Characterization of two classes of pancreatic shock factors: functional differences exhibited by hydrophilic and hydrophobic shock factors

Will mesenchymal stem cells be future directions for treating radiation-induced skin injury?

Radiation-induced skin injury (RISI) is one of the common serious side effects of radiotherapy (RT) for patients with malignant tumors. Mesenchymal stem cells (MSCs) are applied to RISI repair in some clinical cases series except some traditional options. Though direct replacement of damaged cells may be achieved through differentiation capacity of MSCs, more recent data indicate that various cytokines and chemokines secreted by MSCs are involved in synergetic therapy of RISI by anti-inflammatory, immunomodulation, antioxidant, revascularization, and anti-apoptotic activity. In this paper, we not only discussed different sources of MSCs on the treatment of RISI both in preclinical studies and clinical trials, but also summarized the applications and mechanisms of MSCs in other related regenerative fields.

The autodigestion hypothesis: Proteolytic receptor cleavage in rheological and cardiovascular cell dysfunction1

Transformation of circulating leukocytes from a dormant into an activated state with changing rheological properties leads to a major shift of their behavior in the microcirculation. Low levels of pseudopod formation or expression of adhesion molecules facilitate relatively free passage through microvessels while activated leukocytes with pseudopods and enhanced levels of adhesion membrane proteins become trapped in microvessels, attach to the endothelium and migrate into the tissue. The transformation of leukocytes into an activated state is seen in many diseases. While mechanisms for activation due to infections, tissue trauma, as well as non-physiological biochemical or biophysical exposures are well recognized, the mechanisms for activation in many diseases have not been conclusively liked to these traditional mechanisms and remain unknown. We summarize our recent evidence suggesting a major and surprising role of digestive enzymes in the small intestine as root causes for leukocyte activation and microvascular disturbances. During normal digestion of food digestive enzymes are compartmentalized in the lumen of the intestine by the mucosal epithelial barrier. When permeability of this barrier increases, these powerful degrading enzymes leak into the wall of the intestine and into the systemic circulation. Leakage of digestive enzymes occurs for example in physiological shock and multi-organ failure. Entry of digestive enzymes into the wall of the small intestine leads to degradation of the intestinal tissue in an autodigestion process. The digestive enzymes and tissue/food fragments generate not only activate leukocytes but also cause numerous cell dysfunctions. For example, proteolytic destruction of membrane receptors, plasma proteins and other biomolecules occurs. We conclude that escape of digestive enzymes from the intestinal track serves as a major source of cell dysfunction, morbidity and even mortality, including abnormal leukocyte activation seen in rheological studies.

Autodigestion: Proteolytic Degradation and Multiple Organ Failure in Shock

There is currently no effective treatment for multiorgan failure following shock other than supportive care. A better understanding of the pathogenesis of these sequelae to shock is required. The intestine plays a central role in multiorgan failure. It was previously suggested that bacteria and their toxins are responsible for the organ failure seen in circulatory shock, but clinical trials in septic patients have not confirmed this hypothesis. Instead, we review here evidence that the digestive enzymes, synthesized in the pancreas and discharged into the small intestine as requirement for normal digestion, may play a role in multiorgan failure. These powerful enzymes are nonspecific, highly concentrated, and fully activated in the lumen of the intestine. During normal digestion they are compartmentalized in the lumen of the intestine by the mucosal epithelial barrier. However, if this barrier becomes permeable, e.g. in an ischemic state, the digestive enzymes escape into the wall of the intestine. They digest tissues in the mucosa and generate small molecular weight cytotoxic fragments such as unbound free fatty acids. Digestive enzymes may also escape into the systemic circulation and activate other degrading proteases. These proteases have the ability to clip the ectodomain of surface receptors and compromise their function, for example cleaving the insulin receptor causing insulin resistance. The combination of digestive enzymes and cytotoxic fragments leaking into the central circulation causes cell and organ dysfunction, and ultimately may lead to complete organ failure and death. We summarize current evidence suggesting that enteral blockade of digestive enzymes inside the lumen of the intestine may serve to reduce acute cell and organ damage and improve survival in experimental shock.

