A new high-content model system for studies of gastrointestinal transit: the zebrafish

The comparative analysis of gastrointestinal toxicity of azithromycin and 3'-decladinosyl azithromycin on zebrafish larvae

The most commonly reported side effect of azithromycin is gastrointestinal (GI) disorders, and the main acid degradation product is 3'-Decladinosyl azithromycin (impurity J). We aimed to compare the GI toxicity of azithromycin and impurity J on zebrafish larvae and investigate the mechanism causing the differential GI toxicity. Results of our study showed that the GI toxicity induced by impurity J was higher than that of azithromycin in zebrafish larvae, and the effects of impurity J on transcription in the digestive system of zebrafish larvae were significantly stronger than those of azithromycin. Additionally, impurity J exerts stronger cytotoxic effects on GES-1 cells than azithromycin. Simultaneously, impurity J significantly increased ghsrb levels in the zebrafish intestinal tract and ghsr levels in human GES-1 cells compared to azithromycin, and ghsr overexpression significantly reduced cell viability, indicating that GI toxicity induced by azithromycin and impurity J may be correlated with ghsr overexpression induced by the two compounds. Meanwhile, molecular docking analysis showed that the highest -CDOCKER interaction energy scores with the zebrafish GHSRb or human GHSR protein might reflect the effect of azithromycin and impurity J on the expression of zebrafish ghsrb or human ghsr. Thus, our results suggest that impurity J has higher GI toxicity than azithromycin due to its greater ability to elevate ghsrb expression in zebrafish intestinal tract.

Radiographic assessment of the impact of sex and the circadian rhythm-dependent behaviour on gastrointestinal transit in the rat

Relatively little is known about the influence of sex and the circadian rhythm on gastrointestinal transit. However, these factors could have an important impact on aspects such as digestion, oral absorption of drugs or the clinical manifestation of gastrointestinal diseases, among others. Remarkably, preclinical models have scarcely taken these factors into consideration. In this study, we assessed the gastrointestinal transit of young adult Wistar Han rats of both sexes, under normal and inverted light cycle. To do this, serial radiographs were taken for 24 h (T0–T24) after intragastric barium administration and subsequently analysed to construct transit curves for each gastrointestinal region. Under a normal light cycle, transit curves were similar, except for a slower transit in females compared with males from T8 to T24. Under the inverted cycle, there was a significant acceleration in stomach emptying (similar in both sexes), emptying of the small intestine (even faster in females) and filling of the caecum and colon (which was also even faster in females). This study confirms, using X-ray non-invasive methods for the first time, that both sex and circadian rhythm (probably through its effect on behaviour) influence gastrointestinal transit in laboratory animals.

Bifidobacterium lactis BL-99 modulates intestinal inflammation and functions in zebrafish models

This study was designed to explore the therapeutics and the mechanisms of a patented and marked gastric acid and intestine juice-resistant probiotics Bifidobacterium lactis BL-99 (B. lactis BL-99) on the intestinal inflammation and functions in the zebrafish models. After feeding for 6 hours, B. lactis BL-99 was fully retained in the larval zebrafish intestinal tract and stayed for over 24 hours. B. lactis BL-99 promoted the intestinal motility and effectively alleviated aluminum sulfate-induced larval zebrafish constipation (p < 0.01). Irregular high glucose diet induced adult zebrafish intestinal functional and metabolic disorders. After fed with B. lactis BL-99, IL-1β gene expression was significantly down-regulated, and IL-10 and IL-12 gene levels were markedly up-regulated in this model (p < 0.05). The intestinal lipase activity was elevated in the adult zebrafish intestinal functional disorder model after B. lactis BL-99 treatment (p < 0.05), but tryptase content had no statistical changes (p > 0.05). B. lactis BL-99 improved the histopathology of the adult zebrafish intestinal inflammation, increased the goblet cell numbers, and up-and-down metabolites were markedly recovered after treatment of B. lactis BL-99 (p < 0.05). These results suggest that B. lactis BL-99 could relieve intestinal inflammation and promote intestinal functions, at least in part, through modulating intestinal and microbial metabolism to maintain intestinal health.

