R. David G. Theakston

Confronting the Neglected Problem of Snake Bite Envenoming: The Need for a Global Partnership

Envenoming resulting from snake bites is an important public health hazard in many regions of the world, yet public health authorities have given little attention to the problem.

Snake venom disintegrins: novel dimeric disintegrins and structural diversification by disulphide bond engineering

We report the isolation and amino acid sequences of six novel dimeric disintegrins from the venoms of Vipera lebetina obtusa (VLO), V. berus (VB), V. ammodytes (VA), Echis ocellatus (EO) and Echis multisquamatus (EMS). Disintegrins VLO4, VB7, VA6 and EO4 displayed the RGD motif and inhibited the adhesion of K562 cells, expressing the integrin alpha5beta1 to immobilized fibronectin. A second group of dimeric disintegrins (VLO5 and EO5) had MLD and VGD motifs in their subunits and blocked the adhesion of the alpha4beta1 integrin to vascular cell adhesion molecule 1 with high selectivity. On the other hand, disintegrin EMS11 inhibited both alpha5beta1 and alpha4beta1 integrins with almost the same degree of specificity. Comparison of the amino acid sequences of the dimeric disintegrins with those of other disintegrins by multiple-sequence alignment and phylogenetic analysis, in conjunction with current biochemical and genetic data, supports the view that the different disintegrin subfamilies evolved from a common ADAM (a disintegrin and metalloproteinase-like) scaffold and that structural diversification occurred through disulphide bond engineering.

Snake Venomics of African Spitting Cobras: Toxin Composition and Assessment of Congeneric Cross-Reactivity of the Pan-African EchiTAb-Plus-ICP Antivenom by Antivenomics and Neutralization Approaches

Venomic analysis of the venoms of Naja nigricollis, N. katiensis, N. nubiae, N. mossambica, and N. pallida revealed similar compositional trends. The high content of cytotoxins and PLA(2)s may account for the extensive tissue necrosis characteristic of the envenomings by these species. The high abundance of a type I α-neurotoxin in N. nubiae may be responsible for the high lethal toxicity of this venom (in rodents). The ability of EchiTAb-Plus-ICP antivenom to immunodeplete and neutralize the venoms of African spitting cobras was assessed by antivenomics and neutralization tests. It partially immunodepleted 3FTx and PLA(2)s and completely immunodepleted SVMPs and CRISPs in all venoms. The antivenom neutralized the dermonecrotic and PLA(2) activities of all African Naja venoms, whereas lethality was eliminated in the venoms of N. nigricollis, N. mossambica, and N. pallida but not in those of N. nubiae and N. katiensis. The lack of neutralization of lethality of N. nubiae venom may be of medical relevance only in relatively populous areas of the Saharan region. The impaired activity of EchiTAb-Plus-ICP against N. katiensis may not represent a major concern. This species is sympatric with N. nigricollis in many regions of Africa, although very few bites have been attributed to it.

Amino acid sequence and crystal structure of BaP1, a metalloproteinase from Bothrops asper snake venom that exerts multiple tissue‐damaging activities

BaP1 is a 22.7‐kD P‐I‐type zinc‐dependent metalloproteinase isolated from the venom of the snake Bothrops asper, a medically relevant species in Central America. This enzyme exerts multiple tissue‐damaging activities, including hemorrhage, myonecrosis, dermonecrosis, blistering, and edema. BaP1 is a single chain of 202 amino acids that shows highest sequence identity with metalloproteinases isolated from the venoms of snakes of the subfamily Crotalinae. It has six Cys residues involved in three disulfide bridges (Cys 117–Cys 197, Cys 159–Cys 181, Cys 157–Cys 164). It has the consensus sequence H142E143XXH146XXGXXH152, as well as the sequence C164I165M166, which characterize the “metzincin” superfamily of metalloproteinases. The active‐site cleft separates a major subdomain (residues 1–152), comprising four α‐helices and a five‐stranded β‐sheet, from the minor subdomain, which is formed by a single α‐helix and several loops. The catalytic zinc ion is coordinated by the Nε2 nitrogen atoms of His 142, His 146, and His 152, in addition to a solvent water molecule, which in turn is bound to Glu 143. Several conserved residues contribute to the formation of the hydrophobic pocket, and Met 166 serves as a hydrophobic base for the active‐site groups. Sequence and structural comparisons of hemorrhagic and nonhemorrhagic P‐I metalloproteinases from snake venoms revealed differences in several regions. In particular, the loop comprising residues 153 to 176 has marked structural differences between metalloproteinases with very different hemorrhagic activities. Because this region lies in close proximity to the active‐site microenvironment, it may influence the interaction of these enzymes with physiologically relevant substrates in the extracellular matrix.

