Natural and synthetic flavonoids, novel blockers of the volume-regulated anion channels, inhibit endothelial cell proliferation

The natural polyphenol fisetin in atherosclerosis prevention: a mechanistic review

The incidence and mortality rate of atherosclerotic cardiovascular disease (ASCVD) is increasing yearly worldwide. Recently, a growing body of evidence has unveiled the anti-atherosclerotic properties of fisetin, a natural polyphenol compound. In this article, we reviewed the pharmacologic actions of fisetin on experimental atherosclerosis and its protective effects on disease-relevant cell types such as endothelial cells, macrophages, vascular smooth muscle cells, and platelets. Based on its profound cardiovascular actions, fisetin holds potential for clinical translation and could be developed as a potential therapeutic option for atherosclerosis and its related complications. Large-scale randomized clinical trials are warranted to ascertain the safety and efficacy of fisetin in patients with or high risk for ASCVD.

Physiology of the volume-sensitive/regulatory anion channel VSOR/VRAC. Part 1: from its discovery and phenotype characterization to the molecular entity identification

The volume-sensitive outwardly rectifying or volume-regulated anion channel, VSOR/VRAC, which was discovered in 1988, is expressed in most vertebrate cell types and is essentially involved in cell volume regulation after swelling and in the induction of cell death. This series of review articles describes what is already known and what remains to be uncovered about the functional and molecular properties as well as the physiological and pathophysiological roles of VSOR/VRAC. This Part 1 review article describes, from the physiological standpoint, first its discovery and significance in cell volume regulation, second its phenotypical properties, and third its molecular identification. Although the pore-forming core molecules and the volume-sensing subcomponent of VSOR/VRAC were identified as LRRC8 members and TRPM7 in 2014 and 2021, respectively, it is stressed that the identification of the molecular entity of VSOR/VRAC is still not complete enough to explain the full set of phenotypical properties.

Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206

Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.

ATP modulation of osmotically activated anionic current in the membrane of Phycomyces blakesleeanus sporangiophore

Ion channels are vital components of filamentous fungi signaling in communication with their environment. We exploited the ability of the apical region of growing sporangiophores of Phycomyces blakesleeanus to form membrane-enveloped cytoplasmic droplets (CDs), to examine ion currents in the filamentous fungi native plasma membrane. In hypoosmotic conditions, the dominant current in the CDs is ORIC, an osmotically activated, anionic, outwardly rectified, fast inactivating instantaneous current that we have previously characterized. Here, we examined the effect of ATP on ORIC. We show that CDs contain active mitochondria, and that respiration inhibition by azide accelerates ORIC inactivation. ATP, added intracellularly, reduced ORIC run-down and shifted the voltage dependence of inactivation toward depolarized potentials, in a manner that did not require hydrolysis. Notably, ATP led to slowing down of ORIC inactivation, as evidenced by an increased time constant of inactivation, τ_in, and slower decline of τ_in during prolonged recordings. Flavonoids (genistein and quercetin) had the effect on ORIC opposite to ATP, acting as current inhibitors, possibly by disrupting the stabilizing effect of ATP on ORIC. The integration of osmotic sensing with ATP dependence of the anionic current, typical of vertebrate cells, is described here for the first time in filamentous fungi.

Trends in volume-regulated anion channel (VRAC) research: visualization and bibliometric analysis from 2014 to 2022

