Extracellular phospholipase A2: causative agent in circulatory collapse of septic shock?

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.

Tenidap sodium inhibits secretory non-pancreatic phospholipase A(2) synthesis by foetal rat calvarial osteoblasts

Tenidap (TD) was initially defined as a dual inhibitor of cyclooxygenase and lipoxygenase. This study was designed to assess its inhibitory activity against proinflammatory phospholipase A(2). This study shows that TD inhibits the synthesis of pro-inflammatory secretory non-pancreatic phospholipase A(2) (sPLA(2)). Concentrations as low as 0.25 mug/ml (0.725 muM) reduced the release of sPLA(2) by 40% from foetal rat calvarial osteoblasts stimulated with IL-1beta and TNFalpha, whereas a concentration of 2.5 mug/ml (7.25 muM) reduced the release by over 80%. TD also markedly reduced the release of sPLA(2) from unstimulated cells. There was no direct inhibition of sPLA(2) enzymatic activity by TD in vitro. Northern blot analysis showed that TD did not affect the sPLA(2) mRNA levels; however, immunoblotting showed a dose-dependent reduction in sPLA(2) enzyme. These results, together with a marked reduction in sPLA(2) enzymatic activity, suggest that TD inhibits sPLA(2) synthesis at the post-transcriptional level. Therefore TD seems to inhibit the arachidonic acid cascade proximally to cyclooxygenase and lipoxygenase and its anti-inflammatory activity may be related at least in part to the inhibition of sPLA(2) synthesis.

Asp49 phospholipase A2–elaidoylamide complex: a new mode of inhibition

The inhibition of phospholipase A(2)s (PLA(2)s) is of pharmacological and therapeutic interest because these enzymes are involved in several inflammatory diseases. Elaidoylamide is a powerful inhibitor of a neurotoxic PLA(2) from the Vipera ammodytes meridionalis venom. The X-ray structure of the enzyme-inhibitor complex reveals a new mode of Asp49 PLA(2) inhibition by a fatty acid hydrocarbon chain. The structure contains two identical homodimers in the asymmetric unit. In each dimer one subunit is rotated by 180 degrees with respect to the other and the two molecules are oriented head-to-tail. One molecule of elaidoylamide is bound simultaneously to the substrate binding sites of two associated neurotoxic phospholipase A(2) molecules. The inhibitor binds symmetrically to the hydrophobic channels of the two monomers. The structure can be used to design anti-inflammatory drugs.

Presence of group IIa secretory phospholipase A2 in mast cells and macrophages in normal human ileal submucosa and in Crohn's disease

Secretory group IIa phospholipase A2 (PLA2-II) is an important regulator of proinflammatory lipid mediator production and may play a role in ileal inflammation in Crohn's disease. The enzyme has previously only been detected in epithelial Paneth cells. However, one characteristic feature of Crohn's disease is the transmural inflammation. Full thickness ileal sections from nine patients with Crohn's disease, and histologically normal sections from patients with colonic cancer (n=7) and chronic severe constipation (n=1) as controls, were used in this study. PLA2-II-positive cells were detected by immunofluorescence and in situ hybridization. Metachromatic staining and esterase staining were used to identify mast cells and macrophages, respectively. It was shown that mast cells and macrophages in the ileal submucosa in both patients and controls showed positive PLA2-II staining. The number of PLA2-II-labeled cells that did not react with metachromasia, e.g. macrophages, was significantly greater in inflamed Crohn's disease compared to controls. This is, to our knowledge, the first study that has described the presence in healthy, while presence and upregulation of PLA2-II-positive cells in inflamed human ileal submucosa. Our findings suggest a proinflammatory potential for secretory PLA2-II in submucosa, while proinflammatory stimulation of mast cells and macrophages in vitro has shown that the enzyme is responsible for delayed prostaglandin formation.

