The use of mrp1-deficient (Danio rerio) zebrafish embryos to investigate the role of Mrp1 in the toxicity of cadmium chloride and benzo[a]pyrene

Cadmium transport by mammalian ATP-binding cassette transporters

Cellular responses to toxic metals depend on metal accessibility to intracellular targets, reaching interaction sites, and the intracellular metal concentration, which is mainly determined by uptake pathways, binding/sequestration and efflux pathways. ATP-binding cassette (ABC) transporters are ubiquitous in the human body-usually in epithelia-and are responsible for the transfer of indispensable physiological substrates (e.g. lipids and heme), protection against potentially toxic substances, maintenance of fluid composition, and excretion of metabolic waste products. Derailed regulation and gene variants of ABC transporters culminate in a wide array of pathophysiological disease states, such as oncogenic multidrug resistance or cystic fibrosis. Cadmium (Cd) has no known physiological role in mammalians and poses a health risk due to its release into the environment as a result of industrial activities, and eventually passes into the food chain. Epithelial cells, especially within the liver, lungs, gastrointestinal tract and kidneys, are particularly susceptible to the multifaceted effects of Cd because of the plethora of uptake pathways available. Pertinent to their broad substrate spectra, ABC transporters represent a major cellular efflux pathway for Cd and Cd complexes. In this review, we summarize current knowledge concerning transport of Cd and its complexes (mainly Cd bound to glutathione) by the ABC transporters ABCB1 (P-glycoprotein, MDR1), ABCB6, ABCC1 (multidrug resistance related protein 1, MRP1), ABCC7 (cystic fibrosis transmembrane regulator, CFTR), and ABCG2 (breast cancer related protein, BCRP). Potential detoxification strategies underlying ABC transporter-mediated efflux of Cd and Cd complexes are discussed.

Progress in characterizing ABC multidrug transporters in zebrafish

Zebrafish have proved to be invaluable for modeling complex physiological processes shared by all vertebrate animals. Resistance of cancers and other diseases to drug treatment can occur owing to expression of the ATP-dependent multidrug transporters ABCB1, ABCG2, and ABCC1, either because of expression of these transporters by the target cells to reduce intracellular concentrations of cytotoxic drugs at barrier sites such as the blood-brain barrier (BBB) to limit penetration of drugs into privileged compartments, or by affecting the absorption, distribution, and excretion of drugs administered orally, through the skin, or directly into the bloodstream. We describe the drug specificity, cellular localization, and function of zebrafish orthologs of multidrug resistance ABC transporters with the goal of developing zebrafish models to explore the physiological and pathophysiological functions of these transporters. Finally, we provide context demonstrating the utility of zebrafish in studying cancer drug resistance. Our ultimate goal is to improve treatment of cancer and other diseases which are affected by ABC multidrug resistance transporters.

Application of CRISPR/Cas9-based genome editing in ecotoxicology

Chemicals are widely used and released into the environment, and their degradation, accumulation, migration, and transformation processes in the environment can pose a threat to the ecosystem. The advancement in analytical methods with high-throughput screening of biomolecules has revolutionized the way toxicologists used to explore the effects of chemicals on organisms. CRISPR/Cas is a newly developed tool, widely used in the exploration of basic science and biologically engineered products given its high efficiency and low cost. For example, it can edit target genes efficiently, and save loss of the crop yield caused by environmental pollution as well as gain a better understanding of the toxicity mechanisms from various chemicals. This review briefly introduces the development history of CRISPR/Cas and summarizes the current application of CRISPR/Cas in ecotoxicology, including its application on improving crop yield and drug resistance towards agricultural pollution, antibiotic pollution and other threats. The benefits by applying the CRISPR/Cas9 system in conventional toxicity mechanism studies are fully demonstrated here together with its foreseeable expansions in other area of ecotoxicology. Finally, the prospects and disadvantages of CRISPR/Cas system in the field of ecotoxicology are also discussed.

