Molecular characterization of protective antibodies raised in mice by Tityus serrulatus scorpion venom toxins conjugated to bovine serum albumin

Evaluation of the immunoprotective power of a multiple antigenic peptide against Aah II toxin of Androctonus australis hector scorpion

Scorpion envenoming (SE) is a public health problem in developing countries. In Algeria, the population exposed to the risk of SE was estimated at 86.45% in 2019. Thus, the development of a vaccine to protect the exposed population against scorpion toxins would be a major advance in the fight against this disease. This work aimed to evaluate the immunoprotective effect of a Multiple Antigenic Peptide against the Aah II toxin of Androctonus australis hector scorpion, the most dangerous scorpion species in Algeria. The immunogen MAP1Aah2 was designed and tested accordingly. This molecule contains a B epitope, derived from Aah II toxin, linked by a spacer to a universal T epitope, derived from the tetanus toxin. The results showed that MAP1Aah2 was non-toxic despite the fact that its sequence was derived from Aah II toxin. The immunoenzymatic assay revealed that the 3 immunization regimens tested generated specific anti-MAP1Aah2 antibodies and cross-reacted with the toxin. Mice immunized with this immunogen were partially protected against mortality caused by challenge doses of 2 and 3 LD50 of the toxin. The survival rate and developed symptoms varied depending on the adjuvant and the challenge dose used. In the in vitro neutralization test, the immune sera of mice having received the immunogen with incomplete Freund's adjuvant neutralized a challenge dose of 2 LD50. Hence, the concept of using peptide dendrimers, based on linear epitopes of scorpion toxins, as immunogens against the parent toxin was established. However, the protective properties of the tested immunogen require further optimizations.

Divergence in toxin antigenicity and venom enzymes in Tityus melici, a medically important scorpion, despite transcriptomic and phylogenetic affinities with problematic Brazilian species

The Brazilian scorpion Tityus melici, native to Minas Gerais and Bahia, is morphologically related to Tityus serrulatus, the most medically significant species in Brazil. Despite inhabiting scorpion-envenomation endemic regions, T. melici venom remains unexplored. This work evaluates T. melici venom composition and function using transcriptomics, enzymatic activities, and in vivo and in vitro immunological analyses. Next-Generation Sequencing unveiled 86 components putatively involved in venom toxicity: 39 toxins, 28 metalloproteases, seven disulfide isomerases, six hyaluronidases, three phospholipases and three amidating enzymes. T. serrulatus showed the highest number of toxin matches with 80-100 % sequence similarity. T. melici is of medical importance as it has a venom LD50 of 0.85 mg/kg in mice. We demonstrated venom phospholipase A2 activity, and elevated hyaluronidase and metalloprotease activities compared to T. serrulatus, paralleling our transcriptomic findings. Comparison of transcriptional levels for T. serrulatus and T. melici venom metalloenzymes suggests species-specific expression patterns in Tityus. Despite close phylogenetic association with T. serrulatus inferred from COI sequences and toxin similarities, partial neutralization of T. melici venom toxicity was achieved when using the anti-T. serrulatus antivenom, implying antigenic divergence among their toxins. We suggest that the Brazilian therapeutic scorpion antivenom could be improved to effectively neutralize T. melici venom.

Synthetic peptides to produce antivenoms against the Cys-rich toxins of arachnids

Scorpion and spider envenomation is treated with the appropriate antivenoms, prepared as described by Césaire Auguste Phisalix and Albert Calmette in 1894. Such treatment requires the acquisition and manipulation of arachnid venoms, both very complicated procedures. Most of the toxins in the venoms of spiders and scorpions are extremely stable cysteine-rich peptide neurotoxins. Many strategies have been developed to obtain synthetic immunogens to facilitate the production of antivenoms against these toxins. For example, whole peptide toxins can be synthesized by solid-phase peptide synthesis (SPPS). Also, epitopes of the toxins can be identified and after the chemical synthesis of these peptide epitopes by SPPS, they can be coupled to protein carriers to develop efficient immunogens. Moreover, multiple antigenic peptides with a polylysine core can be designed and synthesized. This review focuses on the strategies developed to obtain synthetic immunogens for the production of antivenoms against the toxic Cys-rich peptides of scorpions and spiders.