Identification of two secreted phospholipases A2 in human epidermis

Phospholipases A2 are enzymes that catalyze the release of fatty acids from the sn-2 position of phospholipids. Fatty acids have been suggested to play a key role in the barrier function of the epidermis. The aim of this study was to identify and characterize the type of secretory phospholipase A2 expressed in human epidermis. We report the molecular cloning of two secretory phospholipase A2 in the human epidermis. The first enzyme is identical to human pancreatic type IB phospholipase A2. Western blots revealed a 14 kDa protein localized in the soluble fraction. The second phospholipase A2 is identical to human synovial type IIA enzyme and is localized in the membrane fraction. By semiquantitative reverse transcription-polymerase chain reaction performed on horizontal sections of the epidermis, we found that the mRNAs of both phospholipases A2 were expressed mainly in the basal layers of the epidermis. Our data thus provide evidence for the expression of two secretory phospholipases A2 in human epidermis. The different localization of these two secretory proteins strongly suggests that each enzyme might have a specific role in skin physiology and probably in the barrier function. Taken together, these data validate the reverse transcription-polymerase chain reaction technique performed on thin sections as a first approach to detect gene expression in different layers of the epidermis.

Tumor necrosis factor-alpha augments contraction and cytosolic Ca(2+) sensitivity through phospholipase A(2) in bovine tracheal smooth muscle

To elucidate the effects of tumor necrosis factor-alpha (TNF-alpha) on tracheal smooth muscle contraction, we simultaneously measured isometric tension and intracellular Ca(2+) ([Ca(2+)](i)) in fura 2-loaded muscle strips. Smooth muscle force generation was evaluated in a high potassium (K(+); 20.0-80.0 mM) solution and with acetylcholine (3 nM-10 microM ). TNF-alpha (1-100 ng/ml) did not directly contract muscle strips. The contractile response to acetylcholine was enhanced after application of 10 ng/ml of TNF-alpha for 30 min but not the response of [Ca(2+)](i). The contractile response and the response of [Ca(2+)](i) to a high K(+) solution were not altered after application of TNF-alpha. The [Ca(2+)](i)-tension curve indicated that TNF-alpha enhanced the responsiveness of tracheal smooth muscle through the acetylcholine-mediated Ca(2+) sensitivity of intracellular contractile elements. The augmentation of the acetylcholine concentration-response curves for muscle tension in the presence of TNF-alpha (10 ng/ml) was inhibited in part after application of manoalide, a phospholipase A(2) inhibitor. We conclude that a low concentration of TNF-alpha enhances smooth muscle responsiveness to acetylcholine by agonist-mediated Ca(2+) sensitivity facilitated by phospholipase A(2).

cis,cis- and trans,trans-ceratospongamide, new bioactive cyclic heptapeptides from the Indonesian red alga Ceratodictyon spongiosum and symbiotic sponge Sigmadocia symbiotica

Chemical investigation of the marine red alga (Rhodophyta) Ceratodictyon spongiosum containing the symbiotic sponge Sigmadocia symbiotica collected from Biaro Island, Indonesia, yielded two isomers of a new and bioactive thiazole-containing cyclic heptapeptide, cis,cis-ceratospongamide (1) and trans, trans-ceratospongamide (2). Isolation of these peptides was assisted by bioassay-guided fractionation using a brine shrimp toxicity assay (Artemia salina). The structures of the ceratospongamides, which each consist of two L-phenylalanine residues, one (L-isoleucine)-L-methyloxazoline residue, one L-proline residue, and one (L-proline)thiazole residue, were established through extensive NMR spectroscopy, including (1)H-(13)C HMQC-TOCSY, and (1)H-(15)N HMBC experiments, as well as chemical degradation and chiral analysis. cis,cis- and trans,trans-ceratospongamide are stable conformational isomers of the two proline amide bonds. Molecular modeling of these two ceratospongamide isomers showed the trans, trans isomer to be quite planar, whereas the cis,cis isomer has a more puckered overall conformation. trans,trans-Ceratospongamide exhibits potent inhibition of sPLA(2) expression in a cell-based model for antiinflammation (ED(50) 32 nM), whereas the cis,cis isomer is inactive. trans,trans-Ceratospongamide was also shown to inhibit the expression of a human-sPLA(2) promoter-based reporter by 90%.

IL-6: insights into novel biological activities

IL-6 has many novel activities both within the adaptive immune system and without. It has therapeutic potential in acute inflammation, such as toxic or septic shock, and it is a potential target for cachexia, multiple myeloma, and osteoporosis. Further work on these aspects of IL-6 biology should yield new insight into the possibility of IL-6 both as a therapeutic agent and as a target for antagonists.

