Vipera ammodytes bites treated with antivenom ViperaTAb: a case series with pharmacokinetic evaluation

CONTEXT

In clinical practice it is difficult to differentiate between V. berus and V. ammodytes venomous bites. In the past this was not a concern, but due to the current shortage in Viperfav™ and European viper venom antiserum availability, V. a. ammodytes venomous bites have recently been treated with ViperaTAb^®, which is a pharmaceutical formulation containing a monospecific ovine Fab fragments against the venom of V. berus.

OBJECTIVE

To evaluate ViperaTAb^® in V. a. ammodytes envenomations.

MATERIALS AND METHODS

This is a prospective case series of three consecutive patients envenomed by V. a. ammodytes snakebite treated with ViperaTAb^®. V. ammodytes venom, neurotoxic ammodytoxins, and Fab fragment levels were determined in serum samples and a pharmacokinetic analysis of the antivenom Fab fragments was carried out.

RESULTS

Three patients bitten by V. a. ammodytes with extensive local swelling, neurological symptoms and recurrent thrombocytopenia were treated with ViperaTAb^®. V. ammodytes venom was detected in serum of all three patients. Ammodytoxins were detected in the serum of only the most severely envenomed patient who developed neurological symptoms. In the presented moderate cases, a dose of 8 mL of ViperaTAb^® reduced swelling and improved systemic effects, such as thrombocytopenia. However, this dose of ViperaTAb^® was not effective in the most severely envenomed patient with the highest serum values of V. ammodytes venom. In this case ViperaTAb^® did not stop local swelling and it had no effect on neurological signs. ViperaTAb^®'s systemic clearance, distribution and elimination half-lives were 4.3-13.4 mL/h/kg, 1.2-3.2 h and 14.1-55.4 h, respectively.

CONCLUSIONS

In patients envenomed by V. a. ammodytes venom, ViperaTAb^® reduces moderate swelling and temporarily improves systemic effects, except neurological symptoms. ViperaTAb^® application induces a decrement of V. ammodytes venom level in the blood, but did not affect serum concentration of neurotoxic ammodytoxins in the one patient with measurable concentrations.

A Single Dose of Viperfav(TM) May Be Inadequate for Vipera ammodytes Snake Bite: A Case Report and Pharmacokinetic Evaluation

Viperfav^TM is a commercial F(ab’)₂ antivenom prepared against European vipers venom. It is safe and effective for treating envenomation caused by Vipera aspis and Vipera berus. Therapeutic efficacy for treating Vipera ammodytes ammodytes (V. a. ammodytes) envenoming has not been yet described, although protective efficacy has been demonstrated in preclinical studies. We report on a 32-year-old man bitten by V. a. ammodytes who was treated with Viperfav™. Viperfav™ promptly reduced local extension and improved systemic pathological signs, but 24 h after the incident a recurrence of thrombocytopenia occurred despite a favorable pharmacokinetic profile with systemic clearance (1.64 (mL·h⁻¹)·kg⁻¹) and elimination half-life (97 h) among the highest ever reported. The recommended dose of Viperfav™ for V. aspis and V. berus bites may be inadequate for serious V. a. ammodytes envenomations. Following V. a. ammodytes bite, serial blood counts and coagulation profiles should be performed to help guide Viperfav™ treatment, along with supplemental administration as indicated.

Factors influencing preclinical in vivo evaluation of mumps vaccine strain immunogenicity

Immunogenicity testing in animals is a necessary preclinical assay for demonstration of vaccine efficacy the results of which are often the basis for the decision whether to proceed or withdraw the further development of the novel vaccine candidate. However, in vivo assays are rarely, if at all, optimized and validated. Here we clearly demonstrate the importance of in vivo assay (mumps virus immunogenicity testing in guinea pigs) optimization for gaining reliable results and the suitability of Fractional factorial design of experiments (DoE) for such a purpose. By the use of DoE with resolution IV (2IV((4-1))) we clearly revealed that the parameters significantly increasing assay sensitivity were interval between animal immunizations followed by the body weight of experimental animals. The quantity (0 versus 2%) of the stabilizer (fetal bovine serum, FBS) in the sample was shown as non-influencing parameter in DoE setup. However, the separate experiment investigating only the FBS influence, and performed under other parameters optimally set, showed that FBS also influences the results of immunogenicity assay. Such finding indicated that (a) factors with strong influence on the measured outcome can hide the effects of parameters with modest/low influence and (b) the matrix of mumps virus samples to be compared for immunogenicity must be identical for reliable virus immunogenicity comparison. Finally the 3 mumps vaccine strains widely used for decades in the licensed vaccines were for the first time compared in an animal model, and results obtained were in line with their reported immunogenicity in human population supporting the predictive power of the optimized in vivo assay.

