Calcium-dependent enzyme activation and vacuole formation in the apical granular region of pancreatic acinar cells

Polarized calcium signaling in exocrine gland cells

Cytosolic Ca2+ signals are crucial for the control of fluid and enzyme secretion from exocrine glands. The highly polarized exocrine acinar cells have evolved sophisticated and complex Ca2+ signaling mechanisms that exercise precise control of the secretory events occurring across the apical plasma membrane bordering the gland lumen. Ca2+ stores in the endoplasmic reticulum, the secretory granules, the lysosomes, and the endosomes all play important roles in the generation of the local apical Ca2+ spikes that switch on Cl(-) channels in the apical plasma membrane as well as exocytotic export of enzymes. The mitochondria are crucial not only for ATP generation but also for the physiologically important subcellular compartmentalization of the cytosolic Ca2+ signals.

Pancreatitis and calcium signalling: report of an international workshop

Pancreatitis and Calcium Signalling was an international research workshop organized by the authors and held at the Liverpool Medical Institution, Liverpool, United Kingdom, from Sunday 12th to Tuesday 14th November 2006. The overall goal of the workshop was to review progress and explore new opportunities for understanding the mechanisms of acute pancreatitis with an emphasis on the role of pathological calcium signaling. The participants included those with significant interest and expertise in pancreatitis research and others who are in fields outside gastroenterology but with significant expertise in areas of cell biology relevant to pancreatitis. The workshop was designed to enhance interchange of ideas and collaborations, to engage and encourage younger researchers in the field, and promote biomedical research through the participating and supporting organizations and societies. The workshop was divided into 8 topic-oriented sessions. The sessions were: (1) Physiology and pathophysiology of calcium signaling; (2) Interacting signaling mechanisms; (3) Premature digestive enzyme activation; (4) Physiology Society Lecture: Aberrant Ca2+ signaling, bicarbonate secretion, and pancreatitis; (5) NFkappaB, cytokines, and immune mechanisms; (6) Mitochondrial injury; (7) Cell death pathways; and (8) Overview of areas for future research. In each session, speakers presented work appropriate to the topic followed by discussion of the material presented by the group. The publication of these proceedings is intended to provide a platform for enhancing research and therapeutic development for acute pancreatitis.

Ca2+-induced pancreatic cell death: roles of the endoplasmic reticulum, zymogen granules, lysosomes and endosomes

Alcohol induces Ca(2+)-dependent intracellular trypsinogen activation in the apical granular area via non-oxidative metabolites, such as fatty acid ethyl esters and fatty acids. Intracellular trypsinogen activation is a crucial initiating event in the development of acute pancreatitis, but the specific organelle in which this process takes place has been unknown. Recent data demonstrate that the Ca(2+)-dependent trypsinogen activation occurs in postexocytotic endocytic vacuoles. These vacuoles are acid due to a bafilomycin-sensitive vacuolar H(+) ATPase and have a very Ca(2+)-permeable membrane. Acid endocytic structures, together with lysosomes, zymogen granules and elements of the endoplasmic reticulum, also play an important role in the physiological Ca(2+) signal generation that normally regulates enzyme and fluid secretion from the exocrine pancreas.

Mitochondrial injury in pancreatitis

Pancreatitis is an increasingly common disease that carries a significant mortality and which lacks specific therapy. Pathological calcium signalling is an important contributor to the initiating cell injury, caused by or acting through mitochondrial inhibition. A principal effect of disordered cell signalling and impaired mitochondrial function is cell death, either by apoptosis that is primarily protective, or by necrosis that is deleterious, both locally and systemically. Mitochondrial calcium overload is particularly important in necrotic injury, which may include damage mediated by the mitochondrial permeability transition pore. The role of reactive oxygen species remains controversial. Present understanding of the part played by disordered pancreatic acinar calcium signalling and mitochondrial inhibition offers several new potential therapeutic targets.

Role of PKC-delta on substance P-induced chemokine synthesis in pancreatic acinar cells

Interaction of the neuropeptide substance P (SP) with its high-affinity neurokinin-1 receptor (NK1R) plays an important role in the pathophysiology of acute pancreatitis. SP is known to stimulate the production of chemokines monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein (MIP)-1 alpha, and MIP-2 in pancreatic acinar cells via the activation of NF-kappaB. However, the signaling mechanisms by which the SP-NK1R interaction induces NF-kappaB activation and chemokine production remain unclear. To that end, in the present study, we investigated the participation of PKC in SP-induced chemokine production in pancreatic acinar cells. In this study, we showed that SP stimulated an early phosphorylation of PKC isoform PKC-delta followed by increased activation of MAPKKK MEKK1 and MAPK ERK and JNK as well as transcription factor NF-kappaB and activator protein-1 driven chemokine production. Depletion of PKC-delta with its inhibitor rottlerin or the specific PKC-delta translocation inhibitor peptide dose dependently decreased SP-induced PKC-delta, MEKK1, ERK, JNK, NF-kappaB, and AP-1 activation. Moreover, rottlerin as well as PKC-delta translocation inhibitor inhibited SP-induced chemokine production in a concentration-dependent manner. We also demonstrated that PKC-delta activation was attenuated by CP96345, a selective NK1R antagonist, thus showing that PKC-delta activation was indeed mediated by SP in pancreatic acinar cells. These results show that PKC-delta is an important proinflammatory signal transducer for SP-NK1R-induced chemokine production in pancreatic acinar cells.

Visualizing formation and dynamics of vacuoles in living cells using contrasting dextran-bound indicator: endocytic and nonendocytic vacuoles

Here we describe a technique that allows us to visualize in real time the formation and dynamics (fusion, changes of shape, and translocation) of vacuoles in living cells. The technique involves infusion of a dextran-bound fluorescent probe into the cytosol of the cell via a patch pipette, using the whole-cell patch-clamp configuration. Experiments were conducted on pancreatic acinar cells stimulated with supramaximal concentrations of cholecystokinin (CCK). The vacuoles, forming in the cytoplasm of the cell, were revealed as dark imprints on a bright fluorescence background, produced by the probe and visualized by confocal microscopy. A combination of two dextran-bound probes, one infused into the cytosol and the second added to the extracellular solution, was used to identify endocytic and nonendocytic vacuoles. The cytosolic dextran-bound probe was also used together with a Golgi indicator to illustrate the possibility of combining the probes and identifying the localization of vacuoles with respect to other cellular organelles in pancreatic acinar cells. Combinations of cytosolic dextran-bound probes with endoplasmic reticulum (ER) or mitochondrial probes were also used to simultaneously visualize vacuoles and corresponding organelles. We expect that the new technique will also be applicable and useful for studies of vacuole dynamics in other cell types.

Hereditary pancreatitis amlodipine trial: a pilot study of a calcium-channel blocker in hereditary pancreatitis

OBJECTIVES

Hereditary pancreatitis (HP) is a form of recurrent acute pancreatitis (AP) mediated by mutations in cationic trypsinogen (PRSS1). Mutations cluster in the calcium-associated regulator regions of PRSS1. In rats, calcium-channel blockers (CCB) prevent hyperstimulation-associated AP. Because of the potential importance of hyperstimulation in triggering episodes of AP in HP, we designed a pilot study to evaluate the safety and potential benefit of CCB use in HP.

