Involvement of specific integrins in apoptosis induced by vascular apoptosis-inducing protein 1

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

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

Three snake venoms from Bothrops genus induced apoptosis and cell cycle arrest in K562 human leukemic cell line

Cancer is indisputably one of the leading causes of death worldwide. Snake venoms are a potential source of bioactive compounds, complex mixtures constituted mainly of proteins and peptides with several pharmacological possibilities, including the potential to inhibit tumoral cell growth. In the present study, it was evaluated the antitumor effect of crude venom of Bothrops erythromelas (BeV), Bothrops jararaca (from Southern and Southeastern- BjsV and BjsdV, respectively) and Bothrops alternatus (BaV) in in vitro Chronic myeloid leukemia (CML) cancer cell line model. After 24 h of cell exposure to 10 and 50 μg/mL, BjsV, BjsdV, and BaV exerted a decrease in cell viability in both concentrations. BeV was not cytotoxic and, therefore wasn't chosen for further mechanism of action investigation. Furthermore, morphological alterations show modification typical of apoptosis. Also, was observes a significant cell cycle arrest in the S phase by BjsdV and BaV treatment. Flow cytometry evidenced the involvement of changes in the cell membrane permeability and the mitochondrial function by BjsV and BjsdV, corroborating with the triggering of the apoptotic pathway by the venom administration. BjsV, BjsdV, and BaV also led to extensive DNA damage and were shown to modulate the gene expression of transcripts related to the cell cycle progression and suppress the expression of the BCR-ABL1 oncogene. Altogether, these findings suggest that the venoms trigger the apoptosis pathway due to mitochondrial damage and cell cycle arrest, with modulation of intracellular pathways important for CML progression. Thus, indicating the pharmacological potential of these venoms in the development of new antitumoral compounds.

Integrinβ1/FAK/ERK signalling pathway is essential for Chinese mitten crab Eriocheir sinensis hemocyte survival

Integrins are cellular adhesion molecules that mediate cell-cell, cell-extracellular matrix, and cell-pathogen interactions. Integrins can stimulate various signaling pathways by binding to different ligands, thereby exerting immunological functions. While integrins have been found to primarily play a role in bacterial agglutination, phagocytosis, and inhibition of apoptosis in invertebrates, the specific signaling pathway and mechanism of action remain unclear. In vertebrates, β1 integrin and extracellular matrix interactions can associate with focal adhesion kinase (FAK) to initiate MAPK/ERK signaling and regulate cell survival; however, in invertebrates (e.g., Chinese mitten crab), the mechanisms of integrins are poorly understood. The purpose of this study was to investigate whether integrinβ1/FAK activation of the MAPK/ERK pathway regulates hemocyte survival and the associated mechanism. Treatment with an integrinβ1 inhibitor RGD (a conserved tripeptide Arg-Gly-Asp), decreased the levels of FAK and ERK expression and phosphorylation, followed by an intensification of apoptosis. Similar results were obtained following siRNA knockdown of integrinβ1 expression. We further found that the attenuation of ERK phosphorylation enhanced the level of Caspase-3 expression. Together, these findings suggest that integrinβ1 activates the FAK/ERK signaling cascade and is involved in the survival of Chinese mitten crab hemocytes.

Structure-Function Relationship of the Disintegrin Family: Sequence Signature and Integrin Interaction

Disintegrins are small cysteine-rich proteins found in a variety of snake venom. These proteins selectively modulate integrin function, heterodimeric receptors involved in cell-cell and cell-matrix interaction that are widely studied as therapeutic targets. Snake venom disintegrins emerged from the snake venom metalloproteinase and are classified according to the sequence size and number of disulfide bonds. Evolutive structure and function diversification of disintegrin family involves a stepwise decrease in the polypeptide chain, loss of cysteine residues, and selectivity. Since the structure elucidation of echistatin, the description of the structural properties of disintegrins has allowed the investigation of the mechanisms involved in integrin-cell-extracellular matrix interaction. This review provides an analysis of the structures of all family groups enabling the description of an expanded classification of the disintegrin family in seven groups. Each group presents a particular disulfide pattern and sequence signatures, facilitating the identification of new disintegrins. The classification was based on the disintegrin-like domain of the human metalloproteinase (ADAM-10). We also present the sequence and structural signatures important for disintegrin-integrin interaction, unveiling the relationship between the structure and function of these proteins.

