High-resolution mass spectrometry of skin mucus for monitoring physiological impacts and contaminant biotransformation products in fathead minnows exposed to wastewater effluent

Demonstrating the reliability of in vivo metabolomics based chemical grouping: towards best practice

While grouping/read-across is widely used to fill data gaps, chemical registration dossiers are often rejected due to weak category justifications based on structural similarity only. Metabolomics provides a route to robust chemical categories via evidence of shared molecular effects across source and target substances. To gain international acceptance, this approach must demonstrate high reliability, and best-practice guidance is required. The MetAbolomics ring Trial for CHemical groupING (MATCHING), comprising six industrial, government and academic ring-trial partners, evaluated inter-laboratory reproducibility and worked towards best-practice. An independent team selected eight substances (WY-14643, 4-chloro-3-nitroaniline, 17α-methyl-testosterone, trenbolone, aniline, dichlorprop-p, 2-chloroaniline, fenofibrate); ring-trial partners were blinded to their identities and modes-of-action. Plasma samples were derived from 28-day rat tests (two doses per substance), aliquoted, and distributed to partners. Each partner applied their preferred liquid chromatography-mass spectrometry (LC-MS) metabolomics workflows to acquire, process, quality assess, statistically analyze and report their grouping results to the European Chemicals Agency, to ensure the blinding conditions of the ring trial. Five of six partners, whose metabolomics datasets passed quality control, correctly identified the grouping of eight test substances into three categories, for both male and female rats. Strikingly, this was achieved even though a range of metabolomics approaches were used. Through assessing intrastudy quality-control samples, the sixth partner observed high technical variation and was unable to group the substances. By comparing workflows, we conclude that some heterogeneity in metabolomics methods is not detrimental to consistent grouping, and that assessing data quality prior to grouping is essential. We recommend development of international guidance for quality-control acceptance criteria. This study demonstrates the reliability of metabolomics for chemical grouping and works towards best-practice.

Assessing Contaminants of Emerging Concern in the Great Lakes Ecosystem: A Decade of Method Development and Practical Application

Assessing the ecological risk of contaminants in the field typically involves consideration of a complex mixture of compounds which may or may not be detected via instrumental analyses. Further, there are insufficient data to predict the potential biological effects of many detected compounds, leading to their being characterized as contaminants of emerging concern (CECs). Over the past several years, advances in chemistry, toxicology, and bioinformatics have resulted in a variety of concepts and tools that can enhance the pragmatic assessment of the ecological risk of CECs. The present Focus article describes a 10+- year multiagency effort supported through the U.S. Great Lakes Restoration Initiative to assess the occurrence and implications of CECs in the North American Great Lakes. State-of-the-science methods and models were used to evaluate more than 700 sites in about approximately 200 tributaries across lakes Ontario, Erie, Huron, Michigan, and Superior, sometimes on multiple occasions. Studies featured measurement of up to 500 different target analytes in different environmental matrices, coupled with evaluation of biological effects in resident species, animals from in situ and laboratory exposures, and in vitro systems. Experimental taxa included birds, fish, and a variety of invertebrates, and measured endpoints ranged from molecular to apical responses. Data were integrated and evaluated using a diversity of curated knowledgebases and models with the goal of producing actionable insights for risk assessors and managers charged with evaluating and mitigating the effects of CECs in the Great Lakes. This overview is based on research and data captured in approximately about 90 peer-reviewed journal articles and reports, including approximately about 30 appearing in a virtual issue comprised of highlighted papers published in Environmental Toxicology and Chemistry or Integrated Environmental Assessment and Management. Environ Toxicol Chem 2023;42:2506-2518. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Expanding non-invasive approaches for fish-health monitoring: A survey of the epidermal mucous metabolomes of phylogenetically diverse freshwater fish species

