Formation of interstrand cross-links in chloroacetaldehyde-treated DNA demonstrated by ethidium bromide fluorescence

Chloroacetaldehyde, the stable metabolite of the human carcinogen vinyl chloride, forms interstrand cross-links in vitro in salmon sperm DNA and in the alternating copolymer, poly(deoxyadenylate-deoxythymidylate) [poly(dA-dT)]. Formation of the cross-link was a function of both time of reaction and concentration of chloroacetaldehyde. Cross-linking in chloroacetaldehyde-treated poly(dA-dT) was detected initially by changes in renaturation hysteresis [Singer et al., Carcinogenesis (Lond.), 5: 1165-1171, 1984]. This has been confirmed and quantitated using the relative fluorescence of ethidium bromide after denaturation and reannealing at 40 degrees C. Three percent cross-linking was detected after 10 min reaction with 20 mM chloroacetaldehyde at 24 degrees C. In DNA the relative fluorescence of ethidium bromide after denaturation and rapid cooling was used to estimate the number of cross-links formed. Three times as much cross-linking occurs in DNA compared to poly(dA-dT) under identical reaction conditions. The postulated structure for an interstrand cross-link in poly(dA-dT) is a hydroxyethyl bridge across the strands between the N6-amino groups of alternate adenine residues. In DNA, other amino groups in the proper configuration can be involved.