Sensational site: the sodium pump ouabain-binding site and its ligands

Cardiotonic steroids (CTS), used by certain insects, toads, and rats for protection from predators, became, thanks to Withering's trailblazing 1785 monograph, the mainstay of heart failure (HF) therapy. In the 1950s and 1960s, we learned that the CTS receptor was part of the sodium pump (NKA) and that the Na+/Ca2+ exchanger was critical for the acute cardiotonic effect of digoxin- and ouabain-related CTS. This "settled" view was upended by seven revolutionary observations. First, subnanomolar ouabain sometimes stimulates NKA while higher concentrations are invariably inhibitory. Second, endogenous ouabain (EO) was discovered in the human circulation. Third, in the DIG clinical trial, digoxin only marginally improved outcomes in patients with HF. Fourth, cloning of NKA in 1985 revealed multiple NKA α and β subunit isoforms that, in the rodent, differ in their sensitivities to CTS. Fifth, the NKA is a cation pump and a hormone receptor/signal transducer. EO binding to NKA activates, in a ligand- and cell-specific manner, several protein kinase and Ca2+-dependent signaling cascades that have widespread physiological effects and can contribute to hypertension and HF pathogenesis. Sixth, all CTS are not equivalent, e.g., ouabain induces hypertension in rodents while digoxin is antihypertensinogenic ("biased signaling"). Seventh, most common rodent hypertension models require a highly ouabain-sensitive α2 NKA and the elevated blood pressure is alleviated by EO immunoneutralization. These numerous phenomena are enabled by NKA's intricate structure. We have just begun to understand the endocrine role of the endogenous ligands and the broad impact of the ouabain-binding site on physiology and pathophysiology.

Effects of Cardiac Glycoside Digoxin on Dendritic Spines and Motor Learning Performance in Mice

Synapse formation following the generation of postsynaptic dendritic spines is essential for motor learning and functional recovery after brain injury. The C-terminal fragment of agrin cleaved by neurotrypsin induces dendritic spine formation in the adult hippocampus. Since the α3 subunit of sodium-potassium ATPase (Na/K ATPase) is a neuronal receptor for agrin in the central nervous system, cardiac glycosides might facilitate dendritic spine formation and subsequent improvements in learning. This study investigated the effects of cardiac glycoside digoxin on dendritic spine turnover and learning performance in mice. Golgi-Cox staining revealed that intraperitoneal injection of digoxin less than its IC50 in the brain significantly increased the density of long spines (≥2 µm) in the cerebral cortex in wild-type mice and neurotrypsin-knockout (NT-KO) mice showing impairment of activity-dependent spine formation. Although the motor learning performance of NT-KO mice was significantly lower than control wild-type mice under the control condition, low doses of digoxin enhanced performance to a similar degree in both strains. In NT-KO mice, lower digoxin doses equivalent to clinical doses also significantly improved motor learning performance. These data suggest that lower doses of digoxin could modify dendritic spine formation or recycling and facilitate motor learning in compensation for the disruption of neurotrypsin-agrin pathway.

Digoxin protects against intervertebral disc degeneration via TNF/NF-κB and LRP4 signaling

Background

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain (LBP). The pathological process of IVDD is associated with inflammatory reactions and extracellular matrix (ECM) disorders. Digoxin is widely used for treating heart failure, and it has been reported to have anti-inflammatory effects.

Objective

This study is to investigate the role of digoxin in the pathogenesis of intervertebral disc degeneration as well as the involved molecular mechanism, particularly the potential target protein.

Methods

We exploited a rat needle model to investigate digoxin's role in intervertebral disc degeneration in vivo. Safranin O staining was used to measure cartilaginous tissue in the intervertebral disc. The morphological changes of intervertebral discs in animal models were determined by Hematoxylin-Eosin (H&E) staining and the pathological score. Primary nucleus pulposus cells (NP cells) from intervertebral discs of patients and murine were used in the present study. Western-Blotting assay, Real-time PCR assay, immunofluorescence staining, and immunochemistry were used to detect the role of digoxin in anti-TNF-α-induced inflammatory effects in vitro. Transfection of siRNA was used to regulate low-density lipoprotein receptor-related protein 4 (LRP4) expression in NP cells to investigate the potential protein target of digoxin.

Results

Digoxin protected against intervertebral disc degeneration in rat needle models. Digoxin was found to exert its disc-protective effects through at least three different pathways by a) suppressing TNF-α-induced inflammation, b) attenuating ECM destruction, c) significantly promoting ECM anabolism. Additionally, LRP4 was found to be the downstream molecule of digoxin in NP cells for anti-inflammation and regulation of ECM metabolism. The knockdown of LRP4 downregulated the protective effect of digoxin in NP cells.

Conclusion

These findings suggest that digoxin may be a potential therapeutic agent for intervertebral disc degeneration through anti-catabolism and pro-anabolism. Digoxin might also work as an alternative for other inflammation-related diseases.

Liver lipophagy ameliorates nonalcoholic steatohepatitis through extracellular lipid secretion

Nonalcoholic steatohepatitis (NASH) is a progressive disorder with aberrant lipid accumulation and subsequent inflammatory and profibrotic response. Therapeutic efforts at lipid reduction via increasing cytoplasmic lipolysis unfortunately worsens hepatitis due to toxicity of liberated fatty acid. An alternative approach could be lipid reduction through autophagic disposal, i.e., lipophagy. We engineered a synthetic adaptor protein to induce lipophagy, combining a lipid droplet-targeting signal with optimized LC3-interacting domain. Activating hepatocyte lipophagy in vivo strongly mitigated both steatosis and hepatitis in a diet-induced mouse NASH model. Mechanistically, activated lipophagy promoted the excretion of lipid from hepatocytes, thereby suppressing harmful intracellular accumulation of nonesterified fatty acid. A high-content compound screen identified alpelisib and digoxin, clinically-approved compounds, as effective activators of lipophagy. Administration of alpelisib or digoxin in vivo strongly inhibited the transition to steatohepatitis. These data thus identify lipophagy as a promising therapeutic approach to prevent NASH progression.

The Cytotoxic Cardiac Glycoside (-)-Cryptanoside A from the Stems of Cryptolepis dubia and Its Molecular Targets

A cardiac glycoside epoxide, (-)-cryptanoside A (1), was isolated from the stems of Cryptolepis dubia collected in Laos, for which the complete structure was confirmed by analysis of its spectroscopic and single-crystal X-ray diffraction data, using copper radiation at a low temperature. This cardiac glycoside epoxide exhibited potent cytotoxicity against several human cancer cell lines tested, including HT-29 colon, MDA-MB-231 breast, OVCAR3 and OVCAR5 ovarian cancer, and MDA-MB-435 melanoma cells, with the IC50 values found to be in the range 0.1-0.5 μM, which is comparable with that observed for digoxin. However, it exhibited less potent activity (IC50 1.1 μM) against FT194 benign/nonmalignant human fallopian tube secretory epithelial cells when compared with digoxin (IC50 0.16 μM), indicating its more selective activity toward human cancer versus benign/nonmalignant cells. (-)-Cryptanoside A (1) also inhibited Na+/K+-ATPase activity and increased the expression of Akt and the p65 subunit of NF-κB but did not show any effects on the expression of PI3K. A molecular docking profile showed that (-)-cryptanoside A (1) binds to Na+/K+-ATPase, and thus 1 may directly target Na+/K+-ATPase to mediate its cancer cell cytotoxicity.

Digoxin as an emerging therapy in noncardiac diseases

The cardiac glycoside (CG) digoxin is a generic drug approved for the treatment of heart failure and supraventricular arrhythmias. Over the past few decades, substantial strides have been made toward repurposing digoxin to treat various noncardiac diseases. Here, we evaluate recent insights into basic and clinical work related to noncardiac use of digoxin.

New uses for an old remedy: Digoxin as a potential treatment for steatohepatitis and other disorders

Repurposing of the widely available and relatively cheap generic cardiac gly-coside digoxin for non-cardiac indications could have a wide-ranging impact on the global burden of several diseases. Over the past several years, there have been significant advances in the study of digoxin pharmacology and its potential non-cardiac clinical applications, including anti-inflammatory, antineoplastic, metabolic, and antimicrobial use. Digoxin holds promise in the treatment of gastrointestinal disease, including nonalcoholic steatohepatitis and alcohol-associated steatohepatitis as well as in obesity, cancer, and treatment of viral infections, among other conditions. In this review, we provide a summary of the clinical uses of digoxin to date and discuss recent research on its emerging applications.

