Release of slow reacting substance from the guinea-pig lung by phospholipases A2 of Vipera russelli snake venom

Secreted Phospholipases A₂ from Animal Venoms in Pain and Analgesia

Animal venoms comprise a complex mixture of components that affect several biological systems. Based on the high selectivity for their molecular targets, these components are also a rich source of potential therapeutic agents. Among the main components of animal venoms are the secreted phospholipases A₂ (sPLA₂s). These PLA₂ belong to distinct PLA₂s groups. For example, snake venom sPLA₂s from Elapidae and Viperidae families, the most important families when considering envenomation, belong, respectively, to the IA and IIA/IIB groups, whereas bee venom PLA₂ belongs to group III of sPLA₂s. It is well known that PLA₂, due to its hydrolytic activity on phospholipids, takes part in many pathophysiological processes, including inflammation and pain. Therefore, secreted PLA₂s obtained from animal venoms have been widely used as tools to (a) modulate inflammation and pain, uncovering molecular targets that are implicated in the control of inflammatory (including painful) and neurodegenerative diseases; (b) shed light on the pathophysiology of inflammation and pain observed in human envenomation by poisonous animals; and, (c) characterize molecular mechanisms involved in inflammatory diseases. The present review summarizes the knowledge on the nociceptive and antinociceptive actions of sPLA₂s from animal venoms, particularly snake venoms.

Hypotensive and vascular relaxant effects of phospholipase A2 toxins from Papuan taipan (Oxyuranus scutellatus) venom

Phospholipase A2 (PLA2) toxins are common and abundant components of Australasian elapid venoms. These toxins are associated with a range of activities including neurotoxicity, myotoxicity and coagulation disturbances. We have recently reported that sudden cardiovascular collapse induced by Papuan taipan (Oxyuranus scutellatus) venom involves a combination of the release of dilator autacoids and a direct effect on the smooth muscle. In this study, we aimed to isolate PLA2 components from Papuan taipan venom and investigate their contribution to the hypotensive action of this venom. O. scutellatus venom was fractionated using size-exclusion high performance liquid chromatography (HPLC), and fractions screened for activity in anaesthetized rats. Fraction three from O. scutellatus venom (i.e. OSC3, 14.2±1.0% of whole venom) produced a 64% decrease in mean arterial pressure. Reverse-phase HPLC indicated that OSC3 consisted of two major components (i.e. OSC3a and OSC3b). OSC3a and OSC3b produced a significant hypotensive response in anaesthetized rats which were attenuated by prior administration of indomethacin or the combination of mepyramine and heparin. N-terminal analysis indicated that OSC3a and b displayed sequence homology to PLA2 toxins isolated from coastal taipan (O. scutellatus scutellatus) venom. These findings indicate that PLA2 components may play an important role in the development of hypotension and vascular relaxation which may contribute to the effects observed after envenoming by these Australasian elapids.

The effects of a chactoid scorpion venom and its purified toxins on rat blood pressure and mast cells histamine release

The effect of the venom of the Chactoid family of scorpions on blood pressure was scantly investigated and was addressed in the present study using the venom of the Israeli scorpion, Scorpio maurus palmatus. Blood pressure in rats was monitored via cannulated femoral artery, while venom and toxins were introduced into femoral vein. Venom injection elicited a biphasic effect, expressed first by a fast and transient hypotensive response, which lasted up to 10 min, followed by a hypertensive response, which lasted up to one hour. It was found that these effects resulted from different venom components. Phospholipase A₂ produced the hypotensive effect, while a non-enzymatic neurotoxic polypeptide fraction produced the hypertensive effect. Surprisingly, the main neurotoxic polypeptide to mice had no effect on blood pressure. In vitro experiments indicated that the hypertensive factors caused histamine release from the peritoneal mast cells, but this effect is assumed to be not relevant to their in vivo effect. In spite of the cytotoxic activity of phospholipase A₂, it did not release histamine. These findings suggest that the effects of venom and isolated fractions on blood pressure parameters are mediated by different mechanisms, which deserve further pharmacological investigation.

