Polyether Ionophore Antibiotic Research Articles

The Biological Activities of Polyether Ionophore Antibiotic Routiennocin is Independent of Absolute Stereochemistry.

Carboxylic polyether ionophores (CPIs) are among the most prevalent agricultural antibiotics (notably in the US) and these compounds have been in use for decades. The potential to reposition CPIs beyond veterinary use, e. g. through chemical modifications to enhance their selectivity window, is an exciting challenge and opportunity, considering their general resilience towards resistance development. Given the very large societal impact of these somewhat controversial compounds, it is surprising that many aspects of their mechanisms and activities in cells remain unclear. Here, we report comparative biological activities of the CPI routiennocin and two stereoisomers, including its enantiomer. We used an efficient convergent synthesis strategy to access the compounds and conducted a broad survey of antibacterial activities against planktonic cells and biofilms as well as the compounds' effects on mammalian cells, the latter assessed both via standard cell viability assays and broad morphological profiling. Interestingly, similar bioactivity of the enantiomeric pair was observed across all assays, strongly suggesting that chiral interactions do not play a decisive role in the mode of action. Overall, our findings are consistent with a mechanistic model involving highly dynamic behaviour of CPIs in biological membranes.

Development of multiplex immunochromatographic assay for the simultaneous detection of three polyether ionophore antibiotics in chicken muscle

ABSTRACT A rapid, reliable, sensitive, and multiplex colloidal gold immunochromatographic assay (CGIA) was developed for the simultaneous detection of three polyether ionophore antibiotics (PEs) in chicken muscle. The IC50 values of the optimized CGIA were 1.63, 1.94, and 1.18 ng/mL with a linear range of 0.87–3.04 ng/mL, 0.85–4.41 ng/mL, and 0.57–2.44 ng/mL for maduramicin (MAD), monensin (MON), and salinomycin (SAL), respectively. The cut-off values were 10, 5, and 5 ng/mL, respectively. The whole testing process was completed within 15 min. A parallel analysis in blind chicken muscle samples was conducted by liquid chromatography–tandem mass spectrometry (LC-MS/MS), the developed CGIA did not appear false-positive and false-negative. The results show that the established method could provide a rapid and effective approach for on-site screening and determination of PEs residues in chicken muscle samples.

Potent salinomycin C20-O-alkyl oxime derivative SAL-98 efficiently inhibits tumor growth and metastasis by affecting Wnt/β-catenin signal pathway

The dysregulation of Wnt/β-catenin signaling pathway is closely related to tumorigenesis, metastasis and cancer stem cell maintenance. Salinomycin is a polyether ionophore antibiotic that selectively eliminates cancer stem cells by inhibiting the Wnt/β-catenin signal pathway. Salinomycin selectively target cancer stem cells, but the toxicity limits its further use. In this study, we explore the anti-tumor mechanism of one most active salinomycin C20-O-alkyl oximederivative SAL-98 and found that SAL-98 exerts 10 times higher anti-tumor and anti-CSCs activities compared with salinomycin, which induces cell cycle arrest, ER stress and mitochondria dysfunction and inhibits Wnt/β-catenin signal pathway in vitro with high efficacy. Moreover, SAL-98 shows good anti-metastasis effect in vivo. In addition, SAL-98 demonstrates same anti-tumor activities as salinomycin with less 5 times concentration in vivo, the ER stress, autophagy and anti-CSCs effects were also confirmed in vivo. Mechanistically, SAL-98 inhibits the Wnt/β-catenin signaling pathway associated with CHOP expression induced by ER stress, the induced CHOP disrupts the β-catenin/TCF4 complex and represses the Wnt targeted genes. This study provides an alternative strategy for rational drug development to target Wnt/β-catenin signaling pathway.

