There’s rarely time to write about every cool science-y story that comes our way. So this year, we’re once again running a special Twelve Days of Christmas series of posts, highlighting one science story that fell through the cracks in 2020, each day from December 25 through January 5. Today: identifying potential biomarkers (in mice) for pegging time of death in waterlogged corpses.
Correctly estimating time of death looks so easy in fictional police procedurals, but it’s one of the more challenging aspects of a forensic pathologist’s job. This is particularly true for 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 at Northumbria University in Newcastle, UK, have hit upon a new method for making that determination, involving the measurement of levels of certain proteins in bones. They described 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 didn’t have 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) to the field, thanks to the influence of a former supervisor, an archaeologist who applied proteomics to bones.
At the time of her PhD, there was little to no research that had been on the proteomics of bone in forensic science, and the subfield is still somewhat in its infancy. The results of such work studying bodies in terrestrial environments were very promising, according to Procopio. But this is the first study involving bodies that have been submerged in water.
Forensic pathologists typically sample the level of decomposition on several body areas (face, neck, torso, and limbs), but when the body has been in water, other factors can make it harder to determine what’s known as the post-mortem submerged interval (PMSI): salinity, temperature, depth of the water, tides, and whether any bacteria or scavengers are present, for example.
Procopio’s prior work on using proteomics to estimate postmortem interval and the age of death involved pigs, the closest to the human body’s composition. For this latest study, she opted to work with mouse bodies, simply for practical reasons. “When you do a pilot exploratory study, it’s better to use some kind of smaller model,” she told Ars.
Using pigs also requires certain legal permissions to keep the pigs, and it’s actually hard to acquire pigs that have died of natural causes, as opposed to slaughtering them for research purposes—something Procopio was reluctant to do. “I think research on animals is fundamental in some respects, for example, medical research,” she said. “But for forensics, I think we can use whatever we have, animals that are already dead, rather than killing something for forensic science.”
So instead, she and her team purchased 22 frozen mice from a reptile food supply center. Fortunately, freezing doesn’t seem to have a large effect on decomposition. “If you just freeze and defrost one time, it’s not a massive deal in terms of decomposition and how it can process,” said Procopio. They defrosted one set of mice at room temperature, and another set at body temperature. Then they placed the mouse carcasses in bottles of tap water, saltwater, pond water, and chlorinated water. The tails were taped to the bottom of the bottles to ensure that all the mice were kept at the same depth.
At one-week and three-week intervals, Procopio et al. collected the lower leg bones (tibia) from the mouse corpses, extracting the proteins and analyzing them with mass spectrometry. They found that the type of water had less of an effect on protein levels than how long the bodies had been submerged. For instance the longer the time of submersion, the more levels of a protein called fructose-bisphosphate aldolase A decreased. 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 of a body initially being submerged in pond water and then moved to a different location.
Conclusion: these proteins could be excellent biomarkers for helping establish time of death in waterlogged corpses. For future studies, Procopio and her colleagues hope to examine the effects of different temperatures on the bone proteomics of submerged corpses, among other variables, and ideally move to human bodies eventually, “because that’s what we need in the end in order to apply our findings to forensic case work,” she said. She is already collaborating with a couple of so-called “body farms” to that end, although the ongoing pandemic has put that work on hold.
DOI: Journal of Proteome Research, 2020. 10.1021/acs.jproteome.0c00060 (About DOIs).