Quantitative approaches to the ototoxicity problem1, 2

This paper describes some of the possible approaches to quantitative evaluation of the biochemical effects of ototoxic agents upon fluids and tissues of the internal ear. Major emphasis is placed upon the ultramicrochemical techniques of Lowry, which offer adequate sensitivity for the quantitative determination of metabolites and enzymes in minutes fluid samples and in microscopic tissue elements and single cells. As specific examples, the effects of ethacrynic acid and of salicylate upon the levels of high energy phosphates in stria vascularis, spiral organ and other internal ear structures are described. In most instances, chemical analyses were preceded by electrophysiological evaluations. Results are compared with those obtained in ischemia and following local application of toxic agents, such as cyanide and dinitrophenol. In respect to the ototoxic effects of aminoglycoside antibiotics, only pilot experiments have been performed to date. Methodological problems are extremely complex in this area. In order to obtain meaningful data, analyses should be performed at a stage when chemical changes are already present, but structural damage is still minimal.     

Investigation of isepamicin in-vitro efficiency in Gram negative bacteria

ContextIsepamicin is a new semisynthetic aminoglycoside derived from gentamicin B and it is effective against Gram negative bacteria. Antibiotic resistance is an emerging problem and new options need for the treatment of infections caused by Gram negative bacteria.AimsIn this study we aimed to investigate the in vitro efficiency in carbapenem susceptible and nonsusceptible Enterobacterales and Pseudomonas aeruginosa.Methods and materialA total of 214 isolates of Gram-negative bacteria (Enterobacterales n = 129 and P. aeruginosa n = 85). Identification of the bacteria was tested in Vitek MS (Biomeriux, France). Susceptibility of isepamicin, amikacin, gentamicin, tobramycin and netilmicin was determined by Kirby Bauer disc diffusion method. The breakpoints for susceptibility to isepamicin, amikacin, gentamicin, streptomycin, tobramycin and netilmicin were evaluated according to the Comité de l’Antibiogramme dela Société Française de Microbiologie (CA-SFM) and EUCAST, respectively. Aminoglycoside modifying enzyme (AME) genes were investigated by multiplex PCR method.ResultsIsepamicin susceptibility was determined as 92.3% for Enterobacterales and 67% for P. aeruginosa and 94.4% for carbapenem resistant Enterobacterales. The most common AME gene was aac (6′)-Ib in both Enterobacterales (76%) and P. aeruginosa (14.1%). Seven of the isepamicin intermediate or resistant isolates were positive aac (6’)-Ib in Enterobacterales and P. aeruginosa.ConclusionsIn this study, isepamicin showed good efficiency against both susceptible and carbapenem nonsusceptible Enterobacterales. But amikacin was prior to isepamicin P. aeruginosa isolates. Isepamicin could be a therapeutic option for the infections caused by Enterobacterales.     

Pharmacokinetics of arbekacin in bronchial epithelial lining fluid of healthy volunteers

IntroductionArbekacin is a unique aminoglycoside antibiotic with anti-methicillin-resistant Staphylococcus aureus activity. The efficacy of aminoglycosides is related to their serum maximum concentration. Local concentration of antibiotics in pulmonary epithelial lining fluid, rather than its serum concentration, can help determine its clinical efficacy more precisely for treatment of respiratory infectious disease. The objective of this study was to sequentially measure arbekacin concentration in epithelial lining fluid after infusion of a single clinically available dose.MethodAfter the initial blood sampling, arbekacin was intravenously infused into 6 healthy volunteers over 1 h. Epithelial lining fluid and serum samples were collected by bronchoscopic microsampling 1, 1.5, 2, 2.5, 3, 4, 5, and 6 h after the start of 200 mg arbekacin infusion.ResultsEach probe sampled 10.1 ± 5.2 μl bronchial epithelial lining fluid. The sample dilution factor was 266.7 ± 157.1. Drug concentration was successfully measured in all but 2 of the epithelial lining fluid samples. The maximum concentration of arbekacin in epithelial lining fluid and serum was 10.4 ± 1.9 μg/ml and 26.0 ± 12.2 μg/ml, respectively. The ratio of the maximum drug concentration in the epithelial lining fluid to that in the serum was 0.47 ± 0.19.ConclusionsThe maximum concentration of epithelial lining fluid reached levels that would effectively treat most clinical strains of methicillin-resistant S. aureus.     

