[Phospholipase A--a probable decisive factor in the pathogenesis of 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.

Experimental models of acute pancreatitis

Acute pancreatitis remains a disease of uncertain pathogenesis and nonspecific therapy. Because of the practical problems plaguing investigation of pancreatitis in man, investigators have developed various experimental animal models of pancreatitis in order to develop rationale concepts regarding pathogenesis and therapy. Despite numerous investigations over the past century, the events involved in the initiation and progression of pancreatitis remain obscure. Indeed, identification of the cellular mechanisms responsible for the initiation of this disease may allow for significant advances in therapy. Previous studies have largely focused on the mechanism of pancreatitis at the organ level. It is now apparent that the early initiating events in acute pancreatitis probably occur at a membrane or intracellular level. The resolution of the cellular events which underlie the development of pancreatitis in combination with the introduction of new therapeutic agents may enable a rational and safe protocol to be developed for the support of patients with pancreatitis. In this review different experimental models of acute pancreatitis are discussed. Emphasis is placed on the relevance of various models to clinical pancreatitis.

Phospholipase A2 induced diffuse alveolar damage--effect of indomethacin and dexamethasone upon morphology and plasma-histamine level

Phospholipase A2, injected as a bolus into the jugular vein of adult male Wistar rats was investigated with respect to its action upon lung morphology and blood- plasma- histamine. In comparison with the injection of saline, phospholipase A2 causes hyperemia of the lungs, sequestration of granulocytes and intraalveolar pulmonary edema; the histamine level is increased to the sixfold. Pretreatment of the animals with indomethacin diminishes the toxic effect of phospholipase A2 upon the lungs and the histamine level.

Ultracytochemistry of pancreatic damage induced by excess lysine

The ultracytochemical changes induced in the pancreas by a single large dose of lysine (400 mg/100 g body weight) were studied in male Wistar rats of 7 weeks old. The first changes in the acinar cells were marked swelling of mitochondria with increase in their calcium content and decrease in their ATP content. Early calcium deposits seemed to occur in the matrices of swollen mitochondria and later various patterns occurred. These findings suggested that damage of the acinar cells by excess lysine resulted in breakdown of the mitochondrial membrane barrier to calcium as a very early abnormality, and that extracellular calcium then entered the mitochondrial matrices and inhibited mitochondrial function. Subsequently focal areas of the cytoplasm were degraded. Autophagic vacuoles appeared in these areas, and then acid phosphatase activity in their periphery as a result of fusion with lysosomes. The reaction of acid phosphatase was demonstrated in the locally degraded rough endoplasmic reticulum within or around autophagic vacuoles, suggesting that the endoplasmic reticulum as well as lysosomes participated in the intracellular degradation of cytoplasmic organelles in damaged acinar cells.

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.

[The effect of p-bromophenacylbromide, a phospholipase A inhibitor, in experimental acute pancreatitis in rats]

In this study the effect of p-bromophenacylbromide (p-BPAB), an inhibitor of phospholipase A, was studied in acute pancreatitis in an experimental rat model. Acute pancreatitis was produced by instillation of 0.4 ml bile into the pancreatic duct. p-BPAB was injected i.p. in a dosage of 0.25 micrograms/g b.wt. 30 min before, 30 min after, or 4h after the onset of pancreatitis. Prophylactic and early administration of p-BPAB inhibited severe morphological changes, such as necrosis and hemorrhages. Moreover, during administration of the inhibitor, decreased plasma concentrations of serum lipase and amylase (P less than 0.001) were monitored and compared with untreated animals. These therapeutic effects of p-BPAB were not seen in rats in which the inhibitor was injected 4 h after the onset of pancreatitis. As a result the phospholipase inhibitor, p-BPAB, reduces the clinical and morphological manifestations of acute pancreatitis. The effect of p-BPAB is dependent on the time of administration.

The effect of early pancreatectomy and peritoneal lavage on the development of experimental haemorrhagic pancreatitis in pigs

Forty-seven piglets were operated on; haemorrhagic pancreatitis was induced in 42 of them. The effects of pancreatic resection and peritoneal lavage on the development of the disease were compared. Since the pancreatic phospholipase A2 value has been shown to be important in the pathophysiology of the disease, the effect of pancreatic resection on the enzyme serum activities was studied. Early pancreatic resection and early peritoneal lavage were equally effective in reducing the mortality of the animals. When the pancreatic resection was performed later, most of the animals died. The difference in mortality between the groups was statistically significant (p less than 0.01). In the animals with late pancreatectomy the high serum phospholipase A2 activities fell to normal levels within a few hours after the operation. This strongly suggests that the enzyme is of pancreatic origin.

Phospholipase A2 inhibitors and their possible clinical use in the treatment of acute pancreatitis

A laboratory method was established for measurement of phospholipase A2 activity in buffer and serum. A series of different phospholipase A2 inhibitors was tested. The most effective inhibitors were Ca2+ chelating compounds like EDTA, DTPA, EGTA, and phytic acid. The calcium salt of EDTA also has some inhibitory effect. Serum phospholipase A2 activity in normal healthy control patients was measured. The activity in 27 patients with acute pancreatitis was tested. The activity was abnormally high in five patients. This activity was in vitro inhibited by EDTA and partly by CaNa2EDTA. The clinical picture of these patients did not differ from that of phospholipase-A2-negative patients. Six patients with acute pancreatitis were treated by intravenous infusion of CaNA2EDTA. Two of them had haemorrhagic pancreatitis and two were suspected of having early haemorrhagic pancreatitis. During the CaNa2EDTA infusion serum amylase and phospholipase A2 activities decreased. All patients recovered. No harmful side effects were noticed.