A Concise Review of Prodigious Salinomycin and Its Derivatives Effective in Treatment of Breast Cancer: (2012–2022)

Cancer stem cells (CSCs) are the cells in a primary tumor that have the opportunity to self-renew as well as differentiate into certain cell types, thus forming a mixed tumor. CSCs have been shown to be involved in every aspect of cancer development, including tumor initiation, proliferation, and metastatic activity; they are also involved in chemotherapeutic drug resistance and the recurrence of certain cancers. Based on these capabilities, CSCs have been explored as the next target for the treatment and management of cancer. Salinomycin (SAL), a polyether ionophore antibiotic being used in the poultry industry, was identified as a powerful anti-cancer compound that possesses broad-spectrum activities, especially against CSCs. Here we point out the noteworthy work reported on SAL’s mechanism of action, anticancer activities, toxicity, and clinic applications. In addition, SAL derivatives synthesized by different research groups and their biological activity will also be highlighted.

Monensin and its analogues show anti‐glioblastoma activity in an organoid model of cancer

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Despite numerous clinical trials, the standard of care therapy has remained unchanged for the last decade. One of the main problems contributing to the limited effective treatment options and poor overall survival is the lack of models which can reliably recapitulate tumor heterogeneity. Organoids are 3D self‐organized structures which mimic tumor architecture, microenvironment, and cellular interactions which makes them an improved model for anti‐cancer drug discovery.Monensin (MON) is a polyether ionophore antibiotic characterized by wide range of biological properties including anti‐cancer activity. In order to identify more potent compounds based on the scaffold of MON, we investigated the anti‐GBM activity of 14 novel esters and urethanes of MON. In 3D mini‐ring cell viability assays, we identified seven analogues (IC50 = 91.5 ± 54.4 ‐ 291.7 ± 68.8 nM) more potent towards GBM than the parental MON (IC50 = 612.6 ± 184.4 nM). These analogues induced DNA fragmentation in an organoid model of GBM, suggestive of apoptotic cell death. Furthermore, the most potent analog, compound 1, significantly reduced GBM cell migration, induced PARP cleavage and degradation, increased ɣH2AX signaling and increased expression of the autophagy marker LCII. To investigate the activity of these novel compounds in a tumor microenvironment, we have developed a host:tumor hybrid 3D organoid system. For host tissue, we generated human cerebral organoids (COs) from hiPSCs. The COs displayed multiple neural rosettes with a proliferative zone of neural stem cells (Nestin+), neurons (TUJ1+), primitive ventricular system (SOX2+/Ki67+), intermediate zone (TBR2+) and cortical plate (MAP2+). These findings suggest the level of differentiation and development of our COs as equivalent to early stage human fetal brain. We then co‐cultured RFP‐labeled U87MG cells with fully formed COs. After establishing U87MG tumor formation, hybrid organoids were treated with MON or compound 1. Compound 1 significantly reduced U87MG tumor size after four days of treatment. Our findings highlight the therapeutic potential of MON analogues towards GBM and support further research and clinical development of these compounds.

Salinomycin induces cell cycle arrest and apoptosis and modulates hepatic cytochrome P450 mRNA expression in HepG2/C3a cells

Salinomycin (SAL) is a monocarboxylic polyether ionophore antibiotic isolated from Streptomyces albus. It exhibits an effective antitumor potential against numerous human cancer cells. This study aimed to assess the antiproliferative effects of SAL in human hepatocellular carcinoma HepG2/C3a cell line. We investigated the effects of SAL on cell growth, DNA damage induction, cell cycle changes and apoptosis; and relative changes in expression of cell cycle-related, apoptosis-related, and CYP450 genes. SAL induced cell cycle arrest in the G2/M phase, upregulation of CDKN1A and GADD45A and downregulation of cyclin genes including CCNB1 and CCNA2. SAL effectively suppressed mRNA levels of CTNNB1 gene, an important oncogene that promotes tumorigenesis. The decrease of HepG2/C3A cells’ survival can also be due to downregulation of antiapoptotic BCL-2 expression, thus promoting the induction of apoptosis by SAL. This study also demonstrated the ability of SAL in modulating hepatic cytochrome P450 (CYP) mRNA expression, such that SAL caused the upregulation of CYP1A members and CYP3A5; and downregulation of CYP3A4. Taken together, these data contribute to the understanding of the mechanism of action of SAL, highlighting that metabolizing enzymes modulated by SAL can interfere with chemotherapy treatment and it must be considered in associated treatments.

