Wetting properties of bile salt solutions and dissolution media

Characterization of luminal contents from the fasted human proximal colon

To treat colonic diseases more effectively, improved therapies are urgently needed. In this respect, delivering drugs locally to the colon is a key strategy to achieve higher local drug concentrations while minimizing systemic side effects. Understanding the luminal environment is crucial to efficiently develop such targeted therapies and to predict drug disposition in the colon. In this clinical study, we collected colonic contents from an undisturbed fasted proximal colon via colonoscopy and characterized their composition with regard to drug disposition. Colonic pH, osmolality, protein content, bile salts, lipids, phospholipids and short-chain fatty acids were investigated in 10 healthy volunteers (8 male and 2 female, age 19-25). The unique environment of the proximal colon was reflected in the composition of the sampled luminal fluids and the effect of the microbiota could be observed on the pH (median 6.55), the composition of bile salts (majority deconjugated and secondary), and the abundance of short-chain fatty acids. At the same time, an increase in phospholipid concentration, osmolality and total protein content compared to reported ileal values was seen, likely resulting from desiccation. Lipids could only be found in low quantities and mainly in the form of cholesterol and free fatty acids, showing almost complete digestion and absorption by the time luminal contents reach the colon. All characteristics also displayed the considerable intersubject variability found in different regions of the gastrointestinal tract. This study contributes to an improved understanding of the luminal conditions in the proximal colon and facilitates the development of new predictive tools to study colonic drug absorption.

Novel polysaccharides-bile acid-cyclodextrin gel systems and effects on cellular viability and bioenergetic parameters

Aim: The novel hydrogel systems made from sodium alginate, pectin, beta-cyclodextrin and deoxycholic acid (DCA) were proposed as potential drug-delivery matrices. Materials & methods: To ensure biocompatibility, rheological parameters were examined and hydrogels' effects on bioenergetic parameters and cellular viability on murine hepatic, and muscle and pancreatic beta cells. Results & conclusion: All hydrogels show non-Newtonian, shear thinning behavior. Cells displayed various oxygen-dependent viability patterns, with the bile acid overall adversely affecting their biological activities. All cells performed best under normoxia, with pancreatic beta cells displaying the most profound oxygen-dependent viability behavior. The cells tolerated the addition of a moderate concentration of beta-cyclodextrin to the polymer matrix.

The effect of buffer species on biorelevant dissolution and precipitation assays - Comparison of phosphate and bicarbonate buffer

Biorelevant solubility and dissolution testing is an important tool during pharmaceutical development, however, solubility experiments performed using biorelevant media often do not properly match the solubility data observed in human intestinal fluids. Even though the bicarbonate buffer is the predominant buffer system in the small intestine, in vitro assays are commonly performed using non-volatile buffer systems like phosphate and maleate. In the current study, bicarbonate- and phosphate-buffered biorelevant media were applied to solubility, dissolution, and precipitation testing for a broad range of model compounds. It was found that the medium affects primarily the dissolution kinetics. However, with the knowledge of the unique buffering properties of bicarbonate buffer in the diffusion layer, it was not always possible to predict the effect of buffer species on solubility and dissolution when changing from phosphate to bicarbonate buffer. This once again highlights the special role of bicarbonate buffer for simulating the conditions in the human intestinal fluids. Moreover, it is necessary to further investigate the factors which may cause the differences in solubility and dissolution behavior when using phosphate- vs. bicarbonate-buffered biorelevant media.

Pharmacological and Advanced Cell Respiration Effects, Enhanced by Toxic Human-Bile Nano-Pharmaceuticals of Probucol Cell-Targeting Formulations

Bile acids have recently been studied for potential applications as formulation excipients and enhancers for drug release; however, some bile acids are not suitable for this application. Unconjugated lithocholic acid (ULCA) has recently shown drug formulation-stabilizing and anti-inflammatory effects. Lipophilic drugs have poor gut absorption after an oral dose, which necessitates the administration of high doses and causes subsequent side effects. Probucol (PB) is a highly lipophilic drug with poor oral absorption that resulted in restrictions on its clinical prescribing. Hence, this study aimed to design new delivery systems for PB using ULCA-based matrices and to test drug formulation, release, temperature, and biological effects. ULCA-based matrices were formulated for PB oral delivery by applying the jet-flow microencapsulation technique using sodium alginate as a polymer. ULCA addition to new PB matrices improved the microcapsule’s stability, drug release in vitro (formulation study), and showed a promising effect in ex vivo study (p < 0.05), suggesting that ULCA can optimize the oral delivery of PB and support its potential application in diabetes treatment.

