Population Pharmacokinetics and Absolute Oral Bioavailability of Lasalocid after Single Intravenous and Intracrop Administration in Laying Hens.

Lasalocid sodium is a polyether carboxylic ionophore agent authorized by the EU for use as a coccidiostat in broilers, turkeys, and pullets up to 16 weeks of age, except for laying hens. However, laying hens are the most common nontarget species exposed to lasalocid sodium, mainly due to cross-contamination from feed mills. This exposure may result in potential drug residue deposition in eggs, which could potentially expose consumers to the drug. The breeds commonly used for commercial egg production in Poland are Isa Brown and Green-legged Partridge hens, which have been found to significantly differ in egg-laying performance. This variability may also affect the pharmacokinetics of lasalocid. Data on lasalocid plasma pharmacokinetics in laying hens are lacking. In this study, we aimed to determine typical population pharmacokinetic parameters, absolute oral bioavailability, and how breed may influence the pharmacokinetics of lasalocid. Twenty-layer hens of the two breeds were used in this study. Lasalocid was administered orally at a single dose of either 1 mg or 5 mg/kg body weight or intravenously at a dose of 1 mg/kg body weight, in a crossover design with a three-week washout period between study periods. Blood samples were collected for 72 h, and lasalocid concentrations were measured using high-performance liquid chromatography with fluorescence detection. A population pharmacokinetic analysis was conducted using nonlinear mixed effects modeling. Standard numerical and graphical criteria were used to select the best model, and a stepwise covariate modeling approach was used to determine any influencing factors. The best model was a three-compartment mammillary model with first-order absorption, transit compartments, and linear elimination. The estimated absolute oral bioavailability was low (36%). It was found that breed significantly influenced not only absorption but also the elimination of lasalocid. This study revealed that lasalocid absorption and elimination varied between the two breeds. This variability in pharmacokinetics may result in breed-related differences in drug residue accumulation in eggs, and ultimately, the risk associated with consumer exposure to drug residues may also vary.

Ruminal modulator additive effect of Stryphnodendron rotundifolium bark in feedlot lambs.

The study aimed to evaluate the inclusion effects of Stryphnodendron rotundifolium (barbatimão) extracts in substitution of the lasalocid sodium on the ingestive behaviour, intake, ruminal parameters, and digestibility of feedlot lambs. Twenty-four pantaneiro lambs were used, with an average age of 150 ± 4.59 days and an initial body weight of 21.2 ± 3.63 kg. The lambs were distributed in three treatments in an experimental design with randomized blocks. The treatments correspond to the additive supplements: LAS (0.019 g of lasalocid sodium/lamb/d); DGB (1.50 g of barbatimão dried ground bark/lamb/d); DHE (0.30 g of barbatimão dry hydroalcoholic extract/lamb/d). The DHE increased 59.74 min in the time spent for ingestion per day, resulting in an efficiency reduction of dry matter (DM) ingestion (127 g of DM/h of feed). There was a reduction of 1.8 mg/dL in the ammoniacal nitrogen concentration with extract supplementation compared to LAS. The DGB reduced total volatile fatty acids by 48.9% compared to the control treatment. The inclusion of barbatimão extracts (DGB and DHE) reduced 12.05% of ruminal butyrate content. The supplementation of barbatimão extracts replacing lasalocid sodium in the diet of feedlot lambs did not affect intake and caused small changes on ingestive behaviour.

Simultaneous Improvement in the Thermostability and Catalytic Activity of Epoxidase Lsd18 for the Synthesis of Lasalocid A.

Enzymes used in the synthesis of natural products are potent catalysts, capable of efficient and stereoselective chemical transformations. Lsd18 catalyzes two sequential epoxidations during the biosynthesis of lasalocid A, a polyether polyketide natural product. We performed protein engineering on Lsd18 to improve its thermostability and catalytic activity. Utilizing structure-guided methods of FoldX and Rosetta-ddG, we designed 15 mutants of Lsd18. Screening of these mutants using thermal shift assay identified stabilized variants Lsd18-T189M, Lsd18-S195M, and the double mutant Lsd18-T189M-S195M. Trypsin digestion, molecular dynamic simulation, circular dichroism (CD) spectroscopy, and X-ray crystallography provided insights into the molecular basis for the improved enzyme properties. Notably, enhanced hydrophobic interaction within the enzyme core and interaction of the protein with the FAD cofactor appear to be responsible for its better thermostability.

