The possible role of phospholipase A in the pathogenesis of acute pancreatitis

Phospholipase A(2) Activity in Gingival Crevicular Fluid from Patients with Periodontal Disease: A possible Marker of Disease Activity

The activity of phospholipase A₂ in human gingival crevicular fluid (GCF) associated with periodontal disease was demonstrated. Based upon the presence or absence of bleeding on probing (BOP), which is a marker for the disease activity, there were higher levels of the enzyme activity in BOP positive, than in negative sites. When the BOP positive sites became negative after periodontal therapy, the enzyme activity decreased dramatically to almost undetectable levels. There were no significant differences between the activity before and after treatment when the BOP positive sites remained unchanged. These results suggest that the activity in GCF reflects periodontal disease conditions and that it can be used as a marker for disease activity.

Vigilin and enzyme expression in isolated pancreatic acini after mellitin and gamma-interferon treatment

BACKGROUND/AIMS

Pancreatitis goes along with changes in exocrine enzyme synthesis and secretion in pancreatic acini. The multi-KH domain protein vigilin is supposed to play an important role in t-RNA trafficking especially in cells with high protein synthesis rates and may reflect the degree of stimulation of translational machinery during pathological processes. In relation to these phenomena we explored in this connection the impact of two different inflammation mediators in a system of isolated rat pancreatic acini.

METHODS

Acini were prepared from male Sprague-Dawley rats by collagenase digestion and incubated with mellitin or gamma interferon. Secretion and cytosolic cell content of pancreatic trypsin and amylase as well as the expression of vigilin were determined.

RESULTS

The phospholipase A(2) activator mellitin caused morphological alterations and increased release of trypsin and amylase, while vigilin expression and the intracellular content of these enzymes decreased. Gamma-interferon, a cytokine which is involved at different steps in inflammation processes, selectively inhibits the release of trypsin(ogen) while not affecting amylase secretion and vigilin expression.

CONCLUSION

Mellitin as well as gamma interferon causes alterations in pancreatic enzyme secretion. Additionally, mellitin seems to influence the expressed gene pattern of pancreatic acini while interferon-gamma has no effect on protein synthesis but enzyme secretion.

Serum free fatty acid concentration in patients with acute pancreatitis

BACKGROUND

The involvement of lipolytic enzymes and liberated fatty acids in ethiology of acute pancreatitis (AP) has been implicated.

AIM

To analyze the level of FFA in the patients with AP in relation to severity of the disease.

MATERIAL AND METHODS

The study included 36 patients with acute edematous AP (group I), 29 patients with necrotizing AP: 16 without (group IIA) and 13 with complications (group IIB), and 12 control subjects. Serum levels of total FFA (by enzymatic method) and the individual fatty acids of the FFA pool (by gas-liquid chromatography) were measured during the first 4 days after admission.

RESULTS

A significant increase in the mean total serum FFA was noted for all the groups with the highest values on admission (p < 0.02-0.01). The per cent contribution was significantly higher as compared to control group for oleic acid (group I, p < 0.02, group IIA, p < 0.05, group IIB, p < 0.005), linoleic acid (group IIB, p < 0.02) and arachidonic acid (group IIA, p < 0.05, group IIB, p < 0.02). Significantly lower percentage was noted for stearic acid (all three groups: p < 0.01, p < 0.005, p < 0.01, respectively) and for palmitic acid (only group IIB: p < 0.005). The ratio of saturated to polyunsaturated fatty acids was significantly lower than in control group on each day of study for group IIB only (p < 0.005-p < 0.001).

CONCLUSION

Polyunsaturated fatty acids, mainly linoleic and arachidonic, may be involved in the development of complications in acute pancreatitis.

Pancreatic phospholipase A2 activity in acute pancreatitis: a prognostic marker for early identification of patients at risk

Remarkably elevated levels of phospholipase A2 (PLA2) are measurable in human blood samples in cases of acute pancreatitis. The source of the enzyme was first thought to be exclusively the pancreas, but now it is generally accepted that two isoenzymes--the pancreatic PLA2, group I, and the extrapancreatic PLA2, group II--contribute to the raised activity. In contrast to the group II-PLA2, the pancreatic PLA2 is heat-resistant for 1 hour at 60 degrees C. The catalytically inactive proenzyme of the pancreatic PLA2 can be activated by trypsin. The aim of our study was to evaluate the diagnostic value of PLA2 isoenzyme activity measurements to identify patients with severe complications in acute pancreatitis. Blood samples from patients suffering from acute pancreatitis were analyzed for catalytically active pancreatic PLA2 on day 1 and 2 of hospitalization with a modified radiometric Escherichia coli-based PLA2 assay. In 10 of 41 patients clearly elevated values of catalytically active, heat-resistant pancreatic PLA2 (7.2 to 81.2 U/l) were observed. This group of patients was characterized by severe complications (necrotizing pancreatitis, shock, sepsis, respiratory problems) of which two patients subsequently died. Patients with low or undetectable activity (<7 U/l) of pancreatic PLA2 recovered rapidly. According to these results the presence of catalytically active pancreatic PLA2 in serum is associated with severe complications of acute pancreatitis. In contrast to total serum-PLA2, the catalytic concentration of pancreatic PLA2 can serve as a prognostic marker in acute pancreatitis.