Venomics of Vipera berus berus to explain differences in pathology elicited by Vipera ammodytes ammodytes envenomation: Therapeutic implications

Vipera berus berus (Vbb) is the most widely distributed and Vipera ammodytes ammodytes (Vaa) the most venomous viper in Europe. In particular areas of the Old continent their toxic bites constitute a considerable public health problem. To make the current envenomation therapy more effective we have analysed the proteome of Vbb venom and compared it with that of Vaa. We found the proteome of Vbb to be much less complex and to contain smaller levels of particularly snaclecs and sPLA2s. Snaclecs are probably responsible for thrombocytopenia. The neurotoxic sPLA2s, ammodytoxins, are responsible for the most specific feature of the Vaa venom poisoning - induction of signs of neurotoxicity in patients. These molecules were not found in Vbb venom. Both venoms induce haemorrhage and coagulopathy in man. As Vaa and Vbb venoms possess homologous P-III snake venom metalloproteinases, the main haemorrhagic factors, the severity of the haemorrhage is dictated by concentration and specific activity of these molecules. The much greater anticoagulant effect of Vaa venom than that of Vbb venom lies in its higher extrinsic pathway coagulation factor-proteolysing activity and content of ammodytoxins which block the prothrombinase complex formation.

BIOLOGICAL SIGNIFICANCE

Envenomations by venomous snakes constitute a considerable public health problem worldwide, and also in Europe. In the submitted work we analysed the venom proteome of Vipera berus berus (Vbb), the most widely distributed venomous snake in Europe and compared it with the venom proteome of the most venomous viper in Europe, Vipera ammodytes ammodytes (Vaa). We have offered a possible explanation, at the molecular level, for the differences in clinical pictures inflicted by the Vbb and Vaa venoms. We have provided an explanation for the effectiveness of treatment of Vbb envenomation by Vaa antiserum and explained why full protection of Vaa venom poisoning by Vbb antiserum should not be always expected, especially not in cases of severe poisoning. The latter makes a strong case for Vaa antiserum production as we are faced with its shortage due to ceasing of production of two most frequently used products.

Nonspecific native elution of proteins and mumps virus in immunoaffinity chromatography

Immunoaffinity chromatography, based on the antigen-antibody recognition, enables specific purification of any antigen (protein, virus) by its antibody. The problem with immunoaffinity chromatography is the harsh elution conditions required for disrupting strong antigen-antibody interactions, such as low pH buffers, which are often deleterious for the immobilized protein and the protein to be isolated since they can also disrupt the intramolecular forces. Therefore, immunoaffinity chromatography can only be partially used for protein and virus purification. Here we report on a nonspecific elution in immunoaffinity chromatography using native conditions by elution with amino acid solution at physiological pH for which we suppose possible competing mechanism of action. Elution potential of various amino acid solutions was tested using immunoaffinity columns specific for ovalbumin and mumps virus, and protein G affinity column. Results have shown that the most successful elution solutions were those containing imidazole and arginine of high molarity. Imidazole represents aromatic residues readily found at the antigen-antibody interaction surface and arginine is most frequently found on protein surface in general. Therefore, results on their eluting power in immunoaffinity chromatography, which increases with increasing molarity, are in line with the competing mechanism of action. Virus immunoaffinity chromatography resulted in removal on nonviable virus particles, which is important for research and biotechnology purposes. In addition, amino acids are proven stabilizers for proteins and viruses making approach presented in this work a very convenient purification method.

Identification of mumps virus protein and lipid composition by mass spectrometry

Background

Mumps virus is a negative-sense, single stranded RNA virus consisting of a ribonucleocapsid core enveloped by a lipid membrane derived from host cell, which causes mumps disease preventable by vaccination. Since virus lipid envelope and glycosylation pattern are not encoded by the virus but dependent on the host cell at least to some extent, the aim of this work was to analyse L-Zagreb (L-Zg) mumps virus lipids and proteins derived from two cell types; Vero and chicken embryo fibroblasts (CEF). Jeryl Lynn 5 (JL5) mumps strain lipids were also analysed.

