Solubility of digitoxin in supercritical CO2: Experimental study and modeling

In this communication, the solubility of digitoxin drug in supercritical CO2 was studied at different operating conditions (311 < T (K) < 343, 120 < P (bar) < 300). The results revealed digitoxin drug solubility (in mole fraction) was between 0.095 × 10-5 to 1.12 × 10-5. In the case of thermodynamic solubility modeling, cubic and non-cubic equation of states i.e. SAFT (statistical associating fluid theory), SRK (Soave-Redlich-Kwong) and sPC-SAFT (simplified perturbed chain SAFT) EoSs and six density-based correlations (Chrastil, Kumar-Johnston (KJ), Mendez-Santiago-Teja (MST), Garlapati and Madras (GM), Bartle et al. and Sung-Shim models) were considered. All used equations indicated reasonable behavior with appropriate accuracy for the solubility of the digitoxin drug. Meanwhile, sPC-SAFT EoS and Kumar-Johnston correlation with AARD% set to 8.96 % and 6.25 %, respectively exhibited greater accuracy in fitting the solubility data. Moreover, total, solvation and vaporization enthalpies of the digitoxin/supercritical carbon dioxide binary mixture were calculated based on KJ, Chrastil and Bartle et al. models.

Simple and safe digitoxin dosing in heart failure based on data from the DIGIT-HF trial

BACKGROUND

The present study aimed to develop a simple dosing score when starting the cardiac glycoside digitoxin in heart failure with reduced ejection fraction (HFrEF) employing first data from the randomized, double-blinded DIGIT-HF trial.

METHODS AND RESULTS

In DIGIT-HF, digitoxin was started with a dose of 0.07 mg once daily (o.d.) in all patients. For score derivation, 317 patients were analyzed who had been randomized to digitoxin. In these patients, after scheduled determination of serum levels at study week 6, the digitoxin dose had remained unchanged or had been reduced to 0.05 mg o.d. (97% of patients) to achieve serum concentrations within a predefined range (10.5-23.6 nmol/l). In logistic regression analyses, sex, age, body mass index (BMI), and estimated glomerular filtration rate (eGFR) were associated with need for dose reduction and, therefore, selected for further developing the dosing score. Optimal cut-points were derived from ROC curve analyses. Finally, female sex, age ≥ 75 years, eGFR < 50 ml/min/1.73 m², and BMI < 27 kg/m² each were assigned one point for the digitoxin dosing score. A score of ≥ 1 indicated the need for dose reduction with sensitivity/specificity of 81.6%/49.7%, respectively. Accuracy was confirmed in a validation data set including 64 patients randomized to digitoxin yielding sensitivity/specificity of 87.5%/37.5%, respectively.

CONCLUSION

In patients with HFrEF, treatment with digitoxin should be started at 0.05 mg o.d. in subjects with either female sex, eGFR < 50 ml/min/1.73m², BMI < 27 kg/m², or age ≥ 75 years. In any other patient, digitoxin may be safely started at 0.07 mg o.d.

Interaction of Odoroside A, A Known Natural Cardiac Glycoside, with Na+/K+-ATPase

The nature of odoroside A, a cardiac glycoside (CG) extracted from Nerium oleander, as well as its chemical structure is quite similar to a well-known CG, ouabain possessing a steroid skeleton, a five-membered unsaturated lactone ring, and a sugar moiety as a common structure. Like ouabain, odoroside A inhibits the activity of Na⁺/K⁺-ATPase (NKA) and shows significant anticancer activity, however its inhibitory mechanism remains unknown. CGs show various physiological activities, including cardiotonic and anticancer activities, through the inhibition of NKA by direct interaction. Additionally, X-ray crystallographic analysis revealed the inhibitory mechanism of ouabain and digoxin in relation to NKA. By using different molecular modeling techniques, docking simulation of odoroside A and NKA was conducted based on the results of these X-ray crystallographic analyses. Furthermore, a comparison of the results with the binding characteristics of three known CGs (ouabain, digoxin, and digitoxin) was also conducted. Odoroside A fitted into the CG binding pocket on the α-subunit of NKA revealed by X-ray crystallography. It had key interactions with Thr797 and Phe783. Also, three known CGs showed similar interactions with Thr797 and Phe783. Interaction modes of odoroside A were quite similar to those of ouabain, digoxin, and digitoxin. Docking simulations indicated that the sugar moiety enhanced the interaction between NKA and CGs, but did not show enhanced NKA inhibitory activity because the sugar moiety was placed outside the entrance of active site. Thus, these results suggest that the inhibitory mechanism of odoroside A to NKA is the same as the known CGs.

