Although amorphous silica particles (SPs) are widely used in cosmetics, foods and medicinal products, it has gradually become evident that SPs can induce substantial inflammation accompanied by interleukin-1beta (IL-1beta) production. Here, to develop safe forms of SPs, we examined the mechanisms of SP-induced inflammation and the relationship between particle characteristics and biological responses. We compared IL-1beta production levels in THP-1 human macrophage like cells in response to unmodified SP of various diameters (30- to 1000-nm) and demonstrated that unmodified microsized 1000-nm SP (mSP1000) induced higher levels of IL-1beta production than did smaller unmodified SPs. Furthermore, we found that unmodified mSP1000-induced IL-1beta production was depended on the sequence of reactive oxygen species (ROS) production, endosomal rupture, and subsequent activation of pro-inflammatory complex NLRP3 inflammasome. In addition, we compared IL-1beta production levels in THP-1 cells treated with mSP1000s modified with a functional group (-COOH, -NH(2), -SO(3)H, -CHO). Although unmodified and surface-modified mSP1000s were taken up with similar frequencies equally into the THP-1 cells, surface modification of mSP1000 dramatically suppressed IL-1beta production by reducing ROS production. Our results reveal a part of NLRP3 activation pathway and provide basic information that should help to create safe and effective forms of SPs.
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