Hypocrellin A from an ethnic medicinal fungus protects against NLRP3-driven gout in mice by suppressing inflammasome activation.

Abnormal activation of NLRP3 inflammasome causes the progression of gout, and no small-molecule inhibitor of NLRP3 has been approved yet for clinical use. In this study we established a nigericin-induced inflammasome activation cell model for screening of a natural product library by measuring IL-1β secretion in cell supernatants. Among 432 compounds tested, we found that hypocrellin A (HA), one of the major active components of a traditional ethnic medicinal fungus Hypocrella bambusea in the Northwest Yunnan of China, exhibited the highest inhibition on IL-1β production (IC(50) = 0.103 μM). In PMA-primed THP-1 cells or bone marrow derived macrophages (BMDMs) treated with multiple stimuli (nigericin, ATP or MSU), HA dose-dependently suppressed the activation of NLRP3 inflammasome, reducing the subsequent release of inflammatory cytokines and LDH. Furthermore, the suppression of inflammasome activation by HA was specific to NLRP3, but not to AIM2 or NLRC4. In LPS-primed BMDMs treated with nigericin, HA inhibited ASC oligomerization and speckle formation, and blocked the NLRP3-NEK7 interaction during inflammasome assembly without influencing the priming stage. Moreover, we demonstrated that HA directly bound to the NACHT domain of NLRP3, and that Arg578 and Glu629 were the critical residues for HA binding to NLRP3. In MSU-induced peritonitis and acute gouty arthritis mouse models, administration of HA (10 mg/kg, i.p., once or twice daily) effectively suppressed the inflammatory responses mediated by NLRP3 inflammasome. We conclude that HA is a broad-spectrum and specific NLRP3 inhibitor, and a valuable lead compound to develop novel therapeutic inhibitors against NLRP3-driven diseases. This study also elucidates the anti-inflammation mechanisms and molecular targets of HA, a major active component in medicinal fungus Hypocrella bambusea that has been long used by Chinese ethnic groups.