Quantification of plant cardenolides by HPLC, measurement of Na(+)/K(+)-ATPase inhibition activity, and characterization of target enzymes

The biosynthesis of cardiac glycosides, broadly classified as cardenolides and bufadienolides, has evolved repeatedly among flowering plants. Individual species can produce dozens or even hundreds of structurally distinct cardiac glycosides. Although all cardiac glycosides exhibit biological activity by inhibiting the function of the essential Na⁺/K⁺-ATPase in animal cells, they differ in their level of inhibitory activity. For within- and between-species comparisons of cardiac glycosides to address ecological and evolutionary questions, it is necessary to not only quantify their relative abundance, but also their effectiveness in inhibiting the activity of different animal Na⁺/K⁺-ATPases. Here we describe protocols for characterizing the amount and toxicity of cardenolides from plant samples and the degree of insect Na⁺/K⁺-ATPase tolerance to inhibition: (1) an HPLC-based assay to quantify the abundance of individual cardenolides in plant extracts, (2) an assay to quantify inhibition of Na⁺/K⁺-ATPase activity by plant extracts, and (3) extraction of insect Na⁺/K⁺-ATPases for inhibition assays.

Gender differences and pharmacological regulation of angiogenesis induced by synovial fluids in inflammatory arthritis

Several mediators including cytokines, growth factors and metalloproteinases (MMP) modulate pathological angiogenesis associated with inflammatory arthritis. The biological factors underlying sex disparities in the incidence and severity of rheumatic musculoskeletal diseases are only partially understood. We hypothesized that synovial fluids (SFs) from rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients would impact on endothelial biology in a sexually dimorphic fashion. Immune cell counts and levels of pro-angiogenic cytokines found in SFs from RA and PsA patients (n = 17) were higher than in osteoarthritis patients (n = 6). Synovial VEGF concentration was significantly higher in male than in female RA patients. Zymography revealed that SFs comprised solely MMP-9 and MMP-2, with significantly higher MMP-9 levels in male than female RA patients. Using in vitro approaches that mimic the major steps of the angiogenic process, SFs from RA and PsA patients induced endothelial migration and formation of capillary-like structures compared to control. Notably, endothelial cells from female donors displayed enhanced angiogenic response to SFs with respect to males. Treatment with the established anti-angiogenic agent digitoxin prevented activation of focal adhesion kinase and SF-induced in vitro angiogenesis. Thus, despite higher synovial VEGF and MMP-9 levels in male patients, the responsiveness of vascular endothelium to SF priming was higher in females, suggesting that gender differences in angiogenic responses were mainly related to the endothelial genotype. These findings may have implications for pathogenesis and targeted therapies of inflammatory arthritis.

