Neutrophil priming by hypoxic preconditioning protects against epithelial barrier damage and enteric bacterial translocation in intestinal ischemia/reperfusion

Abstract

Intestinal ischemia/reperfusion (I/R) induces mucosal barrier dysfunction and bacterial translocation (BT). Neutrophilderived oxidative free radicals have been incriminated in the pathogenesis of ischemic injury in various organs, but their role in the bacteria-containing intestinal tract is debatable. Primed neutrophils are characterized by a faster and higher respiratory burst activity associated with more robust bactericidal effects on exposure to a second stimulus. Hypoxic preconditioning (HPC) attenuates ischemic injury in brain, heart, lung and kidney; no reports were found in the gut. Our aim is to investigate whether neutrophil priming by HPC protects against intestinal I/R-induced barrier damage and bacterial influx. Rats were raised in normoxia (NM) or kept in a hypobaric hypoxic chamber (380 Torr) 17 h/day for 3 weeks for HPC, followed by sham operation or intestinal I/R. Gut permeability was determined by using an ex vivo macromolecular flux assay and an in vivo magnetic resonance imaging-based method. Liver and spleen homogenates were plated for bacterial culturing. Rats raised in HPC showed diminished levels of BT, and partially improved mucosal histopathology and epithelial barrier function compared with the NM groups after intestinal I/R. Augmented cytokineinduced neutrophil chemoattractant (CINC)-1 and -3 levels and myeloperoxidase activity correlated with enhanced infiltration of neutrophils in intestines of HPC-I/R compared with NM-I/R rats. HPC alone caused blood neutrophil priming, as shown by elevated production of superoxide and hydrogen peroxide on stimulation, increased membrane translocation of cytosolic p47 phox and p67 phox , as well as augmented bacterial-killing and phagocytotic activities. Neutrophil depletion reversed the mucosal protection by HPC, and aggravated intestinal leakiness and BT following I/R. In conclusion, neutrophil priming by HPC protects against I/R-induced BT via direct antimicrobial activity by oxidative respiratory bursts and through promotion of epithelial barrier integrity for luminal confinement of enteric bacteria.

Ischemic preconditioning ameliorates intestinal injury induced by ischemia-reperfusion in rats

“…Neutrophils are a critical component of the inflammatory response that characterizes intestinal IR [18,19] . Activated neutrophils, which infiltrate the intestine during IR, produce inflammatory mediators, including TNF-a, ICAM-1, and VCAM-1, in the development of intestinal IR by releasing neutrophil proteases and reactive oxygen species, and sequestering polymorphonuclear neutrophils (PMNs) into ischemic intestinal tissue [20][21][22] .…”

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

“…Interaction with matrix proteins further increased FCgR expression in the setting of hypoxia [63], which may reflect the in vivo environment more accurately. Likewise, phagocytosis of zymosan by neutrophils isolated from rabbits after experimental acute ischaemia [64], phagocytosis of E. coli by neutrophils isolated from hypoxic pre-conditioned rats [65] and phagocytosis of S. aureus by neutrophils isolated from volunteers exposed to intermittent hypoxia [66] were all increased. These in vitro assays were performed under normoxic conditions; however, similar results were obtained using isolated human neutrophils with in vitro assays performed under hypoxia [67].…”

“…Studies of neutrophils isolated from human volunteers or mice exposed to hypoxia have shown an increase in ROS production [44,56,65], although, of note, all cell isolation and in vitro assays were conducted under normoxic conditions. Whilst HIF-1a manipulation did not affect ROS release [55,60], in vitro assays conducted under hypoxia have consistently shown decreased intracellular and extracellular superoxide anion production, restored by re-oxygenation [54] and further increased under hyperbaric oxygen conditions.…”

The Microbiota Protects against Ischemia/Reperfusion-Induced Intestinal Injury through Nucleotide-Binding Oligomerization Domain-Containing Protein 2 (NOD2) Signaling

“…We observed an accumulation of spliced Xbp1 mRNA in the injured tissue of both WT and Nod2 À/À mice ( Figure 4A). In addition, cytokine expression has been used as an indicator of hypoxia in I/R-induced injury, 33 as well as in related models of hypoxia in vitro 34 and in vivo. 6e8, 35 Therefore, we evaluated Tnfa, Il-6, and Il-1b mRNA accumulation in ileal tissue of WT and Nod2 À/À mice that underwent I/R-induced injury.…”