Chitosan nanoparticles as a delivery platform for neurotoxin II from Androctonus australis hector scorpion venom: Assessment of toxicity and immunogenicity

In recent years, biodegradable polymers based nanoparticles received high interest for the development of vaccine delivery vehicles. In this study, chitosan nanoparticles encapsulating Aah II toxin (AahII-CNPs) isolated from Androctonus australis hector venom, were investigated as vaccine delivery system. Particles obtained by ionotropic gelation were characterized for their size, surface charge, morphology and toxin release profile from Aah II-CNPs. Toxin-nanoparticles interactions were assessed by Fourier Transform Infrared Spectrometry and X-Ray Diffraction. An immunization protocol was designed in mice to investigate anti-toxin immunity and the protective status induced by different Aah II immune formulations. Unloaded chitosan nanoparticles presenting a spherical shape and smooth surface, were characterized by a size of 185 nm, a dispersion index (PDI) of 0.257 and a zeta potential of +34.6 mV. Aah II toxin was successfully entrapped into chitosan nanoparticles as revealed by FTIR and XRD data. Entrapment efficiency (EE) and Loading capacity (LC) were respectively of 96.66 and 33.5%. Aah II-CNPs had a diameter of 208 nm, a PDI of 0.23 and a zeta potential of +30 mV. Encapsulation of Aah II reduced its toxicity and protected mice until 10 LD₅₀. Mice were immunized via a dual prime-boost scheme. Nanoentrapped Aah II immunogen elicited systemic innate and humoral immune responses as well as local spleen parenchyma hyperplasic alterations. Aah II-CNPs immunized mice withstood high lethal doses of native Aah II, one-month post-boost inoculation. This study provided encouraging and promising results for the development of preventive therapies against scorpion envenoming mainly for the populations at-risk.

Venom diversity in the Neotropical scorpion genus Tityus: Implications for antivenom design emerging from molecular and immunochemical analyses across endemic areas of scorpionism

Scorpions of the Neotropical genus Tityus are responsible for most severe envenomations in the Caribbean, South America, and Lower Central America (LCA). Although Tityus is taxonomically complex, contains high toxin polymorphism, and produces variable clinical manifestations, treatment is limited to antivenoms produced against species with restricted distributions. In this study, we explored the compositional and antigenic diversity of Tityus venoms to provide improved guidelines for the use of available antivenoms at a broader geographic scale. We used immunoblotting, competitive ELISA, and in vivo studies to compare reactivity against commercial antivenoms from Brazil, Venezuela, and Mexico, as well as MALDI-TOF mass spectrometry, cDNA sequencing, and phylogenetic analyses to assess venom sodium channel-active toxin (NaTx) content from medically important Tityus populations inhabiting Brazil, Colombia, Costa Rica, Ecuador, Panama, Trinidad and Tobago, and Venezuela. Additionally, we raised rabbit antibodies against Tityus venoms from LCA to test for cross-reactivity with congeneric species. The results suggest that Tityus spp. possess high venom antigenic diversity, underlying the existence of four toxinological regions in Tropical America, based on venom composition and immunochemical criteria: LCA/Colombia/Amazonia (Region I), Venezuela (Region II), southeast South America (Region III), and a fourth region encompassing species related to toxinologically divergent Tityus cerroazul. Importantly, our molecular and cross-reactivity results highlight the need for new antivenoms against species inhabiting Region I, where scorpions may produce venoms that are not significantly reactive against available antivenoms.

Engineered protein containing crotoxin epitopes induces neutralizing antibodies in immunized rabbits

Crotoxin (Ctx) is the main lethal component of Crotalus durissus terrificus venom. It is a neurotoxin, composed of two subunits associated by noncovalent interactions, the non-toxic acid subunit (CA), named Crotapotin, and the basic subunit (CB), with phospholipase A₂ (PLA₂) activity. Employing the SPOT synthesis technique, we determined two epitopes located in the C-terminal of each Ctx subunit. In addition, 3 other epitopes were mapped in different regions of Ctx using subcutaneous spot implants surgically inserted in mice. All epitopes mapped here were expressed together as recombinant multi-epitopic protein (rMEPCtx), which was used to immunize New Zealand rabbits. Anti-rMEPCtx rabbit serum cross-reacted with Ctx and crude venoms from C. d. terrificus, Crotalus durissus ruruima, Peruvian C. durissus and Bothrops jararaca (with lower intensity). Furthermore, anti-rMEPCtx serum was able to neutralize Ctx lethal activity. As the recombinant multiepitopic protein is not toxic, it can be administered in larger doses without causing adverse effects on the immunized animals health. Therefore, our work evidences the identification of neutralizing epitopes of Ctx and support the use of recombinant multiepitopic proteins as an innovation to immunotherapeutics production.