Polyether ionophore kijimicin inhibits growth of Toxoplasma gondii and controls acute toxoplasmosis in mice.

The natural polyether ionophore antibiotics may be important chemotherapeutic agents. Among them, kijimicin represents an important type of ionophore compound because it inhibits Eimeria tenella and human immunodeficiency virus. The ionophore monensin displays potent activities against several coccidian parasites including the opportunistic pathogen of humans, Toxoplasma gondii. At first, we evaluated the anti-Toxoplasma activity of kijimicin, monensin as a reference control, and anti-Toxoplasma drugs such as clindamycin, in vitro. The half inhibitory concentrations (IC50) for the anti-Toxoplasma activities of kijimicin, monensin, and clindamycin were 45.6 ± 2.4nM, 1.3 ± 1.8nM, and 238.5 ± 1.8nM, respectively. Morphological analyses by electron microscopy revealed cellular swelling and multiple intracellular vacuole-like structures in the T. gondii tachyzoites after treatment with kijimicin and monensin. Kijimicin and monensin also inhibited the invasion of extracellular parasites (IC50 = 216.6 ± 1.9pM and 531.1 ± 1.9pM, respectively). Importantly, kijimicin treatment resulted in decreased mitochondrial membrane potential and generation of reactive oxygen species in T. gondii as monensin did. Furthermore, mice treated with kijimicin at 10mg/kg/day and 3mg/kg/day showed 91.7% and 66.7% survival rates, respectively, 30days after infection with T. gondii. The control mice all died within 18days of infection. The present study shows that kijimicin inhibits T. gondii growth and changes the ultrastruct of the parasites. This finding may lead to validation of kijimicin as new drug to control T. gondii growth.

Maduramicin arrests myocardial cells at G0/G1 phase of the cell cycle through inhibiting AKT-Cyclin D1 signaling.

Maduramicin, a polyether ionophore antibiotic used as an anticoccidial feed additive in poultry, is toxic to animals and humans and can cause heart failure. The present study was initiated to explore the underlying mechanism of toxicity in H9c2 myocardial cells. We observed using cell imaging and counting methods that maduramicin inhibited cell growth in a concentration-dependent manner. Furthermore, MTT assays showed that maduramicin inhibited cell proliferation in a concentration- and time-dependent manner, and was also confirmed by the finding that maduramicin time dependently blocked the incorporation of BrdU into DNA in H9c2 myocardial cells. Further studies revealed that maduramicin induced accumulation of the cells at G0/G1 phase of the cell cycle and concurrently, there was down regulation of expression of Cyclin D1. In addition, exposure to maduramicin pruned phosphorylation of AKT at both T308 and S473 sites. Finally, we found that pre-treatment of H9c2 myocardial cells with AKT activator SC79, attenuated the inhibitory effects of maduramicin on Cyclin D1 expression and cell proliferation. Collectively, our results suggest that maduramicin-suppressed AKT-Cyclin D1 signaling which results in G0/G1 phase cell cycle arrest, leading to the inhibition of myocardial cell proliferation.

