Changes in high-energy phosphate metabolism and cell morphology in four models of acute experimental pancreatitis

The Role of Phosphate in Alcohol-Induced Experimental Pancreatitis

BACKGROUND & AIMS

Heavy alcohol consumption is a common cause of acute pancreatitis; however, alcohol abuse does not always result in clinical pancreatitis. As a consequence, the factors responsible for alcohol-induced pancreatitis are not well understood. In experimental animals, it has been difficult to produce pancreatitis with alcohol. Clinically, alcohol use predisposes to hypophosphatemia, and hypophosphatemia has been observed in some patients with acute pancreatitis. Because of abundant protein synthesis, the pancreas has high metabolic demands, and reduced mitochondrial function leads to organelle dysfunction and pancreatitis. We proposed, therefore, that phosphate deficiency might limit adenosine triphosphate synthesis and thereby contribute to alcohol-induced pancreatitis.

METHODS

Mice were fed a low-phosphate diet (LPD) before orogastric administration of ethanol. Direct effects of phosphate and ethanol were evaluated in vitro in isolated mouse pancreatic acini.

RESULTS

LPD reduced serum phosphate levels. Intragastric administration of ethanol to animals maintained on an LPD caused severe pancreatitis that was ameliorated by phosphate repletion. In pancreatic acinar cells, low-phosphate conditions increased susceptibility to ethanol-induced cellular dysfunction through decreased bioenergetic stores, specifically affecting total cellular adenosine triphosphate and mitochondrial function. Phosphate supplementation prevented ethanol-associated cellular injury.

CONCLUSIONS

Phosphate status plays a critical role in predisposition to and protection from alcohol-induced acinar cell dysfunction and the development of acute alcohol-induced pancreatitis. This finding may explain why pancreatitis develops in only some individuals with heavy alcohol use and suggests a potential novel therapeutic approach to pancreatitis. Finally, an LPD plus ethanol provides a new model for studying alcohol-associated pancreatic injury.

The Role of Extracellular Adenosine Triphosphate in Ischemic Organ Injury

OBJECTIVES

Ischemic tissue injury contributes to significant morbidity and mortality and is implicated in a range of pathologic conditions, including but not limited to myocardial infarction, ischemic stroke, and acute kidney injury. The associated reperfusion phase is responsible for the activation of the innate and adaptive immune system, further accentuating inflammation. Adenosine triphosphate molecule has been implicated in various ischemic conditions, including stroke and myocardial infarction.

STUDY SELECTION

Adenosine triphosphate is a well-defined intracellular energy transfer and is commonly referred to as the body's "energy currency." However, Laboratory studies have demonstrated that extracellular adenosine triphosphate has the ability to initiate inflammation and is therefore referred to as a damage-associated molecular pattern. Purinergic receptors-dependent signaling, proinflammatory cytokine release, increased Ca influx into cells, and subsequent apoptosis have been shown to form a common underlying extracellular adenosine triphosphate molecular mechanism in ischemic organ injury.

CONCLUSIONS

In this review, we aim to discuss the molecular mechanisms behind adenosine triphosphate-mediated ischemic tissue injury and evaluate the role of extracellular adenosine triphosphate in ischemic injury in specific organs, in order to provide a greater understanding of the pathophysiology of this complex process. We also appraise potential future therapeutic strategies to limit damage in various organs, including the heart, brain, kidneys, and lungs.

Breakdown of bioenergetics evoked by mitochondrial damage in acute pancreatitis: Mechanisms and consequences

Acute pancreatitis is a severe inflammatory disease with unacceptably high mortality and without specific therapy. Clinical studies revealed that energy supplementation of patients via enteral feeding decreases systemic infections, multi-organ failure and mortality. These clinical observations have been supported by in vitro and in vivo experimental studies which showed that the most common pancreatitis inducing factors, such as bile acids, ethanol and non-oxidative ethanol metabolites induce intracellular ATP depletion and mitochondrial damage both in pancreatic acinar and ductal cells. Notably, the in vitro supplementation of ATP prevented the cellular damage and restored cell functions in both cell types. These observations suggest that either prevention of mitochondrial damage or restoration of intracellular ATP level might provide therapeutical benefits.