Increased Expression of Integrin Alpha 6 in Nucleus Pulposus Cells in Response to High Oxygen Tension Protects against Intervertebral Disc Degeneration

The destruction of the low oxygen microenvironment in nucleus pulposus (NP) cells played a critical role in the pathogenesis of intervertebral disc degeneration (IVDD). The purpose of this study was to determine the potential role of integrin alpha 6 (ITG α6) in NP cells in response to high oxygen tension (HOT) in IVDD. Immunofluorescence staining and western blot analysis showed that the levels of ITG α6 expression were increased in the NP tissue from IVDD patients and the IVDD rat model with mild degeneration, which were reduced as the degree of degeneration increases in severity. In NP cells, the treatment of HOT resulted in upregulation of ITG α6 expression, which could be alleviated by blocking the PI3K/AKT signaling pathway. Further studies found that ITG α6 could protect NP cells against HOT-induced apoptosis and oxidative stress and protect NP cells from HOT-inhibited ECM protein synthesis. Upregulation of ITG α6 expression by HOT contributed to maintaining NP tissue homeostasis through the interaction with hypoxia-inducible factor-1α (HIF-1α). Furthermore, silencing of ITG α6 in vivo could obviously accelerate puncture-induced IVDD. Taken together, these results revealed that the increase of ITG α6 expression by HOT in NP cells might be a protective factor in IVD degeneration as well as restore NP cell function.

Size Matters: An Evaluation of the Molecular Basis of Ontogenetic Modifications in the Composition of Bothrops jararacussu Snake Venom

Ontogenetic changes in venom composition have been described in Bothrops snakes, but only a few studies have attempted to identify the targeted paralogues or the molecular mechanisms involved in modifications of gene expression during ontogeny. In this study, we decoded B. jararacussu venom gland transcripts from six specimens of varying sizes and analyzed the variability in the composition of independent venom proteomes from 19 individuals. We identified 125 distinct putative toxin transcripts, and of these, 73 were detected in venom proteomes and only 10 were involved in the ontogenetic changes. Ontogenetic variability was linearly related to snake size and did not correspond to the maturation of the reproductive stage. Changes in the transcriptome were highly predictive of changes in the venom proteome. The basic myotoxic phospholipases A₂ (PLA₂s) were the most abundant components in larger snakes, while in venoms from smaller snakes, PIII-class SVMPs were the major components. The snake venom metalloproteinases (SVMPs) identified corresponded to novel sequences and conferred higher pro-coagulant and hemorrhagic functions to the venom of small snakes. The mechanisms modulating venom variability are predominantly related to transcriptional events and may consist of an advantage of higher hematotoxicity and more efficient predatory function in the venom from small snakes.

Vipers of the Middle East: A Rich Source of Bioactive Molecules

Snake venom serves as a tool of defense against threat and helps in prey digestion. It consists of a mixture of enzymes, such as phospholipase A2, metalloproteases, and l-amino acid oxidase, and toxins, including neurotoxins and cytotoxins. Beside their toxicity, venom components possess many pharmacological effects and have been used to design drugs and as biomarkers of diseases. Viperidae is one family of venomous snakes that is found nearly worldwide. However, three main vipers exist in the Middle Eastern region: Montivipera bornmuelleri, Macrovipera lebetina, and Vipera (Daboia) palaestinae. The venoms of these vipers have been the subject of many studies and are considered as a promising source of bioactive molecules. In this review, we present an overview of these three vipers, with a special focus on their venom composition as well as their biological activities, and we discuss further frameworks for the exploration of each venom.

Structures and Functions of Snake Venom Metalloproteinases (SVMP) from Protobothrops venom Collected in Japan

Snake venom metalloproteinases (SVMP) are widely distributed among the venoms of Crotalinae and Viperidae, and are organized into three classes (P-I, P-II and P-III) according to their size and domain structure. P-I SVMP are the smallest SVMP, as they only have a metalloproteinase (M) domain. P-II SVMP contain a disintegrin-like (D) domain, which is connected by a short spacer region to the carboxyl terminus of the M domain. P-III SVMP contain a cysteine-rich (C) domain, which is attached to the carboxyl terminus of the D domain. Some SVMP exhibit hemorrhagic activity, whereas others do not. In addition, SVMP display fibrinolytic/fibrinogenolytic (FL) activity, and the physiological functions of SVMP are controlled by their structures. Furthermore, these proteinases also demonstrate fibrinogenolytic and proteolytic activity against synthetic substrates for matrix metalloproteinases and ADAM (a disintegrin and metalloproteinase). This article describes the structures and FL, hemorrhagic, and platelet aggregation-inhibiting activity of SVMP derived from Protobothrops snake venom that was collected in Japan.