Identification of sites in the cysteine-rich domain of the class P-III snake venom metalloproteinases responsible for inhibition of platelet function

Atrolysin A and jararhagin are class P‐III snake venom metalloproteinases (SVMPs) with three distinct domains: a metalloproteinase, a disintegrin‐like and a cysteine‐rich. The metalloproteinase and the disintegrin‐like domains of atrolysin A and jararhagin contain peptide sequences that interact with α2β1 integrin and inhibit the platelet responses to collagen. Recently, the recombinant cysteine‐rich domain of atrolysin A was shown to have similar effects, but the sequence(s) responsible for this is unknown. In this report, we demonstrate two complete peptide sequences from the homologous cysteine‐rich domains of atrolysin A and jararhagin that inhibit both platelet aggregation by collagen and adhesion of α2‐expressing K562 cells to this protein. In addition, the peptide effects on platelets do not seem to involve an inhibition of GPVI. These results identify, for the first time, sites in the cysteine‐rich domain of SVMPs that inhibit cell responses to collagen and reveal the complexity of the potential biological effects of these enzymes with multifunctional domains.

Crotaline snake bite in the Ecuadorian Amazon: randomised double blind comparative trial of three South American polyspecific antivenoms

Abstract Objective To compare the efficacy and safety of three polyspecific antivenoms for bites by pit vipers. Design Randomised double blind comparative trial of three antivenoms. Setting Shell, Pastaza, southeastern Ecuador. Participants 210 patients with incoagulable blood were recruited from 221 consecutive patients admitted with snake bite between January 1997 and December 2001. Intervention One of three antivenoms manufactured in Brazil, Colombia, and Ecuador, chosen for their preclinical potency against Ecuadorian venoms. Main outcome measures Permanent restoration of blood coagulability after 6 and 24 hours. Results The snakes responsible for the bites were identified in 187 cases: 109 patients (58%) were bitten by Bothrops atrox, 68 (36%) by B bilineatus, and 10 (5%) by B taeniatus, B brazili, or Lachesis muta. Eighty seven patients (41%) received Colombian antivenom, 82 (39%) received Brazilian antivenom, but only 41 (20%) received Ecuadorian antivenom because the supply was exhausted. Two patients died, and 10 developed local necrosis. All antivenoms achieved the primary end point of permanently restoring blood coagulability by 6 or 24 hours after the start of treatment in > 40% of patients. Colombian antivenom, however, was the most effective after initial doses of 20 ml (two vials), < 70 ml, and any initial dose at both 6 and 24 hours. An initial dose of 20 ml of Colombian antivenom permanently restored blood coagulability in 64% (46/72) of patients after 6 hours (P = 0.054 compared with the other two antivenoms) and an initial dose of < 70 ml was effective at 6 hours (65%, P = 0.045) and 24 hours (99%, P = 0.06). Early anaphylactoid reactions were common (53%, 73%, and 19%, respectively, for Brazilian, Colombian, and Ecuadorian antivenoms, P < 0.0001) but only three reactions were severe and none was fatal. Conclusions All three antivenoms can be recommended for the treatment of snakebites in this region, though the reactogenicity of Brazilian and Colombian antivenoms is a cause for concern.

The effect of jararhagin, a metalloproteinase from Bothrops jararaca venom, on pro-inflammatory cytokines released by murine peritoneal adherent cells.

The release of pro-inflammatory cytokines (IL-1beta, IL-6 and TNF-alpha) from murine peritoneal adherent cells (MPAC) was studied after exposure to jararhagin, a metalloproteinase/disintegrin isolated from Bothrops jararaca venom. MPACs were treated with LPS (lipopolysaccharide), jararhagin, or EDTA-inactivated jararhagin for up to 24h. Following incubation, the culture supernatant was assayed by ELISA for the presence of cytokines, while the cells were analysed for viability and cytokine mRNA expression. The cells exposed to native jararhagin released TNF-alpha and IL-1beta after 4 and 24h respectively. When MPACs were exposed to Jararhagin treated with EDTA, TNF-alpha and IL-1beta production was sustained throughout the culture period and IL-6 production was observed. TNF-alpha, IL-6 and IL-1beta mRNA were detected 4h after stimulation with either native or EDTA-treated jararhagin. Addition of jararhagin to LPS stimulated cells resulted in a dramatic decrease in the release of IL-6 and TNF-alpha. RT-PCR showed that this inhibition does not occur at the transcriptional level and further experiments showed that jararhagin degraded soluble cytokines by proteolytic activity. This study suggests that jararhagin induces TNF-alpha, IL-1beta and IL-6 expression, which may be rapidly degraded by its proteolytic activity.

