CCK independently activates intracellular trypsinogen and NF-kappaB in rat pancreatic acinar cells

Trypsin in pancreatitis: The culprit, a mediator, or epiphenomenon?

Pancreatitis is a common, life-threatening inflammatory disease of the exocrine pancreas. Its pathogenesis remains obscure, and no specific or effective treatment is available. Gallstones and alcohol excess are major etiologies of pancreatitis; in a small portion of patients the disease is hereditary. Pancreatitis is believed to be initiated by injured acinar cells (the main exocrine pancreas cell type), leading to parenchymal necrosis and local and systemic inflammation. The primary function of these cells is to produce, store, and secrete a variety of enzymes that break down all categories of nutrients. Most digestive enzymes, including all proteases, are secreted by acinar cells as inactive proforms (zymogens) and in physiological conditions are only activated when reaching the intestine. The generation of trypsin from inactive trypsinogen in the intestine plays a critical role in physiological activation of other zymogens. It was proposed that pancreatitis results from proteolytic autodigestion of the gland, mediated by premature/inappropriate trypsinogen activation within acinar cells. The intra-acinar trypsinogen activation is observed in experimental models of acute and chronic pancreatitis, and in human disease. On the basis of these observations, it has been considered the central pathogenic mechanism of pancreatitis - a concept with a century-old history. This review summarizes the data on trypsinogen activation in experimental and genetic rodent models of pancreatitis, particularly the more recent genetically engineered mouse models that mimic mutations associated with hereditary pancreatitis; analyzes the mechanisms mediating trypsinogen activation and protecting the pancreas against its' damaging effects; discusses the gaps in our knowledge, potential therapeutic approaches, and directions for future research. We conclude that trypsin is not the culprit in the disease pathogenesis but, at most, a mediator of some pancreatitis responses. Therefore, the search for effective therapies should focus on approaches to prevent or normalize other intra-acinar pathologic processes, such as defective autophagy leading to parenchymal cell death and unrelenting inflammation.

Sphingosine 1-phosphate receptor 2 mediated early stages of pancreatic and systemic inflammatory responses via NF-kappa B activation in acute pancreatitis

In acute pancreatitis, activation of inflammatory signaling, including the nuclear factor-kappa B (NF-κB) pathway, within acinar cells is known to be an early intracellular event occurring in parallel with pathologic trypsinogen activation. Sphingosine 1-phosphate receptor 2 (S1PR2) plays a critical role in endothelial inflammation, and our previous studies reported that S1PR2 deficiency significantly reduced the inflammatory response in liver injury under cholestasis conditions. However, the role of S1PR2 in inflammatory signaling activation within acinar cells and inflammatory responses during acute pancreatitis has not been elucidated. Here we report that S1PR2 was upregulated in the whole pancreas during acute pancreatitis. Blockade of S1PR2 by pharmacologic inhibition of S1PR2 by JTE-013 or AAV-mediated knockdown of S1PR2 improved the severity of pancreatic injury, as indicated by a significant reduction in inflammation and acinar cells death in acute pancreatitis mice. Moreover, S1PR2 is the predominant S1PRs expressed in pancreatic acinar cells and mediates NF-κB activation and the early inflammatory response within acinar cells under acute pancreatitis conditions via ROCK signaling pathways, not extracellular signal-regulated kinase pathways or p38 mitogen-activated protein kinase pathways. In addition, S1PR2 mediated macrophage NF-κB activation, migration and polarization toward the M1 phenotype. Therefore, these results demonstrated that the S1PR2-mediated early inflammatory response in acinar cells promotes the progression of acute pancreatitis, successfully linking local events to the systematic inflammatory response and leading to a novel therapeutic target for acute pancreatitis aimed at halting the progression of the inflammatory response.

Associations between gastrointestinal humoral factors and pancreatic proteolytic enzymes in alcohol-related versus non-alcohol-related pancreatitis

BACKGROUND

Alcohol-related pancreatitis is common and the gastrointestinal tract plays an important role in the regulation of pancreatic exocrine function. While the relationship between pancreatic proteolytic enzymes and insulin (as well as other pancreatic hormones) has been investigated in detail, little is known about the relationship between pancreatic proteolytic enzymes and gastrointestinal humoral factors. The aim of this study was to study the associations between trypsin, chymotrypsin, and a panel of gastrointestinal humoral factors in patients after an episode of alcohol-related versus non-alcohol-related pancreatitis.

METHODS

Fasting venous blood samples were analyzed for trypsin, chymotrypsin, cholecystokinin, gastrin, ghrelin, gastrin-related peptide, neuropeptide Y, peptide YY, secretin, and vasoactive intestinal peptide. Linear regression analysis was used in three statistical models, adjusting for covariates (age, sex, ethnicity, smoking, exercise, body mass index, dysglycemia, recurrence of pancreatitis, duration of pancreatitis, and severity of pancreatitis).

RESULTS

The study included 21 patients with alcohol-related pancreatitis and 72 with non-alcohol-related pancreatitis. Gastrin, cholecystokinin, and vasoactive intestinal peptide were significantly associated with chymotrypsin in all three statistical models and resulted in a 1.06, 1.98, and 2.74 times higher chymotrypsin level in alcohol-related pancreatitis, respectively. Ghrelin was significantly associated with trypsin in all three statistical models and resulted in a 2.64 times higher trypsin level in alcohol-related pancreatitis. Other associations did not demonstrate a consistent significant pattern.

CONCLUSION

In alcohol-related pancreatitis, several gut-related peptides are significantly associated with pancreatic exocrine function. Further studies to investigate the effect of alcohol on the interaction between cholecystokinin (as well as gastrin, ghrelin, and vasoactive intestinal peptide) and pancreatic exocrine function are warranted.

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.

Protective effects of carbon monoxide releasing molecule‑2 on pancreatic function in septic mice

The present study aimed to investigate the effect of carbon monoxide (CO)‑releasing molecule‑2 (CORM‑2) on pancreatic function in sepsis‑model mice. To perform the present investigation, mice were rendered septic by cecal ligation and puncture (CLP). Then, mice were either treated with or without CORM‑2 (8 mg/kg, intravenous) for different durations (6, 12 and 24 h) immediately following CLP. The levels of serum amylase and lipase, tumor necrosis factor α, interleukin‑1β and interleukin‑6 in addition to myeloperoxidase (MPO) activity in pancreatic tissues were determined at 6, 12 and 24 h post‑CLP. Histological scores and the expression of intercellular adhesion molecule 1 (ICAM‑1), vascular cell adhesion molecule 1 (VCAM‑1), nuclear factor‑κB (NF‑κB) and phosphorylated inhibitor of κB (p‑IκB‑α) in the pancreas were also evaluated at 24 h post‑CLP. The results of the present study revealed that compared with CLP‑alone group, CORM‑2 treatment significantly (P<0.05) reduced the levels of serum amylase, lipase and pro‑inflammatory cytokines. In parallel, the severity of pancreatic histology, MPO activity and the expression levels of ICAM‑1 and VCAM‑1 in the pancreas of CORM‑2 treated CLP mice were substantially decreased compared with the untreated group. Furthermore, CORM‑2 treatment inhibited the expression levels of NF‑κB and P‑IκB‑α in the pancreas of mice following CLP compared with the untreated group. CORM‑2‑liberated CO exerted protective effects on the pancreatic function of septic mice, and the beneficial effects may be due to the suppression of NF‑κB activation and subsequent regulation of NF‑κB‑dependent expression of cytokines.

Paeonia lactiflora Pall. regulates the NF-κB-NLRP3 inflammasome pathway to alleviate cholestasis in rats

OBJECTIVES

Cholestasis is a critical risk factor for severe hepatic disease or cirrhosis. The anti-inflammatory effect of Paeonia lactiflora Pall. (PLP), named Chishao in traditional Chinese medicine (TCM), on alpha-naphthylisothiocyanate (ANIT)-induced cholestasis model was tried to be elucidated in this research.

