Pathobiology of acute pancreatitis: focus on intracellular calcium and calmodulin

Mitochondrial depolarization and ATP loss during high frequency nanosecond and microsecond electroporation

It is predicted that ultra-short electric field pulses (nanosecond) can selectively permeabilize intracellular structures (e.g., mitochondria) without significant effects on the outer cell plasma membrane. Such a phenomenon would have high applicability in cancer treatment and could be employed to modulate cell death type or immunogenic response. Therefore, in this study, we compare the effects of 100 µs x 8 pulses (ESOPE - European Standard Operating Procedures on Electrochemotherapy) and bursts of 100 ns pulses for modulation of the mitochondria membrane potential. We characterize the efficacies of various protocols to trigger permeabilization, depolarize mitochondria (evaluated 1 h  after treatment), the extent of ATP depletion and generation of reactive oxygen species (ROS). Finally, we employ the most prominent protocols in the context of Ca2+ electrochemotherapy in vitro. We provide experimental proof that 7.5-12.5 kV/cm x 100 ns pulses can be used to modulate mitochondrial potential, however, the permeabilization of the outer membrane is still a prerequisite for depolarization. Similar to 100 µs x 8 pulses, the higher the permeabilization rate, the higher the mitochondrial depolarization. Nevertheless, 100 ns pulses result in lesser ROS generation when compared to ESOPE, even when the energy input is several-fold higher than for the microsecond procedure. At the same time, it shows that even the short 100 ns pulses can be successfully used for Ca2+ electrochemotherapy, ensuring excellent cytotoxic efficacy.

Lighting Up Ca2+ Dynamics in Animal Models

Calcium (Ca2+) signaling coordinates are crucial processes in brain physiology. Particularly, fundamental aspects of neuronal function such as synaptic transmission and neuronal plasticity are regulated by Ca2+, and neuronal survival itself relies on Ca2+-dependent cascades. Indeed, impaired Ca2+ homeostasis has been reported in aging as well as in the onset and progression of neurodegeneration. Understanding the physiology of brain function and the key processes leading to its derangement is a core challenge for neuroscience. In this context, Ca2+ imaging represents a powerful tool, effectively fostered by the continuous amelioration of Ca2+ sensors in parallel with the improvement of imaging instrumentation. In this review, we explore the potentiality of the most used animal models employed for Ca2+ imaging, highlighting their application in brain research to explore the pathogenesis of neurodegenerative diseases.

Over-the-Counter Drug Causing Acute Pancreatitis

Acute pancreatitis is caused by alcohol, gall stone disease, drugs, trauma, infections, and metabolic causes such as hypercalcemia and hyperlipidemia. Hypercalcemia-induced acute pancreatitis has been well documented but only rarely occurs due to over-the-counter calcium carbonate. In this article, we present a case of over-the-counter calcium carbonate–induced acute pancreatitis.

Nuclear Factor-κB Increases Intracellular Calcium by Upregulation of Na+-Ca2+ Exchanger 1 in Cerulein-Induced Acute Pancreatitis

OBJECTIVES

The mechanisms underlying pathogenesis of acute pancreatitis (AP) are still not completely understood. An early, critical feature of AP is aberrant calcium (Ca) signaling, termed Ca overload, within pancreatic acinar cells. This study aimed to develop a model system in rats for AP induction to study the contribution of the Na-Ca exchanger 1 (NCX1) ion channel in AP pathogenesis.

METHODS

To establish a rat model of AP induction, cerulein or L-arginine were intraperitoneally injected and tissue was histologically analyzed by hematoxylin and eosin staining. A cell culture-based model for AP induction was similarly created through cerulein treatment of AR42J cells. Induction of AP was also examined following exposure to the NXC1-targeted inhibitor KB-R7943. The expression of each gene was detected by Western blotting, immunofluorescence, immunohistochemistry, or quantitative reverse transcription polymerase chain reaction. Transcriptional regulation by nuclear factor (NF)-κB was detected using an NCX1 promoter-fusion dual luciferase reporter system. Cytosolic Ca was measured using a fluorescent calcium indicator.

RESULTS

We found that cerulein induced NCX1 expression via activation of nuclear factor NF-κB, which potentially binds to the NCX1 promoter to induce its transcription.

CONCLUSIONS

Our findings reveal a regulatory pathway through NF-κB/NCX1 governing Ca overload in AP development, thus providing potential targets for AP treatment.

