Disruption of Ca(2+) homeostasis can lead to severe damage of the pancreas, resulting in premature activation of digestive enzymes, vacuolisation and necrotic cell death, features typical of acute pancreatitis (AP). Therefore a fine balance between Ca(2+) release from internal stores, Ca(2+) entry and extrusion mechanisms is necessary to avoid injury. Precipitants of AP induce Ca(2+) overload of the pancreatic acinar cell that causes mitochondrial dysfunction, via formation of the mitochondrial permeability transition pore (MPTP), loss of ATP production and consequent necrosis. Oxidative stress has been shown to occur in the development of AP and may modify Ca(2+) signalling events in the acinar cell. However, the precise pathophysiological involvement is currently unclear and antioxidant therapy in the clinic has largely proved ineffective. Possible reasons for this are discussed, including evidence that ROS generation may determine cell death patterns. In contrast, recent evidence has indicated the potential for AP therapy via the prevention of Ca(2+)-dependent mitochondrial damage. Multiple approaches are indicated from preclinical findings; 1) inhibition of Ca(2+) release by IP3R blockade, 2) inhibition of Ca(2+) entry through Orai1 blockade and 3) prevention of MPTP formation. Clinical trials of drugs which prevent mitochondrial dysfunction induced by Ca(2+) overload of pancreatic acinar cells are imminent and may provide patient benefit for a disease that currently lacks specific therapy.

There is a convincing body of evidence that oxidative stress is involved in the pathogenesis of acute pancreatitis. The effects of different radical scavengers suggested that reactive oxygen metabolites are generated at very early stage of disease and contribute to amplify the pancreatic damage. Oxidative stress is also involved in the progression of the disease from a local damage to a systemic organ failure. However, therapeutic use of antioxidants failed to clearly show a clinical benefit in different trials. Therefore, although antioxidants alone seem to be not enough for the treatment of severe acute pancreatitis, future combined therapeutic strategies should include antioxidants in its composition.

Oxidative stress has been implicated in the pathogenesis of acute pancreatitis, a severe and debilitating inflammation of the pancreas that carries a significant mortality, and which imposes a considerable financial burden on the health system due to patient care. Although extensive efforts have been directed towards the elucidation of critical underlying mechanisms and the identification of novel therapeutic targets, the disease remains without a specific therapy. In experimental animal models of acute pancreatitis, increased oxidative stress and decreased antioxidant defences have been observed, changes also detected in patients clinically. However, despite the promise of studies evaluating the effects of antioxidants in these model systems, translation to the clinic has thus far been disappointing. This may reflect many factors involved in the design of both preclinical and clinical evaluations of antioxidant therapy, not least the fact that most experimental studies have focussed on pre-treatment rather than post-injury assessment. This review has examined evidence relating to the involvement of oxidative stress in the pathophysiology of acute pancreatitis, focussing on experimental models and the clinical experience, including the experimental techniques employed and potential of antioxidant therapy.

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.

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.

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.

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.

Reactive oxygen and nitrogen species (ROS and RNS) play an important role in signal transduction and cell injury processes. Nitric oxide synthase (NOS)-the key enzyme producing nitric oxide (NO)-is found in neuronal structures, vascular endothelium and, possibly, in acinar and ductal epithelial cells in the pancreas. NO is known to regulate cell homeostasis, and its effects on the acinar cells are reviewed here. ROS are implicated in the early events within the acinar cells, leading to the development of acute pancreatitis. The available data on ROS/RNS involvement in the apoptotic and necrotic death of pancreatic acinar cells will be discussed.

Chronic and acute pancreatitis can be understood as distinct stages of an inflammatory spectrum in the pancreas. Although its pathogenesis is not well defined, oxidative stress seems to be clearly involved in its development. During acute pancreatitis, there is an extraordinary and rapid formation of reactive oxygen species that leads to the extinction of pancreatic antioxidant reserves, causes direct tissue damage and activates oxidative cellular mediators, giving rise to the lesion. However, classical antioxidants have not been shown to have clear benefits in patients with acute pancreatitis. Chronic pancreatitis seems to be the result of a recurrent lesion and defective repair, leading to pancreatic atrophy and fibrosis. In this process, oxidative stress is an efficient stimulus to maintain pancreatic stellar cells active, the fibrogenic motor of chronic pancreatitis. Although antioxidant supplements relieve abdominal pain in these patients, the direction of future antioxidant therapies lies in identifying oxidative mechanisms with the potential for intervention.

