathogens for which high resolution structures are as yet unavailable. In this review, we will focus the discussion on comparative mechanisms of mammalian ABCG and fungal PDR transporters, owing to their close evolutionary relationships. In fact, the atomic structures of ABCG2 offer excellent models for a better understanding of fungal PDR transporters. Based on comparative structural models of ABCG transporters and fungal PDRs, we propose closely related or even conserved catalytic cycles, thus offering new therapeutic perspectives for preventing MDR in infectious disease settings.

The genome of the marine water flea Diaphanosoma celebensis: Identification of phase I, II, and III detoxification genes and potential applications in marine molecular ecotoxicology

To assemble the genome of the marine water flea Diaphanosoma celebensis, a sentinel model for marine environmental monitoring, we constructed a high-quality genome using PromethION and HiSeq 2500 platforms. The total length of the assembled genome was 100.08 Mb, with N50 = 2.56 Mb (benchmarking universal single-copy orthologs, 96.9%) and consisted of 179 scaffolds. A total of 15,427 genes were annotated, and orthologous gene clusters in D. celebensis were analyzed and compared with those of the cladocerans Daphnia magna and Daphnia pulex. In addition, phase I, II, and III detoxification gene families of cytochrome P450s, glutathione S-transferases, and ATP-binding cassette were fully identified and revealed lineage-specific gene loss and/or expansion, suggesting that the evolution of detoxification gene families likely modulates fitness and susceptibility in response to environmental stressors. The study improves our understanding of the detoxification-related gene system and should contribute to future studies of molecular ecotoxicology in cladoceran species and their responses to emerging pollutants.

Toxin- and species-dependent regulation of ATP-binding cassette (ABC) transporters in scallops after exposure to paralytic shellfish toxin-producing dinoflagellates

ATP-binding cassette (ABC) transporters are membrane-bound proteins involved in exporting various xenobiotic compounds from living cells. Bivalve mollusks can accumulate large amounts of paralytic shellfish toxins (PSTs) from marine dinoflagellates. For aquatic invertebrates, the importance of ABC proteins in multi-xenobiotic resistance has been demonstrated, however, the systematic identification of ABC transporters is very limited. In this study, 64 and 67 ABC genes containing all eight described subfamilies (A to H) were identified in Yesso scallop (Patinopecten yessoensis) and Zhikong scallop (Chlamys farreri), respectively, with massive gene expansion being observed in the ABCC and ABCG subfamilies. The kidney harbored more specifically expressed ABC genes than other organs/tissues, most of which belonged to ABCB, ABCC, and ABCG subfamilies. After feeding the scallops with PST-producing dinoflagellates, the expression of scallop ABC genes in the kidney was regulated in toxin- and species-dependent manners. In total, 20 and 24 ABC genes in Zhikong scallop (CfABCs) were induced after exposure to Alexandrium minutum and A. catenella, with the up-regulated members from both ABCC and ABCG subfamilies mainly showing acute and chronic induction by A. minutum and A. catenella, respectively, while the up-regulated CfABCBs mainly showing chronic induction by both dinoflagellates. In Yesso scallop, only eight ABC genes (PyABCs) were regulated after A. catenella exposure, and all the five up-regulated PyABCs were acutely induced. Our findings imply the functional diversity of scallop ABC genes in coping with PST accumulation, which may contribute to the lineage-specific adaptation of scallops for dealing with algal toxins challenge.

The first intracellular loop is essential for the catalytic cycle of the human ABCG2 multidrug resistance transporter

The human multidrug transporter ABCG2 is required for physiological detoxification and mediates anticancer drug resistance. Here, we identify pivotal residues in the first intracellular loop (ICL1), constituting an intrinsic part of the transmission interface. The architecture includes a triple helical bundle formed by the hot spot helix of the nucleotide‐binding domain, the elbow helix, and ICL1. We show here that the highly conserved ICL1 residues G462, Y463, and Y464 are essential for the proper cross talk of the closed nucleotide‐binding domain dimer with the transmembrane domains. Hence, ICL1 acts as a molecular spring, triggering the conformational switch of ABCG2 before substrate extrusion. These data suggest that the ABCG2 transmission interface may offer therapeutic options for the treatment of drug‐resistant malignancies.

