Retention of bile salts in micellar electrokinetic chromatography: relation of capacity factor to octanol-water partition coefficient and critical micellar concentration

How do different bile acid derivatives affect rat macrophage function - Friends or foes?

Due to an increased need for new immunomodulatory agents, many previously known molecules have been structurally modified in order to obtain new drugs, preserving at the same time some of the benevolent characteristics of the parent molecule. This study aimed to evaluate the immunomodulatory potential of a selected library of bile acid derivatives (BAD) using a broad spectrum of assays, evaluating rat peritoneal macrophages viability, cell membrane damage, lysosomal and adhesion function, and nitric oxide and cytokine production as a response to lipopolysaccharide stimulation. Also, in silico studies on two bile acid-activated receptors were conducted and the results were related to the observed in vitro effects. All tested BAD exerted significant toxicity in concentrations higher than 10 μM, which was determined based on mitochondria and cell membrane damage in a panel of assays. On the other hand, at lower concentrations, the tested BAD proved to be immunomodulatory since they affected lysosomal function, cell adhesion capacities and the ability to produce inflammatory cytokines in response to a stimulus. One of the compounds proved to exhibit significant toxicity toward macrophages, but also caused a concentration-dependent decrease in nitric oxide levels and was identified as a potential farnesoid X receptor agonist.

Pharmaceutical suspensions of ursodeoxycholic acid for pediatric patients: in vitro and in vivo studies

Ursodeoxycholic acid (UDCA) is used in the oral therapy of hepatobiliary cholestatic diseases. Due to UDCA low aqueous solubility, two pediatric oral suspensions (25 mg/mL) were formulated with a few excipients, suspension A (SA) and suspension B (SB) with a vehicle, including two suspending agents. Physical, chemical and microbiological stability and a rheological study were performed at three different conditions (5 °C ± 3 °C, 25 °C ± 2 °C/60% RH ± 5% RH and 40 °C ± 2 °C/75% RH ± 5% RH) for 120 days. Moreover, dissolution study, content uniformity, related substances, and a study of relative oral bioavailability were also carried out. Both suspensions were physically, chemically and microbiologically stable throughout the study. SA and SB can be stored at 25 °C and 5 °C for at least 120 days whereas SA can be kept at 40 °C for at least 90 days and SB for 120 days. They both met USP specifications for dissolution, content uniformity, and related substances. SA and SB showed an improved relative oral bioavailability compared to the solid dosage form and they both displayed similar relative oral bioavailability with no significant differences between them. The developed suspensions proved to be safe and adequate and they are ideal for pediatric use for their acceptability, accurate dose administration and treatment adherence.

Analysis of bile acids in human biological samples by microcolumn separation techniques: A review

Bile acids are a group of compounds essential for lipid digestion and absorption with a steroid skeleton and a carboxylate side chain usually conjugated to glycine or taurine. Bile acids are regulatory molecules for a number of metabolic processes and can be used as biomarkers of various disorders. Since the middle of the twentieth century, the detection of bile acids has evolved from simple qualitative analysis to accurate quantification in complicated mixtures. Advanced methods are required to characterize and quantify individual bile acids in these mixtures. This article overviews the literature from the last two decades (2000-2020) and focuses on bile acid analysis in various human biological samples. The methods for sample preparation, including the sample treatment of conventional (blood plasma, blood serum, and urine) and unconventional samples (bile, saliva, duodenal/gastric juice, feces, etc.) are shortly discussed. Eventually, the focus is on novel analytical approaches and methods for each particular biological sample, providing an overview of the microcolumn separation techniques, such as high-performance liquid chromatography, gas chromatography, and capillary electrophoresis, used in their analysis. This is followed by a discussion on selected clinical applications.