Human Retinal Organoids Provide a Suitable Tool for Toxicological Investigations: A Comprehensive Validation Using Drugs and Compounds Affecting the Retina

Retinal drug toxicity screening is essential for the development of safe treatment strategies for a large number of diseases. To this end, retinal organoids derived from human pluripotent stem cells (hPSCs) provide a suitable screening platform due to their similarity to the human retina and the ease of generation in large-scale formats. In this study, two hPSC cell lines were differentiated to retinal organoids, which comprised all key retinal cell types in multiple nuclear and synaptic layers. Single-cell RNA-Seq of retinal organoids indicated the maintenance of retinal ganglion cells and development of bipolar cells: both cell types segregated into several subtypes. Ketorolac, digoxin, thioridazine, sildenafil, ethanol, and methanol were selected as key compounds to screen on retinal organoids because of their well-known retinal toxicity profile described in the literature. Exposure of the hPSC-derived retinal organoids to digoxin, thioridazine, and sildenafil resulted in photoreceptor cell death, while digoxin and thioridazine additionally affected all other cell types, including Müller glia cells. All drug treatments caused activation of astrocytes, indicated by dendrites sprouting into neuroepithelium. The ability to respond to light was preserved in organoids although the number of responsive retinal ganglion cells decreased after drug exposure. These data indicate similar drug effects in organoids to those reported in in vivo models and/or in humans, thus providing the first robust experimental evidence of their suitability for toxicological studies.

Inhibition of the Na+/K+-ATPase by cardiac glycosides suppresses expression of the IDO1 immune checkpoint in cancer cells by reducing STAT1 activation

Despite extensive basic and clinical research on immune checkpoint regulatory pathways, little is known about the effects of the ionic tumor microenvironment on immune checkpoint expression and function. Here we describe a mechanistic link between Na+/K+-ATPase (NKA) inhibition and activity of the immune checkpoint protein indoleamine-pyrrole 2',3'-dioxygenase 1 (IDO1). We found that IDO1 was necessary and sufficient for production of kynurenine, a downstream tryptophan metabolite, in cancer cells. We developed a spectrophotometric assay to screen a library of 31 model ion transport-targeting compounds for potential effects on IDO1 function in A549 lung and MDA-MB-231 breast cancer cells. This revealed that the cardiac glycosides ouabain and digoxin inhibited kynurenine production at concentrations that did not affect cell survival. NKA inhibition by ouabain and digoxin resulted in increased intracellular Na+ levels and downregulation of IDO1 mRNA and protein levels, which was consistent with the reduction in kynurenine levels. Knockdown of ATP1A1, the ɑ1 subunit of the NKA and target of cardiac glycosides, increased Na+ levels to a lesser extent than cardiac glycoside treatment and did not affect IDO1 expression. However, ATP1A1 knockdown significantly enhanced the effect of cardiac glycosides on IDO1 expression and kynurenine production. Mechanistically, we show that cardiac glycoside treatment resulted in curtailing the length of phosphorylation-mediated stabilization of STAT1, a transcriptional regulator of IDO1 expression, an effect enhanced by ATP1A1 knockdown. Our findings reveal cross talk between ionic modulation via cardiac glycosides and immune checkpoint protein expression in cancer cells with broad mechanistic and clinical implications.

Comparative Therapeutic Potential of Cardioactive Glycosides in Doxorubicin Model of Heart Failure

In the present study, we investigated the cardioactive glycosides oleandrin and ouabain, and compared them to digoxin in a model of cardiotoxicity induced by doxorubicin. Adult rats were distributed into four experimental groups. Each group was challenged with a single intraperitoneal application of doxorubicin at a dose of 12 mg/kg. Then, they were treated with saline solution and the glycosides oleandrin, ouabain, and digoxin at a dose of 50 µg/kg, for 7 days. They underwent echocardiography, electrocardiography, hematologic, biochemical tests, and microscopic evaluation of the heart. All animals presented congestive heart failure, which was verified by a reduction in the ejection fraction. Oleandrin and digoxin were able to significantly reduce (p < 0.05) the eccentric remodeling caused by doxorubicin. Oleandrin and digoxin were significantly lower (p < 0.05) than the control group in maintaining systolic volume and left ventricular volume in diastole. Other parameters evaluated did not show significant statistical differences. All animals showed an increase in erythrocyte count, and an increase in the duration of the QRS complex on the ECG and myocardial necrosis at the histopathological analysis. It is concluded that the glycosides oleandrin, ouabain, and digoxin in the used dosage do not present therapeutic potential for the treatment of congestive heart failure caused by doxorubicin.

Depth of the Steroid Core Location Determines the Mode of Na,K-ATPase Inhibition by Cardiotonic Steroids

Cardiotonic steroids (CTSs) are specific inhibitors of Na,K-ATPase (NKA). They induce diverse physiological effects and were investigated as potential drugs in heart diseases, hypertension, neuroinflammation, antiviral and cancer therapy. Here, we compared the inhibition mode and binding of CTSs, such as ouabain, digoxin and marinobufagenin to NKA from pig and rat kidneys, containing CTSs-sensitive (α1S) and -resistant (α1R) α1-subunit, respectively. Marinobufagenin in contrast to ouabain and digoxin interacted with α1S-NKA reversibly, and its binding constant was reduced due to the decrease in the deepening in the CTSs-binding site and a lower number of contacts between the site and the inhibitor. The formation of a hydrogen bond between Arg111 and Asp122 in α1R-NKA induced the reduction in CTSs’ steroid core deepening that led to the reversible inhibition of α1R-NKA by ouabain and digoxin and the absence of marinobufagenin’s effect on α1R-NKA activity. Our results elucidate that the difference in signaling, and cytotoxic effects of CTSs may be due to the distinction in the deepening of CTSs into the binding side that, in turn, is a result of a bent-in inhibitor steroid core (marinobufagenin in α1S-NKA) or the change of the width of CTSs-binding cavity (all CTSs in α1R-NKA).

Rate control strategies for atrial fibrillation

Atrial fibrillation (AF) is one of the main cardiac arrhythmias associated with higher risk of cardiovascular morbidity and mortality. AF can cause adverse symptoms and reduced quality of life. One of the strategies for the management of AF is rate control, which can modulate ventricle rate, alleviate adverse associated symptoms and improve the quality of life. As primary management of AF through rate control or rhythm is a topic under debate, the purpose of this review is to explore the rationale for the rate control approach in managing AF by considering the guidelines, recommendations and determinants for the choice of rate control drugs, including beta blockers, digoxin and non- dihydropyridine calcium channel blockers for patients with AF and other comorbidities and atrioventricular nodal ablation and pacing. Despite the limitations of rate control treatment, which may not be effective in preventing disease progression or in reducing symptoms in highly symptomatic patients, it is widely used for almost all patients with atrial fibrillation. Although rate control is one of the first line management of all patient with atrial fibrillation, several issues remain debateable.

Identification of the organic anion transporting polypeptides responsible for the hepatic uptake of the major metabolite of epyrifenacil, S-3100-CA, in mice

Epyrifenacil is a novel herbicide that acts as an inhibitor of protoporphyrinogen oxidase (PPO) and produces hepatotoxicity in rodents by inhibiting PPO. Our previous research revealed that the causal substance of hepatotoxicity is S-3100-CA, a major metabolite of epyrifenacil, and that human hepatocyte uptake of S-3100-CA was significantly lower than rodent one, suggesting less relevant to hepatotoxicity in humans. To clarify the species difference in the uptake of S-3100-CA, we focused on organic anion transporting polypeptides (OATPs) and carried out an uptake assay using human, rat, and mouse OATP hepatic isoforms-expressing 293FT cells. As a result, all the examined OATPs were found to contribute to the S-3100-CA uptake, suggesting that the species difference was not due to the differences in selectivity toward OATP isoforms. When [14 C]epyrifenacil was administered to mice, the liver concentration of S-3100-CA was higher in males than in females. Furthermore, when [14 C]epyrifenacil was administered with OATP inhibitors, the liver/plasma ratio of S-3100-CA was significantly decreased by rifampicin, an Oatp1a1/Oatp1a4 inhibitor in mice, but not by digoxin, an Oatp1a4-specific inhibitor. This result indicates that Oatp1a1, the predominant transporter in male mice, is the main contributor to the hepatic transport of S-3100-CA, and consequently to the gender difference. Moreover, we conclude that the species difference in the hepatic uptake of S-3100-CA observed in our previous research is not due to differences in the selectivity toward OATP isoforms but rather to the significantly higher expression of OATPs which mediate uptake of S-3100-CA in rodents than in humans.

