Translocation of nanoparticles and Mycobacterium marinum across the intestinal epithelium in zebrafish and the role of the mucosal immune system

Microplastics and Anthropogenic Particles in Recreationally Caught Freshwater Fish from an Urbanized Region of the North American Great Lakes

BACKGROUND

Microplastics are a pervasive contaminant cycling through food webs-leading to concerns regarding exposure and risk to humans.

OBJECTIVES

We aimed to quantify and characterize anthropogenic particle contamination (including microplastics) in fish caught for human consumption from the Humber Bay region of Lake Ontario. We related quantities of anthropogenic particles to other factors (e.g., fish size) that may help in understanding accumulation of microplastics in fish.

METHODS

A total of 45 samples of six fish species collected from Humber Bay in Lake Ontario near Toronto, Ontario, Canada, were examined for anthropogenic particles in their gastrointestinal (GI) tracts and fillets. Using microscopy and spectroscopy, suspected anthropogenic particles were identified and characterized.

RESULTS

We observed anthropogenic particles in the GI tracts and fillets of all species. Individual fish had a mean ± standard deviation of 138 ± 231 anthropogenic particles, with a single fish containing up to 1,508 particles. GI tracts had 93 ± 226 particles/fish (9.8 ± 32.6 particles/gram), and fillets had 56 ± 61 particles/fish (0.5 ± 0.8 particles/gram). Based on a consumption rate of 2 servings/week, the average yearly human exposure through the consumption of these fish fillets would be 12,800 ± 18,300 particles.

DISCUSSION

Our findings suggest that consumption of recreationally caught freshwater fish can be a pathway for human exposure to microplastics. The elevated number of particles observed in fish from Humber Bay highlights the need for large-scale geographic monitoring, especially near sources of microplastics. Currently, it is unclear what the effects of ingesting microplastics are for humans, but given that recreationally caught freshwater fish are one pathway for human exposure, these data can be incorporated into future human health risk assessment frameworks for microplastics. https://doi.org/10.1289/EHP13540.

Alleviative effects of quercetin of Botrytis cinerea-induced toxicity in zebrafish (Danio rerio) larvae

Quercetin is a kind of flavonoid substance extensively existing in the plant, which has antioxidant, anti-inflammatory, and anti-apoptosis effects. It was reported that the higher concentration of spores present in the environment could cause abnormal development in zebrafish larvae. Therefore, this study set out to investigate whether quercetin could reduce the zebrafish larvae damage caused by Botrytis cinerea exposure as well as to examine the molecular basis for this action. The findings demonstrated that 50 μM quercetin improved the developmental dysplasia of zebrafish larvae induced by 102 CFU/mL Botrytis cinerea spore suspension, reduced abnormal apoptosis, enhanced antioxidant system, relieved inflammation, reshaped intestinal morphology and recovered intestinal motility. At the molecular level, quercetin decreased the transcriptional abundance of pro-apoptotic factors (bax, p53, caspase3, and caspase9) and up-regulated the anti-apoptotic gene (bcl-2) expression to reduce apoptosis. Moreover, quercetin enhanced the activities of downstream antioxidant enzymes (SOD and CAT) to clear excess ROS and MDA due to Botrytis cinerea exposure by up-regulating the expression of antioxidant genes (nrf2, ho-1, sod, and cat) in the Keap1-Nrf2 pathway. Additionally, quercetin inhibited the elevation of TNF-α by regulating the gene expression of key targets (jak3, pi3k, pdk1, akt, and ikk2) and the content of major proteins NF-κB (P65) and IκB in the NF-κB pathway. In conclusion, this work enriched the contents of the biological research of Botrytis cinerea and provided a new direction for the drug development and targeted therapy of quercetin.

