Ionophore Antibiotic Research Articles

Salinomycin induces primary chicken cardiomyocytes death via mitochondria mediated apoptosis

Salinomycin, as a polyether ionophore antibiotic, is extensively used as a feed additive against coccidiosis in poultry and as a growth promoter of ruminants worldwide. Owing to its narrow therapeutic index, numerous intoxication have been reported in target/non-target animals by overdosage, misuse or drug interactions as well as human who consumed salinomycin accidently. Salinomycin-induced cardiotoxicity in chicken and non-target animals is considered as a major contributor to animal death. In the current study, we aim to elucidate the underlying mechanism of its myocardial toxicity using primary chicken myocardial cell as an in vitro model. The results showed that salinomycin altered cellular morphology and induced cell death in a concentration-dependent manner. Salinomycin treatment elevated the permeability of the cell membrane and leaded to the efflux of enzymes, including creatine kinase (CK) and lactate dehydrogenase (LDH). Flow cytometry analysis indicated the number of apoptotic cells increased significantly by salinomycin exposure. Furthermore, caspase-3 and caspase-9 were activated at gene and protein level rather than caspase-8, along with the up-regulation of apoptosis genes Bax, Cytochrome C, Apoptotic peptidase activating factor 1 (Apaf-1) and the down-regulation of Bcl-2. Salinomycin-induced mitochondrial dysfunction was accompanied by the significant decrease of mitochondrial membrane potential (MMP) and the severe ultrastructure damage. In conclusion, these findings suggest that the toxic dose of salinomycin induces severe cardiomyocytes death through mitochondria mediated apoptosis pathway.

Applied strategies for the control of coccidiosis in poultry.

Abstract Apicomplexan parasites of the genus Eimeria are widespread in poultry flocks and if present in sufficient numbers can cause the intestinal disease coccidiosis. For many years, the disease has been controlled either by incorporating drugs in the feed (prophylaxis) or by immunization with live parasites (vaccination). Efficacy of anticoccidial drugs has been compromised by the acquisition of resistance which has been documented for all drugs introduced including those most widely used, the ionophorous antibiotics. A consequence of limited efficacy is that these drugs permit some parasite development thus allowing the acquisition of immunity. Combined with improvements in management, this may explain the continued use of drugs for the control of coccidiosis in broiler and turkey production. In recent years vaccination, utilizing live attenuated or non-attenuated parasites has made a significant contribution to the control of coccidiosis in chickens. Vaccines are administered on a single occasion by a variety of methods to newly hatched chicks and initiate an immune response in the bird. Full protective immunity requires secondary exposure to vaccinal oocysts in the litter, an aspect of vaccination over which the producer has little control. Exposure to wild-type parasites already present in the litter may cause clinical coccidiosis, as evident by characteristic intestinal lesions in birds, before protective immunity has time to fully develop. Several vaccines comprise parasites that have never been exposed to anticoccidial drugs and it has been shown that their use in a commercial setting may replace drug-resistant organisms resulting in a restoration of drug-sensitivity. Programs involving alternation of chemotherapy and vaccination have been introduced with the objective of prolonging the life of anticoccidial drugs that have been compromised by drug-resistance. This is the only known example of restoration of drug sensitivity in veterinary parasitology. So-called 'natural' products that include herbs, herbal and fungal extracts, and probiotics are claimed to alleviate Eimeria infections in poultry, but few have been thoroughly investigated. Advances have been made in our knowledge of the structure of proteins released during parasite invasion of host cells and may eventually result in novel vaccines based upon molecular technology. Hens immunized with proteins isolated from gametocyte stages of the life cycle of one species of Eimeria pass antibodies to developing embryos and this may provide short-term passive protection to young chickens' post-hatch. As with other approaches to vaccination, protection is dependent upon exposure to wild-type parasites present in the environment.

