Therapeutic Myeloperoxidase Inhibition Attenuates Neutrophil Activation, ANCA-Mediated Endothelial Damage, and Crescentic GN
Authors: Antonelou Marilina , Michaëlsson Erik , Evans Rhys D.R. , Wang Chun Jing , Henderson Scott R. , Walker Lucy S.K. , Unwin Robert John , Salama Alan D. ,   RAVE-ITN Investigators
Published: December 2019

Significance Statement
Myeloperoxidase released after neutrophil and monocyte activation can generate reactive oxygen species, leading to tissue damage. Free myeloperoxidase is deposited in glomeruli in various forms of crescentic GN and is elevated in ANCA-associated crescentic GN. The authors evaluated renal biopsy samples and studied the effect of a novel myeloperoxidase inhibitor, AZM198, in vivo and in vitro. They demonstrate that myeloperoxidase mediates neutrophil degranulation and neutrophil extracellular trap formation and contributes to ANCA-mediated endothelial damage. Their findings critically implicate myeloperoxidase in crescentic GN pathogenesis and show that use of AZM198 significantly attenuates these pathways and reduces disease severity in a preclinical crescentic GN model. These data suggest that clinical myeloperoxidase inhibition might represent a novel therapeutic strategy for diverse forms of crescentic GN.

Background
Myeloperoxidase released after neutrophil and monocyte activation can generate reactive oxygen species, leading to host tissue damage. Extracellular glomerular myeloperoxidase deposition, seen in ANCA-associated vasculitis, may enhance crescentic GN through antigen-specific T and B cell activation. Myeloperoxidase-deficient animals have attenuated GN early on, but augmented T cell responses. We investigated the effect of myeloperoxidase inhibition, using the myeloperoxidase inhibitor AZM198, to understand its potential role in treating crescentic GN.

Methods
We evaluated renal biopsy samples from patients with various forms of crescentic GN for myeloperoxidase and neutrophils, measured serum myeloperoxidase concentration in patients with ANCA-associated vasculitis and controls, and assessed neutrophil extracellular trap formation, reactive oxygen species production, and neutrophil degranulation in ANCA-stimulated neutrophils in the absence and presence of AZM198. We also tested the effect of AZM198 on ANCA-stimulated neutrophil-mediated endothelial cell damage in vitro, as well as on crescentic GN severity and antigen-specific T cell reactivity in the murine model of nephrotoxic nephritis.

Results
All biopsy specimens with crescentic GN had extracellular glomerular myeloperoxidase deposition that correlated significantly with eGFR and crescent formation. In vitro, AZM198 led to a significant reduction in neutrophil extracellular trap formation, reactive oxygen species production, and released human neutrophil peptide levels, and attenuated neutrophil-mediated endothelial cell damage. In vivo, delayed AZM198 treatment significantly reduced proteinuria, glomerular thrombosis, serum creatinine, and glomerular macrophage infiltration, without increasing adaptive T cell responses.

Conclusions
Myeloperoxidase inhibition reduced neutrophil degranulation and neutrophil-mediated endothelial cell damage in patients with ANCA-associated vasculitis. In preclinical crescentic GN, delayed myeloperoxidase inhibition suppressed kidney damage without augmenting adaptive immune responses, suggesting it might offer a novel adjunctive therapeutic approach in crescentic GN.