Taxonomic applicability of inflammatory cytokines in adverse outcome pathway (AOP) development

Review of ecologically relevant in vitro bioassays to supplement current in vivo tests for whole effluent toxicity testing - Part 2: Non-apical endpoints

Whole effluent toxicity (WET) testing uses whole animal exposures to assess the toxicity of complex mixtures, like wastewater. These assessments typically include four apical endpoints: mortality, growth, development, and reproduction. In the last decade, there has been a shift to alternative methods that align with the 3Rs to replace, reduce, and refine the use of animals in research. In vitro bioassays can provide a cost-effective, high-throughput, ethical alternative to in vivo assays. In addition, they can potentially include additional, more sensitive, environmentally relevant endpoints than traditional toxicity tests. However, the ecological relevance of these endpoints must be established before they are adopted into regulatory frameworks. This is Part 2 of a two-part review that aims to identify in vitro bioassays that are linked to ecologically relevant endpoints that could be included in WET testing. Part 2 of this review focuses on non-apical endpoints that should be incorporated into WET testing. In addition to the four apical endpoints addressed in Part 1, this review identified seven additional toxic outcomes: endocrine disruption, xenobiotic metabolism, carcinogenicity, oxidative stress, inflammation, immunotoxicity and neurotoxicity. For each, the response at the molecular or cellular level measured in vitro was linked to the response at the organism level through a toxicity pathway. Literature from 2015 to 2020 was used to identify suitable bioassays that could be incorporated into WET testing.

Machine learning-based biomarkers identification from toxicogenomics - Bridging to regulatory relevant phenotypic endpoints

One of the major challenges in realization and implementations of the Tox21 vision is the urgent need to establish quantitative link between in-vitro assay molecular endpoint and in-vivo regulatory-relevant phenotypic toxicity endpoint. Current toxicomics approach still mostly rely on large number of redundant markers without pre-selection or ranking, therefore, selection of relevant biomarkers with minimal redundancy would reduce the number of markers to be monitored and reduce the cost, time, and complexity of the toxicity screening and risk monitoring. Here, we demonstrated that, using time series toxicomics in-vitro assay along with machine learning-based feature selection (maximum relevance and minimum redundancy (MRMR)) and classification method (support vector machine (SVM)), an "optimal" number of biomarkers with minimum redundancy can be identified for prediction of phenotypic toxicity endpoints with good accuracy. We included two case studies for in-vivo carcinogenicity and Ames genotoxicity prediction, using 20 selected chemicals including model genotoxic chemicals and negative controls, respectively. The results suggested that, employing the adverse outcome pathway (AOP) concept, molecular endpoints based on a relatively small number of properly selected biomarker-ensemble involved in the conserved DNA-damage and repair pathways among eukaryotes, were able to predict both Ames genotoxicity endpoints and in-vivo carcinogenicity in rats. A prediction accuracy of 76% with AUC = 0.81 was achieved while predicting in-vivo carcinogenicity with the top-ranked five biomarkers. For Ames genotoxicity prediction, the top-ranked five biomarkers were able to achieve prediction accuracy of 70% with AUC = 0.75. However, the specific biomarkers identified as the top-ranked five biomarkers are different for the two different phenotypic genotoxicity assays. The top-ranked biomarkers for the in-vivo carcinogenicity prediction mainly focused on double strand break repair and DNA recombination, whereas the selected top-ranked biomarkers for Ames genotoxicity prediction are associated with base- and nucleotide-excision repair The method developed in this study will help to fill in the knowledge gap in phenotypic anchoring and predictive toxicology, and contribute to the progress in the implementation of tox 21 vision for environmental and health applications.

Prediction of the skin sensitization potential of polyhexamethylene guanidine phosphate, oligo(2-(2-ethoxy)ethoxyethyl) guanidinium chloride, triclosan, and mixtures of these compounds with the excipient propylene glycol through the local lymph node assay: BrdU-FCM