Digitoxin promotes apoptosis and inhibits proliferation and migration by reducing HIF-1α and STAT3 in KRAS mutant human colon cancer cells

Colon cancer patients with mutant KRAS are resistant to cetuximab, an antibody directed against the epidermal growth factor receptor. New treatment options are needed to improve survival in patients with KRAS mutated colorectal cancer. Digitoxin is a cardiotonic drug, which has been demonstrated to exhibit anticancer effects in a number of cancers. However, the anticancer mechanisms of digitoxin in KRAS mutant human colon cancer cells remain elusive. Our result demonstrated that digitoxin but not cetuximab markedly decreased the expression of hypoxia-inducible factor-1α (HIF-1α), signal transducer and activator of transcription 3 (STAT3) and p-STAT3 protein in KRAS mutant colon cancer cells. Further analysis revealed that digitoxin inhibited HIF-1α protein synthesis, without affecting the expression level of HIF-1α mRNA or degradation of HIF-1α protein. The phosphorylation levels of ribosomal protein S6 kinase (p70S6K) and eIF4E binding protein-1 (4E-BP1) were significantly suppressed by digitoxin. Digitoxin inhibited the expression and activation of STAT3 through upregulation of phosphatase and tensin homolog deleted on chromosome ten (PTEN), SHP1 and protein inhibitors of activated STAT3 (PIAS3) and direct binding to STAT3. Meanwhile, digitoxin inhibited HIF-1α in STAT3-independent manner in KRAS mutant colon cancer cells. Moreover, digitoxin promoted apoptosis and inhibited proliferation and migration, which was potentially mediated by suppression of HIF-1α and STAT3. We also found that digitoxin administration inhibited tumor growth in a mouse xenograft model. Taken together, our findings highlight the therapeutic potential of digitoxin for the treatment of cetuximab-resistant human colon cancer.

The Natural Product β-Escin Targets Cancer and Stromal Cells of the Tumor Microenvironment to Inhibit Ovarian Cancer Metastasis

Simple Summary

β-escin, a component of horse chestnut seed extract, was first identified as an inhibitor of ovarian cancer (OvCa) adhesion/invasion in our high-throughput screening program using a three-dimensional organotypic model assembled from primary human cells and extracellular matrix. The goal of the study presented here is to determine if β-escin and structurally-similar compounds have a therapeutic potential against OvCa metastasis. β-escin and cardiac glycosides inhibit ovarian cancer adhesion/invasion to the omental microenvironment in vivo, and β-escin inhibits ovarian cancer metastasis in the prevention and intervention setting. Additionally, β-escin was found to decrease the stemness of ovarian cancer cells, inhibit extracellular matrix production in the tumor microenvironment, and inhibit HIF1α stability in ovarian cancer cells and the tumor microenvironment. This study reveals that the natural compound β-escin has therapeutic potential because of its ability to prevent OvCa dissemination by targeting both cancer and stromal cells in the OvCa tumor microenvironment.

Abstract

The high mortality of OvCa is caused by the wide dissemination of cancer within the abdominal cavity. OvCa cells metastasize to the peritoneum, which is covered by mesothelial cells, and invade into the underlying stroma, composed of extracellular matrices (ECM) and stromal cells. In a study using a three-dimensional quantitative high-throughput screening platform (3D-qHTS), we found that β-escin, a component of horse chestnut seed extract, inhibited OvCa adhesion/invasion. Here, we determine whether β-escin and structurally similar compounds have a therapeutic potential against OvCa metastasis. Different sources of β-escin and horse chestnut seed extract inhibited OvCa cell adhesion/invasion, both in vitro and in vivo. From a collection of 160 structurally similar compounds to β-escin, we found that cardiac glycosides inhibited OvCa cell adhesion/invasion and proliferation in vitro, and inhibited adhesion/invasion and metastasis in vivo. Mechanistically, β-escin and the cardiac glycosides inhibited ECM production in mesothelial cells and fibroblasts. The oral administration of β-escin inhibited metastasis in both OvCa prevention and intervention mouse models. Specifically, β-escin inhibited ECM production in the omental tumors. Additionally, the production of HIF1α-targeted proteins, lactate dehydrogenase A, and hexokinase 2 in omental tumors was blocked by β-escin. This study reveals that the natural compound β-escin has a therapeutic potential because of its ability to prevent OvCa dissemination by targeting both cancer and stromal cells in the OvCa tumor microenvironment.