METHODS

Subjects 6 years or older had a PRSS1 mutation, recurrent AP, and pain. Total study duration was 16 weeks. Amlodipine was given during weeks 0 to 11. Dose (2.5, 5, or 10 mg) was based on weight (range, 0.08-0.17 mg x kg(-1) x d(-1)). Subjects filled a daily diary including pain (0-10 scale) and blood pressure reading. Clinical assessments occurred at weeks -4, 0, 1, 2, 6, 10, 11, and 12. Subjects filled a Medical Outcomes Study Short-Form Survey version 2 (SF-10 for children <14 years old) at weeks -4, 0, 6, and 10. Data were compared for weeks -4 to 0 and 6 to 10.

RESULTS

Nine subjects signed informed consent (4 males; 12-52 years old). Four were excluded during the screening phase. Drug was discontinued in one due to development of unilateral lower-extremity numbness. Four subjects (12-31 years old) completed the study. Mean blood pressure, laboratory tests, physical findings, and daily pain scores did not clinically significantly differ before and during drug therapy, but all reported reduced symptoms. Three reduced analgesic use. Three had improved scores on the Medical Outcomes Study Short-Form Survey version 2.

CONCLUSIONS

Amlodipine is generally safe in subjects with HP and does not increase pain or episodes of AP. Further research into the mechanism of CCB on pancreatitis would be important to provide a pathophysiologic basis to support further trials in HP.

Acinar cell membrane disruption is an early event in experimental acute pancreatitis in rats

OBJECTIVE

To test the hypothesis that disruption of acinar cell membranes is the earliest event that takes place after the onset of acute pancreatitis.

METHODS

Cerulein and taurocholate pancreatitis were induced in rats. Furthermore, stimulation with different doses of bombesin, pilocarpine, and cerulein was performed. Five to 180 minutes after initiation of treatment, animals were killed. Disruption of cell membranes was detected by the penetration of the experimental animal's own albumin or immunoglobulin G (IgG) into acinar cells by immunocytological localization. Tissue was further analyzed by electron microscopy and electron microscopic immunostaining.

RESULTS

Animals with pancreatitis displayed significantly greater antialbumin and anti-IgG immunostaining in the cytoplasm of acinar cells and in vacuoles in comparison with controls, confirming membrane disruption. This was not detectable after stimulation with bombesin, pilocarpine, and nonsupramaximal doses of cerulein. The first changes were seen after 5 minutes of induction of pancreatitis. Results were verified by electron microscopy and electron microscopic immunohistochemistry.

CONCLUSIONS

The penetration of albumin and IgG into acinar cells indicates that wounding of their plasma membrane occurs at the onset of acute pancreatitis. Disruption of the membranes could be expected to allow the influx of calcium ions, causing massive intracellular alterations, and exit of molecules, such as enzymes from acinar cells.

ATP depletion inhibits Ca2+ release, influx and extrusion in pancreatic acinar cells but not pathological Ca2+ responses induced by bile

Here, we describe novel mechanisms limiting a toxic cytosolic Ca(2+) rise during adenosine 5'-triphosphate (ATP) depletion. We studied the effect of ATP depletion on Ca(2+) signalling in mouse pancreatic acinar cells. Measurements of ATP in isolated cells after adenovirus-mediated expression of firefly luciferase revealed that the cytosolic ATP concentration fell from approximately 1 mM to near zero after treatment with oligomycin plus iodoacetate. ATP depletion resulted in the inhibition of Ca(2+) extrusion, which was accompanied by a remarkably synchronous inhibition of store-operated Ca(2+) influx. Alternative inhibition of Ca(2+) extrusion by carboxyeosin had a much smaller effect on Ca(2+) influx. The coordinated metabolic inhibition of Ca(2+) influx and extrusion suggests the existence of a common ATP-dependent master regulator of both processes. ATP-depletion also suppressed acetylcholine (ACh)-induced Ca(2+) oscillations, which was due to the inhibition of Ca(2+) release from internal stores. This could be particularly important for limiting Ca(2+) toxicity during periods of hypoxia. In contrast, metabolic control of Ca(2+) influx and Ca(2+) release from internal stores spectacularly failed to prevent large toxic Ca(2+) responses induced by bile acids-activators of acute pancreatitis (a frequent and often fatal disease of the exocrine pancreas). The bile acids taurolithocholic acid 3-sulphate (TLC-S), taurochenodeoxycholic acid (TCDC) and taurocholic acid (TC) were used in our experiments. Neither Ca(2+) release from internal stores nor Ca(2+) influx triggered by bile acids were inhibited by ATP depletion, emphasising the danger of these pathological mechanisms.

The pancreas misled: signals to pancreatitis

Acute pancreatitis is an increasingly common and sometimes severe disease for which there is little specific therapy. Chronic pancreatitis is a common and grossly debilitating sequel that is largely irreversible, whatever treatment is adopted. In the face of these burdens, the absence of specific treatments is a spur to research. The acinar cell is the primary target of injury from alcohol metabolites, bile, hyperlipidaemia, hyperstimulation and other causes. These induce abnormal, prolonged, global, cytosolic calcium signals, the prevention of which also prevents premature digestive enzyme activation, cytokine expression, vacuole formation and acinar cell necrosis. Such agents increase calcium entry through the plasma membrane and/or increase calcium release from intracellular stores, shown to result from effects on calcium channels and calcium pumps, or their energy supply. A multitude of signalling mechanisms are activated, diverted or disrupted, including secretory mechanisms, lysosomal regulators, inflammatory mediators, cell survival and cell death pathways, together with or separately from calcium. While recent discoveries have increased insight and suggest prophylaxis or treatment targets, more work is required to define the mechanisms and interactions of cell signalling pathways in the pathogenesis of pancreatitis.

Pancreatic cellular injury after cardiac surgery with cardiopulmonary bypass: frequency, time course and risk factors

Although often clinically silent, pancreatic cellular injury (PCI) is relatively frequent after cardiac surgery with cardiopulmonary bypass; and its etiology and time course are largely unknown. We defined PCI as the simultaneous presence of abnormal values of pancreatic isoamylase and immunoreactive trypsin (IRT). The frequency and time evolution of PCI were assessed in this condition using assays for specific exocrine pancreatic enzymes. Correlations with inflammatory markers were searched for preoperative risk factors. One hundred ninety-three patients submitted to cardiac surgery were enrolled prospectively. Blood IRT, amylase, pancreatic isoamylase, lipase, and markers of inflammation (alpha1-protease inhibitor, alpha2-macroglobulin, myeloperoxidase) were measured preoperatively and postoperatively until day 8. The postoperative increase in plasma levels of pancreatic enzymes and urinary IRT was biphasic in all patients: early after surgery and later (from day 4 to 8 after surgery). One hundred thirty-three patients (69%) experienced PCI, with mean IRT, isoamylase, and alpha1-protease inhibitor values higher for each sample than that in patients without PCI. By multiple regression analysis, we found preoperative values of plasma IRT >or=40 ng/mL, amylase >or=42 IU/mL, and pancreatic isoamylase >or=20 IU/L associated with a higher incidence of postsurgery PCI (P < 0.005). In the PCI patients, a significant correlation was found between the 4 pancreatic enzymes and urinary IRT, total calcium, myeloperoxidase, alpha1-protease inhibitor, and alpha2-macroglobulin. These data support a high prevalence of postoperative PCI after cardiac surgery with cardiopulmonary bypass, typically biphasic and clinically silent, especially when pancreatic enzymes were elevated preoperatively.

