(C) Means to enhance penetration

Lipid Core Peptide System for Gene, Drug, and Vaccine Delivery

A vast number of biologically active compounds await efficient delivery to become therapeutic agents. Lipidation has been demonstrated to be a convenient and useful approach to improve the stability and transport across biological membranes of potential drug molecules. The lipid core peptide (LCP) system has emerged as a promising lipidation tool because of its versatile features. This review discusses the progress in the development of the LCP system to improve cell permeability of nucleotides, physicochemical properties of potential drugs, and vaccine immunogenicity. Emphasis was put on the application of the LCP system to deliver antigens for the prevention of group A streptococcus infection, novel techniques of conjugation of target molecules to the LCP, and new alterations of the LCP system itself.

New Pharmaceutical Microemulsion System for Encapsulation and Delivery of Diospyrin, a Plant-Derived Bioactive Quinonoid Compound

A new vegetable oil based oil-in-water microemulsion is developed and characterized as a prospective delivery system for in vivo application A particular weight percent composition 5/30/65 (clove oil/Tween-20/water) was selected (V1) from the clear oil-in-water zone of the pseudoternary phase diagram comprising clove oil, polyoxyethylene sorbitan monolaurate (Tween-20), and water. Two modifications of V1, (V2 and V3) were prepared by addition of dipalmitoyl phosphatidyl choline (DPPC), and a mixture of DPPC and cholesterol, respectively. A model drug diospyrin (a plantderived quinonoid compound) was encapsulated in the dispersed clove oil droplets of the three systems and designated as DV1, DV2, and DV3, respectively. The size of the dispersed clove oil droplets ranged between 9-20 nm as determined by dynamic light scattering. The stability of the vehicles, before and after encapsulation, was assessed under varying conditions of time and temperature and was found to be stable for 1 year and over a temperature range of 4-40 degrees C. The ultraviolet-visible spectrum of diospyrin after encapsulation in the compartmentalized medium remained almost identical to that dissolved in chloroform. The single-dose acute toxicity of V1 and DV1 was assessed in vivo by carrying out survival study and enzyme assay in Swiss Albino mice. The vehicle was safe at a volume of 0.05 ml when injected intraperitoneally into the mice.

Self-Microemulsifying Drug Delivery Systems (SMEDDS) for Improving In Vitro Dissolution and Oral Absorption of Pueraria Lobata Isoflavone

The aim of our investigation was to develop and characterize self-microemulsifying drug delivery systems (SMEDDS) of Pueraria lobata isoflavone to improve its in vitro dissolution and oral absorption in beagle dogs. SMEDDS consisted of oil (ethyl oleate), a surfactant (Tween 80), and a cosurfactant (Transcutol P). In all the SMEDDS, the level of Pueraria lobata isoflavone was fixed at 20% w/w of the vehicle. The in vitro self-microemulsification properties and droplet size analysis of SMEDDS were studied following their addition to water under mild agitation. A pseudoternary phase diagram was constructed identifying the efficient self-microemulsification region. From these investigations, an optimized formulation was selected and its dissolution and bioavailability were compared with a tablet formulation in beagle dogs. The in vitro dissolution rate of puerarin from SMEDDS was more than threefold faster than that from Yufengningxin tablets (Pueraria lobata isoflavone tablets). A 2.5-fold increase in the relative bioavailability was observed for the SMEDDS compared with Yufengningxin tablets. The absolute bioavailability of the SMEDDS was 82.32 +/- 15.51%, which was significantly improved compared with that of Yufengningxin tablets. These results demonstrate the potential of SMEDDS as an efficient way of improving the oral absorption of Pueraria lobata isoflavone.

Viability and permeability across Caco-2 cells of CBZ solubilized in fully dilutable microemulsions

The purpose of this study was to evaluate the viability and permeability of carbamazepine (CBZ) solubilized in fully dilutable non-ionic microemulsions across Caco-2 cells used as a model for intestinal epithelium. Maximum solubilization capacity (SC) of CBZ was determined within water-in-oil (W/O), bicontinuous and oil-in-water (O/W) structures formed upon dilution. The effect of the nature of the oil phase, surfactant type, and the ratio between the oil phase and surfactant on the quantity of solubilized CBZ, droplets size, the viability of the cells and drug permeability was elucidated. We found that: (1) several fully dilutable microemulsions based on pharma-grade ingredients can be loaded with very significant amounts of CBZ, (2) W/O microemulsions (10wt% water) exhibit up to 3-fold higher solubilization capacity over the drug's solubility in oil (triacetin), (3) CBZ in the O/W microemulsions (80wt% water) exhibit up to 29-fold higher solubilization than in water, (4) the O/W droplets of the examined systems are 9-11nm in size, (5) the highest permeability was obtained in systems containing triacetin/alpha-tocopherol acetate/ethanol in 3/1/4wt% ratio as oil phase and Tween 60 as surfactant, (6) the replacement of alpha-tocopherol acetate by alpha-tocopherol inhibits CBZ release, (7) replacement of a saturated chain of Tween 60 by an unsaturated (Tween 80) or shorter chain (Tween 40) inhibited drug release, (8) the decrease in the oil phase to surfactant ratio leads to enhancement of drug release (dilution line 64>dilution line 73).

