Neutralization of cardiac toxins oleandrin, oleandrigenin, bufalin, and cinobufotalin by digibind: monitoring the effect by measuring free digitoxin concentrations

Oleandrin: A bioactive phytochemical and potential cancer killer via multiple cellular signaling pathways

Nerium oleander, a member of family Apocynaceae, is commonly known as Kaner in various countries of Asia and Mediterranean region. This plant has been renowned to possess significant therapeutic potential due to its various bioactive compounds which have been isolated from this plant e.g., cardiac glycosides, oleandrin, α-tocopherol, digitoxingenin, urosolic acid, quercetin, odorosides, and adigoside. Oleandrin, a saponin glycoside is one of the most potent and pharmacologically active phytochemicals of N. oleander. Its remarkable pharmacotherapeutic potential have been interpreted as anticancer, anti-inflammatory, anti-HIV, neuroprotective, antimicrobial and antioxidant. This particular bioactive entity is known to target the multiple deregulated signaling cascades of cancer such as NF-κB, MAPK, and PI3K/Akt. The main focus of the current study is to comprehend the action mechanisms of oleandrin against various pathological conditions. The current review is a comprehensive summary to facilitate the researchers to understand the pharmacological position of the oleandrin in the arena of drug discovery, representing this compound as a new drug candidate for further researches. Moreover, in vivo and in silico based studies are required to explore the mechanistic approaches regarding the pharmacokinetics and biosafety profiling of this compound to completely track its candidature status in natural drug discovery.

New therapeutic aspects of steroidal cardiac glycosides: the anticancer properties of Huachansu and its main active constituent Bufalin

Aim of the review

In the past decade, increasing research attention investigated the novel therapeutic potential of steroidal cardiac glycosides in cancer treatment. Huachansu and its main active constituent Bufalin have been studied in vitro, in vivo and clinical studies. This review aims to summarize the multi-target and multi-pathway pharmacological effects of Bufalin and Huachansu in the last decade, with the aim of providing a more comprehensive view and highlighting the recently discovered molecular mechanisms.

Results

Huachansu and its major derivative, Bufalin, had been found to possess anti-cancer effects in a variety of cancer cell lines both in vitro and in vivo. The underlying anti-cancer molecular mechanisms mainly involved anti-proliferation, apoptosis induction, anti-metastasis, anti-angiogenesis, epithelial-mesenchymal transition inhibition, anti-inflammation, Na⁺/K⁺-ATPase activity targeting, the steroid receptor coactivator family inhibitions, etc. Moreover, the potential side-effects and toxicities of the toad extract, Huachansu, and Bufalin, including hematological, gastrointestinal, mucocutaneous and cardiovascular adverse reactions, were reported in animal studies and clinic trails.

Conclusions

Further research is needed to elucidate the potential drug-drug interactions and multi-target interaction of Bufalin and Huachansu. Large-scale clinical trials are warranted to translate the knowledge of the anticancer actions of Bufalin and Huachansu into clinical applications as effective and safe treatment options for cancer patients in the future.

Oleander and Datura Poisoning: An Update

India has a very high incidence of poisoning. While most cases are due to chemicals or drugs or envenomation by venomous creatures, a significant proportion also results from consumption or exposure to toxic plants or plant parts or products. The exact nature of plant poisoning varies from region to region, but certain plants are almost ubiquitous in distribution, and among these, Oleander and Datura are the prime examples. These plants are commonly encountered in almost all parts of India. While one is a wild shrub (Datura) that proliferates in the countryside and by roadsides, and the other (Oleander) is a garden plant that features in many homes. Incidents of poisoning from these plants are therefore not uncommon and may be the result of accidental exposure or deliberate, suicidal ingestion of the toxic parts. An attempt has been made to review the management principles with regard to toxicity of these plants and survey the literature in order to highlight current concepts in the treatment of poisoning resulting from both plants.

