Human group II phospholipase A2. Characterization of monoclonal antibodies and immunochemical quantitation of the protein in synovial fluid

Secreted phospholipase A2 is increased in meconium-stained amniotic fluid of term gestations: potential implications for the genesis of meconium aspiration syndrome

BACKGROUND

Meconium-stained amniotic fluid (MSAF) represents the passage of fetal colonic content into the amniotic cavity. Meconium aspiration syndrome (MAS) is a complication that occurs in a subset of infants with MSAF. Secreted phospholipase A2 (sPLA2) is detected in meconium and is implicated in the development of MAS. The purpose of this study was to determine if sPLA2 concentrations are increased in the amniotic fluid of women in spontaneous labor at term with MSAF.

MATERIALS AND METHODS

This was a cross-sectional study of patients in spontaneous term labor who underwent amniocentesis (n = 101). The patients were divided into two study groups: (1) MSAF (n = 61) and (2) clear fluid (n = 40). The presence of bacteria and endotoxin as well as interleukin-6 (IL-6) and sPLA2 concentrations in the amniotic fluid were determined. Statistical analyses were performed to test for normality and bivariate analysis. The Spearman correlation coefficient was used to study the relationship between sPLA2 and IL-6 concentrations in the amniotic fluid.

RESULTS

Patients with MSAF have a higher median sPLA2 concentration (ng/mL) in amniotic fluid than those with clear fluid [1.7 (0.98-2.89) versus 0.3 (0-0.6), p < 0.001]. Among patients with MSAF, those with either microbial invasion of the amniotic cavity (MIAC, defined as presence of bacteria in the amniotic cavity), or bacterial endotoxin had a significantly higher median sPLA2 concentration (ng/mL) in amniotic fluid than those without MIAC or endotoxin [2.4 (1.7-6.0) versus 1.7 (1.3-2.5), p < 0.05]. There was a positive correlation between sPLA2 and IL-6 concentrations in the amniotic fluid (Spearman Rho = 0.3, p < 0.05).

CONCLUSION

MSAF that contains bacteria or endotoxin has a higher concentration of sPLA2, and this may contribute to induce lung inflammation when meconium is aspirated before birth.

Secretory and cytosolic phospholipase A(2)regulate the long-term cytokine-induced eicosanoid production in human keratinocytes

The involvement of cytosolic phospholipase A(2)(cPLA(2)) and secretory non-pancreatic PLA(2)(npPLA(2)) in release of arachidonic acid (AA) preceding eicosanoid formation in the human keratinocyte cell line HaCaT was examined. Interleukin 1beta (IL-1beta) and tumour necrosis factor-alpha (TNF), phorbol myristate acetate (PMA) and calcium ionophore A(23187)increased the extracellular AA release, and stimulated eicosanoid synthesis as determined by HPLC analysis. The main metabolites after stimulation with IL-1beta, PMA or A(23187)were PGE(2), an unidentified PG and LTB(4), while TNF stimulated HETE-production. Both cPLA(2)and npPLA(2)message and enzyme activity were detected in unstimulated HaCaT cells. IL-1beta, PMA and TNF increased both cPLA(2)enzyme activity and expression, but did not lead to any increase in npPLA(2)expression or activity. The selective npPLA(2)inhibitors LY311727 and 12-epi-scalaradial, or the cPLA(2)inhibitor arachidonyl trifluoro methyl ketone (AACOCF(3)) reduced IL-1beta-induced eicosanoid production in a concentration dependent manner. The results presented strongly suggest that both cPLA(2)and npPLA(2)contribute to the long-term generation of AA preceding eicosanoid production in differentiated, human keratinocytes. Inhibitors against npPLA2 or cPLA2 enzymes should be useful in treating inflammatory skin diseases, such as psoriasis.

