Perfluorooctane Sulfonamide Induced Autotoxic Effects on the Zebrafish Immune System.

Perfluorooctane sulfonamide (PFOSA) is an immediate perfluorooctanesulfonate (PFOS) precursor (PreFOS). Previous studies have shown PFOSA to induce stronger toxic responses compared to other perfluorinated compounds (PFCs). However, the specific nature of PFOSA-induced toxicity, whether autonomous or mediated by its metabolite PFOS, has not been fully elucidated. This study systematically investigates the immunomodulatory effects of PFOSA and PFOS in zebrafish (Danio rerio). Exposure to PFOSA compromised the zebrafish's ability to defend against pathogenic infections, as evidenced by increased bacterial adhesion to their skin and reduced levels of the biocidal protein lysozyme (LYSO). Moreover, PFOSA exposure was associated with disruptions in inflammatory markers and immune indicators, along with a decrease in immune cell counts. The findings from this study suggest that the immunotoxicity effects of PFOSA are primarily due to its own toxicity rather than its metabolite PFOS. This conclusion was supported by dose-dependent responses, the severity of observed effects, and multivariate analysis. In addition, our experiments using NF-κB-morpholino knock-down techniques further confirmed the role of the Nuclear factor-κappa B pathway in mediating PFOSA-induced immunotoxicity. In conclusion, this study reveals that PFOSA impairs the immune system in zebrafish through an autotoxic mechanism, providing valuable insights for assessing the ecological risks of PFOSA.

Sodium valproate effects on the morphological and neurobehavioral phenotype of zebrafish.

The anticonvulsant sodium valproate (SV) is frequently administered as a medicament but bears several negative effects in case of exposure during development. We analyzed extensively these early development effects of using the zebrafish model. Zebrafish embryos were exposed as eggs to two sublethal concentrations of SV, 10 and 25mg/L. A general embryo toxicity analysis revealed extended anomalies in the cardiovascular system, and in the craniofacial and the spinal skeleton, as well as high mortality, in the embryos exposed to SV. The teratogenic potential of SV was confirmed in hacthed larvae by morphometric and cartilage profile analysis. Last, neurobehavioral impairments due to SV were highlighted in subjects' activity, anxiety, response to stimulations, habituation learning, and daily synchronization of locomotor activity, overall mirroring typical phenotypes associated with autistic spectrum disorders. In conclusion, our results confirmed the presence of extended and multifaced impacts of exposure to SV during development.

Acute warming tolerance (CTmax) in zebrafish (Danio rerio) appears unaffected by changes in water salinity.

Tolerance against acute warming is an essential trait that can determine how organisms cope during heat waves, yet the mechanisms underlying it remain elusive. Water salinity has previously been suggested to modulate warming tolerance in fish and may therefore provide clues towards these limiting mechanisms. Here, using the critical thermal maximum (CTmax) test, we investigated whether short (2 hours) and long (10 days) term exposure to different water salinities (2 hours: 0-5 ppt, 10 days: 0-3 ppt) affected acute warming tolerance in zebrafish (N = 263). We found that water salinity did not affect the warming tolerance of zebrafish at either time point, indicating that salinity does not affect the mechanism limiting acute warming tolerance in zebrafish at these salinity ranges, and that natural fluctuations in salinity levels might not have a large impact on acute warming tolerance in wild zebrafish.

Comprehensive in vitro and in vivo evaluation of therapeutic potential of Bacopa-derived asiatic acid against a human oral pathogen Streptococcus mutans.