METHODS

Therapeutic effect indices on hepatic function, including ALT, AST, TBIL, DBIL, ALP, TBA and γ-GT, were measured. To further investigate the protective mechanism of PLP, the mRNA and protein expression levels of NF-κB-NLRP3 inflammasome pathway were detected.

RESULTS

Our results showed that compared with the model group, PLP could significantly reduce the increased serum indices such as ALT, AST, TBIL, DBIL, ALP, TBA and γ-GT induced by ANIT in a dose-dependent way. Moreover, we found that PLP downregulated the mRNA expression levels including IKK, p65, NLRP3, caspase-1 and IL-1β, especially at the large dose. Furthermore, PLP also significantly inhibited NF-κB-NLRP3 inflammasome pathway by decreasing the protein levels of p65, p-p65, p-IKK, NLRP3, caspase-1 and IL-1β.

CONCLUSIONS

The results indicated that PLP could ameliorate ANIT-induced cholestasis in rats and the anti-inflammatory effect of PLP might be related to regulating NF-κB-NLRP3 inflammasome pathway. This study will provide scientific evidence for PLP as a potential drug candidate for cholestasis.

Immunopathogenesis of pancreatitis

The conventional view of the pathogenesis of acute and chronic pancreatitis is that it is due to a genetic- or environment-based abnormality of intracellular acinar trypsinogen activation and thus to the induction of acinar cell injury that, in turn, sets in motion an intra-pancreatic inflammatory process. More recent studies, reviewed here, present strong evidence that while such trypsinogen activation is likely a necessary first step in the inflammatory cascade underlying pancreatitis, sustained pancreatic inflammation is dependent on damage-associated molecular patterns-mediated cytokine activation causing the translocation of commensal (gut) organisms into the circulation and their induction of innate immune responses in acinar cells. Quite unexpectedly, these recent studies reveal that the innate responses involve activation of responses by an innate factor, nucleotide-binding oligomerization domain 1 (NOD1), and that such NOD1 responses have a critical role in the activation/production of nuclear factor-kappa B and type I interferon. In addition, they reveal that chronic inflammation and its accompanying fibrosis are dependent on the generation of IL-33 by injured acinar cells and its downstream induction of T cells producing IL-13. These recent studies thus establish that pancreatitis is quite a unique form of inflammation and one susceptible to newer, more innovative therapy.

The p21-activated kinase, PAK2, is important in the activation of numerous pancreatic acinar cell signaling cascades and in the onset of early pancreatitis events

In a recent study we explored Group-1-p21-activated kinases (GP.1-PAKs) in rat pancreatic acini. Only PAK2 was present; it was activated by gastrointestinal-hormones/neurotransmitters and growth factors in a PKC-, Src- and small-GTPase-mediated manner. PAK2 was required for enzyme-secretion and ERK/1-2-activation. In the present study we examined PAK2's role in CCK and TPA-activation of important distal signaling cascades mediating their physiological/pathophysiological effects and analyzed its role in pathophysiological processes important in early pancreatitis. In rat pancreatic acini, PAK2-inhibition by the specific, GP.1.PAK-inhibitor, IPA-3-suppressed cholecystokinin (CCK)/TPA-stimulated activation of focal-adhesion kinases and mitogen-activated protein-kinases. PAK2-inhibition reversed the dual stimulatory/inhibitory effect of CCK/TPA on the PI3K/Akt/GSK-3β pathway. However, its inhibition did not affect PKC activation. PAK2-inhibition protected acini from CCK-induced ROS-generation; caspase/trypsin-activation, important in early pancreatitis; as well as from cell-necrosis. Furthermore, PAK2-inhibition reduced proteolytic-activation of PAK-2p34, which is involved in programmed-cell-death. To ensure that the study did not only rely in the specificity of IPA-3 as a PAK inhibitor, we used two other approaches for PAK inhibition, FRAX597 a ATP-competitive-GP.1-PAKs-inhibitor and infection with a PAK2-dominant negative(DN)-Advirus. Those two approaches confirmed the results obtained with IPA-3. This study demonstrates that PAK2 is important in mediating CCK's effect on the activation of signaling-pathways known to mediate its physiological/pathophysiological responses including several cellular processes linked to the onset of pancreatitis. Our results suggest that PAK2 could be a new, important therapeutic target to consider for the treatment of diseases involving deregulation of pancreatic acinar cells.

Src kinases play a novel dual role in acute pancreatitis affecting severity but no role in stimulated enzyme secretion

In pancreatic acinar cells, the Src family of kinases (SFK) is involved in the activation of several signaling cascades that are implicated in mediating cellular processes (growth, cytoskeletal changes, apoptosis). However, the role of SFKs in various physiological responses such as enzyme secretion or in pathophysiological processes such as acute pancreatitis is either controversial, unknown, or incompletely understood. To address this, in this study, we investigated the role/mechanisms of SFKs in acute pancreatitis and enzyme release. Enzyme secretion was studied in rat dispersed pancreatic acini, in vitro acute-pancreatitis-like changes induced by supramaximal COOH-terminal octapeptide of cholecystokinin (CCK). SFK involvement assessed using the chemical SFK inhibitor (PP2) with its inactive control, 4-amino-7-phenylpyrazol[3,4-d]pyrimidine (PP3), under experimental conditions, markedly inhibiting SFK activation. In CCK-stimulated pancreatic acinar cells, activation occurred of trypsinogen, various MAP kinases (p42/44, JNK), transcription factors (signal transducer and activator of transcription-3, nuclear factor-κB, activator protein-1), caspases (3, 8, and 9) inducing apoptosis, LDH release reflective of necrosis, and various chemokines secreted (monocyte chemotactic protein-1, macrophage inflammatory protein-1α, regulated on activation, normal T cell expressed and secreted). All were inhibited by PP2, not by PP3, except caspase activation leading to apoptosis, which was increased, and trypsin activation, which was unaffected, as was CCK-induced amylase release. These results demonstrate SFK activation is playing a dual role in acute pancreatitis, inhibiting apoptosis and promoting necrosis as well as chemokine/cytokine release inducing inflammation, leading to more severe disease, as well as not affecting secretion. Thus, our studies indicate that SFK is a key mediator of inflammation and pancreatic acinar cell death in acute pancreatitis, suggesting it could be a potential therapeutic target in acute pancreatitis.

NF-κB in acute pancreatitis: Mechanisms and therapeutic potential

The incidence of acute pancreatitis (AP) is increasing globally and mortality could be high among patients with organ failure and infected necrosis. The predominant factors responsible for the morbidity and mortality of AP are systemic inflammatory response syndrome and multiorgan dysfunction. Even though preclinical studies have shown antisecretory agents (somatostatin), antioxidants (S-adenosyl methionine [SAM], selenium), protease inhibitors, platelet activating factor inhibitor (Lexipafant), and anti-inflammatory immunomodulators (eg. prostaglandin E, indomethacin) to benefit AP in terms of reducing the severity and/or mortality, most of these agents have shown heterogeneous results in clinical studies. Several years of experimental studies have implicated nuclear factor-kappa B (NF-κB) activation as an early and central event in the progression of inflammation in AP. In this manuscript, we review the literature on the role of NF-κB in the pathogenesis of AP, its early intraacinar activation, and how it results in progression of the disease. We also discuss why anti-protease, antisecretory, and anti-inflammatory agents are unlikely to be effective in clinical acute pancreatitis. NF-κB, being a central molecule that links the initial acinar injury to systemic inflammation and perpetuate the inflammation, we propose that more studies be focussed towards targeted inhibition of NF-κB activity. Direct NF-κB inhibition strategies have already been attempted in patients with various cancers. So far, peroxisome proliferator activator receptor gamma (PPAR-γ) ligand, pyrrolidine dithiocarbamate (PDTC), proteasome inhibitor and calpain I inhibitor have been shown to have direct inhibitory effects on NF-κB activation in experimental AP.

