Therapeutic application of natural inhibitors against snake venom phospholipase A(2)

Ethnomedicinal breakthroughs in snake bite therapy: From folklore to forefront

Snakebite envenomation is a critical public health issue, especially in tropical regions like India, resulting in significant morbidity and mortality. This review explores the potential of ethnomedicinal herbs as adjunct therapies to conventional antivenoms, addressing challenges such as the high cost, limited availability, and side effects of traditional antivenoms. The study emphasizes regional and species-specific variations in snake venom that complicate antivenom development and highlights the pharmacological potential of certain medicinal plants in mitigating venom effects. These plants offer an affordable, accessible alternative, though their efficacy can vary due to regional venom differences. Additionally, the review discusses the role of bioinformatics in advancing antivenom research, aiming to combine traditional knowledge with modern science to develop effective and accessible snakebite treatments in resource-limited settings.

Doxycycline-Mediated Inhibition of Snake Venom Phospholipase and Metalloproteinase

INTRODUCTION

Warfighters are exposed to life-threatening injuries daily and according to the Joint Trauma System Military Clinical Practice Guideline-Global Snake Envenomation Management snakebites are a concerning threat in all theaters of operation. Snake venom is a complex mixture of toxins including phospholipases A2 (PLA2) and snake venom metalloproteinases (SVMP) that produce myotoxic, hemotoxic, and cytotoxic injuries. Antibody-based antivenom is the standard of care but new approaches including small-molecule inhibitors have gained attention in recent years. Doxycycline is an effective inhibitor of human metalloproteinases and PLA2. The enzymatic activities of 3 phylogenetically distinct snakes: Agkistrodon piscivorus, Naja kaouthia, and Daboia russelii were tested under inhibitory conditions using doxycycline.

MATERIALS AND METHODS

Enzymatic activity of PLA2 and SVMP was measured in N. kaouthia, D. russelii, and A. piscivorus venom alone and with doxycycline using EnzChek Phospholipase A2 and Gelatinase Assay Kits. A 1-way ANOVA with Tukey's post-hoc test was used to conduct comparative analysis. The median lethal dose of the venoms, the effective dose of doxycycline, and creatine kinase (CK) inhibition levels were measured in a murine model with adult Bagg Albino (BALB/c) mice using intramuscular injections. Median lethal and effective doses were determined using Spearman-Karber's method and a 1-way ANOVA with Tukey's post-hoc test was used to compare CK inhibition levels.

RESULTS

Phospholipases A2 activity was reduced to 1.5% to 44.0% in all 3 venoms in a dose-dependent manner using 0.32, 0.16, and 0.08 mg/mL doxycycline when compared to venom-only controls (P < .0001) (Fig. 1A). Snake venom metalloproteinases activity was reduced to 4% to 62% in all 3 venoms in a dose-dependent manner using 0.32, 0.16, and 0.08 mg/mL doxycycline (P < .0001) (Fig. 1B). The lethal dose (LD50) values of the venoms in the murine model were calculated as follows: A. piscivorus = 20.29 mg/kg (Fig. 2A), N. kaouthia = 0.38 mg/kg (Fig. 2B), and D. russelii = 7.92 mg/kg (Fig. 2C). The effective dose (ED50) of doxycycline in A. piscivorus was calculated to be 20.82 mg/kg and 72.07 mg/kg when treating D. russelii venom. No ED50 could be calculated when treating N. kaouthia venom (Fig. 3). Creatine kinase activity was significantly decreased in all 3 venoms treated with doxycycline (P < .0001) (Fig. 4).

CONCLUSION

Doxycycline reduced PLA2- and SVMP-related lethality, particularly in A. piscivorus envenomings and in a limited capacity with D. russelii revealing its promise as a treatment for snakebites. In addition, CK activity, a common indicator of muscle damage was inhibited in mice that received doxycycline-treated venom. The doxycycline concentrations identified in the ED50 studies correspond to 1,456 to 5,061 mg dosages for a 70 kg human. Factors including venom yield and snake species would affect the actual dosage needed. Studies into high-dose doxycycline safety and its effectiveness against several snake species is needed to fully translate its use into humans. Based on this work, doxycycline could be used as a treatment en route to higher echelons of care, providing protection from muscle damage and reducing lethality in different snake species.

Alkaloids from Siparuna (Siparunaceae) are predicted as the inhibitors of proteolysis and plasma coagulation caused by snake venom and potentially counteract phospholipase A2 activity of Bothrops jararaca

ETHNOPHARMACOLOGICAL RELEVANCE

Snakebite envenomation (SBE) is the world's most lethal neglected tropical disease. Bothrops jararaca is the species that causes the greatest number of SBEs in the South and Southeastern of Brazil. The main symptoms are local (inflammation, edema, hemorrhage, and myonecrosis) and systemic (hemorrhage, hemostatic alterations with consumptive coagulopathy, and death) effects. Species of the genus Siparuna, Siparunaceae, are used in folk and traditional medicine to treat SBE. However, limited information is available concerning Brazilian Siparuna species against SBE.

AIM OF THE STUDY

To investigate the correlation between the compounds present in the extracts of five Siparuna species as potential agents against proteolytic activity, plasma coagulation, and phospholipase A2 (PLA2) activity caused by B. jararaca venom, using data obtained by UHPLC-MS/MS, biological activity, and multivariate statistics.

MATERIALS AND METHODS

The ethanol extracts from leaves of S. ficoides, S. decipiens, S. glycycarpa, S. reginae, and S. cymosa were fractionated by liquid-liquid extraction using different solvents of increasing polarity (hexane, dichloromethane, ethyl acetate, and n-butanol), affording their respective extracts, totaling 25 samples that were assayed through in vitro plasma coagulation and proteolytic activity assays. Moreover, the extracts were analyzed by UHPLC-MS/MS, using electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI) in negative and positive ionization modes. The data was processed in MZmine v. 2.53 and evaluated by multivariate statistical tests (PLS) using the software UnscramblerX v. 10.4. These data were also used to build molecular networks (GNPS), and some ions of interest could be annotated using the library of molecules on the GNPS platform.

