Host-pathogen interactions made transparent with the zebrafish model

Zebrafish as an effective model for evaluating phage therapy in bacterial infections: a promising strategy against human pathogens

The escalating prevalence of antibiotic-resistant bacterial infections necessitates urgent alternative therapeutic strategies. Phage therapy, which employs bacteriophages to specifically target pathogenic bacteria, emerges as a promising solution. This review examines the efficacy of phage therapy in zebrafish models, both embryos and adults, which are proven and reliable for simulating human infectious diseases. We synthesize findings from recent studies that utilized these models to assess phage treatments against various bacterial pathogens, including Enterococcus faecalis, Pseudomonas aeruginosa, Mycobacterium abscessus, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Escherichia coli. Methods of phage administration, such as circulation injection and bath immersion, are detailed alongside evaluations of survival rates and bacterial load reductions. Notably, combination therapies of phages with antibiotics show enhanced efficacy, as evidenced by improved survival rates and synergistic effects in reducing bacterial loads. We also discuss the transition from zebrafish embryos to adult models, emphasizing the increased complexity of immune responses. This review highlights the valuable contribution of the zebrafish model to advancing phage therapy research, particularly in the face of rising antibiotic resistance and the urgent need for alternative treatments.

A new protocol for multispecies bacterial infections in zebrafish and their monitoring through automated image analysis

The zebrafish Danio rerio has become a popular model host to explore disease pathology caused by infectious agents. A main advantage is its transparency at an early age, which enables live imaging of infection dynamics. While multispecies infections are common in patients, the zebrafish model is rarely used to study them, although the model would be ideal for investigating pathogen-pathogen and pathogen-host interactions. This may be due to the absence of an established multispecies infection protocol for a defined organ and the lack of suitable image analysis pipelines for automated image processing. To address these issues, we developed a protocol for establishing and tracking single and multispecies bacterial infections in the inner ear structure (otic vesicle) of the zebrafish by imaging. Subsequently, we generated an image analysis pipeline that involved deep learning for the automated segmentation of the otic vesicle, and scripts for quantifying pathogen frequencies through fluorescence intensity measures. We used Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae, three of the difficult-to-treat ESKAPE pathogens, to show that our infection protocol and image analysis pipeline work both for single pathogens and pairwise pathogen combinations. Thus, our protocols provide a comprehensive toolbox for studying single and multispecies infections in real-time in zebrafish.

Identification of kinase inhibitors as potential host-directed therapies for intracellular bacteria

The emergence of antimicrobial resistance has created an urgent need for alternative treatments against bacterial pathogens. Here, we investigated kinase inhibitors as potential host-directed therapies (HDTs) against intracellular bacteria, specifically Salmonella Typhimurium (Stm) and Mycobacterium tuberculosis (Mtb). We screened 827 ATP-competitive kinase inhibitors with known target profiles from two Published Kinase Inhibitor Sets (PKIS1 and PKIS2) using intracellular infection models for Stm and Mtb, based on human cell lines and primary macrophages. Additionally, the in vivo safety and efficacy of the compounds were assessed using zebrafish embryo infection models. Our screen identified 11 hit compounds for Stm and 17 hit compounds for Mtb that were effective against intracellular bacteria and non-toxic for host cells. Further experiments were conducted to prioritize Stm hit compounds that were able to clear the intracellular infection in primary human macrophages. From these, two structurally related Stm hit compounds, GSK1379738A and GSK1379760A, exhibited significant activity against Stm in infected zebrafish embryos. In addition, we identified compounds that were active against intracellular Mtb, including morpholino-imidazo/triazolo-pyrimidinones that target PIK3CB, as well as 2-aminobenzimidazoles targeting ABL1. Overall, this study provided insights into kinase targets acting at the host-pathogen interface and identified several kinase inhibitors as potential HDTs.

Predatory Bacteria in the Treatment of Infectious Diseases and Beyond

Antimicrobial resistance (AMR) is an increasing problem worldwide, with significant associated morbidity and mortality. Given the slow production of new antimicrobials, non-antimicrobial methods for treating infections with significant AMR are required. This review examines the potential of predatory bacteria to combat infectious diseases, particularly those caused by pathogens with AMR. Predatory bacteria already have well-known applications beyond medicine, such as in the food industry, biocontrol, and wastewater treatment. Regarding their potential for use in treating infections, several in vitro studies have shown their potential in eliminating various pathogens, including those resistant to multiple antibiotics, and they also suggest minimal immune stimulation and cytotoxicity by predatory bacteria. In vivo animal studies have demonstrated safety and efficacy in reducing bacterial burden in various infection models. However, results can be inconsistent, suggesting dependence on factors like the animal model and the infecting bacteria. Until now, no clinical study in humans exists, but as experience with predatory bacteria grows, future studies including clinical studies in humans could be designed to evaluate their efficacy and safety in humans, thus leading to the potential for approval of a novel method for treating infectious diseases by bacteria.

A review of cumulative toxic effects of environmental endocrine disruptors on the zebrafish immune system: Characterization methods, toxic effects and mechanisms

Environmental endocrine disrupting chemicals (EDCs), are a type of exogenous organic pollutants, are ubiquitous in natural aquatic environments. Currently, in addition to neurological, endocrine, developmental and reproductive toxicity, ecotoxicology studies on immunotoxicity are receiving increasing attention. In this review, the composition of immune system of zebrafish, the common indicators of immunotoxicity, the immunotoxicity of EDCs and their molecular mechanism were summarized. We reviewed the immunotoxicity of EDCs on zebrafish mainly in terms of immune organs, immunocytes, immune molecules and immune functions, meanwhile, the possible molecular mechanisms driving these effects were elucidated in terms of endocrine disruption, dysregulation of signaling pathways, and oxidative damage. Hopefully, this review will provide a reference for further investigation of the immunotoxicity of EDCs.

Transcriptomic changes in the microsporidia proliferation and host responses in congenitally infected embryos and larvae

Congenital infection caused by vertical transmission of microsporidia N. bombycis can result in severe economic losses in the silkworm-rearing industry. Whole-transcriptome analyses have revealed non-coding RNAs and their regulatory networks in N. bombycis infected embryos and larvae. However, transcriptomic changes in the microsporidia proliferation and host responses in congenitally infected embryos and larvae remains unclear. Here, we simultaneously compared the transcriptomes of N. bombycis and its host B. mori embryos of 5-day and larvae of 1-, 5- and 10-day during congenital infection. For the transcriptome of N. bombycis, a comparison of parasite expression patterns between congenital-infected embryos and larva showed most genes related to parasite central carbon metabolism were down-regulated in larvae during infection, whereas the majority of genes involved in parasite proliferation and growth were up-regulated. Interestingly, a large number of distinct or shared differentially expressed genes (DEGs) were revealed by the Venn diagram and heat map, many of them were connected to infection related factors such as Ricin B lectin, spore wall protein, polar tube protein, and polysaccharide deacetylase. For the transcriptome of B. mori infected with N. bombycis, beyond numerous DEGs related to DNA replication and repair, mRNA surveillance pathway, RNA transport, protein biosynthesis, and proteolysis, with the progression of infection, a large number of DEGs related to immune and infection pathways, including phagocytosis, apoptosis, TNF, Toll-like receptor, NF-kappa B, Fc epsilon RI, and some diseases, were successively identified. In contrast, most genes associated with the insulin signaling pathway, 2-oxacarboxylic acid metabolism, amino acid biosynthesis, and lipid metabolisms were up-regulated in larvae compared to those in embryos. Furthermore, dozens of distinct and three shared DEGs that were involved in the epigenetic regulations, such as polycomb, histone-lysine-specific demethylases, and histone-lysine-N-methyltransferases, were identified via the Venn diagram and heat maps. Notably, many DEGs of host and parasite associated with lipid-related metabolisms were verified by RT-qPCR. Taken together, simultaneous transcriptomic analyses of both host and parasite genes lead to a better understanding of changes in the microsporidia proliferation and host responses in embryos and larvae in N. bombycis congenital infection.

