People are always looking for the “next big thing.” In sports, they are looking for the next Michael Jordan. In medicine, they are looking for the ultimate tool to defeat cancer. In forensic science, they are looking for a breakthrough technology in human identification. Once upon a time, DNA was that breakthrough, then it was next-generation sequencing, and now it may be proteomics.
In a first-of-its-kind study, Northumbria University professor Noemi Procopio and colleagues have applied the principles of forensic proteomics to the estimation of postmortem submerged interval (PMSI) in aquatic environments. While there are a few established methods for calculating the postmortem submerged interval of a corpse, they can be subjective, they require the presence of the whole cadaver, and they are not applicable in the early stages of decomposition.
Procopio and her team were looking for an alternative method that could meet these challenges head on. In their study, the researchers examined whether four different types of water affected the proteome of mouse bones submerged in water for 1 or 3 weeks. To limit the complexity of the experiment and focus solely on water and time, all other environmental variables, such as water temperature and depth, were fixed.
After a PMSI of 1 or 3 weeks, the team collected the tibia from the corpses, extracted the top 30 proteins and analyzed them by mass spectrometry. The proteins clustered according to their PMSI, and there was a clear distinction between the 1-week cluster, the 3-week cluster and the controls.
Importantly, the researchers determined that the time since submersion had a greater effect on protein levels than the different types of water. According to the study results, the 1-week cluster was characterized by a higher abundance of bone-specific and serum proteins. The researchers say this is because ubiquitous and water-soluble proteins are released from the body first, leaving an abundance of proteins in the first few days of decomposition. After 3 weeks, however, muscle protein finally decays and there is a noticeable reduction.
Only one protein was found to be significantly more abundant in the controls than in any of the water environments, leading the researchers to conclude PMSI is a much more important variable than type of water.
“Despite the fact that different types of water have been shown to alter the decomposition rate, proteins in bones are quite ‘protected’ by the mineral matrix itself,” Procopio told Forensic. “This is the same reason why proteins can be recovered from very old bone specimens, such as archaeological ones, and are better preserved than DNA. The fact that different types of water didn’t affect the proteomic composition encourages us to proceed in this direction.”
Overall, the study identified novel potential biomarker candidates that may be useful for the estimation of PMSI in criminal investigations. Driven by the promising results, Procopio said she would next like to explore the effects that different water temperatures and prolonged decomposition times may have on proteins to develop a regression model that could help in the prediction of PMSI starting from bone proteins and working backward.
“These results are only the starting point for more research in order to implement this, in the future, in crime investigations,” Procopio said. “Due to the cost of instrumentation and proteomic analyses, we will have to find and validate specific protein biomarkers first that can be targeted and analyzed with instruments commonly available in forensic laboratories. This is definitely a key priority on my team and we will continue to work to get to the point in which the proposed biomarkers can be used in forensic investigations to help solve real cases.”
Procopio’s team is also working on the correlation between the age of a person and their proteomic profile, which could eventually be an interesting tool in the human identification puzzle.
Other researchers have already shown the power of proteomics in identification, including how peptide biomarkers can be used to identify a person when DNA is not an option, and how they can determine the biological sex of a corpse when only small body fragments are available.