Statistical analysis of histopathological endpoints

Dietary Protein Quality Affects the Interplay between Gut Microbiota and Host Performance in Nile Tilapia

Dietary protein quality plays a key role in maintaining intestinal mucosal integrity, but also modulates the growth of luminal microorganisms. This work assessed the effect of dietary protein sources on the performance, gut morphology, and microbiome in Nile tilapia. Four isonitrogenous and isolipidic diets comprising equivalent amounts of the protein supply derived from either PLANT, ANIMAL, INSECT, or BACTERIAL (bacterial biomass) sources were fed to triplicate groups of fish (IBW: 12 g) for 46 days. Fish fed the ANIMAL and BACTERIAL diets showed significantly higher weight gains than those fed the PLANT and INSECT diets (p < 0.05). Relative abundance at the phylum level showed that Bacteroidetes, Fusobacteria, and Proteobacteria were the more abundant phyla in tilapia's intestine, while Cetobacterium was the most representative genus in all treatments. Interesting patterns were observed in the correlation between amino acid intake and genus and species abundance. Metabolism prediction analysis showed that BACTERIAL amine and polyamine degradation pathways are modulated depending on diets. In conclusion, different protein sources modulate the relationship between bacteria functional pathways and amino acid intake.

Historical control histopathology data from amphibian metamorphosis assays and fathead minnow fish short term reproductive assays: A tool for data interpretation

The Amphibian Metamorphosis Assay (AMA) is used to determine if a tested chemical has potential to impact the hypothalamic-pituitary-thyroid (HPT) axis of Xenopus laevis tadpoles, while the Fish Short Term Reproduction Assay (FSTRA) assesses potential effects on the hypothalamic-pituitary-gonadal (HPG) axis of fish such as the fathead minnow (Pimephales promelas). Several global regulatory programs routinely require these internationally validated tests be performed to determine the potential endocrine activity of chemicals. As such, they are conducted in accordance with standardized protocols and test criteria, which were originally developed more than a decade ago. Sizeable numbers of AMA and FSTRA studies have since been carried out, which allows for the mining of extensive historical control data (HCD). Such data are useful for investigating the existence of outlier results and aberrant control groups, identifying potential confounding variables, providing context for rare diagnoses, discriminating target from non-target effects, and for refining current testing paradigms. The present paper provides histopathology HCD from 55 AMA studies and 45 fathead minnow FSTRA studies, so that these data may become publicly available and thus aid in the interpretation of future study outcomes. Histopathology is a key endpoint in these assays, in which it is considered to be one of the most sensitive indicators of endocrine perturbation. In the current review, granular explorations of HCD data were used to identify background lesions, to assess the utility of particular diagnostic findings for distinguishing endocrine from non-endocrine effects, and to help determine if specific improvements to established regulatory guidance may be warranted. Knowledge gleaned from this investigation, supplemented by information from other recent studies, provided further context for the interpretation of AMA and FSTRA histopathology results. We recommend HCDs for the AMA and FSTRA be maintained to support the interpretation of study results.

Comparative subchronic toxicity of copper and a tertiary copper mixture to early life stage rainbow trout (Oncorhynchus mykiss): impacts on growth, development, and histopathology

This research aimed to characterize and compare the subchronic impacts of Cu to a Cu, Cd, and Zn mixture in early life stages of rainbow trout (Oncorhynchus mykiss) by examining uptake, survival, growth, development, and histopathology parameters. To accomplish this, rainbow trout were exposed for 31 days from eyed embryos to the swim-up fry life stage to waterborne Cu (31, 47, 70, and 104 μg/L) individually or as mixture containing Cd (4.1, 6.2, 9.3, and 14 μg/L) and Zn (385, 578, 867, and 1300 μg/L). Exposures elicited pronounced effects on survival when Cu was administered as a mixture (LC25 = 32.9 μg/L Cu) versus individually (LC25 = 46.3 μg/L Cu). Mixtures of Cu, Cd, and Zn also elicited more pronounced sublethal toxicity relative to equivalent Cu treatments with respect to reduced yolk sac resorption and increased incidence and/or severity of gill, liver, and kidney lesions. Our findings of reduced body weight (EC10, Cu = 55.0 μg/L Cu; EC10, Cu+Cd+Zn = 58.9 μg/L Cu), yolk sac resorption (LOECCu = 70 μg/L Cu; LOECCu+Cd+Zn = 70 μg/L Cu), coelomic fat (LOECCu = 47 μg/L Cu; LOECCu+Cd+Zn = 70 μg/L Cu), and increased hepatocellular cytoplasmic vacuolation (LOECCu = 70 μg/L Cu; LOECCu+Cd+Zn = 47 μg/L Cu) collectively indicate a complicated metabolic interference by metals in exposed fish. These lethal and sublethal effects observed in the laboratory could translate to reduced survival and fitness of wild salmonid populations inhabiting waterbodies receiving wastewater or runoff containing multiple metals at elevated concentrations.

