Tobramycin-mediated self-assembly of DNA nanostructures for targeted treatment of Pseudomonas aeruginosa-infected lung inflammation

Pseudomonas aeruginosa (PA) is one of the most common multidrug-resistant pathogens found in clinics, often manifesting as biofilms. However, due to the emergence of superbugs in hospitals and the overuse of antibiotics, the prevention and treatment of PA infections have become increasingly challenging. Utilizing DNA nanostructures for packaging and delivering antibiotics presents an intervention strategy with significant potential. Nevertheless, construction of functional DNA nanostructures with multiple functionalities and enhanced stability in physiological settings remains challenging. In this study, the authors propose a magnesium-free assembly method that utilizes tobramycin (Tob) as a mediator to assemble DNA nanostructures, allowing for the functionalization of DNA nanostructures by combining DNA and antibiotics. Additionally, our study incorporates maleimide-modified DNA into the nanostructures to act as a targeting moiety specifically directed towards the pili of PA. The targeting ability of the constructed functional DNA nanostructure significantly improves the local concentration of Tob, thereby reducing the side effects of antibiotics. Our results demonstrate the successful construction of a maleimide-decorated Tob/DNA nanotube (NTTob-Mal) for the treatment of PA-infected lung inflammation. The stability and biocompatibility of NTTob-Mal are confirmed, highlighting its potential for clinical applications. Furthermore, its specificity in recognizing and adhering to PA has been validated. In vitro experiments have shown its efficacy in inhibiting PA biofilm formation, and in a murine model, NTTob-Mal has exhibited significant therapeutic effectiveness against PA-induced pneumonia. In summary, the proposed antibiotic drug-mediated DNA nanostructure assembly approach holds promise as a novel strategy for targeted treatment of PA infections.

pH-Responsive, Charge-Reversing Layer-by-Layer Nanoparticle Surfaces Enhance Biofilm Penetration and Eradication

Microbes entrenched within biofilms can withstand 1000-fold higher concentrations of antibiotics, in part due to the viscous extracellular matrix that sequesters and attenuates antimicrobial activity. Nanoparticle (NP)-based therapeutics can aid in delivering higher local concentrations throughout biofilms as compared to free drugs alone, thereby enhancing the efficacy. Canonical design criteria dictate that positively charged nanoparticles can multivalently bind to anionic biofilm components and increase biofilm penetration. However, cationic particles are toxic and are rapidly cleared from circulation in vivo, limiting their use. Therefore, we sought to design pH-responsive NPs that change their surface charge from negative to positive in response to the reduced biofilm pH microenvironment. We synthesized a family of pH-dependent, hydrolyzable polymers and employed the layer-by-layer (LbL) electrostatic assembly method to fabricate biocompatible NPs with these polymers as the outermost surface. The NP charge conversion rate, dictated by polymer hydrophilicity and the side-chain structure, ranged from hours to undetectable within the experimental timeframe. LbL NPs with an increasingly fast charge conversion rate more effectively penetrated through, and accumulated throughout, wildtype (PAO1) and mutant overexpressing biomass (ΔwspF) Pseudomonas aeruginosa biofilms. Finally, tobramycin, an antibiotic known to be trapped by anionic biofilm components, was loaded into the final layer of the LbL NP. There was a 3.2-fold reduction in ΔwspF colony forming units for the fastest charge-converting NP as compared to both the slowest charge converter and free tobramycin. These studies provide a framework for the design of biofilm-penetrating NPs that respond to matrix interactions, ultimately increasing the efficacious delivery of antimicrobials.

Thymus vulgaris essential oil + tobramycin within nanostructured archaeolipid carriers: A new approach against Pseudomonas aeruginosa biofilms

BACKGROUND

Pseudomonas aeruginosa biofilms in the respiratory tract of patients with an excessive inflammatory context are difficult to eradicate. New medicines that simultaneously target biofilms and inflammation should be developed.

HYPOTHESIS

Co-delivery of Thymus vulgaris essential oil (EOT) and tobramycin (TB) by nanostructured archaeolipids carriers (NAC) could support nebulization as well as improve EOT and TB antioxidant, anti-inflammatory and antibiofilm activity.

METHODS

NAC_(EOT+TB) were prepared by loading EOT and TB in NAC having a compritol and miglyol core, covered with a shell of archaeolipids, extracted from the hyperhalophylic archaebacteria Halorubrum tebenquichense, and Tween 80. NAC_(EOT+TB) were structurally characterized, including DSC thermograms, Raman spectra, TB release profile, EOT volatilization and in vitro antioxidant activity. In addition, stability upon nebulization, autoclaving and storage were assessed. The antibiofilm activity on P. aeruginosa PAO1 established biofilm of NAC_(EOT+TB) and the cytotoxicity on human lung epithelial cells and macrophage were determined, as well as intracellular reactive oxygen species (ROS) production and cytokines release on LPS stimulated cells.

RESULTS

NAC_(EOT+TB) showed a size of 197 ± 16 nm with PdI of 0.3 ± 0.1 and ζ Potential of -38 ± 3 mV. Structural characterization suggested that EOT was trapped in the compritol-miglyol core and TB was distributed between the surface of nanoparticles and free in solution. NAC_(EOT+TB) displayed a dual release profile of TB, a delayed release of EOT and improved EOTs in vitro antioxidant activity. While NAC_(EOT+TB) preserved its structural features after nebulization, autoclaving and 18 months of storage, carriers without archaeolipids gelled at room temperature and showed a significant increase of size after the same storage time. Below cytotoxic concentration, NAC_(EOT+TB) decreased bacteria viability and enhanced the disruption of established PAO1 biofilms compared to free TB and EOT. Also, the strong entrapment of EOT in NAC_(EOT+TB) delayed its volatilization, decreased intracellular ROS production and maintained its anti-inflammatory activity in LPS stimulated cells.

CONCLUSION

Combination of EOT + TB within NAC_(EOT+TB) result in a stable and nebulizable formulation that enhanced the antioxidant and anti-biofilm activity of free ingredients, improved their ability to decrease intracellular ROS and provided anti-inflammatory activity, at non-cytotoxic concentrations on eukaryotic cells.

Structural and phylogenetic analyses of resistance to next-generation aminoglycosides conferred by AAC(2') enzymes

Plazomicin is currently the only next-generation aminoglycoside approved for clinical use that has the potential of evading the effects of widespread enzymatic resistance factors. However, plazomicin is still susceptible to the action of the resistance enzyme AAC(2')-Ia from Providencia stuartii. As the clinical use of plazomicin begins to increase, the spread of resistance factors will undoubtedly accelerate, rendering this aminoglycoside increasingly obsolete. Understanding resistance to plazomicin is an important step to ensure this aminoglycoside remains a viable treatment option for the foreseeable future. Here, we present three crystal structures of AAC(2')-Ia from P. stuartii, two in complex with acetylated aminoglycosides tobramycin and netilmicin, and one in complex with a non-substrate aminoglycoside, amikacin. Together, with our previously reported AAC(2')-Ia-acetylated plazomicin complex, these structures outline AAC(2')-Ia's specificity for a wide range of aminoglycosides. Additionally, our survey of AAC(2')-I homologues highlights the conservation of residues predicted to be involved in aminoglycoside binding, and identifies the presence of plasmid-encoded enzymes in environmental strains that confer resistance to the latest next-generation aminoglycoside. These results forecast the likely spread of plazomicin resistance and highlight the urgency for advancements in next-generation aminoglycoside design.