Increased sensitivity to endotoxemia in the bile duct-ligated cirrhotic Rat

Sepsis is a common complication of cirrhosis with a high mortality. In this study, we have investigated some of the pathways that may be involved in tissue injury and death. Bile duct-ligated (BDL) cirrhotic and control rats were challenged with lipopolysaccharide (LPS). Sensitivity to LPS was markedly enhanced in the BDL group, and was associated with increased liver injury and mortality. There was a 5-fold constitutive activation of nuclear factor kappa B (NFkappaB) in the liver of BDL rat controls (P <.001), and this was activated further, but to a similar extent, in the liver of both sham and BDL rats after injection of LPS. Plasma tumor necrosis factor alpha (TNF-alpha) increased more markedly in the BDL cirrhotic rats (2,463 +/- 697 pg/mL in BDL rats versus 401 +/- 160 pg/mL in the controls at 3 hours; P <.01). Plasma nitrite/nitrate concentrations were increased in the BDL controls at baseline, and increased further after LPS (P <.05), but did not differ from sham controls at 6 hours. Plasma F(2)-isoprostanes increased 6-fold in the cirrhotic rats and 2-fold in the controls (P <.01) indicative of lipid peroxidation. Esterified F(2)-isoprostanes in the liver increased 2- to 3-fold at 1 hour in control and BDL rats, but returned to baseline levels by 3 hours. Esterified F(2)-isoprostanes in the kidney increased by 2-fold in the BDL rats after LPS administration, but remained unchanged in sham controls. We conclude that there is a marked increase in sensitivity to LPS in BDL cirrhotic rats. This is associated with an enhanced TNF-alpha response and increased lipid peroxidation. These may be directly and causally related to mortality.

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.

Differential activation of human neutrophil cytosolic phospholipase A2 and secretory phospholipase A2 during priming by 1,2-diacyl- and 1-O-alkyl-2-acylglycerols

We have shown previously that both 1,2-diacylglycerol (AAG) and 1-O-alkyl-2-acylglycerol (EAG) prime neutrophil release of arachidonic acid via uncharacterized phospholipases A2. Therefore, we investigated the actions of EAG and AAG specifically on neutrophil cytosolic (cPLA2) and secretory (sPLA2) phospholipase A2s. We hypothesized that AAG as a protein kinase activator would activate cPLA2 via phosphorylation events. EAG is antagonistic to the AAG activation of PKC, thus it was not expected to act via phosphorylation of cPLA2. Neutrophils were primed with either AAG or EAG and then stimulated with fMLP. When neutrophils were primed with 5-20 microM 1,2-diacylglycerol, a shift was observed in cPLA2 migration on SDS-PAGE gels, consistent with phosphorylation of the protein. This gel shift was not seen after exposure to EAG. AAG also caused a parallel increase in enzymatic activity of cPLA2 that was not seen with EAG. We also investigated whether either diglyceride would cause similar priming or direct secretion of sPLA2. Both AAG and EAG directly caused significant secretion of neutrophil sPLA2. EAG also increased the release of sPLA2 in cells subsequently stimulated with fMLP. Thus, AAG activated cPLA2 and stimulated secretion of sPLA2. In contrast, EAG did not activate cPLA2, but directly activated secretion of sPLA2. We also demonstrated that human synovial fluid sPLA2 increased AA release from resting and fMLP-stimulated neutrophils. Given that diglycerides prime for release of AA, PAF, and LTB4, these current data support the hypothesis that such priming may be mediated by phosphorylation dependent (cPLA2) or phosphorylation independent (e.g. secretion of sPLA2) events.

Mobilization of potent plasma bactericidal activity during systemic bacterial challenge. Role of group IIA phospholipase A2

Extracellular mobilization of Group IIA 14-kD phospholipase A2 (PLA2) in glycogen-induced rabbit inflammatory peritoneal exudates is responsible for the potent bactericidal activity of the inflammatory fluid toward Staphylococcus aureus (1996. J. Clin. Invest. 97:250-257). Because similar levels of PLA2 are induced in plasma during systemic inflammation, we have tested whether this gives rise to plasma bactericidal activity not present in resting animals. Baboons were injected intravenously (i.v.) with a lethal dose of Escherichia coli and plasma or serum was collected before and at hourly intervals after injection. After infusion of bacteria, PLA2 levels in plasma and serum rose > 100-fold over 24 h to approximately 1 microg PLA2/ml. Serum collected at 24 h possessed potent bactericidal activity toward S. aureus, Streptococcus pyogenes, and encapsulated E. coli not exhibited by serum collected from unchallenged animals. Bactericidal activity toward S. aureus and S. pyogenes was nearly completely blocked by a monoclonal antibody to human Group IIA PLA2 and addition of purified human Group IIA PLA2 to prechallenge serum conferred potent antistaphylococcal and antistreptococcal activity equal to that of the 24 h post-challenge serum. PLA2-dependent bactericidal activity was enhanced approximately 10x by factor(s) present constitutively in serum or plasma. Bactericidal activity toward encapsulated E. coli was accompanied by extensive bacterial phospholipid degradation mediated, at least in part, by the mobilized Group IIA PLA2 but depended on the action of other bactericidal factors in the 24-h serum. These findings further demonstrate the contribution of Group IIA PLA2 to the antibacterial potency of biological fluids and suggest that mobilization of this enzyme during inflammation may play an important role in host defense against invading bacteria.