The use of lipid-based formulations to increase the oral bioavailability of Panax notoginseng saponins following a single oral gavage to rats

PURPOSE

This article was intended to improve the absorption of ginsenoside Rg1 and Rb1 of Panax notoginseng saponins (PNS).

METHODS

PNS-Phospholipid complex and a lipid-based formulation by dissolving the complex in the medium chain fattyglycerides were prepared, and their oral relative bioavailability was determined in rats and compared with an aqueous solution of PNS for each component.

RESULTS

The study gave evidence that the phospholipids could combine with the two active constitutes of PNS and form a PNS-phospholipid complex. The complex efficiently increased the solubility of hydrophilic ginsenoside Rg1 and Rb1 in some selected hydrophobic esters, such as fatty glycerides, and constructed the lipid-based formulations of PNS. The experimental result in rats in vivo showed that the oral relative bioavailability was enhanced remarkably by these lipid-based formulations composed of the PNS-Phospholipid complex and various esters. The absorption enhancement of the medium-chain glyceride (Labrafac cc and Capmul MCM (3:1)) was somewhat greater than that of other fatty glyceride. The area under the plasma concentration-time curve (AUC) of ginsenoside Rg1 and Rb1 of the PNS-complex in the medium-chain glyceride were 27.38 microg.mL-1.h and 600.08 microg.mL-1.h, compared with 2.52 microg.mL-1.h and 92.29 microg.mL-1.h of the PNS aqueous solution, respectively.

CONCLUSIONS

The oral relative bioavailability of ginsenoside Rg1 and Rb1 of PNS was enhanced remarkably by the lipid-based formulations. These findings reveal a new strategy to increase oral bioavailability by lipophilicity enhancement for some highly water-soluble but poorly absorbed drugs.

Physical and biological considerations for the use of nonaqueous solvents in oral bioavailability enhancement

This review addresses the use of nonaqueous solvents as components of oral formulations in discovery and preclinical studies. Pharmacology, pharmacokinetic, and safety studies are frequently conducted with solution formulations that use a solvent to solubilize poorly aqueous soluble drugs. The physical chemical basis for solubilization and the precipitation of solubilized drug following administration both contribute to the utility of nonaqueous solvent solutions as oral vehicles. While many of these solvents are considered nontoxic, they are not completely inert biologically. The effects of common nonaqueous solvents on the structural integrity of the epithelia, the inherent permeability of and flux across the GI membrane, the activity of efflux and metabolic enzymes, and the effects on GI motility and GI transit times will be described through an examination of available literature. The practical relevance of these factors to the development of early formulations will be examined critically and suggestions made for the suitability of nonaqueous solvents for a variety of purposes.

Mechanistic Understanding of Oral Drug Absorption Enhancement of Cromolyn Sodium by an Amino Acid Derivative

PURPOSE

Examine the oral absorption enhancement mechanism of cromolyn sodium by sodium N-[8-(2-hydroxybenzoyl) amino] caprylate (SNAC) by evaluating the effect of SNAC on cromolyn sodium lipophilicity and changes in Caco-2 cell membrane fluidity.

MATERIALS AND METHODS

Standard Shake-flask method was used to evaluate the effect of SNAC on the lipophilicity of cromolyn sodium. The measurements were carried out in three partitioning solvents with varying hydrogen-bonding properties. Steady state fluorescence emission anisotropy technique was used to evaluate the effect of SNAC with/without cromolyn sodium on Caco-2 cell membrane fluidity.

RESULTS

The lipophilicity measurements showed that SNAC had no influence on the lipophilicity of cromolyn sodium in the three partitioning solvent systems. The findings of the steady-state fluorescence anisotropy showed that SNAC increases the membrane fluidity of the Caco-2 cells in a concentration dependent manner. The increase in fluidity with SNAC was seen in the presence and absence of cromolyn sodium and the presence of cromolyn sodium did not augment the effect of SNAC on membrane fluidity.

CONCLUSIONS

The increase in membrane fluidity by SNAC plays a pivotal role in the permeation enhancement mechanism of cromolyn sodium. Therefore, the increase in permeation is a result of changing Caco-2 cell membrane fluidity resulting in change in membrane integrity and not due to an increase in the lipophilicity of cromolyn sodium through its interaction with SNAC.

