Synovial-type (group II) phospholipase A2 human seminal plasma

Quantitative Analysis of the Human Semen Phosphorometabolome by 31P-NMR

Phosphorus-containing metabolites occupy a prominent position in cell pathways. The phosphorometabolomic approach in human sperm samples will deliver valuable information as new male fertility biomarkers could emerge. This study analyzed, by 31P-NMR, seminal plasma and whole semen from asthenozoospermic and normozoospermic samples (71% vs. 27% and 45% vs. 17%, total and progressive sperm motility, respectively), and also ejaculates from healthy donors. At least 16 phosphorus-containing metabolites involved in central energy metabolism and phospholipid, nucleotide, and nicotinamide metabolic pathways were assigned and different abundances between the samples with distinct sperm quality was detected. Specifically, higher levels of phosphocholine, glucose-1-phosphate, and to a lesser degree, acetyl phosphate were found in the asthenozoospermic seminal plasma. Notably, the phosphorometabolites implicated in lipid metabolism were highlighted in the seminal plasma, while those associated with carbohydrate metabolism were more abundant in the spermatozoa. Higher levels of phosphocholine, glucose-1-phosphate, and acetyl phosphate in the seminal plasma with poor quality suggest their crucial role in supporting sperm motility through energy metabolic pathways. In the seminal plasma, phosphorometabolites related to lipid metabolism were prominent; however, spermatozoa metabolism is more dependent on carbohydrate-related energy pathways. Understanding the presence and function of sperm phosphorylated metabolites will enhance our knowledge of the metabolic profile of healthy human sperm, improving assessment and differential diagnosis.

Molecular determinants of bacterial sensitivity and resistance to mammalian Group IIA phospholipase A2

Group IIA secretory phospholipase A2 (sPLA(2)-IIA) of mammalian species is unique among the many structurally and functionally related mammalian sPLA(2) in their high net positive charge and potent (nM) antibacterial activity. Toward the Gram-positive bacteria tested thus far, the global cationic properties of sPLA(2)-IIA are necessary for optimal binding to intact bacteria and penetration of the multi-layered thick cell wall, but not for the degradation of membrane phospholipids that is essential for bacterial killing. Various Gram-positive bacterial species can differ as much as 1000-fold in sPLA(2)-IIA sensitivity despite similar intrinsic enzymatic activity of sPLA(2)-IIA toward the membrane phospholipids of various bacteria. d-alanylation of wall- and lipo-teichoic acids in Staphylococcus aureus and sortase function in Streptococcus pyogenes increase bacterial resistance to sPLA(2)-IIA by up to 100-fold apparently by affecting translocation of bound sPLA(2)-IIA to the cell membrane. Action of the sPLA(2)-IIA and other related sPLA(2) against Gram-negative bacteria is more dependent on cationic properties of the enzyme near the amino-terminus of the protein and collaboration with other host defense proteins that produce alterations of the unique Gram-negative bacterial outer membrane that normally represents a barrier to sPLA(2)-IIA action. This article is part of a Special Issue entitled: Bacterial Resistance to Antimicrobial Peptides.

Detection and quantification of microparticles from different cellular lineages using flow cytometry. Evaluation of the impact of secreted phospholipase A2 on microparticle assessment

Microparticles, also called microvesicles, are submicron extracellular vesicles produced by plasma membrane budding and shedding recognized as key actors in numerous physio(patho)logical processes. Since they can be released by virtually any cell lineages and are retrieved in biological fluids, microparticles appear as potent biomarkers. However, the small dimensions of microparticles and soluble factors present in body fluids can considerably impede their quantification. Here, flow cytometry with improved methodology for microparticle resolution was used to detect microparticles of human and mouse species generated from platelets, red blood cells, endothelial cells, apoptotic thymocytes and cells from the male reproductive tract. A family of soluble proteins, the secreted phospholipases A₂ (sPLA₂), comprises enzymes concomitantly expressed with microparticles in biological fluids and that catalyze the hydrolysis of membrane phospholipids. As sPLA₂ can hydrolyze phosphatidylserine, a phospholipid frequently used to assess microparticles, and might even clear microparticles, we further considered the impact of relevant sPLA2 enzymes, sPLA2 group IIA, V and X, on microparticle quantification. We observed that if enriched in fluids, certain sPLA₂ enzymes impair the quantification of microparticles depending on the species studied, the source of microparticles and the means of detection employed (surface phosphatidylserine or protein antigen detection). This study provides analytical considerations for appropriate interpretation of microparticle cytofluorometric measurements in biological samples containing sPLA2 enzymes.

