Hemorrhagic shock is associated with metabolic defects, including hyperglycemia and insulin resistance but the mechanisms are unknown. We recently demonstrated that reduction of the extracellular domain of the insulin receptor by degrading proteases may lead to a reduced ability to maintain normal plasma glucose values. In shock, transfer of digestive enzymes from the lumen of the intestine into the systemic circulation after breakdown of the intestinal mucosal barrier causes inflammation and organ dysfunction. Suppression of the digestive enzymes in the lumen of the intestine with protease inhibitors is effective in reducing the level of the inflammatory reactions. To determine the degree to which blockade of digestive enzymes affects insulin resistance in shock, rats were exposed to acute hemorrhagic shock (mean arterial pressure of 30 mmHg for 2 hours) at which time all shed blood volume was returned. Digestive proteases in the intestine were blocked with a serine protease inhibitor (tranexamic acid in polyethylene glycol and physiological electrolyte solution) and the density of the insulin receptor was measured with immunohistochemistry in the mesentery microcirculation. The untreated rat without enzyme blockade had significantly attenuated levels of insulin receptor density as compared to control and treated rats. Blockade of the digestive proteases after 60 min of hypotension in the lumen of the small intestine lead to a lesser decrease in insulin receptor density compared to controls without protease blockade. Glucose tolerance test indicates a significant increase in plasma glucose levels two hours after hemorrhagic shock, which are reduced to control values in the presence of protease inhibition in the lumen of the intestine. The transient reduction of the plasma glucose levels after an insulin bolus is significantly attenuated after shock, but is restored in when digestive enzymes in the lumen of the intestine are blocked. These results suggest that in hemorrhagic shock elevated microvascular extracellular digestive enzyme activity causes insulin receptor dysfunction, hyperglycemia and reduced ability to regulate blood glucose values.
Glucose tolerance; pancreatic enzymes; proteases; auto-digestion; mesentery microvessels; leukocytes; Wistar rat
Shock and multi-organ failure have one of the highest levels of inflammatory markers, morbidities and mortality. The underlying mechanisms are currently unknown and no effective intervention exists. We present evidence for a previously untested mechanism due to autodigestion by the digestive enzymes synthesized in the pancreas and transported in the lumen of the intestine as normal part of food digestion. We summarize experimental evidence in support of the autodigestion hypothesis and a new approach for possible intervention against multi-organ failure that is currently entering clinical trials.
Intestine; digestive pancreas; inflammation; trypsin; chymotrypsin; elastase; intestinal mucosa; hemorrhagic shock; sepsis
Recent evidence suggests that the spontaneously hypertensive rat (SHR) has an elevated level of proteases, including matrix metalloproteinases (MMPs), involved in cell membrane receptor cleavage. We hypothesize that SHR red blood cells (RBCs) may be subject to an enhanced glycocalyx cleavage compared to the RBCs of the normotensive Wistar-Kyoto (WKY) rats. By direct observation of RBC rouleaux, we found no significant difference in RBC aggregation for unseparated SHR and WKY RBCs. However, lighter SHR RBCs have a greater tendency to aggregate than WKY RBCs when separated by centrifugation. When SHR plasma was mixed with WKY RBCs, SHR plasma proteases cleaved the glycocalyx of WKY RBCs, a process that can be blocked by MMP inhibition. When treated with MMPs, WKY RBCs showed strong aggregation in dextran but not in fibrinogen, indicating that RBC membrane glycoproteins from the inner core of the glycocalyx were cleaved and that dextran was able to bind to the lipid portion of the RBC membrane. In contrast, treatment with amylases produced fibrinogen-induced aggregation with fibrinogen binding to the protein core. MMP cleavage of RBC glycocalyx reduces RBC adhesion to macrophages as a mechanism to remove old RBCs from the circulation.
