Molecular analysis, developmental function and heavy metal-induced expression of ABCC5 in zebrafish

Genome-wide analysis of ATP-binding cassette (ABC) transporter in Penaeus vannamei and identification of two ABC genes involved in immune defense against Vibrio parahaemolyticus by affecting NF-κB signaling pathway

The ATP-binding cassette (ABC) transporters have crucial roles in various biological processes such as growth, development and immune defense in eukaryotes. However, the roles of ABC transporters in the immune system of crustaceans remain elusive. In this study, 38 ABC genes were systematically identified and characterized in Penaeus vannamei. Bioinformation analysis revealed that PvABC genes were categorized into ABC A-H eight subfamilies with 17 full-transporters, 11 half transporters and 10 soluble proteins, and multiple immunity-related cis-elements were found in gene promoter regions. Expression analysis showed that most PvABC genes were widely and highly expressed in immune-related tissues and responded to the stimulation of Vibrio parahaemolyticus. To investigate whether PvABC genes mediated innate immunity, PvABCC5, PvABCF1 and PvABCB4 were selected for dsRNA interference experiment. Knockdown of PvABCF1 and PvABCC5 not PvABCB4 increased the cumulative mortality of P. vannamei and bacterial loads in hepatopancreas after infection with V. parahaemolyticus. Further analysis showed that the PvABCF1 and PvABCC5 knockdown decreased expression levels of NF-κB pathway genes and antimicrobial peptides (AMPs). Collectively, these findings indicated that PvABCF1 and PvABCC5 might restrict V. parahaemolyticus challenge by positively regulating NF-κB pathway and then promoting the expression of AMPs, which would contribute to overall understand the function of ABC genes in innate immunity of invertebrates.

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.

Assessment of Lactobacillus rhamnosus mediated protection against arsenic-induced toxicity in zebrafish: a qPCR-based analysis of Firmicutes and Bacteroidetes groups and embryonic development

Arsenic poses a significant health risk worldwide, impacting the gut microbiota, reproductive health, and development. To address this issue, a cost-effective method like probiotic supplementation could be beneficial. However, the interplay between arsenic toxicity, probiotics, gut microbiota, and maternal transcript modulation remains unexplored. This study investigates the impact of Lactobacillus rhamnosus (L. rhamnosus) DSM 20021 on the proportions of Firmicutes and Bacteroidetes, as well as its effects on embryonic development in zebrafish induced by arsenic trioxide (As2O3). Adult zebrafish were exposed to both high and environmentally relevant concentrations of As2O3 (10, 50, and 500 ppb) for 1, 6, and 12 weeks. qPCR analysis revealed increased proportions of Firmicutes and Bacteroidetes in all As2O3-exposed and As2O3 + L. rhamnosus-exposed groups, while no significant changes were observed in groups exposed only to L. rhamnosus DSM 20021. The larvae, exposed to 500 ppb of As2O3 for 12 weeks, exhibited low growth, decreased survival rates, and morphological deformities. However, these adverse effects were reversed upon exposure to only L. rhamnosus DSM 20021. Furthermore, the expression of DVR1 and ABCC5, which are involved in defense against xenobiotics and embryo development, decreased significantly in As2O3 (500 ppb) and As2O3 (500 ppb) + L. rhamnosus-exposed groups, whereas ameliorative effects were observed in only L. rhamnosus DSM 20021-exposed groups.

Effects of antimony exposure on DNA damage and genome-wide variation in zebrafish (Danio rerio) liver

Antimony (Sb) is a potentially toxic and carcinogenic cumulative contaminant that poses a serious threat to aquatic ecosystems. To better clarify the genotoxicity of Sb and its mechanism of action. In this study, we investigated DNA damage and genome-wide variation in the liver of a model organism, zebrafish (Danio rerio), under subacute Sb exposure and explored its potential toxicological mechanisms. The results showed that medium and high concentrations of Sb significantly reduced the total antioxidant capacity and increased the content of reactive oxygen species in zebrafish liver, and further studies revealed that it increased oxidative DNA damage and DNA-DNA cross-link (DDC), but had little effect on DNA-protein cross-link (DPC). The result of resequencing showed that the mutation sites of the genes with high concentrations of Sb were higher than those with medium concentrations, and the mutation was mainly a single nucleotide. The pathways significantly enriched for nonsynonymous single nucleotide polymorphisms (SNPs) and insertion/deletion mutations (InDels) variant genes in the coding regions of both the medium and high Sb-treated groups were ECM-receptor interactions, and the high Sb-treated group also included lysine degradation, hematopoietic cell lineage, and cytokine-cytokine receptor interactions. This suggests that ECM-receptor interactions play an important role in the mechanism of antimony toxicity to the liver of zebrafish.

New loci for refractive errors and ocular biometric parameters in young Chinese Han adults

Myopia has become a major public health issue with an increasing prevalence. There are still individuals who experience similar environmental risk factors and, yet, remain non-myopic. Thus, there might be genetic factors protecting people from myopia. Considering the opposite ocular characteristics of primary angle closure glaucoma (PACG) to myopia and possible common pathway between them, we propose that certain risk genes for PACG might act as a protective factor for myopia. In this study, 2,678 young adults were genotyped for 37 targeted single nucleotide polymorphisms. Compared with emmetropia, rs1401999 (allele C: OR=0.795, P=0.03; genotype in dominant model: OR=0.759, P=0.02) and rs1258267 (allele A: OR=0.824, P=0.03; genotype in dominant model: OR=0.603, P=0.01) were associated with low to moderate myopia and high myopia, respectively. Genotype under recessive model of rs11024102 was correlated with myopia (OR=1.456, P=0.01), low to moderate myopia (OR=1.443, P=0.02) and high myopia (OR=1.453, P=0.02). However, these associations did not survive Bonferroni correction. Moreover, rs1401999, rs1258267, and rs11024102 showed associations with certain ocular biometric parameters in different groups. Our study suggests that ABCC5, CHAT and PLEKHA7 might be associated with refractive errors by contributing to the regulation of ocular biometry, in terms of uncorrected results and their biological functions.

