Structural and functional studies of a bothropic myotoxin complexed to rosmarinic acid: new insights into Lys49-PLA₂ inhibition

Inhibitors and activators for myotoxic phospholipase A2-like toxins from snake venoms - A structural overview

Snakebite envenomations result in acute and chronic physical and psychological health effects on their victims, leading to a substantial socio-economic burden in tropical and subtropical countries. Local necrosis is one of the serious effects caused by envenomation, primarily induced by snake venoms from the Viperidae family through the direct action of components collectively denominated as myotoxins, including the phopholipase A2-like (PLA2-like) toxins. Considering the limitations of antivenoms in preventing the rapid development of local tissue damage caused by envenomation, the use of small molecule therapeutics has been suggested as potential first-aid treatments or as adjuvants to antivenom therapy. In this review, we provide an overview of the structural interactions of molecules exhibiting inhibitory activity toward PLA2-like toxins. Additionally, we discuss the implications for the myotoxic mechanism of PLA2-like toxins and the molecules involved in their activation, highlighting key differences between activators and inhibitors. Finally, we integrate all these results to propose a classification of inhibitors into three different classes and five sub-classes. Taking into account the structural and affinity information, we compare the different inhibitors/ligands to gain a deeper understanding of the structural basis for the effective inhibition of PLA2-like toxins. By offering these insights, we aim to contribute to the search for new and efficient inhibitor molecules to complement and improve current therapy by conventional antivenoms.

Tissue damaging toxins in snake venoms: mechanisms of action, pathophysiology and treatment strategies

Snakebite envenoming is an important public health issue responsible for mortality and severe morbidity. Where mortality is mainly caused by venom toxins that induce cardiovascular disturbances, neurotoxicity, and acute kidney injury, morbidity is caused by toxins that directly or indirectly destroy cells and degrade the extracellular matrix. These are referred to as 'tissue-damaging toxins' and have previously been classified in various ways, most of which are based on the tissues being affected (e.g., cardiotoxins, myotoxins). This categorisation, however, is primarily phenomenological and not mechanistic. In this review, we propose an alternative way of classifying cytotoxins based on their mechanistic effects rather than using a description that is organ- or tissue-based. The mechanisms of toxin-induced tissue damage and their clinical implications are discussed. This review contributes to our understanding of fundamental biological processes associated with snakebite envenoming, which may pave the way for a knowledge-based search for novel therapeutic options.

BthTX-I, a phospholipase A2-like toxin, is inhibited by the plant cinnamic acid derivative: chlorogenic acid

Snakebite is a significant health concern in tropical and subtropical regions, particularly in Africa, Asia, and Latin America, resulting in more than 2.7 million envenomations and an estimated one hundred thousand fatalities annually. The Bothrops genus is responsible for the majority of snakebite envenomings in Latin America and Caribbean countries. Accidents involving snakes from this genus are characterized by local symptoms that often lead to permanent sequelae and death. However, specific antivenoms exhibit limited effectiveness in inhibiting local tissue damage. Phospholipase A2-like (PLA2-like) toxins emerge as significant contributors to local myotoxicity in accidents involving Bothrops species. As a result, they represent a crucial target for prospective treatments. Some natural and synthetic compounds have shown the ability to reduce or abolish the myotoxic effects of PLA2-like proteins. In this study, we employed a combination approach involving myographic, morphological, biophysical and bioinformatic techniques to investigate the interaction between chlorogenic acid (CGA) and BthTX-I, a PLA2-like toxin. CGA provided a protection of 71.8% on muscle damage in a pre-incubation treatment. Microscale thermophoresis and circular dichroism experiments revealed that CGA interacted with the BthTX-I while preserving its secondary structure. CGA exhibited an affinity to the toxin that ranks among the highest observed for a natural compound. Bioinformatics simulations indicated that CGA inhibitor binds to the toxin's hydrophobic channel in a manner similar to other phenolic compounds previously investigated. These findings suggest that CGA interferes with the allosteric transition of the non-activated toxin, and the stability of the dimeric assembly of its activated state.

Structural basis of the myotoxic inhibition of the Bothrops pirajai PrTX-I by the synthetic varespladib

Varespladib (LY315920) is a potent inhibitor of human group IIA phospholipase A₂ (PLA₂) originally developed to control inflammatory cascades of diseases associated with high or dysregulated levels of endogenous PLA₂. Recently, varespladib was also found to inhibit snake venom PLA₂ and PLA₂-like toxins. Herein, ex vivo neuromuscular blocking activity assays were used to test the inhibitory activity of varespladib. The binding affinity between varespladib and a PLA₂-like toxin was quantified and compared with other potential inhibitors for this class of proteins. Crystallographic and bioinformatic studies showed that varespladib binds to PrTX-I and BthTX-I into their hydrophobic channels, similarly to other previously characterized PLA₂-like myotoxins. However, a new finding is that an additional varespladib binds to the MDiS region, a particular site that is related to muscle cell disruption by these toxins. The present results further advance the characterization of the molecular interactions of varespladib with PLA₂-like myotoxins and provide additional evidence for this compound as a promising inhibitor candidate for different PLA₂ and PLA₂-like toxins.

Structural and functional studies of a snake venom phospholipase A2-like protein complexed to an inhibitor from Tabernaemontana catharinensis

Snake envenomation is an ongoing global health problem and tropical neglected disease that afflicts millions of people each year. The only specific treatment, antivenom, has several limitations that affects its proper distribution to the victims and its efficacy against local effects, such as myonecrosis. The main responsible for this consequence are the phospholipases A₂ (PLA₂) and PLA₂-like proteins, such as BthTX-I from Bothrops jararacussu. Folk medicine resorts to plants such as Tabernaemontana catharinensis to palliate these and other snakebite effects. Here, we evaluated the effect of its root bark extract and one of its isolated compounds, 12-methoxy-4-methyl-voachalotine (MMV), against the in vitro paralysis and muscle damage induced by BthTX-I. Secondary and quaternary structures of BthTX-I were not modified by the interaction with MMV. Instead, this compound interacted in an unprecedented way with the region inside the toxin hydrophobic channel and promoted a structural change in Val31, loop 58-71 and Membrane Disruption Site. Thus, we hypothesize that MMV inhibits PLA₂-like proteins by preventing entrance of fatty acid into the hydrophobic channel. These data may explain the traditional use of T. catharinensis extract and confirm MMV as a promising candidate to complement antivenom or a structural guide to develop more effective inhibitors.