Successful Treatment of Severe Digitoxin Intoxication with CytoSorb® Hemoadsorption

While several intoxications can be successfully treated with specific antidotes, intoxications with the steroid glycoside digitoxin still represent a major challenge. Besides conventional approaches, CytoSorb® hemoadsorption might be another treatment option. We report on an 81-year-old female patient treated in our intensive care unit (ICU) with severe digitoxin intoxication, acute renal failure, and urinary tract infection (UTI). As physiological digitoxin elimination kinetics are known to appear slow, and also in regard to the renal failure, the decision was made to initiate continuous renal replacement therapy combined with CytoSorb hemoadsorption. The patient was hemodynamically stabilized within the first 4 h of treatment and initially required catecholamines to be stopped within 24 h of treatment. Pre- and post-adsorber drug level measurements showed a rapid elimination of digitoxin. Antibiotic treatment with piperacillin/tazobactam was initiated, and despite CytoSorb hemoadsorption therapy and its known potential to reduce plasma concentrations of several drugs, the UTI was successfully treated. After 3 days of CytoSorb treatment, digitoxin plasma levels were stable and almost normalized, and no clinical signs of intoxication were present. Five days after presentation, the patient was transferred from the ICU in a stable condition. CytoSorb hemoadsorption may be an easily available, efficient, and less cost-intensive therapy option than treatment with the Fab fragment, which is the currently recommended therapy for digitalis intoxications. Therefore, the use of CytoSorb might represent an alternative treatment for life-threatening complications of digitoxin intoxications.

Potential antitumor activity of digitoxin and user-designed analog administered to human lung cancer cells

BACKGROUND

Cardiac glycosides (CGs), such as digitoxin, are traditionally used for treatment of congestive heart failure; recently they also gained attention for their anticancer properties. Previous studies showed that digitoxin and a synthetic L-sugar monosaccharide analog treatment decreases cancer cell proliferation, increases apoptosis, and pro-adhesion abilities; however, no reports are available on their potential to alter lung cancer cell cytoskeleton structure and reduce migratory ability. Herein, we investigated the anticancer effects of digitoxin and its analog, digitoxigenin-α-L-rhamnoside (D6MA), to establish whether cytoskeleton reorganization and reduced motility are drug-induced cellular outcomes.

METHODS

We treated non-small cell lung carcinoma cells (NSCLCs) with sub-therapeutic, therapeutic, and toxic concentrations of digitoxin and D6MA respectively, followed by both single point and real-time assays to evaluate changes in cellular gene and protein expression, adhesion, elasticity, and migration.

RESULTS

Digitoxin and D6MA induced a decrease in matrix metalloproteinases expression via altered focal adhesion signaling and a suppression of the phosphoinositide 3-kinases / protein kinase B pathway which lead to enhanced adhesion, altered elasticity, and reduced motility of NSCLCs. Global gene expression analysis identified dose-dependent changes to nuclear factor kappa-light-chain-enhancer, epithelial tumor, and microtubule dynamics signaling.

CONCLUSIONS

Our study demonstrates that digitoxin and D6MA can target antitumor signaling pathways to alter NSCLC cytoskeleton and migratory ability to thus potentially reduce their tumorigenicity.

SIGNIFICANCE

Discovering signaling pathways that control cancer's cell phenotype and how such pathways are affected by CG treatment will potentially allow for active usage of synthetic CG analogs as therapeutic agents in advanced lung conditions.

Combined amiodarone and digitalis therapy before heart transplantation is associated with increased post-transplant mortality

Aims

Amiodarone and digitalis are frequently used drugs in patients with heart failure. Both have separately been linked to reduced post‐transplant survival, but their combined impact on mortality after HTX remains uncertain. This study investigated the effects of combined amiodarone and digitalis use before HTX on post‐transplant outcomes.