Maduramicin-activated protein phosphatase 2A results in extracellular signal-regulated kinase 1/2 inhibition, leading to cytotoxicity in myocardial H9c2 cells

Maduramicin, a polyether ionophore antibiotic used as an anticoccidial agent in poultry industry, has been reported to be toxic to animals and humans if improperly used or by accident, resulting in heart failure, skeletal muscle degeneration and even death. However, the molecular mechanism underlying its cardiotoxicity remains elusive. Mitogen activated protein kinases (MAPKs) and protein phosphatases signaling pathways have been documented to be involved in the cell survival regulation. The present study was set to investigate the role of above pathways in maduramicin-induced myocardial cytotoxicity. Here we observed that maduramicin inhibited cell proliferation and reduced cell viability in H9c2 cells. Furthermore, we found that maduramicin suppressed extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in a concentration-dependent manner. Ectopic expression of constitutively active MKK1 partially prevented the cytotoxicity of maduramicin. Moreover, we showed that maduramicin concentration-dependently activated protein phosphatase 2A (PP2A) by decreasing its phosphorylation and increasing its methylation. Inhibition of PP2A with okadaic acid attenuated maduramicin’s toxicity. Overexpression of dominant negative PP2A partially rescued cells from maduramicin-inhibited ERK1/2 contributing to its cytotoxicity. The results indicate that maduramicin activates PP2A and consequently inhibits ERK1/2, leading to cytotoxicity in H9c2 cells. Our data suggest that manipulation of PP2A-ERK1/2 pathway may be a potential approach to prevent maduramicin-induced cardiotoxicity.

A Novel TetR Family Transcriptional Regulator, CalR3, Negatively Controls Calcimycin Biosynthesis in Streptomyces chartreusis NRRL 3882.

Calcimycin is a unique ionophoric antibiotic that is widely used in biochemical and pharmaceutical applications, but the genetic basis underlying the regulatory mechanisms of calcimycin biosynthesis are unclear. Here, we identified the calR3 gene, which encodes a novel TetR family transcriptional regulator and exerts a negative effect on calcimycin biosynthesis. Disruption of calR3 in Streptomyces chartreusis NRRL 3882 led to significantly increased calcimycin and its intermediate cezomycin. Gene expression analysis showed that the transcription of calR3 and its adjacent calT gene were dramatically enhanced (30- and 171-fold, respectively) in GLX26 (ΔcalR3) mutants compared with the wild-type strains. Two CalR3-binding sites within the bidirectional calR3-calT promoter region were identified using a DNase I footprinting assay, indicating that CalR3 directly repressed the transcription of its own gene and the calT gene. In vitro electrophoretic mobility shift assays suggested that both calcimycin and cezomycin can act as CalR3 ligands to induce CalR3 to dissociate from its binding sites. These findings indicate negative feedback for the regulation of CalR3 in calcimycin biosynthesis and suggest that calcimycin production can be improved by manipulating its biosynthetic machinery.

Comparative effects of Moringa oleifera root bark and monensin supplementations on ruminal fermentation, nutrient digestibility and growth performance of growing lambs

Two comparative in vitro and in vivo experiments were accomplished to assess the effects of Moringa oleifera root bark (MRB) and ionophore antibiotic monensin as dietary feed additives for ruminants' diets. In the in vitro experiment, the effects of graded levels of MRB (0, 25 and 50g/kg DM) and monensin (40mg/kg DM) on ruminal fermentation and degradability parameters were evaluated using the semi-automatic gas production (GP) system. Results were subjected to regression analysis (dose-response analysis) and ANOVA to select the MRB effective dose. In the in vivo experiment, eighteen Barki lambs (BW; 25±3.1kg) were randomly allotted into three dietary treatments (n=6/treatment) as: control (basal diet without additive), monensin (40mg/kg DM) and MRB (25g/kg DM). The experiment lasted for 70 days to collect ruminal samples and evaluate lamb performance, while the subsequent 7 days were assigned for the nutrient digestibility and nitrogen balance trial. The GC–MS analysis of MRB showed that the most abundant phytochemicals were organosilicons, alkaloids and benzoic acid ester. Results of the in vitro assay showed that both MRB doses inhibited (P<0.01) CH4 production (ml/g DM) without adverse effects on GP and degradability compared to control. Diet supplemented with 25gMRB/kg DM resulted in the highest increase (P=0.03) of propionate compared to control. Ammonia concentration was decreased (P<0.01) by monensin, while protozoal counts were not affected by all experimental diets. The in vivo effects of MRB on ruminal fermentation profile were different from those of in vitro assay. MRB enhanced (P<0.05) the total short chain fatty acids, acetate production and nutrients digestibility, while monensin enhanced propionate (P<0.01) compared to other diets. Both monensin and MRB exhibited similar reductions (P<0.01) in protozoal counts, urine N excretions and estimated CH4 produced per unit of body weight gain while enhanced (P<0.05) the body N retention, average daily gain, and feed efficiency compared to control. These results suggested that, although MRB was less effective than monensin, it favourably modified the ruminal fermentation process and nutrients digestibility, thus it could be used as a novel dietary feed additive for ruminant diets.