Bothropoides pauloensis venom effects on isolated perfused kidney and cultured renal tubular epithelial cells

Snake envenomation (Bothrops genus) is common in tropical countries and acute kidney injury is one of the complications observed in Bothrops snakebite with relevant morbidity and mortality. Here, we showed that Bothropoides pauloensis venom (BpV) decreased cell viability (IC50 of 7.5 μg/mL). Flow cytometry with annexin V and propidium iodide showed that cell death occurred predominantly by apoptosis and late apoptosis, through caspases 3 and 7 activation, mitochondrial membrane potential collapse and ROS overproduction. BpV reduced perfusion pressure, renal vascular resistance, urinary flow, glomerular filtration rate, percentage of sodium, chloride or potassium tubular transportation. These findings demonstrated that BpV cytotoxicity on renal epithelial cells might be responsible for the nephrotoxicity observed in isolated kidney.

Snake venom metalloproteinases

Recent proteomic analyses of snake venoms show that metalloproteinases represent major components in most of the Crotalid and Viperid venoms. In this chapter we discuss the multiple activities of the SVMPs. In addition to hemorrhagic activity, members of the SVMP family also have fibrin(ogen)olytic activity, act as prothrombin activators, activate blood coagulation factor X, possess apoptotic activity, inhibit platelet aggregation, are pro-inflammatory and inactivate blood serine proteinase inhibitors. Clearly the SVMPs have multiple functions in addition to their well-known hemorrhagic activity. The realization that there are structural variations in the SVMPs and the early studies that led to their classification represents an important event in our understanding of the structural forms of the SVMPs. The SVMPs were subdivided into the P-I, P-II and P-III protein classes. The noticeable characteristic that distinguished the different classes was their size (molecular weight) differences and domain structure: Class I (P-I), the small SVMPs, have molecular masses of 20-30 kDa, contain only a pro domain and the proteinase domain; Class II (P-II), the medium size SVMPs, molecular masses of 30-60 kDa, contain the pro domain, proteinase domain and disintegrin domain; Class III (P-III), the large SVMPs, have molecular masses of 60-100 kDa, contain pro, proteinase, disintegrin-like and cysteine-rich domain structure. Another significant advance in the SVMP field was the characterization of the crystal structure of the first P-I class SVMP. The structures of other P-I SVMPs soon followed and the structures of P-III SVMPs have also been determined. The active site of the metalloproteinase domain has a consensus HEXXHXXGXXHD sequence and a Met-turn. The "Met-turn" structure contains a conserved Met residue that forms a hydrophobic basement for the three zinc-binding histidines in the consensus sequence.

Functional analysis of a recombinant PIII-SVMP, GST-acocostatin; an apoptotic inducer of HUVEC and HeLa, but not SK-Mel-28 cells

Disintegrins and disintegrin-like peptides interact with integrins and interfere with cell-cell and cell-matrix interactions. A disintegrin-like snake venom gene, Acocostatin was cloned from the venom gland mRNA of Agkistrodon contortrix contortrix. Acocostatin belongs to the PIII-SVMP subfamily of disintegrin-like peptides. The recombinant acocostatin peptide was produced and purified as GST-fusion. The GST-acocostatin peptide, at 44 μg/mL, inhibited platelet aggregation by 30% in PRP and 18% in whole blood. In addition GST-acocostatin, at 220 μg/mL, inhibited SK-Mel-28 cell migration by 48%, but did not inhibit T24 cell migration. The GST-acocostatin peptide ability to induce apoptosis on HUVEC, HeLa, and SK-Mel-28 cells was determined using Annexin V-FITC and chromatin fragmentation assays after 24 h of treatment. At 5 μM GST-acocostatin peptide, 19.68%+/- 3.09 of treated HUVEC, and 35.86% +/- 2.05 of treated HeLa cells were in early apoptosis. The GST-acocostatin peptide also caused chromatin fragmentation of HUVEC and HeLa cells as determined by fluorescent microscopy and Hoechst staining. The GST-acocostatin peptide failed to induce apoptosis of SK-Mel-28 cells. We characterized the HUVEC, HeLa, and T24 integrin expression by flow cytometry, as the first step in determining GST-acocostatin binding specificity. Our results indicate that HUVEC express αv, αvβ3, αvβ5, α6, β1, and β3 integrin receptors. HeLa cells express α1, α2, α6, αv, αvβ5, and β1 integrin receptors. T24 cells express α1, α3, α6, αv, αvβ3, αvβ5, β1, β3, and β6 integrin receptors.

