Contortrostatin, a homodimeric snake venom disintegrin, is a potent inhibitor of osteoclast attachment

Effect of minor amounts of β-calcium pyrophosphate and hydroxyapatite on the physico-chemical properties and osteoclastic resorption of β-tricalcium phosphate cylinders

β-Tricalcium Phosphate (β-TCP), one of the most used bone graft substitutes, may contain up to 5 wt% foreign phase according to standards. Typical foreign phases include β-calcium pyrophosphate (β-CPP) and hydroxyapatite (HA). Currently, the effect of small amounts of impurities on β-TCP resorption is unknown. This is surprising since pyrophosphate is a very potent osteoclast inhibitor. The main aim of this study was to assess the effect of small β-CPP fractions (<1 wt%) on the in vitro osteoclastic resorption of β-TCP. A minor aim was to examine the effect of β-CPP and HA impurities on the physico-chemical properties of β-TCP powders and sintered cylinders. Twenty-six batches of β-TCP powder were produced with a Ca/P molar ratio varying between 1.440 and 1.550. Fifteen were further processed to obtain dense and polished β-TCP cylinders. Finally, six of them, with a Ca/P molar ratio varying between 1.496 (1 wt% β-CPP) and 1.502 (1 wt% HA), were incubated in the presence of osteoclasts. Resorption was quantified by white-light interferometry. Osteoclastic resorption was significantly inhibited by β-CPP fraction in a linear manner. The presence of 1% β-CPP reduced β-TCP resorption by 40%, which underlines the importance of controlling β-CPP content when assessing β-TCP biological performance.

Bothrops moojeni Venom and Its Components Strongly Affect Osteoclasts' Maturation and Protein Patterns

Osteoclasts (OCs) are important for bone maintenance, calcium balance, and tissue regeneration regulation and are involved in different inflammatory diseases. Our study aimed to evaluate the effect of Bothrops moojeni's venom and its low and high molecular mass (HMM and LMM) fractions on human peripheral blood mononuclear cell (PBMC)-derived OCs' in vitro differentiation. Bothrops moojeni, a Brazilian lanced-head viper, presents a rich but not well-explored, venom composition. This venom is a potent inducer of inflammation, which can be used as a tool to investigate the inflammatory process. Human PBMCs were isolated and induced to OC differentiation following routine protocol. On the fourth day of differentiation, the venom was added at different concentrations (5, 0.5, and 0.05 µg/mL). We observed a significant reduction of TRAP+ (tartrate-resistant acid phosphatase) OCs at the concentration of 5 µg/mL. We evaluated the F-actin-rich OCs structure's integrity; disruption of its integrity reflects bone adsorption capacity. F-actin rings phalloidin staining demonstrated that venom provoked their disruption in treated OCs. HMM, fraction reduces TRAP+ OCs at a concentration of 5 µg/mL and LMM fraction at 1 µg/mL, respectively. Our results indicate morphological changes that the venom induced cause in OCs. We analyzed the pattern of soluble proteins found in the conditioned cell culture medium OCs treated with venom and its fractions using mass spectrometry (LC-MS/IT-Tof). The proteomic analyses indicate the possible pathways and molecular mechanisms involved in OC reduction after the treatment.

Preclinical studies of a novel snake venom-derived recombinant disintegrin with antitumor activity: A review

Snake venoms consist of a complex mixture of many bioactive molecules. Among them are disintegrins, which are peptides without enzymatic activity, but with high binding affinity for integrins, transmembrane receptors that function to connect cells with components of the extracellular matrix. Integrin-mediated cell attachment is critical for cell migration and dissemination, as well as for signal transduction pathways involved in cell growth. During tumor development, integrins play key roles by supporting cancer cell proliferation, angiogenesis, and metastasis. The recognition that snake venom disintegrins can block integrin functions has spawned a number of studies to explore their cancer therapeutic potential. While dozens of different disintegrins have been isolated, none of them as yet has undergone clinical evaluation in cancer patients. Among the best-characterized and preclinically most advanced disintegrins is vicrostatin (VCN), a recombinant disintegrin that was rationally designed by fusing 62 N-terminal amino acids derived from the disintegrin contortrostatin with 6 C-terminal amino acids from echistatin, the disintegrins from another snake species. Bacterially produced VCN was shown to target multiple tumor-associated integrins, achieving potent anti-tumor and anti-angiogenic effects in in vitro and in vivo models in the absence of noticeable toxicity. This review will introduce the field of snake venom disintegrins as potential anticancer agents and illustrate the translational development and cancer-therapeutic potential of VCN as an example.

