Proteases and protease inhibitors in taurocholate-induced acute pancreatitis in rats

Role of Bile Acids and Bile Salts in Acute Pancreatitis: From the Experimental to Clinical Studies

ABSTRACT

Acute pancreatitis (AP) is one of the most common gastroenterological disorders leading to hospitalization. It has long been debated whether biliary AP, about 30% to 50% of all cases, is induced by bile acids (BAs) when they reach the pancreas via reflux or via the systemic blood circulation.Besides their classical function in digestion, BAs have become an attractive research target because of their recently discovered property as signaling molecules. The underlying mechanisms of BAs have been investigated in various studies. Bile acids are internalized into acinar cells through specific G-protein-coupled BA receptor 1 and various transporters. They can further act via different receptors: the farnesoid X, ryanodine, and inositol triphosphate receptor. Bile acids induce a sustained Ca2+ influx from the endoplasmic reticulum and release of Ca2+ from acidic stores into the cytosol of acinar cells. The overload of intracellular Ca2+ results in mitochondrial depolarization and subsequent acinar cell necrosis. In addition, BAs have a biphasic effect on pancreatic ductal cells. A more detailed characterization of the mechanisms through which BAs contribute to the disease pathogenesis and severity will greatly improve our understanding of the underlying pathophysiology and may allow for the development of therapeutic and preventive strategies for gallstone-inducedAP.

Octreotide prevents L-asparaginase-induced pancreatic injury in rats

OBJECTIVE

L-asparaginase (ASNase) is one of the most effective chemotherapeutic means for inducing remission in acute lymphoblastic leukemia. However, because of unknown risk factors, severe pancreatitis sometimes occurs in patients receiving ASNase. We assessed the effect of ASNase on pancreatic acinar cells and then investigated the preventive effects of octreotide against ASNase-induced pancreatic injury in rats.

MATERIALS AND METHODS

Rats received intraperitoneal injections of an Escherichia coli ASNase solution (200, 500, or 1000 IU/kg) or normal saline as a control every 24 hours for 5 days. Octreotide (3 microg/kg) was injected subcutaneously with ASNase (1000 IU/kg) every 8 hours for 5 days. Rats were sacrificed 24 hours after the last injection of ASNase or normal saline.

RESULTS

Only the rats given 1000 IU/kg ASNase had significantly increased levels of pancreatic amylase (1962 +/- 152 vs 2179 +/- 84 IU/L, p < 0.01), trypsin (27.3 +/- 3.6 vs 41.1 +/- 22.8 IU/L, p < 0.05), and pancreatic secretory trypsin inhibitor (0.03 +/- 0.09 vs 0.27 +/- 0.10 ng/mL, p < 0.01) as compared to the control group. In addition, the acinar cells showed histological damage; however, octreotide injection provided protection against histological damage and the pancreatic enzymes remained within normal limits.

CONCLUSIONS

Although ASNase by itself did not cause pancreatitis, it did cause increased levels of pancreatic enzymes and histological damage to the pancreas associated with pancreatic injury or pre-pancreatitis. Prior treatment with octreotide prevented the development of ASNase-induced pancreatic injury.

C1 inhibitor: molecular and clinical aspects

C1 inhibitor (C1-INH) is a serine protease inhibitor (serpins) that inactivates several different proteases in the complement, contact, coagulation, and fibrinolytic systems. By its C-terminal part (serpin domain), characterized by three beta-sheets and an exposed mobile reactive loop, C1-INH binds, and blocks the activity of its target proteases. The N-terminal end (nonserpin domain) confers to C1-INH the capacity to bind lipopolysaccharides and E-selectin. Owing to this moiety, C1-INH intervenes in regulation of the inflammatory reaction. The heterozygous deficiency of C1-INH results in hereditary angioedema (HAE). The clinical picture of HAE is characterized by bouts of local increase in vascular permeability. Depending on the affected site, patients suffer from disfiguring subcutaneous edema, abdominal pain, vomiting and/or diarrhoea for edema of the gastrointestinal mucosa, dysphagia, and dysphonia up to asphyxia for edema of the pharynx and larynx. Apart from its genetic deficiency, there are several pathological conditions such as ischemia-reperfusion, septic shock, capillary leak syndrome, and pancreatitis, in which C1-INH has been reported to either play a pathogenic role or be a potential therapeutic tool. These potential applications were identified long ago, but controlled studies have not been performed to confirm pilot experiences. Recombinant C1-INH, produced in transgenic animals, has recently been produced for treatment of HAE, and clinical trials are in progress. We can expect that the introduction of this new product, along with the existing plasma derivative, will renew interest in exploiting C1-INH as a therapeutic agent.

