Ca2+ signaling in pancreatic acinar cells: physiology and pathophysiology

Mitochondrial dysfunction in pancreatic acinar cells: mechanisms and therapeutic strategies in acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disease of the pancreas and a complex process involving multiple factors, with mitochondrial damage playing a crucial role. Mitochondrial dysfunction is now considered a key driver in the development of AP. This dysfunction often presents as increased oxidative stress, altered membrane potential and permeability, and mitochondrial DNA damage and mutations. Under stress conditions, mitochondrial dynamics and mitochondrial ROS production increase, leading to decreased mitochondrial membrane potential, imbalanced calcium homeostasis, and activation of the mitochondrial permeability transition pore. The release of mitochondrial DNA (mtDNA), recognized as damage-associated molecular patterns, can activate the cGAS-STING1 and NF-κB pathway and induce pro-inflammatory factor expression. Additionally, mtDNA can activate inflammasomes, leading to interleukin release and subsequent tissue damage and inflammation. This review summarizes the relationship between mitochondria and AP and explores mitochondrial protective strategies in the diagnosis and treatment of this disease. Future research on the treatment of acute pancreatitis can benefit from exploring promising avenues such as antioxidants, mitochondrial inhibitors, and new therapies that target mitochondrial dysfunction.

Computational Model of Complex Calcium Dynamics: Store Operated Ca2+ Channels and Mitochondrial Associated Membranes in Pancreatic Acinar Cells

This proposed model explores the intricate Ca2+ dynamics within the pancreatic acinar cells (PACs) by emphasizing the role of store-operated Ca2+ entry (SOCE) and the mitochondrial-associated membranes (MAMs) in the secretory region (apical) of the PACs. Traditionally, Ca2+ releases from the endoplasmic reticulum (ER) via calcium-induced calcium release (CICR). It has been shown to be important in regulating functions such as secretion of digestive enzymes in PACs. However, this model posits that upon the depletion of Ca2+ in the ER, the signaling protein stromal interaction molecule (STIM1) is activated. Activated STIM1, then facilitates the opening of Orai channels, allowing Ca2+ influx through the store-operated calcium channels (SOCCs). The model highlights the complexity of the Ca2+ dynamics, and the importance of SOCE and MAMs in the PACs Ca2+ homeostasis. The numerical and bifurcation analysis illustrate how changes in agonist concentrations can lead to the diverse Ca2+ oscillation patterns, such as thin to broader oscillations, sinusoidal patterns, and baseline fluctuations, driven by the feedback mechanisms involving Ca2+ and inositol 1,4,5 trisphosphate (IP3). This understanding could have broader implications for cellular physiology and the development of therapies targeting Ca2+ signaling pathways.

Novel Functional Features of cGMP Substrate Proteins IRAG1 and IRAG2

The inositol triphosphate-associated proteins IRAG1 and IRAG2 are cGMP kinase substrate proteins that regulate intracellular Ca²⁺. Previously, IRAG1 was discovered as a 125 kDa membrane protein at the endoplasmic reticulum, which is associated with the intracellular Ca²⁺ channel IP₃R-I and the PKGIβ and inhibits IP₃R-I upon PKGIβ-mediated phosphorylation. IRAG2 is a 75 kDa membrane protein homolog of IRAG1 and was recently also determined as a PKGI substrate. Several (patho-)physiological functions of IRAG1 and IRAG2 were meanwhile elucidated in a variety of human and murine tissues, e.g., of IRAG1 in various smooth muscles, heart, platelets, and other blood cells, of IRAG2 in the pancreas, heart, platelets, and taste cells. Hence, lack of IRAG1 or IRAG2 leads to diverse phenotypes in these organs, e.g., smooth muscle and platelet disorders or secretory deficiency, respectively. This review aims to highlight the recent research regarding these two regulatory proteins to envision their molecular and (patho-)physiological tasks and to unravel their functional interplay as possible (patho-)physiological counterparts.

