Xuanfei Baidu Formula Ameliorates Influenza A Virus-induced Lung Inflammation by Repressing the NLRP3 Inflammasome in Macrophages

The NOD-like receptor family pyrin domain-containing protein 3 (NLRP3) inflammasome is an intracellular protein complex containing a nucleotide-binding oligomerization domain, leucine-rich repeats, and a pyrin domain. It is a key regulator of inflammation in viral pneumonia (VP). Small-molecule inhibitors targeting various NLRP3 binding sites are advancing into early clinical trials, but their therapeutic utility is incompletely established. Xuanfei Baidu Formula (XF), clinically used for VP treatment, attenuates NLRP3 activation by hampering caspase-11 to impede polarization of pro-inflammatory macrophages in a model of lipopolysaccharide (LPS)-induced lung injury inmice. Herein, we demonstrate that XF attenuated influenza A virus (IAV)-induced lung inflammation as well as lung injury in immunocompetent (but not in macrophage-depleted) mice. RNA-sequencing of sorted lung macrophages from IAV-infected mice revealed that XF inhibited activation of the NLRP3 inflammation and interleukin (IL)-1β production. Quantitative nuclear magnetic resonance of XF enabled us to develop XF-Comb1, a fixed-ratio combination of five bioactive compounds that recapitulated the bioactivity of XF in suppressing NLRP3 activation in macrophages in vitro and in vivo. Interestingly, XF-Comb1 inhibited assembly of the NLRP3 inflammasome through multi-site interactions with functional residues of NLRP3, apoptosis-associated speck-like protein containing caspase recruitment domain (CARD) (ASC), and caspase-1. Taken together, this work advances the development of NLRP3 inhibitors by translating a complex herbal formula into defined bioactive compounds.