Effects on behaviour and EEG of single chain phospholipases A2 from snake and bee venoms injected into rat brain: search for a functional antagonism

Brachial artery thrombosis following bee sting, case report

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Bee sting are the most common insect emergencies.

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Often bee stings occur only with local allergic reactions.

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A very rare case of brachial artery thrombosis after a honey bee sting is presented.

Introduction

Bee stings are the most common among insect emergencies.

Presentation of case

We present a 47-year-old male patient who was admitted to the emergency department with complaints of pallor, chills, numbness and bruising on the left palm one hour after a bee sting on his left leg, and a very rare case of brachial artery stenosis in Dopler ultrasonography.

Discussion

Often bee stings occur only with local allergic reactions; sometimes it can also cause myocardial infarction, pulmonary edema, bleeding, hemolytic anemia, and kidney disease and neurological manifestations. Side effects are generally thought to be related to the dose of this venom in these patients who are admitted to the emergency room with a bruise extending from the left hand to the arm after bee bites.

Conclusion

With this case presented, we wanted to emphasize that thrombosis may occur due to bee stings, albeit rarely, and doctors in emergency departments should recognize these very rare cases.

A Novel Phospholipase A2 Isolated from Palythoa caribaeorum Possesses Neurotoxic Activity

Zoanthids of the genus Palythoa are distributed worldwide in shallow waters around coral reefs. Like all cnidarians, they possess nematocysts that contain a large diversity of toxins that paralyze their prey. This work was aimed at isolating and functionally characterizing a cnidarian neurotoxic phospholipase named A2-PLTX-Pcb1a for the first time. This phospholipase was isolated from the venomous extract of the zoanthid Palythoa caribaeorum. This enzyme, which is Ca²⁺-dependent, is a 149 amino acid residue protein. The analysis of the A2-PLTX-Pcb1a sequence showed neurotoxic domain similitude with other neurotoxic sPLA₂´s, but a different catalytic histidine domain. This is remarkable, since A2-PLTX-Pcb1a displays properties like those of other known PLA₂ enzymes.

Neurotoxicity of coral snake phospholipases A2 in cultured rat hippocampal neurons

The neurotoxicity of two secreted Phospholipases A2 from Brazilian coral snake venom in rat primary hippocampal cell culture was investigated. Following exposure to Mlx-8 or Mlx-9 toxins, an increase in free cytosolic Ca(2+) and a reduction in mitochondrial transmembrane potential (ΔΨm) became evident and occurred prior to the morphological changes and cytotoxicity. Exposure of hippocampal neurons to Mlx-8 or Mlx-9 caused a decrease in the cell viability as assessed by MTT and LDH assays. Inspection using fluorescent images and ultrastructural analysis by scanning and transmission electron microscopy showed that multiphase injury is characterized by overlapping cell death phenotypes. Shrinkage, membrane blebbing, chromatin condensation, nucleosomal DNA fragmentation and the formation of apoptotic bodies were observed. The most striking alteration observed in the electron microscopy was the fragmentation and rarefaction of the neuron processes network. Degenerated terminal synapses, cell debris and apoptotic bodies were observed among the fragmented fibers. Numerous large vacuoles as well as swollen mitochondria and dilated Golgi were noted. Necrotic signs such as a large amount of cellular debris and membrane fragmentation were observed mainly when the cells were exposed to highest concentration of the PLA2-neurotoxins. PLA2s exposed cultures showed cytoplasmic vacuoles filled with cell debris, clusters of mitochondria presented mitophagy-like structures that are in accordance to patterns of programmed cell death by autophagy. Finally, we demonstrated that the sPLA2s, Mlx-8 and Mlx-9, isolated from the Micrurus lemniscatus snake venom induce a hybrid cell death with apoptotic, autophagic and necrotic features. Furthermore, this study suggests that the augment in free cytosolic Ca(2+) and mitochondrial dysfunction are involved in the neurotoxicity of Elapid coral snake venom sPLA2s.

An unusual presentation of bee sting: subarachnoid hemorrhagia

A person consists of a variety of immune reactions as a result of bee stings, depending on his/her immunologic structure. A 49-year-old male patient was brought to the emergency department because of generalized tonic clonic seizure and loss of consciousness after an hour of wild bee bite from the anterior abdomen in a rural area. After cardiopulmonary resuscitation, he was admitted to intensive care unit. Although cranial computed tomography taken in the emergency department was normal, control cranial computed tomography at the 36th hour after admission was consisted with subarachnoid hemorrhagia (SAH). The patient was diagnosed as SAH due to exposure to bee stings. The patient was treated for a month in an intensive care unit and discharged in a vegetative state. We present and discuss the case that had epileptic seizures and SAH after a bee bite, with the review of the literature.

