Preliminary Study on Amino Acid Profiles in Postmortem Rat Myocardial Tissue

Carcass decomposition is a natural process that is characterized by a series of chemical transformations. During postmortem degradation, macromolecules are broken down into smaller molecules. Because proteins constitute a large proportion of the dry cell mass, protein degradation is the dominant postmortem decomposition process. Currently, the characteristics of protein degradation postmortem are largely unknown. Metabolomics enables the quantitative analysis of all metabolites within organisms or cells and has been used to investigate metabolite changes during physiological and pathological processes. Recently, forensic researchers have also applied metabolomics to postmortem challenges. In this study, we used targeted metabolomics with gas chromatography-mass spectrometry (GC-MS) to quantitatively analyze amino acid changes in rat myocardial tissue and assess protein degradation with the postmortem interval (PMI). First, the GC-MS method was validated and yielded satisfactory results. Quantitative analysis revealed good correlations between the concentrations of 14 amino acids (alanine, glycine, valine, leucine, isoleucine, proline, methionine, phenylalanine, tryptophan, glutamine, tyrosine, glutamic acid, histidine, and arginine) and early PMI. Among the 14 amino acids, the concentrations of nearly all neutral nonpolar amino acids consistently increased during the 0-6 days postmortem, while that of glutamic acid increased up to 10 days postmortem. Higher ambient temperatures increased the rate of protein degradation. A total of 9 amino acids (alanine, glycine, valine, leucine, isoleucine, phenylalanine, tryptophan, tyrosine, and glutamic acid) that exhibit regular increases at different temperatures during specific PMI show potential as biomarkers for PMI estimation.