Mitochondrial mechanisms of death responses in pancreatitis

PINK1/PARK2 dependent mitophagy effectively suppresses NLRP3 inflammasome to alleviate acute pancreatitis

BACKGROUND

Acute pancreatitis (AP) is a clinically common acute inflammatory disease in digestive system, leading to systemic inflammatory response syndrome (SIRS) and severe acute pancreatitis (SAP). It was reported that PINK1/PARK2 dependent mitophagy played an important role in various inflammatory diseases. However, its role in AP has not been elucidated. Herein, we explore the effect of mitophagy in the pathogenesis of AP.

METHODS

Firstly, we established cerulein-induced AP group and arginine-induced SAP group based on wild, PINK1^-/- and PARK2^-/- mice. Pancreatic samples were harvested for further investing the mitochondrial dynamics, mitophagy alterations, NLRP3 inflammatory pathway etc. Furthermore, peripheral blood mononuclear cells from SAP patients were collected to examine the expression of mitophagy-related indicators. Additionally, the interrelationship between mitophagy and NLRP3 inflammasome was also explored in AP.

RESULTS

It was confirmed that mitochondria were damaged in both AP and SAP models. The expressions of PINK1, PARK2 and mitochondrial autophagosomes were elevated in wild AP group, which were decreased in SAP group over time. Similarly, the expressions of PINK1 and PAKR2 in peripheral blood mononuclear cells were significantly lower in SAP patients. Besides, in PINK1^-/- and PARK2^-/- mice AP groups, more pronounced inflammatory infiltration, increased apoptotic and necrotic levels and upregulated NLRP3 inflammasome pathway were detected. After injection with MCC950, NLRP3 inflammasome production was notably reduced in PINK1^-/-and PARK2^-/-mice, which effectively alleviated the pancreatic damage and inflammatory cell infiltration.

CONCLUSION

Our study suggested that mitochondrial dysfunction activated PINK1/PARK2-mediated mitophagy in AP, while mitophagy was impaired in SAP. PINK1^-/- and PARK2^-/- mice were more sensitive to onset of SAP and the deficiency of mitophagy could lead to the formation of NLRP3 inflammasome.

Dehydrocholic Acid Ameliorates Sodium Taurocholate-Induced Acute Biliary Pancreatitis in Mice

Acute biliary pancreatitis (ABP) with a high mortality rate is an incurable digestive system disease induced by abnormal bile acid regurgitation due to the biliary obstruction. Dehydrocholic acid (DA) alleviates the severity of cholestatic hepatitis related to biliary inflammation, suggesting DA is potential to develop for the incurable ABP management. Here we identified DA potency and explored the underlying mechanism in ABP. Our data showed that DA administration not only reduced typically clinicopathological parameters including serum levels of amylase and lipase but also suppressed pancreatic tissue edema, necrosis and trypsin activation in ABP mice. We also found that DA significantly reduced the necrosis of pancreatic acinar cells induced by sodium taurocholate (NaT). Further experimental data showed the significant inhibitions of DA on mitochondrial membrane potential depolarization, ATP exhaustion, calcium overload and reactive oxygen species (ROS) erupted in acinar cells induced by NaT, indicating DA could avert acinar cell death through protecting the mitochondrial function, scavenging excessive oxidative stress and balancing calcium. The comprehensive study found DA elevated the expression of transcription factor EB (TFEB) in vitro thus to increase the functional lysosome content. Indeed, DA decreased the Microtubule-associated protein light chain 3 (LC3) II/I ratio as well as ubiquitin-binding protein p62 and Parkin expressions in vivo and in vitro, revealing autophagy restoration maybe through the improvement of TFEB-mediated lysosome biogenesis. These data indicate that DA improves ABP through the mitochondrial protection, antioxidant ability enhancement and autophagy recovery. In conclusion, our study proposes a potential therapy strategy for the incurable ABP.

