Differences in xenobiotic detoxifying activities between bone marrow stromal cells from mice and rats: Implications for benzene-induced hematotoxicity

Benzene is a human carcinogen; exposure to benzene can result in a plastic anemia and leukemia. Data from animal models are frequently used in the risk assessment for benzene. In rodent studies, mice have been shown to be more sensitive to benzene-induced hemato- toxicity than rats. In this regard, we have observed that bone marrow stromal cells from mice were significantly more susceptible to the cytotoxicity induced by the benzene metabolites hydroquinone (HQ) and benzoquinone (BQ) than cells from rats. Since cellular glutathione (CSH) and quinone reductase (QR) are known to play critical roles in modulating HQ- induced cytotoxicity, we have measured the GSH content and the QR and glutathione S- transferase (GST) activity in stromal cells from both species. In rat cells, the GSH content and the QR specific activity were 2 and 28 times as much as those from mice, respectively. GSH and QR in both mouse and rat stromal cells were inducible by 1,2-dithiole-3-thione (D3T). D3 T pretreatment of both mouse and rat stromal cells resulted in a marked protection against HQ-induced toxicity. Pretreatment of both mouse and rat stromal cells with GSH ethyl ester also provided a dramatic protection against HQ-induced toxicity. Conversely, dicoumarol, an inhibitor of QR, enhanced the HQ-induced toxicity in stromal cells from both mice and rats, indicating an important role for QR in modulating HQ-induced stromal toxicity in both species. Buthionine sulfoximine (BSO), which depleted GSH significantly in both species, potentiated the HQ-induced toxicity in mouse but not in rat stromal cells. Surprisingly, incubation of stromal cells with BSO resulted in a significant induction of QR, especially in rats. The failure of BSO to potentiate HQ-induced toxicity in rat stromal cells may be due to the concomitant induction of QR by BSO. Overall, this study demonstrates that the differences in stromal cellular GSH content and QR activity between mice and rats contribute to their respective susceptibility to HQ-induced cytotoxicity in vitro, and may be involved in the greater in vivo sensitivity of mice to benzene-induced hematotoxicity.