Antigen identification strategies and preclinical evaluation models for advancing tuberculosis vaccine development

In its myriad devastating forms, Tuberculosis (TB) has existed for centuries, and humanity is still affected by it. Mycobacterium tuberculosis (M. tuberculosis), the causative agent of TB, was the foremost killer among infectious agents until the COVID-19 pandemic. One of the key healthcare strategies available to reduce the risk of TB is immunization with bacilli Calmette-Guerin (BCG). Although BCG has been widely used to protect against TB, reports show that BCG confers highly variable efficacy (0-80%) against adult pulmonary TB. Unwavering efforts have been made over the past 20 years to develop and evaluate new TB vaccine candidates. The failure of conventional preclinical animal models to fully recapitulate human response to TB, as also seen for the failure of MVA85A in clinical trials, signifies the need to develop better preclinical models for TB vaccine evaluation. In the present review article, we outline various approaches used to identify protective mycobacterial antigens and recent advancements in preclinical models for assessing the efficacy of candidate TB vaccines.

Evaluating the In Vivo Virulence of Environmental Pseudomonas aeruginosa Using Microinjection Model of Zebrafish (Danio rerio)

(1) Background: Microinjection of zebrafish (Danio rerio) embryos offers a promising model for studying the virulence and potential environmental risks associated with Pseudomonas aeruginosa. (2) Methods: This work aimed to develop a P. aeruginosa infection model using two parallel exposition pathways on zebrafish larvae with microinjection into the yolk and the perivitelline space to simultaneously detect the invasive and cytotoxic features of the examined strains. The microinjection infection model was validated with 15 environmental and clinical strains of P. aeruginosa of various origins, antibiotic resistance profiles, genotypes and phenotypes: both exposition pathways were optimized with a series of bacterial dilutions, different drop sizes (injection volumes) and incubation periods. Besides mortality, sublethal symptoms of the treated embryos were detected and analyzed. (3) Results: According to the statistical evaluation of our results, the optimal parameters (dilution, drop size and incubation period) were determined. (4) Conclusions: The tested zebrafish embryo microinjection infection model is now ready for use to determine the in vivo virulence and ecological risk of environmental P. aeruginosa.

A novel DSP zebrafish model reveals training- and drug-induced modulation of arrhythmogenic cardiomyopathy phenotypes

Arrhythmogenic cardiomyopathy (AC) is an inherited disorder characterized by progressive loss of the ventricular myocardium causing life-threatening ventricular arrhythmias, syncope and sudden cardiac death in young and athletes. About 40% of AC cases carry one or more mutations in genes encoding for desmosomal proteins, including Desmoplakin (Dsp). We present here the first stable Dsp knock-out (KO) zebrafish line able to model cardiac alterations and cell signalling dysregulation, characteristic of the AC disease, on which environmental factors and candidate drugs can be tested. Our stable Dsp knock-out (KO) zebrafish line was characterized by cardiac alterations, oedema and bradycardia at larval stages. Histological analysis of mutated adult hearts showed reduced contractile structures and abnormal shape of the ventricle, with thinning of the myocardial layer, vessels dilation and presence of adipocytes within the myocardium. Moreover, TEM analysis revealed "pale", disorganized and delocalized desmosomes. Intensive physical training protocol caused a global worsening of the cardiac phenotype, accelerating the progression of the disease. Of note, we detected a decrease of Wnt/β-catenin signalling, recently associated with AC pathogenesis, as well as Hippo/YAP-TAZ and TGF-β pathway dysregulation. Pharmacological treatment of mutated larvae with SB216763, a Wnt/β-catenin agonist, rescued pathway expression and cardiac abnormalities, stabilizing the heart rhythm. Overall, our Dsp KO zebrafish line recapitulates many AC features observed in human patients, pointing at zebrafish as a suitable system for in vivo analysis of environmental modulators, such as the physical exercise, and the screening of pathway-targeted drugs, especially related to the Wnt/β-catenin signalling cascade.

Immunotoxicity and transcriptome analysis of zebrafish embryos exposure to Nitazoxanide

Nitazoxanide (NTZ) is a broad-spectrum immunomodulatory drug, and little information is about the immunotoxicity of aquatic organisms induced by NTZ. In the present study, reduced body length and decreased yolk sac absorption in the NTZ-treated group were observed. Meanwhile, the number of innate immune cells and adaptive immune cells was substantially reduced upon NTZ exposure, and the migration and retention of macrophages and neutrophils in the injured area were inhibited. Following NTZ stimulation, oxidative stress levels in the zebrafish increased obviously. Mechanistically, RNA-seq, a high-throughput method, was performed to analyze the global expression of differentially expressed genes (DEGs) in zebrafish embryos treated with NTZ. 531 DEGs were identified by comparative transcriptome analysis, including 121 up-regulated and 420 down-regulated genes in zebrafish embryos after NTZ exposure. The transcriptome sequences were further subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology (GO) and analysis, showing phototransduction and metabolic pathway, respectively, and were most enriched. In addition, some immune-related genes were inhibited after NTZ exposure. RNA-seq results confirmed by qRT-PCR were used to verify the expression of the 6 selected genes. The other immune-related genes such as two pro-inflammatory cytokines (IL-1β, tnfα) and two chemokines (CXCL8b.3, CXCL-c1c) were further confirmed and were differentially regulated after NTZ exposure. In summary, NTZ exposure could lead to immunotoxicity and increased ROS in zebrafish embryos, this study provides valuable information for future elucidating the molecular mechanism of exogenous stimuli-induced immunotoxicity in aquatic ecosystems.

Teleost leukocyte immune-type receptors

Leukocyte immune-type receptors (LITRs) are a large family of teleost immunoregulatory receptor-types belonging to the immunoglobulin superfamily. These immune genes are phylogenetically and syntenically related to Fc receptor-like protein genes (fcrls) present in other vertebrates, including amphibians, birds, mice, and man. In vitro-based functional analyses of LITRs, using transfection approaches, have shown that LITRs have diverse immunoregulatory potentials including the activation and inhibition of several innate immune effector responses such as cell-mediated killing responses, degranulation, cytokine secretion, and phagocytosis. The purpose of this mini review is to provide an overview of fish LITR-mediated immunoregulatory potentials obtained from various teleost model systems, including channel catfish, zebrafish, and goldfish. We will also describe preliminary characterization of a new goldish LITR-specific polyclonal antibody (pAb) and discuss the significance of this tool for further investigation of the functions of fish LITRs.

In vitro and ex vivo proteomics of Mycobacterium marinum biofilms and the development of biofilm-binding synthetic nanobodies

The antibiotic-tolerant biofilms present in tuberculous granulomas add an additional layer of complexity when treating mycobacterial infections, including tuberculosis (TB). For a more efficient treatment of TB, the biofilm forms of mycobacteria warrant specific attention. Here, we used Mycobacterium marinum (Mmr) as a biofilm-forming model to identify the abundant proteins covering the biofilm surface. We used biotinylation/streptavidin-based proteomics on the proteins exposed at the Mmr biofilm matrices in vitro to identify 448 proteins and ex vivo proteomics to detect 91 Mmr proteins from the mycobacterial granulomas isolated from adult zebrafish. In vitro and ex vivo proteomics data are available via ProteomeXchange with identifier PXD033425 and PXD039416, respectively. Data comparisons pinpointed the molecular chaperone GroEL2 as the most abundant Mmr protein within the in vitro and ex vivo proteomes, while its paralog, GroEL1, with a known role in biofilm formation, was detected with slightly lower intensity values. To validate the surface exposure of these targets, we created in-house synthetic nanobodies (sybodies) against the two chaperones and identified sybodies that bind the mycobacterial biofilms in vitro and those present in ex vivo granulomas. Taken together, the present study reports a proof-of-concept showing that surface proteomics in vitro and ex vivo proteomics combined are a valuable strategy to identify surface-exposed proteins on the mycobacterial biofilm. Biofilm-surface-binding nanobodies could be eventually used as homing agents to deliver biofilm-targeting treatments to the sites of persistent biofilm infection.

