Mass Spectrometric Assessment of the Reactivity and Target Sites of 3‐Aminopropanal and 3‐Aminopropanal‐Released Acrolein in Peptides and Proteins

Living cells are frequently exposed to aldehydes, as these compounds are produced during metabolism, found in natural dietary sources, and present as contaminants, drugs, and pollutants. For instance, acrolein is well-known as a toxic pollutant, but is also produced in the metabolism of polyamines, threonine, and polyunsaturated fatty acids. Another aldehyde, 3-aminopropanal, is a byproduct of polyamine oxidation, and its cytotoxicity has been implicated in various diseases, especially those involving oxidative stress and cellular damage. 3-Aminopropanal can readily convert to acrolein through ammonia elimination. Our objective was to compare the reactivity of these two compounds toward biomolecules. Amino acids such as cysteine and lysine, along with model peptides and proteins, were reacted with an excess of each compound. The reacted molecules were analyzed by MALDI-TOF mass spectrometry to assess the extent of modification by examining the difference in molecular mass. Modified peptides, including those obtained by enzymatic digestion of the reacted model proteins, were subjected to tandem mass spectrometry to identify modification sites and determine the structure of the modified amino acids. The most characteristic modifications were Michael addition to cysteine and Schiff base formation with lysine, consistent with known acrolein-induced protein modifications. Compared to acrolein, 3-aminopropanal exhibited substantially reduced reactivity, though it generally targeted the same sites. These results represent the first experimental characterization of 3-aminopropanal-induced protein modifications at the molecular level, and support the notion that 3-aminopropanal is converted to acrolein, which acts as the modifying agent.