Cardiac Glycosides as Autophagy Modulators

Traditional Chinese medicine bufalin inhibits infectious hematopoietic necrosis virus infection in vitro and in vivo

Infectious hematopoietic necrosis virus (IHNV) causes infectious hematopoietic necrosis and severe economic losses to salmon and trout aquaculture worldwide. Currently, the only commercial vaccine against IHNV is a DNA vaccine with some biosafety concerns. Hence, more effective vaccines and antiviral drugs are needed to prevent IHNV infection. In this study, 1,483 compounds were screened from a traditional Chinese medicine monomer library, and bufalin showed potential antiviral activity against IHNV. The 50% cytotoxic concentration of bufalin was >20 µM, and the 50% inhibitory concentration was 0.1223 µΜ against IHNV. Bufalin showed the inhibition of diverse IHNV strains in vitro, which confirmed that it had an inhibitory effect against all IHNV strains, rather than random activity against a single strain. The bufalin-mediated block of IHNV infection occurred at the viral attachment and RNA replication stages, but not internalization. Bufalin also inhibited IHNV infection in vivo and significantly increased the survival of rainbow trout compared with the mock drug-treated group, and this was confirmed by in vivo viral load monitoring. Our data showed that the anti-IHNV activity of bufalin was proportional to extracellular Na+ concentration and inversely proportional to extracellular K+ concentration, and bufalin may inhibit IHNV infection by targeting Na+/K+-ATPase. The in vitro and in vivo studies showed that bufalin significantly inhibited IHNV infection and may be a promising candidate drug against the disease in rainbow trout.

IMPORTANCE

Infectious hematopoietic necrosis virus (IHNV) is the pathogen of infectious hematopoietic necrosis (IHN) which outbreak often causes huge economic losses and hampers the healthy development of salmon and trout farming. Currently, there is only one approved DNA vaccine for IHN worldwide, but it faces some biosafety problems. Hence, more effective vaccines and antiviral drugs are needed to prevent IHNV infection. In this study, we report that bufalin, a traditional Chinese medicine, shows potential antiviral activity against IHNV both in vitro and in vivo. The bufalin-mediated block of IHNV infection occurred at the viral attachment and RNA replication stages, but not internalization, and bufalin inhibited IHNV infection by targeting Na+/K+-ATPase. The in vitro and in vivo studies showed that bufalin significantly inhibited IHNV infection and may be a promising candidate drug against the disease in rainbow trout.

Qiliqiangxin: A multifaceted holistic treatment for heart failure or a pharmacological probe for the identification of cardioprotective mechanisms?

The active ingredients in many traditional Chinese medicines are isoprene oligomers with a diterpenoid or triterpenoid structure, which exert cardiovascular effects by signalling through nutrient surplus and nutrient deprivation pathways. Qiliqiangxin (QLQX) is a commercial formulation of 11 different plant ingredients, whose active compounds include astragaloside IV, tanshione IIA, ginsenosides (Rb1, Rg1 and Re) and periplocymarin. In the QUEST trial, QLQX reduced the combined risk of cardiovascular death or heart failure hospitalization (hazard ratio 0.78, 95% confidence interval 0.68-0.90), based on 859 events in 3119 patients over a median of 18.2 months; the benefits were seen in patients taking foundational drugs except for sodium-glucose cotransporter 2 (SGLT2) inhibitors. Numerous experimental studies of QLQX in diverse cardiac injuries have yielded highly consistent findings. In marked abrupt cardiac injury, QLQX mitigated cardiac injury by upregulating nutrient surplus signalling through the PI3K/Akt/mTOR/HIF-1α/NRF2 pathway; the benefits of QLQX were abrogated by suppression of PI3K, Akt, mTOR, HIF-1α or NRF2. In contrast, in prolonged measured cardiac stress (as in chronic heart failure), QLQX ameliorated oxidative stress, maladaptive hypertrophy, cardiomyocyte apoptosis, and proinflammatory and profibrotic pathways, while enhancing mitochondrial health and promoting glucose and fatty acid oxidation and ATP production. These effects are achieved by an action of QLQX to upregulate nutrient deprivation signalling through SIRT1/AMPK/PGC-1α and enhanced autophagic flux. In particular, QLQX appears to enhance the interaction of PGC-1α with PPARα, possibly by direct binding to RXRα; silencing of SIRT1, PGC-1α and RXRα abrogated the favourable effects of QLQX in the heart. Since PGC-1α/RXRα is also a downstream effector of Akt/mTOR signalling, the actions of QLQX on PGC-1α/RXRα may explain its favourable effects in both acute and chronic stress. Intriguingly, the individual ingredients in QLQX - astragaloside IV, ginsenosides, and tanshione IIA - share QLQX's effects on PGC-1α/RXRα/PPARα signalling. QXQL also contains periplocymarin, a cardiac glycoside that inhibits Na+ -K+ -ATPase. Taken collectively, these observations support a conceptual framework for understanding the mechanism of action for QLQX in heart failure. The high likelihood of overlap in the mechanism of action of QLQX and SGLT2 inhibitors requires additional experimental studies and clinical trials.

