Zebrafish as a visual and dynamic model to study the transport of nanosized drug delivery systems across the biological barriers

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

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

To see or not to see: In vivo nanocarrier detection methods in the brain and their challenges

Nanoparticles have a great potential to significantly improve the delivery of therapeutics to the brain and may also be equipped with properties to investigate brain function. The brain, being a highly complex organ shielded by selective barriers, requires its own specialized detection system. However, a significant hurdle to achieve these goals is still the identification of individual nanoparticles within the brain with sufficient cellular, subcellular, and temporal resolution. This review aims to provide a comprehensive summary of the current knowledge on detection systems for tracking nanoparticles across the blood-brain barrier and within the brain. We discuss commonly employed in vivo and ex vivo nanoparticle identification and quantification methods, as well as various imaging modalities able to detect nanoparticles in the brain. Advantages and weaknesses of these modalities as well as the biological factors that must be considered when interpreting results obtained through nanotechnologies are summarized. Finally, we critically evaluate the prevailing limitations of existing technologies and explore potential solutions.

Retinal organoid and gene editing for basic and translational research

The rapid evolution of two technologies has greatly transformed the basic, translational, and clinical research in the mammalian retina. One is the retinal organoid (RO) technology. Various induction methods have been created or adapted to generate species-specific, disease-specific, and experimental-targeted retinal organoids (ROs). The process of generating ROs can highly mimic the in vivo retinal development, and consequently, the ROs resemble the retina in many aspects including the molecular and cellular profiles. The other technology is the gene editing, represented by the classical CRISPR-Cas9 editing and its derivatives such as prime editing, homology independent targeted integration (HITI), base editing and others. The combination of ROs and gene editing has opened up countless possibilities in the study of retinal development, pathogenesis, and therapeutics. We review recent advances in the ROs, gene editing methodologies, delivery vectors, and related topics that are particularly relevant to retinal studies.

Antioxidant Effects of Quercetin Nanocrystals in Nanosuspension against Hydrogen Peroxide-Induced Oxidative Stress in a Zebrafish Model

Quercetin, a flavonoid compound rich in hydroxyl groups, possesses antioxidant properties, whereas its poor water solubility limits its bioavailability. In pursuit of addressing the water solubility of quercetin and comprehending the impact of nanocrystal particle size on antioxidant efficacy, we prepared three different-sized quercetin nanocrystals, namely small (50 nm), medium (140 nm), and large (360 nm), using a nanosuspension method in this study. Within the in vitro setting, assessments employing solubility and radical scavenging assays revealed that quercetin nanocrystals displayed superior solubility (26, 21, and 13 fold corresponding to small, medium, and large particle sizes) and antioxidant performance compared to the coarse quercetin. Furthermore, quercetin nanocrystals of three particle sizes all demonstrated significant protection effects on the survival rate of H2O2-treated zebrafish at 72 h (77.78%, 73.33%, and 66.67% for small, medium, and large particle sizes, respectively), while the coarse quercetin group exhibited a low survival rate (53.3%) similar to the H2O2-treated group (47.8%). Moreover, all quercetin nanocrystals exhibited potent antioxidant capacity on both the antioxidants and enzymatic antioxidant system in H2O2-treated zebrafish to restore zebrafish to a normal state under oxidative stress. For instance, the levels of reactive oxygen species were reduced to 101.10%, 108.83%, and 109.77% of the normal levels for small, medium, and large particle-sized quercetin nanocrystals, respectively. In conclusion, quercetin nanocrystals demonstrated enhanced solubility, robust antioxidant capacity, and protective effects in zebrafish compared to coarse quercetin.

Nobiletin with AIEE Characteristics for Targeting Mitochondria and Real-Time Dynamic Tracking in Zebrafish

Nobiletin is a natural product with multiple physiological activities and is the main ingredient of Pericarpium Citri Reticulatae. We successfully discovered that nobiletin exhibits aggregation induced emission enhancement (AIEE) properties and it has significant advantages such as a large Stokes shift, good stability and excellent biocompatibility. The increase in methoxy groups endows nobiletin a greater fat-solubility, bioavailability and transport rate than the corresponding unmethoxylated flavones. Ulteriorly, cells and zebrafish were used to explore the application of nobiletin in biological imaging. It emits fluorescence in cells and is specifically targeted at mitochondria. Moreover, it has a noteworthy affinity for the digestive system and liver of zebrafish. Due to the unique AIEE phenomenon and stable optical properties of nobiletin, it paves the way for discovering, modifying and synthesizing more molecules with AIEE characteristics. Furthermore, it has a great prospect with regard to imaging cells and cellular substructures, such as mitochondria, which play crucial roles in cell metabolism and death. Indeed, three-dimensional real-time imaging in zebrafish provides a dynamic and visual tool for studying the absorption, distribution, metabolism and excretion of drugs. In this article, more directions and inspiration can be presented for the exploration of non-invasive pharmacokinetic research and intuitive drug pathways or mechanisms.

