[Determination of the fluorescence intensity of coenzymes NADH and FAD in the skeletal muscle of the rat depending on the post-mortem interval]

[The forensic implications of the relationship between the proteolytic enzymes activity and the changes in NADH and FAD fluorescence intensity in skeletal muscle when determining the time of death (experimental study)]

OBJECTIVE

Evaluation of the relationship between the activity of proteolytic enzymes (cathepsin D and calpains) and the dynamics of the fluorescence intensity of the coenzymes nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) in the rats' skeletal muscles in relation to the time of death. The proteolytic activity of enzymes in rat skeletal muscle was determined at the postmortem time points corresponding to the most significant changes in the dynamics of coenzymes NADH and FAD fluorescence intensity. The proteolytic enzymes activity was found to be low during the period of increasing intensity of NADH fluorescence observed within 3 hours after death. An increase in the activity of proteolytic enzymes was registered in 4.5 hours after death which corresponds to the initial point of decrease in NADH fluorescence intensity. In 24 hours post-mortem, corresponding to increased FAD fluorescence intensity a significant decrease in the activity of calpains was found. The results of the study suggest that the nature of the postmortem dynamics of the fluorescence intensity of coenzymes is largely due to the peculiarities of intracellular proteolysis. The study results suggest that the pattern of post mortem changes in coenzyme fluorescence intensity is largely attributable to the specifics of intracellular proteolysis. The relationship between coenzyme fluorescence and molecular mechanisms of cell death confirms the viability and feasibility of laser-induced spectroscopy for post-mortem changes assessment when determining the time of death.

Patterns of changes in the fluorescence of nadh and fad coenzymes and their relationship in skeletal muscle in the early post-mortem period (an experimental study)

Background.The paper presents changes and mathematical models of autofluorescence of reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) and their redox ratio (RR) in rat skeletal muscle during the first 24 hours after death.Aim.To establish a pattern of change in the fluorescence intensity of NADH and FAD coenzymes, as well as their relationship in skeletal muscle during the first 24 hours after death using mathematical modeling.Material and methods.The experiment was performed on Sprague Dawley rats. The fluorescence intensity of FAD and NADH coenzymes in skeletal muscle was measured in situ in living rats under general anesthesia, 5 minutes after euthanasia, and at intervals of 1.53 h during the 24-hour postmortem period. To estimate the fluorescence intensity of NADH and FAD coenzymes and to calculate the RR, a Lasma MC-3 fluorescence measuring device with special software was used. The obtained data were analyzed by non-linear regression analysis. The summary, accuracy estimation, and significance of the regression equation coefficients were assessed using SigmaPlot 10.0 software. The significance of the regression model was tested using the Fisher F-criterion.Results.During the first 3 hours of the postmortem period, an increase in the mean values of RR and NADH fluorescence was detected; starting from 4.5 and lasting until 24 hours post mortem, their gradual decrease was observed. The relationship between NADH, RR, and time since death is characterized by the Weibull equation. The statistical significance of the NADH and RR models, based on the obtained equations, was considered high.Conclusion.The analysis of the obtained data allowed us to create mathematical models describing the relationship between RR and NADH fluorescence intensity and time after death, which confirms the non-randomness and regularity of the discovered patterns.