Research Progress on the Relationship Between Acute Pancreatitis and Calcium Overload in Acinar Cells

Acute pancreatitis is a human disease with multiple causes that leads to autodigestion of the pancreas. There is sufficient evidence to support the key role of sustained increase in cytosolic calcium concentrations in the early pathogenesis of the disease. To clarify the mechanism of maintaining calcium homeostasis in the cell and pathological processes caused by calcium overload would help to research directly targeted therapeutic agents. We will specifically review the following: intracellular calcium homeostasis and regulation, the occurrence of calcium overload in acinar cells, the role of calcium overload in the pathogenesis of AP, the treatment strategy proposed for calcium overload.

ABT-199 (Venetoclax), a BH3-mimetic Bcl-2 inhibitor, does not cause Ca2+ -signalling dysregulation or toxicity in pancreatic acinar cells

BACKGROUND AND PURPOSE

Many cancer cells depend on anti-apoptotic B-cell lymphoma 2 (Bcl-2) proteins for their survival. Bcl-2 antagonism through Bcl-2 homology 3 (BH3) mimetics has emerged as a novel anti-cancer therapy. ABT-199 (Venetoclax), a recently developed BH3 mimetic that selectively inhibits Bcl-2, was introduced into the clinic for treatment of relapsed chronic lymphocytic leukaemia. Early generations of Bcl-2 inhibitors evoked sustained Ca²⁺ responses in pancreatic acinar cells (PACs) inducing cell death. Therefore, BH3 mimetics could potentially be toxic for the pancreas when used to treat cancer. Although ABT-199 was shown to kill Bcl-2-dependent cancer cells without affecting intracellular Ca²⁺ signalling, its effects on PACs have not yet been determined. Hence, it is essential and timely to assess whether this recently approved anti-leukaemic drug might potentially have pancreatotoxic effects.

EXPERIMENTAL APPROACH

Single-cell Ca²⁺ measurements and cell death analysis were performed on isolated mouse PACs.

KEY RESULTS

Inhibition of Bcl-2 via ABT-199 did not elicit intracellular Ca²⁺ signalling on its own or potentiate Ca²⁺ signalling induced by physiological/pathophysiological stimuli in PACs. Although ABT-199 did not affect cell death in PACs, under conditions that killed ABT-199-sensitive cancer cells, cytosolic Ca²⁺ extrusion was slightly enhanced in the presence of ABT-199. In contrast, inhibition of Bcl-xL potentiated pathophysiological Ca²⁺ responses in PACs, without exacerbating cell death.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that apart from having a modest effect on cytosolic Ca²⁺ extrusion, ABT-199 does not substantially alter intracellular Ca²⁺ homeostasis in normal PACs and should be safe for the pancreas during cancer treatment.

LINKED ARTICLES

This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Ca2+ signalling underlying pancreatitis

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

Novel lipophilic probe for detecting near-membrane reactive oxygen species responses and its application for studies of pancreatic acinar cells: effects of pyocyanin and L-ornithine

AIMS

The aim of this study was to develop a fluorescent reactive oxygen species (ROS) probe, which is preferentially localized in cellular membranes and displays a strong change in fluorescence upon oxidation. We also aimed to test the performance of this probe for detecting pathophysiologically relevant ROS responses in isolated cells.

RESULTS

We introduced a novel lipophilic ROS probe dihydrorhodamine B octadecyl ester (H2RB-C18). We then applied the new probe to characterize the ROS changes triggered by inducers of acute pancreatitis in pancreatic acinar cells. We resolved ROS changes produced by L-ornithine, L-arginine, cholecystokinin-8, acetylcholine, taurolithocholic acid 3-sulfate, palmitoleic acid ethyl ester, and the bacterial toxin pyocyanin. Particularly prominent ROS responses were induced by pyocyanin and L-ornithine. These ROS responses were accompanied by changes in cytosolic Ca(2+)concentration ([Ca(2+)]i), mitochondrial membrane potential (ΔΨ), and NAD(P)H concentration.

INNOVATION

The study describes a novel sensitive lipophilic ROS probe. The probe is particularly suitable for detecting ROS in near-membrane regions and therefore for reporting the ROS environment of plasma membrane channels and pumps.

