DNA cross‐link induced by trans‐4‐hydroxynonenal

Trans-4-Hydroxynonenal (HNE) is a peroxidation product of omega-6 polyunsaturated fatty acids. Michael addition of HNE to deoxyguanosine yields four diastereomeric 1,N(2)-dG adducts. The adduct of (6S,8R,11S) stereochemistry forms interstrand N(2)-dG:N(2)-dG cross-links in the 5'-CpG-3' sequence. It has been compared with the (6R,8S,11R) adduct, incorporated into 5'-d(GCTAGCXAGTCC)-3' . 5'-d(GGACTCGCTAGC)-3', containing the 5'-CpG-3' sequence (X = HNE-dG). Both adducts rearrange in DNA to N(2)-dG aldehydes. These aldehydes exist in equilibrium with diastereomeric cyclic hemiacetals, in which the latter predominate at equilibrium. These cyclic hemiacetals mask the aldehydes, explaining why DNA cross-linking is slow compared to related 1,N(2)-dG adducts formed by acrolein and crotonaldehyde. Both the (6S,8R,11S) and (6R,8S,11R) cyclic hemiacetals are located within the minor groove. However, the (6S,8R,11S) cyclic hemiacetal orients in the 5'-direction, while the (6R,8S,11R) cyclic hemiacetal orients in the 3'-direction. The conformations of the diastereomeric N(2)-dG aldehydes, which are the reactive species involved in DNA cross-link formation, have been calculated using molecular mechanics methods. The (6S,8R,11S) aldehyde orients in the 5'-direction, while the (6R,8S,11R) aldehyde orients in the 3'-direction. This suggests a kinetic basis to explain, in part, why the (6S,8R,11S) HNE adduct forms interchain cross-links in the 5'-CpG-3' sequence, whereas (6R,8S,11R) HNE adduct does not. The presence of these cross-links in vivo is anticipated to interfere with DNA replication and transcription, thereby contributing to the etiology of human disease.