Assessment of Toxicological Perturbations and Variants of Pancreatic Islet Development in the Zebrafish Model

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.

Comparing the effects of developmental exposure to alpha lipoic acid (ALA) and perfluorooctanesulfonic acid (PFOS) in zebrafish (Danio rerio)

Alpha lipoic acid (ALA) is a dietary supplement that has been used to treat a wide range of diseases, including obesity and diabetes, and have lipid-lowering effects, making it a potential candidate for mitigating dyslipidemia resulting from exposures to the per- and polyfluoroalkyl substance (PFAS) family member perfluorooctanesulfonic acid (PFOS). ALA can be considered a non-fluorinated structural analog to PFOS due to their similar 8-carbon chain and amphipathic structure, but, unlike PFOS, is rapidly metabolized. PFOS has been shown to reduce pancreatic islet area and induce β-cell lipotoxicity, indicating that changes in β-cell lipid microenvironment is a mechanism contributing to hypomorphic islets. Due to structural similarities, we hypothesized that ALA may compete with PFOS for binding to proteins and distribution throughout the body to mitigate the effects of PFOS exposure. However, ALA alone reduced islet area and fish length, with several morphological endpoints indicating additive toxicity in the co-exposures. Individually, ALA and PFOS increased fatty acid uptake from the yolk. ALA alone increased liver lipid accumulation, altered fatty acid profiling and modulated PPARɣ pathway signaling. Together, this work demonstrates that ALA and PFOS have similar effects on lipid uptake and metabolism during embryonic development in zebrafish.

Tris(4-chlorophenyl)methane and tris(4-chlorophenyl)methanol disrupt pancreatic organogenesis and gene expression in zebrafish embryos

OBJECTIVES

Tris(4-chlorophenyl) methane (TCPM) and tris(4-chlorophenyl)methanol (TCPMOH) are anthropogenic environmental contaminants believed to be manufacturing byproducts of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT) due to environmental co-occurrence. TCPM and TCPMOH are persistent, bioaccumulate in the environment, and are detected in human breast milk and adipose tissues. DDT exposures have been previously shown to disrupt insulin signaling and glucoregulation, increasing risk for diabetes. We have previously shown that embryonic exposures organochlorines such as polychlorinated biphenyls disrupted pancreatic development and early embryonic glucoregulatory networks. Here, we determined the impacts of the similar compounds TCPM and TCPMOH on zebrafish pancreatic growth and gene expression following developmental exposures.

METHODS

Zebrafish embryos were exposed to 50 nM TCPM or TCPMOH beginning at 24 hr postfertilization (hpf) and exposures were refreshed daily. At 96 hpf, pancreatic growth and islet area were directly visualized in Tg(ptf1a::GFP) and Tg(insulin::GFP) embryos, respectively, using microscopy. Gene expression was assessed at 100 hpf with RNA sequencing.

RESULTS

Islet and total pancreas area were reduced by 20.8% and 13% in embryos exposed to 50 nM TCPMOH compared to controls. TCPM did not induce significant morphological changes to the developing pancreas, indicating TCPMOH, but not TCPM, impairs pancreatic development despite similarity in molecular responses. Transcriptomic responses to TCPM and TCPMOH were correlated (R²  = .903), and pathway analysis found downregulation of processes including retinol metabolism, circadian rhythm, and steroid biosynthesis.

CONCLUSION

Overall, our data suggest that TCPM and TCPMOH may be hazardous to embryonic growth and development.

Nrf2a dependent and independent effects of early life exposure to 3,3'-dichlorobiphenyl (PCB-11) in zebrafish (Danio rerio)