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.

Antibacterial properties of chicken intestinal phospholipase A2

Background

The presence of chicken group-IIA PLA2 (ChPLA2-IIA) in the intestinal secretion suggests that this enzyme plays an important role in systemic bactericidal defence. We have analyzed the bactericidal activity of purified ChPLA2-IIA, on several gram-positive and gram-negative bacteria by using the diffusion well and dilution methods.

Results

ChPLA2-IIA displays potent bactericidal activity against gram-positive bacteria but lacks bactericidal activity against gram negative ones. We have also demonstrated a synergic action of ChPLA2-IIA with lysozyme when added to the bacteria culture prior to ChPLA2-IIA. The bactericidal efficiency of ChPLA2-IIA was shown to be dependent upon the presence of calcium ions and then a correlation could be made to its hydrolytic activity of membrane phospholipids. Interestingly ChPLA2-IIA displays a higher dependence to Ca2+ ions than to Mg2+ions.

Conclusion

We conclude that the main physiological role of ChPLA2-IIA could be the defence of the intestine against bacterial invasions.

Catalytic and non-catalytic functions of human IIA phospholipase A2

Group IIA phospholipase A2 (PLA2) is a low-molecular-mass secreted PLA2 enzyme that has been identified as an acute phase protein with a role in the inflammatory response to infection and trauma. The protein is possibly unique in being highly cationic and having a global distribution of surface arginine and lysine residues. This structure supports two functions of the protein. (1) An anti-bacterial role where the enzyme is targeted to the anionic cell membrane of Gram-positive bacteria and phospholipid hydrolysis assists in bacterial killing. (2) A proposed non-catalytic role in which the protein forms supramolecular aggregates with anionic phospholipid vesicles or debris. These aggregates are then internalized via interactions with cell surface heparin sulphate proteoglycans and macropinocytosis for disposal by macrophages.

The major bactericidal activity of human seminal plasma is zinc-dependent and derived from fragmentation of the semenogelins

One of the major roles of seminal plasma is to provide antimicrobial protection for the spermatozoa in the female reproductive tract. We found that the bactericidal activity of seminal plasma was highest after resolution of the seminal clot and that this antibacterial activity subsequently became greatly diminished. The antibacterial activity was derived from peptides generated by fragmentation of the semenogelins while the semenogelin holoproteins displayed no antibacterial activity. After ejaculation the semenogelin-derived peptides were fragmented to smaller and smaller fragments over time and thereby lost antibacterial activity. This paralleled the loss of antibacterial activity of whole seminal plasma both in vitro and after sexual intercourse. Moreover, the antibacterial activity of the semenogelin-derived peptides generated in seminal plasma was strictly zinc-dependent both at neutral and low pH. These data provide novel roles for the resolution of seminal clots and for the high zinc concentration in human seminal plasma.

The antibacterial chemokine MIG/CXCL9 is constitutively expressed in epithelial cells of the male urogenital tract and is present in seminal plasma

The integrity of the urogenital tract against potentially invasive pathogens is important for the health of the individual, fertilization, and continuance of species. Antibiotic peptides with broad antimicrobial activity, among them chemokines, are part of the innate immune system. We investigated the presence of the antibacterial interferon (IFN)-dependent CXC chemokines, MIG/CXCL9, IP-10/CXCL10, and I-TAC/CXCL11, in the human male reproductive system. MIG/CXCL9 was detected at 25.0 nM (range 8.1-40.6 nM; n = 14), whereas IP-10/CXCL10 and I-TAC/CXCL11 were detected at lower levels (mean 1.8 nM, range 0.3-5.8 nM and mean 0.6, 0.2-1.6 nM, respectively) in seminal plasma of fertile donors. The levels of MIG/CXCL9 are more than 300-fold higher than those previously reported in blood plasma. In vasectomized donors, significantly lower levels of MIG/CXCL9 (mean 14.7 nM, range 6.6-21.8) were found, suggesting that the testis and epididymis, in addition to the prostate, significantly contribute to the MIG/CXCL9 content of seminal plasma. Strong expression of MIG/CXCL9 was found in the epithelium of testis, epididymis, and prostate, as detected by immunohistochemistry. MIG/CXCL9 at concentrations in the order of those found in seminal plasma possessed antibacterial activity against the urogenital pathogen Neisseria gonorrhoeae. The relatively high levels of MIG/CXCL9 in seminal plasma point to roles for this chemokine in both host defense of the male urogenital tract and during fertilization.