Release and swelling studies of an innovative antidiabetic-bile acid microencapsulated formulation, as a novel targeted therapy for diabetes treatment

In previous studies carried out in our laboratory, a bile acid formulation exerted a hypoglycaemic effect in a rat model of type 1 diabetes (T1D). When the antidiabetic drug gliclazide was added to the bile acid, it augmented the hypoglycaemic effect. In a recent study, we designed a new formulation of gliclazide-deoxycholic acid (G-DCA), with good structural properties, excipient compatibility and which exhibited pseudoplastic-thixotropic characteristics. The aim of this study is to test the slow release and pH controlled properties of this new formulation. The aim is also to examine the effect of DCA on G release kinetics at various pH values and different temperatures. Microencapsulation was carried out using our Buchi-based microencapsulating system developed in our laboratory. Using sodium alginate (SA) polymer, both formulations were prepared including: G-SA (control) and G-DCA-SA (test) at a constant ratio (1:3:30), respectively. Microcapsules were examined for efficiency, size, release kinetics, stability and swelling studies at pH 1.5, 3, 7.4 and 7.8 and temperatures of 25 °C and 37 °C. The new formulation is further optimised by the addition of DCA. DCA reduced bead-swelling of the microcapsules at pH 7.8 and 3 at 25 °C and 37 °C, and even though bead size remains similar after DCA addition, the percentage of G release was enhanced at high pH values (pH 7.4 and 7.8, p < 0.01). The new formulation exhibits colon-targeted delivery and the addition of DCA prolonged G release suggesting its suitability for the sustained and targeted delivery of G and DCA to the lower intestine.

Stability and Release Kinetics of an Advanced Gliclazide-Cholic Acid Formulation: The Use of Artificial-Cell Microencapsulation in Slow Release Targeted Oral Delivery of Antidiabetics

Introduction

In previous studies carried out in our laboratory, a bile acid (BA) formulation exerted a hypoglycaemic effect in a rat model of type-1 diabetes (T1D). When the antidiabetic drug gliclazide (G) was added to the bile acid, it augmented the hypoglycaemic effect. In a recent study, we designed a new formulation of gliclazide-cholic acid (G-CA), with good structural properties, excipient compatibility and exhibits pseudoplastic-thixotropic characteristics. The aim of this study is to test the slow release and pH-controlled properties of this new formulation. The aim is also to examine the effect of CA on G release kinetics at various pH values and different temperatures.

Method

Microencapsulation was carried out using our Buchi-based microencapsulating system developed in our laboratory. Using sodium alginate (SA) polymer, both formulations were prepared: G-SA (control) and G-CA-SA (test) at a constant ratio (1:3:30), respectively. Microcapsules were examined for efficiency, size, release kinetics, stability and swelling studies at pH 1.5, pH 3, pH 7.4 and pH 7.8 and temperatures of 20 and 30 °C.

Results

The new formulation is further optimised by the addition of CA. CA reduced microcapsule swelling of the microcapsules at pH 7.8 and pH 3 at 30 °C and pH 3 at 20 °C, and, even though microcapsule size remains similar after CA addition, percent G release was enhanced at high pH values (pH 7.4 and pH 7.8, p < 0.01).

Conclusion

The new formulation exhibits colon-targeted delivery and the addition of CA prolonged G release suggesting its suitability for the sustained and targeted delivery of G and CA to the lower intestine.

The design of controlled-release formulations resistant to alcohol-induced dose dumping--a review

The concomitant intake of alcoholic beverages together with oral controlled-release opioid formulations poses a serious safety concern since alcohol has the potential to alter the release rate controlling mechanism of the dosage form which may result in an uncontrolled and immediate drug release. This effect, known as alcohol-induced dose dumping, has drawn attention of the regulatory authorities. Thus, the Food and Drug Administration (FDA) recommends that in vitro drug release studies of controlled-release dosage forms containing drugs with narrow therapeutic range should be conducted in ethanolic media up to 40%. So far, only a limited number of robust dosage forms that withstand the impact of alcohol are available and the development of such dosage forms is still a challenge. This review deals with the physico-chemical key factors which have to be considered for the preparation of alcohol-resistant controlling dosage forms. Furthermore, appropriate matrix systems and promising technological strategies, which are suitable to prevent alcohol-induced dose dumping, are discussed.