Gut Barrier Dysfunction Induced by Aggressive Fluid Resuscitation in Severe Acute Pancreatitis is Alleviated by Necroptosis Inhibition in Rats

Fluid resuscitation is the first-line antishock treatment in severe acute pancreatitis (SAP). Currently, although mentions of complications related to aggressive fluid resuscitation are very frequent, a lack of proper handling of complications remains. One of the most important complications is intestinal barrier injury, including intestinal ischemia-reperfusion injury following aggressive fluid resuscitation. Once injured, the intestinal barrier may serve as the source of additional diseases, including systemic inflammatory response syndrome and multiple organ dysfunction syndrome, which aggravate SAP. This study focused on the underlying mechanisms of gut barrier dysfunction in rats induced by aggressive fluid resuscitation in SAP. This study further indicated the important role of necroptosis in intestinal barrier injury which could be relieved by using necroptosis-specific inhibitor Nec-1 before aggressive fluid resuscitation, thus reducing intestinal barrier damage. We also found pancreas damage after intestinal ischemia/reperfusion challenge and indicated the effects of high mobility group protein B1 in the vicious cycle between SAP and intestinal barrier damage.

Novel mitochondrial transition pore inhibitor N-methyl-4-isoleucine cyclosporin is a new therapeutic option in acute pancreatitis

KEY POINTS

•Bile acids, ethanol and fatty acids affect pancreatic ductal fluid and bicarbonate secretion via mitochondrial damage, ATP depletion and calcium overload. •Pancreatitis-inducing factors open the membrane transition pore (mPTP) channel via cyclophilin D activation in acinar cells, causing calcium overload and cell death; genetic or pharmacological inhibition of mPTP improves the outcome of acute pancreatitis in animal models. •Here we show that genetic and pharmacological inhibition of mPTP protects mitochondrial homeostasis and cell function evoked by pancreatitis-inducing factors in pancreatic ductal cells. •The results also show that the novel cyclosporin A derivative NIM811 protects mitochondrial function in acinar and ductal cells, and it preserves bicarbonate transport mechanisms in pancreatic ductal cells. •We found that NIM811 is highly effective in different experimental pancreatitis models and has no side-effects. NIM811 is a highly suitable compound to be tested in clinical trials.

ABSTRACT

Mitochondrial dysfunction plays a crucial role in the development of acute pancreatitis (AP); however, no compound is currently available with clinically acceptable effectiveness and safety. In this study, we investigated the effects of a novel mitochondrial transition pore inhibitor, N-methyl-4-isoleucine cyclosporin (NIM811), in AP. Pancreatic ductal and acinar cells were isolated by enzymatic digestion from Bl/6 mice. In vitro measurements were performed by confocal microscopy and microfluorometry. Preventative effects of pharmacological [cylosporin A (2 µm), NIM811 (2 µm)] or genetic (Ppif^-/- /Cyp D KO) inhibition of the mitochondrial transition pore (mPTP) during the administration of either bile acids (BA) or ethanol + fatty acids (EtOH+FA) were examined. Toxicity of mPTP inhibition was investigated by detecting apoptosis and necrosis. In vivo effects of the most promising compound, NIM811 (5 or 10 mg kg^-1 per os), were checked in three different AP models induced by either caerulein (10 × 50 µg kg^-1 ), EtOH+FA (1.75 g kg^-1 ethanol and 750 mg kg^-1 palmitic acid) or 4% taurocholic acid (2 ml kg^-1 ). Both genetic and pharmacological inhibition of Cyp D significantly prevented the toxic effects of BA and EtOH+FA by restoring mitochondrial membrane potential (Δψ) and preventing the loss of mitochondrial mass. In vivo experiments revealed that per os administration of NIM811 has a protective effect in AP by reducing oedema, necrosis, leukocyte infiltration and serum amylase level in AP models. Administration of NIM811 had no toxic effects. The novel mitochondrial transition pore inhibitor NIM811 thus seems to be an exceptionally good candidate compound for clinical trials in AP.

