Supra-molecular association and polymorphic behaviour in systems containing bile acid salts

In situ interaction of pea peptides and bile salts under in vitro digestion: Potential impact on lipolysis

The present work evaluated how a native pea protein isolate (PPI) affects the key roles carried out by bile salts (BS) in lipid digestion by means of the in vitro static INFOGEST protocol. Two gastric residence times were evaluated (10 and 60 min), and then the peptides obtained (GPPP) were mixed with BS at physiological concentration in simulated intestinal fluid to understand how they interact with BS both at the bulk and at the interface. Both GPPP give rise to a film with a predominant viscous character that does not constitute a barrier to the penetration of BS, but interact with BS in the bulk duodenal fluid. When the peptides flushing from the stomach after the different gastric residence times undergo duodenal digestion, it was found that for the longer gastric residence time the percentage of soluble fraction in the duodenal phase, that perform synergistically with BS micelles, was twice that of the lower residence time, leading to an increase in the solubilization of oleic acid. These results finally lead to a greater extent of lipolysis of olive oil emulsions. This work demonstrates the usefulness of in vitro models as a starting point to study the influence of gastric residence time of pea protein on its interaction with BS, affecting lipolysis. Pea proteins were shown to be effective emulsifiers that synergistically perform with BS improving the release and bioaccessibility of bioactive lipids as olive oil.

Potentials and limitations of pharmaceutical and pharmacological applications of bile acids in hearing loss treatment

Hearing loss is a worldwide epidemic, with approximately 1.5 billion people currently struggling with hearing-related conditions. Currently, the most wildly used and effective treatments for hearing loss are primarily focus on the use of hearing aids and cochlear implants. However, these have many limitations, highlighting the importance of developing a pharmacological solution that may be used to overcome barriers associated with such devices. Due to the challenges of delivering therapeutic agents to the inner ear, bile acids are being explored as potential drug excipients and permeation enhancers. This review, therefore, aims to explore the pathophysiology of hearing loss, the challenges in treatment and the manners in which bile acids could potentially aid in overcoming these challenges.

Using Nuclear Magnetic Resonance Spectroscopy to Probe Hydrogels Formed by Sodium Deoxycholate

Hydrogels of bile acids and their salts are promising materials for drug delivery, cellular immobilization, and other applications. However, these hydrogels are poorly understood at the molecular level, and further study is needed to allow improved materials to be created by design. We have used NMR spectroscopy to probe hydrogels formed from mixtures of formic acid and sodium deoxycholate (NaDC), a common bile acid salt. By assaying the ratio of deoxycholate molecules that are immobilized as part of the fibrillar network of the hydrogels and those that can diffuse, we have found that 65% remain free under typical conditions. The network appears to be composed of both the acid and salt forms of deoxycholate, possibly because a degree of charge inhibits excessive aggregation and precipitation of the fibrils. Spin-spin relaxation times provided a molecular-level estimate of the temperature of gel-sol transition (42 °C), which is virtually the same as the value determined by analyzing macroscopic parameters. Saturation transfer difference (STD) NMR spectroscopy established that formic acid, which is present mainly as formate, is not immobilized as part of the gelating network. In contrast, HDO interacts with the network, which presumably has a surface with exposed hydrophilic groups that form hydrogen bonds with water. Moreover, the STD NMR experiments revealed that the network is a dynamic entity, with molecules of deoxycholate associating and dissociating reversibly. This exchange appears to occur preferentially by contact of the hydrophobic edges or faces of free molecules of deoxycholate with those of molecules immobilized as components of the network. In addition, DOSY experiments revealed that gelation has little effect on the diffusion of free NaDC and HDO.

Advances in self-assembled injectable hydrogels for cancer therapy

Non-specific toxicity of chemotherapeutics and evolution of malignant tumors against them are major challenges for existing cancer chemotherapeutic regimens. Engineering of nanomaterials has attempted to minimize the toxicity of anticancer drugs, but systemic delivery of these nanomaterials still imposes many hurdles in their clinical use like burst release of chemotherapeutics and toxicity and immunogenicity associated with excipients of nanomaterials. However, there has been a surge in the development of natural and synthetic nanomaterials to deliver anticancer agents to the diseased (tumor) site as it can minimize the systemic circulation of anticancer drugs and reduce the toxicity-related challenges. Therefore, localized drug delivery is considered as the most effective way to deliver therapeutics but is further challenged by poor biodegradability, high immunogenicity, poor drug entrapment efficacy and inability to maintain sustained release of anticancer agents at the tumor site. This review maps out recent advancements in engineering of low molecular weight hydrogels derived from amino acid, fatty acyl, steroidal lipid and drug conjugated amphiphilic scaffolds. We have summarized the efforts for the development of molecular hydrogels in terms of biocompatibility, therapeutic potential and challenges associated with existing molecular hydrogels for cancer therapy.