Evaluation of multigenerational effects of 2-ethylhexyl 4-hydroxybenzoate in Japanese medaka

The Japanese medaka (Oryzias latipes) extended one-generation reproduction test (MEOGRT) (Test Guideline 890.2200) is a Tier 2 test within the Endocrine Disruptor Screening Program of the US Environmental Protection Agency (US EPA). A modified MEOGRT was used to evaluate multigenerational effects of 2-ethylhexyl 4-hydroxybenzoate (2-EHHB) under flow-through conditions starting with adults (parent generation, F0) through a 3-week reproductive phase of the second generation (F2). Fish were exposed to one of five 2-EHHB test concentrations or a dechlorinated tap water control. Fecundity was affected at the lowest exposure (5.32 μg/L) and greater sensitivity occurred in the F1 and F2 generations. Percent fertility was also diminished from no effect level observed in the F0 generation to 101 and 48.8 μg/L in the F1 and F2 generations, respectively. Growth indices were decreased for F0 adult females and F1 subadults and adults at 48.8 μg/L 2-EHHB. Histopathologic examination of gonads, liver, kidney, and thyroid yielded possible delayed reproductive tract development in F1 subadult males, masculinization of the renal phenotype in F1 adult females (renal tubular eosinophilia) and reduced hepatic energy storage (liver glycogen vacuoles) in F1 (11.3 and 48.8 μg/L) and F2 (48.8 and 101 μg/L) males and females, respectively. Endocrine-related findings included a decrease in anal fin papillae in F2 adult males at 101 μg/L. Results of this study demonstrate effects on growth, development, and reproduction that may be mediated by endocrine (weak estrogenic) and nonendocrine mechanisms. Duration of the MEOGRT should not be routinely extended beyond the OCSPP 890 guideline study design.

Ability of Lactobacillus brevis 47f to Alleviate the Toxic Effects of Imidacloprid Low Concentration on the Histological Parameters and Cytokine Profile of Zebrafish (Danio rerio)

In the present article, the possible mitigation of the toxic effect of imidacloprid low-concentration chronic exposure on Danio rerio by the probiotic strain Lactobacillus brevis 47f (1 × 108 CFU/g) was examined. It was found that even sublethal concentration (2500 µg/L) could lead to the death of some fish during the 60-day chronic experiment. However, the use of Lactobacillus brevis 47f partially reduced the toxic effects, resulting in an increased survival rate and a significant reduction of morphohistological lesions in the intestines and kidneys of Danio rerio. The kidneys were found to be the most susceptible organ to toxic exposure, showing significant disturbances. Calculation of the histopathological index, measurement of morphometric parameters, and analysis of principal components revealed the most significant parameters affected by the combined action of imidacloprid and Lactobacillus brevis 47f. This effect of imidacloprid and the probiotic strain had a multidirectional influence on various pro/anti-inflammatory cytokines (IL-1β, TNF-α, IL-6, IL-8). Therefore, the results suggest the possibility of further studying the probiotic strain Lactobacillus brevis 47f as a strain that reduces the toxic effects of xenobiotics. Additionally, the study established the possibility of using imidacloprid as a model toxicant to assess the detoxification ability of probiotics on the kidney and gastrointestinal tract of fish.

Case Study in 21st-Century Ecotoxicology: Using In Vitro Aromatase Inhibition Data to Predict Reproductive Outcomes in Fish In Vivo

To reduce the use of intact animals for chemical safety testing, while ensuring protection of ecosystems and human health, there is a demand for new approach methodologies (NAMs) that provide relevant scientific information at a quality equivalent to or better than traditional approaches. The present case study examined whether bioactivity and associated potency measured in an in vitro screening assay for aromatase inhibition could be used together with an adverse outcome pathway (AOP) and mechanistically based computational models to predict previously uncharacterized in vivo effects. Model simulations were used to inform designs of 60-h and 10-21-day in vivo exposures of adult fathead minnows (Pimephales promelas) to three or four test concentrations of the in vitro aromatase inhibitor imazalil ranging from 0.12 to 260 µg/L water. Consistent with an AOP linking aromatase inhibition to reproductive impairment in fish, exposure to the fungicide resulted in significant reductions in ex vivo production of 17β-estradiol (E2) by ovary tissue (≥165 µg imazalil/L), plasma E2 concentrations (≥74 µg imazalil/L), vitellogenin (Vtg) messenger RNA expression (≥165 µg imazalil/L), Vtg plasma concentrations (≥74 µg imazalil/L), uptake of Vtg into oocytes (≥260 µg imazalil/L), and overall reproductive output in terms of cumulative fecundity, number of spawning events, and eggs per spawning event (≥24 µg imazalil/L). Despite many potential sources of uncertainty in potency and efficacy estimates based on model simulations, observed magnitudes of apical effects were quite consistent with model predictions, and in vivo potency was within an order of magnitude of that predicted based on in vitro relative potency. Overall, our study suggests that NAMs and AOP-based approaches can support meaningful reduction and refinement of animal testing. Environ Toxicol Chem 2023;42:100-116. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Amphibian Metamorphosis Assay: Investigation of the potential effects of five chemicals on the hypothalamic-pituitary thyroid axis of Xenopus laevis

