Effect of Crotalus viridis viridis snake venom on the ultrastructure and intracellular survival of Trypanosoma cruzi

A Review of Rattlesnake Venoms

Venom components are invaluable in biomedical research owing to their specificity and potency. Many of these components exist in two genera of rattlesnakes, Crotalus and Sistrurus, with high toxicity and proteolytic activity variation. This review focuses on venom components within rattlesnakes, and offers a comparison and itemized list of factors dictating venom composition, as well as presenting their known characteristics, activities, and significant applications in biosciences. There are 64 families and subfamilies of proteins present in Crotalus and Sistrurus venom. Snake venom serine proteases (SVSP), snake venom metalloproteases (SVMP), and phospholipases A2 (PLA2) are the standard components in Crotalus and Sistrurus venom. Through this review, we highlight gaps in the knowledge of rattlesnake venom; there needs to be more information on the venom composition of three Crotalus species and one Sistrurus subspecies. We discuss the activity and importance of both major and minor components in biomedical research and drug development.

Unlocking the potential of snake venom-based molecules against the malaria, Chagas disease, and leishmaniasis triad

Malaria, leishmaniasis and Chagas disease are vector-borne protozoal infections with a disproportionately high impact on the most fragile societies in the world, and despite malaria-focused research gained momentum in the past two decades, both trypanosomiases and leishmaniases remain neglected tropical diseases. Affordable effective drugs remain the mainstay of tackling this burden, but toxicicty, inneficiency against later stage disease, and drug resistance issues are serious shortcomings. One strategy to overcome these hurdles is to get new therapeutics or inspiration in nature. Indeed, snake venoms have been recognized as valuable sources of biomacromolecules, like peptides and proteins, with antiprotozoal activity. This review highlights major snake venom components active against at least one of the three aforementioned diseases, which include phospholipases A2, metalloproteases, L-amino acid oxidases, lectins, and oligopeptides. The relevance of this repertoire of biomacromolecules and the bottlenecks in their clinical translation are discussed considering approaches that should increase the success rate in this arduous task. Overall, this review underlines how venom-derived biomacromolecules could lead to pioneering antiprotozoal treatments and how the drug landscape for neglected diseases may be revolutionized by a closer look at venoms. Further investigations on poorly studied venoms is needed and could add new therapeutics to the pipeline.

Antibacterial Activity of Venom from the Puff Adder (Bitis arietans), Egyptian Cobra (Naja haje), and Red Spitting Cobra (Naja pallida)

Bitis arietans (Puff adder), Naja haje (Egyptian cobra), and Naja pallida (Red spitting cobra) venoms were tested for antimicrobial activity. This evaluation employed disc diffusion and microbroth dilution techniques. Gram-positive bacteria (Bacillus cereus and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Klebsiella pneumonia, and Salmonella typhi) were used. Aztreonam (30 µg), cefpodoxime (10 µg), cefoxitine (30 µg), streptomycin (25 µg), ceftriaxone (30 µg), nalidixic acid (30 µg), tetracycline (30 µg), and sulfamethoxazole (25 µg) were used as controls. All tests were conducted in triplicate (n = 3). Results. The activity of B. arietans venom against Gram-negative bacteria was significantly lower (p < 0.001) than that of controls. The efficacy of B. arietans venom and sulfamethoxazole against both Gram-positive and Gram-negative bacteria was not significantly different (p > 0.9999). The efficacy of B. arietans venom against Gram-positive bacteria was significantly lower (p < 0.001) than cefoxitin, streptomycin, and tetracycline. The efficacy of N. haje venom against Gram-negative bacteria was significantly lower (p < 0.001) than that of controls. There was no significant difference in the antimicrobial efficacy of N. haje venom and controls against Gram-positive bacteria (p=0.3927 to p=0.9998). There was no significant difference in the efficacy of N. pallida venom and controls against Gram-negative bacteria (p=0.3061 to p=0.9981). There was no significant difference in the efficacy of N. pallida venom and controls against Gram-positive bacteria (p=0.2368 to p > 0.9999). Conclusions. Of all the tested venoms, only Naja pallida venom showed good efficacy against both Gram-positive and Gram-negative bacteria.

