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

Phospholipase A2 subclasses in acute respiratory distress syndrome

Phospholipases A2 (PLA2) catalyse the cleavage of fatty acids esterified at the sn-2 position of glycerophospholipids. In acute lung injury-acute respiratory distress syndrome (ALI-ARDS) several distinct isoenzymes appear in lung cells and fluid. Some are capable to trigger molecular events leading to enhanced inflammation and lung damage and others have a role in lung surfactant recycling preserving lung function: Secreted forms (groups sPLA2-IIA, -V, -X) can directly hydrolyze surfactant phospholipids. Cytosolic PLA2 (cPLA2-IVA) requiring Ca2+ has a preference for arachidonate, the precursor of eicosanoids which participate in the inflammatory response in the lung. Ca(2+)-independent intracellular PLA2s (iPLA2) take part in surfactant phospholipids turnover within alveolar cells. Acidic Ca(2+)-independent PLA2 (aiPLA2), of lysosomal origin, has additionally antioxidant properties, (peroxiredoxin VI activity), and participates in the formation of dipalmitoyl-phosphatidylcholine in lung surfactant. PAF-AH degrades PAF, a potent mediator of inflammation, and oxidatively fragmented phospholipids but also leads to toxic metabolites. Therefore, the regulation of PLA2 isoforms could be a valuable approach for ARDS treatment.

Contractions to histamine in pulmonary and mesenteric arteries from endotoxemic rabbits: modulation by vascular expressions of inducible nitric-oxide synthase and histamine H1-receptors

The inducible isoform of nitric-oxide synthase (iNOS) is highly expressed after induction of endotoxemia and contributes to vascular hypocontractility in endotoxemia. Circulating levels of histamine are elevated in animal models of sepsis and in patients with septic shock. This study assessed whether the vascular effects of histamine play a significant role in the pathophysiology of endotoxemic shock despite the hyporesponsiveness to vasoconstrictors associated with iNOS up-regulation. Rabbits were rendered endotoxemic by lipopolysaccharide (LPS; 100 microg/kg, i.v.). In mesenteric arteries taken from animals at 6 h of LPS administration, the contractile response to histamine was significantly impaired but histamine-evoked contractions in pulmonary arteries were unchanged. Western blot revealed a drastic increase in iNOS expression in mesenteric vessels after LPS, but endotoxin-induced iNOS increase was not so marked in pulmonary vessels. On the other hand, expression of endothelial nitric-oxide synthase was suppressed under LPS challenge in both types of vessels. In the presence of NG-nitro-l-arginine or (S)-ethylisothiourea used for iNOS inhibition, histamine-evoked contractions of endotoxemic pulmonary and mesenteric vessels were significantly enhanced. This was possibly associated with a dramatic increase in H1-receptor expression at the gene and protein levels, as determined by Northern blot and immunoblot analyses. Furthermore, we found that LPS-induced endotoxemia caused prominent increases in production of histamine through induction of histidine decarboxylase in tissues, including blood vessels. From these results, we propose that histamine may contribute to the development of endotoxin-induced pulmonary hypertension.

Serum phospholipases A2 in patients undergoing panproctocolectomy because of severe ulcerative colitis

A major role has been proposed for group II phospholipase A2 in the pathogenesis of local and generalised inflammatory reactions. Elevated catalytic activity and mass concentrations of this enzyme have been found in serum and tissue samples of the colon in patients with active ulcerative colitis. The cellular source(s) of group II phospholipase A2 in the blood circulation is (are) unknown. In the current prospective study, we investigated the mass concentration of group II phospholipase A2 and the catalytic activity concentration of phospholipase A2 in serial serum samples of 15 consecutive patients who underwent a standard panproctocolectomy operation for severe ulcerative colitis. Both the catalytic activity concentrations of phospholipase A2 and the mass concentrations of group II phospholipase A2 increased rapidly in serum samples to maximum values on the first postoperative day and then decreased (p = 0.002 and p < 0.001, respectively) in patients who recovered uneventfully. Three patients had postoperative complications that further increased the enzyme concentrations at the time of respective complications. The pattern of group II phospholipase A2 mass concentration profiles was similar to the profiles of C-reactive protein. The results show that the removal of the large bowel does not eliminate the potential to secrete group II phospholipase A2 into the blood circulation in these patients. Secretion of group II phospholipase A2 into the circulation after surgery seems to be a normal host response to a major abdominal operation and postoperative complications. Consequently, we conclude that the large bowel is not an important source of group II phospholipase A2 in sera of patients with ulcerative colitis. The results also support the assumptions that the catalytic activity of phospholipase A2 in serum is attributable to group II phospholipase A2 and that this enzyme is an acute phase protein.

