The endothelin ETA receptor exists in the caudal solitary tract nucleus of the rat brain

1. The receptor autoradiographic method done on the rat lower brain stem and cerebellum plus 125I-endothelin-1, BQ-123, an antagonist for the endothelin ETA receptor, and sarafotoxin S6c, an agonist for the ETB receptor, revealed minute amounts of the ETA receptor coexisting with the ETB receptor in the caudal solitary tract nucleus of the rat lower brain stem. 2. The ETB receptor is present predominantly in other parts of the lower brain stem. 3. Knowledge of the heterogeneous distribution of the central endothelin receptor subtypes aids in understanding the neurophysiology of endothelins.

Delayed administration of Vipera xanthina palaestinae antivenin

INTRODUCTION

Vipera xanthina palaestinae is the most widely distributed venomous snake in Israel, accounting for most envenomations. A specific equine antivenin is efficacious against both systemic and local manifestations if given within hours. This study sought to determine if delayed vipera xanthina palaestinae antivenin can be effective.

METHODS

Patients who had been bitten by vipera xanthina palaestinae during 1991-1995 were evaluated. Those who continued to deteriorate beyond 24 h post envenomation, in spite of treatment or because of delayed diagnosis, were given vipera xanthina palaestinae antivenin.

RESULTS

Ten patients were included in the study. Vipera xanthina palaestinae was identified in seven and diagnosis was considered probable in three patients. On admission, eight patients had local signs and seven patients had mild to severe systemic manifestations. The local signs were remarkable and progressive in all patients. In five, systemic signs and laboratory abnormalities were delayed as well. The time range for delayed antivenin administration was 1-6 days after envenomation. Following antivenin administration, progression of local signs ceased in all patients and swelling regressed within 24 h. In nine patients this occurred within 6 h.

CONCLUSION

Vipera xanthina palaestinae antivenin administration should be considered in patients with envenomations complicated by marked and progressive local signs, delayed systemic signs and laboratory abnormalities more than 24 h after envenomation.

Protein and cDNA structures of an acidic phospholipase A2, the enzymatic part of an unusual, two-component toxin from Vipera palaestinae

In the venom of Vipera palaestinae an unusual, two-component toxin was found. The two components of the toxin are an acidic phospholipase A2 (VpaPLA2) and a basic protein, both with an apparent molecular mass of about 15 kDa. Each component alone is not toxic; however, their mixture is lethal. We have determined the amino acid and cDNA sequences of VpaPLA2. The protein primary structure was solved by sequencing the peptides generated by chemical cleavage of the molecule using CNBr, formic acid and hydroxylamine-hydrochloride and by enzymatic fragmentation with trypsin and chymotrypsin. VpaPLA2 consists of 122 amino acid residues and has all the structural characteristics of subgroup IIA PLA2s. It shows the highest amino acid similarity to a non-toxic phospholipase A2 from Eristocophis macmahoni (82%), whereas the most similar toxic phospholipases A2 share about 70% of residues with VpaPLA2. The substitution of His20 for a hydrophobic residue (Leu) in VpaPLA2 might be one of the reasons that its complex with the basic protein could not be observed.

Role of the activation peptide domain in human factor X activation by the extrinsic Xase complex

The activation of factor X by the extrinsic coagulation system results from the action of an enzyme complex composed of factor VIIa bound to tissue factor on phospholipid membranes in the presence of calcium ions (extrinsic Xase complex). Proteolysis at the Arg52-Ile53 peptide bond in the heavy chain of factor X leads to the formation of the serine protease, factor Xa, and the generation of a heavily glycosylated activation peptide comprising residues 1-52 of the heavy chain. The role of the activation peptide region in mediating substrate recognition and cleavage by the extrinsic Xase complex is unclear. The protease Agkistrodon rhodostoma hydrolase gamma (ARHgamma), from the venom of the Malayan pit viper, was used to selectively cleave human factor X in the activation peptide region. Three cleavage sites were found within this region and gave products designated Xdes1-34, Xdes1-43, and Xdes1-49. The products were purified to yield Xdes 1-49 and a mixture of Xdes 1-34 and Xdes 1-43. Reversed phase high pressure liquid chromatography analysis indicated that the cleaved portion of the activation peptide was likely removed during purification. All cleaved species were inactive and could be completely activated to factor Xa by the extrinsic Xase complex or by a purified activator from Russell's viper venom. Steady state kinetic studies using tissue factor reconstituted into membranes yielded essentially equivalent kinetic constants for the activation of intact factor X and the cleaved derivatives under a wide range of conditions. Since Xdes 1-49 lacks all but three residues of the activation peptide and is devoid of the carbohydrate present in this region, the data suggest that the specific recognition of human factor X by the extrinsic Xase complex is not achieved through specific interactions with residues 1-49 of the activation peptide or with carbohydrate structures attached to these residues.