Placental BCRP transporter reduces cadmium accumulation and toxicity in immortalized human trophoblasts

Cadmium (Cd) is a ubiquitous environmental metal detectable in most pregnant women. Animal and human studies demonstrate that in utero exposure to Cd reduces birth weight and impairs perinatal growth due to placental toxicity. BCRP is a prominent transporter that can efflux xenobiotics from the placenta. This study sought to investigate Cd transport and toxicity in cultured human BeWo trophoblasts with reduced expression and function of the placental barrier transporter BCRP. Knockdown (KD) of BCRP protein expression and function in BeWo trophoblasts increased the intracellular accumulation of Cd by 100% following treatment with 1 μM CdCl2. No change in the expression of Cd uptake transporters was observed between control and BCRP-KD cells. Reduced BCRP expression impaired viability of BeWo cells exposed to CdCl2 for 48 hr (BCRP-KD IC50: 11 μM, control cells IC50: 18 μM). Moreover, BCRP-KD cells were more sensitive to CdCl2-induced cytotoxicity compared to control BeWo cells. CdCl2 treatment strongly induced the expression of the metal-binding protein metallothionein (MT) in both control and BCRP-KD cells, with significantly greater MT upregulation in Cd-treated BCRP-KD cells. These data suggest that the BCRP transporter reduces Cd accumulation in syncytiotrophoblasts, which may be one mechanism to reduce subsequent toxicity to the placenta and developing fetus.

ABC transporter-mediated MXR mechanism in fish embryos and its potential role in the efflux of nanoparticles

ATP-binding cassette (ABC) transporters are believed to protect aquatic organisms by pumping xenobiotics out, and recent investigation has suggested their involvement in the detoxification and efflux of nanoparticles (NPs), but their roles in fish embryos are poorly understood. In this regard, this paper summarizes the recent advances in research pertaining to the development of ABC transporter-mediated multi-xenobiotic resistance (MXR) mechanism in fish embryos and the potential interaction between ABC transporters and NPs. The paper focuses on: (1) Expression, function, and modulation mechanism of ABC proteins in fish embryos; (2) Potential interaction between ABC transporters and NPs in cell models and fish embryos. ABC transporters could be maternally transferred to fish embryos and thus play an important role in the detoxification of various chemical pollutants and NPs. There is a need to understand the specific mechanism to benefit the protection of aquatic resources.

Effects of atorvastatin on the Sirtuin/PXR signaling pathway in Mugilogobius chulae

Atorvastatin (ATV) is a hypolipidemic drug widely detected in the aquatic environment. Nevertheless, limited information is provided about the toxic effects of ATV on estuary or coastal species and the underlying mechanisms. In the present study, the responses of genes expression in pregnane X receptor (PXR) signaling pathway and enzymatic activities in the liver of the estuarine benthic fish (Mugilogobius chulae) were investigated under acute and sub-chronic ATV exposure. Results showed that PXR was significantly inhibited in the highest exposure concentration of ATV for a shorter time (24 h, 500 μg L^-1) but induced in a lower concentration (72 h, 5 μg L^-1). The downstream genes in PXR signaling pathway such as CYP3A, SULT, UGT, and GST showed similar trends to PXR. P-gp and MRP1 were repressed in most treatments. GCLC associated with GSH synthesis was mostly induced under ATV exposure for a long time (168 h), suggesting that reactive oxygen species (ROS) were generated under ATV exposure. Similarly, GST and SOD enzymatic activities significantly increased in most exposure treatments. Under ATV exposure, SIRT1 and SIRT2 displayed induction to some extent in most treatments, suggesting that SIRTs may affect PXR expression by regulating the acetylation levels of PXR. The investigation demonstrated that ATV exposure affected the expression of the Sirtuin/PXR signaling pathway, thus further interfered adaption of M. chulae to the environment.

