Lysine 49 phospholipase A2 proteins

Varespladib in the Treatment of Snakebite Envenoming: Development History and Preclinical Evidence Supporting Advancement to Clinical Trials in Patients Bitten by Venomous Snakes

The availability of effective, reliably accessible, and affordable treatments for snakebite envenoming is a critical and long unmet medical need. Recently, small, synthetic toxin-specific inhibitors with oral bioavailability used in conjunction with antivenom have been identified as having the potential to greatly improve outcomes after snakebite. Varespladib, a small, synthetic molecule that broadly and potently inhibits secreted phospholipase A2 (sPLA2s) venom toxins has renewed interest in this class of inhibitors due to its potential utility in the treatment of snakebite envenoming. The development of varespladib and its oral dosage form, varespladib-methyl, has been accelerated by previous clinical development campaigns to treat non-envenoming conditions related to ulcerative colitis, rheumatoid arthritis, asthma, sepsis, and acute coronary syndrome. To date, twenty-nine clinical studies evaluating the safety, pharmacokinetics (PK), and efficacy of varespladib for non-snakebite envenoming conditions have been completed in more than 4600 human subjects, and the drugs were generally well-tolerated and considered safe for use in humans. Since 2016, more than 30 publications describing the structure, function, and efficacy of varespladib have directly addressed its potential for the treatment of snakebite. This review summarizes preclinical findings and outlines the scientific support, the potential limitations, and the next steps in the development of varespladib's use as a snakebite treatment, which is now in Phase 2 human clinical trials in the United States and India.

South American snake venoms with abundant neurotoxic components. Composition and toxicological properties. A literature review

In South America there are three snake genera with predominantly neurotoxic venoms: Crotalus, Micrurus and Hydrophis, which include nine species/subspecies, 97 species and a single marine species, respectively. Although accidents with neurotoxic venoms are less frequent than those with anticoagulant, cytotoxic or necrotic venoms (e.g. from Bothrops), they are of major public health importance. Venoms from genus Crotalus have been extensively studied, while data on the venoms from the other two genera are very limited, especially for Hydrophis. The venoms of North and South American Crotalus species show biochemical and physiopathological differences. The former species cause bothrops-like envenomation symptoms, while the latter mainly have neurotoxic and myotoxic effects, leading to respiratory paralysis and, occasionally, renal failure by myoglobinuria and death, often with no local lesions. Micrurus and Hydrophis also cause neurotoxic envenomations. Many studies have isolated, identified and characterized new enzymes and toxins, thus expanding the knowledge of snake venom composition. The present review summarizes the currently available information on neurotoxic venoms from South American snakes, with a focus on protein composition and toxicological properties. It also includes some comments concerning potential medical applications of elapid and crotalic toxins.

Synergism of in vitro plasmodicidal activity of phospholipase A2 isoforms isolated from panamanian Bothrops asper venom

Bothrops asper is one of the most important snake species in Central America, mainly because of its medical importance in countries like Ecuador, Panama and Costa Rica, where this species causes a high number of snakebite accidents. Several basic phospholipases A₂ (PLA₂s) have been previously characterized from B. asper venom, but few studies have been carried out with its acidic isoforms. In addition, since snake venom is a rich source of bioactive substances, it is necessary to investigate the biotechnological potential of its components. In this context, this study aimed to carry out the biochemical characterization of PLA₂ isoforms isolated from B. asper venom and to evaluate the antiparasitic potential of these toxins. The venom and key fractions were subjected to different chromatographic steps, obtaining nine PLA₂s, four acidic ones (BaspAc-I, BaspAc-II, BaspAc-III and BaspAc-IV) and five basic ones (BaspB-I, BaspB-II, BaspB-III, BaspB-IV and BaspB-V). The isoelectric points of the acidic PLA₂s were also determined, which presented values ranging between 4.5 and 5. The findings indicated the isolation of five unpublished isoforms, four Asp49-PLA, corresponding to the group of acidic isoforms, and one Lys49-PLA₂-like. Acidic PLA₂s catalyzed the degradation of all substrates evaluated; however, for the basic PLA₂s, there was a preference for phosphatidylglycerol and phosphatidic acid. The antiparasitic potential of the toxins was evaluated, and the acidic PLA₂s demonstrated action against the epimastigote forms of T. cruzi and promastigote forms of L. infantum, while the basic PLA₂s BaspB-II and BaspB-IV showed activity against P. falciparum. The results indicated an increase of up to 10 times in antiplasmodial activity, when the Asp49-PLA₂ and Lys49-PLA₂ were associated with one another, denoting synergistic action between these PLA₂ isoforms. These findings correspond to the first report of synergistic antiplasmodial action for svPLA₂s, demonstrating that these molecules may be important targets in the search for new antiparasitic agents.

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.

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.