Dental caries is a common human oral disease worldwide, caused by an acid-producing bacteria Streptococcus mutans. The use of synthetic drugs and antibiotics to prevent dental caries has been increasing, but this can lead to severe side effects. To solve this issue, developing and developed countries have resorted to herbal medicines as an alternative to synthetic drugs for the treatment and prevention of dental caries. Therefore, there is an urgent need for plant-derived products to treat such diseases. Bacopa monnieri, a well-documented medicinal plant, contains 52 phytocompounds, including the pentacyclic triterpenoid metabolite known as asiatic acid (ASTA). Hence, this study aimed to demonstrate, for the first time, the antibacterial activity of phytocompound ASTA against S. mutans. The findings revealed that ASTA significantly inhibited the growth of S. mutans and the production of virulence factors such as acidurity, acidogenicity, and eDNA synthesis. Molecular docking analysis evaluated the potential activity of ASTA against S. mutans virulence genes, including VicR and GtfC. Furthermore, toxicity assessment of ASTA in human buccal epithelial cells was performed, and no morphological changes were observed. An in vivo analysis using Danio rerio (zebrafish) confirmed that the ASTA treatment significantly increased the survival rates of infected fish by hindering the intestinal colonization of S. mutans. Furthermore, the disease protection potential of ASTA against the pathognomonic symptom of S. mutans infection was proven by the histopathological examination of the gills, gut, and kidney. Overall, these findings suggest that ASTA may be a promising therapeutic and alternative drug for the treatment and prevention of oral infection imposed by S. mutans.

Green synthesis of chitosan gum acacia based biodegradable polymeric nanoparticles to enhance curcumin's antioxidant property: an in vivo zebrafish (Danio rerio) study.

Green-synthesis of biodegradable polymeric curcumin-nanoparticles using affordable biodegradable polymers to enhance curcumin's solubility and anti-oxidative potential. The curcumin-nanoparticle was prepared based on the ionic-interaction method without using any chemical surfactants, and the particle-size, zeta-potential, surface-morphology, entrapmentefficiency, and in-vitro drug release study were used to optimise the formulation. The antioxidant activity was investigated using H2DCFDA staining in the zebrafish (Danio rerio) model. The mean-diameter of blank nanoparticles was 178.2 nm (±4.69), and that of curcuminnanoparticles was about 227.7 nm (±10.4), with a PDI value of 0.312 (±0.023) and 0.360 (±0.02). The encapsulation-efficacy was found to be 34% (±1.8), with significantly reduced oxidative-stress and toxicity (∼5 times) in the zebrafish model compared to standard curcumin. The results suggested that the current way of encapsulating curcumin using affordable, biodegradable, natural polymers could be a better approach to enhancing curcumin's water solubility and bioactivity, which could further be translated into potential therapeutics.

Assessment of toxicity of pyriproxyfen, Bacillus thuringiensis, and malathion and their mixtures used for mosquito control on embryo-larval development and behavior of zebrafish.

Pyriproxyfen (PPF), Bacillus thuringiensis israelensis (BTI), and malathion (MLT) are widely used worldwide to control the population of mosquitos that transmit arboviruses. The current work aimed to evaluate the toxicity of these single pesticides and their binary mixtures of PPF + BTI, PPF + MLT, and MLT + BTI on the embryo-larval stage of zebrafish (Danio rerio) as an animal model. Epiboly, mortality, apical endpoints, affected animals, heart rate, morphometric, thigmotaxis, touch sensitivity, and optomotor response tests were evaluated. PPF and MLT and all mixtures reduced the epiboly percentage. Mortality increased significantly in all exposed groups, except BTI, with MLT being the most toxic. The observed apical endpoints were pericardial and yolk sac edemas, and tail and spine deformation. Exposure to MLT showed a higher percentage of affected animals. A reduction in heart rate was also observed in MLT- and PPF + MLT-exposed groups. The PPF + MLT mixture decreased head measurements. Behavioral alterations were observed, with a decrease in thigmotaxis and touch sensitivity responses in PPF + MLT and MLT + BTI groups. Finally, optomotor responses were affected in all groups. The above data obtained suggest that the MLT + PFF mixture has the greatest toxicity effects. This mixture affected embryo-larval development and behavior and is close to the reality in several cities that use both pesticides for mosquito control rather than single pesticides, leading to a reevaluation of the strategy for mosquito control.

Anticonvulsant and anxiolytic-like potential of the essential oil from the Ocimum basilicum Linn leaves and its major constituent estragole on adult zebrafish (Danio rerio).

