Crystallization and preliminary X-ray diffraction studies of a toxic phospholipase A2 from the venom of Vipera ammodytes meridionalis complexed to a synthetic inhibitor

Effect of Vipera ammodytes ammodytes Snake Venom on the Human Cytokine Network

Local inflammation is a well-known symptom of envenomation by snakes of the family Viperidae, attributed primarily to the phospholipase A₂s, metalloproteinases and L-amino acid oxidases contained in their venom. The inflammatory effect of snake venoms has been associated with a marked increase of the cytokines IL-1β, IL-6, IL-8, IL-10 and TNF-α. To determine the impact of Vipera ammodytes ammodytes snake venom on the expression of inflammation-related genes, we incubated human U937 monocyte cells with dilutions of snake venom. Gene expression was quantified for 28 different genes using a TaqMan^® Array Human Cytokine Network 96-well Plate in a RT-qPCR system. Our results have demonstrated that 1.0 μg/mL Vipera ammodytes ammodytes venom solution induces a notable change in the expression of several cytokine network genes. Among the upregulated genes, there were several that encode interleukins, interferons, and tumor necrosis factors. We further report the downregulation of three interleukin-related genes. Our findings come as supportive information for the known complex effect of snake venoms on the human cytokine network. It also provides relevant new information regarding the expression of genes that have not been previously associated with the effect of snake venoms.

Inhibition of Naja naja venom enzymes by the methanolic extract of Leucas aspera and its chemical profile by GC-MS

Purpose

The present investigation was aimed at evaluating the anti-ophidian properties of ethnomedicinal herb Leucas aspera against Indian cobra, Naja naja venom enzymes.

Methods

Methanolic extract of Leucas aspera was evaluated, in vitro, for its ability to inhibit the major enzyme activities of Naja naja venom including protease, phospholipase A₂, hyaluronidase and hemolytic factors. The type of phytochemicals present in the extract was analyzed. Also, the major phytoconstituents in the extract was determined by gas chromatography–mass spectrometry (GC–MS).

Results

Venom protease and hyaluronidase activities (two isoforms) were completely (100%) neutralized by the L. aspera methanolic extract at ratio of 1:50 w/w (venom: plant extract) and venom hemolytic activity was also completely neutralized at a ratio of 1:80 w/w by the plant extract. However, the extract failed to neutralize phospholipase A₂ activity even at the highest concentration used. Phytochemical analysis revealed the presence of alkaloids, acidic compounds, flavonoids, steroids and cardiac glycosides in the extract. GC–MS analysis indicated that a total of 14 compounds were present in the extract. The major bioactive constituents were found to be 6-octadecenoic acid (32.47%), n-hexadecanoic acid (25.97%), and 17-octadecen-14-yn-1-ol (14.22%) along with the minor constituents, sitosterol (2.45%) and stigmasterol (2%), which was previously reported to exhibit antivenom activity.

Conclusion

The results obtained demonstrate for the first time that the methanolic extract of Leucas aspera possesses anti-venom activity and could be considered as a potential source for the anti-ophidian metabolites.

Snake venom PLA2s inhibitors isolated from Brazilian plants: synthetic and natural molecules

Ophidian envenomation is an important health problem in Brazil and other South American countries. In folk medicine, especially in developing countries, several vegetal species are employed for the treatment of snakebites in communities that lack prompt access to serum therapy. However, the identification and characterization of the effects of several new plants or their isolated compounds, which are able to inhibit the activities of snake venom, are extremely important and such studies are imperative. Snake venom contains several organic and inorganic compounds; phospholipases A₂ (PLA₂s) are one of the principal toxic components of venom. PLA₂s display a wide variety of pharmacological activities, such as neurotoxicity, myotoxicity, cardiotoxicity, anticoagulant, hemorrhagic, and edema-inducing effects. PLA₂ inhibition is of pharmacological and therapeutic interests as these enzymes are involved in several inflammatory diseases. This review describes the results of several studies of plant extracts and their isolated active principles, when used against crude snake venoms or their toxic fractions. Isolated inhibitors, such as steroids, terpenoids, and phenolic compounds, are able to inhibit PLA₂s from different snake venoms. The design of specific inhibitors of PLA₂s might help in the development of new pharmaceutical drugs, more specific antivenom, or even as alternative approaches for treating snakebites.