Antimalarial activity of basic phospholipases A2 isolated from Paraguayan Bothrops diporus venom against Plasmodium falciparum

Malaria is a parasitic infectious disease and was responsible for 400.000 deaths in 2018. Plasmodium falciparum represents the species that causes most human deaths due to severe malaria. In addition, studies prove the resistance of P. falciparum to drugs used to treat malaria, making the search for new drugs with antiplasmodial potential necessary. In this context, the literature describes snake venoms as a rich source of molecules with microbicidal potential, including phospholipases A2 (PLA2s). In this sense, the present study aimed to isolate basic PLA2s from Paraguayan Bothrops diporus venom and evaluate their antiplasmodial potential. Basic PLA2s were obtained using two chromatographic steps. Initially, B. diporus venom was subjected to ion exchange chromatography (IEC). The electrophoretic profile of the fractions from the IEC permitted the selection of 3 basic fractions, which were subjected to reverse phase chromatography, resulting in the isolation of the PLA2s. The toxins were tested for enzymatic activity using a chromogenic substrate and finally, the antiplasmodial, cytotoxic potential and hemolytic activity of the isolated toxins were evaluated. The electrophoretic profile of the fractions from the IEC permitted the selection of 3 basic fractions, which were subjected to reverse phase chromatography, resulting in the isolation of the two enzymatically active PLA2s, BdTX-I and BdTX-II and the PLA2 homologue BdTX-III. The antiplasmodial potential was evaluated and the toxins showed IC50 values of: 2.44, 0.0153 and 0.59 μg/mL respectively, presenting PLA2 selectivity according to the selectivity index results (SI) calculated against HepG2 cells. The results show that the 3 basic phospholipases isolated in this study have a potent antiparasitic effect against the W2 strain of P. falciparum. In view of the results obtained in this work, further research are necessary to determine the mechanism of action by which these toxins cause cell death in parasites.

Insights into the antiviral activity of phospholipases A2 (PLA2s) from snake venoms

Viruses are associated with several human diseases that infect a large number of individuals, hence directly affecting global health and economy. Owing to the lack of efficient vaccines, antiviral therapy and emerging resistance strains, many viruses are considered as a potential threat to public health. Therefore, researches have been developed to identify new drug candidates for future treatments. Among them, antiviral research based on natural molecules is a promising approach. Phospholipases A₂ (PLA₂s) isolated from snake venom have shown significant antiviral activity against some viruses such as Dengue virus, Human Immunodeficiency virus, Hepatitis C virus and Yellow fever virus, and have emerged as an attractive alternative strategy for the development of novel antiviral therapy. Thus, this review provides an overview of remarkable findings involving PLA₂s from snake venom that possess antiviral activity, and discusses the mechanisms of action mediated by PLA₂s against different stages of virus replication cycle. Additionally, molecular docking simulations were performed by interacting between phospholipids from Dengue virus envelope and PLA₂s from Bothrops asper snake venom. Studies on snake venom PLA₂s highlight the potential use of these proteins for the development of broad-spectrum antiviral drugs.

Muscle proteolysis via ubiquitin-proteasome system (UPS) is activated by BthTx-I Lys49 PLA2 but not by BthTx-II Asp49 PLA2 and Bothrops jararacussu venom

Bites by viperid snakes belonging to Bothrops genus produce fast and intense local edema, inflammation, bleeding and myonecrosis. In this study, we investigated the role of Myogenic Regulatory Factors (MRFs: MyoD; Myog), negatively regulated by GDF-8 (Myostatin), and ubiquitin-proteasome system pathway (UPS: MuRF-1; Fbx-32) in gastrocnemius muscle regeneration after Bothrops jararacussu snake venom (Bjussu) or its isolated phospholipase A₂ myotoxins, BthTx-I (Lys-49 PLA₂) and BthTx-II (Asp-49 PLA₂) injection. Male Swiss mice received a single intra-gastrocnemius injection of crude Bjussu, at a dose/volume of 0.83 mg/kg/20 μl, and BthTx-I or BthTx-II, at a dose/volume of 2.5 mg/kg/20 μl. Control mice (Sham) received an injection of sterile saline solution (NaCl 0.9%; 20 μl). At 24, 48, 72 and 96 h post injection, right gastrocnemius was collected for protein expression analyses. Based on the temporal expressional dynamics of MyoD, Myog and GDF-8/Myostatin, it was possible to propose that the myogenesis pathway was impacted most badly by BthTx-II followed by BthTx-I and lastly by B. jararacussu venom, thus suggesting that catalytic activity has likely inhibitory role on the satellite cells-mediated reparative myogenesis pathway. Inversely, the catalytic activity seems to be not a determinant for the activation of proteins ubiquitination by MuRF-1 and Fbx-32/Atrogin-1 E3 proteasome ligases, given proteolysis pathway through UPS was activated neither after Bjussu, nor after BthTx-II, but just after the catalytically-inactive BthTx-I Lys-49 PLA₂-homologue exposure. The findings of this study disclose interesting perspective for further mechanistic studies about pathways that take part in the atrophy and repair after permanent damage induced by bothropic snakebites.

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.