The mojastin mutant Moj-DM induces apoptosis of the human melanoma SK-Mel-28, but not the mutant Moj-NN nor the non-mutated recombinant Moj-WN

In this study, three recombinant mojastin peptides (Moj-WN, Moj-NN, and Moj-DM) were produced and compared functionally. Recombinant Moj peptides were purified as GST-fusions. GST-Moj-WN and GST-Moj-NN inhibited ADP-induced platelet aggregation in platelet rich plasma. The GST-Moj-WN had an IC(50) of 160nM, while the GST-Moj-NN had an IC(50) of 493nM. The GST-Moj-DM did not inhibit platelet aggregation. All three GST-Moj peptides inhibited SK-Mel-28 cell adhesion to fibronectin. The GST-Moj-WN inhibited the binding of SK-Mel-28 cells to fibronectin with an IC(50) of 11nM, followed by the GST-Moj-NN (IC(50) of 28nM), and the GST-Moj-DM (IC(50) of 46nM). The GST-Moj peptides' ability to induce apoptosis on SK-Mel-28 cells was determined using Annexin-V-FITC and nuclear fragmentation assays. Cells were incubated with 5muM GST-Moj peptides for 24h. At 5microM GST-Moj-DM peptide, 13.56%+/-2.08 of treated SK-Mel-28 cells were in early apoptosis. The GST-Moj-DM peptide also caused nuclear fragmentation as determined by fluorescent microscopy and Hoechst staining. The GST-Moj-WN and GST-Moj-NN peptides failed to induce apoptosis. We characterized the SK-Mel-28 integrin expression, as the first step in determining r-Moj binding specificity. Our results indicate that SK-Mel-28 cells express alphavbeta3, alphav, alpha6, beta1, and beta3 integrin receptors.

Cell death induced by Bothrops asper snake venom metalloproteinase on endothelial and other cell lines

Two adherent cell lines, BAEC and HeLa, and non-adherent Jurkat, were treated with snake venom metalloproteinase BaP1 to determine whether cytotoxicity, previously reported for this toxin, could be mediated by the process of anoikis. It was observed that there was no correlation between the ability of this toxin to induce loss of adherence, and the cytotoxic effect, since concentrations that do not induce loss of adherence (3-6 microg/mL), were able to trigger 50% of cytotoxicity in BAEC. In the case of HeLa, where toxicity was very low (less than 20% at maximun concentrations and times of exposure), significant detachment and no toxicity was observed at concentrations of 1.5 microg/mL, showing also no correlation between both events. We also observed differences between BAEC toxicity measured by XTT reduction and DNA fragmentation determined by flow cytometry (as an indicator of apoptosis), since concentrations that induce 100% of cytotoxicity barely showed any DNA fragmentation (12% at 24h), suggesting that if apoptosis was involved, DNA damage is still not present, although chromatin condensation, another indicator of apoptosis, is observed in 40% of the cells. Inhibition of BAEC cytotoxicity by caspase inhibitors indicate that apoptosis is playing a role in this process, but other mechanisms of cell death could be participating also. Another way to determine whether the mechanism of cell death was related to anoikis was using a non-adherent cell line, which should show substrate independence. We determined by TUNEL that at 50 microg/ml BaP1 triggered 50% of apoptosis at 96 h, an effect that was seen earlier, suggesting also that if this toxin was inducing apoptosis in a non-adherent cell line, the mechanism could not be related to loss of attachment. Cell cycle arrest in S phase was also observed in Jurkat cells, an effect that could be leading to apoptosis. In conclusion, since there was no correlation between cell detachment and cytotoxicity (and apoptosis) in adherent cell lines and due to the ability of BaP1 to induce apoptosis in a non-adherent cell line, we suggest that this enzyme is toxic by a mechanism not related to anoikis, and that in the case of Jurkat cells, it is likely to be related to its ability to induce cell cycle arrest. Processes other than apoptosis could be also involved in the cell death mechanism mediated by BaP1 on BAEC.