Hypoxia-Inducible Factor-1α Knockdown Plus Glutamine Supplementation Attenuates the Predominance of Necrosis over Apoptosis by Relieving Cellular Energy Stress in Acute Pancreatitis

The present study was conducted to investigate the effect and potential mechanism of hypoxia-inducible factor-1α (HIF-1α) genetic inhibition plus glutamine (Gln) supplementation on necrosis-apoptosis imbalance during acute pancreatitis (AP), with a specific focus on the regulations of intracellular energy metabolism status. Wistar rats and AR42J cells were used to establish AP models. When indicated, a HIF-1α knockdown with or without a Gln supplementation was administered. In vivo, local and systemic inflammatory injuries were assessed by serum cytokine measurement, H&E staining, and transmission electron microscope (TEM) observation of pancreatic tissue. In vitro, intracellular energy metabolism status was evaluated by measuring the intracellular adenosine triphosphate (ATP), lactic acid, and Ca²⁺ concentrations and the mitochondrial potential. In addition, changes in the apoptotic activity were analyzed using TUNEL staining in vivo and an apoptosis assay in vitro. HIF-1α knockdown alleviated AP-related inflammatory injury as indicated by the measurements of serum cytokines and examinations of TEM and H&E staining of pancreatic tissues. HIF-1α knockdown played an antioxidative role against AP-related injuries by preventing the increase in the intracellular Ca²⁺ concentration and the decrease in the mitochondrial membrane potential and subsequently by suppressing the glycolysis pathway and increasing energy anabolism in AR42J cells after AP induction. Apoptosis was significantly upregulated when HIF-1α was knocked down before AP induction due to an attenuation of the translocation of nuclear factor-kappa B to the nuclei. Furthermore, these merits of HIF-1α knockdown in the relief of the metabolic stress and upregulation of apoptosis were more significant when Gln was administered concomitantly. In conclusion, Gln-supplemented HIF-1α knockdown might be promising for the future management of AP by relieving the intracellular energy stress, thereby attenuating the predominance of necrosis over apoptosis.

GC-MS based metabolomics strategy to distinguish three types of acute pancreatitis

Acute pancreatitis (AP) is a progressive systemic inflammatory response with high morbidity and high mortality, which is mainly caused by alcohol, bulimia, gallstones and hyperlipidemia. The early diagnosis of different types of AP and further explore potential pathophysiological mechanism of each type of AP is beneficial for optimized treatment strategies and better patient's care. In this study, a metabolomics approach based on gas chromatography-mass spectrometry (GC-MS), and random forests algorithm was established to distinguish biliary acute pancreatitis (BAP), Hyperlipidemia acute pancreatitis (HLAP), and alcoholic acute pancreatitis (AAP), from healthy controls. The classification accuracies for BAP, HLAP, and AAP patients compared with healthy control, were 0.886, 0.906 and 0.857, respectively, by using 5-fold cross-validation method. And some special metabolites for each type of AP were discovered, such as l-Lactic acid, (R)-3-Hydroxybutyric acid, Phosphoric acid, Glycine, Erythronic acid, l-Phenylalanine, d-Galactose, l-Tyrosine, Arachidonic acid, Glycerol 1-hexadecanoate. Furthermore, associations between these metabolites with the metabolism of amino acids, fatty acids were identified. Our studies have illuminated the biomarkers and physiological mechanism of disease in a clinical setting, which suggested that metabolomics is a valuable tool for identifying the molecular mechanisms that are involved in the etiology of BAP, AAP, HLAP and thus novel therapeutic targets.

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.

Human Pancreatic Acinar Cells: Proteomic Characterization, Physiologic Responses, and Organellar Disorders in ex Vivo Pancreatitis

Knowledge of the molecular mechanisms of acute pancreatitis is largely based on studies using rodents. To assess similar mechanisms in humans, we performed ex vivo pancreatitis studies in human acini isolated from cadaveric pancreata from organ donors. Because data on these human acinar preparations are sparse, we assessed their functional integrity and cellular and organellar morphology using light, fluorescence, and electron microscopy; and their proteome by liquid chromatography-tandem mass spectrometry. Acinar cell responses to the muscarinic agonist carbachol (CCh) and the bile acid taurolithocholic acid 3-sulfate were also analyzed. Proteomic analysis of acini from donors of diverse ethnicity showed similar profiles of digestive enzymes and proteins involved in translation, secretion, and endolysosomal function. Human acini preferentially expressed the muscarinic acetylcholine receptor M3 and maintained physiological responses to CCh for at least 20 hours. As in rodent acini, human acini exposed to toxic concentrations of CCh and taurolithocholic acid 3-sulfate responded with trypsinogen activation, decreased cell viability, organelle damage manifest by mitochondrial depolarization, disordered autophagy, and pathological endoplasmic reticulum stress. Human acini also secreted inflammatory mediators elevated in acute pancreatitis patients, including IL-6, tumor necrosis factor-α, IL-1β, chemokine (C-C motif) ligands 2 and 3, macrophage inhibitory factor, and chemokines mediating neutrophil and monocyte infiltration. In conclusion, human cadaveric pancreatic acini maintain physiological functions and have similar pathological responses and organellar disorders with pancreatitis-causing treatments as observed in rodent acini.