Advancement in Analytical Techniques for Determining the Activity of β-Site Amyloid Precursor Protein Cleaving Enzyme 1

Alzheimer's disease (AD) is a degenerative disease of the central nervous system. The pathogenesis is still not fully clear. One of the main histopathological manifestations is senile plaques formed by β-amyloid (Aβ) accumulation. Aβ is generated from the sequential proteolysis of amyloid precursor protein (APP) by β-secretase [i.e. β-site APP cleaving enzyme 1 (BACE1)] and γ-secretase, with a rate-limiting step controlled by BACE1 activity. Therefore, inhibiting BACE1 activity has become a potential therapeutic strategy for AD. The development of reliable detection methods for BACE1 activity plays an important role in early diagnosis of AD and evaluation of the therapeutic effect of new drugs for AD. This article has reviewed the recent advances in BACE1 activity detection techniques. The challenges of applying these analysis techniques to early clinical diagnosis of AD and development trends of the detection techniques have been prospected.

Apoptosis-Sensing Xenograft Zebrafish Tumor Model for Anticancer Evaluation of Redox-Responsive Cross-Linked Pluronic Micelles

A suitable animal model for preclinical screening and evaluation in vivo could vastly increase the efficiency and success rate of nanomedicine development. Compared with rodents, the transparency of the zebrafish model offers unique advantages of real-time and high-resolution imaging of the whole body and cellular levels in vivo. In this research, we established an apoptosis-sensing xenograft zebrafish tumor model to evaluate the anti-cancer effects of redox-responsive cross-linked Pluronic polymeric micelles (CPPMs) visually and accurately. First, doxorubicin (Dox)-loaded CPPMs were fabricated and characterized with glutathione (GSH)-responsive drug release. Then, the B16F10 xenograft zebrafish tumor model was established to mimic the tumor microenvironment with angiogenesis and high GSH generation for redox-responsive tumor-targeting evaluation in vivo. The high GSH generation was first verified in the xenograft zebrafish tumor model. Compared with ordinary Pluronic polymeric micelles, Dox CPPMs had a much higher accumulation in zebrafish tumor sites. Finally, the apoptosis-sensing B16F10-C3 xenograft zebrafish tumor model was established for visual, rapid, effective, and noninvasive assessment of anti-cancer effects at the cellular level in vivo. The Dox CPPMs significantly inhibited the proliferation of cancer cells and induced apoptosis in the B16F10-C3 xenograft zebrafish tumor model. Therefore, the redox-responsive cross-linked Pluronic micelles showed effective anti-cancer therapy in the xenograft zebrafish tumor model. This xenograft zebrafish tumor model is available for rapid screening and assessment of anti-cancer effects in preclinical studies.

FRET as the tool for in vivo nanomedicine tracking

Advanced drug delivery system utilizing a nanocarrier is the major application of nanotechnology on pharmacotherapeutics. However, despite the promising benefits and a leading trend in pharmaceutical research, nanomedicine development suffers from a poor clinical translation problem as only a handful of nanomedicine products reach the market yearly. The conventional pharmacokinetic study generally focuses only on monitoring the level of a free drug but ignores the nanocarrier's role in pharmacokinetics. One hurdle is that it is difficult to directly track intact nanocarriers in vivo to explore their pharmacokinetics. Although several imaging techniques such as radiolabeling, nuclear imaging, fluorescence imaging, etc., have been developed over the past few years, currently, one method that can successfully track the intact nanocarriers in vivo directly is by Förster resonance energy transfer (FRET). This review summarizes the application of FRET as the in vivo nanoparticle tracker for studying the in vivo pharmacokinetics of the organic nanocarriers and gives elaborative details on the techniques utilized.

FRET Ratiometric Nanoprobes for Nanoparticle Monitoring

Fluorescence labelling is often used for tracking nanoparticles, providing a convenient assay for monitoring nanoparticle drug delivery. However, it is difficult to be quantitative, as many factors affect the fluorescence intensity. Förster resonance energy transfer (FRET), taking advantage of the energy transfer from a donor fluorophore to an acceptor fluorophore, provides a distance ruler to probe NP drug delivery. This article provides a review of different FRET approaches for the ratiometric monitoring of the self-assembly and formation of nanoparticles, their in vivo fate, integrity and drug release. We anticipate that the fundamental understanding gained from these ratiometric studies will offer new insights into the design of new nanoparticles with improved and better-controlled properties.