Electrophysiological and structural aspects in the frontal cortex after the bee (Apis mellifera) venom experimental treatment

The aim of this study is to evaluate the bioelectrical and structural-functional changes in frontal cortex after the bee venom (BV) experimental treatments simulating both an acute envenomation and a subchronic BV therapy. Wistar rats were subcutaneously injected once with three different BV doses: 700 μg/kg (T(1) group), 2100 μg/kg (T(3) group), and 62 mg/kg (sublethal dose-in T(SL) group), and repeated for 30 days with the lowest dose (700 μg/kg-in T(S) group). BV effects were assessed by electrophysiological, histological, histochemical, and ultrastructural methods. Single BV doses produced discharges of negative and biphasic sharp waves, and epileptiform spike-wave complexes. The increasing frequency of these elements suggested a dose-dependent neuronal hyperexcitation or irritation. As compared to the lower doses, the sublethal dose was responsible for a pronounced toxic effect, confirmed by ultrastructural data in both neurons and glial cells that underwent extensive, irreversible changes, triggering the cellular death. Subchronic BV treatment in T(S) group resulted in a slower frequency and increased amplitude of cortical activity suggesting neuronal loss. However, neurons were still stimulated by the last BV dose. Structural-functional data showed a reduced cellular density in frontal cortex of animals in this group, while the remaining neurons displayed both specific (stimulation of neuronal activity) and unspecific modifications (moderate alterations to necrotic phenomena). Molecular mechanisms involved in BV interactions with the nervous tissue are also discussed. We consider all these data very important for clinicians who manage patients with multiple bee stings, or who intend to set an appropriate BV therapy.

Mass spectrometry analysis of the phospholipase A(2) activity of snake pre-synaptic neurotoxins in cultured neurons

Snake pre-synaptic phospholipase A(2) neurotoxins paralyse the neuromuscular junction by releasing phospholipid hydrolysis products that alter curvature and permeability of the pre-synaptic membrane. Here, we report results deriving from the first chemical analysis of the action of these neurotoxic phospholipases in neurons, made possible by the use of high sensitivity mass spectrometry. The time-course of the phospholipase A(2) activity (PLA(2)) hydrolysis of notexin, beta-bungarotoxin, taipoxin and textilotoxin acting in cultured neurons was determined. At variance from their enzymatic activities in vitro, these neurotoxins display comparable kinetics of lysophospholipid release in neurons, reconciling the large discrepancy between their in vivo toxicities and their in vitro enzymatic activities. The ratios of the lyso derivatives of phosphatidyl choline, ethanolamine and serine obtained here together with the known distribution of these phospholipids among cell membranes, suggest that most PLA(2) hydrolysis takes place on the cell surface. Although these toxins were recently shown to enter neurons, their intracellular hydrolytic action and the activation of intracellular PLA(2)s appear to contribute little, if any, to the phospholipid hydrolysis measured here.

Neurotoxicity and other pharmacological activities of the snake venom phospholipase A2 OS2: the N-terminal region is more important than enzymatic activity

Several snake venom secreted phospholipases A2 (sPLA2s) including OS2 exert a variety of pharmacological effects ranging from central neurotoxicity to anti-HIV activity by mechanisms that are not yet fully understood. To conclusively address the role of enzymatic activity and map the key structural elements of OS2 responsible for its pharmacological properties, we have prepared single point OS2 mutants at the catalytic site and large chimeras between OS2 and OS1, a homologous but nontoxic sPLA2. Most importantly, we found that the enzymatic activity of the active site mutant H48Q is 500-fold lower than that of the wild-type protein, while central neurotoxicity is only 16-fold lower, providing convincing evidence that catalytic activity is at most a minor factor that determines central neurotoxicity. The chimera approach has identified the N-terminal region (residues 1-22) of OS2, but not the central one (residues 58-89), as crucial for both enzymatic activity and pharmacological effects. The C-terminal region of OS2 (residues 102-119) was found to be critical for enzymatic activity, but not for central neurotoxicity and anti-HIV activity, allowing us to further dissociate enzymatic activity and pharmacological effects. Finally, direct binding studies with the C-terminal chimera, which poorly binds to phospholipids while it is still neurotoxic, led to the identification of a subset of brain N-type receptors which may be directly involved in central neurotoxicity.

