Extraction and Untargeted Analysis of Metabolome from Undemineralised Cortical Bone Matrix

Abstract

Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) untargeted
metabolomics has become the gold standard for the profiling of low-molecular-weight compounds.
Recently, this discipline has raised great interest in forensic sciences, especially in the field of toxicology
and for post-mortem interval estimation. The current study aims at evaluating three extraction
protocols and two LC-MS/MS assays run in both positive and negative mode to identify the most suitable method to conduct post-mortem metabolomic profiling of bone tissue. A fragment of the anterior tibia of a 82 years-old male sampled from a Human Taphonomy Facility was powdered via freeze-milling. The powdered sub-samples were extracted in five replicates per protocol. Methods tested were (I) a biphasic chloroform-methanol-water protocol (II) a single phase methanol-water protocol and (III) a single phase methanol-acetonitrile-water protocol. LC-MS/MS analyses were carried out via High Performance Liquid Chromatography, either on hydrophilic interaction (HILIC) or on reversed-phase (C18) columns in both positive and negative ionisation modes, coupled with a Q-TOF mass spectrometer. Results suggest that the highest consistency between replicates and quality control samples was obtained with the single phase extractions (i.e., methanol-acetonitrile-water), whilst the ideal combination of instrumental set up HILIC chromatography in positive ionisation mode and of C18 chromatography in negative ionisation mode. For the purpose of forensic investigations, a combination of a single phase extraction and the two aforementioned chromatographic and mass spectrometry modes could represent an ideal set up for obtaining bone metabolomic profiles from taphonomically altered bones.