The Ocimum species present active compounds with the potential to develop drugs for treating chronic disease conditions, such as anxiety and seizures. The present study aims to investigate the anticonvulsant and anxiolytic-like effect of the essential oil from O. basilicum Linn (OEFOb) leaves and its major constituent estragole (ES) in vivo on adult zebrafish (aZF) and in silico. The aZF were treated with OEFOb or ES or vehicle and submitted to the tests of toxicity, open-field, anxiety, and convulsion and validated the interactions of the estragole on the involvement of GABAergic and serotonergic receptors by molecular docking assay. The results showed that the oral administration of OEFOb and ES did not have a toxic effect on the aZF and showed anxiolytic-like effects with the involvement of GABAA, 5-HT1, 5-HT2A/2C and 5-HT3A/3B as well on anxiety induced by alcohol withdrawal. The OEFOb and ES showed anticonvulsant potential attenuating the seizures induced by pentylenetetrazole (PTZ) by modulation of the GABAA system. Both anxiolytic and anticonvulsant effects were corroborated by the potential of the interaction of ES by in silico assay. These study samples demonstrate the pharmacological evidence and potential for using these compounds to develop new anxiolytic and anticonvulsant drugs.

Investigating the Potential of Essential Oils from Citrus reticulata Leaves in Mitigating Memory Decline and Oxidative Stress in the Scopolamine-Treated Zebrafish Model.

Petitgrain essential oil (PGEO) is derived from the water distillation process on mandarin (Citrus reticulata) leaves. The chemical constituents of PGEO were analyzed by gas chromatography/mass spectrometry (GC/MS) method which revealed the presence of six compounds (100%). The major peaks were for methyl-N-methyl anthranilate (89.93%) and γ-terpinene (6.25%). Over 19 days, zebrafish (Tubingen strain) received PGEO (25, 150, and 300 µL/L) before induction of cognitive impairment with scopolamine immersion (SCOP, 100 µM). Anxiety-like behavior and memory of the zebrafish were assessed by a novel tank diving test (NTT), Y-maze test, and novel object recognition test (NOR). Additionally, the activity of acetylcholinesterase (AChE) and the extent of the brain's oxidative stress were explored. In conjunction, in silico forecasts were used to determine the pharmacokinetic properties of the principal compounds discovered in PGEO, employing platforms such as SwissADME, Molininspiration, and pKCSM. The findings provided evidence that PGEO possesses the capability to enhance memory by AChE inhibition, alleviate SCOP-induced anxiety during behavioral tasks, and diminish brain oxidative stress.

Effects of 2-ethylhexyl diphenyl phosphate (EHDPP) on glycolipid metabolism in male adult zebrafish revealed by targeted lipidomic analyses.

The present study aims to evaluate the effects of 2-ethylhexyldiphenyl phosphate (EHDPP) on glycolipid metabolism in vivo. Adult male zebrafish were exposed to various concentrations (0, 1, 10, 100 and 250 µg/L) of EHDPP for 28 days, and changes in lipid and glucose levels were measured. Results indicated significant liver damages in the 100 and 250 µg/L EHDPP groups, which both exhibited significant decreases in hepatic somatic index (HSI), elevated activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in serum and liver, as well as hepatocyte vacuolation and nuclear pyknosis. Exposure to 100 and 250 µg/L EHDPP led to significant reductions in serum and liver cholesterol (TC), triglycerides (TGs), and lipid droplet deposition, indicating a significant inhibition of EHDPP on hepatic lipid accumulation. Lipidomic analyses manifested that 250 µg/L EHDPP reduced the levels of 103 lipid metabolites which belong to glycerides (TGs, diglycerides, and monoglycerides), fatty acyles (fatty acids), sterol lipids (cholesterol, bile acids), sphingolipids, and glycerophospholipids, and downregulated genes involved in de novo synthesis of fatty acids (fas, acc, srebp1, and dagt2), while upregulated genes involved in fatty acid ß-oxidation (pparα and cpt1). KEGG analyses revealed that EHDPP significantly disrupted glycerolipid metabolism, steroid biosynthesis and fatty acid biosynthesis pathways. Collectively, the results showed that EHDPP induced lipid reduction in zebrafish liver, possibly through inhibiting lipid synthesis and disrupting glycerolipid metabolism. Our findings provide a theoretical basis for evaluating the ecological hazards and health effects of EHDPP on glycolipid metabolism.