Effects of heavy metals on fish physiology - A review

The pollution by heavy metals poses a serious threat to the aquatic environment and to the organisms if the concentration of heavy metals in the environment exceeds the safe limits. Due to their non-biodegradable and long persistence nature in the environment, heavy metals cause toxicity in fish by producing oxygen reactive species through oxidizing radical production. In this review, we investigated the effects of heavy metals on fish physiology with special emphasis on hemato-biochemical properties, immunological parameters especially hormones and enzymes, histopathology of different major organs and underlying molecular mechanisms. All those parameters are significantly affected by heavy metal exposure and are found to be important bio-monitoring tools to assess heavy metal toxicity. Hematological and biochemical alterations have been documented including cellular and nuclear abnormalities in different fish species exposed to different concentrations of heavy metals. Major fish organs (gills, liver, kidneys) including intestine, muscles showed different types of pathology specific to organs in acute and chronic exposure to different heavy metals. This study also revealed the expression of different genes involved in oxidative stress and detoxification of heavy metals. In a nutshell, this article shades light on the manipulation of fish physiology by the heavy metals and sought attention in the prevention and maintenance of aquatic environments particularly from heavy metals contaminations.

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.

ATP-binding cassette transporters at the zebrafish blood-brain barrier and the potential utility of the zebrafish as an in vivo model

The brain is protected from toxins by a tightly regulated network of specialized cells, including endothelial cells, pericytes, astrocyes, and neurons, known collectively as the blood-brain barrier (BBB). This selectively permeable barrier permits only the most crucial molecules essential for brain function to enter and employs a number of different mechanisms to prevent the entry of potentially harmful toxins and pathogens. In addition to a physical barrier comprised of endothelial cells that form tight junctions to restrict paracellular transport, there is an active protective mechanism made up of energy-dependent transporters that efflux compounds back into the bloodstream. Two of these ATP-binding cassette (ABC) transporters are highly expressed at the BBB: P-glycoprotein (P-gp, encoded by the ABCB1 gene) and ABCG2 (encoded by the ABCG2 gene). Although a number of in vitro and in vivo systems have been developed to examine the role that ABC transporters play in keeping compounds out of the brain, all have inherent advantages and disadvantages. Zebrafish (Danio rerio) have become a model of interest for studies of the BBB due to the similarities between the zebrafish and mammalian BBB systems. In this review, we discuss what is known about ABC transporters in zebrafish and what information is still needed before the zebrafish can be recommended as a model to elucidate the role of ABC transporters at the BBB.

Potential mechanism of lead poisoning to the growth and development of ovarian follicle

With the rapid development of economic globalization and industrialization, lead (Pb), one of the most important heavy metals, has been used widely since antiquity for several purposes. In fact, its impact on the health of animals and humans is a significant public health risk all the time. Pb could be accumulated in the body for a long time, causing irreversible damage to the health of animals and humans, including hostile reproductive health. Up to now, although there are some published studies on impeding the normal development of ovarian folliculogenesis of female resulted from Pb exposure, with the damage of structure in uterine tissue, the imbalance of female menstrual status, and the change of hormone levels. The potential mechanism of Pb exposure on female reproduction system, however, remains enigmatic. How to alleviate the damage of Pb toxicity to reproductive function of female has become an urgent problem. Therefore, the aim of the present review is to discuss the information on the growth and development of ovarian follicle of mammalians and the potential toxic mechanism when exposed to Pb. The literatures were collected via various websites and consulting books, reports, etc. In summary, Pb impair folliculogenesis of mammalians, which may be related to the interference to the hypothalamic-pituitary-gonadal (HPG) axis and the production of reactive oxygen species (ROS), in turn impairs various molecules including proteins, lipids and DNA, as well as the disruption of the antioxidant defense system, ionic equilibrium and endoplasmic reticulum homeostasis.

Updates on Genes and Genetic Mechanisms Implicated in Primary Angle-Closure Glaucoma

Primary angle-closure glaucoma (PACG) is estimated to affect over 30 million people worldwide by 2040 and is highly prevalent in the Asian population. PACG is more severe and carries three times the higher risk of blindness than primary open-angle glaucoma, thus representing a significant public health concern. High heritability and ethnic-specific predisposition to PACG suggest the involvement of genetic factors in disease development. In the recent past, genetic studies have led to the successful identification of several genes and loci associated with PACG across different ethnicities. The precise cellular and molecular roles of these multiple loci in the development and progression of PACG remains to be elucidated. Nonetheless, these studies have significantly increased our understanding of the emerging cellular processes and biological pathways that might provide more significant insights into the disease’s genetic etiology and may be valuable for future clinical applications. This review aims to summarize and update the current knowledge of PACG genetics analysis research.

Generation of Knockout and Transgenic Zebrafish to Characterize Abcc4 Functions in Detoxification and Efflux of Lead

Lead (Pb) is one of the major heavy metals that are toxic to vertebrates and usually considered as environmental pollutants. ABCC4/MRP4 is an organic anion transporter that mediates cellular efflux of a wide range of exogenous and endogenous compounds such as cyclic nucleotides and anti-cancer drugs; however, it remains unclear whether ABCC4 and its orthologs function in the detoxification and excretion of toxic lead. In this study, we found that the transcriptional and translational expression of zebrafish abcc4 was significantly induced under lead exposure in developing zebrafish embryos and adult tissues. Overexpression of zebrafish Abcc4 markedly decreased the cytotoxicity and accumulation of lead in pig renal proximal tubule cell line (LLC-PK1 cells). To further understand the functions of zebrafish Abcc4 in lead detoxification, the clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 system was used to create an abcc4^−/− mutant zebrafish line. In comparison with the wild-type (WT) zebrafish, the abcc4^−/− mutants showed a higher death rate and lead accumulation upon exposure to lead. Furthermore, a stable abcc4-transgenic zebrafish line was successfully generated, which exerted stronger ability to detoxify and excrete lead than WT zebrafish. These findings indicate that zebrafish Abcc4 plays a crucial role in lead detoxification and cellular efflux and could be used as a potential biomarker to monitor lead contamination in a water environment.

