Occupational injuries with captive lance-headed vipers (Bothrops moojeni): experience from a snake farm in Brazil

We studied occupational injuries with captive lance-headed vipers (Bothrops moojeni) that occurred in a snake farm in south-eastern Brazil from February 1981 to May 1999. The risk of injury, taking into account 13 cases of snake-associated injuries (12 of them snake bites) was 2.73 per 10,000 person-days of work, and 3.51 per 100,000 venom extractions. Thirteen cases of injury occurred in seven workers, whereas 18 workers were never injured, suggesting that some individuals have a higher risk of injury than others perhaps due to lack of concentration or overconfidence. Eight episodes of occupational injuries occurring in four technicians, including a case of eye injury due to splashed venom during extraction, are reported. Assessment of whether envenoming occurred was facilitated by knowledge of the snake species and size, history of recent venom extraction and snake feeding, and examination of snake venom glands. Hypersensitivity reactions (anaphylaxis and serum sickness) to antivenom are a risk particularly to those workers who were bitten more than once and medicated previously. Antivenom therefore should not be administered to these individuals unless there is clear evidence that envenoming occurred or is likely to have occurred. Hypersensitivity to the venom is also a health concern for workers from snake farms.

Imaging pulmonary emboli and deep venous thrombi with 99mTc-bitistatin, a platelet-binding polypeptide from viper venom

An imaging test that could locate both pulmonary emboli (PE) and their source, active deep venous thrombi (DVT), would be valuable in patient management. Bitistatin, an 83-amino-acid polypeptide isolated from Bitis arietans venom, binds avidly to the glycoprotein IIb/IIIa receptor on platelets. The goal of this study was to label bitistatin with 99mTc and assess its potential for imaging thrombi and emboli in vivo.

METHODS

Molecular modeling of bitistatin indicated that its primary amines are located on the opposite side of the molecule from the receptor-binding domain. The primary amines were reacted with succinimidyl-4-hydrazino nicotinate hydrochloride to place 2.4 hydrazino nicotinate (Hn) chelating groups per peptide molecule. Hn-bitistatin was labeled by incubation with 99mTc-glucoheptonate to 96 TBq/mmol and then tested for binding to platelets in vitro and for imaging of 24-h-old DVT and PE in a canine model used previously for other thrombus tracers.

RESULTS

99mTc-Hn-bitistatin bound to stimulated platelets with a dissociation constant (Kd) = 32 nmol/L, similar to that of 125I-bitistatin (Kd = 41 nmol/L). In vivo, focal uptake was observed in planar images as early as 30 min (DVT) and 60 min (PE) after injection. Lesion uptake of 99mTc-Hn-bitistatin at 4 h after injection was calculated in terms of percentage injected dose per gram (%ID/g) of tissue and averaged 0.89 %ID/g PE and 0.79 %ID/g DVT. Lesion-to-background ratios averaged 34:1 (PE-to-lung), 18:1 (DVT-to-blood), and 284:1 (DVT-to-muscle). These values were not significantly different from iodinated bitistatin, but uptakes were higher than other tracers tested in the same model.

CONCLUSION

99mTc-Hn-bitistatin retains the functional activity of the iodinated peptide, has higher DVT and PE uptakes than other thrombus tracers in this standardized model, and has target-to-background characteristics suitable for imaging both PE and DVT in a single test.

Crystal structure of flavocetin-A, a platelet glycoprotein Ib-binding protein, reveals a novel cyclic tetramer of C-type lectin-like heterodimers

Snake venom contains a number of the hemostatically active C-type lectin-like proteins, which affect the interaction between von Willebrand factor (vWF) and the platelet glycoprotein (GP) Ib or platelet receptor to inhibit/induce platelet activation. Flavocetin-A (FL-A) is a high-molecular mass C-type lectin-like protein (149 kDa) isolated from the habu snake venom. FL-A binds with high affinity to the platelet GP Ibalpha-subunit and functions as a strong inhibitor of vWF-dependent platelet aggregation. We have determined the X-ray crystal structure of FL-A and refined to 2.5 A resolution. This is a first elucidation of a three-dimensional structure of the platelet GP Ib-binding protein. The overall structure reveals that the molecule is a novel cyclic tetramer (alphabeta)(4) made up of four alphabeta-heterodimers related by a crystallographic 4-fold symmetry. The tetramerization is mediated by an interchain disulfide bridge between cysteine residues at the C-terminus of the alpha-subunit and at the N-terminus of the beta-subunit in the neighboring alphabeta-heterodimer. The high affinity of FL-A for the platelet GP Ib alpha-subunit could be explained by a cooperative-binding action through the multiple binding sites of the tetramer.

