Pretreatment with valproic acid, a histone deacetylase inhibitor, enhances the sensitivity of the peripheral blood micronucleus assay in rodents

Micronucleus (MN) assay is widely used for the determination of the genotoxic potential of new chemical entities. Improvement in the sensitivity of MN assay will be advantageous for the successful detection of marginally active genotoxins. In the past, several improvements have been made in the automated scoring of micronuclei, while very few attempts have been taken to improve the sensitivity of manual micronuclei detection. The present study aims to validate the effect of valproic acid (VPA) pretreatment on the sensitivity of peripheral blood micronucleus (PBMN) assay using cyclophosphamide (CP, 50mg/kg), methotrexate (MTX, 20mg/kg) and zidovudine (AZT, 400mg/kg) in rodents. However, to find out the optimum VPA pretreatment time as well as to detect the effect of species and age difference, separate experiments were conducted on young Swiss albino mice (24-28 days) and Sprague-Dawley rats (21-24 days), in which significant increase in MN induction was observed with 3-day VPA pretreatment in both the species. Based on these results, studies on adult mice were conducted with 3-day VPA pretreatment along with CP or MTX or AZT. The results of the present study clearly demonstrate that the 3-day VPA pretreatment significantly enhances the sensitivity of PBMN assay in peripheral blood (PB) in adult mice. After validation with other standard genotoxins as well as other HDAC (histone deacetylase) inhibitors, this model may be useful for the detection of marginally active DNA damaging agents.