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Background Myeloperoxidase (MPO) activity increases in myocardial infarction due to neutrophil infiltration. MPO together with H2O2 and Cl- leads to the formation of HOCl, which induces plasmalogen modification. HOCl attacks the vinylether bond of plasmalogens inducing formation of alpha-chlorofatty aldehydes, like 2-chlorohexadecanal (2-ClHDA). 2-ClHDA impacts protein function by covalent modification, triggering cytotoxic responses. Methods To study 2-ClHDA-mediated protein modification in cardiomyocytes, click-chemistry with proteomic approaches was used. Therefore, an alkyne containing bioortholog of 2-ClHDA, 2-chlorohexadec-15-yn-1-al (2-ClHDyA), was synthesized. Protein lysates of 2-ClHDyA-modified cardiomyocytes were clicked with tetramethylrhodamine (TAMRA) azide and separated by 2-DE. TAMRA-positive spots were trypsinized and identified by LC-MS/MS. Results During these analyses 51 2-ClHDyA-modified proteins were identified. Those proteins were mainly attributed to cellular processes involved in stress response, the cytoskeleton, and enzymes responsible for energy metabolism. These results suggest that cellular damage following myocardial infarction could be caused by impaired protein function due to modification by 2-ClHDA.

Recent observations link myeloperoxidase (MPO) activation to neurodegeneration. In multiple sclerosis MPO is present in areas of active demyelination where the potent oxidant hypochlorous acid (HOCl), formed by MPO from H(2)O(2) and chloride ions, could oxidatively damage myelin-associated lipids. The purpose of this study was (i) to characterize reaction products of sphingomyelin (SM) formed in response to modification by HOCl, (ii) to define the impact of exogenously added SM and HOCl-modified SM (HOCl-SM) on viability parameters of a neuronal cell line (PC12), and (iii) to study alterations in the PC12 cell proteome in response to SM and HOCl-SM. MALDI-TOF-MS analyses revealed that HOCl, added as reagent or generated enzymatically, transforms SM into chlorinated species. On the cellular level HOCl-SM but not SM induced the formation of reactive oxygen species. HOCl-SM induced severely impaired cell viability, dissipation of the mitochondrial membrane potential, and activation of caspase-3 and DNA damage. Proteome analyses identified differential expression of specific subsets of proteins in response to SM and HOCl-SM. Our results demonstrate that HOCl modification of SM results in the generation of chlorinated lipid species with potent neurotoxic properties. Given the emerging connections between the MPO-H(2)O(2)-chloride axis and neurodegeneration, this chlorinating pathway might be implicated in neuropathogenesis.