Activation of the NLRP3 inflammasome in myeloid cells follows exposure to pathogen-associated molecular patterns (first signal) and ATP (second signal). This leads to oligomerization and assembly of a high molecular weight (~700 kDa) multimeric inflammasome complex, which leads to the conversion of pro-caspase-1 into the catalytically active form. Inflammatory caspases, such as caspase-1, or interleukin-converting enzyme (ICE), play a central role in innate immunity by recognizing cytosolic foreign danger signals and initiating a two-fold response. First, caspase-1 proteolytically converts the proforms of the two important pro-inflammatory cytokines, interleukin-1ß (IL-1ß) and interleukin-18 (IL-18), into their active forms, which are secreted. Second, caspase-1 or caspase-11 triggers a form of lytic, programmed cell death known as pyroptosis.
Nigericin is a potent microbial toxin derived from Streptomyces hygroscopicus. It acts as a potassium ionophore, inducing a net decrease in intracellular levels of potassium, which is crucial for oligomerization of the NLRP3 inflammasome and activation of caspase-1. Nigericin requires signaling through pannexin-1 to induce caspase-1 activation and IL-1ß processing and release. It has been shown to generate a robust caspase-1 activation response in various cell lines, including Jurkat and THP-I cells.
- Reconstitute each vial of Nigericin with 100 µL DMSO to form the 5 mM stock concentrate. Once reconstituted, it may be aliquoted and stored at ≤ -20°C for 1 year protected from light and thawed no more than twice during that time.
- Immediately prior to addition to the samples and controls, dilute 5 mM Nigericin stock 1:10 in diH2O to form a 500 µM working solution for use in treating samples. For example, dilute 1:10 by adding 20 µL stock concentrate to 180 µL diH2O.
- Use Nigericin at 1-20 µM to induce NLRP3 inflammasome activation in cells. For example, to use at 10 µM, dilute 500 µM working solution 1:50 in samples; e.g., spike 294 µL cell suspension/overlay medium with 6 µL of 500 µM working solution. Typical treatment periods range from 3-24 hours at 37°C. Each investigator should adjust the concentration of Nigericin and treatment period to accommodate the particular cell line and research conditions.
- NLRP3 inflammasome activation can be detected by ELISA or Western blot measuring secreted pro-inflammatory cytokines IL-1β or IL-18, or through the use of caspase-1 activation assays, such as ICT’s Caspase-1 Assay Kits or Pyroptosis/Caspase-1 Assay Kit.