Progress in research on the determination of entrapment efficiency of liposomes / 中国药科大学学报

@#Liposome, a new dosage form, has become important in improving in vivo behavior of drugs or realizing targeted drug delivery. Study and control of its critical processes and quality attributes are the main challenges in the current research on liposomes. The degree of encapsulation can determine drug''s effect in vivo directly, thus entrapment efficiency (EE) has turned into one of the critical quality attributes of liposome.In this paper some methods commonly used for the determination of EE and their characteristics are summarized and analyzed, and the main factors to be considered for the determination are discussed.

Preparation of ligustrazine microemulsion and comparative study on in vitro release of different size microemulsions / 中草药

Objective: To study the preparation process of ligustrazine microemulsion delivery system and evaluate its physical pharmacy properties; Microemulsions of different particle sizes were prepared in different oil phases, and the effect of particle size factors on the release behavior of the preparation was investigated. Methods: Taking the solubility of ligustrazine as index, the oil phase, emulsifier, and co-emulsifier were screened. The microemulsion formulation was optimized by pseudo-ternary phase diagram method. The encapsulation efficiency and drug loading was studied by ultrafiltration centrifugation. The particle size and potential were detected by the particle size analyzer. The release behavior of microemulsions with different particle sizes was compared by dialysis bag method. Results: The tetramethylpyrazine microemulsion was successfully prepared, and the appearance was clear and transparent. The average pH value was about 5.46. The detection method of microemulsion encapsulation rate was successfully established. When the drug loading of ligustrazine was 1.2 mg/mL, the encapsulation efficiency was (87.43 ± 0.20)%. The microemulsions of different particle sizes were prepared by changing the oil phase (ethyl oleate, oleic acid, and IPM). When the drug loading was 1.2 mg/mL, the three particle sizes were (16.80 ± 0.91), (129.50 ± 1.21), and (18.51 ± 0.24) nm, respectively. The release test showed that the release rate of all three could reach more than 90% within 4 h, and there was no significant difference. Conclusion: The uniform and stable tetramethylpyrazine microemulsion is successfully prepared; The release behavior of different tetramethylpyrazine microemulsions is not affected by the particle size factor.

A study on characteristic of different sample pretreatment methods to evaluate the entrapment efficiency of liposomes.

To examine how methods affect the evaluation of entrapment efficiency (EE) of liposomes, four different sample pretreatment methods were adopted in the experiment. The four sample pretreatment methods were size-exclusion chromatography (SEC), solid-phase extraction (SPE), centrifugation ultrafiltration (CF-UF) and hollow fiber centrifugal ultrafiltration (HF-CF-UF). Amphotericin B (AmB), which could self-associate to form aggregates in water is adopted as the model drugs in this paper. In the present work, it was found that the characterization results of four methods were quite different. The EE of liposome by SEC was about 93%, only 5-13% using C18 or HLB columns, and approximately 100% by CF-UF. The EE of HF-CF-UF reached up to nearly 99.0%. Further, this paper revealed the reasons making the difference of EE among four methods. Conventional SEC may distort the authentic of EE of liposomes with mainly employing some small liposomes or excessive water as eluent. For SPE, cholesterol on liposome surface could interact with the stationary phase making it hard to elute with water, and increase the risk of liposome leakage. While for CF-UF, concentration polarization was a main limitation hindering unentrapped drug to pass through membrane, making unentrapped drug undetectable in liposome. HF-CF-UF could truly reflect EE of liposomes with the concentration of unentrapped AmB lower than 25.0µg/mL. However, when the concentration was higher than 25.0µg/mL, AmB aggregates could be entrapped by hollow fiber. From the above analysis, this paper came to the conclusion that each method had its own feature in characterization. This study provided a reasonable guideline for choosing methods to character the EE of liposome.

Accuracy assessment on the analysis of unbound drug in plasma by comparing traditional centrifugal ultrafiltration with hollow fiber centrifugal ultrafiltration and application in pharmacokinetic study.

