Detection of honeybee venom in envenomed tissues by direct MALDI MSI

A new analytical approach using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) for the study of honeybee venom is shown. In vitro and in vivo models simulating the bee sting have been developed using live honeybees and, as the envenomation sites, pig ears and rat legs; MALDI MSI has been used to map, over time, the diffusion and distribution of three venom allergens (Api m 1, Api m 4, and Api m 6) and two venom toxins (apamine and mast cell degranulating peptide). In conjunction with other classical biochemical techniques and high resolution mass spectrometry (HRMS), structural data have been obtained that contribute to current understanding of honeybee venom composition. Initial data have also been obtained demonstrating the feasibility of mapping the organism's response to the sting. The opportunity to monitor venom diffusion and the organism's response at the same time might open new pathways for in vivo preclinical studies in designing and testing new venom immunotherapy (VIT).

Attenuated free cholesterol loading-induced apoptosis but preserved phospholipid composition of peritoneal macrophages from mice that do not express group VIA phospholipase A2

Mouse macrophages undergo ER stress and apoptosis upon free cholesterol loading (FCL). We recently generated iPLA(2)beta-null mice, and here we demonstrate that iPLA(2)beta-null macrophages have reduced sensitivity to FCL-induced apoptosis, although they and wild-type (WT) cells exhibit similar increases in the transcriptional regulator CHOP. iPLA(2)beta-null macrophages are also less sensitive to apoptosis induced by the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor thapsigargin and the scavenger receptor A ligand fucoidan, and restoring iPLA(2)betaexpression with recombinant adenovirus increases apoptosis toward WT levels. WT and iPLA(2)beta-null macrophages incorporate [(3)H]arachidonic acid ([(3)H]AA]) into glycerophosphocholine lipids equally rapidly and exhibit identical zymosan-induced, cPLA(2)alpha-catalyzed [(3)H]AA release. In contrast, although WT macrophages exhibit robust [(3)H]AA release upon FCL, this is attenuated in iPLA(2)beta-null macrophages and increases toward WT levels upon restoring iPLA(2)beta expression. Recent reports indicate that iPLA(2)beta modulates mitochondrial cytochrome c release, and we find that thapsigargin and fucoidan induce mitochondrial phospholipid loss and cytochrome c release into WT macrophage cytosol and that these events are blunted in iPLA(2)beta-null cells. Immunoblotting studies indicate that iPLA(2)beta associates with mitochondria in macrophages subjected to ER stress. AA incorporation into glycerophosphocholine lipids is unimpaired in iPLA(2)beta-null macrophages upon electrospray ionization-tandem mass spectrometry analyses, and their complex lipid composition is similar to WT cells. These findings suggest that iPLA(2)beta participates in ER stress-induced macrophage apoptosis caused by FCL or thapsigargin but that deletion of iPLA(2)beta does not impair macrophage arachidonate incorporation or phospholipid composition.

Effect of chronic CB1 cannabinoid receptor antagonism on livers of rats with biliary cirrhosis

Recent studies have shown that the activated endocannabinoid system participates in the increase in IHR (intrahepatic resistance) in cirrhosis. The increased hepatic production of vasoconstrictive eicosanoids is involved in the effect of endocannabinoids on the hepatic microcirculation in cirrhosis; however, the mechanisms of these effects are still unknown. The aim of the present study was to investigate the effects of chronic CB(1) (cannabinoid 1) receptor blockade in the hepatic microcirculation of CBL (common bile-duct-ligated) cirrhotic rats. After 1 week of treatment with AM251, a specific CB(1) receptor antagonist, IHR, SMA (superior mesenteric artery) blood flow and hepatic production of eicosanoids [TXB(2) (thromboxane B(2)), 6-keto PGF(1alpha) (prostaglandin F(1alpha)) and Cys-LTs (cysteinyl leukotrienes)] were measured. Additionally, the protein levels of hepatic COX (cyclo-oxygenase) isoforms, 5-LOX (5-lipoxygenase), CB(1) receptor, TGF-beta(1) (transforming growth factor beta(1)), cPLA(2) [cytosolic PLA(2) (phospholipase A(2))], sPLA(2) (secreted PLA(2)) and collagen deposition were also measured. In AM251-treated cirrhotic rats, a decrease in portal venous pressure was associated with the decrease in IHR and SMA blood flow. Additionally, the protein levels of hepatic CB(1) receptor, TGF-beta(1), cPLA(2) and hepatic collagen deposition, and the hepatic levels of 5-LOX and COX-2 and the corresponding production of TXB(2) and Cys-LTs in perfusates, were significantly decreased after 1 week of AM251 treatment in cirrhotic rats. Furthermore, acute infusion of AM251 resulted in a decrease in SMA blood flow and an increase in SMA resistance in CBL rats. In conclusion, the chronic effects of AM251 treatment on the intrahepatic microcirculation were, at least partly, mediated by the inhibition of hepatic TGF-beta(1) activity, which was associated with decreased hepatic collagen deposition and the activated PLA(2)/eicosanoid cascade in cirrhotic livers.

Butyrate inhibits oral cancer cell proliferation and regulates expression of secretory phospholipase A2-X and COX-2

Although surgical resection is the first choice for oral cancer, the development of new anti-cancer drugs is of great interest. The effect of the histone deacetylation inhibitor, sodium butyrate (NaBu) on oral cancer cell (OCC) HSC-3 and HSC-4 proliferation in vitro was investigated. The synthesis of rate-limiting enzymes such as sPLA2 (-IIA, -V, -X) and COX-2 was examined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, as well as PGE2 by ELISA. NaBu acted in a concentration-dependent manner. Over 3 mM, it inhibited OCC proliferation, due to increased p21 expression and cell cycle arrest in the G2/M-phase. At low concentration (< or = 1 mM), NaBu showed no effects or enhanced cell proliferation. NaBu also regulated COX-2 and sPLA2-X expression, and augmented PGE2 synthesis in OCC. These results indicate that NaBu is a novel candidate agent for the treatment of oral cancer. The treatment efficacy must be investigated in additional experiments considering NaBu concentration and tumor cell heterogeneity.

Role of phospholipase A2 in the induction of drip loss in porcine muscle

The role of phospholipase A2 in the induction of drip loss from pig muscle has been investigated. In samples from porcine M. longissimus dorsi, total PLA2 activity as well as mRNA and protein levels of the group VIA iPLA2 (iPLA2-VIA) increased during the initial 4 h post-mortem period. Morphological studies of porcine muscle showed that at 4 h post-mortem, gaps had formed between muscle fibers and that the sarcolemma membrane borders appeared blurred. At the same time iPLA2-VIA protein levels were increased inside muscle fibers and at the sarcolemma. iPLA2-VIA mRNA abundance in samples from different breeds of pigs with variations in drip loss revealed no clear correlation between drip loss level and iPLA2-VIA expression. Together, these data indicate that during the post-mortem period, iPLA2-VIA expression and activity is increased at the muscle fiber membranes. PLA2 activity may affect membrane permeability and consequently the progression of drip formation in porcine muscle.

A new photoprobe for studying biological activities of secreted phospholipases A2

Ammodytoxin (Atx) is a snake venom phospholipase A2 (sPLA2s) with presynaptic toxicity, anticoagulant activity and the ability to influence cell cycle progression. These multiple physiological activities make this molecule a promising tool for studying processes influenced by the highly homologous mammalian sPLA2s-for example cell proliferation and apoptosis. Secreted PLA2s can act on cells as enzymes or as ligands for cellular receptors. To further characterize the sPLA2-binding molecules in cells we have developed a new method based on AtxC and a biotin-containing cross-linking reagent sulfo-SBED which possesses both an amine-reactive and a photo-reactive site, together with a biotin moiety that enables specific detection and affinity-based concentration. The biological activity of the AtxC derivatized by sulfo-SBED was demonstrated by biotin-tagging of calmodulin and R25, both known AtxC targets, but not of other proteins. In addition, using the new protocol we specifically labelled 14-3-3 proteins, protein disulfide isomerase and two unknown proteins of 45 and 46kDa in the mitochondrial-synaptosomal fraction of porcine cerebral cortex, none of which could be tagged by the previously used methods. The new methodology, which can be used for any sPLA2, constitutes a novel approach to discovering and purifying sPLA2-binding proteins, to studying the topology of their respective complexes and to following sPLA2s in different biological systems.