Ultrastructural localization of secretory type II phospholipase A2 in atherosclerotic and nonatherosclerotic regions of human arteries

We recently reported on the immunolocalization of type II secretory nonpancreatic phospholipase A2 (snpPLA2) in human atherosclerotic lesions. In the present study, we present data on the distribution and ultrastructural localization of snpPLA2 in adjacent nonatherosclerotic and atherosclerotic regions of human arteries. Electron microscopy (EM) of immunogold labeling techniques with a monoclonal antibody was used to analyze arterial tissue. The human specimens analyzed were obtained from autopsy and surgery cases. The results with EM showed a stronger snpPLA2 immunoreactivity in regions of arteries with atherosclerotic lesions than in regions without lesions from the same individual. snpPLA2 immunoreactivity was stronger in the arterial intima of atherosclerotic than of nonatherosclerotic tissue. EM-immunogold examination revealed that the majority of snpPLA2 was localized along the extracellular matrix, associated with collagen fibers and other extracellular matrix structures. Intracellular snpPLA2 was observed in electron-dense vesicles in intimal cells. snpPLA2 was also found in contact with large, extracellular lipid droplets. These results support the hypothesis that extracellular snpPLA2 is localized at sites where it may hydrolyze phospholipids from lipoproteins and lipid aggregates retained in the extracellular matrix of the arterial wall. This may be a mechanism for in situ release of proinflammatory lipids, free fatty acids, and lysophosphatidylcholine in regions of apolipoprotein B accumulation, which are abundant in atherosclerotic lesions.

Secretory and cytosolic phospholipases A2 are activated during TNF priming of human neutrophils

Cytokines alter neutrophil (PMN) function during inflammation, and Tumor Necrosis Factor (TNF) in vitro primes PMN such that receptor-mediated stimulation causes markedly enhanced release of arachidonic acid. We hypothesized that two Ca(2+)-dependent PLA2's in PMN might be activated during priming of the cell, thus affecting arachidonate release. A low molecular weight, secretory PLA2 was identified by enzymatic activity in the cell free supernates of primed or stimulated PMN, and in PMN disrupted by nitrogen cavitation. The enzymatic activity was calcium-dependent, acid stable, destroyed by dithiothreitol, and blocked by anti-sPLA2 antibodies. TNF caused secretion of sPLA2 and also caused an increase in cell-associated sPLA2 enzymatic activity. Activation and release were maximal with fMLP stimulation of TNF-primed PMN. Neutrophils also contained a cytosolic PLA2 (cPLA2) characterized by enzymatic activity which was calcium dependent, enhanced by dithiothreitol, and blocked by anti-cPLA2 antibody. TNF caused a doubling of cPLA2 enzymatic activity which was associated with phosphorylation of the enzyme as judged by a migration shift on Western blots. Thus, TNF priming of human PMN caused marked increase in fMLP stimulated AA release in parallel to enhanced activity of two different PLA2's.

Melittin binds to secretory phospholipase A2 and inhibits its enzymatic activity

Synthetic melittin inhibited the enzymatic activity of secretory phospholipase A2 (PLA2) from various sources, including bee and snake venoms, bovine pancreas, and synovial fluid from rheumatoid arthritis patients, irrespective of substrate (e.g., [14C]-phosphatidylcholine or phosphatidylethanolamine vesicles and [3H]-oleic acid-labeled E.coli). A Lineweaver-Burk analysis showed that melittin was a noncompetitive inhibitor of bee venom PLA2, causing a change in Vmax from 200 to 50 units/min/mg of protein. The Km remained unchanged (0.75 nmole). Melittin inhibited approximately 50% of purified bee venom PLA2 activity in a 30:1 molar ratio (melittin:enzyme). Because the enzyme kinetics indicated a PLA2-melittin interaction, a melittin-sepharose affinity column was used to purify a PLA2 from human serum. Further, an enzyme-linked assay was developed to quantitate PLA2 activity in biological fluids using avidin-peroxidase and ELISA plates coated with biotinylated melittin. These observations may have potential therapeutic significance, as well as provide a convenient basis for the isolation and quantitation of PLA2.