The Gut-Brain-Microbiome Axis and Its Link to Autism: Emerging Insights and the Potential of Zebrafish Models

Research involving autism spectrum disorder (ASD) most frequently focuses on its key diagnostic criteria: restricted interests and repetitive behaviors, altered sensory perception, and communication impairments. These core criteria, however, are often accompanied by numerous comorbidities, many of which result in severe negative impacts on quality of life, including seizures, epilepsy, sleep disturbance, hypotonia, and GI distress. While ASD is a clinically heterogeneous disorder, gastrointestinal (GI) distress is among the most prevalent co-occurring symptom complex, manifesting in upward of 70% of all individuals with ASD. Consistent with this high prevalence, over a dozen family foundations that represent genetically distinct, molecularly defined forms of ASD have identified GI symptoms as an understudied area with significant negative impacts on quality of life for both individuals and their caregivers. Moreover, GI symptoms are also correlated with more pronounced irritability, social withdrawal, stereotypy, hyperactivity, and sleep disturbances, suggesting that they may exacerbate the defining behavioral symptoms of ASD. Despite these facts (and to the detriment of the community), GI distress remains largely unaddressed by ASD research and is frequently regarded as a symptomatic outcome rather than a potential contributory factor to the behavioral symptoms. Allowing for examination of both ASD's impact on the central nervous system (CNS) as well as its impact on the GI tract and the associated microbiome, the zebrafish has recently emerged as a powerful tool to study ASD. This is in no small part due to the advantages zebrafish present as a model system: their precocious development, their small transparent larval form, and their parallels with humans in genetics and physiology. While ASD research centered on the CNS has leveraged these advantages, there has been a critical lack of GI-centric ASD research in zebrafish models, making a holistic view of the gut-brain-microbiome axis incomplete. Similarly, high-throughput ASD drug screens have recently been developed but primarily focus on CNS and behavioral impacts while potential GI impacts have not been investigated. In this review, we aim to explore the great promise of the zebrafish model for elucidating the roles of the gut-brain-microbiome axis in ASD.

Probiotics Modulate Intestinal Motility and Inflammation in Zebrafish Models

This study was aimed to assess effects of three strains of probiotics Lactobacillus acidophilus NCFM, Lactobacillus rhamnosus HN001, and Bifidobacterium animalis subsp. lactis Bi-07 on the intestinal motility and inflammation in the zebrafish models. The intestinal motility model was established using 5 days postfertilization (dpf) zebrafish administered with a fluorescent dye Nile red at 10 ng/mL for 16 h, followed by probiotics treatment for 24 h and the intestinal motility was inversely proportional to the intestinal fluorescence intensity that was quantitatively measured by image analysis. The intestinal inflammation was induced by treating 3 dpf neutrophil fluorescent zebrafish with 0.0125% of trinitrobenzenesulfonic acid for 48 h. Probiotics were administered at low, moderate, and high concentrations determined based on maximum tolerable concentration through soaking. All three strains of probiotics promoted intestinal movement, of which B. animalis subsp. lactis Bi-07 was most potent at lower concentrations. L. rhamnosus HN001 and B. animalis subsp. lactis Bi-07 had the therapeutic effects on the intestinal inflammation and the inflammation-associated mucosal damage recovery. The anti-inflammatory mechanisms of L. rhamnosus HN001 was related to both reduce inflammatory factor interleukin-6 (IL-6) and restored tissue repair factor transforming growth factor-β-1 (TGFβ-1); whereas B. animalis subsp. lactis Bi-07 was probably only associated with TGFβ-1 elevation. Using larval zebrafish models for probiotics screening and assessment would speed up product research and development and improve products' efficacy and quality.

Screening of intestinal peristalsis-promoting probiotics based on a zebrafish model

Based on the difference of the intestinal tract fluorescence intensity of zebrafish, the precise screening of strains with high retention capacity in vivo was completed and probiotics for intestinal peristalsis were quickly screened from strains with high retention capacity using the transparent visibility of zebrafish. In order to study the relationship between probiotic retention and intestinal peristalsis and develop constipation-resistant probiotics, this study used 2 types of strain and 6 potential functional strains and screened them based on the fluorescence intensity and intestinal peristalsis-promoting in the zebrafish model. The methods and results were as follows: (1) the zebrafish were immersed in the strains labeled with fluorescein isothiocyanate (FITC), and the intestinal fluorescence intensity was taken as the index. The strain L. paracasei X11 with good retention capacity was screened out. (2) 220 zebrafish were randomly selected and divided into 11 groups with 20 tails in each group. 1 group was the normal control group and the other 10 groups were used to construct the constipation zebrafish model by the loperamide hydrochloride method, namely, 1 model control group, 1 model + positive drug control group (domperidone), 2 model + type strains control groups, and 6 model + potential strain treatment groups. The intestinal peristalsis frequency of each group within 1 min was calculated after immersing the model zebrafish in 108 CFU mL-1 strain solution. The results showed that L. paracasei X11 had a better function of intestinal peristalsis-promotion.