cDNA Cloning and Some Additional Peptide Characterization of a Single-Chain Vascular Apoptosis-Inducing Protein, VAP2

Vascular apoptosis-inducing proteins (VAPs) from hemorrhagic snake venom are apoptosis-inducing toxins targeting vascular endothelial cells. Well-characterized VAPs consist of disulfide-bridged double chains (ddVAPs). The authors previously described a single-chain VAP (scVAP), VAP2 from Crotalus atrox, which also induces apoptosis in endothelial cells (Masuda et al., 1998, European Journal of Biochemistry, 253, 36-41). The authors report here the whole cDNA sequences and some additional peptide characteristics of VAP2. In addition to the apoptosis-inducing activity of VAP2, the toxin displays a cell-detaching activity after incubation in high-salt conditions. These observations indicate that the apoptosis and cell-detaching functions can be discriminated. Analysis of the cell-detaching activity also revealed that VAP2 consists of two similar peptides, VAP2A and VAP2B, which are members of the PIII-type snake venom metalloproteases (SVMPs). The VAP2A cDNA encodes a 609-amino acid protein. In contrast, the peptide sequences of VAP2B were identical to that of catrocollastatin, an inhibitor of platelet aggregation. VAP2A and VAP2B interact with each other to form a noncovalent dimer similar to the ddVAPs, which was detected by native polyacrylamide gel electrophoresis. These data show some new characteristics of VAPs, which are important to clarify the apoptotic pathways in vascular endothelial cells.

Cytoskeletal rearrangement and cell death induced by Bothrops alternatus snake venom in cultured Madin–Darby canine kidney cells

Bothrops snake venoms cause renal damage, with renal failure being the main cause of death in humans bitten by these snakes. In this work, we investigated the cytoskeletal rearrangement and cytotoxicity caused by Bothrops alternatus venom in cultured Madin–Darby canine kidney (MDCK) cells. Incubation with venom (10 and 100 µg/mL) significantly (p <0.05) decreased the cellular uptake of neutral red dye after 1 and 3 h. Venom (100 µg/mL) also markedly decreased the transepithelial electrical resistance (RT) across MDCK monolayers. Staining with rhodamine-conjugated phalloidin revealed disarray of the cytoskeleton that involved the stress fibers at the basal cell surface and focal adhesion-associated F-actin in the cell–matrix contact region. Feulgen staining showed a significant decrease in the number of cells undergoing mitosis and an increase in the frequency of altered nuclei. Scanning electron microscopy revealed a decrease in the number of microvilli and the presence of cells with a fusiform format. Flow cytometry with annexin V and propidium iodide showed that cell death occurred by necrosis, with little apoptosis, a conclusion supported by the lack of DNA fragmentation characteristic of apoptosis. Pretreating the cells with catalase significantly attenuated the venom-induced loss of viability, indicating a possible involvement of H2O2 in the cellular damage; less protection was observed with superoxide dismutase or Nω-nitro-l-arginine methyl ester. These results indicate that Bothrops alternatus venom is cytotoxic to cultured MDCK cells, possibly via the action of reactive oxygen species. This cytotoxicity could contribute to nephrotoxicity after envenoming by this species.

Crystal structures of catrocollastatin/VAP2B reveal a dynamic, modular architecture of ADAM/adamalysin/reprolysin family proteins

Catrocollastatin/vascular apoptosis-inducing protein (VAP)2B is a metalloproteinase from Crotalus atrox venom, possessing metalloproteinase/disintegrin/cysteine-rich (MDC) domains that bear the typical domain architecture of a disintegrin and metalloproteinase (ADAM)/adamalysin/reprolysin family proteins. Here we describe crystal structures of catrocollastatin/VAP2B in three different crystal forms, representing the first reported crystal structures of a member of the monomeric class of this family of proteins. The overall structures show good agreement with both monomers of atypical homodimeric VAP1. Comparison of the six catrocollastatin/VAP2B monomer structures and the structures of VAP1 reveals a dynamic, modular architecture that may be important for the functions of ADAM/adamalysin/reprolysin family proteins.