2-Ethylhexyl 4-hydroxybenzoate (2-EHHB), 4-tert-octylphenol (4-OP), 4-nonylphenol-branched (4-NP), benzyl butyl phthalate (BBP) and dibutyl phthalate (DBP) were evaluated using a 21-day Amphibian Metamorphosis Assay (AMA). Xenopus laevis larvae were exposed nominally to each chemical at 3.6, 10.9, 33.0, and 100 μg/L, except 4-NP concentrations were 1.8, 5.5, 16.5 and 50 μg/L. Endpoints included mortality, developmental stage, hind limb length (HLL), snout-vent length (SVL), body weight (BW), and thyroid histopathology. BBP and 4-OP accelerated development compared to controls at the mean measured concentration of 3.5 and 39.8 μg/L, respectively. An increase in developmental stage frequency distribution was observed for 4-OP at 39.8 and 103 µg/L, BBP at all concentrations and DBP at 143 µg/L. Normalized HLL was increased on study day (SD) 21 for all tested substances except 4-NP. Histopathology revealed accelerated development and mild thyroid follicular cell hypertrophy at all BBP concentrations, but moderate severity at 105 μg/L. Increased BW occurred for all chemicals except 4-OP. Increased SVL was observed for 4-NP, BBP and DBP on SD 21. There was insufficient evidence that 4-NP and 2-EHHB affected the hypothalamic-pituitary thyroid axis, however, BBP, DBP and 4-OP showed potential effects on amphibian metamorphosis and thyroid activity, albeit through different lines of evidence.

Effects of sodium perchlorate and 6-propylthiouracil on metamorphosis and thyroid gland histopathology in the European common frog (Rana temporaria)

Several chemicals have been identified as thyroid hormone axis disrupting chemicals (THADCs) able to interfere with the thyroid hormone system during fetal life and early life stages, thereby impairing neurodevelopment in mammals and inducing development and growth disorders in fish and amphibians. However, identification of THADCs is particularly challenging, and thyroid modalities are currently only assessed in vivo by mammalian and amphibian tests. The aquatic African clawed frog (Xenopus laevis/tropicalis) is the model species of the amphibian test guidelines developed by the OECD and the United States Environmental Protection Agency, but as most European amphibians are semi-aquatic, concern has been raised whether the sensitivity of native European species is comparable to Xenopus. A shortened version of the OEDC test guideline 241 (Larval Amphibian Growth and Development Assay, LAGDA) was used to investigate the effects of two model THADCs on the metamorphosis and thyroid histopathology in the European common frog (Rana temporaria). R. temporaria eggs were collected on the field and exposed till metamorphic climax to sodium perchlorate (11.9-426.5 μg/L perchlorate concentrations) and 6-propylthiouracil (PTU: 1.23-47.7 mg/L). PTU severely delayed metamorphosis and affected several thyroid gland histopathological endpoints at slightly lower concentrations compared to Xenopus. As opposed to what was described in similar Xenopus studies, we observed no effect of perchlorate on the investigated endpoints. Interspecies differences may be linked to mechanisms of action.

Effects of a 28-day early life stage exposure to carbaryl on fathead minnow long-term growth and reproduction

The US Environmental Protection Agency conducts ecological risk assessments with a battery of fish toxicity tests that include acute, early life stage, and reproduction tests. While endpoints in these tests (survival, growth and reproduction) are conceptually related, because they are measured in separate exposures, the quantitative relationships between them are difficult to determine and largely ignored. In the current test, fathead minnows (FHM) were exposed for 28 days to 1 mg/L or 2 mg/L carbaryl, a well-studied carbamate insecticide, in early life stages and then reared in clean water until adulthood, when reproduction was assessed. Also. weekly growth measurements were taken throughout the test to determine growth rates during and after exposure. Growth curves derived from these measurements were then compared to the reproductive output. The data indicate that carbaryl reduced growth rate only for a brief time early in the exposure. However, this brief effect impacted overall growth into adulthood and lowered the reproductive output of exposed FHM. The effect of a transient exposure early in life to carbaryl could have later population-level impacts by causing mortality, lowering growth rates, and reducing reproductive output.

A Critical Review of Morphologic Findings and Data From 14 Toxicological Studies Involving Fish Exposures to Diclofenac

A number of studies have investigated the potential toxicity of the analgesic agent diclofenac (DCF) in various fish species under a diverse array of experimental conditions. Reported evidence of toxicity in these investigations is often strongly reliant on morphologic end points such as histopathology, immunohistochemistry, and transmission electron microscopy. However, it may be challenging for scientists who perform environmental hazard or risk determination to fully appreciate the intricacies of these specialized endpoints. Therefore, the purpose of the current review was to critically assess the quality of morphologic data in 14 papers that described the experimental exposure of fish to DCF. Areas of focus during this review included study design, diagnostic accuracy, magnitude of reported changes, data interpretation and presentation, and the credibility of individual reported findings. Positive attributes of some studies included robust experimental designs, accurate diagnoses, and straightforward and transparent data reporting. Issues identified in certain articles included diagnostic errors, failure to account for sampling and/or observer bias, failure to evaluate findings according to sex, exaggeration of lesion severity, interstudy inconsistencies, unexplained phenomena, and incomplete or ambiguous data presentation. It is hoped that the outcome of this review will be of value for personnel involved in regulatory decision-making.

Evaluating the bone-regenerative role of the decellularized porcine bone xenograft in a canine extraction socket model

Objective

To evaluate the efficacy of a novel decellularized porcine bone xenograft, produced by supercritical carbon dioxide extraction technology, on alveolar socket healing after tooth extraction compared to a commercially available deproteinized bovine bone (Bio‐Oss®).