Lysophosphatidylcholine induces apoptosis in AR42J cells

Phospholipase A2 (PLA2) has been suggested to play an important role in the pathogenesis of acute pancreatitis, in part through the PLA2-generated phospholipid by-products, most notably lysophosphatidylcholine (lyso-PC). The effects of lyso-PC on pancreatic acinar cells, other than the induction of necrosis, are poorly characterized. Here we examined the effects of lyso-PC on the induction of apoptosis in rat pancreatic AR42J cells. Lyso-PC induced apoptosis in a dose-dependent manner at 10 and 25 microM, but induced cell lysis at > or = 50 microM. Lyso-PC-induced (at 25 microM) apoptosis was not blocked by a protein kinase C inhibitor (staurosporine) or by inhibitors of caspases (acetyl-DEVD-aldehyde and benzoyloxycarbonyl-VAD-fluoromethylketone). Lyso-PC at 10 and 25 microM induced the expression of clusterin mRNA and wild-type p53. Apoptosis induction by lyso-PC (at 25 microM) was not inhibited by a specific antagonist of platelet-activating factor (PAF) receptor, suggesting that the action was independent of th

Phospholipase A2: its usefulness in laboratory diagnostics

Phospholipase A2 (PLA2) is an enzyme that catalyzes the hydrolysis of membrane phospholipids. This article reviews the source and structure of PLA2, the involvement of the enzyme in various biological and pathological phenomena, and the usefulness of PLA2 assays in laboratory diagnostics. Of particular importance is the role of PLA2 in the cellular production of mediators of inflammatory response to various stimuli. Assays for PLA2 activity and mass concentration are discussed, and the results of enzyme determinations in plasma from patients with different pathological conditions are presented. The determination of activity and mass concentration in plasma is particularly useful in the diagnosis and prognosis of pancreatitis, multiple organ failure, septic shock, and rheumatoid arthritis. A very important result is the demonstration that PLA2 is an acute phase protein, like CRP. Indeed, there is a close correlation between PLA2 mass concentration and CRP levels in several pathological conditions. Although the determination of C-reactive protein is much easier to perform and is routinely carried out in most clinical laboratories, the assessment of PLA2 activity or mass concentration has to be considered as a reliable approach to obtain a deeper understanding of some pathological conditions and may offer additional information concerning the prognosis of several disorders.

Inhibition of serum phospholipase-A2 in acute pancreatitis by pharmacological agents in vitro

Phospholipase-A2 has been suggested as having a role in the pathophysiology of acute pancreatitis. The inhibition of phospholipase-A2 was studied in vitro using 17 pharmacological agents in the search for a specific therapy for acute pancreatitis. The inhibitory effect was tested using an isotopic assay system with 2-palmitoyl-(1-14C)-labelled dipalmitoyl phosphatidylcholine as a substrate and 10 microliters of serum from patients with acute necrotizing pancreatitis as an enzyme source. Among all agents tested, anti-inflammatory drugs inhibited enzyme activity most significantly: indomethacin (9.0 x 10(-3) mol l-1) decreased the phospholipase-A2 activity to one- tenth. The weak inhibitory effect could also be demonstrated using a lower concentration of 2 x 10(-5) mol l-1, which can be achieved after intravenous administration of 50 mg of this drug. The other drugs inhibited the enzyme activity at concentrations higher than those achieved after intravenous injections in clinical use. Diclofenac (3.1 x 10(-2) mol l-1) reduced the phospholipase-A2 activity by 93%, ketoprofen (2.0 x 10(-2) mol l-1) or chlorpromazine (1.4 x 10(-2) mol l-1) by 90%, tobramycin (1.7 x 10(-2) mol l-1) by 84%, doxycycline (9.0 x 10(-3) mol l-1) by 61%, dexamethasone (1.7 x 10(-3) mol l-1) by 62%, methylprednisolone (3.8 x 10(-2) mol l-1) by 50%, and pindolol (1.0 x 10(-4) mol l-1) by 59%. A weak inhibition of phospholipase-A2 activity was demonstrated by betamethasone, bupivacaine, digoxin, hydrocortisone, lidocaine, metoprolol, propranolol, and vancomycin. Indomethacin proved the most potent of the tested agents in inhibiting phospholipase-A2 activity in serum from patients with acute pancreatitis and should be further studied in vivo.

Role of hypertriglyceridemia in the pathogenesis of experimental acute pancreatitis in rats

CONCLUSION

The pancreatic damage initiated via different pathogenetic pathways can be increased by triglycerides. Thus, triglycerides seem to play an important role in the pathogenesis of acute pancreatitis.

BACKGROUND

Lipolytic enzymes and their substrates may play a role in the pathogenesis of acute necrotizing pancreatitis. We investigated, therefore, whether triglycerides alter the course of acute pancreatitis in three experimental models of rats.

METHODS

1. Edematous acute pancreatitis induced by repeated sc injections of cerulein; 2. Necrotizing acute pancreatitis by retrograde duct injection of sodium taurocholate; and 3. Pancreatic edema by ligation of: a. The bile duct at the liver hilus; b. The common bile/pancreatic duct close to the duodenal wall; or c. A combination of a. and b. Six hours later, rats were sacrificed and the isolated perfused pancreas prepared. The pancreases were perfused with either HEPES/Ringer/HAES alone or in combination with various concentrations of triglycerides (1-5% wt/vol). The activities of lipase and amylase in the portal venous effluents were regarded as a marker of pancreatic injury. In addition, the pancreases were evaluated by light microscopy.

RESULTS

In both cerulein and taurocholate acute pancreatitis, amylase/lipase activities were significantly higher compared to controls during 45 min of perfusion. In both models, addition of triglycerides caused a dose-dependent marked elevation of enzymes. Ligation (a) did not cause any rise in enzymes in the venous effluent; triglycerides had no effect. Ligation (b) or (c) caused a significant increase of pancreatic enzymes, which was further increased by triglycerides. Histology showed various degrees of severity of tissue damage depending on the model used. The additional damaging effect of a 45-min perfusion with triglycerides, however, could not be detected by histology.

