Zebrafish as an alternative animal model in human and animal vaccination research

Integrated transcriptomic and proteomic analysis of hepatotoxic effects of Venenum Bufonis in zebrafish

BACKGROUND

Venenum Bufonis (VB), a traditional Chinese medicine (TCM), is renowned for its therapeutic detoxification, pain relief, and cognitive enhancement effects. VB has been classified as a toxic TCM in medical literature, and its clinical usage is currently subject to several limitations. However, the toxicological characteristics of VB and underlying mechanisms remain unclear.

METHODS

We conducted a comprehensive assessment to confirm the target organs affected by VB using the zebrafish model. Subsequently, network pharmacology, transcriptomic and proteomic analyses were performed to explore the associated mechanisms, with the aim of providing a basis for its clinical application.

RESULTS

VB exhibited dose-dependent toxic effects on zebrafish, particularly causing gross morphological abnormalities in the liver along with aggravated hepatocyte apoptosis. Pericardial edema and an enlarged atrioventricular septum were also observed. The combined analyses revealed significant alterations induced by VB in gene expression enriched in multiple pathways and biological processes. Importantly, TLR4/RIPK2/NF-κB and Wnt signaling-mediated inflammation, fibrosis, and apoptosis were identified as the key functional signaling pathways underlying VB-mediated liver toxicity.

CONCLUSION

Our results present robust and direct evidence of the hepatotoxic effects induced by VB in zebrafish, while also providing novel insights into the molecular pathways involved. These results establish a solid theoretical foundation for the appropriate clinical application of VB.

Temperature effects on development and lifelong behavior in zebrafish

In recent decades, global warming has intensified temperature changes, placing substantial pressure on organism survival. Understanding how temperature variations impact development and behavior is crucial for conservation strategies. This study examined how temperature affects zebrafish embryo development and behavior, focusing on mRNA expression changes under thermal challenges. Zebrafish embryos were reared at 27 °C (control), 22 °C, and 30 °C, monitored from 24 to 120 hpf for structural development, and tested for optomotor responses at 7 dpf. Juvenile (30 dpf) and adult (90 dpf) fish reared at 27 °C were subjected to acute temperature shifts (22 °C and 30 °C for 2 h), followed by behavioral assessments and brain sampling for hsp90a and hspb1 mRNA expression analysis. Survival rates were significantly lower at 22 °C, with higher hatching rates at 30 °C but decreased at 22 °C. Developmental abnormalities varied: head malformations were more common at 30 °C, pericardial and yolk sac edema at 22 °C, and tail malformations at both extremes. Optomotor responses were impaired in fish from 22 °C. Social and aggressive behaviors were mostly unaffected, but fish from extreme temperatures showed increased risk-taking and reduced response to alarm substances. hsp90a mRNA expression was elevated in fish raised at 30 °C and those exposed to the 30 °C challenge, while hspb1 mRNA expression remained stable across temperatures. Cooling environments detrimentally affected embryo growth and survival, while warmer conditions induced pronounced growth defects. Elevated temperatures posed greater risks, triggering heightened hsp90a expression crucial for stress adaptation. Understanding thermal variation impacts on embryo development is crucial for mitigating climate change effects on species' viability and reproduction.

Protein bioactive complexes promote osteogenesis under microgravity environment

The space microgravity environment and cosmic radiation pose a significant threat to musculoskeletal health, particularly bone mass. However, the critical mechanism underlying space-induced bone loss and its relation to cellular oxidative stress remains unclear. Currently used bone-loss-reversing drugs face limitations like poor efficacy and metabolic defects. Herein, we revealed that simulated microgravity (SMG) induces reactive oxygen species (ROS), negatively impacting osteoblasts, causing cytoskeletal damage, and downregulating osteogenic genes. To combat this, we designed protein-zein nanocages loaded with a chimeric non-enzymatic cocktail (ZNAC) containing ascorbic acid, resveratrol, luteolin, coenzyme Q, and glutathione. These nanocages (~200 nm) demonstrated excellent stability, biocompatibility, and antioxidant properties compared to free drugs. We investigated the effects of ZNAC under SMG using two experimental models: MC3T3 pre-osteoblast/MG63 osteoblasts and regenerating zebrafish scales that represent compositional and physiological/pathophysiological analogy with mammalian system. ZNAC effectively reduced SMG-induced ROS, preserved cytoskeletal integrity, and enhanced alkaline phosphatase (ALP) activity along with the expression of osteogenic genes such as RUNX2 and Col1A1. In zebrafish scales, it increased osteogenic gene expression, calcification, and the calcium/phosphorus ratio, indicating enhanced scale regeneration. These findings suggest that ZNAC is a promising candidate for bone regeneration, offering potential solutions for maintaining astronaut health during extended space missions.

Synthesis of immunomodulatory biomimetic lipid polymer hybrid nanoparticles and application of zebrafish larvae in immunomodulation screening

Since the antibiotic golden era of the mid-20th century, there have been limited antibiotics approved, while antibiotic resistance continues to escalate disproportionately, outpacing the rate of novel antibiotic discovery. This imbalance poses a serious global health concern, with an estimated annual death toll of 10 million due to antibiotic resistance by 2050. There is a growing interest in immunotherapy as an alternative approach to conventional antibiotics due to its ability to target and stimulate immune system, leveraging its innate ability to self-eradicate pathogens. This study synthesized lipid polymer hybrid nanoparticles (LPHNPs) conjugated with two immunomodulatory agents, namely, curdlan and mycolic acid (MA), as a potential immunotherapy for bacterial infections. LPHNPs were synthesized using lecithin and polycaprolactone (PCL) at a 15 % lipid-to-polymer (w/w) ratio. Additionally, PCL-curdlan copolymer, comprising 15 % w/w curdlan, was successfully synthesized and used to conjugate the LPHNPs with various curdlan concentrations. Furthermore, The LPHNPs were conjugated with varying MA concentrations, with or without curdlan. In-vivo assessment of the immunomodulatory effect of the LPHNPs was conducted using a larval zebrafish model assessing behaviour and immunofluorescence, as indicators of immune stimulation. The data suggests that curdlan exhibits a more complex immunoregulatory role as demonstrated by the countered stimulated behavioural effect while inflammation remained heightened. This work also provides new insights that zebrafish larvae are a valuable screening tool in the development of nanoparticle immunotherapies.

Low concentrations of complex mixtures of pesticides and metabolites are toxic to common Carp brain cells (Cyprinus carpio carpio)

Pesticide use increases annually, and Brazil is the world's largest consumer. However, unlike the European Union (EU), there is no established limit value for pesticide mixtures in drinking water, and therefore the concentration of pesticides can reach 3354 times the EU limit. Thus, determining the risk of exposure to pesticide mixtures and their main metabolites is challenging and requires the use of alternative methods. In the present study, the Common Carp Brain (CCB) cell line was used to evaluate the in vitro toxicity of relevant pesticide mixtures (glyphosate, 2,4-D, atrazine, and mancozeb) and their main metabolites after 72 h of exposure. The tested concentrations were based on the Acceptable Daily Intake (ADI) defined by Brazilian legislation. The results showed that cells exposed to lower concentrations of the pesticide mixtures and the pesticide + metabolite mixtures were affected by a decrease in cell confluence, resazurin metabolism, and wound healing capacity. The IBR index showed that lower concentrations had more severe effects, suggesting the absence of safe concentrations of these pesticide and metabolite mixtures for the CCB cell line within the tested concentration range. These findings raise concerns about the effects of exposure to these substances on animal and human health.

Comparative ovarian morphophysiology of Wistar rats and Zebrafish after exposure to nandrolone decanoate

This study aimed to compare the effects of nandrolone decanoate on the morphology and physiology of ovarian tissues in two experimental models, Zebrafish and rats, after in vitro cultivation. A total of 136 animals were used (Wistar rats, n=36, and Zebrafish, n=100). In both experiments, the animals were divided into two groups (Control and Deca) and were exposed to nandrolone decanoate for seven weeks. At the end of the administrations, the animals were euthanized, and the tissues were collected for morphological and biochemical analyses. Data were expressed as mean ± SEM. Tukey and Shapiro-Wilk tests were used. ANOVA and chi-square tests were applied for group comparisons. Differences were considered significant when P<0.05. The results showed an increase in body weight in Wistar rats, while Zebrafish body weight was decreased. In both experiments, the number of atretic follicles increased throughout the in vitro culture, from day 0 to day 7, in the Control group (CTRLr and CTRLz), while in the DECA group (DECAr and DECAz), atretic follicles were reduced from D0 to D7. The antioxidant environment, represented by increased the thiol content, which was significantly higher on day zero in CTRLz compared to CTRLr. SOD activity increased in Zebrafish (group DECAz), while CAT activity decreased in both models (group DECAr and DECAz). In conclusion, the study demonstrated similarity in ovarian physiology between the models exposed or not exposed to nandrolone decanoate, suggesting that, when convenient, researchers could consider changing the experimental model.