FV peptide induces apoptosis in HEp 2 and HeLa cells: an insight into the mechanism of induction

The present study is an attempt to evaluate the antiproliferative potential of peptide (7.6 kDa) from lionfish (Pterios volitans) venom on cultured HEp2 and HeLa cells. Different dose of purified peptide (1, 2 and 4 μg/ml) at different time points (12, 24 and 36 hrs) were tested for antiproliferative index of the peptide. Among them, 2 μg/ml at 24 hrs was found to effectively inhibit cancer cell growth in vitro and did not cause any adverse effect on normal human lymphocytes. Apoptosis was examined by propidium iodide staining, confirmed by the expression of caspase-8 and caspase-3, down regulation of Bcl-2 expression and DNA fragmentation in treated cells, when compared to untreated HEp2 and HeLa cells. Thus fish venom peptide was found to selectively induce apoptosis in cancer cell.

Epithelial laminin alpha5 is necessary for distal epithelial cell maturation, VEGF production, and alveolization in the developing murine lung

Laminin alpha5 is prominent in the basement membrane of alveolar walls, airways, and pleura in developing and adult lung. Targeted deletion of laminin alpha5 in mice causes developmental defects in multiple organs, but embryonic lethality has precluded examination of the latter stages of lung development. To identify roles for laminin alpha5 in lung development, we have generated an inducible lung epithelial cell-specific Lama5 null (SP-CLama5(fl/-)) mouse through use of the Cre/loxP system, the human surfactant protein C promoter, and the reverse tetracycline transactivator. SP-CLama5(fl/-) embryos exposed to doxycycline from E6.5 died a few hours after birth. Compared to control littermates, SP-CLama5(fl/-) lungs had dilated, enlarged distal airspaces, but basement membrane ultrastructure was preserved. Distal epithelial cell differentiation was perturbed, with a marked reduction of alveolar type II cells and a virtual absence of type I cells. Cell proliferation was reduced and apoptosis was increased. Capillary density was diminished, and this was associated with a decrease in total lung VEGF production. Overall, these findings indicate that epithelial laminin alpha5, independent of its structural function, is necessary for murine lung development, and suggest a role for laminin alpha5 in signaling pathways that promote alveolar epithelial cell differentiation and VEGF expression.

Jararhagin, a snake venom metalloproteinase, induces a specialized form of apoptosis (anoikis) selective to endothelial cells

Jararhagin is a snake venom metalloproteinase (SVMP) from Bothrops jararaca involved in several hemostatic and inflammatory disorders that occur in human envenomings. In this study, we evaluated the effect of jararhagin on endothelial cells (tEnd). The exposure of tEnd to jararhagin (20 and 40microg/ml) resulted in apoptosis with activation of pro-caspase-3 and alterations in the ratio between Bax/Bcl-xL. We observed that apoptosis was followed by decrease of cell viability and the loss of cell adhesion. Jararhagin induced changes in cell shape with a decrease in cell spreading, rounding up and detachment. This was accompanied by a rearrangement of actin network and a decrease in FAK association to actin and in tyrosine phosphorylated proteins. Morphological alterations and apoptosis were abolished when jararhagin catalytic activity was inhibited, indicating the importance of catalysis. Treatment of murine peritoneal adherent cells or fibroblasts with jararhagin did not result in apoptosis. The data indicate that the pro-apoptotic effect of jararhagin is selective to endothelial cells, interfering with the adhesion mechanisms and inducing anoikis. The present model might be useful for the study of the relationships between the architectural changes in the cytoskeleton and the complex phenomenon named anoikis.

Severe cell fragmentation in the endothelial cell apoptosis induced by snake apoptosis toxin VAP1 is an apoptotic characteristic controlled by caspases

Hemorrhagic snake venom induces apoptosis in vascular endothelial cells (VEC). Vascular apoptosis-inducing protein 1 (VAP1), which is identified as an apoptosis toxin against vascular endothelial cells, induces apoptosis accompanied by severe cell fragmentation compared with that of apoptosis due to other inducers. The mechanism of this morphologic feature is not known. In this report, we examine the roles of the caspases in the apoptosis induced by VAP1. Measurement of the caspase activities shows that activation of caspases occurred in this type of cell death. In the presence of certain caspase inhibitors, the severe cell fragmentation was strongly inhibited. The other hand, cell death induced by VAP1 was not affected by caspase inhibitors. These data suggest that the severe cell fragmentation induced by the snake toxin is a special characteristic of this apoptosis. Apoptosis with severe cell fragmentation may be regarded as a new category of endothelial cell apoptosis.