Spontaneously hypertensive rat; matrix metalloproteinases; red blood cell aggregation; glycocalyx cleavage; dextran; fibrinogen
Intestinal ischemia is associated with high morbidity and mortality but the underlying mechanisms are uncertain. We hypothesize that during ischemia the intestinal mucosal barrier becomes disrupted, allowing digestive enzymes access into the intestinal wall initiating autodigestion. We used a rat model of splanchnic ischemia by occlusion of the superior mesenteric and celiac arteries up to 30 min with and without luminal injection of tranexamic acid as a trypsin inhibitor. We determined the location and activity of digestive proteases on intestinal sections with in-situ zymography and we examined the disruption of two components of the mucosal barrier: mucin isoforms and the extra- and intracellular domains of E-cadherin with immunohistochemistry and western blot techniques. The results indicate that non-ischemic intestine has low levels of protease activity in its wall. After 15 min ischemia protease activity was visible at the tip of the villi and after 30 min enhanced activity was seen across the full thickness of the intestinal wall. This activity was accompanied by disruption of the mucin layer and loss of both intra- and extracellular domains of E-cadherin. Digestive protease inhibition in the intestinal lumen with tranexamic acid reduced morphological damage and entry of digestive enzymes into the intestinal wall. This study demonstrates that disruption of the mucosal epithelial barrier within minutes of intestinal ischemia allows entry of fully activated pancreatic digestive proteases across the intestinal barrier triggering autodigestion.
Shock; mucin; serine proteases; e-cadherin
Recent evidence indicates that several experimental pathophysiological conditions are associated with elevated protease activity in plasma, which impacts endothelial function. We hypothesize that extracellular structures bound to the endothelial cell (EC) membrane may be degraded by proteolytic activity and cause the cells to respond abnormally to physiological shear stress (12 dyn/cm2). To test this hypothesis, cultured bovine aortic endothelial cells (BAECs) were exposed to low levels of a serine protease, trypsin. Extracellular mechanosensor densities of the glycocalyx and vascular endothelial growth factor receptor 2 (VEGFR-2) were determined. Metabolic dysfunction was tested by examining insulin receptor and glucose uptake levels. Protease treatment impaired the cells’ ability to align in the direction of fluid flow after 12 hours of shear stress; however, cells realigned after an additional 12 hours of shear stress with protease inhibition. Proteases caused reduction in the densities of glycocalyx, VEGFR-2, and insulin receptor in static and shear conditions, except for static VEGFR-2 cells. Under static conditions, protease-treated endothelial cells had reduced glucose uptake compared to untreated controls. Under shear, however, glucose uptake for protease-treated BAECs was greater than untreated controls. In conclusion, protease activity in plasma alters the exofacial membrane components of ECs and may interfere with mechanotransduction.
Mechanotransduction; VEGFR-2; insulin resistance; lectin; glycocalyx; autodigestion
Leukocyte adhesion to the endothelium is abnormal in hypertension. We have recently shown that spontaneously hypertensive rats (SHRs) have circulating leukocytes with enhanced CD18 receptor cleavage. In the current study, we investigate expression levels of its counter receptor, intercellular adhesion molecule (ICAM-1), and its possible proteolytic cleavage in the SHR and control Wistar rat.
ICAM-1 was labeled on tissue sections with two antibodies targeting its extracellular and intracellular domains and evaluated by light absorption measurements. The in situ cleavage of ICAM-1 was assessed by treating vessel sections with matrix metalloproteinase (MMP)-7, MMP-9 and elastase.
SHRs showed a significant increase in ICAM-1 expression in liver and kidney compared with Wistar rats. The liver and kidney glomeruli exhibit a discrepancy in label density between intra- and extracellular antibodies, which suggests that enzymatic cleavage may be a factor determining ICAM-1 distribution. MMP-7 and MMP-9, which are elevated in SHR plasma, and elastase, which has elevated activity in SHR neutrophils, cleave the extracellular domain of ICAM-1 when applied to the tissue.
ICAM-1 expression in SHRs is upregulated in a tissue-specific manner. Proteolytic cleavage of the extracellular domain of ICAM-1 and accumulation in kidney glomeruli may play a role in the renal involvement of inflammation.