Transgenic Schizochytrium as a Promising Oral Vaccine Carrier: Potential Application in the Aquaculture Industry

Schizochytrium limacinum SR21, a kind of eukaryotic heterotrophic organism rich in unsaturated fatty acids, is an emerging microbial alternative to fish oil. The dietary inclusion of 15% SR21 was optimal for the growth performance of zebrafish. Previous studies demonstrated that fructose-1,6-bisphosphate aldolase (FBA) of Edwardsiella tarda is a valuable broad-spectrum antigen against various pathogens in aquaculture (e.g., Aeromonas hydrophila, Vibro anguillarum, Vibro harveyi, Vibro alginolyticus). We pioneered the development of stable S. limacinum SR21 transformants expressing the antigen protein FBA, exploring their potential as a novel oral vaccine for the aquaculture industry. The model animal zebrafish (Danio rerio) and ornamental fish koi carp (Cyprinus carpio koi) were harnessed to assess the immunoprotective effect, respectively. According to the quantitative expression analysis, zebrafish fed with recombinant Schizochytrium expressing FBA exhibited specific immune responses in the intestine. The expression levels of MHC-I and MHC-II, involved in cell-mediated adaptive immune responses, were significantly upregulated on the 14th and 28th days post-immunization. Additionally, the expression of highly specialized antibody genes IgZ1 and IgZ2 in mucosal immunity were significantly triggered on the 14th day post-immunization. Feeding koi carp with recombinant S. limacinum SR21-FBA increased the production of myeloperoxidase and FBA-specific antibodies in the sera. Furthermore, the sera of koi fed with recombinant S. limacinum SR21-FBA exhibited significant bactericidal activities against pathogen E. tarda. Thus, S. limacinum SR21 is a natural and highly promising oral vaccine carrier that not only provides essential nutrients as a functional feed ingredient but also offers specific immune protection to aquatic animals. This dual application is vital for promoting the sustainable development of the aquaculture industry.

Zebrafish (Danio rerio) as a Model System to Investigate the Role of the Innate Immune Response in Human Infectious Diseases

The zebrafish (Danio rerio) has emerged as a valuable model for studying host-pathogen interactions due to its unique combination of characteristics. These include extensive sequence and functional conservation with the human genome, optical transparency in larvae that allows for high-resolution visualization of host cell-microbe interactions, a fully sequenced and annotated genome, advanced forward and reverse genetic tools, and suitability for chemical screening studies. Despite anatomical differences with humans, the zebrafish model has proven instrumental in investigating immune responses and human infectious diseases. Notably, zebrafish larvae rely exclusively on innate immune responses during the early stages of development, as the adaptive immune system becomes fully functional only after 4-6 weeks post-fertilization. This window provides a unique opportunity to isolate and examine infection and inflammation mechanisms driven by the innate immune response without the confounding effects of adaptive immunity. In this review, we highlight the strengths and limitations of using zebrafish as a powerful vertebrate model to study innate immune responses in infectious diseases. We will particularly focus on host-pathogen interactions in human infections caused by various bacteria (Clostridioides difficile, Staphylococcus aureus, and Pseudomonas aeruginosa), viruses (herpes simplex virus 1, SARS-CoV-2), and fungi (Aspergillus fumigatus and Candida albicans).

The screening of α-glucosidase inhibitory peptides from β-conglycinin and hypoglycemic mechanism in HepG2 cells and zebrafish larvae

Inhibition of carbohydrate digestive enzymes is a key focus across diverse fields, given the prominence of α-glucosidase inhibitors as preferred oral hypoglycaemic drugs for diabetes treatment. β-conglycinin is the most abundant functional protein in soy; however, it is unclear whether the peptides produced after its gastrointestinal digestion exhibit α-glucosidase inhibitory properties. Therefore, we examined the α-glucosidase inhibitory potential of soy peptides. Specifically, β-conglycinin was subjected to simulated gastrointestinal digestion by enzymatically cleaving it into 95 peptides with gastric, pancreatic and chymotrypsin enzymes. Eight soybean peptides were selected based on their predicted activity; absorption, distribution, metabolism, excretion and toxicity score; and molecular docking analysis. The results indicated that hydrogen bonding and electrostatic interactions play important roles in inhibiting α-glucosidase, with the tripeptide SGR exhibiting the greatest inhibitory effect (IC50 = 10.57 μg/mL). In vitro studies revealed that SGR markedly improved glucose metabolism disorders in insulin-resistant HepG2 cells without affecting cell viability. Animal experiments revealed that SGR significantly improved blood glucose and decreased maltase activity in type 2 diabetic zebrafish larvae, but it did not result in the death of zebrafish larvae. Transcriptomic analysis revealed that SGR exerts its anti-diabetic and hypoglycaemic effects by attenuating the expression of several genes, including Slc2a1, Hsp70, Cpt2, Serpinf1, Sfrp2 and Ggt1a. These results suggest that SGR is a potential food-borne bioactive peptide for managing diabetes.

Analysis of Antiangiogenic Potential and Cell Death Mechanism of a Kinetically Inert Platinum Antitumor Agent

Cancer is a multifaceted disease involving various pathological processes, including uncontrolled proliferation, development of resistance, angiogenesis, metastasis, etc. Therefore, chemotherapeutic agents capable of simultaneously inhibiting proliferation, circumventing chemoresistance, and inhibiting angiogenesis can address multiple aspects of cancer progression. We recently identified a highly promising kinetically inert platinum antitumor agent, namely, Pt-1, that can circumvent cisplatin resistance and showed negligible nephrotoxicity. In this study, we explored the antiangiogenic potential and elucidated the detailed mechanism of cell death through which it exerts its antitumor activity. Pt-1 strongly inhibited angiogenesis in a zebrafish in vivo model at its therapeutically relevant nontoxic dose. Further, Pt-1 exerted antitumor activity through necroptosis- and paraptosis-mediated cell death. Taken together, the combination of antitumor activity with antiangiogenic property in Pt-1 makes it a highly promising antitumor candidate.

The potential of zebrafish as drug discovery research tool in immune-mediated inflammatory disease

Immune-mediated inflammatory disease (IMID) prevalence is estimated at 3-7% for Westernised populations, with annual incidence reported at almost 1 in 100 people globally. More recently, drug discovery approaches have been evolving towards more targeted therapies with an improved long-term safety profile, while the requirement for individualisation of medicine in complex conditions such as IMIDs, is acknowledged. However, existing preclinical models-such as cellular and in vivo mammalian models-are not ideal for modern drug discovery model requirements, such as real-time in vivo visualisation of drug effects, logistically feasible safety assessment over the course of a lifetime, or dynamic assessment of physiological changes during disease development. Zebrafish share high homology with humans in terms of proteins and disease-causing genes, with high conservation of physiological processes at organ, tissue, cellular and molecular level. These and other unique attributes, such as high fecundity, relative transparency and ease of genetic manipulation, positions zebrafish as the next major role player in IMID drug discovery. This review provides a brief overview of the suitability of this organism as model for human inflammatory disease and summarises the range of approaches used in zebrafish-based drug discovery research. Strengths and limitations of zebrafish as model organism, as well as important considerations in research study design, are discussed. Finally, under-utilised avenues for investigation in the IMID context are highlighted.

