A new C-type lectin (RVsnaclec) purified from venom of Daboia russelii russelii shows anticoagulant activity via inhibition of FXa and concentration-dependent differential response to platelets in a Ca²⁺-independent manner

This is the first report on the characterization of a snaclec (RVsnaclec) purified from Daboia russelii russelii venom. The RVsnaclec is a heterodimer of two subunits, α (15.1 kDa) and β (9 kDa). These subunits are covalently linked to form multimeric (αβ)₂ and (αβ)₄ structures. Peptide mass fingerprinting analysis of RVsnaclec via LC-MS/MS demonstrated its similarity to snaclecs purified from other viperid snake venoms. Two tryptic peptide sequences of RVsnaclec revealed the putative conserved domains of C-type lectin (CTL). RVsnaclec dose-dependently increased the Ca-clotting time and prothrombin time of platelet-poor plasma (PPP); however, it did not affect the partial thromboplastin time (APTT) or thrombin time of PPP. The in vitro and in vivo anticoagulant activity of RVsnaclec is correlated to its binding and subsequent uncompetitive inhibition of FXa (Ki = 0.52 μmole) in a Ca(2+)-independent manner; however, supplementation with 0.25 mM Ca(2+) enhanced the Xa binding potency of RVsnaclec. Monovalent or polyvalent antivenom failed to neutralize its anticoagulant potency, and RVsnaclec did not inhibit trypsin, chymotrypsin, thrombin or plasmin. RVsnaclec was devoid of hemolytic activity or cytotoxicity against several human cancer cell lines, demonstrated concentration-dependent aggregation and deaggregation of human platelets, and inhibited the ADP-induced aggregation of platelet. RVsnaclec (5.0 mg/kg body weight) was non-lethal to mice and showed no adverse pharmacological effects, suggesting that it has potential as a lead compound for future therapeutic applications in cardiovascular disorders.

Evaluation of the lethal potency of scorpion and snake venoms and comparison between intraperitoneal and intravenous injection routes

Scorpion stings and snake bites are major health hazards that lead to suffering of victims and high mortality. Thousands of injuries associated with such stings and bites of venomous animals occur every year worldwide. In North Africa, more than 100,000 scorpion stings and snake bites are reported annually. An appropriate determination of the 50% lethal doses (LD₅₀) of scorpion and snake venoms appears to be an important step to assess (and compare) venom toxic activity. Such LD₅₀ values are also commonly used to evaluate the neutralizing capacity of specific anti-venom batches. In the present work, we determined experimentally the LD₅₀ values of reference scorpion and snake venoms in Swiss mice, and evaluated the influence of two main venom injection routes (i.e., intraperitoneal (IP) versus intravenous (IV)). The analysis of experimental LD₅₀ values obtained with three collected scorpion venoms indicates that Androctonus mauretanicus (Am) is intrinsically more toxic than Androctonus australis hector (Aah) species, whereas the latter is more toxic than Buthus occitanus (Bo). Similar analysis of three representative snake venoms of the Viperidae family shows that Cerastes cerastes (Cc) is more toxic than either Bitis arietans (Ba) or Macrovipera lebetina (Ml) species. Interestingly, the venom of Elapidae cobra snake Naja haje (Nh) is far more toxic than viper venoms Cc, Ml and Ba, in agreement with the known severity of cobra-related envenomation. Also, our data showed that viper venoms are about three-times less toxic when injected IP as compared to IV, distinct from cobra venom Nh which exhibited a similar toxicity when injected IP or IV. Overall, this study clearly highlights the usefulness of procedure standardization, especially regarding the administration route, for evaluating the relative toxicity of individual animal venoms. It also evidenced a marked difference in lethal activity between venoms of cobra and vipers, which, apart from the nature of toxins, might be attributed to the rich composition of high molecular weight enzymes in the case of viper venoms.

The polyphenol 3, 4, 5 - tri-hydroxy benzoic acid inhibits indian daboia russelli venom and its hemorrhagic complex induced local toxicity

Despite a long history on treatment and management of snakebite, as of now, no satisfactory cure exists to treat local toxicity, including anti-venom therapy. Several natural compounds from plants and their synthetic analogs have shown to be protective. In this study 3, 4, 5-tri-hydroxy benzoic acid, the gallic acid (GA) was tested against the local toxicity of Daboia russelli (DR) venom and its purified hemorrhagic complex (HC). GA inhibited in vitro proteolytic activity of both DR venom and HC but, it did not inhibit phospholipase activity of DR venom. GA inhibited hemorrhage, edema forming, dermo- and myonecrotic activities of both HC and DR venom in in vivo experiments. GA was particularly effective against hemorrhagic activity but, GA inhibition had a greater effect on HC when compared to DR venom. The inhibition was likely due to GA induced structural changes in HC as revealed by alterations in fluorescence emission and CD spectral properties. However, the inhibition was not due to chelating property of GA as suggested by UV-visible spectral studies. Inhibition of collagen type IV, laminin and fibronectin degradation essentially provided the biochemical basis for GA which inhibited local effects of HC as well as DR venom. Thus, the study appears highly promising to explore GA and its generics against ruthless local effects and perhaps systemic hemorrhage of DR and other snake bites as well. Further, these agents will possibly find an immense value in the regulation of matrix metalloproteases (MMPs) in processes such as wound healing, inflammation and in the treatment of cancer.