cDNA cloning and deduced amino acid sequence of fibrinolytic enzyme (lebetase) from Vipera lebetina snake venom

The complete amino acid sequence of lebetase is deduced from the nucleotide sequence of a cDNA clone isolated by screening a venomous gland c DNA library of Central Asian Vipera lebetina snake. The cDNA sequence with 2011 basepairs encodes an open reading frame of 478 amino acids which includes an 18 amino acid signal peptide, plus an 175 amino acid segment of zymogen-like propeptide, a mature protein of 204 amino acids, a spacer of 18 amino acids and a disintegrin-like peptide of 63 amino acids. The mature protein lebetase as isolated from the crude venom has the molecular weight of approximately 23.7 kD and, thus, lebetase as well as several other snake venom metalloproteinases is translated as a precursor protein, which may be processed posttranslationally. The lebetase proprotein has a "cysteine switch" motif (PKMCGV) similar to that involved in the activation of matrix metalloproteinase zymogens. The mature protein (residues 223-427) shows the strongest similarity with fibrolase (63% identity), fibrinolytic enzyme from Agkistrodon contortrix contortrix venom. The metalloproteinase domain has a typical zinc-chelating sequence (HEXXHXXGXXH). In the disintegrin-like domain of protein, the RGD sequence is replaced by VGD.

Cellular localization of endothelin receptor subtypes in the rat kidney following in vitro labelling

1. We have previously shown that [125I]-endothelin (ET) receptor binding is localized almost exclusively to the fenestrated endothelial cells of glomerular capillaries and peritubular capillaries in the rat kidney following systemic administration of the radioligand in vivo. Because of the lack of specific ET receptor binding in other glomerular and tubular structures following in vivo labelling, we undertook further studies, using electron microscopic autoradiography and ET receptor subtype selective ligands, to investigate whether other renal components also contain ET receptor binding and, if so, to determine the cellular localization of the ET receptor subtypes, ETA and ETB, following in vitro labelling. 2. At the electron microscopic level, ET binding sites were localized primarily to the fenestrated endothelium of glomerular and peritubular capillaries of the cortex, inner stripe of the outer medulla and the inner medulla. ET binding sites also occurred overlying renomedullary interstitial cells (RMIC) of the inner medulla. 3. The ETB receptor selective agonist, sarafotoxin 6c (S6c), abolished ET binding in the vascular endothelium throughout the kidney, while the ETA receptor selective antagonist, BQ123, was without effect. Both BQ123 and S6c partially inhibited the binding in the RMIC of the inner medulla. 4. These results indicate that ET receptor binding in the fenestrated endothelium in the glomerular capillaries and peritubular capillaries belongs mainly to the ETB subtype, whereas both ETA and ETB subtypes are present in the RMIC.

Isolation and characterization of carinactivase, a novel prothrombin activator in Echis carinatus venom with a unique catalytic mechanism

The venom of the viper Echis carinatus contains a metalloprotease, ecarin, that is a potent prothrombin activator. We here show that the venom is also rich in another prothrombin activator, which does not belong to any known category of prothrombin activators. The novel enzyme, designated carinactivase-1 (CA-1), consists of two subunits held together non-covalently but very tightly. One subunit is a 62-kDa polypeptide that has metalloprotease activity and is homologous to the single-chain enzyme ecarin; the other subunit of 25 kDa consists of two disulfide-linked polypeptides of 17 and 14 kDa, and this subunit resembles the anticoagulant in the habu snake venom, IX/X-bp, that specifically binds the Gla domains of coagulation factors IX and X in a Ca2+-dependent fashion. The activation of prothrombin by CA-1 requires Ca2+ ions at millimolar concentrations and in the absence of Ca2+ ions this enzyme is virtually inactive. By contrast, activation by ecarin is completely independent of Ca2+ ions. CA-1, unlike ecarin, does not activate prothrombin derivatives, in which binding of Ca2+ ions has been perturbed, namely prethrombin-1 and acarboxyprothrombin. Furthermore, the isolated catalytic subunit, although its activity is greatly reduced as compared to that of the holoenzyme, no longer requires Ca2+ ions for the activation of prothrombin. Reconstitution with the non-catalytic 25-kDa subunit restores high level activity and the dependence on Ca2+ ions. Finally, prothrombin activation by CA-1 is inhibited by prothrombin fragment 1, and the isolated non-catalytic subunit is capable of binding fragment 1 in the presence of Ca2+ ions. From these observations, we postulate the following unique mechanism for the activation of prothrombin by CA-1. The enzyme primarily recognizes the Ca2+-bound conformation of the Gla domain in prothrombin via the 25-kDa regulatory subunit, and the subsequent conversion of prothrombin to active thrombin is catalyzed by the 62-kDa catalytic subunit.