Materials and methods

Nine dogs (about 18 months old and weighing between 20 kg and 30 kg) underwent extractions of lower second to fourth premolars, bilaterally. The dogs were randomly selected and allocated to the following groups: Group 1: control unfilled socket; Group 2: socket filled with decellularized porcine bone xenograft (ABCcolla®) and covered by a commercially available porcine collagen membrane (Bio‐Gide®); Group 3: socket filled with Bio‐Oss® and covered by Bio‐Gide® membrane. One dogs from each group was sacrificed at 4‐, 12‐, and 24‐week to evaluate the socket healing after tooth extraction. The mandible bone blocks were processed without decalcification and specimens were embedded in methyl methacrylate and subjected to histopathology analyses to evaluate the bone regeneration in the extraction sockets.

Results

At 24‐week after socket healing, ABCcolla® treated defects demonstrated significantly higher histopathology score in new bone formation and bone bridging, but significantly lower score in fluorescent labeling than those of the Bio‐Oss®. In the microphotographic examination, decellularized porcine bone xenograft showed similar characteristics of new bone formation to that of Bio‐Oss®. However, there was significantly less remnant implant materials in the decellularized porcine bone xenograft compared to the Bio‐Oss® group at 24‐week. Thus, the decellularized porcine bone graft seems to have promising bone regeneration properties similar to that of Bio‐Oss® with less remnant grafted material in a canine tooth extraction socket model.

Conclusions

Within the limits of the study, we concluded that ABCcolla® treated defects demonstrated significantly more new bone formation and better bone bridging, but less amount of fluorescent labeling than those of the Bio‐Oss® group. However, clinical studies in humans are recommended to confirm these findings.

Fundamental Concepts for Semiquantitative Tissue Scoring in Translational Research

Failure to reproduce results from some scientific studies has raised awareness of the critical need for reproducibility in translational studies. Macroscopic and microscopic examination is a common approach to determine changes in tissues, but text descriptions and visual images have limitations for group comparisons. Semiquantitative scoring is a way of transforming qualitative tissue data into numerical data that allow more robust group comparisons. Semiquantitative scoring has broad uses in preclinical and clinical studies for evaluation of tissue lesions. Reproducibility can be improved by constraining bias through appropriate experimental design, randomization of tissues, effective use of multidisciplinary collaborations, and valid masking procedures. Scoring can be applied to tissue lesions (eg, size, distribution, characteristics) and also to tissues through evaluation of staining distribution and intensity. Semiquantitative scores should be validated to demonstrate relevance to biological data and to demonstrate observer reproducibility. Statistical analysis should make use of appropriate tests to give robust confidence in the results and interpretations. Following key principles of semiquantitative scoring will not only enhance descriptive tissue evaluation but also improve quality, reproducibility, and rigor of tissue studies.

Medaka (Oryzias latipes) Multigeneration Test with Triclosan

The medaka extended one-generation reproduction test (MEOGRT) is a tier-2 study in the US Environmental Protection Agency's Endocrine Disruptor Screening Program and a level-5 study in the Organisation for Economic Co-operation and Development's conceptual framework. Integrating nonspecific apical and endocrine-specific mechanistic endpoints, results of a MEOGRT can be used, with other data, in a weight-of-evidence evaluation to establish a dose-response relationship for risk assessment and identify potential causal relationships between an endocrine mode of action and adverse effects. The MEOGRT test design was used to evaluate the multigenerational effects of the antimicrobial agent triclosan. Japanese medaka were exposed to nominal concentrations of 1.4, 2.8, 5.6, 11, and 23 μg/L triclosan and a dilution water control starting with adult medaka (F0) through hatch in the second generation (F2). No consistent or concentration-related responses occurred in the 182-d test that suggested an endocrine-mediated effect. There were no impacts on hepatic vitellogenin, secondary sex characteristics, or sex ratio that were linked to an adverse reproductive outcome. Histopathological responses were consistent with a toxic or stress effect, particularly when considered in context with observed reductions in growth. The overall population-relevant no-observed-effect concentration was 11 µg/L based on effects on growth. The results of the present study support a previously conducted weight-of-evidence evaluation concluding that triclosan does not act as an agonist or antagonist within estrogen, androgen, thyroid, or steroidogenic pathways. Environ Toxicol Chem 2019;38:1770-1783. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

The effects of continuous diazinon exposure on growth and reproduction in Japanese medaka using a modified Medaka Extended One Generation Reproduction Test (MEOGRT)