Luminescent Amphiphilic Aminoglycoside Probes to Study Transfection

We report the characterization of amphiphilic aminoglycoside conjugates containing luminophores with aggregation-induced emission properties as transfection reagents. These inherently luminescent transfection vectors are capable of binding plasmid DNA through electrostatic interactions; this binding results in an emission "on" signal due to restriction of intramolecular motion of the luminophore core. The luminescent cationic amphiphiles effectively transferred plasmid DNA into mammalian cells (HeLa, HEK 293T), as proven by expression of a red fluorescent protein marker. The morphologies of the aggregates were investigated by microscopy as well as ζ-potential and dynamic light-scattering measurements. The transfection efficiencies using luminescent cationic amphiphiles were similar to that of the gold-standard transfection reagent Lipofectamine® 2000.

Antibacterial activity of iron oxide, iron nitride, and tobramycin conjugated nanoparticles against Pseudomonas aeruginosa biofilms

BACKGROUND

Novel methods are necessary to reduce morbidity and mortality of patients suffering from infections with Pseudomonas aeruginosa. Being the most common infectious species of the Pseudomonas genus, P. aeruginosa is the primary Gram-negative etiology responsible for nosocomial infections. Due to the ubiquity and high adaptability of this species, an effective universal treatment method for P. aeruginosa infection still eludes investigators, despite the extensive research in this area.

RESULTS

We report bacterial inhibition by iron-oxide (nominally magnetite) nanoparticles (NPs) alone, having a mean hydrodynamic diameter of ~ 16 nm, as well as alginate-capped iron-oxide NPs. Alginate capping increased the average hydrodynamic diameter to ~ 230 nm. We also investigated alginate-capped iron-oxide NP-drug conjugates, with a practically unchanged hydrodynamic diameter of ~ 232 nm. Susceptibility and minimum inhibitory concentration (MIC) of the NPs, NP-tobramycin conjugates, and tobramycin alone were determined in the PAO1 bacterial colonies. Investigations into susceptibility using the disk diffusion method were done after 3 days of biofilm growth and after 60 days of growth. MIC of all compounds of interest was determined after 60-days of growth, to ensure thorough establishment of biofilm colonies.

CONCLUSIONS

Positive inhibition is reported for uncapped and alginate-capped iron-oxide NPs, and the corresponding MICs are presented. We report zero susceptibility to iron-oxide NPs capped with polyethylene glycol, suggesting that the capping agent plays a major role in enabling bactericidal ability in of the nanocomposite. Our findings suggest that the alginate-coated nanocomposites investigated in this study have the potential to overcome the bacterial biofilm barrier. Magnetic field application increases the action, likely via enhanced diffusion of the iron-oxide NPs and NP-drug conjugates through mucin and alginate barriers, which are characteristic of cystic-fibrosis respiratory infections. We demonstrate that iron-oxide NPs coated with alginate, as well as alginate-coated magnetite-tobramycin conjugates inhibit P. aeruginosa growth and biofilm formation in established colonies. We have also determined that susceptibility to tobramycin decreases for longer culture times. However, susceptibility to the iron-oxide NP compounds did not demonstrate any comparable decrease with increasing culture time. These findings imply that iron-oxide NPs are promising lower-cost alternatives to silver NPs in antibacterial coatings, solutions, and drugs, as well as other applications in which microbial abolition or infestation prevention is sought.

Ultraselective antibiotic sensing with complementary strand DNA assisted aptamer/MoS2 field-effect transistors

Although aptamer has been demonstrated as an important probe for antibiotic determination, the selective sensing of different antibiotics is still a challenge due to their structure similarities and wide folding degrees of aptamer. Herein, a field-effect transistor using MoS₂ nanosheet as the channel and an aptamer DNA (APT) with its configuration shaped by a complementary strand DNA (CS) is employed for kanamycin (KAN) determination. This probe structure contributes to an enhanced selectivity and reliability with reduced device-to-device variations. This MoS₂/APT/CS sensor shows time-dependent performance in antibiotic sensing. Prolonged detection time (20 s-300 s) leads to an enhanced sensitivity (1.85-4.43 M^-1) and a lower limit of detection (1.06-0.66 nM), while a shorter detection time leads to a broader linear working range. A new sensing mechanism relying on charge release from probe is proposed, which is based on the "replacement reaction" between KAN and APT-CS. This sensor exhibits an extremely high selectivity (selectivity coefficient of 12.8) to kanamycin over other antibiotics including streptomycin, tobramycin, amoxicillin, ciprofloxacin and chloramphenicol. This work demonstrates the merits of probe engineering in label-free antibiotic detection with FET sensor, which presents significant promises in sensitive and selective chemical and biological sensing.

Enhanced of antibacterial activity of antibiotic-functionalized silver nanocomposites with good biocompatibility

Antimicrobial resistance to traditional antibiotics leads to a serious concern for medical care owing to ineffective antibiotic therapies. This study focused on the preparation of silver nanocomposites (AgNPs@Tob&PAGA) by modifying AgNPs with tobramycin (Tob) and carbohydrate polymer of poly(2-(acrylamido) glucopyranose) (PAGA). The enhanced antibacterial activities of nanocomposites against common pathogens of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were explored. The introduction of PAGA onto silver nanocomposites improved both citocompatibility and antibacterial activity. Compared with nude Tob, AgNPs@Tob&PAGA showed more fascinating antimicrobial effect against E. coli and S. aureus with about 20-fold increase in the antibacterial activity, simultaneously no detectable resistance was observed. Consequently, the silver nanocomposite as an antimicrobial agent presents promising prospects in the treatment of bacterial infections caused by antimicrobial resistant bacteria.

All-in-one NIR-activated nanoplatforms for enhanced bacterial biofilm eradication

The chronic infection of humans by antibiotic-resistant bacteria and their related biofilm have, so far, not been properly addressed. In the present work, we developed a novel antibacterial nanoplatform showing the most efficient antibiotic-resistant bacteria inhibition and biofilm eradication. This particular formulation contains tobramycin-conjugated graphene oxide, for efficiently capturing bacteria through electrostatic interactions and eliminating bacteria as a "nano-knife", and copper sulphide nanoparticles for enhancing the photothermal and photodynamic properties. This novel formulation can selectively eliminate bacteria over NIH 3T3 cells, and the biofilm eradication capacity was up to 70%. Importantly, the nanoplatforms can inhibit bacterial growth and promote the repair of antibiotic-resistant bacteria-infected wounds on rats without non-specific damage to normal tissue. This work provides an effective, simple, and rapid method for the design and fabrication of near-infrared light-induced nanoplatforms that offer possibilities to treat biofilm-related infections.

Pharmacokinetics and pharmacodynamics of high doses of inhaled dry powder drugs

For many years, administration of drugs by inhalation has been the mainstay treatment for obstructive respiratory disorders such as asthma and chronic obstructive pulmonary disease. Antibiotics and other drugs have been administered for decades as aerosols to treat other pulmonary disease in a clinical setting, but it was until the early 1980's that colistin was formally marketed as a solution for nebulization in Europe (Colomycin, Pharmax, Bexley). The solubility of other drugs and the size of the dose required to achieve therapeutic concentrations at the site of action, made treatment times long and difficult to be performed at home. High dose dry powder delivery is a potentially effective way to deliver low potency drugs such as antibiotics. There are three major barriers to achieving the desired pharmacodynamic effect with these compounds: aerosol delivery, lung deposition and clearance. The powder formulation and device technology influence aerosol generation and may influence the size of the dose that can be achieved by inhalation in one puff. The site of deposition in the lungs is dictated by mechanisms of deposition which are influenced by the aerosol properties, particularly aerodynamic particle size distribution and the anatomy and physiology of the lungs. Finally, mechanisms of clearance dictate the local and systemic disposition of the drug, which in turn affects its pharmacokinetics and ultimately the pharmacodynamic effect and efficacy of treatment. Each of these factors will be considered and the implications for antimicrobial agent delivery as a high dose delivery example will be given.