Chemical effects on dye efflux activity in live zebrafish embryos and on zebrafish Abcb4 ATPase activity

ATP-binding cassette (ABC) transporter proteins include efflux pumps that confer multixenobiotic resistance to zebrafish embryos, a valuable toxico/pharmacological model. Here, we established an automated microscopy-based rhodamine B dye accumulation assay in which enhanced dye accumulation in live zebrafish embryos indicates inhibition of multixenobiotic efflux transporter activity. Twenty structurally divergent known substrates and/or inhibitors of human ABC transporters and environmentally relevant compounds were examined using this assay and the ATPase activity of recombinant zebrafish Abcb4 as readouts. These two assays confirmed that Abcb4 functions as an efflux transporter in zebrafish, whereas they gave discordant results for some of the tested substances. The dye accumulation assay in zebrafish embryos could be useful to screen environmental pollutants and other chemicals for efflux transporter interaction in a medium-throughput fashion.

The genetics of angle closure glaucoma

Glaucoma, the leading cause of irreversible blindness worldwide, can be divided into two major types: primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG). PACG could lead to severe vision loss and has a high prevalence among Asian populations. The worldwide population affected by PACG is estimated to exceed 20 million by 2020. Recent studies have shown that there are at least eight genetic loci significantly associated with risk of PACG, possibly contributing to the phenotype by interacting with environmental factors. This review presents the progress that has been achieved in the genetics of PACG and its future perspectives. This article should be considered as a memorial article to honor Dr. R. Rand Allingham's remarkable contribution to genetic association studies in glaucoma. We are deeply saddened by the loss of Dr. Allingham, not only a huge loss for ophthalmology, but also loss of a dear friend. Looking back to his extraordinary career, Dr. Allingham devoted his whole life and passion into establishing the genetic basis of different forms of glaucoma such as open angle, angle closure, and exfoliation glaucoma. He had a special interest in analyses of populations from African ancestry, which greatly boosted the understanding of glaucoma genetics.

Involvement of LeMRP, an ATP-binding cassette transporter, in shikonin transport and biosynthesis in Lithospermum erythrorhizon

Shikonin and its derivatives are important medicinal secondary metabolites accumulating in roots of Lithospermum erythrorhizon. Although some membrane proteins have been identified as transporters of secondary metabolites, the mechanisms underlying shikonin transport and accumulation in L. erythrorhizon cells still remain largely unknown. In this study, we isolated a cDNA encoding LeMRP, an ATP-binding cassette transporter from L. erythrorhizon, and further investigated its functions in the transport and biosynthesis of shikonin using the yeast transformation and transgenic hairy root methods, respectively. Real-time PCR was applied for expression analyses of LeMRP and shikonin biosynthetic enzyme genes. Functional analysis of LeMRP using the heterologous yeast cell expression system showed that LeMRP could be involved in shikonin transport. Transgenic hairy roots of L. erythrorhizon demonstrated that LeMRP overexpressing hairy roots produced more shikonin than the empty vector (EV) control. Real-time PCR results revealed that the enhanced shikonin biosynthesis in the overexpression lines was mainly caused by highly up-regulated expression of genes coding key enzymes (LePAL, HMGR, Le4CL and LePGT) involved in shikonin biosynthesis. Conversely, LeMRP RNAi decreased the accumulation of shikonin and effectively down-regulated expression level of the above genes. Typical inhibitors of ABC proteins, such as azide and buthionine sulphoximine, dramatically inhibited accumulation of shikonin in hairy roots. Our findings provide evidence for the important direct or indirect role of LeMRP in transmembrane transport and biosynthesis of shikonin.

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

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

Involvement of LeMDR, an ATP-binding cassette protein gene, in shikonin transport and biosynthesis in Lithospermum erythrorhizon

BACKGROUND

Shikonin is a naphthoquinone secondary metabolite with important medicinal value and is found in Lithospermum erythrorhizon. Considering the limited knowledge on the membrane transport mechanism of shikonin, this study investigated such molecular mechanism.

RESULTS

We successfully isolated an ATP-binding cassette protein gene, LeMDR, from L. erythrorhizon. LeMDR is predominantly expressed in L. erythrorhizon roots, where shikonin accumulated. Functional analysis of LeMDR by using the yeast cell expression system revealed that LeMDR is possibly involved in the shikonin efflux transport. The accumulation of shikonin is lower in yeast cells transformed with LeMDR-overexpressing vector than that with empty vector. The transgenic hairy roots of L. erythrorhizon overexpressing LeMDR (MDRO) significantly enhanced shikonin production, whereas the RNA interference of LeMDR (MDRi) displayed a reverse trend. Moreover, the mRNA expression level of LeMDR was up-regulated by treatment with shikonin and shikonin-positive regulators, methyl jasmonate and indole-3-acetic acid. There might be a relationship of mutual regulation between the expression level of LeMDR and shikonin biosynthesis.

CONCLUSIONS

Our findings demonstrated the important role of LeMDR in transmembrane transport and biosynthesis of shikonin.

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

Previous studies in our lab have revealed that both P-glycoprotein (Pgp) and multi-resistance associated protein (Mrp) 1 played important roles in the detoxification of heavy metals and polycyclic aromatic hydrocarbon (PAH) in zebrafish embryos. This paper aims to extend this research by using mrp1-deficient model to illustrate the individual function of Mrp1. In this respect, CRISPR/Cas9 system was employed to generate a frameshift mutation in zebrafish mrp1 causing premature translational stops in Mrp1. Significant reduction on the efflux function of Mrps was found in mutant zebrafish embryos, which correlated well with the significantly enhanced accumulation and toxicity of cadmium chloride (CdCl₂) and benzo[a]pyrene (BαP), indicating the protective role of the corresponding protein. The different alteration on the accumulation and toxicity of Cd²⁺ and BαP could be attributed to the fact that Cd²⁺ and its metabolites were mainly excreted by Mrp1, while BαP was primarily pumped out by Pgp. More importantly, the compensation mechanism for the absence of Mrp1, including elevated glutathione (GSH) level and up-regulated expression of pgp and mrp2 were also found. Thus, mrp1-deficient zebrafish embryo could be a useful tool in the investigation of Mrp1 functions in the early life stages of aquatic organisms. However, compensation mechanism should be taken into consideration in the interpretation of results obtained with mrp1-deficient fish.