Antiprotozoal Effect of Snake Venoms and Their Fractions: A Systematic Review

Background: Protozoal infection is a lingering public health issue of great concern, despite efforts to produce drugs and vaccines against it. Recent breakthrough research has discovered alternative antiprotozoal agents encompassing the use of snake venoms and their components to cure these infections. This study collated the existing literature to examine the antiprotozoal effect of snake venoms and their fractions. Methods: We conducted a systematic review following the PRISMA guidelines. The PubMed and Embase databases were searched from their inception until 13 October 2021. Articles were screened at the title, abstract and full-text phases. Some additional studies were obtained through the manual search process. Results: We identified 331 studies via the electronic database and manual searches, of which 55 reporting the antiprotozoal effect of snake venoms and their components were included in the review. Around 38% of studies examined the effect of whole crude venoms, and a similar percentage evaluated the effect of a proportion of enzymatic phospholipase A2 (PLA2). In particular, this review reports around 36 PLA2 activities and 29 snake crude venom activities. We also report the notable phenomenon of synergism with PLA2 isoforms of Bothrops asper. Importantly, limited attention has been given so far to the antiprotozoal efficacies of metalloproteinase, serine protease and three-finger toxins, although these venom components have been identified as significant components of the dominant venom families. Conclusion: This study highlights the impact of snake venoms and their fractions on controlling protozoal infections and suggests the need to examine further the effectiveness of other venom components, such as metalloproteinase, serine protease and three-finger toxins. Future research questions in this field must be redirected toward synergism in snake venom components, based on pharmacological usage and in the context of toxicology. Ascertaining the effects of snake venoms and their components on other protozoal species that have not yet been studied is imperative.

Panacea within a Pandora's box: the antiparasitic effects of phospholipases A2 (PLA2s) from snake venoms

Parasitic diseases affect millions of individuals worldwide, mainly in low-income regions. There is no cure for most of these diseases, and the treatment relies on drugs that have side effects and lead to drug resistance, emphasizing the urgency to find new treatments. Snake venom has been gaining prominence as a rich source of molecules with antiparasitic potentials, such as phospholipases A₂ (PLA₂s). Here, we compile the findings involving PLA₂s with antiparasitic activities against helminths, Plasmodium, Toxoplasma, and trypanosomatids. We indicate their molecular features, highlighting the possible antiparasitic mechanisms of action of these proteins. We also demonstrate interactions between PLA₂s and some parasite membrane components, shedding light on potential targets for drug design that may provide better treatment for the illnesses caused by parasites.

A Meta-Analysis of the Protein Components in Rattlesnake Venom

The specificity and potency of venom components give them a unique advantage in developing various pharmaceutical drugs. Though venom is a cocktail of proteins, rarely are the synergy and association between various venom components studied. Understanding the relationship between various components of venom is critical in medical research. Using meta-analysis, we observed underlying patterns and associations in the appearance of the toxin families. For Crotalus, Dis has the most associations with the following toxins: PDE; BPP; CRL; CRiSP; LAAO; SVMP P-I and LAAO; SVMP P-III and LAAO. In Sistrurus venom, CTL and NGF have the most associations. These associations can predict the presence of proteins in novel venom and understand synergies between venom components for enhanced bioactivity. Using this approach, the need to revisit the classification of proteins as major components or minor components is highlighted. The revised classification of venom components is based on ubiquity, bioactivity, the number of associations, and synergies. The revised classification can be expected to trigger increased research on venom components, such as NGF, which have high biomedical significance. Using hierarchical clustering, we observed that the genera's venom compositions were similar, based on functional characteristics rather than phylogenetic relationships.