Hemorrhage induced by snake venom metalloproteinases: biochemical and biophysical mechanisms involved in microvessel damage

Zinc-dependent metalloproteinases are responsible for the hemorrhagic activity characteristic of viperid snake venoms. Snake venom metalloproteinases (SVMPs) are classified in various groups (P-I-IV), according to their domain composition. P-III SVMPs, comprising metalloproteinase, disintegrin-like and cysteine-rich domains, exert more potent hemorrhagic activity than P-I SVMPs, which present only the metalloproteinase domain. SVMPs degrade various components of the basement membrane and are also able to hydrolyze endothelial cell membrane proteins, such as integrins and cadherins, involved in cell-matrix and cell-cell adhesion. In addition, disintegrin-like and cysteine-rich domains interact with endothelial cell integrins, interfering with their adhesion to extracellular matrix. Hemorrhage induced by SVMPs is an extremely rapid event in vivo, with capillary endothelial cells showing drastic structural alterations within few minutes. In contrast, observations in cell culture conditions do not evidence such rapid endothelial cell damage. Instead, the main effect is detachment and rounding of these cells; it is only after several hours of incubation that cells show evidence of apoptotic damage. This apparent discrepancy between in vivo and in vitro observations can be explained if biophysical forces operating on microvessels in vivo are taken into consideration. It is proposed that SVMP-induced hemorrhage occurs in vivo by a 'two-step' mechanism. Initially, SVMPs degrade basement membrane and adhesion proteins, thus weakening the capillary wall and perturbing the interactions between endothelial cells and the basement membrane. Then, transmural pressure acting on the weakened capillary wall causes distention. As a consequence, endothelial cells become very thin, until the integrity of the capillary wall is lost at some points, where extravasation occurs. In addition, endothelial cells become more susceptible to blood flow-dependent shear stress, which further contributes to capillary wall disruption.

Characterization of events associated with apoptosis/anoikis induced by snake venom metalloproteinase BaP1 on human endothelial cells

Human endothelial EA.hy926 cells were incubated with BaP1, a hemorrhagic metalloproteinase purified from Bothrops asper snake venom. Since the first hour of incubation with the proteinase, cells started showing DNA fragmentation, detected by a terminal deoxynucleotidyl transferase-mediated dUDP nick-end labeling (TUNEL)-based photometric enzyme-linked immunosorbent assay (ELISA). At later times, DNA fragments were predominantly located outside the cells, evidencing plasma membrane rupture. DNA fragmentation was completely abolished by Batimastat, a potent inhibitor of metalloproteinase enzymatic activity. Apoptosis induced by BaP1 on endothelial cells was independent of two Bcl-2 family members (anti-apototic Bcl-xL and pro-apoptotic Bax), that did not show any changes in their expression during a 24 h-treatment period. Interestingly, IkappaBalpha, an inhibitor of NFkappaB, decreased after 24 h of treatment, suggesting further activation of the transcription factor. When some elements of the apoptotic extrinsic pathway were assessed, it was observed that procaspase-8 completely disappeared after 24 h of treatment with BaP1, probably indicating its activation by a death receptor, whereas caspase-8 inhibitor, cellular FLICE-inhibitory protein (cFLIP(L)), increased its expression since the first hours of BaP1 incubation. In conclusion, treatment of human endothelial cells with BaP1 induces apoptosis/anoikis, independently of Bcl-2 family members Bax and Bcl-xL and associated with caspase-8 activation and cFLIP(L) up-regulation. Apoptosis was completely dependent on BaP1 enzymatic activity. Similarities between this and other endothelial cell anoikis-related systems suggest that BaP1 and other snake venom metalloproteinases may be useful experimental tools in the study of death-related events that occur when adherent cells loose contact with extracellular matrix.

Rattlesnake venom induces apoptosis by stimulating PC-PLC and upregulating the expression of integrin β4, P53 in vascular endothelial cells

In the previous studies, we found that phosphatidylcholine-specific phospholipase C (PC-PLC) was implicated in apoptosis induced by rattlesnake venom in vascular endothelial cells (VEC) [Biochem. Biophys. Res. Commun. (1997b) 223, 182]. In order to find out other signal elements in this pathway and the mechanisms by which PC-PLC mediates apoptosis induced by rattlesnake venom in VEC, the expression of integrin beta4 and P53 was evaluated when the activity of PC-PLC was suppressed by D609 (tricyclodecan-9-yl-xanthogenate), a specific inhibitor of this enzyme. The increase of integrin beta4 and P53 expression induced by the venom was markedly suppressed when apoptosis of VEC was inhibited by D609. The data indicated that integrin beta4 and P53 play important roles in signal transduction of apoptosis induced by rattlesnake venom, and that PC-PLC might regulate apoptosis by up-regulating the expression of integrin beta4 and P53 in VEC.