The osteoclasts attach to the bone surface where the extracellular calcium concentration decreases

Osteoclasts demineralize and resorb bone once they attach to its surface. However, it's still unclear how the osteoclasts choose the specific sites for their attachments. It is postulated in this article that the decreased extracellular free ionized calcium concentration (Ca²⁺_[e]) can provide a microenvironment for osteoclasts to recognize and then initiate the attachment process. The osteoclasts initially attach to the bone surface via integrating its integrin α_vβ₃ and RGD containing ligands in bone matrix. Through the interaction with RGD-containing ligand, the integrin α_vβ₃ forms carboxylate oxygen noncovalent, which is further stabilized by accompanied electrostatic interaction between the Ca²⁺ and the β₃ subunit. There are two types of cation-binding sites on the β₃ subunit: the high affinity Ca²⁺ binding site ("LC" site) that activates the osteoclasts by promoting the combination; the low affinity Ca²⁺ binding site ("I" site, also named ADMIDAS) that deactivates the osteoclasts by dissociating the combination and it can override the "LC" site's positive effect on osteoclasts when necessary. Normally the Ca²⁺ concentration of bone extracellular fluid is maintained within a normal range by osteocytes, keeping the "I" sites activated. When the osteocytes' function stalls and the ambient Ca²⁺ concentration falls below the affinity discrimination threshold between the "I" site and the "LC" site, the "LC" site's promoting function starts to out compete the "I" site in its inhibitory effect, in which case the inactive integrin α_vβ₃ turns into an extended active form and the osteoclasts start to attach, signifying the initiation of bone resorption.

Thrombin-dependent modulation of β1-integrin-mediated signaling up-regulates prolidase and HIF-1α through p-FAK in colorectal cancer cells

Products of prolidase [E.C. 3.4.13.9] activity, proline or hydroxyproline, contribute to up-regulation of hypoxia-inducible factor-1α (HIF-1α). Prolidase activity is regulated by β(1)-integrin signaling. We studied the effects of echistatin (a well-known disintegrin) and thrombin (a serine protease capable of activation of integrin α(2)β(1) receptor) on prolidase activity and expressions of prolidase, α(2)β(1)-integrin receptor, focal adhesion kinase (FAK), MAP-kinases (ERK(1) and ERK(2)), and nuclear HIF-1α in human colon adenocarcinoma (DLD-1) cells. It has been found that treatment of the cells with thrombin contributes to decrease in the expression of prolidase and simultaneously increase in its phosphorylation, resulting in maintenance of the enzyme activity. The phenomenon was accompanied by thrombin-dependent recovery of depressed autophosphorylation of FAK (pY(397)) under the effect of FAK inhibitor (1,2,4,5-benzenetetramine tetrahydrochloride). Although integrin α(2)β(1) receptor expression was not affected by thrombin, the signaling induced by thrombin up-regulated nuclear HIF-1α expression. It was accompanied by increase in the expression of MAP kinases, ERK1 and ERK2. It suggests that integrin-dependent signaling through p-FAK is up-regulated in DLD-1 cells and it may represent potential target for anti-cancer therapy.

ADAM-17: the enzyme that does it all

This review focuses on the role of ADAM-17 in disease. Since its debut as the tumor necrosis factor converting enzyme (TACE), ADAM-17 has been reported to be an indispensible regulator of almost every cellular event from proliferation to migration. The central role of ADAM-17 in cell regulation is rooted in its diverse array of substrates: cytokines, growth factors, and their receptors as well as adhesion molecules are activated or inactivated by their cleavage with ADAM-17. It is therefore not surprising that ADAM-17 is implicated in numerous human diseases including cancer, heart disease, diabetes, rheumatoid arthritis, kidney fibrosis, Alzheimer's disease, and is a promising target for future treatments. The specific role of ADAM-17 in the pathophysiology of these diseases is very complex and depends on the cellular context. To exploit the therapeutic potential of ADAM-17, it is important to understand how its activity is regulated and how specific organs and cells can be targeted to inactivate or activate the enzyme.

Colombistatin: a disintegrin isolated from the venom of the South American snake (Bothrops colombiensis) that effectively inhibits platelet aggregation and SK-Mel-28 cell adhesion

Snake venoms are complex mixtures of proteins, which affect the vital biologic systems of prey, as well as humans. Envenomation leads to immobilization by paralysis, cardiac, and circulatory failure. These same venom proteins that cause havoc in the physiologic system could be used as therapeutic agents. Disintegrins and disintegrin-like proteins are molecules found in the venom of four snake families (Atractaspididae, Elapidae, Viperidae, and Colubridae). The disintegrins are non-enzymatic proteins that inhibit cell-cell interactions, cell-matrix interactions, and signal transduction. These proteins may have potential in the treatment of strokes, heart attacks, cancers, osteoporosis, and diabetes. The present study describes the isolation and characterization of a disintegrin (colombistatin) found in the venom of the Venezuelan snake mapanare (Bothrops colombiensis). Colombistatin was purified by a two-step high-performance liquid chromatography procedure, which included reverse phase C18 and size exclusion protein Pak 60. Colombistatin inhibited ADP-induced platelet aggregation, human urinary (T24) and skin melanoma (SK-Mel-28) cancer cell adhesion to fibronectin, and cell migration. Colombistatin contained 72 amino acids with a mass of 7.778 kDa as determined by mass spectrometry. Colombistatin could be used as a therapeutic tool in the treatment of melanoma cancers and also thrombotic diseases.

