Polymethacrylate based microparticulates of insulin for oral delivery, part II: solid state characterization

The objectives of the present study were (A) to characterize insulin microparticles prepared by the coprecipitation process by size exclusion chromatography, differential scanning calorimetry, fourier-transform IR spectroscopy, and powder X-ray diffractometry, and (B) to study the solid state conformation of insulin before and after entrapment in the polymeric carrier. Microparticles were prepared by dissolving insulin in 0.01 N HCI and alcohol USP to get a final concentration of 32% v/v. Eudragit L100, a representative polymethyacrylate polymer, was then dissolved in this solution which was transferred to a beaker containing cold water with homogenization to obtain microparticulates. Insulin powder, microcapsules, and a physical mixture of insulin and Eudragit L100 were then analyzed by SEC-HPLC, DSC, FTIR, and XRD to observe changes in protein conformation as result of the manufacturing process. While DSC, XRD and FTIR results were of limited value due to limits of instrument sensitivity, size exclusion chromatography data indicated that higher order aggregates were not formed during microcapsule formation. It was concluded that formulating insulin into microparticles by the coprecipitation process is an attractive and stable method for protein delivery and might be suitable for oral delivery of insulin.     

Chitosan phthalate microspheres for oral delivery of insulin: preparation, characterization, and in vitro evaluation

Chitosan phthalate polymer was synthesized and its microspheres were prepared by emulsion phase separation technique. The characterization of microspheres was determined by means of FTIR spectroscopy, electron microscopy, particle size, and zeta potential. The insulin was loaded to the microspheres by passive absorption technique. The peptic and tryptic enzymes degradation of insulin in microspheres was investigated. The in vitro release behavior of the microspheres was investigated under different pH conditions (pH 2.0 and pH 7.4). The degree of phthalate substitution in the synthesized polymer was 20%. The prepared microspheres were spherical with an average diameter 46.34 μ m. The insulin-loading capacity was 62%. Chitosan phthalate microspheres protect the insulin from gastric enzymes degradation that may enhance the oral stability of insulin. The encapsulated insulin was quickly released in a phosphate buffer saline (pH 7.4), whereas a small amount of insulin was released under acidic condition (0.1N HCl; pH 2.0) because under acidic conditions, carboxylic groups present in the system exist in nonionized form and are poorly hydrophilic. However, in alkaline conditions, it exists in ionized form and is considerably hydrophilic. The results suggest that chitosan phthalate microspheres may be used as a potential carrier for oral insulin delivery.     

Proliposomes for oral delivery of dehydrosilymarin: preparation and evaluation in vitro and in vivo

Aim:

To formulate proliposomes with a polyphase dispersed system composed of soybean phospholipids, cholesterol, isopropyl myristate and sodium cholate to improve the oral bioavailability of dehydrosilymarin, an oxidized form of herbal drug silymarin.

Methods:

Dehydrosilymarin was synthesized from air oxidation of silymarin in the presence of pyridine, and proliposomes were prepared by a film dispersion-freeze drying method. Morphological characterization of proliposomes was observed using a transmission electron microscope. Particle size and encapsulation efficiency of proliposomes were measured. The in vitro release of dehydrosilymarin from suspension and proliposomes was evaluated. The oral bioavailability of dehydrosilymarin suspension and proliposomes was investigated in rabbits.

Results:

The proliposomes prepared under the optimum conditions were spherical and smooth with a mean particle size in the range of 7 to 50 nm. Encapsulation efficiency was 81.59%±0.24%. The in vitro accumulative release percent of dehydrosilymarinloaded proliposomes was stable, which was slow in pH 1.2, and increased continuously in pH 6.8, and finally reached 86.41% at 12 h. After oral administration in rabbits, the relative bioavailability of proliposomes versus suspension in rabbits was 228.85%.

Conclusion:

Proliposomes may be a useful vehicle for oral delivery of dehydrosilymarin, a drug poorly soluble in water.     