Endogenous Amyloid-formed Ca2+-permeable Channels in Aged 3xTg AD Mice

Alzheimer's disease (AD), the leading cause of dementia, is characterized by the accumulation of beta-amyloid peptides (Aβ). However, whether Aβ itself is a key toxic agent in AD pathogenesis and the precise mechanism of Aβ-elicited neurotoxicity are still debated. Emerging evidence demonstrates that the Aβ channel/pore hypothesis could explain Aβ toxicity, because Aβ oligomers are able to disrupt membranes and cause edge-conductivity pores that may disrupt cell Ca2+ homeostasis and drive neurotoxicity in AD. However, all available data to support this hypothesis have been collected from "in vitro" experiments using high concentrations of exogenous Aβ. It is still unknown whether Aβ channels can be formed by endogenous Aβ in AD animal models. Here, we report an unexpected finding of the spontaneous Ca2+ oscillations in aged 3xTg AD mice but not in age-matched wild-type mice. These spontaneous Ca2+ oscillations are sensitive to extracellular Ca2+, ZnCl2, and the Aβ channel blocker Anle138b, suggesting that these spontaneous Ca2+ oscillations in aged 3xTg AD mice are mediated by endogenous Aβ-formed channels.

Understanding Necroptosis in Pancreatic Diseases

Intermediate between apoptosis and necrosis, necroptosis is a regulated caspase-independent programmed cell death that induces an inflammatory response and mediates cancer development. As our understanding improves, its role in the physiopathology of numerous diseases, including pancreatic diseases, has been reconsidered, and especially in pancreatitis and pancreatic cancer. However, the exact pathogenesis remains elusive, even though some studies have been conducted on these diseases. Its unique mechanisms of action in diseases are expected to bring prospects for the treatment of pancreatic diseases. Therefore, it is imperative to further explore its molecular mechanism in pancreatic diseases in order to identify novel therapeutic options. This article introduces recent related research on necroptosis and pancreatic diseases, explores necroptosis-related molecular pathways, and provides a theoretical foundation for new therapeutic targets for pancreatic diseases.

Reduction in O-GlcNAcylation Mitigates the Severity of Inflammatory Response in Cerulein-Induced Acute Pancreatitis in a Mouse Model

Acute pancreatitis (AP) involves premature trypsinogen activation, which mediates a cascade of pro-inflammatory signaling that causes early stages of pancreatic injury. Activation of the transcription factor κB (NF-κB) and secretion of pro-inflammatory mediators are major events in AP. O-GlcNAc transferase (OGT), a stress-sensitive enzyme, was recently implicated to regulate NF-κB activation and inflammation in AP in vitro. This study aims to determine whether a pancreas-specific transgenic reduction in OGT in a mouse model affects the severity of AP in vivo. Mice with reduced pancreatic OGT (OGT^Panc+/-) at 8 weeks of age were randomized to cerulein, which induces pancreatitis, or saline injections. AP was confirmed by elevated amylase levels and on histological analysis. The histological scoring demonstrated that OGT^Panc+/- mice had decreased severity of AP. Additionally, serum lipase, LDH, and TNF-α in OGT^Panc+/- did not significantly increase in response to cerulein treatment as compared to controls, suggesting attenuated AP induction in this model. Our study reveals the effect of reducing pancreatic OGT levels on the severity of pancreatitis, warranting further investigation on the role of OGT in the pathology of AP.

IRAG2 Interacts with IP3-Receptor Types 1, 2, and 3 and Regulates Intracellular Ca2+ in Murine Pancreatic Acinar Cells

The inositol 1,4,5-triphosphate receptor-associated 2 (IRAG2) is also known as Jaw1 or lymphoid-restricted membrane protein (LRMP) and shares homology with the inositol 1,4,5-triphosphate receptor-associated cGMP kinase substrate 1 (IRAG1). IRAG1 interacts with inositol trisphosphate receptors (IP₃ receptors /IP₃R) via its coiled-coil domain and modulates Ca²⁺ release from intracellular stores. Due to the homology of IRAG1 and IRAG2, especially in its coiled-coil domain, it is possible that IRAG2 has similar interaction partners like IRAG1 and that IRAG2 also modulates intracellular Ca²⁺ signaling. In our study, we localized IRAG2 in pancreatic acinar cells of the exocrine pancreas, and we investigated the interaction of IRAG2 with IP₃ receptors and its impact on intracellular Ca²⁺ signaling and exocrine pancreatic function, like amylase secretion. We detected the interaction of IRAG2 with different subtypes of IP₃R and altered Ca²⁺ release in pancreatic acinar cells from mice lacking IRAG2. IRAG2 deficiency decreased basal levels of intracellular Ca²⁺, suggesting that IRAG2 leads to activation of IP₃R under unstimulated basal conditions. Moreover, we observed that loss of IRAG2 impacts the secretion of amylase. Our data, therefore, suggest that IRAG2 modulates intracellular Ca²⁺ signaling, which regulates exocrine pancreatic function.

