Platelet aggregation and sphingomyelinase D activity of a purified toxin from the venom of Loxosceles reclusa

Exogenous phospholipase D generates lysophosphatidic acid and activates Ras, Rho and Ca2+ signaling pathways

BACKGROUND

Phospholipase D (PLD) hydrolyzes phospholipids to generate phosphatidic acid (PA) and a free headgroup. PLDs occur as both intracellular and secreted forms; the latter can act as potent virulence factors. Exogenous PLD has growth-factor-like properties, in that it induces proto-oncogene transcription, mitogenesis and cytoskeletal changes in target cells. The underlying mechanism is unknown, although it is generally assumed that PLD action is mediated by PA serving as a putative second messenger.

RESULTS

In quiescent fibroblasts, exogenous PLD (from Streptomyces chromofuscus) stimulated accumulation of the GTP-bound form of Ras, activation of mitogen-activated protein (MAP) kinase and DNA synthesis, through the pertussis-toxin-sensitive inhibitory G protein Gi. Furthermore, PLD mimicked bioactive lysophospholipids (but not PA) in inducing Ca2+ mobilization, membrane depolarization and Rho-mediated neurite retraction. PLD action was mediated by Iysophosphatidic acid (LPA) derived from Iysophosphatidylcholine acting on cognate G-protein-coupled LPA receptor(s). There was no evidence for the involvement of PA in mediating the effects of exogenous PLD.

CONCLUSIONS

Our results provide a molecular explanation for the multiple cellular responses to exogenous PLDs. These PLDs generate bioactive LPA from pre-existing Iysophosphatidylcholine in the outer membrane leaflet, resulting in activation of G-protein-coupled LPA receptors and consequent activation of Ras, Rho and Ca2+ signaling pathways. Unscheduled activation of LPA receptors may underlie, at least in part, the known pathogenic effects of exogenous PLDs.

Sphingomyelinase D activity of brown recluse spider (Loxosceles reclusa) venom as studied by 31P-NMR: effects on the time-course of sphingomyelin hydrolysis

The time-course for the hydrolysis of the D linkage of chicken egg yolk sphingomyelin in a Triton X-100 mixed micelle and of lysophosphotidylcholine micelles, as catalyzed by brown recluse spider venom and brown recluse spider toxin, was followed by phosphorous-31 nuclear magnetic resonance spectroscopy. The overall rate of hydrolysis of sphingomyelin in mixed micelles was found to be an order of magnitude faster than the hydrolysis of lysophosphotidylcholine. Incorporation of lysophosphotidylcholine into mixed micelles with Triton X-100 inhibited the lipase activity of brown recluse spider venom and brown recluse spider venom toxin. The effects of increased rates of overall reaction were observed with increased temperature and also with decreased ionic strength. The presence of divalent calcium ions was found to be necessary for hydrolytic activity, but only in catalytic amounts (less than 1 mM).

Brown recluse spider envenomation: a prospective trial of hyperbaric oxygen therapy

OBJECTIVES

Loxosceles reclusa (brown recluse) spider bites can produce severe skin lesions that may necessitate extensive surgical repair. This study delineated the effects of hyperbaric oxygen (HBO) therapy on these lesions by performing a prospective controlled animal study.

METHODS

After approval by the Institutional Animal Care and Use Committee, 41 New Zealand white rabbits received 64 intradermal injections of 73 microL of raw venom extract mixed with physiologic buffered saline (Dulbecco's solution). Control injections were made with buffer. The animals were divided into 5 groups: 1) venom and no HBO; 2) venom and 1 immediate HBO treatment (100% O2); 3) venom and immediate HBO with 10 treatments (100% O2); 4) venom and then delayed (48 hr) HBO therapy with 10 treatments (100% O2); and 5) venom and immediate hyperbaric treatment with normal inspired PO2 for 10 treatments (8.4% O2). Three animals in group 2 also received a control sodium citrate buffer injection. HBO treatments were at 2.5 atm absolute (ATA) for 90 minutes twice daily. Daily measurements were made of the lesion diameter, and skin blood flow using a laser Doppler probe.

