Cell-free fat extract protects septic lethality via restraining NLRP3 inflammasome activation.

Background: Sepsis is a dysregulated host response to infection with high mortality and current management cannot reach optimal remission. Previous studies have shown that cell-free fat extract (CEFFE) is a kind of bioactive extraction from adipose tissues and exhibits a potent anti-inflammatory effect on wound healing and inflammatory diseases. However, the potential role of CEFFE in sepsis remains unclear.

Methods: CEFFE was extracted from healthy donors and was intraperitoneally injected into septic mice. The septic mice models were constructed using lipopolysaccharide (LPS), E. coli, and cecal ligation and puncture (CLP). The survival of septic mice was detected for 96 h and Kaplan-Meier analysis was used to analyze the differences of survival rates. Lung tissues that were collected from septic mice were subjected to HE staining to evaluate the extent of lung injury, and the mice serum was obtained for inflammasome-related cytokines detection. Moreover, peritoneal macrophages were extracted from C57 mice and treated with CEFFE and/or inflammasome activators. The level of IL-1β, IL-18, IL-6, and TNF-α was detected by ELISA, and the activation of NLRP3 were evaluated by Western Blot. Total mtDNA and mitochondrial permeability transition pore were determined to explore the mitochondrial dysfunction in the activation of NLRP3 inflammasome with or without CEFEE. Coimmunoprecipitation (Co-IP) assays were performed to confirm the mechanism of NLRP3 activation induced by CEFFE.

Results: CEFFE significantly improved the survival of sepsis mice and alleviate sepsis-induced lung injury. Moreover, CEFFE significantly decreased the level of inflammasome-cytokines (IL-1β and IL-18) but not the pro-inflammatory cytokines such as IL-6 and TNF-α. Moreover, CEFFE markedly suppressed the canonical activation of NLRP3 inflammasome without affecting inflammasomes NLRC4 and AIM2. Additionally, the non-canonical activation of NLRP3 inflammasome was significantly inhibited by CEFFE. CEFFE treatment attenuated the mtDNA outflow and the increase of mitochondrial permeability induced by both canonical and non-canonical pathway of NLRP3 inflammasome activation. The results of Co-IP assays revealed that CEFFE remarkably attenuated the oligomerization of ASC and inhibited the association between NLRP3 and ASC.

Conclusion: Our study revealed that CEFFE could significantly alleviate sepsis-related injuries possibly by suppressing NLRP3 inflammasome activation. CEFFE was a promising approach for sepsis treatment.