Abstract PS18-46: Inhibition of breast cancer stem cells in 2- and 3-dimensional culture by novel salinomycin analogs

Abstract Breast cancer remains one of the leading cancers among women and an estimated 90% of breast cancer deaths are due to metastasis. Cancer stem cells (CSCs) are a sub-population of cancer cells which are responsible for its initiation, progression and metastasis. CSCs are resistant to conventional chemo- and radio-therapies and therefore therapeutic strategies targeting CSCs hold great potential for novel advances in cancer treatment. Salinomycin (SAL) is a naturally occurring polyether ionophore antibiotic which was shown to effectively target breast CSCs. A library of 17 novel SAL analogs was synthesized and screened to identify compounds with improved selectivity against breast cancer stem cells. SAL analogs were either single modified esters or amides in the C1 position or double-modified C20-oxo derivatives. Eight single- and two double-modified analogs were more potent (IC50 range of 1.13 ± 0.19 to 3.93 ± 0.39 µM) towards the breast cancer cell line MDA-MB-231 compared to parent SAL (IC50 of 4.90 ± 1.60 µM). These analogs induced DNA fragmentation suggestive of apoptotic cell death. Compounds 2 (butyl ester analog of SAL) and 17 (double-modified C20-oxosalinomycin with benzhydroxamic acid) have been chosen for follow-up screening due to their improved activity and selectivity versus parent SAL. This included clonogenic assays to assess the ability of the compounds to affect cell renewal, and wound healing assays to assess cell migratory properties. In both assays, compound 17 showed superior properties over SAL. Furthermore, analog 17 showed improved targeting of breast CSCs in both cell monolayer and organoid culture as assessed in assays measuring the CD44+/CD24- stem cell sub-population. Analogs and parent compound were further studied examining (ADP-ribose) polymerase (PARP) cleavage and Bcl-2 levels by immunoblotting. All three compounds induced loss of 116 kDa PARP expression within 48h, with the highest effect induced by analog 17. In addition, treatment with compound 17 caused a decrease in Bcl-2 expression as early as 24 h. Select analogs were next screened against the NCI-60 Human Tumor Cell Line Panel. The described above double-modified analog was found to be more potent than SAL towards all 6 breast cancer cell lines in the panel as well as other tumor types. The present findings highlight the therapeutic potential of SAL analogs towards breast stem cells and support further research and clinical development of these compounds. Funding: The present study was funded by grants (to AM and TCC) from the Arkansas Breast Cancer Research Program. Testing was performed by the Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, http://dtp.cancer.gov. Citation Format: Alicja Joanna Urbaniak, Megan R. Reed, Michał Antoszczak, Michał Sulik, Adam Huczyński, Robert L. Eoff, Melanie C. MacNicol, Timothy C. Chambers, Angus M. MacNicol. Inhibition of breast cancer stem cells in 2- and 3-dimensional culture by novel salinomycin analogs [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-46.

Expanding the antibacterial selectivity of polyether ionophore antibiotics through diversity-focused semisynthesis.

Polyether ionophores are complex natural products capable of transporting cations across biological membranes. Many polyether ionophores possess potent antimicrobial activity and a few selected compounds have ability to target aggressive cancer cells. Nevertheless, ionophore function is believed to be associated with idiosyncratic cellu-lar toxicity and, consequently, human clinical development has not been pursued. Here, we demonstrate that structurally novel polyether ionophores can be efficiently constructed by recycling components of highly abundant polyethers to afford analogues with enhanced anti-bacterial selectivity compared to a panel of natural polyether ionophores. We used classic degradation reactions of the natural polyethers lasalocid and monensin and combined the resulting fragments with building blocks provided by total synthesis, including halogen-functionalized tetronic acids as cation-binding groups. Our results suggest that structural optimization of polyether ionophores is possible and that this area represents a potential opportunity for future methodological innovation.