Comprehensive review of cardiovascular toxicity of drugs and related agents

Cardiovascular diseases are a leading cause of morbidity and mortality in most developed countries of the world. Pharmaceuticals, illicit drugs, and toxins can significantly contribute to the overall cardiovascular burden and thus deserve attention. The present article is a systematic overview of drugs that may induce distinct cardiovascular toxicity. The compounds are classified into agents that have significant effects on the heart, blood vessels, or both. The mechanism(s) of toxic action are discussed and treatment modalities are briefly mentioned in relevant cases. Due to the large number of clinically relevant compounds discussed, this article could be of interest to a broad audience including pharmacologists and toxicologists, pharmacists, physicians, and medicinal chemists. Particular emphasis is given to clinically relevant topics including the cardiovascular toxicity of illicit sympathomimetic drugs (e.g., cocaine, amphetamines, cathinones), drugs that prolong the QT interval, antidysrhythmic drugs, digoxin and other cardioactive steroids, beta-blockers, calcium channel blockers, female hormones, nonsteroidal anti-inflammatory, and anticancer compounds encompassing anthracyclines and novel targeted therapy interfering with the HER2 or the vascular endothelial growth factor pathway.

Cinobufotalin impedes Sw.71 cytotrophoblast cell line function via cell cycle arrest and apoptotic signaling

Preeclampsia (preE) is a hypertensive disorder of pregnancy. Cardiotonic steroids (CTS) are endogenous inhibitors of Na⁺/K⁺ ATPase, and at least one CTS, marinobufagenin (MBG), is elevated in a rat model of preE prior to the development of the syndrome. MBG and ouabain impair cytotrophoblast (CTB) cell function, which is critical for placental development. We evaluated the effect of a CTS, cinobufotalin (CINO), on CTB cell function in vitro. CINO at ≥1 nM inhibited CTB cell proliferation, migration, and invasion (p < 0.05), but had no effect on cell viability. There was a higher (p < 0.05) percentage of G0/G1 phase cells in groups treated with CINO at ≥1 nM. CINO caused an increase in stress signaling p38 MAPK and a positive annexin-V staining in CTB cells, indicating the activation of apoptotic signaling. However, the CINO-induced apoptotic signaling was prevented by p38 inhibition. These data demonstrate that CINO impairs CTB cell function via cell cycle arrest and apoptotic signaling.

Toad Intoxication in the Dog by Rhinella marina : The Clinical Syndrome and Current Treatment Recommendations

Oral exposure to the secretions of Rhinella marina (formerly Bufo marinus ) can carry a high fatality rate without early and appropriate treatment. In dogs, the clinical syndrome, which is evident almost immediately, manifests in profuse ptyalism along with gastrointestinal, respiratory, and neurologic signs. Severe cardiac arrhythmias develop less frequently. This review will cover the history, toxicology, and clinical syndrome of Rhinella marina intoxication, and will discuss the recommended therapies for stabilization.

A comparison of simulation-based education versus lecture-based instruction for toxicology training in emergency medicine residents

Simulation-based teaching (SIM) is a common method for medical education. SIM exposes residents to uncommon scenarios that require critical, timely actions. SIM may be a valuable training method for critically ill poisoned patients whose diagnosis and treatment depend on key clinical findings. Our objective was to compare medical simulation (SIM) to traditional lecture-based instruction (LEC) for training emergency medicine (EM) residents in the acute management of critically ill poisoned patients. EM residents completed two pre-intervention questionnaires: (1) a 24-item multiple-choice test of four toxicological emergencies and (2) a questionnaire using a five-point Likert scale to rate the residents' comfort level in diagnosing and treating patients with specific toxicological emergencies. After completing the pre-intervention questionnaires, residents were randomized to SIM or LEC instruction. Two toxicologists and three EM physicians presented four toxicology topics to both groups in four 20-min sessions. One group was in the simulation center, and the other in a lecture hall. Each group then repeated the multiple-choice test and questionnaire immediately after instruction and again at 3 months after training. Answers were not discussed. The primary outcome was comparison of immediate mean post-intervention test scores and final scores 3 months later between SIM and LEC groups. Test score outcomes between groups were compared at each time point (pre-test, post-instruction, 3-month follow-up) using Wilcoxon rank sum test. Data were summarized by descriptive statistics. Continuous variables were characterized by means (SD) and tested using t tests or Wilcoxon rank sum. Categorical variables were summarized by frequencies (%) and compared between training groups with chi-square or Fisher's exact test. Thirty-two EM residents completed pre- and post-intervention tests and comfort questionnaires on the study day. Both groups had higher post-intervention mean test scores (p < 0.001), but the LEC group showed a greater improvement compared to the SIM group (5.6 [2.3] points vs. 3.6 [2.4], p = 0.02). At the 3-month follow-up, 24 (75 %) tests and questionnaires were completed. There was no improvement in 3-month mean test scores in either group compared to immediate post-test scores. The SIM group had higher final mean test scores than the LEC group (16.6 [3.1] vs. 13.3 [2.2], p = 0.009). SIM and LEC groups reported similar diagnosis and treatment comfort level scores at baseline and improved equally after instruction. At 3 months, there was no difference between groups in comfort level scores for diagnosis or treatment. Lecture-based teaching was more effective than simulation-based instruction immediately after intervention. At 3 months, the SIM group showed greater retention than the LEC group. Resident comfort levels for diagnosis and treatment were similar regardless of the type of education.