Methods and results

This registry study analysed 600 patients receiving HTX at Heidelberg Heart Center between 1989 and 2016. Patients were stratified by amiodarone and digitalis use before HTX. Analysis included patient characteristics, medication, echocardiographic features, heart rates, permanent pacemaker implantation, atrial fibrillation, and post‐transplant survival including causes of death. One hundred eighteen patients received amiodarone before HTX (19.7%), hereof 67 patients with digitalis (56.8%) and 51 patients without digitalis before HTX (43.2%). Patients with and without amiodarone before HTX showed a similar 1 year post‐transplant survival (72.0% vs. 78.4%, P = 0.11), but patients with combined amiodarone and digitalis before HTX had a worse 1 year post‐transplant survival (64.2%, P = 0.01), along with a higher percentage of death due to transplant failure (P = 0.03). Echocardiographic analysis of these patients showed a higher percentage of an enlarged right ventricle (P = 0.02), left atrium (P = 0.02), left ventricle (P = 0.03), and a higher rate of reduced left ventricular ejection fraction (P = 0.03). Multivariate analysis indicated combined amiodarone and digitalis use before HTX as a significant risk factor for 1 year mortality after HTX (hazard ratio: 1.69; 95% confidence interval: 1.02–2.77; P = 0.04).

Conclusions

Combined pre‐transplant amiodarone and digitalis therapy is associated with increased post‐transplant mortality.

Gene therapy-emulating small molecule treatments in cystic fibrosis airway epithelial cells and patients

Background

Several small molecule corrector and potentiator drugs have recently been licensed for Cystic Fibrosis (CF) therapy. However, other aspects of the disease, especially inflammation, are less effectively treated by these drugs. We hypothesized that small molecule drugs could function either alone or as an adjuvant to licensed therapies to treat these aspects of the disease, perhaps emulating the effects of gene therapy in CF cells. The cardiac glycoside digitoxin, which has been shown to inhibit TNFα/NFκB signaling in CF lung epithelial cells, may serve as such a therapy.

Methods

IB3–1 CF lung epithelial cells were treated with different Vertex (VX) drugs, digitoxin, and various drug mixtures, and ELISA assays were used to assess suppression of baseline and TNFα-activated secretion of cytokines and chemokines. Transcriptional responses to these drugs were assessed by RNA-seq and compared with gene expression in AAV-[wildtype]CFTR-treated IB3–1 (S9) cells. We also compared in vitro gene expression signatures with in vivo data from biopsied nasal epithelial cells from digitoxin-treated CF patients.

Results

CF cells exposed to digitoxin exhibited significant suppression of both TNFα/NFκB signaling and downstream secretion of IL-8, IL-6 and GM-CSF, with or without co-treatment with VX drugs. No evidence of drug-drug interference was observed. RNA-seq analysis showed that gene therapy-treated CF lung cells induced changes in 3134 genes. Among these, 32.6% were altered by digitoxin treatment in the same direction. Shared functional gene ontology themes for genes suppressed by both digitoxin and gene therapy included inflammation (84 gene signature), and cell-cell interactions and fibrosis (49 gene signature), while genes elevated by both were enriched for epithelial differentiation (82 gene signature). A new analysis of mRNA data from digitoxin-treated CF patients showed consistent trends in expression for genes in these signatures.

Conclusions

Adjuvant gene therapy-emulating activities of digitoxin may contribute to enhancing the efficacy of currently licensed correctors and potentiators in CF patients.

Rationale and design of the DIGIT-HF trial (DIGitoxin to Improve ouTcomes in patients with advanced chronic Heart Failure): a randomized, double-blind, placebo-controlled study

AIMS

Despite recent advances in the treatment of chronic heart failure (HF), mortality and hospitalizations still remain high. Additional therapies to improve mortality and morbidity are urgently needed. The efficacy of cardiac glycosides - although regularly used for HF treatment - remains unclear. DIGIT-HF was designed to demonstrate that digitoxin on top of standard of care treatment improves mortality and morbidity in patients with HF and a reduced ejection fraction (HFrEF).