Proteolytic receptor cleavage in the pathogenesis of blood rheology and co-morbidities in metabolic syndrome. Early forms of autodigestion

Abnormal blood rheological properties seldom occur in isolation and instead are accompanied by other complications, often designated as co-morbidities. In the metabolic syndrome with complications like hypertension, diabetes and lack of normal microvascular blood flow, the underlying molecular mechanisms that simultaneously lead to elevated blood pressure and diabetes as well as abnormal microvascular rheology and other cell dysfunctions have remained largely unknown. In this review, we propose a new hypothesis for the origin of abnormal cell functions as well as multiple co-morbidities. Utilizing experimental models for the metabolic disease with diverse co-morbidities we summarize evidence for the presence of an uncontrolled extracellular proteolytic activity that causes ectodomain receptor cleavage and loss of their associated cell function. We summarize evidence for unchecked degrading proteinase activity, e.g. due to matrix metalloproteases, in patients with hypertension, Type II diabetes and obesity, in addition to evidence for receptor cleavage in the form of receptor fragments and decreased extracellular membrane expression levels. The evidence suggest that a shift in blood rheological properties and other co-morbidities may in fact be derived from a common mechanism that is due to uncontrolled proteolytic activity, i.e. an early form of autodigestion. Identification of the particular proteases involved and the mechanisms of their activation may open the door to treatment that simultaneously targets multiple co-morbidities in the metabolic syndrome.

Pancreatic digestive enzyme blockade in the intestine increases survival after experimental shock

Shock, sepsis, and multiorgan failure are associated with inflammation, morbidity, and high mortality. The underlying pathophysiological mechanism is unknown, but evidence suggests that pancreatic enzymes in the intestinal lumen autodigest the intestine and generate systemic inflammation. Blocking these enzymes in the intestine reduces inflammation and multiorgan dysfunction. We investigated whether enzymatic blockade also reduces mortality after shock. Three rat shock models were used here: hemorrhagic shock, peritonitis shock induced by placement of cecal material into the peritoneum, and endotoxin shock. One hour after initiation of hemorrhagic, peritonitis, or endotoxin shock, animals were administered one of three different pancreatic enzyme inhibitors--6-amidino-2-naphtyl p-guanidinobenzoate dimethanesulfate, tranexamic acid, or aprotinin--into the lumen of the small intestine. In all forms of shock, blockade of digestive proteases with protease inhibitor attenuated entry of digestive enzymes into the wall of the intestine and subsequent autodigestion and morphological damage to the intestine, lung, and heart. Animals treated with protease inhibitors also survived in larger numbers than untreated controls over a period of 12 weeks. Surviving animals recovered completely and returned to normal weight within 14 days after shock. The results suggest that the active and concentrated digestive enzymes in the lumen of the intestine play a central role in shock and multiorgan failure, which can be treated with protease inhibitors that are currently available for use in the clinic.

2008 Landis Award lecture. Inflammation and the autodigestion hypothesis

Although long recognized in microvascular research, an increasing body of evidence suggests that inflammatory markers are present in human diseases. Since the inflammatory cascade serves as a repair mechanism, the presence of inflammatory markers in patient groups has raised an important question about the mechanisms that initiate the inflammatory cascade (i.e., the mechanisms that cause tissue injury). Using a severe form of inflammation, shock, and multiorgan failure, for which there is no accepted injury mechanism, we summarize studies that suggest that the powerful pancreatic digestive enzymes play a central role in the destruction of the intestine and other tissues if their compartmentalization in the lumen of the intestine and in the pancreas is compromised. Further, we summarize evidence that uncontrolled degrading enzyme activity in plasma causes proteolytic cleavage of the extracellular domain of membrane receptors and loss of associated cell functions. For example, in a model of metabolic disease with type II diabetes, proteolytic cleavage of the insulin receptor causes the inability of insulin to signal glucose transport across membranes. The evidence suggests that uncontrolled proteolytic and lipolytic enzyme activity may trigger the mechanism for tissue injury. The significance of such mechanisms remain to be explored in human diseases.