RESULTS

A total of 19 extracts inhibited B. jararaca-induced plasma coagulation, with emphasis on S. cymosa and S. reginae (800 s). The inhibition of the proteolytic activity was also promising, ranging from 16% (S. glycycarpa) to 99% (S. cymosa, S. decipiens, and S. reginae). In addition, most extracts from S. cymosa and S. reginae inhibited 70-90% of PLA2 activity. Based on data from positive mode APCI analyses, it was possible to obtain a statistic model with reliable predictive capacity which exhibited an average R2 of 0.95 and a Q2 of 0.88, indicating a robust fit. This process revealed five ions, identified as the alkaloids: coclaurine (1), stepholidine (2) O-methylisopiline (3), nornantenine (4) and laurolitsine (5). This is the first study to evidence the potential antivenom of alkaloids from Siparuna species.

CONCLUSIONS

Altogether, our results give support to the popular use of Siparuna extracts in SBE accidents, suggesting their potential as an alternative or complementary strategy against envenoming by B. jararaca venom. The predicted ions in the chemometric analysis for the assayed activities can also be correlated with the blocking activity and encourage the continuation of this study for possible isolation and testing of individual compounds on the used models.

Exploring the inhibitory potential of phytochemicals from Vernonia glaberrima leaves against snake venom toxins through computational simulation and experimental validation

Phospholipase A2 (PLA2) is an enzyme present in appreciable quantity in snake venoms which catalyze the hydrolysis of glycerophospholipids at sn-2 position and promote the release of lysophospholipids and fatty acids. 5-methylcoumarin-4-β-glucoside (5MC4BG) and lupeol were previously isolated from the leaves of V. glaberrima. The aim of this research was to evaluate effect of these compounds as potential inhibitors of snake venom toxins of Naja nigricollis using an in vitro and in silico studies. Antisnake venom studies was conducted using acidimetry while the molecular docking analysis against PLA2 enzyme from N. nigricollis was performed using Auto Dock Vina and ADME-Tox analysis was evaluated using swissADME and ProTox-II online servers. The two compounds (5MC4BG and Lupeol) were able to inhibit the hydrolytic actions of PLA2 enzyme with percentage inhibition ranging from 23.99 to 72.36 % and 21.97-24.82 % at 0.0625-1.00 mg/mL respectively while the standard ASV had 82.63 % at 1.00 mg/mL after 10 min incubation at 37 °C. Similar effects were observed after 30 min incubation, although there was significant increase in percentage inhibition of 5MC4BG and lupeol ranging from 66.51 to 83.73 % and 54.87-59.60 % at similar concentrations. Furthermore, the compounds were able to bind to the active site of PLA2 enzyme with high affinity (-7.7 to -6.3 kcal/mol); the standard ligand, Varespladib had a docking score of -6.9 kcal/mol and they exhibited favorable drug-likeness and pharmacokinetic properties and according to toxicity predictions, the two compounds are toxic. In conclusion, the leaf of V. glaberrima contains phytoconstituents with antisnake activity and thus, validates the hypothesis that, the phytoconstituents of V. glaberrima leaves has antisnake venom activity against N. nigricollis venom and thus, should be studied further for the development as antisnake venom agents.

Molecular dynamics simulation analysis of alpha-cobra toxin docked with phytochemical compounds

It is of interest to document data on the molecular dynamics simulation analysis of alpha-cobratoxin docked with phytochemical compounds. This can be used as effective drug candidates against the snake and scorpion venom. It should be noted experimental verification is needed to further validate the current data.

A First Look at the Inhibitory Potential of Urospatha sagittifolia (Araceae) Ethanolic Extract for Bothrops atrox Snakebite Envenomation

Bothrops atrox snakebites are a relevant problem in the Amazon basin. In this biodiverse region, the ethnomedicinal approach plays an important role as an alternative to antivenom therapy. Urospatha sagittifolia (Araceae) is a plant used for this purpose; however, its neutralizing properties have not been scientifically accessed. To fill this gap, we investigated the ability of U. sagittifolia to modulate the catalytic activity of Bothrops atrox venom, and their toxic consequences, such as local damage and lethality. The venom profile of B. atrox was assessed by chromatography and electrophoresis. Inhibition of the three main enzymatic and medically important toxins from the venom was evaluated using synthetic substrates and quantified by chromogenic activity assays. Additionally, the neutralization of lethality, hemorrhage and edema were investigated by in vivo assays. The possible interactions between venom proteins and plant molecules were visualized by polyacrylamide gel electrophoresis. Finally, the phytochemical constituents present in the ethanolic extract were determined by qualitative and quantitative analyses. The ethanolic extract reduced the activity of the three main enzymes of venom target, achieving ranges from 19% to 81% of inhibition. Our in vivo venom neuralizations assays showed a significant inhibition of edema (38.72%) and hemorrhage (42.90%). Additionally, lethality was remarkably counteracted. The highest extract ratio evaluated had a 75% survival rate. Our data support the biomedical value of U. sagittifolia as a source of natural enzyme inhibitors able to neutralize catalytically active B. atrox venom toxins and their toxic effects.

A comparative study of endogenous phospholipase A2 inhibitors in the serum of Brazilian pit vipers

This work compared the presence of phospholipase A₂ inhibitors (PLIs) in the serum of 19 snake species maintained at Instituto Butantan to better understand the mechanisms of venom resistance in snakes and improve the treatment of snakebite. PLI was isolated from blood of 19 snake species by one-step chromatography and identified in all samples, besides its identity was confirmed through the interaction with both phospholipase A₂ and anti-γPLI. These findings highlight the diversity of snake serum PLIs and emphasize the importance of structure-function studies.