Inflammasome Activation Induced by a Snake Venom Lys49-Phospholipase A2 Homologue

Background: Snake venom phospholipases A₂ (PLA₂s) have hemolytic, anticoagulant, myotoxic, oedematogenic, bactericidal, and inflammatory actions. BthTX-I, a Lys49-PLA₂ isolated from Bothrops jararacussu venom, is an example of Lys49-PLA₂ that presents such actions. NLRP3 is a cytosolic receptor from the NLR family responsible for inflammasome activation via caspase-1 activation and IL-1β liberation. The study of NLRs that recognize tissue damage and activate the inflammasome is relevant in envenomation. Methods: Male mice (18–20 g) received an intramuscular injection of BthTX-I or sterile saline. The serum was collected for creatine-kinase (CK), lactate dehydrogenase (LDH), and interleukin-1β (IL-1β) assays, and muscle was removed for inflammasome activation immunoblotting and qRT-PCR expression for nucleotide and oligomerization domain, leucine-rich repeat-containing protein family, pyrin-containing domain 3 receptor (NLRP3) inflammasome components. Results: BthTX-I-induced inflammation and myonecrosis, shown by intravital microscope, and LDH and CK release, respectively. Mouse treatment with A438079, a P2X7 receptor antagonist, did not modify these effects. BthTX-I induced inflammasome activation in muscle, but P2X7R participation in this effect was not observed. Conclusion: Together, the results showed for the first time that BthTX-I in gastrocnemius muscle induces inflammation and consequently, inflammasome activation via NLRP3 with caspase-1 activation and IL-1β liberation.

Beyond the 'big four': Venom profiling of the medically important yet neglected Indian snakes reveals disturbing antivenom deficiencies

Background

Snakebite in India causes the highest annual rates of death (46,000) and disability (140,000) than any other country. Antivenom is the mainstay treatment of snakebite, whose manufacturing protocols, in essence, have remained unchanged for over a century. In India, a polyvalent antivenom is produced for the treatment of envenomations from the so called ‘big four’ snakes: the spectacled cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Daboia russelii), and saw-scaled viper (Echis carinatus). In addition to the ‘big four’, India is abode to many other species of venomous snakes that have the potential to inflict severe clinical or, even, lethal envenomations in their human bite victims. Unfortunately, specific antivenoms are not produced against these species and, instead, the ‘big four’ antivenom is routinely used for the treatment.

Methods

We characterized the venom compositions, biochemical and pharmacological activities and toxicity profiles (mouse model) of the major neglected yet medically important Indian snakes (E. c. sochureki, B. sindanus, B. fasciatus, and two populations of N. kaouthia) and their closest ‘big four’ congeners. By performing WHO recommended in vitro and in vivo preclinical assays, we evaluated the efficiencies of the commercially marketed Indian antivenoms in recognizing venoms and neutralizing envenomations by these neglected species.

Findings

As a consequence of dissimilar ecologies and diet, the medically important snakes investigated exhibited dramatic inter- and intraspecific differences in their venom profiles. Currently marketed antivenoms were found to exhibit poor dose efficacy and venom recognition potential against the ‘neglected many’. Premium Serums antivenom failed to neutralise bites from many of the neglected species and one of the ‘big four’ snakes (North Indian population of B. caeruleus).

Conclusions

This study unravels disturbing deficiencies in dose efficacy and neutralisation capabilities of the currently marketed Indian antivenoms, and emphasises the pressing need to develop region-specific snakebite therapy for the ‘neglected many’.

Snakebite is a ‘neglected tropical disease’ that majorly affects the rural populations in developing countries. India bears the brunt of snakebites with over 46,000 deaths and 140,000 disabilities, annually. A significant number of these bites are attributed to the widely distributed ‘big four’ snakes, namely spectacled cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Daboia russelii), and saw-scaled viper (Echis carinatus). The commercial antivenoms marketed in India are only manufactured against these four species, while neglecting many other medically relevant snakes with restricted geographic distribution. Snakebite pathology is dependent on the venom composition of the population/species, which can, in turn, vary intra- and inter-specifically. Though this variation severely limits the cross-population/species antivenom efficacy, envenomations by the neglected snakes in India are treated with the ‘big four’ antivenom. Therefore, to unravel the underlying venom variability, we investigated venom proteomic, biochemical/pharmacological and toxicity profiles of the major neglected Indian snakes and their ‘big four’ relatives. To assess the effectiveness of the ‘big four’ antivenom in treating bites from these neglected snakes, we performed preclinical experiments, which revealed alarming inadequacies of the commercial antivenoms. Our findings accentuate the compelling necessity for the innovation of highly efficacious next-generation snakebite therapy in India.

Isolation, Biochemical Characterization and Antiparasitic Activity of BmatTX-IV, A Basic Lys49-Phospholipase A2 from the Venom of Bothrops mattogrossensis from Paraguay

Background:

Functional and structural diversity of proteins of snake venoms is coupled with a wide repertoire of pharmacological effects. Snake venoms are targets of studies linked to searching molecules with biotechnological potential.

Methods:

A homologue phospholipase A2 (BmatTX-IV) was obtained using two chromatographic techniques. Mass spectrometry and two-dimensional gel electrophoresis were used to determine the molecular mass and isoelectric point, respectively. By means of Edman degradation chemistry, it was possible to obtain the partial sequence of amino acids that comprise the isolated toxin. Trypanocidal, leishmanicidal and cytoxic activity against Trypanosoma cruzi, Leishmania infantum and murine fibrobasts was determinated.

Results:

Combination of both chromatographic steps used in this study demonstrated efficacy to obtain the PLA2-Lys49. BmatTX-IV showed molecular mass and isoelectric point of 13.55 kDa and 9.3, respectively. Amino acid sequence of N-terminal region (51 residues) shows the presence of Lys49 residue at position 49, a distinctive trait of enzymatically inactive PLA2. Bothrops mattogrossensis snake venom showed IC50 values of 11.9 μg/mL against Leishmania infantum promastigotes and of 13.8 μg/mL against Trypanosoma cruzi epimastigotes, respectively. On the other hand, the venom showed a high cytotoxic activity (IC50 value of 16.7 μg/mL) against murine fibroblasts, whereas the BmatTX-IV showed IC50 value of 81.2 μg/mL.