Polysaccharide coated niosomes for oral drug delivery: formulation and in vitro stability studies

Non-ionic surfactant vesicles (niosomes) were prepared and appended with a polysaccharide cap using hydrophobic anchors. Hydrophobized polysaccharides, O-palmitoyl pullulan (OPPu) and cholesteroyl pullulan (CHPu) were anchored onto propranolol.HCL containing preformed niosomes. The coated niosomes were characterized for average vesicle size, size distribution, shape, encapsulation efficiency and in vitro release profile and were compared with their uncoated counterparts. No significant difference was observed in % encapsulation (P > 0.05 in a rank sum test) of polysaccharide coated and uncoated vesicles. In vitro release studies however, revealed a significant lowering (P < 0.01) of drug release for the coated systems in simulated gastric and intestinal fluids with a biphasic release profile. The influence of the hydrophobized polysaccharide cap on niosomal membrane integrity and stabilization against harsh bio-environment conditions was also investigated. The parameters investigated include detergent and bile (bile salts and fresh-pooled rat bile) challenge, freeze-thaw cycling, osmotic stress, and long term and shelf stability studies. It was seen that at higher bile salt concentrations and detergent content, uncoated niosomes underwent bilayer solubilization into intermediate micellar structures, whereas coated niosomes were able to maintain their structural integrity as reflected from their higher % latency for the entrapped water soluble agent. Similarly, freeze-thaw cycling could not bring any fusion or collapse of the niosomal membrane (unlike uncoated ones). Furthermore, the exceptional shelf stability of the coated vesicles both at 37 +/- 1 degrees and at 4 +/- 1 degrees C establishes the potential of polysaccharide coated niosomes as an oral delivery system for water-soluble agents. Results from OPPu and CHPu coated niosomal systems for their oral stability potential are compared.     

Development of PEGDMA: MAA based hydrogel microparticles for oral insulin delivery

An oral insulin delivery system based on copolymers of poly(ethylene glycol) dimethacrylate and methacrylic acid was developed and its functional activity was tested in non-obese diabetic rats. Poly(ethylene glycol) dimethacrylates (PEGDMA) were synthesized by esterification reaction of different molecular weight poly(ethylene glycol) with methacrylic acid (MAA) in presence of acid catalyst. PEG dimethacrylates of molecular weight ranging from 400 to 4000 and methacrylic acid were further copolymerized by suspension polymerization to obtain pH sensitive hydrogel microparticles. The diameter of poly(PEGDMA:MAA) microparticles increased with increasing the molecular weight of the poly(ethylene glycol) dimethacrylate used for respective microparticle synthesis. Insulin was loaded into the hydrogel microparticles by partitioning from concentrated insulin solution. In vitro release studies of insulin loaded microparticles were performed by simulating the condition of gastrointestinal tract, which showed the minimal insulin leakage (18-25%) at acidic pH (2.5) and significantly higher release at basic pH (7.4). Animal studies were carried out to investigate the abilities of the insulin loaded hydrogel microparticles to influence the blood glucose levels of the diabetic rats. In studies with diabetic rats, the blood glucose level reduced for animals that received the insulin loaded hydrogel microparticles and the effect lasted for 8-10h. It was also observed, two capsules per day of poly(PEGDMA4000:MAA) hydrogel microparticles containing 80 I.U./kg of insulin dose were sufficient to control the blood glucose level of fed diabetic rats between 100 and 300 mg/dl.     

In vitro assessment of archaeosome stability for developing oral delivery systems

The in vitro stability of archaeosomes made from the total polar lipids of Methanosarcina mazei, Methanobacterium espanolae or Thermoplasma acidophilum, was evaluated under conditions encountered in the human gastrointestinal tract. At acidic pH, multilamellar vesicles (MLV) prepared from T. acidophilum lipids were the most stable, releasing approximately 80, 20, 10 and 5% of encapsulated 14C-sucrose at pH 1.5, 2.0, 2.5 and 6.2, respectively, after 90 min at 37 degrees C. Archaeosomes from M. mazei lipids were the least stable. For each type of total polar lipid, unilamellar vesicles (ULV) were less stable than the corresponding MLV vesicles. Pancreatic lipase had relatively minor effect on the stability of archaeosomes made from either of the three types of total polar lipids, causing the release of 12-27% of the encapsulated 5(6)-carboxyfluorescein (CF) from ULV and MLV after 90 min at 37 degrees C. In simulated human bile at pH 6.2, MLV from M. mazei total polar lipids lost 100% of the encapsulated CF after 90 min at 37 degrees C, whereas those from the polar lipids of M. espanolae or T. acidophilum lost approximately 85% of the marker. Pancreatic lipase and simulated human bile had no synergistic effect on the release of carboxyfluorescein from ULV or MLV prepared from any of the total polar lipids. After 90 min in the combined presence of these two stressors at pH 6.2, the leakage of fluorescein conjugated bovine serum albumin from MLV prepared from T. acidophilum lipids was similar to that of CF, and 13% of the initially present vesicles appeared to be intact. These results indicate that archaeosomes show stability properties indicative of potential advantages in developing applications as an oral delivery system.     