RESULTS

There was no significant effect of HBO on blood flow at the wound center or 1-2 cm from the wound center. Standard HBO significantly decreased wound diameter at 10 days (p < 0.0001; ANOVA), whereas hyperbaric treatment with normoxic gas had no effect. Histologic preparations from 2 animals in each group revealed that there were more polymorphonuclear leukocytes in the dermis of all the HBO-treated animals when compared with the venom-alone and sodium-citrate controls.

CONCLUSION

HBO treatment within 48 hours of a simulated bite from L. reclusa reduces skin necrosis and results in a significantly smaller wound in this model. The mechanism appears unrelated to augmented local blood flow between treatments.

Comparison of hyperbaric oxygen and dapsone therapy for loxosceles envenomation

OBJECTIVE

To determine whether hyperbaric O2 (HBO), dapsone, or HBO plus dapsone affects lesion size in a swine model of Loxosceles envenomation.

METHODS

In a randomized controlled animal laboratory experiment, 32 piglets were assigned to 1 of 4 equal groups. Each piglet received 15 microliters, of purified venom intradermally on day zero. Group 1 received no treatment; group 2 received HBO at 2 atm for 2 hours on days 1-3; group 3 received 50 mg of dapsone orally on days 1-3; and group 4 received dapsone 50 mg orally and HBO at 2 atm for 2 hours on days 1-3. On days 1-7, 14, and 21, an investigator blinded to the treatment groups measured necrosis and induration. Mean necrosis and induration rates were compared using analysis of variance for repeated measures.

RESULTS

Comparing groups on any day, no significant difference was noted in necrosis, induration, reduction in necrosis from day 1, or rate of change in lesion size from days 1-7. A difference was seen in the reduction of induration between all 3 treatment groups and the control group on days 7 and 14 only. The sample size permitted a power of 0.8 to detect a 12-mm mean change in lesion size.

CONCLUSION

Compared with the control, neither dapsone, HBO, nor the combination of dapsone and HBO reduced necrosis from Loxosceles envenomation on days 3-21. An increase was seen in the rate of reduction in induration between all 3 treatment groups and the control group on days 7-21. However, the magnitude of this effect was clinically insignificant. In this animal model, treatment with either dapsone or HBO or a combination offers little clinical benefit in Loxosceles envenomation.

Biochemical and molecular analysis of phospholipase C and phospholipase D activity in mycobacteria

Resurgence of mycobacterial infections in the United States has led to an intense effort to identify potential virulence determinants in the genus Mycobacterium, particularly ones that would be associated with the more virulent species (e.g., Mycobacterium tuberculosis). Thin-layer chromatography (TLC) using radiolabeled phosphatidylcholine and sphingomyelin as substrates indicated that cell extracts of M. tuberculosis contain both phospholipase C (PLC) and phospholipase D (PLD) activities. In contrast, only PLD activity was detected in cell extracts of M. smegmatis. Neither activity was detected in cell-free culture supernatants from these organisms. We and others recently identified two open reading frames in M. tuberculosis with the potential to encode proteins which are highly homologous to the nonhemolytic (PlcN) and hemolytic (PlcH) phospholipase C enzymes of Pseudomonas aeruginosa. In contrast to the plc genes in P. aeruginosa, which are considerably distal to each other (min 34 and 64 on the chromosome), the mycobacterial genes, designated mpcA and mpcB, are tandemly arranged in the same relative orientation and separated by only 191 bp. Both the mpcA and the mpcB genes were individually cloned in M. smegmatis, and PLC activity was expressed from each gene in this organism. Hybridization experiments using the mpcA and the mpcB genes as probes under conditions of moderate stringency identified sequences homologous to these genes in M. bovis, M. bovis BCG, and M. marinum but not in several other Mycobacterium species, including M. smegmatis, M. avium, and M. intracellulare. TLC analysis using radiolabeled substrates indicated that M. bovis and M. marinum cell extracts contain PLC and PLD activities, but only PLD activity was detected in M. bovis BCG cell extracts. Sphingomyelinase activity was also detected in whole-cell extracts of M. tuberculosis, M. marinum, M. bovis, and M. bovis BCG, but this activity was not detected in extracts of M. smegmatis. Sphingomyelinase activity was detected in cell extracts from M. smegmatis harboring either recombinant mpcA or mpcB. These data indicate that PLC and sphingomyelinase activities are associated with the most virulent mycobacterial species, while PLD activity was detected in both virulent and saprophytic strains.