Platelet-activating factor and phospholipase A2 in patients with septic shock and trauma

OBJECTIVE

To study blood and bronchoalveolar lavage (BAL) fluid levels of platelet activating factor (PAF-acether) and phospholipase A2 (PLA2) in patients with septic shock or following severe trauma.

DESIGN

Prospective controlled clinical study.

SETTING

An intensive care unit (ICU) of a university hospital.

PATIENTS AND PARTICIPANTS

The study comprised 12 patients, 8 with septic shock and 4 with trauma, consecutively admitted to the ICU. Healthy volunteers were used as controls.

MEASUREMENTS AND RESULTS

Blood PAF-acether and plasma PLA2 levels were measured within 24 h after the patients arrival to the ICU. The Apache II score and outcome were registered. Median values for PAF-acether and PLA2 in the septic shock patients were 10.5 x 10(-10) M and 5300 units/ml, respectively, whereas corresponding values in the trauma patients were 1.3 x 10(-10) M and 770 units/ml. Normal healthy individuals had no detectable PAF-acether in the circulating blood (< 0.5 x 10(-10) M), and normal plasma PLA2 activity was < 300 units/ml. Moreover, both PLA2 and PAF-acether levels correlated well with the severity of the disease as assessed by the Apache II scoring system (p < 0.01 for PLA2 and p < 0.05 for PAF-acether). In addition, PAF-acether and PLA2 were determined in BAL fluid of patients with septic shock (n = 5) and trauma (n = 3); increased PAF-acether levels were found in four patients with septic shock and one patient with trauma.

CONCLUSION

These results demonstrate a significant increase of both PLA2 and PAF-acether in the circulation of trauma patients, and a further increase in septic shock patients. It is possible that PAF-acether and PLA2 can be used as markers for the severity of the disease in septic shock and following severe trauma.

Pancreatic phospholipase A2 in cerulein-induced acute pancreatitis in the rat

We investigated the concentration of immunoreactive pancreatic phospholipase A2 (pan-PLA2) and the catalytic activity of phospholipase A2 (CA-PLA2) in plasma and pancreases of rats with cerulein-induced acute pancreatitis. Edematous pancreatitis with ascites and fat necroses in the abdominal cavity developed after 8 h infusion of cerulein (5 micrograms/kg/h). Large vacuoles were found in acinar cells and there were small areas of acinar cell necrosis. No pathological changes were seen in saline-infused control animals. Pancreatic PLA2 was localized by immunohistochemistry in pancreatic acinar cells in both groups of animals and in the proximal tubular cells of the kidney in cerulein-infused animals. The lungs and kidneys appeared normal by light microscopy in all animals. The pan-PLA2 values increased markedly, whereas the CA-PLA2 values did not change during the cerulein-infusion. The CA-PLA2 values in the homogenates of pancreatic tissue of cerulein-infused animals did not differ significantly from those of saline-infused controls. The results indicate that the CA-PLA2 in plasma is independent from the concentration of pan-PLA2 in cerulein-induced acute pancreatitis in rat.

Systemic phospholipase A2 and cachectin levels in adult respiratory distress syndrome and multiple-organ failure

In this clinical study we have prospectively measured plasma phospholipase A2 (PLA2) activity and tumor necrosis factor (TNF) levels in ventilated intensive care unit (ICU) patients with (n = 9) and without (n = 12) evidence of respiratory distress syndrome (ARDS) and multiple-organ failure (MOF). The median peak TNF concentration in control patients was 40 ng/L (range less than 40-100 ng/L) and in ARDS patients 231 ng/L (range 100-2550 ng/L; p less than 0.001). All of the control patients were discharged alive from the ICU, whereas 6 of 9 ARDS patients died in the ICU. In 6 ARDS patients, it was possible to measure more than 4 consecutive plasma TNF levels. Of these 6 patients, the 3 with persistent elevations in systemic TNF above 230 ng/L succumbed (p less than 0.05, one-tailed). Patients with ARDS also had parallel elevations in plasma PLA2 activity above controls. These elevations were significant for arterial PLA2 activity but not for venous PLA2 activity. Our study suggests that serial measurement of plasma (arterial or venous) TNF levels may have (1) prognostic and (2) etiologic significance in ICU patients with ARDS and MOF.

Phospholipase A2--a mediator between proximal and distal effectors of inflammation

Phospholipase A2 (PLA2) is known to play an important intracellular role in inflammatory processes but does it also perform a vital function extracellularly? Here, W. Pruzanski and P. Vadas marshall the evidence supporting PLA2 as a mediator of inflammation, specifically in linking local and systemic effects.

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.