Π-Π interactions stabilize PeptoMicelle-based formulations of Pretomanid derivatives leading to promising therapy against tuberculosis in zebrafish and mouse models

Tuberculosis is the deadliest bacterial disease globally, threatening the lives of millions every year. New antibiotic therapies that can shorten the duration of treatment, improve cure rates, and impede the development of drug resistance are desperately needed. Here, we used polymeric micelles to encapsulate four second-generation derivatives of the antitubercular drug pretomanid that had previously displayed much better in vivo activity against Mycobacterium tuberculosis than pretomanid itself. Because these compounds were relatively hydrophobic and had limited bioavailability, we expected that their micellar formulations would overcome these limitations, reduce toxicities, and improve therapeutic outcomes. The polymeric micelles were based on polypept(o)ides (PeptoMicelles) and were stabilized in their hydrophobic core by π-π interactions, allowing the efficient encapsulation of aromatic pretomanid derivatives. The stability of these π-π-stabilized PeptoMicelles was demonstrated in water, blood plasma, and lung surfactant by fluorescence cross-correlation spectroscopy and was further supported by prolonged circulation times of several days in the vasculature of zebrafish larvae. The most efficacious PeptoMicelle formulation tested in the zebrafish larvae infection model almost completely eradicated the bacteria at non-toxic doses. This lead formulation was further assessed against Mycobacterium tuberculosis in the susceptible C3HeB/FeJ mouse model, which develops human-like necrotic granulomas. Following intravenous administration, the drug-loaded PeptoMicelles significantly reduced bacterial burden and inflammatory responses in the lungs and spleens of infected mice.

Molecular Actors of Inflammation and Their Signaling Pathways: Mechanistic Insights from Zebrafish

Inflammation is a hallmark of the physiological response to aggressions. It is orchestrated by a plethora of molecules that detect the danger, signal intracellularly, and activate immune mechanisms to fight the threat. Understanding these processes at a level that allows to modulate their fate in a pathological context strongly relies on in vivo studies, as these can capture the complexity of the whole process and integrate the intricate interplay between the cellular and molecular actors of inflammation. Over the years, zebrafish has proven to be a well-recognized model to study immune responses linked to human physiopathology. We here provide a systematic review of the molecular effectors of inflammation known in this vertebrate and recapitulate their modes of action, as inferred from sterile or infection-based inflammatory models. We present a comprehensive analysis of their sequence, expression, and tissue distribution and summarize the tools that have been developed to study their function. We further highlight how these tools helped gain insights into the mechanisms of immune cell activation, induction, or resolution of inflammation, by uncovering downstream receptors and signaling pathways. These progresses pave the way for more refined models of inflammation, mimicking human diseases and enabling drug development using zebrafish models.

Specificity of the innate immune responses to different classes of non-tuberculous mycobacteria

Mycobacterium avium is the most common nontuberculous mycobacterium (NTM) species causing infectious disease. Here, we characterized a M. avium infection model in zebrafish larvae, and compared it to M. marinum infection, a model of tuberculosis. M. avium bacteria are efficiently phagocytosed and frequently induce granuloma-like structures in zebrafish larvae. Although macrophages can respond to both mycobacterial infections, their migration speed is faster in infections caused by M. marinum. Tlr2 is conservatively involved in most aspects of the defense against both mycobacterial infections. However, Tlr2 has a function in the migration speed of macrophages and neutrophils to infection sites with M. marinum that is not observed with M. avium. Using RNAseq analysis, we found a distinct transcriptome response in cytokine-cytokine receptor interaction for M. avium and M. marinum infection. In addition, we found differences in gene expression in metabolic pathways, phagosome formation, matrix remodeling, and apoptosis in response to these mycobacterial infections. In conclusion, we characterized a new M. avium infection model in zebrafish that can be further used in studying pathological mechanisms for NTM-caused diseases.

Localized Infections with P. aeruginosa Strains Defective in Zinc Uptake Reveal That Zebrafish Embryos Recapitulate Nutritional Immunity Responses of Higher Eukaryotes

The innate immune responses of mammals to microbial infections include strategies based on manipulating the local concentration of metals such as iron (Fe) and zinc (Zn), commonly described as nutritional immunity. To evaluate whether these strategies are also present in zebrafish embryos, we have conducted a series of heart cavity-localized infection experiments with Pseudomonas aeruginosa strains characterized by a different ability to acquire Zn. We have found that, 48 h after infection, the bacterial strains lacking critical components of the Zn importers ZnuABC and ZrmABCD have a reduced colonization capacity compared to the wild-type strain. This observation, together with the finding of a high level of expression of Zur-regulated genes, suggests the existence of antimicrobial mechanisms based on Zn sequestration. However, we have observed that strains lacking such Zn importers have a selective advantage over the wild-type strain in the early stages of infection. Analysis of the expression of the gene that encodes for a Zn efflux pump has revealed that at short times after infection, P. aeruginosa is exposed to high concentrations of Zn. At the same time, zebrafish respond to the infection by activating the expression of the Zn transporters Slc30a1 and Slc30a4, whose mammalian homologs mediate a redistribution of Zn in phagocytes aimed at intoxicating bacteria with a metal excess. These observations indicate that teleosts share similar nutritional immunity mechanisms with higher vertebrates, and confirm the usefulness of the zebrafish model for studying host-pathogen interactions.

Investigating Potential Cardiovascular Toxicity of Two Anti-Leukemia Drugs of Asciminib and Ponatinib in Zebrafish Embryos

BCR-ABL, a fusion protein kinase, is a druggable target exclusively expressed in patients with chronic myeloid leukemia (CML). Several anti-leukemia medicines targeting this protein have been developed in recent years. However, therapeutic options are limited for CML patients bearing multiple BCR-ABL1 mutations. Ponatinib (PON), a potent tyrosinase inhibitor, was one of the approved drugs for managing BCR-ABL1 T315I mutant disease. However, treatment of patients with PON reported severe side effects related to cardiovascular events. Asciminib (ASC) was the first allosteric inhibitor approved to target the myristoyl pocket of BCR-ABL protein to inhibit protein activity. The different mechanism of inhibition opens the possibility of co-exposure with both medicines. Reports on cardiovascular side effects due to the combination use of PON + ASC in pre-clinical and clinical studies are minimal. Thus, this study aimed to observe the potential cardiovascular-related side effect after co-exposure to ASC and PON using zebrafish as an animal model. In this study, zebrafish were acutely exposed to both compounds. The cardiovascular physiology parameters and gene expression related to cardiovascular development were evaluated. We demonstrate that combining ASC with PON at no observed effect concentration (NOEC) did not cause any significant change in the cardiac performance parameter in zebrafish. However, a significant increase in nkx2.5 expression level and a substantial decrease in blood flow velocity were recorded, suggesting that combining these compounds at NOEC can cause mild cardiovascular-related side effects.

Zebrafish facilitates drug screening: potential of 3-deoxy-andrographoside from Chuanxinlian ) as an anti-inflammatory agent

OBJECTIVE

To systematically evaluate the anti-inflammatory potential of diterpene lactones from Chuanxinlian () (AP).

METHODS

We firstly adopted zebrafish, a novel and ideal animal model for high-throughput drug screening, to investigate the anti-inflammatory activities of 17 diterpene lactones isolated from AP.

RESULTS

The results showed that most of diterpene lactones displayed significant anti-inflammatory effects in lipopolysaccharide microinjection-, copper sulfate exposure- or tail transection-induced zebrafish inflammation models. Moreover, diterpene lactone 3-deoxy-andrographoside (AP-5) was firstly found to attenuate inflammatory responses, which was closely associated with the myeloid differentiation primary response 88/nuclear factor-kappa B and signal transducer and activator of transcription 3 pathways.

CONCLUSION

Our research sheds light on the inestimable roles of zebrafish in high-throughput drug screening, elucidates the potent inhibitory effects of diterpene lactones against inflammation and indicates that AP-5 may serve as a potential alternative agent for the treatment of inflammatory diseases.

