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Sensitization of the respiratory tract is an important occupational health challenge, and understanding the mechanistic basis of this effect is necessary to support the development of toxicological tools to detect chemicals that may cause it. Here we use the adverse outcome pathway (AOP) framework to organize information that may better inform our understanding of sensitization of the respiratory tract, building on a previously published skin sensitization AOP, relying on literature evidence linked to low-molecular-weight organic chemicals and excluding other known respiratory sensitizers acting via different molecular initiating events. The established key events (KEs) are as follows: (1) covalent binding of chemicals to proteins, (2) activation of cellular danger signals (inflammatory cytokines and chemokines and cytoprotective gene pathways), (3) dendritic cell activation and migration, (4) activation, proliferation, and polarization of T cells, and (5) sensitization of the respiratory tract. These events mirror the skin sensitization AOP but with specific differences. For example, there is some evidence that respiratory sensitizers bind preferentially to lysine moieties, whereas skin sensitizers bind to both cysteine and lysine. Furthermore, exposure to respiratory sensitizers seems to result in cell behavior for KEs 2 and 3, as well as the effector T cell response, in general skewing toward cytokine secretions predominantly associated with T helper 2 (Th2) response. Knowledge gaps include the lack of understanding of which KE(s) drive the Th2 polarization. The construction of this AOP may provide insight into predictive tests that would in combination support the discrimination of respiratory-sensitizing from non- and skin-sensitizing chemicals, a clear regulatory need.

Background: The introduction of whole new foods in a population may lead to sensitization and food allergy. This constitutes a potential public health problem and a challenge to risk assessors and managers as the existing understanding of the pathophysiological processes and the currently available biological tools for prediction of the risk for food allergy development and the severity of the reaction are not sufficient. There is a substantial body of in vivo and in vitro data describing molecular and cellular events potentially involved in food sensitization. However, these events have not been organized in a sequence of related events that is plausible to result in sensitization, and useful to challenge current hypotheses. The aim of this manuscript was to collect and structure the current mechanistic understanding of sensitization induction to food proteins by applying the concept of adverse outcome pathway (AOP). Main body: The proposed AOP for food sensitization is based on information on molecular and cellular mechanisms and pathways evidenced to be involved in sensitization by food and food proteins and uses the AOPs for chemical skin sensitization and respiratory sensitization induction as templates. Available mechanistic data on protein respiratory sensitization were included to fill out gaps in the understanding of how proteins may affect cells, cell-cell interactions and tissue homeostasis. Analysis revealed several key events (KE) and biomarkers that may have potential use in testing and assessment of proteins for their sensitizing potential. Conclusion: The application of the AOP concept to structure mechanistic in vivo and in vitro knowledge has made it possible to identify a number of methods, each addressing a specific KE, that provide information about the food allergenic potential of new proteins. When applied in the context of an integrated strategy these methods may reduce, if not replace, current animal testing approaches. The proposed AOP will be shared at the www.aopwiki.org platform to expand the mechanistic data, improve the confidence in each of the proposed KE and key event relations (KERs), and allow for the identification of new, or refinement of established KE and KERs. © 2017 The Author(s).

Concerted international efforts are underway to build networks of AOPs with shared key events (KEs) to enable the database of known AOPs to eventually serve as a framework for contextualizing results of predictive test methods across varied biological mechanisms. The development of an AOP for sensitization of the respiratory tract by low-molecular-weight (LMW) organic chemicals was envisioned to build upon a skin sensitization AOP published by OECD in 2012, since KEs may be common to both pathways. Indeed, the established KEs, which are 1) Covalent binding of LMW chemicals to proteins, 2) Cellular Danger Signals: Activation of inflammatory cytokines and chemokines and cytoprotective gene pathways, 3) Dendritic cell activation and migration, 4) Activation and proliferation of T cells, and 5) B Cell activation and class switching, are very similar. However, there are differences. For example, though the Molecular Initiating Event (MIE), covalent binding to proteins, is common to the two AOPs, there is some evidence that respiratory sensitizers bind preferentially to lysine, whereas skin sensitizers bind to both cysteine and lysine. In some cases this preference may be consequential enough to the respiratory sensitization pathway that it warrants separate description from the MIE for skin sensitization. Other events that may be similarly discriminatory include KEs 2 and 5; in fact, there has been some success separating skin and respiratory sensitizers by assessing specific profiles of inflammatory mediators expressed after in vitro exposure to sensitizers. The construction of this AOP highlights knowledge gaps and may provide insight into which predictive tests would be most useful to develop further to support the discrimination of respiratory-sensitizing from skin-sensitizing chemicals, a clear regulatory need.