Bile salt-reinforced alginate-chitosan beads

A polymeric delayed release protein delivery system was investigated with albumin as the model drug. The polysaccharide chitosan was reacted with sodium alginate in the presence of calcium chloride to form beads with a polyelectrolyte. In this study, attempts were made to extend albumin release in the phosphate buffer at pH 6.8 from the alginate-chitosan beads by reinforcing the matrix with bile salts. Sodium taurocholate was able to prevent albumin release at pH 1.2, protecting the protein from the acidic environment and extending the total albumin release at pH 6.8. This effect was explained by an interaction between the permanent negatively charged sulfonic acid of sodium taurocholate with the amino groups of chitosan. Mild formulation conditions, high bovine serum albumin (BSA) entrapment efficiency, and resistance to gastrointestinal release seem to be synergic and promising factors toward the development of an oral protein delivery form.

Dissolution and Solubility Behavior of Fenofibrate in Sodium Lauryl Sulfate Solutions

The solubility of fenofibrate in pH 6.8 McIlvaine buffers containing varying concentrations of sodium lauryl sulfate was determined. The dissolution behavior of fenofibrate was also examined in the same solutions with rotating disk experiments. It was observed that the enhancement in intrinsic dissolution rate was approximately 500-fold and the enhancement in solubility was approximately 2000-fold in a pH 6.8 buffer containing 2% (w/v) sodium lauryl sulfate compared to that in buffer alone. The micellar solubilization equilibrium coefficient (k*) was estimated from the solubility data and found to be 30884+/-213 L/mol. The diffusivity for the free solute, 7.15x10(-6) cm2/s, was calculated using Schroeder's additive molal volume estimates and Hayduk-Laurie correlation. The diffusivity of the drug-loaded micelle, estimated from the experimental solubility and dissolution data and the calculated value for free solute diffusivity, was 0.86x10(-6) cm2/s. Thus, the much lower enhancement in dissolution of fenofibrate compared to its enhancement in solubility in surfactant solutions appears to be consistent with the contribution to the total transport due to enhanced micellar solubilization as well as a large decrease (approximately 8-fold) in the diffusivity of the drug-loaded micelle.

Enhancing intestinal drug solubilisation using lipid-based delivery systems

Lipid-based delivery systems are finding increasing application in the oral delivery of poorly water-soluble, lipophilic drugs. Whilst lipidic dose forms may improve oral bioavailability via several mechanisms, enhancement of gastrointestinal solubilisation remains argueably the most important method of absorption enhancement. This review firstly describes the mechanistic rationale which underpins the use of lipid-based delivery systems to enhance drug solubilisation and briefly reviews the available literature describing increases in oral bioavailability after the administration of lipid solution, suspension and self-emulsifying formulations. The use of in vitro methods including dispersion tests and more complex models of in vitro lipolysis as indicators of potential in vivo performance are subsequently described, with particular focus on recent data which suggests that the digestion of surfactants present in lipid-based formulations may impact on formulation performance. Finally, a series of seven guiding principles for formulation design of lipid-based delivery systems are suggested based on an analysis of recent data generated in our laboratories and elsewhere.

Influence of culture heterogeneity in cell surface charge on adhesion and biofilm formation by Enterococcus faecalis

Biofilm formation is an increasing problem in medicine, due to the intrinsic resistance of microorganisms in the biofilm mode of growth against the host immune system and antimicrobial therapy. Adhesion is an important step in biofilm formation, influenced, among other factors, by the surface hydrophobicities and charges of both the substratum and the adhering microorganisms. Enterococcus faecalis strains generally display subpopulations with different surface charges, expressed as bimodal zeta potential distributions. Two-thirds of E. faecalis strains isolated from clogged biliary stents displayed such heterogeneity of surface charges in culture. In this study, the influence of this culture heterogeneity on initial adhesion and subsequent biofilm formation was investigated. Heterogeneous strains were retained in higher numbers on polystyrene than homogeneous strains. Also, biofilm formation was much more pronounced for heterogeneous strains than for homogeneous strains. In a population enriched to display only one subpopulation, fewer bacteria were retained than in its original heterogeneous culture. Also, the enriched subpopulation formed less biofilm than its original heterogeneous culture. The presence of ox bile during adhesion resulted in fewer retained bacteria, although heterogeneous strains were still retained in significantly higher numbers than were homogeneous strains, and, in general, the presence of ox bile reduced biofilm formation. The initial adhesion and biofilm formation were independent of the presence of the gene encoding the enterococcal surface protein (esp) or the expression of gelatinase (GelE). It is concluded that heterogeneity in cell surface charge represents an advantage for bacteria in the colonization of surfaces.