Establishment of a Drug Screening Model for Cardiac Complications of Acute Renal Failure

Acute renal failure (ARF) is a clinical critical syndrome with rapid and severe decline of renal function. Complications of ARF, especially its cardiac complications (cardiorenal syndrome type 3, CRS-3), are the main causes of death in patients with ARF. However, the shortage and limited efficacy of therapeutic drugs make it significant to establish new large-scale drug screening models. Based on the Nitroreductase/Metronidazole (NTR/MTZ) cell ablation system, we constructed a Tg(cdh17:Dendra2-NTR) transgenic zebrafish line, which can specifically ablate renal tubular epithelial cells. The absence of renal tubular epithelial cells can lead to ARF in zebrafish larvae. The ARF symptoms, such as heart enlargement, slow heart rate and blood stasis, are similar to the clinical manifestations of human CRS-3. Furthermore, two therapeutic drugs (digoxin and enalapril) commonly used in the clinical treatment of heart failure were also effective in alleviating the symptoms of CRS-3 in zebrafish, which proved the effectiveness of this model. Drug screening further discovered a potential drug candidate, α-lipoic acid, which can effectively alleviate the symptoms of CRS-3 through its antioxidant function. Accordingly, we established a new ARF model of zebrafish, which laid a foundation for large-scale screening of new therapeutic drugs for its complications.

The effect of Guanxin Shutong capsule on alleviating the myocardial fibrosis in heart failure rats

ETHNOPHARMACOLOGICAL RELEVANCE

Guanxin Shutong (GXST) capsule is a renowned traditional Chinese medicine widely used for the treatment of cardiovascular diseases in the clinic. However, no pharmacological experimental studies of GXST has been reported on the treatment of pressure overload-induced heart failure. This study aimed to investigate the effects of GXST capsule on ameliorating myocardial fibrosis conditions in pressure overload-induced heart failure rats.

MATERIAL AND METHODS

Rats were randomly divided into 6 groups: Normal group, Model group, GXST-treated group at a dose of 0.5 g/kg, 1 g/kg, 2 g/kg, respectively, and digoxin positive control group at a dose of 1 mg/kg. After 4 weeks of administration, cardiac function was evaluated by echocardiography. Cardiac injury and fibrotic conditions were evaluated by H&E staining, Masson staining, and Sirius Red staining. Myocardial fibrosis was evaluated by immunohistochemistry staining and Western blot.

RESULTS

GXST significantly inhibited cardiac fibrosis, reduced the excessive deposition of collagen, and finally improved cardiac function. GXST reversed ventricular remodeling might be through the TGF-β/Smad3 pathway.

CONCLUSION

GXST capsule demonstrated a strong anti-fibrosis effect in heart failure rats by inhibiting the TGF-β/Smad3 signaling pathway.

Inhibition of the IL-17A axis in adipocytes suppresses diet-induced obesity and metabolic disorders in mice

Overnutrition causes obesity, a global health problem without any effective therapy. Obesity is characterized by low-grade inflammation, which predisposes individuals to metabolic syndrome via unknown mechanisms. Here, we demonstrate that abolishing the interleukin-17A (IL-17A) axis in mice by inhibition of RORγt-mediated IL-17A production by digoxin, or by ubiquitous deletion of IL-17 receptor A (Il17ra), suppresses diet-induced obesity (DIO) and metabolic disorders, and promotes adipose-tissue browning, thermogenesis and energy expenditure. Genetic ablation of Il17ra specifically in adipocytes is sufficient to completely prevent DIO and metabolic dysfunction in mice. IL-17A produced in response to DIO induces PPARγ phosphorylation at Ser273 in adipocytes in a CDK5-dependent manner, thereby modifying expression of diabetogenic and obesity genes, which correlates with IL-17A signalling in white adipose tissues of individuals with morbid obesity. These findings reveal an unanticipated role for IL-17A in adipocyte biology, in which its direct action pathogenically reprograms adipocytes, promoting DIO and metabolic syndrome. Targeting the IL-17A axis could be an efficient antiobesity strategy.

Effect of Digoxin vs Bisoprolol for Heart Rate Control in Atrial Fibrillation on Patient-Reported Quality of Life: The RATE-AF Randomized Clinical Trial

IMPORTANCE

There is little evidence to support selection of heart rate control therapy in patients with permanent atrial fibrillation, in particular those with coexisting heart failure.

OBJECTIVE

To compare low-dose digoxin with bisoprolol (a β-blocker).

DESIGN, SETTING, AND PARTICIPANTS

Randomized, open-label, blinded end-point clinical trial including 160 patients aged 60 years or older with permanent atrial fibrillation (defined as no plan to restore sinus rhythm) and dyspnea classified as New York Heart Association class II or higher. Patients were recruited from 3 hospitals and primary care practices in England from 2016 through 2018; last follow-up occurred in October 2019.

INTERVENTIONS

Digoxin (n = 80; dose range, 62.5-250 μg/d; mean dose, 161 μg/d) or bisoprolol (n = 80; dose range, 1.25-15 mg/d; mean dose, 3.2 mg/d).

MAIN OUTCOMES AND MEASURES

The primary end point was patient-reported quality of life using the 36-Item Short Form Health Survey physical component summary score (SF-36 PCS) at 6 months (higher scores are better; range, 0-100), with a minimal clinically important difference of 0.5 SD. There were 17 secondary end points (including resting heart rate, modified European Heart Rhythm Association [EHRA] symptom classification, and N-terminal pro-brain natriuretic peptide [NT-proBNP] level) at 6 months, 20 end points at 12 months, and adverse event (AE) reporting.

RESULTS

Among 160 patients (mean age, 76 [SD, 8] years; 74 [46%] women; mean baseline heart rate, 100/min [SD, 18/min]), 145 (91%) completed the trial and 150 (94%) were included in the analysis for the primary outcome. There was no significant difference in the primary outcome of normalized SF-36 PCS at 6 months (mean, 31.9 [SD, 11.7] for digoxin vs 29.7 [11.4] for bisoprolol; adjusted mean difference, 1.4 [95% CI, -1.1 to 3.8]; P = .28). Of the 17 secondary outcomes at 6 months, there were no significant between-group differences for 16 outcomes, including resting heart rate (a mean of 76.9/min [SD, 12.1/min] with digoxin vs a mean of 74.8/min [SD, 11.6/min] with bisoprolol; difference, 1.5/min [95% CI, -2.0 to 5.1/min]; P = .40). The modified EHRA class was significantly different between groups at 6 months; 53% of patients in the digoxin group reported a 2-class improvement vs 9% of patients in the bisoprolol group (adjusted odds ratio, 10.3 [95% CI, 4.0 to 26.6]; P < .001). At 12 months, 8 of 20 outcomes were significantly different (all favoring digoxin), with a median NT-proBNP level of 960 pg/mL (interquartile range, 626 to 1531 pg/mL) in the digoxin group vs 1250 pg/mL (interquartile range, 847 to 1890 pg/mL) in the bisoprolol group (ratio of geometric means, 0.77 [95% CI, 0.64 to 0.92]; P = .005). Adverse events were less common with digoxin; 20 patients (25%) in the digoxin group had at least 1 AE vs 51 patients (64%) in the bisoprolol group (P < .001). There were 29 treatment-related AEs and 16 serious AEs in the digoxin group vs 142 and 37, respectively, in the bisoprolol group.

CONCLUSIONS AND RELEVANCE

Among patients with permanent atrial fibrillation and symptoms of heart failure treated with low-dose digoxin or bisoprolol, there was no statistically significant difference in quality of life at 6 months. These findings support potentially basing decisions about treatment on other end points.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02391337 and clinicaltrialsregister.eu Identifier: 2015-005043-13.