Serum pancreatic phospholipase A2 and prophospholipase A2 in acute pancreatitis and after endoscopic retrograde pancreatography

Serum immunoreactive pancreatic phospholipase A2 (IP-PLA2) levels and the proportion of active pancreatic PLA2 in the serum IP-PLA2 were determined by radioimmunoassay with an antibody directed against active human PLA2. The subjects of this study included eight patients who underwent endoscopic retrograde pancreatography (ERP), nine patients with acute pancreatitis, and six healthy controls. The serum IP-PLA2 levels were elevated after ERP and during acute pancreatitis. The amount of active pancreatic PLA2 in the serum was determined after its separation from pancreatic prophospholipase A2 using reverse-phase high-performance liquid chromatography (HPLC). The serum IP-PLA2 was separated into two peaks on reverse-phase HPLC. The one which eluted faster contained the PLA2 activity; the other peak did not. The latter IP-PLA2 peak consisted of pancreatic prophospholipase A2 as judged by HPLC analysis and PLA2 activity determination of the products after treatment with trypsin. The proportion of active pancreatic PLA2 in the serum IP-PLA2 of patients after ERP (13.9 +/- 0.5%) increased slightly compared with that in fasting, healthy controls (8.0 +/- 1.1%). For those with acute pancreatitis, the proportion of active pancreatic PLA2 within 48 hours of hospital admission increased more markedly (44.0 +/- 5.7%) than that after ERP. These findings demonstrate that the proportion of active pancreatic PLA2 in the serum IP-PLA2 markedly increases during the early stage of acute pancreatitis, and that an ERP-induced rise in the intraductal pressure leads to the leakage of pancreatic PLA2 into the circulation, but not to a marked activation of the leaked enzyme.

Distribution of pancreatic (group I) and synovial-type (group II) phospholipases A2 in human tissues

The catalytic activity of phospholipase A2 (cat-PLA2) and the concentration of pancreatic (group I) phospholipase A2 (pan-PLA2) and synovial-type (group II) phospholipase A2 (syn-PLA2) were studied in 19 human tissues in order to find potential sources of circulating phospholipase A2. Five specimens of each tissue were collected at autopsies or from normal deliveries (placentas and amnionic membranes). The concentrations of pan-PLA2 and syn-PLA2 were measured by specific time-resolved fluoroimmunoassays. The cat-PLA2 was measured by radioactive dipalmitoyl phosphatidylcholine as substrate. The concentration of pan-PLA2 was negligible in all tissue homogenates except the pancreas. Immunoreactive syn-PLA2 was found in the homogenates of the digestive tract, cartilage, and prostatic and parotid glands. By immunohistochemistry, syn-PLA2 was localized in Paneth cell secretory granules, chondrocytes, cartilage matrix, and glandular cells of prostate.

Impaired mononuclear phagocyte function in patients with severe acute pancreatitis: evidence from studies of plasma clearance of trypsin and monocyte phagocytosis

Activated proteases in plasma are complexed by alpha 2-macroglobulin. Although the complexes retain peptidase activity, they are usually eliminated promptly by mononuclear phagocytes. In severe acute pancreatitis, almost 30% of plasma alpha 2-macroglobulin becomes complexed, suggesting impaired clearance. In the present study, plasma [methyl-14C]trypsin clearance and monocyte phagocytosis were investigated. Attacks complicated by major organ-system failure, pancreatic pseudocyst, abscess, or necrosis were graded severe (median Ranson score 5.5). Plasma [methyl-14C]trypsin half-life was significantly increased in severe attacks (N = 7, median 21.1 min), compared to mild attacks (N = 14, median 15.4 min, P < 0.05) and healthy controls (N = 4, median 10.8 min, P < 0.02). Monocyte phagocytosis was significantly lower in severe attacks (N = 9, median 3.6%) compared to mild attacks (N = 20, median 20.8%, P < 0.01) and healthy controls (N = 8, median 26.9%, P < 0.01). Plasma [methyl-14C]trypsin half-life and monocyte phagocytosis were significantly inversely correlated (r = -0.51, P < 0.01). Impaired clearance of circulating trypsin in acute pancreatitis is potentially deleterious but may be reversed by stimulating mononuclear phagocytes.

Comparison of different treatment modalities in experimental pancreatitis in rats

Lipolytic enzymes may play a role in the pathogenesis of acute pancreatitis. Therefore, the effects of a lipase inhibitor, THL (tetrahydrolipstatin), a protease inhibitor, FUT (nafamostat mesilate), and albumin under different conditions in rats were investigated. (a) Isolated pancreatic acini were incubated with pancreatic homogenates and triglycerides or lecithin with or without albumin and the degree of cellular destruction quantitated. (b) Taurocholate was injected into the pancreatic duct of isolated pancreas and the organ continuously perfused with either FUT, THL, or albumin. Organ damage was evaluated by measurement of pancreatic enzymes in the portal effluence. (c) Necrotizing pancreatitis was induced in vivo via retrograde taurocholate injection. FUT, THL, or albumin was applied either intravenously or injected into the pancreatic parenchyma. (a) Albumin prevented the cellular damage caused by both fatty acids and lysolecithin. (b) THL was ineffective, FUT lowered the release of pancreatic enzymes into the portal effluence, and albumin was most effective. (c) Albumin prevented the development of panlobular necrosis and lowered the degree of extrapancreatic fat necrosis. Albumin, via its ability to bind detergents, may have therapeutic implications.

Isolated rat pancreatic acini as a model to study the potential role of lipase in the pathogenesis of acinar cell destruction

We have recently reported that lipase may play a role in the pathogenesis of acute pancreatitis by its ability to release fatty acids from triglycerides. The aim of this study was to further investigate the effect of lipase and its various digestive products on the integrity of isolated pancreatic rat acini. Pancreatic acini were prepared by collagenase digestion and their newly synthesized proteins labeled with 35S-methionine. Acini were later incubated in buffer to which various factors were added: Products of lipolytic digestion, such as various fatty acids and monoglycerides, fat tissue, nonactivated or trypsin activated homogenized pancreatic tissue, and a specific lipase inhibitor (THL, tetrahydrolipstatin). Cellular destruction was quantified by the degree of radiolabeled proteins released. Short chain fatty acids and monoglycerides (up to C-12) caused cellular destruction, whereas long chain fatty acids and their respective monoglycerides were not harmful. With regard to unsaturated fatty acids, long chain fatty acids (C-18 to C-22) were also able to destroy cells. The degree of cellular necrosis correlated with incubation time and fatty acid concentration. The cellular damage caused by incubation of acini with either inactive or trypsin activated pancreatic homogenates together with triglycerides could be completely inhibited by the specific lipase inhibitor THL. Bile alone caused no damage. When bile was combined with activated-pancreatic homogenates, about 25% of newly synthesized proteins were released by acini within 30 min. Incubation with a combination out of bile activated pancreatic homogenates and triglycerides resulted in the most pronounced damage. This acinar destruction could only be partly inhibited by THL. These studies suggest that both lipase and phospholipase-A2 may play an important role in the pathogenesis of acinar cell destruction.