Self-association of sodium isoursodeoxycholate and sodium isohenodeoxycholate in water

Bile salts (BS) form hydrophobic Small's primary micelles at concentrations above the critical micelle concentration (CMC), while at concentrations above 3CMC they form secondary micelles (by the association of primary micelles via H-bonds). In this paper the self-associations of the anions of isohenodeoxycholic acid (3-epimer of henodeoxycholic acid, ICD) and the anions of isoursodeoxycholic acid (3-epimer of ursodeoxycholic acid, IUD) are examined, since the thermodynamic parameters of their self-association have not yet been published. Forming of IUD aggregates with two or three building units is slightly more favorable via α sides of steroid skeletons, regarding hydrophobicity, while regarding steric repulsive interactions it is more favorable to associate via β sides. Due to this, IUD in the vicinity of the CMC can form primary micelles by association of IUD particles both from the convex side and from the concave side of the steroid ring system. Therefore, IUD is significantly more prone to initial micellization than bile salt derivatives whose steroidal skeletons contain equatorially oriented OH groups.

Studies on the interactions between bile salts and food emulsifiers under in vitro duodenal digestion conditions to evaluate their bile salt binding potential

During the last decade a special interest has been focused on studying the relationship between the composition and structure of emulsions and the extent of lipolysis, driven by the necessity of modulate lipid digestion to decrease or delay fats absorption or increase healthy fat nutrients bioavailability. Because bile salts (BS) play a crucial role in lipids metabolism, understanding how typical food emulsifiers affect the structures of BS under duodenal conditions, can aid to further understand how to control lipids digestion. In the present work the BS-binding capacity of three emulsifiers (Lecithin, Tween 80 and β-lactoglobulin) was studied under duodenal conditions. The combination of several techniques (DLS, TEM, ζ-potential and conductivity) allowed the characterization of molecular assemblies resulting from the interactions, as modulated by the relative amounts of BS and emulsifiers in solution.

Bile Acids and Their Derivatives as Potential Modifiers of Drug Release and Pharmacokinetic Profiles

Bile acids have received considerable interest in the drug delivery research due to their peculiar physicochemical properties and biocompatibility. The main advantage of bile acids as drug absorption enhancers is their ability to act as both drug solubilizing and permeation-modifying agents. Therefore, bile acids may improve bioavailability of drugs whose absorption-limiting factors include either poor aqueous solubility or low membrane permeability. Besides, bile acids may withstand the gastrointestinal impediments and aid in the transporter-mediated absorption of physically complexed or chemically conjugated drug molecules. These biomolecules may increase the drug bioavailability also at submicellar levels by increasing the solubility and dissolution rate of non-polar drugs or through the partition into the membrane and increase of membrane fluidity and permeability. Most bile acid-induced effects are mediated by the nuclear receptors that activate transcriptional networks, which then affect the expression of a number of target genes, including those for membrane transport proteins, affecting the bioavailability of a number of drugs. Besides micellar solubilization, there are many other types of interactions between bile acids and drug molecules, which can influence the drug transport across the biological membranes. Most common drug-bile salt interaction is ion-pairing and the formed complexes may have either higher or lower polarity compared to the drug molecule itself. Furthermore, the hydroxyl and carboxyl groups of bile acids can be utilized for the covalent conjugation of drugs, which changes their physicochemical and pharmacokinetic properties. Bile acids can be utilized in the formulation of conventional dosage forms, but also of novel micellar, vesicular and polymer-based therapeutic systems. The availability of bile acids, along with their simple derivatization procedures, turn them into attractive building blocks for the design of novel pharmaceutical formulations and systems for the delivery of drugs, biomolecules and vaccines. Although toxic properties of hydrophobic bile acids have been described, their side effects are mostly produced when present in supraphysiological concentrations. Besides, minor structural modifications of natural bile acids may lead to the creation of bile acid derivatives with the reduced toxicity and preserved absorption-enhancing activity.