Resolvin D1 protects against inflammation in experimental acute pancreatitis and associated lung injury

Acute pancreatitis is an inflammatory condition that may lead to multisystemic organ failure with considerable mortality. Recently, resolvin D1 (RvD1) as an endogenous anti-inflammatory lipid mediator has been confirmed to protect against many inflammatory diseases. This study was designed to investigate the effects of RvD1 in acute pancreatitis and associated lung injury. Acute pancreatitis varying from mild to severe was induced by cerulein or cerulein combined with LPS, respectively. Mice were pretreated with RvD1 at a dose of 300 ng/mouse 30 min before the first injection of cerulein. Severity of AP was assessed by biochemical markers and histology. Serum cytokines and myeloperoxidase (MPO) levels in pancreas and lung were determined for assessing the extent of inflammatory response. NF-κB activation was determined by Western blotting. The injection of cerulein or cerulein combined with LPS resulted in local injury in the pancreas and corresponding systemic inflammatory changes with pronounced severity in the cerulein and LPS group. Pretreated RvD1 significantly reduced the degree of amylase, lipase, TNF-α, and IL-6 serum levels; the MPO activities in the pancreas and the lungs; the pancreatic NF-κB activation; and the severity of pancreatic injury and associated lung injury, especially in the severe acute pancreatitis model. These results suggest that RvD1 is capable of improving injury of pancreas and lung and exerting anti-inflammatory effects through the inhibition of NF-κB activation in experimental acute pancreatitis, with more notable protective effect in severe acute pancreatitis. These findings indicate that RvD1 may constitute a novel therapeutic strategy in the management of severe acute pancreatitis.

Innate Immune Molecule Surfactant Protein D Attenuates Sepsis-induced Acute Pancreatic Injury through Modulating Apoptosis and NF-κB-mediated Inflammation

Sepsis causes multiple-organ dysfunction including pancreatic injury, thus resulting in high mortality. Innate immune molecule surfactant protein D (SP-D) plays a critical role in host defense and regulating inflammation of infectious diseases. In this study we investigated SP-D functions in the acute pancreatic injury (API) with C57BL/6 Wild-type (WT) and SP-D knockout (KO) mice in cecal ligation and puncture (CLP) model. Our results confirm SP-D expression in pancreatic islets and intercalated ducts and are the first to explore the role of pancreatic SP-D in sepsis. CLP decreased pancreatic SP-D levels and caused severe pancreatic injury with higher serum amylase 24 h after CLP. Apoptosis and neutrophil infiltration were increased in the pancreas of septic KO mice (p < 0.05, vs septic WT mice), with lower Bcl-2 and higher caspase-3 levels in septic KO mice (p < 0.05). Molecular analysis revealed increased NF-κB-p65 and phosphorylated IκB-α levels along with higher serum levels of TNF-α and IL-6 in septic KO mice compared to septic WT mice (p < 0.01). Furthermore, in vitro islet cultures stimulated with LPS produced higher TNF-α and IL-6 (p < 0.05) from KO mice compared to WT mice. Collectively, these results demonstrate SP-D plays protective roles by inhibiting apoptosis and modulating NF-κB-mediated inflammation in CLP-induced API.

The role of inflammation in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with an extremely poor prognosis. Inflammatory processes have emerged as key mediators of pancreatic cancer development and progression. In genetically engineered mouse models, induction of pancreatitis accelerates PDAC development, and patients with chronic pancreatitis are known to have a higher risk of developing pancreatic cancer. In recent years, much effort has been given to identify the underlying mechanisms that contribute to inflammation-induced tumorigenesis. Many inflammatory pathways have been identified and inhibitors have been developed in order to prevent cancer development and progression. In this chapter, we discuss the role of inflammatory pathways in the initiation and progression of pancreatic cancer as well as the role of inhibitors used in treatment and prevention of pancreatic cancer.

New insights into the pathogenesis of pancreatitis

PURPOSE OF REVIEW

In this article, we review important advances in our understanding of the mechanisms of pancreatitis.

RECENT FINDINGS

The relative contributions of intrapancreatic trypsinogen activation and nuclear factor kappa B (NFκB) activation, the two major early independent cellular events in pancreatitis, have been investigated using novel genetic models. Trypsinogen activation has traditionally held the spotlight for many decades as the central pathogenic event of pancreatitis. However, recent experimental evidence points to the role of trypsin activation in early acinar cell damage but not in the inflammatory response of acute pancreatitis, which was shown to be induced by NFκB activation. Further, chronic pancreatitis developed independently of trypsinogen activation in the caerulein model. Sustained NFκB activation, but not persistent intra-acinar expression of active trypsin, was shown to result in chronic pancreatitis. Calcineurin-NFAT (nuclear factor of activated T-cells) signaling was shown to mediate downstream effects of pathologic rise in intracellular calcium. Interleukin-6 was identified as a key cytokine mediating pancreatitis-associated lung injury.

SUMMARY

Recent advances challenge the long-believed trypsin-centered understanding of pancreatitis. It is becoming increasingly clear that activation of intense inflammatory signaling mechanisms in acinar cells is crucial to the pathogenesis of pancreatitis, which may explain the strong systemic inflammatory response in pancreatitis.

Src Dependent Pancreatic Acinar Injury Can Be Initiated Independent of an Increase in Cytosolic Calcium

Several deleterious intra-acinar phenomena are simultaneously triggered on initiating acute pancreatitis. These culminate in acinar injury or inflammatory mediator generation in vitro and parenchymal damage in vivo. Supraphysiologic caerulein is one such initiator which simultaneously activates numerous signaling pathways including non-receptor tyrosine kinases such as of the Src family. It also causes a sustained increase in cytosolic calcium- a player thought to be crucial in regulating deleterious phenomena. We have shown Src to be involved in caerulein induced actin remodeling, and caerulein induced changes in the Golgi and post-Golgi trafficking to be involved in trypsinogen activation, which initiates acinar cell injury. However, it remains unclear whether an increase in cytosolic calcium is necessary to initiate acinar injury or if injury can be initiated at basal cytosolic calcium levels by an alternate pathway. To study the interplay between tyrosine kinase signaling and calcium, we treated mouse pancreatic acinar cells with the tyrosine phosphatase inhibitor pervanadate. We studied the effect of the clinically used Src inhibitor Dasatinib (BMS-354825) on pervanadate or caerulein induced changes in Src activation, trypsinogen activation, cell injury, upstream cytosolic calcium, actin and Golgi morphology. Pervanadate, like supraphysiologic caerulein, induced Src activation, redistribution of the F-actin from its normal location in the sub-apical area to the basolateral areas, and caused antegrade fragmentation of the Golgi. These changes, like those induced by supraphysiologic caerulein, were associated with trypsinogen activation and acinar injury, all of which were prevented by Dasatinib. Interestingly, however, pervanadate did not cause an increase in cytosolic calcium, and the caerulein induced increase in cytosolic calcium was not affected by Dasatinib. These findings suggest that intra-acinar deleterious phenomena may be initiated independent of an increase in cytosolic calcium. Other players resulting in acinar injury along with the Src family of tyrosine kinases remain to be explored.