Characterization of recombinant human and rat pancreatic phospholipases A2 secreted from Saccharomyces cerevisiae: difference in proteolytic processing

An expression plasmid for human pancreatic phospholipase A2 in Saccharomyces cerevisiae was constructed by insertion of cDNA encoding its preprophospholipase A2 into a yeast expression vector pAM82. The resulting product secreted in the yeast culture medium was mainly prophospholipase A2, which was the same as the natural proenzyme in all aspects examined, including the higher order structure. However, when the rat preprophospholipase A2 cDNA was manipulated in the same manner, the active phospholipase A2 of the intact mature form was secreted with the proenzyme being hardly detected in the medium. This unexpected favorable result would occur due to cleavage of rat phospholipase A2 pro-peptide by a trypsin-like proteinase in S. cerevisiae. Based on this finding, we constructed a plasmid carrying the sequence coding for the prepro-peptide of rat pancreatic phospholipase A2 behind the PHO5 promoter in the pAM82 vector, which leads to the secretion of heterologous proteins as their mature form. The use of this plasmid led to secretion of biologically active human pancreatic secretory trypsin inhibitor and a glutamic acid-specific endopeptidase from Staphylococcus aureus ATCC 12600, which are eukaryote and prokaryote proteins, respectively, in the culture medium of S. cerevisiae.

Phospholipase A2 in rat gingival tissue

Phospholipase A2 (PLA2) is a proinflammatory enzyme in the synovial fluids of all--and sera of some--patients with rheumatoid arthritis. Due to the similarities in pathogenesis between rheumatoid arthritis and periodontitis, we sought to study the enzymatic properties of PLA2 in periodontal tissue. In this study, we demonstrated PLA2 activity in rat gingival tissue, about 80% of which was present in the cytosolic fraction. We characterized the cytosolic PLA2 enzyme with respect to substrate specificity, sensitivity to detergent, Ca2+ ion dependency and optimum pH. We found that phosphatidylethanolamine, rather than phosphatidylcholine, was the preferred substrate, the Ca2+ ion was essential for the expression of PLA2 activity, the enzyme was active over a broad pH range, with the optimum at pH 9.0, and sodium-deoxycholate inhibited the enzyme activity strongly in a concentration-dependent manner. These results are consistent with those which have been obtained with synovial fluid PLA2 and suggest that gingival PLA2 may be involved in the pathogenic processes of gingivitis and periodontitis.

Impaired hepatic energy metabolism in rat acute pancreatitis: protective effects of prostaglandin E2 and synthetic protease inhibitor ONO 3307

To evaluate the effects of acute pancreatitis on the energy metabolism of the liver and on the fragility of hepatic cells and subcellular organelles, we studies (1) the arterial blood ketone body ratio (BKBR) (aceto acetate/beta-hydroxy butyrate), which is in equilibrium with the free NAD+/NADH ratio in liver mitochondria; (2) the hepatic energy charge (EC) = (ATP + 1/2 ADP)/(ATP + ADP + AMP); (3) the cathepsin B leakage from hepatic lysosomes and the malate dehydrogenase leakage from hepatic mitochondria in vitro; and (4) the protective effects of prostaglandin E2 (PGE2) and a new synthetic protease inhibitor ONO 3307 on hepatic injury in acute pancreatitis induced in rats by a supramaximal dose of caerulein. Decreased BKBR and hepatic EC as well as increased hepatic lysosomal and mitochondrial fragility were observed in rats with this type of acute pancreatitis, and both PGE2 and ONO 3307 had a significant protective effect against hepatic injury in these rats, especially ONO 3307. These results suggest that impaired hepatic energy metabolism is closely related to increased hepatic lysosomal and mitochondrial fragility and that some proteases, which are derived from pancreatitis and are susceptible to inhibition by ONO 3307, seem to play an important pathological role in this liver injury induced by pancreatitis. Therefore, it is important to take care of the liver in patients with acute pancreatitis.

Cytoprotective effects of prostaglandins and a new potent protease inhibitor in acute pancreatitis

The redistribution of cathepsin B, a lysosomal enzyme, from the lysosomal pellet to the zymogen pellet in the subcellular fractionation, the colocalization of cathepsin B with digestive enzyme, and increased cellular, lysosomal, and mitochondrial fragility within acinar cells have been found during the early stages of caerulein-induced acute pancreatitis in rats. In the present study, the authors investigated the protective effects of prostaglandin E1 and E2, a combined therapy of these prostaglandins, and a new, synthetic, low molecular weight protease inhibitor, ONO3307, on the exocrine pancreas in this noninvasive model of experimental pancreatitis in vivo and in vitro. Prostaglandin E2, but not E1, prevented hyperamylasemia, congestion of amylase and trypsinogen in the acinar cells, redistribution of cathepsin B, and amylase and lactate dehydrogenase discharge from the dispersed acini. It also prevented cathepsin B leakage from the lysosomes and malate dehydrogenase leakage from the mitochondria in an almost dose-dependent manner, particularly at the dose of 100 micrograms/kg/hr continuous infusion. Furthermore, the combined therapy of prostaglandin E2 with ONO3307 strongly inhibited all the parameters tested in this study. This combination therapy seems to be the most effective against secretagogue-induced pancreatic injuries. These results indicate that cellular and subcellular organellar fragility seem to be closely involved in the pathogenesis of acute pancreatitis. Prostaglandin E2 seems to have important cytoprotective effects on the biologic membranes, such as a stabilizer of lysosomal or mitochondrial membranes. In addition, these findings also suggest the crucial roles of some unknown proteases in the etiology of acute pancreatitis, and indicate the clinical effectiveness of prostaglandins and this type of low molecular weight protease inhibitor for acute pancreatitis.