Transcriptome profile analysis reveals cardiotoxicity of maduramicin in primary chicken myocardial cells.

Maduramicin, an excellent ionophore antibiotic, is extensively used to control coccidiosis in poultry. Numerous maduramicin intoxications have been reported in farm animal and human due to its relatively narrow safety range, with necrosis or degeneration of cardiac and skeletal muscles as hallmark. To date, the mechanisms of maduramicin-induced cardiotoxicity remain unclear in chicken and other animals. Maduramicin (5µg/mL)-treated primary chicken myocardial cells were used for RNA sequencing (RNA-Seq) and bioinformatics analysis in this study. A total of 1442 differential expressed genes were identified. 810 genes were up-regulated and the rest 632 genes were down-regulated. Transcriptome analysis revealed that the cytokine-cytokine receptor interaction, apoptosis, calcium signal and cytoplasmic vacuolization pathways were significantly affected. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis showed that gene expression patterns were consistent with RNA-Seq analysis. Pro-inflammatory cytokines including tumor necrosis factor alpha (TNF-α) and interleukin-8 (IL-8), apoptosis ratios, cleaved caspase-3, intracellular calcium level and Ca2+-ATPase activity were elevated after maduramicin (0.05, 0.5 and 5µg/mL) treatment. Massive vacuole formation was found in the cytoplasm by morphology and transmission electron microscopy observation. Taken together, the results suggested that maduramicin exerted its cardiotoxicity by multiple molecular mechanisms in primary chicken myocardial cells.

Comparative effects of meso-2,3- dimercaptosuccinic acid, monensin, and salinomycin on cadmium-induced brain dysfunction in cadmium-intoxicated mice.

Cadmium (Cd) is a risk factor for neurodegenerative diseases. The purpose of this study was to compare the effects of meso-2,3-dimercaptosuccinic acid (DMSA) and the polyether ionophorous antibiotics monensin and salinomycin on Cd-induced neurodegenerative alterations in mice. The results show that subacute intoxication of mice with Cd (II) acetate (20 mg/kg body weight (BW) for 14 days) caused a significant accumulation of cadmium (Cd) in the brain. Treatment of Cd-exposed mice with DMSA (20 mg/kg BW for 14 days) significantly increased the Cd concentration in the brains compared to those of the Cd-treated group. However, administration of monensin (20 mg/kg BW for 14 days) or salinomycin (20 mg/kg BW for 14 days) significantly reduced the Cd concentration in the brains of Cd-treated mice compared to the toxic control group. Histopathological analysis of brain tissues from the Cd-treated mice revealed that Cd induced neuronal necrosis, characterized by many shrunken, darkly stained pyknotic neurons with prominent perineuronal spaces. Whereas monensin and salinomycin significantly reduced the adverse effects of Cd on brain morphology of Cd-treated mice, DMSA did not. Monensin slightly increased the copper and iron endogenous levels in the brains of Cd-exposed mice compared to those of the untreated mice. Salinomycin did not affect the concentrations of biometal ions in the brain of Cd-exposed mice compared to untreated controls. The results demonstrated salinomycin to be a better potential chelating agent for treatment of Cd-induced brain injury compared to DMSA and monensin.