In vitro trichomonocidal potency of Naja nigricollis and Bitis arietans snake venom

Background and Aim: Trichomonas vaginalis drug's limited efficacy and high toxicity, justify the need to explore other therapeutic agents, including animal toxins. In this study, the Naja nigricollis and Bitis arietans snake venoms were used to assess such trichomonocidal effect. Materials and Methods: The median lethal dose (LD50) value for both snake species was calculated by probit analysis using a statistical package for the sciences version 20.0 with an LD50 of 4.04 μg/mL for the N. nigricollis, and no mortality was observed in the B. arietans envenomed rats. Results: The trichomonocidal potency of the snake venom on T. vaginalis was evident with a growth inhibitory concentration of 89% with a half-maximal inhibitory concentration (IC50) of 0.805 μg/mL in B. arietans while 95% for N. nigricollis at an IC50 of 0.411 μg/mL. Conclusion: The statistical analysis of one-way analysis of variance shows a significant difference (p<0.05) between the venoms and positive control group (p<0.001), and there is no significant difference between each venom and its varying concentration (p>0.05). As the least concentration can be useful, interestingly, there is no significant difference in the efficacy of N. nigricollis and B. arietans to T. vaginalis (p>0.05); as such, either of the venom can be used for the treatment of trichomoniasis.

The functions of CAP superfamily proteins in mammalian fertility and disease

BACKGROUND

Members of the cysteine-rich secretory proteins (CRISPS), antigen 5 (Ag5) and pathogenesis-related 1 (Pr-1) (CAP) superfamily of proteins are found across the bacterial, fungal, plant and animal kingdoms. Although many CAP superfamily proteins remain poorly characterized, over the past decade evidence has accumulated, which provides insights into the functional roles of these proteins in various processes, including fertilization, immune defence and subversion, pathogen virulence, venom toxicology and cancer biology.

OBJECTIVE AND RATIONALE

The aim of this article is to summarize the current state of knowledge on CAP superfamily proteins in mammalian fertility, organismal homeostasis and disease pathogenesis.

SEARCH METHODS

The scientific literature search was undertaken via PubMed database on all articles published prior to November 2019. Search terms were based on following keywords: 'CAP superfamily', 'CRISP', 'Cysteine-rich secretory proteins', 'Antigen 5', 'Pathogenesis-related 1', 'male fertility', 'CAP and CTL domain containing', 'CRISPLD1', 'CRISPLD2', 'bacterial SCP', 'ion channel regulator', 'CatSper', 'PI15', 'PI16', 'CLEC', 'PRY proteins', 'ASP proteins', 'spermatogenesis', 'epididymal maturation', 'capacitation' and 'snake CRISP'. In addition to that, reference lists of primary and review article were reviewed for additional relevant publications.

OUTCOMES

In this review, we discuss the breadth of knowledge on CAP superfamily proteins with regards to their protein structure, biological functions and emerging significance in reproduction, health and disease. We discuss the evolution of CAP superfamily proteins from their otherwise unembellished prokaryotic predecessors into the multi-domain and neofunctionalized members found in eukaryotic organisms today. At least in part because of the rapid evolution of these proteins, many inconsistencies in nomenclature exist within the literature. As such, and in part through the use of a maximum likelihood phylogenetic analysis of the vertebrate CRISP subfamily, we have attempted to clarify this confusion, thus allowing for a comparison of orthologous protein function between species. This framework also allows the prediction of functional relevance between species based on sequence and structural conservation.

WIDER IMPLICATIONS

This review generates a picture of critical roles for CAP proteins in ion channel regulation, sterol and lipid binding and protease inhibition, and as ligands involved in the induction of multiple cellular processes.

The effect of the biflavonoid 2″,3″-dihydroochnaflavone on Trypanosoma cruzi Y strain