Quantitation of human tissue and immune cell type II 14 kDa phospholipase A2 by enzyme immunoassay

The metabolism of arachidonic acid into inflammatory mediators (e.g. prostaglandin, leukotrienes) is dependent upon the rate-limiting enzyme phospholipase A(2). Localization and quantification of type II 14 kDa phospholipase A(2) (PLA(2)) in cells or tissue preparations has historically been accomplished through activity measurements, a process that can provide variable results due to interference by exogenous substances with hydrolysis assessment. Others have reported on the use of sandwich enzyme immunoassays (EIA) to measure 14 kDa PLA(2) by mass in serum and exudate fluids, e.g. synovial fluid. Herein, we report the utilization of a human recombinant type II 14 kDa PLA(2) sandwich EIA to directly measure cell or tissue-residing 14 kDa PLA(2). It is known that type II 14 kDa PLA(2) resists acid treatment, and this technique was applied to cell fractions which liberated the enzyme from cellular membrane components prior to quantitation by EIA. Two human immune cell populations were assessed and shown to contain measurable levels of 14 kDa PLA(2). Neutrophil or monocyte cytosolic fractions contained no measurable levels whereas the respective 100 000g particulate fractions contained 2.6+/-0.8 pg (neutrophil) and 2.1+/-0.6 pg (monocyte) 14 kDa PLA(2)/mug protein. Human placenta cytosolic fractions contained no measurable levels while 100 000g particulate contained approximately 25 ng 14 kDa PLA(2)/mg protein. This EIA, in conjunction with acid extraction, provides an easy and reproducible assay to identify and quantify this enzyme in cells and whole tissues, expanding our ability to study the relationship of this enzyme to inflammatory processes.

Localization of nonpancreatic secretory phospholipase A2 in normal and atherosclerotic arteries. Activity of the isolated enzyme on low-density lipoproteins

Secretory nonpancreatic type II phospholipase A2 (snpPLA2) hydrolyzes fatty acids at the sn-2 position in phospholipids releasing free fatty acids (FFAs) and lysophospholipids. These products may act as intracellular second messengers or can be further metabolized into proinflammatory lipid mediators. The presence of snpPLA2 in extracellular fluids and serum during inflammation has suggested a role of the enzyme in this process. However, the presence of snpPLA2 in a variety of normal tissues suggests that snpPLA2 may also have physiological functions. Atherosclerosis appears to have an inflammatory component. Here we report on the snpPLA2 localization in normal and atherosclerotic lesions and on the properties of the isolated enzyme. A strong snpPLA2 immunoreactivity was observed in the arterial media that was colocalized with alpha-actin-positive vascular smooth muscle cells (SMCs) in both normal and atherosclerotic vessels. In aortic atherosclerotic lesions, snpPLA2 was observed colocalized with CD68-positive macrophages and HHF-35-positive SMCs and extracellularly in the lipid core. snpPLA2 was isolated from human normal arteries and from aorta with lesions. The enzyme was isolated by acid extraction of normal arterial tissues followed by immunoaffinity chromatography. The purified snpPLA2 had an expected molecular weight of 14 kD by polyacrylamide gel electrophoresis and appeared as a single band in immunoblotting. The enzymatic activity was followed by measuring release of fatty acids from phospholipid liposomes or LDL as substrates. The enzymatic activity was inhibited with two specific inhibitors for human snpPLA2: (1) monoclonal antibody 187 and (2) LY311727, a synthetic selective inhibitor. The mRNA for snpPLA2 was detected with reverse transcriptase polymerase chain reaction. These results indicate that snpPLA2 is present in human arteries and that it is able to hydrolyze phospholipids in LDL. The results support the hypothesis that snpPLA2 can release proinflammatory lipids at places of LDL deposition in the arterial wall.