Oxidative stress plays an important role in the early stage of acute pancreatitis, as well as in the associated multiple organ injury. This study tests the hypothesis that M40401, a new superoxide dismutase mimetic, attenuates experimental acute pancreatitis. Intraperitoneal injection of cerulein in mice resulted in a severe, acute pancreatitis that was characterized by edema, neutrophil infiltration, tissue hemorrhage, and cell necrosis, as well as increases in the serum levels of amylase and/or lipase. The infiltration of the pancreatic tissue of these animals with neutrophils (measured as an increase in myeloperoxidase activity) was associated with expression of intercellular adhesion molecule-1, as well as signs of enhanced lipid peroxidation (e.g., increased tissue levels of malondialdehyde). Immunohistochemical examination demonstrated a marked increase in the staining (immunoreactivity) for nitrotyrosine and poly (ADP-ribose) polymerase in the pancreas of cerulein-treated mice. In contrast, the degree of pancreatic inflammation and tissue injury (histological score), the expression of intercellular adhesion molecule-1, the staining for nitrotyrosine and poly (ADP-ribose) polymerase, and lipid peroxidation were markedly reduced in pancreatic tissue sections obtained from cerulein-treated mice administered with M40401. These results confirm our hypothesis that superoxide anions play an important role in cerulein-mediated acute pancreatitis and support the possible clinical use of low-molecular-weight synthetic superoxide dismutase mimetics in those conditions that are associated with overproduction of superoxide.

The course of pancreatitis is paralleled by a drastic reduction in organ perfusion and increased ICAM-1-mediated leukocyte-endothelial interaction. We aimed to evaluate the effect of oxygen radicals on ICAM-1 expression and the microcirculation in severe acute pancreatitis using the oxygen radical scavenger dimethylsulfoxide (DMSO).

Severe pancreatitis was induced in rats (n = 32) who were randomly assigned to one of two groups: either 4 ml/kg 50% DMSO/saline (v/v) started 3 h after induction of pancreatitis or 4 ml/kg saline (control). Microcirculation was evaluated by intermittent intravital microscopy. Serum amylase and lipase, histomorphometric changes, immunohistochemistry for ICAM-1 expression and 24-hour survival were investigated.

Leukocyte adherence was significantly reduced (4.4 +/- 0.47 vs. 5.58 +/- 0.69 sticker/100 micro m, p < 0.05), and mean capillary (0.96 +/- 0.06 vs. 0.45 +/- 0.13 mm/s; p < 0.01) and venous erythrocyte velocity (1.16 +/- 0.12 vs. 0.58 +/- 0.16 mm/s, p < 0.01) were significantly increased by DMSO treatment. Microcirculatory disturbances were paralleled by an increase in endothelial ICAM-1 expression, whereas DMSO reduced ICAM-1 expression.

DMSO improves pancreatic microcirculation and reduces ICAM-1 expression and subsequent leukocyte adhesion, suggesting an important role of oxygen free radicals in the pathway of endothelial ICAM-1 expression and microcirculatory disturbances in acute pancreatitis.

Intrapancreatic activation of digestive enzymes is a key event in the parenchymal cell injury of pancreatitis. We hypothesized that neutrophils recruited to the pancreas during pancreatitis may contribute to such activation.

To cause experimental pancreatitis, rats and mice were treated with high doses of cerulein. Activation of the digestive enzyme, trypsin, was measured in pancreatic homogenates using a fluorogenic assay and localized immunocytochemically with antibody to trypsin-activation peptide (TAP).

Compared with controls, rats depleted of neutrophils with antineutrophil serum exhibited a marked attenuation in intrapancreatic trypsin activation and acinar cell TAP labeling induced by high-dose cerulein. To examine the mechanism, mice deficient in either nicontinamide adenine dinucleotide phosphate (NADPH) oxidase, or myeloperoxidase (MPO) were studied for trypsin activation. Mice deficient in NADPH oxidase exhibited attenuation of the cerulein-induced trypsin activation, but those deficient in MPO did not. Using measurements of Western blot analysis, generation of reactive oxygen species, and immunocytochemistry, we demonstrated the NADPH oxidase activity is in neutrophils and not pancreatic acinar tissue.

The results demonstrate a novel role for neutrophils infiltrating the pancreas in pathologic activation of digestive enzymes in acute pancreatitis and indicate that this effect is mediated by products of NADPH oxidase.