The critical role of nanoparticle sizes in the interactions between gold nanoparticles and ABC transporters in zebrafish embryos

Despite the increasing evidences for adenosine triphosphate-binding cassette (ABC transporters)-mediated efflux of nanoparticles, the universality of these phenomena and the determining factors for the process remained to be clarified. This paper aimed to systemically investigate the role of nanoparticle size in the interactions between adenosine triphosphate-binding cassette (ABC transporters) and gold nanoparticles (AuNPs, 3 nm, 19 nm, and 84 nm, named as Au-3, Au-19, and Au-84) in zebrafish embryos. The results showed that all the three AuNPs induced significant toxicity as reflected by delayed hatching of embryos, decreased glutathione (GSH) contents, and increased reactive oxygen species (ROS) levels. Under the hindrance of embryo chorions, smaller AuNPs could more easily accumulate in the embryos, causing higher toxicity. Addition of transporter inhibitors enhanced the accumulation and toxicity of Au-3 and Au-19, and these nanoparticles induced the expressions of abcc2 and abcb4, indicating a fact that Au-3 and Au-19 were the potential substrates of ABC transporters, but these phenomena were barely found for Au-84. On the contrary, Au-84 suppressed the gene expressions of various ABC transporters like abcc1, abcg5, and abcg8. With specific suppressors, transcription factors like nuclear factor-erythroid 2-related factor-2 (Nrf2) and pregnane X receptor (Pxr) were found to be important in the induction of ABC transporters by AuNPs. After all, these results revealed a vital role of nanoparticle sizes in the interactions between ABC transporters and AuNPs in zebrafish embryos, and the critical size could be around 19 nm. Such information would be beneficial in assessing the environmental risk of nanoparticles, as well as their interactions with other chemical toxicants.

Zinc oxide/graphene oxide nanocomposites efficiently inhibited cadmium-induced hepatotoxicity via releasing Zn ions and up-regulating MRP1 expression

Environmental cadmium (Cd) pollution has been verified to associated with various hepatic diseases, as Cd has been classified as one of the TOP 20 Hazardous Substances and liver is the main target of Cd poisoning. However, to design efficient hepatic antidotes with excellent detoxification capacity and reveal their underlying mechanism(s) are still challenges in Cd detoxification. Herein, ZnO/GO nanocomposites with favorable biocompatibility was uncovered their advanced function against Cd-elicited liver damage at the in situ level in vivo by 9.4 T magnetic resonance imaging (MRI). To explore the cellular detoxification mechanism, ZnO/GO nanocomposites was found to effectively inhibit the cyto- and geno-toxicity of Cd with the maximum antagonistic efficiency to be approximately 90%. Mechanistically, ZnO/GO nanocomposites competitively inhibited the cellular Cd uptake through releasing Zn ions, and significantly promoted Cd excretion via targeting the efflux pump of multidrug resistance associated protein1 (MRP1), which was confirmed by mass spectra and immunohistochemical analysis in kidney, a main excretion organ of Cd. Our data provided a novel approach against Cd-elicited hepatotoxic responses by constructed ZnO/GO nanocomposites both in vitro and in vivo, which may have promising application in prevention and detoxification for Cd poisoning.

Determining the Biological Mechanisms of Action for Environmental Exposures: Applying CRISPR/Cas9 to Toxicological Assessments

Toxicology is a constantly evolving field, especially in the area of developing alternatives to animal testing. Toxicological research must evolve and utilize adaptive technologies in an effort to improve public, environmental, and occupational health. The most commonly cited mechanisms of toxic action after exposure to a chemical or particle test substance is oxidative stress. However, because oxidative stress involves a plethora of genes and proteins, the exact mechanism(s) are not commonly defined. Exact mechanisms of toxicity can be revealed using an emerging laboratory technique referred to as CRISPR (clustered regularly interspaced short palindromic repeats). This article reviews the most common CRISPR techniques utilized today and how each may be applied in Toxicological Sciences. Specifically, the CRISPR/CRISPR-associated protein complex is used for single gene knock-outs, whereas CRISPR interference/activation is used for silencing or activating (respectively) ribonucleic acid. Finally, CRISPR libraries are used for knocking-out entire gene pathways. This review highlights the application of CRISPR in toxicology to elucidate the exact mechanism through which toxicants perturb normal cellular functions.