Trypanosoma cruzi is the causative agent of Chagas disease which affects 8 million people in Latin America. The parasite possesses high capacity to evade host immune system and the available drugs to treat Chagas disease present low efficacy combined to serious side effects to patients. Therefore, the identification of alternative therapeutics is essential. Brazilian flora exhibits an immense diversity of metabolites with great potential to be developed into new drugs. We investigated the action of 2″,3″-dihydroochnaflavone a biflavonoid extracted from Luxemburgia nobilis Eichler ex Engl. (Ochnaceae) against T. cruzi (Y strain). Our experiments showed that this compound is effective against parasite epimastigote forms, presenting IC₅₀ value of (2.5 ± 0.1) μM after 96 h of treatment. Ultrastructure alterations were also detected in treated epimastigotes especially mitochondrial enlargement at the kinetoplast region. At the concentration of 30 μM, the compound killed (61.6 ± 3.37)% of the parasite in its amastigote form. In addition, at the same concentration, the compound killed all trypamastigotes growing within murine macrophages after 7-9 days of infection. Nonetheless, the biflavonoid concentrations were harmless to murine enriched population of lymphocytes and peritoneal macrophages. These results indicate that 2″,3″- dihydroochnaflavone presents activity against T. cruzi.

Screening Snake Venoms for Toxicity to Tetrahymena Pyriformis Revealed Anti-Protozoan Activity of Cobra Cytotoxins

Snake venoms possess lethal activities against different organisms, ranging from bacteria to higher vertebrates. Several venoms were shown to be active against protozoa, however, data about the anti-protozoan activity of cobra and viper venoms are very scarce. We tested the effects of venoms from several snake species on the ciliate Tetrahymena pyriformis. The venoms tested induced T. pyriformis immobilization, followed by death, the most pronounced effect being observed for cobra Naja sumatrana venom. The active polypeptides were isolated from this venom by a combination of gel-filtration, ion exchange and reversed-phase HPLC and analyzed by mass spectrometry. It was found that these were cytotoxins of the three-finger toxin family. The cytotoxins from several cobra species were tested and manifested toxicity for infusorians. Light microscopy revealed that, because of the cytotoxin action, the infusorians’ morphology was changed greatly, from teardrop-like to an almost spherical shape, this alteration being accompanied by a leakage of cell contents. Fluorescence microscopy showed that the fluorescently labelled cytotoxin 2 from cobra N. oxiana was localized mainly at the membrane of killed infusorians, indicating that cytotoxins may kill T. pyriformis by causing membrane rupture. This work is the first evidence of the antiprotozoal activity of cobra venom cytotoxins, as demonstrated by the example of the ciliate T. pyriformis.

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.

Analysis of snake venom composition and antimicrobial activity

With the threat of a post-antibiotic era looming, the search for new and effective antibiotics from novel sources is imperative. Not only has crude snake venom been shown to be effective, but specific components within the venoms, such as Phospholipase A₂s and l-amino acid oxidases have been isolated and demonstrated to be effective as well. Despite numerous studies being completed on snake venoms, there is a heavy bias towards utilizing the venoms from the highly toxic Elapidae and Viperidae species. Very few studies have been conducted on the less toxic, but taxonomically more diverse, Colubridae. Furthermore, an extensive review of the literature examining the efficacy and potential specificity of these venoms has not been completed. Therefore, the aims of this study were to elucidate any similarities in snake venoms as well as investigate the efficacy of snake venom antimicrobial properties towards morphologically and metabolically diverse microbial classes and the prevalence of snake species with antimicrobial properties within each snake family. The results indicate that snake venoms and their isolated components are powerful antimicrobial agents but vary in efficacy towards different microbial classes. Furthermore, due to similarities in venom composition, and limited preliminary studies, the less toxic Colubridae family may be a fruitful area of research to find novel antimicrobial agents that are less harmful to humans.

Trypanocidal activity of mastoparan from Polybia paulista wasp venom by interaction with TcGAPDH

Chagas disease, considered a neglected disease, is a parasitic infection caused by Trypanosoma cruzi, which is endemic throughout the world. Previously, the antimicrobial effect of Mastoparan (MP) from Polybia paulista wasp venom against bacteria was described. To continue the study, we report in this short communication the antimicrobial effect of MP against Trypanosoma cruzi. MP inhibits all T. cruzi developmental forms through the inhibition of TcGAPDH suggested by the molecular docking. In conclusion, we suggest there is an antimicrobial effect also on T. cruzi.

In vitro antischistosomal activity of venom from the Egyptian snake Cerastes cerastes

INTRODUCTION:

We studied the potential in vitro antischistosomal activity of Cerastes cerastes venom on adult Schistosoma mansoni worms.