MALDI-TOF mass spectrometry analysis of substrate specificity of lebetase, a direct-acting fibrinolytic metalloproteinase from Vipera lebetina snake venom

Lebetase is a direct-acting fibrinolytic zinc metalloendopeptidase related in amino acid sequence to reprolysins which include both hemorrhagic and non-hemorrhagic proteinases. Despite apparent structural similarities, fibrinolytic and hemorrhagic proteinases differ significantly in substrate specificity. In this study, we have examined the activity of lebetase I against biologically active peptides (bradykinin, kallidin, substance P) and 6-10 amino acid residues containing peptides synthesized according to cleavage regions of alpha(2)-macroglobulin, pregnancy zone protein (PZP) and fibrinogen. Lebetase was found to have no activity against studied hexapeptides. Surprisingly, the best substrates for lebetase were substance P, and peptide fragment of PZP, both were cleaved at position Pro-Gln. Identification of the hydrolysis products of 15 peptides by MALDI-TOF mass spectrometry analysis indicates that lebetase possesses broad substrate specificity. The MALDI-TOF MS technique was proven to be highly efficient for the recovery and identification of the peptides released by lebetase hydrolysis.

Contortrostatin, a homodimeric disintegrin, binds to integrin alphavbeta5

Contortrostatin is a homodimeric disintegrin from snake venom. We have shown that contortrostatin binds to integrins alphaIIbbeta3, alpha5beta1, and alphavbeta3. We now use several criteria to demonstrate the binding of contortrostatin to alphavbeta5. First, incubation of T24 cells, which express alphavbeta3 and alphavbeta5, with antibody against alphavbeta3 failed to completely inhibit adhesion of cells to vitronectin. However, pretreatment of the cells with contortrostatin or the combination of antibodies against alphavbeta3 and alphavbeta5 completely blocked adhesion to vitronectin. By contrast, either anti-alphavbeta5 alone or contortrostatin blocked adhesion of an alphavbeta3-negative T24 subline. Second, contortrostatin as well as anti-alphavbeta5 inhibits invasion of OVCAR-5, which express only alphavbeta5. Third, contortrostatin binds to purified alphavbeta5 in a saturable manner. Finally, radioligand binding assays yielded a K(d) value of 24 nM for [(125)I]contortrostatin binding to alphavbeta5. This investigation identifies alphavbeta5 as a binding site for contortrostatin. Blockage of alphavbeta5 by contortrostatin inhibits alphavbeta5-mediated adhesion and invasion.

Glycoprotein Ib-binding protein from the venom of Deinagkistrodon acutus--cDNA sequence, functional characterization, and three-dimensional modeling

Agkicetin-C, a potent glycoprotein Ib antagonist from the venom of the Chinese pit viper, Deinagkistrodon acutus, has been purified and characterized (5). It is a disulfide-linked heterodimer containing subunits of 132 and of 123 amino acid residues. Herein, the complete amino acid sequences were resolved by cloning and nucleotide sequencing of the cDNAs. The sequences of its subunits are homologous to those of other snake venom proteins of the C-type (Ca2+-dependent) lectin superfamily. A three-dimensional model of agkicetin-C was constructed based on the crystal structure of habu coagulation factor IX/X-binding protein. By careful alignment of all the related sequences available and comparing the 3D-model of agkicetin-C with structures of other homologous proteins of different functions, some variable residues of agkicetin-C were identified, which possibly are responsible for the specificity of this distinct subtype of the C-type lectin-like venom proteins.