Evaluation of the increase of the thymoquinone permeability formulated in polymeric micelles: In vitro test and in vivo toxicity assessment in Zebrafish embryos

Thymoquinone (TQ) is a natural compound present in the essential oil and in the fixed oil of Nigella sativa L. Like many natural substances, it is characterized by poor aqueous solubility and low stability which limit its bioavailability. Soluplus®-Solutol® HS15 polymeric micelles (TQ-MP) were developed to increase the permeability of TQ with particular attention to overcoming intestinal barrier and the blood brain barrier, for possible oral and parenteral administration. The optimized micelles have dimensions < 100 nm and PdI < 0.2 indicating that the formulation was homogeneous as confirmed also by TEM experiments. EE% was 92.4 ± 0.3%. Stability studies showed a stable formulation following subsequent dilutions and in the gastric-intestinal media. In vitro studies have revealed that the carrier enhances the permeability of TQ in the intestine and in the blood-brain barrier using Parallel Artificial Membrane Permeability Assay (PAMPA) assay and cellular tests with Caco-2 cells and hCMEC/D3 monolayer cells. Up-take study, cell viability and cytotoxicity studies were also conducted. Fluorescent micelles (FITC-MP), were also optimized to perform in vitro up-take study in Caco-2 cells and to study their toxicity in Zebrafish model. The toxicity was evaluated on three lines of Zebrafish: wild type, transgenic line Tg(Myl7:EGFP) in which cardiomyocytes are marked with green fluorescence protein and Tg(flk1-GFP) line which expresses GFP under the control of the vascular endothelial growth factor receptor 2 (vegfr2) promoter.

Particle Integrity and Size Effect on the Journey of Polymeric Nanocarriers in Zebrafish Model and the Correlation with Mice

Polymeric nanocarriers have high biocompatibility for potential drug delivery applications. After entering bloodstream, nanocarriers will circulate, interact with proteins, dissociate, or be cleared by reticuloendothelial system. Zebrafish as a visual animal model, can serve as a tool for screening nanomedicines and monitoring nanocarrier behaviors in vivo. However, a comprehensive correlation between zebrafish and rodent models is currently deficient. Here, different-sized poly(caprolactone) nanocarriers (PCL NCs) are fabricated with or without PEGylation to investigate correlation between zebrafish and mice regarding their biofate via Förster resonance energy transfer technique. Results show that PEGylated PCL NCs have higher integrity in both zebrafish and mice. Small PEG-PCL NCs have longer circulation, while large PEG-PCL NCs have dramatically higher macrophage sequestration in zebrafish and mice spleen, leading to poor circulation. PCL NCs dissociate rapidly with less macrophage sequestration. Moreover, in 7 days postfertilization (dpf) zebrafish, polymers are eliminated via hepatobiliary pathway, which is not fully functional at earlier stages of development. The effects of nanocarrier integrity on macrophage sequestration in zebrafish and good correlation with mice spleen are pioneered to be demonstrated. The findings suggest that 7 dpf zebrafish are suitable as an in vivo screening model of nanocarriers and predict their biofate in rodents.

Zebrafish Models for the Safety and Therapeutic Testing of Nanoparticles with a Focus on Macrophages

New nanoparticles and biomaterials are increasingly being used in biomedical research for drug delivery, diagnostic applications, or vaccines, and they are also present in numerous commercial products, in the environment and workplaces. Thus, the evaluation of the safety and possible therapeutic application of these nanomaterials has become of foremost importance for the proper progress of nanotechnology. Due to economical and ethical issues, in vitro and in vivo methods are encouraged for the testing of new compounds and/or nanoparticles, however in vivo models are still needed. In this scenario, zebrafish (Danio rerio) has demonstrated potential for toxicological and pharmacological screenings. Zebrafish presents an innate immune system, from early developmental stages, with conserved macrophage phenotypes and functions with respect to humans. This fact, combined with the transparency of zebrafish, the availability of models with fluorescently labelled macrophages, as well as a broad variety of disease models offers great possibilities for the testing of new nanoparticles. Thus, with a particular focus on macrophage-nanoparticle interaction in vivo, here, we review the studies using zebrafish for toxicological and biodistribution testing of nanoparticles, and also the possibilities for their preclinical evaluation in various diseases, including cancer and autoimmune, neuroinflammatory, and infectious diseases.

Phosphonate as a Stable Zinc-Binding Group for "Pathoblocker" Inhibitors of Clostridial Collagenase H (ColH)

Microbial infections are a significant threat to public health, and resistance is on the rise, so new antibiotics with novel modes of action are urgently needed. The extracellular zinc metalloprotease collagenase H (ColH) from Clostridium histolyticum is a virulence factor that catalyses tissue damage, leading to improved host invasion and colonisation. Besides the major role of ColH in pathogenicity, its extracellular localisation makes it a highly attractive target for the development of new antivirulence agents. Previously, we had found that a highly selective and potent thiol prodrug (with a hydrolytically cleavable thiocarbamate unit) provided efficient ColH inhibition. We now report the synthesis and biological evaluation of a range of zinc-binding group (ZBG) variants of this thiol-derived inhibitor, with the mercapto unit being replaced by other zinc ligands. Among these, an analogue with a phosphonate motif as ZBG showed promising activity against ColH, an improved selectivity profile, and significantly higher stability than the thiol reference compound, thus making it an attractive candidate for future drug development.

