A biological system is more than the sum of its parts – it accomplishes many functions via synergy. Deconstructing the system down to the molecular mechanism level necessitates the complement of reconstructing functions on all levels, i.e., in our conceptualization of biology and its perturbations, our experimental models and computer modelling.

Toxicology contains the somewhat arbitrary subclass “systemic toxicities”; however, there is no relevant toxic insult or general disease that is not systemic. At least inflammation and repair are involved that require coordinated signaling mechanisms across the organism. However, the more body components involved, the greater the challenge to reca­pitulate such toxicities using non-animal models. Here, the shortcomings of current systemic testing and the development of alternative approaches are summarized.

We argue that we need a systematic approach to integrating existing knowledge as exemplified by systematic reviews and other evidence-based approaches. Such knowledge can guide us in modelling these systems using bioengineering and virtual computer models, i.e., via systems biology or systems toxicology approaches. Experimental multi-organ-on-chip and microphysiological systems (MPS) provide a more physiological view of the organism, facilitating more comprehensive coverage of systemic toxicities, i.e., the perturbation on organism level, without using substitute organisms (animals). The next challenge is to establish disease models, i.e., micropathophysiological systems (MPPS), to expand their utility to encompass biomedicine. Combining computational and experimental systems approaches and the chal­lenges of validating them are discussed. The suggested 3S approach promises to leverage 21^st century technology and systematic thinking to achieve a paradigm change in studying systemic effects.

The traditional approaches to toxicity testing have posed multiple challenges for evaluating the safety of commercial chemicals, pesticides, food additives/contaminants, and medical products. The challenges include the numbers of chemicals that need to be tested, time and resource intensive nature of traditional toxicity tests, and unexpected adverse effects that occur in pharmaceutical clinical trials despite the extensive toxicological testing. Over a decade ago, the U.S. Environmental Protection Agency (EPA), National Toxicology Program (NTP), National Center for Advancing Translational Sciences (NCATS), and the Food and Drug Administration (FDA) formed a federal consortium for “Toxicology in the 21^st Century” (Tox21) with a focus on developing and evaluating in vitro high-throughput screening (HTS) methods for hazard identification and providing mechanistic insights. The Tox21 consortium generated data on thousands of pharmaceuticals and data poor chemicals, developed better understanding of the limits and applications of in vitro methods, and enabled incorporation of HTS data into regulatory decisions. To more broadly address the challenges in toxicology, Tox21 has developed a new strategic and operational plan that expands the focus of its research activities. The new focus areas include developing an expanded portfolio of alternative test systems, addressing technical limitations of in vitro test systems, curating legacy in vivo toxicity testing data, establishing scientific confidence in the in vitro test systems, and refining alternative methods for characterizing pharmacokinetics and in vitro assay disposition. The new Tox21 strategic and operational plan addresses key challenges to advance toxicology testing and will benefit both the organizations involved and the toxicology community.

Food contamination due to unintentional leakage of chemicals from food contact materials (FCM) is a source of increasing concern. Since for many of these substances only limited or no toxicological data are available, the devel­opment of alternative methodologies to rapidly and cost-efficiently establish the level of safety concern is critical to ensure adequate consumer protection. Computational toxicology methods are considered the most promising solutions to cope with this data gap. In particular, mutagenicity assessment has a particular relevance and is a mandatory requirement for all substances released from plastic FCM, regardless how low migration and exposure are. In the present work, a strategy integrating a number of (Quantitative) Structure Activity Relationship ((Q)SAR) models for Ames mutagenicity predictions is proposed. A list of chemicals representing moieties likely migrating from FCM was selected to test the value of the newly defined strategy and the possibility to combine predictions given by the different algorithms was evaluated. In particular, a scheme to integrate mutagenicity estimations into a single final assessment was developed, resulting in an increased domain of applicability. In most cases, a deeper analysis of experimental data, where available, allowed fixing misclassification errors, highlighting the importance of data curation in the devel­opment, validation and application of in silico methods. The high accuracy of the strategy provided the rationale for its application for toxicologically uncharacterized chemicals. Finally, the overall strategy of integration will be automated through its implementation into a freely available software application.