Free radicals and their scavengers are supposed to be involved in pancreatitis.

To investigate the expression of superoxide dismutase (SOD) in rat pancreatic acinar cell injury.

As an in vivo model, male WBN/Kob rats were used. Chronic pancreatitis developed spontaneously at 12 weeks in this model and progressed thereafter, but acinar regeneration was recognized at 20 weeks. By semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), manganese SOD (MnSOD) mRNA expression peaked at 8 and 20 weeks, whereas copper/zinc SOD (CuZnSOD) mRNA expression peaked at 12 and 20 weeks. Immunohistochemistry confirmed the localization of SOD in acinar cells. Acinar cell apoptosis peaked at 12 and 20 weeks. In an in vitro study, MnSOD mRNA expression peaked at 2 hours after the addition of arginine to culture medium, whereas apoptosis was increased at 24 hours.

Thus, the induction of SOD around the onset and at the late stage of chronic pancreatitis in the WBN/Kob rats implies pancreatic ischemia and acinar remodeling, respectively. From the in vitro results, MnSOD expression might reflect a defensive mechanism of acinar cells against oxidative stress or pro-apoptotic stimuli.

To evaluate the therapeutic potential of lazaroids in severe necrotizing acute pancreatitis and to investigate the association between oxidative stress, protease activation, and local production of proinflammatory cytokines and the severity and lethality of the disease.

Oxidative stress is a crucial factor in the pathophysiology of acute pancreatitis and its systemic complications. Treatment with antioxidants, however, failed to improve survival in most studies performed so far. Lazaroids are a novel class of antioxidants that potently protect pancreatic acinar cells against oxidant attack in vitro.

Prospective, randomized, controlled experimental study.

University research laboratory.

Seventy-five anesthetized male Wistar rats (300-350 g).

Severe acute pancreatitis was induced by retrograde injection of 3.5% taurocholate-sodium into the common bile-pancreatic duct. Interventions were performed to mimic the clinical situation, including continuous intravenous fluid substitution and administration of lazaroids in a therapeutic protocol. Therapy was started 1 hr after injection of the bile salt by using three different lazaroids, lactated Ringer's solution (placebo), and methylprednisolone as a corticosteroid control (n = 15 in each group). All the substances were given by continuous intravenous infusion throughout the 20-hr trial period.

Pancreatic homogenates and ascites were analyzed for indicators of oxidative stress, antioxidants, proteases, and proinflammatory cytokines. Pancreatic edema, morphologic pancreatitis severity, and pancreatic histopathology also were assessed. All three lazaroids and methylprednisolone diminished pancreatic tumor necrosis factor-alpha concentrations. Lethality was 33% in the placebo group. Neither the lazaroids nor methylprednisolone influenced survival. The local pancreatic and peritoneal concentrations of lipid peroxidation products, antioxidants, and proteases did not differ among the five groups. Nonsurviving rats, however, had a higher total protease activity in the pancreas and higher concentrations of trypsinogen activation peptide in ascites, as compared with surviving animals. There were no differences between survivors and nonsurvivors with regard to variables of oxidative stress and cytokines.

Lazaroid application under clinically relevant conditions (i.e., after induction of fulminant acute pancreatitis) does not influence lethality or biochemical variables relevant to this disease. Protease activation rather than oxidative stress or local pancreatic cytokine production is an important determinant of disease severity and survival in acute pancreatitis. In experimental studies evaluating novel therapeutics, the same strict criteria should be applied as in the human setting.

Acute experimental pancreatitis (induced by cerulein) recently has been reported to cause marked diaphragmatic dysfunction, which may contribute to respiratory distress in this setting. In cerulein-induced acute pancreatitis, expression of inducible nitric oxide synthase is induced to produce a large amount of nitric oxide. Nitric oxide excessively produced has been implicated in diaphragmatic dysfunction induced by a variety of etiologies. The aims of the current study were, first, to examine whether nitric oxide overproduced through inducible nitric oxide synthase is involved in cerulein-induced impairment of diaphragmatic function, and second, if demonstrated, to assess effects of ONO-1714, an inducible nitric oxide synthase inhibitor, on diaphragmatic dysfunction associated with cerulein-induced acute pancreatitis.

Prospective, randomized animal study.

University research laboratory.

Ninety-one male Sprague-Dawley rats, weighing 200-250 g.