Lys49 myotoxins, secreted phospholipase A2-like proteins of viperid venoms: A comprehensive review

Muscle necrosis is a potential clinical complication of snakebite envenomings, which in severe cases can lead to functional or physical sequelae such as disability or amputation. Snake venom proteins with the ability to directly damage skeletal muscle fibers are collectively referred to as myotoxins, and include three main types: cytolysins of the "three-finger toxin" protein family expressed in many elapid venoms, the so-called "small" myotoxins found in a number of rattlesnake venoms, and the widespread secreted phospholipase A₂ (sPLA₂) molecules. Among the latter, protein variants that conserve the sPLA₂ structure, but lack such enzymatic activity, have been increasingly found in the venoms of many viperid species. Intriguingly, these sPLA₂-like proteins are able to induce muscle necrosis by a mechanism independent of phospholipid hydrolysis. They are commonly referred to as "Lys49 myotoxins" since they most often present, among other substitutions, the replacement of the otherwise invariant residue Asp49 of sPLA₂s by Lys. This work comprehensively reviews the historical developments and current knowledge towards deciphering the mechanism of action of Lys49 sPLA₂-like myotoxins, and points out main gaps to be filled for a better understanding of these multifaceted snake venom proteins, to hopefully lead to improved treatments for snakebites.

Anxiolytic and antidepressive potentials of rosmarinic acid: A review with a focus on antioxidant and anti-inflammatory effects

Depression and anxiety are the most prevalent neuropsychiatric disorders that have emerged as global health concerns. Anxiolytic and antidepressant drugs, such as benzodiazepines, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors, and tricyclics, are the first line used in treating anxiety and depression. Although these drugs lack efficacy and have a delayed response time and numerous side effects, their widespread abuse and market continue to grow. Over time, traditional practices using natural and phytochemicals as alternative therapies to chemical drugs have emerged to treat many pathological conditions, including anxiety and depression. Recent preclinical studies have demonstrated that the phenolic compound, rosmarinic acid, is effective against several neuropsychiatric disorders, including anxiety and depression. In addition, rosmarinic acid showed various pharmacological effects, such as cardioprotective, hepatoprotective, lung protective, antioxidant, anti-inflammatory, and neuroprotective effects. However, the potentialities of the use of rosmarinic acid in the treatment of nervous system-related disorders, such as anxiety and depression, are less or not yet reviewed. Therefore, the purpose of this review was to present several preclinical and clinical studies, when available, from different databases investigating the effects of rosmarinic acid on anxiety and depression. These studies showed that rosmarinic acid produces advantageous effects on anxiety and depression through its powerful antioxidant and anti-inflammatory properties. This review will examine and discuss the possibility that the anxiolytic and anti-depressive effects of rosmarinic acid could be associated with its potent antioxidant and anti-inflammatory activities.

Mechanistic Insights into Biological Activities of Polyphenolic Compounds from Rosemary Obtained by Inverse Molecular Docking

Rosemary (Rosmarinus officinalis L.) represents a medicinal plant known for its various health-promoting properties. Its extracts and essential oils exhibit antioxidative, anti-inflammatory, anticarcinogenic, and antimicrobial activities. The main compounds responsible for these effects are the diterpenes carnosic acid, carnosol, and rosmanol, as well as the phenolic acid ester rosmarinic acid. However, surprisingly little is known about the molecular mechanisms responsible for the pharmacological activities of rosemary and its compounds. To discern these mechanisms, we performed a large-scale inverse molecular docking study to identify their potential protein targets. Listed compounds were separately docked into predicted binding sites of all non-redundant holo proteins from the Protein Data Bank and those with the top scores were further examined. We focused on proteins directly related to human health, including human and mammalian proteins as well as proteins from pathogenic bacteria, viruses, and parasites. The observed interactions of rosemary compounds indeed confirm the beforementioned activities, whereas we also identified their potential for anticoagulant and antiparasitic actions. The obtained results were carefully checked against the existing experimental findings from the scientific literature as well as further validated using both redocking procedures and retrospective metrics.

BthTX-II from Bothrops jararacussu venom has variants with different oligomeric assemblies: An example of snake venom phospholipases A2 versatility

Phospholipases A₂ (PLA₂s) are found in almost every venomous snake family. In snakebites, some PLA₂s can quickly cause local myonecrosis, which may lead to permanent sequelae if antivenom is administered belatedly. They hydrolyse phospholipids in membranes through a catalytic calcium ions-dependent mechanism. BthTX-II is a basic PLA₂ and the second major component in the venom of Bothrops jararacussu. Herein, using the software SEQUENCE SLIDER, which integrates crystallographic, mass spectrometry and genetic data, we characterized the primary, tertiary and quaternary structure of two BthTX-II variants (called a and b), which diverge in 7 residues. Crystallographic structure BthTX-IIa is in a Tense-state with its distorted calcium binding loop buried in the dimer interface, contrarily, the novel BthTX-IIb structure is a monomer in a Relax-state with a fatty acid in the hydrophobic channel. Structural data in solution reveals that both variants are monomeric in neutral physiological conditions and mostly dimeric in an acidic environment, being catalytic active in both situations. Therefore, we propose two myotoxic mechanisms for BthTX-II, a catalytic one associated with the monomeric assembly, whereas the other has a calcium independent activity related to its C-terminal region, adopting a dimeric conformation similar to PLA₂-like proteins.