Leukocyte adhesion; Endothelium; Receptor cleavage; Arterioles; Venules
Microvascular rarefaction, defined by a loss of terminal arterioles, small venules and/or capillaries, is a common characteristic of the hypertension syndrome. While rarefaction has been associated with vessel specific free radical production, deficient leukocyte adhesion, and cellular apoptosis, the relationships of rarefaction with structural alterations at the network and cellular level remain largely unexplored. The objective of this study was to examine the architecture and perivascular cell phenotypes along microvascular networks in hypertensive versus normotensive controls in the context of imbalanced angiogenesis. Mesenteric tissues from age-matched adult male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats were harvested and immnolabeled for PECAM and neuron-glia antigen 2 (NG2). Evaluation of intact rat mesenteric microvascular networks rats suggests that network alterations associated with hypertension are more complex than just a loss of vessels. Typical SHR versus WKY networks demonstrate a reduced branching architecture marked by more proximal arteriole/venous anastomoses and an absence of NG2 labeling along arterioles. Although less frequent, larger SHR microvascular networks display regions of dramatically increased vascular density. SHR and WKY lymphatic networks demonstrate increased vessel diameters and vascular density compared to networks in normotensive Wistar rats (the strain from which both the SHR and WKY originated). These observations provide a rationale for investigating the presence of local angiogenic factors and response of microvascular networks to therapies aimed at reversing rarefaction in genetic hypertension.
A complication of the spontaneously hypertensive rat (SHR) is microvascular rarefaction, defined by the loss of microvessels. However, the molecular mechanisms involved in this process remain incompletely identified. Recent work in our laboratory suggests that matrix metalloproteinases (MMPs) may play a role by cleavage of the vascular endothelial growth factor receptor 2 (VEGFR-2). In order to further delineate the role for MMPs in microvascular rarefaction, the objective of the current study was to examine the relationship in the same tissue between MMP activity, VEGFR-2 cleavage and rarefaction. Using an in-vivo microzymographic technique we show significantly enhanced levels of MMP-1, -1/-9, -7, and -8 activities, but not MMP-2 and-3 activities, along mesenteric microvessels of the SHR compared to its normotensive control, Wistar Kyoto (WKY) rat. Based on immunohistochemical methods, the SHR exhibited a decreased labeling of the extracellular, but not the intracellular, domain of VEGFR-2 along mesenteric microvessels. Chronic MMP inhibition served to attenuate VEGFR-2 cleavage and microvascular network rarefaction in the SHR mesentery. These results spatially link MMP-induced VEGFR-2 cleavage and rarefaction in the mesentery of the SHR and thus support the hypothesis that MMPs serve as regulators of microvascular dysfunction in hypertension.
Spontaneously Hypertensive Rat; Wister Kyoto rat; capillary; arteriole; venule; microzymography; matrix metalloproteinase inhibition
Chronic venous disease (CVD) has a range of clinical presentations, including tortuous, distended veins in lower extremities, increasing skin pigmentation, and in severe cases ulceration of the affected skin. Venous insufficiency, a precursor to CVD characterized by improper return of blood from the lower extremities to the heart, must be studied in its earliest stages at a time when preventative measures could be applied in man. This underscores the need for basic research into biomarkers and genetic predisposing factors affecting the progression of venous disease. Investigation over the past decade has yielded insight into these specific genetic, cellular and molecular mechanisms underlying the development of venous disease. Among the many advances include the elucidation of an increasing role for matrix metalloproteinases as important mediators of the degenerative process involved with venous insufficiency. This may be preceded by an inflammatory process which further contributes to venular degeneration and endothelial dysfunction seen in advanced presentation of disease. Furthermore, genomic analyses have shed light upon temporal expression patterns of matrix remodeling proteins in diseased tissue samples. In this review we examine some of the current findings surrounding cellular, molecular and genetic advances in delineating the etiology of chronic venous disease.