METHODS

Patients with chronic HF, New York Heart Association (NYHA) functional class III-IV and left ventricular ejection fraction (LVEF) ≤ 40%, or patients in NYHA functional class II and LVEF ≤ 30% are randomized 1:1 in a double-blind fashion to treatment with digitoxin (target serum concentration 8-18 ng/mL) or matching placebo. Randomization is stratified by centre, sex, NYHA functional class (II, III, or IV), atrial fibrillation, and treatment with cardiac glycosides at baseline. A total of 2190 eligible patients will be included in this clinical trial (1095 per group). All patients receive standard of care treatment recommended by expert guidelines upon discretion of the treating physician. The primary outcome is a composite of all-cause mortality or hospital admission for worsening HF (whatever occurs first). Key secondary endpoints are all-cause mortality, hospital admission for worsening HF, and recurrent hospital admission for worsening HF.

CONCLUSION

The DIGIT-HF trial will provide important evidence, whether the cardiac glycoside digitoxin reduces the risk for all-cause mortality and/or hospital admission for worsening HF in patients with advanced chronic HFrEF on top of standard of care treatment.

Compound Library Screening Identified Cardiac Glycoside Digitoxin as an Effective Growth Inhibitor of Gefitinib-Resistant Non-Small Cell Lung Cancer via Downregulation of α-Tubulin and Inhibition of Microtubule Formation

Non-small-cell lung cancer (NSCLC) dominates over 85% of all lung cancer cases. Epidermal growth factor receptor (EGFR) activating mutation is a common situation in NSCLC. In the clinic, molecular-targeting with Gefitinib as a tyrosine kinase inhibitor (TKI) for EGFR downstream signaling is initially effective. However, drug resistance frequently happens due to additional mutation on EGFR, such as substitution from threonine to methionine at amino acid position 790 (T790M). In this study, we screened a traditional Chinese medicine (TCM) compound library consisting of 800 single compounds in TKI-resistance NSCLC H1975 cells, which contains substitutions from leucine to arginine at amino acid 858 (L858R) and T790M mutation on EGFR. Attractively, among these compounds there are 24 compounds CC50 of which was less than 2.5 μM were identified. We have further investigated the mechanism of the most effective one, Digitoxin. It showed a significantly cytotoxic effect in H1975 cells by causing G2 phase arrest, also remarkably activated 5' adenosine monophosphate-activated protein kinase (AMPK). Moreover, we first proved that Digitoxin suppressed microtubule formation through decreasing α-tubulin. Therefore, it confirmed that Digitoxin effectively depressed the growth of TKI-resistance NSCLC H1975 cells by inhibiting microtubule polymerization and inducing cell cycle arrest.

Xysmalobium undulatum (uzara) - review of an antidiarrhoeal traditional medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Xysmalobium undulatum, commonly known as uzara, is traditionally used as an antidiarrhoeal and to treat stomach cramps, dysmenorrhoea and afterbirth cramps. In addition, it was reportedly used to treat anxiety and other conditions relating to mental health.

AIM OF THE REVIEW

To unite the botanical aspects, ethnopharmacology, phytochemistry, biological activity, pharmacokinetic and pharmacodynamic data, toxicity and commercial aspects of the scientific literature available on uzara.

METHOD

An extensive review of the literature covering 1917-2014 was carried out. Electronic databases including Scopus, Pubmed, Google Scholar and Google were used to assemble the data. All abstracts, full-text articles and books written in English and German were examined and included.

RESULTS

The phytochemistry of uzara has been comprehensively investigated and at least 18 compounds have been isolated and characterised. Uzara contains mainly cardenolide glycosides such as uzarin and xysmalorin and cardenolide aglycones such as uzarigenin and xysmalogenin. Limited scientific studies on the biological activity of uzara have been done. In vitro antisecretory antidiarrhoeal action was confirmed. Central nervous system activity was conflicting, in vitro and in vivo (animals) studies were inconclusive and no clinical studies have been performed. No antimutagenic effects have been reported and no toxicity up to date has been associated with uzara consumption. Significant cross-reactivity of uzara compounds with commercial digoxin and digitoxin assays may interfere with therapeutic drug monitoring.

