The effect of surface modification of amorphous silica particles on NLRP3 inflammasome mediated IL-1β production, ROS production and endosomal rupture

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-1β (IL-1β) 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-1β 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-1β production than did smaller unmodified SPs. Furthermore, we found that unmodified mSP1000–induced IL-1β 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-1β production levels in THP-1 cells treated with mSP1000s modified with a functional group (–COOH, –NH2, –SO3H, –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-1β 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.