A novel, reliable method for repeated blood collection from aquarium fish

Vitamin D3 Regulates Energy Homeostasis under Short-Term Fasting Condition in Zebrafish (Danio Rerio)

Vitamin D3 (VD3) is a steroid hormone that plays pivotal roles in pathophysiology, and 1,25(OH)2D3 is the most active form of VD3. In the current study, the crucial role of VD3 in maintaining energy homeostasis under short-term fasting conditions was investigated. Our results confirmed that glucose-depriving pathways were inhibited while glucose-producing pathways were strengthened in zebrafish after fasting for 24 or 48 h. Moreover, VD3 anabolism in zebrafish was significantly suppressed in a time-dependent manner under short-fasting conditions. After fasting for 24 or 48 h, zebrafish fed with VD3 displayed a higher gluconeogenesis level and lower glycolysis level in the liver, and the serum glucose was maintained at higher levels, compared to those fed without VD3. Additionally, VD3 augmented the expression of fatty acids (FAs) transporter cd36 and lipogenesis in the liver, while enhancing lipolysis in the dorsal muscle. Similar results were obtained in cyp2r1-/- zebrafish, in which VD3 metabolism is obstructed. Importantly, it was observed that VD3 induced the production of gut GLP-1, which is considered to possess a potent gluconeogenic function in zebrafish. Meanwhile, the gene expression of proprotein convertase subtilisin/kexin type 1 (pcsk1), a GLP-1 processing enzyme, was also induced in the intestine of short-term fasted zebrafish. Notably, gut microbiota and its metabolite acetate were involved in VD3-regulated pcsk1 expression and GLP-1 production under short-term fasting conditions. In summary, our study demonstrated that VD3 regulated GLP-1 production in zebrafish by influencing gut microbiota and its metabolite, contributing to energy homeostasis and ameliorating hypoglycemia under short-term fasting conditions.

Synthesis and molecular docking studies of new aryl imeglimin derivatives as a potent antidiabetic agent in a diabetic zebrafish model

Diabetes mellitus (DM) is a persistent, progressive, and multifaceted disease characterized by elevated blood glucose levels. Type 2 diabetes mellitus is associated with a relative deficit in insulin mainly due to beta cell dysfunction and peripheral insulin resistance. Metformin has been widely prescribed as a primary treatment option to address this condition. On the other hand, an emerging glucose-reducing agent known as imeglimin has garnered attention due to its similarity to metformin in terms of chemical structure. In this study, an innovative series of imeglimin derivatives, labeled 3(a-j), were synthesized through a one-step reaction involving an aldehyde and metformin. The chemical structures of these derivatives were thoroughly characterized using ESI-MS, 1H, and 13C NMR spectroscopy. In vivo tests on a zebrafish diabetic model were used to evaluate the efficacy of the synthesized compounds. All compounds 3(a-j) showed significant antidiabetic effects. It is worth mentioning that compounds 3b (FBS = 72.3 ± 7.2 mg/dL) and 3g (FBS = 72.7 ± 4.3 mg/dL) have antidiabetic effects comparable to those of the standard drugs metformin (FBS = 74.0 ± 5.1 mg/dL) and imeglimin (82.3 ± 5.2 mg/dL). In addition, a docking study was performed to predict the possible interactions between the synthesized compounds and both SIRT1 and GSK-3β targets. The docking results were in good agreement with the experimental assay results.

Dynamics of Chromosome Aberrations and Cell Death in Zebrafish Embryos Exposed to 137Cs Total-Body Irradiation

Ionizing radiation exposure induces significant DNA damage and cell death in aquatic species. Accurate sensing and quantification play pivotal roles in environmental monitoring and surveillance. Zebrafish (Danio rerio) is a well-suited animal model for research into this aspect, especially with recent development of cytogenetic and transgenic tools. In this study, we present time-course studies of chromosome aberrations and cell death in zebrafish embryos exposed to 2 Gy 137Cs total-body irradiation. Using a cytogenetic approach, we quantified chromosome and chromatid aberrations in irradiated embryos at 6, 14, 20, and 24 h postirradiation. Metaphases with aberrations showed rapid declining kinetics, accompanied by incomplete karyotypes and irregular chromatin contents. Using an apoptosis-reporting transgenic zebrafish, we found increasing cell death along these time points, with the embryonic eyes and brain contributing the majority of the cell death volumes. We provide evidence that self-proliferating progenitor cells form the underlying linkage between the two kinetics and their positions define radiosensitive niches in zebrafish embryos. Our results provide detailed chromosome aberration and cell death dynamics in 137Cs-irradiated zebrafish embryos and unveil the appropriate timeline and tissue positions for accurate sensing and quantification of radiation-induced damages in zebrafish embryos.

Pharmacokinetics of the analgesic and anti-inflammatory drug meloxicam after administration of multiple doses to nursehound sharks (Scyliorhinus stellaris)

OBJECTIVE

To determine the pharmacokinetics of meloxicam in the nursehound shark (Scyliorhinus stellaris) during multiple dose administration.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

A total of eight clinically healthy adult nursehounds (four males, four females).

METHODS

Meloxicam was administered intramuscularly at a dose of 1.5 mg kg-1 once daily for 7 days. Blood samples were collected from the caudal vein for pharmacokinetic analysis at 2.5 hours and 24 hours after drug administration. After a 4 week washout period, meloxicam was administered orally at the same dose at 12 hour intervals for three repeated doses. Blood samples were collected at 1, 2, 4, 6, 8, 12, 24, 36 and 48 hours after the first administration. Sharks were visually monitored during each study and 4 weeks afterwards for side effects or signs of toxicity. Time required to achieve steady state was assessed by visual inspection and statistical comparison of peak and trough concentrations using a Friedman test; comparison between sexes was performed using a Mann-Whitney U test and p-value was set at 0.05.

RESULTS

No animal died or showed clinical signs of toxicity during the study. Meloxicam administered orally did not produce detectable concentrations in plasma. After intramuscular administration, steady state was achieved after five doses, and mean trough and peak plasma concentrations at steady state were 1.76 ± 0.21 μg mL-1 and 3.02 ± 0.23 μg mL-1, respectively. Mean peak concentration accumulation ratio was 2.50 ± 0.22.

CONCLUSIONS AND CLINICAL RELEVANCE

This study shows that intramuscular posology produces plasma concentrations considered therapeutic for other species. However, meloxicam was not detected in plasma after oral administration. These results suggest that meloxicam administered intramuscularly may be a useful non-steroid anti-inflammatory drug in nursehound sharks. Further pharmacodynamic studies are needed to fully evaluate its clinical use in this species.

Endotoxin of Porphyromonas gingivalis amplifies the inflammatory response in hyperglycemia-induced zebrafish through a mechanism involving chitinase-like protein YKL-40 analogs

Porphyromonas gingivalis (P. gingivalis), a key pathogen in periodontal diseases, is also associated with hyperglycemia-associated systemic diseases, including diabetes mellitus (DM). Gingipains are the most important endotoxins of P. gingivalis, and in vivo studies using gingipains are scarce. Zebrafish (Danio rerio) is a vertebrate with high physiological and genetic homology with humans that has multiple co-orthologs for human genes, including inflammation-related proteins. The aim of our study was to determine the effects of gingipain in a hyperglycemia-induced zebrafish model by evaluating inflammation, oxidant-antioxidant status, and the cholinergic system. Adult zebrafish were grouped into the control group (C), hyperglycemia-induced group subjected to 15 days of overfeeding (OF), gingipain-injected group (GP), and gingipain-injected hyperglycemic group (OF + GP). At the end of 15 days, an oral glucose tolerance test (OGTT) was performed, and fasting blood glucose (FBG) levels were measured. Lipid peroxidation (LPO), nitric oxide (NO), glutathione (GSH), glutathione S-transferase, catalase, acetylcholinesterase (AChE), alkaline phosphatase (ALP), and sialic acid (SA) levels were determined spectrophotometrically in the hepatopancreas. The expression levels of tnf-⍺, il-1β, ins, crp, and the acute phase protein YKL-40 analogs chia.5 and chia.6 were evaluated by RT‒PCR. After two weeks of overfeeding, significantly increased weight gain, FBG, and OGTT confirmed that the zebrafish were hyperglycemic. Increased oxidative stress, inflammation, and AChE and ALP activities were observed in both the overfeeding and GP groups. Amplification of inflammation and oxidative stress was evident in the OF + GP group through increased expression of crp, il-1β, chia.5, and chia.6 and increased LPO and NO levels. Our results support the role of gingipains in the increased inflammatory response in hyperglycemia-associated diseases.

