Mathematical modeling of the interaction between yolk utilization and fish growth in zebrafish, Danio rerio

Effects of Metabolic Disruption on Lipid Metabolism and Yolk Retention in Zebrafish Embryos

A subgroup of endocrine-disrupting chemicals have the ability to disrupt metabolism. These metabolism-disrupting chemicals (MDCs) can end up in aquatic environments and lead to adverse outcomes in fish. Although molecular and physiological effects of MDCs have been studied in adult fish, few studies have investigated the consequences of metabolic disruption in fish during the earliest life stages. To investigate the processes affected by metabolic disruption, zebrafish embryos were exposed to peroxisome proliferator-activated receptor gamma (PPARγ) agonist rosiglitazone, the PPARγ antagonist T0070907, and the well-known environmentally relevant MDC bisphenol A. Decreased apolipoprotein Ea transcript levels indicated disrupted lipid transport, which was likely related to the observed dose-dependent increases in yolk size across all compounds. Increased yolk size and decreased swimming activity indicate decreased energy usage, which could lead to adverse outcomes because the availability of energy reserves is essential for embryo survival and growth. Exposure to T0070907 resulted in a darkened yolk. This was likely related to reduced transcript levels of genes involved in lipid transport and fatty acid oxidation, a combination of responses that was specific to exposure to this compound, possibly leading to lipid accumulation and cell death in the yolk. Paraoxonase 1 (Pon1) transcript levels were increased by rosiglitazone and T0070907, but this was not reflected in PON1 enzyme activities. The present study shows how exposure to MDCs can influence biochemical and molecular processes involved in early lipid metabolism and may lead to adverse outcomes in the earliest life stages of fish. Environ Toxicol Chem 2024;43:1880-1893. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Maternal PFOS exposure affects offspring development in Nrf2-dependent and independent ways in zebrafish (Danio rerio)

Perfluorooctanesulfonic acid (PFOS) is a ubiquitous legacy environmental contaminant detected broadly in human samples and water supplies. PFOS can cross the placenta and has been detected in cord blood and breastmilk samples, underscoring the importance of understanding the impacts of maternal PFOS exposure during early development. This study aimed to investigate the effects of a preconception exposure to PFOS on developmental endpoints in offspring, as well as examine the role of the transcription factor Nuclear factor erythroid-2-related factor (Nrf2a) in mediating these effects. This transcription factor regulates the expression of several genes that protect cells against oxidative stress including during embryonic development. Adult female zebrafish were exposed to 0.02, 0.08 or 0.14 mg/L PFOS for 1 week (duration of one cycle of oocyte maturation) and then paired with unexposed males from Nrf2a mutant or wildtype strains. Embryos were collected for two weeks or until completion of 5 breeding events. PFOS was maternally transferred to offspring independent of genotype throughout all breeding events in a dose-dependent manner, ranging from 2.77 to 23.72 ng/embryo in Nrf2a wildtype and 2.40 to 15.80 ng/embryo in Nrf2a mutants. Although embryo viability at collection was not impacted by maternal PFOS exposure, developmental effects related to nutrient uptake, growth and pancreatic β-cell morphology were observed and differed based on genotype. Triglyceride levels were increased in Nrf2a wildtype eggs from the highest PFOS group. In Nrf2a wildtype larvae there was a decrease in yolk sac uptake while in Nrf2a mutants there was an increase. Additionally, there was a significant decrease in pancreatic β-cell (islet) area in wildtype larvae from the 0.14 mg/L PFOS accompanied by an increase in the prevalence of abnormal islet morphologies compared to controls. Abnormal morphology was also observed in the 0.02 and 0.08 mg/L PFOS groups. Interestingly, in Nrf2a mutants there was a significant increase in the pancreatic β-cell area in the 0.02 and 0.08 mg/L PFOS groups and no changes in the prevalence of abnormal islet morphologies. These results suggest that the regulation of processes like nutrient consumption, growth and pancreatic β-cell development are at least partially modulated by the presence of a functional Nrf2a transcriptomic response. Overall, preconception exposure to environmental pollutants, such as PFOS, may impact the maturing oocyte and cause subtle changes that can ultimately impact offspring health and development.

Chronotropic and vasoactive properties of the gut bacterial short-chain fatty acids in larval zebrafish

Short-chain fatty acids (SCFAs) produced by the gut bacteria have been associated with cardiovascular dysfunction in humans and rodents. However, studies exploring effects of SCFAs on cardiovascular parameters in the zebrafish, an increasingly popular model in cardiovascular research, remain limited. Here, we performed fecal bacterial 16S sequencing and gas chromatography/mass spectrometry (GC-MS) to determine the composition and abundance of gut microbiota and SCFAs in adult zebrafish. Following this, the acute effects of major SCFAs on heart rate and vascular tone were measured in anesthetized zebrafish larvae using fecal concentrations of butyrate, acetate, and propionate. Finally, we investigated if coincubation with butyrate may lessen the effects of angiotensin II (ANG II) and phenylephrine (PE) on vascular tone in anesthetized zebrafish larvae. We found that the abundance in Proteobacteria, Firmicutes, and Fusobacteria phyla in the adult zebrafish resembled those reported in rodents and humans. SCFA levels with highest concentration of acetate (27.43 µM), followed by butyrate (2.19 µM) and propionate (1.65 µM) were observed in the fecal samples of adult zebrafish. Immersion in butyrate and acetate produced a ∼20% decrease in heart rate (HR), respectively, with no observed effects of propionate. Butyrate alone also produced an ∼25% decrease in the cross-sectional width of the dorsal aorta (DA) at 60 min (*P < 0.05), suggesting compensatory vasoconstriction, with no effects of either acetate or propionate. In addition, butyrate significantly alleviated the decrease in DA cross-sectional width produced by both ANG II and PE. We demonstrate the potential for zebrafish in investigation of host-microbiota interactions in cardiovascular health.NEW & NOTEWORTHY We highlight the presence of a core gut microbiota and demonstrate in vivo short-chain fatty acid production in adult zebrafish. In addition, we show cardio-beneficial vasoactive and chronotropic properties of butyrate, and chronotropic properties of acetate in anesthetized zebrafish larvae.