Mechanisms of respiration intensification of rat pancreatic acini upon carbachol-induced Ca(2+) release

AIM

Acetylcholine as one of the main secretagogues modulates mitochondrial functions in acinar pancreacytes, presumably due to increase in ATP hydrolysis or Ca(2+) transport into mitochondria. The aim of this work was to investigate the mechanisms of carbachol (CCh) action on respiration and oxidative phosphorylation of isolated pancreatic acini.

METHODS

Respiration of intact or permeabilized rat pancreatic acini was studied at 37 °C using a Clark oxygen electrode.

RESULTS

Respiration rate of isolated acini in rest was 0.27 ± 0.01 nmol O2 s(-1) 10(-6) cells. Addition of 10 μM CCh into respiration chamber evoked biphasic stimulation of respiration. Rapid increase of respiration by 20.1% lasted for approx. 1 min, followed by decrease to level by 11.5% higher than control. Addition of 1 μm CCh caused monophasic increase by 11.5%. Preincubation (5 min) with 1 or 10 μm CCh elevated respiration rate by 12.5 or 11.2% respectively. FCCP prevented the effect of CCh. Preincubation with 1 (but not 10) μm CCh increased FCCP-uncoupled respiration rate. Thapsigargin slightly elevated respiration, but ryanodine did not. Application of 2-aminoethoxydiphenyl borate or ruthenium red prevented the effects of CCh on respiration, while oligomycin abolished them. Preincubation with 1 μm CCh prior to cell permeabilization increased respiration rate at pyruvate+malate oxidation, but not at succinate oxidation. In contrast, preincubation with 10 μm CCh decreased pyruvate+malate oxidation.

CONCLUSION

Medium CCh dose (1 μm) intensifies respiration and oxidative phosphorylation of acinar pancreacytes by feedforward mechanism via Ca(2+) transport into mitochondria and activation of Ca(2+) /ADP-sensitive mitochondrial dehydrogenases. Prolonged action of high CCh dose (10 μm) might impair mitochondrial functions.

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

SIGNIFICANCE

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

RECENT ADVANCES

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

CRITICAL ISSUES

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

FUTURE DIRECTIONS

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

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

BACKGROUND & AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Polarized calcium signaling in exocrine gland cells

Cytosolic Ca2+ signals are crucial for the control of fluid and enzyme secretion from exocrine glands. The highly polarized exocrine acinar cells have evolved sophisticated and complex Ca2+ signaling mechanisms that exercise precise control of the secretory events occurring across the apical plasma membrane bordering the gland lumen. Ca2+ stores in the endoplasmic reticulum, the secretory granules, the lysosomes, and the endosomes all play important roles in the generation of the local apical Ca2+ spikes that switch on Cl(-) channels in the apical plasma membrane as well as exocytotic export of enzymes. The mitochondria are crucial not only for ATP generation but also for the physiologically important subcellular compartmentalization of the cytosolic Ca2+ signals.

The pancreas misled: signals to pancreatitis

Acute pancreatitis is an increasingly common and sometimes severe disease for which there is little specific therapy. Chronic pancreatitis is a common and grossly debilitating sequel that is largely irreversible, whatever treatment is adopted. In the face of these burdens, the absence of specific treatments is a spur to research. The acinar cell is the primary target of injury from alcohol metabolites, bile, hyperlipidaemia, hyperstimulation and other causes. These induce abnormal, prolonged, global, cytosolic calcium signals, the prevention of which also prevents premature digestive enzyme activation, cytokine expression, vacuole formation and acinar cell necrosis. Such agents increase calcium entry through the plasma membrane and/or increase calcium release from intracellular stores, shown to result from effects on calcium channels and calcium pumps, or their energy supply. A multitude of signalling mechanisms are activated, diverted or disrupted, including secretory mechanisms, lysosomal regulators, inflammatory mediators, cell survival and cell death pathways, together with or separately from calcium. While recent discoveries have increased insight and suggest prophylaxis or treatment targets, more work is required to define the mechanisms and interactions of cell signalling pathways in the pathogenesis of pancreatitis.

Calcium signalling and pancreatic cell death: apoptosis or necrosis?

