Inca H. Hundscheid

New insights in intestinal ischemia-reperfusion injury: implications for intestinal transplantation.

Purpose of reviewIschemia–reperfusion injury is inevitable during intestinal transplantation and can negatively affect the transplant outcome. Here, an overview is provided of the recent advances in the pathophysiological mechanisms of intestinal ischemia–reperfusion injury and how this may impact graft survival. Recent findingsThe intestine hosts a wide range of microorganisms and its mucosa is heavily populated by immune cells. Intestinal ischemia–reperfusion results in the disruption of the epithelial lining, affecting also protective Paneth cells (antimicrobials) and goblet cells (mucus), and creates a more hostile intraluminal microenvironment. Consequently, both damage-associated molecular patterns as well as pathogen-associated molecular patterns are released from injured tissue and exogenous microorganisms, respectively. These ‘danger’ signals may synergistically activate the innate immune system. Exaggerated innate immune responses, involving neutrophils, mast cells, platelets, dendritic cells, as well as Toll-like receptors and complement proteins, may shape the adaptive T-cell response, thereby triggering the destructive alloimmune response toward the graft and resulting in transplant rejection. SummaryInnate immune activation as a consequence of ischemia–reperfusion injury may compromise engraftment of the intestine. More dedicated research is required to further establish this concept in man and to design more effective therapeutic strategies to better tolerize intestinal grafts.

Goblet cell compound exocytosis in the defense against bacterial invasion in the colon exposed to ischemia-reperfusion

In recent years, the importance of the mucus layer in the colon has become increasingly clear. Disturbance of the mucus layer has been implicated in a variety of intestinal diseases. We have recently investigated the importance of the mucus layer in colon ischemia-reperfusion (IR). Using a newly developed human and rat colon IR model, we showed that colon ischemia leads to mucus barrier breakdown. This allowed intraluminal bacteria to interact with the colonic epithelium, which was associated with an inflammatory response. Intriguingly, we found goblet cells to respond immediately by expelling their mucin granules into the gut lumen, which flushed bacteria from the colonic crypts and resulted in rapid restoration of the mucus layer during reperfusion. Our study might explain why ischemic colitis tends to have favorable outcomes and can often be treated conservatively.

The Human Colon Is More Resistant to Ischemia-reperfusion-induced Tissue Damage Than the Small Intestine An Observational Study

OBJECTIVE Aim of this study was to draw comparisons between human colonic and jejunal ischemia-reperfusion sequelae in a human in vivo experimental model. BACKGROUND In patients, colonic ischemia-reperfusion generally has a milder course than small intestinal ischemia-reperfusion. It is unclear which pathophysiologic processes are responsible for this difference. METHODS In 10 patients undergoing colonic surgery and 10 patients undergoing pancreaticoduodenectomy, 6 cm colon or jejunum was isolated and exposed to 60 minutes ischemia followed by various reperfusion periods. Morphology (hematoxylin and eosin), apoptosis (M30), tight junctions (zonula occludens 1), and neutrophil influx (myeloperoxidase) were assessed using immunohistochemistry. Quantitative polymerase chain reaction and enzyme-linked immunosorbent assay were performed for interleukin-6 and tumor necrosis factor-α. RESULTS Hematoxylin and eosin staining revealed intact colonic epithelial lining, but extensive damage in jejunal villus tips after 60 minutes ischemia. After reperfusion, the colonic epithelial lining was not affected, whereas the jejunal epithelium was seriously damaged. Colonic apoptosis was limited to scattered cells in surface epithelium, whereas apoptosis was clearly observed in jejunal villi and crypts, (42 times more M30 positivity compared with colon, P < 0.01). Neutrophil influx and increased tumor necrosis factor-α mRNA expression were observed in jejunum after 30 and 120 minutes of reperfusion (P < 0.05). Interleukin-6 mRNA expression was increased in jejunum after 120 minutes of reperfusion (3.6-fold increase, P < 0.05), whereas interleukin-6 protein expression was increased in both colon (1.5-fold increase, P < 0.05) and small intestine (1.5-fold increase, P < 0.05) after 30 and 120 minutes of reperfusion. CONCLUSIONS Human colon is less susceptible to IR-induced tissue injury than small intestine.

Enteroendocrine L Cells Sense LPS after Gut Barrier Injury to Enhance GLP-1 Secretion

Glucagon-like peptide 1 (GLP-1) is a hormone released from enteroendocrine L cells. Although first described as a glucoregulatory incretin hormone, GLP-1 also suppresses inflammation and promotes mucosal integrity. Here, we demonstrate that plasma GLP-1 levels are rapidly increased by lipopolysaccharide (LPS) administration in mice via a Toll-like receptor 4 (TLR4)-dependent mechanism. Experimental manipulation of gut barrier integrity after dextran sodium sulfate treatment, or via ischemia/reperfusion experiments in mice, triggered a rapid rise in circulating GLP-1. This phenomenon was detected prior to measurable changes in inflammatory status and plasma cytokine and LPS levels. In human subjects, LPS administration also induced GLP-1 secretion. Furthermore, GLP-1 levels were rapidly increased following the induction of ischemia in the human intestine. These findings expand traditional concepts of enteroendocrine L cell biology to encompass the sensing of inflammatory stimuli and compromised mucosal integrity, linking glucagon-like peptide secretion to gut inflammation.

Human small intestine is capable of restoring barrier function after short ischemic periods

AIM To assess intestinal barrier function during human intestinal ischemia and reperfusion (IR). METHODS In a human experimental model, 6 cm of jejunum was selectively exposed to 30 min of ischemia (I) followed by 30 and 120 min of reperfusion (R). A sham procedure was also performed. Blood and tissue was sampled at all-time points. Functional barrier function was assessed using dual-sugar absorption tests with lactulose (L) and rhamnose (R). Plasma concentrations of citrulline, an amino acid described as marker for enterocyte function were measured as marker of metabolic enterocytes restoration. Damage to the epithelial lining was assessed by immunohistochemistry for tight junctions (TJs), by plasma marker for enterocytes damage (I-FABP) and analyzed by electron microscopy (EM) using lanthanum nitrate as an electrondense marker. RESULTS Plasma L/R ratio’s were significantly increased after 30 min of ischemia (30I) followed by 30 min of reperfusion (30R) compared to control (0.75 ± 0.10 vs 0.20 ± 0.09, P < 0.05). At 120 min of reperfusion (120R), ratio’s normalized (0.17 ± 0.06) and were not significantly different from control. Plasma levels of I-FABP correlated with plasma L/R ratios measured at the same time points (correlation: 0.467, P < 0.01). TJs staining shows distortion of staining at 30I. An intact lining of TJs was again observed at 30I120R. Electron microscopy analysis revealed disrupted TJs after 30I with paracellular leakage of lanthanum nitrate, which restored after 30I120R. Furthermore, citrulline concentrations closely paralleled the histological perturbations during intestinal IR. CONCLUSION This study directly correlates histological data with intestinal permeability tests, revealing that the human gut has the ability of to withstand short episodes of ischemia, with morphological and functional recovery of the intestinal barrier within 120 min of reperfusion.