The environmental pollutant 3,3'-dichlorobiphenyl (PCB-11) is a lower-chlorinated polychlorinated biphenyl (PCB) congener present in air and water samples. Both PCB-11 and its metabolite, 4-PCB-11-Sulfate, are detected in humans, including in pregnant women. Previous research in zebrafish (Danio rerio) has shown that 0.2 μM exposures to 4-PCB-11-Sulfate starting at 1 day post fertilization (dpf) increase hepatic neutral lipid accumulation in larvae at 15 dpf. Here, we explored whether nuclear factor erythroid 2-related factor 2 (Nrf2), known as the master-regulator of the adaptive response to oxidative stress, contributes to metabolic impacts of 4-PCB-11-Sulfate. For this work, embryos were collected from homozygous wildtype or Nrf2a mutant adult zebrafish that also express GFP in pancreatic β-cells, rendering Tg(ins:GFP;nrf2afh318+/+) and Tg(ins:GFP;nrf2afh318-/-) lines. Exposures were conducted from 1-15 dpf to either 0.05% DMSO or DMSO-matched 0.2 µM 4-PCB-11-Sulfate, and at 15 dpf subsets of larvae were imaged for overall morphology, primary pancreatic islet area, and collected for fatty acid profiling and RNAseq. At 15 dpf, independent of genotype, fish exposed to 4-PCB-11-Sulfate survived significantly more at 80-85% compared to 65-73% survival for unexposed fish, and had primary pancreatic islets 8% larger compared to unexposed fish. Fish growth at 15 dpf was dependent on genotype, with Nrf2a mutant fish a significant 3-5% shorter than wildtype fish, and an interaction effect was observed where Nrf2a mutant fish exposed to 4-PCB-11-Sulfate experienced a significant 29% decrease in the omega-3 fatty acid DHA compared to unexposed mutant fish. RNAseq revealed 308 differentially expressed genes, most of which were dependent on genotype. These findings suggest that Nrf2a plays an important role in growth as well as for DHA production in the presence of 4-PCB-11-Sulfate. Further research would be beneficial to understand the importance of Nrf2a throughout the lifecourse, especially in the context of toxicant exposures.

Exposure to perfluorooctane sulfonate reduced cell viability and insulin release capacity of β cells

Per- and polyfluoroalkyl substances (PFAS) are found to have multiple adverse outcomes on human health. Recently, epidemiological and toxicological studies showed that exposure to PFAS had adverse impacts on pancreas and showed association with insulin abnormalities. To explore how PFAS may contribute to diabetes, we studied impacts of perfluorooctane sulfonate (PFOS) on cell viability and insulin release capacity of pancreatic β cells by using in vivo and in vitro methods. We found that 28-day administration with PFOS (10 mg/(kg body weight•day)) caused reductions of pancreas weight and islet size in male mice. PFOS administration also led to lower serum insulin level both in fasting state and after glucose infusion among male mice. For cell-based in vitro bioassay, we used mouse β-TC-6 cancer cells and found 48-hr exposure to PFOS decreased the cell viability at 50 μmol/L. By measuring insulin content in supernatant, 48-hr pretreatment of PFOS (100 μmol/L) decreased the insulin release capacity of β-TC-6 cells after glucose stimulation. Although these concentrations were higher than the environmental concentration of PFOS, it might be reasonable for high concentration of PFOS to exert observable toxic effects in mice considering mice had a faster removal efficiency of PFOS than human. PFOS exposure (50 μmol/L) to β-TC-6 cells induced intracellular accumulation of reactive oxidative specie (ROS). Excessive ROS induced the reactive toxicity of cells, which eventually invoke apoptosis and necrosis. Results in this study provide evidence for the possible causal link of exposure to PFOS and diabetes risk.

The Nrf2a pathway impacts zebrafish offspring development with maternal preconception exposure to perfluorobutanesulfonic acid

Since the voluntary phaseout of perfluorooctanesulfonic acid (PFOS), smaller congeners, such as perfluorobutanesulfonic acid (PFBS) have served as industrial replacements and been detected in contaminated aquifers. This study sought to examine the effects of a maternal preconception PFBS exposure on the development of eggs and healthy offspring. Adult female zebrafish received a one-week waterborne exposure of 0.08, 0.14, and 0.25 mg/L PFBS. After which, females were bred with non-exposed males and embryos collected over 5 successful breeding events. PFBS concentrations were detected in levels ranging from 99 to 253 pg/embryo in the first collection but were below the limit of quantitation by fourth and fifth clutches. Therefore, data were subsequently binned into early collection embryos in which PFBS was detected and late collections, in which PFBS was below quantitation. In the early collection, embryo 24 h survival was significantly reduced. In the late collection, embryo development was impacted with unique patterns emerging between Nrf2a wildtype and mutant larvae. Additionally, the impact of nutrient loading into the embryos was assessed through measurement of fatty acid profiles, total cholesterol, and triglyceride content. There were no clear dose-dependent effects, but again unique patterns were observed between the genotypes. Preconception PFBS exposures were found to alter egg and embryo development, which is mediated by direct toxicant loading in the eggs, nutrient loading into eggs, and the function of Nrf2a. These findings provide insight into the reproductive and developmental effects of PFBS and identify maternal preconception as a novel critical window of exposure.