High versus low energy administration in the early phase of acute pancreatitis (GOULASH trial): protocol of a multicentre randomised double-blind clinical trial

INTRODUCTION

Acute pancreatitis (AP) is an inflammatory disease with no specific treatment. Mitochondrial injury followed by ATP depletion in both acinar and ductal cells is a recently discovered early event in its pathogenesis. Importantly, preclinical research has shown that intracellular ATP delivery restores the physiological function of the cells and protects from cell injury, suggesting that restoration of energy levels in the pancreas is therapeutically beneficial. Despite several high quality experimental observations in this area, no randomised trials have been conducted to date to address the requirements for energy intake in the early phase of AP.

METHODS/DESIGN

This is a randomised controlled two-arm double-blind multicentre trial. Patients with AP will be randomly assigned to groups A (30 kcal/kg/day energy administration starting within 24 hours of hospital admission) or B (low energy administration during the first 72 hours of hospital admission). Energy will be delivered by nasoenteric tube feeding with additional intravenous glucose supplementation or total parenteral nutrition if necessary. A combination of multiorgan failure for more than 48 hours and mortality is defined as the primary endpoint, whereas several secondary endpoints such as length of hospitalisation or pain will be determined to elucidate more detailed differences between the groups. The general feasibility, safety and quality checks required for high quality evidence will be adhered to.

ETHICS AND DISSEMINATION

The study has been approved by the relevant organisation, the Scientific and Research Ethics Committee of the Hungarian Medical Research Council (55961-2/2016/EKU). This study will provide evidence as to whether early high energy nutritional support is beneficial in the clinical management of AP. The results of this trial will be published in an open access way and disseminated among medical doctors.

TRIAL REGISTRATION

The trial has been registered at the ISRCTN (ISRTCN 63827758).

Methylene blue attenuates mitochondrial dysfunction of rat kidney during experimental acute pancreatitis

OBJECTIVE

The disturbance of mitochondrial functions has been considered as one of the mechanisms of pathogenesis of acute pancreatitis (AP) followed by kidney failure. This study was aimed to investigate the effects of methylene blue (MB) on pancreas and kidney mitochondrial respiratory functions during experimental acute pancreatitis in rats.

METHODS

AP was induced by administrating sodium taurocholate into the pancreatic duct of male Wistar rats. The rats were divided into three groups: the MB group, MB (5 mg/kg) was injected intravenously 10 min prior to AP induction; the AP group, saline solution was injected intravenously 10 min prior to AP induction; and the sham operation group, isotonic sodium chlorine was used instead of sodium taurocholate. The animals were sacrificed after 24 h. The pancreas and kidney were removed for mitochondrial assay by oxygraphic and spectrophotometric methods.

RESULTS

Intravenous injection of MB did not prevent AP-induced inhibition of pancreatic mitochondrial respiration; however, MB significantly improved kidney mitochondrial respiratory functions with complex I-dependent substrates glutamate and malate. The activity of complex I of mitochondria isolated from AP-damaged kidney was increased after pretreatment with MB. However, MB did not affect AP-inhibited kidney mitochondrial respiration with succinate. MB had no protective effects on amylase activity or on urea content in serum in AP.

CONCLUSION

The disturbances of kidney mitochondrial energy metabolism in experimental model of severe AP can be ameliorated by MB administration.