Effects of acute pancreatitis on hepatic secretion of lysosomal enzymes into bile and hepatic lysosomal fragility: protective effects of a new synthetic protease inhibitor, ONO 3307

To evaluate the effects of acute pancreatitis on hepatic function and hepatic cellular and subcellular organellar fragility, we studied 1) the hepatic secretion of lysosomal enzymes (beta-glucuronidase, beta-galactosidase, and N-acetyl-beta-glucosaminidase) into bile in the isolated perfused rat liver model; 2) the aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT), and lysosomal enzyme levels in the effluent in an isolated liver model; 3) hepatic lysosomal fragility in an in vitro incubation study; and 4) protective effects of a new low molecular weight synthetic protease inhibitor, ONO 3307, against hepatic injury in doses of 2 and 5 mg/kg.h in acute pancreatitis induced by a supramaximal dose of cerulein in rats. Decreased hepatic secretion of lysosomal enzymes into bile and accelerated hepatic lysosomal fragility were observed in acute pancreatitis induced by cerulein. ONO 3307 showed a significant protective effect against this hepatic injury in acute pancreatitis, the dose of 5 mg/kg.h showing a more potent effect than the dose of 2 mg/kg.h. These results suggest that the impaired hepatic function, including depressed hepatic secretion of lysosomal enzymes, seems to be closely related to accelerated hepatic fragility and that some unknown protease, which is present in pancreatitis and is susceptible to inhibition by ONO 3307, plays a crucial pathologic role in the development of this liver injury during acute pancreatitis.

The diagnostic value of serum pancreatic phospholipase A2 (PLA2) in pancreatic diseases

The diagnostic significance of serum immunoreactive pancreatic phospholipase A2 (PLA2) was studied in 119 patients with pancreatic disease, 200 with various non-pancreatic disease, and 203 healthy controls using radioimmunoassay (RIA) specific to human pancreatic PLA2. This newly developed RIA using monoclonal antibody was satisfactorily sensitive and reliable. Serum PLA2 was elevated in all six patients with acute pancreatitis. Frequency of abnormal serum PLA2 levels was 60% in chronic pancreatitis (n = 52) and 67% in pancreatic cancer (n = 61). Serum PLA2 levels were low in chronic pancreatitis with severe exocrine insufficiency and advanced pancreatic cancer. In chronic pancreatitis, patients with low serum PLA2 level showed lower enzyme output in secretin test than patients with normal or high serum PLA2 level. Frequency of abnormal PLA2 levels was 27% in non-pancreatic disease and, in particular, patients with renal failure showed high PLA2 levels. Sensitivity (62%) and efficiency (69%) of serum PLA2 assay in pancreatic disease were superior to those of amylase. In conclusion, serum PLA2 determination using RIA was useful for the diagnosis of acute pancreatitis by high serum PLA2 levels and the diagnosis of severe exocrine pancreatic insufficiency by low serum PLA2 levels.

Evidence of intracellular activation of serine proteases in acute cerulein-induced pancreatitis in rats

It is believed that activation of zymogen proteases occurs in the early development of acute pancreatitis. This hypothesis was proved on subcellular fractions of rat pancreas after induction of pancreatitis by infusion of high doses of cerulein for 2 h. Secretory enzyme activities were measured spectrophotometrically in subcellular fractions obtained by differential ultracentrifugation. Additionally, trypsin and chymotrypsin activities were detected by enzyme blots after isoelectric focusing. Finally immunoblotting (Western-blot analysis) for amylase, lipase, trypsin/ogen, and chymotrypsin/ogen was carried out on fractions separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). In cerulein pancreatitis, subcellular fractions of secretory granules and vacuoles showed significant amounts of free trypsin and chymotrypsin activities compared with controls. The presence of free activities of serine proteases was paralleled by the appearance of numerous low molecular weight peptides detected by 2-dimensional electrophoresis and SDS-PAGE, which in part represented proteolytically cleaved secretory proteins. It is concluded that the intracellular activation of serine proteases that occurs in cerulein pancreatitis could contribute to further acinar cell destruction.

The role of phospholipase A2 in pancreatic acinar cell injury

The integrity of rat pancreatic acinar cells under the influence of human phospholipase A2 (PLA2) was studied. Isolated pancreatic acini showed no increased discharge of aspartylaminotransferase (ASAT) when incubated either in solutions containing human pancreatic PLA2 or the bile salt sodium deoxycholate (DEC), the latter in concentrations that augment PLA2 activity but have no destructive detergent effect. When human pancreatic PLA2 was injected into the rat pancreatic duct, uneven distribution was observed at 15 min and 3 h in immunohistochemical sections. Edema and a mild inflammatory reaction were the main changes in the pancreas. The necrotic areas seen by light and electron microscopy were quite small and located mostly at the periphery of lobules corresponding the spread of the injected material. Necrosis was of the coagulation type and showed equal extent after the injection of PLA2 with or without DEC. Internalized human pancreatic PLA2 was present already 15 min after the injection in the cytoplasm of some intact acinar cells, indicating a functioning protective mechanism. It was concluded that pancreatic acinar cells are quite resistant to PLA2-catalyzed hydrolysis of membrane phospholipids in vitro, but additional trauma, e.g., pressure caused by intraductal injection, and tissue related factors, such as the mediators of the inflammatory reaction, make acinar cells susceptible to the effect of PLA2.