Methods

Virus lipids were isolated by organic phase extraction and subjected to 2D-high performance thin layer chromatography followed by lipid extraction and identification by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). Virus samples were also subjected to gel electrophoresis under denaturating conditions and protein bands were excised, in-gel trypsinized and identified by MS as well as tandem MS.

Results

Results showed that lipids of both mumps virus strains derived from Vero cells contained complex glycolipids with up to five monosaccharide units whereas the lipid pattern of mumps virus derived from CEF was less complex. Mumps virus was found to contain expected structural proteins with exception of fusion (F) protein which was not detected but on the other hand, V protein was detected. Most interesting finding related to the mumps proteins is the detection of several forms of nucleoprotein (NP), some of which appear to be C-terminally truncated.

Conclusions

Differences found in lipid and protein content of mumps virus demonstrated the importance of detailed biochemical characterization of mumps virus and the methodology described here could provide a means for a more comprehensive quality control in vaccine production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0463-0) contains supplementary material, which is available to authorized users.

Stability of Minimum Essential Medium functionality despite L-glutamine decomposition

L-Glutamine (L-Gln) instability in liquid media is a well-known fact. Also, negative effect of ammonia, one of the L-Gln degradation products, on viability of many cell cultures and on replication of different viruses has been described. However, negative effects of ammonia have been reported in doses excessively exceeding those that could be generated in regularly used liquid culture media due to spontaneous L-Gln breakdown (below 2 mM). Traditional virus vaccine production processes have been established and registered involving L-Gln containing media use. Eventual culture media replacement in the regular production process belongs to the major regulative changes that require substantial financial expenses. The aim of this study was to evaluate the effect of storage of Minimum Essential Media with Hanks salts on their relevant biological functions during virus vaccine production process in relation to L-Gln decrease. Our results show a cell type dependent effect of spontaneous L-Gln degradation during medium storage. They also suggest that for cell cultures used in measles, mumps, and rubella virus production the media retain their functionality in respect to cell viability or virus growth over a certain time window despite L-Gln degradation.

Structural and biochemical characterisation of VaF1, a P-IIIa fibrinogenolytic metalloproteinase from Vipera ammodytes ammodytes venom

A high molecular mass metalloproteinase with α-fibrinogenolytic activity, termed VaF1, was purified from nose-horned viper (Vipera ammodytes ammodytes) venom. Subcutaneous injection of 9 μg of VaF1 did not induce bleeding in rats. Nevertheless, in vitro it degraded collagen IV, nidogen and fibronectin, components of the extracellular matrix, although with low efficacy and narrow specificity. VaF1 would be expected to exert anti-coagulant action, due to its hydrolysis of fibrinogen, factor X, prothrombin and plasminogen, plasma proteins involved in blood coagulation. The enzyme is a single-chain glycoprotein with a molecular mass of 49.7 kDa, as determined by mass spectrometry, and multiple isoelectric points centred at pH 5.8. The complete amino acid sequence of the precursor of VaF1 was deduced by cloning and sequencing its cDNA. Composed of metalloproteinase, disintegrin-like and cysteine-rich domains, VaF1 is a typical P-IIIa subclass snake venom metalloproteinase. Although it possesses a collagen-binding sequence in its disintegrin-like domain, VaF1 displayed no effect on collagen-induced platelet aggregation in vitro. Two consensus N-glycosylation sites are present in the sequence of VaF1, however, the extent of its glycosylation is low, only 5.2% of the total molecular mass. Interestingly, in standard experimental conditions VaF1 is not recognised by antiserum against the whole venom, so it can contribute to post-serotherapy complications, such as ineffective blood coagulation, in the envenomed patient.