Microplastics in marine mammal blubber, melon, & other tissues: Evidence of translocation

Marine mammals consume large quantities of microplastic particles, likely via trophic transfer (i.e., through prey who have consumed plastic) and direct consumption from seawater or sediment. Microplastics have been found in the stomachs, gastro-intestinal tracts, and feces of cetaceans and pinnipeds. Translocation of ingested microplastics has been documented in other organs of several aquatic species, but has not been examined in marine mammals. Marine mammals have highly specialized lipid-rich tissues which may increase susceptibility to lipophilic microplastics. Here we demonstrate the occurrence of microplastics, ranging in size, mass concentration, and particle count concentration from 24.4 μm - 1387 μm, 0.59 μg/g - 25.20 μg/g, and 0.04 - 0.39 particles/g, respectively, in four tissues (acoustic fat pad, blubber, lung, & melon) from twelve marine mammal species inclusive of mysticetes, odontocetes, and phocids. Twenty-two individuals were examined for microplastics using a combination of Raman spectroscopy and pyrolysis gas chromatography with mass spectrometry. Overall, 68% of individuals had at least one microplastic particle in at least one of the four tissue types, with the most common polymer and shape observed being polyethylene and fibers, respectively. These findings suggest some proportion of ingested microplastics translocate throughout marine mammal bodies posing an exposure risk to both marine mammals and people. For people, exposure could be directly through consumption for those who rely on marine mammals as food and indirectly to peoples globally who consume the same prey resources as marine mammals. Some individuals examined represent samples obtained over two decades ago, suggesting that this process, and thus exposure risk, has occurred for some time.

Polygoni multiflori radix exacerbates idiosyncratic inflammatory liver injury through the FXR-SHP pathway and altered pharmacokinetic behavior

Polygoni multiflori radix (PM) is a well-known tonic herb. It has been reported that PM could cause idiosyncratic inflammatory liver injury in some individuals. In this study, we investigated the mechanism of PM-induced idiosyncratic inflammatory liver injury in zebrafish and rat models based on pharmacodynamics and pharmacokinetics. The zebrafish were administered with polygoni multiflori radix extract (PME), emodin (EMO), and 2,3,5,4'-tetrahydroxystilbene-2-Ο-β-D-glucoside (TSG) after lipopolysaccharide (LPS) treatment, to establish an idiosyncratic inflammation model. In zebrafish with idiosyncratic inflammation, PME, EMO, and TSG decreased liver area and brightness and increased the number of immune cells around the colliculi. PME+LPS produced hepatocyte damage, aggravated mitochondrial and endoplasmic reticulum damage, and increased AST and ALT activity. RT-PCR showed that PME and EMO up-regulated the expression of IL-6, IL-1β, and INF-γ, and PME down-regulated expression of FXR and SHP. In rats with idiosyncratic inflammation, AST and ALT activities increased significantly, and liver tissues showed pathological damage. An efficient and sensitive LC-MS/MS method was established for the pharmacokinetic study of EMO and TSG in rats with idiosyncratic inflammation. The AUC_0-t was higher for EMO and TSG in the model group compared with the normal group. The MRT_0-t was significantly prolonged in EMO, while CL_z/F was significantly reduced. The present results suggested that the absorption of potentially toxic components of PM increased and metabolism slowed down under inflammatory stress, and PM induced idiosyncratic liver injury via the FXR-SHP axis.

Lympho-Hematopoietic Microenvironments and Fish Immune System

In the last 50 years information on the fish immune system has increased importantly, particularly that on species of marked commercial interest (i.e., salmonids, cods, catfish, sea breams), that occupy a key position in the vertebrate phylogenetical tree (i.e., Agnatha, Chondrichtyes, lungfish) or represent consolidated experimental models, such as zebrafish or medaka. However, most obtained information was based on genetic sequence analysis with little or no information on the cellular basis of the immune responses. Although jawed fish contain a thymus and lympho-hematopoietic organs equivalents to mammalian bone marrow, few studies have accounted for the presumptive relationships between the organization of these cell microenvironments and the known immune capabilities of the fish immune system. In the current review, we analyze this topic providing information on: (1) The origins of T and B lymphopoiesis in Agnatha and jawed fish; (2) the remarkable organization of the thymus of teleost fish; (3) the occurrence of numerous, apparently unrelated organs housing lympho-hematopoietic progenitors and, presumably, B lymphopoiesis; (4) the existence of fish immunological memory in the absence of germinal centers.