Therapy of brown spider envenomation: a controlled trial of hyperbaric oxygen, dapsone, and cyproheptadine

STUDY OBJECTIVE

To determine whether hyperbaric oxygen (HBO), dapsone, or cyproheptadine decreases the severity of skin lesions resulting from experimental Loxosceles envenomation.

DESIGN

Randomized, blinded, controlled study.

SETTING

Animal care facility.

INTERVENTIONS

We used New Zealand white rabbits. All groups received 20 micrograms of pooled L deserta venom intradermally. Our control group received 4 ml of a 5% ethanol solution by oral gavage every 12 hours for 4 days. The HBO group received hyperbaric oxygen at 2.5 ATA for 65 minutes every 12 hours for 2 days, plus 5% ethanol solution for 4 days. The dapsone group received dapsone 1.1 mg/kg in 5% ethanol by gavage every 12 hours for 4 days. The cyproheptadine group received cyproheptadine .125 mg/kg in 5% ethanol by gavage every 12 hours for 4 days.

RESULTS

Total lesion size and ulcer size were followed for 10 days. The lesions were then excised, examined microscopically, and ranked by the severity of the histopathology. The groups did not differ significantly with respect to lesion size, ulcer size, or histopathologic ranking.

CONCLUSION

Given the negative result in this study with adequate power to detect meaningful treatment benefits, we cannot recommend hyperbaric oxygen, dapsone, or cyproheptadine in the treatment of Loxosceles envenomation.

The involvement of collagenase in the necrosis induced by the bites of some spiders

1. The midgut extracts of 13 Australian spider species produced cellular disruption in mouse skin in tissue culture conditions. 2. Microbial collagenase and the venoms of some of these species had similar effects. 3. Five venoms also caused severe dermonecrosis in living mice. 4. Pre-mixing the venoms with L-cysteine caused complete in vivo and partial in vitro inhibition of their effects. 5. It was concluded that collagenase is a major factor in the aetiology of necrotic arachnidism.

Loxoscelism

Loxoscelism, or envenomation by the brown recluse spider, may result in necrotic lesions and systemic reactions, including hemolytic anemia. Histologically, it resembles a cutaneous Arthus reaction. The reaction mechanism involves interactions between complement, neutrophils, and the clotting system. It is best treated with analgesics, avoidance of early surgical debridement, and oral dapsone.

Studies of the necrotic actions of the venoms of several Australian spiders

1. Raw venoms from a number of Australian Araneomorph spiders were found to cause epidermal disruption in cultured skin from both mice and humans. 2. The more potent ones also caused loss of epidermal cell-cell adhesion of mouse skin in vivo. 3. Raw venoms from three Mygalomorph species did not have these actions. 4. Venom gland extracts from the Araneomorph species were also ineffective. 5. It was concluded that where spider venoms appear to possess necrogenic activity the most likely reason for this is contamination of the venoms with digestive tract secretions.

Serum amyloid P component: its role in platelet activation stimulated by sphingomyelinase D purified from the venom of the brown recluse spider (Loxosceles reclusa)

Serum amyloid P component or serum amyloid protein is a ubiquitous, highly conserved glycoprotein whose function is unknown. Although the related pentraxin, C-reactive protein, is an acute phase reactant in man, there is no direct evidence that human serum amyloid protein is involved in an inflammatory response. Here we show that serum amyloid protein is required by sphingomyelinase D, the principal necrotic agent of the venom of Loxosceles reclusa, for the in vitro-activation of human platelets. Furthermore, this platelet activation is dependent upon the presence of only serum amyloid protein; no other plasma components are necessary. Secretion of [3H]-serotonin and aggregation of platelets are nearly maximal following incubation of the platelets with purified sphingomyelinase D (0.3 micrograms/ml) and 5 micrograms/ml pure serum amyloid protein in the presence of calcium. Since the platelets are no longer activated when this 10% physiologic amount of serum amyloid protein is omitted, serum amyloid protein is likely to have a role in the necrosis caused by brown recluse spider venom.