Genotoxicity evaluation induced by Tityus serrulatus scorpion venom in mice

Tityus serrulatus is the scorpion associated with the most severe cases of scorpion envenoming in Brazil. However, there are no studies reporting the genotoxic effects of this venom in natural or experimental envenomations. It is well known that DNA-damage responses are providing opportunities for improving disease detection and management. In this study was evaluating the genotoxicity of the T. serrulatus venom in different organs (hippocampus, cortex, striatum, blood, heart, lung, liver and kidney) and periods in mice experimentally envenomed. ELISA and the Comet assays were used to quantification of venoms antigens and DNA damage, respectively. Forty-eight Swiss mice were divided into five groups and 0.5 DL₅₀ of T. serrulatus venom (0.90 mg/kg) was administered intraperitoneally in each animal. Euthanasia was performed by cervical dislocation in the period of 0h (control group) 1h, 2h, 6h and 12h, where it the tissues were removed. The results showed high DNA damage in all structures analyzed, suggesting that T. serrulatus venom presented genotoxic activity or some secondary effect generated by venom injection. In the ELISA test, toxic circulant antigens were verified in practically all organs at the time intervals analyzed. Therefore, the distribution of the venom changes from organ to organ. We conclude that scorpion envenoming affects DNA in all organs analyzed even when the venom concentration is lower or no detectable, DNA damage persists.

Toxicity of crude and detoxified Tityus serrulatus venom in anti-venom-producing sheep

Specific anti-venom used to treat scorpion envenomation is usually obtained from horses after hyperimmunization with crude scorpion venom. However, immunized animals often become ill because of the toxic effects of the immunogens used. This study was conducted to evaluate the toxic and immunogenic activities of crude and detoxified Tityus serrulatus (Ts) venom in sheep during the production of anti-scorpionic anti-venom. Sheep were categorized into three groups: G1, control, immunized with buffer only; G2, immunized with crude Ts venom; and G3, immunized with glutaraldehyde-detoxified Ts venom. All animals were subjected to clinical exams and supplementary tests. G2 sheep showed mild clinical changes, but the other groups tolerated the immunization program well. Specific antibodies generated in animals immunized with either Ts crude venom or glutaraldehyde-detoxified Ts venom recognized the crude Ts venom in both assays. To evaluate the lethality neutralization potential of the produced sera, individual serum samples were pre-incubated with Ts crude venom, then subcutaneously injected into mice. Efficient immune protection of 56.3% and 43.8% against Ts crude venom was observed in G2 and G3, respectively. Overall, the results of this study support the use of sheep and glutaraldehyde-detoxified Ts venom for alternative production of specific anti-venom.

Mapping of the continuous epitopes displayed on the Clostridium perfringens type D epsilon-toxin

The epsilon toxin, produced by Clostridium perfringens, is responsible for enterotoxemia in ruminants and is a potential bioterrorism agent. In the present study, 15 regions of the toxin were recognized by antibodies present in the serum, with different immunodominance scales, and may be antigen determinants that can be used to formulate subunit vaccines.

Biotechnological Trends in Spider and Scorpion Antivenom Development

Spiders and scorpions are notorious for their fearful dispositions and their ability to inject venom into prey and predators, causing symptoms such as necrosis, paralysis, and excruciating pain. Information on venom composition and the toxins present in these species is growing due to an interest in using bioactive toxins from spiders and scorpions for drug discovery purposes and for solving crystal structures of membrane-embedded receptors. Additionally, the identification and isolation of a myriad of spider and scorpion toxins has allowed research within next generation antivenoms to progress at an increasingly faster pace. In this review, the current knowledge of spider and scorpion venoms is presented, followed by a discussion of all published biotechnological efforts within development of spider and scorpion antitoxins based on small molecules, antibodies and fragments thereof, and next generation immunization strategies. The increasing number of discovery and development efforts within this field may point towards an upcoming transition from serum-based antivenoms towards therapeutic solutions based on modern biotechnology.