Environmental pro-oxidants induce altered envelope protein profiles in human keratinocytes.

Cornified envelopes (CEs) of human epidermis ordinarily consist of transglutaminase-mediated cross-linked proteins and are essential for skin barrier function. However, in addition to enzyme-mediated isopeptide bonding, protein cross-linking could also arise from oxidative damage. Our group recently demonstrated abnormal incorporation of cellular proteins into CEs by pro-oxidants in woodsmoke. In this study, we focused on 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), mesquite liquid smoke (MLS), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), to further understand the mechanisms through which environmental pro-oxidants induce CE formation and alter the CE proteome. CEs induced by the ionophore X537A were used for comparison. Similar to X537A, DMNQ- and MLS-induced CE formation was associated with membrane permeabilization. However, since DMNQ is non-adduct forming, its CEs were similar in protein profile to those from X537A. By contrast, MLS, rich in reactive carbonyls that can form protein adducts, caused a dramatic change in the CE proteome. TCDD-CEs were found to contain many CE precursors, such as small proline-rich proteins and late cornified envelope proteins, encoded by the epidermal differentiation complex. Since expression of these proteins is mediated by the aryl hydrocarbon receptor (AhR), and its well-known downstream protein, CYP1A1, was exclusively present in the TCDD group, we suggest that TCDD alters the CE proteome through persistent AhR activation. This study demonstrates the potential of environmental pro-oxidants to alter the epidermal CE proteome and indicates that the cellular redox state has an important role in CE formation.

New Hydrophilic Derivatives of Lasalocid and Their Complexes with Selected Metal Cations.

Two new esters of lasalocid, that are more hydrophilic, with glucose (LasGlu) and xylitol (LasX), have been synthesized, and their complexation of monovalent cations has been studied by various spectrometric and spectroscopic methods, such as ESI mass spectrometry, 1H, 13C NMR and FT-IR. Analyses of the results confirmed the synthesis of new esters with good yields. In order to carry out further studies, it was necessary to purify them using "flash" liquid chromatography. It was confirmed that the newly obtained molecules, as well as their complexes with lithium, sodium and potassium cations, were stabilized by a strong system of intramolecular hydrogen bonds. It was found that the hydroxyl groups of esters derived from xylitol and glucose were also involved in the complexation of cations. The results of the PM6 semiempirical calculations permitted determination of the heat of formation (HOF), and visualization of the structure of the new esters and their complexes with the cations studied. All computation results are in agreement with the spectroscopic data.

Effects of lasalocid, narasin, or virginiamycin supplementation on rumen parameters and performance of beef cattle fed forage-based diet.

Two experiments were designed to evaluate the impacts of supplementing lasalocid (LAS), narasin (NAR), or virginiamycin (VRM) on rumen fermentation parameters, apparent nutrient digestibility, and blood parameters (Exp. 1), as well as feed intake and performance (Exp. 2) of Nellore cattle consuming a forage-based diet. In Exp. 1, 32 rumen-fistulated Nellore steers (initial shrunk body weight [BW] = 355 ± 4.4 kg) were assigned to a randomized complete block design. Within block, animals were randomly assigned to one of four treatments: 1) forage-based diet without feed additives (CON), 2) CON diet plus 13 mg/kg of dry matter (DM) of NAR, 3) CON diet plus 20 mg/kg of DM of sodium LAS, or 4) CON diet plus 20 mg/kg of DM of VRM. No treatment effects were detected (P ≥ 0.32) for intake and apparent digestibility of nutrients. Steers fed NAR had the lowest (P ≤ 0.01) molar proportion of acetate on day 28, 56, and 112 vs. CON, LAS, and VRM steers, whereas acetate did not differ (P ≥ 0.25) between LAS, VRM, and CON steers from day 28 to 84. On day 112, steers fed LAS had a lower (P < 0.02) molar proportion of acetate vs. VRM and CON, whereas it did not differ between CON and VRM (P > 0.33). Steers receiving NAR had a greater (P ≤ 0.04) ruminal propionate vs. CON, LAS, and VRM, whereas LAS steers had greater (P < 0.04) propionate vs. CON and VRM steers on day 28 and 112, and it did not differ (P > 0.22) between CON and VRM. In Exp. 2, 160 Nellore bulls were blocked by initial shrunk BW (212 ± 3.1 kg) in a 140-d feedlot trial. Diets contained the same treatments used in Exp. 1. Bulls fed NAR had greater (P < 0.02) average daily gain (ADG) vs. CON and VRM, and similar (P = 0.17) ADG between NAR and LAS, whereas ADG did not differ (P > 0.28) between LAS, VRM, and CON bulls. A treatment effect was detected (P = 0.03) for dry matter intake, being greater in NAR vs. CON, LAS, and VRM bulls, and similar (P > 0.48) between CON, LAS, and VRM bulls. A tendency was detected (P = 0.09) for feed efficiency, which was greater (P < 0.02) in NAR bulls vs. CON and VRM, and similar (P = 0.36) between NAR and LAS bulls. From day 112 to 140, bulls receiving NAR were heavier (P < 0.03) vs. CON, LAS, and VRM bulls, but no differences were observed (P > 0.51) between CON, LAS, and VRM bulls. Collectively, ruminal fermentation profile and intake were impacted by NAR supplementation, which partially contributed to the enhanced performance of Nellore bulls receiving a forage-based diet.