Crystal structure of vipoxin at 2.0 A: an example of regulation of a toxic function generated by molecular evolution

Vipoxin is the main toxic component in the venom of the Bulgarian snake Vipera ammodytes meridionalis, the most toxic snake in Europe. Vipoxin is a complex between a toxic phospholipase A2 (PLA2) and a non-toxic protein inhibitor. The structure is of genetic interest due to the high degree of sequence homology (62%) between the two functionally different components. The structure shows that the formation of the complex in vipoxin is significantly different to that seen in many known structures of phospholipases and contradicts the assumptions made in earlier studies. The modulation of PLA2 activity is of great pharmacological interest, and the present structure will be a model for structure-based drug design.

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.

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.

Mechanism of inhibition of human nonpancreatic secreted phospholipase A2 by the anti-inflammatory agent BMS-181162

Many important mediators of inflammation result from the liberation of free arachidonic acid from phospholipid pools which is thought to result from the action of phospholipase A2 (PLA2). It is believed, therefore, that the inhibition of PLA2 would be an important treatment in many inflammatory disease states. The anti-inflammatory agent BMS-181162 (4-(3'-carboxyphenyl)-3,7-dimethyl-9-(2",6",6"-trimethyl-1"-cyclohexenyl )-2Z,4E , 6E,8E-nonatetraenoic acid) selectively inhibits PLA2 and has been shown to block arachidonic acid release in whole cells. The mechanism of inhibition of human non-pancreatic-secreted PLA2 by BMS-181162 is investigated in this paper. A scooting mode assay in which the enzyme is irreversibly bound to vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphomethanol containing 5 mol % of 1-palmitoyl-2-[1-14C]arachidonoyl-sn-glycero-3-phosphocholine, was used to characterize the inhibition. With this assay system, BMS-181162 inhibited the enzyme in a dose-dependent manner. Compounds which inhibit in the scooting mode have been shown to be competitive inhibitors in the interface (Gelb, M. H., Berg, O., and Jain, M. K. (1991) Curr. Op. Struct. Biol. 1, 836-843). This was verified by demonstrating that the inhibition was not due to the desorption of the enzyme from the lipid-water interface. Additionally, the compound did not measurably affect the rate of association onto the vesicles. Therefore, the inhibition was not the result of a modulation of the bilayer morphology nor an interaction with the interfacial binding site on the enzyme. The degree of inhibition was dependent on the reaction volume which indicates that the inhibitor is only partially partitioned into the bilayer. After compensating for this partitioning, the dose-dependent inhibition could be defined by kinetic equations describing competitive inhibition at the interface. The equilibrium dissociation constant for the inhibitor bound to the enzyme at the interface (KI*) was determined to be 0.013 mol fraction, thus demonstrating that BMS-181162 represents a novel structural class of tight-binding competitive inhibitors of human nonpancreatic secreted PLA2. Using Escherichia coli membranes as substrate, to which the enzyme binds to the interface reversibly, the inhibition showed a nonclassical kinetic pattern which is also consistent with a partial partitioning of the inhibitor into the bilayer. This was verified by a direct measurement of the amount of inhibitor remaining in solution. The implications for in vivo efficacy which result from this mechanism are discussed.

Selective inhibition of group II phospholipase A2 by quercetin

The influence of quercetin, chlorpromazine, aristolochic acid, and indomethacin on group I phospholipase A2 (PLA2) from porcine pancreas and on group II PLA2 from Vipera russelli was compared. Quercetin and chlorpromazine were found to inhibit PLA2 activity in lower concentrations (< 100 microM), while aristolochic acid and indomethacin were inhibitory only in higher concentrations (> 100 microM). The order of potency against Vipera PLA2 was: quercetin > chlorpromazine > aristolochic acid > indomethacin, while the order of potency against pancreatic PLA2 was: chlorpromazine > aristolochic acid > indomethacin >> quercetin. Thus, quercetin was a potent inhibitor towards group II PLA2 (IC50 = 2 microM), but a very weak inhibitor against group I PLA2, with maximum 30% inhibition. Aristolochic acid and indomethacin were three to four times more potent towards group II PLA2 than towards group I PLA2, while chlorpromazine was equally potent towards the two PLA2 types. Quercetin and chlorpromazine were also tested against two PLA2 fractions purified from the plasma of septic shock patients; chlorpromazine was then equally potent towards the two PLA2 fractions, whereas quercetin was a potent inhibitor of only one of the two PLA2 fractions (IC50 = 4 microM). Together, these results indicate that (1) different PLA2 inhibitors have different potency depending on which type of PLA2 they are used against, (2) quercetin selectively inhibits group II PLA2 and may therefore be used to discriminate between different PLA2 forms in biological materials, and (3) both PLA2 of group I and group II are present in septic shock plasma.