Nanoparticle strategies for the oral delivery of insulin

Since its discovery, insulin remains the major treatment for Type 1 diabetes and many Type 2 diabetic patients, with insulin being administered parenterally. The oral route of insulin delivery, being the most comfortable, would also be the most physiologically advantageous in taking advantage of the portal-hepatic route of absorption. However, insulin is less absorbed by the intestinal mucosa and is rapidly degraded enzymatically in the gastrointestinal tract. Polymeric biodegradable and biocompatible nanoparticles have been developed. These nanoparticles protect insulin against degradation and facilitate the uptake of insulin (associated or not associated to the nanoparticles) through a paracellular or a transcellular pathway. In this review, the physicochemical characteristics of polymer composition, in vitro release kinetics and the biological effects of insulin-loaded nanoparticles in experimental diabetes and healthy animals are discussed.     

In vitro comparative study of three pancreatic enzyme preparations: dissolution profiles, active enzyme release and acid stability

Background  Various pancreatic enzyme preparations are used for the treatment of pancreatic insufficiency but their bioequivalence is often unknown.
Aim  To determine in vitro the pH-dependent release and acid resistance of enzymes from three commercially available pancreatin capsules, two containing enteric-coated (Creon 25000; Eurobiol 25000) and one uncoated (Eurobiol 12500) microspheres.
Methods  Dissolution experiments were performed at pH values ranging from 4.0 to 5.8. Lipase, chymotrypsin and amylase activities were measured in the solution as a function of time.
Results  Eurobiol 25000 started to release its enzymes significantly at pH 5.0 ( t _1/2 = 71 min), whereas the enzymes from Creon 25000 were only released at higher pH value (5.4; t _1/2 = 49.2 min). Unlike chymotrypsin, lipase and amylase were highly sensitive to acidic conditions at the lowest pH values tested. Both enzymes were also found to be sensitive to proteolytic inactivation at the highest pH values tested. Overall, Eurobiol 25000 released higher amounts of active amylase and lipase than Creon 25000 at the pH values usually found in duodenal contents. The uncoated Eurobiol 12500 preparation was, however, the only one that could immediately release rather high levels of active chymotrypsin and lipase at low pH (4.5).
Conclusion  These findings suggest that pH-sensitive enteric-coated pancreatin products containing similar amounts of enzymes might not be bioequivalent depending on the pH of duodenal contents.     

Oil-based formulations for oral delivery of insulin

Several oil-based solution formulations of insulin were prepared, in which insulin was solubilized in the form of anhydrous reverse micelles. The preparation process involved micellar dissolution of insulin followed by freeze drying, then reconstitution of lyophilized product with an oil phase. These formulations were stable at room temperature for up to 12 months. No significant changes in the appearance were observed and no degradation products of insulin were detected during the course of the stability study. The efficacy of these formulations was evaluated in-vivo using diabetic Wistar rat as an animal model and then a specific formulation was chosen for further study in non-diabetic New Zealand rabbits. It was found that the efficacy of insulin oil solution was dose dependent and insulin oil solution had the same efficacy as insulin emulsion with the same formulation composition. If ethylene-diaminetetraacetic acid (EDTA) was pre-delivered 40 min before the delivery of insulin oil solution, the hypoglycaemic effect of insulin oil solution was greatly enhanced, with an AUC (% glucose reduced) value increase from 28.5 +/- 14.7 to 167.1 +/- 72.3. The improvement of oral absorption induced by predelivery of EDTA might be attributed to enzyme inhibition, reduced gut mobility and the opening of paracellular routes.     