Antiviral activity of digoxin and ouabain against SARS-CoV-2 infection and its implication for COVID-19

The current coronavirus (COVID-19) pandemic is exacerbated by the absence of effective therapeutic agents. Notably, patients with COVID-19 and comorbidities such as hypertension and cardiac diseases have a higher mortality rate. An efficient strategy in response to this issue is repurposing drugs with antiviral activity for therapeutic effect. Digoxin (DIG) and ouabain (OUA) are FDA drugs for heart diseases that have antiviral activity against several coronaviruses. Thus, we aimed to assess antiviral activity of DIG and OUA against SARS-CoV-2 infection. The half-maximal inhibitory concentrations (IC50) of DIG and OUA were determined at a nanomolar concentration. Progeny virus titers of single-dose treatment of DIG, OUA and remdesivir were approximately 103-, 104- and 103-fold lower (> 99% inhibition), respectively, than that of non-treated control or chloroquine at 48 h post-infection (hpi). Furthermore, therapeutic treatment with DIG and OUA inhibited over 99% of SARS-CoV-2 replication, leading to viral inhibition at the post entry stage of the viral life cycle. Collectively, these results suggest that DIG and OUA may be an alternative treatment for COVID-19, with potential additional therapeutic effects for patients with cardiovascular disease.

Digoxin: Pharmacology and toxicology-A review

Digoxin is a cardiac glycoside used as drug in case of heart problems, including congestive heart failure, atrial fibrillation or flutter, and certain cardiac arrhythmias. It has a very narrow therapeutic window of the medication. Digoxin is toxic substance with well known cardiotoxic effect. In this work, pharmacology and toxicology of digoxin are summarized; Its pharmacokinetics, pharmacodynamics, available acute toxicity data (different species, different administration routes) are summarized in this article. Moreover, its treatment side effect and human poisonings are thoroughly discussed. Finally, appropriate therapy regimen is proposed.

Effects of digoxin on full-type hyperactivation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades

Previous researches of our laboratory reported that addition of cAMP analog cBiMPS and protein phosphatase inhibitor calyculin A (stimulators of cAMP signaling cascades) improved the capacity of incubation medium to induce full-type hyperactivation in bovine ejaculated spermatozoa. However, this modified medium was valid only for samples with relatively good survivability for incubation with stimulators of cAMP signaling cascades. Thus, it is necessary to make further modified medium for evaluation of potentials to exhibit full-type hyperactivation in bovine sperm samples with relatively lower survivability. Na⁺/K⁺-ATPase is an integral membrane protein and involved with the regulation of rodent sperm motility. To make further modification of the medium, we examined effects of Na⁺/K⁺-ATPase inhibition with digoxin on motility, full-type hyperactivation and protein tyrosine phosphorylation in bovine ejaculated spermatozoa with relatively lower survivability for incubation with stimulators of cAMP signaling cascades and also performed the immunodetection of bovine sperm Na⁺/K⁺-ATPase. The addition of Na⁺/K⁺-ATPase inhibitor digoxin to the incubation medium containing cBiMPS and calyculin A had the tendency to lessen the decreases in the percentages of motile spermatozoa in all of 12 samples after the incubation for 1-3 h and significantly increased the percentages of full-type hyperactivation in one group of 4 samples (Sample-A1) and another group of 4 samples (Sample-A2) after 1 and 2 h respectively, though it had no significant effects on full-type hyperactivation in the other group of 4 samples (Sample-B). In addition, incubation time-related changes in the sperm protein tyrosine phosphorylation (a good marker for sperm capacitation) were correlated with those in the percentages of full-type hyperactivation in Sample-A1 containing digoxin. Immunodetection showed that Na⁺/K⁺-ATPase is present in the middle and principal pieces of the flagella, indicating that Na⁺/K⁺-ATPase has possible relations with sperm motility. These results obtained with bull ejaculated spermatozoa with relatively lower survivability indicate that incubation method using digoxin is useful to evaluate potentials of sperm samples to exhibit full-type hyperactivation, that digoxin has effects on suppressing reduction of sperm motility, and that prolonged incubation with digoxin induces reduction of capacitation state which may suppress the maintenance of full-type hyperactivation.

Resolution of Fetal Hydrops Dependent on Sustained Fetal Supraventricular Tachycardia after Digoxin Therapy

We present a special case of fetal supraventricular tachycardia detected at 34 weeks gestation. Fetal hydrops was noted on ultrasound upon admission. Normal fetal heart rate was maintained for three weeks by maternal administration of digoxin. A live infant was delivered via caesarian section at 37 weeks gestation. This clinical case demonstrated that pharmacological treatment can be effective and helps to prolong pregnancy safely.

Na+/K+-ATPase-Targeted Cytotoxicity of (+)-Digoxin and Several Semisynthetic Derivatives

(+)-Digoxin (1) is a well-known cardiac glycoside long used to treat congestive heart failure and found more recently to show anticancer activity. Several known cardenolides (2-5) and two new analogues, (+)-8(9)-β-anhydrodigoxigenin (6) and (+)-17-epi-20,22-dihydro-21α-hydroxydigoxin (7), were synthesized from 1 and evaluated for their cytotoxicity toward a small panel of human cancer cell lines. A preliminary structure-activity relationship investigation conducted indicated that the C-12 and C-14 hydroxy groups and the C-17 unsaturated lactone unit are important for 1 to mediate its cytotoxicity toward human cancer cells, but the C-3 glycosyl residue seems to be less critical for such an effect. Molecular docking profiles showed that the cytotoxic 1 and the noncytotoxic derivative 7 bind differentially to Na⁺/K⁺-ATPase. The HO-12β, HO-14β, and HO-3'aα hydroxy groups of (+)-digoxin (1) may form hydrogen bonds with the side-chains of Asp121 and Asn122, Thr797, and Arg880 of Na⁺/K⁺-ATPase, respectively, but the altered lactone unit of 7 results in a rotation of its steroid core, which depotentiates the binding between this compound and Na⁺/K⁺-ATPase. Thus, 1 was found to inhibit Na⁺/K⁺-ATPase, but 7 did not. In addition, the cytotoxic 1 did not affect glucose uptake in human cancer cells, indicating that this cardiac glycoside mediates its cytotoxicity by targeting Na⁺/K⁺-ATPase but not by interacting with glucose transporters.

21-Benzylidene digoxin decreases proliferation by inhibiting the EGFR/ERK signaling pathway and induces apoptosis in HeLa cells

Cardiotonic steroids (CTS) are agents traditionally known for their capacity to bind to the Na,K-ATPase (NKA), affecting the ion transport and the contraction of the heart. Natural CTS have been shown to also have effects on cell signaling pathways. With the goal of developing a new CTS derivative, we synthesized a new digoxin derivative, 21-benzylidene digoxin (21-BD). Previously, we have shown that this compound binds to NKA and has cytotoxic actions on cancer, but not on normal cells. Here, we further studied the mechanisms of actions of 21-BD. Working with HeLa cells, we found that 21-BD decreases the basal, as well as the insulin stimulated proliferation. 21-BD reduces phosphorylation of the epidermal growth factor receptor (EGFR) and extracellular-regulated kinase (ERK), which are involved in pathways that stimulate cell proliferation. In addition, 21-BD promotes apoptosis, which is mediated by the translocation of Bax from the cytosol to mitochondria and the release of mitochondrial cytochrome c to the cytosol. 21-BD also activated caspases-8, -9 and -3, and induced the cleavage of poly (ADP-ribose) polymerase-1 (PARP-1). Altogether, these results show that the new compound that we have synthesized exerts cytotoxic actions on HeLa cells by inhibition of cell proliferation and the activation of both the extrinsic and intrinsic apoptotic pathways. These results support the relevance of the cardiotonic steroid scaffold as modulators of cell signaling pathways and potential agents for their use in cancer.

A novel source of the cardiac glycoside digoxin from the endophytic fungus Epicoccum nigrum: isolation, characterization, production enhancement by gamma irradiation mutagenesis and anticancer activity evaluation

AIMS

Different endophytic fungi were isolated and screened for their digoxin-producing ability. Strain improvement and different culture conditions were studied for more effective production of digoxin.