Objective: In this study, we utilized bibliometric methods to assess the worldwide scientific output and identify hotspots related to the research on the volume-regulated anion channel (VRAC) from 2014 to 2022. Methods: From Web of Science, we obtained studies related to VRAC published from 2014 to 2022. To analyzed the data, we utilized VOSviewer, a tool for visualizing network, to create networks based on the collaboration between countries, institutions, and authors. Additionally, we performed an analysis of journal co-citation, document citation, and co-occurrence of keywords. Furthermore, we employed CiteSpace (6.1. R6 Advanced) to analyzed keywords and co-cited references with the strongest burst. Results: The final analysis included a total of 278 related articles and reviews, covering the period from 2014 to 2022. The United States emerged as the leading country contributing to this field, while the University of Copenhagen stood out as the most prominent institution. The author with most publications and most citations was Thomas J. Jentsch. Among the cited references, the article by Voss et al. published in Science (2014) gained significant attention for its identification of LRRC8 heteromers as a crucial component of the volume-regulated anion channel VRAC. Pflügers Archiv European Journal of Physiology and Journal of Physiology-London were the leading journals in terms of the quantity of associated articles and citations. Through the analysis of keyword co-occurrence, it was discovered that VRAC is involved in various physiological processes including cell growth, migration, apoptosis, swelling, and myogenesis, as well as anion and organic osmolyte transport including chloride, taurine, glutamate and ATP. VRAC is also associated with related ion channels such as TMEM16A, TMEM16F, pannexin, and CFTR, and associated with various diseases including epilepsy, leukodystrophy, atherosclerosis, hypertension, cerebral edema, stroke, and different types of cancer including gastric cancer, glioblastoma and hepatocellular carcinoma. Furthermore, VRAC is involved in anti-tumor drug resistance by regulating the uptake of platinum-based drugs and temozolomide. Additionally, VRAC has been studied in the context of pharmacology involving DCPIB and flavonoids. Conclusion: The aim of this bibliometric analysis is to provide an overall perspective for research on VRAC. VRAC has become a topic of increasing interest, and our analysis shows that it continues to be a prominent area. This study offers insights into the investigation of VRAC channel and may guide researchers in identifying new directions for future research.

Osmotically Activated Anion Current of Phycomyces Blakesleeanus-Filamentous Fungi Counterpart to Vertebrate Volume Regulated Anion Current

Studies of ion currents in filamentous fungi are a prerequisite for forming a complete understanding of their physiology. Cytoplasmic droplets (CDs), obtained from sporangiophores of Phycomyces blakesleeanus, are a model system that enables the characterization of ion currents in the native membrane, including the currents mediated by the channels not yet molecularly identified. Osmotically activated anionic current with outward rectification (ORIC) is a dominant current in the membrane of cytoplasmic droplets under the conditions of hypoosmotic stimulation. We have previously reported remarkable functional similarities of ORIC with the vertebrate volume regulated anionic current (VRAC), such as dose-dependent activation by osmotic difference, ion selectivity sequence, and time and voltage dependent profile of the current. Using the patch clamp method on the CD membrane, we further resolve VRAC-like ORIC characteristics in this paper. We examine the inhibition by extracellular ATP and carbenoxolone, the permeation of glutamate in presence of chloride, selectivity for nitrates, and activation by GTP, and we show its single channel behavior in excised membrane. We propose that ORIC is a functional counterpart of vertebrate VRAC in filamentous fungi, possibly with a similar essential role in anion efflux during cell volume regulation.

Pharmacological properties of total flavonoids in Scutellaria baicalensis for the treatment of cardiovascular diseases

BACKGROUND

Scutellaria baicalensis, a medicinal herb belonging to the Lamiaceae family, has been recorded in the Chinese, European, and British Pharmacopoeias. The medicinal properties of this plant are attributed to the total flavonoids of Scutellaria baicalensis (TFSB), particularly the main component, baicalin. This study provides a systematic and comprehensive list of the identified TFSB components and their chemical structures. The quality control process, pharmacokinetics, clinical application, and safety of Scutellaria baicalensis are discussed, and its pharmacological effect on cardiovascular diseases (CVDs) is detailed. Finally, the future research trends and prospects of this medicinal plant are provided.

METHODS

The Chinese and English papers related to TFSB were collected from the PubMed and CNKI databases using the relevant keywords. To highlight the pharmacological mechanism, clinical application, and safety of TFSB, the collected articles were screened and classified based on their research content.

RESULTS

TFSB contains at least 100 different kinds of flavonoids, of which baicalin, baicalein, wogonin, wogonoside, scutellarin, and scutellarein are the main active ingredients. The preparation process of TFSB is relatively well established, and the extraction rate can be significantly increased by enzymatic pretreatment and ultrasonication. The low oral availability of TFSB may be effectively enhanced using nanoformulations. The available pharmacokinetic data show that flavonoid glycosides and aglycones with the same parent nucleus may be converted to structures that are conducive to absorption in vivo. Moreover, TFSB can protect against CVDs by inhibiting apoptosis, regulating oxidative stress response, participating in inflammatory response, protecting against myocardial fibrosis, inhibiting myocardial hypertrophy, and regulating blood vessels. In terms of clinical application and animal safety, the available studies show that TFSB can be applied in a wide range of clinical treatments and is safe to use is animals.