In present study, accuracy assessment on the analysis of unbound drug in plasma was made by comparing traditional centrifugal ultrafiltration (CF-UF) with hollow fiber centrifugal ultrafiltration (HFCF-UF). We used metformin (MET) as a model drug and studied the influence of centrifugal time, plasma condition and freeze-thaw circle times on the ultrafiltrate volume and related effect on the measurement of MET. Our results demonstrated that ultrafiltrate volume was a crucial factor which influenced measurement accuracy of unbound drug in plasma. For traditional CF-UF, the ultrafiltrate volume cannot be well-controlled due to a series of factors. Compared with traditional CF-UF, the ultrafiltrate volume by HFCF-UF can be easily controlled by the inner capacity of the U-shaped hollow fiber inserted into the sample under enough centrifugal force and centrifugal time, which contributes to a more accurate measurement. Moreover, the developed HFCF-UF method achieved a successful application in real plasma samples and exhibited several advantages including high precision, extremely low detection limit and perfect recovery. The HFCF-UF method offers the advantage of highly satisfactory performance in addition to being simple and fast in pretreatment, with these characteristics being consistent with the practicability requirements in current scientific research.

Preparation technology of sinomenine hydrochloride liposomes / 中草药

Objective: To prepare sinomenine hydrochloride (SIN-HCl) liposomes with high entrapment efficiency (EE) and to illustrate the effects of drug quantity and particle size on EE. Methods: Centrifugation sedimentation-centrifugation ultrafiltration was employed to determine EE of liposomes. Thin film hydration (TFH), reverse phase evaporation (REV), and ether injection (EI) were screened based on EE and formability of liposomes. The effects of water type, pH value, ion concentration of hydration liquid, pH gradient active drug loading, lecithin-cholesterol ratio, and drug-lipid ratio on EE of liposomes were investigated. The relationship between EE and the factors affecting the drug quantity and particle size was probed with a comprehensive design experiment. The stability of typical liposomes was evaluated at 4 °C. Results: The optimal preparation technology was TFH for SIN-HCl liposomes and citrate buffer solution (CBS) was the best hydration liquid. The liposome EE increased with the increase of pH values of CBS. When the pH value of CBS was fixed, the EE increased as a result of decrease in the ion concentration of CBS. pH gradient active drug loading led to increase of EE. The preferable hydration liquid for liposomes was CBS with pH value of 2.5. The optimal ratio of soybean lecithin to cholesterol was 6:1. Increasing ratios of SIN-HCl to soybean lecithin from 1:6 to 6:6 led to a slight decrease in EE of liposomes without probe signification. A quantitative relationship was established between the EE and drug quantity and liposome size. The EE of SIN-HCl liposomes prepared by certain particle size and drug quantity could reach over 80%. The typical liposomes showed a good stability. Conclusion: The technology of pH gradient active drug loading is able to prepare SIN-HCl liposomes with high EE.

Determination of entrapment efficiency of sinomenine hydrochloride liposomes with centrifugation sedimentation combined with centrifugation ultrafiltration / 中草药

Objective: To develop a method for determining the entrapment efficiency of sinomenine hydrochloride (SM-HCl) liposomes and to illuminate the drug retention property in the liposomes. Methods: Thin film hydration method was employed to prepare SM-HCl liposomes. HPLC was used to determine drug content of the liposomes. A Kromasil ODS C18 column (250 mm x 4.6 mm, 5 μ) was used with an isocratic elution composed of methanol, water, and ethylenediamine in the ratio of 55 : 45 : 0.225 at a flow rate of 1.0 mL/min. The column was maintained at 30 °C. The UV detector was set at 265 nm. Centrifugation sedimentation combined with centrifugation ultrafiltration was used to determine drug entrapment efficiency of the liposomes. The entrapment efficiencies of an SM-HCl liposome sample (hydrated with citric buffer solution at pH 7.0) and its diluted sample were compared. Results: The pharmaceutical excipients and solvents for analysis had no interference with the determination of sinomenine. Sinomenine had a good linear relation in the range of 9.82-78.6 μg/mL (r = 0.999 7), the intra-day and inter-day precisions were with RSD≤2.1% and the averaged recovery was within 99.29%-100.8%. SM-HCl solution (50 μL) was able to saturate the drug absorption of ultrafiltration films. The entrapment efficiencies of the SM-HCl liposome sample (hydrated with citric buffer solution at pH 7.0) and its double-volume diluted sample were 33.16% and 14.75%, respectively. Conclusion: HPLC and centrifugation sedimentation combined with centrifugation ultrafiltration are able to determine the entrapment efficiency of SM-HCl liposomes efficiently and accurately. Initial filtrate (50 μL) should be discarded in the process of ultrafiltration in order that the drug concentration in filtrate may be equal to that of external aqueous phase of liposomes. The retention of sinominine in the liposomes is poor, although it has considerable affinity to the lipid bilayers.