Zebrafish gut microbiota composition in response to tick saliva biomolecules correlates with allergic reactions to mammalian meat consumption

The α-Gal syndrome (AGS) is an IgE-mediated tick borne-allergy that results in delayed anaphylaxis to the consumption of mammalian meat and products containing α-Gal. Considering that α-Gal-containing microbiota modulates natural antibody production to this glycan, this study aimed to evaluate the influence on tick salivary compounds on the gut microbiota composition in the zebrafish (Danio rerio) animal model. Sequencing of 16 S rDNA was performed in a total of 75 zebrafish intestine samples, representing different treatment groups: PBS control, Ixodes ricinus tick saliva, tick saliva non-protein fraction (NPF), tick saliva protein fraction (PF), and tick saliva protein fractions 1-5 with NPF (F1-5). The results revealed that treatment with tick saliva and different tick salivary fractions, combined with α-Gal-positive dog food feeding, resulted in specific variations in zebrafish gut microbiota composition at various taxonomic levels and affected commensal microbial alpha and beta diversities. Metagenomics results were corroborated by qPCR, supporting the overrepresentation of phylum Firmicutes in the tick saliva group, phylum Fusobacteriota in group F1, and phylum Cyanobacteria in F2 and F5 compared to the PBS-control. qPCRs results at genus level sustained significant enrichment of Plesiomonas spp. in groups F3 and F5, Rhizobium spp. in NPF and F4, and Cloacibacterium spp. dominance in the PBS control group. This study provides new results on the role of gut microbiota in allergic reactions to tick saliva components using a zebrafish model of AGS. Overall, gut microbiota composition in response to tick saliva biomolecules may be associated with allergic reactions to mammalian meat consumption in AGS.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

Zebrafish as Versatile Model for Assessing Animal Venoms and Toxins: Current Applications and Future Prospects

Animal venoms and toxins hold promise as sources of novel drug candidates, therapeutic agents, and biomolecules. To fully harness their potential, it is crucial to develop reliable testing methods that provide a comprehensive understanding of their effects and mechanisms of action. However, traditional rodent assays encounter difficulties in mimicking venom-induced effects in human due to the impractical venom dosage levels. The search for reliable testing methods has led to the emergence of zebrafish (Danio rerio) as a versatile model organism for evaluating animal venoms and toxins. Zebrafish possess genetic similarities to humans, rapid development, transparency, and amenability to high-throughput assays, making it ideal for assessing the effects of animal venoms and toxins. This review highlights unique attributes of zebrafish and explores their applications in studying venom- and toxin-induced effects from various species, including snakes, jellyfish, cuttlefish, anemones, spiders, and cone snails. Through zebrafish-based research, intricate physiological responses, developmental alterations, and potential therapeutic interventions induced by venoms are revealed. Novel techniques such as CRISPR/Cas9 gene editing, optogenetics, and high-throughput screening hold great promise for advancing venom research. As zebrafish-based insights converge with findings from other models, the comprehensive understanding of venom-induced effects continues to expand, guiding the development of targeted interventions and promoting both scientific knowledge and practical applications.

Alternatives of Animal Models for Biomedical Research: a Comprehensive Review of Modern Approaches

Biomedical research has long relied on animal models to unravel the intricacies of human physiology and pathology. However, concerns surrounding ethics, expenses, and inherent species differences have catalyzed the exploration of alternative avenues. The contemporary alternatives to traditional animal models in biomedical research delve into three main categories of alternative approaches: in vitro models, in vertebrate models, and in silico models. This unique approach to artificial intelligence and machine learning has been a keen interest to be used in different biomedical research. The main goal of this review is to serve as a guide to researchers seeking novel avenues for their investigations and underscores the importance of considering alternative models in the pursuit of scientific knowledge and medical breakthroughs, including showcasing the broad spectrum of modern approaches that are revolutionizing biomedical research and leading the way toward a more ethical, efficient, and innovative future. Models can insight into cellular processes, developmental biology, drug interaction, assessing toxicology, and understanding molecular mechanisms.

Single-Cell Oral Delivery Platform for Enhanced Acid Resistance and Intestinal Adhesion

Oral delivery of cells, such as probiotics and vaccines, has proved to be inefficient since cells are generally damaged in an acidic stomach prior to arrival at the intestine to exert their health benefits. In addition, short retention in the intestine is another obstacle which affects inefficiency. To overcome these obstacles, a cell-in-shell structure was designed with pH-responsive and mucoadhesive properties. The pH-responsive shell consisting of three cationic layers of chitosan and three anionic layers of trans-cinnamic acid (t-CA) was made via layer-by-layer (LbL) assembly. t-CA layers are hydrophobic and impermeable to protons in acid, thus enhancing cell gastric resistance in the stomach, while chitosan layers endow strong interaction between the cell surface and the mucosal wall which facilitates cell mucoadhesion in the intestine. Two model cells, probiotic L. rhamnosus GG and dead Streptococcus iniae, which serve as inactivated whole-cell vaccine were chosen to test the design. Increased survival and retention during oral administration were observed for coated cells as compared with naked cells. Partial removal of the coating (20-60% removal) after acid treatment indicates that the coated vaccine can expose its surface immunogenic protein after passage through the stomach, thus facilitating vaccine immune stimulation in the intestine. As a smart oral delivery platform, this design can be extended to various macromolecules, thus providing a promising strategy to formulate oral macromolecules in the prevention and treatment of diseases at a cellular level.

BODIPY-Based Analogue of the TREM2-Binding Molecular Adjuvant Sulfavant A, a Chemical Tool for Imaging and Tracking Biological Systems

Recently, we described synthetic sulfolipids named Sulfavants as a novel class of molecular adjuvants based on the sulfoquinovosyl-diacylglycerol skeleton. The members of this family, Sulfavant A (1), Sulfavant R (2), and Sulfavant S (3), showed important effects on triggering receptor expressed on myeloid cells 2 (TREM2)-induced differentiation and maturation of human dendritic cells (hDC), through a novel cell mechanism underlying the regulation of the immune response. As these molecules are involved in biological TREM2-mediated processes crucial for cell survival, here, we report the synthesis and application of a fluorescent analogue of Sulfavant A bearing the 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene moiety (Me4-BODIPY). The fluorescent derivative, named PB-SULF A (4), preserving the biological activity of Sulfavants, opens the way to chemical biology and cell biology experiments to better understand the interactions with cellular and in vivo organ targets and to improve our comprehension of complex molecular mechanisms underlying the not fully understood ligand-induced TREM2 activity.

Current Status of the Zebrafish Euthanasia and Humane Endpoint in the Republic of Korea and Guideline Suggestion from Nationwide Expert Elicitation: A Model for Other Countries

Since its introduction as a model organism in the 1980s, the use of zebrafish (Danio rerio) in research has expanded worldwide. Despite its now widespread use in research, guidelines to safeguard the ethical treatment of zebrafish, particularly with regard to euthanasia and humane endpoint practices, remain inadequate. One well-recognized example is the use of excess tricaine methanesulfonate (MS-222) as a means to euthanize zebrafish, regardless of life stage. In this study, through nationwide expert elicitation, we provide a detailed account of zebrafish research practices within the Republic of Korea and the challenges of implementing appropriate methods for euthanasia as a humane endpoint, with many opting for hypothermic shock. We report a local expert consensus for establishing national guidelines to improve zebrafish welfare and good research practice. Suggestions and recommendations for national guidelines were offered. Taken together, our findings raise awareness broadly among zebrafish research practitioners in the field, offer an accurate account of the welfare and treatment of zebrafish in research within the Republic of Korea, and advocate for the development and implementation of national guidelines. As such, our study is useful as a model to adopt the expert elicitation approach to investigate, quantify, and address welfare concerns in zebrafish research, and to establish best practice guidelines.

Beyond compliance: harmonising research and husbandry practices to improve experimental reproducibility using fish models

Reproducibility in animal research is impacted by the environment, by husbandry practices in the laboratory and by the animals' provenance. These factors, however, are often not adequately considered by researchers. A disconnect between researchers and animal care staff can result in inappropriate housing and husbandry decisions for scientific studies with those animals. This is especially the case for the research in neuro-behaviour, epigenetics, and the impact of climate change, as heritable phenotypic, behavioural or physiological changes are known to result from the animals' environmental housing, husbandry, provenance and prior experience. This can lead to greater variation (even major differences) in data outcomes among studies, driving scientific uncertainties. Herein, we illustrate some of the endpoints measured in fish studies known to be intrinsically linked to the environment and husbandry conditions and assess the significance of housing and husbandry practice decisions for research adopting these endpoints for different fish species. We highlight the different priorities and challenges faced by researchers and animal care staff and how harmonising their activities and building greater understanding of how husbandry practices affect the fish will improve reproducibility in research outcomes. We furthermore illustrate how improving engagement between stakeholders, including regulatory bodies, can better underpin fish husbandry decisions and where researchers could help to drive best husbandry practices through their own research with fish models.

Pharmacological potential of Jussiaea repens L. against CuSO4 and bacterial lipopolysaccharide O55:B5 induced inflammation using in-vivo zebrafish models

ETHNOPHARMACOLOGICAL RELEVANCE

The Northeastern state of India is known for its remarkable biodiversity and untapped medicinal resources. Jussiaea repens L., commonly known as water primrose, is a plant found in this region that has been traditionally used by indigenous communities for various purposes. It has been employed to treat skin ulcerations, bone fractures, rheumatism, stomach pain, and intestinal worms. Despite its long-standing ethnopharmacological usage, there is limited scientific research on the bioactivity of Jussiaea repens L. However, preliminary studies have shown its potential antioxidant properties and cytotoxicity against cancer cells. Further exploration of its medicinal properties, particularly its potential as an anti-inflammatory agent, is warranted.