[Inflammatory pancreatic disease due to enzyme autodigestion: an exceptional model of glandular crinophagy]

The exocrine pancreas is a functionally dangerous structure since it is exposed to digestion by its most aggressive enzymes (proteases, etc) despite self-protective measures such as the synthesis of some of these enzymes in the form of inactive zymogens (trypsinogen, etc.). We review inflammatory pancreatic disease by separately analyzing its classical forms of onset: acute and chronic pancreatitis (AP and CP). There is general consensus that the initial pathogenic event in AP is intraacinar activation of trypsinogen into trypsin, followed by that of the remaining proenzymes, giving rise to an unusual model of autophagic inflammation. In contrast, consensus is lacking on the initial pathogenic event in CP (toxic-metabolic lesion, oxidative stress, ductal hypertension, etc.?), although in some cases a <<necrosis-fibrosis>> sequence due to recurrent episodes of AP seems evident. The pathogenic features shared by both forms of the disease and which justify some recent attempts to formulate an overall explanation of the pathogenesis of pancreatitis are discussed. Such an explanation would place both forms of pancreatitis within the conceptual framework of an <<inflammatory pancreatic disease due to enzyme autodigestion>>.

Twenty years of calcium imaging: cell physiology to dye for

The use of fluorescent dyes over the past two decades has led to a revolution in our understanding of calcium signaling. Given the ubiquitous role of Ca(2+) in signal transduction at the most fundamental levels of molecular, cellular, and organismal biology, it has been challenging to understand how the specificity and versatility of Ca(2+) signaling is accomplished. In excitable cells, the coordination of changing Ca(2+) concentrations at global (cellular) and well-defined subcellular spaces through the course of membrane depolarization can now be conceptualized in the context of disease processes such as cardiac arrhythmogenesis. The spatial and temporal dimensions of Ca(2+) signaling are similarly important in non-excitable cells, such as endothelial and epithelial cells, to regulate multiple signaling pathways that participate in organ homeostasis as well as cellular organization and essential secretory processes.

Pathobiology of alcoholic pancreatitis

This paper provides a summary of the effects of alcohol abuse on the pathobiologic responses that occur during acute and chronic pancreatitis considering both the human disease and animal/tissue models. The effects are multiple and include ones on cell death leading to necrosis; on inflammation resulting in a sensitized response to pancreatic stress; and fibrosis through effects of ethanol on pancreatic stellate cells and the plasminogen system. Although the effects of alcohol are multiple and complex, it is likely that a combination of a few key effects on these pathobiologic responses drive the increased sensitivity of the pancreas to acute pancreatitis with pancreatic stress and the promotion of chronic pancreatitis with pancreatic injury occurring during acute pancreatitis.

Initiation site of Ca(2+) entry evoked by endoplasmic reticulum Ca(2+) depletion in mouse parotid and pancreatic acinar cells

PURPOSE

In non-excitable cells, which include parotid and pancreatic acinar cells, Ca(2+) entry is triggered via a mechanism known as capacitative Ca(2+) entry, or store-operated Ca(2+) entry. This process is initiated by the perception of the filling state of endoplasmic reticulum (ER) and the depletion of internal Ca(2+) stores, which acts as an important factor triggering Ca(2+) entry. However, both the mechanism of store-mediated Ca(2+) entry and the molecular identity of store-operated Ca(2+) channel (SOCC) remain uncertain.

MATERIALS AND METHODS

In the present study we investigated the Ca(2+) entry initiation site evoked by depletion of ER to identify the localization of SOCC in mouse parotid and pancreatic acinar cells with microfluorometeric imaging system.

RESULTS

Treatment with thapsigargin (Tg), an inhibitor of sarco/endoplasmic reticulum Ca(2+)-ATPase, in an extracellular Ca(2+) free state, and subsequent exposure to a high external calcium state evoked Ca(2+) entry, while treatment with lanthanum, a non-specific blocker of plasma Ca(2+) channel, completely blocked Tg-induced Ca(2+) entry. Microfluorometric imaging showed that Tg-induced Ca(2+) entry started at a basal membrane, not a apical membrane.

CONCLUSION

These results suggest that Ca2+ entry by depletion of the ER initiates at the basal pole in polarized exocrine cells and may help to characterize the nature of SOCC.

Caerulein-induced intracellular pancreatic zymogen activation is dependent on calcineurin

Aberrant cytosolic Ca(2+) flux in pancreatic acinar cells is critical to the pathological pancreatic zymogen activation observed in acute pancreatitis, but the downstream effectors are not known. In this study, we examined the role of Ca(2+)-activated protein phosphatase 2B (or calcineurin) in zymogen activation. Isolated pancreatic acinar cells were stimulated with supraphysiological caerulein (100 nM) with or without the calcineurin inhibitors FK506 or cell-permeable calcineurin inhibitory peptide (CiP). Chymotrypsin activity was measured as a marker of zymogen activation, and the percent amylase secretion was used as a measure of enzyme secretion. Cytosolic Ca(2+) changes were recorded in acinar cells loaded with the intermediate Ca(2+)-affinity dye fluo-5F using a scanning confocal microscope. A 50% reduction in chymotrypsin activity was observed after pretreatment with 1 microM FK506 or 10 microM CiP. These pretreatments did not affect amylase secretion or the rise in cytosolic Ca(2+) after caerulein stimulation. These findings suggest that calcineurin mediates caerulein-induced intra-acinar zymogen activation but not enzyme secretion or the initial caerulein-induced cytosolic Ca(2+) signal.