Improving Oral Bioavailability of Luteolin Nanocrystals by Surface Modification of Sodium Dodecyl Sulfate

Luteolin suffers from drawbacks like low solubility and bioavailability, thus hindering its application in the clinic. In this study, we employed sodium dodecyl sulfate (SDS), an efficient tight junction opening agent, to modify the surface of luteolin nanocrystals, aiming to enhance the bioavailability of luteolin (LUT) and luteolin nanocrystals (LNC). The particle sizes of SDS-modified luteolin nanocrystals (SLNC) were slightly larger than that of LNC, and the zeta potential of LNC and SLNC was -25.0 ± 0.7 mV and -43.5 ± 0.4 mV, respectively. Both LNC and SLNC exhibited enhanced saturation solubility and high stability in the liquid state. In the cellular study, we found that SDS has cytotoxicity on caco-2 cells and could open the tight junction of the caco-2 monolayer, which could lead to an enhanced transport of luteolin across the intestinal membrane. The bioavailability of luteolin was enhanced for 1.90-fold by luteolin nanocrystals, and after modification with SDS, the bioavailability was enhanced to 3.48-fold. Our experiments demonstrated that SDS could efficiently open the tight junction and enhance the bioavailability of luteolin thereafter, revealing the construction of SDS-modified nanocrystals is a good strategy for enhancing the oral bioavailability of poorly soluble drugs like luteolin.

Polymeric Nanoparticles-Based Brain Delivery with Improved Therapeutic Efficacy of Ginkgolide B in Parkinson's Disease

Purpose

Ginkgolide B (GB) is a terpene lactone derivative of Ginkgo biloba that is believed to function in a neuroprotective manner ideal for treating Parkinson’s disease (PD). Despite its promising therapeutic properties, GB has poor bioavailability following oral administration and cannot readily achieve sufficient exposure in treated patients, limiting its clinical application for the treatment of PD. In an effort to improve its efficacy, we utilized poly(ethylene glycol)-co-poly(ε-caprolactone) (PEG-PCL) nanoparticles as a means of encapsulating GB (GB-NPs). These NPs facilitated the sustained release of GB into the blood, thereby improving its ability to accumulate in the brain and to treat PD.

Methods and Results

Using Madin-Darby canine kidney (MDCK) cells, we were able to confirm that these NPs could be taken into cells via multiple nonspecific mechanisms including micropinocytosis, clathrin-dependent endocytosis, and lipid raft/caveolae-mediated endocytosis. Once internalized, these NPs tended to accumulate in the endoplasmic reticulum and lysosomes. In zebrafish, we determined that these NPs were readily able to undergo transport across the chorion, gastrointestinal, blood–brain, and blood-retinal barriers. In a 1-methyl-4-phenylpyridinium ion (MPP⁺)-induced neuronal damage model system, we confirmed the neuroprotective potential of these NPs. Following oral administration to rats, GB-NPs exhibited more desirable pharmacokinetics than did free GB, achieving higher GB concentrations in both the brain and the blood. Using a murine PD model, we demonstrated that these GB-NPs achieved superior therapeutic efficacy and reduced toxicity relative to free GB.

Conclusion

In conclusion, these results indicate that NPs encapsulation of GB can significantly improve its oral bioavailability, cerebral accumulation, and bioactivity via mediating its sustained release in vivo.

In vitro kinetic release study, antimicrobial activity and in vivo toxicity profile of a kojic acid ester-based nanoemulsion for topical application

Nanoemulsions have emerged as novel vehicles for drug delivery that allow sustained or controlled release for topical application. In this study, kojic acid ester-based nanoemulsion (KAE-NA) was analyzed for in vitro permeation evaluation, kinetic release study, in vitro antimicrobial activity and in vivo toxicity profile on embryonic zebrafish (Danio rerio). Based on KAE-NA in vitro permeation evaluation, the percentage of permeation was significantly improved from 4.94% at 1 h to 59.64% at 8 h of application. The permeation rate of KAE-NA at 8 h was 4659.50 μg cm-2 h-1 (initial concentration, C 0 = 2000 μg mL-1) with a permeability coefficient (K p) value of 0.48 cm h-1. The kinetic release analysis showed the Korsmeyer-Peppas model was the best fitted kinetic model with high linearity [R 2 = 0.9964]. Antimicrobial activity of KAE-NA was studied against the skin pathogen bacteria Staphylococcus aureus ATCC 43300. The results indicated that the inhibition zone size of the KAE-NA (8.00 ± 0.0 mm) was slightly bigger than that of its active ingredient, kojic acid ester (6.5 ± 0.0 mm). The toxicity profile of KAE-NA on embryonic zebrafish revealed less toxicity with LC50 (50% lethal concentration) more than 500 μg mL-1. The survival rate of the embryonic zebrafish was more than 80% when treated at doses ranging from 7.81-250 μg mL-1 and showed normal development throughout the experiment without any observed deformation. Hence, KAE-NA proved to be less toxic on the embryonic zebrafish.