Genetic variation and urine cadmium levels: ABCC1 effects in the Strong Heart Family Study

Genetic effects are suspected to influence cadmium internal dose. Our objective was to assess genetic determinants of urine cadmium in American Indian adults participating in the Strong Heart Family Study (SHFS). Urine cadmium levels and genotyped short tandem repeat (STR) markers were available on 1936 SHFS participants. We investigated heritability, including gene-by-sex and smoking interactions, and STR-based quantitative trait locus (QTL) linkage, using a variance-component decomposition approach, which incorporates the genetic information contained in the pedigrees. We also used available single nucleotide polymorphisms (SNPs) from Illumina's Metabochip and custom panel to assess whether promising QTLs associated regions could be attributed to SNPs annotated to specific genes. Median urine cadmium levels were 0.44 μg/g creatinine. The heritability of urine cadmium concentrations was 28%, with no evidence of gene-by-sex or -smoking interaction. We found strong statistical evidence for a genetic locus at chromosome 16 determining urine cadmium concentrations (Logarithm of odds score [LOD] = 3.8). Among the top 20 associated SNPs in this locus, 17 were annotated to ABCC1 (p-values from 0.0002 to 0.02), and attenuated the maximum linkage peak by a ∼40%. Suggestive QTL signals (LOD>1.9) in chromosomes 2, 6, 11, 14, and 19, showed associated SNPs in the genes NDUFA10, PDE10A, PLEKHA7, BAZ1A and CHAF1A, respectively. Our findings support that urinary cadmium levels are heritable and influenced by a QTL on chromosome 16, which was explained by genetic variation in ABCC1. Studies with extended sets of genome-wide markers are needed to confirm these findings and to identify additional metabolism and toxicity pathways for cadmium.

Involvement of ABC transporters in the detoxification of non-substrate nanoparticles in lung and cervical cancer cells

This paper aimed to systemically investigate the role of adenosine triphosphate-binding cassette (ABC transporters) in the detoxification of non-substrate nanoparticles including titanium dioxide (n-TiO₂, 5-10 nm) and gold (AuNPs, 3 nm, 15 nm, and 80 nm, named as Au-3, Au-15 and Au-80) in human lung cancer (A549) and human cervical cancer (HeLa) cells. All these nanoparticles were of larger hydrophilic diameters than the channel sizes of ABC transporters, thus should not be the substrates of membrane proteins. After 24-h treatment, they induced significant cytotoxicity as reflected by the reduction in cell viability and glutathione (GSH) contents, as well as the increase in reactive oxygen species (ROS) level. At median-lethal concentrations (10 mg/L n-TiO₂, 2 mg/L Au-3, 5 mg/L Au-15, and 10 mg/L Au-80 for A549 cells; 20 mg/L n-TiO₂, 2 mg/L Au-3, 5 mg/L Au-15, and 10 mg/L Au-80 for Hela cells), all the nanoparticles significantly induced the gene expressions and activities of ABC transporters including P-glycoprotein (PGP) and multidrug resistance associated protein 1 (MRP1). Addition of transporter inhibitors enhanced the ROS levels produced by nanoparticles, but didn't alter their death-inducing effects and intracellular accumulations. With specific suppressors, transcription factors like nuclear factor-erythroid 2-related factor-2 (NRF2) and pregnane X receptor (PXR) were proved to be important in the induction of ABC transporters by nanoparticles. After all, this paper revealed a damage-dependent modulation of ABC transporters by non-substrate nanoparticles. The up-regulated ABC transporters could help in reducing the oxidative stress produced by nanoparticles. Such information should be useful in assessing the environmental risk of nanoparticles, as well as their interactions with other chemical toxicants or drugs.

Application of CRISPR/Cas9 System to Reverse ABC-Mediated Multidrug Resistance

Multidrug resistance (MDR) is the main obstacle in cancer chemotherapy. ATP-binding cassette (ABC) transporters can transport a wide range of antitumor drugs out of cells, which is the most common reason in the development of resistance to drugs. Currently, various therapeutic strategies are used to reverse MDR, among which CRISPR/Cas9 gene editing technique is expected to be an effective way. Here, we reviewed the research progress of reversing ABC-mediated drug resistance by CRISPR/Cas9 system.