Crystallization and preliminary X-ray diffraction studies of BmooPLA2-I, a platelet-aggregation inhibitor and hypotensive phospholipase A2 from Bothrops moojeni venom

Phospholipases A(2) (PLA(2)s) are enzymes that cause the liberation of fatty acids and lysophospholipids by the hydrolysis of membrane phospholipids. In addition to their catalytic action, a wide variety of pharmacological activities have been described for snake-venom PLA(2)s. BmooPLA(2)-I is an acidic, nontoxic and catalytic PLA(2) isolated from Bothrops moojeni snake venom which exhibits an inhibitory effect on platelet aggregation, an immediate decrease in blood pressure, inducing oedema at a low concentration, and an effective bactericidal effect. BmooPLA(2)-I has been crystallized and X-ray diffraction data have been collected to 1.6 Å resolution using a synchrotron-radiation source. The crystals belonged to space group C222(1), with unit-cell parameters a = 39.7, b = 53.2, c = 89.2 Å. The molecular-replacement solution of BmooPLA(2)-I indicated a monomeric conformation, which is in agreement with nondenaturing electrophoresis and dynamic light-scattering experiments. A comparative study of this enzyme with the acidic PLA(2) from B. jararacussu (BthA-I) and other toxic and nontoxic PLA(2)s may provide important insights into the functional aspects of this class of proteins.

BE-I-PLA2, a novel acidic phospholipase A2 from Bothrops erythromelas venom: isolation, cloning and characterization as potent anti-platelet and inductor of prostaglandin I2 release by endothelial cells

A novel acidic Asp49 phospholipase A(2) was isolated from Bothrops erythromelas (jararaca malha-de-cascavel) snake venom by four chromatographic steps. BE-I-PLA2 present a molecular weight of 13,649.57 Da as estimated by mass spectrometry. N-terminal and four internal peptides were sequenced, covering around one-third of the complete toxin sequence. The complete BE-I-PLA2 cDNA was cloned from a B. erythromelas venom-gland cDNA library. The cDNA sequence possesses 457 bp and encodes a protein with significant sequence similarity to many other phospholipase A(2) from snake venoms. When tested in platelet rich plasma, the enzyme showed a potent inhibitory effect on aggregation induced by arachidonic acid and collagen, but not ADP. On the other hand, BE-I-PLA2 did not modify aggregation in washed platelet. Furthermore, no action of BE-I-PLA2 on the principal platelets receptors was observed. Chemical modification with p-bromophenacyl bromide abolished the enzymatic activity of BE-I-PLA2, but its anti-platelet activity was only partially inhibited. In human umbilical-cord veins endothelial cells, BE-I-PLA2 was neither apoptotic nor proliferative but stimulated endothelial cells to release prostaglandin I(2), suggesting an increase of its potential anti-platelet activity in vivo. Further studies are required in order to determine the exact mechanism of action of BE-I-PLA2 in the inhibition of platelet aggregation.

Haemodynamics in leptospirosis: Effects of plasmapheresis and continuous venovenous haemofiltration

BACKGROUND

Haemodynamics in leptospirosis may differ from that of sepsis because of frequently obeserved myocarditis and severe cholestatic jaundice. A haemodynamic study was therefore made in 10 patients with severe leptospirosis.

METHODS AND RESULTS

All patients had pulmonary complications with a chest X-ray showing either pulmonary oedema or infiltration. Renal failure was present in nine patients. Three patterns of haemodynamics were revealed. The first pattern was observed in six patients who showed increased cardiac index, decreased systemic vascular resistance, normal pulmonary capillary wedge pressure, normal pulmonary vascular resistance and hypotension. The pattern resembled that of sepsis. The second pattern shown in two patients with haemoptysis consisted of a normal cardiac index, normal systemic vascular resistance, normal blood pressure, normal pulmonary capillary wedge pressure and increased pulmonary vascular resistance. The third pattern was observed in two patients with severe jaundice who had hypotension, a relatively low cardiac index, increased systemic vascular resistance and normal pulmonary capillary wedge pressure, and pulmonary vascular resistance. Plasmapheresis performed in two patients and continuous venovenous haemofiltration performed in two patients improved systemic haemodynamics and normalized blood pressure with a resolution of lung signs.

Characterization, amino acid sequence and evolution of edema-inducing, basic phospholipase A2 from Trimeresurus flavoviridis venom