Impact of a novel homozygous mutation in nicotinamide nucleotide transhydrogenase on mitochondrial DNA integrity in a case of familial glucocorticoid deficiency

BACKGROUND

Familial Glucocorticoid Deficiency (FGD) is a rare autosomal recessive disorder that is characterized by isolated glucocorticoid deficiency. Recently, mutations in the gene encoding for the mitochondrial nicotinamide nucleotide transhydrogenase (NNT) have been identified as a causative gene for FGD; however, no NNT activities have been reported in FGD patients carrying NNT mutations.

METHODS

Clinical, biochemical and molecular analyses of lymphocytes from FDG homozygous and heterozygous carriers for the F215S NNT mutation.

RESULTS

In this study, we described an FGD-affected Japanese patient carrying a novel NNT homozygous mutation (c.644T>C; F215S) with a significant loss-of-function (NNT activity = 31% of healthy controls) in peripheral blood cells' mitochondria. The NNT activities of the parents, heterozygous for the mutation, were 61% of controls.

CONCLUSIONS

Our results indicated that (i) mitochondrial biogenesis (citrate synthase activity) and/or mtDNA replication (mtDNA copy number) were affected at ≤60% NNT activity because these parameters were affected in individuals carrying either one or both mutated alleles; and (ii) other outcomes (mtDNA deletions, protein tyrosine nitration, OXPHOS capacity) were affected at ≤30% NNT activity as also observed in murine cerebellar mitochondria from C57BL/6J (NNT^-/-) vs. C57BL/6JN (NNT^+/+) substrains.

GENERAL SIGNIFICANCE

By studying a family affected with a novel point mutation in the NNT gene, a gene-dose response was found for various mitochondrial outcomes providing for novel insights into the role of NNT in the maintenance of mtDNA integrity beyond that described for preventing oxidative stress.

Serum profiles of M30, M65 and interleukin-17 compared with C-reactive protein in patients with mild and severe acute pancreatitis

BACKGROUND

Several studies state that a test of severity early in the course of acute pancreatitis is still needed. In this prospective study, an assay of the biomarkers M30 and M65 as well as of interleukin 17 (IL-17) is investigated.

METHODS

One hundred and fifty patients and 70 controls were evaluated. The prognostic value of M30, M65 and their ratio M30/M65 is assessed by ELISA. The same method is used for the study of IL-17.

RESULTS

At 24 h after symptom onset, the concentrations of M30 and M65 as well as their ratio, differed significantly in severe compared to mild disease (P = 0.016). C-reactive protein (CRP) was significantly higher (P < 0.001) in severe pancreatitis on the same day. The sensitivity of M65 to show severe acute pancreatitis at 24 h was 100% for values above the cut-off point of 428.15 U/l. The sensitivity of CRP was 100% as well. Concerning IL-17, its concentrations were higher in patients than in the control group (P < 0.001) in the first 24 h.

CONCLUSIONS

Plasma concentrations of M65 and the M30/M65 ratio can be useful in predicting the severity of acute pancreatitis as early as 24 h after the onset of symptoms. The rates of IL-17 early in the course of acute pancreatitis are indicative of the disease.

Differences in the degree of cerulein-induced chronic pancreatitis in C57BL/6 mouse substrains lead to new insights in identification of potential risk factors in the development of chronic pancreatitis

A frequently used experimental model of chronic pancreatitis (CP) recapitulating human disease is repeated injection of cerulein into mice. C57BL/6 is the most commonly used inbred mouse strain for biomedical research, but widespread demand has led to generation of several substrains with subtly different phenotypes. In this study, two common substrains, C57BL/6J and C57BL/6NHsd, exhibited different degrees of CP, with C57BL/6J being more susceptible to repetitive cerulein-induced CP as assessed by pancreatic atrophy, pancreatic morphological changes, and fibrosis. We hypothesized that the deficiency of nicotinamide nucleotide transhydrogenase (NNT) protein in C57BL/6J is responsible for the more severe C57BL/6J phenotype but the parameters of CP in NNT-expressing transgenic mice generated on a C57BL6/J background do not differ with those of wild-type C57BL/6J. The highly similar genetic backgrounds but different CP phenotypes of these two substrains presents a unique opportunity to discover genes important in pathogenesis of CP. We therefore performed whole mouse genome Affymetrix microarray analysis of pancreatic gene expression of C57BL/6J and C57BL/6NHsd before and after induction of CP. Genes with differentially regulated expression between the two substrains that might be candidates in CP progression included Mmp7, Pcolce2, Itih4, Wdfy1, and Vtn. We also identified several genes associated with development of CP in both substrains, including RIKEN cDNA 1810009J06 gene (trypsinogen 5), Ccl8, and Ccl6.

