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

ADP-ribosylation factor 1 protein regulates trypsinogen activation via organellar trafficking of procathepsin B protein and autophagic maturation in acute pancreatitis

Several studies have suggested that autophagy might play a deleterious role in acute pancreatitis via intra-acinar activation of digestive enzymes. The prototype for this phenomenon is cathepsin B-mediated trypsin generation. To determine the organellar basis of this process, we investigated the subcellular distribution of the cathepsin B precursor, procathepsin B. We found that procathepsin B is enriched in Golgi-containing microsomes, suggesting a role for the ADP-ribosylation (ARF)-dependent trafficking of cathepsin B. Indeed, caerulein treatment increased processing of procathepsin B, whereas a known ARF inhibitor brefeldin A (BFA) prevented this. Similar treatment did not affect processing of procathepsin L. BFA-mediated ARF1 inhibition resulted in reduced cathepsin B activity and consequently reduced trypsinogen activation. However, formation of light chain 3 (LC3-II) was not affected, suggesting that BFA did not prevent autophagy induction. Instead, sucrose density gradient centrifugation and electron microscopy showed that BFA arrested caerulein-induced autophagosomal maturation. Therefore, ARF1-dependent trafficking of procathepsin B and the maturation of autophagosomes results in cathepsin B-mediated trypsinogen activation induced by caerulein.

Emodin promoted pancreatic claudin-5 and occludin expression in experimental acute pancreatitis rats

AIM: To investigate the effect of emodin on pancreatic claudin-5 and occludin expression, and pancreatic paracellular permeability in acute pancreatitis (AP).

METHODS: Experimental pancreatitis was induced by retrograde injection of 5% sodium taurocholate into the biliopancreatic duct. Emodin was injected via the external jugular vein 0 or 6 h after induction of AP. Rats from sham operation and AP groups were injected with normal saline at the same time. Samples of pancreas were obtained 6 or 12 h after drug administration. Pancreatic morphology was examined with hematoxylin and eosin staining. Pancreatic edema was estimated by measuring tissue water content. Tumor necrosis factor (TNF)-α and interleukin (IL)-6 level were measured by enzyme-linked immunosorbent assay. Pancreatic paracellular permeability was assessed by tissue dye extravasation. Expression of pancreatic claudin-5 and occludin was examined by immunohistology, quantitative real-time reverse transcriptase polymerase chain reaction and western blotting.

RESULTS: Pancreatic TNF-α and IL-6 levels, wet/dry ratio, dye extravasation, and histological score were significantly elevated at 3, 6 and 12 h following sodium taurocholate infusion; treatment with emodin prevented these changes at all time points. Immunostaining of claudin-5 and occludin was detected in rat pancreas, which was distributed in pancreatic acinar cells, ductal cells and vascular endothelial cells, respectively. Sodium taurocholate infusion significantly decreased pancreatic claudin-5 and occludin mRNA and protein levels at 3, 6 and 12 h, and that could be promoted by intravenous administration of emodin at all time points.

CONCLUSION: These results demonstrate that emodin could promote pancreatic claudin-5 and occludin expression, and reduce pancreatic paracellular permeability.

Mitochondrial calcium in the life and death of exocrine secretory cells

The remarkable recent discoveries of the proteins mediating mitochondrial Ca(2+) transport (reviewed in this issue) provide an exciting opportunity to utilise this new knowledge to improve our fundamental understanding of relationships between Ca(2+) signalling and bioenergetics and, importantly, to improve the understanding of diseases in which Ca(2+) toxicity and mitochondrial malfunction play a crucial role. Ca(2+) is an important activator of exocrine secretion, a regulator of the bioenergetics of exocrine cells and a contributor to exocrine cell damage. Exocrine secretory cells, exocrine tissues and diseases affecting exocrine glands (like Sjögren's syndrome and acute pancreatitis) will, therefore, provide worthy research areas for the application of this new knowledge of the Ca(2+) transport mechanisms in mitochondria.

Pharmacological and genetic inhibition of calcineurin protects against carbachol-induced pathological zymogen activation and acinar cell injury

Acute pancreatitis is a major health burden for which there are currently no targeted therapies. Premature activation of digestive proenzymes, or zymogens, within the pancreatic acinar cell is an early and critical event in this disease. A high-amplitude, sustained rise in acinar cell Ca(2+) is required for zymogen activation. We previously showed in a cholecystokinin-induced pancreatitis model that a potential target of this aberrant Ca(2+) signaling is the Ca(2+)-activated phosphatase calcineurin (Cn). However, in this study, we examined the role of Cn on both zymogen activation and injury, in the clinically relevant condition of neurogenic stimulation (by giving the acetylcholine analog carbachol) using three different Cn inhibitors or Cn-deficient acinar cells. In freshly isolated mouse acinar cells, pretreatment with FK506, calcineurin inhibitory peptide (CiP), or cyclosporine (CsA) blocked intra-acinar zymogen activation (n = 3; P < 0.05). The Cn inhibitors also reduced leakage of lactate dehydrogenase (LDH) by 79%, 62%, and 63%, respectively (n = 3; P < 0.05). Of the various Cn isoforms, the β-isoform of the catalytic A subunit (CnAβ) was strongly expressed in mouse acinar cells. For this reason, we obtained acinar cells from CnAβ-deficient mice (CnAβ-/-) and observed an 84% and 50% reduction in trypsin and chymotrypsin activation, respectively, compared with wild-type controls (n = 3; P < 0.05). LDH release in the CnAβ-deficient cells was reduced by 50% (n = 2; P < 0.05). The CnAβ-deficient cells were also protected against zymogen activation and cell injury induced by the cholecystokinin analog caerulein. Importantly, amylase secretion was generally not affected by either the Cn inhibitors or Cn deficiency. These data provide both pharmacological and genetic evidence that implicates Cn in intra-acinar zymogen activation and cell injury during pancreatitis.

Zymophagy: selective autophagy of secretory granules

Timing is everything. That's especially true when it comes to the activation of enzymes created by the pancreas to break down food. Pancreatic enzymes are packed in secretory granules as precursor molecules called zymogens. In physiological conditions, those zymogens are activated only when they reach the gut, where they get to work releasing and distributing nutrients that we need to survive. If this process fails and the enzymes are prematurely activated within the pancreatic cell, before they are released from the gland, they break down the pancreas itself causing acute pancreatitis. This is a painful disease that ranges from a mild and autolimited process to a severe and lethal condition. Recently, we demonstrated that the pancreatic acinar cell is able to switch on a refined mechanism that could explain the autolimited form of the disease. This is a novel selective form of autophagy named zymophagy, a cellular process to specifically detect and degrade secretory granules containing activated enzymes before they can digest the organ. In this work, we revise the molecules and mechanisms that mediate zymophagy, a selective autophagy of secretory granules.

Chemokine receptor CXCR3 is involved in the acute pancreatitis-associated lung injury

Acute pancreatitis is a common disease, which is divided into mild pancreatitis and severe pancreatitis. For the latter, a systemic inflammatory response may occur and lead to distant organ damage and the development of multiple organ dysfunction syndrome (MODS), which accounts for significant morbidity and mortality in humans. Chemokines and their receptors are being believed to play a pivotal role in the pathogenesis of acute pancreatitis. Chemokine receptor CXCR3 is reported to be involved in acute tissue injury, for example acute lung injury induced by cigarette smoking, but its role in acute pancreatitis is not yet known. In this study, two animal models of acute pancreatitis (cerulein- and arginine-induced pancreatitis) were applied in CXCR3⁻/⁻ mice and wild-type mice, in order to explore the role of CXCR3 in acute pancreatitis. Serum amylase, lipase and histological observations revealed that CXCR3 knockout did not affect the severity of acute pancreatitis. However, edema and inflammatory cell infiltrate in the lung tissue were attenuated in CXCR3⁻/⁻ mice when acute pancreatitis was induced. In conclusion, chemokine receptor CXCR3 is not involved in acute pancreatic injury, but has a connection with acute pancreatitis-associated lung injury. Acute pulmonary injury is attenuated in CXCR3 knockout mice in experimental acute pancreatitis.

