INTRODUCTION: The NLRP3 inflammasome is a key factor in innate immunity and plays a pivotal role in driving acute lung injury via IL-1ß and IL-18. Recent studies highlighted the immunomodulatory effects of tetracyclines (TET) in the treatment of inflammatory diseases and identified inhibition of NLRP3 inflammsome as a potential mechanism.

AIM: We investigated in a murine model whether TET reduces NLRP3 inflammasome-mediated lung inflammation and improves outcome.

METHODS: Mice were challenged with LPS i.t. and treated by i.p. injection of TET from d 0 for 10 d. Lung injury was determined by measurement of i) albumin concentration by ELISA, ii) neutrophil population by flow cytometry (both in BALF) and iii) histopathology. Concentration of IL-1ß, IL-6, IL-18 and TNFa was measured by multiplex assay in BALF. The effect of TET on NLRP3 inflammasome was tested in BMDMs after stimulation with LPS plus nigericin. Concentration of IL-1ß and TNFa was determined by ELISA and cleavage of caspase-1 via western blot.

RESULTS: TET treated mice showed significantly reduced weight loss and mortality (43% vs. 7%) compared to PBS treated animals. TET treatment diminished lung injury in terms of lower albumin (325±35 vs 144±16µg/ml) concentration and number of neutrophils. Histopathology showed reduced lung injury in TET-treated animals. TET decreased exclusively the concentration of IL-1ß (152±16 vs 86±8 pg/ml) and IL-18 in BALF. TET selectively inhibited IL-1ß secretion and caspase-1 activation after NLRP3 stimulation.

CONCLUSIONS: Current study demonstrates that TET reduces acute lung injury in mice via inhibiting NLRP3 inflammasome activation, thereby reducing morbidity and mortality.