Production of a tributyltin-binding protein 2 knockout mutant strain of Japanese medaka, Oryzias latipes

Tributyltin-binding proteins (TBT-bps), members of the lipocalin family, bind TBT in fish blood and are presumed to contribute to detoxification of TBT. Recent studies have shown that many fish species have TBT-bp genes, and that these genes are induced by stresses such as exposure to chemicals or fish pathogenic bacteria. However, the function of TBT-bps, and the mechanisms of their induction and detoxification activity are still unclear. Here, towards elucidating the functions of TBT-bp2, we produced a TBT-bp2 knockout (TBT-bp2^-/-) strain of Japanese medaka, Oryzias latipes, by using the CRISPR/Cas9 system. Gene expression of the mutated TBT-bp2 was reduced, and the cDNA sequencing and predicted protein structure suggested possible loss of function. However, the fish could be grown under normal conditions. Exposure of the TBT-bp2^-/- strain of medaka to various stresses in future experiments is expected to contribute to our understanding of this novel detoxification system in aquatic organisms.

A method for CRISPR/Cas9 mutation of genes in fathead minnow (Pimephales promelas)

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 genome editing allows for the disruption or modification of genes in a multitude of model organisms. In the present study, we describe and employ the method for use in the fathead minnow (Pimephales promelas), in part, to assist in the development and validation of adverse outcome pathways (AOPs). The gene coding for an enzyme responsible for melanin production, tyrosinase (tyr), was the initial target chosen for development and assessment of the method since its disruption results in abnormal pigmentation, a phenotype obvious within 3-4 d after injection of fathead minnow embryos. Three tyrosinase-targeting guide strands were generated using the fathead minnow sequence in tandem with the CRISPOR guide strand selection tool. The strands targeted two areas: one stretch of sequence in a conserved region that demonstrated homology to EGF-like or laminin-like domains as determined by Protein Basic Local Alignment Search Tool in concert with the Conserved Domain Database, and a second area in the N-terminal region of the tyrosinase domain. To generate one cell embryos, in vitro fertilization was performed, allowing for microinjection of hundreds of developmentally-synchronized embryos with Cas9 proteins complexed to each of the three guide strands. Altered retinal pigmentation was observed in a portion of the tyr guide strand injected population within 3 d post fertilization (dpf). By 14 dpf, fish without skin and swim bladder pigmentation were observed. Among the three guide strands injected, the guide targeting the EGF/laminin-like domain was most effective in generating mutants. CRISPR greatly advances our ability to directly investigate gene function in fathead minnow, allowing for advanced approaches to AOP validation and development.

Translational Toxicology in Zebrafish

A major goal of translational toxicology is to identify adverse chemical effects and determine whether they are conserved or divergent across experimental systems. Translational toxicology encompasses assessment of chemical toxicity across multiple life stages, determination of toxic mode-of-action, computational prediction modeling, and identification of interventions that protect or restore health following toxic chemical exposures. The zebrafish is increasingly used in translational toxicology because it combines the genetic and physiological advantages of mammalian models with the higher-throughput capabilities and genetic manipulability of invertebrate models. Here, we review recent literature demonstrating the power of the zebrafish as a model for addressing all four activities of translational toxicology. Important data gaps and challenges associated with using zebrafish for translational toxicology are also discussed.

MicroRNA-mediated suppression of P-glycoprotein by quantum dots in lung cancer cells