Early proteome analysis of rat pancreatic acinar AR42J cells treated with taurolithocholic acid 3-sulfate

BACKGROUND

Bile acids are the initiating factors of biliary acute pancreatitis. Bile acids can induce the activation of intracellular zymogen, thus leading injury in pancreatic acinar cells. Pathological zymogen activation in pancreatic acinar cells is a common feature of all types of acute pancreatitis. The proteins expressed in pancreatic acinar cells during the activation of zymogen may determine the severity of acute pancreatitis. The present study aims to determine the differentially expressed proteins in taurolithocholic acid 3-sulfate-stimulated pancreatic acinar cells as an in vitro model for acute pancreatitis.

METHODS

Rat pancreatic acinar AR42J cells were treated with taurolithocholic acid 3-sulfate for 20 min. Laser confocal scanning microscopy and flow cytometry were used to detect activated trypsinogen in pancreatic acinar AR42J cells. After the determination of trypsinogen activation, proteome analysis was performed to identify the proteins differentially expressed in taurolithocholic acid 3-sulfate-treated cells and non-treated cells.

RESULTS

After treatment with taurolithocholic acid 3-sulfate for 20 min, the activation of trypsinogen in AR42J cells was concurrent with changes in the protein expression profile. Thirty-nine differentially expressed proteins were detected; among these, 23 proteins were up-regulated and 16 proteins were down-regulated. KEGG analysis indicated that these proteins are involved in cellular metabolic pathways, cellular defensive mechanisms, intracellular calcium regulation and cytoskeletal changes.

CONCLUSION

The expression of proteins in the pancreatic acinar cell changes at the early stage of biliary acute pancreatitis. These differentially expressed proteins will provide valuable information to understand the pathophysiologic mechanism biliary acute pancreatitis and may be useful for prognostic indices of acute pancreatitis.

Melatonin ameliorates acute necrotizing pancreatitis by the regulation of cytosolic Ca2+ homeostasis

OBJECTIVES

This study aims to investigate the relationship between the protective effects of melatonin in pancreas and the expression of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) and Na(+)/Ca(2+) exchanger (NCX) in rats with acute necrotizing pancreatitis (ANP), to verify whether melatonin ameliorates ANP by alleviating calcium overload.

METHODS

Ninety-six male Sprague-Dawley rats were randomly divided into four groups (sham operation group, ANP group, melatonin treatment group, melatonin contrast group). ANP was induced by the retrograde injection of 4% taurocholate (1 ml/kg body weight) into the biliopancreatic duct. Melatonin (50 mg/kg body weight) was administered 30 min before the induction of ANP in the melatonin treatment group. Rats in each group were euthanized at 1, 4, and 8 h after ANP induction. Pancreatic tissues were removed to measure SERCA and NCX levels and cytosolic calcium ion (Ca(2+)) concentration ([Ca(2+)](i)).

RESULTS

At each time point, SERCA and NCX levels in the melatonin treatment group were significantly higher than that in the ANP group, and lower than that in the sham group and the melatonin contrast group. These levels did not differ between the 4- and 8-h time points in the ANP group. [Ca(2+)](i) in pancreatic acinar cells was higher in the melatonin treatment group than in the sham group and the melatonin contrast group, but lower than in the ANP group, at each time point.

CONCLUSION

Melatonin can reduce pancreatic damage via the up-regulation of SERCA and NCX expression, which can alleviate calcium overload in pancreatic acinar cells.

STIM and Orai proteins and the non-capacitative ARC channels

The ARC channel is a small conductance, highly Ca²⁺-selective ion channel whose activation is specifically dependent on low concentrations of arachidonic acid acting at an intracellular site. They are widely distributed in diverse cell types where they provide an alternative, store-independent pathway for agonist-activated Ca²⁺ entry. Although biophysically similar to the store-operated CRAC channels, these two conductances function under distinct conditions of agonist stimulation, with the ARC channels providing the predominant route of Ca²⁺ entry during the oscillatory signals generated at low agonist concentrations. Despite these differences in function, like the CRAC channel, activation of the ARC channels is dependent on STIM1, but it is the pool of STIM1 that constitutively resides in the plasma membrane that is responsible. Similarly, both channels are formed by Orai proteins but, whilst the CRAC channel pore is a tetrameric assembly of Orai1 subunits, the ARC channel pore is formed by a heteropentameric assembly of three Orai1 subunits and two Orai3 subunits. There is increasing evidence that the activity of these channels plays a critical role in a variety of different cellular activities.

Cinnamtannin B-1, a natural antioxidant that reduces the effects of H(2)O(2) on CCK-8-evoked responses in mouse pancreatic acinar cells

This work was designed in order to gain an insight on the mechanisms by which antioxidants prevent pancreatic disorders. We have examined the properties of cinnamtannin B-1, which belongs to the class of polyphenols, against the effect of hydrogen peroxide (H(2)O(2)) in mouse pancreatic acinar cells. We have studied Ca(2+) mobilization, oxidative state, amylase secretion, and cell viability of cells treated with cinnamtannin B-1 in the presence of various concentrations of H(2)O(2). We found that H(2)O(2) (0.1-100 μM) increased CM-H(2)DCFDA-derived fluorescence, reflecting an increase in oxidation. Cinnamtannin B-1 (10 μM) reduced H(2)O(2)-induced oxidation of CM-H(2)DCFDA. CCK-8 induced oxidation of CM-H(2)DCFDA in a similar way to low micromolar concentrations of H(2)O(2), and cinnamtannin B-1 reduced the oxidant effect of CCK-8. In addition, H(2)O(2) induced a slow and progressive increase in intracellular free Ca(2+) concentration ([Ca(2+)](c)). Cinnamtannin B-1 reduced the effect of H(2)O(2) on [Ca(2+)](c), but only at the lower concentrations of the oxidant. H(2)O(2) inhibited amylase secretion in response to cholecystokinin, and cinnamtannin B-1 reduced the inhibitory action of H(2)O(2) on enzyme secretion. Finally, H(2)O(2) reduced cell viability, and the antioxidant protected acinar cells against H(2)O(2). In conclusion, the beneficial effects of cinnamtannin B-1 appear to be mediated by reducing the intracellular Ca(2+) overload and intracellular accumulation of digestive enzymes evoked by ROS, which is a common pathological precursor that mediates pancreatitis. Our results support the beneficial effect of natural antioxidants in the therapy against oxidative stress-derived deleterious effects on cellular physiology.

Calcium and reactive oxygen species in acute pancreatitis: friend or foe?

SIGNIFICANCE

Acute pancreatitis (AP) is a debilitating and, at times, lethal inflammatory disease, the causes and progression of which are incompletely understood. Disruption of Ca(2+) homeostasis in response to precipitants of AP leads to loss of mitochondrial integrity and cellular necrosis.

RECENT ADVANCES

While oxidative stress has been implicated as a major player in the pathogenesis of this disease, its precise roles remain to be defined. Recent developments are challenging the perception of reactive oxygen species (ROS) as nonspecific cytotoxic agents, suggesting that ROS promote apoptosis that may play a vital protective role in cellular stress since necrosis is avoided.

CRITICAL ISSUES

Fresh clinical findings have indicated that antioxidant treatment does not ameliorate AP and may actually worsen the outcome. This review explores the complex links between cellular Ca(2+) signaling and the intracellular redox environment, with particular relevance to AP.

FUTURE DIRECTIONS

Recent publications have underlined the importance of both Ca(2+) and ROS within the pathogenesis of AP, particularly in the determination of cell fate. Future research should elucidate the subtle interplay between Ca(2+) and redox mechanisms that operate to modulate mitochondrial function, with a view to devising strategies for the preservation of organellar function.