Secreted phospholipase A2 potentiates glutamate-induced calcium increase and cell death in primary neuronal cultures

Secreted phospholipases A2 (sPLA2s) modulate neuronal survival and neurotransmitter release. Here we show that sPLA2 (group III) synergistically increases glutamate-induced cell death and intracellular calcium ([Ca2+]i) in cultured primary cortical and hippocampal neurons. Whereas 1 microM glutamate elicited transient [Ca2+]i increases in all neurons that recovered 66% to baseline, 25 ng/ml sPLA2 pretreatment resulted in sustained [Ca2+]i increases, with only 5% recovery. At 250 nM glutamate, 25% of neurons failed to respond, and the average recovery time was 101 +/- 12 sec; sPLA2 increased recovery time to 158 +/- 6 sec, and only 2% of cells failed to respond. Both the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and the calcium-channel blocker cobalt inhibited this effect. Experiments with the glutamate uptake inhibitor L-trans-pyrollidine-2,4-dicarboxylic acid (2.5 microM) indicated that glutamate uptake sites are not a likely modulation point by sPLA2, whereas arachidonic acid (AA) potentiated calcium responses to glutamate. Thus the enhancement of glutamate-induced [Ca2+]i increases by sPLA2 may be due to modulation at NMDA receptors and/or calcium channels by AA. These results indicate that sPLA2 affects neuronal responses to both nontoxic (0.1-10 microM) and toxic (=25 microM) concentrations of glutamate, implicating this enzyme in neuronal functions in pathology.

Inhibition of crotoxin phospholipase A(2) activity by manoalide associated with inactivation of crotoxin toxicity and dissociation of the heterodimeric neurotoxic complex

Crotoxin (CACB complex) is a convulsant heterodimeric neurotoxic phospholipase A(2) (PLA(2)). The role of phospholipid hydrolysis in its epileptogenic properties remains unresolved. We, thus, studied the effect of manoalide (MLD), a PLA(2) inhibitor, on the toxin catalytic activity and its central and peripheral toxicity. Incubation of crotoxin with MLD fully and irreversibly inactivated its enzymatic activity. Interestingly, crotoxin also lost its central neurotoxicity after intracerebroventricular injection and peripheral toxicity after intravenous administration. MLD-treated crotoxin prevented the high affinity binding of [125I]-radiolabeled crotoxin on rat cortex synaptic plasma membranes. Further analysis of MLD-treated crotoxin by non-denaturing PAGE and surface plasmon resonance indicated that the crotoxin complex was dissociated after MLD treatment. Although the loss of MLD-treated crotoxin peripheral neurotoxicity could not be attributed to this dissociation, the presence of free CA subunit might explain the observed competition in binding experiments. In conclusion, the dissociation of the crotoxin complex by MLD, as demonstrated in this study, did not permit to specify the role of the enzymatic activity in crotoxin epileptogenic properties. Other approaches would be required to resolve this question.

Both group IB and group IIA secreted phospholipases A2 are natural ligands of the mouse 180-kDa M-type receptor

Snake venom and mammalian secreted phospholipases A2 (sPLA2s) have been associated with toxic (neurotoxicity, myotoxicity, etc.), pathological (inflammation, cancer, etc.), and physiological (proliferation, contraction, secretion, etc.) processes. Specific membrane receptors (M and N types) for sPLA2s have been initially identified with snake venom sPLA2s as ligands, and the M-type 180-kDa receptor was cloned from different animal species. This paper addresses the problem of the endogenous ligands of the M-type receptor. Recombinant group IB and group IIA sPLA2s from human and mouse species have been prepared and analyzed for their binding properties to M-type receptors from different animal species. Both mouse group IB and group IIA sPLA2s are high affinity ligands (in the 1-10 nM range) for the mouse M-type receptor. These two sPLA2s are expressed in the mouse tissues where the M-type receptor is also expressed, making it likely that both types of sPLA2s are physiological ligands of the mouse M-type receptor. This conclusion does not hold for human group IB and IIA sPLA2s and the cloned human M-type receptor. The two mouse sPLA2s have relatively high affinities for the mouse M-type receptor, but they can have much lower affinities for receptors from other animal species, indicating that species specificity exists for sPLA2 binding to M-type receptors. Caution should thus be exerted in avoiding mixing sPLA2s, cells, or tissues from different animal species in studies of the biological roles of mammalian sPLA2s associated with an action through their membrane receptors.