Inhibition of hemorrhagic activity of viper venoms by N-acetyl cysteine: involvement of N-acetyl and thiol groups

The mortality rate due to snakebite is reduced markedly by the use of anti-venoms, which are the only medically approved remedial agents available. The anti-venoms effectively neutralize the systemic toxicity but offer no protection towards local tissue degradation. In viperid snake envenomations, SVMPs and SVHYs are the major agents responsible for brutal local tissue damage as they degrade ECM and basement membrane surrounding the blood vessels. Thus, the usage of inhibitor(s) against ECM degrading enzymes in the treatment of viper bites is an affirmative therapeutic choice. The present study assessed the efficacy of N-acetyl cysteine (NAC) to inhibit gelatinase, hyaluronidase, hemorrhagic and defibrinogenating activities of Vipera russelli and Echis carinatus venoms. NAC inhibited these activities dosedependently, but it did not inhibit the PLA2, 5' nucleotidase, procoagulant and edema inducing activities of both the venoms. NAC showed complete inhibition of hemorrhagic activity when incubated with venom prior to testing. Whereas little inhibition was observed when venom and NAC were injected independently. Inhibition of the basement membrane degradation and accumulation of inflammatory leukocytes at the site of venom injection in histological sections further corroborate the inhibitory property of NAC. The observed inhibition of hemorrhage was likely due to zinc chelation as supported by spectral studies. Further, docking predictions suggested the role of -SH and -NH-CO-CH3 groups of NAC in the inhibition of SVMPs and SVHYs. Future studies related to the protective role of NAC against the venom induced systemic hemorrhage and secondary complications are highly exciting.

Chronic Activation of Endothelin B Receptors

Endothelin (ET) exerts powerful pressor actions primarily through activation of the ET(A) receptor subtype. The ET(B) receptor (ET(B)R) subtype, on the other hand, is generally thought to initiate physiological actions that decrease arterial pressure. Such actions include clearing ET from the bloodstream, initiating endothelium-mediated vasodilation, and facilitating renal sodium and water excretion. The effect of long-term activation of the ET(B)R on arterial pressure, however, never has been directly tested. In this study we evaluated cardiovascular responses to chronic (5-day) activation of ET(B)R in male rats using continuous intravenous infusion of the selective agonist sarafotoxin 6c. Surprisingly, we found that sarafotoxin 6c caused a sustained increase in arterial pressure that rapidly reversed on termination of infusion. The hypertension was associated with increased renal excretion of sodium and water and decreased plasma volume. Alterations in daily sodium intake did not affect the magnitude of the hypertension. Hemodynamic studies revealed a decreased cardiac output and increased total peripheral resistance during sarafotoxin 6c infusion. Infusion of sarafotoxin 6c caused a small increase in plasma ET levels. Nevertheless, the hypertension was not affected by coadministration of a selective ET(A) receptor antagonist (atrasentan) but was completely prevented by treatment with a combined ET(A) receptor and ET(B)R antagonist (A186280). These experiments reveal for the first time that chronic activation of ET(B)R in rats causes sustained hypertension.

Venom of Indian monocellate cobra and Russell's viper show anticancer activity in experimental models

Indian monocellate cobra (Naja kaouthia) and Russell's viper (Vipera russelli) are common snakes of the East Indian sub-peninsula. The anticarcinogenic activities of their crude venoms were studied on carcinoma, sarcoma and leukemia models. Sub-lethal doses of venoms showed cytotoxicity on Ehrlich ascites carcinoma (EAC) cells in vivo. The venoms increased lifespan of EAC mice and strengthened the impaired host antioxidant system. Sarcoma formation in mice (3-methylcholanthrene induced) after venom treatment was significantly less (p < 0.005). Histopathological examination of tumors showed tissue necrosis. The venoms displayed potent cytotoxic and apoptogenic effect on human leukemic cells (U937/K562). The venoms reduced cell proliferation rate (p < 0.005) and produced morphological alterations indicative of apoptosis induction. Different degree and nature of anticarcinogenic property of cobra and viper venoms may be attributed to the difference in their constituents.

Ammodytase, a metalloprotease from Vipera ammodytes ammodytes venom, possesses strong fibrinolytic activity

Ammodytase, a high molecular mass metalloproteinase with fibrinogenolytic and fibrinolytic activities, was purified from long-nosed viper (Vipera ammodytes ammodytes) venom by gel filtration, affinity and ion-exchange chromatographies. The enzyme is a single-chain glycoprotein with apparent molecular mass of 70 kDa and isoelectric point of 6.6. Ammodytase shows very weak hemorrhagic activity, and only at doses higher than 20 microg. Consistent with this, it partially degrades some components of the extracellular matrix in vitro. It cleaves the Aalpha-chain of fibrinogen preferentially at peptide bonds Glu(441)-Leu(442) and Glu(539)-Phe(540). Its preference for bulky and hydrophobic amino acids at the P1' position in substrates is demonstrated by its hydrolysis of only the Gln(4)-His(5) and Tyr(16)-Leu(17) bonds in the B-chain of insulin. Ammodytase is able to dissolve fibrin clots. It neither activates nor degrades plasminogen and prothrombin, and has no effect on collagen- or ADP-induced platelet aggregation in vitro. LC/MS and MS/MS analyses of its tryptic fragments demonstrated that ammodytase is a P-III class snake venom metalloproteinase composed of metalloproteinase, disintegrin-like and cysteine-rich domains. Its similarity to hemorrhagins from V. a. ammodytes venom, accompanied by very low toxicity, makes ammodytase a promising candidate as an antigen to prepare antisera against these most dangerous components of the viper's venom. Moreover, its ability to degrade fibrin clots suggests its clinical use as an antithrombotic agent.