Embryonic Exposure to Benzotriazole Ultraviolet Stabilizer 327 Alters Behavior of Rainbow Trout Alevin

Benzotriazole ultraviolet (UV) stabilizers (BUVSs) are used in great quantities during industrial production of a variety of consumer and industrial goods. As a result of leaching and spill, BUVSs are detectable ubiquitously in the environment. As of May 2023, citing concerns related to bioaccumulation, biomagnification, and environmental persistence, (B)UV(S)-328 was recommended to be listed under Annex A of the Stockholm Convention on Persistent Organic Pollutants. However, a phaseout of UV-328 could result in a regrettable substitution because the replacement chemical(s) could cause similar or unpredicted toxicity in vivo, relative to UV-328. Therefore, the influence of UV-327, a potential replacement of UV-328, was investigated with respect to early life development of newly fertilized rainbow trout embryos (Oncorhynchus mykiss), microinjected with environmentally relevant concentrations of UV-327. Developmental parameters (standard length), energy consumption (yolk area), heart function, blue sac disease, mortality, and behavior were investigated. Alevins at 14 days posthatching, exposed to 107 ng UV-327 g-1 egg, presented significant signs of hyperactivity; they moved on average 1.8-fold the distance and at 1.5-fold the velocity of controls. Although a substantial reduction in body burden of UV-327 was observed at hatching, it is postulated that UV-327, due to its lipophilic properties, interfered with neurological development and signaling from the onset of neurogenesis. If these results hold true across multiple taxa and species, a potential contributor to neurodevelopmental disorders might have been identified. These findings suggest that UV-327 poses an unknown hazard to rainbow trout embryos and alevins, rendering UV-327 a potential regrettable substitution to UV-328. However, a qualified statement on a regrettable substitution requires a comparative investigation on the teratogenic effects between the two BUVSs. Environ Toxicol Chem 2024;00:1-10. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Quantitative characterization of zebrafish development based on multiple classifications using Mueller matrix OCT

Organ development analysis plays an important role in assessing an individual' s growth health. In this study, we present a non-invasive method for the quantitative characterization of zebrafish multiple organs during their growth, utilizing Mueller matrix optical coherence tomography (Mueller matrix OCT) in combination with deep learning. Firstly, Mueller matrix OCT was employed to acquire 3D images of zebrafish during development. Subsequently, a deep learning based U-Net network was applied to segment various anatomical structures, including the body, eyes, spine, yolk sac, and swim bladder of the zebrafish. Following segmentation, the volume of each organ was calculated. Finally, the development and proportional trends of zebrafish embryos and organs from day 1 to day 19 were quantitatively analyzed. The obtained quantitative results revealed that the volume development of the fish body and individual organs exhibited a steady growth trend. Additionally, smaller organs, such as the spine and swim bladder, were successfully quantified during the growth process. Our findings demonstrate that the combination of Mueller matrix OCT and deep learning effectively quantify the development of various organs throughout zebrafish embryonic development. This approach offers a more intuitive and efficient monitoring method for clinical medicine and developmental biology studies.

A PBPK model to evaluate zebrafish eleutheroembryos' actual exposure: bisphenol A and analogs' (AF, F, and S) case studies

The zebrafish eleutheroembryo model is increasingly used to assess the toxicity and developmental adverse effects of xenobiotics. However, the actual exposure is seldom measured (poorly accessible), while a predictive model could estimate these concentrations. The predictions with a new eleutheroembryo physiologically based pharmacokinetic (PBPK) model have been evaluated using datasets obtained from literature data for several bisphenols. The model simulated the toxicokinetics of bisphenols A (BPA), AF, F, and S through the eleutheroembryo tissues while considering the body and organ growth. We further improved the predictions by adding dynamic flows through the embryo and/or its chorion, impact of experimental temperature, metabolic clearance, and saturation of the absorption by Bayesian calibration. The model structure was determined using the BPA dataset and generalized to the other bisphenols. This model revealed the central role of the chorion in the compound uptake in the first 48 h post-fertilization. The predictions for the BPA substitutes estimated by our PBPK model were compared to available toxicokinetics data for zebrafish embryos, and 63% and 88% of them were within a twofold and fivefold error intervals of the corresponding experimental values, respectively. This model provides a tool to design new eleutheroembryo assays and evaluate the actual exposure.