Gestational Zearalenone Exposure Causes Reproductive and Developmental Toxicity in Pregnant Rats and Female Offspring

Zearalenone (ZEN) is an oestrogenic mycotoxin commonly found in food and feed products and can affect reproduction and development in both humans and animals. This study aimed to determine the toxic effects of ZEN on maternal SD rats and the F1 female offspring. Sixty-four pregnant rats were divided into 4 groups and exposed to feed contaminated with ZEN (0, 5, 10, and 20 mg/kg feed) on gestational days (GDs) 0–21. Compared with the controls, the groups exposed to 10 and 20 mg/kg ZEN showed significantly decreased feed intake and body weight of pregnant rats and/or female offspring. Meanwhile, 20 mg/kg ZEN significantly decreased the birth weight and viability of F1 newborn rats. Moreover, 10 and 20 mg/kg ZEN diets increased follicle-stimulating hormone concentrations but decreased oestradiol in both maternal and F1 adult rats. In the F1 generation, ZEN caused no pathological changes in ovaries and uterus in weaned rats, but significant follicular atresia and a thinning uterine layer were found in F1 female adult rats in the 20 mg/kg ZEN group. These impairments concurred with the inhibited mRNA and protein levels of oestrogen receptor-alpha (Esr1) and 3β-hydroxysteroid dehydrogenase (HSD) in the adult uterus and/or ovaries. Furthermore, 10 and/or 20 mg/kg ZEN exposure significantly reduced Esr1, gonadotropin-releasing hormone receptor (GnRHr), and ATP binding cassette transporters b1 and c1 (ABCb1 and ABCc1) in the placenta and foetal and weaned F1 brains, and also produced a dose-dependent increase in 3β-HSD in the placenta. Additionally, 20 mg/kg ZEN significantly upregulated ABCc5 expression in the placenta and ovaries of weaned rats. These results suggested that prenatal ZEN exposure in rats affected maternal and foetal development and may lead to long-term reproductive impairment in F1 adult females.

A multivariate assessment of innate immune-related gene expressions due to exposure to low concentration individual and mixtures of four kinds of heavy metals on zebrafish (Danio rerio) embryos

Concerns over the potential health effects of mixtures of low concentration heavy metals on living organisms keep growing by the day. However, the toxicity of low concentration metal mixtures on the immune system of fish species has rarely been investigated. In this study, the zebrafish model was employed to investigate the effect on innate immune and antioxidant-related gene expressions, on exposure to environmentally relevant concentrations of individual and mixtures of Pb (0.01 mg/L), Hg (0.001 mg/L), As (0.01 mg/L) and Cd (0.005 mg/L). Messenger-RNA (mRNA) levels of IL1β, TNF-α, IFNγ, Mx, Lyz, C3B and CXCL-Clc which are closely associated with the innate immune system were affected after exposing zebrafish embryos to metals for 120 h post fertilization (hpf). Individual and mixtures of metals exhibited different potentials to modulate innate-immune gene transcription. IL1β genes were significantly up regulated on exposure to Pb + As (2.01-fold) and inhibited on exposure to Pb + Hg + Cd (0.13-fold). TNF-α was significantly inhibited on exposure to As (0.40-fold) and Pb + As (0.32-fold) compared to control. Metal mixtures generally up regulated IFNγ compared to individual metals. Additionally, antioxidant genes were affected, as CAT and GPx gene expressions generally increased, whiles Mn-SOD and Zn/Cu-SOD reduced. Multivariate analysis showed that exposure to individual metals greatly influenced modulation of innate immune genes; whiles metal mixtures influenced antioxidant gene expressions. This suggests that beside oxidative stress, there may be other pathways influencing gene expressions of innate immune and antioxidant-related genes. Low concentration heavy metals also affect expression of development-related (wnt8a and vegf) genes. Altogether, the results of this study clearly demonstrate that low concentration individual and mixtures of metals in aquatic systems will greatly influence the immune system. It is indicative that mechanisms associated with toxicity of metal mixtures is complex, however, further studies to elucidate them are ongoing in our research laboratory.

ATP-binding cassette transporters in reproduction: a new frontier

BACKGROUND

The transmembrane ATP-binding cassette (ABC) transporters actively efflux an array of clinically relevant compounds across biological barriers, and modulate biodistribution of many physiological and pharmacological factors. To date, over 48 ABC transporters have been identified and shown to be directly and indirectly involved in peri-implantation events and fetal/placental development. They efflux cholesterol, steroid hormones, vitamins, cytokines, chemokines, prostaglandins, diverse xenobiotics and environmental toxins, playing a critical role in regulating drug disposition, immunological responses and lipid trafficking, as well as preventing fetal accumulation of drugs and environmental toxins.

METHODS

This review examines ABC transporters as important mediators of placental barrier functions and key reproductive processes. Expression, localization and function of all identified ABC transporters were systematically reviewed using PubMed and Google Scholar websites to identify relevant studies examining ABC transporters in reproductive tissues in physiological and pathophysiological states. Only reports written in English were incorporated with no restriction on year of publication. While a major focus has been placed on the human, extensive evidence from animal studies is utilized to describe current understanding of the regulation and function of ABC transporters relevant to human reproduction.

RESULTS

ABC transporters are modulators of steroidogenesis, fertilization, implantation, nutrient transport and immunological responses, and function as 'gatekeepers' at various barrier sites (i.e. blood-testes barrier and placenta) against potentially harmful xenobiotic factors, including drugs and environmental toxins. These roles appear to be species dependent and change as a function of gestation and development. The best-described ABC transporters in reproductive tissues (primarily in the placenta) are the multidrug transporters p-glycoprotein and breast cancer-related protein, the multidrug resistance proteins 1 through 5 and the cholesterol transporters ABCA1 and ABCG1.