Secretagogues, such as cholecystokinin and acetylcholine, utilise a variety of second messengers (inositol trisphosphate, cADPR and nicotinic acid adenine dinucleotide phosphate) to induce specific oscillatory patterns of calcium (Ca(2+)) signals in pancreatic acinar cells. These are tightly controlled in a spatiotemporal manner, and are coupled to mitochondrial metabolism necessary to fuel secretion. When Ca(2+) homeostasis is disrupted by known precipitants of acute pancreatitis, for example, hyperstimulation or non-oxidative ethanol metabolites, Ca(2+) stores (endoplasmic reticulum and acidic pool) become depleted and sustained cytosolic [Ca(2+)] elevations replace transient signals, leading to severe consequences. Sustained mitochondrial depolarisation, possibly via opening of the mitochondrial permeability transition pore (MPTP), elicits cellular ATP depletion that paralyses energy-dependent Ca(2+) pumps causing cytosolic Ca(2+) overload, while digestive enzymes are activated prematurely within the cell; Ca(2+)-dependent cellular necrosis ensues. However, when stress to the acinar cell is milder, for example, by application of the oxidant menadione, release of Ca(2+) from stores leads to oscillatory global waves, associated with partial mitochondrial depolarisation and transient MPTP opening; apoptotic cell death is promoted via the intrinsic pathway, when associated with generation of reactive oxygen species. Apoptosis, induced by menadione or bile acids, is potentiated by inhibition of an endogenous detoxifying enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1), suggesting its importance as a defence mechanism that may influence cell fate.

Menadione-induced reactive oxygen species generation via redox cycling promotes apoptosis of murine pancreatic acinar cells

Oxidative stress may be an important determinant of the severity of acute pancreatitis. One-electron reduction of oxidants generates reactive oxygen species (ROS) via redox cycling, whereas two-electron detoxification, e.g. by NAD(P)H:quinone oxidoreductase, does not. The actions of menadione on ROS production and cell fate were compared with those of a non-cycling analogue (2,4-dimethoxy-2-methylnaphthalene (DMN)) using real-time confocal microscopy of isolated perfused murine pancreatic acinar cells. Menadione generated ROS with a concomitant decrease of NAD(P)H, consistent with redox cycling. The elevation of ROS was prevented by the antioxidant N-acetyl-l-cysteine but not by the NADPH oxidase inhibitor diphenyliodonium. DMN produced no change in reactive oxygen species per se but significantly potentiated menadione-induced effects, probably via enhancement of one-electron reduction, since DMN was found to inhibit NAD(P)H:quinone oxidoreductase detoxification. Menadione caused apoptosis of pancreatic acinar cells that was significantly potentiated by DMN, whereas DMN alone had no effect. Furthermore, bile acid (taurolithocholic acid 3-sulfate)-induced caspase activation was also greatly increased by DMN, whereas DMN had no effect per se. These results suggest that acute generation of ROS by menadione occurs via redox cycling, the net effect of which is induction of apoptotic pancreatic acinar cell death. Two-electron detoxifying enzymes such as NAD(P)H:quinone oxidoreductase, which are elevated in pancreatitis, may provide protection against excessive ROS and exert an important role in determining acinar cell fate.

Fatty acid ethyl esters cause pancreatic calcium toxicity via inositol trisphosphate receptors and loss of ATP synthesis

BACKGROUND & AIMS

Fatty acid ethyl esters are ethanol metabolites inducing sustained, toxic elevations of the acinar cytosolic free calcium ion concentration ([Ca(2+)](C)) implicated in pancreatitis. We sought to define the mechanisms of this elevation.

METHODS

Isolated mouse pancreatic acinar cells were loaded with fluorescent dyes for confocal microscopy to measure [Ca(2+)](C) (Fluo 4, Fura Red), endoplasmic reticulum calcium ion concentration ([Ca(2+)](ER), Mg Fluo 4), mitochondrial membrane potential (TMRM), ADP:ATP ratio (Mg Green), and NADH autofluorescence in response to palmitoleic acid ethyl ester and palmitoleic acid (10-100 micromol/L). Whole-cell patch clamp was used to measure the calcium-activated chloride current and apply ethanol metabolites and/or ATP intracellularly.