Phospholipases in biology and medicine

Phospholipases, a group of enzymes that catalyze the hydrolysis of membrane phospholipids, are classified according to the bond cleaved in a phospholipid into PLA1 (EC 3.1.1.3), PLA2 (EC 3.1.1.4), PLB (EC 3.1.1.5), PLC (EC 3.1.4.3), and PLD (EC 3.1.4.4). This paper reviews source and structure of PLA2 and the involvement of PLA2 and PLC in several biological phenomena, such as, signal transduction, photoreception, biosynthesis of lung surfactant, sperm motility, and fertilization. New assays for PLA2 activity and concentration in biological fluids are discussed. Phospholipases are involved in many inflammatory reactions by making arachidonate available for eicosanoid biosynthesis. The determination of PLA2 activity and mass concentration in plasma is useful in the diagnosis and prognosis of pancreatitis and of septic shock. Naturally occurring phospholipase inhibitors, such as lipocortins act as second messengers in the anti-inflammatory response to steroids. Lipocortins may be valuable therapeutic agents, because they are more specific in their anti-inflammatory action than glucocorticoids; therefore, they are less likely to produce harmful side effects.

Phospholipase A2 activity and concentration in several body fluids in patients with acute pancreatitis

According to recent studies, phospholipase A2 (PLA2) may be an important factor in the pathogenesis and pathophysiology of acute pancreatitis. Increased serum PLA2 activities and concentrations have been measured in patients with acute pancreatitis. Serum PLA2 activities have been shown to correlate with the severity and prognosis of the disease. To study the different methods of PLA2 determination, we measured the PLA2 activity by means of an isotopic assay method and the concentration by a radioimmunologic method in several body fluids of 52 consecutive patients with acute pancreatitis. PLA2 activity and concentration were detected in all of the patient body fluids. The serum PLA2 activities were 2.5-fold higher (mean +/- SD, 7.6 +/- 6.0) than normal activities, and the concentrations were 9.6-fold higher (mean +/- SD, 41 +/- 88). The enzyme activities and concentrations correlated well in ascites, fluids from the pleural cavity, and peritoneal lavation and poorly in serum, urine, and fluid from pancreatic pseudocyst.

Serum enzymes and other laboratory tests in acute pancreatitis

This review evaluates selective enzymes and blood tests available for the diagnosis and prognosis of acute pancreatitis. It is concluded that serum amylase and lipase measurements represent the best available diagnostic methods. Newer alternative assays still require careful evaluation.

Role of phospholipase A2 in human acute pancreatitis

In a prospective clinical trial, 85 patients with acute pancreatitis, including 50 with acute interstitial-edematous pancreatitis and 35 with necrotizing pancreatitis, were recruited. Serum pancreatic immunoreactive phospholipase A2 (IR-PLA2), serum phospholipase A catalytic activity (CA-PLA), and serum phospholipase A2 catalytic activity (CA-PLA2) were determined daily between day 1 and day 10 after the onset of the disease. The serum course of IR-PLA2 values for patients with acute interstitial-edematous pancreatitis was comparable to that for patients with necrotizing pancreatitis. In contrast, the determination of CA-PLA and of CA-PLA2 specific activity in the serum revealed a high differentiation between patients with interstitial edematous and those with necrotizing pancreatitis. The overall accuracy for differentiating patients with necrotizing pancreatitis from those with the interstitial-edematous type was 79% for CA-PLA and 77% for CA-PLA2 (cut-off level: CA-PLA, 15 U/L, day 1-5; CA-PLA2, 3.5 U/L, day 1-5). Patients with pancreatitis-associated pulmonary complications showed significantly higher CA-PLA and CA-PLA2 values in the serum. This study demonstrates the role of serum catalytic phospholipase A2 in human acute pancreatitis where the development of pancreatic necrosis and pulmonary failure is concerned.

Alterations in digestive function caused by pancreatic disease

Pancreatic exocrine secretion is regulated by a complex interaction of meal-stimulated neurohormonal reflexes. Pancreatic enzyme output must be reduced to less than 10 per cent of normal before fat absorption is appreciably impaired, proving that the pancreas secretes a large surplus of enzymes. Surgical therapy does not improve pancreatic exocrine insufficiency, and partial pancreatic resection frequently precipitates steatorrhea in patients with chronic pancreatitis. Therefore, pancreatic resection should be undertaken cautiously in patients who do not yet have clinically evident exocrine insufficiency. In most patients, oral pancreatic enzymes will control diarrhea secondary to steatorrhea. In others, concurrent administration of an H2 blocker is required to reduce gastric acidity and prevent enzyme inactivation in the stomach. Formulations with an acid-resistant coating are also effective in some patients. However, complete normalization of fat absorption with restoration of body weight and nutritional well-being requires careful management of multiple dietary and behavioral factors, as well as long-term follow-up. Unfortunately, this appears to be an elusive goal, as many patients with chronic pancreatitis continue to die of malnutrition.

Inhibition of porcine pancreas phospholipase A2 activation by gabexate mesilate

We investigated the effect of gabexate mesilate on the catalytic activity of phospholipase A2 in homogenized porcine pancreatic tissue. Gabexate mesilate is a potent inhibitor of serine proteases. There is no direct inhibition of phospholipase A2 catalytic activity in concentrations up to 6 mmol/l. Preincubation of homogenized pancreatic tissue with gabexate mesilate leads to a reduction of phospholipase A2 activity even in concentrations as low as 6 mumol/l. The activation of purified porcine prophospholipase A2 added to pancreatic tissue can be completely inhibited. Thus gabexate mesilate might influence the activation of phospholipase A2 administered in therapeutic concentrations in inflamed pancreatic tissue.

Serum phospholipase--regulatory and pathophysiological aspects

The development of a photometric procedure to measure phospholipase A activity has extended previous observations that this enzyme activity increases in several pathological states including pancreatic and inflammatory diseases. Serum phospholipase A in pancreatitis was characterized as a mixture of the pancreatic enzyme and a different phospholipase with a pH optimum at 8.0. The latter enzyme was also observed in nonpancreatic diseases like septicemia and acute lung failure which are characterized by an increase in tissue phagocyte activity. The possible pathogenic role of phospholipase(s) A, their intracellular regulation and the proposed mechanisms of release into the blood stream are discussed with respect to the present pathobiochemical knowledge. This includes the mechanism of activation of phagocytosis and the possible role of lipocortins known to be stimulated by glucocorticoid treatment.