The role of autophagy protein Atg5 in multiple sclerosis

Multiple sclerosis (MS) is a neurological disease which has a strong autoimmune component to its pathology. Although there are currently many approved immunomodulatory treatments that reduce the rate of relapse and slow down the progression of the disease, the cure is still elusive. This may be due to the underlying etiology still being unknown. Autophagy is the potential link between neurodegeneration and autoimmunity. Specifically, this review will focus on the autophagy protein Atg5 and examine the in vitro cell culture, animal and human studies that have examined its expression and effects in the context of MS. The findings of these investigations are summarized, and a model is proposed in which elevated Atg5 levels leads to dysfunctional autophagy, neurodegeneration, inflammation, and eventually clinical disability. While there are currently no drugs that specifically target Atg5, our review recommends that further investigations into the role that Atg5 plays in MS pathophysiology may eventually lead to the development of autophagy-specific treatments of MS.

The mechanistic role of cardiac glycosides in DNA damage response and repair signaling

Cardiac glycosides (CGs) are a class of bioactive organic compounds well-known for their application in treating heart disease despite a narrow therapeutic window. Considerable evidence has demonstrated the potential to repurpose CGs for cancer treatment. Chemical modification of these CGs has been utilized in attempts to increase their anti-cancer properties; however, this has met limited success as their mechanism of action is still speculative. Recent studies have identified the DNA damage response (DDR) pathway as a target of CGs. DDR serves to coordinate numerous cellular pathways to initiate cell cycle arrest, promote DNA repair, regulate replication fork firing and protection, or induce apoptosis to avoid the survival of cells with DNA damage or cells carrying mutations. Understanding the modus operandi of cardiac glycosides will provide critical information to better address improvements in potency, reduced toxicity, and the potential to overcome drug resistance. This review summarizes recent scientific findings of the molecular mechanisms of cardiac glycosides affecting the DDR signaling pathway in cancer therapeutics from 2010 to 2022. We focus on the structural and functional differences of CGs toward identifying the critical features for DDR targeting of these agents.

Autophagy, innate immunity, and cardiac disease

Autophagy is an evolutionarily conserved mechanism of cell adaptation to metabolic and environmental stress. It mediates the disposal of protein aggregates and dysfunctional organelles, although non-conventional features have recently emerged to broadly extend the pathophysiological relevance of autophagy. In baseline conditions, basal autophagy critically regulates cardiac homeostasis to preserve structural and functional integrity and protect against cell damage and genomic instability occurring with aging. Moreover, autophagy is stimulated by multiple cardiac injuries and contributes to mechanisms of response and remodeling following ischemia, pressure overload, and metabolic stress. Besides cardiac cells, autophagy orchestrates the maturation of neutrophils and other immune cells, influencing their function. In this review, we will discuss the evidence supporting the role of autophagy in cardiac homeostasis, aging, and cardioimmunological response to cardiac injury. Finally, we highlight possible translational perspectives of modulating autophagy for therapeutic purposes to improve the care of patients with acute and chronic cardiac disease.

Dual targets of lethal apoptosis and protective autophagy in liver cancer with periplocymarin elicit a limited therapeutic effect

