Immune function, hepatic CYP1A, and reproductive biomarker responses in the gulf killifish, Fundulus grandis, during dietary exposures to endocrine disrupters

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

Oxidative stress responses of gulf killifish exposed to hydrocarbons from the Deepwater Horizon oil spill: Potential implications for aquatic food resources

Ecosystem effects of polycyclic aromatic hydrocarbons (PAHs) remain under investigation following the Gulf of Mexico Deepwater Horizon oil spill. Fundulus grandis, an established indicator of aquatic ecosystem health, was investigated because this species shares genes and biochemical pathways with higher trophic-level fish and plays an important role in the gulf food chain. Oxidative stress responses including hepatic cytochrome P4501A (CYP1A) and serum antioxidant capacity were evaluated in fish exposed to PAHs. Fish were exposed to water-accommodated fractions (WAFs) of crude oil (7.0  ± 0.10 mg/L C6-C28) after which solutions were diluted below the level of detection over 8 h using 15 ppt aerated artificial seawater. Before euthanasia, fish remained in aquaria for 12 h, 24 h, or 48 h. Three replicate experiments were conducted at each time point using unexposed fish as experimental controls. Significant differences (p < 0.05) in CYP1A induction were observed in exposed versus control fish at 24 h. Expression of CYP1A increased by 25%, 66%, and 23% in exposed fish at 12 h, 24 h, and 48 h, respectively. Significant increases were observed in antioxidant capacity of nonenzymatic antioxidants in exposed versus control fish at each time point. Given the activity of CYP1A, radicals formed during PAH detoxification likely resulted in increased oxidant load requiring elevated antioxidant defenses. Research is needed to determine the duration of oxidative stress responses considering the potential for lipid oxidation in exposed fish or species feeding on exposed fish.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Evolution of tolerance to PCBs and susceptibility to a bacterial pathogen (Vibrio harveyi) in Atlantic killifish (Fundulus heteroclitus) from New Bedford (MA, USA) harbor

A population of the non-migratory estuarine fish Fundulus heteroclitus (Atlantic killifish) resident to New Bedford (NB), Massachusetts, USA, an urban harbor highly contaminated with polychlorinated biphenyls (PCBs), demonstrates recently evolved tolerance to some aspects of PCB toxicity. PCB toxicology, ecological theory, and some precedence supported expectations of increased susceptibility to pathogens in NB killifish. However, laboratory bacterial challenges of the marine pathogen Vibrio harveyi to wild fish throughout the reproductive season and to their mature laboratory-raised progeny demonstrated comparable survival by NB and reference killifish, and improved survival by NB males. These results are inconsistent with hypothesized trade-offs of adaptation, and suggest that evolved tolerance in NB killifish may include mechanisms that minimize the immunosuppressive effects of PCBs. Compensatory strategies of populations persisting in highly contaminated environments provide a unique perspective for understanding the long-term ecological effects of toxic chemicals.

Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics

A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms.

Molecular markers of endocrine disruption in aquatic organisms

A wide range of organic contaminant compounds prevalent in the aquatic environment has been shown to exhibit hormone-disrupting activity. The actual potency of such compounds are low compared with endogenous hormones, such as 17beta-estradiol, but may still produce detrimental biological effects. Induced hormone levels are routinely measured using commercial testing kits, though these fail to relate to actual effects. Field and laboratory studies on the biological effects of environmental estrogens have, in the past, largely relied on assays of vitellogenin (vtg) induction in male fish, reduced growth in testes formation, and intersex incidence. Here, we critically review the current and potential application of molecular techniques in assessing the adverse biological reproductive effects of endocrine-disrupting chemicals in aquatic organisms. The role of fish (estrogen, androgen, and progestogen) hormone receptors and invertebrate (ecdysone) hormone receptor, egg production (vtg and chorion) proteins, steroid biosynthesis enzymes (aromatase, sulfotransferase, and hydroxysteroid dehydrogenase), DNA damage, apoptosis, and their potential development as biomarkers are discussed in turn. In each case, the sequences characterized are presented and homologies across species are highlighted. Molecular methods of gauging vtg and zona radiata (ZR) expression and protein concentrations have included immunoassay and reverse transcription polymerase chain reaction (RT-PCR). Suggestions for the isolation for key gene expression products (aromatase, ZR, and vtg, for instance), from a wider range of fish species using degenerate primers, are given. Endocrine disruption in invertebrates has received less attention compared with fish, partly because the knowledge regarding invertebrate endocrinology is limited. Here we review and suggest alternate isolation strategies for key players in the imposex induction process: vitellin (Vn), aromatase, and Ala-Pro-Gly-Trp (APGW) amide neurohormone. Current molecular-level techniques rely on ligand-binding assays, enzyme-linked immunosorbent assay (ELISA), and, more recently, gene expression. In the future, more reliance will be placed on the development of gene expression assays using reporter systems combined with cross-species PCR-based or polyclonal antibody-based assays. We discuss the use of recombinant receptors as a means of primary screening of environmental samples for estrogenicity and antiestrogenicity, which avoids species and seasonal variation in receptor response to ligand binding, a recognized problem of earlier bioassays. Most exciting is the potential that microarray and proteomics approaches have to offer. Such techniques are now used routinely in medical research to identify specific genes and proteins affected by treatment with endocrine disruptors, including estradiol. The technique has yet to be used to screen aquatic organisms, but it has the potential to implicate previously unsuspected estradiol-sensitive genes that may later become molecular markers of endocrine disruption.