Evaluation of Protection by Caffeic Acid, Chlorogenic Acid, Quercetin and Tannic Acid against the In Vitro Neurotoxicity and In Vivo Lethality of Crotalus durissus terrificus (South American Rattlesnake) Venom

Systemic envenomation by Crotalus durissus terrificus (South American rattlesnake) can cause coagulopathy, rabdomyolysis, acute kidney injury, and peripheral neuromuscular blockade, the latter resulting in flaccid paralysis. Previous studies have shown that plant products such as tannic acid and theaflavin can protect against the neuromuscular blockade caused by C. d. terrificus venom in vitro. In this work, we used mouse-isolated phrenic nerve-diaphragm preparations to examine the ability of caffeic acid, chlorogenic acid, and quercetin to protect against C. d. terrificus venom-induced neuromuscular blockade in vitro. In addition, the ability of tannic acid to protect against the systemic effects of severe envenomation was assessed in rats. Preincubation of venom with caffeic acid (0.5 mg/mL), chlorogenic acid (1 mg/mL), or quercetin (0.5 mg/mL) failed to protect against venom (10 μg/mL)-induced neuromuscular blockade. In rats, venom (6 mg kg⁻¹, i.p.) caused death in ~8 h, which was prevented by preincubation of venom with tannic acid or the administration of antivenom 2 h post-venom, whereas tannic acid given 2 h post-venom prolonged survival (~18.5 h) but did not prevent death. Tannic acid (in preincubation protocols or given 2 h post-venom) had a variable effect on blood creatinine and urea and blood/urine protein levels and prevented venom-induced leukocytosis. Tannic acid attenuated the histological lesions associated with renal damage in a manner similar to antivenom. The protective effect of tannic acid appeared to be mediated by interaction with venom proteins, as assessed by SDS-PAGE. These findings suggest that tannic acid could be a potentially useful ancillary treatment for envenomation by C. d. terrificus.

The Search for Natural and Synthetic Inhibitors That Would Complement Antivenoms as Therapeutics for Snakebite Envenoming

A global strategy, under the coordination of the World Health Organization, is being unfolded to reduce the impact of snakebite envenoming. One of the pillars of this strategy is to ensure safe and effective treatments. The mainstay in the therapy of snakebite envenoming is the administration of animal-derived antivenoms. In addition, new therapeutic options are being explored, including recombinant antibodies and natural and synthetic toxin inhibitors. In this review, snake venom toxins are classified in terms of their abundance and toxicity, and priority actions are being proposed in the search for snake venom metalloproteinase (SVMP), phospholipase A2 (PLA2), three-finger toxin (3FTx), and serine proteinase (SVSP) inhibitors. Natural inhibitors include compounds isolated from plants, animal sera, and mast cells, whereas synthetic inhibitors comprise a wide range of molecules of a variable chemical nature. Some of the most promising inhibitors, especially SVMP and PLA2 inhibitors, have been developed for other diseases and are being repurposed for snakebite envenoming. In addition, the search for drugs aimed at controlling endogenous processes generated in the course of envenoming is being pursued. The present review summarizes some of the most promising developments in this field and discusses issues that need to be considered for the effective translation of this knowledge to improve therapies for tackling snakebite envenoming.

Gallic acid anti-myotoxic activity and mechanism of action, a snake venom phospholipase A2 toxin inhibitor, isolated from the medicinal plant Anacardium humile

Snakebite envenoming is the cause of an ongoing health crisis in several regions of the world, particularly in tropical and neotropical countries. This scenario creates an urgent necessity for new practical solutions to address the limitations of current therapies. The current study investigated the isolation, phytochemical characterization, and myotoxicity inhibition mechanism of gallic acid (GA), a myotoxin inhibitor obtained from Anacardium humile. The identification and isolation of GA was achieved by employing analytical chromatographic separation, which exhibited a compound with retention time and nuclear magnetic resonance spectra compatible with GA's commercial standard and data from the literature. GA alone was able to inhibit the myotoxic activity induced by the crude venom of Bothrops jararacussu and its two main myotoxins, BthTX-I and BthTX-II. Circular dichroism (CD), fluorescence spectroscopy (FS), dynamic light scattering (DLS), and interaction studies by molecular docking suggested that GA forms a complex with BthTX-I and II. Surface plasmon resonance (SPR) kinetics assays showed that GA has a high affinity for BthTX-I with a K_D of 9.146 × 10^-7 M. Taken together, the two-state reaction mode of GA binding to BthTX-I, and CD, FS and DLS assays, suggest that GA is able to induce oligomerization and secondary structure changes for BthTX-I and -II. GA and other tannins have been shown to be effective inhibitors of snake venoms' toxic effects, and herein we demonstrated GA's ability to bind to and inhibit a snake venom PLA₂, thus proposing a new mechanism of PLA₂ inhibition, and presenting more evidence of GA's potential as an antivenom compound.

The synthetic varespladib molecule is a multi-functional inhibitor for PLA2 and PLA2-like ophidic toxins

BACKGROUND

The treatment for snakebites is early administration of antivenom, which can be highly effective in inhibiting the systemic effects of snake venoms, but is less effective in the treatment of extra-circulatory and local effects. To complement standard-of-care treatments such as antibody-based antivenoms, natural and synthetic small molecules have been proposed for the inhibition of key venom components such as phospholipase A₂ (PLA₂) and PLA₂-like toxins. Varespladib (compound LY315920) is a synthetic molecule developed and clinically tested aiming to block inflammatory cascades of several diseases associated with high PLA₂s. Recent studies have demonstrated this molecule is able to potently inhibit snake venom catalytic PLA₂ and PLA₂-like toxins.

METHODS

In vivo and in vitro techniques were used to evaluate the inhibitory effect of varespladib against MjTX-I. X-ray crystallography was used to reveal details of the interaction between these molecules. A new methodology that combines crystallography, mass spectroscopy and phylogenetic data was used to review its primary sequence.

RESULTS

Varespladib was able to inhibit the myotoxic and cytotoxic effects of MjTX-I. Structural analysis revealed a particular inhibitory mechanism of MjTX-I when compared to other PLA₂-like myotoxin, presenting an oligomeric-independent function.

CONCLUSION

Results suggest the effectiveness of varespladib for the inhibition of MjTX-I, in similarity with other PLA₂ and PLA₂-like toxins.

GENERAL SIGNIFICANCE

Varespladib appears to be a promissory molecule in the treatment of local effects led by PLA₂ and PLA₂-like toxins (oligomeric dependent and independent), indicating that this is a multifunctional or broadly specific inhibitor for different toxins within this superfamily.

