Some parameters of affinity chromatography in the purification of antibody against Naja naja siamensis toxin 3

A Quest for a Universal Plasma-Derived Antivenom Against All Elapid Neurotoxic Snake Venoms

This review describes the research aimed at the development of universal antivenom against elapid neurotoxic snake venoms. The antivenoms produced in Thailand in the 1980s were of low potency, especially against the elapid venoms. This was thought to be due to the low immunogenicity of the α-neurotoxins, which are the most lethal toxins in these venoms. Comparisons of various α-neurotoxin conjugates and polymers, and also different immunological adjuvants, showed that the adjuvant used is the major determinant in the antibody response in horses. The potent Freund's adjuvant was not used due to its severe local side-effect in horses. Therefore, a novel immunization protocol termed 'low dose, low volume multi-site' was developed for use in horses. This immunization protocol has led to the production of highly potent monospecific antivenoms against several elapid and viperid venoms, and two potent polyspecific antivenoms, one against 4 neurotoxic and another against 3 hematotoxic venoms. The immunization protocol has also led to other improvements in antivenom production including: several fold increases in antiserum potency, a reduction in the time required to reach therapeutically useful antibody titers, a 90% reduction in the amount of venom used, and 100% of the horses responding to the immunization program. This development is partly responsible for significant decrease in the Thailand's annual snakebite death toll from a few dozens to mostly nil in recent years. Finally, a simple and novel immunization strategy, using a 'diverse toxin repertoire' composed of numerous elapid toxin fractions as immunogen, was proposed and tested. This immunization procedure has resulted in the successful production of a widely paraspecific antiserum against at least 36 neurotoxic venoms of 28 species encompassing 10 genera and from 20 countries on four continents, and possibly against all elapid venoms with α-neurotoxins as the lethal toxins. These results indicate that, with optimizations of the composition of the 'diverse toxin repertoire', the immunization scheme and antibody fractionation to increase the antivenom neutralizing potency, an effective universal antivenom against the neurotoxic elapid snakes of the world can be produced.

Quality-Related Properties of Equine Immunoglobulins Purified by Different Approaches

Whole IgG antivenoms are prepared from hyperimmune animal plasma by various refinement strategies. The ones most commonly used at industrial scale are precipitation by sodium or ammonium sulphate (ASP), and caprylic acid precipitation (CAP) of non-immunoglobulin proteins. The additional procedures, which have so far been used for experimental purposes only, are anion-exchange (AEX) and cation-exchange chromatography (CEX), as well as affinity chromatography (AC) using IgG’s Fc-binding ligands. These protocols extract the whole IgG fraction from plasma, which contains both venom-specific and therapeutically irrelevant antibodies. Such preparations represent a complex mixture of various IgG subclasses whose functional and/or structural properties, as well as relative distribution, might be affected differently, depending on employed purification procedure. The aim of this work was to compare the influence of aforementioned refinement strategies on the IgG subclass distribution, venom-specific protective efficacy, thermal stability, aggregate formation and retained impurity profile of the final products. A unique sample of Vipera ammodytes ammodytes specific hyperimmune horse plasma was used as a starting material, enabling direct comparison of five purification approaches. The highest purity was achieved by CAP and AC (above 90% in a single step), while the lowest aggregate content was present in samples from AEX processing. Albumin was the main contaminant in IgG preparations obtained by ASP and CEX, while transferrin dominantly contaminated IgG sample from AEX processing. Alpha-1B-glycoprotein was present in CAP IgG fraction, as well as in those from ASP- and AEX-based procedures. AC approach induced the highest loss of IgG(T) subclass. CEX and AEX showed the same tendency, while CAP and ASP had almost no impact on subclass distribution. The shift in IgG subclass composition influenced the specific protective efficacy of the respective final preparation as measured in vivo. AC and CEX remarkably affected drug’s venom-neutralization activity, in contrary to the CAP procedure, that preserved protective efficacy of the IgG fraction. Presented data might improve the process of designing and establishing novel downstream processing strategies and give guidance for optimization of the current ones by providing information on potency-protecting and purity-increasing properties of each purification principle.

Immunological properties of Hypnale hypnale (hump-nosed pit viper) venom: antibody production with diagnostic and therapeutic potentials

Envenomation by hump-nosed pit viper (Hypnale hypnale, Hh) in Sri Lanka has caused significant morbidity and mortality, attributed to 35% of total venomous snakebites. In Southwestern India (Kerala), H. hypnale was increasingly identified as a dangerous and common source of envenomation, second to the Russell's viper but ahead of the cobra bites. Unfortunately, there is still no specific antivenom to date. This study aims to investigate the immunological properties of the venom and to assess the feasibility of specific Hh antivenom production as well as the development of a diagnostic assay. Hh venom elicited satisfactory titers of anti-Hh IgG in rabbits after 3rd immunization. The anti-Hh IgG, isolated with caprylic acid precipitation method, was effective in neutralizing the venom lethality (potency=48 LD(50) per ml IgG) as well as its procoagulant, hemorrhagic and necrotic effects, indicating the possibility to produce the specific antivenom using the common immunization regime. Cross-reactivity studies using indirect ELISA showed that anti-Hh IgG cross-reacted extensively with several Asiatic crotalid venoms, particularly that of Calloselasma rhodostoma (73.6%), presumably due to the presence of venom antigens common to both snakes. Levels of immunological cross-reactivity were vastly reduced with double-sandwich ELISA. Further work demonstrated that the assay was able to distinguish and quantify venoms of H. hypnale, Daboia russelii and Echis carinatus sinhaleyus (three common local viperid) used to spike human sera at various concentrations. The assay hence may be a useful investigating tool for diagnosing biting species and studying the time course profile of venom concentrations in blood.