A TRPV6 expression atlas for the mouse

The transient receptor potential vanilloid 6 (TRPV6) channel is highly Ca²⁺-selective and has been implicated in mediating transcellular Ca²⁺ transport and thus maintaining the Ca²⁺ balance in the body. To characterize its physiological function(s), a detailed expression profile of the TRPV6 channel throughout the body is essential. Capitalizing on a recently established murine Trpv6-reporter strain, we identified primary TRPV6 channel-expressing cells in an organism-wide manner. In a complementary experimental approach, we characterized TRPV6 expression in different tissues of wild-type mice by TRPV6 immunoprecipitation (IP) followed by mass spectrometry analysis and correlated these data with the reporter gene expression. Taken together, we present a TRPV6 expression atlas throughout the entire body of juvenile and adult mice, providing a novel resource to investigate the role of TRPV6 channels in vivo.

Dual Mode of Action of Acetylcholine on Cytosolic Calcium Oscillations in Pancreatic Beta and Acinar Cells In Situ

Cholinergic innervation in the pancreas controls both the release of digestive enzymes to support the intestinal digestion and absorption, as well as insulin release to promote nutrient use in the cells of the body. The effects of muscarinic receptor stimulation are described in detail for endocrine beta cells and exocrine acinar cells separately. Here we describe morphological and functional criteria to separate these two cell types in situ in tissue slices and simultaneously measure their response to ACh stimulation on cytosolic Ca2+ oscillations [Ca2+]c in stimulatory glucose conditions. Our results show that both cell types respond to glucose directly in the concentration range compatible with the glucose transporters they express. The physiological ACh concentration increases the frequency of glucose stimulated [Ca2+]c oscillations in both cell types and synchronizes [Ca2+]c oscillations in acinar cells. The supraphysiological ACh concentration further increases the oscillation frequency on the level of individual beta cells, inhibits the synchronization between these cells, and abolishes oscillatory activity in acinar cells. We discuss possible mechanisms leading to the observed phenomena.

The p.E152K-STIM1 mutation deregulates Ca2+ signaling contributing to chronic pancreatitis

Since deregulation of intracellular Ca²⁺ can lead to intracellular trypsin activation, and stromal interaction molecule-1 (STIM1) protein is the main regulator of Ca²⁺ homeostasis in pancreatic acinar cells, we explored the Ca²⁺ signaling in 37 STIM1 variants found in three pancreatitis patient cohorts. Extensive functional analysis of one particular variant, p.E152K, identified in three patients, provided a plausible link between dysregulated Ca²⁺ signaling within pancreatic acinar cells and chronic pancreatitis susceptibility. Specifically, p.E152K, located within the STIM1 EF-hand and sterile α-motif domain, increased the release of Ca²⁺ from the endoplasmic reticulum in patient-derived fibroblasts and transfected HEK293T cells. This event was mediated by altered STIM1-sarco/endoplasmic reticulum calcium transport ATPase (SERCA) conformational change and enhanced SERCA pump activity leading to increased store-operated Ca²⁺ entry (SOCE). In pancreatic AR42J cells expressing the p.E152K variant, Ca²⁺ signaling perturbations correlated with defects in trypsin activation and secretion, and increased cytotoxicity after cholecystokinin stimulation.This article has an associated First Person interview with the first author of the paper.

Sustained bile drainage decreases the organs injuries via inflammation-associated factors modulation in a severe acute pancreatitis rat model

The timely and effective treatment for severe acute pancreatitis (SAP) is favorable to prognosis. Decompression of the bile duct might be a feasible way to decrease the progression of SAP. The present study investigated the effects of sustained bile external drainage on organs injury caused by SAP in Sprague-Dawley (SD) rats and the mechanisms involved. A total of 72 female SD rats weighting 190-230 g were randomly divided into four groups (n=18): Sham operation group (SOG), SOG + bile drainage group (BDG), SAP group, and SAP + BDG. Sodium taurocholate solution (4%; 1 mg/kg body weight) was used to set up SAP model via injection of retrograde puncture of biliopancreatic duct through the duodenum. A cannula was inserted into the bile duct and fixed externally to establish BDG model. At each time points (t=3, 6, 12; n=6), tissues from the liver, lung, and pancreas, and blood samples were collected. Serum amylase (AMY) was analyzed in all the samples. The levels of tumor necrosis factor-α (TNF-α), heme oxygenase-1 (HO-1), interleukin-10 (IL-10) and high mobility group box 1 (HMGB1) were detected by ELISA. Hematoxylin-eosin staining was performed to observe the histopathological changes, and nuclear transcription factor (NF)-κB-p65 levels in the pancreas were analyzed by western blotting. The data indicated that BDG alleviated the SAP progression and multiple organs injuries. Meanwhile, the histopathological changes of the pancreas, liver, and lungs were improved by BDG. BDG decreased the pathological scores of pancreas significantly (P<0.05). The levels of AMY, TNF-α, HMGB1, and NF-κB-p65 were significantly downregulated by BDG (P<0.05), while the level of HO-1 was upregulated and IL-10 was unchanged. In summary, BDG may attenuate the multiple organs injuries caused by SAP via downregulation of TNF-α, HMGB1, NF-κB-p65 and upregulation of HO-1.

