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Acute Systemic Toxicity

Predictive Models for Acute Oral Systemic Toxicity

The ICCVAM Acute Toxicity Workgroup is initiating a global project to develop in silico models of acute oral systemic toxicity that predict five specific endpoints needed by regulatory agencies. NICEATM invites scientists to develop in silico models that predict any or all of these endpoints. NICEATM and the EPA National Center for Computational Toxicology (NCCT) have collected a large body of rat oral acute toxicity data. Subsets of these data will be used by project participants to build and test their models, and by NICEATM and the project organizing committee to evaluate the models. Models are due to NICEATM by February 16, and submitted models will be discussed at an April workshop.

Replacing Animals for Acute Systemic Toxicity Testing

ICCVAM, with support from NICEATM, is developing a U.S. strategy and roadmap for implementing alternative approaches for required acute systemic toxicity testing. Development and implementation of these approaches will involve four key steps: (1) defining testing needs, (2) identifying available alternatives, (3) developing integrated approaches to testing and assessment, and (4) addressing both scientific and non-scientific challenges.

The ICCVAM Acute Toxicity Workgroup is coordinating activities relevant to these goals. Initial efforts have focused on identifying existing alternatives and activities needed to advance their development and utilization. Some information for these efforts will be drawn from ongoing efforts resulting from workshops held by NICEATM and collaborators in 2015 and 2016.

Past and ongoing activities relevant to these goals include:

  • Evaluating the usefulness of additivity formulas (as used by the United Nations Globally Harmonized System of Classification and Labeling of Chemicals) for classifying formulations and mixtures for acute systemic toxicity
  • Evaluating in vitro and in silico approaches for predicting acute systemic toxicity, including approaches using high throughput screening data and quantitative structure-activity relationship models
  • Developing a scoping document that outlines the current requirements and testing needs for U.S. and international government agencies
    Strickland J et al. 2018. Status of acute toxicity testing requirements and data uses by U.S. regulatory agencies [published online ahead of print 3 February 2018]. Reg Toxicol Pharmacol
  • Collecting and reviewing acute toxicity data to determine if acute oral hazard classifications can be used to assign U.S. Environmental Protection Agency (EPA) acute dermal hazard classifications; results of this review supported EPA guidance for waiving the acute dermal toxicity test for pesticide formulations

EURL ECVAM Validation Study in the Field of Toxicokinetics and Metabolism

The European Union Reference Laboratory for Alternatives to Animal Testing (EURL ECVAM) coordinated a validation study of two in vitro assays to evaluate human liver metabolism and toxicity. Representatives from NICEATM and ICCVAM participated on the management team for this validation study.

In humans and other animals, chemical metabolism often involves liver enzymes called cytochrome P450s (CYPs). An EURL ECVAM study completed in 2013 assessed the potential for CYP enzyme induction at clinically relevant doses of pharmaceuticals in a human hepatoma cell line (HepaRG®) and cryopreserved human liver cells. This study provides a starting point for the development of novel in vitro platforms to assess chemical and drug metabolism and toxicity, with the ultimate goal of providing a metabolically competent in vitro alternative for long-term toxicity studies.

The EURL ECVAM validation report for this study was submitted to the EURL ECVAM Scientific Advisory Committee for peer review in 2014. A draft test guideline for in vitro measurement of CYP enzyme induction is currently under consideration by the Organisation for Economic Co-operation and Development. EURL ECVAM is currently drafting a background document on integrating this method into regulatory processes.

Evaluation and Validation Study of In Vitro Cytotoxicity Test Methods

In vitro methods that use mammalian cell cultures and various cytotoxicity endpoints, while not currently regarded as suitable replacements for rodent acute oral toxicity tests, are useful for establishing the starting dose for acute oral toxicity tests. ICCVAM recommends, where appropriate, the use of validated in vitro basal cytotoxicity tests in a weight-of-evidence approach for this purpose. Using these in vitro methods can reduce the number of animals required for each toxicity test.

The use of in vitro cytotoxicity test methods to reduce animal use in acute oral systemic toxicity testing was evaluated at a workshop on In Vitro Methods for Assessing Acute Systemic Toxicity (2000). A Guidance Document on Using In Vitro Data to Estimate In Vivo Starting Doses for Acute Toxicity was prepared by ICCVAM with the assistance of the workshop participants.

Scientific Workshop on Acute Chemical Safety Testing: Advancing In Vitro Approaches and Humane Endpoints for Systemic Toxicity Evaluations

NICEATM, ICCVAM, and international partners sponsored a workshop to explore alternative methods for acute chemical safety testing. The goals of this 2008 meeting were to:

  1. Review the state-of-the-science and identify knowledge gaps (at the whole organism, organ system, cellular, and/or molecular levels) relevant to key in vivo pathways involved in acute systemic toxicity
  2. Recommend how these knowledge gaps can be addressed by collecting mechanistic biomarker data during currently required in vivo safety testing
  3. Recommend how in vivo key pathway information can be used to develop more predictive mechanism-based in vitro test systems and to identify biomarkers that may serve as earlier, more humane endpoints for in vivo test methods
  4. Recommend how mechanism-based in vitro test systems and earlier, more humane endpoints can be used to further reduce, refine, and eventually replace animal use for acute systemic toxicity testing while ensuring the protection of human and animal health

Oral Up-and-Down Procedure

The oral up-and-down procedure (UDP) is an alternative to the traditional LD50 test that reduces animal use. A peer review panel sponsored by NICEATM and ICCVAM met in 2000 and 2001 to evaluate the revised oral UDP and develop recommendations for use. U.S. regulatory agencies adopted the ICCVAM recommendations on the revised oral UDP in 2003 and now accept oral UDP methods issued by the Organisation for Economic Co-operation and Development and EPA, which replaced the conventional acute oral systemic toxicity test method.