Wall teichoic acid deficiency in Staphylococcus aureus confers selective resistance to mammalian group IIA phospholipase A(2) and human beta-defensin 3

Wall teichoic acids (WTAs) and membrane lipoteichoic acids (LTAs) are the major polyanionic polymers in the envelope of Staphylococcus aureus. WTAs in S. aureus play an important role in bacteriophage attachment and bacterial adherence to certain host cells, suggesting that WTAs are exposed on the cell surface and could also provide necessary binding sites for cationic antimicrobial peptides and proteins (CAMPs). Highly cationic mammalian group IIA phospholipase A(2) (gIIA PLA(2)) kills S. aureus at nanomolar concentrations by an action(s) that depends on initial electrostatic interactions, cell wall penetration, membrane phospholipid (PL) degradation, and activation of autolysins. A tagO mutant of S. aureus that lacks WTA is up to 100-fold more resistant to PL degradation and killing by gIIA PLA(2) and CAMP human beta-defensin 3 (HBD-3) but has the sensitivity of the wild type (wt) to other CAMPs, such as Magainin II amide, hNP1-3, LL-37, and lactoferrin. In contrast, there is little or no difference in either gIIA PLA(2) activity toward cell wall-depleted protoplasts of the wt and tagO strains of S. aureus or in binding of gIIA PLA(2) to wt and tagO strains. Scanning and transmission electron microscopy reveal increased surface protrusions in the S. aureus tagO mutant that might account for reduced activity of bound gIIA PLA(2) and HBD-3 toward the tagO mutant. In summary, the absence of WTA in S. aureus causes a selective increase in bacterial resistance to gIIA PLA(2) and HBD-3, the former apparently by reducing access and/or activity of bound antibacterial enzyme to the bacterial membrane.

Analysis of expression of secreted phospholipases A2 in mouse tissues at protein and mRNA levels

Secreted phospholipases A(2) (sPLA(2)) form a group of low-molecular weight enzymes that catalyze the hydrolysis of phospholipids. Some sPLA(2)s are likely to play a role in inflammation, cancer, and as antibacterial enzymes in innate immunity. We developed specific and sensitive time-resolved fluroimmunoassays (TR-FIA) for mouse group (G) IB, GIIA, GIID, GIIE, GIIF, GV and GX sPLA(2)s and measured their concentrations in mouse serum and tissues obtained from both Balb/c and C57BL/6J mice. We also analyzed the mRNA expression of the sPLA(2)s by quantitative real-time reverse transcriptase PCR (qPCR). In most tissues, the concentrations of sPLA(2) proteins corresponded to the expression of sPLA(2)s at the mRNA level. With a few exceptions, the sPLA(2) proteins were found in the gastrointestinal tract. The qPCR results showed that GIB sPLA(2) is synthesized widely in the gastrointestinal tract, including esophagus and colon, in addition to stomach and pancreas. Our results also suggest that the loss of GIIA sPLA(2) in the intestine of GIIA sPLA(2)-deficient C57BL/6J mice is not compensated by other sPLA(2)s under normal conditions. Outside the gastrointestinal tract, sPLA(2)s were expressed occasionally in a number of tissues. The TR-FIAs developed in the current study may serve as useful tools to measure the levels of sPLA(2) proteins in mouse serum and tissues in various experimental settings.

Secretory phospholipase A2 of group IIA: Is it an offensive or a defensive player during atherosclerosis and other inflammatory diseases?