Scratching below the surface: wound healing and alanine mutagenesis provide unique insights into interactions between eristostatin, platelets and melanoma cells

To study the molecular mechanism of the disintegrin eristostatin, cellular functional studies were performed using ten recombinant alanine mutants. ADP-induced platelet aggregation revealed critical contributions of seven residues within the 'RGD loop' (R24, R27, G28, N31) and C-terminus (W47, N48, G49) of this disintegrin. Using an in vitro scratch wound healing assay, four human melanoma cell lines yielded similar results when exposed to wildtype eristostatin. All eristostatin-treated cells healed less of the wounded area than control conditions. This phenomenon was reproduced when using fibronectin as the matrix. C8161 cells showed significant delay in wound closure with the N-terminal mutant P4A but not with R24A or G28A. Evidence from our laboratory and others suggests neither alpha IIb, alpha 4 nor alpha 5 integrins are directly involved in eristostatin's interactions. Eristostatin did not affect the number of melanoma cells in culture after 24 h or the development of apoptosis. However, phosphorylation studies performed after these melanoma cells were exposed to eristostatin revealed changes in several tyrosine phosphorylated molecules.

Functional atomic force microscopy investigation of osteopontin affinity for silicon stabilized tricalcium phosphate bioceramic surfaces

Resorbable silicon stabilized tricalcium phosphate (Si-TCP)-based bioceramics are characterized from a biological perspective by measuring the intermolecular interaction force between osteopontin (OPN) protein and the material surface using atomic force microscopy (AFM). OPN protein was covalently bound to silicon nitride AFM tips and adsorption and adhesion forces were measured in an electrolyte with a composition similar to that of physiological fluids. A strong relationship exists between the adhesion force of OPN on the material surface, the number of adherent osteoclasts (OC) and the resorption of the material. OPN adhesion is strongest on hydroxyapatite (HA) surfaces, or in samples that induce a HA-like surface through a precipitation reaction in electrolytic media. It is proposed that the increased biological response of the Si-TCP phase can be attributed in part to its reactivity in a physiological electrolyte, which involves a rapid conversion to a calcium deficient HA phase with a corresponding increase in the adhesion strength of OPN to the material, with a consequentially higher OC resorption response.

A novel disintegrin, jerdonatin, inhibits platelet aggregation and sperm-egg binding

A novel disintegrin, jerdonatin, was purified to homogeneity from Trimeresurus jerdonii venom by gel filtration and reversed-phase high-pressure liquid chromatography. We isolated the cDNA encoding jerdonatin from the snake venom gland. Jerdonatin cDNA precursor encoded pre-peptide, metalloprotease and disintegrin domain. Jerdonatin is composed of 72 amino acid residues including 12 cysteines and the tripeptide sequence Arg-Gly-Asp (RGD), a well-known characteristic of the disintegrin family. Molecular mass of jerdonatin was determined to be 8011 Da by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). Jerdonatin inhibited ADP- and collagen-induced human platelet aggregation with IC50 of 123 and 135 nM, respectively. We also investigated the effect of jerdonatin on the binding of B6D2F1 hybrid mice spermatozoa to mice zona-free eggs and their subsequent fusion. Jerdonatin significantly inhibited sperm-egg binding in a concentration-dependent manner, but had no effect on the fusion of sperm-egg. These results indicate that integrins on the egg play a role in mammalian fertilization.

Differential effects of echistatin and thrombin on collagen production and prolidase activity in human dermal fibroblasts and their possible implication in beta1-integrin-mediated signaling

