Unpredicted human safety events in clinical trials for new drugs are costly in terms of human health and money. The drug discovery industry attempts to minimize those events with diligent preclinical safety testing. Current standard practices are good at preventing toxic compounds from being tested in the clinic; however, false negative preclinical toxicity results are still a reality. Continual improvement must be pursued in the preclinical realm. Higher-quality therapies can be brought forward with more information about potential toxicities and associated mechanisms. The zebrafish model is a bridge between in vitro assays and mammalian in vivo studies. This model is powerful in its breadth of application and tractability for research. In the past two decades, our understanding of disease biology and drug toxicity has grown significantly owing to thousands of studies on this tiny vertebrate. This Review summarizes challenges and strengths of the model, discusses the 3Rs value that it can deliver, highlights translatable and untranslatable biology, and brings together reports from recent studies with zebrafish focusing on new drug discovery toxicology.

Dimethyl sulfoxide (DMSO) is a popular solvent for developmental toxicity testing of chemicals and pharmaceuticals in zebrafish embryos. In general, it is recommended to keep the final DMSO concentration as low as possible for zebrafish embryos, preferably not exceeding 100 μL/L (0.01%). However, higher concentrations of DMSO are often required to dissolve compounds in an aqueous medium. The aim of this study was to determine the highest concentration of DMSO that can be safely used in our standardized Zebrafish Embryo Developmental Toxicity Assay (ZEDTA). In the first part of this study, zebrafish embryos were exposed to different concentrations (0–2%) of DMSO. No increase in lethality or malformations was observed when using DMSO concentrations up to 1%. In a follow-up experiment, we assessed whether compounds that cause no developmental toxicity in the ZEDTA remain negative when dissolved in 1% DMSO, as false positive results due to physiological disturbances by DMSO should be avoided. To this end, zebrafish embryos were exposed to ascorbic acid and hydrochlorothiazide dissolved in 1% DMSO. Negative control groups were also included. No significant increase in malformations or lethality was observed in any of the groups. In conclusion, DMSO concentrations up to 1% can be safely used to dissolve compounds in the ZEDTA.

The zebrafish (Danio rerio) has been increasingly explored in pharmaceutical research as a promising alternative model for toxicological screens. This necessitates a thorough knowledge on the biotransformation processes for a correct interpretation of pharmacological and toxicological data. Physiologically, cytochrome P450 (CYP) enzymes, specifically CYP families 1-3, play a pivotal role in drug metabolism. And yet, information regarding activity of CYP, its isoforms, and conjugation enzymes in zebrafish is either scarce or conflicting. To account for this discrepancy, the available spatiotemporal, modulation and activity data on zebrafish CYP 1-3 families are reviewed in this paper and compared with human CYP data. The CYP genetic features and synteny are well characterized, as is their expression in different organ systems. Moreover, several substrates metabolized by humans also show metabolism in zebrafish, with other CYP isoforms possibly involved. Altogether, the five CYP1 members, 41 CYP2 members and five CYP3 members in zebrafish show distinct evolutionary and orthological similarities with humans.

During the prenatal, neonatal and post-weaning periods, the mammalian gastrointestinal tract undergoes various morphological and physiological changes alongside with an expansion of the immune system and microbial ecosystem. This review focuses on the time period before weaning and summarizes the current knowledge regarding i) structural and functional aspects ii) the development of the immune system, and iii) the establishment of the gut ecosystem of the porcine intestine. Structural and functional maturation of the gastrointestinal tract gradually progress with age. In the neonatal period colostrum induces gut closure, leads to an increase in intestinal weight, absorptive area and brush border enzyme activities. During the first weeks of life, an increased secretion of stomach and pancreatic enzymes and an increased uptake of monosaccharides and amino acids are observed. The development in digestive function coincides with development in both the adaptive and innate immune system. This secures a balanced immune response to the ingested milk-derived macromolecules, and colonizing bacteria. Husbandry and dietary interventions in early life appear to affect the development of multiple components of the mucosal immune system. Furthermore, the composition of the intestinal microbial communities seems to be affected by the early postnatal environment, which might also contribute to gut maturation, metabolic and immune development. Understanding the interplay between morphological, functional and immunological maturation, as influenced by early microbial colonization and ingestion of dietary factors, is of utmost importance to identify management and feeding strategies to optimize intestinal health. We discuss some possible implications related to intrauterine growth restriction, and preterm delivery as these both dramatically increase the risk of mortality and morbidity. In addition, some nutritional interventions during the perinatal period in both sows and piglets will be discussed in the light of possible health consequences early in life and later on.