Immunotoxic effects of metal-based nanoparticles in fish and bivalves

There is a global research interest in metal nanoparticles (MNPs) due to their diverse applications, rapidly increasing use, and increased presence in the aquatic environment. Currently, most MNPs in the environment are at levels unlikely to cause overt toxicity. Sub-lethal effects that MNPs may induce, notable immunotoxicity, could however have significant health implications. Thus, deciphering the immunological interactions of MNPs with aquatic organisms constitutes a much-needed area of research. In this article, we critically assess the evidence for immunotoxic effects of MNPs in bivalves and fish, as key wildlife sentinels with widely differing ecological niches that are used as models in ecotoxicology. The first part of this review details the properties, fate, and fundamental physicochemical behavior of MNPs in the aquatic ecosystem. We then consider the toxicokinetics of MNP uptake, accumulation, and deposition in fish and bivalves. The main body of the review then focuses on immune reactions in response to MNPs exposure in bivalves and fish illustrating their immunotoxic potential. Finally, we identify major knowledge gaps in our current understanding of the implications of MNPs exposure for immunological functions and the associated health consequences for bivalves and fish, as well as the general lessons learned on the immunotoxic properties of the emerging class of nanoparticulate contaminants in fish and bivalves.

Gut Immune System and the Implications of Oral-Administered Immunoprophylaxis in Finfish Aquaculture

The gastrointestinal immune system plays an important role in immune homeostasis regulation. It regulates the symbiotic host-microbiome interactions by training and developing the host's innate and adaptive immunity. This interaction plays a vital role in host defence mechanisms and at the same time, balancing the endogenous perturbations of the host immune homeostasis. The fish gastrointestinal immune system is armed with intricate diffused gut-associated lymphoid tissues (GALTs) that establish tolerance toward the enormous commensal gut microbiome while preserving immune responses against the intrusion of enteric pathogens. A comprehensive understanding of the intestinal immune system is a prerequisite for developing an oral vaccine and immunostimulants in aquaculture, particularly in cultured fish species. In this review, we outline the remarkable features of gut immunity and the essential components of gut-associated lymphoid tissue. The mechanistic principles underlying the antigen absorption and uptake through the intestinal epithelial, and the subsequent immune activation through a series of molecular events are reviewed. The emphasis is on the significance of gut immunity in oral administration of immunoprophylactics, and the different potential adjuvants that circumvent intestinal immune tolerance. Comprehension of the intestinal immune system is pivotal for developing effective fish vaccines that can be delivered orally, which is less labour-intensive and could improve fish health and facilitate disease management in the aquaculture industry.

Teleost Fish as an Experimental Model for Vaccine Development

Advances in vaccine development depend on animal models to test innovative therapies. Recent studies have reported the successful introduction of teleost fish as a new vertebrate model in scientific research, with emphasis on the species Danio rerio (zebrafish). This chapter aims to give an overview of important aspects related to the immune system of fish, as well as the current progress of the successful use of these animals in studies for the development of vaccines, assisting in the determination of efficacy and clinical safety. Among the advantages of using fish for the development of vaccines and immunomodulatory drugs, it is worth highlighting the reproductive capacity of these animals resulting in a high number of individuals belonging to the same spawning, transparent embryos, low cost of breeding and high genetic similarity that favor translational responses to vertebrate organisms like humans.

Evidence of Microplastic Translocation in Wild-Caught Fish and Implications for Microplastic Accumulation Dynamics in Food Webs

The presence of microplastics within the gut of animals is well documented. Whether microplastics bioaccumulate in organisms and biomagnify in food webs remains unclear and relies on the ability of microplastics to translocate to other tissues. Here, we demonstrate the widespread presence of microplastics and other anthropogenic microparticles in the gastrointestinal tract, fillet, and livers of seven species of sportfish from Lake Simcoe, Ontario, Canada. Larger fish had a higher microplastic load compared to smaller fish, but the opposite trend was observed with translocated microplastics standardized by fish mass (i.e., smaller fish contained more translocated particles per gram wet weight than larger fish). Moreover, we observed no evidence of biomagnification as there was no significant relationship between the trophic level and total or translocated microplastics per individual. Overall, this suggests that microplastics are translocating, but that excretion of translocated particles or growth dilution may be occurring rather than bioaccumulation and biomagnification. Moreover, the assemblages of shapes and material types varied among tissues, suggesting that particle characteristics may predict biological fate. Our findings highlight the need for further work to understand the mechanisms of microplastic translocation and excretion and the implications for the dynamics of microplastics accumulation in food webs and human exposure.