Effects of Russell's viper venom fractions on systemic and renal hemodynamics

Changes in systemic and renal hemodynamics induced by Russell's viper venom are well established. The component of the venom responsible for hemodynamic alteration has not been identified. By Sephadex column chromatography five fractions of Russell's viper (Daboia russellii siamensis) venom were isolated. Each venom fraction consisted of phospholipase A2, proteolytic enzyme, phosphomonoesterase, phosphodiesterase, arginine ester hydrolase and hyaluronidase of varying activities. Hemodynamic effects of each venom fraction including mean arterial pressure, cardiac output, systemic and renal vascular resistance, renal blood flow and glomerular filtration rate were studied in five groups of dogs; each group had four dogs. Minimal hemodynamic changes were observed in dogs receiving venom fraction I. Increased renal vascular resistance with diminution of renal blood flow and glomerular filtration rate was observed in dogs receiving venom fractions II, III, IV and V. A markedly increased renal vascular resistance with maximal decrease in renal blood flow and glomerular filtration rate was caused by fraction III of the venom with highest PLA2 and proteolytic enzyme activities. However, renal hemodynamic changes appeared to correlate better with proteolytic enzyme activity than PLA2 activity. The findings suggested the proteolytic enzyme as an important determinant of hemodynamic alteration. Fractional excretion of Na was increased in dogs injected with venom fraction IV, and is presumed to be due to the inhibition of tubular reabsorption of Na by a natriuretic factor in this venom fraction.

Functional roles of the two distinct domains of halysase, a snake venom metalloprotease, to inhibit human platelet aggregation

Halysase, a hemorrhagic metalloprotease, has an apparent molecular weight of 66kDa and belongs to the class P-III snake venom metalloprotease. Class P-III snake venom metalloproteases have multifunctional domains including a protease domain and a disintegrin-like domain. Halysase was able to preferentially hydrolyze the alpha-chain of fibrinogen. Proteolytic activity of the enzyme was completely inhibited by metal chelating agents but not by other typical protease inhibitors. The enzyme principally cleaves X-Leu, X-Tyr, X-Phe, and X-Ala peptide bonds of the oxidized insulin B-chain. Halysase strongly suppresses collagen-induced human platelet aggregation in a dose-dependent manner. Apohalysase that is devoid of its metalloprotease activity was also able to inhibit the platelet aggregation to a certain extent. Experimental evidence clearly indicates that each of the two distinct domains of halysase, the metalloprotease and the disintegrin-like domains, plays its characteristic role to inhibit human platelet aggregation.

Intravenous apyrase administration reduces arterial thrombosis in a rabbit model of endothelial denudation in vivo

The role of adenine nucleotides on vascular and platelet functions has long been established. Apyrase (CD39) takes part of a family of ecto-enzymes that hydrolyze adenosine diphosphate and adenosine triphosphate. The participation of apyrase in the thromboregulatory system is under study. An in vivo experimental model of acute arterial thrombosis was used to test the hypothesis that administering a soluble form of potato apyrase could prevent thrombus formation. Twenty-five white New Zealand male rabbits suffered balloon aortic endothelium denudation and, after 15 days, they were submitted to a thrombosis-triggering protocol with a procoagulant (Russel's viper venom) and epinephrine. After the thrombosis-triggering protocol, 12 animals received two soluble apyrase administrations intravenously (with 90 min intervals), while 13 control animals received no apyrase. Three hours after the triggering protocol, the animals were killed and the rate and area of arterial thrombosis were analyzed. The rate of thrombosis in the apyrase group was significantly lower than that of the control group (16.7 versus 69%, respectively; P = 0.015), as was the area of thrombosis (1.7 +/- 4.3 versus 21.7 +/- 37.4 mm2, respectively; P = 0.008). Our results confirm that apyrase participates in homeostasis through a potent anti-thrombotic effect.

[Protective effect of Vipera raddei venom damage of peripheral nerve]

In rats, single pulse activity of inter- and motoneurons of the spinal cord lumbar segment was studied in stimulation of cut. n. ischiadicus, extensor (n. gastrocnemius) and flexor (n. peroneus communis) after treatment with the Viper raddei venom for 4 weeks. In the control rats, no responses occurred in the n. ischiadicus distal stump, whereas the responses to contralateral nerve stimulation did occur. On the intact side, the responses occurred in opposite sequence. The absence of effects of the cut nerve distal stump stimulation in control rats resulted from the coalescence absence in the proximal stump which suggests atrophy of the distal stump. Morphological data prove a distal stump hypertrophy and restoration of the affected limb motor activity. The findings suggest a possibility of application of the Viper raddei venom for regeneration of injured peripheral nerve.