CONCLUSION

This article systematically reviews the therapeutic effect and underlying pharmacological mechanism of TFSB against CVDs. The available studies clearly suggest that TFSB has great potential for the treatment of CVDs and is worthy of in-depth research and development.

The Potential Therapeutic Properties of Prunetin against Human Health Complications: A Review of Medicinal Importance and Pharmacological Activities

BACKGROUND

Flavonoids are polyphenolic compounds found to be present in nature and abundant in flowers and fruits. Flavonoidal class phytochemicals have gained interest in the scientific field because of their important pharmacological activities. Several scientific studies have revealed anti-bacterial, anti-oxidant, anti-fungal, analgesic, anti-viral, anti-inflammatory, anti-tumor, anti-parasitic and anti-allergic activities of flavonoidal class phytochemicals. Prunetin is an O-methylated isoflavone that belongs to the phytochemical phytoestrogen class, found to be present in licorice, red cherry, soybean and legumes.

METHODS

Biological potential and pharmacological activities of prunetin have been investigated in the present work through scientific data analysis of numerous scientific research works. Numerous literature databases have been searched in order to collect the scientific information on prunetin in the present work. Pharmacological activities of prunetin have been investigated in the present work through literature data analysis of different scientific research works. Scientific data have been collected from Google Scholar, Google, PubMed, Science Direct and Scopus. Analytical data on prunetin has been collected from literature sources and analyzed in the present work.

RESULTS

Scientific data analysis revealed the biological importance of prunetin in medicine. Prunetin was found to be present in the pea, peach, Oregon cherry, skimmed cheese, cheese, cow kefir and goat kefir. Prunetin is also present in the Prunus avium, Andira surinamensis, Butea superba, Dalbergia sympathetica, Ficus nervosa, Pterospartum tridentatum and Pycnanthus angolensis. Pharmacological data analysis revealed the biological importance of prunetin on bone disorders, cancers, especially hepatocellular carcinoma, urinary bladder cancer, gastric cancer, ovarian cancer, human airway, gut health and enzymes. Scientific data analysis revealed biological effectiveness of prunetin for their angiogenic effects, anti-inflammatory, anti-oxidant, antimicrobial, estrogenic and vasorelaxant potential. Analytical data revealed the importance of modern analytical techniques for qualitative and quantitative analysis of prunetin in the scientific fields.

CONCLUSION

Scientific data analysis in the present investigation revealed the biological importance and pharmacological activities of prunetin in medicine.

4-(2-Butyl-6,7-dichloro-2-cyclopentyl-indan-1-on-5-yl) oxobutyric acid inhibits angiogenesis via modulation of vascular endothelial growth factor receptor 2 signaling pathway

4-(2-Butyl-6,7-dichloro-2-cyclopentyl-indan-1-on-5-yl) oxobutyric acid (DCPIB), was discovered to be a potent and specific antagonist of volume-regulated anion channel that is closely linked to angiogenesis. However, the effect of DCPIB on angiogenesis remains unclear. Here, we found that DCPIB inhibited angiogenesis in the corneal suture and myocardial infarction in vivo model. In addition, DCPIB inhibited human umbilical vein endothelial cell migration, tube formation and proliferation in vitro. Moreover, DCPIB repressed the activation and expression of vascular endothelial growth factor receptor 2 (VEGFR2) and its downstream signaling pathway. Computer modeling further confirmed that DCPIB binds with high affinity to VEGFR2. Collectively, we present evidence supporting an antiangiogenic role of DCPIB by targeting VEGFR2 signaling pathway, which suggests that DCPIB is a valuable lead compound for the treatment of angiogenesis-related diseases.

