Background/Purpose: Neutrophils are potential instigators of autoimmunity and effectors of organ damage in lupus. However, there is presently no consensus as to whether inhibition of neutrophil effector functions can be pursued as a therapeutic strategy. For example, NADPH oxidase inhibition prevents neutrophil extracellular trap release (NETosis), but exacerbates lupus (likely by interfering with the function of suppressive neutrophil subsets). Similarly, peptidylarginine deiminase inhibitors prevent NETosis and protect against lupus-mediated vascular damage, but raise the levels of key autoantibodies such as anti-double-stranded DNA. Here, we characterize neutrophil elastase, a key effector of neutrophil-mediated organ damage. Neutrophil elastase is required for NETosis and has also been reported to circulate at high levels in lupus patients; however, this key serine protease has been surprisingly little studied in lupus.

Methods: We tested the effects of specific inhibition of the serine protease neutrophil elastase in a mouse model of lupus, namely NZWxBXSB F₁ mice (which develop immune-complex nephritis, and also display a strong prothrombotic diathesis). NZWxBXSB F₁ mice were treated with daily oral administration of the potent, selective elastase inhibitor GW311616A. Endpoints assessed NETosis efficiency, circulating autoantibody levels, glomerulonephritis, cardiac fibrosis, and venous thrombosis.

Results: In vitro, the neutrophil elastase inhibitor GW311616A mitigated NETosis in response to stimulation with either phorbol 12-myristate 13-acetate (PMA) or lupus serum. Neutrophils isolated from GW311616A-treated mice also demonstrated reduced NETosis when challenged with stimuli such as PMA and lipopolysaccharide. In NZWxBXSB F₁ mice, a six-week course of daily oral GW311616A or vehicle control (n=24 per group) protected against several aspects of the lupus phenotype. Specifically, treated mice demonstrated reduced levels of autoantibodies against cathelicidin-related antimicrobial peptide (CRAMP, the mouse orthologue of LL-37) and beta-2 glycoprotein I (β₂GPI, the key autoantigen in antiphospholipid syndrome); in contrast, the levels of anti-double-stranded DNA antibodies were not affected. GW311616A-treated mice demonstrated improved proteinuria-free survival, reduced deposition of complement C3 in kidneys, and reduced expansion of CD4+ CD44+ CD62L- effector T cells in spleens. Cardiac fibrosis (a measure of the prothrombotic phenotype of NZWxBXSB F₁ mice) was reduced by GW311616A. Finally, a brief course of GW311616A in aged NZWxBXSB F₁ mice was effective in mitigating macroscopic venous thrombosis in response to inferior vena cava flow restriction.

Conclusion: These data reveal neutrophil elastase as a novel therapeutic target in lupus. Administration of the specific neutrophil elastase inhibitor GW311616A reduced autoantibody levels, and protected against nephritis as well as both arterial and venous thrombosis. This work once again emphasizes that the method of neutrophil inhibition must be carefully considered in lupus.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/inhibition-of-neutrophil-elastase-protects-against-glomerulonephritis-and-thrombosis-in-a-mouse-model-of-lupus/