There is a pressing need for more-holistic approaches to fisheries assessments along with growing demand to reduce the health impacts of sample collections. Metabolomic tools enable the use of sample matrices that can be collected with minimal impact on the organism (e.g., blood, urine, and mucus) and provide high-throughput, untargeted biochemical information without the requirement of a sequenced genome. These qualities make metabolomics ideal for monitoring a wide range of fish species, particularly those under protected status. In the current study, we surveyed the relative abundances of 120 endogenous metabolites in epidermal mucus across eight freshwater fish species belonging to seven phylogenetic orders. Principal component analysis was used to provide an overview of the data set, revealing strong interspecies relationships in the epidermal mucous metabolome. Normalized relative abundances of individual endogenous metabolites were then used to identify commonalities across multiple species, as well as those metabolites that showed notable species specificity. For example, taurine was measured in high relative abundance in the epidermal mucus of common carp (Cyprinus carpio), northern pike (Esox lucius), golden shiner (Notemigonus crysoleucas), rainbow trout (Oncorhynchus mykiss), and rainbow smelt (Osmerus mordax), whereas γ-amino butyric acid (GABA) exhibited a uniquely high relative abundance in flathead catfish (Pylodictis olivaris). Finally, hierarchical cluster analysis was used to evaluate species relatedness as characterized by both the epidermal mucous metabolome (phenotype) and genetic phylogeny (genotype). This comparison revealed species for which relatedness in the epidermal mucous metabolome composition closely aligns with phylogenetic relatedness (e.g., N. crysoleucas and C. carpio), as well as species for which these two measures are not well aligned (e.g., P. olivaris and Polyodon spathula). These, and other findings reported here, highlight novel areas for future research with fish, including development of epidermal mucous-based markers for non-invasive health monitoring, sex determination, and hypoxia tolerance.

Environmental metabolomics uncovers oxidative stress, amino acid dysregulation, and energy impairment in Daphnia magna with exposure to industrial effluents

Anthropogenic activities are regarded as point sources of pollution entering freshwater bodies worldwide. With over 350,000 chemicals used in manufacturing, wastewater treatment and industrial effluents are comprised of complex mixtures of organic and inorganic pollutants of known and unknown origins. Consequently, their combined toxicity and mode of action are not well understood in aquatic organisms such as Daphnia magna. In this study, effluent samples from wastewater treatment and industrial sectors were used to examine molecular-level perturbations to the polar metabolic profile of D. magna. To determine if the industrial sector and/or the effluent chemistries played a role in the observed biochemical responses, Daphnia were acutely (48 h) exposed to undiluted (100%) and diluted (10, 25, and 50%) effluent samples. Endogenous metabolites were extracted from single daphnids and analyzed using targeted mass spectrometry-based metabolomics. The metabolic profile of Daphnia exposed to effluent samples resulted in significant separation compared to the unexposed controls. Linear regression analysis determined that no single pollutant detected in the effluents was significantly correlated with the responses of metabolites. Significant perturbations were uncovered across many classes of metabolites (amino acids, nucleosides, nucleotides, polyamines, and their derivatives) which serve as intermediates in keystone biochemical processes. The combined metabolic responses are consistent with oxidative stress, disruptions to energy metabolism, and protein dysregulation which were identified through biochemical pathway analysis. These results provide insight into the molecular processes driving stress responses in D. magna. Overall, we determined that the metabolic profile of Daphnia could not be predicted by the chemical composition of environmentally relevant mixtures. The findings of this study demonstrate the advantage of metabolomics in conjunction with chemical analyses to assess the interactions of industrial effluents. This work further demonstrates the ability of environmental metabolomics to characterize molecular-level perturbations in aquatic organisms exposed to complex chemical mixtures directly.