Mechanistic Effects of Baicalein on Aqueous Humor Drainage and Intraocular Pressure

Elevated intraocular pressure (IOP) is a major risk factor for glaucoma that results from impeded fluid drainage. The increase in outflow resistance is caused by trabecular meshwork (TM) cell dysfunction and excessive extracellular matrix (ECM) deposition. Baicalein (Ba) is a natural flavonoid and has been shown to regulate cell contraction, fluid secretion, and ECM remodeling in various cell types, suggesting the potential significance of regulating outflow resistance and IOP. We demonstrated that Ba significantly lowered the IOP by about 5 mmHg in living mice. Consistent with that, Ba increased the outflow facility by up to 90% in enucleated mouse eyes. The effects of Ba on cell volume regulation and contractility were examined in primary human TM (hTM) cells. We found that Ba (1–100 µM) had no effect on cell volume under iso-osmotic conditions but inhibited the regulatory volume decrease (RVD) by up to 70% under hypotonic challenge. In addition, Ba relaxed hTM cells via reduced myosin light chain (MLC) phosphorylation. Using iTRAQ-based quantitative proteomics, 47 proteins were significantly regulated in hTM cells after a 3-h Ba treatment. Ba significantly increased the expression of cathepsin B by 1.51-fold and downregulated the expression of D-dopachrome decarboxylase and pre-B-cell leukemia transcription factor-interacting protein 1 with a fold-change of 0.58 and 0.40, respectively. We suggest that a Ba-mediated increase in outflow facility is triggered by cell relaxation via MLC phosphorylation along with inhibiting RVD in hTM cells. The Ba-mediated changes in protein expression support the notion of altered ECM homeostasis, potentially contributing to a reduction of outflow resistance and thereby IOP.

Therapeutic importance and pharmacological activities of karanjin in the medicine for the treatment of Human disorders: A review through scientific data analysis

Backgrounds:

Plant and derived herbal drugs have been used in the traditional system of medicine for the treatment of various forms of human health complications since a very early age. Commercial products prepared from natural herbs have been always valuable for the society in the form of health supplement to medicament. In the ancient time, herbal products were mainly prepared from plants and their derived phytochemical. Plants contain a rich source of pure phytochemical called secondary metabolite and examples are flavonoids, glycosides, tannins and terpenoids etc. Plants and their parts including fruits, flowers, vegetables etc. are the best source of Flavonoid class phytochemicals.

Methods:

Present work summarized the scientific information of karanjin for their health beneficial aspects and pharmacological activities including its analytical aspects. In the present investigation, scientific data of karanjin have been collected from various scientific databases such as Google, Goggle Scholar, Science Direct and PubMed and analyzed to know the health beneficial aspects of karanjin in the medicine. Further pharmacological activity data has been collected and analyzed in the present work to know their biological potential in the medicine. Analytical methods used for the separation, isolation, and identification of karanjin for the standardization of different natural products have been also discussed in the present work.

Results:

Scientific data analysis signified the biological importance of Flavonoid class phytochemicals in the medicine as they are well known for their anti-ischemic, vasodilatory, anti-bacterial, anti-inflammatory, anti-oxidant, anti-viral, and anti-cancer activities. Scientific data analysis revealed the presences of karanjin in numerous medicinal plants such as Fordia cauliflora, Lonchocarpus latifolius, Millettia pinnata, Millettia pubinervis, Pongamia pinnata, and Tephrosia purpurea. Pharmacological activity data revealed the biological potential of karanjin against cancerous disorders, glucose metabolism abnormalities, gastrointestinal disorders, arthritis, inflammatory disorders, colitis, psoriasis and brain related disorders. However, analytical data signified the importance of RP-HPLC, TLC, HPTLC, UPLC-ESI-MS/MS and HSCCC techniques in the medicine for the quantification of karanjin in different samples.

Conclusion:

Presented information about karanjin in this review paper will be beneficial to the scientific peoples of the world to know the health beneficial aspects of karanjin in the medicine.