mRNA for pancreatic uncoupling protein 2 increases in two models of acute experimental pancreatitis in rats and mice

Uncoupling-protein 2 (UCP2) is a mitochondrial protein that appears to be involved in cellular oxidant defense and in the regulation of oncotic cell death, both of which are important features of acute pancreatitis. However, UCP2 expression in acute pancreatitis has not been previously reported. In the current experiments, pancreatic gene expression was studied by real-time reverse-transcription/polymerase chain reaction and Northern blots. Two models of acute experimental pancreatitis were investigated: cerulein-induced pancreatitis in mice at two different time points and taurocholate-induced pancreatitis in rats at two degrees of severity. After cerulein administration, acinar injury and leukocyte infiltration was significantly higher at 24 h compared with 12 h after the first injection of cerulein (P<0.05, P<0.005, respectively). UCP2 mRNA was unchanged at 12 h but was nearly 12-fold greater than control levels after 24 h (P<0.001). UCP2 gene expression correlated with acinar injury (r=0.69; P<0.001). By 72 h after taurocholate administration, the severe group had more necrosis than the mild group (P<0.005). Pancreatic UCP2 mRNA was increased fourfold in the severe group compared with controls (P<0.01). UCP2 expression correlated with parenchymal necrosis (r=0.61; P<0.01). Thus, pancreatic UCP2 mRNA increased in two models of acute pancreatitis. The increase in UCP2 gene expression was correlated with the severity of the disease. Up-regulation of UCP2 in the pancreas may be a protective response to oxidative stress, but this increase may also have a negative influence on cellular energy metabolism. Therefore, acinar UCP2 may be an important modifier of the severity of acute pancreatitis.

Disorders of hemostasis during the surgical management of severe necrotizing pancreatitis

OBJECTIVES

Several clinical studies of severe necrotizing pancreatitis (SNP) suggest profound activation of coagulation as well as activation of the fibrinolytic system. The aim of this study was to evaluate the hemostatic derangements in patients who were managed for SNP.

METHODS

Forty-one operated-on patients with SNP were analyzed regarding clinical outcome and activation of the coagulation systems. Serial measurement of coagulation, anticoagulation, and fibrinolysis parameters: prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, antithrombin III (AT III), protein C, plasminogen activator inhibitor-1 (PAI-1), d-dimer, alpha2-antiplasmin, and plasminogen were performed on days 1, 3, 5, 7, 10, and 14 after the initial operation. According to treatment outcome at the end of study, groups of 26 survivors and 15 nonsurvivors were compared.

RESULTS

Nonsurvivors had significantly lower levels of activity of protein C and AT III, and higher concentrations of d-dimer and PAI-1 than survivors. The other measured parameters did not show significant differences between the compared groups of patients.

CONCLUSIONS

Changes in protein C, AT III, d-dimer and PAI-1 levels indicate exhaustion of fibrinolysis and coagulation inhibitors in patients with poor outcome during the course of SNP.

Multimodal management - of value in fulminant acute pancreatitis?

BACKGROUND

The multiple organ dysfunction syndrome (MODS) is the major cause of morbidity and mortality associated with acute pancreatitis. Presently, therapy is merely organ supportive as no effective therapy against underlying causative pathophysiological mechanisms exists.

AIMS

To evaluate the effect of treatment with a platelet-activating factor inhibitor (PAFI), a monoclonal antibody against platelet endothelial cell adhesion molecule 1 (PECAM-1-MAb) and an oxygen free radical scavenger (N-acetylcystein; NAC), alone or in combination, on systemic organ dysfunction in experimental acute pancreatitis.