Negative Regulator Nlrc3-like Maintain the Balanced Innate Immune Response During Mycobacterial Infection in Zebrafish

The NOD-like receptors (NLRs) have been shown to be involved in infection and autoinflammatory disease. Previously, we identified a zebrafish NLR, nlrc3-like, required for macrophage homeostasis in the brain under physiological conditions. Here, we found that a deficiency of nlrc3-like leads to decreased bacterial burden at a very early stage of Mycobacterium marinum infection, along with increased production of pro-inflammatory cytokines, such as il-1β and tnf-α. Interestingly, myeloid-lineage specific overexpression of nlrc3-like achieved the opposite effects, suggesting that the impact of nlrc3-like on the host anti-mycobacterial response is mainly due to its expression in the innate immune system. Fluorescence-activated cell sorting (FACS) and subsequent gene expression analysis demonstrated that inflammasome activation-related genes were upregulated in the infected macrophages of nlrc3-like deficient embryos. By disrupting asc, encoding apoptosis-associated speck-like protein containing a CARD, a key component for inflammasome activation, the bacterial burden increased in asc and nlrc3-like double deficient embryos compared with nlrc3-like single deficient embryos, implying the involvement of inflammasome activation in infection control. We also found extensive neutrophil infiltration in the nlrc3-like deficient larvae during infection, which was associated with comparable bacterial burden but increased tissue damage and death at a later stage that could be alleviated by administration of dexamethasone. Our findings uncovered an important role of nlrc3-like in the negative regulation of macrophage inflammasome activation and neutrophil infiltration during mycobacterial infection. This highlights the importance of a balanced innate immune response during mycobacterial infection and provides a potential molecular basis to explain how anti-inflammatory drugs can improve treatment outcomes in TB patients whose infection is accompanied by a hyperinflammatory response.

Assessment of 2-Pentadecyl-2-oxazoline Role on Lipopolysaccharide-Induced Inflammation on Early Stage Development of Zebrafish (Danio rerio)

Lipopolysaccharide (LPS), or bacterial endotoxin, is an important virulence factor in several human and animal pathologies. Oxazoline of Palmitoylethanolamide (PEAOXA) has shown strong anti-inflammatory activity in several animal models. LPS was applied for 24 h to zebrafish embryos to induce inflammation, and then the anti-inflammatory action of PEAOXA was evaluated for the first time in the zebrafish model (Danio rerio). Different concentrations of PEAOXA were tested for toxicity on zebrafish embryonic development; only the highest concentration of 30 mg/L showed toxic effects. Quantitative RT-PCR was applied to detect Tumor necrosis factor-α, Interleukin 1β, 6, and 8, and members of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB). Exposure to LPS induced an increase in pro-inflammatory cytokines (tumor necrosis factor and interleukin 1, 6, and 8) in both gene and protein expression, as well as an increase of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) and the nuclear factor kappa light polypeptide enhancer in B-cells inhibitor (IκBα) gene expression. Furthermore, acute LPS exposure also induced an increase in tryptase release, related to mast cell activity, and in the production of apoptosis-related proteins (caspase 3, bax, and bcl-2). Treatment with PEAOXA 10 mg/L significantly counteracts LPS-induced inflammation in terms of cytokine expression and decreases tryptase release and the apoptosis pathway.

Host-directed therapies for tuberculosis: quantitative systems pharmacology approaches

Host-directed therapies (HDTs) that modulate host-pathogen interactions offer an innovative strategy to combat Mycobacterium tuberculosis (Mtb) infections. When combined with tuberculosis (TB) antibiotics, HDTs could contribute to improving treatment outcomes, reducing treatment duration, and preventing resistance development. Translation of the interplay of host-pathogen interactions leveraged by HDTs towards therapeutic outcomes in patients is challenging. Quantitative understanding of the multifaceted nature of the host-pathogen interactions is vital to rationally design HDT strategies. Here, we (i) provide an overview of key Mtb host-pathogen interactions as basis for HDT strategies; and (ii) discuss the components and utility of quantitative systems pharmacology (QSP) models to inform HDT strategies. QSP models can be used to identify and optimize treatment targets, to facilitate preclinical to human translation, and to design combination treatment strategies.

A fresh look at mycobacterial pathogenicity with the zebrafish host model

The zebrafish has earned its place among animal models to study tuberculosis and other infections caused by pathogenic mycobacteria. This model host is especially useful to study the role of granulomas, the inflammatory lesions characteristic of mycobacterial disease. The optically transparent zebrafish larvae provide a window on the initial stages of granuloma development in the context of innate immunity. Application of fluorescent dyes and transgenic markers enabled real-time visualization of how innate immune mechanisms, such as autophagy and inflammasomes, are activated in infected macrophages and how propagating calcium signals drive communication between macrophages during granuloma formation. A combination of imaging, genetic, and chemical approaches has revealed that the interplay between macrophages and mycobacteria is the main driver of tissue dissemination and granuloma development, while neutrophils have a protective function in early granulomas. Different chemokine signaling axes, conserved between humans and zebrafish, have been shown to recruit macrophages permissive to mycobacterial growth, control their microbicidal capacity, drive their spreading and aggregation, and mediate granuloma vascularization. Finally, zebrafish larvae are now exploited to explore cell death processes, emerging as crucial factors in granuloma expansion. In this review, we discuss recent advances in the understanding of mycobacterial pathogenesis contributed by zebrafish models.

The Proapoptotic Gene Bad Regulates Brain Development via p53-Mediated Stress Signals in Zebrafish

Studies have shown that the BH3-only domain Bad regulates brain development via the control of programmed cell death (PCD), but very few studies have addressed its effect on the molecular signaling of brain development in the system. In this work, we examined the novel role of zebrafish Bad in initial programmed cell death for brain morphogenesis through the priming of p53-mediated stress signaling. In a biological function study on the knockdown of Bad by morpholino oligonucleotides, at 24 h post-fertilization (hpf) Bad defects induced abnormal hindbrain development, as determined in a tissue section by means of HE staining which traced the damaged hindbrain. Then, genome-wide approaches for monitoring either the upregulation of apoptotic-related genes (11.8%) or the downregulation of brain development-related genes (29%) at the 24 hpf stage were implemented. The p53/caspase-8-mediated apoptotic death pathway was strongly involved, with the pathway being strongly reversed in a p53 mutant (p53^M214K) line during Bad knockdown. Furthermore, we propose the involvement of a p53-mediated stress signal which is correlated with regulating Bad loss-mediated brain defects. We found that some major genes in brain development, such as crybb1, pva1b5, irx4a, pax7a, and fabp7a, were dramatically restored in the p53^M214K line, and brain development recovered to return movement behavior to normal. Our findings suggest that Bad is required for (PCD) control, exerting a p53 stress signal on caspase-8/tBid-mediated death signaling and brain development-related gene regulation.

Characterization of a member of the CEACAM protein family as a novel marker of proton pump-rich ionocytes on the zebrafish epidermis

In humans, several members of the CEACAM receptor family have been shown to interact with intestinal pathogens in an inflammatory context. While CEACAMs have long been thought to be only present in mammals, recent studies have identified ceacam genes in other vertebrates, including teleosts. The function of these related genes remains however largely unknown. To gain insight into the function of CEACAM proteins in fish, we undertook the study of a putative member of the family, CEACAMz1, identified in Danio rerio. Sequence analysis of the ceacamz1 gene product predicted a GPI-anchored extracellular protein containing eleven immunoglobulin domains but revealed no evident orthology with human CEACAMs. Using a combination of RT-PCR analyses and in situ hybridization experiments, as well as a fluorescent reporter line, we showed that CEACAMz1 is first expressed in discrete cells on the ventral skin of zebrafish larvae and later on in the developing gills. This distribution remains constant until juvenile stage is reached, at which point CEACAMz1 is almost exclusively expressed in gills. We further observed that at late larval stages, CEACAMz1-expressing cells mostly localize on the afferent side of the branchial filaments and possibly in the inter-lamellar space. Using immunolabelling and 3D-reconstructions, we showed that CEACAMz1 is expressed in cells from the uppermost layer of skin epidermis. These cells are embedded within the keratinocytes pavement and we unambiguously identified them as proton-pump rich ionocytes (HR cells). As the expression of ceacamz1 is turned on concomitantly to that of other known markers of HR cells, we propose that ceacamz1 may serve as a novel marker of mature HR cells from the zebrafish epidermis.