Rat liver mitochondrial phospholipase A2 is an endotoxin-stimulated membrane-associated enzyme of Kupffer cells which is released during liver perfusion

A novel fluorescence assay for phospholipase A2 [Wilton (1990) Biochem. J. 266, 435-439] has been used to study the Group-II rat liver mitochondrial enzyme, and a number of novel properties of this enzyme were identified. (1) The enzyme activity was located in the liver macrophages (Kupffer cells) while negligible activity was associated with hepatocytes. (2) Although subcellular fractionation of whole liver confirmed the predominantly mitochondrial location of this enzyme activity, the analysis of the hepatocyte-free Kupffer-cell-enriched fraction revealed a different enzyme distribution, with the majority of activity being associated with the microsomal membrane fraction. (3) Bacterial endotoxin has been previously shown to be scavenged by Kupffer cells in rats. Treatment of rats with bacterial lipopolysaccharide (endotoxin) resulted in a dramatic time- and dose-dependent increase in liver phospholipase A2 activity. (4) It is known that injection of endotoxin into rodents results in elevated serum phospholipase A2 activity, while a similar phenomenon is seen in the condition of septic shock in man. The source of this serum enzyme was unknown. In this study perfusion of livers from rats pretreated with lipopolysaccharide with physiological saline demonstrated a 6-fold increase in phospholipase A2 activity in the perfusate compared with sham-treated controls, with only minor release of hepatic lipase. (5) Western-blot analysis confirmed an increased release of this Group-II phospholipase A2 into the perfusate of lipopolysaccharide-treated rats compared with sham-treated controls. These results suggest that liver Kupffer cells are a major source of the endotoxin-induced serum Group-II phospholipase A2 activity associated with bacterial infection and trauma.

Effect of a series of 1-alkyl ether lipids on inhibition of phospholipase A2 activity and PAF responses

Several 1-alkyl ether lipids were studied for their ability to inhibit PLA2 and antagonize PAF responses. Studies with synthetic micellar substrate (1-stearyl-2-arachidonyl phosphocholine), at concentrations ranging from 0.02 to 1000 microM, demonstrate that CL 118326 inhibits porcine pancreatic PLA2 in vitro. As the substrate concentration increases, there is a dose-dependent increase in the IC50 value (IC50 ranges: 1.6-84.6 micrograms/ml or 2.6-137 microM). CL 118326 inhibits mammalian pancreatic PLA2, but not snake or bee venom PLA2. CL 118326 inhibits thrombin (IC50 = 7.9 microM), but not Na arachidonate- (IC50 > 100 microM) induced platelet aggregation, indicative of inhibition of cellular PLA2. CL 118326 inhibits other PLA2-dependent processes such as antigen-induced leukotriene (LTC4) release (IC50 = 2.3 micrograms/ml or 3.8 microM) and histamine release (IC50 = 1.4 micrograms/ml or 2.2 microM) in basophil-enriched WBCs. Intradermal coinjection of CL 118326 (10 micrograms) with PLA2 into guinea pig skin inhibits pancreatic PLA2-induced increase in vascular permeability and leakage, but not snake or bee venom PLA2-induced leakage. CL 118326 shows no PAF-like agonist activity in stimulating rabbit platelet-rich plasma. It inhibits PAF-induced aggregation (IC50 = 5.8 microM), but not ADP-induced aggregation. CL 118326 has greater efficacy as a PLA2 inhibitor than as a PAF antagonist since the IC50-substrate concentration ratio for PLA2 inhibition is < or = 1.0 at substrate concentrations of 10-1000 microM while the IC50-agonist ratio for PAF antagonism is > 100. Results for four other compounds related to CL 118326 are also presented.

