Diepoxybutane induces caspase and p53-mediated apoptosis in human lymphoblasts

Abstract

Diepoxybutane (DEB) is the most potent metabolite of the environmental chemical 1,3-butadiene (BD), which is prevalent in petrochemical industrial areas. BD is a known mutagen and human carcinogen, and possesses multiorgan systems toxicity that includes bone marrow depletion, spleen, and thymus atrophy. Toxic effects of BD are mediated through its epoxy metabolites. In working towards elucidating the cellular and molecular mechanisms of BD toxicity, we investigated the ability of DEB to induce apoptosis in human lymphoblasts. DEB induced a concentration and exposure time-dependent apoptosis, which accounted for the DEB-induced loss of cell viability observed in TK6 lymphoblasts. The DEB-induced apoptosis was inhibited by inhibitors of caspases 3 and 9. The role of p53 in mediating the DEB-induced apoptosis was also investigated. DEB induced elevated p53 levels in direct correlation to the extent of DEB-induced apoptosis, as the concentration of DEB increased up to 5 μM. The extent of DEB-induced apoptosis was dramatically higher in TK6 lymphoblasts as compared to the genetically paired p53-deficient NH32 lymphoblasts under the same experimental conditions. Our results confirm and extend observations on the occurrence of apoptosis in DEB exposed cells, and demonstrate for the first time the elevation of p53 levels in human lymphoblasts in response to DEB exposure. In addition, our results demonstrate for the first time that DEB-induced apoptosis is mediated by caspases 3 and 9, as well as the p53 protein. It is possible that DEB-induced apoptosis may explain BD-induced bone marrow depletion, spleen and thymus atrophy in BD-exposed animals.