National Toxicology Program

National Toxicology Program

Acute Systemic Toxicity

NICEATM Evaluation of Use of Acute Oral Systemic Toxicity Data to Determine EPA Acute Dermal Hazard Classification

The results of acute oral and dermal systemic toxicity tests are used to determine pesticide hazard labels to protect users, workers, and handlers. Dermal systemic toxicity test data are also used to determine the type of personal protective equipment required for occupational users of pesticides. NICEATM is conducting an evaluation to determine whether acute oral toxicity data could be used to determine EPA acute dermal hazard classifications. If oral acute toxicity data could be used for this purpose, animal use for acute systemic toxicity testing could be reduced. NICEATM is analyzing data for both pesticide active ingredients and pesticide formulations to determine whether data for both routes are needed.

EURL ECVAM Validation Study in the Field of Toxicokinetics and Metabolism

The European Union Reference Laboratory for Alternatives to Animal Testing coordinated a validation study with the aim of providing a standard in vitro assay for evaluating human liver metabolism and toxicity. Representatives from NICEATM and ICCVAM participated on the management team for the validation study.

Biotransformation is a process that converts a substance into a chemically different substance. In humans and other animals, hepatic (liver) enzymes called cytochrome P450s (CYPs) play a major role in biotransformation. Interactions between chemicals or drugs and CYP enzymes have been shown to cause hormonal disturbances, increased liver weight, drug-drug interactions, and increased toxic effects.

Because of the importance of CYP enzymes in the role of biotransformation in vivo, which can potentially increase or decrease chemical toxicity, measuring CYP enzyme activity is important to the development of in vitro toxicity assays. Establishment of metabolically competent systems is a key issue in the development of in vitro toxicity assays that can better mimic in vivo systems. An in vitro system that can assess changes in CYP activity is likely to be a metabolically competent system, as CYP induction has a complex underlying mechanism.

The EURL ECVAM study used a human hepatoma cell line (HepaRG®) and cryopreserved human hepatocytes (liver cells) to assess the potential for CYP induction at clinically relevant doses of pharmaceuticals. The study could provide a starting point for a novel in vitro platform for assessing metabolism and toxicity, ultimately providing a metabolically competent in vitro alternative for long-term studies.

The EURL ECVAM study is complete and the validation study report will be submitted to the EURL ECVAM Scientific Advisory Committee for peer review in late 2013. A standard project submission form was submitted to the Organisation for Economic Co-operation and Development (OECD) in 2013 to support the development of a Performance-Based Test Guideline for the establishment of human-derived hepatic system to investigate biotransformation and toxicity of compounds by evaluation of cytochrome P450 induction competence.

Validation Study of In Vitro Cytotoxicity Test Methods

In February 2008, ICCVAM forwarded recommendations on the use of two in vitro test methods to estimate starting doses for acute oral systemic toxicity tests. ICCVAM recommended that these test methods be considered before using animals for acute oral systemic toxicity testing, and that the methods should be used where determined appropriate. Data from the in vitro test methods should be used in a weight-of-evidence approach for determining starting doses for in vivo studies. Using these in vitro methods where appropriate is expected to reduce the number of animals required for each toxicity test.

Evaluation of In Vitro Cytotoxicity Test Methods

In vitro methods that use mammalian cell cultures and various cytotoxicity endpoints have been proposed as alternatives to in vivo acute oral systemic toxicity tests that use rodents. In vitro cytotoxicity test methods that measure basal cytotoxicity (general cytotoxicity that affects structures or processes intrinsic to all cell types) are not currently regarded as suitable replacements for rodent acute oral toxicity tests. However, some methods can be useful for establishing the starting dose for acute oral toxicity tests and thus reduce and refine animal use for such testing.

The use of in vitro cytotoxicity test methods to reduce animal use in acute oral systemic toxicity testing was evaluated at an October 2000 Workshop on In Vitro Methods for Assessing Acute Systemic Toxicity. 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.

Development of OECD Test Guidelines for the Evaluation of Acute Systemic Toxicity

NICEATM and ICCVAM actively participate in the development of OECD Test Guidelines and Guidance Documents relevant to toxicology and safety testing. OECD Test Guidelines are based on the most relevant internationally agreed-upon testing methods used by government, industry, and independent laboratories.

NICEATM and the ICCVAM Acute Toxicity Working Group have contributed to the development of a number of OECD Test Guidelines and Guidance Documents. Click on the heading above to view summaries of these activities.

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 February 2008 meeting of international experts in the fields of in vitro and in vivo toxicology and human and veterinary medicine were to:

  1. Review the state-of-the-science and identify knowledge gaps (at the whole organism, organ system, cellular, and/or molecular levels) regarding the 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 oral median lethal dose (LD50) test that reduces animal use. In the oral UDP, one animal is tested at a time, and the response of each animal to a test substance determines whether the next animal receives a higher or lower dose. A peer review panel sponsored by NICEATM and ICCVAM met in 2000 and 2001 to evaluate the revised oral UDP and develop recommendations. U.S. regulatory agencies adopted the ICCVAM recommendations on the revised oral UDP in 2003 and now accept oral UDPs methods issued by OECD and the U.S. Environmental Protection Agency, which have replaced the conventional acute oral systemic toxicity test method.

NTP is located at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.