Since its discovery in the serum of patients with severe inflammation and in rheumatoid arthritic fluids, the secretory phospholipase A2 of group IIA (sPLA2-IIA) has been chiefly considered as a proinflammatory enzyme, the result of which has been very intense interest in selective inhibitors of sPLA2-IIA in the hope of developing new and efficient therapies for inflammatory diseases. The recent discovery of the antibacterial properties of sPLA2-IIA, however, has raised the question of whether the upregulation of sPLA2-IIA during inflammation is to be considered uniformly negative and the hindrance of sPLA2-IIA in every instance beneficial. The aim of this review is for this reason, along with the results of various investigations which argue for the proinflammatory and proatherogenic effects of an upregulation of sPLA2-IIA, also to array data alongside which point to a protective function of sPLA2-IIA during inflammation. Thus, it could be shown that sPLA2-IIA, apart from the bactericidal effects, possesses also antithrombotic properties and indeed plays a possible role in the resolution of inflammation and the accelerated clearance of oxidatively modified lipoproteins during inflammation via the liver and adrenals. Based on these multipotent properties the knowledge of the function of sPLA2-IIA during inflammation is a fundamental prerequisite for the development and establishment of new therapeutic strategies to prevent and treat severe inflammatory diseases up to and including sepsis.

[Secreted phospholipases A2 (sPLA2): friends or foes? Are they actors in antibacterial and anti-HIV resistance?]

In this paper the authors update on the deletereous or beneficial roles of human and animal secretory phospholipases A2 (sPLA2). Although human sPLA2-IIA (inflammatory) was initially thought as a foe because its pathogenic implication in sepsis, multiorganic failure or other related syndromes, recent data indicates its role in in the antiinfectious host resistance. Thus, sPLA2-IIA exhibits potent bactericidal activities against gram-negative and gram-positive (in this case, together with other endogenous inflammatory factors) bacteria. Surprisingly, human sPLA-IIA does not show in vitro anti-human immunodeficiency virus (HIV) activity, whilst several sPLA2-IA isolated from bee and serpent venons do it: this is the case for crotoxin, a sPLA2-IA isolated from the venon of Crotalus durissus terrificus (sPLA2-Cdt). The mechanism for the in vitro anti-HIV activity of sPLA2-Cdt (inhibition of Gag p24) appears to be related to the ability of the drug to desestabilize ancorage (heparans) and fusion (cholesterol) receptors on HIV target cells.

Phospholipase A2 group IIA expression in gastric adenocarcinoma is associated with prolonged survival and less frequent metastasis

We analyzed gene expression patterns in human gastric cancers by using cDNA microarrays representing approximately equal 30,300 genes. Expression of PLA2G2A, a gene previously implicated as a modifier of the Apc(Min/+) (multiple intestinal neoplasia 1) mutant phenotype in the mouse, was significantly correlated with patient survival. We confirmed this observation in an independent set of patient samples by using quantitative RT-PCR. Beyond its potential diagnostic and prognostic significance, this result suggests the intriguing possibility that the activity of PLA2G2A may suppress progression or metastasis of human gastric cancer.

Biological effects of secretory phospholipase A(2) group IIA on lipoproteins and in atherogenesis

Secretory phospholipase A(2) group IIA(sPLA(2) IIA) can be produced and secreted by various cell types either constitutionally or as an acute-phase reactant upon stimulation by proinflammatory cytokines. The enzyme prefers phosphatidylethanolamine and phosphatidylserine as substrates. One important biological function may be the hydrolytic destruction of bacterial membranes. It has been demonstrated, however, that sPLA(2) can also hydrolyse the phospholipid monolayers of high density lipoprotein (HDL) and low density lipoprotein (LDL) in vitro. Secretory phospholipase A(2)-modified LDL show increased affinity to glycosaminoglycans and proteoglycans, a tendency to aggregate, and an enhanced ability to deliver cholesterol to cells. Incubation of cultured macrophages with PLA(2)-treated LDL and HDL is associated with increased intracellular lipid accumulation, resulting in the formation of foam cells. Elevated sPLA(2)(IIA) activity in blood serum leads to an increased clearance of serum cholesterol. Secretory phospholipase A(2)(IIA) can also be detected in the intima, adventitia and media of the atherosclerotic wall not only in developed lesions but also in very early stages of atherosclerosis. The presence of DNA of Chlamydia pneumoniae, herpes simplex virus, and cytomegalovirus was found to be associated with sPLA(2)(IIA) expression and other signs of local inflammation. Thus, sPLA(2)(IIA) appears to be one important link between the lipid and the inflammation hypothesis of atherosclerosis.

