Inhibitors of Snake Venoms and Development of New Therapeutics

Alternative Targets for sPLA2 Activity: Role of Membrane-Enzyme Interactions

The secreted phospholipases A2 (sPLA2s) play important roles both physiologically and pathologically, with their expression increasing significantly in diseases such as sepsis, inflammation, different cancers, glaucoma, obesity, Alzheimer's disease and even COVID-19. The fact has led to a large-scale search for inhibitors of these enzymes. In total, several dozen promising molecules have been proposed, but not a single one has successfully passed clinical trials. The failures in clinical studies motivated in-depth fundamental studies of PLA2s. Here we review alternative ways to control sPLA2 activity, outside its catalytic site. The concept can be realized by preventing sPLA2 from attaching to the membrane surface; by binding to an external protein which blocks sPLA2 hydrolytic activity; by preventing sPLA2 from orienting properly on the membrane surface; and by preventing substrate binding to the enzyme, keeping the catalytic site unaltered. Evidence in the literature is summarized in the review with the aim to serve as a starting point for new types of sPLA2 inhibitors.

Snake Envenomation

SNAKE ENVENOMATION REPRESENTS AN IMPORTANT HEALTH PROBLEM IN much of the world. In 2009, it was recognized by the World Health Organization (WHO) as a neglected tropical disease, and in 2017, it was elevated into Category A of the Neglected Tropical Diseases list, further expanding access to funding for research and antivenoms. However, snake envenomation occurs in both tropical and temperate climates and on all continents except Antarctica. Worldwide, the estimated number of annual deaths due to snake envenomation (80,000 to 130,000) is similar to the estimate for drug-resistant tuberculosis and for multiple myeloma.^, In countries with adequate resources, deaths are infrequent (e.g., <6 deaths per year in the United States, despite the occurrence of 7000 to 8000 bites), but in countries without adequate resources, deaths may number in the tens of thousands. Venomous snakes kept as pets are not rare, and physicians anywhere might be called on to manage envenomation by a nonnative snake. Important advances have occurred in our understanding of the biology of venom and the management of snake envenomation since this topic was last addressed in the Journal two decades ago. For the general provider, it is important to understand the spectrum of snake envenomation effects and approaches to management and to obtain specific guidance, when needed.

Advances in the Therapeutic Application of Small-Molecule Inhibitors and Repurposed Drugs against Snakebite

The World Health Organization has declared snakebite as a neglected tropical disease. Antivenom administration is the sole therapy against venomous snakebite; however, several limitations of this therapy reinforce the dire need for an alternative and/or additional treatment against envenomation. Inhibitors against snake venoms have been explored from natural resources and are synthesized in the laboratory; however, repurposing of small-molecule therapeutics (SMTs) against the principal toxins of snake venoms to inhibit their lethality and/or obnoxious effect of envenomation has been garnering greater attention owing to their established pharmacokinetic properties, low-risk attributes, cost-effectiveness, ease of administration, and storage stability. Nevertheless, SMTs are yet to be approved and commercialized for snakebite treatment. Therefore, we have systematically reviewed and critically analyzed the scenario of small synthetic inhibitors and repurposed drugs against snake envenomation from 2005 to date and proposed novel approaches and commercialization strategies for the development of efficacious therapies against snake envenomation.

Phytochemical composition, antisnake venom and antibacterial activities of ethanolic extract of Aegiphila integrifolia (Jacq) Moldenke leaves

Snakebites are considered a major neglected tropical disease, resulting in around 100,000 deaths per year. The recommended treatment by the WHO is serotherapy, which has limited effectiveness against the toxins involved in local tissue damage. In some countries, patients use plants from folk medicines as antivenoms. Aegiphila species are common plants from the Brazilian Amazon and are used to treat snakebites. In this study, leaves from Aegiphila integrifolia (Jacq) Moldenke were collected from Roraima state, Brazil and its ethanolic extract was evaluated through in vitro and in vivo experiments to verify their antiophidic activity against Bothrops atrox crude venom. The isolated compounds from A. integrifolia were analyzed and the chemical structures were elucidated on the basis of infrared, ultraviolet, mass, ¹H and ¹³C NMR spectrometry data. Among the described compounds, lupeol (7), betulinic acid (1), β-sitosterol (6), stigmasterol (5), mannitol (4), and the flavonoids, pectolinarigenin (2) and hispidulin (3), were identified. The ethanolic extract and flavonoids (2 and 3) partially inhibited the proteolytic, phospholipase A2 and hyaluronidase activities of B. atrox venom, and the skin hemorrhage induced by this venom in mice. Antimicrobial activity against different bacteria was evaluated and the extract partially inhibited bacterial growth. Thus, taken together, A. integrifolia ethanolic extract has promising use as an antiophidic and antimicrobial.