Vein; Venous disease; Molecular; Genetics; Valves; Endothelial; Blood vessel
Recent evidence suggests that inflammation in the spontaneously hypertensive rat (SHR) is associated with an uncontrolled matrix metalloproteinase (MMP) activity. We hypothesize that the transcription factor nuclear factor kappa B (NF–κB) is overexpressed in the SHR, enhancing its MMP activity and enzymatic cleavage of the beta-2 adrenergic receptor (β2AR), thereby diminishing catecholamine-mediated arteriolar vasodilation. NF-κB expression level and translocation were compared between Wistar Kyoto rat (WKY) and SHR kidney, heart and brain. The animals were treated with a NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC), for ten weeks and correlations between NF-κB and MMP activity were determined. Immunohistochemistry showed that NF-κB expression is increased in untreated SHR kidney (~ 14%) and brain hypothalamus (~ 22%) compared to that in WKY (p <0.05), but not in myocardium and cerebral cortex. After PDTC treatment, the SHR systolic blood pressure was reduced close to WKY levels. NF-κB expression level in treated-SHR was also decreased in kidney and hypothalamus compared to non-treated animals (p <0.05). Furthermore, MMP-2 and -9 activities in SHR plasma were significantly reduced (~41%) by PDTC treatment. Additionally, zymographic analyses and in situ zymography showed decreased MMP-2 activity in kidney homogenates and decreased MMP-1,-9 activities in brain. The level of the β2AR extracellular, but not intracellular, domain density was found reduced in kidney showing a receptor cleavage process that can be blocked by PDTC treatment. These results suggest NF-κB is an important transcription factor in the SHR and may be involved in the enhanced MMP activity and consequently receptor cleavage.
Microcirculation; matrix metalloproteinases; beta-2 adrenergic receptor; receptor cleavage; NF-κB inhibitor; pyrrolidine dithiocarbamate
Venous hypertension is associated with microvascular inflammation, restructuring, and apoptosis, but the cellular and molecular mechanisms underlying these events remain uncertain. In the present study we tested the hypothesis that elevated venous pressure and reduction of shear stress induces elevated enzymatic activity. This activity in turn may affect endothelial surface receptors and promote their dysfunction. Using a rodent model for venous hypertension using acute venular occlusion, microzymographic techniques for enzyme detection, and immunohistochemistry for receptor labeling, we found increased activity of the matrix metalloproteases (MMPs) -1, -8 and -9 and tissue inhibitors of metalloproteases (TIMPs) -1,-2 in both high and low-pressure regions. In this short time frame we also observed that elevated venule pressure led to two different fates for the vascular endothelial growth factor receptor-2 (VEGFR2); in higher-pressure upstream regions some animals exhibited higher VEGFR2 expression, while others displayed lower levels upstream compared to their downstream counterparts with lower pressure. VEGFR2 expression was, on average, more pronounced upon application of MMP inhibitor, suggesting possible cleavage of the receptor by activated enzymes in this model. We conclude that venous pressure elevation increases enzymatic activity which may contribute to inflammation and endothelial dysfunction associated with this disease by influencing critical surface receptors.
matrix metalloproteases; inflammation; vascular endothelial growth factor-2; occlusion; mesentery; venule; endothelial cell
One of the most important unresolved issues in diabetes is the mechanism for the attenuated response to insulin, i.e. insulin resistance.
Aims and methods
We hypothesize that the mechanism for the insulin resistance is due to uncontrolled protease activity in the plasma, on endothelial cells and in the tissue parenchyma. To examine this hypothesis we use of microzymographic techniques in the microcirculation, plasma zymography, and receptor labeling techniques with antibodies against an extracellular domain of the insulin receptor α.
The spontaneously hypertensive rat has an enhanced proteolytic activity and significant cleavage of the receptor with attenuated glucose transport. We present evidence for insulin receptor cleavage in a high fat diet and a transgenic model of diabetes.
These results suggest that cleavage of the extracellular domain of the insulin receptor, a situation that interferes with the ability for insulin to bind and provide an intracellular signal for glucose transport, may be involved in insulin resistance.