A Kinetic Approach to Determining Drug Distribution in Complex Biphasic Systems

Pharmaceutical emulsions contain multiple components, such as micellar, aqueous, and oil phases, leading to complex drug transfer and equilibrium phenomena. These complex components present challenges for the bioequivalence assessment of the drug products. The objective of the study was to develop a method that can probe the underlying mechanism and process of drug distribution. The concept of drug partitioning into biphasic systems was used to simplify the complex transfer phenomenon. A kinetic method was developed taking into account the biphasic diffusion. Using this approach, both the rate (kinetics) and the extent (equilibrium) of distribution can be determined. For method development purpose, 3 model compounds (triamcinolone acetonide, difluprednate, and cyclosporine), with expected partition coefficient values ranging from 2 to 6, were tested using the kinetic method and the traditional shake-flask method. The values obtained by the 2 methods for all compounds correlated well (r² = 0.825). Various organic and aqueous solvents which are commonly encountered in formulations were also tested to determine the impact of phase composition on drug distribution. The kinetic method was found to offer more flexibility in terms of solvent composition and can lead to better understanding for drug distribution and potential drug release in complex biphasic systems.

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.

Lithocholic acid as a biomarker of intrahepatic cholestasis of pregnancy during ursodeoxycholic acid treatment

BACKGROUND

The diagnosis and treatment of intrahepatic cholestasis of pregnancy (ICP) has important implications on fetal health. The biochemical parameter commonly used in the diagnosis of ICP is the determination of the concentration of total serum bile acids (TSBA). However, bile acid profile, especially lithocholic acid (LCA) analysis is a more sensitive and specific biomarker for differential diagnosis of this pathology and also could be an alternative to evaluate the efficiency of ursodeoxycholic acid (UDCA) for ICP treatment.

METHODS

Serum bile acid (SBA) profiles including LCA determination, were studied in 28 ICP patients using a capillary electrophoresis method. The effects of UDCA treatment on bile acid profile, were analysed in 23 out of 28 ICP patients and the two samples obtained before and 15 days after treatment were compared. Two samples taken as controls were also obtained from each of five patients without therapy.

RESULTS

A dramatic decrease in LCA concentrations and maintenance of TSBA concentrations were found in all patients after UDCA therapy, whereas SBA profiles together with LCA values did not change in patients without therapy.

CONCLUSION

We propose LCA as an alternative biomarker and a more sensitive parameter than TSBA to evaluate the effectiveness of UDCA treatment, at least in ICP patients from Argentina.

Sodium cholate aggregation and chiral recognition of the probe molecule (R,S)-1,1'-binaphthyl-2,2'-diylhydrogenphosphate (BNDHP) observed by 1H and 31P NMR spectroscopy

Bile salt micelles can be employed as a pseudostationary phase in micellar electrokinetic capillary chromatography (MEKC) separations of chiral analytes. To improve MEKC separations of chiral analytes, a molecular level understanding of micelle aggregation in the presence of analyte is needed. Here, aggregation of sodium cholate has been observed by exploiting the presence of a model analyte molecule. The 31P and 1H nuclear magnetic resonance spectroscopy (NMR) chemical shifts of (R,S)-1,1'-binaphthyl-2,2'-diylhydrogenphosphate ((R,S)-BNDHP), a model analyte in chiral MEKC separations, are demonstrated to be very sensitive to the aggregation state of the bile salt sodium cholate. In addition to probing micellar aggregation, the NMR spectral resolution of enantiomeric species is also stronglycorrelated with chiral separations in MEKC. In this work, the aggregation of sodium cholate in basic solutions (pH 12) has been observed over the concentration range 0-100 mM. The primary critical micelle concentration (cmc) was found to be 14 +/- 1 mM for basic solutions of sodium cholate. In addition, a primitive aggregate is clearly observed to form at 7 +/- 1 mM sodium cholate. The data also show pseudo-cmc behavior for secondary aggregation observed in the regime of 50-60 mM cholate. Finally, the H5-H7 edge of BNDHP is shown to be sensitive to chirally selective interactions with primary cholate micelles.