Pharmacological characterization of endothelin receptors in the rabbit iris sphincter muscle: suggestion for the presence of atypical receptors

Pharmacological profiles of endothelin (ET) receptors in the isolated rabbit iris sphincter were characterized. ET isopeptides caused dose-dependent contraction of the preparation. The respective EC50 values for ET-1, ET-2 and ET-3 were 39.4, 58.0 and 84.3 nM, so that ET-1 was twice as potent as ET-3. Sarafotoxin (SRTX) -b, an ET(A)/ET(B) non-selective agonist, caused very potent contraction with an EC50 of 1.13 nM. However, selective ET(B) receptor agonists SRTX-c and IRL 1620 showed no contractile activity up to 1 microM. BQ-123, a selective ET(A) receptor antagonist, shifted the dose-response curves of ET isopeptides to the right. The pA2 value for ET-1 was 5.52 with a slope of 1.06, which is not different from unity, and the pK(B) value for ET-2 was 5.06. Interestingly, very low doses of BQ-123 antagonized responses to ET-3 and SRTX-b, with a Schild plot slope of approximately 0.7 which is significantly different from unity, suggesting receptor heterogeneity. The abscissal intercepts of the Schild plots were -9.29 for ET-3 and -8.53 for SRTX-b. FR 139317, another ET(A) receptor antagonist, also preferentially antagonized responses to ET-3. RES-701-1, a selective ET(B) receptor antagonist, did not shift dose-response curves for ET-1 and ET-3. These results suggest that ET receptors in the rabbit iris sphincter muscle cannot be classified into the ET(A), ET(B) or ET(C) receptor subtypes, so far established. When compared to the established receptor subtypes, ET receptors in this preparation were quite different from the ET(B) receptor, but apparently showed a pharmacological profile most similar to the ET(A) receptor, suggesting the presence of heterogeneous and atypical ET(A) receptors.

Endothelial regeneration during the repair process following Habu-snake venom induced glomerular injury

In this study, the kinetics of glomerular endothelial cells during the repair process following glomerular injury was investigated in a model of mesangial proliferative glomerulonephritis induced by Habu-snake venom (HSV) in rats. Intravenous injection of HSV led to a cystic ballooning type lesion at day 1. Subsequently a marked segmental proliferative lesion was observed in the cystic areas at day 5. Thereafter cellularity decreased and reconstruction of the glomerular tuft was gradually observed with time. The histological structure of the glomeruli had almost returned to normal 21 days following HSV injection. After prominent depletion at day 1, the number of endothelial cells increased rapidly and reached a plateau at day 7, not significantly different from that of the control group. Morphologically endothelial cell elongation from the vascular pole into the cystic lesion was seen together with premature capillary formation in the proliferative lesion. Accompanying the reduction of mesangial expansion, the endothelial cells gradually formed definite capillary lumens. We conclude that the mesangial proliferative glomerulonephritis induced by HSV recovers to its original structural state and that the migration and proliferation of endothelial cells with accompanying capillary formation are essential for the repair process, in addition to mesangial cell proliferation.

[Detection of lupus anticoagulant using a modified diluted Russell's viper venom time test]

Lupus anticoagulants (LA) are considered to be a significant risk factor in patients with unexplained thrombosis and are often present in women who have recurrent miscarriages. According to Petri et al, LA detectable using a diluted Russell's Viper Venom time (dRVVT) test are more closely linked with thrombosis in patients with systemic lupus erythematosus than are anticardiolipin antibodies. We evaluated a new simplified dRVVT test, that is, a combination of LUPO-TESTII and LUCOR, and found that the ratio of LUPO-TESTII/LUCOR values is a good indicator for detection of LA. The cut-off point of the ratio based on receiver-operating characteristic (ROC) analysis was set at 1.07. The sensitivity and specificity were 92.3% and 96.8%, respectively. The ratio of LUPO-TESTII/LUCOR values of 24 (92.3%) of 26 LA-positive patients was significantly higher than those of warfarin-treated patients, patients with hereditary clotting-factor deficiency and patients positive for specific clotting-factor inhibitors (p < 0.01). It was shown that the result was not influenced by warfarin and/or heparin treatment and the presence of specific clotting-factor inhibitors. The ratio of LUPO-TESTII/LUCOR values is regarded as a more useful indicator for the detection of LA than the platelet neutralization procedure test.