Microbial recognition regulates intestinal epithelial growth in homeostasis and disease

The intestine is constantly exposed to a dynamic community of microbes. Intestinal epithelial cells respond to microbes through evolutionarily conserved recognition pathways, such as the immune deficiency (IMD) pathway of Drosophila, the Toll-like receptor (TLR) response of flies and vertebrates, and the vertebrate nucleotide-binding oligomerization domain (NOD) pathway. Microbial recognition pathways are tightly controlled to respond effectively to pathogens, tolerate the microbiome, and limit intestinal disease. In this review, we focus on contributions of different model organisms to our understanding of how epithelial microbe recognition impacts intestinal proliferation and differentiation in homeostasis and disease. In particular, we compare how microbes and subsequent recognition by the intestine influences barrier integrity, intestinal repair and tumorigenesis in Drosophila, zebrafish, mice, and organoids. In addition, we discuss the importance of microbial recognition in homeostatic intestinal growth and discuss how immune pathways directly impact stem cell and crypt dynamics.

Aquatic toxicity of chemically defined microplastics can be explained by functional additives

A novel, systematic approach to relate plastic toxicity with chemical composition is undertaken. Using industrial methods, three petroleum-based polymers, low-density polyethylene (PE), polyvinyl chloride (PVC), and polyamide (PA), and the biopolymer polyhydroxybutyrate (PHB) were manufactured in different formularies including conventional and alternative additives, and microplastics of two sizes (<250 and <20 µm) were obtained with the aim to relate their composition with environmental impact in aquatic environments. Internationally accepted standard tests of regulatory use with marine organisms representative of microalgae (Tisochrysis lutea population growth), crustaceans (Acartia clausi larval survival), and echinoderms (Paracentrotus lividus sea-urchin embryo test) support the following conclusions. Aquatic toxicity of microplastics made from conventional oil-based polymers is due to leaching of chemical additives, and not to ingestion of microplastics. Use of alternative formulations based on natural rather than synthetic chemical additives did not consistently reduce aquatic toxicity except for the replacement of triclosan by the alternative biocide lawsone. In contrast, the biopolymer tested, PHB, seemed to impact marine plankton through different mechanisms associated to the higher abundance of plastic particles within the nanometric range found in this resin and absent in other materials.

Dietary uptake and effects of copper in Sticklebacks at environmentally relevant exposures utilizing stable isotope-labeled 65CuCl2 and 65CuO NPs

Copper oxide nanoparticles (CuO NPs) accumulating in sediment can be taken up by invertebrates that serve as prey for fish. Thus, it is likely that the latter are exposed to CuO NPs via the gut. However, to this day it is unknown if CuO NPs can be taken up via the gastrointestinal tract and if and in which tissues/organs they accumulate. To address this knowledge gap, we synthesized CuO NPs enriched in the stable isotope ⁶⁵Cu and incorporated them at low concentration (5 μg ⁶⁵Cu g^-1 ww food) into a practical diet prepared from worm homogenate, which was then fed to Three-spined Stickleback (Gasterosteus aculeatus) for 16 days. For comparison, fish were exposed to a diet spiked with a ⁶⁵CuCl₂ solution. Background Cu and newly taken up ⁶⁵Cu in fish tissues/organs including gill, stomach, intestine, liver, spleen, gonad and carcass and feces were quantified by ICP-MS. In addition, expression levels of genes encoding for proteins related to Cu uptake, detoxification and toxicity (ctr-1, gcl, gr, gpx, sod-1, cat, mta and zo-1) were measured in selected tissues using RT-qPCR. The obtained results showed that feces of fish fed ⁶⁵CuO NP-spiked diet contained important amounts of ⁶⁵Cu. Furthermore, there was no significant accumulation of ⁶⁵Cu in any of the analyzed internal organs, though ⁶⁵Cu levels were slightly elevated in liver. No significant modulation in gene expression was measured in fish exposed to ⁶⁵CuO NP-spiked diet, except for metallothionein, which was significantly upregulated in intestinal tissue compared to control fish. Altogether, our results suggests that dietary absorption efficiency of CuO NPs, their uptake across the gastrointestinal barrier into the organism, and effects on Cu-related genes is limited at low, environmentally relevant exposure doses (0.2 μg ⁶⁵Cu ^-1 fish ww day^-1).