RESULTS

Intracellular delivery of ester induced oscillatory increases of [Ca(2+)](C) and calcium-activated currents, inhibited acutely by caffeine (20 mmol/L), but not atropine, indicating involvement of inositol trisphosphate receptor channels. The stronger effect of extracellular ester or acid caused depletion of [Ca(2+)](ER), not prevented by caffeine, but associated with depleted ATP, depleted NADH autofluorescence, and depolarized mitochondria, suggesting calcium-ATPase pump failure because of lack of ATP. Intracellular ATP abolished the sustained rise in [Ca(2+)](C), although oscillatory signals persisted that were prevented by caffeine. Inhibition of ester hydrolysis markedly reduced its calcium-releasing effect and consequent toxicity.

CONCLUSIONS

Fatty acid ethyl ester increases [Ca(2+)](C) through inositol trisphosphate receptors and, following hydrolysis, through calcium-ATPase pump failure from impaired mitochondrial ATP production. Lowering cellular fatty acid substrate concentrations may reduce cell injury in pancreatitis.

In vivo imaging of human pancreatic microcirculation and pancreatic tissue injury in clinical pancreas transplantation

Pancreatitis remains to be a major complication following clinical pancreas transplantation. We performed orthogonal polarized spectral (OPS) imaging for direct in vivo visualization and quantification of human pancreatic microcirculation in six healthy donors for living donor liver transplantation and 13 patients undergoing simultaneous pancreas-kidney transplantation. We further determined the impact of microvascular dysfunction during early reperfusion on pancreatic graft injury. Exocrine and endocrine pancreatic impairment was determined by analysis of serum lipase, amylase and C-peptide levels. Compared to normal pancreas in liver donors (homogeneous acinar perfusion) functional capillary density (FCD) and capillary red blood flow velocity of reperfused grafts were significantly decreased. Elevated CRP concentrations on day 2 post-transplant and serum lipase and amylase levels determined on days 4-5 significantly correlated with microvascular dysfunction during the first 30 min of graft reperfusion. Post-transplant serum C-peptide also correlated significantly with pancreatic capillary perfusion. OPS imaging allows to intra-operatively assess physiologic pancreatic microcirculation and to determine microcirculatory impairment during early graft reperfusion. This impairment correlated with the manifestation of post-transplant dysfunction of both exocrine and endocrine pancreatic tissue. OPS imaging may be used clinically to determine the efficacy of interventions, aiming at attenuating microcirculatory impairment during the acute post-transplant reperfusion phase.

Activation of adenosine A1-receptor pathway induces edema formation in the pancreas of rats

BACKGROUND & AIMS

Adenosine has been shown to modulate various pathophysiologic conditions through receptor-mediated mechanisms. However, the role of adenosine in the pathogenesis of acute pancreatitis has not been described. We examined the effect of adenosine-receptor stimulation or inhibition on the pathologic changes of the pancreas.

METHODS

Rats received intraperitoneal injections of selective agonists of A1, A2a, and A3 adenosine receptors: 2-chloro-N(6)-cyclopentyladenosine (CCPA), CGS-21680 (CGS), or 1-deoxy-1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-N-methyl-be ta-D-ribofuranuronamide (IB-MECA), respectively. Serum amylase activity and pathologic changes of the pancreas were evaluated. The effects of a specific A1-receptor antagonist (FK-838) on the pathologic findings of cerulein- and taurocholate-induced pancreatitis were also examined.

RESULTS

Administration of a selective A1 agonist induced hyperamylasemia and morphologic changes in the pancreas characterized by interstitial edema and leukocyte infiltration; neither A2a nor A3 agonist produced such changes. Treatment with an A1-receptor antagonist significantly attenuated the outcome induced by A1 agonist stimulation. In addition, the A1-receptor antagonist significantly ameliorated pancreatic edema in both pancreatitis models, although it did not improve the acinar cell damage of the pancreas or the increase of serum amylase.

CONCLUSIONS

Activation of the adenosine A1-receptor pathway may have an important role in the pathogenesis of acute pancreatitis.