Inotropic effects of ETB receptor stimulation and their modulation by endocardial endothelium, NO, and prostaglandins

Endothelin (ET)-1 acts on ETA and ETB receptors. The latter include ETB1 (endothelial) and ETB2 (muscular) subtypes, which mediate opposite effects on vascular tone. This study investigated, in rabbit papillary muscles ( n = 84), the myocardial effects of ETB stimulation. ET-1 (10−9 M) was given in the absence or presence of BQ-123 (ETA antagonist). The effects of IRL-1620 (ETB1 agonist, 10−10–10−6 M) or sarafotoxin S6c (ETB agonist, 10−10–10−6 M) were evaluated in muscles with intact or damaged endocardial endothelium (EE); intact EE, in the presence of NG-nitro-l-arginine (l-NNA); and intact EE, in the presence of indomethacin (Indo). Sarafotoxin S6c effects were also studied in the presence of BQ-788 (ETB2 antagonist). ET-1 alone increased 64 ± 18% active tension (AT) but decreased it by 4 ± 2% in the presence of BQ-123. In muscles with intact EE, sarafotoxin S6c alone did not significantly alter myocardial performance. Sarafotoxin S6c (10−6 M) increased, however, AT by 120 ± 27% when EE was damaged and by 39 ± 8% or 23 ± 6% in the presence of l-NNA or Indo, respectively. In the presence of BQ-788, sarafotoxin S6c decreased AT (21 ± 3% at 10−6 M) in muscles with intact EE, an effect that was abolished when EE was damaged. IRL-1620 also decreased AT (22 ± 3% at 10−6 M) in muscles with intact EE, an effect that was abolished when EE was damaged or in the presence of l-NNA or Indo. In conclusion, the ETB-mediated negative inotropic effect is presumably due to ETB1 stimulation, requires an intact EE, and is mediated by NO and prostaglandins, whereas the ETB-mediated positive inotropic effect, observed when EE was damaged or NO and prostaglandins synthesis inhibited, is presumably due to ETB2 stimulation.

Effects of 60Co gamma radiation on toxicity and hemorrhagic, myonecrotic, and edema-forming activities of Cerastes cerastes venom

Antisera are used as effective antidotes against the local effects of snake bites. To improve antisera production and extend the life of surrogates used to produce antibodies, the chronic effects of venom toxicity must be reduced. The present study evaluated the effectiveness of gamma irradiation to reduce the local effects associated with viperid snake bites by evaluating in NMRI mice the toxicity and edematic, hemorrhagic, and myonecrotic activities of native and irradiated Cerastes cerastes venoms. These results indicated that the toxicity of irradiated venoms (1 and 2 kGy) decreased as compared with that of native venom. The edematic and hemorrhagic activities were also reduced in the detoxified samples, particularly with the 2-kGy radiation dose. Futhermore, the creatine phosphokinase (CPK) activity was significantly increased in the serum and decreased in the myocardium after envenomation with native venom, but no significant enzymatic changes were observed in mice envenomated with irradiated venom. Histopathologic evaluation showed that native venom caused severe degenerative changes in the myocardium. In the case of 2-kGy-irradiated venom, no tissue alterations were observed. These results indicate that irradiation of venom with a 2-kGy dose may offer an effective method for reducing the chronic toxic effects of venom in immunized animals.Key words: venom, Cerastes cerastes, gamma radiation, histopathological change.

Evaluation of the effect of gamma rays on the venom of Vipera lebetina by biochemical study

Snake bites represent a serious public health problem in many areas of the world. In Algeria, two widespread snakes are Vipera lebetina and Cerastes cerastes. Vipera lebetina venom causes local hemorrhage and necrosis, and it may lead to permanent limb loss. The principal causes of mortality after snakebites are acute renal failure and hemorrhage, which occur not only locally, at the site of the bite, but also systemically, contributing to the cardiovascular shock characteristic of severe envenomation. Gamma radiation has been shown to be effective for attenuating venom toxicity. Vipera lebetina venom was irradiated with two doses of gamma rays (1 and 2 kGy) from a 60Co source, and the venom's toxic, enzymatic, and structural properties were analyzed. Intraperitoneal injection of the irradiated venoms (100–500 µg/20 g mouse body mass) revealed a significant decrease of the toxicity. Irradiated venoms with 1 and 2 kGy doses were four and nine times less toxic, respectively, than the native venom. A biochemical characterization of in vitro enzymatic activities was performed. Vipera lebetina displayed in vitro caseinolytic, amidolytic, esterasic, coagulant, and phospholipase A2 activities. Caseinolytic, amidolytic, esterasic, and coagulative activities were reduced for the irradiated venoms; only phospholipase A2 activity was abolished in the irradiated venom with a dose of 2 kGy. The native and irradiated venoms were separated by gel filtration and electrophoresis. Chromatographic and electrophoretic profiles were drastically changed as compared with the native venom. Vipera lebetina venom detoxified by gamma rays was used for active immunization, and the presence of antibody in the immune sera was detected by ELISA. The immunogenic properties were preserved and the antisera obtained with the irradiated venoms could cross-react. Antisera were able to neutralize the toxic effect of V. lebetina native venom. These results indicate that irradiation of V. lebetina venom with a dose of 2 kGy can promote a significant detoxification, keeping the immunological properties intact.Key words: Vipera lebetina venom, gamma radiation, enzymes, detoxification, immune sera, immunoreactivity.