Oxidant-impaired intracellular Ca2+ signaling in pancreatic acinar cells: role of the plasma membrane Ca2+-ATPase

Pancreatitis is an inflammatory disease of pancreatic acinar cells whereby intracellular calcium concentration ([Ca(2+)](i)) signaling and enzyme secretion are impaired. Increased oxidative stress has been suggested to mediate the associated cell injury. The present study tested the effects of the oxidant, hydrogen peroxide, on [Ca(2+)](i) signaling in rat pancreatic acinar cells by simultaneously imaging fura-2, to measure [Ca(2+)](i), and dichlorofluorescein, to measure oxidative stress. Millimolar concentrations of hydrogen peroxide increased cellular oxidative stress and irreversibly increased [Ca(2+)](i), which was sensitive to antioxidants and removal of external Ca(2+), and ultimately led to cell lysis. Responses were also abolished by pretreatment with (sarco)endoplasmic reticulum Ca(2+)-ATPase inhibitors, unless cells were prestimulated with cholecystokinin to promote mitochondrial Ca(2+) uptake. This suggests that hydrogen peroxide promotes Ca(2+) release from the endoplasmic reticulum and the mitochondria and that it promotes Ca(2+) influx. Lower concentrations of hydrogen peroxide (10-100 muM) increased [Ca(2+)](i) and altered cholecystokinin-evoked [Ca(2+)](i) oscillations with marked heterogeneity, the severity of which was directly related to oxidative stress, suggesting differences in cellular antioxidant capacity. These changes in [Ca(2+)](i) also upregulated the activity of the plasma membrane Ca(2+)-ATPase in a Ca(2+)-dependent manner, whereas higher concentrations (0.1-1 mM) inactivated the plasma membrane Ca(2+)-ATPase. This may be important in facilitating "Ca(2+) overload," resulting in cell injury associated with pancreatitis.

Recent insights into the cellular mechanisms of acute pancreatitis

In acute pancreatitis, initiating cellular events causing acinar cell injury includes co-localization of zymogens with lysosomal hydrolases, leading to premature enzyme activation and pathological exocytosis of zymogens into the interstitial space. This is followed by processes that accentuate cell injury; triggering acute inflammatory mediators, intensifying oxidative stress, compromising the microcirculation and activating a neurogenic feedback. Such localized events then progress to a systemic inflammatory response leading to multiorgan dysfunction syndrome with resulting high morbidity and mortality. The present review discusses some of the most recent insights into each of these cellular processes postulated to cause or propagate the process of acute pancreatitis, and also the role of alcohol and genetics.

Role of NADPH oxidase and calcium in cerulein-induced apoptosis: involvement of apoptosis-inducing factor

Apoptosis linked to oxidative stress has been implicated in pancreatitis. NADPH oxidase has been considered as a major source of reactive oxygen species (ROS) during inflammation and apoptosis in pancreatic acinar cells. Recently we demonstrated that NADPH oxidase subunits Nox1, p27phox, p47phox, and p67phox are constitutively expressed in pancreatic acinar cells and may contribute to apoptosis in pancreatic acinar AR42J cells stimulated with cerulein. The present study aims to investigate the apoptotic mechanism of pancreatic acinar cells stimulated with cerulein by determining whether cerulein induces apoptosis-inducing factor (AIF) expression and whether cerulein-induced expression of AIF is inhibited by transfection with antisense oligonucleotide (AS ODN) of p47phox or p67phox or treatment with a Ca2+ chelator BAPTA-AM. As a result, cerulein induced the expression of apoptotic gene AIF. Transfection with AS ODN of p47phox or p67phox or treatment with BAPTA-AM inhibited cerulein-induced AIF expression in pancreatic acinar AR42J cells. These results demonstrate that NADPH oxidase and calcium have a role in cerulein-induced apoptosis in pancreatic acinar AR42J cells by inducing the expression of AIF. In conclusion, the increase in intracellular Ca2+ and NADPH oxidase activity may be the upstream event of apoptotic gene (AIF) expression, which contributes to cerulein-induced apoptosis in pancreatic acinar AR42 cells.

Why does pancreatic overstimulation cause pancreatitis?

Many animal models are available to investigate the pathogenesis of pancreatitis, an inflammatory disorder of the pancreas. However, the secretagogue hyperstimulation model of pancreatitis is the most commonly used. Animals infused with high doses of cholecystokinin (CCK) exhibit hyperamylasemia, pancreatic edema, and acinar cell injury, which closely mimic pancreatitis in humans. Intra-acinar zymogen activation is an essential early event in the pathogenesis of secretagogue-induced pancreatitis. Early in the course of pancreatitis, lysosomal hydrolases colocalize with digestive zymogens and activate them. These activated zymogens then cause acinar cell injury and necrosis, a characteristic of pancreatitis. Besides being the site of initiation of injury in pancreatitis, acinar cells also synthesize and release cytokines and chemokines very early in the course of pancreatitis, which then attract and activate inflammatory cells and initiate the disease's systemic phase.

Calcium signalling and pancreatic cell death: apoptosis or necrosis?

Secretagogues, such as cholecystokinin and acetylcholine, utilise a variety of second messengers (inositol trisphosphate, cADPR and nicotinic acid adenine dinucleotide phosphate) to induce specific oscillatory patterns of calcium (Ca(2+)) signals in pancreatic acinar cells. These are tightly controlled in a spatiotemporal manner, and are coupled to mitochondrial metabolism necessary to fuel secretion. When Ca(2+) homeostasis is disrupted by known precipitants of acute pancreatitis, for example, hyperstimulation or non-oxidative ethanol metabolites, Ca(2+) stores (endoplasmic reticulum and acidic pool) become depleted and sustained cytosolic [Ca(2+)] elevations replace transient signals, leading to severe consequences. Sustained mitochondrial depolarisation, possibly via opening of the mitochondrial permeability transition pore (MPTP), elicits cellular ATP depletion that paralyses energy-dependent Ca(2+) pumps causing cytosolic Ca(2+) overload, while digestive enzymes are activated prematurely within the cell; Ca(2+)-dependent cellular necrosis ensues. However, when stress to the acinar cell is milder, for example, by application of the oxidant menadione, release of Ca(2+) from stores leads to oscillatory global waves, associated with partial mitochondrial depolarisation and transient MPTP opening; apoptotic cell death is promoted via the intrinsic pathway, when associated with generation of reactive oxygen species. Apoptosis, induced by menadione or bile acids, is potentiated by inhibition of an endogenous detoxifying enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1), suggesting its importance as a defence mechanism that may influence cell fate.

Phosphatidylinositol 3-kinase facilitates bile acid-induced Ca(2+) responses in pancreatic acinar cells

Bile acids are known to induce Ca(2+) signals in pancreatic acinar cells. We have recently shown that phosphatidylinositol 3-kinase (PI3K) regulates changes in free cytosolic Ca(2+) concentration ([Ca(2+)](i)) elicited by CCK by inhibiting sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA). The present study sought to determine whether PI3K regulates bile acid-induced [Ca(2+)](i) responses. In pancreatic acinar cells, pharmacological inhibition of PI3K with LY-294002 or wortmannin inhibited [Ca(2+)](i) responses to taurolithocholic acid 3-sulfate (TLC-S) and taurochenodeoxycholate (TCDC). Furthermore, genetic deletion of the PI3K gamma-isoform also decreased [Ca(2+)](i) responses to bile acids. Depletion of CCK-sensitive intracellular Ca(2+) pools or application of caffeine inhibited bile acid-induced [Ca(2+)](i) signals, indicating that bile acids release Ca(2+) from agonist-sensitive endoplasmic reticulum (ER) stores via an inositol (1,4,5)-trisphosphate-dependent mechanism. PI3K inhibitors increased the amount of Ca(2+) in intracellular stores during the exposure of acinar cells to bile acids, suggesting that PI3K negatively regulates SERCA-dependent Ca(2+) reloading into the ER. Bile acids inhibited Ca(2+) reloading into ER in permeabilized acinar cells. This effect was augmented by phosphatidylinositol (3,4,5)-trisphosphate (PIP(3)), suggesting that both bile acids and PI3K act synergistically to inhibit SERCA. Furthermore, inhibition of PI3K by LY-294002 completely inhibited trypsinogen activation caused by the bile acid TLC-S. Our results indicate that PI3K and its product, PIP(3), facilitate bile acid-induced [Ca(2+)](i) responses in pancreatic acinar cells through inhibition of SERCA-dependent Ca(2+) reloading into the ER and that bile acid-induced trypsinogen activation is mediated by PI3K. The findings have important implications for the mechanism of acute pancreatitis since [Ca(2+)](i) increases and trypsinogen activation mediate key pathological processes in this disorder.