Aberrant Ca(2+) signalling through acidic calcium stores in pancreatic acinar cells

Pancreatic acinar cells possess a very large Ca(2+) store in the endoplasmic reticulum, but also have extensive acidic Ca(2+) stores. Whereas the endoplasmic reticulum is principally located in the baso-lateral part of the cells, although with extensions into the granular area, the acidic stores are exclusively present in the apical part. The two types of stores can be differentiated pharmacologically because the endoplasmic reticulum accumulates Ca(2+) via SERCA pumps, whereas the acidic pools require functional vacuolar H(+) pumps in order to maintain a high intra-organellar Ca(2+) concentration. The human disease acute pancreatitis is initiated by trypsinogen activation in the apical pole and this is mostly due to either complications arising from gall bladder stones or excessive alcohol consumption. Attention has therefore been focussed on assessing the acute effects of bile acids as well as alcohol metabolites. The evidence accumulated so far indicates that bile acids and fatty acid ethyl esters - the non-oxidative products of alcohol and fatty acids - exert their pathological effects primarily by excessive Ca(2+) release from the acidic stores. This occurs by opening of the very same release channels that are also responsible for normal stimulus-secretion coupling, namely inositol trisphosphate and ryanodine receptors. The inositol trisphosphate receptors are of particular importance and the results of gene deletion experiments indicate that the fatty acid ethyl esters mainly utilize sub-types 2 and 3.

Phenotypic changes in mouse pancreatic stellate cell Ca2+ signaling events following activation in culture and in a disease model of pancreatitis

The specific characteristics of intracellular Ca 2+ signaling and the downstream consequences of these events were investigated in mouse pancreatic stellate cells (PSC) in culture and in situ using multiphoton microscopy in pancreatic lobules. PSC undergo a phenotypic transformation from a quiescent state to a myofibroblast-like phenotype in culture. This is believed to parallel the induction of an activated state observed in pancreatic disease such as chronic pancreatitis and pancreatic cancer. By day 7 in culture, the complement of cell surface receptors coupled to intracellular Ca 2+ signaling was shown to be markedly altered. Specifically, protease-activated receptors (PAR) 1 and 2, responsive to thrombin and trypsin, respectively, and platelet-derived growth factor (PDGF) receptors were expressed only in activated PSC (aPSC). PAR-1, ATP, and PDGF receptor activation resulted in prominent nuclear Ca 2+ signals. Nuclear Ca 2+ signals and aPSC proliferation were abolished by expression of parvalbumin targeted to the nucleus. In pancreatic lobules, PSC responded to agonists consistent with the presence of only quiescent PSC. aPSC were observed following induction of experimental pancreatitis. In contrast, in a mouse model of pancreatic disease harboring elevated K-Ras activity in acinar cells, aPSC were present under control conditions and their number greatly increased following induction of pancreatitis. These data are consistent with nuclear Ca 2+ signaling generated by agents such as trypsin and thrombin, likely present in the pancreas in disease states, resulting in proliferation of "primed" aPSC to contribute to the severity of pancreatic disease.

The acinar-ductal tango in the pathogenesis of acute pancreatitis

There is an unacceptably high mortality in acute pancreatitis, which is due to the lack of specific treatments for the disease. A major reason stated to account for the inability to develop effective treatments is that there are multiple pathobiologic pathways activated in the acinar cell mediating pancreatitis making it difficult to choose molecular targets for therapeutic strategies. However, this reasoning limits opportunities for therapeutic development because it does include another important participant in pancreatitis - the pancreatic duct cells. The most recent advance in pancreatitis research is that depletion of both glycolytic and oxidative ATP synthesis is a common event in both acinar and ductal cells. Although ATP has a very short half-life in the blood and is hydrolysed to ADP, there is clear evidence that encapsulating ATP into liposomes can effectively drive ATP into the cells which can be effective in protecting them from necrosis. In this review, we will examine the effects of different insults associated with pancreatitis on both the acinar and ductal components of the exocrine pancreas pointing out the role of the ductal epithelial responses in both attenuating and increasing the severity of pancreatitis. In addition, we propose that exogenous ATP administration may restore ductal and acinar function providing therapeutic benefit.

Calmodulin protects against alcohol-induced pancreatic trypsinogen activation elicited via Ca2+ release through IP3 receptors

Alcohol abuse is a major global health problem, but there is still much uncertainty about the mechanisms of action. So far, the effects of ethanol on ion channels in the plasma membrane have received the most attention. We have now investigated actions on intracellular calcium channels in pancreatic acinar cells. Our aim was to discover the mechanism by which alcohol influences calcium homeostasis and thereby understand how alcohol can trigger premature intracellular trypsinogen activation, which is the initiating step for alcohol-induced pancreatitis. We used intact or two-photon permeabilized acinar cells isolated from wild-type mice or mice in which inositol trisphosphate receptors of type 2 or types 2 and 3 were knocked out. In permeabilized pancreatic acinar cells even a relatively low ethanol concentration elicited calcium release from intracellular stores and intracellular trypsinogen activation. The calcium sensor calmodulin (at a normal intracellular concentration) markedly reduced ethanol-induced calcium release and trypsinogen activation in permeabilized cells, effects prevented by the calmodulin inhibitor peptide. A calmodulin activator virtually abolished the modest ethanol effects in intact cells. Both ethanol-elicited calcium liberation and trypsinogen activation were significantly reduced in cells from type 2 inositol trisphosphate receptor knockout mice. More profound reductions were seen in cells from double inositol trisphosphate receptor (types 2 and 3) knockout mice. The inositol trisphosphate receptors, required for normal pancreatic stimulus-secretion coupling, are also responsible for the toxic ethanol action. Calmodulin protects by reducing calcium release sensitivity.

Ethanol enhances carbachol-induced protease activation and accelerates Ca2+ waves in isolated rat pancreatic acini

Alcohol abuse is a leading cause of pancreatitis, accounting for 30% of acute cases and 70-90% of chronic cases, yet the mechanisms leading to alcohol-associated pancreatic injury are unclear. An early and critical feature of pancreatitis is the aberrant signaling of Ca(2+) within the pancreatic acinar cell. An important conductor of this Ca(2+) is the basolaterally localized, intracellular Ca(2+) channel ryanodine receptor (RYR). In this study, we examined the effect of ethanol on mediating both pathologic intra-acinar protease activation, a precursor to pancreatitis, as well as RYR Ca(2+) signals. We hypothesized that ethanol sensitizes the acinar cell to protease activation by modulating RYR Ca(2+). Acinar cells were freshly isolated from rat, pretreated with ethanol, and stimulated with the muscarinic agonist carbachol (1 μM). Ethanol caused a doubling in the carbachol-induced activation of the proteases trypsin and chymotrypsin (p < 0.02). The RYR inhibitor dantrolene abrogated the enhancement of trypsin and chymotrypsin activity by ethanol (p < 0.005 for both proteases). Further, ethanol accelerated the speed of the apical to basolateral Ca(2+) wave from 9 to 18 μm/s (p < 0.0005; n = 18-22 cells/group); an increase in Ca(2+) wave speed was also observed with a change from physiologic concentrations of carbachol (1 μM) to a supraphysiologic concentration (1 mM) that leads to protease activation. Dantrolene abrogated the ethanol-induced acceleration of wave speed (p < 0.05; n = 10-16 cells/group). Our results suggest that the enhancement of pathologic protease activation by ethanol is dependent on the RYR and that a novel mechanism for this enhancement may involve RYR-mediated acceleration of Ca(2+) waves.

Low extracellular pH induces damage in the pancreatic acinar cell by enhancing calcium signaling

Low extracellular pH (pHe) occurs in a number of clinical conditions and sensitizes to the development of pancreatitis. The mechanisms responsible for this sensitization are unknown. Because abnormal Ca(2+) signaling underlies many of the early steps in the pathogenesis of pancreatitis, we evaluated the effect of decreasing pHe from 7.4 to 7.0 on Ca(2+) signals in the acinar cell. Low pHe significantly increased the amplitude of cerulein-induced Ca(2+) signals. The enhancement in amplitude was localized to the basolateral region of the acinar cell and was reduced by pretreatment with ryanodine receptor (RYR) inhibitors. Because basolateral RYRs also have been implicated in the pathogenesis of pancreatitis, we evaluated the effects of RYR inhibitors on pancreatitis responses in acidic conditions. RYR inhibitors significantly reduced the sensitizing effects of low pHe on zymogen activation and cellular injury. These findings suggest that enhanced RYR-mediated Ca(2+) signaling in the basolateral region of the acinar cell is responsible for the injurious effects of low pHe on the exocrine pancreas.