CONCLUSIONS

The ABC transporters have various roles across multiple reproductive tissues. Knowledge of efflux direction, tissue distribution, substrate specificity and regulation of the ABC transporters in the placenta and other reproductive tissues is rapidly expanding. This will allow better understanding of the disposition of specific substrates within reproductive tissues, and facilitate development of novel treatments for reproductive disorders as well as improved approaches to protecting the developing fetus.

Two novel multidrug resistance associated protein (MRP/ABCC) from the Mediterranean mussel (Mytilus galloprovincialis): characterization and expression patterns in detoxifying tissues

Multidrug resistance associated proteins (MRP) belong to the ABCC branch of the ABC transporters. The MRP together with P-gp (P-glycoprotein; MDR1; ABCB1) and BCRP (breast cancer resistance protein; ABCG2) confer multixenobiotic resistance (MXR) in marine vertebrates. In aquatic invertebrates, little is known about the presence and role of these ABC transporters. The ABC transporters play an important role in the absorption, distribution, and excretion of drugs, xenobiotics, and endogenous compounds and are predominantly expressed in excretory organs. In the present study, we identified and characterized two MRP/ABCC transporters (mrp1 and mrp2) from the Mediterranean mussel (Mytilus galloprovincialis Lamarck, 1819). The two cDNAs finally obtained were 4648 bp for mrp1 and 5065 bp for mrp2 with open reading frames of 1500 and 1524 residues, respectively. Analysis of the amino acid sequences revealed the structural organization of ABC transporters with the typical and highly conserved motifs. The expression levels of these genes revealed that the highest expression of mrp1 and mrp2 genes was found in the digestive gland followed by gills, and the lowest expression of the three tissues was detected in the mantle. The expression of these genes was also studied in mussels naturally contaminated with okadaic acid (from a bloom of Dinophysis acuminata Claparède and Lachmann, 1859). The overexpression of mrp2 in the digestive gland suggests that this gene is involved in the process of detoxification of okadaic acid in M. galloprovincilais. These expression patterns agree with the suggested role of these genes in the protection against endogenous or exogenous compounds in aquatic organisms.

Individual and joint toxic effects of cadmium sulfate and α-naphthoflavone on the development of zebrafish embryo

This paper aims to evaluate the individual and joint toxicities of cadmium sulfate (CdSO4) and α-naphthoflavone (ANF) in zebrafish embryos. As a result, CdSO4 caused both lethal and sub-lethal effects, such as 24 h post-fertilization (hpf) death and 72 hpf delayed hatching. However, ANF only caused sub-lethal effects, including 48 hpf cardiac edema and 72 hpf delayed hatching. Taking 24 hpf death and 48 hpf cardiac edema as endpoints, the toxicities of CdSO4 and ANF were significantly enhanced by each other. Consistently, both CdSO4 and ANF caused significant oxidative stress, including decreases in the reduced glutathione (GSH) level, inhibition of superoxide dismutase (SOD) activity, as well as increases in malondialdehyde (MDA) content in zebrafish embryos, but these mixtures produced much more significant alterations on the biomarkers. Co-treatment of CdSO4 and ANF significantly down-regulated the mRNA level of multidrug resistance-associated protein (mrp) 1 and cytochrome P450 (cyp) 1a, which constituted the protective mechanisms for zebrafish embryos to chemical toxins. In conclusion, co-treatment of CdSO4 and ANF exhibited a much more severe damage in zebrafish embryos than individual treatment. Meanwhile, production of oxidative stress and altered expression of mrp1 and cyp1a could be important components of such joint toxicity.

Silver nanoparticles affect the neural development of zebrafish embryos

Silver nanoparticles (AgNPs) have been widely used in commercial products. This study aims to understand the impact of AgNPs on the early developmental stages in zebrafish (Danio rerio) embryos. Embryos were exposed to two sizes of AgNPs at three dose levels, as well to free Ag(+) ions, for a range of 4-96 h post-fertilization (hpf). The acute exposure study showed that exposure to AgNPs affected the neurological development, and the exposed embryos exhibited anomalies such as small head with hypoplastic hindbrain, small eye and cardiac defects. At the molecular level, AgNPs altered the expression profiles of neural development-related genes (gfap, huC and ngn1), metal-sensitive metallothioneins and ABCC genes in exposed embryos. The expression of AhR2 and Cyp1A, which are usually considered to mediate polycyclic aromatic hydrocarbon toxicity, were also significantly changed. A size-dependent uptake of AgNPs was observed, whereby 4 nm AgNPs were more efficiently taken up compared with the 10 nm-sized particles. Importantly, the head area accumulated AgNPs more efficiently than the trunk area of exposed zebrafish embryos. No free Ag(+) ions, which can be potentially released from the AgNP solutions, were detected. This study suggests that AgNPs could affect the neural development of zebrafish embryos, and the toxicity of AgNPs may be partially attributed to the comparatively higher uptake in the head area. These results indicate the potential neurotoxicity of AgNPs and could be extended to other aquatic organisms.

Effects of tetracycline on developmental toxicity and molecular responses in zebrafish (Danio rerio) embryos

The extensive use of pharmaceuticals has resulted in the intensive contamination of water bodies. Tetracycline is a type of antibiotic and its potential toxicity is causing environmental concern. The effects of developmental toxicity and the mechanisms of tetracycline on fish embryos are not well understood. Zebrafish embryos are used in this study to investigate the developmental toxicity of this compound. Four hour post-fertilization (hpf) zebrafish embryos are exposed to different concentrations of tetracycline until 96 hpf. The larvae display developmental delay phenotypes, including hatching delay, shorter body length, increased yolk sac area and uninflated swim bladder upon exposure to tetracycline. Delayed yolk sac absorption and swim bladder deficiency at 96 hpf are observed in the zebrafish larvae upon exposure to 20 μg/L of tetracycline. To test whether tetracycline causes oxidative damage and the resulting oxidative stress-induced apoptosis, the generation of reactive oxygen species (ROS), Acridine Orange staining and real time polymerase chain reaction have been performed in this study. The results indicate that tetracycline exposure results in significant increases in ROS production and cell apoptosis, mainly in the tail areas at 96 hpf. The gene expression pattern demonstrates that tetracycline induces ROS which causes apoptosis in the zebrafish larvae, and the results also indicate that caspase-dependent apoptotic pathways may greatly contribute to tetracycline-induced apoptosis in the early-life stages of the zebrafish. In addition, we have investigated the effects of tetracycline on marker genes related to resistance mechanisms and gene regulating drug biotransformation. The results of these gene expression studies indicate that tetracycline could induce zebrafish to resist pharmaceuticals and Cytochrome P450s that are involved in the biotransformation of tetracycline in zebrafish larvae. The overall results indicate that tetracycline can produce oxidative stress and induce apoptosis, which brings about significant developmental delay in zebrafish embryos.

