Bone tissue (osseous tissue), which is also called bone in the uncountable sense of that word, is hard tissue, a type of specialized connective tissue.

Forensic anthropology is the blooming division which will the future era of investigation.

This branch deals with the application and techniques of anatomical structures.

Bones carry the evidence that helps to identify the person and can be used forensically. Bone proteome (protein) is the tool in solving the crime with the potential estimation PMI (Post Mortem Interval) , AAD( Age at Death).

However, the preservation of such proteins is highly dependent on intrinsic and extrinsic factors that can hinder the potential application of molecular techniques to forensic sciences.

Furthermore, several potential “stable” protein markers (i.e., proteins not affected by the burial environment) are identified for PMI and AAD estimation.

Overall, these results show that the two burial environments play a role in the differential preservation of noncollagenous proteins, confirming the potential of LC-MS/MS-based proteomics in forensic sciences.

This article gives an idea of bone proteome preservation and their use in investigation.

Bone

Bone is a metabolically active connective tissue that provides structural support, facilitates movement, and protects vital organs.

Depending upon species, age, and type of bone, bone cells represent up to 15 percent of the volume of bone; in mature bone in most higher animals, they usually represent only up to 5 percent.

The nonliving intercellular material of bone consists of an organic component called collagen with small amounts of proteinpolysaccharides, glycoaminoglycans (formerly known as mucopolysaccharides) chemically bound to protein and dispersed within and around the collagen fibre bundles, and an inorganic mineral component in the form of rod-shaped crystals.

What is Forensic Anthropology?

The Forensic anthropology is extensive and is increasing every day. It includes the collection preservation and analysis of human skeletal remains for identification and reconstruction of the events surrounding the death of an individual.

Many killers dump the dead bodies of their victims in remote sites, meaning that most often the police will have skeletal remains to aid in their investigation.

It is then left to the forensic anthropologist to use this evidence to shed some light on the case with his expertise.

Bone Proteome Forensic Identification

The study of proteomics applies to bones as the pieces are composed of approximately 70% of the inorganic phase, hydroxyapatite crystals, while 30% are the organic phase made up by proteins (predominantly collagenous proteins).

The proteins are vital to the formation of bones and their remodeling, while the hydroxyapatite crystals prevent proteins from degrading.

However, the interactions within the molecules existing in the bones are disrupted from the filtering of proteins from the burial environment.

Damages may occur in proteins due to the unstable reaction from the hydrolysis of peptide bonds, leaving little amounts of collagen to be present.

The changes in deamidation may provide more specifics into calculating decay for its dependency on time.

The rate of this non-enzymatic hydrolysis occurring in glutamine and asparagine amino acid residues are influenced by external conditions that may reveal the geological age of the bones. 

Through these biomolecule interactions in bone tissues, the rate at which protein decay may provide efficient time estimates during post-mortem.

Factors That Affect PMI and ADD

• Taphonomic changes are highly dependent on different environmental conditions (e.g., temperature, precipitation, humidity, soil composition).

• Among those, the burial modality (e.g., exposed, buried in the ground or in coffins, submerged in water) and the accessibility of the carcass to bacteria, insects, and scavengers play central roles in decomposition and its rate.

• There are also intrinsic biological factors that can affect post-mortem changes such as body size, age, and trauma.

• All of these variables must be considered when developing estimation methods for forensic purposes.

• One of the most commonly utilized methods for PMI estimation is the evaluation of the formation of adipocere.

Stages of Corpse Decomposition

• Rigor mortis appears in the body starting from top and going downwards. It is fully developed in about 12 hours in whole body. It persists for next 12 hours and afterwards disappears from whole body in next 12 hours following the same sequence.

• Decomposition starts around 24 hours after death comprising of putrefactive and autolytic changes.

• Marbling, colliquitive liquefaction and ultimately skeletonization occur after death upto 1 month.

• Depending upon environmental factors instead of decomposition the dead body may go for adipocere formation as well as mummification.

How is Proteomes used in Forensics?

The context of the current study, it is essential to summarize the events that lead to cadaveric decomposition.

Immediately after death, autolytic processes caused by the breakdown of cellular membranes result in the release of hydrolytic enzymes that lead to the digestion of the surrounding tissues.

The corpse’s environment is then rapidly converted from aerobic to fully anaerobic.

This change establishes the ideal conditions for anoxic bacteria from the gut, commonly referred to as endogenous bacteria or the thanatomicrobiome, to travel into the body and to proliferate rapidly.

This marks the beginning of the putrefactive stage, at ∼1h post-mortem, and continues throughout the next 48 h.

During this stage, bacteria transmigrate to the rest of the body via the blood vessels and reach the skeletal system within a day of death.

Reductive catalysis promoted by endogenous bacteria results in the bloating of the corpse, caused by the accumulation of gases in the inner body cavities.

When the accumulation of gases applies sufficient pressure on the soft tissues, the abdomen is ruptured, and internal tissues are exposed.

This situation offers an ideal environment for the colonization of the body by insects and by exogenous microbial communities present in the surrounding environment.

The decomposing body is a natural reservoir of nutrients that enhances the proliferation of exogenous communities, which start to replace the endogenous bacterial population. 

With the progression of the decomposition, specific bacterial species are attracted in a quite consistent way, regardless of the type of burial environment and condition (e.g., soil type, buried vs exposed).

For this reason, microbial succession has been studied by several authors as a means of estimating the PMI.

Despite the fact that it is well known that bacteria are the main drivers for bone bioerosion and the consequent protein decay, the origin (e.g., endogenous, or exogenous) of the microorganisms responsible for the degradation of biomolecules is not yet fully clarified.

Despite the fact that proteomics has been useful for successfully discriminating microbially versus nonmicrobially driven decomposition in an animal model,  the specific role that endogenous and exogenous microbes may have in bone biomolecules still has to be elucidated, especially considering the lack of specific studies on human cadavers.

The analysis can be done with vibrational spectroscopy, fluorescence spectroscopy,  mass spectrometry, LC-MS etc. 

Conclusion

This study helps in identification of PMI and ADD of the buried corpse.

Preservation of the bone proteome can be useful for the forensic purpose.

The cons of this is that the condition of the environment varies  according to the certain environment. However, this field will led to the opening of new blooming era of investigation.

References:

1. Insights into the Differential Preservation of Bone Proteomes in Inhumed and Entombed Cadavers from Italian Forensic Caseworks - Andrea Bonicelli, Aldo Di Nunzio, Ciro Di Nunzio, and Noemi Procopio (March 22, 2022).

2. Protein-based forensic identification using genetically variant peptides in human bone - Katelyn Elizabeth Mason1, Deon Anex2, Todd Grey3, Bradley Hart2, Glendon Parker4