Bile acids as constituents for dental composites: in vitro cytotoxicity of (meth)acrylate and other ester derivatives of bile acids

Methacrylic derivatives of bile acids have been synthesized for use as monomers in dental composites. Polymeric dental materials are known to leach cytotoxic unreacted monomers and degradation products. In this study, the in vitro cytotoxicity of bile acids and their derivatives towards 3T3 fibroblasts has been evaluated by colorimetric MTT assay and compared with that of the common dental monomers BisGMA, UDMA and TEGDMA. In general, the bile acids and their derivatives induced mitochondrial dysfunction at similar or higher concentrations than the commercial dental monomers. Certain monomers did not influence MTT response over their entire range of solubility.

Correlation between CMC and chromatographic index: simple and effective evaluation of the hydrophobic/hydrophilic balance of bile acids

The discovery that bile acids are involved in the modulation of nuclear steroid receptors has prompted renewed interest in this field of research. Due to the nature of research in this field, a technique that enables simple and effective assessment of the hydrophobic/hydrophilic balance, thus improving and speeding up evaluations of the biological profiles of these compounds, is greatly needed. In this context, both CMC value determination and RP-HPLC mobility evaluation were explored as possible approaches. While the CMC was calculated using the noninvasive conductimetric method, the RP-HPLC mobility was assessed by measuring the retention factor at several mobile phase compositions and extrapolating back to the pure aqueous mobile phase. The correlation of the CMC with the derived chromatographic hydrophobic index phi0 was satisfactory.

Beta-blockers and benzodiazepines location in SDS and bile salt micellar systems. An ESR study

The work here described aimed to find out the location of the different species of two families of pharmaceutical substances, namely two beta-blockers (atenolol and nadolol) and two benzodiazepines (midazolam and nitrazepam) in synthetic (sodium dodecyl sulphate, SDS) and natural (bile salts-sodium cholate and sodium deoxycholate) micellar aggregate solutions. Electronic spin resonance spectroscopy studies were carried out, at 25 degrees C and at an ionic strength of 0.10 M in NaCl, using 5-, 12- and 16-doxylstearic acid probes (AS). The immobilization degree of solubilized stearic acid spin probes was found to vary with the position of the nitroxide group in the sequence 5-doxylstearic acid>12-doxylstearic acid>16-doxylstearic acid for SDS and 12-doxylstearic acid>5-doxylstearic acid>16-doxylstearic acid for both bile salts investigated. Therefore, from the rotational correlational time values obtained, it can be inferred that the structure of bile salt micelles is markedly different from that of SDS micelles and the results suggest that the bile salt micelles studied have similar structure independently of differences in the molecular structure of the respective bile salts. Drug location studies were performed at pH 4.0 (SDS solutions) or 7.0 (bile salt solutions) and 10.8 in order to study the effect of the drug ionisation on its relative position on micelles. The results have shown that drug location is controlled by the (i) drug hydrophilicity and acid/base properties, with the more soluble compound in water (atenolol) exhibiting smaller variation of rotational correlational time (in SDS and bile salts solutions), and with both beta-blockers exhibiting smaller deviations in the protonated forms and (ii) the bile salt monomers, with the dihydroxylic bile salt (deoxycholate) producing larger differences. The work described herein allow us to conclude that the (protonated) beta-blockers are probably located on the surface of the detergent micelles, and linked to them by means of essentially electrostatic forces, while the (neutral) benzodiazepines are probably located deeper in the interior of the micelles.

Noninvasive methods to determine the critical micelle concentration of some bile acid salts