LPS exacerbates endothelin-1 induced activation of cytosolic phospholipase A2 and thromboxane A2 production from Kupffer cells of the prefibrotic rat liver

BACKGROUND/AIMS

Thromboxane A2 (TXA2) has been suggested to play a significant role in the development of portal hypertension in fibrosis, and Kupffer cell (KC) derived TXA2 has been shown to mediate the hyperresponsiveness of the portal circulation to the vasoconstrictive actions of endothelin-1 (ET-1) during endotoxemia. The aim of this study was to determine whether the double stresses of prefibrotic changes and endotoxemia additively activate KC to increase release of TXA2 in response to ET-1, resulting in elevated portal resistance.

METHODS

One week Bile duct ligation (BDL) rats and sham-operated controls were subjected to isolated liver perfusions following LPS or saline for 6h. In a separate experiment, KC were isolated from BDL or sham rats and incubated with LPS or saline for 6h before the ET-1 treatment.

RESULTS

The double stresses of early fibrosis and LPS resulted in a greater sustained increase in portal pressure in response to ET-1 in BDL rats, and this increase correlated well with the much enhanced release of TXA2 in the perfusate. Media from the cultured KC showed significantly greater TXA2 release in response to ET-1 in BDL group than those in sham group, and LPS exacerbated this effect. Protein levels of cytosolic phospholipase A2 (cPLA2), cyclooxygenase-2, and thromboxane synthase were also significantly elevated in KC from BDL rats. ET-1 produced a marked increase in cPLA2 activation as measured by the phosphorylation of cPLA2 in KC of both BDL and sham groups. LPS greatly exacerbated the activation of cPLA2.

CONCLUSIONS

The data suggest that the double stresses additively activate KC with an upregulation of the key enzymes in the TXA2 biosynthesis and release increased amount of TXA2 via the augmented activation of cPLA2 in response to ET-1, which leads to the increased portal resistance and ultimately hepatic microcirculatory dysfunction.

PCB 50 stimulates release of arachidonic acid and prostaglandins from late gestation rat amnion fibroblast cells

Amniotic phospholipase A2 activity contributes to elevated levels of arachidonic acid and prostaglandins observed during labor. Polychlorinated biphenyls (PCBs) activate PLA2 and have been associated with shortened gestation length. To determine if PCBs stimulate amniotic PLA2, cell cultures of rat amnion fibroblasts (RAF) were established from gestation day (gd) 20 rats and labeled with 0.5 micro Ci [3H]-arachidonic acid prior to a 0.5- or 4-h exposure to 0.1% DMSO (solvent control), PCB 50 (1-50 micro M) or TNFalpha (positive control). PCB 50 and TNFalpha induced significant release of [3H]-arachidonic acid from amnion fibroblast cells in time-dependent manners (p<0.001), an effect associated with a significant increase in iPLA2 expression (p<0.05). PCB 50 also stimulated prostaglandin production from RAF cells independent of changes in immunoreactive COX-2. These data suggest that amnion may serve as a target for PCB-induced release of arachidonic acid and uterotonic prostaglandins, with a potential for adverse pregnancy outcomes.

Differential expression of cyclooxygenase 1 and cyclooxygenase 2 in the bovine oviduct

The aim of the present study was to investigate the enzymes for the local prostaglandin (PG) biosynthesis present in the bovine oviduct during the estrous cycle to influence early reproductive events. Bovine oviducts were classified into four phases: pre-ovulatory, post-ovulatory, early-to-mid luteal, and late luteal phase, subdivided further into ipsi- or contralateral site and separated into ampulla or isthmus. Oviductal cells were gained by flushing the oviductal regions. Quantitative real-time reverse transcriptase-PCR was performed for the secretory and cytosolic phospholipases A(2) (sPLA(2)IB, cPLA(2)alpha, and cPLA(2)beta) and cyclooxygenases (COX-1 and COX-2) as the first step enzymes of PG synthesis. COX-1 and cPLA(2)beta showed significant highest mRNA expression around and before ovulation compared with the luteal phase respectively. sPLA(2)IB and cPLA(2)alpha mRNA expression was unregulated during the estrous cycle. Regional differences in mRNA content were found for sPLA(2)IB with higher mRNA expression in the ampulla than in the isthmus. Western blot analysis revealed the highest COX-1 protein content in the early-to-mid luteal phase. Immunohistochemistry demonstrated that COX-1 was localized in epithelial and smooth muscle cells, whereas COX-2 was only localized in epithelial cells. COX-2 showed a differential distribution within the epithelial cell layer suggesting a regulation on a cellular level, although the COX-2 mRNA and protein amounts did not vary throughout the estrous cycle. A COX activity assay of oviductal cells revealed that COX activity originated predominantly from COX-1 than from COX-2. Treatment of primary oviductal cells with 10 pg/ml 17beta-estradiol or 10 ng/ml progesterone resulted in a higher expression of COX-2 and cPLA(2)alpha, but not of the other enzymes. The expression pattern of these enzymes suggests that an estrous-cycle dependent and region-specific PG synthesis in the bovine oviduct may be required for a successful reproduction.

Expression profiling of auxin-treated Arabidopsis roots: toward a molecular analysis of lateral root emergence

Treating Arabidopsis roots with exogenous auxin results in dramatic changes in cellular processes including de novo induction of lateral roots which later emerge through the overlying cells. Microarray experiments reveal approximately 80 genes that are substantially up-regulated in the root over the first 12 h following auxin treatment. We hypothesize that the observed increase in expression of pectate lyase family genes leads to degradation of the pectin-rich middle lamellae, allowing cells in the parent root to separate cleanly. Differences in the degree of pectin methylation in lateral and parent roots may explain why lateral roots are not degraded themselves.

Early diet-induced non-alcoholic steatohepatitis in APOE2 knock-in mice and its prevention by fibrates

BACKGROUND/AIMS

The molecular mechanisms leading to Non-Alcoholic Steatohepatitis (NASH) are not fully understood. In mice, NASH can be inhibited by fenofibrate, a synthetic agonist for the nuclear receptor peroxisome proliferator activated receptor alpha, which regulates hepatic triglyceride metabolism. This study aimed to elucidate the relation between steatosis and inflammation in NASH in a human-like hyperlipidemic mouse model.

METHODS

Liver phenotype and gene expression were assessed in APOE2 knock-in mice that were fed a western-type high fat diet with or without co-administration of fenofibrate.

RESULTS

In response to a western diet, APOE2 knock-in mice developed NASH characterized by steatosis and inflammation. Strikingly, macrophage accumulation in the liver preceded the steatosis during progression of the disease. This phenotype was in line with gene expression patterns, which showed regulation of two major groups of genes, i.e. inflammatory and lipid genes. Fenofibrate treatment decreased hepatic macrophage accumulation and abolished steatosis. Moreover, a marked reduction in the expression of inflammatory genes occurred immediately after fenofibrate treatment.

CONCLUSIONS

These data indicate that inflammation might play an instrumental role during the development of NASH in this mouse model. Inhibition of NASH by fenofibrate may be due, at least in part, to its inhibitory effect on pro-inflammatory genes.

A continuous fluorescence assay for phospholipase A2 with nontagged lipid

Human nonpancreatic secreted phospholipase A2 (hnps PLA2) is considered to be an important drug target for antiinflammation therapy. We have established a new fluorescence assay by using 1-anilinonaphthalene-8-sulfonate (ANS) as an interfacial probe for hydrophobic environment detection. The fitted apparent k(cat)/K(m) of hnps PLA2 is 0.0181 +/- 0.0005 RFU/microMs. Tests on known synthesized inhibitor gave IC50 values similar to those from isotope-labeled assay. Because ANS is a commonly used probe for hydrophobic environment detection that needs no modification in the current assay, this strategy may be widely applicable for interfacial catalytic reactions.