Bile Acids and Their Derivatives as Potential Modifiers of Drug Release and Pharmacokinetic Profiles

Bile acids have received considerable interest in the drug delivery research due to their peculiar physicochemical properties and biocompatibility. The main advantage of bile acids as drug absorption enhancers is their ability to act as both drug solubilizing and permeation-modifying agents. Therefore, bile acids may improve bioavailability of drugs whose absorption-limiting factors include either poor aqueous solubility or low membrane permeability. Besides, bile acids may withstand the gastrointestinal impediments and aid in the transporter-mediated absorption of physically complexed or chemically conjugated drug molecules. These biomolecules may increase the drug bioavailability also at submicellar levels by increasing the solubility and dissolution rate of non-polar drugs or through the partition into the membrane and increase of membrane fluidity and permeability. Most bile acid-induced effects are mediated by the nuclear receptors that activate transcriptional networks, which then affect the expression of a number of target genes, including those for membrane transport proteins, affecting the bioavailability of a number of drugs. Besides micellar solubilization, there are many other types of interactions between bile acids and drug molecules, which can influence the drug transport across the biological membranes. Most common drug-bile salt interaction is ion-pairing and the formed complexes may have either higher or lower polarity compared to the drug molecule itself. Furthermore, the hydroxyl and carboxyl groups of bile acids can be utilized for the covalent conjugation of drugs, which changes their physicochemical and pharmacokinetic properties. Bile acids can be utilized in the formulation of conventional dosage forms, but also of novel micellar, vesicular and polymer-based therapeutic systems. The availability of bile acids, along with their simple derivatization procedures, turn them into attractive building blocks for the design of novel pharmaceutical formulations and systems for the delivery of drugs, biomolecules and vaccines. Although toxic properties of hydrophobic bile acids have been described, their side effects are mostly produced when present in supraphysiological concentrations. Besides, minor structural modifications of natural bile acids may lead to the creation of bile acid derivatives with the reduced toxicity and preserved absorption-enhancing activity.

Formation of a Bile Salt-Drug Hydrogel to Predict Human Intestinal Absorption

The unique character of bile salts to self-assemble into hydrogels in the presence of halide salts was exploited in this work to facilitate the prediction of human intestinal absorption (%HIA) for a set of 25 compounds. This was achieved by firstly incorporating each compound separately within the process of gel formation to create a series of gel-drug membranes. Scanning electron microscopy analysis of the freeze-dried samples of the blank bile salt hydrogels and drug-loaded bile salt hydrogels indicated a unique microstructure made of a network of intertwined fibrils. Drug-loaded sodium deoxycholate hydrogels were then utilized as the donor phase to study permeability using flow-through and static diffusion cells. The resulting values of the release-permeability coefficient (K_p) were then analyzed, along with other molecular descriptors, for the %HIA using multiple linear regression. Overall, when comparing predicted values (using the systems presented in this study) with known literature values, it can be seen that both methods (i.e., using static and flow-through cells) had good predictability with R²_PRED values of 79.8% and 79.7%, respectively. This study therefore proposes a novel, accurate, and precise way to predict HIA for compounds of pharmaceutical interest using a simple in vitro permeation system. It is important to develop alternatives to the current methods used in prediction of HIA, which are expensive and time-consuming or include the use of animals. Therefore, the proposed method in this study being economic and time-saving provides superiority over these current methods and suggests the possibility of its use as an alternate to such methods for prediction of HIA.

Gallstone-Formation-Inspired Bimetallic Supra-nanostructures for Computed-Tomography-Image-Guided Radiation Therapy