Alternagin-C, a Disintegrin-like Protein, Induces Vascular Endothelial Cell Growth Factor (VEGF) Expression and Endothelial Cell Proliferation in Vitro

Alternagin-C (ALT-C), a disintegrin-like protein purified from the venom of the Brazilian snake Bothrops alternatus, interacts with the major collagen I receptor, the alpha(2)beta(1) integrin, inhibiting collagen binding. Here we show that ALT-C also inhibits the adhesion of a mouse fibroblast cell line (NIH-3T3) to collagen I (IC(50) 2.2 microm). In addition, when immobilized on plate wells, ALT-C supports the adhesion of this cell line as well as of human vein endothelial cell (HUVEC). ALT-C (3 microm) does not detach cells that were previously bound to collagen I. ALT-C (5 nm) induces HUVEC proliferation in vitro, and it inhibits the positive effect of vascular endothelial growth factor (VEGF) or FGF-2 on the proliferation of these cells, thus suggesting a common mechanism for these proteins. Gene expression analysis of human fibroblasts growing on ALT-C- or collagen-coated plates showed that ALT-C and collagen I induce a very similar pattern of gene expression. When compared with cells growing on plastic only, ALT-C up-regulates the expression of 45 genes including the VEGF gene and down-regulates the expression of 30 genes. Fibroblast VEGF expression was confirmed by RT-PCR and ELISA assay. Up-regulation of the VEGF gene and other growth factors could explain the positive effect on HUVEC proliferation. ALT-C also strongly activates Akt/PKB phosphorylation, a signaling event involved in endothelial survival and angiogenesis. In conclusion, ALT-C acts as a survival factor, promoting adhesion and endothelial cell proliferation.

Integrin β4 is a target of rattlesnake venom during inducing apoptosis of vascular endothelial cells

To find more effective components which can trigger apoptosis in crude rattlesnake venom, and the possible mechanisms by which the venom causes apoptosis in vascular endothelial cells (VECs), we investigated the function of integrin beta4 by using the monoclonal antibody (mAb) of this integrin. We added anti-beta4 mAb 5 microg.ml(-1) to the cells treated with 2 microg.ml(-1) rattlesnake venom; apoptosis of these cells was completely inhibited 6 h after the treatment. Furthermore, the increase of P53 expression induced by the venom was markedly suppressed. The results first demonstrated that there was at least one important component target to integrin beta4 in crude rattlesnake (Crotalus atrox) venom; moreover, this component played its role in the early phase of apoptosis. The results also showed that integrin beta4 participated in signal transduction of apoptosis induced by rattlesnake venom in VEC by up-regulating the expression of p53.

Serum from rabbit orally administered cobra venom inhibits growth of implanted hepatocellular carcinoma cells in mice

AIM: To investigate the inhibitory effect of serum preparation from rabbits orally administered cobra venom (SRCV) on implanted hepatocellular carcinoma (HCC) cells in mice.

METHODS: An HCC cell line, HepA, was injected into mice to prepare implanted tumors. The animals (n = 30) were divided randomly into SRCV, 5-fluorouracil (5-FU), and distilled water (control) groups. From the second day after transplantation, 20 mg/kg 5-FU was administered intraperitoneally once a day for 9 d. SRCV (1000 mg/kg) or distilled water (0.2 mL) was given by gastrogavage. Tumor growth inhibition was described by the inhibitory rate (IR). Apoptosis was detected by transmission electron microscopy (TEM), flow cytometry (FCM), and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL). Student’s t-test was performed for statistical analysis.

RESULTS: The tumor growth was inhibited markedly by SRCV treatment compared to that in the control group (P < 0.01). The treatment resulted in a significant increase in the apoptotic rate of cancer cells by the factors of 10.5% ± 2.4% and 20.65% ± 3.2% as demonstrated through TUNEL and FCM assays, respectively (P < 0.01). The apoptotic cells were also identified by characteristic ultrastructural features.

CONCLUSION: SRCV can inhibit the growth of implanted HepA cells in mice, and the apoptosis rate appears to elevate during the process.