[Safe improvement of drug absorption by combinatorial use of sodium laurate with amino acids: cytoprotection by amino acids and its mechanisms]

The development of combinatorial chemistry and high-throughput screening techniques has made it possible to generate many new drug candidates very rapidly, but it has also resulted in a number of poorly soluble and/or poorly absorbable candidates. A new trend in drug development based on pharmacogenomics or the development of molecular-targeted drugs is also spurring the tendency, and it does not necessarily lead to good output in terms of the development of new drugs. It is attractive to improve membrane permeability as well as solubility by using adjuvants, because this method could be applicable for various drugs. However, the practical use of absorption-enhancing adjuvants has been limited because of the potential local toxicity. Therefore suppressing the potential local toxicity would lead to the successful development of safe preparations with improved absorption using adjuvants. Our biochemical and histopathologic studies showed that several amino acids such as taurine and L-glutamine had cytoprotective activity, and it has been found that the combinatorial use of sodium laurate (C12) with these amino acids could maintain the absorption-enhancing ability of C12. A suppository preparation containing C12 and taurine remarkably improved the rectal absorption of rebamipide, classified as BCS class IV, and the preparation was safe to the rectal mucosa. For the mechanisms of cytoprotective action by these amino acids, it has been found that they suppress the intracellular calcium level, induce the expression of heat-shock protein 70, and inhibit the release of histamine and apoptosis.

Nanoparticles as potential oral delivery systems of proteins and vaccines: a mechanistic approach

Peptides and proteins remain poorly bioavailable upon oral administration. One of the most promising strategies to improve their oral delivery relies on their association with colloidal carriers, e.g. polymeric nanoparticles, stable in gastrointestinal tract, protective for encapsulated substances and able to modulate physicochemical characteristics, drug release and biological behavior. The mechanisms of transport of these nanoparticles across intestinal mucosa are reviewed. In particular, the influence of size and surface properties on their non-specific uptake or their targeted uptake by enterocytes and/or M cells is discussed. Enhancement of their uptake by appropriate cells, i.e. M cells by (i) modeling surface properties to optimize access to and transport by M cells (ii) identifying surface markers specific to human M cell allowing targeting to M cells and nanoparticles transcytosis is illustrated. Encouraging results upon in vivo testing are reported but low bioavailability and lack of control on absorbed dose slow down products development. Vaccines are certainly the most promising applications for orally delivered nanoparticles.

Enhanced bioavailability of silymarin by self-microemulsifying drug delivery system

The main purpose of this study was to prepare lipid-based self-microemulsifying drug delivery system (SMEDDS) to improve peroral bioavailability of silymarin. SMEDDS was a system consisting of silymarin, Tween 80, ethyl alcohol, and ethyl linoleate. Particle size change of the microemulsion was evaluated upon dilution with aqueous media and loading with incremental amount of silymarin. In vitro release was investigated by a dialysis or an ultrafiltration method. Results showed that release of silymarin from SMEDDS was limited, incomplete, and typical of sustained characteristics. Pharmacokinetics and bioavailability of silymarin suspension, solution, and SMEDDS were evaluated and compared in rabbits. Plasma silybin, which was treated as the representing component of silymarin, was determined by high-performance liquid chromatography. After gavage administration of silymarin suspension, plasma silybin level was very low and fell below limit of detection 4h after. As for silymarin solution and SMEDDS, double peak of maximum concentrations were observed, which was characteristic of enterohepatic circulation. Relative bioavailability of SMEDDS was dramatically enhanced in an average of 1.88- and 48.82-fold that of silymarin PEG 400 solution and suspension, respectively. It was concluded that bioavailability of silymarin was enhanced greatly by SMEDDS. Alternative mechanisms, such as improved lymphatic transport pathway, other than improved release may contribute to enhancement of bioavailability of silymarin.

Optimization of Suppository Preparation Containing Sodium Laurate and Taurine That Can Safely Improve Rectal Absorption of Rebamipide

We previously reported that the fatty base suppository containing sodium laurate (C12) and taurine (Tau) (C12-Tau suppository) could enhance the colonic absorption of rebamipide, a poorly water-soluble and poorly absorbable drug, without any serious mucosal damages in rats. In the preset study, in order to make C12-Tau suppositories available for practical use, the scaling-up studies of animal and formulation size were performed, compared with the suppositories containing sodium caprate (C10) (C10 suppository) at the same amounts as those contained in the commercial products. Twenty-mg C12 improved the dissolution of rebamipide from suppository remarkably and the addition of 30-mg Tau only slightly decreased the dissolution rate. The absorption of rebamipide from rabbit rectum was more markedly improved by suppositories containing C12 than C10 suppositories. Although Tau tended to attenuate the absorption-enhancing effect of C12, several C12-Tau suppositories kept high bioavailability values, which were much higher than control. Histopathological studies showed that Tau exerted the cytoprotective action and that C12-Tau suppositories were better than C10 suppositories in safety. Considering the balance between efficacy and safety, the suppository containing 10- or 20-mg C12 with 30-mg Tau is better than C10 suppositories as commercial products and could be promising for practical use in human.