Effect of sublethal concentrations of glyphosate-based herbicides (Roundup Active®) on skin of the tropical frog (Dendropsophus molitor)

In Colombia, glyphosate (GP) is used to control weeds, with Roundup Active® being the most widely used. This use has affected aquatic ecosystems, causing malformations in amphibians. The Savannah frog (D. molitor) is a tropical frog inhabiting the mountain of Colombia. In the present study, we determined the effect of sublethal concentrations of GP (Roundup Active®) on the skin of D. molitor. Twenty-four tadpoles were exposed to concentrations of GP (T1: 0, T2: 1.4, T3: 3.6, and T4: 5.6 a.e mg/L) during 31 days. In 10 individuals per treatment, two skin regions were evaluated: dorsal cranial and caudal ventral to determine histopathological alterations. Morphometric analysis of the layers of the skin was performed: epidermis, dermis, and hypodermis-muscular. T1 did not present histopathological alterations. Since T2 was identified, glandular cell hyperplasia and hypertrophy increased melanophores and melanin accumulations in the highest concentrations of GP. The ultrastructure revealed an increase in excretory glands in the dermis. In the other layers, an increase of melanophores and melanocyte clusters was observed accompanied by vacuolization of basal cells. The morphometry showed an increase in the thickness of the dermis in the dorso-cranial region in T2 compared to the other treatments, while the ventral caudal region exhibited a variation in the thickness of the dermis from T2 and a decrease in T4. Despite evaluating sublethal concentrations, the skin of D. molitor tadpoles presents histopathological, ultrastructural, and morphometric alterations that could affect the survival of the species in the natural environment.

Untargeted MSn-Based Monitoring of Glucuronides in Fish: Screening Complex Mixtures for Contaminants with Biological Relevance

The complexity of contaminant mixtures in surface waters has presented long-standing challenges to the assessment of risks to human health and the environment. As a result, novel strategies for both identifying contaminants that have not been routinely monitored through targeted methods and prioritizing detected compounds with respect to their biological relevance are needed. Tracking biotransformation products in biofluids and tissues in an untargeted fashion facilitates the identification of chemicals taken up by the resident species (e.g., fish), so by default ensuring that detected compounds are biologically relevant in terms of exposure. In this study, we investigated xenobiotic glucuronidation, which is arguably the most important phase II metabolism pathway for many pharmaceuticals, pesticides, and other environmental contaminants. The application of an untargeted high-resolution mass spectrometry-based approach tentatively revealed the presence of over 70 biologically relevant xenobiotics in bile collected from male and female fathead minnows exposed to wastewater treatment plant effluents. The majority of these were not targets of conventional contaminant monitoring. These results highlight the utility of biologically based untargeted screening methods when evaluating chemical contaminants in complex environmental mixtures.

Characterization of vitellogenin concentration in male fathead minnow mucus compared to plasma, and liver mRNA

The objective of this study was to characterize vitellogenin (VTG) protein in male fathead minnow (Pimephales promelas) mucus compared with more conventional measures in plasma and mRNA isolated from liver. To assess the intensity and duration of changes in mucus VTG concentrations, male fathead minnows were exposed to 17α-ethinylestradiol (EE2) for 7 days with a subsequent depuration period of 14 days. The experiment was conducted in a flow-through system to maintain a consistent concentration of EE2 at a nominal EC₅₀ concentration of 2.5 ng/L and high concentration of 10 ng/L as a positive control. Mucus, plasma and liver were sampled at regular intervals throughout the study. Relative abundance of vtg mRNA increased after 2 days of exposure and returned to control levels after 4 days of depuration. VTG protein concentration displayed similar induction kinetics in both mucus and plasma, however, it was found to be significantly increased after 2 days of exposure using the mucus-based assays and 7 days with the plasma-based assay. Significantly elevated levels of VTG were detected by both assays throughout the 14-day depuration period. The elimination of the laborious plasma collection step in the mucus-based workflow allowed sampling of smaller organisms where blood volume is limiting. It also resulted in significant gains in workflow efficiency, decreasing sampling time without loss of performance.

