Identification of a nitric oxide-dependent hypotensive effect of anticoagulation factor II from the venom of Agkistrodon acutus

Vasodilator and hypotensive effects of the spider peptide Lycosin-I in vitro and in vivo

Lycosin-I, a spider peptide isolated from the venom of the spider Lycosa singoriensis, has anti-bacteria and anti-cancer properties in organisms. However, cardiovascular effects of Lycosin-I have not been studied. In this study, we investigated for the first time the vasodilator and hypotensive effects of Lycosin-I and the possible mechanisms, in order to develop a promising treatment for hypertension-related diseases. For in vitro experiments, thoracic aortas were isolated, and divided into two groups, endothelium-intact and endothelium-denuded aortic rings. Lycosin-I induced a remarkable dose-dependent relaxation in endothelium-intact aortic rings pre-treated with phenylephrine (p < 0.05), while it showed no obvious vasodilator effects in endothelium-denuded aortic rings (p > 0.05). The vasodilator effects of Lycosin-I were significantly weakened by a nitric oxide synthase (NOS) inhibitor, L-NAME (p < 0.001) and a selective inhibitor of nitric oxide (NO)-sensitive soluble guanylate cyclase (sGC), ODQ (p < 0.05), respectively. The levels of endothelial nitric oxide synthase (eNOS) phosphorylation and the NO production were significantly higher in human umbilical vascular endothelial cells pre-cultured with Lycosin-I than the control (p < 0.001), determined via western blot analysis and ozone-chemiluminescence technology. For in vivo experiments, arterial and venous catheters were inserted for mean arterial pressure (MAP) recording and drug administration in anaesthetized spontaneously hypertensive rats. Lycosin-I caused a transient drop of MAP 2 min after the administration compared with the control (p < 0.001). In conclusion, Lycosin-I has the potential to be an anti-hypertensive drug by endothelium-dependent vasodilatation, in which eNOS and NO-sensitive sGC are two main involved factors.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.

Vascular effects and electrolyte homeostasis of the natriuretic peptide isolated from Crotalus oreganus abyssus (North American Grand Canyon rattlesnake) venom

Crotalus oreganus abyssus is a rattlesnake that is usually found in the Grand Canyon, United States of America. Knowledge regarding the composition of C. o. abyssus venom is scarce. New natriuretic peptides (NPs) have been isolated and characterized from the venoms of members of the Crotalinae family. The NP family comprises three members, ANP (atrial natriuretic peptide), BNP (b-type natriuretic peptide) and CNP (c-type natriuretic peptide), and has an important role in blood pressure regulation and electrolyte homeostasis. The aim of the present study was to characterize a novel natriuretic-like peptide (Coa_NP2), isolated from C. o. abyssus venom. The Coa_NP2 presents an average molecular mass of 3419.88Da (theoretical average molecular mass 3418.94Da, monoisotopic molecular mass 3416.66Da and theoretical PI 7.78) and its amino acid sequence presents the loop region that is characteristic of natriuretic peptides. The peptide has 32 amino acids and its complete sequence is SYGISSGCFGLKLDRIGTMSGLGCWRLLQDSP. Coa_NP2 is a natriuretic peptide of the ANP/BNP-like family, since the carboxyterminal region of CNP has its own NP domain. We demonstrate, herein, that Coa_NP2 produces a dose-dependent decrease in mean arterial pressure in rats, followed by significant increases in concentrations of markers of nitric oxide formation measured in the plasma and vasorelaxation in a thoracic aortic ring bath. The structural and biological aspects confirm Coa_NP2 as a new natriuretic peptide, isolated from snake venom.

Ca(2+) -induced binding of anticoagulation factor II from the venom of Agkistrodon acutus with factor IX

Anticoagulation factor II (ACF II), a coagulation factor X- binding protein from the venom of Agkistrodon acutus has both anticoagulant and hypotensive activities. Previous studies show that ACF II binds specifically with activated factor X (FXa) in a Ca(2+) -dependent manner and inhibits intrinsic coagulation pathway. In this study, the inhibition of extrinsic coagulation pathway by ACF II was measured in vivo by prothrombin time assay and the binding of ACF II to factor IX (FIX) was investigated by native polyacrylamide gel electrophoresis and surface plasmon resonance (SPR). The results indicate that ACF II also inhibits extrinsic coagulation pathway, but does not inhibit thrombin activity. ACF II also binds with FIX with high binding affinity in a Ca(2+) -dependent manner and their maximal binding occurs at about 0.1 mM Ca(2+) . ACF II has similar binding affinity to FIX and FX as determined by SPR. Ca(2+) has a slight effect on the secondary structure of FIX as determined by circular dichroism spectroscopy. Ca(2+) ions are required to maintain in vivo function of FIX Gla domain for its recognition of ACF II. However, Ca(2+) at high concentrations (>0.1 mM) inhibits the binding of ACF II to FIX. Ca(2+) functions as a switch for the binding between ACF II and FIX. ACF II extends activated partial thromboplastin time more strongly than prothrombin time, suggesting that the binding of ACF II with FIX may play a dominant role in the anticoagulation of ACF II in vivo.