METHODS

Severe acute pancreatitis was induced in rats by the intraductal administration of taurodeoxycholate. Treatment was given after 1 or 3 h, and evaluations were performed 6 h after induction. Organ dysfunction was evaluated by means of endothelial integrity impairment expressed as endothelial barrier leakage index.

RESULTS

Severe acute pancreatitis caused a significant impairment in endothelial integrity in all organs studied and decreased levels of protease inhibitors compared to controls. The endothelial barrier impairment was significantly ameliorated by all treatment modalities, either given early or later. Combinations of NAC and the PECAM-1-MAb or the PECAM-1-MAb and the PAFI were the only schedules to restore endothelial barrier integrity to normal levels in most of the organs studied.

CONCLUSION

Combination therapy with NAC and PECAM-1-MAb and/or PAFI may offer effective, causative-directed supplements to organ-supportive therapy of MODS in severe acute pancreatitis.

Gut barrier permeability, reticuloendothelial system function and protease inhibitor levels following intestinal ischaemia and reperfusion--effects of pretreatment with N-acetyl-L-cysteine and indomethacin

BACKGROUND

Pathophysiological mechanisms and ways to intervene on intestinal barrier dysfunction following small intestinal ischaemia and prolonged reperfusion are still not fully clarified.

AIMS

To evaluate the effect of oxygen free radical and prostaglandin inhibition on intestinal barrier injury following intestinal ischaemia/reperfusion.

METHODS

Endothelial and epithelial barrier permeability was evaluated by clearance of radiolabelled albumin. Parameters included 125I-Escherichia coli uptake rate index, host reticuloendothelial system function and organ distribution, as well as protease inhibitor and proenzyme activities in rats subjected to small intestinal ischaemia for 40 minutes followed by 12 hours reperfusion (ischaemia/reperfusion), pretreated with N-acetyl-L-cysteine or indomethacin.

RESULTS

Following ischaemia/reperfusion, endothelial and epithelial permeability increased, reticuloendothelial system activation occurred and plasma protease inhibitors were consumed. N-acetyl-L-cysteine pretreatment resulted in improved endothelial and epithelial barrier integrity, a decrease in protease inhibitor consumption and less pronounced reticuloendothelial system activation. Pretreatment with indomethacin was not effective.

CONCLUSION

Oxygen free radicals seem to play an important role in the development of intestinal barrier impairment following ischaemia/reperfusion. N-acetyl-L-cystine may be a potential agent for preventing ischaemia/reperfusion damage.

Regional effects of nafamostat, a novel potent protease and complement inhibitor, on severe necrotizing pancreatitis

BACKGROUND

We evaluated the effect of the novel protease inhibitor nafamostat on rat necrotizing pancreatitis through different routes of administration.

METHODS

Three hours after the induction of severe pancreatitis, the rats received intravenous gabexate or intravenous or local mesenteric intra-arterial nafamostat. At 9 hours, ascites and bronchoalveolar lavage fluid were collected for the evaluation of capillary leakage (Evans blue extravasation). Pancreas and lung were excised for histologic features, myeloperoxidase, and trypsinogen activation peptide. Twenty-four hour survival was evaluated.

RESULTS

Only the intravenous infusion of nafamostat significantly reduced myeloperoxidase (11.7 +/- 2.3 vs 18.3 +/- 1.8 mU/mg; P <.05) and capillary leakage in lungs (Evans blue dye, 1.6 +/- 0.3 vs 2.6 +/- 0.3; P <.05). Only intra-arterial infusion of nafamostat significantly diminished capillary peritoneal leakage (Evans blue dye, 3.6 +/- 0.9 vs 9.4 +/- 0.4; P <.01). Typsinogen activation peptide levels were significantly reduced in all groups, but only intra-arterial infusion did so to baseline. Histologic inflammation in the pancreas was most significantly reduced after intra-arterial infusion (0.92 +/- 0.08 vs 2.91 +/- 0.06; P <.05). No form of protease inhibition reduced mortality rates.