The interactions between adenosine triphosphate-binding cassette (ABC) transporters and nano-sized materials are attracting increasing attention, due to their great potential in overcoming the multidrug resistance (MDR) phenomena in cancer treatment. However, the inner mechanisms involved in the interactions are largely unknown. In this study, two commercial quantum dots (QDs), CdSe/ZnS-MPA and CdSe/ZnS-GSH, were tested for their interactions with P-glycoprotein (P-gp), as well as the relating mechanisms in lung cancer (A549) cells. Both QDs significantly suppressed the gene and protein expressions of P-gp in A549 cells. To explain this, the gene expressions of nine relating microRNAs (miRNAs) were evaluated. The results indicated a shared up-regulation of miR-34b and miR-185 by both QDs. Furthermore, mimics and inhibitors of miR-34b and miR-185 significantly enhanced and suppressed the gene and protein expressions of P-gp, respectively, confirming the modulatory function of these two miRNAs on P-gp. Interestingly, expressions of both miRNAs were suppressed during treatment with Cd²⁺ and doxorubicin, which induced the expression of P-gp, indicating the universality of these miRNAs-related mechanisms. Thus, as miR-34b and miR-185 participated in the suppression of P-gp functions in A549 cells they could be interesting targets for the treatment of lung cancer.

Hybrid silica aerogel nanocomposite adsorbents designed for Cd(II) removal from aqueous solution

Hybrid silica aerogel (HSA) nanoparticles were synthesized by sol-gel method and drying at ambient pressure. Also, two magnetic nanocomposites of HSA with Fe₃ O₄ nanoparticles and chitosan (CS) were prepared including HSA-Fe₃ O₄ and HSA-Fe₃ O₄ -CS. The morphology, structure, and magnetic properties of the HSA as well as its nanocomposites were analyzed by SEM, XRD, TGA, VSM, and ATR-FTIR techniques. The saturation magnetization (M_s ) values for the Fe₃ O₄ NPs, HSA-Fe₃ O_4, and HSA-Fe₃ O₄ -CS nanocomposite film were 69.93, 19.04, and 5.77 emu/g, respectively. Furthermore, the abilities of the HSA, HSA-Fe₃ O₄ , CS, and HSA-Fe₃ O₄ -CS adsorbents were assessed for removal of cadmium(II) heavy metal ions (100 ppm) from aqueous solution. All adsorbents removed/adsorbed the maximum Cd(II) ions in 120 min when adsorbent dosage = 20 mg and pH = 8. Moreover, the highest adsorption capacities were 58.5, 69.4, 65.8, and 71.9 mg/g for the HSA, CS, HSA-Fe₃ O_4, and HSA-Fe₃ O₄ -CS, respectively. Kinetic studies using all adsorbents verified that Cd(II) adsorption obeyed the second-order model illustrating the analyte chemisorption was happened on the adsorbent surfaces. All adsorption data were well consistent with the Langmuir isotherms. The reusability experiment confirmed that all of adsorbents could preserve >95% of their initial adsorption capacities even after five series of adsorption/desorption tests. PRACTITIONER POINTS: Hybrid silica aerogel (HSA), HSA-Fe₃ O_4, and HSA-Fe₃ O₄ -CS adsorbents were produced. Nanocomposites were characterized by XRD, TGA, SEM, VSM, and ATR-FTIR analysis. Adsorption of cadmium(II) ions by adsorbents was examined in aqueous solution. The highest adsorption capacity was obtained for the HSA-Fe₃ O₄ -CS (71.9 mg/g). Cd(II) adsorption followed second-order kinetics and Langmuir isotherm model.

Pxr- and Nrf2- mediated induction of ABC transporters by heavy metal ions in zebrafish embryos