Short report: treatment of snake envenomations by a new polyvalent antivenom composed of highly purified F(ab)2: results of a clinical trial in northern Cameroon

A clinical trial was conducted in 2 health centers in northern Cameroon to assess the safety and efficacy of a new polyvalent antivenom composed of highly purified and pasteurized F(ab')2 (FAV-Africa). Forty-six patients with objective signs of envenomation, including 67% with hemorrhage, were included in the study. Each patient received at least 20 ml of FAV-Africa by direct, slow intravenous injection; 172 10-ml ampules were administered. All patients were clinically cured after treatment. Two patients (4.3%) showed minor immediate adverse events that may have been related to FAV-Africa (induration, light-headedness); no other treatment-related adverse event occurred. No patient had serum sickness. This trial confirms the safety of FAV-Africa administered by intravenous injection and its efficacy in the treatment of snake envenomations in sub-Saharan Africa.

Sudden pressure elevation can trigger acute muscle cell death of the heart and aorta

The object of this study was to clarify whether or not the acute muscle cell death of the aortic media observed in normal rabbits treated with Russell's viper venom (RVV) and angiotensin II (Ang) is a result of either acute hypertension or the apoptotic effect of angiotensin II. The incidence and mean % area necrosis of the aorta and left ventricle in the rabbits receiving RVV and Ang (group 1) were compared with those in rabbits receiving Ang and saline (group 2), RVV and saline (group 3), RVV, Ang type 1 receptor blocker (CV 11974) and Ang (group 4), RVV, Ang and nicardipine, dihydropyridine derivative (group 5) and RVV, Ang type 2 receptor blocker (PD 123319) and Ang (group 6). The incidence as well as the mean % area of acute muscle necrosis of the aortic media and left ventricle in groups 3, 4 and 5 were found to be significantly lower than those in either group 1 or group 6. The mean % area of acute spotty myocardial necrosis in group 2 (Ang, saline) was also significantly higher than that in groups 3, 4 and 5. There was no evidence of cells with positive in situ nick end labeling (TUNEL reaction). As a result, the acute muscle necrosis of the aortic media and left ventricle was considered to be due to the sudden elevation in the blood pressure, but not due to apoptosis mediated through Ang type 2 receptor. We thus conclude that a sudden increase in blood pressure may be one of the triggering mechanisms for an acute onset of cardiovascular disorders.

Purification and amino acid sequence of MP-III 4R D49 phospholipase A2 from Bothrops pirajai snake venom, a toxin with moderate PLA2 and anticoagulant activities and high myotoxic activity

MP-III 4R PLA2 was purified from the venom of Bothrops pirajai venom (Bahia's jararacussu) after three chromatographic steps which started with RP-HPLC. The complete amino acid sequence of MP-III 4R PLA2 from Bothrops pirajai was determined by amino acid sequencing of reduced and carboxymethylated MP-III 4R and the isolated peptides from clostripain and protease V8 digestion. MP-III 4R is a D49 PLA2 with 121 amino acid residues and has a molecular weight estimated at 13,800 Da, with 14 half-cysteines. This protein showed moderate PLA2 and anticoagulant activity. This PLA2 does not have a high degree of homology with other bothropic PLA2-like myotoxins (approximately 75%) and nonbothropic myotoxins (approximately 60%). MP-III 4R is a new PLA2, which was isolated using exclusively analytical and preparative HPLC methods. Based on the N-terminal sequence and biological activities, MP-III 4R was identified as similar to piratoxin-III (PrTX-III), which was isolated by conventional chromatography based on molecular exclusion ion exchange chromatography. Clinical manifestations indicate that at the site of toxin injection, there may be pain of variable intensity, because animals continue to lick the limb. No clinical sign indicating general toxicity was noticed. Myotoxicity was observed in gastrocnemius muscle cells after exposure to MP-III 4R, with a high frequency (70%) of affected muscle fibers.

Signal transduction pathways mediated by glycoprotein Ia/IIa in human platelets: comparison with those of glycoprotein VI

Human platelets were activated either by glycoprotein (GP) Ia/IIa agonist (rhodocytin) or by a GPVI agonist (collagen-related peptide, CRP), and the intracellular signal transduction pathways were compared in the presence of various inhibitors. Rhodocytin isolated from Calloselasma rhodostoma venom was verified as a GPIa/IIa agonist, based on the inhibitory effects of three mAbs directed against GPIa. Platelet activation mediated by GPIa/IIa led to overt platelet aggregation, elevation of intracellular Ca2+, and tyrosine phosphorylation of several proteins, similar to that of GPVI. p72(syk) and phospholipase Cgamma2 (PLCgamma2) tyrosine phosphorylation were also observed with GPIa/IIa-mediated platelet aggregation, although they peaked slightly later than that of GPVI. In contrast to GPVI-mediated platelet activation, most of these phenomena induced by GPIa/IIa activation were markedly suppressed by acetylsalicylic acid (ASA) or cytochalasin D. These findings suggest that the requirements for thromboxane A2 (TXA2) production and actin polymerization, which are the characteristics of collagen-induced platelet activation, are derived from the GPIa/IIa-mediated signal transduction, but not from that of GPVI.