Development, Characterization, and In Vitro Testing of Co-Delivered Antimicrobial Dry Powder Formulation for the Treatment of Pseudomonas aeruginosa Biofilms

Pseudomonas aeruginosa is an opportunistic bacteria responsible for recurrent lung infections. Previously, we demonstrated that certain materials improved the activity of tobramycin (Tob) against P. aeruginosa biofilms in vitro. We aimed to develop prototype dry powder formulations comprising Tob and a mixture of excipients and test its aerodynamic properties and antimicrobial activity. First, we evaluated different combinations of excipients with Tob in solution against P. aeruginosa biofilms. We selected the compositions with the highest activity, to prepare dry powders by spray drying. The powders were characterized by morphology, bulk density, water content, and particle size distributions. Finally, the antimicrobial activity of the powders was tested. The combinations of Tob (64 μg/mL) with l-alanine and l-proline (at 10 and 20 mM; formulations 1 and 2, respectively) and with l-alanine and succinic acid (at 20 mM; formulation 3) showed the highest efficacies in vitro and were prepared as dry powders. Formulation 1 had the best aerodynamic performance as indicated by the fine particle fraction and the best in vitro activity against P. aeruginosa biofilms. Formulation 3 represents a good candidate for further optimization because it demonstrated good dispersibility potential and optimization of the particle size distribution may achieve high delivery efficiencies.

Differential Effects of Linkers on the Activity of Amphiphilic Tobramycin Antifungals

As the threat associated with fungal infections continues to rise and the availability of antifungal drugs remains a concern, it becomes obvious that the need to bolster the antifungal armamentarium is urgent. Building from our previous findings of tobramycin (TOB) derivatives with antifungal activity, we further investigate the effects of various linkers on the biological activity of these aminoglycosides. Herein, we analyze how thioether, sulfone, triazole, amide, and ether functionalities affect the antifungal activity of alkylated TOB derivatives against 22 Candida, Cryptococcus, and Aspergillus species. We also evaluate their impact on the hemolysis of murine erythrocytes and the cytotoxicity against mammalian cell lines. While the triazole linker appears to confer optimal activity overall, all of the linkers incorporated into the TOB derivatives resulted in compounds that are very effective against the Cryptococcus neoformans species, with MIC values ranging from 0.48 to 3.9 μg/mL.

Quorum-Quenching Human Designer Cells for Closed-Loop Control of Pseudomonas aeruginosa Biofilms

Current antibiotics gradually lose their efficacy against chronic Pseudomonas aeruginosa infections due to development of increased resistance mediated by biofilm formation, as well as the large arsenal of microbial virulence factors that are coordinated by the cell density-dependent phenomenon of quorum sensing. Here, we address this issue by using synthetic biology principles to rationally engineer quorum-quencher cells with closed-loop control to autonomously dampen virulence and interfere with biofilm integrity. Pathogen-derived signals dynamically activate a synthetic mammalian autoinducer sensor driving downstream expression of next-generation anti-infectives. Engineered cells were able to sensitively score autoinducer levels from P. aeruginosa clinical isolates and mount a 2-fold defense consisting of an autoinducer-inactivating enzyme to silence bacterial quorum sensing and a bipartite antibiofilm effector to dissolve the biofilm matrix. The self-guided cellular device fully cleared autoinducers, potentiated bacterial antibiotic susceptibility, substantially reduced biofilms, and alleviated cytotoxicity to lung epithelial cells. We believe this strategy of dividing otherwise coordinated pathogens and breaking up their shielded stronghold represents a blueprint for cellular anti-infectives in the postantibiotic era.

Elution Profiles of Two Methods of Antibiotic Tibial Nail Preparations

Interlocking nails coated with antibiotic-supplemented cement provide effective treatment of infected long bone nonunion, but the thicker coating on guidewires may provide greater antibacterial activity. This study compared the properties of cement cured on each construct by evaluating 2-cm segments of 8-mm interlocking nails and 3.5-mm guidewires coated with antibiotic-supplemented cement. Each construct (n=7 for each group) was coated with polymethylmethacrylate cement (Simplex; Stryker Orthopaedics, Mahwah, New Jersey) containing either 1 g tobramycin or 1 g vancomycin powder plus 2.2 g tobramycin powder. A No. 40 French polyvinyl chloride chest tube was used as a mold for all constructs. Segments were soaked in sterile phosphate-buffered saline, and entire aliquots were exchanged at various intervals over a 6-week period. Antibiotic concentration, antibacterial activity, cement curing temperature, and porosity were measured. At least half of the total elution of antibiotics occurred within the first 24 hours for all constructs. For the tobramycin-only cement, no differences between constructs were observed. For constructs containing both antibiotics, interlocking nails showed more antibiotic release than guidewires at most time points (P<.05-P<.001). Antibiotics were released for 6 weeks and continued to inhibit Staphylococcus aureus growth. Cement curing temperatures for interlocking nails were lower than those for guidewires (P<.05). Guidewires coated with cement containing tobramycin and vancomycin showed significantly greater porosity compared with the other 3 groups (P<.05), but the amount of antibiotic released did not directly relate to porosity for any construct type. Interlocking nails coated with antibiotic-supplemented cement may provide greater antibiotic delivery to infected long bone nonunion compared with guidewires. A thin mantle of cement may allow greater elution, possibly as a result of cooler exothermic reactions. [Orthopedics. 2017; 40(3):e436-e442.].

Thermodynamics of an aminoglycoside modifying enzyme with low substrate promiscuity: The aminoglycoside N3 acetyltransferase-VIa

Kinetic, thermodynamic, and structural properties of the aminoglycoside N3-acetyltransferase-VIa (AAC-VIa) are determined. Among the aminoglycoside N3-acetyltransferases, AAC-VIa has one of the most limited substrate profiles. Kinetic studies showed that only five aminoglycosides are substrates for this enzyme with a range of fourfold difference in k_cat values. Larger differences in K_M (∼40-fold) resulted in ∼30-fold variation in k_cat /K_M . Binding of aminoglycosides to AAC-VIa was enthalpically favored and entropically disfavored with a net result of favorable Gibbs energy (ΔG < 0). A net deprotonation of the enzyme, ligand, or both accompanied the formation of binary and ternary complexes. This is opposite of what was observed with several other aminoglycoside N3-acetyltransferases, where ligand binding causes more protonation. The change in heat capacity (ΔCp) was different in H₂ O and D₂ O for the binary enzyme-sisomicin complex but remained the same in both solvents for the ternary enzyme-CoASH-sisomicin complex. Unlike, most other aminoglycoside-modifying enzymes, the values of ΔCp were within the expected range of protein-carbohydrate interactions. Solution behavior of AAC-VIa was also different from the more promiscuous aminoglycoside N3-acetyltransferases and showed a monomer-dimer equilibrium as detected by analytical ultracentrifugation (AUC). Binding of ligands shifted the enzyme to monomeric state. Data also showed that polar interactions were the most dominant factor in dimer formation. Overall, thermodynamics of ligand-protein interactions and differences in protein behavior in solution provide few clues on the limited substrate profile of this enzyme despite its >55% sequence similarity to the highly promiscuous aminoglycoside N3-acetyltransferase. Proteins 2017; 85:1258-1265. © 2017 Wiley Periodicals, Inc.

