The role of NLRP3 inflammasome activation in proinflammatory and cytotoxic effects of metal nanoparticles.

Exposure to metal nanoparticles (NPs) is known to induce inflammatory responses in various tissues, thus limiting their therapeutic potential. NOD-like receptor protein 3 (NLRP3) inflammasome activation is an essential component of innate immunity playing a significant role in inflammation and development of inflammatory diseases. Therefore, the objective of the present review was to summarize data on the role of NLRP3 inflammasome in proinflammatory effects induced by metal NPs, and to discuss the underlying molecular mechanisms, including its dependence on the physical and chemical properties of metal NPs. Titanium, zinc, silver, aluminum, iron, cobalt, nickel, vanadium, and tungsten nanoparticles, as well as metal-based quantum dots have all been shown to induce NLRP3 inflammasome activation in vitro in macrophages and monocytes, dendritic cells, keratinocytes, hepatocytes, enterocytes, microglia, astrocytes, lung epithelial cells, endotheliocytes, as well as certain types of cancer cells. In vivo studies confirmed the role of NLRP3 pathway activation in development of colitis, pulmonary inflammation, liver damage, osteolysis, and neuroinflammation induced by various metal nanoparticles. Briefly, particle endocytosis with subsequent lysosomal damage, induction of ROS formation, K⁺ efflux, increased intracellular Ca²⁺ levels, and NF-κB pathway activation results in NLRP3 inflammasome complex assembly, caspase-1 activation, and cleavage of pro-IL-1β and pro-IL-18 to mature proinflammatory cytokines, while gasdermin D cleavage induces pyroptotic cell death. Moreover, small-sized and rod-shaped metal NPs exert a more profound stimulatory effect on NLRP3 inflammasome activation, but contrary findings have also been reported. Taken together, it is concluded that NLRP3 inflammasome may mediate both adverse proinflammatory effects of metal nanoparticles, as well as their beneficial effect when used as antitumor agents.