The role of protein synthesis and digestive enzymes in acinar cell injury

The exocrine pancreas is the organ with the highest level of protein synthesis in the adult--each day the pancreas produces litres of fluid filled with enzymes that are capable of breaking down nearly all organic substances. For optimal health, the pancreas must produce sufficient enzymes of the right character to match the dietary intake. Disruption of normal pancreatic function occurs primarily as a result of dysfunction of the acinar cells that produce these digestive enzymes, and can lead to acute or chronic diseases. For many years, the prevailing dogma has been that inappropriate intracellular activation of the digestive enzymes produced by acinar cells was the key to pancreatic inflammatory diseases, as digestive enzymes themselves are potentially harmful to the cells that secrete them. However, we now know that many stressors can affect pancreatic acinar cells, and that these stressors can independently trigger pancreatic pathology through various mechanisms. This Review focuses on protein synthesis and active digestive enzymes--two key stressors faced by the acinar cell that are likely to be the major drivers of pathology encountered in the pancreas.

Effects of curcumin on proinflammatory cytokines and tissue injury in the early and late phases of experimental acute pancreatitis

BACKGROUND & AIMS

Acute pancreatitis (AP) varies from mild to severe necrotizing changes with high mortality. The objective of the current study was to investigate the effects of curcumin on tissue injury and proinflammatory cytokines in the early and late phases of AP.

METHODS

AP was induced by sodium taurocholate in rats (n = 140). First group was left untreated. Group II received 100 mg/kg curcumin daily starting 20 days before AP induction. The rats were allocated into 7 sub-groups (n:5) and were sacrificed at 2, 6, 12, 24, 72, 144 and 288 h following the induction of AP. Blood and pancreatic tissue samples were collected for biochemical and histopathologic evaluations and the assessment of protein and mRNA levels, as well.

RESULTS

Curcumin decreased total histopathologic scores in comparison with those of the taurocholate group (P < 0.05). Curcumin increased Caspase-3 activity and decreased trypsin activity, while inhibited nuclear factor-κ (NF-κB) at all time points (P < 0.05) and moreover reduced activator protein-1 (AP-1). Curcumin decreased chemokine (except for 288 h), TNF-α (except for 2 and 24 h), IL-6 (except for 2, 6 and 288 h) and iNOS (except for 144 and 288 h) mRNA levels (P < 0.05). Curcumin serum nitric oxide (NO) (except for 144 and 288 h) levels were reduced, as well.

CONCLUSIONS

In conclusion, curcumin reduced tissue injury, trypsin activation and inhibited NF-κB and AP-1. However TNF-α, IL-6 and iNOS and NO were not inhibited at all time points. Therefore no direct correlation was detected in the subgroups between tissue injury, proinflammatory cytokines and oxidative enzymes.

Cerulein-induced chronic pancreatitis does not require intra-acinar activation of trypsinogen in mice

BACKGROUND & AIMS

Premature activation of trypsinogen activation can cause pancreatic injury and has been associated with chronic pancreatitis (CP). Mice that lack intra-acinar activation of trypsinogen, such as trypsinogen-7-null (T(-/-)) and cathepsin B-null (CB(-/-)) mice, have been used to study trypsin-independent processes of CP development. We compared histologic features and inflammatory responses of pancreatic tissues from these mice with those from wild-type mice after the development of CP.

METHODS

CP was induced in wild-type, T(-/-), and CB(-/-) mice by twice-weekly induction of acute pancreatitis for 10 weeks; acute pancreatitis was induced by hourly intraperitoneal injections of cerulein (50 μg/kg × 6). Pancreatic samples were collected and evaluated by histologic and immunohistochemical analyses. Normal human pancreas samples, obtained from the islet transplant program at the University of Minnesota, were used as controls and CP samples were obtained from surgical resections.

RESULTS

Compared with pancreatic tissues from wild-type mice, those from T(-/-) and CB(-/-) mice had similar levels of atrophy, histomorphologic features of CP, and chronic inflammation. All samples had comparable intra-acinar activation of nuclear factor (NF)-κB, a transcription factor that regulates the inflammatory response, immediately after injection of cerulein. Pancreatic tissue samples from patients with CP had increased activation of NF-κB (based on nuclear translocation of p65 in acinar cells) compared with controls.

CONCLUSIONS

Induction of CP in mice by cerulein injection does not require intra-acinar activation of trypsinogen. Pancreatic acinar cells of patients with CP have increased levels of NF-κB activation compared with controls; regulation of the inflammatory response by this transcription factor might be involved in the pathogenesis of CP.

Noggin attenuates cerulein-induced acute pancreatitis and impaired autophagy

OBJECTIVES

To investigate the role of bone morphogenetic protein (BMP) signaling in acute pancreatitis (AP) by administration of noggin, an endogenous BMP antagonist, in a cerulein-induced AP model.

METHODS

Acute pancreatitis was induced by 9 hourly intraperitoneal injections of cerulein (50 μg/kg). Control mice received phosphate-buffered saline injections. In a separate group, noggin (0.5 mg/kg) was given intraperitoneally at 1 hour before and 2, 4, and 6 hours after AP induction. The mice were euthanized at 1 hour after completion of AP induction. The blood samples and the pancreas were harvested for analysis. Isolated pancreatic acini from normal mice and AR42J cells were treated with BMP2 and cerulein. AR42J cells were also treated with noggin. Phosphorylation of Smad1/5/8 was measured.

RESULTS

Bone morphogenetic protein signaling was up-regulated in AP mouse pancreas. Bone morphogenetic protein 2 and cerulein-induced phosphorylation of Smad1/5/8 in the acinar cells in vitro, which was blocked by noggin. Noggin administration in vivo attenuated AP induction, decreased vacuole formation in acinar cells, blocked LC3-II levels, and partially restored Beclin-1 and lysosomal-associated membrane protein 2 levels.

CONCLUSIONS

Bone morphogenetic protein signaling seems to promote AP induction and autophagy, as suggested by our study showing that noggin ameliorates AP and partially restores autophagic homeostasis.

Activation of nuclear factor-κB in acinar cells increases the severity of pancreatitis in mice

BACKGROUND & AIMS

Nuclear factor-κB (NF-κB) is activated during early stages of pancreatitis. This transcription factor regulates genes that control many cell activities, including inflammation and survival. There is evidence that activation of NF-κB protects against pancreatitis, and, in other cases, that it promotes this disease. We compared the effects of NF-κB in different mouse models of pancreatitis to understand these complications.

METHODS

To model constitutive activation of NF-κB, we expressed a transgene that encodes its p65 subunit or the inhibitor of κB kinase (IKK)2 in pancreatic acinar cells of mice. We analyzed effects on pancreatic tissues and levels of NF-κB target genes in these mice and compared them with mice that did not express transgenic p65 or IKK2 (controls).

RESULTS

Transgenic expression of p65 led to compensatory expression of the inhibitory subunit IKB-α and, therefore, no clear phenotype. However, p65 transgenic mice given injections of cerulein, to induce acute pancreatitis, had higher levels of NF-κB activity in acinar cells, greater levels of inflammation, and more severe outcomes than control mice. In contrast, constitutive expression of IKK2 directly increased the activity of NF-κB in acinar cells and induced pancreatitis. Prolonged activity of IKK2 (3 months) resulted in activation of stellate cells, loss of acinar cells, and fibrosis, which are characteristics of chronic pancreatitis. Co-expression of IKK2 and p65 greatly increased the expression of inflammatory mediators and the severity of pancreatitis, compared with control mice.

CONCLUSIONS

The level of NF-κB activation correlates with the severity of acute pancreatitis in mice. Longer periods of activation (3 months) lead to chronic pancreatitis. These findings indicate that strategies to inactivate NF-κB might be used to treat patients with acute or chronic pancreatitis.

Pathogenic mechanisms of acute pancreatitis

PURPOSE OF REVIEW

In this article, recent advances in the pathogenesis of acute pancreatitis have been reviewed.