In vitro anti-venom potential of various solvent based leaf extracts of Andrographis serpyllifolia (Rottler ex Vahl) Wight against Naja naja and Daboia russelli

ETHNOPHARMACOLOGICAL RELEVANCE

Snake bite is a major occupational hazard in tropical and subtropical countries including India as per the World Health Organization. Naja naja (Indian cobra) and Daboia russelli (Russell's viper) are the two poisonous snakes commonly associated with human mortality in India. Andrographis serpyllifolia (Rottler ex Vahl) Wight has been documented in ethnobotanical records as a plant possessing potent anti-snake venom activity.

AIM OF THE STUDY

The present study is aimed for systematic evaluation of in vitro anti-venom potential of various solvent based leaf extracts of A. serpyllifolia against toxic venom enzymes of Naja naja and Daboia russelli.

MATERIALS AND METHODS

Different solvent based leaf extracts of A. serpyllifolia were tested against the snake venoms of Naja naja and Daboia russelli obtained from Irula Snake Catchers Industrial Co-operative Society Limited, Kancheepuram, Tamil nadu, India. Three different in vitro neutralization assays such as indirect hemolysis, procoagulent and lytic activities and seven in vitro enzyme inhibition assays such as protease, acetylcholinesterase, phosphomonoesterase, phosphodiesterase, 5'nucleotidase, phospholipase A2, hyaluronidase and post synaptic acetylcholine receptor binding activity were carried out according to standard protocols. The results were analyzed using the standard ANOVA procedures.

RESULTS

Among various solvent based leaf extracts of A. serpyllifolia tested, aqueous extract showed maximum neutralizing and inhibitory activities against Naja naja and Daboia russelli venoms.

CONCLUSIONS

The various in vitro enzymatic studies reveal that the aqueous leaf extract of A. serpyllifolia plant could inhibit most of the toxic enzymes of the Naja naja and Daboia russelli venoms which could be further confirmed by in vivo studies.

The interaction between the natural metalloendopeptidase inhibitor BJ46a and its target toxin jararhagin analyzed by structural mass spectrometry and molecular modeling

Snakebite envenoming affects millions of people worldwide, being officially considered a neglected tropical disease by the World Health Organization. The antivenom is effective in neutralizing the systemic effects of envenomation, but local effects are poorly neutralized, often leading to permanent disability. The natural resistance of the South American pit viper Bothrops jararaca to its venom is partly attributed to BJ46a, a natural snake venom metalloendopeptidase inhibitor. Upon complex formation, BJ46a binds non-covalently to the metalloendopeptidase, rendering it unable to exert its proteolytic activity. However, the structural features that govern this interaction are largely unknown. In this work, we applied structural mass spectrometry techniques (cross-linking-MS and hydrogen-deuterium exchange MS) and in silico analyses (molecular modeling, docking, and dynamics simulations) to understand the interaction between BJ46a and jararhagin, a metalloendopeptidase from B. jararaca venom. We explored the distance restraints generated from XL-MS experiments to guide the modeling of BJ46a and jararhagin, as well as the protein-protein docking simulations. HDX-MS data pinpointed regions of protection/deprotection at the interface of the BJ46a-jararhagin complex which, in addition to the molecular dynamics simulation data, reinforced our proposed interaction model. Ultimately, the structural understanding of snake venom metalloendopeptidases inhibition by BJ46a could lead to the rational design of drugs to improve anti-snake venom therapeutics, alleviating the high morbidity rates currently observed.