Rapid detection of the active cardiac glycoside convallatoxin of lily of the valley using LOCI digoxin assay

OBJECTIVES

To explore the luminescent oxygen channeling technology-based digoxin immunoassay (LOCI digoxin assay) for rapid detection of lily of the valley extract and convallatoxin. The potential in vitro binding of convallatoxin with Digibind was also evaluated.

METHODS

Aliquots of a drug-free serum pool and a digoxin serum pool were supplemented with lily of the valley extract or convallatoxin, and then apparent digoxin concentrations were measured using the LOCI digoxin assay. Mice were administered lily of the valley extract or 50 μg of convallatoxin, and digoxin concentrations in serum specimens were measured 1 and 2 hours after gavage. Aliquots of a serum pool supplemented with convallatoxin or lily of the valley extract were further supplemented with various concentrations of Digibind and free apparent digoxin concentrations were measured.

RESULTS

Apparent digoxin concentrations were observed when aliquots of a drug-free serum pool were supplemented with convallatoxin or lily of the valley extract, and also with convallatoxin or herbal extract. Bidirectional interference of convallatoxin and lily of the valley extract with serum digoxin measurement using the LOCI assay was also observed. Digibind was capable of binding convallatoxin in vitro.

CONCLUSIONS

LOCI digoxin assay can be used for rapid detection of convallatoxin, and Digibind can bind convallatoxin in vitro.

Rapid detection of convallatoxin using five digoxin immunoassays

CONTEXT

Cardiac glycosides of plant origin are implicated in toxic ingestions that may result in hospitalization and are potentially lethal. The utility of commonly available digoxin serum assays for detecting foxglove and oleander ingestion has been demonstrated, but no studies have evaluated the structurally similar convallatoxin found in Convallaria majalis (lily of the valley) for rapid laboratory screening, nor has digoxin immune Fab been tested as an antidote for this ingestion.

OBJECTIVE

We aimed to (1) evaluate multiple digoxin assays for cross-reactivity to convallatoxin, (2) identify whether convallatoxin could be detected in vivo at clinically significant doses, and (3) determine whether digoxin immune Fab could be an effective antidote to convallatoxin.

MATERIALS AND METHODS

Cross-reactivities of purified convallatoxin and oleandrin with five common digoxin immunoassays were determined. Serum from mice challenged with convallatoxin was tested for apparent digoxin levels. Binding of convallatoxin to digoxin immune Fab was determined in vitro.

RESULTS

Both convallatoxin and oleandrin were detectable by a panel of commonly used digoxin immunoassays, but cross-reactivity was variable between individual assays. We observed measurable apparent digoxin levels in serum of convallatoxin intoxicated mice at sublethal doses. Convallatoxin demonstrated no binding by digoxin immune Fab.

CONCLUSION

Multiple digoxin immunoassays detect botanical cardiac glycosides including convallatoxin and thus may be useful for rapid determination of severe exposures, but neutralization of convallatoxin by digoxin immune Fab is unlikely to provide therapeutic benefit.