Compound mouse mutants of bZIP transcription factors Mafg and Mafk reveal a regulatory network of non-crystallin genes associated with cataract

Although majority of the genes linked to early-onset cataract exhibit lens fiber cell-enriched expression, our understanding of gene regulation in these cells is limited to function of just eight transcription factors and largely in the context of crystallins. We report on small Maf transcription factors Mafg and Mafk as regulators of several non-crystallin human cataract-associated genes in fiber cells and establish their significance to this disease. We applied a bioinformatics tool for cataract gene discovery iSyTE to identify Mafg and its co-regulators in the lens, and generated various null-allelic combinations of Mafg:Mafk mouse mutants for phenotypic and molecular analysis. By age 4 months, Mafg-/-:Mafk+/- mutants exhibit lens defects that progressively develop into cataract. High-resolution phenotypic characterization of Mafg-/-:Mafk+/- mouse lens reveals severely disorganized fiber cells, while microarray-based expression profiling identifies 97 differentially regulated genes (DRGs). Integrative analysis of Mafg-/-:Mafk+/- lens-DRGs with (1) binding motifs and genomic targets of small Mafs and their regulatory partners, (2) iSyTE lens expression data, and (3) interactions between DRGs in the String database, unravel a detailed small Maf regulatory network in the lens, several nodes of which are linked to cataract. This approach identifies 36 high-priority candidates from the original 97 DRGs. Significantly, 8/36 (22%) DRGs are associated with cataracts in human (GSTO1, MGST1, SC4MOL, UCHL1) or mouse (Aldh3a1, Crygf, Hspb1, Pcbd1), suggesting a multifactorial etiology that includes oxidative stress and misregulation of sterol synthesis. These data identify Mafg and Mafk as new cataract-associated candidates and define their function in regulating largely non-crystallin genes linked to human cataract.

Zebrafish Abcb4 is a potential efflux transporter of microcystin-LR

Microcystin-LR (MC-LR) is one of the most common microcystins (MCs), which are hepatotoxic and released into a water body during a period of cyanobacterial blooms. These toxicants can be accumulated in aquatic animals and transferred along the food chain and thus pose adverse effects on aquatic environment and public health. Zebrafish Abcb4 is reported to mediate the cellular efflux of ecotoxicologically relevant compounds including galaxolide, tonalide and phenanthrene; however, it remains unclear whether Abcb4 functions in the detoxification of MC-LR. Here, we demonstrated the role of zebrafish Abcb4 in cellular efflux of MC-LR. Transcripts of zebrafish abcb4 were detected in all of adult tissues examined. MC-LR was able to induce the expression of abcb4 gene and overexpression of Abcb4 significantly decreased the cytotoxicity and accumulation of MC-LR in LLC-PK1 cells and developing embryos. In contrast, overexpression of an Abcb4-G1177D mutant abolished its transporter function but not substrate binding activity, and sensitized LLC-PK1 cells and developing embryos to this cyanobacterial toxin. Moreover, ATPase activity in developing embryos can be induced by MC-LR. Thus, zebrafish Abcb4 plays crucial roles in cellular efflux of MC-LR and is a potential molecular marker for the monitoring of cyanobacteria contamination in the aquatic environment.

Characterization of zebrafish Abcc4 as an efflux transporter of organochlorine pesticides

DDT and lindane are highly toxic organochlorine pesticides and posing adverse effects on the environment and public health due to their frequent usage in developing countries. ABCC4/MRP4 is an organic anion transporter that mediates cellular efflux of a wide range of exogenous and endogenous compounds such as cyclic nucleotides and anti-cancer drugs; however, it remains unclear whether ABCC4 and its orthologs function in the detoxification of organochlorine pesticides. Here, we demonstrated the roles of zebrafish Abcc4 in cellular efflux of DDT and lindane. Zebrafish abcc4 was maternally expressed in the oocytes and its transcripts were detected in the lens, pancreas, gills, liver, intestine and bladder of developing embryos and in adult tissues examined. DDT and lindane were able to induce the expression of abcc4 gene and overexpression of Abcc4 significantly decreased the cytotoxicity and accumulation of DDT and lindane in LLC-PK1 cells and developing embryos. In contrast, overexpression of an Abcc4-G1188D mutant abolished its transporter function without effects on its substrate binding activity, and sensitized LLC-PK1 cells and developing embryos to toxic pesticides. Moreover, glutathione (GSH) was involved in the efflux of cellular pesticides and ATPase activity in developing embryos can be induced by DDT or lindane. Thus, zebrafish Abcc4 plays crucial roles in cellular efflux of organochlorine pesticides and can be used a potential molecular marker for the monitor of DDT and lindane contamination in the aquatic environment.

Histopathological lesions, P-glycoprotein and PCNA expression in zebrafish (Danio rerio) liver after a single exposure to diethylnitrosamine

The presence of carcinogenic compounds in the aquatic environment is a recognized problem. ABC transporters are well known players in the multidrug-resistance (MDR) phenomenon in mammals associated with resistance to chemotherapy, however little is known in fish species. Thus, the aim of this study was to induce hepatic tumours and evaluate long-term effects on P-glycoprotein (P-gp) and proliferating cell nuclear antigen (PCNA) proteins in Danio rerio liver, after exposure to diethylnitrosamine (DEN). Several hepatic histopathological alterations were observed in zebrafish after exposure to DEN including pre-neoplastic lesions 6 and 9 months post-exposure. After 3, 6 and 9 months of exposure to DEN, P-gp and PCNA proteins expression were up-regulated. In conclusion, this study has shown that zebrafish ABC transporters can play a similar role as in human disease, hence zebrafish can be used also as a biological model to investigate in more deep mechanisms involved in disease processes.