Early Intra-Acinar Events in Pathogenesis of Pancreatitis

Premature activation of digestive enzymes in the pancreas has been linked to development of pancreatitis for more than a century. Recent development of novel models to study the role of pathologic enzyme activation has led to advances in our understanding of the mechanisms of pancreatic injury. Colocalization of zymogen and lysosomal fraction occurs early after pancreatitis-causing stimulus. Cathepsin B activates trypsinogen in these colocalized organelles. Active trypsin increases permeability of these organelles resulting in leakage of cathepsin B into the cytosol leading to acinar cell death. Although trypsin-mediated cell death leads to pancreatic injury in early stages of pancreatitis, multiple parallel mechanisms, including activation of inflammatory cascades, endoplasmic reticulum stress, autophagy, and mitochondrial dysfunction in the acinar cells are now recognized to be important in driving the profound systemic inflammatory response and extensive pancreatic injury seen in acute pancreatitis. Chymotrypsin, another acinar protease, has recently been shown be play critical role in clearance of pathologically activated trypsin protecting against pancreatic injury. Mutations in trypsin and other genes thought to be associated with pathologic enzyme activation (such as serine protease inhibitor 1) have been found in familial forms of pancreatitis. Sustained intra-acinar activation of nuclear factor κB pathway seems to be key pathogenic mechanism in chronic pancreatitis. Better understanding of these mechanisms will hopefully allow us to improve treatment strategies in acute and chronic pancreatitis.

Heterogeneity of cannabinoid ligand-induced modulations in intracellular Ca2+ signals of mouse pancreatic acinar cells in vitro

We recently reported that a CB₂R agonist, GW405833 (GW), reduced both the ACh-induced Ca²⁺ oscillations and the L-arginine-induced Ca²⁺ signal enhancement in mouse pancreatic acinar cells, suggesting that GW-induced inhibition may prevent the pathogenesis of acute pancreatitis. In this study, we aim to evaluate the effects of other cannabinoid ligands on Ca²⁺ signaling in acinar cells. Patch-clamp whole-cell recordings were applied to measure ACh-induced intracellular Ca²⁺ oscillations in pancreatic acinar cells acutely dissociated from wild-type (WT), CB₁R knockout (KO), and CB₂R KO mice, and the pharmacological effects of various cannabinoid ligands on the Ca²⁺ oscillations were examined. We found that all the 8 CB₂R agonists tested inhibited ACh-induced Ca²⁺ oscillations. Among them, GW, JWH133, and GP1a caused potent inhibition with IC₅₀ values of 5.0, 6.7, and 1.2 μmol/L, respectively. In CB₂R KO mice or in the presence of a CB₂R antagonist (AM630), the inhibitory effects of these 3 CB₂R agonists were abolished, suggesting that they acted through the CB₂Rs. The CB₁R agonist ACEA also induced inhibition of Ca²⁺ oscillations that existed in CB₁R KO mice and in the presence of a CB₁R antagonist (AM251), suggesting a non-CB₁R effect. In WT, CB₁R KO, and CB₂R KO mice, a nonselective CBR agonist, WIN55,212-2, inhibited Ca²⁺ oscillations, which was not mediated by CB₁Rs or CB₂Rs. The endogenous cannabinoid substance, 2-arachidonoylglycerol (2-AG), did not show an inhibitory effect on Ca²⁺ oscillations. In conclusion, CB₂R agonists play critical roles in modulating Ca²⁺ signals in mouse pancreatic acinar cells, while other cannabinoid ligands modulate Ca²⁺ oscillations in a heterogeneous manner through a CB receptor or non-CB-receptor mechanism.