Maduramicin induces apoptosis and necrosis, and blocks autophagic flux in myocardial H9c2 cells.

Maduramicin, a polyether ionophore antibiotic, is widely used as an anticoccidial agent in the poultry industry. It has been reported that maduramicin may cause heart and skeletal muscle cell damage, resulting in heart failure, skeletal muscle degeneration and even death in animals and humans, if improperly used. However, the molecular mechanism behind its capability to cause death of cardiac cells is not known. Here, we show that maduramicin induced apoptosis and necrosis in rat myocardial cells (H9c2). Maduramicin did not apparently upregulate the expression of pro-apoptotic proteins (e.g., BAD, BAK and BAX) or downregulate the expression of anti-apoptotic proteins (e.g. Bcl-2, Bcl-xL, Mcl-1 and survivin). Interestingly, maduramicin increased the expression of DR4 and TRAIL, activating caspases 8/3 and triggering cleavage of poly ADP ribose polymerase (PARP). In addition, maduramicin induced nuclear translocation of apoptosis inducing factor. Furthermore, maduramicin blocked autophagic flux, as evidenced by inducing accumulation of both LC3-II and p62/SQSTM1. Taken together, the above results suggest that maduramicin executes its toxicity in the myocardial cells at least by inducing caspase-dependent cell death through TRAIL/DR4-mediated extrinsic pathway and caspase-independent cell death by inducing apoptosis inducing factor nuclear translocation and blocking autophagic flux. Our findings provide a new insight into the molecular mechanism of maduramicin's toxicity in myocardial cells.

Marine Mammal Microbiota Yields Novel Antibiotic with Potent Activity Against Clostridium difficile.

The recent explosion of research on the microbiota has highlighted the important interplay between commensal microorganisms and the health of their cognate hosts. Metabolites isolated from commensal bacteria have been demonstrated to possess a range of antimicrobial activities, and it is widely believed that some of these metabolites modulate host behavior, affecting predisposition to disease and pathogen invasion. Our access to the local marine mammal stranding network and previous successes in mining the fish microbiota poised us to test the hypothesis that the marine mammal microbiota is a novel source of commensal bacteria-produced bioactive metabolites. Examination of intestinal contents from five marine mammals led to the identification of a Micromonospora strain with potent and selective activity against a panel of Gram-positive pathogens and no discernible human cytotoxicity. Compound isolation afforded a new complex glycosylated polyketide, phocoenamicin, with potent activity against the intestinal pathogen Clostridium difficile, an organism challenging to treat in hospital settings. Use of our activity-profiling platform, BioMAP, clustered this metabolite with other known ionophore antibiotics. Fluorescence imaging and flow cytometry confirmed that phocoenamicin is capable of shifting membrane potential without damaging membrane integrity. Thus, exploration of gut microbiota in hosts from diverse environments can serve as a powerful strategy for the discovery of novel antibiotics against human pathogens.

Bioconjugation of Ionophore Antibiotics: A Way to Obtain Hybrids with Potent Biological Activity

Bioconjugation of Ionophore Antibiotics: A Way to Obtain Hybrids with Potent Biological Activity

Hops (Humulus lupulus L.) Bitter Acids: Modulation of Rumen Fermentation and Potential As an Alternative Growth Promoter.

Antibiotics can improve ruminant growth and efficiency by altering rumen fermentation via selective inhibition of microorganisms. However, antibiotic use is increasingly restricted due to concerns about the spread of antibiotic-resistance. Plant-based antimicrobials are alternatives to antibiotics in animal production. The hops plant (Humulus lupulus L.) produces a range of bioactive secondary metabolites, including antimicrobial prenylated phloroglucinols, which are commonly called alpha- and beta-acids. These latter compounds can be considered phyto-ionophores, phytochemicals with a similar antimicrobial mechanism of action to ionophore antibiotics (e.g., monensin, lasalocid). Like ionophores, the hop beta-acids inhibit rumen bacteria possessing a classical Gram-positive cell envelope. This selective inhibition causes several effects on rumen fermentation that are beneficial to finishing cattle, such as decreased proteolysis, ammonia production, acetate: propionate ratio, and methane production. This article reviews the effects of hops and hop secondary metabolites on rumen fermentation, including the physiological mechanisms on specific rumen microorganisms, and consequences for the ruminant host and ruminant production. Further, we propose that hop beta-acids are useful model natural products for ruminants because of (1) the ionophore-like mechanism of action and spectrum of activity and (2) the literature available on the plant due to its use in brewing.