K+-induced ion-exchanges trigger trypsin activation in pancreas acinar zymogen granules

Trypsin premature activation has been thought to be a key event in the initiation phase of acute pancreatitis. Here we test a hypothesis that a sustained increase of cytosolic Ca(2+) concentration ([Ca(2+)](C)) can trigger K(+) influx into pancreas acinar zymogen granules (ZGs) via a Ca(2+)-activated K(+) channel (K(Ca)), and this influx of K(+) then mobilizes bound-Ca(2+) by K(+)/Ca(2+) ion-exchange to increase free Ca(2+) concentration in the ZGs ([Ca(2+)](G)) and release bound-H(+) by K(+)/H(+) ion-exchange to decrease the pH in ZGs (pH(G)). Both the increase of [Ca(2+)](G) and the decrease of pH(G) will facilitate trypsinogen autoactivation and stabilize active trypsin inside ZGs that could lead to acute pancreatitis. The experimental results are consistent with our hypothesis, suggesting that K(+) induced ion-exchanges play a critical role in the initiation of trypsin premature activation in ZGs.

Substance P treatment stimulates chemokine synthesis in pancreatic acinar cells via the activation of NF-kappaB

Acinar cell injury early in acute pancreatitis leads to a local inflammatory reaction and to the subsequent systemic inflammatory response, which may result in multiple organ dysfunction and death. Inflammatory mediators, including chemokines and substance P (SP), are known to play a crucial role in the pathogenesis of acute pancreatitis. It has been shown that pancreatic acinar cells produce the chemokine monocyte chemoattractant protein-1 (MCP-1) in response to caerulein hyperstimulation, demonstrating that acinar-derived MCP-1 is an early mediator of inflammation in acute pancreatitis. Similarly, SP levels in the pancreas and pancreatic acinar cell expression of neurokinin-1 receptor, the primary receptor for SP, are both increased during secretagogue-induced experimental pancreatitis. This study aims to examine the functional consequences of exposing mouse pancreatic acinar cells to SP and to determine whether it leads to proinflammatory signaling, such as production of chemokines. Exposure of mouse pancreatic acini to SP significantly increased synthesis of MCP-1, macrophage inflammatory protein-1alpha (MIP-1alpha), as well as MIP-2. Furthermore, SP also increased NF-kappaB activation. The stimulatory effect of SP was specific to chemokine synthesis through the NF-kappaB pathway, since the increase in chemokine production was completely attenuated when pancreatic acini were pretreated with the selective NF-kappaB inhibitor NF-kappaB essential modulator-binding domain peptide. This study shows that SP-induced chemokine synthesis in mouse pancreatic acinar cells is NF-kappaB dependent.

Emerging perspectives in store-operated Ca2+ entry: Roles of Orai, Stim and TRP

Depletion of intracellular Ca2+ stores induces Ca2+ influx across the plasma membrane through store-operated channels (SOCs). This store-operated Ca2+ influx is important for the replenishment of the Ca2+ stores, and is also involved in many signaling processes by virtue of the ability of intracellular Ca2+ to act as a second messenger. For many years, the molecular identities of particular SOCs, as well as the signaling mechanisms by which these channels are activated, have been elusive. Recently, however, the mammalian proteins STIM1 and Orai1 were shown to be necessary for the activation of store-operated Ca2+ entry in a variety of mammalian cells. Here we present molecular, pharmacological, and electrophysiological properties of SOCs, with particular focus on the roles that STIM1 and Orai1 may play in the signaling processes that regulate various pathways of store-operated entry.

Failure of calcium microdomain generation and pathological consequences

Normal physiological regulation depends on Ca(2+) microdomains, because there is a need to spatially separate Ca(2+) regulation of different cellular processes. It is only possible to generate local Ca(2+) signals transiently; so, there is an important functional link between Ca(2+) spiking and microdomains. The pancreatic acinar cell provides a useful cell biological model, because of its clear structural and functional polarization. Although local Ca(2+) spiking in the apical (granular) microdomain regulates fluid and enzyme secretion, prolonged global elevations of the cytosolic Ca(2+) concentration are associated with the human disease acute pancreatitis, in which proteases in the granular region become inappropriately activated and digest the pancreas and its surroundings. A major cause of pancreatitis is alcohol abuse and it has now been established that fatty acid ethyl esters and fatty acids, non-oxidative alcohol metabolites, are principally responsible for causing the acinar cell damage. The fatty acid ethyl esters release Ca(2+) from the endoplasmic reticulum and the fatty acids inhibit markedly mitochondrial ATP generation, which prevents the acinar cell from disposing of the excess Ca(2+) in the cytosol. Because of the abolition of ATP-dependent Ca(2+) pump activity, all intracellular Ca(2+) concentration gradients disappear and the most important part of the normal regulatory machinery is thereby destroyed. The end stage is necrosis.

Role of Ca2+ in pancreatic cell death induced by alcohol metabolites

Whereas alcohol itself, even in high concentrations, has little effect on the functional performance of isolated pancreatic acinar cells, non-oxidative metabolites (fatty acid ethyl esters [FAEE] and fatty acids [FA]) can cause Ca(2+)-dependent necrosis. The mechanism of action of FAEE has been investigated using a combination of patch clamp whole-cell current recording and Ca(2+) imaging. At low stimulation intensities, FAEE evoke repetitive short-lasting cytosolic Ca(2+) spikes, which are inhibited by caffeine, used as an inositol trisphosphate receptor antagonist. With more intense stimulation, sustained elevations of the cytosolic Ca(2+) concentration are observed, which can be prevented by pharmacological inhibition of the conversion of FAEE to FA. It is therefore the FA and not the FAEE that cause necrosis. The effect of FA cannot be blocked by inositol trisphosphate receptor antagonists. Fatty acids elicit a marked reduction in the cytosolic adenosine triphosphate (ATP) level. The patch clamp experiments show that the toxic sustained Ca(2+) signal generation induced by FA can be prevented by adding ATP to the cell interior. The toxic alcohol effects are principally due to FAEE produced under non-oxidative conditions and their subsequent conversion to FA. The FA-induced necrosis is Ca(2+)-dependent. The destructive sustained Ca(2+) signals are due to inhibition of mitochondrial function with failure of ATP generation.