Structure of a potassium salt of Lasalocid A and an investigation of solid–state conformational variance of the Lasalocid A backbone in known complexes

The structure of a potassium salt of the polyether ionophore antibiotic Lasalocid A has been determined by single–crystal X–ray crystallography. A dimeric structure is revealed in which two antibiotic molecules present hemispheric oxygen co–ordination environments for two potassium centres. Co–ordination for both cations is further fulfilled by contact with the oxygen atoms of two discrete dimethylformamide molecules that bridge the two potassium centres. Close analysis using directional statistics of the conformation of the backbone of the Lasalocid A molecule in all previously reported crystal structures, as well as the potassium salt reported here, reveals that conformation is substantially conserved throughout the series, aside from some variation in the twist of the carboxylate group with respect to the plane of the aromatic ring, and the orientation of the tetrahydrofuran ring. The Lasalocid A molecule in the potassium complex presented here is the closest fit to the averaged Lasalocid structure, derived from the family of known complexes,

Ionophore antibiotic X-206 is a potent inhibitor of SARS-CoV-2 infection in vitro

Pandemic spread of emerging human pathogenic viruses, such as the current SARS-CoV-2, poses both an immediate and future challenge to human health and society. Currently, effective treatment of infection with SARS-CoV-2 is limited and broad spectrum antiviral therapies to meet other emerging pandemics are absent leaving the World population largely unprotected. Here, we have identified distinct members of the family of polyether ionophore antibiotics with potent ability to inhibit SARS-CoV-2 replication and cytopathogenicity in cells. Several compounds from this class displayed more than 100-fold selectivity between viral-induced cytopathogenicity and inhibition of cell viability, however the compound X-206 displayed >500-fold selectivity and was furthermore able to inhibit viral replication even at sub-nM levels. The antiviral mechanism of the polyether ionophores is currently not understood in detail. We demonstrate, e.g. through unbiased bioactivity profiling, that their effects on the host cells differ from those of cationic amphiphiles such as hydroxychloroquine. Collectively, our data suggest that polyether ionophore antibiotics should be subject to further investigations as potential broad-spectrum antiviral agents.

The biosynthetic pathway to tetromadurin (SF2487/A80577), a polyether tetronate antibiotic.

The type I polyketide SF2487/A80577 (herein referred to as tetromadurin) is a polyether tetronate ionophore antibiotic produced by the terrestrial Gram-positive bacterium Actinomadura verrucosospora. Tetromadurin is closely related to the polyether tetronates tetronasin (M139603) and tetronomycin, all of which are characterised by containing a tetronate, cyclohexane, tetrahydropyran, and at least one tetrahydrofuran ring. We have sequenced the genome of Actinomadura verrucosospora to identify the biosynthetic gene cluster responsible for tetromadurin biosynthesis (the mad gene cluster). Based on bioinformatic analysis of the 32 genes present within the cluster a plausible biosynthetic pathway for tetromadurin biosynthesis is proposed. Functional confirmation of the mad gene cluster is obtained by performing in-frame deletions in each of the genes mad10 and mad31, which encode putative cyclase enzymes responsible for cyclohexane and tetrahydropyran formation, respectively. Furthermore, the A. verrucosospora Δmad10 mutant produces a novel tetromadurin metabolite that according to mass spectrometry analysis is analogous to the recently characterised partially cyclised tetronasin intermediate lacking its cyclohexane and tetrahydropyran rings. Our results therefore elucidate the biosynthetic machinery of tetromadurin biosynthesis and lend support for a conserved mechanism of cyclohexane and tetrahydropyran biosynthesis across polyether tetronates.

Treatment of Lasalocid A, Salinomycin and Semduramicin as ionophore antibiotics in pharmaceutical wastewater by PAMAM-coated membranes