CONCLUSIONS

The key traditional uses associated with uzara have been investigated in vitro and in vivo (animal), but clinical trial data is lacking.

Real-time analysis of the effects of toxic, therapeutic and sub-therapeutic concentrations of digitoxin on lung cancer cells

Digitoxin belongs to a naturally occurring class of cardiac glycosides (CG); digitoxin is clinically approved for heart failure and known for its anti-cancer effects against non-small lung cancer cells (NSCLC). However, concerns associated with its narrow therapeutic index and its concentration-dependent mechanism of action are rising. Thus, before digitoxin implementation in designing and developing safer and more effective CG-based anti-cancer therapies, its pharmacological and safety profiles need to be fully elucidated. In this research we used a combinatorial approach to evaluate the anti-cancer mechanisms of digitoxin in real-time. Our approach employed a non-invasive electric cell impedance sensing technique as a proxy to monitor NSCLC behavior post-exposure to toxic, therapeutic and sub-therapeutic concentrations of the drug. By developing structure-function combinatorial relations we showed that digitoxin targets cancer cells in a time and dose-dependant manner by activating pro-apoptotic and anti-proliferative signaling cascades that results in strengthening cellular adhesion and sequestration of key regulatory proliferation protein from the nucleus.

Evaluation of a straightforward and rapid method for the therapeutic drug monitoring of digitoxin by LC-MS/MS

OBJECTIVES

Therapeutic drug monitoring of digitoxin is strongly recommended but metabolites of digitoxin and digitoxin-like immunoreactive substances may interfere with widely used immunoassays. Recently evaluated assays on LC-MS/MS have the drawback of long turnaround time. We sought to evaluate a specific method on LC-MS/MS optimizing sample preparation thereby significantly reducing turnaround time.

DESIGN AND METHODS

Linearity, functional sensitivity, and precision of the method were established. External quality control samples were used for the evaluation of accuracy of the LS-MS/MS method. In addition, digitoxin concentrations in 221 samples were measured by LC-MS/MS and immunoassay.

RESULTS

Linearity was validated between 0.15 and 80 ng/mL. Limit of quantification was established at 0.14 ng/mL. Between-day imprecision lay between 1.4 and 4.9% and meets the conditions required for routine analysis. Comparison to results obtained by immunoassay revealed a mean difference of -1.2 ng/mL.

CONCLUSIONS

By optimizing preparation steps turnaround time was shorter for LC-MS/MS than for immunoassay. This did not result in increased susceptibility to matrix effects. Analytical performance was sufficient for routine analysis. Therefore, the method is suitable for routine therapeutic drug monitoring of digitoxin.

Determination of digitoxin and digoxin contents in first and second passage calli and organ redifferentiating calli of several Digitalis species by radioimmunoassay

With first and second passage calli induced from seedlings of Digitalis purpurea, D. lanata, D. lutea, D. mertonensis, D. ambigua and D. ferruginea Gigantea and those induced from leaf discs of D. purpurea and D. lanata, the contents of digitoxin and digoxin equivalents were assayed and compared with the contents involved in the inocula. Although the total contents of digitoxin and digoxin equivalents in the first passage calli induced from seedlings varied between zero and nine times as high as in the original seedlings, those in the second passage calli were almost undetectable. The total contents of digitoxin equivalents in the first passage calli induced from leaf discs of D. purpurea were approximately equal to those in the original leaf discs, but those in the second passage calli were less than those in the inocula. In the first passage calli induced from leaf discs of D. lanata, the total contents of digitoxin equivalents decreased but those of digoxin equivalents slightly increased. However, in the second passage calli, the amounts of both cardenolides decreased. Root-forming calli accumulated no more digitoxin nor digoxin equivalents than completely dedifferentiated calli. However, shoot-forming calli accumulated considerable amounts of cardenolides, which were assayed as digitoxin and digoxin equivalents by radioimmunoassay.