DNA cross-linking by dehydromonocrotaline lacks apparent base sequence preference.

Area of Science:

• Toxicology
• Molecular Biology
• Organic Chemistry

Background:

• Pyrrolizidine alkaloids (PAs) are widespread plant toxins.
• Metabolic activation of PAs by hepatic enzymes generates reactive pyrrolic electrophiles.
• These electrophiles form DNA-DNA and DNA-protein cross-links, contributing to PA toxicity and carcinogenicity.

Purpose of the Study:

• To investigate whether the activated PA dehydromonocrotaline (DHMO) exhibits DNA base sequence preferences during cross-linking.
• To assess the influence of specific nucleotide sequences on DHMO-DNA adduct formation.
• To identify cellular nucleophiles that may compete with DNA for DHMO cross-linking.

Main Methods:

• Electrophoretic mobility shift assay (EMSA) was used to detect DHMO-DNA cross-links in labeled oligonucleotides.
• High-performance liquid chromatography (HPLC) analysis of enzymatically digested, cross-linked DNA was performed.
• Competition assays were conducted with various amino acids and glutathione to assess their interaction with DHMO.

Main Results:

• The extent of DHMO-DNA cross-linking was dependent on DHMO concentration, not on the oligonucleotide base sequence.
• HPLC analysis revealed no discernible sequence preference for DHMO cross-linking across any nucleotide.
• Glutathione, tyrosine, cysteine, and aspartic acid competed with DNA for DHMO cross-linking, unlike phenylalanine, threonine, serine, lysine, and methionine.

Conclusions:

• DHMO does not exhibit a strong base sequence preference when forming cross-links with DNA.
• Cellular nucleophiles like glutathione and certain amino acids can inhibit DHMO-induced DNA cross-linking.
• These findings contribute to understanding the mechanism of PA-induced genotoxicity and potential protective strategies.