Ophelia (1852) by John Everett Millais, inspired by Shakespeare’s character Hamletwho goes mad and drowns in a brook. It can be challenging for forensic scientists to determine how long a dead body has been submerged in water. “/>There is rarely time to write about every cool science story that comes our way. So this year, we’re once again running a special Twelve Day Christmas series of posts, each day from December 25th through January 5th highlighting a science story that fell through the cracks in 2020. Today: Identifying potential biomarkers (in mice) for recording the time of death in soggy corpses.
Correctly estimating the time of death seems so easy in fictional police procedures, but it is one of the more challenging aspects of a forensic pathologist’s job. This is especially true of corpses found in water, where a multitude of additional variables make it even more difficult to determine how long a body has been submerged. A team of scientists from Northumbria University in Newcastle, UK has come up with a new method to make that determination, measuring the level of certain proteins in bones. They detailed their findings in an April paper in the Journal of Proteome Research.
Co-author Noemi Procopio has been interested in forensic science since she was 14, but initially studied biotechnology because her home country of Italy had no forensic science programs. When she moved to the University of Manchester in the UK to complete her PhD, she chose to specialize in the application of proteomics (the large-scale study of proteins) in the field, thanks to the influence of a former supervisor, a archaeologist who applied proteomics to bones.
At the time of her PhD, there was little to no research on the proteomics of bone in forensic science, and the subfield is still somewhat in its infancy. The results of such research on bodies in terrestrial environments were promising, according to Procopio. But this is the first study with bodies submerged in water.
Forensic pathologists typically measure the level of decomposition on different body parts (face, neck, trunk, and limbs), but if the body has been in the water, other factors can make it more difficult to determine what is known as the post-mortem immersion interval (PMSI ): salinity, temperature, depth of the water, tides and whether, for example, bacteria or scavengers are present.
Procopio’s previous work on using proteomics to estimate post-mortem interval and age of death involved pigs, which are closest to the composition of the human body. For this latest study, she chose to work with mouse bodies for practical reasons. “If you’re doing a pilot exploratory study, it’s better to use some sort of smaller model,” she told Ars.
Using pigs also requires some legal permission to keep the pigs, and it’s actually hard to get pigs that have died of natural causes, unlike slaughtering them for research purposes – something Procopio didn’t like to do. “I think animal research is fundamental in some ways, such as medical research,” she said. “But for forensics, I think we can use whatever we have, animals that are already dead, instead of killing anything for forensic science.”
So instead, she and her team bought 22 frozen mice from a reptile food center. Fortunately, freezing doesn’t seem to have a major effect on decomposition. “If you freeze and thaw just once, it’s not that big of a deal in terms of decomposition and how it can be processed,” Procopio said. They thawed one set of mice at room temperature and another set at body temperature. Then they placed the mouse carcasses in bottles of tap water, salt water, pond water and chlorinated water. The tails were taped to the bottom of the bottles to ensure that all mice were kept at the same depth.
At weekly and three-week intervals, Procopio et al. collected the lower leg bones (tibia) of the mouse bodies, extracted the proteins and analyzed them by mass spectrometry. They found that the type of water had less impact on protein levels than how long the bodies were submerged. The longer the immersion time, the more levels of the protein fructose bisphosphate aldolase A decrease. Water type did have an effect on one type of protein: fetuin-A was more likely to change chemically (deamidation) in pond water than in the other types of water. This could be an indication that a body is initially submerged in pond water and then moved to another location.
Conclusion: These proteins could be excellent biomarkers to help determine the time of death in soggy corpses. For future studies, Procopio and her colleagues hope to investigate the effects of different temperatures on the bone proteomics of submerged corpses, among other variables, and ideally eventually move to human bodies, “because that is what we ultimately need to make our findings for forensic casework. , “she said. She is already working with a number of so-called “body farms” on this, although the ongoing pandemic has delayed that work.
DOI: Journal of Proteome Research, 2020.10.1021 / acs.jproteome.0c00060 (About DOIs).