Novel Approaches for Postmortem Interval Estimation: Biochemical, Histopathological, Immunohistochemical, and Comet Assay Study in Heart Tissue.

Background: The postmortem interval (PMI) is a commonly researched issue. The significance of getting a precise PMI in medicolegal death investigations is vital because it helps in making decisions about suspects, identifying the time of assault versus time of death and formulation of conclusions regarding suspects. Aim: Using a time-dependent experiment in the heart of an adult male albino rat model; the study attempted to estimate postmortem interval using certain biochemical parameters, histopathological changes, immunohistochemical variations, and comet assay results. Materials and methods: In this in-vivo experimental study, thirty rats were divided into five groups at the 0, 6, 12, 24, and 48-hour postmortem points. Hearts were removed from each group, and oxidative stress biomarkers (CAT, GSH, NO, and MDA) were assessed. Additionally, histopathological analysis using hematoxylin and eosin (H&E) stain, immunohistochemical labelling of Bcl-2, and comet assay was used to measure the rate of DNA degradation. Results: In the cardiac tissue of all rats with increasing postmortem interval, there was a significant increase in MDA and NO levels. At the same time, there was a significant decrease in CAT and GSH levels. The histopathological findings revealed normal histological structures in the 0 and 6 hrs postmortem groups. After 12 hrs, there was slight endomysium oedema and after 24 hrs increased interstitial oedema and a mild number of mononuclear cell infiltrates with vacuolated sarcoplasm of some myofibers were found. Moreover, in the 48 hrs postmortem group, more interstitial oedema, fragmented myofibers, and coagulation necrosis of myofibers were found. Immunohistochemical staining of Bcl-2 showed reduced expression with increased postmortem interval with non-noticeable expressed cells in the 48 hrs postmortem group. Also, comet assay revealed a significant increase in Tail length, Tail DNA % and Tail moment mean values with increasing PMI.