Review on Toxic Effects of Di(2-ethylhexyl) Phthalate on Zebrafish Embryos

Di(2-ethylhexyl) phthalate (DEHP) is widely used as a plasticizer in consumer products. People are continuously exposed to DEHP through ingestion, inhalation and dermal absorption. From epidemiological studies, DEHP has been shown to associate with various adverse health effects, such as reproductive abnormalities and metabolic diseases. Health concerns have been raised regarding DEHP exposures; therefore, relevant risk assessment has become necessary through toxicological testing of DEHP. In the past 10 years, an increasing number of DEHP toxicity studies have been using zebrafish embryos as an in vivo model due to their high fecundity, rapid embryonic development as well as optical transparency, which have now been established as an alternative of the more conventional rodent model. The aim of the present paper is to review the effects of acute (from embryo stage to ≤1 week) and chronic (from embryo stage to >1 week) DEHP exposures on zebrafish, which start from the embryonic stage, and to analyze acute and potential long-term effects induced by acute exposure and effects induced by chronic exposure of DEHP upon subjecting to exposures, starting from the embryonic stage to different developmental stages, with a view to facilitate risk assessments on DEHP exposures.

Modulation of PPAR signaling disrupts pancreas development in the zebrafish, Danio rerio

Peroxisome Proliferator Activated Receptors (PPARs) are transcription factors that regulate processes such as lipid and glucose metabolism. Synthetic PPAR ligands, designed as therapeutics for metabolic disease, provide a tool to assess the relationship between PPAR activity and pancreas development in vivo, an area that remains poorly characterized. Here, we aim to assess the effects of PPAR agonists and antagonists on gene expression, embryonic morphology and pancreas development in transgenic zebrafish embryos. To evaluate developmental perturbations, we assessed gross body and pancreas morphology at 4 days post fertilization (dpf) in response to developmental exposures with PPARα, PPARγ, and PPARβ/δ agonists and antagonists at 0, 0.01, 0.1, 1, and 10 μM concentrations. All ligand exposures, with the exception of the PPARα agonist, resulted in significantly altered fish length and yolk sac area. PPARγ agonist and antagonist had higher incidence of darkened yolk sac and craniofacial deformities, whereas PPARα antagonist had higher incidence of pericardial edema and death. Significantly reduced endocrine pancreas area was observed in both PPARγ ligands and PPARα agonist exposed embryos, some of which also exhibited aberrant endocrine pancreas morphology. Both PPARβ/δ ligands caused reduced exocrine pancreas length and novel aberrant phenotype, and disrupted gene expression of pancreatic targets pdx1, gcga, and try. Lipid staining was performed at 8 dpf and revealed altered lipid accumulation consistent with isoform function. These data indicate chronic exposure to synthetic ligands may induce morphological and pancreatic defects in zebrafish embryos.

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

Optimal embryonic development plays a major role in the health of an individual beyond the developmental stage. Nutritional perturbation during development is associated with cardiovascular and metabolic disease later in life. With both nutritional uptake and overall growth being risk factors for eventual health, it is necessary to understand not only the behavior of the processes during development but also their interactions. In this study, we used differential equations, image analyses, curve fittings, parameter estimation and laboratory experiments to quantify the rate of yolk absorption and its effect on early development of a vertebrate model (Danio rerio). Findings from this study establish a nonlinear functional relationship between nutrient absorption and early fish growth. We found that the rate of change in fish length and yolk utilization is logistic, that is the yolk decays rapidly for a period of time before leveling out. An interesting finding from this study is that yolk utilization reaches its maximum at 84 h post-fertilization. We validated our mathematical models against experimental observations, making them powerful tools for replication and future simulations.