Natural Inhibitors of Snake Venom Metalloproteinases

Snakebites are a hazard in the tropical world. Although antivenom therapy is effective, it is beset with inherent drawbacks. A better understanding of the major components of snake venoms and their neutralisation will help in improving snakebite treatment. Snake venom metalloproteinases (SVMPs) are responsible for severe haemorrhage, the inhibition of coagulation and platelet aggregation, observed in the victims of snakebite envenoming. Inhibitors from various sources including medicinal plants, animal venoms, and sera are sought to block the pharmacological functions of SVMPs. In this review, we describe the interaction of natural inhibitors with SVMPs. To understand their inhibitory mechanisms, we focussed on the complex structures of these inhibitors and SVMPs. There are three distinct classes of inhibitors; namely, chelators, competitive inhibitors, and non-competitive inhibitors. A small number of inhibitors show their anti-hemorrhagic activity in invivo animal models in treatment mode, but most studies evaluate either invitro neutralisation of enzymatic activity or invivo effects in pre-incubation protocols. We propose the distinct strategies and limitations to design either broad-spectrum or highly selective SVMP inhibitors. The goal of designing broad-spectrum inhibitors against SVMPs capable of effective treatment of snakebites without toxicity has been elusive, probably because of the narrow molecular footprint of inhibitors against a large number of SVMPs with distinct molecular surfaces. Our ability to design highly selective inhibitors is limited by the lack of information of interactions between selective inhibitors and SVMPs. Comparisons of structures of hemorrhagic and non-hemorrhagic SVMPs revealed different distributions of electric charge on the surface of SVMPs, which may be exploited to design specific inhibitors. The specific inhibitors may also be useful to identify target molecules of the SVMPs and help to understand their mechanism of action.

Zoanthid mucus as new source of useful biologically active proteins

Palythoa caribaeorum is a very common colonial zoanthid in the coastal reefs of Brazil. It is known for its massive production of mucus, which is traditionally used in folk medicine by fishermen in northeastern Brazil. This study identified biologically active compounds in P. caribaerum mucus. Crude mucus was collected during low tides by the manual scraping of colonies; samples were maintained in an ice bath, homogenized, and centrifuged at 16,000 g for 1 h at 4 °C; the supernatant (mucus) was kept at -80 °C until use. The enzymatic (proteolytic and phospholipase A₂), inhibitory (metallo, cysteine and serine proteases), and hemagglutinating (human erythrocyte) activities were determined. The results showed high levels of cysteine and metallo proteases, intermediate levels of phosholipase A₂, low levels of trypsin, and no elastase and chymotrypsin like activities. The mucus showed potent inhibitory activity on snake venom metalloproteases and cysteine proteinase papain. In addition, it showed agglutinating activity towards O⁺, B⁺, and A⁺ erythrocyte types. The hemostatic results showed that the mucus prolongs the aPTT and PT, and strongly inhibited platelet aggregation induced by arachidonic acid, collagen, epinephrine, ADP, and thrombin. The antimicrobial activity was tested on 15 strains of bacteria and fungi through the radial diffusion assay in agar, and no activity was observed. Compounds in P. caribaeorum mucus were analyzed for the first time in this study, and our results show potential pharmacological activities in these compounds, which are relevant for use in physiopathological investigations. However, the demonstration of these activities indicates caution in the use of crude mucus in folk medicine. Furthermore, the present or absent activities identified in this mucus suggest that the studied P. caribaeorum colonies were in thermal stress conditions at the time of sample collection; these conditions may precede the bleaching process in zoanthids. Hence, the use of mucus as an indicator of this process should be evaluated in the future.

The effects of Cissampelos pareira extract on envenomation induced by Bothropsdiporus snake venom

ETHNOPHARMACOLOGICAL RELEVANCE

Ophidian accidents are a serious public health problem in Argentina; the Bothrops species is responsible for 97% of these accidents, and in particular, B. diporus is responsible for 80% of them. In the northeast of the country (Corrientes Provinces), Cissampelos pareira L. (Menispermaceae) is commonly used against the venom of B. diporus; its use is described in almost all ethnobotanical literature from countries where the plant grows.

AIM OF THE STUDY

In this study, the in vitro and in vivo antivenom activities of C. pareira extracts were evaluated against B. diporus venom, with a particular focus on the local effects associated with envenoming. The seasonal influence on the chemical composition of the active extracts was also studied, in order determine the associated range of variability and its influence on the antivenom activity.

