In vitro comet and micronucleus assays do not predict morphological transforming effects of silica samples in Syrian Hamster Embryo cells

Crystalline silica and asbestos have both been classified as carcinogenic by the International Agency for Research on Cancer (IARC). However, because of the limited data available, amorphous silica was not classifiable.
On the other hand, in vitro, the carcinogenic potential of silica can be revealed by the Syrian Hamster Embryo (SHE) cell transformation assay. However, a number of questions remain unanswered regarding the SHE transforming events and the responses of those substances in genotoxicity assays. We therefore decided to test different silica materials and to investigate possible correlations between genotoxic events using the in vitro micronucleus assay and the comet assay in SHE and V79 hamster-lung cells and the SHE transformation assay.
Three silica samples of different crystallinity were used: natural amorphous silica, partially crystallized silica and quartz silica particles. In the micronucleus and the comet assays, none of the samples were capable of inducing genotoxic effects in SHE cells and only the amorphous silica induced genotoxic effects in V79 cells. However in the SHE cell transformation assays, only the partially crystallized and quartz silica were able to induce morphological cell transformation. Together, these data suggest that short-term genotoxic assays alone cannot predict the carcinogenic potential of this type of particle.