Bufalin-loaded mPEG-PLGA-PLL-cRGD nanoparticles: preparation, cellular uptake, tissue distribution, and anticancer activity

BACKGROUND

Recent studies have shown that bufalin has a good antitumor effect but has high toxicity, poor water solubility, a short half-life, a narrow therapeutic window, and a toxic dose that is close to the therapeutic dose, which all limit its clinical application. This study aimed to determine the targeting efficacy of nanoparticles (NPs) made of methoxy polyethylene glycol (mPEG), polylactic-co-glycolic acid (PLGA), poly-L-lysine (PLL), and cyclic arginine-glycine-aspartic acid (cRGD) loaded with bufalin, ie, bufalin-loaded mPEG-PLGA-PLL-cRGD nanoparticles (BNPs), in SW620 colon cancer-bearing mice.

METHODS

BNPs showed uniform size. The size, shape, zeta potential, drug loading, encapsulation efficiency, and release of these nanoparticles were studied in vitro. The tumor targeting, cellular uptake, and growth-inhibitory effect of BNPs in vivo were tested.

RESULTS

BNPs were of uniform size with an average particle size of 164 ± 84 nm and zeta potential of 2.77 mV. The encapsulation efficiency was 81.7% ± 0.89%, and the drug load was 3.92% ± 0.16%. The results of in vitro cytotoxicity studies showed that although the blank NPs were nontoxic, they enhanced the cytotoxicity of bufalin in BNPs. Drug release experiments showed that the release of the drug was prolonged and sustained. The results of confocal laser scanning microscopy indicated that BNPs could effectively bind to human umbilical vein endothelial cells. In the SW620 xenograft mice model, the BNPs could effectively target the tumor in vivo. The BNPs were significantly more effective than other NPs in preventing tumor growth.

CONCLUSION

BNPs had even size distribution, were stable, and had a slow-releasing and tumor-targeting effect. BNPs significantly inhibited colon cancer growth in vitro and in vivo. As a novel drug carrier system, BNPs are a potentially promising targeting treatment for colon cancer.

In vitro and in vivo neuroprotective activity of the cardiac glycoside oleandrin from Nerium oleander in brain slice-based stroke models

The principal active constituent of the botanical drug candidate PBI-05204, a supercritical CO(2) extract of Nerium oleander, is the cardiac glycoside oleandrin. PBI-05204 shows potent anticancer activity and is currently in phase I clinical trial as a treatment for patients with solid tumors. We have previously shown that neriifolin, which is structurally related to oleandrin, provides robust neuroprotection in brain slice and whole animal models of ischemic injury. However, neriifolin itself is not a suitable drug development candidate and the FDA-approved cardiac glycoside digoxin does not cross the blood-brain barrier. We report here that both oleandrin as well as the full PBI-05204 extract can also provide significant neuroprotection to neural tissues damaged by oxygen and glucose deprivation as occurs in ischemic stroke. Critically, we show that the neuroprotective activity of PBI-05204 is maintained for several hours of delay of administration after oxygen and glucose deprivation treatment. We provide evidence that the neuroprotective activity of PBI-05204 is mediated through oleandrin and/or other cardiac glycoside constituents, but that additional, non-cardiac glycoside components of PBI-05204 may also contribute to the observed neuroprotective activity. Finally, we show directly that both oleandrin and the protective activity of PBI-05204 are blood brain barrier penetrant in a novel model for in vivo neuroprotection. Together, these findings suggest clinical potential for PBI-05204 in the treatment of ischemic stroke and prevention of associated neuronal death.

Structural characterization of a pectic polysaccharide from Nerium indicum flowers

A polysaccharide fraction, J6, was isolated from the hot-water extract of flowers of oleander Nerium indicum Mill., using ethanol precipitation, cetyltrimethylammonium bromide (CTAB) complexing, anion-exchange chromatography and gel permeation chromatography. J6 was found to contain L-rhamnose, L-arabinose, D-galactose, and D-galacturonic acid, in the ratio of 10.1:49.8:30.1:10.0. Its structure was investigated by methylation analysis, periodate oxidation, Smith degradation, partial acid hydrolysis, electrospray ionization mass spectrometry and NMR spectroscopic methods. It was found that J6 is an RG-I type polysaccharide, which contains a rhamnogalacturonan backbone, with various branches attached to O-4 of L-rhamnose. The branches probably involve (1-->4)-beta-D-galactan, branched L-arabino-(1-->3)(1-->6)-beta-D-galactan, and (1-->5)-alpha-L-arabinan. J6 stimulated NO production of macrophage RAW264.7 cells in a preliminary test.