Modulating glutathione thiol status alters pancreatic β-cell morphogenesis in the developing zebrafish (Danio rerio) embryo

Emerging evidence suggests that redox-active chemicals perturb pancreatic islet development. To better understand potential mechanisms for this, we used zebrafish (Danio rerio) embryos to investigate roles of glutathione (GSH; predominant cellular redox buffer) and the transcription factor Nrf2a (Nfe2l2a; zebrafish Nrf2 co-ortholog) in islet morphogenesis. We delineated critical windows of susceptibility to redox disruption of β-cell morphogenesis, interrogating embryos at 24, 48 and 72 h post fertilization (hpf) and visualized Nrf2a expression in the pancreas using whole-mount immunohistochemistry at 96 hpf. Chemical GSH modulation at 48 hpf induced significant islet morphology changes at 96 hpf. Pro-oxidant exposures to tert-butylhydroperoxide (77.6 μM; 10-min at 48 hpf) or tert-butylhydroquinone (1 μM; 48-56 hpf) decreased β-cell cluster area at 96 hpf. Conversely, exposures to antioxidant N-acetylcysteine (bolsters GSH pools; 100 μM; 48-72 hpf) or sulforaphane (activates Nrf2a; 20 μM; 48-72 hpf) significantly increased islet areas. Nrf2a was also stabilized in β-cells: 10-min exposures to 77.6 μM tert-butylhydroperoxide significantly increased Nrf2a protein compared to control islet cells that largely lack stabilized Nrf2a; 10-min exposures to higher (776 μM) tert-butylhydroperoxide concentration stabilized Nrf2a throughout the pancreas. Using biotinylated-GSH to visualize in situ protein glutathionylation, islet cells displayed high protein glutathionylation, indicating oxidized GSH pools. The 10-min high (776 μM) tert-butylhydroperoxide exposure (induced Nrf2a globally) decreased global protein glutathionylation at 96 hpf. Mutant fish expressing inactive Nrf2a were protected against tert-butylhydroperoxide-induced abnormal islet morphology. Our data indicate that disrupted redox homeostasis and Nrf2a stabilization during pancreatic β-cell development impact morphogenesis, with implications for disease states at later life stages. Our work identifies a potential molecular target (Nrf2) that mediates abnormal β-cell morphology in response to redox disruptions. Moreover, our findings imply that developmental exposure to exogenous stressors at distinct windows of susceptibility could diminish the reserve redox capacity of β-cells, rendering them vulnerable to later-life stresses and disease.

Perfluorobutanesulfonic Acid Disrupts Pancreatic Organogenesis and Regulation of Lipid Metabolism in the Zebrafish, Danio rerio

Following the phase-out of highly persistent perfluorosulfonates in the United States from non-stick and stain-resistant products in the early 2000s, perfluorobutanesulfonic acid (PFBS) has replaced these compounds as a primary surfactant. Measurements of PFBS in environmental and human samples have been rising in recent years, raising concerns about potential negative health effects. We previously found that embryonic exposures to a related compound, perfluorooctanesulfonic acid (PFOS), decreased pancreas length and insulin-producing islet area in zebrafish embryos (Danio rerio). The objective of this study was to compare the effects of PFBS exposures on pancreatic organogenesis with our previous PFOS findings. Dechorionated zebrafish embryos from two different transgenic fish lines (Tg[insulin:GFP], Tg[ptf1a:GFP]) were exposed to 0 (0.01% DMSO), 16, or 32 µM PFBS daily beginning at 1 day post fertilization (dpf) until 4 and 7 dpf when they were examined using fluorescent microscopy for islet area and morphology, and exocrine pancreas length. PFBS-exposed embryos had significantly increased caudal fin deformities, delayed swim bladder inflation, and impaired yolk utilization. Incidence of fish with significantly stunted growth and truncated exocrine pancreas length was significantly increased, although these two effects occurred independently. Islet morphology revealed an increased incidence of severely hypomorphic islets (areas lower than the 1st percentile of controls) and an elevated occurrence of fragmented islets. RNA-Seq data (4 dpf) also identify disruptions in regulation of lipid homeostasis. Overall, this work demonstrates that PFBS exposure can perturb embryonic development, energy homeostasis, and pancreatic organogenesis.

Xenobiotic mediated diabetogenesis: Developmental exposure to dichlorvos or atrazine leads to type 1 or type 2 diabetes in Drosophila

