pH-Sensitive oral insulin delivery systems using Eudragit microspheres

In this paper, we present in vitro and in vivo release data on pH-sensitive microspheres of Eudragit L100, Eudragit RS100 and their blend systems prepared by double emulsion-solvent evaporation technique for oral delivery of insulin. Of the three systems developed, Eudragit L100 was chosen for preclinical studies. Insulin was encapsulated and in vitro experiments performed on insulin-loaded microspheres in pH 1.2 media did not release insulin during the first 2?h, but maximum insulin was released in pH 7.4 buffer media from 4 to 6?h. The microspheres were characterized by scanning electron microscopy to understand particle size, shape and surface morphology. The size of microspheres ranged between 1 and 40?µm. Circular dichroism spectra indicated the structural integrity of insulin during encapsulation as well as after its release in pH 7.4 buffer media. The in vivo release studies on diabetic-induced rat models exhibited maximum inhibition of up to 86%, suggesting absorption of insulin in the intestine.     

pH-Sensitive and mucoadhesive microspheres for duodenum-specific drug delivery system

Particulate systems that could deliver drug specifically to duodenum have not yet been reported. The aim of this study was to develop a novel duodenum-specific drug delivery system based on thiolated chitosan and hydroxypropyl methylcellulose acetate maleate (HPMCAM) for the duodenal ulcer application. Berberine hydrochloride was used as model drug. Thiolated chitosan was synthesized and further used for the preparation of mucoadhesive microspheres. HPMCAM, which is insoluble below pH 3.0 was synthesized and used for the coating of thiolated chitosan microspheres (TCM). The resulting thiolated chitosan immobilized on chitosan was 268.21?±?18 μmol/g. In vitro mucoadhesion study showed that the mucoadhesion property of TCM was better than that of chitosan microspheres. Morphological observation showed that the HPMCAM coating would maintain its integrity in simulated gastric fluid (SGF) for 2?h and dissolved quickly in simulated pathological duodenal fluid (SPDF; pH 3.3). In vitro drug release studies showed that only 4.75% of the drug was released in SGF for 2?h, while nearly 90% of the drug was released within 6?h after transferring into SPDF.     

Mucoadhesive and pH-sensitive thiolated Eudragit microspheres for oral delivery of Pasteurella multocida antigens containing dermonecrotoxin

In this study, cysteine was conjugated to the Eudragit to have mucoadhesive and pH-sensitive properties. Pasteurella multocida dermonecrotoxin (PMT) is a major virulence factor as a causative agent of atrophic rhinitis (AR) in swine and, therefore, inactivated P. multocida was used as a candidate vaccine in the current study. PMT-loaded thiolated Eudragit microspheres (TEMS) prepared using W/O/W emulsion-solvent evaporation method were characterized to assess their efficacy in oral vaccination. PMT-loaded TEMS were observed as spherical shapes with smooth surfaces and average particle sizes were 5.2 +/- 0.55 microm. The loading efficiency of PMT in the TEMS was about 75.3%. A significantly higher percentage of PMT from PMT-loaded TEMS was released at pH 7.4 than at pH 1.5. Murine macrophage stimulated with PMT-loaded TEMS facilitated a gradual secretion of tumor necrosis factor-alpha and nitric oxide as immune stimulatory mediators in a time dependent manner, suggesting that the released PMT from PMT-loaded TEMS had immune stimulating activity of AR vaccine in vitro.     

Erythrocytes as oral delivery systems for human insulin

The use of different forms of human red blood cells as oral carrier systems for human insulin in vivo was the subject of this investigation. Male Wistar rats were made diabetic by a single intraperitoneal injection of streptozocin (100 mg/kg). Three days after the injection, rats were found diabetic as evidenced by elevated fasted blood glucose concentration (200 mg/dl or higher). Rats received orally one of the following (100 U, 2 ml): an insulin solution, a ghosts-insulin suspension, a vesicles-insulin suspension, a liposomes-ghosts-insulin suspension, or a liposomes-vesicles-insulin suspension. Free carrier suspensions or sodium chloride solution (0.9%) were also given orally as controls. Blood glucose concentration was determined just before administration and at 1, 2, 3, 4, 5, 6, and 7 hr post administration. The results show that all treatment groups, except liposomes-ghosts-insulin, were significantly different statistically from their respective controls (i.e., the free carriers).     

