The analysis of post-mortem fluorescent signatures in discarded cell lysate from DNA extractions: a comparative study...

Post-mortem interval (PMI) estimation remains a complex yet crucial task in medico-legal death investigations, as accurate and reliable estimates could establish timelines and contextualize physical evidence. Taphonomic studies often use pig carcasses as human analogues, and while they perform well in some entomology experiments, comparative studies have shown interspecies differences in biomolecular degradation during decomposition. Further, few studies use fluorimetry, leaving the degradation of fluorophores understudied in both species. Herein, we integrated PMI analysis into DNA extraction protocols by probing typically discarded cell lysates, enabling multiple analyses from a single sample. Our dataset included human and pig remains: 50 biopsy punches collected from 14 human donors at the Research in Experimental and Social Thanatology (REST) facility in Québec, Canada and 21 biopsy punches from two pigs placed in Oshawa, Canada, with PMIs ranging from 0-1185 days (9.9-11 281.7 accumulated degree days; ADD). An excitation-emission matrix was acquired for each lysate and deconvoluted using parallel factor analysis (PARAFAC) to identify individual fluorophores. PARAFAC models revealed similar fluorophores and time-dependent trends in both species. Tryptophan fluorescence decreased over time, while fluorescence between 400-500 nm increased as PMI progressed, attributed to an accumulation of fluorescent oxidation products and advanced glycation end-products. Although partial least squares discriminant analysis demonstrated fluorescence differences between species, principal component analysis did not yield species-specific groupings and displayed common PMI/ADD-related trends for both species. Our findings suggest that interspecies differences are not primarily driven by PMI/ADD, and that pig carcasses are a useful human analogue in taphonomic studies using fluorimetry.