In vitro release profiles of eristostatin from biodegradable polymeric microspheres: protein aggregation problem

Eristostatin, a low molecular weight polypeptide (MW 5725), was encapsulated within two biodegradable poly(lactic acid-glycolic acid) microspheres. In vitro release profiles from the microspheres exhibited fast initial release for up to several days, followed by very slow or no release. The later stage of the slow release was due to protein aggregation within the microspheres. A simple, noninvasive method to detect the protein aggregation within the microspheres has been developed: extraction of radiolabeled protein from the microspheres by a DC electric field into a polyacrylamide gel and subsequent exposure to a gamma-ray sensitive film. Direct application of the degrading microspheres onto the sample loading zone of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) could successfully extract the monomeric and oligomeric proteins into the autoradiogram of a gel slab, while unextractable protein aggregates within the microspheres could be directly visualized in their loading position.

Purification and properties of the L-amino acid oxidase from Malayan pit viper (Calloselasma rhodostoma) venom

The L-amino acid oxidase of Malayan pit viper (Calloselasma rhodostoma) venom was purified to electrophoretic homogeneity. The molecular weight of the enzyme was 132,000 as determined by Sephadex G-200 gel filtration chromatography and 66,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is a glycoprotein, has an isoelectric point of 4.4, and contains 2 mol of flavin mononucleotide per mole of enzyme. The N-terminal amino acid sequence of the enzyme was A-D-D-R-N-P-L-A-E-E-F-Q-E-N-N-Y-E-E-F-L. Kinetic studies suggest the presence of a alkyl side-chain binding site in the enzyme and that the binding site comprises at least four hydrophobic subsites. The characteristics of the binding site differ slightly from those of cobra venom L-amino acid oxidases.

Monospecific antivenin therapy in Russell's viper bite

Venom antigenemia was detected in 24 out of 30 Russell's viper bites. Those who suffered clinical bleeding (N = 14) had higher venom antigenemia than those who did not. The mean value of the amount of monospecific antivenin correcting blood incoagulability was 165 +/- 59.3 ml. Consequently, the recommended treatment is 60 ml of antivenin being administered intravenously at 6-hour intervals until blood coagulability is restored. There were no serious complications after antivenin administration. Renal complication (3 cases) was the major problem following this snake bite. One patient with clinical diagnosis of central nervous system bleeding died on admission.

Snake bites in Zimbabwe: a clinical study with emphasis on the need for antivenom

A retrospective analysis of 83 consecutive patients (42 males and 41 females) treated for snake bites at Mpilo Central Hospital between January 1990 and June 1992 is presented. In Zimbabwe poisonous snakes belong to four families; Colubrids (Boomslang), Vipers (Puff Adder), Elapids (Mambas and Cobras) and Atractaspids (Bibron Stilleto snake). The Puff Adder is responsible for three quarters of the bites. Forty eight pc (40/83) of the patients were below 20 years of age (range 1 year 10 months to 72 years). Most bites occurred at night (61 pc) in the rainy season (November to April). The majority of snake bites occurred on the lower limb, 64 pc (53/83), with most of the remainder occurring on the upper limb, 34 pc (28/83). The most common clinical features were; pain (95 pc), swelling (87 pc), tachycardia (20 pc), fever (13 pc) and vomiting (8 pc). This study, carried out at a time when there was no antivenom in stock at Mpilo Hospital, shows a considerable mortality (5 pc, 4/83) and morbidity (37 pc, 31/83) rate from poisonous snake bites in Zimbabwe. These observations highlight the need to maintain adequate stocks of antivenom in the major hospitals in Zimbabwe.

[A fatal case of viper bite in an adult in France]

Vipera bites in France are supposed to be benign. We report here, the case of a snake bite with fatal outcome due to hypoxemia and shock, occurring in a young woman without previous disease. This case could lead to reevaluate the indication of antivenomous serotherapy in the severe envenomations. However the tolerance of the new serums has to the confirmed.

Raynaud's phenomenon and gangrene following snake envenomation

Local necrosis and gangrene at the site of the bite are commonly observed after snake envenomation. However, Raynaud's phenomenon and gangrene occurring in a limb other than that bitten by the snake is encountered rarely. So far, there is only one report of such an episode in literature. Here we are reporting a case of patient with snake bite on the right foot following which he developed Raynaud's phenomenon of the left upper limb and dry gangrene of the tips of the left index and middle fingers. The snake was identified as Russel's viper.

Purification and characterization of a Kunitz-type trypsin inhibitor from Leaf-nosed viper venom

A Kunitz-type trypsin inhibitor was purified from Leaf-nosed viper venom and the primary structure determined by peptide analysis. In relation to other trypsin inhibitors, the protein has an extended C-terminal segment and a distinct pattern of residue alterations at the functionally important contact sites with proteases.