Properties, Structures, and Physiological Roles of Three Types of Anion Channels Molecularly Identified in the 2010's

Molecular identification was, at last, successfully accomplished for three types of anion channels that are all implicated in cell volume regulation/dysregulation. LRRC8A plus LRRC8C/D/E, SLCO2A1, and TMEM206 were shown to be the core or pore-forming molecules of the volume-sensitive outwardly rectifying anion channel (VSOR) also called the volume-regulated anion channel (VRAC), the large-conductance maxi-anion channel (Maxi-Cl), and the acid-sensitive outwardly rectifying anion channel (ASOR) also called the proton-activated anion channel (PAC) in 2014, 2017, and 2019, respectively. More recently in 2020 and 2021, we have identified the S100A10-annexin A2 complex and TRPM7 as the regulatory proteins for Maxi-Cl and VSOR/VRAC, respectively. In this review article, we summarize their biophysical and structural properties as well as their physiological roles by comparing with each other on the basis of their molecular insights. We also point out unsolved important issues to be elucidated soon in the future.

Herbal Phytomedicine 'Irisolidone' in Chronic Diseases: Biological Efficacy and Pharmacological Activity

BACKGROUND

Plant-derived products have been used in medicine as a source of bioactive molecules, mainly due to their medicinal importance and therapeutic potential. Nowadays, plant derived products have been used in the medicine for the development of novel drug leads. Polyphenols are an important class of secondary metabolites found to be present in plants and their derived products. Polyphenols play an important role in the nutrition of human beings and also have a significant role in plant resistance against pests and diseases. Scientific studies have proven the biological importance of flavonoids in medicine and other allied health sectors. Anti-oxidant, analgesic, anti-microbial, anti-inflammatory, anti-viral, anti-tumor and anti-allergic activities are the important pharmacological features of flavonoids. Irisolidone is an important isoflavone found to be present in Pueraria lobata flowers.

METHODS

To know the medicinal importance and therapeutic potential of irisolidone in the medicine, numerous scientific research data have been collected from Google, Google Scholar, PubMed, Science Direct, and Scopus. Pharmacological activity data of irisolidone has been collected and analyzed in the present works to know their health beneficial aspects in the medicine. Detailed pharmacological activities of irisolidone have been investigated through scientific data analysis of scientific research works.

RESULTS

Scientific research data analysis of irisolidone revealed the anti-inflammatory, antiangiogenic, anti-cancer, anti-platelet, anti-oxidant, anti-hyperlipidemic, immunomodulating, hepatoprotective and estrogenic potential. However, the biological effect of irisolidone on the gastric system, aldose reductase enzymes, malignant gliomas, and JC virus has also been investigated. Scientific data analysis revealed the significance of analytical tools for the separation and identification of irisolidone.

CONCLUSION

Present work signified the biological importance and therapeutic potential of irisolidone in medicine.

Anticancer Activity of Natural and Synthetic Chalcones

Cancer is a condition caused by many mechanisms (genetic, immune, oxidation, and inflammatory). Anticancer therapy aims to destroy or stop the growth of cancer cells. Resistance to treatment is theleading cause of the inefficiency of current standard therapies. Targeted therapies are the most effective due to the low number of side effects and low resistance. Among the small molecule natural compounds, flavonoids are of particular interest for theidentification of new anticancer agents. Chalcones are precursors to all flavonoids and have many biological activities. The anticancer activity of chalcones is due to the ability of these compounds to act on many targets. Natural chalcones, such as licochalcones, xanthohumol (XN), panduretin (PA), and loncocarpine, have been extensively studied and modulated. Modification of the basic structure of chalcones in order to obtain compounds with superior cytotoxic properties has been performed by modulating the aromatic residues, replacing aromatic residues with heterocycles, and obtaining hybrid molecules. A huge number of chalcone derivatives with residues such as diaryl ether, sulfonamide, and amine have been obtained, their presence being favorable for anticancer activity. Modification of the amino group in the structure of aminochalconesis always favorable for antitumor activity. This is why hybrid molecules of chalcones with different nitrogen hetercycles in the molecule have been obtained. From these, azoles (imidazole, oxazoles, tetrazoles, thiazoles, 1,2,3-triazoles, and 1,2,4-triazoles) are of particular importance for the identification of new anticancer agents.

Structural bioinformatics used to predict the protein targets of remdesivir and flavones in SARS-CoV-2 infection

BACKGROUND

During the current SARS-CoV-2 pandemic, the identification of effective antiviral drugs is crucial. Unfortunately, no specific treatment or vaccine is available to date.