Polyether ionophore antibiotics such as Lasalocid A, Salinomycin and Semduramicin, which are used a lot in veterinary medicine, have high toxicity among other antibiotics. They cannot be eliminated by conventional wastewater treatment and leak into surface and ground water which can have detrimental damage on aquatic environment. Membrane processes like ultrafiltration can be a solution as tertiary and advanced treatment for this issue. Unfortunately, they can be easily fouled by dissolved substances. In this study, poly(amidoamine) (PAMAM) dendrimers were used as novel antifouling agents and chemically coated on the amidoximated membranes with different half-generations (G0-G2.5). New membranes exhibited great performances in the treatment of pharmaceutical wastewater with these antibiotics. G2.5 PAMAM-coated ultrafiltration membranes were selected as optimum membranes with 120.4 L/m 2 .h of pure water flux, 91.3% of Semduramicin rejection, low contact angle (51.2°) and zeta potential (-56.1 mV). The flux profiles of these membranes revealed that the flux reduction does not occur after 1–1.5 h of filtration. These profiles were fitted by power law model. In addition to the surface charge and pore size, the branches of dendrimers, which had negative charges, acted great roles during the filtration. • New antifouling agents have been synthesized on acrylic ultrafiltration membranes. • PAMAM dendrimers were used to minimize antibiotic accumulation on surface membranes. • Surface became more hydrophilic and negative because of terminal carboxylic acid. • Fouling decreased notably for G2.5 PAMAM-coated membranes. • Rejection of drugs was below toxicological level.

Monensin inhibits glioblastoma angiogenesis via targeting multiple growth factor receptor signaling

Glioblastoma is characterized by the extensive vascularization with poor prognosis. Targeting both tumor cell and angiogenesis may present an effective therapeutic strategy for glioblastoma. Monensin, a polyether ionophore antibiotic, has been recently recognized as promising anticancer drug candidate due to its potent and selective anti-tumor activities. However, little is known on the effects of monensin on tumor angiogenesis. In this work, we investigated the effects and underlying mechanisms of monensin on glioblastoma angiogenesis and growth. We show that monensin at nanomolar concentrations inhibits early stages of capillary network formation of glioblastoma endothelial cell. Monensin inhibited multiple endothelial cellular events, including migration, growth and survival, without affecting adhesion to Matrigel. We further demonstrate that monensin acts on endothelial cells via suppressing VEGFR- and EGFR-mediated signaling pathways. Monensin also inhibits proliferation and induces apoptosis in a panel of glioblastoma cells. However, monensin is more effective in targeting endothelial cells than tumor cells. Using glioblastoma growth xenograft mice model, we show that monensin at tolerable dose effectively inhibits glioblastoma growth. Of note, there is a significant decreased tumor vascularization from monensin-treated mice. Our work clearly demonstrates the anti-angiogenic activity of monensin and its ability in suppressing multiple tyrosine kinase receptor-mediated pathways. Our findings suggest that is a useful addition to the treatment armamentarium for glioblastoma.

Novel Salinomycin Analogs Show Improved Selectivity Towards Breast Cancer Stem Cells

Breast cancer tumor metastasis is the leading cause of mortality among women. Cancer stem cells (CSCs) are the tumor‐initiating cells which drive initiation, progression, metastasis, and tumor reoccurrence. Their resistance to conventional chemo‐ and radiotherapies and their ability to survive such treatment enables tumor reestablishment. Thus, therapeutic strategies targeting CSCs hold great potential for novel advances in cancer treatment. Salinomycin (SAL) is a naturally occurring polyether ionophore antibiotic with anti‐cancer activity towards various types of tumor cells, but its toxicity towards normal cells limits broad application. A library of 21 novel SAL analogs was screened to identify compounds with improved selectivity especially against breast cancer stem cells. SAL analogs were either single modified with ester or amide in the C1 position or double‐modified C20‐oxo derivatives. Eight single‐ and two double‐modified derivatives were more potent (IC50 range of 1.13 ± 0.19 to 3.93 ± 0.39 μM) towards the breast cancer cell line MDA‐MB‐231 compared to SAL (IC50 of 5.81 ± 1.50). These derivatives induced DNA fragmentation suggestive of apoptotic cell death. Further, most of these derivatives had improved selectivity toward MDA‐MB‐231 cells compared to SAL when also tested against normal breast epithelial MCF10A cells. In addition, a butyl ester derivative of SAL, chosen based on increased potency and selectivity versus SAL, significantly reduced the colony‐forming efficiency of MDA‐MB‐231 cells in association with selective loss of the CD44+/CD24−/low stem‐cell‐like subpopulation. Select derivatives were next screened against the NCI‐60 Human Tumor Cell Line Panel. A double‐modified analog of C20‐oxo‐SAL with hydroxamic acid was found to be more potent than SAL towards all 6 breast cancer cell lines in the panel as well as other tumor types especially leukemia. Studies are underway to test the analogs in three dimensional culture using breast cancer organoids derived from both cell lines and patients. The present findings highlight the therapeutic potential of SAL analogs towards breast cancer and breast cancer stem cells and support further research and clinical development of these compounds.Support or Funding InformationThe present study was funded by grants (to AMM and TCC) from the Arkansas Breast Cancer Research Program. Testing was performed by the Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, http://dtp.cancer.gov.