MATERIALS AND METHODS

This research was conducted using aerial parts (leaves, flowers, tender stems) and roots of Cissampelos pareira collected from two different phytogeographic regions of Corrientes (Argentina); Paso de la Patria and Lomas de Vallejos. In addition, to perform a seasonal analysis and to evaluate the metabolic stability, material was collected at three different growth stages. In vivo and in vitro anti-snake venom activities were tested, and a bio-guided chromatographic separation was performed in order to determine the active chemicals involved. The fractions obtained were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and the chemical profile of the most active constituent was analyzed by ultra high-performance liquid chromatography coupled to quadrupole/high-resolution mass spectrometry (Q-Orbitrap). (UHPLC-MS).

RESULTS

The alcoholic extract was found to be the most active The bio-guided fractionation allowed selection one fraction to be analyzed by UHPLC-MS in order to identify the components responsible for the activities found; this identified five possible flavonoids.

CONCLUSIONS

Our studies of the activity of C. pareira against the venom of B. diporus have confirmed that this species possesses inhibitory effects in both in vitro and in vivo models. Moreover, the present data demonstrate that certain flavonoids may mitigate some of the venom-induced local tissue damage.

Isolation and characterization of a novel metalloprotease inhibitor from Bothrops alternatus snake serum

Resistance of snakes and some other animals to snake envenomation has been attributed to soluble factors present in their tissues. Here we report the isolation of a novel metalloprotease inhibitor from Bothrops alternatus snake serum (named BaltMPI) with high purity, using a four-step chromatographic method. BaltMPI has molecular weights of 60.5 and 42.4kDa, as determined by SDS-PAGE and mass spectrometry, respectively, and pI=5.27. The first 60 amino acids from the N-terminal region of BaltMPI, determined by Edman's degradation, showed high homology (97%) with the snake venom metalloprotease inhibitor (SVMPI) BJ46a and other SVMPIs (78-82%). The chromatographic fractions and purified BaltMPI exhibited anti-hemorrhagic activity against Batroxase and BjussuMP-I. BaltMPI was stable over wide ranges of pH (1, 5, 8, and 9) and temperature (-80, -20, 4, 60, and 100°C), and suppressed the fibrinogenolytic, fibrinolytic, and azocaseinolytic activities of Batroxase. BaltMPI specifically inhibited the activity of metalloproteases, without affecting the activity of serine proteases. Together, our results suggest that BaltMPI and other SVMPIs are promising molecules for the treatment of snake envenomation, in particular that caused by Bothrops sp.

Venom Resistance as a Model for Understanding the Molecular Basis of Complex Coevolutionary Adaptations

SynopsisVenom and venom resistance are molecular phenotypes widely considered to have diversified through coevolution between predators and prey. However, while evolutionary and functional studies on venom have been extensive, little is known about the molecular basis, variation, and complexity of venom resistance. We review known mechanisms of venom resistance and relate these mechanisms to their predicted impact on coevolutionary dynamics with venomous enemies. We then describe two conceptual approaches which can be used to examine venom/resistance systems. At the intraspecific level, tests of local adaptation in venom and resistance phenotypes can identify the functional mechanisms governing the outcomes of coevolution. At deeper evolutionary timescales, the combination of phylogenetically informed analyses of protein evolution coupled with studies of protein function promise to elucidate the mode and tempo of evolutionary change on potentially coevolving genes. We highlight case studies that use each approach to extend our knowledge of these systems as well as address larger questions about coevolutionary dynamics. We argue that resistance and venom are phenotypic traits which hold exceptional promise for investigating the mechanisms, dynamics, and outcomes of coevolution at the molecular level. Furthermore, extending the understanding of single gene-for-gene interactions to the whole resistance and venom phenotypes may provide a model system for examining the molecular and evolutionary dynamics of complex multi-gene interactions.

