Intrapulmonary aquaporin-5 expression as a possible biomarker for discriminating smothering and choking from sudden cardiac death: A pilot study

The diagnosis of mechanical asphyxia as a cause of death, especially smothering and choking lacking evident injury, is one of the most difficult tasks in forensic pathology. The present study investigated the intrapulmonary expressions of aquaporins (AQPs; AQP-1 and AQP-5), as markers of water homeostasis, in forensic autopsy cases (total n = 64, within 48 h postmortem) of mechanical asphyxiation due to neck compression (strangulation, n = 24), including manual/ligature strangulation (n = 12) and atypical hanging (n = 12), smothering (n = 7) and choking (n = 8), compared with sudden cardiac death (n = 14) and acute brain injury (n = 11). Quantification of mRNA using a Taqman real-time PCR assay system demonstrated suppressed expression of AQP-5, but not AQP-1, in smothering and choking, compared with that in strangulation as well as sudden cardiac death and acute brain injury death. Immunostaining of AQP-5 was weakly detected in a linear pattern in the type I alveolar epithelial cells in smothering and choking cases, while cardiac and brain injury death showed marked positivity, and most strangulation cases had AQP-5-positive granular aggregates and fragments in intra-alveolar spaces. These observations indicate a partial difference in pulmonary molecular pathology among these causes of death, suggesting a procedure for possible discrimination of smothering and choking from sudden cardiac death.