Background/Purpose: Gout is an inflammatory arthropathy due to the deposition of uric acid (monosodium urate: MSU) crystals in synovial tissue. MSU leads to activate nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome and following IL-1beta secretion via caspase-1 activation in human monocytes. Synthesis of mature IL-1beta is a 2-step processes. In the 1^st step, microbial-derived signals (binding of bacterial products such as LPS) up-regulate pro-IL-1beta, resulting in synthesis of pro-IL-1beta. However, priming signals for NLRP3 infammasome pathway had not been completely elucidated in sterile inflammatory arthritis including gout. In this study, we investigated the role of TNF-alpha on MSU-mediated IL-1beta induction in human neutrophils.

Methods: Venous peripheral blood was collected from healthy volunteers. Human neutrophils were stimulated with MSU (200 µg/ml), in the presence or absence of TNF-alpha priming (2 to 50 ng/ml). The cellular supernatants were analyzed for IL-1beta, IL-18 and caspase-1 by ELISA. Pro-IL-1beta mRNA expressions in human neutrophils were analyzed by real-time PCR.

Results: TNF-alpha stimulation induced pro-IL-1beta mRNA expression, however, MSU stimulation alone did not induce pro-IL-1beta mRNA expression in neutrophils. TNF-alpha alone or MSU stimulation did not result in efficient IL-1beta secretion. Whereas MSU stimulation to TNF-alpha-primed neutrophils resulted in a marked IL-1beta (Figure 1) as well as IL-18 secretion. TNF-alpha-primed neutrophils secreted cleaved caspase-1 (p20) with MSU stimulation.

Conclusion: These results indicate that priming of human neutrophils with TNF-alpha promotes uric acid-mediated NLRP-3 activation and IL-1beta secretion in the absence of microbial stimulation, that provide new insights into the neutrophils-mediated inflammatory processes in gouty arthritis.

Figure 1. MSU induces IL-1beta synthesis from TNF-alpha-pretreated neutrophils.