Paraspecificity of Vipera a. ammodytes-specific antivenom towards Montivipera raddei and Macrovipera lebetina obtusa venoms

Antivenom raised against the venom of nose-horned viper, Vipera ammodytes (V. a.) ammodytes (European viper venom antiserum, Zagreb antivenom), contains neutralising equine F(ab')₂ fragments that are clinically successful against homologous venom, but also against the venoms of several others medically important European snakes due to its paraspecific action. In this work we demonstrated that Zagreb antivenom is preclinically effective in neutralising lethal toxicity and hemorrhagicity of venoms of Armenian mountain snakes--Montivipera raddei and Macrovipera lebetina obtusa as well. In order to better understand the biochemical basis of the observed paraspecificity, the ability of anti-V. a. ammodytes serum to recognise and neutralise proteinases of the two venoms was also investigated. Anti-V. a. ammodytes serum showed surprisingly low capacity to inhibit metalloproteinases of both venoms included in the study, probably due to weak immunorecognition of their P-I representatives. Also, it completely failed to abolish enzymatic action of serine proteinases from Macrovipera lebetina obtusa venom. Relevance of such finding is yet to be established.

Hemorrhagin VaH4, a covalent heterodimeric P-III metalloproteinase from Vipera ammodytes ammodytes with a potential antitumour activity

In the envenomation caused by a bite of Vipera ammodytes ammodytes, the most venomous snake in Europe, hemorrhage is usually the most severe consequence in man. Identifying and understanding the hemorrhagic components of its venom is therefore particularly important in optimizing medical treatment of patients. We describe a novel high molecular mass hemorrhagin, VaH4. The isolated molecule is a covalent dimer of two homologous subunits, VaH4-A and VaH4-B. Complete structural characterization of A and partial characterization of B revealed that both belong to the P-III class of snake venom metalloproteinases (SVMPs), comprising a metalloproteinase, a disintegrin-like domain and a cysteine-rich domain. However, neither VaH4-A nor VaH4-B possess the Cys174 involved in the inter-subunit disulphide bond of P-III SVMPs. A three-dimensional model of the VaH4 dimer suggests that Cys132 serves this function. This implies that dimers in the P-III class of SVMPs can be formed either between their Cys132 or Cys174 residues. The proteolytic activity and stability of VaH4 depend on Zn²⁺ and Ca²⁺ ions and the presence of glycosaminoglycans, which indicates physiological interaction of VaH4 with the latter element of the extracellular matrix (ECM). The molecular mass of VaH4, determined by MALDI/TOF mass spectrometry, is 110.2 kDa. N-deglycosylation reduced the mass of each monomer by 8.7 kDa. The two possible N-glycosylation sites in VaH4-A are located at completely different positions from those in homodimeric P-IIIc VaH3 from the same venom, however, without any evident functional implications. The hemorrhagic activity of this slightly acidic SVMP is ascribed to its hydrolysis of components of the ECM, particularly fibronectin and nidogen, and of some blood coagulation proteins, in particular the α-chain of fibrinogen. VaH4 is also significant medically as we found it cytotoxic against cancer cells and due to its substantial sequence similarity to ADAM/ADAMTS family of physiologically very important human proteins of therapeutic potential.

Influence of charge ratio of liposome/DNA complexes on their size after extrusion and transfection efficiency

BACKGROUND

Physicochemical characteristics of liposome/DNA complexes influence transfection efficiency and affect each other in a very intricate way. The result of this is discrepancies in conclusions drawn about the individual influence of each one.

METHODS

Aiming to elucidate the influence of liposome/DNA charge ratio and size on transfection efficiency and on each other, we used liposome/DNA complexes with charge ratio (+/-) in the range of 1-50 and extruded through membranes of 400, 200, and 100 nm. Plasmid DNA encoding green fluorescent protein was used to measure transfection efficiency by flow cytometry. Sizes of liposome/DNA complexes were measured by dynamic light scattering.

RESULTS

Liposome size was reduced after extrusion but this was mainly driven by the charge ratio and not by the size of the membrane pores. Reduction of complex size at each charge ratio positively correlated with transfection efficiency. When the size of the complexes was approximately constant, increasing the charge ratio was found to promote transfection efficiency. Cationic lipid N-(1-(2,3-dioleoyloxy)propyl)N,N,N trimethylammonium chloride was used for modulation of positive charge and a cytotoxicity test showed that increasing its amount increases cytotoxicity.

CONCLUSION

It can be concluded that charge ratio dictates the size of the complex whereas overall size reduction and higher charge ratios promote transfection efficiency in vitro.

