Environmental Toxicology Assays Using Organ-on-Chip

Wildlife ecological risk assessment in the 21st century: Promising technologies to assess toxicological effects

Despite advances in toxicity testing and the development of new approach methodologies (NAMs) for hazard assessment, the ecological risk assessment (ERA) framework for terrestrial wildlife (i.e., air-breathing amphibians, reptiles, birds, and mammals) has remained unchanged for decades. While survival, growth, and reproductive endpoints derived from whole-animal toxicity tests are central to hazard assessment, nonstandard measures of biological effects at multiple levels of biological organization (e.g., molecular, cellular, tissue, organ, organism, population, community, ecosystem) have the potential to enhance the relevance of prospective and retrospective wildlife ERAs. Other factors (e.g., indirect effects of contaminants on food supplies and infectious disease processes) are influenced by toxicants at individual, population, and community levels, and need to be factored into chemically based risk assessments to enhance the "eco" component of ERAs. Regulatory and logistical challenges often relegate such nonstandard endpoints and indirect effects to postregistration evaluations of pesticides and industrial chemicals and contaminated site evaluations. While NAMs are being developed, to date, their applications in ERAs focused on wildlife have been limited. No single magic tool or model will address all uncertainties in hazard assessment. Modernizing wildlife ERAs will likely entail combinations of laboratory- and field-derived data at multiple levels of biological organization, knowledge collection solutions (e.g., systematic review, adverse outcome pathway frameworks), and inferential methods that facilitate integrations and risk estimations focused on species, populations, interspecific extrapolations, and ecosystem services modeling, with less dependence on whole-animal data and simple hazard ratios. Integr Environ Assess Manag 2024;20:725-748. © 2023 His Majesty the King in Right of Canada and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Biomimetic microfluidic chips for toxicity assessment of environmental pollutants

Various types of pollutants widely present in environmental media, including synthetic and natural chemicals, physical pollutants such as radioactive substances, ultraviolet rays, and noise, as well as biological organisms, pose a huge threat to public health. Therefore, it is crucial to accurately and effectively explore the human physiological responses and toxicity mechanisms of pollutants to prevent diseases caused by pollutants. The emerging toxicological testing method biomimetic microfluidic chips (BMCs) exhibit great potential in environmental pollutant toxicity assessment due to their superior biomimetic properties. The BMCs are divided into cell-on-chips and organ-on-chips based on the distinctions in bionic simulation levels. Herein, we first summarize the characteristics, emergence and development history, composition and structure, and application fields of BMCs. Then, with a focus on the toxicity mechanisms of pollutants, we review the applications and advances of the BMCs in the toxicity assessment of physical, chemical, and biological pollutants, respectively, highlighting its potential and development prospects in environmental toxicology testing. Finally, the opportunities and challenges for further use of BMCs are discussed.

The suitability of a polydimethylsiloxane-based (PDMS) microfluidic two compartment system for the toxicokinetic analysis of organophosphorus compounds

Organ-on-a-chip platforms are an emerging technology in experimental and regulatory toxicology (species-specific differences, ethical considerations). They address gaps between in vivo and in vitro models. However, there are still certain limitations considering material, setup and applicability. The current study examined the suitability of a commercially available polydimethylsiloxane-based (PDMS) organ-chip for the toxicokinetic characterization of the highly toxic nerve agent VX and the organophosphate pesticide parathion. The respective concentrations of 1000 µmol/L and 100 µmol/L VX and parathion were chosen deliberately high in order to study concentrations even if high compound absorption by PDMS might occur. Neuronal and liver spheroids, totaling 2 × 106 cells were used to study concentration changes of VX and parathion. In addition, VX enantiomers were quantified. The current study suggests a significant absorption of VX, respectively parathion by PDMS. This might require future investigation of alternative materials or coatings to limit absorption for organophosphorus compounds in toxicokinetic studies.

Development of fish liver PLHC-1 spheroids and its applicability to investigate the toxicity of plastic additives

Fish liver cell lines are valuable tools to understand the toxicity of chemicals in aquatic vertebrates. While conventional 2D cell cultures grown in monolayers are well established, they fail to emulate toxic gradients and cellular functions as in in-vivo conditions. To overcome these limitations, this work focuses on the development of Poeciliopsis lucida (PLHC-1) spheroids as a testing platform to evaluate the toxicity of a mixture of plastic additives. The growth of spheroids was monitored over a period of 30 days, and spheroids 2-8 days old and sized between 150 and 250 µm were considered optimal for conducting toxicity tests due to their excellent viability and metabolic activity. Eight-day-old spheroids were selected for lipidomic characterization. Compared to 2D-cells, the lipidome of spheroids was relatively enriched in highly unsaturated phosphatidylcholines (PCs), sphingosines (SPBs), sphingomyelins (SMs) and cholesterol esters (CEs). When exposed to a mixture of plastic additives, spheroids were less responsive in terms of decreased cell viability and generation of reactive oxygen species (ROS), but were more sensitive than cells growing in monolayers for lipidomic responses. The lipid profile of 3D-spheroids was similar to a liver-like phenotype and it was strongly modulated by exposure to plastic additives. The development of PLHC-1 spheroids represents an important step towards the application of more realistic in-vitro methods in aquatic toxicity studies.