METHODS:

Live specimens of the horned viper snake, C. cerastes were collected from the Aswan Governorate (Egypt). Venom was collected from snakes by manual milking. Worms of S. mansoni were obtained from infected hamsters by perfusion and isolated from blood using phosphate buffer. Mortality rates of worms were monitored after 3 days of exposure to snake venom at LC50 and various sublethal concentrations (10, 5, 2.5µg/ml). Scanning electron microscopy was used to investigate tegumental changes in treated worms after exposure to LC50 doses of venom.

RESULTS:

The LC50 of C. cerastes venom was 21.5µg/ml. The effect of C. cerastes venom on Schistosoma worms varied according to their sex. The mortality rate of male and female worms after 48-h exposure was 83.3% and 50%, respectively. LC50 of C. cerastes venom induced mild to severe tegumental damage in Schistosoma worms in the form of destruction of the oral sucker, shrinkage and erosion of the tegument, and loss of some tubercle spines.

CONCLUSIONS:

The present study demonstrated that C. cerastes venom exerts potential in vitro antischistosomal activity in a time and dose-dependent manner. These results may warrant further investigations to develop novel schistosomicidal agents from C. cerastes snake venom.

Rapid changes in gene expression direct rapid shifts in intestinal form and function in the Burmese python after feeding

Snakes provide a unique and valuable model system for studying the extremes of physiological remodeling because of the ability of some species to rapidly upregulate organ form and function upon feeding. The predominant model species used to study such extreme responses has been the Burmese python because of the extreme nature of postfeeding response in this species. We analyzed the Burmese python intestine across a time series, before, during, and after feeding to understand the patterns and timing of changes in gene expression and their relationship to changes in intestinal form and function upon feeding. Our results indicate that >2,000 genes show significant changes in expression in the small intestine following feeding, including genes involved in intestinal morphology and function (e.g., hydrolases, microvillus proteins, trafficking and transport proteins), as well as genes involved in cell division and apoptosis. Extensive changes in gene expression occur surprisingly rapidly, within the first 6 h of feeding, coincide with changes in intestinal morphology, and effectively return to prefeeding levels within 10 days. Collectively, our results provide an unprecedented portrait of parallel changes in gene expression and intestinal morphology and physiology on a scale that is extreme both in the magnitude of changes, as well as in the incredibly short time frame of these changes, with up- and downregulation of expression and function occurring in the span of 10 days. Our results also identify conserved vertebrate signaling pathways that modulate these responses, which may suggest pathways for therapeutic modulation of intestinal function in humans.

Crovirin, a snake venom cysteine-rich secretory protein (CRISP) with promising activity against Trypanosomes and Leishmania

Background

The neglected human diseases caused by trypanosomatids are currently treated with toxic therapy with limited efficacy. In search for novel anti-trypanosomatid agents, we showed previously that the Crotalus viridis viridis (Cvv) snake venom was active against infective forms of Trypanosoma cruzi. Here, we describe the purification of crovirin, a cysteine-rich secretory protein (CRISP) from Cvv venom with promising activity against trypanosomes and Leishmania.

Methodology/Principal Findings

Crude venom extract was loaded onto a reverse phase analytical (C8) column using a high performance liquid chromatographer. A linear gradient of water/acetonitrile with 0.1% trifluoroacetic acid was used. The peak containing the isolated protein (confirmed by SDS-PAGE and mass spectrometry) was collected and its protein content was measured. T. cruzi trypomastigotes and amastigotes, L. amazonensis promastigotes and amastigotes and T. brucei rhodesiense procyclic and bloodstream trypomastigotes were challenged with crovirin, whose toxicity was tested against LLC-MK₂ cells, peritoneal macrophages and isolated murine extensor digitorum longus muscle. We purified a single protein from Cvv venom corresponding, according to Nano-LC MS/MS sequencing, to a CRISP of 24,893.64 Da, henceforth referred to as crovirin. Human infective trypanosomatid forms, including intracellular amastigotes, were sensitive to crovirin, with low IC₅₀ or LD₅₀ values (1.10–2.38 µg/ml). A considerably higher concentration (20 µg/ml) of crovirin was required to elicit only limited toxicity on mammalian cells.