Metal ion binding to anticoagulation factor II from the venom of Agkistrodon acutus: stabilization of the structure and regulation of the binding affinity to activated coagulation factor X

Anticoagulation factor II (ACF II) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X (FXa)-binding protein with both anticoagulant and hypotensive activities. The thermodynamics of the binding of alkaline earth metal ions to ACF II and their effects on the stability of ACF II and the binding of ACF II to FXa were investigated by isothermal titration calorimetry, fluorescence, differential scanning calorimetry, and surface plasmon resonance. The binding of ACF II to FXa does not have an absolute requirement for Ca(2+). Mg(2+), Sr(2+), and Ba(2+) can induce the binding of ACF II to FXa. The radii of the cations bound in ACF II crucially affect the binding affinity of ACF II for cations and the structural stability of ACF II against guanidine hydrochloride and thermal denaturation, whereas the radii of cations bound in FXa markedly affect the binding affinity between ACF II and FXa. The binding affinities of ACF II for cations and the capacities of metal-induced stabilization of ACF II follow the same trend: Ca(2+) > Sr(2+) > Ba(2+). The metal-induced binding affinities of ACF II for FXa follow the trend Mg(2+) > Ca(2+) > Sr(2+) > Ba(2+). Although Mg(2+) shows significantly low binding affinity with ACF II, Mg(2+) is the most effective to induce the binding of ACF II with FXa. Our observations suggest that in blood the bindings of Ca(2+) in two sites of ACF II increase the structural stability of ACF II, but these bindings are not essential for the binding of ACF II with FXa, and that the binding of Mg(2+) and Ca(2+) to FXa may be essential for the recognition between FXa and ACF II. Like Ca(2+), the abundant Mg(2+) in blood also plays an important role in the anticoagulation of ACF II.

Binding of Ca2+ and Zn2+ to factor IX/X-binding protein from venom of Agkistrodon halys Pallas: stabilization of the structure during GdnHCl-induced and thermally induced denaturation

Coagulation factor IX/coagulation factor X binding protein from the venom of Agkistrodon halys Pallas (AHP IX/X-bp) is a unique coagulation factor IX/coagulation factor X binding protein (IX/X-bp). Among all IX/X-bps identified, only AHP IX/X-bp is a Ca(2+)- and Zn(2+)-binding protein. The binding properties of Ca(2+) and Zn(2+) ions binding to apo-AHP IX/X-bp and their effects on the stability of the protein have been investigated by isothermal titration calorimetry, fluorescence spectroscopy, and differential scanning calorimetry. The results show that AHP IX/X-bp has two metal binding sites, one specific for Ca(2+) with lower affinity for Zn(2+) and one specific for Zn(2+) with lower affinity for Ca(2+). The bindings of Ca(2+) and Zn(2+) in the two sites are entropy- and enthalpy-driven. The binding affinity of AHP IX/X-bp for Zn(2+) is 1 order of magnitude higher than for Ca(2+) for either high-affinity binding or low-affinity binding, which accounts for the existence of one Zn(2+) in the purified AHP IX/X-bp. Guanidine hydrochloride (GdnHCl)-induced and thermally induced denaturations of Ca(2+)-Ca(2+)-AHP IX/X-bp, Zn(2+)-Zn(2+)-AHP IX/X-bp, and Ca(2+)-Zn(2+)-AHP IX/X-bp are all a two-state processes with no detectable intermediate state(s), indicating the Ca(2+)/Zn(2+)-induced tight packing of the protein. Ca(2+) and Zn(2+) increase the structural stability of AHP IX/X-bp against GdnHCl or thermal denaturation to a similar extent. Although Ca(2+) and Zn(2+) have no obvious effect on the secondary structure of AHP IX/X-bp, they induce different rearrangements in local conformation. The Zn(2+)-stabilized specific conformation of AHP IX/X-bp may be helpful to its recognition of the structure of coagulation factor IX. This work suggests that in vitro, Ca(2+) plays a structural rather than an active role in the anticoagulation of AHP IX/X-bp, whereas Zn(2+) plays both structural and active roles in the anticoagulation. In blood, Ca(2+) binds to AHP IX/X-bp and stabilizes its structure, whereas Zn(2+) cannot bind to AHP IX/X-bp owing to the low Zn(2+) concentration. AHP IX/X-bp prolongs the clotting time in vivo through its binding only with coagulation factor X/activated coagulation factor X.