At the IVTIP (In Vitro Testing Industrial Platform) meeting of November 26th 2009 entitled 'Toxicology in the 21st century ('21C') - working our way towards a visionary reality' all delegates endorsed the emerging concept of the '21C' vision as the way forward to enable a thorough, reliable and systematic approach to future toxicity testing without the use of animals. One of the emerging concepts focused on integrating a defined number of tests modelling in vivo-relevant and well-characterised toxicity pathways representing mechanistic endpoints. At this meeting the importance of Integrated Testing Strategies (ITS) as tools towards reduction and eventually replacement of the animals currently used for hazard identification and risk assessment was recognised.A follow-up IVTIP Spring 2010 meeting entitled 'Integrated In Vitro Testing Strategies (ITS) - Implementation Challenges' was organised to address pending questions about ITS. This report is not a review of the ITS literature, but a summary of the discussions triggered by presented examples on how to develop and implement ITS. Contrasts between pharmaceutical and chemical industry, as well as a list of general but practical aspects to be considered while developing an ITS emerged from the discussions. In addition, current recommendations on the validation of ITS were discussed.In conclusion, the outcome of this workshop improved the understanding of the participants of some important factors that may impact the design of an ITS in function of its purpose (e.g. screening, or early decision making versus regulatory), the context in which they need to be applied (e.g. ICH guidelines, REACH) and the status and quality of the available tools. A set of recommendations of best practices was established and the importance of the applicability of the individual tests as well as the testing strategy itself was highlighted. © 2012 Elsevier Ltd.

In November 2009 the In Vitro Testing Industrial Platform (IVTIP) organized a meeting entitled '. Toxicology in the 21st century - working our way towards a visionary reality'. Participating delegates included scientists, key opinion leaders, developers and users of 3Rs-related tests and testing strategies. This paper summarizes the discussions with respect to the conditions required to move the vision towards an applicable reality. It should not be considered as a comprehensive review of technologies that could be relevant for moving the in vitro testing and risk assessment field forward.Overall, the US National Research Council (NRC) vision and strategy for toxicity testing in the 21st century was unanimously considered as the right approach to enable future toxicity testing without animal experimentation. Many elements of this vision were identified in the European initiatives aimed at the development of non-animal based methods. However, the need for concerted actions moving the current state-of-the-art towards a thorough, reliable and systematic approach to future toxicity testing was made evident by the discussions.Among the difficulties and hurdles on the way forward, the lack of physiologically relevant, metabolic competent and robust in vivo, ex vivo and in vitro models of both healthy and diseased people was frequently mentioned. In addition, there was a call for immediate implementation of emerging technologies and paradigms considered to be essential for transferring the vision into the reality of a toxicity-testing system assessing biologically significant perturbations in key pathways which are relevant for human biology. While the unique strengths of each of the available and emerging technologies was recognized, integration of available data and emerging technologies to integrated testing strategies (ITS) was highlighted as the preferred way forward. Method harmonization and standardization, as well as procedures and guidelines for putting together ITS, were urgently requested in order to facilitate proper implementation and acceptance.There was an urgent call for better coordination of the efforts that are ongoing or initiated in the 3Rs arena at national and international level. Education, training, communication and dissemination were addressed. It was recognised that the EPAA, through its 'Platform for Communication and Dissemination', has a very important and central role in this area. © 2011 Elsevier Ltd.

The European cosmetics legislation foresees a review in 2011 and possible postponement of the 2013 marketing ban to enforce the testing ban for systemic and repeated-dose animal tests. For this purpose, a 119-page report commissioned by the European Commission was published recently. Here, a group of 17 independent experts from the US, Europe, and Japan was brought together to evaluate the report. The expert panel strongly endorsed the report and its conclusions. A number of important options not considered were identified; these do not, however, affect the overall conclusions regarding the current lack of availability of a full replacement, especially for the areas of repeated dose toxicity, carcinogenicity testing, and reproductive toxicity, though a roadmap for change is emerging. However, some of these options may provide adequate data for replacement of some animal studies in the near future pending validation. Various recommendations expand the original report. The reviewers agree with the report that there is greater promise in the short term for the areas of sensitization and toxicokinetics. Additional opportunities lie in more global collaborations and the inclusion of other industry sectors.