The guanidine family of antimicrobial agents, which includes polyhexamethylene guanidine phosphate (PHMG) and oligo(2-(2-ethoxy)ethoxyethyl) guanidinium chloride (PGH), and chlorophenol biocidal chemicals such as 2,4,4′-trichloro-2′-hydroxydiphenyl ether (triclosan) are used in various occupational and environmental biocidal applications. The excipient propylene glycol (PG) is used to dissolve the active ingredients. The skin sensitization (SS) potential of these substances has not been systemically investigated and is still debated. Moreover, mixtures of PHMG, PGH, or triclosan with PG have not been evaluated for SS potency. An in vivo assay known as the local lymph node assay: 5-bromo-2-deoxyuridine-flow cytometry method (LLNA: BrdU-FCM) was recently adopted as an alternative testing method and was used to address these issues. Via the LLNA: BrdU-FCM, PHMG, PGH, and triclosan were predicted to be sensitizers, while PG was predicted to be a nonsensitizer. In addition, d-limonene, which is used as a flavoring in various consumer products, was also predicted to be a sensitizer, although no unanimous conclusion has been reached regarding its SS potential. Mixtures of PHMG, PGH, triclosan, or d-limonene with PG at ratios of 9:1, 4:1, and 1:4 (w/w) were all positive in terms of SS potential, indicating that the PG excipient does not influence the SS predictions of these chemicals. Since humans can be occupationally and environmentally exposed to mixtures of excipients with active ingredients, the present study may give insight into further investigations of the SS potentials of various chemical mixtures.

Global Transcriptional Analysis of Nontransformed Human Intestinal Epithelial Cells (FHs 74 Int) after Exposure to Selected Drinking Water Disinfection By-Products

BACKGROUND

Drinking water disinfection inadvertently leads to the formation of numerous disinfection by-products (DBPs), some of which are cytotoxic, mutagenic, genotoxic, teratogenic, and potential carcinogens both in vitro and in vivo.

OBJECTIVES

We investigated alterations to global gene expression (GE) in nontransformed human small intestine epithelial cells (FHs 74 Int) after exposure to six brominated and two chlorinated DBPs: bromoacetic acid (BAA), bromoacetonitrile (BAN), 2,6-dibromo-p-benzoquinone (DBBQ), bromoacetamide (BAM), tribromoacetaldehyde (TBAL), bromate (BrO3-), trichloroacetic acid (TCAA), and trichloroacetaldehyde (TCAL).

METHODS

Using whole-genome cDNA microarray technology (Illumina), we examined GE in nontransformed human cells after 4h exposure to DBPs at predetermined equipotent concentrations, identified significant changes in gene expression (p≤0.01), and investigated the relevance of these genes to specific toxicity pathways via gene and pathway enrichment analysis.

RESULTS

Genes related to activation of oxidative stress-responsive pathways exhibited fewer alterations than expected based on prior work, whereas all DBPs induced notable effects on transcription of genes related to immunity and inflammation.

DISCUSSION

Our results suggest that alterations to genes associated with immune and inflammatory pathways play an important role in the potential adverse health effects of exposure to DBPs. The interrelationship between these pathways and the production of reactive oxygen species (ROS) may explain the common occurrence of oxidative stress in other studies exploring DBP toxicity. Finally, transcriptional changes and shared induction of toxicity pathways observed for all DBPs caution of additive effects of mixtures and suggest further assessment of adverse health effects of mixtures is warranted. https://doi.org/10.1289/EHP4945.

Prediction of the skin sensitization potential of didecyldimethylammonium chloride and 3,7-dimethyl-2,6-octadienal and mixtures of these compounds with the excipient ethylene glycol through the human Cell Line Activation Test and the Direct Peptide Reactivity Assay

In commercial products such as household deodorants or biocides, didecyldimethylammonium chloride (DDAC) often serves as an antimicrobial agent, citral serves as a fragrance agent, and the excipient ethylene glycol (EG) is used to dissolve the active ingredients. The skin sensitization (SS) potentials of each of these substances are still being debated. Moreover, mixtures of DDAC or citral with EG have not been evaluated for SS potency. The in vitro alternative assay called human Cell Line Activation Test (h-CLAT) and Direct Peptide Reactivity Assay (DPRA) served to address these issues. On three independent runs of h-CLAT, DDAC and citral were predicted to be sensitizers while EG was predicted to be a non-sensitizer and also by the DPRA. Mixtures of DDAC or citral with EG at ratios of 7:3 and 1:4 w/v were all positive by the h-CLAT in terms of SS potential but SS potency was mitigated as the proportion of EG increased. Citral and its EG mixtures were all positive but DDAC and its EG mixtures were all negative by the DPRA, indicating that the DPRA method is not suitable for chemicals with pro-hapten characteristics. Since humans can be occupationally or environmentally exposed to mixtures of excipients with active ingredients, the present study may give insights into further investigations of the SS potentials of various chemical mixtures.