CONCLUSIONS

The effects of protease inhibition depend on the route of administration. Nafamostat has maximal effects on the pancreas and peritoneal capillary leakage when delivered by way of local intra-arterial infusion, and shows a greater reduction of lung leukocyte infiltration and capillary leakage by the intravenous route. Nafamostat is more effective than gabexate.

Minor role of oxidative stress during intermediate phase of acute pancreatitis in rats

Reactive oxygen species have been implicated in the pathogenesis of acute pancreatitis. Few studies have focused on the loss of endogenous antioxidants and molecular oxidative damage. Two acute pancreatitis models in rats; taurocholate (3% intraductal infusion) and cerulein (10 microg/kg/h), were used to study markers of oxidative stress: Glutathione, ascorbic acid, and their oxidized forms (glutathione disulfide and dehydroascorbic acid), malondialdehyde, and 4-hydroxynoneal in plasma and pancreas, as well as 7-hydro-8-oxo-2'-deoxyguanosine in pancreas. In both models, pancreatic glutathione depleted by 36-46% and pancreatic ascorbic acid depleted by 36-40% (p <.05). In the taurocholate model, plasma glutathione was depleted by 34% (p <.05), but there were no significant changes in plasma ascorbic acid or in plasma and pancreas dehydroascorbic acid, malondialdehyde, and 4-hydroxynoneal, and no significant changes in the pancreas glutathione disulfide/glutathione ratio. While pancreas glutathione disulfide/glutathione ratio increased in the cerulein model, there were no significant changes in plasma glutathione, plasma, or pancreas ascorbic acid, dehydroascorbic acid, 4-hydroxynoneal, and malondialdehyde, or in pancreas 7-hydro-8-oxo-2'-deoxyguanosine. Reactive oxygen species have a minor role in the intermediate stages of pancreatitis models.

Acute pancreatitis

Acute pancreatitis is a process that continues to interest physicians and research scientists. Understanding potential factors initiating acute pancreatitis, mechanisms regulating the local and distant inflammatory response, methods for accurately predicting outcome, and possible therapeutic interventions continue to be investigated. Current interest in inflammatory response of the acute injury focuses on proinflammatory and anti-inflammatory cytokines as markers for disease severity and predictors of outcome. Recent studies confirm the utility of physical examination and existing markers such as C-reactive protein and interleukin-6 in predicting the severity of acute pancreatitis. Understanding the molecular mechanism of lung injury remains a major focus for future therapeutic targets, since pancreatitis-associated pulmonary injury results in significant morbidity and is a major indication for intensive care unit admissions.

Proteases and protease inhibitors in cerulein-induced acute pancreatitis in rats

BACKGROUND

Proteases and protease inhibitors are important in acute pancreatitis (AP), although little is known about the time course in cerulein-induced AP in the rat.

MATERIALS AND METHODS

AP was induced by supramaximal stimulation of cerulein, 10 microgram/kg/h, and during 72 h we measured lipase, amylase, albumin, prekallikrein, factor X, alpha(1)-protease inhibitor, alpha(1)-macroglobulin, alpha(2)-antiplasmin, antithrombin III (all in plasma) and macroscopic and histologic variables.

RESULTS

Within 12 h an edematous pancreatitis was evident with peak values of peritoneal exudate, pancreatic wet weight ratio, and plasma amylase and lipase activities. Histologically, edema and vacuolization were prominent already after 3 and 6 h, respectively, while inflammation, necrosis, and total histological score gradually increase to reach peak levels at 48 h. Proenzymes and most plasma protease inhibitors decreased to low levels after 6-12 h followed by a gradual increase. The sequential changes over time indicate that kallikrein - kinin activation, and plasminogen activation are probably early events in cerulein-induced AP in rats. alpha(1)-Macroglobulin and alpha(1)-protease inhibitor gradually decreased during the whole study period, probably being "second line" defense inhibitors. Levels above normal were seen for alpha(2)-antiplasmin and factor X at 48 h, normalizing at 72 h.

CONCLUSIONS

These results suggest that protease activation and protease inhibitor consumption occur in cerulein-induced AP in the rat.