The increased incidence of diabetes to the magnitude of a global epidemic is attributed to non-traditional risk factors, including exposure to environmental chemicals. However, the contribution of xenobiotic exposure during the development of an organism to the etiology of diabetes is not fully addressed. Developing stages are more susceptible to chemical insult, but knowledge on the consequence of the same to the onset of diabetes is residual. In this context, by using Drosophila melanogaster having conserved Insulin/Insulin growth factor-like signaling (IIS) as well as glucose homeostasis as a model, we evaluated the potential of developmental exposure to dichlorvos (DDVP, an organophosphorus pesticide) or atrazine (herbicide) to cause diabetes in exposed organisms. Flies exposed to DDVP during their development display insulin deficiency or type 1 diabetes (T1D) while those exposed to atrazine show insulin resistance or type 2 diabetes (T2D), suggesting that exposure to these xenobiotics during organismal development can result in diabetes and that different mechanisms underlie pesticide mediated diabetes. We show that oxidative stress-mediated c-Jun N-terminal kinase (JNK) signaling activation underlies insulin resistance in flies exposed to atrazine during their development while DDVP-mediated T1D involves activation of caspase-mediated cell death pathway. Mitigation of oxidative stress through over-expression of SOD2 in atrazine (20μg/ml) exposed flies, revealed significantly decreased oxidative stress levels and reduced phosphorylation of JNK. Moreover, glucose and Akt phosphorylation levels in SOD2 over-expression flies exposed to atrazine were comparable to those in controls, suggesting restoration in insulin sensitivity. Therefore, exposure to xenobiotics during development is a common risk factor for the development of type 1 or type 2 diabetes. Accordingly, the present study cautions against the use of such diabetogenic pesticides. Also, mitigation of oxidative stress or anti-oxidant supplementation could be a potential therapy for xenobiotic mediated type 2 diabetes.

Redox stress and signaling during vertebrate embryonic development: Regulation and responses

Vertebrate embryonic development requires specific signaling events that regulate cell proliferation and differentiation to occur at the correct place and the correct time in order to build a healthy embryo. Signaling pathways are sensitive to perturbations of the endogenous redox state, and are also susceptible to modulation by reactive species and antioxidant defenses, contributing to a spectrum of passive vs. active effects that can affect redox signaling and redox stress. Here we take a multi-level, integrative approach to discuss the importance of redox status for vertebrate developmental signaling pathways and cell fate decisions, with a focus on glutathione/glutathione disulfide, thioredoxin, and cysteine/cystine redox potentials and the implications for protein function in development. We present a tissue-specific example of the important role that reactive species play in pancreatic development and metabolic regulation. We discuss NFE2L2 (also known as NRF2) and related proteins, their roles in redox signaling, and their regulation of glutathione during development. Finally, we provide examples of xenobiotic compounds that disrupt redox signaling in the context of vertebrate embryonic development. Collectively, this review provides a systems-level perspective on the innate and inducible antioxidant defenses, as well as their roles in maintaining redox balance during chemical exposures that occur in critical windows of development.

Pancreatic beta cells are a sensitive target of embryonic exposure to butylparaben in zebrafish (Danio rerio)

BACKGROUND

Butylparaben (butyl p-hydroxybenzoic acid) is a common cosmetic and pharmaceutical preservative reported to induce oxidative stress and endocrine disruption. Embryonic development is sensitive to oxidative stress, with redox potentials playing critical roles in progenitor cell fate decisions. Because pancreatic beta cells have been reported to have low antioxidant gene expression, they may be sensitive targets of oxidative stress. We tested the hypotheses that butylparaben causes oxidative stress in the developing embryo, and that pancreatic beta cells are a sensitive target of butylparaben embryotoxicity.

METHODS

Transgenic insulin:GFP zebrafish embryos (Danio rerio) were treated daily with 0, 250, 500, 1,000, and 3,000 nM butylparaben. Pancreatic islet and whole embryo development were examined though 7 days postfertilization, and gene expression was measured by quantitative real-time PCR. Glutathione (GSH) and cysteine redox content were measured at 28 hr postfertilization using HPLC.

RESULTS

Butylparaben exposure caused intestinal effusion, pericardial edema, and accelerated yolk utilization. At 250 nM, beta cell area increased by as much as 55%, and increased incidence of two aberrant morphologies were observed-fragmentation of the islet cluster and ectopic beta cells. Butylparaben concentrations of 500 and 1,000 nM increased GSH by 10 and 40%, respectively. Butylparaben exposure downregulated transcription factor pdx1, as well as genes involved in GSH synthesis, while upregulating GSH-disulfide reductase (gsr).

CONCLUSIONS

The endocrine pancreas is a sensitive target of embryonic exposure to butylparaben, which also causes developmental deformities and perturbs redox conditions in the embryo.

