Immunohistochemical cerebral cortex expression of aquaporin 4, aquaporin 5, aquaporin 9 Vasopressin and GFAP in saltwater drowning and freshwater drowning

Abstract Autopsy assessment of drowning deaths remains a challenging task for forensic pathologists, requiring a comprehensive multidisciplinary approach. Drowning is typically diagnosed by exclusion, relying on careful evaluation of autopsy, toxicological, and histological findings. However, definitive pathognomonic autopsy features remain elusive. In recent years, numerous immunohistochemical studies on drowning cases have yielded intriguing results. Yet, despite promising findings in the literature, no specific marker is currently employed in routine forensic practice to provide a definitive diagnosis. This study delves into the cerebral cortex expression of AQP4, AQP5, AQP9, AVP, and GFAP, aiming to: (1) identify novel markers potentially useful for drowning diagnosis; (2) explore different pathways in saltwater drowning (SWD) and freshwater drowning (FWD), which can help in understanding the pathophysiology. A retrospective analysis was conducted, selecting 10 cases of FWD (Lake Geneva) from the University Center of Legal Medicine, Lausanne, Geneva (Switzerland) and cases of SWD (Mediterranean Sea) from the Institute of Legal Medicine of Genoa (Italy). As a control group (CC), we included 10 cases of death by acute external bleeding. A strong expression of AQP4 was significantly ( p < 0.05) more evident in FWD cases compared to SWD and control cases. Our study findings suggest an activation of AQP4 in response to the osmotic stimulus and haemodilution that occur during FWD. These markers hold promise for differential diagnosis between freshwater and saltwater drowning. The identification of AQP4 as potential differential diagnostic markers for drowning represents a significant step forward in the forensic evaluation of these cases. Further research is warranted to validate these findings and establish their applicability in routine forensic practice.