Emerging trends in the methodology of environmental toxicology: 3D cell culture and its applications

Human diseases and health concerns caused by environmental pollutants are globally emerging. Therefore, rapid and efficient evaluation of the effects of environmental pollutants on human health is essential. Due to the significant differences between humans and animals and the lack of physiologically related environments, animal models and two-dimensional (2D) culture cannot accurately describe toxicological effects and predict actual in vivo responses. To make up for the limitations of traditional environmental toxicology screening, three-dimensional (3D) culture has been developed. The 3D culture could provide a good organizational structure comparable to the complex internal environment of humans and produce a more realistic response to environmental pollutants, which has been used in drug development, toxicity evaluation, personalized therapy and biological mechanism research. The goal of environmental toxicology is to provide clues and support for the risk assessment and management of environmental pollutants. With the development of 3D culture that can reproduce specific physiological aspects loaded with specific cells that reflect human biology, interactions between pollutants and target tissues and organs can be explored to assess the acute and chronic adverse health effects of exposure to various environmental toxins. The 3D culture with great potential shows broad prospects in toxicology research and is expected to bridge the gap between 2D culture and animal models eventually. In this sense, we strongly recommend that 3D culture be used to identify and understand environmental toxins, which will greatly facilitate the public's comprehensive understanding of environmental toxins.

Di(2-ethylhexyl) phthalate induced thyroid toxicity via endoplasmic reticulum stress: In vivo and in vitro study

Di(2-ethylhexyl) phthalate (DEHP) could induce thyroid injury but the mechanism was unclear. This study combined in vivo and in vitro experiments to clarify the mechanism. In vivo, the offspring of Sprague Dawley rats were gavaged with different doses of DEHP (5, 50, and 250 mg/[kg⋅d]) from in utero to 12 weeks-old. Transcriptome sequencing was used to detect the mRNA expression profile of the offspring's thyroids. Differentially expressed genes were identified, followed by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. In vitro, Nthy-ori 3-1 cells were exposed to DEHP's metabolite mono (2-ethylhexyl) phthalate (MEHP) to verify the pathway we found by KEGG analysis. The results indicated that DEHP could disorder the thyroid hormones. Compared with the offspring in control group, the mRNA levels of 656 genes were upregulated in the offspring exposed to 50 mg/(kg⋅d) DEHP. The upregulated genes were enriched in the pathway of "protein processing in the endoplasmic reticulum (ER)." It indicated that the ER stress might play significant role in the thyroid toxicity induced by DEHP. In vitro, the mitochondrial membrane potential (ΔΨm) level of cells was decreased while the reactive oxygen species level was increased after MEHP exposure. MEHP increased the intracellular Ca²⁺ level and induced ER stress. After ER stress was inhibited by the 4-phenylbutyric acid, the thyroid toxicity caused by MEHP was alleviated. Taken together, our results indicated that DEHP could induce thyroid toxicity by activating ER stress.

High-throughput screening paradigms in ecotoxicity testing: Emerging prospects and ongoing challenges

The rapidly increasing number of new production chemicals coupled with stringent implementation of global chemical management programs necessities a paradigm shift towards boarder uses of low-cost and high-throughput ecotoxicity testing strategies as well as deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity that can be used in effective risk assessment. The latter will require automated acquisition of biological data, new capabilities for big data analysis as well as computational simulations capable of translating new data into in vivo relevance. However, very few efforts have been so far devoted into the development of automated bioanalytical systems in ecotoxicology. This is in stark contrast to standardized and high-throughput chemical screening and prioritization routines found in modern drug discovery pipelines. As a result, the high-throughput and high-content data acquisition in ecotoxicology is still in its infancy with limited examples focused on cell-free and cell-based assays. In this work we outline recent developments and emerging prospects of high-throughput bioanalytical approaches in ecotoxicology that reach beyond in vitro biotests. We discuss future importance of automated quantitative data acquisition for cell-free, cell-based as well as developments in phytotoxicity and in vivo biotests utilizing small aquatic model organisms. We also discuss recent innovations such as organs-on-a-chip technologies and existing challenges for emerging high-throughput ecotoxicity testing strategies. Lastly, we provide seminal examples of the small number of successful high-throughput implementations that have been employed in prioritization of chemicals and accelerated environmental risk assessment.