Detection and analysis of endogenous polar volatile organic compounds (PVOCs) in urine for human exposome research

Background: The human exposome, defined as '…everything that is not the genome', comprises all chemicals in the body interacting with life processes. The exposome drives genes x environment (GxE) interactions that can cause long-term latency and chronic diseases. The exposome constantly changes in response to external exposures and internal metabolism. Different types of compounds are found in different biological media. Objective: Measure polar volatile organic compounds (PVOCs) excreted in urine to document endogenous metabolites and exogenous compounds from environmental exposures. Methods: Use headspace collection and sorbent tube thermal desorption coupled with bench-top gas chromatography-mass spectrometry (GC-MS) for targeted and non-targeted approaches. Identify and categorize PVOCs that may distinguish among healthy and affected individuals. Results: Method is successfully demonstrated to tabulate a series of 28 PVOCs detected in human urine across 120 samples from 28 human subjects. Median concentrations range from below detect to 165 ng/mL. Certain PVOCs have potential health implications. Conclusions: Headspace collection with sorbent tubes is an effective method for documenting PVOCs in urine that are otherwise difficult to measure. This methodology can provide probative information regarding biochemical processes and adverse outcome pathways (AOPs) for toxicity testing.

Pollution Biomarkers in Environmental and Human Biomonitoring

Environmental pollutants generate harmful conditions for living organisms, including humans. This accounts for the growing interest to early warning tools for detection of adverse biological responses to pollutants in both humans and wildlife. Molecular and cellular biomarkers of pollution meet this requirement. A pollution biomarker is defined as an alteration in a biological response occurring at molecular, cellular or physiological levels which can be related to exposure to or toxic effects of environmental chemicals.

Pollution biomarkers have known a growing development in human and environmental biomonitoring representing a valuable tool for early pollutant exposure detection or early effect assessment (exposure/effect biomarkers).

The review discusses the recent developments in the use of pollution biomarker in human and environmental biomonitoring and analyzes future perspectives in the application of this tool such as their potentiality for bridging human and environmental issued studies.

Correlation between mast cell-mediated allergic inflammation and length of perfluorinated compounds

Perfluorinated compounds (PFC) have widely been used in numerous applications including clothing, food packaging, and nonstick coating. With the widespread use of PFC, concerns regarding potential adverse health effects in humans and wildlife have increased. In spite of the known PFC-mediated immunotoxiciy, correlation with PFC and allergic inflammation still requires elucidation. The aim of this study was to examine the effect of four types of PFC (perfluoroheptanoic acid [PFHpA], perfluorononanoic acid [PFNA], perfluorodecanoic acid [PFDA], and perfluoroundecanoic acid [PFUnA]) on mast cell-mediated allergic inflammation in the presence of high-affinity immunoglobulin (Ig) E receptor (FcεRI) cross-linking. Among PFC family, long-chain PFDA and PFUnA increased release of histamine and β-hexosaminidase by up-regulation of intracellular calcium levels in IgE-stimulated mast cells. In addition, PFDA and PFUnA enhanced gene expression of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-8 by activation of nuclear factor-κB in IgE-stimulated mast cells. In ovalbumin (OVA)-induced model of systemic anaphylaxis in the presence of hypothermia, PFNA, PFDA, and PFUnA exacerbated allergic symptoms accompanied by elevation in serum histamine, TNF-α, IgE, and IgG₁. Our data indicate that some PFC aggravated high-affinity IgE receptor (FcεRI)-mediated mast cell degranulation and allergic symptoms. Consequently, the results demonstrated that carbon-chain length of PFC may serve as a factor in allergic inflammation.

Human biomarker interpretation: the importance of intra-class correlation coefficients (ICC) and their calculations based on mixed models, ANOVA, and variance estimates

Human biomonitoring is the foundation of environmental toxicology, community public health evaluation, preclinical health effects assessments, pharmacological drug development and testing, and medical diagnostics. Within this framework, the intra-class correlation coefficient (ICC) serves as an important tool for gaining insight into human variability and responses and for developing risk-based assessments in the face of sparse or highly complex measurement data. The analytical procedures that provide data for clinical and public health efforts are continually evolving to expand our knowledge base of the many thousands of environmental and biomarker chemicals that define human systems biology. These chemicals range from the smallest molecules from energy metabolism (i.e., the metabolome), through larger molecules including enzymes, proteins, RNA, DNA, and adducts. In additiona, the human body contains exogenous environmental chemicals and contributions from the microbiome from gastrointestinal, pulmonary, urogenital, naso-pharyngeal, and skin sources. This complex mixture of biomarker chemicals from environmental, human, and microbiotic sources comprise the human exposome and generally accessed through sampling of blood, breath, and urine. One of the most difficult problems in biomarker assessment is assigning probative value to any given set of measurements as there are generally insufficient data to distinguish among sources of chemicals such as environmental, microbiotic, or human metabolism and also deciding which measurements are remarkable from those that are within normal human variability. The implementation of longitudinal (repeat) measurement strategies has provided new statistical approaches for interpreting such complexities, and use of descriptive statistics based upon intra-class correlation coefficients (ICC) has become a powerful tool in these efforts. This review has two parts; the first focuses on the history of repeat measures of human biomarkers starting with occupational toxicology of the early 1950s through modern applications in interpretation of the human exposome and metabolic adverse outcome pathways (AOPs). The second part reviews different methods for calculating the ICC and explores the strategies and applications in light of different data structures.