Transcription factors including pregnane X receptor (Pxr) and nuclear factor-erythroid 2-related factor-2 (Nrf2) are important modulators of Adenosine triphosphate-binding cassette (ABC) transporters in mammalian cells. However, whether such modulation is conserved in zebrafish embryos remains largely unknown. In this manuscript, pxr- and nrf2-deficient models were constructed with CRISPR/Cas9 system, to evaluate the individual function of Pxr and Nrf2 in the regulation of ABC transporters and detoxification of heavy metal ions like Cd²⁺ and Ag⁺. As a result, both Cd²⁺ and Ag⁺ conferred extensive interactions with ABC transporters in wild type (WT) embryos: their accumulation and toxicity were affected by the activity of ABC transporters, and they significantly induced the mRNA expressions of ABC transporters. These induction effects were reduced by the mutation of pxr and nrf2, but elevations in the basal expression of ABC transporters compensated for the loss of their inducibility. This could be an explanation for remaining transporter function in both mutant models as well as the unaltered toxicity of metal ions in pxr-deficient embryos. However, mutation of nrf2 disrupted the production of glutathione (GSH), resulting in the enhanced toxicity of Cd²⁺/Ag⁺ in zebrafish embryos. In addition, elevated expressions of other transcription factors like aryl hydrocarbon receptor (ahr) 1b, peroxisome proliferator-activated receptor (ppar)-β, and nrf2 were found in pxr-deficient models without any treatment, while enhanced induction of ahr1b, ppar-β and pxr could only be seen in nrf2-deficient embryos after the treatment of metal ions, indicating different compensation phenomena for the absence of transcription factors. After all, pxr-deficient and nrf2-deficient zebrafish embryos are useful tools in the functional investigation of Pxr and Nrf2 in the early life stages of aquatic organisms. However, the compensatory mechanisms should be taken into consideration when interpreting the results and need in-depth investigations.

Xenobiotic transporter activity in zebrafish embryo ionocytes

Ionocytes are specialized cells in the epidermis of embryonic zebrafish (Danio rerio) that play important roles in ion homeostasis and have functional similarities to mammalian renal cells. Here, we examined whether these cells might also share another functional similarity with renal cells, which is the presence of efflux transporter activities useful for elimination of toxic small molecules. Xenobiotic transporters (XTs), including the ATP-Binding Cassette (ABC) family, are a major defense mechanism against diffusible toxic molecules in aquatic embryos, including zebrafish, but their activity in the ionocytes has not previously been studied. Using fluorescent small molecule substrates of XT, we observed that specific populations of ionocytes uptake and efflux fluorescent small molecules in a manner consistent with active transport. We specifically identified a P-gp/ABCB1 inhibitor-sensitive efflux activity in the H⁺-ATPase-rich (HR) ionocytes, and show that these cells exhibit enriched expression of the ABCB gene, abcb5. The results extend our understanding of the functional significance of zebrafish ionocytes and indicate that these cells could play an important role in protection of the fish embryo from harmful small molecules.

Making Waves: New Developments in Toxicology With the Zebrafish

The laboratory zebrafish (Danio rerio) is now an accepted model in toxicologic research. The zebrafish model fills a niche between in vitro models and mammalian biomedical models. The developmental characteristics of the small fish are strategically being used by scientists to study topics ranging from high-throughput toxicity screens to toxicity in multi- and transgenerational studies. High-throughput technology has increased the utility of zebrafish embryonic toxicity assays in screening of chemicals and drugs for toxicity or effect. Additionally, advances in behavioral characterization and experimental methodology allow for observation of recognizable phenotypic changes after xenobiotic exposure. Future directions in zebrafish research are predicted to take advantage of CRISPR-Cas9 genome editing methods in creating models of disease and interrogating mechanisms of action with fluorescent reporters or tagged proteins. Zebrafish can also model developmental origins of health and disease and multi- and transgenerational toxicity. The zebrafish has many advantages as a toxicologic model and new methodologies and areas of study continue to expand the usefulness and application of the zebrafish.

Altered Gene expression of ABC transporters, nuclear receptors and oxidative stress signaling in zebrafish embryos exposed to CdTe quantum dots