Liver organ-on-chip models for toxicity studies and risk assessment

The liver is a key organ that plays a pivotal role in metabolism and ensures a variety of functions in the body, including homeostasis, synthesis of essential components, nutrient storage, and detoxification. As the centre of metabolism for exogenous molecules, the liver is continuously exposed to a wide range of compounds, such as drugs, pesticides, and environmental pollutants. Most of these compounds can cause hepatotoxicity and lead to severe and irreversible liver damage. To study the effects of chemicals and drugs on the liver, most commonly, animal models or in vitro 2D cell cultures are used. However, data obtained from animal models lose their relevance when extrapolated to the human metabolic situation and pose ethical concerns, while 2D static cultures are poorly predictive of human in vivo metabolism and toxicity. As a result, there is a widespread need to develop relevant in vitro liver models for toxicology studies. In recent years, progress in tissue engineering, biomaterials, microfabrication, and cell biology has created opportunities for more relevant in vitro models for toxicology studies. Of these models, the liver organ-on-chip (OoC) has shown promising results by reproducing the in vivo behaviour of the cell/organ or a group of organs, the controlled physiological micro-environment, and in vivo cellular metabolic responses. In this review, we discuss the development of liver organ-on-chip technology and its use in toxicity studies. First, we introduce the physiology of the liver and summarize the traditional experimental models for toxicity studies. We then present liver OoC technology, including the general concept, materials used, cell sources, and different approaches. We review the prominent liver OoC and multi-OoC integrating the liver for drug and chemical toxicity studies. Finally, we conclude with the future challenges and directions for developing or improving liver OoC models.

Analyzing Human Periodontal Soft Tissue Inflammation and Drug Responses In Vitro Using Epithelium-Capillary Interface On-a-Chip

The gingival epithelium–capillary interface is a unique feature of periodontal soft tissue, preserving periodontal tissue homeostasis and preventing microorganism and toxic substances from entering the subepithelial tissue. However, the function of the interface is disturbed in periodontitis, and mechanisms of the breakdown of the interface are incompletely understood. To address these limitations, we developed a microfluidic epithelium–capillary barrier with a thin culture membrane (10 μm) that closely mimics the in vivo gingival epithelial barrier with an immune micro-environment. To test the validity of the fabricated gingival epithelial barrier model, epithelium–capillary interface-on-a-chip was cultured with human gingival epithelial cells (HGECs) and human vascular endothelial cells (HUVEC). Their key properties were tested using optical microscope, transepithelial/transendothelial electrical resistance (TEER), and permeability assays. The clear expression of VE-cadherin revealed the tight junctions in endothelial cells. Live/dead assays indicated a high cell viability, and the astrocytic morphology of HGE cells was confirmed by F-actin immunostaining. By the third day of cell culture, TEER levels typically exceeded in co-cultures. The resultant permeability coefficients showed a significant difference between 70 kDa and 40 kDa FITC-dextran. The expression of protein intercellular cell adhesion molecule (ICAM-1) and human beta defensin-2 (HBD2) decreased when exposed to TNF-α and LPS, but recovered with the NF-κB inhibitor treatment- Pyrrolidinedithiocarbamic acid (PDTC), indicating the stability of the fabricated chip. These results demonstrate that the developed epithelium-capillary interface system is a valid model for studying periodontal soft tissue function and drug delivery.

Microscopic Imaging Methods for Organ-on-a-Chip Platforms

Microscopic imaging is essential and the most popular method for in situ monitoring and evaluating the outcome of various organ-on-a-chip (OOC) platforms, including the number and morphology of mammalian cells, gene expression, protein secretions, etc. This review presents an overview of how various imaging methods can be used to image organ-on-a-chip platforms, including transillumination imaging (including brightfield, phase-contrast, and holographic optofluidic imaging), fluorescence imaging (including confocal fluorescence and light-sheet fluorescence imaging), and smartphone-based imaging (including microscope attachment-based, quantitative phase, and lens-free imaging). While various microscopic imaging methods have been demonstrated for conventional microfluidic devices, a relatively small number of microscopic imaging methods have been demonstrated for OOC platforms. Some methods have rarely been used to image OOCs. Specific requirements for imaging OOCs will be discussed in comparison to the conventional microfluidic devices and future directions will be introduced in this review.