Role of oxygen-derived free radicals in protease activation after pancreas transplantation in the pig

The role of oxygen-derived free radicals in pancreatitis after pancreas transplantation was examined in a porcine pancreatic transplantation model. Trypsin activation, protease inhibitor consumption, kininogen consumption, and postoperative graft function were investigated in 24 pigs subjected to whole organ pancreaticoduodenal transplantation. The animals were divided into one control group and two groups treated with free radical scavengers. One group was given allopurinol, and one group was treated with superoxide dismutase in combination with catalase. In the early phase (within 1 hr) after reperfusion, no differences were seen between the groups as to protease activation. Neither trypsin-protease inhibitor imbalance nor any signs of kininogen consumption were seen. In a later phase (1-3 days after the transplantation), the trypsin activation, measured as high molecular weight immunoreactive cationic trypsin in plasma, was significantly less pronounced in allopurinol-treated animals. This finding indicates a less severe form of reperfusion pancreatitis in this group compared with the other groups. A tendency toward better function in the allopurinol-treated group was also seen. We conclude that oxygen-derived free radicals seem to be of importance in the development of reperfusion pancreatitis after pancreas transplantation in the pig. We also conclude that allopurinol, but not superoxide dismutase/catalase, possibly due to the administration regimens used in this series, is able to attenuate the trypsin activation and the development of pancreatitis in the later phase in this model.

Ischemia-reperfusion-induced pancreatic microvascular injury. An intravital fluorescence microscopic study in rats

With the concept that ischemia-reperfusion injury may contribute to the pathogenesis of acute pancreatitis, we have quantitatively analyzed the pancreatic microcirculation of rats during postischemic reperfusion using intravital fluorescence microscopy. Ischemia to the pancreas of Sprague-Dawley rats (N = 7) was induced by clamping the arteriae gastroduodenalis, lienalis, gastrica sinistra, and gastricae breves for 60 min followed by 120 min of reperfusion. Ischemic conditions were verified by measurement of microvascular hemoglobin oxygenation using reflection spectrophotometry (n = 9). Postischemic reperfusion was characterized by a significant (P < 0.05) reduction of functional capillary density to approximately 69% of baseline (no reflow). Reperfusion-induced inflammatory response was reflected by a marked increase (100-fold; P < 0.01) of the number of permanently adherent leukocytes in postcapillary venules (reflow paradox). Postischemic reperfusion was further associated with increased serum lipase activities, and histomorphological analysis revealed alterations, similar as known in acute interstitial pancreatitis, ie, neutrophil infiltration, interstitial edema, and hemorrhagic lesions. We, therefore, conclude that ischemia-reperfusion- associated events, ie, no reflow and reflow paradox, may be considered as trigger mechanisms in the manifestation of distinct types of acute pancreatitis, in particular posttransplant pancreatitis.

Ischaemia-reperfusion mechanisms in acute pancreatitis

The role of ischaemia in the pathogenesis of acute pancreatitis is unknown. Some experimental studies have shown that ischaemia has little effect on the pancreas, while others have found an association with pancreatic injury. Ischaemia-reperfusion damage has been well documented in other sites such as the intestine, cardiac muscle, and skeletal muscle. However, in the pancreas, injury is usually seen only after complete ischaemia, which is uncommon clinically. Experimental chronic pancreatitis is characterized by low pancreatic blood flow, low interstitial pH, and impaired pancreatic tissue oxygenation, which are all findings consistent with the ischaemia-reperfusion mechanisms. Acute pancreatitis is also associated with a reduction in pancreatic blood flow and evidence of free radical generation, similarly suggesting the possibility of ischaemia-reperfusion injury. Ethanol ingestion, which is commonly associated clinically with both chronic and acute pancreatitis, may itself contribute to an ischaemic-reperfusion injury. We have shown that administration of ethanol to cats decreases pancreatic blood flow and may also directly activate neutrophils. Further investigation is needed to determine whether or not these findings are also associated with an ischaemia-reperfusion injury.

Ischemia reperfusion of the pancreas: a new in vivo model for acute pancreatitis in rats

