Toxicovenomics and antivenom profiling of the Eastern green mamba snake ( Dendroaspis angusticeps )

Abstract

Envenomings by elapid snakes of the genus Dendroaspis, collectively known as mambas, represent a serious medical problem in sub-Saharan Africa. The development of novel antivenoms and of recombinant neutralizing antibodies demands the identification of the most relevant toxins in these venoms. In this study, a bottom-up approach was followed for the study of the proteome of the venom of the Eastern green mamba, D. angusticeps. Forty-two different proteins were identified, among which the three-finger toxin (3FTx) family, characteristic of elapid venoms, was the most abundant, followed by the Kunitz-type proteinase inhibitor family. In addition, several other protein families were present in the venom, together with the nucleoside adenosine. No α-neurotoxins were identified within the family of 3FTxs in the venom of D. angusticeps, in contrast to the venom of Dendroaspis polylepis, in which α-neurotoxins are largely responsible for the toxicity. With one exception, HPLC fractions from D. angusticeps venom did not kill mice at the doses tested. This underscores that the toxicity of the whole venom is due to the synergistic action of various components, such as fasciculins and dendrotoxins, and probably other synergistically-acting toxins. Thus, the venoms of these closely related species (D. angusticeps and D. polylepis) seem to have different mechanisms to subdue their prey, which may be related to different prey preferences, as D. angusticeps is predominantly arboreal, whereas D. polylepis lives mostly in open bush country and feeds mainly on mammals. It is therefore likely that the predominant clinical manifestations of human envenomings by these species also differ, although in both cases neurotoxic manifestations predominate. Polyspecific antivenoms manufactured in South Africa and India were effective in the neutralization of venom-induced lethality in mice and showed a pattern of broad immunorecognition of the various venom fractions. It is necessary to identify the toxins responsible for the synergistic mode of toxicity in this venom, since they are the targets for the development of recombinant antibodies for the treatment of envenomings.

High-throughput immuno-profiling of mamba (Dendroaspis) venom toxin epitopes using high-density peptide microarrays

“…The results for 40 additional short chain three-fingered toxins are available in Fig. 4, including 19 aminergic (muscarinic) toxins known to act synergistically21. However, a further exploration of these antivenom-toxin interactions is beyond the scope of this communication.…”

“…Key findings within the most important toxin families in mamba and cobra venoms are presented in the following subsections, where focus is directed on toxins of high medical importance as judged by their Toxicity Scores determined in previous studies2122.…”

“…Fasciculins are another medically important subfamily of short chain three-finger toxins found primarily in D. angusticeps venom2123. As venom from D. angusticeps is included in the immunisation mixture for the SAIMR antivenom, the detected epitopes are likely to be a result of specific antibodies.…”

“…Mamba envenomings are known for their rapid onset of neurotoxicity1920, which may manifest itself already after 15 min via clinical signs such as flaccid paralysis, dyspnea due to respiratory muscle paralysis, and involuntary skeletal muscle contractions or fasciculations19. These effects are explained by the venom compositions, which are dominated by potent small neurotoxins belonging to the three-finger toxin family and Kunitz-type serine protease inhibitor family212223. α-neurotoxins bind to nicotinic cholinergic receptors at the motor end-plate of muscle fibers, thereby blocking neuromuscular transmission24.…”

“…In addition, fasciculins, which are inhibitors of acetylcholinesterase (AChE), have been isolated from D. angusticeps venom, and these quite unique AChE inhibitors may induce increased synaptic concentrations of acetylcholine causing fasciculation26. Although many toxins have been isolated and sequenced from Dendroaspis venoms, only the venoms of D. polylepis and D. angusticeps have so far undergone a thorough toxicovenomics analysis2122. In spite of the significant differences in venom compositions, many similar toxins exist in Dendroaspis venoms, although in different relative proportions, which is to be expected given the phylogenetic proximity of the four species27.…”