METHODS AND RESULTS

Among the isolated fungi, an isolate produced digoxin in a concentration of 2·07 mg l^-1 . The digoxin-producing fungal isolate was identified as Epicoccum nigrum Link according to the morphological features and phylogenetic analyses. The potentiality of the fungal strain for production enhancement of digoxin was performed by gamma radiation mutagenesis. Gamma irradiation dose of 1000 Gy intensified the digoxin yield by five-fold. Using this dose, a stable mutant strain with improved digoxin productivity was isolated and the stability for digoxin production was followed up across four successive generations. In the effort to increase digoxin magnitude, selection of the proper cultivation medium, addition of some elicitors to the most proper medium and several physical fermentation conditions were tested. Fermentation process carried out in malt extract autolysate medium (pH 6·5) supplemented by methyl jasmonate and inoculated with 2 ml of 6-day-old culture and incubated at 25°C for 10 days stimulated the highest production of digoxin to attain 50·14 mg l^-1 . Moreover, cytotoxicity of digoxin separated from the fungal culture was tested against five different cancer cell lines. Based on the MTT assay, digoxin inhibited the proliferation of the five different cancer cell lines and the recorded 50% inhibitory concentration ranged from 10·76 to 35·14 μg ml^-1 .

CONCLUSIONS

This is the first report on the production and enhancement of digoxin using fungal fermentation as a new and alternate source with high productivity.

SIGNIFICANCE AND IMPACT OF THE STUDY

These findings offer new and alternate sources with excellent biotechnological potential for digoxin production by fungal fermentation. Moreover, digoxin proved to be a promising anticancer agent whose anticancer potential should be assessed in prospective cancer therapy.

Restoration and Enhancement of Immunogenic Cell Death of Cisplatin by Coadministration with Digoxin and Conjugation to HPMA Copolymer

Complete tumor eradication is the ultimate goal of cancer therapy. However, the majority of anticancer drugs cause nonimmunogenic cell death and only exert on-site anticancer activities. The intrinsic genomic instability of cancer allows for the persistence and later expansion of treatment-resistant clones after surviving a sort of Darwinian selection of chemotherapy. Additional incorporation of immunotherapy, which is robust and individualized could be game-changing. Herein, we report a combination strategy that delivers nonimmunogenic cell death inducer Cisplatin to treat primary tumors and converts the tumor cells into vaccines that spurs a long-lasting immune response against residual tumors to prevent tumor recurrence and metastasis. Cisplatin(IV) prodrug was linked to the N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer (P-Cis) and coadministered with digoxin (Dig), which eventually launched two attacks to cancer cells. First, P-Cis exhibited superior tumor retention and cytotoxicity over free Cisplatin (to inhibit the primary tumor growth). Then, Dig reversed the inability of Cisplatin to trigger calreticulin exposure, and HPMA copolymer-amplified Cisplatin-induced ATP release. These complementary mechanisms induced potent immunogenic cell death that promotes dendritic cell maturation and activates CD8⁺ T cell responses. In established tumor models, P-Cis + Dig combination completely eradicate tumors with no residual cancer cells remaining. Cancer cells succumbing to P-Cis + Dig could protect syngeneic mice against the subsequent challenge with living cells of the same type and stimulated robust abscopal and antimetastatic effects. Such a strategy might be promising to restore the immunogenicity of nonimmunogenic drugs and generate vaccine-like functions for improved immunochemotherapy.

Prophylactic digoxin treatment reduces IL-17 production in vivo in the neonatal calf and moderates RSV-associated disease

Respiratory syncytial virus (RSV) is a leading cause of morbidity and mortality in human infants. Bovine RSV infection of neonatal calves is pathologically and immunologically similar to RSV infection in infants, and is therefore a useful preclinical model for testing novel therapeutics. Treatment of severe RSV bronchiolitis relies on supportive care and may include use of bronchodilators and inhaled or systemic corticosteroids. Interleukin-17A (IL-17) is an inflammatory cytokine that plays an important role in neutrophil recruitment and activation. IL-17 is increased in children and rodents with severe RSV infection; and in calves with severe BRSV infection. It is currently unclear if IL-17 and Th17 immunity is beneficial or detrimental to the host during RSV infection. Digoxin was recently identified to selectively inhibit IL-17 production by antagonizing its transcription factor, retinoid-related orphan receptor γ t (RORγt). Digoxin inhibits RORγt binding to IL-17 and Th17 associated genes, and suppresses IL-17 production in vitro in human and murine leukocytes and in vivo in rodent models of autoimmune disease. We demonstrate here that in vitro and in vivo digoxin treatment also inhibits IL-17 production by bovine leukocytes. To determine the role of IL-17 in primary RSV infection, calves were treated prophylactically with digoxin and infected with BRSV. Digoxin treated calves demonstrated reduced signs of clinical illness after BRSV infection, and reduced lung pathology compared to untreated control calves. Digoxin treatment did not adversely affect virus shedding or lung viral burden, but had a significant impact on pulmonary inflammatory cytokine expression on day 10 post infection. Together, our results suggest that exacerbated expression of IL-17 has a negative impact on RSV disease, and that development of specific therapies targeting Th17 immunity may be a promising strategy to improve disease outcome during severe RSV infection.

Indexes of the erythropoietin level in the blood plasma of chronic heart failure patients with anemia

BACKGROUND

Anemia aggravates the disease course and the survival rate of chronic heart failure (CHF) patients. The purpose of the study was to investigate the level of erythropoietin (EPO) in CHF patients with anemic syndrome, with the aim to more accurately assess the severity of the disease and its treatment, depending on the anemia degree.

METHODS

Patients with ischemic CHF of I-IV functional class (FC) with and without anemia were examined (total number of patients=208, patients with anemia=174). The EPO was determined using the enzyme-linked immunosorbent assay. Before treatment, the patients underwent the following medical therapy: angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers, long-acting nitrates, diuretics, digoxin, and beta-blockers at individual doses. Depending on the plasma EPO level, the CHF patients with anemia were divided into four randomized groups in terms of treatment.

RESULTS

Normal erythropoietinemia was found in 36.2% of the CHF patients with anemic syndrome (I-III FC), hypoerythropoietinemia in 44.8% (III-IV FC), and hypererythropoietinemia in 18.96% (III-V FC). The EPO level in the blood plasma of the patients with I-II FC CHF with hypoerythropoietinemia, who were treated with methoxy polyethylene glycol-epoetin β (MEB), increased by 2.2 times. Combination therapy with disease-modifying drugs and MEB led to a significant increase in the plasma EPO level in the CHF patients with hypoerythropoietinemia.

CONCLUSIONS

It was shown that the EPO level in patients with CHF and anemia did not always drop. Hypererythropoietinemia in patients with CHF and anemia leads to an unfavorable treatment prediction. This necessitates the investigation of the EPO level in all patients with CHF before and after treatment, with the aim of correcting the anemic syndrome. The research showed that the combined therapy of patients with CHF and anemia using MEB medication and iron with regard to the EPO level in the blood plasma improved their overall physical condition, reduced heart failure symptoms and hospitalization frequency, and demonstrated a clear tendency to reduce the general mortality rate.

WWOX controls hepatic HIF1α to suppress hepatocyte proliferation and neoplasia

Liver cancer is one of the most lethal malignancies with very poor prognosis once diagnosed. The most common form of liver cancer is hepatocellular carcinoma (HCC). The WW domain-containing oxidoreductase (WWOX) is a large gene that is often perturbed in a wide variety of tumors, including HCC. WWOX has been shown to act as a tumor suppressor modulating cellular metabolism via regulating hypoxia-inducible factor 1α (HIF-1α) levels and function. Given that WWOX is commonly inactivated in HCC, we set to determine whether specific targeted deletion of murine Wwox affects liver biology and HCC development. WWOX liver-specific knockout mice (Wwox ΔHep ) showed more potent liver regeneration potential and enhanced proliferation as compared with their control littermates. Moreover, WWOX deficiency in hepatocytes combined with diethylnitrosamine treatment increased the tumor burden, which was associated with increased HIF1α levels and target gene transactivation. Inhibition of HIF1α by systemic treatment with digoxin significantly delayed HCC formation. Our work suggests that WWOX inactivation has a central role in promoting HCC through rewiring of cellular metabolism and modulating proliferation.

New insights in the in vitro characterisation and molecular modelling of the P-glycoprotein inhibitory promiscuity

The presence of several binding sites for both substrates and inhibitors is yet a poorly explored thematic concerning the assessment of the drug-drug interactions risk due to interactions of multiple drugs with the human transport protein P-glycoprotein (P-gp or MDR1, gene ABCB1). In this study we measured the inhibitory behaviour of a set of known drugs towards P-gp by using three different probe substrates (digoxin, Hoechst 33,342 and rhodamine 123). A structure-based model was built to unravel the different substrates binding sites and to rationalize the cases where drugs were not inhibiting all the substrates. A separate set of experiments was used to validate the model and confirmed its suitability to either detect the substrate-dependent P-gp inhibition and to anticipate proper substrates for in vitro experiments case by case. The modelling strategy described can be applied for either design safer drugs (P-gp as antitarget) or to target specific sub-site inhibitors towards other drugs (P-gp as target).