General characterization of Tityus fasciolatus scorpion venom. Molecular identification of toxins and localization of linear B-cell epitopes

This communication describes the general characteristics of the venom from the Brazilian scorpion Tityus fasciolatus, which is an endemic species found in the central Brazil (States of Goiás and Minas Gerais), being responsible for sting accidents in this area. The soluble venom obtained from this scorpion is toxic to mice being the LD50 is 2.984 mg/kg (subcutaneally). SDS-PAGE of the soluble venom resulted in 10 fractions ranged in size from 6 to 10-80 kDa. Sheep were employed for anti-T. fasciolatus venom serum production. Western blotting analysis showed that most of these venom proteins are immunogenic. T. fasciolatus anti-venom revealed consistent cross-reactivity with venom antigens from Tityus serrulatus. Using known primers for T. serrulatus toxins, we have identified three toxins sequences from T. fasciolatus venom. Linear epitopes of these toxins were localized and fifty-five overlapping pentadecapeptides covering complete amino acid sequence of the three toxins were synthesized in cellulose membrane (spot-synthesis technique). The epitopes were located on the 3D structures and some important residues for structure/function were identified.

Evolution of alternative methodologies of scorpion antivenoms production

Scorpionism represents a serious public health problem resulting in the death of children and debilitated individuals. Scorpion sting treatment employs various strategies including the use of specific medicines such as antiserum, especially for patients with severe symptoms. In 1909 Charles Todd described the production of an antiserum against the venom of the scorpion Buthus quinquestriatus. Based on Todd's work, researchers worldwide began producing antiserum using the same approach i.e., immunization of horses with crude venom as antigen. Despite achieving satisfactory results using this approach, researchers in this field have developed alternative approaches for the production of scorpion antivenom serum. In this review, we describe the work published by experts in toxinology to the development of scorpion venom antiserum. Methods and results describing the use of specific antigens, detoxified venom or toxins, purified toxins and or venom fractions, native toxoids, recombinant toxins, synthetic peptides, monoclonal and recombinant antibodies, and alternative animal models are presented.

Molecular, immunological, and biological characterization of Tityus serrulatus venom hyaluronidase: new insights into its role in envenomation

Background

Scorpionism is a public health problem in Brazil, and Tityus serrulatus (Ts) is primarily responsible for severe accidents. The main toxic components of Ts venom are low-molecular-weight neurotoxins; however, the venom also contains poorly characterized high-molecular-weight enzymes. Hyaluronidase is one such enzyme that has been poorly characterized.

Methods and principal findings

We examined clones from a cDNA library of the Ts venom gland and described two novel isoforms of hyaluronidase, TsHyal-1 and TsHyal-2. The isoforms are 83% identical, and alignment of their predicted amino acid sequences with other hyaluronidases showed conserved residues between evolutionarily distant organisms. We performed gel filtration followed by reversed-phase chromatography to purify native hyaluronidase from Ts venom. Purified native Ts hyaluronidase was used to produce anti-hyaluronidase serum in rabbits. As little as 0.94 µl of anti-hyaluronidase serum neutralized 1 LD₅₀ (13.2 µg) of Ts venom hyaluronidase activity in vitro. In vivo neutralization assays showed that 121.6 µl of anti-hyaluronidase serum inhibited mouse death 100%, whereas 60.8 µl and 15.2 µl of serum delayed mouse death. Inhibition of death was also achieved by using the hyaluronidase pharmacological inhibitor aristolochic acid. Addition of native Ts hyaluronidase (0.418 µg) to pre-neutralized Ts venom (13.2 µg venom+0.94 µl anti-hyaluronidase serum) reversed mouse survival. We used the SPOT method to map TsHyal-1 and TsHyal-2 epitopes. More peptides were recognized by anti-hyaluronidase serum in TsHyal-1 than in TsHyal-2. Epitopes common to both isoforms included active site residues.