A study of the necrotic actions of the venom of the wolf spider, Lycosa godeffroyi, on mouse skin

1. The venom of the wolf spider, Lycosa godeffroyi, caused cutaneous necrosis when injected into mice. 2. A strong inflammatory response and total loss of epidermal cellularity were features of this in vivo necrosis. 3. Mouse skin envenomated while in tissue culture showed epidermal detachment and reduced cellular adhesion. 4. Triprolidine and methysergide, used together, indomethacin, heparin and human and mouse sera all failed to inhibit the necrosis significantly. 5. The venom caused moderate haemolysis, complement consumption and inhibition of clotting, these apparently not being the main reasons for the necrosis. 6. Neither Atrax infensus venom nor hyaluronidase caused similar epithelial damage.

Effects of snake venom proteins on blood platelets

Snake venoms are complex mixtures which contain pharmacologically active polypeptides and proteins. Several snake venom constituents interfere in platelet aggregation, an important cellular process in thrombosis and hemostasis. These components range in size from small molecular weight polypeptides to high molecular weight proteins. Some of the proteins are enzymes, such as phospholipase A2, proteinases, nucleotidases, or L-amino acid oxidase, while others do not exhibit enzymatic activity. These components may initiate and/or inhibit platelet aggregation. Some venom factors induce platelet agglutination. This review deals with the physical characteristics of these venom factors, the mechanisms of their platelet effects, structure-function relationships, and their physiological significance.

Acute arthropod envenomation. Incidence, clinical features and management

Black widow spider (Latrodectus mactans) envenomation is found throughout both the temperate and tropical latitudes, and is one of the leading causes of death from arthropod envenomations worldwide. The venom is highly neurotoxic, affecting the presynaptic motor endplate to allow massive noradrenaline (norepinephrine) and acetylcholine release into synapses causing excessive stimulation and fatigue of the motor end plate and muscle. Clinically, patients develop a bite site lesion and pain, abdominal pain and tenderness, and lower extremity pain and weakness within minutes to hours of envenomation. Symptoms progress over several hours, then subside over 2 to 3 days. The recommended treatment of 'common' envenomation is calcium gluconate 10% intravenously, titrated to relief of symptoms; antivenin, although effective, may cause hypersensitivity and serum sickness reactions, and should be restricted to life-threatening envenomations only. Brown recluse spider (Loxosceles reclusa) envenomations are seen in the Americas and in Europe, and are endemic to the south and central United States. The venom contains at least 8 enzymes, consisting of various lysins (facilitating venom spread) and sphingomyelinase D, which causes cell membrane injury and lysis, thrombosis, local ischaemia, and chemotaxis. Local envenomations begin as pain and itching that progresses to vesiculation with violaceous necrosis and surrounding erythema, and ultimately ulcer formation. Systemic envenomations may be life threatening, and present with fever, constitutional symptoms, petechial eruptions, thrombocytopenia, and haemolysis with haemoglobinuric renal failure. Treatment of local envenomations is conservative (local wound care, cryotherapy, elevation, tetanus prophylaxis, and close follow-up); systemic envenomation requires supportive care and treatment of arising complications, corticosteroids to stabilise red blood cell membranes, and support of renal function. Dapsone 100mg daily has emerged as a promising therapeutic agent in both animal studies and clinical trials. Over 650 species of scorpions are known to cause envenomation (mostly in children under 10 years); they are endemic mostly in arid and tropical areas. Different venoms and clinical presentations are seen across the different species. Most commonly, an inflammatory local reaction occurs with envenomation, which is treated with wound debridement and cleaning, tetanus prophylaxis, and antihistamines. Occasionally the venom is allergenic, and the resultant allergic reaction is treated in a standard fashion.(ABSTRACT TRUNCATED AT 400 WORDS)

Wound care of spider and snake envenomations

Venomous bites and stings are numerous but severe local tissue damage is uncommon. Venoms may be simple substances or complex mixtures of many poorly characterized components whose interactions are still not fully understood. The best studied example of a dermonecrotic venom is that produced by the brown recluse spider (Loxosceles reclusa). Rattlesnake envenomation also causes significant wound injuries. Many spider and snake envenomation management modalities are controversial and the evidence is mounting against the use of a number of these treatments.