Inspired by the gallstone formation mechanism, we report a fast one-pot synthesis of high-surface-area bimetallic hierarchical supra-nanostructures. As gallstones are generated from metal cholate complexes, cholate bile acid molecules with Au/Ag metal precursors formed stable nanocomplexes aggregated with metal Au ions and preformed ~2 nm silver halide nanoparticles before reduction. When a reducing agent was added, the metal cholate nanocomplexes quickly formed noble bimetallic hierarchical supra-nanostructures. The morphology of bimetallic supra-nanostructures could be tailored by changing the feeding ratio of each metal precursor. In situ synchrotron small-angle X-ray scattering measurement with a custom-designed reaction cell showed two-step growth and attachment behavior toward hierarchical supra-nanostructures from the gallstone-formation-inspired metal cholate nanocomplexes in a 60 s reaction. Additional wide-angle X-ray scattering, X-ray absorption near-edge structure, in situ Fourier transform infrared, and high-resolution scanning transmission electron microscopy investigations subsequently revealed the mechanism for the evolution of bimetallic hierarchical supra-nanostructures. The gallstone-formation-inspired synthesis mechanism can be universally applied to other metals, for example, Pt-Ag and Pd-Ag bimetallic nanostructures. Finally, the synthesized high-surface-area bimetallic supra-nanostructures demonstrated significantly enhanced X-ray computed tomography imaging contrast and radiosensitizing effect for a potential image-guided nanomedicine application. We believe that our synthetic method inspired by gallstone formation and understanding represents an important step toward the development of hierarchical nanoparticles for various applications.

Two sides of the coin. Part 2. Colloid and surface science meets real biointerfaces

Part 1 revisited developments in lipid and surfactant self assembly over the past 40 years [1]. New concepts emerged. Here we explore how these developments can be used to make sense of and bring order to a range of complex biological phenomena. Together with Part 1, this contribution is a fundamental revision of intuition at the boundaries of Colloid Science and Biological interfaces from a perspective of nearly 50 years. We offer new insights on a unified treatment of self assembly of lipids, surfactants and proteins in the light of developments presented in Part 1. These were in the enabling disciplines in molecular forces, hydration, oil and electrolyte specificity; and in the role of non Euclidean geometries-across the whole gammut of physical, colloid and surface chemistry, biophysics and membrane biology and medicine. It is where the early founders of the cell theory of biology and the physiologists expected advances to occur as D'Arcy Thompson predicted us 100 years ago.

pKa values of hyodeoxycholic and cholic acids in the binary mixed micelles sodium-hyodeoxycholate-Tween 40 and sodium-cholate-Tween 40: Thermodynamic stability of the micelle and the cooperative hydrogen bond formation with the steroid skeleton

Due to a relatively small size of bile acid salts, their mixed micelles with nonionic surfactants are analysed. Of the special interests are real binary mixed micelles that are thermodynamically more stable than ideal mixed micelles. Thermodynamic stability is expressed with an excess Gibbs energy (G^E) or over an interaction parameter (β_ij). In this paper sodium salts of cholic (C) and hyodeoxycholic acid (HD) in their mixed micelles with Tween 40 (T40) are analysed by potentiometric titration and their pKa values are determined. Examined bile acids in mixed micelles with T40 have higher pKa values than free bile acids. The increase of ΔpKa acid constant of micellary bound C and HD is in a correlation with absolute values of an interaction parameter. According to an interaction parameter and an excess Gibbs energy, mixed micelle HD-T40 are thermodynamically more stable than mixed micelles C-T40. ΔpKa values are higher for mixed micelles with Tween 40 whose second building unit is HD, related to the building unit C. In both micellar systems, ΔpKa increases with the rise of a molar fraction of Tween 40 in binary mixtures of surfactants with sodium salts of bile acids. This suggests that, ΔpKa can be a measure of a thermodynamic stabilization of analysed binary mixed micelles as well as an interaction parameter. ΔpKa values are confirmed by determination of a distribution coefficient of HD and C in systems: water phase with Tween 40 in a micellar concentration and 1-octanol, with a change of a pH value of a water phase. Conformational analyses suggests that synergistic interactions between building units of analysed binary micelles originates from formation of hydrogen bonds between steroid OH groups and polyoxyethylene groups of the T40. Relative similarity and spatial orientation of C₃ and C₆ OH group allows cooperative formation of hydrogen bonds between T40 and HD - excess entropy in formation of mixed micelle. If a water solution of analysed binary mixtures of surfactants contains urea in concentration of 4M significant decreases of an interaction parameter value happens which confirms the importance of hydrogen bonds in synergistic interactions (urea compete in hydrogen bonds).