Intraspecies variability in Vipera ammodytes ammodytes venom related to its toxicity and immunogenic potential

Vipera ammodytes is the most venomous European snake, whose venom has been used as antigen for immunization of antivenom-producing animals. Same as venom of any other snake, it is a complex mixture of proteins, peptides and other compounds which biochemical and pharmacological variability has been demonstrated at interspecies and intraspecies level. In this work we demonstrated intraspecific variability between 8 venom production batches using both the conventional and the new methodology. Moreover, in contrast to the literature on different venoms' variability, for the first time we were able to select those biochemical differences that are related to and give information on the venom's toxicity and immunogenicity. We have shown that methods quantifying ammodytoxin (the most toxic compound identified so far in the Vipera ammodytes ammodytes venom) content of the venom clearly distinguish between high and low immunogenic venoms.

Studying disulfide bond rearrangement by MALDI-RTOF PSD and MALDI-TOF/RTOF high-energy CID (20 keV) experiments of peptides derived from ammodytoxins

Ammodytoxins (Atxs) are presynaptically neurotoxic phospholipases present in Vipera ammodytes ammodytes snake venom. Atxs show a high sequence homology and contain 14 cysteines which form seven biologically relevant disulfide bridges-connecting non-neighboring cysteines. Formic acid cleavage was performed to confirm protein sequences by MALDI RTOF MS and resulted in 95.6% sequence coverage exhibiting only few formylations. Cysteine-containing peptides showed adjacent signals 2 and/or 4 Da lower (according to the number of cysteines present in the peptide) than the theoretical molecular weight indicating disulfide bridge rearrangement. Post-source decay (PSD) and high-energy collision-induced dissociation (CID) at 20 keV experiments showed fragmentation pattern unique for the reduced, thiol group containing and the oxidized, disulfide bridge harboring peptides. Besides typical low-energy fragment ions observed during PSD experiments (a-, b-, y-type ions), additional high-energy fragment ions (c-, x-, w-, d-type and internal fragments) of significant intensity were generated during fragmentation at 20 keV. In the case of charge directing N- and C-termini, x- and w-type ions were also observed during PSD. Good and up to complete sequence coverage was achieved for all studied peptides from Atxs in the case of high-energy CID, whereas PSD lacked information particularly for larger peptides.

Ammodytoxin content of Vipera ammodytes ammodytes venom as a prognostic factor for venom immunogenicity

Venoms are complex mixtures of proteins, peptides and other compounds whose biochemical and biological variability has been clearly demonstrated. These molecules have been used as antigens for immunization of anti-venom-producing animals (horses or sheep). Ammodytoxins (Atx) are potently neurotoxic compounds, and the most toxic compounds isolated so far from the Vipera ammodytes ammodytes (Vaa) venom. Recently we have shown that the level of antibodies specific to Vaa venom's most toxic component, ammodytoxin A (AtxA), (anti-AtxA IgG) in Vaa venom immunized rabbit sera highly correlated to the venom toxicity-neutralization potential of these sera. Here we investigated whether Atx content of Vaa venom could influence the outcome of immunization procedure. The novel ELISA was developed for precise determination of Atx content and Atx was quantified in venom samples used for immunization of rabbits. We clearly showed that animals immunized with the venom containing lower amount of Atx produced sera with significantly lower venom toxicity-neutralizing power and, vice versa, animals immunized with venoms containing higher amount of Atx produced sera with higher venom toxicity-neutralizing ability. Thus, the content of Atx in Vaa venom is a relevant parameter of its suitability in the production of highly protective Vaa anti-venom.

Comparative study of structurally related peptidoglycan monomer and muramyl dipeptide on humoral IgG immune response to ovalbumin in mouse

Structurally related peptidoglycan monomer (PGM) and muramyl dipeptide (MDP) differ in several aspects of biological activity but have in common immunostimulating properties. Comparative study of the effects of these adjuvants on humoral IgG immune response specific for protein antigen ovalbumin (OVA) was carried out in two inbred mouse strains, CBA and NIH/OlaHsd, and their ability to modulate the bias of immune response towards Th1/Th2 was evaluated. MDP had better adjuvant activity at some points than PGM, whereas both adjuvants stimulated Th2-biased immune response specific for OVA. In comparison to Complete Freund's adjuvant (CFA), as a golden standard of adjuvant action, both PGM and MDP exhibited considerably lower activity. Addition of PGM to Incomplete Freund's adjuvant (IFA) on humoral immune response was studied also, and the effect of such adjuvant formulation was compared to the effect of CFA. While CFA induced the switch towards Th1-biased immune response, the addition of PGM into IFA did have no impact on modulating the immune response towards more pronounced Th2-type of immune response, defined by IFA itself.