Based on the concept that ischemia is an important factor in the pathogenesis of acute pancreatitis, we developed a new model of complete ischemia/reperfusion of the pancreas in the rat. The aim of this study was to investigate the microcirculation of the pancreas after complete and reversible ischemia at different times after reperfusion by using intravital fluorescence microscopy. In addition, the effect of ischemia/reperfusion on the pancreas was assessed by means of light and electron microscopy and measurement of serum pancreas amylase concentration. In 35 adult Sprague-Dawley rats ischemia of the pancreas was induced by temporary occlusion of the four supplying arteries. Sham-operated animals served as controls (group A). After periods of 30 min (group B), 60 min (group C) or 120 min (group D) of ischemia the organ was reperfused. To exclude the influence of hypovolemia on microcirculation in group E (120 min ischemia) hydroxyethylstarch (HES) was given i.v. to maintain central venous pressure at baseline values. For intravital fluorescence microscopy the pancreas was exteriorized on a stage and quantitative analysis of microcirculation, including functional capillary density and leukocyte-endothelium interaction, was performed after 30 min, 1 h and 2 h of reperfusion. Serum pancreas-amylase was measured at control (prior ischemia) and at 2 h after reperfusion. Tissue samples for light and electron microscopy were taken 2 h after reperfusion. In sham-operated animals, functional capillary density (FCD) remained within baseline values (FCD 407.7 +/- 9 cm-1) during reperfusion. Dependent on the time of ischemia and time of reperfusion a gradual reduction in functional capillary density was observed; after 2 h of ischemia only 35% of capillaries were perfused (FCD 140.9 +/- 28.3 cm-1). Reduced functional capillary density was associated with an increase of perfusion heterogeneity to a maximum of 0.65 +/- 0.12, as against 0.13 +/- 0.02 in control animals. With a 2 h ischemia leukocyte-endothelium interaction was enhanced after 0.5 h of reperfusion (8-fold increase of adherent leukocytes in comparison to control) followed by a further significant increase until 2 h after the beginning of reperfusion. Amylase concentration after ischemia of 2 h (2967 +/- 289 U/l) was significantly higher as compared to controls (1857 +/- 99 U/l). Differences between group E and D were not observed. Pancreatic tissue injury was ascertained by histopathological studies. These results indicate that complete ischemia/reperfusion of the pancreas induces pancreatic microvascular failure. The severity of changes depends on duration of ischemia and duration of reperfusion. The morphological and biochemical changes suggest that ischemia/reperfusion causes an inflammatory reaction as observed in acute pancreatitis.

Evidence for early oxidative stress in acute pancreatitis. Clues for correction

Pancreatic oxidative stress with depletion of pancreatic glutathione is an early feature in all tested models of acute pancreatitis, and sooner or later the problem extends to the lung, irrespective of disease severity, whether toward spontaneous recovery or death from multisystem organ failure. We, therefore, sought evidence of oxidative stress in the human disease by analyzing admission blood samples. We found it from high concentrations of oxidatively altered linoleic acid in serum and vitamin C in plasma (p < 0.001 vs controls or a group of other acute abdominal crises where the proportion of patients with admission Apache II scores < or > 8 was similar). These changes were accompanied by subnormal levels of ascorbic acid in plasma (p < 0.001); selenium (p < 0.001), beta-carotene (p < 0.001), and alpha-tocopherol in serum (p = 0.005 for its molar ratio to cholesterol). Paradoxically, the plasma concentration of S-adenosylmethionine was elevated (p = 0.02), suggesting that this proximate bioactive metabolite of the essential amino acid had backtracked because its intracellular metabolism down the methionine trans-sulfuration pathway toward glutathione synthesis was disrupted. The aberrations transcended putative etiological factor, duration of symptoms, or disease severity. We conclude: (1) that oxidative stress has pervaded the vascular compartment by the time of admission in patients with acute pancreatitis, and, (2) that blood micronutrient antioxidant profiles at this stage are consistent not only with compromised intracellular capacity to synthesize/refurbish glutathione, but also vulnerability of intra- and extracellular lipid targets.

A method for in vivo assessment of reversible rat pancreatic ischemia using 31P NMR spectroscopy at 2.0 tesla

A surgical method is described which allows in vivo assessment of reversible rat pancreatic ischemia using 31P NMR spectroscopy at 2.0 T. Phosphorous-31 NMR spectra acquired during the ischemic period show the expected increase in inorganic phosphate with a concomitant decrease in ATP levels and pH as compared to controls. Upon reperfusion, inorganic phosphate and ATP returned to control levels while pH recovered to a more alkaline value. This method provides a means of studying in vivo changes in high energy metabolite associated with acute pancreatitis (AP) and maintains the secretory ability of the gland so that different forms of AP, such as those arising from pancreatic juice edema, can be studied.

