Shikonin inhibits NLRP3 inflammasome activation and controls inflammatory disease

Inflammasomes are multimeric cytosolic protein complexes found in various cells, including macrophages, neutrophils, dendritic cells (DCs), and cardiomyocytes1. Among them, the NLRP3 (nucleotide-binding oligomerization domain-like receptor family pyrin domain-containing 3) inflammasome is an intracellular sensor complex that plays a vital role in innate immunity, comprising NLRP3, ASC, and caspase-12. Upon stimulation, NLRP3 recruits ASC and pro-caspase-1 to form a helical fibrillary complex known as the NLRP3 inflammasome. Assembly of the NLRP3 inflammasome induces the maturation of pro-caspase-1, enhancing the production of mature IL-1β and IL-18. Additionally, NLRP3 activation can trigger Gasdermin D (GSDMD)-induced pyroptosis1.
Appropriate activation of the NLRP3 inflammasome is crucial for host defense against pathogens and inflammation3,4. However, abnormal NLRP3 activation has been implicated in various diseases, including non-alcoholic fatty liver disease (NAFLD), gout, Alzheimer’s disease, type II diabetes, ulcerative colitis, and septic shock5,6. Consequently, the NLRP3 inflammasome is a promising therapeutic target for related diseases. Both damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) can activate the NLRP3 inflammasome. DAMPs include nucleic acids, proteins, ions, glycans, and metabolites, while PAMPs encompass lipopolysaccharides, oligopeptide sugars, yeast polysaccharides, and phosphatidylserine7. Key mechanisms of NLRP3 activation include intracellular ionic fluxes, lysosomal damage, and ROS generation8, with ROS being particularly significant9,10. ROS can activate the NLRP3 inflammasome by dissociating thioredoxin-interacting protein (TXNIP) from the TXNIP-TXN complex11. Our team found that ROS induces cytochrome C translocation into the cytoplasm, where it activates the NLRP3 inflammasome by binding to NLRP3. Meanwhile, ROS converts mitochondrial DNA (mtDNA) into its oxidized form (ox-mtDNA), which is recognized as the ultimate ligand for NLRP312,13,14. However, previous research has shown that ROS can also trigger the formation of the pro-caspase-1-ASC complex, leading to NLRP3 inflammasome activation15. Collectively, antioxidant strategies may be beneficial in treating NLRP3-associated diseases.
Shikonin (SHK), a bioactive molecule found in the roots of Radix Lithospermi, has demonstrated anti-infective, anti-tumor, anti-inflammatory, and wound-healing properties. Previous studies reported that SHK exhibits significant anti-inflammatory effects by inhibiting chemokine receptor function16. Additionally, in mouse models of lethal endotoxemia, SHK reduced serum levels of the inflammatory mediator high-mobility group box 1 (HMGB1) protein, protecting mice from LPS-induced mortality. SHK also suppresses the maturation of pro-IL1β via the NLRP3 inflammasome in response to soluble and particulate NLRP3 activators17. However, the precise mechanism of SHK’s anti-inflammatory action remains unclear.