Partitioning into Colloidal Structures of Fasted State Intestinal Fluid Studied by Molecular Dynamics Simulations

We performed molecular dynamics (MD) simulations to obtain insights into the structure and molecular interactions of colloidal structures present in fasted state intestinal fluid. Drug partitioning and interaction were studied with a mixed system of the bile salt taurocholate (TCH) and 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLiPC). Spontaneous aggregation of TCH and DLiPC from unconstrained MD simulations at the united-atom level using the Berger/Gromos54A7 force fields demonstrated that intermolecular hydrogen bonding between TCH molecules was an important factor in determining the overall TCH and DLiPC configuration. In bilayered systems, these intermolecular hydrogen bonds resulted in embedded transmembrane TCH clusters. Free energy simulations using the umbrella sampling technique revealed that the stability of these transmembrane TCH clusters was superior when they consisted of 3 or 4 TCH per bilayer leaflet. All-atom simulations using the Slipids/GAFF force fields showed that the TCH embedded in the bilayer decreased the energy barrier to penetrate the bilayer (ΔG_pen) for water, ethanol, and carbamazepine, but not for the more lipophilic felodipine and danazol. This suggests that diffusion of hydrophilic to moderately lipophilic molecules through the bilayer is facilitated by the embedded TCH molecules. However, the effect of embedded TCH on the overall lipid/water partitioning was significant for danazol, indicating that the incorporation of TCH plays a crucial role for the partitioning of lipophilic solutes into e.g. lipidic vesicles existing in fasted state intestinal fluids. To conclude, the MD simulations revealed important intermolecular interactions in lipidic bilayers, both between the bile components themselves and with the drug molecules.

The effect of hydroxyl moieties and their oxosubstitution on bile acid association studied in floating monolayers

Bile salt aggregates are promising candidates for drug delivery vehicles due to their unique fat-solubilizing ability. However, the toxicity of bile salts increases with improving fat-solubilizing capability and so an optimal combination of efficient solubilization and low toxicity is necessary. To improve hydrophilicity (and decrease toxicity), we substituted hydroxyl groups of several natural bile acid (BA) molecules for oxogroups and studied their intrinsic molecular association behavior. Here we present the comparative Langmuir trough study of the two-dimensional (2D) association behavior of eight natural BAs and four oxoderivatives (traditionally called keto-derivatives) floated on an aqueous subphase. The series of BAs and derivatives showed systematic changes in the shape of the compression isotherms. Two types of association could be distinguished: the first transition was assigned to the formation of dimers through H-bonding and the second to the hydrophobic aggregation of BA dimers. Hydrophobic association of BA molecules in the films is linked to the ability of forming H-bonded dimers. Both H-bond formation and hydrophobic association weakened with increasing number of hydroxyl groups, decreasing distance between hydroxyl groups, and increasing oxosubstitution. The results also show that the Langmuir trough method is extremely useful in selecting appropriate BA molecules to design drug delivery systems.

Formation and dynamics of "waterproof" photoluminescent complexes of rare earth ions in crowded environment

Understanding behavior of rare-earth ions (REI) in crowded environments is crucial for several nano- and bio-technological applications. Evolution of REI photoluminescence (PL) in small compartments inside a silica hydrogel, mimic to a soft matter bio-environment, has been studied and explained within a solvation model. The model uncovered the origin of high PL efficiency to be the formation of REI complexes, surrounded by bile salt (DOC) molecules. Comparative study of these REI-DOC complexes in bulk water solution and those enclosed inside the hydrogel revealed a strong correlation between an up to 5×-longer lifetime of REIs and appearance of the DOC ordered phase, further confirmed by dynamics of REI solvation shells, REI diffusion experiments and morphological characterization of microstructure of the hydrogel.

Wittig reaction (with ethylidene triphenylphosphorane) of oxo-hydroxy derivatives of 5β-cholanic acid: Hydrophobicity, haemolytic potential and capacity of derived ethylidene derivatives for solubilisation of cholesterol