CONCLUSIONS

In our experimental conditions, the novel probe was more sensitive than 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein (CM-H2DCF) and dihydrorhodamine123 (H2R123) and allowed us to resolve ROS responses to secretagogues, pyocyanin, and L-ornithine. Changes in the fluorescence of the new probe were particularly prominent in the peripheral plasma membrane-associated regions. Our findings suggest that the new probe will be a useful tool in studies of the contribution of ROS to the pathophysiology of exocrine pancreas and other organs/tissues.

Milk-alkali-induced pancreatitis in a chronically hypocalcemic patient with DiGeorge syndrome

BACKGROUND

Pancreatitis is a common diagnosis in the emergency department (ED), and milk-alkali syndrome (MAS) is an uncommon etiology for pancreatitis. MAS is caused by increased calcium and alkali ingestion, causing hypercalcemia accompanied by metabolic alkalosis and renal failure. Once considered rare, MAS is an increasingly common cause of hypercalcemia. Awareness of the resurgence of this syndrome is important for emergency physicians when recalling the causes of renal failure and pancreatitis. We present a case of pancreatitis and acute renal failure (ARF) in a chronically hypocalcemic DiGeorge syndrome patient, resulting from hypercalcemia secondary to excessive ingestion of calcium carbonate tablets.

CASE REPORT

A patient with DiGeorge syndrome and chronic abdominal pain due to gastroesophageal reflux disease (GERD) presented to our ED for severe abdominal pain. He reported nausea and vomiting, as well as epigastric pain that seemed worse than his typical pain. Laboratory evaluation revealed pancreatitis and ARF, although the patient had no prior history of these conditions. Upon further questioning, his mother divulged that the patient had been taking large quantities of calcium carbonate tablets for his worsening GERD symptoms. The patient was admitted to the intensive care unit where his pancreatitis and ARF eventually resolved as his calcium levels returned to his baseline. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: MAS is a relatively uncommon diagnosis, but can lead to serious sequelae such as pancreatitis and ARF. Questioning the patient about calcium ingestion is an important facet to the diagnosis and work-up of pancreatitis and ARF. Recognition of this etiology can improve patient outcomes and prevent recurrences.

Calcium signaling of pancreatic acinar cells in the pathogenesis of pancreatitis

Pancreatitis is an increasingly common and sometimes severe disease that lacks a specific therapy. The pathogenesis of pancreatitis is still not well understood. Calcium (Ca²⁺) is a versatile carrier of signals regulating many aspects of cellular activity and plays a central role in controlling digestive enzyme secretion in pancreatic acinar cells. Ca²⁺ overload is a key early event and is crucial in the pathogenesis of many diseases. In pancreatic acinar cells, pathological Ca²⁺ signaling (stimulated by bile, alcohol metabolites and other causes) is a key contributor to the initiation of cell injury due to prolonged and global Ca²⁺ elevation that results in trypsin activation, vacuolization and necrosis, all of which are crucial in the development of pancreatitis. Increased release of Ca²⁺ from stores in the intracellular endoplasmic reticulum and/or increased Ca²⁺ entry through the plasma membrane are causes of such cell damage. Failed mitochondrial adenosine triphosphate (ATP) production reduces re-uptake and extrusion of Ca²⁺ by the sarco/endoplasmic reticulum Ca²⁺-activated ATPase and plasma membrane Ca²⁺-ATPase pumps, which contribute to Ca²⁺ overload. Current findings have provided further insight into the roles and mechanisms of abnormal pancreatic acinar Ca²⁺ signals in pancreatitis. The lack of available specific treatments is therefore an objective of ongoing research. Research is currently underway to establish the mechanisms and interactions of Ca²⁺ signals in the pathogenesis of pancreatitis.

Anti-inflammatory effects of reactive oxygen species - a multi-valued logical model validated by formal concept analysis

Background

Recent findings suggest that in pancreatic acinar cells stimulated with bile acid, a pro-apoptotic effect of reactive oxygen species (ROS) dominates their effect on necrosis and spreading of inflammation. The first effect presumably occurs via cytochrome C release from the inner mitochondrial membrane. A pro-necrotic effect – similar to the one of Ca²⁺ – can be strong opening of mitochondrial pores leading to breakdown of the membrane potential, ATP depletion, sustained Ca²⁺ increase and premature activation of digestive enzymes. To explain published data and to understand ROS effects during the onset of acute pancreatitis, a model using multi-valued logic is constructed. Formal concept analysis (FCA) is used to validate the model against data as well as to analyze and visualize rules that capture the dynamics.