Ingestion of false hellebore plants can cross-react with a digoxin clinical chemistry assay

INTRODUCTION

We report a case of digoxin-like toxicity because of ingestion of foraged plants. This patient presented with nausea, vomiting, bradycardia, and hypotension after ingesting Veratrum viride (false hellebore). The patient's serum specimen demonstrated a positive digoxin level (0.38 ng/mL) measured by a clinical tubidimetric immunoassay. We hypothesize that steroidal alkaloid compounds contained in V. viride cross-react with the Multigent Digoxin immunoassay reagent antibodies.

RESULTS

Plant extracts from V. viride demonstrated cross-reactivity to Multigent reagent antibodies but did not bind therapeutic DigiFab antibodies. Gas chromatography/mass spectrometry analyses identified several steroidal alkaloid compounds present in the V. viride extracts: jervine, ribigirvine, solanidine, and veratraman.

CONCLUSIONS

This study indicates that compounds extracted from V. viride can cross-react with a clinical Digoxin immunoassay. Yet these extracts did not bind DigiFab antibody fragments used for therapeutic intervention. Providers should not unnecessarily administer DigiFab fragments as an antidote in symptomatic V. viride toxic patients.

Cardioactive steroid poisoning: a comparison of plant- and animal-derived compounds

INTRODUCTION

Cardioactive steroids (CASs) are found in plants, animals, and insects. Their affinity for Na+-K+ ATPase is attenuated by the type of lactone at carbon 17 (C17) of the steroid backbone: those with 5-membered lactone rings, or cardenolides, are derived mostly from plants with 6-membered rings or from animals with bufadienolides. A systematic review of CAS poisoning was performed to compare the mortality rate of cardenolides and bufadienolides.

METHODS

MEDLINE was searched for articles using commonly reported names of CASs, and keywords were limited to human cases only. We searched cases from 1982 to 2003, so that supportive care was similar and digoxin-specific Fab was available. Identified reports of CAS poisoning were read to exclude cases involving licensed pharmaceuticals. Inclusion criteria included hyperkalemia, gastrointestinal symptoms, electrocardiographic evidence of CAS toxicity, digoxin serum concentration, or history of exposure to a substance containing a CAS. Clinical data was collected, including information about treatment with digoxin-specific Fab and treatment outcome.

RESULTS

Fifty-nine articles, describing 924 patients, were identified. Eight hundred ninety-seven patients (97%) ingested a CAS with a 5-membered lactone ring, and mortality was 6% (n = 54). Twenty-seven patients (2.9%) ingested a CAS with a 6-membered lactone ring, and mortality was 29.6% (n = 8). The difference in mortality rates was statistically significant (p < 0.001, [X2]). CASs with 6-member rings accounted for the highest percentage of nonsuicidal exposures.

CONCLUSION

Although cardenolides accounted for the majority of exposures, bufadienolides were five times more lethal than cardenolides.

Changing Characteristics of the TDx Digoxin II Assay in Detecting Bufadienolides in a Traditional Chinese Medicine

In 1992, apparent digoxin concentrations determined by the Abbott TDx II assay 5 hours after the ingestion of 10 pills of traditional Chinese medicine containing toad secretions (chan su) by 7 volunteers, yielded results that were equimolar to bufalin measured by 2 in-house bufalin radioimmunoassays (RIAs). Recently, a 17-year-old Chinese female unintentionally took 100 (instead of 10) of these pills for a sore throat but suffered no ill effects. The blood bufalin concentration at 3 hours by 1 of the 2 RIAs was 10.93 nmol/L, which was commensurate with the dose. However, the apparent digoxin measured by a TDx II assay produced in 2004 was only 3.08 nmol/L, which probably reflects the change in the specificity of the polyclonal digoxin antisera used in the assay over the years. In 1989, the TDx assay was commended for its ability to detect poisoning from plant and animal cardenolides, a property that seems to be waning and, thus, bad news for those wishing to use the assay to detect alternative cardenolides. But, on the other hand, it possibly eliminates the "specter" of digoxin-like immunoreactive substance (DLIS) that has afflicted some digoxin assays, which can only be good news.