A pH-dependent colon-targeted oral drug delivery system using methacrylic acid copolymers. II. Manipulation of drug release using Eudragit L100 and Eudragit S100 combinations

Tablets containing mesalazine as a model drug were coated using various combinations of two methacrylic acid copolymers, (Eudragit® L100 and Eudragit S100) by spraying from aqueous systems. The Eudragit L100-Eudragit S100 (w/w) combinations studied were 1:0, 4:1, 3:2, 1:1, 2:3, 1:4, 1:5, and 0:1. The coated tablets were tested in vitro for their suitability for pH-dependent colon-targeted oral drug delivery. The dissolution profiles of the drug obtained from the studied tablets demonstrate that the release of the drug could be manipulated by changing the Eudragit L100-Eudragit S100 ratios in the combinations within the pH range between 6.0 and 7.0 in which the individual polymers are soluble, and a coating formulation consisting of a combination of the two polymers can overcome the issue of high gastrointestinal (GI) pH variability among individuals. The results also demonstrate the feasibility of using aqueous dispersions of Eudragit L100-Eudragit S100 combinations for coating tablets for colon-targeted delivery of drugs, and that the formulation can be adjusted to deliver drug(s) at any other desirable site of the intestinal region of the GI tract in which pH of the fluid is within the range 6.0 to 7.0. For colon-targeted delivery of drugs, the proposed combination system is superior to tablets coated with either Eudragit L100 or Eudragit S100 alone.     

Controlled drug delivery systems based on thiolated chitosan microspheres

The aim of the present study was to verify the potential of chitosan-thio-butyl-amidine (TBA) microspheres as carrier systems for controlled drug delivery. In this study microspheres were prepared utilizing water in oil (w/o) emulsification solvent evaporation technique. A concentration of 0.5% of chitosan-TBA conjugate displaying 100 µM thiol groups per gram polymer was used in the aqueous phase of the emulsion in order to prepare microspheres. The obtained non-aggregated free-flowing microspheres were examined with conventional light microscope as well as scanning electron microscopy (SEM). The microscopic images indicated that the prepared chitosan-TBA microspheres were of spherical shape and smooth surface while microparticles obtained from the unmodified chitosan were of porous structure and non-spherical shape. Particle size distribution was determined to be in the range from 1 to 59 µm. The free thiol group content of chitosan-TBA microspheres prepared with an aqueous phase of pH 2, 5, and 6.5 were determined to be 71.4, 49.4, and 8.2 µM/g polymer, respectively. Furthermore, results attained from in vitro release studies with fluorescein isothiocyanate labelled dextran (FITC-dextran) loaded chitosan-TBA microspheres showed a controlled release rate for more than three hours while the control reached the maximum peak level of release already within an hour. According to these results, chitosan-TBA microspheres seem to be a promising tool in transmucosal drug delivery for poorly absorbed therapeutic agents.     

Eudragit coating of chitosan-prednisolone conjugate microspheres and in vitro evaluation of coated microspheres

Chitosan-prednisolone conjugate microspheres (Ch-SP-MS) were prepared, and Eudragit coating was applied in order to efficiently deliver the microspheres and drug to the intestinal disease sites. The Eudragit L100-coated microspheres (Ch-SP-MS/EuL100) were examined for particle characteristics and the release of drug and Ch-SP-MS in different pH media at 37°C. Ch-SP-MS were spherical, with a mean size of 4.5 μm and prednisolone content of 3.3% (w/w). Ch-SP-MS/EuL100 were fairly spherical, with a mean size of 22. 5 μm and drug content of 0.32% (w/w). At pH 1.2, the release extent was less than 5% even at 48 h, and Eudragit coating tended to suppress the release. In contrast, at pH 6.8 and 7.4, Ch-SP-MS/EuL100 tended to show somewhat faster drug release than Ch-SP-MS. Ch-SP-MS/EuL100 displayed a release extent of 23 and 27% at pH 6.8 and 7.4, respectively. Ch-SP-MS aggregated at pH 1.2, but almost kept their initial size and shape at pH 6.8 and 7.4. Ch-SP-MS/EuL100 almost maintained their original shape and size at pH 1.2, and gradually released Ch-SP-MS at pH 6.8 and 7.4 due to dissolution of the Eudragit layer. Eudragit coating is suggested to be useful to efficiently deliver Ch-SP-MS to the intestinal disease sites.     

