, 2010). The inter-gender comparison is justified because the amounts of cross-link adducts were 2–2.5-fold higher in females of both species compared to males when subjected to the same exposure

conditions ( Goggin et al., 2009). The ratio of (±)-DEB in mouse blood compared to rat blood increases from 4.5 at near to 0 ppm BD up to 16 at 625 ppm BD (calculated using the one-phase exponential association functions). The ratio of 1,4-bis-(guan-7-yl)-2,3-butanediol increases from 4.2 at 62.5 ppm BD up to 11 at 625 ppm BD. In the exposure range between 0.5 and 625 ppm BD, ratios of between 6 and 15 can be calculated for the DEB exposure marker N,N-(2,3-dihydroxy-1,4-butadiyl)-valine. All three studies show that the DEB burden is substantially higher in mice than in rats and that the difference increases at BD concentrations Inhibitor Library purchase above 200 ppm. Not expected from the present DEB data are the drastically larger mouse-to-rat ratios in the N,N-(2,3-dihydroxy-1,4-butadiyl)-valine levels which were reported for longer BD exposures (6 h/d, 5 d/w, 4 w) ( Georgieva

et al., 2010 and Swenberg Pirfenidone chemical structure et al., 2007). It has been speculated that the exposure of the erythrocytes to DEB decreased the lifespan of the rat erythrocytes and diluted the adduct levels in rat erythrocytes by increased hematopoiesis ( Georgieva et al., 2010). The present data help to explain the findings on the species-specific carcinogenic potency of tuclazepam BD in mice and rats. In blood of male rats, mean concentrations of DEB do not surpass 0.1 μmol/l, a concentration reached at an exposure concentration of 19 ppm in blood of male mice. In male mice, the lowest statistically significant carcinogenic BD exposure concentration was 62.5 ppm in a two-year inhalation study (Melnick et al., 1990),

which corresponds to a DEB concentration of 0.3 μmol/l in blood. Considering that male rats never reach this blood concentration, it seems probable that BD induced gland tumors in rats exposed to 1000 and 8000 ppm BD (Owen et al., 1987) resulted not so much from the DEB burden but primarily from the burdens of both 1,2-epoxy-3-butene and 3,4-epoxy-1,2-butanediol as has already been suggested earlier (Filser et al., 2007 and Fred et al., 2008). In the blood of rats, concentrations of 1,2-epoxy-3-butene and 3,4-epoxy-1,2-butanediol of about 1 μmol/l and 2 μmol/l, respectively, are found at BD concentrations of 1000 ppm (Filser et al., 2007). As a starting point for the estimation of the risk of BD to humans who may be exposed to low BD concentrations, knowledge of the internal burden by the epoxy-metabolites of BD is required. In addition to the earlier sensitive methods for the determination of 1,2-epoxy-3-butene and 3,4-epoxy-1,2-butanediol in blood (Filser et al., 2007 and Filser et al., 2010), we have now a very sensitive and highly specific method for the analysis of DEB in our hands.