Prognostic value of serum phospholipase A in acute pancreatitis

Serum from 48 patients with acute pancreatitis (21 with interstitial-edematous and 27 with necrotizing pancreatitis) was monitored for immunoreactive (IR) phospholipase A2 (PLA2) protein concentration and PLA catalytic activity. In both groups within 48 h after start of acute pancreatitis an up to tenfold increase of IR-PLA2 was demonstrable. Determination of IR-PLA2 revealed no differences between the groups. In contrast, determination of PLA catalytic activity allowed us to differentiate between patients with interstitial-edematous and necrotizing pancreatitis.

Phospholipase A2 activity in taurocholate-induced acute pancreatitis in the rat model

The activity of phospholipase A2 (PA2) was measured in the plasma of rats after the induction of acute pancreatitis. Buffered sodium taurocholate (3.75% w/v), injected into the pancreatico-biliary duct, was used to induce acute pancreatitis. Blood was taken at 1-h intervals for the measurement of phospholipase A2, glucose, lipase, and arterial gases. Plasma lipase was markedly elevated in the test groups, indicating acute pancreatitis, but no significant difference in PA2 activity was seen between the controls and the test group. However, in four animals the PA2 activity was elevated and in all cases this was accompanied by a low arterial pO2. This supports the theoretical role of PA2 in the pathogenesis of the respiratory complications observed in severe acute pancreatitis.

The effect of gabexate mesilate on the outcome of acute hemorrhagic pancreatitis in pigs

The effects of gabexate mesilate (GM) on hemodynamics and phospholipase A2 activities (PLA2) during acute hemorrhagic pancreatitis (AHP) were studied in 17 piglets which were randomly divided into three groups: The control group (CG) received only the fluid replacement, whereas the pretreatment group (PG) was given an infusion of GM (20 mg/kg/5h), which was started 30 min before and in the treatment group (TG) 30 min after the induction of AHP. AHP was induced by infusing a mixture of trypsin and sodiumtaurocholate (1 ml/kg) into the pancreatic duct, and the animals were followed up for 5h. Two animals of the CG died, but no mortality was observed in the other groups. Histologically, acute hemorrhagic pancreatitis was detected in all animals, but no significant differences were observed between the groups. PLA2 activity in the serum increased rapidly after the induction of AHP in the CG, and it was significantly (P less than 0.05) higher 5h after the induction in the CG than in TG or PG. No significant differences developed between the groups in cardiac indices or hemodynamic pressure parameters during the 5h of surveillance, but the volume of secreted exudate into the peritoneal cavity was significantly (P less than 0.05) smaller in the PG than in the CG. In conclusion, GM treatment and pretreatment reduced mortality and the amount of the secreted ascitic fluid during AHP. Moreover, the activity of circulating PLA2 was inhibited in the groups receiving GM.

A simple isotopic assay method for human serum phospholipase A2 activity

An assay using 2-(1-14C)palmitoyl-labelled dipalmitoyl phosphatidylcholine substrate for the determination of serum phospholipase A2 (PLA2) activity is described and validated. The rapid determination of the enzyme activity is enabled by a simple liquid-liquid partition system to replace the laborious thin-layer chromatography used in earlier studies. The PLA2 activity of human pancreatic juice was used for the optimization of the assay. Interference by serum phospholipids can be avoided by using 10 microliter aliquots of serum in the assay, whereas larger amounts caused a progressive inhibition of the enzyme activity. Virtually no enzyme activity is determined in serum from normal healthy subjects (range from 1.2 to 3.0 IU/l). In acute haemorrhagic pancreatitis the PLA2 activity is markedly elevated (range from 10.7 to 42.0 IU/l). Due to the simple extraction of the reaction products the results can be obtained the same day. Therefore, the assay can conveniently be used for the rapid clinical identification of subjects with acute haemorrhagic pancreatitis.

The generation of lysolecithin by enterokinase in trypsinogen prophospholipase A2 lecithin mixtures, and its relevance to the pathogenesis of acute necrotising pancreatitis

The cascade enterokinase-trypsinogen-prophospholipase A2 lecithin, generating trypsin, phospholipase A2 and lysolecithin, respectively, was studied in vitro using a novel phospholipase A2 assay. The rate of enterokinase catalysed activation of trypsinogen was maximal at 4 mmol/1 glycodeoxycholic acid; higher concentrations of bile salt progressively inhibited enterokinase activity. Net phospholipase A2 activity in reaction mixtures was critically dependent on the trypsin/prophospholipase A2 molar ratio. Lecithin hydrolysis by phospholipase A2 was dependent on the bile salt/lecithin molar ratio and was optimal at 1.25 to 1. The addition of enterokinase to lecithin and bile salt mixtures, containing trypsinogen and prophospholipase A2 at presumed pathophysiological concentrations, resulted in the generation of concentrations of lysolecithin lytic for pancreatic acinar cells within 5 min. These findings would support the concept that the entry of bile containing active enterokinase into the pancreatic duct system in vivo may in some cases be involved in the initiation of necrotising acute pancreatitis in man.

Gabexate mesilate and camostate: new inhibitors of phospholipase A2 and their influence on the alpha-amylase activity in serum of patients with acute pancreatitis

The new synthetic polyvalent protease inhibitors gabexate mesilate (ethyl-p[6-guanidinohexanoyloxy]-benzoate methansulfonate) and camostate (N,N-dimethylcarbamoylmethyl-4-[4-guanidinobenzoyloxy]-phenylacetate methansulfonate) were tested for possible inhibition of phospholipase A2 activity. In a pilot study, we treated 17 patients suffering from acute pancreatitis with continuous intravenous administration of gabexate mesilate, 450 mg/d. The results were compared with a placebo group (same standard therapy) of 21 patients suffering from acute pancreatitis. In vitro experiments showed that, at concentrations between 10(-4) and 5 X 10(-4) mol/L (depending on the enzyme assay employed) for gabexate mesilate and between 10(-3) and 5 X 10(-4) mol/L for camostate, a 50% reduction in phospholipase A2 activity was effected. Comparing the two groups of acute pancreatitis patients after 6 days of treatment with gabexate mesilate, we observed a statistically significantly lower alpha-amylase activity in the serum of treated patients compared with the placebo group.