Seeing is believing: real-time cellular activity assay for phospholipase A2

Quantitative real-time in situ activity assays are necessary for determining the physiological function and regulation of enzymes. A paper in this issue reports the synthesis of a series of new fluorogenic phospholipids that allow fast real-time measurements of cellular activity and head group selectivity of an important family of enzyme, phospholipases.

Expression of phospholipase A2 group IVA (PLA2G4A) is upregulated by human chorionic gonadotropin in bovine granulosa cells of ovulatory follicles

Prostaglandins are required for the ovulatory process, and their biosynthesis depends on the initial release of arachidonic acid from membrane phospholipids. We hypothesized that phospholipase A2 group IVA (PLA2G4A) expression is upregulated in granulosa cells (GC) at ovulation. We have characterized bovine PLA2G4A cDNA, and investigated its spatiotemporal regulation at the mRNA and protein levels in hCG-induced ovulatory follicles and in vitro, using forskolin-stimulated GC. Regulation of PLA2G4A mRNA expression was studied in GC obtained from bovine follicles collected at different developmental stages: small follicles (2-4 mm), dominant follicles at Day 5 (D5) of the estrous cycle, ovulatory follicles 24 h following injection of hCG, and corpus luteum at D5. PLA2G4A mRNA increased by 14-fold in GC of hCG-stimulated versus dominant follicles (P < 0.0001). Follicular walls obtained from ovulatory follicles recovered at 0, 6, 12, 18, and 24 h post-hCG injection showed an initial 16-fold increase in PLA2G4A transcript at 12 h that reached a 45-fold increase at 24 h, as compared to 0 h (P < 0.0001). Immunoblots of GC extracts showed an initial induction of the PLA2G4A protein at 18 h post-hCG, reaching a maximum at 24 h. Immunohistochemistry observations showed that PLA2G4A signal was mainly observed in mural GC compared to antral GC in hCG-stimulated follicles. Stimulation of cultured bovine GC with 10 microM of forskolin caused an increase in PLA2G4A mRNA and protein. Ovulation is associated with an LH/hCG-dependent induction of PLA2G4A in GC via the adenylyl cyclase/cAMP pathway.

Analysis of gene and protein expression in healthy and carious tooth pulp with cDNA microarray and two-dimensional gel electrophoresis

Complementary DNA (cDNA) microarray and two-dimensional (2-D) gel electrophoresis, combined with mass spectrometry, enable simultaneous analysis of expression patterns of thousands of genes, but their use in pulp biology has been limited. Here we compared gene and protein expression of pulp tissues from sound and carious human teeth using cDNA microarray and 2-D gel electrophoresis to evaluate their usefulness in pulp biology research and to identify the genes with changes in carious teeth. The cDNA microarray revealed several differentially expressed genes and genes with a high expression in both tissues. These genes have various functions, e.g. effects on vascular and nerve structures, inflammation, and cell differentiation. Variability between cDNA hybridizations indicates that the overall gene expression pattern may vary significantly between individual teeth. The 2-D gel electrophoresis revealed no change between healthy and diseased tissue. The identification of 96 proteins in the pulp tissue revealed none of the gene products with corresponding high/different mRNA expression in cDNA microarray. Interestingly, we detected also a hypothetical protein (putative nucleoside diphosphate kinase), and present therefore the first evidence for the existence of this protein. Even though the methods reveal potentially important gene expression, they may currently have only limited value in in vivo pulp biology research.

Lipoprotein-associated phospholipase A2 as a biomarker for coronary disease and stroke

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), also known as platelet-activating factor acetylhydrolase, is a plasma enzyme that circulates bound to lipoproteins. The association between Lp-PLA(2) and atherosclerosis is ambiguous, as it can both degrade and generate potentially damaging vasoactive molecules. In this article, we speculate that Lp-PLA(2) associated with HDL might have cardioprotective properties, whereas the same enzyme bound to LDL might contribute directly to atherosclerosis at all stages, from lipoprotein oxidation to endothelial dysfunction, and plaque initiation and growth. Genetic and animal model studies give varying indications as to the contribution of Lp-PLA(2) to atherogenesis and tend to support the view that higher Lp-PLA(2) levels are cardioprotective. By contrast, a series of population studies point clearly to a positive association between plasma Lp-PLA(2) levels or activity levels and risk of coronary heart disease or stroke. Typically, people with Lp-PLA(2) levels in the highest quintile of the population have about a twofold greater risk than those in the lowest quintile. It is, perhaps, too early to introduce Lp-PLA(2) as a population-wide biomarker for coronary heart disease risk; however, with accumulating evidence, it might find a place in a stepwise risk assessment of individuals who require more aggressive intervention to prevent vascular disease.

Crystal Structure Analysis of Phosphatidylcholine−GM2-Activator Product Complexes: Evidence for Hydrolase Activity,

GM2-activator protein (GM2AP) is a lysosomal lipid transfer protein with important biological roles in ganglioside catabolism, phospholipid metabolism, and T-cell activation. Previous studies of crystal structures of GM2AP complexed with the physiological ligand GM2 and platelet activating factor (PAF) have shown binding at two specific locations within the spacious apolar pocket and an ordering effect of endogenous resident lipids. To investigate the structural basis of phospholipid binding further, GM2AP was cocrystallized with phosphatidylcholine (PC), known to interact with GM2AP. Analysis of three crystal forms revealed binding of single chain lipids and fatty acids only and surprisingly not intact PC. The regions of best defined electron density are consistent with the presence of lyso-PC and oleic acid, which constitute deacylation products of PC. Their acyl tails are in stacking contact with shorter, less well-defined stretches of electron density that may represent resident fatty acids. The GM2AP associated hydrolytic activity that generates lyso-PC was further confirmed by mass spectrometry and enzymatic assays. In addition, we report the structures of (i) mutant Y137S, assessing the role of Tyr137 in lipid transfer via the hydrophobic cleft, and (ii) apo-mouse GM2AP, revealing a hydrophobic pocket with a constricted opening. Our structural results provide new insights into the biological functions of GM2AP. The combined effect of hydrolytic and lipid transfer properties has profound implications in cellular signaling.

Isolation and pharmacological characterization of cannitoxin, a presynaptic neurotoxin from the venom of the Papuan Taipan (Oxyuranus scutellatus canni)

The Papuan taipan (Oxyuranus scutellatus canni) is widely distributed throughout much of Papua New Guinea. Although neurotoxicity is a major symptom of envenomation, no neurotoxins have been isolated from this venom. Using a series of size exclusion chromatography steps, we report the isolation of cannitoxin, a presynaptic neurotoxin (44,848 Da) that represents approximately 16% of the whole venom. The toxin displayed high phospholipase A2 (PLA2 activity (330 +/- 5 micromol/min/mg) and caused concentration-dependent (11-66 nM) inhibition of indirect (0.2 ms; 0.1 Hz; supramaximal V) twitches of the chick biventer cervicis nerve-muscle preparation without effecting nicotinic receptor agonists. Prior addition of CSL Taipan antivenom (5 U/ml) or inhibition of phospholipase A2 activity by incubation with 4-bromophenacyl bromide prevented the inhibition of twitches. Cannitoxin is composed of three different subunits, alpha, beta, and gamma, with the possibility of two beta isomers. However, only the alpha subunit displayed in vitro neurotoxic activity of its own. Thus, cannitoxin is similar in structure and pharmacology to taipoxin, which has been isolated from the closely related Australian species O. scutellatus scutellatus (coastal taipan).