OBJECTIVE

Here, we aimed to predict the interactions between SARS-CoV-2 proteins and protein targets from the human body for some flavone molecules (kaempferol, morin, pectolinarin, myricitrin, and herbacetin) in comparison to synthetic compounds (hydroxychloroquine, remdesivir, ribavirin, ritonavir, AMD-070, favipiravir).

METHODS

Using MOE software and advanced bioinformatics and cheminformatics portals, we conducted an extensive analysis based on various structural and functional features of compounds, such as their amphiphilic field, flexibility, and steric features. The structural similarity analysis of natural and synthetic compounds was performed using Tanimoto coefficients. The interactions of some compounds with SARS-CoV-2 3CLprotease or RNA-dependent RNA polymerase were described using 2D protein-ligand interaction diagrams based on known crystal structures. The potential targets of considered compounds were identified using the SwissTargetPrediction web tool.

RESULTS

Our results showed that remdesivir, pectolinarin, and ritonavir present a strong structural similarity which may be correlated to their similar biological activity. As common molecular targets of compounds in the human body, ritonavir, kaempferol, morin, and herbacetin can activate multidrug resistance-associated proteins, while remdesivir, ribavirin, and pectolinarin appear as ligands for adenosine receptors.

CONCLUSION

Our evaluation recommends remdesivir, pectolinarin, and ritonavir as promising anti-SARS-CoV-2 agents.

ClC-3: A Novel Promising Therapeutic Target for Atherosclerosis

Chloride channel 3 (ClC-3), a Cl^-/H⁺ antiporter, has been well established as a member of volume-regulated chloride channels (VRCCs). ClC-3 may be a crucial mediator for activating inflammation-associated signaling pathways by regulating protein phosphorylation. A growing number of studies have indicated that ClC-3 overexpression plays a crucial role in mediating increased plasma low-density lipoprotein levels, vascular endothelium dysfunction, pro-inflammatory activation of macrophages, hyper-proliferation and hyper-migration of vascular smooth muscle cells (VSMCs), as well as oxidative stress and foam cell formation, which are the main factors responsible for atherosclerotic plaque formation in the arterial wall. In the present review, we summarize the molecular structures and classical functions of ClC-3. We further discuss its emerging role in the atherosclerotic process. In conclusion, we explore the potential role of ClC-3 as a therapeutic target for atherosclerosis.

Targeting Chloride Ion Channels: New Insights into the Mechanism of Action of the Marine Toxin Azaspiracid

Azaspiracids (AZAs) are marine toxins produced by dinoflagellates belonging to the genera Azadinium and Amphidoma that caused human intoxications after consumption of contaminated fishery products, such as mussels. However, the exact mechanism for the AZA induced cytotoxic and neurotoxic effects is still unknown. In this study several pharmacological approaches were employed to evaluate the role of anion channels on the AZA effects that demonstrated that cellular anion dysregulation was involved in the toxic effects of these compounds. The results presented here demonstrated that volume regulated anion channels (VRACs) are affected by this group of toxins, and, because there is not any specific activator of VRACs besides the intracellular application of GTPγ-S molecule, this group of natural compounds could represent a powerful tool to analyze the role of these channels in cellular homeostasis. In addition to this, in this work, a detailed pharmacological approach was performed in order to elucidate the anion channels present in human HEK293 cells as well as their regulation by the marine toxins azaspiracids. Altogether, the data presented here demonstrated that the effect of azaspiracids in human cells was completely dependent on ATP-regulated anion channels, whose upregulation by these toxins could lead to regulatory volume decrease and underlie the reported toxicity of these compounds.