Eudragit S-100 entrapped chitosan microspheres of valdecoxib for colon cancer

COX-2 inhibitors have demonstrated beneficial effects in colorectal cancer. The purpose of this study was to prepare and evaluate the colon specific microspheres of COX-2 inhibitors using valdecoxib as a model drug. Mucoadhesive core microspheres were prepared using chitosan as polymer and entrapped within Eudragit S 100 for colon targeting. FTIR spectrum of selected, coated microspheres showed peaks of valdecoxib at 3377, 3250, 1334 and 1155 cm⁻¹. XRD showed amorphous character and DSC showed depressed broad endotherm of valdecoxib at 169.07°C, which may be attributed to dilution effect by the amorphous polymer. The coated microspheres were spherical with an average size of 90 μm. Storage of the microspheres at 40°C/75% relative humidity for 6 months indicated no significant drug degradation. The coated microspheres did neither release the drug in acidic pH of stomach (pH 1.2) nor in small intestinal pH between 5 to 6.8, and the release started at pH 7.4, indicting perfect colonic delivery. The coated microspheres pretreated with phosphate buffer pH 7.4 for 30 min, when applied to mucosal surface of freshly excised goat colon, showed good mucoadhesion. The drug release at pH 7.4 and good mucoadhesive property of the microspheres make the system ideal for colonic delivery.     

Acyl modified chitosan derivatives for oral delivery of insulin and curcumin

In the present investigation, bioadhesive property of chitosan (CS) was enhanced by the N-acylation with hexanoyl, lauroyl and oleoyl chlorides. The chemical structure of the modified polymer was characterized by FTIR and zeta potential measurements. The swelling ability was evaluated at alkaline pH. Mucin interactions and mucoadhesion experiments were performed under in vitro experimental conditions. Cytotoxicity experiments were employed to confirm the applicability of these particles as drug carriers. Finally in vitro evaluation of hydrophobic and hydrophilic drug release profile at acidic and alkaline pH was also conducted. A strong interaction between CS acyl derivatives and mucin was detected, which was further confirmed by an in situ mucoadhesion experiments with excised intestinal tissue. CS modified with oleoyl chloride showed better mucoadhesion property, as compared to the one modified with lower fatty acid groups. CS derivatives were found non-toxic on L-929 cell lines and provided sustained release of hydrophobic drugs under in vitro experimental conditions. From these studies it seems that hydrophobically modified CS is an interesting system for drug delivery applications.     

Calcium alginate nanocarriers as possible vehicles for oral delivery of insulin

In the present investigation, alginate nanoparticles have been prepared and characterised by various techniques such as FTIR, SEM, particle size analysis and surface charge measurements. It was found from both the SEM and particle size analysis that average size of the particle was about 40?nm. The particles were loaded with insulin and the release kinetics of insulin was studied in PBS medium. The results indicated that when percent loading increases from 11.7 to 38.9, the released amount of insulin increased from 18% to 60% of the loaded drug. The effect of composition of nanoparticles, pH and temperature of the release medium was examined on the amount of released insulin. It was observed when that amount of alginate in the feed mixture was varied from 1.0 to 2.0?g, the prepared nanoparticles showed a decreasing tendency to release insulin. Similarly, upon increasing the concentration of crosslinker in the range 0.5–1.1?mM, the release of insulin constantly decreased. The chemical stability of the loaded drug was assessed especially under highly acidic conditions of artificial gastric juice and it was noticed that even in harsh acidic environment (pH 1.2) the insulin remains chemically stable. The invitro blood compatibility of nanoparticles was also investigated and it was found that for a definite composition of nanoparticles, protein adsorption and percent haemolysis were minimum which suggested for an optimum blood compatibility of alginate nanoparticles of definite composition. Thus, it can be conclusively stated that the calcium alginate nanoparticles prepared by emulsion crosslinking method show potential to be developed as oral formulation for insulin delivery.     