Significant progress has been made in the development and validation of non-animal test methods for skin sensitization assessment. At present, three of the four key events of the adverse outcome pathway (AOP) are assessable by OECD-accepted in vitro methods. The fourth key event describes the immunological response in the draining lymph node where activated den­dritic cells present major histocompatibility complex-bound chemically modified peptides to naïve T cells, thereby priming the proliferation of antigen-specific T cells. Despite substantial efforts, modelling and assessing this adaptive immune response to sensitizers with in vitro T cell assays still represents a challenge. The Cosmetics Europe Skin Tolerance Task Force organized a workshop, bringing together academic researchers, method developers, industry representatives and regulatory stakeholders to review the scientific status of T cell-based assays, foster a mutual scientific understanding and conceive new options to assess T cell activation. Participants agreed that current T cell assays have come a long way in predicting immunogenicity, but that further investment and collaboration is required to simplify assays, optimize their sensitivity, better define human donor-to-donor variability and evaluate their value to predict sensitizer potency. Furthermore, the potential role of T cell assays in AOP-based testing strategies and subsequent safety assessment concepts for cosmetic ingredients was discussed. It was agreed that it is currently difficult to anticipate uses of T cell assay data for safety assessment and concluded that experience from case studies on real-life risk assessment scenarios is needed to further consider the usefulness of assessing the fourth AOP key event.

Under the new Directive 2010/63/EU, member states have to publish non-technical summaries (NTS) of the projects involving animals that they authorise. These summaries must include information on the objectives of the project including the predicted harm and benefits and the number and types of animals to be used. Summaries should also demonstrate compliance with the 3Rs. The intention was that NTS would help increase the transparency of animal research in the EU. In this article, we review the status of the publication of NTS across member states and give some general observations on publication speed, identification, accessibility and quality. We also review in more detail the quality of reporting in a selection of NTS from Germany and the UK. We consistently found that NTS from Germany and the UK were deficient in their description of what is being done to the animals and what they might experience as a result. Using examples taken from specific NTS we highlight what we view to be good and bad examples to assist member states and researchers in producing better NTS in the future. The NTS can also be an important tool in sharing of best practice in the 3Rs and the avoidance of duplicative animal testing. For this to happen, however, member states need to publish timely, ensure that NTS are accurate and, ideally, there needs to be some centralisation of the NTS.

The air-blood barrier is mainly composed of alveolar epithelial cells and macrophages. Whereas the epithelium acts as a diffusional barrier, macrophages represent an immunological barrier, in particular for larger molecules and nanoparticles.

This paper describes a new co-culture of human cell lines representing both cell types. Acquiring, culturing and maintaining primary alveolar epithelial cells presents significant logistical and technical difficulties. The recently established human alveolar epithelial lentivirus immortalized cell line, hAELVi, when grown on permeable filters, form monolayers with high functional and morphological resemblance to alveolar type I cells. To model alveolar macrophages, the human cell line THP-1 was seeded on pre-formed hAELVi monolayers.

The co-culture was characterized regarding cellular morphology, viability and barrier function. Macrophages were homogenously distributed on the epithelium and could be kept in co-culture for up to 7 days. Transmission electron microscopy showed loose contact between THP-1 and hAELVi cells. When grown at air liquid interface, both cells were covered with extracellular matrix-like structure, which was absent in THP-1 mono‑culture. In co-culture with macrophages, hAELVi cells displayed similar, sometimes even higher, trans-epithelial electrical resistance than in mono-cultures. When exposed to silver and starch NPs, hAELVi mono-cultures were more tolerant to the particles than THP-1 mono-cultures. The viability in the co-culture was similar to that of hAELVi monocultures. Transport studies with sodium fluorescein in presence/absence of EDTA proved that the co‑culture acts as functional diffusion barrier. These data demonstrate that hAELVi-/THP-1 co-cultures represent a promising model for safety and permeability studies of inhaled chemicals, drugs and nanoparticles.