Probiotic Yeasts and Vibrio anguillarum Infection Modify the Microbiome of Zebrafish Larvae

The host microbiome plays an essential role in health and disease. Microbiome modification by pathogens or probiotics has been poorly explored especially in the case of probiotic yeasts. Next-generation sequencing currently provides the best tools for their characterization. Debaryomyces hansenii 97 (D. hansenii 97) and Yarrowia lipolytica 242 (Y. lipolytica 242) are yeasts that protect wildtype zebrafish (Danio rerio) larvae against a Vibrio anguillarum (V. anguillarum) infection, increasing their survival rate. We investigate the effect of these microorganisms on the microbiome and neutrophil response (inflammation) in zebrafish larvae line Tg(Bacmpx:GFP)ⁱ¹¹⁴. We postulated that preinoculation of larvae with yeasts would attenuate the intestinal neutrophil response and prevent modification of the larval microbiome induced by the pathogen. Microbiome study was performed by sequencing the V3-V4 region of the 16S rRNA gene and prediction of metabolic pathways by Piphillin in conventionally raised larvae. Survival and the neutrophil response were both evaluated in conventional and germ-free conditions. V. anguillarum infection resulted in higher neutrophil number in the intestinal area compared to non-infected larvae in both conditions. In germ-free conditions, infected larvae pre-inoculated with yeasts showed fewer neutrophil numbers than infected larvae. In both conditions, only D. hansenii 97 increased the survival of infected larvae. Beta diversity of the microbiota was modified by V. anguillarum and both yeasts, compared to non-inoculated larvae. At 3 days post-infection, V. anguillarum modified the relative abundance of 10 genera, and pre-inoculation with D. hansenii 97 and Y. lipolytica 242 prevented the modification of 5 and 6 of these genera, respectively. Both yeasts prevent the increase of Ensifer and Vogesella identified as negative predictors for larval survival (accounting for 40 and 27 of the variance, respectively). In addition, yeast pre-inoculation prevents changes in some metabolic pathways altered by V. anguillarum’s infection. These results suggest that both yeasts and V. anguillarum can shape the larval microbiota configuration in the early developmental stage of D. rerio. Moreover, modulation of key taxa or metabolic pathways of the larval microbiome by yeasts can be associated with the survival of infected larvae. This study contributes to the understanding of yeast–pathogen–microbiome interactions, although further studies are needed to elucidate the mechanisms involved.

Animal models of chronic and recurrent Pseudomonas aeruginosa lung infection: significance of macrolide treatment

Animal models of human diseases are invaluable and inevitable elements in identifying and testing novel treatments for serious diseases, including severe infections. Planning and conducting investigator-initiated human trials are generally accepted as being enormously challenging. In contrast, it is often underestimated how much planning, including background and modifying experiments, is needed to establish a relevant infectious disease animal model. However, representative animal infectious models, well designed to test generated hypotheses, are useful to improve our understanding of pathogenesis, virulence factors and host response and to identify novel treatment candidates and therapeutic strategies. Such results can subsequently proceed to clinical testing if suitable. The present review aims at presenting all the pulmonary Pseudomonas aeruginosa infectious models we have knowledge of and the detailed descriptions of established animal models in our laboratory focusing on macrolide therapy are presented.

Gentamicin Combined With Hypoionic Shock Rapidly Eradicates Aquaculture Bacteria in vitro and in vivo

Bacterial pathogens are a major cause of infectious diseases in aquatic animals. The abuse of antibiotics in the aquatic industry has led to the proliferation of antibiotic resistance. It is therefore essential to develop more effective and safer strategies to increase the efficacy and extend the life span of the antibiotics used in aquaculture. In this study, we show that six aquaculture bacterial pathogens (i.e., Aeromonas hydrophila, Vibrio alginolyticus, Edwardsiella tarda, Streptococcus iniae, Vibrio harveyi, and Vibrio fluvialis) in the stationary phase can be rapidly killed after immersion in gentamicin- or neomycin-containing, ion-free solutions for a few minutes. Such hypoionic shock treatment enhances the bacterial uptake of gentamicin in an ATP-dependent manner. Importantly, we demonstrate, as a proof of concept, that gentamicin under hypoionic shock conditions can effectively kill A. hydrophila in vivo in a skin infection model of zebrafish (Danio rerio), completely curing the infected fish. Given that pathogenic bacteria generally adhere to the skin surface and gills of aquatic animals, our strategy is of potential significance for bacterial infection control, especially for small-scale economic fish farming and ornamental fish farming. Further, the combined treatment can be completed within 5 min with a relatively small volume of solution, thus minimizing the amount of residual antibiotics in both animals and the environment.

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

Tuberculosis (TB) remains a global health problem despite almost universal efforts to provide patients with highly effective chemotherapy, in part, because many infected individuals are not diagnosed and treated, others do not complete treatment, and a small proportion harbor Mycobacterium tuberculosis (Mtb) strains that have become resistant to drugs in the standard regimen. Development and approval of new drugs for TB have accelerated in the last 10 years, but more drugs are needed due to both Mtb's development of resistance and the desire to shorten therapy to 4 months or less. The drug development process needs predictive animal models that recapitulate the complex pathology and bacterial burden distribution of human disease. The human host response to pulmonary infection with Mtb is granulomatous inflammation usually resulting in contained lesions and limited bacterial replication. In those who develop progressive or active disease, regions of necrosis and cavitation can develop leading to lasting lung damage and possible death. This review describes the major vertebrate animal models used in evaluating compound activity against Mtb and the disease presentation that develops. Each of the models, including the zebrafish, various mice, guinea pigs, rabbits, and non-human primates provides data on number of Mtb bacteria and pathology resolution. The models where individual lesions can be dissected from the tissue or sampled can also provide data on lesion-specific bacterial loads and lesion-specific drug concentrations. With the inclusion of medical imaging, a compound's effect on resolution of pathology within individual lesions and animals can also be determined over time. Incorporation of measurement of drug exposure and drug distribution within animals and their tissues is important for choosing the best compounds to push toward the clinic and to the development of better regimens. We review the practical aspects of each model and the advantages and limitations of each in order to promote choosing a rational combination of them for a compound's development.

A Novel Function of TLR2 and MyD88 in the Regulation of Leukocyte Cell Migration Behavior During Wounding in Zebrafish Larvae

Toll-like receptor (TLR) signaling via myeloid differentiation factor 88 protein (MyD88) has been indicated to be involved in the response to wounding. It remains unknown whether the putative role of MyD88 in wounding responses is due to a control of leukocyte cell migration. The aim of this study was to explore in vivo whether TLR2 and MyD88 are involved in modulating neutrophil and macrophage cell migration behavior upon zebrafish larval tail wounding. Live cell imaging of tail-wounded larvae was performed in tlr2 and myd88 mutants and their corresponding wild type siblings. In order to visualize cell migration following tissue damage, we constructed double transgenic lines with fluorescent markers for macrophages and neutrophils in all mutant and sibling zebrafish lines. Three days post fertilization (dpf), tail-wounded larvae were studied using confocal laser scanning microscopy (CLSM) to quantify the number of recruited cells at the wounding area. We found that in both tlr2^-/- and myd88^-/- groups the recruited neutrophil and macrophage numbers are decreased compared to their wild type sibling controls. Through analyses of neutrophil and macrophage migration patterns, we demonstrated that both tlr2 and myd88 control the migration direction of distant neutrophils upon wounding. Furthermore, in both the tlr2 and the myd88 mutants, macrophages migrated more slowly toward the wound edge. Taken together, our findings show that tlr2 and myd88 are involved in responses to tail wounding by regulating the behavior and speed of leukocyte migration in vivo.