Protective effect of oral treatment with Cordia verbenacea extract against UVB irradiation deleterious effects in the skin of hairless mouse

Photochemoprotection of the skin can be achieved by inhibiting inflammation and oxidative stress, which we tested using Cordia verbenacea extract, a medicinal plant known for its rich content of antioxidant molecules and anti-inflammatory activity. In vitro antioxidant evaluation of Cordia verbenacea leaves ethanolic extract (CVE) presented the following results: ferric reducing antioxidant power (886.32 μM equivalent of Trolox/g extract); IC50 of 19.128 μg/ml for scavenging 2,2-diphenyl-1-picrylhydrazyl; IC50 of 12.48 μg/mL for scavenging 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid); decrease of hydroperoxides from linoleic acid (IC50 of 10.20 μg/mL); inhibition of thiobarbituric acid reactive substances (IC50 8.90 μg/mL); iron-chelating ability in bathophenanthroline iron assay (IC50 47.35 μg/mL); chemiluminescence triggered by free radicals in the H2O2/horseradish peroxidase/luminol (IC50 0.286 μg/mL) and xanthine/xanthine oxidase/luminol (IC50 0.42 μg/mL) methods. CVE (10-100 mg per kg, 30 min before and immediately after UVB exposure) treatment was performed by gavage in hairless mice. CVE inhibited skin edema, neutrophil infiltration, and overproduction of MMP-9; reduced levels of TNF-α, IL-1β, and IL- 6; numbers of skin mast cells, epidermal thickening, number of epidermal apoptotic keratinocytes, and collagen degradation. CVE increased the skin's natural antioxidant defenses as observed by Nrf-2, NAD(P)H quinone oxidoreductase 1, and heme oxygenase 1 mRNA expression enhancement. Furthermore, CVE inhibited lipid peroxidation and superoxide anion production and recovered antioxidant reduced glutathione, catalase activity, and ROS scavenging capacity of the skin. Concluding, CVE downregulates the skin inflammatory and oxidative damages triggered by UVB, demonstrating its potentialities as a therapeutic approach.

In silico and in vitro neutralization of PLA2 activity of Daboxin P by butein, mimosine and bakuchiol

Medicinal plants have always been used for snakebite treatment by traditional healers but they lack scientific evidence of action. However secondary metabolites of such plants have been explored and found to inhibit the toxic effect of venom proteins. Literature survey from 2003 to 2019 resulted in identification of 251 secondary metabolites with such properties. In silico docking studies of these metabolites with modelled structure of Daboxin P, a PLA₂ from Indian Daboia russelii revealed that butein, mimosine and bakuchiol bind to Daboxin P with high affinity. Butein interacted with the catalytic triad but mimosine and bakuchiol interacted with the Ca²⁺ binding residues of Daboxin P. In vitro validation showed that the molecules inhibited the sPLA₂ activity of Daboxin P. Interestingly, mimosine and bakuchiol could also neutralize the anti-coagulatory activity of Daboxin P. Further, it was observed that butein and mimosine could neutralize the PLA₂ activity of Indian big four venoms dose dependently. On the other hand, mimosine and bakuchiol could also neutralize the pro/anti-coagulatory effect of big four crude venom. Thus, in this study, three molecules have been identified which can neutralize the PLA₂ activity and pro/anti-coagulatory effect of Daboxin P as well as crude venom of big four.

In-solution structural studies involving a phospholipase A2-like myotoxin and a natural inhibitor: Plasticity of oligomeric assembly affects mechanisms of inhibition

Snakebite envenomation has been categorized by World Health Organization as a category A neglected tropical disease, since it causes chronic psychological disorders, physical disablement and death. Ophidian accidents may cause local myonecrosis that cause drastic sequelae, which are not efficiently neutralized via serum therapy. Phospholipase A₂-like (PLA₂-like) myotoxins have a major role in the local effects caused by several snake venoms. We previously demonstrated that chicoric acid (CA) is an efficient inhibitor of the BthTX-I myotoxin and solved the X-ray structure of complex. Herein, we assess the oligomeric behavior of the BthTX-I/CA complex in solution under different physical-chemical conditions and using toxin obtained by two different biochemical methodologies to fully elucidate structural bases of inhibition of myotoxins by CA. We demonstrated the ability of PLA₂-like proteins to form different oligomeric assemblies in the presence of certain inhibitors, which can also be modulated by buffer polarity change. In the presence of ethanol, BthTX-I/CA remains predominantly in a monomeric conformation, which prevents it from being in its active form (dimeric conformation). In contrast, in the absence of ethanol, the tetramer assembly was observed, which hid key regions of the protein responsible for docking and disruption of the muscle membrane. Therefore, the "plasticity" of these proteins with regard to their abilities to form oligomeric assemblies is a key issue for the future development of therapeutic agents to complement of serum therapy.

An updated review of protective effects of rosemary and its active constituents against natural and chemical toxicities

Natural and chemical toxic agents cause severe adverse effects on people's health in a variety of exposing ways. Herbal medications have taken into consideration as alternative safe treatments for toxicities. Rosmarinus officinalis also known as rosemary belongs to the Lamiaceae family. Rosemary and its constituents including carnosic acid, rosmarinic acid, and carnosol have a lot of benefits such as anti-inflammatory, antioxidant, anti-mutagenic, anti-bacterial, antiviral, antinociceptive, and neuroprotective activities. In this literate review, we focused on the protective effects of rosemary and its main compounds against natural and chemical toxicities in both in vitro and in vivo studies. The protective effects of rosemary and its components are mostly mediated through different mechanisms such as the inhibition of oxidative stress, reduction of inflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-17 (IL-17), cyclooxygenase-2 (COX-2) and nuclear factor ĸB (NF-ĸB) as well as the modulation of apoptosis and mitogen-activated protein kinase (MAPK) signaling pathways.

The allosteric activation mechanism of a phospholipase A2-like toxin from Bothrops jararacussu venom: a dynamic description

The activation process of phospholipase A₂-like (PLA₂-like) toxins is a key step in their molecular mechanism, which involves oligomeric changes leading to the exposure of specific sites. Few studies have focused on the characterization of allosteric activators and the features that distinguish them from inhibitors. Herein, a comprehensive study with the BthTX-I toxin from Bothrops jararacussu venom bound or unbound to α-tocopherol (αT) was carried out. The oligomerization state of BthTX-I bound or unbound to αT in solution was studied and indicated that the toxin is predominantly monomeric but tends to oligomerize when complexed with αT. In silico molecular simulations showed the toxin presents higher conformational changes in the absence of αT, which suggests that it is important to stabilize the structure of the toxin. The transition between the two states (active/inactive) was also studied, showing that only the unbound BthTX-I system could migrate to the inactive state. In contrast, the presence of αT induces the toxin to leave the inactive state, guiding it towards the active state, with more regions exposed to the solvent, particularly its active site. Finally, the structural determinants necessary for a molecule to be an inhibitor or activator were analyzed in light of the obtained results.