AIM OF THE STUDY

This study aimed to investigate the anti-inflammatory properties of Jussiaea repens L., a plant species found in the biodiverse Northeastern region of India. The plant has been traditionally used by indigenous communities for various ailments. By utilizing zebrafish as an animal model and evaluating its effects in different inflammation models, the study aimed to uncover the plant's potential as an anti-inflammatory agent. The research contributes to the scientific understanding of this traditional remedy and its potential therapeutic applications.

METHODS

Jussiaea repens L. extract was obtained from the stem and leaves using methanol as the solvent. Zebrafish embryos were used for in vivo assays. The anti-inflammatory study included two models: CuSO4-induced inflammation and tail wounding followed by bacterial lipopolysaccharide-induced inflammation. The activities of catalase (CAT) and superoxide dismutase (SOD) were measured in CuSO4-induced inflammation. Leukocyte migration at the injury site was observed in the tail wounding model. The extract's inhibition of the 15-LOX enzyme was assessed. All procedures followed established protocols and ethical guidelines.

RESULTS AND CONCLUSION

Jussiaea repens L. extract exhibited anti-inflammatory activity in two in vivo zebrafish models: CuSO4-induced inflammation and tail wounding combined with bacterial lipopolysaccharide-induced inflammation. The extract reduced mortality rates and showed antioxidant effects by increasing catalase (CAT) and superoxide dismutase (SOD) activities in the CuSO4 model. In the tail wounding model, the extract reduced leukocyte migration in a concentration-dependent manner. Additionally, the extract demonstrated dose-dependent inhibition of the 15-LOX enzyme in the in vitro assay. These results suggest that Jussiaea repens L. extract possesses anti-inflammatory properties and inhibits the 15-LOX enzyme.

β-Carboline (FG-7142) modulates fear but not anxiety-like behaviour in zebrafish

The β-Carboline FG-7142 is a partial inverse agonist at the benzodiazepine allosteric site on the GABA-A receptor that induces anxiogenic, proconvulsant, and appetite-reducing effects in many species, including humans. Seizure-kindling effects have been well studied, however anxiogenic properties are relatively unexplored. This study aimed to investigate concentration-dependent effects of FG-7142 on anxiety-like behaviour and fear responses in zebrafish (Danio rerio) using the open-field test (OF) and novel object approach test (NOA). A U-shaped distribution was found with maximal responses in increased immobility and reduced distance moved at 10 µM in the NOA but not the OF. Follow up experiments demonstrated a lack of effect in repeated OF testing and no changes in opercular movements. Furthermore, the effect of FG-7142 was reversed with ethanol treatment. These results suggest that FG-7142 elicits a 'freezing' response in zebrafish via the introduction of novelty, suggesting fear-induction. These findings indicate that FG-7142 may act as an agent to promote acute fear responses in zebrafish.

The zebrafish as a potential model for vaccine and adjuvant development

INTRODUCTION

Zebrafishes represent a proven model for human diseases and systems biology, exhibiting physiological and genetic similarities and having innate and adaptive immune systems. However, they are underexplored for human vaccinology, vaccine development, and testing. Here we summarize gaps and challenges.

AREAS COVERED

Zebrafish models have four potential applications: 1) Vaccine safety: The past successes in using zebrafishes to test xenobiotics could extend to vaccine and adjuvant formulations for general safety or target organs due to the zebrafish embryos' optical transparency. 2) Innate immunity: The zebrafish offers refined ways to examine vaccine effects through signaling via Toll-like or NOD-like receptors in zebrafish myeloid cells. 3) Adaptive immunity: Zebrafishes produce IgM, IgD,and two IgZ immunoglobulins, but these are understudied, due to a lack of immunological reagents for challenge studies. 4) Systems vaccinology: Due to the availability of a well-referenced zebrafish genome, transcriptome, proteome, and epigenome, this model offers potential here.

EXPERT OPINION

It remains unproven whether zebrafishes can be employed for testing and developing human vaccines. We are still at the hypothesis-generating stage, although it is possible to begin outlining experiments for this purpose. Through transgenic manipulation, zebrafish models could offer new paths for shaping animal models and systems vaccinology.

Zebrafish Experimental Animal Models for AD: A Comprehensive Review

AD disease (AD) is a multifaceted and intricate neurodegenerative disorder characterized by intracellular neurofibrillary tangle (NFT) formation and the excessive production and deposition of Aβ senile plaques. While transgenic AD models have been found instrumental in unravelling AD pathogenesis, they involve cost and time constraints during the preclinical phase. Zebrafish, owing to their simplicity, well-defined behavioural patterns, and relevance to neurodegenerative research, have emerged as a promising complementary model. Zebrafish possess glutaminergic and cholinergic pathways implicated in learning and memory, actively contributing to our understanding of neural transmission processes. This review sheds light on the molecular mechanisms by which various neurotoxic agents, including okadaic acid (OKA), cigarette smoke extract, metals, and transgenic zebrafish models with genetic similarities to AD patients, induce cognitive impairments and neuronal degeneration in mammalian systems. These insights may facilitate the identification of effective neurotoxic agents for replicating AD pathogenesis in the zebrafish brain. In this comprehensive review, the pivotal role of zebrafish models in advancing our comprehension of AD is emphasized. These models hold immense potential for shaping future research directions and clinical interventions, ultimately contributing to the development of novel AD therapies.

Zebrafish (Danio rerio) as a Model for the Study of Developmental and Cardiovascular Toxicity of Electronic Cigarettes

The increasing popularity of electronic cigarettes (e-cigarettes) as an alternative to conventional tobacco products has raised concerns regarding their potential adverse effects. The cardiovascular system undergoes intricate processes forming the heart and blood vessels during fetal development. However, the precise impact of e-cigarette smoke and aerosols on these delicate developmental processes remains elusive. Previous studies have revealed changes in gene expression patterns, disruptions in cellular signaling pathways, and increased oxidative stress resulting from e-cigarette exposure. These findings indicate the potential for e-cigarettes to cause developmental and cardiovascular harm. This comprehensive review article discusses various aspects of electronic cigarette use, emphasizing the relevance of cardiovascular studies in Zebrafish for understanding the risks to human health. It also highlights novel experimental approaches and technologies while addressing their inherent challenges and limitations.

Artificial Neural Network (ANN)-Based Pattern Recognition Approach Illustrates a Biphasic Behavioral Effect of Ethanol in Zebrafish: A High-Throughput Method for Animal Locomotor Analysis

Variations in stress responses between individuals are linked to factors ranging from stress coping styles to the sensitivity of neurotransmitter systems. Many anxiolytic compounds can increase stressor engagement through the modulation of neurotransmitter systems and are used to investigate stress response mechanisms. The effect of such modulation may vary in time depending on concentration or environment, but those effects are hard to dissect because of the slow transition. We investigated the temporal effect of ethanol and found that ethanol-treated individual zebrafish larvae showed altered behavior that is different between drug concentrations and decreases with time. We used an artificial neural network approach with a time-dependent method for analyzing long (90 min) experiments on zebrafish larvae and found that individuals from the 0.5% group begin to show locomotor activity corresponding to the control group starting from the 60th minute. The locomotor activity of individuals from the 2% group after the 80th minute is classified as the activity of individuals from the 1.5% group. Our method shows three clusters of different concentrations in comparison with two clusters, which were obtained with the usage of a statistical approach for analyzing just the speed of fish movements. In addition, we show that such changes are not explained by basic behavior statistics such as speed and are caused by shifts in locomotion patterns.

Identification of metabolites generated in the biotransformation process by the Danio rerio (zebrafish) exposed to the fungicide tebuconazole

Tebuconazole is a triazole fungicide widely used in agricultural crops for control of multiple fungal, mainly foliar and soil-borne diseases. Due to its intense use, this pesticide has been detected on aquatic matrices in different countries, which makes it necessary to identify metabolites capable to be used in its exposure monitoring. The aim of this work was to evaluate tebuconazole metabolites in zebrafish water tanks using liquid chromatography coupled to a high-resolution mass spectrometer (LCHRMS) to highlight analytical targets to monitor tebuconazole exposure in aquatic environments. Two Phase I metabolites, TEB-OH and TEB-COOH, and one Phase II metabolite, TEB-S, were identified. Target metabolomics pointed TEB-S as the most important metabolite for discrimination between treatment and negative control group and potential surrogate for detection and monitoring of tebuconazole exposure in aquatic environments. To the best of our knowledge, this is the first study to suggest the sulphation of tebuconazole (TEB-S) by zebrafish metabolism. Moreover, the use of water samples proved to be a promising approach when compared to the usual biological matrices (e.g. plasma) for evaluating the exposure of aquatic animals to tebuconazole because it is a clean and easy to obtain matrix. Water samples presented a higher concentration of metabolites when compared to plasma samples. The results suggest the applicability of this assay model for the identification of potential biomarkers for monitoring the presence of xenobiotics in water.