Bile acid salts are biosurfactants which form mixed micelles with phospholipids in vertebrates. These mixed micelles are suitable for solubilisation of cholesterol. For therapeutic purposes some bile acid salts as sodium ursocholate are used. However, bile acid anions possess low capacity for solubilisation of cholesterol. Thus, synthesis of more hydrophobic and less membranotoxic bile acid derivatives is of the great interest. In this paper Wittig reaction between ethylidene triphenylphosphorane and different bile acids oxo derivatives is examined. Wittig reaction of bile acids has not been studied much. C12 oxo group is inert in this reaction. If Wittig reaction happens on C7 oxo group stereospecifically E ethylidene stereoisomer is obtained, while the same reaction on C3 oxo group leads to more reactive not sterospecific product. In this paper stereochemical course of investigated Wittig reactions is thoroughly analysed. Hydrophobicity of derived products is determined over the temperature (T) dependence on retention coefficients (k) in reversed phase high resolution chromatography. Using method of principle components on k=f(T) matrix it is found that values of first principle components best describe hydrophobicity of analysed bile acids, while the second principal component is responsible for their hydrophilicity. By in silico molecular descriptors: valence connectivity index of order 3 (X3v) and packing density index (PDI), linear regression equations are obtained that can be used to predict hydrophobicity (over retention coefficient) of bile acids that belong to set of more congeneric groups. Membranotoxicity is determined by haemolytic potential. Monoethylidene derivatives of bile acids (in the form of anions) have lower membranotoxicity than deoxycholic acids anion. Sodium salt of deoxycholic acid 7-ethylidene derivative has 11% greater capacity for solubilisation of cholesterol monohydrate than sodium salt of deoxycholic acid.

Mixed micelles of sodium cholate and sodium dodecylsulphate 1:1 binary mixture at different temperatures--experimental and theoretical investigations

Micellisation process for sodium dodecyl sulphate and sodium cholate in 1∶1 molar ratio was investigated in a combined approach, including several experimental methods and coarse grained molecular dynamics simulation. The critical micelle concentration (cmc) of mixed micelle was determined by spectrofluorimetric and surface tension measurements in the temperature range of 0–50°C and the values obtained agreed with each other within the statistical error of the measurements. In range of 0–25°C the cmc values obtained are temperature independent while cmc values were increased at higher temperature, which can be explained by the intensive motion of the monomers due to increased temperature. The evidence of existing synergistic effect among different constituent units of the micelle is indicated clearly by the interaction parameter (β_1,2) calculated from cmc values according to Rubingh. As the results of the conductivity measurements showed the negative surface charges of the SDS-NaCA micelle are not neutralized by counterions. Applying a 10 µs long coarse-grained molecular dynamics simulation for system including 30-30 SDS and CA (with appropriate number of Na⁺ cations and water molecules) we obtained semi-quantitative agreement with the experimental results. Spontaneous aggregation of the surfactant molecules was obtained and the key steps of the micelle formation are identified: First a stable SDS core was formed and thereafter due to the entering CA molecules the size of the micelle increased and the SDS content decreased. In addition the size distribution and composition as well as the shape and structure of micelles are also discussed.

Formation and properties of gels based on lipo-plexes

Aqueous systems containing sodium taurodeoxycholate and, eventually, soybean lecithin were investigated. Depending on the relative amounts of two such species, molecular, micellar, vesicular, liquid crystalline, and solid phases were formed. In the presence of bovine serum albumin, micellar and vesicular systems form lipo-plexes. The latter self-organize into gels, depending on composition and thermal treatments. According to scanning electron microscopy, vesicle-based gels obtained from lipo-plexes form sponge-like entities, whereas micelle-based ones self-arrange in fibrous organizations. Gels are characterized by a significant viscoelasticity in a wide temperature and frequency range. Rheological data were interpreted by assuming strict relations between the system response and the self-organization of the lipo-plexes into gels. It was inferred that differences in the gel properties depend on the different self-assembly modes of the aggregates formed by the mentioned lipo-plexes. Use of the above systems in biomedical applications, mostly in the preparation of matrices requiring the use of smart and biocompatible gels, is suggested.

Comparison of solubilization capacity of resveratrol in sodium 3α, 12α -dihydroxy-7-oxo-5 β-cholanoate and sodium dodecyl sulfate