Regulatory Patterns of Crp on Monensin Biosynthesis in Streptomyces cinnamonensis

Monensin, produced by Streptomyces cinnamonensis, is a polyether ionophore antibiotic widely used as a coccidiostat and a growth-promoting agent in agricultural industry. In this study, cyclic AMP receptor protein (Crp), the global transcription factor for regulation of monensin biosynthesis, was deciphered. The overexpression and antisense RNA silencing of crp revealed that Crp plays a positive role in monensin biosynthesis. RNA sequencing analysis indicated that Crp exhibited extensive regulatory effects on genes involved in both primary metabolic pathways and the monensin biosynthetic gene cluster (mon). The primary metabolic genes, including acs, pckA, accB, acdH, atoB, mutB, epi and ccr, which are pivotal in the biosynthesis of monensin precursors malonyl-CoA, methylmalonyl-CoA and ethylmalonyl-CoA, are transcriptionally upregulated by Crp. Furthermore, Crp upregulates the expression of most mon genes, including all PKS genes (monAI to monAVIII), tailoring genes (monBI-monBII-monCI, monD and monAX) and a pathway-specific regulatory gene (monRI). Enhanced precursor supply and the upregulated expression of mon cluser by Crp would allow the higher production of monensin in S. cinnamonensis. This study gives a more comprehensive understanding of the global regulator Crp and extends the knowledge of Crp regulatory mechanism in Streptomyces.

Comparative study on the effects of salinomycin, monensin and meso-2,3-dimercaptosuccinic acid on the concentrations of lead, calcium, copper, iron and zinc in lungs and heart in lead-exposed mice

Background and aimEnvironmental lead (Pb) exposure damages the lungs and is a risk factor for death from cardiovascular disease. Pb induces toxicity by a mechanism, which involves alteration of the essential elements homeostasis. In this study we compare the effects of salinomycin (Sal), monensin (Mon) and meso-2,3-dimercaptosuccinic acid (DMSA) on the concentrations of lead (Pb), calcium (Ca), copper (Cu), iron (Fe) and zinc (Zn) in the lungs and heart of lead-exposed mice. MethodsSixty days old male ICR mice were divided into five groups: control (Ctrl) – untreated mice obtained distilled water for 28 days; Pb-intoxicated group (Pb) – exposed to 80 mg/kg body weight (BW) Pb(NO3)2 during the first 14 days of the experimental protocol; DMSA-treated (Pb + DMSA) – Pb-exposed mice, subjected to treatment with an average daily dose of 20 mg/kg BW DMSA for two weeks; Monensin-treated (Pb + Mon) – Pb-exposed mice, obtained an average daily dose of 20 mg/kg BW tetraethylammonium salt of monensic acid for 14 days; Pb + Sal - Pb-exposed mice, treated with an average daily dose of 20 mg/kg BW tetraethylammonium salt of salinomycinic acid for two weeks. On the 29th day of the experiment the samples (lungs and heart) were taken for atomic absorption analysis. ResultsThe results revealed that exposure of mice to Pb for 14 days significantly increased the concentration of the toxic metal in both organs and elevated the cardiac concentrations of Ca, Cu and Fe compared to untreated mice. Pb exposure diminished the lung concentrations of Ca and Zn compared to that of untreated controls. DMSA, monensin and salinomycin decreased the concentration of Pb in the lungs and heart. Among the tested chelating agents, only salinomycin restored the cardiac Fe concentration to normal control values. ConclusionThe results demonstrated the potential application of polyether ionophorous antibiotic salinomycin as antidote for treatment of Pb-induced toxicity in the lungs and heart. The possible complexation of the polyether ionophorous antibiotics with Ca(II) and Zn(II), which can diminish the endogenous concentrations of both ions in the lungs should be taken into account.