Polycationic lipophilic-core dendrons as penetration enhancers for the oral administration of low molecular weight heparin

Two polycationic lipophilic-core carbohydrate-based dendrons 2a-b and five polycationic lipophilic-core peptide dendrons 3-6, containing four arginine or lysine terminal residues, were synthesized and then tested in rats as penetration enhancers for the oral delivery of low molecular weight heparin. Better results were obtained with dendrons containing terminal lysine residues than terminal arginine. A significant anti-factor Xa activity was obtained when low molecular weight heparin was coadministered with dendron 5.

Correlation between epithelial toxicity and surfactant structure as derived from the effects of polyethyleneoxide surfactants on caco-2 cell monolayers and pig nasal mucosa

The cell toxic effects of nonionic surfactants were investigated by means of two in vitro models, namely pig nasal mucosa mounted in horizontal Ussing chambers, and Caco-2 cell monolayers. A series of homologous polyethyleneoxide (PEO) surfactants with a wide span in hydrophilic head-group size and hydrophobic chain lengths were screened for concentration-dependent effects on the transepithelial electrical resistance (TEER) and mannitol permeability across Caco-2 cell monolayers. Trends in effects on permeability in the presence of increasing surfactant concentration coincided with the effects seen on TEER. Correlation of surfactant molecular structure with cell toxicity showed the size of the PEO group to be a more critical parameter than the size of the hydrocarbon chain. More specifically, the presence of very long PEO groups (>30 EO units) were found to lead to a decrease in cell toxicity. Similar trends were observed in the studies of the effects of PEO surfactants on pig nasal mucosa mounted in horizontal Ussing chambers. However, the nasal mucosa was somewhat more tolerant towards high surfactant concentrations than the Caco-2 cells. The relation between surfactant molecular structure and cell toxic effects is discussed in terms of micellar surface adsorption and micellar solubilization. The effect of the surfactants on the solubility of budesonide was investigated at two different surfactant concentrations (0.01 and 1 mg/mL). At the lower concentration, the solubilizing capacity of all of the surfactants was marginal, and there was no correlation between solubilizing capacity and cmc. At the higher concentration, on the other hand, all surfactants substantially increased the solubility of budesonide. The C18 PEO-ester with 40 EO units in the head group was found to be an efficient micellar solubilizer for budesonide, without causing adverse effects on the Caco-2 cell monolayers.

Ubidecarenone nanoemulsified composite systems

The nanoemulsified composite (NEC) delivery system is a patented technology based on the incorporation of a double microemulsion into microporous carrier. This approach was applied on the very water insoluble ubidecarenone drug. The resulting composite powder showed good technological properties such as flowability; also good stability was evidentiated, with size of the nano-droplets released from the systems maintained equal to the starting size also after a long storage. Furthermore very good biopharmaceutical properties were originated, with water solubility concentrations up to 50-fold higher than pure ubidecarenone and oral absorption in rats up to three-fold greater than standard commercial products in terms of plasma levels and AUC.

Oral Delivery of Peptide Drugs

A wide variety of peptide drugs are now produced on a commercial scale as a result of advances in the biotechnology field. Most of these therapeutic peptides are still administered by the parenteral route because of insufficient absorption from the gastrointestinal tract. Peptide drugs are usually indicated for chronic conditions, and the use of injections on a daily basis during long-term treatment has obvious drawbacks. In contrast to this inconvenient and potentially problematic method of drug administration, the oral route offers the advantages of self-administration with a high degree of patient acceptability and compliance. The main reasons for the low oral bioavailability of peptide drugs are pre-systemic enzymatic degradation and poor penetration of the intestinal mucosa. A considerable amount of research has focused on overcoming the challenges presented by these intestinal absorption barriers to provide effective oral delivery of peptide and protein drugs. Attempts to improve the oral bioavailability of peptide drugs have ranged from changing the physicochemical properties of peptide molecules to the inclusion of functional excipients in specially adapted drug delivery systems. However, the progress in developing an effective peptide delivery system has been hampered by factors such as the inherent toxicities of absorption-enhancing excipients, variation in absorption between individuals, and potentially high manufacturing costs. This review focuses on the intestinal barriers that compromise the systemic absorption of intact peptide and protein molecules and on the advanced technologies that have been developed to overcome the barriers to peptide drug absorption.