Results

Simulations for two different levels of bile stimulation and for inhibition or addition of antioxidants reproduce the qualitative behaviour shown in the experiments. Based on reported differences of ROS production and of ROS induced pore opening, the model predicts a more uniform apoptosis/necrosis ratio for higher and lower bile stimulation in liver cells than in pancreatic acinar cells. FCA confirms that essential dynamical features of the data are captured by the model. For instance, high necrosis always occurs together with at least a medium level of apoptosis. At the same time, FCA helps to reveal subtle differences between data and simulations. The FCA visualization underlines the protective role of ROS against necrosis.

Conclusions

The analysis of the model demonstrates how ROS and decreased antioxidant levels contribute to apoptosis. Studying the induction of necrosis via a sustained Ca²⁺ increase, we implemented the commonly accepted hypothesis of ATP depletion after strong bile stimulation. Using an alternative model, we demonstrate that this process is not necessary to generate the dynamics of the measured variables. Opening of plasma membrane channels could also lead to a prolonged increase of Ca²⁺ and to necrosis. Finally, the analysis of the model suggests a direct experimental testing for the model-based hypothesis of a self-enhancing cycle of cytochrome C release and ROS production by interruption of the mitochondrial electron transport chain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-014-0101-7) contains supplementary material, which is available to authorized users.

Molecular mechanisms of alcohol associated pancreatitis

Alcohol abuse is commonly associated with the development of both acute and chronic pancreatitis. Despite this close association, the fact that only a small percentage of human beings who abuse alcohol develop pancreatitis indicates that alcohol abuse alone is not sufficient to initiate clinical pancreatitis. This contention is further supported by the fact that administration of ethanol to experimental animals does not cause pancreatitis. Because of these findings, it is widely believed that ethanol sensitizes the pancreas to injury and additional factors trigger the development of overt pancreatitis. How ethanol sensitizes the pancreas to pancreatitis is not entirely known. Numerous studies have demonstrated that ethanol and its metabolites have a number of deleterious effects on acinar cells. Important acinar cells properties that are affected by ethanol include: calcium signaling, secretion of zymogens, autophagy, cellular regeneration, the unfolded protein response, and mitochondrial membrane integrity. In addition to the actions of ethanol on acinar cells, it is apparent that ethanol also affects pancreatic stellate cells. Pancreatic stellate cells have a critical role in normal tissue repair and the pathologic fibrotic response. Given that ethanol and its metabolites affect so many pancreatic functions, and that all of these effects occur simultaneously, it is likely that none of these effects is “THE” effect. Instead, it is most likely that the cumulative effect of ethanol on the pancreas predisposes the organ to pancreatitis. The focus of this article is to highlight some of the important mechanisms by which ethanol alters pancreatic functions and may predispose the pancreas to disease.

Identification of serum microRNAs as diagnostic and prognostic biomarkers for acute pancreatitis

BACKGROUND/OBJECTIVES

To identify serum microRNA (miRNA) as diagnostic and prognostic biomarkers for acute pancreatitis (AP).

MATERIALS AND METHODS

Sera microRNA expression was profiled from 12 AP patients with varying disease severity and three healthy controls. Differentially expressed miRNAs were validated in a larger cohort of patients and controls. The diagnostic and prognostic potentials of differentially expressed miRNAs were evaluated using receiver operating characteristic (ROC) curve analysis and compared to that of classic prognostic markers for AP.

RESULTS

miRNA microarray analyses identified 205 differentially expressed miRNAs between sera from AP patients and that from controls. Nine miRNAs were differentially expressed between severe and mild AP patients. Further validation confirmed the down-regulation of miR-92b, miR-10a, and miR-7 in AP patients, and ROC analysis revealed that these miRNAs can differentiate AP from health cases. Furthermore, the serum miR-551b-5p level was significantly higher in patients with disease complications or a low plasma calcium level. ROC analysis showed that the serum miR-551b-5p level can distinguish between severe and mild AP.

CONCLUSION

The expressions of miR-92b, miR-10a, and miR-7 in AP might be used for the early diagnosis of AP and miR-551b-5p may be used for predicting AP severity.

