Carrageenan‐induced inflammation promotes ROS generation and neutrophil extracellular trap formation in a mouse model of peritonitis

Abstract

Neutrophil extracellular traps (NETs) are a combination of DNA fibers and granular proteins, such as neutrophil elastase (NE). NETs are released in the extracellular space in response to different stimuli. Carrageenan is a sulfated polysaccharide extracted from Chondrus crispus, a marine algae, used for decades in research for its potential to induce inflammation in different animal models. In this study, we show for the first time that carrageenan injection can induce NET release in a mouse model of acute peritonitis. Carrageenan induced NET release by viable neutrophils with NE and myeloperoxidase (MPO) expressed on DNA fibers. Furthermore, although this polysaccharide was able to stimulate reactive oxygen species (ROS) generation by peritoneal neutrophils, NADPH oxidase derived ROS were dispensable for NET formation by carrageenan. In conclusion, our results show that carrageenan-induced inflammation in the peritoneum of mice can induce NET formation in an ROS-independent manner. These results may add important information to the field of inflammation and potentially lead to novel anti-inflammatory agents targeting the production of NETs.Keywords: Carrageenan r Myeloperoxidase r Neutrophil Elastase r Neutrophil Extracellular Traps r Neutrophils Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionNeutrophils are the first cells involved in defense against pathogens and present a mechanism called neutrophil extracellular traps (NETs), which are extracellular structures able to trap and kill pathogens [1,2]. NETs are fibers made of Correspondence: Prof. Márcio V. F. Donadio e-mail: mdonadio@pucrs.br decondensed chromatin (histones and DNA) decorated with antimicrobial proteolytic enzymes present in the granules of neutrophils (such as neutrophil elastase (NE) and myeloperoxidase (MPO)) [3] and other nuclear components, all apparently involved in its mechanism of action [4]. There are a variety of stimuli yet described in the literature including proteins, bacteria, fungi, viruses, and cytokines capable of inducing NETs release [1,[5][6][7]. NETs are present in a plenty of in vivo inflammatory conditions, such as endometriosis [8] importance of exploring inflammatory stimuli involved in NETs formation.Carrageenan is a sulfated polysaccharide extracted from Chondrus crispus, a marine algae, used for decades in research for its potential to induce inflammation [13]. Also, carrageenan is widely used by the food industry as a gelling agent [13]. Due to the potential induction of inflammation, carrageenan is often used as a model of pleurisy [14,15], peritonitis [16,17], and edema [17,18] in experimental animals. The injection of carrageenan triggers an acute inflammation associated with hyperalgesy, which is characterized by edema and an exacerbated response to thermal and mechanical stimuli [13]. Bhattacharyya and colleagues found that carrageenan-induced inflammation in vitro in human colonocytes occurs through activation of Tolllike receptor...

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“…Recent studies have revealed that neutrophil extracellular traps (NET), which consist mainly of the DNA-histone complex and neutrophil elastase, can directly activate factor XII (5,6). Considering that thyroid hormone induces reactive oxygen species (ROS) production in neutrophils and ROS can induce NET formation (7,8), it is plausible that NET may be actively formed in hyperthyroidism. NET can activate the contact system (3,5).…”