Transcriptome Analysis Reveals the Molecular Basis of Overfeeding-Induced Diabetes in Zebrafish

Diabetes has gradually become a serious disease that threatens human health. It can induce various complications, and the pathogenesis of diabetes is quite complex and not yet fully elucidated. The zebrafish has been widely acknowledged as a useful model for investigating the mechanisms underlying the pathogenesis and therapeutic interventions of diabetes. However, the molecular basis of zebrafish diabetes induced by overfeeding remains unknown. In this study, a zebrafish diabetes model was established by overfeeding, and the molecular basis of zebrafish diabetes induced by overfeeding was explored. Compared with the control group, the body length, body weight, and condition factor index of zebrafish increased significantly after four weeks of overfeeding. There was a significant elevation in the fasting blood glucose level, accompanied by a large number of lipid droplets accumulated within the liver. The levels of triglycerides and cholesterol in both the serum and liver exhibited a statistically significant increase. Transcriptome sequencing was employed to investigate changes in the livers of overfed zebrafish. The number of up-regulated and down-regulated differentially expressed genes (DEGs) was 1582 and 2404, respectively, in the livers of overfed zebrafish. The DEGs were subjected to KEGG and GO enrichment analyses, and the hub signaling pathways and hub DEGs were identified. The results demonstrate that sixteen genes within the signal pathway associated with fatty acid metabolism were found to be significantly up-regulated. Specifically, these genes were found to mainly participate in fatty acid transport, fatty acid oxidation, and ketogenesis. Furthermore, thirteen genes that play a crucial role in glucose metabolism, particularly in the pathways of glycolysis and glycogenesis, were significantly down-regulated in the livers of overfed zebrafish. These results indicate insulin resistance and inhibition of glucose entry into liver cells in the livers of overfed zebrafish. These findings elucidate the underlying molecular basis of zebrafish diabetes induced by overfeeding and provide a model for further investigation of the pathogenesis and therapeutics of diabetes.

Hepatotoxicity screening and ranking of structurally different pyrrolizidine alkaloids in zebrafish

Pyrrolizidine alkaloids (PAs) are phytotoxins distributed in ∼6000 plant species. PA-contaminated/containing foodstuffs/herbs/supplements pose a potential threat to human health. Various regulatory authorities established different PA margins of exposure assuming an equal hepatotoxic potency of structurally diverse PAs, although they exhibit different toxic potencies. Therefore, understanding hepatotoxic potencies of different PAs would facilitate a more appropriate risk assessment of PA exposure. In this study, a zebrafish model, which mimics physiological processes of absorption, distribution, metabolism, and excretion, was selected to evaluate acute hepatotoxic potency of different PAs (7 PAs and 2 PA N-oxides) and explore possible physiological pathways involved in PA-induced hepatotoxicity. After 6 h oral administration, PAs caused distinct structure-dependent hepatotoxicity with a series of biochemical and histological changes in zebrafish. Based on the measured toxicological endpoints, the relative toxic potency order of different PAs was derived as lasiocarpine ∼ retrorsine > monocrotaline > riddelliine > clivorine > heliotrine > retrorsine N-oxide ∼ riddelliine N-oxide≫>platyphyline. Further, compared to control group, different upregulation/downregulation of mRNA expression in PA-treated groups indicated that inflammation, apoptosis, and steatosis were involved in PA-induced hepatotoxicity in zebrafish. These findings demonstrate that zebrafish model is useful for screening and ranking hepatotoxicity of PAs with diverse structures, which would facilitate the more accurate risk assessment of PA exposure.

Loss of glyoxalase 2 alters the glucose metabolism in zebrafish

Glyoxalase 2 is the second enzyme of the glyoxalase system, catalyzing the detoxification of methylglyoxal to d-lactate via SD-Lactoylglutathione. Recent in vitro studies have suggested Glo2 as a regulator of glycolysis, but if Glo2 regulates glucose homeostasis and related organ specific functions in vivo has not yet been evaluated. Therefore, a CRISPR-Cas9 knockout of glo2 in zebrafish was created and analyzed. Consistent with its function in methylglyoxal detoxification, SD-Lactoylglutathione, but not methylglyoxal accumulated in glo2^-/- larvae, without altering the glutathione metabolism or affecting longevity. Adult glo2^-/- livers displayed a reduced hexose concentration and a reduced postprandial P70-S6 kinase activation, but upstream postprandial AKT phosphorylation remained unchanged. In contrast, glo2^-/- skeletal muscle remained metabolically intact, possibly compensating for the dysfunctional liver through increased glucose uptake and glycolytic activity. glo2^-/- zebrafish maintained euglycemia and showed no damage of the retinal vasculature, kidney, liver and skeletal muscle. In conclusion, the data identified Glo2 as a regulator of cellular energy metabolism in liver and skeletal muscle, but the redox state and reactive metabolite accumulation were not affected by the loss of Glo2.

Pharmacokinetics of the Anti-Inflammatory Drug Meloxicam after Single 1.5 mg/kg Intramuscular Administration to Undulate Skates (Raja undulata)

The therapy database currently used in elasmobranchs is still mostly based on empirical data, and there are few efficacy and safety studies supporting clinical practice. In this study, meloxicam pharmacokinetics (PK) were evaluated after a single 1.5 mg/kg IM administration to a group of seven clinically healthy adult undulate skates (Raja undulata Lacepède, 1802). Blood samples were collected before administration and at 15, 30, 60 and 90 min and 2, 4, 8, 12, 24 and 48 h after the IM injection. The meloxicam concentrations in plasma were determined using high-performance liquid chromatography, and PK parameters were calculated using a non-compartmental model approach. The mean ± SEM values of the main PK values were 1.84 ± 0.31 μg/mL for peak plasma concentration, 1.5 ± 0.24 h for time to maximum plasma concentration, 11.43 ± 2.04 h·µg/mL for area under the plasma concentration vs. time curve, 3.55 ± 0.65 h for elimination half-life, and 5.37 ± 0.94 h for mean residency time. No adverse reactions were detected. The relatively high plasma concentration and short time to maximum plasma concentration suggest that meloxicam could turn into an efficient analgesic and anti-inflammatory candidate drug to be used in skates. Further efficacy, pharmacodynamic, and multiple-dose studies with meloxicam are needed in elasmobranchs.

Non-Lethal Sampling Supports Integrative Movement Research in Freshwater Fish

Freshwater ecosystems and fishes are enormous resources for human uses and biodiversity worldwide. However, anthropogenic climate change and factors such as dams and environmental contaminants threaten these freshwater systems. One way that researchers can address conservation issues in freshwater fishes is via integrative non-lethal movement research. We review different methods for studying movement, such as with acoustic telemetry. Methods for connecting movement and physiology are then reviewed, by using non-lethal tissue biopsies to assay environmental contaminants, isotope composition, protein metabolism, and gene expression. Methods for connecting movement and genetics are reviewed as well, such as by using population genetics or quantitative genetics and genome-wide association studies. We present further considerations for collecting molecular data, the ethical foundations of non-lethal sampling, integrative approaches to research, and management decisions. Ultimately, we argue that non-lethal sampling is effective for conducting integrative, movement-oriented research in freshwater fishes. This research has the potential for addressing critical issues in freshwater systems in the future.