Rats were randomly divided into seven groups (n = 8 each): CONT-SAL, CAER-SAL, CONT-ONO, CAER-DEX, CAER-AMI, CAER-ONOhigh, and CAER-ONOlow. Groups labeled CAER received two consecutive intraperitoneal doses (50 microg/kg) of cerulein, whereas groups labeled CONT received two consecutive intraperitoneal injections of saline. Groups labeled SAL received intraperitoneal saline before cerulein or saline. The group labeled DEX received 2 mg/kg intraperitoneal dexamethasone, and the group labeled AMI received 100 mg/kg intraperitoneal aminoguanidine. The groups labeled ONO, ONOhigh, and ONOlow received ONO-1714 at 0.1 mg/kg, 0.1 mg/kg, and 0.03 mg/kg, respectively, before cerulein or saline.

Diaphragmatic contractility and fatigability were assessed in vitro by using muscle strips excised from the costal diaphragms 6 hrs after the first dose of cerulein or saline. Expression of inducible nitric oxide synthase protein in the diaphragm was assessed by immunohistochemistry by using anti-inducible nitric oxide synthase antibody. Plasma concentrations of nitrite plus nitrate and diaphragmatic concentrations of malondialdehyde were measured. With another set of rats (n = 5 each group), diaphragmatic inducible nitric oxide synthase activity was determined. Twitch and tetanic tensions and tensions generated during fatigue trial were lower in group CAER-SAL than in group CONT-SAL. Cerulein increased diaphragmatic malondialdehyde and plasma nitrite plus nitrate concentrations. Positive immunostaining for inducible nitric oxide synthase protein was found in group CAER-SAL. Dexamethasone and aminoguanidine attenuated the diaphragmatic mechanical damages. A high dose of ONO-1714 attenuated cerulein-induced impairment of diaphragmatic contractility and endurance capacity, although a low dose of the drug failed to do so.

Cerulein-induced diaphragmatic dysfunction was attributable, in part, to nitric oxide overproduced via inducible nitric oxide synthase. Pretreatment with ONO-1714 at a dose of 0.1 mg/kg attenuated diaphragmatic dysfunction associated with cerulein-induced pancreatitis in rats assessed by contractile profiles and endurance capacity. This beneficial effect of ONO-1714 may be attributable, in part, to inhibition of diaphragmatic lipid peroxidation induced by nitric oxide-derived free radicals.

Reactive oxygen species have been implicated in the pathogenesis of acute pancreatitis. Few studies have focused on the loss of endogenous antioxidants and molecular oxidative damage. Two acute pancreatitis models in rats; taurocholate (3% intraductal infusion) and cerulein (10 microg/kg/h), were used to study markers of oxidative stress: Glutathione, ascorbic acid, and their oxidized forms (glutathione disulfide and dehydroascorbic acid), malondialdehyde, and 4-hydroxynoneal in plasma and pancreas, as well as 7-hydro-8-oxo-2'-deoxyguanosine in pancreas. In both models, pancreatic glutathione depleted by 36-46% and pancreatic ascorbic acid depleted by 36-40% (p <.05). In the taurocholate model, plasma glutathione was depleted by 34% (p <.05), but there were no significant changes in plasma ascorbic acid or in plasma and pancreas dehydroascorbic acid, malondialdehyde, and 4-hydroxynoneal, and no significant changes in the pancreas glutathione disulfide/glutathione ratio. While pancreas glutathione disulfide/glutathione ratio increased in the cerulein model, there were no significant changes in plasma glutathione, plasma, or pancreas ascorbic acid, dehydroascorbic acid, 4-hydroxynoneal, and malondialdehyde, or in pancreas 7-hydro-8-oxo-2'-deoxyguanosine. Reactive oxygen species have a minor role in the intermediate stages of pancreatitis models.

Using a retrograde infusion sodium taurocholate pancreatitis model in the rat treatment with oxygen radical scavengers or monoclonal anti-ICAM-1 antibody decreased tissue damage and polymorphonuclear leukocytes (PMN) infiltration. Scavengers or anti-ICAM-1 treatment attenuated the activating capacity of blood PMNs following zymosan stimulation. The local production of oxygen free radicals in the pancreas by systemic infusion of hypoxanthine and regional infusion of xanthine oxidase did not induce acute pancreatitis, although an increase of infiltrating PMNs was observed. Our data suggest that oxygen free radicals and infiltrating PMNs aggravate acute pancreatitis and that both are important mediators of local destruction and systemic activation of PMNs.