Self-emulsifying drug delivery systems (SEDDS) for improved oral delivery of lipophilic drugs

The oral delivery of hydrophobic drugs presents a major challenge because of the low aqueous solubility of such compounds. Self-emulsifying drug delivery systems (SEDDS), which are isotropic mixtures of oils, surfactants, solvents and co-solvents/surfactants, can be used for the design of formulations in order to improve the oral absorption of highly lipophilic drug compounds. SEDDS can be orally administered in soft or hard gelatin capsules and form fine relatively stable oil-in-water (o/w) emulsions upon aqueous dilution owing to the gentle agitation of the gastrointestinal fluids. The efficiency of oral absorption of the drug compound from the SEDDS depends on many formulation-related parameters, such as surfactant concentration, oil/surfactant ratio, polarity of the emulsion, droplet size and charge, all of which in essence determine the self-emulsification ability. Thus, only very specific pharmaceutical excipient combinations will lead to efficient self-emulsifying systems. Although many studies have been carried out, there are few drug products on the pharmaceutical market formulated as SEDDS confirming the difficulty of formulating hydrophobic drug compounds into such formulations. At present, there are four drug products, Sandimmune and Sandimmun Neoral (cyclosporin A), Norvir (ritonavir), and Fortovase (saquinavir) on the pharmaceutical market, the active compounds of which have been formulated into specific SEDDS. Significant improvement in the oral bioavailability of these drug compounds has been demonstrated for each case. The fact that almost 40% of the new drug compounds are hydrophobic in nature implies that studies with SEDDS will continue, and more drug compounds formulated as SEDDS will reach the pharmaceutical market in the future.

Studies on the Intestinal Absorption of Low Molecular Weight Heparin Using Saturated Fatty Acids and Their Derivatives as an Absorption Enhancer in Rats

Intestinal absorption of low molecular weight heparin (LMWH) as well as unfractionated heparin (UFH) is limited due to its large molecular size and extensive negative charge. Development of its oral formulations would allow outpatient treatment with LMWH and UFH, and contribute a reduction in hospital expenses. The present study was aimed at evaluating the absorption enhancers Labrasol and Gelucire 44/14, which mainly consist of glycerides and fatty acids esters, to improve the intestinal absorption of LMWH. The absorption effects of saturated fatty acids with several carbon chain lengths (C6-C14) were also investigated. LMWH formulated with or without absorption enhancer was administered to the duodenum of fasted rats. The doses of LMWH and absorption enhancer were 20 mg/kg and 30 mg/kg, respectively. Plasma anti-Xa activity was measured as a marker of the LMWH absorption. By administration of the LMWH formulation with Labrasol but not with Gelucire 44/14, the plasma anti-Xa activity was increased to a level above 0.2 IU/ml which is the critical level for elucidation of its anticoagulant activity. Saturated fatty acids also enhanced the intestinal absorption of LMWH, and the order of absorption-enhancing effect was C10=C12>C14>C16>C8> or =C6. These results suggest that the intestinal absorption of LMWH varies with carbon chain lengths of the saturated fatty acids.

Bile salt/lecithin mixed micelles optimized for the solubilization of a poorly soluble steroid molecule using statistical experimental design

Bile salts and lecithin combine physiologically to form mixed micelles which aid the solubilization and absorption of dietary fats and drug molecules. In this series of experiments, we have shown how experimental design procedures aid the optimization of a formulation incorporating a bile salt, lecithin, and water with fluticasone propionate (FP) as the model poorly soluble drug. The initial inclusion of a categorical variable ruled out the use of classic response surface designs; therefore the experimental design was constructed using a d-optimal selection from a candidate set of all possible experimental combinations. A separate 2-factor central composite design was used to determine the optimum lecithin and bile salt concentrations over an extended range after the categorical variable had been eliminated. It has been demonstrated that an increase in either lecithin or cholic acid concentration produces an increase in solubility of FP, while sodium taurocholate appears to depress the solubility of FP compared with the other two bile salts. The increase in solubility associated with the increase in bile salt and lecithin is further demonstrated by a linear relationship between FP solubility and the total lipid in the formulation. The influence of molar ratio of lecithin to bile salt in the formulation is also significant. The physical properties of the mixed micellar system (solution turbidity and viscosity ranking) were used to further discriminate between formulations. The optimization showed that the dominant effect was the lecithin, which improves the solubilizing characteristics of the formulation with increasing concentration. The effect of salt concentration is less marked though slightly quadratic in nature. The overall increase in solubility demonstrated was from <1 microg/mL in water to 205 microg/mL in the optimized mixed micellar system.