Combined effects of polyethylene terephthalate and abamectin on enzymatic activity and histopathology response in juvenile zebrafish (Danio rerio).

One of the most pressing global environmental issues is the widespread abundance and distribution of microplastics (MPs). MPs can act as vectors for other contaminants in the environment making these small plastic particles hazardous for ecosystems. The presence of MPs in aquatic environments may pose threats to aquatic organisms that ingest them. This study examined effects of abamectin (ABM) and polyethylene terephthalate (PET) MP fragments on histopathological and enzymatic biomarkers in zebrafish (Danio rerio). Zebrafish were exposed for 96 h to pristine PET-MPs at concentrations of 5 mg/L and 10 mg/L, ABM alone at 0.006 mg/L, and the same concentration of ABM in the presence of PET-MPs in aquaria. Histopathological analysis revealed tissue content changes in liver and kidney in the presence of ABM individually and in combination with MPs. Results of enzymatic analysis showed that MPs increased the bioavailability and toxicity of pesticides due to inhibition of catalase (CAT) and acid phosphatase (ACP) enzymes. However, MPs did not affect the toxicity of ABM for glutathione s-transferase (GST) enzyme. Despite the inhibition of acetylcholinesterase (AChE) in MPs or ABM treatments, and some neurotoxicity, no change in activity of this enzyme and neurotoxicity was observed in the combined MPs and ABM treatments, although toxicity effects of MPs and ABM on zebrafish require more detailed studies.

Ecotoxicological assessment of UV filters benzophenone-3 and TiO2 nanoparticles, isolated and in a mixture, in developing zebrafish (Danio rerio).

The increasing use of UV filters, such as benzophenone-3 (BP-3) and titanium dioxide nanoparticles (TiO2 NPs), has raised concerns regarding their ecotoxicological effects on the aquatic environment. The aim of the present study was to examine the embryo-larval toxicity attributed to BP-3 or TiO2 NPs, either alone or in a mixture, utilizing zebrafish (Danio rerio) as a model after exposure to environmentally relevant concentrations of these compounds. Zebrafish embryos were exposed to BP-3 (10, 100, or 1000 ng/L) or TiO2 NPs (1000 ng/L) alone or in a mixture (BP-3 10, 100, or 1000 ng/L plus 1000 ng/L of TiO2 NPs) under static conditions for 144 hr. After exposure, BP-3 levels were determined by high-performance liquid chromatography (HPLC). BP-3 levels increased in the presence of TiO2 NPs, indicating that the BP-3 degradation decreased in the presence of the NPs. In addition, in the presence of zebrafish, BP-3 levels in water decreased, indicating that zebrafish embryos and larvae might absorb BP-3. Data demonstrated that, in general, environmentally relevant concentrations of BP-3 and TiO2 NPs, either alone or in a mixture, did not significantly induce changes in heart and spontaneous contractions frequencies, levels of reactive oxygen species (ROS), morphological and morphometric parameters as well as mortality rates during 144 hr exposure. However, the groups exposed to TiO2 NPs alone and in a mixture with BP-3 at 10 ng/L exhibited an earlier significant hatching rate than the controls. Altogether, the data indicates that a potential ecotoxicological impact on the aquatic environment exists.

Dynamics in cortisol levels in Danio rerio fish under the influence of a synthetic analog of kisspeptin 1.

The effect of a synthetic analog of kisspeptin 1, a peptide involved in the regulation of the hypothalamicpituitary- gonadal (HPG) stress axis, on the cortisol level of Danio rerio fish was investigated. Kisspeptin 1 was administered at doses of 2 µg/kg and 8 µg/kg followed by resting for 1 h and 4 h. We found that kisspeptin at doses of 2 µg/kg and 8 µg/kg increased cortisol levels, with a significant spike in cortisol levels at 1 h post-injection.