Cardiac glycosides (CGs) are candidate anticancer agents that function by increasing [Ca²⁺]i to induce apoptotic cell death in several types of cancer cells. However, new findings have shown that the anti‑cancer effects of CGs involve complex cell‑signal transduction mechanisms. Hence, exploring the potential mechanisms of action of CGs may provide insight into their anti‑cancer effects and thus aid in the selection of the appropriate CG. Periplocymarin (PPM), which is a cardiac glycoside, is an active ingredient extracted from Cortex periplocae. The role of PPM was evaluated in HepG2 cells and xenografted nude mice. Cell proliferation, real‑time ATP rate assays, western blotting, cell apoptosis assays, short interfering RNA transfection, the patch clamp technique, electron microscopy, JC‑1 staining, immunofluorescence staining and autophagic flux assays were performed to evaluate the function and regulatory mechanisms of PPM in vitro. The in vivo activity of the PPM was assessed using a mouse xenograft model. The present study demonstrated that PPM synchronously activated lethal apoptosis and protective autophagy in liver cancer, and the initiation of autophagy counteracted the inherent pro‑apoptotic capacity and impaired the anti‑cancer effects. Specifically, PPM exerted a pro‑-apoptotic effect in HepG2 cells and activated macroautophagy by initiation of the AMPK/ULK1 and mTOR signaling pathways. Activation of macroautophagy counteracted the pro‑apoptotic effects of PPM, but when it was combined with an autophagy inhibitor, the anti‑cancer effects of PPM in mice bearing HepG2 xenografts were observed. Collectively, these results indicated that a self‑limiting effect impaired the pro‑apoptotic effects of PPM in liver cancer, but when combined with an autophagy inhibitor, it may serve as a novel therapeutic option for the management of liver cancer.

Exploring the Complex Link between Autophagy, Regulated Cell Death, and Cell Fate Pathways in Cancer Pathogenesis and Therapy

Autophagy is a catabolic lysosomal-dependent pathway involved in the degradation of cellular materials, supplying precursor compounds and energy for macromolecule synthesis and metabolic needs [...].

The role of autophagic cell death in cardiac disease

Cardiomyocytes undergo various forms of cell death during heart disease such as myocardial infarction and heart failure. Understanding the mechanisms of cell death in cardiomyocytes is one of the most fundamental issues in the treatment of heart failure. Among the several kinds of cell death mechanisms, this review will focus on autophagy-related cardiomyocyte cell death. Although autophagy plays an essential role in mediating cellular quality control mechanisms for cell survival, dysregulation of autophagy can cause cell death, referred to as autophagy-dependent cell death or type II programmed cell death. The recent discovery of autosis as a modality of autophagy-dependent cell death with unique morphological and biochemical features has allowed us to broaden our understanding of the mechanistic role of autophagy in cell death. Here, we discuss autophagy-dependent cardiomyocyte cell death, including autosis, in pathophysiological conditions of the heart.

Proscillaridin A induces mitochondrial damage and autophagy in pancreatic cancer and reduces the stability of SMAD4 in Panc-1 cells

Background

Pancreatic cancer (PC) is a highly metastatic and lethal cancer with a very low overall 5-year survival rate. There is an urgent need for identifying new therapeutic agents for this deadly disease. Cardiac glycosides (CGs) have been traditionally used for their potent cardiovascular activities and have also recently been reported to exhibit anti-tumor effects. Proscillaridin A (Pro A), a natural CG, has been shown to display anti-tumor effects on multiple cancer types.

Methods

The cytotoxic effect of Pro A on PC cells was determined using cell viability assay, colony formation assay and transwell assay in vitro. Cell apoptosis, cell cycle, reactive oxygen species (ROS) generation, intracellular Ca²⁺ levels and mitochondrial membrane potential (MMP) were assayed by flow cytometry. Panc-1-xenografted mice model was used to evaluate Pro A’s effect in tumor growth. Mitochondria morphology was observed by transmission electron microscopy. LC3 aggregation was assessed by GFP-LC3 fluorescence microscopy. Gene expression was assayed by western blot or real-time quantitative polymerase chain reaction (qPCR).

Results

Pro A inhibits the proliferation, migration and invasion of Panc-1, BxPC-3 and AsPC-1 PC cells in vitro, and Panc-1 cells display the highest sensitivity with an IC50 at the nano-molar level. In vivo, Pro A treatment inhibits tumor progression in Panc-1 xenograft nude mice. Pro A treatment promotes both cell apoptosis and autophagy, and Pro A-treated PC cells display characteristics of mitochondrial damage including increased ROS generation, intracellular Ca²⁺ levels and disruption of MMP. In addition, high sensitivity towards Pro A of Panc-1 cells compared to BxPC-3 and AsPC-1 cells could be partially attributed to the loss of endogenous SMAD4 expression in the latter.

Conclusions

Our findings suggest that Pro A constitutes a promising therapeutic candidate for certain types of PC.