Experimental acute pancreatitis induces mitochondrial dysfunction in rat pancreas, kidney and lungs but not in liver

BACKGROUND/AIMS

Excessive systemic inflammatory response syndrome during severe acute pancreatitis (AP) leads to multiple organ dysfunction syndrome, which is the main cause of death and may be associated with primary mitochondrial disturbances. The aim of our study was to evaluate the role of mitochondria during experimental AP in pancreas and vital organs like kidney, lungs and liver within the first 48 h.

METHODS

AP was induced in 39 male Wistar rats by intraductal application of sodium taurocholate (5%, 1.75 ml/kg). Animals were divided into groups reflecting the time from induction of the AP till collection of tissues (control and 1, 3, 6, 12, 24, 48 h). Mitochondria were isolated by differential centrifugation and mitochondrial respiration rates were measured oxygraphically.

RESULTS

(1) Mitochondria in pancreas are affected within the first 6 h after onset of AP, (2) kidney mitochondria are affected 24 h after onset of AP, (3) lungs mitochondria are affected within 48 h after onset of AP whereas (4) liver mitochondria remain well preserved within the first 48 h. Severe AP-induced decrease in the oxidative phosphorylation of pancreas, kidney and lungs mitochondria was more pronounced with Complex I-linked (glutamate/malate) than with Complex II-linked (succinate) substrates and was associated with inhibition of Complex I.

CONCLUSION

Our data show that the disturbances of mitochondrial energy metabolism in pancreas, kidney and lungs may play an important role in the development and progression of AP as a systemic disease.

Central role of mitochondrial injury in the pathogenesis of acute pancreatitis

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

Impaired autophagy and organellar dysfunction in pancreatitis

Recent findings from our group, obtained on experimental in vivo and ex vivo models of pancreatitis, reveal that this disease causes a profound dysfunction of key cellular organelles, lysosomes and mitochondria. We found that autophagy, the main cellular degradative, lysosome-driven process, is activated but also impaired in acute pancreatitis because of its' inefficient progression/resolution (flux) resulting from defective function of lysosomes. One mechanism underlying the lysosomal dysfunction in pancreatitis is abnormal processing (maturation) and activation of cathepsins, major lysosomal hydrolases; another is a decrease in pancreatic levels of key lysosomal membrane proteins LAMP-1 and LAMP-2. Our data indicate that lysosomal dysfunction plays an important initiating role in pancreatitis pathobiology. The impaired autophagy mediates vacuole accumulation in acinar cells; furthermore, the abnormal maturation and activation of cathepsins leads to increase in intra-acinar trypsin, the hallmark of pancreatitis; and LAMP-2 deficiency causes inflammation and acinar cell necrosis. Thus, the autophagic and lysosomal dysfunctions mediate key pathologic responses of pancreatitis. On the other hand, we showed that pancreatitis causes acinar cell mitochondria depolarization, mediated by the permeability transition pore (PTP). Genetic (via deletion of cyclophilin D) inactivation of PTP prevents mitochondrial depolarization and greatly ameliorates the pathologic responses of pancreatitis. Further, our data suggest that mitochondrial damage, by stimulating autophagy, increases the demand for efficient lysosomal degradation and therefore aggravates the pathologic consequences of lysosomal dysfunction. Thus, the combined autophagic, lysosomal and mitochondrial dysfunctions are key to the pathogenesis of pancreatitis.