The role of calcium in acute pancreatitis

Until recently, it was unclear whether calcium is more than a bystander in the development of acute pancreatitis. Now important evidence has been accumulated supporting a pivotal role of intracellular levels of calcium in the early pathogenesis of the disease. A sustained increase of cytosolic calcium concentrations, as observed in various models of acute pancreatitis, was identified as sabotaging crucial cellular defense mechanisms and initiating premature trypsinogen activation. These processes lead the acinar cell to necrosis, with spillage of activated proteases into the interstitial space, affecting surrounding acinar cells and initiating a vicious circle that ends in macroscopic acute pancreatitis and systemic inflammatory response syndrome. Comprehensive knowledge of the pathobiology of cytosolic calcium in the pancreatic acinar cell is leading to the understanding of coherent molecular pathways of early events in the pathogenesis of acute pancreatitis and is opening horizons for research into directly targeted therapeutic agents.

Urinary plasmin inhibits TRPV5 in nephrotic-range proteinuria

Urinary proteins that leak through the abnormal glomerulus in nephrotic syndrome may affect tubular transport by interacting with membrane transporters on the luminal side of tubular epithelial cells. Patients with nephrotic syndrome can develop nephrocalcinosis, which animal models suggest may develop from impaired transcellular Ca(2+) reabsorption via TRPV5 in the distal convoluted tubule (DCT). In nephrotic-range proteinuria, filtered plasminogen reaches the luminal side of DCT, where it is cleaved into active plasmin by urokinase. In this study, we found that plasmin purified from the urine of patients with nephrotic-range proteinuria inhibits Ca(2+) uptake in TRPV5-expressing human embryonic kidney 293 cells through the activation of protease-activated receptor-1 (PAR-1). Preincubation with a plasmin inhibitor, a PAR-1 antagonist, or a protein kinase C (PKC) inhibitor abolished the effect of plasmin on TRPV5. In addition, ablation of the PKC phosphorylation site S144 rendered TRPV5 resistant to the action of plasmin. Patch-clamp experiments showed that a decreased TRPV5 pore size and a reduced open probability accompany the plasmin-mediated reduction in Ca(2+) uptake. Furthermore, high-resolution nuclear magnetic resonance spectroscopy demonstrated specific interactions between calmodulin and residues 133-154 of the N-terminus of TRPV5 for both wild-type and phosphorylated (S144pS) peptides. In summary, PAR-1 activation by plasmin induces PKC-mediated phosphorylation of TRPV5, thereby altering calmodulin-TRPV5 binding, resulting in decreased channel activity. These results indicate that urinary plasmin could contribute to the downstream effects of proteinuria on the tubulointerstitium by negatively modulating TRPV5.

Expression of calmodulin in germ cells is associated with fenvalerate-induced male reproductive toxicity

Exposure to fenvalerate was demonstrated to be toxic to the male reproductive system. Our previous data revealed that intracellular calcium plays an important role in regulating the above toxicity, through actions on both T-type calcium channels and endoplasmic reticulum calcium signals. The present study explored the effects of fenvalerate on the expression of calmodulin in mouse testis and GC-2spd(ts) cells, and its association with fenvalerate-induced male reproductive toxicity. Male mice were subjected to different doses (3.71, 18.56, 37.12, 92.81 mg/kg bw) of fenvalerate or vehicle control for 4 weeks. Expression of calmodulin was determined by real-time polymerase chain reaction (PCR) and Western blot analysis in mouse testis. Similar approaches were utilized in GC-2spd(ts) cells cultured with 5 μM fenvalerate at different time points. In the in vivo study, all mice survived through the entire 4 weeks. Administration of fenvalerate resulted in a dose-dependent reduction in testis weight/body weight, sperm motility, and increased head abnormality rate. By histological staining, mice treated with fenvalerate at higher doses showed dilated seminiferous tubules and disturbed arrangement of spermatogenic cells. Meanwhile, both mRNA and protein expression of calmodulin were significantly increased in the testes of mice exposed to fenvalerate compared to control mice. Moreover, in the in vitro study, 5 μM fenvalerate significantly increased the expression of calmodulin at the mRNA and protein levels in GC-2spd(ts) cells after 8 h of incubation and sustained these levels for at least 24 h. Collectively, these data suggested that enhanced expression of calmodulin correlates with male reproductive damage induced by fenvalerate.