State-of-the-art polymeric nanoparticles as promising therapeutic tools against human bacterial infections

Infectious diseases kill over 17 million people a year, among which bacterial infections stand out. From all the bacterial infections, tuberculosis, diarrhoea, meningitis, pneumonia, sexual transmission diseases and nosocomial infections are the most severe bacterial infections, which affect millions of people worldwide. Moreover, the indiscriminate use of antibiotic drugs in the last decades has triggered an increasing multiple resistance towards these drugs, which represent a serious global socioeconomic and public health risk. It is estimated that 33,000 and 35,000 people die yearly in Europe and the United States, respectively, as a direct result of antimicrobial resistance. For all these reasons, there is an emerging need to find novel alternatives to overcome these issues and reduced the morbidity and mortality associated to bacterial infectious diseases. In that sense, nanotechnological approaches, especially smart polymeric nanoparticles, has wrought a revolution in this field, providing an innovative therapeutic alternative able to improve the limitations encountered in available treatments and capable to be effective by theirselves. In this review, we examine the current status of most dangerous human infections, together with an in-depth discussion of the role of nanomedicine to overcome the current disadvantages, and specifically the most recent and innovative studies involving polymeric nanoparticles against most common bacterial infections of the human body.

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.

An end to the controversy over the microscopic detection and effects of pristine microplastics in fish organs

The aquatic environment and the associated fish assemblages are being exposed to an increasing amount of microplastics. Despite the high number of publications on the presence of microplastics in fish, little is known about their uptake, translocation and accumulation within fish organs. Experimental studies on the detection and effects of pristine microplastics in fish have shown controversial and ambiguous results, respectively. Here, we conducted two experiments to detect and assess the impacts of dietary exposure of Danio rerio to different types of pristine microplastics. Our results show that D. rerio recognizes plastic particles as inedible materials but ingests them when mixed with food or fish oil. Accidental ingestion occurs in fish exposed to relatively small (1–5 µm) microplastic particles without associated food or fish oil. Additionally, D. rerio effectively eliminated pristine microplastics 24 h after ingestion; however, retention time was associated with increasing particle size and the intake of additional meals. Clinical signs, such as anorexia and lethargy, are present in fish fed relatively large microplastics (120–220 µm). The ingestion of microplastics does not induce any histopathological changes. To the best of our knowledge, we are able, for the first time, to fully demonstrate the uptake and translocation of plastic microbeads using confocal microscopy. Our results question the findings of previous studies on the detection and effects of pristine microplastics in fish and state that inaccurate interpretations of the histological findings regarding microplastics in fish organs is a prevalent flaw in the current scientific literature.

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.

Kleptoprotein bioluminescence: Parapriacanthus fish obtain luciferase from ostracod prey

Through their diet, animals can obtain substances essential for imparting special characteristics, such as toxins in monarch butterflies and luminescent substances in jellyfishes. These substances are typically small molecules because they are less likely to be digested and may be hard for the consumer to biosynthesize. Here, we report that Parapriacanthus ransonneti, a bioluminescent fish, obtains not only its luciferin but also its luciferase enzyme from bioluminescent ostracod prey. The enzyme purified from the fish's light organs was identical to the luciferase of Cypridina noctiluca, a bioluminescent ostracod that they feed upon. Experiments where fish were fed with a related ostracod, Vargula hilgendorfii, demonstrated the specific uptake of the luciferase to the fish's light organs. This "kleptoprotein" system allows an organism to use novel functional proteins that are not encoded in its genome and provides an evolutionary alternative to DNA-based molecular evolution.

Zebrafish as a preclinical in vivo screening model for nanomedicines

The interactions of nanomedicines with biological environments is heavily influenced by their physicochemical properties. Formulation design and optimization are therefore key steps towards successful nanomedicine development. Unfortunately, detailed assessment of nanomedicine formulations, at a macromolecular level, in rodents is severely limited by the restricted imaging possibilities within these animals. Moreover, rodent in vivo studies are time consuming and expensive, limiting the number of formulations that can be practically assessed in any one study. Consequently, screening and optimisation of nanomedicine formulations is most commonly performed in surrogate biological model systems, such as human-derived cell cultures. However, despite the time and cost advantages of classical in vitro models, these artificial systems fail to reflect and mimic the complex biological situation a nanomedicine will encounter in vivo. This has acutely hampered the selection of potentially successful nanomedicines for subsequent rodent in vivo studies. Recently, zebrafish have emerged as a promising in vivo model, within nanomedicine development pipelines, by offering opportunities to quickly screen nanomedicines under in vivo conditions and in a cost-effective manner so as to bridge the current gap between in vitro and rodent studies. In this review, we outline several advantageous features of the zebrafish model, such as biological conservation, imaging modalities, availability of genetic tools and disease models, as well as their various applications in nanomedicine development. Critical experimental parameters are discussed and the most beneficial applications of the zebrafish model, in the context of nanomedicine development, are highlighted.

