Acute pancreatitis:The stress factor

Acute pancreatitis is an inflammatory disorder of the pancreas that may cause life-threatening complications.Etiologies of pancreatitis vary,with gallstones accounting for the majority of all cases,followed by alcohol.Other causes of pancreatitis include trauma,ischemia,mechanical obstruction,infections,autoimmune,hereditary,and drugs.The main events occurring in the pancreatic acinar cell that initiate and propagate acute pancreatitis include inhibition of secretion,intracellular activation of proteases,and generation of inflammatory mediators.Small cytokines known as chemokines are released from damaged pancreatic cells and attract inflammatory cells,whose systemic action ultimately determined the severity of the disease.Indeed,severe forms of pancreatitis may result in systemic inflammatory response syndrome and multiorgan dysfunction syndrome,characterized by a progressive physiologic failure of several interdependent organ systems.Stress occurs when homeostasis is threatened,and stressors can include physical or mental forces,or combinations of both.Depending on the timing and duration,stress can result in beneficial or harmful consequences.While it is well established that a previous acute-short-term stress decreases the severity of experimentally-induced pancreatitis,the worsening effects of chronic stress on the exocrine pancreas have received relatively little attention.This review will focus on the influence of both prior acute-short-term and chronic stress in acute pancreatitis.

Chronic stress sensitizes rats to pancreatitis induced by cerulein:Role of TNF-α

AIM:To investigate chronic stress as a susceptibility factor for developing pancreatitis,as well as tumor necrosis factor-α (TNF-α) as a putative sensitizer.METHODS:Rat pancreatic acini were used to analyze the influence of TNF-α on submaximal (50 pmol/L) cholecystokinin (CCK) stimulation.Chronic restraint (4 h every day for 21 d) was used to evaluate the effects of submaximal (0.2 μg/kg per hour) cerulein stimulation on chronically stressed rats.RESULTS:In vitro exposure of pancreatic acini toTNF-α disorganized the actin cytoskeleton.This was further increased by TNF-α/CCK treatment,which additionally reduced amylase secretion,and increased trypsin and nuclear factor-κB activities in a protein-kinase-C δ and ε-dependent manner.TNF-α/CCK also enhanced caspases' activity and lactate dehydrogenase release,induced ATP loss,and augmented the ADP/ATP ratio.In vivo,rats under chronic restraint exhibited elevated serum and pancreatic TNF-α levels.Serum,pancreatic,and lung inflammatory parameters,as well as caspases' activity in pancreatic and lung tissue,were substantially enhanced in stressed/cerulein-treated rats,which also experienced tissues' ATP loss and greater ADP/ATP ratios.Histological examination revealed that stressed/cerulein-treated animals developed abundant pancreatic and lung edema,hemorrhage and leukocyte infiltrate,and pancreatic necrosis.Pancreatitis severity was greatly decreased by treating animals with an anti-TNF-αantibody,which diminished all inflammatory parameters,histopathological scores,and apoptotic/necrotic markers in stressed/cerulein-treated rats.CONCLUSION:In rats,chronic stress increases susceptibility for developing pancreatitis,which involves TNF-α sensitization of pancreatic acinar cells to undergo injury by physiological cerulein stimulation.

Munc18/SNARE proteins’ regulation of exocytosis in guinea pig duodenal Brunner’s gland acini

AIM: To examine the molecular mechanism of exocytosis in the Brunner’s gland acinar cell. METHODS: We used a submucosal preparation of guinea pig duodenal Brunner’s gland acini to visualize the dilation of the ductal lumen in response to cholinergic stimulus. We correlated this to electron microscopy to determine the extent of exocytosis of the mucin-filled vesicles. We then examined the behavior of SNARE and interacting Munc18 proteins by confocal microscopy. RESULTS: One and 6 μmol/L carbachol evoked a dose- dependent dilation of Brunner’s gland acini lumen, which correlated to the massive exocytosis of mucin. Munc18c and its cognate SNARE proteins Syntaxin-4 and SNAP-23 were localized to the apical plasma membrane, and upon cholinergic stimulation, Munc18c was displaced into the cytosol leaving Syntaxin-4 and SNAP-23 intact. CONCLUSION: Physiologic cholinergic stimulation induces Munc18c displacement from the Brunner’s gland acinar apical plasma membrane, which enables apical membrane Syntaxin-4 and SNAP-23 to form a SNARE complex with mucin-filled vesicle SNARE proteins to affect exocytosis.