Conclusion:

Physicochemical and biological characterization of snake venoms components is critically important, since these complex mixtures provide a source of molecules with antiparasitic potential, making further studies necessary to identify and characterize components with higher efficacy and selectivity.

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.

Cytotoxic and inflammatory potential of a phospholipase A2 from Bothrops jararaca snake venom

Background

Snake venom phospholipases A₂ (PLA₂s) have been reported to induce myotoxic, neurotoxic, hemolytic, edematogenic, cytotoxic and proinflammatory effects. This work aimed at the isolation and functional characterization of a PLA₂ isolated from Bothrops jararaca venom, named BJ-PLA₂-I.

Methods and Results

For its purification, three consecutive chromatographic steps were used (Sephacryl S-200, Source 15Q and Mono Q 5/50 GL). BJ-PLA₂-I showed acidic characteristics, with pI~ 4.4 and molecular mass of 14.2 kDa. Sequencing resulted in 60 amino acid residues that showed high similarity to other Bothrops PLA₂s, including 100% identity with BJ-PLA₂, an Asp49 PLA₂ previously isolated from B. jararaca venom. Being an Asp49 PLA₂, BJ-PLA₂-I showed high catalytic activity, and also inhibitory effects on the ADP-induced platelet aggregation. Its inflammatory characterization showed that BJ-PLA₂-I was able to promote leukocyte migration in mice at different concentrations (5, 10 and 20 μg/mL) and also at different response periods (2, 4 and 24 h), mainly by stimulating neutrophil infiltration. Furthermore, increased levels of total proteins, IL-6, IL-1β and PGE₂ were observed in the inflammatory exudate induced by BJ-PLA₂-I, while nitric oxide, TNF-α, IL-10 and LTB₄ levels were not significantly altered. This toxin was also evaluated for its cytotoxic potential on normal (PBMC) and tumor cell lines (HL-60 and HepG2). Overall, BJ-PLA₂-I (2.5–160 μg/mL) promoted low cytotoxicity, with cell viabilities mostly varying between 70 and 80% and significant values obtained for HL-60 and PBMC only at the highest concentrations of the toxin evaluated.

Conclusions

BJ-PLA₂-I was characterized as an acidic Asp49 PLA₂ that induces acute local inflammation and low cytotoxicity. These results should contribute to elucidate the action mechanisms of snake venom PLA₂s.

Venom Complexity in a Pitviper Produced by Facultative Parthenogenesis

Facultative parthenogenesis (FP) is asexual reproduction in plant and animal species that would otherwise reproduce sexually. This process in vertebrates typically results from automictic development (likely terminal fusion) and is phylogenetically widespread. In squamate reptiles and chondrichthyan fishes, FP has been reported to occur in nature and can result in the production of reproductively viable offspring; suggesting that it is of ecological and evolutionary significance. However, terminal fusion automixis is believed to result in near genome-wide reductions in heterozygosity; thus, FP seems likely to affect key phenotypic characters, yet this remains almost completely unstudied. Snake venom is a complex phenotypic character primarily used to subjugate prey and is thus tightly linked to individual fitness. Surprisingly, the composition and function of venom produced by a parthenogenetic pitviper exhibits a high degree of similarity to that of its mother and conspecifics from the same population. Therefore, the apparent loss of allelic diversity caused by FP appears unlikely to have a significant impact on the prey-capturing ability of this snake. Accordingly, the pitviper offspring produced by FP retained complex phenotypic characteristics associated with fitness. This result reinforces the potential ecological and evolutionary importance of FP and questions our understanding of the inheritance of venom-associated genes.

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.

Purification and characterization of the first γ-phospholipase inhibitor (γPLI) from Bothrops jararaca snake serum

Phospholipases A₂ (PLA₂) are enzymes acting on the cell membrane phospholipids resulting in fatty acids and lysophospholipids and deconstructing the cell membrane. This protein is commonly found in snake venoms, causing tissue inflammation in the affected area. Evidence indicates that snakes have natural resistance to their own venom due to protective properties in plasma, that inhibit the action of proteins present in their venom. Given that, this study aimed to purify and characterize a γPLI from Bothrops jararaca serum, named γBjPLI. PLA₂ inhibitor was isolated using two chromatographic steps: an ion exchange column (DEAE), followed by an affinity column (crotoxin coupled to a CNBr-activated Sepharose resin). The purity and biochemical characterization of the isolated protein were analyzed by RP-HPLC, SEC, SDS-PAGE, circular dichroism and mass spectrometry. The ability to inhibit PLA₂ was determined by enzymatic activity, neutralization of paw edema and myonecrosis. The protein purity was confirmed by RP-HPLC and SEC, whilst an apparent molecular mass of 25 kDa and 20 kDa was obtained by SDS-PAGE, under reducing and non-reducing conditions, respectively. According to mass spectrometry analysis, this protein showed 72% and 68% of coverage when aligned to amino acid sequences of two proteins already described as PLIs. Thus, the inhibitory activity of enzymatic, edema and myonecrotic activities by γBjPLI suggests a role of this inhibitor for protection of these snakes against self-envenomation.