NMR Tube Degradation Method for Sugar Analysis of Glycosides

The sugar subunits of natural glycosides can be conveniently determined by acid hydrolysis and (1)H NMR spectroscopy without isolation or derivatization. The chemical shifts, coupling constants, and integral ratios of the anomeric signals allow each monosaccharide to be identified and its molar ratio to other monosaccharides to be quantified. The NMR data for the anomeric signals of 28 monosaccharides and three disaccharides are reported. Application of the method is demonstrated with the flavonoid glycoside naringin (1), the aminoglycoside antibiotics kanamycin (2) and tobramycin (3), and the saponin digitonin (4).

Validated spectrofluorimetric method for determination of selected aminoglycosides

New, sensitive, and selective spectrofluorimetric method was developed for determination of three aminoglycoside drugs in different dosage forms, namely; neomycin sulfate (NEO), tobramycin (TOB) and kanamycin sulfate (KAN). The method is based on Hantzsch condensation reaction between the primary amino group of aminoglycosides with acetylacetone and formaldehyde in pH 2.7 yielding highly yellow fluorescent derivatives measured emission (471 nm) and excitation (410 nm) wavelengths. The fluorescence intensity was directly proportional to the concentration over the range 10-60, 40-100 and 5-50 ng/mL for NEO, TOB and KAN respectively. The proposed method was applied successfully for determination of these drugs in their pharmaceutical dosage forms.

Antimicrobial efficacy of tobramycin polymeric nanoparticles for Pseudomonas aeruginosa infections in cystic fibrosis: formulation, characterisation and functionalisation with dornase alfa (DNase)

Inhaled antibiotics, such as tobramycin, for the treatment of Pseudomonas aeruginosa pulmonary infections are associated with the increase in life expectancy seen in cystic fibrosis (CF) patients over recent years. However, the effectiveness of this aminoglycoside is still limited by its inability to penetrate the thick DNA-rich mucus in the lungs of these patients, leading to low antibiotic exposure to resident bacteria. In this study, we created novel polymeric nanoparticle (NP) delivery vehicles for tobramycin. Using isothermal titration calorimetry, we showed that tobramycin binds with alginate polymer and, by exploiting this interaction, optimised the production of tobramycin alginate/chitosan NPs. It was established that NP antimicrobial activity against P. aeruginosa PA01 was equivalent to unencapsulated tobramycin (minimum inhibitory concentration 0.625mg/L). Galleria mellonella was employed as an in vivo model for P. aeruginosa infection. Survival rates of 90% were observed following injection of NPs, inferring low NP toxicity. After infection with P. aeruginosa, we showed that a lethal inoculum was effectively cleared by tobramycin NPs in a dose dependent manner. Crucially, a treatment with NPs prior to infection provided a longer window of antibiotic protection, doubling survival rates from 40% with free tobramycin to 80% with NP treatment. Tobramycin NPs were then functionalised with dornase alfa (recombinant human deoxyribonuclease I, DNase), demonstrating DNA degradation and improved NP penetration of CF sputum. Following incubation with CF sputum, tobramycin NPs both with and without DNase functionalisation, exhibited anti-pseudomonal effects. Overall, this work demonstrates the production of effective antimicrobial NPs, which may have clinical utility as mucus-penetrating tobramycin delivery vehicles, combining two widely used CF therapeutics into a single NP formulation. This nano-antibiotic represents a strategy to overcome the mucus barrier, increase local drug concentrations, avoid systemic adverse effects and improve outcomes for pulmonary infections in CF.

Engineering persister-specific antibiotics with synergistic antimicrobial functions

Most antibiotics target growth processes and are ineffective against persister bacterial cells, which tolerate antibiotics due to their reduced metabolic activity. These persisters act as a genetic reservoir for resistant mutants and constitute a root cause of antibiotic resistance, a worldwide problem in human health. We re-engineer antibiotics specifically for persisters using tobramycin, an aminoglycoside antibiotic that targets bacterial ribosomes but is ineffective against persisters with low metabolic and cellular transport activity. By giving tobramycin the ability to induce nanoscopic negative Gaussian membrane curvature via addition of 12 amino acids, we transform tobramycin itself into a transporter sequence. The resulting molecule spontaneously permeates membranes, retains the high antibiotic activity of aminoglycosides, kills E. coli and S. aureus persisters 4-6 logs better than tobramycin, but remains noncytotoxic to eukaryotes. These results suggest a promising paradigm to renovate traditional antibiotics.

Chemical and structural insights into the regioversatility of the aminoglycoside acetyltransferase Eis

A recently discovered cause of tuberculosis resistance to a drug of last resort, the aminoglycoside kanamycin, results from modification of this drug by the enhanced intracellular survival (Eis) protein. Eis is a structurally and functionally unique acetyltransferase with an unusual capability of acetylating aminoglycosides at multiple positions. The extent of this regioversatility and its defining protein features are unclear. Herein, we determined the positions and order of acetylation of five aminoglycosides by NMR spectroscopy. This analysis revealed unprecedented acetylation of the 3''-amine of kanamycin, amikacin, and tobramycin, and the γ-amine of the 4-amino-2-hydroxybutyryl group of amikacin. A crystal structure of Eis in complex with coenzyme A and tobramycin revealed how tobramycin can be accommodated in the Eis active site in two binding modes, consistent with its diacetylation. These studies, describing chemical and structural details of acetylation, will guide future efforts towards designing aminoglycosides and Eis inhibitors to overcome resistance in tuberculosis.

Physicochemical compatibility of nebulizable drug admixtures containing colistimethate and tobramycin

Inhalation therapy with nebulizable antibiotic drugs is a mainstay in treating Pseudomonas aeruginosa infections in cystic fibrosis patients. The combination of tobramycin and colistin was found to be superior to monotherapy in killing P. aeruginosa in biofilms. The simultaneous inhalation of tobramycin and colistin might be an option to increase the compliance of patients. The objective of this in-vitro study was to determine whether admixtures of inhalation solutions containing colistin methanesulfonate (CMS) and tobramycin are physicochemically compatible. Physical compatibility was determined by measuring pH and osmolality. Chemical compatibility was determined by testing the antibiotic activity of the mixtures by the pharmacopoeial microbiological assay and comparing the results to those of standard solutions. Samples were analyzed immediately after mixing and after 24 h. Values of pH and osmolality remained unchanged and in physiologically acceptable ranges. Neither for colistin methanesulfonate (CMS) nor for tobramycin losses of antibiotic potency were registered at any time. Admixtures of nebulizer solutions containing CMS and tobramycin were shown to be physicochemically compatible. Further investigations are needed to determine whether drug delivery is affected by mixing the nebulizer solutions to ensure that simultaneous inhalation is recommendable.

The effect of PAMAM dendrimers on the antibacterial activity of antibiotics with different water solubility

Erythromycin (EM) and tobramycin (TOB) are well-known and widely used antibiotics, belonging to different therapeutic groups: macrolide and aminoglycoside, respectively. Moreover, they possess different solubility: EM is slightly soluble and TOB is freely soluble in water. It was previously demonstrated that PAMAM dendrimers enhanced the pharmacological activity of antifungal drugs by increasing their solubility. Therefore, it appears interesting to investigate the effect of PAMAM-NH2 and PAMAM-OH dendrimers generation 2 (G2) and generation 3 (G3) on the antibacterial activity of antibiotics with different water solubility. In this study it was shown that the aqueous solubility of EM was significantly increased by PAMAM dendrimers (PAMAM-NH2 and PAMAM-OH caused about 8- and 7- fold solubility increases, respectively). However, it was indicated that despite the increase in the solubility, there was only slight influence on the antibacterial activity of EM (2- and 4-fold decreases in the MBC values of EM in the presence of PAMAM-OH G3 and PAMAM-NH2 G2 or G3 for strains of Staphylococcus aureus were noted, respectively). It was also found that there was no influence of PAMAM on the antibacterial activity of hydrophilic TOB.