A journey with Tony Hugli up the inflammatory cascade towards the auto-digestion hypothesis

My association with Tony Hugli, long-term editor of Immunopharmacology and International Immunopharmacology, came about by a specific and long-standing problem in inflammation research. What is the trigger mechanism of inflammation in physiological shock? This is an important clinical problem due to the high mortality associated with physiological shock. We joined forces in the search of the answer to this question for more than a decade. Our journey eventually led to development of the hypothesis that shock may be associated with pancreatic enzymes, a set of powerful digestive enzymes that are an integral part of human digestion. The digestive enzymes need to be compartmentalized in the lumen of the intestine where they break down a broad spectrum of biological molecules into their building blocks, suitable for molecular transport across the mucosal epithelium into the circulation. The mucosal epithelial barrier is the key element for compartmentalization of the digestive enzymes. But under conditions when the mucosal barrier is compromised, the fully activated digestive enzymes in the lumen of the intestine are transported into the wall of the intestine, starting an auto-digestion process. In the process several classes of mediators are generated that by themselves have inflammatory activity and upon entry into the central circulation generate the hallmarks of inflammation and eventually cause multi-organ failure. Thus, our journey led to a new hypothesis, which is potentially of fundamental importance for death by multi-organ failure. The auto-digestion hypothesis is in line with the century old observation that the intestine plays a special role on shock - indeed it is the organ for digestion. Auto-digestion may be the prize to pay for life-long nutrition.

PANCREATIC ENZYMES GENERATE CYTOTOXIC MEDIATORS IN THE INTESTINE

Recent evidence indicates that shock is accompanied by a failure of the mucosal barrier in the intestine and entry of pancreatic digestive enzymes into the wall of the intestine. To investigate the formation of cytotoxic mediators produced by enzymatic digestion of the intestine, we applied homogenates of rat small intestinal wall to human neutrophils and used flow cytometry measurements of propidium iodide uptake to determine cytotoxicity. We show that homogenates of the small intestine after ischemia by occlusion of the superior mesenteric and celiac arteries for 3 h, but not without ischemia, are cytotoxic. Digestion of homogenates of nonischemic intestinal wall with purified trypsin, chymotrypsin, or elastase, proteases normally present in the intestinal lumen, yielded cytotoxic mediators. Before cell death, we saw cell damage in the form of bleb formation and flow cytometry measurements of cell size changes due to blebbing. Cytotoxicity was prevented by serine protease inhibition with phenylmethylsulfonyl fluoride (PMSF) before, but not after proteolytic digestion of the wall homogenates, indicating that enzymatic action of proteases on the homogenate is necessary for cytotoxicity. Cytotoxicity of wall homogenates digested by enzymes in the fluid collected from the lumen of the intestine was greater than digests by the individual purified proteases. Cytotoxicity is undetectable if digestive enzymes in the luminal fluid are inhibited with a combination of enzyme inhibitors PMSF and 6-amidino-2-naphthyl p-guanidinobenzoate dimethanesulfonate before addition of wall homogenates. Passage of digested intestinal wall homogenates across a hydrophobic glass-fiber filter reduced cytotoxicity. Furthermore, we found that luminal fluid itself may be cytotoxic, possibly because of digestion of ingested food. To test whether digested food can be cytotoxic, we homogenized rat food and digested it in vitro with chymotrypsin or endogenous enzymes in luminal fluid. Cytotoxicity was significantly increased after digestion of food by luminal fluid compared with luminal fluid or undigested food. These results indicate the presence of a previously unknown mechanism for hemorrhagic necrosis in shock.

INTRALUMINAL PANCREATIC SERINE PROTEASE ACTIVITY, MUCOSAL PERMEABILITY, AND SHOCK

Shock states are characterized by a pronounced activation of numerous cell types that lead to an acute inflammatory reaction. The exact mechanism by which these inflammatory cells are activated is not known. Numerous studies have implicated the gastrointestinal tract as one of the main sites for the generation of inflammatory mediators and initiation of an acute systemic response. The pancreas is known to secrete powerful digestive enzymes, and we hypothesize that they may play a leading role in the pathogenesis of multiorgan failure after the onset of shock. We carried out a search in PubMed for all relevant studies related to the role of the pancreas in shock. Studies that included information concerning the role of pancreatic enzymes in shock were then summarized. Our article serves to review the current hypotheses on how digestive enzymes produced by the pancreas may play a pivotal role in initiating the systemic inflammatory response. We further hypothesize how these enzymes and/or their products may ultimately contribute to multiorgan failure and death.