Two phospholipases A2 (PLA2s) were purified from the venom of Trimeresurus flavoviridis (Crotalinae) inhabiting Tokunoshima island, Japan, and named PLA-A and PLA-B in the order of elution on a cation-exchange column. Lipolytic activities of PLA-A and PLA-B toward mixed micelles and liposomes were substantially lower than that of PLA2 (an [Asp49]PLA2) which had been isolated from the same venom. Both PLA-A and PLA-B consisted of 122 amino acids and contained aspartate at position 49 (the numbering according to the aligned sequences of PLA2s in Fig. 8), thus belonging to an [Asp49]PLA2 subgroup. PLA-A and PLA-B were identical in sequence with an exception at position 79. PLA-B contained Asn-Gly at positions 79 and 80 which are located in the beta-sheet region. On the other hand, PLA-A had beta-Asp-Gly and alpha-Asp-Gly in high and low proportion, respectively, at the corresponding positions which were produced from Asn-Gly through the base-catalyzed formation and hydrolysis of the succinimide type intermediate. Thus, PLA-A is derived from PLA-B. PLA-B is similar in sequence to PL-X, which had been purified from the venom of T. flavoviridis inhabiting Amami-Oshima island, Japan, and to PL-X', whose cDNA had been cloned from Tokunoshima T. flavoviridis venom gland, rather than PLA2. PLA-B showed strong edema-inducing activity, while PLA-A exhibited rather lower activity. The sequence around position 79 which constitutes a beta-turn segment seems to be crucial for edema-inducing activity. Phylogenetic tree of Tokunoshima T. flavoviridis venom PLA2 isozymes indicated that PLA-B and PL-X' diverged from PLA2 after branching of [Asp49]PLA2 forms and [Lys49]PLA2 forms.

Purification and properties of three new phospholipase A2 isoenzymes from Micropechis ikaheka venom

Three new phospholipase A2 (PLA2) isoenzymes were purified from the Micropechis ikaheka venom by successive chromatographies. The homogeneity of them was accessed by capillary zone electrophoresis and mass spectrometry. Their N-terminal sequences showed high identity (94, 88 and 90, respectively) with MiPLA-1, a group IB PLA2 also from this venom. In addition, strong immuno-cross-reaction with anti-MiPLA-1 serum was observed. These results suggested that three newly purified PLA2 belonged to group IB. Beside enzymatic activity, they induced various pharmacological effects, including myotoxic, anticoagulant effects and insulin secretion stimulating effects. Our results indicated that enzymatic activity is essential for their myotoxic and anticoagulant effects. On the other hand, no direct correlation between their insulin secretion stimulating effect and enzymatic activity was observed, suggesting that they may stimulate insulin secretion through a non-enzymatic mechanism.

Sea snake Hydrophis cyanocinctus venom. I. Purification, characterization and N-terminal sequence of two phospholipases A2

Two phospholipases A2 (PLA2, H1 and H2) from sea snake Hydrophis cyanocinctus venom were purified to homogeneity in a single step using reversed-phase high performance liquid chromatography on a Nucleosil 7C18 column. The molecular weights of H1 and H2, as estimated by MALDI MS, were 13588.1 and 13247.2 Da, respectively. The N-terminal 60 amino acid residues were determined by direct automated Edman degradation analysis. Since both PLA2s show close sequence homologies to those of PLA2s from other Elapid snakes (60-84%) they have been tentatively classified as belonging to group-IA and Asp-49 phospholipases A2. Despite the sequence variation (18%) between H1 and H2, their general structural organization is very similar as shown by their clearly related CD spectra. Furthermore, both enzymes are quite thermostable (60-65 degrees C) as determined by temperature variable CD spectra, indicating that the enzymes contain compact folded structure, mainly based on the core structure of disulfide bridges. However, the major PLA2 (H1) shows higher toxicity to albino rats (LD50 i.p. 0.04 mg/kg) and purification resulted in 18-fold increase in toxicity over the crude or whole venom (LD50 i.p. 0.80 mg/kg). H1 also shows edema-inducing and indirect haemolytic but no haemorrhagic activity. Unlike the toxic PLA2-H1, enzyme H2 was not toxic to albino rats but showed edema-inducing and indirect haemolytic activities.

Purification, properties, and amino acid sequence of a hemoglobinuria-inducing phospholipase A(2), MiPLA-1, from Micropechis ikaheka venom

Dark-colored urine is one of the clinical symptoms of envenomation by Micropechis ikaheka (New Guinea small-eyed snake). We have purified a phospholipase A(2), MiPLA-1, which induces dark-colored urine in experimental mice, to homogeneity. The analysis of the dark-colored urine by electrophoresis and N-terminal sequence determination indicated that the color of mouse urine is due to hemoglobin in the urine but not myoglobin. MiPLA-1 is the first hemoglobinuria-inducing toxin. Insignificant hemolytic activity of MiPLA-1 indicates that hemoglobinuria is not due to lysis of erythrocytes by MiPLA-1. This suggests that hemoglobinuria induced by MiPLA-1 may be due to kidney leakage caused by unknown mechanisms. MiPLA-1 also showed other biological effects, including myotoxicity as well as anticoagulant and antiplatelet effects. Structural studies show that MiPLA-1 is a basic protein with a molecular mass of 14041.60 +/- 1.78 as determined by electrospray mass spectrometry. We have determined the complete amino acid sequence of MiPLA-1. It is a 124-amino-acid protein with a "pancreatic loop" and belongs to group IB phospholipase A(2) enzymes. Two short segments flanked by proline brackets are found in the sequence of MiPLA-1. These segments are on the surface of the molecule and hence may be involved in protein-protein recognition.