In Search of a Target Gene for a Desirable Phenotype in Aquaculture: Genome Editing of Cyprinidae and Salmonidae Species.

Aquaculture supplies the world food market with a significant amount of valuable protein. Highly productive aquaculture fishes can be derived by utilizing genome-editing methods, and the main problem is to choose a target gene to obtain the desirable phenotype. This paper presents a review of the studies of genome editing for genes controlling body development, growth, pigmentation and sex determination in five key aquaculture Salmonidae and Cyprinidae species, such as rainbow trout (Onchorhynchus mykiss), Atlantic salmon (Salmo salar), common carp (Cyprinus carpio), goldfish (Carassius auratus), Gibel carp (Carassius gibelio) and the model fish zebrafish (Danio rerio). Among the genes studied, the most applicable for aquaculture are mstnba, pomc, and acvr2, the knockout of which leads to enhanced muscle growth; runx2b, mutants of which do not form bones in myoseptae; lepr, whose lack of function makes fish fast-growing; fads2, Δ6abc/5Mt, and Δ6bcMt, affecting the composition of fatty acids in fish meat; dnd mettl3, and wnt4a, mutants of which are sterile; and disease-susceptibility genes prmt7, gab3, gcJAM-A, and cxcr3.2. Schemes for obtaining common carp populations consisting of only large females are promising for use in aquaculture. The immobilized and uncolored zebrafish line is of interest for laboratory use.

Comparing Prion Proteins Across Species: Is Zebrafish a Useful Model?

Despite the considerable body of research dedicated to the field of neurodegeneration, the gap in knowledge on the prion protein and its intricate involvement in brain diseases remains substantial. However, in the past decades, many steps forward have been taken toward a better understanding of the molecular mechanisms underlying both the physiological role of the prion protein and the misfolding event converting it into its pathological counterpart, the prion. This review aims to provide an overview of the main findings regarding this protein, highlighting the advantages of many different animal models that share a conserved amino acid sequence and/or structure with the human prion protein. A particular focus will be given to the species Danio rerio, a compelling research organism for the investigation of prion biology, thanks to its conserved orthologs, ease of genetic manipulation, and cost-effectiveness of high-throughput experimentation. We will explore its potential in filling some of the gaps on physiological and pathological aspects of the prion protein, with the aim of directing the future development of therapeutic interventions.

A multi-evidence approach in an Amazonian river based on land use, water quality, histopathological effects and habitat selection behavior in fish.

The Amazon rivers constitute the largest river basin in the world, with a high level of biodiversity. The Tocantins River is one of the most important rivers in this region, which has been impacted by different land uses. The objective of this study was to carry out a multi-evidence analysis focusing on the water quality of the Tocantins River, close to the municipality of Marabá-PA. We analyzed forest cover and water quality and, using the model organism Danio rerio, performed toxicity tests for histopathological effects, as well as the habitat selection approach by exposing fish to different river water samples in a multi-compartment device. The results showed that the studied area has already lost almost 30% of its forests in recent decades. Regarding water quality, the upstream (C1) and downstream (C5) points are the least impacted. On the other hand, the other points (C2-C4), closer to the city, greater input of pollutants was detected. Fish exposed to water samples from the most impacted sites showed several oedemas and hyperplastic cells in the gills. Regarding habitat selection behavior, there was a marked avoidance by samples with the highest contamination load. The results of this study lead to the understanding of the potential negative effects of human activities on local Amazonian biodiversity, since the potential toxicity of the environment, in conjunction with changes in the habitat selection process, could lead to a decline in populations of aquatic organisms, altering the environmental balance.

Copy number variation and population-specific immune genes in the model vertebrate zebrafish.