Conclusions

Hyaluronidase inhibition and immunoneutralization reduced the toxic effects of Ts venom. Our results have implications in scorpionism therapy and challenge the notion that only neurotoxins are important to the envenoming process.

In Brazil, accidents with scorpion stings have been a serious public health problem, and Tityus serrulatus (Ts) is primarily responsible for severe accidents. Therefore, efforts have been made to understand the characteristics of the molecules present in scorpion venoms. These venoms are complex mixtures, in which neurotoxins are the main toxic components. Ts venom also contains enzymes, such as hyaluronidase, that have not been well characterized. In this study, we described for the first time two sequences of Ts hyaluronidase isoforms: TsHyal-1 and TsHyal-2. We purified native hyaluronidase from Ts venom and produced anti-hyaluronidase serum in rabbits. This serum neutralized hyaluronidase activity present in Ts venom. In vivo neutralization assays showed that anti-hyaluronidase serum inhibited and delayed mouse death after injection of a lethal dose (50% lethal dose, LD₅₀) of Ts venom. This work confirms the influence of hyaluronidase in Ts venom lethality and paves the way for the development of new strategies for scorpionism therapy.

Synthetic peptides for in vitro evaluation of the neutralizing potency of Loxosceles antivenoms

An important step in the development of therapeutic antivenoms is the pre-clinical testing using in vivo methods to assess their neutralizing potency. For spider antivenoms (Loxosceles species), horse serum potency against the necrotizing activities of Loxosceles intermedia crude venom is currently tested in rabbits. These procedures are time consuming and involve a large number of animals. The aim of this study was to develop an in vitro method to assess the neutralizing potency of anti-Loxosceles sera. We first demonstrated that it was not possible to establish a correlation between the ELISA antibody reactivity of horse anti-Loxosceles serum and their neutralizing potency. We then showed that the antivenoms recognized several peptide epitopes from different regions of SMase-D proteins, which are toxic antigens from Loxosceles venoms. The recognition of some peptides was observed only when high neutralizing potency sera was used. Based on these results, three peptides (peptide 1, DNRRPIWNLAHMVNA and peptide 3, DFSGPYLPSLPTLDA corresponding to residues 2-16 and 164-178, respectively, of SMase-1 protein from Loxosceles laeta, and peptide 2, EFVNLGANSIETDVS corresponding to residues 22-36 of A1H - LoxGa protein from Loxosceles gaucho and LiD1 protein from L. intermedia) were selected. The peptides were synthesized, coupled to bovine serum albumin (BSA), and used as antigens in indirect ELISA to test their reactivity with horse anti-Loxosceles serum of varying neutralizing potencies. We found certain assay conditions that discriminated between the high and low neutralizing potency sera. This study introduced an in vitro and peptide-based neutralization assay for anti-Loxosceles antivenoms.

Mimotopes of mutalysin-II from Lachesis muta snake venom induce hemorrhage inhibitory antibodies upon vaccination of rabbits

Mutalysin-II (mut-II) from Lachesis muta snake venom is an endopeptidase with hemorrhagic activity. A mAb against mutalysin-II that neutralized the hemorrhagic effect was produced previously. To identify the mAb epitopes, sets of 15-mer overlapping peptides covering the mut-II amino acid sequence were synthesized using the SPOT method and tested but failed to react with the mAb. Using a phage-display approach seventeen clones reactive with mAb were identified. Additional immunoassays with the peptides and mAb identified the QCTMDQGRLRCR, TCATDQGRLRCT, HCFHDQGRVRCA, HCTMDQGRLRCR and SCMLDQGRSRCR sequences as possible epitopes. Immunization of rabbits with these peptides induced antibodies that recognize mut-II and protected against the hemorrhagic effects of Lachesis venom.

F0F1-ATPase activity regulated by external links on beta subunits

F(o)F(1)-ATPase activity is regulated by external links on beta subunits with different molecular weight. It is inhibited when anti-beta subunit antibody, streptavidin and H9 antibody link on the beta subunits successively, but is activated when virus was binded. Western blotting indicated that the employed anti-beta antibody target was on the non-catalytic site of the beta subunit. Furthermore, an ESR study of spin-labeled ATP (SL-ATP) showed that the affinity of ATP to the holoenzyme increases with increasing external links on the beta subunits. This simple regulation method may have great potential in the design of rapid, free labeled, sensitive and selective biosensors.