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.

Transport in technicolor: mapping ATP-binding cassette transporters in sea urchin embryos

One quarter of eukaryotic genes encode membrane proteins. These include nearly 1,000 transporters that translocate nutrients, signaling molecules, and xenobiotics across membranes. While it is well appreciated that membrane transport is critical for development, the specific roles of many transporters have remained cryptic, in part because of their abundance and the diversity of their substrates. Multidrug resistance ATP-binding cassette (ABC) efflux transporters are one example of cryptic membrane proteins. Although most organisms utilize these ABC transporters during embryonic development, many of these transporters have broad substrate specificity, and their developmental functions remain incompletely understood. Here, we review advances in our understanding of ABC transporters in sea urchin embryos, and methods developed to spatially and temporally map these proteins. These studies reveal that multifunctional transporters are required for signaling, homeostasis, and protection of the embryo, and shed light on how they are integrated into ancestral developmental pathways recapitulated in disease.

Embryonic exposure to sodium arsenite perturbs vascular development in zebrafish

Exposure to arsenic in its inorganic form, arsenite, causes adverse effects to many different organs and tissues. Here, we have investigated arsenite-induced adverse effects on vascular tissues in the model organism zebrafish, Danio rerio. Zebrafish embryos were exposed to arsenite at different exposure windows and the susceptibility to vascular tissue damage was recorded at 72hours post fertilization (hpf). Intersegmental vessel sprouting and growth was most perturbed by exposure to arsenite during the 24-48hpf window, while disruption in the condensation of the caudal vein plexus was more often observed at the 48-72hpf exposure window, reflecting when these structures develop during normal embryogenesis. The vascular growth rate was decreased by arsenite exposure, and deviated from that of control embryos at around 24-26.5hpf. We further mapped changes in expression of key regulators of angiogenesis and vasculogenesis. Downregulation of vascular endothelial growth factor receptor 1/fms-related tyrosine kinase 1 (vegfr1/flt1) expression was evident already at 24hpf, coinciding with the decreased vascular growth rate. At later time points, matrix metalloproteinase 9 (mmp9) expression was upregulated, suggesting that arsenite affects the composition of the extracellular matrix. In total, the expression of eight key factors involved in different aspects of vascularization was significantly altered by arsenic exposure. In conclusion, our results show that arsenite is a potent vascular disruptor in the developing zebrafish embryo, a finding that calls for an evaluation of arsenite as a developmental vascular toxicant in mammalian model systems.

ABCC5, a gene that influences the anterior chamber depth, is associated with primary angle closure glaucoma

Anterior chamber depth (ACD) is a key anatomical risk factor for primary angle closure glaucoma (PACG). We conducted a genome-wide association study (GWAS) on ACD to discover novel genes for PACG on a total of 5,308 population-based individuals of Asian descent. Genome-wide significant association was observed at a sequence variant within ABCC5 (rs1401999; per-allele effect size = −0.045 mm, P = 8.17×10⁻⁹). This locus was associated with an increase in risk of PACG in a separate case-control study of 4,276 PACG cases and 18,801 controls (per-allele OR = 1.13 [95% CI: 1.06–1.22], P = 0.00046). The association was strengthened when a sub-group of controls with open angles were included in the analysis (per-allele OR = 1.30, P = 7.45×10⁻⁹; 3,458 cases vs. 3,831 controls). Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants influencing anterior chamber dimensions.

The anterior chamber is the space within the eye which is bound by the cornea, and the anterior surfaces of the iris and lens. Anterior chamber depth (ACD) is the distance measured along the eye's optical axis, from the cornea to the lens surface. ACD is an important risk factor for primary angle closure glaucoma (PACG), a major cause of irreversible blindness worldwide, and in particular, individuals of Asian ethnicity. In order to identify the genes that underlie PACG susceptibility, we conducted a two-staged study. We first conducted a large scale genetic study on a total of 5,308 population-based individuals of Asian descent to identify the genetic variants that influence ACD. This was followed by testing for associations between the identified genetic variant and PACG in another independent collection of 4,276 PACG cases and 18,801 controls. We found that a genetic variant within ABCC5 was associated with an increased risk of having PACG. Our findings suggest that the increase in PACG risk could in part be mediated by genetic sequence variants that influence the anterior chamber dimensions of the eye.

Proline-induced changes in acetylcholinesterase activity and gene expression in zebrafish brain: reversal by antipsychotic drugs

Hyperprolinemia is an inherited disorder of proline metabolism and hyperprolinemic patients can present neurological manifestations, such as seizures, cognitive dysfunctions, and schizoaffective disorders. However, the mechanisms related to these symptoms are still unclear. In the present study, we evaluated the in vivo and in vitro effects of proline on acetylcholinesterase (AChE) activity and gene expression in the zebrafish brain. For the in vivo studies, animals were exposed at two proline concentrations (1.5 and 3.0mM) during 1h or 7 days (short- or long-term treatments, respectively). For the in vitro assays, different proline concentrations (ranging from 3.0 to 1000 μM) were tested. Long-term proline exposures significantly increased AChE activity for both treated groups when compared to the control (34% and 39%). Moreover, the proline-induced increase on AChE activity was completely reverted by acute administration of antipsychotic drugs (haloperidol and sulpiride), as well as the changes induced in ache expression. When assessed in vitro, proline did not promote significant changes in AChE activity. Altogether, these data indicate that the enzyme responsible for the control of acetylcholine levels might be altered after proline exposure in the adult zebrafish. These findings contribute for better understanding of the pathophysiology of hyperprolinemia and might reinforce the use of the zebrafish as a complementary vertebrate model for studying inborn errors of amino acid metabolism.