Multi-omics analysis of zebrafish response to tick saliva reveals biological processes associated with alpha-Gal syndrome

The alpha-Gal syndrome (AGS) is a tick-borne allergy. A multi-omics approach was used to determine the effect of tick saliva and mammalian meat consumption on zebrafish gut transcriptome and proteome. Bioinformatics analysis using R software was focused on significant biological and metabolic pathway changes associated with AGS. Ortholog mapping identified highly concordant human ortholog genes for the detection of disease-enriched pathways. Tick saliva treatment increased zebrafish mortality, incidence of hemorrhagic type allergic reactions and changes in behavior and feeding patterns. Transcriptomics analysis showed downregulation of biological and metabolic pathways correlated with anti-alpha-Gal IgE and allergic reactions to tick saliva affecting blood circulation, cardiac and vascular smooth muscle contraction, behavior and sensory perception. Disease enrichment analysis revealed downregulated orthologous genes associated with human disorders affecting nervous, musculoskeletal, and cardiovascular systems. Proteomics analysis revealed suppression of pathways associated with immune system production of reactive oxygen species and cardiac muscle contraction. Underrepresented proteins were mainly linked to nervous and metabolic human disorders. Multi-omics data revealed inhibition of pathways associated with adrenergic signaling in cardiomyocytes, and heart and muscle contraction. Results identify tick saliva-related biological pathways supporting multisystemic organ involvement and linking α-Gal sensitization with other illnesses for the identification of potential disease biomarkers.

Evaluation of Disinfection Methods for Artificial Plants in Zebrafish (Danio rerio) Recirculating Water Systems

The use of artificial plants as environmental enrichment for zebrafish (Danio rerio) in biomedical research facilities has been shown to provide benefits in animal welfare and care. Despite the benefits of artificial plants to zebrafish welfare, some research facilities are hesitant to incorporate them into their routine husbandry practices due to concerns about disease transmission and a lack of guidance on effective disinfection practices between tanks. Limited published information is available on how to adequately disinfect artificial plants, which creates concerns regarding their reuse between tanks in recirculating water systems. Proper sanitation and disinfection of these items is crucial to preventing the spread of disease in the system. We evaluated 2 disinfection methods- a commercial-grade laboratory glassware dishwasher and an ethylene oxide (ETO) sterilizer-by using ATP detection and bacterial culture of the artificial plants before and after the disinfection process. Plants were placed in the dirty sump of 2 separate recirculating systems (2,500 to 3,000 fish per system) for 2 wk before the start of the study. High ATP levels and various bacterial organisms were detected prior to disinfection. The commercial-grade labo- ratory glassware dishwasher and ETO sterilizer both significantly reduced ATP levels and resulted in complete eradication of live bacteria that were present before treatment. This study demonstrates 2 effective methods for disinfecting artificial plants in zebrafish facilities.

Assessment of acute toxicity of crude extract rich in carotenoids from Cantaloupe melon (Cucumis melo L.) and the gelatin-based nanoparticles using the zebrafish (Danio rerio) model

Cantaloupe melon is known for its carotenoid-rich orange pulp. However, carotenoids are sensitive to oxygen, light, and heat, potentially reducing their benefits. Nanoencapsulation can preserve these benefits but raises concerns about toxicity. We aimed to assess the safety and bioactive potential of crude extract-rich carotenoids (CE) and nanoparticles based on gelatin loaded with CE (EPG) by investigating parameters such as cardio or neurotoxicity, especially acute toxicity. EPG was obtained by O/W emulsification and characterized by different methods. Zebrafish embryos were exposed to CE and EPG at 12.5 mg/L and 50 mg/L for 96h and were investigated for survival, hatching, malformations, and seven days post fertilization (dpf) larvae's visual motor response. Adult fish underwent behavioral tests after acute exposure of 96h. CE and EPG showed no acute toxicity in zebrafish embryos, and both improved the visual motor response in 7dpf larvae (p = 0.01), suggesting the potential antioxidant and provitamin A effect of carotenoids in cognitive function and response in the evaluated model. Adult fish behavior remained with no signs of anxiety, stress, swimming pattern changes, or sociability that would indicate toxicity. This study highlights the safety and potential benefits of carotenoids in zebrafish. Further research is needed to explore underlying mechanisms and long-term effects.

Assessment of Risperidone Toxicity in Zebrafish (Danio rerio) Embryos

Risperidone is an antipsychotic medication used in the treatment of conditions like autism and schizophrenia. The goal of the current study was to examine the effects of risperidone in zebrafish embryos ( Danio rerio ) with regard to survival, development, and cardiac and neural systems. The results showed that concentrations above 100 μM were associated with deaths, teratogenic effects, and cardiotoxic and neurotoxic effects. The findings support the utility of zebrafish for toxicological screening studies.

The Zebrafish Embryo as a Model Organism for Testing mRNA-Based Therapeutics

mRNA-based therapeutics have revolutionized the world of molecular therapy and have proven their potential in the vaccination campaigns for SARS-CoV2 and clinical trials for hereditary disorders. Preclinical studies have mainly focused on in vitro and rodent studies. However, research in rodents is costly and labour intensive, and requires ethical approval for all interventions. Zebrafish embryonic disease models are not always classified as laboratory animals and have been shown to be extremely valuable for high-throughput drug testing. Zebrafish larvae are characterized by their small size, optical transparency and high number of embryos, and are therefore also suited for the study of mRNA-based therapeutics. First, the one-cell stage injection of naked mRNA can be used to assess the effectivity of gene addition in vivo. Second, the intravascular injection in older larvae can be used to assess tissue targeting efficiency of (packaged) mRNA. In this review, we describe how zebrafish can be used as a steppingstone prior to testing mRNA in rodent models. We define the procedures that can be employed for both the one-cell stage and later-stage injections, as well as the appropriate procedures for post-injection follow-up.

Exposure of adult zebrafish (Danio rerio) to SARS-CoV-2 at predicted environmentally relevant concentrations: Outspreading warns about ecotoxicological risks to freshwater fish

While the multifaceted social, economic, and public health impacts associated with the COVID-19 pandemic are known, little is known about its effects on non-target aquatic ecosystems and organisms. Thus, we aimed to evaluate the potential ecotoxicity of SARS-CoV-2 lysate protein (SARS.CoV2/SP02.2020.HIAE.Br) in adult zebrafish (Danio rerio) at predicted environmentally relevant concentrations (0.742 and 2.226 pg/L), by 30 days. Although our data did not show locomotor alterations or anxiety-like or/and anxiolytic-like behavior, we noticed that exposure to SARS-CoV-2 negatively affected habituation memory and social aggregation of animals in response to a potential aquatic predator (Geophagus brasiliensis). An increased frequency of erythrocyte nuclear abnormalities was also observed in animals exposed to SARS-CoV-2. Furthermore, our data suggest that such changes were associated with a redox imbalance [↑ROS (reactive oxygen species), ↑H2O2 (hydrogen peroxide), ↓SOD (superoxide dismutase), and ↓CAT (catalase)], cholinesterasic effect [↑AChE (acetylcholinesterase) activity], as well as the induction of an inflammatory immune response [↑NO (nitric oxide), ↑IFN-γ (interferon-gamma), and ↓IL-10 (interleukin-10)]. For some biomarkers, we noticed that the response of the animals to the treatments was not concentration-dependent. However, principal component analysis (PCA) and the "Integrated Biomarker Response" index (IBRv2) indicated a more prominent ecotoxicity of SARS-CoV-2 at 2.226 pg/L. Therefore, our study advances knowledge about the ecotoxicological potential of SARS-CoV-2 and reinforces the presumption that the COVID-19 pandemic has negative implications beyond its economic, social, and public health impacts.

Behavioral Study of 3- and 5-Halocytisine Derivatives in Zebrafish Using the Novel Tank Diving Test (NTT)

Anxiety is a serious mental disorder, and recent statistics have determined that 35.12% of the global population had an anxiety disorder during the COVID-19 pandemic. A mechanism associated with anxiolytic effects is related to nicotinic acetylcholine receptor (nAChR) agonists, principally acting on the α4β2 nAChR subtype. nAChRs are present in different animal models, including murine and teleosteos ones. Zebrafish has become an ideal animal model due to its high human genetic similarities (70%), giving it high versatility in different areas of study, among them in behavioral studies related to anxiety. The novel tank diving test (NTT) is one of the many paradigms used for studies on new drugs related to their anxiolytic effect. In this work, an adult zebrafish was used to determine the behavioral effects of 3- and 5-halocytisine derivatives, using the NTT at different doses. Our results show that substitution at position 3 by chlorine or bromine decreases the time spent by the fish at the bottom compared to the control. However, the 3-chloro derivative at higher doses increases the bottom dwelling time. In contrast, substitution at the 5 position increases bottom dwelling at all concentrations showing no anxiolytic effects in this model. Unexpected results were observed with the 5-chlorocytisine derivative, which at a concentration of 10 mg/L produced a significant decrease in bottom dwelling and showed high times of freezing. In conclusion, the 3-chloro and 3-bromo derivatives show an anxiolytic effect, the 3-chlorocytisine derivative being more potent than the 3-bromo derivative, with the lowest time at the bottom of the tank at 1mg/L. On the other hand, chlorine, and bromine at position 5 produce an opposite effect.