Zymophagy, a novel selective autophagy pathway mediated by VMP1-USP9x-p62, prevents pancreatic cell death

Autophagy has recently elicited significant attention as a mechanism that either protects or promotes cell death, although different autophagy pathways, and the cellular context in which they occur, remain to be elucidated. We report a thorough cellular and biochemical characterization of a novel selective autophagy that works as a protective cell response. This new selective autophagy is activated in pancreatic acinar cells during pancreatitis-induced vesicular transport alteration to sequester and degrade potentially deleterious activated zymogen granules. We have coined the term "zymophagy" to refer to this process. The autophagy-related protein VMP1, the ubiquitin-protease USP9x, and the ubiquitin-binding protein p62 mediate zymophagy. Moreover, VMP1 interacts with USP9x, indicating that there is a close cooperation between the autophagy pathway and the ubiquitin recognition machinery required for selective autophagosome formation. Zymophagy is activated by experimental pancreatitis in genetically engineered mice and cultured pancreatic acinar cells and by acute pancreatitis in humans. Furthermore, zymophagy has pathophysiological relevance by controlling pancreatitis-induced intracellular zymogen activation and helping to prevent cell death. Together, these data reveal a novel selective form of autophagy mediated by the VMP1-USP9x-p62 pathway, as a cellular protective response.

Cannabinoid agonist WIN55,212 in vitro inhibits interleukin-6 (IL-6) and monocyte chemo-attractant protein-1 (MCP-1) release by rat pancreatic acini and in vivo induces dual effects on the course of acute pancreatitis

BACKGROUND

Cannabinoids (CBs) evoke their effects by activating the cannabinoid receptor subtypes CB1-r and CB2-r and exert anti-inflammatory effects altering chemokine and cytokine expression. Various cytokines and chemokines are produced and released by rodent pancreatic acini in acute pancreatitis. Although CB1-r and CB2-r expressed in rat exocrine pancreatic acinar cells do not modulate digestive enzyme release, whether they modulate inflammatory mediators remains unclear. We investigated the CB-r system role on exocrine pancreas in unstimulated conditions and during acute pancreatitis.

METHODS

We evaluated in vitro and in vivo changes induced by WIN55,212 on the inflammatory variables amylasemia, pancreatic edema and morphology, and on acinar release and content of the cytokine interleukin-6 (IL-6) and chemokine monocyte chemo-attractant protein-1 (MCP-1) in untreated rats and rats with caerulein (CK)-induced pancreatitis.

KEY RESULTS

In the in vitro experiments, WIN55,212 (10(-6) mol L(-1)) inhibited IL-6 and MCP-1 release from acinar cells of unstimulated rats and after CK-induced pancreatitis. In vivo, when rats were pretreated with WIN55,212 (2 mg kg(-1), intraperitoneally) before experimentally-induced pancreatitis, serum amylase, pancreatic edema and IL-6 and MCP-1 acinar content diminished and pancreatic morphology improved. Conversely, when rats with experimentally-induced pancreatitis were post-treated with WIN55,212, pancreatitis worsened.

CONCLUSIONS & INFERENCES

These findings provide new evidence showing that the pancreatic CB1-r/CB2-r system modulates pro-inflammatory factor levels in rat exocrine pancreatic acinar cells. The dual, time-dependent WIN55,212-induced changes in the development and course of acute pancreatitis support the idea that the role of the endogenous CB receptor system differs according to the local inflammatory status.

Time-resolved release of calcium from an epithelial cell monolayer during mucin secretion

A significant amount of Ca²+ is contained in secretory mucin granules. Exchange of Ca²+ for monovalent cations drives the process of mucin decondensation and hydration after fusion of granules with the plasma membrane. Here we report direct observation of calcium secretion with a Ca²+ ion-selective electrode (ISE) in response to apical stimulation with ATP from HT29-Cl.16E cells, a subclone of the human colonic cancer cell line HT29. No increase in Ca²+ level was seen for the sister cell line Cl.19A, which lacks mucin granules, or for Cl.16E cells after inhibition of granule fusion with wortmannin. Further, the measured concentration was used to estimate the time-resolved rate of release of Ca²+ from the cell monolayer, by use of a deconvolution-based method developed previously (Nair and Gratzl in Anal Chem 77:2875-2881, 2005). The results argue that Ca²+ release by Cl.16E cells is associated specifically with mucin secretion, i.e., that the measured Ca²+ increase in the apical solution is derived from granules after fusion and mucin exocytosis. The Ca²+ ISE in conjunction with deconvolution provides a minimally disturbing method for assessment of Ca²+ secretion rates. The release rates provide estimates of exocytosis rates and, when combined with earlier capacitance measurements, estimates of post-stimulation endocytosis rates also.

Dantrolene mitigates caerulein-induced pancreatitis in vivo in mice

Acute pancreatitis is a painful, inflammatory disorder for which adequate treatments are lacking. An early, critical step in its development is the aberrant signaling of Ca(2+) within the pancreatic acinar cell. This Ca(2+) release is modulated by the intracellular Ca(2+) channel the ryanodine receptor (RYR). We have previously shown that RYR inhibition reduces pathological intra-acinar protease activation, an early marker of pancreatitis. In this study, we examined whether pretreatment with the RYR inhibitor dantrolene attenuates the severity of caerulein-induced pancreatitis in mice. Immunofluorescent labeling for RYR from mouse pancreatic sections showed localization to the basolateral region of the acinar cell. After 1 h of caerulein hyperstimulation in vivo, dantrolene 1) reduced pancreatic trypsin activity by 59% (P < 0.05) and 2) mitigated early ultrastructural derangements within the acinar cell. Eight hours after pancreatitis induction, dantrolene reduced pancreatic trypsin activity and serum amylase by 61 and 32%, respectively (P < 0.05). At this later time point, overall histological severity of pancreatitis was reduced by 63% with dantrolene pretreatment (P < 0.05). TUNEL-positive cells were reduced by 58% (P < 0.05). These data suggest that the RYR plays an important role in mediating early acinar cell events during in vivo pancreatitis and contributes to disease severity. Blockade of Ca(2+) signals and particularly RYR-Ca(2+) may be useful as prophylactic treatment for this disease in high-risk settings for pancreatitis.

Dynamic changes in cytosolic and mitochondrial ATP levels in pancreatic acinar cells

BACKGROUND & AIMS

Previous studies of pancreatic acinar cells characterized the effects of Ca(2+)-releasing secretagogues and substances, inducing acute pancreatitis on mitochondrial Ca(2+), transmembrane potential, and NAD(P)H, but dynamic measurements of the crucial intracellular adenosine triphosphate (ATP) levels have not been reported. Here we characterized the effects of these agents on ATP levels in the cytosol and mitochondria.

METHODS

ATP levels were monitored using cytosolic- or mitochondrial-targeted luciferases.

RESULTS

Inhibition of oxidative phosphorylation produced a substantial decrease in cytosolic ATP comparable to that induced by inhibition of glycolysis. Cholecystokinin-8 (CCK) increased cytosolic ATP in spite of accelerating ATP consumption. Acetylcholine, caerulein, and bombesin had similar effect. A bile acid, taurolithocholic acid 3-sulfate (TLC-S); a fatty acid, palmitoleic acid (POA); and palmitoleic acid ethyl ester (POAEE) reduced cytosolic ATP. The ATP decrease in response to these substances was observed in cells with intact or inhibited oxidative phosphorylation. TLC-S, POA, and POAEE reduced mitochondrial ATP, whereas physiological CCK increased mitochondrial ATP. Supramaximal CCK produced a biphasic response composed of a small initial decline followed by a stronger increase.

CONCLUSIONS

Both glycolysis and oxidative phosphorylation make substantial contributions to ATP production in acinar cells. Ca(2+)-releasing secretagogues increased ATP level in the cytosol and mitochondria of intact isolated cells. TLC-S, POA, and POAEE reduced cytosolic and mitochondrial ATP. When cells rely on nonoxidative ATP production, secretagogues as well as TLC-S, POA, and POAEE all diminish cytosolic ATP levels.