Nano-emulsification of Aeollanthus suaveolens Mart. Ex Spreng essential oil modifies its neuroeffects?

Oil in water nano-emulsions are drug delivery systems constituted by liquid lipophilic nano-droplets dispersed through the external aqueous phase, often reaching the kinetic stability with surfactant as stabilizers. Essential oils can be the oily phase or the source of bioactive compounds. In this study, the essential oil of Aeollanthus suaveolens-a plant used in folk medicine due to its psychopharmacological effects-was used for preparation of fine nano-emulsions by a low-energy titrating method. Monodisperse small nano-droplets (ca. 70 nm; PdI 0.200) were assembled by using blends of non-ionic surfactants, indicating modulation on surfactant system lead to altering the physical property. In a separate set of experiments, we investigated the role of this modulation on biological properties of the optimal nano-emulsion. The zebrafish embryos were more susceptible to the nano-emulsion than the bulk essential oil, showing the improved bioactivity due to nano-sizing. Therefore, adult zebrafish was treated, and paralysis was observed in the groups treated with the nano-emulsion, being this finding in accordance with hypnosis. At the same essential oil dose, another behavior was observed, suggesting that expected dose-dependent effects associated to sedative-hypnotics can be achieved by nano-sizing of psychoactive essential oils. This paper contributes to the state-of-art drug delivery systems by opening perspectives for novel sedative-hypnotics nano-emulsified essentials oils that can reach hypnotic effects at considerably lower dose, when compared with bulk materials, being useful for further completed dose-response studies.Graphical abstract.

Nanoparticles Mediating the Sustained Puerarin Release Facilitate Improved Brain Delivery to Treat Parkinson's Disease

Recent work has highlighted the potential of puerarin (PU) as a valuable compound to treat Parkinson's disease (PD), but its undesirable water solubility and bioavailability have constrained its utility. In this study, we sought to develop nanoparticles (NPs) that could be used to encapsulate PU, thereby extending its in vivo half-life and improving its bioavailability and accumulation in the brain to treat the symptoms of PD. We prepared spherical NPs (88.36 ± 1.67 nm) from six-armed star-shaped poly(lactide-co-glycolide) (6-s-PLGA) NPs that were used to encapsulate PU (PU-NPs) with 89.52 ± 1.74% encapsulation efficiency, 42.97 ± 1.58% drug loading, and a 48 h sustained drug release. NP formation and drug loading were largely mediated by hydrophobic interactions, while changes in the external environment led these NPs to become increasingly hydrophilic, thereby leading to drug release. Relative to PU alone, PU-NPs exhibited significantly improved cellular internalization, permeation, and neuroprotective effects. Upon the basis of Förster resonance energy transfer (FRET) of NPs-administered zebrafish, we were able to determine that these NPs were rapidly absorbed into circulation whereupon they were able to access the brain. We further conducted oral PU-NPs administration to rats, revealing significant improvements in PU accumulation within the plasma and brain relative to rats administered free PU. In MPTP-mediated neurotoxicity in mice, we found that PU-NPs treatment improved disease-associated behavioral deficits and depletion of dopamine and its metabolites. These findings indicated that PU-NPs represent a potentially viable approach to enhancing PU oral absorption, thus improving its delivery to the brain wherein it can aid in the treatment of PD.

Zebrafish embryo as a replacement model for initial biocompatibility studies of biomaterials and drug delivery systems

The development of new biomaterials and drug delivery systems necessitates animal experimentation to demonstrate biocompatibility and therapeutic efficacy. Reduction and replacement of the requirement to conduct experiment using full-grown animals has been achieved through utilising zebrafish embryos, a promising bridge model between in vitro and in vivo research. In this review, we consider how zebrafish embryos have been utilised to test both the biocompatibility of materials developed to interact with the human body and drug release studies. Furthermore, we outline the advantages and limitations of this model and review legal and ethical issues. We anticipate increasing application of the zebrafish model for biomaterial evaluation in the near future. STATEMENT OF SIGNIFICANCE: This review aims to evaluate the potential application and suitability of the zebrafish model in the development of biomaterials and drug delivery systems. It creates scientific impact and interest because replacement models are desirable to the society and the scientific community. The continuous development of biomaterials calls for the need to provide solutions for biological testing. This review covers the topic of how the FET model can be applied to evaluate biocompatibility. Further, it explores the zebrafish from the wild-type to the mutant form, followed by a discussion about the ethical considerations and concerns when using the FET model.

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.