The proximal tubule is the primary site for renal solute reabsorption and secretion and thus a main target for drug-induced toxicity. Current nonclinical methods using 2D cell cultures are unable to fully recapitulate clinical drug responses mainly due to limited in vitro functional lifespan. Since extracellular matrices are known to be key regulators of cell development, culturing cells on classic 2D plastic surfaces inevitably results in loss of differentiation. Hence, 3D models of the human proximal tubule that recapitulate the in vivo morphology would allow for improved drug screening and disease modeling. Here, the development and characterization of a 3D proximal tubule model using RPTEC/TERT1 cells is presented. RPTEC/TERT1 cells self-assembled in matrigel to form highly differentiated and stable 3D tubular structures characterized by a branched network of monolayered cells encircling a cell-free lumen, thus mimicking the proximal tubule. In vitro tubuli resembled the polarity of a proximal tubule epithelium as indicated by polar expression of Na+/K+-ATPase and ZO-3. Furthermore, 3D cultured RPTEC/TERT1 cells showed overall increased mRNA expression of xenobiotic transporters, e.g., OCTs and MATEs and de novo expression of OAT3 when compared to cultures on plastics or membrane inserts. Finally, this model was used to assess delayed cisplatin-induced nephrotoxicity and demonstrated increased sensitivity when compared to 2D culture. Thus, the easy-to-use model described here may prove to be useful for mechanistic investigations, e.g., in discovery of compounds interfering with tubule formation, differentiation and polarization, as well for the detection and understanding of pharmaceutical induced nephrotoxicity.

The (developmental) neurotoxicity hazard is still unknown for most chemicals. Establishing a test battery covering most of the relevant adverse outcome pathways may close this gap without requiring a huge animal experimentation program. Ideally, each of the assays would cover multiple mechanisms of toxicity. One candidate test is the human LUHMES cell-based NeuriTox test. To evaluate its readiness for larger-scale testing, a proof of concept library, assembled by the U.S. National Toxicology Program (NTP), was screened. Out of the 75 unique compounds, seven were defined as specifically neurotoxic after the hit-confirmation phase and ten further compounds were generally cytotoxic within the concentration range of up to 20 μM. As complementary approach, the library was screened in the PeriTox test, which identifies toxicants affecting the human peripheral nervous system. Of the eight PeriTox hits, five were similar to the NeuriTox hits: rotenone, colchicine, diethylstilbestrol, berberine chloride, and valinomycin. The unique NeuriTox hit, methyl-phenylpyridinium (MPP⁺), is known from in vivo studies to affect only dopaminergic neurons (which LUHMES cells are). Conversely, the known peripheral neurotoxicant acrylamide was picked up in the PeriTox, but not in the NeuriTox assay. All of the five common hits had also been identified in the published neural crest migration (cMINC) assay, while none of them emerged as a cardiotoxicant in a previous screen using the same library. These comparative data suggest that complementary in vitro tests can pick up a broad range of toxicants, and that multiple test results might help to predict organ specificity patterns.

Many types of assays in cell biology, pharmacology and toxicology generate data in which a parameter is measured in a reference system (negative control) and then also under conditions of increasing stress or drug exposure. To make such data easily comparable, they are normalized, i.e., the initial value of the system (e.g., viability or transport function) is set to 100%, and all data are indicated relative to this value. Then, curves are fitted through the data points and summary data of the system behavior are determined. For this, a benchmark response (BMR) is given (e.g., a curve drop by 15 or 50%), and the corresponding benchmark concentration (BMC15 or BMC50) is determined. Especially for low BMRs, this procedure is not very robust and often results in incorrect summary data. It is often neglected that a second normalization (re-normalization) is necessary to make the data suitable for curve fitting. It is also frequently overlooked that this requires knowledge of the system behavior at very low stress conditions. Here, good in vitro practice guidance for the re-normalization procedure is provided so that data of higher fidelity can be generated and presented.