Suspect screening of antimicrobial agents transformation products in environmental samples development of LC-QTrap method running in pseudo MRM transitions

The aim of the work was to develop a new HPLC-MS/MS method that allows for the simultaneous detection of antimicrobials agents (targeted analysis) and their transformation products (non-targeted analysis), which enabled the elucidation of their transformation pathways in the environment. Targeted analysis was performed for 16 selected antimicrobials agents (AMs) in wastewater collected at different stages of the treatment process and river water from sections before and after wastewater discharge. The samples were collected in the Łyna sewage treatment plant (Olsztyn, Poland) in three measuring periods at different seasons. Analytes were selected from tetracyclines, fluoroquinolones, β-lactams, macrolides, glycopeptides, lincosamides and synthetic antibiotics. As a part of the targeted analysis, 13 AMs were detected in wastewater samples, and 7 of them in river water samples. However, their presence and concentrations were closely related to the type of the sample and the season in which the sample was taken. The highest concentrations of AMs were detected in samples collected in September (max. 1643.7 ng L^-1 TRI), while the lowest AMs concentrations were found in samples collected in June (max. 136.1 ng L^-1 CLR). The total content of AMs in untreated wastewater was in the range of 1.42-1644 ng L^-1, while in the river water was for upstream 1.22-48.73 ng L^-1 and for downstream 2.24-149 ng L^-1. In the non-target analysis, 33 degradation products of the selected AMs were identified, and the transformation pathways of their degradation were speculated. In the course of the research, it was found that as a result of the processes taking place in wastewater treatment plant, the parent substances are transformed into a number of stable transformation products. Transformation products resulted from hydroxylation, ring opening, oxidation, methylation or demethylation, carboxylation, or cleavage of the CN bond of the parent AMs.

The use of non-lethal sampling for transcriptomics to assess the physiological status of wild fishes

Fishes respond to different abiotic and biotic stressors through changes in gene expression as a part of an integrated physiological response. Transcriptomics approaches have been used to quantify gene expression patterns as a reductionist approach to understand responses to environmental stressors in animal physiology and have become more commonly used to study wild fishes. We argue that non-lethal sampling for transcriptomics should become the norm for assessing the physiological status of wild fishes, especially when there are conservation implications. Processes at the level of the transcriptome provide a "snapshot" of the cellular conditions at a given time; however, by using a non-lethal sampling protocol, researchers can connect the transcriptome profile with fitness-relevant ecological endpoints such as reproduction, movement patterns and survival. Furthermore, telemetry is a widely used approach in fisheries to understand movement patterns in the wild, and when combined with transcriptional profiling, provides arguably the most powerful use of non-lethal sampling for transcriptomics in wild fishes. In this review, we discuss the different tissues that can be successfully incorporated into non-lethal sampling strategies, which is particularly useful in the context of the emerging field of conservation transcriptomics. We briefly describe different methods for transcriptional profiling in fishes from high-throughput qPCR to whole transcriptome approaches. Further, we discuss strategies and the limitations of using transcriptomics for non-lethally studying fishes. Lastly, as 'omics' technology continues to advance, transcriptomics paired with different omics approaches to study wild fishes will provide insight into the factors that regulate phenotypic variation and the physiological responses to changing environmental conditions in the future.

Pathway-Based Approaches for Assessing Biological Hazards of Complex Mixtures of Contaminants: A Case Study in the Maumee River

Assessment of ecological risks of chemicals in the field usually involves complex mixtures of known and unknown compounds. We describe the use of pathway-based chemical and biological approaches to assess the risk of chemical mixtures in the Maumee River (OH, USA), which receives a variety of agricultural and urban inputs. Fathead minnows (Pimephales promelas) were deployed in cages for 4 d at a gradient of sites along the river and adjoining tributaries in 2012 and during 2 periods (April and June) in 2016, in conjunction with an automated system to collect composite water samples. More than 100 industrial chemicals, pharmaceuticals, and pesticides were detected in water at some of the study sites, with the greatest number typically found near domestic wastewater treatment plants. In 2016, there was an increase in concentrations of several herbicides from April to June at upstream agricultural sites. A comparison of chemical concentrations in site water with single chemical data from vitro high-throughput screening (HTS) assays suggested the potential for perturbation of multiple biological pathways, including several associated with induction or inhibition of different cytochrome P450 (CYP) isozymes. This was consistent with direct effects of water extracts in an HTS assay and induction of hepatic CYPs in caged fish. Targeted in vitro assays and measurements in the caged fish suggested minimal effects on endocrine function (e.g., estrogenicity). A nontargeted mass spectroscopy-based analysis suggested that hepatic endogenous metabolite profiles in caged fish covaried strongly with the occurrence of pesticides and pesticide degradates. These studies demonstrate the application of an integrated suite of measurements to help understand the effects of complex chemical mixtures in the field. Environ Toxicol Chem 2021;40:1098-1122. © 2020 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Sex-dependent changes in the skin mucus metabolome of discus fish (Symphysodon haraldi) during biparental care

