探討擱淺鯨豚體內銀沉積/分布與組織病變程度及傳染性疾病關聯性

Abstract

銀及奈米銀近年被廣泛應用於各類生活用品、醫療器材和電子產品，進而加劇環境中銀汙染的程度。鯨豚作為海洋高階掠食者可能因食物鏈生物的放大作用，而使其體內累積高量的銀。本研究回溯性調查101隻擱淺鯨豚，除分析銀在鯨豚體內的組織分佈外，也針對銀濃度和某些病原感染是否有關進行評估，以了解銀對鯨豚健康造成的不良影響。本研究應用金屬自顯影技術（Autometallography, AMG）標示銀在臟器組織的分布，擱淺鯨豚肝臟銀濃度是以鯨豚組織銀測定法（Cetacean histological Ag assay, CHAA）估計，此方法為AMG於福馬林固定石蠟包埋（Formalin-fixed paraffin-embedded, FFPE）組織所建立的推估模組。在銀濃度和病原相關性的評估，以組織病理學評估擱淺鯨豚病灶狀況，同時以即時聚合酶鏈鎖反應（real-time PCR）檢測鯨豚麻疹病毒、布氏桿菌與弓蟲，評估這些病原在台灣擱淺鯨豚的感染情形。結果顯示在肝臟銀濃度高的個體，神經細胞、神經膠質細胞、肺細胞、睪丸萊狄氏細胞、腎上腺皮質細胞和嗜鉻細胞中存有AMG陽性訊號。相較之前的研究，鯨豚AMG陽性訊號細胞的分布模式與實驗動物囓齒類動物的陽性細胞分布模式不同，顯示鯨豚可能有不同的銀代謝途徑。高銀濃度組別具病灶的鯨豚比例顯著高於低銀濃度組別，顯示銀汙染對於鯨豚健康狀況可能有明顯的負面影響。銀的環境污染不容忽視，其對生物造成的危害需要進一步的研究，特別是奈米銀免疫毒性之研究。另一方面，鯨豚麻疹病毒、布氏桿菌與弓蟲皆在本次研究被檢出，顯示銀及傳染病原對於鯨豚健康的風險需要謹慎評估。

Silver (Ag), such as silver nanoparticles (AgNPs), has been used in varieties of commercial products and may be eventually released into environment. Cetaceans as apex predator of ocean have an evidence of relatively high level of Ag deposition in their bodies through food chain. Therefore, the present study investigated the systemic Ag distribution and its correlation with the lesions or infectious pathogens in stranded cetaceans. The study was to perform comprehensive evaluation of the negative health effects caused by Ag deposition in 101 stranded cetaceans around Taiwanese coast. The Ag deposition in cetaceans was demonstrated by autometallography (AMG). The Ag concentrations of the liver tissue from stranded cetaceans were estimated by cetacean histological Ag assay (CHAA), a regression model developed by using AMG on formalin-fixed paraffin-embedded (FFPE) tissues. For evaluating the correlation between Ag concentration and the lesions or disease status, each individual was assessed by histopathology. In addition, AMG positive signals were frequently found in neuron, glial cells, pneumocytes, Leydig cells, adrenocortical cells and pheochromocytes of animals having higher Ag concentration in liver. Comparing with previous studies, the patterns of AMG positive signals in cetacean are different from those found in laboratory rodents. It suggests that cetaceans may have different silver metabolic pathway. High Ag concentration group of stranded cetaceans have higher frequency of having lesions in visceral organs than low Ag concentration group. The results suggest that environmental pollution, especially the emerging heavy metal, Ag, should not be overlooked. Simultaneously, emerging infectious pathogens of cetaceans, including cetacean morbillivirus, Brucella spp. and Toxoplasma gondii, were detected by real-time PCR. All of three pathogens investigated were detected in the present study. The potential risk of the pathogens to cetaceans and human under the background of silver pollution should be seriously concerned. Hence, further investigations, such as in vitro immunotoxic studies of Ag and/or AgNPs, are warranted.