The Medaka Extended One Generation Reproduction Test (MEOGRT) is a Tier 2 test within U.S. Environmental Protection Agency's (USEPA) Endocrine Disruptor Screening Program (EDSP), designed to characterize the potential adverse effects to fish of exposure to chemical that can cause disruption of the endocrine system. The MEOGRT focuses primarily on adverse effects to reproduction while collecting information regarding effects on growth, survival, and endocrine-related endpoints. However, the risk assessment process for fish, as mandated by legislation such as the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) or the Toxic Substances Control Act (TSCA), could benefit from a more detailed assessment of effects on growth. Typically, fish growth data in support of risk assessment are obtained from full life-cycle tests or early life stage tests using the fathead minnow. As an alternative to these tests, a modified MEOGRT was conducted to assess the effects of diazinon on the various parameters measured in the MEOGRT. Diazinon is an organophosphate insecticide that is detected in the environment, and whose efficacy is a result of inhibition of the acetylcholine esterase enzyme at neuromuscular junctions and synapses of the nervous system. Diazinon (2.9, 5.2, 10.3, 19.8, and 40.2 μg/L) was tested with the MEOGRT protocol, and the lowest observable effect concentrations of 2.9 μg/L for fecundity and 5.2 μg/L for growth were determined. Additional growth measurements were added to the MEOGRT protocol to more robustly define growth rates and to determine the impact size has on reproductive performance. Fish size starting at the first measurement day (i.e. 21 days post-fertilization), and continuing through the duration of the test was reduced with exposure to 5.2 μg/L and higher, and asymptotic size predicted from growth modeling was reduced at 10.3 μg/L and higher. By simply adding non-destructive growth measurements at two additional time points, the MEOGRT provided enough data for the parameterization of growth models, which could be used to characterize the reproductive implications of growth impairment.

Effects of multiple life stage exposure to the fungicide prochloraz in Xenopus laevis: Manifestations of antiandrogenic and other modes of toxicity

The Larval Amphibian Growth and Development Assay (LAGDA) is an internationally harmonized testing guideline for evaluating effects of chronic chemical exposure in amphibians. In order to evaluate the effects of chronic exposure to an antiandrogenic chemical in an amphibian model, prochloraz was tested using a variation of the LAGDA design. Exposure was initiated with <1d post-fertilization embryos at nominal concentrations of 0, 6.7, 20, 60 and 180 μg/L (0, 18, 53, 159, 478 nM) and continued in flow-through conditions until two months following the median time that controls completed metamorphosis. Growth, developmental rate, circulating thyroid hormone and thyroid gland histopathology were evaluated in a subsample at completion of metamorphosis. There were no effects on growth or development at this stage, but circulating thyroid hormone was elevated in the 20, 60 and 180 μg/L treatments and minimal to mild thyroid follicular cell hypertrophy was observed histologically in the 180 μg/L treatment. Growth, overt toxicity, and reproductive development were evaluated at test termination. There were no effects on growth in either gender, but livers and kidneys exhibited treatment-related pathologies consistent with organ toxicity related to metabolism and presumably impaired excretion of prochloraz metabolites. Histological assessments of female ovaries resulted in minimal pathologies only in the 180 μg/L treatment while male testes exhibited numerous treatment-related pathologies that are consistent with previously reported antiandrogenic effects of prochloraz in other species. The most severe testis pathologies occurred in the 180 μg/L treatment; however, incidences of treatment-related pathologies occurred in all prochloraz treatments. Müllerian duct regression in males was inhibited by prochloraz exposure while Müllerian duct maturation in females was accelerated, characteristic of a feminizing effect. Gene expression levels of potential biomarkers of testis function were also measured. Relative abundance of cyp17a1 transcripts was generally unaffected by prochloraz exposure whereas the Insl3 orthologue, rflcii, was elevated by 3 and >5-fold in the 60 and 180 μg/L treatments, respectively, indicating impaired Leydig cell maturation and testosterone signaling. Overall, prochloraz exposure caused effects characteristic of an antiandrogenic mode of action, which is consistent with previously reported results in other species and supports the utility of the LAGDA design for chemical testing.

Comparing apples and oranges and pears and kumquats: The misuse of index systems for processing histopathology data in fish toxicological bioassays

Histopathology index systems involve the application of weighted scores to various diagnostic findings for the purpose of calculating overall organ and/or whole-animal health measurements. Such systems were originally developed as tools for monitoring the general health of fish populations. More recently, index systems have been applied to hypothesis-based toxicological studies, the goal of which is to investigate whether a cause-and-effect relationship exists between exposure to a particular test substance or environmental contaminant and morphologic effects in fish tissues. However, the application of index systems in that context is problematic for various reasons: a dependency on untested assumptions of toxicological importance for different types of histopathologic findings; organ scores that combine mechanistically unrelated and potentially contradictory diagnoses; calculations that include excessive numbers of findings, some of which may be incidental to the study outcome; failure to incorporate additional relevant results into the data interpretation, such as clinical observations, macroscopic findings, organ/body weights, clinical pathology data, and the results of hormonal or other biochemical assays; the inappropriate mathematical manipulation of ordinal categorical data (e.g., severity scores and "importance factors"); and a tendency of these systems to amplify, mask, and divert attention from methodological weaknesses and inaccurate diagnoses. The purpose of the present article is to demonstrate why the use of index systems is a misguided approach for handling histopathology data in studies of potential fish toxicants. Environ Toxicol Chem 2018;37:1688-1695. © 2018 SETAC.