Insulin protects pancreatic acinar cells from cytosolic calcium overload and inhibition of plasma membrane calcium pump

Acute pancreatitis is a serious and sometimes fatal inflammatory disease of the pancreas without any reliable treatment or imminent cure. In recent years, impaired metabolism and cytosolic Ca(2+) ([Ca(2+)](i)) overload in pancreatic acinar cells have been implicated as the cardinal pathological events common to most forms of pancreatitis, regardless of the precise causative factor. Therefore, restoration of metabolism and protection against cytosolic Ca(2+) overload likely represent key therapeutic untapped strategies for the treatment of this disease. The plasma membrane Ca(2+)-ATPase (PMCA) provides a final common path for cells to "defend" [Ca(2+)](i) during cellular injury. In this paper, we use fluorescence imaging to show for the first time that insulin treatment, which is protective in animal models and clinical studies of human pancreatitis, directly protects pancreatic acinar cells from oxidant-induced cytosolic Ca(2+) overload and inhibition of the PMCA. This protection was independent of oxidative stress or mitochondrial membrane potential but appeared to involve the activation of Akt and an acute metabolic switch from mitochondrial to predominantly glycolytic metabolism. This switch to glycolysis appeared to be sufficient to maintain cellular ATP and thus PMCA activity, thereby preventing Ca(2+) overload, even in the face of impaired mitochondrial function.

The crucial role of early mitochondrial injury in L-lysine-induced acute pancreatitis

AIMS

Large doses of intraperitoneally injected basic amino acids, L-arginine, or L-ornithine, induce acute pancreatitis in rodents, although the mechanisms mediating pancreatic toxicity remain unknown. Another basic amino acid, L-lysine, was also shown to cause pancreatic acinar cell injury. The aim of the study was to get insight into the mechanisms through which L-lysine damages the rat exocrine pancreas, in particular to characterize the kinetics of L-lysine-induced mitochondrial injury, as well as the pathologic responses (including alteration of antioxidant systems) characteristic of acute pancreatitis.

RESULTS

We showed that intraperitoneal administration of 2 g/kg L-lysine induced severe acute necrotizing pancreatitis. L-lysine administration caused early pancreatic mitochondrial damage that preceded the activation of trypsinogen and the proinflammatory transcription factor nuclear factor-κB (NF-κB), which are commonly thought to play an important role in the development of acute pancreatitis. Our data demonstrate that L-lysine impairs adenosine triphosphate synthase activity of isolated pancreatic, but not liver, mitochondria.

INNOVATION AND CONCLUSION

Taken together, early mitochondrial injury caused by large doses of L-lysine may lead to the development of acute pancreatitis independently of pancreatic trypsinogen and NF-κB activation.

Organellar dysfunction in the pathogenesis of pancreatitis

SIGNIFICANCE

Acute pancreatitis is an inflammatory disease of exocrine pancreas that carries considerable morbidity and mortality; its pathophysiology remains poorly understood. During the past decade, new insights have been gained into signaling pathways and molecules that mediate the inflammatory response of pancreatitis and death of acinar cells (the main exocrine pancreas cell type). By contrast, much less is known about the acinar cell organellar damage in pancreatitis and how it contributes to the disease pathogenesis.

RECENT ADVANCES

This review summarizes recent findings from our group, obtained on experimental in vivo and ex vivo models, which reveal disordering of key cellular organelles, namely, mitochondria, autophagosomes, and lysosomes, in pancreatitis. Our results indicate a critical role for mitochondrial permeabilization in determining the balance between apoptosis and necrosis in pancreatitis, and thus the disease severity. We further investigate how the mitochondrial dysfunction (and hence acinar cell death) is regulated by Ca(2+), reactive oxygen species, and Bcl-xL, in relation to specific properties of pancreatic mitochondria. Our results also reveal that autophagy, the principal cellular degradative, lysosome-driven pathway, is impaired in pancreatitis due to inefficient lysosomal function, and that impaired autophagy mediates two key pathological responses of pancreatitis-accumulation of vacuoles in acinar cells and the abnormal, intra-acinar activation of digestive enzymes such as trypsinogen.

CRITICAL ISSUES AND FUTURE DIRECTIONS

The findings discussed in this review indicate critical roles for mitochondrial and autophagic/lysosomal dysfunctions in the pathogenesis of pancreatitis and delineate directions for detailed investigations into the molecular events that underlie acinar cell organellar damage.

