Uptake and molecular impact of aluminum-containing nanomaterials on human intestinal caco-2 cells

Aluminum (Al) is one of the most common elements in the earth crust and increasingly used in food, consumer products and packaging. Its hazard potential for humans is still not completely understood. Besides the metallic form, Al also exists as mineral, including the insoluble oxide, and in soluble ionic forms. Representatives of these three species, namely a metallic and an oxidic species of Al-containing nanoparticles and soluble aluminum chloride, were applied to human intestinal cell lines as models for the intestinal barrier. We characterized physicochemical particle parameters, protein corona composition, ion release and cellular uptake. Different <i>in vitro</i> assays were performed to determine potential effects and molecular modes of action related to the individual chemical species. For a deeper insight into signaling processes, microarray transcriptome analyses followed by bioinformatic data analysis were employed. The particulate Al species showed different solubility in biological media. Metallic Al nanoparticles released more ions than Al₂O₃ nanoparticles, while AlCl₃ showed a mixture of dissolved and agglomerated particulate entities in biological media. The protein corona composition differed between both nanoparticle species. Cellular uptake, investigated in transwell experiments, occurred predominantly in particulate form, whereas ionic Al was not taken up by intestinal cell lines. Transcellular transport was not observed. None of the Al species showed cytotoxic effects up to 200 µg Al/mL. The transcriptome analysis indicated mainly effects on oxidative stress pathways, xenobiotic metabolism and metal homeostasis. We have shown for the first time that intestinal cellular uptake of Al occurs preferably in the particle form, while toxicological effects appear to be ion-related.

铝（Al）是地壳中最常见的元素之一，如今在食品、消费品及包装材料中的应用日益广泛，但其对人类的潜在危害仍未完全阐明。除金属形态外，铝还以矿物形式存在（包括难溶的氧化物）以及可溶性离子形态。选取这三类形态的代表性物质——含铝纳米颗粒的金属态、氧化态物种，以及可溶性氯化铝——作用于人肠上皮细胞系，以模拟肠道屏障环境。我们对其理化颗粒参数、蛋白冠（protein corona）组成、离子释放情况及细胞摄取行为进行了表征。开展了多组体外（in vitro）实验，以明确与各化学形态相关的潜在生物学效应及分子作用模式。为深入解析信号通路过程，本研究采用了微阵列转录组分析结合生物信息学数据分析的方法。颗粒态铝物种在生物介质中的溶解度存在显著差异：金属铝纳米颗粒的离子释放量高于三氧化二铝（Al₂O₃）纳米颗粒，而氯化铝（AlCl₃）在生物介质中则同时存在溶解态与团聚态颗粒实体。两种纳米颗粒的蛋白冠组成存在显著差异。通过Transwell实验开展的细胞摄取研究显示，细胞对铝的摄取主要以颗粒形式发生，而离子态铝并未被肠上皮细胞系摄取，且未检测到跨细胞转运现象。在铝浓度最高达200 µg Al/mL的条件下，所有铝形态均未表现出细胞毒性。转录组分析结果显示，铝主要影响氧化应激通路、异生物质代谢及金属稳态相关生物学过程。本研究首次证实：肠道细胞对铝的摄取优选颗粒形态，而其毒理效应则与离子形态密切相关。