Testicular oocytes in smallmouth bass in northeastern Minnesota in relation to varying levels of human activity

Testicular oocytes (TOs) have been found in black bass (Micropterus spp.) from many locations in North America. The presence of TOs is often assumed to imply exposure to estrogenic endocrine disrupting compounds (EDCs); however, a definitive causal relationship has yet to be established, and TO prevalence is not consistently low in fish from areas lacking evident EDC sources. This might indicate any of a number of situations: 1) unknown or unidentified EDCs or EDC sources, 2) induction of TOs by other stressors, or 3) testicular oocytes occurring spontaneously during normal development. In the present study, we analyzed TO occurrence in smallmouth bass (Micropterus dolomieu) from 8 populations in northeastern Minnesota watersheds with differing degrees of human development and, hence, presumed likelihood of exposure to anthropogenic chemicals. Three watersheds were categorized as moderately developed, based on the presence of municipal wastewater discharges and higher human population density (4-81 per km² ), and 5 watersheds were minimally developed, with very low human population density (0-1 per km² ) and minimal built environment. Testicular tissues from mature fish were evaluated using a semiquantitative method that estimated TO density, normalized by cross-sectional area. Testicular oocyte prevalence and density among populations from moderately developed watersheds was higher than in populations from minimally developed watersheds. However, TO prevalence was unexpectedly high and variable (7-43%) in some populations from minimally developed watersheds, and only weak evidence was found for a relationship between TO density and watershed development, suggesting alternative or more complex explanations for TO presence in smallmouth bass from this region. Environ Toxicol Chem 2017;36:3424-3435. © 2017 SETAC.

Summary of the development the US Environmental Protection Agency's Medaka Extended One Generation Reproduction Test (MEOGRT) using data from 9 multigenerational medaka tests

In response to various legislative mandates, the US Environmental Protection Agency (USEPA) formed its Endocrine Disruptor Screening Program (EDSP), which in turn, formed the basis of a tiered testing strategy to determine the potential of pesticides, commercial chemicals, and environmental contaminants to disrupt the endocrine system. The first tier of tests is intended to detect the potential for endocrine disruption mediated through estrogen, androgen, or thyroid pathways, whereas the second tier is intended to further characterize the effects on these pathways and to establish a dose-response relationship for adverse effects. One of these tier 2 tests, the Medaka Extended One Generation Reproduction Test (MEOGRT), was developed by the USEPA for the EDSP and, in collaboration with the Japanese Ministry of the Environment, for the Guidelines for the Testing of Chemicals of the Organisation for Economic Co-operation and Development (OECD). The MEOGRT protocol was iteratively modified based on knowledge gained after the successful completion of 9 tests with variations in test protocols. The present study describes both the final MEOGRT protocol that has been published by the USEPA and the OECD, and the iterations that provided valuable insights into nuances of the protocol. The various tests include exposure to 17β-estradiol, 4-t-octylphenol, o,p'- dichlorodiphenyltrichloroethane, 4-chloro-3-methylphenol, tamoxifen, 17β-trenbolone, vinclozolin, and prochloraz. Environ Toxicol Chem 2017;36:3387-3403. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Gonadal intersex in smallmouth bass Micropterus dolomieu from northern Indiana with correlations to molecular biomarkers and anthropogenic chemicals

Over the past decade, studies have shown that exposure to endocrine disrupting chemicals (EDCs) can cause gonadal intersex in fish. Smallmouth bass (Micropterus dolomieu) males appear to be highly susceptible to developing testicular oocytes (TO), the most prevalent form of gonadal intersex, as observed in various areas across the U.S. In this study, prevalence and severity of TO was quantified for smallmouth bass sampled from the St. Joseph River in northern Indiana, intersex biomarkers were developed, and association between TO prevalence and organic contaminants were explored. At some sites, TO prevalence reached maximum levels before decreasing significantly after the spawning season. We examined the relationship between TO presence and expression of gonadal and liver genes involved in sex differentiation and reproductive functions (esr1, esr2, foxl2, fshr, star, lhr and vtg). We found that vitellogenin (vtg) transcript levels were significantly higher in the liver of males with TO, but only when sampled during the spawning season. Further, we identified a positive correlation between plasma VTG levels and vtg transcript levels, suggesting its use as a non-destructive biomarker of TO in this species. Finally, we evaluated 43 contaminants in surface water at representative sites using passive sampling to look for contaminants with possible links to the observed TO prevalence. No quantifiable levels of estrogens or other commonly agreed upon EDCs such as the bisphenols were observed in our contaminant assessment; however, we did find high levels of herbicides as well as consistent quantifiable levels of PFOS, PFOA, and triclosan in the watershed where high TO prevalence was exhibited. Our findings suggest that the observed TO prevalence may be the result of exposures to mixtures of nonsteroidal EDCs.

I: Biomarker quantification in fish exposed to crude oil as input to species sensitivity distributions and threshold values for environmental monitoring

The aim of this study was to determine a suitable set of biomarker based methods for environmental monitoring in sub-arctic and temperate offshore areas using scientific knowledge on the sensitivity of fish species to dispersed crude oil. Threshold values for environmental monitoring and risk assessment were obtained based on a quantitative comparison of biomarker responses. Turbot, halibut, salmon and sprat were exposed for up to 8 weeks to five different sub-lethal concentrations of dispersed crude oil. Biomarkers assessing PAH metabolites, oxidative stress, detoxification system I activity, genotoxicity, immunotoxicity, endocrine disruption, general cellular stress and histological changes were measured. Results showed that PAH metabolites, CYP1A/EROD, DNA adducts and histopathology rendered the most robust results across the different fish species, both in terms of sensitivity and dose-responsiveness. The reported results contributed to forming links between biomonitoring and risk assessment procedures by using biomarker species sensitivity distributions.