Feed additives are nutritional tools that benefit dietary digestibility and nutrient utilization, alter ruminal fermentation routes, and improve cattle growth and efficiency, thus increasing productivity and profitability in beef cattle systems. Nonetheless, most of the current research focuses on supplementing feed additives in high-concentrate diets. Leaving a significant gap in understanding the influence of feed additives in cattle consuming forage-based diets, especially molecules capable of altering the fermentation process and, consequently, beef cattle performance. Therefore, this experiment aimed to evaluate the impacts of supplementing narasin (NAR), lasalocid (LAS), or virginiamycin (VRM) on rumen fermentation parameters, apparent nutrient digestibility, feed intake, and performance of Bos indicus Nellore cattle consuming a forage-based diet. Including commercially available feed additives into forage-based diets did not impact nutrient intake and digestibility of nutrients. The inclusion of NAR affected ruminal fermentation parameters toward propionate production, positively contributing to animal performance. Ruminal fermentation characteristics and animal growth were not impacted by dietary LAS and VRM, which could be attributed to the dose used in the current experiment, despite the manufacturer's recommendation. This research provides insights into NAR as an important feed additive for forage-based beef cattle diets.

Comparison effect of lasalocid, diclazuril, probiotic and symbiotic on histomorpholical changes of small intestine induced by E. tenella.

This study aimed to investigate the comparison of effect of anticoccidal drugs including lasalocid and diclazuril with probiotic and synbiotic on the growth performance and intestinal morphology in broiler chicken. One hundred eighty chickens (Ross 308, 1 day old) were randomly divided into 6 equal groups (n=30) including the negative control (basal diet), the positive control (basal diet+oral inoculation of 3×104 sporulated oocytes of E. tenella, and four treatment groups. At days of 28 and 49 of age, 9 chickens were blindly chosen from each group were scarified by decapitation and their various segments of small intestine including ileum, jejunum, and duodenum were evaluated histomorphologically. We found that the economic losses resulted from coccidial infection in the poultry industry are caused by the decreased performance of broiler chicken induced by morphological changes in the any three segments specially jejunum. The anticoccidial drugs, synbiotic and probiotic can partially prevent morphological changes in any three segments of small intestine in broiler chicken with coccidiosis. Since morphological changes in the jejunum begin earlier than in other parts and surface area of jejunal villi is important for nutrition absorbance as well as growth performance, lasolacid was found to a be more efficient treatment in this regard.

Analysis of electrochemical and liver microsomal transformation products of lasalocid by LC/HRMS.

