TPPU treatment of burned mice dampens inflammation and generation of bioactive DHET which impairs neutrophil function

Christian B Bergmann,Falk Gogolla,Debin Wan,Dorothy M Supp,Bruce D Hammock,Holly Goetzman,Charles C Caldwell

doi:10.1038/s41598-021-96014-2

Abstract

Oxylipins modulate the behavior of immune cells in inflammation. Soluble epoxide hydrolase (sEH) converts anti-inflammatory epoxyeicosatrienoic acid (EET) to dihydroxyeicosatrienoic acid (DHET). An sEH-inhibitor, TPPU, has been demonstrated to ameliorate lipopolysaccharide (LPS)- and sepsis-induced inflammation via EETs. The immunomodulatory role of DHET is not well characterized. We hypothesized that TPPU dampens inflammation and that sEH-derived DHET alters neutrophil functionality in burn induced inflammation. Outbred mice were treated with vehicle, TPPU or 14,15-DHET and immediately subjected to either sham or dorsal scald 28% total body surface area burn injury. After 6 and 24 h, interleukin 6 (IL-6) serum levels and neutrophil activation were analyzed. For in vitro analyses, bone marrow derived neutrophil functionality and mRNA expression were examined. In vivo, 14,15-DHET and IL-6 serum concentrations were decreased after burn injury with TPPU administration. In vitro, 14,15-DHET impaired neutrophil chemotaxis, acidification, CXCR1/CXCR2 expression and reactive oxygen species (ROS) production, the latter independent from p38MAPK and PI3K signaling. We conclude that TPPU administration decreases DHET post-burn. Furthermore, DHET downregulates key neutrophil immune functions and mRNA expression. Altogether, these data reveal that TPPU not only increases anti-inflammatory and inflammation resolving EET levels, but also prevents potential impairment of neutrophils by DHET in trauma.

Highlights

The concept that oxylipins can modulate the behavior of immune cells in inflammatory diseases has evolved over the last decades[1,2,3]
We hypothesized that a beneficial clinical effect can be seen reflected by the decrease of systemic interleukin 6 (IL-6) levels and that the product 14,15-dihydroxyeicosatrienoic acid (DHET) impairs neutrophil functionality
These results suggest that the impairment of neutrophil Reactive Oxygen Species (ROS) production by 14,15-DHET is independent from p38MAP kinase and PI3K signaling pathways

Summary

Introduction

The concept that oxylipins can modulate the behavior of immune cells in inflammatory diseases has evolved over the last decades[1,2,3]. Administering sEH reduced the release of pro-inflammatory cytokines in murine endotoxemia[10,11], increased survival in a mouse sepsis model[12], and reduced neuronal death in an intracerebral hemorrhage model[13] Some studies attributed these effects to the anti-inflammatory properties of E ETs11,12, which are increased upon inhibition of sEH. Previous studies examining modulation of inflammation by oxylipins focused on the effect on macrophages[12,24], the regulation of neutrophil functionality is not yet well characterized Based upon this limited literature, we tested whether TPPU would alter systemic inflammation after burn injury and hypothesized that sEH-derived DHETs alter immune function in neutrophils that play key roles in burn induced inflammation

Methods

Results

Conclusion