Local inflammatory mediators alterations induced by Daboia siamensis venom

The ability of Russell's viper (Daboia siamensis) venom (total RVV) and phospholipase A₂ (purified PLA₂) to induce the local pathological effects were investigated by the local inflammatory events and the release of inflammatory mediators. Both 0.5 μg of total RVV/mouse and 0.15 μg of purified PLA₂/mouse were administered via intra-peritoneal injection. After 30 min, 1 h, 2 h, and 4 h incubation time, the peritoneal cavity was flooded with normal saline and the total leukocytes were collected. The eicosanoids (lipid mediators) and the leukocyte expression of cyclooxygenase (COX-1 and COX-2) were investigated by ELISA assay and western blotting, respectively. The amounts of total leukocytes were increased from 30 min to 2 h, then decreased at 4 h, by both total RVV and purified PLA₂. Both treatments also induced the expression of COX-2 which was increased at 2 h and then decreased at 4 h, whereas only purified PLA₂ induced the expression level of a COX-1 protein which was increased at 30 min, then constantly expressed until 4 h. In addition, total RVV and purified PLA₂ caused the release of the eicosanoids; PGE₂, TXB₂, and LTB₄, which reached the peak after 2 h. The findings of this study indicate that purified PLA₂ has the potential effects to induce the local inflammation relating the amounts of leukocytes cells, lipid mediators and COX-2 more than the total RVV.

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Purified phospholipase A₂ or the venom could induce eicosanoids and cyclooxygenase-2 expression relating to leukocytes cells.

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Thromboxane B₂ could be the important mediator induced by Russell's viper venom and purified phospholipase A₂.

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Russell's viper venom and purified phospholipase A₂ involved the cyclooxygenase-2 expression, but not cyclooxygenase-1.

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The purified phospholipase A₂ showed more predominant inflammatory response at site than total Russell's viper venom.

BoaγPLI from Boa constrictor Blood is a Broad-Spectrum Inhibitor of Venom PLA2 Pathophysiological Actions

The use of venom in predation exerts a corresponding selection pressure for the evolution of venom resistance. One of the mechanisms related to venom resistance in animals (predators or prey of snakes) is the presence of molecules in the blood that can bind venom toxins, and inhibit their pharmacological effects. One such toxin type are venom phospholipase A₂s (PLA₂s), which have diverse effects including anticoagulant, myotoxic, and neurotoxic activities. BoaγPLI isolated from the blood of Boa constrictor has been previously shown to inhibit venom PLA₂s that induced myotoxic and edematogenic activities. Recently, in addition to its previously described and very potent neurotoxic effect, the venoms of American coral snakes (Micrurus species) have been shown to have anticoagulant activity via PLA₂ toxins. As coral snakes eat other snakes as a major part of their diet, neonate Boas could be susceptible to predation by this sympatric species. Thus, this work aimed to ascertain if BoaγPLI provided a protective effect against the anticoagulant toxicity of venom from the model species Micrurus laticollaris in addition to its ability shown previously against other toxin types. Using a STA R Max coagulation analyser robot to measure the effect upon clotting time, and TEG5000 thromboelastographers to measure the effect upon clot strength, we evaluated the ability of BoaγPLI to inhibit M. laticollaris venom. Our results indicate that BoaγPLI is efficient at inhibiting the M. laticollaris anticoagulant effect, reducing the time of coagulation (restoring them closer to non-venom control values) and increasing the clot strength (restoring them closer to non-venom control values). These findings demonstrate that endogenous PLA₂ inhibitors in the blood of non-venomous snakes are multi-functional and provide broad resistance against a myriad of venom PLA₂-driven toxic effects including coagulotoxicity, myotoxicity, and neurotoxicity. This novel form of resistance could be evidence of selective pressures caused by predation from venomous snakes and stresses the need for field-based research aimed to expand our understanding of the evolutionary dynamics of such chemical arms race.

Moringa oleifera leaf fractions attenuated Naje haje venom-induced cellular dysfunctions via modulation of Nrf2 and inflammatory signalling pathways in rats

Naja haje envenoming could activate multiple pathways linked to haematotoxic, neurological, and antioxidant systems dysfunctions. Moringa oleifera has been used in the management of different snake venom-induced toxicities, but there is no scientific information on its antivenom effects against Naja haje. This study thus, investigated the antivenom activities of different extract partitions of M. oleifera leaves against N. haje envenoming. Forty five male rats were divided into nine groups (n = 5). Groups 2 to 9 were envenomed with 0.025 mg/kg (LD50) of N . haje venom while group 1 was given saline. Group 2 was left untreated, while group 3 was treated with polyvalent antivenom, groups 4, 6 and 8 were treated with 300 mg/kg-1 of N-hexane, ethylacetate and ethanol partitions of M. oleifera, respectively. Groups 5, 7 and 9 were also treated with 600 mgkg-1of the partitions, respectively. Ethanol extract and ethyl acetate partition of M. oleifera significantly improved haematological indices following acute anaemia induced by the venom. Likewise, haemorrhagic, haemolytic and anti-coagulant activities of N. haje venom were best inhibited by ethanol partition. Envenoming significantly down-regulated Nuclear factor erythroid 2-related factor 2 (Nrf2) with the consequent elevation of antioxidant enzymes activities in the serum and brain. Treatment with extract partitions however, elevated Nrf2 levels while normalising antioxidant enzyme activities. Furthermore, there were reduction in levels of pro-inflammatory cytokines (TNF-α and interleukin-1β) in tissues of treated envenomed rats. This study concludes that ethanol partition of M. oleifera was most effective against N. haje venom and could be considered as a potential source for antivenom metabolites.