Trauma-hemorrhagic shock mesenteric lymph from rat contains a modified form of albumin that is implicated in endothelial cell toxicity

It has been proposed that factors originating from the gut after severe trauma/shock are introduced into the systemic circulation through the mesenteric lymphatics and are responsible for the cellular injury and inflammation that culminates in acute multiple organ dysfunction syndrome (MODS). Indeed, it has been shown that lymph collected from shocked but not sham-shocked animals causes endothelial cell death, neutrophil activation, and bone marrow (BM) colony growth suppression in vitro. In an attempt to isolate the factor(s) in lymph responsible for endothelial cell toxicity, lymph from shock and sham animals was fractionated by solid phase extraction (SPE) and ion exchange chromatography (IEX). The separation of shock lymph by both methodologies yielded two fractions having major detectable toxicity to endothelial cells, whereas no toxicity was detected from sham lymph separations by either method. Subsequent analysis of each SPE toxic fraction by gel electrophoresis and mass spectrometry suggests the toxicity is associated with a modified form of rat serum albumin (mod-RSA) and multiple lipid-based factors. Therefore, we have been able to demonstrate by two different separation techniques that shock lymph contains two or more factors that may account for the toxicity to endothelial cells. Further investigations are needed to determine the type of RSA modification and the identity of the lipid factors and their role in MODS.

A new hypothesis for microvascular inflammation in shock and multiorgan failure: self-digestion by pancreatic enzymes

Shock is accompanied by a severe inflammatory cascade in the microcirculation, the origin of which has been hypothesized in the past to be associated with specific mediators such as endotoxin, oxygen free radicals, nitric oxide, cytokines, and lipid products. But no intervention with clinical effectiveness has been derived from these ideas to date. The authors propose here a new hypothesis suggesting that degradative enzymes, synthesized in the pancreas as part of normal digestion, may play a central role in shock and multiorgan failure. These powerful enzymes have the ability to digest almost every biological material. Self-digestion (i.e. autodegradation) is prevented by compartmentalizing the fully activated degradative enzymes in the intestinal lumen by the mucosal barrier. In shock, maintenance of the mucosal barrier is impaired and it becomes permeable to pancreatic enzymes. Digestive enzymes thereby gain access to the wall of the intestine and initiate self-digestion of submucosal extracellular matrix proteins and interstitial cells. The process leads to generation and release of a host of strong inflammatory mediators. The authors hypothesize that inhibition of pancreatic enzymes in the lumen of tile intestine can serve to attenuate formation of these inflammatory mediators in ischemic tissues following hemorrhagic shock, and consequently prevent cell and tissue injury as well as multiorgan failure.

Pancreatic proteases and inflammatory mediators in peritoneal fluid during splanchnic arterial occlusion and reperfusion

Pancreatic enzymes in the ischemic intestine are involved in the production of in vivo inflammatory mediators. These mediators stimulate cells in the cardiovascular system during shock and initiate multiorgan failure. An important aspect that controls the extent of the inflammation is the dispersion of these mediators from the ischemic intestine. In the past, two pathways for dispersion of these inflammatory mediators have been identified, absorption into the intestinal venous circulation and uptake into the lymphatics. We hypothesize here that the inflammatory mediators produced by pancreatic digestive enzymes in the lumen of the intestine may also be released directly into the peritoneal space. To assess the presence of inflammatory mediators in the peritoneal cavity in response to splanchnic arterial occlusion (90 min) and reperfusion (SAO shock), we measured the ability of fluid collected from this cavity to activate naive donor granulocytes. After SAO in control rats, peritoneal lavage fluid caused activation of naive donor granulocytes when tested in vitro. In contrast, when the lumen of the small intestine was flushed with a broad-acting pancreatic enzyme inhibitor (6-amidino-2-naphtyl p-guanidinobenzoate dimethanesulfate), the fluid no longer caused leukocyte activation. Reduction of the levels of inflammatory mediators in the peritoneal fluid was associated with an attenuation in the fall of blood pressure after SAO shock. These results indicate that the inflammatory mediators, which are produced by pancreatic digestive enzymes, can be absorbed directly into the systemic circulation via a transperitoneal route and play a part in the development of multiorgan failure.

