Peptidomimetic hydroxamate metalloproteinase inhibitors abrogate local and systemic toxicity induced by Echis ocellatus (saw-scaled) snake venom.

The ability of two peptidomimetic hydroxamate metalloproteinase inhibitors, Batimastat and Marimastat, to abrogate toxic and proteinase activities of the venom of Echis ocellatus from Cameroon and Ghana was assessed. Since this venom largely relies for its toxicity on the action of zinc-dependent metalloproteinases (SVMPs), the hypothesis was raised that toxicity could be largely eliminated by using SVMP inhibitors. Both hydroxamate molecules inhibited local and pulmonary hemorrhagic, in vitro coagulant, defibrinogenating, and proteinase activities of the venoms in conditions in which venom and inhibitors were incubated prior to the test. In addition, the inhibitors prolonged the time of death of mice receiving 4 LD50s of venom by the intravenous route. Lower values of IC50 were observed for in vitro and local hemorrhagic activities than for systemic effects. When experiments were performed in conditions that simulated the actual circumstances of snakebite, i.e. by administering the inhibitor after envenoming, Batimastat completely abrogated local hemorrhage if injected immediately after venom. Moreover, it was also effective at inhibiting lethality and defibrinogenation when venom and inhibitor were injected by the intraperitoneal route. Results suggest that these, and possibly other, metalloproteinase inhibitors may become an effective adjunct therapy in envenomings by E. ocellatus when administered at the anatomic site of venom injection rapidly after the bite.

Comparison of the adjuvant activity of emulsions with different physicochemical properties on the antibody response towards the venom of West African carpet viper (Echis ocellatus).

Adjuvant emulsions are widely used to enhance the antibody response of the animals used as immunoglobulin source for producing antivenoms. Usually, the adjuvant activity of emulsions is attributed both to their ability to trigger "danger" signals from cells in which they induce death, and to form depots from which immunogens are slowly released. However, there is contradictory evidence suggesting that adjuvant activity of emulsions is independent of the dispersion type and the rate of immunogen release. In order to test how physical properties of emulsions, composed of mineral oil and water, affect their ability to enhance the antibody response towards snake venoms, we compared water-in-oil (W/O) emulsions prepared at volume ratios of 70/30, 50/50 or 30/70, a 50/50 oil-in-water (O/W) emulsion, and a water-in-oil-in-water (W/O/W) multiple emulsion. Comparison included their droplet-size, viscosity, rate of immunogen release and ability to enhance the antibody response of mice immunized with the venom of the African viperid snake Echis ocellatus. It was found that all emulsions released a low amount of venom, and that the 50/50 (W/O) and the multiple emulsion (W/O/W) were those that induced the higher anti-venom antibody response. Our results suggest that the ability of emulsions to enhance the anti-venom response is not associated to their ability to form depots from which the venom is slowly released.

Effect of geographical variation of Echis ocellatus, Naja nigricollis and Bitis arietans venoms on their neutralization by homologous and heterologous antivenoms.

Two antivenoms prepared by using Echis ocellatus, Bitis arietans and Naja nigricollis venoms from different locations in sub-Saharan Africa were compared for their neutralizing ability. Both antivenoms were similarly effective in the neutralization of the venoms of the three species from different locations. However in the case of E. ocellatus venom, antivenom prepared using venom from Nigerian specimens was more effective than antivenom prepared with venom from Cameroon specimens in the neutralization of coagulant activity.

Evaluation of the preclinical efficacy of four antivenoms, distributed in sub-Saharan Africa, to neutralize the venom of the carpet viper, Echis ocellatus, from Mali, Cameroon, and Nigeria.

Snakebite envenoming causes a heavy toll in sub-Saharan Africa in terms of mortality and sequelae. In the West African savannah, the viperid Echis ocellatus is responsible for the vast majority of bites. In the last decades, several new antivenoms have been introduced for the treatment of these envenomings, although the assessment of their preclinical efficacy against the venom of E. ocellatus has been studied only for some of them. This work analyzed comparatively the ability of four antivenoms (FAV Afrique, EchiTAb G, EchiTAB-Plus-ICP(®), and Inoserp™ Panafricain) to neutralize lethal, hemorrhagic, and in vitro coagulant activities of the venoms of E. ocellatus from Mali, Cameroon, and Nigeria. In addition, an immunoaffinity chromatography antivenomic protocol was used to assess the ability of the four antivenoms to bind to the proteins of these venoms. Results showed that all the antivenoms were effective in the neutralization of the three effects investigated, and were able to immunocapture, completely or partially, the most abundant components in the E. ocellatus venoms from the geographical origins sampled. Our observations also highlighted quantitative differences between antivenoms in their neutralizing and antivenomics profiles, especially regarding neutralization of in vitro coagulant activity, suggesting that different doses of these antivenoms are probably needed for an effective treatment of human envenomings by this species.