Recent Advancement in Breast Cancer Research: Insights from Model Organisms-Mouse Models to Zebrafish

Animal models have been utilized for decades to investigate the causes of human diseases and provide platforms for testing novel therapies. Indeed, breakthrough advances in genetically engineered mouse (GEM) models and xenograft transplantation technologies have dramatically benefited in elucidating the mechanisms underlying the pathogenesis of multiple diseases, including cancer. The currently available GEM models have been employed to assess specific genetic changes that underlay many features of carcinogenesis, including variations in tumor cell proliferation, apoptosis, invasion, metastasis, angiogenesis, and drug resistance. In addition, mice models render it easier to locate tumor biomarkers for the recognition, prognosis, and surveillance of cancer progression and recurrence. Furthermore, the patient-derived xenograft (PDX) model, which involves the direct surgical transfer of fresh human tumor samples to immunodeficient mice, has contributed significantly to advancing the field of drug discovery and therapeutics. Here, we provide a synopsis of mouse and zebrafish models used in cancer research as well as an interdisciplinary 'Team Medicine' approach that has not only accelerated our understanding of varied aspects of carcinogenesis but has also been instrumental in developing novel therapeutic strategies.

Toxicity assessment of lead, nickel and cadmium on zebra fish augmented with Bacillus xiamenensis VITMSJ3: An insight on the defense mechanism against oxidative stress due to heavy metals

Increase urbanization in recent years has let to discharge of heavy metals into the environment which has caused severe impacts on soil as well as water. Therefore the current study was aimed to assess the toxicity of lead (Pb), nickel (Ni), and cadmium (Cd) from the contaminated water using zebra fish Danio rerio and detoxification of metals upon augmentation with Bacillus xiamenensis. Exposure doses till 150 mg L^-1 of Pb, Ni and Cd in water showed lethal effects on fish. Similarly the histopathological analysis showed severe tissue disruption in the gills and liver which were less upon supplementation with bacterial strain VITMSJ3. On the 20th day, the uptake concentration of Pb, Ni and Cd in zebra fish was found to be 87 mg L^-1, 89 mg L^-1 and 91 mg L^-1 respectively with VITMSJ3, from the water. Antioxidant enzymatic activities showed an increase upon bacterial supplementation, which reduced the oxidative stress. Further SEM-EDAX analysis confirmed the presence of Pb, Ni and Cd ions adsorbed on the gills. The results clearly showed less oxidative damages in fish with increased head and reduced tail %. Overall, the results showed a significant difference (p < 0.05) among the treatments compared with the control.

Short-term effects of various non-steroidal anti-inflammatory drugs (NSAIDs) on Danio rerio embryos

Due to the widespread use of non-steroidal anti-inflammatory drugs (NSAIDs) without a medical prescription and their frequent prevalence in aquatic habitats, there are major health and environmental issues. NSAIDs have been found in surface water and wastewater in concentrations ranging from ng/L to μg/L all over the world. The purpose of this study was to determine the relationship between NSAIDs (diclofenac, ketoprofen, paracetamol and ibuprofen) exposure and associated adverse effects in the assessment of indirect human health risks posed by Danio rerio (zebrafish) and Environmental Risk Assessment (ERA) of these NSAIDs in aquatic environments. Therefore, the objectives of this study were to (i) reveal abnormality endpoints of early developmental stages, after exposure of zebrafish and (ii) perform an ecological risk assessment of aquatic organisms upon exposure to NSAIDs detected in surface waters based on the risk quotients (RQs) method. According to the toxicity data collected, all of the malformations appeared after diclofenac exposure at all concentrations. The most notable malformations were the lack of pigmentation and an increase in yolk sac volume, with EC₅₀ values of 0.6 and 1.03 mg/L, respectively. The results obtained for the ERA revealed RQs higher than 1 for all the four NSAIDs chosen, posing ecotoxicological pressure in aquatic environments. Overall, our findings provide a critical contribution to the formulation of high-priority actions, sustainable strategies and strict regulations that minimize the negative effects of NSAIDs on the aquatic ecosystem.•To determine the LC₅₀, lethal conditions such as coagulation, absence of heartbeat and blood flow, absence of tail separation and development of somites were taken into account.•The EC₅₀ was calculated using sublethal parameters such as blood coagulation, pericardial edema, yolk sac edema or hypertrophy.•The 4 compounds present a high risk individually and in mixture with a RQ >> 1.

Effects of carnosine on the embryonic development and TiO2 nanoparticles-induced oxidative stress on Zebrafish

Oxidative stress is due to an unbalance between pro-oxidants, such as reactive oxygen (ROS) and nitrogen (RNS) species, and antioxidants/antioxidant system. Under physiological conditions these species are involved in different cellular processes such as cellular homeostasis and immune response, while an excessive production of ROS/RNS has been linked to the development of various diseases such as cancer, diabetes, and Alzheimer's disease. In this context, the naturally occurring dipeptide carnosine has shown the ability to scavenge ROS, counteract lipid peroxidation, and inhibit proteins oxidation. Titanium dioxide nanoparticles (TiO2-NPs) have been widely used to produce cosmetics, in wastewater treatment, in food industry, and in healthcare product. As consequence, these NPs are often released into aquatic environments. The Danio rerio (commonly called zebrafish) embryos exposure to TiO2-NPs did not affect the hatching rate, but induced oxidative stress. According to this scenario, in the present study, we first investigated the effects of carnosine exposure and of a sub-toxic administration of TiO2-NPs on the development and survival of zebrafish embryos/larvae measured through the acute embryo toxicity test (FET-Test). Zebrafish larvae represent a useful model to study oxidative stress-linked disorders and to test antioxidant molecules, while carnosine was selected based on its well-known multimodal mechanism of action that includes a strong antioxidant activity. Once the basal effects of carnosine were assessed, we then evaluated its effects on TiO2-NPs-induced oxidative stress in zebrafish larvae, measured in terms of total ROS production (measured with 2,7-dichlorodihydrofluorescein diacetate probe) and protein expression by immunohistochemistry of two cellular stress markers, 70 kDa-heat shock protein (Hsp70) and metallothioneins (MTs). We demonstrated that carnosine did not alter the phenotypes of both embryos and larvae of zebrafish at different hours post fertilization. Carnosine was instead able to significantly decrease the enhancement of ROS levels in zebrafish larvae exposed to TiO2-NPs and its antioxidant effect was paralleled by the rescue of the protein expression levels of Hsp70 and MTs. Our results suggest a therapeutic potential of carnosine as a new pharmacological tool in the context of pathologies characterized by oxidative stress such as neurodegenerative disorders.

Cellular activity of autophagy and multivesicular bodies in lens fiber cells during early lens development in rbm24a mutant of zebrafish: Ultrastructure analysis

Use of zebrafish as animal model for various diseases during early developmental stages has been exponentially increased with the aim to achieve the best representative results in this transparent fish. Recent studies documented that Rbm24a mutant causes cataract formation and resulted in blindness using the zebrafish model. Therefore, correct interpretation of studies that aimed for molecular approaches, a description of comparative and in-depth analysis of development of lens in wildtype and mutant is crucial to obtain the correct conclusion. In this study, we use a gold standard method the Transmission Electron Microscopy (TEM) to analysis the lens development in rbm24a mutant zebrafish. Firstly, we compare the cellular structures at 16-20 h post fertilization (hpf), the lens placode in ectoderm indicated delay lens development in rbm24a mutant than wildtype (siblings) zebrafish. At 33 hpf, loosely appeared lens fiber cells showed heterogenous electron density with numbers of mitochondria in lens of rbm24a mutant, revealed the influence of gene mutation in lens development. A detail ultrastructure of lens of rbm24a mutant also presented at 33 hpf. Comparatively in wildtype (siblings) at 33 hpf, lens exhibited homogenous electron density in tightly packed lens fiber cells with few mitochondria. Furthermore, to characterize the lens in rbm24a mutant we obtained data of cellular structures on 25 hpf and 1.5 days' post fertilization (dpf). At 25 hpf in mutant zebrafish, the detached solid sphere lens mass from ectoderm showed karyorrhexis, mitophagy and vesicles (also multivesicular bodies), these cellular structures supposed to hamper the development of future fiber cells. Moreover, at 1.5 dpf in mutant, nuclear excisosome, multilamellar bodies and irregular shaped mitochondria in heterogenous electron dense cytoplasm of lens fiber cells, collectively shown affected lens transparency. In summary the ultrastructure results of lens of rbm24a mutant zebrafish expand our knowledge and give reflection of different cellular activities like autophagy, apoptosis, vesicles (multivesicular bodies) and nuclear excisosomes which play their role in transparency achievement.