Alpha-type phospholipase A2 inhibitors from snake blood

It is of popular and scientific knowledge that toxins from snake venom (among them the PLA2 and myotoxins) are neutralized by various compounds, such as antibodies and proteins purified from animal blood. Venomous and nonvenomous snakes have PLA2 inhibitory proteins, called PLIs, in their blood serum. One hypothesis that could explain the presence of these PLIs in the serum of venomous snakes would be self-protection against the enzymes of their own venom, which eventually could reach the circulatory system. However, the presence of PLIs in non-venomous snakes suggests that their physiological role might not be restricted to protection against PLA2 toxins, but could be extended to other functions, as in the innate immune system and local regulation of PLA2s. The present study aimed to review the currently available literature on PLA2 and myotoxin alpha inhibitors present in snake plasma, thus helping to improve the research on these molecules. Furthermore, this review includes current information regarding the mechanism of action of these inhibitors in an attempt to better understand their application, and proposes the use of these molecules as new models in snakebite therapy. These molecules may help in the neutralization of different types of phospholipases A2 and myotoxins, complementing the conventional serum therapy.

Structural determinants of the hyperalgesic activity of myotoxic Lys49-phospholipase A2

BACKGROUND

Bothropstoxin-I (BthTx-I) is a Lys49-phospholipase A₂ (Lys49-PLA₂) from the venom of Bothrops jararacussu, which despite of the lack of catalytic activity induces myotoxicity, inflammation and pain. The C-terminal region of the Lys49-PLA₂s is important for these effects; however, the amino acid residues that determine hyperalgesia and edema are unknown. The aim of this study was to characterize the structural determinants for the Lys49-PLA₂-induced nociception and inflammation.

METHODS

Scanning alanine mutagenesis in the active-site and C-terminal regions of BthTx-I has been used to study the structural determinants of toxin activities. The R118A mutant was employed as this substitution decreases PLA₂ myotoxicity. In addition, K115A and K116A mutants - which contribute to decrease cytotoxicity - and the K122A mutant - which decreases both myotoxicity and cytotoxicity - were also used. The H48Q mutant - which does not interfere with membrane damage or myotoxic activity - was used to evaluate if the PLA₂ catalytic site is relevant for the non-catalytic PLA₂-induced pain and inflammation. Wistar male rats received intraplantar injections with mutant PLA₂. Subsequently, hyperalgesia and edema were evaluated by the paw pressure test and by a plethysmometer. Native and recombinant BthTx-I were used as controls.

RESULTS

Native and recombinant BthTx-I induced hyperalgesia and edema, which peaked at 2 h. The R118A mutant did not induce nociception or edema. The mutations K115A and K116A abolished hyperalgesia without interfering with edema. Finally, the K122A mutant did not induce hyperalgesia and presented a decreased inflammatory response.

CONCLUSIONS

The results obtained with the BthTx-I mutants suggest, for the first time, that there are distinct residues responsible for the hyperalgesia and edema induced by BthTx-I. In addition, we also showed that cytolytic activity is essential for the hyperalgesic effect but not for edematogenic activity, corroborating previous data showing that edema and hyperalgesia can occur in a non-dependent manner. Understanding the structure-activity relationship in BthTx-I has opened new possibilities to discover the target for PLA₂-induced pain.

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.

Privileged frameworks from snake venom

Venom as a form of chemical prey capture is a key innovation that has underpinned the explosive radiation of the advanced snakes (Caenophidia). Small venom proteins are often rich in disulfide bonds thus facilitating stable molecular scaffolds that present key functional residues on the protein surface. New toxin types are initially developed through the venom gland over-expression of normal body proteins, their subsequent gene duplication and diversification that leads to neofunctionalisation as random mutations modify their structure and function. This process has led to preferentially selected (privileged) cysteine-rich scaffolds that enable the snake to build arrays of toxins many of which may lead to therapeutic products and research tools. This review focuses on cysteine-rich small proteins and peptides found in snake venoms spanning natriuretic peptides to phospholipase enzymes, while highlighting their three-dimensional structures and biological functions as well as their potential as therapeutic agents or research tools.

Alkylation of histidine residues of Bothrops jararacussu venom proteins and isolated phospholipases A2: a biotechnological tool to improve the production of antibodies

Crude venom of Bothrops jararacussu and isolated phospholipases A₂ (PLA₂) of this toxin (BthTX-I and BthTX-II) were chemically modified (alkylation) by p-bromophenacyl bromide (BPB) in order to study antibody production capacity in function of the structure-function relationship of these substances (crude venom and PLA₂ native and alkylated). BthTX-II showed enzymatic activity, while BthTX-I did not. Alkylation reduced BthTX-II activity by 50% while this process abolished the catalytic and myotoxic activities of BthTX-I, while reducing its edema-inducing activity by about 50%. Antibody production against the native and alkylated forms of BthTX-I and -II and the cross-reactivity of antibodies to native and alkylated toxins did not show any apparent differences and these observations were reinforced by surface plasmon resonance (SPR) data. Histopathological analysis of mouse gastrocnemius muscle sections after injection of PBS, BthTX-I, BthTX-II, or both myotoxins previously incubated with neutralizing antibody showed inhibition of the toxin-induced myotoxicity. These results reveal that the chemical modification of the phospholipases A₂ (PLA₂) diminished their toxicity but did not alter their antigenicity. This observation indicates that the modified PLA₂ may provide a biotechnological tool to attenuate the toxicity of the crude venom, by improving the production of antibodies and decreasing the local toxic effects of this poisonous substance in animals used to produce antivenom.