In this work the critical micelle concentrations (cmc) of four bile salts, sodium cholate, sodium glycocholate, sodium deoxycholate, and sodium glycodeoxycholate, are determined and presented. Three independent noninvasive methodologies (potentiometry, derivative spectrophotometry, and light scattering) were used for cmc determination, at 25 degrees C with ionic strength adjusted to 0.10 M with NaCl. Spectrophotometric and potentiometric studies of some bile salts were also executed at various ionic strength values, thus allowing the influence of the ionic strength on the cmc value of the bile salt to be assessed. A critical comparison of the cmc values obtained with data collected from the literature is presented. Furthermore, this work makes an evaluation of the conceptual bases of different methodologies commonly used for cmc determination, since variations in the results obtained can be related mainly to different intrinsic features of the methods used (such as sensitivity or the need to include tracers or probes) or to the operational cmc definition applied. The undoubted definition of the experimental bile salt concentration that corresponds to cmc (operational cmc) is essential since in the case of these amphiphiles the formation of micelles is not as abrupt as in the case of ordinary association colloids. The biphasic nature of their aggregation leads to a "round-shaped" variation of the experimental parameters under analysis, which makes difficult the evaluation of the cmc values and can be responsible for the different results obtained.

Analysis of anticancer platinum(II)-complexes by microemulsion electrokinetic chromatography: separation of diastereomers and estimation of octanol-water partition coefficients

Microemulsion electrokinetic chromatography (MEEKC) was applied for the separation and lipophilicity estimation of oxaliplatin and eight novel anticancer oxaliplatin derivatives. Solubility and permeability have to be balanced in modern drug development, and the octanol-water partition coefficient (log P) still represents one of the most useful quantifiable parameters providing a reasonable estimation of a drug's lipophilicity. Therefore, the capacity factors from MEEKC were correlated to log P values derived by the traditional shake flask method. The MEEKC method was accomplished using a microemulsion of heptane/sodium dodecyl sulfate (SDS)/butanol in phosphate buffer at pH 7.4 and 37 degrees C with all analytes being in a neutral state during the run. This experimental setup allowed a baseline separation of all platinum complexes within 11 min. Remarkably, beside the very good resolution and precision of the measurements, separation of diastereomers of the complexes and quantification of the diastereomeric ratios could be achieved. Correlating the capacity factors with the corresponding log P values resulted in a linear dependency with a correlation factor of r = 0.9935. Consequently, the applied MEEKC method was found to be a highly valuable technique not only for the separation of platinum complexes but as well for the estimation of the octanol-water partition coefficient with many advantages in comparison to other methods.

Determination of critical micelle concentration of surfactants by capillary electrophoresis

Capillary electrophoresis (CE) has been proven to be a convenient and useful technique for the determination of the critical micelle concentration (CMC) of a surfactant in an electrophoretic system under operating conditions. In this review, methodological approaches to the determination of the CMC of surfactants by CE technique are described. The practical requirements for making such measurements and the CMC values of surfactants determined by CE methods are presented. In addition, difficulties and uncertainty, as well as misconceptions that may arise in the CMC determination are discussed.

Relation between retention factors of immunosuppressive drugs in microemulsion electrokinetic chromatography with biosurfactants and octanol–water partition coefficients

Retention (capacity) factors (k' values) of immunosuppressive drugs were determined in microemulsion electrokinetic chromatography (MEEKC) systems as a tool for the indirect estimation of partition coefficients (POW) between 1-octanol and water. The microemulsions were based on phosphatidylcholine (PC) and bile acids (BAs) as biosurfactants and isopropyl myristate (IPM) as oil. Immunosuppressants were azathioprine (AZA), mycophenolate mofetil (MMF), tacrolimus (FK506) and cyclosporine A (CyA). Capacity factors of the analytes were determined from electrophoretic mobilities using an aqueous phosphate buffer (20 mM; pH 7.5) for all the systems. Retention was compared with that in the most commonly used microemulsion based on sodium dodecyl sulphate (SDS). logPOW versus logk' calibration lines were constructed using reference compounds with known POW. In addition, data of logPOW of the immunosuppressants were determined by partitioning between octanol and water, and were calculated by the aid of computer program. A different sequence of logPOW for two analytes was found in the biosurfactant-based systems compared with the SDS-containing one. Excellent agreement was observed between the logPOW values derived from the microemulsions containing deoxycholate compared with the data determined by partitioning between octanol and water. It was concluded that the retention factors in the systems with biosurfactants are good estimators for the partitioning in biological systems.