Innate Immunity Provides Biomarkers of Health for Teleosts Exposed to Nanoparticles

In recent years, the unique properties of nanoparticles have fostered novel applications in various fields such as biology, pharmaceuticals, agriculture, and others. Unfortunately, their rapid integration into daily life has also led to environmental concerns due to uncontrolled release of nanoparticles into the aquatic environment. Despite increasing awareness of nanoparticle bioaccumulation in the aquatic environment, much remains to be learned about their impact on aquatic organisms and how to best monitor these effects. Herein, we provide the first review of innate immunity as an emerging tool to assess the health of fish following nanoparticle exposure. Fish are widely used as sentinels for aquatic ecosystem pollution and innate immune parameters offer sensitive and reliable tools that can be harnessed for evaluation of contamination events. The most frequent biomarkers highlighted in literature to date include, but are not limited to, parameters associated with leukocyte dynamics, oxidative stress, and cytokine production. Taken together, innate immunity offers finite and sensitive biomarkers for assessment of the impact of nanoparticles on fish health.

Comparative tissue distribution and depuration characteristics of copper nanoparticles and soluble copper in rainbow trout (Oncorhynchus mykiss)

The continuously growing number of products containing nanoparticles (NPs) makes their presence in the environment inevitable, and given the well-known toxicity of dissolved metals, concerns regarding the toxicity of metal-based NPs have been raised. Whether metal-based NPs present similar or different toxicological effects compared with metal salts is an emerging field. In the present study, rainbow trout were intraperitoneally injected with CuSO₄ or copper NPs (CuNPs) to investigate tissue distribution and depuration characteristics. Fish injected with Cu showed an initial accumulation of Cu in the liver, kidney, gills, intestine, and carcass. The Cu concentration in the liver of CuNP-injected fish increased over time. It appears as though CuNPs accumulated in the liver at a greater rate than they were excreted. In livers of fish injected with CuSO₄ , the Cu concentration appeared to increase and reach an equilibrium, suggesting that copper was accumulated and excreted at the same rate. The possibility that CuNPs can accumulate at a higher rate than it is excreted in the liver warrants further investigation. The present study demonstrates the possibility of dietary uptake of CuNPs because elevated Cu concentrations were observed in carcass, gills, kidney, and intestine of fish gavaged with CuNPs. In conclusion, the results suggest that dietary CuNPs are taken up by the gut and preferentially accumulate in the liver. Environ Toxicol Chem 2019;38:80-89. © 2018 SETAC.

Oral Intubation of Adult Zebrafish: A Model for Evaluating Intestinal Uptake of Bioactive Compounds

Most pathogens invade organisms through their mucosa. This is particularly true in fish as they are continuously exposed to a microbial-rich water environment. Developing effective methods for oral delivery of immunostimulants or vaccines, which activate the immune system against infectious diseases, is highly desirable. In devising prophylactic tools, good experimental models are needed to test their performance. Here, we show a method for oral intubation of adult zebrafish and a set of procedures to dissect and prepare the intestine for cytometry, confocal microscopy and quantitative polymerase chain reaction (qPCR) analysis. With this protocol, we can precisely administer volumes up to 50 µL to fish weighing approximately 1 g simply and quickly, without harming the animals. This method allows us to explore the direct in vivo uptake of fluorescently labelled compounds by the intestinal mucosa and the immunomodulatory capacity of such biologics at the local site after intubation. By combining downstream methods such as flow cytometry, histology, qPCR and confocal microscopy of the intestinal tissue, we can understand how immunostimulants or vaccines are able to cross the intestinal mucosal barriers, pass through the lamina propria, and reach the muscle, exerting an effect on the intestinal mucosal immune system. The model could be used to test candidate oral prophylactics and delivery systems or the local effect of any orally administered bioactive compound.