Histopathological studies of the acute inflammation in synovial tissue of rat knee joint following intra-articular injection of PLA2 from Chinese Cobra (Naja naja atra) venom

A phospholipase A2 was purified from Chinese Cobra Naja naja atra by a two-step procedure: gel filtration on Superdex 75 and reverse-phase high-performance liquid chromatography (HPLC) on a NUCLEOSIL 5 C18 column. Purified phospholipase A2 was homogeneous, as indicated by capillary electrophoresis and electrospray mass spectrometry. It was a basic protein (pI = 8.2 +/- 0.03) with a molecular mass of 13,258 Da. Amino acid sequence analysis of the N-terminal demonstrated a high degree of homology with other related PLA2 from elapid venoms. The histopathological effects of the purified PLA2 on synovial tissue of knee joint were studied in Wistar rats. Rats were injected intra-articularly with 100 microl solution of PLA2 of different concentrations. Synovial tissue samples with patella were taken for light microscope study. Histopathological evaluation revealed a significant induction of acute inflammation in synovial tissue after injection, as indicated by synovial lining-cell hyperplasia, subsynovial cellular infiltration, and peri-articular soft-tissue cellular infiltration. Marked inflammatory and proliferative changes in synovial tissue were evident after repeated intra-articular injections of 100 microg PLA2. This study failed to show any significant histological changes in cartilage of patella as well as in the surrounding muscle tissue of the knee joints. These results suggest that PLA2 purified from Chinese Cobra venom induce time- and dose-dependent inflammatory changes in the synovial tissue of rat knee joint.

At the interface: crystal structures of phospholipases A2

The protein content of many snake venoms often includes one or more phospholipases A2 (PLA2). In recent years a growing number of venoms from snakes of Agkistrodon, Bothrops and Trimeresurus species have been shown to contain a catalytically inactive PLA2-homologue in which the highly conserved aspartic acid at position 49 (Asp49) is substituted by lysine (Lys49). Although demonstrating little or no catalytic activity, these Lys49-PLA2s disrupt membranes by a Ca2+-independent mechanism of action. In addition, this family of PLA2s demonstrates myotoxic and cytolytic pharmacological activities, however the structural bases underlying these functional properties are poorly understood. Through the application of X-ray crystallography in combination with biophysical and bioinformatics techniques, we are studying structure/function relationships of Lys49-PLA2s. We here present results of a systematic X-ray crystallographic and amino acid sequence analysis study of Lys49 PLA2s and propose a model to explain the Ca2+-independent membrane damaging activity.

Purification and characterization of three acidic, cytotoxic phospholipases A2 from Indian cobra (Naja naja naja) venom

Three acidic phospholipases A2 (NN-I2c-PLA2, NN-I2d-PLA2 and NN-I2c-PLA2) were purified by successive chromatography of Indian cobra (Naja naja naja) venom on CM-Sephadex C-25, Sephadex G-50 and QAE Sephadex A-25 columns. They have molecular weights of 13,000-14,500 by sodium dodecyl sulphate polyacrylamide gel electrophoresis. They showed tryptophan specific fluorescence emission spectra (approximately 345 nm). All the three phospholipases A2 were enzymatically highly active with specific activities 9-17 micromol min(-1) mg(-1). They were non-lethal to mice when injected intraperitoneally in doses up to 10 mg kg(-1) body weight. They induced edema in mouse foot pads and were cytotoxic to Ehrlich ascites tumour cells. They did not exhibit direct haemolytic and anticoagulant activities.

Crystallization of piratoxin I, a myotoxic Lys49-phospholipase A2 homologue isolated from the venom of Bothrops pirajai

Large single crystals of piratoxin I. a Lys49-PLA2 homologue with low enzymatic activity, have been obtained. The crystals belong to the orthorhombic system space group P2(1)2(1)2(1), and diffract X-rays to a resolution of 2.8 A. Preliminary analysis reveals the presence of two molecules in the crystallographic asymmetric unit.