PLGA nanoparticles for the oral delivery of nuciferine: preparation,physicochemical characterization and in vitro/in vivo studies

This article reports a promising approach to enhance the oral delivery of nuciferine (NUC), improve its aqueous solubility and bioavailability, and allow its controlled release as well as inhibiting lipid accumulation. NUC-loaded poly lactic-co-glycolic acid nanoparticles (NUC-PLGA-NPs) were prepared according to a solid/oil/water (s/o/w) emulsion technique due to the water-insolubility of NUC. PLGA exhibited excellent loading capacity for NUC with adjustable dosing ratios. The drug loading and encapsulation efficiency of optimized formulation were 8.89?±?0.71 and 88.54?±?7.08%, respectively. NUC-PLGA-NPs exhibited a spherical morphology with average size of 150.83?±?5.72?nm and negative charge of ?22.73?±?1.63?mV, which are suitable for oral administration. A sustained NUC released from NUC-PLGA-NPs with an initial exponential release owing to the surface associated drug followed by a slower release of NUC, which was entrapped in the core. In addition, ～77?±?6.67% was released in simulating intestinal juice, while only about 45.95?±?5.2% in simulating gastric juice. NUC-PLGA-NPs are more efficient against oleic acid (OA)-induced hepatic steatosis in HepG₂ cells when compared to naked NUC (n-NUC, *p < 0.05). The oral bioavailability of NUC-PLGA-NPs group was significantly higher (**p < 0.01) and a significantly decreased serum levels of total cholesterol (TC), triglycerides (TG) and low-density lipoprotein cholesterol (LDL-C), as well as a higher concentration of high-density lipoprotein cholesterol (HDL-C) was observed, compared with that of n-NUC treated group. These findings suggest that NUC-PLGA-NPs hold great promise for sustained and controlled drug delivery with improved bioavailability to alleviating lipogenesis.     

Developments in polymeric devices for oral insulin delivery

BACKGROUND: Development of improved oral insulin administration is necessary for the treatment of diabetes mellitus, to overcome the problem of daily subcutaneous injections. The vast amount of literature data on oral insulin delivery prompted us to cover this area in a review. OBJECTIVE: Insulin delivery using polymeric devices is discussed, with an ultimate aim of addressing the technological development in this area. METHODS: The development of oral delivery devices for insulin using hydrogels and micro/nanoparticles is discussed with reference to polymers. These efforts must be directed to increase the residence time of insulin near the intestinal absorptive cells. RESULTS/CONCLUSION: The published results on oral insulin delivery devices, particularly on inter-polymer complexes of the grafted copolymers, are discussed in greater depth. The use of absorption enhancers like cyclodextrins, bile salts and surfactants is covered. The state-of-the-art technology and challenges in this area are discussed, with typical examples.     

Oil based nanocarrier for improved oral delivery of silymarin: In vitro and in vivo studies

In this study the influence of hydrogen bonding interaction between niosomal membrane and solutes on the drug loading and release was investigated. Salicylic acid (SA) and p-hydroxyl benzoic acid (p-BA) were selected as models. Niosomes were prepared with 1:1 molar ratios of various surfactants and cholesterol by film hydration technique, and the corresponding formulation variables were optimized to achieve the maximum entrapment efficiencies (EE%). The EE% of different formulations followed the trend Span 60>Span 40>Span 20>Span 80. Additionally, it was also found that the EE% of p-BA was much higher than that of SA. This difference may be due to the formation of hydrogen bond between p-BA and niosomal membrane, and the corresponding interaction diagram has been proposed and confirmed indirectly by UV spectroscopy method. The quantitative analysis of hydrogen binding interaction between solutes and niosome has been finished firstly, and the corresponding entrapment equilibrium constant K has been calculated as well. Moreover, in vitro the release of both drugs from niosomes was examined in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF), respectively. The results indicated that the release of p-BA in SIF was much slower than that in SGF, and the release rate of SA in SGF is apparently slower than that in SIF. The possible mechanism was given as well.     