The combination of digoxin and GSK2606414 exerts synergistic anticancer activity against leukemia in vitro and in vivo

Digoxin is a member of cardiac glycosides and recent studies show that digoxin plays anticancer role in several types of cancer. However, the anticancer effects and mechanism of digoxin in leukemia is largely unknown. Her, our data show that digoxin treatment significantly inhibits leukemia cell viability. In addition, digoxin treatment significantly induced apoptosis and G2/M cell cycle arrest in leukemia cells. Furthermore, we demonstrated that digoxin treatment inactivate that oncogenic pathway Akt/mTOR signaling in leukemia cells. In addition, our data show that digoxin treatment induces activation of unfolded protein response (UPR) signaling in leukemia cells. Interestingly, our in vitro and in vivo experiments show that combination treatment of digoxin and UPR inhibitor can synergistically suppress leukemia growth and induces apoptosis and cell cycle arrest compared to single drug treatment. In summary, our findings indicate that digoxin has potential anticancer effects on leukemia. The combination of digoxin and UPR signaling inhibitor can exerts synergistic anticancer activity against leukemia. © 2017 BioFactors, 43(6):812-820, 2017.

Digoxin reveals a functional connection between HIV-1 integration preference and T-cell activation

HIV-1 integrates more frequently into transcribed genes, however the biological significance of HIV-1 integration targeting has remained elusive. Using a selective high-throughput chemical screen, we discovered that the cardiac glycoside digoxin inhibits wild-type HIV-1 infection more potently than HIV-1 bearing a single point mutation (N74D) in the capsid protein. We confirmed that digoxin repressed viral gene expression by targeting the cellular Na⁺/K⁺ ATPase, but this did not explain its selectivity. Parallel RNAseq and integration mapping in infected cells demonstrated that digoxin inhibited expression of genes involved in T-cell activation and cell metabolism. Analysis of >400,000 unique integration sites showed that WT virus integrated more frequently than N74D mutant within or near genes susceptible to repression by digoxin and involved in T-cell activation and cell metabolism. Two main gene networks down-regulated by the drug were CD40L and CD38. Blocking CD40L by neutralizing antibodies selectively inhibited WT virus infection, phenocopying digoxin. Thus the selectivity of digoxin depends on a combination of integration targeting and repression of specific gene networks. The drug unmasked a functional connection between HIV-1 integration and T-cell activation. Our results suggest that HIV-1 evolved integration site selection to couple its early gene expression with the status of target CD4+ T-cells, which may affect latency and viral reactivation.

HIV-1 integrates more frequently within transcribed host genes, however we do not understand the biological significance of this. We found that a drug called digoxin inhibits wild type HIV-1 more potently than an HIV-1 bearing a single point mutation in the capsid protein. Here we show that digoxin represses HIV-1 gene expression and in parallel inhibits CD4+ T-cell activation and metabolism. When we analysed the integration sites of wild type and mutant HIV-1, we discovered that wild type virus integrates within or near genes involved in CD4⁺ T-cell activation and metabolism more often than the mutant virus. Because these are the very same genes repressed by digoxin, the integration bias of wild type virus makes it more susceptible than mutant virus to silencing by the drug. Digoxin unmasked a functional link between HIV-1 integration and T-cell activation, which may affect HIV-1 latency and reactivation.

MUC1 and HIF-1alpha Signaling Crosstalk Induces Anabolic Glucose Metabolism to Impart Gemcitabine Resistance to Pancreatic Cancer

Poor response to cancer therapy due to resistance remains a clinical challenge. The present study establishes a widely prevalent mechanism of resistance to gemcitabine in pancreatic cancer, whereby increased glycolytic flux leads to glucose addiction in cancer cells and a corresponding increase in pyrimidine biosynthesis to enhance the intrinsic levels of deoxycytidine triphosphate (dCTP). Increased levels of dCTP diminish the effective levels of gemcitabine through molecular competition. We also demonstrate that MUC1-regulated stabilization of hypoxia inducible factor-1α (HIF-1α) mediates such metabolic reprogramming. Targeting HIF-1α or de novo pyrimidine biosynthesis, in combination with gemcitabine, strongly diminishes tumor burden. Finally, reduced expression of TKT and CTPS, which regulate flux into pyrimidine biosynthesis, correlates with better prognosis in pancreatic cancer patients on fluoropyrimidine analogs.

Implants composed of digoxin and poly(ε-caprolactone): development, characterization, anti-proliferative and anti-angiogenic activities

Drug delivery systems could be applied to locally treat cervical cancer, thus preventing the drawbacks of conventional therapy. In this study, anti-proliferative and anti-angiogenic effects of digoxin incorporated into poly(ε-caprolactone) implants were evaluated, aiming at the local treatment of cervical cancer. Implants were characterized, and the in vitro release profile of digoxin was demonstrated. Anti-proliferative and anti-angiogenic activities of digoxin were investigated by using chorioallantoic membrane and human cervix carcinoma (HeLa) cells, respectively. The chemical structure of digoxin and the semi-crystalline nature of poly(ε-caprolactone) were preserved after designing implants. The hydrophobicity of drug and polymer as well as the semi-crystalline structure provided a controlled diffusion of digoxin from implants. Digoxin released from implantable devices exhibited anti-proliferative activity against HeLa cells. The anti-angiogenic effect was also shown. Finally, implants composed of digoxin and poly(ε-caprolactone) could be applied as a therapeutic alternative to treat the early stage of cervical cancer, once they were able to locally control the release of this anti-angiogenic and anti-proliferative drug, minimizing its systemic side effects and toxicity.

[Digoxin inhibits migration and invasion of human gastric carcinoma MKN45 cells through down-regulation of AEG-1]

This study was designed to investigate the effect of digoxin on migration and invasion of human gastric carcinoma MKN45 cells and its possible mechanism. MKN45 cells were treated with different concentrations of digoxin for 24 h. The shRNA-AEG-1 plasmid was transfected into MKN45 cells via lipofectamine to block the expression of astrocyte elevated gene-1 (AEG-1). Western blot was used to analyze the protein levels of matrix metalloproteinase-9 (MMP-9), E-cadherin and AEG-1. The result showed that digoxin reduced the abilities of migration and invasion (P < 0.05), up-regulated the protein level of E-cadherin (P < 0.05), and down-regulated the protein levels of MMP-9 and AEG-1 (P < 0.05) in MKN45 cells in a dose-dependent manner. Compared with shControl group, shAGE-1 group showed inhibited cellular migration and invasion, higher expression level of E-cadherin, and lower expression levels of MMP-9 and AEG-1. These results suggest that digoxin suppresses the migration and invasion of human gastric carcinoma MKN45 cells in a dose-dependent manner through inhibiting the expression of AEG-1, and then resulting in the up-regulation of the protein expression of E-cadherin and the down-regulation of the protein expression of MMP-9.

(+)-Strebloside-Induced Cytotoxicity in Ovarian Cancer Cells Is Mediated through Cardiac Glycoside Signaling Networks

(+)-Strebloside, a cardiac glycoside isolated from the stem bark of Streblus asper collected in Vietnam, has shown some potential for further investigation as an antineoplastic agent. A mechanistic study using an in vitro assay and molecular docking analysis indicated that (+)-strebloside binds and inhibits Na⁺/K⁺-ATPase in a similar manner to digitoxin. Inhibition of growth of different high-grade serous ovarian cancer cells including OVCAR3, OVSAHO, Kuramochi, OVCAR4, OVCAR5, and OVCAR8 resulted from treatment with (+)-strebloside. Furthermore, this compound blocked cell cycle progression at the G2 phase and induced PARP cleavage, indicating apoptosis activation in OVCAR3 cells. (+)-Strebloside potently inhibited mutant p53 expression through the induction of ERK pathways and inhibited NF-κB activity in human ovarian cancer cells. However, in spite of its antitumor potential, the overall biological activity of (+)-strebloside must be regarded as being typical of better-known cardiac glycosides such as digoxin and ouabain. Further chemical alteration of cardiac glycosides might help to reduce negative side effects while increasing cancer cell cytotoxicity.