Isolation and structural characterization of bioactive compound from Aristolochia sprucei aqueous extract with anti-myotoxic activity

A bioactive compound isolated from the stem extract of Aristolochia sprucei through High Performance Liquid Chromatography (HPLC) was identified via Nuclear Magnetic Resonance (NMR) as the aristolochic acid (AA). This compound showed an inhibitory effect over the myotoxic activity of Bothrops jararacussu and Bothrops asper venoms, being also effective against the indirect hemolytic activity of B. asper venom. Besides, AA also inhibited the myotoxic activity of BthTX-I and MTX-II with an efficiency greater than 60% against both myotoxins. Docking predictions revealed an interesting mechanism, through which the AA displays an interaction profile consistent with its inhibiting abilities, binding to both active and putative sites of svPLA₂. Overall, the present findings indicate that AA may bind to critical regions of myotoxic Asp 49 and Lys49-PLA₂s from snake venoms, highlighting the relevance of domains comprising the active and putative sites to inhibit these toxins.

Neutralization of a bothropic PLA2-like protein by caftaric acid, a novel potent inhibitor of ophidian myotoxicity

Envenoming by snakebite is an important global health issue that has received little attention, leading the World Health Organization to naming it as neglected tropical disease. Several snakebites present serious local symptoms manifested on victims that may not be efficiently neutralized by serum therapy. Phospholipase A₂-like (PLA₂-like) toxins are present in Viperidae venoms and are responsible for local myotoxic activity. Herein, we investigated the association between BthTX-I toxin and caftaric acid (CFT), a molecule present in plants. CFT neutralized neuromuscular blocking and muscle-damaging activities promoted by BthTX-I. Calorimetric and light-scattering assays demonstrated that CFT inhibitor interacted with dimeric BthTX-I. Bioinformatics simulations indicated that CFT inhibitor binds to the toxin's hydrophobic channel (HCh). According to the current myotoxic mechanism, three different regions of PLA₂-like toxins have specific tasks: protein allosteric activation (HCh), membrane dockage (MDoS), and membrane rupture (MDiS). We propose CFT inhibitor interferes with the allosteric activation, which is related to the conformation change leading to the exposure/alignment of MDoS/MDiS region. This is the first report of a PLA₂-like toxin fully inhibited by a compound that interacts only with its HCh region. Thus, CFT is a novel candidate to complement serum therapy and improve the treatment of snakebite.

Structural basis for phospholipase A2-like toxin inhibition by the synthetic compound Varespladib (LY315920)

The World Health Organization recently listed snakebite envenoming as a Neglected Tropical Disease, proposing strategies to significantly reduce the global burden of this complex pathology by 2030. In this context, effective adjuvant treatments to complement conventional antivenom therapy based on inhibitory molecules for specific venom toxins have gained renewed interest. Varespladib (LY315920) is a synthetic molecule clinically tested to block inflammatory cascades of several diseases associated with elevated levels of secreted phospholipase A₂ (sPLA₂). Most recently, Varespladib was tested against several whole snake venoms and isolated PLA₂ toxins, demonstrating potent inhibitory activity. Herein, we describe the first structural and functional study of the complex between Varespladib and a PLA₂-like snake venom toxin (MjTX-II). In vitro and in vivo experiments showed this compound’s capacity to inhibit the cytotoxic and myotoxic effects of MjTX-II from the medically important South American snake, Bothrops moojeni. Crystallographic and bioinformatics analyses revealed interactions of Varespladib with two specific regions of the toxin, suggesting inhibition occurs by physical blockage of its allosteric activation, preventing the alignment of its functional sites and, consequently, impairing its ability to disrupt membranes. Furthermore, based on the analysis of several crystallographic structures, a distinction between toxin activators and inhibitors is proposed.

Antimyotoxic Activity of Synthetic Peptides Derived from Bothrops atrox Snake Gamma Phospholipase A2 Inhibitor Selected by Virtual Screening

Background:

Several studies have aimed to identify molecules that inhibit the toxic actions of snake venom phospholipases A2 (PLA2s). Studies carried out with PLA2 inhibitors (PLIs) have been shown to be efficient in this assignment.

Objective:

This work aimed to analyze the interaction of peptides derived from Bothrops atrox PLIγ (atPLIγ) with a PLA2 and to evaluate the ability of these peptides to reduce phospholipase and myotoxic activities.

Methods:

Peptides were subjected to molecular docking with a homologous Lys49 PLA2 from B. atrox venom modeled by homology. Phospholipase activity neutralization assay was performed with BthTX-II and different ratios of the peptides. A catalytically active and an inactive PLA2 were purified from the B. atrox venom and used together in the in vitro myotoxic activity neutralization experiments with the peptides.

Results:

The peptides interacted with amino acids near the PLA2 hydrophobic channel and the loop that would be bound to calcium in Asp49 PLA2. They were able to reduce phospholipase activity and peptides DFCHNV and ATHEE reached the highest reduction levels, being these two peptides the best that also interacted in the in silico experiments. The peptides reduced the myotubes cell damage with a highlight for the DFCHNV peptide, which reduced by about 65%. It has been suggested that myotoxic activity reduction is related to the sites occupied in the PLA2 structure, which could corroborate the results observed in molecular docking.

Conclusion:

This study should contribute to the investigation of the potential of PLIs to inhibit the toxic effects of PLA2s.

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.

Essential Oil from Lippia origanoides (Verbenaceae): Haemostasis and Enzymes Activity Alterations

BACKGROUND

The search for natural inhibitors of snake venom toxins is essential to supplement or even replace the serum therapy. The aim of this work was to evaluate the pharmacological properties of essential oil from Lippia origanoides Kunth. (Verbenaceae).

METHODS

The oil was extracted by hydrodistillation and the constituents were identified and quantified by GC-MS and GC-FID. The essential oil from L. origanoides was evaluated in hemolysis tests, on the activities of phospholipases A2 and serine proteases and in coagulation and thrombolysis induced by different snake venoms.