Hydrolytic activities of human pancreatic phospholipase A2 and endotoxin-stimulated endogenous phospholipase A2 toward membrane phospholipids of erythrocytes

The problem of whether human pancreatic phospholipase A2 (PLA2) can really hydrolyze membrane phospholipids in vitro was studied to understand pathophysiology of acute pancreatitis. Total amount of lysophospholipids generated in erythrocytes by exogenously added human pancreatic PLA2 (2 micrograms/ml) was only 12% of the amount of sphingomyelin, which was not decomposed by the enzyme. About fivefold the amount of lysophospholipids was generated in ghost membranes during one-sixth of the incubation time compared to that in intact erythrocyte membranes. Escherichia coli lipopolysaccharide (LPS) (10 micrograms/ml) was able to stimulate membrane-associated PLA2 of erythrocytes, the amount of lysophospholipids generated being 12.5% of that of sphingomyelin without adding the exogenous PLA2. The stimulation of membrane-associated PLA2 in erythrocytes was inhibited by pretreatment of lipopolysaccharide with polymyxin-B sulfate. When intact erythrocytes were incubated with human pancreatic PLA2 and LPS, the amount of generated lysophospholipids was 24% of that of sphingomyelin. These results suggested that the exogenously added human pancreatic PLA2 cannot degrade phospholipids of intact erythrocytes so extensively under physiological conditions, and, in acute pancreatitis, unknown factors may be involved in the hydrolysis of phospholipids. LPS, which activates membrane-associated PLA2, may be one of the factors, and thus membrane phospholipids are hydrolyzed in the disease.

A rational approach to the specific chemotherapy of pancreatitis

Oedematous pancreatitis is pancreatic acinar cell damage with leakage into the peritoneal cavity and circulation of the inactive zymogens of digestive enzymes and active amylase and lipase. Pancreatic oedema and intra-abdominal fat necrosis occur. Necrotising pancreatitis is pancreatic acinar cell damage accompanied by the specific conversion of trypsinogens to trypsins, at a rate, and on a scale, sufficient to overwhelm local defences. Rapid release of the whole spectrum of activated pancreatic enzymes leads to necrosis of parts of the pancreas and blood vessels, and the disseminated enzyme-mediated damage which characterises the molecular pathology of the established severe disease. Chronic pancreatitis, although less well understood, is also associated with trypsinogen activation within the gland. Two mechanisms have emerged as initiators of trypsinogen activation, lysosomal cathepsins and bile-borne enterokinase. Chemotherapeutic strategies against disease initiation include preparation of synthetic enterokinase and Cathepsin B inhibitors. Chemotherapeutic strategies against second-stage mediation of multi-organ damage in the disease, include oligopeptide or organic functionalities with novel catalytic site-directed moieties (such as fluoromethyl ketones) suitable for in vivo use and the specific inhibition of the relevant range of enzymes in complex with alpha 2-macroglobulin. Interference with pancreatic enzyme biosynthesis using proteolysis-resistant constructs mimicking receptor-binding domains of inhibitor peptide hormones as well as inhibitors of pancreatic signal peptidase are promising additional chemotherapeutic approaches worthy of active investigation.

A randomized double-blind study using CaNa2EDTA, a phospholipase A2 inhibitor, in the management of human acute pancreatitis

In a randomized double-blind study the effect of CaNa2EDTA, a phospholipase A2 inhibitor, was tested as a treatment for acute pancreatitis. CaNa2EDTA was infused intravenously during the first 2 days after admission to hospital, in addition to normal conservative treatment. CaNa2EDTA decreased the serum phospholipase A2 activity and appeared to promote recovery from the illness. To what extent the inhibition of serum phospholipase activity may prevent the progress of severe haemorrhagic pancreatitis or diminish mortality and morbidity in acute pancreatitis should be investigated in further studies.

Effects of the serine protease inhibitor gabexate mesilate on purified pancreatic phospholipase A2

The catalytic activity of purified porcine pancreatic phospholipase A2 is competitively inhibited by the cationic amphiphilic serine protease inhibitor gabexate mesilate (ethyl 4-(6-guanidinohexanoyloxy) benzoate methanesulfonate). A Ki of 1.3 X 10(-4)M was found when 1,2-dioctanoyl-sn-glycero-3-phosphorylcholine was used as a substrate. The main metabolites of this drug, 6-guanidinocaproic acid and ethyl p-hydroxy-benzoate, had no effect in concentrations up to 10(-2)M. From the high gabexate mesilate concentrations required to reduce phospholipase A2 activity and from the considerably lower drug concentrations sufficient to cause beneficial effects in acute pancreatitis it is concluded that direct inhibition of pancreatic phospholipase A2 cannot be the cause of the therapeutic results, improvement of the symptoms and prognosis of acute pancreatitis.

Effects of urinary trypsin inhibitor on pancreatic enzymes and experimental acute pancreatitis

Therapeutic effect and the mechanism of the action of human urinary trypsin inhibitor (MTI) on experimental acute pancreatitis were studied. MTI significantly increased survival rate of animals with experimental acute pancreatitis induced by the infusion of trypsin or phospholipase A2 into pancreas or by a closed duodenal loop. The efficacy of MTI on these types of pancreatitis were higher than those of aprotinin. Pancreatic enzymes were released from pancreatic slice by trypsin or phospholipase A2, and this release was inhibited by MTI. Further, these pancreatic enzymes caused a secondary release of enzymes from other pancreatic slice, suggesting that these enzymes injured pancreatic tissue and that a chain reaction of pancreatic enzyme activation may play an important role in the pathogenesis of acute pancreatitis. MTI suppressed the secondary enzyme-induced pancreatic injury more strongly than aprotinin. These results suggest that MTI may suppress pathogenesis and development of pancreatitis by inhibiting the chain reaction of pancreatic enzyme activation.