In this study we investigated resveratrol (trans-3,5,4'-trihydroxystilbene) solubilization with sodium 3α,12 α-dihydroxy-7-oxo-5 β-cholanoate (S7-OD) and sodium dodecyl sulfate (SDS). The investigation was aimed at determining whether large spherical micelles (SDS) or small longitudinal micelles (S7-OD) are more convenient for incorporation of resveratrol. Also, we studied resveratrol behavior in mixed micelles with mentioned surfactants using spectroflourimetric method as well as the effects of sodium chloride and urea on resveratrol solubilization capacity in the applied surfactants. Resveratrol solubilization curve was different in the investigated surfactants. Resveratrol solubilization curve for sodium 3α,12 α-dihydroxy-7-oxo-5 β-cholanoate at concentration 0.9 CMC reached saturation level of 60% dissolved resveratrol. The curve for sodium dodecyl sulfate was linear within the whole range of the investigated concentration; resveratrol solubilization rate reached 13% at 2 CMC. In S7-OD, NaCl increased capacity of resveratrol solubilization up to 1.4 CMC surfactant concentration, whilst maximum level of dissolved resveratrol (90%) was observed at 0.9 CMC. In SDS, NaCl decreased resveratrol solubilization capacity. Urea reduced resveratrol solubilization rate in sodium 3α ,12 α-dihydroxy-7-oxo-5 β-cholanoate, whereas it had inverse effect in sodium dodecyl sulfate. The obtained results strongly suggest that structure, that is, shape, of the surfactant micelles significantly affects their capacity of resveratrol solubilization. Also, presence of NaCl and urea influences solubilization capacities of investigated surfactants.

Synthesis and quantitative structure-property relationships of side chain-modified hyodeoxycholic acid derivatives

Bile acids have emerged as versatile signalling compounds of a complex network of nuclear and membrane receptors regulating various endocrine and paracrine functions. The elucidation of the interconnection between the biological pathways under the bile acid control and manifestations of hepatic and metabolic diseases have extended the scope of this class of steroids for in vivo investigations. In this framework, the design and synthesis of novel biliary derivatives able to modulate a specific receptor requires a deep understanding of both structure-activity and structure-property relationships of bile acids. In this paper, we report the preparation and the critical micellization concentration evaluation of a series of hyodeoxycholic acid derivatives characterized by a diverse side chain length and by the presence of a methyl group at the alpha position with respect to the terminal carboxylic acid moiety. The data collected are instrumental to extend on a quantitative basis, the knowledge of the current structure-property relationships of bile acids and will be fruitful, in combination with models of receptor activity, to design and prioritize the synthesis of novel pharmacokinetically suitable ligands useful in the validation of bile acid-responsive receptors as therapeutic targets.

Physicochemical Study of Bile Salt-Polymer Micellar Aggregates

The micellar behavior of Sodium Deoxycholate (NaDC), a bile salt in presence of a neutral water soluble polymer Poly(vinylpyrrolidone) (PVP) has been investigated at four different temperatures (10–40 ºC) using conductometric, tensiometric, viscometric and fluorometric methods. NaDC is found to associate co-operatively with the polymer beyond a critical concentration, saturate the polymer completely and then undergo micellization at a higher concentration. The counter-ion binding capacity to the micelles is considerably reduced in presence of PVP. The thermodynamic properties of micellization and interfacial adsorption depend on the polymer concentration and the entropic contributions are observed to control the complexation process. The NaDC-PVP aggregate exhibits polyelectrolytic behavior. The aggregation number (N) and polarity index (I1/I3) of the NaDC-PVP mixed entities have been explored by pyrene fluorescence probing technique. The values of N and I1/I3 are found to be affected by [PVP] and temperature: the N values decrease with temperature while those of I1/I3 show increasing trend. The dependence of N and I1/I3 values on [PVP] and temperature reveal interesting insights into the NaDC-PVP complexation phenomenon.

The role of bile salts in digestion

Bile salts (BS) are bio-surfactants present in the gastrointestinal tract (GIT) that play a crucial role in the digestion and absorption of nutrients. The importance of BS for controlled release and transport of lipid soluble nutrients and drugs has recently stimulated scientific interest in these physiological compounds. BS are so-called facial amphiphiles showing a molecular structure that is very distinct from classical surfactants. This peculiar molecular structure facilitates the formation of dynamic aggregates able to solubilise and transport lipid soluble compounds. The detergent nature of BS has been studied in the literature, mostly concentrating on the self-assembly behaviour of BS in solution but also in relation to protein denaturation and its effect on improving proteolysis. In contrast, the affinity of BS for hydrophobic phases has received less attention and studies dealing directly with the interfacial behaviour of BS are very limited in the literature. This is despite the fact that the interfacial activity of BS plays a vital role in fat digestion since it is closely involved with lypolisis. BS adsorb onto fat droplets and can remove other materials such as proteins, emulsifiers and lipolysis products from the lipid surface. The unusual surface behaviour of BS is directly related to their intriguing molecular structure and further knowledge could provide an improved understanding of lipid digestion. This review aims to combine the new insights gained into the surface properties of BS and their role in digestion. A better understanding of surface activity of BS would allow manipulation of physico-chemical and interfacial properties to modulate lipid digestion, improve bioavailability of lipid soluble nutrients and reduce absorption of saturated fats, cholesterol and trans fats.