Chemotaxonomy of the ethnic antidote Aristolochia indica for aristolochic acid content: Implications of anti-phospholipase activity and genotoxicity study

ETHNOPHARMACOLOGICAL RELEVANCE

Aristolochia indica L. (Aristolochiaceae) is a common medicinal plant described in many traditional medicine as well as in Ayurveda used against snakebites. Besides, the plant has also been reported traditionally against fever, rheumatic arthritis, madness, liver ailments, dyspepsia, oedema, leishmaniasis, leprosy, dysmenorrhoea, sexual diseases etc. The plant is known to contain its major bioactive constituent aristolochic acid (AA) known for its anti-snake venom, abortifacient, antimicrobial and antioxidant properties.

MATERIALS AND METHODS

This present work describes a validated, fast and reproducible high performance thin layer chromatography (HPTLC) method to estimate AA from the roots of 20 chemotypes of A. indica procured from 20 diverse geographical locations from the state of West Bengal, India. Further, an evidence-based approach was adopted to investigate the reported anti-venom activity of the aqueous extracts of the A. indica roots by assessing its phospholipase A₂ (PLA₂) inhibitory properties since PLA₂ is a major component of many snake-venoms. Finally, the cytotoxicity and genotoxicity of the aqueous root extract of the Purulia (AI 1) chemotype were assessed at various concentrations using Allium cepa root meristematic cells.

RESULTS

The highest amount of AA (7643.67 μg/g) was determined in the roots of A. indica chemotype collected from Purulia district followed by the chemotypes collected from Murshidabad, Jalpaiguri and Birbhum districts (7398.34, 7345.09 and 6809.97 μg/g respectively). This study not only determines AA in the plants to select pharmacologically elite chemotypes of A. indica, but it also identifies high AA producing A. indica for further domestication and propagation of the plants for pharmacological and industrial applications. The method was validated via analyzing inter-day and intra-day precision, repeatability, reproducibility, instrumental precision, limit of detection (LOD) and limit of quantification (LOQ) and specificity. Chemotypes with high AA content exhibited superior anti-PLA₂ activity by selectively inhibiting human-group PLA₂. Moreover, A. indica root extract significantly inhibited mitosis in Allium cepa root tips as a potent clastogen.

CONCLUSIONS

The present quick, reproducible and validated HPTLC method provides an easy tool to determine AA in natural A. indica plant populations as well as in food and dietary supplements, a potential antivenin at one hand and a possible cause of aristolochic acid nephropathy (AAN) at another. Besides, the cytotoxic and mitotoxic properties of the root extracts should be used with caution especially for oral administration.

Ethnopharmacological Use and Biological Activities of Tragia involucrata L

Plants have been utilized as medicines to treat various ailments since ancient times. Formulations made by plant materials have been used in traditional, complementary, and alternative medicine and remain widespread in both developing and developed countries. In developing countries, traditional medicines are widely practiced due to its accessibility and affordability, while in developed countries, complementary and alternative medicine are widely popular due to the adverse effects of chemical drugs. Tragia involucrata Linn. (family: Euphorbiaceae) is a highly used medicinal plant used in both Sri Lankan and Indian traditional medical systems. Since this plant is a weed, it is being extensively destroyed due to the lack of knowledge regarding the medicinal value of this plant. Hence, the objective of this study was to collect data on the medicinal value of this plant by correlating its scientifically validated biological activities with its ethnopharmacological uses. An attempt was made to gather as much information available regarding the ethnopharmacological uses and scientifically validated biological activities of Tragia involucrata through authentic traditional texts, scientific journals, and other authentic texts regarding medicinal plants. Thus, the review provides an insight to the capability of Tragia involucrata to be used as a monoherbal formulation for diseases pertaining to multiple systems of the body. With all the scientifically validated biological activities and the ethnopharmacological uses, Tragia involucrata may qualify as a potent candidate to be developed into a phytomedicine to be utilized as both a preventive and as a therapeutic agent.

Green synthesis of silver nanoparticles using Indian male fern (Dryopteris Cochleata), operational parameters, characterization and bioactivity on Naja naja venom neutralization

Snakebite is considered as one of the acute severe medical problems across the world. Snake venoms composed of various group of toxins, enzymes and non-toxic enzymes. Phospholipases A₂ present in Naja naja snake venom plays a significant role in lipid signalling and contributes to different inflammation in the human body. Dryopteris cochleata rhizomes have antioxidant, antimicrobial property and used to treat lesions, gonorrhoea, sores, muscular pain, rheumatic and also useful in dog and snake bites. In this study, Indian male fern D. cochleata rhizomes have been used for green synthesis of silver nanoparticles with the aim to increase the bioactivity of plant extract and to evaluate N. naja snake venom inhibition activity of prepared nanoparticles. Green synthesized nanoparticles were characterized with the help of ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray powder diffraction and atomic force microscopy. Naja naja venom inhibition activity of nanoparticles was performed using in vitro phospholipases A₂ assay and tissue damage activity. The results showed that surface plasmon resonance maxima peaks of nanoparticles were observed at 424 nm. Average particle size was around 35 nm, with a spherical shape. Neutralization results exhibited that synthesized silver nanoparticles from D. cochleata decreased percentage of tissue damage, resulting in significant inhibition of phospholipase A₂ and N. naja snake venom. Results concluded that green synthesized silver nanoparticles from D. cochleata rhizome neutralize N. naja snake venom activity.