Screening of plants containing Naja naja siamensis cobra venom inhibitory activity using modified ELISA technique

Enzyme-linked immunosorbent assay (ELISA) has been modified for screening plants with antagonistic activity to Naja naja siamensis cobra venom. Aqueous extracts from plants were investigated for their inhibitory effects on the binding of anti-cobra venom antibody to antigen, cobra venom, fixed onto 96-well microtiter plates. Ingredients in extracts were allowed to react with immobilized venom before the subsequent addition of antivenom antibody. Venom components affected by exposure to the extracts, unable to interact with their specific antibody, were predicted to be unable to bind to their native destinations or natural receptors. Curcuma cf. zedoaria, an old Thai medicinal plant, showed clear inhibitory activity in the ELISA test. Neurotoxin and protein degradative enzymes, major components in venom, were identified as targets of this extract in Western immunoblotting analysis. Ingredients in the extract showed high affinity to the toxin in competition assay by immunoprecipitation. The extract attenuated toxin activity by extending contraction time of diaphragm muscle after envenomation and had a potency to protect cellular proteins from venom degradative enzymes. Curcuma parviflora, with less activity in ELISA, exhibited acceptable results in two experiments but negative results in two experiments, whereas Curcuma longa, having low activity in the ELISA test, never showed any favorable results. Screening of 36 samples could classify plants into an inhibition range of 0 to 86%. This modified ELISA is recommended as a preliminary screening method for inhibitors with a large number of samples.

Asp49 phospholipase A2–elaidoylamide complex: a new mode of inhibition

The inhibition of phospholipase A(2)s (PLA(2)s) is of pharmacological and therapeutic interest because these enzymes are involved in several inflammatory diseases. Elaidoylamide is a powerful inhibitor of a neurotoxic PLA(2) from the Vipera ammodytes meridionalis venom. The X-ray structure of the enzyme-inhibitor complex reveals a new mode of Asp49 PLA(2) inhibition by a fatty acid hydrocarbon chain. The structure contains two identical homodimers in the asymmetric unit. In each dimer one subunit is rotated by 180 degrees with respect to the other and the two molecules are oriented head-to-tail. One molecule of elaidoylamide is bound simultaneously to the substrate binding sites of two associated neurotoxic phospholipase A(2) molecules. The inhibitor binds symmetrically to the hydrophobic channels of the two monomers. The structure can be used to design anti-inflammatory drugs.

Interactions of the neurotoxin vipoxin in solution studied by dynamic light scattering

The neurotoxin vipoxin is the lethal component of the venom of Vipera ammodytes meridionalis. It is a heterodimer of a basic toxic His-48 phospholipase A2 (PLA2) and an acidic nontoxic Gln-48 PLA2. The shape of the neurotoxin and its separated components in solution as well as their interactions with calcium, the brain phospholipid phosphatidylcholine, and two inhibitors, elaidoylamide and vitamin E, were investigated by dynamic light scattering. Calcium binding is connected with a conformational change in vipoxin observed as a change of the hydrodynamic shape from oblate ellipsoid to a shape closer to a sphere. The Ca2+-bound form of vipoxin, which is catalytically active, is more compact and symmetric than the calcium-free heterodimer. Similar changes were observed as a result of the Ca2+-binding to the two separated subunits. In the presence of aggregated phosphatidylcholine, the neurotoxic complex dissociates to subunits. It is supposed that only the toxic component binds to the substrate, and the other subunit, which plays a chaperone function, remains in solution. The inhibition of vipoxin with the synthetic inhibitor elaidoylamide and the natural compound vitamin E changes the shape of the toxin from oblate to prolate ellipsoid. The inhibited toxin is more asymmetric in comparison to the native one. Similar, but not so pronounced, effects were observed after the inhibition of the monomeric and homodimeric forms of the toxic His-48 PLA2. Circular dichroism measurements in the presence of urea, methylurea, and ethylurea indicate a strong hydrophobic stabilization of the neurotoxin. Hydrophobic interactions stabilize not only the folded regions but also the regions of intersubunit contacts.