The Study On The Expression Of Pulmonary Surfactant-associated Protein A And Aquaporin-5of Drowned Rat

【Backgroundandaims】Identificationofbodies recovered out ofwater is a major part inforensic investigation. The key question is to distinguish whether the victim died due to―true‖drowning. In forensic practice, the diagnosis of drowning usually relies onpostmortem phenomena and laboratory tests. the plume of froth and aqueous emphysemacan be considered as valuable information，but these signs are non-specific. In present,diatom test regarded as golden standard for drowning, but the pitfall is the threat ofcontamination, heavy workload, and low sensitivity. Therefore, seeking for valuableindicator for drowning is still a major theme in forensic study.It has always been a hotspot for the research on drowning standard among theforensic field, but most results remain not progressive. Animal experiments have confirmedthat surfactant-associated protein A (SP-A) and aquaporin-5play an important role inmaintaining lung homeostasis. SP-A can decrease pulmonary surface tension, preventingfrom over-scale extension or atrophy. Forensic research on SP-A almost focus onretrospective studies, lacking of relevant animal experiment confirmation. AQP-5plays animportant role in clearing excess liquid in lung. The foreign scholars found decreasedAQP-5gene expression in drowning through animal experiment which was established bywater administration intratracheally after anesthesia. Because the animal model can not reflect the actual drowning process, it still need more improved animal model.In addition, hemodilution can cause increased organ weight in drowning process, sosome scholars suggested that organ weight can be used as an indicator for identification ofdrowning. Hamann S proposed a concept called―drowning index‖, which is the ratiobetween the total weight of the lungs and pleural effusion and the weight of spleen, but thisconcept has not been universally accepted.Therefore, the purpose of our study is to study changes in SP-A and AQP-5proteinexpression in early stage of drowning through the establishment of an animal model, and toexamine whether these two proteins have value in identification of drowning, combiningwith the pathological changes in lung. At the same time, we will discuss about the role oforgan coefficient and relation between wet-to-dry ratio of lung tissue and AQP-5proteinexpression in the investigation of drowning.【Materials and Methods】21S-D rats were selected and divided randomly into threegroups, including freshwater drown group, postmortem immersion group and control group.The freshwater drown group: the rats were killed by drowning in freshwater. Thepostmortem immersion group: the rats were killed by cervical dislocation followed byimmersion. The control group: the rats were killed by cervical dislocation. The lung, liver,spleen and kidney were removed to measure organ coefficient and wet-to-dry ratio of lung.Some lungs were taken to perform histological analyses, immunohistolochemistry andwestern-blotting of SP-A and AQP-5were examined.【Result】(1) The result revealed that lung coefficient, liver coefficient and wet-to-dry ratio oflung in the freshwater drowned group were significantly larger than other two groups (P＜0.01). Kidney coefficient and spleen coefficient were not different significantly amongthree groups (P＞0.05).(2) Lung tissue of freshwater drowned group had more sever emphysema than othergroups and all groups had mild pulmonary edema. (3) The expression of SP-A were located in interface of intra-alveolar epithelia andbronchial epithelial of three groups. In freshwater drowned group and control group,macrophage have positive expression of SP-A. The degree of SP-A expression in thefreshwater group was more lower than other groups, especially in emphysema areas.(4) The expression of AQP-5could be detected in the apical membrane of alveolarepithelial cells, bronchial epithelial cells and vascular endothelial cells in all groups. Thedegree of AQP-5expression in freshwater group was slightly lower than other groups.(5) The protein expression of SP-A and AQP-5in the freshwater drowned group weresignificantly lower than other groups（P＜0.01）.There were no significant differencebetween postmortem immersion group and control group（P＞0.05）.【Conclusion】(1) There is severe pulmonary emphysema in drowned group.the weight of lung andliver were increased in freshwater drowned group. Lung water content is relative with lungweight change.(2) The protein expression of SP-A and AQP-5in the freshwater drowned group weresignificantly decreased. The mechanism need more research.