Fab antibody fragments: some applications in clinical toxicology

This review provides current information on the use of antigen-binding fragments (Fab) from cleaved antibodies to treat poisoning with digoxin and other potent, low formula mass poisons, such as colchicine and tricyclic antidepressants. Anti-digoxin Fab fragments have been used successfully for many years in the management of severe poisoning with digoxin, digitoxin, and a range of other structurally related compounds, including cardiotoxins from Nerium and Thevetia sp. (oleander) and Bufo sp. (toads). However, their main use remains treating digoxin poisoning. Equimolar doses of anti-digoxin Fab fragments completely bind digoxin in vivo. The approximate dose of Fab fragments (mg) is 80 times the digoxin body burden (mg). If neither the dose ingested nor the plasma digoxin/digitoxin concentration is known, in an adult 380 mg of anti-digoxin Fab fragments should be given. The dose for elderly patients or those with renal impairment should be similar to that for those with normal renal function. Fab fragments have a plasma half-life of 12-20 hours, but this can be prolonged in patients with renal impairment. Analysis of serum ultrafiltrate using an immunoassay shown not to have matrix bias remains the most accurate approach to measuring free digoxin in the presence of anti-digoxin Fab fragments. The antibody fragments are given intravenously over 15-30 minutes after dilution to at least 250 mL with plasma protein solution, 0.9% (w/v) sodium chloride, or deionised water, except in infants where the volume infused can be reduced. Factors limiting the efficacy of Fab fragments are the dose, the duration of the infusion and any delay in administration. Guidelines for Fab fragment administration in children include (i) dilution to a final Fab concentration of 10 g/L in either 5% (w/v) dextrose or 0.9% (w/v) sodium chloride; (ii) infusion through a 0.22 microm filter; (iii) administration of the total dose over a minimum of 30 minutes; and (iv) avoiding coadministration of other drugs and/or electrolyte solutions. Fab fragments are generally well tolerated. Adverse effects attributable to Fab treatment include hypokalaemia and exacerbation of congestive cardiac failure; renal function could be impaired in some patients. Fab fragment preparations for treating acute colchicine and tricyclic antidepressant poisoning have been developed, but are not available commercially. Colchicine poisoning is rare in Western countries, and pharmacological management together with supportive care is usually effective even in severe tricyclic antidepressant overdosage. Attempts have been made to produce anti-paraquat antibodies capable of enhancing paraquat elimination from the lung, but thus far all such attempts have proved unsuccessful.

Characterization of the neutralizing activity of digoxin-specific Fab toward ouabain-like steroids

Digoxin-specific Fab (Digibind) is a mixture of antidigoxin Fab fragments prepared from sheep sera and is used as a treatment for digoxin poisoning. Digoxin-specific Fab has been shown to neutralize an endogenous Na+/K+ ATPase inhibitor (endogenous digoxin-like Na+/K+ ATPase regulatory factor; EDLF) in rats and humans and to lower blood pressure. Although the exact structure of EDLF is unknown, compounds identical to or structurally related to ouabain, bufalin, and marinobufagenin have been detected in mammalian plasma. In this study, some structural characteristics of EDLF were inferred from the ability of digoxin-specific Fab to neutralize the Na+/K+ ATPase inhibitory activity of several known cardenolides and bufodienolides. Additional structural information was obtained from [3H]ouabain binding and enzyme-linked immunosorbent assay experiments. Digoxin-specific Fab had the ability to interact to some extent with all of the cardenolides and bufodienolides tested. However, digoxin-specific Fab was more than 20-fold more potent in neutralizing ouabain and bufalin than marinobufagenin. The antihypertensive effect of digoxin-specific Fab seen in preeclampsia and animal models of hypertension may therefore be due to a molecule identical to or structurally similar to ouabain or bufalin.