RESULTS

The major constituents of essential oil were carvacrol, p-cymene, γ-terpinene, and thymol. The oil inhibited approximately 10 % of the phospholipase A2 activity induced by Bothrops atrox, Bothrops jararaca, Bothrops jararacussu and Bothrops moojeni venoms and was not cytotoxic against erythrocytes. However, previous incubation of the oil with B. jararacussu, B. moojeni, and Crotalus durissus terrificus (C.d.t.) venoms resulted in potentiation of hemolytic activity (30 % and 50 % for 0.6 µL mL-1 and 1.2 µL mL-1, respectively). The essential oil presented a procoagulant effect on human citrated plasma, potentiated the thrombolytic action of proteases and phospholipases A2 present in B. jararacussu venom, and serine protease activity induced by B. jararaca and Lachesis muta venoms. When pre-incubated with the C.d.t. venom, however, prothrombotic activity was observed.

CONCLUSION

The results obtained in this work amplify the pharmacological characterization of the essential oil from L. origanoides. However, new studies are fundamental to define the action mechanisms and determine pharmaceutical applications.

Search for efficient inhibitors of myotoxic activity induced by ophidian phospholipase A2-like proteins using functional, structural and bioinformatics approaches

Ophidian accidents are considered an important neglected tropical disease by the World Health Organization. Particularly in Latin America, Bothrops snakes are responsible for the majority of the snakebite envenomings that are not efficiently treated by conventional serum therapy. Thus, the search for simple and efficient inhibitors to complement this therapy is a promising research area, and a combination of functional and structural assays have been used to test candidate ligands against specific ophidian venom compounds. Herein, we tested a commercial drug (acetylsalicylic acid, ASA) and a plant compound with antiophidian properties (rosmarinic acid, RA) using myographic, crystallographic and bioinformatics experiments with a phospholipase A2-like toxin, MjTX-II. MjTX-II/RA and MjTX-II/ASA crystal structures were solved at high resolution and revealed the presence of ligands bound to different regions of the toxin. However, in vitro myographic assays showed that only RA is able to prevent the myotoxic effects of MjTX-II. In agreement with functional results, molecular dynamics simulations showed that the RA molecule remains tightly bound to the toxin throughout the calculations, whereas ASA molecules tend to dissociate. This approach aids the design of effective inhibitors of PLA2-like toxins and, eventually, may complement serum therapy.

Effects of Two Fractions of Swietenia macrophylla and Catechin on Muscle Damage Induced by BothropsVenom and PLA₂

Plant natural products can attenuate the myonecrosis caused by Bothrops snake venom and their phospholipases A₂ (PLA₂). In this study, we evaluated the effects of two fractions (F4 and F6) from Swietenia macrophylla and purified catechin on the muscle damage caused by a myotoxic PLA₂ from Colombian Bothrops asper venom (BaColPLA₂) in mice and by Bothrops marmoratus venom from Brazil in mouse phrenic nerve-diaphragm muscle (PND) preparations in vitro. Male mice were injected with PLA₂ (50 µg) in the absence or presence of F4, F6, and catechin, in the gastrocnemius muscle and then killed 3, 7, 14, and 28 h later for histopathological analysis of myonecrosis, leukocyte infiltration, and the presence of collagen. Fractions F4 and F6 (500 µg) and catechin (90 µg) significantly reduced the extent of necrosis at all-time intervals. These two fractions and catechin also attenuated the leukocyte infiltration on day 3, as did catechin on day 14. There was medium-to-moderate collagen deposition in all groups up to day 7, but greater deposition on days 14 and 28 in the presence of F6 and catechin. Bothrops marmoratus venom (100 µg/mL) caused slight (~25%) muscle facilitation after 10 minutes and weak neuromuscular blockade (~64% decrease in contractile activity after a 120-minute incubation). Pre-incubation of venom with F4 or F6 abolished the facilitation, whereas catechin, which was itself facilitatory, did not. All three fractions attenuated the venom-induced decrease in muscle contractions. These findings indicate that fractions and catechin from S. macrophylla can reduce the muscle damage caused by Bothrops venom and PLA₂. These fractions or their components could be useful for treating venom-induced local damage.

Structural and functional characterization of suramin-bound MjTX-I from Bothrops moojeni suggests a particular myotoxic mechanism

Local myonecrosis is the main event resulting from snakebite envenomation by the Bothrops genus and, frequently, it is not efficiently neutralized by antivenom administration. Proteases, phospholipases A₂ (PLA₂) and PLA₂-like toxins are found in venom related to muscle damage. Functional sites responsible for PLA₂-like toxins activity have been proposed recently; they consist of a membrane docking-site and a membrane rupture-site. Herein, a combination of functional, biophysical and crystallographic techniques was used to characterize the interaction between suramin and MjTX-I (a PLA₂-like toxin from Bothrops moojeni venom). Functional in vitro neuromuscular assays were performed to study the biological effects of the protein-ligand interaction, demonstrating that suramin neutralizes the myotoxic effect of MjTX-I. Calorimetric assays showed two different binding events: (i) inhibitor-protein interactions and (ii) toxin oligomerization processes. These hypotheses were also corroborated with dynamic light and small angle X-ray scattering assays. The crystal structure of the MjTX-I/suramin showed a totally different interaction mode compared to other PLA₂-like/suramin complexes. Thus, we suggested a novel myotoxic mechanism for MjTX-I that may be inhibited by suramin. These results can further contribute to the search for inhibitors that will efficiently counteract local myonecrosis in order to be used as an adjuvant of conventional serum therapy.

PLA2-like proteins myotoxic mechanism: a dynamic model description

Phospholipase A₂-like (PLA₂-like) proteins contribute to the development of muscle necrosis in Viperidae snake bites and are not efficiently neutralized by current antivenom treatments. The toxic mechanisms of PLA₂-like proteins are devoid of catalytic activity and not yet fully understood, although structural and functional experiments suggest a dimeric assembly and that the C-terminal residues are essential to myotoxicity. Herein, we characterized the functional mechanism of bothropic PLA₂-like structures related to global and local measurements using the available models in the Protein Data Bank and normal mode molecular dynamics (NM-MD). Those measurements include: (i) new geometric descriptions between their monomers, based on Euler angles; (ii) characterizations of canonical and non-canonical conformations of the C-terminal residues; (iii) accessibility of the hydrophobic channel; (iv) inspection of ligands; and (v) distance of clustered residues to toxin interface of interaction. Thus, we described the allosteric activation of PLA₂-like proteins and hypothesized that the natural movement between monomers, calculated from NM-MD, is related to their membrane disruption mechanism, which is important for future studies of the inhibition process. These methods and strategies can be applied to other proteins to help understand their mechanisms of action.