Malnutrition in Pancreatic Ductal Adenocarcinoma (PDA): Dietary Pancreatic Enzymes Improve Short-Term Health but Stimulate Tumor Growth

Pancreatic ductal adenocarcinoma (PDA) is a deadly cancer that resists efforts to identify better chemotherapeutics. PDA is associated with chronic pancreatitis and acinar cell dedifferentiation. This reduces enzyme production by the exocrine pancreas, resulting in digestive insufficiencies. Malabsorption of partially digested food causes bloating, overfilled intestines, abdominal pain, excessive feces, steatorrhea, and malnutrition. These maladies affect quality of life and restrict treatment options for pancreatitis and PDA. Here, we characterize health benefits and risks of dietary pancreatic enzymes in three mouse models of PDA-KC, KCR8-16, and KIC. KC expresses oncogenic Kras^G12D in pancreatic tissue whereas KCR8-16 also has deletions of the Rgs8 and Rgs16 genes. Rgs proteins inhibit the release of digestive enzymes evoked by G-protein-coupled-receptor agonists. KC and KCR8-16 mice developed dedifferentiated exocrine pancreata within 2 months of age and became malnourished, underweight, hypoglycemic, and hypothermic. KC mice adapted but KCR8-16 mice rapidly transitioned to starvation after mild metabolic challenges. Dietary pancreatic enzyme supplements reversed these symptoms in KC and KCR8-16 animals, and extended survival. Therefore, we tested the benefits of pancreatic enzymes in an aggressive mouse model of PDA (KIC). Median survival improved with dietary pancreatic enzyme supplements and was extended further when combined with warfarin and gemcitabine chemotherapy. However, dietary pancreatic enzymes stimulated tumor growth in the terminal stages of disease progression in KIC mice.

Ca2+ signalling underlying pancreatitis

In spite of significant scientific progress in recent years, acute pancreatitis (AP) is still a dangerous and in up to 5% of cases deadly disease with no specific cure. It is self-resolved in the majority of cases, but could result in chronic pancreatitis (CP) and increased risk of pancreatic cancer (PC). One of the early events in AP is premature activation of digestive pro-enzymes, including trypsinogen, inside pancreatic acinar cells (PACs) due to an excessive rise in the cytosolic Ca²⁺ concentration, which is the result of Ca²⁺ release from internal stores followed by Ca²⁺ entry through the store operated Ca²⁺ channels in the plasma membrane. The leading causes of AP are high alcohol intake and biliary disease with gallstones obstruction leading to bile reflux into the pancreatic duct. Recently attention in this area of research turned to another cause of AP - Asparaginase based drugs - which have been used quite successfully in treatments of childhood acute lymphoblastic leukaemia (ALL). Unfortunately, Asparaginase is implicated in triggering AP in 5-10% of cases as a side effect of the anti-cancer therapy. The main features of Asparaginase-elicited AP (AAP) were found to be remarkably similar to AP induced by alcohol metabolites and bile acids. Several potential therapeutic avenues in counteracting AAP have been suggested and could also be useful for dealing with AP induced by other causes. Another interesting development in this field includes recent research related to pancreatic stellate cells (PSCs) that are much less studied in their natural environment but nevertheless critically involved in AP, CP and PC. This review will attempt to evaluate developments, approaches and potential therapies for AP and discuss links to other relevant diseases.

Cannabinoid receptor subtype 2 (CB2R) agonist, GW405833 reduces agonist-induced Ca(2+) oscillations in mouse pancreatic acinar cells

Emerging evidence demonstrates that the blockade of intracellular Ca(2+) signals may protect pancreatic acinar cells against Ca(2+) overload, intracellular protease activation, and necrosis. The activation of cannabinoid receptor subtype 2 (CB2R) prevents acinar cell pathogenesis in animal models of acute pancreatitis. However, whether CB2Rs modulate intracellular Ca(2+) signals in pancreatic acinar cells is largely unknown. We evaluated the roles of CB2R agonist, GW405833 (GW) in agonist-induced Ca(2+) oscillations in pancreatic acinar cells using multiple experimental approaches with acute dissociated pancreatic acinar cells prepared from wild type, CB1R-knockout (KO), and CB2R-KO mice. Immunohistochemical labeling revealed that CB2R protein was expressed in mouse pancreatic acinar cells. Electrophysiological experiments showed that activation of CB2Rs by GW reduced acetylcholine (ACh)-, but not cholecystokinin (CCK)-induced Ca(2+) oscillations in a concentration-dependent manner; this inhibition was prevented by a selective CB2R antagonist, AM630, or was absent in CB2R-KO but not CB1R-KO mice. In addition, GW eliminated L-arginine-induced enhancement of Ca(2+) oscillations, pancreatic amylase, and pulmonary myeloperoxidase. Collectively, we provide novel evidence that activation of CB2Rs eliminates ACh-induced Ca(2+) oscillations and L-arginine-induced enhancement of Ca(2+) signaling in mouse pancreatic acinar cells, which suggests a potential cellular mechanism of CB2R-mediated protection in acute pancreatitis.

