الفهرس 
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Abstract
This study aimed to determine different causes of death in relation to postmortem interval through histopathological examination of the brain and lung tissues in addition to analysis of expression of miRNA-23b-3p and miRNA-381-3p in the same tissues using RT-PCR at intervals of 0, 12 and 24hrs postmortem.
This study was carried out in the Department of Forensic Medicine and Clinical Toxicology, Faculty of Medicine, Minia University from May 2023 to June 2023. The study included ninety adult albino rats, weighing between 200 and 250 grams. They were divided into three main groups (30 rats in each group) according to manner of death: control group (natural death), drowning group (drowning death) and electrocution group (electrocution death). Each group was subdivided into three subgroups (each contain 10 rats) according to PMI (0,12,24hrs).
The first group of rats were killed by cervical dislocation (control group), second group were drowned by submersion in fresh water basin till death (drowning group) and third group were electrocuted until death by a 220 V alternating current (electrocution group). The rats were stored at room temperature for the duration of the experiment.
This study strictly followed the guidelines for the care and use of laboratory animals according to Minia University Faculty of Medicine’s Ethical Committee. This study examined postmortem histological changes in brain and lung tissues from rats using H&E-stained sections. The results showed a gradual deterioration of these tissue structure with increasing time after death.
Brain sections obtained from rats of CG at 0hr PM, showed almost normal brain tissues with normal histological structures of neurons of cerebral cortex with mild vacuolation. At 12hrs PM there were moderate vacuolation of the brain stroma increasing to marked vacculation in the parenchyma at 24hrs PM.
As regard results of brain tissues in DG, there were progressively increasing brain parenchymal vacuolation from 0hr to 24hrs PM with appearane of pyknotic nuclei. Similar features were shown in EG but more prominent and severe in comparison to DG and CG.
Lung sections obtained from rats of CG at 0hr PM, showed almost normal architecture with normal bronchi, mild congestion and slight distention of alveoli. At 12hrs PM, mild distention of the alveoli, moderate dissolution of interstitial cells, and more congestion has appeared and progressed to marked distention of the alveoli and marked dissolution of interstitial cells at 24hrs PM. The histopathological changes in lung tissues progressively increased in DG and EC respectively.
The genetic analysis of miRNA-23b-3p levels expression revealed a statistically significant strong negative correlation with the PM intervals in DG and EG in both lung and brain tissues and a statistically significant fair and moderate negative correlation in CG in brain and lung tissues respectively.
While, the analysis of miRNA-381-3p levels showed a statistically significant strong positive correlation with the PM intervals in CG and DG. Also, there were a statistically significant moderate positive correlation in EG in both brain and lung tissues.
The simple linear regression analysis for miRNA-23b-3p levels with RT-PCR in brain tissues showed higher accuracy for estimation of PMI in electrocution group (R2=0.756) followed by drowning group (R2=0.569) and finally control group (R2=0.205). But, in lung tissues showed higher accuracy for estimation of time since death in electrocution group (R2=0.792) followed by drowning group (R2=0.709) and finally control group (R2=0.252).
The simple linear regression analysis for miR-381-3p levels with RT-PCR in brain tissues showed higher accuracy for estimation of PMI in drowning group (R2=0.665) followed by control group (R2=0.573) and finally electrocution group (R2=0.407), However, in lung tissues it showed higher accuracy for estimation of time since death in control group (R2=0.763) followed by drowning group (R2=0.581) and finally electrocution group (R2=0.370).
The following new equations were extracted for PMI estimation in different causes of death by; simple linear regression analysis} PMI =Constant+( B × independent variable) ±SEE {, where the independent variable is miR-23b-3p or miR-381-3p levels.
The findings of this study showed that postmortem histopathological alterations, as well as the expression of miRNA-23b-3p and miRNA-381-3p levels in all tissues investigated, are time and cause dependent. As a result, they may be utilized to determine cause of death and estimate the PMI as new good predictors and also anticipates the cause of death at different postmortem interval.