Plasma components are required for platelet activation by the toxin of Loxosceles reclusa

We have used a partially purified toxin from the venom of the brown recluse spider, Loxosceles reclusa, to study its effects on human platelets isolated from plasma proteins. This toxin, which produced skin necrosis in rabbits, contained sphingomyelinase D activity. The toxin induced platelet aggregation and secretion of [3H]serotonin in human plasma but not in buffer or in human neonate plasma. Ca2+ was required for the interaction of toxin, platelets, and plasma factor(s). The addition of C-reactive protein restored aggregation and serotonin release of platelets incubated in human neonate plasma. The ADP-degrading enzyme, apyrase, and the non-steroidal, anti-inflammatory drug, indomethacin, inhibited platelet aggregation, suggesting that ADP secreted from platelet storage granules and indomethacin-sensitive pathway(s) are involve in the toxin-induced human platelet activation (aggregation and serotonin release). Generation of platelet activating factor (PAF) from the platelet by brown recluse toxin is not likely since the PAF receptor antagonist, BN 52021, did not inhibit platelet aggregation induced by the brown recluse toxin.

Interactions between membranes and cytolytic peptides

The physico-chemical and biological properties of cytolytic peptides derived from diverse living entities have been discussed. The principal sources of these agents are bacteria, higher fungi, cnidarians (coelenterates) and the venoms of snakes, insects and other arthropods. Attention has been directed to instances in which cytolytic peptides obtained from phylogenetically remote as well as from related sources show similarities in nature and/or mode of action (congeneric lysins). The manner in which cytolytic peptides interact with plasma membranes of eukaryotic cells, particularly the membranes of erythrocytes, has been discussed with emphasis on melittin, thiolactivated lysins and staphylococcal alpha-toxin. These and other lytic peptides are characterized in Table III. They can be broadly categorized into: (a) those which alter permeability to allow passage of ions, this process eventuating in colloid osmotic lysis, signs of which are a pre-lytic induction or latent period, pre-lytic leakage of potassium ions, cell swelling and inhibition of lysis by sucrose. Examples of lysins in which this mechanism is involved are staphylococcal alpha-toxin, streptolysin S and aerolysin; (b) phospholipases causing enzymic degradation of bilayer phospholipids as exemplified by phospholipases C of Cl. perfringens and certain other bacteria; (c) channel-forming agents such as helianthin, gramicidin and (probably) staphylococcal delta-toxin in which toxin molecules are thought to embed themselves in the membrane to form oligomeric transmembrane channels.

Immunotoxicology of brown recluse spider (Loxosceles reclusa) venom

A purified toxic protein from Loxosceles reclusa venom was assayed for its in vitro effects on the human immunological and blood clotting systems. The toxin caused inhibition of neutrophil chemotaxis, depletion of serum hemolytic complement, prolongation of the activated partial thromboplastin time and depletion of clotting factors XII, XI, IX and VIII by an average of 44% in human plasma. The prothrombin time of human plasma was also prolonged by 1.5-2.0 sec. No effect of the purified toxin was observed on microbicidal ability of neutrophils, the release of enzymes from neutrophils or the adherence of neutrophils to glass beads.

