Hydrogen sulfide exposure induces NLRP3 inflammasome-dependent IL-1β and IL-18 secretion in human mononuclear leukocytes in vitro.

Amina Basic,Gunnar Dahlén,Ulf Dahlgren,Sara Alizadehgharib

doi:10.1002/cre2.69

Amina Basic, Gunnar Dahlén + Show 2 more

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https://doi.org/10.1002/cre2.69

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Abstract

The aim was to investigate if hydrogen sulfide (H2S) induces the formation of the NLRP3 inflammasome and subsequent IL‐1β and IL‐18 secretion in human peripheral blood mononuclear cells (PBMCs) and in the human monocyte cell line THP1. Bacterial production of H2S has been suggested to participate in the inflammatory host response in periodontitis pathogenesis. H2S is a toxic gas with pro‐inflammatory properties. It is produced by bacterial degradation of sulfur‐containing amino acids, for example, cysteine. We hypothesize that H2S affects the inflammatory host response by inducing formation of the NLRP3 inflammasome and thereby causes the secretion of IL‐1ß and IL‐18. PBMCs from eight healthy blood donors, the human monocyte cell line THP1 Null, and two variants of the THP1 cell line unable to form the NLRP3 inflammasome were cultured in the presence or absence of 1 mM sodium hydrosulfide (NaHS) in 24‐well plates at 37°C for 24 hr. Supernatants were collected and the IL‐1β and IL‐18 concentrations were measured with DuoSet ELISA Development kit. PBMCs exposed to NaHS produced more IL‐1ß and IL‐18 than unexposed control cells (p = .023 and p = .008, respectively). An increase of extracellular potassium ions (K+) inhibited the secretion of IL‐1ß and IL‐18 (p = .008). Further, NaHS triggered the secretion of IL‐1ß and IL‐18 in human THP1‐Null monocytes (p = .0006 and p = .002, respectively), while the NaHS‐dependent secretion was reduced in the monocyte cell lines unable to form the NLRP3 inflammasome. Hence, the results suggest that NaHS induces the formation of the NLRP3 inflammasome and thus the secretion of IL‐1ß and IL‐18. Enhanced NLRP3 inflammasome‐dependent secretion of IL‐1β and IL‐18 in human mononuclear leukocytes exposed to NaHS in vitro is reported. This may be a mode for H2S to contribute to the inflammatory host response and pathogenesis of periodontal disease.

Highlights

Periodontitis, a bacteria‐induced inflammation, is the result of a disruption of the homeostasis between the bacteria and the host
The results showed a statistically significant increase in cytokine secretion in the THP1‐Null cell line when the cells were exposed to NaHS, illustrating that monocytes do secrete IL‐1β and IL‐18 in the presence of NaHS (Figure 2)
The production of pro‐inflammatory cytokines is essential in the induction and development of inflammatory diseases such as periodontal disease

Summary

Introduction

Periodontitis, a bacteria‐induced inflammation, is the result of a disruption of the homeostasis between the bacteria and the host. This dysbiosis is characterized by a high bacterial diversity and the growth of anaerobic, Gram‐negative, and proteolytic bacteria in the subgingival pocket (Kilian, Chapple, Hannig, et al, 2016). H2S is produced by bacterial degradation of sulfur‐containing amino acids, for example, cysteine (Kuester & Williams, 1964) by many different bacterial strains (Basic, Blomqvist, Carlén, & Dahlén, 2015; Persson, Claesson, & Carlsson, 1989), and its presence has been reported in gingival crevicular fluid (Persson, 1992). Monocytes/macrophages play an important role in the immune response of the host because they are able to produce a large variety of cytokines, for example, IL‐1β. H2S can induce pro‐inflammatory cytokine IL‐8 production from gingival and oral epithelial cells in vitro (Chen, Kajiya, Giro, et al, 2010), but it has been shown to cause cell death in lymphocytes and reduce their IL‐2 production. (Mirandola, Gobbi, Sponzilli, et al, 2007)

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