BoaγPLI: Structural and functional characterization of the gamma phospholipase A2 plasma inhibitor from the non-venomous Brazilian snake Boa constrictor

Plasma in several organisms has components that promote resistance to envenomation by inhibiting specific proteins from snake venoms, such as phospholipases A2 (PLA2s). The major hypothesis for inhibitor's presence would be the protection against self-envenomation in venomous snakes, but the occurrence of inhibitors in non-venomous snakes and other animals has opened new perspectives for this molecule. Thus, this study showed for the first time the structural and functional characterization of the PLA2 inhibitor from the Boa constrictor serum (BoaγPLI), a non-venomous snake that dwells extensively the Brazilian territory. Therefore, the inhibitor was isolated from B. constrictor serum, with 0.63% of recovery. SDS-PAGE showed a band at ~25 kDa under reducing conditions and ~20 kDa under non-reducing conditions. Chromatographic analyses showed the presence of oligomers formed by BoaγPLI. Primary structure of BoaγPLI suggested an estimated molecular mass of 22 kDa. When BoaγPLI was incubated with Asp-49 and Lys-49 PLA2 there was no severe change in its dichroism spectrum, suggesting a non-covalent interaction. The enzymatic assay showed a dose-dependent inhibition, up to 48.2%, when BoaγPLI was incubated with Asp-49 PLA2, since Lys-49 PLA2 has a lack of enzymatic activity. The edematogenic and myotoxic effects of PLA2s were also inhibited by BoaγPLI. In summary, the present work provides new insights into inhibitors from non-venomous snakes, which possess PLIs in their plasma, although the contact with venom is unlikely.

Free-radical and biochemical reactions involving polar part of glycerophospholipids

The review summarizes and critically discusses data on biochemical and free-radical transformations of glycerophospholipids. The results presented therein demonstrate that hydroxyl-containing glycerophospholipids, such as cardiolipin, lyso-lipids and others, can undergo fragmentation upon interaction with radical agents forming the biologically active products. Hydrolysis of glycerophospholipids catalyzed by different phospholipases was shown to yield compounds, which can be involved in the free-radical fragmentation leading to significant changes in structures of original lipids.

Perspective on the Therapeutics of Anti-Snake Venom

Snakebite envenomation is a life-threatening disease that was recently re-included as a neglected tropical disease (NTD), affecting millions of people in tropical and subtropical areas of the world. Improvement in the therapeutic approaches to envenomation is required to palliate the morbidity and mortality effects of this NTD. The specific therapeutic treatment for this NTD uses snake antivenom immunoglobulins. Unfortunately, access to these vital drugs is limited, principally due to their cost. Different ethnic groups in the affected regions have achieved notable success in treatment for centuries using natural sources, especially plants, to mitigate the effects of snake envenomation. The ethnopharmacological approach is essential to identify the potential metabolites or derivatives needed to treat this important NTD. Here, the authors describe specific therapeutic snakebite envenomation treatments and conduct a review on different strategies to identify the potential agents that can mitigate the effects of the venoms. The study also covers an increased number of literature reports on the ability of natural sources, particularly plants, to treat snakebites, along with their mechanisms, drawbacks and future perspectives.

Pharmacological characterization of cnidarian extracts from the Caribbean Sea: evaluation of anti-snake venom and antitumor properties

BACKGROUND

Cnidarians produce toxins, which are composed of different polypeptides that induce pharmacological effects of biotechnological interest, such as antitumor, antiophidic and anti-clotting activities. This study aimed to evaluate toxicological activities and potential as antitumor and antiophidic agents contained in total extracts from five cnidarians: Millepora alcicornis, Stichodactyla helianthus, Plexaura homomalla, Bartholomea annulata and Condylactis gigantea (total and body wall).

METHODS

The cnidarian extracts were evaluated by electrophoresis and for their phospholipase, proteolytic, hemorrhagic, coagulant, fibrinogenolytic, neuromuscular blocking, muscle-damaging, edema-inducing and cytotoxic activities.

RESULTS

All cnidarian extracts showed indirect hemolytic activity, but only S. helianthus induced direct hemolysis and neurotoxic effect. However, the hydrolysis of NBD-PC, a PLA2 substrate, was presented only by the C. gigantea (body wall) and S. helianthus. The extracts from P. homomalla and S. helianthus induced edema, while only C. gigantea and S. helianthus showed intensified myotoxic activity. The proteolytic activity upon casein and fibrinogen was presented mainly by B. annulata extract and all were unable to induce hemorrhage or fibrinogen coagulation. Cnidarian extracts were able to neutralize clotting induced by Bothrops jararacussu snake venom, except M. alcicornis. All cnidarian extracts were able to inhibit hemorrhagic activity induced by Bothrops moojeni venom. Only the C. gigantea (body wall) inhibited thrombin-induced coagulation. All cnidarian extracts showed antitumor effect against Jurkat cells, of which C. gigantea (body wall) and S. helianthus were the most active; however, only C. gigantea (body wall) and M. alcicornis were active against B16F10 cells.

CONCLUSION

The cnidarian extracts analyzed showed relevant in vitro inhibitory potential over the activities induced by Bothrops venoms; these results may contribute to elucidate the possible mechanisms of interaction between cnidarian extracts and snake venoms.

Developing Small Molecule Therapeutics for the Initial and Adjunctive Treatment of Snakebite

The World Health Organization (WHO) recently added snakebite envenoming to the priority list of Neglected Tropical Diseases (NTD). It is thought that ~75% of mortality following snakebite occurs outside the hospital setting, making the temporal gap between a bite and antivenom administration a major therapeutic challenge. Small molecule therapeutics (SMTs) have been proposed as potential prereferral treatments for snakebite to help address this gap. Herein, we discuss the characteristics, potential uses, and development of SMTs as potential treatments for snakebite envenomation. We focus on SMTs that are secretory phospholipase A2 (sPLA2) inhibitors with brief exploration of other potential drug targets on venom molecules.