Structure-function properties of venom components from Australian elapids

A comprehensive review of venom components isolated thus far from Australian elapids. Illustrated is that a tremendous structural homology exists among the components but this homology is not representative of the functional diversity. Further, the review illuminates the overlooked species and areas of research.

Venom phospholipase A2-induced impairment of glutamate uptake: an indirect and nonselective effect related to phospholipid hydrolysis

In a nominally calcium-free medium, a toxic phospholipase A2, paradoxin, PDX (1-200nM) was able to significantly decrease glutamate uptake by rat hippocampal mini-slices. Under the same experimental conditions, PDX could also inhibit the reuptake of choline and dopamine, suggesting a nonselective action. Furthermore, we found no evidence of competition between PDX and [3H]L-Aspartate described as a marker of glutamate carrier proteins. A direct blockage of glutamate uptake by binding to the glutamate transporters is thus unlikely to occur. Implication of the free fatty acids (FFAs), or their metabolites, was clearly shown by the total suppression of PDX effect on reuptake in a medium inhibiting its catalytic activity (EGTA/Sr2+ buffer). Moreover, analysis of the FFAs liberated showed a significant increase in polyunsaturated fatty acid (PUFA) levels. Arachidonic acid (AA) concentration reached in the water phase, though in the low micromolar range, may be especially relevant in explaining this effect. Much higher concentrations are found in the membranes and may also participate in the action on reuptake. Evidence for the involvement of FFAs was also provided by the antagonistic, although partial, action of bovine serum albumine (BSA, 1%). Finally, free radicals or eicosanoids did not seem to play a significant role given the persistence of inhibition in the presence of NDGA (1 microM) or indomethacin (10 microM), inhibitors of the two major AA metabolic pathways. Altogether, PDX-induced uptake impairment may thus be related to the direct action of AA and other PUFAs on the glutamate transporter, as well as through less selective actions.

Cloning, chromosomal mapping, and expression of a novel human secretory phospholipase A2

Secretory phospholipases A2 (sPLA2s) represent a rapidly expanding family of structurally related enzymes found in mammals as well as in insect and snake venoms. In this report, a cDNA coding for a novel sPLA2 has been isolated from human fetal lung, and its gene has been mapped to chromosome 16p13.1-p12. The mature sPLA2 protein has a molecular mass of 13.6 kDa, is acidic (pI 5.3), and made up of 123 amino acids. Key structural features of the sPLA2 include: (i) a long prepropeptide ending with an arginine doublet, (ii) 16 cysteines located at positions that are characteristic of both group I and group II sPLA2s, (iii) a C-terminal extension typical of group II sPLA2s, (iv) and the absence of elapid and pancreatic loops that are characteristic of group I sPLA2s. Based on these structural properties, this sPLA2 appears as a first member of a new group of sPLA2s, called group X. A 1.5-kilobase transcript coding for the human group X (hGX) sPLA2 was found in spleen, thymus, and peripheral blood leukocytes, while a less abundant 0.8-kilobase transcript was detected in the pancreas, lung, and colon. When the hGX sPLA2 cDNA was expressed in COS cells, sPLA2 activity preferentially accumulated in the culture medium, indicating that hGX sPLA2 is an actively secreted enzyme. It is maximally active at physiological pH and with 10 mM Ca2+. hGX sPLA2 prefers phosphatidylethanolamine and phosphatidylcholine liposomes to those of phosphatidylserine.

Localization of structural elements of bee venom phospholipase A2 involved in N-type receptor binding and neurotoxicity

We have shown previously that neurotoxic venom secretory phospholipases A2 (sPLA2s) have specific receptors in brain membranes called N-type receptors that are likely to play a role in the molecular events leading to neurotoxicity of these proteins. The sPLA2 found in honey bee venom is neurotoxic and binds to this receptor with high affinity. In this paper, we have used a number of mutants of bee venom sPLA2 produced in Escherichia coli to determine the structural elements of this protein that are involved in its binding to N-type receptors. Mutations in the interfacial binding surface, in the Ca2+-binding loop and in the hydrophobic channel lead to a dramatic decrease in binding to N-type receptors, whereas mutations of surface residues localized in other parts of the sPLA2 structure do not significantly modify the binding properties. Neurotoxicity experiments show that mutants with low affinity for N-type receptors are devoid of neurotoxic properties, even though some of them retain high enzymatic activity. These results provide further evidence for the involvement of N-type receptors in neurotoxic processes associated with venom sPLA2s and identify the surface region surrounding the hydrophobic channel of bee venom sPLA2 as the N-type receptor recognition domain.