A contribution to the study of hydrophobicity (lipophilicity) of bile acids with an emphasis on oxo derivatives of 5β-cholanoic acid

Due to their promotory action on the transport of some drugs through various membranes (lipophilic barriers), oxo derivatives of bile acids have recently been increasingly used in biopharmacy. These compounds exhibit also a lower membranolytic (toxic) activity than their hydroxy analogues. Because of that it is of special importance to find out the descriptors that would adequately describe the structure of bile acids and their biological activity and be used to model the quantitative structure-activity relationship. In view of this, the present work is concerned with the application of the chromatographic parameter RM0 obtained by normal-phase thin-layer chromatography in the solvent system toluene-butanol and silica gel as stationary phase to describe the lipophilicity of bile acids. Also, the work introduces a new molecular descriptor (ND) that reflects both 2D and 3D topological characteristics of the molecule. Between the retention constant, RM0 and the descriptor ND there is a good correlation, and both RM0, and ND describe sufficiently well the structural (conformational) changes that arise in the process of oxidation of the OH group of the steroid skeleton to an oxo group. On the other hand, the in silico descriptors of lipophilicity, logP (atomic-based prediction) and ClogP (fragment-based prediction) predict the hydrophobicity of bile acid oxo derivatives with a certain error.

QSPR study of the effect of steroidal hydroxy and oxo substituents on the critical micellar concentration of bile acids

Measurements of the fluorescence intensity of 1,6-diphenylhexatriene (DPH) as a probe molecule allowed the determination of critical micellar concentrations (CMCs) for 30 bile acid (BA) molecules belonging to three linear congeneric groups, with three (Group I) and two (Group II) oxygen atoms from OH or oxo groups bound to the steroid skeleton, and glyco conjugated cholic acid and glyco conjugated cholic acid derivatives (Group III). The CMC values are related to the structure of the steroid nucleus by constructing novel molecular descriptors with 2D and 3D characteristics of topological descriptors. Namely, with conventional topological descriptors (first-order connectivity index, third-order connectivity index, Wiener-index, Balaban-index, molecular topological index, cluster count, etc.) BA molecules from the same congeneric group have identical values, so that these descriptors cannot be used to form a new model for the given congeneric group. The linear regressions (models) obtained in this work for each congeneric group relate the CMCs to this new descriptor. Statistical parameters of these models, as well as their predictivity, indicate the significance of the obtained equations, that is that the micelle formation is influenced not only by the number of OH and oxo groups in the steroid nucleus but also by their steric environment.

Effect of sodium salts of 3α,12α-dihydroxy-7-oxo-5β-cholanoic and 3,7,12-trioxo-5β-cholanoic acids on verapamil hydrochloride in biophysical-chemical model experiments

It is known that certain bile acids have a promotive effect on the action of some drugs. Special attention is paid to bile acids having oxo groups instead of OH groups in the steroid skeleton of their molecule, since these derivatives have a lower hemolytic potential (membrane toxicity). This study examined the effects of sodium salts of 3?,12?-dihydroxy-7-oxo-5?-cholanoic acid (7-oC) and 3,7,12-trioxo-5?- cholanoic acid (3,7,12-toC) on the adsorption of verapamil hydrochloride on activated carbon (model of the cell membrane). The interaction was followed by measuring the effect of verapamil on the functional dependence between the spin-lattice relaxation time T1 (protons of the C18 angular group of the bile acid molecule) and the bile acid concentration in deuterated chloroform (model of the cell membrane lipid phase). Whether a depot effect of verapamil exists when 7-oC and 3,7,12-toC (in the form of methyl esters) are present in chloroform was also investigated. It was found that 7-oC exhibited a significant effect in the experiments with verapamil, whereas 3,7,12-toC showed no difference of the measured parameters with respect to the control. This indicates that bile acid molecules should have OH groups bound to the steroid nucleus, in order to exhibit an effect on the monitored physico-chemical parameters of verapamil.