Surfactant‐facilitated crystallization of dihydrate carbamazepine during dissolution of anhydrous polymorph

The influence of two structurally different anionic surfactants on the anhydrous-to-dihydrate transformation of carbamazepine (CBZ) was investigated. The surfactants studied were sodium lauryl sulfate (SLS), a surfactant commonly used in compendial dissolution methods, and sodium taurocholate (STC), an important surfactant in the solubilization and absorption of drugs and lipids in the gastrointestinal tract. Results show that both surfactants promoted the crystallization of CBZ dihydrate [CBZ(D)] during dissolution of the anhydrous monoclinic polymorph [CBZ(A)]). Examination of crystal surfaces showed that SLS facilitated the surface-mediated nucleation of CBZ(D) on CBZ(A) crystals at surfactant concentrations below the critical micelle concentration (cmc). Solubilization of a dye and related color changes provided visual evidence for adsorbed SLS assemblies on CBZ(A) crystal faces below the cmc. Above the cmc, both surfactants promoted the transformation by increasing the bulk nucleation of CBZ(D). STC changed the crystal morphology of CBZ(D) from acicular to prismatic, depending on STC concentration. Such morphology changes originate from interactions between STC and molecular structures of CBZ(D) crystal faces that interfere with the formation of a hydrogen-bonded chain of water molecules and carboxamide dimers.

Dry adsorbed emulsion: 2. Dissolution behaviour of an intricate formulation

The behaviour of a pharmaceutical form, called dry adsorbed emulsion (DAE), containing a sparingly soluble drug (i.e. theophylline) was studied for dissolution drug release kinetic, in relation with DAE structure characterisation. In vitro dissolution testings were performed under different experimental conditions (medium at pH 1.2 and 7.4, medium with or without surfactant addition, different particle sizes, discrete or densified particles). Discrete DAE particles showed an extended release, in comparison with the native drug powder, depending on both drug solubility in the medium and particle size. The relevance of dissolution data was not improved by surfactant addition (0.1% sodium lauryl sulfate: SLS). After an initial release due to theophylline of the DAE superficial layer, the dissolution followed the Higuchi model. This suggested that DAE behaved as an inert matrix, which controlled drug release by diffusion through the hydrophobic part of the DAE. Densified DAE particles showed a slower dissolution rate than discrete DAE particles, because of their weak wettability and their poor disintegrant properties due to the particulate rearrangement under pressure. Lastly in a technological point of view, DAE could be considered as a potential drug delivery system in capsules or tablets to better control bioavailability of drugs.

In vitro assessment of oral lipid based formulations

In recent years there has been an increase in interest in the utility of lipid based delivery systems, at least in part as a result of the effective development of lipid based products such as Sandimmun Neoral (cyclosporin), Norvir (ritonavir) and Fortovase (saquinavir). The development pathway for lipid based formulations, however, is still largely empirical, and in vitro models that are predictive of oral bioavailability enhancement are lacking. The use of modified dissolution media, reflecting the bile salt and phospholipid levels in the intestine, has met with some success in terms of the ability to predict the bioavailability of poorly water soluble drugs and the potential bioavailability enhancing effects of food. These approaches, however, do not have the flexibility or complexity to deal with the interactions inherent in the digestion, dispersion and solubilisation of a lipid based formulation and the coincident dissolution profile of a co-administered drug. In this review, the utility of modified dissolution media to predict the impact of food on the absorption of poorly water soluble, lipophilic drugs, is explored. These dissolution based systems are subsequently contrasted with the use of lipid digestion models which have found increasing application in assessment of the interaction of digestible dose forms with the gastrointestinal milieu.

Wetting behavior of bile salt-lipid dispersions and dissolution media patterned after intestinal fluids

The wetting properties of bile salt-lipid solutions and dispersions patterned after the contents of the upper intestine in the fed and fasted states were evaluated using poly(methyl methacrylate) (PMMA) as a model substrate. The surface tension of the solutions and their contact angles on PMMA were measured. Media compositions for the intestinal fed and fasted states were estimated on the basis of physiologic data. The effect of various individual lipids and media composition was also evaluated relative to the adhesional, immersional, and spreading stages of wetting. In micellar systems, both the type and concentration of lipid present in the bile salt solution had an influence on wetting. The wetting of media patterned after gastrointestinal contents showed marked differences with respect to the fed or fasted state compositions. For the fed state compositions, alteration of the solution pH from 7.5 to 5.0 resulted in a significant change in wetting. The surface tension of the medium representative of the fasted state was 15 mN/m higher than that of the fed state. The wetting properties of the physiologically representative media formulated in this study were markedly different compared with other media proposed in the literature. Analysis of the wetting behavior of individual lipids as a function of concentration in bile salt solutions showed that they adsorb in a manner that progressively reduces the expected wetting of the surface. The results have implications for the design and formulation of both biorelevant and surfactant-based dissolution media.