Detailed characterization of experimental acute alcoholic pancreatitis

BACKGROUND

With the ex vivo perfused canine pancreas preparation, the infusion of acetaldehyde, the primary metabolite of ethanol oxidation, plus a short period of ischemia to convert xanthine dehydrogenase to xanthine oxidase, results in the physiologic injury response of acute pancreatitis (edema, weight gain, hyperamylasemia). The free radical scavengers superoxide dismutase and catalase and a xanthine oxidase inhibitor, allopurinol, ameliorate this injury response, suggesting that toxic oxygen metabolites generated by xanthine oxidase play an intermediary role.

METHODS

The isolated ex vivo canine pancreas preparation was perfused for 4 hours, and weight gain of the preparation and amylase activity in the perfusate were monitored. Changes in pancreatic acinar cell architecture were characterized by light and electron microscopy, and intracellular phosphate metabolism was followed by magnetic resonance spectroscopy in control preparations and in glands simulating alcoholic pancreatitis.

RESULTS

Control preparations and preparations with a 1-hour period of ischemia before perfusion gained little weight (7 +/- 3 gm and 8 +/- 1 gm), amylase activity in the perfusate remained normal (933 +/- 513 units/dl and 1537 +/- 553 units/dl), and no changes in architecture were observed. Weight gain (5 +/- 6 gm) and amylase activity (1188 +/- 173 units/dl) were also normal in the preparations receiving acetaldehyde without preceding ischemia, but mild vascular and islet cell injury were observed on electron microscopy. One hour of ischemia followed by acetaldehyde infusion resulted in edema, increased weight gain (21 +/- 12 gm [p < 0.05]), and amylase activity (2487 +/- 1484 units/dl [p < 0.05]). Microscopy showed mild acinar cell damage and greater injury to the capillaries and the islets. The capillary and islet cell changes were reduced by superoxide dismutase and catalase. Intracellular adenosine triphosphate levels remained at baseline levels in the control preparations. Adenosine triphosphate decreased during ischemia but quickly recovered during perfusion without a significant difference whether acetaldehyde was infused after ischemia. An iron chelator desferoxamine ameliorated the injury response in the preparations simulating acute pancreatitis (weight gain, 13 +/- 6 gm [p = 0.09] and amylase activity, 1198 +/- 471 units/dl [p = 0.08]), but a cholecystokinin receptor antagonist L364,718 did not have an effect. A sulfhydryl group protector, dithiothreitol, decreased weight gain (10 +/- 7 gm [p = 0.06]), and amylase activity was not significantly increased over that of the control group (1582 +/- 641 units/dl), but a serine protease inhibitor phenylmethylsulphonylfluoride was ineffective.

CONCLUSIONS

In this model simulating acute alcoholic pancreatitis, both the early physiologic injury response and the early morphologic changes are mediated at least in part by free radicals, which are generated by xanthine oxidase converted reversibly from xanthine dehydrogenase. In addition to the superoxide radical, the hydroxyl radical may also be an important early intermediate step, but the cholecystokinin receptor is not.

Effect of antioxidant treatment in rats with acute hemorrhagic pancreatitis

The purpose of this study was to evaluate the effect of free radical ablation therapy in acute hemorrhagic pancreatitis. Acute pancreatitis was induced in 64 rats by retrograde injection of 5% sodium taurocholate. Thirty animals were pretreated with 100,000 units/kg/hr of superoxide dismutase (SOD) and 400,000 units/kg catalase within the first 3 hr. After 0.5, 3.5, and 12 hr of observation time, serum enzymes and the tissue content of conjugated dienes, malondialdehyde, reduced and oxidized glutathione, as well as ATP, ADP and AMP were measured. In addition, tissue samples were examined by light microscopy. Untreated rats (N = 34) developed within 12 hr an acute hemorrhagic necrotizing pancreatitis with a concomitant increase in serum enzyme levels and a decrease in reduced glutathione and ATP. Within the 12-hr observation period, 57% of the animals died. Scavenger treatment improved the tissue damage and attenuated the increase of the serum enzyme levels and the decrease in reduced glutathione and ATP. Moreover, the lethality rate was significantly lower. Oxygen radicals seem to be instrumental for the development of acute hemorrhagic pancreatitis. Thereby, antioxidant treatment reduces tissue damage, biochemical alterations and extrapancreatic complications, thus improving the final outcome.

