Synthesis, isolation, and characterization of the adduct formed in the reaction of p-hydroxyphenylacetaldehyde with the amino headgroup of phosphatidylethanolamine and phosphatidylserine

The adducts that form when aldehydes modify proteins have been implicated in the pathogenesis of vascular disease and aging. Our previous studies indicated that p-hydroxyphenylacetaldehyde (pHA), the major product of L-tyrosine oxidation by the myeloperoxidase/hydrogen peroxide/chloride system of phagocytes, covalently modifies the ε-amino group of lysine residues at sites of inflammation. Here, we report that pHA also reacts with the amino group of synthetic phospholipids and red blood cell model systems. Using fast atom bombardment mass spectrometric analysis of ethanolamine glycerophospholipid or serine glycerophospholipid incubated with pHA and NaBH₃CN, we detected products that were consistent with reduced phospholipid Schiff base adducts. We confirmed the reaction of the aldehyde with the amino group through ¹H NMR and mass spectrometric analysis of polar headgroups recovered from the modified and reduced parent lipid. When phospholipid model systems and cell membranes were exposed to physiological levels of L-tyrosine and the myeloperoxidase/hydrogen peroxide/chloride system followed by treatment with NaBH₃CN, reduced Schiff base adducts of pHA with ethanolamine glycerophospholipid and serine glycerophospholipid (pHA-PE and pHA-PS, respectively) were produced. The reaction required myeloperoxidase, hydrogen peroxide, L-tyrosine, and chloride ion; it was inhibited by catalase or heme poisons, implicating hydrogen peroxide and peroxidase in the pathway. Collectively, these results demonstrate that an aldehyde generated by the myeloperoxidase system of phagocytes can covalently modify the amino groups of phosphatidylethanolamine and phosphatidylserine. Because amino glycerophospholipids are critical components of cell membranes and circulating lipoproteins such as LDL, similar reactions may play important roles in the initiation or progression of disease at sites of inflammation.