Crosslinking of DNA by dehydroretronecine, a metabolite of pyrrolizidine alkaloids.

Dehydroretronecine (DHR), a major metabolite of the pyrrolizidine alkaloids, has been shown to bind and crosslink pBR322 plasmid DNA and M13 viral DNA, as monitored by electron microscopy and agarose gel electrophoresis. The crosslinking was alkali-stable and varied with time, temperature, pH and reactant ratios. Although the binding of DHR to single-stranded M13 DNA was 3-fold higher than to double-stranded M13 DNA, only the double-stranded DNA was crosslinked. Intra- and inter-molecular crosslinking occurred with both linear and circular forms of double-stranded DNA. Electron microscopy showed that incubations with low DHR/DNA ratios yielded mostly DNA monomers and dimers while higher ratios produced larger aggregations, some of which were equivalent in size to dozens of individual DNA molecules. The average number of intermolecular crosslinks per molecule estimated by Poisson statistics was essentially the same using data from electron microscopy or DHR-binding. DHR generated single strand scissions equally well in both single- and double-stranded molecules.