RECENT FINDINGS

Pathologic intra-acinar trypsinogen activation had been hypothesized to be the central mechanism of pancreatitis for over a century. This hypothesis could be explored for the first time with the development of a novel mouse model lacking pathologic intra-acinar trypsinogen activation. It became clear that intra-acinar trypsinogen activation contributes to early acinar injury, but local and systemic inflammation progress independently during pancreatitis. Early intra-acinar nuclear factor kappa B (NFκB) activation, which occurs parallel to but independent of trypsinogen activation, may be crucial in pancreatitis. Although the mechanism of NFκB and trypsinogen activation is not entirely clear, further insights have been made into key pathogenic cellular events such as calcium signaling, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, autophagy and impaired trafficking, and lysosomal and secretory responses. Cellular intrinsic damage-sensing mechanisms that lead to activation of the inflammatory response aimed at repair, but lead to disease when overwhelmed, are beginning to be understood.

SUMMARY

New findings necessitate a paradigm shift in our understanding of acute pancreatitis. Intra-acinar trypsinogen activation leads to early pancreatic injury, but the inflammatory response of acute pancreatitis develops independently, driven by early activation of inflammatory pathways.

Intra-acinar trypsinogen activation mediates early stages of pancreatic injury but not inflammation in mice with acute pancreatitis

BACKGROUND & AIMS

The role of trypsinogen activation in the pathogenesis of acute pancreatitis (AP) has not been clearly established.

METHODS

We generated and characterized mice lacking trypsinogen isoform 7 (T7) gene (T(-/-)). The effects of pathologic activation of trypsinogen were studied in these mice during induction of AP with cerulein. Acinar cell death, tissue damage, early intra-acinar activation of the transcription factor nuclear factor κB (NF-κB), and local and systemic inflammation were compared between T(-/-) and wild-type mice with AP.

RESULTS

Deletion of T7 reduced the total trypsinogen content by 60% but did not affect physiologic function. T(-/-) mice lacked pathologic activation of trypsinogen, which occurs within acinar cells during early stages of AP progression. Absence of trypsinogen activation in T(-/-) mice led to near complete inhibition of acinar cell death in vitro and a 50% reduction in acinar necrosis during AP progression. However, T(-/-) mice had similar degrees of local and systemic inflammation during AP progression and comparable levels of intra-acinar NF-κB activation, which was previously shown to occur concurrently with trypsinogen activation during early stages of pancreatitis.

CONCLUSIONS

T7 is activated during pathogenesis of AP in mice. Intra-acinar trypsinogen activation leads to acinar death during early stages of pancreatitis, which accounts for 50% of the pancreatic damage in AP. However, progression of local and systemic inflammation in AP does not require trypsinogen activation. NF-κB is activated early in acinar cells, independently of trypsinogen activation, and might be responsible for progression of AP.

Molecular mechanisms of pancreatic injury

PURPOSE OF REVIEW

Despite being a subject of much scientific scrutiny, the pathogenesis of acute pancreatitis is still not well understood. This article reviews recent advances in our understanding of acute pancreatitis.

RECENT FINDINGS

Zymogen activation, observed within acini early during acute pancreatitis for a long time, was shown to be sufficient to induce acute pancreatitis. Another key early event, NFκB activation, has previously been shown to induce acute pancreatitis. The relationship between these two key early steps is beginning to be clarified. Mechanisms of zymogen activation - pathologic calcium signaling, pH changes, colocalization and autophagy, and of NFκB activation have been investigated intensively along with potential therapeutic targets both upstream and downstream of these key events. Additional key findings have been elucidation of the role of bioenergetics and the dual role of oxidative stress in acute pancreatitis, recognition of endoplasmic reticulum stress as an early step and the status of duct cells as important entities in pancreatic injury.

SUMMARY

Current findings have provided further insight into the roles and mechanisms of zymogen activation and inflammatory pathways in pancreatic injury. Future studies, which will be of great importance in identifying therapeutic targets, are being undertaken to establish the relative contributions of these pathways during acute pancreatitis.

Transcriptional regulation of CXC-ELR chemokines KC and MIP-2 in mouse pancreatic acini

Neutrophils and their chemoattractants, the CXC-ELR chemokines keratinocyte cytokine (KC) and macrophage inflammatory protein-2 (MIP-2), play a critical role in pancreatitis. While acute pancreatitis is initiated in acinar cells, it is unclear if these are a source of CXC-ELR chemokines. KC and MIP-2 have NF-κB, activator protein-1 (AP-1) sites in their promoter regions. However, previous studies have shown increased basal and reduced caerulein-induced AP-1 activation in harvested pancreatic tissue in vitro, which limits interpreting the caerulein-induced response. Moreover, recent studies suggest that NF-κB silencing in acinar cells alone may not be sufficient to reduce inflammation in acute pancreatitis. Thus the aim of this study was to determine whether acinar cells are a source of KC and MIP-2 and to understand their transcriptional regulation. Primary overnight-cultured murine pancreatic acini were used after confirming their ability to replicate physiological and pathological acinar cell responses. Upstream signaling resulting in KC, MIP-2 upregulation was studied along with activation of the transcription factors NF-κB and AP-1. Cultured acini replicated critical responses to physiological and pathological caerulein concentrations. KC and MIP-2 mRNA levels increased in response to supramaximal but not to physiological caerulein doses. This upregulation was calcium and protein kinase C (PKC), but not cAMP, dependent. NF-κB inhibition completely prevented upregulation of KC but not MIP-2. Complete suppression of MIP-2 upregulation required dual inhibition of NF-κB and AP-1. Acinar cells are a likely source of KC and MIP-2 upregulation during pancreatitis. This upregulation is dependent on calcium and PKC. MIP-2 upregulation requires both NF-κB and AP-1 in these cells. Thus dual inhibition of NF-κB and AP-1 may be a more successful strategy to reduce inflammation in pancreatitis than targeting NF-κB alone.

Regulator of calcineurin 1 controls growth plasticity of adult pancreas

BACKGROUND & AIMS

Growth of exocrine pancreas is regulated by gastrointestinal hormones, notably cholecystokinin (CCK). CCK-driven pancreatic growth requires calcineurin (CN), which activates Nuclear Factor of Activated T cells (NFATs), but the genetic underpinnings and feedback mechanisms that regulate this response are not known.

METHODS

Pancreatic growth was stimulated by protease inhibitor (PI)-containing chow, which induces secretion of endogenous CCK. Expression profiling of PI stimulation was performed on Affymetrix 430A chips, and CN was inhibited via FK506. Exocrine pancreas-specific overexpression of CN inhibitor Regulator of Calcineurin 1 (Rcan1) was achieved by breeding elastase-Cre(estrogen receptor [ER]) transgenics with "flox-on" Rcan1 mice.

RESULTS

CN inhibitor FK506 blocked expression of 38 genes, as confirmed by quantitative polymerase chain reaction. The CN-dependent genes were linked to growth-related processes, whereas their promoters were enriched in NFAT and NFAT/AP1 sites. Multiple NFAT targets, including Rcan1, Rgs2, HB-EGF, Lif, and Gem, were validated by chromatin immunoprecipitation. One of these, a CN feedback inhibitor Rcan1, was induced >50 fold during 1-8 hours course of pancreatic growth and strongly inhibited (>99%) by FK506. To examine its role in pancreatic growth, we overexpressed Rcan1 in an inducible, acinar-specific fashion. Rcan1 overexpression inhibited CN-NFAT signaling, as shown using an NFAT-luciferase reporter and quantitative polymerase chain reaction. Most importantly, the increase in exocrine pancreas size, protein/DNA content, and acinar proliferation were all blocked in Rcan1 overexpressing mice.

CONCLUSIONS

We profile adaptive pancreatic growth, identify Rcan1 as an important new feedback regulator, and firmly establish that CN-NFAT signaling is required for this response.