Importance of metalloproteinases and macrophages in viper snake envenomation-induced local inflammation

The inflammatory action of jararhagin, a hemorrhagic metalloproteinase from Bothrops jararaca venom, was studied in mice using dorsal air pouches. The injection of the toxin in 6-day-old air pouches resulted in a leukocyte accumulation comparable to that induced by LPS and whole venom. Polymorphonuclear and mononuclear cells were present in this infiltrate, with a predominance of neutrophils. Treatment of jararhagin with 1,10-phenantroline abolished its proteolytic activity and reduced the pro-inflammatory effect in approximately 50%. Cell influx was not observed when jararhagin was injected into 1-hr air pouches devoid of macrophages, except when it was injected together with 10(6) syngeneic peritoneal macrophages. Supernatants of macrophages stimulated in vitro with jararhagin did not induce leukocyte influx in 1-hr air pouches; the influx occurred after injection of the pellets of stimulated cultures. In summary, jararhagin is an important pro-inflammatory component of B. jararaca venom, and its activity is dependent upon the proteolytic activity and the presence of macrophages.

[Effect of Macrovipera lebetina and Cerastes cerastes venoms on adherence to integrins of cancerous cells (IGR39, HT29-D4 and IGROV1)]

In this work, we provide experimental arguments in favor of the fact that components from Macrovipera lebetina and Cerastes cerastes venoms bind to IGR39 melanoma cells but not to HT29D4 cells that derive from carcinoma adenome. Furthermore, Macrovipera lebetina and Cerastes cerastes venoms inhibit the adherence of IGR39 and HT 29-D4 to various extracellular matrix proteins. Macrovipera lebetina and Cerastes cerastes venoms did not inhibit the non specific adherence of IGR 39 cells to polylysine. In addition, binding of components from Cerastes cerastes venom to IGR39 cells is inhibited by GRGDS peptide and by monoclonal antibidy anti-av, while these two components have no effect on the adherence of IGR39 to Macrovipera lebetina venom.

Endothelin receptor mediating contraction of isolated bovine coronary artery

We studied endothelin (ET) receptors and their subtypes on isolated bovine coronary arteries. Endothelin receptors that mediated contraction of isolated bovine coronary artery were characterized by the use of antagonists and agonists. Contractions induced by the nonselective agonist ET-1 (10-10-10-7 M) were not affected by the removal of the endothelium (pEC50: 8.52, maximal contraction: 105% of that induced by 60 mM KCl). BQ-123 (3 x 10-7 M) antagonized contractions of endothelium-denuded coronary rings induced by low concentrations of ET-1 (10-10 or 10-9 M), but potentiated the contractions induced by higher concentrations of ET-1 (3 x 10-8 and 10-7 M). BQ-788 (10-6 M) potentiated contractions induced by ET-1 (3 x 10-10 and 10-7 M). In the presence of BQ-788 (10-6 M), BQ-123 (3 x 10-8-3 x 10-6 M) concentration - dependently inhibited contractions induced by ET-1 (3 x 10-10 and 10-7 M) (pA2: 6.61). Sarafotoxin S6b (10-9-3 x 10-7 M) evoked contractions in the denuded coronary artery (pEC50: 8.49, maximal contraction: 139% of 60 mM KCl). The BQ-123 caused a concentration-dependent rightward shift of contractions induced by sarafotoxin S6b (pA2: 7.89). The present study indicates that ET-1 and sarafotoxin S6b contract the isolated bovine coronary artery by stimulating ETA receptors on smooth muscle cells, and that ETB receptors might suppress the ET-1-induced contractions.

Antagonization of TNF attenuates systemic hemodynamic manifestations of envenomation in a rat model of Vipera aspis snakebite

OBJECTIVES

Tumor necrosis factor (TNF) has been reported as a mediator of local tissue injury following snake envenomation in an intact rat model. We investigated whether systemic release of TNF occurs following Vipera aspis envenomation. We further analyzed the possible connection between envenomation-related hemodynamic depression and TNF antagonization (TNF antibodies or soluble TNF receptor).

DESIGN

A prospective, randomized, controlled experimental study using a rat model for snake envenomation.

SETTINGS

A medical university hospital research laboratory.

INTERVENTION

Eighty rats (300-400 g) were divided into four groups (n = 20): control and three experimental groups. Intramuscular injection of V. asis 500 microg/kg was administered to the three experimental groups: venom only (group 1), venom and 40 microg anti-TNF antibodies (group 2), venom and 250 microg soluble TNF receptor (p55-R; group 3). Hemodynamic parameters were monitored up to 4 h following venom injection.

MEASUREMENTS AND RESULTS

A significant hemodynamic deterioration (reduction in heart rate and blood pressure) occurred 30 min following venom injection in group 1 compared to groups 2 and 3, where hemodynamic parameters remained stable throughout the 4 h observation period. Serum levels of TNF were detected 15 min after venom injection and peaked after 2 h at 485+/-12 pg/ml.

CONCLUSIONS

The hemodynamic consequences of intramuscular injection of V. aspis venom can be blunted in a rat by systemic antagonization of TNF activity prior to venom injection. The poisonous hemodynamic effects of the V. aspis venom might be caused by systemic release of TNF.

Constriction to ETB receptor agonists, BQ-3020 and sarafotoxin s6c, in human resistance and capacitance vessels in vivo

AIMS

The aim of the study was to examine the effects of the ETB receptor selective agonists sarafotoxin S6c (SFTX6c) and BQ-3020 on the forearm resistance and capacitance vessels in healthy subjects in vivo.

METHODS

The local response to intra-arterial or intravenous infusion of SFTX6c (5 pmol min-1) or BQ-3020 (50 pmol min-1) was assessed, on separate occasions, in eight healthy men (aged 20-28 years). Data (mean +/- s.e.mean) were examined by ANOVA. Results are expressed as percentage change from baseline at 90 min.