An in vivo protective response against toxic effects of the dermonecrotic protein from Loxosceles intermedia spider venom elicited by synthetic epitopes

Loxoscelism is a necrotic-hemolytic syndrome caused by bites of brown spiders belonging to the genus Loxosceles. Many approaches for the treatment of Loxosceles poisoning have already been proposed, among which administration of specific antivenom is thought to be the more specific. We have evaluated the use of peptides as immunogen to raise in rabbits an antibody response that could protect animals from a challenge by the Loxtox isoform LiD1, one of the main toxic component of Loxosceles intermedia venom. Six antigenic regions of LiD1 were mapped by using the SPOT method. The corresponding peptides were further chemically synthesized, mixed, and used as immunogens in rabbits. Control animal received recombinant LiD1 alone or together with peptides. We found that the rabbit antibody response to peptides was cross-reactive with LiD1, although only one peptide from the mix of six was immunogenic. The dermonecrotic, hemorrhagic and oedema forming activities induced by LiD1 in naïve rabbits were inhibited by 82%, 35% and 35% respectively, by preincubation of LiD1 with anti-peptide antibodies prepared from immunized rabbits. Animals that were immunized with peptides or LiD1r, were found to be protected from the dermonecrotic, hemorrhagic and oedema forming activities induced by a challenge with LiD1. The protection conferred by peptides was, however, lower than that provided by the peptide protein combination or by the full-length protein. These results encourage us in the utilization of synthetic peptides for therapeutic serum development or vaccination approaches.

Diversity of long-chain toxins in Tityus zulianus and Tityus discrepans venoms (Scorpiones, Buthidae): molecular, immunological, and mass spectral analyses

In Venezuela, stings by Tityus zulianus scorpions produce cardiorespiratory arrest, whereas envenoming by Tityus discrepans involves gastrointestinal/pancreatic complications, suggesting structural and/or functional differences. We sought to compare their toxin repertoires through immunological, molecular, and mass spectral analyses. First, in vivo tests showed that neutralization of T. zulianus venom toxicity by the anti-T. discrepans antivenom was not complete. To compare T. discrepans and T. zulianus long-chain (sodium channel-active) toxins, their most toxic Sephadex G-50 fractions, TdII and TzII, were subjected to acid-urea PAGE, which showed differences in composition. Amplification of toxin-encoding mRNAs using a leader peptide-based oligonucleotide rendered cDNAs representing twelve T. discrepans and two T. zulianus distinct toxin transcripts, including only one shared component, indicating divergence between T. zulianus and T. discrepans 5' region-encoded, toxin signal peptides. A 3'-UTR polymorphism was also noticed among the transcripts encoding shared components Tz1 and Td4. MALDI-TOF MS profiling of TdII and TzII produced species-specific spectra, with seven of the individual masses matching those predicted by cDNA sequencing. Phylogenetic analysis showed that the unique T. zulianus transcript-encoded sequence, Tz2, is structurally related to Tityus serrulatus and Centruroides toxins. Together with previous reports, this work indicates that T. zulianus and T. discrepans toxin repertoires differ structurally and functionally.

The neutralizing effect of a polyclonal antibody raised against the N-terminal eighteen-aminoacid residues of birtoxin towards the whole venom of Parabuthus transvaalicus

Scorpion venom is composed among other things of a large number of neurotoxic peptides affecting all major types of ion channels. The majority of the toxicity of the venom is attributed to the presence of these peptides. In our previous studies using a combination of HPLC and mass spectrometry, we showed that birtoxin like peptides are the major peptidic components of the venom of Parabuthus transvaalicus. These peptides are quite similar to each other differing by only few amino acid residues. In addition they all share a common N-terminus of eighteen amino acid residues. We hypothesize that neutralization of this domain will decrease the toxicity of the whole venom of P. transvaalicus. Polyclonal antibodies against the common N-terminal region of the peptides are generated. Here we show by bioassays that the polyclonal antibodies neutralize the venom of P. transvaalicus in a dose dependent manner and by mass spectrometry and western blotting that these peptides indeed react with the polyclonal antibodies. Previously antibodies generated against a single major toxic component of venom have proven to be an effective strategy for antivenin production. In the case of P. transvaalicus the generated antibody is against the majority of the peptidic fraction due to the presence of several highly similar and highly toxic components in this venom. We show that using the knowledge obtained through biochemical characterization studies it is possible to design very specific antibodies that will be useful for clinical applications against Parabuthus envenomation.

