Xiaoguang Tao

Polypeptide-based vesicles: formation, properties and application for drug delivery

It is well known that amphiphilic block copolymers can self-assemble in selective solvents to adopt various morphologies, such as micelles, vesicles, and cylinders. Polypeptide-containing amphiphilic block copolymers have received a great deal of attention due to their unique physicochemical and biological features. They can form vesicular structures, spontaneously mimicking the self-assemblies of virus capsids. This article focuses on recent advances involving polypeptide-based vesicles, including their formation and properties, which are significantly different from those of conventional coil–coil copolymers. The preparation of vesicles with a tunable size is also described. Unlike other polymers, polypeptides can adopt different conformations and undergo conformation transitions under specific conditions. The stimuli–responses of the vesicles based on conformation transitions will be highlighted. Polypeptides are ideal materials for gene and drug delivery because they are highly biocompatible, biodegradable, and exhibiting precise secondary conformations and inherent functionality. Polypeptide-based vesicles have shown much promise with regard to anti-cancer drug delivery.

A floating multiparticulate system for ofloxacin based on a multilayer structure: In vitro and in vivo evaluation.

The purpose of this research was to develop a novel gastroretentive multiparticulate system with floating ability. This system was designed to provide drug-loaded pellets coated with three successive coatings-the retarding film (ethyl cellulose), the effervescent layer (sodium bicarbonate) and the gas-entrapped polymeric membrane (Eudragit RL 30D). The floating pellets were evaluated for SEM, floating characteristic parameters, in vitro release and bioavailability in New Zealand rabbits. The zero-order release theory model is designed to interpret the release processes. Due to the swelling property, high flexibility and high water permeability, Eudragit RL 30D was used as a gas-entrapped polymeric membrane. The obtained pellets exhibit excellent floating ability and release characteristics. Analysis of the release mechanism showed a zero-order release for the first 8h because of the osmotic pressure of the saturated solution inside of the membrane, which was in accordance with that predicted. Abdominal X-ray images showed that the gastroretention period of the floating barium sulfate-labeled pellets was no less than 6h. The relative bioavailability of the floating pellets compared with reference tablets was 113.06 ± 23.83%. All these results showed that the floating pellets are a feasible approach for the gastroretentive drug delivery system.

Strategies for improving the payload of small molecular drugs in polymeric micelles

Abstract In the past few years, substantial efforts have been made in the design and preparation of polymeric micelles as novel drug delivery vehicles. Typically, polymeric micelles possess a spherical core–shell structure, with a hydrophobic core and a hydrophilic shell. Consequently, poorly water‐soluble drugs can be effectively solubilized within the hydrophobic core, which can significantly boost their drug loading in aqueous media. This leads to new opportunities for some bioactive compounds that have previously been abandoned due to their low aqueous solubility. Even so, the payload of small molecular drugs is still not often satisfactory due to low drug loading and premature release, which makes it difficult to meet the requirements of in vivo studies. This problem has been a major focus in recent years. Following an analysis of the published literature in this field, several strategies towards achieving polymeric micelles with high drug loading and stability are presented in this review, in order to ensure adequate drug levels reach target sites. Graphical abstract The strategies for improve the payload of micelles. Figure. No Caption available.

Improved oral bioavailability of core-shell structured beads by redispersion of the shell-forming nanoparticles: preparation, characterization and in vivo studies.

In order to increase the dissolution rate and oral bioavailability of bifendate, coated beads with core-shell structure were prepared via a combination use of wet media milling method and bead layering process. Hydroxypropyl cellulose (HPC-SL) and sodium lauryl sulfate (SLS) were found to be the best pair to stabilize the nanosuspension during milling process. A 10:1 ratio of mixture of mannitol and SLS was chosen as most suitable coating matrix to maintain the redispersability of dried nanoparticles in the shell of beads. The mean particle size of the nanosuspension was 139 nm and the zeta potential was -20.2 mV. Nanoscale bifendate particles with a mean diameter of 360 nm could be generated when redispersing the prepared beads in water. The differential scanning calorimetry (DSC) and X-ray powder diffraction (XRPD) analysis indicated that the crystalline state of the drug was not changed. The stability test confirmed that coated beads showed no distinct difference in particle size and dissolution velocity during 6 month storage while liquid nanosuspension was stable no more than 3 weeks. Dissolution rate of coated beads was increased significantly compared with commercially available pills. Likewise, the Cmax and AUC (0→24) of nanosuspension based beads in beagle dogs were 2.40-fold and 1.66-fold greater than that of commercially available pills, respectively. The present work is a reliable approach to stabilize nanosuspension based product, and improve dissolution velocity and bioavailability of poor soluble drugs.