Cytotoxicity evaluation of enzyme inhibitors and absorption enhancers in Caco-2 cells for oral delivery of salmon calcitonin

The usefulness of enzyme inhibitors and absorption enhancers with least mucosal cell cytotoxicity was evaluated on Caco-2 cell monolayers. The temporal cytotoxicity of several protease inhibitors at 500 microg/mL (e.g., turkey and chicken ovomucoids, aprotinin, and Protease Inhibitor Cocktail) and absorption enhancers [e.g., cholate (3%), glycocholate (3%), glycosursodeoxycholate (3%), ethylenediaminetetraacetic acid (EDTA, 0.1%), hydroxypropyl-beta-cyclodextrin (HP-beta-CD, 5%), hydroxypropyl-gamma-cylcodextrin (HP-gamma-CD, 5%), gamma-cylcodextrin (gamma-CD, 5%), tetradecyl-beta-D-maltoside (0.25%), octylglucoside (0.25%), citric acid (10%), glycyrrhetinic acid (0.34 mM), and Tween-80 (0.1%)] was measured by monitoring their effect on Caco-2 cell viability. Cell viability was measured by mannitol permeability measurements, transepithelial electrical resistance (TEER) measurements, DNA-propidium iodide staining assay, and WST-1 assay (tetrazolium salt based assay). Sodium dodecyl sulfate (0.1%), a potent surfactant, was used as a positive control. Chicken and turkey ovomucoids were nontoxic to cells as evaluated by all the methods used. Aprotinin decreased the TEER, whereas plasma membrane damage was seen with Protease Inhibitor Cocktail after a 24-h period. With respect to the absorption enhancers, the toxicity increased directly as a result of an increase in the time of incubation. The enhancers EDTA and HP-beta-CD can be used safely for a short period of time, whereas glycosursodeoxycholate, glycyrrhetinic acid, octylglucoside, HP-gamma-CD, and gamma-CD can be used for a longer period.     

Colon targeting: an emerging frontier for oral insulin delivery

Subcutaneous administration of insulin is associated with several limitations such as discomfort, local pain, irritation, infections, immune reactions and lipoatrophy as well as lipohypertrophy manifestations at the injection site. To overcome these drawbacks, enormous research is currently going on worldwide for designing of an alternative noninvasive route of administration. Pulmonary and oral route seem to be the most promising ones, with respect to the market value. However, after the letdown by pulmonary delivery of insulin, oral colon targeted delivery of insulin has gained tremendous interest among researchers. Although bioavailability remains a challenge for oral colon specific delivery of insulin, the employment of protease inhibitors, permeation enhancers and polymeric delivery systems have proved to be advantageous to overcome the said problem. This Editorial article is not intended to offer a comprehensive review on drug delivery, but shall familiarize the readers with the strategies employed for attaining non-erratic bioavailability of insulin, and to highlight some of the formulation technologies that have been developed for attaining oral colon-specific delivery of insulin.     

口服纳米粒递送胰岛素研究进展

药物治疗糖尿病的最新进展当属口服胰岛素,而制备口服胰岛素需要将胰岛素包埋进载体使其避免胃肠降解。可突破肠上皮屏障达到良好降糖效果的口服载体多种多样,其中利用纳米材料制备胰岛素载体(INS-NPs)的研究最热,主要有以下优势:加强药物稳定性,大大提升生物利用率;实现靶向定位释药,降低药物对机体的毒副作用;控制释放药物时量,使药物在体内的作用更加明显等。针对上述优势并结合相关研究结论,本文从生物利用率、降糖时效和控释作用3个方面简述口服纳米粒在糖尿病治疗中的新进展。     

溃结康微丸的制备和体外溶出度考察

目的:制备渍结康微丸并进行处方优化,考察微丸的体外溶出度.方法:用挤出滚圆造粒机制备溃结康微丸,优化制剂处方组成;采用高效液相色谱法以黄芩苷和芍药苷为指标,对其体外溶出度进行考察.结果:制得微丸圆整度好.大小均匀,收率在75%以上.黄芩苷和芍药苷的溶出度45 min内均达80%以上.结论:本法研制的溃结康微丸,处方合理,工艺可行.     