Inhibition of enteral enzymes by enteroclysis with nafamostat mesilate reduces neutrophil activation and transfusion requirements after hemorrhagic shock

BACKGROUND

The gut origin of the inflammatory response in trauma patients has been difficult to define. "In vivo" generation of neutrophil-activating factors by gut proteases may be a cause of multiorgan failure after hemorrhagic shock, and can be prevented with the serine protease inhibitor nafamostat mesilate (Futhan). The objective of this study was to determine the effect of nafamostat mesilate given by enteroclysis on enteric serine protease activity, neutrophil activation, and transfusion requirements during hemorrhagic shock.

METHODS

Sixteen pigs weighing 21 to 26 kg were divided into control and treatment groups. A laparotomy was performed under anesthesia, and catheters were placed in the duodenum, midjejunum, and terminal ileum. Pigs were bled 30 mL/kg over 30 minutes and maintained at a mean arterial pressure of 30 mm Hg for 60 minutes. Shed blood was then used to maintain a mean arterial pressure of 45 mm Hg for another 3 hours. Treated animals received 100 mL/kg of 0.37 mmol/L nafamostat mesilate in GoLYTELY through the duodenal catheter at 1 L/h. Control animals received GoLYTELY only. Samples of enteral content and blood were taken at baseline, after shock, and at 30-minute intervals during resuscitation. Animals were killed after 3 hours of resuscitation. Enteral trypsin-like activity at the three gut sites was measured by spectrophotometry. Activation of naive human neutrophils by pig plasma was measured by the percentage of cells having pseudopods larger than 1 microm on microscopy. Lung, liver, and small bowel were analyzed by histology and myeloperoxidase assay.

RESULTS

Both control and nafamostat mesilate-treated groups had significant reductions in protein and protease levels in the duodenum during enteroclysis; however, only nafamostat mesilate-treated animals had persistent suppression of protease activity throughout the experiment. Nafamostat mesilate-treated animals had a lower transfusion requirement of shed blood, 18.1 +/- 4.5 mL/kg versus 30 +/- 0.43 mL/kg (p = 0.002). Nafamostat mesilate-treated animals had significantly less neutrophil activation than controls at 150 minutes after resuscitation (33.7 +/- 6.48% vs. 42.4 +/- 4.57%,p = 0.01) and 180 minutes after resuscitation (31.1 +/- 3.31% vs. 46.9 +/- 4.53%, p = 0.0002). Lung myeloperoxidase activity was lower in nafamostat mesilate-treated animals (0.31 +/- 0.14) than in control animals (0.16 +/- 0.04, p = 0.04). Histology of liver and small intestine showed less injury in nafamostat mesilate-treated animals.

CONCLUSION

Nafamostat mesilate given by means of enteroclysis with GoLYTELY significantly reduces enteral protease levels, leukocyte activation, and transfusion requirements during resuscitation from hemorrhagic shock. This strategy may have clinical promise.

Pancreatic trypsin increases matrix metalloproteinase-9 accumulation and activation during acute intestinal ischemia-reperfusion in the rat

Ischemia-reperfusion of the intestine produces a set of inflammatory mediators, the origin of which has recently been shown to involve pancreatic digestive enzymes. Matrix metalloproteinase-9 (MMP-9) participates in a variety of inflammatory processes including myocardial, hepatic, and pancreatic ischemia-reperfusion. In the present study, we explore the role of neutrophil-derived MMP-9 in acute intestinal ischemia-reperfusion and its interaction with pancreatic trypsin. Male Sprague-Dawley rats were subjected to 45 minutes of superior mesenteric arterial occlusion followed by 90 minutes of reperfusion. In situ zymography of the proximal jejunum reveals increased gelatinase activity in the intestinal wall after ischemia-reperfusion. Gel electrophoresis zymography and immunofluorescence co-localization suggests that this gelatinase activity is derived from MMP-9 released from infiltrating neutrophils. The role of intraluminal trypsin in this process was investigated using an in vivo isolated jejunal loop model of intestinal ischemia-reperfusion. Trypsin increased the inflammatory response after reperfusion, with an augmented neutrophil infiltration of the intestinal wall. Furthermore, trypsin stimulated a rapid conversion of neutrophil-released proMMP-9 into the lower molecular weight enzymatically active MMP-9. This process represents a powerful in vivo pathophysiological mechanism for trypsin-induced MMP-9 activation and is likely to play a central role in the development of acute intestinal inflammation and shock.