National Toxicology Program

In Vitro Methods for Assessing Acute Systemic Toxicity

In vitro methods that use mammalian cell cultures and various cytotoxicity endpoints have been proposed as alternatives to in vivo acute oral 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 have been validated for establishing the starting dose for acute oral toxicity tests so as to reduce and refine the use of animals for such testing.

The use of in vitro cytotoxicity test methods to reduce animal use in acute 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. ICCVAM recommended that near-term validation studies should focus on two standard basal cytotoxicity assays: one using a human cell system and one using a rodent cell system. The results of the validation study can be found in the Test Method Evaluation Report.

In February 2008, ICCVAM forwarded recommendations on the use of these two in vitro test methods for estimating starting doses for acute oral systemic toxicity tests. ICCVAM recommended that these test methods be considered before using animals for acute oral toxicity testing, and that the methods should be used where determined appropriate. Data from the 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. To follow up on this recommendation, NICEATM and ICCVAM will conduct a study to determine how the two recommended cell culture test methods can be used to set the starting doses for acute toxicity tests of mixtures.

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

NICEATM and ICCVAM, in partnership with ECVAM (European Centre for the Validation of Alternative Methods) and JaCVAM (Japanese Center for the Validation of Alternative Methods) 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

The Up-and-Down Procedure (UDP) is an acute oral toxicity test alternative to the traditional oral median lethal dose (LD₅₀) test. For the UDP, one animal is tested at a time. The response of the animal to a test substance determines whether the next animal receives a higher or lower dose. The Organisation for Economic Co-operation and Development (OECD) UDP test guideline adopted in 1998 was revised to conform with a new globally harmonized hazard classification scheme and to include a limit test for nontoxic substances and a primary test for the remaining substances. A peer review panel sponsored by NICEATM and ICCVAM evaluated the revised UDP in July 2000 and in August 2001.