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

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.

H2S mediates increased interleukin (IL)-1β and IL-18 production in leukocytes from patients with periodontitis

“…When the cells were exposed to H 2 S, the secretion of IL-1β and IL-18 was increased from the cells of the majority of the subjects in both groups. These results are in accordance with those of our previous in vitro study of unknown blood donors [13] and confirm that H 2 S induces PBMCs to secrete proinflammatory cytokines. The level of secretion was, however, highly variable between the individuals tested, and some individuals (N = 9, IL-1β and N = 4, IL-18) actually secreted lower levels of IL-1β and IL-18 after H 2 S exposure than unexposed control cells.…”

“…The blood samples were analyzed for C-reactive protein (CRP), and transferrin at the Clinical Chemistry Laboratory of Sahlgrenska University Hospital, Gothenburg, Sweden. PBMCs were isolated and exposed to a hydrogen sulfide generator as previously described [13]. Briefly, PBMCs were isolated by centrifugation with Ficoll-Paque TM Plus (GE Healthcare Bio-Sciences AB, Uppsala, Sweden), washed with PBS, and resuspended in Dulbecco's Modified Eagle Medium plus GlutaMAX TM (Gibco, Life Technologies, Paisley, UK) supplemented with 5% human serum (Sigma-Aldrich) and penicillin-streptomycin (Sigma-Aldrich).…”

“…The initial in vitro experiments of a small pilot study with PBMCs derived from buffy coats [13] showed large variations in the levels of secreted IL-1β, from 0 μg/ml to 1,181 μg/ml. Based on these results, a power analysis was conducted.…”

“…We hypothesize that H 2 S takes part in the pathogenesis of periodontitis by stimulating the secretion of proinflammatory cytokines from monocytes. In a previous in vitro study [13], we showed elevated secretion of interleukin (IL)-1β and IL-18 from human peripheral blood mononuclear cells (PBMCs) exposed to a hydrogen sulfide generator. The oral status of the donors was unknown.…”

Osteoimmunology: Inflammatory osteolysis and regeneration of the alveolar bone

“…Helicobacter pylori predominantly activates the NLRP3 inflammasome through a process that requires TLR2‐dependent action (Koch & Muller, ). Sulphated bacterial products enhance NLRP3 inflammasome‐dependent cytokine secretion by human mononuclear leucocytes (Basic, Alizadehgharib, Dahlen, & Dahlgren, ), and dental calculus stimulates IL‐1β secretion via NLRP3 inflammasome in macrophages (Montenegro Raudales et al., ). Further, Td92, a surface protein of T. denticola activated NLRP3 in macrophages (Jun, Lee, Lee, & Choi, ) and bone matrix components, activates the NLRP3 inflammasome and promotes osteoclast differentiation (Alippe et al., ).…”