A new method for calculating the exact time of death, even after as much as 10 days, has been developed by a group of researchers at the University of Salzburg. Currently, there are no reliable ways to determine the time since death after approximately 36 hours. Initial results suggest that this method can be applied in forensics to estimate the time elapsed since death in humans.
By observing how muscle proteins and enzymes degrade in pigs, scientists at the University of Salzburg have developed a new way of estimating time since death that functions up to at least 240 hours after death.
During the course of the study, they found that some of the proteins analysed (tropomyosin and actinin) showed no form of degradation until after 240 hours. “It is highly likely that all muscle proteins undergo detectable changes at a certain point in time, and this would extend the currently analysed timeframe even further,” says Dr Peter Steinbacher, who is leading the research.
Specific degradation products of proteins appear at a specific time after death. By studying the timing of their appearance, the researchers were able to calculate time since death. The researchers have already started running experiments on human samples and initial results are promising: “We were able to detect similar changes and exactly the same degradation products in human muscle tissue as we had in our pig study”, says Steinbacher.
The use of muscle tissue in post-mortem studies is a novel approach which presents several advantages: first, muscle tissue is the most abundant tissue of the human body and can therefore be sampled easily. Secondly, proteins in muscle tissue are well known. Thirdly, this method is simple and can deliver results within a day.
Estimating the time since death is a very important aspect in forensic sciences which is pursued by a variety of methods. The most precise method to determine the postmortem interval (PMI) is the temperature method which is based on the decrease of the body core temperature from 37 °C. However, this method is only useful in the early postmortem phase (~0–36 h). The aim of the present work is to develop an accurate method for PMI determination beyond this present limit. For this purpose, we used sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting, and casein zymography to analyze the time course of degradation of selected proteins and calpain activity in porcine biceps femoris muscle until 240 h postmortem (hpm). Our results demonstrate that titin, nebulin, desmin, cardiac troponin T, and SERCA1 degraded in a regular and predictable fashion in all samples investigated. Similarly, both the native calpain 1 and calpain 2 bands disintegrate into two bands subsequently. This degradation behavior identifies muscular proteins and enzymes as promising substrates for future molecular-based PMI determination technologies.