An Engineered Rare Codon Device for Optimization of Metabolic Pathways.

Rare codons generally arrest translation due to rarity of their cognate tRNAs. This property of rare codons can be utilized to regulate protein expression. In this study, a linear relationship was found between expression levels of genes and copy numbers of rare codons inserted within them. Based on this discovery, we constructed a molecular device in Escherichia coli using the rare codon AGG, its cognate tRNA (tRNA(Arg) (CCU)), modified tRNA(Asp) (GUC → CCU), and truncated aspartyl-tRNA synthetase (TDRS) to switch the expression of reporter genes on or off as well as to precisely regulate their expression to various intermediate levels. To underscore the applicability of our work, we used the rare codon device to alter the expression levels of four genes of the fatty acid synthesis II (FASII) pathway (i.e. fabZ, fabG, fabI, and tesA') in E. coli to optimize steady-state kinetics, which produced nearly two-fold increase in fatty acid yield. Thus, the proposed method has potential applications in regulating target protein expression at desired levels and optimizing metabolic pathways by precisely tuning in vivo molar ratio of relevant enzymes.

Novel osmotic pump tablet using core of drug-resin complexes for time-controlled delivery system.

A novel elementary osmotic pump tablet was developed. The system uses the core of drug-resin complexes (DRCs) loaded with propranolol hydrochloride (PNH) for time-controlled delivery. In traditional osmotic pump tablets (OPTs), the lag time was always minimized. However, in the DRCs osmotic pump tablet (DRCOPT), the lag time was increased to achieve the time-controlled delivery. The quantity of osmotic agent in the core and channeling agent in the coating solution as well as weight gain were confirmed to be essential for the release behavior. A spherical symmetric design was applied to the optimization of the DRCOPT. The optimal formulation mainly consisted of DRC 100 mg, polyethyleneoxide (N80) 182 mg, and NaCl 30 mg. The ratio of cellulose acetate (CA)/polyethylene glycol 4000 was 15:3 (w/w) in coating solution, and the weight gain was 8%. The release behavior of the optimal DRCOPT was evaluated in media with different pH, rotation speeds, and ionic strength. It was found to generate a 2-h lag time, to deliver PNH at a rate of zero order from 2 h to 14 h in the medium of NaCl 0.15 mol/l, and the cumulative release at 24 h was 94%. Drug relee was independent of pH and rotation speed, but was proportional to ionic strength. In summary, the lag time could be used in therapeutic regimens with the characteristics of chronotherapy because of the lag time and provides a new concept for the development of osmotic pumps.

A novel time-controlled release system based on drug-resin complexes and elementary osmotic pump.

A novel time-controlled system based on elementary osmotic pump tablet containing a drug-resin complexes (DRCs) core is presented. In the traditional osmotic pump tablets (OPTs), the lag time was always minimized. On the contrary, in the DRCs osmotic pump tablet (DRCOPT), the lag time was increased to achieve time-controlled delivery. The system led to a zero-order drug release after an initial lag time. Polyethylene oxide (PEO) N80 was used as suspension agent and NaCl was applied as ion-exchange, osmotic pressure (electrolyte supplementary) agent, respectively. To examine the mechanism of this system, drug release behaviors were investigated under conditions of various osmotic pressures. A new method of combination of conductivity and HPLC was applied to determine the different fractions of NaCl in producing osmotic pressure, ion-exchange and electrolyte supplement. The pharmacokinetic studies conducted in beagle dogs showed that a steadier and controlled drug release behavior was obtained compared with the traditional formulations. On the basis of prescription of the DRCOPT, a good in-vitro-in-vivo correlation (IVIVC, R(2)=0.9541) was achieved. In addition, a lag time of 4 h was observed in in vivo experiment, which indicated that the DRCOPT can be used in therapeutic regimens with the characteristics of chronotherapy.

Investigation of high shear wet granulation processes using different parameters and formulations.

This study compared the granulation processes for different formulations using a laboratory-scale high shear mixer. The effects of critical process parameters (impeller speed, chopper speed and kneading time) on granule characteristics were evaluated. The characteristics of the granules studied included the size distribution, friability and morphological properties. The flow profiles of the wet mass and material deposition during the process were also studied. The results obtained showed that the effect of the impeller speed was determined by the starting material system. On the other hand, chopper speeds from 1200 to 3600 rpm and kneading times from 120 to 240 s had a consistent influence on all formulations. Moreover, it was found that the toroidal flow pattern of the wet mass could be maintained for a longer period and granules with a good spherical shape were obtained by removing the chopper during the last 120 s of the granulation process. In addition, the use of the pregelatinized starch in the formulation also led to a reduction in the wall adhesion of the material. It was concluded that the effectiveness of high shear wet granulation could be improved by choosing a proper combination of starting material and process parameters and by monitoring the mass motion during the process.

Development and optimization of solid dispersion containing pellets of itraconazole prepared by high shear pelletization.

This study investigated the solid dispersion containing pellets of itraconazole for enhanced drug dissolution rate. The influence of process parameters used during high shear pelletization on the pellet properties including pellet size and dissolution rate was also studied. Solid dispersions of itraconazole were prepared with Eudragit E100, a hydrophilic polymer, by a simple fusion method followed by powdered and characterized by differential scanning calorimetry and X-ray powder diffraction. Solid dispersions containing pellets were consequently prepared using a lab-scale high shear mixer. In order to improve the product quality, a central composite design was applied to optimize the critical process variables, such as impeller speed and kneading time, and the results were modeled statistically. Itraconazole was presented as an amorphous state in the solid dispersion prepared at a drug to polymer ratio of 1:2. Both studied parameters had great effect on the responses. Powdered solid dispersion and pellets prepared using the optimal parameter settings showed approximately 30- and 70-fold increases in dissolution rate over the pure drug, respectively. Solid dispersion prepared by simple fusion method could be an option for itraconazole solubility enhancement. Pelletization process in high shear mixer can be optimized effectively by central composite design.