Model studies on the influence of high hydrostatic pressure on the formation of glycated arginine modifications at elevated temperatures

Aqueous solutions of N^α-acetylarginine and glucose were reacted for 2 h with pressure application from 0 to 600 MPa and varying temperatures between 90 and 120°C. After enzymatic deacetylation of the reaction products, the glycated amino acids were separated by means of a self-assembled preparative ion exchange chromatography system using ninhydrin detection. On the basis of the use of eight synthesized reference compounds known in the literature as posttranslational arginine modifications, first, the presence of several glycated amino acids could be excluded. On the other hand, N⁵-[[(1-carboxyethyl)amino]iminomethyl]ornithine [N ⁷-(1-carboxyethyl)arginine; N⁷-CEA; 12] was identified as a previously unknown arginine modification based on LC-MS, NMR measurements, and synthesis. In addition, N⁵-(5-hydro-5-methyl-4-imidazolon-2-yl)-L- ornithine (1) was identified as a further major reaction product. In further experiments, the formation of 1 and 12 was quantitatively followed at different pressures and/or temperatures. The results indicated that high hydrostatic pressure at elevated temperatures significantly increased the amounts of both arginine modifications. 2-Oxopropanal, known to form 1 in a reaction with arginine, was also quantified to explain the different yields observed after pressure application. A new formation mechanism leading to 12 by a reaction of the guanidine group or arginine with 2-oxopropanal is discussed.