Chemical Genomics, Structure Elucidation, and in Vivo Studies of the Marine-Derived Anticlostridial Ecteinamycin.

A polyether antibiotic, ecteinamycin (1), was isolated from a marine Actinomadura sp., cultivated from the ascidian Ecteinascidia turbinata. 13C enrichment, high resolution NMR spectroscopy, and molecular modeling enabled elucidation of the structure of 1, which was validated on the basis of comparisons with its recently reported crystal structure. Importantly, ecteinamycin demonstrated potent activity against the toxigenic strain of Clostridium difficile NAP1/B1/027 (MIC = 59 ng/μL), as well as other toxigenic and nontoxigenic C. difficile isolates both in vitro and in vivo. Additionally, chemical genomics studies using Escherichia coli barcoded deletion mutants led to the identification of sensitive mutants such as trkA and kdpD involved in potassium cation transport and homeostasis supporting a mechanistic proposal that ecteinamycin acts as an ionophore antibiotic. This is the first antibacterial agent whose mechanism of action has been studied using E. coli chemical genomics. On the basis of these data, we propose ecteinamycin as an ionophore antibiotic that causes C. difficile detoxification and cell death via potassium transport dysregulation.

Characterization of three pathway-specific regulators for high production of monensin in Streptomyces cinnamonensis.

Monensin, a polyether ionophore antibiotic, is produced by Streptomyces cinnamonensis and worldwide used as a coccidiostat and growth-promoting agent in the field of animal feeding. The monensin biosynthetic gene cluster (mon) has been reported. In this study, the potential functions of three putatively pathway-specific regulators (MonH, MonRI, and MonRII) were clarified. The results from gene inactivation, complementation, and overexpression showed that MonH, MonRI, and MonRII positively regulate monensin production. Both MonH and MonRI are essential for monensin biosynthesis, while MonRII is non-essential and could be completely replaced by additional expression of monRI. Transcriptional analysis of the mon cluster by semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) and electrophoresis mobility shift assays (EMSAs) revealed a co-regulatory cascade process. MonH upregulates the transcription of monRII, and MonRII in turn enhances the transcription of monRI. MonRII is an autorepressor, while MonRI is an autoactivator. MonH activates the transcription of monCII-monE, and upregulates the transcription of monT that is repressed by MonRII. monAX and monD are activated by MonRI, and upregulated by MonRII. Co-regulation of those post-polyketide synthase (post-PKS) genes by MonH, MonRI, and MonRII would contribute to high production of monensin. These results shed new light on the transcriptional regulatory cascades of antibiotic biosynthesis in Streptomyces.

Effects of Geraniol and Camphene on in Vitro Rumen Fermentation and Methane Production

Abstract The objective of this study was to determine the effects of geraniol and camphene at three dosages (300, 600, and 900 mg l-1) on rumen microbial fermentation and methane emission in in vitro batch culture of rumen fluid supplied with a 60 : 40 forage : concentrate substrate (16.2% crude protein, 33.1% neutral detergent fibre). The ionophore antibiotic monensin (8 mg/l) was used as positive control. Compared to control, geraniol significantly (P &lt; 0.05) reduced methane production with increasing doses, with reductions by 10.2, 66.9, and 97.9%. However, total volatile fatty acids (VFA) production and in vitro dry matter digestibility were also reduced (P &lt; 0.05) by all doses of geraniol. Camphene demonstrated weak and unpromising effects on rumen fermentation. Camphene did not decrease (P &gt; 0.05) methane production and slightly decreased (P &lt; 0.05) VFA production. Due to the strong antimethanogenic effect of geraniol a careful selection of dose and combination with other antimethanogenic compounds may be effective in mitigating methane emission from ruminants. However, if a reduction in total VFA production and dry matter digestibility persisted in vivo, geraniol would have a negative effect on animal productivity.