Effect of Liposomal Formulations and Immunostimulating Peptidoglycan Monomer (PGM) on the Immune Reaction to Ovalbumin in Mice

The adjuvant activity of liposomes and immunostimulating peptidoglycan monomer (PGM) in different formulations has been studied in mice model using ovalbumin (OVA) as an antigen. PGM is a natural compound of bacterial origin with well-defined chemical structure: GlcNAc-MurNAc-L-Ala-D-isoGln-mesoDpm(epsilonNH2)-D-Ala-D-Ala. It is a non-toxic, non-pyrogenic, and water-soluble immunostimulator. The aim of this study was to investigate the influence of different liposomal formulations of OVA, with or without PGM, on the production of total IgG, as well as of IgG1 and IgG2a subclasses of OVA-specific antibodies (as indicators of Th2 and Th1 type of immune response, respectively). CBA mice were immunized s.c. with OVA mixed with liposomes, OVA with PGM mixed with liposomes, OVA encapsulated into liposomes and OVA with PGM encapsulated into liposomes. Control groups were OVA in saline, OVA with PGM in saline, and OVA in CFA/IFA adjuvant formulation. The entrapment efficacy of OVA was monitored by HPLC method. The adjuvant activity of the mixture of OVA and empty liposomes, the mixture of OVA, PGM, and liposomes and PGM encapsulated with OVA into liposomes on production of total anti-OVA IgG was demonstrated. The mixture of PGM and liposomes exhibited additive immunostimulating effect on the production of antigen-specific IgGs. The analysis of IgG subclasses revealed that encapsulation of OVA into liposomes favors the stimulation of IgG2a antibodies, indicating the switch toward the Th1 type of immune response. When encapsulated into liposomes or mixed with liposomes, PGM induced a switch from Th1 to Th2 type of immune response. It could be concluded that appropriate formulations of antigen, PGM, and liposomes differently affect the humoral immune response and direct the switch in the type of immune response (Th1/Th2).

The role of antibodies specific for toxic sPLA2s and haemorrhagins in neutralizing potential of antisera raised against Vipera ammodytes ammodytes venom

The contribution of antibodies directed against the two main toxic groups of proteins in the Vipera ammodytes ammodytes venom, haemorrhagic metalloproteinases (H) and neurotoxic sPLA2s (Atxs), to the overall protective efficacy of the whole venom antisera was investigated. Using ELISA assays we established a high correlation between the protective efficacy of the whole venom antisera in mice and their anti-Atxs antibody content. As the haemorrhage is the prevailing toxic effect of the venom in human, the lack of correlation also with anti-H IgG content exposed that the mouse model might not be optimal to evaluate the neutralizing potential of the venom-specific antisera for human therapy. We further revealed that Atxs and structurally very similar but non-toxic AtnI2 from the venom are not immuno cross-reactive.

Dose dependent effects of standardized nose-horned viper (Vipera ammodytes ammodytes) venom on parameters of cardiac function in isolated rat heart

Direct, dose dependent effects of the nose-horned vipers (Vipera ammodytes ammodytes) venom on various parameters of cardiac action in isolated rat hearts were examined. Biochemical (protein content, SDS polyacrylamide gel electrophoresis) and biological (minimum haemorrhagic and necrotizing dose and lethal dose (LD(50))) characterization of the venom was performed before testing. The hearts were infused with venom doses of 30, 90 and 150 microg/mL for 10 min followed by 30 min of wash out period. Left ventricular pressure, coronary flow, heart rate, atrioventricular conduction, myocardial oxygen consumption, incidence and duration of arrhythmias were measured and relative cardiac efficiency was calculated. Cardiac CPK, LDH, AST and troponin I were measured as biochemical markers of myocardial damage. The venom caused dose dependent electrophysiological instability and depression of contractility and coronary flow. Effects on the heart rate were biphasic; transient increase followed by significant slowing of the frequency. Relative cardiac efficiency decreased as oxygen consumption remained high relative to the heart rate-contractility product, indicating purposeless expenditure of oxygen and energy. Effects by the dose of 30 microg/mL were highly reversible while the dose of 90 mug/mL caused damages that were mostly irreversible. The dose of 150 mug/mL induced irreversible asystolic cardiac arrest.