Synovial-type (group II) phospholipase A2 in serum of febrile patients with haematological malignancy

Elevated concentrations of synovial-type (group II) phospholipase A2 (PLA2-II) in serum are associated with septic bacterial infections. We measured the concentrations of PLA2-II in serum in 24 fever episodes involving patients suffering from haematological malignancies and having fever after cytotoxic treatment. We applied a novel time-resolved fluoroimmunoassay using a polyclonal antibody raised against recombinant human synovial-type PLA2. The concentrations of PLA2-II in serum were 194.7 +/- 204.4 micrograms/l (mean +/- SD, median 141.9, range 4.6-931.5 micrograms/l). The concentrations of PLA2-II correlated well to the concentrations of C-reactive protein (CRP) in serum (r = 0.688, p < 0.001). The PLA2-II concentrations increased faster than the corresponding CRP values and began to decrease 12 hours after the beginning of antimicrobial treatment. Inverse correlations were found between the concentrations of PLA2-II and blood neutrophil and platelet counts. No correlation was found between the concentrations of PLA2-II and the duration of the time interval from the onset of preceding cytotoxic and corticosteroid treatment to the first blood sample. The concentration of pancreatic PLA2 was within the reference interval in all samples. The present results indicate that PLA2-II resembles an acute-phase protein and is not of blood cell or pancreatic origin.

Novel inhibitor of phospholipase A2 with topical anti-inflammatory activity

Activation of a phospholipase A2 (PLA2) is a key step in the production of precursors for the biosynthesis of lipid mediators of inflammation. Inhibition of this enzyme could result in the suppression of three important classes of inflammatory lipids, prostaglandins, leukotrienes and platelet activating factor (PAF), and offers an attractive therapeutic approach to design novel agents for the treatment of inflammation and tissue injury. In this report we describe a novel compound, BMS-181162 4(3'-carboxyphenyl)-3,7-dimethyl-9(2",6"6"-trimethyl-1"-cyclohexenyl),++ +2Z,4E,6E, 8E-nonatetraenoic acid which specifically inhibits a 14 kD human PLA2 and effectively blocks phorbol ester induced skin inflammation in mice. BMS-181162 is the first reported specific inhibitor of PLA2 and its specificity may make useful tool in the dissection of the role of PLA2 in the inflammatory process.

Hyperphospholipasemia A2 in human volunteers challenged with intravenous endotoxin

Phospholipase A2 (PLA2) activity was measured in the serum of 23 individuals infused intravenously with endotoxin (EN) at a dose of 4 ng/kg body weight. A marked increase in PLA2 was noted 3 h after EN challenge (mean 828 +/- 513 units/ml), reached its maximum at 24 h after the challenge (mean 2667 +/- 2442 units/ml), and was still evident at 48 h (mean 763 +/- 366 units/ml). In contrast, TNF levels were maximal (mean 712 +/- 375 pg/ml) 90 min after the EN challenge and subsided to very low values (5 +/- 5 pg/ml) 5 h after the challenge. There was a positive correlation between the maximum response of TNF and that of PLA2 (r = 0.82, P < 0.01). Administration of ibuprofen or pentoxifylline did not alter the PLA2 response. EN challenge did not affect serum pancreatic PLA2 concentration or that of the lysosomal cationic enzyme, lysozyme. Neutralizing antibody against human recombinant (synovial type) PLA2 completely abolished PLA2 activity in the sera tested. We conclude that EN infusions cause marked intravascular release of nonpancreatic secretory PLA2 and that the magnitude of this response seems to be related to the prior generation of TNF.

Induction of circulating group II phospholipase A2 expression in adults with malaria

High levels of interleukin 1 and tumor necrosis factor are found in both cases of malaria and cases of septic shock. Since both interleukin 1 and tumor necrosis factor induce expression of the proinflammatory enzyme phospholipase A2 (PLA2), we examined serum PLA2 levels in 14 adults with malaria. Mean serum PLA2 activity was elevated 40-fold above normal (P less than 0.001). Serum PLA2 activity correlated with PLA2 immunoreactivity (r = 0.987; P less than 0.001) by an enzyme-linked immunosorbent assay specific for human group II PLA2, showing that serum PLA2 in cases of malaria is host derived. This article describes the novel finding of elevated PLA2 levels in cases of malaria, further strengthening the notion that mediators of the host response in cases of malaria are similar to those in cases of septic shock.