Synthesis and evaluation of hetero- and homodimers of ribosome-targeting antibiotics: antimicrobial activity, in vitro inhibition of translation, and drug resistance

In this study, we describe the synthesis of a full set of homo- and heterodimers of three intact structures of different ribosome-targeting antibiotics: tobramycin, clindamycin, and chloramphenicol. Several aspects of the biological activity of the dimeric structures were evaluated including antimicrobial activity, inhibition of in vitro bacterial protein translation, and the effect of dimerization on the action of several bacterial resistance mechanisms that deactivate tobramycin and chloramphenicol. This study demonstrates that covalently linking two identical or different ribosome-targeting antibiotics may lead to (i) a broader spectrum of antimicrobial activity, (ii) improved inhibition of bacterial translation properties compared to that of the parent antibiotics, and (iii) reduction in the efficacy of some drug-modifying enzymes that confer high levels of resistance to the parent antibiotics from which the dimers were derived.

Amikacin, kanamycin and tobramycin binding to melanin in the presence of Ca(2+) and Mg(2+) ions

The aim of the presented work was to examine the interaction of amikacin, kanamycin and tobramycin with melanin in the presence of Ca(2+ )and Mg(2+) ions. It has been demonstrated that the analyzed aminoglycosides form complexes with melanin in the presence of metal ions and the amount of drugs bound to the polymer increases with increasing initial antibiotics concentration. It has been also shown that two classes of binding sites participate in the formation of amikacin, kanamycin and tobramycin complexes with melanin containing Ca(2+) or Mg(2+) ions: high affinity binding sites (n1) with the association constant K1 approximately 10(4)-10(5)M(-1) and low affinity binding sites (n2) with K2 approximately 10(3)M(-1). It has been demonstrated that calcium and magnesium significantly decrease the number of total binding sites (ntot) as compared with aminoglycoside-melanin complexes obtained in the absence of metal ions.

Interaction of amikacin and tobramycin with melanin in the presence of Cu2+ and Zn2+ ions

Aminoglycoside antibiotics such as amikacin and tobramycin are the most commonly used treatment against Gram-negative bacterial infections. The widely used aminoglycosides have the unfortunate side-effect of targeting sensory hair cells of the inner ear, so that treatment often results in permanent hair cell loss. Because melanin can act as an antioxidant as well as drug and metal chelator, evidence for its role in protecting the stria and organ of Corti against noise, ototoxins, and aging has long been sought. Protective properties of melanin may derive from its ability to bind cations and metals and to scavenge free radical. The aim of the presented work was to examine the amikacin and tobramycin binding to melanin in the presence of Cu2+ and Zn2+ ions. It has been demonstrated that amikacin and tobramycin form stable complexes with melanin in the presence of metal ions and the amount of aminoglycoside antibiotics bound to melanin increases with the increasing of initial drugs concentration. For amikacin and tobramycin complexes with [melanin-Cu2+] and [melanin-Zn2+] one class of binding sites with the association constant K 10(3)M(-1) has been found. It has been also shown that Cu2+ and Zn2+ ions administered to melanin before complexing with drugs decrease the amount of aminoglycosides bound to melanin, probably by blocking some active centers in the melanin molecule.

NMR resonance assignments of an engineered neomycin-sensing riboswitch RNA bound to ribostamycin and tobramycin

The neomycin-sensing riboswitch is an engineered riboswitch developed to regulate gene expression in vivo in the lower eukaryote Saccharomyces cerevisiae upon binding to neomycin B. With a size of only 27nt it is the smallest functional riboswitch element identified so far. It binds not only neomycin B but also related aminoglycosides of the 2'-deoxystreptamine class with high affinity. The regulatory activity, however, strongly depends on the identity of the aminoglycoside. As a prerequisite for the structure determination of riboswitch-ligand complexes we report here the (1)H, (15)N, (13)C and partial (31)P chemical shift assignments for the minimal functional 27nt neomycin sensing riboswitch RNA in complex with the 4,5-linked neomycin analog ribostamycin and the 4,6-linked aminoglycoside tobramycin.

Generic tobramycin elutes from bone cement faster than proprietary tobramycin

Elution of antibiotics from antibiotic-loaded polymethylmethacrylate (AL-PMMA) increases when soluble particulate filler is added to increase the permeability of the PMMA. Antibiotic powder is in itself soluble particulate filler. For greater volume fractions of filler, greater elution occurs. The volume of generic tobramycin powder is more than 3.5 times the volume of proprietary tobramycin powder for a 1.2 g dose leading to the question: Does generic tobramycin elute from AL-PMMA faster than proprietary tobramycin? We performed elution studies on AL-PMMA beads made with 1.2 g of either generic tobramycin or proprietary tobramycin per batch of PMMA. Generic tobramycin eluted more than two times faster than proprietary tobramycin. The release mechanism started as dissolution-driven zero-order release for the generic bead set but for the proprietary bead set the released mechanism started as anomalous diffusion. The release mechanism progressed to diffusion-driven first-order release in both. The increased volume of the generic tobramycin caused more tobramycin to be available for release. The increased elution of tobramycin associated with the greater volume of generic tobramycin powder could lead to clinically higher levels of tobramycin in wound fluid and local tissues; however, the higher volume of powder could potentially cause greater mechanical compromise of the PMMA.

Biaxial flexural modulus of antibiotic-impregnated orthopedic bone cement

Previously reported antibiotic-impregnated cement strengths have been based on uniaxial and fatigue testing methodologies. These methods may not provide an accurate characterization of bone cement's true load-bearing capacity in total joint replacement (TJR). The present study utilized biaxial testing to report on the properties of antibiotic-impregnated cement. Test groups included: PMMA mixed with Vancomycin, Gentamicin, Tobramycin, or no antibiotic (control). In comparison to the control group, PMMA samples mixed with powdered gentamicin resulted in an increase in the mean elastic modulus by 6.50% versus a drop noted with powdered vancomycin and tobramycin by 2.65 and 1.37% respectively. The mean elastic modulus in samples containing liquid gentamicin dropped by 11.6%. This study supports the continued use of powdered antibiotics when clinically indicated, but suggest caution in the use of liquid gentamicin in TJR.

An aminoglycoside microarray platform for directly monitoring and studying antibiotic resistance

Antibiotic resistance is a major threat to human health. Since resistance to the aminoglycoside class of antibiotics is most commonly caused by enzymatic modification, we developed a high-throughput microarray platform for directly assaying resistance enzyme activity on aminoglycosides. After modification, the array can be hybridized with the therapeutic target, a bacterial rRNA A-site mimic, to study the effect that modification has on binding. Such studies will help identify important factors that contribute to high-affinity recognition of therapeutic targets and low-affinity recognition of and modification by resistance enzymes. This platform may also be useful for screening chemical libraries to discover new antibiotics that evade resistance.