Review of inflammation in fish and value of the zebrafish model

Inflammation is a crucial step in the development of chronic diseases in humans. Understanding the inflammation environment and its intrinsic mechanisms when it is produced by harmful stimuli may be a key element in the development of human disease diagnosis. In recent decades, zebrafish (Danio rerio) have been widely used in research, due to their exceptional characteristics, as a model of various human diseases. Interestingly, the mediators released during the inflammatory response of both the immune system and nervous system, after its integration in the hypothalamus, could also facilitate the detection of injury through the register of behavioural changes in the fish. Although there are many studies that give well-defined information separately on such elements as the recruitment of cells, the release of pro- and anti-inflammatory mediators or the type of neurotransmitters released against different triggers, to the best of our knowledge there are no reviews that put all this knowledge together. In the present review, the main available information on inflammation in zebrafish is presented in order to facilitate knowledge about this important process of innate immunity, as well as the stress responses and behavioural changes derived from it.

Drug Resistance in Nontuberculous Mycobacteria: Mechanisms and Models

The genus Mycobacteria comprises a multitude of species known to cause serious disease in humans, including Mycobacterium tuberculosis and M. leprae, the responsible agents for tuberculosis and leprosy, respectively. In addition, there is a worldwide spike in the number of infections caused by a mixed group of species such as the M. avium, M. abscessus and M. ulcerans complexes, collectively called nontuberculous mycobacteria (NTMs). The situation is forecasted to worsen because, like tuberculosis, NTMs either naturally possess or are developing high resistance against conventional antibiotics. It is, therefore, important to implement and develop models that allow us to effectively examine the fundamental questions of NTM virulence, as well as to apply them for the discovery of new and improved therapies. This literature review will focus on the known molecular mechanisms behind drug resistance in NTM and the current models that may be used to test new effective antimicrobial therapies.

Predatory bacteria as living antibiotics - where are we now?

Antimicrobial resistance (AMR) is a global health and economic crisis. With too few antibiotics in development to meet current and anticipated needs, there is a critical need for new therapies to treat Gram-negative infections. One potential approach is the use of living predatory bacteria, such as Bdellovibrio bacteriovorus (small Gram-negative bacteria that naturally invade and kill Gram-negative pathogens of humans, animals and plants). Moving toward the use of Bdellovibrio as a 'living antibiotic' demands the investigation and characterization of these bacterial predators in biologically relevant systems. We review the fundamental science supporting the feasibility of predatory bacteria as alternatives to antibiotics.

Modeling Inflammation in Zebrafish for the Development of Anti-inflammatory Drugs

Dysregulation of the inflammatory response in humans can lead to various inflammatory diseases, like asthma and rheumatoid arthritis. The innate branch of the immune system, including macrophage and neutrophil functions, plays a critical role in all inflammatory diseases. This part of the immune system is well-conserved between humans and the zebrafish, which has emerged as a powerful animal model for inflammation, because it offers the possibility to image and study inflammatory responses in vivo at the early life stages. This review focuses on different inflammation models established in zebrafish, and how they are being used for the development of novel anti-inflammatory drugs. The most commonly used model is the tail fin amputation model, in which part of the tail fin of a zebrafish larva is clipped. This model has been used to study fundamental aspects of the inflammatory response, like the role of specific signaling pathways, the migration of leukocytes, and the interaction between different immune cells, and has also been used to screen libraries of natural compounds, approved drugs, and well-characterized pathway inhibitors. In other models the inflammation is induced by chemical treatment, such as lipopolysaccharide (LPS), leukotriene B4 (LTB4), and copper, and some chemical-induced models, such as treatment with trinitrobenzene sulfonic acid (TNBS), specifically model inflammation in the gastro-intestinal tract. Two mutant zebrafish lines, carrying a mutation in the hepatocyte growth factor activator inhibitor 1a gene (hai1a) and the cdp-diacylglycerolinositol 3-phosphatidyltransferase (cdipt) gene, show an inflammatory phenotype, and they provide interesting model systems for studying inflammation. These zebrafish inflammation models are often used to study the anti-inflammatory effects of glucocorticoids, to increase our understanding of the mechanism of action of this class of drugs and to develop novel glucocorticoid drugs. In this review, an overview is provided of the available inflammation models in zebrafish, and how they are used to unravel molecular mechanisms underlying the inflammatory response and to screen for novel anti-inflammatory drugs.

Zebrafish Models to Study Inflammasome-Mediated Regulation of Hematopoiesis

Hematopoiesis is a complex process through which immature bone marrow precursor cells mature into all types of blood cells. Although the association of hematopoietic lineage bias (including anemia and neutrophilia) with chronic inflammatory diseases has long been appreciated, the causes involved are obscure. Recently, cytosolic multiprotein inflammasome complexes were shown to activate inflammatory and immune responses, and directly regulate hematopoiesis in zebrafish models; this was deemed to occur via cleavage and inactivation of the master erythroid transcription factor GATA1. Herein summarized are the zebrafish models that are currently available to study this unappreciated role of inflammasome-mediated regulation of hematopoiesis. Novel putative therapeutic strategies, for the treatment of hematopoietic alterations associated with chronic inflammatory diseases in humans, are also proposed.

Anti-tuberculosis effect of isoniazid scales accurately from zebrafish to humans

Background and Purpose

There is a clear need for innovation in anti‐tuberculosis drug development. The zebrafish larva is an attractive disease model in tuberculosis research. To translate pharmacological findings to higher vertebrates, including humans, the internal exposure of drugs needs to be quantified and linked to observed response.

Experimental Approach

In zebrafish studies, drugs are usually dissolved in the external water, posing a challenge to quantify internal exposure. We developed experimental methods to quantify internal exposure, including nanoscale blood sampling, and to quantify the bacterial burden, using automated fluorescence imaging analysis, with isoniazid as the test compound. We used pharmacokinetic–pharmacodynamic modelling to quantify the exposure–response relationship responsible for the antibiotic response. To translate isoniazid response to humans, quantitative exposure–response relationships in zebrafish were linked to simulated concentration–time profiles in humans, and two quantitative translational factors on sensitivity to isoniazid and stage of infection were included.

Key Results

Blood concentration was only 20% of the external drug concentration. The bacterial burden increased exponentially, and an isoniazid dose corresponding to 15 mg·L⁻¹ internal concentration (minimum inhibitory concentration) leads to bacteriostasis of the mycobacterial infection in the zebrafish. The concentration–effect relationship was quantified, and based on that relationship and the translational factors, the isoniazid response was translated to humans, which correlated well with observed data.

Conclusions and Implications

This proof of concept study confirmed the potential of zebrafish larvae as tuberculosis disease models in translational pharmacology and contributes to innovative anti‐tuberculosis drug development, which is very clearly needed.

Drug Administration Routes Impact the Metabolism of a Synthetic Cannabinoid in the Zebrafish Larvae Model

Zebrafish (Danio rerio) larvae have gained attention as a valid model to study in vivo drug metabolism and to predict human metabolism. The microinjection of compounds, oligonucleotides, or pathogens into zebrafish embryos at an early developmental stage is a well-established technique. Here, we investigated the metabolism of zebrafish larvae after microinjection of methyl 2-(1-(5-fluoropentyl)-1H-pyrrolo[2,3-b]pyridine-3-carboxamido)-3,3-dimethylbutanoate (7'N-5F-ADB) as a representative of recently introduced synthetic cannabinoids. Results were compared to human urine data and data from the in vitro HepaRG model and the metabolic pathway of 7'N-5F-ADB were reconstructed. Out of 27 metabolites detected in human urine samples, 19 and 15 metabolites were present in zebrafish larvae and HepaRG cells, respectively. The route of administration to zebrafish larvae had a major impact and we found a high number of metabolites when 7'N-5F-ADB was microinjected into the caudal vein, heart ventricle, or hindbrain. We further studied the spatial distribution of the parent compound and its metabolites by mass spectrometry imaging (MSI) of treated zebrafish larvae to demonstrate the discrepancy in metabolite profiles among larvae exposed through different administration routes. In conclusion, zebrafish larvae represent a superb model for studying drug metabolism, and when combined with MSI, the optimal administration route can be determined based on in vivo drug distribution.

