Estimation of time passed since death by ultrastructure, histopathology and DNA degradation detection by gel electrophoresis in albino rats

ABSTRACT

The estimation of postmortem interval [PMI] is of great importance in both criminal and civil cases. However this aim remains critical, difficult if not impossible but an imprecise task in forensic investigation. While the traditional thanatochronological changes upon the dead had been used for estimation of PMI inaccurately, advances in molecular biology, have propelled the analysis of DNA to criminal laboratories. Upon the death of an individual, internal nucleases contained within the cell should cause chromosomal DNA to degrade into increasingly smaller fragments over time that can be used as a predictor of PMI. Liver cells for being rich in nuclear DNA and mitochondria were proved to be the best material for the purpose. The aim of the work was to determine the time passed since death by measuring the rate of DNA degradation in samples of livers of albino rats at different post mortem intervals by using gel electrophoresis method, and to asses the changes of liver cells by histopatological examination at the same periods, with exploring the nature of the post mortem liver cell changes by using the Transmission Electron Microscope [TEM]. Passive engorgement of the sinusoids and extravasations of blood elements appeared early after death in histopathology then cell necrosis, shrunken cells, and apoptotic bodies were increasing by time. TEM examinations revealed the presence of chromatin condensations and fragmentation of the nuclear material. Finally cell lysis and apoptotic bodies appeared while cell necrosis was prominent. Electron microscope could add much to understanding postmortem cellular changes, also assessment of the relative existence of necrosis stages in histopathology might help in identifying PMI. The Gel Electrophorsis detection, measurement and analysis by computer pro analyzer revealed the presence of sequential relationship between DNA degradation level and time passed since death at the DNA visualizing positions [200 bp, 400 bp, 600 bp] up to 24 hours. Statistical evaluation showed a highly significant dependence of DNA degradation on time with P < 0.001. By using linear regression analysis an equation to define the time passed since death could be conducted where Time after death=[DNA degradation - constant] / B. So it is recommended to apply the method of the gel electrophoresis to detect time passed since death by measuring DNA fragmentation from liver cells. These mathematical relations offer a simple and valuable means of estimating the PMI, and its validity should be tested for human being