Pharmacokinetic Studies in Elasmobranchs: Meloxicam Administered at 0.5 mg/kg Using Intravenous, Intramuscular, and Oral Routes to Nusehound Sharks (Scyliorhinus stellaris)

Infectious and inflammatory diseases are the most frequently diagnosed pathologies in elasmobranchs maintained under human care. Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently used in veterinary medicine for their anti-inflammatory, analgesic, and antipyretic properties. Meloxicam is a commonly prescribed NSAID in elasmobranchs, but there are still no published pharmacokinetic (PK) studies supporting its use in this group of animals. In this study, meloxicam was administered at a single dose of 0.5 mg/kg to eight healthy adult nursehound sharks (Scyliorhinus stellaris) intravenously (IV), intramuscularly (IM), and orally (PO), with a minimum 4-week washout period between administrations. Blood samples were obtained both beforehand and at predetermined times after each administration. Plasma concentrations were measured using a validated high performance liquid chromatography method, and PK data was obtained using a non-compartmental analysis. Meloxicam administered orally did not produce detectable concentrations in blood plasma, while mean peak plasma concentration was 0.38 ± 0.08 μg/ml after IM administration. The mean terminal half-life was 10.71 ± 2.77 h and 11.27 ± 3.96 h for IV and IM injections, respectively. The area under the curve extrapolated to infinity was 11.37 ± 2.29 h·μg/ml after IV injections and 5.98 ± 0.90 h·μg/ml after IM injections. Meloxicam administered IM had a mean absolute bioavailability of 56.22 ± 13.29%. These numbers support meloxicam as a promising drug to be used IM in nursehounds, questions the efficacy of its single PO use in elasmobranchs, elucidate the need for higher dosage regimes, and evidence the need for further PK studies in sharks and rays.

Does blood sampling from caudal vessels in fish produce parameter values different from those obtained by heart puncture?

Analyses of blood samples in ichthyology are of importance for assessment of fish health as well as fish responses to environmental stressors. The measurement results may be affected by multiple factors. This study aimed at assessment of the influence of the blood collection site by comparing dual values of indices measured in samples obtained both from the heart and puncturing caudal vessels in the same fish specimens. Our results revealed that the sampling site did not significantly influence measured variables including haematological indices, the plasma biochemistry profile, acid-base balance parameters and the phagocytic activity. To conclude, for the rainbow trout (Oncorhynchus mykiss) both sampling methods are interchangeable with regard to the above-mentioned indices.

Bisphenol A reveals its obesogenic effects through disrupting glucose tolerance, oxidant-antioxidant balance, and modulating inflammatory cytokines and fibroblast growth factor in zebrafish

Obesogens affect lipid metabolism, and genetic or epigenetic factors may also contribute to the progression of obesity. Endocrine-disrupting chemicals (EDCs) are the most striking among obesogens. Bisphenol A (BPA) is an estrogenic EDC used in food containers, adhesives, dye powders, and dental fillers. We aimed to elucidate molecular mechanisms of BPA's obesogenic effects focusing on obesogenic pathways in the liver including fibroblast growth factor (FGF) and Dnmt3a which is its epigenetic regulator, oxidant-antioxidant status, and inflammatory cytokines. Zebrafish were divided into three groups as control, low-dose BPA (1 μm BPA), and high-dose BPA groups (10 μm BPA). At the end of 30 days, oral glucose tolerance test (OGTT) was performed, fasting blood glucose levels were measured, and hepatopancreas tissues were taken. Malondialdehyde (MDA) levels, superoxide dismutase (SOD), glutathione S-transferase (GST), and nitric oxide (NO) activities were examined in the hepatopancreas. Inflammatory cytokines, lepa, fgf21, and dnmt3a expressions were determined by RT-PCR. BPA exposure increased the body weights, il1ß, tnfα, il6, lepa, fgf21, and dnmt3a expressions, impaired glucose tolerance, and oxidant-antioxidant status in a dose-dependent manner. Hepatocyte degeneration, lipid vacuolization, and vasocongestion were observed in both BPA-exposed groups. Our study suggests impaired glucose tolerance, oxidant-antioxidant balance, increased inflammatory response, fgf21 expression, and dnmt3a expressions as the possible mechanisms for the BPA-induced obesity model in zebrafish.

Stevioside ameliorates hyperglycemia and glucose intolerance, in a diet-induced obese zebrafish model, through epigenetic, oxidative stress and inflammatory regulation

Obesity is an independent risk factor for type 2 diabetes and epigenetic regulatory mechanisms affect obesity-related mechanisms. Due to weight gain concern in society, artificial sweeteners with no nutritional value have been increasingly consumed. Stevia is a sweet natural glycoside and a calorie-free sweetner extracted from the leaves of Stevia rebaudiana Bertoni and used as a substitute for artificial sweetners. This study evaluates the effects of stevioside on glucose tolerance, epigenetic and metabolic regulators of insulin resistance, oxidant-antioxidant status and tissue histology in a diet-induced obese (DIO) zebrafish model. After 15 days of overfeeding body weight, and fasting blood glucose, lipid peroxidation and nitric oxide levels and the expressions of fbf21, lepa, ll21, tnfα were elevated, where as there was impaired glucose tolerance and lower superoxide dismutase and glutathione S-transferase activities, dnmt3a expression which is an epigenetic tool of insulin resistance. Beneficial effects of stevioside were observed on glucose tolerance, oxidative stress and inflammatory mediators linking obesity to insulin resistance and its epigenetic regulation, in DIO model.

Assessment of Insulin, GLUT2 and inflammatory cytokines genes expression in pancreatic β-Cells in zebrafish (Danio rario) with overfeeding diabetes induction w/o glucose

Abstract

In recent years, zebrafish have been proposed as a model for rapid analysis of gene function and biological activity due to high genetic similarities with humans. The aim of this study was to determine the effects of overfeeding-induced diabetes w/o glucose on inflammatory cytokine as well as insulin and glucose transporter-2 genes (GLUT2) genes expression in the pancreas in zebrafish.

Materials and methods

The experiment was performed on 120 zebrafish (duplicated sample) with a specific genetic mapping (AB-Wild type). A total of 8 tanks, each containing 15 fish per 2-liter water, were used and divided into four groups: (1) Control group, (2) regular diet with glucose,3) Only Artemia overfeeding and 4) Combined Artemia with glucose. We induced T2DM zebrafish using glucose monohydrate solution in water and repeated daily Artemia feeding. In this model, fasting blood glucose increase is preceded by obesity and glucose intolerance. The experiment lasted for two months. Blood glucose and fish biometrics were measured in two steps. The expression of TNFα, IFNγ, GLUT2 and Insulin genes were quantified by a Real-Time qPCR System (Applied Biosystems, USA) using a set of specific primers.

Results

The highest mortality rate was observed in combined Artemia and glucose (p < 0.05). We showed significantly higher expression of IL-1B and TNF-α as well as inhibitory cytokines such as IFNγ genes in overfeeding induced diabetes(OID) which was highest in the combined Artemia and glucose group.(p < 0.05)The GLUT2 gene expression was higher in the pure artemia group which decreased to a lower level by adding glucose to Artemia in the diet. (p < 0.05). Also, the lowest insulin gene expression was observed in the combined group (p < 0.05).

Conclusions

In zebrafish, diabetes induction with overfeeding and supraphysiological glucose in diet accompanied with higher expression of inflammatory cytokines genes in the pancreas as well as lower insulin and GLU2 genes. These epigenetic factors appeared to initiate pancreatic beta dysfunction alongside insulin resistance and could have a crucial role in the pathogenesis of overfeeding-induced diabetes using primitive animal models.

Bone Phenotyping Approaches in Human, Mice and Zebrafish - Expert Overview of the EU Cost Action GEMSTONE ("GEnomics of MusculoSkeletal traits TranslatiOnal NEtwork")

A synoptic overview of scientific methods applied in bone and associated research fields across species has yet to be published. Experts from the EU Cost Action GEMSTONE ("GEnomics of MusculoSkeletal Traits translational Network") Working Group 2 present an overview of the routine techniques as well as clinical and research approaches employed to characterize bone phenotypes in humans and selected animal models (mice and zebrafish) of health and disease. The goal is consolidation of knowledge and a map for future research. This expert paper provides a comprehensive overview of state-of-the-art technologies to investigate bone properties in humans and animals - including their strengths and weaknesses. New research methodologies are outlined and future strategies are discussed to combine phenotypic with rapidly developing -omics data in order to advance musculoskeletal research and move towards "personalised medicine".

