TOXI 111 |
| 1,3-butadiene (BD) is a known rodent and human carcinogen. In human lymphoblastoid cells, 50% of all BD-induced base substitution mutations occur at A:T sites. Site directed mutation studies showed that the N1-(1-hydroxybutene-2-yl)-2'-deoxy-inosine (N1-1HB-dIno) adduct is the most mutagenic BD derived DNA adduct studied thus far. To study the formation of N1-inosine adducts in vivo, a sensitive mass spectrometric assays was developed. For method validation ctDNA was treated with 0.01 to 12.5 µM of EB or DEB, concentrations that are achieved in blood of rodents after exposure to ~1-1000 ppm BD. The formation of N1-(HB)-dIno and N6(HB)-dAde adducts were detected at treatments greater then 1 µM. The N1-2,3,4-trihydroxybutyl-dIno adducts were detected in ctDNA treated with DEB greater than 0.02 µM. The formation of N1inosine and N6-adenine adducts was ~200 and ~10 fold less, respectively, than that of N7-guanine adducts. Subsequently, Liver DNA was analyzed from mice exposed to 625 ppm BD for 2 weeks and no inosine or adenine adducts were detected, suggesting that they either do not form or were rapidly repaired in vivo. Comparison of N7-guanine adducts in liver DNA with ctDNA suggest that the adduct formation was about ~200 fold less efficient in vivo than in vitro. This may be explained by the presence of tissue protein and other molecules that compete for the availability of epoxides to bind to DNA. Consequently, the adduct levels are expected to be 1 adduct / 109 nucleotides and thus these adducts are probably not biologically significant, since endogenous adducts form constantly in much greater amounts. In conclusion, it is shown that inosine and adenine alkyl adducts are unlikely to be responsible for mutations at A:T sites and therefore ring adducts derived from DEB or cross links may be more important BD mutagenesis. |
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Poster Session and Awards
6:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- 204 A/B, Poster
Sci-Mix
Division of Chemical Toxicology |