Glutathione and ATP levels, subcellular distribution of enzymes, and permeability of duct system in rabbit pancreas following intravenous administration of alcohol and cerulein

In order to reproduce what might occur during the initial phase in some cases of acute alcohol-induced pancreatitis, rabbits were infused with diluted ethanol and low-dose cerulein. The duct permeability was assessed by recovery of fluoresceinated dextran (molecular weight 19,500) in central venous blood following orthograde duct perfusion with this substance in the anesthetized animal. Serum ethanol, lipase, and amylase were measured; pancreatic duct morphology was examined by light microscopy and electron microscopy. ATP and glutathione were measured, as were amylase, trypsinogen/trypsin, cathepsin B, and DNA levels in differential centrifugates. As expected, acinar amylase and trypsinogen showed a significant decrease in the experimental group; cathepsin B activity was similarly diminished. Compared with the control group, the activity of serum amylase and lipase in the experimental group demonstrated a significant increase. However, no differences between saline-infused control animals and the treated group regarding pancreatic duct permeability, continuity of lumen-lining epithelium, ATP and glutathione levels, and the relative subcellular distribution of pancreatic digestive and lysosomal enzymes were observed. Thus, our findings do not support the relevance of some of the most common hypotheses on the pathophysiology of acute pancreatitis in its early stage for at least a certain subgroup of patients with acute alcohol-induced pancreatitis.

Induction of anaerobic glucose metabolism during the development of acute pancreatitis

OBJECTIVE

Studies were performed with the ex vivo perfused canine pancreas preparation to characterize acinar cell metabolism during the development of acute pancreatitis.

SUMMARY BACKGROUND DATA

Acute pancreatitis can be initiated in the ex vivo perfused canine pancreas preparation by five different stimuli as follows: (1) the infusion of oleic acid (FFA), (2) partial obstruction of the pancreatic duct and secretin stimulation (POSS), (3) a 2-hour ischemic period before perfusion (ISCH 2), (4) a 1-hour ischemic period followed by acetaldehyde infusion (ISCH 1 + AA), and (5) supramaximal stimulation by cerulein (CER-HIGH). In each model, weight gain, edema formation, and hyperamylasemia occur, signifying the development of pancreatitis. Previously, the authors demonstrated that intracellular adenosine triphosphate (ATP) levels decline during the development of pancreatitis in the FFA model but not in the other four models.

METHODS

The ex vivo perfused canine pancreas preparation was used to study five different stimuli that result in the initiation of acute pancreatitis, as manifested by weight gain, edema formation, and hyperamylasemia during a 4-hour perfusion period. Glucose metabolism (using 13C-labeled glucose) and intracellular pH and ATP levels were monitored by magnetic resonance spectroscopy. Oxygen consumption and pancreatic secretion were measured directly.

RESULTS

In control preparations, a glucose signal appeared in the 13C-labeled spectra within 15 minutes, and a signal from glycogen appeared at the end of the 4-hour perfusion. In the preparations with an ischemic period (ISCH 2 and ISCH 1 + AA), a lactate signal appeared during the ischemia, disappeared during the early perfusion, and appeared again later during the perfusion as the physiologic injury response of pancreatitis developed. Similarly, in the POSS and CER-HIGH pancreatitis preparations, lactate accumulated in the pancreas during the perfusion period. In these four preparations, the intracellular pH did not differ significantly during the perfusion from that of the control preparations. Oxygen consumption was unchanged during the perfusion in the ISCH 2 and ISCH 1 + AA preparations and increased in the POSS and CER-HIGH preparations. In the FFA pancreatitis preparations, only a trace of glycogen was observed, and the metabolites of glucose were not detected. Intracellular pH and oxygen consumption both dropped significantly during the perfusion.

CONCLUSIONS

In four of the five acute experimental pancreatitis models, anaerobic glucose metabolism was induced, despite continuous oxygen extraction by the pancreas. This induction of anaerobic glucose metabolism may be important in maintaining normal levels of intracellular ATP early after the induction of pancreatitis because the absence of anaerobic glucose metabolism in the FFA model was associated with a remarkable decrease in intracellular ATP levels and pH. The FFA model of pancreatitis is the most severe of the five models.