A 32P-postlabeling method is described that specifically detects and quantifies the 1,N2-propanodeoxyguanosine adducts derived from acrolein (AdG) and crotonaldehyde (CdG) and 1,N2-ethenodeoxyguanosine (EdG) in DNA. These exocyclic adducts are potential DNA lesions caused by exposure to enals as environmental pollutants and as endogenous compounds. This method was developed with the use of the synthetic adduct standards of these exocyclic adducts. The assay relies on HPLC for adduct enrichment prior to labeling and for quantitation and identification after labeling. The labeling efficiencies of adducts at the 1 fmol level ranged from 74 to 96%, whereas they were only 49-60% at the 100 fmol level. This method can detect as low as 0.2 fmol of adduct and allows the detection and quantitative determination of stereoisomers of AdG and CdG. The method was validated by using a sample of enzyme digests of 180 micrograms calf thymus DNA spiked with 25 or 75 fmol of adducts, which is equivalent to 5 or 15 adducts in 10(8) nucleotides. The recovery rates of these adducts in DNA ranged from 30 to 90% at the 25 fmol level and 21 to 55% at the 75 fmol level. Similar to the labeling efficiency, a greater recovery was observed with a lower amount of adduct in DNA. Overall, this method allows the simultaneous identification and quantification of exocyclic adducts AdG, CdG and EdG in DNA. Therefore, it provides a potential tool for studies of the in vivo formation of exocyclic adducts.
Monoclonal antibodies specific for N2,3-ethenodeoxyguanosine (N2,3-epsilon dGuo) and 1,N2-ethenodeoxyguanosine (1,N2-epsilon dGuo) were developed. In a competitive ELISA, 50% inhibition of binding of the N2,3-epsilon dGuo specific antibody (ETH1) was achieved with 18 fmol of N2,3-epsilon dGuo. Fifty per cent inhibition of the 1,N2-epsilon dGuo-specific antibody (ETH2) required 11 pmol 1,N2-epsilon dGuo. Immunoassays for N2,3-epsilon dGuo and 1,N2-epsilon dGuo in single-stranded DNA were developed using these antibodies. The immunoassays could detect as little as 48 fmol of N2,3-epsilon dGuo or 340 fmol 1,N2-epsilon dGUO in 25 micrograms of single stranded DNA. These assays and previously developed immunoassays for 1,N6-ethenodeoxy-adenosine (1,N6-epsilon dAdo) and 3,N4-ethenodeoxycytidine (3,N4-epsilon dCyd) were used to measure etheno adduct levels in DNA of cells exposed to chloroacetaldehyde. The cells used were V79 cells with an inactivated hprt gene and a single copy of the bacterial gpt gene (G12 cells). The most abundant etheno adduct was 1,N6-epsilon dAdo, followed by 3,N4-epsilon dCyd and N2,3-epsilon dGuo. 1,N2-epsilon dGuo was not detected in chloro-acetaldehyde-treated G12 cells. Chloroacetaldehyde was also shown to be mutagenic in these same cells.
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