Conclusions

This is the first report of CRISP anti-protozoal activity, and suggests that other members of this family might have potential as drugs or drug leads for the development of novel agents against trypanosomatid-borne neglected diseases.

The pathogenic trypanosomatid parasites of the genera Leishmania and Trypanosoma infect over 20 million people worldwide, with an annual incidence of ∼3 million new infections. An additional 400 million people are at risk of infection by exposure to parasite-infected insects which act as disease vectors. Trypanosomatid-borne diseases predominant in poorer nation and are considered neglected, having failed to attract the attention of the pharmaceutical industry. However, novel therapy is sorely needed for Trypanosoma and Leishmania infections, currently treated with ‘dated’ drugs that are often difficult to administer in resource-limiting conditions, have high toxicity and are by no means always successful, partly due to the emergence of drug resistance. The last few decades have witnessed a growing interest in examining the potential of bioactive toxins and poisons as drugs or drug leads, as well as for diagnostic applications. In this context, we isolated and purified crovirin, a protein from the Crotalus viridis viridis (Cvv) snake venom capable to inhibiting and/or lysing infective forms of trypanosomatid parasites, at concentrations that are not toxic to host cells. This feature makes crovirin a promising candidate protein for the development of novel therapy against neglected diseases caused by trypanosomatid pathogens.

Melittin peptide kills Trypanosoma cruzi parasites by inducing different cell death pathways

Antimicrobial peptides (AMPs) are components of the innate immune response that represent desirable alternatives to conventional pharmaceuticals, as they have a fast mode of action, a low likelihood of resistance development and can act in conjunction with existing drug regimens. AMPs exhibit strong inhibitory activity against both Gram-positive and Gram-negative bacteria, fungi, viruses, metazoans and other parasites, such as the protozoan Leishmania. Melittin is a naturally occurring AMP, which comprises 40-50% of the dry weight of Apis mellifera venom. Our group has recently shown that crude A. mellifera venom is lethal to Trypanosoma cruzi, the Chagas disease etiologic agent, and generates a variety of cell death phenotypes among treated parasites. Here, we demonstrate that the melittin affected all of T. cruzi developmental forms, including the intracellular amastigotes. The ultrastructural changes induced by melittin suggested the occurrence of different programmed cell death pathways, as was observed in A. mellifera-treated parasites. Autophagic cell death appeared to be the main death mechanism in epimastigotes. In contrast, melittin-treated trypomastigotes appeared to be dying via an apoptotic mechanism. Our findings confirm the great potential of AMPs, including melittin, as a potential source of new drugs for the treatment of neglected diseases, such as Chagas disease.

Apis mellifera venom induces different cell death pathways in Trypanosoma cruzi

Chagas disease chemotherapy is based on drugs that exhibit toxic effects and have limited efficacy, such as Benznidazole. Therefore, research into new chemotherapeutic agents from natural sources needs to be exploited. Apis mellifera venom consists of many biologically active molecules and has been reported to exhibit remarkable anti-cancer effects, often promoting an apoptosis-like death phenotype. This study demonstrates that A. mellifera venom can affect the growth, viability and ultrastructure of all Trypanosoma cruzi developmental forms, including intracellular amastigotes, at concentrations 15- to 100-fold lower than those required to cause toxic effects in mammalian cells. The ultrastructural changes induced by the venom in the different developmental forms led us to hypothesize the occurrence of different programmed cell death pathways. Autophagic cell death, characterized by the presence of autophagosomes-like organelles and a strong monodansyl cadaverine labelling, appears to be the main death mechanism in epimastigotes. In contrast, increased TUNEL staining, abnormal nuclear chromatin condensation and kDNA disorganization was observed in venom-treated trypomastigotes, suggesting cell death by an apoptotic mechanism. On the other hand, intracellular amastigotes presented a heterogeneous cell death phenotype profile, where apoptosis-like death seemed to be predominant. Our findings confirm the great potential of A. mellifera venom as a source for the development of new drugs for the treatment of neglected diseases such as Chagas disease.