Snake Venom PLA2, a Promising Target for Broad-Spectrum Antivenom Drug Development

Snakebite envenomation is a neglected global health problem, causing substantial mortality, disability, and psychological morbidity, especially in rural tropical and subtropical zones. Antivenin is currently the only specific medicine for envenomation. However, it is restricted by cold storage, snakebite diagnosis, and high price. Snake venom phospholipase A₂s (svPLA₂s) are found in all kinds of venomous snake families (e.g., Viperidae, Elapidae, and Colubridae). Along with their catalytic activity, svPLA₂s elicit a wide variety of pharmacological effects that play a pivotal role in envenomation damage. Hence, neutralization of the svPLA₂s could weaken or inhibit toxic damage. Here we overviewed the latest knowledge on the distribution, pathophysiological effects, and inhibitors of svPLA₂s to elucidate the potential for a novel, wide spectrum antivenom drug targeting svPLA₂s.

Non-Clinical Studies for Evaluation of 8-C-Rhamnosyl Apigenin Purified from Peperomia obtusifolia against Acute Edema

Compound 8-C-rhamnosyl apigenin (8CR) induced a moderate reduction in the enzymatic activity of secretory phospholipase A2 (sPLA2) from Crotalus durissus terrificus and cytosolic phospholipase A2 (cPLA2), but the compound also significantly inhibited the enzymatic activity of the enzyme cyclooxygenase. In vitro assays showed that the compound induced a slight change in the secondary structure of sPLA2 from Crotalus durissus terrificus snake venom. In vivo assays were divided into two steps. In the first step, the 8CR compound was administered by intraperitoneal injections 30 min prior to administration of sPLA2. In this condition, 8CR inhibited edema and myonecrosis induced by the sPLA2 activity of Crotalus durissus terrificus in a dose-dependent manner by decreasing interleukin-1β (IL-1β), tumor necrosis factor α (TNF-α), prostaglandin E2 (PGE2), and lipid peroxidation. This has been demonstrated by monitoring the levels of malondialdehyde (MDA) in rat paws after the course of edema induced by sPLA2. These results, for the first time, show that sPLA2 of Crotalus durissus terrificus venom induces massive muscle damage, as well as significant edema by mobilization of cyclooxygenase enzymes. Additionally, its pharmacological activity involves increased lipid peroxidation as well as TNF-α and IL-1β production. Previous administration by the peritoneal route has shown that dose-dependent 8CR significantly decreases the enzymatic activity of cyclooxygenase enzymes. This resulted in a decrease of the amount of bioactive lipids involved in inflammation; it also promoted a significant cellular protection against lipid peroxidation. In vivo experiments performed with 8CR at a concentration adjusted to 200 μg (8 mg/kg) of intraperitoneal injection 15 min after sPLA2 injection significantly reduced sPLA2 edema and the myotoxic effect induced by sPLA2 through the decrease in the enzymatic activity of cPLA2, cyclooxygenase, and a massive reduction of lipid peroxidation. These results clearly show that 8CR is a potent anti-inflammatory that inhibits cyclooxygenase-2 (COX-2), and it may modulate the enzymatic activity of sPLA2 and cPLA2. In addition, it was shown that Crotalus durissus terrificus sPLA2 increases cell oxidative stress during edema and myonecrosis, and the antioxidant properties of the polyphenolic compound may be significant in mitigating the pharmacological effect induced by sPLA2 and other snake venom toxins.

A Review on Venom Enzymes Neutralizing Ability of Secondary Metabolites from Medicinal Plants

OBJECTIVES

Medicinal plants are vital sources of bioactive compounds that are useful for the treatment of patients with snake bites or are indirectly applicable for boosting the effects of conventional serum therapy. These plants are being used traditionally by local healers and tribes for the treatment of patients with snake bites and therefore can be used as an alternative against snake envenomation. Scientifically, using the secondary metabolites of plants to neutralize venom enzymes has an extra benefit of being based on traditional knowledge; also, the use of such metabolites for the treatment of patients with snake bites is cheaper and the treatment can be started sooner.

METHODS

All the available information on various secondary metabolites exhibiting venom neutralizing ability were collected via electronic search (using Google books, Pubmed, SciFinder, Scirus, Google Scholar, and Web of Science) and articles of peer-reviewed journals.

RESULTS

Recent interest in different plant has focused on isolating and identifying of different phytoconstituents that exhibit Phospholipase A2 activity and other venom enzyme neutralizing ability. In this support convincing evidence in experimental animal models are available.

CONCLUSION

Secondary metabolites are naturally present, have no side effect, are stable for a long time, can be easily stored, and can neutralize a wide range of snake enzymes, such as phospholipase A2, hyaluronidase, protease, L-amino acid oxidase, 5'nucleotidase, etc. The current review presents a compilation of important plant secondary metabolites that are effective against snake venom due to enzyme neutralization.

Phospholipase A2 Inhibitor from Crotalus durissus terrificus rattlesnake: Effects on human peripheral blood mononuclear cells and human neutrophils cells

Crotalus Neutralizing Factor (CNF) is an inhibitor of phospholipase A₂ (PLA₂), present in the blood plasma of Crotalus durissus terrificus snake. This inhibitor neutralizes the lethal and enzymatic activity of crotoxin, the main neurotoxin from this venom. In this study, we investigated the effects of CNF on the functionality of human peripheral blood mononuclear cells (PBMCs) and human neutrophils. The following parameters were evaluated: viability and proliferation, chemotaxis, cytokines and LTB₄ production, cytosolic PLA₂s activity, myeloperoxidase (MPO) and superoxide anion (O₂^-) production. CNF showed no toxicity on PBMCs or neutrophils, and acts by stimulating the release of TNF-α and LTB₄, but neither stimulates IL-10 and IL-2 nor affects PBMCs proliferation and O₂^- release. In neutrophils, CNF induces chemotaxis but does not induce the release of both MPO and O₂^-. However, it induces LTB₄ and IL-8 production. These data show the influence of CNF on PBMCs' function by inducing TNF-α and LTB₄ production, and on neutrophils, by stimulating chemotaxis and LTB₄ production, via cytosolic PLA₂ activity, and IL-8 release. The inflammatory profile produced by CNF is shown for the first time. Our present results suggest that CNF has a role in activation of leukocytes and exert proinflammatory effects on these cell.