Discriminatory recognition of membrane phospholipids by lysine-49-phospholipases A2 from Trimeresurus flavoviridis venom

Basic proteins I and II (BP-I and BP-II) isolated from Trimeresurus flavoviridis venom, which are classified into a group of lysine-49-phospholipases A2 (Lys-49-PLA2), exhibited only limited lipolytic activity for the mixed micelles of various phospholipids. Based on the finding that BP-II elicits a strong contraction of guinea pig ileum due to the release of arachidonic acid, BP-II together with BP-I has been tested for their interaction with artificial phospholipid bilayer membranes. The dye leakage experiments indicated that BP-II interacts strongly with liposomes of beta-arachidonoyl-gamma-stearoyl-L-alpha-phosphatidylcholine. The perturbation of liposomes was observed only in the Ca(2+)-containing buffer, and as demonstrated by HPLC analyses, accompanied by the release of arachidonic acid. The concentration of Ca2+ which gave a half maximal activity of BP-II was 3.0 x 10(-4) M, suggesting that the affinity of BP-II for Ca2+ is more than 10 times stronger than that of BP-II without liposomes. These observations clearly show that Lys-49-PLA2 of BP-II is the enzyme responsible for the hydrolysis of membrane phospholipids and that Ca2+ is essential for such enzymatic activity. The interaction of BP-I with liposomes was much weaker than BP-II BP-I and BP-II share a common sequence except for Asp-67 (BP-I) and Asn-67 (BP-II) in the aligned sequences. This implies that the amino acid at position 67 of Lys-49-PLA2s is the residue required for discriminatory recognition of phospholipid membranes.

Phospholipase A2--a structural review

Phospholipases A2 (PLA2) are widely distributed in nature and are well characterized proteins with respect to their catalytic and pharmacological activities. A wealth of structural information has recently become available both from X-ray diffraction and NMR studies, and although a detailed model of the catalytic mechanism of PLA2 has been proposed, the structural bases of other aspects of PLA2 function, such as interfacial activation and venom PLA2 pharmacological activities, are still under debate. An appreciation of the PLA2 protein structure will yield new insights with regard to these activities. The salient structural features of the class I, II and III PLA2 are discussed with respect to their functional roles.

Properties of receptors for neurotoxic phospholipases A2 in different tissues

A radioiodinated derivative of OS2 (125I-OS2), a neurotoxic monochain phospholipase A2 isolated from taipan venom, was previously found to bind to a specific brain membrane receptor with very high affinity. 125I-OS2 is now used to identify the properties of neurotoxic phospholipase receptors in other tissues. Heart, skeletal muscle, kidney, lung, liver, pancreas, and smooth muscle membranes also contain high-affinity binding sites for toxic phospholipases A2. In most tissues, two different types of receptor sites have been characterized for 125I-OS2 with Kd1 and Kd2 values in the 1-5 pM and the 10-50 pM range respectively. Whereas all receptors are similar in the different tissues in terms of their affinity for 125I-OS2, maximal binding site capacities were very different, varying from 1.3 pmol/mg of protein in brain to 0.01 pmol/mg of protein in pancreas. In brain, heart, and skeletal muscle, receptor densities vary with in vivo development. Affinity labeling experiments have identified the subunit composition of OS2 receptors and indicated that these receptors do not have identical structures in the different tissues. Binding competition studies with OS2 and other toxic phospholipases showed tissue-dependent pharmacological profiles. All these results taken together suggest the existence of a family of receptors for neurotoxic phospholipases.

Phospholipase A2 activation is the pivotal step in the effector pathway of inflammation

Our understanding of the mechanisms of initiation and propagation of local and systemic inflammatory processes is clearly imperfect if one uses the available therapeutic modalities as a yardstick. While glucocorticoids are potent anti-inflammatory drugs, the pharmacologic target of this class of agents has not been identified with certainty, and the use of steroids is fraught with the risk of considerable and potentially dangerous side effects. On the other hand, non-steroidal anti-inflammatory drugs (NSAIDS), while more specific, are relatively weak anti-inflammatory compounds and frequently require the addition of more potent agents. Cytotoxic drugs or anti-metabolites effectively suppress acute and chronic inflammatory reactions, but also predispose to infection and initiate the development of neoplasms following long-term exposure. The inadequacy and relative non-specificity of these approaches underscore the deficiencies in our understanding of the principles that govern these responses. A better understanding of these processes will be applicable to broad categories of human disease including autoimmunity, the collagen vascular diseases, aberrations in host defense and the response to trauma and infection.