Dual-controlled oral colon-targeted delivery of bovine insulin based on mesoporous phosphonate

The time- and pH-controlled oral colon-targeted delivery system for bovine insulin was developed by dip-coating lag-time films on tablet comprising bovine insulin-loaded pH-sensitive mesoporous phosphonate (ZrBPMP-3) as tablet core and absorption enhancer of insulin, sodium glycocholate, in outer layer, in which the lag time can be controlled via adjusting coating times of lag-time films and the release of bovine insulin in the colon can be triggered by pH-sensitive ZrBPMP-3. The pH transition release experiments show that the tablet with four times lag-time films coating can carry bovine insulin passing through the stomach and small intestine with a minimum release and trigger off the release of loaded bovine insulin in the colon under dual control, time control and pH value control. Furthermore, the released bovine insulin can still retain its native conformation, as evidenced by circular dichroism spectroscopy, indicating that bovine insulin cannot denature and lose its bioactive conformation during the loading, lag-time films coating, delivery and release. In addition, it is worth mentioning that ZrBPMP-3 almost exhibits non-cytotoxicity at low concentration in MTT assays. Thus, ZrBPMP-3 as a new kind of carrier and based on which developing controllable colon-targeted delivery system have potential application in oral delivery of insulin and even other therapeutic peptides and proteins.     

Transdermal delivery of propranolol using mixed grades of Eudragit: design and in vitro and in vivo evaluation

A matrix-dispersion-type transdermal drug delivery system of propranol was developed using different ratios of mixed polymeric grades of Eudragit. Formulations were evaluated for in vitro dissolution characteristics using a Cygnus' sandwich patch holder. Selected formulations followed zero-order release kinetics. In vivo evaluation was carried out on healthy human volunteers following a balanced incomplete block design (BIBD). In vitro dissolution rate constant k and pharmacokinetic parameters generated from plasma and urine were evaluated statistically. Statistically excellent correlation was found between percentages of drug absorbed from patch versus C_max, AUC_0-24, and AUC_0-∞. A highly significant difference was observed when C_max and AUC_0- generated from plasma and urine data were compared, but when k_e, t_1/2e, k_a, t_1/2awere compared, the difference was not significant. Urinary excretion data are suggested as a simpler alternative to blood-level data in studying the kinetics of absorption and deriving the absorption parameter.     

Synthesis and characterization of insulin/zirconium phosphate@TiO2 hybrid composites for enhanced oral insulin delivery applications

Abstract

In this work, a series of composites of insulin (Ins)/zirconium phosphate (ZrP) were synthesized by intercalation method, then, these composites were coated with TiO₂ by sol-gel method to prepare Ins/ZrP@TiO₂ hybrid composites and the drug release of the composites was investigated by using UV-Vis spectroscopy. Ins/ZrP (10, 30, 60?wt%) composites were prepared by intercalation of insulin into the ZrP layers in water. Then Ins/ZrP composites were coated with different amounts of TiO₂ (30, 50, 100?wt %) by using titanium tetra n-butoxide, as precursor. Formation of intercalated Ins/ZrP and Ins/ZrP@TiO₂ hybrid composites was characterized by FT-IR, FE-SEM, BET and XRD analysis. Zeta potential of the optimized Ins/ZrP@TiO₂ hybrid composite was determined ?27.2?mV. Cytotoxic effects of the optimized Ins/ZrP@TiO₂ hybrid composite against HeLa and Hek293T cell lines were evaluated using MTT assay and the results showed that designed drug delivery system was not toxic in biological environment. Compared to the Ins/ZrP composites, incorporation of TiO₂ coating enhanced the drug entrapment considerably, and reduced the drug release. The Ins/ZrP composites without TiO₂ coating released the whole drug after 30?min in pH 7.4 (phosphate buffer solution) while the TiO₂-coated composites released the entrapped drug after 20?h. In addition to increasing the shelf life of hormone, this nanoencapsulation and nanocoating method can convert the insulin utilization from injection to oral and present a painless and more comfortable treatment for diabetics.     

