The casts of the corpses of a group of human victims of the 79 AD eruption of Vesuvius, found in the so-called “Garden of the Fugitives” in Pompeii. Credit: Lance Vortex © 2000
Working with the remains of victims of Mt. Vesuvius in Pompeii and Herculaneum, Italian researchers have conducted the first proteomic analyses of bones exposed to eruptive conditions. While comparison between the two sets of victims yielded surprising data, the researchers say the results are an “encouraging” step toward potential biomarkers that could impact future development of forensic bone proteomics.
Burned skeletal remains are, unfortunately, a somewhat frequent type of evidence in forensic casework, especially in scenarios that require disaster victim identification.
“Bones can be considered time capsules, and individual history can be imprinted on their organic content,” the authors explain in their paper, published today in Scientific Reports.
These bone proteins can yield a lot of information about how people lived and died. Unlike DNA, proteins have greater longevity and—as this study shows—are not nearly as vulnerable to extreme heat.
The Pompeii and Herculaneum sites together are ideal for anthropological and forensic study. Remains are plentiful, well-preserved and the victims lives and deaths reflect one another—with one crucial difference, according to the results of this study by Georgia Ntasi and colleagues at the University of Naples Federico II, University of Salerno and University of Copenhagen.
In Herculaneum, victims were killed by a pyroclastic surge of approximately 500˚C, which caused the immediate destruction of soft tissue. This was followed by a period of rapid cooling and the burial of the victims in ash. These burials were then preserved in the waterlogged conditions of the seaside town.
Conversely, in Pompeii, the surge temperature only reached about 300˚C—hot enough to instantly kill but not hot enough to cause the immediate loss of soft tissue. Therefore, the victims’ corpses were preserved intact inside the ash deposit after its rapid cooling, allowing soft tissues to slowly decompose over time. The burial conditions in Pompeii were also less wet compared with Herculaneum.
While the bone proteins of all victims showed expected characteristics like extensive deamidation, backbone cleavage and oxidative chemical modifications, bone proteins of Herculaneum victims were better preserved than victims from Pompeii, despite the substantial temperature differences. In fact, the scientists recorded an almost complete absence of non-collagenous proteins (NCPs) in the bones of Pompeii victims compared with Herculaneum victims.
In five of the seven Pompeii bones samples, collagen chains were the only proteins to be detected, and in the other two samples, beside collagen, only chondroadherin and biglycan were identified.
“The lower NCPs content, the higher deamidation level and, in general, the higher extent of modification of collagen in the bones from Pompeii in respect to the bone samples from Herculaneum, demonstrate a more degraded state possibly as a result of the slower decomposition of soft tissue,” write the researchers.
Only proteins stabilized by the binding to collagen or to the inorganic component of bones survived in Herculaneum. Interestingly, the researchers detected Vitronectin in six of the seven samples, just as frequently as biglycan. Vitronectin is an abundant multifunctional glycoprotein found in serum, extracellular matrix, and bone, involved in various physiological processes such as cell attachment, spreading, and migration, which interacts also with collagen type.
Ultimately, the researchers conclude perseveration comes down to environment. At Herculaneum, after the rapid vanishing of soft tissue, the permanently waterlogged ash bed in which the skeleton was buried must have inhibited microbial chemical modifications, allowing the long-term survival of organic matter. This team believes this environment explains the good preservation of proteins, as well as the survival of collagen and DNA they detected throughout their study.
The researchers noted that while forensic proteomics has been used to estimate age-at-death, post-mortem interval of skeletal tissue and to distinguish individuals, its applications have been limited thus far. They believe their study results could change this in the future.
“Our results suggest that additional information can be found by expanding the set of modifications of proteins to look for, unveiling more details about taphonomic agents that may affect bone death processes, leading to potential biomarkers for medicolegal investigations that can provide information about environmental parameters at the time of death,” the study authors conclude.