Molecular characterization of a neutralizing murine monoclonal antibody against Tityus serrulatus scorpion venom

Monoclonal antibodies (mAbs) against Tityus serrulatus venom were obtained by the fusion of SP2/0 murine myeloma cells and spleen cells from BALB/c mice immunized with a toxic fraction (TstFG50) of the Tityus venom (this G50 chromatography fraction represents most of the toxicity of the crude venom) conjugated to bovine serum albumin (BSA) with glutaraldehyde. From the initial screening of over 200 hybridoma fusion wells, a panel of 9 anti-TstFG50 secreting hybridomas was established. The capacity of mAbs to neutralize the TstFG50 toxic fraction toxic was determined by in vitro neutralization assays and by inhibition of the binding of 125I-TsVII to its site on rat brain synaptosomes. Only mAbTs1 neutralized 50% of the toxic effects produced by scorpion venom and showed 35% inhibition of the binding of 125I-TsVII at 10(-7) M. To map the epitope recognized by the protective mAbTs1, we prepared a comprehensive series of overlapping 15-mer synthetic peptides covering the amino acid sequences of the four Tityus proteins. MAbTs1 reacted with peptide 26 of TsIV (KKSKDKKADSGYSYW), peptide 30 of TsVII (KKGSSGYSAWPASYS) and peptide 31 of TsNTxP (KKGSSGYSAWPASYS). MAbTs1 was not reactive with any peptide from TsII. The N-terminal lysine residue from the epitope was found to be critical for mAbTs1 binding. The epitope was positioned on the available three-dimensional structure of TsVII together with the recently identified residues from the pharmacophore of beta-scorpion toxins. The neutralizing properties of mAbTs1 might be explained by spatial vicinity of epitope residues with pharmacophore residues.

Biomaterial with chemically engineered surface for protein immobilization

The last 3 decades have been a revolution in the area of sol-gel-derived materials. They can be used to encapsulate biomolecules such as enzymes, antibodies, hormones, and proteins retaining their functional state. Proteins can be immobilized in many ways but it is crucial that they retain their native conformational structure and, therefore, bioactivity. Porous silica gel matrixes with modified surfaces offer unlimited possibilities to control the protein-solid interaction behavior. The bioimmobilization process on sol-gel biomaterials with chemically engineered surface has driven applications on solid-phase materials, affinity chromatography, biosensors and many others. In the present work, we have aimed to produce surface-modified silica glass materials obtained via sol-gel route to be used as solid support on drug delivery systems and as solid-phase in immunodiagnostic. The functionalization process was carried out by reacting alkoxysilanes with 5 different silane surface modifying chemical groups: tetraethoxysilane (TEOS), 3-mercaptopropyltrimethoxysilane (MPTMS) and 3-aminopropyltriethoxysilane (APTES), 3-glycidoxypropyltrimethoxysilane (GPTMS) and 3-isocyanatopropyltriethoxysilane (ICPES). The bioactivity assays were based on two main tests: (a) An in vivo bioresponse of rats with sol-gel disk implants with insulin protein incorporated. In vivo tests with adult male rats were used to verify the immobilized insulin bioactivity after implantation of different biomaterial with functionalized surfaces. All surface modified materials have presented hypoglycemic peak response associated with the insulin bioactivity. (b) The produced solid-phase sol-gel disks with protein substrates were tested through Enzyme Linked Immuno Sorbent Assay (ELISA). The immunoassay results have showed that glasses with chemically functionalized surfaces regulated the extent of bioimmobilization of protein. The amine, thiol and hydroxyl terminated porous gels have showed significant interaction with the antibody-antigen, during the coupling process. We believe that it is due to balance of forces associated with Van der Waals interaction, hydrophilic and hydrophobic forces and steric hindrance acting at the surface. Therefore, such novel biomaterial could be advantageously used in drug delivery systems and in immunoassays of diagnostic kits.