Research Progress on the Construction and Application of a Diabetic Zebrafish Model

Diabetes is a metabolic disease characterized by high blood glucose levels. With economic development and lifestyle changes, the prevalence of diabetes is increasing yearly. Thus, it has become an increasingly serious public health problem in countries around the world. The etiology of diabetes is complex, and its pathogenic mechanisms are not completely clear. The use of diabetic animal models is helpful in the study of the pathogenesis of diabetes and the development of drugs. The emerging vertebrate model of zebrafish has many advantages, such as its small size, large number of eggs, short growth cycle, simple cultivation of adult fish, and effective improvement of experimental efficiency. Thus, this model is highly suitable for research as an animal model of diabetes. This review not only summarizes the advantages of zebrafish as a diabetes model, but also summarizes the construction methods and challenges of zebrafish models of type 1 diabetes, type 2 diabetes, and diabetes complications. This study provides valuable reference information for further study of the pathological mechanisms of diabetes and the research and development of new related therapeutic drugs.

Healing Wounds Efficiently with Biomimetic Soft Matter: Injectable Self-Healing Neutral Glycol Chitosan/Dibenzaldehyde-Terminated Poly(ethylene glycol) Hydrogel with Inherent Antibacterial Properties

The high prevalence of acquiring skin wounds, along with the emergence of antibiotic-resistant strains that lead to infections, impose a threat to the physical, mental, and socioeconomic health of society. Among the wide array of wound dressings developed, hydrogels are regarded as a biomimetic soft matter of choice owing to their ability to provide a moist environment ideal for healing. Herein, neutral glycol chitosan (GC) was cross-linked via imine bonds with varying concentrations of dibenzaldehyde-terminated polyethylene glycol (DP) to give glycol chitosan/dibenzaldehyde-terminated polyethylene glycol hydrogels (GC/DP). These dynamic Schiff base linkages (absorption peak at 1638 cm^-1) within the hydrogel structure endowed their ability to recover from damage as characterized by high-low strain exposure in continuous step strain rheology. Along with their good injectability and biodegradability, the hydrogels exhibited remarkable inhibition against E. coli, P. aeruginosa, and S. aureus. GC/DP hydrogels demonstrated high LC50 values in vivo using zebrafish embryos as a model system due to their relative biocompatibility and a remarkable 93.4 ± 0.88% wound contraction at 30-dpw against 49.1 ± 3.40% of the control. To the best of our knowledge, this is the first study that developed injectable glycol chitosan/dibenzaldehyde-terminated polyethylene glycol self-healing hydrogels for application in wound healing with intrinsic bacteriostatic properties against the three bacteria.

Zebrafish models of COVID-19

Although COVID-19 has only recently appeared, research studies have already developed and implemented many animal models for deciphering the secrets of the disease and provided insights into the biology of SARS-CoV-2. However, there are several major factors that complicate the study of this virus in model organisms, such as the poor infectivity of clinical isolates of SARS-CoV-2 in some model species, and the absence of persistent infection, immunopathology, severe acute respiratory distress syndrome, and, in general, all the systemic complications which characterize COVID-19 clinically. Another important limitation is that SARS-CoV-2 mainly causes severe COVID-19 in older people with comorbidities, which represents a serious problem when attempting to use young and immunologically naïve laboratory animals in COVID-19 testing. We review here the main animal models developed so far to study COVID-19 and the unique advantages of the zebrafish model that may help to contribute to understand this disease, in particular to the identification and repurposing of drugs to treat COVID-19, to reveal the mechanism of action and side-effects of Spike-based vaccines, and to decipher the high susceptibility of aged people to COVID-19.

Gene Expression Analysis in gla-Mutant Zebrafish Reveals Enhanced Ca2+ Signaling Similar to Fabry Disease

Fabry disease (FD) is an X-linked inborn metabolic disorder due to partial or complete lysosomal α-galactosidase A deficiency. FD is characterized by progressive renal insufficiency and cardio- and cerebrovascular involvement. Restricted access on Gb3-independent tissue injury experimental models has limited the understanding of FD pathophysiology and delayed the development of new therapies. Accumulating glycosphingolipids, mainly Gb3 and lysoGb3, are Fabry specific markers used in clinical follow up. However, recent studies suggest there is a need for additional markers to monitor FD clinical course or response to treatment. We used a gla-knockout zebrafish (ZF) to investigate alternative biomarkers in Gb3-free-conditions. RNA sequencing was used to identify transcriptomic signatures in kidney tissues discriminating gla-mutant (M) from wild type (WT) ZF. Gene Ontology (GO) and KEGG pathways analysis showed upregulation of immune system activation and downregulation of oxidative phosphorylation pathways in kidneys from M ZF. In addition, upregulation of the Ca2+ signaling pathway was also detectable in M ZF kidneys. Importantly, disruption of mitochondrial and lysosome-related pathways observed in M ZF was validated by immunohistochemistry. Thus, this ZF model expands the pathophysiological understanding of FD, the Gb3-independent effects of gla mutations could be used to explore new therapeutic targets for FD.

Neuromasts and Olfactory Organs of Zebrafish Larvae Represent Possible Sites of SARS-CoV-2 Pseudovirus Host Cell Entry

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the acute respiratory disease coronavirus disease 2019 (COVID-19), which has resulted in millions of deaths globally. Here, we explored the mechanism of host cell entry of a luciferase-ZsGreen spike (SARS-CoV-2)-pseudotyped lentivirus using zebrafish embryos/larvae as an in vivo model. Successful pseudovirus entry was demonstrated via the expression of the luciferase (luc) gene, which was validated by reverse transcription-PCR (RT-PCR). Treatment of larvae with chloroquine (a broad-spectrum viral inhibitor that blocks membrane fusion) or bafilomycin A1 (a specific inhibitor of vacuolar proton ATPases, which blocks endolysosomal trafficking) significantly reduced luc expression, indicating the possible involvement of the endolysosomal system in the viral entry mechanism. The pharmacological inhibition of two-pore channel (TPC) activity or use of the tpcn2^dhkz1a mutant zebrafish line also led to diminished luc expression. The localized expression of ACE2 and TPC2 in the anterior neuromasts and the forming olfactory organs was demonstrated, and the occurrence of endocytosis in both locations was confirmed. Together, our data indicate that zebrafish embryos/larvae are a viable and tractable model to explore the mechanism of SARS-CoV-2 host cell entry, that the peripheral sense organs are a likely site for viral host cell entry, and that TPC2 plays a key role in the translocation of the virus through the endolysosomal system. IMPORTANCE Despite the development of effective vaccines to combat the COVID-19 pandemic, which help prevent the most life-threatening symptoms, full protection cannot be guaranteed, especially with the emergence of new viral variants. Moreover, some resistance to vaccination remains in certain age groups and cultures. As such, there is an urgent need for the development of new strategies and therapies to help combat this deadly disease. Here, we provide compelling evidence that the peripheral sensory organs of zebrafish possess several key components required for SARS-CoV-2 host cell entry. The nearly transparent larvae provide a most amenable complementary platform to investigate the key steps of viral entry into host cells, as well as its spread through the tissues and organs. This will help in the identification of key viral entry steps for therapeutic intervention, provide an inexpensive model for screening novel antiviral compounds, and assist in the development of new and more effective vaccines.

Evaluation of establishment and maintenance of primary cell cultures from several strains of common carp (Cyprinus carpio L.)

As a surrogate for the whole organism, primary cultures and cell lines serve as valuable tools for investigating exogenous and endogenous cytopathy. Studying cell responsiveness to diseases and contaminants is considered a less demanding and more readily accessible research approach that minimizes animal distress and provides more specific data. In the current work, the authors established primary cultures from several different organs and tissues of common carp (Cyprinus carpio L.) for subsequent use in other applications. They investigated the technical challenges in obtaining successful and durable carp-derived tissue cultures. The trials indicate that the type of tissue grown, carp strain and fish age impact equally upon culturing success, as do the cultivating conditions. Cells from gill epithelia, head and trunk kidneys, spleen, skin, gonads and ocular tissue were successfully established and maintained for further use in in-vitro testing. The primary cultures were, therefore, used to investigate and assess pathogens and pollutants emerging in carp's environment.