Application and functional characterization of POVACOAT, a hydrophilic co-polymer poly(vinyl alcohol/acrylic acid/methyl methacrylate) as a hot-melt extrusion carrier

Abstract Objective: The aim of this study was to evaluate the applicability of POVACOATTM, a hydrophilic PVA copolymer, as a solid dispersion (SD) carrier for hot-melt extrusion (HME). Methods: Bifendate (DDB), a water-insoluble drug, was chosen as the model drug. DDB was hot-melt extruded by a co-rotating twin screw extruder with POVACOATTM. The SD formability of POVACOATTM was investigated by varying the composition ratios. Solid state characterization was evaluated by differential scanning calorimetry, powder X-ray diffraction, scanning electron microscopy and Fourier transformation infrared spectroscopy. In order to have a better knowledge of the mechanism of dissolution enhancement, dissolution study, phase solubility study and crystallization study of DDB from supersaturated solutions were performed. In addition, the storage stability of the extrudate containing 10% DDB was investigated. Results: Physical characterizations showed that DDB was amorphous up to 15% drug loading. The phase solubility study revealed an AL-type curve. Moreover, POVACOATTM was found to have an inhibitory effect on crystallization from supersaturated solutions. Compared with the pure DDB and physical mixture, the dissolution rate and solubility of extrudates were significantly enhanced and the drug loading markedly affected the dissolution of SDs. Furthermore, the stability test indicated that 10% DDB-SD was stable during storage (40 °C/75% RH). Conclusion: The results of this study demonstrate that POVACOATTM is a valuable excipient for the formulation of solid dispersions prepared by HME to improve dissolution of poorly water-soluble drugs.

Preparation, characterization, stability and in vitro-in vivo evaluation of pellet-layered Simvastatin nanosuspensions

The objective of the present study was to develop stable pellets-layered Simvastatin (SIM) nanosuspensions with improved dissolution and bioavailability. The nanosuspensions were prepared with 7% HPMC, antioxidant 0.03% butylated hydroxyanisole and 0.2% citric acid (m/v) by low temperature grinding. After that, SDS with SIM was in a ratio of 1:5 (m/m), was evenly dispersed in the nanosuspensions. Then, they were layered on the surface of sugar pellets. The mean particle size of the SIM nanosuspensions was 0.74 µm, and 80.6% of the particles was below 1 µm in size. The pellets could re-disperse into nanoparticle status in the dissolution medium. In 900 mL pH 7.0 phosphate solutions, the dissolution of the layered pellets was better than that of commercial tablets. Also, nearly 100% of the drug dissolved from the pellets within 5 min under sink conditions. During the stability studies, SIM pellets exhibited good physical and chemical stability. The relative bioavailability of SIM and Simvastatin β-hydroxy acid (SIMA) for nanosuspensions layered pellets compared with commercial tablets was 117% and 173%, respectively. The bioavailability of SIMA was improved significantly (p < 0.05), confirming the improvement of bioavailability. Thus, the present study demonstrates that the pellet-layered SIM nanosuspensions improved both the dissolution and bioavailability of SIM.

Preparation and in vitro–in vivo evaluation of none gastric resident dipyridamole (DIP) sustained-release pellets with enhanced bioavailability

The objective of this study was to develop none gastric resident sustained-release pellets loaded with dipyridamole with a high bioavailability. Two different kinds of core pellets, one containing citric acid as a pH-modifier (CAP) and, the other without pH-modifier (NCAP) were prepared by extrusion-spheronization and then coated with mixtures of enteric soluble and insoluble polymers (referred to as CAP(1) and NCAP(1)) or insoluble polymer alone (referred to as CAP(2) and NCAP(2)). The relative bioavailability of the sustained-release pellets was studied in fasted beagle dogs after oral administration using a commercially available immediate release tablet (IRT) as a reference. The in vitro release, in vivo absorption and in vitro-in vivo correlation were also evaluated. Results revealed that the plasma drug concentrations after administration of CAP(2), NCAP(1) and NCAP(2) were undetectable, indicating that the drug release was almost zero from the preparations throughout the gastro-intestinal tract. The C(max), T(max) and AUC((0→24)) of CAP(1) were 0.78 ± 0.23 (μg/ml), 3.80 ± 0.30 (h), and 6.74 ± 0.47 (μg/mlh), respectively. While the corresponding values were 2.23 ± 0.32 (μg/ml), 3.00 ± 0.44 (h) and 9.42 ± 0.69 (μg/mlh) for IRT. The relative bioavailability of CAP(1) was 71.55% compared with IRT. By combined incorporation of a pH-modifier into the core of pellets to modify the inner micro-environment and employing mixtures of enteric soluble and insoluble polymers as a retarding layer, drugs with high solubility in stomach and limited solubility in small intestine, such as DIP, could be successfully formulated as sustained release preparations with no pH-dependence in drug release and enhanced bioavailability.

