Norwegian Institute of Public Health, Division of Environmental Medicine, Oslo, Norway.
Part Fibre Toxicol. 2012 Aug 10;9:32. doi: 10.1186/1743-8977-9-32.
Respirable crystalline silica (silicon dioxide; SiO₂, quartz) particles are known to induce chronic inflammation and lung disease upon long-term inhalation, whereas non-crystalline (amorphous) SiO₂ particles in the submicrometre range are regarded as less harmful. Several reports have demonstrated that crystalline, but also non-crystalline silica particles induce IL-1β release from macrophages via the NALP3-inflammasome complex (caspase-1, ASC and NALP3) in the presence of lipopolysaccharide (LPS) from bacteria. Our aim was to study the potential of different non-crystalline SiO₂ particles from the nano- to submicro-sized range to activate IL-1β responses in LPS-primed RAW264.7 macrophages and primary rat lung macrophages. The role of the NALP3-inflammasome and up-stream mechanisms was further explored in RAW264.7 cells.
In the present study, we have shown that 6 h exposure to non-crystalline SiO₂ particles in nano- (SiNPs, 5-20 nm, 50 nm) and submicro-sizes induced strong IL-1β responses in LPS-primed mouse macrophages (RAW264.7) and primary rat lung macrophages. The primary lung macrophages were more sensitive to Si-exposure than the RAW-macrophages, and responded more strongly. In the lung macrophages, crystalline silica (MinUsil 5) induced IL-1β release more potently than the non-crystalline Si50 and Si500, when adjusted to surface area. This difference was much less pronounced versus fumed SiNPs. The caspase-1 inhibitor zYVAD and RNA silencing of the NALP3 receptor reduced the particle-induced IL-1β release in the RAW264.7 macrophages. Furthermore, inhibitors of phagocytosis, endosomal acidification, and cathepsin B activity reduced the IL-1β responses to the different particles to a similar extent.
In conclusion, non-crystalline silica particles in the nano- and submicro-size ranges seemed to induce IL-1β release from LPS-primed RAW264.7 macrophages via similar mechanisms as crystalline silica, involving particle uptake, phagosomal leakage and activation of the NALP3 inflammasome. Notably, rat primary lung macrophages were more sensitive with respect to silica-induced IL-1β release. The differential response patterns obtained suggest that silica-induced IL-1β responses not only depend on the particle surface area, but on factors and/or mechanisms such as particle reactivity or particle uptake. These findings may suggest that bacterial infection via LPS may augment acute inflammatory effects of non-crystalline as well as crystalline silica particles.
已知可吸入结晶二氧化硅（硅二氧化物；SiO₂，石英）颗粒在长期吸入后会引起慢性炎症和肺部疾病，而亚微米范围内的非结晶（无定形）SiO₂颗粒则被认为危害较小。有几项报告表明，结晶二氧化硅颗粒，甚至非结晶二氧化硅颗粒，在细菌脂多糖（LPS）存在的情况下，通过 NALP3-炎症小体复合物（半胱天冬酶-1、ASC 和 NALP3）从巨噬细胞中诱导释放白细胞介素-1β（IL-1β）。我们的目的是研究不同纳米至亚微米大小的非结晶 SiO₂颗粒在 LPS 预刺激的 RAW264.7 巨噬细胞和原代大鼠肺巨噬细胞中激活 IL-1β反应的潜力。进一步在 RAW264.7 细胞中探索了 NALP3-炎症小体和上游机制的作用。
在本研究中，我们表明，6 小时暴露于纳米（SiNPs，5-20nm，50nm）和亚微米大小的非结晶 SiO₂颗粒会在 LPS 预刺激的小鼠巨噬细胞（RAW264.7）和原代大鼠肺巨噬细胞中诱导强烈的 IL-1β反应。原代肺巨噬细胞比 RAW-巨噬细胞对 Si 暴露更敏感，反应更强烈。在肺巨噬细胞中，与非结晶 Si50 和 Si500 相比，结晶二氧化硅（MinUsil 5）在调整表面积后更能有效地诱导白细胞介素-1β的释放。与发烟二氧化硅相比，这种差异要小得多。半胱天冬酶-1 抑制剂 zYVAD 和 NALP3 受体的 RNA 沉默降低了 RAW264.7 巨噬细胞中颗粒诱导的白细胞介素-1β释放。此外，吞噬作用、内体酸化和组织蛋白酶 B 活性抑制剂将不同颗粒的 IL-1β 反应降低到相似的程度。
总之，纳米和亚微米范围内的非结晶二氧化硅颗粒似乎通过与结晶二氧化硅类似的机制，即颗粒摄取、吞噬体渗漏和 NALP3 炎症小体的激活，诱导 LPS 预刺激的 RAW264.7 巨噬细胞释放白细胞介素-1β。值得注意的是，大鼠原代肺巨噬细胞对二氧化硅诱导的白细胞介素-1β释放更为敏感。所获得的差异反应模式表明，二氧化硅诱导的白细胞介素-1β反应不仅取决于颗粒的表面积，还取决于颗粒反应性或颗粒摄取等因素和/或机制。这些发现可能表明，细菌感染通过 LPS 可能会增强非结晶和结晶二氧化硅颗粒的急性炎症效应。