Group II phospholipase A2 induced by interleukin-1 beta in cultured rat gingival fibroblasts

Previously, we reported the presence of group II-like phospholipase A2 activity in the soluble fraction of rat gingiva. In the present study, we found that treatment of rat gingival cells with human recombinant interleukin-1 beta resulted in dose-dependent stimulation of intracellular and extracellular phospholipase A2 activity. Antisera against group II phospholipase A2 totally blocked the interleukin-1 beta-induced phospholipase A2 activity, but antisera against group I phospholipase A2 did not. Moreover, immunoblot analysis showed that the induced phospholipase A2 was group II phospholipase A2. These findings suggest that the induced enzyme belongs to the group II phospholipase A2 family of proinflammatory enzymes.

Serum phospholipase A2 enzyme activity and immunoreactivity in a prospective analysis of patients with septic shock

Massive elevations of serum phospholipase A2 activity have been documented in patients with septic shock. Serum PLA2 activity correlated to the degree and duration of circulatory collapse, while purified native PLA2 reproduced hypotension in experimental animals. In a prospective study of patients with septic shock, we have determined the relationship of PLA2 enzyme activity to PLA2 immunoreactivity using radiolabelled E. coli phospholipid substrate and an ELISA specific for group II human nonpancreatic PLA2. In all patients, there was a clear concordance of the two assays. Maximal PLA2 concentration was increased a mean of 554-fold over normal levels. We found no evidence to support the presence of activating or inhibitory proteins. These data confirm that the observed increase in serum PLA2 activity in septic shock is due to intravascular release of group II nonpancreatic PLA2.

Structure of recombinant human rheumatoid arthritic synovial fluid phospholipase A2 at 2.2 A resolution

Phospholipases A2 (PLA2s) may be grouped into distinct families of proteins that catalyse the hydrolysis of the 2-acyl bond of phospholipids and perform a variety of biological functions. The best characterized are the small (relative molecular mass approximately 14,000) calcium-dependent, secretory enzymes of diverse origin, such as pancreatic and venom PLA2s. The structures and functions of several PLA2s are known. Recently, high-resolution crystal structures of complexes of secretory PLA2s with phosphonate phospholipid analogues have provided information about the detailed stereochemistry of transition-state binding, confirming the proposed catalytic mechanism of esterolysis. By contrast, studies on mammalian nonpancreatic secretory PLA2s (s-PLA2s) have only recently begun; s-PLA2s are scarce in normal cells and tissues but large amounts are found in association with local and systemic inflammatory processes and tissue injury in animals and man. Such s-PLAs have been purified from rabbit and rat inflammatory exudate, from synovial fluid from patients with rheumatoid arthritis and from human platelets. Cloning and sequencing shows that the primary structure of the human s-PLA2 has about 37% homology with that of bovine pancreatic PLA2 and 44% homology with that of Crotalus atrox PLA2. The human s-PLA2 is an unusually basic protein, yet contains most of the highly conserved amino-acid residues and sequences characteristic of the PLA2s sequenced so far. Here we report the refined, three-dimensional crystal structure at 2.2 A resolution of recombinant human rheumatoid arthritic synovial fluid PLA2. This may aid the development of potent and specific inhibitors of this enzyme using structure-based design.

Comparison of group I and II soluble phospholipases A2 activities on phagocytic functions of human polymorphonuclear and mononuclear phagocytes

Soluble phospholipase A2 (PLA2) purified from rheumatoid synovial fluid (group II) and repurified Naja naja venom PLA2 (group I) were compared for their influence on phagocytic activity of human polymorphonuclear (PMN) and mononuclear (MO) phagocytes. Group II PLA2 reduced chemotaxis, adhesiveness, and intracellular bactericidal activity (ICBA) and induced release of muramidase from PMNs. Group I PLA2 suppressed chemotaxis, and enhanced ICBA but had no influence on other phagocytic functions. Group II PLA2 purified from synovial fluid or from placenta caused marked spontaneous superoxide generation followed by inhibition of phagocytosis-induced burst of energy. Group I Naja naja and porcine pancreatic PLA2 had no effect on superoxide generation. Group II but not group I PLA2 reduced markedly ICBA of monocytes. It may be concluded that human group II soluble PLA2, in concentrations comparable to those present in inflamed joints or in sera of patients with active arthritis or septic shock, causes spontaneous formation of the oxygen radical superoxide and release of lysosomal enzymes, and suppresses conventional phagocytic activities of PMNs and monocytes. Marked differences between group I and group II PLA2s may mean that these enzymes exert different influences on cell membrane.