Assessment of material-induced procoagulant activity by a modified Russell viper venom coagulation time test

Platelet activation is an inevitable consequence of blood-material interactions. The ability of those activated platelets and platelet-derived microparticles to enhance coagulation reactions leading to thrombin/fibrin formation has not been well studied despite its potential significance. Activated platelets and platelet-derived microparticles are known to dramatically enhance the catalytic efficiencies of the tenase and prothrombinase complexes. In this paper, a modified Russell viper venom coagulation time test is used to quantitate material-induced procoagulant activity due to the generation of activated phospholipid surfaces. In our test system, polyethylene and Silastic tubes were filled with heparinized whole blood and left to gently flow back and forth at 37 degrees C. After 1 h, the blood within the tubes was gravity drained and the plasma fraction assayed for procoagulant activity. The clotting times were determined by a Coag-A-Mate X2 instrument after the automated addition of Russell viper venom (to activate factors V and X) and calcium ions. Appreciable procoagulant activity was generated during whole blood contact within polyethylene and Silastic tubes although significantly greater activity was generated by the latter surface. As previously reported, platelet-derived microparticles also were detected by flow cytometry. Filtration of the plasma after material contact through a 0.1 microm filter led to substantial gains in clotting times and to near complete removal of microparticles, indicating that the material-induced microparticles likely were responsible for the procoagulant activity.

Viper venom disintegrins and related molecules

The term "disintegrin" was first used in 1990 to describe a group of viper venom-derived, nonenzymatic small proteins that shared numerous structural and functional properties. These proteins, which have been found in a great number of viper species studied since that time possess both a remarkable sequence homology and an equally notable variability in potency and selectivity in their interactions with integrin receptors. The discovery that small disintegrins may actually have been derived from much larger mosaic proteins possessing catalytic activity, and that species other than snakes (both plant and animal) produce proteins containing disintegrin-like domains, has led to much research related to both the proteins themselves and the receptors to which they bind. The purpose of this review is to discuss the literature and the authors' own data on the structure and function of disintegrins and their relevance to the studies on proteins containing disintegrin-like domains, such as hemorrhagins and ADAMs.

Characterization of an apoptosis-inducing factor in Habu snake venom as a glycyrrhizin (GL)-binding protein potently inhibited by GL in vitro

By means of successive heparin-affinity and glycyrrhizin (GL)-affinity column chromatographies (HPLC), a 55 kDa GL-binding protein (gp55) was purified to apparent homogeneity from the Superdex P-I fraction of Habu snake venom. This gp55 was identified as an apoxin I-like protein, because (i) its 20 N-terminal amino acid residues (AHDRNPLEEYFRETDYEEFL) are 95% identical with the corresponding sequence of apoxin I (apoptosis-inducing factor, approx. 55 kDa) in the venom of the western diamondback rattlesnake; and (ii) L-amino acid oxidase (LAO) activity of gp55 is detected when incubated with L-leucine, but not with D-leucine. GL inhibited the LAO activity of gp55 in a dose-dependent manner, but had no effect on the activity of a 65 kDa LAO also purified from Habu snake venom. In addition, GL reduced the ability of gp55 to induce the hemolysis of sheep red blood cells. These results suggest that GL is a potent inhibitor of apoxin I-like proteins in harmful snake venoms.

