MRC/University of Edinburgh, Centre for Inflammation Research, Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh, EH16 4TJ, UK.
Part Fibre Toxicol. 2012 Dec 2;9:47. doi: 10.1186/1743-8977-9-47.
The objective of this study was to examine the threshold fibre length for the onset of pulmonary inflammation after aspiration exposure in mice to four different lengths of silver nanowires (AgNW). We further examined the effect of fibre length on macrophage locomotion in an in vitro wound healing assay. We hypothesised that exposure to longer fibres causes both increased inflammation and restricted mobility leading to impaired clearance of long fibres from the lower respiratory tract to the mucociliary escalator in vivo.
Nine week old female C57BL/6 strain mice were exposed to AgNW and controls via pharyngeal aspiration. The dose used in this study was equalised to fibre number and based on 50 μg/ mouse for AgNW(14). To examine macrophage migration in vitro a wound healing assay was used. An artificial wound was created in a confluent layer of bone marrow derived macrophages by scraping with a pipette tip and the number of cells migrating into the wound was monitored microscopically. The dose was equalised for fibre number and based on 2.5 μg/cm(2) for AgNW(14).
Aspiration of AgNW resulted in a length dependent inflammatory response in the lungs with threshold at a fibre length of 14 μm. Shorter fibres including 3, 5 and 10 μm elicited no significant inflammation. Macrophage locomotion was also restricted in a length dependent manner whereby AgNW in the length of ≥5 μm resulted in impaired motility in the wound closure assay.
We demonstrated a 14 μm cut-off length for fibre-induced pulmonary inflammation after aspiration exposure and an in vitro threshold for inhibition of macrophage locomotion of 5 μm. We previously reported a threshold length of 5 μm for fibre-induced pleural inflammation. This difference in pulmonary and pleural fibre- induced inflammation may be explained by differences in clearance mechanism of deposited fibres from the airspaces compared to the pleural space. Inhibition of macrophage migration at long fibre lengths could account for their well-documented long term retention in the lungs compared to short fibres. Knowledge of the threshold length for acute pulmonary inflammation contributes to hazard identification of nanofibres.
本研究的目的是检测在四种不同长度的银纳米线（AgNW）吸入暴露后，小鼠肺部炎症起始的纤维长度阈值。我们进一步研究了纤维长度对体外伤口愈合试验中巨噬细胞迁移的影响。我们假设，较长纤维的暴露会导致炎症增加和运动受限，从而导致下呼吸道中较长纤维清除到黏液纤毛清除器的能力受损。
9 周龄雌性 C57BL/6 品系小鼠通过咽吸入暴露于 AgNW 和对照物。本研究中的剂量是根据纤维数量来平衡的，对于 AgNW（14），剂量为 50μg/只。为了研究巨噬细胞在体外的迁移，我们使用了伤口愈合试验。通过用移液管尖端刮擦，在骨髓来源的巨噬细胞的汇合层中创建人工伤口，并通过显微镜监测细胞迁移到伤口中的数量。剂量是根据纤维数量来平衡的，对于 AgNW（14），剂量为 2.5μg/cm（2）。
AgNW 吸入导致肺部炎症呈长度依赖性，纤维长度阈值为 14μm。较短的纤维（3、5 和 10μm）不会引起明显的炎症。巨噬细胞的迁移也受到长度的限制，在长度≥5μm 的 AgNW 中，伤口闭合试验中的运动能力受损。
我们证明了吸入暴露后纤维引起的肺部炎症的 14μm 截止长度，以及体外抑制巨噬细胞迁移的 5μm 阈值。我们之前报道了纤维引起的胸膜炎症的 5μm 阈值长度。肺部和胸膜纤维引起的炎症的这种差异可能是由于沉积纤维从气腔清除与从胸膜空间清除的机制不同所致。在长纤维长度下抑制巨噬细胞迁移可能解释了它们与短纤维相比在肺部的长期保留。急性肺炎症的阈值长度有助于纳米纤维的危害识别。
