Gold nanoparticles ingested by oyster larvae are internalized by cells through an alimentary endocytic pathway

The biological fate of nanoparticles (NPs) taken up by organisms from their environment is a crucial issue for assessing ecological hazard. Despite its importance, it has scarcely been addressed due to the technical difficulties of doing so in whole organism <i>in vivo</i> studies. Here, by using transmission electron microscopy and energy dispersive X-ray spectroscopy (TEM-EDS), we describe the key aspects that characterize the interaction between an aquatic organism of global ecological and economic importance, the early larval stage of the Japanese oyster (<i>Crassostrea gigas</i>), and model gold NPs dispersed in their environment. The small size of the model organism allowed for a high-throughput visualization of the subcellular distribution of NPs, providing a comprehensive and robust picture of the route of uptake, mechanism of cellular permeation, and the pathways of clearance counterbalancing bioaccumulation. We show that NPs are ingested by larvae and penetrate cells through alimentary pinocytic/phagocytic mechanisms. They undergo intracellular digestion and storage inside residual bodies, before excretion with feces or translocation to phagocytic coelomocytes of the visceral cavity for potential extrusion or further translocation. Our mechanistically-supported findings highlight the potential of oyster larvae and other organisms which feature intracellular digestion processes to be exposed to man-made NPs and thus any risks associated with their inherent toxicity.

生物体从环境中摄取的纳米颗粒（nanoparticles, NPs）的生物学归趋，是评估生态危害的核心议题。尽管该议题意义重大，但由于整体生物体的体内研究存在技术难题，相关研究至今仍较为匮乏。本研究借助透射电子显微镜与能量色散X射线能谱仪（Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy, TEM-EDS），针对兼具全球生态与经济价值的水生生物——日本牡蛎（Crassostrea gigas）的早期幼体阶段，与环境中分散的模型金纳米颗粒之间的相互作用，阐述其关键特征。该模式生物体型微小，可实现纳米颗粒亚细胞分布的高通量可视化，从而全面且可靠地呈现纳米颗粒的摄取路径、细胞渗透机制，以及抵消生物累积的清除通路。本研究证实，纳米颗粒可被幼体摄取，并通过消化道内的胞饮/吞噬机制穿透细胞。纳米颗粒会经历细胞内消化并储存于残余体中，随后随粪便排出，或是转移至内脏腔的吞噬性体腔细胞，以实现潜在的外排或进一步转运。本研究基于机制层面的实验发现表明，牡蛎幼体及其他具备细胞内消化过程的生物，均存在接触人工合成纳米颗粒的可能性，进而可能面临其固有毒性带来的相关风险。