Purification and characterization of a myotoxic phospholipase A2 from Indian cobra (Naja naja naja) venom

A major phospholipase A2 (NN-XIII-PLA2) which constitutes 20% of the whole Naja naja naja venom was purified to homogeneity on CM-Sephadex C-25 column chromatography. NN-XIII-PLA2 is a basic protein with a mol. wt of 11,200 by SDS-PAGE. This enzyme has low enzymatic activity but is more toxic to mice than the whole venom. The LD50 value (i.p.) of NN-XIII-PLA2 is 2.4 mg/kg body weight (whole venoms LD50 is 2.8 mg/kg body weight). It induces neurotoxic-like signs in experimental animals. It induces myotoxicity when injected i.m. into the thigh muscle of mice and edema when injected into the foot pads of mice. This enzyme has a fluorescence maxima between 310-316 nm which is typical of tyrosine residues.

Edema formation and degranulation of mast cells by a basic phospholipase A2 purified from Trimeresurus mucrosquamatus snake venom

The basic phospholipase A2 (PLA2) purified from Trimeresurus mucrosquamatus snake venom was injected into the subplantar in order to induce edema formation in the rat hind paw. The maximum edema induced by PLA2 was induced at 1-2 hr after injection, and the per cent swelling curve showed a dose-dependent increase by PLA2 injection (2.5-10.0 micrograms). The rate of edema formation is different from the acute swelling induced by T. mucrosquamatus venom (TMV). Pretreatment with dexamethasone (4 mg/kg, s.c.), indomethacin (10 mg/kg, per 05) and diphenhydramine (100 mg/kg s.c.) inhibited the edema induced by the purified phospholipase A2. The injection of purified PLA2 or venom into rabbit skin resulted in an increase in vascular permeability which could be decreased by pretreatment with three antiinflammatory drugs. However, the pharmacological effect of dexamethasone (4 mg/kg) demonstrated a more effective inhibition than the other drugs in the PLA2-induced edema and vascular permeability change. Injection (i.p.) of PLA2 caused marked degranulation of mast cells in the rat mesentery which was facilitated by addition of calcium ion (10 mM) but antagonized by pretreating with three antiinflammatory agents. After incubating peritoneal mast cells with PLA2 (1.0 micrograms/ml), the release of histamine from the mast cell was approximately 36%, this effect was inhibited by preincubating the mast cell with three antiinflammatory agents.

Edema-inducing activity of phospholipase A2 purified from human synovial fluid and inhibition by aristolochic acid

A neutral-active, Ca2+-dependent phospholipase A2 (PLA2) purified 11,000-fold from human synovial fluid (HSF) induced edema when injected into the mouse foot pad. The edema produced by HSF-PLA2 was dose-dependent and was positively correlated with the dose-dependent in vitro expression of PLA2 activity. Maximum edema was achieved within 45 min after the injection and persisted for at least 6 h. Aristolochic acid [8-methoxy-6-nitrophenanthro(3,4-d)-1,3-dioxole-5-carboxylic acid], a major chemical component derived from various species of Aristolochia plant, produced a dose-dependent inhibition of in vitro phospholipid hydrolysis by HSF-PLA2, porcine pancreatic PLA2, snake venom (Naja naja) PLA2, and PLA2 isolated from human platelet. The sensitivity of these PLA2s to inhibition by aristolochic acid varied markedly: HSF-PLA2 greater than N. naja PLA2 greater than human platelet PLA2 greater than porcine pancreatic PLA2. The inhibition of HSF-PLA2 by aristolochic acid was independent of substrate concentration (18-144 microM) and Ca2+ concentration (0.1-4.0 mM). These observations indicate that inhibition of HSF-PLA2 by aristolochic acid may result from direct interaction with the enzyme. When aristolochic acid was mixed with HSF-PLA2 and then injected into the mouse foot pad, edema was inhibited in a dose-dependent manner and was positively correlated with in vitro inhibition of PLA2 activity. Alkylation of HSF-PLA2 with p-bromophenacyl bromide concomitantly inhibited both enzyme and edema-inducing activity. These results clearly demonstrate that the neutral-active, Ca2+-dependent PLA2 isolated from human synovial fluid is proinflammatory and that catalytic activity is positively correlated with in vivo proinflammatory effects.