Expression of group IIA secretory phospholipase A2 is elevated in prostatic intraepithelial neoplasia and adenocarcinoma

Phospholipase A2 (PLA2) enzymes release arachidonic acid from cellular phospholipids in a variety of mammalian tissues, including prostate. Group IIa secretory PLA2 (sPLA2) can generate arachidonate from cellular phospholipids. We examined the group IIa sPLA2 expression in benign prostatic tissues, prostatic intraepithelial neoplasia (PIN), and adenocarcinoma to determine whether sPLA2 expression is altered in the carcinogenesis of human prostatic cancer. Thirty-three of 74 total cases (45%) of benign prostatic tissue showed positive immunohistochemical staining for group IIA sPLA2, whereas 63 of 69 total cases (91%) of high-grade PINs and 70 of 78 total cases (90%) of adenocarcinomas gave positive results. Four of 10 cases of low-grade PIN showed positive immunoreactivity for sPLA2. The number of cells staining for sPLA2 was significantly less in benign epithelium (4%) and low-grade PIN (4%) compared to high-grade PIN (40%) or adenocarcinoma (38%) (P < 0.001). There was no significant difference between high-grade PIN and adenocarcinoma in the number of cells staining positively for sPLA2. The intensity of sPLA2 immunoreactivity was also different among benign prostatic tissue, low-grade PIN, high-grade PIN, and prostatic adenocarcinoma specimens. The malignant cells demonstrated more intense immunohistochemical staining (moderate to strong staining in 81% and 69% cases for high-grade PIN and adenocarcinoma, respectively) than benign glands (moderate staining in 11% of cases). No strong staining was observed in benign glands or low-grade PIN. Our data are consistent with the contention that group IIA sPLA2 expression is elevated in neoplastic prostatic tissue and support the hypothesis that dysregulation of sPLA2 may play a role in prostatic carcinogenesis.

Basic residues of human group IIA phospholipase A2 are important for binding to factor Xa and prothrombinase inhibition comparison with other mammalian secreted phospholipases A2

Human secreted group IIA phospholipase A2 (hGIIA) was reported to inhibit prothrombinase activity because of binding to factor Xa. This study further shows that hGIIA and its catalytically inactive H48Q mutant prolong the lag time of thrombin generation in human platelet-rich plasma with similar efficiency, indicating that hGIIA exerts an anticoagulant effect independently of phospholipid hydrolysis under ex vivo conditions. Charge reversal of basic residues on the interfacial binding surface (IBS) of hGIIA leads to decreased ability to inhibit prothrombinase activity, which correlates with a reduced affinity for factor Xa, as determined by surface plasmon resonance. Mutation of other surface-exposed basic residues, hydrophobic residues on the IBS, and His48, does not affect the ability of hGIIA to inhibit prothrombinase activity and bind to factor Xa. Other basic, but not neutral or acidic, mammalian secreted phospholipases A2 (sPLA2s) exert a phospholipid-independent inhibitory effect on prothrombinase activity, suggesting that these basic sPLA2s also bind to factor Xa. In conclusion, this study demonstrates that the anticoagulant effect of hGIIA is independent of phospholipid hydrolysis and is based on its interaction with factor Xa, leading to prothrombinase inhibition, even under ex vivo conditions. This study also shows that such an interaction involves basic residues located on the IBS of hGIIA, and suggests that other basic mammalian sPLA2s may also inhibit blood coagulation by a similar mechanism to that described for hGIIA.

Phospholipase A2 in serum and colonic mucosa in ulcerative colitis

Group II phospholipase A2 is involved in the pathogenesis of various inflammatory diseases and in the host defence against bacteria. The enzyme is expressed in the epithelial cells of colonic mucosa in ulcerative colitis. In this study, we measured the concentration of group II phospholipase A2 in serum and colonic mucosa of patients with ulcerative colitis of different severity and of control patients without any inflammatory disease. The activity of ulcerative colitis was assessed by endoscopy. The concentration of group II phospholipase A2 was measured with an immunoassay. The concentrations of group II phospholipase A2 in serum and colonic mucosa were significantly higher in patients with active and inactive ulcerative colitis than in controls. However, the group II phospholipase A2 levels did not separate patients with different disease activity. The concentration of group II phospholipase A2 in colonic mucosa corresponded with the mucosal inflammatory activity (higher in active colonic areas) intra-individually, but not between different patients with ulcerative colitis. Serum group II phospholipase A2 values were above the normal reference range more often than the values of 11 standard laboratory blood tests widely used for the follow-up of inflammatory activity in ulcerative colitis. These results indicate that the concentration of group II phospholipase A2 is increased in serum and colonic mucosa of patients with ulcerative colitis. The clinical value of the measurement of group II phospholipase A2 in the follow-up of ulcerative colitis remains to be clarified.