Congo red modulates ACh-induced Ca(2+) oscillations in single pancreatic acinar cells of mice

AIM

Congo red, a secondary diazo dye, is usually used as an indicator for the presence of amyloid fibrils. Recent studies show that congo red exerts neuroprotective effects in a variety of models of neurodegenerative diseases. However, its pharmacological profile remains unknown. In this study, we investigated the effects of congo red on ACh-induced Ca(2+) oscillations in mouse pancreatic acinar cells in vitro.

METHODS

Acutely dissociated pancreatic acinar cells of mice were prepared. A U-tube drug application system was used to deliver drugs into the bath. Intracellular Ca(2+) oscillations were monitored by whole-cell recording of Ca(2+)-activated Cl(-) currents and by using confocal Ca(2+) imaging. For intracellular drug application, the drug was added in pipette solution and diffused into cell after the whole-cell configuration was established.

RESULTS

Bath application of ACh (10 nmol/L) induced typical Ca(2+) oscillations in dissociated pancreatic acinar cells. Addition of congo red (1, 10, 100 μmol/L) dose-dependently enhanced Ach-induced Ca(2+) oscillations, but congo red alone did not induce any detectable response. Furthermore, this enhancement depended on the concentrations of ACh: congo red markedly enhanced the Ca(2+) oscillations induced by ACh (10-30 nmol/L), but did not alter the Ca(2+) oscillations induced by ACh (100-10000 nmol/L). Congo red also enhanced the Ca(2+) oscillations induced by bath application of IP3 (30 μmol/L). Intracellular application of congo red failed to alter ACh-induced Ca(2+) oscillations.

CONCLUSION

Congo red significantly modulates intracellular Ca(2+) signaling in pancreatic acinar cells, and this pharmacological effect should be fully considered when developing congo red as a novel therapeutic drug.

Endoplasmic reticulum stress is chronically activated in chronic pancreatitis

The pathogenesis of chronic pancreatitis (CP) is poorly understood. Endoplasmic reticulum (ER) stress has now been recognized as a pathogenic event in many chronic diseases. However, ER stress has not been studied in CP, although pancreatic acinar cells seem to be especially vulnerable to ER dysfunction because of their dependence on high ER volume and functionality. Here, we aim to investigate ER stress in CP, study its pathogenesis in relation to trypsinogen activation (widely regarded as the key event of pancreatitis), and explore its mechanism, time course, and downstream consequences during pancreatic injury. CP was induced in mice by repeated episodes of acute pancreatitis (AP) based on caerulein hyperstimulation. ER stress leads to activation of unfolded protein response components that were measured in CP and AP. We show sustained up-regulation of unfolded protein response components ATF4, CHOP, GRP78, and XBP1 in CP. Overexpression of GRP78 and ATF4 in human CP confirmed the experimental findings. We used novel trypsinogen-7 knock-out mice (T(-/-)), which lack intra-acinar trypsinogen activation, to clarify the relationship of ER stress to intra-acinar trypsinogen activation in pancreatic injury. Comparable activation of ER stress was seen in wild type and T(-/-) mice. Induction of ER stress occurred through pathologic calcium signaling very early in the course of pancreatic injury. Our results establish that ER stress is chronically activated in CP and is induced early in pancreatic injury through pathologic calcium signaling independent of trypsinogen activation. ER stress may be an important pathogenic mechanism in pancreatitis that needs to be explored in future studies.

Modelling the transition from simple to complex Ca²⁺ oscillations in pancreatic acinar cells

A mathematical model is proposed which systematically investigates complex calcium oscillations in pancreatic acinar cells. This model is based on calcium-induced calcium release via inositol trisphosphate receptors (IPR) and ryanodine receptors (RyR) and includes calcium modulation of inositol (1,4,5) trisphosphate (IP3) levels through feedback regulation of degradation and production. In our model, the apical and the basal regions are separated by a region containing mitochondria, which is capable of restricting Ca2+ responses to the apical region. We were able to reproduce the observed oscillatory patterns, from baseline spikes to sinusoidal oscillations. The model predicts that calcium-dependent production and degradation of IP3 is a key mechanism for complex calcium oscillations in pancreatic acinar cells. A partial bifurcation analysis is performed which explores the dynamic behaviour of the model in both apical and basal regions.

