Early Postmortem Changes in NADH Fluorescence Lifetime Parameters in Rat Skeletal Muscle: Potential for Postmortem...

Investigation of the molecular mechanisms of postmortem processes to identify postmortem interval (PMI) markers is highly relevant in forensic medicine, given the insufficient accuracy and substantial limitations of current routine PMI estimation methods. This exploratory study aimed to describe changes in NADH fluorescence decay parameters in rat skeletal muscle during the early postmortem period and to assess their potential for PMI estimation. Using time-resolved fluorescence spectroscopy, the short- and long-lifetime components (τ₁ and τ₂), the amplitude-weighted mean fluorescence lifetime (τ_m), the relative contributions of the short- and long-lifetime components (α₁ and α₂, respectively) and fluorescence intensity were measured in 10 Wistar rats before death, immediately after death, every 30 min during the first 6 h, and at 24 h postmortem. Immediately after death, τ₁ decreased compared with the antemortem value (p = 0.02). τ₁, τ_m, α₁, and α₂ were dependent on the postmortem interval. For PMI prediction within the first 6 h after death, a partial least squares regression model combining α₁, τ_m, and the difference between rectal and room temperatures was constructed. The model demonstrated promising predictive performance, with a root mean square error (RMSE) of 0.89 h (95% CI: 0.63-0.99), a mean absolute error (MAE) of 0.68 h (95% CI: 0.49-0.82) and an R² of 0.762 (95% CI: 0.689-0.886); the prediction error did not exceed 1 h in 73.2% of cases. These data are preliminary and require confirmation in studies with larger samples under different ambient temperature conditions and subsequent validation on human cadaveric material.