Chemoprevention of benzene-induced bone marrow and pulmonary genotoxicity.

Our earlier studies documented the ability of 7,8-diacetoxy-4-methylcoumarin (DAMC) to cause irreversible inhibition of cytochrome P-450 linked mixed function oxidases (MFO) mediated by membrane bound DAMC: protein transacetylase. Since P-450 catalyzed oxidation of benzene is crucial to its toxic effects, the action of DAMC and related analogues were considered promising in preventing the genotoxicity due to benzene. For this purpose rats were pretreated with various acetoxy-4-methylcoumarins (test compounds), which was followed by the administration of benzene either intratracheally (IT) or intraperitoneally (IP), and sacrificed 26 h after the injection of benzene. The incidence of micronuclei (MN) in bone marrow (BM) and lung (LG) were assessed by light and fluorescent microscopy, respectively. A dose-dependent induction of MN in BM and LG cells was observed in rats administered with benzene. A significant reduction in benzene-induced MN in BM and LG was observed as a result of DAMC administration to rats; a higher dose of DAMC resulted in greater inhibition of clastogenic action of benzene as revealed by MN incidence. 7,8-dihydroxy-4-methylcoumarin (DHMC), the deacetylated product of DAMC, demonstrated relatively lesser potency to inhibit the clastogenic action of benzene. This observation is consistent with the ability of DAMC to inhibit the formation of benzene oxide as well as to scavenge the oxygen radicals formed during the course of benzene metabolism. The fact that DHMC can only scavenge the oxygen radicals and is ineffective in inhibiting benzene oxidation in vivo explains the reduced capability of dihydroxy coumarin to prevent MN due to benzene. 7-Acetoxy-4-methylcoumarin (MAC) inhibits the MN due to benzene being roughly 50% of that produced by DAMC. DAMC is also effective in normalizing the cell cycle alterations produced by benzene in BM and LG. These observations further substantiate our hypothesis that the biological effects of acetoxy coumarins are mediated by the action of membrane bound transacetylase that catalyzes the acetylation of concerned proteins. Teratogenesis Carcinog. Mutagen. 21:181-187, 2001.