[Digoxin and atrial fibrillation in 2016]

Various properties of digoxin have been exploited for decades, amongst which are its positive inotropy used in the treatment of heart failure, and its vagotonic effect used to slow ventricular response to atrial fibrillation. Pharmacologic properties of digoxin are however characterised by a narrow therapeutic interval, and recent observational studies suggest a potential association with increased mortality in patients with atrial fibrillation. As a result and because of available alternative therapeutic strategies, current guidelines do not recommend digoxin as first line treatment of atrial fibrillation. Digoxin may be considered in patients with heart failure and atrial fibrillation with rapid ventricular response when other therapeutic options cannot be pursued.

Is Heart Rate a Norepiphenomenon in Heart Failure?

There has been an increased focus on heart rate as a target in the management of cardiovascular disease and more specifically in heart failure with preserved ejection fraction in recent years with several studies showing the benefit of a lower resting heart rate on outcomes. This review paper examines the pathophysiology behind the benefits of lowering heart rate in heart failure and also the evidence for and against the pharmacological agents available to achieve this.

Effect of Chronic Kidney Diseases on Mortality among Digoxin Users Treated for Non-Valvular Atrial Fibrillation: A Nationwide Register-Based Retrospective Cohort Study

PURPOSE

This study investigated the impact of chronic kidney disease on all-causes and cardiovascular mortality in patients with atrial fibrillation treated with digoxin.

METHODS

All patients with non-valvular atrial fibrillation and/or atrial flutter as hospitalization diagnosis from January 1, 1997 to December 31, 2012 were identified in Danish nationwide administrative registries. Cox proportional hazard model was used to compare the adjusted risk of all-causes and cardiovascular mortality among patients with and without chronic kidney disease and among patients with different chronic kidney disease stages within 180 days and 2 years from the first digoxin prescription.

RESULTS

We identified 37,981 patients receiving digoxin; 1884 patients had the diagnosis of chronic kidney disease. Cox regression analysis showed no statistically significant differences in all-causes (Hazard Ratio, HR 0.89; 95% confident interval, CI 0.78-1.03) and cardiovascular mortality (HR 0.88; 95%CI 0.74-1.05) among patients with and without chronic kidney disease within 180 days of follow-up period. No statistically significant differences was found using a 2 years follow-up period neither for all causes mortality (HR 0.90; 95%CI 0.79-1.03), nor for cardiovascular mortality (HR 0.87; 95%CI 0.74-1.02). No statistically significant differences was found comparing patients with and without estimated Glomerular Filtration Rate <30ml/min/1.73m2 and patients with different stages of chronic kidney disease, for all-causes and cardiovascular mortality within 180 days and 2 years from the first digoxin prescription.

CONCLUSIONS

This study suggest no direct effect of chronic kidney disease and chronic kidney disease stages on all-causes and cardiovascular mortality within both 180 days and 2 years from the first digoxin prescription in patients treatment-naïve with digoxin for non-valvular atrial fibrillation.

Inhibition of the Nuclear Receptor RORγ and Interleukin-17A Suppresses Neovascular Retinopathy: Involvement of Immunocompetent Microglia

OBJECTIVE

Although inhibitors of vascular endothelial growth factor (VEGF) provide benefit for the management of neovascular retinopathies, their use is limited to end-stage disease and some eyes are resistant. We hypothesized that retinoic acid-related orphan nuclear receptor γ (RORγ) and its downstream effector, interleukin (IL)-17A, upregulate VEGF and hence are important treatment targets for neovascular retinopathies.

APPROACH AND RESULTS

Utilizing a model of oxygen-induced retinopathy, confocal microscopy and flow cytometry, we identified that retinal immunocompetent cells, microglia, express IL-17A. This was confirmed in primary cultures of rat retinal microglia, where hypoxia increased IL-17A protein as well as IL-17A, RORγ, and tumor necrosis factor-α mRNA, which were reduced by the RORγ inhibitor, digoxin, and the RORα/RORγ inverse agonist, SR1001. By contrast, retinal macroglial Müller cells and ganglion cells, key sources of VEGF in oxygen-induced retinopathy, did not produce IL-17A when exposed to hypoxia and IL-1β. However, they expressed IL-17 receptors, and in response to IL-17A, secreted VEGF. This suggested that RORγ and IL-17A inhibition might attenuate neovascular retinopathy. Indeed, digoxin and SR1001 reduced retinal vaso-obliteration, neovascularization, and vascular leakage as well as VEGF and VEGF-related placental growth factor. Digoxin and SR1001 reduced microglial-derived IL-17A and Müller cell and ganglion cell damage. The importance of IL-17A in oxygen-induced retinopathy was confirmed by IL-17A neutralization reducing vasculopathy, VEGF, placental growth factor, tumor necrosis factor-α, microglial density and Müller cell, and ganglion cell injury.

CONCLUSIONS

Our findings indicate that an RORγ/IL-17A axis influences VEGF production and neovascular retinopathy by mechanisms involving neuroglia. Inhibition of RORγ and IL-17A may have potential for the improved treatment of neovascular retinopathies.

ABC- and SLC-Transporters in Murine and Bovine Mammary Epithelium--Effects of Prochloraz

Some chemicals are ligands to efflux transporters which may result in high concentrations in milk. Limited knowledge is available on the influence of maternal exposure to chemicals on the expression and function of transporters in the lactating mammary gland. We determined gene expression of ABC and SLC transporters in murine mammary tissue of different gestation and lactation stages, in murine mammary cells (HC11) featuring resting and secreting phenotypes and in bovine mammary tissue and cells (BME-UV). Effects on transporter expression and function of the imidazole fungicide prochloraz, previously reported to influence BCRP in mammary cells, was investigated on transporter expression and function in the two cell lines. Transporters studied were BCRP, MDR1, MRP1, OATP1A5/OATP1A2, OCTN1 and OCT1. Gene expressions of BCRP and OCT1 in murine mammary glands were increased during gestation and lactation, whereas MDR1, MRP1, OATP1A5 and OCTN1 were decreased, compared to expressions in virgins. All transporters measured in mammary glands of mice were detected in bovine mammary tissue and in HC11 cells, while only MDR1 and MRP1 were detected in BME-UV cells. Prochloraz treatment induced MDR1 gene and protein expression in both differentiated HC11 and BME-UV cells and increased protein function in HC11 cells, resulting in decreased accumulation of the MDR1 substrate digoxin. In conclusion, our results demonstrate that murine (HC11) and bovine (BME-UV) mammary epithelial cells can be applied to characterize expression and function of transporters as well as effects of contaminants on the mammary transporters. An altered expression, induced by a drug or toxic chemical, on any of the transporters expressed in the mammary epithelial cells during lactation may modulate the well-balanced composition of nutrients and/or secretion of contaminants in milk with potential adverse effects on breast-fed infants and dairy consumers.

[Digoxin in elderly patients: therapeutic drug monitoring to increase the efficiency of therapy (a review)]

The focus of this review is on cardiac and non-cardiac effects of digoxin, a drug used for treating the heart failure, and on link between these effects and the serum digoxin concentration (SDC) in different dosing regimens. Elderly patients are at the spotlight, as they are both at high risk and high potential benefit from digoxin therapy, explaining potential usefulness from SDC monitoring in this cohort of patients. The laboratory and clinical approaches used to prevent digitalis intoxication are reviewed, with regard to their fidelity, clinical value, and practical usefulness. The role of endogenous cardiotonic steroids, sharing structural and functional similarity to digoxin and affecting the diagnostic value of laboratory tests, is also discussed.

