Preweanling rats were exposed to 600 p.p.m. (4h/day) of the human carcinogen vinyl chloride for 5 days to determine the molecular dosimetry of DNA adducts in liver, lung and kidney. 7-(2'-Oxoethyl)guanine (7OEG) was the major DNA adduct detected, representing approximately 98% of all adducts. N2,3-Ethenoguanine (epsilon G) and 3,N4-etheno-2'-deoxycytidine (epsilon dC) were present at approximately 1% of the 7OEG concentration, while 1,N6-etheno-2'-deoxyadenosine was present in even lower concentrations. Liver had 3- to 8-fold higher amounts of the DNA adducts than lung and kidney. The persistence of all four adducts was determined at 3, 7 and 14 days post-exposure. Whereas 7OEG had a t 1/2 of -62 h, all three etheno adducts were highly persistent. After accounting for dilution due to growth-related cell proliferation, epsilon G had a t 1/2 of approximately 30 days, while epsilon dC and epsilon dA were not repaired. These data suggest that these cyclic adducts are poorly recognized by liver DNA repair enzymes and have the potential for accumulation upon chronic exposure. This, coupled with the known miscoding properties of the ethenobases, provides a strong rational for examining their role in vinyl chloride-induced cancer and their utility as biomarkers of exposure.

1,N6-Etheno-2'-deoxyadenosine (epsilon dAdo) and 3,N4-etheno-2'-deoxycytidine (epsilon dCyd) are formed in vitro by reaction of DNA with the electrophilic metabolites of vinyl chloride (VC), chloroethylene oxide and chloroacetaldehyde. To detect and quantitate these DNA adducts in vivo, we have raised a series of specific monoclonal antibodies (Mab). Among those, Mab EM-A-1 and Mab EM-C-1, respectively, were used for detection of epsilon dAdo and epsilon dCyd by competitive radioimmunoassay (RIA), following pre-separation of the etheno adducts from DNA hydrolysates by high performance liquid chromatography. At 50% inhibition of tracer-antibody binding, both Mab had a detection limit of 187 fmol and antibody affinity constants (K) of 2 x 10(9) l/mol. The levels of epsilon dAdo and epsilon dCyd were quantitated in the DNA of lung and liver tissue of young Sprague-Dawley rats exposed to 2000 p.p.m. of VC for 10 days. The epsilon dAdo/2'-deoxyadenosine and epsilon dCyd/2'-deoxycytidine molar ratios were 1.3 x 10(-7) and 3.3 x 10(-7), respectively, in lung DNA, and 5.0 x 10(-8) and 1.6 x 10(-7) in liver DNA. When hydrolysates of 3 mg of DNA were analyzed by RIA at 25% inhibition of tracer-antibody binding, epsilon dAdo and epsilon dCyd were not detected in liver DNA from untreated rats above the limiting epsilon dAdo/2'-deoxyadenosine and epsilon dCyd/2'-deoxycytidine molar ratios of 2.2 x 10(-8) and 3.1 x 10(-8), respectively.

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