MALDI-TOF MS as a Novel Tool for the Estimation of Postmortem Interval in Liver Tissue Samples

Chengzhi Li,Qinghua Zhang,Yijiu Chen,Yan Shi,Dong Ma,Kaifei Deng,Ping Huang,Ya Tuo,Zhengdong Li,Zhenyuan Wang,Xianyi Zhuo

doi:10.1038/s41598-017-05216-0

Abstract

Estimation of the postmortem interval (PMI) is a complicated task in forensic medicine, especially during homicide and unwitnessed death investigations. Many biological, chemical, and physical indicators can be used to determine the postmortem interval, but most are not accurate. Here, we present a novel matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method that can be used for the estimation of PMI using molecular images and multivariate analyses. In this study, we demonstrate that both rat and human liver tissues of various PMIs (0, 2, 4, and 6days) can be discriminated using MALDI imaging and principal component analysis (PCA). Using genetic algorithm (GA), supervised neural network (SNN), and quick classifier (QC) methods, we built 6 classification models, which showed high recognition capability and good cross-validation. The histological changes in all the samples at different time points were also consistent with the changes seen in MALDI imaging. Our work suggests that MALDI-TOF MS, along with multivariate analysis, can be used to determine intermediate PMIs.

Highlights

Postmortem interval (PMI) estimation is an important task in daily forensic casework
matrix-assisted laser desorption ionization (MALDI) imaging of liver samples from rats and humans
Precise estimation of the postmortem interval (PMI) has been difficult since the very beginning of forensic medicine

Summary

Introduction

Postmortem interval (PMI) estimation is an important task in daily forensic casework. The physical changes that occur after death, including the cooling of the body, rigor mortis, and the development of lividity, have long been recognized as early postmortem phenomena[1] These signs continue to be the main basis for estimating the PMI1. As a rat or human body decomposes, the relative signal intensities from different peptides or proteins within the internal organs will change. To assess this hypothesis, we measured rat and human liver samples at various time intervals after death (range = 0–144 hours) using MALDI-TOF MS on peptides and proteins, and used a profiling acquisition, imaging, and bioinformatics package for inspection and comparison of data sets

Methods

Results

Conclusion