Competitive electrochemical immunosensor for maduramicin detection by multiple signal amplification strategy via hemin@Fe-MIL-88NH2/AuPt

Maduramicin (MD) is a type of monoglycoside polyether ionophore antibiotic that can effectively treat coccidiosis and facilitate animal growth. However, its extensive and excessive use brings potential risk to human health. Herein, an electrochemical immunosensor based on indirect competitive format was fabricated for analysis of MD residue in eggs by a multiple signal amplification system. Initially, Au nanoparticles were deposited onto glassy carbon electrode surface to load the coating antigen MD-BSA and to improve conductivity. Then the signal amplification platform was constructed by encapsulating hemin into Fe-MIL-88 NH2 metal-organic frameworks (hemin@MOFs), and then the obtained composites were decorated with AuPt nanoparticles. The synthesized hemin@MOFs/AuPt was not only used as a signal amplification mediator, but also utilized as a carrier for immobilization of horseradish peroxidase-conjugated affinipure goat anti-mouse antibody (Ab2-HRP) and horseradish peroxidase (HRP). The constructed hemin@MOFs/AuPt-Ab2-HRP bioconjugates could effectively amplify the current signal since hemin@MOFs, AuPt and HRP all exhibited high catalytic activity towards the hydrogen peroxide. Moreover, the established immunosensor showed high sensitivity and stability during the detection procedure. With the synergistic catalytic effect of hemin@MOFs, AuPt and HRP, a wide detection range of 0.1–50 ng mL−1 and a low detection limit of 0.045 ng mL−1 were achieved (S/N = 3), respectively. Ultimately, the developed method displayed excellent performance in practical applications, providing a promising probability to detect other veterinary drug residues to guarantee food safety.

Maduramicin inactivation of Akt impairs autophagic flux leading to accumulated autophagosomes-dependent apoptosis in skeletal myoblast cells.

It has been clinically documented that maduramicin (Mad), a polyether ionophore antibiotic widely used in the control of coccidiosis in poultry worldwide, can elicit skeletal muscle degeneration, heart failure, and even death in animals and humans, if improperly used. Here, we show that Mad induced apoptosis dose-dependently, which was associated with impaired autophagic flux in skeletal myoblast (C2C12 and L6) cells. This is supported by the findings that Mad treatment resulted in increase of autophagosomes with a concomitant elevation of LC3-II and p62 in the cells. Also, Mad increased co-localization of mCherry and GFP tandem-tagged LC3 puncta in the cells, suggesting a blockage of autophagic flux. Furthermore, addition of chloroquine (CQ) strengthened the basic and Mad-enhanced LC3-II and p62 levels, autophagosome formation and cell apoptosis, whereas pretreatment with rapamycin alleviated the effects in the cells exposed to Mad. Moreover, we noticed that Mad treatment inactivated Akt dose-dependently. Inhibition of Akt with inhibitor X potentiated Mad-induced decrease in phosphorylated Akt, and increases in LC3-II and p62 levels, autophagosome formation and cell apoptosis, whereas ectopic expression of constitutively active Akt rendered resistance to these events. Collectively, these results indicate that Mad inactivation of Akt impairs autophagic flux leading to accumulated autophagosomes-dependent apoptosis in skeletal myoblast cells. Our findings suggest that manipulation of Akt activity to improve autophagic flux is a promising strategy against Mad-induced myotoxicity.