Protease activity; matrix metalloproteases; insulin resistance; receptor cleavage; leukocyte; adhesion; integrin
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 forms of inflammation, shock and multi-organ failure, for which there is no accepted injury mechanism, we summarize studies which suggest that the powerful pancreatic digestive enzymes play a central role in destruction of the intestine and other tissues if their compartmentalization in the lumen of the intestine and in the pancreas is compromised. Furthermore, 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 mechanism for tissue injury. The significance of such mechanisms remain to be explored in human diseases.
Microcirculation; inflammation; pancreatic enzymes; matrix metalloproteinases; shock; multi-organ failure; hypertension
Increasing evidence suggests that most cardiovascular diseases, tumors and other ailments are associated with an inflammatory cascade. The inflammation is accompanied by activation of cells in the circulation and fundamental changes in the mechanics of the microcirculation, expression of pro-inflammatory genes and downregulation of anti-inflammatory genes, attachment of leukocytes to the endothelium, elevated permeability of the endothelium, and many other events. The evidence has opened great opportunities for medicine to develop new anti-inflammatory interventions. But it also raises a fundamental question: What is the origin of inflammation? I will discuss a basic series of studies that was designed to explore trigger mechanisms for inflammation in shock and multi-organ failure, an important clinical problem associated with high mortality. We traced the source of the inflammatory mediators to the powerful digestive enzymes in the intestine. Synthesized in the pancreas as part of normal digestion, they have the ability to degrade almost all biological tissues and molecules. In the lumen of the intestine, digestive enzymes are fully activated and self-digestion of the intestine is prevented by compartmentalization in the lumen of the intestine facilitated by the mucosal epithelial barrier. Under conditions of intestinal ischemia, however, the mucosal barrier becomes permeable to pancreatic enzymes allowing their entry into the wall of the intestine. The process leads to auto-digestion of the intestinal wall and production of inflammatory mediators. The hypothesis that multi-organ failure in shock may be due an auto-digestion process by pancreatic enzymes is ready to be tested in a variety of shock conditions.
shock; intestinal ischemia; digestive enzymes; transport; epithelial barrier
Arterial hypertension is associated with organ dysfunctions, but the mechanisms are uncertain. We hypothesize that enhanced proteolytic activity in the microcirculation of spontaneously hypertensive rats (SHRs) may be a pathophysiological mechanism causing cell membrane receptors cleavage and examine this for two different receptors. Immunohistochemistry of matrix-degrading metalloproteinases (MMP-9) protein shows enhanced levels in SHR microvessels, mast cells, and leukocytes compared to normotensive Wistar-Kyoto (WKY) rats. In-vivo micro-zymography shows cleavage by MMP-1,9 in SHRs that co-localizes with MMP-9 and is blocked by metal chelation. SHR plasma also has enhanced protease activity. We demonstrate with an antibody against the extracellular domain that the insulin receptor-α density is reduced in SHR, in line with elevated blood glucose levels and glycated hemoglobin. There is also cleavage of the binding domain of the leukocyte integrin receptor CD18 in line with previously reported reduced leukocyte adhesion. Blockade of MMPs with broad acting inhibitor (doxycycline, 5.4mg/kg/day) reduces protease activity in plasma and microvessels, blocks the proteolytic cleavage of the insulin receptor, the reduced glucose transport, normalizes blood glucose levels and glycated hemoglobin levels, as well as reduces blood pressure and enhanced microvascular oxidative stress of SHRs. The results suggest that elevated MMP activity leads to proteolytic cleavage of membrane receptors in the SHR, e.g. cleavage of the insulin receptor-binding domain associated with insulin resistance.
Microcirculation; matrix metalloproteinases; insulin receptor; integrin; receptor cleavage; oxygen free radical
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.
