Michael addition of acrolein to lysinyl and N-terminal residues of a model peptide: targets for cytoprotective hydrazino drugs

The antihypertensive drug hydralazine blocks acrolein-mediated toxicity by trapping both free aldehyde- and acrolein-adducted proteins, with the latter property more closely related to cytoprotection in cellular models. Here we report the identification of products from 'protein adduct-trapping' reactions using electrospray ionisation mass spectrometry (ESI-MS). Reaction of a 13-residue peptide containing a single lysine with acrolein for 30 min generated ions corresponding to mono- and bis-Michael-adducted peptides. An ion corresponding to a cyclic species formed from bis-adducted lysine was conspicuous at later times (60, 180 min). Tandem mass spectrometric (MS/MS) analysis revealed Michael adduction also occurred on the N-terminus, with a novel N-terminal (3-formyl-3,4-dehydropiperidino) species formed on this residue. Addition of hydralazine to acrolein-adducted peptides generated a diverse range of hydrazones that were also characterised by MS/MS analysis. The results confirm that mass spectrometry is a powerful tool for characterising the reactions of noxious electrophiles with biological macromolecules.