RESULTS

SFTX6c and BQ-3020 reduced forearm blood flow, following local intra-arterial infusion (-25 +/- 7% and -27 +/- 7%, respectively; P < 0.001) and reduced hand vein diameter, following local intravenous infusion (-30 +/- 8% and -16 +/- 7%, respectively; P < 0.001).

CONCLUSIONS

We have shown that locally active infusions of the selective ETB receptor agonists SFTX6c and BQ-3020 cause arterial constriction and venoconstriction in healthy human blood vessels in vivo. These results indicate that ETB receptor stimulation may mediate vasoconstriction in humans.

Endothelin-1 induced bronchial hyperresponsiveness in the rabbit: an ET(A) receptor-mediated phenomenon

Endothelin-1 (ET-1) is a potent and efficacious spasmogen of airway smooth muscle. Recent observations suggest that an increased intrapulmonary production of ET-1 may occur in asthma. Our previous study showed that endothelin-1 induced bronchial hyperresponsiveness to inhaled histamine in the rabbit. The aim of this study was to investigate whether the ET(A) and ET(B) receptors mediate the bronchial hyperresponsiveness induced by endothelin-1 in the rabbit. Our data showed that bronchial hyperresponsiveness induced by ET-1 was significantly inhibited (P<0.01) by the ET(A) receptor-selective antagonist, FR 139317 (from 2.5 to 10 mg kg(-1)). Moreover, bosentan (from 2.5 mg kg(-1) to 10 mg kg(-1)), an ET(A)/ET(B) receptor antagonist, also inhibited the bronchial hyperresponsiveness achieved 24 h following endothelin-1 challenge (P<0.01), but with no difference from FR 139317. The ET(B) receptor agonist, sarafotoxin S6c (from 25 microg to 2.5 mg kg(-1)) did not modify airway responsiveness to inhaled histamine in the rabbit. These results indicate that bronchial hyperresponsiveness induced by ET-1 may be mediated by ET(A) receptor activation.

Effect of some variables on the in vivo determination of scorpion and viper venom toxicities

An adequate assessment of scorpion and snake venom LD50 is an important step for accurate evaluation of antivenom sera potencies and the optimization of serotherapy. The LD50 variation of Tunisian scorpion (Androctonus australis garzonii: Aag and Buthus occitanus tunetanus: Bot) venoms with body weight, sex and strain (Swiss or C57BI/6) of mice used, the route of venom injection, the venom-milking procedures (manually or electrically) and the venom batches have been studied over a 7-year period (1990-1996). Aag venom is 3-4 times more toxic than Bot venom. However for both venoms, the LD50 determined in C57BI/6 mice, in small body weight animal or by intraperitoneal route were respectively significantly lower than those determined in Swiss mice, in high body weight or by subcutaneous route. Significant LD50 variations (25-50%) were also seen from one electrically prepared batch to another. A good correlation (r = 0.982) was observed between the concentrations of the crude venom toxic fraction determined by ELISA and LD50 values when assessed in vivo. The LD50 variation of Tunisian viper (Cerastes cerastes: Cc and Vipera lebetina: VI) venoms with the strain (Swiss or BALB/c), sex and body weight of mice used, the season and the year of venom milking were also investigated over a 3-year period (1990-1992). No significant LD50 variations were observed with the mouse strain, the sex or the season of venom milking. However, LD50 varies significantly with the year of the venom collection and the body weight of mice used. Furthermore, SDS-PAGE analysis shows annual variation for VI venom composition where no such variations were observed for Cc venom. These results stress the need either for the standardization of the venom LD50 evaluation or of the venom quality used for the development of an efficient antivenom.

Preclinical assessment of immunoreactivity of a new purified equine F(ab')2 against European viper venom

The immunological and pharmacokinetic properties of a new, further purified, pasteurized preparation of equine F(ab')2 (VIPERFAV) against Vipera aspis, Vipera berus, and Vipera ammodytes venom were compared with the current equine F(ab')2 preparation (IPSER Europe). Affinity constants of the V. aspis-specific F(ab')2 were determined using biosensor technology and found to be in the range of 10(8) M-1 for the four antigenic fractions of V. aspis toxins and for both F(ab')2 preparations. The improvement of 51% in the specific activity (LD50 mg-1) of the new F(ab')2 was in close agreement with the 1.8-fold increase in the immunoreactive fraction of the new preparation. In vivo investigations of venom immunocomplexation by F(ab')2 in rabbits confirmed the ability of F(ab')2 to neutralize and redistribute toxin venom. Infusion of a stoichiometric molar ratio (i.e., 1 mg kg-1) of the new antivenom induced a 2.3-fold elevation of the plasma venom concentration with a Tmax observed 8 h after F(ab')2 administration and a decline in the terminal half-life from 31.92 +/- 4.49 h to 16.73 +/- 4.34 h, in contrast, for the venom alone. The area under the curve was 1.4-fold greater in the VIPERFAV group than in the IPSER Europe group during the post-F(ab')2 infusion period. Increasing the F(ab')2 dose to 3 mg kg-1 increased by 27% the percent of venom bound to F(ab')2. Finally, the greater the venom distribution, the smaller and less pronounced the plasma redistribution. These results demonstrate that the purification and pasteurization steps involved in the preparation of the new F(ab')2 have no deleterious influence on F(ab')2 affinity but, on the contrary, improve the protective efficacy. Alteration of viper venom kinetics by specific F(ab')2 antivenom was also shown to be dependent on the interval between of F(ab')2 administration and venom bite and on the specific F(ab')2 dose administered.