Experimental Study of a New Vascular Graft Prebonded with Antibiotic: Healing, Toxicity, and Antibiotic Retention

Despite refinements in surgical techniques, routine antibioprophylaxis, and anesthesiology, vascular prosthetic infections remain a serious complication of reconstructive vascular surgery. The purpose of this study was to evaluate the healing, the toxicity, and the antibiotic delivery of a new vascular graft, preloaded with rifampin and tobramycin. Sixteen dogs underwent infrarenal aortic bypass. They were divided into three groups. In test group 1 (n = 8), dogs received grafts loaded with a standard concentration of antibiotics. In test group 2 (n = 4), dogs received grafts loaded with twice the standard concentration of antibiotics. A control group (n = 4) received a commercial gelatin-sealed graft. Grafts were harvested after different periods of time and submitted to histological evaluation and antibiotic dose determination. Liver and kidney toxicities were evaluated from dosages performed on serum samples taken at different time periods between graft implantation and harvesting. The healing of antibiotic-loaded grafts was similar to that of commercial grafts, without any signs of toxicity. These results suggest resistance to infection of these prebonded grafts in an animal model.

EstimatingIn VivoAirway Surface Liquid Concentration in Trials of Inhaled Antibiotics

Antibiotic drugs exhibit concentration dependence in their efficacy. Therefore, ensuring appropriate concentration of these drugs in the relevant body fluid is important for obtaining the desired therapeutic and physiological action. Until recently there had been no suitable method available to measure or estimate concentration of drugs in the human airways resulting from inhaled aerosols or to determine the amount of inhaled antibiotics required to ensure minimum inhibitory concentration of a drug in the airway surface liquid (ASL). In this paper a numerical method is used for estimating local concentration of inhaled pharmaceutical aerosols in different generations of the human tracheobronchial airways. The method utilizes a mathematical lung deposition model to estimate amounts of aerosols depositing in different lung generations, and a recent ASL model along with deposition results to assess the concentration of deposited drugs immediately following inhalation. Examples of concentration estimates for two case studies: one for the antibiotic tobramycin against Pseudomonas aeruginosa, and another for taurolidine against Burkholderia cepacia are presented. The aerosol characteristics, breathing pattern and properties of nebulized solutions were adopted from two recent clinical studies on efficacy of these drugs in cystic fibrosis (CF) patients and from other sources in the literature. While the clinically effective tobramycin showed a concentration higher than the required in vivo concentration, that for the ineffective taurolidine was found to be below the speculated required in vivo concentration. Results of this study thus show that the mathematical ASL model combined with the lung deposition model can be an effective tool for helping decide the optimum dosage of inhaled antibiotic drugs delivered during human clinical trials.

Does antibiotic elution from PMMA beads deteriorate after 1-year shelf storage?

Antibiotic-impregnated polymethylmethacrylate beads are widely used as an adjunct in the treatment of orthopaedic infections. Because there is no commercially available bead in the United States, surgeons must manufacture bead sets at the time of implantation. This can be time consuming and wasteful. We hypothesized antibiotic-impregnated beads would maintain consistent elution for up to 1 year after manufacturing and storage. Tobramycin-impregnated antibiotic beads were manufactured using a bead mold. The antibiotic was either hand-mixed into the polymethylmethacrylate powder (1.2 g/40 g) or came premixed from the factory (1 g/40 g). Packages of beads were gas-sterilized and stored at room temperature. Beads were tested at 0, 1, 2, 3, 6, and 12 months. Antibiotic levels in the eluent from each day of the month were measured. We were unable to detect any difference in the amount of antibiotic elution between beads tested immediately after manufacture and beads manufactured and stored for 6 or 12 months. Beads with hand-mixed antibiotics eluted higher levels of antibiotics than the beads prepared with factory-mixed antibiotics. We conclude antibiotic beads can be made, sterilized, and used after 1 year of storage with no deleterious effect on antibiotic elution characteristics.

Crystallographic studies of Homo sapiens ribosomal decoding A site complexed with aminoglycosides

Aminoglycosides are highly effective antibacterial drugs that decrease translation accuracy by binding to the aminoacyl-tRNA decoding site (A site) of 16S ribosomal RNA. On the other hand, they are highly toxic to mammals through kidney and ear-associated illnesses by binding to ribosomal A sites. To understand the mechanism of toxicity of aminoglycosides to mammals at atomic level, crystallographic studies have been carried out with a number of Homo sapiens mitochondrial and cytoplasmic A sites complexed with aminoglycosides. Several X-ray diffraction data sets were successfully collected. Initial phases of mitochondrial A site with tobramycin and cytoplasmic A site with paromomycin were derived by the molecular replacement method. Refinements of atomic parameters are now under progress.

HPLC retention behavior on hydride-based stationary phases

Two stationary phases attached to a silica hydride surface, cholesterol and bidentate C18, are investigated with a number of pharmaceutically related compounds in order to illustrate the various retention mechanisms that are possible for these bonded materials. The test solutes range from hydrophilic to hydrophobic based on log P (octanol/water partition coefficient) and pKa values. The mobile phases consist of acidified (formic and perchloric acid) water/methanol or water/ACN mixtures. Of particular interest are the high organic content mobile phase compositions where the retention would increase if the bonded material was operating in the aqueous normal phase (ANP) mode. Plots of retention factor (k) versus mobile phase composition are used to elucidate the retention mechanism. A number of examples are presented where solutes are retained based on RP, ANP, or dual retention mechanisms. The silica hydride-based stationary phases can also retain compounds in the organic normal phase.

Interaction of neomycin, tobramycin and amikacin with melanin in vitro in relation to aminoglycosides-induced ototoxicity

The aim of this study was to examine in vitro the interaction between aminoglycoside antibiotics displaying adverse ototoxic effects and melanin which is a constituent of the inner ear. The binding of neomycin, tobramycin and amikacin to model synthetic melanin was studied. It has been demonstrated that all the investigated aminoglycosides form stable complexes with melanin biopolymer. The obtained results show that the amount of drug bound to melanin increases with the increase of initial drug concentration and the incubation time. An analysis of drugs binding to melanin by the use of Scatchard plots has shown that at least two classes of independent binding sites must be implicated in the studied aminoglycoside antibiotic-melanin complexes formation: strong binding sites (n1) with the association constant K1 approximately 0.2-2.0 x 10(5) M(-1) and weak binding sites (n2) with K2 approximately 1.0-4.9 x 10(3) M(-1). Based on the values of association constants the following order of drugs affinity to DOPA-melanin was found: tobramycin > amikacin >> neomycin. The ability of the analyzed aminoglycoside antibiotics to form complexes with melanin in vitro may be one of the reasons for their ototoxicity in vivo, as a result of their accumulation in melanin in the inner ear.