Determination of neomycin sulfate and impurities using high-performance anion-exchange chromatography with integrated pulsed amperometric detection

Neomycin B is one of a class of aminoglycoside antibiotics that lack a good chromophore, and is therefore difficult to determine using reversed-phase HPLC with absorbance detection. This is especially true for determining the quantity of each impurity. We show that neomycin sulfate and its major impurities, including neamine (neomycin A), can be separated on a strong anion-exchange column using a weak potassium hydroxide eluent (2.40 mM) at a column temperature of 30 degrees C, and directly detected by integrated pulsed amperometric detection (IPAD). The resolution (United States Pharmacopeia (USP) definition) between neomycin B and the closest major impurity ranged from 6.56 and 7.45 over 10 days of consecutive analysis (7.24+/-0.10, n=836 injections). Due to the difficulty of producing weak hydroxide eluents of the required purity (i.e. carbonate-free), this method depends on automatic eluent generation to ensure method ruggedness. This method exhibited good long-term (10 days, 822 injections) retention time stability with a R.S.D. of 0.6%. Peak area R.S.D. (10 microM) was 1.3%. Method robustness was evaluated by intentionally varying the flow rate, eluent concentration, column temperature, and column. The spike recoveries of neomycin B from extractions of three different topical ointments and cream formulations ranged from 95 to 100%. The measured concentration of neomycin B in these formulations ranged from 119 to 154% of the label concentration. The R.S.D. for the measured concentration of one of the formulations tested over three separate days, n=11 extracts, was 3.2%. Based on the results of these evaluations, we believe this method can be used for neomycin sulfate identity, assay, and purity.     

HPLC-ELSD法在硫酸庆大霉素及其制剂质量控制中的影响因素考察

目的 以硫酸庆大霉素片为研究对象,分析HPLC-ELSD法在质量控制中的影响因素,探讨氨基糖苷类抗生素质量控制方法的发展趋势。方法 采用Apollo C18色谱柱(250mm×4.6mm, 5μm),流动相为0.2mol/L三氟乙酸溶液:甲醇(96:4,V/V),柱温35℃。ELSD检测：漂移管温度110℃,载气流速2.5L/min,增益1。结果 方法存在溶剂效应,应优先选择流动相做溶剂;溶液浓度超载从而使色谱峰平顶,对组分测定结果有影响;采用西索米星对照品外标法测定有关物质,对照品溶液浓度的高低对测定结果无影响;采用随行标准曲线,色谱峰保留时间的改变对组分和有关物质测定无影响。结论     

Investigation on the Mechanism of Exacerbation of Myasthenia Gravis by Aminoglycoside Antibiotics in Mouse Model

Myasthenia gravis ( MG) is an autoi mmuneneuromuscular disease caused by the autoi mmuneresponse of lymphocytes tothe acetylcholine recep-tor (AChR)[1]. Autoantibodies against AChR playan i mportant role in the pathogenesis of the dis-ease . The therapy of MG patients with antibioticsis needed because it is very easy for these patientsto suffer the infections , especially respiratory in-fections[2]. However ,some kinds of antibiotics canaggravate the obstruction of neuromuscular junc-tion …     

The aminoglycoside G418 suppresses muscarinic receptor-activated calcium release in stably transfected murine N1E-115 neuroblastoma cells

The aminoglycoside G418 inhibited the release of calcium (Ca²⁺) from internal stores coupled to muscarinic receptors in murine N1E-115 neuroblastoma cells carrying the aminoglycoside resistance gene neomycin phosphotransferase (NPT). No significant effect was observed on responses coupled to histamine or bradykinin receptors. Cells were transfected using the eukaryotic expression vector pHβAPr-1-neo and selected using G418. Two groups were differentiated either in the continued presence of G418 or in the absence of G418. Carbachol (1 mM), histamine (200 μM) and bradykinin (100 nM) were administered to cells for thirty seconds and changes in [Ca²⁺]_i were measured with fluorescence video microscopy of single cells loaded with the Ca²⁺ indicator fura-2. The effects of G418 on carbachol evoked Ca²⁺ release included a 73% reduction in the number of cells responding, a two fold increase in the time to reach half-maximal response, a 35% reduction of the peak [Ca²⁺]_i in response to agonist and an elevation of resting [Ca²⁺]_i from 99± 14 nM (mean ± S.E.M.) to 155 ± 27 nM. Acute application (20 min) of G418 to transfected cells differentiated without G418 also reduced the percentage of cells responding to carbachol. This effect was less pronounced in non-transfected parent cells. Thus, the mechanism might involve a metabolite of G418 produced in cells expressing NPT. These results indicate that G418 attenuates Ca²⁺ release coupled to muscarinic receptors.     

Use of the Tn903 neomycin-resistance gene for promoter analysis in the fission yeast Schizosaccharomyces pombe

Summary The bacterial neo gene from transposon Tn903 (Tn601) was used for dominant transformation of the fission yeast Schizosaccharomyces pombe. It was found that high transformation efficiency was dependent on a high level of promoter activity, mediated by the strong promoter of the Schizosaccharomyces pombe alcohol dehydrogenase gene (adh1), as shown by comparing the efficiency of transformation to G418-resistance, the resistance levels of transformed cells, and the in vitro aminoglycoside phosphotransferase activity. On the other hand, the heterologous promoter of the Saccharomyces cerevisiae alcohol dehydrogenase I gene (adc1) is shown to be a weak promoter in Schizosaccharomyces pombe, though its activity is significantly enhanced in cells grown on glycerol as a carbon source. This system for selection and detection of promoter-active sequences may provide a useful basis for the analysis of promoter elements in fission yeast.