Effects of endothelin-1 on capsaicin-induced nociception in mice

The influence of endothelin-1 on nociception induced by capsaicin was assessed in the mouse hindpaw. Local endothelin-1 injection (1 to 20 pmol/paw) 30 min prior to ipsilateral injection of capsaicin (0.1 microg/paw) increased, in a graded fashion, the time spent licking the injected paw. Maximal hyperalgesia was obtained with 10 pmol/paw of endothelin-1 (capsaicin-induced hindpaw licking time increased from 43 +/- 3 s to 114 +/- 7 s, n = 6), but no hyperalgesia was evident following 30 pmol/paw of endothelin-1. The selective endothelin ET(B) receptor agonists sarafotoxin S6c (< or = 30 pmol/paw) and IRL 1620 (i.e., Suc[Glu9,Ala11,15]endothelin-1-(10-21); < or = 100 pmol/paw) failed to induce hyperalgesia. Local treatment with BQ-123 (i.e., cyclo[DTrp-DAsp-Pro-DVal-Leu] 1 nmol/paw selective endothelin ET(A) receptor antagonist), 10 min before endothelin-1 (10 pmol/paw), fully blocked the hyperalgesic response, whereas similar treatment with the selective endothelin ET(B) receptor antagonist BQ-788 (i.e., N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D- 1-methoxy-carboyl-D-norleucine) was ineffective. Intravenous injection of bosentan (17 and 52 micromol/kg a non-peptidic mixed endothelin ET(A)/ET(B) receptor antagonist) or BMS 182874 (i.e., 5-[dimethylamino]-N-[3,4-dimethyl-5-isoxazolyl]-1-naphthalenesulph onamide; 10 and 30 micromol/kg; a non-peptidic selective endothelin ET(A) receptor antagonist), 1 h before endothelin-1, inhibited its hyperalgesic effect in a graded fashion and abolished the response at the higher doses. None of the antagonists modified nociception induced by capsaicin alone or the hyperalgesia induced by local injection of 5-hydroxytryptamine (5-HT; 2 nmol/paw, 30 min before capsaicin). Hyperalgesia induced by 5-HT was abolished by simultaneous injection of endothelin-1 or the endothelin ET(B) receptor agonist IRL 1620 (each at 30 pmol/paw). Therefore, local endothelin-1 exerts a dual influence in this model: at low doses it causes endothelin ET(A) receptor-mediated hyperalgesia (i.e., it potentiates capsaicin-induced nociception), whereas at higher doses it induces an anti-hyperalgesic effect against 5-HT which seems to be mediated via distinct endothelin ET (possibly ET(B)) receptors.

Separation of phospholipase A2 in Habu snake venom by glycyrrhizin (GL)-affinity column chromatography and identification of a GL-sensitive enzyme

By means of glycyrrhizin (GL)-affinity and Mono S column chromatographies (HPLC), at least four GL-binding proteins (p25, p17, p15-1 and p15-2) in the two Superdex fractions (P-II and P-III fractions) from Habu snake venom were selectively purified. By determination of their N-terminal partial amino acid sequences, a metalloprotease (p25) and three GL-binding phospholipases A2 (gbPLA2s) [PA2Y (p17), PA21 (p15-1) and PA2B (p15-2)] were identified. PA2B (lysine-49 PLA2) was found to be the most sensitive to GL because (i) it strongly bound to a GL-affinity column; and (ii) its enzyme activity was selectively inhibited by low dose (ID50 = approx. 1.5 microM) of GL, but not by GA. Furthermore, these three gbPLA2s were phosphorylated by casein kinase II (CK-II) in vitro and GL inhibited the CK-II-mediated stimulation of their enzyme activities in vitro.

[Poisonous snakes of Europe]

Characteristics of poisonous snakes and their toxines are described. The appearance and biology of all European poisonous snakes, eight vipers (family Viperidae) and one opisthoglyph colubride snake (family Colubridae) are given in detail.

[Snake bites in dogs]

Altogether 11 cases of stings in dogs are reported. In at least nine cases, common vipers (Vipera berus) were identified to be the causes. The most frequently observed symptoms were haemorrhagic and oedematous inflammations of the area of the wounds, furthermore haemolysis and intense leukocytosis with relative and absolute neutrophilia and in some cases shock symptoms. One dog died 17 days after the accident from multiple organ insufficiencies, all the other dogs improved. As a therapy, bandage of the injured limb, quieting of the dog, snake antitoxin, corticosteroids, antihistaminics, antibiotics, and symptomatic therapy depending on the clinical signs are recommended.