Localization and functional interrelationships among cytosolic Group IV, secreted Group V, and Ca2+-independent Group VI phospholipase A2s in P388D1 macrophages using GFP/RFP constructs

P388D(1) cells exposed to bacterial lipopolysaccharide (LPS) mobilize arachidonic acid (AA) for prostaglandin synthesis in two temporally distinct pathways. The "immediate pathway" is triggered within minutes by receptor agonists such as platelet-activating factor (PAF) but only if the cells have previously been primed with LPS for 1 h. The "delayed pathway" occurs in response to LPS alone over the course of several hours. We have now investigated the subcellular localization of both the Group IV cytosolic phospholipase A(2) (cPLA(2)) and the Group V secreted PLA(2) (sPLA(2)) during these two temporally distinct routes of AA release. We have prepared cells overexpressing fusion proteins of sPLA(2)-GFP and cPLA(2)-RFP. In the resting cells, cPLA(2)-RFP was uniformly located throughout the cytoplasm, and short-term treatment with LPS did not induce translocation to perinuclear and/or Golgi membranes. However, such a translocation occurred almost immediately after the addition of PAF to the cells. Long-term exposure of the cells to LPS led to the translocation of cPLA(2)-RFP to intracellular membranes after 3 h, and correlates with a significant release of AA in a cPLA(2)-dependent manner. At the same time period that the delayed association of cPLA(2) with perinuclear membranes is detected, an intense fluorescence arising from the sPLA(2)-GFP was found around the nucleus in the sPLA(2)-GFP stably transfected cells. In parallel with these changes, significant AA release was detected from the sPLA(2)-GFP transfectants in a cPLA(2)-dependent manner, which may reflect cross-talk between sPLA(2) and cPLA(2). The subcellular localization of the Group VIA Ca(2+)-independent PLA(2) (iPLA(2)) was also investigated. Cells overexpressing iPLA(2)-GFP showed no fluorescence changes under any activation condition. However, the iPLA(2)-GFP-expressing cells showed relatively high basal AA release, confirming a role for iPLA(2) in basal deacylation reactions. These new data illustrate the subcellular localization changes that accompany the distinct roles that each of the three kinds of PLA(2) present in P388D(1) macrophages play in AA mobilization.

A multifaceted analysis of viperid snake venoms by two-dimensional gel electrophoresis: an approach to understanding venom proteomics

The complexity of Viperid venoms has long been appreciated by investigators in the fields of toxinology and medicine. However, it is only recently that the depth of that complexity has become somewhat quantitatively and qualitatively appreciated. With the resurgence of two-dimensional gel electrophoresis (2-DE) and the advances in mass spectrometry virtually all venom components can be visualized and identified given sufficient effort and resources. Here we present the use of 2-DE for examining venom complexity as well as demonstrating interesting approaches to selectively delineate subpopulations of venom proteins based on particular characteristics of the proteins such as antibody cross-reactivity or enzymatic activities. 2-DE comparisons between venoms from different species of the same genus (Bothrops) of snake clearly demonstrated both the similarity as well as the apparent diversity among these venoms. Using liquid chromatography/tandem mass spectrometry we were able to identify regions of the two-dimensional gels from each venom in which certain classes of proteins were found. 2-DE was also used to compare venoms from Crotalus atrox and Bothrops jararaca. For these venoms a variety of staining/detection protocols was utilized to compare and contrast the venoms. Specifically, we used various stains to visualize subpopulations of the venom proteomes of these snakes, including Coomassie, Silver, Sypro Ruby and Pro-Q-Emerald. Using specific antibodies in Western blot analyses of 2-DE of the venoms we have examined subpopulations of proteins in these venoms including the serine proteinase proteome, the metalloproteinase proteome, and the phospholipases A2 proteome. A functional assessment of the gelatinolytic activity of these venoms was also performed by zymography. These approaches have given rise to a more thorough understanding of venom complexity and the toxins comprising these venoms and provide insights to investigators who wish to focus on these venom subpopulations of proteins in future studies.

Biochemical characterization of Toxoplasma gondii 1-Cys peroxiredoxin 2 with mechanistic similarities to typical 2-Cys Prx

TgPrx2 represents a recently discovered cytosolic 1-Cys peroxiredoxin (Prx) from the intracellular parasite Toxoplasma gondii. Over-expression of the respective gene confers protection against H(2)O(2), suggesting that the protein possesses peroxidase activity. According to the current nomenclature eukaryotic typical and atypical 2-Cys Prx contain a second conserved resolving cysteine residue whereas 1-Cys Prx work on the basis of a monothiol mechanism. Only a few 1-Cys peroxiredoxins have been biochemically characterized to date. Here we describe the mechanistic characterization of TgPrx2 in vitro, including site directed mutagenesis studies, gel filtration chromatography, and molecular modeling. TgPrx2 has general antioxidant properties as indicated by its ability to protect glutamine synthetase against a dithiothreitol Fe(3+)-catalyzed oxidation system. However, TgPrx2 does not reduce H(2)O(2) nor tert-butyl hydroperoxide at the expense of glutaredoxin, thioredoxin or glutathione. Cys(47) was identified as the active site cysteine residue. Most interestingly, Cys(47) was found to form an intermolecular disulfide with Cys(209) from the C-terminal domain of a second subunit which acts as the resolving cysteine. This is a mechanism analogous to typical peroxiredoxins. In contrast to the latter, however, dimeric TgPrx2 does not oligomerize to decamers but is able to form tetramers and hexamers which are non-covalently associated. To our knowledge, TgPrx2 is the first eukaryotic 'so called' 1-Cys peroxiredoxin shown to act on the basis of a 2-Cys mechanism. Our data indicate that mechanistic studies are essential for classifying peroxiredoxins.

Mitochondrial localization of cyclooxygenase-2 and calcium-independent phospholipase A2 in human cancer cells: Implication in apoptosis resistance

Cyclooxygenase-2 (COX-2) is inducible by myriad stimuli. The inducible COX-2 in primary cultured human cells has been reported to localize to nuclear envelope, endoplasmic reticulum, nucleus and caveolae. As COX-2 plays an important role in tumor growth, we were interested in its subcellular location in cancer cells. We examined COX-2 localization in several cancer cell lines by confocal microscopy. A majority of COX-2 was colocalized with heat shock protein 60, a mitochondrial protein, in colon cancer (HT-29, HCT-15 and DLD-1), breast cancer (MCF7), hepatocellular cancer (HepG2) and lung cancer cells (A549) with a similar distribution pattern. By contrast, COX-2 was not localized to mitochondria in human foreskin fibroblasts or endothelial cells. Immunoblot analysis of COX-2 in mitochondrial and cytosolic fractions confirmed localization of COX-2 to mitochondria in HT-29 and DLD-1 cells but not in fibroblasts. Calcium-independent phospholipase A2 was colocalized with heat shock protein 60 to mitochondria not only in cancer cells (HT-29 and DLD-1) but also in fibroblasts. HT-29 which expressed more abundant mitochondrial COX-2 than DLD-1 was highly resistant to arachidonic acid and H2O2-induced apoptosis whereas DLD-1 was less resistant and human fibroblasts were highly susceptible. Treatment of HT-29 cells with sulindac or SC-236, a selective COX-2 inhibitor, resulted in loss of resistance to apoptosis. These results suggest that mitochondrial COX-2 in cancer cells confer resistance to apoptosis by reducing the proapoptotic arachidonic acid.

Cross-presentation of a CMV pp65 epitope by human dendritic cells using bee venom PLA2 as a membrane-binding vector

We have used bee venom phospholipase A2 as a vector to load human dendritic cells ex vivo with a major histocompatibility complex (MHC) class I-restricted epitope fused to its C-terminus. The fusion protein bound to human monocyte-derived dendritic cells and was internalized into early endosomes. In vitro immunization experiments showed that these dendritic cells were able to generate specific CD8 T cell lines against the epitope carried by the fusion protein. Cross-presentation did not require proteasome, transporter associated with antigen processing, or endosome proteases, but required newly synthesized MHC molecules. Comparison of the antigen presentation pathway observed in this study to that followed by other toxins used as vectors is discussed.

An ultrastructural and a cytochemical study of candidal invasion of reconstituted human oral epithelium

BACKGROUND

Opportunistic yeast, Candida albicans causes superficial and systemic mycoses in compromised patients. Adhesion to host tissues, morphogenesis and extracellular phospholipases (PL) are thought to contribute to its virulence. The nature of numerous host-parasite interactions at the invasive phase of oral candidiasis is not fully understood. Hence in this study, we explore the ultrastructural features of oral candidiasis using a tissue culture model based on reconstituted human oral epithelium (RHOE).