Dominant negative p38 mitogen-activated protein kinase expression inhibits NF-kappaB activation in AR42J cells

BACKGROUND

The role of the p38 mitogen-activated protein (MAP) kinase in acute pancreatitis pathogenesis is controversial. We hypothesize that p38 plays a role in regulating NF-kappaB activation in exocrine pancreatic cells.

METHODS

AR42J cells incorporating an NF-kappaB-responsive luciferase reporter, with and without adenoviral transduction of DNp38, were stimulated with cholecystokinin (CCK) or tumor necrosis factor-alpha (TNF-alpha) prior to measuring NF-kappaB activation.

RESULTS

CCK- or TNF-alpha-stimulated NF-kappaB-dependent gene transcription (luciferase assay) was substantially subdued by DNp38 expression. These findings were confirmed by electrophoretic mobility shift assay. Nuclear translocation of the p65 NF-kappaB subunit following agonist stimulation was evident (supershift). Characterization studies showed excellent adenoviral infection efficiency and cell viability in our AR42J cell model. Agonist-stimulated dose- and time-dependent p38 activation, with inhibition by DNp38 expression, was also confirmed.

CONCLUSION

The p38 MAP kinase regulates NF-kappaB pathway activation in exocrine pancreatic cells, and thus potentially plays a role in the mechanism of acute pancreatitis pathogenesis..

Nelfinavir/ritonavir reduces acinar injury but not inflammation during mouse caerulein pancreatitis

There is no clinical treatment that reduces acinar injury during pancreatitis. Human immunodeficiency virus (HIV) protease inhibitors (PI), including nelfinavir (NFV) and ritonavir (RTV), may reduce the rate of pancreatitis in HIV-infected patients. Since permeability transition pore (PTPC)-mediated mitochondrial dysfunction occurs during pancreatitis, and we have shown that PI prevents PTPC opening, we studied its effects in a model of pancreatitis. The effect of NFV plus RTV (NFV/RTV) or vehicle on caerulein-induced pancreatitis in mice was compared by measuring changes in mitochondrial membrane potential in vitro and cytochrome c leakage in vivo. Histological and inflammatory makers were also compared. NFV/RTV improved DiOC6 retention in acini exposed to caerulein in vitro. In vivo NFV prevented cytosolic leakage of cytochrome c and reduced pancreatic acinar injury, active caspase-3 staining, TUNEL-positive acinar cells, and serum amylase (P < 0.05). Conversely, trypsin activity, serum cytokine levels, and pancreatic and lung inflammation were unaffected. NFV/RTV reduces pancreatic injury and acinar cell death in experimental mouse caerulein-induced pancreatitis but does not impact inflammation.

Intracellular trypsin induces pancreatic acinar cell death but not NF-kappaB activation

Premature intracellular activation of the digestive enzyme trypsinogen is considered to be the initiating event in pancreatitis. However, the direct consequences of intracellular trypsin activity have not previously been examined. In the current study, a mutant trypsinogen (paired basic amino acid cleaving enzyme (PACE)-trypsinogen), which is activated intracellularly by the endogenous protease PACE, was developed. This new construct allowed for the first time direct examination of the effects of intracellular trypsin on pancreatic acinar cells. We found that PACE-trypsinogen was expressed in the secretory pathway and was activated within acinar cells. Expression of PACE-trypsinogen induced apoptosis of HEK293 cells and pancreatic acinar cells, as indicated by histology, DNA laddering, PARP cleavage, and caspase-3 activation. Cell death was blocked by the trypsin inhibitor Pefabloc but not by the pancaspase inhibitor benzyloxycarbonyl-VAD, indicating that caspase-independent pathways were also involved. However, intracellular trypsin had no significant effect on the activity of the proinflammatory transcription factor NF-kappaB. In contrast, extracellular trypsin caused cell damage and dramatically increased NF-kappaB activity. These data indicate that localization of active trypsin determines its effects on pancreatic acinar cells. This new model will greatly improve our understanding of the role of active trypsin in pancreatitis and its associated inflammatory response.

Relationship between carbachol hyperstimulation-induced pancreatic intracellular trypsinogen and NF-kappa B activation in rats in vitro

The relationship between intracellular trypsinogen activation and NF-kappa B activation in rat pancreatic acinar cells induced by M3 cholinergic receptor agonist (carbachol) hyperstimulation was studied. Rat pancreatic acinar cells were isolated, cultured and treated with carbachol, the active protease inhibitor (pefabloc) and NF-kappa B inhibitor (PDTC) in vitro. Intracellular trypsin activity was measured by using a fluorogenic substrate. The activity of NF-kappa B was monitored by using electrophoretic mobility shift assay. The results showed that after pretreatment with 2 mmol/L pefabloc, the activities of trypsin and NF-kappa B in pancreatic acinar cells treated with high concentrations of carbachol (10(-3) mol/L) in vitro was significantly decreased as compared with control group (P<0.01). The addition of 10(-2) mol/L PDTC resulted in a significant decrease of NF-kappa B activities in pancreatic acinar cells after treated with high concentrations of carbachol (10(-3) mol/L) in vitro, but the intracellular trypsinogen activity was not obviously inhibited (P>0.05). It was concluded that intracellular trypsinogen activation is likely involved in the regulation of high concentrations of carbachol-induced NF-kappa B activation in pancreatic acinar cells in vitro. NF-kappa B activation is likely not necessary for high concentrations of carbachol-induced trypsinogen activation in pancreatic acinar cells in vitro.

Inhibition of Rac1 decreases the severity of pancreatitis and pancreatitis-associated lung injury in mice

Pancreatitis is a disease with high morbidity and mortality. In vitro experiments on pancreatic acini showed that supramaximal but not submaximal cholecystokinin (CCK) stimulation induces effects in the acinar cell that can be correlated with acinar morphological changes observed in the in vivo experimental model of cerulein-induced pancreatitis. The GTPase Rac1 was previously reported to be involved in CCK-evoked amylase release from pancreatic acinar cells. Here, we demonstrate that pretreatment with the Rac1 inhibitor NSC23766 (100 microM, 2 h) effectively blocked Rac1 translocation and activation in CCK-stimulated pancreatic acini, without affecting activation of its closely related GTPase, RhoA. This specific Rac1 inhibition decreased supramaximal (10 nM) CCK-stimulated acinar amylase release (27.% reduction), which seems to be connected to the reduction observed in serum amylase (46.6% reduction) and lipase levels (46.1% reduction) from cerulein-treated mice receiving NSC23766 (100 nmol h(-1)). The lack of Rac1 activation also reduced formation of reactive oxygen species (ROS; 20.8% reduction) and lactate dehydrogenase release (LDH; 24.3% reduction), but did not alter calcium signaling or trypsinogen activation in 10 nM CCK-stimulated acini. In the in vivo model, the cerulein-treated mice receiving NSC23766 also presented a decrease in both pancreatic and lung histopathological scores (reduction in oedema, 32.4 and 66.4%; haemorrhage, 48.3 and 60.2%; and leukocyte infiltrate, 53.5 and 43.6%, respectively; reduction in pancreatic necrosis, 65.6%) and inflammatory parameters [reduction in myeloperoxidase, 52.2 and 38.9%; nuclear factor kappaB (p65), 61.3 and 48.6%; and nuclear factor kappaB (p50), 46.9 and 44.9%, respectively], together with lower serum levels for inflammatory (TNF-alpha, 40.4% reduction) and cellular damage metabolites (LDH, 52.7% reduction). Collectively, these results suggest that pharmacological Rac1 inhibition ameliorates the severity of pancreatitis and pancreatitis-associated lung injury through the reduction of pancreatic acinar damage induced by pathological digestive enzyme secretion and overproduction of ROS.