[Reversal of adriamycin resistance by digoxin in human breast cancer cell line MCF-7/adriamycin and its mechanism]

The aim of this study was to investigate the effects of digoxin on the chemoresistance of human breast cancer cell line MCF-7/adriamycin (ADR) and its underlying mechanism. MCF-7 and MCF-7/ADR cells were designated as control and ADR groups, respectively. MCF-7/ADR cells in ADR + digoxin group received 48 h of digoxin (10 nmol/L) treatment; MCF-7/ADR cells transfected with pLKO.1-shHIF-1α and pLKO.1-shcontrol plasmids were named shHIF-1α and shcontrol groups, respectively. CCK-8 assay was employed to detect the cytotoxic effect of ADR on MCF-7/ADR cells, and IC50 value and resistance index were calculated according to CCK-8. RT-PCR was used to measure the mRNA levels of hypoxia inducible factor-1α (HIF-1α) and multidrug resistance-1 (MDR1). Western blot was used to analyze the protein levels of HIF-1α and MDR1. Flow cytometry was used to determine the apoptosis. The result showed that the resistance index of MCF-7/ADR cells was 115.6, and it was reduced to 47.2 under the action of digoxin (P < 0.05). In comparison with control group, ADR groups showed increased protein and mRNA levels of HIF-1α and MDR1 (P < 0.05). Digoxin reduced the protein levels of HIF-1α and MDR1, as well as the mRNA level of MDR1, but did not affect the mRNA level of HIF-1α. After HIF-1α gene was silenced, the protein levels of HIF-1α and MDR1 were down-regulated (P < 0.05), and the pro-apoptotic effect of ADR on MCF-7/ADR cells was enhanced. Although it was also observed that digoxin promoted cell apoptosis in both shcontrol and shHIF-1α groups, the difference between the two groups was not significant. In conclusion, the results suggest that digoxin may partially reverse the ADR resistance in human breast cancer cell line MCF-7/ADR by means of down-regulating the expression levels of HIF-1α and MDR1 and promoting apoptosis via HIF-1α-independent pathway.

Targeting Th17 Cells with Small Molecules and Small Interference RNA

T helper 17 (Th17) cells play a central role in inflammatory and autoimmune diseases via the production of proinflammatory cytokines interleukin- (IL-) 17, IL-17F, and IL-22. Anti-IL-17 monoclonal antibodies show potent efficacy in psoriasis but poor effect in rheumatoid arthritis (RA) and Crohn's disease. Alternative agents targeting Th17 cells may be a better way to inhibit the development and function of Th17 cells than antibodies of blocking a single effector cytokine. Retinoic acid-related orphan receptor gamma t (RORγt) which acts as the master transcription factor of Th17 differentiation has been an attractive pharmacologic target for the treatment of Th17-mediated autoimmune disease. Recent progress in technology of chemical screen and engineering nucleic acid enable two new classes of therapeutics targeting RORγt. Chemical screen technology identified several small molecule specific inhibitors of RORγt from a small molecule library. Systematic evolution of ligands by exponential enrichment (SELEX) technology enabled target specific aptamers to be isolated from a random sequence oligonucleotide library. In this review, we highlight the development and therapeutic potential of small molecules inhibiting Th17 cells by targeting RORγt and aptamer mediated CD4(+) T cell specific delivery of small interference RNA against RORγt gene expression to inhibit pathogenic effector functions of Th17 lineage.

The Use of Chemical-Chemical Interaction and Chemical Structure to Identify New Candidate Chemicals Related to Lung Cancer

Lung cancer causes over one million deaths every year worldwide. However, prevention and treatment methods for this serious disease are limited. The identification of new chemicals related to lung cancer may aid in disease prevention and the design of more effective treatments. This study employed a weighted network, constructed using chemical-chemical interaction information, to identify new chemicals related to two types of lung cancer: non-small lung cancer and small-cell lung cancer. Then, a randomization test as well as chemical-chemical interaction and chemical structure information were utilized to make further selections. A final analysis of these new chemicals in the context of the current literature indicates that several chemicals are strongly linked to lung cancer.

Cytotoxicity of cardiotonic steroids in sensitive and multidrug-resistant leukemia cells and the link with Na(+)/K(+)-ATPase

Cardiotonic steroids have long been in clinical use for treatment of heart failure and are now emerging as promising agents in various diseases, especially cancer. Their main target is Na(+)/K(+)-ATPase, a membrane protein involved in cellular ion homeostasis. Na(+)/K(+)-ATPase has been implicated in cancer biology by affecting several cellular events and signaling pathways in both sensitive and drug-resistant cancer cells. Hence, we investigated the cytotoxic activities of 66 cardiotonic steroids and cardiotonic steroid derivatives in sensitive CCRF-CEM and multidrug-resistant CEM/ADR5000 leukemia cells. Data were then subjected to quantitative structure-activity relationship analysis (QSAR) and molecular docking into Na(+)/K(+)-ATPase, which both indicated a possible differential expression of the pump in the mentioned cell lines. This finding was confirmed by western blotting, intracellular potassium labeling and next generation sequencing which showed that Na(+)/K(+)-ATPase was less expressed in multidrug-resistant than in sensitive cells.

Digoxin Suppresses Tumor Malignancy through Inhibiting Multiple Src-Related Signaling Pathways in Non-Small Cell Lung Cancer

Non-small cell lung cancer is the predominant type of lung cancer, resulting in high mortality worldwide. Digoxin, a cardiac glycoside, has recently been suggested to be a novel chemotherapeutic agent. Src is an oncogene that plays an important role in cancer progression and is therefore a potential target for cancer therapy. Here, we investigated whether digoxin could suppress lung cancer progression through the inhibition of Src activity. The effects of digoxin on lung cancer cell functions were investigated using colony formation, migration and invasion assays. Western blotting and qPCR assays were used to analyze the mRNA and protein expression levels of Src and its downstream proteins, and a cell viability assay was used to measure cellular cytotoxicity effects. The results of the cell function assays revealed that digoxin inhibited the proliferation, invasion, migration, and colony formation of A549 lung cancer cells. Similar effects of digoxin were also observed in other lung cancer cell lines. Furthermore, we found that digoxin significantly suppressed Src activity and its protein expression in a dose- and time-dependent manner as well as reduced EGFR and STAT3 activity. Our data suggest that digoxin is a potential anticancer agent that may suppress lung cancer progression through inhibiting Src and the activity of related proteins.

21-Benzylidene digoxin: a proapoptotic cardenolide of cancer cells that up-regulates Na,K-ATPase and epithelial tight junctions

Cardiotonic steroids are used to treat heart failure and arrhythmia and have promising anticancer effects. The prototypic cardiotonic steroid ouabain may also be a hormone that modulates epithelial cell adhesion. Cardiotonic steroids consist of a steroid nucleus and a lactone ring, and their biological effects depend on the binding to their receptor, Na,K-ATPase, through which, they inhibit Na+ and K+ ion transport and activate of several intracellular signaling pathways. In this study, we added a styrene group to the lactone ring of the cardiotonic steroid digoxin, to obtain 21-benzylidene digoxin (21-BD), and investigated the effects of this synthetic cardiotonic steroid in different cell models. Molecular modeling indicates that 21-BD binds to its target Na,K-ATPase with low affinity, adopting a different pharmacophoric conformation when bound to its receptor than digoxin. Accordingly, 21-DB, at relatively high µM amounts inhibits the activity of Na,K-ATPase α1, but not α2 and α3 isoforms. In addition, 21-BD targets other proteins outside the Na,K-ATPase, inhibiting the multidrug exporter Pdr5p. When used on whole cells at low µM concentrations, 21-BD produces several effects, including: 1) up-regulation of Na,K-ATPase expression and activity in HeLa and RKO cancer cells, which is not found for digoxin, 2) cell specific changes in cell viability, reducing it in HeLa and RKO cancer cells, but increasing it in normal epithelial MDCK cells, which is different from the response to digoxin, and 3) changes in cell-cell interaction, altering the molecular composition of tight junctions and elevating transepithelial electrical resistance of MDCK monolayers, an effect previously found for ouabain. These results indicate that modification of the lactone ring of digoxin provides new properties to the compound, and shows that the structural change introduced could be used for the design of cardiotonic steroid with novel functions.

Effects of digoxin and Na, K-ATPase immunoexpression on human oral squamous carcinomas

AIM

The present study evaluated the expression of α1 and β1 Na,K-ATPase, as well as the effects of digoxin (DGX) on oral squamous cell carcinomas (OSCCs).

PATIENTS AND METHODS

Immunohistochemical expression of α1 and β1 Na,K-ATPase were evaluated in 60 patients who underwent treatment at the São João de Deus Hospital. SCC-25 viability was assessed by the colorimetric assay. Chi-square or Fisher's exact tests were used to analyze the association of α1 and β1 Na,K-ATPase expression with the variables.

RESULTS

Immunoexpression of α1 and β1 Na,K-ATPase were observed in 28% and 55% of the tumors, however these proteins were not significant prognostic factors. Tobacco was significantly associated with α1 expression. SCC-25 viability decreased significantly after treatment with 1 μM DGX at 24 h.

CONCLUSION

The smoking status of OSCC patients was significantly associated with α1 expression and DGX affected the SCC-25 viability in a dose- and duration-dependent manner.