Inositol 1,4,5-trisphosphate receptor-isoform diversity in cell death and survival

Cell-death and -survival decisions are critically controlled by intracellular Ca(2+) homeostasis and dynamics at the level of the endoplasmic reticulum (ER). Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) play a pivotal role in these processes by mediating Ca(2+) flux from the ER into the cytosol and mitochondria. Hence, it is clear that many pro-survival and pro-death signaling pathways and proteins affect Ca(2+) signaling by directly targeting IP3R channels, which can happen in an IP3R-isoform-dependent manner. In this review, we will focus on how the different IP3R isoforms (IP3R1, IP3R2 and IP3R3) control cell death and survival. First, we will present an overview of the isoform-specific regulation of IP3Rs by cellular factors like IP3, Ca(2+), Ca(2+)-binding proteins, adenosine triphosphate (ATP), thiol modification, phosphorylation and interacting proteins, and of IP3R-isoform specific expression patterns. Second, we will discuss the role of the ER as a Ca(2+) store in cell death and survival and how IP3Rs and pro-survival/pro-death proteins can modulate the basal ER Ca(2+) leak. Third, we will review the regulation of the Ca(2+)-flux properties of the IP3R isoforms by the ER-resident and by the cytoplasmic proteins involved in cell death and survival as well as by redox regulation. Hence, we aim to highlight the specific roles of the various IP3R isoforms in cell-death and -survival signaling. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

Chemopreventive effects of resveratrol in a rat model of cerulein-induced acute pancreatitis

In the past decades, a greater understanding of acute pancreatitis has led to improvement in mortality rates. Nevertheless, this disease continues to be a health care system problem due to its economical costs. Future strategies such as antioxidant supplementation could be very promising, regarding to beginning and progression of the disease. For this reason, this study was aimed at assessing the effect of exogenous administration of resveratrol during the induction process of acute pancreatitis caused by the cholecystokinin analog cerulein in rats. Resveratrol pretreatment reduced histological damage induced by cerulein treatment, as well as hyperamylasemia and hyperlipidemia. Altered levels of corticosterone, total antioxidant status, and glutathione peroxidase were significantly reverted to control levels by the administration of resveratrol. Lipid peroxidation was also counteracted; nevertheless, superoxide dismutase enzyme was overexpressed due to resveratrol pretreatment. Related to immune response, resveratrol pretreatment reduced pro-inflammatory cytokine IL-1β levels and increased anti-inflammatory cytokine IL-10 levels. In addition, pretreatment with resveratrol in cerulein-induced pancreatitis rats was able to reverse, at least partially, the abnormal calcium signal induced by treatment with cerulein. In conclusion, this study confirms antioxidant and immunomodulatory properties of resveratrol as chemopreventive in cerulein-induced acute pancreatitis.

Central role of mitochondrial injury in the pathogenesis of acute pancreatitis

Acute pancreatitis is an inflammatory disease with no specific treatment. One of the main reasons behind the lack of specific therapy is that the pathogenesis of acute pancreatitis is poorly understood. During the development of acute pancreatitis, the disease-inducing factors can damage both cell types of the exocrine pancreas, namely the acinar and ductal cells. Because damage of either of the cell types can contribute to the inflammation, it is crucial to find common intracellular mechanisms that can be targeted by pharmacological therapies. Despite the many differences, recent studies revealed that the most common factors that induce pancreatitis cause mitochondrial damage with the consequent breakdown of bioenergetics, that is, ATP depletion in both cell types. In this review, we summarize our knowledge of mitochondrial function and damage within both pancreatic acinar and ductal cells. We also suggest that colloidal ATP delivery systems for pancreatic energy supply may be able to protect acinar and ductal cells from cellular damage in the early phase of the disease. An effective energy delivery system combined with the prevention of further mitochondrial damage may, for the first time, open up the possibility of pharmacological therapy for acute pancreatitis, leading to reduced disease severity and mortality.