Two-photon excitation imaging of exocytosis and endocytosis and determination of their spatial organization

Two-photon excitation imaging is the least invasive optical approach to study living tissues. We have established two-photon extracellular polar-tracer (TEP) imaging with which it is possible to visualize and quantify all exocytic events in the plane of focus within secretory tissues. This technology also enables estimate of the precise diameters of vesicles independently of the spatial resolution of the optical microscope, and determination of the fusion pore dynamics at nanometer resolution using TEP-imaging based quantification (TEPIQ). TEP imaging has been applied to representative secretory glands, e.g., exocrine pancreas, endocrine pancreas, adrenal medulla and a pheochromocytoma cell line (PC12), and has revealed unexpected diversity in the spatial organization of exocytosis and endocytosis crucial for the physiology and pathology of secretory tissues and neurons. TEP imaging and TEPIQ analysis are powerful tools for elucidating the molecular and cellular mechanisms of exocytosis and certain related diseases, such as diabetes mellitus, and the development of new therapeutic agents and diagnostic tools.

Movement of calcium signals and calcium-binding proteins: firewalls, traps and tunnels

In the board game 'Snakes and Ladders', placed on the image of a pancreatic acinar cell, calcium ions have to move from release sites in the secretory region to the nucleus. There is another important contraflow - from calcium entry channels in the basal part of the cell to ER (endoplasmic reticulum) terminals in the secretory granule region. Both transport routes are perilous as the messenger can disappear in any place on the game board. It can be grabbed by calcium ATPases of the ER (masquerading as a snake but functioning like a ladder) and tunnelled through its low buffering environment, it can be lured into the whirlpools of mitochondria uniporters and forced to regulate the tricarboxylic acid cycle, and it can be permanently placed inside the matrix of secretory granules and released only outside the cell. The organelles could trade calcium (e.g. from the ER to mitochondria and vice versa) almost depriving this ion the light of the cytosol and noble company of cytosolic calcium buffers. Altogether it is a rich and colourful story.

Cholecystokinin and gastrin receptors

Cholecystokinin and gastrin receptors (CCK1R and CCK2R) are G protein-coupled receptors that have been the subject of intensive research in the last 10 years with corresponding advances in the understanding of their functioning and physiology. In this review, we first describe general properties of the receptors, such as the different signaling pathways used to exert short- and long-term effects and the structural data that explain their binding properties, activation, and regulation. We then focus on peripheral cholecystokinin receptors by describing their tissue distribution and physiological actions. Finally, pathophysiological peripheral actions of cholecystokinin receptors and their relevance in clinical disorders are reviewed.

Dichotomy of fates of pancreatic epithelia in chronic pancreatitis: apoptosis versus survival

Chronic pancreatitis is now thought to have a multifactorial etiology. New concepts integrating cellular, molecular and genetic knowledge of the disease have been proposed to explain its pathogenesis. However, the mechanisms responsible for early exocrine parenchymal destruction and preservation of endocrine islets were unexplored until recently. In the course of chronic inflammation, pancreatic acini lose their "immunoprotective" status by neo-expressing death receptors. Therefore, they become susceptible to apoptosis that is triggered by their respective ligands expressed on lymphocytes and released by pancreatic stellate cells. By contrast, islets retain their immunoprotective status and activate nuclear factor-kappaB (NF-kappaB)-induced anti-apoptotic factors, thus enabling survival. This knowledge might be exploited for devising therapeutic approaches to retard acinar loss and to prolong islet survival.

Caerulin-induced pancreatitis in rats: Histological and genetic expression changes from acute phase to recuperation

AIM: To study the histological and pancreatitis-associated protein mRNA accumulation changes of pancreas from acute phase of caerulin-induced pancreatitis to recuperation in rats.

METHODS: Acute pancreatitis was induced by caerulein in male Wistar rats and followed up for 90 d by histological and mRNA analyses of pancreas. Pancreases were dissected at 0, 9, 24 h and 3, 5, 15, 30, 60, 90 d post-induction. Edema (E), polymorphonuclear neutrophil (PMN) infiltration, cytoplasmic vacuolization (V), zymogen granule depletion (ZD) and acinar disorganization (AD) were microscopically evaluated. Accumulation of pancreatitis-associated protein (PAP) and L13A mRNAs were quantified by real-time PCR.

RESULTS: The main histological changes appeared at 9 h post-induction for PMN infiltration and cytoplasmic V, while at 24 h and 3 d for E and ZD, respectively. All the parameters were recovered after 5 d, except for ZD which delayed more than 30 d. The main AD was observed after 15 d and values returned to normal after 30 d. Similarly to histological changes, accumulation of the PAP mRNA was increased at 9 h with the highest accumulation at 24 h and differences disappeared after 5 d.

CONCLUSION: From the acute phase to recuperation of pancreatitis, regeneration and re-differentiation of pancreas occur and PAP expression is exclusively an acute response of pancreatitis.

Store-operated calcium channels and pro-inflammatory signals

In non-excitable cells such as T lymphocytes, hepatocytes, mast cells, endothelia and epithelia, the major pathway for calcium [Ca2+] entry is through store-operated Ca2+ channels in the plasma membrane. These channels are activated by the emptying of intracellular Ca2+ stores, however, neither the gating mechanism nor the downstream targets of these channels has been clear established. Here, I review some of the proposed gating mechanisms of store-operated Ca2+ channels and the functional implications in regulating pro-inflammatory signals.

Trypsinogen mutations in pancreatic disorders

There are multiple PRSS1 mutations described in hereditary pancreatitis but only a minority of these are clinically relevant. The two most frequent point mutations are in exon 2 (N29I) and exon3 (R122H), found in diverse racial populations. Both mutations result in early onset pancreatitis but the mechanism underlying this phenotype is unclear. The frequency of these mutations in such diverse populations suggests they have spontaneously occurred many times. The origin of the major mutations may be explained by gene conversions, accounting for multiple founders. The implications are discussed in terms of mechanism of action of the mutations and clinical presentation.

Zymogen activation in a reconstituted pancreatic acinar cell system

Pathological activation of digestive zymogens within the pancreatic acinar cell initiates acute pancreatitis. Cytosolic events regulate this activation within intracellular compartments of unclear identity. In an in vivo model of acute pancreatitis, zymogen activation was detected in both zymogen granule-enriched and microsomal cellular fractions. To examine the mechanism of this activation in vitro, a reconstituted system was developed using pancreatic cytosol, a zymogen granule-enriched fraction, and a microsomal fraction. Addition of cytosol to either particulate fraction resulted in a prominent increase in both trypsin and chymotrypsin activities. The percentage of the pool of trypsinogen and chymotrypsinogen activated was about twofold and sixfold greater, respectively, in the microsomal than in the zymogen granule-enriched fraction. Activation of chymotrypsinogen but not trypsinogen was significantly enhanced by ATP (5 mM) but not by the inactive ATP analog AMP-PNP. The processing of procarboxypeptidase B to its mature form also demonstrated a requirement for ATP and cytosol. E64d, an inhibitor of cathepsin B, a thiol protease that can activate trypsin, completely inhibited trypsin activity but did not affect chymotrypsin activity or carboxypeptidase B generation. These studies demonstrate that both zymogen granule-enriched and microsomal fractions from the pancreas can support cytosol-dependent zymogen activation. A component of the activation of some zymogens, such as chymotrypsinogen and procarboxypeptidase, may depend on ATP but not on trypsin or cathepsin B.