Antivenom effects of 1,2,3-triazoles against Bothrops jararaca and Lachesis muta snakes

Snake venoms are complex mixtures of proteins of both enzymes and nonenzymes, which are responsible for producing several biological effects. Human envenomation by snake bites particularly those of the viperid family induces a complex pathophysiological picture characterized by spectacular changes in hemostasis and frequently hemorrhage is also seen. The present work reports the ability of six of a series of 1,2,3-triazole derivatives to inhibit some pharmacological effects caused by the venoms of Bothrops jararaca and Lachesis muta. In vitro assays showed that these compounds were impaired in a concentration-dependent manner, the fibrinogen or plasma clotting, hemolysis, and proteolysis produced by both venoms. Moreover, these compounds inhibited biological effects in vivo as well. Mice treated with these compounds were fully protected from hemorrhagic lesions caused by such venoms. But, only the B. jararaca edema-inducing activity was neutralized by the triazoles. So the inhibitory effect of triazoles derivatives against some in vitro and in vivo biological assays of snake venoms points to promising aspects that may indicate them as molecular models to improve the production of effective antivenom or to complement antivenom neutralization, especially the local pathological effects, which are partially neutralized by antivenoms.

In Vitro and In Vivo Evaluation of Polyherbal Formulation against Russell's Viper and Cobra Venom and Screening of Bioactive Components by Docking Studies

The present study emphasizes to reveal the antivenom activity of Aristolochia bracteolata Lam., Tylophora indica (Burm.f.) Merrill, and Leucas aspera S. which were evaluated against venoms of Daboia russelli russelli (Russell's viper) and Naja naja (Indian cobra). The aqueous extracts of leaves and roots of the above-mentioned plants and their polyherbal (1 : 1 : 1) formulation at a dose of 200 mg/kg showed protection against envenomed mice with LD₅₀ doses of 0.44 mg/kg and 0.28 mg/kg against Russell's viper and cobra venom, respectively. In in vitro antioxidant activities sample extracts showed free radical scavenging effects in dose dependent manner. Computational drug design and docking studies were carried out to predict the neutralizing principles of type I phospholipase A₂ (PLA₂) from Indian common krait venom. This confirmed that aristolochic acid and leucasin can neutralize type I PLA₂ enzyme. Results suggest that these plants could serve as a source of natural antioxidants and common antidote for snake bite. However, further studies are needed to identify the lead molecule responsible for antidote activity.

Active compound from the leaves of Vitex negundo L. shows anti-inflammatory activity with evidence of inhibition for secretory Phospholipase A(2) through molecular docking

Novel compounds with significant medicinal properties have gained much interest in therapeutic approaches for treating various inflammatory disorders like arthritis, odema and snake bites and the post-envenom (impregnating with venom) consequences. Inflammation is caused by the increased concentration of secretory Phospholipases A(2) (sPLA(2)s) at the site of envenom. A novel compound Tris(2,4-di-tert-butylphenyl) phosphate (TDTBPP) was isolated from the leaves of Vitex negundo and the crystal structure was reported recently. The acute anti-inflammatory activity of TDTBPP was assessed by Carrageenan-induced rat paw odema method. TDTBPP reduced the raw paw odema volume significantly at the tested doses of 50 mg/kg and 70 mg/kg body weight. Molecular docking studies were carried out with the X-ray crystal structures of Daboia russelli pulchella's (Vipera russelli, Indian Russell's viper) venom sPLA(2) and Human non-pancreatic secretory PLA(2) (Hnps PLA(2)) as targets to illustrate the antiinflammatory and antidote activities of TDTBPP. Docking results showed hydrogen bond (H-bond) interaction with Lys69 residue lying in the anti-coagulant loop of D. russelli's venom PLA(2), which is essential in the catalytic activity of the enzyme and hydrophobic interactions with the residues at the binding site (His48, Asp49). Docking of TDTBPP with Hnps PLA(2) structure showed coordination with calcium ion directly as well as through the catalytically important water molecule (HOH1260) located at the binding site.

Traditional use of plants against snakebite in Indian subcontinent: a review of the recent literature

Snakebite has been a major cause of mortality across the tropical countries including Indian subcontinent. The present review deals with the enormous amount of ethnobotanical work performed in the last few years involving use of different plants against snakebite in Indian subcontinent (India, Bangladesh, Pakistan and Nepal). From a variety of literature sources the data has been compiled mentioning the plants, parts used, dosage, mode of administration, name of the ethnic communities, geographical locations etc. depending on the availability of information.