Integrating fish models in tuberculosis vaccine development

Tuberculosis is a chronic infection by Mycobacterium tuberculosis that results in over 1.5 million deaths worldwide each year. Currently, there is only one vaccine against tuberculosis, the Bacillus Calmette–Guérin (BCG) vaccine. Despite widespread vaccination programmes, over 10 million new M. tuberculosis infections are diagnosed yearly, with almost half a million cases caused by antibiotic-resistant strains. Novel vaccination strategies concentrate mainly on replacing BCG or boosting its efficacy and depend on animal models that accurately recapitulate the human disease. However, efforts to produce new vaccines against an M. tuberculosis infection have encountered several challenges, including the complexity of M. tuberculosis pathogenesis and limited knowledge of the protective immune responses. The preclinical evaluation of novel tuberculosis vaccine candidates is also hampered by the lack of an appropriate animal model that could accurately predict the protective effect of vaccines in humans. Here, we review the role of zebrafish (Danio rerio) and other fish models in the development of novel vaccines against tuberculosis and discuss how these models complement the more traditional mammalian models of tuberculosis.

Summary: In this Review, we discuss how zebrafish (Danio rerio) and other fish models can complement the more traditional mammalian models in the development of novel vaccines against tuberculosis.

In vivo safety assessment of rhodomyrtone, a potent compound, from Rhodomyrtus tomentosa leaf extract

BACKGROUND

Rhodomyrtus tomentosa (Aiton) Hassk. has been traditionally used to relieve various diseases. Rhodomyrtone, a bioactive acylphloroglucinol compound isolated from the leaves of Rhodomyrtus tomentosa, has been scientifically evidenced as a potential antibacterial agent. This study aimed to assess safety of rhodomyrtone in both invertebrate and vertebrate models.

MATERIAL AND METHODS

Safety of rhodomyrtone was determined in an invertebrate model, Galleria mellonella as well as vertebrate models including zebrafish (Danio rerio) and murine. In addition, toxicity to human erythrocytes was also measured.

RESULTS

Treatment of Galleria mellonella with rhodomyrtone at 100 mg/kg body weight up to four days showed no visible toxic effects (100 % survival). In zebrafish embryo model, at least 80 % survival of embryos was demonstrated when treated with rhodomyrtone at 0.5 μg/mL for three days. Prior to clinical trial, it is a prerequisite that rhodomyrtone has to be evaluated for its biocompatibility with human blood components. The results displayed that rhodomyrtone at 256 μg/mL did not cause any observable human erythrocyte haemolysis. Furthermore, preclinical assessment of rhodomyrtone formulation justified potential applications of rhodomyrtone in humans. Oral toxicity testing in a mouse model indicated the absence of systemic toxicity when the animals received up to 5000 mg/kg body weight of rhodomyrtone formulation for a period of fourteen days.

CONCLUSIONS

As the minimal inhibitory concentration of rhodomyrtone against most Gram-positive pathogens is 0.5-1 μg/mL, the results suggest that it should produce no toxic effects at concentrations used in human, thus support further development in pharmaceutical industries and public health applications.

DNA-based fluorescent probes of NOS2 activity in live brains

Innate immune cells destroy pathogens within a transient organelle called the phagosome. When pathogen-associated molecular patterns (PAMPs) displayed on the pathogen are recognized by Toll-like receptors (TLRs) on the host cell, it activates inducible nitric oxide synthase (NOS2) which instantly fills the phagosome with nitric oxide (NO) to clear the pathogen. Selected pathogens avoid activating NOS2 by concealing key PAMPs from their cognate TLRs. Thus, the ability to map NOS2 activity triggered by PAMPs can reveal critical mechanisms underlying pathogen susceptibility. Here, we describe DNA-based probes that ratiometrically report phagosomal and endosomal NO, and can be molecularly programmed to display precise stoichiometries of any desired PAMP. By mapping phagosomal NO produced in microglia of live zebrafish brains, we found that single-stranded RNA of bacterial origin acts as a PAMP and activates NOS2 by engaging TLR-7. This technology can be applied to study PAMP-TLR interactions in diverse organisms.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Review of diseases and health management in zebrafish Danio rerio (Hamilton 1822) in research facilities

The use of zebrafish (Danio rerio) in biomedical research has expanded at a tremendous rate over the last two decades. Along with increases in laboratories using this model, we are discovering new and important diseases. We review here the important pathogens and diseases based on some 20 years of research and findings from our diagnostic service at the NIH-funded Zebrafish International Resource Center. Descriptions of the present status of biosecurity programmes and diagnostic and treatment approaches are included. The most common and important diseases and pathogens are two parasites, Pseudoloma neurophilia and Pseudocapillaria tomentosa, and mycobacteriosis caused by Mycobacterium chelonae, M. marinum and M. haemophilum. Less common but deadly diseases are caused by Edwardsiella ictaluri and infectious spleen and kidney necrosis virus (ISKNV). Hepatic megalocytosis and egg-associated inflammation and fibroplasia are common, apparently non-infectious, in zebrafish laboratories. Water quality diseases include supersaturation and nephrocalcinosis. Common neoplasms are spindle cell sarcomas, ultimobranchial tumours, spermatocytic seminomas and a small-cell carcinoma that is caused by a transmissible agent. Despite the clear biosecurity risk, researchers continue to use fish from pet stores, and here, we document two novel coccidia associated with significant lesions in zebrafish from one of these stores.

Early Life Glucocorticoid Exposure Modulates Immune Function in Zebrafish (Danio rerio) Larvae

In this study we have assessed the effects of increased cortisol levels during early embryonic development on immune function in zebrafish (Danio rerio) larvae. Fertilized eggs were exposed to either a cortisol-containing, a dexamethasone-containing (to stimulate the glucocorticoid receptor selectively) or a control medium for 6 h post-fertilization (0–6 hpf). First, we measured baseline expression of a number of immune-related genes (socs3a, mpeg1.1, mpeg1.2, and irg1l) 5 days post-fertilization (dpf) in larvae of the AB and TL strain to assess the effectiveness of our exposure procedure and potential strain differences. Cortisol and dexamethasone strongly up-regulated baseline expression of these genes independent of strain. The next series of experiments were therefore carried out in larvae of the AB strain only. We measured neutrophil/macrophage recruitment following tail fin amputation (performed at 3 dpf) and phenotypical changes as well as survival following LPS-induced sepsis (150 μg/ml; 4–5 dpf). Dexamethasone, but not cortisol, exposure at 0–6 hpf enhanced neutrophil recruitment 4 h post tail fin amputation. Cortisol and dexamethasone exposure at 0–6 hpf led to a milder phenotype (e.g., less tail fin damage) and enhanced survival following LPS challenge compared to control exposure. Gene-expression analysis showed accompanying differences in transcript abundance of tlr4bb, cxcr4a, myd88, il1β, and il10. These data show that early-life exposure to cortisol, which may be considered to be a model or proxy of maternal stress, induces an adaptive response to immune challenges, which seems mediated via the glucocorticoid receptor.

The immunotoxicity and neurobehavioral toxicity of zebrafish induced by famoxadone-cymoxanil

As a new protective and therapeutic fungicide, studies on famoxadone-cymoxanil are rare, and its toxicity to aquatic organisms has not been reported. In the present study, zabrafish embryos were exposed to several concentrations of famoxadone-cymoxanil at 10 hpf. Then, the changes of their shape, heart rate, development and function of innate and adaptive immune cells, oxidative stress, apoptosis, the expression of apoptosis-related genes and immune-related genes, the locomotor behavior were observed and detected in acute toxicity of famoxadone-cymoxanil. Our studies showed that, after exposure to famoxadone-cymoxanil, zebrafish embryos had decreased heart rate, shortened body length, swollen yolk sac. Secondly, the number of innate and adaptive immune cells was significantly reduced; and neutrophil migration and retention at the injury area were inhibited, indicating the developmental toxicity and immunotoxicity of famoxadone-cymoxanil on the zebrafish. We also found that the oxidative stress related indicators of embryos were changed significantly, and apoptosis were substantially increased. Further investigation of changes of some key genes in TLR signaling including TLR4, MYD88 and NF-κB p65 revealed that the mRNA expression of these genes was up-regulated. Meanwhile, the mRNA expression of some proinflammatory cytokines such as TNF-α, IFN-γ, IL6 and IL-1β was also up-regulated. In addition, the activity, the total distance, time and average speed were decreased along with the increase of exposure concentration. The absolute turn angle, sinuosity and the enzymatic activity of acetylcholinesterase (AChE) were also increased. These results suggested that famoxadone-cymoxanil can induce developmental toxicity, immunotoxicity and neurobehavioral toxicity in zebrafish larvae.

