Humoral response and neutralization capacity of sheep serum inoculated with natural and Cobalt 60-irradiated Crotalus durissus terrificus venom (Laurenti, 1768)

Use of irradiated elapid and viperid venoms for antivenom production in small and large animals

This work evaluated the feasibility of using toxoids obtained by gamma radiation in the production of antivenoms in small and large animals. Mixtures of African snake venoms from viperids or elapids were used. The viperid mixture contained the crude venom of five species of the genera Echis and Bitis, while the elapid mixture contained the crude venom of six species of the genera Naja and Dendroaspis. The viperid mixture had an LD₅₀ of 1.25 mg/kg in mice, and the elapid mixture had an LD₅₀ of 0.46 mg/kg. Both viper and elapid aqueous mixtures were subjected to Cobalt-60 gamma irradiation in three physical states: lyophilized, frozen and liquid. Radiation doses ranged from 0.5 to 100 kGy. The LD₅₀s of the lyophilized and frozen mixtures of both viperid and elapid mixtures remained unaltered with radiation doses as high as 100 kGy; nevertheless, in the liquid state, doses of 3.5 and 5.5 kGy reduced the venom toxicity of both the viperid and elapid mixtures to 7.25 mg/kg and 1.74 mg/kg; less toxic by factors of 5.8 and 3.8, respectively. Groups of four rabbits and three horses were immunized with either irradiated or non-irradiated mixtures. In vitro and in vivo analysis of the rabbit and horse sera revealed that neutralizing antibodies were produced against both irradiated (toxoids) and native venom mixtures. None of the animals used in this study, either immunized with native venom or toxoids, developed severe local effects due to the application of venoms mixtures. Gamma-irradiated detoxified venoms mixtures, under well-controlled and studied conditions, could be a practical alternative for the production of polyvalent equine serum with high neutralization potency against snake venoms.

Assessment of the neutralizing potency of antisera raised against native and γ-irradiated Naja nigricollis (black-necked spitting cobra) venom in rabbits, concerning its cardiotoxic effect

The present study was designed to prepare a specific safe antiserum for Naja nigricollis using γ-irradiated (1.5KGy and3KGy) venoms. Rabbits were used for active immunization using irradiated venoms (1.5 and 3 kGy) as a toxoid, mice were used for determination of LD₅₀ post immunization and the rats were used for neutralization of the cardiotoxic effect of venom. Results of the immunodiffusion test indicated that the sera of rabbits raised against non-irradiated, 1.5- and 3-kGy γ-irradiated venom, had the same results of precipitin bands. A significant inhibition of phospholipase A₂ activities was obtained when neutralized with native, γ-irradiated (1.5KGy and3KGy) venoms. On the other hand, preincubation of the venom ½ LD₅₀ (0.154 mg/kg i.p.) with each antiserum (non-irradiated or irradiated venom) at 37°C for 1 h in a ratio (1:4) produced a significant reduction in the values of creatine kinase and creatine kinase isoenzyme-MB. However, significant elevation in aspartate aminotransferase level and no change in lactate dehydrogenase level were observed. So the results of this study indicated that the irradiated venom treatment reduces the cardiotoxic effect of venom in immunized immunization animals for preparing vaccines.

Immunological cross-reactivity and neutralization of the principal toxins of Naja sumatrana and related cobra venoms by a Thai polyvalent antivenom (Neuro Polyvalent Snake Antivenom)

The low potency of cobra antivenom has been an area of concern in immunotherapy for cobra envenomation. This study sought to investigate factors limiting the neutralizing potency of cobra antivenom, using a murine model. We examined the immunological reactivity and neutralizing potency of a Thai polyvalent antivenom against the principal toxins of Naja sumatrana (Equatorial spitting cobra) venom and two related Asiatic cobra venom α-neurotoxins. The antivenom possesses moderate neutralizing potency against phospholipases A2 (P, potency of 0.98mg/mL) and moderately weak neutralizing potency against long-chain α-neurotoxins (0.26-0.42mg/mL) but was only weakly effective in neutralizing the short-chain α-neurotoxins and cardiotoxins (0.05-0.08mg/mL). The poor neutralizing potency of the antivenom on the low molecular mass short-chain neurotoxins and cardiotoxins is presumably the main limiting factor of the efficacy of the cobra antivenom. Our results also showed that phospholipase A2, which exhibited the highest ELISA reactivity and avidity, was most effectively neutralized, whereas N. sumatrana short-chain neurotoxin, which exhibited the lowest ELISA reactivity and avidity, was least effectively neutralized by the antivenom. These observations suggest that low immunoreactivity (low ELISA reactivity and avidity) is one of the reasons for poor neutralization of the cobra venom low molecular mass toxins. Nevertheless, the overall results show that there is a lack of congruence between the immunological reactivity of the toxins toward antivenom and the effectiveness of toxin neutralization by the antivenom, indicating that there are other factors that also contribute to the weak neutralization capacity of the antivenom. Several suggestions have been put forward to overcome the low efficacy of the cobra antivenom. The use of a 'proper-mix' formulation of cobra venoms as immunogen, whereby the immunogen mixture used for hyperimmunization contains a mix of various types of α-neurotoxins and cardiotoxins in sufficient amount, may also help to improve the efficacy and broaden the neutralization spectrum of the antivenom.

New nanostructured silica adjuvant (SBA-15) employed to produce antivenom in young sheep using Crotalus durissus terrificus and Apis mellifera venoms detoxified by cobalt-60

Equine antivenom is considered the only treatment for animal-generated envenomations, but it is costly. The study aimed to produce Apis mellifera (Africanized honeybee) and Crotalus durissus terrificus (C.d.t.) antivenoms using nanostructured silica (SBA-15) as adjuvant and cobalt-60 ((60)Co)-detoxified venoms utilizing young sheep. Natural and (60)Co-irradiated venoms were employed in four different hyperimmunization protocols. Thus, 8 groups of 60- to 90-d-old sheep were hyperimmunized, enzyme-linked immunosorbent assay (ELISA) serum titers collected every 14 d were assessed clinically daily, and individual weight were measured, until d 84. Incomplete Freund's (IFA) and nanostructured silica (SBA15) adjuvants were compared. The lethal dose (LD(50)) for both venoms was determined following intraperitoneal (ip) administration to mice. High-performance liquid chromatography on reversed phase (HPLC-RP) was used also to measure the (60)Co irradiation effects on Apis venom. At the end of the study, sheep were killed in a slaughterhouse. Kidneys were histologically analyzed. LD(50) was 5.97 mg/kg Apis and 0.07 mg/kg C.d.t. for native compared to 13.44 mg/kg Apis and 0.35 mg/kg C.d.t. for irradiated venoms. HPLC revealed significant differences in chromatographic profiles between native and irradiated Apis venoms. Native venom plus IFA compared with SBA-15 showed significantly higher antibody titers for both venoms. Apis-irradiated venom plus IFA or SBA-15 displayed similar antibody titers but were significantly lower when compared with native venom plus IFA. Weight gain did not differ significantly among all groups. (60)Co irradiation decreased toxicity and maintained venom immunogenic capacity, while IFA produced higher antibody titers. SBA-15 was able to act as an adjuvant without producing adverse effects. Hyperimmunization did not affect sheep weight gain, which would considerably reduce the cost of antiserum production, as these sheep were still approved for human consumption even after being subjected to hyperimmunization.