RATIONALE: Lasalocid (LAS), an ionophore, is used in cattle and poultry farming as feed additive for its antibiotic and growth-promoting properties. Literature on transformation products (TP) resulting from LAS degradation is limited. So far, only hydroxylation is found to occur as the metabolic reaction during the LAS degradation. To investigate potential TPs of LAS, we used electrochemistry (EC) and liver microsome (LM) assays to synthesize TPs, which were identified using liquid chromatography high-resolution mass spectrometry (LC/HRMS). METHODS: Electrochemically produced TPs were analyzed online by direct coupling of the electrochemical cell to the electrospray ionization (ESI) source of a Sciex Triple-TOF high resolution mass spectrometer. Then, EC-treated LAS solution was collected and analyzed offline using LC/HRMS to confirm stable TPs and improve their annotation with a chemical structure due to informative MS/MS spectra. In a complementary approach, TPs formed by rat and human microsomal incubation were investigated using LC/HRMS. The resulting data were used to investigate LAS modification reactions and elucidate the chemical structure of obtained TPs. RESULTS: The online measurements identified a broad variety of TPs, resulting from modification reactions like (de-)hydrogenation, hydration, methylation, oxidation as well as adduct formation with methanol. We consistently observed different ion complexations of LAS and LAS-TPs (Na+ ; 2Na+ K+ ; NaNH4 + ; KNH4 + ). Two stable methylated EC-TPs were found, structurally annotated, and assigned to a likely modification reaction. Using LM incubation, seven TPs were formed, mostly by oxidation/hydroxylation. After the identification of LM-TPs as Na+ -complexes, we identified LM-TPs as K+ -complexes. CONCLUSION: We identified and characterized TPs of LAS using EC- and LM-based methods. Moreover, we found different ion complexes of LAS-based TPs. This knowledge, especially the different ion complexes, may help elucidate the metabolic and environmental degradation pathways of LAS.

The In Vitro Cytotoxic Effects of Ionophore Exposure on Selected Cytoskeletal Proteins of C2C12 Myoblasts.

Carboxylic ionophores, such as monensin, salinomycin and lasalocid, are polyether antibiotics used widely in production animals for the control of coccidiosis, as well as for the promotion of growth and feed efficiency. Although the benefits of using ionophores are undisputed, cases of ionophore toxicosis do occur, primarily targeting the cardiac and skeletal muscles of affected animals. The 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide (MTT) viability assay was used to determine the cytotoxicity of monensin, salinomycin and lasalocid on mouse skeletal myoblasts (C2C12). Immunocytochemistry and immunofluorescent techniques were, in turn, performed to investigate the effects of the ionophores on the microfilament, microtubule and intermediate filament, i.e., desmin and synemin networks of the myoblasts. Monensin was the most cytotoxic of the three ionophores, followed by salinomycin and finally lasalocid. Monensin and salinomycin exposure resulted in the aggregation of desmin around the nuclei of affected myoblasts. The synemin, microtubule and microfilament networks were less affected; however, vesicles throughout the myoblast's cytoplasm produced gaps within the microtubule and, to a limited extent, the synemin and microfilament networks. In conclusion, ionophore exposure disrupted desmin filaments, which could contribute to the myofibrillar degeneration and necrosis seen in the skeletal muscles of animals suffering from ionophore toxicosis.

The co-administration effects of florfenicol and lasalocid on performance, biochemical and pathological parameters of muscle, heart, liver, kidney and sciatic nerve in broiler chickens.

The study aimed to examine the effect of simultaneous application of florfenicol and lasalocid on the performance and vital organ function of chickens. For this, 300 chicks were divided into four groups. Group one to three received florfenicol, lasalocid and lasalocid plus florfenicol, respectively. Group four as the control group received a basic diet without lasalocid or florfenicol. Lasalocid was used from 7 to 35 days old, continuously. Florfenicol was used at 21 days old for 5 days. The growth indices were measured at the end of each week. The chickens were euthanized at the ages of 28 and 35 days old after collecting blood samples with and without anticoagulants. The liver, heart, muscle, kidney and sciatic nerve were collected in formalin 10% for histopathological examination. The blood and serum samples were used to determine clinical pathologic and hematologic indices. The ratio of internal organs to body weight and ratio of the right ventricle to the total ventricles (RV/TV) of the heart was measured. Results showed, the use of lasalocid decreased feed conversion rate and triglyceride, and increased total protein. Simultaneous administration of lasalocid and florfenicol affected histopathology of the liver and heart and significantly increased creatine phosphokinase, uric acid and the ratio of RV/TV of heart. The eosinophil percentage in the chickens who received florfenicol plus lasalocid was significantly higher than chickens who received florfenicol alone (p < 0.05). In conclusion, it seems that simultaneous administration of the florfenicol and lasalocid induces side-effects especially on cardiac function and it is not recommended.