Inhibition of TMEM16A Ca2+-activated Cl- channels by avermectins is essential for their anticancer effects

Transmembrane member 16A (TMEM16A) encoded Ca²⁺-activated Cl^- channels were found to be involved in tumorigenesis. Previous studies suggest the effect of TMEM16A gene amplification on tumorigenic proliferation is exerted through its channel function. TMEM16A-specific and potent small molecule inhibitors have been proposed to potentially be useful for the treatment of cancer. Thus, we screened six analogues of avermectin for their inhibitory activities on TMEM16A mediated currents. A whole-cell patch technique was used to record the currents. The IC₅₀ and E_max values for TMEM16A inhibition of five tested avermectins (avermectin B₁, ivermectin, doramectin, selamectin, and moxidectin) were 0.15-1.32 μM and 65-87 %, respectively. In addition, these avermectins significantly inhibited endogenous TMEM16A mediated currents and thus, the proliferation, migration, inducing apoptosis of LA795 cancer cells. Eprinomectin (4"-(acetylamino)-4"-deoxy-avermectin B₁) and two other important macrolides (erythromycin and azithromycin), which have minimal or no TMEM16A inhibitory effects, were used as negative control drugs. These drugs were found to have limited effects on the proliferation, migration, and apoptosis of LA795 cells. Finally, avermectin B₁ and ivermectin dramatically inhibited the growth of xenograft tumors in mice. These data demonstrate that avermectins are novel TMEM16A inhibitors and are potentially useful in specific cancer therapies. These findings also provide a new opportunity to develop TMEM16A modulators.

Effect of plant flavonoids on the volume regulation of rat thymocytes under hypoosmotic stress

BACKGROUND

Cell volume regulation and volume-regulated anion channels are critical for cell survival in non-isosmotic conditions, and dysregulation of this system is detrimental. Although genes and proteins underlying this basic cellular machinery were recently identified, the pharmacology remains poorly explored.

METHODS

We examined effects of 16 flavonoids on the regulatory volume decrease (RVD) of thymocytes under hypoosmotic stress assessed by light transmittance and on the activity of volume-sensitive chloride channel by patch-clamp technique.

RESULTS

Comparison of effects of flavonoids on RVD revealed a group of four active substances with lehmannin being the strongest inhibitor (IC50 = 8.8 μM). Structure-functional comparison suggested that hydrophobicity brought about by methoxy, prenyl or lavandulyl groups as well as by the absence of glucosyl fragment together with localization of the phenyl ring B at the position C2 (which is at C3 in totally inactive isoflavones) are important structural determinants for the flavonoids activity as volume regulation inhibitors. All active flavonoids suppressed RVD under Gramicidin D-NMDG hypotonic stress conditions when cationic permeability was increased by an ionophore, gramicidin D, with all extracellular monovalent cations replaced with bulky NMDG+ suggesting that they target volume-sensitive anionic permeability. While effects of hispidulin and pulicarin were only partial, lehmannin and pinocembrin completely abolished RVD under Gramicidin D-NMDG conditions. In direct patch-clamp experiments, lehmannin and pinocembrin produced a strong inhibiting effect on the swelling-induced whole-cell chloride conductance in a voltage-independent manner.

CONCLUSION

Lehmannin, pinocembrin, and possibly hispidulin and pulicarin may serve as leads for developing effective low-toxic immunomodulators.

Tannins, novel inhibitors of the volume regulation and the volume-sensitive anion channel

The volume-sensitive outwardly rectifying anion channel (VSOR) is a key component of volume regulation system critical for cell survival in non-isosmotic conditions. The aim of the present study was to test the effects of four tannin extracts with defined compositions on cell volume regulation and VSOR. Preparation I (98% of hydrolysable tannins isolated from leaves of sumac Rhus typhina L.) and Preparation II (100% of hydrolysable tannins isolated from leaves of broadleaf plantain Plantago major L) completely and irreversibly abolished swelling-activated VSOR currents in HCT116 cells. Both preparations profoundly suppressed the volume regulation in thymocytes with half-maximal effects of 40.9 μg/ml and 12.3 μg/ml, respectively. The inhibition was more efficient at lower concentrations but reverted at higher doses due to possible non-specific membrane-permeabilizing activity. Preparations III and IV (54,7% and 54.3% of hydrolysable tannins isolated, respectively, from roots and aboveground parts of Fergana spurge Euphorbia ferganensis B.Fedtch) inhibited VSOR activity in a partially reversible manner and suppressed the volume regulation with substantially higher half-maximal doses of 270 and 278 μg/ml, respectively, with no secondary reversion at higher doses. Hydrolysable tannins represent a novel class of VSOR channel inhibitors with the capacity to suppress the cell volume regulation machinery.

