Introduction In Cystic Fibrosis (CF), infection and local hypoxia causes increased cell death, cytokine release and damage-associated molecular patterns (DAMPS) which results in hyper-inflammation. The accumulation of misfolded CFTR protein within the cell, along with loss of function leads to excessive cellular stress, defective autophagy and a disruption of ionic balance, all of which contribute to this hyper-inflammatory state. The accumulation of the faulty CFTR, along with the lack of expression of a functional CFTR channel on the cell membrane, leads to perturbation of autophagy in epithelial cells. This, in turn, leads to increased proteasomal degradation of the peroxisome proliferator activated receptor (PPAR)-γ, an anti-inflammatory protein that downregulates expression of genes involved in inflammation.

Method Serum cytokines were measured in patients with CF and controls. In vitro assays were used to characterise effects of small molecules on NLRP3 inflammasome activation in airway epithelial cells and immune cells. A p value<0.05 was considered significant.

Results Levels of IL-18 were significantly increase in patients with CF vs controls. Immune and epithelial cells harbouring CF mutations had increased IL-1Β and IL-18 cytokine production, which was blocked by the addition of inhibitors targeting the NLRP3. The activation of NLRP3 appeared to be mediated by increased K⁺ efflux following dysregulation of ENaC and high sodium flux. Lumacaftor/ivacaftor significantly reduced the levels of inflammatory cytokines in patients within three months of treatment (n=8) as well as in immune and epithelial cells in vitro. The addition of Na⁺ channel inhibitor, Amiloride, and S18 (peptide based on endogenous ENaC inhibitor SPLUNK1) in vitro inhibited secretion of cytokines processed by the NLRP3 inflammasome. This potential mechanism was further corroborated by the failure of EIPA which targets all Na⁺ channels except ENaC to replicate the anti-inflammatory effects. The addition of the small molecule, cysteamine, recovered autophagy and resulted in down-regulation of inflammasome components and decrease in cytokine secretion.

Conclusion Collectively, we have shown that auto-inflammation in CF can be restored with the use of small molecule therapies which target CFTR and ENaC. Data also suggests that correction and potentiators of CFTR will help reverse auto-inflammation in this complex disease