Pharmacotherapy for acute pancreatitis

Our knowledge of acute pancreatitis is still far from complete and there is no unanimous agreement concerning the pathophysiological processes leading to typical alterations during the course of acute pancreatitis. We reviewed the paper published in the last decade on the pathophysiology and treatment of acute pancreatitis. It is difficult to translate the experimental therapeutic results into clinical practice. For example, lexipafant was efficacious in decreasing the severity and mortality of lethal pancreatitis in rats, but seems to have no effect on severe acute pancreatitis in humans. Thus, the main problem in acute pancreatitis, especially in the severe form of the disease, is the difficulty of designing clinical studies capable of giving reliable statistically significant answers regarding the benefits of the various proposed therapeutic agents previously tested in experimental settings. Thus, analgesia, supportive care, and treatment of the pulmonary and renal complications remain the cornerstones of the treatment of acute pancreatitis, especially in the severe form of the disease.

STAT5-glucocorticoid receptor interaction and MTF-1 regulate the expression of ZnT2 (Slc30a2) in pancreatic acinar cells

The exocrine pancreas plays an important role in endogenous zinc loss by regulating excretion into the intestinal tract and hence influences the dietary zinc requirement. The present experiments show that the zinc transporter ZnT2 (Slc30a2) is localized to the zymogen granules and that dietary zinc restriction in mice decreased the zinc concentration of zymogen granules and ZnT2 expression. Excess zinc given orally increased ZnT2 expression and was associated with increased pancreatic zinc accumulation. Rat AR42J acinar cells when induced into a secretory phenotype, using the glucocorticoid analog dexamethasone (DEX), exhibited increased ZnT2 expression and labile zinc as measured with a fluorophore. DEX administrated to mice also induced ZnT2 expression that accompanied a reduction of the pancreatic zinc content. ZnT2 promoter analyses identified elements required for responsiveness to zinc and DEX. Zinc regulation was traced to a MRE located downstream from the ZnT2 transcription start site. Responsiveness to DEX is produced by two upstream STAT5 binding sites that require the glucocorticoid receptor for activation. ZnT2 knockdown in the AR42J cells using siRNA resulted in increased cytoplasmic zinc and decreased zymogen granule zinc that further demonstrated that ZnT2 may mediate the sequestration of zinc into zymogen granules. We conclude, based upon experiments with intact mice and pancreatic acinar cells in culture, that ZnT2 participates in zinc transport into pancreatic zymogen granules through a glucocorticoid pathway requiring glucocorticoid receptor and STAT5, and zinc-regulated signaling pathways requiring MTF-1. The ZnT2 transporter appears to function in a physiologically responsive manner involving entero-pancreatic zinc trafficking.

Ethanol consumption as inductor of pancreatitis

Alcohol abuse is a major cause of pancreatitis, a condition that can manifest as both acute necroinflammation and chronic damage (acinar atrophy and fibrosis). Pancreatic acinar cells can metabolize ethanol via the oxidative pathway, which generates acetaldehyde and involves the enzymes alcohol dehydrogenase and possibly cytochrome P4502E1. Additionally, ethanol can be metabolized via a nonoxidative pathway involving fatty acid ethyl ester synthases. Metabolism of ethanol by acinar and other pancreatic cells and the consequent generation of toxic metabolites, are postulated to play an important role in the development of alcohol-related acute and chronic pancreatic injury. This current work will review some recent advances in the knowledge about ethanol actions on the exocrine pancreas and its relationship to inflammatory disease and cancer.

N-acetylcysteine in acute pancreatitis

Premature trypsinogen activation and production of oxygen free radicals (OFR) are early pathogenic events which occur within acinar cells and trigger acute pancreatitis (AP). OFR exert their harmful effects on various cell components causing lipid peroxidation, disturbances in calcium homeostasis and DNA damage, which lead to increased cell injury and eventually cell death. This review presents the most recent data concerning the effects of N-Acetylcysteine (NAC), in the treatment of AP. NAC is an antioxidant capable of restoring the levels of Glutathione, the most important cellular antioxidant. Studies show the beneficial effects of NAC treatment in preventing OFR production and therefore attenuating oxidative damage. Additionally, NAC treatment has been shown to prevent the increase in cytosolic Ca²⁺ concentration and reduce the accumulation of enzymes in acinar cells during AP. The prevention, by NAC, of these pathological events occurring within acinar would contribute to reducing the severity of AP. NAC is also capable of reducing the activation of transcription factors especially sensitive to the cellular redox state, such as Nuclear factor-κB, signal transducer and activator of transcription-3 and mitogen-activated protein kinase. This leads to a down-regulation of cytokines, adhesion molecules and chemokine expression in various cell types during AP. These findings point to NAC as a powerful therapeutic treatment, attenuating oxidative-stress-induced cell injury and other pathological events at early stages of AP, and potentially contributing to reducion in the severity of disease.

Cholecystokinin-58 and cholecystokinin-8 exhibit similar actions on calcium signaling, zymogen secretion, and cell fate in murine pancreatic acinar cells

The gastrointestinal hormone CCK exists in various molecular forms, with differences in bioactivity between the well-characterized CCK-8 and larger CCK-58 previously reported. We have compared the effects of these peptides on cytosolic calcium concentration ([Ca(2+)](c)), mitochondrial metabolism, enzyme secretion, and cell fate in murine isolated pancreatic acinar cells using fluorescence confocal microscopy and patch-clamp electrophysiology. CCK-58 (1-10 pM) induced transient, oscillatory increases of [Ca(2+)](c), which showed apical to basolateral progression and were associated with a rise of mitochondrial NAD(P)H. CCK-58 (10 pM) induced zymogen exocytosis in isolated cells and amylase secretion from isolated cells and whole tissues. Hyperstimulation with supraphysiological CCK-58 (5 nM) induced a single large increase of [Ca(2+)](c) that declined to a plateau, which remained above the basal level 20 min after application and was dependent on external Ca(2+) entry. In cells dispersed from the same tissues, CCK-8 induced similar patterns of responses to those of CCK-58, with oscillatory increases of [Ca(2+)](c) at lower (pM) concentrations and sustained responses at 5 nM. CCK-58 and CCK-8 exhibited similar profiles of action on cell death, with increases in necrosis at high CCK-58 and CCK-8 (10 nM) that were not significantly different between peptides. The present experiments indicate that CCK-8 and CCK-58 have essentially identical actions on the acinar cell at high and low agonist concentrations, suggesting an action via the same receptor and that the differences observed in an intact rat model may result from indirect effects of the peptides. Our data strengthen the argument that CCK-58 is an important physiological form of this gastrointestinal hormone.

Pancreas-specific aquaporin 12 null mice showed increased susceptibility to caerulein-induced acute pancreatitis

Aquaporin 12 (AQP12) is the most recently identified member of the mammalian AQP family and is specifically expressed in pancreatic acinar cells. In vitro expression studies have revealed that AQP12 is localized at intracellular sites. To determine the physiological roles of AQP12 in the pancreas, we generated knockout mice for this gene (AQP12-KO). No obvious differences were observed under normal conditions between wild-type (WT) and AQP12-KO mice in terms of growth, blood chemistry, pancreatic fluid content, or histology. However, when we induced pancreatitis through the administration of a cholecystokinin-8 (CCK-8) analog, the AQP12-KO mice showed more severe pathological damage to this organ than WT mice. Furthermore, when we analyzed exocytosis in the pancreatic acini using a two-photon excitation imaging method, the results revealed larger exocytotic vesicles (vacuoles) in the acini of AQP12-KO mice at a high CCK-8 dose (100 nM). From these results, we conclude that AQP12 may function in the mechanisms that control the proper secretion of pancreatic fluid following rapid and intense stimulation.