Towards sustained delivery of small molecular drugs using hydroxyapatite microspheres as the vehicle

The aim of this work is to explore the possibilities of using hydroxyapatite microspheres (HAP-MS) and polymer coated HAP-MS as the vehicles for the sustained release of small molecular drugs. The adsorption/desorption behaviors of model drug, doxycycline hydrochloride (Dox·HCl), on HAP-MS were systemically studied. Drug loaded HAP-MS was encapsulated by biodegradable PLGA using S/O/W emulsion–solvent evaporation method, and the in vitro drug release was tested. The adsorption kinetics of Dox·HCl onto HAP-MS fitted well to Freundlich model at lower drug concentrations, but when the HAP-MS was incubated in concentrated drug solutions higher than a critical concentration, precipitation of drug from solutions occurred. Rapid desorption or release of Dox·HCl from HAP-MS was observed. While, the release profile of Dox·HCl from PLGA coated microspheres showed steady slow drug release lasted for at least 7 days without obvious burst release. PLGA coated HAP-MS may provide a novel, injectable carrier for loading and long-period sustained release of small molecular, water-soluble drugs.     

Differentiation of preosteoblasts using a delivery system with BMPs and bioactive glass microspheres

Bone morphogenetic proteins (BMPs) and 45S5 Bioglass microspheres (bioactive GM) can increase the differentiation of osteoblasts. Recombinant human BMP-2 (rhBMP-2) is presently the BMP most frequently used in delivery systems and it has already been used in clinical bone healing studies. We have developed a delivery system that combines a collagen Type I gel, BMP and bioactive GM. Since BMP-9 seems to be more osteogenic than BMP-2, we compared the differentiation of MC3T3-E1 preosteoblasts induced by our delivery system containing either a peptide derived from BMP-9 (pBMP-9), or rhBMP-2, both at 100 ng/mL. After 5 days, alkaline phosphatase staining showed that pBMP-9 induced more differentiation than rhBMP-2 in all experimental conditions. Also, bioactive GM increased this BMP effect. Since preosteoblasts secreted matrix metalloproteinases (MMPs) that can degrade collagen, we then studied the influence of the delivery system on MMPs production. We observed that MMP-2 was the major MMP involved in all experimental conditions. In addition, pBMP-9 with bioactive GM generated less MMP-2 than did rhBMP-2 on days 3 and 5. Thus, a delivery system using collagen Type I gel with pBMP-9 and bioactive GM seems to be a promising system for bone regeneration.     

Ketoprofen spray-dried microspheres based on Eudragit RS and RL: study of the manufacturing parameters

The preparation of ketoprofen spray-dried microspheres can be affected by the long drug recrystallization time. Polymer type and drug-polymer ratio as well as manufacturing parameters affect the preparation. The purpose of this work was to evaluate the possibility to obtain ketoprofen spray-dried microspheres using the Eudragit RS and RL; the influence of the spray-drying parameters on morphology, dimension, and physical stability of microspheres was studied. Ketoprofen microspheres based on Eudragit blend can be prepared by spray-drying and the nebulization parameters do not influence significantly particle properties; nevertheless, they can be affected by drying and storage methods. No effect of the container material is found.     