Contribution of endogenous endothelin-1 to the maintenance of vascular tone: role of nitric oxide

Studies were designed to compare the effect of the nitric oxide inhibitor, N omega-nitro-L-arginine (L-NNA), and the novel ETB receptor antagonist, RES-701-1, on changes in blood pressure and renal blood flow induced by exogenous endothelin receptor agonists and to determine the effect of L-NNA on basal hemodynamics in conscious, chronically instrumented rats. Infusion of low (nonpressor) doses of L-NNA or RES-701-1 potentiated systemic and renal vasoconstriction induced by bolus injections of endothelin-1 or sarafotoxin 6c. Bolus intravenous injection or sustained infusion of L-NNA alone resulted in dose-dependent increases in blood pressure and decreases in renal blood flow, similar to our recently reported results with RES-701-1. Vasoconstriction induced by inhibition of nitric oxide was attenuated by SB 209670, a mixed ETA/B receptor antagonist, but not by BQ123, an ETA receptor antagonist; neither antagonist altered basal hemodynamics. Collectively, the results indicate that: (1) endothelin plays an important role in the control of basal vascular tone by mediating both vasodilation and vasoconstriction; (2) these effects are mediated by different ETB receptor subtypes in the rat, one located on the endothelium that mediates vasodilation via the nitric oxide pathway, the other located on the vascular smooth muscle that mediates contraction.

Non-epithelial endothelin-A receptors activate adenylate cyclase in rat trachea: biochemical mechanisms and physiological implications

In the present study, we investigated the mechanisms underlying the differential effects of endothelins (ETs) in the rat trachea. Sarafotoxin-S6c (SRTX-c) and ET-3 were more potent spasmogens to rat tracheal strips than ET-1. The EC50 values were 12, 14.1 and 89.1 nM, respectively. Tension responses to ET-1 and ET-3, but not to SRTX-c, were enhanced by either indomethacin or the ET(A) blocker, BQ-610 (1 microM). In epithelium-intact tracheal rings, both ET-1 and ET-3 activated adenylate cyclase (AC) in a concentration-dependent manner. The activation by ET-1 of AC was significantly higher than that of ET-3. Thus, EC50 values for ET-1 and ET-3 were 71 and 200 nM, and maximal cAMP increments were 196% and 62% above baseline, respectively. SRTX-c, up to 1 microM, did not alter basal cAMP level. Mechanical removal of the epithelium neither had an effect on AC activation by ET-1 or ET-3, nor did it alter the inability of SRTX-c to modulate AC activity. Conversely, pre-incubation of tracheal strips with indomethacin (1 microM) virtually ablated the increments in cAMP by the ETs. Likewise, BQ-610 attenuated AC activation, concentration-dependently (IC50=28.2 nM). Taken together, the present study suggests that ET(A) receptors, from non-epithelial source, are functionally-linked to AC activation via a prostanoid-dependent pathway. This ET(A)-initiated cascade acts to negatively regulate muscle contraction. Such a cross-talk between ET signals most likely accounts for variation of tension responses to ET homologs.

The disulphide bond pattern of bitistatin, a disintegrin isolated from the venom of the viper Bitis arietans

The disulphide bond pattern of the long disintegrin bitistatin (83 amino acids, 14 cysteines) was established using structural information gathered by amino acid analysis, N-terminal sequencing, and molecular mass determination of fragments isolated by reversed-phase HPLC after polypeptide degradation with trypsin and oxalic acid. A computer program was used to calculate all possible combinations of disulphide-bonded peptides matching the mass spectrometric data, and the output was filtered using compositional and sequence data. Disulphide bonds between cysteines 16-34, 18-29, 28-51, 42-48, 47-72, and 60-79 are conserved in medium-long disintegrins flavoridin and kistrin (70 amino acids, 12 cysteines), and the two cysteine residues at positions 5 and 24 found in bitistatin but not in other disintegrin molecules are disulphide-bridged. This linkage creates an extra, large loop, which, depending on whether the NMR structure of flavoridin or kistrin is used for modelling the structure of bitistatin, lies opposite or nearly parallel, respectively, to the biologically active RGD-containing loop.