Globin Digest Improves Visceral Adiposity Through UCP1 Upregulation in Diet-Induced Obese Zebrafish and Mice

Globin digest (GD), a bioactive oligopeptide derived from porcine hemoglobin proteins, has been demonstrated to have beneficial effects on improving postprandial hyperlipidemia, hyperglycemia, and liver injury. We previously reported the lipid-lowering effects of GD using a zebrafish obesogenic test. Here, we sought to evaluate the effect of GD on visceral adiposity and the underlying molecular mechanisms using zebrafish and mouse obesity models. GD ameliorated dyslipidemia and suppressed the accumulation of visceral adipose tissue (VAT) in adult obese zebrafish. Transcriptomic analysis by RNA sequencing of GD-treated adult zebrafish revealed that GD upregulated UCP1-related pathways. Further, we performed mouse experiments and found that GD intake (2 mg/g body weight/day) was associated with lowered plasma triglyceride and total cholesterol levels, decreased VAT accumulation, and improved adipocyte hypertrophy with the upregulation of Ucp1 expression in white adipose tissue at both the mRNA and protein levels. Taken together, these results indicate that GD improves visceral adiposity by upregulating UCP1 expression, providing a novel perspective on combating obesity.

Early, nonlethal ploidy and genome size quantification using confocal microscopy in zebrafish embryos

Ploidy transitions through whole genome duplication have shaped evolution by allowing the sub- and neo-functionalization of redundant copies of highly conserved genes to express novel traits. The nuclear:cytoplasmic (n:c) ratio is maintained in polyploid vertebrates resulting in larger cells, but body size is maintained by a concomitant reduction in cell number. Ploidy can be manipulated easily in most teleosts, and the zebrafish, already well established as a model system for biomedical research, is therefore an excellent system in which to study the effects of increased cell size and reduced cell numbers in polyploids on development and physiology. Here we describe a novel technique using confocal microscopy to measure genome size and determine ploidy non-lethally at 48 h post-fertilization (hpf) in transgenic zebrafish expressing fluorescent histones. Volumetric analysis of myofiber nuclei using open-source software can reliably distinguish diploids and triploids from a mixed-ploidy pool of embryos for subsequent experimentation. We present an example of this by comparing heart rate between confirmed diploid and triploid embryos at 54 hpf.

Flavin Adenine Dinucleotide Depletion Caused by electron transfer flavoprotein subunit alpha Haploinsufficiency Leads to Hepatic Steatosis and Injury in Zebrafish

The electron transfer flavoprotein (ETF) complex, made up of the ETF alpha subunit (ETFA), ETF beta subunit (ETFB), and ETF dehydrogenase (ETFDH), regulates fatty acid β-oxidation activity while scavenging leaked electrons through flavin adenine dinucleotide (FAD)/reduced form FAD (FADH₂) redox reactions in mitochondria. Here, we hypothesized that ETF dysfunction-mediated FAD deficiency may result in increased mitochondrial oxidative stress and steatosis and subsequent liver injury. We report that etfa haploinsufficiency caused hyperlipidemia, hypercholesterolemia, and hepatic steatosis and injury in adult zebrafish. Further, etfa^{+/ -} mutant livers had reduced levels of FAD and glutathione and an increase in reactive oxygen species. Because FAD depletion might be critical in the pathogenesis of the liver lesion identified in etfa^{+/ -} mutants, we used riboflavin to elevate FAD levels in the liver and found that riboflavin supplementation significantly suppressed hepatic steatosis and injury in etfa^{+/ -} mutants through suppression of oxidative stress and de novo lipogenesis in the liver. Additionally, we found that adenosine triphosphate-linked mitochondrial oxygen consumption and mitochondrial membrane potential were reduced in etfa^{+/ -} primary hepatocytes and that riboflavin supplementation corrected these defects. Conclusion: FAD depletion caused by etfa haploinsufficiency plays a key role in hepatic steatosis and oxidative stress-mediated hepatic injury in adult zebrafish. This raises the possibility that people with ETFA haploinsufficiency have a high risk for developing liver disease.

Preventive Effects of Green Tea Extract against Obesity Development in Zebrafish

Various natural products (NPs) have been used to treat obesity and related diseases. However, the best way to fight obesity is preventive, with accurate body weight management through exercise, diet, or bioactive NPs to avoid obesity development. We demonstrated that green tea extract (GTE) is an anti-obesity NP using a zebrafish obesity model. Based on a hypothesis that GTE can prevent obesity, the objective of this study was to assess GTE's ability to attenuate obesity development. Juvenile zebrafish were pretreated with GTE for seven days before obesity induction via a high-fat diet; adult zebrafish were pretreated with GTE for two weeks before obesity induction by overfeeding. As a preventive intervention, GTE significantly decreased visceral adipose tissue accumulation in juveniles and ameliorated visceral adiposity and plasma triglyceride levels in adult zebrafish obesity models. RNA sequencing analysis was performed using liver tissues from adult obese zebrafish, with or without GTE administration, to investigate the underlying molecular mechanism. Transcriptome analysis revealed that preventive GTE treatment affects several pathways associated with anti-obesity regulation, including activation of STAT and downregulation of CEBP signaling pathways. In conclusion, GTE could be used as a preventive agent against obesity.

Which Hyperglycemic Model of Zebrafish (Danio rerio) Suites My Type 2 Diabetes Mellitus Research? A Scoring System for Available Methods

Despite extensive studies on type 2 diabetes mellitus (T2DM), there is no definitive cure, drug, or prevention. Therefore, for developing new therapeutics, proper study models of T2DM is necessary to conduct further preclinical researches. Diabetes has been induced in animals using chemical, genetic, hormonal, antibody, viral, and surgical methods or a combination of them. Beside different approaches of diabetes induction, different animal species have been suggested. Although more than 85% of articles have proposed rat (genus Rattus) as the proper model for diabetes induction, zebrafish (Danio rerio) models of diabetes are being used more frequently in diabetes related studies. In this systematic review, we compare different aspects of available methods of inducing hyperglycemia referred as T2DM in zebrafish by utilizing a scoring system. Evaluating 26 approved models of T2DM in zebrafish, this scoring system may help researchers to compare different T2DM zebrafish models and select the best one regarding their own research theme. Eventually, glyoxalase1 (glo1-/-) knockout model of hyperglycemia achieved the highest score. In addition to assessment of hyperglycemic induction methods in zebrafish, eight most commonly proposed diabetic induction approval methods are suggested to help researchers confirm their subsequent proposed models.

Ca2+-Dependent Glucose Transport in Skeletal Muscle by Diphlorethohydroxycarmalol, an Alga Phlorotannin: In Vitro and In Vivo Study

Diphlorethohydroxycarmalol (DPHC), a type of phlorotannin isolated from the marine alga Ishige okamurae, reportedly alleviates impaired glucose tolerance. However, the molecular mechanisms of DPHC regulatory activity and by which it exerts potential beneficial effects on glucose transport into skeletal myotubes to control glucose homeostasis remain largely unexplored. The aim of this study was to evaluate the effect of DPHC on cytosolic Ca2+ levels and its correlation with blood glucose transport in skeletal myotubes in vitro and in vivo. Cytosolic Ca2+ levels upon DPHC treatment were evaluated in skeletal myotubes and zebrafish larvae by Ca2+ imaging using Fluo-4. We investigated the effect of DPHC on the blood glucose level and glucose transport pathway in a hyperglycemic zebrafish. DPHC was shown to control blood glucose levels by accelerating glucose transport; this effect was associated with elevated cytosolic Ca2+ levels in skeletal myotubes. Moreover, the increased cytosolic Ca2+ level caused by DPHC can facilitate the Glut4/AMPK pathways of the skeletal muscle in activating glucose metabolism, thereby regulating muscle contraction through the regulation of expression of troponin I/C, CaMKII, and ATP. Our findings provide insights into the mechanism of DPHC activity in skeletal myotubes, suggesting that increased cytosolic Ca2+ levels caused by DPHC can promote glucose transport into skeletal myotubes to modulate blood glucose levels, thus indicating the potential use of DPHC in the prevention of diabetes.