More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels

The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.

The Volume-Regulated Anion Channel LRRC8/VRAC Is Dispensable for Cell Proliferation and Migration

Cells possess the capability to adjust their volume for various physiological processes, presumably including cell proliferation and migration. The volume-regulated anion channel (VRAC), formed by LRRC8 heteromers, is critically involved in regulatory volume decrease of vertebrate cells. The VRAC has also been proposed to play a role in cell cycle progression and cellular motility. Indeed, recent reports corroborated this notion, with potentially important implications for the VRAC in cancer progression. In the present study, we examined the role of VRAC during cell proliferation and migration in several cell types, including C2C12 myoblasts, human colon cancer HCT116 cells, and U251 and U87 glioblastoma cells. Surprisingly, neither pharmacological inhibition of VRAC with 4-[(2-Butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid (DCPIB), carbenoxolone or 5-nitro-2-(3-phenylpropyl-amino)benzoic acid (NPPB), nor siRNA-mediated knockdown or gene knockout of the essential VRAC subunit LRRC8A affected cell growth and motility in any of the investigated cell lines. Additionally, we found no effect of the VRAC inhibition using siRNA treatment or DCPIB on PI3K/Akt signaling in glioblastoma cells. In summary, our work suggests that VRAC is dispensable for cell proliferation or migration.

A 30-year journey from volume-regulated anion currents to molecular structure of the LRRC8 channel

Strange et al. review recent advances in our understanding of the molecular and structural basis of volume-regulated anion channel function within the framework of classical biophysical and physiological studies.

The swelling-activated anion channel VRAC has fascinated and frustrated physiologists since it was first described in 1988. Multiple laboratories have defined VRAC’s biophysical properties and have shown that it plays a central role in cell volume regulation and possibly other fundamental physiological processes. However, confusion and intense controversy surrounding the channel’s molecular identity greatly hindered progress in the field for >15 yr. A major breakthrough came in 2014 with the demonstration that VRAC is a heteromeric channel encoded by five members of the Lrrc8 gene family, Lrrc8A–E. A mere 4 yr later, four laboratories described cryo-EM structures of LRRC8A homomeric channels. As the melee of structure/function and physiology studies begins, it is critical that this work be framed by a clear understanding of VRAC biophysics, regulation, and cellular physiology as well as by the field’s past confusion and controversies. That understanding is essential for the design and interpretation of structure/function studies, studies of VRAC physiology, and studies aimed at addressing the vexing problem of how the channel detects cell volume changes. In this review we discuss key aspects of VRAC biophysics, regulation, and function and integrate these into our emerging understanding of LRRC8 protein structure/function.

An Intermediary Role of Adenine Nucleotides on Free Fatty Acids-Induced Hyperglycemia in Obese Mice

Increased plasma free fatty acids (FFA) level plays a central role in the development of type 2 diabetes. Our previous studies have shown that plasma 5'-adenosine monophosphate (5'-AMP) elevates and acts as a potential upstream regulator of hyperglycemia in diabetic db/db mice. The relationship between FFA and plasma adenosine nucleotides in type 2 diabetes remains unclear. Here we found that plasma 5'-AMP level was also increased in diabetic mice induced by a high-fat diet and streptozotocin (HFD-STZ), as observed in diabetic db/db mice. The metabolites of adenosine nucleotides in plasma were increased in obese mice compared to lean mice. An acute oil gavage to lean mice increased both FFA and plasma purine metabolites, accompanying with glucose intolerance. 5'-AMP administration resulted in an increase in dose-dependent purine metabolites and different levels of glucose intolerance. FFA induced a release of adenine nucleotides from cultural human umbilical vein endothelial cells (HUVECs) prior to induction of their apoptosis. FFA also reduced red blood cells (RBCs) resistance to reactive oxygen species (ROS), leading to hemolysis, thereby increasing plasma nucleotides. Our results suggest that plasma adenine nucleotides play an intermediary role in FFA-induced glucose intolerance and hyperglycemia in obese mice.