Effect of ETA receptor antagonists on cardiovascular responses induced by centrally administered sarafotoxin 6b: role of sympathetic nervous system

The present study was carried out to investigate the cardiovascular effects of centrally administered SRT6b in saline, BQ123 and BMS182874 pretreated male Sprague-Dawley rats, using a radioactive microsphere technique. SRT6b (100 ng, ICV) produced a transient increase (40%) in blood pressure at 5 min followed by a sustained decrease (-42%) at 30 and 60 min in control rats. Total peripheral resistance and heart rate were not significantly altered. Cardiac output increased (16%) at 5 min and decreased 30 and 60 min following SRT6b administration. Central venous pressure was not affected by SRT6b. Regional blood flow and vascular resistance did not change at 5 min following administration of SRT6b. However, a significant decrease in blood flow to the brain, heart, kidneys, liver, spleen, gastrointestinal tract and mesentery and pancreas was observed 30 and 60 min following administration of SRT6b in control (saline treated) rats. Pretreatment with ETA selective receptor antagonists, BQ123 (10 micrograms, ICV) or BMS182874 (50 micrograms, ICV) significantly attenuated the pressor and depressor effects of centrally administered SRT6b. SRT6b induced decrease in blood flow was completely blocked by pretreatment with BQ123 or BMS182874. ET-1 (100 ng, ICV) produced an increase followed by a decrease similar to SRT6b. Reserpine (5 mg/kg, IP) pretreatment attenuated the cardiovascular effects of ET-1. Role of sympathetic nervous system was determined by measuring splanchnic nerve activity. SRT6b when administered in the lateral cerebral ventricle did not produce any significant effect at 5 min, however, a significant decrease in sympathetic nerve activity was observed 30 min after its administration. It is concluded that centrally administered SRT6b produces significant changes in systematic and regional blood circulation which can be completely blocked by ETA receptor antagonist. The cardiovascular effects of centrally administered SRT6b appear to be mediated through the sympathetic nervous system.

Activation of the endothelin B receptor causes a dose-dependent accumulation of cyclic GMP in human platelets

Endothelins modulate in vitro aggregation of human platelets in a bi-directional manner. Thus endothelin-1 has been shown to act as a potentiator of primary aggregation and an inhibitor of secondary aggregation. The endothelin receptors and corresponding second messengers which cause these effects have not yet been characterised. This study investigated the effect of endothelin-1, an agonist at both the ETA and the ETB receptors and sarafotoxin (SRTX) S6c, a selective ETB agonist, on human platelet cyclic nucleotide levels. Neither endothelin-1 (10(-11) -10(-7) M) nor SRTX S6c (10(-11) -10(-7) M) significantly altered platelet cAMP levels. In contrast, both agonists produced a dose-dependent increase in platelet cGMP. From these data, we conclude that activation of the ETB receptor in human platelets is responsible for an increase in platelet cGMP and may contribute to the inhibition of platelet aggregation caused by the endothelins.

Effect of ammodytin L from the venom of Vipera ammodytes on Xenopus laevis differentiated muscle fibres and regenerating limbs

Ammodytin L is a non-catalytic, phospholipase-like snake venom toxin from Vipera ammodytes, which shows a cytotoxic activity on differentiated myotubes when tested in vitro. In the range of concentrations in which ammodytin L induced necrosis of myogenic cells in culture, other cell types (erythrocytes, platelets, fibroblasts) did not appear to be affected. To test the in vivo toxicity and the effective cytolytic specificity of ammodytin L we have followed the morphological changes in muscle tissue of Xenopus laevis limbs after intramuscular toxin injection. Only muscular cells were affected by ammodytin L, and the toxin did not induce any morphological change in other cell types. Further evidence of the muscle-specific action of the toxin was obtained from experiments carried out using the Xenopus kidney cell line B3.2 in culture. Ammodytin L was unable to affect parameters of cell viability such as lactate dehydrogenase leakage, [3H]thymidine incorporation, growth curves and morphological changes. Moreover, direct ammodytin L application to cultured regenerative limbs did not provoke alterations in undifferentiated myoblasts. These data suggest that ammodytin L, like other phospholipase-like toxins, exerts its toxicity by selectively damaging differentiated muscle fibres.

A new animal model of coronary thrombosis and effects of antithrombotic agents

The model was established in male rabbits with experimental atherosclerosis, which was induced by diet cholesterol (0.5 g per day for 8 weeks), by means of intravenous injection of one unit of pituitrin (P.P.). To evaluate the effects of aspirin, heparin and viper venom (VV) on this model, 26 male rabbits were divided randomly into four groups: group A (GA) as control, group B (GB) treated with heparin (10mg, i.v.), group C (GC) with VV (0.08 arginine esterase activity units), group D (GD) with both heparin and VV. Aspirin (30 mg) was given orally before experiment. The results showed that the rate of coronary thrombosis was 11.26% in GA, 8.10% in GB, 9.17% in GC, and 7.56% in GD respectively. The difference between each of three treated groups and the control one was significant (P < 0.005, 0.05, 0.001, respectively). Such a difference can also be found between GA and that without oral aspirin (11.26% vs 16.39%, P < 0.001). The beneficial effects of heparin and VV may be due to their inhibitory effects on different steps of thrombosis, i.e., heparin can prolong the coagulation time, and VV can inhibit platelet aggregation and decrease the concentration of plasma fibrinogen. It is concluded that heparin, viper venom, and especially their combination would be useful in the treatment of human acute coronary syndromes.