Mechanism of hepatotoxicity of first-line tyrosine kinase inhibitors: Gefitinib and afatinib

AIMS

Both gefitinib and afatinib are epidermal growth factor tyrosine kinase inhibitors (EGFR-TKI) in the treatment of non-small cell lung cancer (NSCLC). It has been reported that gefitinib and afatinib could cause hepatotoxicity during the clinic treatment, therefore it is critical to investigate their hepatotoxicity systematically. In this study, zebrafish (Danio rerio) were used as model animals to compare the hepatotoxicity and their toxic mechanism.

MAIN METHODS

The zebrafish transgenic line [Tg (fabp10a: dsRed; ela3l:EGFP) was used in this study. After larvae developed at 3 days post fertilization (dpf), they were put into different concentrations of gefitinib and afatinib. At 6 dpf, the viability, liver area, fluorescence intensity, histopathology, apoptosis, transaminase reflecting liver function, the absorption of yolk sac, and the expression of relative genes were observed and analyzed respectively.

KEY FINDINGS

Both gefitinib and afatinib could induce the larvae hepatotoxicity dose-dependently. Based on the liver morphology, histopathology, apoptosis and function assessments, gefitinib showed higher toxicity, causing more serious liver damage. Both gefitinib and afatinib caused abnormal expressions of genes related to endoplasmic reticulum stress (ERS) pathway and apoptosis. For example, jnk, perk, bip, chop, ire1, bid, caspase3 and caspase9 were up-regulated, while xbp1s, grp78, bcl-2/bax, and caspase8 were down-regulated. The hepatotoxicity difference of gefitinib and afatinib might be due to the different expression level of related genes.

Anti-Obesity Natural Products Tested in Juvenile Zebrafish Obesogenic Tests and Mouse 3T3-L1 Adipogenesis Assays

(1) Background: The obesity epidemic has been drastically progressing in both children and adults worldwide. Pharmacotherapy is considered necessary for its treatment. However, many anti-obesity drugs have been withdrawn from the market due to their adverse effects. Instead, natural products (NPs) have been studied as a source for drug discovery for obesity, with the goal of limiting the adverse effects. Zebrafish are ideal model animals for in vivo testing of anti-obesity NPs, and disease models of several types of obesity have been developed. However, the evidence for zebrafish as an anti-obesity drug screening model are still limited. (2) Methods: We performed anti-adipogenic testing using the juvenile zebrafish obesogenic test (ZOT) and mouse 3T3-L1 preadipocytes using the focused NP library containing 38 NPs and compared their results. (3) Results: Seven and eleven NPs reduced lipid accumulation in zebrafish visceral fat tissues and mouse adipocytes, respectively. Of these, five NPs suppressed lipid accumulation in both zebrafish and 3T3-L1 adipocytes. We confirmed that these five NPs (globin-digested peptides, green tea extract, red pepper extract, nobiletin, and Moringa leaf powder) exerted anti-obesity effects in diet-induced obese adult zebrafish. (4) Conclusions: ZOT using juvenile fish can be a high-throughput alternative to ZOT using adult zebrafish and can be applied for in vivo screening to discover novel therapeutics for visceral obesity and potentially also other disorders.

Adult zebrafish as an in vivo drug testing model for ethanol induced acute hepatic injury

Chronic alcohol abuse is common and a leading cause of alcoholic liver disease (ALD). However, a safe and effective therapy for ALD is still elusive. In this study, we evaluated the utility of adult zebrafish as an in vivo model for rapid assessment of drug efficacy in ethanol-induced acute hepatic injury. We exposed adult zebrafish to 0.5 % ethanol for 24, 48, and 72 hours and measured serum alanine aminotransferase (ALT) activities. This treatment resulted in a significant increase in ALT levels at 48 and 72 h of ethanol treatment, compared to untreated control groups. Accompanying this, significant increases in mRNA expression of genes associated with inflammation was observed in the liver during ethanol exposure. To evaluate the effectiveness of drug testing using our zebrafish model for ethanol-induced acute hepatic injury, we investigated the protective function of nicotinamide riboside, a substrate for NAD⁺, previously shown to be protective in a rodent model of alcoholic liver disease and TES-1025, an inhibitor of α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD), that increases NAD⁺. We found that both nicotinamide riboside and TES-1025 treatment suppressed ethanol-induced serum ALT levels, post 48 h of ethanol exposure. In a similar manner, riboflavin supplementation also suppressed ethanol-induced serum ALT increase during ethanol exposure. Additionally, both nicotinamide riboside and riboflavin supplementation inhibited the upregulation of mRNA expression of genes associated with inflammation and de novo lipogenesis. In conclusion, we established an adult zebrafish model of ethanol-induced acute hepatic injury that will be valuable for cost-effective in vivo drug screening, which may in the future offer identification of novel therapeutics to mitigate hepatic injury, associated with excessive alcohol consumption.

Evaluation of the Percutaneous Absorption of Drug Molecules in Zebrafish

In recent decades, zebrafish (Danio rerio) has become a widely used vertebrate animal model for studying development and human diseases. However, studies on skin medication using zebrafish are rare. Here, we developed a novel protocol for percutaneous absorption of molecules via the zebrafish tail skin, by applying a liquid solution directly, or using a filter paper imbibed with a chemical solution (coating). Human skin is capable of absorbing felbinac and loxoprofen sodium hydrate (LSH), but not glycyrrhetinic acid (GA) and terbinafine hydrochloride (TH). To evaluate the possibility and the quality of transdermal absorption in zebrafish, we transdermally administered these four drugs to zebrafish. Pharmacokinetics showed that felbinac was present in the blood of zebrafish subjected to all administration methods. Felbinac blood concentrations peaked at 2 h and disappeared 7 h after administration. GA was not detected following transdermal administrations, but was following exposure. LSH was not found in the circulatory system after transdermal administration, but TH was. A dose-response correlation was observed for felbinac blood concentration. These findings suggest that zebrafish are capable of absorbing drug molecules through their skin. However, the present data cannot demonstrate that zebrafish is a practical model to predict human skin absorption. Further systemic studies are needed to observe the correlations in percutaneous absorption between humans and zebrafish.

Best practices for non-lethal blood sampling of fish via the caudal vasculature

Blood sampling through the caudal vasculature is a widely used technique in fish biology for investigating organismal health and physiology. In live fishes, it can provide a quick, easy and relatively non-invasive method for obtaining a blood sample (cf. cannulation and cardiac puncture). Here, a general set of recommendations are provided for optimizing the blood sampling protocol that reflects best practices in animal welfare and sample integrity. This includes selecting appropriate use of anaesthetics for blood sampling as well as restraint techniques for situations where sedation is not used. In addition, ideal sampling environments where the fish can freely ventilate and strategies for minimizing handling time are discussed. This study summarizes the techniques used for extracting blood from the caudal vasculature in live fishes, highlighting the phlebotomy itself, the timing of sampling events and acceptable blood sample volumes. This study further discuss considerations for selecting appropriate physiological metrics when sampling in the caudal region and the potential benefits that this technique provides with respect to long-term biological assessments. Although general guidelines for blood sampling are provided here, it should be recognized that contextual considerations (e.g., taxonomic diversity, legal matters, environmental constraints) may influence the approach to blood sampling. Overall, it can be concluded that when done properly, blood sampling live fishes through the caudal vasculature is quick, efficient and minimally invasive, thus promoting conditions where live release of focal animals is possible.

Exposição crônica ao cloridrato de metformina e à glibenclamida causa alterações comportamentais, glicêmicas e de mortalidade em Hemigrammus caudovittatus e Danio rerio

RESUMO Hemigrammus caudovittatus e Danio rerio foram expostos aos hipoglicemiantes orais (HOs) cloridrato de metformina a 40µg/L e 120µg/L e glibenclamida a 0,13µg/L e 0,39µg/L durante 100 dias. Foram avaliados os efeitos tóxicos dos fármacos em relação ao peso, ao comportamento animal, à glicemia e à mortalidade. H. caudovittatus expostos à menor concentração dos fármacos apresentaram aumento significativo (P<0,05) no evento Respiração Aérea. Ainda, foi observado aumento no comportamento Descansar quando os animais foram expostos à glibenclamida a 0,39µg/L. Em D. rerio expostos ao cloridrato de metformina a 120µg/L, foi observado aumento (P<0,05) no comportamento Descansar. A glibenclamida provocou redução (P<0,05) na glicemia de H. caudovittatus. Ambos os fármacos causaram efeito letal na espécie D. rerio, contudo a glibenclamida foi mais tóxica, causando 100% de mortalidade em 30 dias de exposição. Os animais que vieram a óbito apresentaram congestão nos arcos branquiais e hemorragia. Os HOs foram desenvolvidos para apresentarem efeitos fisiológicos em mamíferos, entretanto efeitos tóxicos foram encontrados nas duas espécies de peixe estudadas. Isso levanta a preocupação sobre possíveis efeitos tóxicos de HOs e sobre quais métodos serão utilizados para a sua degradação no ambiente aquático.