Quantitation of the cytosolic phospholipase A2 (type IV) in isolated human peripheral blood eosinophils by sandwich-ELISA

Sandwich enzyme-linked immunosorbent assay (sELISA) was developed for precise quantitation of cytosolic phospholipase A2 (cPLA2 type IV) concentration in isolated human peripheral blood eosinophils as an alternative to semiquantitative chemiluminescent assay employing immunoprecipitation/Western blot analysis. In this assay, monoclonal mouse anti-human cPLA2 antiserum was used as the capture antibody, polyclonal rabbit anti-human cPLA2 antiserum as the secondary antibody, and alkaline phosphatase-conjugated goat anti-rabbit IgG as the tertiary, reporter antibody. Purified human cPLA2 (0-1000 ng/ml) dissolved in Tris-HCl buffered saline was used as the standard protein. The detection limit for cPLA2 in 10(6) eosinophils was 0.109 ng/ml, and coefficients of inter- and intra-assay variation were 4.23% and 7.07%, respectively. There was no cross-reactivity with other (secretory) isoforms of PLA2 (sPLA2 types I-III) either from porcine pancreas, human synovial fluid, or bee venom. In separate studies, the recovery of cPLA2 was > 83% when eosinophil lysate was supplemented exogenously with two different concentrations of cPLA2. From a total protein content of 22.3 +/- 1.7 micrograms/10(6) cells, the baseline concentration of cPLA2 was 0.38 +/- 0.18 ng/10(6) cells in eosinophils obtained from mildly atopic donors. Immunoblotting studies confirmed the complete specificity for the type IV isoform as detected by sELISA. This sELISA method permits the precise quantitative assessment of cPLA2 in nanogram quantities per million cells, which has not previously been possible by immunoblotting analysis.

Transgenic model for the discovery of novel human secretory non-pancreatic phospholipase A2 inhibitors

Transgenic mice were created which overexpress human secretory non-pancreatic phospholipase A2 (sPLA2) pansomatically as a potential disease and drug-testing model. The mice were produced using a DNA construct in which the inducible mouse metallothionein gene promoter drives expression of a human sPLA2 minigene. High levels of sPLA2 were detected in several tissues by immunofluorescence localization. Expression in the testes caused hypospermia and male infertility. Circulating catalytically active sPLA2 could be induced to levels observed in patients undergoing a systemic inflammatory response but had no detectable effect on the mice. Therefore, these results suggest that sPLA2 hyperphospholipasemia alone may have only limited pathophysiological consequences. We further show that 3-[3-acetamide-1-benzyl-2-ethylindolyl-5-oxy]propane phosphonic acid LY311727), a potent new inhibitor of phospholipase A2 catalysis developed by our group, dramatically suppresses the circulating enzyme activity in these animals whereas 3-[3-acetamide-1-benzyl-2-propylindolyl-5-oxy]propane phosphonic acid (LY314024), a substantially less potent LY311727 analog, is without effect. These later results thus motivate the further development of this compound as a potential new therapeutic agent and valuable research tool.

The potent anti-Staphylococcus aureus activity of a sterile rabbit inflammatory fluid is due to a 14-kD phospholipase A2

The cell-free fluid (ascitic fluid, AF) of a sterile inflammatory peritoneal exudate elicited in rabbits is potently bactericidal for complement-resistant gram-negative as well as gram-positive bacterial species. This activity is absent in plasma. We now show that essentially all activity in AF against Staphylococcus aureus is attributable to a group II 14-kD phospholipase A2 (PLA2), previously purified from AF in this laboratory. Antistaphylococcal activity of purified PLA2 and of whole AF containing a corresponding amount of PLA2 was comparable and blocked by anti-AF-PLA2 serum. At concentrations present in AF (approximately 10 nM), AF PLA2 kills > 2 logs of 10(6) S. aureus/ml, including methicillin-resistant clinical isolates, and other species of gram-positive bacteria. Human group II PLA2 displays similar bactericidal activity toward S. aureus (LD90 approximately 1-5 nM), whereas 14-kD PLA2 from pig pancreas and snake venom are inactive even at micromolar doses. Bacterial killing by PLA2 requires Ca2+ and catalytic activity and is accompanied by bacterial phospholipolysis and disruption of the bacterial cell membrane and cell wall. These findings reveal that group II extracellular PLA2, the function of which at inflammatory sites has been unclear, is an extraordinarily potent endogenous antibiotic against S. aureus and other gram-positive bacteria.