METHODS

Reconstituted human oral epithelium (Skinethic Laboratory, Nice, France) was inoculated with C. albicans SC5314 and incubated up to 48 h. The infected tissue was harvested at 12, 24 and 48 h and examined using light, scanning (SEM) and transmission electron microscopy (TEM). Localized activity of PLs of C. albicans during tissue invasion was also examined using a cytochemical method.

RESULTS

Over a period of 48 h C. albicans invaded the RHOE, and histological examination revealed characteristic hallmarks of pathological tissue invasion. Hyphal penetration into the superficial epithelium, particularly at cell junctions, together with features of cellular internalization of yeasts was noted. Phospholipase activity was visible at the tips of hyphae and initial sites of bud formation. Further, SEM studies revealed cavitations on the surface epithelial cells particularly pronounced at the sites of hyphal invasion. Hyphal invasion was seen both at cell surfaces and intercellular cell junctions of the epithelium, the latter resembling thigmotropic behaviour.

CONCLUSIONS

Our findings confirm that multiple cellular interactions such as internalization, thigmotropism and extracellular PLs contribute to invasive candidiasis. The RHOE model, described here, appears to be a satisfactory model for the investigation of ultrastructural and histochemical features of invasive candidiasis in humans.

Function of neisserial outer membrane phospholipase a in autolysis and assessment of its vaccine potential

Outer membrane phospholipase A (OMPLA) is an outer membrane-localized enzyme, present in many gram-negative bacterial species. It is implicated in the virulence of several pathogens. Here, we investigated the presence, function, and vaccine potential of OMPLA in the human pathogen Neisseria meningitidis. Immunoblot analysis showed the presence of OMPLA in 28 out of 33 meningococcal strains investigated. The OMPLA-negative strains all contained a pldA gene, but these alleles contained premature stop codons. All six Neisseria gonorrhoeae strains tested, but only two out of seven commensal neisserial strains investigated, expressed OMPLA, showing that OMPLA is expressed by, but not limited to, many pathogenic neisserial strains. The function of OMPLA was investigated by assessing the phenotypes of isogenic strains, expressing no OMPLA, expressing wild-type levels of OMPLA, or overexpressing OMPLA. OMPLA exhibited phospholipase activity against endogenous phospholipids. Furthermore, OMPLA was characterized as an autolysin that acted under specific conditions, such as prolonged growth of the bacteria. The vaccine potential of the protein was investigated by immunizing mice with in vitro refolded, recombinant OMPLA. High levels of antibody titers were obtained, but the murine sera were neither bactericidal nor protective. Also, convalescent patients and vaccinee sera did not contain detectable levels of anti-OMPLA antibodies, indicating that OMPLA may not be sufficiently immunogenic to be included in a meningococcal vaccine.

Expression and localization of adipophilin and perilipin in human fetal membranes: association with lipid bodies and enzymes involved in prostaglandin synthesis

Lipid storage droplets (LSDs) are subcellular storage depots for triglycerides (TGs) and cholesterol esters surrounded by specific populations of proteins that are necessary for their formation. We have previously described the appearance of LSDs in human fetal membranes with advancing gestation and labor. Perilipin and adipophilin are functional/structural proteins located on the surfaces of intracellular LSDs. Adipophilin and perilipin were both immunolocalized to the amnion epithelium and amnion fibroblasts in human fetal membranes. Adipophilin was also localized to the choriodecidual layer, whereas perilipin was localized to the chorion trophoblasts. Although immunohistochemical data show an apparent increase in adipophilin, but not perilipin, expression in fetal membranes with advancing gestation and labor, Western analysis of tissue homogenate supernatant revealed no significant changes in adipophilin and perilipin expression. However, Western analysis of the floating lipid-rich layer from the tissue homogenate revealed an abundance of adipophilin and perilipin as well as other enzymes (cytosolic phospholipase A2, prostaglandin endoperoxide, and microsomal-associated prostaglandin E synthase-1) involved in prostaglandin synthesis. The association of these enzymatically active proteins with LSDs suggests that LSDs may be foci for signaling via the arachidonic acid cascade in fetal membranes. The structural and functional roles of adipophilin and perilipin in gestation and labor remain to be determined.

Distribution of cyclooxygenase-1, cyclooxygenase-2, and cytosolic phospholipase A2 in the luteal phase human endometrium and ovary

OBJECTIVE

To identify the distribution of the enzymes cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), and cytosolic phospholipase A(2) (cPLA(2)) in the human ovary and endometrium.

DESIGN

Prospective clinical study.

SETTING

Hospital-based unit for reproductive health and research laboratories.

PATIENT(S)

Twenty-nine healthy fertile women with normal menstrual cycles.

INTERVENTION(S)

Endometrial and ovarian biopsy samples were obtained from healthy, fertile women in the luteal phase of the menstrual cycle or during caesarean section.

MAIN OUTCOME MEASURE(S)

Pinopode formation and immunohistochemical staining of cPLA(2), COX-1, and COX-2.

RESULT(S)

In the endometrium, the immunostaining of cPLA(2) was most intense in the luminal epithelium when pinopodes were present. The staining of both COX-1 and COX-2 was most intense in the epithelial cells, with the stroma staining positive only for COX-2. The endometrial vessels expressed COX-2 but not COX-1. The staining of COX-1 and COX-2 was intense on the surface epithelial cells on the outer lining of the ovary.

CONCLUSION(S)

This study details the distribution of these prostaglandin synthase enzymes and emphasizes their importance for the functions of both the endometrium and the ovary.

Crystallization of the Lys49 PLA2 homologue, myotoxin II, from the venom of Atropoides nummifer

Myotoxin II, a Lys49 catalytically inactive phospholipase A(2) homologue from Atropoides nummifer venom, was purified, characterized and crystallized. The crystals belongs to the tetragonal system, space group P4(3)2(1)2, with unit cell parameters (a=b=68.66 and c=63.87 angstroms). Diffraction data were collected to a resolution of 2.32 angstroms. The crystal structure is currently being determined using molecular replacement techniques.

Advanced strategies in liposomal cancer therapy: problems and prospects of active and tumor specific drug release

Tumor specific drug delivery has become increasingly interesting in cancer therapy, as the use of chemotherapeutics is often limited due to severe side effects. Conventional drug delivery systems have shown low efficiency and a continuous search for more advanced drug delivery principles is therefore of great importance. In the first part of this review, we present current strategies in the drug delivery field, focusing on site-specific triggered drug release from liposomes in cancerous tissue. Currently marketed drug delivery systems lack the ability to actively release the carried drug and rely on passive diffusion or slow non-specific degradation of the liposomal carrier. To obtain elevated tumor-to-normal tissue drug ratios, it is important to develop drug delivery strategies where the liposomal carriers are actively degraded specifically in the tumor tissue. Many promising strategies have emerged ranging from externally triggered light- and thermosensitive liposomes to receptor targeted, pH- and enzymatically triggered liposomes relying on an endogenous trigger mechanism in the cancerous tissue. However, even though several of these strategies were introduced three decades ago, none of them have yet led to marketed drugs and are still far from achieving this goal. The most advanced and prospective technologies are probably the prodrug strategies where non-toxic drugs are carried and activated specifically in the malignant tissue by overexpressed enzymes. In the second part of this paper, we review our own work, exploiting secretory phospholipase A2 as a site-specific trigger and prodrug activator in cancer therapy. We present novel prodrug lipids together with biophysical investigations of liposome systems, constituted by these new lipids and demonstrate their degradability by secretory phospholipase A2. We furthermore give examples of the biological performance of the enzymatically degradable liposomes as advanced drug delivery systems.