Medical studies of poisonous land and sea snakes

The comparative toxicity and pathophysiology of thirteen (13) of poisonous snakes indigenous to the area in and around Saudi Arabia were determined. Four snakes from the Viperidae family, six from the Elapidae family, and three representative sea snakes from the family Hydrophiodae were included. Anesthetized adult Beagle dogs and anesthetized monkeys were used in the study. Vital physiologic functions were recorded continuously as were changes in the blood coagulation system and any tissue damage produced by the venom at the site of envenomation. Venom was administered intravenously or by an actual bite. Venom from the snakes of the family Viperidae produced death in an average of 3 hours. The average lethal dose was 1.13 mg/kg. Depression of 1st and 2nd stage clotting factors and a decrease in fibrinogen levels and in platelet counts were observed with these venoms. Findings suggestive of intravascular coagulation also were observed with moderate hemolysis of the formed elements. Some local hemorrhage was seen at the site of envenomation. Venom from the Elapidae family of snakes produced death at an average of 1.7 hours. The average lethal dose was 0.70 mg/kg. Death appeared to be primarily due to respiratory paralysis after blockade at the neuromuscular junction. Only moderate hemolysis was seen with these venoms. No intravascular coagulation or tissue damage was seen. The venom of the family Hydrophiodae consistently produced death in less than 30 minutes at an average dose of 0.06 mg/kg. Tissue damage was not observed, and changes were not observed in the hematologic parameters monitored.(ABSTRACT TRUNCATED AT 250 WORDS)

The efficacy of compression immobilization technique in retarding spread of radio-labeled Russell's viper venom in rhesus monkeys and 'mock venom' NaI131 in human volunteers

The efficacy of the modified compression immobilization technique in retarding spread of radio-labeled Russell's viper venom in 3 rhesus monkeys (Macaca mulata) and "mock venom" NaI131 in 14 human volunteers was studied. 0.1 microgram of Russell's viper venom having 10 microCi radioactivity in 0.2 ml normal saline containing 0.5% bovine serum albumin was injected subcutaneously at the lateral aspect of the right hind limb of a rhesus monkey. A hand-tight bandaging of a rubber pad measuring 55 x 28 x 16 mm over the injection site and splinting effectively retard spread of radio-labeled venom for the entire length of time applied, although complete immobilization was not achieved. In human volunteers, application of a pad measuring 60 x 50 x 17 mm over the subcutaneous injection site of 20 microCi or 12 microCi/0.2 ml NaI131 with a hand-tight bandaging (60 +/- 10 mmHg) and immobilization of limb was found to be effective in retarding the movement of radioactive NaI131. These results suggested that the compression pads tried in this study effectively retard the spread of radio-labeled Russell's viper venom (MW ranging from 20,000-90,000) and radioactive NaI131 (MW 150) from the site of injection. Thus, it is highly likely that the present compression pad will be useful as a first-aid measure in Russell's viper bite victims.

The endothelin peptides ET-1, ET-2, ET-3 and sarafotoxin S6b are co-mitogenic with platelet-derived growth factor for vascular smooth muscle cells

We have investigated whether any of the three isoforms of endothelin (ET) ET-1, ET-2 and ET-3 or the structurally similar peptide sarafotoxin S6b is mitogenic on its own for rat vascular smooth muscle cells in culture. DNA synthesis was determined by a peroxidase-linked double antibody technique to detect bromodeoxyuridine incorporation into the nucleus and stained nuclei were counted by image analysis. None of the ET peptides or sarafotoxin S6b (up to 100 nM) was capable of initiating DNA synthesis in the absence of platelet derived growth factor (PDGF) or fetal calf serum. All the peptides potentiated the mitogenic effect of low concentrations of PDGF. ET-1 and ET-2 (10 nM) caused a 2-fold increase in the number of stained nuclei induced by 5 nM and 10 nM PDGF, whereas ET-3 and sarafotoxin S6b were less potent. These findings demonstrate that ET is a co-mitogen for rat vascular smooth muscle cells. The release of ET at sites of endothelial injury may therefore enhance the mitogenic action of locally acting PDGF on vascular smooth muscle cells and potentiate the proliferative response.

Relationship of administered dose to blood venom levels in mice following experimental envenomation by Russell's viper (Vipera russelli) venom

I125 labelled Russell's viper venom was administered i.m. into mice at various doses. Radioactivity in the blood at different intervals was determined and related to the amount injected. A mathematical equation was formulated to represent the relationship of administered dose to blood venom levels. This study suggests that the derivation of such an equation is also possible in humans in order to predict the amount envenomated.

Effects of Russell's viper venom on blood coagulation, platelets and the fibrinolytic enzyme system

The effects of Russell's viper venom (RVV) on blood coagulation, platelts and fibrinolysis were studied in vivo and in vitro in rabbits and dogs as experimental subjects. RVV was shown to be a strong coagulant, and at the time of manifestation of bleeding due to consumption coagulopathy, the most striking hemostatic abnormalities were fall of fibrinogen level, reduction in platelet count, delayed ADP aggregation of platelets, increased fibrinolytic activity and presence of fibrin degradation products. These findings showed that RVV interfered with blood coagulation, caused abnormalities of platelet function and also activated the fibrinolytic enzyme system.