Neutrophil Extracellular Traps Induce Trypsin Activation, Inflammation, and Tissue Damage in Mice With Severe Acute Pancreatitis

Mohammed Merza, Hannes Hartman, Milladur Rahman, Rundk Hwaiz, Enming Zhang, Erik Renström, Lingtao Luo, Matthias Mörgelin, Sara Regner, Henrik Thorlacius
Gastroenterology 2015, 149 (7): 1920-1931.e8

BACKGROUND & AIMS: Neutrophils are involved in the development of acute pancreatitis (AP), but it is not clear how neutrophil-induced tissue damage is regulated. In addition to secreting antimicrobial compounds, activated neutrophils eliminate invading microorganisms by expelling nuclear DNA and histones to form extracellular web-like structures called neutrophil extracellular traps (NETs). However, NETs have been reported to contribute to organ dysfunction in patients with infectious diseases. We investigated whether NETs contribute to the development of AP in mice.

METHODS: AP was induced in C57BL/6 mice by infusion of taurocholate into the pancreatic duct or by intraperitoneal administration of L-arginine. Pancreata were collected and extracellular DNA was detected by Sytox green staining, levels of CXC chemokines, histones, and cytokines also were measured. Cell-free DNA was quantified in plasma samples. Signal transducer and activator of transcription 3 phosphorylation and trypsin activation were analyzed in isolated acinar cells. NETs were depleted by administration of DNase I to mice. Plasma was obtained from healthy individuals (controls) and patients with severe AP.

RESULTS: Infusion of taurocholate induced formation of NETs in pancreatic tissues of mice and increased levels of cell-free DNA in plasma. Neutrophil depletion prevented taurocholate-induced deposition of NETs in the pancreas. Administration of DNase I to mice reduced neutrophil infiltration and tissue damage in the inflamed pancreas and lung, and decreased levels of blood amylase, macrophage inflammatory protein-2, interleukin 6, and high-mobility groups protein 1. In mice given taurocholate, DNase I administration also reduced expression of integrin α M (macrophage-1 antigen) on circulating neutrophils. Similar results occurred in mice with L-arginine-induced AP. Addition of NETs and histones to acinar cells induced formation of trypsin and activation of signal transducer and activator of transcription 3; these processes were blocked by polysialic acid. Patients with severe AP had increased plasma levels of NET components compared with controls.

CONCLUSIONS: NETs form in the pancreata of mice during the development of AP, and NET levels are increased in plasma from patients with AP, compared with controls. NETs regulate organ inflammation and injury in mice with AP, and might be targeted to reduce pancreatic tissue damage and inflammation in patients.

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