Labour is associated with increased expression of type-IIA secretory phospholipase A2 but not type-IV cytosolic phospholipase A2 in human myometrium

Human labour is associated with increased prostaglandin synthesis within the uterus. The aim of this study was to examine the expression of the type-IV cytosolic phospholipase A2 (cPLA2-IV) and the type IIA secretory phospholipase A2 (sPLA2-IIA) in myometrium in association with labour onset at term and preterm deliveries. These enzymes are important for the release of the prostaglandin precursor, arachidonic acid, from phospholipid membrane stores. RT-PCR was used to determine differences in gene expression between non-labour and labour groups. Expression of sPLA2-IIA in human myometrium was significantly increased with pregnancy, and with labour, both at term and preterm. Expression of cPLA2-IV in myometrium was not significantly altered with respect to pregnancy or labour. Immunohistochemical analysis demonstrated differences in the spatial localization of cPLA2-IV and sPLA2-IIA protein in upper and lower segment myometrium. cPLA2-IV was predominantly in vascular endothelial cells, while sPLA2-IIA was observed in vascular, endothelial and smooth muscle cells. In addition, sPLA2-IIA showed a distinct nuclear or perinuclear localization in myometrial smooth muscle cells of the lower segment. We postulate that the increased expression of sPLA2-IIA rather than cPLA2-IV in the myometrium may play a role in the onset and/or maintenance of human parturition.

Experimental Helicobacter felis infection in transgenic mice expressing human group IIA phospholipase A2

BACKGROUND

Both various virulence factors of Helicobacter pylori and host factors influence the clinical outcome of H. pylori infection. In animal experiments with Helicobacter felis, large variations in the severity of disease have been observed between different mouse strains infected with a single isolate of H. felis. C57BL/6 J mouse strain that lacks the expression of group IIA phospholipase A2 has been shown to develop more severe gastric inflammation than other mouse strains. Thus, group IIA phospholipase A2 has been suggested to play a role in regulating inflammation in gastric mucosa. The aim of this study was to examine the possible role of group IIA phospholipase A2 in experimental Helicobacter infection.

MATERIALS AND METHODS

Transgenic mice expressing human group IIA phospholipase A2 and their group IIA phospholipase A2 deficient nontransgenic C57BL/6 J littermates were infected with H. felis. The mice were killed 3, 8, and 19 weeks after inoculation of bacteria to determine the histopathological changes in gastric mucosa.

RESULTS

The infected mice developed chronic inflammation in gastric mucosa. We found no differences in the colonization of bacteria between transgenic and nontransgenic mice. At 3 and 8 weeks, no difference was found in the severity of inflammation between the two groups. Nineteen weeks after the administration of bacteria the inflammation was more marked in nontransgenic than transgenic mice. Group IIA phospholipase A2 was expressed by in situ hybridization in the neck cells of the glandular stomach in transgenic mice.

CONCLUSIONS

The results of the present study suggest that the endogenous expression of group IIA phospholipase A2 diminishes chronic inflammation in gastric mucosa in experimental H. felis infection in mice.

Assaying phospholipase A2 activity

Mammalian cells contain many structurally and functionally diverse phospholipases A2 (PLA2) that catalyze the hydrolysis of sn-2 fatty acid from membrane phospholipid. Assays are described for measuring the activity of Group IVA cytosolic PLA2alpha(cPLAalpha) and for secreted PLA2s (sPLA2) that are suitable for purified enzymes and for measuring activity in crude cell lysates and culture medium. The assay for cPLA2alpha involves measuring the calcium-dependent release of radiolabeled sn-2 arachidonic acid from small unilamellar vesicles of phosphatidylcholine. Methods are described for distinguishing cPLA2alpha activity in cell lysates from other PLA2s. sPLA2 activity is monitored using a fluorimetric assay that measures the continuous calcium-dependent formation of albumin-bound pyrene fatty acid from the sn-2 position of phosphatidylglycerol.

Secretory Phospholipase A2Deposition on Contact Lenses and Its Effect on Bacterial Adhesion

PURPOSE

Secretory phospholipase A2 (sPLA2) is a potent antibacterial enzyme in tears and has been found to kill Staphylococcus aureus rapidly in vitro. The purpose was to determine whether sPLA2 deposition is associated with contact lens (CL) type, if sPLA2 remains active on CLs, and if this has an effect on bacterial adhesion.

METHODS

Ionic (etafilcon A) and nonionic (Polymacon) high-water, soft CLs were used. CLs were worn for 6 hours (daily wear, n = 39) or 6 nights on an extended-wear schedule (n = 25). Tears were collected from patients and worn contact lenses were removed and protein and active enzymes extracted for estimation of their levels. The number of S. aureus adhering to sPLA2-soaked CLs in vitro was also quantified.

RESULTS

There was no significant difference in the concentration of sPLA2 in tears between groups of daily CL wearers. Significantly less sPLA2 was recovered from Polymacon CLs for both daily and extended wear compared with etafilcon A CLs (daily wear: 3 vs. 5 ng/lens; extended wear: 3 vs. 6 ng/lens; P < 0.05). sPLA2 activity correlated with protein amounts from lenses. Relatively less active sPLA2 was recovered from Polymacon contact lenses. sPLA2 reduced adhesion of Staphylococcus to contact lenses in vitro.

CONCLUSIONS

Etafilcon A CLs absorb more active sPLA2 than Polymacon CLs, which increases with length of CL wear. The sequestering of sPLA2 onto CLs did not affect amounts of the enzyme in tears. sPLA2 adsorbed to a CL can reduce the viable Staphylococcus adhering to the CL, which may protect the eye from colonization by this pathogen.

Is circulating phospholipase A2 removed by large-pore continuous venovenous hemodiafiltration in septic acute renal failure?

Group II A phospholipase A2 (PLA2) produces many inflammatory lipid mediators, and the elevation in the level during sepsis has been correlated positively with the decrease in the arterial blood pressure. We studied the effect of large-pore continuous venovenous hemodiafiltration (LP-CVVHDF) on the plasma PLA2 concentration and the clearance mechanism during septic acute renal failure. The subjects were 10 consecutive patients with septic acute renal failure receiving CVVHDF. Simultaneous samples of arterial, and filter inlet and outlet blood, and ultradiafiltrate were collected before starting CVVHDF (0 hr), and 4 hr, 12 hr and 24 hr after starting CVVHDF. PLA2 activity was measured in plasma and ultradiafiltrate. We eluted PLA2 bound to hemofilter from patient and the classification of PLA2 type of eluting solution and ultradiafiltrate was done using Western blot analysis. Plasma clearance (mL/min) was 28.1+/-7.6 at 4 hr, 23.2+/-8.9 at 12hr and 17.5+/-8.0 at 24 hr. Plasma clearance at 4 hr was higher than that at either 12 hr or 24 hr. Plasma clearance mainly consisted of adsorption by LP-CVVHDF. The changes in arterial plasma PLA2 activity were not statistically significant. One mg/mL of heparin eluted PLA2 bound to the large-pore hemofilter. The PLA2 in eluting solution and in ultradiafiltrate were identified as an approximately 70 kD band in Western blot analysis using anti-human secretory II A-PLA2 monoclonal antibody. The results show that circulating PLA2 can be removed by adsorption with LP-CVVHDF to some extent and that plasma PLA2 activity is not significantly decreased. Because PLA2 clearance with LP-CVVHDF is estimated as <1% of total body PLA2 clearance, LP-CVVHDF could not be a clinically efficient therapy to remove the circulating PLA2.

Effect of crotapotin on the biological activity of Asp49 and Lys49 phospholipases A(2) from Bothrops snake venoms

Myonecrosis, in addition to edema and other biological manifestations, are conspicuous effects of Bothrops snake venoms, some of them caused by phospholipases A(2) (PLA(2)s). Asp49-PLA(2)s are catalytically active, whereas Lys49-PLA(2)s, although highly toxic, have little or no enzymatic activity upon artificial substrates, due to a substitution of lysine for aspartic acid at position 49. Crotapotin (CA), the acidic counterpart of crotoxin PLA(2) (CB), is a PLA(2)-like protein from Crotalus durissus terrificus snake venom, and is considered a chaperone protein for CB, able to increase its lethality about ten fold, but to inhibit the formation of the rat paw edema induced by carrageenin and by snake venoms. In this study, we demonstrate that CA significantly inhibits the edema induced by BthTX-I (23% inhibition), BthTX-II (27%), PrTX-I (25%), PrTX-III (35%) and MjTX-II (10%) on the mouse paw. CK levels evoked by isolated Asp49 or Lys49-PLA(2)s were reduced by 40% to 54% in the presence of CA and, in all cases, the membrane damaging activity of the toxins was also reduced. Circular dichroism spectra of the PLA(2)s in the presence and absence of CA showed that there was not any detectable secondary structural modification due to association between CA and the myotoxins. However, Fourier Transformed Infrared (FT-IR) analysis indicated that ionic and hydrophobic contacts contributed to stabilize this interaction.