Electrostatic assay of phospholipase A activity: an application of the second harmonic method of monitoring membrane boundary potentials

To evaluate phospholipase A activity a new assay is suggested. This assay is based on the recording of boundary potential changes of the planar bilayer lipid membrane during enzymatic hydrolysis of lipids. To register these changes, a second harmonic method is used. Sensitivity of the assay is about 0.0002 units/ml regardless of the impurities that may be present in the samples. One analysis takes about 5 min.

Enhanced expression of group II phospholipase A2 gene in the tissues of endotoxin shock rats and its suppression by glucocorticoid

We studied the regulation of group II phospholipase A2 (PLA2-II) gene in vivo, using endotoxin shock rat as a model for systemic inflammation. Administration of endotoxin into rats increased PLA2 activity in the plasma, as described by Vadas and Hay, using endotoxin-challenged rabbit. Specific absorption of this activity by anti-PLA2-II antibody indicated that the released PLA2 was PLA2-II. The levels of PLA2-II mRNA were elevated in the aorta, spleen, lung, and thymus but not in the liver and kidney. The tissues with high PLA2-II mRNA contents released a greater amount of PLA2-II than the tissues of control rats. These results suggest that in endotoxin shock rats, PLA2-II is synthesized de novo in the above tissues and released into circulation. Furthermore, our present study demonstrates that glucocorticoid suppresses the enhanced expression of the PLA2-II gene in the tissues of endotoxin shock rats.

Compartmental heterogeneity of soluble phospholipases A

Multiple forms of soluble phospholipase A2 (PLA2) are known to coexist in venoms of individual reptilian species. While similar observations in several mammalian species suggest that this is a common phenomenon, the functional implications are not yet understood. In attempting to devise therapeutic strategies for treatment of inflammatory disorders by inhibition of PLA2, it is imperative to define the various PLA2 species in the relevant compartments. Herein, we report the presence of three PLA2 isotypes in rheumatoid arthritis serum, one pancreatic and two nonpancreatic phospholipases A2. The pancreatic and one of the nonpancreatic forms were optimally active in 7 mM calcium at pH 7.5. The other nonpancreatic form was calcium-independent and optimally active at pH 7.0. Only the calcium-dependent nonpancreatic form was observed in rheumatoid synovial fluid. Of the three serum isotypes, only the calcium-dependent nonpancreatic form correlated with markers of disease activity, such as the joint count and Landsbury index. Therefore, not all soluble or circulating phospholipases A2 are relevant to inflammatory processes. Selective inhibition of the proinflammatory form of PLA2 may prove to have some therapeutic benefit while minimizing the possible adverse effects of this form of intervention.

Group II phospholipase A2 mRNA synthesis is stimulated by two distinct mechanisms in rat vascular smooth muscle cells

Two potent inflammatory mediators, interleukin 1 (IL-1) and tumor necrosis factor (TNF) as well as lipopolysaccharide (LPS) increased group II phospholipase A2 (PLA2) mRNA levels, which resulted in enhanced secretion of the PLA2 enzyme from rat smooth muscle cells. cAMP-elevating agents also stimulated the release of PLA2 and increased the mRNA, but IL-1, TNF and LPS did not affect cAMP levels. Furthermore, the effects of TNF and cAMP-elevating agents were not additive but synergistic. Therefore, we concluded that the level of rat group II PLA2 mRNA is controlled at least by two distinct mechanisms, one involves cAMP and the other is mediated by TNF, IL-1 and LPS. This study also suggests important roles of group II PLA2 in pathogenesis of vascular inflammation.