Elevated group II phospholipase A2 mass concentration in serum and colonic mucosa in Crohn's disease

Group II phospholipase A2 has been proposed to play an important role in the pathophysiology of inflammatory bowel diseases. This enzyme has also been linked to host defence mechanisms against bacteria. The current study aimed at measuring the mass concentrations of group II phospholipase A2 in serum and colonic mucosa of patients with Crohn's disease of different severity and of appropriate control patients without any inflammatory disease. The activity of the disease was determined by clinical factors (the simple index score) and endoscopic and histological scoring. The mass concentration of group II phospholipase A2 was measured by a time-resolved fluoroimmunoassay. The mass concentrations of group II phospholipase A2 in serum and colonic mucosa were significantly higher both in patients with active and inactive Crohn's disease when compared with controls. There was statistically significant difference in the mass concentration of group II phospholipase A2 in colonic mucosa but not in serum between inactive and active Crohn's disease. The current results indicate that the mass concentration of group II phospholipase A2 is increased in serum and colonic mucosa of patients with Crohn's disease and that the latter is associated with the degree of the inflammatory activity in the intestinal wall. These results support the idea that group II phospholipase A2 is involved in the local and generalised pathological processes of Crohn's disease.

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.

Group II phospholipase A2 in human male reproductive organs and genital tumors

BACKGROUND

Group II phospholipase A2 (PLA2) is a lipolytic enzyme suggested to play a role in inflammation and antibacterial defence. In seminal fluid, the concentration of PLA2 is exceedingly high under normal circumstances (about 1,000 times the concentration in blood plasma of healthy humans). To elucidate the origin of the enzyme present in seminal plasma, we investigated the expression of group II PLA2 in male reproductive organs both at protein and mRNA levels. In addition, the presence of the enzyme was studied in common male genital tumors.

METHODS

The methods used were immunocytochemistry, in situ hybridization, and Northern blotting.

RESULTS

Northern blotting gave positive results for group II PLA2 mRNA in normal prostate, whereas other normal genital tissues gave negative results. Immunohistochemistry and in situ hybridization of group II PLA2 gave identical results. The enzyme was produced exclusively by the secretory epithelial cells of the prostatic gland. Surprisingly, expression was restricted to the posterior lobe and paraurethral glands of the prostate. Cells of prostatic adenocarcinoma expressed group II PLA2, whereas cells of other male genital tumors contained neither the enzyme protein nor the mRNA of group II PLA2. In some cases prostatic cancer cell seemed to express group II PLA2 at a higher rate than normal prostatic gland cells.

CONCLUSIONS

The high content of group II PLA2 in seminal plasma is due to the local production and secretion of the enzyme by the epithelial cells of the prostatic glands. Group II PLA2 is expressed focally, suggesting that specialized prostatic glands secrete this enzyme. All prostatic adenocarcinomas tested expressed group II PLA2 in variable amounts.

Secretory phospholipase A2 is the principal bactericide for staphylococci and other gram-positive bacteria in human tears

We examined human tears for molecules that killed gram-positive bacteria. The principal mediator of bactericidal activity against staphylococci proved to be a calcium-dependent enzyme, secretory phospholipase A2. Whereas the concentration of secretory phospholipase A2 in the normal tear film exceeded 30 microg/ml, only 1.1 ng (<0.1 nM) of the enzyme per ml sufficed to kill Listeria monocytogenes and 15 to 80 ng/ml killed Staphylococcus aureus. Despite its efficacy against gram-positive bacteria, secretory phospholipase A2 lacked bactericidal activity against gram-negative organisms (Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa) when tested in the ionic environment of tears. Given the presence of secretory phospholipase A2 in tears, intestinal secretions, and leukocytes, this enzyme may play a substantial role in innate mucosal and systemic bactericidal defenses against gram-positive bacteria.