Molecular mechanism of pancreatic and salivary gland fluid and HCO3 secretion

Fluid and HCO(3)(-) secretion is a vital function of all epithelia and is required for the survival of the tissue. Aberrant fluid and HCO(3)(-) secretion is associated with many epithelial diseases, such as cystic fibrosis, pancreatitis, Sjögren's syndrome, and other epithelial inflammatory and autoimmune diseases. Significant progress has been made over the last 20 years in our understanding of epithelial fluid and HCO(3)(-) secretion, in particular by secretory glands. Fluid and HCO(3)(-) secretion by secretory glands is a two-step process. Acinar cells secrete isotonic fluid in which the major salt is NaCl. Subsequently, the duct modifies the volume and electrolyte composition of the fluid to absorb the Cl(-) and secrete HCO(3)(-). The relative volume secreted by acinar and duct cells and modification of electrolyte composition of the secreted fluids varies among secretory glands to meet their physiological functions. In the pancreas, acinar cells secrete a small amount of NaCl-rich fluid, while the duct absorbs the Cl(-) and secretes HCO(3)(-) and the bulk of the fluid in the pancreatic juice. Fluid secretion appears to be driven by active HCO(3)(-) secretion. In the salivary glands, acinar cells secrete the bulk of the fluid in the saliva that is driven by active Cl(-) secretion and contains high concentrations of Na(+) and Cl(-). The salivary glands duct absorbs both the Na(+) and Cl(-) and secretes K(+) and HCO(3)(-). In this review, we focus on the molecular mechanism of fluid and HCO(3)(-) secretion by the pancreas and salivary glands, to highlight the similarities of the fundamental mechanisms of acinar and duct cell functions, and to point out the differences to meet gland-specific secretions.

The role of nitric oxide in the physiology and pathophysiology of the exocrine pancreas

SIGNIFICANCE

Nitric oxide (NO), a ubiquitous gaseous signaling molecule, contributes to both pancreatic physiology and pathophysiology.

RECENT ADVANCES

The present review provides a general overview of NO synthesis, signaling, and function. Further, it specifically discusses NO metabolism and its effects in the exocrine pancreas and focuses on the role of NO in the pathogenesis of acute pancreatitis and pancreatic ischemia/reperfusion injury.

CRITICAL ISSUES

Unfortunately, the role of NO in pancreatic physiology and pathophysiology remains controversial in numerous areas. Many questions regarding the messenger molecule still remain unanswered.

FUTURE DIRECTIONS

Probably the least is known about the downstream targets of NO, which need to be identified, especially at the molecular level.

Pancreatic exocrine function and cardiac iron in patients with iron overload and with thalassemia

Patients with β-thalassemia major at risk of cardiac iron overload have to be identified to undergo myocardial iron measurements by magnetic resonance imaging (MRI), especially, in areas and centers with restricted access to MRI. Measurements of heart iron, liver iron, and pancreatic exocrine function were performed in 44 patients by MRI-R2* [the transverse relaxation rate R2* (= 1/T2*) characterizes the magnetic resonance decay from protons not being in phase with each other in contrast to R2 (= 1/T2)], biomagnetic liver susceptometry (LIC), and pancreatic serum amylase (PAM) and lipase (LIP), respectively. ROC analysis (area: 0.88) for detecting patients with cardiac R2* > 50 sec(-1) (T2* < 20 msec) by LIP revealed a cut-off level of 19 U/L. In conclusion, patients at risk of elevated cardiac iron levels could be identified by the exocrine pancreatic lipase and amylase function parameters.

Cardiocirculatory pathophysiological mechanisms in severe acute pancreatitis

Acute pancreatitis (AP) is a common and potentially lethal acute inflammatory process. Although the majority of patients have a mild episode of AP, 10%-20% develop a severe acute pancreatitis (SAP) and suffer systemic inflammatory response syndrome (SIRS) and/or pancreatic necrosis. The main aim of this article is to review the set of events, first localized in the pancreas, that lead to pancreatic inflammation and to the spread to other organs contributing to multiorganic shock. The early pathogenic mechanisms in SAP are not completely understood but both premature activation of enzymes inside the pancreas, related to an impaired cytosolic Ca²⁺ homeostasis, as well as release of pancreatic enzymes into the bloodstream are considered important events in the onset of pancreatitis disease. Moreover, afferent fibers within the pancreas release neurotransmitters in response to tissue damage. The vasodilator effects of these neurotransmitters and the activation of pro-inflammatory substances play a crucial role in amplifying the inflammatory response, which leads to systemic manifestation of AP. Damage extension to other organs leads to SIRS, which is usually associated with cardiocirculatory physiology impairment and a hypotensive state. Hypotension is a risk factor for death and is associated with a significant hyporesponsiveness to vasoconstrictors. This indicates that stabilization of the patient, once this pathological situation has been established, would be a very difficult task. Therefore, it seems particularly necessary to understand the pathological mechanisms involved in the first phases of AP to avoid damage beyond the pancreas. Moreover, efforts must also be directed to identify those patients who are at risk of developing SAP.