RNA-seq Based Transcriptome Analysis of the Anti-Obesity Effect of Green Tea Extract Using Zebrafish Obesity Models

Green tea is a popular beverage that is rich in polyphenolic compounds such as catechins. Its major content, (-)-epigallocatechin-3-gallate, has been shown to have beneficial effects on several diseases including cancer, metabolic syndrome, cardiovascular diseases, and neurodegenerative diseases. The aim of this study was to assess the anti-obesity effects and the underlying molecular mechanisms of green tea extract (GTE) using zebrafish larva and adult obesity models. We administered 100 μg/mL GTE to zebrafish larvae and performed a short-term obesogenic test. GTE significantly decreased the visceral adipose tissue volume induced by a high-fat diet. Oral administration (250 µg/g body weight/day) of GTE to adult diet-induced obese zebrafish also significantly reduced their visceral adipose tissue volume, with a reduction of plasma triglyceride and total cholesterol levels. To investigate the molecular mechanism underlying the GTE effects, we conducted RNA sequencing using liver tissues of adult zebrafish and found that GTE may ameliorate the obese phenotypes via the activation of Wnt/β-catenin and adenosine monophosphate-activated protein kinase (AMPK) pathway signaling. In addition, the comparative transcriptome analysis revealed that zebrafish and mammals may share a common molecular response to GTE. Our findings suggest that daily consumption of green tea may be beneficial for the prevention and treatment of obesity.

Therapeutic Silencing of Centromere Protein X Ameliorates Hyperglycemia in Zebrafish and Mouse Models of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is characterized by persistent hyperglycemia and is influenced by genetic and environmental factors. Optimum T2DM management involves early diagnosis and effective glucose-lowering therapies. Further research is warranted to improve our understanding of T2DM pathophysiology and reveal potential roles of genetic predisposition. We have previously developed an obesity-induced diabetic zebrafish model that shares common pathological pathways with humans and may be used to identify putative pharmacological targets of diabetes. Additionally, we have previously identified several candidate genes with altered expression in T2DM zebrafish. Here, we performed a small-scale zebrafish screening for these genes and discovered a new therapeutic target, centromere protein X (CENPX), which was further validated in a T2DM mouse model. In zebrafish, cenpx knockdown by morpholino or knockout by CRISPR/Cas9 system ameliorated overfeeding-induced hyperglycemia and upregulated insulin level. In T2DM mice, small-interfering RNA-mediated Cenpx knockdown decreased hyperglycemia and upregulated insulin synthesis in the pancreas. Gene expression analysis revealed insulin, mechanistic target of rapamycin, leptin, and insulin-like growth factor 1 pathway activation following Cenpx silencing in pancreas tissues. Thus, CENPX inhibition exerted antidiabetic effects via increased insulin expression and related pathways. Therefore, T2DM zebrafish may serve as a powerful tool in the discovery of new therapeutic gene targets.

Palmitic Acid-Enriched Diet Induces Hepatic Steatosis and Injury in Adult Zebrafish

Palmitic acid (PA) is the most abundant saturated fatty acid in fast foods and is known to induce inflammation and cellular injury in various tissues. In this study, we investigated whether a PA-enriched diet can induce hepatic steatosis and injury in adult zebrafish. The adult zebrafish exhibited increased body weight, hyperlipidemia, hyperglycemia, and steatosis and a hepatic injury phenotype after being fed with a PA-enriched diet for 6 weeks. The quantitative polymerase chain reaction analysis demonstrated that genes associated with hepatic injury were all significantly increased in the liver. Furthermore, livers from the PA-fed group showed an increased messenger RNA (mRNA) expression associated with oxidative stress and endoplasmic reticulum (ER) stress responses. We also found significant upregulation of genes involved in lipid metabolism and triacylglyceride accumulation. Ultrastructural analysis revealed mitochondrial cristae injury and a dilated ER phenotype in the PA-fed hepatocytes, which can be causes of hepatic injury. PA-enriched diet induced hepatic steatosis and injury in adult zebrafish that recapitulated typical metabolic changes and pathophysiological changes as well as increased oxidative stress and ER stress observed in patients with nonalcoholic fatty liver disease.

Purification and functional characterization of serum transferrin from Nile tilapia (Oreochromis niloticus)

Transferrin (TF), an iron-binding multifunctional protein, could participate in the iron-withholding strategy, an effective antimicrobial defense mechanism in innate immunity, and is involved in host defense against pathogenic infection. In this study, a TF homologue (OnTF) was purified from serum of Nile tilapia (Oreochromis niloticus) through a two-step affinity chromatography, and characterized its antibacterial function and the role in inflammatory response. The identification by mass spectrometry showed that peptide sequence of the purified OnTF was highly consistent with its amino acids sequence, containing two conserved iron binding lobes: N-lobe and C-lobe. The native OnTF was able to bond iron ions, and possessed capability to inhibit the growth of both bacterial pathogens (Streptococcus agalactiae and Aeromonas hydrophila) in vitro. Upon infections of S. agalactiae and A. hydrophila, the expression of OnTF protein was significantly up-regulated in vivo and in vitro. In addition, the OnTF participated in the regulation of inflammation, migration, and enhancement of phagocytosis and respiratory burst activity in head kidney macrophages/monocytes. Taken together, the results of this study indicated that OnTF is likely to involve in innate immunity to play a role in host defense against bacterial infection in Nile tilapia.

Microbiome Alteration in Type 2 Diabetes Mellitus Model of Zebrafish

Understanding the gut microbiota in metabolic disorders, including type 2 diabetes mellitus (T2DM), is now gaining importance due to its potential role in disease risk and progression. We previously established a zebrafish model of T2DM, which shows glucose intolerance with insulin resistance and responds to anti-diabetic drugs. In this study, we analysed the gut microbiota of T2DM zebrafish by deep sequencing the 16S rRNA V3-V4 hypervariable regions, and imputed a functional profile using predictive metagenomic tools. While control and T2DM zebrafish were fed with the same kind of feed, the gut microbiota in T2DM group was less diverse than that of the control. Predictive metagenomics profiling using PICRUSt revealed functional alternation of the KEGG pathways in T2DM zebrafish. Several amino acid metabolism pathways (arginine, proline, and phenylalanine) were downregulated in the T2DM group, similar to what has been previously reported in humans. In summary, we profiled the gut microbiome in T2DM zebrafish, which revealed functional similarities in gut bacterial environments between these zebrafish and T2DM affected humans. T2DM zebrafish can become an alternative model organism to study host-bacterial interactions in human obesity and related diseases.

Model-based serial blood sampling protocol for minimal mortality and better recovery in small to medium sized tilapia

Serial blood sampling involving sampling blood from the same individual at different time points is essential in time-based studies including xenobiotic toxicokinetics and biochemical studies. However, high fish mortality due to phlebotomy-induced anaemia (PIA) constrains serial blood sampling in small to medium sized fish. The aim of the study was to develop and implement a model-based serial blood sampling protocol that minimises fish mortality by regulating anaemia within levels that sustain fish survival and recovery. A model simulating the reduction in haemoglobin was developed from blood sampling data of sixteen (N=16) medium sized Oreochromis mossambicus The model was incorporated into a serial blood sampling protocol whose performance was tested on eight (N=8) fish. The protocol avoided fish mortality and the fish recovered from PIA within three weeks of the post-sampling period. Therefore, managing anaemia minimises mortality and improves the applicability of serial blood sampling in small to medium sized fish.This article has an associated First Person interview with the first author of the paper.