Purification and biochemical characterization of three myotoxins from Bothrops mattogrossensis snake venom with toxicity against Leishmania and tumor cells

Bothrops mattogrossensis snake is widely distributed throughout eastern South America and is responsible for snakebites in this region. This paper reports the purification and biochemical characterization of three new phospholipases A₂ (PLA₂s), one of which is presumably an enzymatically active Asp49 and two are very likely enzymatically inactive Lys49 PLA₂ homologues. The purification was obtained after two chromatographic steps on ion exchange and reverse phase column. The 2D SDS-PAGE analysis revealed that the proteins have pI values around 10, are each made of a single chain, and have molecular masses near 13 kDa, which was confirmed by MALDI-TOF mass spectrometry. The N-terminal similarity analysis of the sequences showed that the proteins are highly homologous with other Lys49 and Asp49 PLA₂s from Bothrops species. The PLA₂s isolated were named BmatTX-I (Lys49 PLA₂-like), BmatTX-II (Lys49 PLA₂-like), and BmatTX-III (Asp49 PLA₂). The PLA₂s induced cytokine release from mouse neutrophils and showed cytotoxicity towards JURKAT (leukemia T) and SK-BR-3 (breast adenocarcinoma) cell lines and promastigote forms of Leishmania amazonensis. The structural and functional elucidation of snake venoms components may contribute to a better understanding of the mechanism of action of these proteins during envenomation and their potential pharmacological and therapeutic applications.

Antitumoral activity of snake venom proteins: new trends in cancer therapy

For more than half a century, cytotoxic agents have been investigated as a possible treatment for cancer. Research on animal venoms has revealed their high toxicity on tissues and cell cultures, both normal and tumoral. Snake venoms show the highest cytotoxic potential, since ophidian accidents cause a large amount of tissue damage, suggesting a promising utilization of these venoms or their components as antitumoral agents. Over the last few years, we have studied the effects of snake venoms and their isolated enzymes on tumor cell cultures. Some in vivo assays showed antineoplastic activity against induced tumors in mice. In human beings, both the crude venom and isolated enzymes revealed antitumor activities in preliminary assays, with measurable clinical responses in the advanced treatment phase. These enzymes include metalloproteases (MP), disintegrins, L-amino acid oxidases (LAAOs), C-type lectins, and phospholipases A2 (PLA2s). Their mechanisms of action include direct toxic action (PLA2s), free radical generation (LAAOs), apoptosis induction (PLA2s, MP, and LAAOs), and antiangiogenesis (disintegrins and lectins). Higher cytotoxic and cytostatic activities upon tumor cells than normal cells suggest the possibility for clinical applications. Further studies should be conducted to ensure the efficacy and safety of different snake venom compounds for cancer drug development.

Action of two phospholipases A2 purified from Bothrops alternatus snake venom on macrophages

The in vitro effects of BaltTX-I, a catalytically inactive Lys49 variant of phospholipase A2 (PLA2), and BaltTX-II, an Asp49 catalytically active PLA2 isolated from Bothrops alternatus snake venom, on thioglycollate-elicited macrophages (TG-macrophages) were investigated. At non-cytotoxic concentrations, the secretory PLA2 BaltTX-I but not BaltTX-II stimulated complement receptor-mediated phagocytosis. Pharmacological treatment of TG-macrophages with staurosporine, a protein kinase C (PKC) inhibitor, showed that this kinase is involved in the increase of serum-opsonized zymosan phagocytosis induced by BaltTX-I but not BaltTX-II secretory PLA2, suggesting that PKC may be involved in the stimulatory effect of this toxin in serum-opsonized zymosan phagocytosis. Moreover, BaltTX-I and -II induced superoxide production by TG-macrophages. This superoxide production stimulated by both PLA2s was abolished after treatment of cells with staurosporine, indicating that PKC is an important signaling pathway for the production of this radical. Our experiments showed that, at non-cytotoxic concentrations, BaltTX-I may upregulate phagocytosis via complement receptors, and that both toxins upregulated the respiratory burst in TG-macrophages.

Cytotoxic activities of [Ser⁴⁹]phospholipase A₂ from the venom of the saw-scaled vipers Echis ocellatus, Echis pyramidum leakeyi, Echis carinatus sochureki, and Echis coloratus

Fractionation by reversed-phase HPLC of venom from four species of saw-scaled viper: Echis ocellatus, Echis pyramidum leakeyi, Echis carinatus sochureki, and Echis coloratus led to identification in each sample of an abundant protein with cytotoxic activity against human non-small cell lung adenocarcinoma A549 cells. The active component in each case was identified by MALDI-TOF mass fingerprinting of tryptic digests as [Ser⁴⁹]phospholipase A₂ ([Ser⁴⁹]PLA₂). An isoform of [Ser⁴⁹]PLA₂ containing the single Ala¹⁸→ Val substitution and a partially characterized [Asp⁴⁹]PLA₂ were also present in the E. coloratus venom. LC₅₀ values against A549 cells for the purified [Ser⁴⁹]PLA₂ proteins from the four species are in the range 2.9-8.5 μM. This range is not significantly different from the range of LC₅₀ values against human umbilical vein endothelial HUVEC cells (2.5-12.2 μM) indicating that the [Ser⁴⁹]PLA₂ proteins show no differential anti-tumor activity. The LC₅₀ value for [Ser⁴⁹]PLA₂ from E. ocellatus against human erythrocytes is >100 μM and the MIC values against Escherichia coli and Staphylococcus aureus are >100 μM. It is suggested that the [Ser⁴⁹]PLA₂ proteins play a major role in producing local tissue necrosis and hemorrhage at the site of envenomation.