Fatty acid ethyl esters cause pancreatic calcium toxicity via inositol trisphosphate receptors and loss of ATP synthesis

BACKGROUND & AIMS

Fatty acid ethyl esters are ethanol metabolites inducing sustained, toxic elevations of the acinar cytosolic free calcium ion concentration ([Ca(2+)](C)) implicated in pancreatitis. We sought to define the mechanisms of this elevation.

METHODS

Isolated mouse pancreatic acinar cells were loaded with fluorescent dyes for confocal microscopy to measure [Ca(2+)](C) (Fluo 4, Fura Red), endoplasmic reticulum calcium ion concentration ([Ca(2+)](ER), Mg Fluo 4), mitochondrial membrane potential (TMRM), ADP:ATP ratio (Mg Green), and NADH autofluorescence in response to palmitoleic acid ethyl ester and palmitoleic acid (10-100 micromol/L). Whole-cell patch clamp was used to measure the calcium-activated chloride current and apply ethanol metabolites and/or ATP intracellularly.

RESULTS

Intracellular delivery of ester induced oscillatory increases of [Ca(2+)](C) and calcium-activated currents, inhibited acutely by caffeine (20 mmol/L), but not atropine, indicating involvement of inositol trisphosphate receptor channels. The stronger effect of extracellular ester or acid caused depletion of [Ca(2+)](ER), not prevented by caffeine, but associated with depleted ATP, depleted NADH autofluorescence, and depolarized mitochondria, suggesting calcium-ATPase pump failure because of lack of ATP. Intracellular ATP abolished the sustained rise in [Ca(2+)](C), although oscillatory signals persisted that were prevented by caffeine. Inhibition of ester hydrolysis markedly reduced its calcium-releasing effect and consequent toxicity.

CONCLUSIONS

Fatty acid ethyl ester increases [Ca(2+)](C) through inositol trisphosphate receptors and, following hydrolysis, through calcium-ATPase pump failure from impaired mitochondrial ATP production. Lowering cellular fatty acid substrate concentrations may reduce cell injury in pancreatitis.

An in vivo study of exocytosis of cement proteins from barnacle Balanus improvisus (D.) cyprid larva

Barnacles, like many marine invertebrates, cause serious biofouling to marine industrial constructions and hulls of vessels as they attach themselves to such surfaces. Precise biochemical understanding of the underwater adhesion to surfaces requires a detailed characterization of the biology of the control of barnacle cement secretion and the proteins that make up the cement. In this study, we have investigated cement secretion by cyprid larvae of Balanus improvisus (D.) and the morphology of their cement glands. We studied the cement protein organization within cement granules and categorized the granules into four different types according to their size and morphology,before and after stimulation of secretion. In addition, we followed the exocytotic process of cement secretion in vivo and discovered that granules undergo a dramatic swelling during secretion. Such swelling might be due to an increased osmotic activity of granule contents, following a process of hydration. We hypothesize that this hydration is essential for exocytotic secretion and conclude that cement protein exocytosis is a more complex process than previously thought and is similar to exocytotic secretion in vertebrate systems, such as histamine secretion from mast cells and exocrine secretion in the salivary gland and the pancreas.

Changes in the morphology of the acinar cells of the rat pancreas in the oedematous and necrotic types of experimental acute pancreatitis

Limited experimental models of the oedematous and necrotic types of acute pancreatitis provide some understanding of the pathophysiology of this disease. Wistar rats were treated with cerulein at 10 mg/kg of body weight or with L-arginine at 1.5 or 3 g/kg of body weight in order to induce the oedematous or necrotic type of acute pancreatitis. After the induction period we examined samples of pancreata with light and electron microscopes. Morphological examination showed profound changes in the histology of the pancreas and its acinar cells and subcellular structures, especially in the group of rats which received a higher dose of L-arginine, amounting to 3 g/kg body weight. These included parenchymal haemorrhage and widespread acinar cell necrotic changes. 4-OH-TEMPO successfully prevented morphological deterioration as well as amylase release, suggesting that the severity of the two types of disease strongly depends on the intensity of the oxidative stress. Our results lend support to the assumption that reactive oxygen species play an axial role in the pathogenesis of both types of acute pancreatitis.

Microdomains of intracellular Ca2+: molecular determinants and functional consequences

Calcium ions are ubiquitous and versatile signaling molecules, capable of decoding a variety of extracellular stimuli (hormones, neurotransmitters, growth factors, etc.) into markedly different intracellular actions, ranging from contraction to secretion, from proliferation to cell death. The key to this pleiotropic role is the complex spatiotemporal organization of the [Ca(2+)] rise evoked by extracellular agonists, which allows selected effectors to be recruited and specific actions to be initiated. In this review, we discuss the structural and functional bases that generate the subcellular heterogeneity in cellular Ca(2+) levels at rest and under stimulation. This complex choreography requires the concerted action of many different players; the central role is, of course, that of the calcium ion, with the main supporting characters being all the entities responsible for moving Ca(2+) between different compartments, while the cellular architecture provides a determining framework within which all the players have their exits and their entrances. In particular, we concentrate on the molecular mechanisms that lead to the generation of cytoplasmic Ca(2+) microdomains, focusing on their different subcellular location, mechanism of generation, and functional role.

Vacuolar sequential exocytosis of large dense-core vesicles in adrenal medulla

Individual exocytic events in intact adrenal medulla were visualized by two-photon extracellular polar-tracer imaging. Exocytosis of chromaffin vesicles often occurred in a sequential manner, involving first vesicles located at the cell periphery and then those present deeper within the cytoplasm. Sequential exocytosis occurred preferentially at regions of the plasma membrane facing the intercellular space. The compound vesicles swelled to more than five times their original volume and formed vacuolar exocytic lumens as a result of expansion of intravesicular gels and their confinement within the lumen by the fusion pore and the narrow intercellular space. Such luminal swelling greatly promoted sequential exocytosis. The SNARE protein SNAP25 rapidly migrated from the plasma membrane to the membrane of fused vesicles. These data indicate that vesicles present deeper within the cytoplasm can be fusion ready like those at the cell periphery, and that swelling of exocytic lumens promotes assembly of the fusion machinery. We suggest the existence of two molecular configurations for fusion-ready states in Ca2+ -dependent exocytosis.

