A new generic column switching system for quantitation in cassette dosing using LC/MS/MS.

Cassette dosing is a method in which multiple drugs are administered to a single animal at the same time, and the plasma concentrations of the individual compounds are simultaneously determined. This method enables high-throughput rapid screening for pharmacokinetic assessment of new drug candidates. An available gradient method was modified for cassette dosing analysis to attain the advantages of high sensitivity and applicability to a wide range of compounds. However, two problems arose; (1). the time-consuming optimization of mobile phases for each compound group, which limited applicability and (2). the remarkable suppression of ionization by polyethyleneglycol, which is commonly used in intravenous administration. To resolve these problems, a new column switching method was established to attain wider applicability and avoid the ionization suppression. This column switching system is very simple because the trap column and the analytical column are specified and the mobile phase is selected from only two species. Method optimization requires only the selection of the mobile phase and takes only a few hours. About 200 compounds, which were administered as about 50 cassettes, were analyzed using this column switching system. Assay validation of one cassette was carried out, and good accuracy and precision were obtained. About 90% of the compounds could be determined within 20% bias. These results showed that this new column switching system for cassette dosing is accurate enough for the screening of drug candidates and offers wide applicability for various compounds. This system was shown to be very useful for the determination of cassette dosing samples, containing multiple compounds.

A novel and simple type of liposome carrier for recombinant interleukin-2.

The strong interaction between recombinant interleukin-2 (IL-2) and liposome was characterized and its possible application to drug-delivery control considered. The liposomes were prepared with egg phosphatidylcholine, distearoyl-phosphatidylglycerol (DSPG), dipalmitoyl-phosphatidylcholine, dipalmitoyl-phosphatidylglycerol or distearoyl-phosphatidylcholine (DSPC). Small and hydrophobic liposomes were selected, which were composed of saturated and long-fatty-acid-chain phospholipids. When the composition and the mixture ratio of IL-2 and the liposomewere optimized, morethan 95% ofthe lyophilized IL-2 (Imunace, 350000 JRU) was adsorbed consistently onto the DSPC-DSPG liposome (molar ratio, 10:1; 25 micromol mL(-1); 30 nm in size). Merely mixing IL-2 lyophilized with liposome suspension is convenient pharmaceutically. After intravenous administration to mice, liposomal IL-2 was eliminated half as slowly from the systemic circulation as free IL-2, with more than 13 and 18 times more IL-2 being delivered to the liver and spleen, respectively. After subcutaneous administration of liposomal IL-2 to mice, the mean residence time of IL-2 in the systemic circulation was 8 times that of free IL-2. These results show that IL-2 consistently adsorbs onto the surface of liposomes after optimization of its composition and mixing ratio. Intravenous and subcutaneous administration to mice demonstrates the gradual release of IL-2. Further trials are warranted using these liposomes.

Stabilization of aerosolized IFN-gamma by liposomes.

Aerosolized IFN-gamma is very unstable. We have improved the stability of IFN-gamma in the jet nebulizer by adding small liposomes. Aerosolized IFN-gamma was recovered in PBS solution by bubbling and its concentration was determined. After nebulization for 30 min, aerosolized IFN-gamma was detected only 0.4+/-0.2% of the initial amount in the PBS solution and 3.1+/-0.7% in the reservoir. On the other hand, the addition of small liposomes (HSPC/DSPG=10/1 (molar ratio), 45+/-24 nm) in the nebulizer increased the stability of IFN-gamma, 27.2+/-4.7% of the initial amount in the PBS solution and 25.7+/-12.6% in the reservoir. The present study also examined the effects of composition and concentration of liposomes on the stabilization of aerosolized IFN-gamma. Liposome prepared from distearoyl phosphatidylcholine (DSPC) or hydrogenated soy phosphatidylcholine (HSPC) was very effective for stabilization of aerosolized IFN-gamma (DSPC/DPPG=10/1, HSPC/DSPG=10/1). HSPC/DSPG liposome was efficient at the concentration higher than 12.5 micromols/ml for the stabilization of 5x10(5) JRU/ml of IFN-gamma. In considering the mechanism of this stabilization, the results of gel filtration chromatography suggest that IFN-gamma is inactivated by polymerization or aggregation in nebulization, while the inactivation is suppressed by liposomes due to their adsorption to IFN-gamma.

pH-sensitive liposomes composed of tocopherol hemisuccinate and of phosphatidylethanolamine including tocopherol hemisuccinate.

The ionic single-chain amphiphile tocopherol hemisuccinate (THS) is water-insoluble but on addition of NaOH, forms vesicles which give an aqueous suspension that is pale-colored and milky. Observation of the permeability of the 5(6)-carboxy-fluorescein-entrapped THS vesicle membranes indicated them to be pH-sensitive liposomes which are stable in the neutral pH region but become leaky at acidic pH. 1-Palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) itself is difficult to form stable liposomes near neutral pH in isotonic buffer but when mixed with THS, gives stable liposomes near physiological pH. These liposomes were found to have a pH-sensitivity that depended on the lipid composition. They were unstable in the presence of rat serum but significantly increased their stability when cholesterol was incorporated (THS/POPE/Chol = 2:8:8). This paper discusses why the ionic single-chain amphiphile THS can form liposome-like vesicles by itself like phosphatidylcholine, which has the diacyl chain.

Gelatin-acacia microcapsules for trapping micro oil droplets containing lipophilic drugs and ready disintegration in the gastrointestinal tract.

Nonhardened gelatin-acacia microcapsules were studied for encapsulation of microdroplets of oil solution containing a lipophilic drug as core material and ready disintegration with release of micro oil droplets in the gastrointestinal tract. Probucol and S-312-d, a Ca-channel blocker, were employed as model lipophilic drugs. Glyceryl tricaprylate and tricaprate mixture solutions containing these drugs were encapsulated according to the complex coacervation method and were recovered as free-flowing powders without any hardening (cross-linking) step. The microcapsules obtained were disintegrated, and the emulsion was reproduced within 3 min at 37 degrees C in the first or second test solution defined in the Japanese Pharmacopeia XII. When the microcapsules were stored as a powder at room temperature in a closed bottle, no significant change in their appearance or disintegration time upon rehydration was observed even after 1 year. Oral bioavailabilities of model drugs from the microcapsules were tested in rats and dogs and compared with those from other conventional formulations. Gastrointestinal absorption of both probucol and S-312-d from the microcapsules was remarkably more efficient than that from other formulations such as powders, granules, or oil solution. The proposed method for microencapsulation could be useful for powdering drug-containing oil solutions or O/W emulsions while maintaining excellent bioavailability.