Novel Anti-Obesity Properties of Palmaria mollis in Zebrafish and Mouse Models

(1) Background: The red seaweed Palmaria mollis (PM), which has a bacon-like taste, is increasingly being included in Western diets. In this study, we evaluate anti-obesity effects of PM using diet-induced obese (DIO) zebrafish and mice models. (2) Methods: We fed PM-containing feed to DIO-zebrafish and mice, and evaluated the anti-obesity effects We also analyzed gene expression changes in their liver and visceral adipose tissues (VAT). (3) Results: PM ameliorated several anti-obesity traits in both animals, including dyslipidaemia, hepatic steatosis, and visceral adiposity. In liver tissues of DIO-zebrafish and mice, PM upregulated gene expressions involved in peroxisome proliferator-activated receptor alpha (PPARA) pathways, and downregulated peroxisome proliferator-activated receptor gamma (PPARG) pathways, suggesting that the lipid-lowering effect of PM might be caused by activation of beta-oxidation and inhibition of lipogenesis. In VAT, PM downregulated genes involved in early and late adipocyte differentiation in zebrafish, but not in mice. (4) Conclusions: We have demonstrated that PM can prevent hepatic steatosis and visceral adiposity for the first time. Dietary supplementation of PM as a functional food may be suitable for obesity prevention and reduction in the prevalence of obesity-related diseases.

Zebrafish as a Model for Obesity and Diabetes

Obesity and diabetes now considered global epidemics. The prevalence rates of diabetes are increasing in parallel with the rates of obesity and the strong connection between these two diseases has been coined as “diabesity.” The health risks of overweight or obesity include Type 2 diabetes mellitus (T2DM), coronary heart disease and cancer of numerous organs. Both obesity and diabetes are complex diseases that involve the interaction of genetics and environmental factors. The underlying pathogenesis of obesity and diabetes are not well understood and further research is needed for pharmacological and surgical management. Consequently, the use of animal models of obesity and/or diabetes is important for both improving the understanding of these diseases and to identify and develop effective treatments. Zebrafish is an attractive model system for studying metabolic diseases because of the functional conservation in lipid metabolism, adipose biology, pancreas structure, and glucose homeostasis. It is also suited for identification of novel targets associated with the risk and treatment of obesity and diabetes in humans. In this review, we highlight studies using zebrafish to model metabolic diseases, and discuss the advantages and disadvantages of studying pathologies associated with obesity and diabetes in zebrafish.

Novel subunit vaccine with linear array epitope protect giant grouper against nervous necrosis virus infection

Viral nervous necrosis caused by nervous necrosis virus (NNV) is one of the most severe diseases resulting in high fish mortality rates and high economic losses in the giant grouper industry. Various NNV vaccines have been evaluated, such as inactivated viruses, virus-like particles (VLPs), recombinant coat proteins, synthetic peptides of coat proteins, and DNA vaccines. However, a cheaper manufacturing process and effective protection of NNV vaccines for commercial application are yet to be established. Hence, the present study developed a novel subunit vaccine composed of a carrier protein, receptor-binding domain of Pseudomonas exotoxin A, and tandem-repeated NNV coat protein epitopes by using the structural basis of epitope prediction and the linear array epitope (LAE) technique. On the basis of the crystal structure of the NNV coat protein, the epitope was predicted from the putative target cell receptor-binding region to elicit neutralizing immune responses. The safety of the LAE vaccine was evaluated, and all vaccinated fish survived without any physiological changes. The coat protein-specific antibody titers in the vaccinated fish increased after vaccine administration and exerted NNV-neutralizing effects. The efficacy tests revealed that the relative percent survival (RPS) of LAE antigen formulated with adjuvant was above 72% and LAE vaccine was effective for preventing NNV infection in giant grouper. This study is the first to develop an NNV vaccine by using epitope repeats, which provided effective protection to giant grouper against virus infection. The LAE construct can be used as a vaccine design platform against various pathogenic diseases.

Evaluating parameter availability for physiologically based pharmacokinetic (PBPK) modeling of perfluorooctanoic acid (PFOA) in zebrafish

Physiologically based pharmacokinetic (PBPK) models are considered useful tools to describe the absorption, distribution, metabolism and excretion of xenobiotics. For accurate predictions, PBPK models require species-specific and compound-specific parameters. Zebrafish are considered an appropriate vertebrate model for investigating the toxicity of a wide variety of compounds. However, no specific mechanistic model exists for the pharmacokinetics of perfluoroalkyl acids (PFAAs) in zebrafish, despite growing concern about this class of ubiquitous environmental contaminants. The purpose of this study was to evaluate the current state of knowledge for the parameters that would be needed to construct such a model for zebrafish. We chose perfluorooctanoic acid (PFOA) as a model PFAA with greater data availability. We have updated a previous PBPK model for rainbow trout to simulate PFOA fate in zebrafish following waterborne exposure. For the first time, the model considers hepatobiliary circulation. In order to evaluate the availability of parameters to implement this model, we performed an extensive literature review to find zebrafish-specific parameters. As in previous approaches, we broadened our search to include mammalian and other fish studies when zebrafish-specific data were lacking. Based on the method used to measure or estimate parameters, or based on their species-specific origin, we scored and ranked the quality of available parameters. These scores were then used in Monte Carlo and partial rank correlation analyses to identify the most critical data gaps. The liver, where fatty acid binding proteins (FABPs) and plasma proteins are considered, represented the best model-data agreement. Lack of agreement in other tissues suggest better parameters are needed. The results of our study highlight the lack of zebrafish-specific parameters. Based on sensitivity and uncertainty analysis, parameters associated with PFAA-protein interactions and passive diffusion need further refinement to enable development of predictive models for these emerging chemicals in zebrafish.

Subchronic toxicity of Nile tilapia with different exposure routes to Microcystis aeruginosa: Histopathology, liver functions, and oxidative stress biomarkers

BACKGROUND

Toxic cyanobacterial blooms (Microcystis aeruginosa contains microcystins [MCs]) have been reported to induce clinicopathological alterations as well as different oxidative stress in aquatic biota.

AIM

Three-week subchronic exposure experiment was carried out on Nile tilapia, to determine their effects on fish behavior, tissues, liver functions, antioxidant enzymes, and lipid peroxidation.

MATERIALS AND METHODS

Fish were exposed to four main treatments; orally fed diet plus toxic cells of M. aeruginosa (containing 3500 µg/g MC-LR), immersion in 500 µg MC-LR/L, intraperitoneal injection of M. aeruginosa MC-LR with a dose of 0.1 ml of extracted toxin at a dose of 200 μg/kg bwt, and the fourth one served as a control group, then the fish were sacrificed at the end of 3^rd week of exposure.

RESULTS

The results revealed no recorded mortality with obvious behavioral changes and an enlarged liver with the congested gall bladder. Histopathology demonstrated fragmentation, hyalinization, and necrosis of the subcutaneous musculature marked fatty degeneration, and vacuolation of hepatopancreatic cells with adhesion of the secondary gill lamellae associated with severe leukocytic infiltration. Furthermore, liver functions enzymes (aspartate aminotransferase and alanine aminotransferase, and the activities of glutathione peroxidase, glutathione reductase, lipid peroxidase, and catalase enzymes) were significantly increased in all treatments starting from the 2^nd week as compared to the control levels.

CONCLUSION

In this context, the study addresses the possible toxicological impacts of toxic M. aeruginosa contain MC-LR to Nile tilapia, and the results investigated that MC-LR is toxic to Nile tilapia in different routes of exposure as well as different doses.