Challenges for the oral delivery of macromolecules

The rapid integration of new technologies by the pharmaceutical industry has resulted in numerous breakthroughs in the discovery, development and manufacturing of pharmaceutical products. In particular, the commercial-scale production of high-purity recombinant proteins has resulted in important additions to treatment options for many large therapeutic areas. In addition to proteins, other macromolecules, such as the animal-derived mucopolysaccharide heparins, have also seen dramatic growth as injectable pharmaceutical products. To date, macromolecules have been limited as therapeutics by the fact that they cannot be orally delivered. This article will address the current status and future possibilities of oral macromolecular drug delivery.

Evaluation of insulin permeability and effects of absorption enhancers on its permeability by an in vitro pulmonary epithelial system using Xenopus pulmonary membrane

The permeability of insulin across Xenopus pulmonary membrane and the effects of various absorption enhancers on insulin permeability were examined using an in vitro Ussing chamber technique. Absorption enhancers used in this study were sodium caprate (NaCap), sodium glycocholate (NaGC), sodium salicylate (NaSal) and ethylenediaminetetraacetic acid disodium salt (EDTA). The permeability of insulin across Xenopus pulmonary membrane significantly increased in the presence of NaCap and NaGC, while EDTA and NaSal did not enhance the permeability. In addition, the enhancing effect of NaGC increased as the concentrations of these enhancers increased. Transmembrane resistance (Rm) of Xenopus lung was markedly decreased in the presence of these enhancers, and NaCap showed a greater effect on Rm than NaGC. Furthermore, the amount of alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) released from the apical side of the Xenopus pulmonary membrane increased in the presence of these enhancers. These results indicate that NaCap and NaGC improve the pulmonary absorption of insulin, but they are toxic to the pulmonary membrane. These findings suggest that this method is useful for estimating the permeability characteristics of peptides across the pulmonary membrane and for evaluating the effects of various additives on their permeability and their membrane toxicity.

Self-emulsifying drug delivery systems (SEDDS) of coenzyme Q10: formulation development and bioavailability assessment

The goals of our investigations are to develop and characterize self-emulsifying drug delivery systems (SEDDS) of coenzyme Q10 (CoQ10), using polyglycolyzed glycerides (PGG) as emulsifiers and to evaluate their bioavailability in dogs. Solubility of CoQ10 was determined in various oils and surfactants. SEDDS consisted of oil, a surfactant and a cosurfactant. Four types of self-emulsifying formulations were prepared using two oils (Myvacet 9-45 and Captex-200), two emulsifiers (Labrafac CM-10 and Labrasol) and a cosurfactant (lauroglycol). In all the formulations, the level of CoQ10 was fixed at 5.66% w/w of the vehicle. The in vitro self-emulsification properties and droplet size analysis of these formulations upon their addition to water under mild agitation conditions were studied. Pseudo-ternary phase diagrams were constructed identifying the efficient self-emulsification region. From these studies, an optimized formulation was selected and its bioavailability was compared with a powder formulation in dogs. Medium chain oils and Myvacet 9-45 provided higher solubility than long chain oils. Efficient and better self-emulsification processes were observed for the systems containing Labrafac CM-10 than formulations containing Labrasol. Addition of a cosurfactant improved the spontaneity of self-emulsification. From these studies, an optimized formulation consisting of Myvacet 9-45 (40%), Labrasol (50%) and lauroglycol (10%) was selected for its bioavailability assessment. A two-fold increase in the bioavailability was observed for the self-emulsifying system compared to a powder formulation. SEDDS have improved the bioavailability of CoQ10 significantly. The data suggest the potential use of SEDDS to provide an efficient way of improving oral absorption of lipophilic drugs.

Intestinal absorption of peptides through the enterocytes

Transport of intact peptides and proteins from the intestinal lumen into the blood is a unique phenomenon, which differs from the regular process of food digestion and absorption. Intestinal absorption of minute amounts of proteins is, however, being considered as a normal physiological process. It is thus important to define and understand the routes for protein transfer from the intestinal lumen to the blood and the mechanisms by which the macromolecules overcome the sieving barrier of the intestinal wall. The study on insulin has demonstrated that, upon proper introduction into the intestinal lumen, insulin is absorbed by the epithelial cells and transferred to the circulation. The peptides absorbed and transferred to the blood retained their biological activity and induced significant lowering of blood glucose levels. The efficiency of the absorption does not differ among the ileum, duodenum, and colon. Morphological examination demonstrated no alteration of the structural integrity of the epithelia, the enterocytes stay intact with well-developed microvilli, and the cells remain joined by tightly closed junctions. Application of immunocytochemistry on thin tissue sections revealed insulin antigenic sites at different locations depending on the time point. Insulin detected in the lumen of the intestinal tract is absorbed through the endosomal compartment of the epithelial cells rather than passing between cells. Internalization occurs through invaginations of the luminal plasma membrane and vesicular structures of the endosomal compartment. In 5-10 minutes, insulin is transferred to the basolateral membrane and released into the interstitial space to reach the circulation. Definition of the transcytotic pathway will contribute to a better understanding of drug delivery for potential therapeutic applications.