Preparation and evaluation of nicotinic acid sustained-release pellets combined with immediate release simvastatin

This study was performed to prepare high-dose nicotinic acid (NA) loaded sustained-release pellets coated with double polymer and simvastatin (SIM). The uncoated pellets were prepared by extrusion-spheronization and the double ethylcellucose (EC) films were coated in a bottom-spray fluidized bed coater. SIM was milled by wet grinding and then the milled suspension was layered on the coated pellets. Results showed that coated with 1.5% subcoating and 1% outer coating composed of EC and polyvinyl pyrrolidone K30 (PVP(K30)) in ratios of 5:1 and 2:1, NA release behavior was very similar to the reference (NER/S; SIMCOR, Abbott) in different media. And SIM was delivered more rapidly than that of the reference, while the SIM layer had no influence on NA release. During 6-month storage at 40°C/75% RH, the two drugs exhibited stable dissolution behavior. It was observed that the content uniformity of SIM was provided by the present preparation and SIM was stable if adding light magnesium oxide in the grinding procedure. Results indicated it was possible to prepare high-dose sustained-release NA pellets combined with little-dose immediate release SIM by spraying double EC polymer and SIM milled suspension on NA pellets in a bottom-spray fluidized bed coater, respectively.

Preparation and characterization of azithromycin--Aerosil 200 solid dispersions with enhanced physical stability.

The main purpose of this study was to investigate the feasibility of azithromycin (AZI)--Aerosil 200 solid dispersions specifically with high stability under accelerated condition (40 °C/75% RH). Ball milling (BM) and hot-melt extrusion (HME) were used to prepare AZI solid dispersions. The physical properties of solid dispersions were evaluated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). For solid dispersions prepared with both methods, no crystalline of AZI was detected (except for AZI: Aerosil 200=75:25) by DSC or PXRD, indicating the amorphous state of AZI in solid dispersions. The FT-IR results demonstrated the loss of crystallization water and the formation of hydrogen bonds between Aerosil 200 and AZI during the preparation of solid dispersions. After 4 weeks storage under accelerated condition, the degree of crystallinity of AZI increased in solid dispersions prepared by BM, whereas for solid dispersions containing AZI, Aerosil 200 and glyceryl behenate (GB) prepared by HME, no crystalline of AZI was identified. This high stability can be attributed to the hydrophobic properties of GB and the presence of hydrogen bonds. Based on the above results, it is inferred the protection of hydrogen bonds between AZI and Aerosil 200 formed during preparation process effectively inhibited the recrystallization of AZI and improved the physical stability of amorphous AZI in the presence of Aerosil 200.

Improvement of dissolution and bioavailability of Ginsenosides by hot melt extrusion and cogrinding

The main purpose of this paper was to improve the dissolution and bioavailability of Ginsenosides (GS) which contained 20(S)-protopanaxadiol (PPD) and 20(S)-protopanaxatriol (PPT) by two methods, and to compare their performance in vitro and in vivo with GS extracts. GS-solid dispersion (SD) were prepared by hot melt extrusion (HME), and GS coground mixture were prepared by cogrinding. In 500 mL 0.1% sodium dodecyl sulfate (SDS) aqueous solution, dissolution of GS-SD and GS coground mixture were both improved comparing with GS extracts. And dissolution of GS-SD was above 90%, which was better than GS coground mixture whose dissolution was about 70%. In GS-SD, GS coground mixture and GS extracts, the AUC0→48 of PPD were 1439.9 ± 435.71, 1618.2 ± 571.9 and 1089.8 ± 359.9 ng·h/mL, and the AUC0→48 of PPT were 683.1 ± 197.7, 736.0 ± 226.0 and 439.8 ± 193.6 ng·h/mL. The results revealed that bioavailability of GS-SD and GS coground mixture was better than GS extracts, but bioavailability of GS-SD was lower than GS coground mixture, which was not consistent with the results of dissolution. The results perhaps caused by the phospholipid in GS coground mixture which played a role as absorption enhancement. It is apparent that both HME and cogrinding can improve the dissolution and bioavailability of GS.