Monitoring of r-hirudin anticoagulation during cardiopulmonary bypass--assessment of the whole blood ecarin clotting time

The use of recombinant (r) hirudin as an anticoagulant in performing extracorporeal circulation systems including cardiopulmonary bypass (CPB) devices requires a specific and easy to handle monitoring system. The usefulness of the celite-induced activated clotting time (ACT) and the activated partial thromboplastin time (APTT) for r-hirudin monitoring has been tested on ex vivo blood samples obtained from eight patients treated with r-hirudin during open heart surgery. The very poor relationship between the prolongation of the ACT and APTT values and the concentration of r-hirudin as measured using a chromogenic factor IIa assay indicates that both assays are not suitable to monitor r-hirudin anticoagulation. As an alternative approach a whole blood clotting assay based on the prothrombin-activating snake venom ecarin has been tested. In vitro experiments using r-hirudin-spiked whole blood samples showed a linear relationship between the concentration of hirudin added and the prolongation of the clotting times up to a concentration of r-hirudin of 4.0 micrograms/ml. Interassay coefficients (CV) of variation between 2.1% and 5.4% demonstrate the accuracy of the ecarin clotting time (ECT) assay. Differences in the interindividual responsiveness to r-hirudin were analyzed on r-hirudin-spiked blood samples obtained from 50 healthy blood donors. CV-values between 1.8% and 6% measured at r-hirudin concentrations between 0.5 and 4 micrograms/ml indicate remarkably slight differences in r-hirudin responsiveness. ECT assay results of the ex vivo blood samples linearily correlate (r = 0.79) to the concentration of r-hirudin. Moreover, assay results were not influenced by treatment with aprotinin or heparin. These findings together with the short measuring time with less than 120 seconds warrant the whole blood ECT to be a suitable assay for monitoring of r-hirudin anticoagulation in cardiac surgery.

Antibiotic prophylaxis for pit viper envenomation: prospective, controlled trial

The efficacy of prophylactic antibiotics for preventing infectious complications at the site of pit viper envenomation has not been well studied. We undertook a prospective, controlled trial of antibiotic treatment versus no antibiotic treatment among 114 victims of crotalid envenomation in Ecuador's Amazon rain forest. A group of 59 patients received intravenous gentamicin and chloramphenicol, and 55 patients did not. All other aspects of care were identical. There were no statistically significant differences between antibiotic-treated and untreated patients with regard to demographics, delay in treatment, clinical and laboratory evidence of severity of envenomation, or use of antivenin. Nine abscesses occurred, six in the antibiotic-treated group and three in the untreated group. The results of this study did not show any statistically significant differences in outcome in terms of the number of abscesses that occurred between antibiotic-treated and untreated patients. Based on this lack of differences, routine use of prophylactic antibiotics for prevention of infectious complications of crotalid envenomation cannot be recommended.

Aortic medial necrosis with or without thrombosis in rabbits treated with Russell's viper venom and angiotensin II

The aim of the present study is primarily to re-examine an animal model of acute myocardial infarction (AMI) and arterial thrombosis, developed by Constantinides and his colleagues in the 1960s, in both heritable hyperlipidemic rabbits and normal rabbits because they did not study these rabbits. The groups in this study consisted of 29 normal rabbits and 29 Watanabe heritable hyperlipidemic (WHHL) rabbits. These rabbits were administered Russell's viper venom (RVV) as a procoagulant, intraperitoneally with serotonin or angiotensin II or saline, intravenously. As a control, 10 normal and 17 WHHL rabbits were administered intravenously with either angiotensin II or saline. These treatments were given on 2 successive days. AMI lesion was found in 8 of 29 normal and 7 of 29 WHHL rabbits receiving RVV and angiotensin or serotonin. Angiotensin II promoted the incidence of aortic thrombosis associated with segmental medial necrosis and an intimal disruption in WHHL rabbits receiving RVV. In the normal rabbits, angiotensin II in addition to RVV induced segmental medial necrosis of the aorta, but angiotensin II alone did not. Thus, we postulated that a synergistic effect of RVV as a cytotoxic substance and a sudden increase in the aortic wall tension by angiotensin II might thus result in acute aortic medial necrosis. The conclusion was that no close correlation between coronary arteriosclerosis and AMI was found in this animal model. The intravenous administration of angiotensin promoted aortic medial necrosis even in normal rabbits treated with RVV and then accelerated aortic thrombosis in the WHHL rabbits treated with RVV.