Quantification of Natural Growth of Two Strains of Mycobacterium Marinum for Translational Antituberculosis Drug Development

The zebrafish infected with Mycobacterium marinum (M. marinum) is an attractive tuberculosis disease model, showing similar pathogenesis to Mycobacterium tuberculosis (M. tuberculosis) infections in humans. To translate pharmacological findings from this disease model to higher vertebrates, a quantitative understanding of the natural growth of M. marinum in comparison to the natural growth of M. tuberculosis is essential. Here, the natural growth of two strains of M. marinum, E11 and M^USA, is studied over an extended period using an established model‐based approach, the multistate tuberculosis pharmacometric (MTP) model, for comparison to that of M. tuberculosis. Poikilotherm‐derived strain E11 and human‐derived strain M^USA were grown undisturbed up to 221 days and viability of cultures (colony forming unit (CFU)/mL) was determined by plating at different time points. Nonlinear mixed effects modeling using the MTP model quantified the bacterial growth, the transfer among fast, slow, and non‐multiplying states, and the inoculi. Both strains showed initial logistic growth, reaching a maximum after 20–25 days for E11 and M^USA, respectively, followed by a decrease to a new plateau. Natural growth of both E11 and M^USA was best described with Gompertz growth functions. For E11, the inoculum was best described in the slow‐multiplying state, for M^USA in the fast‐multiplying state. Natural growth of E11 was most similar to that of M. tuberculosis, whereas M^USA showed more aggressive growth behavior. Characterization of natural growth of M. marinum and quantitative comparison with M. tuberculosis brings the zebrafish tuberculosis disease model closer to the quantitative translational pipeline of antituberculosis drug development.

Host monitoring of quorum sensing during Pseudomonas aeruginosa infection

Pseudomonas aeruginosa rapidly adapts to altered conditions by quorum sensing (QS), a communication system that it uses to collectively modify its behavior through the production, release, and detection of signaling molecules. QS molecules can also be sensed by hosts, although the respective receptors and signaling pathways are poorly understood. We describe a pattern of regulation in the host by the aryl hydrocarbon receptor (AhR) that is critically dependent on qualitative and quantitative sensing of P. aeruginosa quorum. QS molecules bind to AhR and distinctly modulate its activity. This is mirrored upon infection with P. aeruginosa collected from diverse growth stages and with QS mutants. We propose that by spying on bacterial quorum, AhR acts as a major sensor of infection dynamics, capable of orchestrating host defense according to the status quo of infection.

Multiple drug resistant Enterococcus spp. causes disease and mortality in Zebra fish (Danio rerio)

The present report describes the isolation and identification of a multiple drug resistant Enterococcus spp. from diseased zebrafish from a commercial rearing facility in Chennai, Tamil Nadu, India. Zebrafish (Danio rerio) has recently gained great significance as a vertebrate animal model, as its immune system is remarkably similar with that of the humans. However, zebrafish are still susceptible to microbial infection. Gram positive diplococci isolated from kidney was identified as Enterococcus spp. using 16S rRNA gene sequencing analysis. The Enterococcus spp. isolate was either resistant and or intermediately resistant to 14 antibiotics assessed by agar disc diffusion method. This communication is the first report on isolation and confirmation of Enterococcus spp. associated with disease and mortality in zebrafish.

The zebrafish as a model for gastrointestinal tract-microbe interactions

The zebrafish (Danio rerio) has become a widely used vertebrate model for bacterial, fungal, viral, and protozoan infections. Due to its genetic tractability, large clutch sizes, ease of manipulation, and optical transparency during early life stages, it is a particularly useful model to address questions about the cellular microbiology of host-microbe interactions. Although its use as a model for systemic infections, as well as infections localised to the hindbrain and swimbladder having been thoroughly reviewed, studies focusing on host-microbe interactions in the zebrafish gastrointestinal tract have been neglected. Here, we summarise recent findings regarding the developmental and immune biology of the gastrointestinal tract, drawing parallels to mammalian systems. We discuss the use of adult and larval zebrafish as models for gastrointestinal infections, and more generally, for studies of host-microbe interactions in the gut.

Temporal modulation of host aerobic glycolysis determines the outcome of Mycobacterium marinum infection

Macrophages are the first-line host defense that the invading Mycobacterium tuberculosis (Mtb) encounters. It has been recently reported that host aerobic glycolysis was elevated post the infection by a couple of virulent mycobacterial species. However, whether this metabolic transition is required for host defense against intracellular pathogens and the underlying mechanisms remain to be further investigated. A pathogenic mycobacterial species, M. marinum, is genetically close to Mtb and was utilized in this study. Through analyzing cellular carbon metabolism of RAW 264.7 (a murine macrophage-like cell line) post M. marinum infection, a strong elevation of glycolysis was observed. Next, three glycolysis inhibitors were examined for their ability to inhibit mycobacterial proliferation inside RAW264.7 macrophages. Among them, a glucose analog, 2-deoxyglucose (2-DG) displayed a protective role against mycobacterial infection. Treatment with 2-DG at concentrations of 0.5 or 1 mM significantly induced autophagy and decreased the phagocytosis of M. marinum by macrophages. Moreover, 2-DG pre-treatment exerted a significantly protective effect on zebrafish larvae by limiting the proliferation of M. marinum, and such effect was correlated to tumor necrosis factor alpha (TNF-α) as the 2-DG pre-treatment increased the expression of TNF-α in both mouse peritoneal macrophages and zebrafish. On the contrary, the 2-DG treatment post infection did not restrain proliferation of M. marinum in WT zebrafish, and even accelerated bacterial replication in TNF-α^-/- zebrafish. Together, modulation of glycolysis prior to infection boosts host immunity against M. marinum infection, indicating a potential intervention strategy to control mycobacterial infection.

The anti-inflammatory effects of formononetin and ononin on lipopolysaccharide-induced zebrafish models based on lipidomics and targeted transcriptomics

INTRODUCTION

Formononetin (MBHS) and its glycosylated derivative ononin (MBHG), as the major isoflavones, have exhibited the anti-inflammatory impacts on the lipopolysaccharide (LPS)-induced inflammation. Although various researches have focused on interpreting the pharmaceutical activities of MBHG and MBHS, the molecular mechanisms in zebrafish models are still unclear.

OBJECTIVE

The purpose of the present work is to investigate the molecular mechanisms of the anti-inflammatory effects of MGHG and MBHS based on lipidomics and targeted transcriptomics.

METHODS

UHPLC-MS was applied for the lipid analyses and RT-PCR was adopted for the mRNA analyses, and the results of different groups were compared for exploring the significantly changed lipids and mRNAs.

RESULTS

The results of lipidomics revealed that phosphatidylcholines (PCs) were drastically down-regulated in the MBHG or MBHS treated LPS-induced inflammatory zebrafish models. Besides, MBHS can also decrease the levels of triacylglycerols (TAGs). For the targeted transcriptomics analyses, 4 cytokines (TNF-α, IL-1β, IL-6 and IFN-γ) and 3 mRNA (JNK1, ERK1 and p38a) involved in the MAPK pathway were down-regulated and IL-10 was up-regulated under the treatment of MBHG or MBHS.

CONCLUSION

Combining the results of lipidomics and targeted transcriptomics, we indicated that MBHG and MBHS exerted potent anti-inflammatory effects on the LPS-induced zebrafish models through the MyD88 or TRIF MAPK/ERK and MAPK/JNK pathways and the glycerophospholipid, glycosylphosphatidylinositol (GPI)-anchor biosynthesis and glycerolipid metabolisms. Our results provided new insights into the anti-inflammatory mechanisms of MBHG or MBHS and supplied an effective method to interpret the pharmacological mechanisms of drugs.