Cardioactive steroid poisoning from an herbal cleansing preparation

We describe a case of unintentional poisoning from a cardioactive steroid and the subsequent analytic investigation. A 36-year-old woman with no past medical history and taking no conventional medications ingested an herbal preparation marketed for "internal cleansing." Its ingredients were neither known to the patient nor listed on the accompanying literature. The next morning, nausea, vomiting, and weakness developed. In the emergency department, her blood pressure was 110/60 mm Hg, and her pulse rate was 30 beats/min. Her ECG revealed a junctional rhythm at a rate of 30 beats/min and a digitalis effect on the ST segments. After empiric therapy with 10 vials of digoxin-specific Fab (Digibind), her symptoms resolved, and she reverted to a sinus rhythm at a rate of 68 beats/min. Her serum digoxin concentration measured by means of the fluorescence polarization immunoassay (Abbott TDx) was 1.7 ng/mL. Further serum analysis with the Tina Quant digoxin assay, a more digoxin-specific immunoassay, found a concentration of 0.34 ng/mL, and an enzyme immunoassay for digitoxin revealed a concentration of 20 ng/mL (therapeutic range 10 to 30 ng/mL). Serum analysis by means of high-performance liquid chromatography revealed the presence of active digitoxin metabolites; the parent compound was not present. When the diagnosis of cardioactive steroid poisoning is suspected clinically, laboratory analysis can confirm the presence of cardioactive steroids by using immunoassays of varying specificity. An empiric dose of 10 vials of digoxin-specific Fab might be beneficial in patients poisoned with an unknown cardioactive steroid.

The Fab fragment of anti-digoxin antibody (digibind) binds digitoxin-like immunoreactive components of Chinese medicine Chan Su: monitoring the effect by measuring free digitoxin

Chan Su, a Chinese medicine prepared from the skin glands of Chinese toads, is used in the treatment of cardiovascular diseases. Severe toxicity and even death has been reported from overdose with Chan Su. The cardiotonic effect of Chan Su is attributed to bufadienolides, which also have apparent digitoxin activity. We demonstrated that these components of Chan Su could be neutralized by digibind, both in vitro and in vivo. For in vitro experiments, we supplemented drug-free serum pools with aqueous extract of Chan Su. Then, to aliquots of serum pool containing Chan Su, various amounts of digibind (10, 25 or 50 microg/ml of serum) were added. After incubation, total and free digitoxin concentrations (in the protein-free ultrafiltrate) were measured using the fluorescence polarization immunoassay (FPIA) and a FLX/TDx analyzer. For in vivo experiments, mice were fed with Chan Su by gavage. After 45 min, 200 microg of digibind was administered by injection. Fifteen minutes after injection, blood was collected for analysis of total and free apparent digitoxin activities. We observed complete removal of apparent digitoxin activity from protein-free ultrafiltrate both in vitro and in vivo by digibind, indicating that digibind successfully binds Chan Su. We conclude that digibind neutralizes Chan Su, and measuring the free digitoxin concentrations can monitor such an effect.

Effects of resibufogenin from toad venom on isolated Purkinje fibers

Chan su (dried toad venom) is a traditional Chinese medicine obtained from the skin venom gland of the toad. Chan su has long been used as a therapeutic agent in China and other Asian countries. Recent reports indicate that Chan su toxicity carries a high mortality rate in the United States. This study focused upon the cardiac electrophysiological and electro-toxicity effects of resibufogenin (RBG), one of the major components in Chan su. Action potentials of isolated sheep and canine heart Purkinje fibers were studied using glass microelectrode recording techniques. The results indicate that RBG significantly affected all parameters of transmembrane action potential, induced delayed after depolarization, and triggered arrhythmias in sheep and canine Purkinje fibers.

Multiresidue screen for cardiotoxins by two-dimensional thin-layer chromatography

A two-dimensional thin-layer chromatographic method was developed for the qualitative determination of the cardiotoxins oleandrin, gitoxin, digitoxin, gitoxigenin, and grayanotoxins I, II, and III in gastrointestinal contents (stomach, rumen, colon, and cecum contents), feces, and plant material. The cardiotoxins were extracted with dichloromethane. The extract was cleaned up by charcoal and reverse phase solid-phase extraction columns. Analysis was performed by two-dimensional thin-layer chromatography on silica gel plates and visualized by aluminum chloride followed by chloramine T spray. The method detection limits were 0.05 microg/g for oleandrin, 0.1 microg/g for gitoxin, and 0.2 microg/g for the other toxicants in gastrointestinal contents and feces and were 5 times higher in plant material. Four replicate fortifications of bovine rumen contents, bovine feces, and alfalfa at these levels were all well recovered. The diagnostic utility of the method was tested by analyzing samples submitted to the veterinary toxicology laboratory.