Development of a Novel Zebrafish Model for Type 2 Diabetes Mellitus

Obesity is a major cause of type 2 diabetes mellitus (T2DM) in mammals. We have previously established a zebrafish model of diet-induced obesity (DIO zebrafish) by overfeeding Artemia. Here we created DIO zebrafish using a different method to induce T2DM. Zebrafish were overfed a commercially available fish food using an automated feeding system. We monitored the fasting blood glucose levels in the normal-fed group (one feed/day) and overfed group (six feeds/day) over an 8-week period. The fasting blood glucose level was significantly increased in DIO zebrafish compared with that of normal-fed zebrafish. Intraperitoneal and oral glucose tolerance tests showed impaired glucose tolerance by overfeeding. Insulin production, which was determined indirectly by measuring the EGFP signal strength in overfed Tg(−1.0ins:EGFP)^sc1 zebrafish, was increased in DIO zebrafish. The anti-diabetic drugs metformin and glimepiride ameliorated hyperglycaemia in the overfed group, suggesting that this zebrafish can be used as a model of human T2DM. Finally, we conducted RNA deep sequencing and found that the gene expression profiling of liver-pancreas revealed pathways common to human T2DM. In summary, we developed a zebrafish model of T2DM that shows promise as a platform for mechanistic and therapeutic studies of diet-induced glucose intolerance and insulin resistance.

Modeling Pancreatic Endocrine Cell Adaptation and Diabetes in the Zebrafish

Glucose homeostasis is an important element of energy balance and is conserved in organisms from fruit fly to mammals. Central to the control of circulating glucose levels in vertebrates are the endocrine cells of the pancreas, particularly the insulin-producing β-cells and the glucagon producing α-cells. A feature of α- and β-cells is their plasticity, an ability to adapt, in function and number as a response to physiological and pathophysiological conditions of increased hormone demand. The molecular mechanisms underlying these adaptive responses that maintain glucose homeostasis are incompletely defined. The zebrafish is an attractive model due to the low cost, high fecundity, and amenability to genetic and compound screens, and mechanisms governing the development of the pancreatic endocrine cells are conserved between zebrafish and mammals. Post development, both β- and α-cells of zebrafish display plasticity as in mammals. Here, we summarize the studies of pancreatic endocrine cell adaptation in zebrafish. We further explore the utility of the zebrafish as a model for diabetes, a relevant topic considering the increase in diabetes in the human population.

Zebrafish Pancreas Development and Regeneration: Fishing for Diabetes Therapies

The zebrafish pancreas shares its basic organization and cell types with the mammalian pancreas. In addition, the developmental pathways that lead to the establishment of the pancreatic islets of Langherhans are generally conserved from fish to mammals. Zebrafish provides a powerful tool to probe the mechanisms controlling establishment of the pancreatic endocrine cell types from early embryonic progenitor cells, as well as the regeneration of endocrine cells after damage. This knowledge is, in turn, applicable to refining protocols to generate renewable sources of human pancreatic islet cells that are critical for regulation of blood sugar levels. Here, we review how previous and ongoing studies in zebrafish and beyond are influencing the understanding of molecular mechanisms underlying various forms of diabetes and efforts to develop cell-based approaches to cure this increasingly widespread disease.

Acute and chronic toxicity of the benzoylurea pesticide, lufenuron, in the fish, Colossoma macropomum

Lufenuron is a benzoylurea insecticide that interfere in chitin synthesis in insects. Although lufenuron is widely used in agriculture and aquaculture, rare are studies described that relates to possible toxic effects in fish. This work aimed to evaluate acute and chronic toxic effects of benzoylurea pesticide (lufenuron) on biological parameters of Colossoma macropomum (Tambaqui). In the acute test, juveniles of Tambaqui were divided into control group and five experimental groups with exposure from 0.1 to 0.9 mg/L of lufenuron for 96 h. Animals were also submitted to chronic toxicity test for four months in concentrations of 0.1 and 0.3 mg/L of lufenuron, the concentration used in the treatment of ectoparasites in fish and 50% of LC50 96 h, respectively. The presence of hemorrhages was observed in eyes, fins and operculum of fish exposed to 0.7 and 0.9 mg/L of lufenuron. Histological analysis showed changes in the morphology of fish gills submitted to acute toxicity test, as lamellar aneurysm and blood congestion inside lamellae. Lufenuron promoted damage in fish retina as in ability to respond to stimuli in photoreceptors and in ON-bipolar cells in acute test. In chronic test, blood glucose analysis and morphometric parameters showed no significant differences (p > 0.05). In general, Tambaqui exhibited behaviors associated with stress when exposed to lufenuron. Thus, lufenuron showed several toxic effects in relation to biological parameters in Tambaqui. This concerns about the use and discard of lufenuron, and indicates the requirement of environmental actions to prevent potential contamination of aquatic biota.

Leptin signaling regulates glucose homeostasis, but not adipostasis, in the zebrafish

Leptin is the primary adipostatic factor in mammals. Produced largely by adipocytes in proportion to total adipose mass, the hormone informs the brain regarding total energy stored as triglycerides in fat cells. The hormone acts on multiple circuits in the brain to regulate food intake, autonomic outflow, and endocrine function to maintain energy balance. In addition to regulating adipose mass, mammalian leptin also plays a role in the regulation of glucose homeostasis and as a gating factor in reproductive competence. Leptin-deficient mice and people exhibit early onset profound hyperphagia and obesity, diabetes, and infertility. Although leptin and the leptin receptor are found in fish, the hormone is not expressed in adipose tissue, but is found in liver and other tissues. Here, we show that adult zebrafish lacking a functional leptin receptor do not exhibit hyperphagia or increased adiposity, and exhibit normal fertility. However, leptin receptor-deficient larvae have increased numbers of β-cells and increased levels of insulin mRNA. Furthermore, larval zebrafish have been shown to exhibit β-cell hyperplasia in response to high fat feeding or peripheral insulin resistance, and we show here that leptin receptor is required for this response. Adult zebrafish also have increased levels of insulin mRNA and other alterations in glucose homeostasis. Thus, a role for leptin in the regulation of β-cell mass and glucose homeostasis appears to be conserved across vertebrates, whereas its role as an adipostatic factor is likely to be a secondary role acquired during the evolution of mammals.

Zebrafish as model organisms for studying drug-induced liver injury

Drug-induced liver injury (DILI) is a major challenge in clinical medicine and drug development. New models are needed for predicting which potential therapeutic compounds will cause DILI in humans, and new markers and mediators of DILI still need to be identified. This review highlights the strengths and weaknesses of using zebrafish as a high-throughput in vivo model for studying DILI. Although the zebrafish liver architecture is different from that of the mammalian liver, the main physiological processes remain similar. Zebrafish metabolize drugs using similar pathways to those in humans; they possess a wide range of cytochrome P450 enzymes that enable metabolic reactions including hydroxylation, conjugation, oxidation, demethylation and de-ethylation. Following exposure to a range of hepatotoxic drugs, the zebrafish liver develops histological patterns of injury comparable to those of mammalian liver, and biomarkers for liver injury can be quantified in the zebrafish circulation. The zebrafish immune system is similar to that of mammals, but the zebrafish inflammatory response to DILI is not yet defined. In order to quantify DILI in zebrafish, a wide variety of methods can be used, including visual assessment, quantification of serum enzymes and experimental serum biomarkers and scoring of histopathology. With further development, the zebrafish may be a model that complements rodents and may have value for the discovery of new disease pathways and translational biomarkers.

Repeated Blood Collection for Blood Tests in Adult Zebrafish

Repeated blood collection is one of the most common techniques performed on laboratory animals. However, a non-lethal protocol for blood collection from zebrafish has not been established. The previous methods for blood collection from zebrafish are lethal, such as lateral incision, decapitation and tail ablation. Thus we have developed a novel "repeated" blood collection method, and present here a detailed protocol outlining this procedure. This method is minimally invasive and results in a very low mortality rate (2.3%) for zebrafish, thus enabling repeated blood sampling from the same individual. The maximum volume of blood sampling is dependent on body weight of the fish. The volume for repeated blood sampling at intervals should be ≤0.4% of body weight every week or ≤1% every 2 weeks, which were evaluated by measurements of blood hemoglobin. Additionally, hemoglobin, fasting blood glucose, plasma triacylglycerol (TG) and total cholesterol levels in male and female adult zebrafish were measured. We also applied this method to investigate the dysregulation of glucose metabolism in diet-induced obesity. This blood collection method will allow many applications, including glucose and lipid metabolism and hematological studies, which will increase the use of zebrafish as a human disease model organism.