In vivo rodent micronucleus assay: protocol, conduct and data interpretation

In vivo rodent micronucleus assay has been widely used to detect genotoxici ty. Evaluation of micronucleus induction is the primary in vivo test in a b attery of genotoxicity tests and is recommended by the regulatory agencies around the globe to be conducted as part of product safety assessment. The assay, when performed appropriately, detects both clastogenicity and aneuge nicity. Methods for performing micronucleus evaluation have evolved since i ts initial description in the 1970s. In recent years, the focus has been di rected toward improving micronucleus detection with high efficiency by prop osing data-based recommendations to the standard initial protocol design. S uch improvements include, e.g., the use of appropriate harvest time(s), inc lusion of one or both sexes, number of doses tested, limit dose, integratin g micronucleus assessment into the routine toxicology studies, use of fluor escent staining, automation of micronucleus detection and assessment of mic ronuclei in multiple tissues. This protocol paper describes: the mechanism of micronucleus formation, a generalized protocol for manual detection, enu meration of micronuclei, and data interpretation in light of published info rmation thus far on the regulatory aspects of this assay. Certain recent pr otocol issues that are practical in nature are equally valid in relation to standard manual method and provide robust database, which are also include d for consideration. It is expected that such improvements of the protocol will continue to drive the utility of this assay in the product safety asse ssment. (C) 2000 Elsevier Science B.V. All rights reserved.