Protease activation during in vivo pancreatitis is dependent on calcineurin activation

The premature activation of digestive proenzymes, specifically proteases, within the pancreatic acinar cell is an early and critical event during acute pancreatitis. Our previous studies demonstrate that this activation requires a distinct pathological rise in cytosolic Ca(2+). Furthermore, we have shown that a target of aberrant Ca(2+) in acinar cells is the Ca(2+)/calmodulin-dependent phosphatase calcineurin (PP2B). In this study, we hypothesized that PP2B mediates in vivo protease activation and pancreatitis severity. To test this, pancreatitis was induced in mice over 8 h by administering hourly intraperitoneal injections of the cholecystokinin analog caerulein (50 microg/kg). Treatment with the PP2B inhibitor FK506 at 1 and 8 h after pancreatitis induction reduced trypsin activities by greater than 50% (P < 0.005). Serum amylase and IL-6 was reduced by 86 and 84% relative to baseline (P < 0.0005) at 8 h, respectively. Histological severity of pancreatitis, graded on the basis of pancreatic edema, acinar cell vacuolization, inflammation, and apoptosis, was reduced early in the course of pancreatitis. Myeloperoxidase activity from both pancreas and lung was reduced by 93 and 83% relative to baseline, respectively (P < 0.05). These data suggest that PP2B is an important target of the aberrant acinar cell Ca(2+) rise associated with pathological protease activation and pancreatitis.

Ethanol exerts dual effects on calcium homeostasis in CCK-8-stimulated mouse pancreatic acinar cells

Background

A significant percentage of patients with pancreatitis often presents a history of excessive alcohol consumption. Nevertheless, the patho-physiological effect of ethanol on pancreatitis remains poorly understood. In the present study, we have investigated the early effects of acute ethanol exposure on CCK-8-evoked Ca²⁺ signals in mouse pancreatic acinar cells. Changes in [Ca²⁺]_i and ROS production were analyzed employing fluorescence techniques after loading cells with fura-2 or CM-H₂DCFDA, respectively.

Results

Ethanol, in the concentration range from 1 to 50 mM, evoked an oscillatory pattern in [Ca²⁺]_i. In addition, ethanol evoked reactive oxygen species generation (ROS) production. Stimulation of cells with 1 nM or 20 pM CCK-8, respectively led to a transient change and oscillations in [Ca²⁺]_i. In the presence of ethanol a transformation of 20 pM CCK-8-evoked physiological oscillations into a single transient increase in [Ca²⁺]_i in the majority of cells was observed. Whereas, in response to 1 nM CCK-8, the total Ca²⁺ mobilization was significantly increased by ethanol pre-treatment. Preincubation of cells with 1 mM 4-MP, an inhibitor of alcohol dehydrogenase, or 10 μM of the antioxidant cinnamtannin B-1, reverted the effect of ethanol on total Ca²⁺ mobilization evoked by 1 nM CCK-8. Cinnamtannin B-1 blocked ethanol-evoked ROS production.

Conclusion

ethanol may lead, either directly or through ROS generation, to an over stimulation of pancreatic acinar cells in response to CCK-8, resulting in a higher Ca²⁺ mobilization compared to normal conditions. The actions of ethanol on CCK-8-stimulation of cells create a situation potentially leading to Ca²⁺ overload, which is a common pathological precursor that mediates pancreatitis.

Impaired autophagic flux mediates acinar cell vacuole formation and trypsinogen activation in rodent models of acute pancreatitis

The pathogenic mechanisms underlying acute pancreatitis are not clear. Two key pathologic acinar cell responses of this disease are vacuole accumulation and trypsinogen activation. We show here that both result from defective autophagy, by comparing the autophagic responses in rodent models of acute pancreatitis to physiologic autophagy triggered by fasting. Pancreatitis-induced vacuoles in acinar cells were greater in number and much larger than those induced with fasting. Degradation of long-lived proteins, a measure of autophagic efficiency, was markedly inhibited in in vitro pancreatitis, while it was stimulated by acinar cell starvation. Further, processing of the lysosomal proteases cathepsin L (CatL) and CatB into their fully active, mature forms was reduced in pancreatitis, as were their activities in the lysosome-enriched subcellular fraction. These findings indicate that autophagy is retarded in pancreatitis due to deficient lysosomal degradation caused by impaired cathepsin processing. Trypsinogen activation occurred in pancreatitis but not with fasting and was prevented by inhibiting autophagy. A marker of trypsinogen activation partially localized to autophagic vacuoles, and pharmacologic inhibition of CatL increased the amount of active trypsin in acinar cells. The results suggest that retarded autophagy is associated with an imbalance between CatL, which degrades trypsinogen and trypsin, and CatB, which converts trypsinogen into trypsin, resulting in intra-acinar accumulation of active trypsin in pancreatitis. Thus, deficient lysosomal degradation may be a dominant mechanism for increased intra-acinar trypsin in pancreatitis.

Calpain-mediated breakdown of cytoskeletal proteins contributes to cholecystokinin-induced damage of rat pancreatic acini

The cytosolic cysteine protease calpain is implicated in a multitude of cellular functions but also plays a role in cell damage. Our previous results suggest that an activation of calpain accompanied by a decrease in its endogenous inhibitor calpastatin may contribute to pancreatic damage during cerulein-induced acute pancreatitis. The present study aimed at the time course of secretagogue-induced calpain activation and cellular substrates of the protease. Isolated rat pancreatic acini were incubated with a supramaximal concentration of cholecystokinin (0.1 microM CCK) for 30 min in the presence or absence of the calpain inhibitor Z-Val-Phe methyl ester (100 microM ZVP). The activation of calpain and the expression of calpastatin and the actin cytoskeleton-associated proteins alphaII-spectrin, E-cadherin and vinculin were studied by immunoblotting. The cell damage was assessed by lactate dehydrogenase release and ultrastructural analysis including fluorescence-labelled actin filaments. Immediately after administration, CCK led to activation of both calpain isoforms, mu- and m-calpain. The protease activation was accompanied by a decrease in the E-cadherin level and formation of calpain-specific breakdown products of alphaII-spectrin. A calpain-specific cleavage product of vinculin appeared concomitantly with changes in the actin filament organization. No effect of CCK on calpastatin was found. Inhibition of calpain by ZVP reduced CCK-induced damage of the actin-associated proteins and the cellular ultrastructure including the actin cytoskeleton. The results suggest that CCK-induced acinar cell damage requires activation of calpain and that the actin cytoskeleton belongs to the cellular targets of the protease.

Calcium elevation in mitochondria is the main Ca2+ requirement for mitochondrial permeability transition pore (mPTP) opening

We have investigated in detail the role of intra-organelle Ca2+ content during induction of apoptosis by the oxidant menadione while changing and monitoring the Ca2+ load of endoplasmic reticulum (ER), mitochondria, and acidic organelles. Menadione causes production of reactive oxygen species, induction of oxidative stress, and subsequently apoptosis. In both pancreatic acinar and pancreatic tumor AR42J cells, menadione was found to induce repetitive cytosolic Ca2+ responses because of the release of Ca2+ from both ER and acidic stores. Ca2+ responses to menadione were accompanied by elevation of Ca2+ in mitochondria, mitochondrial depolarization, and mitochondrial permeability transition pore (mPTP) opening. Emptying of both the ER and acidic Ca2+ stores did not necessarily prevent menadione-induced apoptosis. High mitochondrial Ca2+ at the time of menadione application was the major factor determining cell fate. However, if mitochondria were prevented from loading with Ca2+ with 10 mum RU360, then caspase-9 activation did not occur irrespective of the content of other Ca2+ stores. These results were confirmed by ratiometric measurements of intramitochondrial Ca2+ with pericam. We conclude that elevated Ca2+ in mitochondria is the crucial factor in determining whether cells undergo oxidative stress-induced apoptosis.