Exploring the mechanisms of graphene oxide behavioral and morphological changes in zebrafish

The presence of natural organic matter such as humic acid (HA) can influence the behavior of graphene oxide (GO) in the aquatic environment. In this study, zebrafish embryos were analyzed after 5 and 7 days of exposure to GO (100 mg L^-1) and HA (20 mg L^-1) alone or together. The results indicated that, regardless of the presence of HA, larvae exposed to GO for 5 days showed an increase in locomotor activity, reduction in the yolk sac size, and total length and inhibition of AChE activity, but there was no difference in enzyme expression. The statistical analysis indicated that the reductions in total larval length, yolk sac size, and AChE activity in larvae exposed to GO persisted in relation to the control group, but there was a recovery of these parameters in groups also exposed to HA. Larvae exposed to GO for 7 days did not show significant differences in locomotor activity, but the RT-PCR gene expression analysis evidenced an increase in the AChE expression. Since the embryos exposed to GO showed a reduction in overall length, they were submitted to confocal microscopy and their muscle tissue configuration investigated. No changes were observed in the muscle tissue. The results indicated that HA is associated with the toxicity risk modulation by GO and that some compensatory homeostasis mechanisms may be involved in the developmental effects observed in zebrafish.

Nanomaterials meet zebrafish: Toxicity evaluation and drug delivery applications

With the rapid development of engineered nanomaterials for various applications, in vivo toxicological studies for evaluating the potential hazardous effects of nanomaterials on environmental and human safety are in urgent need. Zebrafish has long been considered as the "gold standard" for biosafety assessments of chemicals and pollutants due to its high fecundity, cost-effectiveness, well-characterized developmental stages, optical transparency, and so forth. Thus, zebrafish holds great potential for high-throughput nanotoxicity screening. In this review, we summarize the in vivo toxicological profiles of different nanomaterials, including Ag nanoparticles (NPs), CuO NPs, silica NPs, polymeric NPs, quantum dots, nanoscale metal-organic frameworks, etc, in zebrafish and focus on how the physicochemical properties (e.g., size, surface charge, and surface chemistry) of these nanomaterials influence their biosafety. In addition, we also report the recent advances of the in vivo delivery of nanopharmaceuticals using zebrafish as the model organism for therapeutic assessment, biodistribution tracking, and the controlled release of loaded drugs. Limitations and special considerations of zebrafish model are also discussed. Overall, zebrafish is expected to serve as a high-throughput screening platform for nanotoxicity and drug delivery assessment, which may instruct the design of safe nanomaterials and more effective nanomedicines.

Let's get small (and smaller): Combining zebrafish and nanomedicine to advance neuroregenerative therapeutics

Several key attributes of zebrafish make them an ideal model system for the discovery and development of regeneration promoting therapeutics; most notably their robust capacity for self-repair which extends to the central nervous system. Further, by enabling large-scale drug discovery directly in living vertebrate disease models, zebrafish circumvent critical bottlenecks which have driven drug development costs up. This review summarizes currently available zebrafish phenotypic screening platforms, HTS-ready neurodegenerative disease modeling strategies, zebrafish small molecule screens which have succeeded in identifying regeneration promoting compounds and explores how intravital imaging in zebrafish can facilitate comprehensive analysis of nanocarrier biodistribution and pharmacokinetics. Finally, we discuss the benefits and challenges attending the combination of zebrafish and nanoparticle-based drug optimization, highlighting inspiring proof-of-concept studies and looking toward implementation across the drug development community.

Application of Förster Resonance Energy Transfer (FRET) technique to elucidate intracellular and In Vivo biofate of nanomedicines

Extensive studies on nanomedicines have been conducted for drug delivery and disease diagnosis (especially for cancer therapy). However, the intracellular and in vivo biofate of nanomedicines, which is significantly associated with their clinical therapeutic effect, is poorly understood at present. This is because of the technical challenges to quantify the disassembly and behaviour of nanomedicines. As a fluorescence- and distance-based approach, the Förster Resonance Energy Transfer (FRET) technique is very successful to study the interaction of nanomedicines with biological systems. In this review, principles on how to select a FRET pair and construct FRET-based nanomedicines have been described first, followed by their application to study structural integrity, biodistribution, disassembly kinetics, and elimination of nanomedicines at intracellular and in vivo levels, especially with drug nanocarriers including polymeric micelles, polymeric nanoparticles, and lipid-based nanoparticles. FRET is a powerful tool to reveal changes and interaction of nanoparticles after delivery, which will be very useful to guide future developments of nanomedicine.

Development of the brain vasculature and the blood-brain barrier in zebrafish

To ensure tissue homeostasis the brain needs to be protected from blood-derived fluctuations or pathogens that could affect its function. Therefore, the brain capillaries develop tissue-specific properties to form a selective blood-brain barrier (BBB), allowing the passage of essential molecules to the brain and blocking the penetration of potentially harmful compounds or cells. Previous studies reported the presence of this barrier in zebrafish. The intrinsic features of the zebrafish embryos and larvae in combination with optical techniques, make them suitable for the study of barrier establishment and maturation. In this review, we discuss the most recent contributions to the development and formation of a functional zebrafish BBB. Moreover, we compare the molecular and cellular characteristic of the zebrafish and the mammalian BBB.