A quantitative high-throughput screen identifies compounds that lower expression of the SCA2-and ALS-associated gene ATXN2

CAG repeat expansions in the ATXN2 (ataxin-2) gene can cause the autosomal dominant disorder spinocerebellar ataxia type 2 (SCA2) as well as increase the risk of ALS. Abnormal molecular, motor, and neurophysiological phenotypes in SCA2 mouse models are normalized by lowering ATXN2 transcription, and reduction of nonmutant Atxn2 expression has been shown to increase the life span of mice overexpressing the TDP-43 (transactive response DNA-binding protein 43 kDa) ALS protein, demonstrating the potential benefits of targeting ATXN2 transcription in humans. Here, we describe a quantitative high-throughput screen to identify compounds that lower ATXN2 transcription. We screened 428,759 compounds in a multiplexed assay using an ATXN2-luciferase reporter in human embryonic kidney 293 (HEK-293) cells and identified a diverse set of compounds capable of lowering ATXN2 transcription. We observed dose-dependent reductions of endogenous ATXN2 in HEK-293 cells treated with procillaridin A, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), and heat shock protein 990 (HSP990), known inhibitors of HSP90 and Na+/K+-ATPases. Furthermore, HEK-293 cells expressing polyglutamine-expanded ATXN2-Q58 treated with 17-DMAG had minimally detectable ATXN2, as well as normalized markers of autophagy and endoplasmic reticulum stress, including STAU1 (Staufen 1), molecular target of rapamycin, p62, LC3-II (microtubule-associated protein 1A/1B-light chain 3II), CHOP (C/EBP homologous protein), and phospho-eIF2α (eukaryotic initiation factor 2α). Finally, bacterial artificial chromosome ATXN2-Q22 mice treated with 17-DMAG or HSP990 exhibited highly reduced ATXN2 protein abundance in the cerebellum. Taken together, our study demonstrates inhibition of HSP90 or Na+/K+-ATPases as potentially effective therapeutic strategies for treating SCA2 and ALS.

Calotropin and corotoxigenin 3-O-glucopyranoside from the desert milkweed Asclepias subulata inhibit the Na+/K+-ATPase activity

Na⁺/K⁺-ATPase is an essential transmembrane enzyme found in all mammalian cells with critical functions for cell ion homeostasis. The inhibition of this enzyme by several cardiotonic steroids (CTS) has been associated with the cytotoxic effect on cancer cell lines of phytochemicals such as ouabain and digitoxin. This study evaluated the inhibitory capacity of cardenolides calotropin and corotoxigenin 3-O-glucopyranoside (C3OG) from Asclepias subulata over the Na⁺/K⁺-ATPase activity in vitro and silico. The inhibitory assays showed that calotropin and C3OG decreased the Na⁺/K⁺-ATPase activity with IC₅₀ values of 0.27 and 0.87 μM, respectively. Furthermore, the molecules presented an uncompetitive inhibition on Na⁺/K⁺-ATPase activity, with K_i values of 0.2 μM to calotropin and 0.5 μM to C3OG. Furthermore, the molecular modeling indicated that calotropin and C3OG might interact with the Thr⁷⁹⁷ and Gln¹¹¹ residues, considered essential to the interaction with the Na⁺/K⁺-ATPase. Besides, these cardenolides can interact with amino acid residues such as Phe⁷⁸³, Leu¹²⁵, and Ala³²³, to establish hydrophobic interactions on the binding site. Considering the results, these provide novel evidence about the mechanism of action of cardenolides from A. subulata, proposing that C3OG is a novel cardenolide that deserves further consideration for in vitro cellular antiproliferative assays and in vivo studies as an anticancer molecule.

Autophagy in asthma and chronic obstructive pulmonary disease

Autophagy (or macroautophagy) is a key cellular process that removes damaged molecules (particularly proteins) and subcellular organelles to maintain cellular homeostasis. There is growing evidence that abnormalities in autophagy may contribute to the pathogenesis of many chronic diseases, including asthma and chronic obstructive pulmonary disease (COPD). In asthma, increased autophagy plays a role in promoting type 2 immune responses and eosinophilic inflammation, whereas decreased autophagy may be important in neutrophilic asthma. Acute exposure to cigarette smoke may activate autophagy, resulting in ciliary dysfunction and death of airway epithelial cells, whereas in stable COPD most studies have demonstrated an impairment in autophagy, with reduced autophagic flux and accumulation of abnormal mitochondria (defective mitophagy) and linked to cellular senescence. Autophagy may be increased or decreased in different cell types and depending on the cellular environment, making it difficult to target autophagy therapeutically. Several existing drugs may activate autophagy, including rapamycin, metformin, carbamazepine, cardiac glycosides and statins, whereas others, such as chloroquine, inhibit this process. However, these drugs are nonspecific and more selective drugs are now in development, which may prove useful as novel agents to treat asthma and COPD in the future.