Pharmacological Properties of Vochysia Haenkeana (Vochysiaceae) Extract to Neutralize the Neuromuscular Blockade Induced by Bothropstoxin-I (Lys49 Phospholipase A2) Myotoxin

Purpose: Bothrops snakes are responsible for more than 70 % of snakebites every year in Brazil and their venoms cause severe local and systemic damages. The pharmacological properties of medicinal plants have been widely investigated in order to discover new alternative treatments for different classes of diseases including neglected tropical diseases as envenomation by snakebites. In this work, we have investigated the ability of Vochysia haenkeana stem barks extract (VhE) to neutralize the neuromuscular effects caused by Bothropstoxin-I (BthTX-I), the major phospholipase A₂ (PLA₂) myotoxin from B. jararacussu venom.

Methods: The biological compounds of VhE were analysed under thin layer chromatography (TLC) and its neutralizing ability against BthTX-I was assessed through twitch-tension recordings and histological analysis in mouse phrenic nerve-diaphragm (PND) preparations. The antimicrobial activity of VhE was assessed against S. aureus, E. coli and P. aeruginosa strains. The aggregation activity of VhE was analysed under protein precipitation assay.

Results: VhE showed the presence of phenolic compound visualized by blue trace under TLC. VhE abolished the neuromuscular blockade caused by BthTX-I applying the pre-toxin incubation treatment and partially neutralized the BthTX-I action under post-toxin incubation treatment; VhE contributed slightly to decrease the myotoxicity induced by BthTX-I. The neutralizing mechanism of VhE may be related to protein aggregation. VhE showed no antimicrobial activity.

Conclusion: V. haenkeana extract which has no antimicrobial activity exhibited neutralizing ability against the neuromuscular blockade caused by BthTX-I and also contributed to decrease its myotoxicity. Protein aggregation involving phenolic compounds may be related in these protective effects.

Heterologous expression of the antimyotoxic protein DM64 in Pichia pastoris

Snakebite envenomation is a neglected condition that constitutes a public health problem in tropical and subtropical countries, including Brazil. Interestingly, some animals are resistant to snake envenomation due to the presence of inhibitory glycoproteins in their serum that target toxic venom components. DM64 is an acidic glycoprotein isolated from Didelphis aurita (opossum) serum that has been characterized as an inhibitor of the myotoxicity induced by bothropic toxins bearing phospholipase A₂ (PLA₂) structures. This antitoxic protein can serve as an excellent starting template for the design of novel therapeutics against snakebite envenomation, particularly venom-induced local tissue damage. Therefore, the aim of this work was to produce a recombinant DM64 (rDM64) in the methylotrophic yeast Pichia pastoris and to compare its biological properties with those of native DM64. Yeast fermentation in the presence of Pefabloc, a serine protease inhibitor, stimulated cell growth (~1.5-fold), increased the rDM64 production yield approximately 10-fold and significantly reduced the susceptibility of rDM64 to proteolytic degradation. P. pastoris fermentation products were identified by mass spectrometry and Western blotting. The heterologous protein was efficiently purified from the culture medium by affinity chromatography (with immobilized PLA₂ myotoxin) and/or an ion exchange column. Although both native and recombinant DM64 exhibit different glycosylation patterns, they show very similar electrophoretic mobilities after PNGase F treatment. rDM64 formed a noncovalent complex with myotoxin II (Lys49-PLA₂) from Bothrops asper and displayed biological activity that was similar to that of native DM64, inhibiting the cytotoxicity of myotoxin II by 92% at a 1:1 molar ratio.

Snakebite envenomation causes medical emergencies that, depending on the species responsible for the bite, involve different organs and tissues. Envenomation by snakebite is a worldwide problem, and Brazil presents a high incidence of Bothrops bites. Bothrops venoms cause pathological alterations with prominent local effects, such as edema, blistering, hemorrhage, dermonecrosis and myonecrosis, usually followed by poor tissue regeneration and permanent sequelae. Bleeding, coagulopathy, cardiovascular shock and renal failure are typical systemic effects of these venoms. The clinical treatment for snakebite envenoming is intravenous administration of the specific antivenom. However, serotherapy does not efficiently protect against local tissue damage. Additional challenges faced by classical antivenom therapy include the wide antigenic variation of venoms across species and even within the same snake species and the frequent occurrence of adverse reactions that are associated with the administration of immunobiologicals. The development of new effective toxin inhibitors based on the structure of natural antiophidic proteins is an attractive therapeutic alternative. DM64 is a myotoxin inhibitor that was isolated from opossum serum, and its expression as a recombinant protein is paramount to the characterization of its structure-function relationship, an essential step toward the development of alternative strategies to better manage bothropic snakebite envenomations.

Gene expression profiling of the venom gland from the Venezuelan mapanare (Bothrops colombiensis) using expressed sequence tags (ESTs)

BACKGROUND

Bothrops colombiensis is a highly dangerous pit viper and responsible for over 70% of snakebites in Venezuela. Although the composition in B. colombiensis venom has been identified using a proteome analysis, the venom gland transcriptome is currently lacking.

RESULTS

We constructed a cDNA library from the venom gland of B. colombiensis, and a set of 729 high quality expressed sequence tags (ESTs) was identified. A total number of 344 ESTs (47.2% of total ESTs) was related to toxins. The most abundant toxin transcripts were metalloproteinases (37.5%), phospholipases A2s (PLA2, 29.7%), and serine proteinases (11.9%). Minor toxin transcripts were linked to waprins (5.5%), C-type lectins (4.1%), ATPases (2.9%), cysteine-rich secretory proteins (CRISP, 2.3%), snake venom vascular endothelium growth factors (svVEGF, 2.3%), L-amino acid oxidases (2%), and other putative toxins (1.7%). While 160 ESTs (22% of total ESTs) coded for translation proteins, regulatory proteins, ribosomal proteins, elongation factors, release factors, metabolic proteins, and immune response proteins. Other proteins detected in the transcriptome (87 ESTs, 11.9% of total ESTs) were undescribed proteins with unknown functions. The remaining 138 (18.9%) cDNAs had no match with known GenBank accessions.

CONCLUSION

This study represents the analysis of transcript expressions and provides a physical resource of unique genes for further study of gene function and the development of novel molecules for medical applications.

