Cathepsin C inhibition reduces neutrophil serine protease activity and improves activated neutrophil-mediated disorders.

Cathepsin C (CatC) is an enzyme which regulates the maturation of neutrophil serine proteases (NSPs) essential for neutrophil activation. Activated neutrophils are key players in the innate immune system, and are also implicated in the etiology of various inflammatory diseases. This study aims to demonstrate a therapeutic potential for CatC inhibitors against disorders in which activated neutrophil-derived neutrophil extracellular traps (NETs) play a significant role. We demonstrate that a CatC inhibitor, MOD06051, dose-dependently suppresses the cellular activity of NSPs, including neutrophil elastase (NE), in vitro. Neutrophils derived from MOD06051-administered rats exhibit significantly lower NE activity and NET-forming ability than controls. Furthermore, MOD06051 dose-dependently ameliorates vasculitis and significantly decreases NETs when administered to a rat model of myeloperoxidase (MPO)-antineutrophil cytoplasmic antibody-associated vasculitis (AAV). These findings suggest that CatC inhibition is a promising strategy to reduce neutrophil activation and improve activated neutrophil-mediated diseases such as MPO-AAV.

Methylprednisolone pulse-enhanced neutrophil extracellular trap formation in mice with imiquimod-induced lupus-like disease, resulting in ischaemia of the femoral head cartilage.

OBJECTIVES: Methylprednisolone (mPSL) pulse therapy is an essential option for patients with active systemic lupus erythematosus, but there is a risk of adverse events related to microcirculation disorders, including idiopathic osteonecrosis of the femoral head (ONFH). Recent studies have revealed that excessive neutrophil extracellular traps (NETs) are involved in microcirculation disorders. This study aimed to demonstrate that mPSL pulse could induce NETs in lupus mice and identify the factors contributing to this induction. METHODS: Six mice with imiquimod (IMQ)-induced lupus-like disease and six normal mice were intraperitoneally injected with mPSL on days 39 to 41, and five mice with IMQ-induced lupus-like disease and six normal mice were injected with phosphate-buffered saline. Pathological examinations were conducted to evaluate the ischaemic state of the femoral head and tissue infiltration of NET-forming neutrophils. Proteome analysis was performed to extract plasma proteins specifically elevated in mPSL-administered mice with IMQ-induced lupus-like disease, and their effects on NET formation were assessed in vitro. RESULTS: Mice with IMQ-induced lupus-like disease that received mPSL pulse demonstrated ischaemia of the femoral head cartilage with tissue infiltration of NET-forming neutrophils. Proteome analysis suggested that prenylcysteine oxidase 1 (PCYOX1) played a role in this phenomenon. The reaction of PCYOX1-containing very low-density lipoproteins (VLDL) with its substrate farnesylcysteine (FC) induced NETs in vitro. The combined addition of IMQ and mPSL synergistically enhanced VLDL-plus-FC-induced NET formation. CONCLUSION: PCYOX1 and related factors are worthy of attention to understand the underlying mechanisms and create novel therapeutic strategies for mPSL-mediated microcirculation disorders, including ONFH.

Bruton's tyrosine kinase is a possible therapeutic target in microscopic polyangiitis.

BACKGROUND: Bruton's tyrosine kinase (Btk) is an enzyme expressed in leukocytes other than T lymphocytes and plasma cells and involved in B-cell receptor- and Fcγ receptor (FcγR)-mediated signal transduction. Btk inhibitors potentially suppress autoantibody production due to the expected inhibitory ability of B lymphocyte differentiation into antibody-producing plasma cells and reduce FcγR-mediated neutrophil activation, including the release of neutrophil extracellular traps (NETs). Microscopic polyangiitis (MPA) is a systemic small-vessel vasculitis characterized by the pathogenic autoantibody, antineutrophil cytoplasmic antibody (ANCA) that reacts with myeloperoxidase (MPO). MPO and MPO-ANCA immune complex (IC)-induced FcγR-mediated NETs are critically involved in MPA pathogenesis. This study aimed to demonstrate the therapeutic efficacy of the Btk inhibitor tirabrutinib on MPA. METHODS: Various doses of tirabrutinib or vehicle were orally administered to Sprague-Dawley rats daily. Four weeks later, the number of peripheral B lymphocytes was counted, and Btk phosphorylation in B lymphocytes was evaluated by flow cytometry. Human peripheral blood neutrophils were stimulated by MPO and anti-MPO antibody ICs (MPO and anti-MPO-ICs), and Btk and its downstream Vav phosphorylation were assessed by western blotting. The effects of tirabrutinib on MPO and anti-MPO-IC-induced NET formation were examined in vitro. Wistar Kyoto rats were immunized with human MPO to induce experimental MPA and given drug-free or tirabrutinib-containing feed (0.0037% or 0.012%) from day 0 or 28. All rats were euthanized on day 42 for serological and histological evaluation. RESULTS: Tirabrutinib inhibited Btk phosphorylation without decreasing B lymphocytes in vivo. Neutrophil Btk and Vav were phosphorylated when stimulated with MPO and anti-MPO-ICs. Tirabrutinib suppressed MPO and anti-MPO-IC-induced NET formation in vitro and ameliorated experimental MPA in a dose-dependent manner in vivo. Although MPO-ANCA production was not affected, NET-forming neutrophils in the blood were significantly reduced by tirabrutinib. CONCLUSIONS: The Btk inhibitor tirabrutinib suppressed MPO and anti-MPO-IC-induced NET formation in vitro and ameliorated experimental MPA by reducing NET-forming neutrophils but not decreasing MPO-ANCA titer in vivo. This study suggests that Btk is a possible therapeutic target in MPA.