Comparison of tobramycin 0.3%/dexamethasone 0.1% and tobramycin 0.3%/loteprednol 0.5% in the management of blepharo-keratoconjunctivitis

In this clinical trial, investigators compared the effectiveness of 2 commercially formulated antibiotic/steroid combinations - tobramycin 0.3%/dexamethasone 0.1% (Tobradex; Alcon, Fort Worth, Tex) and tobramycin 0.3%/loteprednol 0.5% (Zylet; Bausch & Lomb Inc., Rochester, NY) - for rapidly controlling inflammation in patients with blepharo-keratoconjunctivitis. Investigators in this randomized, parallel-group, double-masked study examined 40 eyes of 40 patients with blepharo-keratoconjunctivitis. Patients received tobramycin 0.3%/dexamethasone 0.1% or tobramycin 0.3%/loteprednol 0.5% twice daily in the test eye, according to the randomization schedule. At baseline, the ocular surface was graded on a scale of 3 (extensive) to 0 (minimum) for 4 components: blepharitis, conjunctivitis, ocular discharge, and corneal punctate epithelial keratopathy (PEK). Only those patients with moderate to extensive inflammation (cumulative score >6) were included in the study. At follow-up 3 to 5 d later, the ocular surface was regraded so that treatment response could be evaluated. No statistically significant difference was noted between groups in pretreatment scores for blepharitis (P=.31), discharge (P=.62), conjunctivitis (P=1.0), and PEK (P=.57), or for total ocular inflammation (P=.87). Mean posttreatment scores were as follows: total ocular surface scores, 1.8 and 3.4 (P=.002); blepharitis scores, 0.9 and 1.35 (P=.017); discharge scores, 0.2 and 0.6 (P=.025); and conjunctivitis scores, 0.15 and 0.6 (P=.013) for tobramycin/dexamethasone and tobramycin/loteprednol, respectively. Corneal PEK scores were not significantly different between treatments. Tobramycin 0.3%/dexamethasone 0.1% significantly decreased clinical signs of ocular inflammation (ie, blepharitis, discharge, conjunctivitis) and total ocular inflammation scores when compared with tobramycin 0.3%/loteprednol 0.5% in patients with moderate to severe blepharo-keratoconjunctivitis. The 2 regimens also provided comparably rapid decreases in corneal PEK.

Formulation and Characterization of Lipid-Coated Tobramycin Particles for Dry Powder Inhalation

PURPOSE

This study was conducted to develop and evaluate the physicochemical and aerodynamic characteristics of lipid-coated dry powder formulations presenting particularly high lung deposition.

METHODS

Lipid-coated particles were prepared by spray-drying suspensions with different concentrations of tobramycin and lipids. The solid-state properties of the formulations, including particle size and morphology, were assessed by scanning electron microscopy and laser diffraction. Aerosol performance was studied by dispersing the powders into a Multistage Liquid Impinger and determining drug deposition by high-performance liquid chromatography.

RESULTS

Particle size distributions of the formulations were unimodal, narrow with more than 90% of the particles having a diameter of less than 2.8 microm. All powder formulations exhibited mass median diameters of less than 1.3 and 3.2 microm, as determined by two different laser diffraction methods, the Malvern's Mastersizer and Spraytec, respectively. The fine particle fraction varied within a range of 50.5 and 68.3%.

CONCLUSIONS

Lipid coating of tobramycin formulations resulted in a reduced agglomeration tendency and in high fine particle fraction values, thus improving drug deposition. The very low excipients content (about 5% m/m) of these formulations offers the benefit of delivering particularly huge concentrations of antibiotic directly to the site of infection, while minimizing systemic exposure, and may provide a valuable alternative treatment of cystic fibrosis.

Late opacification of a silicone intraocular lens caused by ophthalmic ointment

A 55-year-old man had uneventful phacoemulsification with implantation of a 3-piece silicone intraocular lens (IOL). Postoperative medications included antibiotic-steroid drops and ointments. Eight months postoperatively, the patient started having recurrent episodes of anterior chamber inflammatory reaction. Suspicion that lens instability was causing the reactions led to a lens repositioning procedure 11 months after the initial surgical implantation and again at 13 months. Eighteen months postoperatively, the IOL had a "greasy" film. Despite antiinflammatory and antibiotic treatment, the clinical outcome did not improve. Twenty-seven months after implantation, the lens was exchanged with a hydrophilic acrylic IOL. The course after the exchange was uneventful. The explanted lens was examined by gross and microscopic evaluations, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and gas chromatography-mass spectrometry (GC-MS) using electronic ionization. Gross and microscopic evaluations confirmed the presence of a thin, oily film covering the IOL optic surface. Surface analyses at the level of the oily substance showed unspecific peaks of sodium, chloride, and potassium. The GC-MS analysis showed the presence of compounds characteristic of hydrocarbons, including docosane, tricosane, and tetracosane, which are commonly found in the vehicle of ophthalmic ointments. The GC-MS analysis of 1 ointment used postoperatively found matching peaks, suggesting deposition of those compounds on the IOL.

Targeted sustained delivery of tobramycin at the site of a femoral osteotomy

Complex fractures are difficult to manage because of the increased risk of secondary infection. Traditional treatments include debridment and local administration of antibiotics. Local antibiotic therapy is a safe technique resulting in high local concentration of antibiotics with minimal systemic levels. Local antibiotics effectively control infection in animal models. The length of implantation and the need for removal of the delivery vehicle places the patient at risk for additional surgical procedure as well as delays the fixation procedure. Development of a bioresorbable carrier that can deposit therapeutic concentrations of antibiotics locally without side-effects will provide positive outcomes for the patient. Tricalcium phosphate lysine (TCPL) ceramic capsules containing tobramycin were implanted at the site of a femoral osteotomy delivered therapeutic concentrations of the drug locally and reduced the incidence of infection compared to TCPL capsule which were uncharged by 50%. In addition, the ceramic material was osteoconductive and animals in TCPL + TOB and TCPL carrier alone showed evidence of osteoblast alkaline phosphatase activity for a period of 15 weeks. Neither the carrier nor the carrier containing antibiotics displayed untoward effects on body weight, vital organs and reproductive organs over a 15 week period. The results from this study demonstrated that TCPL can be used as an effective osteoconductive material capable of delivering therapeutic concentrations of antibiotics over 15 week period.

From ultrathin capsules to biaqueous vesicles

The layer-by-layer (LbL) adsorption of anionic polyelectrolytes (PE) and tobramycin sulfate (TbS) multilayers on zinc oxide core particles followed by the controlled core-removal process leads to the formation of ultrathin capsules, which gradually convert to biaqueous vesicles and emulsionlike systems depending on the hydrophilicity/hydrophobicity of the PE backbone, PE/TbS ratio, and Zn2+ concentration. The unique characteristics of the PE/TbS multilayer capsules result because of the formation of PE/TbS/H2O biphasic liquid systems unlike the other LbL capsular systems that form stiff PE coacervates when mixed together in water. This paper investigates the PE/TbS ultrathin capsule to biaqueous vesicle transition and its physicochemical properties.

Electrospray ionization of nucleic acid aptamer/small molecule complexes for screening aptamer selectivity

Molecular recognition of small molecule ligands by the nucleic acid aptamers for tobramycin, ATP, and FMN has been examined using electrospray ionization mass spectrometry (ESI-MS). Mass spectrometric data for binding stoichiometry and relative binding affinity correlated well with solution data for tobramycin aptamer complexes, in which aptamer/ligand interactions are mediated by hydrogen bonds. For the ATP and FMN aptamers, where ligand interactions involve both hydrogen bonding and significant pi-stacking, the relative binding affinities determined by MS did not fully correlate with results obtained from solution experiments. Some high-affinity aptamer/ligand complexes appeared to be destabilized in the gas phase by internal Coulombic repulsion. In CAD experiments, complexes with a greater number of intermolecular hydrogen bonds exhibited greater gas-phase stability even in cases when solution binding affinities were equivalent. These results indicate that in at least some cases, mass spectrometric data on aptamer/ligand binding affinities should be used in conjunction with complementary techniques to fully assess aptamer molecular recognition properties.

A clinical comparison of two formulations of tobramycin 0.3% eyedrops in the treatment of acute bacterial conjunctivitis

PURPOSE

To compare the safety and efficacy of a new enhanced viscosity ophthalmic formulation of tobramycin, given twice daily (BID), with the existing four times daily (QID) treatment regimen in patients with acute bacterial conjunctivitis.