Efficacy evaluations of Mimosa pudica tannin isolate (MPT) for its anti-ophidian properties

AIM OF THE STUDY

Evaluations of the anti-snake venom efficacy of Mimosa pudica tannin isolate (MPT) obtained from root of the plant.

MATERIALS AND METHOD

MPT was investigated in vitro and in vivo for its efficacy against the venom of Naja kaouthia snake.

RESULTS

In vitro: (1) mice injected i.p. with MPT pre-incubated with Naja kaouthia venom at concentrations as low as 0.625 mg/ml showed 100% survival after a 24-h observation period. (2) In the proteomics study, mice injected with MPT pre-incubated with the Naja kaouthia venom showed down-regulation of five serum proteins. (3) In the protein-dye-binding study, the percentage of Bradford dye-protein binding showed a reduction relative to the decrease in MPT concentration used to incubate with the venom. In vivo: the results from the animal studies showed that MPT had no in vivo protection against the Naja kaouthia venom (0.875 mg/kg) in four different rescue modes and in an oral pre-treatment experiment.

CONCLUSION

The study indicated the promising ability of MPT to neutralize the Naja kaouthia venom in in vitro experiments but fell short in its in vivo potential. As such, the use of Mimosa pudica (Mimosaceae) as therapeutics for snake bites is questionable as all the possible in vivo rescue studies and pre-treatment of the active constituents showed no protection against the affected mice.

Purification and characterization of a metalloproteinase, Porthidin-1, from the venom of Lansberg's hog-nosed pitvipers (Porthidium lansbergii hutmanni)

Porthidium lansbergii hutmanni is a small pit viper found on Margarita Island, Venezuela. Local tissue damage is one of the most obvious characteristics of P. l. hutmanni envenomation, which can lead to diverse pathological effects, such as hemorrhage, edema, blistering, necrosis, lymphatic vessel damage and degradation of extracellular matrix. Metalloproteinases are one of the major components in venoms responsible for these effects. To date, very little is known or has been reported on P. l. hutmanni venom. Crude P. l. hutmanni venom had a LD(50) of 2.5 mg/kg and was considered very hemorrhagic (minimal hemorrhagic dose [MHD]: 0.98 μg) when compared to other hemorrhagic (Bothrops) venoms in Venezuela. Crude P. l. hutmanni venom also inhibited ADP-induced platelet aggregation. A metalloproteinase, Porthidin-1, from this venom was isolated by three chromatography steps (Sephadex G100, Superose 12 HR10/30 and Bioscale Q2). Porthidin-1 falls in the SVMP P-I class having a molecular weight of 23 kDa, verified by both SDS-PAGE and mass spectrometry. High-resolution mass spectrometry and a database search identified a peptide from Porthidin-1 (YNGDLDK) belonging to the SVMP family of proteins. Porthidin-1 contained hemorrhagic, fibrino(geno)lytic, caseinolytic and gelatinolytic activities, and these activities were capable of being neutralized by metalloproteinase inhibitors but not serine proteinase inhibitors. The peptide YNGDLDK shared similarities with five venom proteins with a BLAST e-value of <1. This work details the biochemical and pathophysiological effects that can result from envenomations, and highlights the importance and significance for characterizing unknown or poorly documented venoms from different geographical regions.

The structure of helokinestatin-5 and its biosynthetic precursor from Gila monster (Heloderma suspectum) venom: evidence for helokinestatin antagonism of bradykinin-induced relaxation of rat tail artery smooth muscle

Here we report the primary structure of a novel peptide, named helokinestatin-5 (VPPPLQMPLIPR), from the venom of the Gila monster (Heloderma suspectum). Helokinestatin-5 differs in structure from helokinestatin-3 by deletion of a single prolyl residue in the N-terminally located polyproline region. Two different biosynthetic precursors were consistently cloned from a venom-derived cDNA library. The first encoded helokinestatins 1-4 and a single copy of C-type natriuretic peptide, as previously described, whereas the second was virtually identical, lacking only a single prolyl codon as found in the mature attenuated helokinestatin-5 peptide. Helokinestatins 1-3 and 5 were synthesized by solid-phase fmoc chemistry and each synthetic replicate was found to antagonize the relaxation effect induced by bradykinin on rat tail artery smooth muscle. Helokinestatins thus represent a novel family of vasoactive peptides from the venom of helodermatid lizards.