The venom of the Lebanese viper, Montivipera bornmuelleri contains vasoactive compounds

Abstract

Snake venoms are rich mixtures of polypeptides, which target, among other physiological networks, the cardiovascular system. Snake toxins such as phospholipase A2 (PLA2), natriuretic peptides (NPs), and bradykinin-potentiating peptides (BPP) exert various effects with vascular consequences (hypotension, vasorelaxation…). Some of these toxins have been developped as drugs with antihypertensive properties, such as Captopril™. We have previously shown that the venom of Montivipera bornmuelleri induces the relaxation of rat aortic rings. Here, we aim to identify and characterize the vasoactive compounds of this venom. The venom was fractionated by HPLC. The fractions were assayed on the endothelial cell line, Mile Sven 1 (MS1) and two different cell lines, which stably expressed muscarinic receptors M1 and M3. We screened for compounds able to inhibit acetylcholine-induced intracellular Ca 2+ rise, using the fluorescence probe FURA-2. Wire myography on isolated mesenteric arteries was used. Proteomic analysis was performed to characterize selected fractions. Among 23 fractions of the M. bornmuelleri venom, one fraction was selected for its ability to reduce acetylcholine-induced Ca 2+ rise in MS1 cells. The proteomic analysis led to identify a novel peptidyl toxin, homologous to a vascular endothelial growth factor toxin from Macrovipera lebetina . However, this novel toxin was unable to antagonize acetylcholine-induced Ca 2+ rise in cells expressing muscarinic receptors M1 or M3, suggesting that this peptide acts indirectly on the Ca 2+ signaling pathway in endothelial cells. In myography, the crude venom exhibited a vasorelaxant effect on mesenteric arteries, but the isolated peptide did not. The M. bornmuelleri venom exerts a vasorelaxant effect on mesenteric arteries. We found a novel toxin homologous to a vascular endothelial growth factor snake toxin, which modulates Ca 2+ signaling pathway in endothelial cells.