Effect of monospecific antibodies against baltergin in myotoxicity induced by Bothrops alternatus venom from northeast of Argentina. Role of metalloproteinases in muscle damage

Myotoxicity, one of the most relevant local manifestations in envenomation by Bothrops genus, may result from a direct action of myotoxins or be due to an indirect vascular degeneration and ischemia. Baltergin, a snake venom metalloproteinase (SVMP), isolated from Bothrops alternatus venom has been used to obtain monospecific IgG, in order to determine the relative role of toxin in myotoxicity induced by whole venom. Bothrops diporus venom, another medical relevant genus of the northeastern region of Argentina, was also studied. Anti-baltergin IgG was able to neutralize completely the hemorrhagic activity of B. alternatus venom at an antibodies:venom ratio of 30:1 (w:w). However, mice injected with B. diporus venom showed a small spot remaining even at the highest ratio of IgG:venom assayed (50:1; w:w). Specific antibodies were efficient to neutralize the myotoxicity of B. alternatus venom at ratio 30:1 (w:w) but did not neutralize the same effects in B. diporus venom. Anti-baltergin polyclonal antibodies were useful tools for revealing the central role of SVMPs in the development of myotoxicity of B. alternatus venom, as well as, helping to suggest indirectly presence of potent myotoxic phospholipases A2 (PLA2s) in B. diporus venom.

A Lys49 phospholipase A2, isolated from Bothrops asper snake venom, induces lipid droplet formation in macrophages which depends on distinct signaling pathways and the C-terminal region

MT-II, a Lys49PLA₂ homologue devoid of catalytic activity from B. asper venom, stimulates inflammatory events in macrophages. We investigated the ability of MT-II to induce formation of lipid droplets (LDs), key elements of inflammatory responses, in isolated macrophages and participation of protein kinases and intracellular PLA₂s in this effect. Influence of MT-II on PLIN2 recruitment and expression was assessed, and the effects of some synthetic peptides on LD formation were further evaluated. At noncytotoxic concentrations, MT-II directly activated macrophages to form LDs. This effect was reproduced by a synthetic peptide corresponding to the C-terminal sequence 115–129 of MT-II, evidencing the critical role of C-terminus for MT-II-induced effect. Moreover, MT-II induced expression and recruitment of PLIN2. Pharmacological interventions with specific inhibitors showed that PKC, PI3K, ERK1/2, and iPLA₂, but not P38^MAPK or cPLA₂, signaling pathways are involved in LD formation induced by MT-II. This sPLA₂ homologue also induced synthesis of PGE₂ that colocalized to LDs. In conclusion, MT-II is able to induce formation of LDs committed to PGE₂ formation in a process dependent on C-terminal loop engagement and regulated by distinct protein kinases and iPLA₂. LDs may constitute an important inflammatory mechanism triggered by MT-II in macrophages.

Combined snake venomics and venom gland transcriptomic analysis of Bothropoides pauloensis

Unraveling the repertoire of venom toxins of Bothropoides pauloensis was assessed by snake venomics and venom gland transcriptomic surveys. Both approaches yielded converging overall figures, pointing to metalloproteinases (~37%), PLA(2)s (26-32%), and vasoactive (bradykinin-potentiating) peptides (12-17%) as the major toxin classes. The high occurrence of SVMPs, PLA(2) molecules, vasoactive peptides, along with serine proteinases, explains the local and systemic effects observed in envenomations by B. pauloensis. Minor (<3%) C-type lectin, serine proteinase, L-amino acid oxidase, nerve growth factor, and CRISP molecules were also identified in the transcriptome and the proteome. Low abundance (0.3%) EST singletons coding for vascular endothelial growth factor (svVEGF), ohanin, hyaluronidase, and 5' nucleotidase were found only in the venom gland cDNA library. At the molecular level, the transcriptomic and proteomic datasets display low compositional concordance. In particular, although there is good agreement between transcriptome and proteome in the identity of BPPs, PLA(2) molecules and L-amino acid oxidase, both datasets strongly depart in their C-type lectin and SVMP complements. These data support the view that venom composition is influenced by transcriptional and translational mechanisms and emphasize the value of combining proteomic and transcriptomic approaches to acquire a more complete understanding of the toxinological profile and natural history of the snake venom.