Pancreatic protease activation by alcohol metabolite depends on Ca2+ release via acid store IP3 receptors

Toxic alcohol effects on pancreatic acinar cells, causing the often fatal human disease acute pancreatitis, are principally mediated by fatty acid ethyl esters (non-oxidative products of alcohol and fatty acids), emptying internal stores of Ca(2+). This excessive Ca(2+) liberation induces Ca(2+)-dependent necrosis due to intracellular trypsin activation. Our aim was to identify the specific source of the Ca(2+) release linked to the fatal intracellular protease activation. In 2-photon permeabilized mouse pancreatic acinar cells, we monitored changes in the Ca(2+) concentration in the thapsigargin-sensitive endoplasmic reticulum (ER) as well as in a bafilomycin-sensitive acid compartment, localized exclusively in the apical granular pole. We also assessed trypsin activity in the apical granular region. Palmitoleic acid ethyl ester (POAEE) elicited Ca(2+) release from both the ER as well as the acid pool, but trypsin activation depended predominantly on Ca(2+) release from the acid pool, that was mainly mediated by functional inositol 1,4,5- trisphosphate receptors (IP(3)Rs) of types 2 and 3. POAEE evoked very little Ca(2+) release and trypsin activation when IP(3)Rs of both types 2 and 3 were knocked out. Antibodies against IP(3)Rs of types 2 and 3, but not type 1, markedly inhibited POAEE-elicited Ca(2+) release and trypsin activation. We conclude that Ca(2+) release through IP(3)Rs of types 2 and 3 in the acid granular Ca(2+) store induces intracellular protease activation, and propose that this is a critical process in the initiation of alcohol-related acute pancreatitis.

Designing protease sensors for real-time imaging of trypsin activation in pancreatic cancer cells

Acute pancreatitis is a serious and potentially fatal disease caused by intracellular trypsinogen activation. Although protease detection has been greatly facilitated by the development of protease probes capable of monitoring protease activation and inhibition, real-time quantitative measurement of protease activity in living cells remains a challenge, and the identification of the cellular compartment for trypsinogen activation is inconclusive. Here we report a novel strategy for developing trypsin sensors by grafting an enzymatic cleavage site into a sensitive location for optical change of chromophore in a single enhanced green fluorescent protein (EGFP). Our designed trypsin sensor exhibits rapid kinetic responses for protease activation and inhibition with a large ratiometric optical signal change. In addition, it has strong specificity, as enzymatic cleavage is not observed with other proteases such as thrombin, cathepsin B, tryptase, and tissue plasminogen activator. Moreover, the developed trypsin sensor allows us for the first time to observe, in real time, trypsinogen activation by caerulein in the pancreatic cancer cell line, MIA PaCa-2 without zymogen granules. These developed protease sensors will facilitate improved understanding of mechanisms and locations of protease activation and further provide screening of protease inhibitors with therapeutic effects.

Fatty acids, alcohol and fatty acid ethyl esters: toxic Ca2+ signal generation and pancreatitis

Pancreatitis, a potentially fatal disease in which the pancreas digests itself as well as its surroundings, is a well recognized complication of hyperlipidemia. Fatty acids have toxic effects on pancreatic acinar cells and these are mediated by large sustained elevations of the cytosolic Ca(2+) concentration. An important component of the effect of fatty acids is due to inhibition of mitochondrial function and subsequent ATP depletion, which reduces the operation of Ca(2+)-activated ATPases in both the endoplasmic reticulum and the plasma membrane. One of the main causes of pancreatitis is alcohol abuse. Whereas the effects of even high alcohol concentrations on isolated pancreatic acinar cells are variable and often small, fatty acid ethyl esters--synthesized by combination of alcohol and fatty acids--consistently evoke major Ca(2+) release from intracellular stores, subsequently opening Ca(2+) entry channels in the plasma membrane. The crucial trigger for pancreatic autodigestion is intracellular trypsin activation. Although there is still uncertainty about the exact molecular mechanism by which this Ca(2+)-dependent process occurs, progress has been made in identifying a subcellular compartment--namely acid post-exocytotic endocytic vacuoles--in which this activation takes place.

Mechanisms regulating cytochrome c release in pancreatic mitochondria

BACKGROUND

Mechanisms of acinar cell death in pancreatitis are poorly understood. Cytochrome c release is a central event in apoptosis in pancreatitis. Here, we assessed the regulation of pancreatic cytochrome c release by Ca(2+), mitochondrial membrane potential (Delta Psi m), and reactive oxygen species (ROS), the signals involved in acute pancreatitis. We used both isolated rat pancreatic mitochondria and intact acinar cells hyperstimulated with cholecystokinin-8 (CCK-8; in vitro model of acute pancreatitis).

RESULTS

Micromolar amounts of Ca(2+) depolarised isolated pancreatic mitochondria through a mechanism different from the "classical" (ie, liver) mitochondrial permeability transition pore (mPTP). In contrast with liver, Ca(2+)-induced mPTP opening caused a dramatic decrease in ROS and was not associated with pancreatic mitochondria swelling. Importantly, we found that Ca(2+)-induced depolarisation inhibited cytochrome c release from pancreatic mitochondria, due to blockade of ROS production. As a result, Ca(2+) exerted two opposite effects on cytochrome c release: Ca(2+) per se stimulated the release, whereas Ca(2+)-induced depolarisation inhibited it. This dual effect caused a non-monotonous dose-dependence of cytochrome c release on Ca(2+). In intact acinar cells, cytochrome c release, caspase activation and apoptosis were all stimulated by ROS and Ca(2+), and inhibited by depolarisation, corroborating the findings on isolated pancreatic mitochondria.

CONCLUSIONS

These data implicate ROS as a key mediator of CCK-induced apoptotic responses. The results indicate a major role for mitochondria in the effects of Ca(2+ )and ROS on acinar cell death. They suggest that the extent of apoptosis in pancreatitis is regulated by the interplay between ROS, Delta Psi m and Ca(2+). Stabilising mitochondria against loss of Delta Psi m may represent a strategy to mitigate the severity of pancreatitis.

Critical Care of the Patient with Acute Pancreatitis

Acute pancreatitis is an inflammatory process of the pancreas with variable involvement of regional tissues and remote organs. This review gives a comprehensive overview of the aetiology, pathophysiology, diagnosis and therapy of acute pancreatitis relevant to the intensivist. Recent international guidelines on the management of acute pancreatitis are summarised.

Eighty percent of acute pancreatitis episodes are related either to gallstones or to alcohol abuse. Independent of its aetiology, the pathophysiologic hallmark of acute pancreatitis is the premature activation of trypsin, which leads to massive pancreas inflammation, systemic overproduction of pro-inflammatory mediators and ultimately remote organ dysfunction. All guidelines agree that the diagnosis of acute pancreatitis should include clinical symptoms, increased serum amylase or lipase levels and/or characteristic findings on computed tomography. Endoscopic retrograde cholangiopancreatography is recommended as a causative therapy in patients with acute cholangitis or a strong suspicion of gallstones. All guidelines underline the importance of vigorous fluid resuscitation and supplemental oxygen therapy and prefer enteral over parenteral nutrition, with the majority favouring the nasojejunal route. In view of lacking scientific evidence, antibiotic prophylaxis to prevent infection of pancreatic necroses is discouraged by most guidelines. Computed tomography-guided fine needle aspiration is the technique of choice to differentiate between sterile and infected pancreas necrosis. While sterile pancreatic necrosis should be managed conservatively, infected pancreatic necrosis requires debridement and drainage supplemented by antibiotic therapy. Surgical necrosectomy is the traditional approach, but less invasive techniques (retroperitoneal or laparoscopic necrosectomy, computed tomography-guided percutaneous catheter drainage) may be equally effective.

Downstream from calcium signalling: mitochondria, vacuoles and pancreatic acinar cell damage

Ca(2+) is one of the most ancient and ubiquitous second messengers. Highly polarized pancreatic acinar cells serve as an important cellular model for studies of Ca(2+) signalling and homeostasis. Downstream effects of Ca(2+) signalling have been and continue to be an important research avenue. The primary functions regulated by Ca(2+) in pancreatic acinar cells--exocytotic secretion and fluid secretion--have been defined and extensively characterized in the second part of the last century. The role of cytosolic Ca(2+) in cellular pathology and the related question of the interplay between Ca(2+) signalling and bioenergetics are important current research lines in our and other laboratories. Recent findings in these interwoven research areas are discussed in the current review.

The role of free fatty acids, pancreatic lipase and Ca+ signalling in injury of isolated acinar cells and pancreatitis model in lipoprotein lipase-deficient mice

AIM AND METHODS

Recurrent pancreatitis is a common complication of severe hypertriglyceridaemia (HTG) often seen in patients carrying various gene mutations in lipoprotein lipase (LPL). This study investigates a possible pathogenic mechanism of cell damage in isolated mouse pancreatic acinar cells and of pancreatitis in LPL-deficient and in wild type mice.

