Innovating the buccal micronucleus cytome assay to improve its utility as a biomarker of <i>in vivo</i> genotoxicity

The Buccal Micronucleus Cytome (B-MNcyt) assay is used worldwide to study chromosomal abnormalities and environmental genotoxicity and cytotoxicity in humans. The aim of this article is to discuss the strengths and limitations of the B-MNcyt assay and to identify emerging opportunities to further improve and validate its use. This can be achieved by innovating and evolving the B-MNcyt assay by identifying and solving important knowledge and technological gaps that hinder its utility. The cells examined in the B-MNcyt assay are squamous epithelial cells that can be easily collected from the inside of the mouth. These cells are postmitotic cells generated from the proliferative basal layer and may contain micronuclei (MN). MN can be generated during mitosis of the basal cells prior to their differentiation into squamous cells. The B-MNcyt assay is increasingly being used to measure DNA damage induced in vivo by environmental genotoxins. Results with this assay have been shown to correlate positively with MN frequency measured using the well-validated lymphocyte cytokinesis-block micronucleus cytome (L-CBMNcyt) assay. However, the B-MNcyt assay has some important limitations that need to be addressed to achieve a similar level of validation and applicability to that of the L-CBMNcyt assay. These include the lack of (i) evidence that the buccal MN frequency predicts disease risk in prospective studies; (ii) an automated scoring system to score MN in buccal cells, which is essential to achieve statistically robust results and to improve the feasibility of the assay in population studies; (iii) sufficient research on the kinetics of MN expression in buccal cells to define optimal time frames to score MN after acute exposure or during chronic genotoxin exposure; and (iv) studies to test the suitability of using the B-MNcyt assay for radiation exposure biodosimetry. This article discusses these issues and provides some suggestions on how to address them.