Salinomycin inhibits canine mammary carcinoma in vitro by targeting cancer stem cells.

Salinomycin (SAL), a polyether ionophore antibiotic, has been demonstrated to selectively kill cancer stem cells (CSCs) in various types of human tumor. The aim of the present study was to investigate the effects of SAL on canine mammary CSCs. CSCs in canine mammary carcinoma cell lines (CMT7364 and CIPp) were identified using a sphere formation assay and flow cytometry. The chemoresistance, invasive potential and expression of stem cell-associated proteins of these spheres was then analyzed. This demonstrated that the spheres exhibited characteristics of CSCs, including a cluster of differentiation (CD)44+/CD24-/low phenotype, upregulation of Wnt/β-catenin signaling pathway-associated proteins and chemoresistance. The viability of the spheres was decreased in a concentration- and time-dependent manner following treatment with SAL, and the spheres did not exhibit increased resistance to SAL compared with their parental cells. In addition, exposure to SAL inhibited sphere-formation and invasive potential in canine mammary CSCs in a dose-dependent manner. Furthermore, SAL decreased the CD44+/CD24-/low population and downregulated the expression of Wnt/β-catenin signaling-associated proteins (β-catenin, Cyclin D1 and octamer-binding transcription factor 4) in the spheres. In conclusion, the present study demonstrated that SAL is an effective inhibitor of canine mammary CSCs in vitro, indicating that SAL is a promising chemotherapeutic agent for the treatment of canine mammary carcinoma.

Salinomycin induces endoplasmic reticulum stress‑mediated autophagy and apoptosis through generation of reactive oxygen species in human glioma U87MG cells.

Salinomycin is a polyether ionophore antibiotic that has recently been shown to induce cell apoptosis in human cancer cells displaying multiple mechanisms of drug resistance. In the present study, we explored the impact of salinomycin on the apoptosis and autophagy as well as the correlation between those effects and endoplasmic reticulum (ER) stress molecular mechanisms in human glioma U87MG cells. Apoptosis, autophagy and reactive oxygen species (ROS) were analyzed using flow cytometry. In addition, expression levels of apoptosis-, autophagy-and ER stress-related proteins were determined by western blotting. The results showed that salinomycin induced apoptosis, ER stress and autophagy in glioma cancer cell lines. In addition, salinomycin also induced ROS generation, and the ROS scavenger N-acetyl-L-cysteine was found to inhibit the salinomycin-induced apoptosis, ER stress and autophagy. The inhibition of ER stress with 4-phenylbutyric acid depressed salinomycin-induced apoptosis and autophagy. Salinomycin increased the expression of autophagy marker protein, LC3B, and accumulation of acidic vesicular organelles. Furthermore, pre-treatment with the autophagy inhibitor 3-methyladenine showed potential in increasing the apoptosis rate induced by salinomycin in the U87MG cells. Taken together, these results revealed that salinomycin induced apoptosis and autophagy via ER stress mediated by ROS, suggesting that ER stress by salinomycin plays a dual function in both promoting and suppressing cell death.

Isolated alkali cation complexes of the antibiotic ionophore nonactin: correlation with crystalline structures.

The antibiotic activity of nonactin is sustained by its ability to transport K+ across lipophilic phases, e.g., the cell membranes. Such a feature can be traced back to a specific ionophoric behavior and to a balanced hydrophobicity modulated by the formation of a cation complex. In this study, the dominant conformations and coordination arrangements in the alkali cation complexes (Na+, K+, Cs+) of nonactin are characterized by means of action vibrational spectroscopy and quantum chemical computations. The low energy conformers of the complexes comprise compact inclusion structures, in which the cation interacts with a varying number of oxygen atoms of the carbonyl and oxolane ring groups of the nonactin macrocycle. The spectroscopy experiments indicate that the three alkali complexes explored are formed in a S4 conformation. This is in contrast with previous crystallography studies, which concluded that the symmetry of the most stable conformer of the complex changes qualitatively with the cation size, from C2 for Na+ to S4 for K+ and Cs+. Computations with different hybrid density functionals lead to contradictory predictions that appear to be quite sensitive to the modelling of the long range interactions in the coordination arrangements. The stabilization of the nonactin-Na+ complex in the C2 or S4 forms emerges as a subtle feature that may be tuned with an appropriate control of the environmental conditions, and constitutes a challenging benchmark to confront novel computational methods for supramolecular systems.