Toxicity evaluation of microplastics to aquatic organisms through molecular simulations and fractional factorial designs

Molecular docking, molecular dynamics modelling, and fractional factorial design methodologies were used in the current work to examine the harmful effects of ten microplastic (MPs) such as polystyrene (PS), polyvinylchloride (PVC), polyurethane (PU), polymethyl methacrylate (PMMA), polyamide (PA), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polychloropene (PCP) and polycarbonate (PC) on the aquatic organism (zebrafish). The toxicity was evaluated based on the docking of the MPs on cytochrome P450 (CYP P450) protein crystals. The binding affinities (ΔG) followed the order, PC (-6.9 kcal/mol) > PET (-6.1 kcal/mol) > PP (-5.8 kcal/mol) > PA (-5.6 kcal/mol) > PS (-5.1 kcal/mol) > PU (-4.1 kcal/mol) > PMMA (-3.9 kcal/mol) > PCP (-3.3 kcal/mol) > PVC (-2.4 kcal/mol) > PE (-2.1 kcal/mol). The primary driving factors for the binding of the MPs and the protein were hydrophobic force, and hydrogen bonding based on the molecular dynamics analysis and surrounding amino acid residues. Furthermore, a 2^10-5 fractional factorial design method was estimated to identify the main effect and second-order effects of MPs in a composite contamination system on binding affinity/energy to CYP450 receptor protein of zebrafish, combined with a fixed effects model. The findings showed that different MPs combinations had varying impacts on aquatic toxicity; as a consequence, the best combination of MPs with the lowest aquatic toxicity effect could be excluded. The factorial designs showed that the PU-PS and PP-PA combination and single PCP, has the most significant main effect on CYP450 receptor protein of zebrafish which translates to an optimum toxicity level of -4.61 kcal/mol. The investigation offers a theoretical foundation for identifying the hazardous impacts of MPs on aquatic life.

Health risks of phthalates: A review of immunotoxicity

Phthalates (PAEs) are known environmental endocrine disruptors that have been widely detected in several environments, and many studies have reported the immunotoxic effects of these compounds. Here, we reviewed relevant published studies, summarized the occurrence and major metabolic pathways of six typical PAEs (DMP, DEP, DBP, BBP, DEHP, and DOP) in water, soil, and the atmosphere, degradation and metabolic pathways under aerobic and anaerobic conditions, and explored the molecular mechanisms of the toxic effects of eleven PAEs (DEHP, DPP, DPrP, DHP, DEP, DBP, MBP, MBzP, BBP, DiNP, and DMP) on the immune system of different organisms at the gene, protein, and cellular levels. A comprehensive understanding of the mechanisms by which PAEs affect immune system function through regulation of immune gene expression and enzymes, increased ROS, immune signaling pathways, specific and non-specific immunosuppression, and interference with the complement system. By summarizing the effects of these compounds on typical model organisms, this review provides insights into the mechanisms by which PAEs affect the immune system, thus supplementing human immune experiments. Finally, we discuss the future direction of PAEs immunotoxicity research, thus providing a framework for the analysis of other environmental pollutants, as well as a basis for PAEs management and safe use.

Calcium Chloride Toxicology for Food Safety Assessment Using Zebrafish (Danio rerio) Embryos

The salt calcium chloride (CaCl₂) is widely used in industry as a food additive; levels for human consumption are regulated by international or governmental agencies. Generally, the food industry relies on toxicity studies conducted in mammals such as mice, rats, and rabbits for determining food safety. However, testing in mammals is time-consuming and expensive. Zebrafish have been used in a range of toxicological analyses and offer advantages with regard to sensitivity, time, and cost. However, information in not available with regard to whether the sensitivity of zebrafish to CaCl₂ is comparable to the concentrations of CaCl₂ used as food additives. The aim of this study was to compare the CaCl₂ tolerance of zebrafish embryos and larvae with concentrations currently approved as food additives. Acute toxicity, embryotoxicity, cardiotoxicity, and neurotoxicity assays were used to determine the threshold toxic concentration of CaCl₂ in zebrafish embryos and larvae. The data showed that doses above 0.4% had toxic effects on development and on the activity of the cardiac and neuronal systems. Furthermore, all embryos exposed to 0.8 and 1.6% of CaCl₂ died after 24 hpf. These findings are consistent with the limits of CaCl₂ concentrations approved by Codex Alimentarius. Therefore, zebrafish embryos could be suitable for screening food additives.

Use of Zebrafish as a Model Organism to Study Oxidative Stress: A Review

Dioxygen is an integral part of every living organism, but its concentration varies from organ to organ. Production of metabolites from dioxygen may result in oxidative stress. Since oxidative stress has the potential to damage various biomolecules in the cell, therefore, it has presently become an active field of research. Oxidative stress has been studied in a wide range of model organisms from vertebrates to invertebrates, from rodents to piscine organisms, and from in vivo to in vitro models. But zebrafish (adults, larvae, or embryonic stage) emerged out to be the most promising vertebrate model organism to study oxidative stress because of its vast advantages (transparent embryo, cost-effectiveness, similarity to human genome, easy developmental processes, numerous offspring per spawning, and many more). This is evidenced by voluminous number of researches on oxidative stress in zebrafish exposed to chemicals, radiations, nanoparticles, pesticides, heavy metals, etc. On these backgrounds, this review attempts to highlight the potentiality of zebrafish as model of oxidative stress compared with other companion models. Several areas, from biomedical to environmental research, have been covered to explain it as a more convenient and reliable animal model for experimental research on oxidative mechanisms.

Development and Applications of a Zebrafish (Danio rerio) CYP1A-Targeted Monoclonal Antibody (CRC4) with Reactivity across Vertebrate Taxa: Evidence for a Conserved CYP1A Epitope

CYP1A is a heme-thiolate enzyme associated with the cytochrome P4501A1 monooxygenase system and is inducible by a wide variety of xenobiotics and endogenous ligands that bind and activate the aryl hydrocarbon receptor (AHR). The AHR-CYP1A axis is important for detoxification of certain xenobiotics and for homeostatic balance of endogenous sex hormones, amine hormones, vitamins, fatty acids, and phospholipids. Herein, we generated and described applications of a zebrafish CYP1A-targeted monoclonal antibody (mAb CRC4) that fortuitously recognizes induced CYP1A across vertebrate taxa, including fish, chicken, mouse, rat, and human. We then demonstrated that mAb CRC4 targets a highly conserved epitope signature of vertebrate CYP1A. The unique complimentary determining region (CDR) sequences of heavy and light chains were determined, and these Ig sequences will allow for the expression of recombinant mAb CRC4, thus superseding the need for long-term hybridoma maintenance. This antibody works well for immunohistochemistry (IHC), as well as whole-mounted IHC in zebrafish embryos. Monoclonal antibody CRC4 may be particularly useful for studying the AHR-CYP1A axis in multiple vertebrate species and within the context of Oceans and Human Health research. By using archived samples, when possible, we actively promoted efforts to reduce, replace, and refine studies involving live animals.

An adult zebrafish model for adherent-invasive Escherichia coli indicates protection from AIEC infection by probiotic E. coli Nissle

Adherent-invasive Escherichia coli (AIEC) is an opportunistic pathogen associated with major inflammatory bowel disease, Crohn disease, and ulcerative colitis. Unfavorable conditions push commensal AIEC to induce gut inflammation, sometimes progressing to inflammation-induced colon cancer. Recently, zebrafish have emerged as a useful model to study human intestinal pathogens. Here, a zebrafish model to study AIEC infection was developed. Bath inoculation with AIEC resulted in colonization and tissue disruption in the zebrafish intestine. Gene expression of pro-inflammatory markers including interleukin-1β (IL-1β), tumor necrosis factor alpha (TNFα), interferon-γ (IFNγ), and S100A-10b (akin to human calprotectin) in the zebrafish intestine was significantly induced by AIEC infection. The probiotic E. coli Nissle 1917 (EcN) was tested as a therapeutic and prophylactic against AIEC infection and reduced AIEC colonization, tissue damage, and pro-inflammatory responses in zebrafish. Furthermore, EcN diminished the propionic-acid-augmented hyperinfection of AIEC in zebrafish. Thus, this study shows the efficacy of EcN against AIEC in an AIEC-zebrafish model.

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AIEC can colonize, invade, and induce inflammation in the zebrafish gut

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Probiotic E. coli Nissle can protect zebrafish from AIEC infection

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EcN is effective both prophylactically and therapeutically against AIEC-induced IBD