Ondansetron-loaded chitosan microspheres for nasal antiemetic drug delivery: an alternative approach to oral and parenteral routes

Background: The aim of this study was to develop chitosan microspheres for nasal delivery of ondansetron hydrochloride (OND). Method: Microspheres were prepared with spray-drying method using glutaraldehyde as the crosslinking agent. Microspheres were characterized in terms of morphology, particle size, zeta potential, production yield, drug content, encapsulation efficiency, and in vitro drug release. Results: All microspheres were spherical in shape with smooth surface and positively charged. Microspheres had also high encapsulation efficiency and the suitable particle size for nasal administration. In vitro studies indicated that all crosslinked microspheres had a significant burst effect, and sustained drug release pattern was observed until 24 hours following burst drug release. Nasal absorption of OND from crosslinked chitosan microspheres was evaluated in rats, and pharmacokinetic parameters of OND calculated from nasal microsphere administration were compared with those of both nasal and parenteral administration of aqueous solutions of OND. In vivo data also supported that OND-loaded microspheres were also able to attain a sustained plasma profile and significantly larger area under the curve values with respect to nasal aqueous solution of OND. Conclusion: Based on in vitro and in vivo data, it could be concluded that crosslinked chitosan microspheres are considered as a nasal delivery system of OND.     

Enhanced oral bioavailability of tacrolimus in rats by self-microemulsifying drug delivery systems

A new self-microemulsifying drug delivery system (SMEDDS) has been developed to increase the solubility, dissolution rate and oral bioavailability of tacrolimus (TAC). The formulations of TAC-SMEDDS were optimized by solubility assay, compatibility tests, and pseudo-ternary phase diagrams analysis. In order to inhibit the efflux of P-glycoprotein (P-gp) for tacrolimus, which is the substrate of P-gp, the excipients which show the inhibition effect to P-gp, such as tocopheryl polyethylene glycol succinate (TPGS) and Cremophor EL40, were chosen in the SMEDDS formulations. According to particle size and the rate of self-emulsification, two optimized formulations were selected: Miglyol 840 as oil phase, Transcutol P as cosurfactant, TPGS as surfactant (TPGS-SMEDDS) or Cremophor EL40 as surfactant (Crem-SMEDDS), respectively. The ratio of oil phase, surfactant and cosurfactant is 1:7.2:1.8. The mean droplet size distribution of the optimized SMEDDS was less than 20?nm. The in vitro dissolution test indicated a significant improvement in release characteristics of TAC. The prepared SMEDDS was compared with the homemade solution by administering the hard capsule to fasted rats. The absorption of TAC from TPGS-SMEDDS and Crem-SMEDDS form resulted in about sevenfold and eightfold increase in bioavailability compared with the homemade solution. Our study illustrated the potential use of SMEDDS for the delivery of hydrophobic compounds, such as TAC by the oral route.     

Cyclosporine A: a review of current oral and intravenous delivery systems

As early as 1978, the immunosuppressive effect of cyclosporine A (CsA), a metabolite of the fungus Tolypocladium inflatum (Borel, 1989), was reported to be effective in inhibiting organ rejection in patients receiving kidney transplants from mismatched cadaver donors (Calne et al., 1978) and in the treatment of graft-versus-host disease in patients with acute leukemia following bone marrow transplants (Powles et al., 1978). Today, CsA is still indicated to prevent rejection following solid organ transplantations, prevent and treat graft-vs-host disease following bone marrow transplants, and has also been used in the treatment of autoimmune disease such as psoriasis, rheumatoid arthritis, and nephrotic syndrome (Canadian Pharmacists Association, 2006). The effectiveness of CsA is derived from its ability to specifically and reversibly inhibit immunocompetent lymphocytes in the G₀ and G₁ phase of the cell cycle. The T-helper cells are the main target, but suppression of the T-suppressor cells also occurs. The production and release of lymphokines, including interleukin-2 are also inhibited (Novartis, 2005a). CsA can be administered intravenously as well as orally in the form of a solution or a soft gelatin capsule. The following review will focus on the evolution of the emulsion-based oral formulations from the first generation as Sandimmune® to the second generation Neoral®, both products of Novartis Pharmaceutical, as well as on the Sandimmune® commercial intravenous formulation. The potential of alternative delivery systems, including micelles, micro- and nanoparticles, and liposomes, will also be discussed.