Fractionation of equine antivenom using caprylic acid precipitation in combination with cationic ion-exchange chromatography

A combined process of caprylic acid (CA) precipitation and ion-exchange chromatography on SP-Sepharose was studied as a means to fractionate pepsin-digested horse antivenom F(ab')(2) antibody. In the CA precipitation, the optimal concentration for fractionation of F(ab')(2) from pepsin-digested horse plasma was 2%, in which 89.61% of F(ab')(2) antibody activity was recovered in the supernatant with 1.5-fold purification. A significant amount of pepsin was not precipitated and remained active under these conditions. An analytical cation exchanger Protein-Pak SP 8HR HPLC column was tested to establish optimal conditions for the effective separation of IgG, albumin, pepsin and CA from the F(ab')(2) product. From these results, the supernatant from CA precipitation of pepsin-digested plasma was subjected to a SP-Sepharose column chromatography using a linear salt gradient. With stepwise elution, a peak containing F(ab')(2) antibody could be obtained by elution with 0.25 M NaCl. The total recovery of antibody was 65.56% with 2.91-fold purification, which was higher than that achieved by ammonium sulfate precipitation. This process simultaneously and effectively removed residual pepsin, high molecular weight aggregates and CA in the final F(ab')(2) product, and should be suitable for large-scale fractionation of therapeutic equine antivenoms.

Quantitative comparison on the refinement of horse antivenom by salt fractionation and ion-exchange chromatography

A quantitative comparison was made on the fractionation of pepsin-digested horse antivenoms by ammonium sulfate (AS) fractional precipitation and ion-exchange chromatography on Q-Sepharose. In the precipitation process, pepsin digested horse anti-Naja kaouthia serum was precipitated by 30% saturated AS followed by 50% saturated AS. The recovery of antibody activity [as measured by an enzyme-linked immunosorbent assay (ELISA) against the cobra postsynaptic neurotoxin 3] from the 30-50% saturated AS precipitate was 53% with a 1.93-fold purification. For the chromatographic process, the behavior of the horse antitoxin antibody and its F(ab')2 fragments was first studied. The pepsin digested horse serum was then desalted on a Bio-gel P-2 column followed by chromatography on Q-Sepharose using a linear gradient (20 mM Tris-HCl, pH 8.0 containing 0.0 to 0.5 M NaCl) A peak containing primarily the F(ab')2 antibody could be obtained. This peak constituted 73% of the total antivenom activity with 2.08-fold purification. The total recovery of antibody activity by the chromatographic process was 90%. The yield of antibody activity was about 2-fold higher than that reported previously with other fractionation procedures. The implications of these results for the refining of horse therapeutic antivenoms are discussed.

Experimental evaluation of ovine antisera to Thai cobra (Naja kaouthia) venom and its alpha-neurotoxin

Conventional treatment of Naja kaouthia (Thai cobra) envenoming requires large volumes (up to 600 ml) of equine antivenom, which results in a high incidence of serum reactions. The inefficiency of the antivenom is assumed to be related to the high percentage (approx. 20%) of alpha-neurotoxin, a relatively weak and highly toxic immunogen, present in the native venom. First, antibodies to N. kaouthia venom were raised in sheep, which protected mice against challenge with whole venom. Second, ovine antibodies to the purified neurotoxin and to three different neurotoxin conjugates were developed and their neutralising abilities against either whole venom or neurotoxin were compared using murine ED50 tests. High titre antibodies, assessed by enzyme immunoassay and Western blot, were obtained from all four neurotoxin immunisation regimens. Neurotoxin conjugated to rabbit anti-sheep IgG produced the highest titres against both neurotoxin and whole venom. This antiserum provided protection against neurotoxin challenge but failed to protect against whole venom. Furthermore, the addition of neurotoxin antibodies to whole venom antiserum did not enhance the neutralisation efficacy of the latter. These findings raise the possibility that in mice other toxins apart from the neurotoxin may significantly contribute to the lethal effect of N. kaouthia venom.

Preparation, characterization and immunogenicity of various polymers and conjugates of elapid postsynaptic neurotoxins

Seven polymeric forms and conjugates of purified principal postsynaptic neurotoxins of Naja naja siamensis (NNS), Ophiophagus hannah (OH) and Bangarus fasciatus (BF) have been synthesized by controlled polymerization in which only 29-60% of the toxins were allowed to react. A carbodiimide (ECDI) and glutaraldehyde (GA) were used as coupling agents while BSA and tetanus toxoid (TT) were used as carriers. The antigenic mosaic of these immunogens was: NNS-ECDI, NNS-BF-OH-ECDI, NNS-BSA-ECDI, NNS-TT-ECDI, NNS-BF-OH-TT-ECDI, NNS-GA and NNS-BF-OH-GA. By using SDS-PAGE and radioactive toxin, each immunogen preparation was characterized in terms of molecular size and abundance of protein components, percent toxin reacted and toxin density. The relative immunogenicities of the immunogens along with those of NNS venom and pure NNS neurotoxin were evaluated in groups of eight rats. The levels of specific antibody against each of the neurotoxins were determined by ELISAs. Multiple comparisons between antibody responses to these immunogens were made. All the chemically modified immunogens were at least as immunogenic as NNS venom. NNS-TT-ECDI gave the highest antibody response (2.7-6.2-fold higher than that induced by NNS venom). All three multispecific immunogens induced comparable specific antibodies to BF, OH and NNS neurotoxins. The results showed that the presence of TT carrier and the relative degree of toxin density affected the immunogenicities. Some of the immunogens reported here should be useful for the production of potent, polyvalent antivenoms against elapid snakes.