Constitutive IKK2 activation in acinar cells is sufficient to induce pancreatitis in vivo

Activation of the inhibitor of NF-kappaB kinase/NF-kappaB (IKK/NF-kappaB) system and expression of proinflammatory mediators are major events in acute pancreatitis. However, the in vivo consequences of IKK activation on the onset and progression of acute pancreatitis remain unclear. Therefore, we modulated IKK activity conditionally in pancreatic acinar cells. Transgenic mice expressing the reverse tetracycline-responsive transactivator (rtTA) gene under the control of the rat elastase promoter were generated to mediate acinar cell-specific expression of IKK2 alleles. Expression of dominant-negative IKK2 ameliorated cerulein-induced pancreatitis but did not affect activation of trypsin, an initial event in experimental pancreatitis. Notably, expression of constitutively active IKK2 was sufficient to induce acute pancreatitis. This acinar cell-specific phenotype included edema, cellular infiltrates, necrosis, and elevation of serum lipase levels as well as pancreatic fibrosis. IKK2 activation caused increased expression of known NF-kappaB target genes, including mediators of the inflammatory response such as TNF-alpha and ICAM-1. Indeed, inhibition of TNF-alpha activity identified this cytokine as an important effector of IKK2-induced pancreatitis. Our data identify the IKK/NF-kappaB pathway in acinar cells as being key to the development of experimental pancreatitis and the major factor in the inflammatory response typical of this disease.

Pancreas-specific RelA/p65 truncation increases susceptibility of acini to inflammation-associated cell death following cerulein pancreatitis

Activation of the transcription factor NF-kappaB/Rel has been shown to be involved in inflammatory disease. Here we studied the role of RelA/p65, the main transactivating subunit, during acute pancreatitis using a Cre-loxP strategy. Selective truncation of the rela gene in pancreatic exocrine cells led to both severe injury of the acinar cells and systemic complications including lung and liver damage. Our data demonstrated that expression and induction of the protective pancreas-specific acute phase protein pancreatitis-associated protein 1 (PAP1) depended on RelA/p65. Lentiviral gene transfer of PAP1 cDNA reduced the extent of necrosis and infiltration in the pancreata of mice with selective truncation of RelA/p65. These results provide in vivo evidence for RelA/p65 protection of acinar cell death via upregulation of PAP1. Moreover, our data underscore the pancreas-specific role of NF-kappaB/Rel and suggest multidimensional roles of NF-kappaB/Rel in different cells and contexts during inflammation.

Why does pancreatic overstimulation cause pancreatitis?

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

Structure and Function of Cationic Amino Acid Transporters (CATs)

The CAT proteins (CAT for cationic amino acid transporter) are amongst the first mammalian amino acid transporters identified on the molecular level and seem to be the major entry path for cationic amino acids in most cells. However, CAT proteins mediate also efflux of their substrates and thus may also deplete cells from cationic amino acids under certain circumstances. The CAT proteins form a subfamily of the solute carrier family 7 (SLC7) that consists of four confirmed transport proteins for cationic amino acids: CAT-1 (SLC7A1), CAT-2A (SLC7A2A), CAT-2B (SLC7A2B), and CAT-3 (SLC7A3). SLC7A4 and SLC7A14 are two related proteins with yet unknown function. One focus of this review lies on structural and functional differences between the different CAT isoforms. The expression of the CAT proteins is highly regulated on the level of transcription, mRNA stability, translation and subcellular localization. Recent advances toward a better understanding of these mechanisms provide a second focus of this review.

Translocation of endothelial nitric-oxide synthase involves a ternary complex with caveolin-1 and NOSTRIN

Recently, we characterized a novel endothelial nitric-oxide synthase (eNOS)-interacting protein, NOSTRIN (for eNOS-trafficking inducer), which decreases eNOS activity upon overexpression and induces translocation of eNOS away from the plasma membrane. Here, we show that NOSTRIN directly binds to caveolin-1, a well-established inhibitor of eNOS. Because this interaction occurs between the N terminus of caveolin (positions 1-61) and the central domain of NOSTRIN (positions 323-434), it allows for independent binding of each of the two proteins to eNOS. Consistently, we were able to demonstrate the existence of a ternary complex of NOSTRIN, eNOS, and caveolin-1 in Chinese hamster ovary (CHO)-eNOS cells. In human umbilical vein endothelial cells (HUVECs), the ternary complex assembles at the plasma membrane upon confluence or thrombin stimulation. In CHO-eNOS cells, NOSTRIN-mediated translocation of eNOS involves caveolin in a process most likely representing caveolar trafficking. Accordingly, trafficking of NOSTRIN/eNOS/caveolin is affected by altering the state of actin filaments or cholesterol levels in the plasma membrane. During caveolar trafficking, NOSTRIN functions as an adaptor to recruit mediators such as dynamin-2 essential for membrane fission. We propose that a ternary complex between NOSTRIN, caveolin-1, and eNOS mediates translocation of eNOS, with important implications for the activity and availability of eNOS in the cell.

Mechanisms of acinar cell injury in acute pancreatitis

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

Expression of mutated cationic trypsinogen reduces cellular viability in AR4-2J cells

Mutations in the human cationic trypsinogen are associated with hereditary pancreatitis. The cDNA coding for human cationic trypsinogen was subcloned into the expression vector pcDNA3. The mutations R122H, N29I, A16V, D22G, and K23R were introduced by site directed mutagenesis. We constructed an expression vector coding for active trypsin by subcloning the cDNA of trypsin lacking the coding region for the trypsin activating peptide behind an appropriate signal peptide. Expression of protein was verified by Western blot and measurement of enzymatic activity. AR4-2J cells were transiently transfected with the different expression vectors and cell viability and intracellular caspase-3 activity were quantified. In contrast to wild-type trypsinogen, expression of active trypsin and mutated trypsinogens reduced cell viability of AR4-2J cells. Expression of trypsin and R122H trypsinogen induced caspase-3 activity. Acinar cells might react to intracellular trypsin activity by triggering apoptosis.

Altered posttranslational processing of glycoproteins in cerulein-induced pancreatitis

Acute pancreatitis is an auto-digestive disease resulting in inflammation. At the cellular level, acute pancreatitis disrupts posttranslational protein processing and traffic in the secretory pathway, and zymogens become activated in the acinar cell. To better understand the disruption of the secretory pathway in pancreatitis, pulse-chase [(35)S]met/cys analysis was used to study the effects of supramaximal cerulein stimulation on posttranslational modification in the secretory pathway of the major sulfated glycoprotein of the mouse pancreas, pro-Muclin, and the lysosomal membrane protein LAMP1. Maximal cerulein or high concentration bombesin stimulation had little effect on glycoprotein processing. By contrast, supramaximal cerulein stimulation strongly inhibited pro-Muclin processing as measured by the failure of Muclin to attain its normal mature size of 300 kDa and to become highly sulfated and decreased proteolytic cleavage of pro-Muclin to produce apactin. Digestion of immunoprecipitated [35S]met/cys-labeled Muclin and LAMP1 with endoglycosidase H demonstrated that the supramaximal cerulein-induced block in processing occurred before the medial Golgi compartment. With supramaximal cerulein stimulation, vacuoles formed which contained Muclin, amylase, and LAMP1. Earlier autoradiographic studies showed that newly synthesized proteins end up in pancreatitis-associated vacuoles, so it is likely that glycoproteins with incomplete posttranslational processing are also present in vacuoles. Because glycoproteins are believed to protect the membranes of lysosomes and zymogen granules, when they are not correctly processed, their defensive mechanisms may be impaired, and this could contribute to vacuole fragility in pancreatitis.