DasR positively controls monensin production at two-level regulation in Streptomyces cinnamonensis

The polyether ionophore antibiotic monensin is produced by Streptomyces cinnamonensis and is used as a coccidiostat for chickens and growth-promoting agent for cattle. Monensin biosynthetic gene cluster has been cloned and partially characterized. The GntR-family transcription factor DasR regulates antibiotic production and morphological development in Streptomyces coelicolor and Saccharopolyspora erythraea. In this study, we identified and characterized the two-level regulatory cascade of DasR to monensin production in S. cinnamonensis. Forward and reverse genetics by overexpression and antisense RNA silence of dasR revealed that DasR positively controls monensin production under nutrient-rich condition. Electrophoresis mobility shift assay (EMSA) showed that DasR protein specifically binds to the promoter regions of both pathway-specific regulatory gene monRII and biosynthetic genes monAIX, monE and monT. Semi-quantitative RT-PCR further confirmed that DasR upregulates the transcriptional levels of these genes during monensin fermentation. Subsequently, co-overexpressed dasR with pathway-specific regulatory genes monRI, monRII or monH greatly improved monensin production.

Voltammetric and corrosion studies of the ionophoric antibiotic–salinomycin and its determination in a soil extract

Salinomycin monosodium salt (SLM) is a widely used ionophoric antibiotic with a broad spectrum of activity. In this paper, a study is reported on the first electrochemical investigation of SLM. The use of square wave voltammetry (SWV) in combination with a renewable silver amalgam film electrode (Hg(Ag)FE) is presented for the determination of SLM in a spiked soil extract. A reduction peak at −1.40V vs. an Ag/AgCl/KCl reference electrode was obtained in Britton–Robinson (B–R) buffer (pH7.0). The influences of conditioning potential and time, frequency, amplitude, step potential and equilibration time were studied. This electroanalytical procedure was used to determine SLM on an Hg(Ag)F electrode at a concentration range of 2.5×10−7–2.5×10−6molL−1. The precision and repeatability of the method were checked. The limit of detection and quantification were 7.8×10−8molL−1 and 2.5×10−7molL−1, respectively. To understand the SLM electrode mechanism, the cyclic voltammetry (CV) technique was applied. Moreover, the effect of SLM on the corrosion properties of stainless steels used to produce metal bowls and feed troughs was studied using the potentiodynamic method.

Inhibitors of Cancer Stem Cells.

The cancer stem cell (CSC) theory is current strategy of cancer treatment. Cancers follow pathways of cancer stem cell such as Notch, Wnt and Hedgehog can be addressed with natural products or synthetic drugs to diminish the chance of new tumours. The cancer growth can also be suppressed by aiming the tumourigenic stem cells alone, instead of targeting at reducing complete tumour dimension. The recurrence of tumours after years of disease-free survival has prompted interest in the concept that cancers may have a stem cell basis. Current assumption holds that &lt; 5% of the tumour mass may be chemo-resistant and radio-resistant, harbouring stem-like properties that impel tumour survival, development, and metastasis. There is intense an investigation to interpret CSCs based on self-renewal and multi-lineage differentiation. Nevertheless, no successful targeted therapies have reached the clinic. The ionophore antibiotic salinomycin that selectively kills breast CSCs seems to be a promising anticancer drug. Clinical trials conducted by the NIH (National Institute of Health) on several synthetic drugs demonstrate the current importance of the issue and predict a bright future for such molecular weapons against cancer.