In vitro antiplasmodial activity of phospholipases A2 and a phospholipase homologue isolated from the venom of the snake Bothrops asper

The antimicrobial and antiparasite activity of phospholipase A₂ (PLA₂) from snakes and bees has been extensively explored. We studied the antiplasmodial effect of the whole venom of the snake Bothrops asper and of two fractions purified by ion-exchange chromatography: one containing catalytically-active phospholipases A₂ (PLA₂) (fraction V) and another containing a PLA₂ homologue devoid of enzymatic activity (fraction VI). The antiplasmodial effect was assessed on in vitro cultures of Plasmodium falciparum. The whole venom of B. asper, as well as its fractions V and VI, were active against the parasite at 0.13 ± 0.01 µg/mL, 1.42 ± 0.56 µg/mL and 22.89 ± 1.22 µg/mL, respectively. Differences in the cytotoxic activity on peripheral blood mononuclear cells between the whole venom and fractions V and VI were observed, fraction V showing higher toxicity than total venom and fraction VI. Regarding toxicity in mice, the whole venom showed the highest lethal effect in comparison to fractions V and VI. These results suggest that B. asper PLA₂ and its homologue have antiplasmodial potential.

Antiplasmodial effect of the venom of Crotalus durissus cumanensis, crotoxin complex and Crotoxin B

The antiplasmodial activity of phospholipases A(2) (PLA(2)) isolated from different animals has been studied. We explored the in vitro anti Plasmodium falciparum effect of a fraction containing crotoxin, Crotoxin B and whole venom of the rattlesnake Crotalus durissus cumanensis. Fraction II (crotoxin complex) was obtained by size exclusion chromatography, whereas Crotoxin B was purified by RP-HPLC. The whole venom is active against the parasite at concentrations of 0.17±0.03 μg/ml, fraction II at 0.76±0.17 μg/ml and Crotoxin B at 0.6±0.04 μg/ml. Differences were observed in the cytotoxic activity against peripheral mononuclear cells, with Crotoxin B exhibiting the highest cytotoxicity. The concentration of Crotoxin B required to exert cytotoxic activity was higher than that required to exert antiplasmodial activity. Lethality in mice confirmed the higher toxicity and neurotoxicity of whole venom and fraction II, whereas Crotoxin B was not lethal at the doses tested. These results suggest the potential of Crotoxin B as a lead compound for antimalarial activity.

Effects of amiodarone and posaconazole on the growth and ultrastructure of Trypanosoma cruzi

The antifungal posaconazole (PCZ) is the most advanced candidate for the treatment of Chagas disease, having potent anti-Trypanosoma cruzi activity in vitro and in animal models of the disease as well as an excellent safety profile in humans. Amiodarone (AMD) is the antiarrhythmic drug most frequently used for the symptomatic treatment of chronic Chagas disease patients, but it also has specific anti-T. cruzi activity. When used in combination, these drugs exhibit potent synergistic activity against the parasite. In the present work, electron microscopy was used to analyse the effects of both compounds, acting individually or in combination, against T. cruzi. The 50% inhibitory concentration (IC(50)) against epimastigote and amastigote forms was 25 nM and 1.0 nM for PCZ and 8 μM and 5.6 μM for AMD, respectively. The antiproliferative synergism of the drugs (fractional inhibitory concentration<0.5) was confirmed and the ultrastructural alterations in the parasite induced by them, leading to cell death, were characterised using electron microscopy. These alterations include intense wrinkling of the protozoan surface, swelling of the mitochondrion, shedding of plasma membrane vesicles, the appearance of vesicles in the flagellar pocket, alterations in the kinetoplast, disorganisation of the Golgi complex, accumulation of lipid inclusions in the cytoplasm, and the formation of autophagic vacuoles, the latter confirmed by immunofluorescence microscopy. These findings indicate that the association of PCZ and AMD may constitute an effective anti-T. cruzi therapy with low side effects.