Collagen-induced secretion-dependent phase of platelet aggregation is inhibited by the snake venom metalloproteinase jararhagin

Jararhagin, a 52 kDa metalloproteinase from Bothrops jararaca snake venom, belongs to the family of enzymes with an N-terminal Zn2+-containing enzymatic domain, a disintegrin-like domain and a cysteine-rich C-terminal domain. Both jararhagin and jararhagin C, a 28 kDa-protein from the same venom identical to the disintegrin-like domain of jararhagin, inhibit collagen-induced platelet aggregation. In this study, jararhagin and synthetic linear peptides based on the disintegrin-like domain of jararhagin overlapping with the RGD sequence of venom disintegrins, were shown for the first time to inhibit the release of 5-hydroxytryptamine (5-HT) from platelets preloaded with [14C]5-HT and stimulated with collagen. The normal phosphorylation of the 21-kDa myosin light chain (p21) in response to the stimulation indicated that jararhagin and the peptides did not interfere with platelet shape change. The selective inhibition of the secretion-dependent phase of the platelet response to collagen by the enzyme and its peptides was confirmed by the defective phosphorylation of pleckstrin, a 47-kDa platelet protein (p47) involved in dense granule secretion.

Preclinical assessment of the efficacy of a new antivenom (EchiTAb-Plus-ICP) for the treatment of viper envenoming in sub-Saharan Africa

A preclinical assessment was performed on the neutralizing efficacy of a whole IgG polyspecific antivenom (EchiTAb-Plus-ICP), designed for the treatment of snakebite envenomings in Nigeria. It was generated by immunizing horses with the venoms of Echis ocellatus, Bitis arietans and Naja nigricollis, the most medically important species in Nigeria. Antivenom was tested against the venoms of E. ocellatus, Echis leucogaster, Echis pyramidum leakeyi, B. arietans, Bitis gabonica, Bitis rhinoceros and Bitis nasicornis. The neutralization of the venom toxins responsible for the lethal, hemorrhagic, coagulant and local necrotizing activities was assessed, since these are the most significant effects that characterize envenoming by these species. Echis sp venoms exerted lethal, hemorrhagic, coagulant and necrotizing effects, whereas the Bitis sp venoms tested induced lethality, hemorrhage and necrosis, but were devoid of coagulant activity. The antivenom was effective in the neutralization of all effects tested in all venoms. Highest neutralization was achieved against the venoms of E. ocellatus and B. arietans, and the lowest neutralizing potency was against the venom of B. nasicornis, a species that has a low clinical relevance. It is concluded that EchiTAb-Plus-ICP, whilst specifically designed for Nigeria, has a good preclinical neutralizing profile against homologous and heterologous viperid venoms from other sub-Saharan African locations. It therefore constitutes a promising therapeutic option for the treatment of snakebite envenoming in this region.

The molecular cloning of a phospholipase A2 from Bothrops jararacussu snake venom: Evolution of venom group II phospholipase A2's may imply gene duplications

The sequence coding for a snake venom phospholipase A2 (PLA2), BJUPLA2, has been cloned from a Bothrops jararacussu venom gland cDNA library. The cDNA sequence predicts a precursor containing a 16-residue signal peptide followed by a molecule of 122 amino acid residues with a strong sequence similarity to group II snake venom PLA2s. A striking feature of the cDNA is the high sequence conservation of the 5′ and 3′ untranslated regions in cDNAs coding for PLA2s from a number of viper species. The greatest sequence variation was observed between the regions coding for the mature proteins, with most substitutions occurring in nonsynonymous sites. The phylogenetic tree constructed by alignment of the amino acid sequence of BJUPLA2 with group II PLA2s in general groups them according to current taxonomical divisions and/or functional activity. It also suggests that gene duplications may have occurred at a number of different points during the evolution of snake venom group II PLA2s.