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.

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.

Expression of human group II PLA2 in transgenic mice results in epidermal hyperplasia in the absence of inflammatory infiltrate

Group II PLA2 has been implicated in inflammatory processes in both man and other animals and has been shown to be involved in inflammatory conditions, such as arthritis and sepsis. Transgenic mice expressing the human group II PLA2 gene have been generated using a 6.2-kb genomic fragment. These mice express the group II PLA2 gene abundantly in liver, lung, kidney, and skin, and have serum PLA2 activity levels approximately eightfold higher than nontransgenic littermates. The group II PLA2 transgenic mice reported here exhibit epidermal and adnexal hyperplasia, hyperkeratosis, and almost total alopecia. The chronic epidermal hyperplasia and hyperkeratosis seen in these mice is similar to that seen in a variety of dermatopathies, including psoriasis. However, unlike what is seen with these dermatopathies, no significant inflammatory-cell influx was observed in the skin of these animals, or in any other tissue examined. These mice provide an important tool for examining group II PLA2 expression, and for determining the role of group II PLA2 in normal and disease physiology. They serve as an in vivo model for identifying inhibitors of group II PLA2 activity and gene expression.

A natural disruption of the secretory group II phospholipase A2 gene in inbred mouse strains

The synovial fluid or group II secretory phospholipase A2 (sPLA2) has been implicated as an important agent involved in a number of inflammatory processes. In an attempt to determine the role of sPLA2 in inflammation, we set out to generate sPLA2-deficient mice. During this investigation, we observed that in a number of inbred mouse strains, the sPLA2 gene was already disrupted by a frameshift mutation in exon 3. This mutation, a T insertion at position 166 from the ATG of the cDNA, terminates out of frame in exon 4, resulting in the disruption of the calcium binding domain in exon 3 and loss of both activity domains coded by exons 4 and 5. The mouse strains C57BL/6, 129/Sv, and B10.RIII were found to be homozygous for the defective sPLA2 gene, whereas outbred CD-1:SW mice had variable genotype at this locus. BALB/c, C3H/HE, DBA/1, DBA/2, NZB/BIN, and MRL lpr/lpr mice had a normal sPLA2 genotype. The sPLA2 mRNA was expressed at very high levels in the BALB/c mouse small intestine, whereas in the small intestine of the sPLA2 mutant mouse strains, sPLA2 mRNA was undetectable. In addition, PLA2 activity in acid extracts of the small intestine were approximately 40 times higher in BALB/c than in the mutant mice. Transcription of the mutant sPLA2 gene resulted in multiple transcripts due to exon skipping. None of the resulting mutant mRNAs encoded an active product. The identification of this mutation should not only help define the physiological role of sPLA2 but also has important implications in mouse inflammatory models developed by targeted mutagenesis.

Immunohistochemical localization of phospholipase A2 in human and bovine male reproductive organs

Phospholipase A2 (PLA2) taken from human seminal plasma and purified about 1450-fold was injected into rabbits to prepare polyclonal antibodies. The antiserum produced and the IgG purified from the antiserum were used to compare the immunohistochemical localization of PLA2 in the human male reproductive system with that in the bull. In Western blot analyses, the polyclonal antibodies cross-reacted with purified PLA2s from human seminal plasma, bovine Cowper's glands and with partly purified PLA2 from bovine seminal vesicle fluid. On the other hand, purified PLA2s from Crotalus adamanteus venom, bovine pancreas or from bovine prostate were not recognized by the polyclonal antibodies. With an indirect peroxidase technique, PLA2 was localized in the epithelial cells of the human prostate and bovine seminal vesicles as well as in the fibrous connective tissue of bovine Cowper's gland. Indirect peroxidase staining also gave an immunoreaction in the enlarged acrosomes of round spermatids in the human testis. Using an indirect immunofluorescence method, ejaculated human spermatozoa revealed an immunoreaction which was not uniform, and the reaction was restricted to the middle piece and the acrosomal and postacrosomal regions. In conclusion, human seminal plasma, spermatozoa and prostate PLA2s were immunohistochemically related to those from bovine Cowper's gland, seminal vesicles and seminal fluid.