Melatonin inhibits snake venom and antivenom induced oxidative stress and augments treatment efficacy

Snakebite is a neglected health hazard. Its patho-physiology has largely been focused on systemic and local toxicities; whereas, venom and antivenom induced oxidative stress has long been ignored. Antivenom therapy although neutralizes venom lethality and saves many lives, remains ineffective against oxidative stress. This prompted us to complement antivenom with an antioxidant molecule melatonin that would protect against oxidative stress and increase the efficacy of the existing snakebite therapy. Here we show that D. russelli and E. carinatus venoms induce strong oxidative stress that persists even after antivenom administration in mice model. Additionally, antivenoms also induce oxidative stress. Polyvalent antivenom induce more oxidative stress than monovalent antivenom. Strikingly, antivenom and melatonin together not only inhibit venom and antivenom induced oxidative stress but also significantly reduce the neutralizing antivenom dose. This study provides a therapeutic potential for enhancing the existing snakebite therapy. The combined treatment of antivenom+melatonin would prevent the upsurge of oxidative stress as well as minimize the antivenom load. Thus the investigation offers immense scope for physicians and toxinologists to reinvestigate, design new strategies and think beyond the conventional mode of antivenom therapy.

Protective Effect of the Plant Extracts of Erythroxylum sp. against Toxic Effects Induced by the Venom of Lachesis muta Snake

Snake venoms are composed of a complex mixture of active proteins that induce toxic effects, such as edema, hemorrhage, and death. Lachesis muta has the highest lethality indices in Brazil. In most cases, antivenom fails to neutralize local effects, leading to disabilities in victims. Thus, alternative treatments are under investigation, and plant extracts are promising candidates. The objective of this work was to investigate the ability of crude extracts, fractions, or isolated products of Erythroxylum ovalifolium and Erythroxylum subsessile to neutralize some toxic effects of L. muta venom. All samples were mixed with L. muta venom, then in vivo (hemorrhage and edema) and in vitro (proteolysis, coagulation, and hemolysis) assays were performed. Overall, crude extracts or fractions of Erythroxylum spp. inhibited (20%-100%) toxic effects of the venom, but products achieved an inhibition of 4%-30%. However, when venom was injected into mice before the plant extracts, hemorrhage and edema were not inhibited by the samples. On the other hand, an inhibition of 5%-40% was obtained when extracts or products were given before venom injection. These results indicate that the extracts or products of Erythroxylum spp. could be a promising source of molecules able to treat local toxic effects of envenomation by L. muta venom, aiding in the development of new strategies for antivenom treatment.

High-affinity selective inhibitor against phospholipase A2 (PLA2): a computational study

Phospholipase A2 (PLA2) is the most abundant protein found in snake venom. PLA2 induces a variety of pharmacological effects such as neurotoxicity, myotoxicity and cardiotoxicity as well as anticoagulant, hemolytic, anti-platelet, hypertensive, hemorrhagic and edema inducing effects. In this study, the three dimensional structure of PLA2 of Naja sputatrix (Malayan spitting cobra) was modeled by I-TASSER, SWISS-MODEL, PRIME and MODELLER programs. The best model was selected based on overall stereo-chemical quality. Further, molecular dynamics simulation was performed to know the stability of the modeled protein using Gromacs software. Average structure was generated during the simulation period of 10 ns. High throughput virtual screening was employed through different databases (Asinex, Hit finder, Maybridge, TOSLab and ZINC databases) against PLA2. The top seven compounds were selected based on the docking score and free energy binding calculations. These compounds were analyzed by quantum polarized ligand docking, induced fit docking and density functional theory calculation. Furthermore, the stability of lead molecules in the active site of PLA2 was employed by MD simulation. The results show that selected lead molecules were highly stable in the active site of PLA2.

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.

Production of high titre antibody response against Russell's viper venom in mice immunized with ethanolic extract of fruits of Piper longum L. (Piperaceae) and piperine

Piper longum L. fruits have been traditionally used against snakebites in north-eastern and southern region of India. The aim of the study was to assess the production of antibody response against Russell's viper venom in mice after prophylactic immunization with ethanolic extract of fruits of Piper longum L. and piperine. The mice sera were tested for the presence of antibodies against Russell's viper venom by in vitro lethality neutralization assay and in vivo lethality neutralization assay. Polyvalent anti-snake venom serum (antivenom) manufactured by Haffkine Bio-Pharmaceutical Corporation Ltd. was used as standard. Further confirmation of presence of antibodies against the venom in sera of mice immunized with PLE and piperine was done using indirect enzyme-linked immunosorbent assay (ELISA) and double immunodiffusion test. Treatment with PLE-treated mice serum and piperine-treated mice serum was found to inhibit the lethal action of venom both in the in vitro lethality neutralization assay and in vivo lethality neutralization assay. ELISA testing indicated that there were significantly high (p<0.01) levels of cross reactions between the PLE and piperine treated mice serum and the venom antigens. In double immunodiffusion test, a white band was observed between the two wells of antigen and antibodies for both the PLE-treated and piperine-treated mice serum. Thus it can be concluded that immunization with ethanolic extract of fruits of Piper longum and piperine produced a high titre antibody response against Russell's viper venom in mice. The antibodies against PLE and piperine could be useful in antivenom therapy of Russell's viper bites. PLE and piperine may also have a potential interest in view of the development of antivenom formulations used as antidote against snake bites.