Ca2+ signalling and pancreatitis: effects of alcohol, bile and coffee

Ca2+ is a universal intracellular messenger that controls a wide range of cellular processes. In pancreatic acinar cells, acetylcholine and cholecystokinin regulate secretion via generation of repetitive local cytosolic Ca2+ signals in the apical pole. Bile acids and non-oxidative alcohol metabolites can elicit abnormal cytosolic Ca2+ signals that are global and sustained and result in necrosis. Necrosis results from excessive loss of Ca2+ from the endoplasmic reticulum, which is mediated by Ca2+ release through specific channels and inhibition of Ca2+ pumps in intracellular stores, followed by entry of extracellular Ca2+. Reduction of the cellular ATP level has a major role in this process. These abnormal Ca2+ signals, which can be inhibited by caffeine, explain how excessive alcohol intake and biliary disease cause acute pancreatitis, an often-fatal human disease in which the pancreas digests itself and its surroundings.

Mechanisms of acinar cell injury in acute pancreatitis

Acute pancreatitis has many causes, all leading to a common pathway of changes within the pancreatic acinar cell. Key amongst these changes is premature intracellular activation of digestive enzymes but this is also accompanied by the appearance of cytosolic vacuoles, co-localization of digestive and lysosomal enzymes, activation of NF-kappaB, and release of pro-inflammatory cytokines. The exact mechanism responsible for enzyme activation remains the subject of much research effort and not a little debate, however it is clear that all of these changes are triggered by an abnormal, sustained rise in cytosolic calcium concentration, which is itself dependent both on release of calcium from endoplasmic reticulum stores and uptake from the extracellular milieu. Activated enzymes are directly damaging to the acinar cell themselves, but recruitment of circulating neutrophils leads to further cellular damage. Cytokines and neutrophil activation are also responsible for the systemic inflammatory response typically seen in severe acute pancreatitis.

The ryanodine receptor mediates early zymogen activation in pancreatitis

Acute pancreatitis is characterized by the pathologic activation of zymogens within pancreatic acinar cells. The process requires a rise in cytosolic Ca(2+) from undefined intracellular stores. We hypothesized that zymogen activation is mediated by ryanodine receptor (RYR)-regulated Ca(2+) release, because early zymogen activation takes place in a supranuclear compartment that overlaps in distribution with the RYR. Ca(2+) signals in the basolateral, but not apical, region of acinar cells observed during supraphysiologic agonist stimulation were dependent on RYR Ca(2+) release. Inhibition of RYR or depletion of RYR-sensitive Ca(2+) pools each reduced pathologic zymogen activation in isolated acinar cells, but neither treatment affected amylase secretion. Inhibition of RYR also inhibited zymogen activation in vivo. We propose that Ca(2+) release from the RYR mediates zymogen activation but not enzyme secretion. The findings imply a role for the RYR in acute pancreatitis.

Secretin differentially sensitizes rat pancreatic acini to the effects of supramaximal stimulation with caerulein

Supramaximal stimulation of the rat pancreas with CCK, or its analog caerulein, triggers acute pancreatitis and a number of pancreatitis-associated acinar cell changes including intracellular activation of digestive enzyme zymogens and acinar cell injury. It is generally believed that some of these various acinar cell responses to supramaximal secretagogue stimulation are interrelated and interdependent. In a recent report, Lu et al. showed that secretin, by causing generation of cAMP and activation of PKA, sensitizes acinar cells to secretagogue-induced zymogen activation, and, as a result, submaximally stimulating concentrations of caerulein can, in the presence of secretin, trigger intracellular zymogen activation. We found that secretin also sensitizes acinar cells to secretagogue-induced cell injury and to subapical F-actin redistribution but that it did not alter the caerulein concentration dependence of other pancreatitis-associated changes such as the induction of a peak plateau intracellular [Ca(2+)] rise, inhibition of secretion, activation of ERK1/2, and activation of NF-kappaB. The finding that secretin sensitizes acinar cells to both intracellular zymogen activation and cell injury is consistent with the concept that these two early events in pancreatitis are closely interrelated and, possibly, interdependent. On the other hand, the finding that, in the presence of secretin, caerulein can trigger subapical F-actin redistribution without inhibiting secretion challenges the concept that disruption of the subapical F-actin web is causally related to high-dose secretagogue-induced inhibition of secretion in pancreatic acinar cells.

NADPH oxidase and apoptosis in cerulein-stimulated pancreatic acinar AR42J cells

Apoptosis linked to oxidative stress has been implicated in pancreatitis. We investigated whether NADPH oxidase mediates apoptosis in cerulein-stimulated pancreatic acinar AR42J cells. We report here that cerulein treatment resulted in the activation of NADPH oxidase, as determined by ROS production, translocation of cytosolic subunits p 47(phox) and p 67(phox) to the membrane, and interaction between NADPH oxidase subunits. Cerulein induced Ca(2+) oscillation, the expression of apoptotic genes p53 and bax, and apoptotic indices (DNA fragmentation, TUNEL staining, caspase 3 activity, decrease in cell viability) in AR42J cells. Treatment with a Ca(2+) chelator, BAPTA-AM, or transfection with antisense oligonucleotides for NADPH oxidase subunits p22(phox) and p 47(phox) inhibited cerulein-induced ROS production, translocation of NADPH oxidase cytosolic subunits p 47(phox) and p 67(phox) to the membrane, and the expression of apoptotic genes and apoptotic indices, as compared to the cells without treatment and those transfected with the corresponding sense oligonucleotides. These results indicate that NADPH oxidase may mediate ROS-induced apoptosis in pancreatic acinar cells in a Ca(2+)-dependent manner.

Early and late complications after pancreatic necrosectomy

BACKGROUND

Surgery for pancreatic necrosis is associated with a high morbidity and mortality. The aim of this study was to review the incidence of early and late complications after pancreatic necrosectomy in a large contemporary series of patients.

METHODS

The clinical outcomes of 88 patients who underwent pancreatic necrosectomy between 1997 and 2003 were reviewed.

RESULTS

The median age was 55.5 (range, 18-85) years, 54 (61%) were males, 68 (77%) had primary pancreatic infection, 71 (81%) had >50% necrosis, and the median admission Acute Physiology and Chronic Health Evaluation score was 9 (range, 1-21). Median time to surgery was 31 (range, 1-161) days; 47 patients underwent minimally invasive necrosectomy and 41 open necrosectomy; 81 (92%) of patients had complications postoperatively, and 25 (28%) died. Multiorgan failure (odds ratio = 3.4, P = .05) and hemorrhage (odds ratio = 6.1, P = .03) were the only independent predictors of mortality. During a median follow-up of 28.9 months, 39 (62%) of 63 surviving patients had one or more late complications: biliary stricture in 4 (6%), pseudocyst in 5 (8%), pancreatic fistula in 8 (13%), gastrointestinal fistula in 1 (2%), delayed collections in 3 (5%), and incisional hernia in 1 (2%); intervention was required in 10 (16%) patients. Sixteen (25%) of 63 surviving patients developed exocrine insufficiency, and 19 (33%) of 58 without prior diabetes mellitus developed endocrine insufficiency.

CONCLUSIONS

Almost all patients undergoing necrosectomy developed significant early or late complications or both. Multiorgan failure and postoperative hemorrhage were independent predictors of mortality. Long-term follow-up was important because 62% developed complications, and 16% of those with complications required surgical or endoscopic intervention.