Secretory group II phospholipase A2 in human atherosclerotic plaques

Atherosclerotic plaques exhibit a series of features that are similar to those of chronic inflammation. Based on the fact that during inflammation several cell types synthesize and secrete a group II phospholipase A2 (PLA2), an immunohistochemical study was undertaken to explore whether this enzyme can be identified in human atherosclerotic lesions. Tissue specimens obtained from 13 patients who had undergone arteriectomy and three specimens with advanced atherosclerotic plaques obtained at autopsy were analyzed and compared to arteries free of atherosclerosis. The results showed that in all areas with atherosclerotic lesions, a staining with monoclonal antibodies raised against group II PLA2 was evident. In normal arteries without thickened intima, this immunostaining was completely negative. With the use of specific monoclonal antibodies against macrophages (anti-KP-1) and smooth muscle cells (anti-alpha-actin), PLA2-positive cells were identified as foam cells mainly derived from macrophages. In addition to these cells, other regions of the thickened intima gave a partially positive reaction with anti-PLA2 antibodies, but could not be stained with either anti-KP-1 or anti-alpha-actin. Some of these regions were localized on edges of calcification and cell necrosis. Other PLA2-positive regions seem to be associated with extracellular matrix structures. In summary, the findings of this study may be regarded as further evidence to support the link between atherosclerosis and chronic inflammatory processes. In view of the fact that the in vitro modification of lipoproteins by PLA2-treatment induces lipid deposition in macrophages, the results of this study suggest that group II PLA2 may actively be involved in the formation of foam cells in vivo.

Solution-phase binding of monoclonal antibodies to bee venom phospholipase A2

The binding of monoclonal anti-bee venom phospholipase A2 antibodies to their antigen was monitored by size-exclusion high performance liquid chromatography. As judged by this panel of six antibodies, honeybee venom phospholipase A2 contains five binding sites, three of which are completely independent epitopes. The study revealed that this PLA2 can accommodate three different antibodies simultaneously. The results demonstrate the utility of size-exclusion high performance liquid chromatography in epitope analyses, such as its ability to compare the relative expansiveness and conformational state of the epitopes and to enumerate the antibodies that the antigen can accommodate simultaneously. The data provide compelling evidence that one of the monoclonal antibodies, M5 (which activates the enzyme), recognizes a different conformation of phospholipase A2 than do the other antibodies. The results also demonstrate that different pairs of monoclonal antibodies differ in their predilection to form high molecular weight complexes with the antigen.

Immunohistologic detection of non-pancreatic phospholipase A2 (type II) in human placenta and its possible involvement in normal parturition at term

Placenta is one of the richest sources of non-pancreatic phospholipase A2 (npPLA2) (type II) in the human body, and the enzyme is the key enzyme releasing unsaturated fatty acids from membrane phospholipids. Prostaglandins (PGs) play a critical role in the initiation and progression of parturition. Cytokines are presumed to play a central role in the initiation of normal labor at term, and cytokines are also found to regulate both synthesis and secretion of npPLA2 enzyme. In an attempt to resolve the physiologic function of the npPLA2 enzyme in placental tissue, immunohistologic localization and enzymatic activity measurements of npPLA2 enzyme were performed. NpPLA2 protein was detected in vascular smooth muscle, endothelial cells and connective tissue cells in placenta and umbilical cord, and the protein was weakly stained in trophoblast cells in placenta. Enzymatic activity was not increased in sera from mother nor child compared to sera from healthy individuals, but the activity in amniotic fluid was considerably higher. Our findings support the candidacy for npPLA2 in enzymatic arachidonic acid release from foetal membranes.

Interleukin-1 beta induces cytosolic phospholipase A2 and prostaglandin H synthase in rheumatoid synovial fibroblasts. Evidence for their roles in the production of prostaglandin E2

OBJECTIVE

In order to investigate potential regulatory mechanisms for the increased production of prostaglandin E2 (PGE2) in interleukin-1 beta (IL-1 beta)-stimulated rheumatoid synovial fibroblasts (RSF), this study examined the induction of phospholipase A2 (PLA2) and prostaglandin H synthase (PGHS) enzymes and the correlation of these events with PGE2 production in IL-1 beta-stimulated RSF.

METHODS

Protein and messenger RNA (mRNA) levels of cytosolic PLA2 (cPLA2) and PGHS-2 enzymes in IL-1 beta-stimulated RSF were measured by Western and Northern blotting, respectively, using specific antisera and complementary DNA probes. Enzymatic activity of cPLA2 was determined in cell-free reaction mixtures utilizing mixed micelles of 14C-phosphatidylcholine and Triton X-100 as the substrate. PGE2 levels were quantitated using a commercial enzyme immunoassay kit.