The genome of the marine monogonont rotifer Brachionus rotundiformis and insight into species-specific detoxification components in Brachionus spp

The monogonont rotifer Brachionus spp. have been widely used for ecotoxicological studies because of their advantages as one of the most suitable laboratory experimental species. In the present study, we obtained and assembled the whole genome sequence of the rotifer Brachionus rotundiformis, consisting of 13,612 annotated genes with 213 scaffolds and 58 Mb in total length. Focusing on ecotoxicological aspects, we conducted a comparative genome analysis on the gene families involved in detoxification, including four to six sulfotransferase gene families, seven uridine 5'-diphospho-glucuronosyltransferase gene families, and 58, 61, or 70 ATP-binding cassette genes in the genus Brachionus including Brachionus koreanus and Brachionus plicatilis. Our results suggest that these gene families have undergone a species- and/or lineage-specific evolution in response to the surrounding environmental pressure. Our genome resource for B. rotundiformis would be highly useful for future ecotoxicological studies and also provides a better understanding on the view of evolutionary mechanism of detoxification in the genus Brachionus spp.

Transcriptional Response of ATP-Binding Cassette (ABC) Transporters to Insecticide in the Brown Planthopper, Nilaparvata lugens (Stål)

The ATP-binding cassette (ABC) transporter superfamily is one of the largest groups of proteins and plays a non-negligible role in phase III of the detoxification process, which is highly involved in the response of insects to environmental stress (plant secondary metabolites and insecticides). In the present study, in Nilaparvata lugens, we identified 32 ABC transporters, which are grouped into eight subfamilies (ABCA–H) based on phylogenetic analysis. The temporal and spatial expression profiles suggested that the nymphal stages (1st–5th) and adult males showed similarity, which was different from eggs and adult females, and NlABCA1, NlABCA2, NlABCB6, NlABCD2, NlABCG4, NlABCG12, NlABCG15, and NlABCH1 were highly expressed in the midgut and Malpighian tubules. In addition, ABCG12, which belongs to the ABC transporter G subfamily, was significantly upregulated after exposure to sulfoxaflor, nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. Moreover, verapamil significantly increased the sensitivity of N. lugens to nitenpyram, clothianidin, etofenprox, chlorpyrifos, and isoprocarb. These results provide a basis for further research on ABC transporters involved in detoxification in N. lugens, and for a more comprehensive understanding of the response of N. lugens to environmental stress.

The genome of the harpacticoid copepod Tigriopus japonicus: Potential for its use in marine molecular ecotoxicology

The copepod Tigriopus japonicus has been widely used as an experimental species in the field of ecotoxicology. We have sequenced and assembled the whole genome of T. japonicus with comparative analysis of gene families that represent detoxification phases in two additional public genomes of Tigriopus spp., namely, T. californicus and T. kingsejongensis. The total length of the T. japonicus assembled genome was 196.6 Mb with an N50 value of 10.65 Mb and consisted of 339 scaffolds and 25,143 annotated genes. The detoxification gene families encoding cytochrome P450s (CYP450s), glutathione S-transferases (GSTs), and ATP-binding cassette (ABC) proteins in Tigriopus spp. have shown species-dependent diversity in several gene sets, suggesting that these genes have undergone a species-specific expansion to increase their fitness to different marine habitats and environmental pressures. Our study will provide a better understanding of the detoxification system in Tigriopus spp. and will contribute to various areas of research, including ecotoxicology.