A Novel Antigen-Sampling Cell in the Teleost Gill Epithelium With the Potential for Direct Antigen Presentation in Mucosal Tissue

In mammals, M cells can take up antigens through mucosal surfaces of the gut and the respiratory tract. Since M cells are deficient of lysosomes and phagosomes, the antigens are directly delivered to the mucosa-associated lymphoid tissue (MALT) without degradation. In teleost fish, the entire body surface (gills, skin, and intestinal system) is covered by mucus; however, specific antigen-sampling cells have not yet been identified in their mucosal tissues. Here, we show that two phenotypes of antigen-sampling cells take up antigens through epithelial surfaces of the rainbow trout gill. One phenotype of antigen-sampling cells has features of monocyte/macrophage/dendritic cell-type cells; they have large vacuoles in the cytoplasm and express PTPRC (CD45), CD83, IL-1β, and IL-12p40b. The second phenotype exhibits similar characteristics to mammalian M cells; the corresponding cells bind the lectin UEA-1 but not WGA and show expression of M cell marker gene Anxa5. In contrast to mammalian M cells, teleost M-type cells were found to exhibit small vacuoles in their cytoplasm and to express almost all genes related to the “phagosome”, “lysosome,” and “antigen processing and presentation” pathways. Furthermore, MHC class II was constitutively expressed on a fraction of M-type cells, and this expression was significantly increased after antigen uptake, suggesting that the MHC class II is inducible by antigen stimulation. Here, we suggest that teleost M-type cells play a role in the phylogenetically primitive teleost immune system, similar to bona-fide M cells. In addition, the presence of MHC class II expression suggests an additional role in antigen presentation in the gills, which are an organ with high T cell abundance, especially in interbranchial lymphoid tissue. The present results suggest an unconventional antigen presentation mechanism in the primitive mucosal immune system of teleosts, which generally lack highly organized lymphoid tissues. Moreover, the results of this work may be valuable for the development of mucosal vaccines that specifically target M-type cells; mucosal vaccines significantly reduce working costs and the stress that is usually induced by vaccination via injection of individual fish.

Control of mycobacteriosis in zebrafish (Danio rerio) mucosally vaccinated with heat-inactivated Mycobacterium bovis

BACKGROUND

Mycobacterial infections greatly affect human and animal health worldwide, and vaccines are effective, sustainable and economic interventions for the prevention and control of these infectious diseases. Recent results support the use of zebrafish as a model for studying the pathophysiology of mycobacterial infection and for the development of novel interventions for tuberculosis (TB) control. Recently, we showed that oral immunization with the heat-inactivated M. bovis vaccine (M. bovis IV) protect wild boar against TB, and suggested that this vaccine may controls mycobacterial infection in other species.

METHODS

In this study we evaluated the effect of M. bovis IV on the control of mycobacteriosis in zebrafish mucosally vaccinated by immersion and challenged intraperitoneally with Mycobacterium marinum.

RESULTS

The results showed that the M. bovis IV administered by immersion protected zebrafish against mycobacteriosis caused by M. marinum by reduction in mycobacterial infection, the number of mycobacteria per granuloma and the number of granulomas per fish. An IgM antibody response against M. bovis antigens was developed in vaccinated fish. Evidences suggested that the protective mechanism elicited by mucosal vaccination with M. bovis IV in zebrafish was based on the activation of the innate immune response through the C3 pathway.

CONCLUSIONS

These results support the use of the M. bovis IV administered by immersion for the control of mycobacteriosis in fish.

Small-Sized mPEG-PLGA Nanoparticles of Schisantherin A with Sustained Release for Enhanced Brain Uptake and Anti-Parkinsonian Activity