RESULTS

Incubation of RSF with IL-1 beta increased the mRNA and protein levels for the high molecular weight cPLA2 as well as for the mitogen/growth factor-responsive PGHS (PGHS-2). The IL-1 receptor antagonist completely abolished the induction of these two enzymes and the stimulation of PGE2 production by IL-1 beta in RSF. In contrast, levels of the other known forms of these enzymes, i.e., the 14-kd secretory group II PLA2 (sPLA2) and the constitutive form of PGHS (PGHS-1), were unaffected by IL-1 beta treatment.

CONCLUSION

These are the first data to demonstrate the coordinate induction by IL-1 of cPLA2 and PGHS-2 in RSF. The time-course for the induction of these enzymes suggests that their increase contributes to the increased production of PGE2 in IL-1-treated RSF, and may help explain the capacity of RSF to produce large amounts of PGE2.

Role of type II phospholipase A2 in the inflammatory process of carrageenan-induced pleurisy in rats

In order to investigate the role of type II phospholipase A2 (PLA2) in the inflammatory process, the effect of a monoclonal antibody specific to type II PLA2 on carrageenan-induced pleurisy was studied in rats. Intravenous injection of the antibody (MB5.2), which inhibits the catalytic activity of type II PLA2, significantly reduced both the pleural exudate volume and the intrapleural leukocyte count, while a control antibody did not have any appreciable effect. MB5.2 caused no change in the level of type II PLA2 in the pleural fluid. These results suggest that type II PLA2 generated at inflamed sites, at least in part, have a crucial role in the pathogenesis of acute inflammation.

Are events after endotoxemia related to circulating phospholipase A2?

OBJECTIVE

The authors sought to determine whether the signs and symptoms of endotoxemia were related to the endotoxin-stimulated increase in circulating phospholipase A2 (PLA2) activity.

BACKGROUND

Because hypotension and pulmonary injury have been associated with elevated PLA2 activity in septic shock and PLA2 levels are reduced with the administration of glucocorticoids, the PLA2 response to endotoxin was investigated in volunteers pretreated with and without hydrocortisone.

METHODS

Carefully screened human subjects were studied under four conditions: (1) saline, (2) hydrocortisone, (3) endotoxin, and (4) hydrocortisone administration before endotoxin exposure. Pulse rate, blood pressure, temperature, and symptoms of endotoxemia were serially measured. Plasma for tumor necrosis factor concentrations and PLA2 activity was obtained.

RESULTS

After lipopolysaccharide, pulse rate and tumor necrosis factor concentrations rose at 1 to 2 hours; temperature increased maximally at 4 hours. PLA2 activity reached peak levels at 24 hours. With hydrocortisone pretreatment, a 50% reduction in the concentrations of tumor necrosis factor and PLA2 occurred. Significant correlations between other variables and PLA2 activity were not observed. The enzyme identified by monoclonal antibody was the secreted nonpancreatic PLA2 (SNP-PLA2).

CONCLUSIONS

The results of this study suggest that elevations in circulating SNP-PLA2 activity and systemic events associated with intravenous endotoxin administration are unrelated.

Elevated expression of human nonpancreatic phospholipase A2 in psoriatic tissue

In involved psoriatic tissue, which is characterized by chronic inflammation in both epidermis and dermis, elevated levels of arachidonic acid and eicosanoids have been measured. This implies that a phospholipase A2 (PLA2) may be involved in the pathogenesis of psoriasis. The PLA2's are a group of enzymes that release unsaturated fatty acids from the sn2-position of membrane phospholipids. Once released, the fatty acids are converted by various enzymes into biologically very important signaling molecules. Release of arachidonate initiates the arachidonate cascade, leading to the synthesis of eicosanoids such as prostaglandins, thromboxanes, leukotrienes, and lipoxines. Eicosanoids are important in a variety of physiological processes and play a central role in inflammatory mediators, such as lyso-PAF (a precursor for PAF) and other lysophospholipids, may also be formed through the action of a PLA2. We report for the first time the detection of transcripts of nonpancreatic phospholipase A2 (npPLA2, type II) and cytosolic (c) PLA2 in human skin, and overexpression of npPLA2 in involved skin from patients with psoriasis (plaque psoriasis and pustular psoriasis). Limited amounts of npPLA2 enzyme are detected immunologically in the uppermost layers of epidermis from healthy persons. Both involved and uninvolved psoriatic epidermis contain higher levels of npPLA2 than normal skin. Positive cells in dermis showed significantly higher levels of npPLA2 than epidermal cells. In dermis from healthy persons, only weak staining of a few cells could be detected. The two PLA2 enzymes detected in psoriatic skin (cytosolic and nonpancreatic) may both be involved in eicosanoid overproduction in psoriatic tissue, and the npPLA2 may also be involved in potentiating cell activation, especially T cells.