Molecular cloning, characterization and expression analysis of a novel wap65-1 gene from Plecoglossus altivelis

Warm temperature acclimation associated 65-kDa protein 1 (WAP65-1) is a specific fish plasma glycoprotein that is possibly involved in various physiological or pathological processes. In this study, we obtained the cDNA and genomic DNA sequences of the Plecoglossus altivelis wap65-1 (Pawap65-1) gene. Multiple sequence alignment showed that Pawap65-1 is similar in structure to wap65-1 in fish. Phylogenetic analysis revealed that Pawap65-1 is most closely related to that of a rainbow trout. Pawap65-1 transcripts are present in various tissues and are most abundant in the liver. We expressed recombinant PaWAP65-1 in Escherichia coli and raised antiserum against it in mouse. Western blot analysis revealed that the higher molecular mass of PaWAP65-1 in blood plasma was caused by post-translational N-glycosylation. Quantitative real-time quantitative PCR (qPCR) and Western blot analysis data showed that the hepatic mRNA and blood plasma levels of PaWAP65-1 were both influenced by warm temperature acclimation and cadmium exposure, but not by Listonella anguillarum infection, hypo-osmotic, or cold temperature acclimation. In conclusion, our data reveals that PaWAP65-1 is a stress-related protein, and may play a role in fish acclimation to warm temperature and cadmium exposure.

Gene expression analysis of ABC efflux transporters, CYP1A and GSTα in Nile tilapia after exposure to benzo(a)pyrene

The aim of this study was to evaluate the response of ABC transporters, CYP1A and class alpha (α) GST genes, upon water and dietary exposures to benzo(a)pyrene (BaP) in Oreochromis niloticus. Partial mRNA sequences of ABC transporters (ABCB1b, ABCB11, ABCC1, ABCC2 and ABCG2) were identified, and their tissue distribution patterns evaluated in liver, gill and intestine, showing similarities with other fish and mammals. After 14 days of water exposure to BaP, ABC transporters mRNA expression was up-regulated, namely ABCC2 in gill (up to 16-fold) and ABCG2 in liver (up to 2-fold) and proximal intestine (up to 7-fold). CYP1A mRNA expression was up-regulated in water exposed animals, with maximum fold inductions of 5, 35 and 155, respectively in liver, gill and proximal intestine. After dietary exposure, intestinal CYP1A mRNA showed a 13-fold increase in exposed animals. No significant changes were seen in ABCB1b, ABCC1 and GSTα mRNA expression after both routes of exposure to BaP. In conclusion, this study has shown that transcriptional expression of some ABC transporters and CYP1A respond to the presence of BaP, indicating a possible involvement and cooperation in the detoxification process in Nile tilapia.

Arsenic-glutathione conjugate transport by the human multidrug resistance proteins (MRPs/ABCCs)

Millions of people world-wide are chronically exposed to inorganic forms of the environmental toxicant arsenic in drinking water. This has led to a public health crisis because arsenic is a human carcinogen, and causes a myriad of other adverse health effects. In order to prevent and treat arsenic-induced toxicity it is critical to understand the cellular handling of this metalloid. A large body of literature describes the importance of the cellular tripeptide glutathione (γ-Glu-Cys-Gly,GSH/GS) in the excretion of arsenic. The triglutathione conjugate of arsenite [As(III)(GS)(3)] and the diglutathione conjugate of monomethylarsonous acid [MMA(III)(GS)(2)] have been isolated from rat bile and mouse urine, and account for the majority of excreted arsenic, suggesting these are important transportable forms. The ATP-binding cassette (ABC) transporter proteins, multidrug resistance protein 1 (MRP1/ABCC1) and the related protein MRP2 (ABCC2), are thought to play an important role in arsenic detoxification through the cellular efflux of arsenic-GSH conjugates. Current knowledge on the cellular handling of arsenic with a special emphasis on the transport pathways of the arsenic-GSH conjugates As(III)(GS)(3), MMA(III)(GS)(2), and dimethylarsenic glutathione DMA(III)(GS), as well as, the seleno-bis(S-glutathionyl) arsinium ion [(GS)(2)AsSe](-) are reviewed.

Molecular characterization and functions of zebrafish ABCC2 in cellular efflux of heavy metals

Multidrug-resistance associated protein 2 (MRP2/ABCC2) plays crucial roles in bile formation and detoxification by transporting a wide variety of endogenous compounds and xenobiotics, but its functions in zebrafish (Danio rerio) remain to be characterized. In this study, we obtained the full-length cDNA of zebrafish abcc2, analyzed its expression in developing embryos and adult tissues, investigated its transcriptional response to heavy metals, and evaluated its roles in efflux of heavy metals including cadmium, mercury and lead. Zebrafish abcc2 gene is located on chromosome 13 and composed of 32 exons. The deduced polypeptide of zebrafish ABCC2 consists of 1567 amino acids and possesses most of functional domains and critical residues defined in human ABCC2. Zebrafish abcc2 gene is not maternally expressed and its earliest expression was detected in embryos at 72hpf. In larval zebrafish, abcc2 gene was found to be exclusively expressed in liver, intestine and pronephric tubules. In adult zebrafish, the highest expression of abcc2 gene was found in intestine followed by those in liver and kidney, while relative low expression was detected in brain and muscle. Expression of abcc2 in excretory organs including kidney, liver and intestine of zebrafish larvae was induced by exposure to 0.5μM mercury or 5μM lead. Moreover, exposure to 0.125-1μM of mercury or lead also significantly induced abcc2 expression in these excretory organs of adult zebrafish. Furthermore, overexpression of zebrafish ABCC2 in ZF4 cells and zebrafish embryos decreased the cellular accumulation of heavy metals including cadmium, mercury and lead as determined by MRE (metal responsive element)- or EPRE (electrophile response element)-driven luciferase reporters and atomic absorption spectrometry. These results suggest that zebrafish ABCC2/MRP2 is capable of effluxing heavy metals from cells and may play important roles in the detoxification of toxic metals.