Inhibitory effect of plant Manilkara subsericea against biological activities of Lachesis muta snake venom

Snake venom is composed of a mixture of substances that caused in victims a variety of pathophysiological effects. Besides antivenom, literature has described plants able to inhibit injuries and lethal activities induced by snake venoms. This work describes the inhibitory potential of ethanol, hexane, ethyl acetate, or dichloromethane extracts and fractions from stem and leaves of Manilkara subsericea against in vivo (hemorrhagic and edema) and in vitro (clotting, hemolysis, and proteolysis) activities caused by Lachesis muta venom. All the tested activities were totally or at least partially reduced by M. subsericea. However, when L. muta venom was injected into mice 15 min first or after the materials, hemorrhage and edema were not inhibited. Thus, M. subsericea could be used as antivenom in snakebites of L. muta. And, this work also highlights Brazilian flora as a rich source of molecules with antivenom properties.

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.

Anti-snake venom activities of ethanolic extract of fruits of Piper longum L. (Piperaceae) against Russell's viper venom: characterization of piperine as active principle

ETHNOPHARMACOLOGICAL RELEVANCE

Piper longum L. fruits have been traditionally used against snakebites in north-eastern and southern region of India.

AIM OF THE STUDY

To examine the ability of ethanolic extract of fruits of Piper longum L., Piperaceae (PLE) and piperine, one of the main active principles of Piper longum, to inhibit the Russell's viper (Doboia russelii, Viperidae) snake venom activities.

MATERIALS AND METHODS

Anti-snake venom activities of ethanolic extract of fruits of Piper longum L. (Piperaceae) and piperine against Russell's viper venom was studied in embryonated fertile chicken eggs, mice and rats by using various models as follows: inhibition of venom lethal action, inhibition of venom haemorrhagic action (in vitro), inhibition of venom haemorrhagic action (in vivo), inhibition of venom necrotizing action, inhibition of venom defibrinogenating action, inhibition of venom induced paw edema, inhibition of venom induced mast cell degranulation, creatine kinase assay and assay for catalase activity.

RESULTS

PLE was found to inhibit the venom induced haemorrhage in embryonated fertile chicken eggs. Administration of PLE and piperine significantly (p<0.01) inhibited venom induced lethality, haemorrhage, necrosis, defibrinogenation and inflammatory paw edema in mice in a dose dependent manner. PLE and piperine also significantly (p<0.01) reduced venom induced mast cell degranulation in rats. Venom induced decrease in catalase enzyme levels in mice kidney tissue and increase in creatine kinase enzyme levels in mice serum were significantly (p<0.01) reversed by administration of both PLE and piperine.

CONCLUSIONS

PLE possesses good anti-snake venom properties and piperine is one of the compounds responsible for the effective venom neutralizing ability of the plant.

Viper venom induced inflammation with Montivipera xanthina (Gray, 1849) and the anti-snake venom activities of Artemisia absinthium L. in rat

The present study was conducted to explore the characterization of Montivipera xanthina crude venom partially by in vitro and in vivo and the anti-snake venom activities of Artemisia absinthium L. in comparison with carrageenan-induced acute inflammation model in rats. The LD50 value was estimated as 8.78 mg/kg within 24 h by different venom doses administrated intraperitoneally in mice. The IC50 value was 0.43 ± 0.18 μg/ml after 48 h treatment while the calculated value was 0.73 ± 0.10 μg/ml for the culture media totally refreshed after 2 h treatment with venom. Wistar rats were treated intraperitoneally with A. absinthium extract, 30 min before venom or carrageenan was injected subplantarly into the left hind paw. Intraperitoneal administration of 25 and 50 mg/kg extract was inhibited venom induced paw swelling at 0.5, 1, 2 and 3 h (p < 0.05) while 12.5, 25 and 50 mg/kg extract treatment was inhibited carrageenan-induced paw swelling at 2, 3, 4 and 5 h (p < 0.05). In conclusion, the in vivo toxicity and inflammatory actions and in vitro cytotoxic actions of crude M. xanthina venom were performed as a first report and inhibition of venom-induced inflammation by methanolic extract of A. absinthium was described.

Humanized-single domain antibodies (VH/VHH) that bound specifically to Naja kaouthia phospholipase A2 and neutralized the enzymatic activity

Naja kaouthia (monocled cobra) venom contains many isoforms of secreted phospholipase A2 (sPLA₂). The PLA₂ exerts several pharmacologic and toxic effects in the snake bitten subject, dependent or independent on the enzymatic activity. N. kaouthia venom appeared in two protein profiles, P3 and P5, after fractionating the venom by ion exchange column chromatography. In this study, phage clones displaying humanized-camel single domain antibodies (VH/V_HH) that bound specifically to the P3 and P5 were selected from a humanized-camel VH/V_HH phage display library. Two phagemid transfected E. coli clones (P3-1 and P3-3) produced humanized-V_HH, while another clone (P3-7) produced humanized-VH. At the optimal venom:antibody ratio, the VH/V_HH purified from the E. coli homogenates neutralized PLA₂ enzyme activity comparable to the horse immune serum against the N. kaouthia holo-venom. Homology modeling and molecular docking revealed that the VH/V_HH covered the areas around the PLA₂ catalytic groove and inserted their Complementarity Determining Regions (CDRs) into the enzymatic cleft. It is envisaged that the VH/V_HH would ameliorate/abrogate the principal toxicity of the venom PLA₂ (membrane phospholipid catabolism leading to cellular and subcellular membrane damage which consequently causes hemolysis, hemorrhage, and dermo-/myo-necrosis), if they were used for passive immunotherapy of the cobra bitten victim. The speculation needs further investigations.