Brown recluse spider bites. A comparison of early surgical excision versus dapsone and delayed surgical excision

In a prospective study, 31 patients with brown recluse spider bites were treated by either immediate surgical excision or with the leukocyte inhibitor, dapsone, followed by delayed surgical excision. Patients were matched for age, gender, and lesion size and were excluded if the typical history and physical findings were not present. In patients treated with immediate surgical excision (N = 14), delayed wound healing (N = 5) and objectional scarring (N = 7) were common complications. However, pretreatment treatment with dapsone reduced the incidence of wound complications (N = 1) and objectional scarring (N = 1) (p less than 0.05), while reducing the need for surgical excision (N = 1). There were no severe drug reactions due to dapsone, although one patient had persistent G.I. upset. Pretreatment with dapsone not only reduced surgical complications but also improved the outcome of patients bitten by the brown recluse spider.

Comparative toxinology of Loxosceles reclusa and Corynebacterium pseudotuberculosis

In contrast to other kinds of phospholipases, phospholipases D that are toxic for humans and animals are not commonly encountered as constituents of venoms or as products of pathogenic microorganisms. Toxic phospholipases D are present, however, in the venom of the brown recluse spider (Loxosceles reclusa) and in supernatants or filtrates of cultures of Corynebacterium pseudotuberculosis. Although the two enzyme toxins are derived from phylogenetically disparate entities, they are similar in molecular weight, charge, substrate specificity, and in several biological activities. They are immunologically distinguishable.

Interrelationships between toxins: studies on the cross-reactivity between bacterial or animal toxins and monoclonal antibodies to two jellyfish venoms

Affinity chromatography on columns of immobilized anti-Chrysaora and anti-Physalia monoclonal antibodies can be an effective purification tool for animal and bacterial toxins. Furthermore, the fact that specific fractions of a given species obtained from immunochromatography columns prepared with either monoclonal antibody possessed identical protein bands, were quantitatively similar in in vitro cardiotoxicity and bound like amounts of antibody, as indicated by the enzyme-linked immunosorbent assay, suggested that antigenic targets of the two monoclonal antibodies are cross-reactive and/or are located on the same molecule. Additional enzyme-linked immunosorbent assays were conducted using non-coelenterate toxins. The significant binding of brown recluse spider venom and purified cholera toxin to both our monoclonal antibodies indicated that these toxic substances shared a common or cross-reacting antigenic site(s) with some coelenterate venoms.

Interaction of brown recluse spider venom on cell membranes: the inciting mechanism?

The venom from the brown recluse spider, Loxosceles reclusa, contains one or more factors which produce skin necrosis. A dermonecrotic factor with sphingomyelinase D activity was purified from the spider's venom sacs which produced skin necrosis when injected intradermally in rabbits. Adsorption of the dermonecrotic activity occurred following incubation with isolated membranes from different cell types or different species in a dose-responsive fashion. Since injection of the complex in rabbits produced skin necrosis, a specific antibody that inhibits the dermonecrotic activity and sphingomyelinase activity was used to identify the venom fraction on the plasma membrane of erythrocytes with electron microscopy. Initiation of cutaneous inflammatory reaction may result from high-affinity interaction of a venom component in the brown recluse spider venom and cell membranes.

Effects of preparatory procedures on the venom from a rattlesnake (Crotalus molossus molossus), as determined by isoelectric focusing

A study was made on the venom of a single specimen of the rattlesnake Crotalus molossus molossus, utilizing isoelectric focusing in polyacrylamide gels, to determine what effects various commonly employed preparative procedures might have on the chemical properties of the venom. The procedures included storage at several temperatures, freezing and thawing, evaporation, desiccation and lyophilization. Results indicated that the numbers and relative positions of the protein bands were constant with each procedure. It was concluded that the various procedures did not cause enzymatic degradation or major shifts in the pI of the bands. The significance of the findings is discussed.

Enzymatic and hemolytic properties of brown recluse spider (Loxosceles reclusa) toxin and extracts of venom apparatus, cephalothorax and abdomen

Loxosceles reclusa venom apparatus extract, toxin, cephalothorax and abdomen extracts were tested for six activities. Protease, lipase, nonspecific hydrolase and direct hemolytic activities were found primarily in abdomen extracts while sphingomyelinase activity appeared predominantly in the toxin. Appreciable complement-mediated hemolysis was not observed.