Profiling of RNA Degradation for Estimation of Post Morterm Interval

Fernanda Sampaio-Silva,Ricardo Jorge Dinis-Oliveira,Félix Carvalho,Ricardo Silvestre,Teresa Magalhães,Manfred Kayser

doi:10.1371/journal.pone.0056507

Abstract

An estimation of the post mortem interval (PMI) is frequently touted as the Holy Grail of forensic pathology. During the first hours after death, PMI estimation is dependent on the rate of physical observable modifications including algor, rigor and livor mortis. However, these assessment methods are still largely unreliable and inaccurate. Alternatively, RNA has been put forward as a valuable tool in forensic pathology, namely to identify body fluids, estimate the age of biological stains and to study the mechanism of death. Nevertheless, the attempts to find correlation between RNA degradation and PMI have been unsuccessful. The aim of this study was to characterize the RNA degradation in different post mortem tissues in order to develop a mathematical model that can be used as coadjuvant method for a more accurate PMI determination. For this purpose, we performed an eleven-hour kinetic analysis of total extracted RNA from murine's visceral and muscle tissues. The degradation profile of total RNA and the expression levels of several reference genes were analyzed by quantitative real-time PCR. A quantitative analysis of normalized transcript levels on the former tissues allowed the identification of four quadriceps muscle genes (Actb, Gapdh, Ppia and Srp72) that were found to significantly correlate with PMI. These results allowed us to develop a mathematical model with predictive value for estimation of the PMI (confidence interval of ±51 minutes at 95%) that can become an important complementary tool for traditional methods.

Highlights

The post mortem interval (PMI) describes the period of time elapsed from the time of death
No significant differences were observed in the RNA quality indicator (RQI) levels during the first 4 hours post mortem, a time dependent decrease in RNA integrity was observed until 11 hours post mortem
A significant correlation was found between total RNA isolated from the heart, femoral quadriceps or liver samples and the PMI

Summary

Introduction

The post mortem interval (PMI) describes the period of time elapsed from the time of death. Forensic pathologists commonly assess physical (algor mortis, livor mortis), physicochemical (rigor mortis), biochemical (electrolyte concentration, enzyme activity), microbiological (decomposition), entomological and botanical processes [2,3] Most of these methods for the estimation of PMI remain relatively inaccurate, and even when applied to the very early post mortem period are of limited practical relevance [1,4]. Novel methods such as flow cytometry, capillary zone electrophoresis, magnetic resonance spectroscopy and immunohistochemistry have been proposed to assess post mortem changes, attempting to extrapolate the time since death [5]. These approaches do not make on their own death time estimation more precise, the combination of different methods has been proposed to narrow down the margins of error associated to individual methods [1,4,5]

Objectives

Methods

Results

Discussion

Conclusion