Unraveling the distinctive features of hemorrhagic and non-hemorrhagic snake venom metalloproteinases using molecular simulations

Snake venom metalloproteinases are important toxins that play fundamental roles during envenomation. They share a structurally similar catalytic domain, but with diverse hemorrhagic capabilities. To understand the structural basis for this difference, we build and compare two dynamical models, one for the hemorrhagic atroxlysin-I from Bothrops atrox and the other for the non-hemorraghic leucurolysin-a from Bothrops leucurus. The analysis of the extended molecular dynamics simulations shows some changes in the local structure, flexibility and surface determinants that can contribute to explain the different hemorrhagic activity of the two enzymes. In agreement with previous results, the long Ω-loop (from residue 149 to 177) has a larger mobility in the hemorrhagic protein. In addition, we find some potentially-relevant differences at the base of the S1' pocket, what may be interesting for the structure-based design of new anti-venom agents. However, the sharpest differences in the computational models of atroxlysin-I and leucurolysin-a are observed in the surface electrostatic potential around the active site region, suggesting thus that the hemorrhagic versus non-hemorrhagic activity is probably determined by protein surface determinants.

Structural and functional evidence for membrane docking and disruption sites on phospholipase A2-like proteins revealed by complexation with the inhibitor suramin

Local myonecrosis resulting from snakebite envenomation is not efficiently neutralized by regular antivenom administration. This limitation is considered to be a significant health problem by the World Health Organization. Phospholipase A2-like (PLA2-like) proteins are among the most important proteins related to the muscle damage resulting from several snake venoms. However, despite their conserved tertiary structure compared with PLA2s, their biological mechanism remains incompletely understood. Different oligomeric conformations and binding sites have been identified or proposed, leading to contradictory data in the literature. In the last few years, a comprehensive hypothesis has been proposed based on fatty-acid binding, allosteric changes and the presence of two different interaction sites. In the present study, a combination of techniques were used to fully understand the structural–functional characteristics of the interaction between suramin and MjTX-II (a PLA2-like toxin).In vitroneuromuscular studies were performed to characterize the biological effects of the protein–ligand interaction and demonstrated that suramin neutralizes the myotoxic activity of MjTX-II. The high-resolution structure of the complex identified the toxin–ligand interaction sites. Calorimetric assays showed two different binding events between the protein and the inhibitor. It is demonstrated for the first time that the inhibitor binds to the surface of the toxin, obstructing the sites involved in membrane docking and disruption according to the proposed myotoxic mechanism. Furthermore, higher-order oligomeric formation by interaction with interfacial suramins was observed, which may also aid the inhibitory process. These results further substantiate the current myotoxic mechanism and shed light on the search for efficient inhibitors of the local myonecrosis phenomenon.

Structural Basis for the Inhibition of a Phospholipase A2-Like Toxin by Caffeic and Aristolochic Acids

One of the main challenges in toxicology today is to develop therapeutic alternatives for the treatment of snake venom injuries that are not efficiently neutralized by conventional serum therapy. Venom phospholipases A2 (PLA2s) and PLA2-like proteins play a fundamental role in skeletal muscle necrosis, which can result in permanent sequelae and disability. This leads to economic and social problems, especially in developing countries. In this work, we performed structural and functional studies with Piratoxin-I, a Lys49-PLA2 from Bothropspirajai venom, complexed with two compounds present in several plants used in folk medicine against snakebites. These ligands partially neutralized the myotoxic activity of PrTX-I towards binding on the two independent sites of interaction between Lys49-PLA2 and muscle membrane. Our results corroborate the previously proposed mechanism of action of PLA2s-like and provide insights for the design of structure-based inhibitors that could prevent the permanent injuries caused by these proteins in snakebite victims.

Combining molecular docking and 3-D pharmacophore generation to enclose the in vivo antigenotoxic activity of naturally occurring aromatic compounds: myricetin, quercetin, rutin, and rosmarinic acid

Considering the controversial results concerning the antimutagenicity of some phenolic compounds recorded in the literature, the antigenotoxic effects of four selected phenolic compounds, myricetin, quercetin, rutin, and rosmarinic acid, against DNA damage induced by alkylation with ethyl methanesulfonate (EMS), were evaluated in Drosophila melanogaster males using the sex-linked recessive lethal (SLRL) test. To assess the protective effects against DNA damage, D. melanogaster males were exposed to a monofunctional alkylating agent EMS in concentration of 0.75 ppm, 24 h prior to one of the selected phenolic compounds in the concentration of 100 ppm. The possible differences in mechanisms of protection by selected compounds were determined by molecular docking, after which structure-based 3-D pharmacophore models were generated. EMS induced considerable DNA damage as shown by significant increase in the frequency of germinative mutations. The frequency decreased with high significance (p<0.001***) after post-treatments with all selected phenolic compounds. Further, docking analysis revealed EMS pre-bond conformations against guanine and thymine as a necessary condition for alkylation, after which resulting O⁶-ethylguanine and O⁴-ethylthimine were docked into the active site of O⁶-alkylguanine-DNA alkyltransferase to confirm that particular lesions are going to be repaired. Finally, myricetin and quercetin protected dealkylated nucleotides from further EMS alkylation by forming the strong hydrogen bonds with O⁶-guanine and O⁴-thymine via B ring hydroxyl group (bond lengths lower than 2.5 Å). On the other side, rutin and rosmarinic acid encircled nucleotides and by fulfilling the EMS binding space they made an impermeable barrier for the EMS molecule and prevented further alkylation.

Neurotoxicity in snakebite--the limits of our knowledge

Snakebite is classified by the WHO as a neglected tropical disease. Envenoming is a significant public health problem in tropical and subtropical regions. Neurotoxicity is a key feature of some envenomings, and there are many unanswered questions regarding this manifestation. Acute neuromuscular weakness with respiratory involvement is the most clinically important neurotoxic effect. Data is limited on the many other acute neurotoxic manifestations, and especially delayed neurotoxicity. Symptom evolution and recovery, patterns of weakness, respiratory involvement, and response to antivenom and acetyl cholinesterase inhibitors are variable, and seem to depend on the snake species, type of neurotoxicity, and geographical variations. Recent data have challenged the traditional concepts of neurotoxicity in snake envenoming, and highlight the rich diversity of snake neurotoxins. A uniform system of classification of the pattern of neuromuscular weakness and models for predicting type of toxicity and development of respiratory weakness are still lacking, and would greatly aid clinical decision making and future research. This review attempts to update the reader on the current state of knowledge regarding this important issue.

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.