Deparment of Preventive Medicine College of Medicine, Chung-Ang University, Seoul, South Korea.
Department of Nanofusion Technology, Hoseo University, Asan, South Korea.
Part Fibre Toxicol. 2019 Jan 7;16(1):2. doi: 10.1186/s12989-018-0286-9.
Information on particle deposition, retention and clearance are important for the evaluation of the risk of inhaled nanomaterials to human health. Recent revised OECD inhalation toxicity test guidelines require to evaluate the lung burden of nanomaterials after rodent subacute and subchronic inhalation exposure (OECD 412, OECD 413). These revised test guidelines require additional post-exposure observation (PEO) periods that include lung burden measurements that can inform on lung clearance behavior and translocation. The latter being particularly relevant when the testing chemical is a solid poorly soluble nanomaterial. Therefore, in the spirit of 3 R's, we investigated whether measurement of retained lung burden of inhaled nanoparticles (NPs) in individual lung lobes is sufficient to determine retained lung burden in the total lung. If it is possible to use only one lobe, it will reduce animal use and maximize the number of endpoints evaluated.
To achieve these goals, rats were exposed nose-only for 1 or 5 days (6 h/day) to an aerosol of 20 nm well-dispersed silver nanoparticles (AgNPs), which is the desired particle diameter resulting in maximum deposition in the pulmonary region when inhaled as singlets. After exposure, the five lung lobes were separated and silver concentration was measured using inductively coupled plasma-mass spectrophotometer (ICP-MS). The results showed that the retention of deposited silver nanoparticle in the different lung lobes did not show any statistically significant difference among lung lobes in terms of silver mass per gram lung lobe. This novel finding of evenness of retention/deposition of inhaled 20 nm NPs in rats for all five lobes in terms of mass per unit tissue weight contrasts with earlier studies reporting greater apical lobe deposition of inhaled micro-particles in rodents. The difference is most likely due to preferred and efficient deposition of inhaled NPs by diffusion vs. additional deposition by sedimentation and impaction for micron-sized particles.
AgNPs following acute inhalation by rats are evenly retained in each lung lobe in terms of mass per unit lung tissue weight. Accordingly, we suggest sampling any of the rat lung lobes for lung burden analysis can be used to determine deposited or retained total lung burden after short-term inhalation of NPs and using the other lobes for collecting and analyzing bronchoalveolar lavage fluid (BALF) and for histopathological analysis. Therefore, by combining lung burden measurement, histopathological tissue preparation, and BALF assay in the same rat will reduce the number of animals used and maximize the number of endpoints measured.
了解颗粒的沉积、滞留和清除对于评估吸入纳米材料对人类健康的风险非常重要。最近修订的 OECD 吸入毒性测试指南要求评估啮齿动物亚急性和亚慢性吸入暴露后纳米材料的肺部负担（OECD 412、OECD 413）。这些修订后的测试指南需要额外的暴露后观察（PEO）期，包括肺部负担测量，以告知肺部清除行为和转移。当测试化学物质是一种固体、难溶性纳米材料时，后者尤为重要。因此，本着 3R 的精神，我们研究了测量吸入纳米颗粒（NPs）在单个肺叶中的滞留肺部负担是否足以确定整个肺部的滞留肺部负担。如果仅使用一个肺叶就可以实现，那么这将减少动物的使用，并最大限度地增加评估的终点数量。
为了实现这些目标，大鼠仅通过鼻腔暴露于 20nm 分散良好的银纳米颗粒（AgNPs）气溶胶中 1 或 5 天（每天 6 小时），这是吸入时单个颗粒最大沉积的理想粒径。暴露后，将五个肺叶分开，并使用电感耦合等离子体质谱仪（ICP-MS）测量银浓度。结果表明，在银质量/克肺叶方面，不同肺叶之间沉积的银纳米颗粒的保留没有任何统计学上的显著差异。这一新颖的发现表明，在所有五个肺叶中，以单位组织重量计，吸入的 20nm NPs 的保留/沉积均匀性，与先前报告的吸入微颗粒在啮齿动物中顶叶沉积较多的研究结果形成对比。这种差异很可能是由于吸入 NPs 优先和有效地通过扩散沉积，而对于微米大小的颗粒则通过沉降和冲击进一步沉积。
大鼠急性吸入 AgNPs 后，以单位肺组织重量计，每个肺叶中的质量均匀保留。因此，我们建议可以使用任何一个大鼠肺叶进行肺部负担分析，以确定在短时间吸入 NPs 后沉积或保留的总肺部负担，并用其他肺叶收集和分析支气管肺泡灌洗液（BALF）并进行组织病理学分析。因此，在同一只大鼠中结合肺部负担测量、组织病理学准备和 BALF 测定，将减少使用的动物数量，并最大限度地增加测量的终点数量。