Prolidase [E.C. 3.4.13.9] is a cytosolic imidodipeptidase that plays an important role in collagen biosynthesis. The enzyme contributes to the recovery of proline from protein degradation products (mainly collagen) for collagen resynthesis. Prolidase activity and collagen biosynthesis are supposed to be regulated by beta(1)-integrins, which initiate a signaling pathway in which several kinases and intracellular proteins are involved, including focal adhesion kinase pp125(FAK) (FAK), Src, Shc, growth factor receptor bound protein 2 (Grb-2), son of sevenless protein (SOS), Ras, Raf and mitogen-activated protein kinases (MAPK), extracellular-signal regulated kinase 1 (ERK(1)) and kinase 2 (ERK(2)). We studied the effects of echistatin, a well-known disintegrin and thrombin, a serine protease capable of activation of platelet integrin alpha(2)beta(1) receptor on collagen production, prolidase activity, expression of prolidase, beta(1)-integrin receptor, FAK, SOS-protein and phosphorylated MAP-kinases (ERK(1) and ERK(2)) in confluent human dermal fibroblasts. It has been found that treatment of the cells with 100nM echistatin contributes to inhibition of collagen production, as well as prolidase activity and expression compared to control cells. These phenomena were accompanied by a decrease in the expression of FAK, SOS-protein and phosphorylated MAP-kinases, ERK(1) and ERK(2). An opposite phenomenon was observed in fibroblasts treated with 0.1IU thrombin. In this case, a significant increase in collagen production and prolidase activity, accompanied by a distinct raise in the expression of prolidase, FAK and phosphorylated MAP-kinases and a slight increase in expression of SOS compared to controls were found. The results suggest that regulation of prolidase activity and collagen biosynthesis in human dermal fibroblasts may involve beta(1)-integrin-dependent signaling.

Bone loss induced by ovariectomy in rats is prevented by gene transfer of parathyroid hormone or an Arg-Gly-Asp-containing peptide

Osteoporosis is a major and growing healthcare concern as the population ages. The genes of both a Arg-Gly-Asp (RGD)-containing peptide and parathyroid hormone (PTH) were used to reduce bone loss induced by ovariectomy (OVX) in rats. Plasmids with either RGD or PTH gene were delivered into the quadriceps of OVX rats. The expression of the genes was detected by RT-PCR and radioimmunoassay. Analysis of bone mineral density, bone mechanical testing and bone mineral content indicated an improvement in bone properties in both RGD-transferred and PTH-transferred rats compared to OVX rats. Gene transfer of either RGD or PTH is therefore a possible approach to prevent bone loss in OVX rats thus providing a potential method to prevent osteoporosis in clinical situations.

RGD- and MLD-disintegrins, jarastatin and EC3, activate integrin-mediated signaling modulating the human neutrophils chemotaxis, apoptosis and IL-8 gene expression

The effects of jarastatin (JT), a monomeric RGD-disintegrin, were compared with those of the heterodimeric MLD-disintegrin, EC3, on human neutrophil activation and functions. Both disintegrins inhibited neutrophil chemotaxis induced by fMet-Leu-Phe and were also potent chemotactic agents. These effects were accompanied by an increase in actin polymerization, and both were inhibited by genistein, a tyrosine kinase inhibitor. While JT, but not other RGD-disintegrins, inhibited EC3-induced chemotaxis, EC3 was not able to inhibit JT effect. The chemotactic effect of JT was blocked by anti-alpha(M) antibody whereas anti-alpha(9)beta(1) inhibited EC3 effect. Both JT and EC3 induced focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K) activation. Accordingly, LY294002, a PI3K inhibitor, impaired their chemotactic effect on neutrophils. JT induced Erk-2 translocation to nucleus and a delay of the spontaneous apoptosis of neutrophils in vitro. In contrast, EC3 inhibited Erk-2 activation and had a proapoptotic effect. These effects were reverted by PD98059, an MEK 1/2 inhibitor and blocked by z-VAD-FMK, a caspase inhibitor. In addition, JT, but not EC3, increased the IL-8 mRNA levels in neutrophils. The data indicate that JT and EC3 directly activate an integrin-coupled signaling and modulate the MAPK pathway in different ways, leading the neutrophils to express different functional response.

Contortrostatin, a homodimeric disintegrin, binds to integrin alphavbeta5

Contortrostatin is a homodimeric disintegrin from snake venom. We have shown that contortrostatin binds to integrins alphaIIbbeta3, alpha5beta1, and alphavbeta3. We now use several criteria to demonstrate the binding of contortrostatin to alphavbeta5. First, incubation of T24 cells, which express alphavbeta3 and alphavbeta5, with antibody against alphavbeta3 failed to completely inhibit adhesion of cells to vitronectin. However, pretreatment of the cells with contortrostatin or the combination of antibodies against alphavbeta3 and alphavbeta5 completely blocked adhesion to vitronectin. By contrast, either anti-alphavbeta5 alone or contortrostatin blocked adhesion of an alphavbeta3-negative T24 subline. Second, contortrostatin as well as anti-alphavbeta5 inhibits invasion of OVCAR-5, which express only alphavbeta5. Third, contortrostatin binds to purified alphavbeta5 in a saturable manner. Finally, radioligand binding assays yielded a K(d) value of 24 nM for [(125)I]contortrostatin binding to alphavbeta5. This investigation identifies alphavbeta5 as a binding site for contortrostatin. Blockage of alphavbeta5 by contortrostatin inhibits alphavbeta5-mediated adhesion and invasion.