Copy number variation in large gene families is well characterized for plant resistance genes, but similar studies are rare in animals. The zebrafish (Danio rerio) has hundreds of NLR immune genes, making this species ideal for studying this phenomenon. By sequencing 93 zebrafish from multiple wild and laboratory populations, we identified a total of 1513 NLRs, many more than the previously known 400. Approximately half of those are present in all wild populations, but only 4% were found in 80% or more of the individual fish. Wild fish have up to two times as many NLRs per individual and up to four times as many NLRs per population than laboratory strains. In contrast to the massive variability of gene copies, nucleotide diversity in zebrafish NLR genes is very low: around half of the copies are monomorphic and the remaining ones have very few polymorphisms, likely a signature of purifying selection.

Humans and other animals have immune systems that protect them from bacteria, viruses and other potentially harmful microbes. Members of a family of genes known as the NLR family play various roles in helping to recognize and destroy these microbes. Different species have varying numbers of NLR genes, for example, humans have 22 NLRs, but fish can have hundreds. 400 have been found in the small tropical zebrafish, also known as zebra danios. Zebrafish are commonly used as model animals in research studies because they reproduce quickly and are easy to keep in fish tanks. Much of what we know about fish biology comes from studying strains of those laboratory zebrafish, including the 400 NLRs found in a specific laboratory strain. Many NLRs in zebrafish are extremely similar, suggesting that they have only evolved fairly recently through gene duplication. It remains unclear why laboratory zebrafish have so many almost identical NLRs, or if wild zebrafish also have lots of these genes. To find out more, Schäfer et al. sequenced the DNA of NLRs from almost 100 zebrafish from multiple wild and laboratory populations. The approach identified over 1,500 different NLR genes, most of which, were previously unknown. Computational modelling suggested that each wild population of zebrafish may harbour up to around 2,000 NLR genes, but laboratory strains had much fewer NLRs. The numbers of NLR genes in individual zebrafish varied greatly ­ only 4% of the genes were present in 80% or more of the fish. Many genes were only found in specific populations or single individuals. Together, these findings suggest that the NLR family has expanded in zebrafish as part of an ongoing evolutionary process that benefits the immune system of the fish. Similar trends have also been observed in the NLR genes of plants, indicating there may be an evolutionary strategy across all living things to continuously diversify large families of genes. Additionally, this work highlights the lack of diversity in the genes of laboratory animals compared with those of their wild relatives, which may impact how results from laboratory studies are used to inform conservation efforts or are interpreted in the context of human health.

A rapid protocol for inducing acute pancreatitis in zebrafish models.

Acute pancreatitis (AP) is an inflammatory disorder that occurs in the exocrine pancreas associated with tissue injury and necrosis. Experimental models of AP typically involve rodents, such as rats or mice. However, rodents exhibit divergent pathophysiological responses after the establishment of AP between themselves and in comparison, with human. The experiments conducted for this manuscript aimed to standardize a new AP model in zebrafish and validate it. Here, we provide a protocol for inducing AP in zebrafish through intraperitoneal injections of synthetic caerulein. Details are provided for solution preparation, pre-injection procedures, injection technique, and monitoring animal survival. Subsequently, validation was performed through biochemical and histological analyses of pancreatic tissue. The administered dose of caerulein for AP induction was 10 µg/kg applied four times in the intraperitoneal region. The histological validation study demonstrated the presence of necrosis within the first 12 h post-injection, accompanied by an excess of zymogen granules in the extracellular milieu. These observations align with those reported in conventional rodent models. We have standardized and validated the AP model in zebrafish. This model can contribute to preclinical and clinical studies of new drugs for AP treatment. Therefore, this novel model expands the toolkit for exploring faster and more effective preventive and therapeutic strategies for AP.

Evaluation of the citalopram toxicity on early development of zebrafish: Morphological, physiological and biochemical responses.