Oral Delivery of Puerarin Nanocrystals To Improve Brain Accumulation and Anti-Parkinsonian Efficacy

Puerarin (PU) has emerged as a promising herb-derived anti-Parkinsonism compound. However, the undesirable water solubility as well as the unwanted bioavailability of PU limit its application. Therefore, this study aimed to develop and characterize PU nanocrystals (PU-NCs) with enhanced oral bioavailability and improved brain accumulation for the treatment of Parkinson's disease (PD). The fabricated PU-NCs were approximately spherical, with a mean size of 83.05 ± 1.96 nm, a PDI of 0.047 ± 0.009, a drug loading of 72.7%, and a rapid dissolution rate in vitro. Molecular dynamics simulation of PU and Pluronic F68 demonstrated the interaction energy and binding energy of -88.1 kJ/mol and -40.201 ± 0.685 kJ/mol, respectively, indicating a spontaneous binding with van der Waals interactions. In addition, the cellular uptake and permeability of PU-NCs were significantly enhanced as compared to PU alone ( p < 0.01). Moreover, PU-NCs exerted a significant neuroprotective effect against the cellular damage induced by the 1-methyl-4-phenylpyridinium ion (MPP⁺). Besides, PU-NCs demonstrated no obvious toxic effects on zebrafish, as evidenced by the unaltered morphology, hatching, survival rate, body length, and heart rate. Fluorescence resonance energy transfer (FRET) imaging revealed that intact nanocrystals were found in the intestine and brain of adult zebrafish gavaged with DiO/DiI/PU-NCs. Increased values of C_max and AUC_{0- t} were observed in the plasma of rats following oral administration of PU-NCs compared to PU suspension. Likewise, brain accumulation of PU-NCs was higher than that of PU suspension. Furthermore, PU-NCs attenuated dopamine depletion, ameliorated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced behavioral deficits, and enhanced the levels of dopamine and its metabolites. Taken altogether, this study provides evidence that PU-NCs could be exploited as a potential oral delivery system to treat PD, by improving the poor bioavailability of PU and enhancing their delivery into the brain.

Stability, Cellular Uptake, and in Vivo Tracking of Zwitterion Modified Graphene Oxide as a Drug Carrier

In this paper, a novel kind of zwitterion modified graphene oxide (GO) for promoting stability and reducing aggregation of GO as a drug carrier was proposed and demonstrated. Specifically, the GO was functionalized with a kind of zwitterion based silane, 3-(dimethyl(3-(trimethoxysilyl)propyl)-ammonio)propane-1-sulfonate (SBS). After zwitterion modification, the SBS functionalized GO (GO-SB) shows significantly enhanced stability in both serum-free and serum-containing solution, especially after loading doxorubicin hydrochloride (DOX). According to drug release profiles, the drug-loaded GO-SB exhibits thermosensitive and sustained release behavior. Meanwhile, in vitro studies show that the DOX loaded GO-SB could be easily internalized by HepG2 cells and exhibit obvious cytotoxicity on the cells. And, in vivo studies demonstrate that the GO-SB drug carrier is capable of being taken by the larvae of zebrafish and can be eliminated from the body within several days.

Transgenic zebrafish model for quantification and visualization of tissue toxicity caused by alloying elements in newly developed biodegradable metal

The cytotoxicity of alloying elements in newly developed biodegradable metals can be assessed through relatively low-cost and rapid in vitro studies using different cell types. However, such approaches have limitations; as such, additional investigations in small mammalian models are required that recapitulate the physiological environment. In this study, we established a zebrafish (Danio rerio) model for cytotoxicity evaluations that combines the physiological aspects of an animal model with the speed and simplicity of a cell-based assay. The model was used to assess the cytotoxicity of five common alloying elements in biodegradable implant materials. Conventional in vitro testing using heart, liver, and endothelial cell lines performed in parallel with zebrafish studies revealed statistically significant differences in toxicity (up to 100-fold), along with distinct changes in the morphology of the heart, liver, and blood vessels that were undetectable in cell cultures. These results indicate that our zebrafish model is a useful alternative to mammalian systems for accurately and rapidly evaluating the in vivo toxicity of newly developed metallic materials.