Re-evaluation of in vitro dissolution techniques for supersaturating drug delivery systems

Conventional dissolution testing using high-performance liquid chromatography (HPLC) analysis was evaluated against fiber optic dissolution method for studying supersaturable drug delivery systems. Two self-microemulsifying (SME) formulations of albendazole (ABZ) (15 mg/capsule and 5 mg/capsule) were prepared. Dissolution study was performed in medium with pH 1.2, 4.5, 6.8 and 7.4. Samples were analyzed simultaneously by HPLC and online fiber optic dissolution system. For 15 mg/capsule formulation, the profiles obtained using HPLC data showed almost 80-100% releases at pH 4.5, 6.8 and 7.4, whereas fiber optic data showed less than 40% release at the end of 60 min. The observed precipitation was due to pH-dependent solubility of ABZ in water and data analysis revealed a supersaturation phenomenon. This difference in release profiles was due to the presence of oil and water phase in the dissolution sample that upon dilution with high organic mobile phase resulted in quantification of the total drug and not the dissolved drug. The 5 mg/capsule formulation showed no difference in release profiles between methods as the concentration was under the saturation solubility. These results pointed out a considerable error in the development of a complex SME formulation, and use of fiber optic dissolution method was found beneficial.     

黄柏微丸的制备和体外溶出度考察

目的：制备黄柏微丸并进行处方优化,考察微丸的体外溶出度。方法：用挤出滚圆造粒机制备黄柏微丸,优化制剂处方组成;采用高效液相色谱法以盐酸小檗碱有为指标,对其体外溶出度进行考察。结果：制得微丸圆整度好,大小均匀,收率在82%以上。盐酸小檗碱的溶出度60min内达88%以上。结论：本法研制的黄柏微丸,处方合理,工艺可行。     

Feasibility, stability and release performance of a time-dependent insulin delivery system intended for oral colon release

The aim of the present work was to evaluate the viability of a time-dependent delivery platform (Chronotopic^TM) in preparing an insulin-based system intended for oral colon delivery. The main objectives were to assess the influence of the manufacturing process and storage conditions on the protein stability. Insulin-loaded cores were manufactured by direct compression and were subsequently coated with hydroxypropyl methylcellulose (HPMC) in a top-spray fluid bed up to increasing weight gains, namely 20%, 60% and 100%. In order to evaluate the impact the operating conditions may have on the protein integrity, insulin and its main degradation products (A21-desamido insulin - A21, Other Insulin-Related Compounds - OIRCs, and High-Molecular Weight Proteins - HMWPs) were assayed on samples collected after each process step by chromatographic methods. Furthermore, long-term (4 °C) and accelerated (25 °C-60% RH) stability studies were carried out on tablet cores and coated systems by assessing insulin, A21, OIRC and HMWP percentages throughout a one-year storage period. In addition, the in vitro release behaviour was investigated during the same study period. The overall results indicated that the manufacturing process is not detrimental for insulin integrity and that 4 °C storage temperature alters neither the protein content nor the release performances of the device.It was therefore concluded that insulin-containing systems intended for oral colon delivery can be obtained by the Chronotopic^TM technology.     

Eligen insulin--a system for the oral delivery of insulin for diabetes

The oral administration of insulin is difficult to achieve because the large peptide hormone is poorly absorbed and is subjected to enzymatic and acidic degradation in the stomach. Emisphere Technologies Inc is developing formulations of insulin co-administered with a drug delivery agent. With the proprietary Eligen technology employed, the carrier agent appears to form a conformational complex with insulin that can protect against degradation and facilitate the absorption of the hormone through the intestinal wall. In animal studies and phase I clinical trials, dosing with Eligen insulin led to a rapid elevation of plasma insulin and subsequent decrease in plasma glucose levels; the onset of activity was more rapid and insulin concentrations were higher with Eligen insulin than with injected insulin. Formulations of Eligen insulin have been well tolerated in all clinical trials performed to date. In a phase II clinical trial in patients with type 2 diabetes, Eligen insulin in combination with metformin failed to achieve significant superior glycemic control over treatment with metformin alone. Eligen oral insulin formulations may have potential as prandial insulin therapies in patients with either type 1 or type 2 diabetes; however, no clinical trials for such treatments appeared to be ongoing at the time of publication.