Discus fish Symphysodon spp. employs an unusual parental care where fry feed on parental skin mucus after hatching. Here, we investigated the mucus metabolites of parental and non-parental discus by using non-targeted metabolomics. Statistical analysis of the skin mucus metabolome revealed sex-dependent changes of mucus between parental and non-parental discus, as well as sex-specific differences between parental fish. Differential metabolites reflected that mucus of both parents was rich in prostaglandin A1, but only male contained more oligosaccharides (gentiobiose and D-melezitose) and nucleotides (guanine and cytosine), and only female detected more thymine. Moreover, differential metabolites revealed the metabolic status of parental discus, including the inhibition of biosynthesis of amino acids, e.g., L-phenylalanine (parents), L-aspartic acid (female) and taurine (male) and the activation of metabolism of these amino acids; the increase of metabolism of fatty acids such as α-Linolenic acid (female), arachidonic acid (female) and linoleic acid (male); the perturbation of metabolism of carbohydrate and energy including starch and sucrose metabolism (parents), ascorbate and aldarate metabolism (parents), amino sugar and nucleotide sugar metabolism (female), pentose and glucuronate interconversions (male) and glyoxylate and dicarboxylate metabolism (male). These results might suggest sex-specific metabolic changes in the skin mucus of discus fish during parental care. SIGNIFICANCE: We detected the low-molecular-weight compounds present in the parental mucus of discus fish evolving for offspring and revealed the possible metabolic changes associated with parental care. These results are helpful to gain further insights on the functional and regulatory aspects of skin mucus of discus during parental care.

Hepatic metabolite profiling of polychlorinated biphenyl (PCB)-resistant and sensitive populations of Atlantic killifish (Fundulus heteroclitus)

Atlantic killifish inhabiting polluted sites along the east coast of the U.S. have evolved resistance to toxic effects of contaminants. One such contaminated site is the Acushnet River estuary, near New Bedford Harbor (NBH), Massachusetts, which is characterized by very high PCB concentrations in the sediments and in the tissues of resident killifish. Though killifish at this site appear to be thriving, the metabolic costs of survival in a highly contaminated environment are not well understood. In this study we compared the hepatic metabolite profiles of resistant (NBH) and sensitive populations (Scorton Creek (SC), Sandwich, MA) using a targeted metabolomics approach in which polar metabolites were extracted from adult fish livers and quantified. Our results revealed differences in the levels of several metabolites between fish from the two sites. The majority of these metabolites are associated with one-carbon metabolism, an important pathway that supports multiple physiological processes including DNA and protein methylation, nucleic acid biosynthesis and amino acid metabolism. We measured the gene expression of DNA methylation (DNA methyltransferase 1, dnmt1) and demethylation genes (Ten-Eleven Translocation (TET) genes) in the two populations, and observed lower levels of dnmt1 and higher levels of TET gene expression in the NBH livers, suggesting possible differences in DNA methylation profiles. Consistent with this, the two populations differed significantly in the levels of 5-methylcytosine and 5-hydroxymethylcytosine nucleotides. Overall, our results suggest that the unique hepatic metabolite signatures observed in NBH and SC reflect the adaptive mechanisms for survival in their respective habitats.