Proceedings of the 2016 National Toxicology Program Satellite Symposium

The 2016 annual National Toxicology Program Satellite Symposium, entitled "Pathology Potpourri" was held in San Diego, CA, at the Society of Toxicologic Pathology's (STP) 35th annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks, along with select images that were used by the audience for voting and discussion. Some lesions and topics covered during the symposium included malignant glioma and histiocytic sarcoma in the rodent brain; a new statistical method designed for histopathology data evaluation; uterine stromal/glandular polyp in a rat; malignant plasma cell tumor in a mouse brain; Schwann cell proliferative lesions in rat hearts; axillary schwannoma in a cat; necrosis and granulomatous inflammation in a rat brain; adenoma/carcinoma in a rat adrenal gland; hepatocyte maturation defect and liver/spleen hematopoietic defects in an embryonic mouse; distinguishing malignant glioma, malignant mixed glioma, and malignant oligodendroglioma in the rat; comparison of mammary gland whole mounts and histopathology from mice; and discussion of the International Harmonization of Nomenclature and Diagnostic Criteria collaborations.

Don't be fooled-A no-observed-effect concentration is no substitute for a poor concentration-response experiment

Renowned mathematician and science historian Jacob Bronowski once defined science as "the acceptance of what works and the rejection of what does not" and noted "that needs more courage than we might think." Such would also seem to be the case with no-observed-effect concentrations (NOECs) and no-observed-effect levels in ecotoxicology. Compelling arguments were advanced more than a quarter of a century ago as to why the use of a model to describe the concentration-response relationship was preferable to an isolated metric, with the NOEC singled out as a particularly poor toxicity measure. In the ensuing years numerous articles critical of the NOEC have been written, with some calling for an outright ban on its use. More recently, arguments have been made for the retention of NOECs, with supporters suggesting that this metric is particularly useful in situations where the concentration-response relationship is weak or nonexistent. In addition, it has been claimed that there are situations in ecotoxicology where suitable models are simply not available. These arguments are not correct, and they also have impeded the decades-overdue incorporation of numerous recommendations based on research that NOECs should no longer be used. In the present study the authors counter some of the most recent claims in support of NOECs and provide new insights for 1 class of problem claimed not to be amenable to such modeling. They are confident that similar insights will be developed as further original research in this area is undertaken. Environ Toxicol Chem 2016;35:2141-2148. © 2016 SETAC.

Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part I: Fathead minnow

In the present study, a hypothesized adverse outcome pathway linking inhibition of thyroid peroxidase (TPO) activity to impaired swim bladder inflation was investigated in two experiments in which fathead minnows (Pimephales promelas) were exposed to 2-mercaptobenzothiazole (MBT). Continuous exposure to 1mg MBT/L for up to 22 days had no effect on inflation of the posterior chamber of the swim bladder, which typically inflates around 6 days post fertilization (dpf), a period during which maternally-derived thyroid hormone is presumed to be present. In contrast, inflation of the anterior swim bladder, which occurs around 14dpf, was impacted. Specifically, at 14dpf, approximately 50% of fish exposed to 1mg MBT/L did not have an inflated anterior swim bladder. In fish exposed to MBT through 21 or 22dpf, the anterior swim bladder was able to inflate, but the ratio of the anterior/posterior chamber length was significantly reduced compared to controls. Both abundance of thyroid peroxidase mRNA and thyroid follicle histology suggest that fathead minnows mounted a compensatory response to the presumed inhibition of TPO activity by MBT. Time-course characterization showed that fish exposed to MBT for at least 4 days prior to normal anterior swim bladder inflation had significant reductions in anterior swim bladder size, relative to the posterior chamber, compared to controls. These results, along with similar results observed in zebrafish (see part II, this issue) are consistent with the hypothesis that thyroid hormone signaling plays a significant role in mediating anterior swim bladder inflation and development in cyprinids, and that role can be disrupted by exposure to thyroid hormone synthesis inhibitors. Nonetheless, possible thyroid-independent actions of MBT on anterior swim bladder inflation cannot be ruled out based on the present results. Overall, although anterior swim bladder inflation has not been directly linked to survival as posterior swim bladder inflation has, potential links to adverse ecological outcomes are plausible given involvement of the anterior chamber in sound production and detection.