Intestinal Transit Time and Cortisol-Mediated Stress in Zebrafish

Intestinal motility, the spontaneous and rhythmic smooth muscle contraction, is a complex process that is regulated by overlapping and redundant regulatory mechanisms. Primary regulators intrinsic to the gastrointestinal tract include interstitial cells of Cajal, enteric neurons, and smooth muscle cells. Extrinsic primary regulators include the autonomic nervous system, immune system, and the endocrine system. Due to this complexity, a reductionist approach may be inappropriate if the ultimate goal is to understand motility regulation in vivo. Motility can be directly visualized in intact zebrafish, with intact regulatory systems, because larvae are transparent. Intestinal motility can therefore be measured in a complete system. However, the intestinal tract may respond to external influences, such as handling, which may invoke a stress response and influence intestinal transit. We used SR4G transgenic zebrafish, which express green fluorescent protein following activation of glucocorticoid receptors, and showed that handling required for the intestinal motility assay induces stress. Separate experiments showed that exogenous application of hydrocortisone did not influence intestinal transit, suggesting that handling may not interfere with transit measurements in intact zebrafish larvae. These experiments contribute to further development of the zebrafish model for intestinal motility research.

Human prokinetic drugs promote gastrointestinal motility in zebrafish

BACKGROUND

Gastrointestinal (GI) motility disorders are highly prevalent in populations worldwide and the development of effective and safe drug treatments for GI motility disorders has proven challenging. In this study, taking advantage of the transparency of larval zebrafish, we developed a novel zebrafish GI motility model for drug screening and efficacy assessment.

METHODS

Zebrafish at 5 days postfertilization were fed 10 μg/L Nile red for 16 h, followed by drug treatment for 6 h. Tested drugs were delivered into the zebrafish by direct soaking. Drug effect on zebrafish GI motility was quantitatively assessed using GI tract fluorescent image-based morphometric analysis. During all the periods of the experiments, the zebrafish were not fed any food.

KEY RESULTS

All four human prokinetic drugs (domperidone, metoclopramide, mosapride, and magnesium sulfate) increased zebrafish GI motility, whereas two drugs that inhibit human GI movement (atropine and anisodamine) and two negative control drugs (glucose and vitamin C) did not show statistically significant effect on zebrafish GI motility.

CONCLUSIONS & INFERENCES

These results suggest that larval zebrafish motility model developed here is a useful tool for whole-animal in vivo GI transit studies and for assessing prokinetic drugs.

Microgavage of zebrafish larvae

The zebrafish has emerged as a powerful model organism for studying intestinal development(1-5), physiology(6-11), disease(12-16), and host-microbe interactions(17-25). Experimental approaches for studying intestinal biology often require the in vivo introduction of selected materials into the lumen of the intestine. In the larval zebrafish model, this is typically accomplished by immersing fish in a solution of the selected material, or by injection through the abdominal wall. Using the immersion method, it is difficult to accurately monitor or control the route or timing of material delivery to the intestine. For this reason, immersion exposure can cause unintended toxicity and other effects on extraintestinal tissues, limiting the potential range of material amounts that can be delivered into the intestine. Also, the amount of material ingested during immersion exposure can vary significantly between individual larvae(26). Although these problems are not encountered during direct injection through the abdominal wall, proper injection is difficult and causes tissue damage which could influence experimental results. We introduce a method for microgavage of zebrafish larvae. The goal of this method is to provide a safe, effective, and consistent way to deliver material directly to the lumen of the anterior intestine in larval zebrafish with controlled timing. Microgavage utilizes standard embryo microinjection and stereomicroscopy equipment common to most laboratories that perform zebrafish research. Once fish are properly positioned in methylcellulose, gavage can be performed quickly at a rate of approximately 7-10 fish/ min, and post-gavage survival approaches 100% depending on the gavaged material. We also show that microgavage can permit loading of the intestinal lumen with high concentrations of materials that are lethal to fish when exposed by immersion. To demonstrate the utility of this method, we present a fluorescent dextran microgavage assay that can be used to quantify transit from the intestinal lumen to extraintestinal spaces. This test can be used to verify proper execution of the microgavage procedure, and also provides a novel zebrafish assay to examine intestinal epithelial barrier integrity under different experimental conditions (e.g. genetic manipulation, drug treatment, or exposure to environmental factors). Furthermore, we show how gavage can be used to evaluate intestinal motility by gavaging fluorescent microspheres and monitoring their subsequent transit. Microgavage can be applied to deliver diverse materials such as live microorganisms, secreted microbial factors/toxins, pharmacological agents, and physiological probes. With these capabilities, the larval zebrafish microgavage method has the potential to enhance a broad range of research fields using the zebrafish model system.

Development of the enteric nervous system and its role in intestinal motility during fetal and early postnatal stages

Motility patterns in the mature intestine require the coordinated interaction of enteric neurons, gastrointestinal smooth muscle, and interstitial cells of Cajal. In Hirschsprung's disease, the aganglionic segment causes functional obstruction, and thus the enteric nervous system (ENS) is essential for gastrointestinal motility after birth. Here we review the development of the ENS. We then focus on motility patterns in the small intestine and colon of fetal mice and larval zebrafish, where recent studies have shown that the first intestinal motility patterns are not neurally mediated. Finally, we review the development of gastrointestinal motility in humans.