Phospholipase A2 stimulated release of lipoxin B4 formation from endogenous sources of arachidonic acid in porcine leukocytes

Incubation of an isoenzyme of phospholipase A2 (PLA2, isolated from snake venom) with porcine leukocytes resulted in the formation of several trihydroxytetraene- containing compounds which were derived from endogenous sources of arachidonic acid. The formation of these endogenous compounds was dose-dependent with an EC50 of approximately 1.25 x 10(-8) M. At this concentration of the isoenzyme and time (10 min) of explosure the cells remained viable as determined by the exclusion of trypan blue. The trihydroxytetraene compounds were purified by RP-HPLC and their identities were analyzed by U.V. spectrometry, GC/MS and by comparison with synthetic materials. The biologically derived compounds proved to be lipoxin B4 (5S, 14R, 15S-trihydroxy-6,10,12-trans-8-cis-eicosatetraenoic acid) and its two structural isomers (8-trans-LXB4 and 14S-8-trans-LXB4). Results of the present study indicate that porcine leukocytes can generate lipoxin B4 and its isomers from endogenous sources of arachidonic acid. Moreover, they suggest that certain PLA2 isoenzymes may stimulate the formation of lipoxins and related compounds.

Purification and partial biochemical characterization of an edema inducing phospholipase A2 from Vipera russelli (Russell's viper) snake venom

A phospholipase A2 (VRV PL-VI) from Vipera russelli venom was purified to homogeneity in a single step on CM-Sephadex C-25 column. VRV PL-VI is a basic protein with a mol. wt of about 12,000 and showed a basic pH optimum and a high temperature maximum. It hydrolysed purified phospholipids in the order of phosphatidylethanolamine greater than phosphatidylcholine much greater than phosphatidylserine greater than phosphatidylinositol = 0. It is toxic with an LD50 value (i.p.) of 3.5 micrograms/g body weight in mice and it induced persistent edema in the mouse foot pad.

A phospholipase A2 isoenzyme provokes lipoxin B formation from endogenous sources of arachidonic acid in porcine leukocytes

Porcine leukocytes incubated with an isoenzyme of phospholipase A2 (PLA2) (isolated from snake venom) produced several trihydroxytetraene- containing compounds which were derived from endogenous sources of arachidonic acid. The formation of these compounds was dose-dependent with an EC50 of approximately 1.25 X 10(-8) M. At this concentration of the isoenzyme and time of exposure the cells remained viable as determined by the exclusion of trypan blue. The compounds were purified by HPLC and their identities were determined by physical criteria which included U.V. spectrometry, GC/MS and by comparison with both synthetic and authentic materials. The biologically derived compounds proved to be lipoxin B (5S, 14R, 15S-trihydroxy-6, 10, 12-trans-8-cis-eicosatetraenoic acid) and its two structural isomers (8-trans-LXB and 14S-8-trans-LXB). Of interest, only small amounts of lipoxin A and its isomers were found in these incubations. Results of the present study indicate that porcine leukocytes can generate lipoxin B and its isomers from endogenous sources of arachidonic acid. Moreover, they suggest that certain PLA2 isoenzymes may initiate the formation of lipoxins and related compounds.

Characterization of three edema-inducing phospholipase A2 enzymes from habu (Trimeresurus flavoviridis) venom and their interaction with the alkaloid aristolochic acid

A basic phospholipase A2 (PLA2) enzyme, TFV PL-X (pI 9.2) and two acidic PLA2 enzymes, TFV PL-Ia (pI 4.9) and TFV PL-Ib (pI 4.5) were purified from Trimeresurus flavoviridis venom on CM-Sephadex C-25 and QAE-Sephadex A-25 columns, respectively. The basic enzyme exists as a monomer, whereas the acidic enzymes are dimers. These enzymes differ in properties such as molecular weight, Km, optimum pH and temperature and pharmacological properties. The basic enzyme hydrolysed purified phospholipids in the order of PC greater than PE greater than PS greater than PI = 0, while for TFV PL-Ia and TFV PL-Ib the order was PC greater than PE greater than PS = PI = 0. TFV PL-X was comparatively more toxic, with an LD50 value of 4.2 micrograms/g (i.p.), while the acidic PLA2 enzymes had LD50 values above 8 micrograms/g (i.p.). All three enzymes induced edema when injected into the mouse foot pad. Aristolochic acid, an alkaloid (8-methoxy-6-nitrophenanthro(3,4-d)-1,3-dioxole-5-carboxylic acid) from the medicinal plant Aristolochia radix, interacts with these PLA2 enzymes. It is a competitive inhibitor with varying affinity when PC is used as substrate. Aristolochic acid inhibits direct and indirect hemolytic activity, as well as edema-inducing activity, of TFV PL-X, but fails to neutralize the lethal potency of the enzyme. On the other hand, it inhibits direct and indirect lytic activity of TFV PL-Ia and TFV PL-Ib only at 10-fold higher concentrations and it enhances the edema-inducing activity of these enzymes. Such effects of aristolochic acid indicates that (1) different mechanisms may be involved in the edema-inducing activity of PLA2 enzymes and (2) catalytic and pharmacological sites are separate on the PLA2 molecule.