Embryonic exposure to Mono(2-ethylhexyl) phthalate (MEHP) disrupts pancreatic organogenesis in zebrafish (Danio rerio)

Mono(2-ethylhexyl) phthalate (MEHP) is the bioactive metabolite of di(2-ethylhexyl) phthalate, a plasticizing agent and persistent environmental contaminant associated with obesity, developmental abnormalities, and oxidative stress. Nrf2 (Nfe2l2) is a transcription factor that regulates cytoprotective genes as part of the adaptive antioxidant response. We previously identified the pancreas as a sensitive target of oxidative stress during embryonic development. The goals of this study were to 1) characterize the effects of MEHP exposure on pancreatic development, and 2) determine whether oxidative stress contributes to MEHP embryotoxicity. Zebrafish (Danio rerio) embryos from AB wildtype and Tg(ins:GFP;nrf2a^fh318/fh318) were exposed to 0 or 200 μg/L MEHP at 3 h post fertilization (hpf) through 168 hpf to assess pancreatic organogenesis. MEHP exposure significantly decreased β-cell area at all timepoints (48, 72, 96, 168 hpf), but Nrf2a did not significantly protect against islet hypomorphism. Tg(gcga:GFP) embryos exposed to MEHP showed a decrease in α-cell area in the islet across the same timepoints. Tg(ptf1a:GFP) embryos were assessed at 80 and 168 hpf for exocrine pancreas length. MEHP exposure decreased growth of the exocrine pancreas. Expression of pancreas genes insa, sst2 and ptf1a was significantly reduced by MEHP exposure compared to controls. Glutathione (GSH) concentrations and redox potentials were quantified at 72 hpf by HPLC, but no significant changes were observed. However, expression of the GSH-related genes gstp1 and gsr were significantly altered by MEHP exposure. These data indicate that the developing pancreas is a sensitive target tissue of embryonic exposure to MEHP.

Developmental Exposure to Endocrine Disrupting Chemicals and Type 1 Diabetes Mellitus

Exposure to endocrine disrupting chemicals (EDCs) may have implications for the development of type 1 diabetes mellitus (T1DM), especially if exposure occurs during development. Exposure to EDCs during fetal or early life can disrupt the development of both the immune system and the pancreatic beta cells, potentially increasing susceptibility to T1DM later in life. Developmental exposure to some EDCs can cause immune system dysfunction, increasing the risk of autoimmunity. In addition, developmental exposure to some EDCs can affect beta cell development and function, influencing insulin secretion. These changes may increase stress on the beta cells, and identify them as a target to the immune system. Developmental exposure to EDCs that disrupt metabolism by increasing insulin resistance or obesity may also stress the beta cells. Exposure to these EDCs during development may play a role in the pathogenesis of T1DM, and requires further research.

Embryonic exposures to perfluorooctanesulfonic acid (PFOS) disrupt pancreatic organogenesis in the zebrafish, Danio rerio

Perfluorooctanesulfonic acid (PFOS) is a ubiquitous environmental contaminant, previously utilized as a non-stick application for consumer products and firefighting foam. It can cross the placenta, and has been repeatedly associated with increased risk for diabetes in epidemiological studies. Here, we sought to establish the hazard posed by embryonic PFOS exposures on the developing pancreas in a model vertebrate embryo, and develop criteria for an adverse outcome pathway (AOP) framework to study the developmental origins of metabolic dysfunction. Zebrafish (Danio rerio) embryos were exposed to 16, 32, or 64 μM PFOS beginning at the mid-blastula transition. We assessed embryo health, size, and islet morphology in Tg(insulin-GFP) embryos at 48, 96 and 168 hpf, and pancreas length in Tg(ptf1a-GFP) embryos at 96 and 168 hpf. QPCR was used to measure gene expression of endocrine and exocrine hormones, digestive peptides, and transcription factors to determine whether these could be used as a predictive measure in an AOP. Embryos exposed to PFOS showed anomalous islet morphology and decreased islet size and pancreas length in a U-shaped dose-response curve, which resemble congenital defects associated with increased risk for diabetes in humans. Expression of genes encoding islet hormones and exocrine digestive peptides followed a similar pattern, as did total larval growth. Our results demonstrate that embryonic PFOS exposures can disrupt pancreatic organogenesis in ways that mimic human congenital defects known to predispose individuals to diabetes; however, future study of the association between these defects and metabolic dysfunction are needed to establish an improved AOP framework.