Zebrafish (Danio rerio) model as an early stage screening tool to study the biodistribution and toxicity profile of doxorubicin-loaded mixed micelles

Doxorubicin (DOX) hydrochloride is a powerful anthracycline antibiotic used for the treatment of various types of malignancies, particularly ovarian and metastatic breast cancer. However, DOX presents severe side effects, such as hepatotoxicity, nephrotoxicity, dose-limiting myelosuppression, brain damage and cardiotoxicity. A liposomal formulation, Doxil®, was approved by the FDA, which has managed to reduce the number of cardiac events in patients with metastatic breast cancer. However, in comparison to free DOX, Doxil® has not shown significant improvements regarding survival. We have previously designed DOX-loaded mixed micelles (MMDOX) composed of D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) and Tetronic® T1107. To assess the potential toxic effects of this novel formulation, in this work the zebrafish (Danio rerio) model was used to evaluate its in vivo toxicity and teratogenicity. This study evaluated and compared the effects of DOX exposure from different formulations (free DOX, MMDOX and Doxil®) on the swimming activity, morphological alterations, cardiac rhythm, lethality rate and DOX biodistribution. MMDOX showed lower lethal effects, morphological alterations and neurotoxic effects than the free drug. This study shows the potential of the MMDOX to be an effective DOX-delivery system because it could reduce the side effects.

The Potential of Zebrafish as a Model Organism for Improving the Translation of Genetic Anticancer Nanomedicines

In the last few decades, the field of nanomedicine applied to cancer has revolutionized cancer treatment: several nanoformulations have already reached the market and are routinely being used in the clinical practice. In the case of genetic nanomedicines, i.e., designed to deliver gene therapies to cancer cells for therapeutic purposes, advances have been less impressive. This is because of the many barriers that limit the access of the therapeutic nucleic acids to their target site, and the lack of models that would allow for an improvement in the understanding of how nanocarriers can be tailored to overcome them. Zebrafish has important advantages as a model species for the study of anticancer therapies, and have a lot to offer regarding the rational development of efficient delivery of genetic nanomedicines, and hence increasing the chances of their successful translation. This review aims to provide an overview of the recent advances in the development of genetic anticancer nanomedicines, and of the zebrafish models that stand as promising tools to shed light on their mechanisms of action and overall potential in oncology.

Zebrafish: A Visual Model To Evaluate the Biofate of Transferrin Receptor-Targeted 7Peptide-Decorated Coumarin 6 Micelles

In the present study, the zebrafish was explored as an in vivo model to assess the biofate of transferrin receptor (TfR)-targeted coumarin 6 (C6) micelles across various biological barriers. Three 7peptide (7pep)-decorated poly(ethylene glycol)-block-poly(ε-caprolactone) micelles loaded with fluorescence coumarin 6 (7pep-M-C6) with different ligand densities were constructed with particle sizes between 30 and 40 nm. Whole-mount immunostaining revealed that the expression level of TfR in the retina, brain, and intestine increased along with development stage. Compared to unmodified micelles, 7pep-M-C6 demonstrated higher uptake efficiency in the larval zebrafish. Preinhibition of TfR with 7pep implicated the TfR-mediated endocytosis pathway in the uptake of 7pep-M-C6. Confocal images of the larval zebrafish eye and brain showed the efficient delivery of C6 across the retinal pigment epithelial to the ganglion cell layer and the significant accumulation of C6 in all brain tissues, respectively, which plateaued when the ligand density was 10%. To investigate the intestinal distribution of C6, micelles were administered to adult zebrafish via gavaging. Notably, 7pep-M-C6 enhanced the transport of C6 across the villi and increased its aggregation into the basolateral membrane of the intestine. After the oral administration of 7pep-M-C6, C6 accumulated in the eye and brain. Förster resonance energy transfer analysis suggested that intact 7pep-modified micelles could enter the epithelial cells of the intestine, brain, and eye after oral administration in adult zebrafish. In conclusion, zebrafish could be used as a model for in vivo visual assessment of the biofate of TfR-targeted drug delivery systems.

Zebrafish: A promising in vivo model for assessing the delivery of natural products, fluorescence dyes and drugs across the blood-brain barrier

The blood brain barrier (BBB) is the network of capillaries that controls the passage of substances from the blood into the brain and other parts of the central nervous system (CNS). As this barrier is the major obstacle for drug delivery into CNS, a credible BBB model is very necessary to assess the BBB permeability of novel neuroactive compounds including thousands of bioactive compounds which have been extracted from medicinal plants and have the potential for the treatment of CNS diseases. Increasing reports indicated that zebrafish has emerged as a timely, reproducible model for BBB permeability assessment. In this review, the development and functions of the BBB in zebrafish, such as its anatomical morphology, tight junctions, drug transporters and enzyme expression, are compared with those in mammals. The studies outlined in this review describe the utilization of the zebrafish as a BBB model to investigate the permeability and distribution of fluorescent dyes and drugs. Particularly, this review focuses on the use of zebrafish to evaluate the delivery of natural products and nanosized drug delivery systems across the BBB. Due to the highly conserved nature of both the structure and function of the BBB between zebrafish and mammals, zebrafish has the potential to be developed as a model for assessing and predicting the permeability of BBB to novel compounds.