Schisantherin A (SA) is a promising anti-Parkinsonism natural product. However, its poor water solubility and rapid serum clearance impose significant barriers to delivery of SA to the brain. This work aimed to develop SA in a nanoparticle formulation that extended SA circulation in the bloodstream and consequently an increased brain uptake and thus to be potentially efficacious for the treatment of Parkinson's disease (PD). Spherical SA nanoparticles with a mean particle size of 70 nm were prepared by encapsulating SA into methoxy poly(ethylene glycol)-block-poly(d,l)-lactic-co-glycolic acid (mPEG-PLGA) nanoparticles (SA-NPs) with an encapsulation efficiency of ∼91% and drug loading of ∼28%. The in vitro release of the SA-NPs lasted for 48 h with a sustained-release pattern. Using the Madin-Darby canine kidney (MDCK) cell model, the results showed that first intact nanoparticles carrying hydrophobic dyes were internalized into cells, then the dyes were slowly released within the cells, and last both nanoparticles and free dyes were externalized to the basolateral side of the cell monolayer. Fluorescence resonance energy transfer (FRET) imaging in zebrafish suggested that nanoparticles were gradually dissociated in vivo with time, and nanoparticles maintained intact in the intestine and brain at 2 h post-treatment. When SA-NPs were orally administrated to rats, much higher C_max and AUC_0-t were observed in the plasma than those of the SA suspension. Furthermore, brain delivery of SA was much more effective with SA-NPs than with SA suspension. In addition, the SA-NPs exerted strong neuroprotective effects in zebrafish and cell culture models of PD. The protective effect was partially mediated by the activation of the protein kinase B (Akt)/glycogen synthase kinase-3β (Gsk3β) pathway. In summary, this study provides evidence that small-sized mPEG-PLGA nanoparticles may improve cross-barrier transportation, oral bioavailability, brain uptake, and bioactivity of this Biopharmaceutics Classification System (BCS) Class II compound, SA.

Specific and Efficient Uptake of Surfactant-Free Poly(Lactic Acid) Nanovaccine Vehicles by Mucosal Dendritic Cells in Adult Zebrafish after Bath Immersion

Activation of mucosal immunity is a key milestone for next-generation vaccine development. Biocompatible polymer-based nanoparticles (NPs) are promising vectors and adjuvants for mucosal vaccination. However, their in vivo uptake by mucosae and their biodistribution in antigen-presenting cells (APCs) need to be better understood to optimize mucosal nanovaccine designs. Here, we assessed if APCs are efficiently targeted in a spontaneous manner by surfactant-free poly(lactic acid) nanoparticles (PLA-NPs) after mucosal administration. Combining histology and flow imaging approaches, we describe and quantify the mucosal uptake of 200 nm PLA-NPs in adult zebrafish. Following bath administration, PLA-NPs penetrated and crossed epithelial barriers from all exposed mucosae. In mucosae, PLA-NPs accumulated in APCs, which were identified as dendritic cells (DCs), macrophages, and IgZ⁺ B cells in gills and skin. PLA-NP uptake by phagocytes was specific to these cell types, as PLA-NPs were not detected in neutrophils. Importantly, quantitative analyses in gills revealed that DCs take up PLA-NPs with specifically high efficiency. This study shows that surfactant-free PLA-NPs, which display optimal biocompatibility, can spontaneously target DCs with high efficiency in vivo following mucosal administration, and highlights PLA-NPs as powerful platforms for mucosal vaccine delivery in the medical and veterinary fields, and particularly in aquaculture.

LLOMe does not release cysteine cathepsins to the cytosol but inactivates them in transiently permeabilized lysosomes

L-leucyl-L-leucine methyl ester (LLOMe) induces apoptosis, which is thought to be mediated by release of lysosomal cysteine cathepsins from permeabilized lysosomes into the cytosol. Here, we demonstrated in HeLa cells that at apoptotic as well as sub-apoptotic concentrations LLOMe caused rapid and complete lysosomal membrane permeabilization (LMP), evidenced by loss of the proton gradient and release into the cytosol of internalized lysosomal markers below 10K molecular weight. However, there was no evidence for the release of cysteine cathepsins B and L into the cytosol; rather they remained within lysosomes, where they were rapidly inactivated and degraded. LLOMe-induced adverse effects, including LMP, loss of cysteine cathepsin activity, caspase activation and cell death could be reduced by inhibition of cathepsin C, but not by inhibiting cathepsins B and L. When incubated with sub-apoptotic LLOMe concentrations, lysosomes transiently lost protons but annealed and re-acidified within hours. Full lysosomal function required new protein synthesis of cysteine cathepsins and other hydrolyses. Our data argue against release of lysosomal enzymes into the cytosol and their proposed proteolytic signaling during LLOMe-induced apoptosis.