Auto-digestion; shock; inflammation; cytokines; leukocytes; microcirculation; pancreatic enzymes; trypsin; chymotrypsin; elastase
Hypertension is a common hereditary syndrome with unclear pathogenesis. Chromogranin A (Chga), which catalyzes formation and cargo storage of regulated secretory granules in neuroendocrine cells, contributes to blood pressure homeostasis centrally and peripherally. Elevated Chga occurs in spontaneously hypertensive rat (SHR) adrenal glands and plasma, but central expression is unexplored. In this report, we measured SHR and Wistar–Kyoto rat (control) Chga expression in central and peripheral nervous systems, and found Chga protein to be decreased in the SHR brainstem, yet increased in the adrenal and the plasma. By re-sequencing, we systematically identified five promoter, two coding and one 3′-untranslated region (3′-UTR) polymorphism at the SHR (versus WKY or BN) Chga locus. Using HXB/BXH recombinant inbred (RI) strain linkage and correlations, we demonstrated genetic determination of Chga expression in SHR, including a cis-quantitative trait loci (QTLs) (i.e. at the Chga locus), and such expression influenced biochemical determinants of blood pressure, including a cascade of catecholamine biosynthetic enzymes, catecholamines themselves and steroids. Luciferase reporter assays demonstrated that the 3′-UTR polymorphism (which disrupts a microRNA miR-22 motif) and promoter polymorphisms altered gene expression consistent with the decline in SHR central Chga expression. Coding region polymorphisms did not account for changes in Chga expression or function. Thus, we hypothesized that the 3′-UTR and promoter mutations lead to dysregulation (diminution) of Chga in brainstem cardiovascular control nuclei, ultimately contributing to the pathogenesis of hypertension in SHR. Accordingly, we demonstrated that in vivo administration of miR-22 antagomir to SHR causes substantial (∼18 mmHg) reductions in blood pressure, opening a novel therapeutic avenue for hypertension.
In intestinal ischemia, inflammatory mediators in the small intestine's lumen such as food byproducts, bacteria, and digestive enzymes leak into the peritoneal space, lymph, and circulation, but the mechanisms by which the intestinal wall permeability initially increases are not well defined. We hypothesize that wall protease activity (independent of luminal proteases) and apoptosis contribute to the increased transmural permeability of the intestine's wall in an acutely ischemic small intestine. To model intestinal ischemia, the proximal jejunum to the distal ileum in the rat was excised, the lumen was rapidly flushed with saline to remove luminal contents, sectioned into equal length segments, and filled with a tracer (fluorescein) in saline, glucose, or protease inhibitors. The transmural fluorescein transport was determined over 2 hours. Villi structure and epithelial junctional proteins were analyzed. After ischemia, there was increased transmural permeability, loss of villi structure, and destruction of epithelial proteins. Supplementation with luminal glucose preserved the epithelium and significantly attenuated permeability and villi damage. Matrix metalloproteinase (MMP) inhibitors (doxycycline, GM 6001), and serine protease inhibitor (tranexamic acid) in the lumen, significantly reduced the fluorescein transport compared to saline for 90 min of ischemia. Based on these results, we tested in an in-vivo model of hemorrhagic shock (90 min 30 mmHg, 3 hours observation) for intestinal lesion formation. Single enteral interventions (saline, glucose, tranexamic acid) did not prevent intestinal lesions, while the combination of enteral glucose and tranexamic acid prevented lesion formation after hemorrhagic shock. The results suggest that apoptotic and protease mediated breakdown cause increased permeability and damage to the intestinal wall. Metabolic support in the lumen of an ischemic intestine with glucose reduces the transport from the lumen across the wall and enteral proteolytic inhibition attenuates tissue breakdown. These combined interventions ameliorate lesion formation in the small intestine after hemorrhagic shock.
Premature infants fed formula are more likely to develop necrotizing enterocolitis (NEC) than if fed breast milk, but the mechanisms of intestinal necrosis in NEC and protection by breast milk are unknown. We hypothesized that after lipase digestion, formula, but not fresh breast milk, contains levels of unbound free fatty acids (FFAs) that are cytotoxic to intestinal cells.