Chemical and histological comparisons between Brevoortia sp. (menhaden) collected in fall 2010 from Barataria Bay, LA and Delaware Bay, NJ following the DeepWater Horizon (DWH) oil spill

Body burdens of PAHs were compared to histological effects in menhaden (Family: Clupeidae, Genus: Brevoortia) collected in fall 2010 from Barataria Bay, LA (BBLA) and Delaware Bay, NJ (DBNJ). Barataria Bay was heavily oiled during the DeepWater Horizon (DWH) oil spill, while Delaware Bay although urbanized had no reported recent oil spills. GCMS analyses of pre-spill 2009, BBLA and DBNJ fish found predominantly C2/C3 phenanthrene (1.28-6.52 ng/mg). However, BBLA also contained five higher molecular weight PAHs (0.06-0.34 ng/mg DW). Fluorescent aromatic compound spectroscopy (FACS) of gastrointestinal (GI) tract tissue showed statistically higher levels of hydroxypyrene-like PAHs in DBNJ than BBLA fish. Histopathologic lesions were more prevalent in BBLA than DBNJ fish. The lesion prevalence (gill, trunk kidney, epidermis, stomach) in the BBLA menhaden were significantly higher and more severe than observed in the DBNJ menhaden. Reversible lesions included gill lamellar hyperplasia, adhesions, edema, and epidermal hyperplasia. The increased pigmented macrophage centers were indicative of activated macrophages responding to connective tissue damage or other antigens. The liver hepatic necrosis and renal tissue mineralization may well have undergone repair, but damage to the kidney nephrons and hepatic/biliary regions of the liver would be slower to resolve and apparently remained after elimination of PAHs. Therefore, a direct cause and effect between DWH oil spill and increased lesion prevalence in BBLA menhaden could not be established.

Endocrine-disrupting effect of the ultraviolet filter benzophenone-3 in zebrafish, Danio rerio

The chemical ultraviolet (UV) filter benzophenone-3 (BP-3) is suspected to be an endocrine disruptor based on results from in vitro and in vivo testing. However, studies including endpoints of endocrine adversity are lacking. The present study investigated the potential endocrine-disrupting effects of BP-3 in zebrafish (Danio rerio) in the Fish Sexual Development Test (Organisation for Economic Co-operation and Development TG 234) and a 12-d adult male zebrafish study. In TG 234, exposure from 0 d to 60 d posthatch caused a monotone dose-dependent skewing of the phenotypic sex ratio toward fewer males and more female zebrafish (no observed effect concentration [NOEC]: 191 μg/L, lowest observed effect concentration [LOEC]: 388 μg/L). Besides, gonad maturation was affected in both female fish (NOEC 191 μg/L, LOEC 388 μg/L) and male fish (NOEC 388 μg/L, LOEC 470 μg/L). Exposure to BP-3 did not affect the vitellogenin concentration in TG 234. After 12 d exposure of adult male zebrafish, a slight yet significant increase in the vitellogenin concentration was observed at 268 μg/L but not at 63 μg/L and 437 μg/L BP-3. Skewing of the sex ratio is a marker of an endocrine-mediated mechanism as well as a marker of adversity, and therefore the conclusion of the present study is that BP-3 is an endocrine-disrupting chemical in accordance with the World Health Organization's definition.

Evaluation of the 5α-reductase inhibitor finasteride on reproduction and gonadal development in medaka, Oryzias latipes

5-α reductase (5αR) inhibitors have an anti-androgenic effect in mammals because they inhibit the conversion of testosterone to the potent androgen, dihydrotestosterone. Finasteride is a type-2 5αR inhibitor that is used as a human pharmaceutical for the treatment of prostate cancer, benign prostate hyperplasia and male pattern baldness. This study evaluated the impacts of finasteride (50, 500 and 5000μg/L) on the development and reproduction of medaka (Oryzias latipes) exposed continuously over multiple generations (F0, F1 and F2). The exposure was initiated with reproductively mature fish (F0 generation) and continued until the hatching of the F2 generation. There were no significant effects on survival, fecundity or fertility in the F0 (50, 500, 5000μg/L) and F1 (50, 500μg/L) generations. The F1 generation exposed to 5000μg/L exhibited significant mortality. Histopathology of the gonads demonstrated that medaka and pre-clinical species respond similarly to finasteride exposure. Intersex condition and maldeveloped gonads were observed in F0 generation males exposed to 5000μg/L and F1 generation males exposed to 500μg/L. F1 generation males exposed to 500μg/L displayed reduced gonadosomatic index with an increased incidence of testicular degeneration. Males in both generations exhibited an increased incidence of Leydig cell hyperplasia at concentrations ⩾500μg/L. F0 generation females exposed to 5000μg/L exhibited increased gonadosomatic index. An increased prevalence of accelerated post-ovulatory follicle involution was observed in females at concentrations ⩾500μg/L in both generations. The gonadal changes induced by finasteride support the idea that 5-α reductase inhibition impacts androgen signaling in fish. Results from this study are discussed in the context of differential expression of the androgen receptor between species of fish.

Nonlesions, Misdiagnoses, Missed Diagnoses, and Other Interpretive Challenges in Fish Histopathology Studies

Differentiating salient histopathologic changes from normal anatomic features or tissue artifacts can be decidedly challenging, especially for the novice fish pathologist. As a consequence, findings of questionable accuracy may be reported inadvertently, and the potential negative impacts of publishing inaccurate histopathologic interpretations are not always fully appreciated. The objectives of this article are to illustrate a number of specific morphologic findings in commonly examined fish tissues (e.g., gills, liver, kidney, and gonads) that are frequently either misdiagnosed or underdiagnosed, and to address related issues involving the interpretation of histopathologic data. To enhance the utility of this article as a guide, photomicrographs of normal and abnormal specimens are presented. General recommendations for generating and publishing results from histopathology studies are additionally provided. It is hoped that the furnished information will be a useful resource for manuscript generation, by helping authors, reviewers, and readers to critically assess fish histopathologic data.