Adaptations of the in vitro MN assay for the genotoxicity assessment of nanomaterials

The issue of appropriate testing strategies has been raised for the genotoxicity assessment of nanomaterials. Recently, efforts have been made to evaluate the adequacy of Organisation for Economic Co-operation and Development-standardised tests to assess the genotoxicity of nanomaterials. The aim of this review was to examine whether the current guideline for the in vitro micronucleus (MN) assay is applicable for testing nanomaterials. From a Pubmed literature search, 21 available studies were identified for analysis. We reviewed all protocols used for testing nanomaterials with the in vitro MN assay. All studies were categorised based on the particle type and size. Different aspects of the protocols were evaluated such as the exposure (duration and doses), the cytochalasin-B treatment, serum levels and cytotoxicity assessment. Sixteen of the 21 studies demonstrated increased frequencies of MN. Some recommendations regarding the protocol were formulated to maximise sensitivity and avoid false negatives. Determination of the cellular dose was advised for a better interpretation of MN frequency results. The level of serum can modulate the cellular response, therefore the serum percentage used should enable cell growth and proliferation and a maximal sensitivity of the assay. Furthermore, different types of cytochalasin-B treatment were used, co-treatment, post-treatment and delayed co-treatment. In order to avoid decreased cellular uptake as a consequence of actin inhibition, post-treatment or delayed co-treatment is suggested. Exposure during mitosis should be recommended to allow contact with the chromatin or mitotic apparatus for nanomaterials that are unable to cross the nuclear membrane. With these adaptations, the in vitro MN assay can be recommended for genotoxicity testing of nanomaterials.