Reversal Effect of ALK Inhibitor NVP-TAE684 on ABCG2-Overexpressing Cancer Cells

Failure of cancer chemotherapy is mostly due to multidrug resistance (MDR). Overcoming MDR mediated by overexpression of ATP binding cassette (ABC) transporters in cancer cells remains a big challenge. In this study, we explore whether NVP-TAE684, a novel ALK inhibitor which has the potential to inhibit the function of ABC transport, could reverse ABC transporter-mediated MDR. MTT assay was carried out to determine cell viability and reversal effect of NVP-TAE684 in parental and drug resistant cells. Drug accumulation and efflux assay was performed to examine the effect of NVP-TAE684 on the cellular accumulation and efflux of chemotherapeutic drugs. The ATPase activity of ABCG2 transporter in the presence or absence of NVP-TAE684 was conducted to determine the impact of NVP-TAE684 on ATP hydrolysis. Western blot analysis and immunofluorescence assay were used to investigate protein molecules related to MDR. In addition, the interaction between NVP-TAE684 and ABCG2 transporter was investigated via in silico analysis. MTT assay showed that NVP-TAE684 significantly decreased MDR caused byABCG2-, but not ABCC1-transporter. Drug accumulation and efflux tests indicated that the effect of NVP-TAE684 in decreasing MDR was due to the inhibition of efflux function of ABCG2 transporter. However, NVP-TAE684 did not alter the expression or change the subcellular localization of ABCG2 protein. Furthermore, ATPase activity analysis indicated that NVP-TAE684 could stimulate ABCG2 ATPase activity. Molecular in silico analysis showed that NVP-TAE684 interacts with the substrate binding sites of the ABCG2 transporter. Taken together, our study indicates that NVP-TAE684 could reduce the resistance of MDR cells to chemotherapeutic agents, which provides a promising strategy to overcome MDR.

MXR response in sea anemones: Effect of temperature, salinity and copper

Multixenobiotic resistance (MXR) phenotype is a cellular defense which can eliminate toxic substances from cells. Several studies describe the MXR activity after pollutant exposure, but little is known about the interference of abiotic factors in this mechanism. The present study aimed to evaluate MXR activity in sea anemones Bunodosoma cangicum after in vivo and in vitro exposures to different temperatures (15, 20 and 25C) and salinities (15, 30 and 45‰) associated or not with copper (0, 7.8 and 15.6 μg/L). Results showed that low temperature inhibited the MXR activity in vivo and in vitro, while salinity did not alter this activity. Copper could change the response, mainly at different temperatures (15 and 25 °C) - 7.8 μg/L Cu activated in vivo and in vitro and 15.6 μg/L Cu in vitro inhibited MXR activity in relation to same copper concentrations at 20 °C. Results for MXR activity found between in vivo and in vitro exposures were similar among temperature treatments and salinities; however, under hyperosmotic shock, in vivo exposure showed that animals has different response than isolated cells. The animals exposed to salinity 45‰ produced a mucus layer as a defense mechanism, because of this protection the response was different between in vivo and in vitro exposures. Concluding, temperature affects MXR activity independently of the presence of copper and each model of exposure contributes with different type of knowledge (cellular mechanism/systemic response).

The genome of the freshwater water flea Daphnia magna: A potential use for freshwater molecular ecotoxicology

The water flea Daphnia magna is a small planktonic cladoceran. D. magna has been used as a model species for ecotoxicology, as it is sensitive to environmental stressors and environmental changes. Since Daphnia is affected by culture environment and each population/strain has its own ecological and genetic characteristics, its population/strain-based genome information is useful for environmental genomic studies. In this study, we assembled and characterized the genome of D. magna. Using a high-density genetic map of D. magna xinb3, the draft genome was integrated to 10 linkage groups (LGs). The total length of the integrated genome was about 123 Mb with N50 = 10.1 Mb, and the number of scaffolds was 4193 including 10 LGs. A total of 15,721 genes were annotated after manual curation. Orthologous genes were characterized in the genome and compared with other genomes of Daphnia. In addition, we identified defense related genes such as cytochrome P450 (CYP) genes, glutathione S-transferase (GST) genes, and ATP-binding cassette (ABC) genes from the assembled D. magna genome for its potential use in molecular ecotoxicological studies in the freshwater environment. This genomic resource will be helpful to study for a better understanding on molecular mechanism in response to various pollutants.