Modular polyketide synthase contains two reaction chambers that operate asynchronously.

Type I modular polyketide synthases are homodimeric multidomain assembly line enzymes that synthesize a variety of polyketide natural products by performing polyketide chain extension and ß-keto group modification reactions. We determined the 2.4-angstrom-resolution x-ray crystal structure and the 3.1-angstrom-resolution cryo­electron microscopy structure of the Lsd14 polyketide synthase, stalled at the transacylation and condensation steps, respectively. These structures revealed how the constituent domains are positioned relative to each other, how they rearrange depending on the step in the reaction cycle, and the specific interactions formed between the domains. Like the evolutionarily related mammalian fatty acid synthase, Lsd14 contains two reaction chambers, but only one chamber in Lsd14 has the full complement of catalytic domains, indicating that only one chamber produces the polyketide product at any given time.

Detection of salinomycin and lasalocid in chicken liver by icELISA based on functional bispecific single-chain antibody (scDb) and interpretation of molecular recognition mechanism.

Salinomycin (SAL) and lasalocid (LAS) are widely used as ionophore antibiotics for coccidiosis control. However, their common use as feed additives has led to the occurrence of feed cross-contamination, which has toxic effects on non-target animals. There have been few reports on multiple-residue detection for SAL and LAS in recent years. In this study, two single-chain antibody fragments (scFvs) capable of specifically recognizing SAL and LAS were constructed. Using LAS-scFv and SAL-scFv as parent antibodies, a complete bispecific single-chain diabody (scDb) against both LAS and SAL was built using splicing by overlap extension polymerase chain reaction (SOE-PCR). In addition, the key amino acid sites and interaction energy of antibody variable regions for small-molecule recognition were preliminarily studied by homology modeling and molecular docking. Finally, IC50 values of 12.9 and 8.6 ng/mL, with a linear range of 6.9-24.0 and 4.7-16.0 ng/mL, were obtained for LAS-scFv and SAL-scFv, respectively. An indirect competitive enzyme-linked immunosorbent assay (icELISA) method was established using scDb to obtain an IC50 of 3.5 ng/mL for LAS and 4.1 ng/mL for SAL, which showed better sensitivity and specificity than those of the parent scFv antibodies. The recoveries of LAS and SAL in chicken liver were 89.2-92.7%(CV<4.7%) and 88.6-90.2% (CV<6.8%)), respectively.

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 the ability to target aggressive cancer cells. Nevertheless, ionophore function is believed to be associated with idiosyncratic cellular 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 antibacterial 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.

A rapid and convenient screening method for detection of restricted monensin, decoquinate, and lasalocid in animal feed by applying SERS and chemometrics.

The surface-enhanced activities of size- and shape-controlled gold nanoparticles (AuNPs) with superior chemical stability were investigated to explore a possible development of a simple and non-destructive spectroscopic method to help the regulatory agency's analytical services for rapid detection and characterization of selected antimicrobials in animal feeds. Feed samples spiked at different concentration ranges of antimicrobials were evaluated using AuNPs as a surface-enhanced Raman spectroscopy (SERS) agent. The collected SERS spectra were mathematically preprocessed for further analysis. The classification models obtained 100% predictive accuracy with zero or little misclassification. The first two canonical variables (p = 0.001) could explain >95% of the variability in preprocessed spectral data. Most chemometric models for predicting MON, DEC, and LAS concentrations showed a high predictive accuracy (r2 > 0.90), lower predictive error (<20 mg/kg), and satisfactory regression quality (slope close to 1.0). The statistical results showed no statistically significant difference between the reference and SERS predicted values (p > 0.05). The findings and implications from the study indicate that SERS would be a powerful and efficient technique possessing a great potential serving as an excellent monitoring and screening tool for antimicrobial contaminated samples in the on-site analysis.

Synthesis and Anticancer Activity of Dimeric Polyether Ionophores.