METHODS

This was a 12-day, multicenter, observer-masked, randomized, parallel group study. Patients received one drop of tobramycin 0.3% (3 mg/mL) enhanced viscosity ophthalmic solution BID or tobramycin 0.3% (3 mg/mL) ophthalmic solution QID in the affected eyes for 7 days. The primary efficacy variable was the percentage of patients with sustained cure/presumed bacterial eradication based on clinical judgment at the test-of-cure visit (Day 12). Pretherapy bacterial isolates were obtained and tested for susceptibility to tobramycin by determination of minimum inhibitory concentrations (MIC).

RESULTS

A total of 276 patients were enrolled in the study and 203 of these were culture positive and attended all follow-up examinations. In this group, 98% of those treated with tobramycin enhanced viscosity ophthalmic solution and 99% of those treated with tobramycin 0.3% ophthalmic solution were categorized as having sustained cure/presumed eradication at the test-of-cure visit (p = 0.6037). Reported adverse events were not serious, mild to moderate in severity, and generally did not prevent continuation in the study. Several pre treatment pathogens demonstrated tobramycin resistance (MIC > 4 mg/mL). However, therapy with both treatments was effective in the majority of the cases.

CONCLUSIONS

Tobramycin enhanced viscosity ophthalmic solution is well tolerated and has equivalent efficacy to the established treatment regimen with a simplified posology. The formulation provides an alternative therapy for acute bacterial conjunctivitis that should improve patient compliance and satisfaction.

From triplex to B-form duplex stabilization: reversal of target selectivity by aminoglycoside dimers

Aminoglycosides have been shown to target A-form nucleic acids. Our work has previously shown that neomycin (and other aminoglycosides) bind and stabilize DNA/RNA triplexes and other A-form nucleic acids. We report herein the unexpected B-form duplex stabilization shown by aminoglycoside dimers (neomycin-neomycin and neomycin-tobramycin). The dimers are highly selective for AT rich duplexes and show high affinity (K(a) approximately 10(8)M(-1)) as determined by isothermal titration calorimetry.

Antibiotic Elution from Hydroxyapatite Cement Cranioplasty Materials

Hydroxyapatite cements (HAC) are a contemporary material used for multiple cranioplasty applications. In an effort to decrease the risk of postoperative infection, mixing antibiotics into the material during intraoperative application is frequently done. It has been assumed, but never substantiated, that significant antibiotic release from the material occurs after implantation. Using standardized morphologies, a mixture of a specific HAC (Mimix bone void filler) and tobramycin antibiotic was prepared, hydrated in phosphate-buffered saline, and tested in vitro for as long as 22 days after preparation. The results show that the majority of the antibiotic (91%) was released within the first 24 hours, with the balance being eluted during the next 8 days. Overall, the release of tobramycin from Mimix bone void filler appears to fit the pattern of antibiotic release demonstrated to occur from other bioabsorbable ceramic-type carriers.

The in vitro elution characteristics of vancomycin and tobramycin from calcium sulfate beads

The purpose of this study was to determine the elution characteristics of vancomycin and tobramycin when mixed with calcium sulfate to form antibiotic beads. Calcium sulfate was combined with vancomycin and tobramycin separately to form 2 types of antibiotic beads, which were packaged and labeled separately. The packaged calcium sulfate beads with vancomycin and tobramycin were then gas sterilized. The beads were placed in phosphate-buffered saline and kept at 36 degrees C for 6 weeks. Two separate series of assays were run simultaneously for both types of beads. In one assay, a bead containing vancomycin was placed in a fresh vial of phosphate buffered saline after each assay. The same was done with beads containing tobramycin. In the second series of assays, 9 vials of phosphate buffered saline each containing 1 vancomycin bead and 9 vials of phosphate buffered saline each containing 1 tobramycin bead was arranged. The phosphate-buffered saline was then assayed at predetermined times for both the vancomycin bead series and the tobramycin bead series. The amount of vancomycin and tobramycin assayed nearly equaled the calculated amount of antibiotic per bead measured before bead construction. Also, the elution of antibiotic from the calcium sulfate was complete within 72 hours. In conclusion, the construction and gas sterilization of calcium sulfate beads containing vancomycin and tobramycin does not destroy vancomycin and tobramycin. Also, the complete elution of available vancomycin and tobramycin in calcium sulfate beads occurs within 72 hours.

Surface plasmon resonance evaluation of various aminoglycoside-RNA hairpin interactions reveals low degree of selectivity

Aminoglycoside antibiotics, which are able to selectively bind to RNA, are considered to be an important lead in RNA-targeting drug discovery. In this study, surface plasmon resonance (SPR) was employed to explore the interaction of aminoglycosides with known tobramycin-binding RNA hairpins (aptamers) and an unrelated RNA hairpin. It was established that aminoglycosides have multiple interactions with RNA hairpins. Unexpectedly, the different hairpins showed comparable affinity for a set of related aminoglycosides. The observed absence of selectivity presents an extra hurdle in the discovery of novel aminoglycosides as specific drugs that target defined RNA hairpins.

Aminoglycoside antibiotics aggregate to form starch-like fibers on negatively charged surfaces and on phage lambda-DNA

The water-soluble (> 200 mg/mL) antibiotics tobramycin, kanamycin, and neomycin spontaneously produce rigid fibers on negatively charged surfaces (mica, graphite, DNA). Atomic force microscopy showed single strands of tobramycin on mica at pH 7 with a length of several hundred nanometers and a diameter of 0.5 nm and double helices with a diameter of 1.0 nm and a helical pitch of 7 nm. At pH 13 (NaOH) up to 15 microm long, rigid fibers with a uniform height of 2.4 nm and an apparent helical pitch of 30 nm were formed along the sodium silicate channels on the surface of mica. Kanamycin and neomycin behaved similarly. Fibers of similar length and width, but without secondary structure, were obtained from aqueous solutions at pH 7 on amorphous, hydrophilized carbon and characterized by transmission electron microscopy. Overstretched phage lambda-DNA strands with a height of 1.0 nm on mica did not interact with tobramycin coils at pH 7. After treatment with EDTA, however, the height of the magnesium-free lambda-DNA strands grew from 1.0 to 3.8 nm after treatment with tobramycin, which suggests a wrapping by the supramolecular fibers. Such fibers may interact with F-actin fibers in biological cells, which would explain the known aggressiveness of aminoglycosides toward bacterial cell membranes and their ototoxicity.

[Electrospray ion trap mass spectrometry of eight aminoglycoside antibiotics]

AIM

To study the dissociation pathways of aminoglycoside antibiotics.

METHODS

In positive mode, eight aminoglycoside antibiotics were elucidated by use of electrospray ion trap mass spectrometry in the multi-stage MS full scan mode.

RESULTS

It was demonstrated that the eight aminoglycoside antibiotics gave abundant product ions at m/z 322 (gentamicin, micronomicin and sisomicin), m/z 350 (etimicin, netilmicin and vetilmicin) and m/z 324 (kanamycin and tobramycin) by loss of the C-ring (amino-alpha-D-glucopyranose) in MS2 full scan mode. In MS3 full scan mode, the prominent fragmentation ions at m/z 163 as well as m/z 191 were formed from the fragmentation ions at m/z 322, m/z 350 and m/z 324 by loss of the A-ring (amino-alpha-D-glucopyranose), separately, while the characteristic fragmentation ions at m/z 160 as well as m/z 162 were formed from m/z 322, m/z 350 and m/z 324 by loss of the B-ring (2-deoxy-D-streptamine), separately.

CONCLUSION

The structural information was obtained via collision-activated dissociation and these characteristics are applicable to the structural elucidation and quantitative analysis of aminoglycoside compounds.