Transcriptional response of ATP-binding cassette (ABC) transporters to insecticides in the cotton bollworm, Helicoverpa armigera

When any living organism is frequently exposed to any drugs or toxic substances, they evolve different detoxification mechanism to confront with toxicants during absorption and metabolism. Likewise, the insects have evolved detoxification mechanisms as they are frequently exposed to different toxic secondary plant metabolites and commercial insecticides. ABC transporter superfamily is one of the largest and ubiquitous group of proteins which play an important role in phase III of the detoxification process. However, knowledge about this gene family remains largely unknown. To help fill this gap, we have identified a total of 54 ABC transporters in the Helicoverpa armigera genome which are classified into eight subfamilies (A-H) by phylogenetic analysis. The temporal and spatial expression profiles of these 54 ABC transporters throughout H. armigera development stages and seven tissues and their responses to five different insecticides, were investigated using RNA-seq analysis. Furthermore, the mRNA expression of eight selected genes in different tissues and six genes responses to insecticides were confirmed by the quantitative real-time PCR (RT-qPCR). Moreover, H. armigera become more sensitive to abamectin and indoxacarb when P-gp was inhibited. These results provide a foundation for further studies of ABCs in H. armigera.

Nanoplastic Ingestion Enhances Toxicity of Persistent Organic Pollutants (POPs) in the Monogonont Rotifer Brachionus koreanus via Multixenobiotic Resistance (MXR) Disruption

Among the various materials found inside microplastic pollution, nanosized microplastics are of particular concern due to difficulties in quantification and detection; moreover, they are predicted to be abundant in aquatic environments with stronger toxicity than microsized microplastics. Here, we demonstrated a stronger accumulation of nanosized microbeads in the marine rotifer Brachionus koreanus compared to microsized ones, which was associated with oxidative stress-induced damages on lipid membranes. In addition, multixenobiotic resistance conferred by P-glycoproteins and multidrug resistance proteins, as a first line of membrane defense, was inhibited by nanoplastic pre-exposure, leading to enhanced toxicity of 2,2',4,4'-tetrabromodiphenyl ether and triclosan in B. koreanus. Our study provides a molecular mechanistic insight into the toxicity of nanosized microplastics toward aquatic invertebrates and further implies the significance of synergetic effects of microplastics with other environmental persistent organic pollutants.

Effects of bisphenol A and its analogs bisphenol F and S on life parameters, antioxidant system, and response of defensome in the marine rotifer Brachionus koreanus

To understand the adverse outcome in response to bisphenol A and its analogs bisphenol F and S (BPA, BPF, and BPS), we examined acute toxicity, life parameter, and defensome in the marine rotifer Brachionus koreanus. Among the bisphenol analogs, BPA showed the highest acute toxicity and then BPF and BPS, accordingly in the view of descending magnitude of toxicity. In life parameters including life span and reproduction, BPA, BPF, and BPS were found to cause adverse effect. Both intracellular ROS level and GST activity were significantly increased (P < 0.05) in response to each dosage of bisphenol analogs exposures. In response to bisphenol analogs, defensomes of phase I, II, and III detoxification mechanism demonstrated inverse relationship between the lipophilicity of bisphenol analogs and the expression patterns of defensomes. BPA and BPF were found to have significant modulation (P < 0.05) in the expression of cytochrome P450 (CYP) and GST genes. In phase III, BPS with comparatively lower lipophilicity demonstrated highly diversified expressional pattern, suggesting that BPS is likely caused less toxicity compared to BPA and BPF. In this study, via phase I, II, and III detoxification mechanism, bisphenol A and its analogs F and S demonstrated specific detoxification mechanism in rotifer.