Comparing continuous wave progressive saturation EPR and time domain saturation recovery EPR over the entire motional range of nitroxide spin labels

The measurement of spin-lattice relaxation rates from spin labels, such as nitroxides, in the presence and absence of spin relaxants provides information that is useful for determining biomolecular properties such as nucleic acid dynamics and the interaction of proteins with membranes. We compare X-band continuous wave (CW) and pulsed or time domain (TD) EPR methods for obtaining spin-lattice relaxation rates of spin labels across the entire range of rotational motion to which relaxation rates are sensitive. Model nitroxides and spin-labeled biological species are used to illustrate the potential complications that arise in extracting relaxation data under conditions typical to biological experiments. The effect of super hyperfine (SHF) structure is investigated for both CW and TD spectra. First and second harmonic absorption and dispersion CW spectra of the nitroxide spin label, TEMPOL, are all fit simultaneously to a model of SHF structure over a range of microwave amplitudes. The CW spectra are novel because all harmonics and microwave phases were acquired simultaneously using our homebuilt CW/TD spectrometer. The effect of the SHF structure on the pulsed free induction decay (FID) and pulsed saturation recovery spectrum is shown for both protonated and deuterated TEMPOL. We present novel pulsed saturation recovery measurements on biological molecules, including spin-lattice relaxation rates of spin-labeled proteins and spin-labeled double-stranded DNA. The impact of structure and dynamics on relaxation rates are discussed in the context of each of these examples. Collisional relaxation rates with oxygen and transition metal paramagnetic relaxants are extracted using both continuous wave and time domain methods. The extent of the errors inherent in the CW method and the advantages of pulsed methods for unambiguously measuring collisional relaxation rates are discussed. Spin-lattice relaxation rates, determined by both CW and pulsed methods, are used to determine the electrostatic potential on the surface of a protein.

[Bromoacyl analogues of phosphatidylcholine with intramolecular fluorescence quenching and their use as substrates for continuous monitoring of phospholipase A2 activity]

Two new derivatives of phosphatidylcholine with intramolecular fluorescence quenching were obtained by substituting residues of pyrene butyric and bromine-containing fatty acids for acyl chains. The two compounds can be used for quantitative evaluation of catalytic activity of pancreatic phospholipase A2 in kinetic mode.

Characterization of a haemolytic phospholipase A2 activity in clinical isolates of Campylobacter concisus

A membrane-bound, haemolytic phospholipase A(2) (PLA(2)) activity was detected in clinical strains of Campylobacter concisus isolated from children with gastroenteritis. The clinical strains were assigned into two molecular groups (genomospecies) based on PCR amplification of their 23S rDNA. This calcium-dependent, heat-stable, haemolytic PLA(2) activity was detected in strains from both genomospecies. A crude haemolysin extract (CHE) was initially prepared from cellular outer-membrane proteins of these isolates and was further fractionated by ultrafiltration. The haemolytic activity of the extracted fraction (R30) was retained by ultrafiltration using a 30 kDa molecular mass cut-off filter, and was designated haemolysin extract (HE). Both CHE and HE had PLA(2) activity and caused stable vacuolating and cytolytic effects on Chinese hamster ovary cells in tissue culture. Primers for the conserved region of pldA gene (phospholipase A gene) from Campylobacter coli amplified a gene region of 460 bp in all tested isolates, confirming the presence of a homologous PLA gene sequence in C. concisus. The detection of haemolytic PLA(2) activity in C. concisus indicates the presence of a potential virulence factor in this species and supports the hypothesis that C. concisus is a possible opportunistic pathogen.

Recent advances in molecular biology and physiology of the prostaglandin E2-biosynthetic pathway

Prostanoids represent a group of lipid mediators that are produced from arachidonic acid via the cyclooxygenase pathway. Once formed, the prostanoids are released from the cells and act on their cognate receptors on cell surfaces to exert their biological actions. Of these, prostaglandin E(2) (PGE(2)) is the most common prostanoid, being produced by a wide variety of cells and tissues and has a broad range of bioactivity. Recent advance in this field has led to identification and characterization of a number of enzymes that play roles in the biosynthesis of PGE(2), namely phospholipase A(2), cyclooxygenase and terminal PGE synthase. Each of these three reactions can be rate-limiting and involves multiple enzymes/isozymes that can act in different phases of cell activation and exhibit distinct functional coupling. In this review, we will overview a recent understanding of the molecular biology, regulatory mechanisms, and physiological functions of these enzymes.

[Diagnostic effect of bronchoalveolar lavage in early lung injury caused by enterogenic infection in rat]

OBJECTIVE

To study the diagnostic effect of bronchoalveolar lavage in early lung injury by observing changes in inflammatory mediators in early lung injury caused by enterogenic infection.

METHODS

Eighty-four Sprague-Dawley rats were randomly divided into infection group and sham-operation group. Cecal ligation and perforation was utilized to produce abdominal infection in rats. Six groups were sacrificed respectively at 0, 24, 48, 72, 96, 120 hours after operation. The differential cell count in bronchoalveolar lavage fluid (BALF) was assessed. The concentrations of endotoxin, phospholipase A2 (PLA2) and tumor necrosis factor-alpha (TNF-alpha) in BALF, lung and plasma were assayed.

RESULTS

The neutrophil percentage of BALF increased progressively. The concentrations of endotoxin, PLA2 and TNF-alpha in BALF, lung and plasma were significantly increased. The levels of endotoxin and PLA2 in lung tissue were respectively correlated positively with those in BALF and plasma (BALF and lung: r=0.904, P<0.05; BALF and plasma: r=0.895, P<0.05; lung and plasma: r=0.946, P<0.01). Significant positive correlation was also present between the TNF-alpha levels in BALF and lung (r=0.952 P<0.01), but not between the TNF-alpha level in plasma and that in lung or BALF (r=0.684, r=0.608, both P>0.05).

CONCLUSION

The examinations of bronchoalveolar lavage may help discover early lung injury caused by enterogenic infection.

Arachidonic acid release from mammalian cells transfected with human groups IIA and X secreted phospholipase A(2) occurs predominantly during the secretory process and with the involvement of cytosolic phospholipase A(2)-alpha

Stable expression of human groups IIA and X secreted phospholipases A(2) (hGIIA and hGX) in CHO-K1 and HEK293 cells leads to serum- and interleukin-1beta-promoted arachidonate release. Using mutant CHO-K1 cell lines, it is shown that this arachidonate release does not require heparan sulfate proteoglycan- or glycosylphosphatidylinositol-anchored proteins. It is shown that the potent secreted phospholipase A(2) inhibitor Me-Indoxam is cell-impermeable. By use of Me-Indoxam and the cell-impermeable, secreted phospholipase A(2) trapping agent heparin, it is shown that hGIIA liberates free arachidonate prior to secretion from the cell. With hGX-transfected CHO-K1 cells, arachidonate release occurs before and after enzyme secretion, whereas all of the arachidonate release from HEK293 cells occurs prior to enzyme secretion. Immunocytochemical studies by confocal laser and electron microscopies show localization of hGIIA to the cell surface and Golgi compartment. Additional results show that the interleukin-1beta-dependent release of arachidonate is promoted by secreted phospholipase A(2) expression and is completely dependent on cytosolic (group IVA) phospholipase A(2). These results along with additional data resolve the paradox that efficient arachidonic acid release occurs with hGIIA-transfected cells, and yet exogenously added hGIIA is poorly able to liberate arachidonic acid from mammalian cells.