From Infections to Anthropogenic Inflicted Pathologies: Involvement of Immune Balance

A temporal trend can be seen in recent human history where the dominant causes of death have shifted from infectious to chronic diseases in industrialized societies. Human influences in the current "Anthropocene" epoch are exponentially impacting the environment and consequentially health. Changing ecological niches are suggested to have created health transitions expressed as modifications of immune balance from infections inflicting pathologies in the Holocene epoch (12,000 years ago) to human behaviors inflicting pathologies beginning in the Anthropocene epoch (300 years ago). A review of human immune health and adaptations responding to environmental (biological, chemical, physical, and psychological) stresses, which are influenced by social conditions, emphasize the involvement of fluctuations in immune cell subsets affecting influential gene-environment interactions. The literature from a variety of fields (anthropological, immunological, and environmental) is incorporated to present an expanded perspective on shifts in diseases within the context of immune balance and function and environmental immunology. The influences between historical and contemporary human ecology are examined in relation to human immunity. Several examples of shifts in human physiology and immunity support the premise that increased incidences of chronic diseases are a consequence of human modification of environment and lifestyle. Although the development of better health care and a broader understanding of human health have helped with better life quality and expectancy, the transition of morbidity and mortality rates from infections to chronic diseases is a cause for concern. Combinations of environmental stressors/pollutants and human behaviors and conditions are modulating the immune-neuroendocrine network, which compromises health benefits.

Risk assessment of benzalkonium chloride in cosmetic products

A risk assessment of benzalkonium chloride (BAC) was conducted based upon its toxicological profile and exposure evaluation. Since 1935, BAC has been used in a wide variety of products such as disinfectants, preservatives, and sanitizers. It is well-established that BAC is not genotoxic nor does it display tumorigenic potential, but safety concerns have been raised in local usage such as for ocular and intranasal applications. The Foundation of Korea Cosmetic Industry Institute (KCII) reported that in a hair conditioner manufactured as a cosmetic or personal product in South Korea, BAC was present at concentrations of 0.5-2%. The systemic exposure dosage (SED) was determined using the above in-use concentrations and a risk assessment analysis was conducted. The Margin of Safety (MOS) values for hair conditioners were calculated to be between 621 and 2,483. The risk of certain personal and cosmetic products was also assessed based upon assumptions that BAC was present at the maximal level of regulation in South Korea and that the maximal amount was used. The MOS values for the body lotion were all above 100, regardless of the application site. Collectively, data indicate that there are no safety concerns regarding use of products that contain BAC under the current concentration restrictions, even when utilized at maximal permitted levels. However, a chronic dermal toxicity study on BAC and comprehensive dermal absorption evaluation needs to be conducted to provide a more accurate prediction of the potential health risks to humans.

Release of chitobiase as an indicator of potential molting disruption in juvenile Daphnia magna exposed to the ecdysone receptor agonist 20-hydroxyecdysone

During arthropod molting, the old exoskeleton is degraded and recycled by the molting fluid. Chitobiase, a major chitinolytic enzyme in the molting fluid, has been widely used as a biomarker to indicate endocrine disruption of molting in arthropods under environmental stress. Although release of chitobiase was extensively studied in organisms exposed to molting-inhibiting chemicals, enzymic association with molting and response of the molting hormone receptor, ecdysone receptor (EcR), is not well understood. The present study was therefore conducted to identify potential linkages between release of chitobiase, molting frequency, and EcR activation in a freshwater crustacean Daphnia magna after short-term (96 hr) exposure to endogenous molting hormone 20-hydroxyecdysone (20E). A suite of bioassays was used for this purpose, including the chitobiase activity, molting frequency, viability, and in vitro EcR activation. Effect concentrations were compared between different assays analyzed. Results showed that exposure to 20E reduced chitobiase release and molting frequency in a concentration-dependent manner. Exposure to as low as 250 nM 20E significantly decreased release of chitobiase after 72 hr exposure, whereas adverse effects on molting frequency and incomplete molting-associated mortality required higher 20E exposure concentrations. The EcR reporter assay further demonstrated that as low as 100 nM 20E may activate EcR in vitro. Data suggest that release of chitobiase may be employed as a sensitive indicator of potential molting disruption in crustaceans after exposure to EcR agonists such as 20E.