Group II phospholipase A2 in synovial fluid and serum in acute arthritis

Increased catalytic activity of synovial-type (group II) phospholipase A2 (syn-PLA2), has been associated with cartilage erosions in rheumatoid arthritis and osteoarthritis. The catalytic activity of phospholipase A2 and the concentration of syn-PLA2 were measured in a prospective study in synovial fluid (SF) samples from 66 patients with acute knee joint effusion. The median (range) of the concentration of syn-PLA2 in SF was 210 micrograms/l (80-1480 micrograms/l) in culture-positive septic arthritis, 460 micrograms/l (270-1040 micrograms/l) in reactive arthritis, 780 micrograms/l (120-2710 micrograms/l) in osteoarthritis and 230 micrograms/l (80-1400 micrograms/l) in traumatic joint effusions. High concentrations of syn-PLA2 are found also in SF of patients with arthritides not expected to lead to permanent destruction of cartilage.

Interleukin-1 beta induces cytosolic PLA2 in parallel with prostaglandin E2 in rheumatoid synovial fibroblasts

We investigated the temporal relationship between the increase in enzymatic activity and protein of a high molecular weight (100 kDa), cytosolic PLA2 (cPLA2) in interleukin-1 beta (IL-1 beta)-treated rheumatoid synovial fibroblasts (RSF). Both of these responses increased according to a similar time-course which correlates with PGE2 production by these cells. In contrast, 14 kDa, secreted PLA2 (sPLA2), which was also produced by RSF, was not affected by IL-1 beta treatment. These findings support that an augmentation of CPLA2 activity, caused by an induction of cPLA2 protein, rather than sPLA2, is temporally associated with increased PGE2 production in IL-1 beta-treated RSF.

Interleukin-1 beta stimulates cytosolic phospholipase A2 in rheumatoid synovial fibroblasts

Phospholipase A2 (PLA2) activities in rheumatoid synovial fibroblasts (RSF) stimulated with interleukin-1 beta (IL-1 beta) were investigated. RSF incubated in the presence of IL-1 beta (120 pg/ml) for 18 h secreted 35 fold more PGE2 than did those incubated without IL-1 beta. IL-1 beta treatment did not increase the level of secretory PLA2 (sPLA2) activity or sPLA2 protein in the conditioned medium or subcellular fractions of lysed RSF. In contrast, the cell-associated PLA2 activity increased 3 to 4 fold in IL-1 beta stimulated RSF when compared with the control. The IL-1 beta stimulated, cell-associated PLA2 required submicromolar concentrations of calcium for activity, a characteristic consistent with the calcium sensitivity of cytosolic PLA2 (cPLA2) activity reported in other cell types, such as U937 cells. These findings demonstrate that an elevation in a cytosolic PLA2, rather than a sPLA2, is associated with increased PGE2 production in IL-1 beta stimulated RSF.

Purification of recombinant human secretory phospholipase A2 (group II) produced in long-term immobilized cell culture

Recombinant human secretory phospholipase A2 (Group II) was expressed in long-term culture of immobilized Chinese hamster ovary cells utilizing a continuous-perfusion airlift bioreactor. The bioreactor was continuously perfused with cell-culture medium supplemented with 5% fetal calf serum at an average flow rate of 5 liters/day for 30 days. Recombinant phospholipase A2, at concentrations ranging from 100 to 500 micrograms/liter, was purified to apparent homogeneity by an efficient two-step procedure involving a silica-based cation-exchange resin and hydrophobic interaction chromatography (greater than 65% recovery of phospholipase A2). The purified recombinant protein has an apparent molecular weight of 16 kDa, identical to that of purified human placental or synovial fluid phospholipase A2, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Application of the purified protein onto several different gel filtration columns resulted in elution of the protein at molecular weights corresponding to 3.1-4.7 kDa, suggesting an interaction of the protein with the column resins. However, analytical ultracentrifugation experiments revealed that the protein behaves as a monomer (13.8-14.2 kDa) over a protein concentration range of approximately 10 micrograms/ml to 5 mg/ml. With autoclaved Escherichia coli membranes as substrate, the recombinant protein has catalytic properties (pH optimum, effects of bovine serum albumin, sodium chloride concentration, and requirement for calcium) similar to those of the protein purified from human placenta.