We digested multiple term and preterm infant formulas or human milk with pancreatic lipase, proteases (trypsin and chymotrypsin), lipase + proteases, or luminal fluid from a rat small intestine and tested FFA levels and cytotoxicity in vitro on intestinal epithelial cells, endothelial cells, and neutrophils.
Lipase digestion of formula, but not milk, caused significant death of neutrophils (ranging from 47–99% with formulas vs. 6% with milk) with similar results in endothelial and epithelial cells. FFAs were significantly elevated in digested formula versus milk and death from formula was significantly decreased with lipase inhibitor pretreatment, or treatments to bind FFAs. Protease digestion significantly increased FFA binding capacity of formula and milk but only enough to decrease cytotoxicity from milk.
FFA-induced cytotoxicity may contribute to the pathogenesis of NEC.
free fatty acids; shock; lipase; cytotoxicity
The small intestine plays a key role in the pathogenesis of multiple organ failure following circulatory shock. Current results show that reduced perfusion of the small intestine compromises the mucosal epithelial barrier, and the intestinal contents (including pancreatic digestive enzymes and partially digested food) can enter the intestinal wall and transport through the circulation or mesenteric lymph to other organs such as the lung. The extent to which the luminal contents of the small intestine mediate tissue damage in the intestine and lung is poorly understood in shock. Therefore, rats were assigned to three groups: No-hemorrhagic shock (HS) control and HS with or without a flushed intestine. HS was induced by reducing the mean arterial pressure (30 mmHg; 90 min) followed by return of shed blood and observation (3 h). The small intestine and lung were analyzed for hemorrhage, neutrophil accumulation, and cellular membrane protein degradation. After HS, animals with luminal contents had increased neutrophil accumulation, bleeding, and destruction of E-cadherin in the intestine. Serine protease activity was elevated in mesenteric lymph fluid collected from a separate group of animals subjected to intestinal ischemia/reperfusion. Serine protease activity was elevated in the plasma after HS but was detected in lungs only in animals with nonflushed lumens. Despite removal of the luminal contents, lung injury occurred in both groups as determined by elevated neutrophil accumulation, permeability, and lung protein destruction. In conclusion, luminal contents significantly increase intestinal damage during experimental HS, suggesting transport of luminal contents across the intestinal wall should be minimized.
Hemorrhagic shock; lung injury; lymph; protease activity; small intestine
In January of 2011, the Biomedical Engineering Society (BMES) and the Society for Physical Regulation in Biology and Medicine (SPRBM) held its inaugural Cellular and Molecular Bioengineering (CMBE) conference. The CMBE conference assembled worldwide leaders in the field of CMBE and held a very successful Round Table discussion among leaders. One of the action items was to collectively construct a white paper regarding the future of CMBE. Thus, the goal of this report is to emphasize the impact of CMBE as an emerging field, identify critical gaps in research that may be answered by the expertise of CMBE, and provide perspectives on enabling CMBE to address challenges in improving human health. Our goal is to provide constructive guidelines in shaping the future of CMBE.
In bowel ischemia, impaired mucosal integrity may allow intestinal pancreatic enzyme products to become systemic and precipitate irreversible shock and death. This can be attenuated by pancreatic enzyme inhibition in the small bowel lumen. It is unresolved, however, whether ischemically-mediated mucosal disruption is the key event allowing pancreatic enzyme products systemic access, and whether intestinal digestive enzyme activity in concert with increased mucosal permeability leads to shock in the absence of ischemia. To test this possibility, the small intestinal lumen of non-ischemic rats was perfused for two hours with either digestive enzymes, a mucin disruption strategy (i.e., mucolytics) designed to increase mucosal permeability, or both, and animals were observed for shock. Digestive enzymes perfused included trypsin, chymotrypsin, elastase, amylase and lipase. Control (n=6) and experimental animals perfused with pancreatic enzymes only (n=6) or single enzymes (n=3 for each of the five enzyme groups) maintained stable hemodynamics. After mucin disruption using a combination of enteral N-acetylcysteine, atropine, and increased flow rates, rats (n=6) developed mild hypotension (p<0.001 compared to groups perfused with pancreatic enzymes only after 90 minutes) and increased intestinal permeability to intralumenally perfused FITC-dextrans-20kD (p<0.05) compared to control and enzyme-only groups, but there were no deaths. All animals perfused with both digestive enzymes and subjected to mucin disruption (n=6) developed hypotension and increased intestinal permeability (p<0.001 after 90 minutes). Pancreatic enzymes were measured in the intestinal wall of both groups subjected to mucin disruption, but not in the enzyme-only or control groups. Depletion of plasma protease inhibitors was found only in animals perfused with pancreatic enzymes plus mucin disruption, implicating increased permeability and intralumenal pancreatic enzyme egress in this group. These experiments demonstrate that increased bowel permeability via mucin disruption in the presence of pancreatic enzymes can induce shock and increase systemic protease activation in the absence of ischemia, implicating bowel mucin disruption as a key event in early ischemia. Digestive enzymes and their products, if allowed to penetrate the gut wall may trigger multiorgan failure and death.