Vitellogenesis in male Fundulus heteroclitus (killifish) induced by selected estrogenic compounds

The response of male Fundulus heteroclitus to estrogenic compounds was assessed in anticipation of using this species in endocrine disrupter field studies in the Chesapeake Bay. Measurements of plasma vitellogenin, gonadosomatic (GSI) and hepatosomatic (HSI) indices, and an assessment of changes in gonadal histology were made. Of the parameters assessed, vitellogenin was found to be the most sensitive biomarker. Plasma vitellogenin production occurred in a dose-dependent manner in males exposed to 4-nonylphenol, 4-(tert-octyl)phenol, bisphenol-A, and 17beta-estradiol. There was some indication that the effect on GSI may be influenced by the season in which the experiments are carried out. Two time course experiments revealed that vitellogenin is a fairly long-lived biomarker in male F. heteroclitus. There was also evidence that fish from two moderately contaminated areas injected with 4-nonylphenol or bisphenol-A produced less vitellogenin than those collected from a more pristine habitat. Production of vitellogenin in male F. heteroclitus appeared similar to two other species dosed with the same compounds.

Interaction between endocrine and immune systems in fish

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

Serum antibody levels against select bacterial pathogens in Atlantic bottlenose dolphins, Tursiops truncatus, from Beaufort NC USA and Charleston Harbor, Charleston, SC, USA

Concern over the emergence of zoonotic diseases in marine organisms is growing. In response to this concern, this study set out to measure antibody activities against bacterial pathogens in Atlantic bottlenose dolphins, Tursiops truncatus, from the coastal estuaries of NC and SC, USA. Individuals from Charleston SC harbor, a heavily industrialized shipping harbor estuary, and from Beaufort NC, a non-shipping estuary, were examined. Purified IgG was obtained from pooled sera using ammonium sulfate precipitation steps and protein-G procedures, which was then used to generate a panel of IgG-specific monoclonal antibodies. Two of these antibodies, mAbs BB-10-2 (IgG1) and BB-32-2 (IgG2b), were then used to determine total serum IgG concentrations using a sandwich capture ELISA. Circulating IgG levels were variable between individuals and between the two pods. MAb BB-10-2 was then used in an indirect ELISA to determine serum antibody activities against several common marine bacteria as well as the human pathogens E. coli and E. coli strain 0157:H7, Vibrio parahemolyticus, V. vulnificus, V. cholerae, Mycobacteria marinum, M. fortuitum, and M. chelonae. The highest antibody activities were against mycobacteria, two of which are zoonotic pathogens. Males had the highest antibody activities, thus suggesting low cell-mediated immunity against intracellular pathogens in these individuals. T-cell proliferation in response to Con-A, an indicator of cell-mediated immune function, was then measured in the Beaufort population. Males had the lowest proliferation responses, however a negative correlation between antibody activities and T-cell proliferation in individuals could not be established for either of the Mycobacteria species. Overall, antibody activities against all bacteria, including innocuous species such as V. anguillarum, V. natrigens, and M. xenopi were highly variable between individual dolphins and the two pods, with some animals exhibiting very high activities. These studies suggests that dolphin populations should be monitored by following the health and seroprevalence of pathogens of interest in select individual animals over time.