Polyether ionophores represent a group of natural lipid-soluble biomolecules with a broad spectrum of bioactivity, ranging from antibacterial to anticancer activity. Three seem to be particularly interesting in this context, namely lasalocid acid, monensin, and salinomycin, as they are able to selectively target cancer cells of various origin including cancer stem cells. Due to their potent biological activity and abundant availability, some research groups around the world have successfully followed semi-synthetic approaches to generate original derivatives of ionophores. However, a definitely less explored avenue is the synthesis and functional evaluation of their multivalent structures. Thus, in this paper, we describe the synthetic access to a series of original homo- and heterodimers of polyether ionophores, in which (i) two salinomycin molecules are joined through triazole linkers, or (ii) salinomycin is combined with lasalocid acid, monensin, or betulinic acid partners to form 'mixed' dimeric structures. Of note, all 11 products were tested in vitro for their antiproliferative activity against a panel of six cancer cell lines including the doxorubicin resistant colon adenocarcinoma LoVo/DX cell line; five dimers (14-15, 17-18 and 22) were identified to be more potent than the reference agents (i.e., both parent compound(s) and commonly used cytostatic drugs) in selective targeting of various types of cancer. Dimers 16 and 21 were also found to effectively overcome the resistance of the LoVo/DX cancer cell line.

Streptomyces lasalocidi sp. nov. (formerly 'Streptomyces lasaliensis'), an actinomycete isolated from soil which produces the polyether antibiotic lasalocid.

Strain ATCC 31180T was isolated from soil collected in Hyde Park, Massachusetts (USA), and found to produce the polyether antibiotic lasalocid. The name 'Streptomyces lasaliensis' has been in common use since 1974, without a recognized taxonomic description. The most closely related type cultures determined by rRNA gene sequence similarity were Streptomyces longwoodensis DSM 41677T (100 %) and Streptomyces galbus DSM 40089T (100 %). OrthoANI values with S. longwoodensis and S. galbus were 95.50 and 94.41 %, respectively. Chemotaxonomic characteristics supported inclusion within the genus Streptomyces. The cell wall peptidoglycan contained ll-diaminopimelic acid, and the major whole-cell sugars were glucose and ribose. Polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol, phosphatidylglycerol, one unidentified lipid and one unidentified glycolipid. The major menaquinones detected were MK9(H4), MK9(H6) and MK9(H8). The major cellular fatty acids were anteiso-C15 : 0, anteiso-C17 : 0, iso-C16 : 0, iso-C15 : 0 and anteiso-C17 : 1. Its DNA had a G+C content of 72.6 %. Differentiation of ATCC 31180T from the closely related species was evident from digital DNA-DNA hybridization values of 61.80 and 56.90 % for S. longwoodensis and S. galbus respectively. Significant differences were seen in the polyphasic phenotypic analyses. ATCC 31180T produced lasalocid, grew from 10 to 45 °C, pH4-8 and in the presence of 0-10 % NaCl, 0.01 % NaN3 and 1 % phenol. Melanin was produced; H2S and indole were not. Nitrate was not reduced. Spore chains were retinaculum-apertum and spore surfaces were smooth. Spore colour, mycelia colour and soluble pigment production were medium-dependent. The proposed name is Streptomyces lasalocidi sp. nov.; the type strain being ATCC 31180T (=NRRL 3382T=DSM 46487T).

Polyether ionophores residues in Minas Frescal cheese by UHPLC-MS/MS.

An analytical method was developed and validated for the determination of three polyether ionophores (monensin, lasalocid, and salinomycin) in 60 samples of Brazilian Minas Frescal cheese by UHPLC-MS/MS. Linearity ranged from 1 to 8 µg kg-1 for monensin and salinomycin, and from 0.50 to 4 µg kg-1 for lasalocid. Limits of detection and quantitation were 0.50 µg kg-1 and 1 µg kg-1, respectively, for both monensin and salinomycin, and 0.25 µg kg-1 and 0.50 µg kg-1, respectively, for lasalocid. Recoveries were between 69% and 84% with coefficients of variation up to 16.28% for repeatability and 13.79% for intermediate precision. A total of 60 samples of Minas Frescal cheese were analysed and only monensin residues were found. Monensin was detected in 55% of the samples and quantified in 5 of them at mean levels varying from 1.00 to 1.73 µg kg-1. The proposed method demonstrated the suitability for monitoring these substances in cheese.