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

Natural inhibitors occupy an important place in the potential to neutralize the toxic effects caused by snake venom proteins and enzymes. It has been well recognized for several years that animal sera, some of the plant and marine extracts are the most potent in neutralizing snake venom phospholipase A(2) (svPLA(2)). The implication of this review to update the latest research work which has been accomplished with svPLA(2) inhibitors from various natural sources like animal, marine organisms presents a compilation of research in this field over the past decade and revisiting the previous research report including those found in plants. In addition to that the bioactive compounds/inhibitor molecules from diverse sources like aristolochic alkaloid, flavonoids and neoflavonoids from plants, hydrocarbones -2, 4 dimethyl hexane, 2 methylnonane, and 2, 6 dimethyl heptane obtained from traditional medicinal plants Tragia involucrata (Euphorbiaceae) member of natural products involved for the inhibitory potential of phospholipase A(2) (PLA(2)) enzymes in vitro and also decrease both oedema induced by snake venom as well as human synovial fluid PLA(2). Besides marine natural products that inhibit PLA(2) are manoalide and its derivatives such as scalaradial and related compounds, pseudopterosins and vidalols, tetracylne from synthetic chemicals etc. There is an overview of the role of PLA(2) in inflammation that provides a rationale for seeking inhibitors of PLA(2) as anti-inflammatory agents. However, more studies should be considered to evaluate antivenom efficiency of sera and other agents against a variety of snake venoms found in various parts of the world. The implications of these new groups of svPLA(2) toxin inhibitors in the context of our current understanding of snake biology as well as in the development of new novel antivenoms therapeutics agents in the efficient treatment of snake envenomations are discussed.

Molecular characterization of an acidic phospholipase A(2) from Bothrops pirajai snake venom: synthetic C-terminal peptide identifies its antiplatelet region

This paper describes a biochemical and pharmacological characterization of BpirPLA(2)-I, the first acidic Asp49-PLA(2) isolated from Bothrops pirajai. BpirPLA(2)-I caused hypotension in vivo, presented phospholipolytic activity upon artificial substrates and inhibitory effects on platelet aggregation in vitro. Moreover, a synthetic peptide of BpirPLA(2)-I, comprising residues of the C-terminal region, reproduced the antiplatelet activity of the intact protein. A cDNA fragment of 366 bp encompassing the mature form of BpirPLA(2)-I was cloned by reverse transcriptase-PCR of B. pirajai venom gland total RNA. A Bayesian phylogenetic analysis indicated that BpirPLA(2)-I forms a clade with other acid Asp49-PLA(2) enzymes from the Bothrops genus, which are characterized by the high catalytic activity associated with anticoagulant or hypotensive activity or both. Comparison of the electrostatic potential (EP) on the molecular surfaces calculated from a BpirPLA(2)-I homology model and from the crystallographic models of a group of close homologues revealed that the greatest number of charge inversions occurred on the face opposite to the active site entrance, particularly in the Ca(2+) ion binding loop. This observation suggests a possible relationship between the basic or acid character of PLA(2) enzymes and the functionality of the Ca(2+) ion binding loop.

Isolation and characterization of two new Lys49 PLA2s with heparin neutralizing properties from Bothrops moojeni snake venom

Among the proteins and peptides already characterized in Bothrops moojeni venom, two novel phospholipases A(2) (PLA(2)) have been purified and fully sequenced by ESI-MS/MS techniques. Both of them belong to the enzymatically non-active Lys49 variants of PLA(2). They consist of 122 amino acids and share a characteristic sequence in their C-terminal region composed of clusters of basic amino acids known to interact with heparin. Thus, as already established, heparin can be used as an antidote to antagonize some myotoxic PLA(2)s from venoms of Bothrops genus. The two PLA(2) variants were shown to interact in vitro with unfractionated heparin (UFH) and low molecular weight heparin (LMWH), neutralizing their anticoagulant properties. Although the influences of PLA(2)s from snake venoms on the blood coagulation system are known, their use to antagonize the anticoagulant effect of heparin in vitro or in vivo has never been proposed. These finding recommend diagnostic and therapeutic applications, which are currently investigated.

Nandrolone stimulates MyoD expression during muscle regeneration in the condition of myonecrosis induced by Bothrops jararacussu venom poisoning

Myonecrosis with permanent loss of muscle mass is a relevant local toxic effect following envenomation with Bothrops jararacussu snake venom. Regeneration of adult skeletal muscle involves the activation of satellite cells, a process regulated by myogenic regulatory factors (MRF). MyoD is an MRF involved in both proliferation and differentiation of satellite cells. Androgens are modulators of skeletal muscle, known to increase muscle mass and strength. This study examined the hypothesis that anabolic androgens improve the muscle regeneration process in mice following envenomation by Bothrops jararacussu snake venom. Myonecrosis was induced by venom injection (30 microg/50 microl in physiological solution) over the extensor digitorum longus (EDL) muscles of mice. Nandrolone (ND) (6 mg/kg, sc) was administered after 12 h, 7 d, and 14 d following venom injection. The histological changes in EDL muscle at 1, 3, 7, and 21 d after muscle injury were analyzed by light microscopy. Cross-sectional areas of fibers were measured. MyoD was evaluated by immunofluorescence technique. Histological examination revealed the presence of a regeneration process in ND-treated animals, characterized by the appearance of some myotubes at 3 d, and numerous myotubes at 7 d from venom injection. Nandrolone treatment reduced the frequency of small fibers at 7 and 21 d after venom administration, and increased the frequency of large fibers at 7 d postinjury. Nandrolone also significantly augmented the expression of MyoD-positive cells at 7 and 21 d after envenomation. These results suggest that ND accelerates muscle regeneration and indicate the involvement of MyoD in this process.