Structure-function relationships of phospholipases. I: Prediction of presynaptic neurotoxicity

The hydropathic indexes of 24 phospholipases have been calculated from their amino acid sequences. The presynaptic neurotoxic potential of venom phospholipases can be predicted by the use of hydropathy profiles. The presynaptically acting phospholipases have a distinct hydrophobic region around the residues 80-110 which is probably involved in the interaction with the presynaptic membranes. This region is present as a separate helix in the tertiary structure of phospholipases. Such a hydrophobic region is absent in non-neurotoxic phospholipases.

Relaxant effect of phospholipase A2 from Vipera russelli snake venom on rat aorta

The effect of the acidic phospholipase A2 (PLA2) from Vipera russelli venom on the rat aortic ring was studied and compared with that of acetylcholine (ACh). PLA2 induced relaxation of the aortic ring precontracted with noradrenaline (NA) in a dose-dependent manner. Removal of the endothelium did not reduce the relaxant effect of PLA2. Replacement of Ca2+ by Sr2+ in the medium to inhibit the PLA2 enzyme activity reduced the relaxant effect. Atropine, a muscarinic receptor antagonist, did not affect the relaxant response. The cyclooxygenase inhibitor indomethacin, when equilibrated for 50 min, potentiated the relaxation. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) partially reduced the relaxation. This relaxation was also partially reduced by the guanylate cyclase inhibitor methylene blue. In contrast, the relaxation elicited by ACh was abolished by de-endothelialization, atropine, NDGA or methylene blue. 6-keto-PGF1 alpha (degradation product of prostacyclin) and PGE2 produced by aortic rings were measured by radioimmunoassay. PLA2 (3 X 10(-6) g/ml) increased the output of 6-keto-PGF1 alpha about 10-fold. The production of PGE2 was also increased but to a lesser extent. ACh also increased the output of 6-keto-PGF1 alpha and PGE2. However, prostacyclin released by PLA2 and ACh appears not to contribute to the relaxant effect, since prostacyclin does not relax the rat aorta. It is concluded that the relaxation elicited by PLA2 in the rat aorta is endothelium-independent and partially mediated by lipoxygenase product(s) and cyclic GMP whereas the relaxation induced by ACh was endothelium-dependent, mediated by lipoxygenase product(s) and cyclic GMP, and blocked by atropine.

Effects of phospholipases A2 from Vipera russelli snake venom on blood pressure, plasma prostacyclin level and renin activity in rats

Vipera russelli venom contains several isoenzymes of phospholipase A2 (PLA2) which were isolated by column chromatography. The effects of PLA2 fractions on blood pressure, plasma prostacyclin level and renin activity were studied in normotensive and renal hypertensive rats. PLA2 fractions II-5, II-7, III-3 and III-6 (0.1 mg/kg) injected i.v. into rats decreased the arterial blood pressure. The hypotensive action of PLA2 fractions was not affected by heat treatment (70-80 degrees C, 30 min, pH 6.8). After indomethacin (30 mg/kg, i.v.), the hypotensive response to PLA2 was markedly reduced. Plasma prostacyclin (PGI2) and thromboxane A2 (TXA2) levels were measured by radioimmunoassays of their degradation products, 6-keto-PGF1 alpha and TXB2, respectively. PLA2 fractions (0.1 mg/kg) induced an increase in plasma PGI2 and TXA2 levels. There was a positive linear correlation between the PLA2-induced hypotensive effect and the ratio of increased 6-keto-PGF1 alpha to TXB2 (r = 0.83) in normotensive rats. In renal hypertensive rats, the increase in PGI2 level was larger than in normotensive rats. Plasma renin activity was also measured by the radioimmunoassay. Plasma renin activity was reduced by PLA2 fractions in renal hypertensive rats, but not in normotensive rats. These results suggest that the hypotensive effect of PLA2 fractions in normotensive rats may be partly due to the increase in plasma prostacyclin and thromboxane A2 levels. In addition to the larger increase in plasma PGI2 level, the reduction in plasma renin activity may also contribute to the greater hypotensive effect of PLA2 fractions in renal hypertensive rats.