Regulation of CCK-induced amylase release by PKC-delta in rat pancreatic acinar cells

PKC is known to be activated by pancreatic secretagogues such as CCK and carbachol and to participate along with calcium in amylase release. Four PKC isoforms, alpha, delta, epsilon, and zeta, have been identified in acinar cells, but which isoforms participate in amylase release are unknown. To identify the responsible isoforms, we used translocation assays, chemical inhibitors, and overexpression of individual isoforms and their dominant-negative variants by means of adenoviral vectors. CCK stimulation caused translocation of PKC-alpha, -delta, and -epsilon, but not -zeta from soluble to membrane fraction. CCK-induced amylase release was inhibited approximately 30% by GF109203X, a broad spectrum PKC inhibitor, and by rottlerin, a PKC-delta inhibitor, but not by Gö6976, a PKC-alpha inhibitor, at concentrations from 1 to 5 microM. Neither overexpression of wild-type or dominant-negative PKC-alpha affected CCK-induced amylase release. Overexpression of PKC-delta and -epsilon enhanced amylase release, whereas only dominant-negative PKC-delta inhibited amylase release by 25%. PKC-delta overexpression increased amylase release at all concentrations of CCK, but dominant-negative PKC-delta only inhibited the maximal concentration; both similarly affected carbachol and JMV-180-induced amylase release. Overexpression of both PKC-delta and its dominant-negative variant affected the late but not the early phase of amylase release. GF109203X totally blocked the enhancement of amylase release by PKC-delta but had no further effect in the presence of dominant-negative PKC-delta. These results indicate that PKC-delta is the PKC isoform involved with amylase secretion.

Intercellular adhesion molecule-1 (ICAM-1) regulates endothelial cell motility through a nitric oxide-dependent pathway

Coordinated regulation of endothelial cell migration is an integral process during angiogenesis. However, molecular mechanisms regulating endothelial cell migration remain largely unknown. Increased expression of cell adhesion molecules has been implicated during angiogenesis, yet the precise role of these molecules is unclear. Here, we examined the hypothesis that intercellular adhesion molecule-1 (ICAM-1) is important for endothelial cell migration. Total cell displacement and directional migration were significantly attenuated in ICAM-1-deficient endothelium. Closer examination of ICAM-1-deficient cells revealed decreased Akt Thr(308) and endothelial nitric-oxide synthase Ser(1177) phosphorylation and NO bioavailability, increased actin stress fiber formation, and a lack of distinct cell polarity compared with wild-type endothelium. Supplementation of ICAM-1 mutant cells with the NO donor DETA NONOate (0.1 microM) corrected the migration defect, diminished stress fiber formation, and enhanced pseudopod and uropod formation. These data demonstrate that ICAM-1 facilitates the development of cell polarity and modulates endothelial cell migration through a pathway regulating endothelial nitric-oxide synthase activation and organization of the actin cytoskeleton.

Phosphatidylinositide 3-kinase gamma regulates key pathologic responses to cholecystokinin in pancreatic acinar cells

BACKGROUND & AIMS

Early events in the pancreatic acinar cell critical for development of pancreatitis include activation of the transcription factor nuclear factor kappa B (NF-kappa B), abnormal Ca(2+) responses, and trypsinogen activation. Mechanisms underlying these responses, which can be studied in isolated pancreatic acini stimulated with supraphysiologic doses of cholecystokinin (CCK-8), remain poorly understood. We here report that these responses are regulated by phosphatidylinositide 3-kinase (PI3K) gamma.

METHODS

To inactivate PI3K, we used mice deficient in the catalytic PI3K gamma subunit p110 gamma as well as the PI3K inhibitors LY294002 and wortmannin. We measured Ca(2+) responses by using Fura-2, NF-kappa B-binding activity by electromobility shift assay, I kappa B degradation by Western blotting, and trypsinogen activation by fluorogenic assay.

RESULTS

CCK-induced intracellular Ca(2+) mobilization, Ca(2+) influx, trypsinogen, and NF-kappa B activation were all diminished in pancreatic acini isolated from p110 gamma(-/-) mice. Both in mouse and rat acini, these responses were inhibited by the PI3K inhibitors. The Ca(2+) signal and trypsinogen activation were similarly reduced in acini isolated from p110 gamma(-/-) and p110 gamma(+/-) mice compared with wild-type mice. By contrast, NF-kappa B activation was inhibited in p110 gamma(-/-) acini but not in p110 gamma(+/-) acini. These differences indicate that the mechanism of NF-kappa B regulation by PI3K gamma differs from those for the Ca(2+) and trypsinogen responses. CCK-induced responses in p110 gamma(-/-) acini were all further inhibited by LY294002, indicating the involvement of other PI3K isoform(s), in addition to PI3K gamma.

CONCLUSIONS

The results show that key pathologic responses of the pancreatic acinar cell are regulated by PI3K gamma and suggest an important role for this PI3K isoform in pancreatitis.

Involvement of M3 cholinergic receptor signal transduction pathway in regulation of the expression of chemokine MOB-1, MCP-1 genes in pancreatic acinar cells

Whether M3 cholinergic receptor signal transduction pathway is involved in regulation of the activation of NF-kappaB and the expression of chemokine MOB-1, MCP-lgenes in pancreatic acinar cells was investigated. Rat pancreatic acinar cells were isolated, cultured and treated with carbachol, atropine and PDTC in vitro. The MOB-1 and MCP-1 mRNA expression was detected by using RT-PCR. The activation of NF-kappaB was monitored by using electrophoretic mobility shift assay. The results showed that as compared with control group, M3 cholinergic receptor agonist (10(-3) mol/L, 10(-4) mol/L carbachol) could induce a concentration-dependent and time-dependent increase in the expression of MOB-1, MCP-1 mRNA in pancreatic acinar cells. After treatment with 10(-3) mol/L carbachol for 2 h, the expression of MOB-1, MCP-1 mRNA was strongest. The activity of NF-kappaB in pancreatic acinar cells was significantly increased (P<0.01) after treated with M3 cholinergic receptor agonist (10(-3) mol/L carbachol) in vitro for 30 min. Either M3 cholinergic receptor antagonist (10(-5) mol/L atropine) or NF-kappaB inhibitor (10(-2) mol/L PDTC) could obviously inhibit the activation of NF-kappaB and the chemokine MOB-1, MCP-1 mRNA expression induced by carbachol (P<0.05). This inhibitory effect was significantly increased by atropine plus PDTC (P<0.01). The results of these studies indicated that M3 cholinergic receptor signal transduction pathway was likely involved in regulation of the expression of chemokine MOB-1 and MCP-lgenes in pancreatic acinar cells in vitro through the activation of NF-kappaB.

In vivo canine cardiac electrophysiologic profile of 1,4-benzodiazepine IKs blockers

Previous cardiac electrophysiologic studies of blockers of the slowly activating delayed rectifier (IKs) current have focused primarily on ventricular repolarization. This report summarizes an extensive in vivo cardiac electrophysiologic profile of four 1,4-benzodiazepine IKs blocker analogues (L-761334, L-763540, L-761710, and L-768673) in dogs. At 3.0 mg/kg intravenously, all four analogues elicited 14.5%-21.4% increases in ventricular refractoriness and 19.2%-22.6% increases in QTc interval. Concomitant 11.1%-13.5% increases in atrial refractoriness were noted with all four analogues. Decreases in sinus heart rate of 8.4%-17.3% were noted with all four compounds. No effects on atrial, His Purkinje, ventricular conduction or atrial and ventricular excitation were observed. One analogue, L-761710, significantly delayed atrioventricular (AV) nodal conduction (40.7+/-17.4% increase in atrial-to-His interval) and increased the AV conduction system functional refractory period 19.9+/-6.2%. The lack of effect of the other three 1,4-benzodiazepine IKs blockers on AV nodal function at dosages producing comparable effects on atrial and ventricular refractoriness suggest that the AV nodal effects of L-761710 were unrelated to IKs blockade. These findings indicate IKs plays important roles in both atrial and ventricular refractoriness as well as pacemaker function in the dog heart, suggesting potential utility for IKs blockers in the treatment of atrial and ventricular arrhythmias.