Effects of some non-ionic surfactants on transepithelial permeability in Caco-2 cells

The effects of the non-ionic surfactants polysorbate 20, polysorbate 60, polysorbate 85, cholesteryl poly (24) oxyethylene ether (Solulan C24) and the lanolin-based poly (16) oxyethylene ether (Solulan 16) on the epithelial integrity of monolayers of human intestinal epithelial (Caco-2) cells has been studied using metformin as a model drug. The aim was to identify the surfactants and their optimal concentrations capable of enhancing drug transport while causing no, or only minor, cellular damage. Effects on cell permeability were assessed by measurements of the transport of metformin, a hydrophilic drug, by monitoring transepithelial electrical resistance. Cell viability was determined by the diphenyltetrazolium bromide test (the MTT test). All the surfactants studied demonstrated concentration-dependent effects on cell permeability and cell viability. The effects on transepithelial electrical resistance correlated with cell viability, i.e. increased transepithelial electrical resistance and increased cell-monolayer permeability for metformin corresponded to decreased cell viability. The results indicate that the Solulan and polysorbate surfactants were active as absorption enhancers, Solulan C24 and 16 being more effective than polysorbates 20, 60 or 85, causing an increase in metformin transport at lower concentrations than the polysorbates. Polysorbate 20 exerted its greatest effect at a concentration of 5%-increasing the flux of metformin after 3 h by a factor of around 20 over the control. Large increases in the transport of metformin, especially at surfactant levels of 0.05%, 0.1% and 0.5%, were related to the effect of Solulan C24 and Solulan 16 on the cell permeability. The Caco-2 cell monolayer experiments confirmed the ability, especially of polysorbate 20, Solulan C24 and Solulan 16, to increase the absorption of metformin. The polysorbates increased permeability as a result of solubilisation of membrane components, while Solulans did so by penetrating and solubilising the membrane. Correlation between increase in membrane permeability and the toxicity of the surfactants towards the cell membrane has been established.

Transcellular uptake mechanisms of the intestinal epithelial barrier Part one

Part one of this two-part review addresses the transport of therapeutics across the intestinal barrier, and focuses on transcellular transport through the intestinal epithelia. The anatomical, biochemical and physiological parameters impacting transcellular uptake of orally administered drugs are described, and methods for overcoming obstacles limiting successful transcellular oral drug delivery are discussed. Part two will cover paracellular transport.

Design of compounds that increase the absorption of polar molecules

Hydrophilic drugs are often poorly absorbed when administered orally. There has been considerable interest in the possibility of using absorption enhancers to promote absorption of polar molecules across membrane surfaces. The bile acids are one of the most widely investigated classes of absorption enhancers, but there is disagreement about what features of bile acid enhancers are responsible for their efficacy. We have designed a class of glycosylated bile acid derivatives to evaluate how increasing the hydrophilicity of the steroid nucleus affects the ability to transport polar molecules across membranes. Some of the glycosylated molecules are significantly more effective than taurocholate in promoting the intestinal absorption of a range of drugs, showing that hydrophobicity is not a critical parameter in transport efficacy, as previously suggested. Furthermore, the most effective glycosylated compound is also far less damaging to membranes than the best bile acid absorption promoters, presumably because it is more hydrophilic. The results reported here show that it is possible to decouple absorption-promoting activity from membrane damage, a finding that should spark interest in the design of new compounds to facilitate the delivery of polar drugs.

Preparation and evaluation of a time-controlled release capsule made of ethylcellulose for colon delivery of drugs

A novel ethylcellulose (EC) capsule which releases drug with a time-controlled fashion has been prepared. This capsule is composed of four parts, drug container, swellable substance, capsule body and cap. At the bottom of the body, micropores are made. As water penetrates through these micropores, the swellable substance such as low substituted hydroxypropyl cellulose (L-HPC) swells. When the cap made of water-insoluble macromolecular substance such as EC cannot persist the swelling pressure, the EC cap disintegrates and the drug in the container is released from the capsule. The lag-time is utilized for the delivery of drug to the colon. The release time of the drug from the capsule was measured both in vitro and in vivo experiments. In the case of an in vitro experiment, after 12mg of fluorescein as a model drug and 238mg of starch were filled into the container, caps having different thickness were attached to the capsule body and release study was performed. The release time of the drug was mainly dependent on the thickness of the cap. Using test capsules of which mean cap thickness were 39.1 +/- 2.3 (SE)microns, 63.1 +/- 5.0 microns and 75.6 +/- 4.1 microns, the in vivo release time was estimated after administration to beagle dogs. As a parameter, the peak time (tmax) when plasma fluorescein concentration reached to its maximum level was determined for the estimation of the release time of the drug from the capsule in the gastrointestinal tract. The in vivo tmax was well correlated with the cap thickness.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative approaches to delineate paracellular diffusion in cultured epithelial cell monolayers

