Glucose-6-Phosphate Dehydrogenase Protects Escherichia coli from Tellurite-Mediated Oxidative Stress

The tellurium oxyanion tellurite induces oxidative stress in most microorganisms. In Escherichia coli, tellurite exposure results in high levels of oxidized proteins and membrane lipid peroxides, inactivation of oxidation-sensitive enzymes and reduced glutathione content. In this work, we show that tellurite-exposed E. coli exhibits transcriptional activation of the zwf gene, encoding glucose 6-phosphate dehydrogenase (G6PDH), which in turn results in augmented synthesis of reduced nicotinamide adenine dinucleotide phosphate (NADPH). Increased zwf transcription under tellurite stress results mainly from reactive oxygen species (ROS) generation and not from a depletion of cellular glutathione. In addition, the observed increase of G6PDH activity was paralleled by accumulation of glucose-6-phosphate (G6P), suggesting a metabolic flux shift toward the pentose phosphate shunt. Upon zwf overexpression, bacterial cells also show increased levels of antioxidant molecules (NADPH, GSH), better-protected oxidation-sensitive enzymes and decreased amounts of oxidized proteins and membrane lipids. These results suggest that by increasing NADPH content, G6PDH plays an important role in E. coli survival under tellurite stress

Liposomal amikacin dry powder inhaler: Effect of fines on in vitro performance

The aim of the present investigation was to prepare and evaluate the influence of adding fines on the in vitro performance of liposomal amikacin dry powder inhaler (AMK LDPI) formulations. Liposomes composed of hydrogenated soyaphosphatidylcholine, cholesterol and saturated soyaphosphatidylglycerol (AMK 1), or stearylamine (AMK 2) were prepared by a reverse phase evaporation technique, extruded to reduce size and separated from unentrapped drug. Purified liposomal dispersion was subjected to lyophilization using optimized cryoprotectant to achieve maximum percentage drug retentio (PDR). Lactose carrier in varying mass ratios with or without addition of fines in different mixing sequences was used to formulate AMK LDPI formulations. AMK LDPI formulations were characterized for angle of repose, compressibility index, dispersibility index, scanning electron microscopy, and fine perticle fraction (FPF). PDR was found to be 97.6%±2.2% for AMK1 and 98.5%±1.9% for AMK2 using sucrose as optimized cryoprotectant in lipid:sucrose ratio of 1∶4. Lactose carrier containing 10% fines (wt/wt) was found to be the optimum blend at 1∶5 mass ratio of liposome:lactose. The addition of fines and the order of mixing of fines were found to influence the FPF with significantly different device fractions. FPF of AMK LDPI formulations using Rotahaler as the delivery device at 30, 60, and 90 L/min were found to be 21.85%±2.2% and 24.6%±2.4%, 25.9% ±1.8% and 29.2%±2.1%, and 29.5%±2.6% and 34.2%±2.0% for AMK1 and AMK2, respectively. From the studies performed in this investigation, it was observed that liposomal charge, addition of fines and order of mixing fines, has a significant effect (P<.05) on in vitro deposition of drug from LDPI formulation