Investigating the pathobiology of alcoholic pancreatitis

Alcohol abuse is one of the most common causes of pancreatitis. The risk of developing alcohol-induced pancreatitis is related to the amount and duration of drinking. However, only a small portion of heavy drinkers develop disease, indicating that other factors (genetic, environmental, or dietary) contribute to disease initiation. Epidemiologic studies suggest roles for cigarette smoking and dietary factors in the development of alcoholic pancreatitis. The mechanisms underlying alcoholic pancreatitis are starting to be understood. Studies from animal models reveal that alcohol sensitizes the pancreas to key pathobiologic processes that are involved in pancreatitis. Current studies are focussed on the mechanisms responsible for the sensitizing effect of alcohol; recent findings reveal disordering of key cellular organelles including endoplasmic reticulum, mitochondria, and lysosomes. As our understanding of alcohol's effects continue to advance to the level of molecular mechanisms, insights into potential therapeutic strategies will emerge providing opportunities for clinical benefit.

Acute pancreatitis

Acute pancreatitis (AP) is an important cause of morbidity and mortality worldwide and the annual incidence appears to be increasing. It presents as a mild self-limiting illness in 80% of patients. However, one-fifth of these develop a severe complicated life-threatening disease requiring intensive and prolonged therapeutic intervention. Alcohol and gallstone disease remain the commonest causes of AP but metabolic abnormalities, obesity and genetic susceptibility are thought be increasingly important aetiological factors. The prompt diagnosis of AP and stratification of disease severity is essential in directing rapid delivery of appropriate therapeutic measures. In this review, the range of diagnostic and prognostic assays, severity scoring systems and radiological investigations used in current clinical practice are described, highlighting their strengths and weaknesses. Increased understanding of the complex pathophysiology of AP has generated an array of new potential diagnostic assays and these are discussed. The multidisciplinary approach to management of severe pancreatitis is outlined, including areas of controversy and novel treatments.

Prosurvival Bcl-2 proteins stabilize pancreatic mitochondria and protect against necrosis in experimental pancreatitis

Acinar cells in pancreatitis die through apoptosis and necrosis, the roles of which are different. The severity of experimental pancreatitis correlates directly with the extent of necrosis and inversely, with apoptosis. Apoptosis is mediated by the release of cytochrome c into the cytosol followed by caspase activation, whereas necrosis is associated with the mitochondrial membrane potential (DeltaPsim) loss leading to ATP depletion. Here, we investigate the role of Bcl-2 proteins in apoptosis and necrosis in pancreatitis. We found up-regulation of prosurvival Bcl-2 proteins in pancreas in various experimental models of acute pancreatitis, most pronounced for Bcl-xL. This up-regulation translated into increased levels of Bcl-xL and Bcl-2 in pancreatic mitochondria. Bcl-xL/Bcl-2 inhibitors induced DeltaPsim loss and cytochrome c release in isolated mitochondria. Corroborating the results on mitochondria, Bcl-xL/Bcl-2 inhibitors induced DeltaPsim loss, ATP depletion and necrosis in pancreatic acinar cells, both untreated and hyperstimulated with CCK-8 (in vitro pancreatitis model). Together Bcl-xL/Bcl-2 inhibitors and CCK induced more necrosis than either treatment alone. Bcl-xL/Bcl-2 inhibitors also stimulated cytochrome c release in acinar cells leading to caspase-3 activation and apoptosis. However, different from their effect on pronecrotic signals, the stimulation by Bcl-xL/Bcl-2 inhibitors of apoptotic responses was less in CCK-treated than control cells. Therefore, Bcl-xL/Bcl-2 inhibitors potentiated CCK-induced necrosis but not apoptosis. Correspondingly, transfection with Bcl-xL siRNA stimulated necrosis but not apoptosis in the in vitro pancreatitis model. Further, in animal models of pancreatitis Bcl-xL up-regulation inversely correlated with necrosis, but not apoptosis. Results indicate that Bcl-xL and Bcl-2 protect acinar cells from necrosis in pancreatitis by stabilizing mitochondria against death signals. We conclude that Bcl-xL/Bcl-2 inhibition would aggravate acute pancreatitis, whereas Bcl-xL/Bcl-2 up-regulation presents a strategy to prevent or attenuate necrosis in pancreatitis.