When using cultured cell monolayers to determine the mechanism of transcellular diffusion of molecules, it may be important to identify the fraction that moves through the paracellular route or passively diffuses through tight junctions. We characterized the apparent diameter of the junctional pore in a variety of epithelial cell monolayers (Caco-2, MDCK, alveolar). Using hydrophilic extracellular permeants varying in molecular radii and charge (neutral, anionic, cationic, zwitterionic), rate-determining steps and factors of the paracellular route were quantitatively delineated by the model for molecular size-restricted diffusion within a negative electrostatic field of force. Protonated amines permeated the pores faster than their neutral images while organic anions were slower. With increasing molecular size the influence of charge diminished. This approach was used to quantify the relationship between permeant radius and transepithelial electrical resistance and to analyze changes in junctional pore size as a function of pharmacological perturbation, such as in the use of absorption promoters or adjuvants.

Enhancement of intestinal insulin absorption by bile salt-fatty acid mixed micelles in dogs

The pharmacokinetics and pharmacodynamics of porcine zinc insulin following intravenous (iv), intrajejunal, and ileocolonic delivery were evaluated in dogs. The concentration-time profile of plasma immunoreactive insulin following iv injection could be best described by a two-compartment model with a mean distribution half-life of 1.1 min and a mean elimination half-life of 5.6 min. Maximum hypoglycemia occurred at 15 min after injection. Intrajejunal administration of 10 units/kg insulin in phosphate-buffered saline resulted in minimal insulin absorption or hypoglycemia. Incorporation of mixed micelles containing 30 mM sodium glycocholate and 40 mM linoleic acid significantly improved enteral insulin absorption. When delivered with mixed micelles, the mean absolute bioavailability of insulin was 1.8%. To study the effect of intestinal site on insulin uptake, the same formulation was delivered to the ileocolonic region. The mean absolute bioavailability of insulin absorbed from this site was 0.6%. Delivery of insulin to both sites caused significant hypoglycemia in all dogs. Insulin combined with mixed micelles is enterally absorbed in dogs; however, the bioavailability is much lower than that observed in similar studies with rats.

Oral administration of insulin in solid form to nondiabetic and diabetic dogs

It was previously demonstrated that a biologically active insulin could cross the mucosal membrane in the gut by using surface active substances. In this report we describe studies in which insulin administered orally, in a solid formulation, was effectively absorbed in the canine model. The insulin was mixed with cholate and soybean trypsin inhibitor. It was delivered orally, as enterocoated microtablets, to nondiabetic and diabetic (pancreatectomized) dogs in a fasting state. The time interval between the administration of the drug and the beginning of a decrease in the plasma glucose levels was 60-140 min. This decrease reached a minimum level of 20-40 % of the initial values and lasted for more than 90 min following administration of the drug. In this model a pronounced increment in plasma insulin levels was shown prior to the drop of plasma glucose concentrations. It is concluded that with this novel oral insulin formulation a beneficial biological effect can be achieved in the treatment of diabetes.

Gastrointestinal parameters that influence oral medications

The successful functioning of oral medication depends primarily on how the gastrointestinal (Gl) tract processes drugs and drug delivery systems. Parameters such as regional pH, motility (and hence residence time), and brush border and colonic microflora enzymatic activity play an important role in the performance of orally administered dosage forms. In addition, medications are required to treat disease states that alter normal functions of the body. This review (which summarizes the symposium of the same title undertaken in the 2nd Jerusalem Conference on Pharmaceutical Sciences and Clinical Pharmacology, Jerusalem, Israel, May 1992) focuses on two aspects: (1) how some physiological parameters of the intestine can be manipulated to achieve control over drug absorption (P. Bass: alteration of the paracellular space of enterocytes with glucose to modulate the passive movement of drugs; E. Ziv: intestinal absorption of insulin) and spatial placement of drugs (D.R. Friend: use of colonic beta-glucosidases to target glycoside prodrugs of steroids to the large bowel; A. Rubinstein: specific degradation of polysaccharide matrices by colonic bacteria); and (2) how abnormalities of the Gl tract affect drug performance (J.B. Dressman: physiological and pathophysiological changes in upper Gl tract pH may lead to alterations in drug bioavailability; W. A. Ritschel: influence of diseases on the pharmacokinetics of drugs).