Ascorbic acid (AA) is an important endogenous antioxidant in plasma and has been shown to be decreased at the time of hospital admission in patients with acute pancreatitis. The aim of this study was to determine whether plasma AA concentration continues to decrease after admission and whether the extent of decrease is related to the severity of pancreatitis.

Consecutive patients with mild (n = 62) and severe (n = 23) acute pancreatitis had plasma AA concentration measured on the day of recruitment and on days 2 and 5 by high-performance liquid chromatography.

The plasma AA concentration in patients with acute pancreatitis was significantly less than that in normal volunteers on days 0, 2 and 5 (P < 0.0001) and this was more marked in those with severe disease. There was a decrease in plasma AA concentration from day 0 to day 2 in patients with mild (P < 0.0001) and severe (P = 0.0005) pancreatitis, and from day 2 to day 5 in patients with severe pancreatitis (P = 0.023).

Endogenous plasma AA continues to decrease over the first 5 days in hospital and the extent is related to the severity of acute pancreatitis. Presented to a meeting of the Australasian Surgical Research Society, Auckland, New Zealand, August 1995 and published in abstract form as Aust N Z J Surg 1996; 66: 243

Direct in vivo histological detection of oxygen-derived free radicals (OFRs) in inflammatory conditions is not fully resolved. We report an application of cerium histochemistry (in which capture of OFRs by Ce atoms results in laser-reflectant cerium-perhydroxide precipitates) combined with reflectance confocal laser scanning microscopy (CLSM) to demonstrate the evolution of oxidative stress in taurocholate-induced acute pancreatitis (AP) in rats. Animals were perfused with CeCl(3) in vivo and cryostat sections of pancreata were studied by CLSM. Vascular endothelium was immunolabeled for PECAM-1. OFR production by isolated polymorphonuclear leukocytes (PMNs) incubated in vitro with CeCl(3) was quantified by image analysis. In the pancreas, strong OFR-derived cerium reflectance signals were seen in acinar cells at 1-2 hr, capillaries and small venules were frequently engorged by cerium precipitates, and adherent PMNs presented weak intracellular reflectance signals. At 8-24 hr, acinar cell OFR production decreased, whereas adherent/transmigrated PMNs displayed abundant intra- and pericellular reflectance. PECAM-1 expression was unchanged. PMNs from ascites or blood showed significant (p<0.01) time-dependent OFR production, plateauing from 2 hr. The modified cerium capture/CLSM method allows the co-demonstration of in vivo oxidative stress and cellular structures labeled with fluorescent markers. In vivo oxidative stress was shown histologically for the first time in experimental AP.

Cyanohydroxybutene (CHB), a glycosinolate breakdown product, causes pancreatic injury when given to animals in large amounts. To determine the course of CHB-induced pancreatopathy, rats were given a single subcutaneous dose of CHB and the pancreas weighed and examined by light and electron microscopy and immunohistochemistry at intervals from 2 h to 28 days. The pancreatic lesion was unusual in that there was marked early oedema with limited inflammatory cell infiltration, rapid synchronous onset of acinar cell apoptosis and early advanced atrophy engendering only a limited regenerative response. Acinar cell apoptosis was atypical in that cell fragmentation was limited and phagocytosis delayed, resulting in extensive secondary necrosis. As ducts were unaffected by CHB, the crowded ducts making up the epithelial component of atrophic lobules could be clearly shown to derive from their condensation and proliferation, not the redifferentiation of pre-existing acinar cells, widely held to produce this lesion. Although the basis of CHB selectivity and toxicity for pancreatic acinar cells remains unknown, the potential therapeutic benefit of such an agent in patients with pancreatitis or pancreatic tumours warrants further investigation.

Cu/Zn-SOD is present in pancreatic juice and tissue. Immunohistochemical studies reveal a localization of this enzyme in islet, duct, and centroacinar cells, but to a much lower extent in pancreatic acinar cells.

It is generally accepted that oxygen radicals are involved in the pathogenesis of acute and chronic pancreatitis. An imbalance of radical-generating and radical-scavenging processes is thought to lead to the damage of pancreatic acinar cells that initiate the autodigestion of the whole organ.