Autodigestion; small intestine permeability; pancreatic enzymes; inflammatory mediators
Methods and Results
We developed a novel, integrative method (combining animal models, transcriptomics, bioinformatics, molecular biology, and trait-extreme phenotypes) to identify candidate genes for essential hypertension and the metabolic syndrome. We first undertook transcriptome profiling on adrenal glands from blood pressure extreme mouse strains: the hypertensive BPH and hypotensive BPL. Microarray data clustering revealed a striking pattern of global underexpression of intermediary metabolism transcripts in BPH. The MITRA algorithm identified a conserved motif in the transcriptional regulatory regions of the underexpressed metabolic genes, and we then hypothesized that regulation through this motif contributed to the global underexpression. Luciferase reporter assays demonstrated transcriptional activity of the motif, via transcription factors HOXA3, SRY, and YY1. We finally hypothesized that genetic variation at HOXA3, SRY, and YY1 might predict blood pressure and other metabolic syndrome traits in humans. Tagging variants for each locus were associated with BP in a human population BP extreme sample, with the most extensive associations for YY1 tagging SNP rs11625658, on SBP, DBP, BMI, and fasting glucose. Meta-analysis extended the YY1 results into two additional large population samples, with significant effects preserved on DBP, BMI, and fasting glucose.
The results outline an innovative, systematic approach to the genetic pathogenesis of complex cardiovascular disease traits, and point to transcription factor YY1 as a potential candidate gene involved in essential hypertension and the cardio-metabolic syndrome.
BPH mouse strain; complex trait; essential (genetic) hypertension; human genetics; metabolic syndrome
One of the major challenges for hypertension research is to identify the mechanisms that cause the comorbidities encountered in many hypertensive patients, as seen in the metabolic syndrome. An emerging body of evidence suggests that human and experimental hypertensives may exhibit uncontrolled activity of proteinases, including the family of matrix metalloproteinases, recognized for their ability to restructure the extracellular matrix proteins and to play a role in hypertrophy. We propose a new hypothesis that provides a molecular framework for the comorbidities of hypertension, diabetes, capillary rarefaction, immune suppression, and other cell and organ dysfunctions due to early and uncontrolled extracellular receptor cleavage by active proteinases. The proteinase and signaling activity in hypertensives requires further detailed analysis of the proteinase expression, the mechanisms causing proenzyme activation, and identification of the proteinase substrate. This work may open the opportunity for reassessment of old interventions and development of new interventions to manage hypertension and its comorbidities.
Matrix metalloproteinase; MMP; ADAM; Metabolic syndrome; Hypertrophy; Insulin resistance; Capillary rarefaction; Immune suppression; Insulin receptor; Beta-adrenergic receptor; Vascular endothelial growth factor receptor; NF-kappaB; Spontaneously hypertensive rat; Essential hypertension; Microcirculation; Artery; Arteriole; Extracellular matrix protein; Proteinase inhibitor; Angiotensin-converting enzyme; Angiotensin; Hypertension; Metabolic syndrome; Pathogenesis