Citalopram, an antidepressant drug have been detected in different environmental matrices due to its high consumption. Previous study has proved that citalopram may alter the behaviour of aquatic organisms at environmentally relevant concentrations. However, scientific knowledge is still lacking on the ecotoxicological effects of citalopram on aquatic organisms. For this reason, the present study is aimed to investigate the potential toxicity of citalopram in terms of development, antioxidant, neurotoxicity, apoptosis, lipogenesis, and bone mineralization in embryonic and larval zebrafish (Danio rerio) at environmentally relevant concentrations. We noticed that citalopram exposure at 1 and 10 µg/L concentration delays hatching and heartbeat at 24, 48, 72 and 96 hpf. Exposure to citalopram also significantly increased mortality at 10 µg/L. Abnormal development with yolk sac edema, pericardial edema and scoliosis were also observed after citalopram treatment. In addition, citalopram significantly (P < 0.001) induced superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST) and lipid peroxidation (LPO) levels. A significant decrease in acetylcholine esterase (AChE) activity was also observed in citalopram exposed groups. We found significant dose-and time-dependent increases in apoptosis, lipogenesis, and bone mineralization. In conclusion, the findings of the present study can provide new insights on the ecotoxicity of citalopram in the aquatic environment.

Evaluation of behavioral and neurochemical changes induced by carbofuran in zebrafish (Danio rerio).

Carbofuran (CF) is a carbamate class pesticide, widely used in agriculture for pest control in crops. This pesticide has high toxicity in non-target organisms, and its presence in the environment poses a threat to the ecosystem. Research has revealed that this pesticide acts as an inhibitor of acetylcholinesterase (AChE), inducing an accumulation of acetylcholine in the brain. Nonetheless, our understanding of CF impact on the central nervous system remains elusive. Therefore, this study explored how CF influences behavioral and neurochemical outcomes in adult zebrafish. The animals underwent a 96-hour exposure protocol to different concentrations of CF (5, 50, and 500 µg/L) and were subjected to the novel tank (NTT) and social preference tests (SPT). Subsequently, they were euthanized, and their brains were extracted to evaluate neurochemical markers associated with oxidative stress and AChE levels. In the NTT and SPT, CF did not alter the evaluated behavioral parameters. Furthermore, CF did not affect the levels of AChE, non-protein sulfhydryl groups, and thiobarbituric acid reactive species in the zebrafish brain. Nevertheless, further investigation is required to explore the effects of environmental exposure to this compound on non-target organisms.

Characterization of medaka (Oryzias latipes) AHRs and the comparison of two model fishes-Medaka vs. zebrafish: The subform-specific sensitivity to dioxin.

Dioxins and the emerging dioxin-like compounds (DLCs) have recruited increasing concerns about their environmental contamination, toxicity, health impacts, and mechanisms. Based on the structural similarity of dioxins and many DLCs, their toxicity was predominantly mediated by the dioxin receptor (aryl hydrocarbon receptor, AHR) in animals (including human), which can be different in expression and function among species and then possibly produce the species-specific risk or toxicity. To date, characterizing the AHR of additional species other than human and rodents can increase the accuracy of toxicity/risk evaluation and increase knowledge about AHR biology. As a key model, the medaka AHR has not been clearly characterized. Through genome survey and phylogenetic analysis, we identified four AHRs (olaAHR1a, olaAHR1b, olaAHR2a, and olaAHR2b) and two ARNTs (olaARNT1 and olaARNT2). The medaka AHR pathway was conserved in expression in nine tested tissues, of which olaAHR2a represented the predominant subform with greater abundance. Medaka AHRs and ARNTs were functional and could be efficiently transactivated by the classical dioxin congener 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), although olaAHR1a did not seem to cooperate with olaARNT2. In terms of function/sensitivity, the EC50 values of medaka olaAHR1a (9.01 ± 1.43 nM), olaAHR1b (4.00 ± 1.10 nM), olaAHR2a (8.75 ± 3.34 nM), and olaAHR2b (3.06 ± 0.81 nM) showed slight differences; however, they were all at the nM level. The sensitivity of four medaka AHRs to TCDD was similar to that of zebrafish dreAHR2 (the dominant form, EC50 = 3.14 ± 4.19 nM), but these medaka AHRs were more sensitive than zebrafish dreAHR1b (EC50 = 27.05 ± 18.51 nM). The additional comparison also indicated that the EC50 values in various species were usually within the nM range, but AHRs of certain subforms/species can vary by one or two orders of magnitude. In summary, the present study will enhance the understanding of AHR and help improve research on the ecotoxicity of dioxins/DLCs.