We investigated the distribution pattern of the cytosolic radical-scavenging enzyme, copper/zinc-superoxide dismutase (Cu/Zn-SOD), in pancreatic juice and tissue. In patients with chronic pancreatitis or pancreatic malignancies, Cu-Zn-SOD was quantitated in different fractions of pancreatic juice by means of an enzyme immunoassay using two Cu/Zn-SOD-specific monoclonal antibodies. Cryostat or paraffin sections of pancreatic tissue were analyzed by immunohistochemical techniques.

We found this enzyme to be present in the first secretin-triggered fraction of endoscopically obtained pancreatic juice in concentrations similar to serum. In contrast, after cholecystokinin stimulation, only low levels could be found in pancreatic juice, indicating that this enzyme is not actively secreted. Interestingly, pancreatic juice of patients with chronic pancreatitis or pancreas tumor contained higher levels (25-29 ng/mL) of Cu/Zn-SOD than juice of controls without pancreatic diseases (15 ng/mL). Immunohistochemical studies of Cu/Zn-SOD in pancreatic tissue revealed a more intense staining of duct cells, islet cells, and centroacinar cells, whereas acinar cells showed almost no staining for Cu/Zn-SOD.

Redistribution of vitamin E in the rat body was studied during acute pancreatitis induced by two intraperitoneal doses of cerulein 40 micrograms/kg of body weight at 1-hr intervals. Hyperamylasemia (2064 +/- 521 vs 6419 +/- 129 U/dL) and pancreatic edema (pancreatic water content, 71 +/- 1.2% vs 78 +/- 2%) were observed. In this model the increased level of lipid soluble fluorophore was also observed (274 +/- 18 vs 120 +/- 9.0 relative fluorescence per g dry wt). Parallel with these changes was a decrease in the level of vitamin E in the serum and an increase in the pancreas. The concentration of vitamin E in the pancreas after 6 h was 162 +/- 8.5 ng/mg dry mass vs 128.1 +/- 6.1 ng/mg dry mass in control animals. The effect of heparin on vitamin E redistribution induced by acute pancreatitis was also investigated. It was found that heparin at a dose of 100 U/kg body mass prevents the drop of the vitamin E level in the serum as well as the increases in the concentration in the pancreas tissue. It was concluded that acute pancreatitis induced redistribution of vitamin E in the rat body. Moreover, we studied the effects of heparin treatment on oxidative stress in the pancreas tissue. Acute pancreatitis caused an increase in lipofuscin accumulation, and a decrease in protein sulfhydryl groups in citrate synthetase (CS) and in malate dehydrogenase (MDH) activity. Heparin treatment that protected vitamin E accumulation in the pancreas tissue did not influence the changes in the level of lipofuscin and proteins sulfhydryl.(ABSTRACT TRUNCATED AT 250 WORDS)

Xanthine oxidoreductase is an enzyme which has the unusual property that it can exist in a dehydrogenase form which uses NAD+ and an oxidase form which uses oxygen as electron acceptor. Both forms have a high affinity for hypoxanthine and xanthine as substrates. In addition, conversion of one form to the other may occur under different conditions. The exact function of the enzyme is still unknown but it seems to play a role in purine catabolism, detoxification of xenobiotics and antioxidant capacity by producing urate. The oxidase form produces reactive oxygen species and, therefore, the enzyme is thought to be involved in various pathological processes such as tissue injury due to ischaemia followed by reperfusion, but its role is still a matter of debate. The present review summarizes information that has become available about the enzyme. Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.

Many previous reports using experimental animal models of pancreatitis have suggested that oxygen free radicals play an important part in initiation and development of pancreatitis. Infiltration of inflammatory cells--that is, neutrophils, lymphocytes, and monocytes--has been seen in damaged pancreatic glands of animal models and patients with pancreatitis. As neutrophils are known to be the highest producer of oxygen free radicals among these inflammatory cells, it seems plausible that oxygen free radicals produced by neutrophils have some pathoaetiological meaning in pancreatitis. This study measured the superoxide production by neutrophils obtained from patients with acute and chronic pancreatitis and then examined the effects of pancreatic enzymes on superoxide production. Patients showed significantly higher superoxide production by 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) stimulated neutrophils than healthy controls. Among the three pancreatic enzymes, amylase, trypsin, and elastase, elastase was the only one that increased the superoxide production by PMA stimulated neutrophils, by an increment of 1.5-fold. It also increased the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase prepared from PMA stimulated neutrophils by a factor of 2.1. High affinity and low affinity binding sites for elastase on neutrophils were identified. These results suggest that elastase plays a part in the development of pancreatitis by enhancing superoxide production of neutrophils.