Linking physiological parameters to perturbations in the human exposome: Environmental exposures modify blood pressure and lung function via inflammatory cytokine pathway

Human biomonitoring is an indispensable tool for evaluating the systemic effects derived from external stressors including environmental pollutants, chemicals from consumer products, and pharmaceuticals. The aim of this study was to explore consequences of environmental exposures to diesel exhaust (DE) and ozone (O₃) and ultimately to interpret these parameters from the perspective of in vitro to in vivo extrapolation. In particular, the objective was to use cytokine expression at the cellular level as a biomarker for physiological systemic responses such as blood pressure and lung function at the systemic level. The values obtained could ultimately link in vivo behavior to simpler in vitro experiments where cytokines are a measured parameter. Human exposures to combinations of DE and O₃ and the response correlations between forced exhaled volume in 1 second (FEV₁), forced vital capacity (FVC), systolic and diastolic blood pressure (SBP and DBP, respectively), and 10 inflammatory cytokines in blood (interleukins 1β, 2, 4, 5, 8, 10, 12p70 and 13, IFN-γ, and TNF-α) were determined in 15 healthy human volunteers. Results across all exposures revealed that certain individuals displayed greater inflammatory responses compared to the group and, generally, there was more between-person variation in the responses. Evidence indicates that individuals are more stable within themselves and are more likely to exhibit responses independent of one another. Data suggest that in vitro findings may ultimately be implemented to elucidate underlying adverse outcome pathways (AOP) for linking high-throughput toxicity tests to physiological in vivo responses. Further, this investigation supports assessing subjects based upon individual responses as a complement to standard longitudinal (pre vs. post) intervention grouping strategies. Ultimately, it may become possible to predict a physiological (systemic) response based upon cellular-level (in vitro) observations.

Crowd-based breath analysis: assessing behavior, activity, exposures, and emotional response of people in groups

A new concept for exhaled breath analysis has emerged wherein groups, or even crowds of people are simultaneously sampled in enclosed environments to detect overall trends in their activities and recent exposures. The basic idea is to correlate the temporal profile of known breath markers such as carbon dioxide, isoprene, or acetone with all other volatile organics in the air space. Those that trend similarly in time are designated as breath constituents. The ultimate goal of this work is to develop technology for assessing group based behaviors, chemical exposures or even changes in stress or mood. Applications are myriad ranging from chemical dose/toxicity screening to health and stress status for national security diagnostics. The basic technology employs real-time mass spectrometry capable of simultaneously measuring volatile chemicals and endogenous breath markers.

Blood-borne biomarkers and bioindicators for linking exposure to health effects in environmental health science

Environmental health science aims to link environmental pollution sources to adverse health outcomes to develop effective exposure intervention strategies that reduce long-term disease risks. Over the past few decades, the public health community recognized that health risk is driven by interaction between the human genome and external environment. Now that the human genetic code has been sequenced, establishing this "G × E" (gene-environment) interaction requires a similar effort to decode the human exposome, which is the accumulation of an individual's environmental exposures and metabolic responses throughout the person's lifetime. The exposome is composed of endogenous and exogenous chemicals, many of which are measurable as biomarkers in blood, breath, and urine. Exposure to pollutants is assessed by analyzing biofluids for the pollutant itself or its metabolic products. New methods are being developed to use a subset of biomarkers, termed bioindicators, to demonstrate biological changes indicative of future adverse health effects. Typically, environmental biomarkers are assessed using noninvasive (excreted) media, such as breath and urine. Blood is often avoided for biomonitoring due to practical reasons such as medical personnel, infectious waste, or clinical setting, despite the fact that blood represents the central compartment that interacts with every living cell and is the most relevant biofluid for certain applications and analyses. The aims of this study were to (1) review the current use of blood samples in environmental health research, (2) briefly contrast blood with other biological media, and (3) propose additional applications for blood analysis in human exposure research.