Supersulphides suppress type-I and type-II interferon responses by blocking JAK/STAT signalling in macrophages.

Interferons (IFNs) are cytokines produced and secreted by immune cells when viruses, tumour cells, and so forth, invade the body. Their biological effects are diverse, including antiviral, cell growth-inhibiting, and antitumour effects. The main subclasses of IFNs include type-I (e.g. IFN-α and IFN-β) and type-II (IFN-γ), which activate intracellular signals by binding to type-I and type-II IFN receptors, respectively. We have previously shown that when macrophages are treated with supersulphide donors, which have polysulphide structures in which three or more sulphur atoms are linked within the molecules, IFN-β-induced cellular responses, including signal transducer and activator of transcription 1 (STAT1) phosphorylation and inducible nitric oxide synthase (iNOS) expression, were strongly suppressed. However, the subfamily specificity of the suppression of IFN signals by supersulphides and the mechanism of this suppression are unknown. This study demonstrated that supersulphide donor N-acetyl-L-cysteine tetrasulphide (NAC-S2) can inhibit IFN signalling in macrophages stimulated not only with IFN-α/β but also with IFN-γ. Our data suggest that NAC-S2 blocks phosphorylation of Janus kinases (JAKs), thereby contributing to the inhibition of phosphorylation of STAT1. Under the current experimental conditions, the hydrogen sulphide (H2S) donor NaHS failed to inhibit IFN signalling. Similar to NAC-S2, the carbohydrate-based supersulphide donor thioglucose tetrasulphide (TGS4) was capable of strongly inhibiting tumour necrosis factor-α production, iNOS expression, and nitric oxide production from macrophages stimulated with lipopolysaccharide. Further understanding of the molecular mechanisms by which supersulphide donors exhibit their inhibitory actions towards JAK/STAT signalling is a necessary basis for the development of supersulphide-based therapeutic strategy against autoimmune disorders with dysregulated IFN signalling.