Adenosine triphosphate-binding cassette (ABC) transporters, including P-glycoprotein (Pgp) and multi-resistance associated proteins (Mrps), have been considered important participants in the self-protection of zebrafish embryos against environmental pollutants, but their possible involvement in the efflux and detoxification of quantum dots (QDs), as well as their regulation mechanism are currently unclear. In this work, gene expression alterations of ABC transporters, nuclear receptors, and oxidative stress signaling in zebrafish embryos after the treatment of mercaptopropionic acid (MPA)CdTe QDs and MPA-CdSCdTe QDs were investigated. It was observed that both QDs caused concentration-dependent delayed hatching effects and the subsequent induction of transporters like mrp1&2 in zebrafish embryos, indicating the protective role of corresponding proteins against CdTe QDs. Accompanying these alterations, expressions of nuclear receptors including the pregnane X receptor (pxr), aryl hydrocarbon receptor (ahr) 1b, and peroxisome proliferator-activated receptor (ppar)-β were induced by QDs in a concentration- and time-dependent manner. Moreover, elevated oxidative stress, reflected by the reduction of glutathione (GSH) level and superoxide dismutase (SOD) activities, as well as the dramatic induction of nuclear factor E2 related factor (nrf) 2, was also found. More importantly, alterations of pxr and nrf2 were more pronounced than that of mrps, and these receptors exhibited an excellent correlation with delayed hatching rate in the same embryos (R² > 0.8). Results from this analysis demonstrated that the induction of mrp1 and mrp2 could be important components for the detoxification of QDs in zebrafish embryos. These transporters could be modulated by nuclear receptors and oxidative stress signaling. In addition, up-regulation of pxr and nrf2 could be developed as toxic biomarkers of CdTe QDs.

iTRAQ-based proteomic profiling of Pycnoporus sanguineus in response to co-existed tetrabromobisphenol A (TBBPA) and hexavalent chromium

In current study, we investigated the changes of proteome profiles of Pycnoporus sanguineus after a single exposure of Cr(VI), TBBPA and a combined exposure of TBBPA and Cr(VI), with the goal of illuminating the cellular mechanisms involved in the interactions of co-existed TBBPA and Cr(VI) with the cells of P. sanguineus at the protein level. The results revealed that some ATP-binding cassette (ABC) transporters were obviously induced by these pollutants to accelerate the transportation, transformation and detoxification of TBBPA and Cr(VI). Cr(VI) could inhibit the bioremoval of its organic co-pollutants TBBPA through suppressing the expression of several key proteins related to the metabolism of TBBPA by P. sanguineus, including two cytochrome P450s, pentachlorophenol 4-monooxygenase and glutathione S-transferases. Furthermore, Cr(VI) possibly reduced the cell vitality and growth of P. sanguineus by enhancing the expression of imidazole glycerol phosphate synthase as well as by decreasing the abundances of proteins associated with the intracellular metabolic processes, such as the tricarboxylic acid cycle, purine metabolism and glutathione biosynthesis, thereby adversely affecting the biotransformation of TBBPA. Cr(VI) also inhibited the expression of peptidyl prolyl cis/trans isomerases, thus causing the damage of cell membrane integrity. In addition, some important proteins participated in the resistance to Cr(VI) toxicity were observed to up-regulate, including heat shock proteins, 26S proteasome, peroxiredoxins and three critical proteins implicated in S-adenosyl methionine synthesis, which contributed to reducing the hazard of Cr(VI) to P. sanguineus. The results of this study provide novel insights into the physiological responses and molecular mechanism of white rot fungi P. sanguineus to the stress of concomitant TBBPA and Cr(VI).

CRISPR-Cas9: A New Addition to the Drug Metabolism and Disposition Tool Box

Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated protein 9 (Cas9), i.e., CRISPR-Cas9, has been extensively used as a gene-editing technology during recent years. Unlike earlier technologies for gene editing or gene knockdown, such as zinc finger nucleases and RNA interference, CRISPR-Cas9 is comparably easy to use, affordable, and versatile. Recently, CRISPR-Cas9 has been applied in studies of drug absorption, distribution, metabolism, and excretion (ADME) and for ADME model generation. To date, about 50 papers have been published describing in vitro or in vivo CRISPR-Cas9 gene editing of ADME and ADME-related genes. Twenty of these papers describe gene editing of clinically relevant genes, such as ATP-binding cassette drug transporters and cytochrome P450 drug-metabolizing enzymes. With CRISPR-Cas9, the ADME tool box has been substantially expanded. This new technology allows us to develop better and more predictive in vitro and in vivo ADME models and map previously underexplored ADME genes and gene families. In this mini-review, we give an overview of the CRISPR-Cas9 technology and summarize recent applications of CRISPR-Cas9 within the ADME field. We also speculate about future applications of CRISPR-Cas9 in ADME research.