Determination of Eight Coccidiostats in Eggs by Liquid-Liquid Extraction-Solid-Phase Extraction and Liquid Chromatography-Tandem Mass Spectrometry.

A method for the simultaneous determination of robenidine, halofuginone, lasalocid, monensin, nigericin, salinomycin, narasin, and maduramicin residues in eggs by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. The sample preparation method used a combination of liquid-liquid extraction (LLE) and solid-phase extraction (SPE) technology to extract and purify these target compounds from eggs. The target compounds were separated by gradient elution using high-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC). Tandem mass spectrometry was used to quantitatively and qualitatively analyze the target compounds via electrospray ionization (ESI+) and multiple reaction monitoring mode. The HPLC-MS/MS and UPLC-MS/MS methods were validated according to the requirements defined by the European Union and the Food and Drug Administration. The limits of detection and limits of quantification of the eight coccidiostats in eggs were 0.23-0.52 µg/kg and 0.82-1.73 µg/kg for HPLC-MS/MS, and 0.16-0.42 µg/kg and 0.81-1.25 µg/kg for UPLC-MS/MS, respectively. The eggs were spiked with four concentrations of the eight coccidiostats, and the HPLC-MS/MS and UPLC-MS/MS average recoveries were all higher than 71.69% and 72.26%, respectively. Compared with the HPLC-MS/MS method, utilizing UPLC-MS/MS had the advantages of low reagent consumption, a short detection time, and high recovery and precision. Finally, the HPLC-MS/MS and UPLC-MS/MS methods were successfully applied to detect eight coccidiostats in 40 eggs.

Lasalocid Acid Antibiotic at a Membrane Surface Probed by Sum Frequency Generation Spectroscopy.

Carboxyl polyether ionophores (CPIs) are widely used as veterinary antibiotics and to increase food utilization in ruminating animals. Furthermore, CPIs can target drug-resistant bacteria, but detailed knowledge about their mode-of-action is needed to develop agents with a reasonable therapeutic index. It has been suggested that ionophores bind to membranes and incur large structural changes to shield a bound ion from the hydrophobic environment of the lipid bilayer for transport. One crucial piece of information is missing, however: Is it necessary for the free ionophore to adsorb on the membrane surface before interacting with a cation to facilitate cross-membrane ion transport? To answer this question, we applied sum-frequency generation (SFG) vibrational spectroscopy and surface tensiometry to identify the interaction between the prototypical CPI lasalocid acid (LA) and a model membrane. Observed changes in the surface pressure demonstrate that the free LA undergoes a self-assembly process with the lipid monolayer. Spectra taken from the lipid monolayer show that the free acid inserts partially into the lipid monolayer and then after complexation with sodium chloride disrupts the lipid monolayer. Overall, this study strongly suggests that this must be the crucial step of LA and metal ion complexation that allows the ionophore to traverse a lipid membrane.

Revisiting Old Ionophore Lasalocid as a Novel Inhibitor of Multiple Toxins.

The ionophore lasalocid is widely used as a veterinary drug against coccidiosis. We found recently that lasalocid protects cells from two unrelated bacterial toxins, the cytotoxic necrotizing factor-1 (CNF1) from Escherichia. coli and diphtheria toxin. We evaluated lasalocid's capacity to protect cells against other toxins of medical interest comprising toxin B from Clostridium difficile, Shiga-like toxin 1 from enterohemorrhagic E. coli and exotoxin A from Pseudomonas aeruginosa. We further characterized the impact of lasalocid on the endolysosomal and the retrograde pathways and organelle integrity, especially the Golgi apparatus. We found that lasalocid protects cells from all toxins tested and impairs the drop of vesicular pH along the trafficking pathways that are required for toxin sorting and translocation to the cytoplasm. Lasalocid also has an impact on the cellular distribution of GOLPH4 and GOLPH2 Golgi markers. Other intracellular trafficking compartments positive for EEA1 and Rab9A display a modified cellular pattern. In conclusion, lasalocid protects cells from multiple deadly bacterial toxins by corrupting vesicular trafficking and Golgi stack homeostasis.