Phospholipase A2 in porifera

Phospholipase A2 (PLA2) catalytic activity was measured in aqueous extracts of 83 freeze-dried specimens representing 55 marine sponge species collected from the east coast of Australia including the Great Barrier Reef. High levels (>500 u/l) of PLA2 activity (defined as the amount of activity that releases 1 micromol of fatty acid per min) were found in four out of 55 species (7%), moderate activities (100-499 u/l) in 6/55 (11%), low activities (1-99 u/l) in 11/55 (20%) and no PLA2 activity in 34/55 (62%). Species with high PLA2 activity levels included Cymbastela coralliophila (2118 u/l, specific activity 10,590 u/g of protein), Acanthella cavernosa (1318 u/l, specific activity 2470 u/g), Spirastrella vagabunda (1036 u/l, specific activity 1727 u/g and Theonella swinhoei (567 u/l, specific activity 354 u/g). It was postulated that poriferan PLA2 may be involved in eicosanoid metabolism and antimicrobial and toxic defence of the animal.

Both A chain and B chain of β-bungarotoxin are functionally involved in the facilitation of spontaneous transmitter release in Xenopus nerve–muscle cultures

In the present study, Xenopus nerve-muscle cultures were used to explore the functional roles of A chain (a phospholipase A(2) subunit) and B chain (a non-phospholipase A(2) subunit) of Bungarus multicinctus beta-bungarotoxin. It was found that beta-bungarotoxin induced an increment of the frequency of spontaneous synaptic currents (SSCs) in the nerve-muscle cultures. Modification of beta-bungarotoxin with pyridoxal-5'-phosphate or substitution of Ca(2+) with Ba(2+) in buffer abolished the phospholipase A(2) activity of beta-bungarotoxin and the facilitatory phase of SSC as well. Antibodies that were directed specifically against A chain or B chain effectively inhibited phospholipase A(2) activity, and as a consequence the SSC frequency was not greatly different from the control rate. These results suggest that both A and B chains are indispensable parts of beta-bungarotoxin for inducing the facilitation of SSC frequency with Xenopus nerve-muscle cultures.

Cytosolic phospholipase A2 type IVA is present in human red cells

Phospholipase A(2) type IVA (IVAPLA(2)) is a cytosolic enzyme that on activation selectively releases arachidonic acid (AA) from cell membrane phospholipids. Both AA and lysophospholipid, products of the enzymic reaction, can function as signal transducers in cellular interactions. The enzyme is present in most cells, including polymorphs, eosinophils, and platelets. This study used affinity purification to extract IVAPLA(2) from red cell lysate prepared from leukocyte- and platelet-depleted human blood to overcome the masking effect of hemoglobin on Western blot detection. We show that IVAPLA(2) is present in red cells as a 90-kDa protein.

Regulation of the water channel aquaporin-1: isolation and reconstitution of the regulatory complex

Aquaporins (AQP) are involved in rapid and active gating of water across biological membranes. The molecular regulation of AQP is unknown. Here we report the isolation, identification and reconstitution of the regulatory complex of AQP-1. AQP-1 and Galphai3 have been implicated in GTP-induced gating of water in zymogen granules (ZG), the secretory vesicles in exocrine pancreas. In the present study, detergent-solubilized ZGs immunoprecipitated with monoclonal AQP-1 antibody, co-isolates AQP-1, PLA2, Galphai3, potassium channel IRK-8, and the chloride channel ClC-2. Exposure of ZGs to either the potassium channel blocker glyburide, or the PLA2 inhibitor ONO-RS-082, blocked GTP-induced ZG swelling. RBC known to possess AQP-1 at the plasma membrane, swell on exposure to the Galphai-agonist mastoparan, and respond similarly to ONO-RS-082 and glyburide, as ZGs. Liposomes reconstituted with the AQP-1 immunoisolated complex from solubilized ZG, also swell in response to GTP. Glyburide or ONO-RS-082 abolished the GTP effect. Immunoisolate-reconstituted planar lipid bilayers demonstrate conductance, which is sensitive to glyburide and an AQP-1 specific antibody. Our results demonstrate a Galphai3-PLA2 mediated pathway and potassium channel involvement in AQP-1 regulation.

Efficient in-gel digestion procedure using 5-cyclohexyl-1-pentyl-beta-D-maltoside as an additive for gel-based membrane proteomics

A cycloalkyl aliphatic saccharide, 5-cyclohexyl-1-pentyl-beta-D-maltoside (CYMAL-5), was evaluated as a novel additive in a high-throughput in-gel protein digestion system using 96-well plates. Addition of 0.1% CYMAL-5 (final concentration) during trypsin treatment was compatible with both matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis, and gave a better digestion efficiency than n-octylglucoside, which we previously reported. In-gel reduction and alkylation of Cys residues under denaturing conditions also improved the sequence coverage of peptides. In-gel tryptic digestion with the optimum combination of 0.5 mm thick gels, negative staining, alkylation under denaturing conditions (6 M guanidine hydrochloride), and digestion in the presence of CYMAL-5, gave excellent performance especially for membrane protein analysis, where recovery of hydrophobic peptides was markedly enhanced. The new protocol is simple and convenient, and should be widely applicable to gel-based proteomics.

A continuous spectrophotometric assay for phospholipase A(2) activity

This paper describes a simple continuous spectrophotometric method for assaying phospholipase A(2) (PLA(2)) activity. The procedure is based on a coupled enzymatic assay, using dilinoleoyl phosphatidylcholine as phospholipase substrate and lipoxygenase as coupling enzyme. The linoleic acid released by phospholipase was oxidized by lipoxygenase and then phospholipase activity was followed spectrophotometrically by measuring the increase in absorbance at 234 nm due to the formation of the corresponding hydroperoxide from the linoleic acid. The optimal assay concentrations of hog pancreatic phospholipase A(2) and lipoxygenase were established. PLA(2) activity varied with pH, reaching its optimal value at pH 8.5. Scans of the deoxycholate concentration pointed to an optimal detergent concentration of 3mM. Phospholipid hydrolysis followed classical Michaelis-Menten kinetics (V(m)=1.8 microM/min, K(m)=4.5 microM, V(m)/K(m)=0.4 min(-1)). This assay also allows PLA(2) inhibitors, such as p-bromophenacyl bromide or dehydroabietylamine acetate, to be studied. This method was proved to be specific since there was no activity in the absence of phospholipase A(2). It also has the advantages of a short analysis time and the use of commercially nonradiolabeled and inexpensive substrates, which are, furthermore, natural substrates of phospholipase A(2).

Effects of Green Tea and High-Fat Diet on Arachidonic Acid Metabolism and Aberrant Crypt Foci Formation in an Azoxymethane-Induced Colon Carcinogenesis Mouse Model

Excessive fat consumption is a risk factor for colon carcinogenesis, and green tea consumption may reduce the risk of colon and other cancers. The current study was designed to investigate the effects of green tea and a high-fat diet on arachidonic acid metabolism and aberrant crypt foci formation in an azoxymethane (AOM)-induced colon carcinogenesis mouse model. We also determined whether green tea consumption altered the size of regional fat pads. CF-1 female mice were maintained on either a high-fat (20% corn oil) or a low-fat (5% corn oil) diet. AOM was given subcutaneous at a dose of 7.5 mg/kg body weight at 6 wk and then a dose of 10 mg/kg at 7 wk of age. Two weeks after the second AOM injection, 0.6% green tea (6 mg tea solids/ml) was given as the drinking fluid and continued for 10 wk until the experiment was terminated. In the AOM-treated mice not receiving green tea, the high-fat diet significantly enhanced colonic levels of 5-lipoxygenase, leukotriene A4 hydrolase, and leukotriene B4, but it did not significantly alter prostaglandin E2 levels and aberrant crypt foci formation. In AOM-treated mice on the high-fat diet, green tea significantly decreased colonic levels of cytosolic phospholipase A2, 5-lipoxygenase, and leukotriene B4; green tea treatment also decreased the number of aberrant crypt foci (P < 0.05). The weights of parametrial and retroperitoneal fat pads were increased by the high-fat diet and decreased by green tea treatment. The current results indicate that green tea consumption and dietary fat modulate 5-lipoxygenase-dependent pathway of arachidonic acid metabolism during AOM-induced colon carcinogenesis. Green tea inhibits ACF formation in mice on a high corn oil diet, suggesting its possible inhibitory effect on colon carcinogenesis in populations such as those in Western countries that consume high amounts of fat.