RESULTS

Addition of free fatty acids (FFA) or of chylomicrons to isolated pancreatic acinar cells caused stimulation of amylase release, and at higher concentrations it also caused cell damage. This effect was decreased in the presence of the lipase inhibitor orlistat. Surprisingly, pancreatic lipase whether in its active or inactive state could act like an agonist by inducing amylase secretion, increasing cellular cGMP levels and converting cell damaging sustained elevations of [Ca(2+)](cyt) to normal Ca(2+) oscillations. Caerulein increases the levels of serum amylase and caused more severe inflammation in the pancreas of LPL-deficient mice than in wild type mice.

CONCLUSION

We conclude that high concentrations of FFA as present in the plasma of LPL-deficient mice and in patients with HTG lead to pancreatic cell damage and are high risk factors for the development of acute pancreatitis. In addition to its enzymatic effect which leads to the generation of cell-damaging FFA from triglycerides, pancreatic lipase also prevents Ca(2+) overload in pancreatic acinar cells and, therefore, counteracts cell injury.

Ethanol impairs calcium homeostasis following CCK-8 stimulation in mouse pancreatic acinar cells

Alcohol consumption has long been associated with cell damage, and it is thought that it is involved in approximately 40% of cases of acute pancreatitis. In the present study, we have investigated the early effects of acute ethanol exposure on cholecystokinin octapeptide (CCK-8)-evoked calcium (Ca2+) signals in mouse pancreatic acinar cells. Cells were loaded with fura-2 and the changes in fluorescence were monitorized using a spectrofluorimeter. Our results show that stimulation of cells with 1 nM CCK-8 led to a transient increase in [Ca2+]c, which consisted of an initial increase followed by a decrease of [Ca2+]c toward a value close to the prestimulation level. In the presence of 50mM ethanol, CCK-8 lead to a greater Ca2+ mobilization compared to that obtained with CCK-8 alone. The peak of CCK-8-evoked Ca2+ response, the "steady-state level" reached 5 min after stimulation, the rate of decay of [Ca2+]c toward basal values and the total Ca2+ mobilization were significantly affected by ethanol pretreatment. Thapsigargin (Tps) induced an increase in [Ca2+]c due to its release from intracellular stores. After stimulation of cells with CCK-8 or Tps in the presence of 50mM ethanol, a greater [Ca2+]c peak response, a slower rate of decay of [Ca2+]c, and higher values of [Ca2+]c were observed. The effects of ethanol might result from a delayed or reduced Ca2+ extrusion from the cytosol toward the extracellular space by plasma membrane Ca2+ adenosine triphosphatase (ATPase), or into the cytosolic stores by the sarcoendoplasmic reticulum Ca2+-ATPase. Participation of mitochondria in Ca2+ handling is also demonstrated. The actions of ethanol on CCK-8 stimulation of cells create a situation potentially leading to Ca2+ overload, which is a common pathological precursor that mediates pancreatitis.

Direct activation of cytosolic Ca2+ signaling and enzyme secretion by cholecystokinin in human pancreatic acinar cells

BACKGROUND & AIMS

Cholecystokinin (CCK) has been thought to act only indirectly on human pancreatic acinar cells via vagal nerve stimulation, rather than by direct CCK receptor activation as on rodent pancreatic acinar cells. We tested whether CCK (CCK-8 and human CCK-58) can act directly on human pancreatic acinar cells.

METHODS

Human acinar cells were freshly isolated from pancreatic transection line samples, loaded with Fluo4-AM or quinacrine, and examined for Ca(2+), metabolic and secretory responses to CCK-8, human CCK-58, or acetylcholine with confocal microscopy.

RESULTS

CCK-8 and human CCK-58 at physiologic concentrations (1-20 pmol/L) elicited rapid, robust, oscillatory increases of the cytosolic Ca(2+) ion concentration, showing apical to basal progression, in acinar cells from 14 patients with unobstructed pancreata. The cytosolic Ca(2+) ion concentration increases were followed by increases in mitochondrial adenosine triphosphate production and secretion. CCK-elicited Ca(2+) signals and exocytosis were not inhibited by atropine (1 mumol/L) or tetrodotoxin (100 nmol/L), showing that CCK was unlikely to have acted via neurotransmitter release. CCK-elicited Ca(2+) signals were inhibited reversibly by caffeine (5-20 mmol/L), indicating involvement of intracellular inositol trisphosphate receptor Ca(2+) release channels. Acetylcholine (50 nmol/L) elicited similar Ca(2+) signals.

CONCLUSIONS

CCK at physiologic concentrations in the presence of atropine and tetrodotoxin elicits cytosolic Ca(2+) signaling, activates mitochondrial function, and stimulates enzyme secretion in isolated human pancreatic acinar cells. We conclude that CCK acts directly on acinar cells in the human pancreas.

Bile acids and signal transduction: role in glucose homeostasis

Bile acids are mainly recognized for their role in dietary lipid absorption and cholesterol homeostasis. However, recent progress in bile acid research suggests that bile acids are important signaling molecules that play a role in glucose homeostasis. Among the various supporting evidence, several reports have demonstrated an improvement of the glycemic index of type 2 diabetic patients treated with diverse bile acid binding resins. Herein, we review the diverse interactions of bile acids with various signaling/response pathways, including calcium mobilization and protein kinase activation, membrane receptor-mediated responses, and nuclear receptor responses. Some of the effects of the bile acids are direct through the activation of specific receptors, i.e., TGR5, CAR, VDR, and FXR, while others imply modulation of the hormonal, growth factor and/or neuromediator responses, i.e., glucagon, EGF, and acetylcholine. We also discuss recent evidence implicating the interaction of bile acids with glucose homeostasis mechanisms, with the integration of our understanding of how the signaling mechanisms modulated by bile acid could regulate glucose metabolism.

The novel protein kinase C isoforms -delta and -epsilon modulate caerulein-induced zymogen activation in pancreatic acinar cells

Isoforms of protein kinase C (PKC) have been shown to modulate some cellular responses such as pathological secretion and generation of inflammatory mediators during acute pancreatitis (AP). We propose that PKC also participates in premature zymogen activation within the pancreatic acinar cell, a key event in the initiation of AP. This hypothesis was examined in in vivo and cellular models of caerulein-induced AP using PKC activators and inhibitors. Phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA, 200 nM), a known activator of PKC, enhanced zymogen activation at both 0.1 nM and 100 nM caerulein, concentrations which mimic physiological and supraphysiological effects of the hormone cholecystokinin, respectively, in preparations of pancreatic acinar cells. Isoform-specific PKC inhibitors for PKC-delta and PKC-epsilon reduced supraphysiological caerulein-induced zymogen activation. Using a cell-free reconstitution system, we showed that inhibition of PKC-delta and -epsilon, reduced zymogen activation in both zymogen granule-enriched and microsomal fractions. In dispersed acinar cells, 100 nM caerulein stimulation caused PKC-delta and -epsilon isoform translocation to microsomal membranes using cell fractionation and immunoblot analysis. PKC translocation was confirmed with in vivo studies and immunofluorescence microscopy in pancreatic tissues from rats treated with or without 100 nM caerulein. PKC-epsilon redistributed from an apical to a supranuclear region following caerulein administration. The signal for PKC-epsilon overlapped with granule membrane protein, GRAMP-92, an endosomal/lysosomal marker, in a supranuclear region where zymogen activation takes place. These results indicate that PKC-delta and -epsilon isoforms translocate to specific acinar cell compartments and modulate zymogen activation.

Ca2+ signalling and Ca2+-activated ion channels in exocrine acinar cells

The development of the calcium signalling field, from its early beginnings some 40 years ago to the present, is described. Calcium signalling in exocrine gland acinar cells and the effects of neurotransmitter- or hormone-elicited rises in the cytosolic calcium ion concentration on ion channel gating are reviewed. The highly polarized arrangement of the organelle systems in living acinar cells is described as well as its importance for the physiologically relevant local and polarized calcium signalling events.