Localization and evolution of two human phospholipase A2 genes and two related genetic elements

Mammals are now known to contain at least two distinct classes of phospholipases A2, the progenitors of which can be seen in the venoms of snakes. Mammalian "Type I" PLA2, synthesized primarily by the pancreas, is also present in smaller amounts in other tissues including lung, spleen, and kidney. Recently, a mammalian "Type II" PLA2 has been sequenced, and shown to occur in platelets, synovial cells and fluid, cells of inflammatory peritoneal exudate, liver, intestine, kidney, and placenta. This form, referred to here as Type IIA PLA2, could play a key role in arachidonate release in both normal and pathologic inflammation. The genes encoding both forms have also been recently cloned. Here, the sites of synthesis and respective roles of the two known enzymes are discussed, along with an analysis of the evolutionary conservation of Type IIA PLA2 gene sequence. In addition, two related genetic elements containing sequences homologous to a portion of Type II PLA2 are described, which map to the same chromosome as the Type IIA PLA2 gene (chromosome 1). Either or both of these could also encode a portion of additional mammalian PLA2s.

The effect of adrenalectomy on interleukin-1 release in vitro and in vivo

1 Peritoneal macrophages (M phi) collected from adrenalectomized (ADX) rats released more interleukin-1 (IL-1) activity and prostaglandin E2 (PGE2) than macrophages from sham-operated (SHO) rats. 2 The increase in IL-1 activity in the supernatants was confirmed by the increase of the cell-associated 33 kD IL-1 alpha precursor in ADX macrophages stimulated by lipopolysaccharide (LPS). 3 After the injection of Complete Freund's Adjuvant (CFA) to induce adjuvant arthritis, 60% of the ADX rats died, while no deaths occurred in the SHO group. 4 The in vivo administration of dexamethasone inhibited both IL-1 and PGE2 release by macrophages as well as protecting ADX animals from CFA-induced death. Indomethacin and BW 755C partially protected the animals from this lethal effect. 5 These results suggest that adrenalectomy induces an increased release of IL-1 both in vitro and in vivo, and are consistent with a feedback mechanism between IL-1 and glucocorticoid hormones.

Release of phospholipase A2 activity from rat vascular smooth muscle cells mediated by cAMP

Primary cultures of smooth muscle cells (SMC) derived from rat aorta release a phospholipase A2 activity into the culture medium. Phospholipase A2 activity was determined with [1-14C]oleate-labelled Escherichia coli as substrate. The enzyme has a neutral pH optimum and the activity is critically dependent on the free calcium concentration, with significant activity in the micromolar range of free calcium. Treatment of SMC with the beta agonist salbutamol, forskolin or cholera toxin, which all activate adenylate cyclase and increase intracellular cAMP concentration, increase the release of phospholipase A2 activity in a dose-dependent manner. Likewise, the addition of the membrane-permeable cAMP analogues, (Sp)-adenosine 3',5'-[thio]phosphate and N6,O-2'-dibutyryladenosine 3',5'-phosphate, enhance the release of phospholipase A2 activity from SMC in a dose-dependent manner. There is a lag period of about 4 h before a significant secretion of phospholipase A2 can be detected under basal, as well as under stimulated conditions. The forskolin analogue 1,9-dideoxyforskolin, which is inactive as a stimulator of adenylate cyclase, has no effect on phospholipase A2 secretion. Likewise, the potent vasoconstrictive peptide angiotensin II activates inositol phospholipid turnover in SMC, but has no effect on phospholipase A2 release. Pretreatment of SMC with actinomycin D or cycloheximide completely suppresses basal and cAMP-stimulated secretion of phospholipase A2 activity, thus demonstrating that transcription and protein synthesis are necessary for enzyme release.

Interleukin 1 and tumor necrosis factor synergistically stimulate prostaglandin synthesis and phospholipase A2 release from rat renal mesangial cells

Treatment of rat glomerular mesangial cells with recombinant human interleukin 1 alpha (rIL-1 alpha), recombinant human interleukin 1 beta (rIL-1 beta) or recombinant human tumor necrosis factor (rTNF) induces prostaglandin E2 (PGE2) synthesis and the release of a phospholipase A2 (PLA2) activity. rIL-1 beta is significantly more potent than rIL-1 alpha or rTNF in stimulating PGE2 as well as PLA2 release from mesangial cells. When given together, rTNF interacts in a synergistic fashion with rIL-1 alpha and rIL-1 beta to enhance both, PGE2 synthesis and PLA2 release. The released PLA2 has a neutral pH optimum and is calcium-dependent. Pretreatment of cells with actinomycin D or cycloheximide inhibits basal and cytokine-stimulated PGE2 and PLA2 release.